STRUCTURE magazine | May 2023

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WOOD AND MASONRY INSIDE: Mass Timber High-Rise 10 Sustainable Use of Timber in CA 32 GFRP-Reinforced Masonry 42 Modernizing Masonry Cavity Walls 44 STRUCTURE NCSEA | CASE | SEI MAY 2023

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EDITORIAL BOARD

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

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

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

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

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

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

Jessica Mandrick, P.E., S.E., LEED AP

Gilsanz Murray Steficek, LLP, New York, NY

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

Brian W. Miller

Cast Connex Corporation, Davis, CA

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

Kenneth Ogorzalek, P.E., S.E. KPFF Consulting Engineers, San Francisco, CA (WI)

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

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

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

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STRUCTURE ® magazine (ISSN 1536 4283) is published monthly by The National Council of Structural Engineers Associations (a nonprofit Association), 20 N. Wacker Drive, Suite 750, Chicago, IL 60606 312.649.4600. Periodical postage paid at Chicago, Il, and at additional mailing offices. STRUCTURE magazine, Volume 30, Number 5, © 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.

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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. 2023 On the Cover: Timber construction over concrete podium at Apex Plaza in Charlottesville, Virginia Photo courtesy of Eric R. Ober, P.E. ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org
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By Eric R. Ober, P.E., and Chelci E. Dell, P.E. Apex Plaza is an approximately 300,000 square foot, mixed-use office/retail/residential high-rise building in Charlottesville, Virginia, with six stories of mass timber framing over a four-story concrete podium parking structure.

32 AN EXAMPLE OF SUSTAINABILITY USING TIMBER

Decarbonization must rapidly advance to avert further changes to our environment. As a signatory of SE 2050, Skidmore, Owings & Merrill has committed to bringing meaningful carbon reductions to a wide spectrum of buildings. The use of mass timber in many buildings can be cost-effective when combined with the building’s architectural design and programmatic needs.

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5 MAY 2023 Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, the Publisher, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions. STRUCTURE magazine is not a peer-reviewed publication. Readers are encouraged to do their due diligence through personal research on topics. 7 Editorial Advancing the Profession, Serving Our Communities By Ryan Kersting, P.E., S.E. 8 Structural Influencers Michael O'Rourke 14 Design Specifications Fire Protection of Mass Timber Connections Based on the 2022 Fire Design Specification By Myles Lacy, P.E., and John “Buddy” Showalter, P.E., M.ASCE 18 Legal Perspectives Climate Change and the Structural Engineer By Gail Kelley 20 Structural Forum Delegated Design of Masonry By Jamie Davis 22 Mass Timber Buckling Restrained Braces In Mass Timber Projects: Three Case Studies By
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26 Business Practices Selling Your Engineering Business By John Allen 38 Code Updates TMS 402 Appendix D: GFRPReinforced Masonry
Ph.D., PE, and Antonio Nanni, Ph.D., PE. 40 Outside the Box Mass Timber for 843 N. Spring Street By
M.S., P.E. and Chris Smith, M.S.,
Brandt Saxey, Alex Zha (SOM), Ilana Danzig (Aspect),
(KPFF)
By Richard Bennett,
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44 Structural Rehabilitation Repairing and Modernizing Masonry Cavity Walls
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Advancing the Profession , Serving Our Communities

As I embark on my year as NCSEA President, I have a renewed sense of awareness and appreciation of all of the great work that CASE, NCSEA, and SEI are doing to advance the Structural Engineering profession. I am also inspired by the engagement of so many individuals within various levels of our organizations, working together with a common purpose. Those who have engaged already recognize the value of participation and the benefits of both investing in their career and doing their part to help advance our profession. If you missed it, I encourage you to read the editorial by Jeannette Torrents from the February issue on “The Value of Participation.” No matter what stage you are in your career, it is never too late, nor too early, to start engaging and investing in your career. We have all heard the testimonials about the value of participation regardless of the timing – from being invited as a younger member as way to gain technical knowledge and build a network; to taking a leadership position as a way to develop additional skills beyond the daily work or get experience otherwise not available at your job; to getting, and staying, involved later as a way to share knowledge and perspective to the next generation. If you are not currently actively participating in CASE, NCSEA, or SEI, now would be a great time to get involved. If you are already participating, I encourage you to invite someone from your professional network to get involved with you, help them feel included, and assist them in finding the right place and time for them to engage.

Each of the organizations have many opportunities for members to get involved and help influence

the direction of our profession in a variety of ways: from committees working on the next editions of our governing codes and standards, to groups sharing and promoting business best practices; from committees charged with developing and delivering continuing education content on a variety of topics and platforms, to groups influencing our profession through initiatives to improve DEI and to strengthen SE licensure; and from groups supporting young members and early career professionals, to groups engaged in developing the next generation through outreach to K-12 and university students. Paraphrasing from the February editorial: When structural engineers go beyond the passive consumption of ideas to actively sharing… they progress along the participation power scale from simply keeping up with the profession to shaping the profession.

In addition to opportunities to advance the profession, structural engineers and our organizations have opportunities, if not inherent responsibilities, to serve our communities directly through the work we do and through how we engage with our fellow citizens. The loss of life, economic impacts, and long-term disruption to daily life caused by natural disasters close to home and around the world are unfortunate reminders of how our communities depend on buildings and critical infrastructure to not just provide a basic level of safety against a number of hazards but to also provide the resources and services to recover and return to daily life in a reasonable amount of time. To help with the emergency response phase of recovery, speciallytrained structural engineers are often involved as part of formal Urban Search and Rescue teams or “second responder” safety evaluation programs. In addition to those emergency response efforts, structural engineers can also serve an important role in communicating with members of the media, elected officials and other policymakers, and the general public.

This year, NCSEA will be using a new “Disaster Response Plan” to help coordinate post-disaster

response within our organization in terms of responding to media requests as well as assisting with requests for deployment of second responders. Being prepared for the next disaster means starting now by providing media training through the NCSEA Communications Committee to engineers designated as official spokespersons and by providing resources through the NCSEA Structural Engineering Emergency Response (SEER) Committee to support efforts at the state and local level to develop second responder programs.

As we reflect on recent natural disasters in the headlines, NCSEA’s Code Advisory Committee and Resilience Committee have engaged in efforts and conversations regarding the role of building codes and standards relative to improving community resilience and will be considering the emerging concept of designing for improved functional recovery in addition to basic safety. We also need structural engineers to engage at the state and local level through outreach to elected officials and other policymakers to explain the expected performance of buildings and critical infrastructure relative to the predominant hazards in a given community and develop programs to mitigate potential vulnerabilities.

