STRUCTURE magazine | February 2023

STRUCTURE

INSIDE: Speed Core 2.0

Chicago Gateway Engineering Lightness

TSX Magic on Broadway

ADVERTISER INDEX

American Concrete Institute

Anthony

Atlas Tube

Bull Moose

ENERCALC

Chicago Clamp Co

Clark Dietrich Building Systems

CSI Computers & Structures Inc

IDEA StatiCa

NCEES

New Millennium Nucor

Max USA Corp

Simpson Strong-Tie

Please support these advertisers

STRUCTURE

CIRCULATION

subscriptions@structuremag.org

EDITORIAL BOARD

Chair John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA chair@STRUCTUREmag.org

Trimble Tekla Williams Form Engineering

Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT

Erin Conaway, P.E. AISC, Littleton, CO

Linda M. Kaplan, P.E. Pennoni, Pittsburgh, PA

Charles “Chuck” F. King, P.E. Urban Engineers of New York, New York, NY

Nicholas Lang, P.E. Masonry Industry Representative

Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY

Jason McCool, P.E. Robbins Engineering Consultants, Little Rock, AR

Brian W. Miller Davis, CA

Evans Mountzouris, P.E. Retired, Milford, CT

John “Buddy” Showalter, P.E. International Code Council, Washington, DC

Eytan Solomon, P.E., LEED AP Silman, New York, NY

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

EDITORIAL STAFF

Executive Editor Alfred Spada aspada@ncsea.com

Production

production@structuremag.org

MARKETING & ADVERTISING SALES

Director for Sales, Marketing & Business Development

Monica Shripka Tel: 773-974-6561 monica.shripka@STRUCTUREmag.org

STRUCTURE ® magazine (ISSN 1536 4283) is published monthly by The National Council of Structural Engineers Associations (a nonprofit Association), 20 N. Wacker Drive, Suite 750, Chicago, IL 60606 312.649.4600. Periodical postage paid at Chicago, Il, and at additional mailing offices. STRUCTURE magazine, Volume 30, Number 2, © 2023 by The National Council of Structural Engineers Associations, all rights reserved. Subscription services, back issues and subscription information tel: 312-649-4600, or write to STRUCTURE magazine Circulation, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606.The publication is distributed to members of The National Council of Structural Engineers Associations through a resolution to its bylaws, and to members of CASE and SEI paid by each organization as nominal price subscription for its members as a benefit of their membership. Yearly Subscription in USA $75; $40 For Students; Canada $90; $60 for Canadian Students; Foreign $135, $90 for foreign students. Editorial Office: Send editorial mail to: STRUCTURE magazine, Attn: Editorial, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606. POSTMASTER: Send Address changes to STRUCTURE magazine, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606.

STRUCTURE is a registered trademark of the National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

Contents

FEBRUARY 2023

Cover Feature 200 PARK AVENUE SPEEDCORE 2.0 FROM THREE PERSPECTIVES

By Ron Klemencic, P.E., S.E., Hon. AIA, Casey Kraning, Casey Wend, Kevin Englund, Chris Grimmer, and Mike Mills

The structural engineer, the developer, and the construction firm relate their experiences building California’s first SpeedCore tower.

Features

FUNCTIONALITY AND FLEXIBILITY KEY TO NEW CHICAGO GATEWAY

By Jennifer Drake, P.E., S.E.

In 2016, the Chicago Department of Aviation (CDA) recognized that Midway International Airport (MDW) required expansion. Since September 11, 2001, the original narrow walkway connecting the landside and airside terminals over a major arterial street/ state highway was unable to meet enhanced security requirements.

ENGINEERING LIGHTNESS

By Thorsten Helbig, Dipl.-Ing., and Florian Meier, M.S., P.E.

The new Academy Museum of Motion Pictures (AMMP) is now the world’s premier museum and event space devoted to the motion picture industry, celebrating the artistry and technology of film.

TSX MAGIC ON BROADWAY IN TIMES SQUARE

By Cawsie Jijina, P.E., and J. Benjamin Alper, P.E., S.E.

Times Square in New York is known for many things, including its Broadway Theaters, luxurious hotels, trendy retail, great entertainment venues, and flashy billboards. In the case of TSX Broadway (1568 Broadway), the project contains all these items in one building

WHY VIRTUAL DESIGN AND CONSTRUCTION IS THE FUTURE OF BUILDING

By Michael Schroeder, CCM

Columns and Departments

7 Editorial The Value of Participation

By Jeannette Torrents, PE, SE, F.SEI, LEED AP.

8 Structural Influencers David Cocke, S.E.

12 Engineers Notebook Commonly Misapplied Welding Symbols

By Jason McCool, P.E.

24 Structural Design Shipping Container Design

By Nabil (Bill) Taha, Ph.D., P.E.

32 In Focus

If there is an Engineer Shor tage, What Caused It?

By John A. Dal Pino, S.E.

36 Structural Performance Architectural Experiments with Foldable Composites

By Joseph Choma

40 Structural Specifications What's New Under the Sun?

By Nestor A. Agbayani, P.E., S.E., M.ASCE, Steven M. Gartner, P.E., M.ASCE, and Alexander E. Coologeorgen, P.E., PMP, M.ASCE

50 Iconic Structures

Houston Astrodome, The Eighth Wonder of the World

By Narendra K. Gosain, PhD., P.E.

54 Construction Issues

Off-site Construction

By Nabil Rahman, Ph.D., P.E., Kirsten Zeydel, S.E., and Andrew Newland, P.E.

58 Historic Structures

Wabasha Street Bridge, St. Paul, Minnesota, 1859

By

Frank Griggs, Jr., Dist. M.ASCE, D.Eng, P.E., P.L.S.

66 Business Practices Creating a Culture of Accountability Within Your Company

By Dr. Tricia Groff, Ph.D.

In Every Issue

Advertiser Index

Resource Guide - Bridge

NCSEA News

SEI Update CASE in Point

Digital

Available Only at STRUCTUREmag.org

The Value of Participation

By Jeannette Torrents, PE, SE, F.SEI, LEED AP

Congratulations! The fact that you’re reading STRUCTURE means that you’re already a member of a structural engineering organization (CASE, NCSEA or SEI). But are you really getting your money’s worth? If you’re not actively involved, you’re not truly leveraging the value of your membership.

“Why do you see serial volunteers within our structural engineering organizations? Because they’ve unlocked the power of participation and the benefits that come along with it.”

In 2014, the Harvard Business Review published an article about the power of participation. The impact and influence you can have when leveraging the power of a group is exponentially greater than that you can achieve on your own. As a member of a committee, your words have a different gravitas when trying to convince an AHJ to amend a code provision. When structural engineers go beyond the passive consumption of ideas to actively sharing content, then adapting content, then creating or delivering content, and finally co-owning content, they progress along the participation power scale from simply keeping up with the profession to shaping the profession.

You’ll find that heavily involved people invariably say that they’ve received much more from their organization than they’ve put into it. What is it that they’re receiving? The list could include:

• A network of structural engineers with access to peer sounding boards, mentors, technical experts, thought partners, and many times new friendships

• An opportunity to advance their careers by practicing soft skills such as public speaking, teamwork, and leadership

• Visibility that helps their firm with recruitment, retention, and reputation

• The personal satisfaction of positively impacting our profession Becoming involved in advancing our profession recenters you and reminds you why you entered this profession in the first place – it removes you from the daily grind for a moment and brings more purpose to your daily activities. Becoming active in your structural engineering organization is a unique opportunity because it allows you to spend time on things that are in service to yourself such as cultivating your interests, building relationships and skills that will help advance your career, and serving your personal purpose all under the umbrella of your day job.

Why does serving your personal purpose matter? As we come out of the pandemic, the focus has shifted from work-life balance to work-life enrichment. Studies show that when employees feel connected to a greater purpose in their work, it not only improves their productivity, but also positively impacts their ability to think clearly and to make decisions efficiently and effectively. Engaging in meaningful work can lead to increased job satisfaction which in turn can help you feel more energized and be more resilient to job-related stress and setbacks, positively impacting your health and life outside of work. How to get started? Reach out to someone who is already involved and ask about opportunities. Where does the organization need help? How do your personal interests align with the mission of the organization? If a prolonged commitment seems insurmountable – sign up to help with a discreet initiative such as a mentoring roundtable at your local university or a job site tour. If you can’t find the right fit

at the local level, consider serving on a national committee. CASE, SEI, and NCSEA all have volunteer opportunities available where you can help advance the objectives of their Joint Vision for the Future of Structural Engineering which include:

• Developing and positioning structural engineers as leaders and innovators on project teams and in society

• Reforming structural engineering education

• Improving mentoring of young structural engineers

• Enhancing the professional development of practicing structural engineers

• Advocating for structural engineering licensure

• Implementing performance-based codes and standards

• Encouraging resilience in the built environment, including disaster response planning

• Promoting diversity within the structural engineering profession

• Collaborating on common causes with related industry organizations

• Advancing the structural engineering profession nationally and globally

Don’t become hung up on whether you have the right skills or credentials to contribute; everyone has something to offer. You don’t have to be a technical expert to contribute to a technical committee. Many subject matter experts are pulled in several different directions; you can help them make things happen by doing the legwork while they provide the ideas and direction. Over time, through osmosis and interaction, you too will become an expert.

How do you find the time? The goals and objectives of our structural engineering organizations mainly reside in the sweet spot of Stephen Covey’s Four Quadrants of Time Management: Important but not Urgent. Is everything you are currently doing with your time truly important? If not, can you reprioritize to find time to become involved now rather than at some theoretical future date when things slow down at work or the kids are older?

It’s time for you to be an active member in your organization. Don’t just do it for the profession; do it for yourself. Why do you see serial volunteers within our structural engineering organizations? Because they’ve unlocked the power of participation and the benefits that come along with it. You already bought the key when you became a member. Isn’t it time to open the door? ■

Jeannette Torrents is a Principal at JVA, Inc. and serves on the NCSEA Board of Directors. She has been active in her local SEA since being voluntold to join a committee as a new grad and has never looked back.

structural INFLUENCERS

David Cocke, S.E.

David Cocke started Structural Focus over twenty years ago in Los Angeles and has grown the firm to nearly 30 employees. David received his B.S. from Virginia Tech and his M.S. from San Jose State University. He is a registered Structural Engineer in California and several other states, with expertise in seismic evaluations and retrofits, historic preservation, and new design.

David was the 2019 President of the Structural Engineers Institute (SEI) of ASCE and is the current President of the Earthquake Engineering Research Institute (EERI). In addition, David has served on the Board of Directors of numerous organizations, including the California Preservation Foundation, Pasadena Heritage, USC Architectural Guild, SEAONC, SEAOSC, SEAOC, and the Board of Los Angeles Conservancy. In 2007, David served as the SEAOC-appointed Alternate Structural Engineer Member on the California Historical Building Safety Board. In 2014, David was named to Los Angeles Mayor Eric Garcetti’s Mayoral Seismic Safety Task Force to perform a year-long study of seismic risk in Los Angeles, resulting in the Mayor’s Resilience by Design report.

David has led the effort to bring post-earthquake building re-occupancy programs to southern California. In 2013, his team worked with DreamWorks to establish southern California’s first such program in the City of Glendale. Now the team is partnering with a multitude of clients and cities throughout Southern California to establish their programs.

We know that Structural Focus is a fairly prominent firm in southern California, but for those outside the region, what could you tell us about your company?

We founded Structural Focus in April 2001, after I moved here in 1995 to open Degenkolb Engineers’ LA office. We wanted to focus on the projects that we enjoyed most: preservation, adaptive reuse, media and film studios, and universities and labs, and today, we are pretty well known in those markets. We have been growing gradually and consistently and now have a staff of over 25. Our strategy has been to find and keep repeat clients, and we have been especially successful with “campus” environments. I think we have a reputation for excellent design, complete documents, and constructability. We have very loyal clients, and most of our work is with Fortune 500 owners. We have not spread out to multiple offices but will work anywhere the client wants us. We are licensed in over 20 states.

On a personal level, that is quite an accomplishment, particularly in a competitive marketplace. So what is your secret, if we might ask?

Starting and growing Structural Focus has been personally very gratifying for me, and most gratifying is finding really great people and giving them the environment where they can succeed. We try to be

pretty picky about our projects and look at a project through the client’s eyes to become their trusted advisor.

Recruiting and retaining talented staff is challenging, particularly since Covid. How have you done it for the long-term and also recently when so many firms struggled?

Again, it’s all about finding high-quality people and taking care of them. We recruit from the best university programs in the country. We have been very successful in hiring summer interns and then having them return after their graduate program. We have an excellent benefits package, but I think it’s about treating our people respectfully and actively supporting their career advancement. We encourage continuing education and professional activities. We want to show them that this profession has a lot to offer and that they can advance their career with some investment by us and themselves. We have a very diverse team, and we try hard to celebrate both professional and personal milestones. We have been named one of the top Best Places to Work in Los Angeles for several years in a row.

For structural engineers thinking about going out on their own, would you provide a few do’s and don’ts that might benefit them? Write a strategic plan and identify the markets that you want to be in. Make sure you have enough cash to cover the first months or so before invoices start getting paid. Do not try to grow too quickly. Don’t be afraid to reach out to your connections; never stop expanding your network. Take care of your clients, be loyal and make them look good. When they move, stay in touch with them. Finally, do not be afraid to hire people that are smarter than you!

Structural Focus team members attending the 2022 SEAOC Convention in Indian Wells, CA

Of all the projects you have worked on, would you describe the one or two that you are most proud of and why?

That’s a difficult question after 41 years of work in this profession! Maybe the Hotel Del Coronado in San Diego because of the complexity of working on, at that time, an almost 120-year-old building with lots of past modifications and little documentation. Maybe the Wilshire Boulevard Temple because of its beauty and our excellent design and construction team. Or maybe the dozens of Warner Bros. projects we worked on since the 1994 Northridge Earthquake. But, I must say that I am also very proud of our efforts to establish accelerated post-earthquake building re-occupancy programs in southern California. We have multiple very large campus clients and are working hard on spreading the word, including my serving as project technical director on a FEMA-funded Applied Technology Council project to publish program guidelines.

Successful firms plan for ownership transition and firm longevity. Without giving away any secrets, what is your philosophy on the subject?

Since we started in 2001, we have always thought we wanted to start a legacy firm. So we planned for an internal ownership transition from the beginning. It might look slightly different from what we initially envisioned, but we are getting there. Of course, along the way, we always said with a wink, “if someone makes us a crazy offer, we’ll talk.”

Firms are looking to have talented staff who reflect the communities they work in. What attributes do you look for?

We like to hire people with a great attitude, good communication skills, a sense of humor, and the drive to be a leader. So when we see great leadership positions on a resume, regardless of what the person did, that interests us more than the grades, assuming they have taken all the appropriate courses.

You have demonstrated a long and dedicated commitment to professional activities. You are a Fellow of SEI, ASCE, and SEAOC. What is the most rewarding aspect of your service, and if we may ask, was it worth it and why?

Again, I am very gratified by having the opportunity to give back to our profession and our communities. My wife Kate and I have served on numerous boards over the years, both in our professions and community. My professional activities started small at the local level, and over the years, I have held national and international leadership positions. Those activities also allowed us to meet some outstanding people from all around the world. I definitely think it was worth the investment. I am driven to help our younger engineers have a rewarding career, so if there is something that

David welcomes the audience to the 2019 SEI/ IStructE Iconic Structures conference in Dubai.

G ng off-s s s w us ng g m s on-s . ps you do you b s wo s ff n y s poss b . F om f m ng o f n s ng, p odu s nds v ss v m ,m nd bo , so you n g job don g nd go g b som p of m nd.

I can do in professional activities that help them or Structural Focus, then I am motivated.

You mentioned your non-engineering community involvement. Would you expand on that?

Great question. Let me start with a story. I was on a local organization’s board and was asked to help on a project. After digging into the issue using skills I have learned from my profession and coming up with a solution, the board president stated at a board meeting, “Wow, we should ALWAYS try to have an engineer on our board!” The point is that we as engineers have a unique skill set to help our communities, even if not in a highly technical manner, by using our analytical and communication skills that we use every day at work. We have a lot to give, and our communities can use our help. For example, I often lecture to engineering students that we can “save the world.” In addition, I have found that it is very fulfilling personally!

Work-life balance has been a hot topic for several years. Recently doing just enough to get by seems to be a trend too. What advice would you give to young engineers?

Funny, I never thought about “just getting by” until you asked this question, but it reminds me that I had a similar attitude my first couple years at work. Finally, my wife Kate sat me down, pointed out that I had been a high achiever in the past, and questioned why I would “settle” now. I’ve given the same talk to several engineers on my staff that needed it after a year or two

in the professional world. At Structural Focus, we do believe that we can work hard and play hard. We want people to go on vacations, and we seek adventures. And we also strive to show that we want them to be a real success!

We all have mentors and people who have helped us be successful. So whom would you like to thank and why?

Wow, over 41 years, I have had many mentors. Obviously, my former bosses and friends at Degenkolb. I was there for 20 years and learned a lot. That was a special group! Since then, I have learned from friends, clients, and others in professional associations and my younger staff. Finally, of course, I must mention my wife, Kate – she has been my best advisor, business partner, and supporter.

In closing, you have mentioned Kate a few times. There must be a lot to unpack, but she obviously played an essential role in your success and that of your team. What does that say about what makes Structural Focus a special place?

When I told Kate back in 2001 that I was going to start a new firm, she enthusiastically volunteered to be a part of it (after leaving a 20-year technical career at Bechtel)! She took on all the duties that did not involve structural engineering or business development. Her presence over the years has had a stabilizing effect on our staff, and she has been a prominent role model for so many of our diverse young staff. (Don’t ask any of our staff who is REALLY in charge!) I do think that our partnership has been a tremendous influence on the Structural Focus culture of teamwork. We would not be the same firm without her!■

The Structural Focus project team attending the topping out ceremony at the new Amazon Studios in Culver City.

David Cocke, Wayne Chang and Jonathan Lehmer.

Commonly Misapplied Welding Symbols

By Jason McCool, P.E.

Welding is a fundamental part of steel construction, but correct performance at the steel fabricator’s shop and the project site requires effective communication of what’s expected. Following are some common mistaken assumptions on structural drawings regarding welding symbols. While most engineers are aware of the American Welding Society’s (AWS) D1.1, Structural Welding Code – Steel, many may not be aware that AWS produces a formal standard for welding symbols: A2.4 – Standard Symbols for Welding, Brazing, and Nondestructive Examination (Figure 1). When in doubt, this thoroughly illustrated reference is an excellent resource.

Assumption 1

I don’t need to show a fillet weld size.

Structural drawings often include welding symbols with unspecified sizes. While a vee-groove weld without a specified throat or depth of preparation is assumed to be a Complete Joint Penetration (CJP) weld, fillet welds have no similar default. Lap joints for materials 1/4 inch or thicker have a maximum leg size of 1/16 inch less than the thickness of the overlapping part unless the weld is specified to be the full thickness of the part. This is not a default but simply a maximum. Specifying the full thickness is discouraged because of the tendency to melt the edge, blurring it and making an undersized weld appear full-thickness. Still, it is an option and a necessary one at times. Therefore, fillet weld sizes should always be specified clearly. Many fillet weld joints, such as the heel of an angle overlapping a gusset plate or a pipe column welded all around to a base plate, do not have any limiting dimension on the leg size other than a common sense guess that the Engineer of Record (EOR) did not need a 2-inch-thick fillet weld at the heel of an L2x2x1/4

kicker brace angle. The EOR is free to specify a typical size outside the welding symbol (such as in a note in the detail or on a general notes sheet), with the understanding that the further information is removed from the point of application, the easier it is to overlook discrepancies. The drawings should be carefully reviewed to verify that the typical size thus specified is adequate and actually achievable at the locations with blank welding symbols. See Figure 2 for a typical plan depiction of a fillet welding symbol.

Assumption 2

I don’t need to show a flare bevel groove weld size, or I can just say “full throat.”

Flare bevel and flare-vee groove welds are unique in that they are necessarily Partial Joint Penetration (PJP) groove welds, and therefore the effective throat must always be shown in parentheses. A groove weld size without parentheses denotes how deep the groove is and not the weld size and is simply the radius for flare bevel groove joints. For other groove welds, depth of preparation should not be specified unless the engineer knows the intended welding process (e.g., SMAW, FCAW, GMAW, SAW, etc.) and position (e.g., horizontal, overhead, etc.). Since the weld capacity is determined by the effective throat, and that depends on one factor known to the structural engineer (the radius of the member being welded) and on one factor known to the welding personnel (the welding process being used), the engineer must always specify the effective throat. Also, note that the AWS formulas for effective throat are based on the joint being filled flush; any depth of underfill must be subtracted from the theoretical throat. Generally, underfill is not a common design issue. However, questions of permissible underfill could arise due to potential repairs if an inspection revealed nonconforming welds or as a means of minimizing welding

Figure 1. AWS A2.4 is an excellent companion to D1.1 for clearly showing design intent on drawings.

Figure 2. A common example where the required fillet weld size is not limited by geometry and must be specified.

for large-radius members. See Figure 3 for a comparison of incorrect versus correct welding symbols.

