STRUCTURE magazine | October 2021

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STRUCTURE magazine

Contents

Cover Feature

O CTO BER 2021

HISTORIC STONE ARCH REQUIRES MODERN APPROACH By Matt Lewellyn, P.E. The rich history of the East Burke Street Bridge dates to the Civil War, surviving a Confederate attack. Structural deficiencies were identified in 2010. The goal was to maintain the existing stone arch while providing an alternate structural system to carry traffic loads. This intricate rehabilitation was achieved with several innovative strategies.

Features IN-SITU EVALUATION OF OLD PAN-GIRDER BRIDGES

ADAPTIVE REUSE OF THE HISTORIC WITHERSPOON BUILDING – PART 2

By Nur Yazdani, Ph.D., P.E., and Eyosias Beneberu, Ph.D., P.E.

By D. Matthew Stuart, P.E., S.E., P.Eng

Historically, pan-girders fell out of favor for economic reasons. Their popular period was before the introduction of AASHTO’s HL-93 design load. This article discusses a visual inspection and condition assessment conducted for the East Bound (EB) US 80 pan-girder bridge in Forney, Texas.

This four-part series discusses the adaptive reuse of the historic Witherspoon Building in Philadelphia, PA. Part 2 includes a discussion of the ongoing adaptations during construction and the structural investigations conducted to better understand the existing structure.

Columns and Departments 7 Editorial

What is Your Career Goal?

By Tina Wyffels, P.E.

8 Structural Monitoring Bridge Vibration Monitoring

By Andrea Zampieri, Ph.D.

12 Structural Specifications Revisiting Wind Loads on Pedestrian Bridges

24 Structural Connections Anatomy of a Mass Timber Bearing Intersection

55 Structural Performance Community Storm Shelter Design – Part 2

By D. Scott Nyseth, S.E., and Jason Smart, P.E.

By Bradford Russell, AIA, P.E., SECB

28 Structural Resilience Adapt and Transform – COVID-19 Lessons

58 Technology Computational Embrace

By the NCSEA Resilience Committee

32 Building Blocks Test-Based Available Strengths for Aluminum Structures – Part 2

By Aaron Gordon, P.E., and Gavin Good, P.E.

16 Structural Systems Hybrid Suspension Bridges for Super-Long Spans

By James LaBelle, P.E.

By Roumen V. Mladjov, S.E., P.E.

By John A. Dal Pino, S.E., and Larisa Enachi

20 Structural Design The Long Road – Part 1

40 Historic Structures Eden Train Wreck

By Matthew Speicher, Ph.D., and John Harris, Ph.D.

By Frank Griggs, Jr., D.Eng, P.E.

Special Section

36 Engineer’s Notebook Approximate Structural Analysis

2021/22

By Phillip Bellis, P.E., and Steve Reichwein, P.E., S.E., SECB

62 Structural Forum Take Time to Save Time

By Heather Todak, P.E.

In Every Issue Advertiser Index NCSEA News SEI Update CASE in Point

STRUCTURAL ENGINEERING Resource Guide

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, the Publisher, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

O C T O B E R 2 0 21

EDITORIAL What is Your Career Goal?

By Tina Wyffels, P.E.

A

s I reflect on everything that has happened since the pandemic started, I recognize I have primarily been operating in a survival mode. For the past year, most of my personal and work-related decisions have been affiliated with day-to-day tasks and very short-term thinking. There were months when I essentially stopped planning or working toward any long-term goals. This was because I was discouraged that the moment I thought I had a plan mapped out, the school teaching model would change, and my kids suddenly had two days off to allow time for the teachers to adjust. Or, a new CDC recommendation would come out, and plans to gather with friends or family were canceled. Planning for anything beyond a few days seemed futile, and I lost focus on any long-term goals.

We have all been through a lot this past year and a half. We transitioned to a largely remote workforce. We navigated different learning models for our kids. We are adjusting business policies to allow more flexibility to working remotely. We are evaluating office cleaning policies and monitoring health regulations to keep employees safe. We are deciding what business policies to have about masks and vaccines.

There has been no shortage of decisions needing to be made that have nothing to do with our engineering education, and it has been easy to lose focus on why we chose to be in this profession.

“

The most important thing is to give thought to what you aspire for in your career and then start making progress so it can become a reality.

When I ask what your career goal is, I am asking about your big picture, long-term career goal (and you may have more than one!).

This is an excellent question if you are entering the workforce, but it can still apply to you regardless of where you are in your career if you have not given it recent thought. What position do you aspire to hold, and what have you set your mind on achieving? Do you want to start your own company? Do you want to be a technical leader? Do you want to teach? Are you interested in becoming an active member in a local or national professional organization to help advance the structural engineering profession? Do you want to be responsible for winning work for your firm? There are several different paths your career can take, and each can be very rewarding. If you have never given this question much thought, I recommend you set aside some STRUCTURE magazine

focused time to think about what you desire for your future. Think about how you define success and align your career goal with your definition of success. Then, as you think about your future, consider if your career goal aligns with other personal goals you may have so that you are not overstretched in your time and energy.

I recently had a conversation with a new entry-level hire at another consulting firm, and she talked about how her work mentor had asked what her career goal was and that she had not given it much thought.

I cannot say I would have been able to answer that question at that point in my career either, but her statement reminded me that I also needed to revisit the goals I have for myself and be more proactive in achieving them. If you have lost your focus as I had, try to revisit your goals and restart your efforts in achieving them. And if you manage other staff, I encourage you to ask them about their career goals. It concerns me to hear statistics like over 30% of millennials are considering changing jobs after the pandemic. I fear that if we do not help our employees understand what options there are within this industry and help them find a career path that they are passionate and motivated about, the demands of our profession may cause them to overlook how rewarding it can be.

When you have your career goal identified, write it down someplace that can be regularly reviewed. Then identify at least one short-term goal that will help progress you toward your overall career goal and start working toward achieving that short-term goal.

Set a timeframe for when you want to accomplish this short-term goal, and if possible, find a mentor that can help keep you accountable.

When one short-term goal is reached, celebrate your achievement before restarting the process with the next short-term goal. Be intentional and set aside time each week to make progress, even if just a few minutes. Time flies, and there is no shortage of work and personal agendas competing for that time. It is very easy to get trapped in a day-to-day mode without achieving any progress toward your goals. If this happens, give yourself grace and adjust to get yourself back on track.

Keep your goals fresh in your mind so that your momentum is not stagnated by days turning into years without any progress. The most important thing is to give thought to what you aspire for in your career and then start making progress so it can become a reality.

I am optimistic that the worst of the pandemic is behind us, and we will experience increased stability as each month passes. With this stability, we can transition into a new normal. And, this is an excellent time for all of us to revisit our career goals to confirm they still reflect our personal aspirations. Now is the time to get back on track with your career, as the pandemic may have changed your priorities and where you need to spend your time moving forward.■ Tina Wyffels is a Principal at BKBM Engineers in Minneapolis, MN, and is Chair of the CASE Guidelines Committee.

O C T O B E R 2 0 21

7

structural MONITORING Bridge Vibration Monitoring State of the Art and Future Outlooks

By Andrea Zampieri, Ph.D.

I

nspection and condition assessment of bridges requires detailed visual examinations that must be conducted at least biennially. This effort involves deploying crews on-site for an extended period of time, depending on structure-specific needs and bridge typology. At times, gaining access to specific structural elements can be a challenge. Such is the case for the main cables and hangers of suspension bridges and the girders of viaducts and arch structures, which sometimes require special rope access. Thus, it should come as no surprise that inspection expenses are one of the most relevant items in the life-cycle cost of bridges. As a limited budget is available to sustain these costs, and given the increasing inspection needs of the U.S. bridges, the bulk of which are nearing the end of their service life, the need for costeffective condition assessment techniques has never been more critical.

Visual inspections are also imperfect because they are subjective, given that they depend on the inspector’s experience and judgment. When the very stability of the structure is in question, inspections may also pose safety hazards to the inspection crew on site.

In recent years, engineers and bridge managers have started to deploy structural health monitoring (SHM) systems to supplement visual examinations. SHM employs various sensors, such as accelerometers, strain gages, displacement transducers, acoustic sensors, and GPS systems, to name a few. These instruments remotely and automatically collect structural response data that can be processed to obtain information on the condition of the bridges. SHM can reduce inspection time and costs, provide objective data, and mitigate access difficulties and safety hazards. Vibration-based approaches to SHM aim to assess bridges’ structural health by using vibration response data, usually collected by accelerometers installed on the structures. These sensors are widely employed because acceleration data are relatively easy and economical to obtain, are well-suited for many applications, and can be easily incorporated into various structural analysis and assessment strategies. As a result, vibration-based SHM plays a prominent role among the various types of SHM implementation as a support tool for structural evaluation and asset management. In the following, an overview of state-of-the-art techniques and an outline of emerging technologies are presented to ultimately offer a primer on the objectives, methodologies, and potential applications of bridge vibration monitoring.

Objectives and General Framework Although different approaches to bridge vibration monitoring exist, a general framework for the practical implementation of the method could be outlined following the flowchart in Figure 1.

A sensor network is installed on the bridge. When new data are available, the digital records are processed to identify the modal parameters of the structure, namely the natural frequencies of vibration, mode shapes, and, in some applications, the damping ratios. It is important to observe that acceleration records target the global behavior of the structure, so the first few lower-frequency global modes of vibration

8 STRUCTURE magazine

Figure 1. General framework for vibration-based SHM, based on Feng et al. 2013.

may be identified. Because these vibration characteristics depend on the mechanical properties of the structural system, the modal parameters identified from the vibration records may be employed to estimate the structural parameters – generally the stiffness – of selected structural elements within the bridge. Results are stored in a database, and values of stiffness that differ more than an established threshold compared to previously identified ones may signal an abnormal structural behavior, damage, or other conditions, depending on the specific application for which the monitoring activity is used. If deemed necessary, corrective interventions are made, and then the monitoring activity resumes.

It is important to understand that determinations on the condition of a bridge are based on detecting changes in its vibration characteristics. Hence, a fundamental principle of vibration-based SHM is that it requires a baseline set of modal parameters and their associated structural stiffness values to detect and quantify those changes. This baseline must represent the bridge in pristine condition or, more generally, the condition prior to the event under investigation has occurred. For instance, if the goal of the analysis is to determine whether a seismic event caused structural damage, which in turn means to detect whether structural stiffness decreased as a result of the event, a baseline set of modal and structural parameters, identified before the shaking, is required. This will enable a comparison with the modal and structural identification results obtained after

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residual capacity of the structure. This allows asset managthe seismic event occurs. Also, it is important to note that records ers to make better-informed decisions on matters such as from multiple datasets collected over a long period yield more determining whether structural rehabilitation is required, reliable baselines than those obtained from short-term monitoring estimating the remaining service life of the bridge, verifying campaigns with only a few records. This is because the parameters if load posting should be imposed, and deciding whether an identified through each set of measurements are affected by the aging bridge should be decommissioned. In addition, from specific operational conditions – primarily temperature – when the perspective of a monitored network of bridges, this may the vibration data are collected. By using multiple datasets, one can enable rational prioritization of interventions and more take statistics of the parameters identified from each set and build effective budgeting. a statistical baseline model of the bridge to account for the effect While long-term vibration monitoring could be helpful on a wide of specific operational conditions.

Even more importantly, the benefits of vibration-based SHM are array of issues, short-term SHM campaigns may still be employed maximized through long-term monitoring deployments. This offers to address specific project needs. For example: an opportunity to study the full history of the bridge, which is key to identifying potential structural concerns promptly, making educated decisions on maintenance interventions, and enabling other asset management provisions.

Some examples of such applications and benefits are: • By comparing the structural parameters identified before and after a potentially damaging event, such as an earthquake or a ship collision, a long-term vibration monitoring deployment enables the engineer to determine whether damage occurred, locate the structural elements affected, and quantify the extent of the damage.

• Tracking changes of a bridge’s modal Prevent condensation and mold and structural parameters throughout its service life makes structural Improve effective R-value of the aging visible and quantifiable. Aging building envelope by up to 50% may be expected to produce small Increase floor temperature by up progressive shifts in bridge vibration to 34°F/19°C adjacent to balcony characteristics associated with gradual Reduce heat loss by up to 90% decrements of structural stiffness over the structure’s life.

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O C T O B E R 2 0 21

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Figure 2. Ambient vibration records collected by eleven sensors installed on a bridge are used to identify the natural modes of vibration of the structure. The frequency domain decomposition plot shows three natural frequencies at approximately 2.9 Hz, 3.8 Hz, and 13.8 Hz. The acceleration records are available in Saiidi, n.d.

• Upon commissioning, bridges may be instrumented with temporary accelerometers to identify modal and structural parameters that can be compared against the design values to conclude whether the actual behavior of the bridge in service complies with the design expectations.

• Temporary accelerometer networks may be employed when bridge repair or strengthening is performed to measure the difference between the modal and structural parameters identified before and after the intervention. This information provides a measure of the effects of the repair or strengthening and allows verification of the design objectives.

Modal and Structural Parameters Identification Much literature has been produced on modal parameter identification using vibration measurements, and different techniques are available for various types of vibration data. In most practical applications, ambient vibrations (e.g., vibrations induced by traffic across the bridge and nearby traffic, or in other words, the vibrations a bridge is subjected to in ordinary operational conditions) are used for modal identification purposes. The process of identifying the modal parameters of bridges from ambient vibration data is called operational modal analysis.

While several operational modal analysis techniques are available, they are all characterized by being output-only analysis methods. This means that bridge vibration response measurements collected by the accelerometers installed on the bridge – i.e., the output data – are sufficient to carry out the analysis, with no need to obtain explicit measurements of the input excitations. The most straightforward operational modal analysis approach is the peak-picking method. This method first transforms the measured digital vibration signals into the frequency domain employing well-known mathematical functions such as the discrete Fourier transform or the power spectral density function. The natural modes of vibration of the bridge are then identified simply by “picking” the peaks of these frequency representations of the vibration data.

However, the most common operational modal analysis technique used in practical applications is perhaps the frequency domain 10 STRUCTURE magazine

decomposition. It also relies on a frequency-domain transformation of the data. In fact, it can be interpreted as a refinement of the peakpicking method through more sophisticated mathematical tools. An example of the frequency domain decomposition method is shown in Figure 2. More details on operational modal analysis can be found in Brincker and Ventura, 2015.

Once the modal parameters are available, the structural parameters of the bridge can be estimated. A variety of techniques have been proposed in the literature to do so. The finite element model updating method discussed in depth by Friswell and Mottershead (1995) may be one of the greatest interest to practicing engineers.

The fundamental principle of this technique is relatively simple. A parametric finite element model of the bridge is constructed, in which the stiffness of selected elements is treated as a variable parameter (i.e., the unknowns). The finite element model updating problem is solved by searching for stiffness values that minimize the difference between the modal parameters identified from the vibration data and the analytical modal parameters obtained from finite element analysis. Thus, structural parameters identification may be very much intended as an optimization problem that can be solved through various optimization algorithms.

Despite its conceptual simplicity, finite element model updating must be applied carefully. Because only a limited number of global modal parameters can be identified from the vibration data, attention must be placed on selecting the structural parameters to be used as unknowns of the finite element model updating problem. Selecting too many variables would make the optimization algorithm ill-conditioned, resulting in multiple possible solutions to the problem rather than a unique solution. This issue may be mitigated by performing a sensitivity analysis to explore the influence of each candidate variable on the bridge’s modal parameters to help select the proper unknowns of the finite element model updating problem.

Future Outlooks In recent years, advances in computer technology have paved the way for data science and artificial intelligence to take on a central role in nearly every scientific research field. And, as sensors become cheaper

and more widely available, novel archetypes of the built environment have come forth through concepts such as smart city and ubiquitous sensing. Bridge vibration monitoring is affected in many ways by these novel scientific and technological perspectives, as they are opening new frontiers in collecting and processing vibration data.

One paradigmatic example is the recent proposal of crowdsensing platforms for bridge vibration monitoring. This technology stems from the observation that today’s sensors are ubiquitous. In fact, it is safe to say that each of us carries an accelerometer in our pocket every day – on smartphones. Thus, the main idea of crowdsensing is to perform operational modal analysis of the structures by taking advantage of aggregate acceleration data collected by the smartphones from users traveling across bridges. Compared to traditional vibration monitoring applications, the clear advantage is that crowdsensing frees bridge owners from the burden of installing and maintaining a sensor network. And this may encourage more extensive adoption of bridge vibration monitoring technologies in the industry, which is still relatively limited compared to the research effort produced in this field. In addition, a crowdsensing platform provides a wealth of data, highly granular both in space and time, that traditional sensor networks are incapable of producing.

Yet, these schemes also present technical difficulties. First and foremost, this is because smartphones are mobile sensors rather than fixed ones, making modal identification of bridges challenging. Additional complexity is added by the fact that the bridge vibration data collected are affected by the dynamics of the car and the disturbance of the user interaction with the smartphone. While crowdsensing platforms

cannot be viewed as market-ready technologies yet, their application to real-life problems may be closer than one would expect.

To appreciate the pace at which research is moving forward, it suffices to note that the first laboratory experiment to test the potential of smartphone sensors for vibration-based SHM was conducted in 2015 (Feng et al. 2015). In 2018, the natural frequencies of a reallife bridge were identified using the data collected by a smartphone mounted on the dashboard of a car over 42 trips across the bridge (Matarazzo et al. 2018).

The crowdsensing paradigm effectively highlights how novel technologies increase the amount of readily available data at an affordable cost and suggests that bridge vibration monitoring may play a more prominent role in bridge condition assessment and management in the future.

From a broader perspective, these technological advances showcase the fast-changing professional landscape that we face today. Such a scenario challenges structural engineers to develop new skills in fields ranging from sensing and computer algorithms to data management and user behavior. Yet, these skills must be integrated with traditional structural engineering knowledge, for it is essential to better understand how to effectively use the wealth of data that will be readily obtainable in the future for the benefit of asset management. ■ Full references are included in the online PDF version of the article at STRUCTUREmag.org.

Andrea Zampieri is a Bridge Engineer at Parsons Corporation in New York City. (andrea.zampieri@parsons.com)

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structural SPECIFICATIONS Revisiting Wind Loads on Pedestrian Bridges

By Aaron Gordon, P.E., and Gavin Good, P.E.

P

edestrian and multi-use trail bridges have become more popular as public and private entities invest in alternative modes of transportation, human-scale design, and user safety. The design of these structures is typically adapted from vehicular bridge design methodology. While the scale of pedestrian bridges simplifies portions of the analysis, such as considering multiple lanes and certain load combinations, it adds several wrinkles, including vibration and increased attention to lateral loads. The American Association of State Highway and Transportation Officials (AASHTO) LRFD Guide Specifications for the Design of Pedestrian Bridges (AASHTO Pedestrian Bridge Guide) addresses these design aspects unique to pedestrian structures. Its use Figure 1. Timeline of code publications and wind load methodology. The 2 nd edition of the AASHTO Pedestrian Bridge Guide is strongly recommended by references the 4 th edition of AASHTO LRFD for wind load factors. Since then, the wind load factors and methodology in AASHTO AASHTO's Load and Resistance LRFD have changed, while the wind load procedure for the AASHTO Pedestrian Bridge Guide has not changed.

Factor Bridge Design Specifications (AASHTO LRFD) when designing pedestrian bridges and other Evolution of Wind Load Criteria structures not carrying full highway loading. In fact, a recent survey of state bridge offices found that over 90% of states explicitly require The approach to wind loading in the AASHTO Pedestrian Bridge the use of the AASHTO Pedestrian Bridge Guide when designing such Guide has evolved since it was first published in 1997. This first facilities in their jurisdiction. Despite a guide specification dedicated to edition used a simplified approach consistent with the AASHTO pedestrian bridges, evaluating wind load on these structures involves Standard Specifications for Highway Bridges (AASHTO Standard consulting and cross-referencing various specifications based on dif- Specifications). In place of correlating wind speeds to applied presferent analysis methods. The indirect approach to wind loading makes sures or more refined analyses, a uniform wind pressure was used it difficult for engineers to ensure appropriate design procedures are based on empirical methods. The 2nd (and latest) edition of the followed and fails to provide consistent reliability across the industry. AASHTO Pedestrian Bridge Guide was published in 2009, with This article reviews the evolution of wind load criteria, examines interim revisions issued in 2015 that do not impact the wind load current wind load criteria for pedestrian bridges, and provides a path criteria. This edition reflected the transition from Load Factor towards establishing a consistent design methodology for wind loading Design (LFD) in AASHTO Standard Specifications to Load and on pedestrian bridges.

Resistance Factor Design in AASHTO LRFD and correlated wind Table of AASHTO LRFD Base Wind Speed and Load Factors. Adapted from Table 3.4.1-1 in AASHTO LRFD 7 th and 8 th Editions and Table 3.8.1.1.2-1 in AASHTO LRFD 8 th Edition. The Strength V load combination is not used for most pedestrian bridge designs since it simultaneously considers live load and wind load.

12 STRUCTURE magazine

We flip the traditional organizational structure

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speeds directly to wind pressures. However, instead of incorporatCurrent Wind Load Criteria ing the wind load procedure in AASHTO LRFD, it requires that wind pressures be calculated using AASHTO Standard Specifications Structural engineers must be aware of the updates to AASHTO for Structural Supports for Highway Signs, Luminaires, and Traffic LRFD since the publication of the AASHTO Pedestrian Bridge Guide Signals (AASHTO Signs) using a mean recurrence interval (MRI) or risk underestimating the wind pressures on the structure. The of 100 years. Per the AASHTO Pedestrian Bridge Guide, the wind AASHTO Pedestrian Bridge Guide references AASHTO LRFD 4th pressures generated using AASHTO Signs are then factored using Edition, but there is no language highlighting the importance of which load combinations from AASHTO LRFD. AASHTO LRFD edition to incorporate. Furthermore, the references This approach to wind loading is due to the similarities between to AASHTO LRFD 4th Edition are not specific to the wind loading pedestrian bridges and overhead sign structures in the United States. and are only found in the design example and the listed references at Both structure types can span over roadways, frequently consist of the end of the specification. As shown in Figure 1, AASHTO LRFD steel truss elements, and are subject to relatively low gravity loads. 4th Edition was published prior to overhauling wind load criteria in Prefabricated steel trusses, which have the most in-common with over- AASHTO LRFD 8th Edition. head signs, are a popular solution for many owners seeking to provide The current AASHTO LRFD wind load criteria use an MRI of 700 pedestrian and bicycle access across roadways and other obstacles. This years for vehicular bridge design, whereas AASHTO Signs uses 100 logic is also reflected in the commentary of the AASHTO Pedestrian years. As shown in Figure 2 (page 14), this discrepancy would have Bridge Guide, which states: been addressed at the time of publication of AASHTO Signs by the The wind loading is taken from AASHTO Signs specification AASHTO LRFD 4th Edition load factors. However, if the load facrather than from AASHTO LRFD due to the potentially flexible tors in the current version of AASHTO LRFD are used in pedestrian nature of pedestrian bridges and also due to the potential for bridge strength design, the wind pressures from AASHTO Signs traffic signs to be mounted to them. would not be increased, and the structure would only be designed When the current AASHTO Pedestrian Bridge Guide was pub- for an MRI of 100 years. This underestimates the wind load on the lished, AASHTO LRFD wind load provisions used the fastest-mile structure since the AASHTO Pedestrian Bridge Guide intended this wind speed approach. The fastest-mile wind calculation was based load to be increased by 40%. While it may be acceptable to design on determining the shortest time a mile-long column of air would some pedestrian bridges for a lower MRI than vehicular bridges, many take to travel past a fixed point. A base wind speed of 100 miles of these structures span critical infrastructure networks or support per hour and a constant base wind pressure were used for structural commuter routes. Reduced reliability of a structure should be an calculations regardless of location. Alternatively, engineers could intentional design decision in coordination with the Owner, not due perform a site-specific wind study. The pressures generated from to discrepancies in the design criteria. This creates a significant tension these wind speeds were then factored according to each load combination, as shown in the Table. This fastestmile wind pressure calculation was What does it mean to be a considered reasonable for most of the United States but was unconservative supportive business organization? in hurricane-prone regions and failed to provide uniform reliability to structural designs.

The 8th edition of AASHTO LRFD sought to provide uniform reliability across the country using a design wind speed that reflects the actual wind speed at a given location. The updated specifications adopted a constant averaging time of 3-seconds per gust, aligning with ASCE-7 Minimum Design Loads for Buildings and Other Structures (ASCE-7) and data from the National Weather Service. This edition and subsequent editions of AASHTO LRFD vary the wind speed based on geographic location and the load combination being applied, as summarized what could that mean for you? kpff.com in the Table. Since wind speeds now vary among load combinations, all load Seattle Sacramento Boise Nashville factors for wind pressures were changed Tacoma San Francisco Salt Lake City Birmingham to 1.0. This is a significant departure Lacey Los Angeles Des Moines Washington, DC Spokane Long Beach St. Louis New York from the previous wind loading critePortland Orange County Chicago ria, and its ramifications have not been KPFF is an Equal Opportunity Employer Eugene San Diego Louisville reflected in the AASHTO Pedestrian Bridge Guide.

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Therefore, the design and cost implications of applied wind pressures will significantly impact owners and end-users. The updated wind load criteria in AASHTO LRFD impact the applied wind pressure, which can dictate superstructure-to-substructure connections, bearing requirements, and substructure design.

Piers and intermediate bents for pedestrian bridges can reach substantial heights to meet vertical clearance requirements over highways or provide users with scenic views. Small differences in lateral loads applied at the top of these tall column elements may dictate their size and govern their foundations. In particular, pile footings can be dramatically affected as many owners discourage or forbid pile uplift forces. Pedestrian bridges have relatively lower dead loads to counteract overturning, so uplift forces frequently control foundation sizes and pile embedment. A conservative approach to wind loading may result in sizable cost increases for the substructure and foundation, which are main factors in the overall cost.

For some pedestrian bridge superstructures and substructures, AASHTO LRFD could be more appropriate than AASHTO Signs if these structural elements are less flexible and less sign-like, such as reinforced concrete slabs, composite steel girders, short span timber, or concrete columns.

Figure 2. Comparison of wind pressures at 30 feet. Wind pressures from AASHTO Signs are factored according to AASHTO LRFD 4 th Edition and 8th Edition. Wind Exposure Category C is assumed. For AASHTO Signs, a drag coefficient of 1.70 is assumed.

for engineers who should consult AASHTO LRFD 4th Edition for wind load factors and later AASHTO LRFD editions for everything else, inviting inconsistencies to designs and built structures. Figure 2 demonstrates the potential variability of wind loading based on the different design criteria.

Wind loads on fences and railings are another area of inconsistency in pedestrian bridge design. AASHTO LRFD stipulates that the design wind load for a chain-link or metal-fabric fence shall be 15 pounds per square foot applied to the full fence height. This clause from AASHTO LRFD is not in the AASHTO Pedestrian Bridge Guide nor AASHTO Signs. Calculating wind load on fences or railings using AASHTO Signs involves determining the obstructed area, estimating the drag coefficient of specific members, and measuring the distance between windward and leeward sides. Many engineers and truss manufacturers simplify this calculation by conservatively applying the superstructure wind pressure to the full projected area of the fence or railing while neglecting the leeward side. While this approach seems reasonable and conservative for most cases, specific guidance on how to accurately account for wind loads on fences and railings could promote more efficient and consistent structural designs.

Fences and railings can constitute most of the superstructure height for pedestrian bridges. Therefore, conservative estimates of these loads may considerably impact the structure and cost.

It is imperative to use engineering judgment when applying wind load specifications to pedestrian bridges. While typical vehicular and highway bridges are rarely governed by wind loading, pedestrian bridges are much more likely to be governed by wind and other lateral loads.

14 STRUCTURE magazine

Conclusion

The stated purpose of load and resistance factor design specifications is to build structures according to a precise statistical method and a specific level of reliability that values user safety. Today, pedestrian bridges can be designed and constructed to a wide range of reliabilities due to the cross-referencing of different specifications which use different analysis methods, without clarity on which edition should be applied. An update to the AASHTO Pedestrian Bridge Guide could include wind load criteria rather than referencing AASHTO Signs and provide more guidance on fence and railing loads. If using AASHTO Signs as a design supplement is preferable, the AASHTO Pedestrian Bridge Guide could provide additional commentary on when it is acceptable to reference AASHTO Signs based on the bridge type, natural frequency, or weight-to-width ratio.

Alternatively, it could refer to a specific edition of AASHTO LRFD for wind load factors or explicitly provide LRFD load combinations.

In the meantime, the authors believe engineers should consider applying the load factors in AASHTO LRFD 4th Edition, rather than the reduced load factors in more recent editions, to align with the original intent of the AASHTO Pedestrian Bridge Guide. Regardless of updates to the wind loading criteria or the design approach, engineers must always rely on sound reasoning and communicate clearly with owners when establishing wind load criteria.■ Aaron Gordon is a Structural Engineer at Kimley-Horn in Dallas, TX, with a focus on public infrastructure projects. (aaron.gordon@kimley-horn.com) Gavin Good is a Structural Engineer at Kimley-Horn in Atlanta, GA, specializing in vehicular and pedestrian bridge design. (gavin.good@kimley-horn.com)

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structural SYSTEMS Hybrid Suspension Bridges for Super-Long Spans

By Roumen V. Mladjov, S.E., P.E.

B

uilding taller, longer, stronger, and faster is one of humanity’s eternal aspirations.

It is not by chance that the construction industry measures achievements by comparing the height of skyscrapers, the size of arenas, and the span of bridges.

Currently, seven bridges exceed 4,921 feet (1,500 m) in span.

The Akashi-Kaikyo Bridge, Japan (1998) has the longest span at 6,532 feet (1,991 m). Figure 1. Hybrid suspension bridge system for super-long spans.

The Çanakkale Strait Bridge in Turkey, to be completed in 2022, will surpass this with a record- with cable-stayed supported cantilevers extending on each side or at breaking 6,637 feet (2,023 m) span. least extending into the main span (Figure 1). These cantilevers support There were projects for longer bridge spans over the English Chanel, the “on-deck pylons” and the central suspension portion. The forces at the Gibraltar Strait, and the Messina Strait, where construction pre- both ends of the pylons are transferred with tension cables to the top paratory work started in 2009, only to be abandoned in 2013. As a of the central tower. The pylons’ vertical reactions are transferred with result, the longest bridge span has not increased for 23 years. When diagonal cables to the top of the main towers; the horizontal tension considering long bridge spans, engineers choose between suspen- forces from the central suspension cables are also transferred to the top sion and cable-stayed bridges, the only systems to achieve spans over of the main towers, but with horizontal cables (Figure 1). The main 3,281 feet (1,000 m) (the longest span by any other system being an cables support the deck-girder in the suspension portion with regular 1,811-foot arch (552-m)). suspenders. In contrast, between the on-deck pylons and the towers, Like all bridge systems, suspension and cable-stayed structures are the deck-girder is supported with cable-stays directly by the towers. continuously enhanced based on the development of high-strength This approach has potential that needs to be verified for feasibilmaterials, newer construction technologies, quality control, and ity and economy. The basic idea for reducing the suspension span maintenance. However, it is no longer sufficient to simply increase is not new. The idea was explored by Joseph Strauss in the early the structural members’ sections to provide longer spans. We are at design of the Golden Gate Bridge (1932), with colossal steel truss the point where it may be necessary to implement new or at least cantilevers from the towers shortening the main suspension span. modified structural systems.

Sergio Musmeci used a different method for a Messina Strait bridge competition (1970) with Lclear = 10,827 feet (3,300 m), and T.Y. Lin for a Gibraltar Strait bridge feasibility study (1990) with sevHybrid Suspension Systems eral 16,404-foot spans (5,000-m). The author also considered the One option for increasing the length of long-spans is using hybrids prospect of a hybrid suspension system for a Messina Strait bridge of suspension and cable-stayed bridge systems, or hybrid suspension. feasibility study (1988) with Lclear = 9,350 feet (2,850 m).

The idea is to reduce the suspension span while maintaining the In principle, shortening the suspension length should result in required clear span length. In hybrid suspension, this is achieved by substantial savings. The reduction of the suspension cable forces adding “on-deck interior” cable-stayed pylons at 1,000-1,600 feet from a classic suspension system with Lmax span to a shorter sus(300-500 m) from the supports, combining cable-stayed cantilevers pended portion Lsusp of a hybrid system, keeping the same free main (extending from the towers) and a central suspension portion. This spans Lmax, is proportional to the square of the ratio of the lengths approach reduces the suspension length, related cable forces, and of the two systems (Lsusp/Lmax)2, if the sag to span ratio ( f/L) for the demand on the structure, so a free span of 11,811 feet (3,600 both systems is kept the same. For example, the reduction of the m) can be obtained using a suspension structure of about 8,202 main cable horizontal force (and all other related forces) resulting feet (2,500 m). from transforming an 11,811-foot classic suspension (3,600-m) to Depending on the span’s requirements, the system may include one hybrid suspension with an 8,268-foot suspension portion (2,520central “main” span plus two side spans or a combination of multiple m) is (8268/11811)2 = 0.49, a reduction by about half, with all “main” spans with two side spans. The towers are structural systems consequent advantages and savings.

