On the Cover: The 2024 Structure of the Year Winner is the Perelman Performing Arts Center, which was announced at the NCSEA Summit in November. Image by Iwan Baan and courtesy of the Perelman Performing Arts Center.
CIRCULATION
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EDITORIAL BOARD
Chair John A. Dal Pino, SE Claremont Engineers Inc., Oakland, CA chair@STRUCTUREmag.org
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
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
Jeannette M. Torrents, PE, SE, LEED AP JVA, Inc., Boulder, CO
The National Council of Structural Engineers Associations is pleased to share winners of the 2024 Excellence in Structural Engineering Awards
FEATURES
Q & A
38
OPPORTUNITY AWAITS: SOFTWARE TRENDS TO WATCH FOR IN THE NEAR FUTURE
By STRUCTURE Magazine
Leaders from structural engineering software firms share their thoughts and analysis regarding the trends in software.
ACCESS AND PROTECTION AT 1,250 FEET
By Robert Belardi, PE
A collaborative means and methods design brought efficiency and safety to the reclad of the Empire State Building Floor 102 Observation deck.
ARCHITECTURAL PRECAST CONCRETE FACADE
By Alexander Stephani, PE, Kevin Poulin, and Filippo Masetti
The coordination between design and construction professionals stands as a cornerstone of successful facade design and construction at the Studio Museum in Harlem.
COLUMNS and DEPARTMENTS
By James Mack, Erika Winters-Downey, Mike Hernandez, and Kyle Kammer
Thank You for Impacting the Next Generation of Structural Engineers!
By Linda Kaplan, PE, F.SEI, M,ASCE
The only way to start off an update about the SEI Futures Fund is to say THANK YOU! Thank you to SEI Futures Fund Donors, and especially Ashraf Habibullah and Computers & Structures, Inc. for the 3-to-1 donation match in 2023! The campaign raised more than $330,000 and increased the number of donors investing in the next generation of structural engineering!
Where Does the Money Go?
This year the SEI Futures Fund approved the largest grant amount in our 11 year history. With more than $400,000 in committed funds for the coming year, we will be supporting:
• A record number of student and young professional scholarships to both the SEI Structures Congress in Phoenix and the Electrical and Transmission and Substation Structures Conference in Dallas.
• A Performance-Based Design Roadmap Development Workshop to bring together SEI leaders and subject matter experts, as well as allied partners working to advance performance-based design into the profession; as well as underwrite the publishing of the ASCE/SEI Pre-standard for Calculation Methodology for Structural Systems in Whole-Building Life Cycle Assessment, so this guidance document can be provided to the profession for free.
• The subsequent SEI Towards Zero Carbon Bootcamp to train and educate the profession, and provide travel funding for SEI young professional members, on the current LCA practices and the many tools, documents, and resources available to help structural engineers achieve embodied carbon reductions.
• Continued Young Professional Travel Support for SEI Standards Committees to ensure that young professionals are able to participate meaningfully with development of SEI standards and codes.
• SEI Chapter Innovative Programs for Student and Professional Involvement to provide local and student chapters small grant money to help with outreach, networking, and other events to encourage the growth of students and young professionals in
structural engineering.
• Efforts to finalize, publish, and distribute an ASCE/SEI 7 Student Primer specifically for students, or early career professionals, to serve as an introduction to the loading provisions of the ASCE/SEI 7-22 standard.
Does It Really Work?
Yes! The SEI Futures Fund’s goals center around getting the next generation of structural engineers engaged with and involved in our profession, as well as providing resources to help practicing engineers design with the future in mind.
The SEI Futures Fund vision is to support the art, science, and practice of structural engineering for a better and brighter future of our profession. Our specific goals as follows, include supporting programs that:
• Invest in the future of the structural engineering profession.
• Promote student interest in structural engineering.
• Support younger member involvement in SEI.
• Provide opportunities for professional development!
Past funding also supported well known efforts including SEI SE 2050 Commitment Program, performance based design development and life-cycle assessment methods which are all becoming more mainstream. Student design workshops and outreach efforts have reached the next batch of structural engineers. Additionally, past SEIFF scholarship winners are now serving on the SEI Board of Governors, ASCE/SEI 7 Standard Committees, and one is even the chair of the SEI Futures Fund Board this year (hint: its ME, who was among the first group of SEIFF scholarship winners in 2012!).
What’s Next?
The future champions of our profession may not even know it yet. The SEI Futures Fund would love to fund more projects targeted through local SEI chapters at K-12 outreach and engaging the next generation of structural
engineers. How can we support those at all levels of the structural engineering career path to build the best future possible? From educating elementary students on what a structural engineer does, to showing undergraduate students why this is a worthy profession, to supporting graduate students and young professionals looking to make changes and improve processes, all the way to helping seasoned professionals give back and pass on their knowledge—the SEI Futures Fund is here to support not only the profession, but the people who make it great. We invest not only in what people are doing now, but what they can and will do in the future.
We also hope to continue growing. The generosity of Habibullah and Computers & Structures, Inc., allowed us to support more projects in the coming year than we have before. But that doesn’t mean we couldn’t do even more. Every year we turn away deserving proposals and excellent scholarship applicants. We are actively looking for new match opportunities and welcome new donors. With your support we will continue to advance and strengthen our profession.
As a reminder the SEI Futures Fund operates in collaboration with the ASCE Foundation so that 100% of your gifts goes directly to profession-building activities authorized by the SEI Futures Fund Board. Donors may be individuals, companies, or other organizations.
This year’s SEI Futures Fund Board members are me,Linda Kaplan, PE, F.SEI, M.ASCE; Jim Harris, Ph.D., PE, NAE, F.SEI, Dist.M.ASCE; Dan Linzell, Ph.D., PE, F.SEI, F.ASCE; Otto Lynch, PE, F.SEI, F.ASCE; and Erleen Hatfield, PE, F.ASCE. Please reach out to any of us if you have questions. We also want to thank Joe Burns for his excellent leadership of the SEI Futures Fund over the past year. Learn more and give at www.asce.org/ SEIFuturesFund. Thank you! ■
Linda Kaplan, P.E., F.SEI is a Senior Structural Engineer with Pennoni in Pittsburgh, PA and the Chair of the SEI Futures Fund for FY 2024-25.
structural INFLUENCERS
Aimee Corn
Aimee Corn, PE, the youngest member to serve on SEI’s national board of governors, is a dam engineer in Gannett Fleming’s Denver office. Highly involved in ASCE, she has won the Edmund Friedman Young Engineer award, co-chaired the Mentoring Committee, enabled student conference scholarships with the Student Initiatives Committee, and has served as the secretary, vice president, and president of Colorado’s chapter of ASCE SEI. Outside of ASCE/SEI, Corn chairs Gannett Fleming’s Employee Resource Group (ERG), Connected Women, serves as the chair of the United States Society on Dams’ (USSD) Young Professionals Committee, and recently chaired the Conference Planning Committee for the 2024 USSD Annual Conference in Seattle, Washington. If you’d like to be a dam engineer. Please reach out to Corn, and she’ll teach you a thing or two!
STRUCTURE: What led you into dam engineering?
Corn: Like many in the industry, I fell into it. I had a family friend who introduced me to Guy Lund, PE, F.SEI, a leader in the evaluation of concrete dams, as I was starting my master’s degree. Guy began mentoring me, and while completing an internship under his guidance, I switched to a thesis-based master’s degree focusing on modeling potential failure modes of post-tensioned anchors in concrete gravity dams. Most civil engineering students are not provided an opportunity to learn about dams, even though they are a vital part of modern society’s infrastructure. Since joining the industry, I have made it a point to get out there and talk more about dams.
STRUCTURE: How does structural engineering for dams differ from structural engineering for buildings or bridges?
Corn: The most significant difference is that in dam engineering there are no codes, only guidelines produced by the federal government. This is a strength and a weakness in the industry. It’s a strength as the dam engineer needs to understand the parameters and justify every decision that they make when analyzing a dam, as there is no code to fall back on. From an innovation perspective, reliance on the federal government can slow things down. Some projects are still using guidelines that date to the 1990s and early 2000s. More recently, the Federal Energy Regulatory Commission (FERC) made updates to their Part 12D program following the 2017 Oroville Spillway Incident, particularly related to the frequency and depth of inspections.
STRUCTURE: How did you get involved in SEI?
Corn: I was a student scholarship recipient, which allowed me to participate in and present my senior design project at the 2013 Structures Congress. After my first Structures Congress, I began attending our local SEI meetings, eventually getting into local leadership roles. In 2017, when the Structures Congress was held in Denver, I participated on the Local Planning Committee.
STRUCTURE: You served on the SEI Board from 2018 to 2022. What was the experience like and what did the board accomplish?
Corn: Serving on the board gave me the opportunity to see how
much SEI was doing. Awesome things. And I worked with and learned from amazing people. SE2050 and the commitment to net zero erupted. The SEI structure was completely reorganized from a five-division organization into a Technical Community and a Professional Community. We also rewrote the by-laws of the Board to create a permanent young professional seat and began CROSS-US to increase the safety of structures.
STRUCTURE: You have been involved in several professional society committees that focus on people. What led you to these committees and can you speak about the role they serve?
Corn: The lack of committees within ASCE and SEI related to dam engineering has caused me to lean more towards the committees centered on people. That said, I have been a huge supporter and cheerleader for fellow engineers. I enjoy mentoring and connecting people. Involvement in professional societies has helped me build my network early on in my career. SEI introduced me to many leaders in the industry. I was able to reach out to one of them, Ron Klemencic, to fill the role of plenary speaker at the USSD Annual Conference. As one of the few dam engineers actively involved in SEI, I get to show students and young engineers that there are structural career paths beyond bridges and vertical construction and advocate for dams.
STRUCTURE: What have been highlights of your work so far as a dam engineer?
Corn: I’ve really enjoyed working on a project in Montana—Basin Creek Dam—as this is the first project I have worked on from start to finish, beginning with the initial site inspection documenting severe freeze-thaw damage, to the analysis and design of alternatives, and finally through the construction of repairs. The dam was originally a granite masonry gravity dam constructed in the 1890s which was raised using mass concrete in the 1910s. A photograph of me sounding the face of the dam even ended up on the front page of the Montana Standard newspaper.
STRUCTURE: You have been involved in planning for Structures Congress and the USSD Annual Conference. How have you approached your role?
Corn: I want people to leave a conference feeling excited and energized about the work they do and I try to channel that into the program. I was impressed when I attended my first USSD conference by how much fun everyone had. As engineers we don’t need to be serious all of the time. We do need to be serious about life safety, but presentations don’t need to go so far into the weeds that they lose the attention of the audience. David Odeh has said that Structures Congress feels like homecoming. It’s an opportunity to connect and grow our skills socially and technically. For USSD, I wanted people to leave the conference advocating for dams. There are some people who want all dams taken out, so it’s important for us as engineers to speak to the important role that dams serve to
keep society moving by providing drinking water, flood protection, power, and recreation.
STRUCTURE: What advice do you offer to young engineers?
Corn: Young people don’t need to know what they want to be when they grow up. As an undergraduate I honestly did not enjoy my reinforced concrete and H&H classes, and now I work on concrete dams. In your career, you are allowed to change your mind. Also, embrace your failures. I thought that the PE would be a breeze, even though in the dam industry I had not used the codes and standards the test is based on since grad school. I had to retake the PE twice. Failure doesn’t define you, and we should all talk more about our own failures, it’s how we learn and grow. (Speaking of failures, damfailures.org is one site that provides case studies and lessons learned from dam incidents. Check it out.)
STRUCTURE: Have you felt supported in your work for professional organizations?
Corn: Involvement in professional society work comes from the top down at Gannet Fleming, so I have always been encouraged and supported in my participation. Professional organizations help us to keep a pulse on the industry, have our work recognized, and network with a variety of stakeholders. That said, it’s important to strike a balance between your professional society involvement and your day-to-day work! ■
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structural DESIGN
Structural Thermal Bridging in Facades
This Part 2 of a three-part series explores thermal bridging of building facade systems, how it relates to structural engineers, and mitigation strategies. Part 1 ran in the November issue of STRUCTURE.
By Jim D’Aloisio, PE, and Ivan Lee, P.Eng.
Thermal bridging in buildings has been gaining more and more attention in recent years not only as a potential cause of condensation and moisture related deterioration but also for its role in degrading the thermal performance of the building enclosure. As we strive to reach low and ultimately net-zero carbon goals, mitigating thermal bridging to enhance building energy performance is critical. While many believe thermal bridging and thermal performance of the building envelope is within the domain of architects and building enclosure consultants, structural engineers also have an important role in mitigating thermal bridging since many of these details have a structural component.
Building Facade Systems
The building facade often refers to the components and systems that enclose the vertical surfaces of a building including exterior walls and windows. Its primary functions are to control heat, air, and moisture flow, as well as provide structural support against lateral wind loads and occasionally gravity loads for load bearing walls. Facades also contribute to the aesthetics of the building since it is a recognizable exterior component.
The opaque sections of the building facade can be composed of many different types of systems that include glazed wall systems such as curtain wall and window wall systems and precast insulated concrete panels. Steel-framed exterior wall assemblies are commonly found in many low to mid-rise commercial buildings. Increasingly, these wall assemblies are fitted with more and more insulation. Although many designers and contractors have added insulation between the studs in the past, many building energy codes and standards are asking for a continuous layer of insulation that often is placed outboard of the steel studs to help mitigate thermal bridging. This presents challenges of how to securely attach exterior cladding to these walls such that wind loads can be transferred back to the structure. The solution many designers have posed is to add exterior cladding support systems to these assemblies along with the exterior continuous insulation. Common solutions that we have seen include: vertical Z-girts, horizontal Z-girts, mixed Z-girts, and intermittent brackets or clips.
Of these four types of cladding support systems, intermittent brackets/clips system offers the best thermal performance since
it minimizes components penetrating the exterior insulation. Many bracket and clip designs include thermal break pads or thermal breaks within the bracket, while others use low thermal conductivity materials such as stainless steel or fiberglass. At first glance, choosing a cladding support system made with low thermal conductivity materials may seem appropriate for optimizing the thermal performance of the building facade. However, other factors should be considered when selecting the right system including structural capacity, fire resistance, and cost. A fiberglass clip may provide low thermal conductive performance compared to an aluminum clip but have less structural capacity. As a result, more fiberglass clips may be required to carry cladding dead load and wind loads than an aluminum clip system. This increases the amount of penetrations through the insulation as well as attachments to the exterior wall, which could drive up material and construction costs since more components are needed. An aluminum clip system may be able to achieve the same thermal performance but with greater clip spacing.
Rail penetration depth into the insulation and orientation impact the thermal performance of many clip systems. Because the clips are intermittent, rails are added to help support the cladding and cladding attachment components. Rails penetrate through the insulation in many North American clip systems. As a result, the rails act as fins that draw heat from the insulation. This effect is greater for clips that are much smaller than the insulation depth since the rails are fitted deeper in the insulation. The orientation of the rails also has an impact on thermal performance. Systems that include rails running horizontally often have shorter overall rail length than vertical rail systems and therefore better thermal performance. Many cladding support systems have vertical clip spacing greater than the horizontal spacing, resulting in fewer horizontal rails because the spacing between the rails is dictated by the clip spacing.
Intermittent Brackets/ Clips
Recent building energy codes have not only begun to recognize thermal bridging of cladding support systems, but some have also provided prescriptive derating values. Energy codes such as the Massachusetts Stretch Code have provided derating values that can range from 27% to over 63% for most typical exterior insulation ranges. With good design that balances both structural and thermal performance, many clip systems are able to achieve higher thermal efficiencies and lower derating values than these prescribed values. A holistic approach, with close collaboration between architect, structural engineer, and building enclosure consultant, is often required to find the optimal design. Many cladding support system manufacturers provide engineering reports of 3D thermal simulations, span charts, and load tables for their systems to help aid in the design. Some will provide engineering services to ensure their system is fully optimized for the building.
