June STRUCTURE 2025

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EDITORIAL BOARD

Chair John A. Dal Pino, S.E. Claremont Engineers Inc., Oakland, CA chair@STRUCTUREmag.org

Kevin Adamson, PE Structural Focus, Gardena, CA

Marshall Carman, PE, SE Schaefer, Cincinnati, Ohio

Erin Conaway, PE AISC, Littleton, CO

Sarah Evans, PE

Walter P Moore, Houston, TX

Linda M. Kaplan, PE Pennoni, Pittsburgh, PA

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On the Cover: The Hangzhou Century Center, also known as “The Gate of Hangzhou,” is a prominent urban development situated in the Xiaoshan District of Hangzhou, China. This iconic development comprises two high-rise towers, each reaching a height of 310 meters, connected at their base by a 60-meter-span steel arch bridge.

Nicholas Lang, PE Vice President Engineering & Advocacy, Masonry Concrete Masonry and Hardscapes Association (CMHA)

Jessica Mandrick, PE, SE, LEED AP Gilsanz Murray Steficek, LLP, New York, NY

Brian W. Miller

Cast Connex Corporation, Davis, CA

Evans Mountzouris, PE Retired, Milford, CT

Kenneth Ogorzalek, PE, SE KPFF Consulting Engineers, San Francisco, CA (WI)

John “Buddy” Showalter, PE International Code Council, Washington, DC

Eytan Solomon, PE, LEED AP Silman, New York, NY

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FIT MORE INTO LESS.

Today’s multi-family residential construction design calls for maximum ceiling height with minimal floor-to-floor depth, enabling developers to fit more into multi-story buildings.

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HANGZHOU CENTURY CENTER: ENGINEERING A LANDMARK

By Jin Chen, PE, SE

MAKER MAXITY

26

By Anantha Chittur, SE, PE and Steven Baldridge, PE, SE

Innovative, unconventional solutions abound in a concrete high-rise hospitality project in India.

A suspended steel grid structure connects two towers in this iconic development in Hangzhou, China.

20

FEATURES Contents JUNE 2025

30

WALKING ON AIR

By David Fields, PE, SE, and Alex Wiley, PE, SE

An eccentric cantilever and stepping perimeter columns allow a Chicago luxury apartment tower to dramatically capture space at height.

CAESARS SUPERDOME RENOVATION

36

By Eric Grusenmeyer, PE

A phased approach to major renovations at the New Orleans stadium allowed it to remain fully functional and continue to host major sports and entertainment events, ensuring a steady stream of revenue and minimal disruption to schedule.

SCIENTIFIC GROWTH OF A CAMPUS

By Michael A. Tecci, P.E., Brooke H. Shannon, Ph.D.

Wesleyan University endeavored to build a state-of-the-art science complex to expand its reach and grow multiple programs. 42

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Photography by Dustin Williams

COLUMNS and DEPARTMENTS

By Luke Lombardi, PE and Lauren Wingo, PE (SE 2050 Co-Chairs)

Nabih Youssef

By William L. Coulbourne, PE, Jessica Mandrick, PE, SE, and Adam Reeder, PE, CFM

By Andrew Sundal, AIA, PE; Dave Martin, SE; Emre Toprak, Ph.D, PE; and JohnMichael Wong, Ph.D, SE

Tara Flaherty, EIT

By John Dal Pino, David Seward, Anders Carpenter, Ruth Todd, Maria Flessas, and Dan Bech

EDITORIAL

Towards Zero Carbon: Call to Action for Structural Engineers

By Luke Lombardi, PE and Lauren Wingo, PE (SE 2050 Co-Chairs)

Structural engineers adapt design and construction methods that change with economics, materials, and current research available to shape the built environment—quite literally. From the carved stone used to build the pyramids to the concrete dome of the Pantheon, our profession has answered the evolving needs of society with ingenuity and resolve. And in the wake of disasters, like the 1994 Northridge earthquake, we respond with creative solutions to keep our communities safe. We observe, gather data, calculate risk, develop design formulas, and establish code changes. As storms grow and disasters worsen, our capabilities are needed and we are called to act.

Today, we stand on the brink of another major shift and face a new defining challenge. One that isn’t sudden but accelerating. The science is clear: our development systems use up vast resources, disrupt ecosystems, and create an imbalance of greenhouse gases destabilizing our climate. Concrete and steel, principal materials that define our profession, are among the most carbon-intensive on Earth—contributing upwards of 15% of global emissions. That is six times that of aviation! Continuing to build as we have will use up remaining carbon budgets needed elsewhere.

And yet, at this existential threshold is an incredible opportunity.

Material advancements, smarter design strategies, and emerging policies are opening the door to better collaboration and more efficient, lowerimpact structures. This shift needs structural engineers, and embracing this challenge is a way towards purpose and resilient business practice.

The Structural Engineering Institute’s (SEI) SE 2050 Commitment Program was founded to support structural engineers in this pivotal moment. The vision of SE 2050 is to lead a transition of the structural engineering profession towards a net zero future. Since SE 2050 was established in 2020, the topic of embodied carbon has gone from rogue to vogue to California code. While structural engineers were traditionally left out of sustainability discussions, that is quickly changing as the environmental impacts of structural materials become better understood.

Addressing embodied carbon in the built environment is an opportunity to show the societal value of our profession and advance our other core principles: economic and sustainable use of resources, the use of innovative technologies, and the creation of inspiring structures.

Now in its fifth year, SE 2050 has over 150 firms of all sizes across more than 30 states signed on to the commitment. These Signatory Firms are showcasing an evolution of the structural engineering profession and sit at the forefront of

adopting efficient design approaches and build ing technologies.

It’s important that structural engineers use our voice because we’re often the only ones that know what we know on a project. It’s structural engineers like Fraser Reid at Buro Happold who can evaluate the inefficiency of column transfers. It’s structural engineers like Alexis Feitel at KL&A who can say that steel can be salvaged. It’s structural engineers like Anthony Dente at Verdant inventing very lowcarbon straw panels. And it’s structural engineers like Don Davies at Davies-Crooks Associates that specify the performance characteristics of concrete. All of these structural engineers are members of SE 2050 Signatory Firms, amongst many others showcasing advancement of the profession. Engaging on embodied carbon puts front and center the importance of several themes:

practices—are available on the website, se2050.org. Another key resource published this year is the SE 2050 Commitment Program: 2023 Data Analysis and Findings Report. The findings provide insights on design parameters that most greatly influence embodied carbon.

• Efficiency and Cost Savings: Optimizing designs to reduce material use, engineers lower project costs while reducing embodied carbon. This puts engineers at the table earlier in the design process.

• Adaptive Reuse and Existing Buildings: In 2022, architects made more revenue from renovations than new builds. There’s growing potential in retrofitting and repurposing existing structures.

• Circularity and Material Reuse: Developing skills in deconstructing and reusing materials from existing buildings creates new revenue streams and value-added services.

Lastly, beyond the rational engineering assessment, this work has a resounding positive impact on people. Nearly two out of three people in the U.S. have a sense of personal responsibility toward climate change, but over half don’t know where to take action. For firm leaders, the power to influence our industry towards a better future offers a lasting legacy. And for young engineers, this work is an opportunity to grow in a career developing solutions to address the generation’s biggest challenge. SE 2050 is building a culture of collaboration that recognizes everyone has a role.

Start Small and Get Involved!

If you feel motivated to act, join SE 2050! SE 2050 Signatory Firms publicly share their accomplishments through annually updated Embodied Carbon Action Plans, which outline each firm’s approach to staff education, project impact tracking, reduction targets, and advocacy for embodied carbon-conscious design. These action plans—alongside free resources for advancing design and specification

You can also join us in person. Later this month, the Towards Zero Carbon 2025: Summit and Symposium will be held in Boulder, Colorado. This event will take education into action, bringing together firms collaboratively working to advance structural engineering towards best practices and technologies that foster sustainable, efficient resource use.

This year’s Towards Zero Carbon Summit will include three key tracks:

• Embodied Carbon Bootcamp—Ideal for engineers beginning their embodied carbon education journey.

• SE 2050 Signatory Firm Summit—A first-ever in-person gathering of SE 2050 Signatory Firms to exchange ideas and shape the program’s future.

• Firm Leader Roundtable—A collaborative space for leadership to drive sustainable transformation in our industry.

These tracks ensure structural engineers of all experience levels can engage, whether they’re just starting their sustainability journey, seeking deeper connections within the SE 2050 network, or guiding their firm’s evolving strategy.

The structural engineering profession is being shaped by the societal shifts occurring as a result of a warming world, while also influencing changes to advance design and construction practices towards a net zero future. SE 2050 provides a framework, and its Signatories show a path forward with tools available now. Whether you’re optimizing a new design or reimagining an old one, this is structural engineering’s moment to lead.

Lauren Wingo, PE (lauren.wingo@arup.com) is co-chair of SE 2050 and an Associate with Arup’s Climate & Sustainability team.

Luke Lombardi, PE (luke.lombardi@burohappold.com) is co-chair of the SE 2050 Program and co-lead of the Carbon Leadership Forum Los Angeles Hub.

Lauren Wingo Luke Lombardi

structural INFLUENCER

Nabih Youssef

Nabih Youssef, a leading California-based structural engineer and seismic design expert and pioneering advocate of steel plate shear walls in areas of high seismic risk, passed away on July 12, 2024, at the age of 80. Born in Egypt, Youssef, SE, F ASCE, FAIA, received a bachelor’s degree in structural engineering from Cairo University in 1967. After emigrating to the United States, he received a master’s degree from California State University, Los Angeles, in 1974 and then a postgraduate diploma in earthquake engineering from UCLA.

As the founder, chair, and CEO of his eponymous firm Nabih Youssef & Associates (NYA), he was a revered expert in the development of earthquake engineering codes and standards. Today NYA is an internationally recognized structural engineering firm with offices in Los Angeles, San Francisco, San Diego, Irvine, South Carolina, and beyond. Youssef’s visionary leadership, innovative engineering, and profound kindness left an enduring mark on the design and construction community. Youssef was a co-author of foundational documents for Performance Based Seismic Design (PBSD), which is a fundamental part of contemporary earthquake engineering.

NYA became known for undertaking landmark projects that had immediate and lasting effects on our communities. His accomplishments were many but those most important are:

• The base isolation of Los Angeles City Hall, a monumental effort to preserve the legacy of the historic tower after the effects of the Northridge earthquake.

• The 54-story LA Live project cited by the American Institute of Steel Construction for special achievement for the use of an innovative steel shear wall system. LA Live’s Ritz Carlton Tower pioneered new applications of PBSD and helped reimagine tall building seismic engineering in high seismic regions.

• The Broad, which houses 2,000 works of art collected by Eli and Edythe Broad, whose prominent collection is now encased in a “veil and vault” concept. To protect the artwork, light filters into the space through a creative honeycomb facade that covers an acre of column-free galleries.

• The base isolation of Our Lady of the Angels Cathedral earned Youssef and team recognition from ENR as Top Seismic Project of the 20th Century in 2006. After the historic Saint Vibiana Cathedral was damaged in an earthquake, the Los Angeles archdiocese commissioned a new $200 million cathedral. The base isolation system consists of 149 rubber bearings and a separate set of 47 steel sliders. The cathedral’s thin concrete walls and alabaster panels allow diffused light to pour inside in a modern take on stained glass windows. Youssef was thrilled to help realize Rafael Moneo’s vision for this contemporary deconstructivist design.

Youssef delighted in historic landmarks and breathing new life into buildings. He saw value in preservation to help neighborhoods thrive, show respect for their past, and bring vibrancy to communities. A few of his passion projects included the restorations and expansions of the Ace Hotel, the Harold Examiner building, the Los Angeles Memorial Coliseum, Dodgers Stadium, and Transbay Terminal in San Francisco. He helped retrofit and restore the Getty Villa, worked on the Walter E Washington Convention Center in DC, and innovated a glass canopy structure to enclose a new atrium supported by the new addition wing of the Cleveland Museum of Art.

Leader in Seismic Design

A registered civil and structural engineer, Youssef was one of the world’s leaders in earthquake engineering and seismic design and the development of associated standards. His position as the Chair of the Vision 2000 Committee and the Seismology Committee for the Structural Engineers Association of California heavily contributed to the enactment of PBSD, a major conceptual breakthrough for the engineering community. Youssef also chaired the City of Los Angeles’ Mayor’s Blue Ribbon Seismic Hazard Reduction Committee. He authored many technical papers, and taught classes at multiple universities, including lectures on engineering concepts and analysis for high-rise buildings. He served on the University of California Seismic Advisory Board, was part of the Building Seismic Safety Council “NEHRP” Special Programs of the National Institute of Building Sciences in Washington DC and was an Associate Editor for the publication “The Structural Design of Tall & Special Buildings” published by Wiley. He was a pioneer in the use of base isolation to protect structures seismically. His dedication to his work and collaboration with peers were leading aspects of his character.

The catastrophic failure of the Olive View Hospital and Sanitarium during the momentous Sylmar temblor of February 9, 1971, was one of the most important early influences on Youssef’s career. A graduate student in structural engineering at California State University in Los Angeles at the time, he had never felt an earthquake. “It was my first awareness of the severity of Mother Nature,” Youssef recalled to Downtown LA News in 2004. The structural failure of the hospital led to two of the 14 fatalities in the Sylmar quake despite the facility’s state-of-the-art design. This underscored the fact that

earthquake engineering was “an open field and earthquake codes were not fully developed. That’s what caught my creative interest and led to my decision to immerse myself in the field,” Youssef said. While Youssef made his name working on construction projects, his most lasting contributions could ultimately come from work that took place out of public view. Youssef sought to transform the entire philosophy underlying traditional earthquake codes. As chair of the Seismic Safety Committee of California’s Buildings Standards Commission, and as a member of many other panels, Youssef investigated the performance of buildings constructed to code standards before the 1994 Northridge earthquake. The investigation showed that steel-framed structures built to the most demanding specifications at the time were not immune to catastrophic failure during a big event. That finding added momentum to an ongoing shift away from force-based code prescriptions that lay out a list of generalized strength features that every building must have. Youssef and others urged regulatory agencies to adopt PBSD standards, which set goals ranging from preventing collapse to protecting property at various seismic intensity levels and performance objectives.

California’s State Historical Building Code is an example of standards that incorporate performance-based guidelines. “While not compromising life safety, it still allows alternative, creative methods of interventions which limit the intrusion and help protect the historic fabric of old buildings,” Youssef said. This transformation in thinking about earthquake safety deserves a good deal of credit for the downtown Los Angeles renaissance, especially along the Historic Core. People widely regarded Youssef as one of the leading thinkers among structural engineers within the adaptive reuse movement. When it came to historic structures, such as steel frame/brick

infill buildings, Youssef wanted to take advantage of the quality of the original designs. “The common view … was that masonry walls had no value. Retrofitting them required tons of shear walls and foundations, which was not feasible,” Youssef said. In fact, the intrusive intervention required under older codes sometimes did more harm than good, he added, not only to the historic character of old buildings but to their structural integrity. A better way to retrofit historic buildings, Youssef said, is to supplement the inherent strength of masonry walls with reinforced concrete frames, carbon fiber mats and other unobtrusive, lightweight materials. Those are also the most cost-effective methods.

Youssef played a key role in the booming reuse of beautiful historic buildings in the downtown, historic core of Los Angeles. Redevelopment was possible because of an improved partnership between developers and city officials who were receptive to novel approaches to earthquake design. “I wouldn’t use ‘flexible’ to describe their approach. Building officials feel guilty about that word,” Youssef said. “But I would say we now have much better collaboration between the city and leading engineering firms and practitioners. That has allowed us to implement cost-effective, elegant solutions, and in a timely manner too.”

Youssef was a husband and father of three. He created a national educational charity for children in need, https://www.copticedu.org/, and co-founded several schools. He changed the lives of countless people with opportunity, and more often with kindness.

With generosity and creativity, Nabih Youssef transformed structural engineering forever, leaving the profession better than he found it. His spirit of innovation and compassion will continue as his firm’s guiding principle as they carry his legacy forward into their next chapter. ■

Clockwise from top left: Nabih Youssef's work included The Broad art museum, Los Angeles City Hall, and LA Live.

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codes and

Major Revisions to ASCE 24— A Standard for Flood-Resistant Design and Construction

The new revisions were primarily influenced by the need to make the standard compatible with ASCE 7-22 Supplement 2 and ten years of post-disaster flood assessments.

By William L. Coulbourne, PE, Jessica Mandrick, PE, SE, and Adam Reeder, PE, CFM

ASCE 24 was last revised in 2014, over a decade ago while major flood events have caused severe damage to the nation’s building inventory and infrastructure. This standard, titled Flood-Resistant Design and Construction was first published in 1998 and was revised in 2005 as well as in 2014. ASCE 24-14 has been adopted into the International Building Codes by reference and is used across the country to guide building and re-building in areas designated as floodplains. This latest revision, ASCE 24-24, has been submitted for consideration in the 2027 IBC and is intended to improve building performance during floods by requiring higher elevations for buildings in floodplains and by strengthening many provisions that address how to construct buildings subject to flooding. This revision also aligns flood design requirements with the recent changes made to ASCE 7-22, Supplement 2 as they relate to more stringent standards being applied to flood load design. This standard revision provides a resource for the practice in the form of a Commentary section that provides examples of buildings in floodplains to illustrate how to use the new provisions, especially as they relate to the new elevation requirements.

New Elevation Requirements

Previous versions of ASCE 24 had minimum elevation tables that required a minimum elevation to the Base Flood Elevation (BFE) plus

some amount of freeboard. The BFE is FEMA’s regulatory minimum elevation or the elevation of the 1% annual chance flood, which is used for the National Flood Insurance Program (NFIP). Freeboard is an additional elevation that provides a margin of safety above the BFE minimum elevation. The NFIP requires communities to adopt minimum construction standards and in exchange makes flood insurance available for properties. In ASCE 24-14 and prior editions, the required amount of freeboard was dictated by the Flood Design Class (FDC) of the building; the higher the class (from 1 to 4), the greater the amount of freeboard generally. ASCE 24 uses FDC to distinguish building use types instead of Risk Categories used by ASCE 7; while the FDC aligns closely with Risk Category, FDC provides more specificity on the use types in each class.