It is also worth noting that fillet welds in skewed T-joints have many of the same issues as the included angle increases above 100 degrees or decreases below 80 degrees. Therefore, that range of fillet welds also requires the engineer to specify the effective throat – not the leg size, as is typical for fillet welds. This is because there is a reduced throat dimension due to joint geometry for included angles above 100 degrees and a “Z-loss” dimension, which depends on the welding process used, for angles between 30 degrees and 60 degrees that must be accounted for. Fillet welds between 60 degrees and 80 degrees actually increase in effective throat relative to the leg size. Therefore, the engineer specifies the throat, and the shop/field welding personnel must determine the appropriate leg size based on the welding process employed.

Assumption 3

The weld-all-around symbol is an acceptable shortcut at complex joints.

AWS actually restricts welding across the common plane (i.e., a “3-D” weld configuration) due to a) the likelihood of insufficient weld throat at the transition causing a potential weld failure under load and b) the masking of improper fitup. The need for actual continuous welds is recognized in D1.1 for conditions like air- or liquid-tight sealing, hot-dip galvanizing, or sanitary washdown service conditions. However, in those cases, the burden is on the specifying engineer to note any required inspection (e.g., magnetic particle, liquid penetrant) at these joints due to the quality challenges mentioned. Yet this is precisely what engineers showing a weld-all-around symbol in some of their typical details are asking the welder to accomplish. See Figure 2 for an appropriate application of a weld-all-around symbol and Figure 4 for an inappropriate application. Other common misapplications of this symbol are when specifying the

3 fillet welds on a full-depth beam web stiffener or at square or rectangular HSS connections with flush members. In the latter case, the joint changes from fillet welds on two sides to flare bevel groove welds on the two flush sides.

Assumption 4

Arrow side/other side = near side/far side.

Another common assumption is that the arrow side (below the reference line) and other side (above the line) symbols are synonymous with near side and far side notation. However, while near side/far side is relative to the observer, the arrow side and other side are relative to the weld joint. For instance, if an angle is reinforced by welding a solid rod or pipe into the heel of the angle, the “other side” of the resulting flare bevel groove joint is actually the inaccessible one in the heel, not the separate joint at the other leg of the angle (Figure 3) Figure 4 also illustrates this distinction: the hidden angle on the far side of the gusset plate should be referenced in the tail rather than using a fillet weld symbol above the reference line.

Clear, correct welding symbols can take additional time to draw and additional space on already-crowded details. But engineers need to specify them accurately on their construction documents using the recognized standard on the topic to avoid ambiguity. Moreover, D1.1 requires welding symbols to conform to the A2.4 standard, making it legally binding in jurisdictions that adopt the International Building Code, incorporating D1.1 by reference. That can become especially important on projects with significant time and labor tied to welding if the design office and the shop or field interpret ambiguous welding instructions differently. ■

Jason McCool is a project engineer for Robbins Engineering Consultants in Little Rock, AR. He graduated with a Bachelor’s degree in Welding Engineering & Materials Joining from LeTourneau University, was an AWS CWI for 18 years, a CWB CWS & CWE, and a co-author of the Steel Joist Institute’s 2nd edition of Technical Digest 8 – Welding of OpenWeb Steel Joists. Jason is also a member of STRUCTURE’s Editorial Board (jmcool@robbins-engineering.com).

Figure 3. The top symbol shows a weld on the other side of the joint, which is behind the round bar and inaccessible. It also does not specify the effective throat correctly.

Figure 4. The weld-all-around symbol here requires not only wrapping the weld around the gusset plate but also welding in the narrow gap between the angles.

SpeedCore 2.0 from Three Perspectives 200 Park Avenue 200 Park Avenue

By Ron Klemencic, P.E., S.E.,

Seattle’s Rainier Square introduced the world to SpeedCore. San Jose’s 200 Park Avenue expands SpeedCore’s possibilities. For decades, a reinforced concrete core surrounded by structural steel floor framing has been the industry’s go-to structural system for high-rise buildings. And why not? It is a cost-effective and efficient way to brace against wind and seismic loads while meeting the needs of architects and leasing agents who seek to offer unencumbered office and residential space. But unfortunately, a concrete core’s lengthy construction cycle can lead to delays before steel erection can begin. In 2005, Purdue University researchers started to explore a new structural system that would satisfy architectural and leasing demands, provide adequate strength and stiffness, eliminate steel erection delays, and reduce the overall construction schedule. The solution? Concrete-Filled, CompositePlate Shear Wall (CF-CPSW) panels. These prefabricated, modular panels – two steel plates spaced apart by interconnecting tie rods – could be stacked atop one another like giant LEGO® blocks to form a traditional structural core. Once erected, the panels could be filled with concrete to create a stiff and strong composite structural core – like an ice cream sandwich, with the

panels serving as the cookies and the concrete serving as the ice cream filling. Initial research results demonstrated exceptional performance and the ability to achieve ambitious improvements in construction speed.

Hon. AIA, Casey Kraning, Casey Wend, Kevin Englund, Chris Grimmer, and Mike Mills

Steel Framing and SpeedCore at 200 Park Ave. | Photo: Jason O'Rear

The structural engineer, the developer, and the construction firm relate their experiences building California’s first SpeedCore tower.

After nearly 10 years of laboratory testing, this new structural system, appropriately dubbed SpeedCore by the American Institute of Steel Construction (AISC), was ready to be incorporated for the first time into a commercial high-rise building – Seattle’s 58-story, 850-foot-tall Rainier Square. Rigorous design and review processes preceded the project’s 2017 groundbreaking. As a result, instead of completing Rainier Square in 32 months using a traditional reinforced concrete core, the team used SpeedCore to complete the project in just 22 months – an astonishing 10 months faster than planned!

The Structural Engineer’s Perspective

Rainier Square’s success encouraged Jay Paul Company, the developer of 200 Park in San Jose, California, to incorporate SpeedCore into its project’s design and construction. This 19-story, 1.3-millionsquare-foot commercial office building includes three parking levels above grade and four below grade extending 46 feet where the tower rests on a mat foundation.Two structural cores centrally located on the floor plates and surrounded by structural steel framing brace the tower. The design and approval processes began in 2019. The project team chose a reinforced concrete, beam-and-slab system for

below-grade construction; this facilitated an early construction start and allowed ample time to plan, procure, and fabricate the SpeedCore panels.

Rainier Square offered numerous lessons and inspired additional research to improve SpeedCore’s efficiency, effectiveness, and constructability. Under the leadership of Dr. Amit Varma at Purdue University and Dr. Michel Bruneau at the University at Buffalo, researchers made advancements to overall panel stability, cross-tie spacing, link beam detailing, foundation connections, and fire protection. These new research results, as well as the lessons learned during Rainier Square’s construction, were incorporated into 200 Park and benefitted the structural design in many ways:

Expanded Cross-Tie Spacing. Rainier Square utilized 240,000 oneinch-diameter cross-ties spaced at 12 inches on-center (o.c.) over the entire extent of the SpeedCore wall panels. The cross-ties are a critical part of each wall panel as they perform multiple functions, including:

• Temporary stability of the prefabricated panels for handling and shipping

• Buckling stability for the wall panels during the erection of the surrounding steel

• Resistance to hydro-static pressures during concreting

• The mechanical connection between the steel plates and the hardened concrete enforces composite action

• Confining pressure for the concrete subject to compressive stresses

Purdue University research showed wider cross-tie spacings were possible where lower demands are expected. For 200 Park, the design specified cross-ties spaced 18 inches on-center (o.c.) above Level 6, resulting in more than a 50% reduction in crosstie density for approximately three-quarters of the wall height. No Cross-Ties in Link Beams. Rainier Square included horizontal and vertical cross-ties over the entire length of all link beams crossing over wall openings throughout the tower. However, Purdue University research indicated these cross-ties were unnecessary; instead, headed

SpeedCore Basics | Image: MKA

SpeedCore Foundation Connection at Rainier Square | Photo: MKA

SpeedCore Erection at Rainier Square, Seattle | Photo: MKA

studs were used to prevent local plate buckling. The design of 200 Park took full advantage of this design improvement and eliminated cross-ties in all of the link beams.

Transition from Concrete to Steel. SpeedCore for Rainier Square started immediately above the tower’s mat foundation, making the connection from the steel wall panels to the concrete foundation straightforward using a series of steel stanchions embedded into the mat. The 200 Park project included a below-grade, cast-in-place concrete parking structure that influenced the location of the concrete-to-steel transition to a floor level well above the tower’s mat foundation. A stanchion approach similar to Rainier Square was used, but 200 Park’s stanchions were embedded into the tight confines of a ductile concrete shear wall. Extraordinary coordination between the reinforcing steel detailer and placers ensured this transition was buildable while achieving strict confinement requirements for the cast-in-place concrete shear walls.

Elimination of Spray-on Fireproofing. Rainier Square adopted spray-on fire protection for the SpeedCore wall panels. However, subsequent research at Purdue indicated that spray-on fireproofing could be eliminated if the SpeedCore wall panels met certain parameters regarding overall wall thickness, wall-plate thickness, and cross-tie spacing. The design team presented these research results to the City of San Jose’s Planning, Building & Code Enforcement officials, who favorably considered the proposal to eliminate

spray-on fire protection of SpeedCore wall panels as long as beam/ wall connections and deck support angles remained protected. Procurement. Procurement of the wall-plate material was a source of great discussion for both Rainier Square and 200 Park. American mills roll plate material to a maximum width of 10 feet. Only South Korean and German mills roll wider plates. For Rainier Square, the plate material was purchased from South Korea, where plates could be produced to match the typical story height of 14 feet. For 200 Park, domestic plates were selected at a width of 10 feet, necessitating shop splicing of plates to prefabricate individual full-story-tall wall panels. In the future, Nucor plans to produce wider plate material in a newly constructed domestic mill.

MEP Coordination. Penetrations through the SpeedCore panels for ductwork, piping, and electrical conduits required careful planning and coordination to facilitate prefabrication. For both projects, detailed coordination efforts during the design phases, including weekly meetings with the various subcontractors, were essential to incorporating the necessary openings into the design, shop drawings, and fabrication process.

Fabrication. The time required to fabricate a single wall panel exceeds the time to erect the same wall panel, necessitating advance fabrication and stockpiling of wall panels for just-intime delivery on site. Careful planning of the overall workflow in the fabrication shop, all the way to the final delivery point, was required to meet the aggressive erection schedule of both projects. Shipping. Planning the shipping routes and understanding the state-by-state trucking requirements were essential for the smooth and timely delivery of SpeedCore wall panels to the site. Rainier Square wall panels were fabricated in Portland, Oregon, requiring shipping on both Oregon and Washington highways. For 200 Park, wall panels were fabricated in Phoenix, AZ, and Stockton, CA, requiring shipping on Arizona, Nevada, and California highways. In both instances, shipments were deemed wide loads, demanding that trucking companies follow each state’s specific laws. Upon arrival at the site, deliveries in downtown Seattle were limited to the early morning hours before downtown office workers arrived. Deliveries in downtown San Jose proved to be more flexible.

200 Park Ave. SpeedCore connection to Special Reinforced Concrete Shear Walls

200 Park Ave. SpeedCore Lobby Openings | Photo: Jason O'Rear

Erection. Rainier Square and 200 Park completed full-scale mock-ups of a portion of the core walls, allowing the contractors to learn how best to handle, erect, connect, and concrete the wall panels. While costly, these mock-ups proved invaluable to the construction teams, allowing the on-site construction work to proceed with a limited learning curve.

One notable item for both projects was the relationship between the fully concreted SpeedCore panels and the tie-ins for the tower cranes. In the case of Rainier Square, the tie-ins and related tower crane jumps were conditioned by the location of the fully concreted SpeedCore wall panels. Construction of 200 Park took a more aggressive approach, using the strength and stability of the “un-concreted” SpeedCore panels to support crane tie-in loads. This approach required rigorous engineering assessments to confirm its application and limits.

The SpeedCore wall panels for Rainier Square and 200 Park exhibited a small amount of warpage in the wall-plate material caused by heat associated with completing the cross-tie connections. In most instances, this modest warpage could easily be managed with the field-welded panel-to-panel wall splice. However, in only one instance was the warpage significant enough that a modified field splice detail was required.

The Developer’s Perspective –Opting for SpeedCore

Implementing a new technology or construction methodology is not without risks, nor is it something to take lightly. As the design concepts progressed for the 200 Park project, the teams at Gensler and MKA brought the SpeedCore system to Jay Paul Company’s attention and suggested that it may be a good fit for the project. As a best-in-class producer of class A office space, the selected process needed to maintain the company’s image and meet four key objectives: Marketable (Leaseable), Permittable, Cost Appropriate, and Schedule Appropriate.

MKA’s confidence in SpeedCore went a long way in Jay Paul Company’s decision to choose SpeedCore for this project. Ron Klemencic and his team at MKA have a unique ability to concisely convey extremely complex engineering elements into a digestible format needed to make ownership’s key decisions. As the first structural concepts for the 200 Park project were being priced and considered, the development team visited Rainier Square to hear firsthand the benefits and challenges of this novel structural system. Ultimately, they came away confident that SpeedCore was a viable option for 200 Park.

MKA took a very active role in early discussions with the City of San Jose, bolstering confidence that City officials would be supportive and have the processes in place to consider, review, and ultimately permit this construction method within the aggressive construction and procurement schedule. The City review, concurrent peer review, and permitting were not without challenges, but all parties came away with lessons learned and, ultimately, a better product.

Level 10 Construction took the lead in analyzing key questions around schedule and cost. Along with partners at Scuff Steel and input from the Special Inspector (Construction Testing Services), Level 10 compared the more traditional concrete core and BRB/ Sheet Plate Shear Wall systems and discovered that schedule and cost gains could be achieved. As a result, the implementation team was confident that it could achieve the desired results.

The 200 Park project and its SpeedCore component have received a lot of press and accolades from the broader building community. However, this did not drive the owner’s decision to build using SpeedCore. Instead, the team was focused on bringing an iconic building to downtown San Jose that meets the needs of our desired tenants. SpeedCore fit well with broader project goals, and confidence in Gensler, MKA, the City of San Jose, Level 10, and the rest of the implementation team made this a rational decision rather than a risky decision.

As 200 Park nears completion and becomes a defining landmark in downtown San Jose, there is pride amongst the project’s team and confidence in its decision to use SpeedCore.

The Contractor’s Perspective –Embracing New Ideas

When Jay Paul Company approached Level 10 Construction about building 200 Park, only the second SpeedCore project in the world, three factors required consideration: confidence in the ability to execute the work, an understanding of the risks, and assurance that the project made financial sense.

Level 10’s VPs of Operations, Casey Wend and Kevin Englund, met with Ron Klemencic to get an overview of the design and key project fundamentals. After multiple meetings, the team toured the first-ever SpeedCore project, Rainier Square, in downtown Seattle to see SpeedCore firsthand and meet the project’s erector, The Erection Company of Lake Stevens, Washington.

Confident in understanding the dynamics of a SpeedCore project, schedule and cost studies were performed to determine if SpeedCore made sense for Jay Paul Company and 200 Park. The study showed

SpeedCore left exposed as lobby "art" at Rainier Square | Photo: MKA

SpeedCore could reduce the project’s structural frame-and-deck schedule by at least three months. In addition, the reduced general conditions and site requirements costs, combined with other trade offs realized from building a CF-CPSW core instead of a traditional reinforced concrete core, ultimately netted a reduction in estimated construction costs. Of course, similar studies would need to occur on future projects, given the price fluctuations in steel and other commodities since the pandemic. Still, after the studies were presented to Jay Paul Company, a decision was made to move forward with the world’s second SpeedCore project and the first such project in California.

The next step was to secure the right subcontractor to fabricate and erect the project. After multiple pre- and post-bid interviews with four different structural steel subcontractors, it was recommended that Schuff Steel be awarded the project. In addition to cost, some of the considerations that went into this decision included fabrication plant capacity, detailing resources, labor and equipment resources, location, and history with past Level 10 projects.

Schuff Steel provided a well-prepared presentation that showed they invested significant time in planning how to fabricate and erect this new design technology successfully. This included substantial pre-modeling and logistical planning graphics and videos as part of their proposal and interview.

SpeedCore requires the early coordination of penetrations for mechanical, electrical, plumbing, and fire protection (MEPF). As a result, MEPF design-build subcontractors participated in design and coordination meetings weekly to fix the locations and sizes of SpeedCore penetrations in time for Schuff Steel to provide detailing and obtain MKA’s approvals to allow fabrication in sequence with all the other standard CF-CPSW units. When building with SpeedCore, slab on metal deck reinforcementsmust be detailed early because dowels or drag bar reinforcing locations require holes. The steel fabricator needs to incorporate the locationsof these holes into the shop drawings. Providing this information in a con trolled shop environment

is more cost-effective than drilling holes in the field.

During the coordination process, elements such as the coupling beams which framed the header of the large core walkway opening had opening restrictions. These restricted locations needed to be identified early so the alternate locations could be established and coordinated with the interfacing trade work. The penetrations also had to be coordinated with additional internal trusses above MKA’s design that Schuff Steel used as a quality control measure for alignment during the fabrication of the composite plate shear wall modules and to ensure no distortion occurred during trucking and rigging of the units.

The time invested in early coordination and review for the reinforcing steel holes and MEPF openings paid off significantly, avoiding costly rework in the field. No SpeedCore field modifications were needed for MEPF penetrations in the core walls.

Another unique consideration during the planning of the project was the evaluation of MKA’s requirements for the placement of concrete in the CPSW panels relative to the concrete placement of the slabs on metal deck and the number of levels of erected steel ahead of filling the core.

MKA’s documents required the 10,000 pounds per square inch (psi) concrete to be placed in the CPSW panels directly below a level and reach a minimum compressive strength of 4,000 psi before any concrete on the metal deck could be placed on that level. This requirement added a constraint to the project schedule, so Level 10 and Schuff Steel partnered with Simpson Gumpertz & Heger (SGH) to evaluate the actual loading conditions and identify solutions. SGH, acting as Schuff Steel’s erection engineer, modeled and calculated that one level of concrete fill on metal deck could be placed above one level of un-grouted CPSW. SGH was also able to design additional internal stiffening of the CPSW, thus providing crews some flexibility in the scheduling and sequencing of the work. These studies and additional measures supported the project’s schedule needs and contributed to its successful execution.

There were many other aspects of unique thinking, planning, and requirements, including a full-size CPSW Steel mock-up, a full-size grout placement mock-up, tower crane sizing, site logistics, fire rating studies, and elevator shaft considerations. Given the success of the design’s implementation on 200 Park, the design technology of SpeedCore should be considered for future projects.

SpeedCore 3.0?

Rainier Square proved SpeedCore’s potential to the world. It also offered myriad lessons and inspired additional research to improve SpeedCore’s efficiency, effectiveness, and constructability – all of which were incorporated into the design and construction today of 200 Park. But, of course, it is only time before another developer chooses to build with SpeedCore. Whatever that project might be remains to be seen. But one thing is certain now – it is an exciting time to witness this evolution in high-rise construction and structural systems. ■

200 Park Ave. Completed | Photo: Jason O'Rear

Ron Klemencic, Chairman and CEO, Magnusson Klemencic Associates. Casey Kraning, Director | Real Estate Development, Jay Paul Company. Casey Wend and Kevin Englund, Partners/VPs Operations, Chris Grimmer, Senior Project Manager, and Mike Mills, Senior Superintendent, Level 10 Construction.

Our new LDSS spline solution for mass timber panel connections includes the LDSS light diaphragm spline strap, PRO300SG2 Quik Drive® tool and collated Strong-Drive® WSV screws. The steel LDSS strap attains high loads at a lower installed cost than plywood. Placed on top of CLT and other types of mass timber panels, it eliminates the need for CNC routing. The strap fastens quickly and easily with the Quik Drive tool, unique noseclip and screws. The Simpson Strong-Tie® LDSS spline strap is tested, widely available and backed by our expert service and technical support.

Switch to the LDSS spline solution for your next design. To learn more, visit go.strongtie.com/LDSS or call (800) 999-5099.

A faster, more economical connection than plywood.

Functionality and Flexibility Key to New Chicago Gateway

The Midway Security Checkpoint Expansion Project

In 2016, the Chicago Department of Aviation (CDA) recognized that Midway International Airport (MDW) required expansion. Since September 11, 2001, the original narrow walkway

By

connecting the landside and airside terminals over a major arterial street/state highway was unable to meet enhanced security requirements, resulting in passenger backups into the adjacent parking garage.

The CDA awarded the Midway Airport Security Checkpoint Expansion project to Muller & Muller, Ltd. (M2) as a prime consultant in collaboration with Jacobs, serving as the bridge structure, civil/roadway, security, and wayfinding consultant. In this capacity, Jacobs designed the structure from the concrete deck level down to the foundation level, provided for utility relocation, designed the reconstructed roadway and sidewalks, coordinated with the Transportation Security Administration (TSA) for its needs for future security equipment, and worked with the client on ideal wayfinding throughout the new terminal. MDW’s location in a dense neighborhood required an innovative approach – expanding the airport’s footprint was cost prohibitive and would disrupt the surrounding community. Instead, using the existing walkway bridge, the Jacobs/M2 team created a new 80,000-square-foot structure that spans above and below active roadways (including during construction) to connect the MDW terminal’s two halves seamlessly.