Shelf Angles at Intermediate Floors
Brick veneer and masonry panels are common cladding types used in buildings. Many types of masonry cladding systems are connected to exterior wall assemblies using intermittent anchors
which are much smaller than typical cladding support clip systems. Although these anchors may have good thermal performance, they are only part of the masonry support system. Shelf angles are often needed at regular intervals to support the weight of the masonry cladding. These angles are commonly structural steel and attached to the primary structure of the building at intermediate floors. Because of the loads these shelf angles must carry they can be hefty and significant thermal bridges in brick and masonry facades.
Most shelf angles are directly attached to the intermediate floor which interrupts the exterior wall continuous insulation and forms a large linear thermal bridge. The solution to mitigating thermal bridging at this detail is to use shelf angles that are offset from the intermediate floor with discrete supports. This reduces the amount of steel penetrating through the insulation as well as direct contact with the primary structure of the building. An offset shelf angle can be 59% to 80% more thermally efficient than a direct anchor shelf angle for exterior insulation ranges between R-5 and R-25.
In cases where offset shelf angles are not feasible, adding low conductivity thermal shims between the shelf angle and intermediate floor may help reduce heat flow by thermally separating the metal angle from the primary structure.
Window to Wall Junction Details
Window to wall junction facade details are often overlooked in terms of thermal bridging. Windows are often installed directly on the interior steel-frame, woodframe, or concrete back up wall for structural support of the window. Although this is effective structurally, a significant thermal bridge may be created when the exterior wall insulation and the thermal resistive parts of the window are not aligned. For mid-rise and highrise buildings with punched windows, the window to wall interface length may be several thousand feet long,
Direct Anchor Shelf Angle
Offset Shelf Angle
Compared to a window directly supported over a steel-frame wall, an angle-supported windowsill (above) reduces heat flow 64% and the intermittent clip supported windowsill (below) reduces heat flow by 95%.
meaning any small reduction in thermal bridging can significantly improve the facade thermal performance.
To reduce thermal bridging at window to wall junction details, the window should be aligned with the mid-point of the wall’s insulation. For framed wall assemblies with insulation in the stud cavity and exterior continuous insulation, the optimal location is over the exterior insulation.
This installation position poses a problem of how to adequately support the window. One solution is to install an angle beneath the windowsill to support the cantilevered window. Another approach is to use intermittent cladding support clips to carry the window, such as the Akira Window Connection detail. Compared to the conventional window installation detail where the window is directly supported over the steel-frame wall, the angle supported windowsill reduces the heat flow by 64% and the intermittent clip supported window sill reduces heat flow by 95%.
Although both of these window support configurations may seem unconventional, both can carry significant loads when designed properly by a structural engineer. Depending on the structural capacity of the clips and its spacing, the intermittent clip supported window can support triple-glazed windows as tall as 6 feet.
As shown in the examples mentioned in this article, structural engineers have many opportunities to help improve the thermal performance of facade systems through mitigating thermal bridging. The next article of this three-part series will cover thermal bridging at roof and foundation details. ■
Jim D’Aloisio, P.E., LEED AP is a Principal with Klepper, Hahn & Hyatt of East Syracuse, NY, focusing on structural engineering and building envelope consulting services.
Ivan Lee, P.Eng., M.A.Sc., LEED APBD+C, WbLCA AP, is a Building Science Engineer and Team Lead in the Building Performance Analysis department with a focus on thermal analysis, hygrothermal analysis, and Life Cycle Assessment. Lee has worked at Morrison Hershfield now Stantec for over 14 years and has been involved with various projects including 3D thermal modelling to assess thermal bridging details for the Building Envelope Thermal Bridging Guide (BETB Guide).
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Successful implementation of aggressive low-carbon goals happens with clear, early communication between all parties.
By James Mack, Erika Winters-Downey, Mike Hernandez, and Kyle Kammer
With increased awareness of the influence of materials on global carbon emissions and initiatives like the SE2050 Commitment, structural engineers are adapting traditional workflows to incorporate embodied carbon reduction goals. In today’s environment of material innovation, practicalities can be lost in translation. This article promotes a nuanced approach to working with low-carbon concrete from the perspective of the supplier and contractor—advocating for increased collaboration, adaptability, and a willingness to embrace innovative solutions in a rapidly evolving industry.
The authors’ collective experience spans the breadth of the industry— from traditional structural design, construction project management, material engineering, field crew operations and logistics, and concrete placement techniques. Many aspects should be considered when implementing novel materials on a project, so authors' recommendations are distilled here into three categories: materials, placement, and design documents to highlight how to start. However, one major theme that will be consistent throughout is the need for open discussion between the Owner, Engineer of Record (EOR), Contractor and Ready-mix Supplier about the project’s sustainability goals.
Materials
In any concrete mix, it’s the cement that dominates the Global Warming Potential (GWP) due to the manufacturing process. While aggregates and cement make up about 70% and 10% of the volume respectively, in a traditional mix, the cement accounts for somewhere between 75 to 90% of the concrete’s GWP (Fig. 1, Reference Cemex)
As such, to reduce a concrete’s CO2 from a materials perspective, one needs to reduce the impact of the cement. Two of the primary levers to reduce cement’s CO2 are:
1. Use Supplementary Cementitious Materials (SCMs).
2. Switch to Portland-Limestone Cement (Type IL cement) or other Blended Cements.
Use Supplementary Cementitious Materials
SCMs include industrial waste materials such as Fly Ash (FA), Blast Furnace Slag (GGBFS or slag), silica fume and other pozzolans that have long been used in concrete to reduce the amount of cement. While these materials have historically been used to reduce costs, they also improve the concrete by:
• Increasing long term strength.
• Increasing material durability against distresses such as Alkalisilica reaction (ASR).
• Reducing heat of hydration.
• Improving workability, though water demand can be an issue with some SCMs.
• Lowering CO2 emissions by replacing cement in the mix. Fly ash, slag, and silica fume are already in use, but are not used to maximum effectiveness in most cases. For example, many specifications limit FA to 15 to 20% but many applications can go higher. Several alternative SCMs are also in development, and in most cases, they perform well. The issue is typically “scalability” and having a consistent, long-term supply of material available to make the effort of dedicating bin space, adding hoppers and developing the new mix designs with the alternative SCM worthwhile.
Glass Pozzolans
An emerging alternative SCM gaining attention for Ready Mix Concrete operations is ground glass pozzolans. However, its local market availability might not lead to widespread use due to the limited volume of material. For example, we know of some plants that have been offered a supply of 40 tons of ground glass per month. Unfortunately, that amount of glass SCM would only produce around 65 truckloads of concrete—less than 1/4 the quantity required every month to have a dedicated silo.
Fig. 1. Comparison of cement and aggregates portion of a concrete mix's volume and embodied CO2
One downside is that SCMs may impact early age strength gain because they typically react with the byproducts of cement hydration and therefore are slower to gain strength. However, the end concrete is a denser, stronger, and more durable material that has lower embodied carbon. SCMs may also affect other plastic properties, but these can be typically addressed by the engineer, contractor, and supplier working together to evaluate the impacts to the overall project.
Switch to Blended Cements
Blended cements are cements where part of the clinker is substituted with other materials such as limestone, slag, FA, silica fume, calcined clays, and other manmade or natural pozzolans at the cement plant (vs the Ready-mix plant as above). Blended cements must conform to the requirements of ASTM C595 (or AASHTO M 240) and are used in all aspects of concrete construction in the same manner as portland cements. Generally, there are four main categories:
• Type IL, portland-limestone cement.
• Type IP, portland-pozzolan cement.
• Type IS, portland blast-furnace slag cement.
• Type IT, Ternary blended cement. The advantage of all blended cements is that they reduce the amount of clinker in the final product and that lowers CO 2. Because of this, we are in a blended cement revolution. Currently, about 53% of all cements sold in the U.S. are blended cement, with 1L cements making up approximately 97% of those cement sales. Still, the use of the other ASTM C595 blended cements (e.g. Ty 1P, 1S, and IT) is also expanding and they make up 15% or more of blended cements usage in states such as New Jersey, Nebraska, Delaware, and parts of New York, (Source: USGS April 2024 Cement Statistics and Information https://www.usgs.gov/centers/ national-minerals-information-center/ cement-statistics-and-information).
Compared to portland cements and for the same cementitious quantities, blended cements tend to have lower early strength and lower heat of hydration, but they also tend to have comparable 28-day strength and higher ultimate strengths. However, it is important to understand that in addition to meeting the engineering requirements for an application, cement content is also based on other project specific issues such as environmental conditions and contractor placement requirements. As such, while early strength may be reduced, the mix could still meet the early opening requirements. Early discussions between the engineer, contractor, and producer, and working together can address most project specific requirements and applications.
Performance and Transitioning to Use
Long term usage in Europe, Canada, and elsewhere, as well as our own experience has shown that using 1L cement does make good concrete (e.g. it is concrete). However, the material can behave differently and while this is usually not a problem, isolated issues related to specific placements or conditions have occurred.
This re-emphasizes the important
Fig. 2. A portable batch plant
point that in transitioning to all types of blended cements, it is NOT always a 1:1 replacement for straight cement mix. While the total amount of cementitious material will most likely be similar to the mix of ordinary portland cement with different amounts of SCMs, performance will vary, and adjustments may need to be made.
To minimize issues, as cement manufacturers move to all types of blended cements into the marketplace, it is critical that they have open dialog, coordination, and communication with the ready-mix suppliers, contractors, engineers, and other customers about their plans. Some specific items that need to be shared include:
1. When will the cement supplier switch to 1L and other Blended Cements and when is the cutoff date?
2. Results of test data to educate contractors, ready mix suppliers, and specifiers on the concrete material’s behavior.
3. Incorporate mockups and other placement testing into budgets, especially with flat work.
While it may be argued that using SCM replacement at the cement plant or the ready-mix plant results in the same overall CO2 reduction; the primary advantage to having the blending occur at the cement plant is the ability optimize the blending so that the final cement has higher consistency, optimum fineness, and improved chemical control so that it behaves better. Using a blended cement product also helps smaller producers who have only limited silos and space to produce low carbon concrete.
However, no matter what cement type is used, specifications should always allow for ready mix suppliers to add additional SCMs at the plants. Because the local producers will know their local materials best and can dial in the mix for most given project specific needs, this will help ensure a low carbon concrete can be obtained. Still, care and appropriate and adequate testing are needed to ensure performance.
Execution
From a contractor’s perspective the goal is to provide the owner with the best combination of schedule, quality, safety, and cost that will make the project a success and enhance a relationship based on mutual trust. Going forward, embodied carbon will also be weighted in the balance of project characteristics. Each project type and location will present a unique combination of challenges that can be modified related to sustainability and would be nearly impossible for an engineering firm to know unless and until there is open communication with the owner, design team, contractors, and local ready mixed producers.
Fig. 3. A large slab-on-grade placement in progress.
The construction team can provide feedback on which elements of the project may have less critical strength needs. The earlier in the construction process the team members are identified and this discussion takes place, the more effective the team will be in addressing the project sustainability goals with minimal or no construction schedule impact. If the closest ready mixed producers do not have enough SCM silos or aggregate capacity to provide low embodied carbon concrete which meets the owners goals, the team will need to be more creative and explore alternate blended cements or different suppliers. Admixture advances have provided the option of longer hauls in remote locations or congested metropolitan areas to use hydration stabilizers to extend set times beyond the traditional 90 minutes while maintaining workability and overall quality. While not an ideal sustainability solution because of the additional hauling, it does open the range of potential producers if material availability, experience, or the timeline to produce Environmental Product Declarations (EPDs) may stop all sustainability efforts.
Finishability and pumpability will need to be tested on novel slab mixes, particularly non-air entrained, troweled mixes with high flatness standards. Many contractors have reported differences or issues with placement of low carbon concrete. Additional lab testing and field mockups large enough for project appropriate equipment testing will reduce the risks. Starting with mixes the team has successful history with and making incremental adjustments is one strategy.
The testing laboratory technicians also will need support for the team to succeed. Many of the blended cements or mixes with higher SCM contents are more sensitive to extreme temperatures, so to maintain the cylinders within the ASTM C31 curing range, adequate preparation and jobsite logistics are needed. High or low initial curing temperatures will yield low breaks, according to multiple studies.
Structural Contract Documents
When presented with a specific project opportunity, it is incumbent upon the structural engineer to understand how the client’s overall
sustainability goals can be successfully applied to the project, and specifically how the structural AND non-structural items, such as sidewalks and duct-banks, inform the full picture of the project’s embodied carbon footprint.
Ensure you are given access to the client’s Basis of Design (BOD) and Division 001 specifications. These hold the key to understanding big picture goals.
Balance areas where you can be aggressive with areas where you can’t. For example, mixes made to achieve high-early strength have proportionally higher cement content. By knowing this, we can balance these mixes with areas like foundations, which traditionally can accommodate a longer curing duration.
Bring non-structural concrete providers into the discussion, such as those providing concrete for hardscape, equipment pads, or duct-bank concrete in the case of data centers.
Come prepared to meetings with an approximate “Carbon Budget” to outline your path to success. Table 1 is an example demonstrating a quick calculation done via spreadsheet to map out early carbon expectations and reductions. Tools like this provide clear communication to clients, designers, and trade partners.
Boilerplate specifications which don’t directly apply to (or even worse contradict) project goals are a frequent source of confusion for concrete contractors.
The authors recommend the following best practices for adapting contract documents for novel mix use:
• Ensure your specification lists the cement product in use in your area. As noted earlier, more than 50% of the U.S. has transitioned to Type 1L cement. Specifying ASTM C150 Type I/II cement where it is not in use will trigger an unnecessary RFI.
• Type 1L cement is an ASTM C595 blended cement—ensure your specification reflects and allows this.
• Understand that ready-mix suppliers need leeway to adjust water/ cement ratios for novel mixes. Some alternative SCMs require more water than traditional cements and additional testing may be needed to verify compliance with project requirements. This should be discussed as early as possible to determine the feasibility
of project sustainability goals.
• Remove notes requiring minimum cement content.
• Remove notes limiting SCM content to 20% or less.
• Add notes regarding minimum cement replacement.
• Consider adding a dedicated page to your drawing sets with specific embodied carbon reduction guidance (similar to a page that was added for special inspection requirements).
• Be specific about ready-mix baseline benchmarks when asked to achieve a verifiable carbon reduction. Become familiar with NRMCA and Carbon Leadership Forum (CLF) ready-mix baselines, their various iterations, and how they continue to evolve.
• Consider whether your specification will note required reductions as a percentage vs. baseline or with a specific Global Warming Parameter (GWP) number. Concrete contractors appreciate the
Sustainable Concrete Communication Recommendations
• Don’t approach your project with a boilerplate spec. Examine your general notes.
• Get to know and keep open communication with local contractors and suppliers.
• Let the materials engineering happen and consider the full picture! Strength is great, but other properties like pumpability, workability, and finishability need to be considered. Blended cements and some SCMs have high water demand. Even with a higher water-cementitious ratio they can still have adequate permeability. Do you need 28 day strength? Can the schedule allow for 56 day strengths? This can really open up options.
• If you want to use a novel mix without much test data, allocate time and potential budget for testing, both in the lab and in the field.
• Be open to new materials and products.
• Submittal reviews matter—the person on the EOR side of things needs to have enough experience and knowledge to know and understand what they are looking at.
• Ensure that proper initial curing is being done in the field. ASTM C31 is frequently violated. Low carbon concrete is being reported as more sensitive to high temperature early curing.
• Carbon budget the overall structure. This will make it easier to maintain the schedule goals.
specificity of knowing a GWP parameter to stay under, but this could lead to annual specification updates. Showing embodied carbon reduction as a percentage leads to more legwork on the contractor’s end but may result in a specification that needs less updating.
• Approve backup mixes in case regional supply constraints arise.
• Assure qualified reviewers examine novel mix design submittals. Even the savviest younger engineers may not know what to look for when regarding mix test data or SCM content.
