STRUCTURE magazine | January 2024 by structuremag

STRUCTURE JANUARY 2024

NCSEA | CASE | SEI

CONCRETE

INSIDE: Austin, Texas Court Facility

Concrete Repairs in New Construction 16 Slab-on-Grade for Rack Loads 20 EVs, Design Loads for Parking Garages 36

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EDITORIAL BOARD Chair John A. Dal Pino, S.E. Claremont Engineers Inc., Oakland, 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. Vice President Engineering & Advocacy, Masonry Concrete Masonry and Hardscapes Association (CMHA) 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 Cast Connex Corporation, Davis, CA Evans Mountzouris, P.E. Retired, Milford, CT Kenneth Ogorzalek, P.E., S.E. KPFF Consulting Engineers, San Francisco, CA (WI) John “Buddy” Showalter, P.E. International Code Council, Washington, DC Eytan Solomon, P.E., LEED AP Silman, New York, NY

On the Cover: The courthouse’s architectural concept provides an equilibrium between openness and safety while also integrating the local community.

Jeannette M. Torrents, P.E., S.E., LEED AP JVA, Inc., Boulder, CO

Photo Courtesy of Andrea Calo.

Executive Editor Alfred Spada

EDITORIAL STAFF aspada@ncsea.com

Managing Editor Shannon Wetzel swetzel@structuremag.org

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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 31, Number 1, © 2024 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.

JANUARY 2024

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Contents Cover Feature

10 COURT ADJOURNED By Kyle Dunning, P. E., LEED Green Associate

After nearly 100 years of operation, the Herman Marion Sweatt Travis County Courthouse, constructed in 1931 in Austin, Texas, was in dire need of replacement after falling into disrepair. The building was unable to support the growth of its constituents.To replace the aging courthouse, Travis County formed a public-private partnership as a design-build project to construct the Travis County Civil and Family Courts Facility. The new courthouse is a 12-story, 448,000-sf structure located in downtown Austin and includes 25 courtrooms, with a single level, below-grade garage.

JANUARY 2024

Columns and Departments 7 Editorial Revisiting the Future of Engineering By Bruce Burt, P. E., P. Eng.

30 Engineer’s Notebook ChatGPT in Structural Engineering By Stephanie Slocum, P. E.

48 Business Practices Why is Legal Advice About Contracts Like Cockroaches and Twinkies? By Karen Erger and Eric Singer

8 Structural Influencers Ron Klemencic, P. E., S. E., F. SEI, F.ASCE, NAC, NAE, Dist. M. ASCE, Hon. AIA

34 Engineer’s Notebook Code Compliance for Cold-Formed Structural Steel Systems By Natasha Zamani, Ph. D., P. E.

16 Structural Systems Use of FRP and FRCM Systems in Repair of New Construction By Kevin Goudarzi, P. E.

36 Insights Engineering Infrastructure to Support Societal Resiliency

50 Code Updates 2024 IBC Significant Structural Changes By John “Buddy” Showalter, P. E. and Sandra Hyde, P. E.

55 Historical Structures 19th Century Mississippi River Bridges By Dr. Frank Griggs, Jr.

By James McDonald, S. E., Joseph Moody, S. E., Michael Perkins, S. E., and Molly Pobiel, P. E.

20 Structural Design Design of Slab-on-Grade for Rack Loads By Rafik Gerges, S. E., Ph. D., Vinay Teja Meda, M. S., and Weian Liu, Ph. D., S. E.

40 Structural Design Design Considerations for Aluminum Structures In South Florida By Antonio De Luca, Ph. D., P. E., S. E., Lauren Millman,

24 Anchoring to Concrete Shear Concrete Breakout Calculations for Anchorages With Multiple Rows By Richard T. Morgan, P. E.

28 Infocus Engineering a Better Work-Life Fit By Erin Conaway, P. E., LEED AP and Rachel Mosier, P. E., Ph. D.

Ph. D., P. E., Derek A. Wassink, P. E., R. A., S. I., STS2, and Matthew J. Olender, P. E., S. I.

46 Structural Forum Importance of Hand Calculations and Rules of Thumb in the Artificial Intelligence Age By Ciro Cuono, P. E.

58 Structural Observations Unwanted Vibration in Structures By Jibreel Mustafa and Craig E. Barnes

66 Codes and Standards FAQ on SEI Standards By Jennifer Goupil, P. E., F. SEI, F. ASCE

In Every Issue 3 Advertiser Index 60 NCSEA News 62 SEI Update 64 CASE in Point

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, the Publisher, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions. STRUCTURE magazine is not a peer-reviewed publication. Readers are encouraged to do their due diligence through personal research on topics. JANUARY 2024

EDITORIAL Revisiting the Future of Engineering By Bruce Burt, P. E., P. Eng.

ASE, NCSEA and SEI have embarked on an update to their jointly prepared Vision of the Future of Structural Engineering. Having just re-read the previous statement released in May of 2019, I am struck by the number of developments that just four years later are reshaping the engineering profession. Many of these issues have been trending for a decade or more, but have gained an increased sense of urgency over the past four years. If you’ve been reading STRUCTURE Magazine, the topics will be familiar: climate change; diversity, equity, inclusion (DEI); an inadequate talent pipeline, changes in structural engineering licensure; artificial intelligence; the evolving built environment; resiliency and sustainability. A comprehensive vision of the future of structural engineering must consider all these challenges. To create an aspirational vision of the future, it is helpful to consider current efforts to address these issues. The engineering community, with contributions from NCSEA, SEI and CASE, are confronting these challenges. Climate Change. There may be no more controversial or discussed topic than climate change. Climate targets are in jeopardy; the effects of climate change, though potentially devastating, are not precisely known. Engineers designing structures with 50-year or greater lifespans need guidance in addressing the current and future needs of their clients and to meet their standard of care. Is a design based on current codes sufficient if sea levels rise as predicted, or if extreme weather events occur with greater frequency than those on which existing codes are predicated? ASCE 7-22, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, has been updated to protect against 500-year floods, rather than the 100-year flood hazard referenced in the 2016 edition. CASE is in the process of updating its suite of contracts for structural engineers, and is incorporating language that will clarify the responsibilities of the engineer for designing beyond current minimum code requirements. The Structural Engineers 2050 Commitment Program, SE2050 for short, is an SEI-led initiative to reduce embodied carbon emissions through the use of more efficient materials. The aims of the program are to educate the structural engineering profession on best practices for design and construction, engage in a carbon STRUCTURE magazine

tracking program, report on impacts and trends of various structural systems, and advocate on behalf of clients, the design community, and the public, all with the goal of achieving net zero embodied carbon emissions by 2050. Diversity, Equity & Inclusion. NCSEA’s Structural Engineering Engagement & Equity (SE3) Committee has developed a series of webinars that discuss ways to develop “multicultural organizations via inclusive policies, programs and practices.” Webinars are available on NCSEA’s website that deal with bias awareness, improving STEM programs and improving the structural engineering talent pipeline. Fostering an inclusive environment within engineering firms is a critical step in providing wider opportunities. However, more opportunity will not in itself address DEI challenges, nor the talent shortage facing the engineering profession. Addressing the diversity issue requires further investment in STEM education and building greater awareness of engineering as a career path at the earliest stages of children’s development. One goal of NCSEA’s WeSEE promotional campaign is to raise awareness of structural engineering as an attainable, rewarding career path. Structural Licensure. Changes are taking place in structural engineering licensure. The format of the PE Structural Engineer Exam has changed. The SE exam is the last of the engineering exams to be converted to a computer-based test. As of April 2024, the exam will have four sections with a total exam time of 21 hours, in contrast to the previous two-part, 16-hour paper exam. The Structural Engineering Licensure Coalition (SELC) is a partnership of SEI, NCSEA and CASE established to promote a common position on structural licensure and to work towards SE licensing in all U.S. jurisdictions (there are currently sixteen states with some form of SE license requirement). The SELC has taken the lead in educating SE-aspiring engineers on these changes. The SELC is also in the process of updating its Significant Structure Model Recommendations, first adopted in 2019. The intent of this document is to identify the types of structures that should be designed under the responsible charge of a Licensed Structural Engineer. Artificial Intelligence. Rapid advances in artificial intelligence will soon cause fundamental changes in the way the typical design firm

conducts business. Among its many potential benefits, AI promises to improve design optimization through generative design and more efficient methods of structural analysis. Proposals, specifications, and reports can be developed more quickly and efficiently with the aid of AI. Increased productivity resulting from the appropriate use of AI could help resolve the talent shortage. However, for the foreseeable future the liability for the accuracy of AI-generated material will remain in human hands. Other risks, such as infringements in confidentiality and intellectual property, must be considered. Evolving Built Environment. The global pandemic greatly accelerated societal change. Remote work became commonplace, reshaped the workplace, and disrupted office building markets across the U.S. As leases expire and tenants downsize, it very likely will require repurposing many of the buildings comprising our urban and suburban communities. Other factors will also help transform the built environment. ASCE’s Future World identifies six trends: autonomous vehicles, climate change, smart cities, advanced materials, and policy and funding. Mega City 2070 is ASCE’s second iteration of an envisioned future city. Resiliency and Sustainability. In 2023 ASCE, in partnership with ACEC and APWA (American Public Works Association), released ASCE/COS 73-23: Standard Practice for Sustainable Infrastructure. This non-mandatory, performance-based consensus standard targets civil infrastructure and “provides guidance for infrastructure owners to develop and implement sustainable solutions through a project’s entire life cycle.” The standard also focuses on reducing embodied carbon. A new generation of structural engineers, using new methods, new technologies and new materials will play a crucial role in reshaping our built environment. Updating the Vision of the Future of Structural Engineering offers an opportunity to provide insight and guidance in this time of change and challenge. Then sometime in the near future our rapidly changing world will necessitate another reappraisal.� Bruce Burt, P. E., P. Eng., is a Senior Principal at Ruby+Associates, a Degenkolb Company.

JANUARY 2024

structural INFLUENCERS Ron Klemencic, P. E., S. E., F. SEI, F. CTBUH, F. ACI, NAC, NAE, Dist. M. ASCE, Hon. AIA Ron Klemencic is Chairman and CEO of Magnusson Klemencic Associates (MKA), an award-winning structural and civil engineering firm headquartered in Seattle, Washington. An industry innovator and preeminent practicing structural engineer, he is recognized for his creativity, “big picture” approach, and ability to produce cost-effective designs. Ron has been involved in the design of tall buildings around the globe, including San Francisco’s Salesforce Tower; Chicago’s St. Regis, 150 North Riverside, and Aqua; and Seattle’s Rainier Square. In addition, he has led the research and development of industry-advancing innovations, including SpeedCore and Performance-Based Seismic Design. He is also a Director of the Charles Pankow Foundation and the MKA Foundation. Ron’s distinguished career has been marked with numerous honors, with some of the most recent including induction into the National Academy of Construction (NAC) and the National Academy of Engineering (NAE), being appointed a Distinguished Member of the American Society of Civil Engineers (ASCE), and being named an ASCE/Structural Engineering Institute (SEI) Fellow. He is a member of the UC Berkeley Civil and Environmental Engineering Department’s Academy of Distinguished Alumni. He received the Distinguished Engineering Alumni Award and Civil Engineering Alumni Achievement Award from Purdue University. The following is STRUCTURE Editorial Board Chair John Dal Pino’s interview with Klemencic. My first experience with Magnusson Klemencic Associates (then called Skilling Ward Magnusson Barkshire) was on 100 First Street in San Francisco, when I met John Skilling. There were significant cost savings with custom steel sections fabricated in Korea and containers of steel arriving at the site for assembly. What does that say about innovation at MKA, then and now? Our firm has a 104-year history of challenging the norms, pushing boundaries, and thinking creatively. These traits are embedded in our culture. In fact, our firm’s mission statement is “Always Striving for Better,” which sums up our collective motivation and approach.

Would you mind describing how you got to where you are at MKA and what aspiring young engineers can learn from your experiences? My career path has been fueled by an insatiable appetite to learn. I constantly seek to understand “why” things are the way they are, which often reveals opportunities to think differently. I am immensely curious and tenaciously competitive—always striving for better. Applying math and science to solve engineering problems simplistically and elegantly always trumps elaborate computer analysis and complicated spreadsheets. The best engineering occurs at the intersection of art and science.

Innovation is a result of culture. Not top-down or bottom-up. As recognized innovators, how do you motivate the staff? Primarily by encouraging them to always question everything. The best ideas can come from anyone and at any time. Working together daily, in person, in our single office in Seattle fosters these opportunities. 8 STRUCTURE magazine

Ron Klemencic. Photo courtesy of Magnusson Klemencic Associates (MKA).

Most companies tend to expand with many branch offices. You have resisted that tendency. What benefits does that offer the firm and its staff? Through our daily, in-person collaborations in a single office, we can accelerate training, avoid costly mistakes, and inspire each other by combining and leveraging our individual skills and expertise. In addition, there is a high degree of camaraderie amongst the employees, resulting in staff longevity.

Every firm strays from its core mission from time to time. Would you cite a good and bad result and what you learned? With 104 years of company history, MKA benefits from the lessons learned of yesteryear, and we are very disciplined in our commitment to our core values and strategies. Occasionally, questions arise and challenge our thinking, but we have remained steadfast in our commitment to what we do and how we do it. One example that comes up with some regularity is the question of opening additional offices in other cities or locations. At one time in our firm’s history, we had five offices. We learned from that experience that (a.) the remote office may not be as skilled as the home office, and the firm’s work product and reputation suffer, and (b.) the remote office may grow to be as strong as the home office, ultimately leading to competition amongst offices. Neither of these scenarios is attractive to us. As such, we maintain a single office in which we can collaborate daily, delivering a consistent and reliable work product.

Most CEOs drift away from doing projects. But you are clearly involved in SpeedCore. What does that say about you and your company? At MKA, the most senior leaders still do the work. We are passionate about contributing to the creative process and providing our clients with consistency, reliability, and creative thinking. With senior leadership intimately involved in the daily engineering tasks, it limits the number of projects we can take on, but we are good with that. We believe in quality over quantity.

MKA was an early leader in Performance-Based Design (PBD) for seismic and wind loads. Where is PBD going to take the profession in the future? Prescriptive codes have become increasingly oppressive, often hindering creative thinking or, worse yet, fundamental engineering thinking. PBD methods unlock code-imposed handcuffs, allowing engineers to use their skills and creativity to design more efficiently, effectively, and with substantially reduced embodied carbon.

Ron Klemencic and Jon Magnusson. Photo courtesy of Luke Abaffy.

Your tall buildings have pushed “the limits” in many aspects. How have you been successful in demonstrating “code compliance”? Over the last 20 years, Third Party Peer Review has become essential to the review and approvals process. Most Authorities Having Jurisdiction (AHJs) are open to such a process, and these reviews have proved invaluable. Better designs have resulted, and the state of our practice has advanced through interactions between the Engineer of Record (EOR) and the Peer Reviewers.

Engineering can seem a little on the humdrum side to many. Without giving away any secrets, what do you think the next big thing will be? We are working on several “next big things.” Most exciting are our advancements with Performance-Based Wind Engineering, embodied carbon reduction, and a modular, prefabricated allsteel floor system that will accelerate construction schedules by upwards of 30 percent.

I think most engineers would agree that current prescriptive code provisions limit innovation and waste engineering fees. If you could eliminate some code provisions, which ones are at the top of your list? 1. Response modification factors for seismic design. 2. Redundancy Factors 3. Torsional Amplification Factors 4. Any other artificial factors that attempt to “simplify” what we can investigate and quantify. Mentorship has been and continues to be a huge topic of discussion. How do you approach it? Would you like to recognize a mentor of yours? Mentorship is about availability and engagement. Mentorship should be driven by the personal choices of the mentee and cannot effectively be forced. Taking the time to engage with thoughtfulness, interest, and care is the most effective approach. Over my career, I have had several mentors, but none more important than Jon Magnusson. Jon has taught me so much about engineering, running the business, and life in general. Words cannot express adequately my gratitude.

In terms of skills, what should future engineers focus on? Think! Don’t fall into the trap of mindlessly following prescriptive building code requirements or relying too heavily on computer analysis, especially the allure of artificial intelligence. Instead, strive to apply “real intelligence,” for it is only through thought leadership and collaboration with others that new innovations will be discovered.

On a personal and a professional level, two separate things, what would you like to be remembered for? Personally, I would like to be remembered as someone who cares deeply about all those around me, particularly my family. Professionally, I would like to be remembered as someone who contributed to advancing our profession in a positive and collegial manner.

Ron Klemencic during Charette. Photo courtesy of MKA.

If you weren’t a structural engineer, what would you be doing? Teaching and growing vegetables. JANUARY 2024

Court Adjourned Travis County Civil and Family Courts Facility in Austin, Texas, uses P3 to construct new building with option to expand. By Kyle Dunning, P. E., LEED Green Associate

fter nearly 100 years of operation, the Herman Marion Sweatt Travis County Courthouse, constructed in 1931 in Austin, Texas, was in dire need of replacement after falling into disrepair. The building was unable to support the growth of its constituents. To replace the aging courthouse, Travis County formed a public-private partnership (P3) as a design-build project to construct the Travis County Civil and Family Courts Facility. The new courthouse is a 12-story, 448,000-sf structure located in downtown Austin and includes 25 courtrooms, with a single level below-grade garage. The adjacent plaza is comprised of five levels of below-grade parking topped with a green roof. Design of the structure began in the summer of 2018 and the project was completed in December 2022. The project has received an Austin Energy Green Building 4 Star Rating (out of 5 stars maximum) and a LEED Gold designation. From the onset, the new courthouse site had a bevy of challenges. For example, there is a 12-foot grade differential from west to east. Therefore, the new courthouse rests on a podium that spans the length of the entire block it occupies. The lower level occupies the podium immediately beneath the building and includes the secured parking area for judges, the MEP rooms as well as additional building support. The west half of the podium below the plaza includes the five levels of below-grade public parking. The green roof above the public parking garage features a landscaped public plaza with elevator banks to service the parking below. More importantly this portion of the podium was also designed to serve as the structural support for a future 14-story office building. Another challenge to the design and construction of the facility was adhering to the fast-track schedule, which included achieving the building permit and accurate guaranteed maximum price with minimum contingencies within nine months. The development team closed an alley, condemned a holdout parcel, rezoned the site, and achieved the site permit with an extraordinarily complex utility in less than nine months through its partnership with the county. In addition, the team managed approximately $6 million in savings from contingency and incorporated scope changes needed by the county beyond the design criteria through the savings with minimum disruption to the schedule, according to Rodney Moss, senior vice president at Hunt Companies.

The design of the Travis County Civil and Family Courts Facility in Austin, Texas, was intended to evoke a sense of calm for visitors and presents itself as an approachable facility. Photo courtesy of Andrea Calo.

Light-filled and airy interiors can be found throughout the new courthouse. Photo courtesy of Andrea Calo.

Furthermore, communication amongst all the building team members was key because the tiebacks were extended below the roadway as there were below grade utilities that could not be disrupted. This was achieved through meetings with the Austin Utility Coordination Committee, to ensure there was no conflict between the utilities and the tiebacks. Within the site, the tiebacks for the garage extend under the building’s concrete foundation to ensure there was not a conflict, according to Ash Bajaj, project manager at Hensel Phelps. The Travis County Civil and Family Courts Facility’s is primarily a concrete structure with precast concrete panel façade walls. The structure is supported by drilled piers that are set at a depth of 18 feet below grade and extend into the stiff Austin Group Limestone below. The piers located adjacent to the sub-grade parking garage were drilled even deeper, up to 40 feet, so as to not impact or interfere with the supports for

Structural Engineering Design Walter P Moore, in concert with Martinez Moore Engineers, provided structural engineering design for the Travis County Civil and Family Courts Facility. The firm also provided secure design services that included vehicle barrier and site securing consulting. Specifications were prepared for fixed and operable barriers rated for vehicle impact. One challenge related to secure design was the provision of K4-rated operable wedge barriers located on an elevated level, so the structural floor system was designed to support forces developed under vehicle impact. This barrier system was located on a split slab, in order to waterproof the occupied space below grade, which required a close examination to provide adequate support without excessive depth. To achieve this, a 14-inch-thick elevated concrete slab acted as the base for a 6-inch-thick topping slab, set on top of a drainage layer, which was doweled into surrounding beam at the perimeter. The wedge barrier was then anchored to the 6-inch slab.

Structural Characteristics Multiple aspects of a design-build project occurring concurrently is not surprising, and the Travis County Civil and Family Courts Facility was no exception as the foundation for the tower was being poured at the same the five-story parking garage was being excavated. To ensure both were constructed safely and efficiently, tiebacks were used as the retention system during the excavation of the foundation. Careful coordination was critical during the foundation excavation of both the tower and the garage as the tiebacks and the tower foundations had to be placed precisely to ensure there were no conflicts between the two. 12 STRUCTURE magazine

Because there is a 12-foot grade differential from west to east, the new courthouse rests on a podium that spans the length of the entire block it occupies. Photo courtesy of Walter P Moore.

the garage which were over 45 feet below the basement level of the courthouse. A mat and pier caps that support shear wall banks were placed as part of the foundation in order to support the main elevator bank as well as the service elevator. The shear walls operate as a lateral support system for the structure. Additionally, the basement walls for the tower’s single-story garage are integral to the support of the complex framing, including all of the planters and stairs, at the first floor. Because some of the courtrooms needed unobstructed space, a pan formed beam system with post-tensioned girders was used throughout the structure. This provided an opportunity to design bays that measured up to 40x45-feet. The 25-inch deep, 7-inch-wide pan formed beams were typically spaced at 53 inches clear and spanned up to 40 feet to reach 25 feet deep, 42-inchwide post-tensioned girders. The five-story below-grade parking garage required a large amount of excavation before

The steel staircase that offsets a two-story stone clad wall in the courthouse’s main lobby underwent a vibration analysis to ensure the comfort and strength requirements outlined in AISC Design Guide 11 were met. Photo courtesy of Andrea Calo.

