STRUCTURE magazine - March 2018

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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March 2018 Wind/Seismic 2018 Structures Congress Fort Worth, Texas April 19 – 21

Inside: Times Square, New York

LeMessurier Calls on Tekla Structural Designer for Complex Projects Interoperability and Time Saving Tools

Tekla Structural Designer was developed specifically to maximize collaboration with other project parties, including technicians, fabricators and architects. Its unique functionality enables engineers to integrate the physical design model seamlessly with Tekla Structures or Autodesk Revit, and to round-trip without compromising vital design data.

“We’re able to import geometry from Revit, design in Tekla Structural Designer and export that information for import back into Revit. If an architect makes geometry updates or changes a slab edge, we’ll send those changes back into Tekla Structural Designer, rerun the analysis and design, and push updated design information back into Revit.”

Tekla Structural Design at Work: The Hub on Causeway

For over 55 years, LeMessurier has provided structural engineering services to architects, owners, contractors, developers and artists. Led by the example of legendary structural engineer and founder William LeMessurier, LeMessurier provides the expertise for some of the world’s most elegant and sophisticated designs while remaining true to the enduring laws of science and engineering.

Known for pushing the envelope of the latest technologies and even inventing new ones, LeMessurier engineers solutions responsive to their clients’ visions and reflective of their experience.

An early adopter of technology to improve their designs and workflow, LeMessurier put its own talent to work in the eighties to develop a software solution that did not exist commercially at the time. Their early application adopted the concept of Building Information Modeling (BIM) long before it emerged decades later.

While LeMessurier’s proprietary tool had evolved over three decades into a powerhouse of capability, the decision to evaluate commercial structural design tools was predicated on the looming effort required to modernize its software to leverage emerging platforms, support normalized data structure integration and keep up with code changes.

After a lengthy and thorough comparison of commercial tools that would “fill the shoes” and stack up to the company’s proprietary tool, LeMessurier chose Tekla Structural Designer for its rich capabilities that addressed all of their workflow needs. According to Derek Barnes, Associate at LeMessurier, ” Tekla Structural Designer offered the most features and the best integration of all the products we tested. They also offered us the ability to work closely with their development group to ensure we were getting the most out of the software.”

One Model for Structural Analysis & Design

From Schematic Design through Construction Documents, Tekla Structural Designer allows LeMessurier engineers to work from one single model for structural analysis and design, improving efficiency, workflow, and ultimately saving time. “Our engineers are working more efficiently because they don’t need to switch between multiple software packages for concrete and steel design. Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product,” said Barnes.

LeMessurier engineers use Tekla Structural Designer to create physical, information-rich models that contain the intelligence they need to automate the design of significant portions of their structures and efficiently manage project changes.

TRANSFORMING THE WAY THE WORLD WORKS

“Tekla Structural Designer has streamlined our design process,” said Craig Blanchet, P.E., Vice President of LeMessurier. “Because some of our engineers are no longer doubling as software developers, it allows us to focus their talents on leveraging the features of the software to our advantage. Had we not chosen to adopt Tekla Structural Designer, we would have needed to bring on new staff to update and maintain our in-house software. So Tekla Structural Designer is not just saving us time on projects, it is also saving us overhead.

Efficient, Accurate Loading and Analysis

Tekla Structural Designer automatically generates an underlying and highly sophisticated analytical model from the physical model, allowing LeMessurier engineers to focus more on design than on analytical model management. Regardless of a model’s size or complexity, Tekla Structural Designer’s analytical engine accurately computes forces and displacements for use in design and the assessment of building performance.

“Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product.”

Positioning a large scale mixed-use development next to an active arena, a below grade parking garage, and an interstate highway, and bridging it over two active subway tunnels makes planning, phasing and engineering paramount. Currently under construction, The Hub on Causeway Project will be the final piece in the puzzle that is the site of the original Boston Garden.

Despite being new to the software, LeMessurier decided to use Tekla Structural Designer for significant portions of the project. “Relying on a new program for such a big project was obviously a risk for us, but with the potential for time savings and other efficiencies, we jumped right in with Tekla Structural Designer. It forced us to get familiar the software very quickly.”

“Tekla Structural Designer allowed us to design the bulk of Phase 1 in a single model,” said Barnes. The project incorporates both concrete flat slabs and composite concrete and steel floor framing. “Tekla Structural Designer has the ability to calculate effective widths based on the physical model which is a big time saver,” said Barnes. “On this project, the integration with Revit, along with the composite steel design features enabled us to work more efficiently. Adding the ability to do concrete design in the same model was a bonus because we had both construction types in the same building.”

“Tekla Structural Designer helped this project run more efficiently, and in the end it was a positive experience,” said Blanchet.

“Tekla Structural Designer gives us multiple analysis sets to pull from, which gives us lots of control. Most programs don’t have the capability to do FE and grillage chase-down. For the design of beam supported concrete slabs, Tekla Structural Designer allows us to separate the slab stiffness from the beam stiffness, so if we choose to we can design the beams without considering the influence of the slab. In the same model we can use a separate analysis set to review the floor system with the beams and slab engaged,” said Barnes.

Barnes also shared similar benefits with concrete column design. “Tekla Structural Designer does grillage take-downs floor-by-floor, finds the reactions and applies them to the next floor. This allows us to view column results both for the 3-dimensional effects of the structure as a whole and from the more traditional floor-by-floor load take-down point of view.

Doing both has always required significant manual intervention, but Tekla Structural Designer puts it all in one place.” “We reduce the possibility for human error because with Tekla Structural Designer less user input is required,” said Barnes. “Tekla Structural Designer automatically computes many of the design parameters, such as column unbraced lengths. The assumptions made by the software are typically correct, but we can easily review and override them when necessary.”

“Tekla Structural Designer provided the best fit for our workflow compared to other commercially available software.”

Want to Evaluate Tekla Structural Designer? tekla.com/TryTekla

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CONTENTS

34 Cover Feature

Columns and Departments

STRUCTURAL LICENSURE

42 Licensure

By J. G. (Greg) Soules, P.E., S.E., P.Eng., SECB

EDITORIAL

7 Structural Engineers

By Marc Hoit, Ph.D.

PRACTICAL SOLUTIONS

9 Wind Loads on Non-Building Structures

By Emily M. Guglielmo, S.E., P.E.

TIMES SQUARE’S NEW ADDITION

STRUCTURAL ANALYSIS

By Cawsie Jijina, P.E., SECB, and Steve Reichwein, P.E., S.E., SECB When completed,20 Times Square

12 Resilient Design and Risk Assessment using FEMA P-58 Analysis

will encompass 378,000 square feet of floor space,

By Curt B. Haselton, Ph.D., P.E.,

rise 550 feet above the street, and have used 2,000

Ronald O. Hamburger, S.E.,

tons of Structural Steel and 21,400 cubic yards of

and Jack W. Baker, Ph.D.

reinforced cast-in-place concrete.

STRUCTURAL PERFORMANCE

Features 26 THE HISTORIC TREFETHEN WINERY

By Marianne Wilson, S.E., Kevin Zucco, S.E., and Brett Shields, P.E. Constructed in 1886, the Trefethen Family Vineyards historic winery building was shaken to its core during the 6.0 magnitude Napa earthquake in 2014. In the aftermath, the historic structure rested in a precarious tilt.

30 HIBERNIA BANK BUILDING

16 An Overview of Fire Protection for Structural Engineers – Part 3

By Frederick W. Mowrer, Ph.D., and Richard L. Emberley, Ph.D.

STRUCTURAL PRACTICES

20 Bad Vibrations

By Charles DeVore, Ph.D., P.E.

and seismic retrofit. The seismic resistance provided by the

STRUCTURAL FAILURES

51 Straight-Line Wind Damage Analysis

By Karyn Beebe, P.E.

INSIGHTS

56 Foreign Engineering Graduates in America

By Dilip Khatri, Ph.D., S.E.

SPOTLIGHT

59 UC Berkeley Bowles Hall Seismic Retrofit and Renewal

By Joe Maffei, S.E., Ph.D., and Karl Telleen, S.E.

STRUCTURAL FORUM

66 Document, Document, Document

By Scott Lowe

24 Remediation of ColdFormed Steel Members and Connections

By Kelly Cobeen, S.E., Terrence Paret, and Owen Rosenboom, Building recently underwent an ambitious historic renovation

By Gail S. Kelley, P.E., Esq.

ENGINEER’S NOTEBOOK

By Roger LaBoube, Ph.D., P.E.

Ph.D., P.E., S.E. San Francisco’s landmark Hibernia Bank

LEGAL PERSPECTIVES

47 A Contract’s “Miscellaneous” Section – Part 2

STRUCTURAL DESIGN

38 Shallow Reinforced Concrete Foundations

massive granite and brick masonry walls had allowed the

By David A. Fanella, Ph.D., S.E., P.E.,

building to survive the 1906 earthquake relatively unscathed.

and Michael Mota, Ph.D., P.E., SECB

IN EVERY ISSUE 8 Advertiser Index 56 Resource Guide – Software Updates 60 NCSEA News 62 SEI Structural Columns 64 CASE in Point

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.

STRUCTURE magazine

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March 2018

Editorial

new trends, new techniques and current industry issues

Structural Engineers Leadership to Address the World’s Challenges

By Marc Hoit, Ph.D., F.SEI, F.ASCE

W

ho better than structural engineers (and civil engineers in general) have the skills, temperament, and understanding of the built environment to lead the next disruptive changes to advance society?

As automation, artificial intelligence, machine learning, and biotech dominate the “4th industrial revolution,” structural engineers are in a perfect position to be leaders and innovators. To become innovative leaders, the collective profession needs to shift its focus to the broader challenges of society to determine how infrastructure will play a dominant role in advancing society. This means growing the profession’s societal involvement and becoming trusted leaders.

To accomplish this, structural engineers have to grow their skills beyond their technical abilities and take on greater leadership in both infrastructure projects and societal issues. The ASCE Report card is an excellent example of how engineers have led newsworthy infrastructure-related societal issues that have also impacted policy changes. Structural engineers need to increase their visible advocacy by serving on boards and city councils. They are often regarded as technically very smart, but improving emotional intelligence is critical to the success of the profession. Most importantly, the profession needs to embrace its responsibility to educate future engineers to be creative, innovative, and a stronger motivational force for positive change.

clearly depend on what industry the structural engineers support and the focus of their professional practice. An engineering career typically spans three stages: Early, Mid, and Late. Part of the career path often includes decisions to remain focused on the technical aspects of engineering or, more often, opportunities move experienced engineers onto a management path. The profession needs to consider developing both technical and management career paths as a way to improve the profession. Currently, most of the financial incentive is focused on the management track.

The SEI Continuing Education committee has developed a strategy.

Continuing education needs based on career stage, as well as much of this editorial, came from that effort. The needs at each stage are: Early-Career: Knowledge of all Basic Building Materials, Design and Detailing Requirements, Communication, Listening, Report Writing, and Computational Literacy Mid-Career: Management skills, Communication, Judgement and Decision Making, Currency with Codes, and Technology Late-Career: Marketing and Selling (Firm Legacy), Stewardship of the Profession, Motivate and Inspire (both inside and outside profession), Mentoring and Leadership, and Subject Matter Expert While technical expertise will always be in demand as an engineer moves through the three career stages, there is an increasing demand for non-technical skills such as communications, business acumen, and leadership. Continuing professional education is an efficient way to help engineers gain the needed additional non-technical skills and expand or deepen technical knowledge and skills.

It is clear that future structural engineers will need a variety of both technical and non-technical skills. This fits the need and the new direction of the SEI Vision. These skills will vary based on personal goals, individual career path, and company focus. Whatever the direction, the opportunity to improve society through the built environment has given engineers the chance to provide a more rational approach to the future.

Get involved and grow your skills to lead: www.asce.org/SEI – Join a Committee or Chapter effort, participate at a conference www.asce.org/advocacy.▪

Educating the Future Engineer Education, and the constant desire to make every new engineer in one’s own image, disrupt reinvention. Engineers often lack soft skills and the profession often focuses on the technical side of education. This occurs despite research that shows that technical skill only covers 15 percent of the skills needed to be successful in this profession. While there are significant differences in degree programs – including general civil, structurally-focused, and architectural engineering degrees – none prepares an engineer for a lifetime career. A bachelor’s degree is considered the bare minimum knowledge required to start as a practicing engineer.

While there are current efforts to “raise the bar” and complaints that a bachelor’s degree has fewer credits and less technical content than in the past, the fact is that a bachelor’s degree – or for that matter, a master’s degree – and a license are only the beginning of the education required to be a structural engineer. This is because the demands of the industry are changing rapidly, as witnessed by the complexity of codes, the breadth of knowledge required, and the pace of technology. Most structural engineering firm leaders say that engineering graduates do not know a fraction of what is needed, so they are hired based on the limited requirement of problem-solving abilities. None of this addresses the required focus and education on the non-technical skills needed for leadership. The most significant innovation in this field is coming from Elon Musk, Physics Ph.D., and entrepreneur who has reinvigorated tunneling.

The bachelor’s and master’s degrees should peak an engineer’s curiosity and instill the desire to learn. This would leverage a more significant role for continuous professional education. All of these issues, however, STRUCTURE magazine

Marc Hoit is Chair of the SEI Structures Congress Committee and member of the ASCE Industry Leaders Council. He serves as Vice Chancellor for Information Technology (VCIT) at North Carolina State University in Raleigh.

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March 2018

ADVERTISER INDEX

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Greg Schindler, P.E., S.E. KPFF Consulting Engineers, Seattle, WA Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA

March 2018, Volume 25, Number 3 ISSN 1536-4283. Publications Agreement No. 40675118.

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F

or the practicing structural engineer, deciphering the wind provisions of ASCE 7 is an ever-present challenge. However, some would argue that the real challenge is addressing commonly encountered situations which are not directly addressed in the code.

In 2011, NCSEA sent out a survey to approximately 10,000 structural engineers to generate data on the wind load provisions of ASCE 7. One of the most consistent responses was a request for more guidance on commonly encountered non-building structure conditions, such as canopies, rooftop mechanical screen walls, and solar photovoltaic panels.

Because of this feedback, NCSEA provided recommendations to ASCE 7 for incorporation into ASCE 7-16.

This article discusses several common non-building structures, how they are currently addressed in ASCE 7, and provides suggestions for addressing areas where the code is silent.

limitation and allows the provisions to be used for rooftop equipment and structures on buildings of all heights.

Provisions It is understood that the wind forces on rooftop equipment and structures will be higher than those determined for wind loads on other nonroof mounted structures (ASCE 7-10 Equation 29.5-1). This increase in wind force is due to several factors: 1) Due to the small size of the rooftop structure in relation to the building, there is an increased correlation between the pressures across the structure surface. In other words, there is more likelihood of the rooftop structure receiving concurrent peak pressures on the windward and leeward surfaces.

2) Higher turbulence is present on the building roof.

3) Accelerated wind speeds are present on the roof.

Practical SolutionS solutions for the practicing structural engineer

Rooftop Units Mechanical units are routinely placed on the roof of buildings. While engineers are accustomed to calculating and accommodating for the gravity loads of these units, the proper application of wind loads to rooftop units has historically been a source of confusion.

ASCE 7-05 provided an equation to generate a horizontal Main Wind Force Resisting System (MWFRS) wind load on rooftop equipment.

While the commentary alluded to a high uplift component of wind loads that should be considered in the design of rooftop structures, ASCE 7-05 provisions did not provide a method for calculating this uplift.

In ASCE 7-10, the design wind force for rooftop structures was revised to include a vertical component of wind force based on research, recently completed at the time, from the University of Western Ontario. Also, a new section was added for determining the Component and Cladding (C&C) loads on rooftop structures and equipment. This section is particularly useful for engineers designing the actual mechanical equipment enclosure or its anchorage.

It is important to note that the applicability of rooftop structures and equipment provisions in ASCE 7-10 was limited to structures less than or equal to 60 feet in height. While this covers the majority of buildings designed in the United States, it does leave a significant gap for the design engineer when generating wind loads on rooftop equipment for structures over 60 feet. ASCE 7-16 removes this 60-foot

Wind Loads on Non-Building Structures The lateral force, Fh, on rooftop structures and equipment is determined by the following equation: Fh = qh(GCr)Af (ASCE 7-10 Equation 29.5-2) qh = velocity pressure evaluated at the mean roof height of the building Ar = horizontal projected area of rooftop structure or equipment GCr = 1.9 for rooftop structures and equipment with Af less than (0.1Bh). GCr shall be permitted to be reduced linearly from 1.9 to 1.0 as the value of Af is increased from (0.1Bh) to (Bh).

The vertical force, Fv, on rooftop structures and equipment is determined by the following equation: Fv = qh(GCr)Ar (ASCE 7-10 Equation 29.5-3) qh = velocity pressure evaluated at the mean roof height of the building Ar = horizontal projected area of rooftop structure or equipment GCr = 1.5 for rooftop structures and equipment with Af less than (0.1BL). GCr shall be permitted to be reduced linearly from 1.5 to 1.0 as the value of Af is increased from (0.1BL) to (BL).

The values of GCr take into account the higher rooftop pressures, discussed above. As the rooftop equipment size grows relative to the building, the values of GCr decrease. continued on next page

STRUCTURE magazine

9

By Emily M. Guglielmo, S.E., P.E., C.E., F.SEI

Emily M. Guglielmo is a Principal with Martin/Martin, Inc. managing their San Francisco Bay Area office. Emily is the secretary of the NCSEA Wind Engineering Committee and serves on the ASCE 7-22 wind loads subcommittee. She may be reached at eguglielmo@martinmartin.com.

GC for rooftop structures.

Rooftop Screen walls Mechanical equipment screens commonly are used to conceal plumbing, electrical, or mechanical equipment from view. Historically, ASCE 7 has not provided guidance on what wind pressure to apply to these rooftop screens. Several approaches have been used within the industry, including applying parapet pressures, using the solid-freestanding wall provisions, and applying the rooftop structures and equipment provisions (discussed above).

Little research is currently available to provide guidance for determining wind loads on screen walls and equipment behind screens.

The ASCE 7-16 commentary to Section 29.5.1 suggests that the provisions for rooftop structures and equipment be used to generate wind forces on screen walls located away from the edge of a building.

Fh = qh(GCr)Af (ASCE 7-10 Equation 29.5-2) The commentary also alludes to the fact that screen walls located close to a building edge should be designed for parapet pressures.

To quantify the appropriate distance from a building edge to differentiate between “parapet” and “rooftop structures and equipment” pressures, the boundary between corner and edge wind zones (zones 2 and 3) versus typical roof zones (zone 1) provides a reasonable delineation. Therefore, a suggested practice would be that screen walls located in Zones 2 and 3 should be designed for parapet pressures, while screen walls located in Zone 1 can be engineered for a “rooftop structures and equipment” pressure.

Research is currently underway to help advance our understanding and support updating code provisions for rooftop screen walls and the equipment behind the screens. The Insurance Institute for Business & Home Safety (IBHS) Research Center and the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) have recently completed the first phase of a relevant study. It focused on the effects of rooftop screens on the wind

loads applied to the equipment being screened.

Preliminary findings suggest that fully enclosed screen wall configurations do lower wind loads on the equipment, while partially enclosed screen configurations do not provide significant wind load reduction. Also, the screen type does not significantly change wind loads on the equipment being screened. The second phase of the study focuses on the wind loads on the screen walls themselves. Results of this phase have not yet been released.

Canopies Canopies are another example of building components that are commonly encountered by structural engineers but lack clear guidance for applying wind loads. However, even when the code lacks direct guidance, there are often ways to interpolate and extrapolate portions of the code to gain an understanding of appropriate loading on commonly encountered conditions.

Studying and understanding Table 27.4-1, which is one of the most long-standing Tables in ASCE 7, provides an excellent basis for the design of canopies. For this instance, the most important value in Table 27.4-1 is the windward wall pressure coefficient, Cp = 0.8.

When designing a canopy, it is important to realize wind loads can act in a downward or upward direction. Depending on the location of the canopy, it is possible for either of these two load cases to control. To bound the solution, consider two extreme cases: 1) a canopy at the base of a tall building, and 2) a canopy at the top of a tall building.

For the first case, the downdraft of wind flowing down the face of the wall imposes a pressure downward on the top of a canopy (downward Cp = 0.8). For the second case, wind flows up the face of the building and applies an uplift pressure on the underside of the canopy (upward Cp = 0.8) that could combine with suction at the upper surface of the canopy.

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March 2018

While this bounded solution provides some guidance for the engineer, it can overestimate the total uplift on a canopy at the top of a building. Further, it does not provide direction for canopies located mid-height of a building.

ASCE 7-16 introduces a procedure for attached canopies and awnings. These provisions provide a chart to find both total downward and upward pressures on a canopy, in addition to a chart to find separate pressures on the upper and lower surfaces of a canopy. To the discerning eye, these charts yield similar pressure coefficients as the study presented above.

It is important to note that the provisions of ASCE 7-16 relating to canopies are applicable only to buildings 60 feet or less in height.

It is the intent to expand these provisions in future codes to encompass canopies on taller buildings.

Tall Parapets Exterior walls are often cantilevered beyond the roof surface to create a parapet. These parapets may serve many purposes, including fall arrest, flashing termination, fire resistance, or visual screening. In recent years, parapet heights have become increasingly taller, often to achieve visual screening of rooftop equipment. Engineers have pondered the effects of these taller parapets and whether they warrant wind load increases, decreases, and step functions. The current parapet provisions of ASCE 7 do not provide guidance on limitations or suggestions for applying wind loads to very tall parapets.

It is important to understand the history of those provisions to provide the context for the parapet provision of ASCE 7. While engineers understood that increased parapet wind pressures were a real phenomenon worthy of consideration, there were no provisions for wind loads on parapets before ASCE 7-02. In ASCE 7-02, a method for generating wind forces on parapets was introduced based on the committee’s collective experience, intuition, and judgment. In ASCE 7-05, these provisions were updated with research from University of Western Ontario and Concordia University.