Conclusion
Start proactively communicating now to your clients that you, as the EOR, need to be involved early to guide this process. A successful implementation of aggressive goals can only happen with clear communication early and often between all parties. This is your chance to show why your firm is invaluable in early project planning. Reach out to your area ready mix suppliers and concrete contractors for a plant tour or stay after a project meeting to understand their workflow and current supply chain. Attend an area ACI Chapter event, Concrete Contractor Society meeting, Structural Engineers’ Association, Carbon Leadership Forum Meeting, or U.S. Green Building Council local chapter event—these are great places to broaden your network and understanding of local capabilities. Be willing to share your successes and failures—everyone will benefit, and you will be a sought-after resource on future projects. ■
Erika Winters-Downey, SE, LEED AP BD+C, is a structural engineer and Director of Material Innovation & Impact for the Clayco/Lamar Johnson Collaborative enterprise.
Mike Hernandez, PE, FACI, LEED AP BD+C, is Technical Director for the American Society of Concrete Contractors. He has over 25 years of construction operations experience constructing concrete buildings and bridges.
Kyle Kammer, PE, is the Director of Quality for Concrete Strategies. He has over 15 years of experience in concrete construction and leads Concrete Strategies’ sustainability efforts in conjunction with the Clayco Enterprise team.
Jim Mack joined CEMEX in September 2007 and is currently Director, Market Development – Infrastructure and Sustainability. In this position, he works with agencies, contractors, and other professionals to identify and develop sustainable concrete and cement-based solutions for pavement and building applications.
Fig. 4. The temporary dry batch plant shown here has the capacity for one cement, one SCM, three aggregate sizes, and sand.
sustainable DESIGN
Data Insights From Over 500 Building Projects for Low-Carbon Structures
Since 2020, the SE 2050 Commitment Program has collected emissions data of over 500 building projects with corresponding structural design characteristics. Key takeaways from the inaugural analysis of the database are shared here.
By Jonathan Broyles, Mel Chafart, Martín Torres, Demi Fang
In 2022, building operations and material production were responsible for 37% of global anthropogenic greenhouse gas emissions. Of these emissions, about three-quarters were from the direct and indirect emissions from energy use in buildings (i.e., operational carbon), and a quarter was from building materials and construction (i.e., embodied carbon). Efforts to reduce embodied carbon in both research and practice have lagged behind efforts for reducing operational emissions. As such, there is an urgent and critical need to understand and reduce embodied carbon in the built environment to mitigate impacts of the climate crisis.
To help address this issue, the Structural Engineers (SE) 2050 Commitment Program, supported by the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE) was formed to catalyze the building design industry’s alignment with the SE 2050 Challenge, in which firms pledge to “understand, reduce, and ultimately eliminate embodied carbon emissions in structural systems by 2050.” Signatory firms, the structural engineering firms who have committed to the pledge, are required to submit project data to an anonymized database hosted by the SE 2050 Committee. While individual signatory firms might be limited to collecting data on their own projects, the SE 2050 Database (currently in beta version) allows simple and secure collection of many relevant project characteristics for hundreds of diverse projects across different firms, locations, and building types.
The SE 2050 Database contains a diverse set of project data with a range of building characteristics, structural engineering design features, and structural system embodied carbon emissions, measured as Global Warming Potential (GWP) (kilogram of carbon dioxide equivalent, kg
CO2e). As of November 1, 2023, the SE 2050 Database had 522 project submissions. The SE 2050 Data Science Team (DST) was formed as an internal working group within the SE 2050 Committee to perform a preliminary analysis of the data. As more data is collected, the collection and analysis will be refined to continue to inform the SE 2050 Commitment Program. This analysis identifies relationships between the embodied carbon of structural systems and building characteristics. These insights are meant to inform structural engineers, building practitioners, and policymakers to facilitate widespread embodied carbon reduction in the structural systems of buildings.
Methodology: Data Filtering and Analysis
A brief overview of the methodology for data filtering and analysis is summarized here. For more details, the reader is referred to the SE 2050 Commitment Program 2023 Data Analysis and Findings Report. Before analyzing the data, the SE 2050 Database was processed to filter out project entries deemed out-of-scope. The filtered project data was categorized into two datasets according to the life-cycle stages reported: stage A with 241 entries; and stages A to C with 100 data entries, referred to as Upfront Carbon and A to C, respectively. After reviewing the filtered data, the Upfront Carbon subset was chosen as the primary dataset to be analyzed because it contained the largest number of projects and represented the life cycle stages where structural engineers have the largest influence on structural embodied carbon emissions.
Definitions
Embodied Carbon: The carbon emissions associated with the production life-cycle of building materials, including material extraction, transportation, production, manufacturing, use, maintenance, replacement, and end-of-life.
Global Warming Potential (GWP, in kg CO2e): A measure of how much energy the emissions of 1 kg of a greenhouse gas will absorb over a given period of time, relative to the emissions of 1 kg of carbon dioxide (CO2). This metric enables a common unit of measure of the global warming impacts of different greenhouse gasses. The larger the GWP, the more that a given gas warms the earth compared to CO2 over a time period (typically 100 years).
Global Warming Potential Intensity (GWP Intensity, in kg CO2e/meter2): A measure of GWP normalized by the Gross Floor Area of a building. Note that biogenic carbon is excluded in this metric due to data limitations.
Gross Floor Area: A measure of the total horizontal area, measured
in plan, taken to the outer edge of the exterior envelope. The gross floor area is consistent with the architectural information of the building project.
Life Cycle Assessment (LCA): A method of environmental accounting in accordance with International Organization for Standardization (ISO) 14040 and ISO 14044 that tracks the inputs from nature (e.g., materials and resources) and outputs to nature (e.g., waste, carbon dioxide, and methane) considering all of the processes that take place during the manufacture, use, and disposal of a product or system. An LCA can assess several outputs, referred to as mid-point indicators, including GWP.
Life Cycle Stage: A temporal subdivision of a product or system’s life cycle. In the context of a building product, these modules are the Product stage (modules A1-A3), Construction stage (modules A4-A5), Use stage (modules B1-B7), and End-of-life stage (modules C1 to C4). This article focuses on the GWP results in the Product and Construction (modules A1-A5) life cycle stages.
GWP Intensity Excluding Biogenic Carbon was selected as the performance objective (i.e., the primary metric studied), herein referred to as GWP Intensity. An exploratory data analysis was first conducted on the Upfront Carbon dataset, which involved creating a series of plots that demonstrate the relationships (or lack thereof) between GWP Intensity and project features. This included building and structural features such as gross floor area, stories above grade, typical floor live load, and primary horizontal gravity system (refer to the full report for the full list of building and structural features). The exploratory data analysis was followed by more detailed statistical analyses to clarify the importance of relationships in the data. These analyses included linear regressions and machine learning regressions with feature importance to confirm the trends between GWP Intensity and salient building features identified in the exploratory data analysis.
Key Results
overlaid with a strip plot showing all design data points in the Upfront Carbon dataset. The median GWP Intensity (gray number) is 234 kg CO2e/m2 and the mean (dark blue number marked with an X) GWP Intensity is 270 kg CO2e/m2
The data exhibits a wide spread of GWP Intensities. The 80th percentile value from this Upfront Carbon dataset is proposed as a recommended limit for upfront (A1-A5) structural embodied carbon: 350 kgCO2e/m2. A GWP Intensity (excluding biogenic carbon) larger than this proposed threshold might warrant further design intervention to reduce its high embodied carbon.
Although not all plots from the analysis are shown in this article, the strongest relationship identified is shown in Figure 2, between Total GWP and gross floor area. The linear regression demonstrated an R2 value of 0.84 (R2=1 indicates a perfect linear relationship; R is the Pearson correlation coefficient, which is a measure of the strength and direction of the linear relationship between two variables.) This result indicates that the size of building projects is a critical design consideration when aiming to reduce embodied carbon emissions.
Another important result from the data analysis is the importance of system selection (including the structural material of the system) on embodied carbon emissions of structures in buildings. As seen in Figure 3, concrete and steel systems tend to have higher GWP intensities, which are seen across all three structural system features (i.e., primary horizontal gravity system, primary vertical gravity system, and primary lateral system).
Lastly, machine learning regression models were trained on different subsets of the Upfront Carbon dataset to distill potentially multivariate relationships into a hierarchy of building features with the largest influence on structural embodied carbon. For more details on these findings, the reader is referred to the full report. In short, the linear regressions and feature importance from the machine learning models showed the following design features to have relatively stronger correlations with GWP Intensity when compared to other design features:
Gross Floor Area
Mean Roof Height
Typical Floor Live Load
Primary Horizontal Gravity System
Primary Vertical Gravity System
LCA Tool
Building Use Type
Implications to Designers
The strongest correlation was found between Total GWP and gross
Fig. 1. Distribution of GWP Intensity Excluding Biogenic Carbon for projects in the Upfront Carbon dataset.
Fig. 2. Scatter plot of GWP against gross floor area for Upfront Carbon projects.
floor area. The machine learning feature importance found gross floor area, typical floor live load, and mean roof height to be the strongest predictors of GWP Intensity. Additional influential features identified with this analysis include the building use type, primary horizontal gravity system, and primary vertical gravity system. These key findings suggest that structural engineers and building designers should consider these building features to more effectively reduce structural embodied carbon emissions.
The wide distribution of GWP Intensity in the current database can be explained by a variety of factors and therefore should not be used to establish benchmarks. With a higher quantity, quality, and granularity of data, a clearer understanding of building projects can emerge to establish meaningful benchmarks. While more data is needed to confidently establish program- or system-specific benchmarks, a recommended threshold for upfront carbon is proposed. Using the 80th percentile GWP Intensity limit for Upfront Carbon (A1-A5) dataset, the recommended threshold for structural embodied carbon emissions is 350 kgCO 2e/m 2. Structural engineers and building designers should use this value to determine if the structural design would have poor embodied carbon performance.
Concluding Remarks
As the SE 2050 Database grows, these results will be regularly updated to ensure that the industry is supplied with the most up-to-date, science-based recommendations to support embodied carbon emission reduction. Furthermore, future iterations of the analysis may be able to make more definitive conclusions, including program- and systemspecific benchmarks.
Current Limitations and Call to Action
The data analysis revealed limitations and opportunities to improve the SE 2050 Database. The underlying LCA tools to obtain embodied carbon performances for design projects have different embodied carbon coefficients and assumptions, inhibiting comparability. Furthermore, due to the database’s anonymity, the SE 2050 team is unable to clarify unusual or unexpected data entries with the signatory firms, so potentially incorrect data are left uncorrected. Thus, the Sustainability Committee under the Structural Engineering Institute has written a pre-standard document to help signatory firms correctly calculate and report the embodied carbon emissions of structural systems. Despite these limitations, this analysis and corresponding results reveal useful trends to inform better project data collection and produce more robust embodied carbon benchmarks.
More high-quality project data entries can improve the findings of this inaugural analysis. Practicing structural engineers are strongly encouraged to submit their project information to the SE 2050 Database to contribute to this effort to illuminate features important to structural embodied carbon. Furthermore, recommendations from this analysis related to improving data collection will be included in future updates to the SE 2050 Database, such as requiring the submission of structural material quantities with each project, requiring embodied carbon emissions to be separated by LCA stages, and providing further guidance on biogenic carbon emissions reporting.
This first analysis of the SE 2050 Database identifies important design considerations for structural engineers to better reduce embodied carbon emissions in buildings. First, designers should consider how much floor area is needed for a project, as gross floor area was found to have the highest correlation to GWP. Structural engineers should pay special attention to the type of structural system selected, as concrete and steel systems trended with higher embodied carbon emissions. These findings may already be intuitive for those designing with embodied carbon in mind but are now quantitatively validated with empirical data from the industry. The quality of such insights will only be improved with future improvements in the database. Importantly, this report highlights that there are different pathways and design choices that can reduce carbon emissions; therefore, it would be beneficial for all building stakeholders to collaborate early and throughout the building design process. The analyses used in this study can be improved upon with more complete and verifiable data to better understand which building characteristics, and combination of building characteristics, are most important to consider for embodied carbon emission reduction. Future iterations of this study can inform data-driven policy and guidelines through feature-importance hierarchies and feature-specific embodied carbon benchmarking. ■
Full references are included in the online version of the article at STRUCTUREmag.org .
Jonathan Broyles, Ph.D, is a Postdoctoral Research Associate and Lecturer at the University of Colorado Boulder, where he researches at the intersection of structural engineering, sustainability, computational design, and acoustics.
Manuel Chafart, PE, is a Research Engineer at the Life Cycle Lab at the University of Washington and a Research Affiliate at the Carbon Leadership Forum. His work focuses on providing more access to data on low carbon design of buildings in North America.
Martín Torres, PE, is a Ph.D student at the University of Colorado Boulder, where he is researching novel methods of uncertainty modeling for whole-building life cycle assessment.
Demi Fang, Ph.D, is incoming Assistant Professor at Northeastern University School of Architecture, with an affiliate appointment in Civil and Environmental Engineering. Her research includes data-driven approaches to mitigating the environmental impacts of structural systems in design.
Fig. 3. Distribution of GWP Intensities by primary horizontal gravity system in the Upfront Carbon dataset.
structural
Challenges of Glass Design
Structural glass design requires a unique approach in the absence of robust codified standards.
By Ted Kraemer, PE
Most materials used for building construction utilize well-established design standards which are adopted by the building code and have evolved over time. Steel, concrete, wood, and aluminum all have codified documents which offer thorough and robust guidance to structural designers. Unfortunately, no such standard exists for glass when it is used in a structural capacity. In the absence of adopted standards, structural glass engineers rely on a collection of industry best-practices and alternative design standards to fill in the gaps. The design of glass presents unique challenges which require special consideration. The best practices for structural glass design can be classified into 6 Rs, resistance, redundancy, residual capacity, retention, replacement, and regulation:
Resistance
Glass has unique properties in comparison to most modern construction materials. Perhaps the most challenging from a structural designer’s perspective is that it is brittle, not ductile. Material ductility is desirable because it provides a predictable onset of yielding which gradually transitions to an ultimate failure. Most traditional building materials either inherently exhibit ductility (e.g. steel) in their load resistance behavior or have incorporated construction techniques which impart ductile qualities to a composite (e.g. concrete rebar). As a brittle material, glass strength is controlled by the presence of
microscopic surface flaws which when loaded will propagate to full fracture without a yielding transition. The unpredictable nature of surface flaws necessitates that a statistical model is used to determine the load resistance of in-service glass. The industry standard for acceptable probabilities of breakage will vary depending on the application, with common probabilities of breakage being 1/1000 and 8/1000. Tempering is a common thermal treatment which effectively strengthens a glass surface against crack propagation. The tempering process increases load resistance by imparting a residual compressive surface stress to the glass. A conceptually similar method of strengthening is observed in post-tensioned concrete slabs, another brittle construction material.
Redundancy
Redundancy is an important concept for all structural design. A redundant structure ensures there are multiple ways for a structure to distribute and transfer any applied loads. This is crucial to ensure that if any individual component fails, the applied loads may be redistributed to other components without a progressive collapse. One of the primary methods by which redundancy is imparted to glass is via lamination of two or more lites of glass with a binding interlayer. Laminated glass is used in a multitude of applications in which glass failure could result in severe injury or fatalities. For example,
Who Is a Glass Consultant?
A glass consultant is a specialist typically contracted by an architect, building engineer, or contractor to provide design services specific to glass. Typically, they will have a structural engineering background and undertake additional professional training from seasoned designers familiar with the intricacies and nuances of glass. Glass consultants need to understand their structural glass system on both a macro and micro scale, as properly detailing connections is every bit as important as understanding the system’s structural load path and stability. To accomplish this, they rely on a strong fundamental understanding of material mechanics, with robust knowledge of the various strengths and weaknesses of glass as well as the many other different building materials with which they interface.
lamination is used for modern automobile windshields for the added safety and redundancy it provides to passengers. In buildings, glass redundancy via lamination can be observed in modern guard and handrail design and sloped overhead applications, such as canopies.