ASCE 24 strives to meet or exceed the NFIP requirements. The elevation requirements in ASCE 24-24 are now driven by the Design Flood Elevation (DFE) which is determined by applying the higher of the locally mandated elevation requirements and a Mean Recurrence Interval (MRI) flood event. The MRI flood event is different for each FDC. FDC 2 buildings (most commercial and residential buildings) require a minimum elevation to the 500-year flood level; FDC 3 buildings require a minimum elevation to the 750-year flood level; and FDC 4 buildings require elevation to the 1,000-year flood level. Since there is very little information about the elevation of 750- and 1,000-year floods, there are scaling factors provided to help designers estimate those higher flood levels. The 500-year flood level is often provided in Flood Insurance

Studies (FIS) and the extent shown on FEMA Flood Insurance Rate Maps (FIRMs). Table 1-2 from the new standard is shown above slightly modified as Table 1 here.

The DFE is calculated as the DFE = FE com or (FEMRI + ΔSLC) where

• FE com = Flood elevation established by the community, and

• FEMRI = Flood elevation based on the required minimum MRI for the flood design class of the building or structure (500-year for Class 2, 750-year for Class 3, 1000-year for Class 4), and

• ΔSLC = Relative sea level change which shall not be taken as less than 0 As noted previously, flood elevations are generally available for 10-, 50-, 100- and 500-year flood events and are shown in the FIS and/or FIRM for the flood source of interest. The needed elevations for 750and 1,000-year elevations are almost never available unless a site-specific study has been performed. Therefore, two new tables were added that designate how to find the needed flood elevation when only certain pieces of information are available. The methods in these tables accommodate the range of flood data available on reports and maps throughout the country and are listed in order of most commonly available. One table describes the methods for noncoastal flood sources, and one describes the methods for coastal flood sources. The noncoastal flood source table (Table 1-3 in the standard) has five possible methods for each of the four FDCs. Table 2 is a slightly modified version of Table 1-3. The coastal flood sources table (Table 1-4 in the standard) has four possible methods for each of the four FDCs. Table 3 is a slightly modified version of Table 1-4. Tables 1-5 and 1-6 of the standard list the scaling factors necessary to calculate for higher return period events for coastal flood sources when the FEMRI information is not available. The intent of including Tables 2 and 3 shown here is to provide a minimum elevation for the structure that will elevate the structure above the MRI flood event and generally limit the MRI flood loads imposed on the structure per ASCE 7-22, Supplement 2. One example of this comparison is provided in this article in the Example Elevation Section.

There are worked examples for finding the correct minimum elevation for the nine cases (five noncoastal and four coastal) in the ASCE 24-24 Commentary for Chapter 1. The examples use various FDCs, and thus various design associated mean recurrence intervals to provide a range of possible approaches to obtaining the correct DFE. Since in each case, there is a minimum required elevation of either the BFE + freeboard or the DFE, there is a comparison in each example of which is higher—the BFE + freeboard or the DFE.

The elevation requirements carry over into other sections of the standard instead of being repeated and only slightly modified. The previous versions of ASCE 24 had separate elevation tables for Chapter 3 (primarily A zones), Chapter 4 (primarily V Zones and Coastal A Zones), Chapter 6 (Dry and Wet Floodproofing), and Chapter 7 (utilities). Those tables have been removed in ASCE 24-24 and the elevation requirements for these flood subjects are covered fully by Chapter 1 and Table 1-2. The other chapters now simply refer to Table 1-2 when elevation requirements are mentioned in each chapter. To further simplify the determination of the minimum elevation requirements, a web-based tool has been developed by the committee and the LSU AgCenter that will be released in conjunction with ASCE 24-24 in order to aid design professionals and local officials with minimum elevation determinations. Sections 2.3 and 4.4 of ASCE 24-24 on Elevation Requirements are measured consistent with ASCE 24-14 in that the minimum required elevation for buildings in noncoastal and coastal areas with small waves is for the top of the lowest floor to be elevated to or above the elevation established in the new Table 1-2 (shown here as Table 1), and in areas where the 100-year wave heights are greater than 1.5 feet, the bottom of the lowest horizontal structural member of buildings must be elevated in accordance with the same Table 1-2 requirements. Tables 2 and 3 shown here describe for the practitioner how to achieve the requirements of Sections 2.3 and 4.4 for different conditions related to the flood elevation data available.

Table 2. FEMRI for Flood Hazard Areas with Noncoastal Flood Sources

elevations (SWEL) available

Method C: Only 100-year flood elevation available

Method E: 100-year flood elevation not available

1 100-year FE100 FE100 FE100 100 com

2 500-year FE500 SWEL500+ [CMRI_100(FE100-SWEL100)]

3 750-year FE750

4 1,000-year FE1000

CMRI_500(SWEL500-Zdatum) + [CMRI_100(FE100-SWEL100)] + Zdatum

CMRI_500(SWEL500-Zdatum) + [CMRI_100(FE100-SWEL100)] + Zdatum

CMRI_100(FE100-Zdatum)+Zdatum

CMRI_100(FE100-Zdatum) + Zdatum

CMRI_100(FE100-Zdatum) + Zdatum

CMRI_100(100com -Zdatum) + Zdatum

CMRI_100(100com -Zdatum) + Zdatum

CMRI_100(100com -Zdatum) + Zdatum

Where SWELMRI represents the stillwater elevation at a specified MRI and CMRI_xxx represents the scaling factor from Table 1-5 or 1-6 (in the standard) depending on the MRI. Zdatum is permitted to be zero for the Gulf of Mexico and all other coastal sites. For Great Lakes and all other coastal lake sites, the Zdatum is the chart datum or low water datum.

Consideration of Sea Level Change Required

The determination of the DFE must now include consideration of sea level change in coastal flood locations. The standard requires that a building service life of 50 years be considered into the future, and that the amount of sea level rise be based on the historic rate of change (over the previous 40 years) at the building site location times the 50-year service life. A sea level change value of less than zero is not allowed. There is information in the commentary that discusses how to find the sea level change for many locations around the country. Data developed and provided by the USACE and NOAA covers many coastal locations around the country. There is no requirement that a site-specific study must be conducted in order to find the rate of sea level change at a specific project site. This requirement to include consideration of sea level change is in line with the requirements in ASCE 7-22, Supplement 2. Designers and owners may wish to consider a greater amount of sea level rise based on projections of future conditions, but such predictions are not required by ASCE 24-24.

Example Elevation Determination Comparison: ASCE 24-24 and ASCE 7-22, S2

Givens:

Building is FDC 2 located on the Gulf Coast Community has adopted ASCE 24-24 and requires 1 foot of freeboard FIRM Map indicates the BFE = 13 feet which is to the top of the wave at this coastal location

FIS at transect of interest indicates SWEL100 = 10.8 feet and SWEL500 = 15.1 feet

Rate of historic sea level rise is 0.015 feet/year and is to be used for a 50-year building life

Elevation at the site taken as 0 feet which is the coastal datum

Find the required minimum elevation in accordance with ASCE 24-24 and the equivalent elevation for loading in ASCE 7-22, S2. Since the FE100, SWEL100 and SWEL500 are all known, use Method B from Table 3 above to find the elevation required by ASCE 24-24.

1. The required minimum elevation to meet the community regulation (see Table 1) = FE100 = 13 feet+1 feet = 14 feet

2. The elevation required to comply with ASCE 24-24 for FDC 2 buildings = SWEL500+[CMRI_100(FE100-SWEL100)] = 15.1 + 1.35 (scaling factor from Table 1-5 in standard)*(13-10.8) = 18.1 feet

ΔSLR must be added to this elevation to determine the final FE500 for DFE comparison, so 18.1 feet + 0.015*50 = 18.9 feet

3. Compare FEcom to FE500 to determine the DFE and then compare to minimum elevation requirements. FEcom = 14 feet < FE500 = 18.9 feet = DFE. DFE = 18.9 > BFE + 1 feet (13 + 1 foot = 14 feet).

The required elevation for ASCE 24-24 = 18.9 feet

4. The elevation for loading in ASCE 7-22, S2 is determined using Equation 5.3-1 (ASCE 7-22) or df = (SWELMRI-Ge) +ΔSLR where df = design stillwater flood depth, Ge = ground elevation and ΔSLR = change in sea level elevation. In this example, df = (15.1 – 0) + 0.75 feet = 15.85 feet

We do not know the wave height for the FE500 event; we only know the SWEL500. Therefore, we must find the FE100 wave height and use a scaling factor from Table 5.3-3 (ASCE 7-22).

We must find the top of wave elevation so the result can be compared to the ASCE 24-24 result. The controlling wave height above the SWEL100 is the BFE = 13 – 10.8 feet = 2.2 feet and the controlling wave height above the SWEL is 70% of the total wave height so the total controlling wave height for the FE100 = 2.2/0.70 = 3.1 feet

The total controlling wave height (HC500) for the 500 year MRI = 3.1 feet*1.3 (scaling factor) = 4 feet The wave portion above the SWEL = 0.70*4 feet = 2.8 feet so the DFE (FE500 elevation equivalent) = 15.85 feet + 2.8 feet = 18.7 feet

5. Therefore the required minimum elevation using ASCE 24-24 is 18.9 feet which is greater than 18.7 feet (ASCE 7-22 DFE) and so it may not be necessary to increase the minimum elevation of the building to minimize loading.

If the ASCE 7-22 DFE was greater than the ASCE 24-24 required minimum elevation, then a designer may consider elevating the floor system to minimize the flood loads on the building.

In addition to changes in required elevations for structures, there were changes to several other important sections in ASCE 24-24. These changes primarily deal with flood proofing methods other than elevation and materials used for flood-prone structures. The change in minimum elevation also required addressing the extent of the 500-year floodplain.

Floodplain Extent (Chapter 1)

ASCE 24-24 expanded the floodplain from the requirements of the previous

version. ASCE 24-14 only required the provisions of the standard to apply to the delineated Special Flood Hazard Area (SFHA) or the 100-year floodplain as shown on FIRMs. A significant change was made to ASCE 24-24 to expand the floodplain to also include the Shaded X Zone (500-year floodplain) where it is mapped. The standard also allows communities to delineate their own floodplain if it is more restrictive than the SFHA and Shaded X Zone shown on the FIRM. This brings ASCE 24-24 further into alignment with ASCE 7-22 Supplement 2.

Materials (Chapter 5)

Significant language is added regarding the use of materials in salt-laden environments and expanded on materials and material standards that should be consulted when the building is to be located near a coastline where salt exposure is prominent. Steel and concrete material especially received additional discussion, particularly as it relates to metal connectors and reinforcing steel for concrete or masonry. Two new ASTM standards are discussed regarding flood damage-resistant materials. ASTM E3075-24 is a Standard Test Method for Water Immersion and Drying for Evaluation of Flood Damage Resistance, and ASTM E3369-24 is a Standard Specification for Determining the Flood Damage Resistance Rating of Building Materials. This is the first time that such an evaluation method for flood damage-resistant materials has been available to designers. This will help address the NFIP requirement that all materials installed below the minimum elevation be resistant to flood damage. It will also provide manufacturers with a method of certifying that new products are indeed flood-damage resistant.

Dry Floodproofing Requirements (Chapter 6)

The requirements for dry floodproofing are allowed in only A Zones (primarily riverine flood areas) and Shaded X Zones (500-year floodplain areas) and similar noncoastal locations and require flood opening barriers to have passed the tests and be certified as described in ANSI 2510, American National Standard for Flood Mitigation Equipment. This means that in order to be used in flood mitigation projects that require compliance with ASCE 24-24, all opening barriers such as shields, flood barriers, closures over doors and windows must meet the ANSI 2510 standard. That also means that designers who will certify compliance, must assure themselves of such compliance.

Designers who certify compliance with the dry floodproofing requirements will need to make sure flood barriers have been tested to the flood depth required of a specific design; they will need to know how the flood barriers are to be installed and design attachments for such flood barriers; they will need to conduct a flood vulnerability assessment of an existing structure where flood barriers are planned and specify how to seal up any other small openings that might exist in the structure’s exterior walls. There is more specific information provided about what type of shields are allowed for each FDC for both new construction and for

substantial improvements. Additionally, more discussion is provided about the use of dry floodproofing techniques for non-residential buildings and non-residential space in mixed-use buildings. Distinctions are made between a barrier for a building opening (i.e. door or window) and a “temporary floodwall.” Floodproofed wall systems must be marked to indicate the level of floodproofing sealant to minimize the potential for unsealed penetrations to be made through a sealed wall system, which would compromise the floodproofing.

There are new inspection, maintenance, and operations plans required to be filed with the

FRP WORKS WHERE OTHER MATERIALS

Authority Having Jurisdiction (AHJ), and actual deployment of equipment and exercising the operations plan is required annually (or as stipulated by the AHJ). Post-disaster assessment indicates that most flood damage to dry floodproofing systems occur because of poor design, poor installation, not knowing where the floodproofing shields or devices are located, and the owner or support personnel not knowing how to install measures properly. There are maximum times allowed for the deployment of active dry floodproofing systems based on Flood Design Class. For wet floodproofed buildings, exceptions were added for the location of flood vents based on restrictions imposed by the geometry of the spaces with only one exterior wall and on sloped sites.

Two Other Important Changes

Additionally, two other changes were made to the standard based upon post-disaster assessments. The standard now addresses elevating existing slab-on-grade buildings, which has been a common practice in some parts of the country as a way to elevate the lowest floor of a house and bring that house into compliance with the NFIP. However, there have been structural slab failures when this has been done, since most slabs have minimal thickness and minimal to no reinforcing steel. Additional language has been added in ASCE 24-24 to make sure the existing slab is assessed for strength, strengthened as needed and connected properly to the new foundation to be able to resist uplift and buoyancy as required. There were also changes to the standard to require that when there is an entrance from the elevated building into an enclosure below the building that the door must be an exterior grade door. This was added based upon elevated buildings being damaged during flood events due to the failure of doors leading into enclosures, leaving the buildings open and unable to be secured.

Summary

The new revisions to ASCE 24-24 were primarily influenced by the need to make this Flood-Resistant Design and Construction Standard compatible with ASCE 7-22 Supplement 2 and ten years of post-disaster flood assessments. Many users will recognize the increase in the floodplain extent and the additional elevation requirements. The committee considered the use of the standard for both design and floodplain management in development of the requirements. Engineers will need to consider the minimum elevation requirements in ASCE 24-24 and the minimum elevation for flood load consideration in ASCE 7-22 Supplement 2 and should use that when determining how high to elevate buildings. The material, slab, and enclosure access provision should further reduce damage to elevated buildings. Innovations in the dry floodproofing requirements should reduce the potential risks for both new and substantially improved floodproofed buildings. The changes are viewed as a major improvement to flood resistant design and are intended to reduce flood losses with increased building flood protection and increased national resiliency. ■

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

William L. Coulbourne, PE, F.SEI, F.ASCE, Coulbourne Consulting, Berlin, MD, member of ASCE 24-24 Standards Committee

Jessica Mandrick, PE, SE, M.ASCE, Partner at Gilsanz, Murray, Steficek in New York City, NY, member of ASCE 24-24 Standards Committee

Adam Reeder, PE, CFM, Principal, CDM Smith, Raleigh, NC, consultant to ASCE 24-24 Standards Committee

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HANGZHOU CENTURY CENTER: Engineering a Landmark

A suspended steel grid structure connects two towers in this iconic development in Hangzhou, China.

By Jin Chen, PE, SE

The Hangzhou Century Center, also known as "The Gate of Hangzhou," is a prominent urban development situated in the Xiaoshan District of Hangzhou, China. Positioned between the Hangzhou International Expo Center to the east and the Olympic Sports Center Training Hall to the west, the project is envisioned as a striking gateway to the city. This iconic development comprises two highrise towers, each reaching a height of 310 meters, connected at their base by a 60-meter-span steel arch bridge. The surrounding commercial blocks form a dynamic mixed-use complex, offering office spaces,

With a total construction area of approximately 526,000 square meters—370,000 square meters above ground and 160,000 square meters below— the twin 63-story towers are designed to resemble the letter "H," a symbol of Hangzhou's identity. A suspended steel grid structure connects the two towers starting at the 21st floor, creating an expansive public space above the bridge, enhancing both the functional and architectural scope of

Towers and Bridge

Hangzhou is located in a region of moderate seismic activity and medium wind pressure. The lateral design of the towers’ structural system is primarily governed by seismic effects. The structural system itself is a highly efficient and robust integration of distinct yet complementary components. It is designed to leverage the stiffness, mass, and damping characteristics of a rigid central core and a ductile perimeter moment frame, optimizing resistance to dynamic wind forces while efficiently dissipating seismic energy.

Each tower features a centrally located reinforced concrete core tube, which transitions from an elongated octagonal shape at the base to a rectangular form by the 44th floor. The core resists the majority of lateral seismic and wind loads. The perimeter frame is a composed of reinforced concrete beams and composite SRC columns which could provide the excellent ductile for seismic and minimize the sizes. The perimeter moment frame is proportioned to ensure effective load sharing, maximizing efficiency as the second defense system for seismic.

Left: Each tower has a central reinforced concrete core tube and a perimeter frame of reinforced concrete beams and composite SRC columns. Right: A steel arch bridge that spans 62 meters between the two towers is supported by rigid connections at the ground level, where it integrates with the steel-reinforced columns of the towers.

The towers’ oval-shaped floor plans taper along their height, resulting in a highly dynamic, aerodynamically optimized massing with a rounded corners and tapered shape, highly integrated with architectural layouts. This shape helps to disrupt wind vortex shedding, thereby reducing wind-induced vibrations and loads, leading to significant material savings.

The floor system consists of one-way reinforced concrete beams and slabs within and beyond the core. Although cast-in-place concrete floors typically extend construction timelines, the contractor was able to implement a three-shift work schedule per day for concrete construction, whereas steel construction was limited to one shift per day due to local regulations. As a result, the concrete system did not delay the schedule while simultaneously achieving structural material cost savings.

The steel arch bridge spans 62 meters between the two towers, elevating 34 meters above the ground. Comprising six parallel arch trusses aligned with the tower columns, the bridge is supported by rigid connections at the ground level, where it integrates with the steelreinforced concrete columns of the towers. The horizontal thrust of the bridge is transferred to the core tubes of the towers via the continuous floor slab system at the ground level, ensuring stability and load distribution.

The bridge serves dual functions: a pedestrian walkway at the 6th floor and a banquet hall at the 3rd floor. The arches of the bridge are defined by the Funicular form-finding to minimize the bending moment under gravity. The diagonal braces are incorporated to enhance lateral stiffness since this building-type bridge still needs to meet with building structural control ratios. The bridge’s natural frequencies are 1.23 seconds

in the X-direction, 1.18 seconds in torsion, and 0.99 seconds in the Y-direction, ensuring its stability under dynamic loads and providing a resilient structure for varied use.