The courthouse’s architectural concept provides an equilibrium between openness and safety while also integrating the local community. Photo courtesy of Andrea Calo.

construction could commence. The piers in the garage were drilled much shallower, only 8 feet, in comparison to those used for the courthouse building due to the deep excavation into the rock. The lateral system utilized for the garage is a combined moment frame and shear wall system with the ability to add additional shear walls through the basement levels for when the 14-story building is eventually constructed. Form savers were added to the several columns as well as sleeves in the slabs that would allow for the future walls to be added. In order to reduce restraint, the basement was detailed so that it is only tied into the perimeter walls at the middle bay in each direction. This method required the columns to be offset from the basement walls and then the perimeter beam framing utilized bond breakers except at the tied in bays. Typically, there is a 5-in. slab on pan forms below grade, but the depth of the slab was increased to 6-1/4 in. with deeper pans underneath the first floor of the garage due to the extensive landscaped areas as well as the loading bays. One thing that further complicated for the garage were the slab slopes required to drain water underneath the landscaping. Ultimately, Gensler developed a landscape model in Revit in order to provide the accuracy required for both design and construction. The green roof on top of the garage includes a small pavilion at one end with a stage on one side and elevators and staircases for the garage on the opposite side. Several planters and trees are located throughout the greenspace. The greenspace is open to the public and is accessible from three different sides of the property. Staggered every two levels in the tower, secure terraces with greenery and outdoor seating provide a soothing environment in which to decompress, according to Luis Santi-Merayo, principal and design director at Gensler. This facility boasts a unique feature wherein it offers access to the outdoors from the waiting areas past security. However, it is also the site where joyful events take place JANUARY 2024

The green roof on top of the garage includes several planters and trees throughout the greenspace, which is open to the public and is accessible from three different sides of the property. Photo courtesy of Walter P Moore.

such as adoptions and weddings. The facility aligns very well with the spirit of Austin and blends nicely with the skyline. The site encourages community engagement, featuring spacious sidewalks, pedestrian benches, bike racks, and a public community plaza, all easily accessible by foot, bus, and bike.

Interior Design The interior design of the courthouse includes a large main entry that has a monumental steel staircase offset a two-story stone clad wall in the main lobby. A vibration analysis was conducted on the stair using an imported forcing function in SAP to ensure all comfort and strength requirements, as outlined in AISC Design Guide 11, were met. The stair design was further complicated by the shared structural support framing with the nearby stone wall, which required deflections to remain under L/600. Besides the lobby, the stone clad walls are also present throughout the building, including the courtrooms, providing a cohesive, elevated design that was not limited to the main entrance. The design of the Travis County Civil and Family Courts Facility was approached with a hospitality mindset that include light-filled, airy interiors and multiple outdoor spaces. The overall design evokes a sense of calm for visitors, many of whom are involved in stressful situations. Overall, the facility exceeded the county’s vision both in terms of scope and delivery method. The delivery method allowed the 14 STRUCTURE magazine

county to make cost effective decisions throughout the process. This included a fully dual piped reclaim water system to substantial enhancements, designing the structure and systems for a future adjacent building, and changing building technology to enhance building security, enable remote trials and hearings, and minimize building occupancy. The result is a building that adds energy and dynamism to the streetscape and presents itself as an approachable facility.�

Project Team Owner: Travis County Courthouse Development Partners, Austin, Texas Structural Engineer: Walter P Moore & Martinez Moore Engineers, Austin, Texas Architect: Gensler, Austin, Texas General Contractor: Hensel Phelps, Greeley, Colorado Developer: Hunt Companies, El Paso, Texas Co-Developer: Chameleon Companies, Austin, Texas Courthouse Designer: CGL Companies, Miami, Florida

Kyle Dunning, P. E., LEED Green Associate, is a Principal at Walter P Moore. He can be reached at (kdunning@walterpmoore.com).

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structural SYSTEMS Use of FRP and FRCM Systems in Repair of New Construction How FRP and FRCM systems can be alternatives to traditional strengthening and repair methods. By Kevin Goudarzi, P. E.

he construction industry is constantly llooking to innovate, research and improve its materials and technologies in pursuit of a sustainable future. Carbon fiber reinforced polymer (CFRP) is used primarily in the strengthening and rehabilitation of structures (Fig.1). This article highlights the use of fiber reinforced polymer (FRP) and fiber reinforced cementitious matrix (FRCM) in the repair of new construction projects.

Reasons for Repair in New Construction Load rating upgrade Several reasons that can cause the change in the loading system includes increasing live loads, installing new equipment, and change of use or building performance. Figure 1 Column wrapped and strengthened with carbon fiber reinforced polymer (CFRP). For example, converting a building that was designed for residential load into a commercial space like a shopping center structural issues can lead to necessary repairs. or parking garage is an example of change of use and increasing Design changes during construction could also necessitate live loads. Also, changes to mechanical units installed in a build- repairs or strengthening of the structure. For instance, changing ing may apply new loads and can require repair or strengthening the bathroom location can change the drain hole locations and of the structure. making new holes in a concrete slab may cut the embedded reinforcement requiring slab strengthening to compensate for Damage a reduction in structural capacity from the cut reinforcement. Damage that can make repair necessary include vehicle or crane impact, fire, and blast. For example, trucks that transport materials like gravel, soil, concrete, etc. can impact the structure and cause damage to the new building. A miscalculation of the loads for selecting the proper crane for the project, or wind damage to the tower cranes, can cause serious damage to new construction projects. Fire can occur during welding or any torch applications. Blast damage could result from improper storage of chemical materials or terrorism attacks.

Environmental issues Environmental issues such as rain, snow or temperature can affect the quality of concrete which may lead to a structural repair in a new construction project.

Design If structural elements are undersized due to improper design, structural deficiencies like deflections can result during new construction or after completion when all loads are applied. These 16 STRUCTURE magazine

Construction Issues Poor construction can cover many items that a contractor can miss or perform improperly, including layout errors, inadequate forming and shoring, overloading the structure during construction, and low concrete strength. Missing or improper placement of rebars or PT cables in a concrete slab, poor quality concrete, and large width cracks are examples of poor construction (Fig.2). Mistakes with structural members such as incorrect concrete column or beam dimensions/sizing or inadequate shoring to support the concrete slab or beam, could lead to excessive deflection that needs repair during the construction process. Storing construction materials on the structure may overload the structure and cause excessive deflection and damage. If the placed concrete strength is below the design strength, major collapse or partial structural failure can occur which makes a structural repair necessary. Other issues could be from the excavation and foundation stage to final completion of the project. Construction errors in the foundation stage may indicate cracks or settlement during construction and after the building is complete. Poor welding in steel structures can require structural repair.

Figure 2 Lack of shear rebar and concrete cover at column.

Fiber Reinforced Polymer (FRP) FRP systems have been used to strengthen and retrofit concrete structure since the mid-1980s. FRP systems were developed as alternatives to traditional external reinforced concrete strengthening techniques, such as steel or concrete jacketing methods. Fiber reinforced polymer (FRP) is a composite material consisting of fiber and polymer. The fiber is made of carbon, glass or Aramid, with carbon the most commonly used in structural retrofitting and strengthening. Fiber provides the strength and stiffness while the polymer acts as cohesive matrix to protect and hold the fibers together. FRP is used for reliable and highperformance structural strengthening systems. FRP systems are widely used for strengthening of dynamically and statically loaded buildings and other structures, providing long-term durability in service. FRP is manufactured as strips, bars and sheets to apply on concrete, steel and masonry surfaces. The structural elements that FRP could be applied are columns, beams, slabs, walls, piles and pier caps (Fig.3). FRP is applicable to many types of structures such as tunnels, pipes and mines, tanks, silos, chimneys, parking garages, bridges, piers, wharfs and commercial and industrial buildings. There are many advantages for using FRP systems as a structural repair or strengthening solution. FRP materials are lightweight materials and ideal for vertical and overhead applications. The repair and strengthening of structures are performed by using a thin layer of material. FRP systems have very low aesthetic impact and conform to existing shapes, have extremely high tensile strength, and has ease in installation. FRP features Figure 4 FRCM versus FRP.

Figure 3 Slab reinforced with CFRP.

excellent chemical and corrosion resistance and the shipping of these materials is nonhazardous. Structural strengthening by FRP is a cost-effective solution and can be performed on concrete and steel structures. Prestressing of FRP is possible in the field if needed and is compatible with many finishes and protective coatings. Like other materials, FRP systems have some disadvantages. FRP does not perform under elevated temperature. High temperatures can cause failure in the epoxy and the FRP matrix. FRP can be affected by ultra-violet (UV) radiation in areas exposed to sun such as bridge columns. The behavior of FRP systems under load is linear elastic to failure which means it does not indicate any sign like deflection before the failure occurs, and the failure mode is sudden without previous notice.

Fiber Reinforced Cementitious Matrix (FRCM) FRCM have been used in Europe the past decade and is now emerging in the United States. This system is like FRP, with the difference that FRCM is applied by cementitious material

JANUARY 2024

Figure 5 FRCM - Phenylene Benzobis Oxazole (PBO) material.

Figure 6 Traditional shotcrete repair (left) vs. FRCM shotcrete repair (right).

in lieu of polymer in the system (Fig. 4). FRCM wrap material could be Phenylene Benzobis Oxazole (PBO) or carbon (Fig. 5). FRCM can also incorporate a carbon grid in a shotcrete application which is thinner than the traditional shotcrete repair (Fig. 6). ACI 549.4R-13 is available as a guide for the design and construction of externally bonded fabric-reinforced cementitious matrix (FRCM) systems for repair and strengthening concrete and masonry structures. FRCM composites have significantly different properties than FRP composites. Mineral mortar used as a matrix is not able to provide good coverage of all fibers versus epoxy resin and causes a slip phenomenon and telescopic effect, and a more ductile nature of the composite. The failure usually occurs as a result of debonding of the composite in the mortar-fiber layer. Due to the nature of the work, the appropriate anchorage of the composite is an important element in strengthening with FRCM composites. Anchorage delays the debonding of the composite and increases load capacity of the element by engaging the mesh properties. The bond strength of FRCM to the substrate material is difficult to quantify as it depends on the type of fibers, fiber sizing, mesh layout, composition of the matrix, substrate properties, and quality of the surface preparation. Unlike FRP, the FRCM fibers are not impregnated; therefore, pulloff tests on concrete substrates typically show the failure within the fabric reinforcement or at the fabric-matrix interface. FRCM has advantages compared to FRP systems. FRCM does not require a dry substrate and works well on damp substrates. FRCM has more resistance to fire than FRP, as it is not affected by high service 18 STRUCTURE magazine

temperature. In most cases, FRCM does not require fire protection. FRCM creates a breathable matrix and is not affected by UV rays.

Conclusion FRP and FRCM systems are being used in the repair of structures in both new construction and existing structures as an effective strengthening technology. Due to their thickness, durability, performance, conformity to existing shapes, corrosion resistance, ease of installation etc, FRP and FRCM systems are great alternatives to traditional strengthening and repair methods and can provide an excellent solution for strengthening of concrete and masonry structures.� This article is a reprint of the article that ran in CRB Bulletin of ICRI in September 2020.

Full references are included in the online version of the article at STRUCTUREmag.org. Kevin Goudarzi, P. E., is a Forensic Structural Engineer at EFI Global in Chantilly, Virginia. Kevin has been serving for three years on the Board of Directors of the ICRI Baltimore/Washington Chapter and chairs the chapter's Industry and Community Outreach Committee and is a member of ASCE.

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Structural DESIGN Design of Slab-on-Grade for Rack Loads Streamlining the design process for slabs-on-grade that support heavy racking loads. By Rafik Gerges, S. E., Ph. D., Vinay Teja Meda, M. S., and Weian Liu, Ph. D., S. E.

lab-on-grade (SOG) is a very important structural component for an industrial facility as it directly supports the building racking system and its loads. The rack loads are influenced by various factors, including pallet weight, pallet height, building clear height, and seismicity. Rack loads act as point loads in both downward and upward directions. Design and analysis of the slab is typically done by numerical modeling and finite element analysis, which is time-consuming and not easy to perform. In this article, a quick and easy design tool is developed based on a parametric study of buildings with different pallet weights, seismicity, and slab thickness and regression analysis of a cluster of data. From this quick lookup tool, it becomes very easy to estimate the slab’s capacity in terms of pallet weight, given the slab thickness and seismicity. Moreover, an adjustment table is developed to calibrate the results of buildings with different clear heights. This tool, combined with the adjustment table, helps the design team and/or owner make a quick decision in terms of building racking functionality at an early stage.

Figure 1 Coupled racking system layout for a typical industrial warehouse.

Warehouse Racking System For an industrial warehouse facility, the main functionality is to store goods and materials, which are typically kept on small platforms called pallets. A typical pallet is 42 inches by 48 inches. They are either placed directly on slab-on-grade (SOG), which is called a bulk storage system or placed on metal rack systems, which is called a palletized racking system. Typically, palletized

Figure 2 Pallet utilization efficiency for different building clear heights.

20 STRUCTURE magazine

racking systems are the preferred approach for storing merchandise in distribution facilities. The typical down-aisle dimension (in the longitudinal direction) of these racks is 8 feet, and the cross-aisle dimension (in the transverse direction) is 4 feet. The racking frame is typically continuous in the longitudinal direction. It is commonly connected back-to-back with an adjacent frame in the transverse direction using a 6-inch coupler in the middle. This configuration is called a coupled rack system, which is very common in the industry. Figure 1 below shows a typical coupled rack geometry for a typical industrial warehouse. The vertical rack spacing and the number of levels within the rack are other important considerations of storage racks. The vertical spacing should accommodate the pallet height plus an 8-inch clearance between pallets and racking frames. The industry standard pallet heights for distribution facilities in the US are 56 inches, 64 inches, and 72 inches. The number of rack levels is greatly dependent on building clear height and pallet heights. The clear height is the height measured from the finished floor to the bottom of the lowest roof framing member. This is the maximum height that racking can extend vertically, and it directly defines the volumetric capacity of the facility. Within the clear height, the maximum number

of rack levels can be determined [2]. Figure 2 presents the pallet utilization configuration for different building clear heights and different pallet heights. The weight of the pallet is highly dependent on the merchandise or material the pallet carries. Typical weights range from 1,000 to 4,000 pounds. For instance, pallets that store dry grocery goods, candies, and freezer items typically weigh 1,200, 1,800, and 2,200 pounds, respectively. Pallets that store construction materials such as building supplies, ceramic tiles, and cement bags typically weigh 2,500, 3,500, and 4,000 pounds, respectively. For an industrial building without an assigned tenant, the industry standard is to assume a pallet weight of 2,000 pounds. Figure 3 shows the pallet weight of each Figure 3 Typical pallet weights for industrial buildings. category. These weights are critical for slabon-grade design in that they directly dictate After combined with gravity loads per the Racking Manufacturer the amount of seismic load that is eventually transferred to the slab. Institute (RMI), net uplift would occur and can be determined. Another important governing factor for seismic load to the slab is The net uplift force tends to pull the slab away from the soil supthe seismicity of the site. The seismic load is directly proportional port, and thus, it is the slab itself that provides resistance to the to the seismicity, and it is directly measured by the short-period uplift. To quantify the net uplift, four pieces of information are spectral acceleration (SDS). This value can be found either through critical, including the building clear height, the pallet weight, the the ASCE 7-16 hazard tool or the geotechnical report. pallet height, and the site seismicity. To evaluate the slab capacity subjected to uplift and down push forces, we follow the flow chart as shown in Figure 4 below. First Design of Slab-on-Grade of all, one needs to determine how many pallets will be utilized to maximize the logistic efficiency of the building based on the clear The racking system inside the building is directly supported by a height. This can be accomplished using Figure 2. Then, the lateral slab-on-grade. Therefore, the slab should be designed to support load to each level of the racking system should be determined per all loads coming from the racking. Typically, two load effects mFs- the RMI guidelines, and its load effects should be combined with lapust be considered during the design of the slab, namely, down gravity load effects to determine the net uplift and down push push and uplift force force to the slab. The next step is to create a numerical model and coming from rack analyze the slab subjected to downward and uplift forces. At this ^ posts. Downward stage, one would start with an initial assumption of slab thickness. forces typically In this finite element analysis, slab-on-grade is typically modeled , do not govern the using shell elements, and the soil below should be modeled using W , W t design as the slab nonlinear compression-only spring elements. After running the ^ will be supported by analysis, the maximum negative moment to the slab can be deterthe soil below, and mined. Figure 5 shows a typical 3D view of the numerical model D an increase of the of the slab subjected to downward and net uplift, as well as the ^ Z ZD/ h base plate dimen- moment contour within the slab. The final step is to determine if > ZD/ sion of rack columns the assumed slab thickness is able to provide the capacity to resist would greatly help the uplift force. This is an iterative process until an adequate slab & D ^ ^ to increase the thickness is determined. capacity to support gravity load. The / uplift force, as a Slab-on-Grade Design Chart ^ / result of the seismic loads on the racking Following the above-mentioned process, we performed a series of system, usually gov- parametric studies of a slab for a typical industrial building with 40 / erns the slab design. feet clear height with combinations of different seismicity and slab During a seismic thickness. The seismicity considered varies from 0.5g to 2.0g, and event, the lateral the slab thickness considered includes 6, 7, 8, 9, and 10 inches. It force imposed on the is assumed that the reinforcement is around 0.1% of the slab area ^ racking system will and that concrete compressive strength is 3500psi. After obtaining a induce tension and cluster data point in terms of Seismicity (SDS), slab thickness, and compression coupled the corresponding pallet weight that the slab can support, a secondFigure 4 Flow chart for design of slab-on-grade. to the rack columns. order regression analysis is then performed to generate contour lines JANUARY 2024

Figure 5 Finite Element Analysis of slab-on-grade.

Figure 6 Slab-on-Grade Design Lookup Chart.

and, thereby, a lookup chart as shown in Figure 6. In this figure, the horizontal axis is the seismicity (SDS), and the vertical axis is the pallet weight that can be accommodated by the slab. In addition, different line types represent different slab thickness, which is overlaid above each line type. This chart clearly shows that as seismicity increases, the maximum pallet weight the slab can accommodate decreases. For the same seismicity, an increase in slab thickness supports more pallet weight. More importantly, from this chart, one can quickly estimate the pallet weight the slab can support based on the seismicity and slab thickness without the need to go through the complete design and check process. Furthermore, the study is extended to buildings with different clear heights, including 32, 36, 42, 46, and 50 feet. Instead of generating different lookup charts for buildings with different clear heights, we used the 40-feet clear building height results as the baseline case, and adjustment factors are determined by correlating the results for a building with different clear heights and baseline case results. This adjustment factor is summarized and provided in the table shown on the lookup chart. Now, utilizing the combined lookup chart and the adjustment table, one is able to very easily determine the maximum accommodated pallet weight considering a given seismicity and slab thickness for buildings with different clear heights.

Examples 1. A 40-foot clear-height warehouse is located on a site with a seismicity of SDS = 1.0g; what is the recommended slab thickness? From the lookup chart, we can easily determine that an 8-inch slab is able to support a racking system with a pallet weight of 3,000 pounds. For 7 and 9-inch slabs, the maximum pallet weights are 1,600 and 4,500 pounds, respectively. Note 22 STRUCTURE magazine

that this chart is for a 40-foot clear building, and the adjusting factor is 1.0 in that case. 2. A 32-foot clear building with seismicity of SDS =1.2g, what is the recommended slab thickness? From the chart, one can determine that 6, 7, and 8-inch slabs can support pallet weights of 400, 1,200, and 2,400 pounds, respectively. In addition, adjustment factors of 3.74, 2.14, and 1.68 should be applied. Therefore, 6, 7, and 8-inch slabs can support pallet weights of 1,496, 2,568, and 4,032 pounds, respectively. In this regard, a 7-inch slab is recommended to meet 2000lb pallet weight industry standards. 3. A 50-foot clear building with seismicity of SDS =0.9g, what is the recommended slab thickness? From the chart, the pallet weight associated with 8, 9, and 10-inch slabs is 3,500, 5,100, and 7,300 pounds, respectively. In addition, adjusting factors of 0.30, 0.39, and 0.40 should be applied. Therefore, 8, 9, and 10-inch slabs can support pallet weights of 1,050, 1,989, and 2,920 pounds, respectively. Therefore, a 10-inch slab is recommended.

Conclusions In the context of an industrial building, the design of a slab-on-grade holds the utmost importance due to its pivotal role in supporting anticipated loads imposed by rack supports. The design process, especially the selection of an optimal slab thickness, proves to be timeconsuming, primarily because it entails intricate numerical modeling. In this study, we conducted a systematic parametric analysis of slabs on grade for buildings with varying pallet weights, clear heights, and seismic conditions. We employed regression analysis to develop a convenient lookup chart, allowing for rapid estimation of the maximum pallet weight the slab can support based on its thickness and seismicity. Additionally, we created an adjustment table for buildings with different clear heights. This tool can greatly assist design teams and owners in making quick decisions, especially during the early stages of building planning, concerning the building's functionality.� Rafik Gerges, Ph. D., P. E., S. E., is a Principal with HSA & Associates and has over 25 years of experience working in consulting Structural Engineering. He is responsible for the design and construction support of major distribution centers, built-to-suit industrial facilities, office buildings, shopping malls, and a variety of other projects. Vinay Teja Meda, M. S., is a senior Structural Designer with HSA & Associates. He has 5 years of experience in Logistics and commercial building structural design. He obtained his Master’s degree from George Institute of Technology. Weian Liu, Ph. D., S. E., is an associate with HSA & Associates. Weian has 7 years of design experience in logistics, commercial, educational, and residential buildings. His key projects include multiple 4-million-sqft fulfillment centers across the nation, LAX Vertical Circulation Cores, Seattle Airport expansion, and many more. Weian obtained his PhD degree in Structural Engineering from UC San Diego.