There are many studies on the effects of parapets on roof wind loads, including varied parapet height. However, primarily due to instrumentation limitations, there are limited studies on wind forces on the parapet itself.

For the tests that do exist, results suggest that wind loads on parapets are independent of parapet height (Mans et al., 2001).

Canopy at Base of Building

Canopy at Top of Building

Due to rapid technological advances in the solar industry and the more extended code cycles of ASCE 7, there will be a cyclical process of adoption and modification of ASCE 7 and the SEAOC Solar PV guides. As a practicing engineer, both documents are useful for providing relevant and up-to-date suggestions for determining wind loads on PV panels.

Conclusions

Use Cp = 0.80 (same as windward wall) on the top of canopy

Use Cp = 0.80 (same as windward wall) on the bottom of the canopy plus the roof uplift on the top

Pressure coefficient for attached canopies.

Solar Photovoltaic (PV) Panels

The online version of the article contains the full reference for (Mans et al., 2001).

Please visit www.STRUCTUREmag.org.

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The rapid rise of renewable energy has led to an increase in rooftop-mounted solar photovoltaic arrays in both commercial and residential applications. While the code has not directly addressed these solar PV panels, engineers have either forced creative implementation of ASCE 7 pressure coefficients or used Wind Design for Low Profile Solar Photovoltaic Arrays on Flat Roofs, published by the Structural Engineers Association of California (SEAOC).

The SEAOC PV committee was formed in September 2011, with the goal of addressing the lack of requirements in the code for PV systems.

In 2012, SEAOC published two guides: PV1-2012: Structural Seismic Requirements and Commentary for Rooftop Solar Photovoltaic Arrays and PV2-2012: Wind Design for Low Profile Solar Photovoltaic Arrays on Flat Roofs.

ASCE 7-16 incorporates and adopts much of the work done in PV2-2012.

However, SEAOC has continued to advance the solar PV guidelines and is preparing to issue PV2-2016, which will supersede PV2-2012. PV2-2016 will reference ASCE 7-16 provisions and incorporate research completed since 2012. In addition to these changes, PV2-2016 will provide updated terminology, guidance on effective wind area determination, and wind tunnel requirements. In some cases, PV2-2016 will provide recommended additional requirements where the ASCE 7-16 requirements may not be adequate.

The SEAOC PV guide covers the following Solar PV applications:

• Arrays with tilted panels on flat or lowslope roof buildings • Parallel-to-roof (flush-mounted) arrays on sloped roofs • Ground-mounted solar arrays The SEAOC PV guide does not cover the following Solar PV applications: • Roof-mounted systems with tilted panels that are not low-profile • Arrays on other roof shapes (e.g., hip, gable, saw-tooth, etc.)

There are many frequently encountered non-building structures which require design with appropriate level wind forces.

As discussed above, ASCE 7 attempts to address some of these commonly encountered conditions, including canopies, rooftop equipment on buildings over 60 feet in height, rooftop screen walls, and solar PV, with future versions. Even when the code does not directly address a condition, it is important to understand the background and intent of the Code so engineers can extrapolate to find an appropriate solution.▪

MCI_5x3.5_02-18.indd 1

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2/19/18 8:44 AM

Structural M analySiS discussing problems, solutions, idiosyncrasies, and applications of various analysis methods

ost building codes worldwide have been developed to protect building occupant health and safety under likely loading, including earthquakes. Severe wind, snow, and live loads frequently occur during a building’s life. Therefore, in addition to protecting life safety, code requirements for these loads also result in a very low probability that buildings will be damaged by these loads. Earthquakes, however, occur rarely and most buildings never experience a significant earthquake. Therefore, building codes do little to limit building damage, repair cost, and building closure time resulting from expected design-level events. Recent studies of code-compliant buildings indicate they may be closed for six to 24 months after a design level earthquake, and demolished after a maximum considered earthquake. Essentially, we are designing “safe but disposable” buildings. Can we do better?

Resilient Design and Risk Assessment using FEMA P-58 Analysis

By Curt B. Haselton, Ph.D., P.E., Ronald O. Hamburger, S.E., and Jack W. Baker, Ph.D. Curt B. Haselton is a Professor and John F. O’Connell Endowed Chair in Civil Engineering at California State University, Chico and Co-Founder of the Seismic Performance Prediction Program (SP3). He can be reached at curt@hbrisk.com.

Ronald O. Hamburger is Senior Principal at Simpson Gumpertz & Heger (SGH) and is the Technical Director for the series of projects that developed the FEMA P-58 methodology. He can be reached at rohamburger@sgh.com.

Jack W. Baker is an Associate Professor of Civil and Environmental Engineering at Stanford University; he is also Co-Founder of the Seismic Performance Prediction Program (SP3). He can be reached at bakerjw@stanford.edu.

In the period from 1971-1994, California experienced damaging earthquakes somewhere in the state every 18 months or so. These frequent and substantial losses prompted owners to ask engineers to evaluate and upgrade existing buildings to perform better, but engineers had no tools to do this. The Federal Emergency Management Agency (FEMA) initiated a series of projects with the Applied Technology Council (ATC) that culminated in 1997 with the publication of FEMA 273/274, Guidelines for Seismic Rehabilitation of Buildings. This landmark document, which has since evolved into the ASCE 41 standard, formed the first generation of true performancebased seismic design criteria. However, owners also wanted better performing new buildings and FEMA 273/274 applied only to existing buildings. Engineers began to demand similar procedures for the design of new buildings.

FEMA again turned to ATC to respond to this need and funded development of the FEMA P-58 methodology through the ATC-58 project series, which ultimately required more than $16 million in funding and produced a comprehensive risk assessment methodology applicable to both new and existing buildings.

Early in the development process, ATC solicited input from stakeholders including engineers, owners, building officials, insurers, and lenders.

These stakeholders indicated that, rather than discrete performance levels inherent in ASCE 41, it would be preferable to acknowledge the continuous range of performance buildings experience, to be quantitative in the description of this

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Figure 1. Overview of the FEMA P-58 analysis method.

performance, and to acknowledge the uncertainties inherent in assessing building performance in future events.

The FEMA P-58 method provides quantitative descriptions of building performance in terms of repair cost, repair time, life safety, occupancy, and environmental impacts. It is building-specific and can be used iteratively to design buildings with desired performance, just as engineers use structural analysis software to design buildings for code compliance (where the goals are limiting drifts, making components strong enough, etc.). It can also be used to assess the risk of an existing building.

Overview of the FEMA P-58 Method Figure 1 shows major steps in the P-58 process: 1) Ground Motions. Expected ground motion intensities are quantified using seismic hazard analysis (or default U.S. Geological Survey data). This step may also include a selection of

Figure 2. Example mean repair cost curve predicted by FEMA P-58 analysis.

ground motions if required for structural analysis (Step 2).

2) Structural Response. Building response quantities are computed for each ground motion level of interest. These include peak story drifts and floor accelerations, residual story drifts, and other predictive parameters. This step can be completed using either response-history analysis or linear static response prediction approaches calibrated to nonlinear analysis based on building strength and modal properties.

3) Component Damage. Damage to individual structural and nonstructural components is computed by combining the structural responses with fragility (damage) functions (e.g., functions for partition walls that relate story drift to wall damage). This step is supported by a comprehensive database of fragility functions provided in the FEMA P-58 documentation.

4) Losses and Repair Times. First, repair costs and repair times are computed for each component based on the predicted damage; then these are aggregated to compute total repair cost and repair time for the building. Repair costs include regional modifiers to reflect construction costs by region and do not typically

Figure 3. Breakdown of repair cost sources for a 10% in 50-year level earthquake motion.

include post-earthquake demand surge (though that could be included).

These four steps of the FEMA P-58 method are combined using Monte Carlo simulation, such that the uncertainties are tracked and the risk predictions quantified by mean values and variability.

Some highlights of the FEMA P-58 method are: • In addition to safety metrics, FEMA P-58 predicts important metrics of building resilience including repair cost, repair time, and potential occupancy tagging • FEMA P-58 predicts building-specific risk using a quantitative engineeringbased assessment process, in contrast to most other loss prediction methods that are empirical or judgment-based, and uses building class rather than building-specific information.

• FEMA P-58 is open-source, standardized, and repeatable, with the assessment process supported by a wide range of databases created in the project (fragility functions, loss functions, etc.).

Figure 2 provides a loss vulnerability curve for an example mid-rise office building in Los Angeles with a reinforced concrete frame. For this example, the 10% in 50-year and 2% in 50-year ground motions produce 0.47g and 0.78g peak ground accelerations and mean

Figure 4. Building closure and repair times for a 10% in 50-year level earthquake motion.

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repair costs of 18% and 42% of replacement cost, respectively. FEMA P-58 also provides full statistical distributions of losses and repair times (e.g., 90th percentiles, etc.).

In addition to the aggregated results of Figure 2, FEMA P-58 also predicts repair costs for specific components. Figure 3 shows a breakdown of repair costs for 10% in 50-year ground motion for the same example building. In this case, two-thirds of the loss comes from items other than structural damage, with significant contributions from partitions and finishes as well as some contribution from excessive post-earthquake drift (“residual drift”), indicating that the building would need to be demolished.

FEMA P-58 also provides detailed information on repair times, which is useful for predicting building closure and business disruption. Companion methods, like the Resilient Design Initiative (REDi) build on FEMA P-58 to provide enhanced repair time estimates. Figure 4, constructed using the REDi procedure, shows the expected repair times for the same 10% in 50-year ground motion level and predicts that it will take six months to reoccupy the building and nine months to have the building restored to preearthquake conditions.

The FEMA P-58 method enables the quantitative resilient design of buildings but is

Figure 5. Rendering of the Long Beach Civic Center, which was designed iteratively using FEMA P-58. Courtesy of Skidmore Owings & Merrill and SEOAC paper.

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Figure 6. Example resilient design showing approximate (a) reduction in repair cost, and (b) reduction in REDi re-occupancy time.

equally applicable to risk assessment of existing buildings (and is commonly used for existing buildings as well).

Recent Developments that Build upon FEMA P-58 The debut of P-58 in 2012 spurred additional research and development to extend and enable effective use of the method.

Examples include the Resilient Design Initiative (REDi) system in 2013 and the U.S. Resiliency Council (USRC) rating system in 2015 – two systems that provide building ratings based in large part on FEMA P-58 calculations. The Seismic Performance Prediction Program (SP3) software was created, and released in 2014, to enable efficient use of the FEMA P-58 method. Additionally, the National Science Foundation has funded the extension of FEMA P-58 to cover other structural systems, including tilt-up buildings.

Uses for FEMA P-58 and Case Studies FEMA P-58 enables engineers to provide a wide range of new services, listed here and illustrated in the following sections.

• Resilient design of new buildings • Retrofit of existing buildings • Risk assessment for mortgage (PML+), insurance, and investment decisions • Risk assessments of special facilities that require post-earthquake operability Quantitative Resilient Design Traditionally, engineers make a building “better” by adding strength or stiffness, or by designing to a higher performance objective (say the immediate occupancy objective using ASCE 41). The result can be difficult to sell to clients, however, because it is hard to quantify the effects of better design. FEMA P-58 enables structural engineers to quantify

the results of better design, in terms that more building owners care about and understand.

Exact design requirements will depend on the circumstance. Common goals are: • Avoid structural damage, and limit residual drifts, to ensure post-earthquake functionality (i.e., no red tag and no damage would require structural repair).

• Prevent damage to non-structural drift sensitive components that would inhibit building functionality.

• Prevent damage to acceleration sensitive components that would inhibit building functionality, including equipment and their anchorages.

Figure 5 ( page 13) shows an example of a recent resilient design project, the Long Beach Civic Center (LBCC) in Southern California (with information coming from the 2016 Structural Engineers Association of California, SEAOC, convention). This complex includes an 11-story building for the City of Long Beach, an 11-story building for the Port of Long Beach, and a one-story city council chambers. This project was designed with the collaboration of Nabih Youssef and Associates and Skidmore Owings & Merrill.

The overall resiliency goals for this design included the following performance goals for 10% in 50-year ground motion: • Safe (code-compliant, low risk of fatality or injury) • Repair cost < 5% of building value • Re-occupancy time < 1 week • Complete recovery time < 1 month The designs of the LBCC buildings were driven directly by iterative FEMA P-58 analysis and redesign. The list below outlines the primary design steps. Figure 6 shows approximately how the repair costs and repair time dropped as each of the resilient design steps where implemented: Step 1: Decide to use a reinforced concrete core wall and start with a code-compliant design.

Step 2: Increase wall strength to limit flexural damage such that repair is not required.

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Step 3: Remove coupling beams (and instead use a punched wall design) such that coupling beams do not require repair.

Step 4: Ensure equipment is functional through strengthening anchorages and prequalifying important equipment.

Step 5: Strengthen one elevator to ensure post-earthquake functionality.

Step 6: Reduce the shear stress in the gravity slab-column connections to limit their damage.

Step 7: Stiffen structural walls (to meet a 1% drift target) to further protect slab-column connections and to protect partition walls.

Exact cost comparisons for this building are not yet available, but other similar projects suggest that this type of resilient design only costs 1-3% more than a baseline codecompliant design.

Figure 7 shows a commercial property developed by Watson Land Company.

Watson Land Company develops and leases their properties and has been designing its properties to exceed minimum requirements for many years as a means of creating more marketable properties, reducing the chance that occupants will be displaced after an earthquake, and reducing required earthquake insurance costs. This building was designed for an Immediate Occupancy objective using ASCE 41. FEMA P-58 is being used to quantify the risk reduction in terms of reduction in dollar losses, which will provide a stronger basis for pursuing an insurance benefit. The current FEMA P-58 study is comparing the repair costs for the Immediate Occupancy (IO) design to those of a typical code-compliant design (for a 10% in 50 year ground motion level) and is finding that the repair costs for the IO design are only half of the repair costs for a typical code-compliant design, but the study is ongoing. When comparing the resilient design to a typical code-compliant design, the building only cost $1.27 more per square foot.

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Figure 7. Rendering of Watson Land Company commercial tilt-up building, designed using an ASCE 41 Immediate Occupancy objective, with a reduction in risk quantified using FEMA P-58. Courtesy of Watson Land Company.

Conclusions

Building-Specific Risk Assessment

The FEMA P-58 assessment methodology represents a great leap forward in capability to quantify and improve earthquake performance. By linking specific building properties to repair cost and repair time, society can better understand and manage earthquake risks.

The examples above show how engineers are using this tool to design resilient buildings and to better quantify the risks posed by existing buildings. Based on the first five years of experience with this tool, evidence shows that new buildings can be designed with greatly improved performance at a very low-cost premium. With each passing year, further research and advances, such as new software tools and rating systems, continue to make this approach more accessible and useful. Engineers can look forward to a day when all building owners and insurers understand their earthquake risk, and when all new buildings are designed to be seismically resilient.▪

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The same FEMA P-58 method is regularly used to complete high-resolution building-specific risk assessments of existing buildings, for a wide range of purposes (retrofit decisions, mortgage risk assessments, insurance risk assessments, investment risk assessments, etc.).

Figure 8 shows an example assessment completed to support a possible building purchase decision. This is an older building that had been structurally upgraded, but which still has older and brittle unreinforced masonry cladding. A full FEMA P-58 assessment was completed by Holmes Structures to estimate building damage and repair costs at multiple levels of ground motion.

Damage to the brittle cladding was a critical component, and Figure 8 illustrates the expected damage states of the cladding on multiple elevations of the building (for a 10% in 50-year ground motion).

Structural M Performance performance issues relative to extreme events

any structural engineers have not traditionally been involved in the analysis or design of building fire safety. When they have been, their focus has generally been on structural fire protection and, with some exceptions, their scope has been limited to ensuring compliance with prescriptive building code requirements for the fire resistance ratings of different building elements. However, structural fire protection is just one aspect of a comprehensive framework for building fire safety. As demonstrated by the Grenfell Tower fire in London, structural fire protection alone does not ensure the fire safety of a building or its occupants. While structural engineers may not practice in the field of fire protection engineering, it is useful for all engineers involved in building design to have at least a basic understanding of building fire safety issues.

Parts 1 and 2 of this series (STRUCTURE, January and February 2018), detailed an overview of fire protection for structural engineers focused on fire safety objectives and the building systems and features used to ensure the objectives are met.

Part 3 provides an overview of the emerging practice of structural fire engineering, which requires close collaboration between fire protection engineers and structural engineers.

Details on the design process and emerging trends and research are highlighted.

An Overview of Fire Protection for Structural Engineers Part 3

By Frederick W. Mowrer, Ph.D., and Richard L. Emberley, Ph.D.

The Role of the Structural Engineer

Frederick W. Mowrer is the Founding Director of Fire Protection Engineering Programs at Cal Poly in San Luis Obispo, CA. Dr. Mowrer is a Fellow of the Society of Fire Protection Engineers and a pastpresident of the Society. He may be reached at fmowrer@calpoly.edu.

Richard L. Emberley is an Assistant Professor in the Mechanical Engineering Department and Fire Protection Engineering Program at California Polytechnic State University (Cal Poly). He may be reached at remberle@calpoly.edu.

and minimize the mass of the building to reduce the overall cost. However, the applied load due to thermal action has traditionally been excluded from structural engineering design and relegated to the fire protection engineer.

ASCE 7 details eight basic combinations of the loads listed above. A structural engineer must first determine which is the most onerous case and, second, design the structural members based on that load combination. The various load combinations are based on the statistics and probability that loads never occur at their full value at the same time. However, fire and the impact of thermal loads are detailed in ASCE 7 as being “extraordinary” or “low-probability” events – the same type of classification of loads as explosions and vehicular impacts. The requirement by ASCE 7 is that the engineer is only required to check the load combination “where required by the owner or applicable code.” However, according to the National Fire Protection Association, 2.93 million structure fires occurred in the U.S. from 2010 to 2015 (NFPA, 2017). Whereas, based on the National Oceanic and Atmospheric Administration data, approximately 2,000 structures have been damaged or destroyed by earthquakes over the same six-year period (NOAA, 2017). While the design for the impact of earthquakes should not be removed or replaced from structural design, especially in areas such as the West Coast of the U.S., structural design against the impact of thermal loads should not be relegated to a low-probability event when the statistics indicate otherwise. Fire is much more than an “extraordinary” event.

Based on the discussion in the previous articles, Structural Response it should be apparent that the traditional role of to Thermal Loads the structural engineer in building fire safety has been limited. However, that has been changing Historically, fire protection of structures has been over the past two decades or so, with the emer- based on the principle of limiting temperatures gence of structural fire engineering as a distinct and the associated strength reduction. For steel design discipline. construction, as an example, the limiting temperaThe design of a structure’s load resisting mem- ture in ASTM E119 is 538°C. This temperature bers account for both gravity (i.e., dead, live, is based on the yield strength reduction of steel snow, and rain) and lateral (seismic and wind) due to increases in temperature. At 538°C, steel loads, and the resulting forces (moment, shear, loses approximately 50% of its yield strength. and axial). In some cases, such as wind loads, complex analyses are involved, from computer modeling to small-scale wind tunnel tests, to correctly design the structural framing and fine tune the architecture to reduce the wind pressure on the building.

An example of this would be the architectural and façade design of the Burj Khalifa to minimize vortex shedding.

Everything about the design, from the curvature of the façade, lateral bracing locations, and the connections, are optimized Figure 1. Thermal expansion in unrestrained vs. restrained support conditions. to reduce the loads applied to the building

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more than the bottom surface, the thermal bowing would be upwards.

Holistically accounting for the structure does have benefits. When heated, a steel beam that is laterally braced by a concrete slab or a two-way spanning concrete slab can utilize tensile membrane action (catenary) and support loads at temFigure 2. Thermal bowing due to differential thermal expansion peratures much greater than the traditional limiting temperatures. from thermal gradients within a member. Unheated Member Concurrently, the surrounding (solid lines). Thermal Bowing Member (dashed lines). structure provides a large amount Fire protection measures, such as gypsum of redundancy and redistribution board or spray-applied fireproofing, are of loads as members increase in temperature, installed to a thickness that prevents the expand, deflect, and, in some cases, fail. temperature of the steel from reaching the While still designating fires as extraordinary limiting temperature during exposure to an events, the 2016 revision of Minimum Design ASTM E119 standard time-temperature Loads and Associated Criteria for Buildings and curve. The underlying principle is that, if Other Structures (ASCE 7) seeks to address the temperature of the steel is kept below the impact of thermal loads on structures 538°C, the structural collapse is prevented through Appendix E, which is a new addition since the strength reduction factor is limited to ASCE 7. The load factor combination that to approximately 50%.

ASCE 7 uses adds the effects of the extraorHowever, highlighted by the Cardington dinary event (Ak) to dead (D), live (L), and Fire Tests (1995-6) and the collapse of World snow loads (S ) with a probability factor of Trade Center 1, 2, and 7, the thermal actions 1.0 (Equation 1). of expansion and bowing occur at relatively (0.9 or 1.2)D + Ak + 0.5L + 0.2S Equation 1 low (150°C) temperatures and have signifiThe reasoning behind the value of 1.0 for cant effects on the structure. When typical the extraordinary event load factor is due to construction materials (steel, concrete, and limited data on the frequency of the events timber) increase in temperature, the materials as well as the inclusion of conservativism in expand linearly proportional to tempera- the design. However, this still relies on “the ture (Figure 1). If the support conditions of owner or applicable code” (ASCE 7-16 Section the member – whether due to the cooler 2.5.1) to require that strength and stability surrounding structural members or the con- checks are completed and to ensure that the nection type – create restraint, the member structure is designed against disproportionate is prevented from expanding. This restricted collapse. While the structural design process for expansion leads to high stresses within the thermal loads is straightforward, the structural beam and can result in local buckling at the mechanics (described above) that are manifest connections during either the heating or cool- when thermal loads are applied are critical in ing phase of a fire. a complete understanding of the performance Concurrently, if the combination of the of a structure in fire conditions and a correct structural member’s thermal properties assessment of the safety of the structure. As our (insulative vs. conductive) and the applied knowledge of structural mechanics increases thermal loads (large vs. small magnitudes) with respect to thermal loads, the safety benefits create thermal gradients within a member, by designing for thermal, mechanical action the differential thermal expansion within (Ak) as a substitute for temperature-limiting the member itself can cause thermal bowing design criteria become more apparent. regardless of restraint conditions (Figure 2).