The resilience of our communities requires experts to engage beyond just project-related work and into the realm of code and standard development as well as local advocacy for mitigation programs relative to the region’s hazard and risk. I hope you agree that structural engineers are uniquely positioned to be these experts by sharing our knowledge about how design of new buildings targets protection of occupant safety, how retrofit of older buildings can mitigate risk of collapse or unacceptable levels of damage, and how enhanced performance can be considered as a way to improve recovery relative to a unique hazard or risk.

As you can see, the structural engineering profession has a range of opportunities for engagement such that everyone should be able to find their way to contribute. I hope you will join me and thousands of others by getting involved in the important work of advancing our profession and serving our communities!■

STRUCTURE magazine MAY 2023 7
Ryan Kersting is an Associate Principal with Buehler in Sacramento, CA and is currently serving as 2023-24 President on the NCSEA Board of Directors.
Structural engineers and our organizations have opportunities, if not inherent responsibilities, to serve our communities directly through the work we do and through how we engage with our fellow citizens.
EDITORIAL

structural INFLUENCERS

Michael O’Rourke

Michael O’Rourke has been a professor in the Civil Engineering Department at Rensselaer Polytechnic Institute (RPI) in Troy, NY, since 1974. He has taught over 4,000 undergraduate and graduate students. In addition, Professor O’Rouke supervised 62 students for Master of Science theses and 10 for Ph. D dissertations. From 1997 to 2017, Professor O’Rouke served as Chair of the Snow and Rain Loads Subcommittee of the American Society of Civil Engineer’s ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. He is a Former Chair of the ASCE 7 Snow and Rain Loads Subcommittee and is a Fellow of the Structural Engineering Institute (SEI). He is the nation’s foremost snow expert and is known for his extensive snow load research, authoring many articles and guides related to snow loads.

How and when did you first develop an interest in snow loads?

Like many things in life, my initial involvement with snow loads was unplanned. Prior to my arriving at Rensseleaar, a colleague of mine, Professor Leon Wang, spent a sabbatical at the United States Army Cold Regions Research and Engineering Lab and subsequently invited Wayne Tobiasson to visit Rensselaer. At that time, Wayne was the chair of the American National Standards Institute’s Snow Loads Subcommittee, ANSI A-58, Design Loads for Buildings and Other Structures. After Wayne’s lecture, we met, and I made some observations about return periods for ground snow loading. Subsequently, we corresponded, which led him to invite me to join the then ANSI A-58 Snow Loads Subcommittee, which eventually morphed into the ASCE 7 Snow and Rain Load Subcommittee.

What have been the highlights of your snow load research and developments? Do you have an interesting standout experience where you gathered a large amount of data that you analyzed, then evaluated extensively to determine the most appropriate result?

The things I’m most proud of are the two relationships for snow drift loads which have been adopted into ASCE 7. Before the mid-1980s, the drift load in ASCE 7 was a simple multiple of the so-called balanced roof snow load. I received National Science Foundation (NSF) funding to improve the then-current relation. I paid Factory Mutual for proprietary information about their observed snow drifts. Graduate students Ulrich Stiefel and Bob Speck helped analyze the data and, with a bit of engineering judgment, we established a relationship in which the drift height was a function of the upwind fetch of the drift snow source area as well as the ground snow load. More recently, a former graduate student, John Cocca, and I developed an improved relation where the drift load is a function of the winter wind speeds and the fetch and ground snow load. These relations are particularly important since snow drifts have historically accounted for roughly 75% of snow-related structural collapses.

What are some major surprises you found from your snow load research?

The Factory Mutual database contained many roof step drifts, many large right triangular snow drifts (peak height at the wall), and a few somewhat smaller non-right triangular drifts (peak height away from the wall). Our database analysis assumed that all leeward drifts had a right triangular shape while all windward drifts had a non-right triangular shape. About 25 years later, a colleague of mine, Professor Thomas Thiis, and his graduate student, Jon Potac, measured drift formations at temporary wooden walls erected at a wind-swept location in Norway. The Norwegian

outdoor experiments confirmed that all leeward roof step-type drifts are, in fact, right triangular in shape. However, they observed that, although windward drifts are initially non-right triangular, with enough wind and a driftable snow source, the non-right triangular drift can morph into a right triangular shape over time. Although the Thiis/Potac measurements disproved my assumption regarding windward drift shape, I was happy to learn the truth because it increased my knowledge of snow drift formation.

Do you have an example of “thinking outside the box,” and if so, how did it help you in your research?

About 15 years ago, I began to receive calls and emails from practitioners saying that as part of a reroofing project, the roof insulation R-value would be increased. They rightly asked about the expected increase in roof snow loads for increased roof R-values. I responded that they were correct in their thinking. Still, unfortunately, since the ASCE 7 thermal factor was based upon buildings characterized as either heat or unheated, the influence of roof R-values could not be determined from currently available roof snow measurements.

I was unhappy with my response since I felt that ASCE 7 should address this issue. Eventually thinking “outside the box,” I recalled an NSF project that estimated the size of roof ice dams, where we used a simple thermal model of the roof/snow layer to estimate the roof snow melt due to heat flow up through the roof. Using our NSF-sponsored research, Scott Russell, a long-time member of the ASCE 7 Snow and Rain Loads Subcommittee, and I developed the Ct factor for unvented roofs in ASCE 7-22, which is a function of the ground snow load and the roof insulation R-value.

Regarding the future of snow loads, what areas do you see as needing more research that will help the structural engineering community?

Since I completed my graduate education in the early 1970s, computer codes and finite element methods have revolutionized structural analysis

STRUCTURE magazine 8

and, to a lesser extent, structural design. In relation to snow loading, I think drift formation at roof steps and other simple geometries is reasonably well understood. However, I expect that in the future, Computational Fluid Mechanics, whereby the path of individual snow particles can be modeled, will result in an enhanced understanding of snow drift formation on geometrically complex roofs.

You have been a professor of civil engineering at Rensselaer Polytechnic Institute for over 40 years. How have you been able to mix your teaching/faculty responsibilities with your snow load research?

The academic reputation of Engineering Departments in the U.S. is based almost exclusively upon the research productivity of its faculty. At Rensselaer, we were encouraged to bring in sponsored research projects which, in turn, were used to support graduate students who did the research work under the direction and supervision of the faculty. Since the teaching load was reduced for faculty with research funding, there was little or no conflict between research and teaching responsibilities at Rensselaer.