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ANCHORING to CONCRETE Shear Concrete Breakout Calculations for Anchorages With Multiple Rows Extrapolating ACI 318-19(22) shear concrete breakout provisions for complex anchorages. By Richard T. Morgan, P. E.

nchoring-to-concrete provisions in the American Concrete Institute (ACI) standard titled Building Code Requirements for Structural Concrete (ACI 318) illustrate how to calculate shear concrete breakout strength for two rows of anchors having one anchor in each row. Many anchorages consist of more than two anchor rows, having multiple anchors in each row, requiring the engineer to extrapolate these provisions. This article discusses how one could extrapolate ACI 318-19(22) provisions to calculate shear concrete breakout strength for anchorages consisting of multiple anchor rows with multiple anchors in each row.

Overview of ACI 318-19(22) Anchoring-toConcrete Provisions for Shear Concrete Breakout Shear concrete breakout occurs at a fixed edge when shear load acts towards that edge. ACI 318-19(22) Section 17.7.2.1 provides equations for calculating nominal concrete breakout strength in shear for a single anchor (Vcb) and an anchor group (Vcbg). These equations are as follows: A Vc Single anchor V cb = A } ed, V } c, V } h, V V b (Eq.17.7.2.1a) Vc0 A Vc

Anchor group V cbg = A

Vc0

} ec,V } ed,V } c,V } h,V V b (Eq.17.7.2.1b)

The parameters in (Eq. 17.7.2.1a) and (Eq. 17.7.2.1b) are defined in Table 1. The parameter ca1 referenced in Table 1 corresponds to the distance in the direction of the applied shear load from the center of a single anchor or from a line through a row of anchors to a fixed concrete edge. When an anchorage consists of multiple anchor rows, the nominal concrete breakout strength in shear for the group of anchors, Vcbg, can be calculated using a ca1 value from a specific row. ACI 318-19(22) considers three cases for determining the value of ca1. Each case considers the spacing between anchor rows in the direction of the applied shear load, which influences where potential concrete breakout failure surfaces can develop, and the magnitude of shear load assumed to act on a particular row. ACI 318-19(22) Fig. R17.7.2.1b (reproduced in Figure 1) illustrates these three cases for a simple anchor arrangement consisting of two anchor rows, with one anchor in each row. Figure 2 illustrates how the three ACI 318-19(22) cases for shear concrete breakout could be extrapolated for an anchorage consisting of three rows with three anchors in each row. Case 1 (Figure 2a) assumes the shear load (Vua) is equally distributed between Rows 1, 2, and 3 if the row spacings, sy,12 and sy,23, are greater than or equal to ca1,row 1. For Rows 1, 2, and 3, if the anchor spacings sx,1 and sx,2 perpendicular to the direction of Vua are less than or equal to 3ca1,row 1, the anchors in each of these rows are considered to act as a group per ACI 318-19(22) 17.5.1.3.1. Since sy,12 and sy,23 are greater

Table 1

Parameter

Description

ACI 318-19 Equation

AVc

projected concrete failure area

AVc0

idealized concrete failure area for a single anchor

A Vc0 = 4.5 ^ c a1 h

W ec,V

modification factor for eccentric load

W ec,V =

reference Fig. R17.7.2.1b 2

Eq. (17.7.2.1.3)

_ 1 + 1.e5lc i V

Eq. (17.7.2.3.1)

W ed,V

modification factor for edge distance (ca2) when ca2 < 1.5ca1

W ed,V = 0.7 + 0.3 1.5ac2a1

W c,V

modification factor for uncracked concrete, or cracked concrete with supplementary reinforcement

W h,V

modification factor for concrete thickness (ha) when ha < 1.5ca1

W h, V =

basic concrete breakout strength (anchors not rigidly attached to fixture)

Vb = _ 7 _ da i

basic concrete breakout strength (anchors rigidly attached to fixture)

Vb = _ 8 _ da i

basic concrete breakout strength (limiting equation)

V b = 9m a

24 STRUCTURE magazine

Eq. (17.7.2.4.1b)

reference Section 17.7.2.5 1.5c a1

Eq. (17.7.2.6.1)

0.2

1.5

da ima

fcl^ c a1 h

da ima

fcl^ c a1 h

1.5

fcl^ c a1 h

1.5

Eq. (17.7.2.2.1a) Eq. (17.7.2.2.2)

Eq. (17.7.2.2.1b)

Figure 1 ACI 318-19(22) Shear Concrete Breakout Assumptions.

than or equal to ca1,row 1, the ca1 value used to calculate Vcbg can be taken as equal to ca1,row 1, and Vua can be assumed to be equally distributed on each anchor row. For the example illustrated in Figure 2a, Case 1 is satisfied if the design concrete breakout Figure 2 Extrapolated ACI 318-19(22) Shear Concrete Breakout Assumptions. strength (zVcbg) calculated with ca1,row 1 is greater than or equal to (Vua/3). precluding the assumptions utilized in Case 2. Examples of anchors not Case 2 (Figure 2b) is an alternative design assumption to Case 1 rigidly attached to a fixture include post-installed anchors and ASTM and assumes a full failure surface could develop from the anchor row (American Society for Testing and Materials) F1554 headed bolts. farthest from the fixed edge (Row 3) if the spacing between rows in However, if anchors are rigidly attached (e.g., welded) to a fixture, Case the direction of Vua is greater than or equal to ca1 for the row nearest 2 is the default assumption when calculating zVcbg because the shear load the fixed edge (ca1,row 1). The total shear load is assumed to act on Row can be redistributed to the back row of anchors, thereby permitting the 3. If the anchor spacings sx,1 and sx,2 perpendicular to the direction assumptions utilized in Case 2. Examples of anchors rigidly attached to of Vua are less than or equal to 3ca1,row 1, the anchors in each of these a fixture include AWS (American Welding Society) D1.1 headed studs. rows are considered to act as a group per ACI 318-19(22) 17.5.1.3.1. Case 2 is satisfied if zVcbg calculated for the anchors in Row 3 using ca1,row 3 is greater than or equal to the total shear load Vua. How To Determine Ca1? – Things To Consider Case 3 (Figure 2c) assumes a full failure surface can only develop from the anchor row nearest to the fixed edge (Row 1) because the As noted on page 1, the parameter ca1 corresponds to the distance in the spacing between rows in the direction of Vua is less than ca1 for the direction of the applied shear load from the center of a single anchor or row nearest the fixed edge (ca1,row 1). The total shear load is assumed to from a line through the center of anchors in a row to the edge where shear act on Row 1. If the anchor spacings sx,1 and sx,2 perpendicular to the concrete breakout is assumed to occur. Shear concrete breakout occurs when direction of Vua are less than or equal to 3ca1,row 1, the anchors in each the applied shear load causes the attached fixture to bear on the anchors such of these rows are considered to act as a group per ACI 318-19(22) that a failure surface develops from the anchors to a fixed concrete edge. 17.5.1.3.1. Since sy,12 and sy,23 are less than ca1,row 1, Case 3 assumes a If anchors are not rigidly attached to a fixture, an annular space full concrete breakout surface cannot develop from either Row 2 or exists between each anchor and the fixture. The origin of a potential Row 3, so the ca1-value used to calculate Vcbg is taken equal to ca1,row 1. failure surface depends on which anchors are assumed to be in bearCase 3 is satisfied if zVcbg calculated for the anchors in Row 1 using ing with the fixture and the spacing between anchors in the direction ca1,row 1 is greater than or equal to the total shear load Vua. of the shear load. For example, if all anchors are centered in the If anchors are not rigidly attached (e.g., not welded) to a fixture, shear fixture holes, bearing could occur simultaneously on each anchor as load cannot necessarily be re-distributed between rows, potentially the shear load is applied, and a failure surface could develop from one or more anchor rows. However, if any anchors are not centered in the fixture holes, the location of potential failure surfaces becomes more difficult to predict because the fixture may be bearing on some anchors but not all of them. Likewise, the spacing between anchors in the direction of the shear load influences whether a full or partial failure surface can develop from a given anchor or anchor row assumed to be in bearing with the fixture. Assuming which anchors are in bearing with the fixture also influences how the shear load can be distributed on those anchors. ACI 318-19(22) design assumptions consider two anchor rows with one anchor in each row. For anchorages consisting of more than two anchor rows with multiple anchors in each row, these design assumptions must be extrapolated to consider which anchor rows are Figure 3 Examples of Potential Load Distribution for Multiple Anchor Rows in Shear. in bearing with the fixture, permitting the formation of JANUARY 2024

Figure 4 Example of Case 3 Load Distribution for Multiple Anchor Rows in Shear.

Figure 5 Example of Multiple Anchor Rows Unequally Spaced and Loaded in Shear.

a potential failure surface, and the shear load distribution among these rows.

Load Distribution On Anchors In Shear – Things To Consider When an anchorage consists of more than two rows resisting shear load, the engineer must decide how the load is distributed on each row. For example, the anchorage shown in Figure 3 consists of five rows. Assume the anchors are not rigidly attached to the plate. Shear load (Vua) acts towards the -y edge. Assuming shear lag, only Rows 1, 2, 3, and 4 will be considered in this example to resist shear load. The edge distance ca1,row 1 corresponds to the distance of the anchors in Row 1 to the -y edge (4 inches). Anchor spacing in the x direction (sx) equals 8 inches, so the anchors in each row act as a group because sx is less than 3ca1,row 1. Spacing in the y direction between each anchor row equals 6 inches, which is greater than ca1, row 1, so both Case 1 and Case 2 can be considered when calculating the design concrete breakout strength in shear (zVcbg). The distribution of Vua among rows 1, 2, 3, and 4 must now be considered. Case 1 assumes equal load distribution per row. Case 2 assumes the total shear load is applied to Row 4; however, consideration could be given to the possibility that some fraction of Vua acts on Rows 1, 2, and 3. Therefore, if Case 2 is considered, zVcbg could be calculated for each row using the ca1-value for that row and checked against some fraction of Vua assumed to be acting on that row. Case 1, shown in Figure 3b, assumes zVcbg is calculated using ca1,row 1, and Vua is distributed equally among Rows 1, 2, 3, and 4. zVcbg,row 1 is checked against (0.25Vua). Case 2, shown in Figure 3c, illustrates how the total shear load is assumed to act on Row 4, while some fraction of Vua is assumed to act on Rows 1, 2, and 3. zVcbg,row n is checked against Vua,row n for each row. The percent utilization for Case 1 (0.25Vua/zVcbg,row 1) must be checked against the highest percent utilization for Case 2 (Vua,row n)/zVcbg,row n). 26 STRUCTURE magazine

The largest value controls the design. For the anchorage shown in Figure 4, assume the anchors are not rigidly attached to the plate. Due to shear lag, only Rows 1, 2, 3, and 4 will be assumed to resist shear. The edge distance ca1,row 1 equals 6 inches and the spacing in the y direction between each anchor row equals 4 inches. The spacing sx equals 8 inches, so the anchors in each row act as a group because sx is less than 3ca1,row 1. Case 3 applies because the spacing in the y direction between all anchor rows is less than ca1, row 1; therefore, a full failure surface can only develop from the anchors in Row 1 because the failure surfaces for the other anchor rows merge with each other. The total shear load (1.0Vua) is assumed to act on Row 1, and the design concrete breakout strength (zVcbg) calculated using ca1,row 1 is checked against Vua. Now consider the anchorage shown in Figure 5. Assume five rows of anchors not rigidly attached to a plate are subjected to a shear load (Vua) acting towards the -y edge. No shear lag is assumed, so all five rows can resist shear load. Assume ca1,row 1 equals 6 inches. The spacing sx equals 8 inches, so the anchors in each row act as a group because sx is less than 3ca1,row 1. The spacing sy between each row varies. Assuming which anchor rows resist shear load becomes more challenging, and it can be difficult to implement the load distribution assumptions of Cases 1, 2, and/or 3. The spacings sy,12, sy,34 and sy,45 shown in Figure 5 are less than ca1,row 1 so Case 3 is relevant to calculating concrete breakout with respect to Rows 1 and 2, as well as Rows 3, 4, and 5. Case 3 assumes the failure surface from Row 2 merges into the failure surface for Row 1, and the failure surfaces from Rows 4 and 5 merge into the failure surface for Row 3. However, sy,23 shown in Figure 5 is equal to ca1,row 1, so Case 2 is also relevant to calculating concrete breakout with respect to Rows 1 and 3. Therefore, the design must consider concrete breakout strength for failure surfaces originating from Row 3 (zVcbg, row 3) and Row 1 (zVcbg, row 1). If Case 3 is considered for these rows, then Vua could be assumed to act on either Row 3 or Row 1, and (Vua /zVcbg, row 3) would be checked versus (Vua /zVcbg, row 1). If Case 2 is considered for these rows, then some fraction of Vua could be assumed to act on each row, and (Vua, row 3 /zVcbg, row 3) would be checked versus (Vua, row 1 /zVcbg, row 1). Finally, the Case 2 results would need to be checked versus the Case 3 results, and the highest percent utilization (Vua,n /zVcbg, n) would control the design. As can be seen, the complexity of the anchor configuration influences where potential failure surfaces can develop, as well as the shear load distribution on the anchors assumed to be resisting shear load.

Summary ACI 318-19(22) provides three design assumptions to calculate shear concrete breakout strength for anchors. Each assumption only considers two anchor rows having one anchor in each row. This article explained how these three design assumptions could be extrapolated to design anchorages consisting of multiple anchor rows with multiple anchors in each row. Consideration must be given to edge distances in the direction of the shear load, spacing between anchor rows in the direction of the shear load, and shear load distribution on anchor rows.� Richard T. Morgan, P. E., is the Manager for Software and Literature in the Technical Marketing Department of Hilti North America.

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INFOCUS Engineering a Better Work-Life Fit A business case for flexibility in the workplace. By Erin Conaway, P. E., LEED AP and Rachel Mosier, P. E., Ph. D.

ver the last few years, the landscape and acceptance of flexible work models have changed dramatically. Having a choice of work environment and location is now a key factor for many job seekers when searching for a better work-life balance and evaluating new career opportunities. The desire for a healthy work-life balance and flexibility only rose during the COVID-19 pandemic. A Randstad 2023 Workmonitor survey revealed that 78% of workers feel they have a good work-life balance, and a majority would not accept a different job with negative work-life balance impacts. Significant data exists across many industries to make the business case for work-life balance, most notably the positive impact on retention and recruitment. In a 2022 annual survey by FlexJobs, 79% of respondents selected “work-life balance” as one of the top three factors when seeking a new position. In this same survey, the number one factor was “remote work options” at 84% of respondents, with 56% indicating “work schedule” as another top ten factor. Flexible work models, including hybrid and remote work options, benefit employees and companies alike. Gallup reports that, on average, it costs one-half to two times an employee’s salary for turnover and replacement. This article lays out the case for a discussion of flexible work models as part of an overall approach to a healthier and more successful work environment for both employees and companies.

What is Work-Life Fit? Initially described as work-family conflict in the early 1980s, the term used to describe the dynamic between work and personal life has changed over time. The conflicts identified in the 1980s focused on marital conflict over work/non-work and home/non-home roles. The discussion focus changed to work-life balance in the mid-1990s as both parents took on career roles, and latch-key kids became a social issue. The term “work-life balance” is what most people are familiar with today. However, the term “work-life fit” has resurfaced over the last decade and supports the idea that “work-life balance” is an outdated concept. “Work-life balance” is based on creating and maintaining clear boundaries between our personal and professional lives. In today’s world, the number of demands on our time has drastically increased, and a 50/50 split between work and personal life is not realistic or even necessary. The concept of “work-life fit” is based on flexibility: individuals fit their personal and work lives together in an effective way that works uniquely for them and achieves their personal business goals (image 1). It is worth noting that work-life fit is not about working less but working differently and more effectively.

Photo courtesy of: https://www.yeoandyeo.com/resource/work-remotely-with-videoconferencing.

realized the benefits of flexible work. As companies continue to redefine their work models moving forward, the physical space may not matter as much as providing resources tailored to help employees reach their full potential. There are three main flexible work models identified by Zweig Group’s “The Right Fit” tool, developed as part of the elevateHER® program. Each model provides a range of implementation options that are applicable to any company. 1. When people work: This model is based on providing flexible schedules using staggered hours, variable schedules with core hours, variable workdays, or a compressed work week. 2. Where people work: This model focuses on flexible office locations via hybrid telecommuting (2-3 days in-office), remote working, or alternating locations throughout a specific period of time. 3. How much people work: This model is less common but offers reduced hours through permanent or transitional parttime positions or job sharing. Ultimately, employees and employers need to identify the right type of flexible work policy that addresses an individual’s needs while supporting the business case for their company.

Flexible Work Models Work-Life Fit Makes Good Business Sense The COVID-19 pandemic changed the landscape and perception of flexible work models dramatically. The traditional model of a 40-hour in-office work week was challenged as both employers and employees 28 STRUCTURE magazine

Creating a work environment that prioritizes work-life fit can result in more engaged employees, positively impacting the bottom line

of a company. The World Health Organization defines employee burnout as exhaustion, negativity, and reduced professional efficacy. Lost productivity associated with employee burnout costs the global economy $1 trillion every year. In turn, burnout in the workplace most often results in employee disengagement, followed by decreased productivity and profitability. Gallup research shows that engaged employees have an 81% lower absenteeism rate, leading to 14% higher productivity. Data from 2022 indicated that 83% of workers supported a hybrid work model (defined as at least 10% of time worked at home, image 2), but only 26% of CEOs were ready to move into this work model (image 3). At that time, 49% of remote-capable workers were using this model. One year later, 59% of remote-capable workers were using this model, with no decrease expected in the future.

Flexible work options work for companies Flexibility is becoming increasingly synonymous with successful companies. Companies offering flexible work are often high-growth companies that rank high in their professional categories. Professional services sectors, such as the Architecture, Engineering, and Construction (AEC) industry, have been identified as having a high potential for remote work with the right considerations. The KPMG 2023 Global Construction Survey, which surveyed representatives from over 300 engineering and construction companies, found that 46% of engineering and construction firms identified that implementing or updating the models for remote work and job construction job site travel played an important part in their response to unforeseen workplace disruptions, including inflation, supply chain issues, and other resource constraints.

8 out of 10 workers support a hybrid work model.

2.5 CEOs support a hybrid work model.

high-profile tech firms reported millions of dollars in savings due to reduced real estate needs based on flexible work models. A flexible work policy is often a low-cost way for small companies to improve a compensation package without offering larger salaries or bonuses, improving their ability to compete with big companies for top talent. Reducing commuting costs for employees can be an attractive portion of an overall compensation package. Flexible work options allow companies to reduce their energy consumption. An environmentally conscious company appeals to a generation of job seekers who care deeply about social and environmental issues. A number of studies, including Global Workplace Analytics, have shown that job seekers are attracted to organizations with sustainable practices.

Moving Forward While Looking Backward

Flexible work options attract and retain talent Flexible work options are a benefit that ensures a business will keep attracting and retaining high-quality employees. In addition, flexible work options expand the talent pool and options for staffing. In Remote.co’s 2022 Work & Financial Wellness Report, 63% of global workers surveyed said they would look for a new job if remote work options were no longer offered.

Flexible work options increase job satisfaction Built-in flexibility reduces employee burnout and improves worklife fit, leading to increased job satisfaction. Flexible work models empower employees by increasing their feeling of personal control over their schedule and work environment. Empowerment appeals to the entrepreneurial spirit and a renewed sense of health and vigor on the job, which is good for employees and businesses. In May 2023, Gallup survey data indicated that employees allowed to work remote or hybrid schedules tend to have significantly higher employee engagement than on-site workers. Furthermore, employees required to work on-site when their job is remote or hybrid-capable have experienced the largest drop in engagement since 2020, while on-site employees with jobs that cannot be done remotely have the lowest engagement.

Flexible work models are not for everyone or every company but can be powerful tools for employees and employers to create meaningful change within an organization. There are a number of factors that should be considered for flexible work policies to be successful for both an individual and a company, including consideration of individual work styles, level of position, security issues, and IT infrastructure investment. Additional impacts, such as office culture, communication with coworkers and clients, and employee morale and engagement, should be taken into account when developing flexible work policies. Many companies have experience with some version of remote or hybrid work policies. Unfortunately, as we move farther away from the COVID-19 pandemic, more and more companies are mandating a return to the office, with or without some form of flexibility offered. Whether or not your company falls into this category, our industry should build its future on the lessons learned over the past few years – good and bad – and not underestimate the positive business impacts of healthy, happy, and engaged employees.� Full references are included in the online version of the article at STRUCTUREmag.org.

Flexible work options are scalable for all company sizes

Erin Conaway, P. E., LEED AP, is the Senior Director of Market Development with the American Institute of Steel Construction, based in Denver, CO (conaway@aisc.org).

Whether a small, medium, or large office, there are financial benefits to the company using flexible work options. Reducing the office footprint and implementing hoteling policies saves money on rent. The larger the office, the larger the savings. Prior to 2020, at least two

Rachel Mosier, P. E., Ph. D., is an Associate Professor in Construction Engineering Technology at Oklahoma State University in Stillwater, OK (rachel.mosier@okstate.edu).