Residual Capacity
Glass breakage can occur during service even with proper design. Accidental or unintended loads from building occupants could stress glass in unanticipated ways. Spontaneous breakage may occur due to virtually indetectable imperfections, such as nickel-sulfide inclusions, created during the manufacturing process. A glass designer must consider glass’ remaining load capacity requirements following a fracture. It may be acceptable for window glass to have little to no residual capacity, but sloped glass or walkways which may be supporting occupants at the time of fracture must be able to accommodate the breakage and still carry the load until occupants can safely relocate.
Retention
Accepting that glass will fracture during service also means considering what will happen to the glass afterwards. What would happen if glass fractured? Would the glass remain entirely secured to the building structure or is falling debris likely? Would falling debris create a significant hazard for occupants? Each glass component’s retention must be considered during design. For example, the designer may decide that it is acceptable for a monolithic window to fracture if the hazard created by falling glass fragments is minimal. Conversely, a laminated canopy (which could fall on occupants directly below) has a relatively higher risk of great bodily harm if not retained to the main building structure. Chapter 24 of the International Building Code (IBC) requires designers to consider the effects of building movement on intact vertical glazing to ensure glass panels in curtain walls and storefronts will not disengage and become a falling hazard.
Replacement
When glass fractures it must be remedied for both temporary and permanent occupation of the building. Lead times for glass
production can vary widely depending on the complexity of the application. A simple insulated glass window panel may be able to be ordered and replaced within a week. More complex, custom applications such as point-supported glass, or oversized units which are produced overseas, may require months of lead time to replace. These delays can significantly hinder the building’s use. Glass connection details can and should be designed to ensure replacement is achievable without compromising other building finishes whenever possible. Careful planning is an important design step to ensure an efficient and swift replacement plan is in place if glass were to be compromised during service.
Regulation
The IBC devotes Chapter 24 to glass and glazing. Topics addressed include a wide range of applications including sloped glazing, safety glazing, and specific use cases like handrails, guards, walkways, and elevators. However, many glass applications in modern building design, such as point-supported glazing and beam-columns (glass fins) are not addressed by the IBC. The IBC has historically updated language in Chapter 24 with each iteration, but additional guidance from outside references remains essential. The IBC also references documents in Chapter 35 which are relevant to glass design, including notable ASTM standards E1300, E2751, and E2358.
Existing documents from other agencies are also very helpful tools to a modern designer. NGA’s GANA Glazing Manual, NCSEA’s Engineering Structural Glass Design Guide, and Eurocode’s BS EN 16612 are excellent resources for understanding and designing modern glass structures. While the IBC does not adopt these documents, they are widely recognized and referenced within the structural glass community. Additional anticipated documents from ASTM and other groups aim to increase the available guidance for structural glass designers moving forward.
Conclusion
Glass design is a complex discipline which requires nuanced thought and care to safeguard building occupants. Until the adopted building code offers more specific guidance, glass designers and engineers must rely upon best-practices and industry standards to do their work. Determining the level of safety required for a particular application requires careful consideration of the risks associated with fracture. It is the responsibility of a glass designer to work with a project’s design team to communicate risks and discuss design decisions associated with these risks as they are made. A knowledgeable and experienced glass design professional will be able to facilitate a smooth and efficient design process. ■
Ted Kraemer, PE, is an Associate at KPFF in Roseville, CA. His engineering specialization focuses on structural glass and building facade. (ted.kraemer@kpff.com)
STRUCTURAL ENGINEERING AWARDS
The National Council of Structural Engineers Associations (NCSEA) is pleased to share winners of the 2024 Excellence in Structural Engineering (SEE) Awards, which were announced during NCSEA’s Structural Engineering Summit, held November 5-8,at the MGM Grand in Las Vegas. The winning entries recognize the most innovative and groundbreaking work of our profession’s top talents. The winners were honored at the Summut during a special awards celebration sponsored by Atlas Tube. The winning projects can also be viewed throughout 2025 during the free, in-depth SEE Awards Webinar Series sponsored by Atlas Tube at www.ncsea.com.
Awards were given in eight categories, with an Outstanding Project awarded in each of the following categories:
• New Buildings under $30 Million
• New Buildings $30 Million to $80 Million
• New Buildings $80 Million to $200 Million
• New Buildings over $200 Million
• New Bridges and Transportation Structures
• Forensic | Renovation | Retrofit | Rehabilitation Structures under $20 Million
• Forensic | Renovation | Retrofit | Rehabilitation Structures over $20 Million
• Other Structures
Judging for each category was completed in two phases. The first round was completed virtually by a group of NCSEA Past Presidents and the second round was conducted by structural engineers from the Northeast Coalition. Judges selected the winning structures based on complexity of criteria or unique problems; creativity of structural design; innovative application of new or existing materials or techniques; commitment to sustainability through efficient use of materials, resilience, circular economy principles, or embodied carbon reduction; and ingenuity of design for constructability challenges and efficient use of labor.
Along with each category award, an overall 2024 Structure of the Year award was selected from the eight Outstanding Projects based on votes by the judging panel and individual attendees of the NCSEA Summit. Voters compared each project based on the complexities and ingenuity required. The winner was announced by the 2024 Awards Committee Chair Carrie Johnson, (Wallace Design Collective, PC, Tulsa, OK).
“We introduced an exciting new voting method for this year’s award,” Johnson said during the awards ceremony. “This innovative approach allowed both the NCSEA Awards Committee and the general audience to select this year’s winner. By combining insights and feedback from industry professionals, we wanted to create a more inclusive and representative selection process. We believe this change reflects the collaborative spirit of our community and enhances the significance of this prestigious award.
Congratulations to the 2024 SEE Award winners! Keep an eye out for in-depth articles on several of these winners in future issues of STRUCTURE
By combining insights and feedback from industry professionals, we wanted to create a more inclusive and representative selection process. We believe this change reflects the collaborative spirit of our community and enhances the significance of this prestigious award.—Carrie Johnson
STRUCTURE YEAR
of the
Perelman Performing Arts Center
NEW YORK CITY, NY
Structural Design Firm
Magnusson Klemencic Associates
Architects
REX, with Davis Brody Bond – A Page Company
General Contractor
Sciame Construction
Approximate Construction Cost
$500 million
A Design for Day to Night
The Perelman Performing Arts Center (PAC NYC) enhances the World Trade Center site with its unique cultural presence. By day, its marble-and-glass facade is understated, but by night, it reveals its versatility. The PAC NYC three main theaters and two adjoining “scene docks” transform into 11 different theater volumes and 60-plus seating configurations, thanks to four retractable, acoustically isolated, gigantic “guillotine” walls.
Existing foundations designed for an entirely differently sized and oriented theater were repurposed—instead of demolished and reconstructed—through load-path mapping. Existing foundation information was evaluated to create a “red dot diagram,” with each red dot identifying an existing support point and its loadcarrying capacity. This revealed no single point of support could support the loads from the new theater configuration, and 60% of the available capacity fell outside PAC NYC’s new footprint.
Seven unique below-grade “interventions” were designed to combine multiple support points and connect them to seven above-grade “super columns” (with up to 20 times more capacity than typical building columns). These seven super columns alone support the entire above-grade 6,300 ton superstructure.
The primary structure supports the heavy Zuccotti Theater floor, which can rise 7.5 feet and lower three feet in minutes. Complex secondary steel supports hoists, mechanisms, and platforms for the heavy guillotine walls, lighting grids, catwalks, and scenery rigging. The team designed 60-plus seating configuration options for PAC NYC; the venue has already used two new configurations. A marvel of engineering, PAC NYC combines security, blast design, and storm resilience, establishing new standards for flexible performance spaces. The 129,000 square-foot facility is a beacon of cutting-edge structural design and engineering creativity.
Fraser Mills Presentation Centre
COQUITLAM, BRITISH COLUMBIA, CANADA
Structural Design Firm: StructureCraft
Architect: Patkau Architects
General Contractor: Beedie Construction
Outstanding Project
Warm Gathering Place for Community
The Presentation Centre at Fraser Mills exemplifies innovative mass timber systems through its inventive structural engineering and community-focused design. Valued at $10M, the Centre serves as a key destination for the 96-acre Fraser Mills development in greater Vancouver, Canada. The building features a distinctive swooping form supported by 26 unique glulam frames, spanning up to 70 feet between cantilevered glulam columns and 33-foot high splayed columns. The complex geometry of each frame required advanced software, including Rhino, Grasshopper, and Karamba, to translate into manufacturable components from plywood and sawn purlins. Notably, the Centre is among the first in British Columbia to use cantilevered glulam columns for lateral support. All timber elements are crafted from locally sourced Douglas Fir, with manufacturing within 500 miles, highlighting a successful local initiative.
Oregon State University Cascades
Edward J. Ray Hall
BEND, OR | CATENA CONSULTING ENGINEERS
Finalist
Edward J. Ray Hall at Oregon State University is a four-story, 50,000-square-foot mass timber building featuring cross-laminated timber (CLT) decking, glued-laminated timber columns and beams, and a mass plywood panel (MPP) monumental stair. Constructed on a steep slope, it required 40 feet of fill and compliance with Seismic Design Category D. The design team used connectors validated through proof-load testing for concealed timber connections, facilitating ease of placement and erection. To counteract long-term creep deflections, the design incorporates composite behavior using advanced methods. The monumental stair utilizes locally sourced MPP for its inclined stringers, treads, and benches. Timber includes 40% restoration and 14% from Native-owned forests, supporting sustainability and regional economic goals. The regular form and repetitive framing reduce fabrication costs and enhance labor efficiency.
U.S. Coast Guard Academy –Maritime Center of Excellence
NEW LONDON, CT | A+F ENGINEERS
The Maritime Center of Excellence, a 20,000 GSF LEED Gold certified building, is situated on the USCG Academy waterfront in New London, CT. Designed to reflect maritime heritage and serve educational and operational needs, this facility features a distinctive roof-oriented northward, echoing traditional navigation. The structural design integrates a hybrid system of steel frames and glulam arches, each uniquely shaped, supporting a massive, cantilevered roof. Engineered to withstand hurricane-level winds and flooding, it employs a combination of steel and wood moment frames alongside concrete shear walls. A+F Engineers crafted this structure to merge architectural elegance with robust, functional engineering, exemplifying practical and efficient design.
Finalist
Innovation in Mass Timber
Outstanding Project
BCIT Tall Timber Student Housing
BURNABY, BRITISH COLUMBIA, CANADA
Structural Design Firm: Fast + Epp
Architect: Perkins & Will
General Contractor: Ledcor
The new Tall Timber Student Housing tower at the British Columbia Institute of Technology (BCIT) in Burnaby, British Columbia, represents a shift forward in tall, hybrid, encapsu lated mass timber construction. The 12-story tower is the first of the next generation of point-supported CLT structures, comprising of flat, two-way spanning Hem-Fir material cross-laminated timber (CLT) floor plates, point-supported on steel columns without beams. The use of local Hem-fir CLT at a large width of 11-feet-6-inches, supported on steel HSS columns, and punching shear reinforcing screws to increase column line spacing, represents a step forward in tall, hybrid structures. The lateral-resisting cores utilize concentrically braced frames, set in self-stabilizing configurations that are shop-installed in 5- and 6-story lifts to further reduce construction time. Utilizing the latest advances in engineered wood products, pre-fabrication, and encapsulation strategies, this project represents significant progress in the field of hybrid-mass timber buildings.
Doug Meijer Medical Innovation Building
GRAND RAPIDS, MI | SMITHGROUP Finalist
The Doug Meijer Medical Innovation Building, part of a 4-acre medical research complex, features a creative structural design to support advanced research and patient care. Key elements include concrete cyclotron vaults and a delay maze constructed with a “box within a box” approach to contain radiation. A tighter column grid on the south side enhances vibration performance for sensitive equipment. The structure uses a 30-foot x 30-foot grid with steel and composite floor framing, supported by nine sloped columns. These columns, which accommodate vehicle access and fit within the grid, have a maximum 15-degree slope. The design prioritizes cost-effectiveness and low embodied carbon.
University of Washington Health Sciences Education Building
SEATTLE, WA |KPFF CONSULTING ENGINEERS
The Health Sciences Education Building was the University of Washington’s first installation of cross-laminated timber (CLT), which also used a hybrid structure to create an inspirational learning environment for future generations of healthcare professionals. The structure combined the benefits of wood and the long-span capacity of composite steel to achieve large, open spaces, while maintaining the health, aesthetic, and sustainability benefits of wood. KPFF teamed with the University of Washington to perform strength and vibration testing for the composite floors. This allowed the design to push beyond the prescriptive limits of the building code and will improve the efficiency of future CLT projects.
Finalist
Alcove – 900 Church
NASHVILLE, TN | DESIMONE CONSULTING ENGINEERING
Outstanding Project
FORTH HOTEL ATLANTA, GA
Structural Design Firm: Uzun+Case, LLC
Architects: HKS and Morri Adjmi
General Contractor: Brasfield & Gorrie
Striking Diagrid Design
The Fourth Ward Social Club & Hotel located in Atlanta, Georgia, is three levels underground and 16 above ground. The hotel featured the exterior “diagrid” column system. Other than the exposed exterior load-bearing diagrid columns, there are only three interior columns and the shear wall. Architecturally, the diagrid columns were to be placed forward of the slab edge to express the diagrid. The building diagrid corners at the top and bottom “folded” inward to create a real three-dimensional complexity to the design. Slab punching shear and diagrid tension forces in the slab made this a project with complex detailing and close
Alcove’s design consists of stacked, shifted cubes organized in pairs, creating four alcoves that host a variety of exterior amenities. The offset stacking required the design of numerous, differently sized, post-tensioned concrete floor plates as the alcoves create alternating openings within the varying tiers. The alternating floor stacks created the need for cantilevered, downturned concrete overhangs, or “mini roofs,” at the alcove floors to complete the transition. On the 34th-floor rooftop, modern amenities include two pools: a traditional deck and saltwater pool, and a clear acrylic-bottomed pool that dramatically overhangs the 27th-floor amenity terrace on the west side of the building, extending eight feet beyond the structure and 34 stories above the street below. To maximize the span of the cantilever, DeSimone designed this area of the structure with posttensioned concrete.
One River North is a 17-story tower featuring a canyon-like facade resembling a slot canyon in Denver, Colorado. The multifamily project includes over 7,000 square feet of outdoor amenities, such as undulating planters, multilevel stairways, and a two-level waterfall. The structure is cast-in-place concrete with post-tensioned floors. Unique structural challenges included each floor’s distinct geometry and loading requirements for the canyon features, wind loading necessitating steel link beams in the core walls, and massive transfer slabs and beams for building offsets. Coordination with MAD Architects and Davis Partnership through multiple BIM models ensured design intent was preserved. The construction phase demanded intensive administration, field question resolution, and frequent site visits to accurately implement the complex design features.
DENVER, CO |JIRSA HEDRICK STRUCTURAL ENGINEERS Finalist
Sphere is a 516-foot-diameter semi-spherical building rising 366 feet above ground with a bowl-shaped theater for 17,600 guests, seated beneath a domed roof and suspended media plane. The team studied several alternate configurations that would facilitate fabrication and erection and finally arrived at a hybrid solution of 14 horizontal continuous ring members and 32 pairs of crisscrossing diagonal geodesic elements, continuous between the base and a ring near the crown. The topmost framing, known as the Oculus, is framed radially. The Exosphere, the venue’s outer latticed grid shell, is composed of steel pipe sections and cast connecting nodes covered with 580,000 square feet of programmable LED lighting, which presents stunning visual displays. Although Sphere is composed of distinct structural systems, they are all interconnected to
Architects: REX, with Davis Brody Bond – A Page Company
General Contractor: Sciame Construction
A Design for Day to Night
The Perelman Performing Arts Center (PAC NYC) enhances the World Trade Center site with its unique cultural presence. By day, its marble-and-glass façade is understated, but by night, it reveals its versatility. The PAC NYC three main theaters and two adjoining “scene docks” transform into 11 different theater volumes and 60-plus seating configurations, thanks to four retractable, acoustically isolated, gigantic “guillotine” walls. Seven unique below-grade “interventions” were designed to combine multiple support points and connect them to seven above-grade “super columns” (with up to 20 times more capacity than typical building columns). These seven super columns alone support the entire above-grade 6,300 ton superstructure. A marvel of engineering, PAC NYC combines security, blast design, and storm resilience, establishing new standards for flexible performance spaces. The 129,000 square-foot facility is a beacon of cutting-edge structural design and engineering creativity.