Typical approaches to fire resistance, such as As shown, the temperature of the bottom those specified in the International Building surface (TB) of the member is greater than Code, place a higher fire resistance rating the top surface (TT). As such, the bottom and thus importance on the primary strucsurface will want to expand more, relative tural frame (columns, bracing members, to the top surface. Since both surfaces are and structural members directly connected part of the same member, curvature (thermal to the columns) than secondary structural bowing) is created to account for the expan- members (not directly connected to the sion difference. Figure 2 shows the bottom columns). Placing a higher priority on prias the heated surface and that the bowing mary structural members protects against the is downwards towards the fire. The reverse disproportionate collapse of the structure. is true as well. If the top surface is heated For designing structural members based on

Figure 3. Open office floor plan. Courtesy of David Sim.

thermal loads, such as recommended in ASCE 7-16 Appendix E, structural members are designed based on design fires representative of the fuel load, compartment and building geometry, and ventilation conditions within the structure. Design fires are identified within the structure and the resulting thermal loads are applied to the vulnerable members. The resulting thermal, mechanical action loads (Ak) are then applied. Where necessary, protection schemes are applied to limit the influence of the thermal loads on the structure. Importance of structural members is given to areas of refuge and egress paths and any project-specifics areas that are deemed important by the owner or AHJ. Each of these steps are described in detail in the next section.

Methodology The first step for designing structural members for thermal loads is to identify the type and amount of fuel within the compartment of the building. The type of fuel drives how quickly the fire reaches maximum heat release rate. Compartment size and ventilation conditions coupled with the amount and type of fuel, dictate the maximum heat release rate and the length of time the fire burns.

Smaller, more compartmentalized architecture lends itself to fully-developed ventilationlimited fires that last upwards to an hour before burnout of the fuel. These types of fires yield localized heating of structural members.

Traditional “fire-resistance” ratings through

Figure 4. External thermal loads on a solid and conduction through the material.

furnace testing (described in a previous section) are based on single-member heating such as this. However, the evolution of space within buildings has dramatically changed over the last 30 years (Figure 3). Numerous small rooms have morphed into larger open floor plates. Fires in open floor plates cannot fully-develop and are thus fuel-limited and burn much more slowly, yielding longer burning durations and heating of a greater number of structural members.

Therefore, the second step is to identify the structural members subjected to thermal loads based on the fire conditions. Knowing whether to account for one heated member versus several is critical in understanding how the building will perform. The location, size, and growth and spread of a fire, as a time-dependent factor in relation to various structural members, allows the engineer to know the thermal load and the length of time the thermal load is applied for both the growth and decay of the fire (structural member heating and cooling stages).

The third step is to quantify the thermal loads and boundary conditions on the structural members. Based on the fire geometry, heat release rate, and burning conditions, an external heat flux (radiation and convection) transfers energy from the fire and/or hot gas layer to the structural member, increasing the temperature through conduction (Figure 4).

The heat transfer analysis can be performed using several tools, such as simple analytical solutions for one-dimensional behavior to finite element software to account for threedimensional behavior. Accounting for the entire duration of the fire allows for quantification of not only the heating periods (increases in heat flux) but also the cooling periods (decreasing heat flux) when the structural member decreases in temperature and contracts in size (reverse thermal expansion).

The fourth and final step is to use the member temperature output from the heat transfer analysis to determine the stresses and strains within the member due to thermal expansions and contractions and temperature strength reductions.

A full structural analysis accounts for material

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properties, support conditions, member geometry, and full frame response of the surrounding structure. Only then can engineers and designers explicitly know the fire performance and degree of safety of the structural frame. Depending on the results of the structural and heat transfer analysis, fire protection schemes for the structural members can be recommended and implemented. Spray-on insulation or intumescent paints can be applied to structural steel to limit the increase in temperature of various critical members. The thickness of concrete cover can be increased to protect reinforcing steel and account for explosive spalling of concrete.

Timber members can be increased to account for combustion and charring.

As new, novel, and emerging construction materials – such as fiber reinforced plastic and engineered mass timber – or other optimized structural solutions and designs enter the market, the need to account for fire and thermal actions within structural engineering is only increasing. Designing for the fuel loads unique to the building leads to an understanding of the safety factors of the fire protection design and, in some cases, can lead to significant cost savings by reducing or eliminating fireproofing. Knowing how a material behaves as a structural member and the correct ways to protect the structure are paramount to delivering a safe building. All of this offers not only a challenge but also an incredible opportunity for structural engineers and fire safety engineers to collaborate early in the design process and produce a truly optimized building for every potential load – seismic, wind, or fire.

Summary Much as it is with the structural performance of buildings, the fire safety of buildings is often taken for granted, until a disaster occurs. Following a disastrous fire such as at the Grenfell Tower, shortcomings become apparent because fire has a way of finding and exploiting the weakest aspects of building fire safety design. In modern buildings, multiple fire safety systems and features are typically part of the design, so multiple failures are generally needed for a catastrophic fire to occur. However, as discussed here, building fire safety does not just happen by chance or good fortune; it requires the careful consideration of fire safety objectives, the coordination of many fire safety systems and features, and effective fire safety management over the lifespan of a building.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

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Structural C PracticeS practical knowledge beyond the textbook

Bad Vibrations Designing for Floor Vibrations Caused by Concerts

By Charles DeVore, Ph.D., P.E.

Charles DeVore is a Senior Engineer at Exponent, Inc. and is an Adjunct Professor at New York University where he teaches structural dynamics. He can be reached at cdevore@exponent.com.

oncerts tend to create a worst case loading scenario for floor vibrations.

Large groups of people are concentrated together, and the musical performance provides a synchronization signal for the audience to sway, bounce, or jump along with the music.

This synchronized excitation creates a harmonic load on the floor which often can be near the natural frequency of the floor structure, resulting in resonance. When this happens, dynamic amplification occurs that may result in an unacceptably large acceleration response.

This article describes the process used to evaluate floor structures subjected to harmonic loading from a concert crowd. The International Organization for Standardization (ISO), American Institute of Steel Construction (AISC), and Concrete Reinforcing Steel Institute (CRSI) vibration standards are used to model harmonic loading parameters and estimate the peak acceleration response for various structural stiffness and damping parameters. With this data, the range of natural frequencies and damping ratios that meet the various acceptance criteria can be determined.

Structural Model

Just like the properties of the continuous floor structure are represented by single parameter values, the crowd force can be represented by a simplified model. In this case, it is assumed that the crowd is distributed along the entire span of the beam and that the crowd acts in unison to apply a harmonic load. With this simplification, the crowd is described by a harmonic forcing function with an amplitude scale factor and an excitation frequency.

Design Factors For floor vibrations, engineers are primarily concerned with the peak acceleration response of the structure. Each standard has a different way of calculating the peak acceleration response, but there are many similarities and commonalities.

This article separates the different components into three non-dimensional design factors: the crowd load factor, the structural amplification factor, and the harmonic load factor. These quantities are themselves functions of the properties of the structure and values given by the vibration standards. When used in the scope of this article, the peak acceleration response is given by the product of the non-dimensional design factors and g, the constant of gravity. The peak acceleration is commonly expressed in units of gravity, in which case the peak acceleration is just the product of the non-dimensional design factors.

Floor structures are composed of a variety of structural systems with diverse materials and configurations. Using the materials, geometry, and loading, the floor structure can be analyzed in terms of its Crowd Load Factor vertical vibration modes. For simple and regular structures, the individual spans can be separated into The first design factor is the crowd load factor. single degree of freedom (SDOF) models (indepen- This is simply the ratio of the static crowd weight dent systems with one dominant mode). divided by the total service load (dead load plus When the overall floor structure is separated static crowd weight). For coordinated crowds in into individual SDOF models, the dynamic open areas, ISO 10137 specifies that a typical model can be described as a set of independent value of the static crowd weight is approximately mass-damper-spring systems. This dynamic model combines the effects of the distributed mass, damping, and stiffness into a simplified model. In this model, the mass is the tributary dead load supported by the beam divided by the constant of gravity. The damping is assumed to be viscous, characterized by a percentage of critical damping, and the spring behavior is equivalent to the vertical stiffness of the floor structure.

Employing these parameters, the natural frequency of the SDOF model can be computed using the properties of the floor structure (dead load, bending stiffness, and span length). Likewise, the dynamic model can be expressed using the mass, natural frequency, and damping ratio if these parameters are determined through other means such Figure 1. Structural amplification factor versus frequency ratio for various damping ratios. as experimental testing.

20 March 2018

11 pounds per square foot (psf ) and the maximum value can be as high as 84 psf, using a 150-pound average person weight. AISC Design Guide 11, Floor Vibrations Due to Human Activity, assumes a static crowd weight of 31 psf for a seated concert. This standard does not provide a static crowd weight for standing room concerts. The CRSI vibration standard contains the same values as Design Guide 11.

As the static crowd weight is increased, the total dynamic mass of the structure changes which, in turn, causes the structure’s natural frequency to decrease.

Structural Amplification Factor The structural amplification factor is the response amplification from a harmonic load applied to a flexible structure. In this case, the crowd is providing a time-varying load at a particular frequency. You can see this behavior in Figure 1, which shows the dynamic amplification versus the frequency ratio (the crowd force frequency divided by the structure’s natural frequency). Several values of the structure’s damping ratio are shown and, as the frequency ratio approaches a value of 1.0,

the dynamic amplification can be quite significant as a result of resonance (i.e., the harmonic load is applied at the natural frequency).

Designers are specifically interested in designing for the worst-case scenario, which occurs when the crowd force frequency is the same as the structure’s natural frequency. Under this resonant condition, the structural amplification factor is a function of the structure’s damping, as Figure 2. Harmonic load factor versus crowd excitation frequency for shown in Figure 1. For low ISO, AISC, and CRSI vibration standards. Note that CRSI follows values of damping (<2%), AISC identically, except for two additional data points. the structural amplification is over 25x, which indicates that even vertical vibrations do not commonly result in a low level of crowd force may cause a large inelastic deformations. ISO provides recomacceleration response. mendations for design damping ratios based Most civil structures are lightly damped on the specific structural system used, with structures (<5%) which can result in high preliminary design values between 1.3–2.0%. structural amplification factors. Also, the AISC and CRSI allow for a damping ratio of damping ratio used for vertical floor vibra- 6% to be used for rhythmic activities because tions is often different from the damping human occupants will act as shock absorbers ratio used for lateral seismic forces because which have an effect similar to damping. continued on next page ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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Figure 3. Response factor for various levels of structure natural frequency and damping ratio using ISO 10137 loading parameters.

Harmonic Load Factor The harmonic load factor is computed based on the design guides and takes into consideration the crowd load frequency to compute the load factor. ISO assumes that the crowd can apply a harmonic load between 1.5–3.5 Hertz (Hz), which is equivalent to 90–210 beats per minute (bpm). A frequency dependent factor is applied for the first three harmonics. The standard also includes a crowd coordination reduction factor to account for the relative ability of crowds to act in unison.

AISC assumes that the crowd can apply a fundamental harmonic load between 1.5 Hz and 2.7 Hz (90–162 bpm) and applies a factor for the first two harmonics. CRSI uses the same values as AISC but extends the upper limit of the crowd frequency to 3 Hz (180 bpm).

The harmonic load factor is shown for each standard in Figure 2.

Acceptance Criteria Each design standard provides its own specific acceptance criteria. However, the two basic types of criteria are the peak acceleration and the response factor. The peak acceleration is the maximum acceleration associated with the harmonic crowd load and is the primary engineering design parameter of interest. The response factor relates to the intensity of vibration felt by human occupants and is defined as the number of times above the baseline of human perception to vibration, which is approximately 0.0005g for frequencies from 4 – 8 Hz. As a relative measure, the response factor is the ratio of acceleration response to the level of human vibration perception at a specific frequency.

Figure 4. Peak acceleration for various levels of structure natural frequency and damping ratio using AISC Design Guide 11 loading parameters.

Different acceptance criteria are used by different standards. At a basic level, the goal is to limit the intensity of the vibrations in the frequency range where humans are sensitive to such vibrations. As a result, each design standard provides similar restrictions even though different acceptance criteria are used.

Design Example To illustrate the design guidance of each standard, a design example is offered where a floor structure with a 100 psf dead load is analyzed for a variety of stiffness and damping ratios.

The results are presented in Figures 3, 4 and 5 for each design standard and using the recommended crowd and harmonic load factors.

ISO recommends that the static crowd weight is 11.5 psf for rhythmic activities in areas without seats. Assuming the structure has a natural frequency of 2.5 Hz and damping ratio of 6%, the peak acceleration response is 0.82g, and the response factor is 900. ISO recommends that the vibration should not exceed a response factor of 200 for crowd comfort or 400 for crowd panic, which is not met for this example. It is necessary to increase the natural frequency to 7 Hz or greater or increase the damping ratio to 10% and the natural frequency to 5 Hz or greater, to meet the crowd panic acceptance criterion.

AISC recommends a static crowd weight of 31 psf for a lively concert with fixed seating but does not provide guidance for standing crowds. The peak acceleration is estimated to be 0.51g, and the response factor is 560, assuming the same structure as before. AISC recommends that the peak acceleration not exceed 0.07g for rhythmic activities, which is not met for this example. It is necessary to

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increase the structure’s natural frequency to 6 Hz or greater to meet the criterion.

CRSI recommends the same static crowd weight as AISC and calculates the same peak acceleration response. However, CRSI recommends an acceptance limit of 0.05g, which is also not met for this example. It is necessary to increase the structure’s natural frequency to 7 Hz or greater to meet the criterion.

Design/Remediation Options There are three basic solutions available to the structural engineer to solve a floor vibration problem: change the natural frequency, increase damping, or add a structural control device.

The first option is to change the natural frequency of the structure so that the structure’s response is outside the frequency range of the crowd’s excitation. The structure’s natural frequency can be raised by increasing the floor’s stiffness or lowered by increasing the floor mass (dead load). Theoretically, both options can achieve the goal of limiting peak accelerations to an acceptable level. However, in practice, adding mass to achieve a low enough natural frequency that is outside the crowd’s excitation range can result in a structure that does not meet deflection or strength requirements. As a result, structural modifications usually aim to add stiffness with the goal of raising the structure’s natural frequency above the crowd excitation frequency’s upper range.

The second option is to increase the damping in the structural system. As previously discussed, damping is difficult to estimate, and there can be mixed guidance as to what damping ratio is appropriate for a specific scenario. However, while it may be difficult to estimate the structure’s damping ratio

The third option available is to utilize a structural control device such as a tuned mass damper (TMD) or an active mass damper (AMD). A TMD is a secondary mass that is suspended from the floor by a system of springs and linear damping devices. The mass, damping, and stiffness of the TMD are specifically designed to tune the secondary mass to a frequency near the structure’s Figure 5. Peak acceleration for various levels of structure natural frequency and damping ratio using CRSI vibration standard loading parameters. natural frequency so that it provides out of accurately, increased damping has a posi- phase forces to decrease the total response of tive effect by decreasing the peak response at the floor. An AMD is like a TMD except that resonance. As a result, a structural engineer an actuator is used to control the motion of can design the support structure to include the secondary mass based on the measured supplemental damping as a way to increase structural response, allowing more efficient the total damping of the system. This can be use of a smaller mass over a wider range of accomplished by using linear damping devices frequencies. Both options can be effective as part of the support structure. for retrofit as they take up a small amount of

space and do not require extensive structural modifications.

Conclusions Concerts often provide a worst-case loading scenario for flexible floor structures. Audience members can bounce, sway, and jump along with the music in such a way that the crowd is synchronized to apply a harmonic load at the same frequency as the music’s tempo. When this excitation frequency corresponds to the natural frequency of the floor structure, significant structural response can occur due to resonance, which may result in unacceptable vibration levels and affect occupants’ comfort.

To prevent unacceptable floor vibrations from occurring during concerts, structural engineers should ensure that the vertical, natural frequency of the floor structure is above 7 Hz. Where this is not feasible, structural engineers can decrease the vibration intensity by adding supplemental damping or including a structural control device.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

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2/6/18 9:02 AM

EnginEEr’s W notEbook aids for the structural engineer’s toolbox

hen damaged members and connections are identified, it is imperative to assess the extent that the damage may impact the structural integrity of the coldformed steel member or connection. As stated in the Engineers Notebook article, Evaluation of Cold-Formed Steel Members and Connections (STRUCTURE, February 2018), assessment should be made quickly to contain the damages or protect the public welfare.

Remediation of damaged cold-formed members and connections may include the following.

Repair of Damaged Coating Because of the galvanic action provided by the zinc coating, AISI S200, North American Standard for Cold-Formed Steel Framing – General Provisions, states that additional corrosion protection shall not be required on edges of metallically coated

Remediation of Cold-Formed Steel Members and Connections

By Roger LaBoube, Ph.D., P.E.

steel framing members that are shop or field cut, punched, or drilled. Thus, small scratches or abrasions in the galvanized coating need not be of concern. Zinc-rich paint may be used to remediate larger damaged areas of the coating.

Damage to the Coating Caused by Welding

Roger LaBoube is Curator’s Distinguished Teaching Professor Emeritus of Civil Engineering and Director of the Wei-Wen Yu Center for Cold-Formed Steel Structures at the Missouri University of Science and Technology. Roger is the current chairman of the American Iron and Steel Institute’s Committee on Framing Standards. He can be reached at laboube@mst.edu.

AISI S200 stipulates that, for welded connections, the weld area is to be treated with an approved treatment to retain corrosion resistance. However, based on when a weld area is not directly exposed to the environment, for example, a weld in the cavity of a properly constructed weather-tight wall or roof, remediation of the coating may not be required.

Damage Caused by White Rust White rust is characterized by the formation of a light film of white powdery residue and frequently occurs on galvanized products. Provided the steel members are well ventilated and well-drained, white rust rarely progresses past the superficial

stage. It can be brushed off but will generally wash off in service with normal weather. No remedial treatment is usually required.

Damage Caused by Red Rust Red rust areas, usually a sign of extensive damage, if not treated, may progress to an undesirable stage and therefore should be wire brushed and the damaged area coated with a zinc-rich paint.

Repair of Screw Connections The available strength of a screw connection may be evaluated using the provisions of Section E4 of the North American Specification for the Design of Cold-Formed Steel Structural Members, AISI S100. In addition to these provisions, AISI S200 provides additional guidance based on the inplace conditions of the connections, e.g., stripped screws, screw spacing, edge distance, etc. To estimate the strength of a screw, refer to CFSEI TN F701, Evaluation of Screw Strength.

Common problems affecting the capacity of screw connections include: Screw Pattern The AISI framing standards are silent regarding the influence that the screw pattern may have on the available strength of the connection. Research

by Sokal and LaBoube has shown that the screw pattern did not influence the available strength of a connection. That is, if the screw connection requires 8 screws, the pattern 2 rows of 4 screws, 4 rows of 2 screws, or screws randomly located achieved the same available strength. This is predicated on proper spacing of the screws as required by AISI S100.

Screw Spacing AISI S100 stipulates that the center-to-center spacing of screws must be at least 3 times the nominal diameter of the screw. However, where the centerto-center spacing of screw fasteners is less than 3 times the nominal diameter but greater than or equal to 2 times the nominal diameter, screw fasteners shall be considered 80 percent effective per AISI S200. Thus, a 20 percent reduction in capacity results with closely spaced fasteners. For connections with closely spaced screws, additional screws may need to be added to the connection to achieve the desired design capacity.

Stripped Screws

Gap between connected members.

24 March 2018

The impact of a stripped screw in a connection depends upon the force being transferred by the screw. AISI S200 provides guidance for assessing the impact of stripped screws. For stripped screws in direct tension, the screw is not to be considered effective. Thus, additional screws must be added to the connection. However, for stripped screws in shear, as many as 25 percent of the screws in the connection may be stripped without a loss in

connection capacity. If more than 25 percent of the screws are stripped, additional screws must be added to achieve the desired capacity.

Gaps between connected members may be a problem and should, if found to affect the capacity of the member or connection, be remediated. When connecting two members, AISI S200 stipulates no separation be present between the components. However, no separation is sometimes difficult to achieve. Tests at both Virginia Tech and the University of Missouri-Rolla have shown that a separation or gap of 0.15 inch is possible with minimal degradation of the connection strength.

Thus, a small gap, for example, equal to the thickness of the thinnest ply, may be deemed acceptable. Therefore, it is suggested that when evaluating the strength of a screw connection using AISI S100 Section E4.3, the criteria shown in the Table should be used.

Remediation

Table of criteria for evaluating the strength of a screw connection.

Case

Distance Between Plies

Gap Between Sheets Fiberglass Insulation Gypsum Wall Board Rigid Foam Insulation

thickness of thinnest ply

Reduction to AISI S100 E4.3 no strength reduction required

≤ 0.15 inch

no strength reduction required

⁄8 inch

0.74 (33 mil or thicker)

2 x 5⁄8 inch

0.65 (43 mil or thicker)

1 inch

0.54 (33 mil or thicker)

2 inch

0.44 (33 mil to 54 mil)

2 inch

0.68 (54 mil or thicker)

4 inch

0.39 (54 mil or thicker)

5

a brace, proper bracing of the member must be maintained if the sheathing material is to be removed during the remediation activity.

For example, to maintain a member for full yield moment capacity, Maxo, bracing intervals should be less than or equal to Lu where Lu is defined by AISI S100 Commentary Eq. C-C3.1.2.1-11.

Be Wary of Loaded Members

Consider the Type of Remediation Carefully

When members or connections are under load, the remediation plan must consider the impact of any remediation activity. For member design that utilized the sheathing as

The use of screw connections is preferable to welding if the wall, floor, or roof cavity has insulation or other combustible materials. Screw connections may be preferable to

bolted connections because of the difficulty with drilling bolt holes.

