STRUCTURE magazine October 2020 by structuremag

STRUCTURE OCTOBER 2020

NCSEA | CASE | SEI

BRIDGES

INSIDE: Cable-Stayed Bridges

Beehive Bridge Miami Bridge Collapse Reinvigorating Historic ROW DTLA

26 30 34

SPECIAL SECTION:

2020 STRUCTURAL ENGINEERING

Resource Guide

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4 STRUCTURE magazine

Contents O CTO BER 2020

Columns and Departments Cover Feature

38 CABLE-STAYED BRIDGES By Roumen V. Mladjov, S.E., P.E.

Most cable-stayed bridges are visually beautiful, and some are among the most impressive of engineering achievements. The efficient range of

7 Editorial Hey Graduates – Give Small Firms a Chance! By Kevin H. Chamberlain, P.E.

8 Structural Practices Mitigating Flood Damage to Bridges By Kevin Johns and Tom Murphy, Ph.D., P.E., S.E.

14 Structural Inspections Inspectability Design By Jennifer Laning, P.E.

cable-stayed bridges is moving towards even longer spans. There is no other bridge structural system

16 Structural Performance 3-D Snow Drifts By Michael O’Rourke, Ph.D., P.E., and Talia Williams

exhibiting such rapid development.

20 Historic Structures Ashtabula Bridge Failure

26 BEEHIVE BRIDGE

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

By Dan Whittemore, P.E.

The Beehive Bridge underwent a road diet to favor pedestrian foot

24 Structural Components Designing Cross-Laminated

Timber Wall Elements

traffic. The spine of the pedestrian enclosure is made up of 138

By Lori Koch, P.E., and Michelle Kam-Biron, P.E., S.E., SECB

individual galvanized structural steel tubes. Between the steel-post

42 Building Blocks Specification Check – Molded Polystyrene

spine is a lattice network of aluminum members arranged into

By Sean O’Keefe

geometric shapes.

44 InSights Bridging the Current Gaps in

30 DEADLY MIAMI PEDESTRIAN BRIDGE COLLAPSE

Bridge Maintenance By Kai Goebel

By Ran Cao, Ph.D., Sherif El-Tawil, Ph.D., P.E., and Anil Kumar Agrawal, Ph.D., P.E.

According to the preliminary report from NTSB on the collapse of the truss bridge, workers were re-tensioning tendons at the time. In this article, a high-fidelity computational model was used to develop a

46 Business Practices Networking Tips for Introverts By Janki DePalma

48 Structural Forum Non-Traditional Career Paths

for Structural Engineers

forensic understanding of the collapse process.

By Brian Quinn, P.E.

34 REINVIGORATING A HISTORIC GIANT By Samuel Mengelkoch, S.E.

ROW DTLA reinvigorates the vast and historic Alameda Square warehouse and industrial building complex. The project updated the area into a vibrant district of offices, retail, and restaurants, and provides a network of public spaces.

56 Special Section

2020

In Every Issue 4 50 52 54

Advertiser Index NCSEA News SEI Update CASE in Point

STRUCTURAL ENGINEERING Resource Guide

October 2020 Bonus Content

Structural Analysis Numerical Analysis Case Study

Additional Content Available Only at – STRUCTUREmag.org By Vitaly B. Feygin, P.E., and Christian P. Gunn

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. OCTOBER 2020

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EDITORIAL Hey Graduates – Give Small Firms a Chance! By Kevin H. Chamberlain, P.E.

s I sit at my desk at work, the view out my window is not a typi• You are more likely to have a chance to design in all the struccal office setting. Our street is a mix of residential and business tural materials, not just steel and concrete, because you are use, near the center of town. I would not trade my view for anything. probably working on smaller projects. This is particularly true I am glad I do not work in a large city in a high rise, or in a bland for wood structures. • You are less likely to be “stuck” on the same project for years. suburban office park along a highway. No offense to colleagues who get to work on stadiums or megasI am also very glad that I work in a small firm. tructures, but I do not think I could devote myself to one project What constitutes a small firm? ACEC categorizes firms with 50 for longer than the extended warranty on my pickup. Small employees or less as small firms, and about 75% of all ACEC member firms have smaller projects that tend to cycle through more firms are “small.” quickly. Variety makes your job more interesting. When I think of a small firm, I think of the six wonderful people • You will learn about dealing with demanding clients, which will at my office who are like a second family. I started at our firm as a benefit you as your career grows towards an ownership position. summer intern over 25 years ago…and never left. As did all of our Knowledge will come by hearing how current engineers. That is rare these days. principals deal with them, and in having Most of my friends who are structural engito respond yourself after some training. neers have worked in no fewer than three • You will become comfortable dealing firms by the time they are 40, and that is with contractors, messy construction probably a low estimate. There seems to be sites, and coarse language, and use To build our ranks, I often attend career fairs those experiences to make you a better at a handful of universities I am familiar with a perception among engineer. Contractors are not shy to recruit graduating students. Over the years, students, and probably about letting an engineer know when I have found that it is tough to stand out as a a detail is not buildable. If you are in small firm without a lot of marketing resources. some of their professors, a firm where you are isolated from the I bring business cards and try to make personal construction trades, you will not benefit connections by sharing my passion for what that you need to take from those learning experiences. I do. I have tried everything, from bringing • You are less likely to be overworked. An along inspection tools we use, to a mockup of a job out of college at a owner who works alongside his employa mortise and tenon timber joint, to a video large firm in a city. ees in a shared office is less likely to turn loop of my partner giving a talk on the WTC off the lights and leave you toiling away collapse, to a huge dish of Halloween candy until midnight because he promised the (the good stuff). I have gone solo, brought client an unrealistic deadline. You are also more likely to be junior engineers, even had our office manager attend. Year after year, paid for every hour you work and less likely to be expected to I leave career fairs feeling optimistic about some bright young engineer put in long unpaid hours. I want to land, only to feel disappointment in the coming weeks when • You are more likely to keep your job when the economy tightthe candidate takes a job somewhere else. Not always, but often. ens, and work is slow. When the 1990 recession hit, our firm There seems to be a perception among students, and probably some took on special inspection work to keep busy. When the 2008 of their professors, that you need to take a job out of college at a large recession hit, we took advantage of the downtime to put our firm in a city. Face it; there is a certain wow factor that students feel people to work building a staff kitchen in the basement. With when they walk up to a career fair table of a big-name national or our modest payroll, we can tighten our belts and retain our international firm with a glitzy backdrop and cool swag. Throw in a best people and ride a crisis through. The firms who survive a signature project like a major bridge or stadium, and they are captivated. downturn with all of their employees…survive. And yet, a small firm is an outstanding place to start a career in structural engineering. Hands down, in my opinion. Here are a few Small businesses are the backbone of America. And engineering firms things for graduates to consider about starting a career in a small firm: are no exception. The majority of structural engineering firms are small • You are more likely to be exposed to a wide variety of work firms and graduating engineering students would benefit from at least tasks. One day you are brainstorming how to give a buildgiving a small firm a chance by talking to engineers like me ing a structure, and the next, you are crunching numbers and scheduling an interview. We do not bite, and you may or building the BIM. You are attending meetings with the be pleasantly surprised at the opportunities awaiting you.■ design team, reviewing the shop drawings, and on the job site Kevin H. Chamberlain is the CEO and Principal of DeStefano & inspecting the work being built. You are not compartmentalChamberlain, Inc. in Fairfield, CT, and the Chair of the CASE Guidelines ized into only performing certain tasks. That is not how small Committee. (kevinc@dcstructural.com) firms typically operate.

“

STRUCTURE magazine

OCTOBER 2020

structural PRACTICES Mitigating Flood Damage to Bridges By Kevin Johns and Tom Murphy, Ph.D., P.E., S.E.

ince 2004, there have been 10 hurricanes in the Atlantic

ηmax

Ocean that have each caused over $20 billion in damage.

Storm Water Level

Since the late 1800s, sea levels have risen by 10 inches (250mm) and are expected to continue to rise, according to the National

F ds

Mean Water Level

Aeronautics and Scape Administration (NASA). Because of this, Departments of Transportation, transit authorities, and private owners have decided it is necessary to add robustness and reliability to new and existing infrastructure, some of which are over 100 years old. Transportation infrastructure, in particular,

Bed Horizontal Forces Pile Group Pile Cap

Wave effect substructure.

is essential, as these weather events sometimes make it necessary to evacuate many people from large areas of the country, and the highway system is the primary evacuation route for most metropolitan areas. Additionally, emergency responders need to be able to move freely, maintaining access to as many areas as possible during and immediately after a storm event. Bridges are one of the most vulnerable and critical components of However, this was an unusual situation in that the line was not in the surface transportation network. A bridge that is out of service in use and was being restored. The bridge was floated out on barges, normal conditions can result in long delays and significant detours. the pier top elevations were increased by three feet, and new bearings What is an inconvenience in normal times can were installed. The rehabilitated superstructure become catastrophic in an emergency. was floated back in place and put into service. Major storm events impart loads on structures bridge has not experienced flood-related Transportation The in several ways, resulting in varying degrees of damage since. damage. Wave action can push and lift the While raising the bridge above the flood level infrastructure, in bridge, creating both global lateral and vertical is the best method to protect the superstrucparticular, is essential, ture, the substructure and foundation will still forces. There are additional local impact loads where waves directly strike the bridge. Both subjected to flooding loads, and damage as these weather events be flooding and wave action impart a vertical can still occur. Wave action and increased upwards force from buoyancy. The buoyant sometimes make it streamflow forces from trapped debris can force can be enough to lift the bridge off its cause increased loads on piers. Higher water bearings and move it away from its supports. necessary to evacuate flow velocities increase the likelihood of scour Floods with moving water can push debris around foundations. Because these issues occur many people from large below the waterline, they are not easily or against the side of the structure or deposit debris on top, which adds to the gravity loads. identified. If no monitoring system is areas of the country... quickly Barges and ships break free from their moorpresent, divers are used to confirm that bridges ings in storm events and can impact bridge are safe to continue carrying traffic. However, superstructures and substructures. there is a limited number of qualified underMost existing bridges were not designed for these additional loads water inspectors – and immediately after an extreme event, there may and may not be able to resist them. The best chance of the structure’s not be enough of them to service an area. Bridges that are designed survival in the event of an extreme storm is to prevent the structure to resist the loads from flood events and increased scour levels are less from being subject to these loads, ideally by ensuring the bottom of the likely to be damaged. They will be less of a concern, reducing the risk superstructure will be above the highest water or wave level. This is easier of not having an inspection immediately after an event. to accomplish on a new bridge as the approaching roadway profile can Movable bridges are used over navigable waterways when the be set to accommodate the necessary bridge elevation. However, it can vertical clearance below the bridge is inadequate for the size of the be difficult on an existing bridge where the travel profile may be set. vessels that traverse the channel. This bridge type is particularly In 2000, Modjeski and Masters raised the Norfolk Southern Shellpot vulnerable to flood damage because their profile usually sets them Swing span three feet to keep it out of the flood zone because the close to the water, and they have sensitive machinery used to opermachinery used to operate the bridge was frequently flooded from ate the bridge. These bridges are opened and closed for marine high water events. Normally, a railroad would not be able to take a traffic with machinery that can be on the pier top or inside rooms line out of commission for the time it would take to raise a span. designed into the piers. These spaces are not watertight once the

“

8 STRUCTURE magazine

water elevation is too high. If the machinery is flooded, the bridge may not be practical due to the requirement of the anchorage system will likely not be able to operate until, at minimum, it is repaired placed into the concrete and limited space at the bearings. and, at worst, completely replaced. In addition to the uplift forces, streamflow and wave effects cause The Florida Avenue Vertical Lift Bridge in New Orleans was opened increased horizontal loading. These loads can be high enough to to traffic in May of 2005. In push the bridge laterally off August of 2005, the costliits supports. Lateral restraints λ est hurricane on record for at the bearings can be used to Z the United States, Hurricane resist these forces. These can Span Cross-Sec�on Rail Katrina, caused $125 billion be added as a retrofit, but it Overhang W in damage and over 1,200 is easier if they are added as Wave W* deaths. New Orleans was in part of the initial design. Propaga�on Deck Direc�on r the direct path of the hurricane Another option for dealing and suffered extreme damage. with lateral loads is to reduce d b dg ηmax The Florida Avenue Bridge their magnitude by using Hmax Zc Storm Water Level survived the storm, but the castellated beams. The large X electrical operating system was holes designed into the webs Storm Surge + Local Wind Setup Water Level severely damaged. Without a of castellated beams create a ds functioning operating system, load path that mimics that of the bridge could not be raised. a truss. These large holes sigBed This meant the waterway was nificantly reduce the area of blocked from allowing emerthe beam, allowing the wave Wave effect superstructure. gency supplies to be brought in to pass through rather than by water. The US Army Corp of Engineers was prepared to demolish impact on the surface. the three-month-old bridge to clear the navigable channel if it could Scour is the result of the increased stream flow velocity around not be made operational. Modjeski and Masters’ engineers were flown bridge piers. Scour results when the flow velocity is high enough to in by helicopter to assess the damage and attempt to make the bridge move supporting soil out from under bridge foundations. Scour can function. After two days of onsite trouble-shooting, the bridge was occur even under base conditions; however, it is much more likely to operating. It was able to be lifted, allowing marine traffic to resume occur in a flood event when flow velocity has significantly increased. and keeping the new bridge from being destroyed. In new designs, scour depths are predicted based on soil properties At the time the Florida Avenue Bridge was designed, there was little and streamflow velocity, which can be selected to reflect an extreme guidance for engineers to anticipate the types of loads caused by such event. The foundation elements are then designed, assuming the an event. In 2008, the American Association of State Highway and scour has occurred. For existing structures that were not designed for Transportation Officials (AASHTO) released the Guide Specifications for scouring, armoring the soils around the piers with riprap can control Bridges Vulnerable to Coastal Storms. The specifications contain guidance the impacts. This has been proven to significantly mitigate the risk for owners and designers on the design of bridges in coastal areas. Methods of scour, even in an extreme flood event. for calculating wave forces on both substructures and superstructures Apart from storm events, flooding can also be caused by a tsunami. based on numerical simulations of wave passage under a bridge, including There are many similarities between the tsunami-generated loadings of local impact forces, are provided in the guidelines. Physical wave tank structures and coastal storm loading. However, the nature of the wavetests and numerical simulations were used to develop the Physics-Based forms can be very different, which changes the interaction between Method (PBM), which is used to calculate the forces and verify the results. the structure and wave and results in significant enough differences Bridge failures due to storm surge and wave loading in Gulf Coast states in structural loading that additional guidelines are needed. Similar to provided field data that was used to verify results. other types of flood load mitigation, raising the superstructure above Loadings, as outlined in the Guide Specifications, are only one side the top of the expected wave elevation is often the best option for a of the design equation. The engineer must still address the resistance designer to consider, if at all practical. Efforts are currently underway of the structure to the load. Various mitigation methods are used to develop design guidance based on numerical and experimental studwhen it is not possible to raise the bridge above flood levels. Some ies of tsunami waves and their interaction with bridges for designers methods can be installed as a retrofit to existing bridges, and others and owners considering this unique threat. must be incorporated as part of the original design. In conclusion, the existing transportation infrastructure – particularly One failure mode observed in previous coastal storms is the unseating bridges – is susceptible to damage from flooding and high-water events. of the superstructure due to the combined effects of buoyancy and Measures are being taken to retrofit existing structures and design vertical wave loading. Air trapped in the areas between the beams can new structures to make them more likely to survive these impacts. also add to the buoyancy effect. To significantly reduce the buoyancy, Research is ongoing to help better understand these events. Practicing relatively small and frequently spaced holes that do not affect the design engineers should become familiar with published structural integrity can be placed in the deck, allowing trapped air guidance, as part of their due diligence, to provide more to escape. This can be done as a retrofit to existing bridges or as part robust and reliable designs.■ of a new design. Alternatively, ensuring air can move longitudinally Kevin Johns is the Movable Bridge Business Unit Director at Modjeski and by not using solid diaphragms can also reduce the forces working to Masters. (kwjohns@modjeski.com) unseat the structure. Additionally, effectively tying the superstructure to the substructure through structural means can prevent unseating. Thomas Murphy is a Vice President and the Chief Technical Officer at However, the vertical loading – including the effects of impact from Modjeski and Masters. (tpmurphy@modjeski.com) waves – can be very large and require robust tie-down systems, which OCTOBER 2020

The print version of the October issue of STRUCTURE (p. 10-12) contains the article, Coating Preparations Reduce the Strength of Bridges. Since publishing this article, STRUCTURE has received feedback that several statements in the article are unsubstantiated and based on limited research that has not been peer-reviewed. As a result, the article has been removed from this digital edition. Please look for further information in the November issue of STRUCTURE.

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structural INSPECTIONS

Inspectability Design Bridge Life Cycle Cost Savings By Jennifer C. Laning, P.E.

tandard practice during bridge design and construction is to consider the biddability of the construction documents, the constructability of the design, and the operability of the asset. Quite often, designers do not consider the inspectability of the bridge over its life cycle. Inspection, required by law on a 24-month cycle at a maximum, presents the bridge owner with costs: labor, equipment expenses, travel impacts, and safety. These costs, especially for complex bridges, signature structures, and high-level river crossings, can be reduced if inspectability is included in the design. The link between bridge design and inspectability is explored in a paper submitted to the SMT Conference 2010 in New York City, entitled Designing Bridges for Inspectability, by Alampalli and Yannotti, and in an ASCE Technical Note by Mahamid, et al., entitled Structural Design and Inspectability of Highway Bridges. In the Technical Note, the authors conducted a workshop on structural design and inspection of highway bridges at the University of Illinois at Chicago in November of 2017, with participants from state agencies, design and inspection companies, and academics. Both of these sources, as well as other sources such as the FHWA-IF-11-016 Framework for Improving Resilience of Bridge Design, placed a focus on improving current inspection challenges and offered proposed modifications for future design practices, intending to facilitate inspection practice. During design, inspectability can be incorporated by improving the ability to inspect the bridge visually. Considering bridge type selection and/or bridge details and providing or improving safe access for inspectors in the design phase is essential. The benefits include improved system preservation because the condition of the bridge can be more accurately monitored, improved safety for inspectors and the public during the performance of the inspection, and overall cost savings from increased inspection efficiency. When considering bridge type selection or design of bridge details, the main objective is to increase the visibility to the inspector by avoiding uninspectable elements. This impacts the owner’s ability to monitor and maintain the overall condition of the bridge; because, as noted in FHWA-IF-11-016, “elements that are difficult to inspect are typically problematic to maintain.” Flaws, cracks, and section loss can occur in inaccessible areas behind end diaphragms or between the ends of box or tub girders. Truss members, tie girders, tub girders, or floorbeam cross girders often have areas that are constrained by the member itself. A prestressed concrete box beam bridge is constructed with internal webs that are not visible. These same areas are susceptible to the accumulation of moisture, debris, roadway deicing materials, and other threats that contribute to the deterioration of the steel or concrete and loss of structural integrity. The inability to have visual access to bridge components means that inspectors cannot monitor the condition of these vulnerable areas over time. In turn, the deterioration will not be reported and maintenance will not be performed, presenting a challenge to system preservation and resulting in costly rehabilitation versus planned routine maintenance. Facilitating safe access to the bridge for both inspectors and the public who would be impacted by inspection operations can be accomplished in several ways. One advantage is that improvements to 14 STRUCTURE magazine

inspection access can be considered at the initial design level or during rehabilitation later in the bridge’s life. On signature or large structures, this can be accomWide sidewalks can provide accessibility. plished by providing catwalks, railings around piers, fall restraint systems, tie-offs on deep girders, and locations where rappelling or traveler systems can be attached to the bridge. A frequently undervalued need is a pull-off or staging area at or under the bridge for safe coordination of inspection operations. For highway structures over roadways, railroads, or waterways, the inspection access considerations are less complicated. Still, even small accommodations can make work safer for inspectors over the life of the bridge. Conversations with experienced bridge inspectors have suggested access improvements such as ensuring an accessible abutment seat height, providing a flat area at the top of slopes to stand or place ladders, locating the girder splices over outer lanes to reduce the need for double lane closures, or making the access hatches to steel tub girders or box floorbeam/cross girders more accessible. Inspection equipment access could also be limited by the width of outboard sidewalks or the placement of high fences and luminaire poles, which may obstruct snoopers, or poor ground conditions underneath the bridge that could be used by manlifts or bucket trucks. There are many factors to consider when looking for ways to optimize inspection access, including reducing or eliminating the need to perform lane closures as much as possible, removing or reducing obstacles to production, improving safety, and allowing inspectors to reach as much of the structure as possible. Ultimately, the goal is to improve safety and efficiency, which has the potential to realize cost savings over the life of the bridge. While these modifications certainly would improve efforts toward best practices in design, it is possible that cost increases in design or construction would impact their implementation. However, the cost savings over the life of the bridge can potentially outweigh the costs in design or construction. For example, consider the low cost of planning to place tie-offs or to analyze the access to various portions of the bridge during the design phase versus not having these in place in the future. An example is a signature cable-stayed bridge that cost more than $100 million to build in the 1990s, which was constructed without tie-offs on the top of the pylons to facilitate rope access inspection. In another case, a functionally obsolete lift truss bridge with extremely narrow lanes that required overnight inspections was retrofitted with a maintenance traveler. Design solutions can also include reducing or eliminating the use of certain bridge types or details, like prestressed adjacent box beam bridges or diaphragm configurations at abutments that prevent visual inspection of the beam ends or abutment backwall. Other solutions include evaluating whether certain areas of a bridge can be accessed by existing equipment configurations (i.e., the largest underbridge inspection vehicle has a 75-foot reach) while in design, and

if not, building in methods of access, such as walkways or connections for travelers or rigging. One suggestion in the ASCE Technical Note was an exciting and innovative discussion point regarding the potential use of BrIM as a way to utilize a digital representation to explore the inspectability of a bridge. If the cost of time spent during the design phase to address inspectability is a barrier, perhaps this innovative solution of using BrIM’s agility can help in making inspectability part of best practices in bridge design. Many agency manuals require that designers consider inspectability during the design process, so a strong case can be made for including an actual review of the plans specifically for inspection considerations. Having a bridge inspection specialist who reviews the plans can provide useful suggestions early in the process. Potential solutions may include flat areas adjacent to the abutments or locating the hatches for tub girders in the bottom face of the tub and making them large enough for extension ladders. And, including a discussion on inspection access improvements in a rehabilitation may provide some value if the improvements can be included at that time. The downside for not addressing inspectability is the potential increase in the costs of inspections due to equipment and lane closures needed to perform the inspections every 24-month interval for the life of the bridge. Remember, there are also impacts on traffic and safety during inspections. Inspection-friendly alternatives considered early, if possible, can be significant improvements. Safety for inspectors and the traveling public is the overarching benefit that can be realized by designing for improved inspectability, particularly when many solutions can reduce or remove the equipment and lane closure demands. Equipment such as underbridge inspection vehicles and traffic control setups cost money. Impacts to traffic on already congested roadways result in economic costs, through delays to commuters and

Traveler rail retrofitted to accommodate a scaffold system for inspections.

the trucking industry, not to mention the cost to the environment from the use of fossil fuels and emissions. By providing alternative methods for access to the bridge, perhaps from beneath or by utilizing rigging, travelers, or walkways, the opportunity exists to be safer and more efficient. Any time that the bridge inspection industry can avoid impacting traffic with equipment and subsequent lane closures, both safety and economic benefits are realized. As a bridge inspection subject matter expert, the author encourages more thoughtful consideration of inspectability by bridge designers. Our industry should encourage bridge designers to consider the long-term cost savings of improving inspectability and the corresponding improvement in safety for inspectors and the traveling public.■ Jennifer C. Laning is Associate Vice President and Bridge Inspection Practice Leader at Pennoni. (jlaning@pennoni.com)

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structural PERFORMANCE

3-D Snow Drifts By Michael O’Rourke, Ph.D., P.E., and Talia Williams

efore the 2016 version of the American Society of Civil Engineer's ASCE 7 Load Standard, Minimum Design Loads for Buildings and Other Structures, all snowdrifts were two dimensional. The height and width (horizontal extension) of the leeward roof step drifts were taken to be constant all along the roof step. The same holds for windward roof step drifts, parapet wall drifts, and over-the-ridge gable roof drifts. As such, the wind direction of interest was nominally perpendicular to the geometric irregularity, i.e., perpendicular in plan to the roof step, the parapet wall, or the gable roof ridgeline. There are some roof geometries where two, 2-D drifts overlap or occupy the same roof area. One such roof geometry is the Northwestern corner of a roof with parapet walls along both the North and West edges. Wind out of the South would result in a two-dimensional drift along the North wall, while wind out of the East would result in a two-dimensional drift along the west wall. Presumably, each of the 2-D drifts would control design for most of the bays along the North and West sides, respectively. The 2-D drift footprints overlap at the corner. Prior to ASCE 7-16, the design snowdrift for the NW corner bay was open to question. Some structural engineers may well have designed the bay for each of the 2-D drifts separately. Other structural engineers may have designed the corner bay for the sum of the two 2-D drifts. ASCE 7-16 clarifies the situation by specifying that the snow depth at any point in the overlap area is taken as the larger of the two 2-D drift depths at that point, as shown in Figure 1. That is, a 3-D drift is not a new drift; instead, it is the drift at locations where well established 2-D drifts overlap. Note that this approach is consistent with the ASCE 7 approach for roof step drifts. In that case, both the leeward and windward drifts are determined, and the larger (not the sum) is used for design. Other roof geometries can lead to 3-D snowdrifts, i.e., the overlapping of two 2-D drifts. A simple gable roof, with a N-S ridgeline and a pediment or parapet at the North end wall, is one such example. For wind out of the South, there would be a regular 2-D parapet wall drift, while for wind out of the West, there would be a regular 2-D gable roof drift on the East side of the gable. These two, 2-D drifts would overlap along a portion of the parapet wall East of the ridgeline, as sketched in Figure 2. Extension of the current 3-D drift provision for parapet wall corners and re-entrant corners to other roof geometries is currently under consideration by the ASCE 7-22 committee. One

Figure 1. Plan view of a 3-D snowdrift at Northwest corner. The dashed line designates the 3-D drift area.

issue is whether such new guidance, which by necessity would increase the length and complexity of the code provisions, is needed. As noted above, there is a single wind direction of interest for the 2-D drifts (e.g., nominally perpendicular to the ridgeline for gable roof drifts). However, there are two wind directions of interest for 3-D drifts (e.g., wind out of South and wind out of the East for the Northwest parapet wall corner case discussed above). This raises the question of the likelihood of multiple wind directions in wintertime. For a site with a single, predominant wind direction (e.g., the winter wind is almost always out of the North), the potential for significant 3-D drift formation would seem limited. On the other hand, 3-D drift formation would seem more likely if winter winds from multiple directions were expected. Boston’s 2014-15 winter season was an example of the latter.