Jennifer Drake, P.E., S.E.

Figure 1. New layout of the security hall and connector bridge section.

Constructing Under the Upper-Level Roadway

The initial CDA concept required construction under 400 linear feet of the upper-level departures roadway. However, the team suggested an approved alternative: two connector bridges – each approximately 50 feet wide (total of 100 feet linear construction under departures) connecting the new elevated security hall to the landside terminal (Figure 1).

The vertical clearance from the bottom of the departures roadway to the top of the arrivals was too low for conventional cranes, so the team wrote a performance specification for prefabricated

rolled beam bridges. The units were transported on a flatbed truck and installed side-by-side with a small crane under short interval closures of the arrivals lanes. The team used two 40-foot units to span the 80 feet between the landside terminal and the main bridge. Interior building columns are attached directly to the piers below. The team designed the exterior columns connection into a concrete curb on the beam bridges (Figure 2).

Distinctive Structural Engineering Obstacles

One unique project aspect was reviewing what design code to follow for building atop a bridge. The design team used the 2014 American Association of State Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD) Bridge Design Specifications, LRFD Guide Specifications for the Design of Pedestrian Bridges, with adherence to the Chicago Building Code. The team quickly found that 100 pounds of force-per-square-foot (psf) pedestrian loading (without live load reductions) and 125 psf in light mechanical areas controlled the design over the H10 maintenance vehicle from the Pedestrian Specification. The team used complex construction staging to meet the CDA’s requirement for the checkpoint to be open continuously during construction, including utilizing Midas Civil to model the various construction stages for stresses in the deck and steel. While the original bridge supported pedestrians, Jacobs designed the north side steel using a splice point located east of Pier 2 (Figure 3); the erection of the remainder of the steel was followed by partial demolition of the airside terminal. Pedestrians

Figure 2. Connector bridge partial cross-section.

Figure 3. Steel erection on north bridge (looking south towards original bridge).

Bathed in natural light, passengers can look toward the soaring, cathedral-like ceiling heights and an extensive clerestory window wall that offers a view of the sky. Grace and beauty, combined with functionality and flexibility, create a positive welcome for travelers in Chicago.

Following an intensive 14-month design phase, the team overcame planning and technical challenges to create an iconic new gateway for the City of Chicago that opened in 2020 (Figure 5).

The resulting space addresses MDW’s capacity requirements and accommodates expanded future capacity. With reduced wait times, expanded retail and concessions, and an enhanced passenger experience, getting in and out of Chicago has never been easier!■

utilized the north bridge after completion during the demolition of the original bridge portion up to a splice. The design called for existing and south bridge construction following partial demolition.

The team developed a framing plan to accommodate upper-level columns, roadway utilities, building column connections, and curtainwall with 34 uniquely sized and spaced beams. Jacobs modeled the deck using MIDAS Civil software to determine localized deck stresses from building columns and the long concrete piers (Figure 3) for thermal forces.

The TSA and curtainwall system mandated strict deflection limits of less than one inch total, requiring the team to design robust, shallow steel beams with camber. In addition, complying with the Americans with Disabilities Act (ADA) was a challenge, as the two building floors of the bridge were at different elevations. The team’s concept involved removing a portion of the original structure, splicing into the original steel, and then regrading with an ADA-compliant slope.

Incorporating Important Architectural Details

The new walkway offers an enhanced experience for passengers moving from the main ticketing hall to the queuing hall featuring integrated lighting in sculptural ceilings (Figure 4).

Project Team

Owner: Chicago Department of Aviation (CDA)

Architect of Record: Muller & Muller, Ltd. (M2)

Contractor: FH Paschen

Prime, Management, Architecture: Muller & Muller, Ltd. (WBE)

Civil, Bridge Structure, TSA Planning, Wayfinding: Jacobs

Building Structure: Matrix Engineering Corporation

Mechanical, Electrical, Plumbing: dbHMS (MBE)

Geotechnical: ECS Midwest, LLC

Surveying: Dynasty Group, Inc. (MBE)

SLighting Design: Schuler Shook

Cost Estimating: Faithful+Gould, Inc.

Building Envelope: Simpson Gumpertz & Heger

Acoustical: Shen Milsom & Wilke

Structural Software: – midas Civil, MDX

Jennifer Drake, P.E., S.E. is Jacobs’ Structures/Rail Group Leader serving Illinois, Wisconsin, Minnesota, and Iowa, residing in Chicagoland (jennifer.drake@jacobs.com).

Figure 4. Completed main ticketing hall. Courtesy of Bill Zbaren.

Figure 5. Looking south at completed bridge. Courtesy of Bill Zbaren.

RECORDS

Eliminate the hassle of resubmitting your College transcripts

Exams results

Employment verifications

Professional references each time you apply for licensure in an additional state.

STRUCTURAL design

Shipping Container Design

What Structural Engineers Need to Know

By Nabil (Bill) Taha, Ph.D., P.E.

It is a shame that many cargo containers are lying around harbors all over the world and, in other places, rusting and wasting away. Would it not be nice to give these very strong structures new life?

Shipping containers have several other names, including sea boxes, cargo containers, conex containers, intermodal containers, International Organization for Standardization (ISO) containers, and sea/ocean containers. However, for this article, they are referred to as shipping containers.

Conex Container: During World War II, standard-sized shipping containers were developed to ship military cargo to the front lines. These boxes were initially called Transporters. The term conex came from the development of Transporters into Container Express or CONEX boxes after the Korean War. Conex containers evolved into modular units that could stack efficiently to store more cargo in one location.

The re-use of cargo containers has produced very efficient and beautiful buildings around the world, such as homes, auxiliary dwelling units (ADU), hotels, apartments, restrooms, restaurants, food courts in open malls, office buildings, portable field offices, commercial buildings, shops, beer gardens, equipment enclosures, storage facilities and much more.

There are many benefits to using shipping containers. They are not combustible, which is especially important in many parts of the world that are susceptible to wildfires. They are also durable and resistant to pests and termites. In addition, shipping containers are stackable up to four and five stories, modular, easily modified to fit user needs, and assembled quickly. With the vast shortage of available labor these days, using shipping containers for modular construction off-site can save tremendous amounts of time and money.

The biggest user of shipping containers for offices, sleeping quarters, kitchen facilities, refrigerators, food/plant processing, and storage buildings is the United States military, where they are found on U.S. military bases all over the world.

One of the most significant cargo container projects in the U.S. is the Obetz Stadium Plaza in Ohio. This structure includes 122 shipping containers arranged to form offices, conference rooms, a cafeteria, a ticketing office, huge restrooms for the stadium, and many more site facilities (Figures 1 and 2).

How Strong are Shipping Containers?

Typical exterior dimensions of shipping containers are 20 feet x 8 feet x 8 feet 6 inches (length x width x height) for standard shipping containers. There are also 40-foot and 45-foot-long containers with the same width and height. High-cubed containers are 9 ft – 6 inches in height. Shipping containers are very strong. They are stronger than required for most buildings. Just as an example, every single container is analyzed, built, and physically tested to resist the following loads:

Vertical dead and live loads

• Individual container 58 kips

• Eight containers stacked above464 kips

Lateral loads

• Short direction 33.75 kips

• Long direction 16.87 kips

A shipping container floor is designed to carry a live load of 250 pounds per square foot (psf). In contrast, the live load requirement is typically 40 psf for residential projects and 100 psf for many commercial projects. So, when a shipping container is used in a typical commercial application, it has a minimum of 2.5 times the required floor capacity.

Also, because containers are designed to be stacked 9 high on ships, the corner posts in the lower container support 464 kips over 4 corners = 116 kips per corner. This is far more capacity than is typically required in 5- or 6-story buildings, considering the small tributary area of the corner columns. For lateral loads, the movement of ships carrying cargo containers on the ocean is several times higher and more aggressive than the strongest seismic forces found anywhere in the U.S. Also, wind loads in ocean areas far exceed the wind loads on land-based structures.

Figure 1. Obetz Stadium Plaza includes 122 shipping containers.

Shipping containers are designed and tested following ISO Standard 1496, Series 1 Freight Containers – Specification and Testing. In addition, they are again tested when shipping goods with the vertical and lateral loads mentioned earlier.

Which traditional type of building material – concrete, steel, or timber – is designed to be 2.5 times the required live load? Designing this way would be considered wasteful. Which traditional building is tested twice, or even once, before giving it a Certificate of Occupancy? For buildings, we know that the answers to these questions are none; only shipping containers have that built-in extra factor of safety. However, since shipping container design is not taught in schools, colleges, or universities, it is understandable that many are hesitant to use or approve a project that uses them. This author had concerns when starting to design with them 20-plus years ago. However, many years of studying and designing shipping container buildings led to the realization that they are incredibly safe.

Structural Analysis and Design

When this author started designing cargo containers for use in buildings, the thought was to do it the way wood structures are designed. So, it would be simple; buy all the available books. Read them, understand them, and then follow them, right? Well, the bad news is, there were not any, at least not 20 years ago. Since this is not taught in schools or colleges, textbooks on the practice were not available either. So, the approach was to use basic engineering principles learned in college and experience with other materials such as steel, aluminum, or concrete.

The following approach is intended to introduce engineers to the structural analysis of shipping container buildings. However, it is not all-inclusive, and you must use your judgment, experience, and patience. But you can get there.

The great news now is that there is finally a standard to rely on – especially when facing a building department unfamiliar with shipping containers used as a building method. As silly as it seems, at least one building department has insisted on adding 2x4 studs and wood sheathing with 8d nails because they did not understand and accept the strength of the steel container.

Components

Structural analysis starts by modeling the containers on commercially-available finite element software such as RISA 3D, StaadPro, or similar software. For this, an engineer needs to know the dimensions of the different parts of the container. Please note that the ISO 1496 Standard that defines the specifications for shipping containers is a performance standard. It specifies the needed capacity of each part of the container. It is then up to the manufacturer to meet these capacities with any structural material. The container is then subjected to rigorous testing and analysis. A designer can start with approximate member sizes, but the analyzed container needs to be visually inspected to verify actual member sizes used for design. The approximate dimensions can be obtained from the manufacturer’s cargo container specification or Intermodal Shipping Container Small Steel Building (Sawyers, Paul. Third Edition, 2017).

The main components of basic shipping units are shown in Figure 3. The corrugated steel decking panels and reinforcement (if any) in the side walls, front, rear, and roof are typically 14-gauge steel. In addition, steel joists as cross members and 11/8-inch, 19-ply hardwood sheathing panels typically make up the container’s floor.

Figure 3. Main components of a shipping container. [Source: DOD MIL-HDBK-138B]

Figure 2. Obetz stadium contains offices, conference rooms, a cafeteria, a ticketing office, and huge restrooms for the stadium.

Codes and Standards

Before starting the design of shipping containers, an engineer should read and understand at least two primary standards and a new section of the 2021 International Building Code® (IBC). ISO 1496 is adopted by all branches of the U.S. military and the federal government. In addition, the ICC G5-2019 Guideline for the Safe Use of ISO Intermodal Shipping Containers Repurposed as Buildings and Building Components is an excellent source of information.

To provide consistency in design, construction, and regulation, IBC Section 3115 has been introduced to provide a consistent and comprehensive set of code provisions specific to intermodal shipping containers. The structural design for the repurposed containers must comply with either the detailed design procedure set forth in Section 3115.8.4 or the simplified structural design method for single-unit containers outlined in Section 3115.8.5.

It would also be prudent to contact the state modular buildings department – there is usually one such department in each state. The city or local jurisdiction may also have some additional requirements. The good news is that if you are modifying the containers in the shop of a state-certified

manufacturer, you may not need to work with the local jurisdiction.

Computer Models

The model for the entire building can be created in structural software according to the building geometry using confirmed dimensions and the proposed layout. Figures 4 and 5 show examples of two different structures. The following modifications were applied to the models. For multiple units, connections were made with rigid links to represent the welded or bolted connections between the units. Portions of the wall steel and metal deck were removed from each unit corresponding to any openings shown on the architectural drawings. Reinforcement was added to those openings, as shown on the structural drawings. Boundary conditions or supports were added to the computer model to represent the foundation used in the project.

Loads were added to the model according to the building code. Examples of loads include dead, live, roof, and/or snow. Wind and seismic loads were modeled in multiple directions as required by ASCE 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. Other loads, including concentrated loads from equipment, are included. Load combinations were evaluated according to the latest version of the IBC adopted by the local building department.

Per the 2021 IBC, section 3115.8.4.2(1): “Where all or portions of the corrugated steel container sides are considered to

Figure 5. Two-story home with a vertical tower container.

Figure 4. Whole building model for an 18-unit, 3-story apartment building.

be the seismic force-resisting system, design and detailing shall be in accordance with ASCE 7, Table 12.2-1 requirements for light-frame bearing-wall systems with shear panels of all other materials.” Accordingly, the Response Modification Coefficient, R = 2.0 for undefined systems.

Per 2021 IBC Section 3115.8.4.2(2): “Where portions of the corrugated steel container sides are retained but are not considered to be the seismic force-resisting system, an independent seismic force-resisting system shall be selected, designed, and detailed in accordance with ASCE 7, Table 12.2-1.” For example, Steel Ordinary Moment Frames per ASCE Table 12.1-1 C.4 are permitted in seismic zones D and E for light-frame construction according to section 12.2.5.6(b) with a building height under 35 feet. In this case, the Response Modification Coefficient, R = 3.5. RISA 3D has a built-in design module for steel components and strength that pairs with RISA Section. All load-bearing or transferring steel members’ shapes, properties, and orientations were modeled in RISA sections and input into RISA 3D for analysis.

Shipping container steel is normally fabricated with CORTEN steel (Fy = 50 ksi, Fu = 70 ksi). However, consider analyzing the steel as a weaker A36 (Fy = 36 ksi, Fu = 58 ksi) for an added factor of safety where the Convention for Safe Containers (CSC) data plate cannot be verified. Containers built, tested, and inspected to ISO standards are identified by a CSC Safety Approval Placard affixed to the container. The placard, also known as a data plate, provides useful information such as the container’s identification number and inspection examination date and provides information to assist in the verification process to confirm that the container was maintained in safe operational condition.

The model was evaluated by finite element analysis according to the loads and load combinations. Model results were then reviewed by a licensed engineer for accuracy, steel code checks, and deflection compatibility.

Conclusion

Intermodal shipping containers are being repurposed worldwide as structures intended for occupancy. Structural engineers should be aware of codes and standards related to their design and use in construction. New provisions of the 2021 IBC have been introduced to provide a consistent and comprehensive set of code

requirements specific to intermodal shipping containers. ISO 1496 is adopted by all branches of the U.S. military and the federal government. ■

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

Bill Taha is the Founder, President, and Principal Engineer of PSE Consulting Engineers and a Former Associate Professor of Civil Engineering at the Oregon Institute of Technology, Civil Engineering Department, Klamath Falls, OR.

Joist Grip Framing Clamp System

Support your rooftop loads in uplift and download conditions. The distributed load capacity of 4,000 lbs per complete system makes the Joist Grip Framing Clamp System the ideal support for rooftop unit installations.

Pipe Header System

Hanger Clamps, rated for 1,000 lbs each allow hanging of equipment below the roof deck while utilizing the ability of the Framing Clamps to distribute the load to panel points on the top chord of the bar joist.

Suspension Clamp System Panel Point Bridge

Utilize the Panel Point Bridge to safely suspend HVAC equipment, conveyors or other ceiling fixtures without welding or drilling using the Suspension Clamp System.

Upper Deck Fall Protection System

Using corrugations in the standard roof deck, the Upper Deck Fall Protection Anchorage System easily clamps to the top chord of the bar joist or wide flange support.

Engineering Lightness

By Thorsten Helbig, Dipl.-Ing., and Florian Meier, M.S., P.E.

The new Academy Museum of Motion Pictures (AMMP) is now the world’s premier museum and event space devoted to the motion picture industry, celebrating the artistry and technology of film. Designed by Pritzker Prize-winning architect Renzo Piano Building Workshop in collaboration with Gensler, the project consists of a sixstory-tall, renovated building and a new spherical building that houses a 1,000-seat theater. Several monumental steel stairs and bridges lead to the Dolby Terrace, directly above the theater. It is covered under a 150-foot-wide steel and glass dome and will be used for events and special exhibitions. The canopy provides weather protection, adds light features and shading elements, supports fire sprinklers, and much more. Developing a well-performing and extremely lightweight structural concept for the dome while integrating all the additional layers of elements necessary to function as envisioned by the architect and client was the main challenge in the design.

Developing a Structural Concept

The structure and façade engineering team at knippershelbig (based in Germany with offices in New York) was brought on board to help address the architects’ concerns regarding the visual heaviness and member sizes of the main structural components of the dome. The ambition was to lighten the initially suggested structural system into a single-layer grid shell. A new structural concept was to run the main members in parallel, east-west arches across the dome, with north-south running members perpendicularly intersecting the dome’s main arches.

The generated single-layer, quadrilateral grid shell was supplemented by diagonal cross-bracing cables, which are essential for generating in-plane shear stiffness. The resulting triangulated grid shell shows good structural performance and redundancy (alternative load paths).

View from Fairfax Ave of the finished project. Courtesy of Patrick W. Price.

Explosion diagram of the connection of the east-west and north-south arches, including glazing assembly.

A structural challenge to be addressed was the large openings towards the north and south ends of the dome. The architect’s goal was to avoid a massive edge beam – as is conventional for shell structures with free, unsupported edges. An edge beam would disrupt the smooth visual lightness of the transition from landscape and sky to the glass roof. To address the low stiffness in this area, the structural engineering team tested several options for reinforcing the edge. The team decided to apply a diagonal cable bracing system based on the work of Russian engineer Vladimir Shukhov (1853-1939) in the early 1900s.

The overall geometry of the glass dome follows an exact 150-footdiameter sphere. The terrace is about 76 feet above ground, and the glass dome’s apex is about 120 feet high. The bottom half of the sphere is cut off; however, it still overlaps partially with the supporting reinforced concrete structure of the Geffen theater. At the area of the overlap, the steel/glass dome leaves a gap to the exposed precast panels, and several steel struts are employed to stabilize and support the E-W arches.

Composition

The primary structure of the steel grid shell consists of 4-inch-diameter round HSS arches in the east-west direction. The arches are oriented parallel to each other in plan and spaced at 4 feet. In the north-south direction, the radially oriented arches are made of custom-milled solid rectangular steel sections (about 2 by 2½ inches) and intersect with the east-west arches perpendicular at every node. The 0.4-inch-diameter twin cables run diagonally and continuously over the entire dome and are clamped at every node of the grid. Secondary T-shaped profiles run approximately 10 inches above the primary east-west structure and serve as a support for the glazing. The glazing consists of flat, laminated glass made of two 12 mm heat-strengthened glass panes with PVB interlayer. All glass panels have the same thickness, but almost every one of the 1,500 glass panels has a unique shape due to the changing dimension of the quadrilateral grid. The signature shingled appearance of the glazing is created by stepping the depth of the supporting T section. Glass panels overlap each other slightly at every step.

The extreme transparency of the shell structure and its glazing required the design and coordination of a complex retractable shading system. In addition, integrating numerous tensioned wires, supporting brackets, and electric conduits required the introduction and coordination of several non-structural elements.

The requirements for glazing maintenance, such as window washing, necessitated a unique solution to provide workers access across the entire dome surface. Whereas most of the dome’s interior surface can be easily cleaned using conventional maintenance platforms, man-lifts, and narrow catwalks between the concrete structure and glazing, the entire exterior surface of the glazing required a creative solution. A maintenance stair leading to the dome’s apex became one of the main design features and showcased what is required to maintain a structure like this – rather than hiding it. Workers can tie off from the stair’s uppermost platform with designated man-rated anchors and can reach every corner of the glass surface.

Structural Behavior

Oriented strictly in the east-west direction, the round HSS arches are the main load-carrying elements. They transfer the gravity loads of the dome to the embed connections and the concrete dome. Due to the spherical geometry of the dome, the arches do not follow the ideal geometry of a catenary arch. The deviation from the catenary form leads to characteristic deformation of spherical domes, with the uppermost area sagging and the lower areas bulging. Some of these effects can be

counteracted for closed spheres by introducing circumferential members. For the Academy Museum’s dome, however, these circumferential lines are interrupted by the large openings. Therefore, this counteracting load mechanism could not fully develop. However, through the introduced cross-bracing, the deflections could be sufficiently controlled within a few inches under self-weight conditions, avoiding a visually observable geometric deviation from the ideal dome shape.

Historically, the structural design of lightweight steel grid shells is usually most sensitive to asymmetrical loads such as wind load effects. Therefore,

Interior view of the grid shell towards the northern opening.

Close-up view of mechanism at roller shades.

a physical model of the dome was tested in a wind laboratory, and the resulting wind pressure assumptions were used for the structural analysis. Although the project is based in California, horizontal acceleration due to an earthquake was less of a concern thanks to the base-isolated construction of the supporting steel-reinforced structure of the Geffen theater. Nevertheless, seismic effects were thoroughly studied in the form of a response spectrum analysis.