Temporary Supports Scaffolds must be engineered and designed to adequately and properly support existing members and connections in a manner that will not compromise the structural integrity of the cold-formed steel framing.▪

The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

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The Historic Trefethen Winery Repair and Retrofit in the Aftermath of the Napa Earthquake

By Marianne Wilson, S.E., Kevin Zucco, S.E., and Brett Shields, P.E.

T

refethen Family Vineyards is a family-owned estate winery located just to the north of Napa, California, within the Oak Knoll District AVA. Their historic winery building, originally known as Eshcol, was constructed in 1886 by Hamden McIntyre, a Scottish civil engineer, honorary ship captain, and well-known builder of wineries in the Napa Valley (Figure 1). McIntyre designed a quartet of similar gravity-fed winery buildings in the Napa Valley during this era: Eshcol, Inglenook, Far Niente, and Greystone, the current home of the Culinary Institute of America. The Trefethen/Eshcol building is unique as an exposed heavy-timber framed structure located on the valley floor, which required a horse-drawn elevator system to hoist grapes to the top level for production. The other three McIntyre wineries were constructed of stone and built against hillsides at the edge of the valley, allowing horse-drawn carts to deliver grapes directly to the upper levels. The Eshcol winery was purchased by the Trefethen family in 1968 and was listed with the National Register of Historic Places in 1987, recognized as the only 19th century, wood-framed, gravity flow winery remaining in Napa County.

Figure 1. Historic Trefethen Winery building (Eshcol Winery c 1915).

Courtesy of Trefethen Family Vineyards.

structure is clad in a simple 10-inch painted straight sheathing/siding, the interior spaces are nearly entirely clad with immaculate redwood tongue and groove sheathing. This creates majestic vaulted spaces at the second floor, showcasing timber construction with minimal hardware and let-in connections likely influenced by the builder’s maritime experience. The existing lateral force resisting system was limited to the exterior, straight sheathing at the building perimeter.

Earthquake

In the immediate aftermath of the 6.0 magnitude Napa earthquake on August 24, 2014, the historic structure rested in a precarious tilt with the second and third story shifted approximately four feet to the west (Figure 2). Nearby ground motion readings indicate specComposition tral accelerations ranged from 0.4g to 1.7g for low-period, one- to The three-story winery structure is 125 feet by 60 feet and approxi- two-story wood framed structures. The largest deflection occurred mately 18,000 total square feet. Before the 2014 Napa earthquake, at the North end of the second-floor level where water-filled tanks the building housed the Trefethen tasting room and offices, though and barrels were stored at the time. The filled water tanks constituted the majority of the space was utilized for storage of wine in barrels. a large concentrated mass at the northern end of the second floor, The building utilizes exposed 10- and 12-inch-square timber post and increasing the seismic forces acting in this area where the larger localbeam construction with exterior wood framed bearing walls. Wood ized horizontal deflections occurred. framed floors are topped with layers of straight sheathing, and trussed With the potential for total building collapse an aftershock away, roof framing is topped with skip sheathing and non-historic plywood. steel shoring and cribbing were immediately erected to prevent further The second-floor diaphragm level is interrupted where the 24-foot- offset and to support displaced gravity members. The timber-framed wide center bay is four feet lower than the adjacent primary levels, gravity system was constructed without positive connection between creating a discontinuity in the diaphragm. While the exterior of the posts and beams, or posts and foundations, allowing posts at the first level to rotate and “walk” without resistance as the building cycled through deflections. While this lack of connection restraint released the lower level posts and beams from sustaining significant damage at connections, the magnitude of the deflection caused several first-floor posts to disengage completely from beneath the beams. Second level posts adjacent to the diaphragm step at the center bay were constrained within a several-foot-tall pony wall between the diaphragm levels. This resulted in a significant amount of flexural damage to the posts directly above the main secondfloor level (Figure 3). Multiple posts at the upper levels sustained damage at let-in Figure 2. Post-earthquake deflection and localized damage at second-floor level.

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beam connections where large splits developed at interior corners of cuts.

Significant structural documentation was performed through multiple site visits to understand the existing framing systems and connections fully. A 3D point cloud survey was also taken of the structure in its deformed state to aid in shoring design and erection. When overlain onto Figure 3. Damaged post at a step in the seconda non-deflected Building floor diaphragm.

Information Model, the 3D point cloud helped to illustrate existing atypical framing and provide further insight into the extent of the deformations developed within the structure (Figure 4 ), as well as shape the retrofit strategy.

Revival When determining the structural approach for repair and retrofit of the historic structure, extensive coordination with the Trefethen family, a historic preservation architect, and a contractor was critical to ensure new elements improving the stability and resiliency of the structure did not detract from the buildingâ&#x20AC;&#x2122;s historic fabric. Discussion regarding the preferred design criteria for retrofit ranged from exclusive use of the California Existing Building Code (CEBC) and California Historic Building Code (CHBC) to minimize addition of new elements in the structure, to a full retrofit utilizing the current California Building Code (CBC) to maximize building performance in a future seismic event. Ultimately, the CHBC and CEBC were used to review existing gravity elements, with a voluntary upgrade to current CBC Life Safety level performance for new lateral resisting elements.

Figure 5. Retrofitted gable end wall framing.

Rebuilding While the existing straight sheathing at the exterior of the structure would have been adequate to resist historical building code lateral loading for most locations, plywood shear walls added to the full exterior increase the structureâ&#x20AC;&#x2122;s seismic capacity and resiliency. To preserve the more unique and fragile interior redwood siding, temporary removal of the exterior straight sheathing, which suffered significant damage in the earthquake, allowed for installation of new plywood.

Additional wall framing members were added to complete the load path for out-of-plane forces and provide minimum stud spacing for the new shear walls (Figure 5). Full height Laminated Strand Lumber (LSL) studs accommodate the stud length required at gable end walls.

As an added benefit to exposing the wall framing, rigid insulation was installed improving the energy performance of the structure.

The straight sheathing was painstakingly labeled before removal for refurbishment to ensure accurate reinstallation, to maintain the correct historic aesthetic at the exterior, and trim elements within the window openings were coordinated with the historical architect to accommodate the additional ½-inch wall thickness.

A new plywood roof diaphragm replaced non-historical roof sheathing and was installed over the historical skip sheathing, with the addition of flat blocking shims over rafters allowing the historical framing elements to remain. New robust continuous concrete stemwall elements added at the building perimeter, and below interior bearing lines, were designed to match the profile of original stone stemwalls.

This preserved the massive existing four-foot-square, mortared granite foundations as coordinated with the geotechnical engineer. The new concrete elements were designed for the full structural demand, transferring bearing and shear forces to the undamaged historic stone foundations through epoxy dowels.

New bolted steel side plates, configured for minimal visual impact, provide positive connections at gravity framing between existing beams, posts, and foundations. Bolted steel flitch plates provide additional flexural strength to floor beams, as required, resulting from occupancy changes at the upper levels. Damaged or split framing members are repaired in-situ with color-matched injected wood epoxy and bolted steel side plates wherever possible. Nearly all original framing members were preserved, with very few completely replaced.

Strengthening Figure 4. REVIT model including deflected shape 3D point cloud.

STRUCTURE magazine

Due to the length of the building and diaphragm discontinuities at the second level, the existing multi-layered, straight sheathed

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floor diaphragms were inadequate for seismic design forces as configured. The addition of new interior lateral force resisting elements reduced the existing diaphragm spans, allowing the diaphragm to remain without strengthening.

Ordinary steel moment frames were selected to maintain the open post and beam feel of the space and to minimize Figure 6. Finished interior at steel moment the prescriptive detailing frame. Courtesy of Adrian Gregorutti and requirements. The flexTrefethen Family Vineyards. ible diaphragms in the east/west direction allow the gable end, wood shear walls to be designed for a standard Response Modification Coefficient (R) of 6.5, and interior ordinary steel moment frames be designed for an R-value of 3.5.

Third-floor wood framed shear walls over moment frames were designed for the moment frame R-value. Steel frame columns were located immediately adjacent to existing timber posts to reduce their impact on the character of the Figure 7. Remembrance post. Courtesy of Adrian space (Figure 6 ). Because Gregorutti and Trefethen Family Vineyards. of installation logistics, including fire risk from welding, the frames are configured into smaller “portal frame” pieces. The moment connections were prefabricated with beam and column stubs, locating bolted splice connections in each beam and welded splices at columns away from the adjacent historical combustible material. This prefabricated portal frame assembly allows smaller pieces to be installed within the confined spaces of the structure with minimal modifications to existing framing. An additional challenge in the design of the moment frame was the offset from the primary bearing line to maintain existing post and beam elements. Custom steel shear transfer plates with vertically slotted holes accommodate the horizontal offset from frame to diaphragm elements, while simultaneously allowing vertical tolerances in existing framing elevation. These were spaced to accommodate the reinstallation of historical knee braces at posts.

Figure 8. Renovations completed in 2017. Courtesy of Adrian Gregorutti and Trefethen Family Vineyards.

multiple generations have grown up in the winery and, specifically within this building, as children playing amongst the barrels as their parents worked. The family considered the earthquake repair of the structure not as something to be hidden, but as another significant chapter in the life of the historic building. With the structural repairs and improvements, not only did the building survive but was made stronger, continuing its legacy as a living piece of winemaking history in Napa Valley. As a final tribute to the earthquake that rocked the structure, additional steel gravity framing was provided so that a single Remembrance Post could be left in its destructed state to illustrate the magnitude of the event the structure withstood at 3:24 am, on August 24, 2014 (Figure 7 ).

Rebirth The structural repair and retrofit were completed in the Fall of 2016.

The revitalization of the winery building continued with interior architectural improvements to provide a new guest experience and improved winemaking facilities. The lower level winemaking areas are now showcased through glazed walls on either side of the center bay, with more barrel storage and the tasting room at the second level.

These features allow guests to appreciate the two-story vaulted space with historical redwood siding and views of the estate vineyard. Renovations were completed for a grand reopening of the tasting room in May 2017 (Figure 8 ).▪

Legacy The Trefethen family placed high importance on saving as much of the existing structural framing as possible to maintain the historic character of the structure, just as the architectural elements were preserved. This included the straight sheathing and historic windows being repaired and reinstalled to the original aesthetic. Since the family’s acquisition, STRUCTURE magazine

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Marianne Wilson, S.E., is a Senior Associate at ZFA Structural Engineers in Santa Rosa, California. She can be reached at mariannew@zfa.com.

Kevin Zucco, S.E., is an Executive Principal at ZFA Structural Engineers in Santa Rosa, California. He can be reached at kevinz@zfa.com.

Brett Shields, P.E., is an Engineer at ZFA Structural Engineers in Santa Rosa, California. He can be reached at bretts@zfa.com.

Project Team Owner: Trefethen Family Vineyards Structural Engineer: ZFA Structural Engineers Historic Preservation Architect: Preservation Architecture Architect: Taylor Lombardo Architects General Contractor: Facility Development Company March 2018

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Hibernia Bank Building

Historic Renovation and Seismic Retrofit

By Kelly Cobeen, S.E., Terrence Paret, and Owen Rosenboom, Ph.D., P.E., S.E.

L

ocated in San Francisco, the landmark Hibernia Bank Building recently underwent an ambitious historical renovation and seismic retrofit. First constructed in 1892, with a major addition just a few years later, the building served as headquarters for the Hibernia Bank for more than 90 years, was briefly used as a police department substation, but was then left vacant for a decade. In the late 2000s, new owner Dolmen Property Group took on the sizable task of renovating the building to allow occupancy once again.

Renovations introduced improved fire safety, access, egress, and seismic safety while leaving the historically significant interiors and exteriors virtually undisturbed. Key to achieving the historic preservation objectives was reliance on the seismic resistance already provided by the massive granite and brick masonry walls that allowed the building to survive the 1906 earthquake relatively unscathed. An analytical study informed retrofit measures that surgically supplemented this seismic resistance to meet current seismic retrofit criteria. This article discusses historical background, the basis for design, and seismic retrofit techniques while illustrating the project philosophy of treating seismic retrofit and historic preservation objectives with equal priority.

Hibernia Bank Building In 1889, architect Albert Pissis and his partner William Moore won a national competition for the design of a new headquarters for the Hibernia Bank at the corner of Jones, McAllister, and Market Streets (Figure 1). The building is dominated by white granite masonry, including colossal fluted granite column shafts, each cut from a single stone. It was one of architect Pissisâ&#x20AC;&#x2122; first structures in San Francisco after returning from instruction at the Ă&#x2030;cole des Beaux-Arts in Paris, STRUCTURE magazine

France. Other Pissis masterpieces include the Flood Building, the Emporium, and Temple Sherith Israel, all of which also survived the 1906 earthquake.

The building interior is dominated by a vast banking Figure 1. Hibernia Bank Building in 1894, before hall with a ceiling the addition. Courtesy of San Francisco History Center, San Francisco Public Library.

35 feet above the banking floor, highly detailed painted plaster, and stone finishes. The banking hall is crowned by two large skylights and matching ceiling level laylights (Figure 2). Two stories of luxury offices are located on the McAllister Street side.

The building is generally rectangular in plan, with dimensions of approximately 130 feet by 120 feet (Figure 3). The primary vertical elements of the structure include four massive perimeter unreinforced brick and granite masonry bearing walls and massive interior brick walls. The roof system uses long-span steel trusses, steel purlins, and a concrete slab. The floor system uses cast concrete topped brick arches supported on steel beams.

Available reports, including a 1906 U.S. Geological Survey report, and photographs suggest that the building survived the 1906 earthquake with little earthquake damage, but with damage from the following fire. Using information on performance and estimated ground shaking intensities from the 1906 earthquake, the design team

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ran analytical studies that corroborated the observed good behavior.

Key to this behavior was the existing massive masonry walls that served to limit drift to modest levels in spite of the tendency towards torsional response (Figure 3). These indications of good seismic performance, combined with the adopted historic preservation objectives, were the primary justification for a focused, surgical seismic retrofit approach.

Basis for Design The historic structures report identified the vast majority of the interior and exterior of the building as “very significant.” The Secretary of the Interior’s Standards for Treatment of Historic Properties, a primary national guideline for historic preservation work, calls for work such as this to “…make possible a compatible use for a property … while preserving those portions or features which convey its historical, cultural, or architectural values.” Attention to the preservation of historic fabric and maintenance of character-defining features were thus determined paramount in guiding the retrofit solution.

The era when a building of this size could economically function as a retail bank has long since passed. Therefore, the owners directed that the building renovation maximize potential future occupancy while meeting historic preservation objectives. This combination barred the banking hall from being broken into smaller rooms, implying Group A assembly occupancy. This potential change from the historic Group B occupancy triggered the structural evaluation of gravity load systems. At the same time, the potential occupant load in the main banking hall implied Occupancy (Risk) Category III. It was also identified that the building had not undergone evaluation or retrofit in response to San Francisco’s 1992 unreinforced masonry building (UMB) ordinance.

The resulting range of work dictated use of a variety of building codes, each relevant for some portion of the work. Use of the 2010 California Historical Building Code (CHBC) is permitted by California state law for determining code criteria for a wide range of work on eligible or designated historic structures, and so was used as the primary starting point. Following the CHBC criteria, gravity systems were checked for live loads consistent with the new occupancy. Following the CHBC and the 2009 and 2012 editions of the International Existing Building Code (IEBC), seismic retrofit minimum criteria were set and were verified to meet the intent of the 1992 UMB ordinance. The CHBC and the 2010 San Francisco Building Code (SFBC) criteria included remediation of the hazard posed by the hollow clay tile (HCT) walls located along exit paths. The new structure, including extensive new egress paths, was designed in accordance with the SFBC. The CHBC provides broad discretion for the use of alternate materials and methods of construction provided that they meet the intent of the CHBC, in recognition of the special conditions encountered in dealing with archaic materials and construction. Based on this, several alternate methods of construction were identified for this project, ranging from a study of adhesive anchors in granite stone masonry to center core systems and beyond. The applicable codes and methods of construction were explained in a basis of design document that was vetted with the building department.

A number of available standards and guidelines were consulted during the design of the seismic retrofit. With design forces remaining in the near-elastic range to protect the masonry, the retrofit is very much in keeping with the spirit of the ASCE 41 linear elastic procedures. Full application of ASCE 41 procedures, however, would have relied on analytical studies of very limited accuracy and benefit. This speaks to the need to maintain the provisions of the CHBC to provide a seismic retrofit basis for buildings with archaic materials and systems that are STRUCTURE magazine

Figure 2. The Hibernia Bank Building main banking hall with banking counters and stained glass laylights overhead. Courtesy of Bruce Schneider.

Figure 3. Hibernia Bank Building floor plan with shaded masonry walls.

Diagonal hatched walls are of combined granite and brick masonry.

beyond the testing and numerical quantification basis of ASCE 41 and similar methodologies.

Seismic Retrofit Techniques Retrofit measures for the primary seismic force-resisting system focused on improved strength and connectivity of the existing roof diaphragm and wall systems. The minimum seismic base shear for evaluation and retrofit used a seismic response modification coefficient (R-factor) of 1.5. As a result, the primary structural elements, both existing and new, are anticipated to stay in a near-elastic stress range with very limited deformations. The following is an overview of seismic retrofit techniques used.

Roof Strengthening Around the perimeter of the building, granite balustrades were temporarily removed to permit installation of reinforced concrete bond beams. The bond beams strengthen the walls by preventing the propagation of cracks to the free edge of the masonry and act as

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for this project was more difficult than usual due to the unpredictable mix of brick masonry and much harder granite masonry over the height of each core. Figure 4 shows center cores on one of the exterior wall elevations.

Corrugated Sheet Steel Shear Wall A secondary lateral bracing system was desired in the executive office wing, but the presence of highly significant finishes presented difficulties. A corrugated sheet, steel shear wall was selected because its relatively high capacity at low drift levels and moderate capacity at larger drift levels provided the best combination of deformation compatibility and control of load path.

Hollow Clay Tile Wall Stabilization In the repairs following the 1906 earthquake, wood partition walls throughout the building were replaced with single-wythe or double-wythe hollow clay tile Figure 4. Center coring at Jones Street elevation. Heavy dashed lines indicate center core (HCT), chosen for its “fireproof ” properties. The location and extent. behavior of such unreinforced, ungrouted HCT chords and collectors for the roof diaphragm. The bond beams also masonry in an earthquake, however, is usually quite poor, so increased serve to anchor the tops of the wall center-cores and as anchorage out-of-plane stability was required along paths of egress, without points for roof-to-wall ties. A number of similar reinforced concrete damaging significant finishes. In locations with significant finishes on members were provided to serve as chords and collectors within the one face, cold-formed steel (CFS) stud walls were installed alongside interior of the roof. To provide a connection between the bond beams the opposite face, and the CFS and HCT walls interconnected with and the existing concrete roof diaphragm, and to create continuity fasteners on a close on-center spacing. In locations with significant between adjacent roof segments, a pre-tensioned “tie plate” was cast finishes on both wall faces and where access was available at the top over each roof diaphragm segment along its perimeter. The interface of the wall from the attic, the HCT was drilled over the full height was pre-compressed with regularly spaced pre-tensioned bolts and using segmental drilling equipment to provide a clear vertical chase steel plates, providing a zero-slip shear friction connection between for installation of vertical reinforcement and grout. the existing roof diaphragm and the bond beams. A carbon fiber reinforced polymer (CFRP) system was used to complete the roof Conclusions strengthening. Surface-mounted CFRP sheets were installed at the top of the slab. Near-surface-mounted CFRP rods were provided Over one hundred years after the Hibernia Bank Building survived around the perimeter and at openings in the diaphragm for chord the 1906 earthquake with little structural damage, the building has strengthening and crack control. Additional surface-mounted sheets undergone an extensive historic renovation and seismic retrofit, were provided on the bottom of the roof slab with through-thickness making it eligible for a range of new uses. Pivotal from a structural CFRP anchors to basket high-stress regions and protect against fall- standpoint was the time taken to understand the inherent positive ing hazard from isolated pieces of roof diaphragm, should localized seismic characteristics of the building, and use of the California degradation occur during an earthquake.

Historical Building Code framework for legal recognition of alternate materials and construction.

Concrete Shear Walls Although the structure has several massive masonry shear walls, the analytical studies identified the need to add a limited number of strategically located new shear walls. One such location is on the north side of the building where a pair of massive parallel masonry walls, only twelve feet apart (the “bookend” in Figure 3), provide significant north-south seismic mass which could be detrimental to the seismic response. To turn this negative attribute into a benefit, the walls were interconnected with reinforced concrete “web” shear walls such that the entire system resists loads as a vertical box girder cantilevering from the basement. Another strategically placed reinforced concrete wall was located in a closet near the entrance to the building.

Acknowledgements The authors would like to acknowledge and thank owner Dolmen Property Group, contractor Landmark Construction, project architect Elevation Architects, and geotechnical engineer Rollo and Ridley. In addition to the authors, the WJE team also included engineers Jeff Rautenberg, Kari Klaboe, and Jason Porto, as well as historic preservation architect Alan Dreyfuss.▪

Center Cored Wall Reinforcement Center coring of the granite and brick masonry walls and piers was included to provide general connectivity and limit slip in masonry joints. The retrofit involved the coring of holes, installation of high strength steel rods as reinforcing, and grouting with a high-strength, low modulus polyester resin-based grout custom designed to reduce shrinkage and heat build-up during curing. The center coring of walls STRUCTURE magazine

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The online version of this article contains references.

Please visit www.STRUCTUREmag.org.

Kelly Cobeen, S.E., is an Associate Principal with Wiss, Janney, Elstner & Associates, San Francisco office.

Terrence Paret is a Senior Principal with Wiss, Janney, Elstner & Associates, San Francisco office.

Owen Rosenboom, Ph.D., P.E., S.E., is a an Associate Principal with Wiss, Janney, Elstner & Associates, San Francisco office.