JANUARY 2024

engineer’s NOTEBOOK ChatGPT in Structural Engineering How can structural engineers leverage Conversational AI benefits while managing its risks? By Stephanie Slocum, P. E.

tructural engineers spend an estimated 20-40% of their work hours writing. Do you ever struggle with writer’s block or spend too much time perfecting work emails? It’s understandable to feel frustrated and wonder if this is what you really signed up for as a structural engineer. Conversational AI tools like ChatGPT can solve this problem, acting as a writing assistant with the potential to drastically cut writing time so you can do more work you enjoy while more effectively communicating your value to teams, clients, and society. In December 2022, based on an entrepreneurial colleague’s enthusiastic recommendation, I first tried ChatGPT. A feeling of “this is going to change everything” came over me as I

Figure 1 ChatGPT is the most quickly adopted tool in the Internet age.

30 STRUCTURE magazine

explored; the last time I felt similarly was when I viewed my first Revit demonstration 20 years prior. I jumped in with both feet to learn all I could. The result has been working with AI experts, sharing my learnings in articles and virtual sessions, and collaborating on a report-writing workshop using this tool. AI language models and OpenAI’s ChatGPT have since made headlines. ChatGPT is the fastest-adopted tool in the Internet age (See Figure 1). The rapid adoption rate means firm leaders must get up to date quickly; an estimated 43% of employees have already used it, yet 68% of those users have not told their bosses they are doing so. AI tools like ChatGPT have the potential to be game-changing in helping engineers communicate effectively. At the same time,

Figure 2 ChatGPT 101 For Structural Engineers: Benefits, Risks, and Examples.

like any other software tool, it must be used with guardrails and a comprehensive understanding of the benefits and risks.

What is ChatGPT? ChatGPT (and other tools like Claude, Google’s Bard, and Microsoft’s Bing) is an AI-powered language model that generates human-like text based on the input - called “prompts” - it receives. Conversational AI tools are built on large language models (LLMs); the current version is GPT-4. For example, GPT-3 was the latest model in December 2022. These models can currently pass standardized exams like the SAT, GRE, and lawyer BAR exams in the top 10% of test takers. Read more about the capabilities in OpenAI’s white paper, available for free here: https://openai.com/research/gpt-4 With each model advancement, the responses to prompts have improved, sometimes dramatically. For example, the model refused to output source data in GPT-3. The current models will share sources. The LLM data used to train ChatGPT and other AI tools is proprietary and not publicly available. The information for developing GPT-3 indicates that it was trained on publicly available Internet data from 2021 and earlier, including Wikipedia and Reddit. Less information is currently known about GPT-4, the latest large language model. Access to GPT-3.5 and earlier is available via multiple free tools, including ChatGPT, Google Bard, and the new Bing search engine. Access to GPT-4 currently requires a ChatGPT Plus paid subscription. It’s also important to understand that access to any of the free (and some of the paid) tools means that any data inputted is being used to train the next model unless you take deliberate steps

available in some (but not all) tools to prevent that access. Any data you share may become public information, as Samsung employees painfully learned when their data leak went viral. The information shared above and herein is current as of 9.1.23; however, these technologies are rapidly advancing and subject to change as new and better tools become available.

Structural Engineering Applications For ChatGPT LLMs have the capabilities for technical applications for structural engineers who understand how to code or have IT departments developing proprietary AI tools. However, this article focuses on applications that any structural engineer can use right now, even without coding knowledge. For most structural engineers, the best application currently is as a writing assistant, helping to automate mundane but required tasks like writing meeting notes or reports. One of the most common complaints among structural engineers is that the industry is becoming commoditized, and clients don’t appreciate structural engineers. There’s also the constant balance of wearing multiple hats in a seller-doer role, especially for project managers and above. Engineers at these levels may be responsible for both internal functions (structural engineering design, coordination, and managing staff) and external processes (client meetings, QA/QC, troubleshooting field issues, producing reports). Seller-doer engineers also participate in business development and building firm reputations through thought leadership. SE leaders, especially of small and mid-size firms, often do all three jobs in their role, resulting in high burnout and overwork, a long-standing issue in structural engineering. JANUARY 2024

It’s here – in this area of communicating value to clients and others without your technical understanding to appreciate your expertise - where tools like ChatGPT can be a game-changer. With good prompts, ChatGPT can output responses in context, allowing it to present and summarize the same information from differing perspectives.

Examples of ChatGPT Use The following are four practical ChatGPT structural engineering application examples: 1. Explaining technical concepts to non-technical decisionmakers: You are working with an architectural client in the early stages of building design. The team is discussing occupancy loads in one public-gathering space. You recognize that the higher occupancy load may drive the building into a higher occupancy category (thus a higher load importance factor and structural costs). You could input your technical understanding into ChatGPT and ask how you would explain it to the bottom-line conscious owner so they can understand and contribute to that decision. In this scenario, you’re using ChatGPT to become the client’s trusted partner/educator to help them make cost-conscious business decisions. 2. Report writing: Structural engineers love going on-site, but only some enjoy writing reports. Imagine returning to the office, inputting your chicken-scratch notes, hitting a button, and immediately having a first report draft to review. This is possible right now (I’ve run workshops on this topic!) and can save you hours in writing. To be clear, I’m not saying the ChatGPT export is the report you hand over to a client in its final form. AI is a technology tool. Like other tools, it must undergo review before leaving the office. However, the most procrastinated and time-consuming part of writing is going from blank page to first draft, and tools like ChatGPT can get you there in a fraction of the time. 3. Writing emails (especially when sharing unwelcome information): You receive an email from a client with a last-minute change the day before a deadline. That change has significant structural implications (such as a column move), and you need to craft an email response that advises that the deadline needs to move if the client requires this change. This type of email used to take me an hour to write (especially in my early career) to strike a balance between setting that boundary and preserving the client relationship. In a post-ChatGPT world, writing a first draft of this email takes minutes. This video shows an example of this type of prompt and output: https://bit.ly/SEChatGPTEmailexample. 4. Thought leadership content: Client-facing engineers must publicly share their expertise to build their reputations. Examples include content creation, such as blogs, presentations, and social media posts. ChatGPT can act as a writing assistant and is especially helpful when repurposing already-written public content. For example, I used ChatGPT to generate an outline and first draft for this article based on my (100% human-written) abstract. Follow along with this ChatGPT example: https://bit.ly/ SEChatGPTExample4 32 STRUCTURE magazine

Even Perfectly-Crafted Input Could Still Equal Garbage Output Structural engineers can harness the power of ChatGPT and similar conversational AI tools to streamline their workflows, write faster and more effectively, and communicate their value better to non-technical stakeholders. Like any other software tool, you must also have the expertise to vet the accuracy of the output. Extra concern is warranted because the output of AI tools like ChatGPT sounds exceptionally knowledgeable, even when factually inaccurate. For example, I asked ChatGPT to write my biography; I have had a robust online presence since before 2021, so it seemed a good test. ChatGPT output was factually incorrect, sharing that I had attended MIT and Stanford instead of my correct alma mater, Penn State. I have also asked ChatGPT to define structural engineering terms with similar inaccuracies. The takeaway: Do not rely on ChatGPT or AI tools to provide accurate outputs. You must have the expertise to vet results for accuracy. From an organizational standpoint, you must have a QA/QC process to use this tool. The alternative is risking your professional reputation because AI output could be wrong or misleading.

Risk Management Concerns for Firm Leaders AI integration in firms raises concerns over data protection, ethics, and reputation. The FTC investigated OpenAI for alleged harmful statements by ChatGPT, emphasizing the importance of risk management strategies. AI writing tools like ChatGPT process large amounts of information and data, including proprietary methodologies, designs, and plans. Free tools currently available often use data inputted to train the model, resulting in concerns around protecting intellectual property (IP). Tech companies are racing to produce tools that will alleviate this concern. One example is Microsoft, which has been Beta-testing the Microsoft Copilot program in large organizations and is expected to roll it out to Office Suite Microsoft 365 users when testing is complete. Other risks include the “black box” nature of the data on which the LLMs are trained. We know that training data includes publicly available Internet data. Therefore, some of that data is guaranteed to be inaccurate. False information, including societal identity-related bias (i.e., age, gender, race, veteran status, etc.), may be included in AI responses. This is especially problematic for documents that must avoid using discriminatory and non-inclusive language, such as job descriptions, promotion qualifications, resumes, or requests for proposals. Organizations must have a robust QA/QC process around any output partially or fully generated by AI tools. Ethical use of AI tools is another risk. It will be years before state licensure and ethics codes catch up with AI. It’s up to engineers and organizations to use engineering judgment on proper use. Broad adoption rates mean many engineers are using it without telling their managers. This scenario raises questions about accountability, responsibility, intellectual property protections, and the potential risks associated with the undisclosed use of AI. Right now, leaders can promote an environment that encourages open discussion regarding AI use, use it with guardrails

to explore benefi ts and risks, and develop policies guiding responsible use. Policy examples are included in this LinkedIn article: https://bit.ly/ SEChatGPTLIpolicy. The other ethics-related issue that has reared its head in recent conversations is the impact on client trust. Because conversational AI is new, many individuals have differing thoughts on “proper use.” Only individual firms can answer the question: If a client learns you wrote something with AI, does that diminish that client’s trust in you? Will they wonder what other shortcuts you took? Or be happy with your faster communication response time?

What Structural Engineers Should Do Now

Figure 3 Technology Inflection Point.

Avoiding or ignoring the advancement of AI tools like ChatGPT isn’t a pragmatic solution. Telling staff not to use it is akin to saying don’t use the internet or smartphones at work – an impractical and arguably short-sighted approach. Instead, focus on understanding the technology, openly discussing its use, exploring best practices, and implementing robust guidelines and safeguards. Developments like Microsoft’s anticipated public rollout of Bing Chat Enterprise and AI tool “Copilot” in Office 365 emphasize that AI capabilities are rapidly becoming mainstream and will soon become integral to how we work. Microsoft copilot Beta users tell me that this AI/GPT-trained tool is designed to integrate seamlessly with the Microsoft Office/Outlook/ Teams platform. This is one example of a tool that will soon be available and expected to have capabilities to keep private data safe from being used to train the public LLM models. When your data can be kept separate from the public models (while still allowing the use of the public model in analysis), the most significant current risk management concerns will be minimized. Technology companies are in a race to provide this capability, and I predict AI tools will become more rapidly adopted for SEs soon after. Individuals and firms taking steps now to understand and harness this technology can give themselves a competitive advantage in the marketplace. Where do you start with ChatGPT and other conversational AI tools? Begin with example 4 (thought leadership content) because that information is or will soon be public knowledge. Report writing is the most advanced of the four examples herein. Reserve this exploration for AFTER your structural engineering organization has decided if reports are an appropriate application for the firm; many firms may prefer to wait until better data protection is available. Structural engineering firms should take immediate action to explore which AI applications are helpful for their organizations and establish usage guidelines around AI use. This includes

safeguarding data and IP and developing a QA/QC policy to vet AI outputs.

AI Tools are Here to Stay Adopting AI writing tools isn’t a trend. It is a fundamental shift promising to bring transformative benefits when navigated with understanding and proper QA/QC practices. We have reached an inflection point in the technological landscape for this technology (Figure 3). This technology is changing quickly and will likely have changed in the months between my writing of this article and your reading of it. Structural engineers and firms must start planning for this future now. The first step is fostering an open discussion and learning environment regarding using AI tools in the workplace. Leaders should promote conversations about AI in the workplace, develop organizational use cases, and encourage experimentation using QA/QC criteria that protect proprietary firm data. This will help ensure ethical use, prevent misuse, and mitigate potential risks. Conversational AI tools like ChatGPT have the potential to solve long-standing communication challenges in helping clients and the public see structural engineers’ value. Those communication challenges lead directly to the fees our industry can command and our ability to attract and retain top talent. By embracing conversational AI as a communication enhancement tool with guardrails in place, we can shape the future of structural engineering using that technology to drive industry progress.� Stephanie Slocum, P. E. is the author of She Engineers and Founder of Engineers Rising LLC, a firm based in State College, PA that specializes in gender-inclusive leadership and communication skills training. She is also SEI President-Elect FY24 (stephanie@engineersrising.com).

JANUARY 2024

engineer’s NOTEBOOK Code Compliance for Cold-Formed Structural Steel Systems Where safety, performance, and innovation meet. By Natasha Zamani, Ph. D., P. E.

valuating products is critical to ensuring safety and performance in the construction industry. For structural steel, there are two main types used in building construction: hotrolled steel shapes and cold-formed steel shapes. While hot-rolled steel has traditionally been commonly utilized, cold-formed steel is gaining popularity due to its flexibility and efficiency. Thus, assessing the safety and performance of cold-formed steel products is important, given their increasing use in construction. While established building codes provide standards for hot-rolled steel, there are limited criteria available for innovative and proprietary coldformed steel support systems. Modular support systems are typically composed of cold-formed steel channels and closed girders and are used primarily to support mechanical, electrical, and plumbing systems. Slotted series of channels offer full flexibility. Various pre-punched slot patterns eliminate the need for precise field measuring and field drilling for hole locations that utilities may require. One of the key considerations in thin-wall cold-formed steel member design is buckling. These sections are associated with high slenderness and are susceptible to buckling. Buckling occurs when a slender member, such as a column or beam, is subjected to compressive forces and begins to deform laterally. This can lead to failure of the member and potentially catastrophic consequences. To prevent buckling, designers must consider several factors, including the shape and size of the member, the material properties, and the load conditions. The American Iron and Steel Institute (AISI) provides guidelines for the design of coldformed steel members. They provide detailed Figure 1 Sub-column test setup provisions and formulas for determining the critical buckling stress of a given member, as well as recom- design provisions of AISI. Therefore, member strength must mendations for selecting the appropriate section shape and be determined by tests or rational engineering analysis with size to minimize the risk of buckling. However, there are some higher safety factors. With the introduction of more innovalimitations on the applications of these design methods; for tive products into the market, it is essential to have a unique example, when the cross-sectional shape is very complicated testing and evaluation process to determine compliance with or when special hole patterns exist in the member. building codes. Members in modular support systems often have sizes, spacing, ICC-ES AC46, Acceptance Criteria for Cold-Formed Steel Framing and configuration of the holes and slots that are beyond the Members, establishes requirements for cold-formed steel members

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to be evaluated in an ICC-ES Evaluation Service Report (ESR) under the International Building Code (IBC). The bases of recognition are the provisions of 1) AISI S100, North American Specification for the Design of Cold-Formed Steel Structural Members, 2) AISI S240, North American Specification for the Design of Cold-Formed Steel Structural Framing, and 3) AISI S220, North American Specification for the Design of ColdFormed Steel Framing-Nonstructural Members, all as referenced in IBC. Testing standards such as AISI S902, Test Standard for Determining the Effective Area of Cold-Formed Steel Compression Members, and AISI S919, Test Standard for Determining the Flexural Strength and Stiffness of Cold-Formed Steel Nonstructural Members, are permitted to be utilized to determine the strength of cold-formed steel members. In working with ICC-ES, this is the first time AC46 has been used to evaluate cold-formed steel products for a modular support system. For example, Hilti’s modular support system has undergone testing and evaluation, and, as a result, ICC-ES ESR-5019 was published containing the effective properties of the product. Effective area is critical in cold-formed steel member design, as it helps determine the member's strength and stiffness. It refers to the portion of the cross-section that can effectively resist the applied load, and is typically smaller than the gross area due to interruptions in the cross-section. The AISI S902 test standard employs stub-column testing to assess the effective area of columns. This standard considers local buckling and residual stresses and can be used for solid or perforated columns with hole patterns in the cross-section. Figure 1 presents Figure 2 Flexural test setup the sub-column test set-up used for the MT channel (a component of the modular support system). The nominal effective cross-sectional area at ultimate Summary load, adjusted to the nominal thickness and minimum specified yield stress, is determined based on testing. The effective area Cold-formed steel traditionally has had limited applications at any working stress level can be further determined using the compared to hot-rolled steel. However, its usage is rising due to provisions of AISI S902. its flexibility and efficiency. As the application of cold-formed The AISI S919 test standard determines the stiffness and steel increases, it is crucial to evaluate products to ensure safety flexural strength of cold-formed steel nonstructural members. and performance in the construction industry. Buckling is a Flexural tests are conducted to ascertain the strength, taking significant concern in the design of cold-formed steel members, into account two potential modes of failure: local buckling susceptible to compressive forces. Organizations such as AISI and distortional buckling. To enable the member to fail in the provide guidelines for the design of cold-formed steel members. intended mode, the spacing and construction of the braces on However, the design of innovative products require unique the compression flanges must be carefully set. Figure 2 dem- testing and evaluation processes to ensure compliance with onstrates the flexural test setup. building codes. In working with ICC-ES, this is the first time Apart from conducting experimental tests to establish the AC46 has been used to evaluate cold-formed steel products for strength of cold-formed members, AC46 requires that an accred- a modular support system. Results are published in ICC-ES ited organization, such as Underwriters Laboratories (UL), ESR-5019 report.� must inspect the manufacturing process periodically to ensure that the products comply with the necessary standards and Natasha Zamani, Ph. D., P. E., is a registered Civil and Structural specifications from which they were sampled and tested. This Engineer in Texas and serves as the Codes and Standards Senior measure is crucial for ensuring the safety and dependability of Manager at Hilti North America. She can be reached at (Natasha. the products and is of equal significance to both manufacturers Zamani@hilti.com). and consumers. JANUARY 2024

INSIGHTS Engineering Infrastructure to Support Societal Resiliency Electric vehicle weights endangering parking structures. By James McDonald, S. E., Joseph Moody, S. E., Michael Perkins, S. E., and Molly Pobiel, P. E.

onverting the US passenger vehicle fleet to electric power is a cornerstone of the national leadership’s proposed response to climate change. The electric vehicle tradeoff of reduced carbon emissions for increased vehicle weight creates a historic opportunity for the engineering and construction industries to adapt infrastructure to support societal resiliency. While the opportunity is historic, it is not without precedent, and the examples are a call to action by engineers and builders. Recent history provides instances of promising technologies nearly eradicated by early failures. The liberty ships essential for the Allied victory in WWII had early catastrophic failures that only with rapid resolution of welding flaws avoided constriction of the war’s sea lifeline. The 1994 Northridge Earthquake brought a moratorium to welded steel moment frame construction after the temblor revealed the lateral system previously codified as the most ductile system to be brittle. Rapid engineering response produced retrofits of existing frames and developed new joint configurations to make welded steel moment frames reliable as originally believed. Failure to enable the shift to heavier electric vehicles (EVs) may impair one of the most broadly recognized remedial measures for climate change. Engineers and builders have an obligation to provide sound infrastructure for EVs to prevent early catastrophic failures from blighting adoption of the technology. Obvious infrastructure vulnerable to damage due to increased vehicle weight are passenger vehicle parking garages. While there are other infrastructures, such as bridges and roads, that are also jeopardized by increased vehicle weight, we use parking structures to illuminate the need for action to compensate for the increased electric vehicle weights.

Figure 1 GVWR of electric pickup trucks sold in America.

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Significantly increasing passenger vehicle weights combined with recently reduced structural design requirements will result in reduced factors of safety and increased maintenance and repair costs for parking structures. The reduced factors of safety will increase the rate of structural deterioration and the frequency of structural failures. Parking structure maintenance and repair costs will increase from heavier wear on traffic coatings, concrete repair of cracking floors and beams, and/or necessary structural strengthening or retrofit of the overall structure. Serviceability will be impaired by increased floor vibrations, increased floor deflections, and visible concrete cracking. These deleterious effects are consequences for code-compliant design and construction; sub-standard parking structures will suffer more. To develop practical and prudent approaches to mitigate the inexorable increase in passenger vehicle weights, we review the structural effect of the added loads to quantify the risks imposed on parking garage owners, users, and stakeholders. Many existing parking structures need repair, and there is a high probability that they do not meet current or historic code-loading requirements. There are many cases of parking structure failures, and the growing demand for EVs will only increase the probability of failure.