16 STRUCTURE magazine

Which system is more efficient – classic suspension or hybrid suspension? Is the hybrid system more efficient as a whole than a classic suspension bridge with the same main span? While the main cable forces are significantly reduced in the hybrid system, there is no change in the total vertical reactions at the towers and foundations, which remain the same regardless of the reduced suspension span.

The hybrid system reduces the length of the suspension. It adds new elements like “on-deck pylons” and diagonal main cable stays. Pylon reactions are transferred to the main supports, and compression is imposed on the deck-girder system between the “on-deck pylons” supports and the main towers. Some of the gain from shortening the suspension span is offset by these transformations of the system.

Hybrid versus Classic Suspension Systems Feasibility Study

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The efficiency of suspension bridges depends mostly on the main cable sag.

Deeper sags reduce the cable force but require taller towers. Classic suspension options have sags, f, ranging from 1/7 to 1/12 of the span, Lmax. While bridges with deeper sag ratios (from 1/7 to 1/9 of Lmax) are more efficient than those with smaller Figure 2. Hybrid suspension alternatives vs. classic suspension systems. sag ratios (from 1/10 to1/12 of Lmax), deeper sags require much taller main towers than smaller sags. The heights same total vertical uniform load q per linear meter. The maximum of the towers are determined as the sum of the initial sag, plus 3% cable force is S=(R^2+Hel^2)^0.5, where R is the maximum reaction longitudinal deck slope (from center to towers), 33-foot allowance and Hel is the maximum elastic horizontal cable force.

(10-m) for the deck structure, plus 213 feet (65 m) of minimum clearance above water. The longitudinal slope is required to remain at least When Clear Spans are the Same 1% after considering the elastic deformation under maximum load q.

The tower heights for an 11,811-foot suspension span (3600-m) The hybrid bridges’ suspension central portion length is 0.6-0.7 of with ratios between 1/7 and 1/9 are 2,037 to 1,663 feet (621 to 507 the clear span, making the corresponding extensions of the towers m), while for ratios from 1/10 to1/12, they are 1,532 to 1,335 feet toward the mid-span 0.15 to 0.2 of Lmax. Consequently, the reduced (467 to 407 m). For practical reasons, engineers have used sags of around 1/9 of L for most of the recent longest bridge spans to optimize balance between the overall efficiency and constructability of the towers.

A simple approach to calculate the total structural quantity for comparing the efficiency of different hybrid options is to calculate the sum of the products of element forces times element lengths.

The smaller the sum, the more efficient the system. The element START WRITING YOUR DCI STORY forces and support reactions are functions of q, the total vertical uniform dead + live load per linear meter. The total structural We’re Hiring! quantity includes the central span of the bridge and the two main towers; for the deck-girder, it includes only the additional comVisit our website pression at the cantilevered (cable-stayed) support portions (since for more details there is no difference in demand on deck-girders in the suspension portions of both compared options). All bridge options are WASHINGTON | OREGON | CALIFORNIA | TEXAS | ALASKA | COLORADO | MONTANA assumed to have the same general structure and width, with the

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for its overall efficiency, and is used for the example above. Additional advantages of this Item Classic Suspension Hybrid System option are that the inclined tower legs result in suspension length reduction and the tower Clear Span (Lmax), feet (meters) 11,811 (3,600 m) 11,811 (3,600 m) space structure provides more stability and Suspension portion, feet (meters) 11,811 (3,600 m) 8,268 (2,520 m), or 70% better resistance to the higher reactions in Max Force of Main Cable (S), q (US tons) 4,629 (4,199 m) 2.977 (2,701), or 64% super-long spans. Other sub-system configurations may be used if the designer and H towers above deck, feet (meters) 1,490 (454 m) 1,211 (369 m), or 81% the builder find them efficient and viable in H towers to foundations, feet (meters) 1,696 (517 m) 1,417 (432), or 84% their detailed analysis.

In addition to studying hypothetical bridges, Total structural quantity, 93,789 (25,930) 79,281 (21,919), or 84.5% the efficiency of hybrid alternatives can be q US ton-feet (ton-meters) x 103 studied and compared across existing longsuspension portions become 8,268 feet (2,520 m) long for an 11,811- span suspension bridges: the Akashi-Kaikyo Bridge, the Great Belt foot bridge (3,600-m) (Figure 1). After exploring different options, East Bridge, and the Izmit Bay Bridge. The results are listed in Table 2, hybrid suspensions with f = 1/8 of Lsusp were considered versus classic along with the potential efficiency of hybrid systems. suspensions with f = 1/9 of Lmax. With these parameters, hybrid tower For super long spans in areas with high winds, it is appropriate for heights are 1,211 feet (369 m) above the deck for an 11,811-foot the deck-girder system to be designed as a steel box with an aerodyspan (3,600-m). The height of on-deck pylons is determined as the namic shape; it may also benefit from additional side bracing with sum of the suspension cable sag + deck slope + calculated deflection cables anchored to the shore. It would be more efficient to use two of the suspension cable under full load. parallel bridge structures in some conditions, one for each traffic As a result of exploring different alternatives for hybrid suspen- direction with some separation, interconnected with horizontal sion bridges, it was determined that hybrid options with Lsusp = 0.7 ties transforming the entire structure into a horizontal Vierendeel Lmax are the most efficient. The study compared classic suspension truss to increase the lateral resistance. If necessary, diagonals can (Figure 2, page 17 ) with the following hybrid variations: be added between the two parallel structures, transforming it into 2a) hybrid suspension a horizontal truss.

2b) hybrid suspension with under-pinned suspension cables 2c) hybrid suspension with inclined main towers Conclusions 2d) hybrid suspension with inclined main towers and inclined on-deck pylons Based on current technical progress and development of suspension The reduction of the suspension length in hybrids allows using sags and cable-stayed bridges, suspension bridges can be expected to reach of 1/8 without requiring very high towers. For example, the result of clear spans of 7,874 to 8,530 feet (2,400 to 2,600 m) in the near replacing a classic suspension system for an 11,811-foot (3,600-m) span future. In comparison, cable-stayed bridges could reach 4,921-foot with a hybrid system (inclined main towers, Figure 2c) with a middle spans (1,500-m). Such design will require total tower heights of about suspension part Lsusp = 0.7 Lmax = 8,268 feet (2,520 m) and the same 1,280 feet (390 m) for suspension systems or 1,411 feet (430 m) for 11,811-foot clear span (3,600-m) is illustrated in Table 1. cable-stayed systems.

In trials of various sub-systems, the sub-system with minimum total Hybrid suspension systems will make possible even longer strucstructural quantity is hybrid with inclined main towers and inclined ture spans of up to 9,843 to 11,811 feet (3,000 to 3,600 m), on-deck pylons (Figure 2d ), providing 17.6% savings. However, for incorporating an internal classic suspension system of only about long spans of 9,843 to11,811 feet (3,000 to3,600 m), the inclined 6,890 to 8,202 feet (2,100 to 2,500 m). Additionally, such hybrid pylons-on-deck need to be about 1,214 feet tall (370 m) above the structures could achieve a 10-15% efficiency of material. While deck. Considering the ease of construction, the next most efficient these savings may not look substantial, for a 3-span bridge with an sub-system, hybrid with inclined main towers but with vertical pylons 11,811-foot main span (3,600-m) and a cost in the range of 4.5 to on deck (Figure 2c), results in about 15% savings, is recommended 4.8 billion dollars, the material savings would be 450-720 million dollars. More importantly, hybrid systems offer the possibility to build much longer spans with main element sizes in the range of those already used for shorter span structures with reduced bridge tower heights and reduced diameter of suspension cables.

Hybrid systems in super-long spans (e.g., 11,811 feet; 3,600 m) would include unprecedented elements, like on-deck interior We are currently looking for: pylons taller than the Eiffel Tower to support the reactions of a considerable suspension portion (e.g., 8,268 feet, 2,520 m), a • Structural Engineers serious challenge. An actual project would require more detailed • Civil Engineers analysis and wind tunnel testing.

• BIM Technicians The results are consistent for a wide range of clear spans (2,461 • Construction Managers to 11,811 feet; 750 to 3,600 m), making hybrid suspensions more • Steel Detailer efficient even in shorter spans of 2,297 to 4,921 feet (700 to 1,500 Please visit klaa.com/open-careers m). The future may see these types of configurations used for more information and to apply. to design and build longer span bridges where necessary, G O L D E N | L O V E L A N D | C A R B O N D A L E | B U F FA L O at a significant reduction in cost, materials, and efforts.■

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Table 1. Comparing classic with hybrid suspension.

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18 STRUCTURE magazine

Table 2. Comparing hybrid suspension options versus as-built for three long-span bridges.

Compared bridge element

Izmit Bay

Great Belt

Akashi-Kaikyo

Main span length L in feet (m)

5,085 (1,550 m)

5,328 (1,624 m)

6,532 (1,991 m)

Main cable sag (f/L)

1/8.7

1/9.37

1/10.64

S cable force of Hybrid option vs. as-built Classic Suspension

0.659

0.625

0.570

Main cable diameter as-built inch (mm)

41 (1,040 mm)

33 (827 mm)

44 (1,120 mm)

Main cable diameter Hybrid inch (mm)

33 (844 mm) 81%

26 (654 mm) (79%)

33 (846 mm)(0.76%)

Main cable as-built, tons (m. tons)

19,842 (18,000 m. t.)

20,008 (18,151 m. t.)

55,423 (50,279 m. t.)

Main cable with Hybrid, tons (m. tons)

13,076 (11,862 m. t.)

12,505 (11,344 m. t.)

31,613 (28,679 m. t.)

Savings with Hybrid, tons (m. tons)

6,138

6,807

21,600

Savings in tons in percent

34.1%

37.5%

42.9%

Main tower height reduction (m)

42.16

31.32

13.72

Classic suspension (as built)

12,059 (3,334)

13,685 (3,784)

21,812 (6,031)

Hybrid option

10,918 (3,018)

11,962 (3,307,)

17,859 (4,938)

Hybrid option vs as built

0.905

0.874

0.819

Total quantity q x t x ft x 1000 (q × m.t × m x 1000)

Note: Saving 34-43% of the main cables’ quantity while reducing their diameter by 19-24% is substantial.

Reducing the total quantity by 9.5-18% is also a significant savings.

This article is a continuation of Cable-Stayed Bridges, STRUCTURE, October 2020.

Roumen V. Mladjov’s expertise comprises structural and bridge engineering and construction management; his main interests are structural performance, seismic resistance, efficiency, and economy. (rmladjov@gmail.com)

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structural DESIGN The Long Road

Advancing First-Generation Performance-Based Seismic Design for Steel Buildings Part 1: Background and Motivation

By Matthew Speicher, Ph.D., and John Harris, Ph.D.

F

irst-generation performance-based seismic design (PBSD) principles are outlined in the latest edition of the American Society of Civil Engineers and the Structural Engineering Institute’s ASCE/SEI 41-17: Seismic Evaluation and Retrofit of Existing Buildings referred to herein as ASCE 41. These PBSD principles have evolved since being introduced in the Federal Emergency Management Agency’s FEMA 273: National Earthquake Hazards Reduction Program (NEHRP) Guidelines for the Seismic Rehabilitation of Buildings (FEMA 1997).

ASCE 41 provides analytical procedures and performance criteria to evaluate an existing building for a defined performance objective and to design seismic retrofit strategies if the criteria are not satisfied. This ability to explicitly define a performance objective and then assess a building against that objective has led practitioners to adopt ASCE 41 for use in new building designs to meet the intent of ASCE 7: Minimum Design Loads for Buildings and Other Structures, of which the latest edition is ASCE/SEI 7-16.

Using ASCE 41 for existing building assessment and new building design has created interest amongst researchers and design professionals about the consistency between ASCE 41 and ASCE 7 (NIST 2009).

Partially motivated to address this matter, the National Institute of Standards and Technology (NIST) initiated a study in 2010 to evaluate the first-generation principles of PBSD as applied to newly constructed steel buildings. A critical aspect of the NIST study was investigating whether the standards for designing new steel buildings and assessing existing steel buildings provide consistent performance levels. With the desire to advance performance-based design, the correlation between the performance of a building designed with the prescriptive provisions of ASCE 7 and assessed with the performancebased provisions of ASCE 41 was largely unknown.

Part 1 of this three-part series provides background on the history of PBSD, compares PBSD with traditional design approaches, and gives an overview of the motivation and outcomes of the NIST study.

This overall series will discuss the past, present, and future work done at NIST to spur the advancement of PBSD.

Performance-Based Seismic Design ASCE/SEI 7-16 Section 1.3 essentially allows two options for the design of a building: 1) a strength-based (or its alternative stress-based) procedure that follows the provisions provided in ASCE 7, or 2) an alternative performance-based procedure. The stated goal of the latter procedure is to give a system “reliability” generally consistent with targets intended to be achieved in the first option; these targets are given in ASCE 7. Since the provisions for the strength-based procedure are prescribed in ASCE 7, this type of design is commonly referred to as prescriptive design.

ASCE 7 prescriptive design requires a building to have adequate strength and stiffness to preclude various limit states (e.g., buckling, yielding, fracture, etc.) and other unacceptable serviceability or functionality performance goals. Along with the prescriptive design designation, this type of design approach is commonly referred to as a limit state design. Moreover, since these attributes are assessed via performance requirements, in the pure sense, prescriptive design can be thought of as a type of performance-based design. ASCE 7 can be considered a performance standard since it prescribes minimum design loads and associated performance criteria. As such, for a defined hazard, prescriptive design represents one point on the performance continuum for a building.

Figure 1. Mapping of ASCE 7-10 and ASCE 41-13 seismic performance objectives based on risk category.

20 STRUCTURE magazine

Similarly, performance-based design is also a limit state design. In particular, for PBSD, a building is designed with defined reliability levels so as not to be damaged beyond certain limit states at specified seismic hazard levels. These limit states are determined based on fundamental mechanics, experimental and field observations, and engineering judgment considering the consequences of the damage associated with these limit states. Generally, consequences are categorized in terms of deaths, dollars, and downtime to assess the following risks implicitly or explicitly: • total or partial collapse of a building; • loss of life or life-threatening injuries to building occupants or the public-at-large; • interruption of building function or occupant mission, either short- or long-term; and • direct economic losses from damage to the building and/or its contents and indirect losses by interruption of provided services.

In the heuristic sense, PBSD provides a way to understand the design of a building and the associFigure 2. Illustration of building performance when subjected to increased earthquake intensities. ated risks that such a design may pose, thus giving a rational estimate of building performance in a future earthquake. PBSD explicitly enables the upfront selection of per- standardization of first-generation PBSD principles in ASCE 41 can formance targets at specific earthquake hazard levels, which results be traced from FEMA 273 as follows: in a clearer expectation of the outcome and greater flexibility in the • FEMA 356, Prestandard and Commentary for Seismic design process (Figure 1).

Rehabilitation of Buildings (FEMA 2000) Understanding the link between the performance objectives of ASCE 7 • ASCE/SEI 41-06 Seismic Rehabilitation of Existing Buildings • ASCE/SEI 41-13 and 41-17 Seismic Evaluation and Retrofit of and ASCE 41 is an integral part of the discussion. In Figure 1, the Existing Buildings seismic hazard used by ASCE 7 (2010 edition and later) is ground • ASCE/SEI 41-23 Seismic Evaluation and Retrofit of Existing motions producing a 1% probability of total or partial collapse in 50 Buildings (under development) years, referred to as the risk-targeted maximum considered earthquake The performance continuum utilized in ASCE 41 is illustrated in (MCER). This hazard has a conditional probability of 10% collapse, given that an MCER event occurs. As such, protection against loss of Figure 2, with each performance level associated with a damage state. life by preventing a collapse of the structural system is the primary In practice, ASCE 41 is one of the referenced standards in the life safety objective (referred to as collapse prevention). ASCE 7 then International Existing Building Code (IEBC) (ICC 2021) to assess the takes two-thirds of this hazard as the “design earthquake.” At this seismic performance of an existing building. ASCE 41 is also utilized level, the secondary life safety objective is that the performance of in some cases in the design of new buildings. For example, ASCE 41 non-structural components is critical to protect life and injuries, is referenced in the following documents: and there exists a margin of safety against collapse (referred to as life • ASCE 7-16, Chapter 16 safety). It is inferred that a building will have a higher performance • An Alternative Procedure for Seismic Analysis and Design of Tall level than life safety for earthquakes occurring more frequently than Buildings Located in the Los Angeles Region (LATBSDC 2020) the design earthquake.

• Guidelines for Performance-Based Seismic Design of Tall Buildings ASCE 41 uses the same terms to define the target performance of (PEER 2017) the structural system but uses different terms to define the target • PBS-P100: Facility Standards for the Public Buildings Service performance of the non-structural system. Therefore, if one wants to (GSA 2018) equate the objectives of the two standards, collapse prevention at the ASCE 41 is a deterministic type assessment procedure; either someMCER is the common performance objective, as the two-thirds factor thing does or does not satisfy the criteria. In recognition of this, FEMA does not result in uniform risk across the nation. Furthermore, ASCE supported the development of “next-generation” PBSD principles, 7 focuses on the performance at the system level, whereas ASCE 41 published in FEMA P-58, Seismic Performance Assessment of Buildings focuses on the performance at the component level. Consequently, (FEMA 2015). FEMA P-58 focuses on evaluating performance “in in the context of linking the two standards, a valid question is what terms of the probability of incurring casualties, repair and replacepercentage of components need to fail the collapse prevention per- ment costs, repair time, selected environmental impacts, and unsafe formance level defined in ASCE 41 to achieve a 10% probability of placarding.” FEMA P-58 provides a probabilistic performance assesscollapse given an MCER event? Questions like this may help enhance ment framework that can be used to explicitly evaluate seismic risks, how PBSD can support risk assessment. relying on fragility and consequence data.

Both ASCE 41 and FEMA P-58 continue to evolve to advance PBSD of buildings. For example, ASCE 41 is currently making refinements State-of-Practice of PBSD to component modeling parameters and capacities for buildings idenASCE 41 continues to be the go-to standard for implementing tified in Recommended Modeling Parameters and Acceptance Criteria first-generation PBSD principles to evaluate existing buildings. The for Nonlinear Analysis in Support of Seismic Evaluation, Retrofit, and O C T O B E R 2 0 21

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Figure 3. Example workflow and results for ASCE 41 nonlinear dynamic analysis.

Design (NIST 2017). Similarly, as new component performance data is generated, updated fragility and consequence functions enhance FEMA P-58. Still, comprehensive efforts to support the application of these two approaches within ASCE 7 are needed.

NIST PBSD Study The NIST study started by designing a set of archetype steel buildings utilizing the prescriptive methods prescribed in the then-current ASCE/SEI 7-10. The archetype design space consisted of 4, 8, and 16-story buildings utilizing special moment frames (SMFs), special concentrically braced frames (SCBFs), eccentrically braced frames (EBFs), and buckling restrained brace frames (BRBFs) as the seismic force-resisting system (SFRS). The buildings are assumed to be in an area of high seismicity and are assigned to Seismic Design Category D as defined by ASCE/SEI 7-10. Each system was designed twice, once with the equivalent lateral force procedure and another with modal response spectral analysis.

The next part of the study involved evaluating the performance of the same structural systems using the different assessment procedures prescribed in ASCE 41. The current standards were used at the time of the respective portions of the NIST study; thus, ASCE/SEI 41-06 was used to assess the SMFs, SCBFs, and EBFs, and ASCE/SEI 41-13 was used to assess the BRBFs. A comparison of the assessment outcomes relative to the level of analytical sophistication was made using the linear static, linear dynamic, nonlinear static, and nonlinear dynamic procedures. Ultimately, the data generated was intended to spur improvements to future editions of ASCE 41, encouraging more confidence in its application. Detailed information regarding this study can be found in the NIST Technical Note 1863 series, Assessment of First Generation Performance-Based Seismic Design Methods for New Steel Buildings (Harris and Speicher 2015a, 2015b, 2015c; Speicher and Harris 2020).

In general, assessment using ASCE 41 (using the respective editions as noted above) tended to show the SFRSs had several challenges in meeting each performance objective. For example, in several cases, the nonlinear dynamic procedure indicated the SMFs had unacceptable performance, illustrated in Figure 3. This finding begs the question of whether the ASCE 41 assessment is overly conservative or if the ASCE 7 design is deficient. To this end, a follow-up study was conducted to verify the probability of collapse of the archetype buildings using FEMA P695, Quantification of Building Seismic Performance Factors (FEMA 2012). Investigating the performance of the SMFs, Speicher et al. (2020) demonstrated that the structural designs do, in fact, meet the objective of ASCE 7-10, suggesting that the respective version of ASCE 41 (in this case, ASCE/SEI 41-06) is conservative for the buildings studied.

22 STRUCTURE magazine

Conclusions PBSD is being used in practice to assess the seismic performance of existing buildings and is increasingly used to design new buildings to satisfy multiple performance levels to meet or exceed the intent of ASCE 7. This article highlights several points of discussion related to the similarities and differences between prescriptive design and performance-based design. Prescriptive design using ASCE 7 can be thought of as one point on a performance-based design continuum.

Assessment using ASCE 41 enables access to more points on this same continuum.

However, the two standards differ in that ASCE 41 evaluates the performance of components, and ASCE 7 designs components for system performance. The starting point for identifying inconsistencies between the two standards is most logical at the collapse prevention performance level considering the maximum considered earthquake.

The constraint of modern design techniques is that a system is defined as the sum of its components. Consequently, component-based limit state design can be inadequate in conveying the consequences of component performance on system performance, limiting its applicability to risk assessment.

The NIST study provides quantitative data demonstrating the inconsistencies between ASCE/SEI 7-10 and ASCE/SEI 41-06 or ASCE/ SEI 41-13. The steel archetype building assessments are found to often result in conservative outcomes when ASCE 41 is applied.

Ultimately, this research has helped spur a critical assessment of the provisions of ASCE 41 and motivated further research to advance the state of practice of PBSD. Part 2 in this series will detail the NIST study’s technical results, which looked at the four structural steel systems introduced previously. Part 3 will discuss the future of PBSD in practice, including its relationship to resilience-based design, which aims to quantitatively support community resilience. With the rise in interest in designing for functional recovery after an earthquake, PBSD will likely be a critical methodology to evaluate the impact of service interruption on the building occupants and the community that the building serves.■ Full references are included in the online PDF version of the article at STRUCTUREmag.org.

Matthew Speicher is a Research Structural Engineer in the Earthquake Engineering Group at NIST. John Harris is the Acting Deputy Director of NEHRP and a Research Structural Engineer in the Earthquake Engineering Group at NIST.

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structural CONNECTIONS Anatomy of a Mass Timber Bearing Intersection

By D. Scott Nyseth, S.E., and Jason Smart, P.E.

P

roper design of bearing intersections between mass timber members is critical to the overall success of a mass timber project. The details of these intersections have a significant effect on cost and schedule. This article focuses on the multi-story column condition, where loads from the column above need to be transferred down through the beam-column intersection, and the beams are supported using a bearing pocket instead of a bearing hanger (Figure 1).

Column Load Transfer

For maximum bearing capacity, wood columns should bear directly on wood columns end-to-end because wood is strongest when bearing parallel to the grain.

For example, if a wood column were to bear directly on a wood beam below, the intersection would have about ⅓ the bearing capacity because compression design values perpendicular-to-grain are lower than compression design values parallel-to-grain.

For efficient member sizes, consider a detail where Constructability an upper column bears directly on the lower column, When initially installed, cambered beam ends may need and a beam also bears on the lower column (Figure 2). special cuts to allow them to sit tight in the bearing Wood columns designed in accordance with the National pocket. Sealing/protecting ends of beams and columns Design Specification® (NDS®) for Wood Construction can is critical because the ends of these members have the have a maximum unbraced length-to-depth ratio of potential to absorb water if wetted during construc50 (up to 75 during construction). Shorter wood coltion, causing swelling and damage to the intersection. umns are controlled primarily by bearing area. Wood Computer Numerical Control (CNC) tolerances are columns used in typical structures must be upsized to small for most cuts, copes, and drillings (⁄16 to ⁄8 control column slenderness and buckling. This means inch); however, they are larger for longer slots that that there is typically more bearing area than required at need to be cut for items such as knife plates (⁄8 to ¼ Figure 1. End column with the ends of a longer wood column, allowing the design inch or more). CNC machine tooling for preparing beam bearing pocket. to incorporate beam pockets in the column without beam pockets and tenons are typically round cutting upsizing the columns. bits; therefore, the resulting surfaces will have rounded surfaces that For column-to-column compression load transfer or any other need to be addressed in the design. parallel-to-grain bearing, NDS 3.10.1 states that “bearing shall be on In the absence of a diaphragm, beam-column intersections should a metal plate or strap, or other equivalently durable, rigid, homogehave some lateral capacity for bracing and racking loads during erection neous material with sufficient stiffness to distribute the applied load” and for leveling and plumbing of the beam-column frame. Column to utilize the full compressive capacity of the wood for bearing. For stability is crucial for projects that use a concrete diaphragm instead end-to-end bearing where a rigid insert is required, NDS 3.10.3 allows of a Cross-Laminated Timber (CLT) diaphragm. In this scenario, the use of a 20 gauge or thicker metal plate placed between bearing multiple stories of columns, beams, and floors can be erected before surfaces to avoid a 25% reduction in bearing capacity. Without the the structural diaphragms are in place. This requires special design bearing plate, a 25% reduction in bearing capacity directly affects the attention, especially at exterior columns. In addition, the contractor amount of wood that can be removed for the beam bearing pocket. needs to provide additional shoring for these columns to stabilize the structure until the concrete diaphragm is in place.

Beam Bearing Pocket Intersections

Figure 2. Column-to-column bearing surface.

24 STRUCTURE magazine

The depth of a beam pocket is often limited by the tooling for a CNC machine. A common limitation is that the beam pocket must be less than or equal to 6 inches deep. This means that the pocket width is the only variable that can be changed by design to make the bearing area large enough for the beam reaction. Therefore, narrow beams with relatively large reactions are not a good combination for a beam bearing pocket intersection.

Beam bearing pocket intersections do not necessarily have a positive connection to the column during installation. Therefore, consideration should be given to provide some type of connection to provide stability during construction. In addition, connections will need to allow the top of beams and floor to shrink down around the columns so that the

bearing on the pocket is not restricted and detailing should address relative movement of the beams and columns so that elements, such as façades and mechanical, electrical, and plumbing (MEP) systems, are not damaged.

fire-resistance rating required of the members or assemblies. As provided in Section 2304.10.1 of the 2021 International Building Code (IBC), fire resistance for protected connections in Type IV-A, IV-B, and IV-C mass timber construction must be determined either: 1) through a standard Movement ASTM E119 or UL 263 fire-resistance For a wood beam bearing on its bottom test in which the protected connection surface, the top of the beam will settle is part of the tested assembly, or 2) downward. The top of beam movement through engineering analysis demcomes from two sources, shrinkage due onstrating that specified temperature to the moisture content change of the rise thresholds are not exceeded within wood and compression of the wood the connection. fiber due to bearing (Figure 3). A rule of Under the engineering analysis thumb is that wood beams may shrink option, calculations must be performed 1% of depth for every 4% of moisture to show that the average temperature Figure 3. Deformation at beam bearing. content change. rise at the interface between the protecAssuming that wet or “green” timber beams would not be used, tion and the connection itself does not exceed 250 degrees Fahrenheit specify timber beams with a maximum wood moisture content of and the maximum temperature rise at any location on that interface 19% (MC19) at the time of manufacture. Glued laminated timber does not exceed 325 degrees Fahrenheit. Both temperature thresholds (glulam) beams are manufactured at a maximum moisture content coincide with conditions of acceptance specified in ASTM E119, of 12% (MC12). pertaining to tests of protective membranes in fire-resistance-rated It is not uncommon for interior building conditions to create assemblies. It is important to note that these temperature limits repmoisture content in wood as low as 5% in an arid environment. As resent temperature rises – or increases above ambient temperatures an extreme example, a 36-inch-deep timber beam with 19% moisture content may shrink 1¼ inches, while a 36-inch-deep glulam beam with 12% moisture content may shrink 5/8 inch, based on 1% shrinkage for every 4% moisture content change.

When evaluating the compression-perpendicular-to-grain strength and deformation of beams, designers should be aware that the ASTM test for this value involves a 2-inch square steel plate bearing on the wood top surface and full-bearing of the wood on the bottom surface, which is different than the wood-on-wood bearing condition where a beam is compressed from roughly equal size bearing on opposite faces (see Characterizing Perpendicular-to-grain Compression Behavior in Wood Construction by Craig Thomas Basta, Rakesh Gupta, Robert J. Leichti, and Arijit Sinha).

For beams loaded on opposing faces, the potential for buckling perpendicular-to-grain is a design consideration for evaluation of strength in addition to bearing (see NDS Commentary). The combined shrinkage and bearing movement also needs to be addressed. In the bearing intersection described in this article, the mass timber floor and beam are detailed to move downward around the column without compromising any of the connections. At roof conditions where wind uplift is a concern, fully threaded 45-degree screws at the top of beams are not an option, as the beam bearing and shrinkage require the freedom of the beam to shrink and take the full bearing load at the base of the beam (Figure 4). This is especially important for fire resistance.

The beam must have full bearing on the column to prevent the formation of any gaps that would allow char intrusion into the beam bearing area.

Fire Design Where the code requires structural members or assemblies to have a fire-resistance rating, structural connections between the members must be protected for a time not less than the

Figure 4. Uplift anchors restraining shrinkage and bearing.

O C T O B E R 2 0 21

25

before fire exposure. It should also be noted that these temperature-rise criteria apply not only to the connection hardware but also to the fasteners and portions of wood members included in the structural design of the connection.

The penetration of ignition into gaps formed by char contraction at unbonded wood member ends and edges must also be addressed. At any given exposure time, ignition is assumed to extend into these gaps at twice the char rate, resulting in a penetration that is twice the char depth, achar, of the wood (2achar versus achar). Protection must be detailed to ensure that no part of the connection, including all previously described components, is exposed to elevated temperatures due to char contraction.

Connection protection may be provided Figure 5. Uncharred bearing interface on the bottom of the beam after a 2-hour fire test. by additional wood cover, Type X gypsum panels, other approved materials, or any combination of these Elimination of char intrusion into the bearing seat is a significant materials. American Wood Council’s Technical Report 10 (TR 10) advancement in the design and economy of this type of bearing conCalculating the Fire Resistance of Wood Members and Assemblies pro- nection. The reduced bearing area must still be accounted for using vides guidance to designers on how to estimate thermal separation a depth of achar instead of 2achar, as shown in Figure 5. The American times provided by wood and gypsum panels in order to demonstrate Wood Council’s newly released 2021 Fire Design Specification (FDS) compliance with the temperature rise limits specified in the engineer- for Wood Construction provides additional design guidance, including ing analysis option of IBC Section 2304.10.1. For protection from an adjustment factor of 1.67 for fire design of bearing perpendicularadditional wood cover or Type X gypsum panels to be effective, char to-grain. The FDS is available on AWC’s website at www.awc.org. contraction of the wood or contraction of the gypsum panel must also be addressed. TR 10 includes examples of how the design of Conclusion this protection is achieved. Notably, recent testing has shown that this gap formation due to char contraction does not occur at bearing A beam-to-column bearing connection, where minimal connection intersections between structural members where the members stay in hardware is used, is an excellent option for designers and contraccontact due to loading (Figure 5). As shown in the graph (Figure 6), tors. Understanding the shrinkage of the beams and how each floor char depths measured at the bearing interface are generally equivalent will move down around the columns as the beams shrink is critical to the char depths, achar, calculated in accordance with the NDS. As a to detailing the connections of the building’s components to the result of this testing, the guidance regarding gap formation due to char structural frame. Understanding and allowing for rounded corners contraction need not be applied to the design of bearing intersections at CNC pockets and tenons will eliminate expensive additional that are even lightly loaded. labor to create square corners. It is important for the design team to have requirements for the submittal of a temporary bracing plan, as the diaphragm and beam-column type significantly affect stability during construction.

Finally, proportioning the correct beam and column sizes to provide adequate bearing through the beam-column intersection (preand post-fire) and eliminating any obstructions or restraint that might prevent full bearing at the intersection starts at the earliest stage of a project. The connection type will dictate a specific layout of the column grid and will likely not be possible to implement on a project where the structural grid is set without the specific bearing connection in mind.■ D. Scott Nyseth is President of Stonewood Structural Engineers, Inc. in Portland, OR. (scott.nyseth@stonewoodstructural.com)

Figure 6. Char depth versus time for bearing intersection.

26 STRUCTURE magazine

Jason Smart is Director of Fire Engineering at the American Wood Council. (jsmart@awc.org)

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structural RESILIENCE Adapt and Transform COVID-19 Lessons for a More Resilient Future

By NCSEA Resilience Committee

“Since 2002, the U.S. has endured seven of the 10 most costly disasters in its history, with Hurricane Katrina and Superstorm Sandy topping the list. As a result, there is a need for best practices for resilience planning that address the increasing value-at-risk of U.S. infrastructure and communities. Communities, as a system, are particularly vulnerable to the effects of natural and human-caused disruptive events. Reliance on rebuild-as-before strategies is impractical and inefficient when dealing with persistent hazards. Instead, communities must break the cycle by enhancing their resilience with a systemic view of short- and long-run time horizons.”