Boston 2015

Boston and other parts of New England experienced significant losses due to a series of four primary snowstorms in January and February of 2015. Based on an insurance arbitration hearing at which Table 1. Snowfall and wind during winter storms in Boston; January thru February, 2015. the senior author attended as an expert witness, the incurred losses due to eave ice dams alone were more than $100 milSnowfall Equivalent Hours with Storm Snowfall Depth Snowfall ≥ 10 MPH Wind lion. Table 1 presents a summary of snowfall and wind for Duration (in.) Weight (psf ) Wind Direction Number each of the four Boston 2015 primary storms. The information in Table 1 is based on National Oceanic and 10 AM 1/26/15 26 6.1 78 300° to 60° 1 to 4 AM 1/28/15 Atmospheric Administration (NOAA) Local Climatological Data Sheets for Logan Airport in Boston. It was assumed that 4 AM 2/2/15 to 17 4.6 57 190° to 70° 2 snow remained driftable for 3 days after the end of the storm 10 PM 2/2/15 snowfall (i.e., snow from Storm #1 was driftable until 4 AM 1 PM 2/7/15 to 25.3 7.3 90 210° to 30° 3 1/31/15)(O’Rourke et al., 2005). Furthermore, the wind speed 1 AM 2/10/15 threshold for snow drifting (i.e., wind-induced snow transport) 4 PM 2/14/15 to 16.8 3.33 63 120° to 10° 4 was taken to be 10 miles per hour (mph)(O’Rourke et al., 1 PM 2/16/15 2005). Hence, for the 114 hours in Storm #1 from the start Total 85.1 21.3 288 of snowfall (10 AM 1/26/15) to assumed cessation of drifting 16 STRUCTURE magazine

(4 AM 1/31/15), drifting was occurring about 68% of the time, assuming the snow source was not depleted. The resulting structural damage, in general, and damage to school buildings in particular, triggered deployment of a Federal Emergency Management Agency (FEMA) Building Science Branch assessment team on February 25, 2015. In early March, the FEMA team inspected four partial school collapses – two south of Boston and two in southern New Hampshire. During the FEMA visit, ground snow depth and load samples were taken. The ground snow depths south of Boston ranged from 2.5 to 2.8 feet, and its ground snow loads ranged from 39 to 44 pounds per square foot (psf). The corresponding southern New Hampshire values were 1.4 to 1.7 feet and 22 to 26.5 psf. Concerning snow drifting, O’Rourke and Cocca (2018) developed parameters to quantify the influence of wind. Specifically, they recommended that the size (cross-sectional area) of the drift surcharge be a function of the ground snow load and the upwind fetch (as is currently), as well as a winter wind parameter. Two wind parameters were considered. The first, W2, is simply the percentage of time during the winter (October through April) during which the wind speed is 10 mph or higher. Note that there is no particular direction associated with W2; all wind directions can contribute. A direction-specific winter wind Figure 2. Plan view of 3-D snowdrift for parapet wall at North end wall of gable with parameter, W4, was also considered. The parameter was defined N-S ridgeline. The dashed line designates the 3-D drift area. as the largest of the eight values for the percentage of time the wind speed was above 10 mph along each of the eight cardinal direcThe Boston 2015 wind roses in Figure 3 demonstrated that a shift in tions (N, NW, W…NE). By its nature: wind direction throughout a single snowstorm or over the course of a W2 = W4N + W4NW + … +W4NE single winter is possible. The single storm version is common enough Table 2 presents the W2 and W4 wind parameters for each of the four that it has been given a name: a Nor’easter. The classic Nor’easter primary Boston 2015 storms. For example, during Storm #1, and the corresponds to a low-pressure system proceeding up the Atlantic three days of potential snow drifting that followed, the wind speed coast. In New England, due to the counter-clockwise rotation about was above 10 mph for 68% of the time, while the wind speed in the a low, there is wind out of the East when the low is south of New north nominal wind direction was above 10 mph for 15% of the time. York City, followed by wind out of the North when the low is East Figure 3, page 18, shows the wind rose for each of the four primary of Boston. Note that the Boston 2015 wind roses (wind out of the Boston 2015 storms. Note that the winds were predominately out North and West) were not due to a Nor’easter (wind out of the North of the Northwest and North, respectively, during Storms #1 and and East). The Boston 2015 Storm #2 was consistent with a Canadian #3. Storm #4 had strong winds out of two directions (NW and W), low traveling along a Southeastern path, somewhat North of Boston. while Storm #2 had three strong wind directions (N, NW, and W). The classic Nor’easter and at least one of the Boston 2015 storms As noted above, wind out of the North and/or West was common in the established that 90° wind shifts are relatively common in New England. Boston 2015 storms. Such a wind pattern, for certain roof geometries, However, this does not establish that such wind shifts are common results in the formation of 3-D snowdrifts. As described in more detail in other parts of the United States. in the Snow Study Summary Report: Observations of Snow Load Effects on Four School Buildings in New England (FEMA, 2016), which can be Winter Wind Shift in the U.S. downloaded https://bit.ly/2wYPiUA, two of the four roof collapses were due to 3-D snowdrifts at relatively complex roof geometries. At Mitchell As shown above, a wind rose is a convenient way of characterizing Elementary in Bridgewater, MA, the damaging 3-D drift was due to an wind direction. Figure 4, page 18, presents a multiyear rose for Boston, overlap of a 2-D gable roof drift due to wind out of the North and a MA. Unlike the individual storm wind roses in Figure 3, the multiyear 2-D windward roof step drift due to wind out of the West. Similarly, at wind rose in Figure 4 is for 65 winters (October through April). Also, Plymouth River Elementary in Hingham, MA, the damaging 3-D drift the wind rose in Figure 4 was not restricted to time during and after was due to an overlap of a 2-D leeward roof step drift due to a North snowstorms. The multiyear winter wind rose for Boston shows the NW wind and a 2-D windward roof step drift due to a West wind. The two wind was the most common winter direction with W4 = 0.19, and the partial collapses observed in Southern New Hampshire were both regular West wind with W4 = 0.16 was the next most common. To use multiyear wind roses for locations across the United States, 2-D drifts at simpler, less complex roof geometries. and to quantify the directional variability of the above-the-driftingTable 2. Wind parameters W2 and W4 for the four primary Boston 2015 snowstorms. threshold-wind, the multiyear wind roses needed to be rotated and normalized. Specifically, each of the multiyear wind roses Storm W2 W4N W4NW W4W W4SW W4S W4SE W4E W4NE was rotated so that the predominant snow drifting wind direction 1 0.68 0.15 0.43 0.0 0.0 0.0 0.0 0.0 0.10 (direction of the largest of the 8 multiyear W4 values) was vertical. For Boston, with NW as the predominant direction, the rose was 2 0.55 0.11 0.11 0.11 0.04 0.07 0.0 0.04 0.07 rotated 45° clock-wise (NW direction now “vertical”). All 272 of 3 0.69 0.59 0.02 0.0 0.0 0.0 0.0 0.0 0.08 the multiyear wind roses were then normalized by dividing each 4 0.60 0.07 0.30 0.23 0.0 0.0 0.0 0.0 0.0 of the eight W4 values by the largest for that location. As a result, OCTOBER 2020

roof areas where the two 2-D drifts overlap, using the larger of 100% of one of the 2-D drift and 60% of the other 2-D drifts is justified.

Conclusion and Recommendation

Figure 3. Winter wind roses for Boston 2015 storms.

each of the 272 multiyear wind roses had an amplitude of 1.0 along the vertical, and smaller amounts for all other directions. Table 3 presents the mean, median, minimum, maximum, and standard deviation of the W4 ratios for all possible wind shifts. That is, 90° CW means 90° clockwise from the predominant direction. Notice that the maximum ratio is close to 100% for all wind directions. That is, there were at least one of the 272 locations where W4 for the next most common wind direction was nominally the same as for the predominant or most common direction. Similarly, the minimum ratio was close to 0% for all directions. That is, for at least one of the 272 locations, there was nominally no snowdrift for some direction other than the predominant direction. Given the rectilinear nature of most roof geometries, it would seem that a 90° or 270° wind shift from the predominant direction are the two directions of most interest with 3-D drift formation. Assuming a normal distribution, the mean plus 1.5 standard deviations would account for about 93% of the locations. The W4 value for either 90° or 270° CW from the predominate would be (using 0.23 as an average standard deviation for 90° CW and 270° CW) (W4)270° = (W4)90° = 0.279 + 1.5(0.23) = 0.62 It turns out that the drift height is, as a first approximation, proportional to the winter wind parameter. As such, one could argue that at

The 2015 Boston case demonstrates that strong winds (capable of causing snow drifting) can change direction during a single storm and over the course of a single winter. The 2015 Boston Winter resulted in 3-D drifts (strong winds from directions 90° apart), which caused partial structural collapses and, in one case, complete closure at one school until the summer. Analysis of winter wind across the whole United States indicates that 3-D drifts are not a “Boston-only” phenomenon. Specifically, the analysis shows that a 3-D drift, composed of or based upon 100% of one of the 2-D drifts and about 60% of the others, seems justified. It is the author’s opinion that, if the current ASCE 7-16 approach for parapet wall corners is expanded to cover other 3-D drift susceptible roof areas, the 100%/100% approach should be used as opposed to the 100%/60% approach mentioned above. This opinion is based on the following reasoning: • The 100%/100% approach is consistent with the current ASCE 7-16 approach for corners (parapet wall and re-entrant) and the long-standing approach for leeward and windward roof step drifts. • The 100%/100% approach is easier to use and understand. The 100%/100% approach requires the structural engineer to determine two 2-D drifts and to consider one combination. The 100%/60% approach requires determination of four 2-D drifts (a 100% and a 60% for both directions) and consideration of two combinations (“100%/60%” and “60%/100%). • One expects that the number of bays susceptible to 3-D drift formation is small in comparison to the number susceptible to 2-D drift formation. In such situations, “simple and conservative” makes more sense than “complex but precise.” Examples of the evaluation of 3-D snow drift using provisions currently in ASCE 7-16 or expected in ASCE 7-22 (i.e., the 100%/100% approach discussed above) are presented in a FEMA guidance document Three-Dimensional Roof Snowdrifts Design Guide (FEMA, 2019), available at https://bit.ly/2VCqMmt.■ The online version of this article contains references. Please visit www.STRUCTUREmag.org. Michael O’Rourke is a Professor of Civil Engineering at Rensselaer Polytechnic Institute, Troy, NY. (orourm@rpi.edu) Talia Williams is an undergraduate civil engineering student of the 2020 graduating class at Rensselaer Polytechnic Institute.

Table 3. W4 values for 272 rotated and normalized wind roses.

Direction

Mean

Median

Minimum

Maximum

St. Deviation

Vertical

1.0

0.0

45° CW

0.440

0.417

0.003

0.993

0.251

90° CW

0.279

0.214

0.001

0.956

0.224

135° CW

0.312

0.271

0.001

0.982

0.242

180° CW

0.413

0.392

0.066

0.999

0.264

225° CW

0.275

0.211

0.002

0.995

0.223

270° CW

0.279

0.218

0.001

0.992

0.237

315° CW

0.458

0.420

0.008

0.998

0.256

18 STRUCTURE magazine

Figure 4. 65-year winter wind rose for Boston, MA.

historic STRUCTURES Ashtabula Bridge Failure By Frank Griggs, Jr., Dist. M.ASCE, D.Eng., P.E., P.L.S.

he Ashtabula Bridge disaster was one of the most publicized American bridge failures

of the 19th century. In 1865, the Lake Shore & Southern Michigan Railroad was faced with the task of replacing a wooden bridge over Ashtabula Creek in northeastern Ohio. The president of the railroad was Amasa Stone, who had purchased the patent rights for the Howe Bridge from William Howe, his brother-in-law, in 1841. Howe’s bridge

The Ashtabula Bridge.

was initially built with wooden top and bottom chords and diagonals; the verticals were wrought-iron rods in tension. Stone had built many successful Howe wooden trusses before the Ashtabula Bridge but built this one entirely of iron with cast iron for junction blocks and wrought iron for tension and compression members. The wrought iron top chord and diagonals were all fabricated from I sections and the bottom chord of wrought iron bars. The span, as built, was 157 feet and cost $75,000. All was well until the night of December 29, 1876. On this night, the eleven-year-old bridge failed, in what was called a blinding snowstorm, carrying the Pacific Express to the creek 69 feet below, resulting in the loss of 80 lives. Stone had rejected the advice of two of his engineers, Charles Collins and Joseph Tomlinson, about the design of the bridge. Collins, who supervised the construction of the bridge, was reported to have said, “This is no bridge of mine; that is the President’s bridge.” After testifying to a Coroner’s Jury, “I never mentioned to anyone that the bridge was not mine and that I did not want anything to do with it since it was placed under the charge of a bridge man; I thought it out of place for me to say anything about it. I never knew of another bridge being built of wrought iron on this plan. I think the bridge was rather an experiment.” After he testified, he committed suicide. Tomlinson, under the supervision of Stone, made the drawings of the bridge but told Stone the braces were not strong enough. Stone then fired Tomlinson. The press of the country, already somewhat critical of the railroads, had a field day pointing fingers, asking embarrassing questions, and wondering over and over again how something like this could happen. The Illustrated London News ran an article in its February 3rd issue, along with a full-page engraving of the train burning amidst the wreckage of the bridge. Harper’s Weekly, on January 20, 1877, ran an article and a full-page illustration of the disaster, asking questions that most people wanted an answer to, when it wrote: “Was it improperly constructed? Was the iron of inferior quality? After eleven years of service, had it suddenly lost its strength? Or had a gradual weakness grown upon it unperceived? Might that weakness have been discovered by frequent and proper examination? Or was the breakage the sudden effect of the intense cold? If so, why had it not happened before in yet more severe weather? Is there no method of making iron bridges of assured safety and who is responsible (so far as responsibility goes) for such an accident –the engineer who designed the bridge, or the contractor, or the builders, 20 STRUCTURE magazine

or the railroad corporation? Was the bridge when made, the best of its kind, or the cheapest of its kind? Was the contract for building “let to the lowest bidder,” or given to the most honest, thorough workmen? These and a hundred similar queries arise in every thoughtful mind and an anxious community desire information and assurance of safety. The majority of people can not, of course, understand the detailed construction of bridges, but they do desire confidence in engineers, builders, contractors, manufacturers, who have to do with the making of them, and in the railroad companies, into whose hands they are constantly putting their own lives and the lives of those dearest to them.” The article's third question (bolded) was most damaging for the civil engineering profession. An iron bridge had been built for railroad traffic by Whipple in 1853, with a span of 147 feet that was still carrying traffic. The B & O had replaced its wooden bridges with iron as well, usually on the Bollman or Fink plan starting in the 1850s. Jacob H. Linville built a 320-foot span bridge at Steubenville, Ohio, in 1864, a year before the construction of the Ashtabula Bridge. As was usually the case when fatalities resulted from a bridge failure, the only means of investigating the underlying causes was to call a coroner’s inquest that went on for 68 days. The Jury had seven conclusions, of which 3, 4, and 5 are the most important for this article, “Third. That the fall of the bridge was the result of defects and errors made in designing, constructing, and erecting it; that a great defect, and one which appears in many parts of the structure, was the dependence of every member for its efficient action upon the probability that all or nearly all the others would retain their position and do the duty for which they were designed, instead of giving to each member a positive connection with the rest, which nothing but a direct rupture could sever...

Fourth. That the railway company used and continued to use this bridge for about eleven years, during all which time a careful inspection by a competent bridge engineer could not have failed to discover all these defects. For the neglect of such careful inspection, the railway company alone is responsible. Fifth. That the responsibility of this fearful disaster and its consequent loss of life rests upon the railway company, which, by its chief executive officer, planned and erected this bridge.” In addition, a special committee of the Ohio state legislature was created. They appointed three prominent engineers, who concluded, after a very comprehensive study, on January 30, 1877, that the factors of safety in the members varied widely, with the tension members very strong and the compression members very weak. They then wrote, “The probability is that the braces failed first, and thereby involved the failure of the top chord also. But inasmuch as both members were weak, and both were involved in the break, it is of little importance which member took precedence in the failure. The factors of safety throughout the compression members were so low that failure must have followed sooner or later. If the several groups of beams composing the braces and top chord had each been combined into a single member, by riveting on their flanges a system of diagonal plates – say three and a half by halfinch – running alternately from right to left and from left to right across the entire group, the bridge would have been abundantly safe. This arrangement would have made each group strongest in the lateral direction and weakest in the direction of the webs of the beams, but in this direction, the beams offer about five times the resistance that they do laterally. The top chord members could then only deflect in single panel lengths, and, on that account,

The failure of the Ashtabula Bridge.

their strength would have been still further increased – twofold. The result would have been that the factors of safety given in the tables would have been increased five times for the braces and ten times for the chord. They would have been so excessively strong that much of the material might have been omitted... Another defect was the absence of any provision for retaining the braces in their places on the angle-blocks. Such provision had been originally made by means of raised lugs on the faces of the blocks at the corner of the flanges of the braces. But, in changing the positions of the braces, these lugs were removed, and no substitute, therefore, was provided. This allowed the braces to

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OCTOBER 2020

Macdonald’s drawing of top chord joints.

slip from their places, and make the already imperfect bearings still more defective... The full legislative committee concluded, 1st – There were from eighty to one hundred lives lost by the failure of the bridge. 2d – The bridge went down under an ordinary load by reason of defects in its original construction. 3d –The defects in the original construction of the bridge could have been discovered at any time after its erection by careful and analytical inspection, such as the importance of the structure demanded, and thus the sacrifice of life and property prevented.” Many engineers weighed in on the failure. Charles Macdonald wrote a long paper for ASCE on the failure. He wrote as an introduction, “At the moment when the pilot of the forward engine reached the western abutment, the top chord of the south truss, which was almost directly under the train, gave way at a point about 23 feet from the west end, causing the immediate fall of the entire structure; the engineer of the first engine, feeling a sudden movement, pulled open his throttle valve and succeeded in landing his engine on [the] solid ground west of the abutment, but the remaining engine and the express cars went down with the bridge, while the passenger cars were dragged one after another over the eastern abutment into a chasm 65 feet in depth, piling one upon the other in a shapeless mass of splintered fragments which immediately caught fire and were consumed.” After describing each element of the bridge and determining its strength, he concluded, “The most important lessons to be learned from the event: In the interval since the accident, we have had a sufficiency of snap judgments to satisfy the most censorious. Judging from the tenor of much that has appeared in the secular press, either as evidence taken under the solemnity of an oath or by way of editorial comment, this bridge must have been conceived in sin and born in iniquity. The President of the Company attempts to execute a difficult piece of construction, with but little special knowledge of the principles involved in his task. He ignores the advice of a chosen professional assistant and neglects to profit by the warnings which are said to have been uttered by the structure itself in the travail of its birth, and now, at the end of all these years, a dire catastrophe brings the misshapen thing back to the source from whence it sprung. In the West, a few scattering efforts had been made, and the subject was beginning to attract the attention of some of 22 STRUCTURE magazine

the best minds in the country. Squire Whipple, Albert Fink, Shaler Smith, Jacob H. Linville, and Thomas C. Clarke had built bridges at that time, it is true, but such names could almost be counted upon the fingers; and even these would, perhaps, now admit that they then “[built it] better than they knew.” If then, the state of knowledge at the time has not been under-estimated, the Ashtabula bridge was the result of an honest effort to improve the bridge practice of the country, undertaken by a man whose experience in wooden bridges warranted him in making the attempt. As to his willful neglect of proffered advice, it would be well to suspend judgment until all the facts are brought to light by the proper tribunals. His worst enemies will, at least, according to Mr. Stone, the possession of common sense... First. The inspection must have been faulty. If anyone of the well-known bridge engineers of today had been asked to examine that structure, he would have pronounced it unsafe, for the principal reason that all the compression members were liable to fail by flexure… Second. A careful study of the behavior of the compression members of this bridge must impress us with the necessity of more perfect experimental knowledge of the strength of iron in the form of struts... Third. The failure of some of the castings conveys a useful lesson in designing details involving the use of cast-iron. Care should always be taken not to pass abruptly from a large to small mass; else, the strains from cooling will surely vitiate the strength of the connection... Fourth. In conclusion, it may with safety be said that the Ashtabula bridge was an exceptional structure, both in its design and execution, and that the reputation of American engineers and bridge constructors of today cannot in the least be affected by its failure when all the facts are known…” Many other engineers, such as Squire Whipple, A. P. Boller, Theodore Cooper, Edward Philbrick, Gouverneur Warren, C. Shaler Smith, Charles Hilton, and Robert Briggs, weighed in on the failure. Whipple wrote, “But it was a much greater fault, and probably the one mainly leading to the fatal result, to divide the material of the braces and upper chord into 5 or 6 slender bars, affording but little mutual support laterally, instead of consolidating a smaller amount of material in single efficient members of large diameter and lateral stiffness.” Boller wrote, “We all know it to have been a conglomeration of errors, and principally astounding in its longevity. Why it lasted a week after the staging was knocked out can only be answered by reference to the doctrine of “special providences.” That it lasted a dozen years is a superb tribute to the value of iron in bridge construction, showing the torture that material will stand before the penalty is paid, that nature exacts of ignorance. Without moralizing over the design, ignorantly conceived and faultily carried out, and one that any bridge expert would have condemned after less than five minutes inspection, the lesson of the disaster is of the highest importance to the whole community.” The cause of the failure was a case of bad design, bad construction, and inadequate inspection. The design was never repeated.■ 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)

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structural COMPONENTS Designing Cross-Laminated Timber Wall Elements By Lori Koch, P.E., and Michelle Kam-Biron, P.E., S.E., SECB

lthough commonly used throughout the building industry, the term “mass timber “will be included in the International Building Code (IBC) for the first time in the 2021 Edition. Mass timber will be defined as structural elements of Type

IV construction primarily of solid, built-up, panelized, or engineered wood products that meet minimum cross-section dimensions of Type IV construction. Cross-laminated Timber, or CLT, is one of the major wood products used in mass timber construction that has started to gain traction in the North American building sector as a viable major building material due to its structural properties, sustainability, and inherent fire-resistance. CLT is a prefabricated engineered wood product consisting of not less than three layers of solid-sawn lumber or structural composite lumber, where the adjacent layers are cross-oriented perpendicularly and bonded with structural adhesive to form a solid wood element. Finished panels are typically 2 to 10 feet wide, with lengths up to 60 feet and thickness up to 20 inches. CLT is commonly used for long spans in walls, floors, and roofs. With its inclusion in the National Design Specification® (NDS®) for Wood Construction and the IBC, the material is becoming more commonly used. However, design examples on the use of this new material remain limited. This article provides information on CLT as a material, its production, and uses, and provides a design example for a CLT wall application.

design values for specific grades of CLT, geometric properties, and adhesive requirements that manufacturers must meet. Structural reference design values for CLT should be obtained from the CLT manufacturer’s literature or code evaluation reports. Although CLT may be used for roof, floor, or wall applications, there are limited design examples available. A conceptual CLT wall design example for axial loads and combined out-of-plane and axial loads is shown below. (Note that the loads are not factored per ASCE 7; the example is shown for proof of concept rather than a complete design example.)

Historical Background and Use

For this exercise, a CLT wall subjected to axial compression and out-of-plane wind load (perpendicular to the face of the wall) is investigated. The design loads and parameters are: Live load = 15,000 plf Dead load (including estimated self-weight) = 7,500 plf Wind load = 25 psf Wall height = L = 10 ft = 120 in The wall will be designed on a unit width basis, so all loads will be calculated based on a 1-foot- wide section. The loads per unit width:

CLT was first introduced in Europe in the 1990s and has grown in popularity in the years since, with over 500 CLT buildings in England alone. Even before being adopted in U.S. codes and standards, CLT was used in buildings such as Long Hall in Whitefish, Montana (the first CLT commercial building), Franklin Elementary School in Franklin, West Virginia (the first CLT school building), and several more. The WoodWorks website reports that there are currently over 350 CLT projects that are either in construction/built or in design, and over 700 projects using other mass timber products throughout the U.S. The Table provides a sampling of projects: In the 2015 and 2018 IBC, CLT is limited in use to low and midrise buildings, mainly of Type III, IV, and V Construction, and may not be used in tall buildings.

Codes and Standards CLT was first standardized in the U.S. in the 2015 NDS and adopted in the 2015 IBC. The production standard in the 2015 and 2018 IBC for CLT is ANSI/APA PRG 320-11 and ANSI/APA PRG 320-17, respectively. However, if designers are considering using CLT for “tall buildings,” ANSI/APA PRG 320-18 should be used due to a change in the adhesive requirements. PRG 320 provides 24 STRUCTURE magazine

Example – Combined Bending and Axial Loads

Axial loads Live load = Plive = 15,000 lbs Dead load = Pdead = 7,500 lbs Total load = Ptotal = Plive + Pdead = 22,500 lbs

Table of U.S. CLT building examples.

Location

No. Stories

Completion Date

The Long Hall

Building

Whitefish, MT

2011

Franklin Elementary School

Franklin, WV

2015

Carbon 12

Portland, OR

2018

Candlewood Suites

Huntsville, AL

2015

John W. Olver Design Building at UMass Amherst

Amherst, MA

2017

Albina Yard

Portland, OR

2016

Bending loads Wind load = wwind = 25 plf The initial design will consist of a 3-ply CLT panel made from 13⁄8-inch × 31⁄2-inch lumber boards (CLT thickness of 41⁄8 inches), grade E1. While the NDS requires designers to use properties from their CLT manufacturer, for this example, general properties from PRG 320 will be used. For CLT grade E1, tabulated properties from PRG 320 Tables A1 and A2 are: Fc,0 = 1,800 psi (Reference compression stress) (FbS)eff,f,0 = 4,525 ft-lb/ft of width (Reference bending moment) (EI)eff,f,0 = 115 * 106 lb-in2/ft of width (Reference bending stiffness) (GA)eff,f,0 = 0.46 * 106 lb/ft of width (Reference shear stiffness) To calculate the effective wall compression capacity, the area parallel to grain is used (NDS 10.3.1). For a 3-ply CLT panel, this includes 2 plies, each of which are 13⁄8 inches thick for the member depth. Since the design is on a unit width, the effective member width is 12 inches. For this example, unless otherwise noted, all adjustment factors are assumed to equal 1.0 (CM = Ct = 1.0). Aparallel = 2 (1.375 in)12 in = 33 in2/ft of width Pc = Fc,0 (Aparallel) = 59,400 lb/ft of width Effective (unadjusted) wall compression capacity To calculate the adjusted allowable compression capacity, the apparent bending stiffness, (EI)app, must first be calculated using the provisions of NDS 10.4.1. Assuming a pinned-pinned column buckling load, NDS Table 10.4.1.1 allows us to determine a Shear Deformation Adjustment Factor, Ks = 11.8. (EI )eff,0 115×106 = = 95*106 lb-in2/ft (EI)app = 6 11.8*115×10 K (EI ) eff,0 of width 1+ 1+ s (0.46×106 )*1202 (GA)eff,0 L2 (EI)app is adjusted per NDS Appendix D and Appendix H to determine (EI)app-min. NDS Commentary C10.4.1 provides additional information on this adjustment. Next, the allowable column capacity is calculated. (EI)app-min = 0.518 (EI)app = 49.0 × 106 lb-in2/ft of width PcE = π2 (EI)app-min / L2 = 34.0 × 103 lb/ft of width (NDS C3.7.1.5) CD = 1.0 (NDS Table 2.3.2) Pc* = Pc(CD)(CM)(Ct) = 59.4 × 103 lb/ft of width (NDS C3.7.1.5) αc = PcE / Pc* = 0.57 c = 0.90 CP =

1+αc − 2c

√( )

2 1+αc − αc CP = 0.52 c 2c

Pc´ = Pc* (CP) = 30.6 × 103 lb/ft of width The capacity of 30,600 lbs per foot of wall exceeds the demand of 22,500 lbs per foot of wall. Next, the bending capacity will be checked. For wind loads, the load duration factor (CD) is assumed to equal 1.6. The applied moment due to wind is calculated as:

( )

L 2 wwind* 12 Mmax = = 312.5 ft-lb/ft of width 8 The beam stability factor is determined based on the provisions in NDS 3.3.3.1. In this example, d = 41⁄8 inches is less than b = 12 inches, so CL = 1.0. The adjusted capacity is then calculated as: (FbS)eff´ = ((FbS)eff,f,0)(CD)(CM)(CL)(Ct) = 7,240 ft-lb/ft of width The capacity exceeds the maximum applied moment, so the design is sufficient for bending. Since the member is subject to combined loads, a bending and axial interaction check is required per NDS 3.9.2. For this example, Equation C3.9.2-3 is used.