March 2018

TIMES SQUARE’S

By Cawsie Jijina, P.E., SECB, and Steve Reichwein, P.E., S.E., SECB

New Addition

Night construction. Courtesy of Ralph D’Angelo.

20

Times Square, or 701 Seventh Avenue, is located on the northeast corner where 47th Street and Seventh Avenue intersect in New York City.

When finished, 20 Times Square will host a variety of functions, including nearly 75,000 square feet of premium retail space and 30,000 square feet of multi-function entertainment spaces, with a premier nightclub and a 7,000 square foot rooftop terrace that overlooks the heart of Times Square. Nestled between the retail space and rooftop is a 150,000 square foot high-end hotel with 452 guest rooms (to be branded as a Marriott Edition, the collaboration between Ian Schrager and Marriott Hotels) and an 18,000 square foot hi-definition LED sign, rising 120 feet above the bustling streets below and wrapping around both the 47th Street and Seventh Avenue facades.

In its finished state, the structure will encompass 378,000 square feet of floor space, rise 550 feet above the street, and have used 2,000 tons of Structural Steel and 21,400 cubic yards of reinforced castin-place concrete.

The Challenges Building a 500-foot-tall tower at one of the busiest pedestrian intersections in the world is an undertaking, to say the least. Additionally, the site is approximately 150 feet east-west by 100 feet north-south, so the design needed to be compact and the floors had to support temporary construction loads, which often dwarf the service design live loads. However, the most significant design challenge was STRUCTURE magazine

imposed by the programming of the building and the New York City zoning codes.

The structure at the base of the tower, or the podium, houses premier and very valuable retail space, so high ceilings and open, column-free volumes were desirable. However, the bulk of the tower is comprised of hotel space, so a thin structural profile was necessary to optimize the number of floors within the prescribed height of the tower, a height which is capped by the New York City zoning code. Since a thin structural floor plate was desirable to optimize the volume of the hotel, columns and walls were needed to thin out the structural profile from floor to floor. However, the zoning code of Manhattan imposed yet another design constraint (the most impactful one of them all) – to maintain the existing building street-wall height of approximately 100 feet versus having a setback at 60 feet height and thus a street wall of 60 feet height, the construction of the building would have to qualify under an alteration permit. To comply, one of three criteria needed to be met: • keep the existing foundations, • keep a minimum of 50% of the existing façade, or • keep a minimum of one-quarter (25%) of the structural floor levels of the existing buildings.

Under an alteration permit, the height of the existing street-wall could remain, and the existing floor level area would be integrated into the podium of the building. That would support the development of an 18,000-square foot wrap-around LED sign. To further compound the issue, there was insufficient documentation available for the existing structures.

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BIM model of the existing structure and temporary support structure.

Courtesy of CNY.

The Existing Structure

An as-built photograph of the existing structure and temporary support structure. Courtesy of Ralph D’Angelo.

were modeled as three-dimensional masses, utilizing point cloud data obtained by the laser scan survey, the new structure was coordinated and designed to avoid conflicts with both the existing structure to remain and the temporary structure. This coordination effort ultimately eased the installation of the new structural framing, saving the construction team and owner crucial time and money.

Site surveying was also conducted by the construction manager and the structural steel erector to verify the information obtained by the three-dimensional laser scan survey and to better pinpoint the detailing requirements associated with integrating and re-supporting the existing structural steel frame with the new structural steel. Having this very detailed survey information not only tightened the coordination and design of the new structure but also helped the structural steel fabricator and Engineer of Record, Severud Associates, detail connections between the new and existing structural steel frames.

The existing structural system of 701 Seventh Avenue, built in 1910, was comprised of a structural steel frame, cinder concrete flat arch floors, and non-bearing masonry walls. The footprint of the building originally formed an “L” along 7th Avenue and 47th Street and rose up 10 stories above the street, topping out around 150 feet in height. This type of construction was revolutionary to that era, as most structures up to that point utilized masonry walls on the exterior as load bearing vertical elements. Very limited documentation was available for both the structural and architectural aspects of the existing structure.

To further complicate retaining 25% of the existing structure, a very intricate bracing system was introduced (designed by Howard Shapiro and Associates) to open key areas of the site to excavation crews while maintaining the stability of the existing structure that was to remain. This temporary bracing system was comprised of two forty-foot-long Pratt Trusses above the ground floor, caisson supported mast towers (which were extended along with the excavation), elevated caisson caps, braced frames, shoring columns, and shoring header beams. Unknown existing structural conditions warranted full-time site supervision by Howard Shapiro and Associates during installation of the temporary bracing and stability systems.

Due to the limited documentation, a three-dimensional laser scan survey was conducted on the architectural shell early in the project and of the existing structure later as the project developed. Additionally, the temporary bracing structure was installed to suit the multitude of different field conditions, which arose during inception. Thus, the laser scan also served as a three-dimensional as-built rendering of the temporary bracing and stability structure. Once the Overall view of the site at the completion of existing and temporary bracing structures foundations. Courtesy of Ralph D’Angelo.

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The Transfer Solution A retail base podium, which favors very long, deep, open structural spans, had to be fused with a hotel tower, which favors a very shallow structural profile. Further, the base podium needed to be designed and detailed around the existing building structure and the concrete tower was scheduled to host a variety of multi-functional volumes.

Achieving these program constraints with one building material or structural system was not possible, so an elegantly designed structural transfer was required. A sturdy structural base had to support a heavy and compact tower.

The hotel tower, a structure composed of a cast-in-place concrete flat plate system, fifteen columns (spaced roughly 25 feet oncenter), two shear wall cores, and a lot-line shear wall, needed to be transferred onto a steel frame which maintained an open floor plan by spanning fifty-plus feet between

Erecting a 10-foot-deep plate girder for the seventh level transfer system.

Courtesy of Ralph D’Angelo.

columns. A well-positioned mechanical level served as the dividing line between the hotel and the retail spaces; nestled in this vast space of mechanical equipment, the transfer structure that supports the hotel tower was proposed. Thirty-five plate girders, ranging in depth from 36 inches to 120 inches, transfer the concrete columns, the largest of which was a ten-foot-deep by three-foot-wide element weighing more than 120,000 pounds.

Fortunately, the lot-line shear wall transfers directly onto a structural steel braced frame below, and one of the shear wall cores spanned from foundation to roof. However, the main hotel elevator core, comprised of two, C-shaped shear walls, transfers to create a vast open retail space below. Two parallel 60-ton Transfer Trusses accomplish the Hotel Core Transfer and deliver the gravity load to four super columns each weighing about 1,200 pounds per linear foot. The lateral forces are transferred through reinforced 9th Floor and 7th Floor slabs that serve as diaphragms, and the combined system delivers all of the hotel tower’s forces to the structural steel system of the RetailEntertainment Podium.

An Open Podium Structure

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The optimal “White Box” retail and entertainment space requires large, open areas with the flexibility to run escalators and elevators, as well as stack merchandise, create unique experiences, entice

STRUCTURE magazine

consumers to enter the space, and make the experience commercially viable; revenue per square foot of floor area is the only driver.

Columns are few and far between in the podium retail structure, due largely to the transfer structure on the 7th floor. Bracing is also scarce, but wind and seismic (lateral) forces are omnipresent; compounding the issue, the main lateral force resisting system of the hotel tower above ceases at the 7th floor. Stability had to be maintained by a minimally intrusive structural system, but large, built-up forces were present.

A megastructural steel “A” frame was introduced on both the 47th Street and 7th Avenue façades to stabilize not only the 120-foot podium structure but also the entire 400-foot-tall hotel and entertainment tower perched on top of the 7th-floor transfer structure. These two A-frames perfectly fit the programming of the retail space, since the perimeter of the building from the 3rd floor up is encapsulated by the wrap-around LED screen.

Hence, exterior structural steel braces and columns stabilized the entire building structure. At the same time, the base of the podium between the street level and the 3rd floor offers prime store-front exposure to the thousands of passersby on Broadway and Seventh Avenue.

Once all forces reach the ground floor, a cast-in-place concrete foundation system, extending 50 feet below grade, collects and resists these forces. The base of the structural steel A-frame is integrated directly into the cast-in-place foundation system to ensure a direct and smooth force transfer.

Cohesive Structural Systems The fusion of structural steel with cast-in-place concrete presents numerous challenges. Going from a cast-in-place concrete foundation to a structural steel podium, and then again to a cast-in-place concrete tower was a logistical challenge solved by creating a nuanced timeline where each trade operated independently of all other trades, and in its own separate vacuum.

While this system posed the most challenges to the design, logistics, and capital cost, it was the most efficient from a schedule perspective and saved a month when compared to other options. The trades were orchestrated to execute like opera performers on a two- and three-shift operation and included steel erected at night.

Given the carrying costs of over $170,000/day, schedule became the driving motivator in many aspects of the project. This meant installing the cast-in-place foundation system, the structural steel skeleton of the podium, the cast-in-place concrete podium floors, and, finally, the cast-in-place concrete system of the hotel tower in rapid linear progression. This process demanded rigorous attention to delivery dates from shop drawings through erection.

The process was accomplished by temporarily stabilizing the base of the building with structural steel braced frames located within the easterly cores of the podium and hotel structure.

These braced frames allowed structural steel erection to seamlessly flow to completion, unimpeded by other trades. While structural steel was being erected, and the braced frame was being encapsulated in concrete, the cast-in-place concrete operations closely followed. Steel frames were minimalistic, designed to support just the amount of weight necessary until the composite system attained design strength and took command.

Above the 7th-floor transfer structure, the cast-in-place concrete

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system continued while the composite concrete and steel structure below gained strength with each passing day.

A design limit of ten floors of concrete superstructure could not be exceeded without completing the concrete encasement below and the platform of plate girders.

The construction (up and down) was coordinated to maximize the efficiency of the schedule.

elevator core of the hotel tower and hang the floor slabs of the two mechanical levels and the roof, thus eliminating all vertical structural elements along the west perimeter of the penthouse suite.

Although the view from the top hotel penthouse suite is indeed impressive, the hard work and dedication of the entire design, construction, and ownership team are evident throughout the project.

Walking through the spaces, one realizes that everything is there because it needs to be there. There are no wasted gestures and flourishes, and systems integration is seamless. That level of design and construction only happens when a cohesive design-construct team, led by a dedicated owner, places the project’s needs above all others. 20 Times Square is greater than the sum of its parts.▪

The View from Up Top No high-rise project is complete without a signature view and, when you are sited in Times Square, every vista needs to be optiTopped out and clad. mally monetized. Walls and columns hinder this monetization. A column-free view was achieved by supporting the mechanical and roof structures above with concrete struts and ties. These outriggers cantilever off the

Cawsie Jijina, P.E., SECB, is a Principal at Severud Associates.

Cawsie participates in the American Council of Engineering Companies of New York (ACECNY) as vice-chair of the Board of Directors, Executive Committee liaison to government affairs committees, chair of the Construction Liaison Committee, and a member of several other committees.

Steve Reichwein P.E., S.E., SECB, is an Associate at Severud Associates. Steve is an active participant in the Concrete Industry Board and is a member of the Structural Engineering Association of New York (SEAoNY), where he is currently active on the Codes and Standards Committee.

Both authors may be reached at info@severud.com.

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March 2018

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Structural T DeSign design issues for structural engineers

his article presents an overview of the design requirements for shallow reinforced concrete foundations (spread footings and mat foundations) supporting buildings assigned to Seismic Design Category (SDC) D, E, or F. Also included is a proposed design method that goes beyond requirements in current codes and standards. Although the following discussion focuses exclusively on spread footings supporting members of the seismic-force-resisting system (SFRS), it is also applicable to mat foundations.

According to ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Section 12.18.9.2, buildings are permitted to be supported on shallow foundations provided the foundations are designed and detailed in accordance with ASCE/SEI 12.13.9.2.1 and the conditions of ASCE/SEI 12.13.9.2 are met.

Shallow Reinforced Concrete Foundations Design for SDC D, E, and F Buildings

By David A. Fanella, Ph.D., S.E., P.E., F.ACI, F.ASCE, and Michael Mota, Ph.D., P.E., SECB, F.ASCE, F.ACI, F.SEI

David A. Fanella is Senior Director of Engineering at the Concrete Reinforcing Steel Institute and can be reached at dfanella@crsi.org.

Michael Mota is Vice President of Engineering at the Concrete Reinforcing Steel Institute and can be reached at mmota@crsi.org.

Determining Base Area Bearing failure is the primary design consideration when footings are subjected to seismic forces.

It is common practice to use service load combinations to size the footing with an allowable bearing capacity that is equal to the static bearing capacity multiplied by a factor to account for the transient nature of the earthquake forces. The 2018 International Building Code (IBC), Section 1806.1, permits the presumptive vertical and lateral bearing pressures values in Table 1806.2 to be increased by one-third where the alternative basic load combinations of IBC 1605.3.2 that include earthquake forces are used. It is also permitted in such cases to use allowable bearing capacities that have been determined from a geotechnical investigation.

ASCE/SEI 12.13 contains requirements for the design of foundations, including spread footings. In lieu of performing a linear analysis that includes foundation flexibility and the loaddeformation characteristics of the foundation soil system (ASCE/SEI 12.13.3), the base dimensions of a footing can be determined utilizing either a strength design method (ASCE/SEI 12.13.5) or an allowable stress design method (ASCE/ SEI 12.13.6).

• For use in load combination 7: E = Eh - Ev = ρQE - 0.2SDS D In these equations, ρ is the redundancy factor determined in accordance with ASCE/SEI 12.3.4, SDS is the design spectral response acceleration at short periods, and QE are the effects due to the horizontal seismic forces.

The combined factored stresses at the base of the footing must be less than or equal to the design soil bearing strength, ϕQns. The resistance factor, ϕ, is given in ASCE/SEI Table 12.13-1 and is equal to 0.45 for bearing strength. ASCE/SEI 12.13.5.2 permits ϕ to be taken as 0.80 where the nominal bearing strength has been determined by in-situ testing of prototype foundations when the testing program has been approved by the authority having jurisdiction.

The nominal soil bearing strength, Qns, is permitted to be determined by the following methods: • Presumptive load-bearing values (organic silts, organic clays, peat, or non-engineered fill are assumed not to have a presumptive load capacity).

• Geotechnical site investigations by a registered design professional, which include field and laboratory testing.

• In-situ testing of prototype foundations.

Strength Design Method In the strength design method, load combinations 1 through 7 in ASCE/SEI 2.3.1 and 2.3.6 are used with the seismic load effects, E, determined in accordance with ASCE/SEI 12.4.2: • For use in load combination 6: E=Eh + Ev = ρQE + 0.2SDS D

38 March 2018

Figure 1. Soil pressure distributions beneath a footing subjected to axial force and bending moment.

Figure 2. Soil pressure distribution beneath a footing assuming full inelastic soil response.

According to ASCE/SEI 12.13.5, overturning effects at the soil-foundation interface are permitted to be reduced by 25% in accordance

with ASCE/SEI 12.13.4 for foundations of buildings where (1) the structure is designed in accordance with the Equivalent Lateral Force Procedure (ELFP) in ASCE/SEI 12.8 and (2) the structure is not an inverted pendulum or cantilevered column type structure. Only the seismic load effects may be reduced by 25% when calculating the bearing pressures; all other load effects must not be reduced.

A 10% decrease of the overturning effects is permitted when a modal analysis in accordance with ASCE/SEI 12.9 is performed.

Analysis of bearing stresses using the strength design method depends on whether inelastic soil response is acceptable or not. If elastic response is required, the maximum factored bearing stress is calculated using the appropriate elastic equations in Figure 1 where factored axial forces, Pu, and bending moments, Mu, are determined by load combinations 1 through 7 in ASCE/SEI 2.3.1 and 2.3.6.

Where inelastic soil response is acceptable, the maximum bearing stress, which is assumed to be constant over the entire contact area, can be calculated assuming full plasticity of the soil (Figure 2). qu,max = Pu /BL´ Regardless of elastic or inelastic soil response, the maximum bearing stress, qu,max, must be less than or equal to the design soil bearing ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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March 2018

strength, ϕQns. The area of the footing is determined based on the governing load combination and the appropriate equation for maximum factored bearing stress.

Allowable Stress Method In the allowable stress design method, load combinations 1 through 10 in ASCE/SEI 2.4.1 and 2.4.5 are used with the seismic load effects, E, calculated in accordance with ASCE/SEI 12.4.2 to determine the maximum bearing stresses at the base of a footing, which must be less than or equal to the allowable bearing capacity. As in the case of the strength design method, reduction of foundation overturning effects is permitted in accordance with ASCE/SEI 12.13.4.

Proposed Design Method The earthquake effects, E, determined in accordance with ASCE/SEI Chapter 12 are less than those that would be expected during a design-level earthquake. Therefore, in the case of footings, the reactions caused by E that are transferred from the supported member to the footing will typically be smaller than those that would be transferred during an actual seismic event. Thus, determining the bearing stresses (and the required flexural and shear strengths) based on code-prescribed

earthquake forces inherently implies that some inelastic behavior is allowed in the footing regardless if strength-level or service-level load combinations are used. Allowing such inelastic behavior may be tolerable for typical buildings assigned to nonessential risk categories (ASCE/SEI Table 1.5-1). However, foundations that are designed in this way may possibly be damaged during a seismic event, and may not perform as intended during subsequent seismic events. Furthermore, inspecting foundations after an earthquake can be very expensive or might not even be possible, so there is usually no direct way of ascertaining if damage has occurred unless the damage is obvious. Repairing foundations is also costly and, in some cases, may not be feasible.

For buildings assigned to SDC D, E, and F, it is recommended to design footings using load combinations 1 through 7 in ASCE/SEI 2.3.1 and 2.3.6, where load combinations 6 and 7 include seismic load effect with overstrength: • Load combination 6: 1.2D + Ev + Emh + L + 0.2S = (1.2 + 0.2SDS)D + ΩoQE + L + 0.2S • Load combination 7: 0.9D - Ev + Emh = (0.9 - 0.2SDS ) + ΩoQE In these equations, Ωo is the overstrength factor given in ASCE/SEI Table 12.2-1 for the SFRS. Like the design of collectors in accordance with current provisions, footings are anticipated to respond primarily in the elastic range when designed using this approach, thereby reducing the likelihood of damage when subjected to a design-level seismic event. Nonlinear response is limited to the supported members, which are correctly detailed according to the appropriate requirements in ACI 31814, Building Code Requirements for Structural Concrete, Chapter 18. As an upper limit, the forces delivered to a footing need not exceed the capacity of the supported structure.

Design Procedure The following design procedure can be used to size the base area of a footing supporting members that are part of the SFRS in buildings assigned to SDC D, E, or F: 1) Determine the factored load effects using load combinations 1 through 7 in ASCE/ SEI 2.3.1 and 2.3.6, where load combinations 6 and 7 include seismic load effect with overstrength.

2) Where elastic soil response is required, determine the base area of the footing, Af, using the appropriate elastic equations in Figure 1 and the design soil bearing strength, ϕQns. 3) Where inelastic soil response is permitted, determine the base area of the footing, Af, using the uniform bearing pressure distribution illustrated in Figure 2 and the design soil bearing strength, ϕQns.

Resistance to Lateral Loads

report, times the density of the soil. IBC Table 1806.2 provides presumptive passive pressure values in pounds-per-square-footper-foot-below-grade for various soil types.

The lateral resistance provided by friction is equal to the total normal force at the base of the footing times an ultimate coefficient of friction. When determining the total normal force, load combination 7 should be used because this results in the smallest normal force at the base. Ultimate coefficients of friction depend on the soil type and are generally reported in a geotechnical report.

ASCE/SEI 12.13.5.1.1 permits the total design lateral strength, ϕQns, to be the sum of the values determined for passive pressure and horizontal sliding (from friction, cohesion, or some combination thereof ). The geotechnical report should specifically designate what type or types of horizontal sliding resistance are applicable at a site.

Allowable Stress Design Method

In general, lateral forces from earthquakes are transferred from a footing to the adjoining soil through friction at the base of the footing and passive bearing pressure along the edge of the footing perpendicular to the direction of analysis (Figure 3). As in the case of bearing pressure at the base of a footing, both strength design and allowable stress design methods can be used to check if resistance to sliding is adequate or not.

In the allowable stress design method, allowable passive bearing pressures and coefficients of friction are used in conjunction with maximum seismic load effects calculated by allowable stress load combinations to determine whether resistance to lateral sliding is adequate or not. As in the case of bearing pressure at the base of a footing, allowable passive pressures may be increased when seismic load combinations are considered to account for transient load effects.

Strength Design Method

Design and Detailing Requirements

In the strength design method, factored lateral forces must be less than or equal to the design lateral strength, ϕQns. The reduction factor, ϕ, is given in ASCE/SEI Table 12.13-1, and is equal to 0.50 for lateral resistance provided by passive bearing pressure and 0.85 for lateral resistance provided by sliding (either friction or cohesion).

ACI 12.13.5.1.1 contains the types of soils that provide lateral sliding resistance from friction and cohesion.

Values of Qns, based on the soil profile at the site, are typically provided in the geotechnical report.

Passive bearing pressure varies linearly with respect to the depth below grade. At a depth ds below grade, the passive pressure is equal to ds times the passive pressure coefficient, Kp, which is typically Figure 3. Lateral load transfer by friction and passive bearing stress. provided in a geotechnical STRUCTURE magazine

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March 2018

The applicable design and detailing requirements given in ACI Chapter 13 and ACI 18.13.2 must be satisfied for footings supporting members of the SFRS in buildings assigned to SDC D through F. Similar to the cases of determining the base area of a footing and checking for sliding resistance, it is recommended that reinforcement for flexure and force transfer at the interface are determined using load combinations 1 through 7 in ASCE/SEI 2.3.1 and 2.3.6, where load combinations 6 and 7 include seismic load effect with overstrength. Shear strength requirements should be satisfied based on those load combinations as well.