NIST Special Publication 1197 – Community Resilience Economic Decision Guide for Buildings and Infrastructure Systems

T

he Federal Emergency Management Agency (FEMA) and, by extension, the architectural engineering profession have embraced the four-phase disaster management cycle as a framework for improving community resilience through capacity building (Figure 1). If cities heed all phases of the disaster management cycle by directing funds or resources to each phase, the presumption is that they will be better able to tolerate and recover from future natural and human-caused disasters. Unfortunately, the COVID-19 pandemic represents a natural disaster that has stress-tested the disaster management cycle. We have witnessed profound political, social, and economic disruptions associated with the constant vacillation between the response and the recovery phase as society struggles to “flatten the curve” and manage infection rates across the county. In this article (first in a series), we contemplate the suitability of the disaster management cycle as a framework to define and enhance community resilience to disasters.

In response to society’s adaptation to a moving recovery target, we consider an alternative disaster management cycle that reflects lessons learned during the COVID-19 pandemic and discuss its application to natural hazards. We introduce the concept of adaptive resilience: the ability to implement immediate changes that minimize the impact of disruptive forces associated with a disaster while working to transform the built environment, real-time, using systems thinking. We also discuss the critical role of a structural engineer in applying advocacy, education, and transformative design solutions to the built environment to enhance community resilience.

Re-Thinking the Disaster Management Cycle Corona Virus Disease 2019 (COVID-19) caused by SARS-CoV-2, a novel (i.e., not previously identified) coronavirus, emerged in December 2019 in Wuhan City, Hubei Province, China. By January 30, 2020, the World Health Organization declared the COVID-19 epidemic an international public health emergency. The scope and 28 STRUCTURE magazine

Figure 1. Disaster Management Cycle.

magnitude of this crisis have exacerbated systemic inequities, disrupted global supply chains, burdened local healthcare capacity, and significantly changed human life and livelihood. How society is applying disaster management techniques in response to this crisis provides ample opportunity to explore ways to improve crisis management for future disasters.

FEMA’s Four Phases of Emergency Management (FEMA 2006), otherwise referred to as the disaster management cycle, includes: preparation, response, recovery, and mitigation. These phases are defined as: 1) Preparation: Activities undertaken in advance of an emergency to develop and enhance operational capacity to respond to and recover from an emergency.

2) Response: Activities conducted to save lives and prevent harm to people and property during an emergency.

3) Recovery: A return to normalcy after a disaster or emergency incident.

4) Mitigation: Any sustained action taken to reduce or eliminate long-term risk to people and property from natural or human-caused hazards and their effects.

The graphic representation of the cycle presented in Figure 1 proportions each phase in the cycle for illustrative purposes only; actual phase duration/effort may vary relative to others. For example, extensive mitigation and preparation guided by community performance goals would limit response and recovery phases.

During the COVID-19 pandemic, we have observed a transition from the response to the recovery phase during a pandemic is unlike the transitions for other natural hazards (earthquake, hurricane, landslide, etc.). Most natural disasters last for a finite time before the immediate threat dissipates (e.g., the storm passes, the ground stops shaking, the floodwaters recede, and the fires are contained). Once the disaster is contained and the damage is triaged, the community can transition from response Figure 2. Disaster Management Cycle during COVID-19.

to recovery. This process is challenged by the state. In some cases, the pre-disaster state COVID-19 pandemic, where society oscilcould leave the community vulnerable to The response to the lates between recovery and response over an future hazards until the mitigation phase recovery phase during extended period. This creates an opportunity is complete. We want to shift the recovery to define and deploy a new phase into the goals to focus on both short-term and a pandemic is unlike long-term time horizons. COVID-19 and FEMA cycle. natural disasters have similarly indicated The cycle associated with the COVID-19 the transitions for that a return to “normal” is not good pandemic more closely aligns with the cycle enough (Hurricane Katrina is an exemshown in Figure 2, where an additional phase, other natural hazards... plary natural hazard for this statement). adapt, occurs between response and recovery.

Adaptation encourages innovative ways The adapt phase covers the period of prolonged to consider new targets for functionalduress, where localities are in a hyper-situaity and how best to construct societal tional state of awareness and are attempting infrastructure to achieve satisfactory results. The authors to slow continued damage and “flatten the curve.” At the same time, recognize that “building back better” may have traditionrecovery efforts adjust to help approach an “end” to the event cycle ally fit that paradigm. Still, in many cases, that approach so that mitigation can start anew. For the COVID-19 pandemic, the increases recovery time, which may undermine societal adapt phase aligns with continual management of restrictions and needs or desires to recover as quickly as possible. Ideally, the messaging until the vaccine can instigate a broader herd immunity so preparation phase includes strategies that consider adaptathat schools, restaurants, etc., can safely open and “normal” activities tion scenarios post-disaster, thereby minimizing the recovery can resume, in some cases at pre-event levels. time following an event.

The adapt phase also has application to disaster management for 2) Replaces the mitigate phase with a transformation phase. natural hazards. After an earthquake or hurricane, for example, it is The term mitigate insinuates risk reduction for the subject feasible that affected populations will live in temporary structures disaster. The term itself assumes that existing operational stanwhile their homes are being rebuilt, but the primary threat has been dards (e.g., building codes) are adequate. While this approach significantly reduced. This is a clear transition from the response works well for known hazards and low-level recovery targets, phase to the recovery phase, with a relatively short adapt phase. For it does not address new hazards or changing paradigms associthe COVID-19 pandemic, society is caught between phases when ated with a range of recovery targets that are acceptable to an infection rates fluctuate. As soon as a city assumes transition to recovaffected community. Transformation intends to broaden the ery, businesses open back up and individuals relax their attention to goal of disaster management beyond mitigation into strategies recommended precautions. As a result, the cases go up and force the that include deployment of new technologies, resiliencecommunity back into a response phase. Arguably, during COVIDfocused planning that considers diversification of critical 19, the recovery phase is only possible post-vaccine/herd immunity, infrastructure in terms of power sources, utility transmission, effective when the threat is significantly diminished. The reference to reconstruction strategies beyond “rebuild in place.” This may recovery, in this case, assumes a return to normal, which is not possible also include deploying innovative solutions that are implewithout a vaccine, herd immunity, or protectionist policies (closing mented or enforced before a disaster occurs. borders to goods, services, restricted travel, etc.).

3) Considering the goal of Resilience itself. A critical evaluaFigure 2 is limited since the insinuation that society cannot advance tion of the disaster management cycle, as it relates to the built to recovery unless a vaccine is widely distributed is not realistic infrastructure, illuminates a need for the building industry with regards to the concept of adaptive resilience. While we have and policymakers responsible for the vaccines for the COVID-19 virus, what built infrastructure to shift disaster about the next pandemic? We want to management and planning toward imagine a disaster management cycle a future-focused target that actuthat applies to all disasters, including ally considers a constantly changing health-related disasters that were previenvironment. While adaptation is ously not considered so widely spread inherently included in the definition and debilitating. of resilience, the distinction between With this in mind, we want the resilresilience and adaptive resilience lies ience planning community to consider in the definition of the recovery goal. an alternative framework for disaster Adaptive resilience is future-focused management. This alternative framework and implores an evolution or iteratakes the vaccine (or guaranteed end of tion of the practitioners’ approach, the disaster) out of the equation and considering all conditions and applyactively manages the recovery process ing systems-thinking to determine through resilience planning and design. the best target that considers societal Figure 3, the alternative disaster management cycle, accomplishes three primary Figure 3. Alternative Disaster Management Cycle post-COVID-19. expectations and needs while avoiding “replacement in-kind” thinking. The objectives: concept of adaptive resilience represents the ability to imple1) Replaces the recovery phase with an adapt phase. This ment immediate and future changes that minimize impacts recharacterization of the post-disaster phase strives to take of disruptive forces, whether from a pandemic or a natural a future-focused approach to recovery. The term recovery disaster, in short-term and long-term time horizons. insinuates a return to normal aligned with the pre-disaster

continued on next page O C T O B E R 2 0 21

29

Structural Engineer as an Advocate and Educator

Figure 4. Port Sulphur Schools (2015).

Ultimately, Figure 3 recalls the roots of resilience theory – the idea that true resilience is observed in the ecological context. Biodiversity (or, in this case, diversity of physical, economic, social systems) enhances the community’s ability to return to an acceptable quality of life while growing, learning, and applying new technologies and the changes they bring. Evolution (i.e., adaption) ensures the survivability of the species.

What This Means for the Structural Engineer

A structural engineer is typically focused on designing a building to meet their client’s needs and ensuring the design meets the requirements of the building code.

As a result, most owners do not participate in defining building performance objectives in various natural hazards but default to the building code, assuming it will provide adequate performance. Unfortunately, many building owners and members of the public do not understand that the building code is focused on minimizing loss of life and does not consider postdisaster recovery.

Structural engineers should discuss post-event performance with their clients and include them in the design process so that they understand that a code-compliant building will be safe but may not be habitable following a natural disaster. These discussions should include real scenario examples that incorporate business interruption costs and recovery costs associated with the loss of building functionality following a natural disaster. Some improvement in post-disaster business recovery can come from planning to reduce downtime (i.e., business continuity plan). In addition, structural engineers can educate themselves on emerging technologies and strategies that can be included in the building design process and enhance long-term building performance in a cost-effective fashion.

There are different general definitions of resilience depending Structural Engineer as a Transformative Thinker on perspective (ecological, psychological, disaster management, engineered) and scale (individual, institutional, community, local, Designing for functional recovery or other performance targets is regional). Some widely accepted definitions of resilience, like that considered a transformative approach to structural engineering design developed by the National Academy of Sciences, focus on “the ability and assessment. Areas affected by Hurricane Katrina present some to prepare and plan for, absorb, recover from, and more success- excellent examples of transformative thinking from which we can fully adapt to adverse events” (NRC 2012). Practicing structural learn. On August 29, 2005, Hurricane Katrina made landfall in engineers play a vital role in making communities more resilient Plaquemines Parish, Louisiana. The associated winds gusted up to 115 through the design and construction of the built environment using mph, bringing a 13-foot storm surge that left a path of destruction, recovery-based performance objectives. Resilience is dependent on and inherent to communities rather than individual buildings. It is focused on community functionality, which requires operational infrastructure and building space rather than just protection of built space. It is measured over time rather than in terms of property damage (Bonowitz, 2020 EERI Distinguished Lecture). The concept is eloquently described in the FEMA/NIST functional recovery report (FEMA P-2090/NIST SP-1254): “…we don’t just want to preserve life, but we want to preserve quality of life”.

In addition to reevaluating how we design buildings, structural engineers need to embrace the multi-disciplinary aspects of community resilience. Many strategies described in this article require input and implementation by other stakeholders (e.g., policymakers, the public, planners, emergency responders, architects).

True resilience can only be achieved through a cross-disciplinary, collaborative, community-focused approach.

There are two ways that structural engineers can affect community resilience: 1) structural engineer as an advocate and educator, and 2) structural engi- Figure 5. The Plaquemines Parish new medical center patient care areas are 23 feet above grade.

Emergency vehicle ramp (background) provides direct access at the second level. neer as a transformative thinker.

30 STRUCTURE magazine

devastating local communities. The hurricane caused over 2,000 casualties and over $200 billion of economic losses. In addition, the school campus at Port Sulfur, Louisiana, suffered extensive hurricane damage associated with storm surge and debris impact.

Instead of “recovering” to existing (pre-hurricane) conditions, the school district adopted an adaptive reconstruction approach. Climate risk and building functionality were considered for the replacement campus. The school district recognized that the replacement campus should withstand storm surge and hurricane wind forces in future events to reduce the operational downtime post-disaster.

The newly completed elementary school campus in Port Sulphur includes elevated classrooms and associated facilities (Figure 4).

While this was a transformative design approach for this specific location, it is a simple design philosophy that can be applied to all disasters. In the case of Plaquemines Parish, this transformative design approach was applied to critical services buildings that include a medical center (Figure 5), a community center, a high school, and teacher housing.

References are included in the online PDF version of the article at STRUCTUREmag.org.

The National Council of Structural Engineers Associations (NCSEA) Resilience Committee was founded to develop positions and recommendations on issues in the emerging field of resilience-based planning and design. The members represent SEAs throughout the U.S., working together to infuse resilience thinking into the practice of Structural Engineering. (ksmoore@sgh.com)

Concluding Thoughts

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COVID-19 has shown us that our strength lies in our capacity for adaptive resilience. Unlike other natural disasters, the virus has affected the global community, with quality of life disrupted by process change instead of physical (infrastructural) damage. The duration of negative consequences to society is significant and prolonged because the singular event recurs and prevents a return to acceptable levels of function. Considering the broader effect on society, COVID-19 has challenged the conventional disaster management framework and illuminated the need for incorporating adaptive resilience into an effective strategy. The pandemic and its aftermath will undoubtedly shift the way we approach disaster management in the future, recognizing how these lessons will inherently promote a more humancentric, health-focused approach. This adaptive resilience approach has implications that translate to the traditional “building back better” recovery strategies. We now may consider building back differently, including techniques and methods that may transform the built environment to better accommodate societal needs following natural disasters. Follow-on articles will explore certain indicators that served as a proxy for the effects of the pandemic on the health of the economy, where one can draw parallels to disaster recovery theory and explore ways to adapt and improve resilience to a disruptive event.■

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building BLOCKS Test-based Available Strengths for Aluminum Structures Part 2

By James LaBelle, P.E., Doc.E.

This is Part 2 of a two-part series. Part 1 (STRUCTURE, September 2021) summarized two methods, including equations for finding available strengths for aluminum based on tests. It also includes plots of calculated safety factors for various conditions. Part 2 compares results from these methods. Please note that Figure numbering continues from Part 1.

T

his second part continues the exploration of Methods 1 and 2 in the 2020 edition of the Specification for Aluminum Structures (Appendix 1; section 1.3) for determining available strengths based on testing.

Comparison of Method 1 and 2 Results Refer to Figures 6 through 9 for plots of the ratio of allowable strengths (ASD) from Method 1 to corresponding values from Method 2 for the sets of variables considered. The same legend (Figure 9) for coefficients of variation applies to each plot.

Quantities include: • RTM: average (mean) test load • R1Ω: Method 1 allowable load • K: statistical coefficient • CV: coefficient of variation • Ω: Method 1 safety factor, from the Specification • R2SF: Method 2 allowable load • m1 = R1Ω / RTM = (1–KCV) / Ω: for Method 1 (see Equation 2 in Part 1), as used for plots.

• m2* = R2SF / RTM = 1/ SF2*: for Method 2 (refer to Equation 7 in Part 1). Here the asterisk indicates that the larger of the calculated safety factor (SF2) and the minimum safety factor (the applicable Ω in the Specification) is used.

Each plotted point corresponds to the ratio m1 / m2*. Each plotted line (“curve”) represents a value of CV, which ranges from 4% to 20%.

Table of bounding values of m1 / m2* for LRFD.

Case

Beam Rupture Tension-Member Rupture Tapping-Screw Connections Welded Connection

Minimum

Maximum

m1 / m2*

m1 / m2*

9%

89%

10%

89%

8%

89%

13%

113%

Figure 6. Ratios of allowable strengths: beam rupture.

The smallest CV is the top line in each figure. The number of samples (N ) extends from 7 to 50.

The target reliability indices, βo (equal to 2.5, 3.0, and 3.5) used in Method 2, correspond to failure probabilities for a 50-year load recurrence of 0.621%, 0.135%, and 0.023%, respectively. Values of βo are given at the top of each figure. For those cases where the Method 1 available load is less than that of Method 2, the failure probability is also less.

As an example (Figure 6: beam rupture), for a set of test specimens with CV = 12%, N = 18, and K = 3.370, the non-dimensional ratios m1 and m2* are equal to 0.305 and 0.513, respectively. Thus, the allowable strength for Method 1 is 30.5% of the test average, and for Method 2, it is 51.3% of the test average. Therefore, m1 / m2* = 0.596, which indicates that R1Ω (the Method 1 allowable strength) is 59.6% of R2SF (the Method 2 allowable strength).

For Method 1 (Equation 2), note that if KCV > 1.0, R1Ω would be negative and thus not a physically usable value. For such a KCV value, no R1Ω meets the criteria of 99% exceedance with 95% confidence. As an illustration, consider CV = 0.20, N = 6 and K = 5.062, for which KCV = 1.012. This is a limitation on Method 1’s range of applicability.

Method 2 does not have this limitation, but it requires a minimum N of 4 versus Method 1’s minimum of 3. Also, Method 2 calls for continued on page 34

32 STRUCTURE magazine

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Figure 7. Ratios of allowable strengths: tension-member rupture.

Figure 8. Ratios of allowable strengths: tapping-screw connections.

three additional tests if any test value deviates from the average by more than 10%.

• Figure 7 (tensile rupture): from 10% to 91%.

• Figure 8 (tapping screw connections): from 8% to 89%.

• Figure 9 (welded connections): from 14% to 117%, which is the largest range.

For LRFD (not plotted), the ranges of the ratio m1 / m2* to the nearest percentage point are given in the Table. All individual LRFD ratios are less than or equal to and within a few percentage points of the corresponding ASD ratios. (The largest difference is 3.9%, for welded connections at N = 50 and CV = 4%.)

Ranges of Ratio m1 / m2* For ASD (Figures 6 through 9), the ranges of the ratio (m1 / m2*) of Method 1 allowable strengths to the corresponding Method 2 values are, to the nearest percentage point: • Figure 6 (flexural rupture): from 9% to 89%.

Overall Trends

Figure 9. Ratios of allowable strengths: welded connection.

34 STRUCTURE magazine

Figures 6 to 8 pertain, respectively, to the limit states of flexural rupture, tensile rupture, and the various failure modes (e.g., fastener tension, pull-out, pull-over, shear, etc.) for connections utilizing tapping screws.

• For these three figures, Method 1 allowable strengths more closely approach the corresponding Method 2 strengths when there is a combination of relatively low CV and large N. • As the number of samples (N ) increases while CV is held constant, Method 1 allowable strengths tend toward those of Method 2.

• For a given N and a decrease in CV, Method 1 allowable strengths also tend toward the corresponding Method 2 strengths.

Figure 9 (welded connections) is an exception. Here, for 4% ≤ CV ≤ 8%, all of the 4% curve and most of the 6% and 8% curves exceed 1.0; i.e., the Method 1 allowable values exceed the corresponding ones from Method 2. This is partly due to the combination of a small and medium CV with a relatively large value of VF (0.15 vs. 0.05) in Method 2. Also, for these three curves at m1 / m2* > 1.0, both a decreasing CV and an increasing N cause the Method 1 allowable strengths to be increasingly larger, on a percentage basis, than the corresponding ones of Method 2.

Small N and Large CV

References are included in Part 1’s online version of this series at STRUCTUREmag.org.

For test sets consisting of a relatively small number of specimens (e.g., 7 to about 12) and which have a large coefficient of variation James LaBelle is a Consultant with experience in the design and (e.g., 15% and 20%) for the test strengths, it is evident that the use investigation of aluminum and other structures. He is retired from CSD of Method 1 entails a substantial “penalty” as compared to Method 2.

Structural Engineers, Milwaukee, WI, and is a member of the Aluminum Recall that Method 1 utilizes a progressively larger factor (K; see Association’s Engineering Design Task Force, FGIA (formerly AAMA), and Figure 1 in Part 1) to address the inherent uncertainty associated ASTM. (jlabelle@csd-eng.com) with small N. If CV is also large, then the combined effect on the allowable strength is quite substantial.

Consider a hypothetical case (tension member rupture; Figure 7) where initial testing includes four specimens. At least one specimen is found to have a strength that differs from the average by more than 10%. Thus, per Method 2, three more samples are tested for a total N = 7. The CV for N = 7 is determined to be 15%. For Method 2, the allowable strength R2SF = 0.406 RTM. For Method 1, the allowable strength (R1Ω) is 0.156 RTM. Therefore, the ratio m1 / m2* = 0.384; the Method 1 allowable strength is 38% of the Method 2 allowable strength. If additional speciESR-3617 mens are tested, the test average and coefficient of variation could be similar to the values for seven specimens. If so, then the allowable strengths would Quick and easy to install increase. Try eight more specimens for from one side a total N = 15. Here, R2SF = 0.429 RTM and R1Ω = 0.242 RTM. These results Designed for standard reflect a 5.6% increase in Method 2’s clearance holes allowable strength and a 55% increase for Method 1. Also, Method 1 allowA fully removable blind able strength would rise to 56% of that for Method 2 (i.e., m1 / m2* = 0.565). fixing available for

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As these comparisons have demonstrated for the cases considered, Method 1 available strengths are generally smaller (more conservative) than the corresponding ones of Method 2. However, Method 1 involves fewer input parameters and is easier to use than Method 2.

The available strength differences can be large, especially for a combination of a small number of specimens (N) and a large coefficient of variation (CV). An exception occurs for welded connections, for most or all N at CV of 4% to 8%, for which Method 1 available strengths are larger than those of Method 2. This is due to a large VF (fabricationvariation parameter) for welded connections.■

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O C T O B E R 2 0 21

35

engineer's NOTEBOOK Approximate Structural Analysis

By John A. Dal Pino, S.E., and Larisa Enachi

E

ngineers routinely need to analyze and design indeterminate structures. Today they would use any one of several analytical software packages commonly loaded on their computers.

The programs are so powerful that it does not take long to develop the input and perform the analysis, even for a major building. Sifting through the output and finding the desired answers might be the greatest effort involved.

However, before the regular use of computers (sorry for the history lesson, but it was not that long ago), the analysis method of choice was the moment distribution method, developed in the 1930s by Professor Hardy Cross of the University of Illinois. Besides being a clever analytical concept, it has an One-story, two-bay frame, with pinned base, under gravity load. inherent simplicity and physical logic that is easy to grasp. It works like this for analyzing a structure with an approximate answer to an indeterminate problem is good enough. continuous beams with multiple supports: 1) every beam-column joint Engineers appreciate that, with ever smaller powerful handheld comin the structure is assumed to be fixed from rotation and appropriate puters, the “right answer” is never that far away. However, there fixed-end bending moments are applied to the joints, and 2) then are many times when calculating an approximate answer, while at each fixed joint is released sequentially, and the fixed-end moments, a job site, on the way home from work, or away from the office, is which at the time of the first joint release are not in equilibrium, are something an engineer needs to do because that is all that is really distributed to adjacent members. The process of fixing, releasing, and needed at the time. re-distributing bending moments is repeated many times until an As is discussed later, these approximate analytical techniques are the equilibrium is reached or until the engineer decides that the amount foundations of structural engineering. Of course, today’s engineers can of undistributed moment is small enough to ignore. consider loading conditions that prior generations knew about but Whether the engineer is working today or in the past, getting the lacked the tools (or the computational desire) to evaluate. They can right answer, or better yet, a “precise” answer (since there is never a also study the post-elastic response of a structure subjected to a suite “right answer”) to the problem, may involve more effort than the of actual earthquake ground motions, with the computer churning engineer wants to exert or has the time or budget to spend. Often, away while they take a long lunch.

One-story, one-bay frames, subjected to lateral load.

36 STRUCTURE magazine

When it comes to hiring entry-level engineering staff, many employers look for candidates having the very advanced knowledge discussed above. But more importantly, they want engineers with solid educational backgrounds who have the ability to think on their feet and quickly assess and solve problems without needing to perform a computer analysis, which, as is commonly known, is just an approximation. Being able to cut through the clutter and get an answer that is in the “ballpark” is highly valued by employers but hard to teach. To underscore the point, how many times has an engineer gotten a confusing answer from a computer model and then needed to go back to first principles to figure out what was wrong and how to fix it? Like troubleshooting a finicky automobile, an engineer needs to assess what is working and what is not using handy and One-story, two-bay frame, with a fixed base, subjected to lateral load. trustworthy tools.

This article discusses four different indeterminate structures that are encountered regularly in engineering primarily from a lateral shearing action or primarily from a lateral practice and that firms also use in their entry-level employee inter- bending response. Once this is done, the rest is just math. views, namely: Lateral Analysis of One-Story, One-Bay Frames 1) Lateral analysis of a one-story, one-bay frames.

2) Gravity analysis of a one-story, two-bay frame There are three variations of this simple structure: a) a pinned base with a pinned base. with beam and columns of approximately equal stiffness, b) a fixed 3) Lateral analysis of a one-story, two-bay frame base with beam and columns of approximately equal stiffness, with a fixed base. and c) a fixed base with a rigid beam and two flexible columns 4) Lateral analysis of a multi-bay, multi-story, of approximately equal stiffness. Assume there is a lateral load slender high-rise frame. applied at the beam level, there is no gravity load, the members It would be fair to say that many older, experienced engineers believe have infinite axial stiffness, the shear in the columns is equal, and that solving these issues quickly and approximately is part and parcel the members have no mass. of being an engineer and would wonder why an interviewer would ask For all three conditions, the first step is to identify the counter-flexure an applicant engineer about these situations. But for those not involved points in the beams and columns. Start this process by drawing the in hiring, it would be surprising to know how many engineers, many deflected shape for each structure. Going back to the job interview educated at our most prestigious universities, have trouble with these process, many applicants have difficulty with the rotation of the beamconcepts, even after accounting for some degree of nervousness and column joint and the curvatures of the beam and column at the joint. the pressure of a job interview. Maybe these concepts are not taught Rather than applying the forces to determine the moment and rotaanymore, or the amount of time allotted to teaching them is too short. tion, they guess and get it all backward. However once the curvatures In either case, this does a disservice to our engineering graduates. Most are drawn correctly, the counter-flexure points can be located. This firms have the capacity to train engineers in more advanced analyti- creates a determinate structure, and the shears and bending moments cal and design techniques. However, if the new hire’s foundation in in the beams and columns can then be determined. The pinned-base statics and mechanics is lacking or weak, more advanced tasks are structure produces the largest bending loads because the base (say the more difficult to learn. ground) helps the least. The fixed-base, rigid-beam structure has equal top and bottom bending moments and the least column bending.

The fixed-base, flexible-beam structure falls somewhere in the middle.

Analyzing the Indeterminate Structure The inflection points in the columns are near (or slightly above) midSolving statically determinate structures is straightforward because height, creating the potential for slightly higher bending moments basic statics can be employed, namely the summing of forces in in the columns than that for the fixed-fixed structure, depending on the x and y directions (for 2-D systems) and the summing of rota- the relative stiffnesses of the beams and columns. Since the analysis tional moments (caused by the applied forces) about a point. Solving is approximate, it is also acceptable to assume the inflection point statically indeterminate structures is mainly the task of turning the is at mid-height. indeterminate structure into a determinate structure. This is done One might wonder – why spend so much time on such a simple by making simplifying assumptions about the location of inflection structure? The answer is that these are the potential conditions for the points (also known as points of counter-flexure) in structural elements first story columns in many kinds of buildings: a structure without that are bending under load (either due to gravity or lateral loads) a basement or any base rigidity, a structure with a basement and and judging whether structures subjected to lateral loads resist loads “normal” second-floor framing, and a structure with a basement and

O C T O B E R 2 0 21

37

by drawing the deflected shape of the structure using the same logic as for the one-bay frames. Assume the inflection points are at mid-length of the beams and mid-height of the columns. This sets the counterflexure points. This creates a determinate structure, and the shears and bending moments in the beams and the shears, bending moments, and axial loads in the columns can then be determined. A fixed-base structure replicates a building with a basement where the columns extend downward to the basement floor level or a building without a basement but with a rigid grade beam system near the surface grade intended to provide column base fixity. A pinned base would replicate a building without a basement or one with a minimal flexible grade beam system.

Lateral Analysis of a Multi-Bay, Multi-Story, Slender High-Rise Frame

Multi-story, multi-bay, slender high-rise frame.

very rigid beams at the second floor. The required sizes of the columns, and the beams but to a lesser extent, can vary greatly.

Gravity Analysis of a One-Story, Two-Bay Frame with a Pinned Base The structure is a one-story, two-bay frame with unequal beam spans.

Assume there is gravity load applied at the beam level, there is no lateral load, the members have infinite axial stiffnesses, and the members have no mass.

It would take a long time to analyze this structure with hand calculations, and it would take a fair amount of time (allowing for a few modeling errors), even with a computer. As with a one-bay frame, the first step is to identify the counter-flexure points in the beams. Start this process by drawing the deflected shape of the beams. Once the beam curvatures are drawn, the counter-flexure points can be located. The beam design aids in the American Society of Steel Construction’s (AISC) Steel Construction Manual show the inflection points for fixed-fixed beams. The inflection points near the center column are more similar to the fixed-fixed condition. Since the exterior beam-column joints rotate to some extent, the inflection points are closer to the columns. The columns do not have inflection points due to the pinned base condition. One should exercise some judgment here, remembering this is an approximate analysis. Adding the inflection points creates a determinate structure, and the shears and bending moments in the beams and the shears, bending moments, and axial loads in the columns can then be determined.

Lateral Analysis of a One-Story, Two-Bay Frame with a Fixed Base A variation of the previous structure is a one-story, two-bay frame with equal beam spans with only lateral loads due to earthquake loads at the floor level. As with the one-bay frame, assume there is no gravity load applied at the beam level, the members have infinite axial stiffnesses, and the members have no mass.

The interior beam-column joint is roughly twice as stiff rotationally as the exterior joints (two beams compared to one beam), so assume that the interior column resists twice as much shear as the exterior columns. This is the basic assumption in the portal frame method.

As with the other structures discussed above, the next step is to identify the counter-flexure points in the beams and columns. Start this process

38 STRUCTURE magazine

For the last structure, a tall, slender building of indeterminate height is examined. The height does not really matter so long as the building is considerably taller than it is wide. The predominant response to lateral loading is flexural bending of the tower as opposed to shearing action.

Assume lateral loads due to earthquakes are applied at each floor level in a triangular shape with the centroid at ⅔ of the height, H; there is no gravity load applied at the beam levels; the beams have infinite axial rigidity; the columns have equal axial stiffnesses; and, the members have no mass.

Rather than identifying the counter-flexure points in the beams and columns as with the other structures whose response is predominately a shearing action, assume the tower bends like a cantilevered pole extending from the ground. Due to the lateral loads only, the columns on one face of the tower are in tension, and the columns on the other face are in compression. For the example building with three columns, sum the moments about the center column (the neutral axis) and determine the axial column’s loads. This simplification is the essence of the cantilever method. Statics dictate that the center column gets no axial load from the lateral load condition.

Suppose the structure has more columns, assuming that plane sections remain plane in bending. In that case, the columns will sustain axial loads proportional to their distance from the neutral axis at the centerline of the building.

If the inflection points are assumed at the mid-lengths of the beams and mid-heights of the columns, the beam and column bending moments and shears can then be determined. Tall buildings have large column axial loads; it would be fair to simply add those to the column’s loads already determined based on tributary area.

Conclusion The ability to determine approximate answers to complicated problems is handy in the real world of engineering. Engineers will be amazed at how much respect they earn when they can provide a contractor with a quick answer in the field without having to go back to the office to figure it out, or when they can, in just a few minutes, help another engineer troubleshoot a computer model that has been frustrating them for several hours. The basics never go out of style and are reliable tools if learned early and well.■ John A. Dal Pino is a Principal with FTF Engineering located in San Francisco, California. He serves as the Chair of the STRUCTURE Editorial Board. (jdalpino@ftfengineering.com) Larisa Enachi is a Designer at FTF Engineering and successful participant in its interview process. (lenachi@ftfengineering.com)

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historic STRUCTURES Eden Train Wreck Dry Creek Bridge Failure

By Frank Griggs, Jr., Dist. M.ASCE, D.Eng, P.E., P.L.S.

O

n the Denver & Rio Grande Railroad running from El Paso on the Rio Grande River through Pueblo to Denver, Colorado, the World’s Fair Flyer was traveling southerly towards Pueblo on the early evening of August 8, 1904, during a severe storm. At approximately 8 miles north of Pueblo, the line crossed an arroyo (generally dry creek bed).

The arroyo was about 100 feet wide and 14 feet deep with steep banks.

A trestle had been built on wooden bents to cross the arroyo and on August 26, 1904, the Railway Age wrote, “...a wooden structure, consisting of three spans, each 32 feet in length, and resting upon four bents. Numbering the bents from north to south, one and four consisted of posts standing on blocking and caps above supporting stringers, ties, and rails. Bents two and three consisted of seven piles driven 13 feet into the bottom of the channel and sawed off Dry Gulch with Pullman cars on the edge of bank and water subsided.