Ptotal +

Mmax

= 0.86 < 1.0 FbS´eff,0* 1− Ptotal PcE The interaction equation summation is less than 1.0, so the design is sufficient for the combined bending and axial loads specified. While CLT has been included in the NDS, there currently is no standard design method for in-plane shear of CLT walls. The existing CLT structures in the U.S. have been designed using the alternate methods and materials provisions allowed in the IBC. These designs would have been conducted using the CLT manufacturer’s specifications, and values are typically derived from testing. Currently, not all manufacturers have design values or procedures available. CLT shear wall shear capacities are not in the 2015 Special Design Provisions for Wind and Seismic (SDPWS), but procedures for the design of CLT shear walls and determination of CLT shear wall shear capacities are being balloted for inclusion in the upcoming 2021 SDPWS. In the interim, some designers, in cooperation with the CLT manufacturer, may choose to go through the exercise of determining appropriate shear values for CLT walls. In contrast, others may use a different vertical lateral resisting system that is included in ASCE 7. Pć

(

)

Fire Design For any products that are utilized in buildings, fire is a significant consideration, and wood is inherently fire resistant because of its innate ability to slow down the progression of the fire. There are seven methods in the IBC for establishing fire resistance; one such method, per Section 722, is calculating fire resistance per Chapter 16 of the NDS. This method determines the depth of char required to provide up to 2 hours of fire resistance. For more information, see the Code Updates article in the June 2020 online issue of STRUCTURE.

Future of CLT Although designers around the world have been constructing taller wood buildings using mass timber (up to 24 stories in height) every year, the current U.S. building codes limit mass timber to 6 stories. However, the tide is changing under the new building codes. In December 2015, in response to requests from building officials, the International Code Council (ICC) Board established the ICC Ad Hoc Committee on Tall Wood Buildings (TWB). The committee was tasked with exploring the science and investigating the feasibility of tall wood buildings, and to take action on developing code changes to the IBC for tall wood buildings. As a result of the thorough research and hard work of this committee, starting with the 2021 IBC, designers will be allowed to design taller mass timber structures up to 18 stories, depending on, among other things, the occupancy, fire protection, egress, and lateral resisting system. Other areas of the world are using mass timber to reach heights of 24 stories. For more in-depth information on the code changes, see https://awc.org/tallmasstimber.■ Lori Koch is the Manager of Educational Outreach with the American Wood Council and is a board member for SEAVa and on the NCSEA Continuing Education Committee. Michelle Kam-Biron is Vice President of Education for the American Wood Council and is Past President of SEAOSC, and volunteers on ASCE/SEI, NCSEA, and SEAOSC committees.

OCTOBER 2020

BEEHIVE BRIDGE Reconnecting Communities through Creative Infrastructure By Dan Whittemore, P.E.

Figure 1. Beehive Bridge elevation.

The

recently constructed Beehive Bridge in New Britain, Connecticut, and winner of the American Council of Engineering Companies (ACEC) Engineering Excellence National Merit Award, is a testament to the power of structures to connect people and connect to people. The Beehive Bridge reconnects longdivided neighborhoods, encourages pedestrian use, and represents its community through its singular design (Figure 1).

A Community Divided When State Route 72 was installed through the center of New Britain in the late 1970s, rapid access to the adjacent interstate system was the driving force behind the construction. At that time, the fact that the sunken roadway ran straight through the middle of the city was a secondary concern. Though several bridges were installed to reconnect the now separate neighborhoods, connectivity to the downtown areas was irrevocably damaged. People found it more convenient to avoid the bridges and stay on their side of the highway. The result was a city divided by a highway installed to serve it.

Merging Form and Function In visualizing a fix to this long-standing condition, New Britain Mayor Erin Stewart initially planned to incorporate public art into one of the Route 72 overpasses to create a public space that would draw people to cross the highway and shelter them from the highway bustle and noise. To help realize this vision, the City hired a design team led by engineering firm Fuss and O’Neill of Manchester, CT, along with design team members Svigals + Partners, Pirie Associates, and Richter & Cegan, Inc. The actualized design takes inspiration from the City’s seal, which includes bees, a beehive, and the motto in Latin of “industry fills the hive and enjoys the honey” that pays homage to the City’s industrial past. The unique focal point of the project is the pedestrian enclosure, which consists of more than 2,100 amber-honey-colored, ½-inch-thick polycarbonate panels arranged in the shape of a giant honeycomb. Its unique appearance shines as a landmark for the City and changes the landscape throughout the day. During daylight hours, the enclosure paints the bridge in ever-changing shades as the sun moves through the sky (Figure 2). At night, programmable LED lighting creates a 21st-century beacon inviting travelers to the City (Figure 3).

Transformation

Figure 2. Pedestrian view from the sidewalk at day.

26 STRUCTURE magazine

The existing bridge carries Main Street over Route 72. The bridge is 270 feet long, split evenly over two 135-foot spans. It is a typical overpass from its time, consisting of 10 haunched steel plate girders supporting a composite concrete deck. Before the redesign, the bridge carried 5 lanes of traffic and had two 10-foot-wide concrete sidewalks on either side, for a total out-to-out width of 86 feet 6 inches. In its finished state, the bridge has undergone a road diet to favor pedestrian foot traffic over vehicular traffic. While the out-to-out width remained unchanged, each sidewalk was expanded from 10 feet wide to as much as 21 feet wide. The sidewalks were edged with a 5-foot-wide brick paver strip embedded in the concrete adjacent to granite curbs. Traffic lanes were reduced to three lanes plus two new bicycle lanes. As part of the artwork, the larger of the two sidewalks has a giant aluminum beehive sculpture on a raised dais. At each of the four corners of the bridge, 11-foot-tall aluminum bees greet

Figure 3. Bee sculpture watching over the structure at dusk.

Figure 4. Approach to the bridge showing widened sidewalks.

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TOGETHER WE BUILD SOLUTIONS

travelers to their hive from their vantage point on raised plinths tied would each have their required edge supports while still keeping bolt to the concrete abutments (Figure 4). holes within tolerances, both at the polycarbonate panels and the The spine of the pedestrian enclosure is made up of 138 individual connection points along the spine. 6-inch x 2-inch x 1⁄4-inch-thick galvanized structural steel tubes evenly The bridge is skewed 18 degrees out of perpendicular to the roadway spaced at 4 feet on-center. The posts form the rough outline of the below it and is built along a vertical highway curve, which adds to the pedestrian enclosure shape, with each post varying in length between geometric complexity of the enclosure. This was a design challenge 3 feet 4 inches to 7 feet 8 inches tall. The posts are all bent inward because, though the two parapets match the vertical curve at the same towards the sidewalks, starting at the same inflection point, creating given point along the highway baseline due to the skew of the bridge, symmetry at eye level. As the post lengths vary, the end of the frame the two pedestrian enclosures on either parapet start and stop at different terminates at different points overhead, creating a dynamic curving points along the curve. The net result for fabrication was that no two and swooping envelope that undulates gradually overhead as one panels of the bridge were precisely alike. In essence, each panel piece walks from one end of the bridge to the other (Figure 5, page 28). (all 137 panels between the 138 posts) had to be custom manufactured Between the steel-post spine is a lattice network of aluminum horizontally and vertically to properly fit its exact spot on the bridge deck. members arranged into geometric shapes continued on next page (mostly triangles, with a few quadrilaterals) to support each edge of every half-inch polycarbonate panel (Figure 6, page 28). The legs of this lattice consist of a structural angle with a third aluminum fin welded onto it, making a lopsided “T.” The fins were individually measured and custom-welded to control the angle of the fin to the aluminum angle base. This was necessary because each of the three sides of every polycarbonate support frame, made up by three separate aluminum “Ts,” need to be co-planer to flush-mount cleanly behind each piece of polycarbonate. Most of the aluminum frame members support two separate polycarbonate panels, one panel resting along one leg of the main structural angle, and another adjacent piece of polycarbonate along the aluminum fin. Each leg of the support needs to be bent at a slightly different CODAworx 2020 CODAawards angle to work as a system, with matching sides of the members under the same Transportation Category Winner Photo: Dylan Evanston piece of polycarbonate being always coplanar, while also following the geometry Barbara Walker Crossing • Portland • OR established by the posts of the installaSt. Louis Seattle Eugene Irvine tion (Figure 5). Significant parametric Chicago Tacoma Sacramento San Diego computer modeling, prototyping, field Louisville Lacey San Francisco Boise Washington, DC Spokane Los Angeles Salt Lake City coordination, and shop work was needed KPFF is an Equal Opportunity Employer New York Portland Long Beach Des Moines www.kpff.com to accomplish this geometric jigsaw. It was imperative to ensure that the panels

OCTOBER 2020

Creation

Figure 5. Closeup of beehive lattice at dusk.

Figure 6. Schematic of panel connections. Each flat piece of polycarbonate panel (transparent) needs a single co-planar aluminum frame (multicolor) to support it. The frames connect at the edges.

Structurally, the pedestrian enclosure had to be designed for the American Association of State Highway Transportation Officials (AASHTO) Bridge Design Guide’s prescribed loadings, including wind, ice, snow, standard pedestrian loadings, and thermal expansion. Geometry from the architect’s computer model was adjusted to account for the latest measurements of the bridge’s existing shape. The model was fed directly into the structural engineer’s finite element analysis software to confirm the frame’s ability to withstand the required loading. The polycarbonate panels were checked against a wind- and vandalism-type impact loading. Thermal movements were designed to be dissipated over the numerous oversized bolted connections throughout the structure’s lattice. The pedestrian enclosure was built on top of reconstructed concrete parapets that were fastened to the existing deck with drilled and epoxied steel dowels. The parapets were built lower than standard to bring the bottom half of the pedestrian enclosure’s shape to eye level and built wider to support the full width of the base plates of the enclosure’s posts. They also conceal several embedded conduits that feed the LED lighting scattered throughout the structure. Paraffin joints, traditional parapet contraction joints coated with paraffin wax, were deliberately spaced to match up with scoring lines in the sidewalk to help blend them into the overall aesthetic. The City’s desire for real brick pavers embedded into the concrete deck to match the streetscape on the approaches was unusual for a bridge. The design team accomplished installation by deepening the notch for the bricks to include a drainage mat at the bottom. This mat is rated for pedestrian and tire loads, and is pitched to deposit water out of the paver notch and toward one of several scupper downspouts on the structure.

A Community Reunited

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28 STRUCTURE magazine

The seals on one end of the bridge proudly state, “Do the Impossible.” The public, press, and civic leaders have recognized this project as the significant innovation that it is. The ribbon-cutting ceremony was a huge event, bringing together the project team, City officials, project stakeholders, community groups, families, the press, and residents. The Connecticut Main Street Center advocated and contributed early financing for transit-oriented development in the area. Under construction is Columbus Commons, a $58M mixeduse transit-oriented development with 160 new apartment units, which is a short walk from the Beehive Bridge. City leaders have pointed at an uptick in commercial and residential activity in both of the previously divided neighborhoods, and they anticipate future returns on their investment. The Beehive Bridge is truly a community showpiece that fosters both its people and its infrastructure.■ Dan Whittemore is a Senior Structural engineer with Fuss & O'Neill in Manchester, CT. He has more than 20 years of experience in bridge design, rehabilitation, and inspection throughout New England.

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Deadly Miami Pedestrian Bridge Collapse Why and How the Structure Failed

By Ran Cao, Ph.D., A.M.ASCE, Sherif El-Tawil, Ph.D., P.E., F.ASCE, F.SEI, and Anil Kumar Agrawal, Ph.D., P.E., M.ASCE, F.ACI

n March 15, 2018, a pedestrian concrete truss bridge in Miami, FL, collapsed during construction. The span that collapsed had been designed as a concrete truss bridge with prestressed members. Figure 1 shows the bridge site before and after the collapse of the main span. The collapse caused multiple fatalities and raised serious concerns regarding the design and construction of the bridge, including the emerging concept of Accelerated Bridge Construction (ABC). ABC usually involves innovative planning, design, and construction methods to reduce the onsite construction time that occurs when building new bridges or replacing existing bridges. In this project, the main span of the bridge was constructed offsite, then transported and placed onto its piers overnight. The bridge collapsed five days later with the roadway underneath it open to traffic. According to the preliminary report from NTSB, workers were re-tensioning tendons in diagonal member 11 (Figure 1) at the time when the bridge collapsed. The National Transportation Safety Board (NTSB) investigated the collapse and released photographs that showed that the bridge exhibited significant signs of distress before the collapse. Most prominent were cracks in the joint area between diagonal member 11, vertical member 12, and the deck. Forensic material testing showed no significant issues in material strength or quality. An investigation of the

Figure 1. Main span of the bridge: a) before collapse; b) after collapse. Courtesy of NTSB.

bridge deck at the north end showed that reinforcement bars were correctly placed. The NTSBâ&#x20AC;&#x2122;s final report judged the design of the concrete joint at the north end (between members 11, 12, and the deck) to be flawed and attributed the failure to it. The NTSB investigation also noted that peer-review of the bridge design was rushed, underfunded, and, therefore, more likely inaccurate and incapable of detecting critical design errors. Although the NTSB investigation identified the north end joint as the cause for failure, the report was not clear on the specific sequence of processes that led to failure. In this article, a high fidelity computational model was used to develop a forensic understanding of the collapse process. A simulation model of the bridge was created based on the as-built drawings and run on the LS-DYNA platform. The different construction stages were simulated using the model, and parametric studies were carried out to investigate how various influential parameters could have influenced the collapse resistance of the bridge.

Computational Modeling The computational model was constructed using the finite element method, wherein the structure and its components were discretized into a multitude of small elements, each with specific properties associated with its parent material. For example, steel bar elements could yield and fracture, while concrete elements could crush, crack, and exhibit confinement and tension stiffening effects. Tension stiffening is the beneficial effect of reinforcement on the mechanical behavior of surrounding concrete. Prestressing was explicitly accounted for through the introduction of prestressing tendon finite elements. The model was designed to represent member separation and falling of debris to represent the failure process faithfully. Figure 2 shows a schematic of the computational model of the main span of the bridge.

Numerical Simulation Results

Figure 2. Simulation setup of the bridge: a) overall computer model of the bridge; b) close-up of reinforcement at the joint; c) steel rebars detailing; d) prestressing tendons detailing.

30 STRUCTURE magazine

Before the bridge collapsed, the main span went through four construction stages: prestressing, transportation, relocation, and re-tensioning. The behavior of the structure under each of the stages was simulated using the computational model. The main findings from the simulations are as follows.

Figure 3. Cracks in the joint area of Member 11 after relocation: a) actual bridge, courtesy of NTSB; b) simulation.

Prestressing Stage The simulation results showed that, after releasing the prestressing force in the truss members and deck, localized concrete cracking occurred around the north end joint in accord with the documented damage. At the time, the observed cracks were deemed benign, and additional construction stages were allowed to proceed. These cracks were initial indicators of a serious design problem.

Transportation Stage After assembly on the ground, the main span was transported on two self-propelled modular transporters (SPMTs) and placed onto the piers. The simulation model indicated that the north end joint of the bridge suffered additional minor damage in the concrete adjacent to the prestressing tendon anchor plates for member 11, which were embedded in the deck. This zone was highly stressed due to the confluence of prestressing tendon forces and other bridge member forces. The damage was internal and likely did not manifest as external cracks on the surface of the joint. The computed deflection at the northern end was small, less than 0.12 inches.

Relocation and Re-tensioning Extensive cracking appeared around the joint at the north end of the bridge after the main span was placed on the piers. Figure 3 shows the concrete cracking observed in the real bridge and computed from the simulation model. There is a reasonable correlation between the observation and the simulation, providing confidence in the simulation modelâ&#x20AC;&#x2122;s fidelity. The east side of the joint experienced severe cracking damage in the heel of member 11 (Figure 3a) due to excessive sliding along the cold joint between members 11 and 12 and the deck. Other cracks extended into the deck, creating a pattern consistent with punch-out failure distress associated with the excessive force demand imposed by diagonal member 11 onto the deck. The simulation model suggests that the bridge was on the verge of two different types of failure modes: sliding along the cold joint and punch-out failure in the deck region. After observing the cracked condition of the bridge at the north end joint, bridge engineers decided to re-tension diagonal member 11 in an attempt to close the cracks in the joint region. During this operation, the bridge collapsed. The simulation model suggests that collapse occurred due to sliding on the cold joint between members 11, 12, and the deck (Figure 4). In essence, the north end joint was pushed out, causing the bridge to fall off its support. Instead of

Figure 4. Sliding action triggered by re-tensioning member 11.

remedying the cracking symptoms as intended, re-tensioning member 11 aggravated the situation and precipitated the progressive collapse process. Figures 5 and 6, page 32, show the collapse process, the final configuration of the actual bridge, and as-computed from the simulation model. The simulation results captured the collapse mode of the bridge reasonably well.

Parametric Studies The simulations clearly showed that the cold-joint design and decision to re-tension were critical factors in the bridge collapse. Parametric studies were conducted using the simulation model to draw broader lessons from the accident to prevent future failures.

Coefficient of Friction The coefficient of friction used in the simulation model was selected as 1.0 based on the as-designed condition of the joint. Since cold joint slip depended on this parameter, the coefficient of friction was increased to 1.4 to see if additional roughening of the cold joint surface could have prevented failure. A coefficient of friction of 1.4 corresponds to an extremely rough surface and represents an extreme value. The simulation showed that, even with this high number, a slip of the joint still occurred and resulted in bridge failure. These results indicate that relying on friction for the stability of the entire structure is risky. Shear keys or some other explicit shear resisting mechanism should have been employed and would have been more reliable and helpful in meeting the horizontal shear demand in the joint.

Re-tensioning Different re-tensioning forces were applied to the tendons in member 11 to reach a stress level that ranged from 55% to 100% of the yield strength of the tendons to study the effect of re-tensioning. The simulation showed that increasing the prestress levels in member 11 led to more damage in the joint area, specifically more heel damage and widespread damage in the body of the joint itself. The simulation clearly showed that increasing the re-tensioning level caused the rate of joint slip to increase significantly. At 95% of the yield strength, the joint quickly slid off the deck. Failure was prevented when the joint was modeled as monolithic (i.e., there was no cold joint). Even if member 11 had not been re-tensioned, the bridge would likely have failed as creep exacerbated sliding at the cold joint or punch-out failure. However, since the process would have been slow and entailed widening cracks that serve as a significant warning sign OCTOBER 2020

of structural distress, action could have been taken to address the situation. Overall, the simulation results suggest that re-tensioning member 11 should not have been considered as an appropriate solution to reduce the cracking symptoms observed in the cold joint area since it aggravated the sliding of the joint and damaged the integrity of the structure in a catastrophic manner.

Conclusions and Lessons Learned The simulation results showed that cracking Figure 5. Failure mode of the bridge from a) accident video frame, courtesy of Instagram/@o2webdev; and damage was initiated as soon as prestressing b) computer simulation. was applied to the concrete members. After placing the bridge on its supports, severe punch-out cracking patreasons unnecessarily introduced complications related to terns developed around the northern joint. The computed damage prestressing and cold joints in the bridge, both of which likely locations coincided reasonably well with the documented pre-failure played critical roles in the collapse of the bridge. crack locations around the cold-joint. The simulation results also 2) Relying on friction at a critical joint (between members 11, suggested that the damaged cold joint at the north end experienced 12, and the deck) is risky in a non-redundant system like that sliding behavior under the re-tensioning forces applied to diagonal used in the bridge. Friction is unreliable by nature and can member 11, which precipitated the collapse of the bridge. Based lead to sudden failure when the demand exceeds capacity. on the detailed analysis and simulations, the authors believe that Shear keys or some other explicit shear resisting mechanism several lessons can be drawn from this accident: placed in the cold joints would have been more reliable and 1) A concrete truss with prestressed members supported the helpful in meeting the horizontal shear demand in the joint. collapsed bridge deck. The use of a concrete truss for aesthetic 3) Re-tensioning diagonal truss members should not have been considered as an appropriate solution to remedy the cracks in the cold joint area since it promoted more sliding across the cold-joint, making the bridge more vulnerable to collapse. Cracks in the cold joint area should be viewed as a meaningful warning sign of impending collapse, and immediate action should be taken to ensure the stability of the structure after detailed calculations or modeling. 4) The collapse of the bridge does not necessarily imply that accelerated bridge construction is risky. Certainly, it shows the need for adequate analysis simulating construction aspects, such as the presence of cold joints or utility conduits, to ensure the safety of the bridge during and after the construction. Peer review should necessarily be concerned with assessing the impact of such details. 5) The bridge was kept open while it was under construction (member 11 was being re-tensioned), probably to showcase the accelerated construction aspect of the project. This accident reemphasizes the lesson that public safety should never be compromised simply to showcase the application of a new construction technology, even though the technology itself may have been shown to be safe in prior applications. Any construction area is, by nature, hazardous to the public.â&#x2013; The online version of this article contains references. Please visit www.STRUCTUREmag.org. Ran Cao, Postdoctoral Researcher, Department of Civil and Environmental Engineering, The City College of the City University of New York, NY. (rcao000@citymail.cuny.edu) Sherif El-Tawil, Professor, Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI. (eltawil@umich.edu)

Figure 6. Close up of failure of member 11 during the collapse: a) simulation; b) accident photo. Courtesy of NTSB.

32 STRUCTURE magazine

Anil Kumar Agrawal, Professor, Department of Civil and Environmental Engineering, The City College of the City University of New York, NY. (agrawal@ccny.cuny.edu)

Reinvigorating a Historic Giant ROW DTLA Building 2

By Samuel Mengelkoch, S.E.

nvisioned by developer Atlas Capital Group and design architect north-west facing views of Downtown Los Angeles, a rare and Rios Clementi Hale Studios, ROW DTLA reinvigorates the vast stunning view of the heart of the city. and historic Alameda Square warehouse and industrial building An ownership change in the middle of the project’s design phase was complex. The project updated the area into a vibrant district of offices, one of the project’s more formidable challenges. The initial owner retail, and restaurants, and provides a network of public spaces for had directed the Structural Focus team to mimic the retrofit design live music, entertainment, and festivals in Downtown Los Angeles. of a similar building on the campus, a strategy with prominent new Renovated in 2017 under the provisions of the California Historical moment frames on the exterior, significantly altering the rhythm Building Code (CHBC), ROW DTLA Building 2 is among the first and proportions of the façade. The new owner had a much different buildings that could be shown to meet the City of Los Angeles’ vision for the project, part of which was to maintain the “New York earthquake hazard reduction requirements for non-ductile concrete City” feel of narrow streets and formidable building façades – a style buildings per Ordinance No. 183893. The project sets a precedent incompatible with highly visible retrofit elements. A series of shear of how a historic, non-ductile concrete building can be retrofitted wall cores down the center of the long, narrow building was the ideal without losing its historical nature and visual appeal. solution for the new owner’s design vision. The architecture of the Building 2 was designed in 1918 by renowned English architect rehabilitation fits well with the new design – the building behavior was John Parkinson and originally built for the Los Angeles Union simplified, and the performance was significantly improved (Figure 1). Terminal Company. The 400,000 square-foot reinforced concrete With no dedicated lateral force-resisting system, the building prebuilding is a significant component of the ROW DTLA develop- sented challenges and opportunities requiring the structural team to ment, one of the newest and largest additions to the burgeoning Arts think quickly, adapt to existing conditions, and make the best use of District redevelopment in Downtown LA. Building 2 is approxi- the building’s characteristics. Utilizing ASCE 41, Seismic Evaluation mately 100 feet by 600 feet in plan and consists of six stories with and Retrofit of Existing Buildings, as specified by the Los Angeles a basement and several ordinance, an ETABS rooftop penthouses as model with existing well as a rooftop water structural elements tower – originally was built for underfor fire suppression, standing the behavior now maintained as of the historic builda familiar beacon in ing and strategically the Arts District. New Figure 1. Typical floor plan, showing four new reinforced concrete shear wall cores (blue). Columns locating the new work added a rooftop highlighted in red received FRP wrapping; typically the outer thirds of the building experienced greater shear wall additions. deck with sweeping, interstory drift due to torsion. With four full-height, 34 STRUCTURE magazine

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specially reinforced concrete of 60 inches. Several thoushear wall cores, the collecsand epoxy dowels were tion of forces was critical. The required to integrate the team employed the robust and existing footings with the generously reinforced existing new mat system. beams and slabs, designed to Each shear wall core has a support a historic warehouse single mat foundation suplive load of 250 pounds per porting it, with the mat square foot, for double duty resisting vertical loads, shear in collecting forces in compresloads, and overturning of the sion, tension, and shear and core. The structural team delivering the load to the new worked with the geotechshear walls (Figure 2). nical engineer to arrive at a Because shear wall cores were rational, allowable bearing employed inside the building, value below the mat in the the contractor was able to utimost extreme seismic load lize the existing structure for cases, permitting settlement construction staging as they greater than typical design went up the building, largely allows. This reflected the eliminating the need for desired performance level Figure 2. Detail at the thru-bolt connection between the new shear wall and existing girder. extensive scaffolding. Existing Also showing vertical wall bars passing through cores in the slab. of Collapse Prevention per beams were attached to new the CHBC. shear walls with thru-bolts, providing easy access and a visible To maintain the early 20th-century charm of the building, engineers link to the existing structure (Figure 3). Suspecting they would carefully surveyed and analyzed the rooftop water tower and façade exhibit good behavior, the team performed nonlinear finite ele- fire escapes to prove that they could safely remain (Figure 5). With a ment analysis on the existing round, spirally-reinforced concrete few suggested upgrades from the team, the water tower sits proudly columns, and compared their inherent ductility to anticipated on top of the finished building; ultimately, however, the five 100building drifts. The goal was to achieve a maximum 2% inter-story year old fire escapes could not be saved. Untenable strengthening drift without inducing a column shear failure. The drift behavior requirements from the City of Los Angeles would have dramatically of each column was analyzed by inputting linear and nonlinear changed their visual character and proved cost-prohibitive. properties and axial loads into the MATLAB program CUMBIA, The building’s size, age, and countless functionalities presented surused for force-displacement response of reinforced concrete mem- prises until the very last days of the project’s construction. Electrical bers under moment. Only columns that could not sustain the transformers from the early 20th century lined a dark room in the imposed drift at the damage control limit were strengthened with basement; in-floor industrial ovens capped with concrete years ago Fiber Reinforced Polymer (FRP). This strategy allowed the team to remained undisturbed, still full of ash and charred concrete; sheet eliminate the need for FRP wrapping on hundreds of sufficiently metal spiral chutes used to deliver packages from upper stories reinforced concrete columns throughout the building. down to the loading dock level were found; hidden slab overload The four new shear wall cores required substantial mat foundations damage that previous tenants had attempted to repair was found; which had to be integrated with the existing spread footings. Each and, even windows that had once been above grade were now original column was supported by a multi-tiered, “weddingcake” style spread footing. In the original construction, there was evidently no set footing elevation. Rather, crews likely excavated only until competent soil was reached, and that is where each footing went. Since the depth to competent soil varied across the large building footprint, footing elevations varied randomly within an approximately five-foot range. The bottom of the mat sloped to accommodate the varying elevations, always matching the bottom elevation (Figure 4). Since the top of the mat was Figure 3. Reinforcement installation at new Figure 4. Crews install foundation reinforcement at the bottom of the new level, the mat thickness varied shear wall core. Note doweling to the existing mat foundation. Notice “wedding-cake” style original concrete foundations as well, while maintaining a corner column and force-transfer bolts into the at varying elevations. required minimum thickness existing girder at the top of the wall. 36 STRUCTURE magazine

below the street level with plywood holding back the soil behind them. Design changes and hidden conditions required many unanticipated drawing submittals, bulletins, and addendums. The $25 million retrofit and adaptive reuse of ROW DTLA Building 2 presented unusual and complex challenges for the design team. However, positive collaboration, flexibility, and adaptability Figure 6. Aerial view. proved key to the project’s successful completion while setting a precedent for the application of the Los Angeles Ordinance No. 183893. ROW DTLA is a considerable part of the revitalization of the Arts District in Los Angeles (Figure 6). Standing as an eclectic and elegant example of adaptive reuse without displacement, ROW demonstrates how maintaining a physical connection to our past is not at odds with a promising economic and cultural future.■

Figure 5. Rooftop water tower elevation from original 1916 Parkinson drawings. Notice support frame is of reinforced concrete.