Additional in-depth information and worked-out design examples can be found in the CRSI publication Design and Detailing of Low-Rise Reinforced Concrete Buildings.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

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Structural licenSure

issues related to the regulation of structural engineering practice

Licensure

Why Additional Credentialing is Necessary for Some Structures

By J. G. (Greg) Soules, P.E., S.E., P.Eng., SECB, F.SEI, F.ASCE

S

tructural engineering licensure is a hotly debated topic within the structural engineering profession. One question that is often raised is “What structures (often referred to as Designated Structures) should structural engineers be required to design?” This article discusses: • What is a Designated Structure?

• What is NOT a Designated Structure?

• Why require a structural engineering (S.E.) license to design Designated Structures?

What is a Designated Structure?

have what is termed a partial practice act.

Designated Structures are defined in a partial practice act, which requires a licensed S.E. to design the Designated Structure. The status of structural engineering licensure in the United States is shown in the Table.

The definition of a Designated Structure also varies in the nine partial practice states and territories listed in the Table. Some states and territories use the term Significant Structures instead of Designated Structures in their licensing laws. Depending on the state or territory, Designated Structures may include: • Schools • Hospitals • Essential facilities • Hazardous facilities • Structures ≥ 45 feet, 4 to 5 stories • Bridges While not obvious, the groupings of Designated Structures shown above do follow a pattern. The Designated Structures contained in these partial practice acts generally fall into the following categories: • Buildings and other structures representing a substantial hazard to human life (ASCE 7/IBC Risk Categories III and IV).

These structures typically are designed for greater loads and have design and detailing restrictions placed on them due to their significant number of occupants (for example, tall buildings), occupants who need assistance in an emergency (for example, school, some healthcare facilities, and the like), or that store explosive or toxic materials.

• Buildings and other structures designated as essential facilities (ASCE 7/IBC Risk Category IV). These structures typically are designed for greater loads, have design and detailing restrictions placed on them, and functionality requirements placed on them because these structures must operate after a design event (for example, hospital, police station, fire station, and the like).

• Buildings and other structures requiring special consideration. Structures falling in this category represents local opinion on the importance of a particular type of structure. For example, a building with fewer occupants than those typically found in Risk Category III may be identified as a Designated Structure.

The Structural Engineering Licensure Coalition (SELC) includes all major organizations specifically representing structural engineers What is Not a throughout the United States and is dedicated to a common position in support of strucDesignated Structure? tural engineering licensure nationwide. SELC The quick answer to this question is “all other is comprised of the Structural Engineering structures not mentioned above.” The strucInstitute (SEI), the National Council of tures listed above as Designated Structures Structural Engineers Associations (NCSEA), represent a relatively small percentage of all the Structural Engineering Certification structures built. Having said this, the moveBoard (SECB), and the Council of Structural ment by the structural engineering profession Engineers (CASE). The SELC states in its to enact partial structural engineering practice Position Statement: acts in all remaining states have made some “SELC advocates that jurisdictions require in the civil engineering profession concerned.

S.E. licensure for anyone who provides Specifically, geotechnical engineers raised a structural engineering services for designated concern that Geo-Structures would be grouped structures.” within Designated Structures by some states.

Structural engineering licensing laws, where Examples of Geo-Structures are: they exist, vary from state to state. A few • Temporary and permanent earthstates identify the discipline of the individual retaining systems engineer in the state’s roster of engineers. This practice is usually referred to Table of current status of structural licensure. as a roster designation. Some structural Full Practice States Partial Practice States Title Restriction Roster Designation engineering licensing laws take the form of a title act. A title act only restricts Hawaii Alaska Idaho Arizona who may use the title of Structural Illinois California (other legislation*) Louisiana Connecticut Engineer but places no restrictions on Nevada Nebraska Massachusetts the practice of structural engineering.

Other structural engineering laws take Oregon New Mexico the form of a practice act. A practice Utah Rhode Island act both restricts who may use the title Washington Texas of Structural Engineer and defines what areas of engineering practice that Guam Vermont may only be performed by a licensed Northern Mariana Islands structural engineer. Some states have Oklahoma what is termed a full practice act, which requires all structures to be designed by *California officially only has a title act. The 1933 Field Act requires that schools be designed by a licensed structural a structural engineer (S.E.). A few states engineer. The 1972 Alquist Act requires that hospitals be designed by a licensed structural engineer.

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Why Require Licensure to Design Designated Structures?

There is only one answer to this question: To protect the health, safety, and welfare of the public.

While the professional engineer (P.E.) laws in all states are intended to protect the health, safety, and welfare of the public, their reliance on self-evaluation of competency dramatically weakens the existing licensing laws. Self-evaluation of competency often leads engineers to do things that they are truly not qualified to do in response to a weak economy or when traditional markets dry up. A STRUCTURE article from March 2011 by Jon A. Schmidt, P.E, SECB, titled Incompetent and Unaware of It discusses the problem of self-evaluation of competency.

So, what do structural engineering practice acts protect the public from? A structural engineering practice act that requires a licensed structural engineer to design Designated Structures protects the public from: • Inexperienced professionals • Unqualified professionals • Professionals not familiar with new and more complex codes • Decrease in engineering education requirements • Inadequate or non-existent structural plan reviews • Advanced design software used by lessqualified/less-experienced engineers

• Professionals not familiar with new and more complex building materials • Professionals not familiar with designing for extreme events The following are actual examples of some of the problems described previously.

Example 1 – Unqualified professionals. A retired aeronautical engineer designs a school building (Risk Category III structure) in a region of high snowfall. The engineer has no experience in masonry design. He cuts and pastes masonry details from another engineer’s project that used a 14-foot-high wall.

Unfortunately, the new project uses 28-foot high walls. Snow load causes the masonry walls to bow and crack and doors to jam, resulting in the closing and later condemnation of the school.

Example 2 – Professionals not familiar with new and more complex codes/ Professionals not familiar with designing for extreme events. The Royal Palm Hotel in Guam (Case Study by R. O. Hamburger at www.selicensure.org) was damaged in a seismic event. Structural design was performed by a licensed civil engineer. The civil engineer of record for the project also served as the special inspector of record. At the time of the project, licensing laws on Guam provided for both a

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o Conventional gravity walls o Modular gravity walls o Mechanically Stabilized Earth (MSE) walls o Non-gravity cantilever walls o Soil nail walls o Landslide stabilization systems (using any of those systems described previously) o “Support of Excavation” systems (permanent or temporary) • Shallow and deep foundations o Drilled shafts o Piles, micropiles, tie-downs o Ground improvement o Rigid inclusions • Underpinning of structures affected by excavations • Shafts and tunnels • Dikes (not used as secondary containment), dams and levees, and soil and rock slopes To address the concerns of geotechnical engineers, a joint task committee of the Geo-Institute (GI) and SEI was formed in 2015 to develop a recommended consensus position statement on the design of specialty geotechnical structures as it relates to S.E. licensure. This consensus document, known as the Oak Brook Accords, was developed and approved by the Board of Governors of both institutes on February 16, 2016.

The joint task committee recommended: • Because the design of both temporary and permanent Geo-Structures may involve structural engineers, geotechnical engineers, civil engineers, or any combination thereof, Geo-Structures should not be subject to designated thresholds contemplated for S.E. licensure, even when these GeoStructures support a Designated Structure.

• In all cases, an appropriately qualified and licensed professional engineer shall be in responsible charge of the work.

The use of the term “appropriately qualified” was meant to convey that geostructures must be designed by engineers (structural, geotechnical, or civil) who have the background, training, knowledge, and experience appropriate for the particular geo-structure.

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Seattle Tacoma Lacey Portland Eugene Sacramento

San Francisco Los Angeles Long Beach Pasadena Irvine San Diego

Boise St. Louis Chicago Louisville New York

civil license and structural title. At the time of the collapse, the civil engineer of record did not possess the structural title authority. A review of the design showed that the analytical model used to design the structure had numerous errors, including several columns that were rotated 90 degrees from their actual orientation. Additional confinement hoops required around column splices were not specified on the drawings. Masonry infill walls used in the construction of the hotel created short-column conditions throughout the structure. Coderequired strong-column weak-beam criteria were not complied with in the design of the

hotel. It was also determined that the contractor did not follow the structural details on the drawings. Special inspection reports, signed by the engineer of record, indicated that the improperly constructed joints had been inspected by the engineer and that he approved of the placement of reinforcing steel.

Further, correspondence and notes on drawings indicate that because the seismic design forces for the structure were less than the wind forces, compliance with the detailing requirements for special moment frames was not essential.

It was clear from the investigation that the civil engineer of record did not have a proper

understanding of the seismic design and detailing requirements in the building code.

Example 3 – Advanced design software used by less-qualified / less-experienced engineers. A pedestrian bridge at NRG Stadium in Houston, Texas (SEAoT Newsletter, Winter 2010), required significant modifications shortly after construction was completed. The pedestrian bridge was required to be a passthrough (Pony) truss bridge. While installing lights on the trusses, the electrical contractor noticed that the trusses swayed back and forth several inches. An investigation of the problem revealed the rigid connections of the truss’ vertical members to the bottom chord, required for a pass-through truss to be stable, were not provided. The original design of the truss used two-dimensional analysis software.

The design engineer missed the fact that the two-dimensional analysis software assumed that the truss was braced out-of-plane. The design engineer was also not familiar with the design procedures required for a “Pony” truss.

Columns were added to the midspan of the pedestrian bridge, and the upper chords of the trusses were braced to correct the design error.

Conclusion

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The above examples demonstrate that structural engineering is not a part-time profession.

A licensed S.E., as opposed to a licensed P.E., is required to design Designated Structures to protect the public. The structural engineering licensing process demonstrates that individuals who are allowed to practice structural engineering are knowledgeable in the use of all structural materials and current structural codes, and experienced in structural design.

While there are licensed professional engineers experienced in structural design, there are many who are not. A professional engineering license (P.E.), by itself, does not demonstrate the competency of the individual to perform structural engineering. Another step is required to demonstrate that competency. A structural engineering license combined with a structural engineering practice act is an effective method to ensure that only those individuals with knowledge in the use of all structural materials, current structural codes, and experience in structural design are allowed to design Designated Structures.▪ J. G. (Greg) Soules is a Principal Engineer with CB&I LLC in Houston, Texas. He is the past Chair of the Structural Engineering Certification Board (SECB) and a past member of the Structural Engineering Licensure Coalition (SELC). He can be reached at greg.soules@cbi.com.

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March 2018

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discussion of legal issues of interest to structural engineers

LegaL PersPectives

A Contract’s “Miscellaneous” Section Governing Law and Forum Selection Provisions: Part 2

By Gail S. Kelley, P.E., Esq.

D

esign agreements often contain a governing law provision which specifies that the laws of a designated jurisdiction will govern any disputes arising from the agreement. Likewise, design agreements often contain forum or venue selection provisions that specify where the adjudication of any disputes will take place. Part 1 of this series (STRUCTURE, February 2018) provided an overview of governing law provisions and the state statutes that apply to these provisions in design agreements. This second part will look at forum and venue selection clauses.

Venue Versus Forum Although the words “venue” and “forum” are often used interchangeably when establishing where an adjudication will take place, there is a difference. Forum refers to the state; venue refers to the actual location of the court. For litigation arising from a design agreement taking place in state court, the venue would be the specific county; for a federal court, the venue would be the specific district.

An example of a forum selection provision would be: Any litigation of disputes arising under this Agreement shall take place in a court of competent jurisdiction in New York. A venue selection clause necessarily also specifies the forum. An example of a venue selection provision for state court would be: Any litigation of disputes arising under this Agreement shall take place in the County of Kings, New York.

An example of a venue selection provision for federal court would be: Any litigation of disputes arising under this Agreement brought in Federal Court shall take place in the Southern District of New York.

Forum Selection Selection of the forum state (the state in which the adjudication of disputes will take place) can have a significant effect on the cost of a litigation. Much of the administrative work required for dispute resolution can be done remotely via electronic filing and conference calls. Nevertheless, a certain amount of travel to the forum state will be required; dispute resolution that takes place in a distant state can result in considerable travel expenses and time for both witnesses and legal personnel. An agreement to submit any disputes to resolution

in a state other than the state where the engineer has its office, or the project is located, should be considered carefully.

Jurisdiction Requirement

enforce laws protecting the welfare, safety, and health of their inhabitants.

Most of the states which require that their law apply to design and construction projects also require that the arbitration or litigation concerning the project take place in the state.

There are a few exceptions, however. While Colorado requires that every construction agreement affecting improvements to real property within the state of Colorado be governed by Colorado law, it does not require that disputes arising from these agreements be adjudicated in Colorado. In contrast, California, Florida, and Virginia require that adjudication take place within the state but do not require that the state’s law governs the dispute. Theoretically, however, if adjudication is taking place in the state’s court,

Forum selection clauses are sometimes worded as jurisdiction selection clauses. Jurisdiction refers to the court’s power to rule on a dispute, or more precisely, the court’s power over the defendant (the party being sued). In general, the courts of a particular state will not have power over a defendant unless it is domiciled in that state, it has “minimum contacts” with the state, or it has consented to jurisdiction.

Thus, a design agreement might contain the provision: The parties agree to submit to the jurisdiction of the courts of New York. The parties are agreeing Table of states with statutes governing forum for resolution of disputes arising from design agreements. that the courts of New York have the power to rule on disputes State Statute arising from the Agreement Arizona Ariz. Rev. Stat. § 32-1129.05 and are waiving their right to California Cal. Civ. Proc. Code § 410.42(a) claim that New York does not Connecticut Conn. Gen. Stat. Ann. § 42-158m have jurisdiction. As worded, however, the provision does not Florida Fla. Stat. Ann. Ch. 47.025 require that disputes be adjuIllinois 815 Ill. Comp. Stat. Ann. 665/10 dicated in New York, it merely Indiana Ind. Code § 32-28-3-17 says they can be. If the parties Kansas Kan. Stat. Ann. § 16-121(e) want to specify that New York will be the forum state, they Louisiana La. Rev. Stat. § 9:2779 would need to state that New Minnesota Minn. Stat. § 337.10 York had exclusive jurisdiction, Montana Mont. Code § 28-2-2116 (1) i.e., The parties agree to submit to the exclusive jurisdiction of the Nebraska Neb. Rev. Stat. § 45-1209 courts of New York or The parties Nevada Nev. Rev. Stat. Ann. 108.2453(2) agree to submit all disputes arising New Mexico N. M. Stat. Ann. § 57-28A-1 under this Agreement to the jurisNew York N.Y. Gen. Bus. Law, Chapter 35-E, § 757 diction of the courts of New York.

Forum Selection Statutes As discussed in Part 1 of this series, 22 states have passed laws which require the state’s laws to govern contracts for design and construction projects in the state, regardless of the parties’ wishes. This is essentially an exercise of the state’s “police” power; under the U.S. Constitution, states are granted the power to establish and

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North Carolina

N.C. Gen. Stat. § 22B-2

Ohio

Ohio Rev. Code § 4113.62 (D)

Oklahoma

Ok. Stat. Ann. tit. 15, § 15-821

Oregon

Or. Rev. Stat. § 701.640

Pennsylvania

73 Pa. Stat Ann. §514 – only applies to claims for payment

Rhode Island

R.I. Gen. Laws § 6-34.1-1(a)

South Carolina

S.C Code Ann. § 15-7-120.A – not law

Tennessee

Tenn. Code § 66-11-208(a)

Texas

Tex. Bus. & Com. Code Ann. § 272.001

Virginia

Va. Code Ann. § 8.01-262.1

Wisconsin

Wis. Stat. § 779.135 (2)

March 2018

the court would be more likely to override a provision requiring the use of another state’s laws, on the grounds that the result would be contrary to the public policy of the forum state.

The Table (page 47 ) provides a listing of the states that have forum selection statutes and a citation to the code section. Many of these statutes use language similar to that found in the Ohio Code: Ohio Rev. Code Ann. § 4113.62(D) (2) Any provision of a construction contract, agreement, understanding, specification, or other document or documentation that is made a part

of a construction contract, subcontract, agreement, or understanding for an improvement, or portion thereof, to real estate in this state that requires any litigation, arbitration, or other dispute resolution process provided for in the construction contract, subcontract, agreement, or understanding to occur in another state is void and unenforceable as against public policy.

Void Versus Voidable The majority of the governing law and forum selection statutes state that a provision which

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specifies that another state’s law will govern the design agreement or requires adjudication of disputes to take place in another state is “void.”

This means that if either party to the agreement challenges the provision and the dispute falls within the provisions of the statute, the court will not enforce the provision.

However, the Rhode Island and Texas statutes state that if a provision specifies that another state’s law will govern the design agreement or adjudication of disputes will take place in another state, the provision is voidable by the party that is obligated by the contract to perform the construction or repair. This means that only the design professional would be entitled to challenge the provision.

Whether a provision is void or voidable, if neither party to the agreement challenges the provision, a court is unlikely to decide it is unenforceable on its own initiative (sua sponte), provided it has jurisdiction over the dispute. For example, if the design agreement for a bottling plant in Cincinnati specified that litigation of any disputes would take place in New Jersey using New Jersey law (because the bottler’s headquarters are in New Jersey), and neither party challenged the provisions, the New Jersey court would probably not sua sponte bring up the fact that the provisions violated Ohio Rev. Code Ann. §4113.62(D).

Conclusion Part 3 of this series will look at some of the issues that might come into play when the parties are negotiating which state’s law will govern a design agreement and will take another look at some of the state statutes for forum selection.▪ Disclaimer: The information in this article is for educational purposes only and is not legal advice. Readers should not act or refrain from acting based on this article without seeking appropriate legal or other professional advice as to their particular circumstances.

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Gail S. Kelley is a LEED AP as well as a professional engineer and licensed attorney in Maryland and the District of Columbia. Her practice focuses on reviewing and negotiating design agreements for architects and engineers. She is the author of Construction Law: An Introduction for Engineers, Architects, and Contractors, published by Wiley & Sons. Ms. Kelley can be reached at Gail.Kelley.Esq@gmail.com.

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investigating failures, along with their consequences and resolutions

Structural FailureS

Straight-Line Wind Damage Analysis

By Karyn Beebe, P.E.

A

straight-line wind event took place in Rockwall, Texas, March 29, 2017, producing significant structural damage resulting in four red- and five yellowtagged homes. The National Weather Service in Fort Worth estimated the storm’s wind speed to be 100 to 110 mph. Before demolition of the most impacted home (Figure 1), APA – The Engineered Wood Association (APA) field staff followed through with an opportunity to survey the damage.

The same fundamental design principle used for resisting tornadoes and hurricanes is also used to resist straight-line winds: create a continuous load path from the point of origin to the foundation. As demonstrated by the March 2017 storm, straight-line winds can be just as destructive as tornados and can produce estimated wind speeds within the bounds of the International Residential Code (IRC).

Continuity in wood-frame construction can be accomplished in many ways, most

Figure 2. This roof had many staples oriented perpendicular to the rafter, and several staples had only one leg in the rafter.

Figure 3. The flexible sheathing tore away from the bottom plate where staples were only partially embedded, allowing the balance of the wall to move inside (note that the arrow is pointing at the carpet).

commonly with continuous wood structural panel (WSP) sheathing of the building envelope. Using a WSP, such as oriented strand board (OSB) or plywood, creates structural redundancy, enhanced puncture resistance from flying debris, and protection from wind- Figure 1. The March 2017 straight-line wind event took place in Rockwall, driven rain. In storm Texas, produced significant structural damage. events, water damage to a building’s contents can be more costly material to the supporting wood studs, resists than the structural repair itself. sliding of the base with anchor bolts, and preIn APA’s assessment of the damage, actual vents overturning of the wall, conventionally construction detail deviated from recom- by using hold downs. mended practices. The following overview In the observed homes, there was a lack highlights some of the more important struc- of load path continuity. The wall sheathing tural issues. panels were not attached to the top plates, WSP roof sheathing was stapled to the roof had no lateral load transfer at the floor line, rafters and, while code allows for staples, and the attachment to the walls studs failed proper installation is critical. The roof in (Figure 3).

Figure 2 had many staples oriented perpenThe detail in Figure 4 shows wall sheathing dicular to the rafter, and several staples had lapped over the Rim Board® and fastened only one leg in the rafter, which combined as one way to create load path continuity to reduce the capacity of the connection by from floor to floor. Another way is to use at least 50 percent. The staple crown should metal plates, such as Simpson Strong-Tie® be parallel to the rafter to assure both legs LTP4s, although neither was done here. are embedded into the supporting member. Instead, flexible sheathing of various grades The staples also appeared to be fastened in an (load capacities: structural grade and noninconsistent pattern. structural grade infill) was fastened using For these wind speeds, APA recommends using 8d ring shank or screw shank nails (0.131-inch x 2½-inch) fastened at 4 inches on-center along the WSP perimeter and 6 inches on-center in the WSP interior. This nailing pattern is closer than the minimum 6- and 12-inch-on-center spacing pattern to provide additional uplift resistance in high-wind events.

The roof diaphragm transfers the lateral load to the shear walls below. In residential construction, this is often the exterior walls of the home in the form of wall bracing or engineered shear walls. Wall bracing is a prescriptive method in the IRC, with the same objective as shear walls. A wood-framed shear wall transFigure 4. Creating load path continuity from floor to floor fers the shear force via the capacity of using WSP wall sheathing lapped over the fastened. the sheathing and the attachment of that

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Figure 7. Use larger washers to tie the structure to the foundation better.

the arrow is pointing at the carpet). The circles on the left of the photo highlight the staples in the wall sheathing and bottom plate. The circle to the right shows the nails that had held the stud to the plate. The nails were rusted and Figure 5. Code-required water-resistive barrier, flashing, and an air the wall sheathing had gap to separate the brick veneer from the wood wall. water stains, indicating that moisture may have played a role in weakening this assembly.

The houses observed were intermittently braced with structurally graded flexible laminated-fiber sheathing, infilled with nonstructural flexible laminated-fiber sheathing panels (Figure 1). Homes fully sheathed with WSP enrich the structural performance of a building. APA Report T2007-73, Full-Scale 3D Wall Bracing Tests, found continuous wood sheathing resists about 80 percent more load than intermittent WSP wall bracing.