6 feet below the surface. On top of these piles rested a sill 12 × 12 and fastened to them with two drift bolts, each ¾-inch in diameter and 36 A wall of water reportedly hit the front of the train as it was passinches long, driven through the sills into each of the piles. Resting on ing over the trestle and carried the engine, baggage car, smoking car, the sills of each bent and extending to the cap above were seven 12 × 12 and chair car (a car with better, more comfortable seats) into the posts, each fastened to the sills with two drift bolts ¾-inch in diameter floodwaters. The two passenger cars were carried downstream by and 22 inches long, driven through the sides of the posts obliquely into the floodwaters, drowning most of the passengers. The engine was the sills. The outer posts on each side of the row of seven rested on the submerged near the bridge; the chair car was found almost a mile sides at an acute angle to afford the structure greater horizontal or side from the bridge buried in sand, and the baggage and smoking cars resistance. On top of the posts were placed caps 16 × 16, which were were found more than 4 miles downriver. fastened to them by two drift bolts ¾-inch in diameter and 26 inches Of the hundred or more people in the two cars that plunged into long, driven through the caps into the top of each post. The stringers the torrent, only three escaped along with the fireman on the engine. were each 8 inches × 10 inches × 32 feet best Oregon timber. Four of The three did so through the fractured roof of the smoking car and these were bolted together and placed under each rail, making eight in swam to shore. The fireman was thrown free of the locomotive. David all stretching from bent to bent. The ends of the stringers were joined Mayfield, the fireman, later stated, by butt joints. Resting on the stringers were the ties and on these the “We did not expect anything at all. We were going along at a good rails. The outer one of each set of four stringers was fastened to the cap speed all the time and never dreamed that anything was wrong. We below by means of a ¾-inch bolt, with [a] nut on each end, which bolt thought that if there were any kind of a flood near Eden, the operator passed through the cap, stringer, and tie above.” there would know, and he would flag us. We passed there but saw no A trestle with two bents in the waterway was standard practice for signals of any kind and never felt any fear… this kind of inexpensive bridge. The bridge had been in place for I scarcely know how it happened, as I was dazed in the mud on the bank years with no signs of weakness. From the record, it does not appear of the creek. It all happened so quickly – and, my God, it is so terrible. A that any significant flooding had taken place during its lifetime. On little while before we reached the bridge that crosses Dry creek, I turned to August 9, 1904, the Colorado Springs Gazette wrote, Charley Hinman, the engineer, and said to him: ‘Charley, is there enough “The engineer, Charles Hinman, had been given a thunderstorm cau- steam to carry us to Pueblo?’ Charley said, ‘No,’ and I began firing up. tion and had slowed the train to 10-15 mph to watch for washaways.

Just as I was putting the second shovelful of coal in, the engine gave After the engine had crossed the creek, a large wave threw the cars a lurch upward. I lost my balance and was thrown from the train on over to the right, broke the coupling to the rear 2 Pullman and dining the bank of the creek. I must have struck partly on my head, as I was cars, and dragged the engine backwards into the river. The Pullman’s dazed and did not know what happened for several minutes. When I porter, Melville Sales of St. Louis, quickly came to, I saw the Pullman cars standing near pulled the emergency air brakes saving the me but could not see the engine or the rest remaining passengers. The front Pullman car of the train. I went up and down the stream was left hanging four feet over the edge of looking for my partner, Charley, the engineer.

When the first crash came, we what remained of the bridge.”

I didn’t notice whether water was running in It is thought that a county road bridge that over the trestle as we approached the bridge were riding along as smoothly had failed upstream was pushed downstream but, when I was thrown out, the water was as one could go…It was just as and may have impacted the Dry Creek Bridge, much higher than the tracks.” contributing to its collapse. However, it is One of the survivors later wrote, “When though the train had struck unclear if the wave of water that hit the train the first crash came, we were riding along as was associated with the upstream bridge smoothly as one could go…It was just as though a stone wall. impacting the Dry Creek Bridge. the train had struck a stone wall. The lights went

40 STRUCTURE magazine

out, the fixtures and everything fell down, and the passengers were thrown forward, and there were the most awful cries for help and the grinding of timbers. I saw the man next to me was down, and I helped him up, but just then, another crash came, and the train seemed to sink about five feet. I lost sight of everybody and couldn’t think of anything but to save myself. I remember well the sensations that I had at that time. I knew I was in terrible danger, and my first thought was that I must get out of the car. At the second crash, I was about up to my waist in water. All the time, the grinding and crushing of timbers was going on. In another crash, I was thrown about a third of the length of the car right up against the front door. I grabbed the top of the door, and the car went over in the water three times. My first instinct when the water went up over my head was to hold my breath. I think I was under water for a full minute.

The car naturally righted, and when it came up, the water was just about my lips. I could breathe all right and saw the transom was just above me.

With my right hand, I smashed out the glass, hoping that I could get out in that way. At that moment, another crash came, and I was struck in the forehead by some floating object and dazed, but managed to keep my head above the water and after a terrific struggle reached the shore.”

When all the bodies were recovered, about 100 persons had drowned in the arroyo, which a few hours later was dry once again. A Pueblo newspaper reported, “Deep gloom has settled down upon the city today following the railroad horror, which snuffed out a hundred or more lives yesterday. Many business houses are closed out of respect to the dead, and more than forty private homes are darkened and in mourning.”

On August 19, the Railway Age quoted J. A. Edson, the Manager of the Denver & Rio Grande, who said, “…the company was in no way responsible for the wreck at Eden, Colo., on the night of August 7. ‘It was one of those unavoidable accidents which are liable to occur on any railroad when a flood of the character that washed out our bridge occurs.’ said Mr. Edson. He further stated, says the dispatch, that the bridge was subjected to regular inspections of the company’s bridge superintendent and was as safe as any other on the Denver & Rio Grande, or, in fact, on any road, and that no bridge could have withstood the torrent that destroyed this one. The under bents of the bridge, he said, were undoubtedly knocked asunder by the washed-out county bridge, thereby leaving no support.”

As was typical in these crashes, a coroner’s jury was convened. They met for 11 days and submitted their 11 findings on August 21, 1904.

They decided, (1) The water not being over the tracks at the bridge, but several inches below the banks, neither the engineer nor the fireman could possibly see it. The track being in line and level, nothing wrong with the bridge could possibly be seen by them. When the first impact took place, the Pullman passengers were not thrown forward out of their seats, besides positive testimony on the point, shows the train was running slow according to order, and the crew is therefore blameless.

(2) If the county bridge was a factor in the destruction of bridge No. 110-B, the railroad company was to blame for not constructing a bridge that would avoid or withstand its impact as it knew the county bridge was there.

(3) Had a bridge of one span on abutments with no obstructions in the channel of the stream to obstruct the flow of water or passage of debris, or stone arches of 110 feet, it would have in all human probability withstood the force of both the volume of water and the impact of the county bridge (if the latter took place) and the catastrophe would not have occurred.

(4) Bridge No. 110-B was not of the best class of bridges used by railroads throughout the country.

(5) Inspection close up to the time of the wreck showed bridge No. 110-B to be in its usual condition. Its weakness consisted, not in its condition, but in the cheap, inferior class to which it belonged.

(6) Had the heavy downpour in the vicinity of Eden at 7:13 pm been reported to the train dispatcher at Pueblo, he might have delivered additional caution orders to No. 11 at Buttes before she left at 7:30, and the disaster might have been averted.

(7) The conductor of No. 7 reported water over the track two miles south of Eden on arrival at Pueblo at 7:55 pm and a downpour at Eden and had a night or operator been stationed at Wigwam, eleven miles from bridge No 110-B, or at Pinion, five miles from it, train No. 11 could have been warned, and the disaster averted.

(8) Had a regular system of track-walkers and flagmen, independent of the section men, been maintained by the company over the track in question, especially in the afternoons, evenings, and nights during the rainy season, No. 11 could have been flagged, and the disaster averted.

(9) Had bridge No. 110-B been under charge of the section gang at Eden, one mile away, instead of the one at Pinon, five miles away, No. 11 would have been flagged, and the disaster averted.

(10) Bridge No. 110- B should have been so constructed as to withstand all the water the arroyo could accommodate. On the night in question, the arroyo accommodated all the water that came down, but the bridge collapsed.

(11) If bridge No. 110-B had been a one-span metal bridge with stone abutments, the probability of damage by the county bridge would have been much lessened. Therefore, the jury finds that the appalling loss of life and property at bridge No. 110-B on August 7, 1904, was due to the negligence of the Denver & Rio Grande Railroad Company as set forth in the foregoing statement of findings and conclusions.

Newspaper headlines following the findings included, RAILROAD IS RESPONSIBLE FOR THE EDEN DISASTER Jury Brings in Set of Vigorous Findings, That the Bridge was not the right class, That there Was No Regular System of Trackwalkers, That D. R. G. was Negligent.

Lawsuits were filed, and the total loss to the Company amounted to almost $250,000 for the lives lost, with some bodies never found.

There is no doubt of the seriousness of this disaster. Still, the Coroner’s Jury findings #3 and #11 that a single span bridge would have prevented the failure is not provable, as many single span wood and iron bridges had been washed out during major storms around the country. Finding #4 is also questionable, as the bridge appeared appropriate for the loads placed on it. It could be argued that it was an Act of God, and the magnitude of the flood and the washing out of a bridge upstream could not have been foreseen. As to #5, it was not a cheap, inferior class of bridge but one that was appropriate for the site on which it was built.

In summary, the sequence of events leading to the failure could not have been planned. In a failed bridge upstream, riding on a flood of unheard-of proportions hitting the bridge at the moment a train was passing over, it was not, and probably could not, have been designed.

It should also be pointed out that Coroner’s Juries did not normally have trained engineers on them but were local laypersons who were, after investigating the failure and talking with survivors and experts, called upon to make an engineering judgment. The other judgments they made were very reasonable given the perfection of hindsight.■ Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He is now an Independent Consulting Engineer. (fgriggsjr@twc.com) O C T O B E R 2 0 21

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In-Situ Evaluation of Old Pan-Girder Bridges

By Nur Yazdani, Ph.D., P.E., F. ASCE, F.SEI, F.ACI, and Eyosias Beneberu, Ph.D., P.E. Figure 1. Metal pan form.

T

he Texas Department of Transportation (TxDOT) employs various concrete bridge superstructure options depending on span length, traffic, and future crossing requirements. Among these, pan-girders were a popular choice in the 1950s and 1960s as a viable alternative for short-span bridges due to their speed of construction, low labor requirements, and cost-effectiveness. The name “pan-girder” came from the pan-shaped formwork that was used in construction. The formwork consisted of an upper semicircular cross-section with straight ends on the bottom of each side (Figure 1). Pan-girder bridges were cast using self-supporting metal forms that spanned between bent caps. Multiple pans could

be placed next to each other to form a concrete web. They were connected with bolts that passed through holes on the sides of the forms (Breña, 2001). The pan forms supported the dead weight of the reinforcement and wet concrete, thus eliminating the need for shoring and falsework.

There are about 4,000 pan-girder bridges still in service in Texas, mainly designed for AASHTO live load designations of H10, H15, H20, HS15, and HS20 trucks. Even though they were originally designed for lesser loads, many pan-girder standards rated out at acceptable levels for HL-93 loading. The standards designed using the lightest AASHTO design loads (H-10 and some H-15) usually did not have an acceptable load rating at the HL-93 level. The decline in the use of pan girders occurred prior to the introduction of the HL-93 design load. Over time, pan-girder construction became labor-intensive, with much time dedicated to tying reinforcing and placing concrete in the pan forms. As the precast industry expanded in Texas, the cast-in-place bridge superstructure types fell out of favor due to economic reasons. With the advent of the heavier current AASHTO HL-93 design load (AASHTO 2011), the use of pan-girder bridges declined even more.

Due to a large number of these types of bridges, pan-girder bridges have been investigated for overall safety assessment and rehabilitation using external composite laminates. Because the bridge pans were not perfectly straight, fresh concrete could flow through gaps between adjacent forms during casting, leaving an irregular surface on the bridge webs. While this irregularity had no impact on the bridge performance, it can influence the placement of composites used to strengthen the bridges. This means composites could not be placed in the middle of the web Figure 2. EB US 80 Bridge over the frontage road top view (map data: ©2018 Google). without first doing some significant surface preparation, increasing labor cost and construction time (Breña, 2001).

For the study discussed here, an in-situ evaluation was conducted of the East Bound (EB) US 80 pan-girder bridge (Figure 2) over a frontage road in Forney, Texas, through visual inspection and condition assessment. TxDOT recommended the inspections to catalog the current bridge condition in order to Figure 3. Detail along the transverse section.

42 STRUCTURE magazine

undertake future load rating and any strength- Table of EB US 80 Bridge condition summary. ening that could be necessary. It is a 10 span Damage Beam Numbers and 252-foot-long bridge constructed in 1955.

Exposed aggregate 6 At each bent, there exist three separate bent Chipped concrete 3 (2), 11 (4), 6, 7, 10 caps. The first, second, and third bent caps support one, 10, and 3 beams, respectively.

Concrete crushing at support 2, 7, 11 (2) The bridge was widened in 1978 when one Delamination 11 beam (Beam 1) was added to the north and Hairline cracks 1, 2 (2), 3, 4 (2), 5 (2), 6 (2) 7 (3), 9 (3) 8, 10 (2), 11 (2), 13 (2) three beams (Beams 12, 13, and 14) were Honeycombing 10 added to the south of the existing bridge.

Longitudinal crack along crest 6, 7, 8, 9 (2), 10, 11, 13, 14 Figure 3 shows the typical detail along the transverse section of the bridge.

Exposed rebar 6, 7, 11 (2) A detailed visual inspection plan was preConcrete scaling 2, 3, 7 (4), 8, 9, 10 (3), 11 (4) pared, and the structural elements were Concrete spalling 2, 7, 11 (2) evaluated for visible signs of distress, damage, Water damage 1 (8), 2 (9), 3 (10), 4 (10), 5 (10), 6 (10), 7 (10), 8 (10), 9 (10) and deterioration. Various types and levels of damage that could jeopardize the overall health and serviceability of the bridge’s structural elements were located The presence of form lowering holes at the crest of the pan girders and cataloged. Deteriorations included, but were not limited to, at quarter-span and mid-span of the girders could be the reason for hairline cracks, concrete crushing and spalling, and water damage. water damage, as the water seeped through the holes. Efflorescence Observed damages are summarized in the Table. Beam numbers are was visible in the form of white and gray residue, which occurs progressive from north to south. Identical beams in various spans when the calcium salts from concrete react with water and air to showed similar levels and types of damage, and these repetitive form insoluble calcium carbonate. This phenomenon is harmful damaged numbers of beams are shown in parenthesis after the cor- to concrete as salt can increase concrete permeability and induce responding beam numbers. For example, 3(2) indicates that beam corrosion of steel rebars. Corrosion propagated from the drainage number three in two spans showed an identical type of damage. In areas in most of the girders, and a few beams had exposed rebars. addition, it is apparent that most beams sustained some form of Rebars were exposed and corroded in some of the beams around the water damage at mid-span, as shown in Figure 4 (page 44). form lowering holes. Such corrosion could occur due to the water ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

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Figure 4. Water damage at mid-span.

Figure 5. Condition in newer beams.

seepage from the holes, which caused concrete scaling and spalling.

However, no corrosion was observed in the primary longitudinal reinforcement, located at the bottom of the stem. If present, corrosion in the rebar could potentially affect the load-carrying capacity of the beams.

It may be noted that beams 1, 12, 13, and 14 displayed little or no water damage. These beams were added in 1978 during the bridge expansion, while the other beams were in service for about 23 additional years. The four newer beams were in much better shape and did not show any extensive visible deterioration and/or water damage (Figure 5). The new bent caps used for the widening were connected to the existing bent caps with dowel bars for continuity.

Beam 11 was the most severely damaged in all spans, with practically all the deterioration mentioned in the Table. Water damage was visible in this beam at every quarter-span location in all spans.

Samples of deterioration are shown in Figure 6. This could be caused by the fact that Beam 11 was on the exterior side before the bridge widening; after widening, it became an interior beam that increased the load it carried and aided in the damage process.

a)

b)

The following recommendations, which can be applied to this and other pan-girder bridges, were made based on findings of the field inspection: 1) A PVC pipe can be glued on the form lowering holes extending beyond the concrete surface of the arch. This will prevent water seepage through the holes and minimize water damage, spalling, and scaling of concrete.

2) Pan-girder bridges were usually designed for a load lighter than the current AASHTO HL-93 live load requirement. Therefore, it is recommended that appropriate load testing, load rating, and analyses be undertaken for such bridges, especially older ones with significant deterioration, to verify the loadcarrying capacity and adequate structural safety.

3) Appropriate retrofitting and repair techniques may be used to upgrade deficient pan-girder bridges with extensive deterioration. For example, experience has shown that externally bonded Carbon Fiber Reinforced Polymer (CFRP) laminate is a viable method for strengthening concrete bridges in general (Mohanamurthy and Yazdani, 2015; Pallempati et al., 2016) and also for under-capacity pan-girder bridges.

Thus, such rehabilitation methods may be suitable to upgrade deficient pan-girder bridges.

In conclusion, the study conducted herein showcased common deteriorations and distresses in a typical pan-girder bridge. The results indicate it is essential to conduct a detailed visual inspection on similar bridges to understand their current condition and undertake strengthening if they are deemed to be unsafe.■ Full references are included in the online PDF version of the article at STRUCTUREmag.org.

Nur Yazdani is a Professor in the Department of Civil Engineering at the University of Texas at Arlington. (yazdani@uta.edu) Eyosias Beneberu is a Structural Engineer with Bridgefarmer & Associates in Dallas, Texas. (eyosias.beneberu@mavs.uta.edu)

c)

Figure 6. Deterioration in beam 11. a) Crushing of concrete; b) Longitudinal crack; c) Exposed and corroded reinforcement.

44 STRUCTURE magazine

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suitable to preserve. It had been repaired in the 1900s with brick rings, and a keystone was inscribed with that date. Five alternative project approaches were presented, ranging from a minimal renovation to a complete replacement with a pre-cast concrete arch.

Ultimately, the bridge owners opted for a major renovation with reinforced concrete to strengthen the historic arch. The phase that followed included both preliminary and final design of the recommended alternative and preparation of right-of-way plans.

Preserving the Stone Arch The project team’s goal was to maintain the existing stone arch while providing an alternate The cracked and deteriorating historic bridge before restoration. structural system to carry traffic loads. A rigid frame was constructed in direct contact above the stone arch to accomplish this. The rigid frame system consists of a concrete rib that follows the existing arch line and a concrete slab that functions as the roadway surface for the bridge. The new frame was constructed by installing falsework under the existing arch barrel, removing the wearing surface and earth fill, and then constructing the new frame on top of the existing arch.

The contractor’s falsework was a series of steel W16 beams, couplers, and posts with diagonal bracing, which supported 3-inchthick timber planking placed just below the B Y M ATT L EWELLYN , P.E. stonework. After mats of epoxy coated rebar were tied into place, the arch rib was formed he East Burke Street Bridge is an important vehicular and pedes- and poured directly on top of the existing stone barrel. The concrete trian connection between downtown Martinsburg, West Virginia, rib was bonded to the stone using an epoxy bonding agent, applied and neighboring residential areas. Equally important as the bridge’s before the pour. Next, gravel fill was installed to fill the voids within function is its rich history dating back to the Civil War. Believed the concrete frame, and the concrete slab was constructed on top to be originally constructed in 1861, the bridge survived a Confederate attack that destroyed an adjacent bridge and other buildings.

Structural deficiencies, including unstable wingwalls, loss of mortar, sidewalk settlement, and missing, cracking, or loose stones were identified in 2010. As a result, the City of Martinsburg and the West Virginia Department of Transportation (WVDOT) sought a solution that would increase load capacity while retaining the historic aspects of the structure. This required a phased and tailored approach that allowed the team to work around the delicate condition of the historic parts of the bridge.

The City and WVDOT worked with design engineers Burgess & Niple using a multi-phased approach. The first phase included survey, mapping, geotechnical borings, condition inspection, hydraulic analysis, and preparation of a bridge renovation study. The initial study included document research to identify the bridge’s historic significance and indicated that the structure was most likely built in the 1860s. This information was used to compare alternatives for renovating and replacing the structure.

The inspection determined that the arch barrel of the A new reinforced concrete arch was designed and placed over the top of the existing arch to provide full live load capacity. bridge was the only portion of the structure that was

H S A R M A T

46 STRUCTURE magazine

of the fill, with the midspan portion constructed integrally with the arch rib.

Like a new bridge, this hidden structural system provided durability and increased load capacity.

The MIDAS Touch The rigid frame support system was analyzed using a MIDAS finite element model that considered construction staging and the effects of soil-structure interaction on the behavior of the frame. The keyed construction joints at the base of the concrete rib were considered classical hinges for the analysis model and were treated as pin supports. The rib and slab elements intersected at a reinforced “knuckle” region and were modeled as moment-continuous. The ends of the slab elements are supported by bearing walls at the abutments and were modeled as pin supports.

The compressive capacity of the existing stone arch was neglected in the analysis, and the existing stonework was included only as dead load. Forces extracted from the model were used to perform design computations for the frame. The frame was designed for the interaction of axial and bending loads, with particular attention given to the reinforcing details in the knuckle regions to control stress concentrations. Support reactions from the model were used to design the micropile foundations. Load combinations producing maximum vertical load, thrust, and overturning effects were identified to determine the controlling design condition.

East Burke Street Bridge MIDAS model.

Use of Micropiles Sensitive ground conditions, steeply sloped bedrock, and adjacent structures made micropiles a good option for the East Burke Street Bridge. A total of 41 micropiles support the forward abutment and parallel wingwalls. Load testing was performed to confirm that the maximum factored axial load of 154,000 pounds per pile would be adequately developed.

The rear abutment is founded on a spread footing placed directly on the bedrock.

Several of the 7⅝-inch-diameter micropiles were installed at an angle to accommodate both axial and lateral loads. The outer casing pipe and drill rods advance through overburdened soils to rock and continue to pile tip elevation. Drill rods and casing were added in 5- or 10-foot lengths. Drill cuttings travel up the inside of the casing using air and water and are discharged through a swivel on the drill head. The piles penetrate 10 feet into bedrock to provide the bond zone for the grout, which is placed through a 1-inch high-density polyethylene (HDPE) tremie pipe to the bottom of the hole.

A single number 11 reinforcing all-thread bar (Grade 75) was placed in the middle of the micropile.

The micropiles provided a strong foundation without using a more traditional driven steel H-pile that could have shaken the ground and caused damage to the stone arch barrel, which would be temporarily supported but still vulnerable to heavy vibration.

Burgess & Niple designed the bridge with micropiles instead of hammer-driven piles to reduce vibrations adjacent to the existing stone masonry.

Technology Helps Preserve History A high-definition survey scan provided a detailed point cloud of existing geometry for stone mapping. The scan was used to

The refurbished bridge used stone facing over the wingwalls and black metal fencing to create a similar aesthetic O C T O B E R 2 0 21

47

As the arch was unearthed, additional issues were discovered. Predictions made about the width of the existing foundation stones were not accurate. The stones were much larger and conflicted with the placement of the concrete foundation as designed. Trimming the stones was discussed, but the team decided not to risk disturbing the arch. Instead, Burgess and Niple adjusted the structural model to account for thrust of the larger span, and revised plans were issued to keep the project moving. This required three additional micropiles and additional battering of the piles.

History Preserved. Safety Restored

The East Burke Street Bridge arch as it is unearthed.

assess the condition of the material and arch structure and helped preserve as much of the viable stonework as possible. As a result, the arch barrel was cleaned and repaired with a lime mortar mix, cracked stones were repaired, and missing or damaged stones and bricks were replaced. In addition, the new concrete spandrel walls, wingwalls, and barriers were faced with stone masonry, some of which were reused from the existing walls. Thus, using the scan helped sustain as much of the bridge’s history and character as possible.

Project Challenges

Through this rehabilitation project, the City of Martinsburg preserved parts of the bridge’s history while increasing safety and load capacity for travelers. This intricate rehabilitation was achieved with several innovative strategies, such as the use of micropiles and high-definition survey software to address design and construction complexities. In addition to the project team’s approach to obstacles, including the proximity of the active railroad and weather-related disruptions, these strategies made this award-winning project a success.■ Matt Lewellyn is a Project Manager in the Burgess & Niple Parkersburg, West Virginia office. He is a national leader in bridge inspection, load rating, preservation, and rehabilitation. (matt.lewellyn@burgessniple.com)

Project Team

Owner: City of Martinsburg, West Virginia The project team faced several challenges during the construction Project Administration: West Virginia Department phase of the project. One of the most significant was the location of Transportation of the bridge approach under a railroad. To allow the railroad to Design Engineer: Burgess and Niple, Inc. remain operational during the rehabilitation, the contractor had Geotechnical Engineer: Terracon, Inc. to provide pre-construction photographs and video of the overGeneral Contractor: Orders Construction Co., Inc. passing railroad abutments and walls. During excavations, survey Micropile Contractor: Coastal Drilling East, LLC monitoring was performed to confirm there was no movement of the railroad structure. In addition, inspections were conducted following the excavation of each stone masonry course to ensure there was no distress caused to the railroad. If issues were observed, a corrective action plan was in place with materials and equipment on hand to immediately restore stability to the railroad. In the end, the action plan was not needed, which confirmed the assumption that the railroad bridge was structurally independent of the arch and supported directly on bedrock.

Another challenge was the amount of rain that fell during construction, causing the Tuscarora Creek that passes under the bridge to rise, resulting in delays. High water resulting from above-average rainfall totals conflicted with the placement of the temporary support structure. To resolve this, the construction team rerouted a portion of the flow around the structure’s footprint by excavating an alternate relief channel The East Burke Street Bridge following the renovation. in the east approach.

48 STRUCTURE magazine

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Adaptive Reuse of the Historic Witherspoon Building Part 2: Adaptive Reuse and Structural Investigations

By D. Matthew Stuart, P.E., S.E., P.Eng, F.ASCE, F.SEI, A.NAFE, SECB

T

his four-part series discusses the adaptive reuse of the Witherspoon Building in Philadelphia, PA (Part 1, STRUCTURE , September 2021). Part 2 includes a discussion of the ongoing adaptations during construction and the structural investigations conducted to better understand the existing structure. Numbered photos are provided in the print version of the articles; lettered photos are provided only within the online versions of the articles.

Adaptive Reuse This adaptive reuse project primarily involved the conversion of an office building to residential units.

The Architect of Record for the project was Deidre DeAscanis, AIA, with JKRP Architects, Philadelphia, PA. Initially, the difference between the minimum required live load capacity for the upper floors of Philadelphia office buildings in the early 20th century (60 psf ) as documented in the 14th Edition of the Architects’ and Builders’ Handbook by Frank E. Kidder (Figure 6) and the current-day live load required for residential areas (40 psf ) were utilized to allow for a 20 psf reserve load-carrying capacity at the upper floor levels.

Fifteen psf of the reserve loadcarrying capacity was dedicated to partition dead loads required by the current governing building code. The remaining 5 psf was dedicated for miscellaneous loads such 50 STRUCTURE magazine

as ceilings, mechanical, electrical, and plumbing dead loads. However, based on the results of an investigation of the 5th and 11th-floor framing, it was determined that the actual capacity of the typical floor beam framing was 100 psf, which provided even more reserve load-carrying capacity than that indicated by the comparison of the building codes.

In addition, earlier references similar to the Architects’ and Builders’ Handbook from the late 19th century indicate that the minimum live load for all floors of an office building in Philadelphia was 100 psf.

Table XLVI. Minimum Live Loads Required by Building Codes The minimum required live Minimum live loads per square foot of floor load capacity for the first floor of San Dept.

Philadelphia office buildings in the PhilaDenClasses of buildings New Boston Chicago Franof York delphia ver late 19th and early 20th centuries 1926 1928 cisco Com1927 1929 1927 1928 merce (100 psf ), as documented in the Dwellings..............

40 40 50 40 60 40 40 Architects’ and Builders’ Handbook, and was used for the evaluation of the 40 adaptive reuse of the first floor, Hotels, Tenements, 40 40 50 40 90 40 40 which included retail space, the and Lodging-houses, Hospitals 70 main entrance lobby, and residenOffice-buildings: tial areas. At the residential areas of First floor........... 100 100 125 125 120 125 100 the first floor, new loft areas were Other floors........ 60 60 60 40 70 40 50 made accessible from the first-floor School class-rooms 75 50 50 75 75 75 50 residential spaces below. At these Buildings or rooms for same areas, the combined loading public assembly: With fixed seats......

100 60 100 75 90 75 50 of two occupied levels of 80 psf Without fixed seats.

100 100 100 125 120 125 100 live load and 40 psf dead load (not Aisles and corridors. 100 100 100 125 120 125 100 including the dead load of the new Garages: Public........ 120 100 150 100 150 100 100 loft floor framing and access stairs), Private....... 120 100 75 100 150 100 80 for a total of 120 psf, exceeded the Warehouses............... 120 150 125-250 125-250 200 125-250 100-250 assumed existing 100 psf capacity Manufacturing: Heavy................. 120 200 250 250 250 250 100 of the first floor. This same assumed Light................... 120 120 125 125 120 125 75 100 psf load-carrying capacity Stores: Wholesale....... 120 110 250 250 120 125 100 established by the code research Retail............. 120 110 125 125 120 100 75 was also subsequently confirmed Sidewalks.................. 300 120 250 150 150 150 250 via the existing 1st-floor framing Figure 6. Reproduction of the data in the Frank Kidder minimum live load table. investigation.

As a result, independently supported loft floor framing was designed using ¾-inch Structural Panel concrete subflooring manufactured by USG. The subflooring spanned between cold-formed steel (CFS) joists supported by new wide flange steel beams that spanned between the existing Gray building columns. The 5% maximum gravity load increase allowed by the International Existing Building Code (IEBC) was used to justify the additional mezzanine loads imposed on the existing columns. Similarly, proposed loft areas associated with the 2nd-floor residential areas had to also be supported by new steel beams spanning between the existing building columns. This is because the assumed existing 100 psf capacity of the second floor was less than the anticipated combined loads of the same multi-level residential areas. However, this aspect of the adaptive reuse plan was not constructed due to limited headroom at the 2nd floor.

The original adaptive reuse plan also included constructing a new rooftop deck assembly area and related enclosed elevator lobby and separate Figure 7. Typical cored hole penetration in a hollow clay tile floor. stair access areas. It was anticipated that new, exposed steel rooftop dunnage framing would span between the require strengthening of the flat, tile arch construction. However, existing main building columns, as required to provide the mini- it was expected that the strengthening, as long as a tie rod was not mum assembly live load capacity of 100 psf. In addition, new stair interrupted, would only involve installing small steel compression and elevator penthouses were required to provide access from the frames that would enable the continuity of the surrounding flat arch 11th floor. However, the new rooftop features were excluded from clay tile units at the new penetrations (Figure F, online). the project due to the excessive cost of the proposed renovations.

In addition, it was anticipated that penetrations that only involved Additional adaptive reuse features that impacted the existing structure small, cored holes would be allowed without reinforcing the tile if included a new trash chute and mechanical chase from the 2nd to the the penetrations could be located to minimize damage to the affected 11th floor. In addition, the new mechanical chase extended up through individual tile (Figure G , online). At similar existing holes that were no the 11th-floor attic and roof framing. Due to the susceptibility of flat, longer needed, the opening and surrounding cavities of the affected hollow clay tile construction to penetrations, it was anticipated that hollow clay tiles were simply infilled with lightweight concrete. these large new openings would involve re-support of the affected arch Lastly, it was also anticipated that infilling the large existing opening framing. Also, it was anticipated that the interruption of any existing in the floors associated with the mechanical penthouse shaft (Figure 7 ), tie rods used as part of flat arch tile construction that occurred within added during the life of the building, would be required. This was the new openings would require that the adjacent affected interior accomplished by constructing new concrete slabs on metal deck that arch spans be strengthened. were supported by new steel beams spanning between the existing floor For reasons similar to that described above for the new floor and beams. The capacity of the existing steel beams around the perimeter roof openings, it was anticipated that smaller utility holes required of the openings to support the new dead and live loads associated for the new residential bathrooms and kitchens could potentially also with the infill framing was also confirmed.

Figure 8. Typical centerline of beam yellow paint line (which was located via a GPR survey on the soffit side of the framing) and core holes.

Figure 9. Typical core holes on top of a beam (left) and beside the beam flange tip (right).

continued on next page O C T O B E R 2 0 21

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The investigation of the beams at the referenced floors was conducted As a part of the initial project in the following manner. Because the design and ongoing adaptive reuse beams were concealed by the existing construction during the project, sevfloor finishes and the plaster ceiling, eral investigations were conducted to it was necessary first to locate the better understand the existing strucbeams via handheld ground penture without any existing drawings. etrating radar (GPR). In addition, A summary of the major investigabecause of the presence of an existtions completed is provided below. ing ±5-inch-thick concrete topping, which also included embedded const th th 1 , 5 , and 11 Floor duits, it was necessary to scan the Framing beams with the GPR from the ceilInvestigations of the typical floor ing side of the framing where only framing at the 1st, 5th, and 11th a few inches of plaster and solid tile floors were conducted to confirm separated the steel beam flange from the load-carrying capacity of the the exposed soffit. existing Carnegie steel beams. The Once the beams were located and investigations concentrated on the the centerline of the members was steel beams rather than the hollow accurately marked on the top of the clay tiles because of the difficulty finished floor, the slab was then cored and cost associated with locating and directly on top of the wide flange measuring the tie rods used with this section to reveal the beam width. A Figure 10. Voussoir arched tiles on each side of and parallel and directly type of masonry flat arch framing, beneath the concealed steel beams. second core was then taken through which is the most accurate method of the entire depth of the topping and estimating the load-carrying capacity of this same framing system. In tile immediately adjacent to the flange tip of the beam to confirm the addition, it is common for the load-carrying capacity of a flat tile arch beam depth (Figures 8 and 9). Both of the core locations allowed the to significantly exceed that of the supporting beams because of the large dimensions of the steel section to be accurately recorded and the thicksafety factors utilized by the original designers for this type of system. ness of the concrete topping, hollow clay tile, and plaster ceiling to be

Structural Investigations

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documented. It was not necessary to confirm the thickness of the tapered I beam flanges because the available Carnegie Steel section property tables (Figure H , online) only included dimensions for the beam depth and flange width and not the variable flange thickness.