Hangzhou Greenland
Century Center
The Greenland Hangzhou Century Center, located just outside of Shanghai, between Hangzhou’s International Expo Center and Olympic Sports Center, is an iconic landmark with its two 302-meter twin towers connected by a gracefully ‘draped’ skybridge. The building’s unique enclosure on the bridge is a parametrically achieved feat of architecture and engineering, creating a geometrically complex curtain wall that resembles a single veil gently draping over the soaring towers and bridge. The design process involved meticulous selection of the bridge and roof shape, resulting in nearly flat glass across the complex. Custom digital tools and close collaboration between design and technical teams ensured the successful integration of geometry and structure.
LAS VEGAS, NV | SEVERUD ASSOCIATES
HANGZHOU, ZHEJIANG, CHINA |SKIDMORE, OWINGS & MERRILL
Finalist
Semi-Integral Pedestrian Bridge Spans Arkansas River
As part of Tulsa’s vision for the Zink Dam area, the Williams Crossing pedestrian bridge spans 1,440 feet with eleven 120-foot arch spans and one 120-foot approach span, linking the east and west banks of the Arkansas River. The semi-integral bridge was designed with extremely slender deck-stiffened arches built from weathering steel plate. The deck-stiffened, plate-arch structure is the first of its kind in the U.S. and the bridge is also the first multi-span, plate arch bridge built in the country. Continuous weathering steel plate is bent at the spandrel locations. In between the spandrels the arch plate is locally stiffened with a 2-inch thick and 24-inch wide plate to increase the vertical bending stiffness of the arch. An efficient and optimized structural design reduced the bridge to its most minimal footprint and contributed to the structure’s sustainable design.
Second Avenue Over I-94 Network
Tied Arch Bridge
Built between 1947 and 1959, Interstate 94 was one of Michigan’s earliest highways, linking more than 100 auto companies to westward factories in Detroit, Michigan. The Michigan Department of Transportation envisioned a bridge without a center pier to enhance the area visually. The Second Avenue Bridge employs innovative accelerated construction methods to minimize traffic disruption and introduces Michigan’s first network-tied arch design and selfpropelled modular transporter (SPMT). The new bridge retains two driving lanes, adds sidewalks and bike lanes, and includes native landscaping and aesthetic lighting. Constructed off-site, the 5-million-pound structure was moved and lowered over the freeway, featuring a vertical curve and 18-degree skew.
The New Frederick Douglass Memorial Bridge
WASHINGTON, DC | AECOM
The New Frederick Douglass Memorial Bridge project transforms Washington DC’s South Capitol Street corridor into a grand boulevard underscoring Major Pierre L’Enfant’s 1791 Plan of the City of Washington. Replacing a deteriorating structure, the bridge features a multi-arch design over the Anacostia River, flanked by park-like transit ovals. The bridge enhances multimodal connections for pedestrians, cyclists, and transit users. Its innovative design includes three lighted, parallel arches that rise above the deck and extend to the water level, allowing the superstructure to expand and contract. With a 540-foot center span and 450-foot flanking spans, the bridge increases navigable waterway width and offers open space above the deck. The design improves mobility, safety, and transit while meeting sustainability
Finalist
The Baird Center Expansion
MILWAUKEE, WI
Structural Design Firm: GRAEF
Architects: TVS Design—Conventional Center Specialist; Eppstein Uhen— Production Architect, Architect of Record
The Baird Center located in Milwaukee, Wisconsin, completed the $456 million renovation and expansion involving complex structural challenges with concrete and steel in May 2024. To accommodate 2024 programming needs, the project included infilling a three-level parking structure and two-level conference rooms beneath an existing exhibit hall. Engineers overcame challenges by lowering existing pile caps and removing a column while supporting live loads. The renovation expanded exhibit space to 300,000 square feet, with a north-end floor extension cantilevering over a sidewalk. Limited structural depth was addressed with a full-story truss supporting the exhibit level’s concrete structure, visible through exhibit hall windows. The project utilized the PS=0 joint coupler for seamless integration and seismic compliance, and the GRAEFaccelerate® system expedited design and detailing to prepare the center for the 2024 RNC.
651 Gateway
SAN FRANCISCO, CA | IMEG
IMEG and Maffei Structural Engineering undertook a comprehensive seismic retrofit and renovations for 651 Gateway Boulevard, a 17-story office building in South San Francisco. Originally built to the 1982 Uniform Building Code (UBC), the building had pre-Northridge deficiencies, including weak beam-to-column connections and inadequate column splices. The retrofit included installing fluid viscous dampers (FVDs) to reduce story drift and improve seismic performance. While lower column splices were retrofitted to prevent fractures, the retrofit addressed significant weaknesses in the building’s lateral force resisting system. The project also involved architectural and MEP upgrades, including floor system stiffening for laboratory use, without changing occupancy classification. IMEG, as the struc tural engineer of record, highlighted the retrofit’s benefits, including enhanced seismic safety, reduced tenant downtime, and extended building lifespan.
Outstanding Project
Dallas County
Records Building Renovation
DALLAS, TX | DATUM ENGINEERS
The Dallas County Records Building Complex project ambitiously rejuvenated a nearly useless complex of three early 1900s historic buildings, converting them into one unified whole, resulting in a connected modern workplace while preserving the historic façades. The design team envisioned an ambitious plan to demolish several floors of the Courts and Annex building, rebuild new floors to match the remaining Records floors plus a new floor on top; build a new central circulation spine to connect all buildings seamlessly; and modernize all building systems. Several upper floors of two of the buildings were demolished while bracing and preserving the skin, then new floors were built back with modern floor heights. The result is a beautiful, functional, connected modern workplace
Finalist
Finalist
Outstanding Project
Minnesota Zoo Treetop Trail
APPLE VALLEY, MN
Structural Design Firm: Buro Happold | Meyer Borgman Johnson
Architects: Snow Kreilich Architects
General Contractor: PCL
Connecting People, Nature, and Animals
Opened in July 2023, the Treetop Trail at the Minnesota Zoo is a remarkable adaptive reuse project. It repurposes a 1970s Corten steel monorail track into the world’s longest elevated pedestrian loop. Spanning 1.25 miles, the 8-foot-wide trail navigates over wildlife exhibits, lakes, marshes, and through the forest canopy. The design addressed complex structural challenges by carefully matching the new lightweight steel-framed decking to the existing Corten structure. Through intelligent strengthening, testing, and repairs, the original steel frame and foundations were reused. Prefabricated in 20-foot modules, the steel structure was installed using a custom trolley system, allowing the zoo to remain operational during construction. The trail embodies the zoo’s mission to connect people, animals, and nature while conserving wildlife.
Downtown Cary Park
The Downtown Cary Park Pavilions, completed in 2023, enhance the six-acre park in Cary, North Carolina with their striking design and functionality. The three pavilions provide shaded gathering spaces and amenities, each crafted with carefully chosen materials that align with their unique geometric forms. The Great Lawn Pavilion, cen trally located, features a multi-purpose stage, concealed green room, and ceiling-suspended AV equipment for events. It combines steel, concrete, glulam, and conventional lumber. The Academy Pavilion, the largest, is the park’s main food and beverage hub, constructed from concrete, steel, conventional lumber, and cold-formed joists. Bark Bar, made of reinforced concrete, serves the adjacent dog play area. The design integrates materiality, structure, and purpose, creating a welcoming environment that has already delighted many visitors.
Real Time Tower
Collins Structural Consulting, PLLC designed an 81-foot, fivelevel tower for MrBeast Studio’s YouTube video “In 10 Minutes This Room Will Explode!”, which has over 105 million views. The tower featured 1,400 square feet of filmable space per floor, clear exterior walls, and various obstacle elements, including trapeze rings and cages, with nearly 20,000 gallons of water on the ground level. With only 45 days and $700,000, traditional construction methods were unfeasible. Instead, recycled shipping containers were used for the main structural columns, secured with off-the-shelf dove-tail connectors and additional steel framing. The C-shaped columns supported the filming stages and allowed for unobstructed filming. Efficient connections and prefabrication ensured the project was completed within 23 days.
Opportunity Awaits: Software Trends to Watch for in the Near Future
Leaders from structural engineering software firms share their thoughts and analysis regarding the trends in software and AI.
By STRUCTURE Magazine
Widespread acceptance of any new technology or innovation comes after a period of wariness and circumspection, but that timeline from introduction to adoption is accelerating. Structural engineers are balancing how to take advantage of new tools that could save them time and improve their work while also being careful to ensure the integrity of the work remains intact.
With this in mind, STRUCTURE approached three experts from software companies that serve structural engineers in different ways to talk about developing trends in technology. They are: Matt Cooper, CEO of BQE Software, a provider of firm management software geared toward architects and engineers; Mark Riffey, CEO of ENERCALC, which contributes structural engineering calculation software; and Josh Taylor, Vice President of Structural Engineering at Bentley, which develops, manufactures, and sells engineering design software for a wide variety of infrastructure assets such as bridges, airports, skyscrapers, and power plants. Their answers focused on the opportunities in general for structural engineers and the advancements in technology, particularly AI. They also shared words of advice for judicious implementation of the evolving tools.
How will AI impact the future use and development of software technology for SEs? In what ways will software further utilize AI to aid structural engineers in their work?
?Matt Cooper, CEO, BQE Software: When it comes to AI, lots of firms are considering how it will impact the practice of structural engineering. However, we anticipate AI will also have a substantial impact on how SEs manage their firms overall. AI will help SEs interact more
effectively with clients, staff projects, forecast project outcomes, improve data analytics, and more. Ultimately, AI will improve business practices and lead to more efficient and profitable firms.
Josh Taylor, VP of Structural Engineering, Bentley: I'm particularly excited about AI's potential to accelerate the earlier stages of the design process by reducing the "overhead" in engineering workflows. By overhead, I mean tasks in which engineers aren't fully utilizing their critical engineering judgement. This would include things like model set up, preliminary loading and design criteria, and establishing the standards for reports and drawings. The real ingenuity and efficiencies that structural engineers contribute to a project come when they are able to see how all the systems in a structure work in unison. This only happens once they have a solid starting point that they can conduct "what if" studies on and fine tune. We can envision AI getting engineers to this starting point much faster than they are able to presently.
Mark Riffey, CEO, ENERCALC: AI is already impacting the use and development of software for SEs.
Larger vendors have significant resources to apply to AI projects. We are already starting to see them roll out AI-based tools in their software (example: Autodesk AI, an Autodesk tool to augment creative exploration, automate tedious tasks, and analyze data to provide predictive insights).
Even starting from a blank screen, you can provide AI with a verbal description of what you want (faster than typing), and even with less than perfect speech recognition, you can get pretty close. You might say, "Pretty close isn't perfect"—and you're right, but that isn't the point. We use these tools because they get to 60-80% of the desired outcome much faster than we do when doing the work without them.
Imagine a programming task that normally takes 3 hours from start to finish, starting from a blank screen. For some types of work, you can get these tools to get you to 80% in 2 minutes. Maybe it takes you another 30 minutes to polish it to where you wanted it, but you're still ahead by almost 2.5 hours.
AI isn't about replacing engineers. It's about empowering engineers by accelerating the mundane work they do, so that they can expend their mental energy on the most important engineering tasks and make better decisions on the things that require engineering judgment.
In what ways will software further utilize AI to aid structural engineers in their work?
?Riffey: It's important to focus on what these tools do better and faster than we do. People are pretty good at finding patterns in visual data. AI is great at finding patterns in high volumes of visual, written, or binary data that would overwhelm us.
AI might also tell you who is more efficient at designing this type of structure vs. that kind.
These tools can be merged into existing systems so they can analyze existing data that's difficult for us to assess quickly. "For this beam, tell me what section sizes we typically use for (your use case) over the last 20 years."
Vendors like Qnect already have software to analyze constructability of a designed structure, work that's related to steel connections. Imagine the types of analysis AI can do across an entire project build with a global analysis tool.
AI can look at project data for something you designed years ago that is now being expanded or upgraded. When you do this work, you have to dig around to figure out what changes are going to be required to meet updated governing codes and design standards. AI could do this in the time it takes to open your analysis and design software.
Is the structural engineering community using software technology to its fullest extent? Which areas of the profession hold the greatest opportunity for improvement through the adoption of available software?
?Cooper: Our purview is firm management software, and within that domain, the SE community is not using software technology to the fullest. More than 50% of small-to-midsized firms continue to use Excel, Quickbooks, or one-off point solutions rather than firm management-software purpose-built for the industry. Most of the firms that are using dedicated firm management software are still on antiquated/legacy platforms and are well past due for a replacement.
In fairness, the software industry has underdelivered in this domain for SE firms in the past. However, there is now easier-to-use software with better functionality that enables firms to drive more efficiencies and insights to run firms more effectively and keep employees happier.
Taylor: One aspect of engineering software that continues to grow in popularity, but I believe is still underutilized, is the use of programming interfaces (APIs) available in the software. APIs allow users with some coding know-how to automate routines that would otherwise take lots of button clicks and manual operation, as well as push and pull data to and from the application to other digital tools. What users are doing with these APIs has grown tremendously in sophistication. Entire digital ecosystems are being built off commercial software by utilizing them. As you might expect, engineers are starting to inject AI into these workflows. In fact, the winner of 2023 Bentley Going Digital Awards for Structural Engineering was Hyundai Engineering, who paired STAAD.Pro with an AI algorithm for optimizing the geometry and framing configurations for mechanical shed structures.
Riffey: Some great structural engineering software is available via open-source and from independent software vendors. Even so, there are significant gaps in functionality, workflow, and interoperability—collectively. For example, software A might talk to software B, but only via a 1990s style import/export of a CSV file. Software C might talk to software A but not to software B—or engineers are forced to cut and paste, or worse.
Other structural engineering software might use more advanced methods (like APIs) to communicate with certain other software. Despite that, there's no end-to-end solution for engineering firms. As a result, they're forced to cobble together a solution from multiple high-quality software packages that fill a specific, necessary purpose, augmented by manual processing.
Engineering firms need full-spectrum holistic solutions. AI is a part of that solution, but is not the sole cure.
Software is a powerful tool but like any tool, misusage can be damaging. What are some pitfalls to be avoided when it comes to employing software? Do you have words of advice or general guidance you tell customers when they are implementing a new tool or product into their systems?
?your spreadsheets, your databases, descriptions of future products, etc.
Cooper: We see three common pitfalls. First, software implementations require BOTH leadership support and an internal owner responsible for the project. Second, these implementations take time, and so adequate capacity needs to be allocated. Finally, firms often try to force-fit the software 100% to their existing internal processes, rather than take the opportunity to refine those processes.
It’s worth noting: any time there is a major project requiring change management, the initial excitement often gives way to temporary dip in sentiment due to the time and effort involved. This dip often occurs right before seeing that proverbial light at the end of the tunnel. It’s important that firms recognize that they are on a journey and commit to completing the implementation so that they can achieve the anticipated benefits.
Riffey: Just like with analysis software, when using an AI tool, it's important to approach it with a clear expectation of the desired outcome—you shouldn't simply follow it blindly. AI tools aren’t designed to think for you. Using them effectively is a skill we can all develop to better leverage their capabilities.
Public large language models (LLMs) like those used by OpenAI's ChatGPT were in large part built on public-facing websites and data on the internet. No matter how you feel about this, I'm quite sure how you would feel if your project data was used while working with a vendor's LLM chat interface and that data ended up as part of the LLM vendor's training database.