Electric Vehicle Trends The excitement about sleek, powerful, and futuristic EVs has overshadowed the fundamental fact that EVs weigh significantly more than an equivalent-sized combustion engine vehicles. While EVs have much smaller and lighter motors than their internal combustion engine (ICE) counterparts’ engines, they typically use heavy lithium-ion batteries that add substantial weight to an EV's drivetrain. The average combustion engine weighs between 300 and 700 pounds, while the battery for most EVs weighs around 1,000 pounds. In fact, the battery of GMC’s Hummer EV truck weighs nearly 3,000 pounds or the weight of an entire Honda Civic. These battery weights dwarf the gasoline weight (180 pounds) of a full, exceptionally large gas tank, 30 gallons. Figures 1 and 2, based on 2023 manufacturer’s gross vehicle weight rating (GVWR) data, depict how much heavier a sample of EV trucks and EV sedans, respectively, are in comparison to a comparable representative ICE vehicle. The average GVWR of the EV trucks is 8,430 pounds, approximately 2,000 pounds more than the gas-powered Ford F-150, the

Figure 2 GVWR of sample of electric sedans sold in America.

best-selling truck in the United States. The electric Ford F-150, the Ford F-150 Lightning, weighs over 25% more than the gas-powered Ford F-150 when trucks of an equivalent wheelbase and drivetrain are compared. In addition, the GMC Hummer EV pickup truck weighs over 10,000 pounds, making it currently the heaviest car on the road and over 4,000 pounds more than the Ford F-150. For sedans, the average EV sedan weighs just over 6,000 pounds, 30% more than the US’s most popular sedan, the Toyota Camry. Although the increased weight of EVs may be a marginal issue if they only represent a small fraction of cars on the road, the percentage of EV cars in the United States has been on the rise, and sales estimates expect a dramatic increase as a part of the vehicle stock. In 2021, EVs only accounted for 3.2% of US auto sales, but in the last two years, they have more than doubled and now represent 7.2% of US auto sales in the first quarter of 2023 (Kelley Blue Book). In fact, as of Q1 2023, the Tesla Model Y has surpassed the Toyota Corolla as the best-selling car in the world. This rapid increase is caused by rising EV popularity and new US legislation aimed at decreasing carbon emissions. According to industry analysis from HIS Markit, US EV sales could reach 25 to 30% of total passenger car sales by 2035 and 45 to 50% of passenger car sales by 2050, under the assumption that the US continues to tighten environmental legislation and at least five states complete the internal combustion engine ban by 2035 (HIS report).

live load by 25%, from 85 psf in 2002 to 64 psf today. We converted the GVWR of the vehicles to area loads in a parking garage to compare the manufacturer’s data to the code requirements, as depicted in Figure 3. We used a standard parking space dimension of 9 feet by 18 feet as a simple representation of the area occupied per vehicle. Then, we compared uniform area loads of EV and internal combustion engine vehicles to the code-specified minimum design live load over time. The average unfactored load for an EV truck is 52 psf, 12 psf higher than the gas-powered Ford F-150, and the average EV sedan is 37 psf, 8 psf higher than the best-selling ICE sedan. When considering the current heaviest EV vehicle, the GMC Hummer EV pickup truck, the unfactored EV load in a 9 feet by 18 feet parking space could be as high as 65 psf. The public trusts regulators, building officials, and engineers to keep the code conservative when considering live load over the building life. According to ASCE 7, the required live load used in the design of buildings and other structures shall be the maximum load expected by the intended use or occupancy. The Commentary of ASCE 7 further explains that the minimum uniformly distributed live loads provided in ASCE 7 are usually far higher than loads measured in live load surveys; however, the buildings must be designed for loads they are likely to be subjected to during some reference period, typically fifty years. Our research shows that the average parking space area loads of EVs are near to or greater than 40 psf, the current minimum live load required by code. Even the gas-powered Ford F-150 is right at the code-specified live load of 40 psf. While most EV vehicle loads are still less than the factored minimum live load, 64 psf, live load factors are meant to consider the variability of live load that could occur over time in the garage, and many parking garages in the United States are consistently filled with vehicles. With the popularity of EVs on the rise, building codes will need to revisit the live load requirements to keep up with increasing vehicle weights. The consequence of inaction is not a sudden wave of parking garage failures in the short term, but rather an increase in parking garage failures and maintenance costs over the long term.

Review of Historical Building Code Requirements Modern EV weights are quickly approaching, and in some cases exceeding, the structural loads specified for design in current building codes. In contrast to the increasing vehicle weights and increasing numbers of EVs in the United States, the strength requirements for parking garage design have been reduced over the last two decades. In 2002, ASCE 7-02 reduced the minimum uniform distributed live load for passenger vehicle garage floors from 50 to 40 psf. At the same time, ACI 318-02 reduced the concrete design load factors for live load from 1.7 to 1.6. The product of these changes reduces the factored design

Figure 3 ASCE 7 parking garage design live load over time compared to truck and sedan loads.

JANUARY 2024

Figure 4 Concrete cracks (a) on underside of beam and (b) vertically through beam.

Serviceability Considerations

parking structures because of its strength, toughness, and durability when designed appropriately. However, all concrete is subject to The serviceability of parking structures includes various consider- cracking and can degrade the performance of the structure over time. ations that are beyond code minimum load requirements, such as Reinforced concrete is the most ubiquitous horizontal framing concrete cracking, structure durability and corrosion resistance, material in parking structures and is subject to flexural demands from wear on the driving surface, and structure vibrations. Neglecting or gravity loading. Flexural cracks in concrete form when the flexural not considering many serviceability items will increase the owner’s stresses exceed the modulus of rupture of the concrete. To provide maintenance costs and decrease the structure’s performance. The an economical structural design, beams and slabs are designed for serviceability considerations listed above are subject to increased strength with little consideration for limiting the tension stress in demands with the increased EV weights. the concrete. Therefore, cracks are expected to form in locations The American Association of State Highway Officials (AASHO) with higher flexural demands, as shown in Figure 4. Road Test in the 1950s resulted in the Law of the Fourth Power, Cracks are the conduit for corrosive elements to penetrate concrete. which postulates that increased axle weight increases road damage by Corrosive elements can include but are not limited to, chlorides the ratio of the increased weight to the fourth power. For example, a from the environment, dirty water, carbon dioxide, and deicing 30% increase in axle load is likely to increase repair costs by 185% salts. Chlorides are particularly corrosive to reinforcing steel, and (nearly tripled). A similar theorem could be applied to the sup- the steel is typically located in the tension regions of concrete where ported decks of a parking garage. However, without the support of cracking is concentrated. The increased loads from EVs increase a road base, parking decks are likely to be even more vulnerable to the crack numbers, widths, and depths, which may decrease the deterioration due to increased axle loads. life of a parking structure. EV charging stations are commonly There are a variety of typical parking garage construction types: rein- grouped to make electrical distribution systems more cost-effective. forced concrete, topped and untopped precast prestressed concrete Grouping EV charging stations will concentrate heavier vehicles, (precast double tees), post-tensioned concrete, or steel structures. intensifying cracking. They all have one element in common: the horizontal structure is A simple analysis can demonstrate how insidious increased loads can concrete. Concrete is a great material to support vehicle loads in be for concrete beam and slab serviceability. For a simply supported beam or slab, the length over which the bending Table 1 Service Load Comparison for Typical Parking Garage Beam. stress exceeds 90% of the maximum bending stress for a given uniform distributed load (i.e., imposed Percent of Code Service Live Load by ICE vehicles) increases by 73% when the uniform Loads (DL + LL) Live Load Source (psf) distributed load increases by 30% (additional load from EVs). In addition, the cracks will be wider and Design Live Load 40 100% deeper. It is easy to understand why repair costs balloon with increasing loads. Average EV Sedans 37 98% Traffic coatings (waterproofing barriers) are commonly used to protect horizontal surfaces on parking structures. When properly maintained, a traffic coating F-150 Gas Trucks 40 100% system can significantly prolong the life of a parking structure. Traffic coatings are common on each level of parking structures in northern climates where Average EV Trucks 52 107% deicing salts are common and tend to only be on the top exposed level in southern climates, if at all. The Heaviest EV Trucks 65 114% service life of traffic coatings can vary from 5 years for 38 STRUCTURE magazine

a lower-grade system to 20 years for a high-performance coating system. Heavier vehicles will increase wear on all traffic coatings due to increased friction and abrasion. Increased coating wear is common around corners, speed bumps, ramps, and braking zones. Vibrations in parking structures can be a nuisance to walking occupants, who may perceive the structure as not performing properly. In the extreme case, the occupant can associate the vibrations with a structural load capacity concern. Vibrations in parking structures are commonly caused by vehicles moving through the structure and are more pronounced at movement joints, precast double-tee joints, and speed bumps. The vertical offset across each of these locations causes vehicles to impose a dynamic load on the structure. Vibrations created by electric vehicles are significantly greater than by ICE vehicles because of their weight, and the structure will be more susceptible to low-frequency excitation due to additional cracking. To explore the potential structural impacts of higher EV weights in parking garages, the authors created and analyzed a computer model of a typical mildly reinforced concrete parking structure beam. The model beam span is 60 feet with a tributary width of 10 feet. The first step was to determine the code-level service demands on the beam by combining the effects of dead load and the codestandard 40 psf live load. Using this combination as our baseline, we subsequently replaced the 40 psf live load with some of the vehicle weights discussed above and compared the total service demands with the code case. As shown in Table 1, a parking garage supporting primarily EV sedans will very nearly exceed the code service loads, which are intended to be conservative. Heavier EVs will exceed the code service loads—some by significant margins.

Vehicle Crash Barrier Public Safety Vehicle crash barriers are a critical component of public safety in parking structures. The primary intent is to restrain moving vehicles and prevent out-of-control vehicles from crashing through. There are several recorded incidents where vehicle crash barriers have failed and resulted in fatalities. ASCE 7 specifies that vehicle crash barrier systems must withstand an impact force of 6,000 pounds at a height of 18 to 27 inches. Developing the required impact force is complicated and varies considerably based on the vehicle’s weight, speed, and energy absorption of the bumper system. Bhargava and Alostaz conducted an extensive study on vehicle impact forces (Bhargava & Alostaz, 2019). The study calculated impact forces by using high-fidelity, physics-based, three-dimensional finite element simulations of various vehicles crashing into vehicle barriers. The study concluded that the smallest vehicle (2,938 pounds) traveling at 5 miles per hour exerted an impact force of 8,990 pounds on a vehicle barrier. The study also demonstrates that the impact force is not linear between the various vehicle weights and that it increases with increased crash barrier stiffness. All the scenarios in the study concluded that the code-required impact force is inadequate. Public safety is decreasing with respect to vehicle crash barriers in parking garages due to the greater EV weights.

Consumer Demands In addition, the single biggest performance constraint that limits EV marketability is range. Increased battery size or technological breakthroughs with greater battery density are potential sources of significantly increased range. It is a prima facia truth that designers

will not constrain increased range based on vehicle weight alone. Hence, the EV range challenge has significant potential to exacerbate the infrastructure challenge.

Conclusion EVs weigh significantly more than their ICE counterparts on which the structural codes were based, and shortly before the popular advent of EVs, the code design requirements were reduced. The disparity between growing loads and reduced design requirements is reducing the margin of safety, increasing the likelihood of structural failure, and will exponentially increase maintenance costs for code-compliant parking structures. For non-compliant parking structures, the consequences could be even more severe. Consequentially, it is possible that the risk of catastrophic structural failures in the future could jeopardize the viability of EV technology as part of national efforts to reduce carbon emissions. Engineers and contractors have an opportunity to contribute to providing sound infrastructure to enable EV technology to be part of the fight against climate change. The authors recommend that engineers and code officials, in collaboration with specialty contractors, implement the following actions with respect to EVs to address this predicament: • Review code load requirements and implement changes as needed. • Survey authorities having jurisdiction and industry organizations (such as AASHTO) for best practices for mitigation. • Perform detailed structural analysis of common parking garage construction types for increased loads. • Develop standardized analysis and strengthening measures to make it more efficient and effective for owners to strengthen their parking garages. • Publish detailed example analysis and strengthening projects as models for assessment and upgrade. • Execute a program of monitoring, measuring, and documenting parking garage performance with significant EV occupancy. • Consider limiting EV access, and especially charging stations, to parts of parking garages less vulnerable to load effects, such as slab-on-grade areas or limited portions of the parking garage strengthened for greater live loads. • Consider vehicle fleet weight cap equivalent to vehicle mileage cap. • Consider standard practice of distributing EV parking spaces to reduce load intensity.� Full references are included in the online version of the article at STRUCTUREmag.org. James McDonald, S. E., Principal, Simpson Gumpertz and Heger (SGH), (jamcdonald@sgh.com) Joseph Moody, S. E., Senior Project Manager, SGH, (jtmoody@sgh.com)

Michael Perkins, S. E., Senior Consulting Engineer, SGH, (mjperkins@sgh.com) Molly Pobiel, P. E., Project Consultant, SGH,(mepobiel@sgh.com) The authors have 60 years of combined experience of designing, evaluating, and rehabilitating parking structures. Our design experience includes parking structures of varying construction types and evaluations are often to address parking structures with performance and condition concerns. Our team has extensive international experience in assessment of overload conditions of structures, including damaged structures supporting vehicular traffic.

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structural DESIGN Design Considerations for Aluminum Structures In South Florida Designing for South Florida’s harsh environmental conditions. By Antonio De Luca, Ph. D., P. E., S. E., Lauren Millman, Ph. D., P. E., Derek A. Wassink, P. E., R. A., S. I., STS2, and Matthew J. Olender, P. E., S. I.

luminum is a widely used building material due to its versatility, malleability, high resistance to corrosion, and high strength-to-weight ratio. Aluminum products come in many shapes and forms. Despite its greater strength-to-weight ratio, aluminum is generally weaker and more flexible than steel. While steel remains the favorable metal for the main load-carrying structure in buildings, aluminum is the first choice for building components or building-like structures such as, cladding and roofing panels, shade structures, window and door frames, balcony guardrails, space trusses, and tanks. Aluminum is also used in highway and bridge light poles, signs, and rails. In south Florida, buildings are threatened by high temperatures, frequent rains, sunlight exposure, strong winds, and salt-spray from the ocean creating harsher environmental conditions throughout the year than most parts of the country. Due to its physical and mechanical properties, as discussed later, aluminum is an economical material choice and often the most cost-effective alternative to steel in the south Florida market.

Figure 1 Schematic representation of an aluminum guardrail design.

Available Material Grades Aluminum is used for structural applications in the form of alloys, which are obtained by combining aluminum with at least another chemical element. Typically, the alloying elements are a small percentage of the compound weight. Structural shapes and thin plates used for manufacturing products in building construction are made of wrought aluminum. Wrought aluminum is made by extrusion, rolling, or forging, and can be classified into seven series, each designated by a four-digit number (1000 through 8000). Sheets and plates used in roofing and cladding systems are often made of the 3000 series alloys. In these alloys, the main alloying element is manganese, which provides corrosion resistance and allows the material to be rolled easily. However, the 3000 series alloys offer limited strength. The 6000 series alloys are primarily used to produce structural shapes. In these alloys, the main alloying elements are magnesium and silicon. These alloys are strong, resistant to corrosion and easily extrudable, but lose strength when welded. Aluminum alloys can be tempered to increase their strength. Tempering can be done by heat treatments or strain hardening. The 6000 series alloys are tempered by heat treatment, while the 3000 series alloys are tempered by strain hardening. Tempering is designated by the letter “T” for heat treatments and “H” for strain hardening. Differences in the tempering process are identified by a digit following the 40 STRUCTURE magazine

letter designation, such as T1 through T6 or H1 though H4. The side effect of tempering is a reduction in ductility. Cast aluminum alloys are generally classified into two groups based on the selected manufacturing process, which can be sand casting or permanent mold casting.

Design Basis In the United States, aluminum shapes for building construction must comply with the Specification for Aluminum Structures, which is included in the Aluminum Design Manual (ADM) published by the Aluminum Association (2020). The minimum strength requirements for aluminum shapes are standardized by the American Society for Testing and Materials (ASTM).

Strength The strength design of aluminum is very similar to that for steel. Aluminum structures can be designed based on the Load and Resistance Factor Design (LRFD) or the Allowable Stress Design (ASD). While aluminum members subjected to flexure, axial, and/or shear loads exhibit similar failure mechanisms as their steel counterparts, the design formulae are different and more rigorous. ADM sets the modulus of elasticity of aluminum equal to

10,100 ksi (approximately 2.9 times lower than that of steel) for all alloy-temper combinations. ADM provides minimum ultimate and yield tensile strengths for aluminum products made of various alloy-temper combinations and that comply with the ASTM specifications. For identical flexural designs, when compared with steel sections, aluminum shapes are expected to be deeper to reduce stresses and are expected to have shorter unbraced lengths to meet buckling limit states. The ultimate and yield tensile strengths of aluminum alloys are significantly dependent on the alloy-temper combinations. A small variation of tempering results in significant changes in mechanical properties. For example, standard structural profiles that are made of wrought aluminum 6061-T6 (i.e., the alloy series and the temper designation, respectively) and that comply with ASTM B308, have design ultimate and yield tensile strengths of 38 and 35 ksi, respectively. Instead, the design ultimate and yield tensile strengths are 22 and 16 ksi, respectively, for the 6063-T5 alloy. Both are commonly used. The mechanical properties of aluminum alloys are inert to temperatures up to approximately 200�F as reported by ADM. At higher temperatures, the strength of the aluminum part reduces depending on alloy, temper, temperature, and time of exposure. The reduction of strength (relative to the strength at room temperature) is greater for aluminum than steel in case of a fire. Thus, aluminum members need a more robust insulation than steel members to resist the effects of fire. Fire protection can be achieved using, for example, plaster boards when required. Fire performance-based design is allowed by ADM. Aluminum shapes can be welded or fastened together. The ultimate and yield strengths of the 6000 series alloys are significantly reduced by welding. The weld-affected zone typically extends up to approximately 1-in. on either side of the weld centerline. ADM publishes welded strengths of available alloy-temper combinations for welds complying with the American Welding Society (AWS) specifications D1.2. The filler used in welded joints is typically of the same chemical composition of the main alloy. Aluminum bolts, nuts and washers are typically made from 2024-T4, 6061-T6, or 7075-T73 alloys. The main advantage of using aluminum bolts to connect aluminum parts is that it virtually eliminates the risk of galvanic corrosion. However, the reduced strength of aluminum alloy bolts as compared to steel bolts makes their use impractical in most applications. Therefore, steel or stainless-steel bolts are often the preferred option when bolting together aluminum parts. High-strength fasteners, such as ASTM A490 bolts, should not be used in contact with aluminum due to the risk of hydrogen embrittlement and galvanic action in exterior applications. The design of aluminum structures is commonly performed through delegated design. The as-designed alloys are specified in the shop drawing submittals and verified in the field by reviewing the fabricator’s documentation. When project data are lacking, the determination of the as-built alloy-temper combination is a challenging task. However, in some cases, it could be estimated through the Vickers Hardness tests (ASTM E384, Standard Test Method for Microindentation Hardness of Materials) performed on material samples extracted from the structural member in question.

Serviceability Due to the lower modulus of elasticity, which has been previously mentioned, aluminum beams are also expected to be deeper

than steel beams to meet code-level deflection requirements. The reduced modulus paired with the lower material density makes aluminum members more susceptible to pedestrian- and/ or wind-induced vibrations than their steel counterparts. When compared to steel, the lower modulus of elasticity makes aluminum members more prone to wind-induced instabilities, such as, vortex shedding. Furthermore, depending on the structure’s design service life, the fatigue strength of aluminum joints is expected to be approximately one-third to one-half that of steel for the same joint detail. Although these characteristics of aluminum alloys can be considered unfavorable, practicing engineers are able to design within their limitations to take advantage of their benefits, such as on lighter weight cladding and roofing panel systems.

Durability Aluminum resists corrosion due to its so-called “self-healing” behavior. When bare aluminum is exposed to oxygen, a film of aluminum oxide forms on the surface of the metal and protects it against corrosion. The 3000 and 6000 series alloys have good corrosion resistance and could be used without protection. However, most building codes do require protection due to contact with dissimilar materials and continued exposure to moisture and other corrosive agents. Aluminum in contact with another metal often results in galvanic corrosion (Fontana and Greene, 1983, and Francis, 2017). This is an electrochemical reaction that occurs when two different metals are joined in the presence of a conductive fluid, such as water. In most galvanic couples that involve a ferrous metal (which contains iron), aluminum will experience galvanic corrosion. On the contrary, aluminum in contact with, for example, magnesium, zinc, cadmium, and passive stainless steel does not experience galvanic corrosion in most environments. The alkaline environment of cement-based products protects embedded steel from corrosion. Differently from steel, the passive oxide film that is normally present on the aluminum surface in neutral environments is destroyed in highly alkaline environments. This reaction occurs when the cementitious materials are in direct contact with the aluminum and water is present. The worst effects occur when fresh concrete is in direct contact to bare aluminum. In the case of cured concrete, water can be present due to the excess of mixing water or from wetting during concrete placement for instance. To compound the issue of a deteriorating aluminum surface, dissimilar metals can be embedded in cementitious materials, either placed in direct contact or near each other. Additionally, chlorides accelerate the corrosion process. In coastal environments, the corrosion process can be particularly accelerated due to the proximity of salt water or wind-driven airborne salt sprays. Case Studies of Aluminum Balcony Guardrails In South Florida The design of balcony guardrails may seem to be a simple task at first sight. If the guardrail system is made of aluminum and the project location is in south Florida, this statement may not be true. The following sections will discuss an overview of most issues found in the design of aluminum guardrail systems when assessing the performance of aluminum structures. Balcony guardrails are often built out of slender aluminum extruded shapes due to their cost effectiveness, ease of fabrication and durability. The guardrail design configuration shown in Figure 1 requires JANUARY 2024

ksi when compared to the 16-ksi unwelded strength. The strength calculations can be simplified by assigning the welded yield strength to the material comprised within the heat-affected zone and the unwelded strength to the material outside of it (Figure 2). For condition assessment, when the as-built strength of a structural member with welded joints is in question, field load testing is a useful tool to assess the existing load-carrying capacity (Section 1708 of the 2021 International Building Code). • A second design consideration is related to the sensitivity of the horizontal pickets to wind-induced instabilities. Vortex shedding of the horizontal pickets can occur at low return period wind speeds. It is not uncommon for this to occur in coastal structures due to low, but steady prevailing winds. The induced across-wind vibrations of the pickets may, in turn, generate a humming sound that can be annoying to the building occupants. For example, -inch diameter cylindriFigure 2 Finite element model of aluminum guardrail post outlining the extent of the cal shapes may be a practical and economical solution for the weld-affected zone. Image courtesy of Thornton Tomasetti, Inc. pickets. While they are adequate to sustain the static design loads, their performance due to dynamic loads, such as wind, special attention. As shown in the figure, the vertical posts are made needs to be further studied. The pickets can be analyzed as of extruded aluminum square shapes spaced at 4-feet on center. The fixed-fixed beams due to the circular fillet weld at the post horizontal pickets are made of extruded aluminum circular shapes, are joints. The natural frequency of the first flexural mode of vertically spaced at 4-inches on center (to meet code requirements), the fixed-fixed picket is calculated to be approximately 52 and their ends are fillet-welded to the post faces. The following design Hz (assuming a picket wall thickness of approximately considerations are unique to aluminum. 1/16-inch and a length of approximately 48-in.). Assuming • The first design consideration is related to the effects of a Strouhal number for circular sections of 0.2 per ADM (or welding to the strength of the vertical posts. As mentioned 0.18 per Holmes, 2001), hand calculations show that a wind above, the heat produced by welding operations causes a speed of approximately 12 mph would be enough to activate significant reduction of the welded material’s tensile strength the pickets first flexural mode. The Strouhal number is a within a narrow band (approximately 1.0 in.) on either side dimensionless number (equal to the ratio between the vortex of the weld. The flexural capacity of the post must be assessed shedding frequency times the characteristic length of the by considering the extent of the weld-induced heat-affected object and the flow velocity) that can be used to predict the zone at the post-to-picket joints. For example, aluminum wind velocity causing vortex-shedding-induced vibrations 6063-T5 has a welded nominal yield tensile strength of 8 in an object. This means that air vortices form around the pickets at wind speeds of approximately 12 mph causing the pickets to oscillate harmonically up and down (Figure 3). Welded structural members have low damping (typically ranging between 0.2 and 0.5%). Assuming a damping ratio of 0.5%, for example, it would take approximately less than 2 seconds for the picket to reach steady-state, resonant vibrations. 12-mph winds are frequent in South Florida. It is good practice to avoid resonant effects at low wind speeds. In addition, depending on the magnitude of the applied cyclic stresses, the wind-induced vibrations may lead to the fatigue failure of the welded picketto-post joint, thus compromising the structural integrity of the guardrail system. At resonance, the maximum dynamic effects on the picket are expected to be (depending on the system’s damping) one or two orders of magnitude Figure 3 Schematic representation of vortex shedding around the cylindrical picket. When the frequency greater than the corresponding equivaof the vortices is separated from the natural frequency of the picket, the picket oscillates up and down, with lent static wind effects. The structural small amplitudes, at the frequency of the vortices. If the two frequencies are sufficiently close to each other (or elements should, therefore, be designed synchronized), the picket’s natural frequency is activated. The result of this resonance is a humming sound that can be felt as uncomfortable to the building occupants. so that their natural frequency is either 42 STRUCTURE magazine

much greater or much lower than the frequency of the applied loading. The ADM-based fatigue design is similar to the one established by AISC for steel structures. • The third design consideration is related to the durability of the guardrail posts in direct contact with the balcony slab concrete. In south Florida, glass railing in-fill panels are often utilized, thus causing high bending forces at the post bases. A typical design has the guardrail posts embedded in the concrete slab due to the high bending forces. The aluminum post is, therefore, in direct contact with concrete on all sides. As mentioned above, the alkalinity of the concrete corrodes the bare aluminum. The corrosion rate is increased by the presence of chloride ions, which are common in coastal regions. Nowadays, extruded aluminum shapes for exterior applications are often coated with organic coatings. These coatings are tested to protect aluminum from corrosive environments as established by the Architectural Aluminum Manufacturers Association (AAMA) requirements, which are considered the highest industry standards of performance for organic coatings on aluminum extrusions. While they can protect aluminum against most aggressive environments, organic coatings can easily be scratched in the field during transportation or installation, thus exposing the bare aluminum to the environment. ADM specifies that aluminum surfaces in contact or embedded in concrete, that