The reserve load-carrying capacity of the floor beams at all three levels was determined to be approximately 100 psf based on the yield strength of the Carnegie beams documented as a part of the Main Roof and Original Mechanical Penthouse investigation described below.

roof beams and the direction of span of both the beams and tile arch were visible from the 11th-floor attic framing because plaster had not been applied to the tile soffit. As a result, the scored bottoms of the 12-inch-wide by 9-inch-long (in the direction of the arch span) hollow clay tiles were visible, with the beam locations identified by the scored bottoms of the end voussoir and beam soffit tiles arranged parallel to and centered about the entire beam span (Figure 10).

Similarly, because the soffit of the high penthouse roof had not been plastered, the location and direction of span of Main Roof and Original book tiles, bulb tees, purlins, and beams Mechanical Penthouse were also readily apparent. In addition, As indicated above, the original adapfull-depth cores were taken at both the tive reuse plan for the building included high penthouse and main roofs to conconstructing an open-air rooftop assemfirm the thickness of the 4-inch book tiles bly space and a new access elevator and (Figure 11) and 12-inch-depth hollow clay stair from the 11th floor for use by the tiles, respectfully, and the associated existresidents. As a result, it was necessary ing roofing. to conduct a structural investigation to Figure 11. Mechanical penthouse high roof 4-inch hollow As indicated in Part 1 of this article, the determine the load-carrying capacity of clay book tile core. southern portion of the main roof was the affected roof framing. not framed with trusses and instead was As previously described, due to the termination of the interior constructed with Carnegie Steel B Beams and built-up, riveted steel building columns at the 11th floor at the north end of the build- plate and angle girders as shown in Figure 12. This area of the building ing, existing fabricated steel roof trusses clear spanned between the was subsequently investigated as a part of the Mechanical Penthouse main east and west sides of the building to support the main roof, and Cooling Tower Dunnage investigation that will be provided in original rooftop mechanical penthouse high roof and floor, and the Part 3 of the article.

11th-floor ceiling framing. Therefore, the intent of the investigation High Mechanical Penthouse Roof Framing involved determining the reserve load-carrying capacity of a typical steel roof truss, high penthouse roof steel purlin and beam, and The analysis of the exposed high roof steel beams indicated that the main roof steel beam. framing had a reserve load carrying capacity of approximately 50 psf The findings of the investigation are provided below and were based in addition to the current-day code-minimum flat roof snow load. on the results of a steel coupon test of a penthouse roof purlin that This maximum load was based on the capacity of the beams; however, indicated an approximate yield strength of 32 ksi. The sample was the purlins had a reserve load-carrying capacity of approximately 75 taken from a portion of the bottom flange at the end of the span psf. Therefore, a determination of the load-carrying capacity of the next to a supporting column. In addition, the location of the main book tiles and supporting bulb tees was not performed.

Main Roof Framing Only the 10-inch-deep north-south support beam along the east wall of the mechanical penthouse could be measured and therefore analyzed. The results of this analysis indicated that the member only had a reserve load carrying capacity of approximately 10 psf in addition to the current day code minimum flat roof live load, including snow drift loads.

Typical Roof Truss The results of the analysis of a typical Warren roof truss (Figure I and J, online) indicated that the member did not have reserve capacity to support the proposed new rooftop assembly space deck; however, it did have adequate capacity to support the reserve capacities noted above for the penthouse high and main roof framing.

Part 3 of this series includes a continuation of the structural investigation, specifically regarding the main roof and original mechanical penthouse.■

Figure 12. South side roof and 11 floor attic framing. th

D. Matthew Stuart is Senior Structural Engineer at Pennoni Associates Inc. in Philadelphia, PA. (mstuart@pennoni.com)

O C T O B E R 2 0 21

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structural PERFORMANCE Community Storm Shelter Design Part 2: A Marriage of Codes and Artistry

By Bradford Russell, AIA, P.E., SECB, F.SEI, F.ASCE

E

ach year severe weather, in the form of storms ripping through our states and along our coasts, leaves a swath of destruction of buildings and infrastructure and many lost lives. The heaviest of these storm events (high wind) is the tornado. However, if you have experienced the power of a tornado, you are likely to agree that the event is much more than wind intensification.

The National Centers for Environmental Information, a division of the National Oceanic and Atmospheric Administration (NOAA), charts a trendline increase in the frequency of tornadoes since 1950, with the occasional spikes like the U.S. saw in 2004 – 1,819 tornadoes.

Studies show that tornado events in the United States do about $400 million dollars in damage to buildings (as exemplified in Figure 1. Extreme storm damage.

Figure 1) and infrastructure and kill an average of 70 people every year. Every U.S. state has experienced twisters, extreme-wind events such as tornadoes and hurricanes. (Figure 2 but Texas holds the record: an annual average of 120. Tornadoes have represents typical FEMA P-361 approved storm shelter signage been reported in Great Britain, India, Argentina, and other countries, designed for the visually impaired.) but they are most often seen in the United States, with an average of Tornadoes and other high wind events are among nature’s most 800 tornadoes each year. destructive forces, more so due to the higher winds and flying debris That average has increased since 2008, causing more than 1,300 associated with these storms. Unfortunately, these types of windstorms injuries each year. In addition, the most violent tornadoes have more continue to cause injury and death to people who cannot safely evacuthan 250 mph wind speeds and leave a damage path a mile wide and ate or find shelter from these events. FEMA has long supported the 50 miles long. Therefore, the need for proper design, documentation, development of hazard-resistant codes and standards by assessing and construction is of great importance today and likely of an even how structures respond to disasters like tornadoes and hurricanes. greater significance tomorrow.

The old scale for F-5 tornadoes had wind speeds This article addresses Community Storm Shelter into the 300 mph (ultimate) range (F-5 – 261-318 design (documentation requirements were mph), while the new scale lists an EF5 as a tornado addressed in Part 1, STRUCTURE, August 2021) with wind speeds above 200 mph and causing and how the codes are used to mitigate risks from damage previously ascribed to the F5 range of these storm events. In addition, we briefly look at wind speeds. The EF Scale was revised from the the release of the new ICC 500-2020 and what original Fujita Scale to reflect better examinations that may include. of tornado damage surveys to align wind speeds more closely with associated storm damage.

The Need for Shelter The FEMA P-361 publication (on which ICC 500 is based), Saferooms for Tornadoes and Hurricanes, provides guidance from the Federal Emergency Management Agency (FEMA) about the planning, design, construction, and operation of safe rooms (storm shelters). It presents essential information about the design and construction of residential and community safe rooms to protect people during

Structural Engineering Considerations

Figure 2. Tornado safe room signage.

Performance issues are the center of engineering design work. As in all structural engineering designs, following the load path is of utmost importance in storm shelter designs to ensure the higher loading is carried to the foundation and accounted for in all connection detailing. Finding O C T O B E R 2 0 21

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the site-specific loadings for a structure can be established by selecting the location on the Applied Technology Council’s (ATC) Hazards by Location website (https://hazards.atcouncil.org). This site covers wind, snow, tornado, and seismic loading for any specific address in the United States.

A review of detailing strength requirements has increased importance when designing for elevated loading conditions to be adequately carried to the foundation. In ordinary loading of a structure, the connections tend to carry a reserve capacity due to the materials’ normal allowable strengths and the typical connection’s buildability. In extreme conditions, the connections may become the weak link in the design due to the concentration of loads in these points. This is where it becomes more important to follow the load path to ensure the extreme demands on the structure are still being met with the design of the connections and the possible junction of several load paths on these points.

The Design Wind speed shall be determined in Figure 3. Map of maximum wind speeds from ICC 500-2014 Figure 304.2(1). accordance with Figure 304.2(1) of the International Code Council’s ICC 500-2014, Standard for the ICC 500-2014, Table 305.1.1 Design and Construction of Storm Shelters, for tornado Speeds for 15-lb Sawn Lumber 2x4 Missile For Tornado Shelters events in the U.S. (Figure 3 ). Unlike code requirements earlier than 2010, design based on Ultimate Design Wind Missile Speed and Shelter Impact Surface Load has become the predominant format provided Speed in wind loading codes. As such, wind load provisions 80 mph Vertical Surfaces of ICC 500-2014 are provided in an Ultimate Load 130 mph 53 mph Horizontal Surfaces format and should be equated against a factored Limit State resistance. Allowable Stress Design can 84 mph Vertical Surfaces 160 mph still be used but requires additional factoring.

56 mph Horizontal Surfaces Along with Wind Loading Requirements are the Impact Loading Requirements of flying debris from 90 mph Vertical Surfaces 200 mph these high wind speed events. This will often govern 60 mph Horizontal Surfaces the design of vertical and horizontal surfaces of the 100 mph Vertical Surfaces shelter. The debris impact test missile for all com250 mph 67 mph Horizontal Surfaces ponents of the shelter envelope of tornado shelters shall be a 15-lb sawn lumber 2×4 traveling at the speeds noted in the Table.

Field Laboratory (WERFL) have tested numerous structural systems The angle of the surfaces (doors, walls, and other shelter surfaces), and documented them for impact. This allows the designer to use 30° or more from the horizontal, will be considered a vertical surface; specific structural systems in their design by a simple selection of less than 30° will be considered a horizontal surface. The Texas Tech details meeting certain pretested load requirements to ensure the National Wind Institute (NWI) and the Wind Engineering Research load is adequately carried to the foundation.

The images shown in Figure 4 are from above-grade protected openings (rolling shutter added to an existing structure on the left and swinging shutter built into a new facility on the right).

Roof live loads are set for a minimum of 100 psf for tornado loadings and 50 psf for hurricane loadings due to the added impact of wind loads carrying debris hazards. Following the load path through the structure, the foundation must be adequately designed and constructed to distribute both the normal loads to the subgrade and the heightened loadings of the storm event. This begins with a site-specific soil report from a repuFigure 4. Different configurations of protective shutters (rolling and swinging). table Geological Engineering firm that qualifies

56 STRUCTURE magazine

the subgrade capacity and continues through the proper foundation design to distribute these loads adequately to the subgrade.

The Art of the shelter continues through the sufficient and efficient design of the structure.

Documentation Requirements Design professionals that have overall design responsibility will be required to ensure the documents adequately show the load path is thoroughly represented in the detailing of the Storm Shelter assembly from the roof to walls, to floor diaphragms, into the Main Wind Force Resisting System (MWFRS), through MWFRS connections, and into the foundation.

Typically falling to the structural engineer is the requirement of a Quality Assurance Plan for each MWFRS and each wind resisting component. Per section 107.3.2 of ICC-500-2014, this Quality Assurance Plan list will include: 1) The MWFRS and wind resisting components.

2) The special inspections and testing to be required.

3) The type and frequency of testing required.

4) The type and frequency of special inspections required.

5) The structural observations to be performed.

6) The required distribution, type, and frequency of reports of tests, inspections, and structural observations.

The Art of the shelter involves preparing and creating a comprehensive set of contract documents by the project design professionals for the contractor to execute.

better understand some of these tools for storm shelter design and the documentation requirements to help control these risks.

In design and life, ‘Always be curious!’ and seek to mitigate your storm shelter design and documentation risks!■ As an Architect and Professional Engineer (structural), Bradford Russell promotes his understanding and leadership in both disciplines relating to the built environment. With multiple A/E/C patents from the USPTO, he brings a unique perspective of innovative approaches.

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Conclusion Simultaneous with the increased tornado frequency is the growth in the population. With this population density increase, the growing need to protect the world’s population is more evident than ever.

The briefly reviewed architectural and engineering concerns stated here begin with performance issues in community storm shelters’ design and documentation requirements. Heightened performance requirements of shelters are of great importance due to the vulnerability of occupants and the importance of the continuation of facilities during these elevated events. The author hopes you

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TECHNOLOGY Computational Embrace

Applying Computational Design Logic to the Quality Control Process

By Phillip Bellis, P.E., and Steve Reichwein, P.E., S.E., SECB

T

he future of structural engineering is inextricably linked with computational design. Algorithms and data will be the basis upon which the industry develops. That is not to say that engineering judgment and expertise will be replaced by artificial intelligence.

Instead, the possibilities of computer programming will continue to enhance the capabilities of structural engineers just as the widespread adoption of the computer did in the 1980s. Some engineers in the industry have been working in the field of computational design for over a decade. Others have been slower to adapt.

Whenever the entry point, engineers will find they can apply the underlying skills and thought processes required for computational design to a far wider range of tasks than expected. It is a common misconception that the methodology is best utilized on high-profile and/or complex projects. While that is an important application, it is not relevant to most of the industry. Most structural engineers can, however, benefit from implementing computation design principles, specifically when utilized within quality control processes.

Computational design has been well documented as a tool used to rapidly develop design alternatives within a defined solution space. Using this methodology, an engineer can find an optimal solution for a given problem by iterating through different combinations of variables. Genetic algorithms ease this process by automatically filtering out the undesirable outcomes, as defined by the user. These algorithms focus on core parameters like volume, cost, performance, etc., and are extraordinarily useful during the schematic design phase, when design options are still rapidly changing. Rather than making the generalized assumptions that were

Computational design tools can assist structural engineers in navigating through an industry with ever-increasing quantities of highly variable data.

once required to maintain aggressive project schedules, structural engineers now have access to timely, meaningful data that can be used to make significant project decisions during schematic design.

Though often viewed as the final deliverable of computational design efforts, schematic design studies should not be the point when the process is abandoned for traditional workflows.

At its essence, computational design is a data management process that can be applied to every facet of a project. It has recently become 58 STRUCTURE magazine

Slab edge comparison between structural analysis model and architectural floor plan.

widely adopted, in part due to the development of visual programming tools such as Grasshopper® for use with Rhinoceros®, and Dynamo® for use with Revit®. Users no longer need to be fluent in a specific programming language to create powerful computer scripts. Using preprogrammed components and a linear logic-based approach, engineers with average computer proficiency can develop scripts to make their workday more efficient. More specifically, engineers can develop scripts that provide quality control checks to ensure that design data (load diagrams, framing layout, beam reactions, column forces, etc.) is accurately considered and documented throughout the duration of projects.

Structural engineers use a multitude of different analysis programs published by competing software developers. Designs are then documented in yet another program to create the drawings upon which contractors base their own plans, which are ultimately used for construction. It is a complicated process that traditionally has relied upon human review to catch errors in data transfer. However, tools such as Grasshopper and Dynamo provide an opportunity to supplement human review with custom-developed scripts that compare the data at each step of the process. This ensures that nothing is outdated, lost, or unintentionally altered. Engineers are thus able to repeatedly check everything from architectural coordination items to the strength of critical connections without devoting company resources away from other tasks.

Architectural Coordination The modern project workflow encourages architectural updates throughout the duration of a project. For better or worse, changes are often made within the architectural drawings without the

structural engineer being notified. Revit users may receive a Major structural analysis programs can export model informacoordination review notification, but this process is incredibly tion in various data formats that Grasshopper and/or Dynamo time-consuming due to the vast number of changes. By combin- understand. Exporting data is often straightforward, but it must ing engineering judgment with data extracted from the design be done logically and in a well-documented, repeatable manner. documents, however, an engineer does not need to review each This point is emphasized because even a small change in exported minute adjustment. data formatting can cause issues with the best-written scripts.

Consider, for example, slab edge adjustments. A computer script However, if the data format remains consistent, generic scripts written within Grasshopper and/or Dynamo can isolate the floor can be used on any analysis model made with a specific software slabs and extract their perimeter curves. That data can then be used program. Thus, an engineer can reliably extract model geometry, to recreate the slab edge within Rhino3D. Corresponding data would support conditions, loading information, member assignments, be extracted from the analysis program used to design the slab and and more, and compare it to the corresponding information within then imported into the same Rhino3D file. The two slabs are compared and subsequently highlighted wherever deviation exceeds a user-specified tolerance using preprogrammed Grasshopper components. An engineer can then focus on the portions of the slab that have significantly changed and update the analysis model accordingly. If greater automation is desired, updating the slab edge within the analysis model may also be written into the script.

A similar approach can be applied to coordinating architectural plans and loading in the structural analysis model.

Using Grasshopper and its data manipulation capabilities, engineers can extract floor loading data from analysis models, filter the loads based on type and magnitude, and then overlay that information on architectural plans. With the relevant information in a single view, it is easier Komponent delivers in design, construction, and in-service for an engineer to verify that the loads in with quality, efficiency, and cost savings! an analysis model are coordinated with the architectural plans. More advanced ADVANTAGES computational designers may take this  Improves structural performance  Up to 60% greater abrasion resistance further by programming the script to  Maximizes design versatility  Increases dimensional stability and durability extract the room and/or floor finish data  Maximizes joint spacing  Enhances compressive and flexural strengths from Revit, associate that information  Speeds time to completion  Minimizes creep and moment with structural loading from a standard Reduces mobilization & formwork  Increases density and lowers permeability ized database, and ultimately compare  Reduces project costs  Prevents curling and drying shrinkage cracking it to the loading over that same area in the analysis model.

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Structural Coordination Coordination and quality control within the inner-office workflow is critical for safe and efficient project delivery. One of the most critical steps in these processes is ensuring data from analytical models is accurately conveyed on design documents. This includes everything from structural framing layouts to connection reactions. Engineers proficient in computational design methodology can write computer scripts to automate many of these tasks in Grasshopper and/ or Dynamo.

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the design documents using Grasshopper and/or Dynamo as the primary user interface.

One of the more valuable tasks that can be completed with this approach is the verification of analysis model geometry and the transfer of associated beam end reactions. Throughout the design and coordination processes, structural framing changes multiple times. Computational programming provides engineers a tool to compare the geometry of the analysis model to the design documents to ensure the analysis model is still fully coordinated or, at a minimum, within an acceptable tolerance. An example method is as follows: Step A: The start/end nodes of framing members are identified, mapped to a geometric coordinate, and then rebuilt within the Grasshopper/ Dynamo interface. It is then important to valiStructural framing location and cross-section comparison between structural analysis model and date the direction of framing members according structural 3-D model. to a standardized convention. Any member not drawn according to the standard must have its start/end nodes geometric location comparison between each member’s start/end reversed. Since reactions may not be the same at either end nodes and then selecting the members with the smallest aggreof a member, this step is critical to ensure the accuracy of the gate absolute distance between these points. If a common origin transferred data. Now that the geometry is drawn and oriented point is not shared between the models, a model translation may properly, the analysis model members must be mapped to the be necessary. corresponding member within the design documents. This can Step B: At this point in the script, the user has enough data corbe done in multiple ways. The most straightforward is a simple rectly linked to each other to discern where and by how much the analysis model deviates from the design documents. The files can then be updated so that any transferred information follows the design intent. After the necessary updates are completed, either manually or automatically, information from the analysis model can be quickly applied to the design documents by using the data mapping that was previously conducted. As a result, tasks that would have previously taken hours to complete, such as including beam end reactions as instance parameters in Revit, are now accomplished efficiently and without the risks associated with the manual transfer of vast amounts of data.

Conclusion Computational design tools can assist structural engineers in navigating through an industry with ever-increasing quantities of highly variable data. From load application in the design phase to including beam end reactions on construction documents, these tasks must be conducted efficiently, minimizing the risk of errors.

Engineers now have access to tools that allow them to accomplish this goal with computational programming logic that would have previously only been possible with a strong knowledge of multiple computer languages. The visual programming interface that these programs use provides all engineers the opportunity to extract, process, and distribute data to improve quality control processes across the industry. These tools are no longer just for use on complex, high-profile projects. Computational programming is for all engineers searching for a way to make their everyday workflows more efficient.■ Phillip Bellis is a Project Engineer with Fast+Epp and a member of the Computational Design Group within their Concept Lab. (pbellis@fastepp.com) Steve Reichwein is a Senior Associate at Severud Associates in New York City. (sreichwein@severud.com)

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structural FORUM Take Time to Save Time

Lessons Learned for Planning a Successful Structural Investigation

By Heather Todak, P.E.

T

he client is on board, the contract is signed, and all eyes are on you – how can you ensure your upcoming structural investigation is successful? After participating in many onsite investigations from coast to coast, here are some tips for successful planning and execution from the author’s perspective as a young engineer beginning to lead project teams.

Choose the Right Team. Assembling the right people for your project is arguably the most crucial decision you will make. Ideally, craft the perfect mix of individual backgrounds, technical expertise, and experience levels. Having all the right colleagues on the job site with you may not be the most costeffective approach, but extra costs associated with seniority and travel expenses pay off in the end. Make sure each team member has a well-defined, unique role and communicate to your colleagues why they are on the team.

Set Expectations. As soon as the team is established, hold a pre-visit meeting before embarking on the trip. A lot goes into planning a successful structural investigation, so enlist the team to assist. Assign pre-investigation tasks that team members can own; this is an opportunity for them to be engaged at the beginning, not just when they arrive on site. For example, junior team members can familiarize themselves with the project scope by developing field sheets, procuring equipment, or collecting existing structural reports and drawings.

Before the site visit, ensure the team knows what to expect regarding how the field investigation will unfold: How long will the days be? What are the working conditions? What if we do not finish in time? What kind of follow-up or reporting assistance is expected of them after the investigation is complete?

Establishing expectations with the client is just as important – if not more important.

Although your project goals and deliverables should be clearly outlined in your signed proposal, take the opportunity to review your intent with the client ahead of the on-site investigation. What are the limitations of your structural investigation or testing techniques?

Is the client providing access, notifications to tenants at the property, coordination with a contractor, or any other necessary support?

Be sure to address any essential matters, such as special safety considerations or protocols.

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Lastly, re-confirm your deliverables. Are they expecting a verbal follow-up, a 40-page written report, or something in between?

Select the Right Equipment and Tech. Ensure that the team is well-equipped with the most appropriate equipment, materials, and technology for the job.

Depending on what type of structural field investigation you are conducting, this may mean anything from a basic tool bag to surveying tools or nondestructive testing equipment.

Keep an eye on the prize – what are the primary goals of the investigation? Keep your focus on the final deliverables – do not plan a ground-breaking science experiment for a client who has asked you to crack-map their parking garage. If your project involves more advanced testing, such as ultrasonic testing or ground-penetrating radar scanning, use equipment your project team is experienced and familiar with. If the equipment is new to the team, arrange a tutorial with the manufacturer and set aside time to learn the platform.

While some level of troubleshooting equipment on site is expected, make sure you are well-prepared to avert disaster on the job site, where your time is most limited.

All structural investigations require an effective way to document observations and findings. This may mean traditional pen and paper or tablets with applications loaded with project-specific toolsets. Higher-tech approaches can be great for large-scale investigations, where multiple users can work on the same document simultaneously. Think through the process dictated by your documentation method and final work product.

For instance, if you plan to take notes on paper field sheets, will you end up digitizing them to include in the report? In this case, working on a digital platform may save hours of work down the road. Like selecting the right tools and testing equipment, be sure to consider the comfort level of your team members with various documentation techniques.

Lastly, if you are hitting the road or traveling by plane for your investigation, do not be afraid to overpack. That extra checked bag containing backup batteries and extra tools is a lot less expensive than sacrificing your

The best advice is to plan for the investigation not to go as planned. valuable time on-site to run to the nearest hardware store for a plumb bob.

React, Revise, and Reset. No matter how much you have planned your structural investigation, there is no way to prepare for everything. The best advice is to plan for the investigation not to go as planned.

Every on-site structural investigation should be designed to be fluid and adaptable. Plan a mid-morning check-in with the team on the first day to re-evaluate the investigative approach relative to the schedule. Will unpredictable conditions require the scope to be adjusted to accomplish the original goal? Take that opportunity to make sure everyone is comfortable with their designated roles in terms of technical expertise and physical demands. Then, adjust accordingly, build in breaks, and keep your team happy.

Keep your client informed without pretending to know all the answers just yet.

Lastly, before you leave the job site, take the time to write a “mental report” in your head before de-mobilizing. Did you collect enough information from your client to prepare an appropriate project background? Have you addressed all tasks outlined in your proposal?

Did you collect representative data, overall photos, or other visuals to include in your report? Asking yourself these questions while on-site can prevent unnecessary heartburn when back in the office.

Learn for Next Time. Once you have finalized your deliverables, take the time to debrief your team and see what you can take away from this project to help improve processes and efficiencies for subsequent structural investigations.■ Heather Todak is an Associate with Wiss, Janney, Elstner Associates, Inc. (htodak@wje.com) O C T O B E R 2 0 21

NCSEA

NCSEA News

National Council of Structural Engineers Associations

Structural Engineering Summit Postponed to February The NCSEA Structural Engineering Summit has a long history of bringing the structural engineering community together to network, learn, and celebrate the successes of our profession. It would have been difficult for the Summit to deliver on that purpose in October as originally planned. As a result, NCSEA has postponed the Summit – both the live event in New York and the virtual event – to February of 2022.

The Summit offers the industry an immersive experience, both in-person and online, with unrivaled educational opportunities, an industry-leading trade show, and unique networking opportunities. Register for the conference and learn more at www.ncsea.com/events.

Excavation Shoring Design Guide Now Available

Reviewing a pertinent worked example bolsters any structural engineer’s confidence. The new Excavation Shoring Design Guide is comprised solely of such detailed work examples and provides the real construction details that are necessary to round out complete designs, including site characterization and earth pressure diagrams, soil/ grout bond strengths, and deflection curves.

Visit www.ncsea.com/publications to download the digital version for $119 (members) / $219 (nonmembers) or order the paperback for $169 (members) / $269 (nonmembers).

Call for NCSEA Committee Volunteers

Are you interested in volunteering with NCSEA? The Council depends on its members to get involved to help advance our mission and further develop our partnership. Our volunteers help educate on codes and standards, develop publications, create courses, advocate for safe structures and post-disaster recovery, and so much more. If you are a new volunteer interested in serving on an NCSEA committee, please visit www.ncsea.com to complete the Committee Volunteer Application. Most committees admit new members on a rolling basis while others add members only once per year. More information about NCSEA committees can be found by visiting www.ncsea.com/committees.

NCSEA Reflects on the 20th Anniversary of September 11th NCSEA collaborated with SEAoNY, AISC, SEI, and the CTBUH on two joint press releases recognizing the contributions of structural engineers in the days, months, and years after the 9/11 tragedy.

NCSEA President Ed Quesenberry, P.E., S.E., shared, “As we reflect on the events of that tragic day, we feel fortunate that our education and training as structural engineers prepared us well to assist in the recovery. We are resolute in our commitment to doing whatever we can to ensure that the buildings we live and work in are safe and to being ready to respond when our communities need us.”

Read the full statements at www.ncsea.com.

follow @NCSEA on social media for the latest news & events!

64 STRUCTURE magazine

News from the National Council of Structural Engineers Associations

Apply for an NCSEA Grant by November 9th to Support your SEA’s Next Initiative The NCSEA SEA Grant Program awards SEAs funding for projects that advance their SEA and the structural engineering profession in accordance with the NCSEA Mission Statement.

Supported by the NCSEA Foundation, the SEA Grant Program has delivered more than $60,000 in Grants since its inception. Past funded initiatives range from building up STEM resources to launching a local SE3 committee.

Applications are due November 9, 2021. Visit www.ncsea.com/awards to apply. Application requests must be reviewed and approved by the Member Organization before being submitted to NCSEA for consideration.

In Need of High-Quality, Expert-Led, Affordable Education?

NCSEA's Webinar Subscription Plan is a cost-effective option for members and nonmembers seeking high-quality continuing education.

By subscribing to NCSEA webinars, you are subscribing to webinars developed by leading experts at an incredible value (as low as $30/hour). With at least 30 live webinars per year and a recorded library of over 170 webinars, NCSEA's Webinar Subscription is designed for the individual engineer as well as the firm; no matter the size, this subscription plan can work for you!

Webinars are available whenever, wherever you need them. Multiple users at the same office, together or remote, can take advantage! Subscribe now by visiting www.ncsea.com and don't miss another webinar in 2021!

NCSEA Webinars

Register on www.ncsea.com/education

October 28, 2021

Design of Insulating Concrete Form (ICF) Walls for High Winds Lionel A. Lemay, P.E., S.E., and Scott Campbell, Ph.D., P.E.

The presentation will discuss the structural design and detailing of ICF walls, including preliminary wall sizing and placement, design details, construction inspections, and high wind and seismic design.

November 9, 2021

The Engineer's Role in Improving Housing Resilience Tim Hart, S.E., LEED AP, and Lizzie Blaisdell Collins, P.E., S.E., LEED AP

Learn more about Build Change, an award winning non-profit social enterprise that works with people in emerging nations to design and build disaster-resistant houses and schools.

November 16, 2021

Retaining Wall Basics Bill Simpson, P.E.

This webinar will provide insight on a variety of retaining wall types and discuss commonly overlooked site issues related to the wall that must not be ignored as part of the retaining wall design.

Courses award 1.5 hours of Diamond Review-approved continuing education after the completion a quiz.

NCSEA webinar subscribers receive access to these webinars and a full year’s worth of live, high-quality continuing education webinars, along with a recorded library of past webinars – all developed by leading experts; available whenever, wherever you need them; and at an affordable price.

O C T O B E R 2 0 21

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SEI Update Advancing the Profession

Call for Comments (through October 11, 2021)

Updated Professional Standard: ASCE/SEI 74-XX Load and Resistance Factor Design (LRFD) for Pultruded Fiber Reinforced Polymer (FRP) Structures

This standard is intended for use in the design of new buildings and other structures constructed of pultruded fiber-reinforced polymer (FRP) composite structural shapes, connections, and prefabricated building products. This standard does not cover tendons and cables.

The standard applies to pultruded fiber-reinforced polymer (FRP) structural shapes with symmetric and balanced reinforcement and fiber architecture with a polymeric matrix.

Accessing the ASCE Public Comment System will require using or creating an ASCE user account if you do not have one. Access ASCE Public Comment at https://bit.ly/3kaUuea. Questions? Contact ASCE Staff James Neckel at jneckel@asce.org.

Get Involved

SEI advances and serves the profession through Committees that produce standards, programs, publications, conferences, and continuing education. Get involved in an SEI volunteer effort in your area of expertise or interest. It’s a great way to advance the profession and increase networking and learning.

Apply/Nominate by November 1 • O.H. Ammann Research Fellowship in Structural Design and Construction • Advance to SEI Fellow recognition – Must be current SEI, actively involved in SEI, 10 years responsible charge (typically post P.E./S.E.) • SEI and ASCE Structural Awards Learn more at www.asce.org/SEI.

Access ASCE COVID-19 Collection

Papers are freely available to help you stay informed of the effect COVID19 is having on the civil engineering profession; the collection will be updated as new content becomes available. Access through December 31. https://ascelibrary.org/covidpapers

EXPLORE THE NEW Career Resources

Find a job Post a job

www.asce.org/freepdh *A Professional Development Hour (PDH) is one contact hour of instruction or presentation. More than 75 percent of U.S. registration boards require continuing education for P.E. license renewal. Visit each registration board’s website to confirm its continuing education requirements. You are required to pass an exam on the webinar’s content to receive a PDH.

Join us this year in celebrating 25 years of SEI – advancing and serving structural engineering!

Errata 66 STRUCTURE magazine

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI.

News of the Structural Engineering Institute of ASCE Learning / Networking

Join Us at SEI Events www.asce.org/SEI

• #SEILive October 13 | 12:30 p.m. EDT on Licensure and Exams • ETS: Powering Past the Pandemic – Wednesday, November 3, 1:00 p.m. ET A unique time of disruption and innovation in the electrical transmission and substation industry Join moderator Ken Sharpless, P.E. F.SEI, F.ASCE, for a big-picture panel discussion on the state of the electrical transmission structures industry as it emerges from pandemic mode. How well did essential businesses adjust to the challenges of COVID, and where does this experience take the industry going forward? Listen to perspectives focusing on essential employees from utilities, contractors, manufacturing, supply chain, engineering, and design. Panelists: Sarah Beckman, ULTEIG; Archie Pugh, American Electric Power; Alex Richards, Aquawolf, LLC; Bill Sales, Sabre Industries, Inc. Register for the live program (1.5 PDHs) OR the post-event recording (no PDHs).

• SEI Standards Series Join for exclusive interaction with expert ASCE/SEI Standard developers on state-of-themarket updates. Participants will learn about technical revisions and review a design example.

Attendees are encouraged to participate in Live Q&A. Each session is LIVE and only available 1:00 - 2:30 p.m. US ET. NOVEMBER 18 – ASCE/SEI 8 Specification for the Design of Cold-Formed Stainless Steel Structural Members Join SEI host Jennifer Goupil for a discussion with the chair of the ASCE/SEI 8 committee Ben Schafer, Ph.D., P.E., F.SEI, M.ASCE ASCE/SEI 8 Specification for the Design of Cold-Formed Stainless Steel Structural Members has been completely revised and updates the 2002 edition of the standard. This standard applies to the design of structural members cold-formed to-shape from annealed and cold-rolled austenitic, ferritic, and duplex stainless steel alloys used for load-carrying purposes in buildings, and structures other than buildings provided allowances are made for dynamic effects. The Specification includes both LRFD and ASD provisions.

