STRUCTURE magazine | November 2021 by structuremag

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INSIDE: Pima Transportation Center Cantilevered Frame Design West Berkeley Medical Office Building 95 State at City Creek

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Errata

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Director for Sales, Marketing & Business Development Monica Shripka Tel: 773-974-6561 monica.shripka@STRUCTUREmag.org

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Creative Director Tara Smith graphics@STRUCTUREmag.org

Based on feedback to the Integrating Shear Lug Design with Anchoring-toConcrete Provisions article in the September 2021 issue of STRUCTURE, the author offers the following correction. Figure 2(b) and Figure 3(b) in the article incorrectly show the bearing area (Aef,sl) as a T-shaped configuration. This configuration is only relevant when stiffeners are used. Since the shear lug in these illustrations does not include stiffeners, the bearing area (Aef,sl) should be shown as a rectangular configuration. If stiffeners are installed, the leading edge of the stiffener and the area of the shear lug extending 2tsl on either side of the stiffener would be included in Aef,sl. The author apologizes for any confusion this may have caused. (This Erratum and corrected figures have been added to the online version of the article, STRUCTUREmag.org.) Figure 1 of the Structural Systems article (Mladjov, October 2021 issue) inadvertently showed an incorrect water level. Please see the corrected figure in the online version at STRUCTUREmag.org. The author apologizes for missing this error.

EDITORIAL BOARD Chair John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA chair@STRUCTUREmag.org Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT Erin Conaway, P.E. AISC, Littleton, CO Linda M. Kaplan, P.E. Pennoni, Pittsburgh, PA Charles “Chuck” F. King, P.E. Urban Engineers of New York, New York, NY Nicholas Lang, P.E. Masonry Industry Representative Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY Jason McCool, P.E. Robbins Engineering Consultants, Little Rock, AR Brian W. Miller Davis, CA Evans Mountzouris, P.E. Retired, Milford, CT

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STRUCTURE ® magazine (ISSN 1536 4283) is published monthly by The National Council of Structural Engineers Associations (a nonprofit Association), 20 N. Wacker Drive, Suite 750, Chicago, IL 60606 312.649.4600. Periodical postage paid at Chicago, Il, and at additional mailing offices. STRUCTURE magazine, Volume 28, Number 11, © 2021 by The National Council of Structural Engineers Associations, all rights reserved. Subscription services, back issues and subscription information tel: 312-649-4600, or write to STRUCTURE magazine Circulation, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606.The publication is distributed to members of The National Council of Structural Engineers Associations through a resolution to its bylaws, and to members of CASE and SEI paid by each organization as nominal price subscription for its members as a benefit of their membership. Yearly Subscription in USA $75; $40 For Students; Canada $90; $60 for Canadian Students; Foreign $135, $90 for foreign students. Editorial Office: Send editorial mail to: STRUCTURE magazine, Attn: Editorial, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606. POSTMASTER: Send Address changes to STRUCTURE magazine, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606. STRUCTURE is a registered trademark of the National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

Contents N OVEM BER 2021

STRUCTURAL

GYMNASTICS IN THE TRANSPORTATION CENTER

Cover Feature By Thomas Kramer, P.E., S.E., et al.

Pima Community College’s new Transportation Center is 43,000 square feet with a total of 27 work bays. An angular geometry, horizontal and vertical, involved intricate load transfers, combinations of transfer girders and custom drag connections, and more.

Features WEST BERKELEY MEDICAL OFFICE BUILDING

Columns and Departments 7 Editorial

We SEE Above & Beyond!™ By Ryan Kersting, P.E., S.E.

By Nick Bucci, S.E., and Ryan Pintar, S.E.

The new Kaiser Permanente medical office building is a 66,000-square-foot structure with open floor plates. The chosen moment frame system allowed for conventional steel framing and a shallow foundation system.

THE WACHENHEIM SCIENCE CENTER By Ron Blanchard, AIA, Michael A. Tecci, P.E., and Julia K. Hogroian, P.E.

By Kenneth Bland, P.E.

8 Practical Solutions

Cantilevered Frame Design Utilizing Joist Girders By Brandon Phillips, P.E.

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

12 Structural Design The Long Road – Part 2 By Matthew Speicher, Ph.D.,

By Sandra Hyde, P.E., and John “Buddy” Showalter, P.E.

20 Structural Systems Structured for Protection

Part 3 of this four-part series continues the discussion of the By April M. Musser, P.E. structural investigations conducted to better understand the existing structure – specifically the main roof and original 24 Structural Carbon mechanical penthouse. The SEI SE 2050 One-Year Anniversary 95 STATE AT CITY CREEK By Mark Sarkisian, S.E., et al.

50 Historic Structures Quebec Bridge, The First Failure, 1907 By Frank Griggs, Jr., D.Eng, P.E.

and John Harris, Ph.D. On a gradually sloping site, three and a half stories of this complex building rise above grade while two and a half levels sit below. Moment frames provide the building’s 16 Codes and Standards lateral load resistance. 2021 IBC Significant Structural Changes – Part 1

ADAPTIVE REUSE OF THE HISTORIC WITHERSPOON BUILDING – PART 3

48 Code Updates States, Cities Adopting Tall Mass Timber Provisions

By Chris Jeseritz, P.E.

The new 95 State facility consists of a 25-story Class A tower with a 5-story podium. In a region of high seismicity 46 Engineer’s Notebook and close to the active Wasatch Fault zone, the design L everaging Professional utilized state-of-the-art performance-based seismic design Relationships By Samuel Harris methodologies and standards.

54 Legal Perspectives Waiver of Consequential Damages By Gail S. Kelley, P.E., Esq.

56 InSights Who Selects Fireproofing? By Charles “Chuck” F. King, P.E., S.E., and Stephen M. Cohen, AIA

59 Spotlight A Face Lift for the Spruce Goose 66 Structural Forum Acceleration in the Pipeline By John Gavan, S.E.

In Every Issue Advertiser Index Resource Guide – Software Updates NCSEA News SEI Update 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. N O V E M B E R 2 0 21

EDITORIAL We SEE Above & Beyond!™ By Ryan Kersting, P.E., S.E.

s a teenager, I had a dramatic introduction to the important role that structural engineers play in our communities. I vividly remember the moment the ground started shaking as I sat in Candlestick Park with my mom and my brother awaiting the start of the third game of the 1989 World Series. It wasn’t too long after the shaking stopped that images of the damage caused by the Loma Prieta Earthquake started appearing on the hand-held TV being watched by the people in front of us. I remember trying to process what just happened: feeling very thankful that the stadium remained standing while thinking about the damaged structures and the lives that were affected. At the time, I did not know if I wanted to become a structural engineer. However, I know that experience ignited a curiosity about what it takes for engineers to design the structures that give us the places in which we live, work, and play. Months of disruption and recovery further demonstrated the impact that structural engineers have on our daily lives and routines. Like many of you, I decided to pursue a career in engineering because I loved math and science, but it wasn’t a foregone conclusion that I would become a structural engineer. My dad was a pastor, my mom was a nurse, and professional engineers were not well known in the small town where I grew up. In fact, one of my elementary school teachers wanted to expose me to some math-related careers and arranged for me to visit a local architect’s office (of all places!). In middle school and high school, I was introduced to careers in engineering. However, I also remember wanting to make sure a career in engineering would allow me to use math and science to connect with and impact my community (the influences of my parents clearly shining through). In college, I was inspired by quotes from Herbert Hoover about the responsibility and opportunity engineers have to improve the way of life in our communities (https://bit.ly/3G8L6AW). In my career, the idea that structural engineering was more than just math and science culminated at the kick-off meeting for a design-build project for a new medical center when a doctor gave the welcoming message to the entire project team. She simply, but passionately, told all of us that each time we picked up a pencil, turned on a computer, or put on a hard hat, our job was not to perform calculations, draw details, or even build the structure. Instead, our job was even bigger: to help the medical center treat cancer and eventually find a cure. These memories about my path to becoming a structural engineer are a lead-in to an ambitious initiative NCSEA has recently embarked on: branding and marketing the entire structural engineering profession. By now, I hope you have seen some of the early announcements, posts, tweets, etc., as the campaign has been revealed with the brand tagline We SEE Above & Beyond. The campaign seeks to raise awareness of the structural engineering profession’s vital role in society and how Structural

Engineering Excellence (SEE) goes above and beyond the calculations, details, and code requirements to thoughtfully and efficiently provide the spaces for our daily experiences and improve the safety and resilience of our communities. NCSEA has enlisted the expertise of an outside agency to develop the content and strategy in close collaboration with a nimble Steering Committee (members listed below) and the NCSEA Board. While the initial efforts target telling the story of the SE profession, raising awareness, and strengthening partnerships within the AEC industry, future efforts include outreach to the general public and students of various ages. The current branding and marketing materials have been created for use in social media by both NCSEA and state and local structural engineering organizations in their local markets. A companion website, www.weseeaboveandbeyond.com, features some of the key campaign messages aligned with the “We SEE Above & Beyond” brand, including: • We SEE the “big picture” vision of a project, its desired outcomes, and its intended impact. • We SEE the structure above, below, in front, and behind the user’s experience. • We SEE the safest, most efficient path for loads so that structures are safe and economical. • We SEE construction solutions using proactive leadership, communication, and creative problem-solving. • We SEE our role in helping to form resilient communities. The website also provides additional resources of interest to the AEC community and the general public. Ultimately, this campaign will demonstrate how structural engineers’ vision, technical expertise, and leadership transcend the basics of code-minimum safety and provide the backbone for the buildings, bridges, and other structures that support almost every daily experience in our communities. Having individual engineers and firms like, share, and re-tweet the campaign messages will help spread the word even further, enhancing the profession’s image and raising awareness about what we do. Embracing opportunities to show and share how We SEE Above & Beyond will make our profession more remarkable and our careers more meaningful and rewarding. Ideally, the campaign will inspire the next generation of structural engineers to join us. Along the way, I hope it inspires you, your colleagues, and our entire profession to continue to SEE Above & Beyond too!■ Ryan Kersting is an Associate Principal with Buehler in Sacramento, CA and is currently serving as Secretary on the NCSEA Board of Directors.

NCSEA Branding and Marketing Campaign Steering Committee: Ed Quesenberry, NCSEA President (SEAO) • David Horos, NCSEA Vice President (SEAOI) • Sarah Appleton, NCSEA Board (SEAOG) Al Spada, NCSEA Executive Director • Ken O’Dell, SEA Participant (SEAOC) • Yunlu Shen, SEA Participant (SEAoNY) Angelina Stasulis, NCSEA External Communications Committee (SEAOG) • Leo Baran, NCSEA MO and Committee Services Director STRUCTURE magazine

N O V E M B E R 2 0 21

practical SOLUTIONS Cantilevered Frame Design Utilizing Joist Girders

Addressing Complexity in an Aircraft Hangar Lateral Load Resisting System By Brandon Phillips, P.E.

n answer to the growing demand for more commercial and defense aircraft, larger-scale maintenance hangar construction is on the rise. These projects are characterized by unobstructed service bays that span hundreds of feet, posing a structural challenge for which architects often specify a cantilevered steel frame. As conceptually shown in Figure 1, the size and complexity of a cantilevered hangar design can present a unique set of engineering challenges. The integration of massive steel trusses and other structural elements can increase project costs. However, steel joist girders, along with steel joists and decks, can offer a cost-effective solution. Steel joist companies are ready to meet these complex challenges, offering a combination of robust engineering knowledge and 3-D modeling tools.

Figure 1. In a conceptual cantilevered system, the cantilevered extension transfers loads to the vertical supports.

Design, Detailing, and Fit-up As shown in Figure 2, a hangar project calls for three cantilevered truss towers. The towers rise at the back side of the building and cantilever over the roof to the front of the hangar. Emanating from the truss towers is a load-resisting system consisting of joists and joist girders. The design establishes the desired open bay space, but it also requires a carefully engineered system that details a range of possible structural fit-up challenges. Figure 3 shows how, as the roof structure slopes to the back of the bay, the steel joists also slope. The joist girders must frame into the cantilever frame to form the roof slope. In addition, as shown in Figure 4, the slope of the hangar roof may require that a horizontal truss fit up with each supporting steel joist girder at varying connection points. A horizontal truss along the front of the bay must be designed for lateral wind and seismic loading. This truss must be detailed to fit with the joist girders and may even be designed to rest on the top

chord of a supporting steel joist girder. As the horizontal truss slopes toward the back of the hangar, the joist girders that support the truss must fit up with the horizontal truss at varying connection points. This requires close collaboration between the structural steel engineer and the steel joist engineer to address varying load/force calculations with related bolting and bracing details.

Vertical and Lateral Loading

Girder deflection on large, open, cantilevered hangar bay designs is often subject to live load deflection limitations related to the movement of supported maintenance equipment and service personnel. The structural engineer (SEOR) may require deflection limits approaching L/700 to ensure the safe, smooth, and reliable operation of suspended cranes and overhead doors. Accordingly, the joist manufacturer conducts loading analyses using the SEOR's requirements to calculate the precise point loads at each brace, crane, and joist location. Each load case must be organized in tabular form and verified with the joist company's design software. The manufacturer needs to check the accuracy of each loading calculation with a redundant review process to assure that, for each load case, the joist girder and truss act as one structure to deflect precisely under live load. The manufacturer signs and seals the calculations as the delegated engineer and submits the calculation package to the SEOR for project review and Figure 2. Cantilevered steel truss systems specified for aircraft maintenance hangars create massive, open-span bays. Cantilevered trusses highlighted in red, joist girders in blue, horizontal trusses in green. approval to ensure overall design 8 STRUCTURE magazine

performance. The SEOR can also use this information from the manufacturer to present to the building official for code review. In addition to taking advantage of the joist manufacturer's engineering expertise, the SEOR can also employ a peer-review process to ensure building performance and public safety.

Joist Girder Bearing A joist girder with a depth of 10 feet and a span of up to 140 feet with significant vertical and lateral loads will have large end reactions (shear). Therefore, establishing adequate joist girder bearing is essential Figure. 3. In a sloping cantilevered bay, the joist girders (blue) frame into the cantilever truss (red) to for proper fit-up and management of these reactions form the roof slope. The supporting joists (orange) slope as well. in a cantilevered frame system. When fitting up the cantilever frame and a joist girder end panel, splice for a given joist girder may not work when considering the large the joist engineer must give adequate seat clearance for the joist girder loads that are characteristic of a cantilevered hangar structure. When connection at the cantilever frame. For example, 12-inch-deep girder designing the girder bottom chord splice for maximum gravity tension seats allow clearance for 8-inch top chord angles and provide the joist and the top chord splice for maximum uplift tension, the capacity of manufacturer the needed design flexibility. In addition, a minimum the splice may not be sufficient. Moving the splice locations to the 12-inch seat length allows adequate space to use four 1-inch structural third points reduces the required tension force. A further tactic may bolts for erection. This provision also supplies acceptable welds to be to increase the tension capacity of the top chord splice by utilizing resist high uplift reactions. a similar splice design generally used on the bottom chord. But these The joist engineer may experiment with the end web slope to change splices typically have a plate on the top chord, affecting fit-up at the the end web size. A steep slope reduces the force in the web, but the joist bearing locations. bearing requirement must balance this. The joist engineer must check Experience dictates that while these tactics can address large splice the eccentricity to minimize end moments while remaining aware of forces, they can also introduce complications due to changes in any required clearances with other structural elements. The 12-inch- the steel joist girder geometry, affecting the horizontal truss, crane deep seat helps with these considerations. The SEOR must be mindful brace, and overhead door brace clearance. The joist manufacturer, of the potential for additional moments due to eccentricity as they along with the steel supplier, can check proper clearances by using consider these connections. 3-D modeling. This solution may require adjustments to joist girder The SEOR may also use the joist girders as part of the lateral load geometry, splice, and brace locations to assure that the splice locations resisting system. As such, the joist engineer must check the girder do not foul with crane and brace load locations while maintaining top chord and seats for these axial forces. The SEOR may also utilize an efficient girder design. large horizontal trusses to manage large lateral loads, which may be Similarly, modeling the joist seat depths and splice locations can guide present in high wind or seismic regions. These trusses may interact the adjustment of the joist seat depths to ensure sufficient clearance with the girders creating challenges for detailing and field erection. for the attachment of the joists to the joist girders at the splice locaThe steel and joist detailers can work together using 3-D modeling tions. The joist manufacturer and the structural steel detailer must to tighten clearances to acceptable shop and field tolerances. coordinate joist seat depth to provide adequate bearing and clearance for the joist seats. In addition, the joist manufacturer must ensure that joist seats do not interfere with the field fit-up of the bolted splices.

Field-bolted Splices

Steel joist girders specified for hangars, along with cantilever frames, can achieve hangar openings up to 450 feet or more. At these spans, joist girders typically require field-bolted splices depending upon shipping and site limitations. However, the location of a midpoint

Project Coordination

For project success, the structural steel supplier must closely coordinate with the joist manufacturer, the SEOR, and the steel erector to ensure ease of design and erection. Early in the project, the structural steel supplier should choose a joist manufacturer experienced with the complexities associated with open bay construction. The joist manufacturer's early involvement ensures enough lead time to produce the required calculations and a 3-D model for approval by the SEOR. The SEOR must provide detailed load diagrams, including all dead, roof live, crane, wind, and seismic loads to the joist manufacturer. They also need to supply serviceability requirements such as maximum deflection under live loads, including cranes and catwalks. In addition, they must consider camber which can be excessive at longer Figure 4. In a sloping, cantilevered hangar structure, horizontal trusses (green) may be supported by interweaving steel joist girders (blue) at different connection points. spans. See SJI technical digest #9 and 45th edition N O V E M B E R 2 0 21

Standard Specifications for more information regarding camber. The SEOR needs to review the joist manufacturer's submittal to ensure building performance. On these complicated projects, the SEOR may delegate the design of the steel connections to another engineer. In many cases, the steel supplier contracts with this delegated engineer and coordinates the connection design between the SEOR, the joist manufacturer, and the connections engineer.

Summary Owners and architects can create massively open and unobstructed aircraft hangar bays by leveraging the unique advantages of the cantilevered frame system paired with joists, joist girders, and deck supplied by an experienced manufacturer. These projects will be highflying successes when the SEOR is supported early by an experienced team of engineers representing both the structural steel supplier and the steel joist manufacturer. Early coordination utilizing 3-D modeling will eliminate costly field errors, saving money and time for the owner.■

Figure 5. The HSS shown was used to drag a 50-kip axial force into two joists. The HSS was connected to the column.

Brandon Phillips currently works for New Millennium Building Systems as an engineer and consultant. He has 25 years of design, manufacturing, and general management experience in the steel joist, joist girder, and deck industry. (brandon.phillips@newmill.com)

Working the Angles A recent cantilevered bay project called for the steel joists to have sloped baseplates designed to support up to 50-kip seismic axial load (Figure 5). The SEOR determined that the most efficient approach was to create an HSS drag to transfer the axial force through two joists back to the lateral resisting system. This HSS was not used for bearing, which created eccentricity, increasing the design moment induced by the axial force plus eccentric bearing. Since the joist bears on the W-section, not on the HSS, the joist seat was designed for eccentric bearing plus a 25-kip axial transfer. The solution introduced complexities to fabrication but allowed this rather large axial force to be transferred through the joist top chord. As can be seen in this example, modern steel joist manufacturers can provide flexible and efficient solutions for complex projects.

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STRUCTURAL ENGINEERING FIRM

Profile

Moving the Industry Forward How KPFF’s Entrepreneurial Culture is Responding to Change Author’s Note: In this time of constant, accelerated change our firms must work together to promote and support our profession. With this in mind, KPFF is proud to be the premiere firm to participate in this new series from STRUCTURE magazine. It allows different firms to promote our noble profession, share current ideas and challenges, and celebrate the unique ways we operate and thrive. “I am pursuing my passion and doing this in collaboration with others that share my enthusiasm for a more sustainable and resilient infrastructure in Southern California.” - Neha Yadav, PE, Principal

Neha and Rodrigo, who are working together to build our transportation and infrastructure practice in Southern California, articulate why KPFF established and continues to be committed to our unique company culture and structure. Their stories highlight the value of combining freedom and support, allowing our team of entrepreneurs to thrive. It illustrates how we successfully leverage our size to provide robust resources and support without being constrained by bureaucracy. KPFF is a supportive business organization, flipping the traditional organizational structure upside down. Our servant leaders focus on supporting our many fully empowered client-facing professionals.

Our unique structure encourages innovation. Ideas and experimentation can happen at an intimate, local scale and then flourish as the larger organization becomes involved. Recent contributions to our profession include: • Chairing ACI 318 Committee. • Collaborating on the latest State of the Practice Book on Structural Design for Physical Security. • Leadership in performance-based design, including authoring early building codes for seismic isolation, pioneering seismic retrofit of hospitals, and initiating design methodology for mass timber tall buildings. Providing opportunities to others feeds a consistent evolving transition. Like a relay race, we get others up to speed while current leaders are running strong, enabling them to strategically and unselfishly pass the baton. This concept allows KPFF to remain privately-held by Principals that are active, engaged and future forward.