Drape Roof and Integrated Design

The suspended roof structure spans approximately 60 meters between the two towers, hanging from the 21st floor. It is composed of bidirectional steel grid members with vertical curvature optimized through the catenary geometry concept; each segment of the grid is straight with the H section. The horizontal curvature is carefully designed to simplify node connections and enhance the architectural aesthetics. Horizontal restraint systems located on the 18th, 14th, and 11th floors provide lateral stability for the suspended roof and incorporate tension cables and compression struts. Vertical steel members support the side walls of the suspended structure, hanging from the edge beams of the roof. These vertical members are laterally restrained at the 6th and 3rd floors of the bridge but are free to move vertically, accommodating differential displacements.

The drape roof is one of the project’s most innovative features, drawing inspiration from the natural shape of a hanging chain, which forms a catenary curve under its own weight. This geometry ensures the roof predominantly carries axial forces to minimize bending moments and optimize material efficiency, which contributes to both structural performance and sustainability.

The suspended roof structure comprises bi-directional steel grid members with vertical curvature.

Each flat glass panel of the bridge roof is supported by a quadrilateral steel grid, with panel edges aligned to the grid lines.

Integrating the steel grid roof and glass panels was a key design challenge.

The initial geometry of the longitudinal drape grid was derived from the classic catenary equation. However, this equation assumes uniform segment lengths and constant gravity loads per segment. Given the varying segment lengths and loads in the drape grid, iterative calculations and adjustments were required to account for the actual gravity loads at each node. This process ensured the final catenary geometry efficiently supports its self-weight

The integration of the steel grid roof and glass panels was a key design challenge, demanding precise coordination to balance structural integrity with aesthetic refinement. The objective was to maintain the majority of the glass panels in a flat configuration while accommodating the doubly curved geometry of the draped roof.

To achieve this, the roof's surface was designed using a scaled-translational approach, beginning with defining a central catenary curve, which is then subdivided into multiple straight-line segments based on the target glass panel dimensions. Due to the tapered form of the tower and different hanging ends, adjacent catenary curves span slightly longer distances. These adjacent curves are generated by scaling the central catenary—preserving the segmentation—and translating it to its designated location. This procedure is repeated to generate the series of catenary curves across the surface. Finally, corresponding division points between adjacent curves are connected with straight lines, forming a quadrilateral grid, which defines the layout for the glazing panels. This method ensured that the glazing panels remained perfectly flat while conforming to the overall curvature of the structure. Each glass panel was supported by a quadrilateral steel grid, with panel edges precisely aligned to the grid lines. The flatness of the panels was meticulously controlled through careful geometric calibration of the grid and strategic orientation of the steel members.

The optimized geometry allows 97% of the grid members to use standard H-section steel (HN300x150x6.5x9), with localized reinforcement (H300x150x10x25) at stress concentration areas. The total steel weight of the roof, including nodes, is approximately 700 tons. The sidewall of the drape roof connects the edge of the drape, which

Each grid node consists of a steel tube with four H-section members connected to it.

The steel bridge was finished in 6 months and the steel drape roof and side walls were constructed in 11 months during the pandemic time. 

is straight in plan, to the edge of the bridge structure, which is curved in plan. It also meets the towers along a line angled in elevation. The hanging mullions of the sidewall are designed to be as evenly spaced as possible while maintaining a funicular shape under gravity to minimize bending.

To achieve these design constraints, 3D graphic statics were employed. In this approach, force magnitudes within the structure are represented by the lengths of lines in a force diagram, while equilibrium at each node is ensured by the closure of force polygons. By imposing geometric constraints on these diagrams, a 3D funicular structure in equilibrium was developed.

Although the structural logic of the sidewall precludes the use of entirely flat glass panels, the relatively shallow curvature ensures that cold-bent glass panel warping remains within acceptable limits, even under wind-induced deflections.

The grid nodes of the suspended roof are designed to simplify construction and ensure structural efficiency. Each node consists of a steel tube with four H-section members connected to it. The flanges of the H-sections are welded to circular plates at the top and bottom of the tube, ensuring continuity of the load path. The orientation of the I-section member axes is carefully specified to ensure that the webs of every I-section intersecting at a node align along a common line, known as the "node axis." This eliminates geometric torsion and simplifies detailing and documentation. The sidewall connections were designed as hinged joints, allowing for construction tolerances and accommodating differential displacements while maintaining structural integrity.

Wind Tunnel and Analysis

Wind tunnel testing was conducted to determine the wind loads on the suspended roof and side walls. The tests provided eight wind load cases for the structural design, with wind pressures ranging

from -2.27 kPa to 1.73 kPa. The natural frequency of the suspended roof was controlled to be around 1 Hz to ensure accurate wind load predictions.

The maximum deformation of the suspended roof under wind loads is 132 millimeters, which is acceptable for a 60-meter span. The lateral deformation of the side walls at the connection points with the towers is 47 millimeters inward and 68 millimeters outward, within the allowable limits for the curtain wall system.

The deformation of the twin towers under wind and seismic loads has a minimal impact on the suspended roof due to the high stiffness of the towers relative to the roof structure. In the integrated structural model, the lateral deformation of the towers at the connection points with the roof is 30 to 50 millimeters, which has a negligible effect on the overall behavior of the grid roof. The porous grid roof reduces wind loads while promoting natural ventilation at the concourse level.

The deformation of the suspended roof is controlled to ensure the safety and functionality of the glass panels. The out-of-plane deformation of the panels is limited to 1/50 of the diagonal length, while the in-plane shear deformation is controlled by designing the panel connections to allow for relative displacements.

The structural performance of the suspended roof was evaluated using finite element analysis. The analysis considered gravity loads, wind loads, and seismic loads, as well as the interaction between the suspended roof and the twin towers. The results confirmed that the roof meets all design requirements, with sufficient stiffness and strength to withstand extreme loading conditions.

Construction

Following the completion of the foundation and basement, construction of the two towers commenced simultaneously from ground level. A climbing formwork system was utilized for the reinforced concrete shear wall core, which progressed approximately two floors ahead of the column, beam, and slab floor system. The typical construction pace averaged six days per floor. Upon reaching level 24, construction of the steel bridge began. The two cores were engineered to resist the thrust forces from the steel bridge. Each bridge arch was prefabricated in two segments at the shop, with the six steel arches erected first, followed by the installation of steel braces, columns, and floor members. The superstructure construction for both towers was completed in 13 months.

The construction of the drape roof presented several challenges, including the need for precise positioning of the grid members and the installation of the glass panels. The construction of the suspended roof involves the following steps:

1. Complete the main structures of the twin towers and the steel bridge.

2. Install temporary scaffolding system on the 6th floor of the top of bridge up to the 20th floor.

3. Assemble large segments 2x2, 2x3, 3x3 grid modules of the roof grid steel in the shop and lift them into position using cranes.

4. Install grid roof steel segments from the lowest mid strip of the roof.

5. Connect the edge beams of the roof to the side walls and install the vertical steel members.

6. Install the horizontal restraint systems at the 18th, 14th, and 11th floors.

7. Install the glass panels on the roof and side walls, ensuring uniform loading.

Conclusion

The Hangzhou Century Center project demonstrates the feasibility of using catenary geometry and advanced structural analysis techniques to design long-span suspended structures. The project’s success provides valuable insights for future projects, particularly in the design of lightweight, efficient, and aesthetically pleasing structures.

The successful realization of the Hangzhou Century Center project would not have been possible without the dedication and expertise of the entire project team. Special acknowledgment is due to structural team members William Baker, Dane Rankin, Toby Mitchell, Han Ding, Max Cooper, and Ben Johnson for their innovative approach to architectural integration and structural aesthetics. Their collective efforts and seamless collaboration were pivotal in transforming this ambitious vision into a tangible landmark.

The suspended grid steel structure of the Hangzhou Century Center stands as a remarkable achievement in contemporary structural engineering. Through the innovative application of catenary geometry, advanced wind tunnel testing, and meticulous construction planning, the project has produced a structure that is not only highly efficient but also visually striking. Its success offers valuable insights for the design and construction of future long-span suspended structures and supertall buildings, pushing the boundaries of engineering excellence. ■

Jin Chen, PE, SE, is an Associate Principal of Skidmore, Owings & Merrill LLP, Chicago, Illinois.

The Greenland Hangzhou Century Center, between Hangzhou’s International Expo Center and Olympic Sports Center, is an iconic landmark with its two 310-meter twin towers connected by a gracefully ‘draped’ skybridge.

MAKER MAXITY

Innovative, unconventional solutions abound in a concrete high-rise hospitality project in India.

By Anantha Chittur, PE, SE and Steven Baldridge, PE, SE

Mumbai, often referred to as India’s financial and commercial capital, is known as the “City of Dreams.” True to this reputation, the city's projects are often ambitious in both scale and vision. One such landmark development is Maker Maxity, a sprawling 20-acre integrated commercial, entertainment, and hospitality complex located in Mumbai's central business district, the Bandra Kurla Complex (BKC).

The hospitality component of Maker Maxity spans 1.2 million square feet and features two tower blocks, each comprising four interconnected towers. These towers, housing luxury-branded hotels, stand 16 stories tall with a combined total of 475 rooms. Beneath them lies a five-story podium stretching more than 800 feet from end to end—notably designed without expansion joints. The structure also includes three basement levels for back-of-house operations, parking, and services. Atop the podium, a roof deck offers a pool and restaurant

with views of the Mithi River. While the design accounted for a future vertical expansion of five additional floors, this plan was ultimately set aside during initial construction.

The project's schematic design was originally based on a structural steel system featuring staggered trusses. However, recognizing that structural steel is relatively uncommon in large-scale hospitality and commercial projects in India, where its use is typically reserved for industrial structures, BASE (the Structural Engineer of Record) and the general contractor, Leighton India Contractors Pvt. Ltd., proposed an alternative solution. They converted the structure into an all-concrete system without altering the original design intent. This revised approach employed long-span post-tensioned beams spanning the building’s width and a distinctive floor system combining composite metal decks with concrete topping supported by the beams. The hybrid system was chosen to reduce or eliminate the extensive

Fig. 1. This wind tunnel testing model shows the curve of the structure’s podium, following the natural flow of the Mithi River. (Courtesy of RWDI)

shoring and reshoring typically required in conventional concrete construction, ultimately accelerating the project’s timeline.

Client: No Expansion Joints!

It's not often that a project begins with a firm "no expansion joint" directive from the client. Their decision was primarily based on the aesthetics of breaking up large open finished lobbies with expansion joints and their expression on the building elevation, in combination with high initial cost and long-term maintenance. Despite numerous discussions and requests early in the design process to incorporate an expansion joint at the podium levels, the response remained a resolute "No."

The podium, overlooking the Mithi River, gracefully follows the river’s flow with an elegant segmented shape. Each tower block comprises four distinct volumes, giving the exterior an architectural expression of independent buildings. The vertical transportation elements, such as elevators and stairs, were strategically clustered within one volume, with corridors extending to the remaining sections. This arrangement effectively reduced restraint to shrinkage and volume changes.

To further minimize restraint, the adjacent interconnected buildings primarily utilized planar shear walls oriented perpendicular to the

shrinkage direction. Perimeter beams spanning between the demising walls of hotel rooms, which also supported the tops of large glazed openings, acted as supplementary moment frames along the building's length. These frames offered less resistance to volume changes compared to shear walls, helping to manage structural movement.

To control initial shrinkage in each tower block, a designated shrinkage strip (marked red) remained open for 28 days in the tower and 56 days in the podium. Additionally, a long delay pour strip (marked green) was incorporated into the podium to allow each tower block to undergo long-term volume changes and reduce cracking (Fig. 2).

The contractor closely monitored the volume change during construction, and the long delay pour strip was closed shortly after the project was topped out.

In addition to shrinkage control, thermal loading was also considered in the design of the vertical and horizontal framing using a comprehensive 3D ETABS analysis model.

Hybrid Floor System

The podium's top at Level 5 was designed to accommodate various functions, including pre-function areas, ballrooms, convention spaces, and indoor pools. Achieving these large open areas using traditional flat

Project Team

Owner: The Indian Film Combine (IFC)

Structural Engineer of Record: BASE

Concept Design: SOM India

Architect of Record: Archgroup Consultants (Dubai)

General Contractor: Leighton-Infra Joint Venture

Wind Tunnel Consultant: RWDI

Fig. 2. To control shrinkage, pour strips were open for 28 days and 56 days (locations in orange), and a long delay pour strip (location in green) was incorporated for long-term volume change during construction in order to reduce cracking.

slabs or one-way slabs would have required transfer girders at Level 6.

To address this challenge, a unique hybrid floor system was introduced starting at Level 6. This system featured long-span post-tensioned beams with clear spans of approximately 58 feet 6 inches, supporting a metal deck spanning roughly 15 to 16 feet, which served as sacrificial formwork. This one-way spanning metal deck hybrid slab was designed for the design loading with conventional reinforcement placed in the flutes. During construction, the metal deck was temporarily supported at mid-span or one-third points using post shores at a single level (Fig.3).

This hybrid system allowed the temporary shores to be removed within six days—significantly faster than traditional post-tensioned or reinforced concrete frames constructed in India, which typically require reshoring for 12 to 28 days. As a result, the system achieved

a 60-75% reduction in framing manpower.

Below Level 5 and in the basement levels, traditional two-way flat plate framing was used.

Transfer Truss

The podium levels beneath Tower 8, located at the southwest end of the project, extended beyond the tower's footprint. This area housed a large double-height ballroom, with one half positioned beneath the tower and the other half occupying the expanded podium. Above the ballroom, a spacious outdoor amenity deck offered impressive views of the city.

Supporting half the tower's weight with a traditional transfer girder,

Fig. 4. A transfer truss extending from Level 5 to Level 6 was the chosen option after a multiple transfer girder study.

Fig. 3. Shown is a cross-section of hybrid floor framing.

as a result of single-span beams spanning the width of the building, proved challenging. The ballroom’s high ceiling requirements con flicted with the placement of a girder, and incorporating one at Level 6 interfered with the lobby’s space planning.

To address this, several design alternatives were explored. One option involved a Vierendeel truss extending from Level 6 to Level 20, while another proposed shallower transfer girders placed at four locations between Levels 6 and 20. However, both solutions resulted in beam and column sizes that clashed with the architectural facade, making them less desirable.

In parallel, a traditional transfer truss option was studied. This design featured a full-height transfer truss extending from Level 5 to Level 6, supporting the exterior columns from Level 6 to the roof (Fig. 4). The truss’s bottom chord spanned the entire floor height between Levels 4 and 5, which housed mechanical services. Openings were incorporated into the bottom chord to allow MEP ducts to pass through.

Ultimately, the transfer truss solution emerged as the most efficient option. It was also well-received by the client and architect, who embraced it as a striking design feature of the planned outdoor bar.

Bathtub Basement

The basement levels of the project are situated below the surrounding water table, leading to significant buoyant forces. Based on seasonal fluctuations, the design water table level created a hydrostatic head of approximately 3 meters (10 feet). To manage the water table during construction, an extensive under-raft drainage system, including sumps and pumps, was implemented.

For the final condition, a hydrostatic slab was designed to withstand hydrostatic pressures of around 11.5 kPa (240 psf). The slab was designed to span between the footings, similar to how a reinforced concrete slab spans between drop panels. It was connected to the footing using pull-out dowels cast into the footing. These dowel bars were straightened during concrete placement for the slab, transferring the load from the slab to the footing (Figure 5).

To create a waterproofed basement (bathtub), a mud slab was laid as the bottommost layer, with a waterproofing layer placed on top. This waterproofing layer extended behind the basement retaining walls (on the soil side) up to the ground floor. The stitch slab and footings were installed above this waterproofing layer.

To reduce the hydrostatic head the slab had to support, a ballast layer of compacted fill was added beneath a slab-on-grade (Fig. 5). This fill layer also accommodated various subgrade plumbing, pipes, and other MEP conduits, facilitating easier installation and future access for maintenance or repairs within the waterproofed "bathtub."

The slab-on-grade was 100 millimeters (4 inches) thick and lightly reinforced, while the stitch slab was reinforced similarly to a two-way reinforced concrete slab, with the reinforcement placed in reverse to address uplift loads.

Conclusion

Turning ambitious visions into reality requires comprehensive analysis, careful planning, and purposeful execution. These elements were pivotal in achieving the client's goal. Various structural design solutions were thoroughly explored, with the final selections—including the hybrid floor framing, transfer truss, and stitch slab—chosen through a methodical process of evaluation and continuous collaboration with the architect and contractor. ■

Anantha Chittur, PE, SE, is Principal at BASE and is based in its Chicago office. He can be reached at achittur@baseengr.com.

Steven M. Baldridge, PE, SE is President at BASE and is based in its Honolulu office. He can be reached at sb@baseengr.com.

Fig. 5. Schematics for the hydrostatic stitch slab are shown above and below. The stitch slab was installed above a water proofing layer and a ballast layer of compacted fill.

An artistic rendering shows how the finished Maker Maxity towers will line the bank of the Mithi River.

Walking on Air

An eccentric cantilever and stepping perimeter columns allow a Chicago luxury apartment tower to dramatically capture space at height.

By David Fields, PE, SE, and Alex Wiley, PE, SE

Floating high above the sea of historic mid- and high-rises framing Grant Park in Chicago’s South Loop neighborhood, 1000M—Helmut Jahn’s final and tallest Chicago tower project—is a masterclass in found space. The 788foot, 73-story luxury apartment tower at 1000 South Michigan Avenue opened in June 2024. Magnusson Klemencic Associates’ (MKA) straight, vertical, and orthogonal design of the tower’s initial 10 floors provides stability to the more structurally complex, space-reclaiming features above, including a cantilever that extends over a neighboring building and incrementally increasing floorplates that create an expanding twist in the building with height. Dual-purpose water tanks located on the tower’s rooftop level serve to dampen the structural response and provide the fire suppression water reservoir.

Building Up, Stepping Out

The development team behind 1000M had the luxury of owning two adjacent sites—1000 South Michigan, where the tower sits, and 1006 South Michigan, home of the eight-story Leightner Building. The 1000M site, only 100 feet wide, abuts that of the Leightner

Project Team

Developer: Time Equities, JK Equities, and Oak Capitals

Architect: Helmut Jahn, Jahn/

Structural Engineer: Magnusson Klemencic Associates

Contractor: James McHugh Construction

Interior Design: Kara Mann

Building, its neighbor to the south. Tearing down the smaller building to increase 1000M’s footprint was not viable due to Leightner’s landmark-protected status. Instead, the development team set its sights on the air rights above and capturing space at height.