Samuel Mengelkoch is an Associate and Project Manager at Structural Focus in Gardena, California. He is currently President of the Southern California Chapter of the Earthquake Engineering Research Institute (EERI) and participates in the Public Policy & Advocacy and Professional Development committees with EERI. (smengelkoch@structuralfocus.com)

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CableStayed

Bridges

DevelOpment, Achievements, and POssibilities By Roumen V. Mladjov, S.E., P.E.

Figure 1. Russky Island Bridge.

able-stayed structures are the youngest, fastest-developing, and most promising bridge systems. Cable-stayed bridges are a subcategory of suspended structures. A cablestayed bridge is similar to a suspension bridge in having towers and a deck-girder supported by cables; however, its diagonal cables transfer the vertical loads from the deck directly to the towers. Thus, the main deckgirder of a cable-stayed bridge works like a continuous beam on cable supports (more flexible than pier supports) with additional compression force throughout the deck. A cable-stayed bridge is also a prestressed system as its cable-stays are additionally tensioned to counterbalance a significant part of the vertical loads on the main deck-girder. The StrĂśmsund Bridge in Sweden, completed in 1956 with a 182-meter (597-foot) main span, is considered the first modern cable-stayed bridge. For the following 65 years, cable-stayed bridges have seen a dramatic increase in both the number of new structures and in long-span achievements. By 1995, there were only 3 cable-stayed bridges with spans over 500 meters (1,640 feet); 25 years later, there are already 67 cable-stayed bridges with spans over 500 meters (including three over 1,000 meters or 3,280 feet). Another 29 with spans over 500 meters, with some over 800 meters (2,624 feet), are currently under construction. The efficient range of cable-stayed bridges is moving towards even longer spans. There is no other bridge structural system exhibiting such rapid development. Most cable-stayed bridges are visually beautiful, and some are among the most impressive of engineering achievements.

Figure 2. Span options: main with two sides spans, asymmetric and multi-span.

38 STRUCTURE magazine

Origins and Precedents The idea for the cable-stayed system was perhaps inspired by the drawbridges of medieval castles and the rope-braced masts of tall ships. The very first documented image of a cable-stayed bridge appears in the Machinae Novae, a book by Fausto Veranzio published in 1615. Predecessors for modern cable-stayed bridges appeared in the 19th century in the form of different hybrid combinations of suspension systems with additional diagonal straight cables, as in the case of the Albert Bridge, UK (1873). The best known of these hybrid structures is the Brooklyn Bridge, New York, 1883, with a 486-meter main span (1,594 feet), for which John Roebling used diagonal cables for stiffening the structure. In the 1960s and 1970s, the system was developed further to replace many of the bridges destroyed in Germany during World War II. In this period, the system was also used for roof structures requiring long, column-free spaces in buildings. Initially, cable-stayed structures were used for bridge spans of 60 to 250 meters (196 to 820 feet) but today they span much longer distances and are the only system that challenges suspension bridges in super-long spans. Their spans grew to 302 meters (990 feet) in 1959 with the Severin Bridge (Germany), to 404 meters (1,325 feet) in 1974 with the Saint Nazaire Bridge (France), and 856 meters (2,808 feet) in 1995 with Michel Virlogeuxâ&#x20AC;&#x2122;s Normandy Bridge (France). Today, the Russky Island Bridge (Russia) has the longest span of this system, 1,104 meters (3,622 feet) achieved in 2012 (Figure 1).

In the United States, we can mention the second Sunshine Skyway Bridge with a span 366-meter (1,200 feet) in 1987 (Florida), the Dames Point Bridge with a 396-meter span (1,300-foot) in Florida, and the Arthur Ravenel Bridge with a 471-meter span (1,545-foot) in 2005 (South Carolina).

System Specifics The main elements of a cable-stayed bridge are towers or pylons, deck girder(s), cable-stays, anchorages, and foundations. Tower and pylon are interchangeable terms; lighter, slender towers are often called pylons. The classic cable-stayed bridges are symmetric with one central span, two side spans, and two towers; such are most cable-stayed bridges with spans above 600 meters. The back-up cables may extend over several side spans. Figure 3. Tower configuration options. Asymmetric cable-stayed bridges have one main span and one side span, with a single tower. Multiple-span cable-stayed bridges For the design of early cable-stayed bridges, engineers used a relatively have two or more (usually equal) main spans. Several examples are small number of cables. After acquiring more experience and with shown in Figure 2. the introduction of structural design software, engineers were able to Some sub-divisions are used for cable-stayed bridges: extradosed, use a larger number of cable stays, reducing the demand on the deck under-spanned (under-deck), cradle, inverted Fink truss, and tenseg- girder and leading to greater efficiency and longer spans. rity. The cables at the towers can be arranged in parallel (harp), fan, The basics of cable-stayed bridge design are as follows: the vertical star, or mixed configuration. Various structural solutions are used for loads on the deck are supported by diagonal cable stays that transfer the towers: single pylons, double-leg portals (vertical, slightly angled, these loads to the towers. At the tower, the horizontal components free-standing, or interconnected as a portal frame, with “A,” “H,” “Y,” of the cables from the main span are in balance with those from the or inverted “Y” shaped arches). side/adjacent spans. The towers support and transfer the vertical load The towers can be continuous above and below the deck supporting to the foundations. Similarly, the cumulative compression horizontal both the deck and the cables, or the upper part can support only the components of the loads from the main span are in balance with the cables while the deck-girder is supported directly by piers. Examples compression load components of the side spans. Therefore, the entire are shown in Figure 3. bridge system is in balance with predominant compression forces in The primary construction materials used in cable-stayed bridges are: the towers and the deck system, and with tension forces in the cable • For decks: reinforced or prestressed concrete, composite stays. The system is self-balanced, provided that all elements are concrete-steel, or orthotropic steel decks; designed correctly to sustain the maximum demand from the highest • For deck-girders: beams of prestressed concrete or steel, box possible combination of loads. girders of prestressed concrete or steel, similar to those in The challenge for the design engineer is to select an appropriate modern suspension bridges; combination of the multiple possible variations of towers, cable• For towers: steel, reinforced or prestressed concrete, composstay arrangements, and deck systems. Like all suspended structures, ite steel-concrete; cable-stayed bridges are sensitive to deformations and it is necessary • For cables: high-strength steel wires, usually 270 grade (270 to check the deformed condition of the system for all load combinaksi, or 1,860 MPa), built from 7-wire, ⅜-inch (9.5 millimetions, including those during the different phases of construction. ters) strands per ASTM A886, other higher-grade steel wires, Today’s structural design software greatly assists engineers in the carbon fiber-reinforced polymers (CFRP), or composites. calculation of cable-stayed bridges. After choosing the main paramPrestressed concrete has been used in the past, but should be eters of the system, it is essential to establish the start-up dimensions avoided as it has been proven unsafe on some failures such as and sections of the deck-girder, cables, and towers. A simple design the Morandi Bridge; approach will help in setting up these dimensions. • For piers and foundations: reinforced concrete with or For a start, the designer can use a substitution simply-supported without piles depending on the soil. beam for determining the approximate bending moments for the For long-span bridges, foundations on soft soils, or for bridges in main span deck-girder. The upward cable-stays pretension can offset high seismic areas, it is preferable to use predominantly steel structures most of the moments from permanent loads on the deck. This is to reduce the self-weight and the related earthquake forces. achieved with additional tensioning of the cables after erecting the main elements to counteract permanent loads, resulting in minimal vertical bending in the deck-girder. The cables should be additionally Conceptual Design tensioned to counteract 50% of the combined temporary downward The most important part of bridge design is the overall concept for the loads (live loads, wind, snow, ice, and earthquake). This way, the workstructure and its elements: the selection of the appropriate structural ing bending moments of the deck-girder will vary during operation system for the bridge considering its specific function, site location, approximately between 50% of the positive moments (from the worst and required spans. A well-selected concept determines the efficiency temporary load combination) to 50% of the negative moments from and economy of the bridge, saves materials, cost, and construction temporary loads. This “first step” determines the design moments for time. Good design concepts minimize problems and future difficulties the main span deck-girder. The compression in the deck-girder due to both in the design office and on the construction site. the horizontal components of cable stays forces is the cumulative sum OCTOBER 2020

Figure 4. Compression forces in deck-girder: at single cable (a); and total compression force for “fan” (b) and “harp” (c) cable configurations.

of these components, approximately 55 to 65% of the total vertical loads on the main span depending on the span, the number of cables, and the height of cable connections at the tower. The cumulative compression force (ΣPc ) in the deck-girder is equal to the sum of all compression forces Pci at cable connections (Figure 4) at the deck: the tension cable force Pcable = Pv /sin α, Pci = Pvi × Li where Ht Pci is the compression force in the deck-girder from the horizontal component of the cable force, Pvi is the vertical DL + LL force applied at the cable connection at the deck-girder plus the vertical component of the additionally-applied tension force, Li is the horizontal distance from this connection to the tower, and Ht is the height of this cable connection at the tower above the deck. A simplified initial calculation for the cumulative compression force is provided by: ΣP × L ΣPc = v max for “fan” configurations 8Ht ΣP × L ΣPc = v gr for “harp” configurations 2Ht where: ΣPc is the cumulative compression force in the deck-girder, maximum at towers, ΣPv is the sum of all downward vertical forces on the main span deck, Lmax is the main span length, Ht is the height of the cable connections at the tower above deck, as shown in Figure 4 for fan or harp cable configuration, and Lgr is the total length of the cable group for harp configuration. The sum of the horizontal forces of all cables at the tower (from the main span) is equal to the cumulative compression force in the main span deck-girder, balanced by an equal force on the opposite side. These calculations will allow the designer to establish the initial design dimensions for the cables, deck-girder, and tower to be used in the computer model for further adjustments and refinements of the system. The deck-girder has to be designed for the compression and bending from the cable-stay system and the typical bridge deck design for vertical dead and live loads. The initial approach described above will help to achieve the desired final goal faster.

bridge systems, with the only competitor being suspension systems, while allowing for more straightforward construction methods. An additional advantage of cable-stayed bridges is their larger efficient span range from 100-meter spans (328 feet) to over 1,000-meter spans (3,280 feet). The multitude of possibilities of the system provide engineers and architects with many design options. The “mid-long range” structures allow more creativity, originality, and possibilities for innovative work. A cable-stayed bridge does not need to be extravagant. The most straightforward bridge with a “sincere” structure is often the best and is usually elegant and attractive. Cable-stayed bridges have a combination of elegance, slenderness, and a feeling of robustness. The national infrastructure’s demand for more bridges requires the priority of efficiency and economy. The art of engineering requires creativity and fantasy, but engineers should avoid repetitive and illogical shapes. Creativity is essential, but “excessive originality” should only be found in justified exceptions (e.g., Christian Menn and Michel Virlogeux).

Pros and Cons The main system advantages are: • Fast and relatively easy construction, requiring less time to build • Less expensive • Multiple design options • Large efficient span range • Strong and resilient structures • Attractive appearance The main system disadvantages are: • Still inferior to suspension bridges for super-long spans • Requires checking deformations at all conditions • Requires experience in both design and construction

Efficiency and Economy Cable-stayed bridges are efficient in cost, materials, and construction time. They have better efficiency than other 40 STRUCTURE magazine

Figure 5. Hybrid cable-stayed and suspension bridge system for super long spans.

Further Development

Conclusions

Like all other bridge systems, cable-stayed bridges are continuously improved based on the development of high-strength materials and new construction technologies. More valuable for engineers are the modifications of established structural systems and newer sub-systems. In addition to the increased number of cable-stayed bridges with longer spans (above 600 meters or approximately 2,000 feet), there is increasing use of the system for pedestrian bridges. The lower loads and shorter spans allow engineers to explore new approaches, transforming the building of these bridges into a testing lab for innovation. As such, we may consider the extradosed, under-spanned, and inverted Fink truss sub-bridge systems, all oriented to improved efficiency. One area of further development is the pursuit of combinations/ hybrids of cable-stayed and suspension bridge systems for achieving super-long spans. The idea is to reduce the suspension span length by moving the suspension support points inward along the span. This not only reduces the suspension span length but the required tower height as well while allowing a longer clear span. This is obtained with “cable-stay cantilevered alternatives” at the bridge towers, adding “ondeck” cable-stayed pylons (Figure 5). With 500-meter (1,640-foot) cantilevers and cable-stayed “on-deck” pylons used on each side of a total clear span of 3,000 meters (9,842 feet), the suspension part is reduced to 2,000 meters (6,561 feet). Such reduction would allow using main suspension cables of the size and type of those already used in bridges, like the Akashi-Kaikyo at 1991 meters (6,532 feet), for a much longer main span.

Based on current technical progress and fast development, cablestayed bridges may reach spans 2,400 to 2,600 meters (7,600 to 8,500 feet) in a short while; such design will require towers about 500 to 570 meters tall (1640 feet to 1,870 feet), something achievable, considering already completed skyscraper structures. This will extend the efficiency range for cable-stayed bridges to very long spans above 2,000 meters (6,561 feet). A hybrid cable-stayed-andsuspension system would make possible even longer spans of up to 3,000 to 3,400 meters (9,842 to over 11,000 feet), incorporating a “pure” suspension bridge of “only” 2,200 to 2,400 meters (7,218 to 7,874 feet). Based on the efficiency and advantages of cable-stayed structures, American engineers and transportation agencies should consider more cable-stayed bridges when planning new projects. Greater use of cable-stayed bridges may upgrade the infrastructure with these efficient, faster built, and elegant structures. Making cable-stayed bridges more popular may also help our bridge engineering profession regain its position of leadership in the design and construction of long-span bridges.■ Roumen V. Mladjov’s field of 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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OCTOBER 2020

building BLOCKS Specification Check – Molded Polystyrene Truths and Insights on Under-Slab Insulations with Structural Implications By Sean O’Keefe

ightweight and versatile, molded polystyrene foam is a common commercial building material that remains misunderstood. Frequently misidentified as Styrofoam, molded polystyrene products range from lightweight structural materials and insulations for commercial construction to packaging for electronics, medicines, and fragile payloads to Original Equipment Manufacturer (OEM) applications like garage doors, jet skis, RVs, and much more. “Molded polystyrene foam is a very versatile material that efficiently solves a lot of common construction challenges,” says Dale Mullikin, a National Account Director for Atlas Molded Products. Structurally, molded polystyrene is well suited to difficult circumstances where a lightweight structural fill is needed. At Snowbird Ski & Summer Resort in Utah, molded polystyrene was used to help stabilize a 45-year-old mountainside cable tram when a new 23,000-square-foot guest center was built on top of Hidden Peak at 14,000 feet. Designers did not want any additional loading in the form of soil settlement to be added to the tram’s foundation wall as a result of the new building. As insulation, molded polystyrene rigid foam is well-suited to many different construction applications where a high-performance building envelope is desired. At Badger State Fruit Processing, a family-owned business serving Wisconsin’s Cranberry industry, molded polystyrene was chosen. Badger State’s insulation needs were not just in the walls and roof, but included foundation perimeter and under-slab applications as well, making it a six-sided challenge. The underslab insulation had a compressive strength able to support the weight of their massive freezers without risk of structural collapse. Though structural loading is never an issue, occasionally proving molded polystyrene’s structural capacity can be. When Mullikin recently approached a company building a large food processing facility about using molded polystyrene rigid foam insulation beneath the cold storage slabs, he got a little more than he expected back from the owner’s engineer. The engineer's reply by email read, in part: “I was forwarded some of your technical brochures. I wanted to verify if you had technical information regarding the insulation foundation modulus (equivalent modulus of subgrade reaction) for your product. We are expecting very high point loads on the slab for this project, so I would like to have that information available for verification and future reference.” “This was a first for me,” says Mullikin. “The term modulus of subgrade reaction was not something I was familiar with.” Fortunately, Mullikin had a reliable resource in Todd Bergstrom, Ph.D., of AFM Corporation. Bergstrom has a Doctorate in material science and engineering from Northwestern University and spent the last 22 years researching, developing, and testing molded polystyrene materials against variables of every sort. From proving R-values to conducting water absorption testing, and quantifying structural performance, Bergstrom has spent his career on the front lines of molded polystyrene material science. “Modulus of subgrade reaction refers to the relative stiffness of the layers of support beneath a concrete slab,” says Bergstrom. 42 STRUCTURE magazine

Quantified, the modulus of subgrade reaction assists engineers in selecting the appropriate molded polystyrene foam to support the pressure of the loaded slab. “In this case, the engineering proved that Foam-Control PLUS+ molded polystyrene insulation would support the same loads as a subgrade composed using XPS (Extruded Polystrene).” As Bergstrom points out, some of the reason for the confusion surrounding rigid cellular polystyrene materials is that rigid cellular polystyrene can be used as both an insulation and a structural fill called geofoam. Though the materials are identical, within ASTM International standards there are two separate designations: ASTM C578 for insulation and ASTM D6817 for geofoam. Rigid cellular polystyrene was first used in commercial construction more than 50 years ago as insulation. It was first tested by the ASTM and published in their standards under ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation. Rigid cellular polystyrene products include both extruded polystyrene and molded polystyrene materials whose practical purposes in commercial construction have grown well beyond the original thermal insulation objectives to now prominently include structural support. “All rigid cellular polystyrene fell under C578 until 2002 when ASTM D6817 was introduced specifically to account for structural applications using geofoam,” says Bergstrom. “Many architects still think of these products exclusively as insulations and, problematically, the original structural capacities listed in the insulation standard for XPS materials are inadequate without adjustment factors. Structural loading should always be specified using the structural capacities in ASTM D6817.” ASTM D6817, Standard Specification for Rigid Cellular Polystyrene Geofoam, determines the structural capacity of rigid cellular polystyrene by compressing the material until it is deformed by only one percent. Conversely, the insulation specification, ASTM C578, compresses the same material until it is deformed by ten percent. “C578 is meant to compare two types of materials against one another,” summarizes Bergstrom. “D6817, however, defines the loading capacity the material can support indefinitely when used structurally.” “Twenty-plus years of working with clients on insulations and structural solutions, and they never run out of questions,” says Mullikin. “For the project at Snowbird Ski & Summer Resort in Utah, by filling the void between the new foundation and the tram wall with Foam-Control Geofoam, designers developed a structural barrier that will never erode. And, in the case of Badger State Fruit Processing, Foam-Control PLUS+ and PLUS+ 400 were selected based on a combination of performance, environmental impact, cost, and strength.”■ Sean O'Keefe writes design and construction industry stories based on 20 years of experience. (sean@sokpr.com)

OCTOBER 2020

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INSIGHTS Bridging Current Gaps in Bridge Maintenance By Kai Goebel

nfrastructure operators are responsible for ensuring the safety and operability of large structures such as bridges, towers, tunnels, and railways. The maintenance process typically requires costly schedule-based routines that rely on periodic manual inspections, which may not always be necessary. A more cost-effective approach involves predictive maintenance policies. Predictive maintenance is a way to remotely monitor the condition and performance of highvalue structures during operations. In this way, operators can understand the structuresâ&#x20AC;&#x2122; current state of health and anticipate the likelihood of future problems. Predictive maintenance systems logically prioritize any needed repairs to prevent failures before they occur, thus saving considerable time, money, and resources. Recent advances in communications networks and advanced sensors have made predictive maintenance feasible through the Industrial Internet of Things (IIoT). New networked sensors and machine learning systems can be designed and trained to recognize structural faults and make accurate predictions about how long until components will fail. A new IIoT System Analytics technology platform called MOXI enables engineers, operators, and maintenance professionals to monitor and proactively manage unexpected maintenance problems remotely. The IIoT suite combines embedded sensing, complex system models, and artificial intelligence technologies to predict adverse system conditions with high accuracy, negligible false alarm rates, and near-zero missed detections.

Predicting Potential Failures The Palo Alto Research Center (PARC) is engaged on a project in Australia called Fibridge, which is sponsored by the Victorian Governmentâ&#x20AC;&#x2122;s Public Sector Innovation Fund and a partnership of Victorian Government agencies, led by VicTrack. The Fibridge project is based on the MOXI smart monitoring system, which has the potential to enable predictive maintenance for bridges and other structures. The system uses fiber-optic (FO) sensors attached to a span to accurately measure and estimate parameters online indicative of the bridge state, 44 STRUCTURE magazine

including structural strain, thermal response, bending moments, shear/impact loads, and corrosion. The system relies on lowcost, high-resolution, compact wavelength-shift detection technology, and intelligent algorithms. Teams from Victorian agencies, VicTrack and VicRoads, have provided their structural engineering expertise to enable effective real-time PARC developed a novel technology to read out signals from monitoring, performance wavelength-encoded optical sensors, like FBG (Fiber Bragg Grating) management, better reliability, sensors, with unprecedented resolution using a compact, low-cost unit that is highly customizable. and improved safety. While Fibridge is initially targeting roadway and rail bridges, over time, it will of a VicRoads bridge in Banksia Street, be extendable to other structures with similar Heidelberg, Victoria, Australia. The signals maintenance and monitoring pain points. were bundled in groups of eight and routed to An initial proof-of-concept demonstration a central computing system for data acquisiusing FO sensors to monitor a VicRoads tion and storage. For power, the system tapped highway bridge in Melbourne, done in into a pre-existing 240V line for the nearby collaboration with AMG Systems and the vehicle messaging system sign. A router was University of Melbourne, has shown promise included to allow remote user access to the thus far. Now the technology is being scaled system. The costs and value proposition up towards an extended pilot trial on multiple of Fibridge over conventionally scheduled rail, road, and transit bridges in Victoria. inspections were estimated for a preliminary Anticipated benefits of this solution include business case assessment. addressing risk and supporting asset manageThe critical pieces of technology affecting ment, as well as the potential for cost-savings sensor costs are the FO sensors, bonding by automating remote bridge inspection with- agents, optical readouts, and supporting edge out the need for access to the structure. devices for online processing and remote FO sensors can simultaneously measure communications. Together, these sensing multiple parameters with high sensitivity in costs are estimated to be $2,000 for 400 multiplexed configurations over very long sense points per bridge. This approach is at FO cables. These parameters include strain, least 5X more economical than commercially temperature, pressure, current, voltage, and available alternatives such as wireless or wired chemical composition. And, the sensors have electric strain gauges. held up well in harsh environments. The most significant expense for Fibridge, Alerts for events of interest for bridge or any other bridge monitoring sensor health can be systematized, and trends in system, involves the one-time installation asset deterioration can enable better planning and setup cost. This step involves some of maintenance and renewals. Finally, the sensor array/structural installation design life of a bridge that is underutilized can be tuning and the cost of equipment such as safely extended due to unused capacity, and boom lifts, trained technicians, and traffic maintenance scheduling can be optimized. management. The setup cost is projected to be roughly over $30,000 per bridge, based on local labor costs in Victoria, Australia. Promising Installation costs are quite variable and Return-on-Investment heavily depend on the asset size, access Over five days in October 2018, 112 FO sen- restrictions, and narrow timeframes due to sors were installed throughout the structure live operating environments, all of which

were the case on the FiBridge trial bridges. However, there is scope to optimize the cost with the design development of the sensors for quick and easy installation, and better training of installation teams. Installation costs would also drop if the sensor system were fitted to new bridges during construction. This would also provide initial data from the early days of structural settling and initial use that could be used for baselining. The preliminary assessment assumes a conservative two-times extension of bridge inspection intervals. This extension will reduce costs and downtime from scheduledriven inspections, avoid liability costs associated with aging bridge structures, and defer investments from being able to safely extend the life of bridges. All taken, Fibridge is estimated to provide a greater than 50 times return-on-investment over the nominal lifetime of a bridge. These savings do not factor in other potential benefits such as savings on follow-up engineering investigation costs, feedback for design and operations teams for improved bridge design, immediate-response ability, wider area congestion management due to

events such as bridges struck by vehicles, and longer-term planning value from having reliable online monitoring into asset usage and performance. Safety is also an area that directly benefits from realtime monitoring of bridges. Recent examples of bridge collapses are reminders that signs of rapid structural degradation due to overload, inclement weather, or hidden structural defects undetectable during visual Installation of the PARC MOXI smart monitoring system on one of the inspections can potentially VicRoads’ bridges in Victoria, Australia. Based on fiber-optic (FO) sensors, MOXI accurately estimates parameters indicative of the bridge provide valuable informahealth state. tion in bridge management. This bridge pilot project in Australia is just one example of the practical than following a rigid timetable for benefits of predictive maintenance to enable regularly scheduled monitoring and self-aware, self-adaptive systems for large repair efforts.■ structures and critical assets. Infrastructure managers can now apply predictive Kai Goebel is a Principal Scientist in the System condition-based technology solutions to proSciences Lab at PARC, a Xerox Company. actively focus their time and resources on the (kgoebel@parc.com) most pressing maintenance problems, rather

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OCTOBER 2020

business PRACTICES Networking Tips for Introverts By Janki DePalma, LEED AP, CPSM

an extrovert, I have a secret to share – I am jealous of introverts! That is because I am surrounded by them daily, and I know their superpowers: an ability to listen well and to engage in thoughtful conversations. But like every superhero, introverts, too, have their kryptonite – networking events. Networking is an essential part of career development. Essentially, people like to work with people they know, like, and trust. So, as an extrovert who is thrilled about the benefits of networking, I would like to share some insight into how you, as an introvert, can wield your superpowers to conquer the intimidating yet important realm of networking. Here’s the thing. Most introverts are uncomfortable because they think they need to network like an extrovert. Just. Don’t. When we think of the “ideal networker,” we often see this gregarious person passing business cards and holding court with throngs of people. When you try to be this person, it fails. You are not this person, and that is ok. In fact, I would argue that it is a good thing! My full-time job is building relationships and teaching engineers how to create and develop their professional network. If you have ever wished you had a secret memo on how to maneuver a networking event, here it is! These tips, combined with your natural powers of listening and developing deeper relationships, can make networking so much easier. How do I approach people? Walking up to a group of strangers with a charming opening line is a lot of pressure. I usually approach a group of three or more people. I stay away from couples or any solo person hovering over his phone. Odds are 3+ people are not having a private conversation. My go-to “line” is direct. “Hey, you guys seem friendly, mind if I join you?” Usually, in a group of 3 or more, there will be one person you can make eye contact with. Focus your opening line to this person. Also, when you tell someone they seem friendly, it forces them to live up to your expectation. Now what do I say? We all hate small talk! Let’s all agree to stop talking about the weather or traffic. I start with some context questions. Something like, “So, how do you guys know the host?” or “which conference sessions did you like?” This helps you establish some 46 STRUCTURE magazine

common ground. When you are first meeting people, it is great to find some commonalities – the threads that bind you. This takes you from a complete stranger to less of a stranger. The “so am I” commonalities help connect you quicker. Should I talk about my work? Making a connection involves charisma, a connection with people through both your warmth and your intelligence. Veer too much into a technical mode, you never really break the surface to a genuine connection. An easy way to connect is to ask questions about someone’s personal interest. Remember, people like to talk about themselves, and you can use your introverted “great listening skills.” This hands-down is where the introvert shines! Ask a few questions and let the other person go. What kind of questions do I ask? I have two go-to’s. One is, “Do you have any exciting travel planned?” The other question I often ask architects is, “Are you working on any personal pet projects?” Given the current situation, I have asked, “Were there any surprise benefits you discovered during quarantine?” Almost everyone has something that makes them light up. Asking these questions can help you move from the small talk into something more meaningful. How do I get out of here? Even when the conversation is amazing, sometimes you want to exit gracefully but do not know how. Here is my exit strategy: “Well, Name, I am so happy that I was able to meet you! Do you mind if I have your business card? I would love to talk with you again.” Simple and straightforward, this formula allows you a graceful exit. Now what? One of the biggest mistakes I see is when people spend time at an event and then fail to follow up. Do not be that person. I am a big procrastinator who hates data entry, so I found that I need to act quickly, or else I will have a stack of untouched business cards. First step – LinkedIn. Connect on the most used business social media platform. Next, if you had an interesting conversation, send a quick email letting her know how much you enjoyed talking with her. If you want to take it to another level, send a small note card. No one gets mail

anymore, so a small note saying how much you enjoyed meeting that person will be unexpected.