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With this unique approach, we have organically grown and expanded throughout our 61-year history. Our team is empowered to “make things happen,” with their contributions benefiting the entire KPFF culture. A great example of this is the intern program in our Special Projects Group, who focus primarily on prime contracts in public infrastructure. Developed by Caressa Bacon, it was nominated for WayUps 2021 Top Internship Programs, with some elements being adopted company wide.

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N O V E M B E R 2 0 21

structural DESIGN The Long Road

Advancing First-Generation PBSD for Steel Buildings Part 2: Case Studies

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

mplementing performance-based seismic design (PBSD) procedures for assessing existing buildings has generated interest in using similar approaches to design new buildings. The advantage of using these procedures is that designers can go outside the more prescriptive requirements of traditional design and have a more direct connection between expected performance and the design process (i.e., performance targets are explicitly defined upfront). This results in the engineer easily communicating the anticipated performance to the client and targeting a design that achieves beyond-code performance if desired. However, as PBSD was gaining popularity in practice approximately a decade ago, there had been limited published information into the relationship between standards for seismic design of new buildings and the seismic assessment of existing buildings. As a result, some engineers were concerned that the existing building standard was too conservative, potentially leading to unnecessarily expensive retrofits for existing buildings or unnecessarily expensive designs for new buildings when utilizing the existing building standard for new building design. The need to understand this relationship was noted in the Research Required to Support Full Implementation of Performance-Based Seismic Design (NIST 2009) and in the Perspectives on ASCE 41 or Seismic Rehabilitation of Buildings (SEAONC 2010). Therefore, the National Institute of Standards and Technology (NIST) began a research initiative to help bridge the gap in understanding and address the perceived challenges of adopting PBSD to assess existing buildings and designing new buildings. Part 1 of this series (STRUCTURE, October 2021) discusses the pertinent history of performance-based design procedures and draws comparisons between performance-based approaches and traditional design approaches. The four-part NIST study, Assessment of First Generation Performance-Based Seismic Design Methods for New Steel Buildings, investigated four steel seismic force-resisting systems (SFRSs) (Harris 2015a, 2015b, 2015c, and Speicher, 2020). Several archetype buildings were designed using the American Society of Civil Engineers’ ASCE 7: Minimum Design Loads for Buildings and Other Structures and then assessed using the provisions in ASCE 41: Seismic Evaluation and Retrofit of Existing Buildings. The results indicated that, in many cases, a building designed to meet the requirements of ASCE 7 did not pass the acceptance criteria in ASCE 41, thus suggesting there is a need for further refinement of PBSD provisions in ASCE 41 to align with a more commonsense outcome.

Archetype Buildings Twenty-four different archetype buildings were designed as part of the NIST study. The buildings were simple in plan layout and framing details to focus on the relationship between new building design and existing building assessment without adding other complexities. Four different SFRS typologies were investigated: special moment frames (SMFs), special concentrically braced frames (SCBFs), eccentrically 12 STRUCTURE magazine

Figure 1. Building schematic.

braced frames (EBFs), and buckling-restrained brace frames (BRBFs). Also, three different heights were investigated: 4-story, 8-story, and 16-story. The moment frames span three bays in the East-West direction, and the braced frames span two bays of the North-South direction. The designs were created using loads from ASCE/SEI 7-10. Each SFRS and height combination was designed twice, using loads via the equivalent lateral force (ELF) procedure and using loads via the modal response spectrum analysis (RSA) procedure. A threedimensional schematic of the 8-story building is shown in Figure 1.

Building Performance Once the designs were completed, each building was assessed using the following four levels of Tier 3 assessment procedures in ASCE 41: linear static, linear dynamic (modal RSA), nonlinear static (pushover), and nonlinear dynamic (response history analysis). These four procedures were used to understand the range of assessment outcomes and see how the assessments related to each other. For the linear and nonlinear procedures, models were created in Computer and Structures, Inc’s (CSI) ETABS and Perform-3D, respectively; full details of modeling approaches are documented in the NIST reports. Each assessment was done considering Life Safety (LS) at the Basic Safety Earthquake Hazard Level 1 (BSE-1) (equivalent to the design level earthquake) and Collapse Prevention (CP) at the BSE-2 Hazard Level (equivalent to the maximum considered earthquake). The assessment of the first three system typologies (SMFs, SCBFs, and EBFs) was done using ASCE/SEI 41-06, and the assessment of the BRBFs was done using ASCE/SEI 41-13; different versions of ASCE 41 were used due to the timing of the different phases of the NIST study.

Table of SMF component performance CP at the BSE-2.

Building Height

4-story 8-story 16-story

Linear Static

Design

Linear Dynamic

Nonlinear Dynamic (mean of 11 records)

Nonlinear Static

ELF

Fail

Pass

RSA

Fail

Pass

Fail

Pass

Fail

Pass

Fail

Pass

ELF

Pass

Fail

Pass

Fail

Pass

Fail

Pass

Fail

Pass

RSA

Fail

Pass

Fail

Pass

Fail

Pass

Fail

ELF

Pass

Fail

Pass

RSA

Fail

Pass

Fail

Pass

Fail

Pass

Sum of Failures

Note: BC = beam-to-column connection, CM = column member, PZ = panel zone

Assessment Results

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Several trends were identified from the assessment results. In general, assessment using ASCE 41 indicated that a new building design is deficient, especially when utilizing both linear static and nonlinear dynamic procedures. The conservative results seen in the linear static procedures may be considered reasonable given the relatively simplistic methodology utilized to account for what is, in reality, complex nonlinear behavior. In contrast, the nonlinear dynamic procedure should arguably have less conservatism, given that the analysis directly accounts for the nonlinear behavior. It is helpful to probe a few issues to understand the reasons why the nonlinear dynamic procedure gave conservative results, including a) the methodology used to select and scale ground motion records, b) the methodology used to derive acceptance criteria (e.g., ASCE 41 permissible rotations of a beam hinge), and c) the potential that the designs did not actually meet the performance intent of ASCE 7. The effects of the methodology used for the selection and scaling of ground motion records was explored in Speicher and Harris (2016) and Uribe et al. (2019). The ground motion selection and scaling methodology followed the provisions of Chapter 16 of ASCE/SEI 7-10, with a few exceptions, including using only records selected from the far-field set (i.e., recorded at sites greater than or equal to 10 km from fault rupture) in Federal Emergency Management Agency’s (FEMA) P695: Quantification of Building Seismic Performance Factors (FEMA 2009). This far-field set was compiled for assessing the validity of ASCE 7 seismic performance factors (i.e., response modification factor, R, deflection amplification factor, Cd, and overstrength factor, Ω0), which may result in a ground motion set that is overly demanding for use in an ASCE 41 assessment. Since the intent of the NIST study was to investigate

generic archetype buildings, it was reasoned that the FEMA P695 farfield set was an appropriate sampling bin. However, after the results from the NIST study showed that nonlinear dynamic procedures yielded conservative results, this approach was re-examined. Uribe et al. (2019) investigated the effects of using a more hazard-consistent ground motion selection and scaling approach, such as the conditional mean spectrum method. The conservatism was reduced using such a method, but not significantly enough to enable all the building components to pass the nonlinear dynamic assessment. The next issue explored was related to ASCE 41 acceptance criteria. These criteria are typically derived from available experimental data coupled with supplemental analytical data and engineering judgment. Most experimental data come from steadily increasing fully-reversed cyclic tests such as the standard protocol described in Chapter K of the American Institute of Steel Construction’s (AISC) 341-16. These test protocols demonstrate a component’s behavior under intensive seismic loading. However, it is well-known that a building component’s behavior is often significantly affected by the loading history; the maximum deformations achieved under fullyreversed cyclic loading protocol can be much less than those under a monotonic loading protocol. Most ASCE 41 acceptance criteria found their origins when nonlinear static (pushover) analysis was the state of practice when advanced analysis was employed. At the time, it was logical to have test data that implicitly capture cyclic effects in the backbone curve, which, in turn, is used to define component acceptance criteria. However, the state of practice has changed in the last few decades with the advances in computing power and the general use of nonlinear dynamic analysis becoming

www.dci-engineers.com

A summary of the SMF assessment outcome is given in the Table. Failures were detected in every level of the assessments conducted, though there was not complete consistency between the linear and nonlinear approaches. For both the linear and nonlinear assessment procedures, deficiencies were detected in the beam-to-column connections and column members. Interestingly, the nonlinear dynamic procedure indicates a few more connection deficiencies than both the linear dynamic and the nonlinear static procedures. This trend counters the idea that the nonlinear dynamic procedure should be the least conservative of the assessment procedures. Similar trends to what was described above were observed for the three different braced frames systems.

N O V E M B E R 2 0 21

Figure 2. The 8-story ELF-designed SMF; a) incremental dynamic analysis curves; b) associated fragility curve.

more prevalent. Therefore, if the response of a building component does not experience fully-reversed cyclic demands to the degree that capacities were derived, the results are often conservative, sometimes to a great degree. This observation is combined with the trend of benchmarking building performance to collapse likelihood. However, several studies have highlighted the tendency for a building to have a one-side response with ratcheting behavior when subject to collapse level shaking (Ibarra and Krawinkler 2005, Lignos and Krawinkler 2011, Maison and Speicher 2016, Speicher and Harris 2016). Therefore, having acceptance criteria that adapt based on loading history would be logical and advantageous. Still, the implementation of such criteria is challenging given the complex failure mechanisms of building components and the limited availability of tests utilizing alternative loading protocols to validate such new criteria. Some ASCE 41 component criteria are used as surrogates to capture other phenomena not captured in typical nonlinear models. Therefore, the challenge remains on how to best address a component’s performance considering loading history. One possible approach is to generate assessment criteria dependent upon loading history, such as energy-based acceptance criteria for certain components. The third issue explored was the potential that the archetype building designs do not actually achieve the intent of ASCE 7, which is specified as less than or equal to a 10% probability of collapse given a risk-targeted maximum considered earthquake (MCER). If the designs do not meet this goal, then ASCE 41 would be justified in flagging the buildings as deficient. Therefore, to validate the designs, NIST conducted additional studies into the seismic performance of the SMFs utilizing the methodology from FEMA P695. New two-dimensional models were generated using OpenSees (the Open System for Earthquake Engineering Simulation) and were compared to the Perform-3D models to verify their consistency. OpenSees is an object-oriented software framework created at the National Science Foundation-sponsored Pacific Earthquake Engineering Research (PEER) Center. Incremental dynamic analysis “spaghetti” curves were generated as shown in Figure 2a, and the associated fragility curve is shown in Figure 2b for the 8-story ELF-designed SMF. Value ST is the median spectral acceleration of the record set at the fundamental period of the building, SMT is the value of the MCER at the fundamental period of the building, and CMR is the collapse margin ratio defined as the ST /SMT value where 50% of the ground 14 STRUCTURE magazine

motion records result in a collapse of the building. The spaghetti curves are generated by incrementally scaling an individual ground motion record and recording the associated maximum interstory drift from the building response. The fragility curve is the cumulative distribution function of the collapse levels obtained from the spaghetti curve results. For the 8-story ELF-designed SMF, the collapse margin ratio is approximately 2.0. This means the entire record set must be scaled by 2.0 before half the records cause collapse. The FEMA P695 methodology further requires the CMR to be adjusted considering the spectral shape of the ground motions. Thus the adjusted collapse margin ratio turns out to be approximately 3.22 for this example. The acceptable collapse margin ratio considering a 10% probability of collapse and a total system uncertainty of 0.53 is 1.96. Therefore, the 8-story ELF-designed SMF has a margin against collapse of approximately 1.64 (= 3.22/1.96) times greater than required to satisfy the 10% conditional goal. A full explanation of the results can be found in Collapse Risk of Steel Special Moment Frames per FEMA P695 (Speicher et al., 2020). Ultimately, the results indicate that the SMFs satisfy the 10% objective, and therefore indicate that the ASCE 41 provisions utilized provide an overly conservative result. Work is ongoing at NIST to investigate the collapse probability of the archetype buildings with the other three SFRSs. PBSD research at NIST has also expanded to several other projects to support further advancement and implementation. For example, given the results from volumes 1-3 published in 2015, NIST sponsored related research to advance the state of practice for PBSD, which resulted in the report titled Recommended Modeling Parameters and Acceptance Criteria for Nonlinear Analysis in Support of Seismic Evaluation, Retrofit, and Design (NIST 2017). This report made recommendations for broad improvements to seismic nonlinear modeling and acceptance criteria requirements for various structural systems. NIST also sponsored an extensive experimental investigation looking at the performance of deep wide-flange steel members, which are often used in special moment frames. The results of this research are published in Seismic Behavior and Design of Deep, Slender Wide-Flange Structural Steel Beam-Columns (NIST 2021). Several recommendations from these reports were considered in the ASCE/ SEI 41-17 update cycle and are currently being considered for the ASCE/SEI 41-23 update cycle.

Conclusions

and acceptance criteria based on new experimental data and stateof-the-art research. Part 3 will discuss the future of PBSD in practice, including its relationship to resilience-based design, which aims to quantitatively support community resilience.■

A set of steel buildings were designed with the loads specified in ASCE/ SEI 7-10 and then assessed with ASCE/SEI 41-06 or ASCE/SEI 41-13. Four levels of analysis were conducted as part of an ASCE 41 Tier 3 assessment. In general, the results indicated that the steel buildings Full references are included in the online PDF studied have deficiencies that would need to be retrofitted to satisfy version of the article at STRUCTUREmag.org. ASCE 41. These results are contingent on the choices made during the design and assessment process, some of which were further critiqued to Matthew Speicher is a Research Structural Engineer in the Earthquake shed light on how the ASCE 41 assessment can be improved so that a Engineering Group at NIST. more logical outcome can be achieved. Of specific note was the seemJohn Harris is the Acting Deputy Director of NEHRP and a Research ingly overly conservative results from the nonlinear dynamic procedure. Structural Engineer in the Earthquake Engineering Group at NIST. The methodology utilized for selecting and scaling ground motions was shown to add to the conservative outcome. However, even with changes to the selection and scaling approach, building designs still failed the ASCE 41 nonlinear dynamic assessment. Other issues related to the accounting of loading history in the acceptance criteria were also explored in the NIST study. ASCE 41 component acceptance criteria are derived from a combination of fully-reversed cyclic tests and engineering judgment. However, it is well-known that component behavior does not necessarily follow a fully-reversed loading pattern during an earthquake, especially ESR-3617 when subjected to near-fault collapse level shaking. Currently, the acceptance criteria do not account for the differQuick and easy to install ences based on loading history, which from one side can add a layer of conservatism to the results. Suggestions have been proposed Designed for standard on how this may be addressed, but the complexities remain. For example, the clearance holes intent of engineering judgment and how a component may be a surrogate for A fully removable blind other behavior is challenging to quantify. ﬁxing available for The final issue discussed is the notion structural connections that the archetype building design may not meet the intended performance goal ASD and LRFD design of ASCE 7; thus, as a corollary, the ASCE 41 assessment rightly flags the designs as resistances available on deficient. An investigation using FEMA our website P695 was conducted to test this idea (See Technical Data) which showed that the designs were, in fact, satisfactory. This confirms the conAvailable in stainless servatism in the ASCE 41 procedures, steel and zinc coated given all the choices and assumptions made to arrive at these conclusions. It Also suitable for Lumber umber to is particularly interesting when using Steel Blind connections ASCE 41 as an alternative approach to Scan to view designing new buildings. The conserinstallation videos vatism seems to take some motivation For questions or technical advice please contact away from utilizing such PBSD proenquiries@blindbolt.com cedures for new designs. The results suggest several areas need improvement in ASCE 41 if alignment with ASCE 7 1217 S Bridge St, Yorkville, IL 60560 is desired. Therefore, additional research (630) 882-9010 funded by NIST has further expanded BLIND BOLT MASTER DISTRIBUTOR the PBSD efforts to update modeling

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N O V E M B E R 2 0 21

CODES and STANDARDS 2021 IBC Significant Structural Changes Part 1: Loads (Chapter 16)

By Sandra Hyde, P.E., and John “Buddy” Showalter, P.E.

his five-part series discusses significant structural changes to the 2021 International Building Code (IBC) by the International Code Council (ICC). Part 1 includes an overview of changes to Chapter 16 on loads. Only a portion of the total number of code changes to this chapter are discussed in this article. More information on the code changes discussed here can be found in the 2021 Significant Changes to the International Building Code, available from ICC. IBC Chapter 16 establishes minimum design requirements so that the structural components of buildings are proportioned to resist the loads that are likely to be encountered. In addition, this chapter assigns buildings and structures to risk categories that are indicative of their intended use. The following modifications were approved for the 2021 IBC. Changes are shown in strikethrough/underline format with a brief description of the change’s significance.

IBC Table 1604.5 Risk Category of Buildings and Other Structures (excerpt).

Construction Document Wind Zones Component and cladding wind zones must now be identified in the construction documents. 1603.1.4 Wind design data. The following information related to wind loads shall be shown, regardless of whether wind loads govern the design of the lateral force-resisting system of the structure: No changes to items 1-4. 5. Design wind pressures and their applicable zones with dimensions to be used for exterior component and cladding materials not specifically designed by the registered design professional responsible for the design of the structure, psf. Change Significance: There has been some confusion about how the 2016 edition of ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, component and cladding (C&C) wind pressure zones are to be applied – specifically what dimensions are prescribed for various building zones. A description of C&C wind pressure zones in the construction documents is intended to show correctly applied requirements for roof and wall assemblies and their coverings.

Risk Categories of Assembly Spaces Mixed occupancy buildings with assembly spaces are now designated as Risk Category III when the total public assembly occupant load exceeds 2,500 people. Change Significance: Group R-1 hotels often have convention center facilities with multiple large ballrooms and other assembly spaces, but public assembly is not the primary occupancy of the building. These buildings have historically been classified as Risk Category II. Conversely, smaller buildings, such as theaters, consist of one or more spaces where the primary occupancy is public assembly with a 16 STRUCTURE magazine

cumulative occupant load of over 300 that must be designed to the higher Risk Category III requirements. However, the total occupant load is much smaller when compared to a Group R-1 hotel. Table 1604.5 includes a new condition under Risk Category III for buildings with multiple occupancies, containing assembly spaces with an occupant load greater than 300 each, while also having a cumulative occupant load for the 300-plus-occupant assembly spaces of more than 2,500. Buildings that meet these criteria are now assigned to Risk Category III rather than Risk Category II. The new threshold requires the existence of the two conditions previously stated to establish a Risk Category III classification. An additional revision addresses daycare facilities classified as Group I-4 occupancies. Consistent with the application for a Group E occupancy in a mixed occupancy building, a building used for daycare purposes is considered Risk Category III when the total occupant load for the Group I-4 occupancy, or combination of Group E and Group I-4 occupancies, exceeds 250.

Load Combinations The strength design and allowable stress design load combinations have been deleted, while direct reference to Chapter 2 of ASCE 7 has been added to Section 1605. 1605.1 General. Buildings and other structures and portions thereof shall be designed to resist the Strength Load Combinations specified in ASCE 7 Section 2.3, the Allowable Stress Design Load Combinations specified in ASCE 7 Section 2.4, or the Alternative Allowable Stress Design Load Combinations of Section 1605.2. Exceptions: 1) The modifications to Load Combinations of ASCE 7 Section 2.3, ASCE 7 Section 2.4, and Section 1605.2 specified in ASCE 7 Chapter 18 and 19 shall apply. 2) When the Allowable Stress Design Load Combinations of ASCE 7 Section 2.4 are used, flat roof snow loads of 30 psf

and roof live loads of 30 psf or less need not be combined with seismic load. Where flat roof snow loads exceed 30 psf, 20 percent shall be combined with seismic loads. 3) Where the Allowable Stress Design Load Combinations of ASCE 7 Section 2.4 are used, crane hook loads need not be combined with roof live loads or with more than threefourths of the snow load or one-half of the wind loads. 1605.3.2 1605.2 Alternative basic allowable stress design load combinations. In lieu of the Load Combinations in ASCE 7 Section 2.4, structures and portions thereof shall be permitted to be designed for the most critical effects resulting from the following combinations… [unchanged text omitted for brevity] Where required by ASCE 7 Chapters 12, 13, and 15, the Load Combinations including overstrength of ASCE 7 Sections 2.3.6 shall be used. D + L + (Lr or S or R) (Equation 16-17 16-1) D + L + 0.6ωW D + L + 0.6W (Equation 16-18 16-2) D + L + 0.6ωW + S/2 D + L + 0.6W + S/2 (Equation 16-19 16-3) D + L + S + 0.6ωW/2 D + L + S + 0.6W/2 (Equation 16-20 16-4) D + L + S + E/1.4 (Equation 16-21 16-5) 0.9D + E/1.4 (Equation 16-22 16-6) Unchanged exceptions and additional deleted text not shown for brevity and clarity. Change Significance: Strength load combinations and basic allowable stress design (ASD) load combinations are replicated directly from ASCE 7. Deletion of the IBC load combinations removes minor variations in the requirements between the IBC and ASCE 7 by eliminating duplication of the equations. The third set of load combinations are from legacy codes that predate the IBC. In previous editions, the alternative ASD load combinations permitted the use of a 1/3 increase in allowable stresses when evaluating load combinations containing short-term transient loads caused by winds. The basic allowable stress combinations did not permit the reduction in loads but applied a factor of 0.75 to transient loads, including live, snow, wind, and seismic loads, when more than one of these loads was considered simultaneously. The omega factor, ω, has been deleted from the alternative ASD load combinations to limit misuse of the stress increase, thus increasing the load due in part to wind forces.