Fabrication and Installation

One of the main goals during manufacturing was maintaining the global structure’s tight tolerance requirements. The structure was assembled in the shop on a template representing a portion of the dome. This assured that the assembled pieces form exactly the final geometry when assembled on site. The pieces were manufactured using several technologies: primarily by conventional welding of flat steel plates, partially by CNC-milling, and some of the pieces were fabricated using drop-forging, such as the cable clamp or the cable end fitting detail.

On-site, the steel pieces arrived in ladder frames consisting of two parallel arch segments already pre-assembled, including the connecting north-south struts. This simplified shipping, handling, and installation for the specialty contractor Josef Gartner / Permasteelisa North America, who fabricated and installed the steel and glass dome. After placing the primary structure on scaffolding, the individual segments were joined using an internal pre-tensioned connection in the east-west arches. Subsequently, the diagonal twin cables were installed and fully pre-tensioned. After the final inspection of the cable pretension, the supporting posts of the

scaffolding were carefully removed so that the structure spans 150 feet without any intermediate supports. From that point onwards, all secondary elements, such as glazing, light fixtures, shading, conduits, and sprinkler pipes, were installed and attached to the filigree structure, which almost seems to disappear among all the additional features around it.

A Rewarding Journey

The Academy Museum of Motion Pictures certainly provides the appropriate setting for the celebration of the craft of filmmaking. As visitors explore its many generous spaces and terraces since its opening on September 30th, 2021, many acknowledge the creativity and care that went into designing and building the structures – a result of a multi-year-long international collaboration between experts in the field of architecture, engineering, and construction.■

Thorsten Helbig is a Founder and Partner at knippershelbig in Stuttgart, New York, and Berlin. He is an Associate Professor at The Cooper Union in New York, a Professor at the University of Applied Sciences in Darmstadt, Germany, and a member of the ASCE Aesthetics in Design Committee.

Florian Meier is leading the New York Office of knippershelbig. He is an expert in complex structures and sustainable design and has been the project leader of the AMMP project. He is an Instructor at The Cooper Union in New York, a Lecturer at the University of Pennsylvania, and a member of the International Association for Shell and Spatial Structures (IASS).

Close-up view of fabrication sample of the upstand, which connects the glazing support profiles to the main structural arches.

Aerial view of the assembly on scaffolding

Test assembly at the fabricator to check geometry and tolerances before final coating, packaging, and shipping to L.A.

since 1922

If There is an Engineer Shortage, What Caused It?

By John A. Dal Pino, S.E.

In the December 2023 issue of STRUCTURE (Stop Trying to OutRecruit the Competition), Anthony LoCicero discussed the current high demand for engineers, and the challenges firms nationwide, large and small, are having with recruitment and retention. In addition, he offered a unique perspective on hiring, namely, looking for candidates that do not fit the typical profile. In this article, I address the hiring issue from a more traditional perspective: hiring recent graduates educated in U.S. university engineering programs. I present my recent experiences and what I believe needs to be done.

For the longest time, I have not been convinced that an engineer shortage existed, although many claimed one did. Demographic group data (students entering or not entering engineering programs, experienced engineers leaving the profession, etc.) was often used to identify trends leading to a long-term shortage. The counter to that prediction is that engineer productivity has increased tremendously over the past few decades because of new technologies. However, this has to be offset by increasing code complexity, which creates more work and the tendency to calculate almost everything. When was the last time you saw the phrase “okay by inspection” in a set of calculations?

Instead of focusing on demographics, I made my judgment using observed marketplace supply and demand. During my career, I observed that on most significant projects I have pursued, multiple firms have always been competing for the work, and the fees being offered were just about right or slightly aggressive on the low side, but certainly not high. To me, this signals that the competing firms have enough staff (supply) for the work in the marketplace (demand). I would suspect that over time, if there were really a shortage of structural engineers, the economic laws of supply and demand would dictate the higher fees required to hire the ever-scarcer engineers. However, I haven’t seen any evidence of this, so I am still doubtful of the numerical shortage argument.

In early 2022, our firm concluded that we had enough forecasted work to recruit and hire additional staff. Many firms lost some staff during the COVID slow times, and we were no exception. A small group of us is charged with sifting through resumes, evaluating candidates, conducting interviews, and making offers. I suppose it should not have been a big surprise, but we quickly discovered that lots of firms were recruiting in the same areas we do, at the same time. In the past, this meant that the number of candidates would be less than we would have liked and that perhaps the most desirable candidates would have many attractive offers. But we did not expect it to be almost impossible to hire engineers with the backgrounds and experience to work in a typical structural engineering office like ours.

To set our search parameters, we typically look for recent graduates or engineers with a few years of experience, generally with Master’s degrees, having:

1)Functional knowledge of basic statics, i.e., an ability to draw a freebody diagram with the forces adding up,

2)An idea of how the various parts of a building work together to resist gravity and lateral loads, i.e., intuition as to how mechanisms work,

3)An engaging personality and communication and writing skills that permit them to interact effectively with our clients and contractors, and

4)An ability to interact with the interviewer and reason a problem out if they don’t have a solution.

We reason that we can teach young engineers everything else via on-the-job training, including how to follow codes and standards and how to use common engineering software.

During the resume review process in the spring of 2022, we deemed roughly 20% of the original applicants worthy of further review and an introductory telephone call. Following the call, we invited roughly half (10% of original applicants) in for an

interview. We made offers to roughly half of those (5% of applicants). Some accepted our offer, and some did not. Doing the math, this is the shortage I observe, with roughly 95% not making it through the entire process. Many applicants had too much education and no practical experience or graduated from college programs that do not appear to be designed to produce employable structural engineers.

More specifically, this is what we found lacking in applicants:

1)Statics is a class everyone takes but does not appear to be stressed nearly enough. In our interviews, candidates who graduated from U.S. undergraduate programs fared worse than candidates educated outside the U.S. This is a significant issue because statics and free-body diagrams are the foundations upon which all other more advanced structural engineering is based. Somewhat like reading and writing, it is very difficult to learn well later if these skills are not learned well early. Most candidates have extensive experience with basic structural analysis software, but often this masks a lack of basic problem-solving skills using rough estimates and pencil and paper.

2)One would expect that after two, three, or more years of college-level work, candidates would have been taught how common structural systems function and resist gravity and lateral loads. But if you assumed that, you would often be wrong. For example, almost everyone we interview has been in a warehouse store like Costco or Walmart. However, a candidate rarely understands how the basic box-store structural system works, even though it is exposed and easy for them to see. We expect candidates who want to be structural engineers to be curious about the structures they see all around them.

3)Carrying on a conversation and

presenting oneself well does not appear to be part of the engineering curriculum, but it easily could be. For example, making a speech in class, explaining a homework assignment to a group, or describing the results of an investigation in a larger setting would offer considerable benefits to students at no cost and with little effort.

4)Defending what you know, showing a willingness to admit what you don’t know, and the ability to think on one’s feet is critical. An experienced interviewer can penetrate the often thin veneer of a candidate’s knowledge within a few minutes. Since the candidates are new to engineering, this is to be expected. But it appears that undergraduate education may focus too much on attending class and earning grades, with insufficient time dedicated to debate, discussion, and critical thinking. I was taught basic structural analysis in college by a professor who served as a U.S. infantryman and fought in the WWII Battle of the Bulge. It was tough sledding and painful at times, but I quickly learned to show up at class ready to engage or to be exposed as unprepared since there were no trees to hide behind.

As you can see, I am often less than impressed with the typical college graduate’s skillset, although I am occasionally blown away by the best of them. I sense that if there is a numerical shortage, it is more a shortage of engineers possessing sufficient employable skills, as noted above, than an overall numerical shortage. Some of this educational deficit can be placed at the feet of the student. Still, it seems that colleges and universities have significant responsibilities, too, since there appears to be a misalignment between the needs and goals of educational institutions and engineering employers, exacerbated by some government policies to be discussed later. The story goes something like this:

1)Tuition must pay for student attendance. That tuition has risen steadily for several decades due to increased administrative overhead costs resulting from government mandates, higher professor salaries and less teaching, and fancier buildings and campus amenities designed to attract students, parents, professors… and perhaps most importantly, donors.Higher-paying first jobs are

obviously attractive to pay for the ever-higher expense of college. It is well known that contractors pay new graduates more than structural engineering firms and that many professions (finance, business, computer science, and technology) pay better than the A/E/C industry. The result is a migration out of engineering.

2)Reduced government funding of public educational institutions has resulted in schools needing to generate more and more income on their own. In addition, since in-state tuition is typically capped or at least controlled via state government oversight, schools need to increase the percentage of international students in student populations since these students pay full tuition compared to the in-state students.

3)The result is a large percentage of international students, educated at least partially at public expense, who, because of government policies, either return to their home countries upon graduation or stay in the U.S. and work via their “student VISA” (actually an F-1 student VISA with OPT (one year) and STEM OPT (two years) extensions for a total of three years), hoping to someday gain H1B or Green Card status with the help of their employer.

Applying for and acquiring an H1B VISA once the F-1 student VISA and OPT extensions expire is time-consuming and expensive for the individual and the sponsoring engineering firm. As a result, many working on their student VISAs reluctantly return home. In addition, the number of H1B VISAs granted is limited by country of origin to protect the employment of U.S. citizen engineers. Still, it discourages the employment of the many high-quality foreignborn engineers trained by U.S. universities.

To make matters worse, if your engineer gets an H1B VISA or your firm hires an existing H1B VISA holder from another firm (there is a cost involved in changing sponsorship from one firm to another, too), there is a government-mandated minimum wage for the H1B VISA holder (but not for the equivalent

U.S. citizen employee). This is the government’s attempt to prevent the exploitation of VISA holders. However, the law actually has the effect of dampening employment opportunities for foreign-born engineers because of the high total cost. The result is the outward migration of engineers.

See the Problem?

So maybe there is a shortage of employable engineers after all! But if there is one, it is not because of the nature of engineering or the reward associated with providing a valuable service to one’s clients and the public. Like many things, it is a problem with several components we, as a society, bring upon ourselves. To address the problem:

1)With all due respect, students need to be smarter about making themselves employable, and the university curriculum needs to focus more on creating well-rounded graduates with solid fundamental skills. Perhaps more career planning is needed. The engineering profession can fill in any gaps. The overall cost of university education has to be reduced so students can become what they want to be rather than what pays the best.

2)Public financing of public universities needs to be restored to past levels so that universities can once again be educational institutions that need to pay their bills rather than businesses chasing dollars and teaching engineering on the side.

3)Change our government’s VISA policies. International students are an overall positive because they increase the educational horsepower of U.S. universities, create a more diverse and interesting student body, and benefit our country in the long term. However, it is unfair and immoral to take advantage of international students for their money when their chance of staying in the U.S. after graduation and working as structural engineers is less likely. ■

John A. Dal Pino is a Principal with FTF Engineering in San Francisco, California. In addition, he serves as the Chair of the STRUCTURE Editorial Board (jdalpino@ftfengineering.com).

As the country comes together to restore the health of our national infrastructure, Atlas Tube is proud to play a supporting role providing quality steel products and components all made right here in America.

B G DREAMS NEED BIG STEEL

Located right here in the U.S., the world’s largest continuous ERW mill rolls Jumbo HSS — the biggest domestic HSS available anywhere. With the high quality and fast delivery times you expect from Atlas Tube, it’s never been easier to start planning big things.

Photo by Max Touhey

FIELD BOLT JUMBO HSS.

structural PERFORMANCE

Architectural Experiments with Foldable Composites

By Joseph Choma

Folding is a systematic method that transforms planar material into threedimensional geometries with structural depth. Through precise calibration, flexible folded hinges can become rigid – capable of withstanding structural loads. Depending on the organization of folds, structures can be flatpacked for ease of transport. Folding can also potentially reduce production costs associated with the complexity of manufacturing parts that have Gaussian curvature. By beginning with a simple flat plane and then folding it, there is the possibility to fabricate geometries that are globally doubly curved but locally developable. Additionally, there are numerous variations possible with one systematic method.

This research seeks to move beyond origami –the art of folding paper – by embracing material and structural constraints. Traditionally, origami is dominantly composed of hidden-under tucked folds, which is neither an efficient use of material nor ideal for resisting structural loads. However, once a folded geometry has a specific orientation to gravity and is considered to have material thickness with the intent of carrying loads, it is no longer “just origami” but a foldable structure. Primarily, the author is inventing new fabrication methods and material logic to expand the possibilities of translating paper folding to materials that have the potential to scale up. In particular, more efficient methods

to manufacture parts are being developed in direct dialogue with the industry to embrace folding as a means to tackle manufacturing applications. These applications include lightweight deployable structures, ultra-thin formwork for concrete casting, and stay-in-place formwork for shell structures and concrete slabs.

Within the field of architecture, we think we have a whole discourse dedicated to foldable structures. However, most structures we label as “folded” are not folded at all but are fold-inspired. For example, in 1923, Eugène Freyssinet designed and engineered two identical aircraft hangars at Orly Airport in Paris. These are considered the first long-span, folded structures. Although Freyssinet’s innovative structural technique was directly linked to the development of reinforced concrete, the structure was not literally folded as we think of folding paper.

With the recent inclusion of fiber-reinforced polymer (FRP) construction in the International Building Code (IBC), textile-based composites are now recognized as viable building materials. Additionally, the Architectural Division of the American Composites Manufacturers Association (ACMA) has produced Guidelines and Recommended Practices for Fiber-Reinforced-Polymer Architectural Products. Significant advances in fire retardant performance suggest that FRP will likely become more widely used in architectural applications. Currently, the IBC and ACMA guides dominantly focus on FRP as cladding systems. This research predicts that FRP might have potential

applications in lightweight, long-span, deployable structures and stay-in-place formwork for concrete casting. This could potentially be the first step to elevating the material beyond decorative cladding (secondary component) to structural applications (primary building material).

This research develops a technique to fold fiberglass – like folding paper by hand – at the architectural scale. Within this research, pliable fiberglass sheets are called “foldable composites.” The concept of foldable composites is straightforward: take a dry fiber reinforcement fabric, mask off seams to create fold points, infuse the unmasked fabric with resin, and cure the resin. This results in a composite laminate with uncured, soft seams that allow the entire structure to be folded for easy on-site transport and installation. After the entire laminate is installed, the dry seams can be infused with resin to solidify the whole structure. The following research explorations advance the current state of foldable composites by developing (and precisely calibrating) this innovative fabrication technique according to geometric constraints. In summary, foldable composites will allow a new range of architectural structures which have yet to be physically realized.

Arch

After numerous small-scale fiberglass studies, the research transitioned into larger inhabitable proof-of-concept built artifacts. The first of these artifacts is an accordion arch based on a variation of the Yoshimura

Detail of curved creases in a foldable composite.

Photograph of the 32-foot 10-inch x 21-foot 9-inch flat fiberglass sheet.

pattern. The lightweight pop-up pavilion was designed, fabricated by hand, and installed by five people. First, two 54-yard-long rolls of 33.3-inch fiberglass cloth were stitched together using a flat felled seam to create one continuous 32-foot 10-inch x 21-foot 9-inch sheet with zero material waste. All the edges were precisely sewn to prevent sharp, rough, or frayed edges.

Next, a crease pattern was drawn on the fabric surface using painter’s masking tape. The intricate pattern was composed of 875 folds, where each accordion fold had a depth of 5 inches. All the planar portions of the structure were then painted with resin. After the resin had cured, the tape was removed, and the structure was folded and compressed into less than a 12-inch width. The flat-packed structure was then easily carried by four individuals and transported to the site. A light scaffolding was constructed on the site in one day. Then, a team of five placed the folded fiberglass above the scaffolding. After another day of applying resin to each crease, the scaffolding was removed, resulting in an extremely thin, lightweight structure spanning 16 feet. This proof-of-concept artifact suggests a means for fiberglass to transition from a secondary component to a primary building material.

Saddle

In the late 1920s, a student in Josef Albers’ Bauhaus studio folded a series

of concentric circles on a piece of paper. A saddle shape emerged as the paper was folded, alternating between mountain and valley folds. A new range of geometric freedom emerges by increasing the number of concentric circles from eight to twenty. It no longer has to remain symmetrical but can be pushed and pulled according to outside forces.

Moving beyond folding concentric circles out of paper, a technique has been developed to allow fiberglass to fold along curved creases. The process begins with a sheet of dry fiber reinforcement fabric selectively coated with resin. Typically, paper models have a particular relaxed state which we can observe after letting go of the model. However, fiberglass does not need to have a relaxed state; any position can be frozen and fixed. After the foldable structure is positioned, resin can be applied to the curved creases to rigidify the structure. Although the structure is at the scale of an object, it suggests

the potential for a larger inhabitable structure. In particular, this was the first time fiberglass had ever been successfully folded along curved creases.

Ceiling or Wall

The crease pattern was inspired by the work of David A. Huffman. In particular, this research develops a means to array Huffman’s initial square with ellipses by systematically mirroring the component. If the tessellation is not iteratively reflected, the surface is not foldable. It can also be calibrated to control a specific structural depth along the surface.

Typically, when looking at a crease pattern, an individual sees a series of mountain and valley folds. However, this tessellated crease pattern could be architecturally interpreted as a reflected ceiling plan, where each square is the location of columns meeting a roof.

The folded fiberglass panel is 8 feet long, 4 feet tall, and has a structural depth of approximately 12 inches. Although it was initially imagined as a roof structure, the same design could be applied to make a wall panel or partition. The piece is able to stand vertically without any additional support. The fiberglass piece was folded out of one continuous flat sheet. It took just two people to hand-fold this crease pattern into place.

The lightweight structure can be folded and compressed into less than a 12-inch width.

Photograph of the folded fiberglass arch spanning 16 feet.

Photograph of the folded fiberglass tessellation on the side of the cube.

Column

The folded column was designed based on intuitive structural and aesthetic criteria. More specifically, the curved creases “kiss” and mirror along vertical lines. This transitions the crease from behaving as a hinge to that of a bi-stable structure – similar to a curved tape spring.

The lightweight column is 8 feet tall and can effortlessly be carried by one person. Since all the creases are mountain folds, it is easy for an individual to fold the entire column. The crease pattern was deliberately designed to have five faces to allow one face to overlap with another. Chopped strand mat was placed in between the two overlapping panels. The connecting seam is nearly invisible because it aligns with the curved creases.

Although the column was imagined as a lightweight foldable structure, the column could be used as a stay-in-place formwork for a concrete column. The fiberglass could also provide additional tensile reinforcement. Alternatively, it could become a reusable formwork with just a few adjustments.

Cube

In the 1980s, the artist Donald Judd created

15 concrete rectilinear tubes in Marfa, Texas. The installation explored the concepts of framing views and defining spatial boundaries in a landscape with a series of geometric primitives. This folding exploration takes inspiration from Judd’s work by creating a folded cube.

First, a globally-flat folded plane was created using a Miura-origami crease pattern (series of folded parallelograms). Then, to allow the crease pattern to turn a corner, a diamond is inserted into the crease pattern. This is similar to the Yoshimura pattern, composed of an array of diamonds. Then, the proportions of the crease pattern on the two long edges are compressed to create a reinforcing frame for the folded geometry. This added step locks the entire crease pattern into a fixed condition. Finally, the crease pattern’s two short edges are connected to form the closed tube.

Cone

Cones are well-understood developable surfaces, and folded cones have been created through various approaches in the past. In particular, alternating a series of mountain and valley arcs defines a folded cone that appears to

be telescoping. Instead of adopting one of these known crease patterns, a new crease pattern is created by combining two different folding logic. Most folded plate structures in architecture are fundamentally based on the Yoshimura pattern (an array of folded diamonds with horizontal valley creases). This commonly used crease pattern is mapped to an unrolled conical projection within this exploration. Curved creases now define the crease pattern that was once defined by straight creases. When the two edges of the conical projection are connected, the curved cells pop inward like a bi-stable structure defined by concentric circles.

Photograph of the folded fiberglass cube.

Crease pattern of the folded cube.

Photograph of the folded fiberglass cone.

Crease pattern of the folded cone.

A-Frame

In many residential buildings, the gable roof is a traditional architectural typology. This research exploration began with the question: How can we transform this traditional profile with curved crease folding? A folded A-Frame is created, taking inspiration from a columnar element designed by David A. Huffman. The proportions of the arcs are precisely calibrated to accommodate the two different angles of the A-Frame geometry. The tubular space is 16 feet long and is defined by a series of curved and straight creases. These creases are only locked in place after the two outer linear edges are anchored to the ground. Although the global A-Frame is a familiar architectural profile, it appears new, unfamiliar, and dynamic in this inhabitable artifact.

Photograph of the folded fiberglass A-Frame.

Vault

A saddle shape emerges when folding a series of concentric circles or ellipses, alternating between mountain and valley folds. The saddle is a doubly-curved geometry with negative Gaussian curvature. This research exploration began with the question: How would one create a doubly-curved (folded) geometry with positive Gaussian curvature (like a vault or dome)? Pulling in some points along a circle could form a star with rounded edges. Intuitively, it might make sense to create a concentric crease pattern with rounded stars to define a folded vault. However, if all alternating mountain and valley creases are simply offset or evenly spaced, the folded surface will want to stay globally flat. Conceptually, the two-dimensional geometry wants to define positive curvature, but the rule of using concentric shapes is wanting to define

negative curvature. This leads to a geometry that is not able to become volumetric. Therefore, it became important to take a step backward to move forward with this crease pattern design. Imagining the crease pattern as a series of straight creases, it becomes evident that the valley folds want to be diagonal and not parallel to the mountain folds. When applying this rule to the curved crease pattern, the valley folds begin to undulate up and down between the mountain folds. This allows the folded geometry to define a shape with positive Gaussian curvature. Unlike a traditional vault, this folded vault gains rigidity through controlled buckling.