Alternative Networking In our post-COVID-19 world, the ways we network may change. No one knows if we will still have large conferences or lunch events. However, the need and ability to network do not change. Some conferences are offering alternative online networking. An easy and active platform is LinkedIn. What do I do on LinkedIn? Without going into too much detail, the biggest thing I would say for LinkedIn is to be a conscientious contributor. Even if a person is barely on LinkedIn, every time she posts, she is opening herself to her network. The single best thing you can do is validate those thoughts by making a legitimate comment, not just the autogenerated ones. Relationships grow stronger based on proximity and frequency. LinkedIn allows you to have both of those, even if you are miles away.

Conclusion Many people place a significant amount of pressure on themselves to be charming, outgoing, and witty at networking events. In reality, as an introvert, your ability to listen and delve into more in-depth conversations gives you the ability to connect in a meaningful way. When in doubt, remember it is better to be interested than interesting!■ Janki DePalma is an Associate and Business Development Manager at DCI Engineers. Janki serves as President-Elect of the Society for Marketing Professional Services Austin chapter, and is an active member of AIA, ULI Next, and CREW. (jdepalma@dci-engineers.com) OCTOBER 2020

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Civil Engineering

MOP 138

Structural Fire Engineering

Prepared by the Fire Protection Committee of the Structural Engineering Institute of ASCE

Structural Fire Engineering

ASCE Manuals and Reports on Engineering Practice No. 138

Structural Fire Engineering

Fire Protection Committee Edited by Kevin J. LaMalva, P.E.

Seismic Loads: Guide to the Seismic Load Provisions of ASCE 7-16

Rain Loads: Guide to the Rain Load Provisions of ASCE 7-16

Wind Loads: Guide to the Wind Provisions of ASCE 7-16

2020 | 108 pp│ SC ISBN: 9780784415535 E-Book ISBN: 9780784482766 List: $60 │ ASCE Member: $45

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Risk Based Structural Evaluation Methods: Best Practices and Development of Standards

Seismic Evaluation and Design of Petrochemical and Other Industrial Facilities, Third Edition

2020 | 187 pp SC ISBN: 9780784415474 E-Book ISBN: 9780784482643 List Price: $100 ASCE Member: $75

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Visit www.asce.org/bookstore American Society of Civil Engineers • 1801 Alexander Bell Drive • Reston, VA 20191 • Ph: 1-800-548-2723 or 1-703-295-6300 • www.asce.org

structural FORUM Non-Traditional Career Paths for Structural Engineers By Brian Quinn, P.E.

“I

really like being a structural engineer, but I do not like many of the tasks associated with the design and construction of projects.” This is a comment I have heard many times from structural engineers who express feeling like a “square peg in a round hole” as a design engineer. We do not want to lose good people from our profession who have an enthusiasm for structural engineering, but who do not enjoy the more conventional career paths as a structural engineer. Many people who experience this frustration end up switching to another industry unrelated to structural engineering, and we lose talented people. The good news is that there are many “non-traditional” career paths available for someone facing this challenge that allow them to utilize their structural engineering background and contribute to the profession in unique ways. Hopefully, sharing my own story provides some additional background. After finishing my MSCE from Purdue in 1991, I was fortunate to find a job with an excellent small consulting structural firm in West Michigan. The three owners of the firm were great mentors. I was able to work on a wide variety of projects, learn an incredible amount about structural engineering, get involved in client meetings, and was given a lot of responsibility. This company was an excellent place to learn as a structural engineer. Yet, something was missing for me in terms of fulfillment. After struggling with what to do, I was able to find a unique position with the structural engineering software company RAM in 1995 (now a part of Bentley®). My role was primarily sales but included technical support and training. I loved using technology related to structural engineering, so this was an excellent position for me, with a great company. It also allowed me to meet a wide range of structural engineers across the country. Also, I was able to get more involved in the structural engineering profession, including being President for the Structural Engineers Association of MI (SEAMi). After twelve great years with RAM, I felt pulled to help structural engineers in another unique way. I started SE Solutions in late 2006 to help match excellent structural

48 STRUCTURE magazine

“

The good news is that there are many “non-traditional” career paths available...

engineers with great companies and unique opportunities so they could find a fulfilling career path and stay in the structural engineering industry. Fast forward to today, and we have seen many ways that structural engineers can make a positive contribution to our profession in non-traditional roles. The “technical” level of these positions can vary significantly, as well as the function of the role. An example of a few possibilities would include: • Helping structural engineers utilize seismic dampers or special seismic connections • Helping trade associations expand their message and outreach in multiple different roles • Helping software companies in sales, training, technical support, or development • Helping companies who make a unique engineered product (roller coasters, ropes courses, stadium bleachers, rack systems, conveyors, to name a few) • Helping investigate the cause/origin of problems (forensic engineering) • Helping building owners or general contractors in the construction, oversight, and maintenance of facilities

So, what are some of the things you can do if you are struggling to find fulfillment as a design engineer? I would recommend seeking out other structural engineers who are in “non-traditional” roles and ask them how they came to do what they are doing. Some approaches include: • Talking to people who come into your office to provide lunch-and-learns • Talking to exhibitors at structural engineering conferences • Using resources like LinkedIn to search for structural engineers doing unique things • Asking family and friends what they see as your strongest traits and skills Structural engineering is a wonderful profession, offering a variety of career paths that can provide a fulfilling career. While the majority of people will enjoy more “traditional” roles, there are multiple other possibilities for those looking for a unique way to still be a part of the structural engineering industry.■ Brian Quinn is the Founder and President of SE Solutions, LLC, based in Holland, MI. (brian. quinn@findyourengineer.com)

OCTOBER 2020

NCSEA NCSEA News

National Council of Structural Engineers Associations

NCSEA Foundation Focused on Advancing Profession

The NCSEA Foundation was established early this year to further support the non-profit activities of NCSEA and its Member Organizations to advance the structural engineering profession through technical development, education, and outreach. The Purpose of the Foundation is to fund qualifying initiatives and activities such as: • Outreach and Education • Research and Technical Development • Publication of Education and Technical Materials • Scholarships The qualifying initiatives that the Foundation funds also are intended to promote engagement within NCSEA’s Member Organizations. The Foundation also supports existing NCSEA initiatives like Young Member Summit Attendance and the SEA Grant Program. The Foundation itself is supported by specialty ticketed events throughout the year as well as individual and corporate donations. Contributions to the NCSEA Foundation support NCSEA's efforts to assist practicing structural engineers to be highly qualified professionals and successful leaders. The NCSEA Foundation is a 501(c)(3) nonprofit organization. Your contribution is tax-deductible to the extent allowed by law. Consider making a donation to help advance the profession.

NCSEA's SEA Grant Program Supports Growth and Advancement

The NCSEA Grant Program was developed in 2015 to award SEAs funding for projects that grow and promote their SEA as well as the structural engineering field in accordance with the NCSEA Mission and Vision Statements. The 2019 Grant recipients are listed below. Learn more about the 2020 Grant Program and submit your project for consideration at www.ncsea.com. • Structural Engineers Association of Central California to enhance their new Structural Engineering, Engagement, and Equity (SE3) Committee • Structural Engineers Association of San Diego to support the EERI San Diego-Tijuana Regional Earthquake Scenario Study and a Special Wind Region Study • Structural Engineers Association of Illinois to host a Young Professionals Workshop • Structural Engineers Association of Kansas/Missouri to launch an SE3 Committee Panel Discussion and Networking Event, and to assist with STEM classes for local elementary school students

• Structural Engineers Association of Massachusetts to launch an SE3 Committee Interactive Seminar Series • Structural Engineers Association of New York for a screening of the documentary Leaning Out with panel • Structural Engineers Association of Ohio for a Young Members’ Track at SEAoO’s Annual Conference • Oklahoma Structural Engineers Association to assist OSEA’s efforts in the Engineering Fair E-week 2020 Bridge Competition • Structural Engineers Association of Texas to support a local SE3 Speed Mentoring event • Structural Engineers Association of Washington to assist with a Joint Special Regions Wind Study

Diversity, Equity, and Inclusion Webinar Series In accordance with the Call to Action released earlier this year, NCSEA is working to identify and eradicate behaviors that perpetuate racism and inequality within our profession. In conjunction with its Foundation and SE3 Committee, NCSEA partnered with a strategic diversity and inclusion practitioner to develop a series of webinars that introduced attendees to diversity, equity, and inclusion, and discuss ways to begin developing multicultural organizations via inclusive policies, programs, and practices. The first session, Cultural Humility & the “You” in Unity aired on September 29, 2020 and introduced participants to cultural humility and its role in creating intentionally inclusive environments. Through interactive activities, participants were able to identify their own dimensions of diversity and consider their role in the “platinum rule.” The second session [October 13, 2020], Bias Awareness and Socialization, introduced participants to biases, how they develop through socialization, and the role of internalized oppression in authoring identities. Through the exploration of the Cycle of Liberation, participants will learn the steps needed to address systemic inequity. Session 3, How Do We Progress Towards Racial Equity in the Structural Engineering Community?, is part of the NCSEA Summit and will take place on Thursday, November 5, 2020. This session, led by the NCSEA SE3 Committee, will highlight common experiences that are reflected in the SE3 survey data as related to race and racial inequities. The Committee will connect everyday experiences in the structural engineering workplace through conversation with experts on racial diversity, equity, and inclusion (DEI) within the AEC industry. Active audience participation will be encouraged and supported through the use of anonymous polls throughout the session. Attendees will leave with ideas on clear, achievable actions to take as individuals and as firm leaders to help advance racial equity in our industry. The first two sessions are free to attend and are available as recordings on www.ncsea.com. If you are interested in attending the third session, we recommend the first two sessions be viewed first to maximize the series' value. Visit the DEI Resources tab on www.ncsea.com for more information. 50 STRUCTURE magazine

News from the National Council of Structural Engineers Associations 2020 Summit Trade Show Open Now...For Everyone As part of this year's Virtual Summit, NCSEA has not only opened the Trade Show a month before the Summit, but it is available for everyone, not just those registered for the Summit. The Virtual Trade Show offers opportunities to visit, learn, and engage with the companies and resources needed by you, practicing structural engineers. Visitors will find leading companies with innovative software, products, services, and resources essential to structural engineering. The virtual trade show features raffles and games, along with opportunities to engage personally with exhibitor representatives! The Virtual Trade Show is open NOW through November 3 for everyone. Visit www.ncsea.com to connect with exhibitors, and to be entered in weekly raffles! But what else does registration to the Summit include? • 26 Hours of Education Available (Most Hours Offered Ever!) • 17 Hours Live-Streamed and On-Demand Education • 9 Hours of Bonus Content • Captivating Keynote Addresses by Expert Speakers • What’s Happening with the Future of the AEC Industry? Jim Malley (Moderator); Glenn Bell, P.E., S.E., Simpson Gumpertz & Heger (Retired); Vibhuti (Vickie) Harris, HKS, Inc.; Greg Gidez, Hensel Phelps • Leading the Human Way: How to Stop Acting Your Age and Lead a Multi-Generational Workforce Matt Havens • Unique Networking Opportunities • Virtual Lounges will be open for topic driven peer-to-peer networking, trivia games, and more! The 2020 Summit will provide the same great education as in prior years – created by structural engineers for practicing structural engineers – delivered to you straight to your desk! Learn more and register by visiting www.ncsea.com.

The Site Tour Reimagined | Minnesota Young Members Host Virtual Site Tour The COVID-19 pandemic has forced the Minnesota Structural Engineers Association's Young Member Group (MNSEA YMG) to get creative when planning events. In June, over 25 MNSEA members participated in a virtual site tour of the University of Minnesota Pillsbury Hall rehabilitation project. Pillsbury Hall was built in 1889, making it the second oldest building on the University of Minnesota Twin Cities campus. Historically, this building has been used for science research and lecture teaching. The building is currently in the process of bring converted from a science teaching space into the new home of the English Department in a comprehensive rehabilitation project. Upon completion, the 62,000 square foot building will be completely revitalized and ready for its new tenants, providing a much more functional space. Members tuned into a Zoom meeting as former MNSEA YMG Chair and BKBM engineer, Ricky Kirchner, led a site tour with JE Dunn job superintendent, Matt Soens, pointing out the more challenging aspects of the structural design. Structural challenges include reinforcement of the existing timber structure, addition of stair and elevator shafts, removal of existing columns, and underpinning of an entire building wing to allow for a basement addition.

NCSEA Webinars

October 8, 2020

Anchor Bolt Design in Masonry Richard Bennett, Ph.D., P.E. This webinar will cover general anchor bolt design in masonry, provide practical design tips, show examples of anchor bolt design, methods for determining the projected tension and shear area, and the two major changes to the anchor bolt design provisions in the 2016 edition of TMS 402.

October 27, 2020

Guide to the Structural Evaluation of Existing Timber Structures, TFEC 3-2019 Thomas E. Nehil, P.E., and Ron Anthony This presentation will discuss key information provided in TFEC 3, laying out an acceptable practice for evaluation of existing structures and explaining why it is necessarily different than design of new timber structures.

Courses award 1.5 hours of Diamond Review-approved continuing education after the completion of a quiz. OCTOBER 2020

SEI Update Learning / Networking

SEI Virtual Events

www.asce.org/structural-engineering/virtual-events • Wednesday, October 7, 12:30 pm ET – #SEILIVE Chat with SEI President Joe DiPompeo, P.E., F.SEI, F.ASCE • Career Path Series: Insights with Glenn Bell and SE Industry Leaders Join discussions for every level of structural engineer: from where to begin to possibilities beyond principal. Live sessions are free for ASCE/SEI Members, but space is limited. Register today! #SEICareerPaths SEI/ASCE Members have free access to July-September sessions and resources online. Session 4: Evolving – To Principal and Beyond – Tuesday, October 20, 1pm US ET Joe DiPompeo, P.E., F.SEI, F.ASCE; and Anne Ellis, P.E., F.ASCE

NEW in the ASCE Bookstore and Library Guidelines for Electrical Transmission Line Structural Loading Edited by Frank Agnew, P.E. Available at www.asce.org

Learning from Failure? By John Cleary, Ph.D., P.E., M.ASCE, Associate Professor, University of South Alabama, Member of SEI Board of Governors

When I was an undergraduate student, several of the faculty would tell me, “you learn more from failure than success.” I don’t know if I fully understood what it meant at the time, but the rest of my time as a student, as a faculty member, and working in professional practice has shown me the importance of this statement. I now tell it to my students all the time. When you think about it, the statement is truer than you might want to admit. Think about in school, when you did well on an exam, did you really learn anything? Sure, you obviously understood the material and prepared well for that exam, but did you determine if it was the best way to prepare? Did you learn if it was the best way to prepare for future exams? Do you even know if it was an efficient way to prepare, or did you use time that could have been allocated to other tasks? The same principles apply to projects and design. Think about the hundreds of projects that are designed, built, and do not have issues throughout their lifetime. Did we learn much from those projects? We can always have lessons learned, maybe about efficiency, project

Errata 52 STRUCTURE magazine

scheduling, or constructability, but what did we really learn? Think about the failures that you heard about as a student. I am sure everyone is overly cautious when designing tension rods on walkways, right? The importance of learning from failures to ensure we do not repeat mistakes cannot be overstated! This is where CROSS-US comes into play. CROSS-US is a confidential reporting system for structural safety issues in the United States. CROSS has been active in the United Kingdom for several years and is now available for projects in the U.S. Whether you are a faculty member teaching structural design or mechanics, a student working on a research project, or a practicing engineer, CROSS-US is an excellent resource for identifying issues that have occurred so we can design to avoid them in the future. I strongly encourage you to take a look and consider incorporating the cases into classes and/or practice. Also, if you have interesting cases, consider submitting them for review! www.cross-us.org

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI-Errata. If you would like to submit errata, contact Jon Esslinger at jesslinger@asce.org.

News of the Structural Engineering Institute of ASCE Advancing the Profession

SEI Board of Governors Thank you to SEI members for voting in the recent online election for new SEI Board members Stephanie Slocum, representing SEI Business Professionals and Activities, and Greg Soules, representing SEI Codes and Standards Activities. The following indicates SEI Board officers elected by the Board at their April 8, 2020 meeting. 2020-2021 SEI Board of Governors are as follows: Joseph G. DiPompeo, P.E., F.SEI, F.ASCE, SEI President Victor E. Van Santen, P.E., S.E., F.SEI, M.ASCE President-Elect Randall P. Bernhardt, P.E., S.E., F.SEI, F.ASCE SEI Treasurer Glenn R. Bell, P.E., S.E., SECB, F.SEI, F.ASCE, SEI Past-President Laura E. Champion, P.E., F.ASCE, SEI Secretary John Cleary, Ph.D., P.E., M.ASCE Aimee Corn, P.E., M.ASCE Satyendra K. Ghosh, Ph.D., F.SEI, F.ASCE Jerome F. Hajjar, Ph.D., P.E., F.SEI, F.ASCE Stephanie Slocum, J. G. (Greg) Soules, Takahiko Kimura, P.E., F.SEI, M.ASCE P.E., M.ASCE P.E., S.E., P.Eng, Robert E. Nickerson, P.E., F.SEI, M.ASCE SECB, F.SEI, F.ASCE Donald R. Scott, P.E., S.E., F.SEI, F.ASCE Thank you to the SEI Board and Officers for serving. And for those who finished terms September 30, thank you for your service and leadership on the SEI Board: David W. Cocke, S.E., F.SEI, F.ASCE, SEI Past President Ronald O. Hamburger, P.E., F.SEI

2021 SEI Futures Fund Grant

For 2021, the SEI Futures Fund Board has committed more than $280,000 in funding for these strategic SEI programs. Some items have been deferred from 2020 due to the impact of the COVID-19 pandemic: • Student Scholarships to Structures Congress • Scholarships for Young Professionals to Participate at Structures Congress • Support to Develop Structural Fire Engineering Curriculum • SEI Standards lecture for SEI Chapters • Student Scholarship to Electrical Transmission and Substation Structures Conference 2021 • Seed Funding for SE2050 Database • Seed Funding for Claims Database Workshops • Strategy Workshop to Address Future Conditions of Environmental Loads and Impacts in SEI Standards • SEI Global Activities Online COVID-19 Symposium Thank you to Donors for their support to make these efforts possible. Learn more and give at www.asce.org/SEIFuturesFund.

Apply/Nominate by November 1 for: • O.H. Ammann Research Fellowship • SEI Fellow • SEI/ASCE Awards Learn more at www.asce.org/SEI.

SEI Online Check out the NEW SEI YouTube Channel including NEW SEI Futures Fund lecture on Structural Fire Protection https://bit.ly/3m6ihuN

SEI News Read the latest at www.asce.org/SEINews SEI Standards Visit www.asce.org/SEIStandards to view ASCE 7 development cycle O C T O B E R 2 02 0

CASE in Point Did you know? CASE has tools and practice guidelines to help firms deal with a wide variety of business scenarios that structural engineering firms face daily. Whether your firm needs to establish a new Quality Assurance Program, update its risk management program, keep track of the skills engineers are learning at each level of experience, or need a sample contract document – CASE has the tools you need! CASE has recently updated its Contract Library and has 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.

CASE Contracts – Usage Guide 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, when 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 an agreement that 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.

Follow ACEC Coalitions on Twitter – @ACECCoalitions. 54 STRUCTURE magazine

News of the Coalition of American Structural Engineers CASE Goes Virtual – Part Two! With in-person meetings at a stand-still, CASE members still found a way to engage with each other and with other ACEC Coalition members. As part of the first ACEC Coalition Virtual Education Series, held August 6-7, CASE committees all met virtually the afternoon of August 7. Below is a recap of all committee work and what new/updated publications are coming to an inbox near you!

CASE Contracts Committee Session:

CASE Guidelines Committee Session:

Presentation on EJCDC contract activities by Alan Steinle, Chairman of EJCDC Contracts committee and member of the CASE Contracts committee. Committee Discussion: • Review and update CASE Commentaries on AIA Document A295 – 2008 and AIA Document A201-2017 • Discussion of adding a Force Majeure clause to all CASE contracts within Terms and Conditions. • Discussion of adding suite of Design-Build contracts to CASE contracts suite

Committee members reviewed and discussed the following new/ updated Practice Guideline topics: New Practice Guideline being developed for release: • National Practice Guidelines for Seismic Design Current Practice Guidelines being updated by the committee: • 962-D: A Guideline Addressing Coordination and Completeness of Structural Construction Documents Future Practice Guideline Topics being developed: • Beyond the Code • Delegated Design Committee members discussed surveying membership about which types of structural systems they opt to delegate design responsibility for.

CASE Programs Committee Session: Committee members discussed participation in the following events: • 2020 ACEC Fall Conference −Participating in the virtual conference; will have at least one session and a roundtable • 2020 NCSEA Structural Engineering Summit – Business of Structural Engineering Seminar −The program has been moved from in-person to virtual and has been moved to (3) weekdays in September • 2021 SEI Structures Congress − Submitted Eric/Karen session • 2021 NASCC Steel Conference −Submission of CASE sponsored topic • 2021 ACEC Annual Convention −Reuse of 2020 submitted session on SEI CROSS system • 2022 NASCC Steel Conference −Submission of a topic in January 2021 • Discussed future topics and reviewed past topics; will survey membership on topics for sessions/roundtables • Committee discussed putting on Virtual Roundtable for membership −Will investigate either Quarterly or every other month basis

Risk Management Tool Committee Session: Committee members reviewed and discussed the following new/ updated and future tool topics:

New Risk Management Tools being developed for release: Tool 2-6: Structural Engineering Job Descriptions Tool 3-6: Succession Planning Tool Tool 5-7: Software Verification

Current Risk Management Tools being updated by the committee: Tool 3-1: Risk Management Program Planning Structure Tool 7-2: Fee Development Tool 8-2: Contract Clauses and Commentary Tool 9-1: Coordination and Completeness of Drawings

Future Tool Topics being developed: • Post Disaster Emergency Business Continuity Plan • Culture of Recruitment and Retention • Change Order Tracking • Earned Value Analysis

ACEC is Going Virtual October 28-30

During these unprecedented times, ACEC is committed to providing you with all the education, networking, and industry content you have come to expect from the Fall Conference – now from the comfort of your home office. Our reimagined event will take place over 3 days and feature high profile speakers, educational sessions on industry hot topics, CEO roundtables, networking lounges, and a virtual Exhibit Hall. Make your schedule work for you – join sessions live or watch on your own time up to 90 days after the event to make the most of your Fall Conference experience. ACEC is thrilled to deliver a dynamic event and space to connect with industry partners across the country. We cannot wait to see you there virtually! Register now at www.acec.org/conferences/fall-convention-2020/register-now. OCTOBER 2020

2020

STRUCTURAL ENGINEERING Resource Guide

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STRUCTURAL ENGINEERING

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RISA

ISA believes structural engineering software should be powerful, accurate, and user-friendly. The RISA Building System designs steel, concrete, timber, masonry, aluminum, and cold-formed steel all in a single, seamlessly integrated model. The following recent case studies illustrate the versatility of our software.

Frozen Fortress at GLOW Nashville

NC A&T Student Center Building Client: North Carolina A&T State University Structural Engineer: Stewart The new $90 million Student Center on the campus of North Carolina A&T State University is the university’s largest on-campus structure and a replacement for the former Memorial Student Union. The 150,000 square feet, LEED Silver facility serves as the “heart of campus” and allows students to come together to study, NC A&T Student Center eat, and socialize.

Waffle Building Building Client: Frederick and Laurie Samitaur Smiths Structural Engineer: NAST Enterprises Corporation The Waffle Building, located in Culver City, CA, is an undulating four-story building that grew out of a collaborative vision between architect Eric Owen Moss and chef Jordan Kahn, whose restaurant, Vespertine, currently occupies the building. The structure, which only occupies a space that is 33 feet by 33 feet, twists along its height and is enveloped in horizontal and vertical steel fins which make up the “waffle” grid and support the glass enclosure. The building is the 2019 Innovative Design in Engineering and Architecture with Structural Steel (IDEAS2) Award winner for projects less than $15 million. The internal supporting structural system closely follows the exterior shape with four, 18-inch-diameter steel pipe columns situated at the corners with steel beams and steel joists supporting each level. The complex geometry of this relatively small structure made collaboration between the architect and structural engineer essential. RISA-3D was used to evaluate the performance of the exterior ¼-inch steel plates specifically due to its submeshing and loading features that allowed for accurate evaluation of stresses in the plates. Additional design challenges Waffle Building included understanding and managing the various deflection “modes” of the structure during construction due to how different the structure performed early in construction (before the exterior steel “fin” plates were installed) as opposed to when the framing was complete.