Individual session: Member $49, Nonmember $99. Student member: Free registration.

REGISTER NOW at https://cutt.ly/9hQDTEo • Save the Date Structures Congress – April 20-23, 2022 in Atlanta Electrical Transmission and Substation Structures Conference – October 2-6, 2022 in Orlando Students and Young Professionals: Apply for SEI Futures Fund Scholarships to participate.

SEI Futures Fund Commitments for FY2022

Thank you, SEI Futures Fund Donors, for investing in the future of structural engineering! Your gifts make possible these strategic initiatives totaling more than $250,000, approved by the Futures Fund Board for FY2022: • Leadership Academy Curriculum Development • Strategy Workshop to Address Future Conditions of Environmental Loads and Impacts in SEI Standards • Student and Young Professional Scholarships to engage at in-person Structures Congress • Student Scholarships to engage at in-person Electrical Transmission and Substation Structures Conference • SE2050 Database • Building Next Engineers Design-Build and Construction Workshop Project for middle/high school students • Claims Database Workshop • Bridge the Gap Project for SEI Chapters/Grad Student Chapters to transition students as lifelong members of SEI • Distribute Engineer’s Agreement Basics via STRUCTURE magazine and promote online • SEI Global Activities Online COVID-19 Symposium Learn more and give at www.asce.org/SEI.

Follow SEI on Social Media: O C T O B E R 2 0 21

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CASE in Point CASE Tools and Resources CASE Contracts – Usage Guide Last year, CASE updated its Contract Library and re-issued updated Contracts that have been reviewed by outside legal counsels. Below is a handy guide for firms to know which contract is appropriate to use in certain situations.

Structural Engineer is Retained CASE Agreement #1 – An Agreement for the Provision of Limited Professional Services.

This agreement is intended for use for small projects or investigations of limited scope and time duration.

CASE Agreement #2 – An Agreement Between Client and Structural Engineer of Record for Professional Services. This agreement is intended for use when the client, e.g., owner, contractor developer, etc., wishes to retain the Structural Engineer of Record directly. This agreement may also be used with a client who is an architect when the architectowner agreement is not an AIA agreement.

CASE Agreement #3 – An Agreement between Owner and Structural Engineer as Prime Design Professional. This agreement is intended for use when the Structural Engineer serves as the Prime Design Professional.

CASE Agreement #4 – An Agreement between Client and Structural Engineer for Special Inspection Services. This agreement is intended for use when the Structural Engineer is hired directly by the Owner to provide Special Inspection services.

CASE Agreement #5 – An Agreement Between Client and Specialty Structural Engineer for Professional Services. This agreement is intended for use when the structural engineer is hired directly by a contractor or sub-contractor for work to be included in a project where you are not the Structural Engineer of Record.

CASE Agreement #6 – An Agreement Between Client and Structural Engineer for a Structural Condition Assessment. This agreement is intended for use when providing a structural condition assessment.

CASE Agreement #7 – An Agreement for Structural Peer Review Services. This agreement is intended for use when performing a peer review for an Owner or another entity

and includes responsibilities and limitations.

CASE Agreement #8 – An Agreement Between Client and Structural Engineer for Forensic Engineering (Expert) Services. This agreement is intended for use when the engineer is engaged as a forensic expert, primarily when the Structural Engineer is engaged as an expert in the resolution of construction disputes. It can be adapted to other circumstances where the Structural Engineer is a qualified expert.

Structural Engineer is Retaining Additional Entity CASE Agreement #9 – An Agreement Between Structural Engineer of Record and Design Professional for Services. This agreement is intended for use when the Structural Engineer of Record, serving in the role of Prime Design Professional or as a Consultant, retains the services of a sub-consultant or architect.

CASE Agreement #10 – An Agreement Between Structural Engineer of Record and Geotechnical Engineer of Record. This agreement is intended for use when the Structural Engineer of Record retains geotechnical engineering services. It can also be altered for use as an agreement between an Owner and the Geotechnical Engineer of Record.

CASE Agreement #11 – An Agreement Between Structural Engineer of Record and Testing Laboratory. This document is intended for use when the structural engineer retains testing services.

Other Situations CASE Agreement #12 – An Agreement Between Structural Engineer of Record (SER) And Contractor for Transfer of Digital

Data (Computer Aided Drafting (CAD) or Building Information Model (BIM)) Files.

This agreement is intended for use when transferring CAD or BIM files to others.

CASE Commentary #A – Agreement for Use with and Commentary on AIA Document C401 Standard Form of Agreement Between Architect and Consultant, 2017 Edition. This document is intended for use as a letter-form of agreement which adopts the AIA C401 by reference. This Agreement is intended for use when the owner-architect agreement is an AIA B-series. A scope of services is included. The purpose of the commentary is to point out provisions that merit special attention.

CASE Commentary #B – Commentary on AIA Document A295 – 2008 General Conditions of the Contract for Integrated Project Delivery, 2008 Edition. This document provides commentary on AIA Document A295 Integrated Project Delivery.

CASE Commentary #C – Commentary on AIA Document A201 General Conditions of the Contract for Construction, 2017 Edition.

This document provides Commentary on AIA document A201-2017 sections which merit special attention.

Additional Contracting Tools: • Tool 6-2: Scope of Work for Engaging Sub-consultants • Tool 6-3: Project Scoping Tool • Tool 8-1: Contract Review • Tool 8-2: Contract Clauses and Commentary

You can purchase these and the other Risk Management Tools at www.acec.org/bookstore.

68 STRUCTURE magazine

News of the Coalition of American Structural Engineers ACEC FALL CONFERENCE IS HERE … Don’t Miss Out! The 2021 Fall Conference will be held on Marco Island, FL, October 27-30, 2021.

Featured Speakers • Technology and Innovation Expert and Best-Selling Author Mitch Joel will speak on The Great Compression – Navigating Your Business in the New World.

• Hear from John Ondrasik, Singer/Songwriter, Five for Fighting, on Creativity, Storytelling, and Innovation.

• Ginny Clarke, Leadership Strategist and Former Director of Executive Recruiting at Google, will speak on Identifying ‘Best Talent’ and Defining Culture in the New Age of Work.

Sessions and Events In addition to the general sessions, forums/roundtables, and the ACEC/PAC events, the Conference also features educational sessions on vital industry issues which are relevant to Structural Engineers, including: • How Cognitive Bias Can Undermine Risk Management, Hosted by CASE, presented by Randy Lewis, AXA XL • Risk Management Challenges with a Virtual Workforce, Hosted by CASE, presented by Karen Erger and Kevin Holland, Lockton Companies For more information and to register, visit www.acec.org/conferences/fall-conference-2021.

ACEC SUMMER MEETING … Highlights CASE members got together in Nashville, TN, for one of the first in-person events for most attendees in over 18 months. CASE members attended risk management and business practices educational sessions, held committee meetings, and engaged with each other and with other ACEC Coalition members during the two-day meeting.

Some of the discussions included: • An update on the infrastructure package from ACEC Chair Robin Greenleaf and ACEC President and CEO Linda Bauer Darr • A roundtable discussion about Building Assessments and Risk Management • Education sessions on CyberSecurity, Current Trends, and Best Practices in Risk management and an overview of the 2020 ACEC Grand Conceptor Award-winning Cooperhill Watershed Restoration project CASE committees all met in person on the afternoon of August 10. Look in next month’s edition for a re-cap of all committee work and what new/updated publications are coming to an inbox near you!

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

O C T O B E R 2 0 21

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BRIDGING THE GAP ON AMERICA’S AGING INFRASTRUCTURE

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2021/22

STRUCTURAL ENGINEERING Resource Guide

Special Section Profiling

STRUCTURE’s Advertising Partners

STRUCTURAL ENGINEERING

Resource Guide

Profile

RISA

R

ISA believes structural engineering software should be powerful, accurate, and user-friendly. With this in mind, RISA software products (including ADAPT) allow engineers to effortlessly analyze and design steel, concrete, post-tensioned concrete, timber, masonry, aluminum, and cold-formed steel structures.

The following case studies illustrate the versatility of our software.

Roy and Diana Vagelos Education Center

Cal Poly Pomona Student Services Building Building Client: California State Polytechnic University, Pomona Structural Engineer: John A. Martin & Associates, Inc., Los Angeles, CA Built to serve a variety of student needs, the Student Services Building at Cal Poly stands as a symbol of the sustainable-focused mission of the university. Inspired by the surrounding topography, including the nearby San Gabriel Mountains, the undulating roof serves an

Riviera Stage at Riverview Park Building Client: City of Des Moines Parks and Recreation Structural Engineer: Raker Rhodes Engineering, Des Moines, IA During most of the 20th century, Riverview Park in Des Moines, Iowa, was home to Riverview Amusement Park, a popular family entertainment oasis that included the nationally known Riviera Ballroom. After its closure in 1978, the site sat empty for decades until it was recently redeveloped to include the new Riviera Stage.

The stage celebrates the city’s history and aims to bring performance back to the island that lies between the Des Moines River.

With the stage as the focal point of the new development, it was important to the designers that the location’s history influenced the design. Thus, the elevated stage includes an open-air canopy that links the design to the former amusement park’s ballroom, while the arch structure serves as a playful reminder of the roller coasters that once stood at the site. The main structural elements used in the stage canopy and arch structure are large round HSS sections (sizes ranging from 12- to 14-inch-diameter). Towering above the stage (60 feet above ground level) is a superstructure comprised of two arched box trusses, each spanning 120 feet. The trusses are connected by a 95-foot-long box truss which supports the signage for the stage.

Engineers utilized the RISA-Revit Link and RISA-3D to create the complex geometry and design the HSS members of both the canopy and arched truss structure. The design team could discern the internal forces at each joint using RISA-3D, helping to simplify the unique challenge of designing the fully welded, angled connections required at the HSS truss intersections.

ADVERTORIAL

Building Client: Columbia University Medical Center Structural Engineer: LERA Consulting Engineers, New York, NY The Roy and Diana Vagelos Education Center is a 107,000-squarefoot, 15-story state-of-the-art medical education facility located on the Washington Heights campus of Columbia University. The building serves as an instrumental tool in the team-based, problem-solvingfocused medical education provided to students. The tower includes a free-flowing “Study Cascade,” which serves as a vertical campus and intentionally designed spaces that focus on specific functions, such as anatomy labs, cadaver examination rooms, and a surgical simulation center. In totality, the building’s design allows for a wide range of learning experiences for medical students.

With the building’s layout creating challenging vertical load paths, engineers utilized cantilevered, high-strength (8 ksi concrete) post-tensioned concrete floors with bonded tendons that were supported by a pair of inclined composite concrete columns that slope up from the foundation level to the 8th Floor and direct load around the column-free auditorium.

ADAPT-Builder’s multi-story features were utilized to capture the load-sharing effects at the cantilevered slabs that are connected by single-story walls and ramps. Additionally, detailed deflection contour plots from ADAPT-Builder were used to coordinate deflections in the slab with the curtain walls above and below, ensuring that the stringent performance criteria were satisfied.

essential role in achieving LEED Platinum certification. The roof, spanning over two separate structures, mitigates the desert climate with its perforated overhangs while shading the exterior glass and reducing the thermal loads as well as glare.

As the main focal point of the structure, the organic, undulating roof consists of long-span tapered steel girders supporting a Kalzip standing-seam roof. The two-way span roof is curved in both directions, which posed considerable challenges for the design, fabrication, connection (19,000 roof panel attachment clips were used), and installation of the steel girders, requiring them to meet incredibly strict deflection tolerances.

Engineers utilized dxf files generated in BIM software to streamline the structural modeling, analysis, and design in RISA-3D. The software then enabled designers to manipulate geometry and loading conditions with ease while closely monitoring individual member deflections under various load combinations, ensuring successful fabrication and construction.

949-951-5815 | info@risa.com | risa.com STRUCTURAL ENGINEERING Resource Guide 2021 SS-71

SOFTWARE Adhesives Technology Corporation Phone: 754-399-1057 Email: jhanley@atcepoxy.com Web: atcepoxy.com/software Product: Pro Anchor Design Software Description: This adhesive anchor-focused design tool aids in meeting the design strength requirements of ACI 318. For use with any of ATC’s IBCcompliant anchoring products. Single pane interface minimizes data input time. Rapid 3-D modeling and real-time optimization of loading conditions, embedment depths, anchor sizes, and more. FREE download!

American Wood Council

Phone: 202-463-4756 Email: info@awc.org Web: www.awc.org Product: Wood Design Calculators Description: The American Wood Council has developed five free, web-, mobile- and tablet-based applications to streamline the process of ensuring new and existing buildings comply with the latest building codes. Apps are available for browsers, as well as iOS, Android, and Windows devices.

ASDIP Structural Software

Phone: 407-284-9202 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP Suite Description: Four intuitive software packages with over 16 modules to help you with all your engineering design tasks. For the past 28 years we have been developing powerful yet simple-to-use tools to easily analyze, design, optimize, and check your structural members.

Bentley Systems®

Phone: 800-BENTLEY Email: structuralinfo@bentley.com Web: www.bentley.com Product: STAAD.Pro Description: Perform comprehensive analysis and design for any size or type of structure faster than ever before using STAAD.Pro. Simplify your BIM workflow by using a physical model in STAAD.Pro that is automatically converted into the analytical model for your structural analysis. Share synchronized models for multi-discipline team collaboration.

Product: RAM Structural System Description: Provides a complete solution for analysis, design, drafting, and documentation for steel and concrete buildings, foundations, and even individual structural components, all in compliance with your local building codes.

CADRE Analytic

Phone: 425-392-4309 Email: j4@cadreanalytic.com Web: www.cadreanalytic.com Product: CADRE Pro Description: General structural application emphasizing on practical analysis of complex structures.

Includes discrete, pressure, hydrostatic, seismic, and dynamic response loading schemes. User friendly features for presenting, displaying, plotting, and tabulating extreme loads and stresses across the structure and across multiple load cases simultaneously. Basic code checking for steel, wood, and aluminum.

SS-72 STRUCTUREmagazine

ClearCalcs

Phone: 603-443-1038 Email: hello@clearcalcs.com Web: www.clearcalcs.com Product: Cloud Software Suite Description: Make design calculations the easiest part of your job. Effortlessly design and analyze everything from the roof down to the foundations in your choice of wood, steel, cold-formed steel, and concrete. Track loads through your whole structure, and use any recent building code with lightning quick FEA based results.

DEWALT Anchors & Fasteners

Phone: 800-524-3244 Email: anchors@dewalt.com Web: http://anchors.dewalt.com Product: DEWALT DESIGN ASSIST™ Description: State-of-the-art structural design software for concrete anchorages. Facilitates design efforts in base plate, equipment, and deck member anchorages, and post-installed rebar designs. Utilize an extensive library of mechanical, adhesive, and castin-place anchors with the Anchor Comparison Tool to easily see differences across anchor types, sizes, and brands. Download at website.

Digital Canal Corp.

Phone: 800-449-5033 Email: info@digitalcanal.com Web: www.digitalcanalstructural.com Product: Cold-Formed Steel Design Description: Please visit the website for New ColdFormed Steel design software information. You receive exceptional value with a one-project return on your investment. You also OWN your licenses. We do not force ongoing payments forever. Our 11,000 clients provide the best testimonial we can offer.

Dlubal Software, Inc.

Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM, RWIND Simulation Description: Wind tunnel numerical simulations for wind flow on all structures. Integrate resulting wind pressures into the FEA program RFEM for further design of steel, concrete, wood, CLT, aluminum, glass, and fabric/membrane structures according to USA/ International standards. Wind loading on specialty structures, not addressed in codes provisions, possible with RWIND Simulation.

Hohmann & Barnard, Inc.

Phone: 800-645-0616 Email: jenniferm@h-b.com Web: h-b.com Product: ProWall Tools Software Description: H&B’s premium, free software, ProWall Tools, allows architects, specifiers, suppliers, and contractors to quickly gather product information, create submittals, ensure that all products are compatible, and create custom take-offs. ProWall Tools now includes our Thermal Brick Support System to help optimize energy efficiency.

IES, Inc.

Phone: 406-586-8988 Email: info@iesweb.com Web: www.iesweb.com Product: IES Building Suite Description: You need practical, affordable tools that really help you solve analysis and design problems efficiently. Fortunately, with IES, Inc., you will get high quality reports from easy-to-use software. Find out for yourself why thousands of engineers rely on VisualAnalysis, VisualFoundation, ShapeBuilder, QuickRWall and our other excellent products.

INTEGRITY SOFTWARE, INC.

Phone: 512-372-8991 Email: sales@softwaremetering.com Web: www.softwaremetering.com Product: SofTrack Description: Use SofTrack to control Bentley Application usage by product code and feature (pipes, ponds, rails). Also control Bentley Passport/Visa usage. Receive idle usage alerts. Seamless operation for local and remote usage including Citrix sessions.

Additionally benefit from Automatic Autodesk named-user tracking and reporting.

Losch Software Ltd

Phone: 323-592-3299 Email: loschinfo@gmail.com Web: www.loschsoft.com Product: LECWall Description: The industry standard for concrete insulated “sandwich” wall panel design and handles multi-story columns as well. LECWall can analyze prestressed and/or mild reinforced wall panels with zero to 100 percent composite action. Flat, hollowcore, and stemmed configurations are supported.

Complete handling analysis is also included.

Product: LECPres Description: Can analyze prestressed and/or mild reinforced simple span or cantilevered concrete beams and slabs. Handling analysis is also included. A 15day trial version is available.

ENERCALC, Inc.

ENERCALC Phone: 949-645-0151 Email: info@enercalc.com Web: https://enercalc.com Product: ENERCALC Structural Engineering Library Description: ENERCALC 3D FEM and RetainPro modules are part of installed/cloud SEL. New FEMpowered Steel Base Plate and Flitch Plated Wood Beam modules. No more hand-calculated Z values!

Subscription seats are now automatically shared between installed/cloud users! SEL’s windows are bigger, cleaner, better organized.

Not listed?

Our monthly 2022 Resource Guide forms are now available on our website.

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Profile

DEWALT® Anchors & Fasteners

mechanical and adhesive anchors matched with cordless tool and dust collection systems to help contractors safely install anchors into concrete and masonry.

New this year, the DEWALT Critical Connection Undercut Anchor (CCU+) combines a robust design with the low displacement characteristics of an undercut anchor built for high performance and applications. For post-installed, critical concrete connections, the new CCU+ delivers on Performance, Productivity, and Range.

Qualified under ICC-ES ESR-4810, the CCU+ Undercut Anchors are for heavy-duty loading in cracked and uncracked concrete. Their published design values offer flexible options, like close anchor spacing and edge distances. Loading performance features high tension and shear loads comparable to cast-in-place anchor bolts. The CCU+ Anchors are Made In The USA and are available in two steel grades: zinc plated carbon steel B7 highstrength steel for interior conditions and 316 Stainless Steel for exterior and wet conditions. Two styles are offered: Pre-Set anchors for installing anchors and fixtures and Thru-Bolt configurations for fixtures already in position.

During installation of CCU+ Anchors, a hollow bit with a stop collar is available for the primary hole, and the undercut is formed with a hollow undercutting bit. Both bits capture silica dust in a HEPA filtration dust extractor and limit exposure as part of the DEWALT DUSTX+™ System. This installation system is available fully cordless as part of the DEWALT 60V MAX* platform.

DEWALT products are sold through a network of construction and industrial supply distributors. In addition, DEWALT Anchors and Fasteners support is available via local field engineer representatives, as well as our engineering direct phone number and email.

Please visit the website for the full DEWALT Anchors and Fasteners offerings. From mechanical and adhesive anchoring to jobsite and engineering support, DEWALT is a Guaranteed Tough™ solution to your commercial and industrial construction needs from DESIGN to BUILD to SUPPORT.

ADVERTORIAL

hen choosing concrete and masonry anchors, both contractors and engineers look for productivity-enhancing solutions. DEWALT® complements its leadership position in Power Tools with a complete range of Anchors and Fasteners to provide such solutions.

Traveling along a customer’s journey, we begin with the construction design. The needs of specifiers and designers have changed, and post-installed concrete anchoring now has its own set of rules set forth by the International Building Code (IBC) code and American Concrete Institute (ACI). Certain anchorage situations call for the utilization of a software solution specifically created to handle the complex calculations required to build modern structures. DEWALT understands these needs and thus created DEWALT DESIGN ASSIST™ (DDA).

DDA is a no-cost/no-fee, state-of-the-art structural design software that streamlines, automates, and optimizes your concrete anchoring design process. DDA includes multiple design standards, a comprehensive library of anchors, numerous reporting options, and unparalleled tools to simplify your design process. Features include Base Plate Anchorage – the standard tool to use when considering anchorage to concrete, allowing complete geometric flexibility with the anchor patterns or base plate shape. Designs are calculated to be compliant with the latest major published design criteria and use products that independent approval bodies have tested for performance and reliability. The included Equipment Anchorage module further extends the functionality of base plate designs, now allowing you to leverage DDA to model wind and seismic forces acting on equipment and helps resolve optimal anchorage solutions at a larger scale. Additional modules include Anchorage to Deck Members, Post-Installed Rebar Design, and Anchors Comparisons, with code compliance to ACI 318-19, ACI 318-14, CSA A23.3-19, and CSA A23.314. Please visit anchors.DEWALT.com/DDA to download the complete program.

Once your designs have been completed, DEWALT offers the commercially available Mechanical and Adhesive Anchors with productivity at the forefront.

DEWALT mechanical anchors include a cracked concrete qualified range of PowerStud+™ carbon steel SD1, SD2, and stainless steel with SD4 and SD6. The Screw-Bolt+™ concrete screw anchor is a cracked concrete qualified, high-performance screw anchor available in both Hex and Flat heads for a finished look. They install quickly with DEWALT impact wrenches and drivers and are removable (as necessary). The UltraCon+ fastening system is a complete family of small diameter screw anchors for light to medium duty applications in concrete, masonry block, brick, and wood base materials.

DEWALT also has post-installed rebar and threaded rod anchor designs and installation covered for your project, as well as

800-524-3244 | anchors@dewalt.com | anchors.dewalt.com STRUCTURAL ENGINEERING Resource Guide 2021 SS-73

SOFTWARE Nanometrics

SkyCiv Engineering

National Council of Examiners for Engineering and Surveying

Strand7 Pty Ltd

Phone: 855-792-6776 Email: sales_mkt@nanometrics.ca Web: www.nanometrics.ca Product: Vantage Structural Health Monitoring Description: An integrated solution for monitoring the structural integrity of critical infrastructure and facilities, the Vantage Structural Health Monitoring portal provides immediate notification of significant events along with automatically compiled incident reports for rapid assessment of any impact to a facility.

Phone: 800-250-3196 Email: jbarker@ncees.org Web: ncees.org Product: Professional Engineering License Description: The National Council of Examiners for Engineering and Surveying (NCEES) is a nonprofit organization dedicated to advancing professional licensure for engineers and surveyors.

RedBuilt™

Phone: 866-859-6757 Email: info@redbuilt.com Web: www.redbuilt.com Product: RedSpec™ Description: A convenient, user-friendly design program that lets you quickly and efficiently create floor and roof design specifications using Red-I™ joists, RedBuilt open-web trusses, RedLam™ LVL, glulam beams and dimensional lumber. RedSpec is provided free of charge to registered users. Contact us if you need support.

RISA

Phone: 949-951-5815 Email: info@risa.com Web: risa.com Product: ADAPT-Builder Description: Powerful and easy-to-use 3-D finite element software for multistory reinforced concrete and post-tensioned buildings and structures. Builder delivers comprehensive workflows for complete analysis and design. Combine gravity, lateral, and post-tensioning actions for efficient, complete, and accurate design. Integrate with various BIM software for seamless project deliverables.

Product: RISAFloor Description: Designs and optimizes building systems constructed of steel (composite and noncomposite), concrete, wood, and CFS, as well as combinations of materials. Automatic live load reduction, additive or exclusive floor area loads, vibration calculations, and more make RISAFloor the first choice for the design of all types of building systems.

Product: RISA-3D Description: Version 19 is the next step in the evolution of the completely redesigned RISA-3D. With new features including the design of coldformed steel walls, AISC and ACI code updates, seismic improvements, and the introduction of orthotropic plates, engineers can effortlessly complete complex projects utilizing any material.

SS-74 STRUCTUREmagazine

Phone: 800-838-0899 Email: support@skyciv.com Web: www.skyciv.com Product: SkyCiv API Description: SkyCiv is excited to announce their structural analysis and design API. Cloud based API lets users connect their tools directly to SkyCiv technology, automating and improving parts of the design process. Functions include: model generation, FEA solver, member design, wind load calculations, 3-D rendering, and much more.

Phone: 252-504-2282 Email: info@strand7.com Web: www.strand7.com Product: Strand7 Description: A general-purpose FEA system comprising integrated pre- and post-processing and solvers. Used for linear and nonlinear analysis of structures and components (static, dynamic, and heat transfer) by engineering companies of all sizes and disciplines. Strand7 has gained worldwide acceptance as a powerful tool for structural analysis, particularly nonlinear analysis.

StructurePoint

Phone: 847-966-4357 Email: info@structurepoint.org Web: www.structurepoint.org Product: Concrete Design Software Suite Description: Concrete design software programs updated to ACI 318-14 for concrete buildings, concrete structures, and concrete tanks. Reinforced concrete structural software includes programs for the design of columns, bridge piers beams, girders, one and two-way slabs, shearwalls, tilt-up walls, mats, foundations, tanks, and slabs-on-grade.

(Formerly the PCA Engineering Software Group)

Trimble

Phone: 770-715-3976 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Tekla Tedds Description: Automates repetitive and error prone structural and civil calculations, allowing engineers to perform 2-D frame analysis, access a large range of automated structural and civil calculations to U.S. codes, and speed up daily structural calculations.

Product: Tekla Structures Description: Create and transfer constructible models throughout the design life cycle, from concept to completion. With Tekla Structures, accurate and information-rich models reduce RFIs, leverage models for drawing production, material take-offs, and collaboration with architects, consultants, fabricators and contractors.

Trimble Monitoring

Phone: 720-376-1909 Email: riley_smith@trimble.com Web: https://monitoring.trimble.com Product: Trimble 4D Control Description: Provides automated movement detection, enabling project stakeholders of critical transportation infrastructure, tunnels, dams, mines, natural hazards, and buildings surrounding construction sites to monitor in real-time with confidence. This customizable platform allows multiple sites to be managed with unparalleled movement analysis and extensive support for a wide variety of monitoring sensors.

Victaulic

Phone: 713-752-1914 Email: stephanie.black@hkstrategies.com Web: www.victaulicsoftware.com Product: Victaulic Tools for AutoCAD® Description: An all-new, free tool that provides AutoCAD users the same classic routing features and drawing productivity gains that were previously only available in the Victaulic Tools for Revit platform. The add-on provides toolsets engineered for civil, industrial, plant, or mechanical projects, and includes features to simplify pipe routing, procurement, and exporting bill-of-materials.

Visicon Inc

Phone: 650-218-0008 Email: info@visicon.com Web: https://visicon.com Product: Visicon Model Review and Checking Description: Gives structural engineers unprecedented visibility into all of the design, analysis, and production BIM models they use and review. No matter the source (Revit, IFC, ETABS, ADAPT, point cloud, etc.), our solution provides an easy and powerful way to understand, compare, and check project models.

WoodWorks® Software

Phone: 800-844-1275 Email: sales@woodworks-software.com Web: www.woodworks-software.com Product: WoodWorks Design Office Suite Description: Conforms to IBC 2015, ASCE 7-10, NDS 2015, SDPWS 2015. SHEARWALLS: designs perforated and segmented shearwalls; generates loads; rigid and flexible diaphragm distribution methods. SIZER: designs beams, columns, studs, joists up to 6 stories; automatic load patterning. CONNECTIONS: Wood-to-wood, wood-to-steel, or wood-to-concrete.

Listings are provided as a courtesy, STRUCTURE is not responsible for errors.

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PORTLAND CEMENT ASSOCIATION

T

healthy lives via structures that withstand natural and man-made disasters. PCA members are committed to delivering products that meet those needs as well as drive down emissions and achieve the industry’s environmental goals. This roadmap enables our member companies and partners along the cement and concrete value chain to continue building a better future, Shaped by Concrete.

About Design and Control of Concrete Mixtures, 17th Edition Design and Control of Concrete Mixtures has been the cement and concrete industry’s primary reference on concrete knowledge for almost 100 years. Since the first edition was published in 1924, the U.S. version has been updated 16 times to reflect advances in cement and concrete technology and to meet the growing needs of architects, engineers, builders, concrete producers, concrete technologists, instructors, and students This fully revised 17th edition was written to provide a concise, current reference on concrete, including the many developments that occurred since the last edition was published in 2016. The text is backed by over 100 years of research by the Portland Cement Association and other industry groups. It reflects the latest guidance on standards, specifications, and test methods of ASTM International (ASTM), the American Association of State Highway and Transportation Officials (AASHTO), and the American Concrete Institute (ACI).

The 17th edition includes an in-depth restructuring of the existing content, presenting a 40% increase in new information over the previous edition. This edition also has added two new chapters on imperfections in concrete and innovations in concrete.

Over 3 million copies of past editions of the book have been distributed, making this book a primary reference on concrete technology.

ADVERTORIAL

he Portland Cement Association (PCA), founded in 1916, is the premier policy, research, education, and market intelligence organization serving America’s cement manufacturers. PCA members have facilities across the United States and represent the majority of American cement production.

The cement and concrete industries, directly and indirectly, employ over 600,000 people and contribute more than $100 billion each year to the nation’s economy. PCA promotes sustainability, safety, and innovation in all aspects of construction, fosters continuous improvement in cement manufacturing and distribution, and generally promotes economic growth and sound infrastructure investment.

Cement producers have a strong culture of innovation. They are in constant pursuit of finding more innovative and efficient ways of producing the high-quality cement our nation needs for things like homes, highways, hospitals, and the infrastructure that delivers safe drinking water. Since 1990, the industry has reduced energy consumption by 35%, emissions intensity by 11%, and company-led improvements have increased the use of alternative fuels, such as industrial byproducts that otherwise would end up in landfills.

In late 2020, PCA released a climate ambition statement: PCA and its members will develop a roadmap by the end of 2021 to facilitate member companies achieving carbon neutrality across the cement and concrete value chain by 2050. This roadmap will guide the industry on perhaps the most ambitious carbon neutrality journey ever attempted. The entire value chain of clinker, cement, concrete, construction, and concrete as a carbon sink is an integral part of tomorrow’s circular economy, and each area has its part to play. This roadmap enables the construction sector to meet this sustainability goal, and collaboration with industry and private partners will be imperative to realize the multitude of solutions outlined.

Cement and concrete have been pivotal in building resilient communities that enable people to live safe, productive, and Chapter List 1 – Introduction to Concrete

13 – Specifying, Designing, and Proportioning Concrete Mixtures

2 – Portland, Blended, and Other Hydraulic Cement

14 – Batching, Mixing, Transporting, and Handling Concrete

3 – Supplementary Cementitious Materials

15 – Placing and Finishing Concrete

4 – Mixing Water for Concrete

16 – Imperfections in Concrete

5 – Aggregates for Concrete

17 – Curing Concrete

6 – Chemical Admixtures for Concrete

18 – Hot Weather Concreting

7 – Fibers

19 – Cold Weather Concreting

8 – Reinforcement

20 – Test Methods

9 – Properties of Concrete

21 – Paving

10 – Volume Changes of Concrete

22 – Structures

11 – Durability

23 – High-Performance Concrete

12 – Sustainability

24 – Innovations in Concrete Technology

Available in both hardcopy and Ebook versions: Purchase your copy here www.cement.org/designandcontrol

For more information, visit www.cement.org or www.shapedbyconcrete.com STRUCTURAL ENGINEERING Resource Guide 2021 SS-75

CONCRETE American Concrete Institute

Commercial Metals Company

CTS Cement Manufacturing|Komponent®

ASDIP Structural Software

Concrete Fiber Solutions

Geopier® Foundation Company

Phone: 248-848-3800 Email: support@concrete.org Web: www.concrete.org/membership Product: Memberships Description: With 30,000 members in more than 100 countries, ACI is the premier, global community dedicated to the best use of concrete. With enhanced benefits, ACI membership provides information on engineering and construction practices worldwide.

Individual, student, organizational, and sustaining memberships are available.

Phone: 407-284-9202 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP CONCRETE Description: Includes easy-to-use intuitive modules for the design of multi-span continuous beams, biaxial slender columns, concrete/masonry bearing walls, and wall opening design, per the latest design codes. ASDIP CONCRETE comes with 3 intuitive modules with powerful interfaces that will substantially simplify timeconsuming calculations for your structural designs.

Phone: 949-405-9161 Email: chromx@cmc.com Web: www.cmc.com/chromx Product: ChromX® Description: High strength rebar with a range of corrosion resistance levels. Designers can select the appropriate level and strength needed, based on the project’s service life. High strength and corrosion resistant properties within the steel result in a reduction in construction costs, shortened build times, reduced congestion issues, and improved safety.