As a professor, how would you describe your teaching style and philosophy?

I received a teaching grant from Rensselaer with the objective of improving our four structural design courses. For each course, I prepared a typed set of course notes which were provided to the students free of charge. This allowed me to cover course material rapidly and in more detail. Some of the classroom time saved was used for “in-class problems,” which I distributed near the end of each class period. Each student was required to show me a correct solution before leaving the classroom. The three main benefits were; improved learning, improved class attendance, and the opportunity to have one-on-one time with each student. Note that I could have used the extra time to present another example problem, but my strong opinion is that one learns best “by doing.” The extra “lecture” example problem would correspond to students reading a new paragraph (a simple task) while the students completing the “in-class” problems would correspond to students writing a new paragraph (a harder task).

How have you engaged your students in gaining an interest in structural engineering?

Most of my teaching at Rensselaer were structural design classes, specifically undergraduate steel design, undergraduate concrete design, graduate-level advanced steel design, and graduate-level advanced concrete design. The two prerequisites for undergraduate classes are statics and strength of materials. As such, the students have already self-selected to pursue structural engineering as a profession before taking my classes. Teaching structural design classes to structural engineering students is a real pleasure since both the instructor and the students have a genuine interest in the topic. I like to think that although I did not “lead the horse to water,” I did make the “horse’s drinking of the water” enjoyable and productive.

What are the most important attributes of being a good instructor?

In my opinion, the objective of lectures and classroom teaching is for the students to learn/understand the material. This may seem obvious to many; however, I have attended presentations consisting of two or three slides on a large number of unrelated projects without explaining any of them in-depth. The only objective, as it seemed to me, was for attendees to be impressed with the “brilliance” of the lecturer.

I like to think I follow the “students learn something” approach instead of the “audience impressed” approach. In following the “learning” approach, I typically ask myself, “what did I not understand when I was first presented with this new material?

What are the most important attributes of being a good engineer?

To my mind, the most important attributes for a good engineer are 1) a level of comfort with math, 2) a curiosity about how or why physical things work, and 3) an ability to communicate one’s ideas clearly to others.

Did you have students help you with your research, and if so, how did this teach and train them and nurture them for their future engineering endeavors?

During my career at Rensselaer, I supervised the research work of about 70 graduate students. The first thing these students typically do is read the relevant technical literature and prepare a list of items that they did not understand. Then, at the start of the new work, I would explain the items on their list and provide suggestions for “next tasks.” Some students never got past the “follow O’Rourke’s directions” phase, while the best students eventually got to a “self-directed” phase.

What advice would you give to a young person trying to make it today in engineering?

As opposed to giving career advice to a young person in engineering, I would instead mention the following opinion and observations. First, I believe there will always be a need for structural engineers. Second, during my career, I have been pleasantly surprised by the number of firm owners who enjoy the actual practice of structural engineering much more than the work associated with being the owner of a structural firm. Structural engineers will always have something to do, and most will enjoy doing it. I always enjoyed sharing this “good news” with students when the opportunity arose.

You have demonstrated a long and dedicated commitment to the structural engineering community, education, activities, and organizations such as ASCE/SEI. What were the most rewarding aspects of those services?

One of the things I enjoy the most is presenting in-person lectures on snow loads to practicing structural engineers at SEI and National Council of Structural Engineers Associations (NCSEA) events. Besides being interested in the lecture material, practicing structural engineers also ask very good questions and raise timely issues during the Q & A.

We all have mentors and people who have influenced and helped us. So, in closing, who would you like to thank and why? And do you have any parting thoughts you would like to share regarding the profession’s future?

I am grateful for all the structural engineers who have influenced me during my professional career. They include the Illinois Institute of Technology (IIT) and Northwestern University professors, my M.S. and Ph.D. thesis advisor, Dr. Richard Parmelee, and our current Department Chair, Dr. Chris Letchford. However, two individuals deserve special recognition. The first is Professor Julian Snyder of the Civil Engineering Department at my undergraduate alma mater, IIT. Besides being a great teacher, Julian would host a get-together for his students at his home. I thought this was a wonderful idea, and I have made it a practice to invite my students for a drink at the end of each semester. The second individual deserving special recognition is Professor Larry Feeser of the Civil Engineering Department at Rensselaer. Larry was hired as Department Chair in 1974, and I was his first structural engineering hire. He was tasked with converting our department from a teaching-only group to a research and teaching group. In my opinion, he was successful with this transition. As my mentor, Larry always gave me useful advice, and I always felt he had my best interest at heart.■

MAY 2023 9

Mass timber construction has gained momentum throughout North America over the past ten years. For example, Apex Plaza is an approximately 300,000 square foot, mixed-use office/retail/ residential high-rise building in Charlottesville, Virginia, with six stories of mass timber framing over a four-story concrete podium parking structure. At the time of its completion in April 2022, Apex Plaza became the largest mass timber-framed building on the east coast.

Recent development in Charlottesville has focused on congested sites near the University of Virginia and the city’s downtown. The site for Apex Plaza has all the challenges associated with urban development, such as property line and existing building constraints on all sides, a high water table, and a limited laydown area for construction.

Apex Clean Energy is the building’s primary tenant, which led the project team to establish sustainability as a guiding principle. William McDonough + Partners (WM+P), the project architect, engaged Simpson Gumpertz & Heger (SGH) as the structural engineer. The project team incorporated features to help to satisfy the sustainability goals, including:

• Mass timber framing using Forest Stewardship Council (FSC) and cradle-to-cradle certified sources for the upper levels.

• Steel-framed canopies support photovoltaic (PV) arrays at the Level 3 terrace and the roof.

• Vegetative roof assemblies at the Level 3 terrace.

A Code Modification

Preliminary design began in early 2018 under the 2012 Virginia Construction Code (VCC). Unfortunately, the scale of the proposed construction (Type IV timber frame over Type IA podium; Figure 1) did not conform to the VCC’s prescriptive construction requirements,

Apex Plaza i

prompting a code modification under VCC Section 106.3. The building official agreed to the code modification, but with stipulations impacting the structural design, including:

• Three-hour fire separation between the podium and timber structure was achieved by an increased cover of reinforcement on the bottom mat.

• Vertical transportation cores enclosed by reinforced concrete walls designed as shear walls.