ADVERTORIAL

Building Client: Exhibau Structural Engineer: Epiq Structural Solutions GLOW Nashville is the ultimate holiday display located at First Tennessee Park in Nashville, TN. The experience for attendees includes one of the tallest Christmas trees in the country (at over 100 feet), more than 4 million holiday lights, Frozen Fortress at GLOW Nashville a 170-foot-long tube park built over the stadium seats and a life-size Santa’s workshop. The focal point of the display is the 3-story viewing platform, known as the Frozen Fortress, which sits at the center of the iceskating rink. The 30-foot-tall, temporary structure includes a spiral staircase in the middle as well as two 70 feet long by 6 feet wide pedestrian bridges that span over the ice-skating rink allowing visitors access to the structure’s viewing platforms. The main structure includes a modular, hot rolled steel system (HSS tubes and wide flanges) that is designed to be easily erected and then taken apart, shipped, stored and ready for the next use. RISA-3D was utilized to model and analyze the entire structure with specific attention paid to the pedestrian bridge and “waffle” floor system. The analysis of the pedestrian bridges were unique due to the fact that the loaded condition would cause the bridge to slide since it was not anchored to the ground. As a result, additional lateral loads were introduced into the model to account for the sliding.

Because of the building’s importance on campus, the architect set out to create an iconic structure. As a result, the structural engineer was faced with the challenge of designing a structure that included large open spaces, multiple cantilevers, and various load conditions based on the changing programmatic space requirements of the building. One of the most challenging aspects of the design was the central atrium bridge. The design went through numerous design iterations and the decision was made to include one central column to support the structure. Due to the stairs mixed use, patterned loading conditions needed to be evaluated for vibration concerns. RISA-3D was instrumental in the design process and was used to quickly evaluate the deflection and free vibration of the bridge in order to determine how the structure would react under various pattern loading conditions as well as failure scenarios of the individual stringers and the supporting column.

949-951-5815 | info@risa.com | risa.com STRUCTURAL ENGINEERING Resource Guide 2020 SS-57

SOFTWARE Adhesives Technology Corporation

CADRE Analytic

Losch Software Ltd

Phone: 754-399-1057 Email: jhanley@atcepoxy.com Web: atcepoxy.com/software Product: Pro Anchor Design Software Description: New Pro Anchor Design software from Adhesives Technology Corp. has an advanced single panel interface updated for all of our IBC compliant products, including two new anchoring adhesives to be introduced in 2020. No need to access the cloud or pay for premium features. It’s free!

Phone: 425-392-4309 Email: cadresales@cadreanalytic.com Web: www.cadreanalytic.com Product: CADRE Pro 6 Description: Finite element structural analysis. Loading conditions include discrete, pressure, hydrostatic, seismic, and dynamic response. 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. Free fully-functioning evaluation version available.

Aegis Metal Framing Phone: 314-851-2200 Email: answers@mii.com Web: www.aegismetalframing.com Product: Steel Engine Description: Software that lets you model your floor, wall, and roof components for an in-depth look at the Ultra-Span truss requirements, giving you an accurate 3-D model of your project with calculated loads. Our precise drawings, combined with faster factory fabrication, saves you time in the field.

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: An advanced software for quick and efficient design of concrete and steel members, foundations, and retaining walls. See immediate graphical results and clean, concise reports with exposed formulas and code references. Focus your attention on engineering and let ASDIP handle the math complexity.

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.

ENERCALC, Inc. ENERCALC Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: Structural Engineering Library/ ENERCALC SE Cloud/RetainPro Description: ENERCALC’s 38th year of Structural Engineering Library brings new modules – including Steel Base Plate and the addition of the RetainPro retaining wall modules. Build 20 includes substantial interface and performance improvements. Save time and money via budget-friendly monthly and annual subscriptions which include updates and support.

GIZA Steel Phone: 314-656-4615 Email: jmoody@gizasteel.com Web: www.gizasteel.com Product: GIZA Description: A structural steel connection design software tool for the shear, moment, vertical brace and horizontal bracing groups. We provide full calculation reports with code references for over 400 different connection configurations. Free 15-day trial at website.

Bentley Systems

IES, Inc.

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.

Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis with Design Description: Once upon a time, there was an engineer overwhelmed with software headaches. As deadlines loomed, he fought against frustration. First the tools were oppressive and clumsy. Then the licensing got ugly. Fortunately, our hero switched to IES and design tasks started feeling more like slaying dragons.

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. SS-58 STRUCTUREmagazine

Product: VisualFoundation 10.0 Description: When engineers need to design foundations, more and more are using IES VisualFoundation. This tool simplifies your use of nonlinear FEA to arrive at solid answers. Create easy models with loading, and then review the clear results. Stay in control of design checks and complete your projects faster.

Product: LECWall Description: The industry standard for precast concrete sandwich wall design handles multi-story columns as well. LECWall can analyze prestressed and/or mild reinforced wall panels with zero to 100 percent composite action. Flat, hollow-core, and stemmed configurations are supported. Complete handling analysis is also included.

LUSAS Phone: 800-975-8727 Email: terry.cakebread@Lusas.com Web: www.lusas.com Product: LUSAS Description: For more than 35 years, LUSAS has helped its clients to analyze, design, and assess all types of infrastructure projects. Our innovative, flexible, and trusted software solution can be applied to diverse applications across a range of industries. Model structure and ground together to consider true interaction.

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

POSTEN Engineering Systems 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.

Qnect LLC Phone: 413-387-4375 Email: christian@qnect.com Web: www.qnect.com Product: Qnect Description: An intelligent, cloud-based connection service giving fabricators, detailers, and engineers fast and flexible connections with significant cost and schedule savings. Connect steel buildings in minutes, with minimal training. Prevent schedule drift, utilize one-station fabrication, and reduce connection material, time to fabricate, and erect.

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ENERCALC – A 38 YEAR LEGACY From Microcomputer Infancy to Global Cloud Computing Our Story

Today, Enercalc Software is Everywhere 16 years later, ENERCALC would again deliver structural engineering applications via ENERCALC SE Cloud. With a proven cloud platform backed by Amazon Web Services (AWS), you can use the Structural Engineering Library, ENERCALC 3D, and our earth retention structure software from anywhere on the globe, using any html5 device on any OS: iPad, tablet, laptop, or desktop. Check out enercalc.com/cloud.

90% of Structural Engineering Work is Low-Rise To gain perspective for the uses of ENERCALC’s structural engineering software, consider your last flight. Before landing, a downtown cluster of skyscrapers, stadiums, and malls appeared. Surrounding them for many square miles are low-rise parking garages, manufacturing facilities, warehouses, retail, hotels, medical complexes, commercial buildings, and other structures that are 90% of structural engineering work. For 38 years, ENERCALC has been committed to supplying structural engineering calculation software for this 90%, while retaining simple entry forms with fast recalculation – just like our original spreadsheets. Today, building codes are complex, with so many load combinations

ENERCALC

and specific design details that hand calculations are no longer feasible. We have added earth retention structure software and ENERCALC 3D, a mature 3D FEM product with broad analysis power with a fresh new ribbon-based UI. These 3 products serve this 90% role completely – bundled with budget-friendly subscription pricing.

Did Your Work Situation Change This Year? In an “My office is where I am” world, ENERCALC is everywhere. With a simple, one-price subscription, you can: • Install the software on any computer, in any location: ENERCALC automatically manages allowed seat usage. • Launch ENERCALC SE Cloud and access the same software globally through a browser. It is the same powerful Windows software – not a trivial subset of our desktop software deployed on the web. • Safely and easily share project files between installed and cloud users. • Access high-performance apps via your browser at the closest of 7 localized Amazon data centers: California, Virginia, Ohio, Tokyo, Mumbai, Sydney and Frankfort.

ADVERTORIAL

In 1982, a young structural engineer named Michael Brooks was working in his father’s SE firm. The IBM PC was getting lots of press and Michael’s $5,000 loan provided for delivery of that beautiful new machine. Lotus 1-2-3 was installed...one of the first programs to make the PC successful. Brooks started creating worksheets to automate typical engineering tasks. By 1983, a small ad appeared for the Structural Engineering Library with a company motto “Innovative Software for the Design Professional.” ENERCALC’s use of spreadsheets was very innovative – surprising even the Lotus 1-2-3 team. Over time, the software evolved from Lotus 1-2-3 using C routines in “FastFrame,” a spreadsheet for full 2-D FEM analysis. Next, a hybrid spreadsheet product gave the user a simple spreadsheet interface that used fast compiled solvers. In the late ‘90s, spreadsheet limitations required a full Windows rewrite. Brooks was convinced that server-based computing was the future. He wrote a Citrix-like server-client system, purchased 24 servers, and launched ENERCALC in the cloud in 2000. It was vision of a future yet to come...the Internet was still too primitive.

Is Revit Part of Your Workflow? SEL will soon debut a Revit add-in that links our software directly into the Revit environment. Click a Revit element and send it to ENERCALC for design, then send it back for a Revit model update. This allows you to generate SEL modules from Revit geometry rapidly, then update the Revit model in real-time based on SEL’s calculations.

A Small Team Working Hard for Structural Engineers 38 years after the birth of those Lotus spreadsheets, ENERCALC remains a small, close-knit team with the same “Innovative Software” focus and some substantial offerings to come in 2021.

800-424-2252 | info@enercalc.com | www.enercalc.com STRUCTURAL ENGINEERING Resource Guide 2020 SS-59

SOFTWARE RISA

S-FRAME Software

Standards Design Group, Inc

Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: RISAConnection Description: The cutting edge of next-generation connection design software; features full 3-D visualization and expandable reports for every limit state. The latest release includes integration with Hilti Profis for anchorage design as well as custom anchor bolt layouts that allow engineers the flexibility to design a variety of anchorage conditions.

Phone: 604-273-7737 Email: info@s-frame.com Web: s-frame.com Product: S-FRAME Analysis Description: An industry standard for over 36 years, analyzes and designs structures regardless of geometric complexity, material type, loading conditions, nonlinear effects, or seismic loads. Integrated concrete, steel, timber, and foundation design ensures maximum productivity. S-FRAME’s continued R&D investment gives users the latest advantages and dedicated technical expertise.

Phone: 806-792-5086 Email: info@standardsdesign.com Web: www.standarddesign.com Product: Wind Loads On Structures 2019 Description: Wind load computations in ASCE 7-05, Section 6 and ASCE 7-10, or 16, Chapters 26-31; “build” structures within the system, enter wind speed or choose basic wind speeds from the ATC Hazards by Location website, input topographic features, different exposures for different wind directions. Computes wind loads by analytical method.

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.

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

Strand7 Pty Ltd

SkyCiv Phone: 800-838-0899 Email: trevor.solie@skyciv.com Web: skyciv.com Product: SkyCiv Software Suite Description: Thanks to SkyCiv Software Suite being cloud-based, software maintenance and downloads are gone. Updates are pushed to the suite automatically, sometimes in as little as two weeks. Simply log into a browser from any device and go. Content and feature updates are available immediately after development.

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IRONORBIT

Phone: 252-504-2282 Email: info@strand7.com Web: www.strand7.com Product: Strand7 Description: 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.

Profile

GPU-Accelerated Cloud Workspaces – Bridging Technology with Innovation and Success • AEC specific solutions to boost efficiency and reduce TCO • Tailored GPU-Accelerated workspaces for every user profile • Perfecting the UX in adopting and utilizing DaaS solutions Matt McGrigg, Global Director of Cloud Business Development at NVIDIA, says, “IronOrbit INFINITY Workspaces are ideal for professional graphics workstations used by engineers, architects, and designers across industries, from AEC to M&E to manufacturing. With Quadro performance from the cloud, on any connected device, professionals working from home can stay productive.” IronOrbit’s AEC clients implement futureproof technology, enabling them to shape their industry and future. Our portfolio includes extended offerings that cover Managed Services (Infrastructure and Advanced Applications) and Thought Leadership Services (Consultation and Professional Services). IronOrbit, a division of SACA Technologies, Inc., founded in 1997 as an MSP provider, is located in beautiful Anaheim Hills, CA. IronOrbit evolved into a cloud solutions provider offering comprehensive cloud technology solutions for almost two decades. IronOrbit delivers optimized, customized, and fully integrated ITC solutions that drive growth for all verticals and industries.

888-753-5060 | sales@ironorbit.com | www.ironorbit.com/aec

ADVERTORIAL

ronOrbit is a privately owned and fully integrated Information and Communications Technology (ICT) Powerhouse. We are a Specialized Cloud Services Leader focused on planning, deploying and fueling Digital Transformations for the AEC industry. IronOrbit innovates, develops, and produces comprehensive ICT solutions, specializing in GPU-Accelerated INFINITY Workspaces, for some of the biggest IT-related challenges facing AEC firms. A Cloud Service Provider for NVIDIA, IronOrbit is strategically positioned as a catalyst for the digitization of end-user workspaces and web-scale applications. Adding the NVIDIA QUADRO® to IronOrbit data centers leverages high-performance and GPU-Acceleration to power our INFINITY Workspaces, which are optimized for today’s modern, demanding, and resource-intensive applications. The result is superior efficiency, creativity, productivity, and end-user experience than a physical workstation. IronOrbit’s future focus is on mid to large enterprise market segments, with a wide base of small enterprises acquired over the years. To target these segments, IronOrbit developed fully customized, dynamic, modular, scalable, and secure Turn-Key solutions that fit specific user profiles within the AEC industry. Key Initiatives include: • Migrate workstations to digitized, cloud-based workspaces

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DEWALT DEWALT is proud to be a leader in the construction industry by offering anchoring solutions to design, build, and maintain jobsites across the country.

To ensure the design process is as productive as possible, we have a full-service team of field engineers dedicated to making sure your business is getting the most out of DDA. Our field engineers work with your structural team to specify anchoring and fastening products, as well as offering assistance during the bidding, submittal, and construction phases of your project. Our team of engineers is available whether you have a question about product substitutions or digital solutions. DEWALT DDA: http://anchors.dewalt.com/anchors/tech-support-software After the site has been designed, the building begins. DEWALT offers an extensive line of mechanical and chemical anchors that are covered by 30+ ICC-ESR approvals. This qualifies our anchor systems as third-party tested and ICC Building code compliant. DEWALT Anchors & Fasteners are reliable and enhance construction productivity. We also offer a full range of installation power tools engineered to drill through the hardest concrete. By combining specific anchors, power tools, and accessories, we have designed a new way to install anchors with the DUSTX+™ Anchor Installation System productively. This code-compliant system eliminates 100% of traditional hole cleaning steps when installing mechanical anchors, such as ScrewBolt-™, and anchoring adhesives such as Pure 110+® or AC200+™. Combine the DEWALT DWV012 dust extractor with 99.97% filter efficiency, DEWALT Hollow Drill Bits, and any DEWALT rotary hammer to remove dust from holes while drilling. This allows our users to achieve OSHA Table 1 compliance while being as productive as possible with anchor installation. Regardless of the job, DEWALT is more than just tools. We are your partner on-site. We work with your teams to identify gaps in your process and offer time-saving solutions to complete projects on-time and within budget. Feedback and customer care are critical components of our innovation process. We listen to the people who rely on us, taking their feedback and using it to create products that drive productivity and profitability.

ADVERTORIAL

ince 1924, construction professionals have relied on DEWALT® for quality, innovative tools. Leading the way in the era of modern construction sites, we are continually developing new technology, products, and software to help improve efficiencies at every stage of the job. We continue to design and optimize professional worksite solutions for the toughest jobsite conditions. DEWALT isn’t just GUARANTEED TOUGH. DEWALT is the total jobsite solution. From design to build to maintain, we offer the expertise, power tools, anchors, and technology to ensure your teams are operating at peak efficiency. DEWALT Design Assist Software provides an innovative way to design your site. Our extensive line of power tools and anchors help you build your site from the ground up. Maintaining your site becomes easier with DEWALT field engineers and service managers within reach. Designing your site is an integral step in the building process. DEWALT is leading innovation within the anchor industry with the DEWALT Design Assist software. This software program is a powerful anchor design and comparison tool. With new innovative features, applications, and products, the interactive and flexible user-interface allows you to model, optimize, and compare multiple anchoring solutions. DDA helps you design your site with 4 key features: 1) Design: Code compliant anchor designs according to ACI 318-14 and CSA A23.3-14. 2) Compare: Quickly compare up to 3 similar or different anchors. 3) Document: Comprehensive design calculations with multiple reporting options. 4) Anchor: Includes a full catalog of DEWALT anchors, standard Cast-In-Place, and more. These key features allow you to model customizable baseplate designs, equipment anchorages, anchorage-to-deck members, composite metal deck slab anchoring, post-installed rebar design (AC308), and more.

800-524-3244 | anchors@dewalt.com | http://anchors.dewalt.com/anchors STRUCTURAL ENGINEERING Resource Guide 2020 SS-61

SOFTWARE StructurePoint

Trimble

Visicon Inc.

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)

Phone: 678-737-7379 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.

Phone: 650-218-0008 Email: florian@visicon.com Web: visicon.com Product: Visicon 3D Model Checker Description: Provides a common platform to review and check Revit, ETABS, and IFC models. It gives greater insight into project models, helps document design progress, identifies model changes, and automates quality control checks. Engineering teams using Visicon to improve overall project coordination and produce higher quality projects.

Trimble Inc. Phone: 800-874-6253 Email: info@geospatial.trimble.com Web: https://monitoring.trimble.com Product: Trimble 4D Control Description: Enables project stakeholders to monitor critical infrastructure including dams, bridges, mines, and buildings surrounding construction sites and tunnels in real-time. Providing unparalleled movement analysis and extensive support for a wide variety of monitoring sensors, multiple sites can be managed from a single, customizable platform.

Product: Tekla Structural Designer Description: The power to analyze and design multi-material buildings efficiently and cost effectively. Fully automated and packed with unique features for optimized concrete and steel design. Helps engineering businesses win more projects and maximize profits. Quick comparison of alternative design schemes through cost-effective change management and seamless BIM collaboration. Product: Tekla Structures Description: Create and transfer constructible models throughout the design life, 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.

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WoodWorks Software Phone: 800-844-1275 Email: sales@woodworks-software.com Web: www.woodworks-software.com Product: WoodWorks® Software Description: Offers three programs: Sizer for beam, joist, columns, wall stud, and CLT design. Shearwalls for wood and gypsum board sheathed walls. Connections for wood-to-wood, wood-to-concrete, and wood-to-steel connections. Use WoodWorks to quickly design components for light-frame and mass timber structures.

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NCEES DISCOVER MORE.

SS-62 STRUCTUREmagazine

ADVERTORIAL

he National Council of Examiners for Engineering and Surveying (NCEES) is a nonprofit organization made up of engineering and surveying licensing boards from all U.S. states and territories. Since its founding in 1920, NCEES has been committed to advancing licensure for engineers and surveyors in order to safeguard the health, safety, and welfare of the U.S. public. NCEES develops, administers, and scores the exams used for engineering and surveying licensure in the United States. It also facilitates professional mobility and promotes uniformity of the U.S. licensure processes through services for its member licensing boards and licensees. These services include the following:  Surveying Exams  Engineering Exams  Exam Prep Materials  Records Program  Credentials Evaluations  CPC Tracking  Surveying Education Award  Engineering Education Award  Speaker’s Link

864-654-6824 | outreach@ncees.org | ncees.org/discover

WOOD American Wood Council

ENERCALC, Inc.

Phone: 202-463-2766 Email: info@awc.org Web: www.awc.org Product: Standards, Resources and Design Tools Description: The American Wood Council develops ANSI-approved standards and other design tools related to the use of wood and wood products. Our popular DCA 6 – Prescriptive Residential Wood Deck Construction Guide is a free document on how to properly build a deck and is available in English or Spanish.

Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: Structural Engineering Library/ ENERCALC SE Cloud Description: Whether working with wood beams, trusses, columns, ledgers, or shear walls, ENERCALC’s Structural Engineering Library will save hours of design time every week. Built-in databases for sawn lumber and engineered wood products (VersaLam, Glu-Lam, etc.) put section properties and allowable stresses at your fingertips. Budget-friendly all-inclusive subscriptions make it easy.

Product: National Design Specification for Wood Construction® (NDS) Description: The 2018 NDS is referenced in the 2018 International Building Code. Significant additions to the 2018 NDS include new Roof Sheathing Ring Shank nails and fastener head pullthrough design provisions to address increased wind loads in ASCE 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structures.

CADRE Analytic Phone: 425-392-4309 Email: cadresales@cadreanalytic.com Web: www.cadreanalytic.com Product: CADRE Pro 6 Description: Finite element structural analysis. Loading conditions include discrete, pressure, hydrostatic, seismic, and dynamic response. 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. Free fullyfunctioning evaluation version available.

CAST CONNEX Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Timber End Connectors™ Description: The leading supplier of cast steel components for use in the design and construction of structures. Timber End Connectors bring off-the-shelf simplicity and reliability to architecturally exposed steel connections at the ends of heavy timber or glulam structural elements, while custom designed components enable unparalleled opportunity for creativity in design.

S-FRAME Software

ENERCALC

Anchors

IES, Inc. Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis + VAConnect Description: Your wood structures start with a model. VisualAnalysis helps you create models easily to obtain accurate analysis and design results. With VAConnect you also get wood connection design to take you a step further toward success. Download free trials of these tools from the website.

RedBuilt 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. 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. For support, contact us by e-mail at RedSpec@RedBuilt.com.

Phone: 604-273-7737 Email: info@s-frame.com Web: s-frame.com Product: S-TIMBER Description: The solution to mass timber, lightframe, and hybrid structural design. Leverages over 38 years of structural engineering expertise into a timber design solution that automates and manages all aspects of the timber design process: modeling, structural analysis, and timber design. S-FRAME Software solutions are backed by best-in-class customer support.

Trimble 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. Product: Tekla Tedds Description: Using Tekla Tedds you can 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).

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.

2020

RISA Phone: 949-951-5815 Email: benf@risa.com Web: risa.com 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.

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STRUCTURAL ENGINEERING Resource Guide 2020 SS-63

MASONRY Concrete Masonry Association of CA & NV Phone: 916-722-1700 Email: info@cmacn.org Web: www.cmacn.org Product: CMD18 Design Tool for Masonry 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).

ENERCALC, Inc.

H&B Powered by MiTek

PROSOCO

Phone: 800-645-0616 Email: tomw@h-b.com Web: h-b.com Product: ENVIRO-BARRIER Air Barrier Description: A single-component, fluid-applied, air, water, and vapor barrier for above-grade wall assemblies. It cures to form a resilient, monolithic, fully adhered, elastomeric membrane that resists air leakage and water penetration, plus acts as a vapor barrier.

Phone: 800-255-4255 Email: brian.barnes@prosoco.com Web: www.prosoco.com Product: PROSOCO Stitch-Ties and Grip-Ties Description: PROSOCO offers a variety of masonry anchors and ties for all kinds of wall stabilization projects, on new construction and on retrofits. New construction anchors establish a secure facade on new masonry buildings, and our restoration anchors restore existing buildings by stabilizing the facade.

Larsen Products Corp. ENERCALC

Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: Structural Engineering Library/ ENERCALC SE Cloud/RetainPro Description: Whether designing masonry slender walls, masonry beams and lintels, or masonry cantilevered retaining wall stems, ENERCALC’s Structural Engineering Library saves time. Masonry design modules feature flexible geometry definition, thorough load combinations, and clear concise output. Instant recalculation allows “what-if ” solutions. Build 20 subscriptions now include RetainPro retaining wall modules.

Phone: 800-633-6668 Email: jlarsen@larsenproducts.com Web: www.larsenproducts.com Product: Weld-Crete® Description: Weld-Crete 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. Listings are provided as a courtesy, STRUCTURE is not responsible for errors.

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Wej-It High-Performance Anchors 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 heavy-duty mechanically-galvanized finish is available to enhance corrosion resistance.

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H&B POWERED BY MITEK The same study shows that offset angles minimize that reduction to between 15 percent and 16.5 percent. Among H&B Powered by MiTek’s thermal offerings is our Thermal Wingnut – the only functional wingnut anchor in the industry. As the wingnut tightens, it presses the insulation tight against the backup wall, maximizing its R-Value. Single-barrel means a single penetration, as opposed to anchors that typically require two fasteners. This means the number of thermal bridges is reduced by half. Using a wall configuration with 4 inches of XPS insulation, at 16- x 16-inch spacings, typical masonry anchors can lead to an R-Value reduction of upward of 20 percent or greater. This anchor limits that effective R-Value reduction to 7.4 percent, or operating at 92.6 percent efficiency. H&B Powered by MiTek offers a line of Thermal 2-SEAL™ anchors, which use a proprietary UL-94 coating to create a thermal break at the insulation, and a stainless-steel barrel that transfers 1⁄7 the thermal energy of a standard zinc barrel. The dual-diameter barrel with EPDM washers makes our 2-SEAL line the only anchors on the market to seal both the insulation and the air barrier. In fact, we make the only anchors that seal the air barrier. The steel-reinforced wing maintains integrity during NFPA 285 testing.

800-645-0616 | weanchor@h-b.com | www.h-b.com SS-64 STRUCTUREmagazine

ADVERTORIAL

&B Powered by MiTek serves both the commercial and residential markets as the leading developer and distributor of reinforcement, anchoring, and moisture protection systems for masonry. An essential part of our anchoring line is our group of thermal products. Our Thermal Brick Support System (TBS) offers many benefits. A groundbreaking brick veneer support system reduces thermal bridging in shelf angles. The TBS system also allows for the installation of continuous insulation behind the support angle. Each job is designed and engineered in-house to meet your specific project needs. In addition, RDH Engineering posted a study showing attached shelf angles will create an effective reduction of the R-Value by between 46 percent and 63 percent.

SEISMIC Adhesives Technology Corporation

Dlubal Software, Inc.

Gripple

Phone: 754-399-1057 Email: ATCinfo@atcepoxy.com Web: atcepoxy.com Product: ULTRABOND® HS-1CC High Strength Anchoring Epoxy Description: The world’s strongest anchoring epoxy, IBC compliant ULTRABOND HS-1CC is available in bulk and cartridge containers. Qualifies for seismic categories A through F, is included on DOT approved materials lists in 31 of the 40 states that maintain such lists (remaining states pending), and is “Made in USA.”

Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM Description: Integrated automatic wind and snow load generators according to ASCE 7-16 for general building-type structures. Calculate a Response Spectra Analysis for all structure types according to ASCE 7-16 or user-defined from accelerogram input data. Structure design and optimization available with the latest design standards such as AISC, ACI, ADM, NDS.

Phone: 630-406-0600 Email: e.balsamo@gripple.com Web: www.gripple.com Product: Seismic Cable Braces for Non-Structural Building Components Description: Specifically-designed and engineered to brace and secure suspended nonstructural equipment and components requiring seismic design. Requiring no tools to install, they are up to 10 times faster than other bracing methods and are suitable for new or retrofit installations. Color-coded by strength for identification ease.