Another observation consistent with previous tornado damage assessments was brick façade failure. Many homes in North Texas have a brick or stone veneer around the exterior of the home. In Figure 6, the brick ties failed; some Figure 6. Damage consistent with previous tornado stayed in the brick veneer and others attached to the wood studs. Installation of continuous assessments – circle shows brick façade failure, WSP sheathing would allow the brick ties to arrow points to mortar buildup between bottom be attached directly to the panels, ensuring plate and brick veneer. a secure hold and reduced failures. From an staples. The non-structural grade sheathing engineering perspective, it is important to eduinstalled over the rim board made it impos- cate clients so that they understand that brick sible to determine the amount of load transfer veneer is merely serving an aesthetic purpose available. The wall sheathing was punctured – it is the sheathing attached to the studs that and missing as shown in Figure 1, which cre- provides the lateral resistance and high-wind ated an opportunity for moisture damage on protection to the building. the interior contents and possible internal Structures with incomplete drainage paths are pressurization of the home leading to more susceptible to water damage and other structural structural damage. problems. Architects and engineers often detail The flexible sheathing tore away from the the drainage system of a structure to avoid these bottom plate (Figure 3) where staples were moisture-related issues. As noted before, rusted only partially embedded, allowing the bal- fasteners and water staining on the sheathing ance of the wall to move inside (note that were indications of moisture exposure. Compare STRUCTURE magazine

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Figure 5 and 6, APA’s recommended drainage assembly with one of the walls observed. In Figure 5, the wall sheathing is protected by a code- required water-resistive barrier, flashing, and an air gap to separate the brick veneer from the wood wall. The arrow in Figure 6 points to mortar buildup which occurred between the bottom plate and the brick veneer. This could trap water behind the wall which could infiltrate the wood wall assembly.

The last takeaway from the straight-line wind event relates to the attachment of the anchor bolts. For high wind areas, APA recommends using an oversized, 0.229-inch x 3-inch x 3-inch slotted square plate washer, four feet on-center or less, to reinforce this connection (Figure 7 ). Wood is weaker when loaded perpendicular to grain and an uplift force on the bottom plate creates such a load in cross-grain bending. The larger washers are a better way to tie the structure to the foundation.

Load path continuity is necessary for all structures, from homes to skyscrapers, built from wood, steel, or concrete to resist earthquakes or winds. Attention to detail and tying the elements together is particularly important for the lateral load path, as contractors may not be as familiar with the intention of the detailing. In wood framing, there are often multiple ways to create a continuous load path. Consider what will be most straightforward to build and even add redundancy when available. For more information on this straight-line wind event, APA recommendations, and related details available for free download, see www.apawood.org/wind-weather-seismic.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

Karyn Beebe is a Member Services Manager with APA – The Engineered Wood Association. She may be reached at karyn.beebe@apawood.org.

Software UpdateS APA - The Engineered Wood Association

Concrete Masonry Association of CA & NV

IES, Inc.

Phone: 253-620-7400 Web: www.apawood.org/ftao Product: APA Force Transfer Around Openings (FTAO) Calculator Description: This free tool assists structural engineers in the design of force transfer around openings (FTAO) shear walls. Provides required hold-down forces, tension strap forces, and wall sheathing capacity. Automatically completes the design check in the final step. Provides shear wall deflection calculations for 3- and 4-term deflection equation options.

Phone: 916-722-1700 Web: cmacn.org Product: CMD15 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 2010 through 2016 CBC or 2009 through 2015 IBC and 2008 through 2013 Building Code Requirements for Masonry Structures (TMS 402/ACI 530/ASCE 5).

Phone: 800-707-0816 Web: www.iesweb.com Product: VisualFoundation Description: All I get are reactions from you. I try to analyze, but there is so much pressure holding me to the ground. I may be unstable. I need you to reinforce me, give me strength to carry your loads. Give me one chance to solve our problems together.

Digital Canal Corporation

Losch Software Ltd

Phone: 563-690-2000 Web: www.DigitalCanalStructural.com Product: Structural Expert Series Library Description: New updates include Design Codes and new features. Time proven, one project ROI and tollfree technical assistance help satisfy your clients and put more money in your own pocket. Visit the website for a free trial.

Phone: 323-592-3299 Web: LoschSoft.com 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.

Bluebeam, Inc. Phone: 866-496-2140 Web: bluebeam.com Product: Bluebeam Revu Description: The digital workflow and collaboration solution trusted by +1 million AEC professionals worldwide. Revu features a suite of mark-up, measurement, estimation, and automation tools that enable businesses to improve project communication, streamline processes, and seamlessly manage project documents. Download a 30-day trial at the website.

CADRE Analytic Phone: 425-392-4309 Web: www.cadreanalytic.com Product: CADE Pro Structural Analysis Description: Finite element structural analysis. New 2018 update. Load distribution functions include discrete, pressure, hydrostatic, seismic, and dynamic response. 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.

Computations & Graphics, Inc. Phone: 303-668-1091 Web: www.cg-inc.com Product: cColumn Description: A powerful Windows program designed specifically for structural engineers to perform axialflexural analysis and design of concrete columns, as well as beams and shear walls, according to ACI 31814/11/08/05/02 and ACI 318-99.

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news and information from software vendors

Dlubal Software Phone: 267-702-2815 Web: www.dlubal.com Product: RFEM Description: Structural analysis and design including USA/International standards for steel, concrete, wood, CLT, aluminum, glass, and fabric/membranes.

Capable of non-linear analysis of member, plate, and solid elements complete with code references and detailed design results. Direct interfaces with Revit, Tekla, and AutoCAD incorporate seamless and bidirectional data exchange.

ENERCALC, Inc. Phone: 800-424-2252 Web: https://enercalc.com Product: Structural Engineering Library/Retain Pro/ ENERCALC SE Cloud Description: New at ENERCALC - 3D component sketches in Structural Engineering Library, plus functionality and performance improvements to ENERCALC SE, a cloud-based, subscription-based application platform. ENERCALC SE’s cloud suite combines Structural Engineering Library, RetainPro (earth retention structure design), and a 3D Finite Element analysis and design application: “ENERCALC 3D”.

MKT Fastening, LLC Phone: 800-336-1640 Web: mktfastening.com Product: MKT Fastening Anchoring Design Software Description: Software that gives the user the ability to input data from a fastening and the software will design a fastening solution based upon that data. Easy to use, fill in the blank software takes the guess work out of anchoring design.

SCIA Inc. Phone: 949-273-8059 Web: www.scia.net Product: SCIA Engineer Description: Links structural modeling, analysis, design, reporting and interoperability in one program.

Design and optimize to the most recent codes. Tackle large projects with advanced non-linear and dynamic analysis. Plug into BIM with IFC support and bidirectional links to Revit, Tekla, and others. Visit the website to learn more.

Simpson Strong-Tie Phone: 800-925-5099 Web: www.strongtie.com Product: CFS Designer™ Software Description: Design CFS beam-column members according to AISI specifications and analyze complex beam loading and span conditions.

Intuitive design tools automate common CFS systems such as wall openings, shearwalls, floor joists, and up to eight stories of load-bearing studs.

Demos at www.struware.com Wind, Seismic, Snow, etc. Struware’s Code Search program calculates these and other loadings for all codes based on the IBC or ASCE7 in just minutes (see online video). Also calculates wind loads on rooftop equipment, signs, walls, chimneys, trussed towers, tanks and more. ($250.00).

CMU or Tilt-up Concrete Walls Analyze solid walls for out of plane loading and panel legs next to or between openings by automatically calculating loads to the wall leg from vertical and horizontal loads at the opening. ($75.00 ea)

Product: Anchor Designer™ Software Description: Quickly and accurately analyze an existing design or suggest anchorage solutions based upon user-defined design elements in various concrete conditions. The software has been updated to include the latest product launches from Simpson Strong-Tie, providing more anchor and adhesive products to choose from.

Floor Vibration Program to analyze floors with steel beams and/or steel joist.

Compare up to 4 systems side by side ($75.00).

Concrete beam/slab Program to provide bending, shear and/or torsional reinforcing.

Quick and easy to use ($45.00).

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news and information from software vendors

Software UpdateS

SkyCiv Engineering

Trimble

Victaulic

Phone: 614-115-71213 Web: www.skyciv.com Product: SkyCiv Structural 3D Description: Announcing some great new product features in next month’s (April) release. The update will automatically push to our users - no updates necessary! This includes: AISC 360 Connection Design - including HSS; ACI 318 Concrete Design; AISC 360 full calculation reporting; and more.

Phone: 770-426-5105 Web: www.tekla.com Product: Tedds Description: Perform 2D frame analysis, access a large range of automated structural and civil calculations to U.S. codes and speed up your daily structural calculations.

Phone: 866-707-0583 Web: www.victaulicsoftware.com Product: Victaulic Tools for Revit 2018® Description: Released in conjunction with Autodesk University, the latest version of Victaulic Tools for Revit 2018 enhances routing with new editing features that make modeling, procurement, and fabrication within Revit a reality for engineers and contractors.

Further simplifies preconstruction, boost productivity, and make projects even faster from the start.

SoilStructure Software, Inc. Phone: 714-321-1816 Web: www.soilstructure.com Product: Substructural Engineering Software Description: Includes Candtilever Shoring, Drilled Pier and Driven Pile Professional Software.

Tilt-Werks® by Dayton Superior® Phone: 720-484-9758 Web: www.tilt-werks.com Product: Tilt-Werks® Description: Go from concept to completion faster with Tilt-Werks, a standardized software package for designing tilt-up buildings and producing precise structural drawings. Its innovative technology, unique in the tilt-up industry, has been used on over 400 tiltup buildings and more than 30 million square feet of building construction.

Product: Tekla Structural Designer Description: Revolutionary software that gives engineers the power to analyze and design buildings efficiently and profitably. From the quick comparison of alternative design schemes through to cost-effective change management and seamless BIM collaboration.

Tekla Structural Designer can transform your business.

Veit Christoph GmbH Phone: +49 711 518573-30 Web: www.vcmaster.com Product: VCmaster - Intelligent Engineering Software Description: Comprehensive, affordable, and userfriendly software solution for compiling professional structural design calculations. A unique combination of reliable calculation capacity and extensive text processing features. Includes more than 60 interactive design aids to AISC 14th edition and ACI-318.

Empowers engineers to automate design calculations.

Free 60-day trial version available!

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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WoodWorks Software Phone: 800-844-1275 Web: www.woodworks-software.com Product: WoodWorks Design Office 11 Description: Conforms to IBC 2015, ASCE7-10, 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, steel, or concrete.

Listings are provided as a courtesy.

STRUCTURE® magazine is not responsible for errors.

InSIghtS

new trends, new techniques and current industry issues

Foreign Engineering Graduates in America

By Dilip Khatri, Ph.D., S.E.

A

merica is a nation built by immigrants. The United States accepts approximately 1,000,000 legal immigrants per year. The U.S. is the most welcoming of all countries and a primary destination for foreign migrants, more than the other top five industrialized nationsâ&#x20AC;&#x2122; immigration rates combined (Germany, United Kingdom, France, Canada, and Switzerland).

One source of U.S. immigration is through an influx of foreign graduates. However, there is a misconception that foreign graduates are impacting the engineering profession negatively and H-1Bs are costing U.S. tax dollars. The lower focus of this article is to open a dialogue on this sensitive topic, share some facts on the numbers/scale of foreign engineering graduates, and examine the national immigration debate as it relates to the engineering profession.

There are several avenues for a foreign graduate to obtain work in the U.S. I am a product of U.S. immigration policy, as my parents came to the United States from India in 1968 when I was only three years old. My parents arrived with $1,500, no car, and no job, but with admissions to the Masters Program at California State University, Fresno, where they both completed Masters Degrees and became teachers.

Migration to the United States has only intensified since that time. A few statistics are important in putting immigration and how it relates to the engineering profession into a perspective of scale. The current U.S. economy consists of a $20 Trillion G.D.P., with approximately 157 million workers in a total population of 310 million. The Civil Engineering population totals roughly 255,000, with approximately 100,000 Licensed Professional Engineers (PEs) in all 50 States and 10,000 registered Structural Engineers (SEs).

One avenue for foreign engineering graduates to obtain work in the U.S. starts with an employment period via the H-1B program.

Established in 1992 for highly skilled/educated professionals, H-1B often leads to permanent immigration status and eventually to U.S. citizenship. The program assists employers seeking to hire nonimmigrant aliens as workers in specialty occupations; as such, the H-1B Visa is targeted to Engineering, Computer Science, Scientists, Doctors, Researchers, and other highly qualified talent. Congress sets the quota at about 85,000 annually (of which 20,000

are reserved for Masters Graduates). There are approximately 450,000 applications each year, which overloads the U.S. Citizenship and Immigration Services (UCICS) website within 3 days of the annual application date. Lottery luck dictates those accepted for H-1B status. From these 85,000 H1-Bs, the vast majority are in Computer Science, Information Systems, and Software Development. In fact, the foremost proponents of the H1-B program are Microsoft, Facebook, Apple, and Google, who sponsor the highest number of applicants.

needed skills and abilities from the U.S. workforce by authorizing the temporary employment of qualified individuals. Certainly, a preferred solution to filling specialized engineering positions would be to encourage our own citizens to pursue advanced degrees and specialize in technical topics. Unfortunately, the data shows that there is no shortage of homegrown American talent for Construction Management, Project Management, Executive MBAs, and Hedge Fund Managers. Conversely, numbers are very small for homegrown talent pursuing a Ph.D. in Nonlinear Finite Element Analysis of often and incorrectly viewed as accepting Rubberized Concrete, Dynamic SoilStructure Interaction, or Nonlinear pay than their American counterparts.

Dynamic Response of PerformanceIn terms of Civil and Structural Engineering, Based High-Rise Buildings to Seismic the H-1B applicant pool is very small (less than ensemble excitations using the Power Spectral 1,000 based on available USICS Data). The Density Method. overall impact on the employment market is In the meantime, Foreign Engineering a trickle when compared to the total employ- Graduates help to fill a void of expertise, posiment of 157 million U.S. workers. Likewise, the tively impacting the engineering community. economic impact for the structural engineering In summary: profession is minimal due to the low numbers 1) The impact of foreign graduates is miniadmitted compared with the size of the industry. mal on the total U.S. Economy and One myth prevalent in the engineering minuscule on the Civil and Structural industry when it comes to foreign engineering Engineering Industry. graduates is related to salary. H-1Bs are often 2) Incoming graduates run research programs and incorrectly viewed as accepting lower pay and contribute positively to the economy than their American counterparts. From my by providing specialized expertise that curown experience, having sponsored H-1Bs in rently does not exist in the U.S. my company over the past 15 years, I can attest 3) Foreign Engineering Graduates do not that this is a falsehood. The H-1B program cost more, and they specialize in areas was explicitly set up to protect both U.S. and that are least pursued by our own citizen H1-B workers. Employers must attest to the engineering population.

Department of Labor that they will pay wages to In the end, remember that foreign graduates the H-1B nonimmigrant workers that are at least eventually become taxpayers and contribute equal to the actual wage paid by the employer significantly to our economic growth. It would to other workers with similar experience and be unwise to lose their financial contribution qualifications, or the prevailing wage for the and intellectual investment in our society.â&#x2013;Ş occupation in the area of intended employment â&#x20AC;&#x201C; whichever is greater. As such, the paperwork Statistics cited in this article were obtained and plethora of reporting often make hiring from U.S. governmental data (USICS and H-1B workers difficult for small businesses.

U.S. Departmental of Labor) and industry Large employers sponsor H-1Bs because they are organizations (ASCE, NSPE, NCEE, NCEES). generally Masters/ Ph.D. graduates with specialized training/education that can be difficult to Dilip Khatri is the Principal of Khatri find among the local population.

International Inc, Civil and Structural Visit a University Engineering Graduate School Engineers, based in Las Vegas, NV, and and you will find a majority of international stuPasadena, CA. He was a Professor of dents. In fact, many Ph.D. engineering students Civil Engineering at Cal Poly Pomona for are foreign applicants that arrive on Student 10 years. He served as a member of the Visas and eventually seek to stay through the STRUCTURE Editorial Board and may H-1B program. The H-1B provisions intend be reached at dkhatri@gmail.com. to help employers who cannot otherwise obtain

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award winners and outstanding projects

Spotlight

UC Berkeley Bowles Hall Seismic Retrofit and Renewal

By Joe Maffei, S.E., Ph.D., LEED AP and Karl Telleen, S.E., LEED AP Maffei Structural Engineering was an Award Winner for its UC Berkeley Bowles Hall Seismic Retrofit and Renewal project in the 2017 Annual Excellence in Structural Engineering Awards Program in the Category – Forensic/Renovation/Retrofit/Rehabilitation Structures over $20M.

B

owles Hall was the first residence hall in the University of California system and the first residential college at any U.S. public university. Built in 1929 in the Collegiate Gothic style, the building features steep gables, a tile roof, and castle-like turrets and chimneys, with eight stories that rise from the hillside site. Architect George W. Kelham and structural engineer H.J. Brunnier (SEAONC’s first president and California Civil PE #3) collaborated to design the structure. It is designated a landmark for the City of Berkeley and is listed in the National Register of Historic Places. A western trace of the Hayward earthquake fault passes beneath the building.

The 2016 renovation and retrofit of Bowles Hall is the University’s first public-private partnership (P3) for a seismic retrofit project. Pyatok Architects and Maffei Structural Engineering worked closely with the Bowles Hall Foundation (owner), Education Realty Trust (developer), and Clark Construction (contractor) to deliver solutions within budget that revitalized the building’s function, strengthened the structure for the site’s extreme earthquake hazard, and restored historic features and character.

A western trace of the Hayward earthquake fault, identified at the site in 2007, passes beneath two corners of the building and the ground-shaking hazard at the site is extreme.

Past earthquakes on the Hayward fault have produced surface fault ruptures with a lateral offset of up to six feet. Seismic retrofit measures carried out in 2009 included new retaining walls and foundations to accommodate earthquake fault displacement, with limited work inside the building. The 2015-2016 project completed foundation work associated with fault displacement and takes advantage of the full building renovation to address seismic deficiencies associated with ground shaking.

Structural retrofit measures improved seismic performance while respecting the building’s historic spaces and aesthetic character: • A new exterior buttress provides shear strength to address an existing discontinuous wall without disrupting interior space in the historic dining room. The base of the buttress is supported on 50-foot-deep micro-piles outside the building perimeter. The buttress’s sloping

cap follows the shape of existing pilasters, and the architectural board-formed finish aligns with board-formed lines in adjacent existing walls.

• New concealed stainless-steel fasteners secure the historic roof tiles to the steeply sloping roof, designed to prevent tiles from dislodging in extreme earthquake shaking. The tens of thousands of roof tiles were individually removed to address leaks in the concrete roof and reinstalled over a new system of waterproofing and redwood battens.

• Historic ceilings in the dining room were preserved and secured with supplementary support to the structure above.

The full renovation provided opportunities to address seismic deficiencies with relatively little additional cost. Enlargement of the original elevator shaft enabled the addition of a concrete core-wall spine. The new elevator accommodates a gurney for medical emergencies and provides accessibility to split floor levels. The new concrete core wall uses thick walls with dense horizontal reinforcement and closelyspaced boundary ties to improve the building’s lateral strength and reduce the likelihood of a story mechanism. Other new concrete walls are located strategically to remove discontinuities and provide lateral support beneath the building’s distinctive octagonal turret.

Upgrading building systems and functionality required a meticulous assessment of existing conditions and coordination during construction to deliver the project on time and budget: • New construction for a two-story building addition uses a unique combination of elements in concrete, shotcrete, steel, CMU, and wood to maximize structural efficiency and economy. At the lower story, concrete retaining walls are supported by a rigid secondfloor diaphragm to minimize foundation costs.

In the plan direction parallel to the juncture of new and existing structure, reinforced masonry walls in an otherwise wood-framed second story maintain stiffness comparable to adjacent, existing concrete walls. In the perpendicular direction, carefully designed floor and roof collectors tie the new wood structure to strengthened concrete walls in the existing building. This makes the best use of rigid and

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Courtesy of David Wakely

flexible seismic elements and avoids the cost and maintenance issues of a seismic joint.

• Rebar scanning and fiber reinforced polymer (FRP) strengthening of existing concrete floors allowed new penetrations at numerous locations for air conditioning and bathrooms within units.

The restoration and improved seismic safety of Bowles Hall enable future UC students to experience an intimate and supportive community within the vast Berkeley Campus. For public universities, the project demonstrates that historic preservation of building stock can be economically viable under public-private partnerships for design, construction, and facility management. For structural engineers, Bowles is of particular interest as an earlier work of H.J. Brunnier and one of a handful of instances addressing historic preservation on an active earthquake fault.

As summarized by the San Francisco Chronicle (August 28, 2016), “On a campus where students typically move off campus after one year in the dorms, the new Bowles Hall offers the antithesis of the typical Berkeley experience: a four-year, all-inclusive academic environment where students learn, eat, and grow in a single residence hall their entire collegiate life.”▪ Joe Maffei is the Founder of Maffei Structural Engineering, with offices in San Francisco and Oakland, California. He may be reached at joe@maffei-structure.com.

Karl Telleen is Senior Engineer at Maffei Structural Engineering. He may be reached at karl@maffei-structure.com.

2018 NCSEA Corporate Members

NCSEA News

News form the National Council of Structural Engineers Associations

NCSEA recognizes and thanks its Corporate Members and Partnering Organizations for their continued support in 2018.

As an NCSEA Corporate Member, your benefits put your company in front of structural engineers across the country. Along with benefits such as webinar savings, Structural Connection (NCSEA’s monthly newsletter), access to NCSEA’s web-based communities, Corporate Members can also receive: • Diamond Review Application discounts.

• A free ad on www.ncsea.com.

• A free job posting on NCSEA’s Career Center.