• Timber design per the 2015 National Design Specification® for Wood Construction (NDS®).

• Timber elements sized to comply with the International Building Code (IBC) Table 602.4 – Wood Member Size Equivalencies and designed for a one-hour fire-resistance rating.

Podium Structural Design

The podium structure is used for parking, retail, and limited office space. Foundations are primarily shallow spread and continuous strip footings bearing on native soils with combined footings at the perimeter to accommodate the eccentricity created by the foundation at the property line. Rammed aggregate pier foundation improvement was implemented in one area with unsuitable fill soil. The transportation cores share a thick mat foundation for shear wall stability. The office floor timber grid was not aligned with the parking layout throughout the footprint, so post-tensioned and conventionally reinforced concrete girders at the top level of the podium transfer loads from ten timber columns to the podium columns. The podium structure is primarily comprised of conventionally reinforced cast-inplace concrete slabs, with drop panels in select locations.

STRUCTURE magazine 10
Figure 1. Timber construction over concrete podium. By Eric R. Ober, P.E., and Chelci E. Dell, P.E. A Mass Timber High-Rise

Timber Frame Design

The upper levels of the building are occupied with office spaces. Floors 4 through 8 and the roof are framed primarily with multi-span crosslaminated timber (CLT) slabs and glued laminated timber (glulam) purlins, girders, and columns. Seven-ply CLT slabs span about 20.75 feet, and glulam beams span up to 27 feet. Floors are topped with gypcrete over an acoustical mat to control sound transmission through the levels as required by the VCC. Floor vibration due to walking was evaluated according to the empirical design approach in the 2nd Edition of the Canadian CLT Handbook

The timber fabricator and supplier, Nordic Structures (Nordic), was engaged early in the design phase of the building. Nordic’s engineering team served in a design-assist role and became a valued contributor to the design. Their suggestions enhanced fabrication efficiency, economy, and constructability.

Most of the timber framing is installed as slabs and beams, allowing long unobstructed views of the exposed CLT from inside and outside of the building. To minimize beam depths, the beams are paired side-byside in depths up to 27 inches and widths up to about 25 inches per pair. Cutting penetrations through glulam beams would have significantly reduced the fire-rating for the upper framed levels, which could have threatened the project’s viability. Instead, the framing is installed in purlin and girder configuration near the building core, with the girders dropped in elevation to allow for M/E/P distribution into the slab and beam framed areas.

The mass timber connection design was delegated to Nordic by performance specification. The beam-to-column connections were designed as bearing-type connections and consisted of notched columns and beams (Figure 2) that fit together without relying on mechanical fasteners to transfer load. This provided economy for the connection design, accommodated cantilevers, and simplified fit-up for columns narrower than the beams.

Compared to conventional dimension lumber construction, wood shrinkage is more easily managed in post-and-beam mass timber systems since vertical loads from above can be transferred parallel to grain. Wood shrinkage is largest tangentially and radially to the grain and is significantly less parallel to grain. The connections between columns at Apex Plaza allowed the columns to stack on top of each other, transferring all vertical load directly in the columns, making shrinkage less of a concern.

Lateral-Force-Resisting System

The building’s lateral-force-resisting system primarily comprises reinforced concrete shear walls at the vertical transportation cores extending from the foundation up to the penthouse roof. At the upper, timber-framed levels, timber braced frames were introduced on the east and south sides of the building to provide additional lateral strength and stiffness at the ends of the building away from the core. Timber braced frames are not a prescriptive seismic force-resisting system included in ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. From a literature search and review of provisions in the Canadian codes and standards, a design approach utilizing a seismic response modification coefficient of R = 3 for the braces and concrete shear walls was implemented. Timber brace connections were designed utilizing an overstrength factor of 2. Dowel-type connection strength was designed for ductility utilizing yield modes III and IV per the NDS. Additional discussion about the brace design can be found at: www.youtube.com/watch?v=E4Or7m1N0AU.

MAY 2023 11
Figure 2. Beam-column bearing connection at braced frame. Figure 3. Timber braced frame with gypsum wrapped connection.

The braced frames are exposed in most locations at the upper levels, creating a unique architectural feature but a connection challenge. The brace connections at columns and beams reduce their cross-section and the members’ fire resistance. This could be addressed by increasing the size of the members, but, in the case of Apex Plaza, this would result in inordinately large members. Instead, connections were wrapped with gypsum to provide passive fire protection (Figure 3).

The design and construction teams recognized the potential for conflicting construction tolerances between concrete and mass timber. Mass timber is fabricated to tolerances much less forgiving than tolerances for reinforced concrete construction. Alteration of the timber framing in the field can be difficult and hinders erection progress. As the concrete cores were erected well in advance of the timber, there was sufficient time to coordinate timber fabrication with the as-built geometry of the cores.

Building Construction

The delivery date for the project was fixed by the needs of Apex Clean Energy which was consolidating its headquarters’ operations from several sites to Apex Plaza. Additionally, Nordic had a dedicated window to fabricate the timber and deliver it to the site. However, the structural design considered several iterations, including a change from five to six stories of timber and various transportation core configurations during the preliminary phases. These iterations put the project at risk of missing the fabrication window. Delaying fabrication would have meant the loss of several months in the schedule and missing the project deadline. Therefore, the team looked at options to expedite construction to allow exterior wall and interior construction to proceed to complete the project on time. The construction team evaluated options and proposed erecting the building using vertical phasing. Rather than constructing the entire building conventionally floor-by-floor as planned, the project was separated into multiple adjacent, full-height phases. Phase 1 involved constructing the concrete podium full-height on the east side of the building. Once the podium was topped out at this location, the timber installation would begin over the completed portion of the building, while podium construction began on the west side. This sequence continued on the west and south sides of the building until construction was complete. Allowing the concrete and timber construction to coincide effectively extended the timber fabrication schedule. Overall, this approach required detailed coordination between the design and the construction teams. Despite numerous logistical challenges, the project was completed on time for occupancy, with the Grand Opening of the building in April 2022 (Figure 4).

Lessons Learned

Through the design and construction of this project, a few key lessons were learned and reinforced:

• Close coordination between the A/E/C team is essential to success.

• Early engagement of the timber fabricator is crucial to secure the fabrication window to meet the project construction schedule.

• Integration of the timber fabricator into the design process offers tremendous opportunities to streamline the project’s design, fabrication, and erection.

• Interface tolerances between different materials must be considered in the design and specifications.