Dead Loads Dead loads at the roof level have been clarified, as well as fixed service equipment concentrated loads. 1606.2 Design dead load. Weights of materials of construction. For purposes of design, the actual weights of materials of construction and fixed service equipment shall be used. In the absence of definite information, values used shall be subject to the approval of the building official. 1606.3 Weight of fixed service equipment. In determining dead loads for purposes of design, the weight of fixed service equipment, including the maximum weight of the contents of fixed service equipment, shall be included. The components of fixed service equipment that are variable, such as liquid contents and movable trays, shall not be used to counteract forces causing overturning, sliding, and uplift conditions in accordance with Section 1.3.6 of ASCE 7. Exceptions: 1) Where force effects are the result of the presence of the variable components, the components are permitted to be used

Figure 1. Examples of roof dead loads – HVAC equipment, solar panels, and vegetative roofs.

to counter those load effects. In such cases, the structure shall be designed for force effects with the variable components present and with them absent. 2) For the calculation of seismic force effects, the components of fixed service equipment that are variable, such as liquid contents and movable trays, need not exceed those expected during normal operation. 1606.3 Photovoltaic panel systems. The weight of photovoltaic panel systems, their support system, and ballast shall be considered as dead load. 1606.3 Vegetative and landscaped roofs. The weight of all landscaping and hardscaping materials for vegetative and landscaped roofs shall be considered as dead load. The weight shall N O V E M B E R 2 0 21

be computed considering both fully saturated soil and drainage layer materials and fully dry soil and drainage layer materials to determine the most severe load effects on the structure. Change Significance: The weights of vegetative roofs, solar panels, and fixed service equipment have been clarified to provide consistency between the IBC and ASCE 7 (Figure 1). The weight of fixed service equipment includes both the equipment’s empty weight and the maximum weight of the contents. For example, the weight of liquids is to be included in the dead load of piping and tanks, and the weight of conduit and wiring is to be included in the dead load of cable trays. In addition, as content weight may be variable, it cannot be assumed to counteract the effects of overturning, sliding, and uplift forces. Exceptions in IBC Section 1606 specifically address the calculation of variable loads for liquids and moveable equipment.

Snow Maps The IBC ground snow load map has been updated to provide consistency with ASCE 7-16 by referencing ASCE 7 snow load tables for states with large case study areas (Figure 2 ). Change Significance: Updating Section 1608 harmonizes snow load provisions with ASCE 7-16. ASCE 7 has a ground snow map that references new ground-snow load tables; these include tables for seven states: Colorado (7.2-2), Idaho (7.2-3), Montana (7.2-4), Washington (7.2-5), New Mexico (7.2-6), Oregon (7.2-7), and New Hampshire (7.2-8). The state tables list ground snow loads and maximum elevations for major cities and towns in each region of a given state. IBC Figure 1608.2 indicates which states have supplemental data within the ASCE 7 standard.

Soil-Caused Uplift Hydrostatic and expansive soil uplift pressures are now addressed in Section 1610 on soil loads. 1610.2 Uplift loads on floor and foundations. Basement floors, slabs on ground, foundations, and similar approximately horizontal elements below grade shall be designed to resist uplift loads where applicable. The upward pressure of water shall be taken as the full hydrostatic pressure applied over the entire area. The hydrostatic load shall be measured from the underside of the element being evaluated. The design for upward loads caused by expansive soils shall comply with Section 1808.6. Change Significance: Section 1610 has not previously addressed uplift loads from hydrostatic pressure or expansive soils. Requirements addressing uplift forces are now to be applied when appropriate and included in the design. The hydrostatic pressure provisions include a

Figure 3. Secondary drainage design assumptions.

18 STRUCTURE magazine

Figure 2. Updated IBC ground snow load map references state-specific snow load tables to provide consistency with ASCE 7-16 (New Hampshire not shown).

required determination of loads based on measuring to the underside of construction per ASCE 7 Section 3.2.2. While this is a straightforward provision of fluid mechanics, the new provisions are intended to prevent the use of common elevations shown on construction drawings, such as floor elevations or the top of foundation construction, as the elevation at which to apply hydrostatic forces. Instead, the new language explicitly states that hydrostatic pressures should be applied to the underside of a foundations’ lowest horizontal element. A pointer has been added to Section 1808.6, Design for Expansive Soils, to help in determining the minimum required uplift due to movement of soils below a building when expansive soils are present.

Rain Loads Secondary drainage system rain loads have been updated to be consistent with ASCE 7. 1611.1 Design rain loads. Each portion of a roof shall be designed to sustain the load of rainwater that will accumulate on it if the primary drainage system for that portion is blocked plus the uniform load caused by water that rises above the inlet of the secondary drainage system at its design flow as per the requirements of Chapter 8 of ASCE 7. The design rainfall shall be based on the 100-year hourly rainfall rate indicated in Figure 1611.1 15-minute duration event or on other rainfall rates determined from approved local weather data. Alternatively, a design rainfall of twice the 100-year hourly rainfall rate indicated in Figure 1611.1 shall be permitted. [Equation unchanged] 1611.2 Ponding instability. Susceptible bays of roofs shall be evaluated for ponding instability in accordance with Section 8.4 Chapters 7 and 8 of ASCE 7.

Change Significance: Secondary (overflow) system design has been harmonized with roof rain load provisions to provide realistic expectations of the roof drainage system and potential roof loading by rainfall (Figure 3). The IBC is now consistent with ASCE 7 provisions. Calculations for the design mean recurrence interval and duration for determining the hydraulic head are available in both ASCE 7 and the IBC. Note that the use of twice the 60-minute duration is close to the 15-minute duration rainfall rate. Also, note that the 2021 IBC rainfall map (Figure 1611.1) provides a 60-minute duration rather than the 15-minute storm duration. However, the 2021 IBC, by giving two options – the 15-minute duration or twice the 60-minute duration – results in values comparable to ASCE 7. Note that the 2021 International Plumbing Code has not yet been updated to reflect the 100-year/15-minute (or twice the 100-year hourly) duration rainfall event design requirement for secondary drainage systems; the structural engineer would be advised to coordinate with the plumbing engineer to assure that the secondary drainage systems are designed for the higher rainfall rate. One source for rainfall data is the National Oceanic and Atmospheric Administration (NOAA) National Weather Service Precipitation Frequency Data Server–Hydrometeorological Design Studies Center (https://bit.ly/3lu1PpS) for precipitation intensity (inches per hour) based on the 100-year mean recurrence interval. HDSC’s data lists both 15-minute and 60-minute duration data.

pressures are now addressed. Secondary drainage system rain loads have been updated to be consistent with ASCE 7. To download published errata for the 2021 IBC, including Table 1604.5, go to iccsafe.org/errata-central.■ An upcoming issue will include an article specifically devoted to rain load calculations with design examples comparing 2021 IBC to 2018 IBC provisions. Sandra Hyde (shyde@iccsafe.org) is Managing Director, and John “Buddy” Showalter (bshowalter@iccsafe.org) is Senior Staff Engineer, both with ICC’s Product Development Group.

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Conclusion Structural engineers should be aware of significant structural changes that have occurred in the 2021 IBC. Many of the new code provisions harmonize the IBC and ASCE 7. Component and cladding wind zones must now be identified in the construction documents. Mixed occupancy buildings with assembly spaces are now designated as Risk Category III when the cumulative occupant load for the 300-plus-occupant assembly spaces exceeds 2,500 people. The strength design and allowable stress design load combinations have been deleted while direct reference to Chapter 2 of ASCE 7 has been added. Dead loads at the roof level have been clarified, as well as fixed service equipment concentrated loads. The IBC ground snow load map has been updated to provide consistency with ASCE 7-16 by referencing ASCE 7 snow load tables for states with large case study areas. Hydrostatic and expansive soil uplift

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N O V E M B E R 2 0 21

structural SYSTEMS

Structured for Protection

The Role of Architectural and Structural Elements in Facility Fire-Protection Schemes By April M. Musser, P.E.

hen most people think of fire protecincluding the International Fire Code (IFC), tion, their minds go straight to fire may include additional structural fire resisalarm systems and sprinkler systems. In realtance requirements based on special hazards ity, these two systems are just small pieces of or uses. Fire-resistance rating requirements for a larger puzzle. Fire protection encompasses building elements prescribed in the IBC (as a “system of systems” that work together to well as other model codes) also allow a reducprovide occupant and facility protection in a tion in the required fire-resistance ratings for fire or other emergency. These systems often certain building elements under specific coninclude many other building systems that are ditions, such as the inclusion of fire sprinkler generally not at the top of mind when considprotection. ering Fire Protection. For example, if a facility The method by which the required firehas duct smoke detection, HVAC controls resistance ratings for building elements can may shut down air handling equipment to be achieved depends on the construction prevent the spread of smoke. In low-light materials. Spray-applied fire-resistive material environments, such as theaters and night(SFRM) is one of the most common methods clubs, lighting controls that automatically used to protect structural steel. In areas where turn on lights may be part of the life safety steel might be exposed, intumescent coatings systems to ensure occupants have adequate may be used instead. Enclosing or “boxing light to evacuate. Fire-resistance-rated conout” structural elements using a listed firestruction to provide compartmentation, exit resistive assembly is also a common approach. separation, and protected egress paths are Concrete structural elements may achieve also part of these systems, which make up the required fire-resistance rating depending the facility’s fire-protection envelope. Other Intumescent coatings can be used to achieve required on the size and aggregate without additional passive fire-protection systems include the fire resistance for structural members. materials to coat or box out the building elefacility’s structural aspects. ments. Structural assemblies are tested by a While many other types of building systems contribute toward the laboratory as outlined in ASTM E119, Standard Test Methods for Fire overall facility fire-protection scheme, this article focuses on facility Tests of Building Construction and Materials, or UL263, Standard design and protection related to the facility structural system(s). for Safety Fire Tests of Building Construction and Materials, to deterCommon sense tells us that the materials providing structural support mine the appropriate methods for fire-proofing structural elements. for a building are subject to damage from the extreme temperatures The above describes the basics of structural fire-protection requireof a fire. For example, concrete can spall (crack or delaminate from ments. What are the potential pitfalls and considerations often substrates), and steel structural members are subject to yield and overlooked in facility design related to structural fire protection? deformation from heat exposure during a fire. The goal of structural fire-protection requirements is to ensure that the facility can Existing Buildings withstand fire conditions long enough to allow for facility egress. Still, it is also concerned with ensuring that firefighters can perform In existing buildings that may be undergoing renovation, addition, or interior firefighting and search and rescue operations without risking changes in use or occupancy, there may not be enough data available a structural failure. from the original construction to determine the fire-resistance rating of the existing structural frame of the building. In cases where changes of use or occupancy or significant renovations or additions require that the The Basics entire building or portions within the area of work be upgraded to the In a fire scenario, a facility is subject to extreme environmental con- current code, this can present a challenge in developing the fire-protection ditions such as heat and water in a relatively short amount of time. envelope. In these cases, there are several options for compliance. As a result, the goals of structural fire protection aim to ensure that 1) Presume that existing elements do not have an inherent a building can withstand these conditions throughout the egress fire-resistance rating and provide fire-resistive assemblies period and through the fire-fighting response and overhaul periods. or materials in accordance with a new assembly listed by a Perhaps the most familiar aspect of structural fire protection is nationally recognized testing laboratory. While this option is related to the fire-resistance requirements of the structural comvalid, it can unnecessarily drive up facility construction costs ponents of the system. Model building codes, including the when the structural elements have some fire-resistive features. International Building Code (IBC), specifically prescribe fire-resis2) Calculate the fire resistance. IBC Section 722, Calculated tance rating requirements for facility structural elements based on Fire Resistance, provides a methodology for determining the building occupancy, height, and area. Furthermore, fire codes, the fire resistance via a mathematical calculation based on

20 STRUCTURE magazine

the building materials and configuration. For example, if an 8-inch-square concrete masonry column is enclosed in 2 layers of ½-inch type X gypsum wallboard, Section 722 can be used to estimate the fire resistance. The masonry column would be assigned a fire-resistance rating of 1-hour while each of the two layers of gypsum would be assigned a fire resistance of 25 minutes each, meaning that it can be assumed that the column has a fire-resistance rating of 110 minutes or 1.8 hours. However, it is important to note that how the assembly was constructed can impact the fire-resistance rating. For example, if the gypsum wallboard in the above example is not properly attached to and sealed where it joins other building elements such as the floor slab or roof deck, that weak spot could lower performance compared to the calculated fire resistance. As a result, the design team must consider that such joints may require additional attention and engineering to ensure the required fire resistance can be maintained at the joints.

Archaic Building Materials

Archaic building materials may present challenges in determining the fire resistance of structural elements.

can be complicated, especially when attic spaces below these roofs are used for equipment, are heavily congested, or have limited access or low clearances.

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When dealing with historic structures, determining the fire-resistance Fire-Resistance-Rated Building Elements rating is even more difficult. However, there are guides available to assist engineers with estimating the fire resistance of archaic building materi- One of the more common oversights made during facility design als. In cases where the structure is part of the facility’s historic fabric, is failure to consider the requirements of IBC Section 704.1 (2018 the fire-resistance rating is of concern and whether archaic materials Edition). This section indicates that structural members must proand age have reduced the load-carrying ability of such materials. It may vide the required fire-resistance rating as specified for the building be necessary to spend extra time understanding archaic construction methods to ensure that recommended structural protection approaches are not undermined by construction methods unfamiliar in the industry today. Special consideration and close coordination between fire protection and structural teammates are necessary to ensure that design approaches aimed at improving structural fire resistance while preserving historic fabric do not degrade these materials further. Understanding how archaic materials that are not in use today may react with newer materials and coatings may be difficult to determine. There may be conditions where engineering judgments must be applied, as there may not always be adequate data or viable means to test assumptions. In such cases, it may be necessary to involve historic preservationists, material science experts, or others who can offer expertise on the EXCELLENCE IN best ways to preserve historical materials Photo is Courtesy of while still meeting the required level of STRUCTURAL ENGINEERING Ben Benschneider fire resistance. S t. Michael Medical Center • Silverdale • Washington Many historic buildings still have wood roofs, and replacing these structures is Seattle Sacramento Boise Nashville not always feasible or desirable. There Tacoma San Francisco Salt Lake City Birmingham Lacey Los Angeles Des Moines Washington, DC are intumescent products available for Spokane Long Beach St. Louis New York application on the underside of roof KPFF is an Equal Opportunity Employer Portland Orange County Chicago structures to increase the fire resistance www.kpff.com Eugene San Diego Louisville of these roofs. However, the application

N O V E M B E R 2 0 21

an industrial aesthetic even where a structural frame requires fire resistance. It looks more like paint, although it is required to be applied in thicker coats. The required depth of the coating depends on the required fire-resistance rating and the specific product being applied. Once it dries, most intumescent coatings are permitted to be covered by a decorative surface finish such as paint. However, when intumescent coatings are exposed to high temperatures, such as those from a fire, the intumescent product expands, sometimes to more than 100 times the original thickness. This then functions as an insulator, thus prolonging the integrity of that element during a fire. Like SFRM, intumescent coatings are also subject to In an automated dry boat storage facility, the structural design must consider the additional weight of fire degradation through mechanical damage over suppression water, which may collect in the stored boats in the event of a fire. the building lifecycle. While it is less brittle than construction type and notes that the structure shall not be less than SFRM, chips, dings, or even sanding the surface to change the paint the ratings required for the fire-resistance-rated assemblies supported color can reduce the fire-resistive performance, especially if sanding by the structure. For example, a six-story Business Occupancy of reduces the depth of the intumescent coating. Type IIA Construction requires only a 1-hour fire-resistance rating for the primary structural frame. However, a six-story building is Weight of Sprinkler Water also required to have 2-hour fire-resistance-rated exit stair and shaft enclosures. Therefore, to comply with Section 704.1 of the IBC, the When SEs think of structural fire protection, they usually consider structural frame supporting the stair and shaft enclosures must have how to protect the structure from fire. However, the structure also at least a 2-hour fire-resistance rating despite only a 1-hour rating needs to be protected from the effects of an activated fire sprinkler required for the primary structural frame by Table 601 of the IBC. system. Consider, for example, a rack storage facility with open-top This is also an important consideration where a facility may have hori- plastic bins or absorbent products. When a sprinkler activates, open zontal shafts penetrating a wall assembly. This kind of rated horizontal storage containers and absorbent materials can absorb water or fill shaft is often necessary where stair pressurization equipment cannot be with water, causing increased structural loads on the rack assembly. co-located with the stair shaft and must be ducted into the stair shaft However, this issue is not reserved to just rack or shelf storage confrom a mechanical room. For example, suppose that a horizontal shaft ditions. Consider, for example, automated dry boat storage. These is required to have a 2-hour fire-resistance rating, and it is the intention facilities allow the boat owner to pull their watercraft into a slip to use the wall assembly it penetrates to support the horizontal shaft. In and enter a code into an automatic storage and retrieval control that case, that wall now requires a 2-hour fire-resistance rating as it is unit. A crane that looks like a boat forklift removes the boat from the supporting element. If structural elements other than walls support the slip and places it in a vertical dry storage bay. The sprinkler the shaft, they also would require an increased fire-resistance rating. protection systems for these indoor vertical boat storage facilities are typically very robust. They are designed to deliver a large sprinkler density, as fiberglass boats with upholstery (floor covering and Facility Lifecycle built-in benches/seats) stored in vertical arrangements constitute a Lifecycle issues can significantly impact the integrity of structural fire- relatively high-challenge fire necessitating aggressive sprinkler design protection components in a building. Take into consideration that discharge densities. However, even with drainage plugs open, the SFRM (spray-applied fire-resistive material) can become brittle and can boats fill with water from a sprinkler system activation faster than be degraded or completely removed by mechanical impact. Therefore, the drains can empty them. The increased weight of water sitting installing SFRM in areas of the facility where electrical or mechanical in these boats could easily cause the collapse of the storage facility equipment is housed could mean a higher likelihood of mechanical if the structure is not designed to anticipate the additional weight impact by ladders or even intentional removal to route new equipment of water-filled boats. In addition, it can be a challenge to determine connections. While most owners know and understand that their fire what design load to use for scenarios where additional structural alarm system requires annual inspection and testing, it is rare to find an loads are caused by sprinkler activation. The additional load varies owner checking the integrity of their SFRM regularly throughout the as the size and capacity of stored products vary, so a conservative building lifecycle. However, damaged SFRM reduces the fire-resistance approach using the worst-case scenario is warranted. rating of the structural elements it is intended to protect. For clients In closing, the structural design of a facility ties into the system who require regular auditing for fire protection and life safety, damaged of systems that defines the full Fire-Protection envelope. Therefore, SFRM is a frequent finding. Therefore, the design team should avoid understanding how structural design and protection tie into the a blanket specification of SFRM throughout a facility without consid- facility’s fire-protection goals is vital to ensuring occupants, ering areas where mechanical impact might be considered likely due first responders, and investments are acceptably protected to operations or co-located equipment and consider using a different in a fire emergency.■ structural fire-protection material in those areas. April Musser is a Certified Fire Protection Specialist (CFPS) and holds a CVI Intumescent coatings may be more durable than SFRM, but they certification from the US Department of Homeland Security. She also serves on are still subject to potential lifecycle issues. For example, consider the NFPA 30 Technical Committee for Flammable and Combustible Liquids and a convention center with an exposed steel structure in an event is an active member of both NFPA and SFPE. (amusser@telgian.com) hall. Intumescent coating is an excellent option for maintaining 22 STRUCTURE magazine

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structural CARBON The SEI SE 2050 One-Year Anniversary By Chris Jeseritz, P.E., LEED AP BD+C

ne year since the launch of the Structural Engineering Institute’s (SEI) Structural Engineers (SE) 2050 Commitment Program, 53 structural engineering firms have committed to embodied carbon neutrality by 2050. The Program’s overarching goal is to provide an accessible sustainability program for structural engineers that includes a commitment of active engagement in reducing the embodied carbon on projects and information sharing. The driver of these objectives is the collective objective of achieving net-zero carbon structures by 2050.