What that means is that your data would become public. Imagine that you asked an LLM to analyze your sales, or a new product you're building, or some valuable new technology that you're working on. Now imagine that the LLM uses that data for training and your competition runs a ChatGPT type query to assess the competitive issues in your market. The data about the new technology you built could become part of the response your competition gets when they run their query.
This is why it's essential to make absolutely sure that your proprietary data is not exposed to public facing systems. This includes your code,
A GPT for Structural Engineers and STRUCTURE Readers
NCSEA launched a free and unique AI tool in October that relies on a library of structural engineering resources—including STRUCTURE articles—to help users find the information they are looking for. When a user prompts SE GPT to answer a structural engineering-related question or provide information on a topic, the system automatically generates a response based on a closed GPT database administered by NCSEA. This database includes only structural engineering-specific content written or produced by professionals and organizations that support structural engineering. SE GPT-generated answers are provided with citations from its database, so users know where the facts and details came from and can seek further knowledge by reading the original source material.
Visit www.ncsea.com/se-gpt to learn more and try it out.
Taylor: Fortunately, structural engineering is governed by some immutable principles, among them the field of engineering mechanics. Regardless of what an engineer uses as an aid (a calculator, spreadsheet, finite element software, or a machine learning tool), the results can be assessed using these principles. Whenever employing any type of new tool, very well understood benchmarks should be employed to gain trust in the tool. Use a past project or a simple verification problem that you understand well. There are design examples available in the public domain. We also ship verification examples with our products that can be used for this purpose.
As AI/ML is concerned, there are many lessons we can take from the emergence of desktop software in structural engineering circa the early 1990s. There was similar skepticism, and I would say healthy skepticism, about the possibility for overreliance on what it produces. For example, the emergence of auto-design functionality required an investment of time for designers to evaluate if they were comfortable with what the software produced. They accordingly made decisions on where they were willing to employ these algorithms and where they felt manual design methods were more appropriate. The game plan for getting confident with AI's possibilities and limitations will be similar.
Do you have any other thoughts on the current and future trends in software for structural engineers that you would like to share?
Taylor: There are an enormous number of possible applications of AI to structural engineering. As a provider of software solutions, conversations with our users are indispensable in learning how we best support the evolution of their AI/ML processes—particularly, what the common needs are across the industry. AI/ML is a means, with the ultimate goal of making our users more productive than they are now while retaining the confidence they have in our solutions.
Riffey: I believe an engineering software vendor's highest purpose is to take the mundane, tedious, complicated, unrewarding work off of engineers’ plates so that they are freed to do the work software can't or shouldn't do. We can do that while leaving critical engineering decisions in the hands of the engineer where they belong. ■
Access and Protection at 1,250 Feet
A collaborative means and methods design brought efficiency and safety to the reclad of the Empire State Building Floor 102 Observation deck.
By Robert Belardi, PE
For many structural engineers, means and methods represent a nebulous cloud of scaffolding, shoring, cranes, and hoists that is swept into a corner labeled “by others.” In the traditional design-bid-build model, the general contractor is responsible for the design and coordination of all means and methods—the combination of temporary structures, sequences, and methodologies that answer the “how to” of getting a design built.
A consequence of this model is that the design of these temporary systems often cascades down a chain of subcontractors and their various engineering consultants. This presents obvious coordination challenges as the responsibility for design moves farther away from the owner and core design team (AOR/EOR). Often, and especially with new construction, coordination may center around timing (demolish this, then build that) or spatial considerations (the scaffold goes here, the crane over there) that can be effectively orchestrated by the general contractor.
However, working on existing buildings requires a higher degree of coordinated design, making the “too many cooks in the kitchen” model inefficient at best and unsafe at worst. When a project occurs at extreme heights, such as on the 102nd floor of the Empire State Building, the means and methods design becomes crucial, requiring an equal amount of time, energy, and collaboration as the final design itself.
This was the case when the Empire State Reality Trust embarked on a major refresh of the 102nd floor observation deck. The project, intended to enhance the visitor experience, called for the complete demolition of the existing envelope to make way for new floor-to-ceiling glass panels that would provide 360-degree views of the Manhattan skyline. A design-assist team consisting of Skanska USA, Plan B Engineering, and Greg Beeche Logistics (GBL) worked closely with the owner and building EOR, Thorton Tomasetti, to design and install an external access and enclosure system, dubbed “the cocoon.”
Over 30 tons of temporary steel and
aluminum framing were assembled from custom, modular pieces at 1,250-plus feet above street level to create three exterior work platforms fully enclosed in high-strength fabric (galvanized steel mesh embedded in a weather resistant fabric). Once completed, the cocoon provided a contained work area that was approved by the New York City Department of Buildings (DOB) as an alternate means of protection under Chapter 33 of the New York City Building Code, which governs pedestrian safety in occupied spaces (Section 3307). This allowed the popular and lucrative 86th floor observation deck to remain open—a key mandate from ownership. Underscoring the challenge of this temporary design was the fact that the installation and dismantling of the cocoon—permitted only between 2 a.m. and 7 a.m.—accounted for nearly two-thirds of the construction schedule.
Early Planning
Plan B was engaged by Skanska early in the planning process to envision an enclosure and access system that met the project needs. The system needed to:
• Provide a solid weather and wind enclosure to execute the exterior work. A wind tunnel study yielded design loads approaching 100 psf (based on 50-year return period and a 1.15 importance factor).
• Gain approval as an alternate means of protection through the CCD-1 review process within the DOB. This required a monthslong dialogue with city officials, which ultimately allowed for the 86th floor observatory to remain open without protection (i.e. a sidewalk shed) covering the exterior viewing deck.
• Provide two 25 psf live load platform levels and a “floor” rated for 300 psf, a new design requirement mandated by the DOB during
the CCD-1 approval process.
• Minimize the number of reinforcements to the existing framing required to support the temporary structure. A lesson learned from previous projects at the Empire State Building was that reinforcements involved significant time and cost to design, coordinate, permit, and install.
• All modular pieces of the system had to fit in a small elevator that was recently renovated for VIP guests. The maximum member size was 8 feet long.
Prior Precedent
The Tower Reconfiguration Project (TRP), a project previously designed by Plan B , provided proof of concept for the construction of a modular enclosure system at extreme heights. The TRP utilized triangular truss sections wrapped in high strength fabric (the same material eventually used for the cocoon) to create an enclosure and worker access to perform structural upgrades to the antenna spire. The TRP was located at the base of the spire, just above the ice shield (a circular, umbrellalike steel bracket that provides a protective “awning” above the exterior walkway on the 103rd floor). This enclosure was attached to the building at the ice shield and laterally tied to the antenna spire above, effectively functioning like a ground-based supported scaffold, albeit at an extreme height. Compared to the TRP project, the observation deck enclosure did not offer such readily available attachment points. However, the TRP project did represent a proof of concept for the construction of a modular enclosure system at extreme heights.
Understanding Existing Conditions
A laser scan conducted as part of the renovation documentation provided an accurate baseline of the building’s geometry. Historic
An isolated rendering of the cocoon is shown with the actual constructed cocoon on the Empire State Building.
structural drawings were useful but fragmented; over the years, the building’s more utilitarian upper levels were modified with little or no documentation. This necessitated multiple site visits, often in tight, claustrophobic spaces, to fully document all existing conditions. Each face of the building showed slight variations, requiring close attention when detailing the final system.
Ice Shield
A previous restoration of the mooring mast glazing utilized a custom suspended scaffold hung from outriggers supported by the 104th floor ice shield. For that project, Plan B collaborated with Thorton Tomasetti to reinforce the ice shield framing and connections. The initial concept was to use this reinforced ice shield as the primary vertical support point for the cocoon. Plan B developed early schematic design loads for this option. However, after presenting this concept to Thorton Tomasetti, it was determined that the required reinforcements to the ice shield were deemed uneconomical. A second option of attaching brackets directly to the existing columns just below the ice shield proved to be the more practical solution.
The reinforced ice shield was nonetheless vital to the overall workplan. The upgraded ice shield incorporated modern OSHA rated lifeline support points that were used during critical exterior work—most notably the removal of the Alford radio antennas and installation of connections to the building columns.
Alford Antennas
On the 102nd floor, a series of 32 Alford radio antennas (formerly the largest combined FM station system in the world, circa 1965) were scheduled for removal. Knowing these attachment points would soon become available, the team conducted a series of probes and
site visits to better understand the framing. Removing the antennas offered access to the building columns just below the work area—an ideal lateral tie point at the floor of the cocoon. The phased removal of the antennas was then integrated into the installation of the cocoon, a benefit to ownership by streamlining the two projects into one.
Such early investigations and vetting of ideas provided vital clarity for such a unique temporary design. Reducing the amount of design and existing condition unknowns allowed Skanska to solicit more accurate bids; and providing the specialty contractor with a viable basis of design for resolving the vertical and lateral loads streamlined the overall design development.
Access Limitations
A small elevator used to transport VIP guests between the 86th and 102nd floors provided limited access to the work zone. This dictated an 8-foot maximum member length, corresponding to the diagonal clearance inside the elevator. From the 102nd floor, all equipment and material had to be carried by hand up a ladder to the 103rd floor. A hatch at the 103rd floor provided access to the “roof” of the building, the 104th floor, where the ice shield is located. All workers at this level were harnessed and tied off to pre-existing lifeline anchors on the ice shield. Additional radiation protection was needed to ensure workers were not exposed to excess radio wave energy from the active television and radio broadcast antennas directly above.
On the 90th floor, at the base of the mooring mast spire, were four small exterior platforms reinforced by Skanska and Plan B for the previous mooring mast project. As with that project, the platforms were identified early on as the only feasible staging area for assembling the cocoon. The north side platform was eventually modified into a partially enclosed “garage” with 8-foot-tall side walls, where the cocoon modules were assembled and rigged up to the work area.
Performance Drawings
Recognizing the coordination and pricing hurdles early on, Skanska engaged Plan B to develop performance drawings. The purpose of these drawings was three-fold:
1. Provide detailed information on the temporary enclosure that was needed, including overall dimensions, work levels , site access limitations, etc., to solicit bids from specialty contractors.
2. Develop schematic level loads imposed for the vertical and lateral attachment points to begin coordination with the EOR for modifying/reinforcing the existing framing.
3. Submit to the NYC-DOB, at the time known as the Building Enforcement Safety Team (BEST), to begin the permit, site safety scopes and protection waiver (known as CCD-1) approval process.
Design Loads
A wind test was conducted by RWDI at its wind tunnel facility in Guelph, Ontario. Peak positive wind pressure was 74 psf and peak negative was -92 psf. The high strength fabric supplied by HAKI was previously tested for the TRP enclosure at Florida International University’s Wall of Wind. It was found to resist real wind speeds up to 140 mph. At the time of the project, the 2014 New York City Building Code modified the ASCE 7 wind speed up to 98 mph (ASD).
Keeping the 86th floor observation deck open to the public during the reclad project was a main priority for the owners. However, the construction variance approved by the city only applied to the completed cocoon system. This required the cocoon to be staged, assembled and then disassembled between the hours of 2 a.m. to 7 a.m. to maintain
An electric winch, dubbed “the crab,” traverses a curved W8 track to rig up modular sections of the cocoon enclosure.
public use of the observation deck during the day and evening. This required modeling the structure in various forms of incompleteness to ensure a proper envelope was developed for loads imposed and member forces.
Construction loads included two platform levels rated for 25 psf and a floor rated for 300 psf to satisfy requirements of the protection variance granted by the DOB. A 23 psf snow load (adding 22 kips to the model) was applied at the roof, and an ice analysis added another 191 kips of vertical load.
Final Concept
Greg Beeche Logistics (GBL) was chosen to furnish and install the framework of the cocoon using its own modular aluminum double
track (ADT) kit of parts developed in-house. Plan B peer-reviewed the final design package and collaborated with GBL engineers and drafters during the design development. GBL’s high level of fabrication precision allowed engineers to collaborate with drafters to identify and resolve detailing and design issues in a design-build style workflow.
Once the design was completed, Plan B led the loads-imposed review process with the Thorton Tomasetti and managed the lengthy DOB approval process. Plan B also prepared the site safety plan (SSP), which was tied directly to the previously mentioned approvals and variances.
The overall configuration of the cocoon consisted of 16 pairs (32 total) of vertical trusses, composed of ADT chords and steel HSS web members. These were assembled in modules on the 90th floor platforms and connected to brackets bolted to building columns on the 103rd floor. Each module was an 8-foot-wide structural bay consisting of two vertical trusses laced together with bolted aluminum HSS3x3 web members to form a moment frame at every other bay around the donut-shaped structure (with the center of the donut being the building itself). The vertical truss web members were optimized by location along the span to reduce weight as much as possible.
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Steel brackets on the 103rd floor were field bolted to structural columns by harnessed workers suspended from the ice shield. The brackets supported a 3D space frame composed of aluminum ADT chords and steel web members, with the top serving as a catwalk platform to provide access to tied- off workers around the exterior of the 103rd floor. The bottom of the cocoon contained another plan diaphragm and tie points to building columns to resolve wind loads. The overall assembly was considered by designers to be a hybrid frame/truss plan bracing system.
The cocoon as seen from the 86th floor observation deck is shown here. Floor 90 platforms can be seen at the base of the mooring mast.
Each module provided two 2-feet 6-inchwide work levels rated at 25 psf, using moment-framed ADT brackets. Small 2-inch to 4-inch aluminum HSS members laced the brackets together in plan to form intermediate diaphragms. Additional stiffness was provided by detailing nailers into the outriggers to fasten 0.5-inch BBOES plywood for the working deck.
A third work level was also provided at the floor of the enclosure. During the DOB approval process, the floor of the enclosure was required to be rated for 300 psf, the protection load then required for NYC sidewalk sheds for construction over 125 feet in height, under 2014 NYC Building Code. This required further customization of the ADT system for the increased load rating. The floor was custom cut to fit snug against the saw tooth profile of the mooring mast glazing.
Enclosure Walls
The exterior cladding consisted of HAKI sheeting (PVC-coated polyester fabric) with an edge termination made of Keder beading wire sewn into the fabric. The beading was slotted into matching continuous aluminum tracks, which were restrained at 12 inches o/c vertically on the outer flange of the inner ADT chord with laser cut plates. The plates worked with the vertical pins connecting the ADT truss pairs to resist the catenary thrust of the HAKI fabric under wind loading.
103rd Floor
The 103rd floor bracket, which supported 90% of the vertical loads, consisted of a combination of GBL’s modular ADT equipment and custom steel brackets. The bracket connections were bolted directly to eight existing building columns around the perimeter of the building. Although field drilling bolt holes at 1,250-plus feet is not ideal, it was considered favorable over the logistics of executing field welds and special inspections in such conditions . This led to an emphasis on bolted detailing as much as possible.
The brackets supported a space frame designed as a plan diaphragm at the roof of the cocoon. Since the cocoon had 16 vertical trusses but only eight building columns, the space frame was designed to span in two directions to deliver vertical and lateral loads directly to the building columns. As with the vertical trusses, the space frame consisted of aluminum ADT chords members and steel web members.
The top surface of the space frames created a 36-inch-wide catwalk for tied off worker access. A pair of W8x21 curved tracks sat on top of the space frame to support “the crab”—an electric winch built of ADT modules that could reach out beyond the façade. Another rail beam was underhung to the bottom of the space frame, supporting a small electric hoist used to move the new glass panels, weighing 450 pounds each, into position.
The crab’s primary purpose was to rig up modular sections of the enclosure assembled at the 90th floor exterior platforms. To ensure rigging stability, a mockup of the panels and crab was built to ensure the rigging aligned with the center of gravity of the completed module. The motorized crab could traverse along the curved W8 tracks, providing 360-degree rigging capabilities essential for the project.
Phased Construction
Once the 103rd floor brackets, space frame and crab were
installed, the 32 Alford antennas floors 102103 were removed by workers in suspended scaffold rigs. Again, the crab proved invaluable as it supplied a four-point suspended support for the work, with 360-degree access to the façade. With the antennas removed, workers were able to access I6 (I-beam, 6 inches depth) vertical mullions that framed out the observation deck to provide a lower phase 2 tie point for the cocoon.