• Multi-span continuous CLT slabs perform substantially more effectively than simple spans for strength and serviceability; however, continuity induces loads on interior supports up to 25% larger than simple tributary loading.

Looking Forward

Apex Plaza is an example of the emerging trend in large timber buildings throughout North America. With many jurisdictions soon to adopt the new tall mass timber provisions in the 2021 IBC, many more exemplar buildings are expected and can benefit from and build on the lessons learned at Apex Plaza.■

Project Team

Development Team: Hourigan Group & Riverbend Development

Strategic Partners: Apex Clean Energy & acac Fitness & Wellness Centers

Structural Engineer: Simpson Gumpertz & Heger

Architect: William McDonough + Partners

MEP Engineer: Staengl Engineering

Timber Supplier: Nordic Structures

General Contractor: Hourigan Construction Corp.

Chelci E. Dell is a Consulting Engineer in the Washington, D.C. office of Simpson Gumpertz & Heger (cedell@sgh.com).

STRUCTURE magazine 12
Eric R. Ober is an Associate Principal in the Washington, D.C. office of Simpson Gumpertz & Heger (erober@sgh.com). Figure 4. Completed construction at the grand opening ceremony.

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your career

At Schaefer, we believe in providing diverse opportunities, both internally + in our communities, to find + elevate our people’s passions.

Forget a one-size-fits-all approach; we believe in customized career paths + professional development plans.

> Technical

> Project manager

> Mentor + people manager

> Thought leader

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It takes all of these types of people (+ more) to make Schaefer a Best Firm to Work For.

How do we support our engineers in developing their career paths? Empowerment + exposure.

> Career path planning documents

> Project diversity (we design for 10 markets!)

> Early project + relationship ownership

> Training budget

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> Feedback – regular check-ins, individual development plans + formal reviews

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At Schaefer, there’s no required path, no predetermined development. We support our people in following their passions.

We’re looking to partner with clients and hire individuals that bring their best every day.

I had found my technical passion –I’m an entertainment engineer. What I craved was an opportunity to develop others. I took advantage of relevant trainings like giving + receiving feedback + leadership development. Schaefer helped me develop + achieve my goal.

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> project diversity

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We’re Schaefer, a structural engineering firm with a national footprint. We’re always looking for smart, creative people to join our team.

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13 MAY 2023 ADVERTORIAL
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design SPECIFICATIONS

Fire Protection of Mass Timber Connections Based on the 2022 Fire Design Specification

It can be cost-effective to design wood structures for resilience and safety during fire events.

With growing public interest in sustainable building and with the addition of “mass timber” Construction Types IV-A, IV-B, and IV-C to the 2021 International Building Code (IBC), design professionals are increasingly required to design mass timber building elements to fire-resistance ratings prescribed by the IBC. While many members of the public, and even building design professionals at times, associate wood construction with inherent fire risks, it is feasible and can even be cost-effective to design wood structures for resilience and safety during fire events.

Specialty engineers and architects routinely handle fire protection design. This standard of design is effective and sensical for non-combustible structural materials as many commercially available products can be used to directly obtain a time-based fire-resistance rating. On the other hand, combustible materials, such as wood, used in building structures are not typically covered with sprayed fire-resistant materials and are often intentionally exposed for aesthetic purposes. The charring of a structural wood member, as well as the associated reduction of the member’s cross-section and material properties, necessitates the involvement of a structural engineer.

Chapter 16 of the American Wood Council’s (AWC) National Design Specification® for Wood Construction 2018 (NDS®) clearly outlines the procedure for calculating a fire-resistance rating for exposed wood members for up to 2 hours. However, the NDS offers only one paragraph of guidance for the fire protection design of wood connections. AWC’s newly published Fire Design Specification (FDS) for Wood Construction was approved as an ANSI standard on September 13, 2022 to fill this gap. The FDS is based largely on AWC’s Technical Report No. 10, Calculating the Fire Resistance of Wood Members and Assemblies (TR10), which supplements the NDS by providing summaries of research progress in the design of fire protection of wood elements, design procedures, and, most notably, design examples. The combination of NDS, FDS, and TR10 provides a well-supported and thorough means of designing fire protection of wood structural members and their connections for different fire ratings.

IBC Provisions

The 2021 IBC expanded Type IV construction to include three new subtypes and changed the previous Type IV to Type IV-HT. Type IV construction now consists of Type IV-A, Type IV-B, Type IV-C, and Type IV-HT, listed from greatest to least fire resistance. Type IV-HT typically does not require fire-resistance ratings for heavy timber

elements unless these elements comprise exterior bearing walls or interior bearing walls supporting more than two floor/ceiling or roof/ ceiling assemblies. Instead, inherent fire protection of heavy timber elements is achieved by requiring the use of prescriptive sizes found in Section 2304.11 of the IBC.

The differences between the new types of Type IV construction consist of required fire-resistance ratings (2021 IBC Tables 601 and 705.5), required non-combustible protection (2021 IBC Section 602.4), and limitations on building heights and areas (2021 IBC Chapter 5).

Fire Design of Wood Members Using Chapter 16 of the NDS

In 2001, AWC first incorporated a chapter on fire design of wood members into the NDS. Chapter 16 of the NDS uses a mechanicsbased approach for determining the fire resistance of exposed wood members for up to two hours. A reduced cross-section can be determined by calculating the amount of effective char a wood member develops over a specific fire exposure time. The reduced cross-sectional dimensions are, in turn, used to calculate a reduced member capacity that can be used to check for the controlling design limit under the appropriate load conditions. Although the section properties are reduced, the reference design values are still used as a starting point for design. These reference design values are multiplied by an adjustment factor specific to fire design as specified in NDS Table 16.2.2 to obtain average ultimate member strengths. When determining the adequacy of a member during fire exposure, it is only necessary to consider service level (allowable stress design) dead and live loads.

Introduction of the 2022 FDS

In September of 2022, AWC obtained ANSI approval for the 2022 FDS. The FDS incorporates the fire design provisions of the NDS and the fire design procedures within TR10 to provide a complete standard for the design of fire-resistance-rated wood members, assemblies, and connections.

While the NDS, FDS, and TR10 provide a methodology for the fire design of exposed structural members used as beams, columns, tension members, decking, floors, and walls, the remainder of this article focuses on the recommended design methodology for fire protection of wood member connections based primarily on the FDS.