History In 2016, the Carbon Leadership Forum (CLF) at the University of Washington created a working group to develop a data-driven commitment program for structural engineering firms to measure and work towards net-zero embodied carbon buildings. The CLF proposed their idea and the Structural Engineers 2050 Challenge framework to the American Society of Civil Engineers (ASCE) SEI Sustainability Committee. The ASCE SEI Sustainability Committee further developed the goals, requirements, and resources to make an official commitment program feasible and realistic to practicing structural engineers. After years of hard work Figure 1. Distribution of SEI SE 2050 commitment firm’s embodied carbon by the ASCE SEI Sustainability Committee volunteers, champion in North America (Map created with mapchart.net). the SEI SE 2050 Commitment Program was endorsed by SEI in late 2019 and launched to the public at Greenbuild Committed Firms Support the Program 2020 as an SEI Program. The Program is run by volunteer members of the SE 2050 Subcommittee of the SEI Sustainability Committee. Since the Program’s launch in October 2020, 53 firms have officially signed on to the SEI SE 2050 Commitment Program. From data submitted by committed firms, approximately 72 percent have no more than 200 employees, with 20 committed firms having 50 or fewer employees. The distribution of firm sizes illustrates that embodied carbon is a critical issue to firms of all sizes in the structural engineering community. The Chart displays the distribution of firm sizes committed to the SEI SE 2050 Commitment Program as of the beginning of August 2021.

Championing Carbon Reduction within the Firm

Distribution of the number of employees at committed firms.

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When a firm commits to the Program, they assign an employee to serve as an embodied carbon reduction champion and act as the main point of contact for the Committee and Program. Additional responsibilities of the champion include educating and advocating for embodied carbon reductions and ensuring the firm meets the yearly requirements of the Program. The state with the largest number of embodied carbon reduction champions is California, with eleven. Washington state follows with six and Massachusetts with four. In addition, two champions are located outside of North America. Figure 1 highlights in blue where the embodied carbon reduction champions

are located in North America and the number per state as of the beginning of August 2021.

A Roadmap to Reduce Carbon Each committed firm must develop and submit an Embodied Carbon Action Plan (ECAP). The purpose of the ECAP is to articulate how a firm educates its staff, reports, documents reduction strategies, and advocates within the Figure 2. Data collected for the SEI SE 2050 database. industry for and on embodied carbon. For companies wishing to simplify their ECAP submission, structural floor systems. Updates will add more framing the SEI SE 2050 website contains an ECAP Google Form submission systems and bay layouts to those already available. Some of option allowing firms to streamline the creation of their ECAP. All the upcoming embodied carbon intensity floor diagrams to committed firms’ ECAPs are publicly available and updated yearly. be released include a reinforced concrete flat plate, concrete Of the 53 firms committed to the Program, 13 have submitted their pan joist, light-framed wood, and a hybrid mass timber/steel first-ever ECAP as of the beginning of August 2021. floor scheme. The SEI SE 2050 website lists the committed companies, the name 3) Embodied Carbon Estimator (ECOM) for structural of their internal embodied carbon reduction champion, the year the materials. Updates to the existing ECOM tool could include company committed to the Program, and a link to their ECAP. The visual updates, report generation, and a user option to input SE 2050 Committee continuously updates this table as new firms custom global warming potential data from a productcommit and ECAPs are submitted. specific Environmental Product Declaration (EPD). The Committee is also developing an ECOM guidance document and examples. Submitting Data to the Program 4) Case Studies. A list of project case studies discussing how In addition to developing an ECAP, committed firms measure the embodied carbon was considered during design and conembodied carbon of multiple projects’ structural systems and submit struction has been added to the SE 2050 website for users their findings to the SE 2050 database. Firms commit to at least two looking for guidance or ideas on their projects. project submissions per North American structural office but need 5) Project specifications guidance. This document will provide guidance to structural engineers on incorporating different not exceed five total projects per year. After months of development embodied carbon reduction strategies into project specificaand testing, the database was officially launched on the SEI SE 2050 tions for multiple types of structural materials. website in September 2021. A committed firm’s embodied carbon reduction champion can access the database from the website, add company users, and begin submitting embodied carbon data. The SE In Closing 2050 Committee has published a user guide to aid users in navigating and reporting their projects to the database. Clients, government officials, and future engineers are interested and The information collected by the database includes project descrip- actively discussing embodied carbon. The SEI SE 2050 website and tors, structural system descriptors, and embodied carbon data. Figure 2 team are dedicated to helping structural engineers learn about and illustrates the different parameters submitted for each project to the reduce embodied carbon. SEI SE 2050 database. After a sufficient amount of data is collected, The structural engineering community has responded enthusiastically embodied carbon benchmarking for different building types can to the SEI SE 2050 Commitment Program and, within the first year, begin to be formed. the Program has picked up significant momentum. The Program provides engineers a platform to play an active role in embodied carbon measurements and reduction strategies. The SE 2050 Committee is Resources for the Structural Engineer continually working to provide additional embodied carbon resources To help committed firms, the SE 2050 Subcommittee continues to and Program improvements to meet this demand and enthusiasm to add and update embodied carbon guidance on its website. Highlights continue the impetus for the next year and beyond. of some of the currently released and upcoming resources include: If your firm is interested in learning more or joining the move1) A guide to embodied carbon-related credits in green rating ment towards net-zero embodied carbon by 2050, please visit systems (USGBC LEED, Green Globes, Envision, etc.). This the SEI SE 2050 Program’s website: se2050.org to learn more.■ resource helps structural engineers learn and advocate for Chris Jeseritz is a Project Manager at PCS Structural Solutions in Seattle, embodied carbon measuring and reduction credits dependWA, and a member of ASCE’s Structural Engineering Institute’s (SEI) ing on the green rating system a project is pursuing. Sustainability Committee and the SE 2050 Commitment Program. 2) Embodied Carbon Intensity Diagrams showing the range (cjeseritz@pcs-structural.com) of embodied carbon intensities associated with common N O V E M B E R 2 0 21

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West Berkeley Medical Office Building Kaiser Permanente Brings Needed Medical Services and Creative Architecture to Its West Berkeley Neighborhood By Nick Bucci, S.E., and Ryan Pintar, S.E.

Figure 1. Aerial view of the building (looking southeast).

he new Kaiser Permanente (KP) medical office building (MOB) in West Berkeley will provide critical medical services to the local community. The L-shaped 66,000-square-foot structure embraces the challenging small infill site with an integrated design that allows for open floor plates and a stunning architectural design. After studying different structural schemes, the ConXtech steel space moment frame was chosen as the structural solution to maximize the flexibility of the ground floor parking and embrace the architectural expression. The steel moment frame scheme allowed for improved seismic performance and allowed for shallow foundations.

Unique Design for a Unique Site The building is located in Berkeley, west of San Pablo Boulevard and bounded by Parker and Tenth Streets. The site, with an existing corner property to remain, necessitated the new structure to be L-shaped in plan to maximize the building volume (Figure 1). The ground level predominantly consists of parking with some office space and a small retail space along San Pablo Ave. The second and third floors have an open floor plan for medical office use and four exterior terraces. The roof includes an enclosed penthouse and a screened-in mechanical space. Laboratory and medical office structures are typically steel-framed and often use steel braced frames for seismic lateral resistance. For this project, steel braced frames were deemed impractical: at the ground floor, the brace locations would impact the ground floor parking and drive aisles, while at the upper levels, the skewed and twisting floor plan did not allow for the brace frames to stack vertically. A concrete structure with concrete Figure 2. ConXtech collar.

shear walls was also considered but ruled out due to the shear wall’s impact on the ground floor parking and the lack of flexibility for future tenant revisions. An additional complexity, there was no specific tenant on board during the project’s design phase. Thus, the building was designed on a specification for future medical office or light laboratory use. Designing a future medical office building is challenging because these buildings have heavy mechanical and equipment demands that frequently add significant loading to the structural framing, not to mention tenant-specific MEP systems and floor plate requirements. Based on the experience of the design team, it was determined that the structure would be steel-framed and use the ConXtech moment connections for the lateral system. The chosen system integrated with the unique architecture, tuck-under parking, and allowed for flexibility with the future tenant needs. The property was sold to Kaiser Permanente after the design was fully permitted, putting the design flexibility of the steel-framed structure to the test. Fortunately, the design team found that with careful planning and leveraging past experiences, the primary structure was designed to accommodate much of the new tenant’s needs without significant structural revisions.

System Advantages The ConXtech steel moment frame system features a proprietary interlocking beam-column connector prequalified for use within ANSI/AISC 358, Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications. The moment frame columns are concrete-filled HSS shapes, and the beams are wide flanges with reduced beam sections (RBS). Fully restrained beam connections are achieved through the ConX collar N O V E M B E R 2 0 21

in the ConXtech system helped maximize the parking area and make the project feasible. The building site consists of up to three feet of compressible fill with some potential for liquefaction settlement and moderate expansion potential; these soil conditions played a major role in determining the chosen structural system. The geotechnical recommendations allowed for the use of shallow spread footings with an allowable bearing pressure of 3,500 psf; however, the design team targeted an allowable gravity bearing pressure of approximately 1,600 psf to reduce the overall differential settlement. Combining the distributed ConXtech moment frame system and the lighter steel-framed structure allowed for the cost-effective use of conventional spread footings. A concrete structure at this site would have incurred additional costs for either soil improvements or a pile foundation system due to the heavier structure.

Specific Details Figure 3. ConXtech bi-axial bolted moment frame connection.

assemblies. Nesting components of the collar are robotically shop welded to the beams and columns, as shown in Figure 2 (page 27). Then, the beams are simply lowered and locked into position at the construction site, and pre-tensioned high-strength bolts are installed (Figure 3). The limited field welding with this system results in substantial time savings in the construction schedule. Furthermore, the ConXtech system allows for moment frame beams to skew in plan up to 15 degrees, facilitating the architectural expression along the west slab edge with minimal impacts to the lateral system design. The distributed bi-axial moment frame layout used with the ConXtech system integrated seamlessly into the typical framing, using 16-inch square-frame columns. Figure 3 shows a typical beam-column connection at a bi-axial moment frame. A diagram showing the distributed lateral system is shown in Figure 4. A conventional special moment frame with wide flange beams and columns works only in the strong direction of the column. It relies upon fewer deeper columns that can have a major impact on the usable space and architecture. The 16-inch square columns utilized

Figure 4. Plan and extrusion of the lateral system.

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The design team collaborated with ConXtech throughout the design and construction of the structure. Like a conventional structure, Tipping Structural Engineers is SEOR for the structural design. ConXtech provides technical design support and serves as the steel subcontractor for the fabrication and erection of the primary steel frame. The building has a 14-foot floor-to-floor height, driven by the city’s zoning requirements for maximum building height. Frame beams are generally 21 inches deep at each level and, therefore, there is limited space below the framing for distributed MEP services. Thus, the SEOR coordinated with the architect and mechanical engineer to limit beam depths to 18 inches deep along major distribution trunks in the corridors to allow more room for mechanical services. The design team used ETABS to analyze the lateral force-resisting system and used RAM Structural System for the gravity framing analysis and design. Figure 5 shows the typical framing with the ConXtech system. Limiting the building’s torsion during a seismic event was another significant design consideration. Since the building is located in Seismic Design Category E, having an Extreme Torsional Irregularity is not permitted by ASCE 7, Minimum Design Loads for Buildings and Other Structures, Chapter 12. Additionally, a design decision was made

Figure 5. Framing at ConXtech corner column.

Project Team Owner: Kaiser Permanente | Oakland, CA Structural Engineer: Tipping Structural Engineers | Berkeley, CA Architect: Gould Evans | San Francisco, CA General Contractor: XL Construction | Milpitas, CA Nick Bucci is an Associate at Tipping Structural Engineers. (n.bucci@tippingstructural.com) Ryan Pintar formerly with Tipping Structural Engineers. (ryan@simplengi.com)

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to limit building torsion below the threshold for Torsional Irregularity to improve the structure’s overall seismic performance. Consideration of torsion also factored into the redundancy check. The structure is classified as an irregular structure, owing to the re-entrant corner. Sufficient moment frames were provided to prevent excessive torsion and improve the structure’s overall seismic performance to keep the redundancy factor at 1.0. The analysis showed that the seismic drift was reasonably uniform and less than 2 percent at the corners owing to the distributed lateral system shown in Figure 4. Base fixity is provided at the moment frame columns. With the distribution of loads facilitated by the space frame concept, it was possible to design fixed base columns using cast-in-place anchor rods with washer plates. The fabricator provided steel templates for aligning the anchor rods with the holes in the base plates, and setting the columns was quick and problem-free. In place of grade beams, it was decided to use the ground floor slab-on-grade to tie together the footings; construction cost and underground routing of utilities both played into this decision. The ground floor foundation and slab-on-grade design required extensive cross-disciplinary collaboration to accommodate the varied ground floor uses and finishes: office, sloped-to-drain parking area, retail, lobby, pavers, ADA access ramps, landscaping, and bioretention planters. A significant advantage of the ConXtech system is the expedited construction installation time and resulting construction schedule reduction. The primary steel frame was installed in approximately a week and a half, equating to about half the time of a conventional steel braced frame structure. The ConXtech system primarily relies upon a field-bolted system for gravity and moment frame connections to expedite the steel erection and field labor. ConXtech leverages a BIM Tekla model and a fully robotic fabrication system to ensure the necessary precision for the field-bolted system. The design team collaborated closely with ConXtech during the design and construction phases, including sharing Revit models to confirm dimensions and steel framing details.

Conclusion The integrated structural design embraced the architecture and non-standard-shaped infill site to provide the West Berkeley community much-needed medical access. The ConXtech moment frame system proved to be the perfect solution for this project. It fits into the typical steel framing without compromising the architecture or usable space and allows for conventional steel framing and a shallow foundation system.■ N O V E M B E R 2 0 21

The Wachenheim Science Center WILLIAMS COLLEGE SCIENCE RENEWAL PROJECT

By Ron Blanchard, AIA, LEED AP BD+C, Michael A. Tecci, P.E., LEED Green Associate, and Julia K. Hogroian, P.E., LEED Green Associate

ith tremendous growth in the sciences and the need for new research, teaching, and equipment space, Williams College in Williamstown, Massachusetts, sought to expand its existing science center to serve the educational demands of the science departments and their students. Nestled within the Berkshire mountains, the original campus buildings are modestly scaled pavilions set in the landscape and define a network of courtyards and outdoor spaces. While recent mega-building clusters were added to the campus, the college favored adding two modestly scaled buildings more in keeping with the original campus fabric over creating another singular megastructure. The buildings could still physically connect to the existing science center via bridge connections but would frame and shape the interconnected landscape that forms the spirit of the campus. Payette Associates Inc., the architect and planner, and Simpson Gumpertz & Heger Inc. (SGH), the structural engineer, designed two buildings to revitalize the science campus. To the south, the Hopper Science Center, completed in 2018, provides new research space for the Biology, Chemistry, and Physics departments and houses new

Section through math department atrium and light monitor looking east.

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Exterior rendering of the Wachenheim Science Center from the northwest.

machine shops and an imaging facility. To the north, the Wachenheim Science Center was constructed on the old Bronfman Science Center site and provides research and teaching space for the Geosciences, Psychology, Mathematics, and Statistics departments. This article focuses on the structural design of the Wachenheim Science Center, completed in February 2021.

Design Overview One of the design goals for the project was the ability to view the mountains from within the science quad. The building notches itself below grade into the bedrock to accomplish this goal. On this gradually sloping site, three and a half stories rise above grade while two and a half levels sit below. The foundation walls extend about forty feet below grade on the sides of the building, where the grade is the highest. The water table is approximately sixteen feet above the bottom of the basement slab elevation. The 26-inch-thick foundation walls and 4-foot-thick structural mat slab constitute the shell of the multi-story deep basement. Shear reinforcement ties in areas of high earth pressure shears are central to optimizing the volumes of wall concrete and reinforcement. The above-grade stories include classrooms, research laboratories, and office spaces. There is a small mechanical penthouse on a portion of the roof. The superstructure consists of structural steel framing acting compositely with a concrete slab on metal deck. A 4½-inch-thick reinforced

normal weight concrete slab on a 3-inch-deep metal deck achieves an uncoated two-hour fire rating for the laboratory chemical control areas, improves vibration performance for microscopy work, and increases flexibility for current and future floor penetrations typical of laboratory occupancies. There are large areas of depressed slabs within the floorplates to accommodate a variety of floor coverings, including locally quarried stone tiles. Dropped steel beams, bolsters, and supplemental deck support angles enabled the complex layout and varying depths of the recesses. The architectural layout and the column grid often do not align from floor to floor because of the mixed-use of Wachenheim. Each level has a number of column transfers; some occur at Architecturally Exposed Structural Steel (AESS) round HSS columns. All connections and splices at these columns fit within the depth of the ceiling cavity to maintain the clean HSS aesthetic. Moment frames provide the building’s lateral load resistance with minimal interference with the building’s complex program. Wind interstory drift control governs the design of the frames. Many of the moment frames have AESS round HSS columns. At the connections, the round columns transition to wide flange column stubs set within the ceiling depth to provide pre-qualified beam-column moment connections and improved panel zone shear strength without compromising the aesthetics of the exposed columns.

Below Grade Among the suite of below-grade classrooms is a 212-person auditorium that will be a valuable asset for the sciences. The auditorium floor is a sloping, formed stepped slab that spans to sloping reinforced concrete raker beams supported by concrete walls. Column transfers around the auditorium space allow unobstructed views. The design team studied various framing options’ varying the location and level of column transfers for the four floors above the auditorium. The adopted scheme has the roof and two stories frame to a column that bears on a 50-foot-long transfer girder at Level 2. Other 50-foot-long girders carry the loads of the roof of the auditorium and of Level 1 to perimeter columns and the foundation wall. This hybrid solution created an efficient compromise of steel tonnage, serviceability, functionality, and constructability.

Partial site plan of Williams College depicting the Wachenheim Science Center to the north and the Hopper Science Center to the south.

Creating “Lightness” Some classrooms were forced below ground despite a desire for exterior views and natural light in all occupiable spaces. The design team added an at-grade exterior glass walk system on the east and west sides of the building to get daylight into these spaces. The glass walkway bears on sloping steel plates that frame between the floor framing and the foundation wall. A combination of tapered bolsters and concrete curbs support the sloped steel plates and glass structure. The building is organized by a main circulation spine, reinforced with a central staircase running alongside it, with hubs of departmental and student social spaces that pinwheel off. These hubs of collaboration

North-south section through the Wachenheim Science Center looking east. N O V E M B E R 2 0 21

space are what give the building its life force. In addition, each department has a double-height volume to mark the heart of the department, giving it an identity and a shared space for faculty and students to congregate. To create these living rooms, spaces needed to be open and column-free to be filled with tables, soft seating, chalk and marker boards, and to produce a collaborative, collegial, and academic environment. Two light monitors provide additional natural lighting, one of which is above the building’s central stair. The north light monitor aligns with the double-height atrium space in the Math Department. The double-height space creates an open atrium between Level 2 and the roof. The Level 3 floor framing hangs from the roof framing, which also supports the light monitor framing, to create additional column-free space on Level 2. For this intertwined area, floor vibration and deflection control the governing design criteria, requiring stiffening of Level 3 and the ultimate supports on the roof. The Psychology double-height atrium is approximately 30 feet by 30 feet in plan and has a double-height curtain wall on the north and east sides. Wide flange columns below Level 2 transition to a series of ganged small hollow structural steel tubes fitting within the backup framing for the brick piers. These eliminate the encroachment of a column cover in the corner of the space and minimize the visual impact of structural columns. The HSS columns bear on the stiffened slab edge at Level 2, run unbraced past Level 3, support the roof, and provide lateral support for the facade systems. There is a column-free entry in the southwest corner of the building. The design team studied various framing options to determine the most efficient system that could accomplish the design intent. Instead of a single massive column transfer girder at Level 1, the team opted for cantilevered floor framing at each level.

Connectivity to Campus While the Wachenheim is a standalone structure, it connects to the existing science center via a pedestrian bridge to provide a sheltered pathway during the Berkshire winters and maintain a physical

Partial plan of typical cantilever framing above the southwest entry.

connection to the rest of the sciences. The bridge is clad in a curtain wall and is structurally independent from the existing Thompson Biology center with an expansion joint between the structures. Directly below the bridge, there is a utility tunnel between the two buildings. The bridge springs off the new Wachenheim Center to a new column that bears on a pre-existing grade beam over the tunnel’s roof. The primary bridge gravity structure is on Level 3. Architecturally exposed plate columns behind the bridge curtain wall mullions act as hangers to support Level 2 and as columns to support the roof. The scheme minimizes the depth of structure and increases the transparency of the bridge at Level 2 and the roof. For wind and seismic loads, the bridge cantilevers horizontally off the Wachenheim center via diaphragm action of the floor and roof decks. The Hopper and Wachenheim Science Centers’ construction, two modestly sized buildings integrated into the existing science center complex via pedestrian bridges and tunnels, provides Williams College additional space and resources for various science departments. By focusing the Wachenheim Center on housing the Geosciences, Psychology, Mathematics, and Statistics Departments, the design team provided distinct educational and collaborative spaces tailored to the needs of each department. Close collaboration by the design team integrated the two new buildings with the campus by providing mixed programming and future flexibility in open, light-filled spaces.■ Ron Blanchard is a Senior Associate at Payette Associates Inc. (rblanchard@payette.com) Michael A. Tecci is a Senior Project Manager at Simpson Gumpertz & Heger Inc. (matecci@sgh.com)

Detail of moment frame connection at round HSS columns that are part of the lateral load resisting system.