Over the past twenty years, there have been numerous intellectual contributions to the mathematical abstraction of folding, such as geometric folding algorithms. There have also been significant advancements in the computational simulation of curved crease folding.

However, many of those advancements have not directly influenced the field of architecture. Most of those contributions ignore materiality, sheet thickness, and gravity – which are fundamental to the built environment. Other folding-related research does focus on construction-based architectural constraints. For example, some research explores prefabricating concrete elements, perforating metal sheet materials, or connecting discrete planar elements. This research into foldable composites conveys a new alternative means and methods of construction for foldable structures and materials. Fundamentally, this research stays true and pure to the paper folding logic even when we scale up.■

Photograph of the folded fiberglass vault.

Crease pattern of the folded vault.

Joseph Choma is the Director of the School of Architecture and a Professor of Architecture at Florida Atlantic University.

Interior photograph of the folded fiberglass A-Frame.

Your success starts with the right steel joist and deck supplier

Make successful connections. Control costs, improve performance and achieve project success using our steel joists and steel deck. Get answers, advice and assistance from our supportive specialists. Find the ideal structural steel building solution for your next project. Together, let’s build it better.

structural SPECIFICATIONS

What’s New Under the Sun?

ASCE/SEI Solar PV Structures Committee Manual of Practice

By Nestor A. Agbayani, P.E., S.E., M.ASCE, Steven M. Gartner, P.E., M.ASCE, and Alexander E. Coologeorgen, P.E., PMP, M.ASCE

As the energy market transitions towards having a larger renewable energy component, the solar energy industry has experienced fastpaced growth. In particular, the solar photovoltaic (PV) industry has grown rapidly over the last decade, which has presented numerous challenges. One significant growing pain has been the lack of design guidance on solar PV structures from the building codes. The building code (referred to herein as the “Code”) is typically some version of the state building code based on the International Building Code (IBC) as adopted by the local Authority Having Jurisdiction (AHJ).

The practice of structural engineering is a technical endeavor, an art, and a business enterprise. The practice benefits when the Code establishes minimum and uniform standards that define a level playing field for producing structural designs and reviewing them for compliance. Another essential function of the Code is to emphasize public safety by defining critical aspects of the engineering “standard of care,” such as the expected basic safety and reliability of engineered structural systems. Unfortunately, these functions are held in delicate balance with and sometimes eroded by a competitive commercial environment in which constant pressure exists to economize/optimize structures.

The Wild West

Some structural engineering practitioners like to describe the current design landscape in the solar PV industry as the Wild West. While the solar industry may contain its share of outlaws and other ornery varmints (i.e., bad actors), it is the Wild West because of the lack of explicit Code design guidance for solar industry structures. The result is a lack of consistency and, in some cases, confusion. Here are a few examples:

• Inconsistent interpretation and application of existing Code provisions that are not readily applicable to solar PV among designers, AHJs, and other reviewers;

• Use of widely different methodologies with varying degrees of design safety, reliability, and effectiveness;

• Inefficient permit review by AHJs due to lack of familiarity with or confusion about industry norms;

• Inconsistent requirements among AHJs; and

• General lack of design guidance on some design issues.

ASCE/SEI Solar PV Structures Committee

To address these challenges, the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE) recently approved the formation of the ASCE/SEI Solar PV Structures Committee. The Committee comprises many solar PV energy industry stakeholders (engineers, AHJs, solar equipment manufacturers, owners, developers, and contractors). It is focused on the consistent and reliable design of structures that support solar PV systems. Structures supporting concentrated solar (i.e., a “mirror farm” focusing light on a central boiler), hot water solar power, or any non-PV-related solar power system are not under the dominion of this committee. The Committee’s mission is defined in its statement of purpose:

To promote advancements in the design, procurement, permitting, and construction of solar photovoltaic (PV) ground-mounted, canopy, and roof-mounted structural systems. The committee, made up of an interdisciplinary team of engineers, manufacturers, contractors, permitting officials, and owners, addresses issues in design and construction, shares lessons learned, develops design guides and standards, and advocates for the reliable and consistent design and development of solar PV power generation structures.

Figure 1. Typical ground-mounted fixed-tilt rack system. Courtesy of ASE.

Currently, the Committee’s primary effort is working towards the mission of “…shares lessons learned, develops design guides and standards…” so that more consistency can be brought to the Wild West by producing a Solar PV Structures Manual of Practice (MOP).

The coming together of stakeholders in an industry to bring some level of consistency to the design process is not new. The Structural Design of Air and Gas Ducts for Power Stations was developed by the Energy Division of ASCE to bring design consistency to large-scale ductwork used in power-generating facilities. The Subcommittee on the Design of Substation Structures of ASCE developed the Substation Structure Design Guide to provide consistency amongst substation design engineers. When the utility-scale wind energy industry was facing similar circumstances a decade ago, stakeholders in the utilityscale wind industry formed a joint committee to address the challenge of bridging and reconciling the industry’s prevalent international design practices with U.S. Code requirements. Under the aegis of the ASCE and the American Wind Energy Association (AWEA), a guidance document was created: ASCE/ AWEA RP2011, Recommended Practice for Compliance of Large Land-based Wind Turbine Support Structures. It was introduced in STRUCTURE’s July 2013 issue in a piece titled Wind Farm Tower Design

The Solar PV Structures Manual of Practice

The MOP is intended to provide needed design guidance to the solar industry for the following benefits: education, consistency, managed risk, and innovation – all contributing to more reliable solar PV power. The developing MOP currently has the following outline:

Chapter 1. Introduction: intent, limitations and scope, solar industry glossary.

Chapter 2.Design Loads: recommended risk categories, wind, wind tunnel testing, dynamic sensitivity, aerodynamic instability, flood and scour, ice and hail, snow, earthquake, frost jacking (heave), effects of stowing, peer review.

Chapter 3.Corrosion: science of corrosion, rational application of unknowns and variables, basis for estimates, and factors of safety applying to solar PV structures.

Chapter 4.Structural Design: load combinations, resistance factors, serviceability and displacements, structural connections. Chapter 5.Foundation Design: Solar PV foundation design using driven piles and drilled piers.

Chapter 6.Construction Quality Assurance: special inspections, preconstruction/pull testing of piles, construction/production pile testing.

Chapter 7.References.

Solar PV Structure Types

The MOP will cover the following types of solar PV systems. Ground-mounted PV (GMPV) support structures:

• Fixed-tilt rack systems. See Figure 1

This system consists of PV panels supported on a steel purlin-beam framework supported on a foundation consisting of driven steel piles, helical anchors, ballast foundations, and sometimes cast-in-drilled-hole piles.

• Single and Dual Axis Tracker systems. See Figure 2

These systems consist of PV panels attached to either a racking system, such as on a dual-axis tracker, or a torque tube, such as on a single-axis tracker, that allows the superstructure assembly to rotate mechanically and actively tilt toward/track the sun during daylight hours. The supporting foundation typically consists of driven steel piles, helical anchors, shallow foundations, or ballast foundations.

Rooftop PV (RPV) support structures:

• Building roof mounted. See Figure 3.

This system consists of PV panels supported on a lowprofile framework that is either ballasted on the roof or mechanically anchored to the roof.

Elevated PV (EPV) support structures:

• Parking lot carport roof mounted. See Figure 3. This system consists of PV panels supported on a roof framework supported on vertical cantilevered columns attached to the top of either piles, cast-in-drilled-hole piles, or spread footings. This configuration allows the solar structure to serve as a parking lot shade structure and produce power.

Floating PV (FPV) support structures:

•Floating solar PV.

This aquatic system consists of a low-profile framework similar to a rooftop framework system but is attached to the top of floats. The floats are then fastened together, and

Figure 2. Typical single-axis tracker system. The torque tube (centered longitudinal tube member, left) rotates (twists) to facilitate tilting the solar PV panels mounted to the superstructure. This way, the tracker system can tilt toward and track the sun. Courtesy of Anubhav Tandon; Array Technologies Inc.

the entire system is anchored to keep it in place on the body of water.

Design Challenges and Recommended Practices

What may be apparent is that solar PV structures are relatively lightweight and flexible compared to other nonbuilding support structures. As such, they tend to be dynamically sensitive structures that, in many cases, exhibit resonant vibrations, galloping, and flutter even at low to intermediate wind speeds far below the Code’s extreme design wind speed. The MOP will attempt to address the many design challenges that the industry faces due to the unique aspects of these structures.

The MOP will provide a snapshot of the current state of the solar PV structure design practice and recommend solutions to a myriad of structural design challenges. The following are some of the significant topics that will be explored in the MOP.

Wind

Due to the characteristics of solar PV structures and their corresponding structural behavior, one of the biggest challenges is establishing Code-compliant wind loading design criteria. Also, the direction from the ASCE 7 on wind loading is wide-ranging. The MOP will provide guidance on how to utilize the existing

ASCE 7 standard design recommendations while filling in key areas that were too new to get into the most recent version of the ASCE 7 standard. These key areas include additional guidance on calculating more refined wind loads in coordination with ASCE 7 and other solar industry standards and how best to apply ASCE 7 wind parameters such as directionality and pressure coefficients to a solar PV structure while considering its unique structural behavior.

Many ground-mounted solar PV structures are relatively lightweight and flexible. Due to this unique trait, these structures are dynamically sensitive and are at a high risk of experiencing aerodynamic instabilities that have been known to result in structural failures. The MOP will provide guidance on dynamic sensitivity, including evaluating aerodynamic instabilities, wake buffeting, and vortex shedding. There will also be guidance on aerodynamic instability for low tilt, stiffness-driven instability (static or cyclical torsional divergence and torsional galloping); high tilt, dampingdriven instability (flutter, vortex lock-in, torsional flutter, stall flutter); wind tunnel testing for instability (section model testing and aero-elastic model testing); and numerical assessment by computational fluid dynamic (CFD) simulation.

Ballasted roof-mounted PV systems that have undergone wind tunnel testing to establish loading requirements are sensitive to vertical lift, which can negatively affect the applicability of the wind tunnel test results. As a result, the current provisions for the Effective Wind Area (as defined in ASCE 7) on solar arrays may be unconservative due to this effect. The MOP will provide guidance on testing rooftop array structures intended to reduce

Figure 3. Combination rooftop and carport/parking lot shade structure solar PV installations are an ideal use of area at large retail establishments. Courtesy of Target Corporation website.

the risk of excessive lift of the array, leading to a more accurate determination of the Effective Wind Area.

Frost Jacking

While the weather becomes increasingly warmer in many areas, the ground still freezes in many parts of the U.S. during winter. Since ground-mounted solar PV structures are relatively lightweight with relatively deep piles, they are susceptible to frost jacking. Frost jacking is an upward, permanent heave that takes place during freeze and thaw cycles and can damage solar PV arrays due to non-uniform differential displacement.

Frost jacking occurs when the three “Ws” happen at the same time:

• Winter (soil temperatures below 32° F),

• Water (in the soil), and

• Wicking (soil types that pull up in-situ moisture from below its elevation, typically clays and silts).

If one of these “Ws” is not present, frost jacking will not occur. Once the potential for frost jacking has been evaluated, it is sometimes possible to reduce the risk of frost jacking forces through mitigation measures. However, one of the challenges with mitigating frost jacking is determining the strength of the bond that develops between a pile and frozen soil (i.e., adfreeze bond stress) to use in design.

The MOP will provide an overview of the mechanics of frost jacking, including the driving forces behind adfreeze bond, and provide engineering solutions to mitigate frost jacking by addressing the primary mechanisms of action and reduce the risk of a pile experiencing uplift.

Corrosion

Utility-scale solar PV projects may have hundreds of thousands of steel piles driven into the earth. While most structural engineers understand the general importance of corrosion above and below grade, few have subject matter expertise specifically in corrosion. The MOP will provide an overview of corrosion mechanisms, testing, and rates. The MOP will also provide guidance in determining service life projections and implications of safety factors with respect to data uncertainties.

Even on larger projects where a specialized “corrosion engineer” subconsultant may be retained, it is prudent that structural engineers understand the subconsultant’s findings and recommendations as they relate to the structural design of the pile foundations. The MOP will provide information on relevant corrosion protection techniques, such as corrosion rate calculation methods incorporating the Romanoff similitude procedures, protective and sacrificial coatings, cathodic protection, modification of the environment, and proper testing, design, and material selection.

Rooftop Solar

Rooftop loads from the solar racking occur as concentrated loads, linear loads, and uniform loads. Considering only aggregate uniform load effects when performing a structural capacity evaluation of the existing roof may overlook roof framing and decking capacity limitations. The MOP will provide design guidance on the importance of considering concentrated, linear, and increased

uniform load effects from PV racking when performing capacity checks of the supporting decking and roof framing elements.

Rooftop solar design and construction have outpaced the development of building Code requirements for this work. Various solar industry guidelines and standards, such as the Structural Engineers Association of California (SEAOC) rooftop solar guidelines, have been written to bridge the gaps while the Code catches up. Also, many local jurisdictions have enacted ordinances specific to rooftop solar to serve as local design requirements. As a result, structural design requirements for rooftop solar evaluation are scattered and not well consolidated. The MOP will consolidate the pertinent Code provisions, industry guidelines, standards, and ordinances for reference by rooftop solar design engineers and others.

Determining existing building roof dead loads and structural capacity can be critically important and should be based heavily on confirmed facts and lightly on assumptions. The MOP will provide best-practice methods for determining existing roof load and capacity information for rooftop solar construction. These methods will cover the investigation of existing/as-built drawings, site investigation, destructive and non-destructive testing, and other tips and tricks.

The MOP will also provide guidance in determining the capacity of the often overlooked roof deck on existing buildings and the mechanical attachments to the roof deck. In addition, the MOP will discuss ICC Evaluation Service report AC467, Acceptance Criteria for Proprietary Attachment Systems of Photovoltaic (PV) Arrays to Roof Assemblies, in which the allowable capacity of the attachment system is based on a safety factor of five. Also discussed will be the importance of reconciling the modeling of roof construction in the test configuration versus the subject roof’s as-built field condition.

Conclusion

Over the past decade, there has been rapid growth in the solar PV industry. As often happens in industries that require unique nonbuilding structures to support the main equipment, the Code is not able to adequately address the solar PV industry’s specialized design needs. Following the tradition that has been set in other industries like fossil fuel power generation, substation design, and wind power, the newly formed ASCE/SEI Solar PV Structures Committee is developing a Manual of Practice that will provide design guidance to the solar PV industry and allow industry stakeholders to design and develop consistent and reliable structures. Check the ASCE website (https://www.asce.org) for Manual of Practice development updates.■

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

Nestor A. Agbayani is a Principal Engineer at Agbayani Structural Engineering (nestor@agbayanistructural.com).

Steven M. Gartner is a Principal Engineer Renewables at HDR (steven. gartner@hdrinc.com).

Alexander E. Coologeorgen is a Principal Consultant at Sargent & Lundy (acoologeorgen@sargentlundy.com).

Times Square in New York is known for many things, including its Broadway Theaters, luxurious hotels, trendy retail, great entertainment venues, and flashy billboards. In the case of TSX Broadway (1568 Broadway), the project contains all these items in one building. What makes TSX Broadway truly special

TSX Magic on Broadway in Times Square

By Cawsie Jijina, P.E., and J. Benjamin Alper, P.E., S.E.

is not just that it contains all the elements of Times Square in one location. How existing elements were shifted, assembled, and juxtaposed with new elements makes this Entertainment complex and hotel tower a unique structural engineering feat.

Act 1 – The Challenges

1568 Broadway (formerly the Doubletree Hotel) stood as a 470-foot-tall structure constructed next to and over the landmarked Palace Theater, with the theater existing in most of the lower floors. The hotel building, initially constructed in the 1990s over the 1910 Palace Theater, no longer met the requirements of a modern hotel. With 8-foot floor-to-ceiling heights, the hotel rooms were not desirable to current hotel chains. Times Square’s streetscape is one of the most valuable retail spaces in the world. A theater sited at the world’s busiest crossroads does not generate revenue during the day as it sits idle, waiting for its doors to open in the evening. And the Palace Theater has a history – as a protected historic landmark, as one of the first vaudeville theaters on Broadway, and as home to some of the most iconic performers and performances over its 110-year life. As such, it could not simply be demolished or replaced to free up space, however valuable that space may be. Additionally, having only one basement limited the service space to serve the multiple occupancies. Severud Associates was contracted for the structural engineering on this project.

Act 2- The Solutions

Demo and Rebuild the Hotel Tower: Demolish and rebuild the upper 30 floors of the hotel tower with higher floor-to-floor

Stacking diagram showing the before (left) and after (right).

heights while still retaining 25% of the original building structure. The 25% retainage is key to maintaining the current zoning floor area. The net increase in building height is approximately 100 feet, significantly increasing wind and seismic forces on this high-rise building.

Dig Another Lower Basement: Add a new subcellar below the existing cellar. Retaining 25% of the existing building implies that existing foundations still support loads imposed from above and, therefore, cannot be undermined during the renovation. Then there are the four “super-columns,” soaring unbraced for over 100+ feet that hold up the transfer trusses that support the existing hotel tower rising above the theater, each supporting over 25 million pounds of weight.

Why Not Just Lift That Theater and Get It Off the Street: Lift the existing theater 30+ feet into the air. This creates a new volume at the street level to add a multilevel retail space and better building access. Unfortunately, the space directly above the existing theater is the location of the existing transfer trusses that hold up the tower over the theater. This brings us to…

Let’s Relocate the Existing Transfer Trusses Higher: Relocate the existing transfer trusses 3 stories higher while maintaining support for the remaining seven levels below.

An almost Column-free Entertainment Space? Why Not?

The lower 12 existing hotel floors were envisioned as a flexible entertainment space. Unfortunately, that requirement increased the load capacity requirements by 250% and necessitated the removal of every other existing column without demolishing the floor itself; remember the 25% floor retainage requirement?

Act 3 – The Execution

Demo and Rebuild

The tower’s upper 30 floors (floors 17-46) were mechanically demolished, and the debris was lowered to the ground floor

for removal off-site. The 25% retainage of the building had to be done in creative ways to avoid having to retain the hotel floors. Based on a zoning interpretation specific to the project, it was permitted to count the raised theater as retained floor area. Creative ways were used to retain slabs and increase their capacities in other areas by bonding them with structural topping slabs. Elsewhere, epoxy pins bonded a reinforced concrete slab to the existing 8-inch concrete flat plate, artfully manipulating the new and existing reinforcement to create a new space that met the higher user needs (larger capacity and longer spans). The increase in building height along with the retainage of the lower floors also meant that a new approach was needed to increase the lateral strength and stiffness of the building. Existing cores were utilized and enhanced by linking them with new frames, increasing their capacities with minimal cost impacts. A new cross-braced frame was added from the foundation to the 16th floor, creating the visual X that makes this the TSX Tower.

Dig a New Basement

Adding a new basement below the existing building is challenging since the excavation inherently undermines the existing footings because it was necessary to keep the existing structure in place throughout. Rather than a costly retrofit, a new concrete system holds the existing structure in place and re-directs the loads to new concrete columns supported by caissons drilled into rock. During their installation, the caissons were fully braced from the cellar and below. As the building rose, the rock and soil around the caissons were demolished for the new subcellar, and the existing floor elevation was lowered by 12 feet. A new concrete superstructure supported by the existing steel frame was designed with the new concrete floor slabs cast through the existing steel columns. Once the new configuration was in place, structural support shifted from old out-of-place columns to new columns, and the old support structure was removed. However, the increased loads on the super-columns

New concrete superstructure with abandoned existing steel columns and beams intertwined before they were burned out.

New concrete ring beam below existing theater walls with jacks engaged supported on new caissons to subgrade below.

demanded a more elaborate foundation. The solution entailed jacking the existing super columns and sliding a new support table founded on new caissons under them.

Move That Theater

The theater is a hollow box – heavy masonry walls on the exterior create a giant box. Balconies are cantilevered off these exterior walls. There are only four interior columns, and they stand as sentries around a magnificent stage. If those exterior walls are compromised, the theater ceases to exist. Therefore, Severud designed a robust concrete ring beam and integrated it with the theater lift system under the walls to minimize the possibility of cracking these century-old masonry walls. Thirty-four lifting

caissons with 4 jacks per caisson lifted the 14-million-pound theater structure at a rate of about 4 inches per hour. The total height of the lift was approximately 30 feet.

Relocate/Redesign Existing Transfer Trusses

The existing transfer truss had to be relocated further up in the building to create a new volume for the raised theater. Logic would dictate a light structural steel truss system. But are you really going to stick-build a steel truss capable of supporting a 600-foot-tall concrete hotel tower, 150 feet above street level and above a 110-year-old theater? Where would the working platform be? What would support it? How does one control the levelness of the tower floors as the steel support structure deflects under increasing loads?