Applied Science International, LLC

DuraFuse Frames

Hexagon

Phone: 919-645-4090 Email: support@appliedscienceint.com Web: www.extremeloading.com Product: Extreme Loading for Structures 8.0 Description: Advanced non-linear structural analysis software tool designed specifically for structural engineers. ELS allows structural engineers to study the 3-D behavior of structures through both the continuum and discrete stages of loading. Includes static and dynamic loads such as those generated by a blast, seismic events, impact, progressive collapse, and wind.

Phone: 801-727-4060 Email: contact@durafuseframes.com Web: www.durafuseframes.com Product: DF360 Description: DuraFuse Frames products are unique seismic resilient systems preventing beam and column damage while also providing repairability. DuraFuse Frames offers the ideal moment-frame and dual-frame solutions for all building types in all Seismic Design Categories, and provides the most versatile SMF/IMF system on the market in addition to resiliency.

Phone: 346-260-8798 Email: andrea.velazquez@hexagon.com Web: https://hexagonppm.com Product: GT STRUDL Description: Engineers build complex geometries using familiar and powerful CAD tools. Automated generation of wind and seismic loads per ASCE 7 with a graphical assignment of wind loads to account for shielding effects on open structures. New in 2019 is the ability to convert seismic response spectra to time history loads.

Cast Connex

Dynamic Isolation Systems

Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: High Strength Connectors™, Cast Bolted Brackets, and Scorpion™ Yielding Connectors Description: High Strength Connectors and Cast Bolted Brackets simplify and improve connections in seismic-resistant concentrically braced frames and moment resisting frames, respectively. Scorpion Yielding Connectors are modular, replaceable, standardized hysteretic fuses that provide enhanced ductility and improved performance in the retrofit of seismically deficient structures or for use in the Seismic Force Resisting System of new structures.

Phone: 775-359-3333 Email: sales@dis-inc.com Web: www.dis-inc.com Product: Lead Rubber Bearing (LRB) Description: Base isolation with LRBs reduces accelerations from an earthquake by isolating the structure from ground motions. Isolated buildings and their contents will be undamaged and functional after an earthquake.

Cintec Reinforcement Systems Ltd Phone: 613-225-3381 Email: rlr@cintec.com Web: www.cintec.com Product: Cintec Anchoring and Reinforcement systems Description: Design features allow for adaptations that meet the specific strengthening and repair requirements individual to each project. Extensive research and development has focused on the contribution Cintec anchors provide in the fields of seismic upgrading and seismic repair while still remaining sensitive to the original architecture.

CoreBrace Phone: 801-280-0701 Email: brandt.saxey@corebrace.com Web: www.corebrace.com Product: CoreBrace Buckling Restrained Braces Description: A sustainable and cost-effective solution to improve seismic performance of structures. This highly ductile system has been used in thousands of projects worldwide for earthquake risk mitigation. CoreBrace’s expert staff works closely with engineers and the entire design and construction team to meet their requirements.

Anchors

ENERCALC, Inc.

ENERCALC

Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: Structural Engineering Library/ ENERCALC SE Cloud Description: SEL automatically incorporates seismic loads in load combinations, including the vertical component, redundancy, and system overstrength factors, as applicable. SEL supports ASCE 7’s Base Shear, Demands on Non-Structural Components, and Wall Anchorage. SEL Build 20 subscriptions now include RetainPro’s retaining wall modules – including the substantially upgraded Segmental Retaining Wall module.

Geopier Foundation Company Phone: 704-439-1790 Email: info@geopier.com Web: geopier.com Product: Geopier Rammed Aggregate Pier® and Rigid Inclusion Systems 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 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.

IES, Inc. Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis Description: Thousands of engineers use VisualAnalysis to design structures for both lateral and gravity loading, including ASCE 7 wind and dynamic analysis for seismic. Customer-proven for over 25 years. the latest version updates material specifications and will help you beat deadlines. Try it today at no cost.

Lindapter Phone: 866-566-2658 Email: inquiries@lindapter.com Web: www.LindapterUSA.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.

Meca Enterprises, Inc Phone: 918-258-2913 Email: rachel@mecaenterprises.com Web: www.mecaenterprises.com Product: MecaWind Software Description: A cost-effective program used by Engineers and Designers to perform wind calculations per ASCE 7-16, ASCE 7-10, and ASCE 7-05. Simple to use and offers a professional looking output with all necessary wind calculations. The software will save you time and is a great tool to have in your business.

SEISMIC RISA

Simpson Strong-Tie®

Trimble

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. Whether using RISA-3D’s automated seismic load generator, or using the built-in dynamic response spectra and time history analysis/design capabilities, you will get designs and reports that will 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.

Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com Product: Tekla Structural Designer Description: Design a lateral force resisting systems with Tekla Structural Designer’s code based 3-D BIM analysis and design tool. 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.

Struware, LLC

S-Frame Software Phone: 604-273-7737 Email: info@s-frame.com Web: s-frame.com Product: S-FRAME Analysis Description: An industry standard for over 36 years, analyzes and designs structures regardless of geometric complexity, material type, loading conditions, nonlinear effects or seismic loads. Integrated concrete, steel, timber, and foundation design ensures your maximum productivity. Our continued R&D investment gives users the latest advantages and dedicated technical expertise.

Phone: 904-302-6724 Email: email@struware.com Web: www.struware.com Product: Struware Code Search Description: Provides you with all pertinent wind, seismic, snow, live and dead loads for your building in just minutes. The program simplifies ASCE 7 and IBC (and codes based on these) by catching the buts, ifs, insteads, footnotes, and hidden items that most people miss. Demo available at the website.

Phone: 408-439-3283 Email: david@zenithengineers.com Web: zenithengineers.com Product: Seismic Retrofitting Service Description: Zenith Engineers has designed and engineered over 600+ seismic retrofits across the west coast ranging from non-ductile concrete, unreinforced masonry, and soft story buildings.

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COREBRACE

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 of its products within its own 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 that is 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, superior quality assurance, and customized schedule performance in every project.

801-280-0701 | info@corebrace.com | corebrace.com SS-66 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 to 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 5) Minimized strengthening of existing structural members and foundations

FOUNDATIONS American Wood Council

Geopier Foundation Company

RISA

Phone: 202-463-2766 Email: info@awc.org Web: www.awc.org Product: Permanent Wood Foundation Design Specification (PWF) Description: PWF covers permanent wood foundation systems which are intended for light frame construction, including residential buildings. This document primarily addresses the structural design requirements.

Phone: 704-439-1790 Email: info@geopier.com Web: geopier.com Product: Geopier Rammed Aggregate Pier® and Rigid Inclusion Systems 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 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.

Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: RISAFoundation Description: The ultimate tool for analysis and design of a variety of different foundation types. Featuring an open modeling environment, finite element analysis, and full integration with superstructure analysis programs; you won’t find a better choice for retaining wall, spread footing, combined footing, mat slab, or pile cap design.

Larsen Products Corp.

STRUCTUREPOINT

Phone: 847-966-4357 Email: software@structurepoint.org Web: www.structurepoint.org Product: spMats Description: Widely used for analysis, design, and investigation of concrete mat foundations, footings, and slabs on grade. spMats is equipped with the American (ACI 318-14) and Canadian (CSA A23.3-14) concrete codes. Utilized by engineers worldwide to optimize complicated foundation design and improve analysis of soil structure interaction.

ENERCALC, Inc. ENERCALC Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: Structural Engineering Library/RetainPro/ ENERCALC SE Cloud Description: ENERCALC’s SEL has you covered when it comes to design of individual pad, continuous wall, or combined footings. The foundation design modules feature flexible geometry definition, thorough load combinations, and clear concise output. Instant recalculation allows “whatif ” solutions. Build 20 subscriptions now include RetainPro’s retaining wall modules. Update today!

Anchors

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DURAFUSE FRAMES

• Added stiffness in connection region results in reduction of overall frame weight • Fewer parts and less fit-up in installation process • No field welding or inspection requirements • Fewer parts and less connection weight • Improvement of project schedule • No prescriptive lateral bracing • No seismic compactness requirements • No protected zone in the beam • Reduction of downtime and repair costs following severe earthquake Three benefits unique to DuraFuse Frames: The only fully-restrained (FR) steel moment frames that do not require prescriptive lateral bracing per AISC 341, D1.2b, which saves money by eliminating braces and creates possibilities for frames where braces are not feasible. The only fully-restrained (FR) steel moment frames that do not have seismic compactness requirements for the beams which enables the use of the most efficient beam shapes and can reduce frame weights. The only fully-restrained (FR) steel moment frames that do not have a protected zone in the beam. DuraFuse Frames is available in RAM Structural Systems, Revit, SDS2, and Tekla.

ADVERTORIAL

uraFuse Frames products are unique seismic resilient systems preventing beam and column damage while also providing repairability. DuraFuse Frames offers the ideal moment-frame and dual-frame solutions for all building types in all Seismic Design Categories and provides the most versatile SMF/IMF system on the market in addition to resiliency. The frame design utilizes bottom fuse plates, which protect the beams and columns, becoming the only parts to be replaced following a severe earthquake event. This innovative design allows buildings to be more resilient to major earthquakes. DuraFuse Frames enjoys full compliance with the performance requirements in AISC 341 with code approvals from IAPMO UES ER 610, including 2018 IBC, CBC, and LA Addendum. Its team of highly competent researchers and developers, project managers, and support staff are dedicated to providing professional, timely, and responsive service. DuraFuse Frames products provide economic seismic protection and industry-leading resilience that are easy to incorporate, fast to install, and commercially competitive. Multiple Technical Bulletins have been published to provide additional details, value analyses, and cost benefits of incorporating DuraFuse Frames products. Unique benefits and features include: • Elimination of typical continuity plates and doubler plates • Reduction of cover plate thickness • Reduction of seismic beam bracing (kickers) • Fewer parts and less fit-up in fabrication process

801-727-4060 | contact@durafuseframes.com | www.durafuseframes.com STRUCTURAL ENGINEERING Resource Guide 2020 SS-67

ANCHORS Adhesives Technology Corporation

H&B Powered by MiTek

Simpson Strong-Tie

Phone: 754-399-1057 Email: atcinfo@atcepoxy.com Web: www.atcepoxy.com Product: ULTRABOND® Anchoring and Doweling Adhesives Description: Now offering four IBC compliant anchoring adhesives. Along with HS-1CC, the world’s strongest anchoring epoxy, we offer new EPX-3CC, a high-performance epoxy for high-volume applications, and new HYB-2CC, the hybrid that cures fast in hot and cold temperatures. ACRYL-8CC provides fast cure and a very broad application temperature range.

Phone: 800-645-0616 Email: tomw@h-b.com Web: h-b.com Product: Thermal Anchor Description: Brick veneer support system reduces thermal bridging in shelf angles. Features job-specific engineering to move the shelf angle away from the wall allowing for continuous insulation behind the shelf angle. 2-SEAL™ Thermal Wingnut Anchor uses a steel reinforced, UL94-rated wing to create a thermal break at the insulation.

Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com 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 bills, and concrete restoration products for concrete and masonry.

ASDIP Structural Software

IES, Inc.

Phone: 407-284-9202 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP STEEL Description: An advanced software for quick and efficient design of steel members, base plates, anchor rods, and shear lugs per the latest ACI anchorage provisions. See immediate graphical results, and condensed or detailed reports with exposed formulas and code references. Save design time and let ASDIP handle the math complexity.

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

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.

DEWALT Anchors & Fasteners

PROSOCO

Phone: 800-524-3244 Email: melanie.rodriguez@sbdinc.com Web: www.anchors.dewalt.com Product: DEWALT Anchor and Fastening Systems Description: Productivity enhancing, reliable, and code approved. Dust X+™ is an ICC-ES approved system combining DEWALT dust extractors, rotary hammers, and hollow drill bits for installation of adhesive and mechanical anchors. Premium epoxy Pure 110+ and hybrid AC200+. Anchor installation systems supported by DDA™, a no fee, in-house engineered software app.

DuraFuse Frames

RISA

Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: RISAConnection Description: The cutting edge of next-generation connection design software features full 3-D visualization and expandable reports for every limit state. The latest release, v11, includes integration with Hilti Profis for anchorage design, support for column cap plate moment connections, and updated HSS tube connection design according to the Canadian steel code.

ENERCALC, Inc.

ENERCALC

Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: Structural Engineering Library/ ENERCALC SE Cloud/RetainPro Description: Design of anchors and anchor bolts typically requires a thorough development of applied loads and may require analysis of full structures or connected components. Structural Engineering Library can assist in determining those loads and performing those analyses through its Loads & Forces modules and its many analysis and design modules. SS-68 STRUCTUREmagazine

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2020

Trimble Phone: 770-715-3976 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Tekla Tedds Description: Automating your everyday 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 www.tekla.com/us/products/tekla-tedds. 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.

Wej-It High-Performance Anchors 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.

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ADHESIVES TECHNOLOGY CORP.

U.S. and California Regulations Drive the Evolution of Anchoring Adhesives

Until recently, anchoring adhesives used in transportation infrastructure have been approved at the discretion of state departments of transportation, while those used in vertical construction were subject to compliance with the International Code Council’s International Building Code (IBC) guidelines. Changes in Federal regulation have now substantially altered the approvals landscape for infrastructure projects. ATC has significantly evolved its adhesive anchoring products in compliance with the new regulatory landscape and offers a full product line to serve the needs of companies building and repairing the country’s vital roadways, bridges, and tunnels.

A Game-Changing FHWA Advisory

Presidential Domestic Content Order In January 2019, an executive order directed government agencies and departments to encourage recipients of federal project dollars to use products made in the United States for every contract, subcontract, purchase order, or sub-award. The order covered many products, including industrial adhesives, which must have 50% or more U.S. content for related projects to qualify for federal funding.

California Weighs In On April 20 of this year, California, the largest recipient of federal construction funds, officially modified the California Department of Transportation (Caltrans) Authorized Materials List to include only products that are IBC compliant. Because of its size and influence, California is often a bellwether of changes to come in the construction industry, and other states are expected to follow its example in the coming months and years. ATC is proud that its ULTRABOND® HS-1CC anchoring and doweling epoxy was the first product on Caltrans’ new materials list to be IBC compliant in both bulk and cartridge packaging. With the more recent approval of new ULTRABOND® HYB-2CC, ATC became the only manufacturer to be listed by Caltrans with both an epoxy and a non-epoxy hybrid approved for all threaded rod and rebar diameters. These products are just a few of the recent developments at ATC, a company that has cultivated a reputation for formulating advanced anchoring adhesives and is considered by many to be the country’s #1 structural adhesives specialist. By focusing on adhesives, ATC has put itself at the forefront of this rapidly evolving sector.

Introducing the Big 4 ATC now offers four IBC compliant anchoring adhesives among a growing list of state DOT approvals. ATC maintains an easyto-use list of DOT approvals sortable by product and state at www.atcepoxy.com/dot-approvals. ULTRABOND® HS-1CC, the world’s strongest 1:1 mix ratio anchoring and doweling epoxy for cracked and uncracked concrete, and the first code-compliant formula available in both cartridge and bulk. Made in USA. ICC-ES approval report ESR-4094 NEW ULTRABOND® HYB-2CC, a high-speed, high-strength hybrid anchoring adhesive that can be applied in temperatures down to 23 °F and is also qualified for post-installed rebar connections. ICC-ES approval report ESR-4535 NEW ULTRABOND® EPX-3CC, the best high-performance and value-optimized adhesive for high-volume anchoring and doweling applications. Made in USA. ICC-ES approval report ESR-4533 FAST CURE ULTRABOND® ACRYL-8CC provides a full cure rate of 45 minutes at 70 °F, and an extended in-service temperature range of 14 °F to 248 °F. ICC-ES approval report ESR-4249 These four products are just part of ATC’s full line of advanced ULTRABOND® anchoring and doweling adhesives, which is complemented by a full line of CRACKBOND® concrete repair and restoration products.

ADVERTORIAL

The Federal Highway Administration issued a technical advisory in January 2018, establishing new guidelines for the installation and inspection of adhesive anchors under sustained loads. These guidelines bring a new national requirement to the use of postinstalled adhesive anchors in transportation infrastructure and now mandate states to comply, or risk losing federal funding on noncompliant projects. Henceforth, anchors used in federally funded infrastructure projects must qualify under the same standards as adhesives specified in accordance with the IBC.

About ATC Founded in 1978, ATC has a proud heritage of research, development, and manufacture of advanced concrete-related construction materials. They are a founding member of the Concrete and Masonry Anchor Manufacturer’s Association (CAMA), offer NCSEA accredited coursework in anchor design accompanied by free anchor design software (Pro Anchor Design), and provide technical training and support to engineers and contractors through their network of field representatives. ATC is a subsidiary of Meridian Adhesives Group which offers a broad array of adhesives for the electronics, flooring, infrastructure, and packaging markets.

754-399-1057 | atcinfo@atcepoxy.com | www.atcepoxy.com STRUCTURAL ENGINEERING Resource Guide 2020 SS-69

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NEW MILLENNIUM BUILDING SYSTEMS

Overcome the Hidden Costs of RFIs

are finding early collaboration and cooperation can mitigate RFIs.

Tainted reputations: Developers and owners have reasonable expectations about their investment and, when they are not met, everyone suffers. If a drawn-out RFI process causes project delays or cost overruns, reputations are damaged. Similarly, delayed RFI responses, inaccurate answers, or unanswered RFIs tarnish the image of the responsible companies.

Your Roadmap Forward A new three-part, in-depth RFI guide provides you the blueprint for success. It features advice from experienced industry specialists, case studies illustrating how to deal with RFIs successfully, and strategies and actions to avoid and mitigate RFIs. Get the free guide at newmill.com/RFIguide.

260-969-3500 | www.newmill.com SS-70 STRUCTUREmagazine

ADVERTORIAL

t is time to fix the problem of incomplete structural drawings. No one likes confusion or misunderstanding or ambiguity. In the construction industry especially, these things lead to damaging results: Project delays. Cost overruns. Tainted reputations. These are the project risks associated with incomplete structural drawings and the related request for information (RFI) process. RFIs are nothing new to the construction industry. Arising out of incomplete or inaccurate structural drawings, they have been a necessary and important part of building design and construction for decades. That said, RFIs appear to be The risks associated with the request-for-information process include project delays and increasing in frequency while decreasing in effectiveness. blown budgets, among others. There is a better way forward that avoids these pitfalls. Navigant Construction Forum researched projects that began between 2001 and 2012 in their paper, Impact & Control of RFIs on Uncover the Solutions Construction Projects. In the 1,362 projects studied, 1.1 million RFIs were submitted for an average of 796 per project. After removing the The problem of incomplete drawings and RFIs is not going away least costly and most costly outliers, the average cost of each RFI was on its own. Progressive firms are pursuing better ways to deal determined to be about $1,080, or $859,680 per project. with them and a better way forward. What is their approach? A The cost impacts are just the beginning. Instead of solving prob- revamped process for project delivery, starting with early design lems as intended, the RFI process has increasingly created other, collaboration with suppliers’ engineering teams. unintended problems. Know your options: In A Guideline Addressing Coordination and Project delays: Resolving an RFI often ensnares representatives Completeness of Structural Construction Documents, the Council of multiple trades working on a project. Navigant found it takes of American Structural Engineers (CASE) calls for coordination an average of eight days before an RFI receives its first response. between the structural engineer of record and suppliers’ engineers Median response time is 12 days. The RFI back-and-forth con- for successful specification and structural drawings. This upfront tributes to extended project timelines, delaying occupancy and coordination pays off with more accurate drawings and fewer resulting in a loss of residential or business revenue. RFIs, especially as project complexity escalates. Change orders: As the RFI process drags on, it often drains a Listen to the experts: STRUCTURE magazine has long been project’s contingency funds. Belated structural design and engi- an advocate for a more collaborative process, as stated in March neering analyses result in the addition, modification, or removal 2010: “Design professionals and engineers should encourage of structural materials, with resulting change orders becoming the questions and should be available to lend their expertise as norm for material costs and fieldwork. As Navigant explains: “It is needed to offer guidance on a project.” Engineers specializing now common to see contractors submitting an exceptional number in long-span floor systems, for instance, can suggest the proper of RFIs and then presenting unapproved change orders which they system needed to achieve optimal spans, support loads efficiently, claim are the result of the design professional’s response to RFIs.” and create shallow floor depths to maximize interior spaces. Depending on project size, actualized material savings can range from 3 percent to 20 percent, but most commonly between 5 percent and 10 percent. Put BIM to work: In a July 2016 survey of the impact of BIM use among architects, engineers, and contractors, Dodge Data & Analytics found that 70 percent of those firms reported at least a 5 percent decrease in requests for information during construction. Using BIM, points of discussion are given immediate clarity in the design phase, removing guesswork and their Want to wipe out RFI risks? Progressive firms are taking on the challenge and related costs.

STEEL Advant Steel

CoreBrace

New Millennium Building Systems

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.

Phone: 801-280-0701 Email: brandt.saxey@corebrace.com Web: www.corebrace.com Product: CoreBrace Buckling Restrained Braces Description: A sustainable and cost-effective solution to improve seismic performance of structures. This highly ductile system has been used in thousands of projects worldwide for earthquake risk mitigation. CoreBrace’s expert staff works closely with engineers and the entire design and construction team to meet their requirements.

Phone: 260-969-3582 Email: rich.madden@newmill.com Web: www.newmill.com Product: Steel Joists and Deck Description: 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. We are the leading provider of special profile steel joists for unique rooflines. And we produce architectural steel deck for highly aesthetic, exposed ceiling applications.

DuraFuse Frames

Qnect LLC

Phone: 413-387-4375 Email: christian@qnect.com Web: www.qnect.com Product: Qnect Description: An intelligent, cloud-based connection service giving fabricators, detailers, and engineers fast and flexible connections with significant cost and schedule savings. Connect steel buildings in minutes, with minimal training. Prevent schedule drift, utilize one-station fabrication, and reduce connection material, time to fabricate and erect.

ENERCALC, Inc.

RISA

Aegis Metal Framing Phone: 314-851-2200 Email: answer@mii.com Web: www.aegismetalframing.com Product: Ultra-Span® CFS/Steel Engine® Description: Our design software does the necessary calculations to determine sizes, shapes, loads, webs, chords, and all the factors involved in your project – bringing ease of fabrication and construction. Sign up for a free account to have access to our specification creator and detail library.

Applied Science International, LLC Phone: 919-645-4090 Email: support@appliedscienceint.com Web: www.appliedscienceint.com Product: SteelSmart Framer Description: Provides designers with a powerful new tool to better design, estimate, and communicate light steel framing on projects using Autodesk® Revit® Building Information Modeling (BIM) software. Product: SteelSmart System Description: Provides structural engineers with a structural design software tool engineered for optimal design and detailing of light steel framing studs, joists, shear walls, and connectors.

Anchors

ENERCALC

Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: Structural Engineering Library/ ENERCALC SE Cloud/RetainPro Description: Save hours on every steel design with ENERCALC’s Structural Engineering Library. Beams, columns, two dimensional frames, force distribution in bolt groups, and more. The clear, simple user interface make it fast and easy to setup, confirm, and “what-if ” your designs. Member optimization improves your efficiency and saves time!

ASDIP Structural Software

GIZA Steel

Phone: 407-284-9202 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP STEEL Description: An advanced software for quick and efficient design of steel beams, composite beams, columns, base plates, anchor rods, shear lugs, and connections. See immediate graphical results and condensed or detailed reports with exposed formulas and code references. Save design time and let ASDIP handle the math complexity.

Phone: 314-656-4615 Email: sales@gizasteel.com Web: www.gizasteel.com Product: GIZA Description: A software tool to help design structural steel connections. The GIZA library covers 415 different connection configurations in the Shear, Moment, Vertical Brace, and Horizontal Brace groups. GIZA works as a stand-alone tool or can integrate with Tekla Structural Designer. Go to our website to try our FREE 15-day trial.

CAST CONNEX Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Innovative Connection Solutions Description: The leading supplier of cast steel components for use in the design and construction of building and bridge structures. Universal Pin Connectors™, Architectural Tapers™, and Diablo Bolted Splices™ bring off-the-shelf simplicity and reliability to AESS, while custom designed components enable unparalleled opportunity for creativity in design.

Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: RISA-3D and RISAFloor Description: Now includes the ability to design coldformed steel wall panels. Easily specify the sheathing, studs, and design methodology in order to analyze and optimize CFS walls for both gravity and lateral loadings, making RISA the place for the design of multi-story buildings utilizing cold-formed steel.

Strongwell 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, cost saving 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.

Trimble IES, Inc. Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis Description: Helps engineers avoid “The Black Box,” with steel design reports to help you understand your project’s behavior. Detailed checks, with intermediate values and code references, minimize your chances of error and maximize productivity. That’s only what we think: customers say, “Easy to Use” and “Excellent Value.”

Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Light Steel Framing Studs and Connectors Description: Create detailed, constructible 3-D models of any steel structure from industrial and commercial buildings to stadiums and high-rise buildings. Integrates with industry-leading construction management and analysis and design software, as well as most of major advanced production or resource planning and machine automation systems for structural steel. Drawings can be extracted from the updated model.

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STRONGWELL

trongwell is the recognized world leader in the manufacture of fiber-reinforced polymer (FRP) composites utilizing the pultrusion process. Strongwell manufactures hundreds of FRP structural shapes, plate, fiberglass gratings, FRP handrails and guardrails, and much more, all made in the USA in one of Strongwell’s three U.S. ISO 9001 certified facilities.

Pultrusion Pultrusion is the manufacturing process where raw materials of a liquid thermoset resin mixture (containing resin, fillers, and specialized additives) and flexible textile reinforcing fibers are pulled (hence the name “PULtrusion”) through a heated steel forming die using a continuous pulling device. This results in constant cross-section shapes that are exceptionally strong (especially in the lengthwise direction), corrosion-resistant, lightweight, RF transparent, and virtually maintenance-free.

EXTREN® Product Line EXTREN is the registered trade name for the proprietary line of standard pultruded fiberglass structural shapes and plate produced by Strongwell. The EXTREN line consists of more than 100 different fiberglass shapes, each with a very specific, proprietary composite design.

Designing with FRP

Temperature and Corrosive Chemicals The coefficient of thermal expansion of EXTREN is slightly less than steel in the 0° direction and significantly less than aluminum. In lower temperatures, EXTREN actually becomes stronger. Independent testing confirms that EXTREN maintains its mechanical and physical properties for temperatures down to at least -60° F. At higher temperatures, engineering and/or resin considerations should be made when the design temperature goes above 150° F. FRP offers resistance to a broad range of chemicals and harsh environments. Strongwell offers a full Corrosion Resistance Guide to ensure the performance of its products in some of the toughest conditions.

Fabricators utilize traditional carpenter’s tools equipped with a carbide- or diamond-grit blade for cutting operations, and carbide tipped drill bits for drilling operations. FRP can be fabricated in many ways, including sawing, drilling, shearing, punching, routing, threading, tapping, grinding, and sanding. EXTREN can be fastened in multiple ways. Surface preparation and the use of fastening devices are encouraged for adhesion and connection. Common attachment methods include screwing, bolting, riveting, and adhesive fastening, or a combination.

Installation Costs Total installed costs are a big way EXTREN structures stand out versus other materials. Composites significantly decrease worksite costs by reducing factors such as involvement of specialty trades, additional lifting equipment, transportation, and additional permitting costs. Installed costs for FRP structures are generally up to 15% less than carbon steel, 30% less than galvanized steel, and 50% less than stainless steel.