32 STRUCTURE magazine

Julia K. Hogroian is a Project Consultant at Simpson Gumpertz & Heger Inc. (jkhogroian@sgh.com)

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At an imposing 80-degree slope, the complex and unique canted brace highlights the slanted entry wall.

Structural Gymnastics By Thomas Kramer, P.E., S.E.,

Elizabeth Brack, P.E., S.E., Diana Gonzalez, EIT, and Geoff Leewaye, EIT

IN THE TRANSPORTATION CENTER

he Transportation Center at Pima Community College’s Center of Excellence for Applied Technology is 43,000 square feet with a total of 27 work bays, including spaces for testing and diagnosis of electric vehicles, faculty offices, classrooms, a dynamometer room, equipment storage, and a large public entry. The unique utility of the building governed its placement, such as the clearance necessary for cars to drive around the lobby and into the work bays. In addition, the structural design focuses on responding to flexibility and visibility, resulting in a state-of-the-art, hands-on learning environment reflected in the vast amount of exposed steel. A high degree of coordination and unique framing concepts, which the team termed “structural gymnastics,” led to the project’s success. DLR Group provided planning, architecture, structural engineering, electrical engineering, interiors, and construction administration services for the Transportation Center.

34 STRUCTURE magazine

Design Creativity The structural system’s creative design focused on flexibility and visibility, revealed in the exposed steel. Allowing daylight into the building was identified as a critical characteristic of the project early in the design. In response, a spectacular 8.5-foot-wide skylight illuminates the high-volume work bay. Creativity in structural design responded to maintaining continuity in load transfer, reflected by the unique stitched-together design at the high bay roof where the diaphragm was made discontinuous by the skylight. Finite element analysis using RAM Structural System was performed using semi-rigid diaphragms and analyzing the “stitching” as a horizontal truss. Transitioning from the ample auto bay space to the administration wing required transferring both the gravity and lateral loads through a non-orthogonal structural grid. The transition was accomplished

through a series of transfer girders and custom drag connections. The lateral load transfer at the interface of the high-volume work bay space and the adjacent two-story classroom building presented a unique challenge. The two-story classroom box is essentially skewed and overlapped into the high-volume work bay space. The lateral force-resisting systems were reimagined to ensure the flexibility of the rooms at the interface of these two different spaces. The solution resulted in a custom transfer girder connection to migrate the load from the classroom roof through a wide-flange girder rotated onto its weak axis and dragged to the high-volume work bay braced frames. Additionally, to create a light and airy shade structure, the large entry canopy was designed to tie into the lateral system of the main building, which eliminated the need for additional bracing. This was achieved with custom drag connections in each direction between the two structures.

Complex Criteria Unique problems arose from the angular layout of the building, horizontally and vertically, that created framing challenges and required extensive detailing. The complex geometry involved a high degree of modeling and coordination for stud soffit supports, exterior wall supports, skylight framing, and high/low roof framing. At an imposing 80-degree slope, the complex and unique canted brace highlights the slanted entry wall. The brace required an intricate degree of analysis due to the increased eccentricity. The 80-degree slope continues into the glass conference room that overlooks the Autolab and lobby. The large corner conference room with a floating effect is another design element that was crucial to the overall design of the building. The placement of columns and the addition of large transfer girders were crucial to delivering the intended visual impact. The tall exterior walls at the high-volume space exceeded 50 feet plus 11-foot cantilevered parapets. These walls required a secondary framing system connected to the main steel frame system and increased the in-plane loading into the roof diaphragm and lateral system. In addition, the wide flange wind girts were orientated with the strong axis horizontally to provide greater strength and deflection control to resist out-of-plane forces while also being in line with the primary structural framing.

8.5-foot-wide skylight illuminates the high-volume work bay.

Innovative Use of Materials Innovation was seen in the application of the exterior panel façade system, resulting in a more cost-effective, lightweight, and easy to install solution. Integrating this system into the structural design involved challenges such as providing custom gravity supports and coordinating the lateral supports for the wall system with the main lateral resisting system – all of which are coplanar. The perimeter structure required a secondary analysis for out-of-plane lateral forces in conjunction with gravity and in-plane lateral forces to support the exterior wall system. The exterior translucent panel system was selected for its best-inindustry thermal performance and light transmission. The panels reduce solar heat gain, which drastically reduces the heating and cooling loads of the building. The diffused light transmission through the panels reduced lighting needs and provided electrical savings. Because the panels are prefabricated and lightweight, savings were

Corner conference room required strategic placement of columns and large transfer girders to deliver the floating effect.

Preliminary detail of transfer girder connection using a wide-flange girder rotated onto its weak axis. N O V E M B E R 2 0 21

Hose reels cantilever from the 50-foot high roof.

also provided on transportation and installation time, approximately 2/3 less than a standard wall system. Structural cold-formed metal framing detailing at the exterior wall system allowed for elevated gravity support, material changes between translucent and insulated panels, and accommodated differential movement at the roof.

Design Efficiency Ingenuity of design for efficiency was at the forefront of the design process from the beginning. Developing specific detailing in the Schematic Design stage minimized late and costly design changes later, which would have impeded the project’s success. Many design complexities required custom solutions, resolved through a high level of coordination and modeling to ensure the structural system was integrated with all other building systems. The transfer girder and steel framing plans were detailed early in the process to ensure smooth coordination and best-in-class design. The exterior façade and structural systems were selected and designed to provide long-term durability and speedy construction sequencing. The CMU walls at the bottom of the exterior walls provided a durable base necessary for the automotive work environment. The structural steel and paneled wall system above enabled quick installation while providing the sought-after thermal and lighting benefits during the life of the building.

Constructability Challenges related to constructability were solved using a high degree of coordination and validation in framing to ensure that the structural

systems worked within the angular layouts of the building. The structural system had to allow for the movement of vehicles through the space, which meant coordination of column locations, providing cantilevered floor systems, and providing moment frames to guarantee open access. The atypical requirements of the automotive equipment meant making sure these systems were accounted for early in design to avoid conflicts during construction. The foundations in the Autolab were coordinated to prevent clashes with under-slab exhaust systems and integrated mechanical systems. Moreover, most mechanical units were installed on the roof of the large auto bay space, and ducts then serviced the lower volume classroom spaces. To access the classroom spaces, however, the ducts had to squeeze through the large transfer girders at the interface of the two spaces, leaving little to no room for error. The team used Navisworks clash detection to identify structural and mechanical issues before they happened in the field to aid in coordination and field challenges when installing mechanical systems. Hose reels that hung from high bay roof structure required custom detailing and an understanding of construction sequencing. In a standard automotive service area, hose reels are hung from the ceiling, typically only 12 feet in height. With a roof that went as high as 50 feet, steel framing had to cantilever down while still meeting equipment deflection limits and providing adequate clearance below. The overall result of the Transportation Center is a bright, open space that is highly functional to its occupants. The seamless transition into different spaces with geometric peculiarities is a true testament to the team’s early vision and high degree of coordination.■

Project Team All authors are with DLR Group. Thomas Kramer is a Project Manager. (tkramer@dlrgroup.com) Elizabeth Brack is a Project Engineer. (ebrack@dlrgroup.com) Diana Gonzalez is a Project Engineer. (dgonzalez@dlrgroup.com) Geoff Leewaye is a Project Engineer. (gleewaye@dlrgroup.com)

36 STRUCTURE magazine

Owner: Pima Community College Structural Engineer and Architect: DLR Group Contractor: Chasse Building Team Structural Software: RAM Structural Systems, RAM Connection, RAM Elements, RAM SBeam, Enercalc, Navisworks

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Adaptive Reuse of the Historic Witherspoon Building Part 3: Structural Investigations By D. Matthew Stuart, P.E., S.E., P.Eng, F.ASCE, F.SEI, A.NAFE, SECB

his four-part series discusses the adaptive reuse of the Witherspoon Building in Philadelphia, Pennsylvania (Part 1, STRUCTURE, September 2021, Part 2, October 2021). Part 3 continues the discussion of the structural investigations – specifically the main roof and original mechanical penthouse – conducted to understand the existing structure better. Numbered photos are provided in the print version of the articles; lettered photos are provided only within the online versions of the articles.

Structural Investigations (continued) Results of the main roof and original mechanical penthouse investigation indicated that the high penthouse roof had sufficient reserve load-carrying capacity to support proposed new mechanical rooftop units (RTUs) that serve the residential units. However, it was necessary to design steel beam support dunnage that clear spanned between the penthouse columns to prevent imposing any load directly on the book tiles and bulb tees (Figure K, online). The increased lateral load on the penthouse due to the raised RTUs also required additional vertical X-bracing (Figure 11) to be installed inside the penthouse

Figure 11. New vertical X-bracing at mechanical penthouse.

38 STRUCTURE magazine

between the existing cast-iron columns and below the high roof beams. In addition, the installation of the X-brace connections was designed to avoid welding to the cast-iron columns by only connecting to the existing beams. During the project’s construction phase, direct tension testing of the penthouse X-brace rods was conducted. This was to ensure correct rod pre-tensioning via turnbuckle rotation was performed without yielding the ½-inchdiameter rods. In addition, during the high roof dunnage construction, it was necessary to remove some of the brick masonry façade wall at the Figure 12. Northeast corner of passenger northeast corner of the pas- elevator penthouse at southwest corner of senger elevator machine room new RTU dunnage. penthouse to access the existing column so that it could support the southwest corner of the dunnage. After removal of the brick, it was discovered that the steel wide flange column that supported the penthouse roof had been spliced on top of an existing Gray column (Figure 12). In addition, corrosion of both the wide flange column and Gray column had occurred due to moisture infiltration from a failed penthouse parapet coping above. The damage was corrected by cleaning the steel of all corrosion by-products to determine the extent of section loss, adding welded headed studs to the column sections, then encasing the members in a reinforced concrete pilaster that recreated the masonry corner of the penthouse. Encasing the steel columns in concrete strengthened them to offset the loss of section and protected the steel from further corrosion. As a part of the investigation, it was also discovered that a few of the mechanical penthouse cast-iron columns were cracked at the

beam web connection clip extensions that proposed new chillers indicated that, in had been cast with the original pipe section general, the existing exposed framing could (Figure 13). The source of the cracking was support the new equipment once the existunclear; however, it was assumed that the ing cooling towers were removed and the cracks occurred during the original handling existing steel was cleaned and repainted to and erection of the columns due to the brittle prevent further corrosion. However, unsafe nature of cast iron. It also appeared that the structural conditions were observed at the clips were intended for lateral support of two easternmost column post supports, the beams during erection only and served immediately adjacent to the building’s edge, no actual structural function in the as-built due to excessive steel corrosion and almost condition. Nevertheless, new bracing angles complete section loss (Figure 14). were added between the affected beams and The building owner was immediately adjacent orthogonally framed beams at the notified of the unsafe conditions; however, same column. the conditions were not corrected until Investigation results also made it necessary much later in the project when similar to design and detail the exterior assembly corrosion was observed at all other dunspace as steel dunnage framing that spanned nage column supports. In the interim, between the existing main building columns. the existing cooling tower equipment was However, reinforcing the lateral resisting removed from the dunnage. Damaged colsystem between the main roof and 11th floor umns were either replaced with new steel was unnecessary because the increase in horiHSS columns or, if the corrosion was not zontal forces was determined to be less than Figure 13. Cracked beam-web connection clip at too severe, encased in a reinforced concrete 10% of the existing lateral loads at the roof a penthouse cast-iron column. plinth that included headed studs welded level, as allowed by the International Existing to the original steel column. Building Code (IEBC). After the equipment was removed, the steel dunnage was cleaned To avoid imposing assembly space dunnage loads on the existing and assessed. This resulted in the discovery that section loss due to clear span roof trusses, it was necessary to extend new columns up corrosion exceeded 5% of the original area; therefore, it was necesfrom the top of the 11th-floor main building columns to create rigid sary to weld reinforcing plates to the wide flange members to offset frames that in turn provided a platform for additional columns, which cross-sectional area loss. It was also necessary to design new steel straddled each side of a truss and supported the new rooftop dunnage grillage framing on top of the existing dunnage to marry the new framing (Figure L, online). Also, a subsequent additional investiga- chiller equipment to the existing framing footprint. New open steel tion was completed at the main roof, 11th floor, and ceiling framing grating catwalks were also provided, along with new support framing impacted by the proposed new elevator and stair penthouses, which for the chiller piping between the existing dunnage and mechanical confirmed the original roof investigation conclusions. Unfortunately, penthouse as required to avoid placing excessive pipe loads on the the design associated with all of the above, except for the RTU main roof framing below. The completed chiller dunnage and pipe dunnage, was excluded from the project due to the high cost of the support framing is shown in Figure M (online). proposed renovations.

Mechanical Penthouse

Mechanical Penthouse and Cooling Tower Dunnage Both the existing mechanical penthouse and cooling tower dunnage had been constructed well after the original building existed. The purpose of their structural investigations was to determine the ability of the same two structures to support the proposed new mechanical equipment and chillers, respectively. The investigation was required because there were no existing drawings available for either structure. Investigation findings are provided below and were based on steel coupon test results of a typical penthouse floor beam and roof joist of approximately 40 ksi and 50 ksi, respectively.

Cooling Tower Dunnage Investigation results of the existing cooling tower steel dunnage for the

Figure 14. Corrosion and excessive section loss at an existing cooling tower steel dunnage column support.

In general, the condition of the existing penthouse structure was fair; however, isolated cracking of the perimeter concrete base wall and moderate corrosion of the interior floor and roof framing were observed. Further, severe corrosion at the exterior steel stair stringers (Figure N, online) between the penthouse and main roof, which had resulted in complete loss of section in some areas, required that the damaged area of the stringer be demolished and replaced. In addition, isolated spalling of the floor slab soffit was also observed. Although the existing 6-inch concrete floor slab capacity could not be accurately determined due to a lack of information concerning internal reinforcing, it was confirmed that the existing steel floor beams had a superimposed, service uniform load-carrying capacity of 100 psf. The open web steel roof joists were determined to have a N O V E M B E R 2 0 21

Figure 15. Partially erected strengthening of the existing freight elevator penthouse.

load-carrying capacity of 16 psf in addition to all existing dead loads associated with the roof structure, roofing, and minimum roof live load of 20 psf. The available capacity of the existing floor was considerably less than that imposed by the new mechanical equipment. As a result, it was necessary to design an independent, steel beam dunnage frame erected immediately above the existing penthouse floor slab to support the new equipment. The new framing clear-spanned between existing perimeter penthouse columns, which could support the new loads, including the existing main building columns below. It was also determined that the existing roof framing had adequate capacity to support the suspended mechanical piping associated with the new penthouse equipment.

Freight Elevator Machine Room Penthouse The existing freight elevator penthouse floor framing consisted of three 15-inch-deep steel wide flange blocking beams that directly supported the elevator machine loads. The blocking beams were supported by W14 machine beams that were in turn supported by W16 beams that spanned east and west between W24 girders. The W24 girders were supported by two perimeter building columns at the north exterior side of the penthouse. One framed into the northernmost roof truss at the south end of the W24 girders, while the other framed into an interior main building column. The penthouse floor, also supported by the beams described above, consisted of a solid concrete slab. The floor beam framing also supported a perimeter, multi-wythe brick 40 STRUCTURE magazine

façade wall, a steel-framed roof, a solid concrete roof slab, and the elevator hoist beams. The existing Otis elevator machinery before its removal is shown in Figure O (online). Penthouse framing analysis included determining the impact of the new loading, provided by the elevator manufacturer, on the moment and shear capacity of the existing framing described above. In addition, the deflection of the framing members was assessed based on the criteria of American Society of Mechanical Engineers A17.1 (ASME A17.1). Analysis results, which were based on a steel coupon test from an existing penthouse roof hoist beam that revealed a yield strength of approximately 47 ksi, indicated that the moment and shear capacities of the 15-inch blocking beams, W14s, W16s, and W24 girders were adequate to support the proposed new elevator loads. As a result, it was also assumed that the existing beam end connections were likewise adequate for the new loading. Based on ASME A17.1 Section 2.9.5, allowable deflections of elevator equipment support beams must be less than span/1666. While the calculated deflections of the blocking beams and W14 beams were less than this same amount due to the proposed new equipment, deflection of the W16 beams and W24 girders would be more than the same allowable deflection and were therefore not capable of safely supporting the proposed new loads. As a result, structural reinforcing was developed for the W16s and W24s. Strengthening the W16 and W24 beams involved installing vertical steel members diagonally between the floor beams and the roof beams above to create story-high trusses (Figure 15). In addition, due to the increase in the minimum-code roof snow load requirements since the existing Otis elevator was installed, the roof truss that supported the W24 penthouse floor girder had to be re-supported with an additional column between the top of an interior 11th floor column and the bottom chord of the existing truss to reduce the span.

Shaft Vertical Rail Supports This investigation did not include an analysis of the existing vertical cab guide rails or counterweight system because they were considered part of the operating equipment for which the elevator manufacturer was responsible. Unlike the vertical cab guide rails, it was also determined that the counterweight system did not impose any additional load on the existing structural supports located within the shaft. Therefore, neither the vertical guide rails nor the counterweight system was included in the investigation and analysis of the existing internal shaft support framing and related floor framing supports. The primary deficiency documented in the shaft as a result of the investigation was the existing connections between the vertical guide rails and the existing horizontal support members at each floor level. Further, it was determined that the existing horizontal support beams, spanning north and south at the east and west guide rails, were also not capable of supporting the new imposed loads. As a result, new rail support beams were designed and installed with the existing supports abandoned in place. However, the related floor support beams located around the perimeter of the shaft could support the new loads. The elevator manufacturer also provided new clamping bolt connections between the existing rails and the new supports and installed a properly-sized bearing plate at the base of the rails on top of the existing concrete pit slab. Part 4 of this series continues the structural investigation discussion, including column capacities and connections, new floor openings, and other renovation-related issues.■ D. Matthew Stuart is Senior Structural Engineer at Pennoni Associates Inc. in Philadelphia, PA. (mstuart@pennoni.com)

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state

at City Creek Salt Lake City, UT By Mark Sarkisian, S.E., Peter Lee, S.E., Rupa Garai, S.E., Jiejing Zhou, P.E., Alex Zha, and Jaskanwal Chhabra, Ph.D.

he new 95 State office and mixed-use facility consists of a 25-story Class A tower with a 5-story podium ecclesiastical meeting house totaling 640,740 square feet. The building is located in the heart of downtown Salt Lake City, Utah. The project is being developed by City Creek Reserve Inc. with Skidmore, Owings & Merrill, architect and structural engineer, and Okland Construction as the general contractor. It is scheduled for completion in late 2021. The integrated urban design of multiple project components includes a complete rehab of the interconnecting pavilion and tunnel under State Street, connects 95 State to Salt Lake’s City Creek Center, and provides connections to neighboring Harmons retail and parking with a new solar canopy. With a client and owner team interested in the long-term performance of the facility located in a region of high seismicity and close to an active segment of Utah’s Wasatch Fault zone, SOM’s structural engineering design team responded to the design challenges of the new 392-foot-tall tower constrained on a narrow corner site using state-of-the-art performance-based seismic design methodologies and standards. Figure 1 shows 95 State from the south nearing completion.

Tower Structural Systems

Figure 1. 95 State nearing completion in late 2021.

42 STRUCTURE magazine

Designed in conformance with the 2015 International Building Code (IBC) with State of Utah 2016 Construction Code Amendments HB310, the 95 State tower and podium structure is assigned a Risk Category III per the occupancy load limits of 2015 IBC Table 1604.5. The tower superstructure uses reinforced concrete core walls as the seismic-forceresisting system extending to an overall building height of approximately 392 feet above adjacent grade with a one-level below-grade basement on the south. The site slopes up to the north approximately 15 feet along State Street, encompassing a second basement below Level 2 on the north. The height exceeds the code-prescribed height limit of 240 feet for the core-wall-only system. Therefore, the design uses a “non-prescriptive” building code design approach using an “alternate procedure” per 2015 IBC Section 104.11. The superstructure is designed based on the acceptance criteria provisions of the 2015 IBC and ASCE 7-16 standard, Minimum Design Loads for Buildings and Other Structures, Section 12.2.1.1 using PEER TBI v.2.03 (2017), Guidelines for Performance-Based Seismic Design of Tall Buildings. The ASCE 7-16 standard was adopted as a project-specific exception to the building code as recommended by PEER TBI v.2.03 Section 1.3. An independent structural design review was provided in conformance with ASCE 7-16 Sections 12.2.1.1 and 16.5 as approved by the authority having jurisdiction, the Salt Lake City Corporation.