Figure 4 Exposed embedment of aluminum post coated with bituminous paint. Photo courtesy of Thornton Tomasetti, Inc.

do not remain dry after curing, shall be coated with a zinc molybdate primer or an alkali resistant bituminous paint (Figure 4). Zinc molybdates are corrosion inhibitors and are used as additives in coatings. Bituminous paints offer waterproofing and corrosion resistant properties.

(a)

(b)

(c) Figure 5 Overall views of aluminum guardrail posts embedded in concrete with cracks in (a) balcony tiles and (b) stucco covering at slab edge. Close-up view of coating failure and aluminum corrosion (c). Photo courtesy of Thornton Tomasetti, Inc.

JANUARY 2024

the section loss of the fastener, thus decreasing the capacity of the connection. Stainless steel fasteners must be used instead. While the contact between aluminum and stainless steel is safe (aluminum and stainless steel are close to each other in the Galvanic chart), in corrosive environments bond breaker tapes between the fasteners and the aluminum connecting plate are recommended. Aluminum coating failures including bubbling, flaking, and/or chalky paint texture may be observed due to the lack of separation between the two materials. Figures 5 and 6 illustrate examples of corrosion in aluminum guardrail post applications due to contact with cementitious materials and dissimilar metals, respectively. Figure 7 shows other examples of aluminum corrosion due to direct contact with stucco and stainless-steel.

Conclusions

Figure 6 Close-up view of steel fasteners’ corrosion at aluminum post base plate. Note the fasteners’ head sheared off due to corrosion-driven section loss. Photo courtesy of Thornton Tomasetti, Inc.

Aluminum structures are becoming more and more competitive in harsh environments due to their extended service life, as opposed to steel. Most structural engineers are comfortable in designing with steel. Although aluminum design has similarities with steel, it has several unique characteristics that should be fully understood by the designer.�

The use of surface-mounted systems with post-installed fasteners can be an effective alternative for railing systems without glass panels in either new construction or for remedial applications. As discussed above, aluminum in contact with dissimilar metals may result in galvanic corrosion. While aluminum fasteners may be the obvious solution, their shear and tensile strengths are limited. Steel fasteners (black, coated, or galvanized) must be avoided at all costs. When aluminum is in contact with steel, the galvanic corrosion results in a movement of electrons from the steel fastener to the aluminum connecting plate. This phenomenon leads to

Full references are included in the online version of the article at STRUCTUREmag.org.

Antonio De Luca, Ph. D., P. E., S. E. (ADeluca@ ThorntonTomasetti.com) is a Senior Associate at the Fort Lauderdale Office of Thornton Tomasetti specializing in forensic investigations and structural diagnostics through analysis, testing and monitoring. Lauren Millman, Ph. D., P. E. (LMillman@ ThorntonTomasetti.com) is a Senior Associate at the Fort Lauderdale Office of Thornton Tomasetti, who specializes in forensic structural and materials engineering and provides litigation support for design and construction defect projects.

Derek A. Wassink, P. E., R. A., S. I., STS2 (DWassink@ThorntonTomasetti.com) is an Associate Principal at the Fort Lauderdale Office of Thornton Tomasetti with more than 30 years of experience in structural design, project management and coordination, and business development.

(a)

(b)

Figure 7 Close-up view of aluminum corrosion (a) due to direct contact with stainless steel washers and (b) due to direct contact between aluminum and stucco. Photo courtesy of Thornton Tomasetti, Inc.

44 STRUCTURE magazine

Matthew J. Olender, P. E., S. I. (MOlender@ ThorntonTomasetti.com) is a Senior Principal at the Fort Lauderdale Office of Thornton Tomasetti specializing in investigating and repairing building deficiencies/defects. Mr. Olender leads the Fort Lauderdale Office and is a leader of Thornton Tomasetti’s Forensics practice.

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structural FORUM Importance of Hand Calculations and Rules of Thumb in the Artificial Intelligence Age The old rules of thumb never looked so important as now. By Ciro Cuono, P. E.

tructural Engineering, as a profession, developed in approximately the mid-19 century mainly from the emerging technologies of the industrial revolution: iron, steel, I-beam production, development of railroads, etc. These emerging technologies helped spur the development of a “specialist” who emerged from the fields of architecture, mathematics, and construction. As structural engineering fully developed into an established profession, structural engineers created standards, codes, and textbooks to guide and train the members of their profession. In an age of pre-computing, their tools consisted of pencil and paper, theory, practical experience, and rules of thumb. This served them well for many years and required

46 STRUCTURE magazine

engineers, who were analytical, proficient at arithmetic and higher-level math, and practical, to be capable of understanding a physical problem and developing a conceptual solution that could be drafted and finally validated with mathematical tools. The mid-20 century Spanish structural engineer, Eduardo Torroja epitomized this notion best in his book, “Philosophy of Structures” (1958), with the following quote: “The calculation of stresses can serve only to check and to correct the sizes of structural members as conceived and proposed by the intuition of the designer. The work itself is never born from the calculation”. This quote summarizes a way of approaching engineering problems that has been endorsed by many past and current engineers in

TAYLOR DAMPED D MOMENT FRAME E™ SIMPLIFIED

JANUARY 2024

Photo credit: John Doogan/WSP

taylor

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our profession. To paraphrase some past professors and men- development of AI create an environment where the structural tors: “you must know the answer to the problem first”; “first do and architectural professions merge into one profession? Nina your thinking on a piece of paper or trace paper, then draft and Rappaport’s book, “Support and Resist: Structural Engineers calculate”; “you must have a feeling for structures,” etc. These are and Design Innovation” explores structural innovations of firms all different forms of Torroja’s quote, which shows that through that have been on the cutting edge of structural expression and study and experience, engineers develop an intuition for struc- collaboration - a timely read in a world of emerging AI. tural behavior. Once this intuition has been developed, a variety Given the legal, moral, and ethical foundations of engineering of solutions can be quickly developed and tested, and the final and our obligation to public safety, the answer to these quesanswer can be validated through a design check. These notions, tions is we need to ensure that the training and development of course, are familiar to most (particularly older) engineers and of the next generation of engineers should be accomplished in have been the basis for good, well-rounded engineers. a way that leads to confident and competent engineers who Our profession, however, like all professions, is constantly can look back at their history with pride and move forward evolving and never static. This evolution sometimes moves at a with new tools and methods and build great structures that faster pace but is indeed a constant force. To summarize a few benefit humankind. key points that illustrate this: the industrial revolution brought The surest way to accomplish this goal is to emphasize hand about new materials such as cast iron, wrought iron and finally calculations and rules of thumb so that the emerging generation steel, which, in turn, brought about new industries such as of structural engineers can develop their structural intuition factories and railroads. This caused the more mathematically and “feeling of structures” and have quick, easy, and meaningful minded architects to break off to form the structural engineering tools to check their designs, which will surely be “spit out” by profession. Parallel to this, the slide rule, which dates to the incredible technology. This does not mean that we should expect 1600s, evolved and became the standard tool for engineers until entry-level engineers to do their designs with slide rules and about the 1960s and ‘70s, when it was replaced by handheld the slope deflection method but rather that a certain amount calculators. Parallel to this, structural analysis of indeterminate of training should be done by simple hand calculation methods structures was born from truss analysis and elasticity methods and rules of thumb. As an entry level engineer advances in his and eventually evolved to computational methods such as the or her career, they can use these techniques, training, and rules slope deflection method of George Maney (1914) and the of thumb to check themselves which will eventually become Moment Distribution Method of Hardy Cross (1930), which their “sanity” checks when they have grey hair and become the had a short learning curve and produced rapid and accurate mentors to the next generation.� answers. At the same time, matrix structural analysis was in its infancy and rapidly developed after World War II, mainly in the aeronautical field, and morphed into the finite element Ciro Cuono P. E., is the founding Principal of Cuono Engineering method, which is the background engine of all structural analyPLLC, a structural engineering firm located in White Plains and sis done by packaged commercial analysis computer programs. Manhattan, NY and is an Adjunct Instructor at Manhattan College. Today rapid computing and advanced graphics have made it He has over 24 years of experience in structural design of new possible for even a small office to analyze complicated structures buildings and renovations and restorations of existing historic effortlessly. Fifty years ago, what would have taken a whole structures. He may be reached at (ccuono@cuonoengineering.com). team of engineers’ days and days to do can now be done in a matter of hours with a smaller team. On the horizon is now the allure of artificial intelligence (AI) and the tantalizing possibility of removing all computational effort from even the devices inc. most complicated designs, freeing engineers from the dog work of calculations to focus solely on testing various forms and solutions and focusing wholly on solving the problems of humanity’s built world. As this next technological revolution (AI) bears upon us, some important questions on the training and development of DAMPER R DESIGN members of our field must be considered. Namely, what is the importance of hand calculations and rules of thumb in the artificial intelligence age? How should we No N o Peer Review wR Required equ uired be teaching and training the next generaNo Tim Time-History m e History A Analysis n a tion of engineers? Do we keep the same curriculum from the last 30 to 50 years? Quick Design Times Should we be teaching the slope deflecThis new procedure decouples special steel moment frame design tion method to engineers who will likely from the damper frame, allowing for easier linear analysis, with full support provided by Taylor Devices’ team of structural engineers. be modeling and designing structures with computing technology that can be (716) 694-0800 | www.taylordevices.com ESR-4769 run from a phone or watch? Will the

business PRACTICES Why is Legal Advice About Contracts Like Cockroaches and Twinkies? Timeless tips for better and more insurable professional services agreements. By Karen Erger and Eric Singer

he answer is that they all endure unchanged forever – at least if you believe the urban myths about cockroaches being able to survive a nuclear blast and Twinkies never going stale. In truth, although cockroaches are six to fifteen times more radiation-resistant than humans, they ultimately succumb to its effects. And Twinkies, according to their manufacturer, only have a shelf-life of 25 days. On the other hand, the contract advice that design professionals receive from lawyers and risk managers really hasn’t changed much over the past three decades. We know because that’s how long we’ve been counseling engineers and architects about their contracts. So, in celebration of our respective fourth decades of construction law practice, here is a brief overview of some timeless contract pointers. Select appropriate clients and projects. Do you and your firm have the experience and capacity necessary to make Consult with your lawyer for the “magic words” to make your clause predictably enforceable the project successful? Make a clear-eyed assessment in your jurisdiction. about the risks of working with this client on this project, and make sure the reward you’ll receive justifies taking those risks. professionals in the same location and time frame. You can, however, change Have a written contract. In some jurisdictions, you are required to have this standard by contract. If you elevate it to “the highest standard of care” or a written contract to perform professional services. Still, even if you’re promise “defect-free design,” you jeopardize professional liability insurance not in one of those places, a written contract helps educate your client coverage and set an unattainable standard for your services. For the same and set reasonable expectations about your services. reason, do not guarantee or warrant your services – these too are unattainable, Don’t start work without a signed contract. We know it doesn’t always happen, uninsurable promises of perfection. but once you begin work, you lose any leverage you might have had to Don’t promise compliance. Promising that the project will comply with negotiate reasonable contract terms. “all laws, codes and standards” is unwise because they can conflict with Use your form contract when possible. If your firm has a standard form con- each other such that it is impossible to comply. They also may be subject tract, try to use it whenever possible. If your client insists on using a different to differing interpretations. Contracting to “conform the services to contract form, comparing it to your standard contract can help you identify applicable laws, codes, and standards consistent with the professional the business and legal terms you want to negotiate. Even if your client won’t standard of care” is more consistent with reality. agree to sign it without revision, this helps set expectations, frame your Don’t guarantee the cost of the Work. Don’t agree to design the project to a discussions and “set the anchor” for your negotiations. fixed budget. You don’t control the market forces that affect bids and the Assess the insurability of contract terms. Have reasonable, attainable insurance cost of construction. Beware any obligation to redesign for free until the requirements. When you receive an RFP or a client’s proposed agreement, bids are within budget. send the “insurance requirements” section to your insurance broker immeIf you agree to an indemnity clause, make it an insurable one. If you agree to diately to verify that you have (or can even purchase) the required coverages. indemnify (“make whole”) your client for damages caused by your negligence, Contracts must be signed by insured entities. Are you and your firm licensed that is probably okay because you’d be responsible for those damages anyway. and registered to practice where the project is located? Don’t wait until it’s But if you agree to indemnify your client for damages caused by parties you time to sign the contract; it takes time to become reciprocally licensed and don’t control, or for non-negligent errors, you assume liability you otherwise register your firm. wouldn’t have, jeopardizing your professional liability insurance coverage. Draft a clear scope of services. Your scope should clearly define the services Include a limitation of liability. Limitations of liability are a reasonable way you will perform, those you could perform as additional services, and those to balance project risk and reward, and they are enforceable in most states. you will not. Do not agree to attach your entire proposal (typically replete Remember that they only bind the parties who signed the contract – your with aspirational marketing language) to the contract to serve as a scope of liability to the rest of the world is not affected. services. A good scope really can save your bacon when disputes arise. Obtain the right to rely on information provided. Suppose your client proSet a reasonable, attainable standard of care. The law requires design provides information about the site or the project. In that case, it is reasonable fessionals to use the degree of care and skill ordinarily exercised by similar to obtain the contractual right to rely on the accuracy and completeness of

48 STRUCTURE magazine

the information provided unless your client is willing to have you verify the information for an appropriate fee and adjustment to the project schedule. Provide for the ability to suspend or terminate your services if you are not paid. If you are not being paid, you will want to have the contractual right to suspend or terminate your services without risking liability for project delays. Observe, don’t inspect. “Inspection” requires a much greater degree of inquiry than “observation.” Unless you really mean to inspect in detail, use the term ‘observe’ in your contracts, site visit reports and notes. Disclaim responsibility for means, methods, or jobsite safety. Your contract should unambiguously provide that the contractor is solely responsible for following the plans and for means, methods, and jobsite safety—failure to include such language subjects you to liability for jobsite injuries and contractor deviations from your design. Limit responsibility for “record drawings.” Use the term “record drawings” rather than “as-builts,” and make clear that your role is to assemble information from the contractor, not to verify every detail of the constructed project. Address copyrights and ownership of documents. If your client wants to own the design documents, find out why. In many cases, granting them a license to use your design for specified purposes will be sufficient. If you decide to give your client ownership of copyrights, consider charging an additional fee, be sure to retain rights to non-unique elements, and obtain an indemnity and disclaimer of responsibility for future use without your professional involvement. Provide for force majeure and delay conditions. Circumstances outside your control (“force majeure”) can prevent you from meeting the project schedule. Your contract should provide for an extension of time (and ideally additional fee) in these situations. Consult with your lawyer for the “magic words” to make your clause predictably enforceable in your jurisdiction. Exercise caution with Latin and Batman phrases. When your contract includes

Latin, legalese, or awkward phrases that would sound normal coming from Batman, but no one else (“Time is of the essence, Robin!”), chances are excellent that they are legal terms of art. Don’t assume those fancy words have ordinary meanings – review them with your lawyer “posthaste.” Use an appropriate contract with sub-consultants. If you retain sub-consultants, make sure your agreements with them are consistent with your upstream agreement. If your agreement with the client says you will litigate all disputes, but your sub-consultant agreements call for arbitration, you will end up with two different proceedings and potentially inconsistent results. If you are a sub-consultant, review the upstream agreement and make sure you can live with its terms. Like the Dude in The Big Lebowski, contract advice abides. Be prepared for the next time your lawyer asks, “What does your contract say?”� Karen Erger is Senior Vice President and Director of Practice Risk Management for Lockton, the world’s largest privately owned independent insurance brokerage. Drawing upon her experience as a construction lawyer in private practice and as a claim supervisor for a major insurer of architects’ and engineers’ professional liability, Karen consults with Lockton’s architect, engineer, and construction contractor clients on practice management issues, including complex claims and contracts, and provides risk management training and resources. (KErger@lockton.com) Eric Singer is a construction lawyer and litigation Partner with Ice Miller LLP in Illinois, concentrating in contracts, insurance, counseling and disputes relating to construction, design and real estate. Eric represents architects, engineers, contractors, owners, lenders, title and liability insurers and others involved in improvement and use of real estate and the built environment. (Eric.Singer@icemiller.com)

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Submit your project now for the 2024 Excellence in Concrete Construction Awards...deadline is April 29, 2024. For more information, visit www.ACIExcellence.org.

JANUARY 2024

code UPDATES 2024 IBC Significant Structural Changes Concrete & Masonry (IBC Chapters 19 & 21)—Part 3. By John “Buddy” Showalter, P. E., M. ASCE, M. NCSEA, and Sandra Hyde P. E., M. ASCE, M. NCSEA

his multi-part series discusses significant structural changes to the 2024 International Building Code (IBC) by the International Code Council (ICC). Part 3 includes an overview of changes to IBC Chapter 19 on concrete and IBC Chapter 21 on masonry. Only a portion of these chapters’ total number of code changes are discussed in this article. More information on the code changes can be found in the 2024 Significant Changes to the International Building Code, available from ICC (Figure 1).

Concrete Structural Concrete with GFRP Reinforcement New provisions and referenced standards have been added to the IBC for structural concrete with glass-fiber reinforced polymer (GFRP) reinforcement. New provisions and referenced standards ACI 440.11

Building Code Requirements for Structural Concrete Reinforced with Glass Fiber Reinforced Polymer (GFRP) Bars (Figure 2) and ASTM D7957 Standard Specification for Solid Round Glass Fiber Reinforced Polymer Bars for Concrete Reinforcement for GFRP bars are added to the IBC expanding options for their use. The addition of these new standards allows the design and construction of cast-in-place reinforced concrete using non-metallic reinforcement. 1901.2.1 Structural concrete with GFRP reinforcement. Cast-in-place structural concrete internally reinforced with glass fiber-reinforced polymer (GFRP) reinforcement conforming to ASTM D7957 and designed in accordance with ACI 440.11 shall be permitted where fire-resistance ratings are not required and only for structures assigned to Seismic Design Category A.

CHAPTER 35 REFERENCE STANDARDS ACI 440.11-22 Building Code Requirements for Structural Concrete Reinforced with Glass Fiber Reinforced Polymer (GFRP) Bars

ASTM D7957/D7957M-17 Standard Specification for Solid Round Glass Fiber Reinforced Polymer Bars for Concrete Reinforcement

Figure 1 2024 Significant Changes to the IBC.