Jahn proposed a unique solution to widen the tower above the Leightner and create more space: a south-facade cantilever that slopes gently over the 100-foot Lightner Building, claiming air rights to maximize leasable floor area and unit count. MKA designed an allconcrete structure to suit, with primarily flat plate floors and lateral stability provided by a central core buttressed at its base.

McHugh Construction, its in-house concrete subcontractor McHugh Concrete, and concrete formwork supplier Peri Formwork Systems collaborated to build the 18-foot, MKA-designed sloped building extension, continuing each floor farther south over the floor below via

With site restrictions that kept the building’s footprint to 100 feet wide, the development team claimed air rights above a smaller landmark-protected building on the adjacent site. A building extension slopes over the 100-foot Leightner Building to increase the leasable floor area and unit count at 1000M. (Photo credit above and opposite page: Angie McMonigal)

continuously evolves as it rises above the podium structure. (Image credit: MKA)

sloping columns between Levels 11 and 20. At Level 11, a 19-foot “fire lid” slab extends over the neighboring Leightner Building, serving as a four-hour fire separation, protecting the 1000M building from potential heat from the roof of the Leightner Building should a fire break out.

At Level 20, where the steeply sloping southern columns resume a vertical path, 1000M’s appearance changes. The building’s lower floors, an aesthetic nod to the Historic Michigan Boulevard District and buildings of 200-foot scale, give way to a slender, carved tower designed to look at a distance like a separate building, complete with differentiating color and sheen.

Unlike the rectangular shape of the building’s base, the upper tower’s form begins in plan with symmetrically curved east and west faces and a flat aspect to the north and south. Diagonal planes then emerge from these straight north and south facades as each floor’s perimeter columns “walk” away from the center of the building to further expand the tower. This expansion continues at each of the top 50 stories of 1000M, growing the exterior bay dimensions from 30 to 43 feet and increasing the individual floorplate area by 900 square feet.

To accommodate the lengthening spans, MKA’s engineers designed a series of increasingly thicker flat slabs to maintain a flat soffit and avoid costly and intrusive beams extending beneath the slab.

Solving for Sway

As is common in the greater Chicago area, suitable soil bearing to support such a tall tower is hidden below layers of fill and soft clay. To reach these soils, large diameter belled caissons were drilled to depths of approximately 75 feet to support elements primarily resisting gravity forces. Due to the narrow site and inherently narrow stance of the lateral system on the foundation, caissons resisting the building overturning were drilled and socketed into bedrock at a depth of approximately 100 feet to achieve their required capacities. The use of deep foundations was also advantageous in bypassing the existing nearby foundations, ensuring the 1000M structure did not surcharge the adjacent properties.

To utilize as much width as possible on the narrow site, the tower is supported by a continuous caisson-supported mat that carries all the tower columns. This solution engages the total dead weight of the building to minimize net uplift demands on the deep foundations, thereby reducing the depth, size, and quantity of expensive rock-socketed caissons.

A building of this height naturally captures enormous lateral wind pressures acting on its surface. Of equal importance was resolving the massive gravity-induced lateral forces created by the steeply sloped building columns, which induce significant horizontal thrusts on the building at the top and bottom of their slope extents. Resistance to these additional forces is provided by the same structural system that resists the wind forces.

A core-only solution to resolving the totality of the lateral forces was infeasible due to a tower height-to-core width aspect ratio of over 20:1. MKA considered two solutions to augment the core: buttress walls or an outrigger system, both of which engage the exterior of the building

1000M’s shape

Sloping columns induce significant horizontal thrusts on the building; the floor plate diaphragm is utilized to complete the load path of these thrusts to the source of lateral resistance. (Image credit: MKA)

to provide a much greater lateral stance.

An outrigger system was deemed too disruptive to the regularity of both the typical floor plan layout and the construction rhythm. Instead, the central concrete core engages with internal buttress walls aligned with core end walls and demise between apartments. The buttress walls extend to mid-height in the building and are end-capped by six-footsquare super-columns for the lowest 10 stories. The south-side sloping columns are tied to this system via heavy bands of high-strength reinforcing bars within the concrete floor slabs. As these heavy bands take up a large volume within the slabs and compete for space in the grid of post-tensioning tendons, a full-size mock-up was created to verify these elements could all be placed within a very tight area while maintaining the necessary configuration.

While the core and buttress systems were sized to ensure the building had all the necessary lateral strength, wind tunnel testing revealed the additional challenge of maintaining occupant comfort during significant wind events. The frequencies at which tall towers sway can resonate with occupants’ senses and lead to motion sickness. This effect is measured in minimal levels of acceleration, with an industry-accepted limit for residential occupancy at 18 milli-g during a 10-year storm. Rather than resolving the issue by adding stiffness through costly and space-taking increases in the size of the shear walls or super-columns, MKA employed two east-west oriented tuned liquid sloshing damper tanks strategically located on 1000M’s rooftop. Together, these dampers contain more than 33,000 gallons of water. These water tanks were tuned to the frequency of the building by careful measurement of as-built building motions and filling the tanks to a specific depth in relation to tank length, creating wave action matching those frequencies. The number and proportions

of tanks were selected to activate sufficient mass to impart meaningful changes to the building’s response to wind excitations. To minimize the impacts of the massive tanks on the roof slab and overall concrete volume, the tanks abut the central core shear walls. This solution utilizes the shear walls themselves as part of the tank enclosure while also relying on the core stiffness to cantilever the tank boxes off the core and stiffen the roof span condition.

In another example of found space at 1000M, the damper tanks double as the building’s fire water reservoir. In the event of a fire, the damper tanks will drain to provide water for firefighting crews. Unlike other damping solutions, a general contractor can build liquid sloshing dampers using materials and crews already mobilized on site. Rebar is tied, walls are formed and cast, and waterproofing liner is installed as it would in a rooftop pool. A case study of NEMA Chicago tower, a similar residential high-rise, found that adding sloshing dampers for a construction cost of $1.4 million saved just under $5 million relative to the next best wind management solution.

1000M is a study in shaking off the constraints of site. As large city lots grow scarce, consider taking advantage of found space using smart engineering solutions that do not massively disrupt the flow of construction. As evidenced by 1000M, small incremental changes can add up to large benefits. ■

David Fields, PE, SE, is a Senior Principal at Magnusson Klemencic Associates. Alex Wiley, PE, SE, is a Senior Associate at Magnusson Klemencic Associates.

Forces generated by the sloshing water in the damper tanks counteract the wind-induced forces, thereby dampening the structural response. (Image credit: MKA)

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Caesars Superdome Renovation

A phased approach to major renovations at the New Orleans stadium allowed it to remain fully functional and continue to host major sports and entertainment events, ensuring a steady stream of revenue and minimal disruption to schedule.

By Eric Grusenmeyer, PE

Fig. 1. A view of the completed North End Zone shows the new bunker clubs and viewing decks. ( Photo by Timothy Hursley)

Caesars Superdome opened its doors in 1975, and with its innovative 680-foot clear span dome roof and iconic hourglass shape, it became a distinctive part of the New Orleans skyline. The Superdome, home to the NFL’s New Orleans Saints, is celebrating its 50th anniversary. But this is no ordinary sports venue. It hosted major concerts from the Rolling Stones in the ‘70s to three consecutive sold-out shows by Taylor Swift last year. The Superdome welcomed Pope John Paul II, Muhammed Ali, and the Republican National Convention and is also the home of the annual Essence Festival and one of the Mardi Gras parades. In addition to the Saints, the Sugar Bowl has been played there since it opened, and the stadium has held five NCAA football championships, six NCAA Final Fours, and eight Super Bowls including Super Bowl LIX in February 2025.

The Superdome is a major economic driver for the city, so when it sustained substantial damage during Hurricane Katrina in summer 2005, an extensive repair and renovation effort was fast-tracked. The building was rebuilt after the hurricane and hosted a home football game the following September 2006.

Renovating the beloved stadium was important to not only preserve its historical and cultural importance to the city of New Orleans but also to maintain the significant and consistent revenue streams stemming from the numerous events hosted there. In addition to the post-Katrina rehabilitation, the stadium has been renovated several times over the years, including notable major renovations in 1995 and 2011. The latest comprehensive renovation sought to modernize the facility, enhance the fan experience, and prepare the venue for many more years of continued use.

The capital improvements project took place over five years, but The Dome had to remain operational for each NFL season as well as major concerts and events including the NCAA Men’s Basketball Final Four. Structural design for Phase 1 began in early 2019, with construction commencing in 2020. The design continued through the 2021 season with rolling design phases and construction being completed prior to the 2024 football season.

The $560-million project consisted of 17 mini-projects spread over the five construction seasons. This article focuses on the corner viewing decks, corner atria and escalators, and corner passenger elevators.

Viewing Decks (aka Super-Voms)

One of the project goals was to enhance ADA accessibility throughout the stadium, including increasing accessible seating. The continuous seating bowl posed a significant challenge due to the unbroken circle formed by the precast tread riser units with only small vomitories, or passageways connecting the circulation concourses to the seating bowl. To address this, the project team introduced eight viewing decks referred to as “super-voms ”: These super-voms, or extra wide vomitories, would include ADA-compliant seating areas and standing-room-only positions in addition to access to the seating bowl (Fig. 2).

Trahan Architects’ design enhanced the overall game day experience by connecting the concourse to the seating bowl, allowing patrons to hear the crowd and catch the action on the field. To achieve this vision, significant structural changes were required. The existing seating bowl consists of a steel-braced frame system with steel raker trusses cantilevering up to 60 feet. The super-voms are located on concourse levels 200 and 500 in each corner. Each super-vom required five existing structural bents and raker trusses to be reconfigured—a total of 40 trusses—to allow the raker and seating bowl to be removed across the width of the new super-vom. This involved reinforcing existing

members and adding new members to create a revised truss layout from which the lower concourse is hung with steel hangers. The result is a new, open cantilevered platform that extends the concourse while also supporting the above stadia, the stepped floor structure supporting the seating and aisles that make up a seating bowl.

The sequencing of the steel installation and demolition of the existing bowl structure required careful planning. The team devised the following steel erection sequencing plan (Fig. 3):

Fig. 3. At each of the eight super-vom locations, five radial raker-trusses were modified in an eight-step process. Existing members are in black. (Image by Thornton Tomasetti.)

Fig. 2. The existing seating bowl created an unbroken ring at Level 200 and 500 with only narrow vomitories connecting the concourse and bowl (inset). New "super-voms" create wide slots in the seating bowl. (Image by Thornton Tomasetti.)

6-FOOT WIDE TYPICAL VOMITORY

STEP 1. Install new steel diagonals and truss chords and reinforce existing members. These elements created the reconfigured truss members.

STEP 2. Demolish the existing precast seating bowl. The existing single tread-riser units were lifted from the bowl as whole pieces.

STEP 3. Install the temporary hanger at each bent. The hanger system (Fig. 4) consisted of an HSS beam below the existing concourse girder with a through-bolt on either side of the girder passing through the slab and a second HSS beam on top of the slab. This allowed for level adjustments as needed. The upper HSS was welded to two pairs of strap plate hangers,

which were supported by a third HSS beam welded to the top of the existing raker. The temporary hanger was located just behind the permanent hanger and near the reconfigured truss work point.

STEP 4. Demolish existing lower raker segments (Fig. 4). Deflections were constantly monitored while sequential torch cuts were made through the webs and flanges of the rakers. Minimal deflections were experienced.

STEP 5 Install new raker tub end and permanent hanger. A stub beam supporting the new cast-in-place stadia tubs, which are found at the front row nearest the playing surface, was field

welded to the existing raker. The new 4-inch diameter solid steel hanger was field welded to gusset plates on the upper raker truss and lower concourse girder.

STEP 6. Gradually de-tension and remove the temporary hanger. Steel elevations were monitored before, during, and after de-tensioning and showed minimal movement.

STEP 7 Install new floor framing and slabs. Concourse floors were filled in between the now cantilevering girders. The leading edge of the concourse was curved to follow the sweeping curvature of the newly formed seating bowl, trimmed with LED video boards.

Fig. 4. The bottom of the temporary hanger assembly consisted of an HSS12X6 cradle beam under the existing wide-flange floor beam. Two pairs of tension rods pass through the floor to an upper HSS8X6 where two pairs of plate hangers were attached. The plate hangers were welded to an upper HSS beam that was welded to the top of the existing raker. (Image by Thornton Tomasetti.)

STEP 8. Install cast-in-place concrete tubs and vomitory walls. The architectural design called for curving vomitory walls that swoop upward and turn into the upturned wall of the cantilevered stadia tubs. Cast-in-place concrete allows the components to be form-fit to the existing structure, avoid heavy crane picks, achieve the architectural curves, and be built faster. It also allowed the tubs to be seamlessly joined to the rakers with the bottom of stadia perfectly flush with the raker ends without joints (Fig. 5).

All eight super-voms with their 40 trusses were demolished and rebuilt in the 2021 offseason owing to the collaboration between Thornton Tomasetti’s structural engineering and construction engineering teams, construction manager Broadmoor LLC, fabricator Postel International, and erector Foster Steel. At the height of structural construction, steel components could be field measured, shop drawings adjusted, steel fabricated, delivered, and erected in as little as one week.

Atria and Escalators

Upon entering the renovated stadium, visitors are greeted by an expansive atrium, which provides a grand entry point while also enhancing the vertical transportation within the structure in three of the four corners. The main entry at the elevated plaza level (Level 100) serves as the primary gateway to the stadium. Fans ascend to

Fig. 5. A shop assembled stub beam detailed for support of the new cast-in-place stadia tub was field welded to the cut end of the existing raker. (Photo by Eric Grusenmeyer/Thornton Tomasetti.)

Fig. 6. The corner atria created new grand entries for patrons accessing all levels of the stadium. (Photo by Timothy Hursley)

Fig. 7. For the existing concrete-framed floors on the lower level, build-back framing consisted of steel beams with composite slabs to form the atrium shape. Black triangles are moment connections. (Image by Thornton Tomasetti.)

designated levels via newly installed escalators. Similar, but shorter, sideline atria were also created in the new sideline clubs—space that was taken back from the original spiral sideline ramps that were demolished in Phase 1.

Creating a corner atrium required cutting 40-foot-wide by 90-foot-long jelly-bean shaped holes at four floor levels. At Level 200, the existing structure consisted of a cast-in-place concrete pan-joist system with concrete girders and columns. The demolition extents were taken to the nearest girder or joist with new steel framing, composite slabs, and curved slab edge plates built-back to create the shape of the opening (Fig. 7).

The existing structure for the upper levels, comprising 2-way flat slabs spanning to girders on column lines, were modified in a similar manner. Additional framing was added as needed to support existing-to-remain 2-way slabs where the new atrium opening created end span (fixedpinned) conditions that were originally designed as interior spans (fixed-fixed). At least one radial flying beam at each level was kept or added to provide support for the long escalators and lateral support for the floor and facade outboard of the atrium.

The engineering challenge extended beyond simply removing existing slabs; it involved rebuilding the lateral load path. The Level 300 structure was particularly challenging because it resolves lateral component forces generated from the sloping, hanging exterior columns, which are under sustained tension. In the existing condition these forces were resolved with in-plane lateral bracing under the

floor. Removal of these braces and select radial girders was facilitated by installing a 20-foot-deep horizontal truss outboard of the atrium under the low roof that redistributes the lateral forces around the large opening (Fig. 8). The truss was assembled in the field with new W12 chords and diagonals but used existing radial low roof beams as the truss “verticals.” Gusset plates and local member reinforcements were field welded to existing steel framing. Sequencing the reinforcement and build-back work with demolition was critically important to maintain structural stability throughout construction, but with careful coordination, the team was able to accomplish this with minimal temporary support.

Each atrium was clad with a “veil” of extruded, serrated aluminum tubes extending the height of the atrium. The veil shape echoes the stadium’s hourglass exterior. Connections between the veil system substructure and the attachment to the superstructure were closely coordinated between Thornton Tomasetti steel detailers and the architectural metals fabricator, Zahner. Steel bent plate brackets and curved slab edge plates were field welded to allow precise placement and supported the shop fabrication and

Project Team

Owner: The Louisiana Stadium and Exposition District

Structural Engineer of Record: Thornton Tomasetti

Architect of Record: Trahan Architects

MEP Engineer: Henderson Engineers

Owner’s Representative: Legends

Construction Manager: Broadmoor, LLC

Steel Fabricator: Postel International, Inc

Steel Erector: Foster Steel, LLC

panelization of the cladding system.

Thornton Tomasetti provided erection engineering support for the construction team and helped devise a plan to assemble the escalator on the Level 100 floor below the atrium, lift it up vertically through the atrium, then rotate it into place with final supports at each end and two intermediate levels.

Elevators

Enhancing ADA accessibility required the addition of 16 new elevators. One challenge was navigating the narrow “waist” of the building, where it comes together and then widens again. The elevator shaft was hemmed in with the circumferential braced frame and girder line on the field side and 14WF facade girts on the exterior (Fig. 10). To provide enough clearance, the girts were reinforced by welding bars to the exterior flanges and top and bottom reinforcing angles to replace the inside flanges. Then the inside flanges, which encroached on the clear hoistway, were removed and a sloping sheet metal shroud was installed to eliminate a ledge condition inside the hoistway.

Foundations for the elevator pits also proved challenging with existing pile caps limiting the pit Dome roof depths and low head-heights limiting equipment sizes. A concrete podium was built to access the elevator entry with a short flight of stairs and a ramp or ADA lift up to the podium. The foundation support for the elevator pit and podium was provided by steel

Fig. 8. The corner atrium horizontal truss redistributes the lateral forces around the large opening. (Photo by Eric Grusenmeyer/Thornton Tomasetti.)

Fig. 9. Each corner atrium is capped with a stretched fabric Barrisol light at the top, creating a skylight effect that changes colors to match the event. (Photo by Eric Grusenmeyer/Thornton Tomasetti.)

open-end pipe piles driven to a depth of around 90 feet. A low-head-height pile driver was used in areas with head-heights as low as 14 feet with pile segments as short as 3 feet.