STRUCTURE magazine 14

Charring Behavior of Wood

To properly protect wood structural connections, one must first understand char depth, effective char depth, and char contraction. Wood members exposed to fire develop a char layer that extends into the member crosssection over an exposure time. This char layer can, in turn, act as an insulator for the member, slowing char growth over time. Due to the insulative properties of the char layer, a linear growth rate tends to underestimate char depth under short time frames and overestimate char depth under longer time frames.

To accommodate the insulative effect of the char layer, FDS, TR10, and NDS recognize a non-linear method of determining char depth as a function of the exposure time (FDS Equation 3.2-1, NDS Equation 16.2-2). Although these equations are applicable for most rectangular wood structural members, cross-laminated timber (CLT) manufactured with certain adhesives exhibits different char growth behavior due to the tendency for char to fall off as the char depth approaches the glue line. This fall-off behavior leads to a speed up and a slowdown of charring encompassed in different equations that consider the thickness of lamination layers and the time of fire exposure (AWC FDS Equation 3.2-5a, NDS Equation 16.2-3). New fire test protocols have been developed and are included in PRG 320-19, Standard for Performance-Rated Cross-Laminated Timber (referenced in 2021 IBC), to ensure adhesives used in CLT will not result in this behavior. After calculating the approximate char depth, the FDS/NDS mandates a reduced member cross-section of 1.2 times the calculated

char depth. This is called the effective char depth. For determining the fire-resistance rating of a structural member, this conservatively increased loss of structural section is all that is required. However, it becomes necessary to consider the effects of char contraction when unbonded members abut, such as at structural connections or where wood trim is used as an insulative protective layer.

As wood members exposed to fire begin to char, the charred wood shrinks such that the volume occupied by the charred member is less than the original volume of the wood before fire exposure. In fact, the actual thickness of char is approximately 70% of the calculated char depth. This gradual member shrinkage is termed char contraction. Char contraction plays a critical role in determining the fire protection of connections. For two abutting but unbonded members, the joint between the two members grows as char contraction occurs at the abutting corners. The gap that forms at the joint reveals the initially protected faces and allows ignition to occur increasingly at the location where the unbonded members meet. At these abutting edges, the FDS recommends using a depth of ignition into the formed gap of twice the calculated approximate char depth (Figure 1).

While the effects of char contraction can affect the strength of a member, they are more likely to expose structural components that, without extra protection, exhibit less fire resistance than required. For example, consider a wood beam and wood column connected by a steel ledger inserted into the beam. At the onset of a fire, the wood beam begins to char, but the ledger is not initially exposed. As char contraction occurs at the interface between the column and beam, the steel ledger is more quickly exposed to elevated temperatures than the calculated effective char depth would suggest.

Wood Member Connection Protection

Understanding char depths and char contraction make it possible to determine protection times for wood member connections. The FDS presents multiple ways to add time to the fire-resistance rating of wood structural members and to protect connections by adding sacrificial wood, type X gypsum board, or non-combustible materials such as mineral wool or fiberglass insulation. These materials can be used in combination, and their impacts on the fire-resistance times can be considered directly additive.

Fire protection of connections designed per the FDS is meant to provide thermal separation that meets the requirements of ASTM

MAY 2023 15
Figure 1. Char Contraction at Unbonded Abutting Wood Members, Courtesy of American Wood Council Figure 2. Effects of Char Contraction on Differently Protected Steel Ledgers

E119, which limits the average temperature rise on the unexposed side of the wood to 250°F over ambient and 325°F at any location. The newly added Section 2304.10.1 of the 2021 IBC, Connection Fire-Resistance Rating, also includes requirements consistent with ASTM E119. Due to steel’s high thermal conductivity, any structural steel connecting element used to fasten a primary structural element must be protected for the duration of the element’s fire-resistance rating to adhere to the ASTM E119 temperature rise limits. On the other hand, fasteners used to attach protection do not need protection themselves; they must be of sufficient length to ensure the protection stays in place for the required time.

The design of wood protection is discussed in FDS Section 3.3.1. For most instances, the protection time (tp) afforded by a layer of wood protection (thickness = dp) used to provide thermal separation for a connection can be determined by using FDS Equation 3.3-2; however, for the base layer of wood protection adjacent to the protected steel, Section 3.5.1 requires the results of Equation 3.3-2 to be modified by a 0.85 multiplier. In areas where char contraction decreases the protection time of the connection, Equation 3.3-2, may be modified as shown to simplify the calculation of the fire protection time. When accounting for the effects of char contraction, the use of a 0.85 multiplier is not required by the FDS.

FDS Equation 3.3-2

FDS Equation 3.3-2 Modified for the Effects of Char Contraction

in mass timber construction types differ slightly from the provisions outlined in the FDS. For example, Table 722.7.1(2) of the 2021 IBC lists the protection time afforded by ½-inch type X gypsum board as 25 minutes which is more conservative than the 30 minutes allowed by the FDS (see FDS Table 3.3.2.1 excerpt in this article). Additionally, the 2021 IBC explicitly requires the use of non-combustible protection in mass timber construction types through Table 722.7.1(1) which allots a portion of the protection time for a specific fire-resistance rating that must come from non-combustible materials. There are also several specific requirements for fastening gypsum board fire protection in Section 722.7.2 of the 2021 IBC, which should be reviewed against the fastening requirements of the FDS during design.

For the base layer of thermal protection of the gypsum board, which is the layer adjacent to the steel being protected, the time of thermal separation shall equal the time of protection provided in FDS Table 3.3.2.1 multiplied by 0.50. It is important to note that gypsum board protection must be specially detailed per the footnotes to Table 3.3.2.1 to limit the effects of contraction and ensure the added protection time outlined in the table during a fire event. As mentioned, FDS Table 3.3.2.1 is excerpted in this article; however, many footnotes

Consider the detail in Figure 2, where two similar fire protection designs are used to protect a CLT floor-to-wall connection. This detail shows the char pattern for a 90-minute exposure on each protection scheme (dark gray represents char). The design on the left incorrectly neglects the effects of char contraction; thus, the steel angle becomes exposed to increased temperatures prior to 90 minutes. The design on the figure’s right correctly protects against the effects of char contraction between the CLT wall and the 2x12 protection by adding a nominal 2x2 trim piece and successfully providing a 90-minute fire-resistance rating.