Never Let Conventional Wisdom Dictate Design

It may seem completely insane and counterintuitive, but in a move that raised eyebrows by the owner and all contractors involved, the design team opted to go with what is now recognized as the longest post-tensioned concrete support system for a vertical build in the world. The proposed system was composed of three post-tensioned concrete super-girders 140 feet long. Each super-girder would be 4.5 feet wide and 41 feet deep. All three super-girders would be linked together at the 12th and 16th floors by cast-in-place concrete slabs that braced them.

New steel caisson to support the concrete superstructure. The caissons were installed at the cellar level in pieces not larger than 8-foot lengths.

Existing super-column with brackets and jacks to transfer loading to new caissons to allow footings to be undermined.

A section through the post-tensioned boxed girder system.

Cross girders of like dimensions would support them in delivering the loads to the four super-columns.

The super-girders would be designed and constructed to be totally self-supporting in 10-foot-deep increments. The first 10-foot-deep section would be supported by falsework bearing on the existing steel trusses and would be post-tensioned. The first 10-foot-deep post-tensioned segment would support the next 10-foot depth. This second segment would then be tensioned to keep everything level. The lower 20-foot segment would now support the third and fourth segments.

Deflections were limited in the support structure to prevent increased costs due to the addition of concrete to level the hotel tower floors. The design team, therefore, devised a system whereby the cables in the post-tensioned support system were re-tensioned as each ten-floor segment of the hotel tower was erected above it. Every ten floors, the super-girders were prestressed to a position calculated to give them a slightly upward camber. The process was repeated four times. When the roof level was finally in place, the super-girders had a total deflection of 0.25 inches over a +140-foot clear span while supporting a 600-foot-tall cast-in-place concrete hotel tower above them.

What’s a Venue on Broadway Without a Stage?

TSX Tower boasts a 51,000-square-foot LED signage wall on its façade that seamlessly slides open on the third floor to project a 4,000-square-foot stage onto Times Square for live performances to be viewed from the crossroads of the world.

The Finale

Most projects have a single challenge that requires creativity. However, it takes out-of-the-box ideas to make the magic when

you have numerous unique, complex challenges within the same project. But once in a while, someone like this owner (L&L Holdings) believes in you, your creativity, and your structural engineering prowess to allow you to respond to complex challenges in unorthodox ways.

The laws of physics are uncompromising. Gravity is not an enemy but a force that can be used and manipulated to counterbalance other forces. And the best designs are those that do not use scads of material to resist loads but those where thrust meets thrust and is held in perfect balance. The structural engineering design of the TSX Tower on Broadway is that design. While Severud may have been the originator of the creative structural engineering design solutions used in this project, the work would be impossible to accomplish and execute without the entire team that was part of this amazing endeavor. The list of “actors” is included in the Project Team (sidebar). In addition, the General Contractor and their sub-contractors are acknowledged for a job well done and for making this a genuine team effort.

Acknowledgment

The authors extend thanks to Ms. Meghan Krupka, Severud's Site Structural Engineer, for her attention in ensuring the design was successfully executed. Ms. Krupka, also an award-winning photographer, is credited for all the photos in this article. ■

Project Team

Owner: L&L Holding Company & Fortress Investment Group

Structural Engineer of Record: Severud Associates Consulting Engineers

Architect of Record: Mancini Duffy

Preservation Architect: Platt Byard Dovell

White

Building Envelope: Perkins Eastman

Means and Methods Engineering: Howard I Shapiro

Foundation/SOE Engineer: Langan

Sign Structural Engineer: Ryan Biggs

Clark Davis

General Contractor: Pavarini

McGovern

Steel Fabricator: Weir Welding

Steel Erector: J.C. Steel Erectors

Steel Detailer: Gress Corp

Concrete Contractor: Sorbara

Construction

Theater Lift Engineer/Contractor and Foundation Contractor: Urban Foundation Engineering

Post-Tensioning Contractor: VSL|Structural

The top of the concrete box girders on the left with the 5-foot-thick transfer slab on the right side.

Cawsie Jijina is a Principal at Severud Associates (cjijina@severud.com). J. Benjamin Alper is an Associate Principal at Severud Associates (jalper@ severud.com).

Why Virtual Design and Construction is the Future of Building

By Michael Schroeder, CCM

As a result of the pandemic, global supply chain issues and inflation rates have led to significant delays in design, architecture, and construction. Yet, now more than ever, architects are being called on to deliver more complex buildings with shorter delivery schedules while remaining on time and within budget. As the industry adjusts to these new circumstances – and the fear of how significant material shortages impact our designs – what has become increasingly evident is that there must be a tightly orchestrated approach between all partners to ensure the seamless planning and execution of a project from the very beginning. By employing this strategy, the Spagnolo Group Architecture (SGA) team recently accomplished a seemingly impossible feat: completing construction on a project in just six months that would typically have taken over two years.

SGA was tapped to work on the latest addition to Gillette Stadium in Foxboro, Massachusetts. Intended to be a multi-purpose space for the New England Patriots, International Forest Products, and parent company The Kraft Group, the team was tasked with designing and building the first phase of a new, four-story mixed-use building.

However, this 120,000-square-foot facility came with its challenges: it had to be built between the New England Patriots’ football seasons and operational by the time fans walked into the stadium for the start of the 2022 NFL season.

Faced with this incredible opportunity, the SGA team understood they had to defy the odds to meet the project’s lofty goals. So, to help drive the design and coordination process to ensure that phase one was completed on time, the firm implemented the SGA Dashboard – a proprietary program and companion tool to its Virtual Design + Construction (VDC) arm, which was developed in recent years. This digital platform functions as a hub to manage projects from concept to completion. Essentially, it bridges the gap between design and construction before the project even begins, opening more effective project planning pathways to line up numerous timelines and priorities. In addition, it resolves issues or questions that often come up between teams later (that can stall the process by weeks or months) and allows planning for and ordering material and equipment much earlier than in typical projects.

The SGA Dashboard; the firm's proprietary VDC project platform

While unconventional, this approach creates a more seamless design and communication process by integrating the essential element in design – the relationship among human beings – with advanced technologies. In addition, this proprietary tool allowed the team to make decisions in real-time when faced with constantly shifting construction challenges such as supply chain constraints, moving timelines, and project changes for this ultra-speed-to-market project. It also helped SGA and the project team evolve the overall design correspondence of the project and track all decision-making in one place. As a result, the team was able to be proactive and collaboratively address issues, preventing them from taking place on the job site.

For example, SGA ordered the steel and MEP equipment very early to account for the current material shortages. In fact, it was decided to order steel even before it was clear what the length of each piece needed to be. While this could have been a major risk, that risk was mitigated by displaying the types of steel sections needed in the design at an early stage, along with a rough estimate of the total amount. This way, the actual cutting of steel could happen at the fabricator’s shop once the construction documents were finalized. Similarly, the significant wait time for HVAC equipment posed another risk to the timeline. To account for this, the SGA Dashboard allowed the engineers and HVAC experts to work together to figure out how much cooling the building would require way ahead of time compared to a typical project, allowing them to order the materials so they would arrive right on schedule.

In designing this facility, the team worked with the stadium’s original architecture and interior building flow. Maintaining the integrity and capacity of the structure was critical to the overall vision and design of the process, especially when accounting for any potential changes that may arise. This particularly came in handy when, during construction and after the majority of the building had been erected, the client requested that the building be flexible to accommodate more floors. In a traditional project, a change at that stage would have presented a major disruption, but the SGA team leaned on VDC and its tools to tweak the foundation and structure. In doing so, they could accommodate several

additional floors should the client choose to pursue this option in the future.

Overall, the months of using the intensive planning and coordination platforms reaped huge benefits, allowing the project to move swiftly without any unanticipated delays or any objections from subcontractors regarding material selections down the line. The SGA team also achieved substantial cost savings, schedule reductions, and the elimination of on-site waste across the board. As a result, the building was substantially complete and issued its certificate by the Patriots’ first preseason game in August 2022, just six months after it broke ground.

Discovering and inventing new technologies that enhance project outcomes is part of SGA’s DNA, so it is beyond encouraging to see how architects, and others in the building industry, can utilize these evolving platforms to elevate their role in project delivery. So far, SGA has collaborated with over 170 professional companies on project dashboards, including 11 other architectural practices, 46 owner organizations ranging from institutional to commercial development, and various consultants and owners. In doing so, they are finding that the right tools and implementations of thoughtfully-created execution success plans are effectively taking confrontation out of the team dynamic while directly addressing the issues of waste, change orders, and cost overruns. As a result, the project delivery process is shifting from adversarial to cooperative and from inflexible to fluid and efficient, resolving problems that have hampered the industry since its inception. By leaning on VDC to improve the process behind complicated projects and building rapport between parts of a team that are often siloed, a new reality for the industry can be presented: one that effectively brings design and construction together. ■

Michael Schroeder is a Partner at and leads SGA’s Virtual Design and Construction arm. Michael created and introduced SGA’s proprietary Dashboard tool in 2021 and continues bringing design and construction teams together to proactively solve the unique challenges facing large developments.

Rendering of the Kraft Group Office at Gillette Stadium, designed by SGA.

The new four-story building was completed in just six months by utilizing SGA’s VDC tools.

Houston Astrodome, The Eighth Wonder of the World

By Narendra K. Gosain, PhD.

Since the inception of the sports, football and baseball fans have been subjected to a wide range of weather conditions ranging from rain, sleet, and snow to hot and humid weather in an open-air environment to watch their favorite teams compete.

That was until the Houston Astrodome was opened in 1965. Touted as the Eighth Wonder of the World, the Astrodome was a catalyst for today’s modern billion-dollar indoor stadiums that dot the worldwide sports landscape.

The dream of a fully air-conditioned domed stadium was that of Roy M. Hofheinz, a Houston politician who served as Houston’s mayor and a Harris County judge during his career. Together with his business partner Bob Smith, they created the Houston Sports Association with the goal of getting a major league baseball franchise in Houston. The Houston Sports Association needed the help of Harris County voters to approve a public bond to build the Astrodome. To pass the bond, the support of African American voters was critical, so Hofheinz and Smith elicited the help of Quentin Mease, one of Houston’s most respected and influential African Americans. Mease and other African American leaders agreed to campaign for the bond on the condition that the stadium was opened as an integrated facility.

In 1961, Harris County voters approved a general bond issue of $42 million for the construction of the Astrodome. Ground was broken on the project in 1962, and construction formally began on the Astrodome in 1963.

Originally called the Harris County (Texas) Domed Stadium, it served as the home to the Houston Colt .45s (Major League Baseball, now known as the Houston Astros) and the Houston Oilers (National Football League, now known as the Tennessee Titans). It was the first time a stadium was built for baseball and football that was totally enclosed and air-conditioned.

Still standing today but currently unused, the Astrodome’s circular shape has an outer diameter of 710 feet, covers 9.14 acres, and the clear span of the domed roof is 642 feet. The diameter of the playing field is 516 feet, and the maximum height of the roof above the playing field is 213 feet. Original seating capacities for the nine-level multi-purpose stadium ranged from 45,772 for baseball, 52,382 for football, 55,000 for conventions, and 66,000 for boxing. In 1989, 10,000 new seats were added to the facility to increase the capacity for baseball and football games. The stadium was constructed for just over $45 million (1960s dollars), and the structural costs totaled $5.3 million for the stadium and $1.5 million for the domed roof.

The Astrodome is a domed circular concrete and steel-framed building. One of the foremost challenges of the project was the dome roof structure. The dome roof had to be affordable and aesthetically pleasing. Structurally, the roof also had to withstand hurricane wind speeds and minimize wind sail. The shape and construction of the roof also had to consider heating/cooling demands to minimize air volume. Even still, it required using equipment with approximately 6,000 tons of cooling capacity circulating approximately 2,000,000 cubic feet of air per minute to cool and heat the stadium. The fresh air intake was required to be approximately 200,000 cubic feet per minute, while any smoke or hot air was to be expelled from the top of the dome.

Competitive design proposals were submitted by interested firms with experience and expertise in long-span roof structures. Each firm

Early stage of erection of dome roof structure using steel erection towers

Ring and lamella steel trusses of partially erected dome roof structure

submitted designs that conformed to the required specifications, which included the following:

• Roof live load 15 psf

• Sonic boom loading 2 psf

• Wind load 40 psf (or load from wind tunnel testing using sustained wind velocity of 135 mph with gusts of 165 mph)

• Dead load: Self-weight of structure

• Superimposed dead load: Three-inch thick Tectum deck on bulb tees with plastic skylights

Unique to the Astrodome was sonic boom loading. In a simple definition, a sonic boom is a manmade thunder caused by shock waves from aircraft flying at speeds faster than sound. Shock waves radiate from the plane in a conical shape exerting pressure. When the lower edge of the pressure cone impinges on the ground, the shock wave is heard as a boom. The speed of sound is 1,125 feet/second or 767 miles per hour. This speed is commonly referred to as Mach 1. After Charles Elwood Yaeger, a United States Air Force officer, broke the sound barrier in 1947 by flying the Bell X-1 aircraft, there was much excitement and discussion about commercial flights flying at speeds greater than sound. The study on supersonic flights started in earnest in 1955. Because the site selected for the Astrodome was only about 8 aerial miles from William P. Hobby Airport, it was considered prudent to consider this sonic boom loading for designing the long-span roof structure of the Astrodome. Indeed, supersonic commercial flights operated in the United States for about 30 years, starting in 1973.

Specifications also required a 1/8-scale model to be tested in a wind tunnel to verify wind forces on the domed structure.

Nine proposals were received for the dome roof design, and Roof Structures, Inc. was awarded the contract. They proposed to use a steel lamella framing for the dome structure.

McDonnell Aircraft Corporation conducted the Astrodome model wind tunnel test in their aeronautical wind tunnel facility in St. Louis, Missouri. Such aeronautical wind tunnels focused on uniform air flow and did not account for the dynamic and turbulent characteristics of wind in the earth’s boundary layer, which is a more realistic simulation of the wind interaction with on-land structures. At the time, unlike today, there were no boundary layer wind tunnel facilities for testing on-land civil engineering structures. The first boundary layer wind tunnel test facility was built in 1965 at the University of Western Ontario in London, Canada. As such, once the aeronautical wind tunnel Astrodome model tests were completed, Dr. Herbert Beckman, Aerodynamicist and Professor of Mechanical Engineering at Rice University, was retained to evaluate the test results independently. In his 1961 report, he wrote that the models were subjected to a steady air stream while hurricane winds consisted of small grain turbulence with a gust diameter of usually not more than 100 or 200 feet. The gusts will impose only partial

loading of the building and, consequently, would be less effective than a steady wind. The wind tunnel data was thus considered to give conservative loads compared with corresponding flow conditions in hurricanes. The Astrodome has successfully withstood four hurricanes with no significant damage since its construction.

Reactions on the dome support columns using the wind tunnel test results were very close to the reactions computed manually by Roof Structures. To verify the analytical procedure using shell analogy for designing the dome, Roof Structures built an extensively instrumented test model and subjected this to various loadings. In addition, the design was extensively peer-reviewed by various experts.

The lamella dome structure has a diamond-shaped pattern on the spherical surface. The arch ribs or ring members are steel trusses with an overall depth of 5.5 feet. The top and bottom chord sizes vary from wide flange WF 16 x 58 to WF 16 x 78. The web members are two angles, 31/2 inches x 31/2 inches x ¼ inch. The short lamellas between ring members are also steel trusses 5.5 feet deep. The top and bottom chords of these trusses vary from WF 14 x 30 to WF 14 x 53. For these trusses, the web members are also two angles, each 31/2 inches x 31/2 inches x ¼ inch. The lamella dome framing is supported on a tension ring, a truss 5 feet, 6 inches deep. The top chord of this highly stressed truss is WF 14 x 370, and the bottom chord is WF 14 x 314. Once again, two angles, 31/2 inches x 31/2 inches x ¼ inch, were also used as web members in the tension ring.

All structural steel used in the lamella dome structure was ASTM A36 steel. Connections between the various elements of the lamella framing were made using ASTM A325 bolts. All welding was done using AWS E7018 electrodes. Continuity in the tension ring’s top and bottom chord members was provided by using full penetration butt weld splices.

The dome roof steel skeleton

Perimeter concrete retaining wall

The dome structure is supported on steel columns WF 12 x 65 located at every five degrees around the dome’s perimeter. These columns were designed to permit the movement of the dome structure toward or away from the centroid but not to allow movement from the tangential shear forces resulting from lateral wind loading. This was accomplished using a knuckled column design conceived by Ken Zimmerman, the lead structural engineer on the Astrodome at Walter P Moore. The knuckled columns have four-inch diameter high-strength steel pins at each end of the column. The lower bearing of the pin was welded to its plate support, and the top side was free to rotate in a close-fitted plate with a milled surface. Anchorage was provided at the top against uplift with U-bolts.

The lateral wind loads were resisted by X-braced bents extending the stadium to the foundation. However, providing the X-braced system in certain areas was not feasible, so moment frames were used instead. In addition, because there are seven expansion joints around the perimeter of the dome structure, each isolated sector had to have its own system of lateral load-resisting frames.

The dome framing required the fabrication and erection of 37 steel shoring towers. The erector placed the dome framing in pie sectors in opposing pairs, with 12 sectors of 30 degrees each. The erection of the steel presented problems because the criteria required that the tension ring stay vertical when dead loads were applied. Jacks were placed at the top of the erection towers to make the adjustments as erection progressed. After the alignment was confirmed and all connections were made, the jacks were gradually retracted over all the towers. Again, there was significant interest in the dome’s deflection. At each lowering of the jacks, tension ring alignment and supporting column plumbness were checked. However, the results of the plumbness of the columns varied daily. This was initially a concern for Roof Structures’ and Walter P Moore’s engineers, and the local elected officials. However, after checking and rechecking the monitoring data carefully and concluding that there was nothing amiss with the design of the supporting columns, the decision was made to retract the jacks and set the frame free. The monitoring of column plumbness continued, and surprisingly, it was observed that the columns did not stay consistently plumb but varied daily. After several days Ken Zimmerman figured out that the variation was due to the temperature effects not being considered in

the monitoring. The columns needed to be checked at the same time on successive days to ensure there was minimal temperature variation. Once the monitoring procedure was adjusted, the columns were noted to perform as predicted. The dead load deflection was calculated to be 1.88 inches. When the jacks were released, and the dome was free from all erection towers, the measured deflection was within 0.25 inches of that prediction. This was remarkably accurate given the limitations of design processes available at the time.

Considering the dome was going to be air-conditioned, a temperature differential of 70 degrees Fahrenheit was used above or below the base temperature of 60 degrees Fahrenheit for temperature stresses and movements. The horizontal movement of the roof for temperature was determined to be +/- 1.80 inches. For the design wind load, the horizontal movement was 5.5 inches. This posed a challenge for architects and engineers to design the expansion joint at the edge of the dome roof structure adjoining the flat roof of the stadium. The joint needed to be designed for a total movement of 11 inches. The design team produced a virtually maintenance-free solution. The solution consisted of a screen attached to the tension ring that extended beyond a concrete curb on the edge of the stadium roof just below the dome. The screen and curb lapped sufficiently to prevent the rain from blowing into the interior, and the curb height was designed to not allow rainwater from spilling down the roof edge.

The foundation structure for the Astrodome was simple and based on the geotechnical recommendations by National Soils Services, Inc. Because of the sandy characteristics of the underlying strata, the differential settlements were negligible. Interestingly, 50 percent of the footings were founded on pure sand located five feet below the playing field. It was only in the 10-foot-deep combined footings at the expansion joints that some wet conditions were encountered. The original water table was at an elevation of 44 feet, the playing field elevation was 33 feet, and the bottom of the deepest excavation was 25 feet. The water table was lowered using a well-point system designed by Lockwood, Andrews & Newnam to accommodate this. Lowering the water table was essential during construction to maintain dry conditions and permanently eliminate the pressures associated with the hydrostatic head of water. Below-grade perforated drainage pipes were installed throughout

Astrodome - interior view during football game

the dome’s interior and circling the exterior of the perimeter basement walls to provide permanent dewatering. Two dewatering lift stations were provided within the perimeter of the Astrodome – one in the southeast quadrant and one in the northeast quadrant – which are still operational. For about 60 percent of the perimeter, the retaining wall extends from the first level to the fourth level of the stadium for a height of 33 feet. The other 40 percent of the perimeter wall extended from the first to the third level for a height of 25 feet. Three concepts were developed to design the walls:

1)Counterfort system

2)Wall braced to interior column footings by diagonal struts and horizontal struts between footings

3)Tie-backs using pre-stressing strands to dead-man anchors around the perimeter of a.the dome structure.

A cost comparison of the three schemes indicated that the system using tie-backs and dead-man anchors was the most economical.

A drained sand backfill was used to reduce the lateral earth pressure against the retaining walls. The geotechnical engineer computed the lateral equivalent fluid pressure to be 30 pcf. All walls were designed to span horizontally, with tie-backs placed at 2.5 degrees around the perimeter. Two levels of tie-backs were provided such that the positive and negative wall moments were equal. The lower tie-back was placed close to the footing, and the second tie-back was placed close to the mid-height of the wall.