At the top of the elevator shafts that access the press boxes, the elevator overruns pass through the existing roof gutter tubs, precast concrete basins that collect rainwater. These pretensioned precast concrete tubs have the important job of catching and draining water collected from nearly 10 acres of roof area. To prevent a cascade of water from pouring into the stadium, a temporary enclosure was built above the gutter to divert it and provide a dry workspace. This enclosure, designed for full hurricane force winds, was supported by wide flange steel framing that can be disassembled and reused for the opposite elevator shaft, during the following offseason construction. Erecting the enclosure structure was perhaps more difficult than the permanent elevator overrun structure itself. Thanks to the creative steel

erector and careful planning and coordination, a scheme was devised to use spliced members that were small enough be lifted to the top of the seating bowl, into the press box, and through a hole in the gutter wall using a series of splayed cable winches guyed off the roof trusses. Once in the gutter, a cable-stayed steel mast supported a cable and trolley that carried the steel into place. After completion of the temporary enclosure, the existing gutter tub was demolished, steel overrun framing installed—respecting the dome roof movement joints—and new cast-in-place gutter tubs were built. Then, the temporary enclosure was disassembled and rebuilt for the elevator at the opposite end of the press box.

Conclusion

The capital improvements at the Caesars Superdome were gradually rolled out to Saints fans after each phase of construction

and when the completed project was unveiled to the world at the hosting of the eighth Super Bowl this past February. The stadium, now equipped with modern amenities and improved accessibility, is poised to welcome a new generation of fans, ensuring its legacy continues for years to come. ■

Eric Grusenmeyer, PE, is a Vice President at Thornton Tomasetti. He has more than a decade of structural engineering experience on a variety of unique and challenging projects in the sports industry. His work includes renovations of historic stadiums such as Lambeau Field in Green Bay, Wisconsin, Penn State’s Beaver Stadium and the Caesars Superdome, as well as additions to existing stadiums like the University of Missouri's South End Zone and new construction projects including US Bank Stadium in Minneapolis.

Fig. 10. Corner passenger elevators had to pass through the narrow “waist” of the building requiring the existing girts to be reduced in depth. (Image by Thornton Tomasetti.)

Scientific Growth of a Campus

Wesleyan University endeavored to build a state-of-the-art science complex to expand its reach and grow multiple programs.

By Michael A. Tecci, PE, Brooke H. Shannon, Ph.D

Wesleyan University, a private liberal arts university in Middletown, CT, began reimagining its science complex more than a decade ago. The New Science Building, scheduled for completion in 2026, will be a signature building for the campus. Working with PAYETTE architects, the Simpson Gumpertz & Heger Inc. (SGH) engineering team designed the structure, taking care to stay true to the campus focus and mix of historic and modern structures. Part of the larger-scale campus plan involves removing Hall-Atwater, located adjacent to the New Science Center, and renovating Shanklin Hall, a 1920s building. The New Science Building supports the growth of Wesleyan

University's science programs and is a focal point on campus with its sweeping glass and stone facades. It stands out amongst the many quintessential New England brick-clad buildings and brownstone facades that dot the campus. The science building incorporates research and support rooms, teaching labs, classrooms, a vivarium, and advanced instrumentation. This programming creates structural design challenges, including differential lateral earth pressures, long-span spaces, transfers, geometric considerations, and vibration performance.

The New Science Building is comprised of steel framing and slabon-metal-deck composite diaphragms, with steel concentric braced frames as the lateral-load-resisting system (LLRS). The building has four stories plus a mechanical penthouse located at the roof level.

Fig. 1. Architectural rendering of exterior northwest corner of the NSB. (Image provided by PAYETTE.)

Laying the Groundwork

The site includes a substantial grade change of approximately 31 feet, allowing for slabs-on-grade at four different levels, with parts of Level 1 and Level 2 on grade in the west and northwest of the building. On top of the grade change, the building incorporates a mechanical trench space that extends 11 feet below the lowest level. The change in grade across the site results in significant differential lateral earth pressures. Transferring the differential pressure through the diaphragm to the LLRS was not practical due to the large floor openings within the load path. Ultimately, the earth pressure was accommodated by designing cantilevered retaining walls to resist it. This design also allowed for backfilling the site earlier than if the walls were designed to span between levels.

In many locations, mat foundations are used to incorporate the foundation wall footing and the adjacent isolated footings. This allows for simplicity of formwork and rebar detailing. The allowable bearing pressure varies based on elevation and location in the site. The foundation design incorporated these aspects to optimize the designs wherever possible.

Let There Be Light

A key architectural feature of the building is the atrium, which incorporates large, irregularly shaped openings that vary at each level. The atrium aligns with a series of four light monitors in the roof that drive natural light into the core of the building. The maximum atrium length is 140 feet east-west and 82 feet north-south. There are no columns within this area, which presented a series of design

challenges to accommodate the unique and varying geometry of the openings, as well as steel depth restrictions along the opening edges and floor finishes that required recesses in the top of the slab-onmetal-deck. The irregular geometric openings range in size from up to 41 feet at the floor levels to 51 feet at roof level. The deepest floor recess includes wood flooring and radiant heating, which only allows for a 4-inch (total depth) slab-on-metal deck, that negatively affects vibration performance over these long spans.

Ultimately, the project team developed a unique framing plan for each level, incorporating cantilever framing around the openings to offset the deeper members from the edge and tapering beam ends to keep a low profile of the framing adding a lighter feel to the space. Cantilever framing supports long-span beams in multiple locations. The team studied to understand the combined deflections, considering the cantilever ends and the long-span beam deflection.

Laying out the beams required careful coordination with PAYETTE to ensure that all the structural steel was concealed within the varying depths of the soffits and ceiling. The irregular geometry and framing also resulted in increased coordination with pipes and ductwork throughout the area. The project benefited from this early coordination with the MEP engineers (van Zelm Engineers) and the general contractor (FIP Construction). At the roof level the framing layout in the atrium also must account for four light monitors with varying geometry to drive natural light into the atrium space. These allow an abundance of natural light to flow through all the floor openings below.

Along the west edge of the building is a double-skin glass curtain wall system. To minimize the visibility of the structure along this edge, SGH designed exposed built-up plate columns aligned with the curtain wall mullions. These columns incorporate three built-up 50 ksi plates. The two outer plates are 8 inches x 2-1/2 inches and the

Fig. 2. Shown is construction progress of atrium framing looking up at light monitor framing.

Fig. 3. Light monitors are highlighted in blue in the Penthouse Structural Framing Plan.

inner plate is 6 inches x 2 inches to allow for a staggered fillet weld to connect the plates. The 7 inches total width blends nicely behind the curtain wall mullions. The wall itself is supported by cantilevers at Level 3, which are tapered W36 members decreasing to about 28 inches at the edge of the building.

The New Science Building features three sets of monumental stairs. Two of these stairs span between the atrium openings from Level 2 to Level 3 and Level 3 to Level 4. As previously mentioned, the atrium

opening framing includes many cantilevers and long spans, which in turn support these stairs at the top and bottom. The floor framing increases the flexibility of the support framing of the stair assemblies; therefore the stair structure requires additional stiffness to offset this additional stiffness and still to meet the stair vibration criteria of AISC Design Guide 11. Per Design Guide 11, the vertical natural frequency of the stairs is greater than 5 Hz and the horizontal natural frequency is greater than 2.5 Hz. Additionally, the stair stringers have depth

Fig. 4 An architectural rendering illustrates the atrium space. (Image provided by PAYETTE ). The structural detail of framing at a typical tapered edge is also shown. (Image provided by SGH.)

restrictions since they are an architectural feature. To meet the depth restriction, the designs incorporate three parallel HSS10x8 stringers to achieve the required stiffness. The stairs also have 1/2-inch-thick fascia plates along the outer edges to conceal the stringers and treads. These plates contribute to the stiffness of the stairs but are not part of the structural design.

Lengthy Ambitions

The building includes a large auditorium between Level 1 and Level 2. This requires a 72-foot clear span to accommodate the openness of the auditorium. This meant transferring out six columns from the upper levels. In the space above the auditorium, one column line aligned with an architectural wall, so a built-up, story-deep truss was designed to create the open space below. The truss consists of wide flange shapes for the chord and web members. The layout of the web members is asymmetric to align the top joints with the column transfers above. The joints were designed and fabricated as nodes with bolted connections to simplify erection. On the other two column lines, there is no wall above, so the transfer was made through built-up box girders. The ceiling had a depth restriction, so two W40x431 beams were designed to act compositely with a 1-1/2-inch-thick continuous plate welded to the top and bottom flanges.

The architectural layout did not allow for braced frames in the northwest area of the building. This is in part because the auditorium is located in this zone. Therefore, the story-deep truss ends up delivering lateral load from the diaphragm due to its relative stiffness. This needed to be accounted for in the lateral analysis of the building. SGH analyzed the system holistically in two ways; one including the truss as a lateral element and one without it. That allowed us to isolate the truss and its connections and properly design for the lateral load they inherently receive, while the LLRS was designed assuming there is no contribution from the truss, so the braced frames are designed for the full lateral load on the building.

Fig. 5. Rendering of stone facade at windows. (Image provided by PAYETTE.)

Fig. 6. Photo of installation of stone facade. (Image provided by PAYETTE.)

Fig. 7. Box girder structural detail.

Shaking Things Up: Designing for Lab Vibration

Many areas in the New Science Building are lab spaces and require a specific vibration performance of 2,000 mips (micro-inches per second). Due to the changes in the column layout from level to level, some column transfers occur in lab spaces. The column transfers result in large beams that help stiffen the floor and help the vibration performance. The vibration performance was studied using both the ETABS building analysis and standalone spreadsheets developed following AISC Design Guide 11 procedures. The lab spaces are large, with beam spans up to 31 feet-2 inches and girder spans up to 18 feet. To meet the vibration requirements, beam sizes range from W18 to W24, and girder sizes range from W21 to W24. Another factor used to help the vibration performance is a 7-1/2-inch total depth slab-on-deck assembly.

Pushing the Envelope

The exterior design of the building emphasizes crisp, modern detailing paired with a grounded, weighty stone mass—paying homage to the rich

legacy of stone architecture found throughout the campus. Between the heavy stone objects, light and floating glazed elements define the welcoming common spaces. A central feature of the design is the articulation of deeply recessed windows within the stone façades, each framed by large custom fluted sill stones that suggest substantial wall thickness. SGH’s team engineered and coordinated bespoke anchoring systems and intricately shaped stones, achieving the visual heft of solid masonry while minimizing the actual volume and weight of stone used.

The New Science Building is a signature building on the campus, joining the historic nature of the surrounding campus with a stateof-the-art science complex. While many of the structural features are concealed, the intricacy of the framing is fitting for such a facility. ■

Michael A. Tecci, PE, is senior project manager-structures at Simpson Gumpertz & Heger Inc. (SGH)

Brooke H. Shannon, Ph.D, is a project consultant-structures at Simpson Gumpertz & Heger Inc. (SGH)

Fig. 8. Structural section through monumental stair.

Fig. 9. Built-up column along double skin facade edge.

Fig. 10. Rendering of NSB within Wesleyan Universities Campus. (Image provided by PAYETTE.)

iconic STRUCTURES

100 McAllister Street, San Francisco

The historic tower is receiving a seismic upgrade and modernization to serve UC Law San Francisco's academic village.

By John Dal Pino, David Seward, Anders Carpenter, Ruth Todd, Maria Flessas, and Dan Bech

The historic 100 McAllister Street building is undergoing a seismic upgrade and interior improvements to further expand campus housing and academic and instructional opportunities for Bay Area institutions of higher education. The project demonstrates UC Law’s commitment to its strategic vision, the implementation of a multi-institutional Academic Village, and an affirmation of its confidence in the revitalization of San Francisco’s Civic Center, Tenderloin, and Mid-Market neighborhoods.

On the heels of the grand opening of UC Law’s new 656-unit campus housing project at 198 McAllister, work has begun on the first of two phases to seismically upgrade and modernize 100 McAllister. Upon completion of both phases in 2027, the renovated and structurally strengthened 355,000 square foot building will add 80 residential units (one to six bedrooms each). The intention to is to provide a range of rent price point options in the building to accommodate students, faculty, and early career professionals, some of whom may share their unit with their partner or family. The lower podium floors of the building are slated to accommodate an academic institutional partner to UC Law and will include potential classroom, seminar, office, and meeting spaces. The building will also preserve and enhance historic gathering spaces including the street level lobby, two ballroom-type spaces, and the Sky Room Lounge on the 24th floor which has sweeping views of the entire city. At the lower level, the basketball court will be converted into a multi-use sports court which will be flanked by a series of spaces for gym equipment and wellness rooms of various sizes and uses. The most compelling historic space is the Great Hall, a former religious sanctuary, which is accessible

by an exterior monumental stair through three archways at street level. This high-volume space is edged with a series of mezzanines and clerestory windows and could be used as an academic institutional partner space, performance space, and/or public assembly space.

• Academic Village

The Academic Village is UC Law’s strategic concept for spurring interdisciplinary engagement among individuals and across institutions on a single urban campus. Student residents of the Academic Village have shared access to all amenities including the library, food services, study areas, and recreational spaces on a campus-wide basis.

• Housing Availability & Affordability

The Bay Area’s housing crisis has intensified the need for affordable student housing, particularly considering increasing rent burdens and longer commutes. San Francisco’s limited housing supply and high costs place significant financial pressure on students.

• San Francisco Urban Revitalization

San Francisco’s recovery from the COVID pandemic and its adverse social impacts has been uneven. Most of the City has regained pre-pandemic activity levels with commercial space performing well, supporting robust sidewalk-level activity. However, not all neighborhoods enjoy the same level of resurgence; the Civic Center, Tenderloin, and Mid-Market neighborhoods continue to lag.

100 McAllister Street is an Art Deco and Gothic Revival high-rise constructed in 1930 with a unique and storied history. Located at the crossroads of the Tenderloin, Civic Center, and Mid-Market neighborhoods, 100 McAllister is important to the development and character of San Francisco. Known as “The Tower,” it has been both witness and contributor to the patterns of history that make these three neighborhoods significant. See Timeline.

Existing Conditions

This historic building has good bones. For a building of this age, it is in great condition with little observed structural deterioration, a testament to UC Law’s deferred maintenance program. The existing structure of 100 McAllister is designed with stepped massing that defines a mid-rise podium, high-rise, and penthouse levels. The lower fourteen floors of the building are contained in an L shaped podium with the balance of the structure rising above the podium in the form of a slender tower. The primary structural system consists of reinforced concrete floors supported on concrete-encased riveted steel beams and columns. The existing seismic load resisting system for the building relies on historic steel wind-brace brackets at beam-column joints; thin, lightly reinforced concrete infill walls; and the non-structural unreinforced masonry (clay brick) infill making up the exterior façade.

The historic foundations are supported on dense to very dense sands of the Colma Formation and therefore are at low risk of liquefactioninduced settlement, as determined by the geotechnical engineers at Langan. The top of the Colma Formation below the basement slab slopes downward from north to south 5 to 15 feet. The building foundations also extend to the same depths below the basement slab for support in the Colma Formation. However, the basement slab is supported on loose to medium dense fill which is below the water level (water level is maintained with pumps beneath the basement slab).

Due to the dual function of the building’s original use as both a church and a hotel, the many different programmatic requirements on the lower floors of the building forced the original engineers to design a highly discontinuous structural system, with many transfer girders. Very little of the seismic force resisting system is continuous to the foundation which creates a significant seismic vulnerability in the building, particularly for the tower and the rear facades of the podium.

Seismic Strengthening Goals

UC Law’s goals for the project are:

• Increase the seismic safety of the building to meet State standards required by UC Law’s Seismic Safety Policy.

• Preserve the historic character of the building which makes it unique and allows for the use of Historic Tax Credits to help fund the project.

Despite its location in a high seismic region, the building has only been subjected to one notable seismic event over its life: the 1989 Loma Prieta Earthquake. The building did not sustain a significant amount of damage during this event because the energy content of the Loma Prieta event was relatively low for this type of building. By modern standards, the historic building contains many undesirable characteristics which can lead to poor seismic performance, such as a discontinuous seismic force-resisting system supported on transfer beams and non-ductile concrete walls. Additionally, the damageability of the

Project Team

• Architect: Perkins & Will

• Structural and Construction Engineer: Holmes Structures

• Historic Preservation Architect: Page & Turnbull

• Cladding Preservation and Waterproofing: Ferarri Moe

• Geotechnical Engineering: Langan

• General Contractor: Plant Construction

• Seismic Review Committee—UC Law San Francisco, Forell Elsesser, Rutherford + Chekene and Engeo

unreinforced masonry and terracotta facade is of interest particularly in the tower portion of the building. The original engineers for the building omitted the steel “wind bracing” elements above the 20th floor which means the tower portion of the building is susceptible to greater seismic damage.

Despite the building’s weaknesses, the building has a highly redundant seismic force-resisting system that provides good resistance for smaller seismic events. In larger seismic events the building is not expected to perform well. Fortunately, engineering and construction techniques have improved tremendously in the past 100 years and these more modern standards can be applied to the retrofit of this building.

According to the USGS, there is a 51% likelihood of a magnitude 7 earthquake striking the San Francisco Bay Area within the next 30 years. By retrofitting this building, UC Law will meet the seismic safety standards required for state-owned structures under Section 317 of the California Existing Building Code (CEBC). This retrofit of 100 McAllister ensures that future generations can continue to benefit from this building for years to come.

Approach to Seismic Strengthening

As structural engineers with an expertise in preservation, Holmes understands the importance of quantifying a building’s inherent strengths and vulnerabilities prior to entertaining any strengthening or retrofit measures. The best, and likely the only, way to do this on a building as complex as this one is through nonlinear performancebased time history analysis. There is no other analysis methodology available to engineers that can lead to a more accurate accounting of seismic performance.

Langan developed site-specific response spectra and spectrally compatible time series for the seismic evaluation and design of the retrofit of the existing tower. The seismic evaluation was performed in accordance with ASCE 41-17, Section 317 of the 2022 California Existing Building Code (CEBC), and the UC Seismic Safety Policy. Horizontal sitespecific spectra were developed for two levels of shaking, Basic Safety Earthquake (BSE) BSE-C and BSE-R, which correspond to a 5 and 20 percent probability of exceedance in 50 years in the maximum direction, respectively. In addition, eleven pairs of amplitude-scaled time series to both BSE-C and BSE-R were developed.