The lateral seismic-force-resisting system consists of special ductile reinforced concrete core shear walls and coupling beam construction extending from a pile and pile cap supported deep foundation system to the penthouse roof at Level 26. The slender core wall depth in the east-west direction is 33 feet, 4 inches, with an aspect ratio of 11.8. Core shear walls range from 24 to 30 inches thick with concrete compressive strength of 8,000 psi. Shear wall thicknesses are constant over the full height of core walls. The shear wall core is interconnected with ductile reinforced coupling beams at openings required for doorways and corridors. Additional openings with coupling beams were introduced to increase seismic inelastic energy dissipation. At Level 26 (El. +356.5 feet), the 2-story MEP penthouse roof lateral and gravity systems consist of a steel-framed core, roof mechanical penthouse, screen walls, and perimeter glazed wall enclosure. The penthouse lateral system combines a steel eccentric braced frame (EBF) and a moment frame structure. The EBF provides sufficient lateral stiffness while accommodating differential vertical displacements compatible with shear wall coupling beams. The moment frame provides a backup system and helps control residual drift. Figure 2 shows the overall 3-D Revit BIM model structural systems. The office tower architectural geometry is defined by Figure 2. Overall 3-D Revit BIM model structural systems. rounded glazed corner curtain wall panels with slightly articulated radiused north-south and east-west walls extending from and the central core. Figure 3 shows a typical framed tower level. Level 3 to 25 on the south and above Level 6 on the north. Levels The composite steel framing and slab system generally consist of 1 to 5 form a podium with larger floor areas encompassing meeting a 3¼-inch lightweight concrete fill over a 2-inch metal deck. At house program facilities clad typically in stone, glazing, and areas with Level 2, Level 4 mechanical rooms, and the Roof Level, the comart glass. The overall footprint is typically 109 by 210 feet in plan posite steel framing system consists of a 4½-inch normal weight at the upper tower levels and 109 by 250 feet at the lower podium concrete fill over a 3-inch metal deck. A 2½-inch normal weight levels. The typical story height is 14 feet, with a story height of 12 concrete fill over a 3-inch metal deck is used at the Level 5 roof feet 10 inches at B1, 18 feet 1 inch at Level 1, 16 feet at Level 4, and garden. At the tower’s north and south curved walls, steel framing 15 feet at Level 25. is cantilevered up to 18 feet to allow for column-free perimeter The gravity system of the tower and podium superstructure floor tenant office areas. plates consists of perimeter steel girders that span between W14 The deep foundation system consists of 24-inch-diameter auger columns located typically at 30 feet, and W18-W21 composite cast-in-place displacement piles supported on pile caps that resist beams typically spaced at 10 feet spanning between the W21 girders superstructure gravity and lateral load reactions at the base of the building. A total of 363 piles extend into primarily gravel and clay deposits to very dense gravel layers at depths of 110 to 115 feet. In upper layers, liquefactioninduced settlements up to 1½ to 2 inches are expected. At the tower core, a single 11-foot-deep mat pile cap is provided, interconnected by tapered grade beam outriggers on primary transverse column lines to perimeter pile caps in the eastwest direction, to resist lateral overturning seismic forces. Grade beams typically interconnect the pile caps and a 10 to 12-inch pile-supported suspended slab on grade. Perimeter foundation walls are also supported by a continuous grade beam that spans on perimeter piles. Level 1 framing construction consists of cast-in-place reinforced concrete with a typical 14-inch slab, beams, drop panels, and Figure 3. Typical tower level framing plan. diaphragm collector elements to transfer N O V E M B E R 2 0 21

Figure 4. Plan of foundation model, outrigger grade beam moment diagram, and core wall mat foundation.

lateral loads from tower core walls to perimeter foundation walls. Figure 4 illustrates foundation modeling of core wall mat and grade beam outriggers.

Site Seismicity and Ground Motions The site in downtown Salt Lake City is located within the Intermountain Seismic Belt, one of the most seismically active areas in the interior western U.S, with a repeated occurrence of earthquakes greater than a moment magnitude of M7 along the Wasatch fault zone. The site is located approximately 1.18 miles from the Salt Lake City Segment of the Wasatch Fault Zone. Seismic loads were developed utilizing site-specific horizontal acceleration response spectra to design the tower – service level earthquake (SLE) at a 43-year return period and risk-targeted maximum considered earthquake (MCER) at a 2,475-year return period by the project geotechnical engineering seismic hazard consultant, Lettis Consultants International, Inc. (LCI), in coordination with site geotechnical investigations by Consolidated Engineering Laboratories (CEL). Peer-reviewed by the Structural Design Review Panel (SDRP), 11 sets of fault-normal and fault-parallel ground motion records were

chosen for MCER using the 2014 Next Generation Attenuation (NGA-West2) model, in conformance with ASCE 7-16 and by following a non-ductile spectral matching approach that conserves the correlation between horizontal components and results in time histories that have peaks and valleys.

Performance-Based Seismic Design

The tower seismic design is based on the PEER TBI v.2.03 (2017) performance-based guideline procedures and the SDRP review. Key unique design aspects of the project included, 1) design of an efficient and well-proportioned lateral load resisting coupled-core wall system that could dissipate seismic energy by controlled yielding of the coupling beams and hinging at the base of the building core, and 2) explicit modeling of the soil-structure interaction to capture the maximum Level 1 transfer diaphragm and basement wall backstay effects, and therefore, determine the upper-bound demands on the transfer diaphragm. The core walls are modeled using nonlinear fiber elements, and the coupling beams are modeled using lumped plasticity flexural/shear hinges in Perform-3D (CSI). Figure 5 shows the core wall horizontal section highlighting the wall fiber arrangement, coupling beams, and core wall strain gauges which capture yielding of longitudinal reinforcement. The coupling beams are modeled according to recommendations in Naish (2010), Galano and Vignoli (2000), and Lim et al. (2016). The stiffness modifiers for the component actions, where nonlinear behavior is not explicitly modeled, are used according to PEER TBI v2.03. Nonlinear analyses are performed with a suite of 11 ground motions for two separate cases to bound the backstay stresses. The upper bound lateral load in the Level 1 transfer diaphragm and perimeter basement walls are modeled using the higher stiffness modifiers per ATC 72-1, Table A-3. The foundation flexibility is Figure 5. Modeling of reinforced concrete core wall nonlinear components (Perform-3D, CSI). accounted for by using soil springs to model

44 STRUCTURE magazine

Figure 6. Illustration of compliance to design criteria: a) Inter-story drift ratio; b) Fiber strain in the RC core wall.

the vertical pile stiffness. The upper bound lateral load remaining in the shear wall core is captured using relatively lower stiffness property modifiers per ATC 72-1, Table A-3. All the elements are modeled as pinned at the top of the pile cap. The structural performance is primarily evaluated by studying the inter-story drift ratios, coupling beam rotations, strain in the core wall fibers, and rotations at the end of the gravity beams in conformance with limits imposed in the detailed structural design criteria. Figure 6 illustrates compliance to design criteria with respect to interstory drift ratios and strain in core wall fibers. The MCER mean base shear force for the maximum backstay case is 15,250-kips (0.145g) in both the transverse and longitudinal directions. NLRHA ground motion analyses were typically completed in 3 to 4 days run-time. With the modeling of piles, run-times extended up to 40 days. Figure 7 shows the in-progress construction of reinforced concrete core walls and steel framing up to Level 6. The new 95 State office tower and mixed-use facility is a bold and iconic addition to Salt Lake City’s downtown urban and livable city center. The performance-based seismic design approach achieves enhanced performance, reductions in embodied carbon impact, and a LEED Gold rating.■ The authors thank the client group at City Creek Reserve, Inc., for their support in achieving project goals, and the entire design and construction team for their contributions.

Project Team Owner/Developer: City Creek Reserve, Inc., Salt Lake City, UT Structural Engineer and Architect: Skidmore, Owings & Merrill, San Francisco, CA General Contractor/Concrete: Okland Construction Company, Salt Lake City, UT Prime Steel Contractor: SME Steel Contractors, West Jordan, UT Concrete Reinforcement Detailer: Harris Rebar Inc, Salt Lake City, UT

Mark Sarkisian is Partner (mark.sarkisian@som.com), Peter Lee is Senior Associate Director (peter.lee@som.com), Rupa Garai is Associate Director (rupa.garai@som. com), Jiejing Zhou is Professional Engineer (jiejing.zhou@som.com), and Alex Zha is Design Engineer (alex.zha@som.com) with the San Francisco office of Skidmore, Owings & Merrill (SOM). Jaskanwal Chhabra is a former Design Engineer with SOM (chhabrajaskanwal@gmail.com).

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The online article contains information regarding the whole-building life-cycle assessment that was performed along with an additional graphic.

Figure 7. Construction of core walls and steel at Level 6.

N O V E M B E R 2 0 21

engineer's NOTEBOOK Leveraging Professional Relationships Staying Ahead of the Rapidly Changing Construction Industry By Samuel Harris

oday’s challenging and fast-paced construction environment forces engineers to take on many responsibilities in the design workflow. The continual evolution of the construction industry makes it difficult for structural design professionals to stay up-to-date on new construction materials, methods, codes, and design technology. Many manufacturers and vendors that regularly support structural engineering consultants offer assistance to help overcome the information gap on many construction applications and technology. These valuable services can help save time and allow design professionals to focus on schedule-critical tasks. There is a vast amount of educational content and design tools that construction vendors make available online via educational forums, webinars, and various software applications. Despite having all of these tools at their disposal, only a small fraction of structural engineering professionals take full advantage of them.

The Dilemma

Where to Start

Structural engineers must continually review new construction inno- One of the greatest challenges vendors and their engineering departvations to meet a variety of design requirements. These requirements ments face is moving beyond being the classification of a vendor to might include: that of a partner. Building material representatives/vendors want • Load capacity to collaborate with engineers to make them more productive and • Compliance with varying load types and serviceability cost-efficient. requirements Start by identifying your local manufacturer representative. Many • Compliance with national and local building code representatives have their P.E. license and come from a structural or requirements Civil engineering background. Invite your field representative to meet • Choosing the correct fastening solution for the application your design team face-to-face or online so that they can understand • Cost of materials and cost of installation labor your processes and projects. Your field representative can provide • Controlling design parameters such as fastener spacing, the following: base material type, and thickness • Design assistance/guidance/quality review • Jobsite considerations and challenges • Customized specification edits º Incorrectly placed or missed • RFI assistance to facilitate better fasteners design and communication of field º Contractor installer training fixes º Incorrect installations • On-site project support and Everyone in the º Environmental considerations hands-on installation training construction industry º Material availability for the installer A designer often consumes large amounts • Answers to challenging software and is extremely busy these of time conducting research, attending projcode provision questions related to days trying to meet ect meetings, and engaging in dialogue with their products the owner/architect/contractor to derive the Certain manufacturers have “preferred condeadlines and support safest and most economical solution. After sultant programs” that offer key structural their clients as design and dedicating countless hours to a project, engineering offices specific benefits such as construction roar back RFIs and re-design work can further concontinuing education, specification modifisume time and budget and possibly cause cation, design assistance, or job site support. to 2019 levels. delays. By leveraging the support services Inquire with your manufacturer’s representaof trusted manufactures and vendors, this tive if your office qualifies. Other (often free) process can be significantly streamlined. services provided to engineers might include:

46 STRUCTURE magazine

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better avoid rework by ensuring products are more likely to be installed correctly. These benefits combine to build a stronger relationship amongst the structural engineer, manufacturer, and contractor. So take the time to reach out to your preferred manufacturers and start this valuable conversation today!■

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Sam Harris is a Lead Structural Field Engineer working for Hilti North Manufacturer representatives provide valuable support tools to the America and covering Colorado and Wyoming. (samuel.harris@hilti.com) design community beyond their face-to-face interactions with structural engineers, including: • Design software – Manufacturers provide some of the best-inclass software packages that can instantly reduce design hours. Many companies offer simplified versions of their software packages for free that can be useful for the most common design problems. • Seminars and webinars – STICK TO THE Continuing education is offered M O S T I M P O R TA NT online or in-person on variSCHEDULE. ous topics; many programs are YO U R S . certified by NCSEA to satisfy state continuing education requirements. • Engineering-specific online landing pages and websites – Online forums such as Ask.Hilti.com are set up expressly to address engineers’ and architects’ technical questions. These sites post various technical content and provide access to technical data, design guides, and product approvals. • Engineering call centers and design offices – Most have a central phone number or email for direct access to an engineering department. Many can respond to technical questions within 24 hours.

Benefits/Conclusion Everyone in the construction industry is extremely busy these days trying to meet deadlines and support their clients as design and construction roar back to 2019 levels. Taking advantage of these services brings value to all parties involved. Structural engineers can confirm that their specification details are up-to-date and communicated correctly to the contractors. Manufacturers can provide design aids and services that save time and prevent costly RFIs. Contractors can work directly with the manufacturers to solve field issues and

Extra steps. More parts and pieces. Skilled labor issues. They all add up to one thing: less of doing what you really love. But with ClarkDietrich, time and innovation work in your favor. Our framing and finishing systems speed up and simplify installation. Because you’ve got better plans waiting. © 2021 ClarkDietrich

N O V E M B E R 2 0 21

code UPDATES States, Cities Adopting Tall Mass Timber Provisions A Variety of Approaches By Kenneth Bland, P.E.

tates and municipalities eager to allow taller mass timber buildings are considering adopting the mass timber provisions in the 2021 International Building Code (IBC). Many have recently finished the adoption of the 2018 I-codes and would otherwise wait several more years to incorporate construction types IV-A, IV-B, and IV-C into their building codes to allow mass timber buildings up to 18 stories tall. The American Wood Council’s (AWC) staff of engineers and former building code officials has been approached by several of these states and localities for technical support and, thus far, California, Georgia, Idaho, Oregon, Utah, Virginia, Washington, and the city of Denver are either in the process of enacting the provisions or are finalizing the process.

Approaches to Early Adoption There have been three main approaches to incorporating the 2021 IBC tall mass timber provisions into state and local building codes. All have the same effect and have been chosen by the State or local jurisdiction based on the most efficient approach to maintain consistency with the rest of the building code. • Incorporate directly into the code. Washington and California are examples where the provisions were incorporated directly into the state code, much like they appear in the 2021 IBC. The International Code Council (ICC) has begun posting statewide amendments adopting the 2021 tall mass timber provisions to its Digital Code website, providing an important resource for other jurisdictions considering adoption. State codes, such as the Washington state building code based on the 2018 IBC, are available for free viewing on the site, where it seamlessly adds the 2021 tall mass timber provisions into the current edition of the code. • Mandatory appendix. The city of Denver added a mandatory appendix for incorporating tall mass timber provisions into the city code. The appendix adds specific provisions to the current building code, allowing designers to use the 2021 IBC tall mass timber criteria. The appendix provisions are identical to the mass timber provisions in the 2021 IBC but are consolidated in one place rather than scattered throughout the code based on the section number. While this example is from a city, a state could undertake the same approach. • Reference the 2021 IBC. Virginia elected to amend the 2018 code by adding a simple reference to the 2021 IBC for the types of tall mass timber construction in Chapter 6. This approach offers a succinct alternative and is consistent with how the state already recognizes the latest changes approved by the 48 STRUCTURE magazine

ICC membership. The added section contains a note that sends the code user to a state-issued supplement containing the consolidated tall mass timber provisions. In many respects, it is similar to the approach used in Denver. However, in AWC’s experience assisting Building Code Boards undertaking the early adoption process, some states may find this approach attractive for its brevity but find it is inconsistent with the rest of the building code.

Amendments to the 2021 Provisions Most states that have incorporated the 2021 IBC tall mass timber provisions into their codes have done so through direct adoption. However, there are a few that amended portions of the model building code. The Oregon Statewide Alternate Methods (SAM) approach was adopted in 2015 and updated in 2019, as the approval process for tall mass timber provisions was underway at ICC and well before the 2021 IBC was finalized. To facilitate the approval of tall mass timber buildings, Oregon added an amendment addressing seismic design coefficients and factors that was eventually replaced with reference to the AWC/ANSI 2021 Special Design Provisions for Wind and Seismic (SDPWS). The 2021 SDPWS provisions apply to buildings less than or equal to 65 feet in height in Seismic Design Category (SDC) A and B. AWC recommends that states and municipalities that have not adopted the 2021 IBC allow the use of 2021 SDPWS, which provides criteria for the design of CLT diaphragms and shear walls. The State of Washington has approved a substantive but straightforward change to their 2021 IBC mass timber provisions based on a code change proposal introduced in the 2024 Code Development Cycle. ICC proposal G15021 clarifies that noncombustible materials that line concealed spaces are not required to be protected in Type IV-HT. AWC is the proponent of the change, which clarifies existing provisions and was recommended for approval by a unanimous vote of the committee.

2024 Code Change Proposals In addition to G150-21, several other code change proposals are being considered in ICC’s 2024 Development Cycle, which are important to tall mass timber code users. For example, a proposal, G147-21, supported by AWC to increase the allowable area of exposed mass timber ceilings from 20% to 100% in buildings up to 12-stories in height, was recommended for approval by the ICC code development committee and during the public comment hearing. Testing conducted by the Research Institute of Sweden (RISE) and sponsored by AWC through a USDA Wood Innovation Grant provided compelling evidence for the committee’s recommendation. An AWC change proposal, F174-21, to delay the installation of the noncombustible topping on CLT floors during construction was also recommended for approval. This proposal was also supported by two mass timber builders that spoke to the challenges of sequencing installation of the topping during construction and the cost savings associated with providing the builder with greater flexibility. G142-21 has been proposed to permit CLT in the exterior walls of Type III construction but was recommended for disapproval. Similarly, FS 34-21 proposes to allow CLT firewall construction in certain combustible construction buildings but was recommended for disapproval, despite strong testimony in support. AWC sought approval of both proposals through the ICC Online Governmental Consensus Vote which closed November 1, 2021.

Conclusion Once a governmental entity takes action to enact ICC’s family of model codes as law, all construction must be designed, constructed,

and inspected for compliance. Adopting the new construction types IV-A, IV-B, and IV-C will allow designers to use strong, low-carbon alternatives to engineer safe, efficient, and sustainable buildings. For additional information on tall mass timber, the 2021 code development process, and the rigorous fire testing performed at the ATF, please refer to www.awc.org/tallmasstimber.■ All graphics are the Apex Clean Energy headquarters under construction in Charlottesville, Virginia. Kenneth Bland is the Vice President, Codes & Regulations for the American Wood Council. AWC is committed to ensuring a resilient, safe, and sustainable built environment on behalf of the industry it represents.

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historic STRUCTURES Quebec Bridge, The First Failure, 1907 By Frank Griggs, Jr., Dist. M.ASCE, D.Eng, P.E., P.L.S.

Winning design by Phoenix Bridge.

bridge had been proposed across the St. Lawrence river for many years when the Phoenix Bridge Company and Theodore Cooper were selected to build an 1,800-foot-span cantilever bridge. The span would be the longest cantilever in the world, surpassing the Firth of Forth Bridge with its two spans of 1,710 feet. Cooper was initially selected as a consultant to the Quebec Bridge & Railway Co. to recommend a design from the many submitted in a design competition. He selected the Phoenix Bridge design as it was “an exceedingly creditable plan from the point of view of its general proportions, outlines, and its constructive features” and was the “best and cheapest plan and proposal of those submitted to me...” At the time, Phoenix Bridge was one of the leading bridge companies in the world, and Cooper had an unblemished record as a bridge engineer. The original proposal was for a 1,600-foot cantilever, but Cooper recommended that the central span be increased to 1,800 feet to save the time to build and the cost of the piers. On November 19, 1900, Cooper was retained as Consulting Engineer, and, shortly after, the Bridge Company received financial support from the Government. Peter Szlapka, working under J. Sterling Deans, started the actual design in accordance with specifications prepared by Cooper. Cooper had significantly modified the standard Canadian specification, placing his mark on the bridge. Two of the changes were,

Plan of bridge showing failed member A9L and planned suspended truss to mid-span.

50 STRUCTURE magazine

• A reduction in wind load. The Original specifications used the Firth of Forth pressure of 56 pounds per square foot. This pressure was adopted after the Firth of Tay Bridge had failed under high wind loads. Cooper reduced the load to 30 pounds per square foot. • An increase in the allowable working stresses in the members to 21,000 pounds-per-square-inch under a Cooper E-30 loading and 24,000 pounds-per-square-inch under a Cooper E-50 loading over the entire length of the bridge. At the time, the usual value was 16,000 psi.