The lower tie points (“receivers”) consisted of built-up plates clamped with custom fabricated beam clamps to the existing I6 mullions that framed out the 102nd floor observation deck immediately above. Steel HSS 3x2 ties with a hammerhead end fixture were then installed from the exterior through existing façade openings left from the Alford antennas and connected with a single .75-inch diameter bolt. These ties lateral restrained the truss modules by providing support points for a horizontal diaphragm—essentially a circular trussed compression ring. The hammerhead end fixtures on the ties created moment connections at the main node points, with pinned truss web members spanning radially between ties. The truss web members consisted of 2-inch Sch 40 pipe struts with threaded end fittings that allowed for effective field fit up.
Cocoon Modules
Modules were assembled on 90th floor garage platform by first building four separate vertical sections that were temporarily nested together within the tight confines of the 90th floor platform walls. The modules were then lifted using the crab and connected in topdown order. The modules were connected to the previously installed tie points at floor 103 via two 1-inch diameter pins and to each other via five 1-inch diameter x 24-inch long (vertically oriented) “module interface pins” to create a double spine. EPDM rubber seals were used at the gaps not filled by structure between the two spines). Once erected and tied in at floors 102 and 103, each module was a fully independent structure that was stable independent of its yetto-be installed neighboring modules.
Conclusion
This was a project where means and methods were as critical as any facet of the new design. A collaborative effort allowed for the seamless removal of existing finishes, the installation of new glass panels and the dismantling of the cocoon from above—all while keeping the 86th floor observation deck operational throughout the project.
The enclosure set an early precedent that paved the way for the Engineered Enclosure System (EES) provisions now in the 2022 New York City Building Code. This system has quickly gained popularity as a strategy to minimize intrusive adjacent property protections. ■
Robert Belardi, PE, is a 2011 Drexel University graduate in architectural engineering and a graduate of the SAHC program in Universidade do Minho, Portugal. He has worked at Plan B Engineering a decade, designing a wide range of access and stabilization systems for new and historic constructions.
A compression ring with adjustable web members on Floor 102 was part of the phased construction.
Architectural Precast Concrete Facade
The coordination between design and construction professionals stands as a cornerstone of successful facade design and construction at the Studio Museum in Harlem.
By Alexander Stephani, PE, Filippo Masetti, and Kevin Poulin
The post-modern architecture of the new Studio Museum in Harlem is both imposing and grand. Its modulated precast concrete facades are interspersed with sleek, curtainwall glazing. The intriguing exterior is designed to pique the interest of visitors, beckoning them to enter and discover the museum’s collection, as well as its artists in residence (Figs. 1 and 2).
The building is a six-story steel structure supported on a con crete mat foundation and clad with architectural precast concrete panels of different sizes and shapes. The building was designed by Adjaye Associates in collaboration with Cooper Robertson. Simpson Gumpertz and Heger Associates Inc., P.C. (SGH) was the Structural Engineer of Record, and they collaborated with consulting engineer Guy Nordenson and Associates (GNA). Sciame Construction was the general contractor, and Beton Prefabrique du Lac (BPDL) was the fabricator and specialty structural engineer for architectural precast panels. The design and construction of the intricate precast concrete facade required significant attention and extensive collaboration among the project team members.
Design Process
A typical precast concrete facade includes several components, and their design is usually shared between the design team (owner, engineer of record (EOR), and architect) and the construction team (general contractor, specialty structural engineer (SSE), and precast fabricator).
This article focuses on the challenge of connecting the large precast panels of varying geometries to the steel superstructure, while controlling both vertical and lateral deflections, so that the size of the panel joints are minimized.
In addition, the design of architectural precast facades is typically iterative and often includes the following steps:
• Determine panel sizes, shapes, and locations.
• Establish required joint sizes and corresponding deflection criteria.
• Design spandrel framing.
Fig. 1. The Studio Museum Harlem's facade on West 125th Street.
• Determine lateral drifts of overall building under wind and seismic loading.
• Complete preliminary design of panels, including connections embedded into the panels and connections that bridge from the panels to the base building structure.
• Analyze joint sizes.
• Iterate until results are satisfactory.
While facade connections are a crucial component of a building’s load path, they are often delegated to specialty structural engineers, leading to potential coordination challenges. Industry resources, including the Architectural Precast Concrete Manual (MNL-122) from the Precast/ Prestressed Concrete Institute (PCI), PCI Design Handbook (MNL120), and American Institute of Steel Construction (AISC) Design Guide 22: Facade Attachments to Steel-Framed Buildings, emphasize the paramount importance of coordination between the design team and the construction team. These documents stress the responsibility of the design team to provide clear guidance, delineate design responsibilities, and review subcontractor submissions carefully.
For example, AISC Code of Standard Practice recognizes that the delineation of responsibilities between EOR and SSE remains a challenge, particularly at connection points where facade components interface with the primary structure. Furthermore, because of myriad options for design delegation, the coordination and communication between design and construction teams is essential. By addressing potential areas of contention, design and construction teams can mitigate risks and ensure alignment with project requirements.
Cognizant of the coordination challenges of a complicated precast facade, the entire project team of the Studio Museum in Harlem began design coordination early in the project. Specifically, the owner engaged
the precast manufacturer to participate in a design-assist exercise right after the completion of the construction documents. During this designassist phase, the design team and the precast facade manufacturer selected a portion of the north elevation to develop typical connection details to be used throughout the facade. The intent was to complete the collaborative and iterative design process on a limited number of connections and identify the “typical” issues that would be expected during the coordination for the remainder of the connections. This exercise also included the fabrication of a full-scale mockup of a section of the facade. This mockup was invaluable, as it allowed the project team to evaluate the facade design and to finalize decisions related to color, aggregate size, panel geometry, and panel joints. From the mockup, we refined the joint analysis and designed portions of the connections bridging the panels and the base building structure. After the mockup, the project team realized that the project would not feature “typical” connections because of limitations on the size of the panels, complicated geometry of the facade, and interior architectural constraints. The final design would include more than 200 different connections of the panels to the base building structure.
Joint Analysis
Precast facades usually consist of individual panel elements connected to the building's structural framing. The gaps between the panels (joints) are often filled with sealant to provide a weatherproof barrier and to accommodate the anticipated movement of the structure without panels bearing on each other and creating unintended load paths. For the Studio Museum in Harlem, the design objective was to maintain joint sizes no larger than 3/4 inch and to align the precast joints with the curtain wall glazing joints and with joints in interior finishes. This alignment aimed for uniformity and harmony between the facade lines and interior spaces. Conventional sealants typically allow for a maximum movement of 50% from the average joint size. Therefore, the typical sealant in a 3/4 inch joint can expand up to 1 1/8 inch and compress down to 3/8 inch without failing.
Despite the original target for joint size appearing manageable, achieving this target posed significant challenges in the design of the base-building structure. The architecture required large open gallery spaces, resulting in spans of 50 feet for several composite steel beams supporting the facade panels. While building codes allow for a maximum live load deflection of L/360 for beams (which exceeds 1 5/8 inch over a span of 50 feet), this large vertical deflection significantly impacted the joint size. Therefore, the team engaged in precise modeling of individual panels and their connections along the spandrel beams to focus on the expected gravity deflections of the base building structure, facade movement, and ultimately joint size (Fig. 3). After the completion of the gravity analysis for the preliminary sizing of the joints, the same modeling approach also allowed the design team to confirm the adequacy of the preliminary joint size for the building’s expected lateral drifts.
Fig. 2. The Studio Museum Harlem's facade on West 124th Street.
Fig. 3. The effect of spandrel deflection on a panel joint is sketched out.
Construction sequencing also played a pivotal role in the joint size analysis. Depending on the construction sequence, deflections from the self-weight of the structure , the self-weight of the facade, superimposed loads from components other than the facade, live loads, snow loads, wind loads, seismic loads, and rain loads needed careful consideration. Given the ability to shim, level, and plumb the facade panels relatively independently of the supporting structure, the joint analysis could solely focus on the expected deflections occurring after the installation and shimming of the panels. As such, the joint analysis did not need to account for the deflections associated with the self-weight of the structure and the facade panels. Finally, the joints were sealed after all the other permanent deflections had taken place (e.g., associated with superimposed dead loads of other building components). In the end, after extensive work and several design iterations, the project team met the general architectural vision of 3/4-inch-sized joints at most locations, except a few panels featuring extreme geometry.
Precast Connection Design
Typically, precast panels are designed to be statically determinate, with few connections per panel. Common types of precast connections include gravity and lateral connections. Gravity connections usually consist of concrete shear keys or embedded steel angles/plates protruding from the back of the precast panel. These protrusions normally bear on and are connected to steel spandrel beams or concrete slabs. As precast connections often introduce eccentricities, the overturning from gravity loads is typically resisted by lateral connections.
At the Studio Museum in Harlem, the gravity connections are constructed from hollow structural section (HSS) steel tube framing connected to the spandrel beams. The lateral connections are adjustable in two directions and constructed from threaded rods in vertically slotted tracks that are embedded into the precast panel and connected to steel channels or angles with horizontally slotted holes. The channel or angles are then welded to the spandrel beams, which are, in turn, connected to the concrete diaphragm by shear studs (Figs. 4 and 5). During the joint analysis, the project team spent significant time locating precast connection points to also avoid interference with curtain wall connections, mechanical, electrical, and plumbing (MEP) systems, and architectural features.
The Studio Museum's articulated facade required unconventional approaches to connection design to support the intricate reveals and soffits in the limited space available. In specific scenarios, substantial box-shaped precast panels positioned below floor levels prompted the
Fig. 4. Precast support details shown for lateral (left) and gravity (right) connections.
Fig. 5. Typical precast facade connections to base building structure. (Lateral type is on the left, and gravity is on the right.)
Fig. 6. Details (top) and photo shown are of an underslung beam for a precast panel connection.
implementation of underslung outriggers to support the gravity connections. These outriggers are designed to attach beneath the structural steel framing while seamlessly integrating into the architectural ceiling space, preserving programming integrity (Fig. 6).
In other scenarios, where spatial constraints are imposed both above the slab (e.g., for architectural programming) and below the slab (e.g., for facade soffits), the project team needed to conceive alternative connection designs. This design includes HSS tubes strategically positioned within the slab's depth, connected to the top of the floor framing, and horizontally extending out to support the panels (Fig. 7). Given the geometrical constraints and the strength and stiffness requirements, the project team considered the novel solution of HSS in-slab supports. Where spatial constraints due to panel geometry were such that the direct extension of outriggers was not feasible, the project team needed another creative connection. This time, the approach includes “kinked” HSS tubes, custom-designed to fit within the slab depth and curb width (Fig. 8).
Conclusion
The coordination between design and construction professionals stands as a cornerstone of a successful facade design and construction, as it did for the Studio Museum in Harlem. By adhering to industry standards, clarifying design responsibilities, and fostering effective communication, design and construction teams can navigate the complexities of facade construction with confidence and precision. After countless hours, extensive coordination, and exceptional dedication, the Studio Museum in Harlem’s team achieved the vision of creating an iconic precast concrete facade worthy of the newly constructed architectural marvel. ■
Alexander Stephani, PE, is a Structural Engineer with Simpson Gumpertz & Heger (SGH), specializing in new design, repair and rehabilitation, and flood resiliency design.
Filippo Masetti, PE, is an Associate Principal at Simpson Gumpertz & Heger Inc. (SGH), specializing in the assessment, repair, and rehabilitation of existing structures, as well as in the evaluation of unusual detailing in ground-up construction.
Kevin Poulin, PE, is a Principal at Simpson Gumpertz & Heger Inc. (SGH), specializing in the restoration and the adaptive reuse of existing buildings, as well as the design of new spaces for arts and culture.
Fig. 7. Details (top) and photo (above) depict HSS outriggers within slab depth.
Fig. 8. An HSS kinked beam is shown in detail and image.
Sentry Bridge at Watkins Glen State Park to be Upgraded
The New York State Office of Parks, Recreation and Historic Preservation (OPRHP) has revealed the design of a new signature footbridge at the entrance of Watkins Glen State Park. Designed by a team led by the New York-based studios of schlaich bergermann partner (sbp) and Snøhetta, the new Sentry Bridge will replace a historic concrete arch structure with stone veneer cladding created in 1908. It will be the most recent structure in a century-long tradition of pedestrian bridges, tunnels, trails, and lookouts along the popular, waterfall-filled Gorge Trail.
The new Sentry Bridge design is a lightweight evolution of the former arch bridge. The stronger rock of the gorge’s north side will support its stainless-steel structure as it spans across the gorge with a total length of 46 feet, creating a new durable emblem for the park. Alluding to the curved form of the previous bridge, the halfarch design disappears behind the rocks, leading visitors into the park’s mystical Gorge Trail that lies beyond.
Although the existing bridge has become a symbol of the park, time and harsh weather have worn away its supporting abutments; a 2022 inspection of the Sentry Bridge found that erosion at the stone abutments had significantly compromised its structural integrity. After carefully studying the site conditions with the design
team, OPRHP determined that a full replacement of the Sentry Bridge was needed to address the unstable rock conditions within the gorge. Given the poor condition of the southern abutment, it was important to find a solution where more of the bridge’s load could be carried by the more stable northern abutment. Under normal conditions, the bridge is designed as a single-span girder supported by both abutments. However, in the case of a failure at the southern abutment, the bridge can act as a cantilever, supporting itself solely on the north abutment. The site and user circulation will also be enhanced with a renovation of the north tunnel that leads to the bridge and the spiral tunnel located further down the trail, a reconfiguration of the bridge’s southern landing, and a new, indirect lighting design to highlight the bridge’s silhouette.
Construction sequencing for the bridge was also considered early in the design process due to the bridge’s difficult to access location. The bridge will be fabricated entirely off site and lifted into place in one piece, allowing for a shorter construction duration and less disturbance to the ecologically sensitive site.
Demolition of the existing bridge and construction of the new Sentry Bridge will commence in the summer of 2025, with opening of the bridge anticipated prior to July 4, 2026. ■
Hampden-Sydney College Gives 19th
Century Gem a 21st Century Restoration
On October 24, Hampden-Sydney College in Virginia held the rededication of Venable Hall. The second-oldest building on the campus, Venable is an architectural and engineering treasure constructed by Jeffersonian-trained masons and enslaved labor between 1824 and 1831. Built in two phases, the building comprises a unique timeline of the architectural and engineering advances that occurred in the eight-year span between the beginning of phase one and phase two of Venable’s construction. The east end of the building, known as Stagger Inn, is constructed of roughly hewn, handmade bricks with wide masonry joints with an oxide stain and white pencil lines to give the appearance of straightness and uniformity and hand-made nails in the original heart pine floors evoking a truly Colonial feel. The center and western portions, known as Tortilla and West End respectively, feature refined bricks uniform in color and shape, thinner joints, and machine-pressed nails. The Schoelkopf Parents and Friends Lounge, situated in West End, is a two-story, 40 feet by 40 feet room with a double corridor and student rooms on top of it, requiring an impressive feat of engineering for the time to make structurally sound then and for the 200 years in which it’s been in use. ■
Hampden-Sydney President Larry Stimpert addresses the attendees of the rededication of Venable Hall in the Schoellkopf Family and Friends Lounge.
The half-arch design of the new bridge alludes to the curved form of the previous bridge.
Photo by Zach Bettis
High Attendance, Inspiring Moments Define the 2024 NCSEA Structural Engineering Summit
The 2024 NCSEA Structural Engineering Summit drew more than 1,000 attendees to Las Vegas from November 5-8, marking another successful gathering for the structural engineering community. This year’s event delivered a dynamic blend of education, networking, exhibits, and celebrations, creating an inspiring experience for all participants.
The Summit featured powerful keynote presentations that captivated attendees, including Glenn R. Bell’s insights on the Champlain Towers South partial collapse investigation, KP Reddy’s panel discussion on AI’s impact on the profession, and Henna Pryor’s energizing session on embracing individual strengths.