Based on the subsurface conditions, the site is classified as a very dense soil and soft rock profile, Site Class C. Langan used subsurface information, including shear wave velocity measurements for the development of site-specific spectra. A probabilistic seismic hazard analysis (PSHA) for 5 and 20 percent probability of exceedance in 50 years, respectively was performed to develop the BSE-C and BSE-R spectra. NGA West 2 ground motion models were used to estimate the level

of shaking. Scaling factors presented in Shahi and Baker (2014) for ratios of SaRotD100/ SaGMRotI50 were used to modify the average results to the maximum direction. The average directivity factors for the site were estimated using the NHR3 directivity based PSHA tool and applied to the PSHA results.

Amplitude scaling (single scalar) was selected by the design team to develop the time series. Section 2.4.3 of ASCE 41-17 requires the development of the ground motion acceleration histories be performed per Section 16.2 of ASCE 7, which requires the average of the maximum direction spectra (ROTD100) from eleven ground motions not fall below 90 percent of the target response spectrum over the period range of interest. Langan developed two suites (11 pairs each) of time series for each hazard level. The selection of the records for each suite was based on calculating the sum of the squared error (SSE) between the target spectrum (BSE-C or BSE-R) and the average of the scaled ROTD100 for each pair of time series. The scaling factors and proposed time series were selected generally based on the least SSE.

ASCE 41-17 defines near-field as sites being 15 km or less from the surface projection of active fault capable of generating a moment magnitude greater than or equal to 7 and requires that the motions be rotated in the fault normal and parallel directions. Studies by Watson-Lamprey and Boore (2007), Huang et al. (2008), and Shahi and Baker (2012) have shown that for sites less than 5 km from a fault that there is strong polarization of the ground motion in the fault normal and fault parallel directions and that the spectral accelerations in fault normal direction are larger than the median value for periods longer than 0.5 second. Beyond 5 km this effect appears to be random, i.e. fault normal is not always the largest. This effect has also been further investigated by Golesorkhi and Gouchon (2023) in a white paper published as part of their involvement with BSSC. Because the site is approximately 13 km from the San Andreas fault, Langan recommended that the selected, scaled motions be applied randomly to the structure. This method was approved by the peer review team.

Through non-linear time-history analysis, Holmes has mitigated the key vulnerabilities in the building by considering each carefully. First, the weak tower portion of the building is strengthened by adding a new concrete core that extends from the roof to a new concrete mat foundation located just below the existing slab level. This new core is in-turn stiffened by new steel outriggers and buckling restrained braces. The new concrete core and

outriggers maximize structural strength and stiffness and minimize impacts to key historic areas. In addition, the new core has the benefit of providing code compliant egress stairs and a modern elevator bank which the students will certainly enjoy in years to come. The retrofit of the tower proved to be the most challenging aspect of the project given the small floor plate which is exacerbated by the wedding cake architecture of the tower. In addition to the new core, key transfer beams that support discontinuous infill walls are stiffened and strengthened as part of the retrofit. The podium portion of the building is strengthened with reinforced concrete overlay walls on the inside of the historic facades. A new 6-footthick mat foundation will be constructed to support gravity and anticipated seismic loads. The fill soil that will remain beneath the new mat foundation is liquefiable and cannot support the anticipated seismic loads. Because of limited access, the high groundwater level, and almost complete coverage of the tower mat area by existing footings, permeation grouting (using vertically aligned overlapping bulbs of soil grouted with microfine cement) was selected to improve the fill beneath the new mat foundation and transfer the seismic loads to the competent Colma Formation. Permeation grouting was

also used to construct shoring walls for the soil excavations. Installation of permeation grouting columns was based on the results of a field test program that investigated various design parameters (bulb size, bulb plan layout, bulb overlaps, etc.) to arrive at an optimal solution. Strategic reinforcement of select building elements achieves the required seismic performance standards set by CEBC and UC Law, while preserving historic features. By enhancing structural rigidity and strength where most needed, this targeted approach optimizes construction costs and maintains the building's historic integrity.

The project has adopted Method B from the CEBC using non-linear time history analysis to demonstrate compliance with state mandated performance objectives. As such, the project is subject to review by UC Law’s Seismic Review Committee consisting of Rutherford + Chekene and Forell Elsesser for structural issues and Engeo for geotechnical issues.

Working closely with Page & Turnbull, areas of significant historical value were identified such that the retrofit is designed to avoid or minimize impact to the historic fabric itself as well as the experience of individuals within the spaces. Special care was taken to eliminate structural options that would interfere with any of these historic resources: terracotta facade, lobby, Walnut Room, Ladies Lounge, Dining Room, window locations, and the basketball/athletic basement area.

One of the joys of working on old buildings are the lessons we learn from studying historic drawings and construction techniques. For this project the team had the benefit of beautifully detailed drawings from the original structural engineer.

—Dan Bech, Holmes Structures

The seismic vulnerabilities of the tall slender tower make it exceptionally difficult to be respectful of these key historic features. With critical input from Page & Turnbull to avoid impacts to historic features, important design decisions on elevators and egress

Many of the original drawings were available. On the left, is the 5th floor plan showing the cross-shaped church space with transfer girders over the entry. To the right is a typical L-shaped upper level floor plan. The floor plans transition to a square shape in the highest levels.

from Perkins & Will, and constructability input from Plant Construction, an elegant structural solution was developed. The structural solution was truly a full team effort.

One of the joys of working on old buildings are the lessons we learn from studying historic drawings and construction techniques. For this project the team had the benefit of beautifully detailed drawings from the original structural engineer; Trygve Rønneberg was also engineer of record for other notable buildings in San Francisco such as the Hobart Building and the Pacific Bell Building (140 New Montgomery) which Holmes and Perkins & Will retrofitted previously. A brief biography of Terres Ronneberg can be found at https://ronneberg.org/blog/ trygve-ronneberg/.

Sustainability—Preserving Existing Structures

The multi-generational use and upkeep of 100 McAllister is more sustainable than new construction. Extending the building's life has a lower carbon footprint than constructing a new building for equivalent functions, even when adding significant strengthening in a high-seismic region.

In collaboration with Perkins & Will, Holmes has completed an in-depth Life Cycle Assessment (LCA) of the project. Holmes has focused on the structural components and Perkins & Will on the balance of the project. When comparing the reused and new building materials at the scale of a 28-story tower, one can grasp the significant volumes of demolition waste that would have to be transported to landfills, and new building materials that must be extracted and manufactured to replace historic elements, it becomes evident that this rehabilitation project honors sustainability goals, especially when calculating the massive amounts of energy (and fossil fuels) needed for transport, manufacturing, construction, and demolition.

Construction Engineering

Given the complexity of the building and a myriad of design constraints imposed on the project, Holmes was engaged to provide construction means and methods support to Plant Construction. Several key construction challenges were part of this project, the most significant of which is the construction of the new concrete core up the center of the tower. To build the core, Plant Construction will use self-climbing formwork within the existing building to expedite construction and reduce

construction costs. To accommodate the core and the self-climbing formwork, several existing transfer beams need to be removed or cut and re-supported. The removal of the existing transfer beams requires careful consideration of construction sequencing including unloading and reloading of existing gravity loads in the structure and foundations. The new floor penetration for the new core requires strategic temporary shoring and strengthening of the existing floors and historic seismic force-resisting system during construction.

Other significant construction challenges where Holmes is providing means and methods support include the design of the tower

crane foundation and tie in, and the design of the construction personnel hoist supports. Construction began in early 2025 and is scheduled to wrap up in the summer of 2027 in time for the start of the 2027-2028 academic year. ■

John

ENGINEERED TO LAST. PROVEN TO PERFORM.

Durable, dimensionally stable concrete with improved structural performance

✓ Eliminates negative volume change and drying shrinkage cracking

✓ Prevents dominant joints and maximizes extended joint spacing

✓ Lowers permeability and improves sulfate resistance

✓ Optimizes sustainable design and maximizes design life

✓ Ultra-Low GWP impact

A. Dal Pino is a Principal with Claremont Engineers, Inc. in Oakland, California. He serves as the Chair of the STRUCTURE Editorial Board. (jdalpino@claremontengineers.com).

David Seward, UC Law San Francisco; Anders Carpenter, Perkins & Will; Ruth Todd, Page & Turnbull; Maria Flessas, Langan Engineering; and Dan Bech, Holmes Structures, were contributing authors.

Shrinkage-Compensating Concrete & Grout Solutions

in FOCUS

Joint Summer Series on Artificial Intelligence (AI)

The webinars and articles focused on AI are a collaboration for the betterment of structural engineering.

By Jeannette Torrents, PE, SE

The Coalition of American Structural Engineers (CASE), the National Council of Structural Engineers Associations (NCSEA), and the Structural Engineering Institute of the American Society of Civil Engineers (SEI) are proud to announce a new joint effort for the betterment of the structural engineering profession. In recent years, the three national structural engineering organizations have been hosting town halls to highlight efforts to fulfill their joint Vision for the Future of Structural Engineering, adopted in 2019 by all three organizations. This year, CASE, NCSEA, and SEI are co-producing their first Joint Summer Series with three free webinars and accompanying STRUCTURE magazine articles centered around a topic with the potential to broadly impact all aspects of structural engineering, from education and research to design and construction and business practice.

2025’s selected topic is artificial intelligence. NCSEA will host the first webinar on June 24, which will be focused on a roadmap for the practicing engineer to get started with AI, offering practical strategies for learning, integration, and long-term growth. Andrew Sundal, AIA, PE and Emre Toprak, Ph.D, PE from NCSEA’s AI Grant Team will provide suggestions for how smaller firms can harness new technologies

AI Webinar Dates

June 24: Towards AI Adoption in the Structural Engineering Profession

July 29: AI Strategy for Engineering Leaders: What You Need to Know

August 26: AI Developments That Will Shape the Practice of Structural Engineering

that amplify their strengths and give them capabilities that were previously not available due to limited resources. They will also provide guidance for midsize and larger firms to navigate the training and deployment challenges of leveraging AI across a larger enterprise.

On July 29, CASE will host “AI Strategy for Engineering Leaders: What You Need to Know” in July, presented by Mehdi Nourbakhsh, Ph.D from the ACEC Technology Committee. Dr. Nourbakhsh will discuss how structural engineering firm leaders can develop a welldefined AI strategy to stay competitive and foster innovation. CASE’s webinar offers a framework for structural engineering companies to assess their AI maturity, enabling leaders to understand their current position and how to elevate their companies to the next level.

SEI will close out the series August 26 with a presentation by Kristopher Dane, D.Eng from SEI’s Digital Design Committee and MZ Nazer, PhD, PE from SEI’s Advances in IT Committee highlighting areas of AI development that will shape the practice of structural engineering. Viewing AI through a practitioner lens, this webinar will outline the current possibilities, risks, and potential for AI to help interpret and improve codes and standards, automate document creation, streamline voting processes for standards approval, assist in real-time monitoring and maintenance of infrastructure, and more. ■

Visit program.acec.org/2025-joint-summer-series-artificialintelligence to register for this summer AI webinar series.

Torrents, PE, SE is the Technical Director of SEI.

Jeannette

Towards AI Adoption in the Structural Engineering Profession

Tools and resources are available now for structural engineers to take their first (or second and third) steps in incorporating artificial intelligence (AI) into their strategic plan.

By Andrew Sundal, AIA, PE; Dave Martin, SE; Emre Toprak, Ph.D, PE; and John-Michael Wong, Ph.D, SE

Artificial Intelligence (AI) is becoming an increasingly important part of project delivery in the Architecture, Engineering, and Construction (AEC) industry. Recognizing this, the National Council of Structural Engineers Associations (NCSEA) Foundation selected AI as the topic for its inaugural Innovation in Structural Engineering (ISE) grant in early 2024. The grant was created to address practical challenges in adopting AI in our industry, including setting a direction for AI in the profession, adoption strategies, and learning outcomes, while considering issues such as accuracy, risks, data privacy, security and ethics.

In February 2024, the AI Grant Team formed with seven licensed structural engineers with input from an industry expert advisory panel. The group met in San Francisco to develop a strategic plan and roadmap for AI adoption, recognizing the unique challenges for the structural engineering industry. The group’s main goals were to encourage innovation, improve collaboration, and share practical resources with the industry. And while AI tools will assuredly add efficiencies, they more importantly should allow us to incorporate more design options and take more risk and scope, while improving sustainability and resiliency outcomes and our impact on projects. The team has since delivered a series of AI-focused webinars, extensive content at the 2024 NCSEA Summit, and online resources, while also building relationships within SEAs across the U.S.

or Copilot, or experimenting with AI-assisted coding, you’re already on the right path. By learning, testing, and breaking these AI tools, you’ll start to see where AI can bring actual value to your practice and understand its pitfalls. And every firm needs to chart a realistic technology strategy: Are you a developer? A consumer? A mix?

In this article and follow-up webinar, we build upon last year’s kickoff publication, "Creating a Foundation for AI in the Structural Engineering Profession." (Scan the QR code and unpack the NCSEA Foundation’s Strategic Plan for AI.) The team has developed approachable and relevant resources that can be used now by firms of all sizes to kickstart their adoption of AI technology and gain an understanding of practical strategies for learning, integration, and long-term growth.

AI Roadmap: Steps in AI Adoption

The first part of the strategic plan is the AI Roadmap, which lays out an ideal path for structural engineers taking their first steps in AI adoption. A simplified version of the roadmap is shown in Figure 1. (Scan the QR code for the full version). The first step is simple: learning and curiosity. If you’re exploring large language models (LLMs) such as ChatGPT

Learning and Strategy

By far the most common perception when talking to executives is that they are behind in adopting technology. Spoiler Alert—you are not behind. In fact, most firms are appropriately still at Step #1: learning what's out there, how this may impact their business models, and strategizing on how AI can best be leveraged to drive value for their clients.

So, let’s collectively demystify AI by using it: Develop a structured learning approach within your firm to understand its underlying principles, ensuring it is not perceived as an impenetrable “black box.” That outcome will not be realized if users have not explored AI firsthand and experienced that “aha” moment (LLMs like ChatGPT in particular). Give project managers, business support, and engineers appropriate and secure LLM access, even if on a limited basis with a small group. The grant team’s sample AI policy can help with this decision and set a foundation for risk-reduced AI use at your firm. (Scan the QR code for the sample policy.) Form user groups to share prompting ideas, recommended workflows,

and insights that will inspire colleagues and build a knowledge base. If your firm has the appetite for programming in engineering workflows, find your tinkerers and support them in acquiring and leveraging coding skills. And if you have compelling cases for machine learning workflows, it has never been easier to implement them.

And we know machine learning, coding, and internal development dominates a lot of discussion in the AI space, but do not overlook commercial AI-startup software tailored to our industry either. While there is much hype in this space, and a lot of unmet promises, there are also glimpses of transformative technology developing—quickly. Our grant team has been meeting with many of these companies to gauge hype, sharing our insights on their value and lessons learned. Whether it be for early design, cost, and option studies, Project Manager support, or quality control/assurance, you need to know what is out there to develop a compelling and competitive strategy.

Connect your staff with valuable company resources in your internal knowledge base. Once the resources are discoverable by AI, they can be used as a basis for new proposals, reports, calculations and beyond using LLMs. This can be done using Copilot and SharePoint Agents, custom development, or using consulting and storage platforms built for AI.

Develop, Implement, and Engage

Once your leadership and user groups have set initial strategy, you will need to set budgets, metrics and measurable goals. Consensus and priorities are often challenging at this stage, where resources and expenditures are limited. Identify practical use cases in technical workflows, project management, or business operations where AI can deliver immediate value. Build on your initial strategy, and engage with stakeholders, to continually assess ROI. Be ready to change direction based on feedback, new models, and AI industry development. This technology is maturing so fast it is likely you will need to shift strategy along the way.

For many firms, that next step may simply represent a $25-30/month subscription to a secure LLM service such as Microsoft 365 Copilot, Google Workspace AI, ChatGPT Plus, or perhaps an AI platform such as Microsoft Azure or Google Cloud. Many of the member firms of the AI grant team have started with Chatbots/RAG to harvest their knowledge base and get AI to their team securely. For others, this might be funding a proposal to modernize or automate workflows of high value or adopting a new piece of AI-infused software or consulting service into your practice. The key here is a well-defined plan and support from stakeholders. If your people are not supportive, adoption of the tech is not likely to grow organically.

Pilot projects can help gain support, measure value, and build small successes: Start by identifying a key group of individuals who want to find ways to leverage technology within your existing processes and workflow. The younger generations are curious, want to engage, and often come with skills essential to leveraging AI and coding. Include them in projects to benefit their development and project outcomes. Additionally, give people the training it takes to use them well. Simply buying a software package is not enough if you don’t know how to use it effectively and properly. Expect that some attempts at AI adoption will not yield the results you had hoped for. Fail fast, learn from and document those experiences, and identify what went well and what went wrong. Be realistic and make things better instead of abandoning technology.

Example Real-World Pilot Projects from the Grant Team

Examples of pilot projects that firms can start with beyond basic LLM adoption, populated by examples Grant Team members are leveraging at their firms include:

• Chat With Your Documents (Retrieval Augmented Generation, RAG):

• AI Transcription, Notetaking and Task Management: Automated notetaking is obvious as a benefit but requires a shift in strategy to get good results with AI. Develop a meeting style where key outcomes, tasks, topics, and agenda items are clearly defined and spoken to so that they will appear in the text transcript. When the meeting is over, tasks should be documented and assigned, with dates, and trackable.

• Business Development, Client Tracking, and CRM Population Automation: How can AI help you win more project work? Track client interactions? Evaluate and respond to RFPs better and faster? Members in our team are using Copilot for Sales to connect to Microsoft Dynamics from Outlook. Other platforms can populate Deltek Vision or Unanet data within Outlook or directly from LLMs.

• Quality Review for BIM, Drawings, and Specifications: Aligning and improving our work products avoids time and waste. AI tools are available that connect to Revit, your specifications and general notes, and product data, giving time back to work on design. Our members are using these workflows to elevate our designs in both 2D and 3D cases and improve cross-discipline collaboration at project milestones Some municipalities are beginning to use AI-enabled tools like CivCheck or Archistar for preliminary plan checking at intake.

• Machine Learning (ML) for Early Design and Prediction: Building a custom ML workflow for early design questions or reductions in compute time may be out of reach for firms without a clear value proposition. However, numerous licensable AI-enabled platforms leverage ML for material-specific early project design estimates. Examples from our members include using ML to predict ASCE41 Tier 1 outcomes, wind surface roughness prediction, flat slab long-term nonlinear deflection results, predicting material quantities for SD designs. While this process has been used for decades in our field, AI makes it easier to structure your data and implement ML. Commercial software tools are also available that generate preliminary floor framing and wall framing layout for steel and wood such as Genia and TangoBuilder.