Project Team

Owner: Harris County, Texas

Structural Engineer: Walter P Moore

Architects: Lloyd & Morgan and Wilson, Morris, Crane & Anderson

Consultants: Praeger Kavanaugh Waterbury Architects, Engineers

Geotechnical Engineer: National Soils Services, Inc.

MEP Engineer: I.A. Naman & Associates and Dale Cooper & Associates

General Contractor: H.A. Lot

Strands with a diameter of 0.25 inches were used. The distance from the wall to the dead-man anchors was approximately 80 feet. Because the strands needed to be buried in the soil, there was a serious concern about the possibility of corrosion over the years and the resulting loss in the cross-section of the strands. As such, it was decided to use the cathodic protection system to protect the strands from the corrosive effects of the soil.

When the dome was completed, the United States had entered into the Space Age with the NASA facility located in Houston. The prefix “Astro” became very popular and synonymous with “gigantic.” The owner of the MLB team renamed them from the Colt .45s to the Astros, and the Harris County Domed Stadium became the Astrodome and was branded as the “Eighth Wonder of the World.”

In the late 1990s, the MLB and NFL teams moved on to new stadiums – and even a new city in the case of the Oilers. The Astrodome sat idle for most of the time aside from the annual Houston Livestock Show and Rodeo, which was last held at the stadium in 2002. In 2005, the Astrodome was used as a shelter for the residents of New Orleans impacted by Hurricane Katrina. By 2008, the Astrodome was officially shut down after inspectors deemed it unsafe for occupancy. In 2014, the Astrodome was listed in the National Register of Historic Places and received a Recorded Texas Historic Landmark Marker in 2018. This is the highest honor the state can bestow on a historic structure. It also adds another level of protection to ensure the Astrodome will exist for the foreseeable future. ■

Narendra K. Gosain was a Senior Principal and Executive Director of structural diagnostics at Walter P Moore. He retired from Walter P Moore in 2020 after 48 years of service.

Construction Materials

The soffit of the exposed steel lamella dome roof structure

CONSTRUCTION issues

Off-site Construction

CFS Load-Bearing Prefabricated Panels

By Nabil Rahman,

Off-site construction is the future of the building industry. It aims to speed up on-site construction schedules, address skilled worker shortages, and achieve better pre-coordination. Given their lightweight nature, cold-formed steel (CFS) framing projects are uniquely situated to use prefabricated panels. The panels can be complete with all the framing, sheathing, and possibly finishes installed in the fabrication facility.

CFS framing is widely used as the primary structural system in mid-rise buildings. It brings the value of reduced building mass that directly affects the design of the building foundation and the design of the lateral force-resisting system to resist lateral forces. Projects that benefit from CFS framing include multi-family housing, assisted living, dorms, hotels, barracks, and mixed-use buildings (see Figure 1 for an example of a 9-story mixed-use building under construction). This article presents the opportunity for off-site construction using prefabricated CFS panels in mid-rise load-bearing wall construction. The design methods, fabrication, and installation techniques for CFS panels are discussed, as well as the coordination between CFS, MEP, and other structural members.

Deciding to Use CFS Panels

Early in the project’s design phase, the project team, including the general contractor, the owner’s representative, the architect, and the engineer of record, typically explore the various structural systems to decide the best system for their project. Factors that affect their decision might include the size of the project (number of floors or total square foot area), the architectural layout, the construction schedule, job site constraints, budget, and consideration of any shortages of skilled field workers. CFS load-bearing panelization can reduce the construction schedule and address on-site skilled worker

shortages and job site constraints; however, added shipping and crane costs should be considered in the analysis.

If the decision is made to use CFS prefabricated panels, it is advantageous to select the panel supplier early in the design process to ensure upfront coordination between the design details and the construction methods. An example of critical early communication is the location of anchorage embed plates in a podium slab. When parties communicate early, shear wall plates can be efficiently located and coordinated with the lateral force resisting system (LFRS) design. However, if this is an afterthought, resolving the forces from the LFRS can be quite complicated.

What Gets Panelized?

It is common to panelize the interior and exterior load-bearing walls in a CFS load-bearing building. The wall segments, historically called panels, are typically one story high and as wide as the panel can be handled in fabrication, transportation, and installation (Figure 2). When the floor and/or the roof design uses CFS framing, they can also be panelized. In some projects, even the non-load-bearing CFS walls are panelized.

Vertical Load Path

Designing panelized load-bearing CFS is similar to the design of field-built CFS framing. Regardless of the system, the normal vertical load path is maintained. Wind, snow, dead, and live loads are considered at the roof level. At the floor level, the various dead and live load conditions are considered. However, panelization can present unique design challenges. For example, during construction, the

Ph.D., P.E., Kirsten Zeydel, S.E., and Andrew Newland, P.E.

Figure 1. A 9-story building with CFS load-bearing prefabricated panels under construction. Courtesy of RGC Inc., Garner, NC.

Figure 2. Installation of CFS prefabricated panels. Courtesy of RGC Inc., Garner, NC.

contractor may stack panels on finished floors before installation. This additional construction loading should be reviewed to ensure that it does not exceed the structural capacity of the framing in the area where stacking may occur. Another example is addressing the in-plane bracing forces generated within a wall panel from vertical loads. Depending on the selected panel width, each panel can have its own anchorage points, or the designer should address the transfer of bracing forces between panels.

Panelized wall framing can be utilized with several different floor and roof systems. The differing systems may affect how the gravity (and lateral) loads are applied to the wall panels. When the floor framing members do not align with the wall framing members, a load distribution member (LDM) may be needed to distribute the gravity load to each wall stud. Some examples of LDMs contained within the floor system are a CFS floor with a ledger track or a concrete deck with a concrete LDM over the wall. Other systems may have the LDM contained within the wall panel. This can be achieved using a properly designed stud and track or an HSS member. These members are then included in the wall panel instead of the floor system (Figure 3).

Wall to Floor/Roof Connections

After installing the floor/roof panels or other floor/roof systems at each level, a discrete positive mechanical attachment should be executed between the floor/roof and the wall. This mechanical attachment can be in the form of screw fastening, power-actuated fasteners, or welds. In the case of ledger-framed floor panels to wall panels (Figure 4), each floor joist is secured to the ledger track utilizing a clip angle and screws, and then the ledger track is fastened with screws to the face of each wall stud. In the case of a concrete slab on steel deck (Figure 5), the deck is welded or screw-fastened to the top track of the wall panel.

Other Materials

There are instances where materials other than CFS framing may be included in a panelized wall. Structural steel is the most common; however, there may be instances where other materials, such as clips, hold-downs, or timber blocking, are included.

Structural steel has several uses in a wall panel and should be properly coordinated. HSS members lend themselves to uses within a CFS wall since the dimensions match typical framing, i.e., 4, 6, or 8 inches, etc. As noted above, an HSS member may be a good LDM solution. In addition, they can be useful when design loads exceed the

capacity of typical CFS framing. This can occur when the number of shear walls is limited and the axial load demand at the lower levels is high. The same goes for posts when axial load accumulates over many floors or posts needed to support special point loads. It should be noted that Section 704.4.1 of the 2021 IBC allows structural steel members located entirely between the top and bottom tracks of CFS wall panels to have their fire-resistance ratings provided by the gypsum board layers on the wall.

Lateral Load Path

As with field-built CFS framing, panelized load-bearing CFS can be used with various lateral force resisting systems (LFRS). Some examples include CFS shear walls with wood sheathing or sheet steel, strap-braced CFS wall panels, steel brace frames, concrete shear walls, and masonry shear walls. However, it is important to note that ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, specifies limitations on the heights of some lateral systems. For example, CFS shear walls and CFS strap braced walls are limited to 65 feet in height for Seismic Design Category D, E, and F projects.

In any structure, it is essential to tie the floor/roof system into the LFRS. Drag members are often required, and those members need to be anchored into the LFRS. This is especially important in seismic areas as the drag members and their connections to the LFRS must be designed, including the overstrength factor or the maximum expected strength. In a CFS floor system, this may be accomplished with steel straps and screws. A concrete deck floor system can handle this with extra reinforcing steel and solid beams in the floor space. It is important to note that the fewer the number of LFRS, the higher the loads, making addressing the drag loads more challenging.

Another critical challenge is anchoring CFS panelized shear walls or strap-braced walls to the foundation or podium slab below. In seismic areas, the overturning forces must be designed for the overstrength factor or the expected strength. These loads can be quite high; thus, standard hold-downs may not work, and specialty plates or rods may be required.

Coordination

Pre-coordination between all trade contractors interacting with the CFS panels can be a critical contributor to the success of a prefabricated panel project. Early inclusion of the panel supplier into the project team allows for coordination with mechanical, electrical, plumbing, and fire protection trades regarding penetrations through

Figure 3a. Single stud LDM

Figure 3b. Double stud LDM

Figure 3c. Steel HSS LDM

walls, floors, and shear walls. Trade coordination is often performed through a shared building information model (BIM) administered by the general contractor or the project manager. BIM has proven to be a successful tool for handling such coordination. Figure 6 shows an example of a detected clash between a CFS wall panel and an MEP component that needs to be resolved.

Pre-coordination with other structural members is also critical. For example, if the design requires concrete shear walls or structural steel beams and columns outside the panels, the construction sequence and accommodations for tolerances need to be determined. At times, accommodating structural steel and concrete tolerances can be difficult, and a project team may decide that field-building those portions of framing is better. Otherwise, the general contractor must hold the steel and concrete trades to a tighter installation tolerance.

Another example of coordination with structural members is anchoring to a post-tensioned concrete deck, as the typical tendon layout will not allow anchors with an embed greater than ¾ inch. Thus, either the tendons will need to be located after the pour with a method like ground penetrating radar or embed plates will be required along the length of the walls. Both options can be costly. An alternative is for the PT tendons to be designed with a thicker cover at the top of the slab, allowing standard post-installed anchors.

Fabrication, Lifting, and Trucking

In a panel, the various framing members (studs, tracks, headers, jambs, etc.) must all be positively connected to transfer the gravity and lateral forces. Two common connectors are screws and welds. They each have their advantages and disadvantages. Screw connections are easy to fabricate and don’t require a special certification. However, screwed panels are less rigid than welded panels. When welded connections are used, the panels are typically stiffer, which is beneficial in trucking and installation. However, welded connections make field adjustments difficult.

Many panelizers use jigs to build their panels. These can be a simple 90-degree frame to ensure the squareness of the panel and saw horses to raise the panel to a better working height. Or motorized framing tables can be used to help ensure the straightness of the panels and assist with seating the studs/joists in the tracks. The motorized framing tables can help build a higher-quality panel but can make installing connections on the backside of the panel challenging and limit the size of the panel being built.

Given the thin-wall nature of CFS framing, special care must be taken when lifting panels. Attention is usually given to lifting panels

in the field, but the moving of panels in the fabrication facility can be just as tricky. For example, using a forklift to move wide panels around can lead to a bending failure of the top and bottom track if the members are not sized to support the cantilevered weight. When lifting a panel with chains/cables, it is critical to use proper connectors with appropriate safety factors in the field and the fabrication facility. It is also important to consider the various lifting conditions that the connectors will experience. For instance, if a panel is lifted from the horizontal position, the loading on the connector is very different than when the panel is in the vertical position. Finally, the increased load on the connectors due to the angle of the lifting cable is another essential element not to forget. Spreader bars can be used to enlarge the angle between the lifting cable and the top of the panel to minimize the increased load.

Trucking the panels from the fabrication facility to the job site is important to consider. Many states allow up to 14.5-foot-wide loads. However, these require special permitting, and some jurisdictions limit the times and days when these wide loads can travel. Panels under 8.5 feet wide usually do not require a special permit, but using this limited width increases the number of panels on a project which can increase the installation time.

Installation, Tolerances, and Deviation from Location

Installation of the panels in the field is where all the hard work pays off. When properly coordinated and executed, CFS panels can be quickly installed in the field with a minimal crew. Often the panel installation can go fast enough that the panel fabricators need to have a large number of panels built before the start of installation.

While all projects allow for installation tolerances, it is essential to note that CFS framing usually supports drywall finishes that typically only allow a ⅛-inch-in-10-feet tolerance. This means it is critical that the CFS framing is accurately installed. This can be especially challenging when the tolerances for the concrete and structural steel elements are significantly less stringent.

When installing CFS panels, it is crucial to carefully install the lowest level of panels as they directly impact the panels above. Concrete podium slabs and slabs on grade can be quite wavy; thus, the lowest level of panels usually requires quite a bit of shimming and possible grinding down of the slab if there is an exceptionally high spot. Ensuring proper installation of the lowest level of panels can be quite tedious and time-consuming, but the rewards pay off during the installation of the upper panels.

Figure 4. Attachment of Ledger-framed CFS floor panels to wall panels

Figure 5. Attachment of concrete slab on steel deck to CFS wall panels

Quality Control and Inspection

All fabrication facilities of CFS panels should have a fabrication procedure and quality control program. Section 1704.2.5 of the 2021 IBC allows the prefabrication of structural assemblies in the facility without special inspection if the facility is pre-approved by an approved agency or the building official. The pre-approval process is typically based on reviewing the fabricator’s written fabrication procedure, quality control manual, and periodic audits. An on-site inspection would still be required for any structural interconnection between prefabricated panels or connections with adjoining site-built structural components.

To develop off-site construction standards, a new standard from the International Code Council and Modular Building Institute,

ICC/MBI 1200-2021, Standard for Off-site Construction: Planning, Design, Fabrication, and Assembly, has just been published. This standard provides a beginning step to defining the design, fabrication, transport, and on-site installation requirements of prefabricated components.

Concluding Remarks

This article presents the opportunity for off-site construction using prefabricated CFS load-bearing panels in mid-rise construction. This construction approach can help to optimize project construction schedules and address the shortage of on-site skilled workers and job site constraints. Pre-coordination and communication are keys to the success of this construction approach. ■

Nabil Rahman is a Principal at FDR Engineers. He is a member of the AISI Committee on Specifications and the AISI Committee on Framing Standards. He has written multiple articles for the STRUCTURE magazine since 2006, advocating using CFS framing in load-bearing wall buildings (nrahman@fdr-eng.com).

Kirsten Zeydel is the Director of Design at Nevell Group, Inc. She is an active participant in the AISI Code Committees. Her passion is ensuring that CFS framing meets the building code and architectural requirements and is easy to manufacture and install (kzeydel@nevellgroup.com).

Andrew Newland is a Specialty Team Leader at ADTEK Engineers, Inc. He is a current member of the AISI Committee on Specification and ASCE-SEI Committee on Cold-Formed Steel and an Executive Committee member of Cold-Formed Steel Engineers Institute (CFSEI), where he previously served as the Chairman (anewland@adtekengineers.com).

BRIDGEresource guide

ASDIP Structural Software

Phone: 407-284-9202

Email: support@asdipsoft.com

Web: www.asdipsoft.com

Product: ASDIP RETAIN

Description: Advanced software for quick and efficient design of cantilever, restrained, counterfort, and sheet pile retaining walls. See immediate results with calculations and reports of load combinations per the latest IBC/ASCE 7 and AASHTO. Includes 4 intuitive modules to help you design and verify structural members with a few clicks.

ENERCALC, Inc.

Phone: 800-424-2252 or 949-645-0151

Email: info@enercalc.com

Web: https://enercalc.com

Product: ENERCALC SEL - ENERCALC for Revit

Description: Tired of complex software for what should be straight-forward analyses? ENERCALC's 3D FEM & Earth Retention modules handle these complex tasks with ease, as do our 33 other modules.

Using Revit? ENERCALC for Revit leverages the analysis power of SEL inside Revit, saving hours of tedious, repetitive work.

POSTEN Engineering Systems

Phone: 510-275-475

Email: sales@postensoft.com

Web: www.postensoft.com

Product: POSTEN

Description: POSTEN - still the Most Comprehensive, Most Powerful & Most Efficient software for the design of Post-tensioned or Conventionally reinforced concrete structures. No fiddling, guessing or time wasting - the only software that Automatically designs the drapes, prestress and mild steel efficiently the first time.

RISA Technologies

Phone: 949 951 5815

Email: benf@risa.com

Web: risa.com

Product: RISA-3D

Description: With RISA-3D’s versatile modeling environment and intuitive graphic interface you can model any structure from bridges to buildings in minutes. Get the most out of your model with advanced features such as moving loads, dynamic analysis, and over 40 design codes. Structural design has never been so thorough or easy!

Williams Form Engineering Corp.

Phone: 616-866-0815

Email: williams@williamsform.com

Web: www.williamsform.com

Product: 150 KSI All-Thread-Bar

Description: Williams Form Engineering Corpora\ on has been providing threaded steel bars and accessories to the bridge construction industry for over 100 years. Williams’ pre-stressing / post tensioning 150 KSI All-Thread-Bars are high tensile steel bars available in seven diameters from 1" to 3" with guaranteed tensile strengths to 1027 kips.

Figure 6. Clash detection during the pre-coordination phase

Wabasha Street Bridge, St. Paul, Minnesota, 1859

19th Century Mississippi River Bridges Series

By Frank Griggs, Jr., Dist. M.ASCE, D.Eng, P.E., P.L.S.

St. Paul, originally called Pig’s Eye, was founded approximately 13 miles downriver from Minneapolis near Fort Snelling. It was the northernmost access on the navigable river for steamboats on the Mississippi. It was settled on the north (east) bank of the Mississippi, on a bluff overlooking the river with low lands to the south (west bank). In 1849, the city was incorporated, and steamboat landings increased rapidly in the early 1850s. Its population reached almost 5,000 people by 1850. The river at the site was divided by Raspberry Island. Passage across the river was by rope ferries, and it soon became apparent that a bridge was necessary if the city continued to grow. As early as 1849, pressure to build a bridge started, and, in 1854, the Territorial Legislature passed Chapter 30, An Act to Incorporate the Saint Paul Bridge Company, on March 4. Sections 12, 14, 15, and 18 stated in part,

Section 12. Said bridge shall be of such material as the stockholders may deem expedient and shall be so constructed as to cover the main navigable channel of the river by a span of at least three hundred feet from pier to pier, the lowest part of which said span shall be at least sixty feet above high water mark – and said company may construct such other abutments, piers, and guards to said bridge, at such distances from each other and at such places as may be deemed necessary either on the street from which said bridge shall lead, on the island opposite said street, in the said river, or on the mainland on the opposite side of the said river. Provided that nothing in this section shall be so construed as to warrant the obstruction of any public street or the navigable channel of said river.

Section 14. No other bridge shall be established within one mile of that erected by the St. Paul Bridge Company without the consent of said company for the period of thirty-five years from the completion of said bridge.

Section 15. The said bridge shall, after the period of thirty-five years, become the joint property of the Counties of Ramsey and Dakota and shall thereafter be a free bridge.

Section 18. Set the tolls at: “For each foot passenger, ten cents; for each horse, mare, or mule, or two ox team, loaded or unloaded with driver, twenty-five cents; for each single horse carriage, twenty-five cents; for each additional cow or ox, ten cents; for each swine or sheep, two cents.” The question was, as usual, what kind of bridge and who would build it. The requirement that there be a vertical clearance of 60 feet and a horizontal clearance of 300 feet to provide for the safe passage of steamboats theoretically set the location and elevation of the abutment and piers closest to St. Paul. From there, the bridge would slope down on bridge spans or filled land until it reached grade on the southerly end. The maximum slope was set by the load a team of horses could pull a wagon up a slope which was generally around 7%. This would set the line and grade. Given the low population and projected tolls, a low-cost bridge was necessary, which pointed to a wooden bridge. The bridge company selected J. S. Sewall as its engineer in June 1856. Sewall was born in Boston

in 1827 and worked on several railroads between 1850 and 1854 when he settled in St. Paul, where he was a respected engineer and surveyor. However, there is no record of his involvement in the design of bridges. The most challenging design was for the main channel bridge that, by the enabling act, had to have a clear passage of 300 feet, but the company sought to decrease this to 220 feet. After the city council and steamboat operators claimed that this clearance would interfere with the safe passage of the steamboats, they agreed to increase it to 240 feet center-to-center of supports. They had already begun the construction of the far pier, so they had to move the first river pier 20 feet closer to shore. With the spans set, Sewall chose to use three lines of trussing with his compression diagonals spanning two panels, similar to William Howe’s design but with wood verticals instead of iron bars as used in the Rock Island Bridge (STRUCTURE, July 2022). In addition, rather than having his deck set on the lower or upper chords, as was the standard, he set variable distances up the verticals to provide a deck slope similar to his shorter spans. His first span was a horizontal deck truss followed by the main channel span. The spans from the end of the channel span were parallel chord deck trusses of 140-foot-span set horizontal with wooden posts of variable heights and beams set on the upper chords to provide a sloping deck. There were seven of these spans down to grade. This was followed by a 330-foot-long wooden trestle to grade and a short bridge across a slough. Sewall designed the foundations and stonework. In the summer of 1856, he advertised with a notice to contractors,

The foundations will be piled. The timber required for the foundations will be furnished by the Company. The masonry must be bid for by the cubic yard, the foundations per pile, and per cubic foot for the cribwork. For further information, inquire at the office of the subscriber, where plans and specifications may be seen.