Resin Choices EXTREN Series 500 and 525 are both premium polyester resin-based products. Both contain UV inhibitors and excellent corrosion resistance properties. Series 525 offers improved fire performance. EXTREN Series 600 and 625 are both premium vinyl ester resin-based products. Both contain UV inhibitors and are designed for more intensive corrosive environments and higher temperature applications. Series 625 offers improved fire performance. The resin makeup of EXTREN and Strongwell’s other FRP products can also be modified to meet specific customer requirements.

Strongwell FRP Strongwell’s website is an invaluable resource for designers and engineers, as it offers design guides, specifications, CAD blocks, case studies, corrosion resistance information, brochures, fabrication worksheets, and much more. Visit the website to learn more about EXTREN, and the complete product lines manufactured by Strongwell.

276-645-8000 | info@strongwell.com | www.strongwell.com SS-72 STRUCTUREmagazine

ADVERTORIAL

Strongwell offers a complete Design Manual for working with EXTREN structural shapes and plate, as well as Strongwell’s other structural FRP products. This manual is available from Strongwell’s website.

FRP Structural Shapes and Connections

CONCRETE American Concrete Institute

IES, Inc.

S-FRAME Software

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 premiere, 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: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: ConcreteBending Description: IES offers practical software tools for concrete designers. Whether you are analyzing frames, slabs, walls, or foundations, IES has economical solutions. Reports include code checks, intermediate values, and specification references to help explain the structural behavior as well as your design choices. Proven by engineers for over 25 years.

Phone: 604-273-7737 Email: info@s-frame.com Web: s-frame.com Product: S-CONCRETE Multistory Designer Description: Shave days off concrete design and detailing projects. Quickly read in all concrete data from an ETABS® model, run a concrete performance assessment to identify problem areas, design and optimize, and generate a detailed engineering report containing all concrete design results.

ASDIP Structural Software

Larsen Products Corp.

Simpson Strong-Tie®

Phone: 407-284-9202 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP CONCRETE Description: An advanced software for quick and efficient design of continuous beams, biaxial columns, and concrete or masonry walls. See immediate graphical results, and condensed or detailed reports with exposed formulas and code references. Save design time and let ASDIP handle the math complexity.

Concrete Masonry Association of CA & NV

Losch Software Ltd

Phone: 800-925-5099 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: 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).

ENERCALC, Inc.

ENERCALC Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: Structural Engineering Library/ ENERCALC SE Cloud/RetainPro Description: Structural Engineering Library (SEL) quickly completes calculations for the design of footings, columns, beams, pedestals, shear walls, etc. Powerful new quad meshing system in ENERCALC 3D simplifies complex mesh building tasks. SEL Build 20 subscriptions include RetainPro retaining wall modules, which provide detailed concrete earth retention design / calculation tools.

Geopier Foundation Company Phone: 704-439-1790 Email: iinfo@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 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.

Anchors

Phone: 323-592-3299 Email: loschinfo@gmail.com Web: www.LoschSoft.com Product: LECPres Description: Analyze prestressed and/or mild reinforced simple span or cantilevered concrete beams and slabs. Handling analysis is also included. A 30day trial version is available. Product: LECWall Description: Theindustr y standard for precast concrete sandwich wall design handles multi-story columns as well. LECWall can analyze prestressed and/or mild reinforced wall panels with zero to 100 percent composite action. Flat, hollow-core, and stemmed configurations are supported. Complete handling analysis is also included.

POSTEN Engineering Systems Phone: 510-275-4750 Email: sales@postensoft.com Web: www.postensoft.com Product: POSTEN Description: Efficient and comprehensive posttensioned concrete software; 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.

RedBuilt Phone: 866-859-6757 Email: info@redbuilt.com Web: www.redbuilt.com Product: RedForm™ LVL and RedForm™ I-joists Description: ThecharacteristicsofR edForm LVL and RedForm I-joists make them ideal for working in concrete forming applications. Thesepr oducts are also reliably engineered to withstand multiple reuses. Visit the RedForm website under Products/ConcreteForming-Shoring for more information.

StructurePoint Phone: 847-966-4357 Email: software@structurepoint.org Web: www.structurepoint.org Product: spMats Description: Widely used for analysis, design, and investigation of concrete mat foundations, footings, and slabs on grade. spMats is equipped with the American (ACI 318-14) and Canadian (CSA A23.3-14) concrete codes. spMats is utilized by engineers worldwide to optimize complicated foundation design and improve analysis of soil structure interaction. Product: spLearn Description: StructurePoint licensed structural engineers have decades of experience with reinforced concrete design. As such, we have multiple resources on our website for the structural engineer’s benefit, including: detailed design examples, technical articles, video tutorials, webinars, and more. Visit our website to learn more and request a webinar or consultation.

Zenith Engineers Phone: 408-439-3283 Email: david@zenithengineers.com Web: zenithengineers.com Product: Seismic Retrofitting Service Description: Zenith Engineers has designed and engineered over 600+ seismic retrofits across the west coast ranging from non-ductile concrete, un-reinforced masonry, and soft story buildings.

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

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CAST CONNEX

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 pinned connections were developed through an iterative design process informed by full-scale destructive testing, 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.

Elegance in Design

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416-806-3521 | info@castconnex.com | www.castconnex.com SS-74 STRUCTUREmagazine

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together (ART+UPC), lending a slenderer overall appearance to structural elements fitted with the connectors. Diablo™ Bolted Splices (DBS) are cast steel fittings that enable unobtrusive field bolted splices in round HSS members. The fittings are designed such that the bolted connection is inboard of the outer diameter of the HSS. Splices made with DBSs can be sheathed in thin-gauge plate to conceal the splice completely or can be left uncovered to provide a more technical aesthetic. Timber End Connectors™ (TEC) are 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. High Strength Connectors™ (HSC) and Cast Bolted Brackets (CBB) are capacity designed connectors for use in Special and Ordinary Concentrically Braced Frames and Special and Ordinary Moment Frames, respectively. Both connector types eliminate the need for field welding, thereby reducing the total installed cost of the structural steel frame while improving quality. High Strength Connectors are also commonly used in AESS, as their use results in smaller gusset plates and because the connectors’ curvaceous appearance is often preferred over slotted-HSS connections that require net section reinforcement. Scorpion™ Yielding Connectors (SYC) are modular, replaceable, standardized hysteretic fuses that provide enhanced ductility and improved performance in the retrofit of seismically deficient structures or for use in the Seismic Force Resisting System of new structures. The system exhibits a full, symmetric hysteresis characterized by an increase in stiffness at deformations above design level. In multistory structures, this post-yield stiffening can decrease the likelihood of the formation of a soft story and results in a more uniform distribution of inelastic demand over the building’s height when compared to other yielding devises that exhibit a low post-yield stiffness. High Integrity Blocks® (HIB) are ultra-heavy weldable solid steel components that exhibit a minimum 50 ksi yield strength and elevated notch toughness in all three directions of loading and through the full cross-section of the section. HIBs are ideal for use at the Disturbed Regions of Connections where lamellar defects in conventional rolled plate may compromise quality and strength of the connection or where the lamination of multiple steel plates to build up a section is not advisable due to the need to transmit forces in multiple directions or orthogonal to the laminations. HIBs are supplied fully engineered and detailed by CAST CONNEX to fit project-specific geometries and loading. Custom Cast Steel Components are designed to address projectspecific 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 related to custom casting supply typically include industrial design and 3-D modeling, engineering including finite element stress analysis, casting detailing, and manufacturing, including oversight.

BRIDGES American Wood Council

Hexagon

Standards Design Group, Inc

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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.

Phone: 800-366-5585 Email: info@standardsdesign.com Web: www.standardsdesign.com Product: Advanced Window Glass Design Description: Performs all required calculations to design window glass according to ASTM E 1300-16 and ASTM E 1300-09, ASTM E 1300-02/03/04, ASTM E 1300-98/00, and ASTM E 1300-94. Includes computations for the E 1300-16 Analytical Method. Facilitates calculations for three-ply laminates. Most comprehensive analysis and design package for glass to date.

CAST CONNEX

IES, Inc.

Phone: 416-806-3521 Email: info@castconnex.com Web: www.castconnex.com Product: Cast Steel Nodes and Connectors Description: The use of cast steel nodes and connectors 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.

Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis Description: Helps engineers bridge the gap between theory and practice. Get analysis and design results. Engineers praise VisualAnalysis as “easy to learn” and an “excellent value.” Try it free on your next project and get answers you need to succeed. Indeed. Proceed to the website.

Cintec Reinforcement Systems Ltd

Anchors

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.

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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, complete with moving load generation (AASHTO library), influence lines, cable form-finding, parametric modeling, and multimaterial design considerations. Powerful yet user friendly FEA software; seamless in the design and analysis of pedestrian and highway cable-stayed, suspension, arch, and beam bridge structures.

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!

Phone: 646-732-7774 Email: info@lusas.com Web: www.lusas.com Product: LUSAS Bridge Description: Use to analyse, 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.

STRUCTUREPOINT Phone: 847-966-4357 Email: software@structurepoint.org Web: www.structurepoint.org Product: spLearn Description: As the former software development team of the Portland Cement Association, StructurePoint is uniquely positioned at the heart of the cement industry. Our licensed structural engineers have decades of experience with reinforced concrete design. For assistance, structural engineers will benefit from the multiple resources on our website. Product: spColumn Description: Visit our Technical Article webpage to see Bridge Pier Design Capacity Evolution where two interaction diagrams using spColumn software are superimposed to compare and contrast capacity before and after the introduction of major code changes at the beginning of the century. This will help bridge designers make money-saving decisions.

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

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STRUCTURAL ENGINEERING Resource Guide 2020 SS-75

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STRUCTURE OCTOBER 2020

Bonus Content

structural ANALYSIS Numerical Analysis Case Study Unreinforced CMU Wall with Diagonal Step Crack By Vitaly B. Feygin, P.E., and Christian P. Gunn

odern CMU construction almost always requires the installation of vertical reinforcement in the grouted cells of the CMU.

However, addressing structural issues associated with unreinforced CMU construction prevalent prior to the 1990s can be daunting. In the author’s experience, today’s engineers do not know how to deal with, or adequately investigate, diagonal cracks in unreinforced CMU

Figure 1. Wall 8-inch strip load diagram.

walls. The discovery of such cracks quite frequently leads to the unjustified conclusion that this type of distress affects the capacity of the wall to resist lateral wind pressure loads. This article investigates the lateral capacity of an ungrouted and unreinforced CMU wall affected by a diagonal step (stair step) crack. The analysis demonstrates why a diagonal corner crack should not be qualified as structural damage.

Known Data A 54-foot by 24-foot structure with 8-inch-thick ungrouted CMU walls is located in an area with wind exposure “B” and an ultimate wind speed of 140 mph. The wall is 8 feet 8 inches high. The roof, which overhangs the wall by 2 feet, is sloped 3:12 and is supported by roof trusses spaced 2 feet apart. The roof dead load is 10 psf and wall self-weight is 42 psf (normal weight of an ungrouted CMU wall). A crack runs diagonally from the top of the wall at the corner down to the base. The analysis is per ASCE 7-10, Minimum Design Loads for Buildings and Other Structures, using Components and Cladding pressures.

Solution Considering the slope of the crack, the horizontal projection of the crack is equal to the wall height of 8.67 feet. The 2.4-foot-wide High-Pressure Zone at the corner is reinforced. Therefore, only the portion of the crack in the unreinforced Normal-Pressure Zone is considered here. Wind pressure loads are based on wind tributary area for components and cladding: • Roof Ultimate wind pressure: p = -35.3 psf • Additional wind pressure [2-foot overhang]: p = -65.7 psf • Wall Ultimate wind pressure: p = -36.2 psf • Critical Wind Load Combination, LC 7, ASCE 7-10, Chapter 2.4 (ASD) LC 7 = 0.6DL + 0.6W Roof load at roof truss to wall attachment: Ax top = -443 lbs tension per 2 feet of wall length, uplift at top of the wall The most critical section is in the middle of the wall, where the wind moment is the largest.

Figure 2. CMU block geometry.

For the load diagram, see Figure 1. Axial load at the middle of the wall (per 8 inches of vertical strip of wall) is: Ax h2 = (-443×0.67 + 0.6×42 psf × 0.67×8.66) 2 = -75.3 lbs tension force at wall mid height Pv = Ax top = 443 lbs/every 2 feet pw = 36.2 psf (Ultimate wind pressure) 2 MW = 0.6×36.2×0.67×8.66 8 = 136 lb-ft per 8-inch horizontal crack or 1,637 lb-in per 8 inches • Tension Stress: Uplift versus Gravity (Figure 2) Note: stresses in the wall are calculated for an 8-inch vertical strip of the wall. -75.3 = -2.60 psi -fa = (2×1.25×8+5.12×(1×1.25×0.5×1)) • Tensile stress due to flexure caused by wind, considering un-cracked section: -1,637 -fa = = -25.70 psi 8×6.375×1.25 • Total tension stress, assuming uncracked section: -fa = -(25.70+2.60) = -28.30 psi • Modulus of rupture, fr , for masonry elements subjected to out-of-plane bending shall be in accordance with the values in Table 9.1.9.2 of ACI 530-13, Building Code Requirements and Specification for Masonry Structures and Companion Commentaries, for Portland cement type N, normal to bed joints for ungrouted CMU: fr = 64 psi This value incorporates a 33% increase in the stress allowed for wind load. This value applies only to the flexural tensile stress developed between the masonry units, mortar, and grout. ASCE 7-10, Chapter 2.4.1, Exceptions, states: “Increase in allowable stress shall not be used OCTOBER 2020 BONUS CONTENT

Figure 3. Effective resistance width of slab for distributable concentrated load.

with the loads or load combinations given in this standard unless it can be demonstrated that such an increase is justified by structural behavior caused by rate or duration of load.” Unmodified Modulus of Rupture becomes: 64 psi fr = = 48 psi 1.33 The analysis must also include redistributed stresses from the cracked section (8-inch-wide horizontal crack) along the uncracked portions of the Effective Resisting Width of the wall panel. Force redistribution theory (Figure 3), based on spring stiffness along the span of the wide plate, was first introduced for the analysis of flat plates with distributable and non-distributable loads by S. Timoshenko in the Theory of Plates and Shells. It was first successfully utilized for the design of Hollow Core Slabs (PCI Manual for Design of Hollow Core Slabs). The same analogy can be utilized for the analysis of CMU walls. The wide plate is viewed as a trampoline having different spring values along the span. The spring is defined by k = δP where, P = 1 kip – a unit force placed anywhere along the span of the 1-foot-wide strip of the plate δ – is a deflection of the 1-foot plate strip under the unit load Since a stiffer spring along the plate span narrows the “effective resistance width,” a softer spring will widen the zone of the distributable load redistribution. Figure 3 shows the boundaries of the distributable width utilized for the distribution of the load applied to the strip with a plastic hinge (a short horizontal crack in the wall strip). However, before confirming the redistribution force model, check the clamping action from the vertical cantilever action created by the shaded area of the wall above the diagonal crack (shown by the magenta line in Figure 3).

STRUCTURE magazine

Figure 4. Partial plastic-hinge resistance.

Limit State I – Cantilever action of the wall above the crack (Figure 3): The shaded portion of the wall is acting as a vertical cantilever with clamping force investigated at locations 3 and 4. • Location 3 is 5 blocks high (5×8 = 40 inches tall) Uplift moment, Mup3 = 443×(24) = 10,632 lb-in Downward moment from self-weight of the CMU above the crack Msw3 = 39,765 lb-in The resisting downward moment, Msw3 = 39,765 lb-in > Uplift moment of Mup3 = 10,632 lb-in • Location 4 is 8 blocks high (8×8 = 64 inches tall) Uplift moment, Mup4 = 443×(48+24) = 31,896 lb-in Downward moment from self-weight of the CMU above the crack Msw4 = 173,525 lb-in The resisting downward moment, Msw4 = 173,525 lb-in > Uplift moment of Mup4 = 31,896 lb-in

Limit State II – The shear stress at critical locations: Allowable shear stress of the CMU block (ACI 530-13, 8.2.6.2) is Fv = 37 psi fV2 = (433−1.33×0.67×42) = 10.14 psi < Fv (2×1.25×16) fV3 = (2×443−3.33×0.67×42) = 7.92 psi < Fv (2×1.25×40) The uplift force from the wind acting on the roof does not affect the assumption of effective resistance width shown in Figure 3.

Clamping action, created by a gravity load of the portion of the wall above the diagonal crack at the two critical locations, allows for the distribution of the distributable load within the effective distributable width.

Limit State III – Effect of the partial limited hinge created by a hairline diagonal step crack: The out-of-plan flexure resistance mechanism activated within the hairline crack is shown in Figure 4. If the cantilever above the crack is not sheared by torsional force induced by flexure, the horizontal crack forms a partial plastic hinge restrained by the wall gravity and CMU shell shear capacity. Partial Plastic-Hinge capacity of the cracked CMU At wall mid-height: M ph@ H2 = 37 psi ×48×1.25+0.5×42 psf × 8.67 × (7.625−1.25) 2 = 15,599 lb-in/ft width At ¾ wall-height: M ph@ 3 H = 37 psi ×24×1.25+0.5×42 psf × 8.67 × (7.625−1.25) 4 4 = 7,799 lb-in/ft width Note: Contribution from the roof DL was conservatively neglected. The allowable flexural capacity of the unconfined wall under simple beam flexure:

(

)

(

)

Mall = fr ×1.25×12×(7.625−1.25) = 48×1.25×12×6.375 = 4,590 lb-in/ft (based on mortar rupture) Mall = ft ×1.25×12×(7.625−1.25) = 25×1.25×12×6.375 = 2,390 lb-in/ft (based on allowable tensile stress of hollow ungrouted CMU with type ‘N’ mortar cement) Both partial hinges exceed the flexural capacity of the unconfined unreinforced CMU wall.

It was analytically proven that a hairline crack forming a partial plastic hinge in the unreinforced wall with a diagonal crack does not degrade the wall’s flexural capacity. Taking into consideration the statement above, additional distributable stress is taken by the uncracked portion of the effective resistance width of the CMU wall (Figure 3). Effective Resisting width at mid-height of the wall is equal to: 0.5H = 0.5×8.66 = 4.33 feet or 52 inches Additional distributable stress ∆fa = -28.30×8 = -5.14 psi 52−8 Where 27.84 psi is total tension stress assuming uncracked section. Adding that additional distributable stress to the stress in the uncracked section of the effective resistance width results in: fa distr = -(28.30+5.14) = 33.44 psi < fr = 48 psi Although analysis for three-quarter wall-height could be provided, net tensile stress at that location is smaller than at the wall mid-height. Therefore, it was proven that the adjacent uncracked cells within the effective resisting width with a diagonal crack could effectively resist the wind load without endangering the stability of the building.

Conclusion Numerical analysis proves that a hairline diagonal crack in the ungrouted CMU walls, in the absence of severe foundation damage, should be categorized as “local distress” rather than “structural damage”.■ Vitaly B. Feygin is a Principal Structural and Geotechnical Engineer, Florida Geotechnical Engineering, Inc. Christian P. Gunn is an Assistant Director of Engineering, Florida Geotechnical Engineering Inc.

OCTOBER 2020 BONUS CONTENT

2020 STRUCTURAL ENGINEERING SUMMIT November 4–6, 2020...& Beyond

Designed by Structural Engineers for Practicing Structural Engineers The 2020 Structural Engineering Virtual Summit is a solution designed for you. It will include three days of live presentations, three days of Bonus Content Presentations with live speaker interaction, and twomonths of access to our virtual trade show. • Access to Our Virtual Trade Show • 26 Hours of Available Education • Unique Networking Opportunities & Virtual Lounges • Captivating Keynote Addresses by Expert Speakers

WEDNESDAY, NOVEMBER 4 24 Hours/Day 8:00-3:00 8:00-8:15 8:15-10:00

Trade Show Open Interactive Lounges Open NCSEA President’s Address Keynote: What’s Happening with the Future of the AEC Industry This session, moderated by James Malley, Degenkolb Engineers, will focus on the trends, technologies, and innovations that will shape the profession. It will showcase a leading architect–Vibhuti Harris, HKS, Inc.; a contractor– Greg Gidez, Hensel Phelps; and a structural engineer–Glenn Bell, Simpson Gumpertz & Heger (retired), to discuss what the future looks like from their perspective and provide a glimpse into the needs of the industry’s customers.

Concurrent Session | 10:45 - 11:45

Mass Timber – Forest to Frame – Part I: Forest This presentation focuses on managed forests and how calculating carbon pollution and carbon storage can make wood a good design solution.

Concurrent Session | 12:45 - 1:45 Tornado Wind Loads for the Practicing Engineer This session will focus on how tornado loads affect the practicing engineer, including an overview of ASCE 7-22 Tornado and ICC-500 Storm Shelter provisions.

Concurrent Session | 12:45 - 1:45

Ask the Experts: Embodied Carbon and Structural Materials This session is a sit-down with representatives from the steel, concrete, and Serviceability Design for the Practicing Engineer wood industries to discuss how these material industries are responding to This session will provide practical information and design examples to the focus on embodied carbon. evaluate the serviceability performance of buildings against the requirements 2:00-3:00 Networking Event of the IBC and ASCE 7.

Concurrent Session | 10:45 - 11:45

THURSDAY, NOVEMBER 5

24 Hours/Day 8:00-3:00 8:00-8:10 8:10-8:30 8:30-9:30

Trade Show Open Interactive Lounges Open NCSEA Vice President’s Address Awards Presentation Keynote: Leading the Human Way: How to Stop Acting Your Age and Lead a Multi-Generational Workforce This session, led by Matt Havens, will share a unique approach to solving all of your generational issues in the workplace (and at home) by rediscovering the similarities among us and learning to lead the Human Way. He will walk you through the steps to resolve your generational differences and show you that the solutions are not as complicated as they seem.

Concurrent Session | 10:15 - 11:15 How Do We Progress Towards Racial Equity in the Structural Engineering Community? This session will highlight common experiences reflected in the SE3 survey data related to race and racial inequities, and will connect the panelists’ experiences in the workplace through conversation with racial diversity, equity, and inclusion experts from the AEC industry.

Concurrent Session | 10:15 - 11:15 Evolving Paradigms in Post-Disaster Safety Assessment: The Structural Engineers’ Role This presentation provides an overview of the FEMA P-2055 publication and focuses on the key conclusions of the document that are applicable to the practicing Structural Engineer.

Concurrent Session | 12:15 - 1:15 Post-Tensioned Concrete Design: Code Requirements The presenter will discuss the current code, and the future relationship of the ACI 318 concrete building code and the ACI/PTI 320 dependent code.

Concurrent Session | 12:15 - 1:15 Community Resilience & Wildfires: The Role of the Structural Engineer This session will overview how fire hazards are assessed, common mitigation methods, and the underlying research that supports those policies. 1:30-2:30 Networking Event

*All Sessions are Listed in Pacific Time*

Learn about the 2020 Structural Engineering Virtual Summit at www.ncsea.com

EVERYONE Can Join us for the Virtual Trade Show! The 2020 Trade Show is open now! ANYONE can access the Exhibit Hall today through November 2. Summit registrants will have expanded access through November 24. Visit www.ncsea.com for the opportunity to visit, learn, and engage. Nucor International Code Council Steel Deck Institute CoreBrace American Concrete Institute International Masonry Institute Peikko USA Steel Joist Institute CRSI ASCE Post-Tensioning Institute Steel Tube Institute DeWalt - Engineered by Powers Keller Atlas Tube RISA Tech, Inc. LNA Solutions Taylor Devices Fabreeka BASF Simpson Strong-Tie Lindapter Trimble Headed Reinforcement Blind Bolt SlipNOT MiTek Hubbell Power Systems Cast Connex 24 Hours/Day 8:00-2:00

Trade Show Open Interactive Lounges Open

FRIDAY, NOVEMBER 6

Concurrent Session | 8:00 - 9:00 An Inside Look at Codes and Standards Development This panel discussion will bring industry leaders together to give a behind-thescenes look at the development of codes and standards.

Concurrent Session | 8:00 - 9:00 Growing an Engineering Firm: Why, How, and When Mark Aden has led DCI’s growth to 13 offices and 350 total staff. Mark will discuss the reasons for growth, organic and M&A growth techniques, costs and financing, and how to define and ensure success.

Concurrent Session | 9:45 - 10:45 Structural Engineering Engagement & Equity: 2020 Survey Results This presentation will focus on the results of the 2020 survey. Attendees will gain an understanding of the challenges facing the profession as well as actionable information and recommended best practices.

Concurrent Session | 11:30 - 12:30 ACSE 7-22 New and Updated Hazards The Structural Engineering Institute of ASCE manages the development of ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. This session will present updates and new developments for the 2022 edition.

Concurrent Session | 9:45 - 10:45

Concurrent Session | 11:30 - 12:30

Performance-Based Design: Where the Profession is Headed As part of the Structural Engineering Institute of ASCE’s vision, this session will present the current state of performance-based design, recent advancements in PBD, and the possible impacts on future standards and building code.

The Evolution of Work Flexibility, Before and After COVID-19 Previous SE3 surveys investigated the demand for various employment benefits, including work flexibility to help achieve work-life balance. This session will review the challenges and adaption in the workplace. 12:45-1:45 Summit Closing

TUESDAY, NOVEMBER 17 8:00-9:00 8 Tips to Avoid the Traps of Unethical Behaviour This session will acquaint the participant with the Canons of, and the application of the Code of Ethics. Tips will be provided to help assess ethical problems and determine when corrective action is required and how to accomplish it. Meet the Newest AISC Standard: AISC 342-20 Seismic Provisions for Evaluation and Retrofit of Existing Structural Steel Buildings This presentation will overview changes and technical developments to AISC 342-20 Seismic Provisions for Evaluation and Retrofit of Existing Structural Steel Building and clarify the relationship to ASCE/SEI 41-17, Chapter 9. 9:45-10:45

Improving the Design of SE’s Subconsultant Agreements Experienced design professional contract lawyers will share key strategies Structural Engineers can use when dealing with the architect prime. 11:30-12:30

BONUS CONTENT SCHEDULE TUESDAY, NOVEMBER 10

TUESDAY, NOVEMBER 24

8:00-9:00

Understanding Changes to the 2021 IEBC Structural Provisions & Frequently Asked Questions This presentation will help practicing structural engineers identify and have an understanding of the most recent changes to the 2021 edition of the IEBC.

8:00-9:00

9:45-10:45

Strategies for Increasing Productivity and Streamlining Workflows This discussion will look at software and concepts that are continuously improving the way the industry operates.

9:45-10:45

11:30-12:30 Workflow Process for Seismic Calculations This session will provide workflow processes for use when preparing structural calculations for seismic design. Calculations and examples will be presented.

11:30-12:30 Mass Timber – Forest to Frame – Part II: Frame This presentation focuses on wood and mass timber products available and the approach to calculating whole-building Life Cycle Assessments (LCA).

Marketing Your SE Firm—Tools for the Structural Engineer at All Levels This discussion will cover why structural engineers at every level should be focused on marketing and the influence they can have on their firm’s brand. 2050 M Street: Designing a Lean Structure to Highlight a Dynamic Façade This session will discuss the structural design approach to 2050 M Street, a new 450,000-sf premier office building in Washington, D.C.

Learn about the 2020 Structural Engineering Virtual Summit at www.ncsea.com