The exhibit hall was bustling with innovative displays, offering hands-on experiences with the latest tools, technologies, and services shaping the industry. Attendees also had the opportunity to earn Professional Development Hours (PDHs) through a broad range of educational sessions exploring the newest advancements and strategies in structural engineering.
This year’s event also celebrated the profession’s best and brightest, with recognition of the 2024 SEE Award winners, along with NCSEA Special Awards, Young Member Group Scholarships, and Diversity
With this success, NCSEA is already gearing up for next year’s Summit in New York City, scheduled for October 14-17, 2025. We look forward to another opportunity to connect, learn, and advance
Summit attendees stop by exhibitor booths between education sessions in Las Vegas this November.
The NCSEA Summit closed with a keynote presentation from Glenn Bell on the NIST’s National Construction Safety Team’s investigation of the Champlain Towers South Partial Collapse.
Announcing the 2025 Structural Engineering Executive Retreat
NCSEA is excited to announce the 2025 Structural Engineering Executive Retreat, designed exclusively for firm leaders looking to gain fresh business insights and elevate their companies. Held at the luxurious Solage Auberge Resort in Napa Valley, this three-day event offers a unique opportunity to focus on strategic growth, leadership development, and future-proofing your firm.
Through interactive sessions and discussions with industry experts and fellow executives, attendees will explore practical strategies to ensure long-term growth, improve firm performance, and strengthen leadership skills. It’s the perfect setting to step beyond daily demands, share ideas, shape a forward-looking vision, and return with actionable insights to guide your firm into the future.
The 2025 Structural Engineering Executive Retreat is March 5-7. Space is limited—secure your spot at www.ncsea.com.
NCSEA Launches SE GPT, a Free AIPowered Tool for Structural Engineers
NCSEA is proud to announce the launch of SE GPT, a groundbreaking, free application designed to provide structural engineers with quick and reliable access to essential information.
Powered by a closed GPT database, SE GPT delivers automatically generated responses based on content curated specifically for the structural engineering profession. The tool draws from trusted resources, including transcripts of NCSEA webinars, an extensive archive of STRUCTURE magazine articles, and additional materials
provided by vetted professionals and organizations supporting structural engineering. Engineers can access SE GPT to streamline research, enhance project efficiency, and stay up-to-date with the latest insights from across the profession—all in one convenient platform. For more information and to start using SE GPT visit www.ncsea.com or launch the website directly at https://gpt-ncsea.amatrium.com.
NCSEA Foundation Awards SEA Grants to Support Structural Engineering Initiatives
The National Council of Structural Engineers Associations (NCSEA) Foundation is pleased to announce the recipients of its 2024 SEA Grants. This year, $10,000 in grant funding will support six Structural Engineers Associations (SEAs) in launching or enhancing initiatives that advance the structural engineering profession.
The SEA Grant Program, funded by the NCSEA Foundation, assists SEAs in expanding their reach through innovative initiatives. The grants provide crucial support for programs that align with the Foundation’s mission of advancing the science and practice of structural engineering.
This year’s grant recipients and their projects are:
• SEANM (New Mexico): SEANM Volunteer Mentoring Program
• SEAC (Colorado): Mental Health Workshop for Firm Leadership
• SEAoT (Texas): Developing Two Student Chapters
• SEAWI (Wisconsin): Young Member Group Support
• SEAOSD (San Diego): Seismic Outreach Program
• SEAOSC (Southern California): Student Member to Active Member Conversion
Each SEA will receive funding ranging from $1,000 to $2,500 to support the development and implementation of their projects. Grant applications were evaluated by a subcommittee of the NCSEA Foundation Board of Directors. Final selections were approved by the full Foundation Board. For more information about the SEA Grant Program or the NCSEA Foundation, visit www.ncsea.com/foundation.
SEI Update
CROSS-US
Mark Your Calendars: First Structural Engineering
Sustainability Symposium in North America
On Feb. 5, 2025, we invite you to attend a free, virtual, half-day event to discuss practical steps that can be taken immediately to meaningfully reduce the carbon impacts of the built environment. An aspirational and practical conversation with structural engineers, carbon and climate experts, and industry advocates – the symposium will go beyond Sustainability 101 and feature lessons learned, best practices, and case studies as well as SEI resources. Discussions will include demystifying LCA, smart material procurement, circular construction successes, and more. Join us to gain practical strategies that can be implemented today wherever you are in your sustainability expertise journey! Sign up to learn more: asceforms.wufoo. com/forms/seistructural-engineering-sustainability-symposium/.
The Collaborative Reporting for Safer Structures US (CROSS-US) System has identified the following industry trends/ concerns regarding Concrete based upon provided reporting from within the U.S. as well as its from partners in the United Kingdom (CROSS-UK) and Australia (CROSS-AUS)]:
• sufficiency of finite element modeling of masonry walls within concrete framed buildings.
• underestimation of bending moments in perimeter columns.
• 2D finite element modeling of pile caps; structural resonance within building floors of commercial gyms.
• improper modeling of concrete frame buildings for analysis during construction. The above listed items indicate that postdesign evaluation and performance of structural systems have identified that current structural design modeling programs and methods for concrete and masonry may fail to accurately identify/predict loading requirements. Additionally, reviews have identified concerns regarding structural failures of falsework and/or formwork during construction and corrosion related to existing bridge elements. To read more about these topics, access published newsletters and safety reports as well as learn about the reporting process, please visit https://www.cross-safety.org/us.
CROSS US is also seeking passionate professionals to collaborate on our mission by serving as Members or Corresponding Members on one of our three subcommittees. Apply here: go.asce.org/applycrossus.
SEI Performance Based Design Committee is seeking new members. The committee is charged to pursue and advance performance-based principles along with engaging, educating and encouraging stakeholders to adopt these principles. Apply to this committee: go.asce.org/sei-committees.
News of the Structural Engineering Institute of ASCE
SEI Futures Fund
Consider donating to the SEI Futures Fund to make a lasting impact on the careers of aspiring engineers. Your support helps provide valuable opportunities like the ones shared by past scholarship recipients:
Learn more about the fund and donate: go.asce.org/seifuturesfund
Calling All Young Professionals and Students
Don’t miss your chance to apply for the prestigious Structures Congress Scholarships! Current SEI membership is required for all scholarships.
SEI Student Scholarship: This scholarship supports full-time undergraduate or graduate students in civil engineering or related fields, providing the opportunity to attend Structures Congress. First-time Structures Congress attendees only.
SEI Young Professional Scholarship: This scholarship promotes active engagement with SEI for young professionals (35 and under) in industry or academia. Additionally, up to five scholarships are available for full-time teaching faculty up to age 40. Eligibility requirements include a one-time award limit per recipient, and the scholarship is not open to students.
SEI Future Leader Scholarship: Supporting both students and young professionals, this scholarship develops leadership and technical communication skills through mentorship and participation in the “Meet the Future of Structural Engineering” session at Structures Congress. You are reliable if you are Interested in presenting at the session. Preference given to previous scholarship recipients or past Structures Congress attendees. Recipients are paired with SEI mentors for presentation preparation and networking
Deadline to apply for scholarships: January 3, 2025. Apply: www.structurescongress.org/program/scholarships
CASE in Point
ACEC Winter Coalition Meeting
February 25-26, 2025
Phoenix, AZ
Hyatt Regency Phoenix
122 N 2nd St, Phoenix, AZ 85004
The 2025 Coalitions Winter Meeting brings together ACEC’s coalition members to discuss strategic initiatives and industry challenges for the year ahead. This year’s Winter Meeting will highlight sustainability efforts and the industry and is a change for the CASE Executive Committee (ExCom) and its subcommittees to work on this year’s publication and education initiatives for CASE members. This gathering provides a valuable opportunity for coalition leaders and attendees to collaborate on solutions impacting the engineering profession.
The ACEC Winter Coalition Meeting is open to everyone. To register for this event Register at www.acec.org/education-events/events/ coalitions-winter-meeting/.
Navigating BIM and Digital Twins: Standards, Reality Capture, Existing Conditions and Collaboration Across the Lifecycle, presented by ACEC’s
Coalition of Professional Surveyors (COPS)and USIBD
This education session on BIM is hosted by the ACEC COPS Coalition and USIBD will focus on standardizing and optimizing building documentation practices across project stages, from design to completion. The session will address developing best practices, ensuring highquality documentation, maintaining ethical standards, and supporting the collaboration between professionals like architects, engineers, and surveyors. The session is a must for professionals seeking to enhance documentation quality, efficiency, and cross-team coordination. For more on USIBD’s mission, visit https://usibd.org/about-us/.
Special Congratulations to our 2024 Scholarship Winner: Alyson McGuire
Alyson McGuire attends George Mason University and was granted $6,500 CASE Scholarship to further her career in Structural Engineering. Support the Future of Structural Engineering: Donate to the CASE Scholarship Fund
The CASE Scholarship Fund is more than just financial support; it’s an investment in the next generation of structural engineers who will shape the built environment and drive innovation forward. Each year, CASE provides scholarships to dedicated students working toward a career in engineering, empowering them to pursue their education and make meaningful contributions to the industry.
Your donation—no matter the amount—can have a lasting impact. It helps cover tuition, supports students’ access to critical resources, and ultimately brings talented, enthusiastic new professionals into the field. Let’s ensure that financial barriers don’t stand in the way of their potential.
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News of the Coalition of American Structural Engineers
CASE Publications
Be sure to explore the latest CASE publications. If you’re not a CASE member, don’t forget to use your discount code, NCSEASEI2022, to save on your purchase.
(Newly Added!) Tool 4-8: Email Best Practices
Clear and descriptive subject lines are essential for effective email communication. Conciseness and directness enhance readability, making short paragraphs and bullet points valuable tools. Personalization and specific calls to action can significantly improve engagement, while proofreading ensures professionalism.
Tool 2-8: Making Remote Work
Flexible work schedules and remote work options have become a top priority for employees today. Many companies are adapting to this shift and seeking long-term solutions, particularly in structural engineering, where finding qualified candidates is becoming more difficult. By expanding candidate pools beyond local offices, companies can attract quality hires. However, this shift also presents challenges related to business operations, insurance, IT and security, productivity, training, and company culture. Tool 2-8 provides guidance on navigating these challenges effectively
Tool 3-7: Succession Planning
Succession planning is a key aspect of talent management. It includes training, career planning, and replacement strategies. Effective succession planning helps organizations manage talent scarcity, identify skill gaps, promote knowledge transfer, boost employee morale, and build a robust skill set.
Tool 5-7: Best Practices for Analysis and Design Software
This tool provides guidelines for verifying analysis and design software results, focusing on linear elastic structures and small deformation/ small strain analysis, which are prevalent in design work.
White Paper: Teaming Agreements
Teaming agreements are essential for joint projects between contractors, design professionals, and structural engineers. These agreements outline the roles of parties before contract award and are often used in design-build projects. This commentary reviews standard teaming agreements from various organizations, including:
• AIA: Contract C102-2015
• EJCDC: Contracts D-580 and E-580
• DBIA: Contract No. 580
• Consensus Docs: Contracts 296 and 498
You can purchase these and other CASE Publications at CASE Resources www.acec.org/member-center/get-involved/coalitions/case/resources/
If you have suggestions for tools that could benefit your business, CASE welcomes your input. Contact coalitions@acec.org.
business PRACTICES
The Arizona Board of Technical Registration Sunset Debacle
By Carl Josephson, PE, SE
On June 14, 2024, one day before the Arizona legislature was scheduled to adjourn, Arizona House Bill 2091 passed, and the Arizona Board of Technical Registration (AZBTR or the Board) was continued for another six years and is now scheduled to terminate on July 1, 2030. However, the Board is now only allowed to investigate and take disciplinary or enforcement action resulting from a complaint if the complainant either: 1) has or had a contractual relations with the person who is the subject of the complaint at the time of the complaint, or 2) was harmed by the alleged misconduct or witnessed the outcome of the misconduct during the course of that person’s contractual duties with complainants.
How did the AZBTR get into this situation? What is the significance? Does this truly protect the public from incompetent or negligent practice? What can we learn from Arizona’s experience, and how can we avoid it?
The Arizona State Board of Registration was established in 1921, and in 1936, it became the Board of Technical Registration. The AZBTR, which is made up of 11 members (five professionals and six public members, all appointed by the Governor), regulates the professions of architecture, engineering, land surveying, landscape architecture, geology, home inspection, and the alarm industry.
Sunset Review and Legislation
The last Sunset Review of the AZBTR took place in 2016, and the board was continued until July 1, 2024. In 2023, the AZBTR prepared its response to the most recent Sunset Audit—a 49-page document that is available online. House Bill 2253 was introduced in January 2024 that would have simply continued the AZBTR for eight years until July 1, 2032. The bill passed easily through the House Commerce Committee and was passed by the House with a vote of 46-10.
In February, the bill continued on to the Senate and was sent to the Senate Government Committee of Reference, which refused to agendize it. On March 21, 2024, the Senate Government Committee proposed a “striker bill,” HB 2632, that would have continued the board for only two years and would have stripped it of its ability to discipline many of its registrants. On May 14, 2024, an amendment to HB 2632 was introduced that would have continued the board for eight years without the proposed changes, but it failed. The Arizona Legislature was scheduled to adjourn on June 15, 2024, and it was too late to introduce new legislation. At that point, the Arizona BTR was scheduled to end on July 1, 2024. Republican members of the Government Senate Committee said the Board was too heavyhanded and believed that online reviews such as Yelp or Google would be adequate enough for consumers to decide if a professional was trustworthy.
On June 14, one day before the Arizona legislature adjourned, a floor amendment to HB 2091 was passed to continue the AZBTR for six years not eight, with the restrictions mentioned at the beginning of this article. The bill was transmitted to the House and then to the Governor, who signed it on June 18, 2024.
Politics at Play
The balance between Democrats and Republicans in the Arizona legislature is on a razor’s edge with Republicans holding a majority in both chambers while the Arizona Governor is a Democrat. The Freedom Caucus is the leading group in Republican politics in Arizona. The Senate has not been confirming many of the Governor’s appointments, creating a tense, acrimonious, and litigious atmosphere. Further complicating matters, the husband of one of the members of the Senate Government Committee is a home inspector who ran afoul of the AZBTR and received a letter of reprimand in January 2024. Also, the chair of the Senate Government Committee is under indictment for his participation in Arizona’s “fake electors” scheme.
What Would Have Happened If the Board “Sunset”?
Ending the board would have thrown the design and construction industry, if not the Arizona economy, into complete disarray. According to AZBTR staff, if the board were to have dissolved, all licenses would have become null and void, expired or not. It would not have been possible for Arizona engineers to transmit their Arizona records to other states and to get licensed in other states by reciprocity. There would have been no enforcement for unlicensed practice, and there would have been no investigation or disciplinary or enforcement actions taken against negligent or incompetent practice.
Most practicing professionals were not aware that this drama was playing out in Arizona at the time. The refusal to agendize the continuation bill came with little notice or fanfare. The proposal to make it more difficult for the Board to investigate, discipline, or take enforcement actions was not subject to any hearings or public review. This flurry of activity and legislation all came at the last minute. By the time SEI/ASCE, NCSEA, and CASE/ACEC were put on notice and began to respond, the die was cast, and the resulting legislation had already been approved. Enforcement is now limited because of who is allowed to make a complaint. The AZBTR is still trying to interpret the meaning of the new language in the law.
What Can We Do to Avoid This in the Future?
Our legislative committees need to be active and nimble in states as well as at a national level. We need members to be familiar with and known by their local representatives. We need to let our representatives know how important it is to ensure we have qualified and ethical licensees; when they are not, they need to be reprimanded and disciplined. We need experienced and responsible members to take the time and effort to serve on their licensing boards. Ideally, and as difficult as it may be for us to imagine, we need to elect engineers to serve in our legislatures. ■
Carl Josephson, PE, SE is a Senior Principal with Josephson-Werdowatz & Associates in San Diego and is the Chair of the Structural Engineering Licensure Coalition. www.selicensure.org