• Damage and Crack Detection, Automated Site Visit Reports: While not a recent advancement, our members are using both custom and commercial offerings to improve and speed up documenting damage in bridges and buildings using image-based AI. Additionally, there are apps using your phone’s camera and microphone to track site visits, transcribe and tag notes, 2D and 3D image capture, and generating a first draft of your site visit report. Expect a lot of advancements in this area as the technology improves.

Fig. 1. AI Roadmap outlines the path forward for AI adoption within any size structural engineering firm.

• Data from Documents: Leverage document intelligence AI to extract structured data from PDFs, such as submittals. Our members are using this to track sustainability metrics across past projects by collecting data from construction administration submittals and create a database of project performance by location and client by integrating this with accounting data. LLMs can also be prompted to output structured data and produce Excel spreadsheets or pre-populate a template form.

• Enable Engineering Automation Tasks: Use AI copilots for coding to write scripts with speed. Leverage AI coding copilots to write scripts and user interfaces that translate one data format into another and allow the computer to handle data while engineers focus on analysis and design. For example, reading shop drawings from open web steel joists to directly import from PDFs into analysis software input so that an engineer can check existing conditions and strengthening for added loads. Cut out the manual data entry, focus on the engineering value. Our members are using programming to automatically import data from API-based services like the ASCE Design Hazard maps and pre-populate report templates with consistent job information like address, client, and project name directly from API-enabled accounting software. Excel calculation sheets can be automated with Power Automate or converted to Python to operate in the cloud.

• Material Quantities and Estimating: AI tools developed to assist with GC estimating can also be used by design professionals to verify basic building design information like floor areas, facade perimeters, opening sizes, and other quantities based on preliminary project criteria documents.

Growth, Focusing Strategy, Disruption, and Transformation

The last phase of a firm’s journey through this roadmap should reflect a developed technology and AI strategy, which engages diverse stakeholders across your firm who use and promote the tools. ROI should be understood and will guide continued development alongside other metrics and feedback loops. And the outcomes of your investments should allow you to add significant value for your clients rather than just realizing efficiencies. This requires an understanding of both your business model and AI tooling to understand the “art of the possible” to drive value for your clients. Those that understand the business side of structural engineering are different than those that understand the AI technology. Getting to this step is not possible without engaging a broad group within the firm and starting early.

The above statements reflect a firm’s journey to transform their practice in the age of AI, potentially disrupting aspects of the industry through innovation. But that outcome goes both ways, as other firms will adopt similar strategies to grow their presence or take on new scope. As AI adoption accelerates, firms must reassess their value proposition constantly in a landscape where startups and established companies are leveraging AI in new ways that were not likely captured in your technology or strategic plans. Being nimble and adaptable is key here.

AI Initiatives: Resources to Help You on the Way

A growing set of resources is available through published documents, partnerships, and continuing education opportunities such as webinars, NCSEA convention presentations, and courses. Along with the upcoming follow-up webinar to this article, NCSEA is hosting a preconference seminar at the 2025 NCSEA Summit in New York, focused on AI applications in structural engineering. This session will offer hands-on strategies, peer collaboration, and actionable takeaways. This hands-on seminar will be hosted in two

specialized tracks—Consumer and Developer—designed to equip and enable participants with different levels of technical skills with AI.

While more publications and short courses are in development, resources available now include (scan the QR code):

Sample AI Policy: A customizable framework for firms to establish AI guidelines, covering ethical use, security, and implementation best practices. This sample policy provides a starting framework and needs to be customized to fit your specific requirements. The details include examples from several firms successfully implementing AI in their operations. It covers a discussion of AI platform considerations, guiding principles and use cases, recommended AI use cases, risks of using AI, ethics and legal considerations, reporting and misuse, confidential and proprietary information, and more.

Getting Started Guide for Generative AI: Provides a description and working definition for Generative AI, and a starting point for general tasks that people can benefit from.

NCSEA Connect Webinars: One introductory webinar and STRUCTURE magazine article on “Creating a Foundation for AI in the Structural Engineering Profession,” two Town Hall Discussions on AI in the SE Profession, and one webinar on introducing beginners to hands-on coding with an AI/ML model. These recordings are available through the NCSEA website.

Quick Start Guide for Working with AI Models: A guided, on-thekeyboard tutorial through working with AI models for beginning coders, with a structural engineering example of using a computer vision model to classify ASCE 7 wind surface roughness categories based on aerial images.

Partnerships: The NCSEA Foundation has initiated several conversations with established software vendors and startups providing solutions using ML and AI. These help to answer the question about what tools and data platforms are coming in the future and provide guidance in terms of whether it makes sense for a firm to build new tools on their own vs. buy in the marketplace today.

NCSEA Summit & Local SEA Participation: The AI Grant Team delivered a series of presentations at the 2024 summit launching into smaller discussions around AI adoption at a local level among several local SEAs across the country.

Conclusion

Today is the time to start on the road to AI adoption and infusion into your everyday practices. The NCSEA Foundation provides essential resources and tools to support the structural engineering profession in successfully adopting AI. The AI Grant Team is eager to support you on your AI journey. For more information, comments, or questions, please email us at ai@ncsea.com. ■

Visit program.acec.org/2025-joint-summer-series-artificialintelligence to register for this summer AI webinar series.

Andrew Sundal, AIA, PE, is a licensed Architect and Structural Engineer at HGA in Minneapolis focused on research, innovation, and computational design.

Dave Martin, SE, is an Associate Principal at Degenkolb based in Oakland and leads firmwide AI adoption and BIM integration.

Emre Toprak, Ph.D, PE, is Asst. Vice President in WSP based in the Washington DC metro area and brings two decades of structural engineering experience across Europe and the Americas, delivering both new building designs and evaluations of existing structures.

John-Michael Wong, Ph.D, SE is the current Project Manager for the NCSEA Foundation’s Innovation in Structural Engineering AI Grant Team, and an Associate at KPFF in San Francisco.

Celebrating connection: 16 Tech Bridge opens to the public in Indianapolis

I

ndianapolis’s 16 Tech Community Corporation celebrated the opening of the signature 16 Tech Innovation District Bridge in May. The wave-like design spans 342 feet over Fall Creek and serves as a vital link between the 16 Tech Innovation District and Indianapolis’ research and medical corridor.

The new multimodal structure prioritizes pedestrians and cyclists, keeping them separated from vehicular traffic with protected pathways that connect to the city’s wider trail and greenway network. With more than half the square footage of its 65-foot-wide deck devoted to non-vehicular use, the bridge’s design encourages pedestrians to pause and enjoy the views along the span of the bridge. A dedicated gathering space on the bridge’s eastern side gently cantilevers over the water, creating opportunities for public programming and events.

Led by bridge designers and engineers schlaich bergermann partner (sbp) and the architects Practice for Architecture and Urbanism (PAU), the design team included Moniteurs Communication Design, Martha Schwartz Partners (MSP), Shrewsberry & Associates, CTL Engineering, Circle Design Group, and People for Urban Progress (PUP). The team was tasked with designing a signature work of public infrastructure that would serve as an example of innovation and collaboration. The result is a unique bridge structure that reinterprets the principles of a classic suspension bridge to create an entirely new form.

The bridge is the first-of-its-kind in the United States and innovates on classic suspension bridge principles while extending sbp’s existing family of steel-plate bridges. By replacing large vertical masts with a fan-like arrangement of smaller masts and substituting traditional suspension cables with 2-inch thick elegant flat steel plates, the bridge achieves its signature wave-like form. This innovative system efficiently distributes internal forces, primarily utilizing tension and compression instead of bending, minimizing material use and enhancing sustainability. Additionally, the bridge is designed as an integral structure, where the superstructure (deck) and substructure (abutments and piers) function as a single,

monolithic unit. This eliminates the need for expansion joints and bearings, reducing maintenance requirements and increasing long-term durability.

The bridge scheme also responds to the site’s unique natural conditions. One of the most striking features of Fall Creek is the seclusion created by the lines of trees on either side. The bridge’s design borrows inspiration from this beautiful setting, creating tree-like vertical supports that mimic the trunk and branches of a tree. The bridge’s defining attribute—its undulating steel ribbon—also mirrors the natural profile of Fall Creek itself, rising with tree canopies on either side of the waterway and lowering towards the center to create unobstructed views up and down the creek.

Given the bridge’s unconventional structural system and the need to minimize environmental impact during construction, constructability was a key challenge. Through advanced digital modeling and close collaboration between engineers and fabricators, the team optimized fabrication and assembly processes to streamline construction while maintaining the bridge’s expressive form. The modular approach allowed for efficient use of materials and labor, reducing waste and ensuring economic feasibility.

While bridges are often viewed as mere transitional spaces, the 16 Tech Bridge challenges this notion by becoming a destination in itself—an inviting public space for gathering, interaction, and connection.

IN BRIEF

NYC releases final investigation report into 2023 fatal parking structure collapse

According to the findings of an investigation report into the deadly 2023 parking garage collapse at 57 Ann Street in Manhattan, a combination of factors led to the collapse, critically the dangerous demolition of a structural brick pier inside the building performed without construction approvals or permits. After an extensive multi-agency investigation, it was determined that employees of the parking garage business improperly removed bricks and mortar from a load-bearing brick pier just below the third floor of the nearly 100-year-old building without implementing proper shoring. It was further determined that this dangerous demolition work, in combination with additional contributing factors, including a flawed engineering assessment of a deteriorated brick pier, poor maintenance, and an apparent design and construction deficiencies during the original construction of the building, led to the collapse. The full report is available at www.nyc.gov.

Cornell structural engineering professor selected for AISC residency program

This summer, the American Institute of Steel Construction (AISC) will welcome its third Innovation Scholar to a two-week residency at the institute’s Chicago headquarters.

Cornell University Professor Reiter, SE, PE, will collaborate with AISC’s engineering and research team on a structural steel-focused project (to be determined) and take part in a variety of industry events, including committee meetings and local facility tours, between July 7–18.

An integral member of Cornell’s School of Civil and Environmental Engineering, Reiter teaches behavior and design related structural engineering courses in addition to serving as faculty director for the Structural MEng program. He brings with him a breadth of experience in structural engineering from his previous work as a project engineer with Thornton Tomasetti and a section manager within Cornell’s facilities engineering department.

In addition to fully reimbursed travel to and from Chicago, fully reimbursed lodging downtown, and a meal stipend, Reiter will receive $5,000 from the AISC Education Foundation.

AISC’s Innovation Scholar program is designed to boost collaboration between engineering educators and the professionals who develop steel design standards. You can learn more about the program and last year’s inaugural cohort of Scholars at aisc.org/innovation-scholar.

Gillespie Field iPark is complete

Construction is complete on Gillespie Field iPark, a built-to-suit manufacturing facility for GKN Aerospace and distribution speculative suite located near Gillespie Field public airport in El Cajon, Calif.

The new industrial development showcases a collaboration between Ware Malcomb, Del Mar-based developer Chesnut Properties, general contractor C2 Building Group, structural engineer Prime Engineering, landscape architect Ridge Landscaping, and utility consultant NV5. The manufacturing tenant, GKN Aerospace, is a leading global tier-one supplier of aftermarket repair, airframe and engine structures, landing gear, electrical interconnection systems and transparencies. Employing tilt-up concrete construction, the industrial building’s exterior architectural features include unique custom canopies that required intricate structural elements, as well as a mural made from steel perforated panels inspired from a photo of a World War II aircraft training at Gillespie Field. Despite airport-related height constraints, the project achieved its interior clear height goal while integrating a variety of sustainability features such as solar panels, energy-efficient equipment, natural ventilation, and daylighting.

More than 50 EV charging stations are also featured on site.

Ware Malcomb’s civil engineering team overcame multiple challenges grading a 30-acre

site comprised of hard rock hills, while still preserving sensitive wetland habitats and maintaining compliance with Federal Aviation Administration height limits. ■

ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

Matthew Reiter

SEI Update

SEI and ASCE Structural Awards recipients

SEI and ASCE honor those who have made significant contributions to the structural engineering profession through publishing outstanding papers, dedication to technical excellence, and by providing exemplary service and leadership. The following were recognized at Structures Congress 2025 in Phoenix. Nominations for next year’s awards are due November 1st. Get inspired — watch the 2025 awards ceremony on YouTube: follow us at @StructuralEngineeringInstituteofASCE.

Dennis L. Tewksbury Award

Daniel G. Linzell, Ph.D., P.E., F.SEI, F.ASCE

George Winter Award

Shortridge Hardesty Award

Moisseff Award

Qian Chen, Ph.D., P.E., M.ASCE; Honfang Wan; Baidurya Bhattacharya, Ph.D., F.ASCE; Sherif El-Tawil, Ph.D., P.E., F.SEI., F.ASCE; Anil K. Agrawal, Ph.D., P.E., F.SEI, Dist.M.ASCE; Waider Wong

Gene Wilhoite Innovations in Transmission Line Engineering Award

C. Reese Research Prize

Alfredo Ang Award on Risk Analysis & Management of Civil Infrastructure

Dan M. Frangopol Medal for LifeCycle Engineering of Civil Structures

David P. Billington Award

SEI Chapter of the Year

SEI Connecticut Chapter

SEI Graduate Student Chapter of the Year

SEI Graduate Student Chapter, Colorado School of Mines

James A. Rossberg Award for Collaboration

SEI President’s Award

Maria E. Moreya Garlock, Ph.D., P.E., F.SEI, F.ASCE

Mahen Mahendarn, Ph.D.,FIEAUST

Raymond

Wenpeng Wu, Ph.D.; Jialong He; Lifeng Li, Ph.D.; Huihui Li, Ph.D., A.M.ASCE

William F. Baker, Jr. P.E., S.E., NAE, F.SEI, Dist.M.ASCE

Walter P. Moore Jr. Award

Daniel T. Cox Ph.D, A.M.ASCE

Phillip J. Samblanet P.E., M.ASCE

Kenneth L. Sharpless P.E., F.SEI, F.ASCE

Sankaran Mahadevan Ph.D., F.EMI, M.ASCE

Fabio Biondini Ph.D., C.Eng., F.SEI, F.ASCE

David O. Prevatt Ph.D., P.E., F.SEI, F.ASCE

News of the Structural Engineering Institute of ASCE

Speakers

and

program announced for the Towards

Zero

Carbon 2025: Summit and Symposium

SEI and the University of Colorado, Boulder are co-hosting the Towards Zero Carbon 2025: Summit and Symposium June 26th27th. Attendees can select from three tracks: Embodied Carbon Bootcamp, SE 2050 Signatory Summit, or Firm Leadership Round Table. All tracks will come together for the welcome reception June 26th and the Symposium: A Structural Engineer’s Vision for the Future on June 27th.

Symposium speakers will focus on answering the following questions:

• What does the structural engineering profession look like in 15 years?

• How will the way we design and build structures evolve and help us move toward zero?

• How will we engage and collaborate with our design partners, clients, and policy makers to drive and adapt to change?

Towards Zero Carbon: A Roadmap for the Structural Engineering Profession

• Jerome Hajjar, Ph.D., P.E., NAE, F.SEI, F.ASCE, Chair, Department of Civil and Environmental Engineering, Northeastern University Motivating a Sustainable Future: Market Drivers, Regulation, and Incentives

• Anish Tilak, Carbon-Free Buildings Program Manager, RMI Building a Sustainable Future: Perspectives from Across the Industry

• Erika Winters Downey, S.E., LEED AP BD+C, Director of Sustainable Structures, Clayco/Lamar Johnson Collaborative

• Kjell Anderson, FAIA, LEED Fellow, Director of Sustainable Design, LMN Architects

• Amanda Kaminsky, Director of Sustainability, Consigli Construction

• Iris Loureiro, Construction Innovation Manager, Prologis The Future of Building Materials

• John Kevern, Ph.D., F.ASCE, National Renewable Energy Laboratory

• Kim Olson, P.E., Nucor

• Will Lepry, Ph.D., Director, Colorado Mass Timber Coalition Structural Design—Visions for the Future

• Ian MacFarlane, P.E., S.E., Senior Principal, Magnusson Klemencic Associates

• Laura Karnath, AIA, Senior Enclosure Consultant, Walter P Moore

• Sheng Zheng, P.E., Martin/Martin Consulting Engineers

SEI Elections

Candidate information and link to the ballot for the 20252026 SEI Board of Governors will go out to all SEI members on July 1st. The ballot will be open from July 1st to July 31st to vote for President-Elect, one At-Large Governor, and one Young Professional Governor. Email sei@asce.org for more information.

SEI announces updated flood provisions on track for incorporation into the 2027 IBC

The IBC-Structural Committee approved SEI’s proposal to align the 2027 IBC with ASCE/SEI 7-22 Supplement 2 and ASCE/ SEI 24-24 at the ICC Code Hearings in Orlando April 27th through May 4th. ASCE/SEI 7-22 Supplement 2 expands the flood hazard area to the 500-year floodplain for Risk Category II, III, and IV structures, incorporates risk-based design for flood loads, and includes requirements to include relative sea level change into design load calculations for coastal sites. ASCE/SEI 24-24 aligns with FEMA Technical Bulletins and includes updated provisions for flood-resistant construction.

Members of the ASCE/SEI 7-22 Flood Load Subcommittee, members of the ASCE/SEI 24-24 committee, and SEI staff testified on behalf of the proposals along with representatives from the Association of Floodplain Managers, BuildStrong America, the Insurance Institute for Business & Home Safety, and the Natural Resources Defense Council. SEI presented several code-change proposals which were approved at Committee Action Hearing #1, ranging from elimination of the alternate ASD load combinations to clarification of design requirements for buildings in tornado-prone regions.

SEI celebrates the adoption of ASCE/SEI 24-24 into the 2027 IBC at CAH #1.

Cole Graveen testifies on behalf of the ASCE 7 Dead and Live Loads Subcommittee.

NCSEA News

Where do 1,000 structural engineers go to find out what’s next?

It’s big. It’s bold. And it’s back. Registration is officially open for the 2025 NCSEA Structural Engineering Summit, the largest event of its kind in the U.S. Join us in New York City on Oct. 14-17 to connect, learn, and see what’s coming next in the field. Set to draw over 1,000 practicing SEs from across the country, the 2025 Summit will offer up to 14 Professional Development

Hours (PDHs) through a curated lineup of educational sessions. With a record number of session proposals submitted this year, the 2025 Summit will provide a power-packed program featuring standout sessions led by top experts, alongside the profession’s largest SE-focused exhibit floor.