Cooper loading E30 designates that each of the driving wheels has a load of 30,000#. It also specifies a load on the leading truck and another load on the trailing axle, plus a load for the following freight cars. At the time of the bridge’s design, a loading of E20 was common, but Cooper specified a loading of E30. All the plans prepared by Szlapka were forwarded to Cooper for his review and approval. While the foundations were being placed between 1899 and late 1903, the design of the superstructure

proceeded, and the anchor spans were to time, it is only very recently that these approved in October 1904. Construction have been in this condition, and their started on the south anchor span in present shape is undoubtedly due to July 1905, and the design of the south the stress they are now receiving. Only cantilever arm followed. Szlapka then a little over a week ago, I measured one determined that the fabricated weight of rib of the 9-L chord of the anchor arm steel was coming in much greater than he here shown, and it was only ¾ inch out had estimated. It so happened that he had of line. Now it is 2¼ inches.” not increased the estimated dead weight McLure took the train to New York, of his cantilever arm and suspended span arriving on the morning of August 29, in going from the 1,600-foot span to the and reported in person to Cooper on his 1,800-foot span that he used to design concerns about the safety of the bridge. his anchor arm. Cooper knew that, short Finally recognizing the critical nature of taking the bridge apart, he could do of the problem, Cooper told McLure to nothing about it and wrote, “I made an telegraph Phoenix Bridge, telling them to estimate of the increased strains due to stop work immediately and sent him to this increased weight and found it to be Phoenixville to discuss the matter more about 7 percent...Realizing that there was Bottom chord cross-section A9L. fully with them. The telegram was sent no remedy and that this 7 percent was at 12:16 PM and arrived at Phoenixville not a fatal increase.” Szlapka then designed the cantilever arm and at 1:15 PM. McLure would not arrive at Phoenixville until 5:30 suspended span to the increased dead weight. PM. At that time, the bridge collapsed into the St. Lawrence River, After the cantilever arm was finished, a smaller traveler was built killing 75 men. to erect one-half of the suspended span. In early August, the splice Harper’s Weekly asked, “was it properly constructed? Was the iron in the lower chord 7-8L of the anchor span showed increased signs of inferior quality? Is there no method of making iron bridges of of distress. Cooper later stated that he began to get “uneasy” about assured safety? And who is responsible (so far as responsibility goes) the lower chord members on August 8 when he got a report from for such an accident – the engineer who designed the bridge, or the his man on the job, Norman McLure, on apparent bending of the contractor, or the builders, or the railroad corporation? Was the bridge web plates on the lower compression chord near the southerly pier. when made the best of its kind, or the cheapest of its kind.” A massive At the time of the collapse, the first three panels of the suspended study was made by a Royal Commission, including a report by C. C. span were in place. Schneider. They concluded, in part: The outside ribs on A9L were each built up of 3 plates – 54 inches × a) The collapse of the Quebec Bridge resulted from the failure of 15 ⁄16 inch and one 37¾ inches × 15⁄16 inch combined with stich rivets. the lower chords in the anchor arm near the main pier. The The interior ribs were built up with 2 plates – 54 inches × 15⁄16 inch failure of these chords was due to their defective design… and two 46 inches × 15⁄16 inch also connected with stich rivets. The c) The design of the chords that failed was made by Mr. P. L. ribs were separated by latticing top and bottom and diaphragms near Szlapka, the designing engineer of the Phoenix Bridge Co. the top. The ends of the plates were milled, and the compressive load d) This design was examined and officially approved by Mr. between the members of the lower chord was to be transferred from Theodore Cooper, consulting engineer of the Quebec Bridge member to member by bearing. However, during erection, they & Railway. Co. encountered many problems bringing the members into full bearing e) The failure cannot be attributed directly to any cause other over the entire joint. than errors in judgment on the part of these two engineers. Between August 7 and August 27, 1907, there were many letf ) These errors of judgment cannot be attributed either to ters, telegrams, and telephone calls between McLure, Cooper, lack of common professional knowledge, to neglect of Szlapka, and Deans regarding the increased bending of the web duty, or to a desire to economize. The ability of the two plates of the lower chord. At first, many of the players believed engineers was tried in one of the most difficult professional the bend had been in the plates problems of the day and from the beginning. McLure could proved to be insufficient for not convince them that the bend the task… was not there initially and was i) We do not believe that the increasing over time as more load fall of the bridge could have been prevented by any action was added to the suspended span. And who is responsible (so far that might have been taken Some of the Phoenix Bridge men after August 27, 1907. Any on the job, including Yenser, the as responsibility goes) for such effort to brace or take down foreman, believed the situation was the structure would have been critical. Birks, the Superintendent, an accident – the engineer impracticable owing to the continued to believe the bend was who designed the bridge, or the manifest risk of human life in the member from the begininvolved. ning. McLure wrote to Cooper, “… contractor, or the builders, or j) The loss of life on August 29, although a number of the chords 1907, might have been preoriginally had ribs more or less wavy, the railroad corporation? vented by the exercise of better as I have reported to you from time

N O V E M B E R 2 0 21

Bridge in the river.

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judgment on the part of those in responsible charge of the work for the Quebec Bridge & Railway Co. and for the Phoenix Bridge Company… m) No one connected with the general designing fully appreciated the magnitude of the work nor the insufficiency of the data upon which they were depending. The special experimental studies and investigations that were required to confirm the judgment of the designers were not made. n) The professional knowledge of the present-day concerning the action of steel columns under load is not sufficient to enable engineers to economically design such structures as the Quebec bridge. A bridge of the adopted span that will

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52 STRUCTURE magazine

L O V E L A N D

C A R B O N D A L E

B U F FA L O

unquestionably be safe can be built, but, in the present state of professional knowledge, a considerably larger amount of material would have to be used than might be required if our knowledge were more exact. o) The professional record of Mr. Cooper was such that his selection for the authoritative position that he occupied was warranted, and the complete confidence that was placed in his judgment by the officials of the Dominion Government, the Quebec Bridge & Railway Company, and the Phoenix Bridge Company was deserved. C. C. Schneider, in his report, wrote of A9L, A9R, and some other members, “Since, however, the lower chord members of the Quebec bridge are butt-jointed, they are neither continuous nor pin connected, and it is impossible to make the whole section bear uniformly under the various conditions of loading… However, there is a deficiency in many of the compression members, as their connections, such as the latticing, are not sufficient to make the parts composing them act as a unit. The most pronounced defect in this respect exists in the lower chord members of the cantilever and anchor.” While not emphasized in his report, in the opinion of many, these were the cause of the buckling and failure of members A9L and A9R. The blame was placed primarily on Cooper and Szlapka, and The Engineering Record wrote on Cooper, “It is seldom that the responsible engineer for any work, great or small, has more authoritatively or more effectively impressed his engineering judgment upon the work in his charge than in this case...Perhaps the most painful part of the evidence is that in which the Consulting Engineer makes the plea of impaired health for not exacting from both the contractor and the Quebec Bridge Co. certain requirements of design and plans in the one case and the necessary organization for the proper performance of the work on the other. Unfortunately, such pleas are admissions of official shortcoming: however much a man may feel the disability of ill health, they give him no relief from official responsibility...The Consulting Engineer makes a further point in his evidence that the fee he received was quite insufficient to enable him to maintain a proper office workforce for the discharge of the duties imposed upon him in his official capacity...When he accepted the fee, he accepted all of the responsibilities of the position. No engineer has any right whatever to consider his responsibilities lessened because his fee is not as large as it should be...” One of the worst and most studied, this failure pointed to the need for meaningful peer review and the need for qualified inspectors, with authority, on major works. It is hard from the perspective of the early 21st century to understand why it was not clear that the lower chord compression members were failing in, and probably before, early August. Accepting that fact would have required the entire design team to recognize that they had made a serious design error, which was not correctable, and that the bridge was doomed to fail. In the early afternoon of August 29, they could not have saved the bridge, but they could have saved the lives of the 75 men who died in the collapse.■ Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19 t h Century cast and wrought iron bridges. He is now an Independent Consulting Engineer. (fgriggsjr@twc.com)

legal PERSPECTIVES Waiver of Consequential Damages By Gail S. Kelley, P.E., Esq.

hile a waiver of consequential damages clause is considered a contractual risk management tool, how these provisions manage risk is not always clear. One reason is that potential consequential damages for one or both parties can vary from virtually nothing to many times the contract amount, depending on the project. Engineers often ask whether they should agree to waive their consequential damages, and likewise, whether they should require the other party to waive their consequential damages. The answer, as is common in contract negotiations, is “it depends.” The concept of consequential damages derives from the 1854 English case, Hadley v. Baxendale. (Because the United States was a British colony, we inherited many of Britain’s legal principles.) The Hadleys were millers who hired Baxendale to transport their broken mill shaft to London for repair. Unfortunately, the repaired shaft was not delivered to the Hadleys by the date the parties had agreed upon, and the mill was shut down for several days. The Hadleys sued for their lost profits but lost, with the court holding that a party injured by a breach of contract can only recover “those injuries which the parties could reasonably have anticipated at the time the contract was entered into.” Because the Hadleys had not told Baxendale that the mill operation depended on the shaft, Baxendale could not be held liable for the lost profits. Over the years, a body of case law has grown around the concept. While many of the cases address specific circumstances and wording, the holding has come to stand for the proposition that a breach of contract can cause two types of damages: direct (or “general”) damages and consequential or “special” damages. Direct damages are those required to correct the breach, for example, the cost to correct a design error. Consequential damages are other economic damages suffered by the non-breaching party that the breaching party knew (or should have known) could occur at the time the contract was entered into. They almost always arise from delays in performance; in the context of construction, this typically involves a delay in project completion.

Construction Contracts One of the best-known cases involving consequential damages arising from construction contracts is Perini Corp. v. Greate Bay Hotel & Casino, Inc., 129 N.J. 479, 610 54 STRUCTURE magazine

If the Client balks at a waiver, this might be a red flag for the Engineer. A.2d 364 (N.J. 1992). In this case, a New Jersey court upheld an arbitration panel’s decision that the construction management firm engaged to manage a casino restoration project owed the owner $14,500,000 in lost profits due to delays in the project. It is generally believed that this case was the impetus for adding a mutual waiver of consequential damages clause to the AIA A201. This clause (subparagraph 15.1.7 of the 2017 A201) includes a broad list of the consequential damages that the Owner waives, including rental expenses, loss of use, income, profit, financing, business and reputation, and loss of employee productivity and services. The Contractor waives the right to claim principal office expenses, lost opportunities and profit, loss of bonding or increased bonding costs, and damages to reputation. There are two important take-away points from the AIA clause – the first is that there is no universally accepted definition of consequential damages. Therefore, the clause should list the types of consequential damages being waived to avoid dispute. The second is that while nominally mutual, the waiver really only impacts the Owner because the most significant component of any consequential damages is lost profits. Whereas the damages that the Contractor is waiving, including lost profits, are limited and could be difficult to prove, the Owner’s lost profits – for example, rental income of apartment or office space – could be substantial. The same holds for an Engineer’s contract – although the waiver clause may be mutual, with both parties giving up the right to claim lost profit and business opportunities, the Engineer’s potential damages for an Owner breach will generally be limited. However, the mutual waiver appropriately reflects the risk/reward ratio for the parties.

Mutual Waivers There are no required words that need to be included in a waiver clause, but the clause should be broadly worded to encompass all claims. An example of a commonly used clause is: Engineer and Client waive all consequential damages, including, but not limited to, loss of use, profits, revenue, business opportunity, or production, for claims, disputes,

or other matters arising out of or relating to the Contract or the services provided by Engineer, regardless of whether such claim or dispute is based upon breach of contract, willful misconduct, or negligent act or omission of either of them or their employees, agents, subconsultants, or other legal theory, even if the affected party has knowledge of the possibility of such damages. This mutual waiver shall survive termination or completion of this Contract.

Subcontracts Parties to a contract can only waive their own rights – they cannot waive the rights of others. This is a key issue for subconsultants – while the Prime Consultant and the Subconsultant may agree to waive consequential damages against each other, if the Owner has not waived its consequential damages and the Subconsultant causes a delay, the Prime Consultant would likely be entitled to pass the Owner’s consequential damages down to the Subconsultant.

Conclusion Engineers generally do not have significant potential consequential damages, so agreeing to waive their own damages typically does not pose much risk. However, the Client’s consequential damages that the Engineer could be held liable for will depend on the client, the type of project, and the Engineer’s role (prime or subconsultant). Engineers may want to include a mutual waiver of consequential damages in their contracts as standard practice. Since there is no universally accepted definition of consequential damages, the clause should include a comprehensive list of potential damages. When a contract includes a one-sided waiver (where only the Engineer waives damages), the Engineer should request that the waiver be mutual. If the Client balks at a waiver, this might be a red flag for the Engineer.■ Gail S. Kelley is a LEED AP and a professional engineer and licensed attorney in Massachusetts, Maryland, and the District of Columbia. She is the author of “Construction Law: An Introduction for Engineers, Architects, and Contractors.” (gail.kelley.esq@gmail.com) N O V E M B E R 2 0 21

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INSIGHTS Who Selects Fireproofing? By Charles “Chuck” F. King, P.E., S.E., and Stephen M. Cohen, AIA

ire is the most common devastating event a building can experience. The structural integrity of a building is vulnerable to high temperatures from a fire because steel melts, wood burns, and concrete cracks! Yet, these are the materials structural engineers use to hold up the building. The materials must maintain integrity during a fire long enough to protect the building occupants and allow firefighters to put out the fire. Building codes provide guidance on protecting buildings and occupants from the effects of fire. Architects and engineers apply the code provisions to contain a fire so all occupants survive and safely escape the premises. The codes specify how long a building must resist fire to achieve this goal. So, who drives the decision for the type of fireproofing used to protect the building elements? Both the architect It is a collaboration between knowledgeable and the engineer have a responsibility to provide these solutions. The structure must be protected, and occupants structural engineers and architects to consider the allowed to escape. So, each professional plays a part in tradeoffs inherent to different approaches. specifying the fireproofing in accordance with the code. When the owner identifies the use of the building and the occupancy load, the architect references the fire codes to classify the building and identify where fire containments (separations) are located. The architect plans the egress avoids the need for sprayed-on fire protection to the underside of the routes (stairs, doors, windows, etc.), applying the fire-resistance rating slab. Of course, exposed beams need to be protected, but eliminating for the walls, ceilings, and floor assemblies. The types of assemblies the need for fire protecting the slab greatly reduces cost. The impact are selected and checked against research from fire prevention labora- of this decision is a slight reduction in the floor-to-ceiling height, tory studies such as Underwriters Laboratory (UL). These reference possibly affecting the architectural design. standards provide precise details for achieving fire ratings for walls, Residential buildings are often constructed with reinforced concrete. floors, etc., that are required to comply with fire codes and, when This material provides built-in fire separation, as concrete has excelapplied, must be constructed precisely as shown. The fire ratings are lent fire resistance, eliminating the need for additional applications or based on lab tests conducted on the various assemblies to assess how assemblies. But the flexibility of the structure for future modifications quickly temperatures reach unacceptable levels. is reduced. It is more difficult to cut a hole in a reinforced concrete In some cases, precise assemblies are not practical for various reasons structure than a steel or wood structure. and, still, the building element must be protected per the code. Faced Numerous options are available for protecting structures; each one with this task, the architect and engineer must now collaborate in has advantages and disadvantages. The priorities of the owner drive preparing, reviewing, and approving fire protection details. the choices. What is the dominant function of the building? Who uses For instance, a popular theme in modern office interiors is an industrial it? What is the expected life cycle? These are questions that should look with an exposed structure. The columns and beams supporting the be answered for all elements of a building design process. And, fire building have an aesthetic appeal desired by the architect. These support protection is a significant consideration when decisions are reached. members must be protected without compromising the aesthetics. A Who should specify? It is a collaboration between knowledgeable popular alternative to sprayed-on cementitious fireproofing, in this case, architects and structural engineers to consider the tradeoffs inheris to employ intumescent paint or mastic coatings that are much thinner ent to different approaches. Sometimes a compromise but, in the and allow the structural elements to be expressed. These coatings have end, protection of life and property drives the final decision. The been developed to swell when heated to protect the structure. They wisdom of these decisions is not apparent immediately but instead protect the steel while satisfying the fire rating requirement. years down the road. If a fire occurs, the owner, residents, and the Sometimes the application of fireproofing impacts the gross square public will be relieved that their building protected the footage calculation the developer wants to maximize. For example, occupants and preserved the property so firefighters could enclosing the columns with a fire-rated assembly reduces the square safely extinguish any fire.■ footage and reduces the rental fee the developer can request from the Charles “Chuck” F. King is Vice President with Urban Engineers of New tenants. With a multi-story building, the reduction in rentable space can York, D.P.C., and the Office Manager of the New York City office. have a substantial negative impact on the cost-benefit to the investors. (cfking@urbanengineers.com) Floor-to-ceiling heights can be affected by the choice of floor fire Stephen M. Cohen is a Managing Director of United Building Sciences, protection. The structural engineer may choose to increase the slab LLC, in New York City. (scohen@ubslny.com) thickness to achieve a fire rating dictated by the code. This approach

56 STRUCTURE magazine

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SOFTWARE updates Adhesives Technology Corporation

Hohmann & Barnard

Phone: 754-399-1057 Email: atcinfo@atcepoxy.com Web: www.atcepoxy.com Product: Pro Anchor Design Software Description: This adhesive-anchor-focused design tool aids in meeting design strength requirements of ACI 318. For use with any ATC IBC-compliant anchoring products. Minimized data input time. Rapid 3-D modeling and real-time optimization of loading conditions, embedment depths, anchor sizes, and more. Accommodates threaded rod, rebar, and internal thread inserts. FREE download!

Phone: 800-645-0616 Email: jenniferm@h-b.com Web: h-b.com Product: ProWall Tools Featuring Thermal Brick Support Description: Free software for architects, mason contractors, specifiers, and designers. Easily incorporate Thermal Brick Support (TBS) System design into projects, allowing brick support design that moves the shelf angle away from the wall, reducing thermal transfer. The TBS module in ProWall Tools allows a fast analysis of a brick support design.

Adit Ltd

IDEA StatiCa

Phone: 00-972-77-5020696 Email: office@adit.org.il Web: www.adit.org.il Product: Adit Anchor Software Description: This is a user-friendly software to design post-installed anchors fit to the ENV 1992-4:2018 requirements or following the extended AAS method. It is a free software and available to download at https://files.adit.org.il/setup.exe.

Phone: 856-642-4070 Email: david.eckrote@ideastatica.com Web: www.ideastatica.com Product: IDEA StatiCa Description: Design any type of steel connection from scratch or import it from your analysis or detailing software. Apply simplified or complex loading. Visualize the connection behavior. Generate connection sketches and bill of material in seconds. IDEA StatiCa gets your connection design done for every configuration of steel connections you need.

ASDIP Structural Software Phone: 407-284-9204 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP SUITE Description: Consists of 4 intuitive software packages with over 16 modules to help you with all your engineering design tasks. For the past 28 years, we have developed powerful yet simple-touse tools to easily analyze, design, optimize, and check your structural members.

Bentley Systems, Inc Phone: 800-BENTLEY Email: structuralinfo@bentley.com Web: www.bentley.com Product: Structural WorkSuite Description: Use what you want, when you want it, with our most comprehensive bundled structural software suite. Design in any infrastructure sector, with multiple materials, using any analysis method that is appropriate for the job. Reduce upfront costs, simplify business transactions, reuse data, and leverage the time saving power of interoperability.

ENERCALC, Inc.

ENERCALC

Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: ENERCALC / ENERCALC For Revit Description: ENERCALC has been the musthave software for structural and civil engineers for 39 years. New ENERCALC for Revit simplifies structural design by bridging the gap between calculation and documentation. It gives engineers access to the familiar power of ENERCALC as a seamless, real-time extension of Autodesk Revit with no import/export. STRUCTURE magazine

IES, Inc. Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: IES ShapeBuilder Description: The fastest way to find section properties for any cross section. Calculates shear and torsion properties as well as stress distribution. Reasonable pricing and licensing options. Try ShapeBuilder free today; it is a 2 minute download and setup.

INTEGRITY SOFTWARE, INC. Phone: 512-372-8991 Email: sales@softwaremetering.com Web: www.softwaremetering.com Product: SOFTRACK Description: Use SofTrack to control Bentley Application usage by product code and feature (pipes, ponds, rails). Also control Bentley Passport/Visa usage. Receive idle usage alerts. Seamless operation for local and remote usage including Citrix sessions. Additionally benefit from Automatic Autodesk named-user tracking and reporting.

Losch Software Ltd Phone: 323-592-3299 Email: Loschinfo@gmail.com Web: loschsoft.com Product: LECWall 3 Description: The industry standard for concrete insulated sandwich wall panel design handles multistory columns as well. Analyze prestressed and/or mild reinforced wall panels with zero, partial, or full composite action. Flat, hollow-core, and stemmed configurations are supported. Complete handling analysis is also included. A free 15-day trial version is available.

RISA Tech, Inc. Phone: 949-951-5815 Email: benf@risa.com Web: risa.com Product: RISACalc Description: Web-based software perfect when building a full 3-D model is not required. Analyze single members (beams, columns) of hot rolled steel, wood, concrete, cold formed steel, aluminum, and stainless steel. Intuitive interface makes it easy to set up a model, apply loads, and view results. Check out RISACalc today!

Struware, LLC Phone: 904-302-6724 Email: mail@struware.com Web: www.struware.com Product: Struware Software Description: Updated version of Code Search adds support for the 2021 IBC, wind on solar panels, calculates wind forces at floors, seismic base shear distribution at floors, seismic diaphragm force distribution at floors, and rain loads. Provides pertinent wind, seismic, snow, live, and dead loads in just minutes. Demos on website.