50 STRUCTURE magazine

Change Significance: Design and construction requirements in ACI 440.11 allow the use of GFRP in Seismic Design Category (SDC) A for the structural frame and in SDC B and SDC C for concrete members that are not part of the seismic force-resisting system. Reasons to use GFRP bars in concrete structures include resistance to corrosion in the presence of chloride ions, lack of interference with electromagnetic fields, and low thermal conductivity. GFRP-reinforced concrete is especially suitable in highly corrosive environments, such as reinforced concrete exposed to salt water, salt air, or de-icing salts. It is primarily used to reinforce highway bridge decks where deicing salts are used on the roads and cause severe corrosion to conventional steel reinforcement. Other applications where GFRP-reinforced concrete is being considered include marine and coastal structures, parking garages, water tanks, and structures supporting magnetic resonance imaging (MRI) equipment. ACI 440.11 establishes minimum requirements for GFRP-reinforced concrete comparable to ACI 318 which establishes minimum requirements for structural concrete with steel reinforcement. Since GFRP reinforcement behaves differently than steel reinforcement, specific standards for this application are required. Among the subjects covered in ACI 440.11 are: • Design and construction for strength, serviceability, and durability • Load combinations, load factors, and strength reduction factors • Structural analysis methods • Deflection limits

SECTION 1905 SEISMIC REQUIREMENTS MODIFICATIONS TO ACI 318 1905.1 General. In addition to the provisions of ACI 318, structural concrete shall comply with the requirements of Section 1905.

1905.2 ACI 318 Section 2.3. Modify existing definitions and add the following definitions to ACI 318, Section 2.3. CAST-IN-PLACE CONCRETE EQUIVALENT DIAPHRAGM. A cast-in-place noncomposite topping slab diaphragm, as defined in Section 18.12.5, or a diaphragm constructed with precast concrete components that uses closure strips between precast components with detailing that meets the requirements of ACI 318 for the Seismic Design Category of the structure. DETAILED PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of [ASCE 7] Chapter 14, and Section 1905.5 of the International Building Code.

ORDINARY PLAIN CONCRETE STRUCTURAL WALL. A wall complying with the requirements of [ASCE 7] Chapter 14, excluding 14.6.2. Figure 2 ACI 440.11-22 Standard for Structural Concrete with GFRP reinforcement.

• Development and splicing of reinforcement • Construction document information • Field inspection and testing • Methods to evaluate the strength of existing structures IBC Section 1901.2.1 and the standard prohibit the use of internally GFRP-reinforced concrete for applications where fire-resistance ratings are required. For a building where reinforced concrete elements require fire-resistance ratings (e.g. in IBC Tables 601 and 705.5), the fire-resistance-rated members and assemblies will continue to need steel reinforcement. See the April 2023 issue of STRUCTURE for an article on GFRP use in new construction and repair of existing structures.

Seismic Requirements for Structural Concrete IBC Section 1902.1.1 has been revised and IBC Section 1905 has been reorganized and revised. The section no longer amends sections of ACI 318, rather focusing on provisions that supplement ACI 318 for seismic design.

PRECAST CONCRETE DIAPHRAGM. A diaphragm constructed with precast concrete components, with or without a cast-in-place topping, that includes the use of discrete connectors or joint reinforcement to transmit diaphragm forces. 1905.3 Intermediate precast structural walls. Intermediate precast structural walls shall comply with Section 18.5 of ACI 318 and this section.

1905.3.1 Connections designed to yield. Connections that are designed to yield shall be capable of maintaining 80 percent of their design strength at the deformation induced by the design displacement or shall use Type 2 mechanical splices. 1905.4 Foundations designed to resist earthquake forces. Foundations resisting earthquake-induced forces or transferring earthquake-induced forces between a structure and ground shall comply with the requirements of Section 18.13 of ACI 318 and other applicable provisions of ACI 318 unless modified by Chapter 18. 1905.5 Detailed plain concrete structural walls.

1902.1.1 Design displacement. Design displacement shall be the Design Earthquake Displacement, bDE, defined in ASCE 7 Section 12.8.6.3. For diaphragms that can be idealized as rigid in accordance with ASCE 7 Section 12.3.1.2, bdi, displacement due to diaphragm deformation corresponding to the design earthquake, is permitted to be taken as zero. Design displacement at each level shall be the total lateral deflection at the level calculated for the design earthquake using the procedures defined in Section 12.8.6 of ASCE 7.

1905.5.1 Reinforcement. 1905.6 Structural plain concrete. 1905.6.1 Seismic Design Categories A and B. 1905.6.2 Seismic Design Categories C, D, E and F. JANUARY 2024

1905.7 Design requirements for anchors 1905.7.1 Anchors in tension.

1905.7.2 Anchors in shear.

Deleted text and text associated with IBC Sections 1905.5 through 1905.7.2 are not shown for brevity. Change Significance: IBC Section 1905 previously contained modifications to ACI 318. Many of the modifications were related to the seismic design of concrete structures. IBC Section 1905 now contains information supplemental to ACI 318 provisions specific to seismic design. Additional edits to IBC Sections 1901, 1902, and 1903 were made to harmonize with changes to IBC Section 1905. Due to the extensive reformatting of IBC Section 1905 and related provisions, Table 1 is provided as a summary of changes. Table 1 Summary of Changes to IBC Section 1905 and Related Provisions

IBC Section

Summary of Changes

1901.2, 1901.3

Reflects conceptual change to Section 1905 supplemental seismic provisions.

1902.1

Two previous subsections were deleted. New Subsection 1902.1.1 was added given the introduction of design earthquake displacement in ASCE/SEI 7-22 Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE 7-22) which includes diaphragm displacement under a design earthquake. To avoid unnecessary calculations, the latter is permitted to be taken as equal to zero for diaphragms that can be idealized as rigid.

1903.2

Deleted since it duplicates 1901.6.

1905.1

Implements conceptual change to Section 1905 supplemental seismic provisions.

1905.2

Two new definitions are added based on ASCE 7-22 Chapter 14 which was not adopted in the 2024 IBC. • Cast-In-Place Concrete Equivalent Diaphragm • Precast Concrete Diaphragm

1905.1.2, Deletions and additions implement the conceptual changes to Section 1905 supplemental seismic 1905.3, 1905.1.4, provisions. 1905.4, 1905.5, 1905.7 1905.6

In addition to reflecting the conceptual changes outlined, an inconsistency regarding structural plain concrete and seismic design category (SDC) was corrected. In structures assigned to SDC A or B, detached one- and two-family dwellings up to three stories constructed with stud bearing walls are permitted to have plain concrete footings without longitudinal reinforcement. Structures in SDC C through F are not permitted to have elements of plain structural concrete with various exceptions.

These changes reorganize IBC Section 1905 and related provisions without introducing any substantive change. The new format is believed to be more user-friendly. As part of this format 52 STRUCTURE magazine

Figure 3 TMS 402/602-22.

change, existing provisions have been relocated to the following new IBC subsections: 1905.3.1, 1905.5.1, 1905.6.1, 1905.7.1, and 1905.7.2.

Masonry Updated Masonry Standards IBC Chapter 21 covers the materials, design, construction, and quality of masonry. Within the chapter are references to masonry design standards and material standards. TMS 402 Building Code Requirements for Masonry Structures, TMS 403 Direct Design Handbook for Masonry Structures and TMS 602 Specification for Masonry Structures are the IBC-referenced design standards for masonry. These standards are developed and published by The Masonry Society (TMS). The masonry provisions comprise allowable stress design, strength design, empirical design, and requirements for glass masonry and masonry fireplaces and chimneys. Masonry veneer is covered in IBC Chapter 14 and TMS 402 Chapter 13. TMS 402 Chapter 1 lists specific masonry items that need to be included in the construction documents. TMS has updated TMS 402 and TMS 602 which are placed in a single volume and often referenced as TMS 402/602 (Figure 3). The new 2022 editions have been revised throughout to update the standards to include new provisions in ASCE 7-22 as well as changes to numerous ASTM Standards. 2101.2 Design methods. Masonry shall comply with the provisions of TMS 402, TMS 403 or TMS 404 as well as applicable requirements of this chapter.

Table 2 Summary of Changes to TMS 402/602-22

TMS 402 Building Code Requirements for Masonry Structures (Chapter/Appendix)

Type and Magnitude of Changes to 2022 Edition from 2016 Edition

1 – General Requirements

Little or No Major Changes

2 – Notation and Definitions

Little or No Major Changes

3 – Quality and Construction

Minor Changes & New Requirements

4 – General Analysis and Design Considerations

Minor Changes & New Requirements

5 – Structural Members

Minor Changes & New Requirements

6 – Reinforcement, Metal Accessories, and Anchor Bolts

Major Changes & New Requirements

7 – Seismic Design Requirements

Moderate Changes & New Requirements

8 – Allowable Stress Design of Masonry

Moderate Changes & New Requirements

9 – Strength Design of Masonry

Major Changes & New Requirements

10 – Prestressed Masonry

Moderate Changes & New Requirements

11 – Strength Design of AAC Masonry

Little or No Major Changes

12 – Design of Masonry Infills

Formerly Appendix B

13 – Veneer

Formerly Chapter 12 – Rewritten

14 – Glass Unit Masonry

Formerly Chapter 13

15 – Masonry Partition Walls

Formerly Chapter 14

A – Empirical Design

Deleted

B – Design of Masonry Infills

Moved to New Chapter 12

C – Limit Design Method

Minor Changes & New Requirements

D – GFRP Reinforced Masonry

New Appendix

TMS 602 Specification for Masonry Structures (Part) 1 – General

Moderate Changes & New Requirements

2 – Products

Moderate Changes & New Requirements

3 – Execution

Moderate Changes & New Requirements

Excerpted from TMS Responds September 2022 – The Masonry Society

CHAPTER 35 REFERENCED STANDARDS TMS 402-22 Building Code Requirements for Masonry Structures

TMS 602-22 Specification for Masonry Structures

Change Significance: Table 2 provides a summary of changes to TMS 402/602-22. Significant changes include: • Compression-controlled section requirements added for Strength Design (Chapter 9) of reinforced masonry under combinations of flexure and axial load • Updated mortar requirements for adhered masonry veneer (see IBC Section 2103.2.4 in this article for more information) • New Appendix D on Glass Fiber Reinforced Polymer (GFRP) Reinforced Masonry which is limited to Seismic Design Categories A through C for elements not designated as part of the seismic-force-resisting system (see Section IBC 1901.2.1 in this article for similar provisions for structural concrete) • Removal of TMS 402 Appendix A: Empirical Design of Masonry (Empirical design of Adobe Masonry remains in IBC Section 2109 with a specific reference to TMS 402-16; see IBC 2109 in this article for a discussion of empirical design)

Mortar for Adhered Masonry Veneer IBC Section 2103.2.4 previously listed the types of mortars that can be used for adhered masonry veneer (Figure 4). Additional general requirements for adhered masonry veneer can be found in IBC Chapter 14. Mortar requirements for adhered veneer have been updated to meet new TMS 402-22 requirements. 2103.2.4 Mortar for adhered masonry veneer. Mortar for use with adhered masonry veneer shall conform to Section 13.3 of TMS 402. ASTM C270 for Type N or S, or shall comply with ANSI A118.4 for latex-modified Portland cement mortar.

Change Significance: Provisions for adhered masonry veneers have been extensively updated in the 2022 edition of TMS 402 to be more rationally based using a minimum mortar/unit bond strength value. Setting bed mortars are required by TMS 402/602-22 to be latexmodified mortars complying with ANSI A118.4 Specifications for Modified Dry-Set Cement Mortar or A118.15 Specifications for Improved Modified Dry-Set Cement Mortar to gain increased bond strength. Setting bed mortars meeting ASTM C270 Standard Specification for Mortar for Unit Masonry Type N or S are only permitted when testing is conducted on the specific mortar/unit combination to be used in construction. JANUARY 2024

Figure 4 Adhered masonry veneer.

Empirical Design of Adobe Masonry The empirical design procedure for adobe masonry is a prescriptive method of sizing and proportioning masonry structures using rules and formulas that were developed over many years. The procedure is based on experience and predates engineering design methods. The empirical method was developed for use in smaller buildings with more interior walls and stiffer floor systems than are commonly built today (Figure 5). The option for empirically designed masonry has been removed from the 2022 edition of TMS 402. However, reference to the previous edition (TMS 402-16) will allow Adobe masonry provisions to remain in the IBC. SECTION 2109 EMPIRICAL DESIGN OF ADOBE MASONRY 2109.1 General. Empirically designed adobe masonry shall conform to the requirements of Appendix A of TMS 402-16, except where otherwise noted in this section.

2109.1.1 Limitations. The use of empirical design of adobe masonry shall be limited as noted in Section A.1.2 of TMS 402-16. In buildings that exceed one or more of the limitations of Section A.1.2 of TMS 402-16, masonry shall be designed in accordance with the engineered design provisions of Section 2101.2 or the foundation wall provisions of Section 1807.1.5. Section A.1.2.23 of TMS 402-16 shall be modified as follows:

A.1.2.23 – Wind. Empirical requirements shall not apply to the design or construction of masonry for buildings, parts of buildings, or other structures to be located in areas where Vasd as determined in accordance with Section 1609.3.1 of the International Building Code exceeds 110 mph. 2109.2 Adobe construction. Adobe construction shall comply with this section and shall be subject to the requirements of this code for Type V construction, Appendix A of TMS 402-16, and this section.

54 STRUCTURE magazine

Figure 5 Adobe masonry construction.

Remaining provisions are unchanged.

Change Significance: In recent years TMS 402 has curtailed the application of empirical design for contemporary masonry materials, construction methods, and building types because these modern buildings and materials no longer rely on the smaller number and size of openings, more frequent cross walls, and shorter walls assumed in the empirical design approach. Additionally, adobe is a material for which there is greater variability in mortar and masonry unit qualities than modern masonry products. As a result, cost-effective adobe construction depends on time-tested and appropriately conservative empirical methods to guide prescriptive solutions for smaller-scale projects, which cannot justify the expense of laboratory testing for each source and product. While TMS 402 Appendix A: Empirical Design of Masonry will no longer be included in 2022 and future editions, retaining reference to the previous edition (TMS 402-16) will allow adobe masonry provisions to remain in the IBC until a standard specific to adobe construction can be created and approved as an IBC-referenced standard. The Masonry Society has indicated that TMS 402-16 will remain available for the foreseeable future. A related change corrects a typographical error to a TMS Appendix A section in IBC Section 2109.1.1.

Conclusion Structural engineers should be aware of significant structural changes in the 2024 IBC for concrete and masonry. New provisions and referenced standards are added for structural concrete reinforced with glass-fiber reinforcement. IBC Section 1905 has been revised and reorganized and no longer amends sections of ACI 318, rather focusing on provisions that supplement ACI 318 for seismic design. TMS 402 and TMS 602 have been updated to 2022 editions. Mortar requirements for adhered veneer are updated to meet new TMS 402-22 requirements. Finally, the option for empirically designed masonry has been removed from the 2022 edition of TMS 402 but reference to the previous edition (TMS 402-16) will allow adobe masonry provisions to remain in the IBC.�

Look for Part 1 of the series in the November 2023 issue and Part 2 in the December 2023 issue of STRUCTURE. John “Buddy” Showalter, P. E., (bshowalter@iccsafe.org) is Senior Staff Engineer of ICC’s Consulting Group. Sandra Hyde, P. E., (shyde@iccsafe.org) is Managing Director of ICC’s Consulting Group.

historical STRUCTURES 19th Century Mississippi River Bridges Louisiana, Missouri Bridge 1873 By Dr. Frank Griggs, Jr.

he Chicago & Alton Railroad was formed in 1862 to run from Chicago on Lake Michigan southerly to Alton on the Mississippi River. Over time a branch line from Bloomington to Roodhouse and then to the Mississippi opposite Louisiana, Missouri was built. From Louisiana west it had a line to Mexico, Louisiana and Jefferson City as well as a line to Kansas City. It used a car ferry for a period but needed a bridge across the Mississippi River to connect these lines. The site of the bridge was described as, “The general features of the river and

surrounding country are a sandy bed, a bold rock bluff on the west near the river, a wide alluvial bottom on the east, rock appearing on the surface at the west shore, and a gradual slope to the east shore, where it is one hundred feet below the river bed. The width of the river on the bridge line is 3,900 feet.” On February 15, 1871 the House approved the bridge and on March 3, 1871 the Senate followed suit. It was entitled “An Act to Authorize the construction of a bridge over the Mississippi River at Louisiana,

Map of Chicago & Alton with branches. Louisiana at bottom of map that also shows location of earlier bridges across the Mississippi at Quincy, Keokuk, Rock Island and Clinton.

JANUARY 2024

The swing span’s superstructure was a Whipple double intersection truss.

Missouri, and also a bridge over the Missouri River at Glasgow in said new company is the Mississippi River Bridge Company, and the bridge state.” Unlike the July 25, 1866 Act that approved bridges across the which it is building is at Louisiana, Mo., for the Chicago & Alton road.” Mississippi requiring for a low level bridge the clear space on either side With the legalities out of the way in the late spring of 1873 the comof the swing pier of 160’, they upped it to 200’ clear stating “Provided, pany decided to proceed with the bridge and received the approval of That if said bridge shall be constructed as a drawbridge, the same shall their plans from the War Department. The plan consisted of from west be constructed with spans of not less than two hundred feet in length (Missouri) to east (Illinois), an embankment 2,800’ long; followed by in the clear on each side of the central or pivot pier of the draw.” This spans of 160’, a 444’ swing span, a 255’ fixed span; a 223’ fixed span increased the length of the swing span from around 360’ to 440’. It addition if a fixed high level span was selected it raised the clearance to 50’ above high water and all fixed spans over the main channel had to be a minimum of 350’ span. These increases were to pacify the shipping interests who were still against any bridge in the channel that would hinder their free passage. On April 4,1873 a charter was granted by the State of Illinois and on April 9, 1873 a charter was given by the state of Missouri. On April 25, 1873 the two entities were combined with the Railroad Gazette reporting on May 31, 1873, “Articles of consolidation between the Mississippi River Bridge Company, an Illinois corporation, and the Louisiana Bridge Company, a Missouri corporation, have been filed with the Secretary of State of Illinois. The title of the When the Missouri Bridge was built in 1873, its 444-ft. swing span was much longer than any typical swing spans in the world. 56 STRUCTURE magazine

In this 3D view of Louisiana, Missouri, a portion of the Missouri Bridge is shown in the lower left. Also visible is the Noix Creek with an American Bridge Company span over it.

and six spans of 160’. The embankment on the east approach was 2,200’ long. They determined they wanted the bridge built before the year was out before the ice closed the river. They, Mississippi River Bridge Company, selected Elmer Corthell as their Chief Engineer. Corthell would go on to become a leader of the profession working closely with George S. Morison and James B. Eads. The masonry piers were built on wooden piles by Reynolds & Saulpaugh of Rock Island for $250,000. The same firm also placed the approach embankments. They had previously worked on several of the earlier Mississippi River bridges. To speed up the process the Company awarded the contract for the superstructure to three different bridge companies. The American Bridge Company built the 140’ span using a Post Truss. The Keystone Bridge Company, under Jacob H. Linville, built the six 160’ standard Keystone Bridge spans and the Kellogg Bridge Company of Buffalo, New York built the 444’ long swing span and the 255’ and 223’ spans, both Pratt Trusses. Charles Kellogg had been with the Detroit Bridge Company when they built the Quincy Bridge and with Kellogg & Clarke when they built the Keokuk Bridge. He started his own firm in Buffalo in 1870. The river was known to shift its main channel over time. In order to ensure the main channel remained under the swing span they chose to build embankments to confine the river and a deflecting dyke upstream to guide the water. The confinement was accomplished by rip-rapped embankments extending into the river 550’ on the west side and 1,260’ on the east side. The report on the bridge noted, “The results obtained thus far are a quickening of the current between the dyke and the levee at Louisiana, the washing away of the bar below the dykes, and a deposit to some extent behind the dyke. The changes on the Upper Mississippi are necessarily slow, but it is confidently expected that this dyke, together with the embankment at the bridge line, will greatly improve the channel between the levee and the bridge, and hold it in its proper place through the draw.” The major span was the 444’ swing span that was much longer than any swing span in the world at the time. The masonry for the pier was

supported on 200 piles and contained 1,200 cubic yards of stone. The superstructure was a Whipple double intersection truss with sloping upper chords, 28’ high at the end and 39’ 8” at the peak, and was all of wrought iron. The trusses were 18’ on center. Surprisingly the total weight of the swing span was only 750,000#. The turntable had a diameter of 36’ and rolled on 48 cast iron wheels on a planed surface. It was said, “One man can move the draw with an ordinary hand-gearing, but it is worked by a double-cylinder engine. At the ends of the draw are cams for raising the ends of the truss on the draw-rest pier. These cams are worked by the engine on the turntable.” The 11th Annual Report of the line stated, “although a steam engine is provided for operating it, so perfect is its construction, that except when high winds prevail, one man can, without the aid of steam, open and close it.” The entire length of the bridge was 2,052’ and the entire cost of bridge and river work was $685,000. A report by the Assistant Engineer, H. W. Parkhurst, that was published in the Railroad Gazette on January 17, 1874 noted, “The third peculiar feature of the work is the unusually short time consumed in the construction of the bridge. When on the 30th day of June last the instructions were given to have the bridge ready for business by Christmas, but few believed it possible to do it; but by planning the work to allow a margin for delays, by putting on a force commensurate with the work and the time in which it was to be done, with favorable weather and reliable and energetic contractors, the work has been done on time. The bridge was formally opened on the 24th of December, and since then all trains have crossed on the bridge.” The bridge was rebuilt on the same piers in 1898 by the Lassig Bridge and Iron Works of Chicago. Several spans were replaced in 1945 and the bridge is now a part of the Kansas City Southern Railroad.� Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19th Century cast and wrought iron bridges. He is now an Independent Consulting Engineer (fgriggsjr@verizon.net).