Type X Gypsum Board can also provide fire protection for wood structural members and connections. To establish a fire protection time with gypsum board, a designer should use Table 3.3.2.1 of the FDS. These values can be directly added when multiple layers of gypsum board are used to protect a structural member or connection. Type X gypsum board can be used for the protection of structural members and connections or, as it has been traditionally used, for the protection of structural assemblies such as a series of floor joists or wall studs. The 2021 IBC requirements for using gypsum board as fire protection

regarding construction requirements and protection time modifications have been omitted.

The FDS provides additional methods of adding to the fire-resistance rating of wood structural members and connections. Section 3.3.3 discusses non-combustible products such as mineral wool and fiberglass insulation and the impact these materials have on fire-resistance ratings. Similar to gypsum board protection, the determination of protection time from insulation can be determined prescriptively, in this case, FDS Table 3.3.3.1. This table provides additional protection times based on the type and thickness of insulation. Insulation protection times cannot be increased from their tabular values even with increased insulation thickness.

Conclusion

As the carbon-neutral and sustainable design market continues to grow, there is an increasing need for structural engineers who can design wood structures for the fire-resistance ratings required by the IBC. AWC’s NDS, FDS, and TR10 are excellent resources for engineers designing mass timber elements and their connections where fire-resistance-rated members and assemblies are required.■

STRUCTURE magazine 16
Myles Lacy, P.E. is a licensed professional engineer focusing on structural design at Martin/Martin, a full-service civil and structural engineering consulting firm based in Colorado. (mlacy@martinmartin.com) John “Buddy” Showalter, P.E., M.ASCE, is a Senior Staff Engineer with the International Code Council (bshowalter@iccsafe.org) Table 3.3.2.1 Fire Resistance Time for Type X Gypsum Panel Products, Courtesy of American Wood Council Table 3.3.3.1 Fire Resistance Time for Protected Wood Surfaces, Courtesy of American Wood Council

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legal PERSPECTIVES

Climate Change and the Structural Engineer

How it may affect the Profession. Part 1

It is almost impossible to open a magazine, pick up a newspaper or listen to the news without seeing a reference to climate change and its effects. Unfortunately, the issue has become very politicized, in part because of the tremendous amounts of money at stake. This three-part series looks briefly at climate change in general, but focuses on how climate change applies to structural engineers and what it could mean for the Standard of Care that their services are held to.

Global Warming Versus Climate Change

While the terms “climate change” and “global warming” are often used interchangeably, they have different, but related meanings. Global warming is the long-term heating of Earth’s surface since the pre-industrial period due to human activities, primarily the burning of fossil fuels, which has increased greenhouse gas levels in the Earth’s atmosphere. In contrast, climate change is a longterm change in the average weather patterns that have come to define the Earth’s local, regional, and global climates. These changes have a broad range of observed effects that have become synonymous with the term. Changes observed in Earth’s climate since the mid-20th century are primarily driven by human activities, particularly fossil fuel burning. The National Aeronautics and Space Administration (NASA) website is a very good source of information on both global warming and climate change. See for example: https://climate.nasa.gov/global-warming-vs-climate-change

Designing for Weather-Related Events

Structural engineers have always had to deal with the challenge of resilient development and designing for weather-related events. Any time we disturb the ground and cover it with buildings, concrete, or asphalt, we disrupt the natural balance of water infiltration and potentially create runoff that can cause flooding. Engineers have usually found solutions to these challenges. But the scale of current weather-related events is creating new and more serious obstacles. At the same time, as real estate costs have soared in many areas of the country, we are often increasing the density of development on land that could be vulnerable to weather-related events.

Extreme Weather Events

Although extreme events and their severity vary geographically, there have been extreme weather events throughout the United States. While these events may not be directly caused by climate change, many in the scientific community believe that climate change is making such events more probable. Looking to the future, it is likely that many parts of this country and the world will face temperature extremes, more frequent and intense storms, more severe droughts, greater risks of wildfires, and increased flooding. Coastal areas will be especially prone to flooding because of rising sea levels. The effects of these events can also interact, exacerbating the potential for damage. Recent prolonged periods of drought have created a greater risk of wildfires; areas damaged by wildfire are especially prone to mudslides during heavy rains because there is no vegetation to aid in slope stabilization.

Climate Action Plans

The terms “decarbonization”, “net zero”, and “carbon neutral” are often heard in discussions of climate change, where decarbonization has the general meaning of reducing or eliminating carbon dioxide emissions, such as by switching away from fossil fuels in buildings and vehicles. Globally, the built environment generates approximately 40% of the total annual carbon dioxide emissions. Approximately 27% of this comes from

STRUCTURE magazine 18

building operations; the other 13% comes from the energy used in producing construction materials, referred to as embodied carbon. Structural engineers and other design professionals can thus play an important role in strategies to reduce greenhouse gas emissions. For more information, see the Architecture2030 website: https://architecture2030.org/why-the-building-sector

Approximately 34 states have climate action plans that include a general outline and steps that the state is going to take to address climate change. Many cities and towns have their own climate action efforts. Nevertheless, climate scientists generally acknowledge that it is too late to prevent or reverse the effects of climate change. Thus, climate adaptation strategies – i.e., adjusting to the current and future effects of climate change – have become crucial to planning, engineering, and related disciplines. However, while there is considerable data and research on climate adaptation strategies, implementation efforts to date have been limited and largely voluntary, reflecting the sometimes controversial political, economic, and social justice implications of climate adaptation. Existing regulatory and statutory requirements addressing climate adaptation have not brought about consistently applied changes in planning, engineering, land use, design, or development practices.

Climate Change Litigation

To date, litigation related to climate change has primarily targeted fossil fuel companies for causing climate change, but this may change as insurance carriers and courts struggle with how to apportion liability for the losses arising from claims related to climate

change. The issue of “climate adaptation liability” and what it means for design professionals is likely to increase in importance as the effects of climate change continue to increase in size and scope. Unfortunately, litigation is sometimes seen as a vehicle for social change. An engineer may thus be caught up in a litigation whose intent is primarily to make a statement; the engineer’s services may be of secondary importance. Nevertheless, the litigation will likely allege that the engineer has not met the Standard of Care and that this breach of the Standard of Care is at least partly responsible for the plaintiff’s damages.

Stakeholders in construction projects, including the authorities having jurisdiction, are increasingly recognizing that structures need to be designed to withstand the climate conditions of the future. This leads to the question of whether engineers can be held liable for failing to anticipate the effects of climate change. While the answer, like many questions related to an engineer’s liability, is tied to the Standard of Care, how to determine the Engineer’s Standard of Care may not be straight forward. In addition, the terms of the design agreement can have a significant effect on the engineer’s potential liability for failing to adapt its designs for climate change.