“The NCSEA Summit is where the most impactful conversations and connections in structural engineering take place,” said Al Spada, NCSEA CEO and Executive Director. “It’s more than a conference —it’s the place to connect, get inspired, and walk away with new ideas that stick long after the final session.”

Check out just a few of the highlights at the 2025 Summit:

• Inspiring Keynotes: This year’s keynote lineup will feature leaders pushing the boundaries in design, leadership, and structural innovation. Stay tuned for upcoming announcements on our speaker roster.

• Huge Exhibit Hall: Explore the latest innovations, products, and services from industry-leading brands in the nation’s largest exhibit hall dedicated entirely to the needs of structural engineers.

• Preconference Artificial Intelligence Symposium: Attendees can kick off the Summit with a focused AI Symposium, featuring two tracks on the transformative impact of artificial intelligence in structural engineering.

• Unmatched Networking: From the high-energy Welcome to New York Party to the SEE Awards Celebration, the Summit creates countless opportunities to connect with colleagues, mentors, and other leaders.

For more information and to register, visit www.ncseasummit.com.

Applications open for young member scholarships, awards

NCSEA is now accepting applications for two programs designed to recognize and support emerging professionals in structural engineering: the Young Member Summit Scholarship and the Young Member Group of the Year Awards.

Young Member Summit Scholarship

This scholarship provides full registration to the 2025 Structural Engineering Summit. First-time recipients will also receive a $1,000 travel stipend to help cover transportation and lodging. Eligible applicants must be under the age of 36 and a member of their local Structural Engineers Association (SEA).

NCSEA Webinars

Young Member Group of the Year Awards

These annual awards celebrate outstanding Young Member Groups (YMGs) across the country. Award categories include YMG of the Year, Breakout YMG, and Best Event/Initiative.

Winners receive complimentary Summit registration, travel stipends, and funding to support future YMG activities and programming. Travel stipends are generously sponsored by Computers & Structures, Inc. (CSI). Applications for both opportunities are open through June 29, 2025.

To learn more or apply, visit https://www.ncsea.com/ education-events/events-conferences/ym-scholarships.

Visit www.ncsea.com/education for the latest news on upcoming webinars and other virtual events.

News from the National Council of Structural Engineers Associations

NCSEA launches inaugural compensation & benefits study

The National Council of Structural Engineers Associations (NCSEA) has released the initial data from its first-ever Compensation & Benefits Study, offering an unprecedented look into structural engineering salaries, benefits, and workplace trends. This interactive platform provides some of the most comprehensive data available to date, giving structural engineers and firm leaders the information they need to benchmark compensation, PTO, bonuses, and more.

For a limited time, NCSEA is offering access to the study at a special introductory rate. Additionally, participants who completed the survey are eligible for a discounted price, and those who haven’t yet participated can still complete the survey by June 15, 2025, to secure the discounted rate.

Explore the data to benchmark salaries, benefits, and bonuses against profession-wide standards; customize data views and export key findings; and visualize emerging trends and inform career decisions.

The strength of the Compensation & Benefits Study depends on widespread participation. By contributing data, structural engineers

not only gain valuable insights, but also help shape the most accurate and impactful compensation benchmarks for the profession.

“This study is a crucial step forward in providing structural engineers with the tools they need to assess and advance their careers,” said Al Spada, NCSEA CEO and Executive Director. “We’re pleased to offer this data and to continue expanding its impact as more participants contribute.”

The NCSEA Compensation & Benefits Study is part of NCSEA’s ongoing commitment to supporting the structural engineering profession with data-driven resources. It is sponsored by SE Impact. To purchase the data or to participate in the survey, visit https:// benchmarking.ncsea.com.

SEAOSD expands seismic outreach program with foundation grant

Withsupport from an NCSEA Foundation SEA Grant, SEAOSD is shaking things up in San Diego classrooms with a hands-on seismic outreach program. Led by UC San Diego undergraduates, the program uses K’Nex design kits and a shake table competition to introduce fourth- through sixth-graders to the basics of structural engineering while sparking early interest in STEM. After engaging 80 students in Fall 2024 and 120 in Winter 2025, SEAOSD plans to reach 160 more in Spring 2025 – and they’re just getting started. Plans are underway to expand the initiative statewide and nationally, bringing more young minds into the world of engineering. This project is one of many supported by NCSEA Foundation SEA Grants.

CASE in Point

Engineering meets the end zone: ACEC-AZ’s STEM Gameday scores big with students

Three years ago, ACEC Arizona saw a problem—and turned it into a playbook for impact. With engineering program enrollments declining and workforce gaps growing, they didn’t just talk about the issue—they took it to the field. Literally.

Enter STEM Gameday, a bold and brilliantly simple idea: bring middle schoolers to major football stadiums and show them how engineering makes game day possible. From infrastructure and utilities to structural design and transportation systems, these iconic venues became hands-on classrooms, turning abstract concepts into real-world inspiration.

The first event launched in 2023 at Arizona State University’s Sun Devil Stadium with 120 students. Fast forward to 2024, and the program had scaled to three universities and over 1,500 students, supported by hundreds of passionate volunteers—from professional engineers to university student mentors.

By 2025, organizers fine-tuned the format, balancing impact with

accessibility, capping attendance around 600 per location while keeping the energy high. With backing from state agencies, engineering firms, and professional societies like ASCE and SAME, the program has become a model of collaboration, creativity, and community.

And here’s the best part: it’s not just the students who leave inspired. From volunteers building connections across generations to engineering leaders watching future talent light up with curiosity, STEM Gameday is creating a ripple effect across Arizona’s entire engineering ecosystem.

Hats off to ACEC-AZ for proving that workforce development doesn’t have to be boring or bureaucratic—it can be fun, immersive, and unforgettable. You’ve built something special here. And for other chapters across the country wondering how to start? Take ACEC-AZ’s advice: “Just try it. Start small. You won’t regret it.”

This is how you grow the future—one stadium, one student, one spark at a time.

From classroom to stadiums: inspiring future engineers

Join us for an engaging episode of Engineering Influence, where we explore ACEC Arizona’s revolutionary initiative, STEM Game Day. Discover how this award-winning program is making waves by immersing middle school students in the engineering world through the excitement of a football game. Chris Bridges, Executive Director of ACEC Arizona, and Nicolai Oliden, Board Member and Workforce Development Chair, share their inspiring journey of addressing workforce challenges by sparking early interest in STEM careers.

Listen as they walk us through the program’s inception, its exponential growth from reaching 120 to over 1,500 students across Arizona, and the impactful collaborations with universities and professionals that make it all possible. Find out how ACEC Arizona’s efforts are creating pipelines for future engineers and fostering community ties, all while providing invaluable learning experiences for students, volunteers, and the engineering sector alike.

Listen to the podcast by scanning the QR code.

Investing in the future: support the CASE Scholarship Fund

Education has the power to transform lives, but for many talented and hardworking students, financial barriers stand in the way of their dreams. The CASE Scholarship Fund is dedicated to breaking down those barriers— ensuring that every deserving student has the opportunity to pursue higher education, regardless of their financial circumstances.

Right now, we have an opportunity to make a real and lasting impact. Every dollar raised goes directly toward helping students achieve their academic goals, empowering the next generation of leaders, innovators, and changemakers. These scholarships don’t just fund tuition—they fuel ambition, progress, and hope for a brighter future.

Do you know an aspiring engineer who could benefit from this opportunity? Share the CASE Scholarship with them and help open the door to a world of possibilities. To find out how to apply go to

We need your support to continue this mission. Whether you contribute $10 or $1,000, your donation makes a difference. Together, we can open doors, create opportunities, and change lives.

Join us in investing in the future. Donate to the CASE Scholarship Fund by scanning the QR code today.

News of the Coalition of American Structural Engineers

Explore CASE’s bestsellers of 2025

Explore CASE’s top publications that inspire and inform professionals like you. From cutting-edge research to actionable insights, this year’s bestsellers are not to be missed. Plus, if you’re not a CASE member, don’t forget to use your discount code NCSEASEI2022 at checkout for exclusive savings.

CASE 962-D: A Guideline Addressing Coordination and Completeness of Structural Construction Documents

This book discusses the purpose of this guideline, the background behind the issue, the important aspects of design relationships, communication, coordination and completeness, guidance for dimensioning of structural drawings, effects of various project delivery systems, document revisions, and closes with recommendations for development and application of quality management procedures. A Drawing Review Checklist is attached.

A companion document is also available: CASE Tool 9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Documents

CASE Tool 9-1: A Guideline Addressing Coordination and Completeness of Structural Construction

Inadequate and/or incomplete design drawings often result in inaccurate competitive bids; delays in schedule; a multiplicity of requests for information (RFIs), change orders and revision costs; increased project costs; and a general dissatisfaction with the project. The guidelines presented in this document will assist not only the structural engineer of record (SER) but also everyone involved with building design and construction in improving the process by which the owner is provided with a successfully completed project.

There are two PDF files included with the Tool: one with Tool 9-1 and the other with the CASE Drawing Review Checklist.

CASE Tool 9-2: Quality Assurance Plan

CASE Tool No. 9-2: Quality Assurance Plan provides guidance to the structural engineering professional for developing a comprehensive detailed Quality Assurance Plan suitable for their firm. A well developed and implemented Quality Assurance Plan ensures consistent high-quality service on all projects and includes:

• Quality Control Review

• Firm-wide Standards

• Construction Quality Assurance

structural FORUM

Makers+Shakers

Hands-on

learning inspires future structural engineers.

By Tara Flaherty, EIT

You’re the structural engineer designing a new multi-story condominium on the Pacific coast. The architect wants clear, unobstructed views of the ocean, high ceilings, and a rooftop pool. The developer wants to maximize the number of sellable units and minimize costs. Your design needs to support the architect’s vision at a cost that works for the developer. And, of course, you need to design the building to withstand an earthquake. Does this sound familiar? This is essentially the problem statement Schaefer team members give students in junior high school participating in the firm’s Makers+Shakers program. Students use K’nex to design their condo towers and test them on a homemade shake table. They get exposed to load path, resonance, torsional irregularities, and mass and stiffness irregularities. They learn to design with constraints and deal with competing objectives. But most importantly, they get exposure to the structural engineers leading the program, and the creativity + technical acumen necessary in our industry.

Makers+Shakers taps into the tangible aspects of ‘build and break’ structural engineering projects that students love and adds a dynamic component more engaging than static load tests.

The Growing Need for Civil Engineers

There is a sizable gap between the expected demand for civil engineers and the number of civil engineers entering the workforce. The U.S. Bureau of Labor Statistics is projecting nearly 23,000 civil engineer job openings each year on average for the rest of this decade. But, according to the National Center for Education Statistics, only 15,051 bachelor’s degrees in civil engineering were awarded in 2021.

How do we bridge the gap? The team at Schaefer believes we can make a difference by sharing our passion with students and introducing a potential career path they may not be familiar with. Age matters – our program is built for seventh and eighth graders for a reason. Many undergraduate engineering programs have math and science prerequisites beyond high school graduation requirements, so we need to meet students when they still have time to plan their high school courses accordingly.

If students don’t see civil or structural engineering as a potential accessible and rewarding profession before high school, they may not have sufficient exposure to the math and science classes required to even apply to a college engineering program.

Fig. 1. The Makers+Shakers shake table uses a servo motor, interlocking chain, and roller skate wheels to simulate ground motions.

Get Involved

Makers+Shakers is an intentionally brief but intensive introduction to structural engineering concepts that can be done as part of a career day activity, within a junior high STEM or engineering class, or as an activity for a club. The entire program can typically be completed in one or two classroom sessions, about one to three hours.

While Makers+Shakers can serve as a launching point to supplement larger scale outreach programs such as Future City or any of the outreach projects that NCSEA promotes on their stem-outreach page, the goal of Makers+Shakers is to grab students’ attention and get them engaged quickly. We’re not lecturing students about engineering—they’re actu ally doing it. We ask them to solve a real-world problem that we, as structural engineering professionals, work through every day.

This small-scale, intensive, one- to two-session approach also makes it easy for facilitators. We’re all busy, so having an impactful outreach activity that can be accomplished in a few hours makes it easier to find volunteers willing and interested in participating.

Schaefer has had great success with our Makers+Shakers program in Cincinnati and Columbus, Ohio, and we’d like to see our partners, peers, and friends participate as well. That’s why we’re publishing all the resources needed to create your own Makers+Shakers program, including building your own shake table.

Following is a high-level overview of the resources and directions; you can find full materials for a prototype shake table on our website (scan the QR code).

How to Build a Homemade Shake Table

You can build a homemade shake table for $200-$400.

The 2-dimensional shake table design enhances visibility of mechanical components while remaining cost-effective. Accessibility and visibility are intentional. This build reinforces the creative “maker” attributes of engineers, it allows the students to intuitively understand how the table works, and by making the tables out of off-the-shelf components (plywood, skateboard parts and servo motor), the build doesn’t seem out of reach for the students themselves.

The prototype shake table consists of a plywood base with stacked plywood cutouts forming shallow foundations and pedestals (Fig. 1). The center pedestal secures the servo motor holding a rotating gear. The two outside pedestals support the roller skate wheels. A pegboard, attached to a wooden block with an interlocking chain, rests on these wheels. During operation, the motor's rotation moves the pegboard horizontally along the chain's length. Our current build of the table replaces the pegboard with a plexiglass board and incorporates the plywood base into a wooden case to make it easy to transport.

The table, controlled by a Raspberry Pi, can simulate ground motions from actual earthquake records! The movement is generated by the servo motor. The large gear and chain convert the rotational velocity of the motor to linear translational velocity of the table. Typical servo motors only have one speed (e.g. they operate at a constant rotational velocity). Our servo operates at 50 Hz, and we provide a pulse every 20 milliseconds (ms). Pulse length within this 20ms interval determines the motor's rotation degree (0.5ms = 0˚, 1.5ms = 90˚, and 2.5ms = 180˚). The motor rotates to the specified rotation degree at the motors default rotational velocity. By using small timestep data and displacement scale, we can control when the servo stops, starts, and reverses to control speed and acceleration.

The Raspberry Pi serves as the control center, running Python code that directs the servo's movement timing and magnitude. Excel files

store the timestep and displacement data. The Python code converts this data into appropriate pulse widths and translates it into a format readable by the Raspberry Pi. The Raspberry Pi transfers the translated data through a series of electrical components (ribbon, GPIO Extender, breadboard) to the servo motor. The breadboard is wired with push buttons and an LCD display to facilitate user interaction.

Educational Components

We’ve developed three primary demonstrations for Makers+Shakers:

1. The first is a standard lollipop resonance demonstration.

2. The second demonstrates relative stiffness differences between general moment frames and braced frames.

3. The third illustrates the influence of additional mass.

Each demonstration illuminates the competing demands of architect and engineer and sets the stage for a classroom competition activity.

Resonance Demonstration

The initial demonstration utilizes sinusoidal motions rather than historical seismic records. This simulation pairs with three "lollipopshaped" building models of varying heights—a single-story structure (house), a mid-rise building (hotel), and a high-rise tower (Fig. 2). Each sinusoidal frequency corresponds to the natural frequency of one of the lollipop models, demonstrating to students that every structure possesses a unique resonant frequency that must be incorporated into design considerations.

Stiffness Demonstration

The second demonstration contrasts the seismic performance of two four-story K'nex structures: a braced frame and a moment frame (Fig. 3). This comparison reveals how different structural systems respond

Fig. 2. In a resonance demonstration, students watch the sinusoidal behavior of three lollipopshaped models to learn about the unique resonant frequencies of structures.

to identical forces, highlighting the relationship between framing methods and building behavior. The demonstration sparks discussions about practical trade-offs, including construction efficiency, material costs, and architectural implications such as window placement and the aesthetic potential of structural bracing.

Mass Demonstration

The final demonstration examines mass influence through identical structures, with one bearing additional weight (Fig. 4). Students observe how the heavier structure exhibits more pronounced responses to seismic forces. This leads to meaningful discussions about real-world design elements that add mass—like rooftop pools, green roofs, solar installations—and their associated cost implications and engineering challenges. Collectively, these demonstrations effectively bridge structural dynamics principles with industry realities and serve as hints and tips for the classroom competition activity.

Competition Activity

After participating in the demonstrations, students are put into teams and tasked with designing and building a tower that meets specific project goals including withstanding an earthquake. A combination of incentives and costs are considered by each team in order to optimize their design. They are given a construction budget, and each K’nex piece has a cost associated with it. The winning structure is the building that creates the most value, at the lowest budget, and survives an earthquake. Rooftop gardens and pools increase the value of the tower but add mass (bean bag) to the roof, increasing seismic loads and overturning. First-floor amenity spaces with a taller floor-to-floor height also create additional value but could create a soft story. Avoiding braces on the ocean-facing side of the tower makes for better views for the tenants but

also impacts building stiffness and could create a torsional irregularity. Facilitators can adjust the accompanying scorecard and activity instructions based upon age of the students and time available for the program. The most important part is that the kids are engaged and excited about engineering.

Start Building

All of the intellectual resources are publicly available in hopes that various ASCE local chapters, student organizations, or outreach minded engineering firms will be interested in building their own tables and engaging with their community schools to inspire the next generation of structural engineers. The Makers+Shakers program goal is to expand students' understanding of engineering's inherent complexities and uncertainties, while fostering appreciation for creative problem-solving in structural design.

Scan the QR code for build instructions for a prototype table. You’ll find parts lists, approximate prices, wiring diagrams and python code to make your own table. In addition, you’ll find the classroom program and score sheets as well as sample demonstrations. Everything is open source. Let us know how it’s going, either through our webpage and/or with the hashtag #MakersandShakers and share what modifications or improvements you’ve made to the table or the program. We’ll add it to the Makers+Shakers website for others to try. ■

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

(tara.flaherty@schaefer-inc.com)

Tara Flaherty is an EIT in Schaefer’s Cincinnati office where in addition to serving as a project engineer, she leads Schaefer’s Makers+Shakers outreach program.

Fig. 3. During the stiffness demonstration, students observe the seismic performance of a braced frame vs. a moment frame.

Fig. 4. In the mass demonstration, students compare two identical moment frames to observe how additional mass magnifies structural movement during seismic events.