• The opportunity to secure a yearly members-only subscription to unlimited live (20+ per year) and recorded educational webinars (from a library of 180+) available online, on-demand, 24/7/365.

• Membership Spotlights on NCSEA’s website.

Visit www.ncsea.com to become a member today!

Associate Members AISC American Wood Council Fabreeka International, Inc.

Insurance Institute for Business & Home Safety International Code Council Metal Building Manufacturers

Precast/Prestressed Concrete Institute Simpson Strong-Tie Steel Tube Institute USG Corporation

Affiliate Members Alpine TrusSteel Atlas Tube AZZ Galvanizing Services Bekaert Blind Bolt Cast Connex Corporation Cold-Formed Steel Engineers DECON USA, Inc. DeWALT Freyssinet, Inc. Geopier

Headed Reinforcement Corp Hexagon PPM Hilti, Inc. ITW Commercial Construction Lindapter USA MeadowBurke MIDASoft, Inc. Mitek Builder Products New Millennium Building Systems Performance Structural Concrete Solutions, LLC

Pieresearch RISA Technologies SE Solutions, LLC SidePlate Systems, Inc. SkyCiv Stabil-Loc Inc. Steel Deck Institute Steel Joist Institute Strand7 Trimble Vector Corrosion Technologies

Gerald E. Kinyon, P.E. Gilsanz Murray Steficek LLP Glotman Simpson Consulting Engineers GRAEF Haskell Holmes Culley Structural Engineers James Ruvolo Joe DeReuil Associates KBR KOMA L.A. Fuess Partners LLC LBYD, Inc. LHB Inc. Mainland Engineer Corp Martin/Martin, Inc. Mercer Engineering, PC Morabito Consultants, Inc.

Mortier-Ang Engineers O’Donnell & Naccarato, Inc. Omega Structural Engineers PSCE Ruby + Associates, Inc. Simpson Gumpertz & Heger Inc. Sound Structures, Inc. Stability Engineering Structural Design Professionals Structural Engineers Group, Inc. STV, Inc. TEG Engineering, LLC TGRWA, LLC The Harman Group Thornton Tomasetti, Inc. Wilson Andrews Wallace

Sustaining Members ARW Engineers Barter & Associates, Inc. Blackwell Structural Engineers Burns & McDonnell Cartwright Engineers Collins Engineers, Inc. Cowen Associates Criser Troutman Tanner CSA Knoxville CTL Group DCI Engineers Inc Degenkolb Engineers DiBlasi Associates, PC Dominick R. Pilla Associates, PC DrJ Engineering, LLC ECM Engineering Solutions LLC

Partnering Organizations Council of Structural Engineers (CASE)

Structural Engineering Institute (SEI)

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Call for 2018 Abstracts

The Best Instructors. The Best Material. Available to you immediately when you register.

The 2018 NCSEA Structural Engineering Summit Committee is seeking 60-minute presentations that deliver pertinent and useful information that is specific to the practicing structural engineer.

In the 2017 post-Summit survey, attendees expressed direct interest in case studies, lessons learned, new codes, snow loads, ethics, communication, recent projects, advanced analysis techniques, and better business practices. The 2018 Summit will feature education specific to the practicing structural engineer, in both technical and non-technical tracks.

Abstracts for the 2018 Structural Engineering Summit in Chicago, IL, are due March 30, 2018.

Visit www.ncsea.com for more details.

NCSEA’s on-demand training provides the most economical SE Exam Preparation Course available. The course includes 30 hours of instruction: 9 Vertical Sessions and 11 Lateral. The course will give you preparation tips and problem-solving skills to pass the exam. All lectures are up-to-date on the most current codes, with handouts and quizzes available.

PLUS…students have access to a virtual classroom exclusively for course attendees! Ask the instructors directly whenever questions arise. This SE Exam Preparation Course allows you to study at your pace but with instant access to the material and instructors. Several registration options are available, visit www.ncsea.com to register yourself or to learn more about special group pricing!

The Save

Date

NCSEA News

Prepare for the SE Exam with NCSEA

2018 STRUCTURAL ENGINEERING SUMMIT October 24–27, 2018 | Sheraton Grand | Chicago, IL

The California Office of Emergency Services (CalOES) Safety Assessment Program (SAP), hosted by NCSEA, is highly regarded as a standard throughout the country for engineer emergency responders. It is one of only two post-disaster assessment programs that will be compliant with the requirements of the forthcoming Federal Resource Typing Standards for engineer emergency responders and has been reviewed and approved by FEMA’s Office of Domestic Preparedness. Based on ATC-20/45 methodologies and forms, the SAP training course provides engineers, architects, and code-enforcement professionals with the basic skills required to perform safety assessments of structures following disasters.

Jason Spotts, P.E., is a civil engineer with the California Governor’s Office of Emergency Services. He served six years as a civil engineer in the United States Navy’s Civil Engineer Corps. His duties included responding to emergencies or planning and preparing for humanitarian assistance and disaster response incidents. Prior to serving in the military, he worked for a geotechnical engineering firm in Glenwood Springs, CO, and a civil design firm in Chico, CA. Jason also has four years of experience as a fire fighter, with two years of that as an EMT. The next live course is Friday, March 16, 2018. Register at www.ncsea.com.

NCSEA Webinars March 29, 2018 Snow Drift Loading – Current Procedures and Future Directions The webinar will provide a detailed review of the current ASCE 7 provisions for snow drift loading as well as expected future improvements.

Speaker: Michael O’Rourke, P.E., Ph.D. April 12, 2018 Preconstruction Estimating: Foundations & Structures This webinar will discuss cost-estimating for the 10 major building systems and the 4 design phases of a project.

Speaker: William R. Davidson April 26, 2018 ASCE 7-16 Component and Cladding Wind Design This webinar will describe the new requirements in ASCE 7-16 for Component and Cladding design including the revised higher roof pressure coefficients for gable and hip roofs.

Speaker: Bill Coulbourne, P.E. Register at www.ncsea.com.

Webinar time: 10:00 am Pacific, 11:00 am Mountain, 12:00 pm Central, 1:00 pm Eastern.

Courses award 1.5 hours of continuing education after the completion of a quiz. Diamond Review approved in all 50 States.

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News from the National Council of Structural Engineers Associations

NCSEA’s CalOES Safety Assessment Program

Learning / Networking

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Structures Congress 2018

Join us for these inspiring keynotes and a great program at Structures Congress in Ft. Worth #structures18 Thursday Morning Guillermo Trotti and Dr. Dava Newman will present on Designing Advanced Structures for Human Space Exploration from the International Space Station (ISS) to the moon to Mars, including large structural systems used to construct the 109-meter ISS currently in low earth orbit and other space vehicles.

Friday Morning Ashraf Habibullah, President/CEO of CSI, will speak on Next Generation Structural Engineering: Redefining the Role of the Structural Engineer in Changing Times. As the world quickly changes, so must our profession to keep up with advancements in materials, construction techniques, computers, and more.

Saturday Lunch Greg Fenves, President of the University of Texas at Austin, presents on Engineering and Leadership.

Learn what educators and professionals can do to enhance leadership in the structural engineering profession.

Learn more about keynotes/speakers and the full program, and register at www.structurescongress.org.

Many SEI committee efforts meet Wednesday before Structures Congress in Ft. Worth, and all are open to visitors. It is a great opportunity to come early, check out a committee, and consider getting involved – www.structurescongress.org/program.

New Book

Significant Changes to the Minimum Design Load Provisions of ASCE 7-16

Includes noteworthy changes to the design load provisions between the 2010 and 2016 editions of ASCE 7. Summarizes changes to the rain, snow, seismic, wind, and other provisions and introduces the new tsunami guidelines. Also explains the rationale behind changes and detailed analysis of implications, with visual aids.

Check out SEI/ASCE Journals Journal of Structural Engineering

2017 Best Paper on Analysis & Computation: Measured buffeting response of a long-span suspension bridge compared with numerical predictions based on design wind spectra, by Aksel Fenerci and Ole Øiseth 2017 Best Paper on Structural Hazards: Methodology for Development of Physics-Based Tsunami Fragilities, Navid Attary, John W. van de Lindt, Vipin U. Unnikrishnan, Andre R. Barbosa and Daniel T. Cox

Journal of Bridge Engineering Practice Periodical on Structural Design and Construction Journal of Management in Engineering

Advancing the Profession

Become an ASCE Key Contact — www.asce.org/keycontacts ASCE Key Contacts influence the policy process of infrastructure at the state and federal levels by developing relationships with elected officials. By meeting and making contacts with your elected officials in several ways, you can influence issues that are important to the profession and become a trusted advisor when bills are drafted or considered.

Errata 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.

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SEI/ASCE Live Webinars - Learn from the Experts March 7 Vibration of Concrete Floors: Evaluation, Acceptance, and Control March 16 Design of Lateral Load Resisting Systems in Masonry Buildings Individual Certificate Fee Discontinued. Register at Mylearning.asce.org for these and much more.

Join or Renew SEI/ASCE

For innovative solutions and learning, to connect with leaders and colleagues, and enjoy member benefits such as SEI Member Update monthly e-news opportunities and resources â&#x20AC;&#x201C; visit www.asce.org/myprofile or call ASCE Customer Service at 800-548-ASCE (2723).

SEI Online

AccessEngineering

NEW ASCE member benefit provides free and unlimited use of online calculators, tutorial videos, guides, handbooks, and more www.asce.org/AccessEngineering.

Highly interactive, 6- to 12-week-long, instructor-led programs. Master the material with video lectures, exercises and case studies, and online discussions. Complete modules at the time and pace that works best for you. Learn more and register. www.asce.org/goc.

ASCE Library With 138,000 technical and professional articles, ASCE Library is the premier information clearinghouse for researchers and practitioners in civil engineering. ascelibrary.org.

Check out the latest SEI News at www.asce.org/SEI SEI is now on Twitter!

Follow @ASCE_SEI and join the conversation to share what inspires you in structural engineering.

Students

SEI Student Career Networking Event April 20 at Structures Congress in Ft. Worth Employers: Sign up now to participate, be included in event promotions, and receive student profiles in advance of the event. www.asce.org/SEI-Sustaining-Org-Membership.

Students: Plan now to connect one-on-one with employers for SE positions and internships. Learn more at www.asce.org/SEI-Students.

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The Newsletter of the Structural Engineering Institute of ASCE

ASCE Guided Online Courses

Structural Columns

Membership

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Practice Guidelines Currently Available Structural Engineer’s Guide to Fire Protection This publication is intended for structural engineers with no prior experience or training in fire protection engineering. It is a comprehensive and concise treatment of prescriptive and performance-based methods for designing structural fire protection systems in an easy to understand format.

CASE 504 – Proposal Preparation Spreadsheet The CASE Proposal Preparation Spreadsheet was developed to assist project managers and administrators in developing cost proposals for a project. The spreadsheet may be easily customized for any organization or project type. It also may be used as a checklist to see that all phases of a project are adequately staffed.

CASE 962-C – Guidelines for International Building Code-Mandated Special Inspections and Tests and Quality Assurance The Guideline is an update of the previous 3rd Edition to bring it current with the requirements of the 2012 International Building Code. The Guideline describes the roles and responsibilities of the parties involved in the special inspection and testing process, how to prepare a special inspection and testing program, the necessary qualifications of the special inspectors, how to conduct the program, and who should pay for the special inspections and test. The Appendix contains sample forms for specifying

special inspections and tests, and sample letters to be filed with code-enforcement agencies after the program is completed.

CASE 962-D – A Guideline Addressing Coordination and Completeness of Structural Construction Documents The guidelines presented in this document will assist not only the structural engineer of record (SER) but also everyone involved with building design and construction in improving the process by which the owner is provided with a successfully completed project. They intend to help the practicing structural engineer understand the importance of preparing coordinated and complete construction documents and providing guidance and direction toward achieving that goal. These guidelines focus on the degree of completeness required in the structural construction documents (“Documents”) to achieve a “successfully completed project” and on the communication and coordination required to reach that goal. They do not attempt to encompass the details of engineering design; instead, they provide a framework for the SER to develop a quality management process.

You can purchase these and the other CASE Risk Management Tools at www.acec.org/case/news/publications.

CASE Winter Planning Meeting Update On February 1 – 2, the CASE Winter Planning Meeting took place in Austin, TX. CASE does two planning meetings a year to allow their committees to meet face to face and interact across all CASE activities. Over thirty CASE committee members and guests were in attendance, making this another well attended and productive meeting. During the meeting, break-out sessions were held by the CASE Contracts, Guidelines, Toolkit, and Programs & Communications Committees.

Current initiatives include: 1) Contracts Committee – Brent Wright (brent@wrighteng.net) • Preparing all CASE Contracts for next legal review in 2019 o Updating all contract documents to included must have terms & conditions o Updating all contract documents to include scope provisions 2) Guidelines Committee – Kirk Haverland (khaverland@larsonengr.com) • Revising the following current Practice Guideline Documents: • 962-D: A Guideline Addressing Coordination and Completeness of Structural Construction Documents • 962: National Practice Guidelines for the Structural Engineer of Record • Working on the following new documents: • Commentary on ASCE-7 Wind Design Provisions • Commentary on ASCE-7 Seismic Design Provisions • Geotech guideline document/white paper • Future publications: • Committee will be reviewing the new AISC COSP and updating the CASE Commentary document with new information STRUCTURE magazine

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• Adding new CASE guidelines that include the 2015 & 2018 version of Special Inspections 3) Programs and Communications Committee – Nils Ericson (nericson@m2structural.com) • Confirmed the session for the 2018 NASCC Steel Conference • Confirmed sessions for the Summer Risk Management Seminar in June o Developed sponsorship program for firms; includes 1- 3 registrations • Discussed options for sessions at the 2018 ACEC Fall Conference • Discussed options for sessions at the 2019 ACEC Annual Convention • Discussed options for the 2019 Business of Structural Engineering 4) Toolkit Committee – Brent White (brentw@arwengineers.com) • Working on the following new documents: o Tool 8-2: Contract Review o Tool 3-5: Short-term Staffing • Future Tools/Activities: o Tool 0-0: Toolkit Index o Will collaborate and work with SEI on a QBS tool o Will updated the tool that links the CASE 962-D Guideline, A Guideline Addressing Coordination and Completeness of Structural Construction Documents, as it is updated by the Guidelines Committee o Review all current tools for possible updates.

March 2018

The CASE Risk Management Convocation will be held in conjunction with the Structures Congress in Fort Worth, TX, April 19 – 21, 2018. For more information and updates go to www.structurescongress.org.

The following CASE Convocation sessions are scheduled to take place on Friday, April 20: 9:30 am – 10:30 am Managing Design Professionals’ Risk in the Design and Construction of Property Line Building Structures Moderator: Benjamin M Cornelius, Leslie E. Robertson Associates, R.L.L.P. Speaker: Kriton A. Pantelidis, Esq., Welby, Brady & Greenblatt, LLP

11:00 am – 12:30 pm The Good and the Bad of Delegated Design: How to Work With/As a Specialty Structural Engineer Moderator/Speaker: Kevin Chamberlain, DeStefano & Chamberlain Inc. 1:30 pm – 3:30 pm Construction Dispute Resolution through Forensic Engineering Moderator/Speaker: Benjamin M Cornelius, Leslie E. Robertson Associates, R.L.L.P. 3:30 pm – 5:00 pm Tackling Today’s Business Practice Challenges – A Structural Engineering Roundtable Moderator: Corey Matsuoka P.E., SSFM International, Inc.

CASE’s Business of Structural Engineering Seminar

CASE in Point

CASE Risk Management Convocation in Fort Worth, TX

June 7 − 8, 2018; Anaheim, CA

so register now to help your firm balance risk management and profitability with greater confidence.

This program will be held June 7-8, 2018, at the Marriott Anaheim, Anaheim, California, and registration and details can be found at http://bit.ly/2mZDfPh. If you are interested in being a sponsor for this event, please contact Heather Talbert (htalbert@acec.org) for more information.

Donate to the CASE Scholarship Fund!

The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at a minimum, in an ABET-accredited engineering program. Since 2009, the CASE Scholarship program has given $25,000 to help engineering students pave their way to a bright future in structural engineering.

We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest

young talent from a dwindling pool of engineering graduates.

One way to enhance the ability of students in pursuing their dreams to become professional engineers is to offer incentives for educational support.

Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for tax deduction, and you do not have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

Market Leaders, Celebrities to Star at ACEC Convention Heading the lineup of political and industry speakers at the 2018 ACEC Convention in Washington, D.C., April 15 – 18, is U.S. Department of Transportation Secretary Elaine Chao.

Steve Schmidt, Republican political strategist and Assistant to President George W. Bush, and Fox News Host Tucker Carlson will both address National Politics in the Age of Trump.

Mike Allen, co-founder of Axios and Politico, will moderate a discussion with prominent lawmakers on Infrastructure and the 2018 Election Cycle.

Energy Under Secretary Paul Dabbar (invited) will examine U.S. energy priorities and programs.

Georgia DOT Commissioner Russell McMurry, Illinois Tollway Chairman Bob Schillerstrom, and Washington Union Station Redevelopment Corp. President/CEO Beverly SwaimStaley will discuss What Works – and What Doesn’t – with Public/ Private Partnerships.

TV star Kevin Nealon will again host the Engineering Excellence Awards Gala.

For more information and to register, http://bit.ly/2ElLEmq.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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CASE is a part of the American Council of Engineering Companies

A proper risk management program can reduce your chances of being sued and allow you to take on more risky projects – which can generate substantial profits for your firm. Developed by the Council of American Structural Engineers (CASE), The Business of Structural Engineering can help reduce your rate of claims against structural engineering projects, increase profitability, and enhance management practices. Firm principals, owners, project managers, and risk managers are all encouraged to attend,

Structural Forum

opinions on topics of current importance to structural engineers

Document, Document, Document The First Three Rules of Construction

By Scott Lowe

O

ne thing savvy contractors have learned is that the first three rules of the construction phase of a project are document, document, and document.

Unfortunately, too many engineers do not adequately document construction activities.

The problem with this is the old maxim, “If it is not in writing, it did not happen.” Though there is wisdom in this old maxim, it does not tell the engineer what to document or how to document.

The first goal of documentation is to collect the facts accurately and then to support these facts with written descriptions and photographs so that construction issues can be quickly and fairly resolved.

Three things to consider are: • Documentation is a must!

• Documentation is related to risk.

• Documentation is only as effective as what is documented, why it is documented, and how it is presented.

Documentation is a Must!

Not everything must be recorded but engineers ought to document everything that may be important, so they have the necessary facts should disputes arise. While a true statement, it is not very helpful and easier said than done.

The information deemed important depends on the situation and what the engineer is trying to communicate.

For example, it is not essential for an owner and engineer to record the cause of a delay if the contractor mitigated the delay, finished the project on time, and did not ask to be paid more money. All is well that ends well. However, the owner and engineer must record the cause of the delay if the contractor causes the delay, accelerates to mitigate the delay, and then asks the owner to pay for the acceleration.

It is not known in advance which contractors will accelerate to mitigate project delays and not ask for additional compensation or which contractors will ask to be paid.

Prudent owners and engineers document all delays.

Documentation is Related to Risk The greater the risk, the greater the need for documentation to mitigate or control that risk. Project documentation, to be useful, should include the specific facts needed to substantiate the engineer’s opinions and conclusions for presentation to the owner.

Engineers also need to protect themselves. For example, owners and contractors can claim that problems are attributed to a poor design. The engineer’s defense and the proper resolution of the issue comes from solid documentation of both the design and the construction activities related to the item(s) in question.

Effective Documentation Three techniques can be used to ensure that valuable information is documented.

Engineers do not have to do all the writing. Some Federal agencies require the contractor to produce daily logs or reports for the project. The logs are then submitted to the owner for review and comment. The owner and engineer can add anything to the daily log that they think should be recorded or comment on the contractor’s entries. This eliminates the need for both the contractor and the owner/engineer to prepare a complete daily log. The same is valid for meeting minutes, submittal logs, RFI logs, and other documents that can (and should) be shared.

Writing is not the only form of documentation.

Pictures are unique tools, but often need an explanation to help the reader understand why the picture was taken. In this digital age, it is easy to add circles and arrows to a photograph to emphasize problems and focus attention, but the value of adding notes should not be underestimated. Without a short paragraph of writing to add clarity, the picture is not nearly as valuable. The writing also memorializes the issue so that, in the future, it is easier to remember the situation accurately.

Document the whole story, not just pieces.

Pictures are powerful tools for documentation, but it is critical to ensure that they tell the whole story. Those doing the documenting

should always keep the story they want to tell in mind.

As an example, an engineer took two pictures of the same bridge, on the same day, to make a point about the causes of delays during construction. Two significant things had happened while the bridge was being built. First, the contractor experienced a form blow-out while constructing one of the tall, slender bridge piers. This pier supported the precast concrete girders that crossed the river. Second, during the erection of the steel girders for another part of the same bridge, a construction document error was discovered and the girders needed to be re-fabricated.

The owner asserted that the form blow-out caused the delay. The contractor asserted that the steel design error caused the delay.

Because the engineer took two pictures on the same day at the expansion joint between the concrete and steel sections of the bridge, the pictures conclusively proved the cause of the delay. One of the pictures was taken of the concrete portion and showed that the bridge deck was yet to be constructed. The second photo, of the steel portion, showed the deck constructed and all but finished and striped.

These two pictures told a defensible story; the form blowout delayed the project – the concrete portion of the bridge was not complete when the deck had already been poured on the steel portion of the bridge. Either one of the photos, by themselves, would not have told that story.

While the old cliché – “If it is not written down, it did not happen” – may be true in some situations, engineers can learn from savvy contractors to stay on-point and effectively document construction activities using reports, photos, and notes.▪ Scott Lowe is a Principal with Trauner Consulting Services, Inc. He is the co-author of the third edition of the book, Construction Delays, and the course developer and lead instructor for the NHI course, Managing Highway Construction Claims: Analysis and Avoidance.

Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, the Publisher, or the STRUCTURE® magazine Editorial Board.

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