S-FRAME Software Phone: 203-421-4800 Email: info@s-frame.com Web: s-frame.com Product: S-FRAME Analysis Description: An industry standard for over 36 years, analyzes and designs structures regardless of geometric complexity, material type, loading conditions, nonlinear effects, or seismic loads. Integrated concrete, steel, timber, and foundation design ensures your maximum productivity. Our continued R&D investment gives users the latest advantages and dedicated technical expertise.

Trimble Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Tekla Structures Description: Create and transfer constructible models throughout the design lifecycle, from concept to completion. With Tekla Structures, accurate and information-rich models reduce RFIs, leverage models for drawing production, material take-offs, and collaboration with architects, consultants, fabricators, and contractors. Product: Tekla Structural Designer Description: Fully automated and packed with unique features for optimized concrete and steel design, Tekla Structural Designer helps engineering businesses win more projects and maximize profits. From quick comparison of alternative design schemes through costeffective change management and seamless BIM collaboration, Tekla Structural Designer can transform your business.

TE A PD

NCSEA

National Council of Structural Engineers Associations

NEW YORK: FEBRUARY 14-17, 2022 VIRTUAL: JANUARY 31-FEBRUARY 24, 2022

Calling All Structural Engineers for the NCSEA Summit

Reconnect with peers and learn from industry experts at this year’s Summit – in both in-person and virtual formats. Engage in educational sessions on wind loads, embodied carbon, steel design, reinforced concrete, forensics, and more. See the latest and greatest building product and software innovations at the Trade Show. Network with the best in the industry.

Keep up with Industry Innovations at the Trade Show Interact with exhibitors and enjoy lunches, breaks, and a cocktail reception all on the trade show floor, as well as virtual networking and educational opportunities.

KEYNOTE SESSIONS 20 Years After 9/11: Lessons Learned & More to Research

Dan Eschenasy, P.E., SECB, F.SEI; James W. Feuerborn Jr., P.E.; Therese McAllister, F.SEI; Moderated by Vicki Arbitrio, P.E., SECB, F.SE

Lighten Up & Lead: Leverage Levity to Boost Client Confidence & Employee Engagement Tami Evans, Employee Engagement & Levity Leadership Expert

Learn more and register at www.ncsea.com/events/annualconference.

THANK YOU TO OUR SPONSORS

SPOTLIGHT A Face Lift for the Spruce Goose

he Spruce Goose Project consists of the seismic retrofit of an aircraft hangar (250 feet x 740 feet) with two additional side buildings and the erection of new high-end office space within the hangar. The hangar comprises two 125-foot-wide portal frame arch structures with a central spine running down the middle. Arup worked in collaboration with the architecture firm, ZGF, to rehabilitate and seismically upgrade the existing timber building to current code requirements and to create four new levels of office and film production spaces inside the hangars. The existing structure was designed and built in the early 1940s using large glue-laminated arches, considered a new technology at the time. The initial seismic design was based on lateral loads equal to 10% of the self-weight of the existing structure. However, the adaptive reuse of the existing facility to a high-end office required the lateral system to be in full compliance with current building standards. Any retrofit methods needed to be benchmarked against the added self-weight to the existing wooden structure. An increase of more than 5% of gravity load would mandate a code-required gravity system retrofit to current building standards. Retrofitting the exiting gravity foundation system consisting of pile caps with wood piles would be very costly and avoided if possible. The structure is a registered national historic building. Any retrofit measures needed to meet the Army Corps of Engineers requirements of minimal interferences with the visual appearance of the existing building. The retrofit consisted of two main processes: a) the addition of a code-compliant lateral system and b) the repair of any decay or damage in the 70-year-old wood elements.

Integration of Lateral System The design team used Grasshopper scripts to define the curved and tapered geometry of the exiting arches in ETABS and evaluate the capacity and behavior of the arches under nonlinear staged loading and deformation load envelopes. Buckling restraint braced frames (BRBF) were selected as the most efficient solution, and the design team decided to place four BRBF cores spaced equally along the center of the building and connect them to the roof diaphragm. These cores served a dual purpose STRUCTURE magazine

as the lateral system for the existing building and the new office building inside. The new office building is a four-story steel frame structure comprised of BRBFs and sits within the existing structure, offset from the walls and roof by a minimum of 20 feet to showcase the beautiful existing timber structure. The BRBF cores in the spine provide lateral resistance to the existing and the new structure in the The hangar, located in Los Angeles, once housed the famous Spruce Goose North/South direction. airplane and is now the LA headquarters for Google. However, the new and existing structures need additional braces glulam elements. Many of the existing glulam at the perimeter in the longitudinal East/ arches showed signs of small to heavy delamiWest direction. nation. Arup evaluated different retrofit and The team was able to get the Los Angeles repair strategies such as reinforcing steel plates Department of Building and Safety’s approval or plywood sheets, in situ timber gluing, and on the use of multi-tier braced frames dowelling options. (MTBF), which were not codified in the Eventually, 17,000 fully threaded and selfBuilding Codes at that time. The 55-foot-tall tapping screws up to 52 inches in length were and only 11-foot-wide MTBFs were designed chosen to retrofit the original glulam arches. to provide strength and stiffness to work with The screws presented a cost-efficient and easy the flexible timber roof diaphragm. The four installation solution since pre-drilling was not MTBFs along each building side in the east- required due to the self-tapping tip of the west direction purely serve the lateral stability screw. This was the most lightweight solution, of the existing building and were located did not lead to any mandated gravity retrofit, directly in front of the existing sheathed and was the first time these screws were used shear walls to minimize visual impact and in Los Angeles. comply with any visual historic requirements. An overview of each of the delamination A merged ETABS model including the new locations per arch in elevation was used to and existing building’s structure was created streamline the procurement and installato analyze the overall behavior of integrating tion of the screws. In addition, construction the retrofit scheme with the new building. documents included retrofit details and Tension tie rods were designed as part of the schedules corresponding to various delamiretrofit scheme and introduced at selected nation classifications. This allowed the arches at an elevation of 53.5 feet above ground contractor to determine the applicable retroto reduce localized bending overstress in the fit detail in the field by measuring existing glulam arches due to seismic drift com- the delamination depth and using patibility checks in the N-S direction. Arup’s schedules.■ An in-plane steel roof truss was introduced to increase roof diaphragm stiffness and tie Arup was an Outstanding Award the existing glulam arches and the BRBF Winner for the Google Spruce Goose cores together.

Retrofit of the Glue Laminated Arches The final and most critical part of the entire retrofit scheme was repairing the existing

project in the 2020 Annual Excellence in Structural Engineering Awards Program in the Category – Forensic/ Renovation/Retrofit/Rehabilitation Structures > $20M.

N O V E M B E R 2 0 21

NCSEA

NCSEA News

National Council of Structural Engineers Associations

SEE Campaign Seeks to Brand, Market Structural Engineering Profession NCSEA wants to raise awareness of the structural engineering profession’s vital contribution to society. That is why we launched a brand and marketing initiative with the help of Agency McKenna. The campaign’s tagline, We SEE Above and Beyond™, describes the valuable ways structural engineers contribute to the design and construction of built structures and resilient communities. Structural Engineering Excellence (SEE) serves as a guiding principle for the profession. NCSEA President Ed Quesenberry, P.E., S.E. shares, “This campaign is about telling the structural engineering story, from celebrating our role in the Architecture, Engineering, and Construction (AEC) industry to building awareness of the many ways our profession advances and supports the safety and resilience in the built environment. Through telling our story, we hope to build connections with people outside our profession so that we can work together to solve the problems of tomorrow. While the initial campaign will target the AEC industry, future goals of the campaign include outreach and awareness-building with consumers, higher education, and grades 5-12 so the public and students can better understand what structural engineers do and how our work is woven into their lives.” The brand and marketing initiative began its outreach in social media in October with a goal to expand to multiple communication platforms in 2022.

Check out the campaign landing page at www.weseeaboveandbeyond.com, which provides easy access to the campaign messages and key resources. Help spread the word about the value structural engineers bring to the industry by following, liking, commenting, and/or sharing posts on NCSEA social media channels – LinkedIn, Facebook, and Twitter.

Online Symposium

Resilience in a Structural Engineering Context December 1, 8, and 15, 12-1:30 p.m. each day

Resilience depends on the ability of infrastructure to withstand anticipated hazards, the users to recover functionality within a specified time frame, and the community to adapt to changing conditions. Built infrastructure plays a crucial role in community resilience. Buildings and infrastructure need to be designed not just for minimum life safety but also for functional recovery. This symposium presents resilience as a concept and summarizes each of the primary natural hazards. We explore what it means to contribute to community resilience as a structural engineer and consider recovery and safety when designing buildings and infrastructure. Pricing and registration at www.ncsea.com/education.

follow @NCSEA on social media for the latest news & events! 60 STRUCTURE magazine

News from the National Council of Structural Engineers Associations

Structural Engineering Summit – Feel the Love this February The NCSEA Structural Engineering Summit is heading to New York City February 14-17 and online January 31 to February 24 – and structural engineers everywhere will be saying “I Love Structural Engineering” this Valentine’s Day season. Reconnecting with your peers, learning from industry experts, networking with product experts at the trade show – what’s not to love! Register for the conference and learn more at www.ncsea.com/events. The top-notch education slate, keynote sessions, exhibitor lists, and hotel reservation details are all available online.

Special Webinar Series

The Excavation Shoring Design Guide: Temporary and Permanent Earth Retention Design and Construction Aspects November 11 and 18, 12-1:30 p.m. each day A digital copy of the guide is included when you register for both days! This webinar series addresses the design and construction aspects of temporary and permanent earth retention systems. Attendees will review the different elements of each earth retention system and when each method is appropriate. Besides sizing the shoring system’s principal members, the series provides basic construction details necessary to round out complete designs. Pricing and registration at www.ncsea.com/education.

NCSEA Webinars

Pricing and registration at www.ncsea.com/education

November 16, 2021

Retaining Wall Basics

Bill Simpson, P.E.

This webinar provides insight on a variety of retaining wall types and discusses commonly overlooked site issues related to the wall that must not be ignored as part of the retaining wall design. December 7, 2021

MSE Retaining Walls and Global Stability

Bill Simpson, P.E.

Mechanically stabilized earth (MSE) walls are one of the most cost-effective and widely used retaining wall systems in the U.S. today. This webinar discusses all of the design conditions associated with an MSE wall and how to ensure they are properly accounted for during the design process, including the important component of global stability.

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

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

N O V E M B E R 2 0 21

SEI Update Learning / Networking

Fall 2021 Fazlur Rahman Khan Distinguished Lecture Series Honoring a Legacy in Structural Engineering and Architecture Wednesday, November 17, 2021 – 4:30 pm EST A Research Perspective on Seismic Performance of Steel Building Structures Presented by Richard Sause, Joseph T. Stuart Professor of Structural Engineering; Director, Advanced Technology for Large Structural Systems (ATLSS) Center; Director, Institute for Cyber Physical Infrastructure & Energy, Lehigh University The lecture is in-person at Lehigh University and live-streamed via Zoom. Register at www.lehigh.edu/~infrk and view past lectures. The Structural Engineering Institute-Lehigh Valley Chapter will award 1 PDH credit for the lecture to eligible attendees.

Congratulations to the Recipients of the O. H. Ammann Research Fellowship Awarded to encourage creation of new knowledge in structural design and construction. Nicole Buck, A.M.ASCE, California Polytechnic State University Seyedomid Sajedi, S.M.ASCE, University at Buffalo: The State University of New York Wanting (Lisa) Wang, Ph.D., A.M.ASCE, University of Colorado Denver Shanglian Zhou, Ph.D., A.M.ASCE, The University of Alabama

Call for New Members – Nuclear Standards Committee

The ASCE/SEI Nuclear Standards Committee is seeking new members to oversee the development of the next editions of three standards: • ASCE/SEI 1, Standard for Geotechnical Analysis, Design, Construction, Inspection and Monitoring of Nuclear Safety-Related Structures, • ASCE/SEI 4, Seismic Analysis of Safety-Related Nuclear Structures, and • ASCE/SEI 43, Seismic Design Criteria for Structures, Systems, and Components in Nuclear Facilities. The chair for this next cycle is Andrew Whittaker, Ph.D., P.E., S.E., F.ASCE, F.SEI, F.ACI, SUNY Distinguished Professor, Department of Civil, Structural, and Environmental Engineering, University at Buffalo. Practicing engineers, researchers, building officials, contractors, and construction product representatives are all needed and welcome. If you are interested in applying for the committee, please submit an application by December 1, 2021, via the online form at www.asce.org/publications-and-news/codes-and-standards/committee-application-form by selecting “SEI” from Institute drop down and then “Nuclear Standards (ASCE/SEI 1, 4, 43).” Carefully indicate the Membership Category for which you are applying. Associate members can be accepted until balloting begins. Eligible regulatory members can qualify for travel reimbursement per ASCE Travel Policy if that occurs. Contact Jennifer Goupil with questions at jgoupil@asce.org.

Thank you to 2021 SEI Sustaining Organization Members Elite ALFRED BENESCH & COMPANY

Members BOSWELL ENGINEERING HARDESTY & HANOVER SCHNABEL FOUNDATION COMPANY SIMPSON STRONG-TIE WALTER P MOORE

Join SEI as a Sustaining Organization Member to reach SEI members year-round, and show your support for SEI to advance and serve the structural engineering profession. www.asce.org/SEI

Follow SEI on Social Media: 62 STRUCTURE magazine

News of the Structural Engineering Institute of ASCE Advancing the Profession

Complete the Survey

Participate by November 30 in SEI Business Practices Survey on the Impact of COVID-19 on the Profession Relative to Office Practices Are you a structural engineer interested in learning about the state of the industry for working-from-home? Do you have a strong opinion about the long-term viability of remote work? Are you wondering if your local or firm experience mirrors the national one? The SEI Business Practices Committee is doing research to get the facts on what’s working and what’s not in structural engineering offices right now in the virtual environment. Data will be used for educational purposes. Share your experience, and get a FREE copy of the results: https://bit.ly/3kz8bUB.

Now Available

Tier 1 Checklists for Seismic Evaluation of Existing Buildings: Fillable Forms for Standard ASCE/SEI 41-17 In Seismic Evaluation and Retrofit of Existing Buildings, Standard ASCE/SEI 41-17, a three-tiered process is established for seismic evaluation according to a range of building performance levels. Tier 1 evaluation focuses on identifying potential deficiencies in existing buildings based on the performance of similar buildings in past earthquakes. The systematic procedure sets forth a methodology to evaluate the entire building in a rigorous manner. Tier 1 Checklists for Seismic Evaluation of Existing Buildings: Fillable Forms for Standard ASCE/SEI 41-17 is a complete collection of the screening checklists included in Chapter 17 and Appendix C of Standard 41-17. The evaluation checklists, covering a variety of building types and seismicity levels, are offered as fillable PDF forms that can be completed using Adobe Acrobat Reader, version 9.0 or later. www.ascelibrary.org

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

• View recent events on SEI YouTube: https://www.youtube.com/c/AmerSocCivilEng • Structures Congress – April 20-23, 2022 in Atlanta View the program and register at www.structurescongress.org. We look forward to seeing you there! Students and Young Professionals: Apply by December 5 for an SEI Futures Fund scholarship to participate. “I am extremely thankful for the opportunity to engage with industry leaders, practicing engineers, fellow researchers, and other students from around the world at Structures Congress- the experience has been inspiring and insightful.” Jacob Choate, EI, S.M.ASCE; Scholarship recipient; Chair, SEI GSC at University of Oklahoma • Electrical Transmission and Substation Structures Conference – October 2-6, 2022 in Orlando Apply for SEI Futures Fund student scholarship to participate.

Get Involved in your Local SEI Chapter

Check out your local SEI professional or Graduate Student Chapter (U.S. and international) for networking, technical and professional events, field visits, construction tours, scholarships, K-12 outreach, etc. SEI Grad Student Chapters (GSC) engage students, enhancing education and transition to practicing professionals from undergraduate to their first job. www.asce.org/SEI

ASCE Free eLearning Webinars

Whether you are a member or looking to become one, check out free, live eLearning webinars to enhance your personal and professional knowledge. www.asce.org/education-and-events/explore-education/elearning-webinars

Errata

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI. N O V E M B E R 2 0 21

CASE in Point News of the Coalition of American Structural Engineers CASE Tools and Resources Did you know? CASE has tools and practice guidelines to help firms deal with a wide variety of business scenarios that structural

engineering firms face daily. Whether your firm needs to establish a new Quality Assurance Program, update its risk management program, keep track of the skills engineers are learning at each level of experience, or need a sample contract document – CASE has the tools you need!

NEW CASE Publication Released!! CASE Tool 3-6: Career Path Planning

Career Path Planning is an important exercise that all firms should employ to better understand and document the strengths, weaknesses, and seniority of individual staff members and the depth of talent within the firm on a holistic level. This allows the firm to identify future recruiting needs as well as strengths and weaknesses within the current staff. CASE recommends firm leaders undertake the exercise in CASE Tool 3-6 in advance of performance reviews to generate talking points during staff reviews (see CASE Tool 2-3: Employee Evaluations). The tool is designed to help the reviewer provide meaningful feedback to staff members during the review. It can also serve as a mechanism to share future growth plans with staff members to encourage their career growth and serve as a retention tool (see CASE Tool 1-4: Creating a Culture of Recruitment and Retention). At a holistic level, this exercise can help a firm identify future retirements and understand the level of recruitment needed to backfill these positions.

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

And the Scholarship Winner Is... The CASE scholarship, administered by the ACEC College of Fellows, is awarded every year to a deserving student seeking a master’s degree in an ABET-accredited engineering program. Since 2010, the CASE Scholarship program has given over $37,000 to engineering students to help pave their way to a bright future in structural engineering. CASE strives to attract the best and brightest to the structural engineering profession, and educational support is the best way to ensure our profession’s future. The 2021 winner, Celeste Carmignani, is working on a bachelor’s degree in structural engineering from the Colorado School of Mines.

Follow ACEC Coalitions on Twitter – @ACECCoalitions. 64 STRUCTURE magazine

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structural FORUM Acceleration in the Pipeline

A Key Aspect of Changing the DEI Landscape in the AEC Professions By John Gavan, S.E.

s our industry looks for ways to change its landscape of diversity, equity, and inclusion (DEI), many are primarily focused on the upstream end of “the pipeline” and who enters it. While efforts to recruit from and build AEC awareness within our underrepresented communities are of critical importance, we cannot lose sight of the diverse and talented people working alongside us every day. Action is required to ensure they are supported, sponsored, and included in an authentic, meaningful way. Many in our profession look to leaders who do not look like them, leaders whose combined identities, backgrounds, and life experiences do not mirror their own. From the opposite direction, many of our leaders look at their teams and recognize only the valuable qualities they have seen before, overlooking the myriad of leadership traits that have yet to be recognized in our industry. Our profession will not be truly representative and inclusive until many of these talented people become influential decisionmakers and join the ranks of leadership. We should focus on supporting talent while also re-evaluating how we define leadership in order to shift the dynamic of who fills these roles. KPFF offers two specific ideas to share with our industry partners: KPFF has created an Inclusive Culture Training Program which encourages vulnerability, open conversation, and education. The program promotes an inclusive culture that is attractive to the talent we seek and the existing workforce, and generates impact and change in our organization. A post-program survey indicates that 95% of participants have found the content valuable.

The inaugural group included Matthew Trotter, Rachel Bascombe, Janiece Williams, Catherine Hernadez, Chris Locke, Duane Williams, Francesca Carney, David Harrop, Darnell Parker, Morgan Bell, Tunmi Da Silva, (with John Gavan, KPFF) and Tremale Berger.

We also recently participated in the creation of a new Leadership Development Program in collaboration with the Southern California Chapter of the National Organization for Minority Architects (NOMA). Our initial cohort of twelve influential professionals from architecture, engineering, and construction have built their skillset, forged important friendships, and made meaningful connections with leaders in our local industry. We hope this is the beginning of a sustained effort

Our profession will not be truly representative and inclusive until many of these talented people become influential decision-makers and join the ranks of leadership.

to helping diverse talent thrive in our industry and ignite this type of program nationally. When thinking about our entire industry, it is critical that we share our new insights and improve our practices rather than forge these improvements as a competitive advantage against each other. This is especially crucial as DE&I is about making holistic change for an improved future for the profession. Our partners in the construction industry are viewing progress in this arena as akin to progress in construction safety; this is truly a place where a rising tide will lift all boats. We urge others to share their best ideas and practices so, together, we can create a diverse, equitable, and inclusive profession that thrives. We encourage all firms to support industry organizations in their DEI efforts. Keep the conversation at the forefront and contact STRUCTURE magazine to share your perspectives and successes.■ John Gavan is the President and CEO at KPFF Consulting Engineers.

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STRUCTURE magazine | November 2021

Articles inside

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Structural Carbon

Historic Structures

Code Updates

Engineer’s Notebook

Codes and Standards

Structural Systems

Structural Design

Editorial