JANUARY 2024

structural OBSERVATIONS Unwanted Vibration in Structures The undergraduate level reader will appreciate that vibration of structures will be a part of their career. By Jibreel Mustafa and Craig E. Barnes

ibration issues for structures have been with us since the beginning of time and will be with us forever. The subject of vibration is not typically part of an engineer’s college education but is a subject worthy of attention and study if one wishes to avoid an embarrassing situation. Noteworthy problems resulting from vibration, i.e., the resonant response of structural elements to load input from outside sources, have certainly been newsworthy, starting with the Angers France Bridge collapse in 1850, to the Tacoma Narrows Bridge in 1940, to the Millennium Pedestrian Bridge that spans London’s River Thames that reopened in 2002 after tuned mass dampers were installed. Unwanted vibrations can develop in structures that are not structurally sound, but more often, a structure that is structurally sound is not psychologically sound to human users. For hundreds of years, structures avoided vibration issues as a natural result of the construction used. You may want to consider that to be the “mass” solution. In other words, in the past, structural systems were more massive, spans were shorter, and supporting elements were thicker. As an example, just compare normally reinforced concrete rib or waffle slab floor construction to the lighter post-tensioned concrete floor construction frequently used today. Architects and engineers did not foresee that 8-inch thick post-tensioned slabs, supported by columns spaced at 20-foot to 30-foot intervals, while structurally sound, would have a “trampoline” feeling that vibration sensitive users imagined to have structural Figure 1 problems. Science and engineering readily dampened this vibration perception issue by providing lightweight, non-structural floor-to-ceiling partitions, realigning travel aisles and display cases, and, in extreme cases, installing mass vibration dampers tuned to counter the natural floor vibration frequency. Architects and engineers often use prescribed methods to ensure precise, safe, and efficient building designs. The vibration of structural systems due to human activity is a serviceability consideration handled primarily by structural engineers. Serviceability aims to meet performance criteria while maintaining comfort, usability,

58 STRUCTURE magazine

and aesthetics. When assessing serviceability, engineers evaluate deflection limits, durability, stability, cracking, and vibration. The American Institute of Steel Construction’s AISC Design Guide 11 – Floor Vibrations Due to Human Activity (2nd Edition) is an extensive resource focusing on floor and stair vibration design in buildings. The guide provides practical advice for structural engineers to assess and control vibrations caused by occupants’ movement. The natural frequency of a building or component represents its inherent vibration when subjected to external forces. Resonance

occurs when dynamic forces from human activity coincide with the envisioning the building’s overall design and functionality, carefully structure’s natural frequency, causing amplified vibrations. The AISC considering factors like traffic flow and seamless integration with the design guide emphasizes analyzing resonance and frequency effects architectural concept. On the other hand, structural engineers bear the to minimize excessive vibrations. By following these guidelines, primary responsibility of ensuring the building’s structural integrity engineers ensure that the building can handle dynamic loads from and serviceability. Engineers can meticulously calculate loads, stresses, human activity without compromising performance. and forces that the stairs must withstand, ensuring compliance with Humans are very sensitive to vibrations, causing discomfort, agi- local building codes and safety regulations, but without a focus on tation, and uncertainty on the building’s overall functionality. vibrations, all is for naught.� According to the AISC Facts for Steel Buildings No. 5 – Vibration, humans can perceive motions of about 0.005 times the acceleration Craig E. Barnes, B. S., M. S., MBA P. E., S. E., was the Founding of gravity (0.5%g). Not only could vibrations be annoying and Principal of CBI Consulting Inc., Structural Engineers, Boston, MA inconvenient, but the overall structural integrity of the building Jibreel Mustafa, B. S., is a Structural Engineer in Training at SOCOTEC, could be perceived as compromised, potentially leading to safety Boston, MA concerns for its occupants and long-term durability issues. Even if the vibrations do not pose any structural risks, the mere sensation of movement can lead to a sense of insecurity and disrupt the perception of stability in the building. Human perception of vibrations is highly sensitive, and even subtle motions can cause discomfort and uncertainty about the building’s overall functionality. In the context of building design, it is essential for the engineer and architect to recognize that From Structure Magazine human perception is beyond only assessing structural risks. Besides thinner structural systems with longer spans lacking damping from partitions, the vibration of basic scissor stairs, and more specifically, the monumental stairs that appear on almost every project present significant challenges to structural engineers. Architects look for a “sleek” design, often utilizing glass railings and treads to achieve the effect. Here again, this beauty, which reduces the mass that contributes to stiffness, may lead to perceptible vibration issues. Annual Publication with Industry Resources for SEs and The vibration in staircases is influenced by Profiles from STRUCTURE’s Advertising Partners various factors, such as the stair structure’s design, material properties, and load distribution. A well-designed staircase should consider all these aspects to minimize vibrations and ensure its structural stability and performance. The AISC Steel Design Guide 11 provides valuable guidelines and recommended practices for designers to assess and control vibrations effectively. Following these prescribed methods is essential to achieve a staircase that not only can withstand the expected loads but also remains comfortable and functional for its intended use. By mitigating excessive vibrations, the overall perception of the structural integrity becomes more favorable. Please see the attached Figure No. 1 from Design Guide 11. While it may appear intimidating, all the elements of the equation should be familiar. Find your next industry partner for anchors, AISC has taken the complex task of determining how they are combined to result in foundations, concrete, software, wood products, a usable vibration equation. steel and cold-formed steel, connections, and more. Architects hold the responsibility of

Available Online

Structural Engineering Resource Guide www.structuremag.org

2023/24

Resource Guide

JANUARY 2024

ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

STRUCTURAL ENGINEERING

NCSEA News Celebrating Excellence: Highlights from the 2023 NCSEA Structural Engineering Summit The 2023 NCSEA Structural Engineering Summit, a nationwide gathering of nearly 1,000 attendees, stood as a testament to the vibrancy of the structural engineering profession. Held in Anaheim, CA, this year’s Summit proved to be a hub of enthusiasm and knowledge exchange, hosting a series of dynamic events that captivated practicing structural engineers, executives, students, trailblazers, educators, and young engineers alike.

Professional Development and Networking Extravaganza This year’s Summit, held in Anaheim, CA, provided an extensive platform featuring more than 14.5 hours of customized professional development for practicing structural engineers. Beyond enriching their knowledge, attendees had the opportunity to engage in social and networking events, complemented by an expansive exhibit hall hosting more than 80 exhibitors.

Letting the Good Times Roll To kick off the Summit in style, the most skilled and vibrant structural engineers from around the country hit the bowling alley and let the good times roll to network in style. Kudos to the Structural Engineers Association of California (SEAOC) for their warm welcome to California.

Knowledge Exchange in the Exhibit Hall The Summit’s Exhibit Hall, the largest and most impactful platform for knowledge exchange and relationship-building, hosted myriad supplier partners offering innovative solutions—our gratitude to all exhibitors for their participation.

Honoring Excellence in Structural Engineering Keynote Insights and Inspirational Sessions The Awards Celebration saw KPFF Consulting Engineers & ERA Structural Engineering receive the coveted Structure of the Year Award for the awe-inspiring Children’s Museum of Eau Claire, Wisconsin. Be sure to visit weseeaboveandbeyond.com/see-awards, to view all this year’s Structural Engineering Excellence (SEE) Awards Winners.

60 STRUCTURE magazine

The Summit’s opening keynote, delivered by John Gavan, CEO/President of KPFF Consulting Engineers and Co-Founder of LeaderFlow, centered around ‘The Diversity Imperative.’ Gavan highlighted the pivotal role of inclusivity in shaping the future success of the structural engineering field through the creation of an environment of equity, inclusion, and belonging. Former NASA Engineer Maureen Zappala joined the Summit to guide attendees on recalibrating their thinking, urging them to overcome ‘impostor syndrome’ and embrace their intelligence.

News from the National Council of Structural Engineers Associations

Nurturing Future Leaders and Building Connections

Empowering Leadership and Collaboration

Committee Collaboration and Ambitious Goals

A series of events brought together aspiring future leaders and experienced professionals to foster inspiration, mentorship, and valuable connections. Highlights included the SEAOC Pathways Program participants’ inaugural engagement, Young Member Speed Mentoring, and the Future Leaders Reception, all celebrating the vision and potential of students, early-career engineers, and emerging leaders.

The Executive Roundtable Breakfast brought together structural engineering leaders and executives for impactful discussions on talent acquisition and retention strategies, providing insights into the challenges and opportunities within the SE industry.

The Summit provided an ideal platform for NCSEA Committees to meet, fostering the exchange of ideas and strengthening bonds within the structural engineering community. Committees played critical roles, with the SE3 Committee organizing its National Symposium, the Code Advisory Council concluding the Summit with the General Session, and the Education Committee curating diverse and impactful sessions.

Looking to the Future As we reflect on the success of the 2023 Summit, we eagerly anticipate the 2024 Structural Engineering Summit scheduled for November 5–8 at the MGM Grand Hotel in Las Vegas, NV. Stay tuned for further details, including a call for abstracts and exhibition opportunities, at ncseasummit.com.

follow @NCSEA on social media for the latest news & events! Visit www.ncsea.com/education for the latest news on upcoming webinars and other virtual events.

NCSEA Webinars January 25, 2024

Boston University Data Science Center

February 6 , 2024

Elevator 101

Purchase an NCSEA webinar subscription and get access to all the educational content you’ll ever need! Subscribers receive access to a full year’s worth of live NCSEA education webinars (25+) and a recorded library of past webinars (170+) – all developed by leading experts; available whenever, wherever you need them!

Recommendations for Performing Structural Engineering Quality Assurance Reviews

JANUARY 2024

SEI Update Hiring for Senior Technical Manager SEI is seeking staff to manage the SEI technical community including facilitation and development of the Institute’s technical and codes and standards activities, technical program development for SEI events, and continuing education content. Learn more and apply at https://asce.applicantpro.com/jobs/2863867

Education

ASCE/SEI Substation Structure Design Guide-MOP 113 Program – January 25 Join us for a discussion on the new guide which provides structural design guidance and function as a comprehensive resource for outdoor electrical substation structures and foundations. The live program will include a dialogue with industry experts, a technical presentation and Q&A with the audience. Register today at www.asce.org/SEIEvents

SEICon24 Join us March 20-22 at NASCC: The Steel Conference for an exciting opportunity to learn, network, and have fun with your SEI community, and take advantage of broader opportunities at NASCC. Check out SEI sessions and program highlights at www.SEICon24.org. For registration and hotel accommodations see www.nascc.aisc.org.

Advancing the Profession

NIST Grant Contractor Report on Advancement in Performance-Based Wind Design Now available from workshop held February 2023 at ASCE. The report was developed by wind engineering practitioners and researchers for buildings, and serves as a roadmap for the standardization and application of performance-based wind design. The impetus for the project was the extensive casualties and property losses that have occurred over the last several decades due to damaging hurricanes, tornadoes, and other wind events affecting the United States. NIST has continued to research and provide leadership in the advancement of knowledge of these hazards and to develop standards that will lead to more resilient communities across the nation. The workshop process included a review of the literature, which identified research needs in the areas of Wind Climate Characteristics, Structural System Reliability, Wind-Structure Interaction, Structural Analysis Techniques, and Structural Design. This review was followed by an extensive workshop preparation process, a two-day workshop to obtain input from experts in these areas, and report preparation and review. The workshop identified a broad range of research and development activities to advance the use of Performance-Based Wind Design with the goal of reducing the impacts of these severe wind events. This report includes discussion and specific recommendations on the following 10 topics: 1. Development of main wind force resisting system reliability; 2. Development of components and cladding reliability;

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News of the Structural Engineering Institute of ASCE 3. Integration of performance between the building structural system and the cladding; 4. Characterization of engineering properties of thunderstorm and tornado wind events; 5. Characterization of the wind hazard and loads for short and long return periods; 6. Improvement of the understanding of structural and material properties; 7. Improvement of physics-informed, computationally efficient methods for nonlinear analysis of wind response over long-period durations; 8. Static pushover for wind engineering to quickly evaluate nonlinear structural performance; 9. Development of wind loading protocol for experimental quantification of system performance in wind; and 10. Economic study to identify existing buildings at risk. Access at http://nvlpubs.nist.gov/nistpubs/gcr/2023/NIST.GCR.23-045-upd1.pdf

Now Available at www.asce.org Substation Structure Design Guide, Second Edition, MOP 113 Documents electrical substation structural design practice and gives guidance and recommendations for the design of outdoor electrical substation structures.

Resilient and Sustainable Buildings Provides a high-level overview of the methods and outcomes of four major projects funded by the National Science Foundation that focuses on different aspects of resilient and sustainable buildings (RSB), ranging from a single building to a full community.

Seismic Evaluation and Retrofit of Existing Buildings Standard, ASCE/SEI 41-23 Describes deficiency-based and systematic procedures that use performance-based principles to evaluate and retrofit existing buildings to withstand the effects of earthquakes.

Infrastructure System Resilience: An Engineering Framework for Assessment, Management, and Governance Describes a framework that demonstrates the interconnected relationships between the main elements that comprise infrastructure system resilience.

Check out Local SEI Chapter and Graduate Student Chapters and get involved www.asce.org/SEILocal

Errata

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI. To submit errata, contact sei@asce.org. JANUARY 2024

CASE in Point Tools To Help Your Business Grow... CASE has committees that work together to produce specific resources available to members, from contract documents to whitepapers, to help your business succeed. If you are a member of CASE, all CASE publications are free to you. NCSEA and SEI members receive a discount on publications. Use discount code - NCSEASEI2022 when you check out. Check out some of the brand new CASE Publications developed by the Guidelines Committee… CASE 976-C: A Review and Commentary on the American Institute of Steel Construction 2022 Code of Standard Practice for Steel Buildings and Bridges The importance of the AISC Code of Standard Practice (AISC 303-22), referred to herein as the Code or COSP) to the construction community is manifested in its almost 100 years of use and development. This Code establishes the trade practices for the steel industry. Generally, this involves the acceptable practices and responsibilities of the Fabricator and Erector and the responsibilities of others such as the Owner’s Designated Representative for Design (ODRD) – (usually the Structural Engineer of Record), the Owner and the Owner’s Designated Representative for Construction (ODRC) – (usually the General Contractor or Construction Manager or similar authority at the jobsite) as they relate to the work of the Fabricator and Erector. The 2022 COSP addresses many recent changes in the practice of designing, purchasing, fabricating, and erecting structural steel and is therefore a continuation of the trend of past improvements and developments of this standard. CASE White Paper Beyond the Code: Shrinkage Cracking

CASE recognizes that the International Building Code or other governing codes do not address all aspects of structural engineering and design. Often, the most common issues where the owners, or the contractor or the design team are not aligned deal with what is not clearly addressed by the various codes or design guidelines. This is the second in a series of “Beyond the Code” white papers that will attempt to collate design considerations that need to be discussed with the owners at the beginning of a project to establish a clear Basis-of-Design for the project. By proactively bringing up the design consideration in front of the owners, the Structural Engineer can set up realistic expectations and discuss the cost impact of alternative designs. This white paper in the “Beyond the Code” series discusses shrinkage cracking in concrete with an explanation of why it occurs, common locations they occur, and strategies to mitigate them becoming a risk in your project. You can purchase these and other Risk Management Tools at You can also browse all of the CASE publications at https://www.acec.org/member-center/get-involved/coalitions/case/resources/ Is there something missing for your business practice? CASE is committed to publishing the right tools for you. Have an idea? We’d love to hear from you!

Follow ACEC Coalitions on LinkedIn: www.linkedin.com/in/acec-coalitions 64 STRUCTURE magazine

News of the Coalition of American Structural Engineers Upcoming Events Joint Town Hall Event with CASE, NCSEA, and SEI February 21, 2024 2:00–3:30 pm ET Online Leadership from CASE, NCSEA, and SEI will host a virtual joint town hall event to discuss how the three organizations are progressing to fulfill the Vision for the Future of Structural Engineering (adopted April 2019), highlighting initiatives to advance the profession and enhance member engagement. The town hall is an opportunity to catch up on things you might have missed and gain insight into what the three organizations are doing moving forward. This complimentary event is open to all CASE, NCSEA and SEI members. https://program.acec.org/ joint-town-hall-event-case-ncsea-and-sei

Coalitions Winter Meeting February 26–27, 2024 New Orleans, LA Innovation Forward: Advancing your Business with Tomorrow’s Technology Are you ready to steer your firm toward success in the ever-evolving landscape of today’s marketplace? Discover the strategies that are propelling companies to new heights, including the game-changing forces of AI and the digital marketplace. Join us at ACEC’s Winter Coalitions Meeting, in New Orleans, where you’ll have the unique opportunity to learn from your peers about their plans for tomorrow to ensure they remain at the forefront of competition in today’s dynamic business world. Don’t miss this opportunity to dive deep into the future of business and technology. Secure your spot at ACEC’s Coalitions Winter Meeting today and set your course for success in the competitive marketplace of tomorrow. Join us at the Coalitions Winter Meeting, where tomorrow’s success begins today! https://program.acec.org/2024-winter-coalitions-meeting

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JANUARY 2024

CODES and STANDARDS FAQ on SEI Standards What you always wanted to ask. By Jennifer Goupil, P. E., F. SEI, F. ASCE

his quarterly article addresses some of the questions received about structural standards developed by the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE). In addition, questions from engineers, building officials, and other design professionals are often considered to develop future editions. Following are some questions received by SEI and responses to clarify the provisions.

ASCE 41, ASCE 7, Fv, And Supplements I have realized that there are corrections for the Fv values in ASCE 7-16 that have been provided in additional supplements, particularly with Supplement 1 and Supplement 3. Since ASCE 41 relies on these values from ASCE 7, how does one find the correct values now in ASCE 41? Fortunately, the ASCE 41 committee has addressed this and also published a correction. Supplement 1 to ASCE 41-17 adopts Supplements 1 and 3 of ASCE 7-16. To expand on the explanation, changes were made to ASCE 7-16 near the end of the cycle, creating a situation where one could not develop the general response spectrum for the Basic Safety Earthquake 1 and 2 (BSE-1E and BSE-2E) on Site Class E because there is no Fv value for Site Class E in ASCE 7-16. To address this, Fv values were provided in ASCE 7-16 Supplement 1. Supplement 1 also contains modifications to Chapter 21 of ASCE 7-16, the site-specific hazard procedures. Supplement 3 of ASCE 7-16 changes the exception to Section 11.4.8 of ASCE 7, which permits users to use the general response spectra with a modified SD1 value as opposed to a site-specific spectrum when situated on Site Class D and E. The original exception required Cs multiplied by 1.5. Because there is no Cs in ASCE 41, one could use the exception without amplifying the BSE-1N and BSE-2N SX1 parameter by 1.5, which is the intent of the exception. Supplement 3 revises the exemption to require the SD1 parameter to be multiplied by 1.5. This is explained fully in the commentary in ASCE 41-17 Supplement 1 Chapter C2 SEISMIC HAZARD as follows: In ASCE 7-16, a provision was added requiring site-specific procedures be used to develop the BSE-1N and BSE-2N hazard parameters or amplification factors on the USGS mapped values be used when a building is on Site Class D or E. Supplement 1 of this standard adopts two supplements of ASCE 7-16 related to this and clarifies that user of this standard would apply the site-specific rules or the appropriate amplification factors to the BSE-1N and BSE-2N hazards as indicated in ASCE 7-16, but that those rules do not apply to the BSE-1E and BSE-2E hazards. While the modified, larger Fa and Fv values for determining the lower limit on site-specific procedures in ASCE 7 Section 21.3 are required for the BSE-1N and BSE-2N, they are not for other seismic hazard levels. This is because the modified, larger Fa and Fv values were developed to correct for the non-conservatism of the 1/T spectral shape at the BSE-2N seismic hazard level for Site Classes D and E. These Fa and Fv values were not developed for other, lower seismic hazard levels, such as the BSE-1E and BSE-2E. Therefore, for other hazard levels, the Fa and Fv values per Chapter 11 of ASCE 7 are referenced instead. The full text of ASCE 41-17 Supplement 1 can be found in the ASCE Library or on www.asce.org/sei. 66 STRUCTURE magazine

Flexural Rigidity For Walls In ASCE 41-17, Table 10-5 Effective Stiffness Values, the equation for Flexural rigidity in Walls-Cracked includes gross Area (Ag). The stiffness for flexural members is not calculated with the area; is this correct? You are correct; flexural rigidity is calculated using the gross moment of inertia of the gross section, Ig, and should be 0.35EcEIg. This was corrected in published errata in Batch 1, published Dec. 3, 2018. This, along with Batch 2 and 3 of the published errata, is available in the ASCE Library or on www.asce.org/sei.

ASCE 41-23 When will the 2023 edition of ASCE 41 be published? Will it be referenced into the 2024 International Existing Building Code? The 2023 edition of ASCE 41 was published in December of 2023 and is available at www.asce.org. ASCE 41-23 was approved for adoption into the 2024 IEBC, however was erroneously omitted during publishing and now appears as an errata in ICC Errata Central and will be corrected when the 2nd edition of the 2024 IEBC is printed. This article’s information is provided for general informational purposes only and is not intended in any fashion to be a substitute for professional consultation. The information provided does not constitute a formal interpretation of the standard. Under no circumstances does ASCE/SEI, its affiliates, officers, directors, employees, or volunteers warrant the completeness, accuracy, or relevancy of any information or advice provided herein or its usefulness for any particular purpose. ASCE/SEI, its affiliates, officers, directors, employees, and volunteers expressly disclaim any and all responsibility for any liability, loss, or damage that you may cause or incur in reliance on any information or advice provided herein. If you have a question you want to be considered in a future issue, please send it to sei@asce.org with FAQ in the subject line. Visit asce.org/sei to learn more about ASCE/SEI Standards. Jennifer Goupil, P. E., F. SEI, F. ASCE, is the Managing Director of the Structural Engineering Institute and the Chief Resilience Officer for the American Society of Civil Engineers.