Lithograph of the bridge, after the wood main span was replaced with a Whipple Iron Truss in 1876.

The contractor for the stonework was Rudolph H. Fitz of St. Paul, and the woodwork by J. & J. Napier also of St. Paul.

Wooden false works were required of various heights to erect the wooden spans, with the highest being over the main channel. Work on the piers was continued in 1857, but with stock sales slowing, the bridge company went to the city to purchase the remaining stock. The city agreed and sold bonds assuming bridge tolls would guarantee their investment. In 1858, Minnesota was admitted to the Union as the 38th State, and St. Paul was designated the Capital of the State.

As built from north to south, the spans were a 100-foot deck span, the 240-foot truss with sloping deck, and seven 140-foot spans with a similar slope to the main span. There were two lanes between the trusses with a total deck width of 17 feet and two 7-foot sidewalks.

The bridge opened in June 1859 at the cost of $161,855, of which the city of St. Paul contributed $114,870. However, tolls were far below the projected amounts, and the city took complete control of the bridge in 1867.

By 1869, the main span was showing signs of decay. It was replaced by a Howe truss with iron verticals in 1870. Shortly after, the seven sloping spans were replaced. In 1875, the main span was again showing signs of decay, and Soulerin and James Company erected a Whipple Iron Truss from Milwaukee, opening in July 1876.

This, the third bridge across the Mississippi, was built of untreated timber, which, uncovered, had a life expectancy of 10 to 12 years. Pictorial evidence exists that the upper chords of the main span were covered with little roofs for a part of the life of the span. It was replaced in 1890 with iron trusses erected as cantilevers and again in 1998 with concrete segmental box girder spans.

The Wabasha Street Bridge was the first to be built with a set of vertical and horizontal clearances to not interfere with steamboat traffic. However, this battle between steamboat captains and bridge builders over the right

of free, unencumbered passage on the nation’s rivers would not be initially settled until 1866, when the Federal Government passed legislation governing horizontal and vertical clearances for high-level and low-level bridges with swing spans.■

Bull Moose is making a major investment in a new 350,000-ton facility in Sinton, TX— with the goal of providing you with the “greenest” steel tube in North America.

• INVESTINGINHSSCAPACITY | Our new mill enables us to produce HSS up to 14” square and 18” round, up to ¾” walls.

• PROMOTINGSUSTAINABILITY | Our state-of-the-art facility will convert electric arc furnace (EAF) coils into some of the lowest global warming potential (GWP) HSS in the market. Additional Bull Moose products means a greater range of possibilities for your designs…while helping you achieve your green initiatives.

Main channel span, three lines of trussing with flanking sidewalks.

Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19th Century cast and wrought iron bridges. He is now an Independent Consulting Engineer (fgriggsjr@verizon.net).

New Opportunities with Diversity Scholarships

In 2021, the NCSEA Foundation established the NCSEA Diversity in Structural Engineering Scholarship Program to award funds to students traditionally underrepresented in structural engineering (including but not limited to Black/African Americans, Native/Indigenous Americans, Hispanics/ Latinos or Spanish, Asian, Native Hawaiian or Pacific Islander, and other people of color, those with disabilities, veterans and LGBTQIA+). Multiple scholarships are presented annually to junior college students, undergraduate students, and/or graduate students pursuing degrees in structural engineering.

In 2022, the NCSEA Foundation awarded six scholarships, including two first-ever partner scholarships in the program. The SEA of Northern California (SEAONC) established an endowed scholarship as part of the NCSEA Foundation program, and the SEA-Metropolitan Washington (SEA-MW) established a named scholarship.

As we begin the 2023 scholarship season, two structural engineering firms and one structural engineering family have generously provided funds to create even more opportunities for aspiring structural engineers in the form of named scholarships. Below is a list of the partner scholarships that will be awarded in 2023 (representing more than $17,000 in scholarships) and the more than $10,000 awarded by the NCSEA Foundation. Entries are due on March 20, 2023. More information about the awards, along with submission instructions, can be found on www.ncsea.com/about/foundation/diversityscholarship/

Endowed Scholarship

SEAONC Diversity in Structural Engineering Scholarship

The Structural Engineers Association of Northern California (SEAONC) established a permanent endowed scholarship to financially support a student from a historically underrepresented minority in structural engineering, preferably with a desire to practice in northern California. The permanent endowed scholarship provides a recipient $3,000 toward their education to assist with tuition, fees, and other mandatory education costs. SEAONC was founded in 1930 with the intent of improving the interchange of technical information and business practices. With 39 charter members, SEAONC now has over 1,000 members focused on structural engineering practice in northern California, a traditional wellspring of earthquake engineering knowledge and skill.

Named Scholarships

The Degenkolb Engineers Diversity in Structural Engineering Scholarship

Degenkolb Engineers established this scholarship, offering the recipient $5,000 towards their education ($2,500 for each of the next two semesters) and an opportunity for a paid internship during the summer of the award in one of their offices on the west coast of the United States. Founded in 1940, Degenkolb Engineers has more than eight decades of commitment to innovation, client service, and life-long learning. They deliver customized structural solutions in a variety of practice areas: healthcare, education, science and technology, forensics, construction engineering and federal buildings.

The Martin/Martin Skyrise Scholarship

Martin/Martin Consulting Engineers established the Skyrise scholarship offering the recipient $5,000 towards their education ($2,500 for each of the next two semesters) to assist with offsetting tuition, fees, and other mandatory education-related costs. This scholarship also includes the possible opportunity to participate as an intern during the summer the award is given in one of Martin/Martin’s offices.

With nine growing offices across the United States, Martin/Martin, Inc is a full-service civil and structural consulting firm built on experience and industry leadership cultivated since the 1940s. Our engineered solutions are developed through a culture of integrity, service, creativity, and quality for the benefit of our clients and the community. In 2020, Martin/Martin,

Inc. founded the Justice, Equity, Diversity, and Inclusion (JEDI) Committee to foster an inclusive culture that celebrates uniqueness, bolsters a sense of belonging, and promotes equitable opportunity for all in the engineering community. This scholarship is part of our company’s commitment to rise above for Justice, Equity, Diversity, and Inclusion within our organization and the industry.

The Steven B. Tipping Memorial Scholarship for Innovation and Excellence in Structural Engineering

Tipping Structural Engineers established this scholarship offering the recipient a $3,500 scholarship towards their education as well as an opportunity to participate in an externship program at Tipping Structural Engineers, Berkeley, California.

For more than 35 years, Steve Tipping advanced the science and art of structural engineering, pioneering creative yet pragmatic design solutions for a broad range of projects. His inventions and accomplishments in seismic retrofit design have been especially crucial to the earthquakeprone Bay Area, while his emphasis on constructability culminated in unparalleled expertise in cost- and resource-efficient solutions. To read more about Steve’s legacy, please visit, https://legacy.seaonc.org/engineer/steven-tipping/

SEA-MW Diversity in Structural Engineering Scholarship

The SEA-Metropolitan Washington (SEA-MW) established a named scholarship offering the recipient $3,000 towards their education.

Call for Abstracts for the NEXT Structural Engineering Summit

NCSEA is seeking abstracts for the 2023 Structural Engineering Summit, scheduled for November 7-10, 2023 in Anaheim, California. at the Disneyland Hotel. Sessions will be 45-60 minutes total, including time for Q&A. Presentations are sought for topics that would appeal to seasoned engineers or younger engineers new to their careers (or both). Summit presentations aim to provide structural engineers with tools, techniques and tips to help them and their firms operate more efficiently and effectively.

Potential submission topics include (but aren’t limited to):

•Best-design practices

•New codes and standards

•Recent project case studies

•Advanced analysis techniques

•Management and business practices

•Diversity and inclusion

•Resilience

•Sustainability

For more information and to submit your abstract, visit https://bit.ly/2023SummitAbstracts or scan this code:

highest-quality webinars

• At least 25 live webinars a year featuring high-quality speakers and relevant subjects.

•All technical webinars are Diamond Review-approved in all 50 states. As an ICC Preferred provider, NCSEA webinars meet the renewal requirements of ICC Certifications.

• Unlimited 24/7/365 access to NCSEA's Recorded Webinar Library – more than 170 recorded webinars available at your fingertips.

Visit

www.ncsea.com/education

• Unlimited free continuing education certificates for each webinar so multiple viewers at the same location can receive credit for every live webinar.

•Available anywhere! NCSEA's webinar subscription can be used wherever you are.

February 9 Repair, Defer, or No Action: Leveraging Structure Movement Monitoring for Efficient Capital Planning and Decision Making

February 22 The 60-Minute MBA for Engineers - BQE Structured Sponsored Webinar*

Courses award 1.0-1.5 hours of Diamond Review-approved continuing education after the completion of a quiz.

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

SEI Standards Series

Join for live session dialogue between industry leaders and experts, a detailed technical presentation, extensive Q&A, and earn PDHs.

February 9 and March 9

ASCE 7 & The Building Codes (Part I & II) - _What Every Young Architect & Structural Engineer Needs to Know

Join SEI host Cherylyn Henry, P.E., F.SEI, M.ASCE, ZAPATA Group, Inc. for a discussion with guests John Paquin, AIA, LEED BD&C, ZAPATA Group, Inc. and Gus Sirakis, P.E., NYC Department of Buildings

Focuses on ASCE 7 - which loads are included, how the loads work together and how ASCE 7 provisions are adopted into IBC and IRC codes. This program will also answer the questions – what do young design professionals have to know about ASCE 7, and the IBC, IRC and where do they find the right resources?

Part I: Overview, presentation & Q&A with industry experts

Part II: Project discussions in breakout rooms with industry experts

Learn about more sessions and register https://collaborate.asce.org/integratedstructures/sei-standards

Sponsor

Engage, network, and learn with the community as we work together to advance the structural engineering profession for a better future.

Anchor

Congratulations to the 2023 SEI Fellows

Amjad Aref, Ph.D., F.SEI, F.ASCE

Robert (Jianqing) Hong, P.E., S.E., P.Eng., F.SEI, M.ASCE

Ahmed Ibrahim, Ph.D., P.E., F.SEI, M.ASCE

Mohsen Issa, Ph.D., P.E., S.E., F.SEI, F.ASCE

Dirk Kestner, P.E., S.E., LEED AP BD+C, ENV SP, F.SEI, M.ASCE

Soliman Khudeira, Ph.D., P.E., S.E., F.SEI, M.ASCE

Kevin LaMalva, P.E., F.SEI, F.ASCE

Marc Levitan, Ph.D., F.SEI, A.M.ASCE

Hussam Mahmoud, Ph.D., F.SEI, M.ASCE

Mustafa Mashal, Ph.D., P.E., CPEng, IntPE (NZ), F.SEI, M.ASCE

Dennis Morgan, P.E., S.E., F.SEI, M.ASCE

Shamsher Bahadur Singh, Ph.D., P.E., C.Eng, F.SEI, F.ASCE

Hema Siriwardane, Ph.D., P.E., B.Sc., F.SEI, F.ASCE

Alexander Whitney, P.E., F.SEI, M.ASCE

The SEI Fellow grade of membership recognizes accomplished SEI members as leaders and mentors in the structural engineering profession. Reach out to congratulate your peers, and encourage your SEI member colleagues to apply to advance to SEI Fellow.

Prospective SEI Fellows must be current SEI, actively involved, licensed P.E./S.E., 10 years responsible charge (typically post P.E.). Learn more and review full list of SEI Fellows at www.asce.org/SEIMembership.

Forensic Engineering 2022: Collaborative Reporting for Safer Structures

This collection contains 9 peer-reviewed papers on the founding and development of CROSS in the UK and its expansion internationally presented at the Ninth Congress on Forensic Engineering, held in Denver, Colorado, November 4-7, 2022. https://doi.org/10.1061/9780784484555

Access your SEI member certificate online

At www.asce.org, login at upper right of page and select ‘Manage my account’. You can renew, update your contact info, professional interests, preferences, bio, education/license details, and download your self-service SEI member certificate now available.

Follow SEI on Social Media:

Tools To Help Your Business Grow...

If you are a member of CASE this tool and all publications are free to you. NCSEA and SEI members receive a discount on publications. Use discount code - NCSEASEI2022 when you check out.

Beyond the Code: Grade-Level Floors over Expansive Soils — CASE recognizes that the International Building Code or other governing codes do not address all aspects of structural engineering and design. Often, the most common issues where the owners, or the contractor or the design team are not aligned deal with what is not clearly addressed by the various codes or design guidelines. This is the first in a series of “Beyond the Code” white papers that will attempt to collate design considerations that need to be discussed with the owners at the beginning of a project to establish a clear Basis-of-Design for the project. By proactively bringing up the design consideration in front of the owners, the Structural Engineer can set up realistic expectations and discuss the cost impact of alternative designs. This first white paper in the “Beyond the Code” series will discuss the pros and cons between two structural design options for the grade level floor in expansive soil regions. Keep an eye out for future installments in the series!

What’s Shaking?

A new publication from CASE about Seismic Design

CASE Guideline 962- J Ð Business Practice Guidelines of Seismic Design for the Structural Engineer. The purpose of this document is to provide insights about structural engineering services in regions where there is a seismic hazard. This document shares key design considerations as well as business practice considerations. Numerous resources are available that provide a much more exhaustive and advanced technical presentation of important considerations when designing for earthquakes. Someone new to designing for earthquakes should consider taking a course in structural dynamics and seismic engineering whether from a university or some other provider such as ASCE or NCSEA.

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

You can also browse all of the CASE publications at www.acec.org/coalitions/coalition-publications/

Is there something missing for your business practice? CASE is committed to publishing the right tools for you. Have an idea? We’d love to hear from you!

Upcoming Events

Coalitions Winter Meeting

March 6-7, 2023 Tampa, FL

The 2023 CASE Winter Member Meeting is going to be in Tampa, FL on March 6-7 this year. The Winter Meeting is open to all CASE members and is a great opportunity to network with your peers and engage in meaningful dialog about the state of the industry. For more information and registration, visit our website https://program.acec.org/coalitions-winter-meeting

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

Upcoming Events

Trends in Decarbonization

March 21, 2023 Online Course

Join the Coalition of American Mechanical and Electrical Engineers (CAMEE) for a broad look at decarbonization beyond specific systems and equipment, as we consider buildings holistically. We will evaluate design choices across the entire building, as well as the importance of building operations. Attendees of this session will gain insight into industry trends and their implications for buildings, the greening of the grid, regulations, and what is practical over the next 15 years.

Now more than ever we need to support the upcoming generation of the workforce. Give to the CASE Scholarship today!

About the CASE Committees...

Do you know someone in your firm that is looking for ways to expand and strengthen their business skillset, gain experience serving on a committee, sharpen their leadership skills, and travel to interesting places? Please consider applying for a position on the committee.

Committee member commitments include a monthly virtual meeting, a few hours a month working on relevant documents, and travel to the Coalitions winter and summer meetings!

To apply, your firm should:

• Be a current member of ACEC

• Be a member of the Coalition of American Structural Engineers (CASE); or be willing to join the Coalition

•Be able to attend the groups' normal face-to-face meetings each year: August, February (hotel, travel partially reimbursable)

• Be available to engage with the committees via email and video/conference call

• Have some specific experience and/or expertise to contribute to the group

Creating a Culture of Accountability Within Your Company

By Dr. Tricia Groff, Ph.D.

Creating a culture of accountability, like most human conundrums in leadership, often makes the most expert and senior leaders want to throw up their hands in frustration and give up. “Why don’t they just do what I told them to do?” “But it’s clearly written in their role description?” “Why am I asking this same question three months later?” And narrowing down a definition of accountability can be difficult, depending on who is part of the conversation. So, for this article, let’s define accountability as a shared understanding that people are responsible for executing their commitments. Underneath the frustration, most leaders struggle to figure out what they can do differently. Other problem-solving scenarios afford logical flows and fit into spreadsheets, while human conundrums are like trying to find a pattern in ever-changing chaos.

Prioritize Accountability

While creating a culture of accountability is not clean or easy, there are fundamental actions that can guide a business in the right direction. First, accountability requires consistency. Training dogs and children is tiring because every parent knows that consistency is critical, yet that knowledge doesn’t help the tired and overwhelmed parent at the end of the day. The same problem occurs in work situations. Leaders usually contend with multiple business decisions, vendor concerns, or team dynamics. The fires to be extinguished and frustrations to be solved create huge energy drains that result in even the most consistent bosses saying, “I just can’t have that conversation today.” While putting off accountability conversations for a day may not create a problem, most are postponed for weeks, or even months, due to the speed of work and competing priorities. Hence, the only way to create a culture of accountability is to hold it as a top priority to ensure consistent feedback and follow-through.

Provide Feedback

Next, accountability and feedback often have negative connotations. Thus, leaders and cultures that value kindness may have difficulty integrating it with their desire to ensure that people feel valued and happy. Leaders can bridge this tension by working to provide positive and negative feedback and checking in on both projects that are going well and those that are problematic. When everyone in a business expects routine follow-up on initiatives, they automatically adjust their behavior. How many students would take accountability for doing homework if the homework was not graded and there were no tests? How many athletes would be excited about winning a game if no one noticed?

Create Clear Outcomes

In addition to verbal follow-up, clear outcomes can also incur accountability. When people know that if they do well, they receive praise, a bonus, or additional autonomy, they are more likely to commit to excellence. Conversely, they are usually more motivated to achieve if they know they will receive a reprimand, fewer resources, or a more limited scope of responsibility for under-achieving. Unfortunately, organizations that struggle with consistency often struggle with elucidating clear outcomes for actions. This combination is fatal to any accountability efforts because there is no simple and repeatable system of people knowing where they stand.

Increase Buy-In

One more complex but highly effective way of generating a culture of accountability in business is to increase buy-in during the decision-making process. Most people have an easier time adhering to decisions they have helped generate. There is added cognitive dissonance if they don’t execute their own ideas. Some leaders believe that buy-in means getting everyone to agree to a process before moving forward. This is not the case. Rather, leaders can say, “this is the problem we are trying to solve. What are your ideas?” Most people don’t need agreement; they need to feel that their voices are heard. The key to achieving buy-in is pulling people into the process early. If a leader says, “here is what we can do; what do you think,” they lower buy-in because the decision has already been made. They are getting feedback, but they are not creating ownership.

Accountability Starts at the Top

The hardest pill to swallow in creating a culture of accountability is that the foundation for creating responsibility starts at the top of an organization. Are the leaders true to their word, able to apologize for miss-steps, and able to correct mistakes? Leaders must understand they are part of the team, so if they cannot take responsibility for the task and human requirements of their role, others in the organization will see any talk of accountability as hypocritical. As a result, the conversation will never become part of the organization’s DNA. Conversely, if the leaders are working on their own integrity, the team sees this and will be more open to taking accountability themselves.

Know When to Let Someone Go

When problematic employees continue to blame others for their mistakes, they need to be fired. Those who consistently find excuses or underdeliver are unlikely to change. When leaders allow employees who are not able to take accountability to remain on teams with those employees who are deeply committed to excellence, they lower the morale of the team. In essence, the leaders are not taking accountability for ensuring the culture of accountability.

Creating a culture of accountability requires consistent communication and feedback on specific expectations. Second, it requires follow-up so that people learn they cannot fly under the radar. Third, it requires that people are valued enough by the organization’s leaders to proactively solicit their opinions at the onset of decision-making and then let them know what decisions were made and why. Finally, it requires praise. When people feel that others notice and appreciate their actions, they feel part of a team and united toward a purpose. At that point, they begin holding themselves accountable not to let down their team and, more importantly, themselves. ■

Dr. Tricia Groff is an Executive Advisor and Executive Coach who works with high achievers and their organizations. She is also a licensed psychologist who brings 20 years of behind-the-scenes conversations to her recommendations for workplace wellness and profitability. Dr. Groff is the author of Relational Genius: The High Achiever’s Guide to Soft-Skill Confidence in Leadership and Life.

BUILD LONG LASTING STRUCTURES WITH POWER PRESERVED GLULAM®

POWER PRESERVED GLULAM® FEATURES

• Manufactured with superior strength southern yellow pine MSR Lumber.

• Offered in two oil-borne preservative treatments: Clear-Guard™ and Cop-Guard® .

• Fast, easy, one-piece installation that’s more efficient than bolting or nailing multi-ply dimension or structural composite lumber members together.

• Excellent choice for decks, boardwalks, pergolas, covered porches and demanding environments such as bridges, highway sound barriers, railroad cross ties, and floating docks.

• 25-year warranty from the treater.

©Anthony Forest Products Company, LLC

Anthony Forest Products is part of the Canfor Group of Companies

CELEBRATING OVER 50 YEARS OF SAP2000 AND ETABS IN OVER 160 COUNTRIES Spanningthedecades,encompassingtheglobe!

Aswecelebrate50yearsofinnovationthathavemadeSAP2000andETABS whattheyaretoday,wewouldliketorecognizetheimmeasurablecontributions ofProfessorEdwardL.Wilson,ProfessorEmeritusattheUniversityofCalifornia atBerkeley,whostarteditallbylaunchingthefirstversionsofSAP2000and ETABSintheearly70s!

THANKYOU,ED!