Phone: 847-495-4700 Email: matthewn@concretefibersolutions.com Web: www.concretefibersolutions.com Product: CFS Steel Fibers Description: Provides better shrinkage crack control than rebar or wire mesh because the fibers are evenly mixed throughout the concrete, meeting micro-cracks where they originate to improve performance and finish. CFS Fibers are clean, free from contaminants, and designed to meet or exceed the requirements of ASTM A820.

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Phone: 714-614-7392 Email: sgoodman@ctscement.com Web: www.ctscement.com Product: Komponent, Type K Cement Description: CTS Cement manufactures CSA cements. Our Komponent shrinkage-compensating cement improves overall structural performance and dimensional stability. It prevents volume change due to drying shrinkage, providing numerous constructability advantages while maximizing inservice performance and design life. From slabs-ongrade to post-tension, containment to pavement, delivering value and performance is what we do.

Phone: 704-439-1790 Email: info@geopier.com Web: geopier.com Product: Geopier Rammed Aggregate Pier® and Rigid Inclusions Description: Geopier provides an efficient and costeffective Intermediate Foundation® solution for the support of settlement structures. Our systems have become effective replacements for massive overexcavation and replacement or deep foundations, including driven piles, drilled shafts, or augered cast-inplace piles. Thousands of structures around the world are currently supported by Geopier technologies.

Profile

CTS CEMENT MANUFACTURING CORPORATION Cement Technology Engineered for Superior Performance and Results

common and costly challenges related to concrete deterioration, repair, and structural failure. Use Komponent technology to minimize or eliminate control joints, alleviate curling and shrinkage cracking, and reduce repair and maintenance costs.

Komponent technology protects the integrity and durability of the concrete, extends the service life of the installation, and reduces lifecycle costs. It offers the most sustainable concrete solution available.

CTS products have been used on notable landmarks like the Hoover Dam Bypass, the Pentagon, the Lincoln Tunnel, the San FranciscoOakland Bay Bridge, as well as major roadways, airports, commercial and industrial projects worldwide.

CTS’ experienced team of engineers, material scientists, technical experts, and field representatives are available to support your next project. Contact us for assistance with product selection, specifications, samples, mix designs, and more.

800-929-3030 | info@ctscement.com | www.ctscement.com SS-76 STRUCTUREmagazine

ADVERTORIAL

CTS Cement manufactures two of the industry’s leading brands in cement for new concrete construction, restoration, and repair – Rapid Set® and Komponent®.

Rapid Set is a full line of professional-grade cement products made with Rapid Set cement, a Belitic Calcium Sulfoaluminate (BCSA) cement technology. Rapid Set cement emits 32% less CO2 than portland cement because of less fuel, lower temperatures, and less limestone being used in the production process. In addition, since Rapid Set cement concrete lasts longer than portland cement concrete, replacement and maintenance are reduced, which means less pollution is released into the environment.

Rapid Set cement products are engineered for high performance, versatility, low shrinkage, and rapid strength gain – performance characteristics that save significant time and money with reduced installation times, labor requirements, and long-term operations and maintenance costs. Rapid Set gains structural strength in one hour. You can build faster, quickly put the structure or area into full service, and achieve durable, long-lasting results.

Komponent is a line of shrinkage-compensating concrete products made with Type K cement technology. These products prevent

CONCRETE Gripple Inc.

PS=Ø®

Somero® Enterprises

MAX USA Corp.

RISA

TAYLOR DEVICES INC

Phone: 630-406-0600 Email: e.balsamo@gripple.com Web: www.gripple.com Product: Spider Cast-in-Place Concrete Insert Description: A versatile cast-in-place insert that accommodates threaded rod sizes from 3⁄8 to 3⁄4 inch or Gripple Cable Hangers. For wood form or metal deck, this provides one product solution across the entire project, giving mechanical, electrical, and piping contractors flexibility to determine how they’ll suspend something after the concrete is poured.

Phone: 800-223-4293 Email: yasaba@maxusacorp.com Web: www.maxusacorp.com Product: PowerLite® System Description: Power beyond the limits of standard 100 PSI pneumatic tools with the PowerLite system. Designed with a lightweight body and engineered for heavy-duty applications, PowerLite tools are built to shoot through steel, concrete, and engineered woods.

Phone: 800-355-8414 Email: sales@pourstrip0.com Web: www.pourstrip0.com Product: PS=Ø Steel Reinforcement Splice System Description: Eliminates pour strips and maintains rebar continuity while allowing for volume change.

Using proven coupler technologies recognized worldwide, the PS=Ø system features a tapered thread on one end and a grout-filled sleeve on the other. The system requires no redesign, is an ACI permitted Type 1 and Type 2 mechanical splice, is ICC approved, and made in the USA.

Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: ADAPT-PT/RC Description: Internationally-recognized and established analysis and design software for reinforced concrete and post-tensioned slabs and beams. The easy-to-use modeling and design environments enable any user to quickly produce optimized designs and quantity take-offs.

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®

Phone: 239-210-6519 Email: sales@somero.com Web: www.somero.com Product: Somero SkyScreed® Laser Screed® Machine Description: Introducing the Somero Sky Screed 36.

Through advancements in technology and feedback from our customers, the Somero Sky Screed machine is the first Laser Screed machine in the world to allow screeding on structural high-rise and slab-ongrade applications. The versatile articulating knuckle boom provides unparalleled versatility.

Phone: 716-694-0800 Email: marketing@taylordevices.com Web: www.taylordevices.com Product: Fluid Viscous Dampers Description: Developed for NASA in the 1960s, fluid viscous dampers have successfully transitioned to the civil engineering community for use in protecting buildings, bridges, and other structures worldwide.

These dampers increase structural damping levels to as much as 50% of critical, the results being a dramatic reduction in stress and deflection.

Profile

MAX USA CORP

The HN120 has a selfcleaning end-cap filter that traps any dirt that enters the tool and expels it when the hose is disconnected. This tool needs service approximately every 200,000 shots, a period that is 40x longer than P.A.T.s and 10x longer than gas tools. The tool also takes air from the compressor, not the environment, decreasing the probability of pulling dirt into the tool.

With a driving force of 2,231-inch-lbs, the HN120 drives .307-inch headpins into concrete or steel. The MAX HN120 can shoot a variety of fasteners, and its sequential trigger adds a layer of safety, preventing the nail from firing unless the nose is depressed. MAX recommends disconnecting the air hose when the tool is not in use.

Very versatile, the PowerLite system shoots a wide variety of pins.

PowerLite fasteners come in 50 or 100 pin coils, which require less reloading and save the operator’s time.

ADVERTORIAL

AX is a leading manufacturer of pneumatic nailers, staplers, and specialty tools with approximately 80 years of manufacturing experience. MAX developed the world’s first 500 psi pneumatic system in 1994. This system is designed to give commercial builders an alternative solution for fastening steel and concrete. No certification or license is necessary.

Engineered to perform at a higher standard in cold temperatures, during low voltage scenarios, or as a replacement to tools with strict operational protocols, PowerLite® system tools can easily fasten engineered woods such as LVL and LSL. The system also effectively fastens wood to concrete, wood to I-beam, steel to concrete, and steel to steel.

PowerLite tools are extremely powerful, yet their size is up to 40% smaller and 30% lighter than conventional 100 PSI tools. The MAX PowerLite system provides a hassle-free pneumatic solution for which no license or certification is needed to operate. Because air is used to power the tools, there is no need for warming or cooling of the environment to maintain the PowerLite® system’s performance.

One notable tool from the PowerLite product line is the HN120 concrete/steel pinner. With the ability to actuate between 150320 psi of compressed air flowing into the small tool body, little air is required to shoot fasteners because of the higher air pressure, which brings higher driving power.

800-223-4293 | yasaba@maxusacorp.com | www.maxusacorp.com STRUCTURAL ENGINEERING Resource Guide 2021 SS-77

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CAST CONNEX

Elegance in Design CAST CONNEX was founded in 2007 with a mission to realize the potential of this research and put castings into service by enabling structural engineers and architects to leverage castings in their building and bridge designs. Since then, the company has put tens of thousands of steel castings into service in hundreds of structures, establishing itself as an enabler of its collaborators’ innovative designs as well as an innovator in its own right.

Today, CAST CONNEX is a rapidly growing multinational organization, and elegance in design remains a core value. To CAST CONNEX, elegance encompasses everything from utility to aesthetics to manufacturability. “All of our solutions are developed with the aim to improve overall structural performance and safety, to simplify steel fabrication and field installation, and to beautify the spaces in which our components are used,” says company President and CEO Carlos de Oliveira.

Company co-founder and Executive Vice President Dr. Michael Gray is equally motivated. “In my ideal world, there would be more incentive to push buildings to higher levels of performance,”

says Gray. “As an industry, we ought to move beyond code minimum; we need to elevate our standards. And not just for structural performance, but for aesthetics in design, too.”

CAST CONNEX Engineers and Technical Sales personnel bring experience in structural engineering consulting and construction to each interaction with specifying practitioners and the construction team for each project.

A Variety of Standardized and Custom Solutions CAST CONNEX offers pre-engineered steel connection solutions ranging in applicability from strictly functional to those ideals for use in architecturally exposed structural steel (AESS) and ranging in weight from 16 pounds to 22 tons. Standardized products are currently available for use in steel, concrete, and timber-steel hybrid construction. The company continues to develop standardized cast steel components.

CAST CONNEX custom cast steel solutions have a virtually limitless scope in application from 10-pound precision machined fittings for custom facades to 10-ton nodes for special structures, are designed to address project-specific needs, and can provide economy in-shop fabrication and field erection as well as create connection details that enable iconic architecture. The company’s design-build services for custom casting supply typically include industrial design and 3-dimensional modeling, engineering including finite element stress analysis, and casting detailing and manufacturing.

(416)806-3521 | info@castconnex.com | www.castconnex.com SS-78 STRUCTUREmagazine

ADVERTORIAL

ixteen years ago, a research group at the University of Toronto was established to explore how steel casting manufacturing could be leveraged to simplify and improve conventionally fabricated structural steel connections.

Cast steel alternatives to codified steel connection types ranging from high-seismic to pin connectors were developed through an iterative design process informed by full-scale destructive testing, a close understanding of manufacturing, and industry insights from practitioners in design and construction. The work not only supported the hypothesis that castings can provide dramatically improved structural performance and resilience over conventionally fabricated steel connections but also emphasized the architectural potential of the geometric freedom afforded by casting manufacturing.

BRIDGES American Galvanizers Association Phone: 720-554-0900 Email: marketing@galvanizeit.org Web: https://galvanizeit.org Product: Hot-Dip Galvanized Steel Description: The American Galvanizers Association (AGA) provides technical support on today’s innovative applications and state-of-the-art technological developments in hot-dip galvanizing for corrosion control.

Adhesives Technology Corporation Phone: 754-399-1057 Email: atcinfo@atcepoxy.com Web: www.atcepoxy.com Product: CRACKBOND® Overlays and Sealers Description: BRIDGE-GARD is the world’s most advanced epoxy polymer concrete formulation.

EPOTHANE T3 is a low-modulus, epoxy urethane skid-resistant overlay. V65 HI-MOD, V120 LOWMOD, and V200 HI-MOD: a suite of healer/sealers with varying viscosities and moduli to extend the life of decks and roadways. ATC is a Meridian Adhesives Group Company.

Cast Connex

Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Standardized Cast Steel Connectors and Custom Cast Steel Connectors Description: The industry leader in the architectural and structural use of cast steel components in the design and construction of building and bridge structures. Our products include pre-engineered connectors that simplify the design and enhance the performance of structures. We also offer design-build services for custom cast steel nodes and components.

Product: Cast Steel Nodes Description: The use of cast steel nodes in steel bridge structures can provide improved fatigue performance, enhanced structural resilience, and can reduce the total life-cycle cost of pedestrian, road, and rail bridges.

CintecReinforcement Systems Ltd

Phone: 613-225-3381 Email: rlr@cintec.com Web: www.cintec.com Product: Archtec Description: Complete diagnostic, design, and installation service, using state-of-the-art technology and drilling methods. Specially designed to strengthen masonry arch bridges internally, while preserving historical value. This novel system of internal strengthening involves inserting and grouting stainless steel reinforcing bars into the masonry. Stainless steel and a high-performance grout enhance durability.

Listings are provided as a courtesy, STRUCTURE is not responsible for errors.

Dlubal Software, Inc.

Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM Description: Capable of linear, non-linear, static, and dynamic analysis, RFEM is complete with moving load generation (AASHTO library), influence lines, cable form-finding, parametric modeling, and multimaterial design considerations. This FEA software is seamless in the design and analysis of pedestrian and highway cable-stayed, suspension, arch, and beam bridge structures.

Anchors

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New Millennium Building Systems

Phone: 260-969-3500 Email: gerald.arvay@newmill.com Web: www.newmill.com Product: Bridge-Dek® Description: Suitable for new bridge construction and rehabilitation, Bridge-Dek stay-in-place deck forming systems offer your project ease and speed of construction, safety, durability, and longevity.

Bridge-Dek is made of high-strength galvanized steel to meet design requirements of steel and concrete bridge structures.

POSTEN Engineering Systems Dynamic Isolation Systems

Phone: 775-359-3333 Email: sales@dis-inc.com Web: www.dis-inc.com Product: Lead Rubber Bearing Description: For Base Isolation of bridges. Allow bridges to survive earthquakes with no damage while providing cost savings on substructures due to reduced forces. They require no maintenance and are extremely durable.

Hexagon

Phone: 346-260-8798 Email: andrea.velazquez@hexagon.com Web: https://hexagonppm.com Product: GT STRUDL Description: A trusted, general-purpose beam and FEA solution. Bridge engineers can leverage the power of the moving load generator, truss wizard for quick model generation, ability to model sloped and skewed geometry, and perform staged construction and cable or dynamic analysis to solve complex projects.

ICC-ES

Phone: 800-423-6587 Email: es@icc-es.org Web: www.icc-es.org Product: Evaluation Service Description: A nonprofit, limited liability company, ICC-ES is the leading evaluation service for innovative building materials, components, and systems. ICC-ES Evaluation Reports (ESRs), Building Product Listings, and PMG Listings provide evidence that products and systems meet requirements of codes and technical standards.

ICC-ES is a member of the ICC family of solutions.

Phone: 510-275-4750 Email: sales@postensoft.com Web: www.postensoft.com Product: POSTEN Description: The most efficient and comprehensive post-tensioned concrete software in the world that, unlike other software, not only automatically designs the tendons, drapes, as well as columns, but also produces highly efficient, cost saving, sustainable designs with automatic documentation of material savings for LEED. The others simply Analyze – POSTEN DESIGNS.

RISA

Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: RISA 3-D Description: With RISA 3-D’s versatile modeling environment and intuitive graphical interface, you can model structures like pedestrian bridges in minutes. Get the most out of your model with advanced features such as moving loads, dynamic analysis, and over 40 design codes. Structural design has never been so easy!

S-FRAME Software

Phone: 203-421-4800 Email: info@s-frame.com Web: s-frame.com Product: S-FRAME Analysis Description: Model, analyze, and design structures regardless of geometric complexity, material type, loading conditions, nonlinear effects or seismic loads.

Integrated concrete design, foundation design, and steel design maximizes your productivity. Our continued investment in R&D gives users the latest analysis advantages and dedicated technical backing.

S-FRAME for faster, better, advanced analysis.

Trimble LUSAS

Phone: 646-732-7774 Email: info@lusas.com Web: www.lusas.com Product: LUSAS Bridge Description: Use to analyze, design, and assess all types of bridge structures and investigate soil/structure interaction effects. Recent releases have extended the engineer’s workflow from analysis into steel and RC frame design, and improved prestress, concrete modeling, and vehicle and rail loading capabilities.

Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Tekla Structures Description: First class structural software for steel, concrete, wood, and composite bridge structures and details. Tekla Structures increases productivity through higher automation of fabrication and 4-D product management. Drawings and reports automated generally from the constructible 3-D model. The detailed model can bring efficiency to bridge maintenance and repairs.

STRUCTURAL ENGINEERING Resource Guide 2021 SS-79

SEISMIC Adhesives Technology Corporation

CoreBrace

Phone: 801-280-0701 Email: brandt.saxey@corebrace.com Web: www.corebrace.com Product: CoreBrace Buckling Restrained Brace Description: CoreBrace, world leader in Buckling Restrained Brace (BRB) design and fabrication, offers a cost-effective and efficient solution for energy dissipation by minimizing forces that buildings must be designed to accommodate, including new construction and retrofits. The CoreBrace team of engineers and experts are available to work with your design team.

Gripple Inc.

Phone: 754-399-1057 Email: atcinfo@atcepoxy.com Web: www.atcepoxy.com Product: ULTRABOND® and CRACKBOND® Adhesives Description: America’s #1 structural adhesive specialist offers four IBC compliant, wind- and seismic-rated adhesives, including HS-1CC, the world’s strongest anchoring epoxy. And CRACKBOND ACCUGROUT HD is a high strength grout designed for onshore and offshore wind farm installations. ATC is a Meridian Adhesives Group Company.

CAST CONNEX®

DuraFuse Frames

Lindapter International

Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Cast Bolted Brackets Description: Prequalified connectors for special and intermediate steel moment frames per AISC 358 and can be used in the retrofit of seismically deficient steel moment framed buildings or in new construction.

Product: High Strength Connectors™ Description: Standardized, capacity-designed brace end connectors that accommodate bolted double-shear connection between round HSS braces and a typical corner gusset plate.

Phone: 801-727-4060 Email: contact@durafuseframes.com Web: www.durafuseframes.com Product: DF360 Description: Steel moment frames with one-of-a-kind resilience, exceptional performance, and improved economy. Seismic energy is dissipated without beam or column damage, minimizing post-earthquake repair cost and duration. Versatile solutions apply to all building types and hazard categories with DuraFuse Frames engineers as seamless extensions of your team providing economical, resilient designs.

STRUCTURAL ENGINEERING

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Phone: 630-406-0600 Email: e.balsamo@gripple.com Web: www.gripple.com Product: Gripple Seismic Cable Bracing Systems Description: Specifically designed and engineered to brace and secure suspended nonstructural equipment and components within a building or structure.

Suitable for bracing new or retrofit installations in a variety of configurations. Ready-to-use kits, fast to install, no tools required, four color-coded kit sizes.

Phone: 866-566-2658 Email: inquiries@lindapter.com Web: www.lindapter.com Product: Hollo-Bolt Description: The original expansion bolt for structural steel; ICC approved for Seismic Design Categories A through F. The Hollo-Bolt is quickly installed from one side of the steel by simply inserting the fastener into a pre-drilled hole and tightening with a torque wrench, saving time and money.

Profile

COREBRACE

5. Minimized strengthening of existing structural members and foundations 6. Availability of advanced modeling and sustainability design aids 7. Integration with structural analysis and detailing software packages 8. Replaceability after a major seismic event, if necessary CoreBrace designs and manufactures all products within its AISC Certified facility utilizing in-house designers, engineers, project management, and sales staff. Added to these capabilities is a strong commitment to collaboration. CoreBrace provides attention to detail that is unmatched in the industry. Through dedication to continuous improvement and innovation, CoreBrace is a progressive company always looking for new perspectives, opportunities to improve, ways to excel, and methods to outperform. CoreBrace provides its clients with confidence that their project is built to the highest standards, using the best options and latest modern approaches available. The global success of CoreBrace is the result of a worldwide need for reliable seismic solutions to protect structures from the devastating effects of earthquakes. CoreBrace provides its clients with complete dependability, high-quality assurance, and customized schedule performance on every project.

801-280-0701 | info@corebrace.com | corebrace.com SS-80 STRUCTUREmagazine

ADVERTORIAL

oreBrace, as a world leader in the construction industry, offers innovative technology to achieve high-performance, resilient structures. CoreBrace designs and fabricates Buckling Restrained Braces (BRBs), seismic protection devices that provide stable energy dissipation, which helps to create safe and sustainable buildings.

BRBs provide a cost-effective and highly efficient solution that allows structures to withstand earthquake demands and continue to be operational after a seismic event. CoreBrace BRBs have been successfully utilized in a wide variety of structures, including high-rise towers, hospitals, schools, stadiums, and industrial facilities in locations such as Azerbaijan, New Zealand, Thailand, Guam, Chile, Mexico, and nearly every state in the United States. CoreBrace’s continuous R&D program provides unparalleled service and extensive support to Design Teams, Steel Fabricators and Erectors, Detailers, and General Contractors during the various stages of a project. This approach offers numerous advantages, including among others: 1. Reduced earthquake forces on the structure and foundation 2. Simple connections to the structural system for faster erection 3. Stable hysteretic behavior through multiple design level events 4. Convenient solution for seismic retrofit or upgrade applications

SEISMIC LNA Solutions, Inc.

RISA

SkyCiv

MAX USA Corp.

Simpson Strong-Tie®

Trimble

Phone: 888-724-2323 Email: inquiries@lnasolutions.com Web: www.lnasolutions.com Product: BoxBolt® Description: BoxBolt Type C is a blind bolt fastener that is ICC ESR-3217 approved for seismic design. It connects tube steel or where access is restricted to one side of structural steel and is used with rectangular, square, or circulation sections. Provides fast, easy installation. IAS certification guarantees load value.

Phone: 800-223-4293 Email: yasaba@maxusacorp.com Web: www.maxusacorp.com Product: PowerLite® System Description: Power beyond the limits of standard 100 PSI pneumatic tools with the PowerLite system.

Designed with a lightweight body and engineered for heavy-duty applications, PowerLite tools are built to shoot through steel, concrete, and engineered woods.

Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: RISA-3D Description: Feeling overwhelmed with the latest seismic design procedures? RISA-3D has you covered with seismic detailing features including full AISC341/358 code checks and buckling restrained braces from Corebrace. Using automated seismic load generator or the built-in dynamic response spectra & time history analysis/design, get designs and reports that meet all your needs.

Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: High Wind-Resistant Construction Application Guide Description: This guide discusses the critical elements of high wind-resistant construction and helps you locate the connectors and fasteners you need for designing in high-wind areas. It also includes information on the effects of wind, corrosion, and uplift to help ensure safe, strong structures.

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Phone: 800-838-0899 Email: trevor.solie@skyciv.com Web: skyciv.com/wind-load-calculator Product: Wind/Snow Load Generator Description: Get rid of your design criteria Excel spreadsheet with the SkyCiv Load Generator. Quickly generate wind and snow design loads for your structure. Take advantage of SkyCiv’s analysis and design tools to complete your structural workflow, directly from an internet browser with no installation necessary.

Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Tekla Structural Designer Description: Built-in loading wizards automatically calculate all wind and seismic forces, generate design cases, and optimize the design of steel and concrete members to the latest AISC, ACI, and ASCE 7 design codes. With Tekla Structural Designer, engineers can review detailed calculations with code clauses and print complete reports for review submittals.

Profile

DURAFUSE FRAMES • Fewer parts, less fit-up, and less connection weight compared to other proprietary moment connections DuraFuse Frames enjoys full compliance with performance requirements in AISC 341 with code approvals from IAPMO UES ER 610, including 2018 IBC, 2019 CBC, and 2020 LA Supplements. Multiple Technical Bulletins have been published to provide additional resources related to performance, modeling, and design. DuraFuse Frames products are available in RAM Structural Systems, Revit, SDS2, and Tekla.

The DuraFuse Frames research, engineering, and design teams are constantly improving the modeling, analysis, and design process to ensure efficient, high performance, and resilient design solutions with quick response times. Our team is looking for opportunities to work with you. We are happy to provide a resilient design alternative using DuraFuse Frames based on your design specifications, meet with you to provide more details on DuraFuse Frames, or provide an in-person technical presentation on DuraFuse Frames systems.

ADVERTORIAL

uraFuse Frames systems are highly ductile steel moment frames with one-of-a-kind resilience, exceptional performance, and improved economy. Seismic energy is dissipated through an innovative fuse plate which prevents beam and column damage. The bottom flange fuse plate and all-bolted connection assembly minimize postearthquake repair duration and cost. After an event, only the fuse plate is replaced. The variety of DuraFuse Frames connection configurations provides the ideal moment-frame solution for all building types in all Seismic Design Categories. Our design and engineering team is dedicated to being a seamless extension of your design team to provide structurally efficient, economical, and uniquely resilient steel momentframes. The benefits of DuraFuse Frames include: • The ONLY resilient, repairable connections • Added panel zone stiffness results in a reduction of overall frame weight • Significant reduction (up to 70%) in seismic lateral beam bracing requirements • No protected zone in the beam • No field welding or inspection requirements • No seismic compactness requirements or span-to-depth limits for beams

800-727-4060 | contact@durafuseframes.com | www.durafuseframes.com STRUCTURAL ENGINEERING Resource Guide 2021 SS-81

WOOD American Wood Council Phone: 202-463-2766 Email: info@awc.org Web: www.awc.org Product: Connection Calculator Description: Provides users with a web-based approach to calculating capacities for single bolts, nails, lag screws, and wood screws per the 2015 NDS. Both lateral (single and double shear) and withdrawal capacities can be determined. Wood-to-wood, wood-toconcrete, and wood-to-steel connections are possible.

Gripple Inc.

S-FRAME Software

IES, Inc.

Trimble

RedBuilt

Product: Tekla Tedds Description: Using Tekla Tedds, design a range of wood elements and produce detailed and transparent documentation for beams (single span, multi-span and cantilever), wood columns, sawn lumber, engineered wood, glulam and flitch options, shear walls (multiple openings: segmented or perforated) and connections (bolted, screwed, nailed, wood/wood, and wood/steel).

Phone: 630-406-0600 Email: e.balsamo@gripple.com Web: www.gripple.com Product: Spider Cast-in-Place Concrete Insert Description: Versatile cast-in-place insert that accommodates threaded rod sizes from 3⁄8- to 3⁄4-inch or Gripple Cable Hangers. For wood form or metal deck, provides one product solution across the entire project, giving mechanical, electrical, and piping contractors flexibility to determine how they will suspend something after the concrete is poured.

Canfor EWP

Phone: 870-310-8168 Email: chris.webb@canfor.com Web: www.anthonyforest.com Product: Power Beam® Description: Designed for use as primary support beams. Power Beam compliments Mass Timber wood framing systems. The strongest engineered wood product (EWP) on the market with design values of 3000Fb - 2.1E - 300Fv. Power Beam is manufactured with superior strength southern yellow pine MSR Lumber.

Product: Power Column® Description: Manufactured with superior strength southern yellow pine MSR Lumber. Power Column compliments Mass Timber wood framing systems.

Available in a range of appearance grades for structural and architectural applications. Framing members such as Power Beam® can easily be attached to Power Column with simple connection detailing.

Product: Power Preserved Glulam® Description: Durable long-term solution for most exterior non-marine use structural applications.

Power Preserved Glulam is offered in two preservative treatments: Clear-Guard® and Cop-Guard®. Both preservatives are applied to Power Preserved Glulam through vacuum pressure impregnation per American Wood Protection Associations (AWPA) Standards.

CAST CONNEX

Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Timber End Connectors™ Description: Clevis-type fittings designed to connect to the ends of heavy timber or glue-laminated structural elements loaded in predominately tension or compression for use in architecturally exposed applications. Visit our website to view the TEC and our custom cast steel connectors for timber projects.

ENERCALC, Inc.

ENERCALC Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: ENERCALC/Structural Engineering Library Description: Designing with wood? Test your designs faster using ENERCALC Structural Engineering Library. SEL includes manufacturer data for Microllam, Parallam, Gang-Lam LVL, Timber Strand, VersaLam, GP Lam LVL, RedLam LVL, RigidLam, X-Beam, and Anthony. Extensive section data for solid-sawn and glued-laminated product accelerates traditional project designs.

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Phone: 406-586-8988 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis Description: Whether you need a simple glue laminated beam design, an entire roof truss system, or post and frame modeling, VisualAnalysis is fast and easy to use. Create models quickly and get NDS code checks for all the members in your project.

Phone: 866-859-6757 Email: info@redbuilt.com Web: www.redbuilt.com Product: Red-I™ joists, RedLam™ LVL and Red-OW Trusses Description: Structural solutions developed to optimize the design of your project and have become an integral part of floor, roof, and ceiling framing.

Visit the Resources section of the website for the complete list of Specifier’s Guides.

RISA

Phone: 949-951-5815 Email: info@risa.com Web: risa.com Product: RISAFloor and RISA-3D Description: Premiere software package for wood design. Create 3-D models of your entire structure and get complete design of wood walls, flexible wood diaphragms, dimensional lumber, glulams, parallams, LVL’s and joists. Custom databases for species, design of strap and hold-downs, as well as panel nailing offer total flexibility.

Product: RISACalc Description: RISACalc brings the power and flexibility of RISA-3D to the cloud, allowing engineers to create, load, and design individual components in a web-based interface. Whether engineered wood beams or columns, RISACalc’s interactive platform allows for detailed reporting and seamless collaboration, ensuring that daily structural design tasks are completed with ease.

Phone: 203-421-4800 Email: info@s-frame.com Web: s-frame.com Product: S-TIMBER Description: Sustainable Building Design with S-TIMBER 2020. Recent update for Mass Timber and Hybrid Timber structural analysis and design solution includes advanced analysis capabilities, orthotropic materials, and enhanced timber design reporting. Flexible enough to adapt to all user needs; backed by over 35 years of structural engineering expertise.

Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Tekla Structures Description: Can be used for wood framing: True BIM model of wood framing; parametric components allow for easy creation and design change; easily add or move doors and windows; library of industry standard wood connections included; clash checking functionality to eliminate change orders. Easily customizable to suit any job requirements.

WoodWorks® Software

Phone: 800-844-1275 Email: sales@woodworks-software.com Web: www.woodworks-software.com Product: WoodWorks Design Office Suite Description: Conforms to IBC 2015, ASCE 7-10, NDS 2015, SDPWS 2015. SHEARWALLS: designs perforated and segmented shearwalls; generates loads; rigid and flexible diaphragm distribution methods. SIZER: designs beams, columns, studs, joists up to 6 stories; automatic load patterning. CONNECTIONS: Wood-to-wood, wood-to-steel, or wood-to-concrete.

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Listings are provided as a courtesy, STRUCTURE is not responsible for errors.

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STRUCTURAL ENGINEERING

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Profile

AGI SENTINEL

GI Sentinel is recognized as one of the premier building manufacturers providing high-quality all-steel buildings globally. Founded in 1987 in Albion, Nebraska, Sentinel Building Systems began as a one-man operation selling Quonset buildings over the telephone. Today, AGI Sentinel building is a full-line building manufacturer that includes engineering through manufacturing and supplies optional accessories to meet customer expectations. AGI Sentinel provides buildings to a wide range of markets, including commercial, industrial, agricultural, retail, and storage, for a global customer base.

All AGI Sentinel buildings are designed and fabricated according to AISI and AISC specifications, and each building is manufactured and shipped from one central location. AGI Sentinel is an IAS accredited building manufacturer and is a member of the Metal Building Manufacturers Association (MBMA). MBMA members

ADVERTORIAL

are committed to providing quality products that meet customer requirements while maintaining a focus on safety, sustainability, and customer and team member engagement to accomplish continuous improvement throughout. AGI Sentinel engineers are registered professionals, and all welders are AWS certified.

The focus is on delivering optimal solutions for customers seeking top quality, reliable structures at an affordable price. All-steel structures are durable, sustainable, and eco-friendly. In addition, steel buildings are highly efficient in material utilization and prefabrication, allowing for shorter construction time on-site.

Choosing all-steel buildings ensures easy expansion and minimal

maintenance for customers. AGI Sentinel focuses on simplifying the buying process for our customers by providing a consultative selling process to assist customers through defining building expectations and offering alternatives to get the most economical building that meets all the customers’ expectations. With more than 30 years of experience, AGI Sentinel has the expertise and fabrication capabilities to develop unique builds for customers.

The buildings are designed and constructed based on each customer’s individual expectations and requirements. The Plainsman model is one of AGI Sentinel’s premier products designed to work well for commercial, industrial, aviation, cattle, riding, farm, retail, office, business, government, and recreational buildings. This versatile product is widely recognized as one of the finest all-steel buildings on the market today. AGI Sentinel building focus is to utilize the highest quality materials. In addition to high-quality materials, Sentinel also pays attention to the small details by providing all fasteners and sealing materials to ensure your build-

ing is weathertight in the most inclement weather. AGI Sentinel also provides accessory components to include windows, doors, insulation packages, and more. Our Self-Storage product provides customers with endless possibilities. AGI Sentinel’s experienced building consultants and engineers can help create unique selfstorage systems that generate maximum profitability at the lowest possible cost regardless of space limitations.

AGI Sentinel goes to great lengths to ensure that customers have no reason to go anywhere else. We provide an unbeatable combination of quality, versatility, value, and support, making AGI Sentinel Building Systems the ideal choice.

800-327-0790 | infosbs@sentinelbuildings.com | www.aggrowth.com STRUCTURAL ENGINEERING Resource Guide 2021 SS-83

ANCHORS Adhesives Technology Corporation

DuraFuse Frames

Simpson Strong-Tie®

Phone: 754-399-1057 Email: atcinfo@atcepoxy.com Web: www.atcepoxy.com Product: ULTRABOND® Anchoring and Doweling Adhesives Description: America’s #1 structural adhesive specialist offers four IBC compliant adhesives. HS1CC, the world’s strongest anchoring epoxy. New EPX-3CC high-performance epoxy for high-volume applications. New HYB-2CC hybrid cures fast in hot and cold temperatures. ACRYL-8CC cures fast with a very broad application temperature range. ATC is a Meridian Adhesives Group Company.

Phone: 801-727-4060 Email: contact@durafuseframes.com Web: www.durafuseframes.com Product: DF360 Description: Steel moment frames with one-of-a-kind resilience, exceptional performance, and improved economy. Seismic energy is dissipated without beam or column damage, minimizing post-earthquake repair cost and duration. Versatile solutions apply to all building types and hazard categories with DuraFuse Frames engineers as seamless extensions of your team providing economical, resilient designs.

Phone: 800-999-5099 Email: web@strongtie.com Web: www.strongtie.com Product: 304|316 Stainless-Steel Titen HD® Heavy-Duty Screw Anchor Description: Now available in Type 304 and 316 stainless steel. Type 316 is the optimal choice for applications in corrosive environments such as near chemicals or saltwater. Type 304 is a cost-effective solution for less extreme applications, including in wet, moist, or damp environments.

Adit Ltd

ENERCALC, Inc.

Phone: 00-972-77-5020696 Email: office@adit.org.il Web: www.adit.org.il Product: Adit Design Anchor Guide 2021 Description: Designing internationally? The Guide allows you to easily consult all the factors used to design anchors in a user-friendly environment. The new version is only available in Hebrew and can be downloaded from the website.

Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: ENERCALC Structural Engineering Library Description: Our latest improvements to SEL include our new Flitch Plated Wood Beam module and new Steel Base Plate by FEM. Both modules can help designers refine their design loads on the anchor rods, common bolts, and framing anchors. Structural Engineering Library subscriptions now provide both installed and cloud use.

ASDIP Structural Software Phone: 407-284-9202 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP STEEL Description: Includes the design of biaxial base plates, anchor rods, and shear lugs, per ACI 318-19. Easily generate detailed reports for complex anchorage design calculations, including the ACI seismic provisions. Both ASD and LRFD can be specified. Load combinations per ASCE 7-05, ASCE 7-10/16, or user-defined.

ENERCALC

Hohmann & Barnard, Inc. Phone: 800-645-0616 Email: jenniferm@h-b.com Web: h-b.com Product: 2-SEAL Thermal Wing Nut Anchor Description: An innovative, single screw veneer tie for metal stud construction. It features a dualdiameter barrel with factory-installed EPDM washers to seal both the face of the insulation and the air/ vapor barrier, and unique Thermal Wings designed to decrease thermal transfer through rigid insulation.

DEWALT Anchors & Fasteners Phone: 800-524-3244 Email: anchors@dewalt.com Web: http://anchors.dewalt.com/anchors Product: CCU+ Critical Connection Undercut™ Description: DEWALT Anchors & Fasteners launches a new heavy-duty concrete anchor for use in critical applications where a robust anchor with low displacement is necessary. The CCU+ Critical Connection Undercut is ICC-ES qualified under ESR-4810 for use in cracked and uncracked concrete.

The anchors are Made in the USA.

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Trimble Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Tekla Tedds Description: Automating your every day structural designs, the Tekla Tedds’ library includes anchor bolt design per ACI 318 Appendix D. The calculation includes comprehensive checks for tensile and shear failure of anchors and is available as part of a free trial by visiting the website.

Product: Tekla Structures Description: An Open BIM modeling software that can model all types of anchors required to create a 100% constructible 3-D model. Anchors can be created inside the software or imported directly from vendors that provide 3-D CAD files of their products.

IES, Inc.

Wej-It High-Performance Anchors

Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VAConnect Description: Design base plates by AISC Design Guide #1 and anchorage calculations for ACI 318.

Both, independently, are difficult by hand! With VAConnect you will get the job done quickly and accurately. Works alone or with IES VisualAnalysis.

Phone: 203-523-5833 Email: julien@toggler.com Web: www.wejit.com Product: POWER-Skru Large Diameter Concrete Screw Description: A high-strength screw anchor with self-tapping threads that offers a unique undercutting design for anchoring into concrete and masonry. No secondary setting is needed. The POWER-Skru Large Diameter Concrete Screw provides high-strength performance with low installation torque. A heavyduty mechanically-galvanized finish is available to enhance corrosion resistance.

LNA Solutions, Inc.

2021/22

Product: Anchoring, Fastening, and Restoration Solutions Product Guide Description: The comprehensive product guide features up-to-date products and technical information to locate the ideal product solution for your job. The Anchoring, Fastening, and Restoration Solutions Product Guide provides information on adhesives, mechanical anchors, direct fastening, carbide drill bits, and concrete restoration products for concrete and masonry.

Phone: 888-724-2323 Email: inquiries@lnasolutions.com Web: www.LNAsolutions.com Product: Box Bolt® Description: A blind bolt fastener that is ICC ESR-3217 approved for seismic design. It connects tube steel or where access is restricted to one side of structural steel and is used with rectangular, square, or circulation sections. Provides fast, easy installation.

IAS certification guarantees load value.

Listings are provided as a courtesy, STRUCTURE is not responsible for errors.

Williams Form Engineering Corp.

Phone: 616-866-0815 Email: williams@williamsform.com Web: www.williamsform.com Product: Anchor Systems Description: Williams Form Engineering Corporation has been providing threaded steel bars and accessories for rock anchors, soil anchors, high capacity concrete anchors, micropiles, tie rods, tiebacks, strand anchors, hollow bar anchors, post tensioning systems, and concrete forming hardware systems in the construction industry for over 95 years.

STRUCTURAL ENGINEERING

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Profile

SOMERO ENTERPRISES

I

n 1986, Somero Enterprises was founded and so marked the first industry-wide revolution upon which the company would embark. Dave and Paul Somero were concrete contractors, and they knew that a machine could get them better quality floors with more efficiency, all with a faster process than the current manual methods of placing concrete. Not wanting to wait on a company to manufacture the machines that would deliver this Faster.Flatter.Fewer solution, they took it upon themselves, and 35 years later, the idea of doing big, quality-driven slab-on-grade projects without a Somero® Laser Screed® Machine is almost unthinkable.

ADVERTORIAL

With this same industry-changing mindset and self-reliance in our DNA, we are embarking on our second revolutionary machine innovation – The SkyLine machine line. Consisting of the SkyScreed® 36 and 25 Laser Screed® Machines and the SkyStrip Machine, we are looking to partner with the structural

high-rise market and deliver quality, safety, and efficiencies never thought possible for concrete floors in this space.

The SkyScreed brings the precision and speed of the laser screed machine to structural projects, and we promise you will not believe the numbers when you hear them. With the right project profile and layouts, the SkyScreed 36 has achieved Fl numbers in the mid-to-high 30s and, in some cases, the low-to-mid 40s. The early adopters of this technology have been blown away, and we believe that it is just a matter of time before the SkyScreed will be the rule on high-rise projects all over North America.

The second machine in the SkyLine machine line is the SkyStrip.

This machine focuses on solving the dangerous and slow process of stripping shoring sheets. This machine is engineered to strip the plywood sheets, lower them to safe hand-off height, and keep going for as long as it takes. Put simply, this machine saves the shoring team a lot of fatigue and keeps them fresh for the more critical, higher-skilled aspects of their jobs. In addition, when job claims and skilled labor shortages keep a developer up at night, this machine will help them all sleep a little easier.

To learn about how the SkyLine machines can revolutionize your projects and provide unparalleled quality, value, and safety to your customers, contact Somero or go to the website to learn more and see these revolutionary machines in action.

239-210-6519 | sales@somero.com | somero.com/skyline STRUCTURAL ENGINEERING Resource Guide 2021 SS-85

FOUNDATIONS Adhesives Technology Corporation

Geopier® Foundation Company

ASDIP Structural Software

IES, Inc.

Phone: 754-399-1057 Email: atcinfo@atcepoxy.com Web: www.atcepoxy.com Product: CONVERGENT Concrete Densification and Finishing Products Description: Adhesives Technology Corporation has acquired Convergent Concrete Technologies, the industry leader in concrete densifiers, hardeners, and finishes. ATC now offers Pentra® products, including Nano-Lithium® technology and Reactive Silicon Hybrid Polymers, and new silica-free, Strontiumbased STRiON® formulas. From densifiers and cures to hardeners and paints, ATC provides innovation engineered to outperform.

Phone: 407-284-9204 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP FOUNDATION Description: An advanced software for quick and efficient design of concrete footings, such as isolated spread footings, two-column combined footings, strap footings, wall footings, and pile caps.

See immediate graphical results, calculations, and detailed or condensed reports with exposed formulas and code references. ASDIP FOUNDATION comes with 5 intuitive modules.

Phone: 704-439-1790 Email: info@geopier.com Web: geopier.com Product: Geopier Rammed Aggregate Pier® and Rigid Inclusions Description: Geopier provides an efficient and cost-effective Intermediate Foundation® solution for the support of settlement structures. Our systems have become effective replacements for massive over-excavation and replacement or deep foundations, including driven piles, drilled shafts, or augered cast-in-place piles. Thousands of structures around the world are currently supported

by Geopier technologies.

Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: RISAFoundation Description: The latest release of RISAFoundation (Version 13) includes full integration with the RISA Building System and adds new features such as expanded load categories, the ability to exclude results, code updates to ACI, and enhanced seismicity. Visit risa.com/new-features/risafoundation to learn about all the new features.

S-FRAME Software

Phone: 406-586-8988 Email: info@iesweb.com Web: www.iesweb.com Product: VisualFoundation Description: Stability calculations alone for a mat footing can drive you mad, not to mention the nonlinear analysis required for soil-supported models. VisualFoundation simplifies advanced FEA, making your work fast and professional.

VisualFoundation handles punching shear, combined footings, grade beams, pile caps and will pay for itself with two jobs.

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RISA

Phone: 203-421-4800 Email: info@s-frame.com Web: s-frame.com Product: S-CONCRETE, S-LINE and S-FOUNDATION Description: The concrete design capabilities in S-CONCRETE, S-LINE, and S-FOUNDATION incorporate not only the best concrete design principles but state-of-the-art analysis techniques.

Designed to be powerful and also easy to use.

S-FRAME Software is the proud solution provider of proven and trusted structural and civil engineering software.

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BLINDBOLT

Design Guide 27. In addition, BlindBolts have been accredited in accordance with AC437 (ICC-ES evaluation report ESR-3617), so they can be specified and used with complete confidence.

For thinner material, including cold-rolled sections, steel sheet, and cladding, the TWBolt (thin wall) is the recommended fixing.

The fixing is blind, with no requirement to access the second side.

The self-contained fixing is inserted and tightened with an electric driver while holding the external nut in a spanner. Expanding legs on the inside splay over a specially-shaped ferrule, clamping the elements together. Quick to install with a neat low-profile finish, the TWBolt is ideal for thinner material – typically 3⁄64 to ¼ inch.

TWBolts have a high shear resistance and are equally capable in tension – the resistance is limited by the deformation of the material, not the fixing.

Comprehensive product data, design resistances, and installation videos are available on the website.

630-882-9010 | enquiries@blindbolt.com | www.blindbolt.com SS-86 STRUCTUREmagazine

ADVERTORIAL

lindBolt manufactures a range of fixings that do precisely what the name implies – they are connectors for steelwork when access is only from one side. It may be that access to the “blind” side is impossible, such as connections to hollow sections, or simply that one-sided access is convenient or leads to faster installation – a typical situation when working at height.

For heavier loads and connections between beams, columns, and similar, BlindBolts are the obvious choice. These fasteners have a gravity-operated toggle secured within the bolt’s shank. The fixing is inserted, turned by 180˚, and the toggle rotates to become an anchor on the blind face of the connection. The fixing can then simply be tightened and the joint completed. The exciting features of the BlindBolt are that they use ordinary tolerance holes, meaning some adjustment of the connection is possible. Also, the fixings are removable – simply loosen the nut, rotate the bolt, and remove.

There is no concern about the engagement of the toggle – a simple gauge can be used to check that the toggle has rotated in position.

Every bolt has a mark on the shank to indicate its orientation.

Designed as bearing-type connections and to be installed to snugtight, the BlindBolt is available in carbon steel (145 ksi) and stainless steel (100 ksi) in a range of diameters up to 13⁄16 inch and is suitable for shear, tension, or a combination of both. The resistances have been proven by test and verified in accordance with AISC 360 and AISC

MASONRY Concrete Masonry Association of CA & NV

IES, Inc.

Simpson Strong-Tie®

Phone: 916-722-1700 Email: info@cmacn.org Web: www.cmacn.org Product: CMD18 Description: Structural design of reinforced concrete and clay hollow unit masonry elements for design of masonry elements in accordance with provisions of Ch. 21 of 2010 through 2019 CBC or 2009 through 2018 IBC and 2008 through 2016 Building Code Requirements for Masonry Structures (TMS 402).

Phone: 406-586-8988 Email: info@iesweb.com Web: www.iesweb.com Product: QuickMasonry Description: To eliminate the guesswork in TMS 402/602 masonry design, turn to QuickMasonry. It designs or checks masonry walls, columns, pilasters, and lintels. Its “Transparent Reporting” lets anyone check your calculations as if you had painstakingly written them by hand. QuickMasonry is value-priced, easy to use, and the best tool available.

Hohmann & Barnard, Inc.

Larsen Products Corp.

The Masonry Society

Phone: 800-645-0616 Email: jenniferm@h-b.com Web: h-b.com Product: Thermal Brick Support System Description: A groundbreaking brick veneer support system that reduces thermal bridging in relief angles, to improve the energy efficiency of your building. Features of our TBS system include allowance for continuous insulation behind the support angle, which saves installation time and improves energy efficiency.

Phone: 800-633-6668 Email: jlarsen@larsenproducts.com Web: www.larsenproducts.com Product: Weld-Crete® Description: A chemical concrete bonding agent incorporates polyvinyl acetate homopolymer in a patented formulation. For exterior and interior use, Weld-Crete will bond new concrete, Portland cement plaster, and cementitious mixes to structurally sound concrete floors, walls, columns, beams, steps, and ramps.

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Phone: 800-999-5099 Email: web@strongtie.com Web: www.strongtie.com Product: Fabric-Reinforced Cementitious Matrix (FRCM) Description: FRCM combines a high-performance sprayable mortar with a carbon-fiber grid to create a thin structural layer that doesn’t add significant weight or volume to an existing structure. FRCM can be used to repair and strengthen concrete and masonry structures for seismic retrofit or load upgrades.

Contact us for design support.

Phone: 303-939-9700 Email: info@masonrysociety.org Web: masonrysociety.org Product: Masonry Codes and Standards Description: The Masonry Society is a non-profit, professional organization of volunteer Members, dedicated to the advancement of masonry knowledge.

Through our Members, all aspects of masonry are discussed. The results are disseminated to provide guidance to the masonry and technical community on various aspects of masonry design, construction, evaluation, and repair.

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NCEES

T

Are You Looking To Practice in Multiple States?

Options for Active-Duty Military and Military Spouses Professional engineers and surveyors actively serving in the military, and their spouses, are eligible to transmit their NCEES Record at no charge when military orders require them to move to a new state. When transmitted to a state licensing board, it will include a military designation to prioritize the application. Please email military@ncees.org for more information.

ADVERTORIAL

he National Council of Examiners for Engineering and Surveying (NCEES) is a nonprofit organization dedicated to advancing professional licensure for engineers and surveyors.

Many professional engineers find that their careers require them to be licensed in more than one state. To do this, a P.E. must apply for comity licensure in additional states.

The NCEES Records program is designed for currently-licensed engineers and surveyors looking for an easier and faster way to complete the licensure process in multiple jurisdictions, including all 50 states, the District of Columbia, Guam, Puerto Rico, Northern Mariana Islands, and the U.S. Virgin Islands. An established NCEES Record will include most – if not all – of the materials you need to apply for comity licensure in additional states and territories.

Eliminate having to resubmit your: College transcripts; Exam results; Employment verifications; and Professional references.

If you are already licensed and want to apply for licensure in an additional U.S. state or territory, apply for an NCEES Record.

NCEES reviews your materials and, after your Record is established, electronically submits them directly to the licensing board on your behalf. This saves time and simplifies the application process when you need to practice in multiple states and territories.

Initial Licensure Are you in the process of becoming licensed and want to establish an NCEES Record? If you have passed the FE and PE exam, some states will allow you to use the NCEES Record for initial licensure.

A limited number of boards offer the initial licensing process, so check your MyNCEES account to find out if this is a path for you. Discover if an NCEES Record is right for you by visiting www.ncees.org/records.

800-250-3196 | ncees.org STRUCTURAL ENGINEERING Resource Guide 2021 SS-87

STEEL Advant Steel Phone: 704-516-1750 Email: tim@advantsteel.com Web: www.advantsteel.com Product: Advant Cold-Formed Steel Truss Description: The first and only CFS truss product designed specifically for use in shallow, parallel chord applications – specifically floors and flat roofs.

ASDIP Structural Software

Phone: 407-284-9202 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP STEEL Description: Includes easy-to-use intuitive modules for the design of steel members and connections, such as composite/non-composite beams, steel columns, base plates, anchoring to concrete, shear connections, and moment connections, per the latest design codes.

ASDIP STEEL comes with 5 intuitive modules that will substantially simplify time-consuming calculations for your structural designs.

CADRE Analytic

Phone: 425-392-4309 Email: j4@cadreanalytic.com Web: www.cadreanalytic.com Product: CADRE Pro Description: General structural application emphasizing on practical analysis of complex structures. Includes discrete, pressure, hydrostatic, seismic, and dynamic response loading schemes.

User friendly features for presenting, displaying, plotting, and tabulating extreme loads and stresses across the structure and across multiple load cases simultaneously. Basic code checking for steel, wood, and aluminum.

Cast Connex

Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Standardized Cast Steel Connectors and Custom Cast Steel Connectors Description: The industry leader in the architectural and structural use of cast steel components in the design and construction of building and bridge structures. Our products include pre-engineered connectors that simplify the design and enhance the performance of structures. We also offer design-build services for custom cast steel nodes and components.

Commercial Metals Company

Phone: 949-405-9161 Email: chromx@cmc.com Web: www.cmc.com/chromx Product: ChromX® Description: High strength rebar with a range of corrosion resistance levels. Designers can select the appropriate level and strength needed, based on the project’s service life. High strength and corrosion resistant properties within the steel result in a reduction in construction costs, shortened build times, reduced congestion issues and improved safety.

Digital Canal Corp.

IES, Inc

Dlubal Software, Inc.

Lindapter International

Phone: 800-449-5033 Email: info@digitalcanal.com Web: www.digitalcanalstructural.com Product: Cold-Formed Steel Design Description: Please visit the website for New ColdFormed Steel design software information. You receive exceptional value with a one-project return on your investment. You also OWN your licenses. We do not force ongoing payments forever. Our 11,000 clients provide the best testimonial we can offer.

Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM, RWIND Simulation Description: Wind tunnel numerical simulations for wind flow on all structures. Integrate resulting wind pressures into the FEA program RFEM for further design of steel, concrete, wood, CLT, aluminum, glass, and fabric/membrane structures according to USA/ International standards. Wind loading on specialty structures, not addressed in codes provisions, possible with RWIND Simulation.

DuraFuse Frames

Phone: 801-727-4060 Email: contact@durafuseframes.com Web: www.durafuseframes.com Product: DF360 Description: Steel moment frames with one-of-a-kind resilience, exceptional performance, and improved economy. Seismic energy is dissipated without beam or column damage, minimizing post-earthquake repair cost and duration. Versatile solutions apply to all building types and hazard categories, with DuraFuse Frames engineers as seamless extensions of your team providing economical, resilient designs.

ENERCALC, Inc.

ENERCALC

Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: ENERCALC Structural Engineering Library Description: Steel design is a breeze with ENERCALC. Beams, columns, 2-D frames, force distribution in bolt groups…SEL handles it all.

The simple user interface makes it easy to set up calculations. Instant recalculation to “what-if ” solutions and find the best fit. Member optimization will improve your efficiency and saves time!

Gripple Inc.

Phone: 630-406-0600 Email: e.balsamo@gripple.com Web: www.gripple.com Product: Gripple Seismic Cable Bracing Systems Description: Specifically designed and engineered to brace and secure suspended nonstructural equipment and components within a building or structure.

Suitable for bracing new or retrofit installations in a variety of configurations. Ready-to-use kits, fast to install, no tools required, four color-coded kit sizes.

Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis 2D Description: When you don’t need the full power (and cost) of 3-D FEA software, try VisualAnalysis 2D. It will tackle beams, columns, moment frames, plane trusses, and braced frames quickly and easily, with AISC design checks. Oh, and it also analyzes and checks 2-D wood models.

Phone: 866-566-2658 Email: inquiries@lindapter.com Web: www.lindapter.com Product: Girder Clamps Description: The only structural steel clamping system approved by ICC-ES. As an alternative to highstrength bolt assemblies, the Girder Clamp (Types AF and AAF) may be used to resist axial tension and slip due to load combinations that include wind or seismic load in all Seismic Design Categories A through F.

LNA Solutions, Inc.

Phone: 888-724-2323 Email: inquiries@lnasolutions.com Web: www.lnasolutions.com Product: BeamClamp® Description: An extensive range of clamping products designed for making steel-to-steel connections without the need for drilling or welding. The clamping system provides a guaranteed connection and a safe working load. Perfect for areas where drilling or welding are not permitted, or access and power are restricted.

MiTek

Phone: 314-851-2200 Email: answers@mii.com Web: www.mitek.com/ultra-span Product: Ultra-Span® CFS/Steel Engine™ Description: Enable your building to be stronger, longer-lasting, and more resilient for the duration of its life with the strength of MiTek’s Ultra-Span CFS and industry-leading design software, Steel Engine™.

MiTek collaborates across the building industry to enable and accelerate transformational breakthroughs in design and construction, both on-site and off-site.

New Millennium Building Systems

Phone: 260-969-3500 Email: gerald.arvay@newmill.com Web: www.newmill.com Product: Structural Steel Joists and Decking Description: New Millennium is a nationwide supplier of custom engineered and manufactured structural steel joist and deck building systems. Called upon early in the design-build process, we can assist in right system specification from our extensive portfolio of building system options. For multi-story projects, we offer the broadest range of long-span, “thin-slab” composite floor systems, including dovetail composite, deep deck composite, and composite joists.

continued on page 90 SS-88 STRUCTUREmagazine

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NEW MILLENNIUM BUILDING SYSTEMS

S

Solve the Top 5 Challenges Facing Building Markets Today

ince March 2020, the pandemic has changed virtually all aspects of our lives. How we live, learn, play, and do business has been disrupted – perhaps permanently. This period for the built environment industries could be called The Great Rethinking.

Building design has already changed to reflect new behaviors and beliefs, circumstances and situations, standards, and requirements.

These changes are especially evident in the education, multi-family residential, multi-story office, and warehouse and data center markets. This evolution is an opportunity and challenge.

How do architecture, engineering, construction, and building owner/developer firms approach future projects in these markets?

Innovative steel building systems from innovative-thinking suppliers are essential in this new era.

A new series of design guides identifies five major challenges in the education, multi-family, multi-story office, and warehouse and data center building markets. These guides teach you how to overcome them using steel joists, steel and composite floor systems, and steel roof deck.

Multi-Story Office Challenges

Education Challenges Innovations in educational facility design have typically been reserved for college campuses and post-secondary education.

However, primary and secondary school design faces an urgent rethinking in the current climate.

New school design priorities include open floor plans that promote safe collaboration; spacious interiors that prioritize health and safety through social distancing; sustainable building methods and materials; modern aesthetics; and controlling interior acoustics. These are the five challenges for school design teams and construction crews.

Steel buildings systems consisting of long-span steel deck systems, including roof deck and composite floor deck; standard joists; and joist girders offer the benefits to efficiently face the new school of design thought.

Multi-Family Challenges While isolating or quarantining at home, millions of people have discovered that

Businesses large and small are rethinking their workspaces to not only safeguard employee health but also to accommodate smaller workforces in the work-from-home era.

Multi-story office designs must change to protect workers’ wellbeing while facilitating safe collaboration. Constructability, work environment, aesthetics, and sustainability join flexibility as the five primary issues in modern-day office design.

Innovative steel building systems – long-span roof and floor structures, standard joists, and special profile joists – are the answer.

ADVERTORIAL

living spaces aren’t adequate substitutes for offices, gyms, restaurants, and other public places. Nor are they designed for social distancing – especially multi-family and multi-story residential structures with common, shared spaces.

To address those concerns, multi-family building design must prioritize flexibility and better living environments while continuing to address longtime issues such as constructability, aesthetics, and sustainability. Together these five factors will guide multi-family design for the foreseeable future.

As this sector could continue to change, nimble steel building systems suppliers become ever more important. The steel building systems from these suppliers provide ideal solutions, among them thin-slab, long-span composite floors, and longspan roof deck.

Warehouse and Data Center Challenges Shopping and interacting online has exploded in popularity during the pandemic. Consequently, the demand for warehouses that store goods and data centers that store digital information has also skyrocketed.

Today’s warehouses and data centers must be designed and built with speed-to-market in mind, along with flexibility, optimized MEP integration, building performance, and sustainability.

To optimize storage space while meeting the five challenges, design teams should consider steel joists, composite joists, joist girders, and long-span roof and floor systems.

Get the guides today that give you the tools to overcome the challenges of education, multi-family, multi-story office, and warehouse and data center markets. https://bit.ly/3niS0MO.

260-969-3500 | info@newmill.com | www.newmill.com STRUCTURAL ENGINEERING Resource Guide 2021 SS-89

STEEL PS=Ø®

Phone: 800-355-8414 Email: sales@pourstrip0.com Web: www.pourstrip0.com Product: PS=Ø Steel Reinforcement Splice System Description: Eliminates pour strips and maintains rebar continuity while allowing for volume change.

Using proven coupler technologies recognized worldwide, the PS=Ø system features a tapered thread on one end and a grout-filled sleeve on the other. The system requires no redesign, is an ACI permitted Type 1 and Type 2 mechanical splice, is ICC approved and made in the USA.

2021/22

STRUCTURAL ENGINEERING Resource Guide

Live on STRUCTUREmag.org for a full year!

RISA

Simpson Strong-Tie®

Product: RISAFloor Description: The latest release of RISAFloor includes the design of cold-formed steel walls according to AISI S400-15 and AISI S240-15. These improvements coupled with RISAFloor’s robust design capabilities for hot rolled steel, composite steel, steel joists, and composite steel joist make RISAFloor the #1 choice for the design of steel building structures.

Strongwell

Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: RISAConnection Description: The cutting edge of next-generation connection design software and features full 3-D visualization as well as expandable reports for every limit state. The latest release, Version 12 includes integration with Hilti Profis for anchorage design including custom anchor bolt layouts, support for Skewed Shear Plate Connections and Flange Plate Column Cap Plate Moment Connections.

Product: RISA-3D Description: Version 19 is the next step in the evolution of the completely redesigned RISA-3D. The latest release includes updates to the AISC code as well as the ability for engineers to design cold-formed steel walls according to AISC codes. This improvement, makes RISA-3D the most comprehensive steel and cold-formed steel design tool on the market.

STRUCTURAL ENGINEERING

Resource Guide

Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: 304|316 Stainless-Steel Titen HD® HeavyDuty Screw Anchor Description: Now available in Type 304 and 316 stainless steel. Type 316 is the optimal choice for applications in corrosive environments such as near chemicals or saltwater. Type 304 is a cost-effective solution for less extreme applications, including in wet, moist, or damp environments.

Phone: 276-645-8000 Email: bmyers@strongwell.com Web: www.strongwell.com Product: EXTREN® Description: Pultruded fiberglass structural shapes and plates replace traditional metals in a wide variety of structural applications. A durable, lightweight, costsaving structural material ideal for turrets, spires, or other features on top of tall buildings. EXTREN holds L.A.R.R. approval for construction of RF transparent screenings or enclosures.

Listings are provided as a courtesy, STRUCTURE is not responsible for errors.

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Eliminate Pour Strips ow you can eliminate pour strips – and the extra costs, construction delays, and safety issues they bring – with the PS=Ø Steel Reinforcement Splice System.

The PS=Ø Steel Reinforcement Splice System eliminates pour strips and maintains rebar continuity while allowing for volume change.

Using proven coupler technologies recognized worldwide, the PS=Ø system features a tapered thread on one end and a grout-filled sleeve on the other. The system requires no redesign, is an ACI permitted Type 1 and Type 2 mechanical splice, is ICC approved, and made in the USA.

Reduce Costs Closing pour strips is the most expensive concrete pour on a project.

Formwork, shoring, and backshoring must stay in place for a week, and crews must reassemble for a small pour. The PS=Ø system eliminates this costly and time-consuming step.

Accelerate Construction Pour strips are a drag on any construction schedule. They not only require re-pouring the leave-out but also restrict worker access. By eliminating pour strips, the PS=Ø system can cut weeks or even months from construction schedules.

Improve Safety An open leave-out in a floor is a major safety hazard. Pour strips are particularly hazardous because they run the entire width of the slab and are impossible to avoid. The PS=Ø system replaces dangerous leave-outs with a narrow, grouted joint.

Eliminate pour strips with the PS=Ø Steel Reinforcement Splice System.

651-247-0123 | jzimmerman@pourstrip0.com | www.pourstrip0.com SS-90 STRUCTUREmagazine

ADVERTORIAL

N

STRUCTURAL ENGINEERING

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QUICK TIE PRODUCTS, INC. Since 1999, Quick Tie Products, Inc. (“QuickTie”) has manufactured and

distributed the QuickTie System, a proprietary, fully engineered, patented hold-down system for high wind and seismic construction.

T

he QuickTieTM System (https://quicktieproducts.com/ wood-quickties) is comprised of aircraft wire rope cable with threaded studs swaged to each end and a steel bearing plate and hex nut on the top end. The system cinches walls to their foundations from the uppermost top plates, resisting roof uplift and building overturning pressures as engineered to meet specified design loads.

Engineers nationwide prefer our system to other hold-down systems for several important reasons (https://quicktieproducts.com/benefits), chiefly among them:

2. Compensate for Wood Shrinkage. QuickTie cables are pre-stressed, compensating for common problems of building settling and long-term wood shrinkage (for which competing products do not account, absent expensive shrinkage compensation devices).

3. Proof-test. Because of premeditated over-tensioning (beyond a particular design load, given cable relaxation over time), if the QuickTie system is going to fail, it will fail at installation when tension is at its peak. In other words, tensioning an assembly – whether epoxied into the foundation or attached to an anchor bolt – “proof-tests” the system when installed.

4. Eliminate Defects. As an active system cinching a structure to its foundation, QuickTie cables eliminate otherwise loose load paths (think threaded rod in particular) and reduce drywall, stucco, and exterior siding cracks (think bowing flat straps).

5. Save builders time and money. The QuickTie system is installed quickly and easily after a building is framed, and is the preferred choice of framers and hardware installers

6. Be Flexible. While QuickTie originated as only a cable system, over the years, we have expanded our product offering to include just about every essential framing and hold-down component on the market. As a result, engineering professionals can choose from a number of QuickTie products in addition to cables when designing their structures.

7. Standardize Corrosion Resistance. When expanding our product offerings, we made a conscious decision to manufacture our framing connectors with a G185 zinc coating.

As a result, design professionals do not have to worry about selecting the right coating when choosing QuickTie connectors (see, for example, https://quicktieproducts.com/face-mount-joist-hangers).

And, in juxtaposition with our competitors, our customers do not have to pay extra for better protection.

ADVERTORIAL

1. Verify embedment depth with 100% certainty. Each threaded stud end of a QuickTie cable has a specific embedment depth that is visually inspectable on the job site.

Threaded rod and conventional hold-down system embedment depths are not visually inspectable, introducing the element of liability should that other system fail.

throughout the country. We continue to innovate and release new products to give engineering professionals better options for designing safe structures while saving their customers time and money. For instance, check out our new SPArtanTM (Sill Plate Anchor), designed to perform on par with other ⅝-inch sill anchors, but with material cost and labor savings. https://quicktieproducts.com/spartan-still-plate-anchor

8. Consider Block Construction. The QuickTie system is equally effective in masonry structures. Masonry walls with QuickTie cables are – counterintuitively – stiffer than conventional systems and eliminate many time-consuming aspects of conventional construction (think vertical downpours, rebar, lintels, and corresponding inspections) https://quicktieproducts.com/masonry-quickties.

Our team of engineers and design professionals is available to answer any questions you may have and assist you in implementing product substitutions. Please see our website for additional information (e.g., our catalog, Technical Evaluation Reports or “TERs,” Florida Product Approval information, design details, etc.), and thank you for your interest and support!

904-281-0525 | info@quicktieproducts.com | https://quicktieproducts.com STRUCTURAL ENGINEERING Resource Guide 2021 SS-91

WHERE VISION BECOMES STRUCTURE

RISA offers a comprehensive suite of design software that work together to simplify even the most complex projects. As a result, engineers can work efficiently on a variety of structures in a mix of materials including steel, concrete, wood, masonry and aluminum. risa.com

®

McDonald's Net-Zero Quick Service Restaurant Structural Steel, Braced Frames, Steel Connections CPH, Inc.