Part Two of this series will take a detailed look at the Engineer’s Standard of Care and how it may be impacted by climate change.■

Gail S. Kelley is a professional engineer as well as a LEED AP and a licensed attorney in Massachusetts, Maryland, and DC.  Ms. Kelley's work is focused on representing design professionals in both contract negotiations and claims management.

Keep building: on your experience + in our communities. With projects in 10 markets + 50 states, project diversity keeps the work fresh, challenges in all the right ways + develops passions. Expect to build a diverse portfolio at Schaefer.

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MAY 2023 19
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Delegated Design of Masonry A

Paradigm Shift

Change is hard. People resist it. It’s easy just to keep going down the known path.

I ask that you humor me by reading this article with an open mind.

The Path that is Known

For years, I have listened to the same two recurring comments from Engineers, Masons, and Educators:

Engineers don’t know how to design masonry (well).

Masonry is not a core class in most Engineering schools; concrete and steel are the focus of most engineering programs. In all my interviews, I have yet to have a new graduate tell me they are comfortable designing masonry, yet they all are comfortable designing concrete and steel.

Engineers don’t know how to detail masonry (well).

There are a lot of moving parts in a masonry system. Coursing, bonding, modularity, etc. A properly detailed masonry system takes TIME and EXPERIENCE. Time to coordinate and dive into the nitty-gritty details and the interface with other structural systems. Experience to know what does and does not work well in the field. If Engineers are not taught masonry design, how can they possibly be expected to know masonry detailing? Even those Engineers that know masonry design struggle with having enough time (and budget) to detail a masonry system properly.

Delegated Design

I want to suggest that the masonry industry take the leap to a delegated design workflow.

What does ‘delegate’ mean? Per the dictionary: delegate is to entrust (a task or responsibility) to someone else.

Specific to structural design, “Delegated Design” is the transfer of design responsibility for certain aspects of the project from the Architect/Engineer to the Contractor.

Delegated Design describes a form of collaboration between a design professional and a contractor where the contractor assumes responsibility for an element or portion of the design. The design professional and contractor typically have separate written contracts with the owner that establish their respective design responsabilities. In the contractor's case, those design responsabilities are often established by performance specifications prepared by the design professional.

Delegating the design of certain specialty systems to the Contractor allows the Contractor to engage Delegate Engineers with the advanced knowledge, skills, and experience to design and detail these systems more efficiently. The Architect/Engineer must still specify all the required performance and design criteria and ultimately review and approve the design. This is not a new concept; it has been used for years in the construction industry. The American Institute of Architects (AIA) and the American Institute of Steel Construction (AISC) have published a paper titled “Design Collaboration on Construction Projects: Delegated Design, Design Assist, and Informal Involvement—what does it all mean?”. This paper is a good summary of the alternative design paths available to designers.

A common question in delegating design is the liability of a Contractor taking on design services. Contractors have commercial general liability insurance but likely do not have professional liability insurance for design and engineering services.

Although the comments have been the same over the last 35 years that I have been working, I haven’t seen any significant changes or improvements to address them.

(Most) Engineers do not design or detail masonry (well). Of course, there are exceptions to the rule. Some firms excel at masonry design and detailing, stay current with advancements in masonry, and take advantage of the most cutting-edge tools for the design, detailing, and modeling of masonry. They do exist; I know several of them through my work with The Masonry Society (TMS). I believe that probably every masonry supplier and contractor knows the Engineers in their region that know how to design and detail masonry…and wish they could be on every job!

The typical approach is for the Contractor to hire a licensed engineer with professional liability insurance to perform the necessary delegated design services. It is important that performance criteria for the project clearly define the delegate engineer’s responsibilities, the expected experience of the delegated engineer, and the required insurance.

Look at the Path of Others

The cold-formed metal framing industry had struggles similar to the masonry industry. Very few Engineers are taught cold-form design in school, and very few excel at the minutia of cold-formed metal framing detailing. When I started my career, we would put together very detailed design drawings for cold-formed metal framing systems; every stud, joist, track, header, sill, jamb, and connection was designed and detailed.

STRUCTURE magazine 20
structural
Excerpt from “Design Collaboration on Construction Projects: Delegated Design, Design Assist, and Informal Involvement—what does it all mean?”.

Then an interesting transformation began.We would receive shop drawings that had an entirely different design!

Along with the shop drawings would be a set of engineered, stamped calculations. We didn’t ASK for this, but we received it, and it was difficult to argue that our design was ‘better’ when calculations and details were showing an alternate solution that was well…more efficient.

Over time, we stopped designing cold-formed metal framing. We allowed the industry to push us to a better solution. We now provide the loading, design criteria, performance specification, basic sizes, and details, but we delegate the design to the Contractor. The Delegate Engineer works with the cold-form contractor/supplier to provide an efficient, well-designed, well-detailed, cold-formed metal framing system that works best for the Contractor.

Delegated Masonry Design

I want to suggest that masonry could follow the same path. What would this look like?

Envision this altered path…

1. The Architect provides the basic architectural parameters: wall locations, wall thickness, wall sections, opening locations, etc.

2. The Engineer of Record (EOR) provides the basic structural parameters: design loads, lateral loads, deflection criteria, etc. It is important to note that the EOR is still responsible for the gravity and lateral design of the building. They must determine all the loads that will be applied to the walls and provide that loading information in the Construction Documents. They are also responsible for reviewing the delegated design submission to ensure that the design and performance criteria have been correctly incorporated into the design.

3. The Mason includes the cost of engineering in his bid, hires a qualified masonry designer/detailer as the Delegate Engineer, and submits both detailed shop drawings and the engineered, stamped calculation package to the EOR for review. This workflow has been used successfully for years for the delegated design of cold-formed metal framing, as well as other specialty items like precast wall systems, steel connections, joist girders, foundation pile systems, metal stair framing, metal-plate connected wood trusses, and pre-engineered metal buildings. Why can’t it work for masonry?

Where to Start?

Admittedly, this is the most challenging question. How do we overcome inertia?

I believe this change has to start with the Masons/Suppliers. As an Engineer, if I delegated my masonry design, I would likely be admonished by my Client when no Mason Contractor would bid on the project! The first step would have to be a consensus among Mason Contractors that this is the best path for the industry.

From there, it would be a matter of Mason Contractors communicating their willingness to do delegated design to the design professionals in their region. Then, they hunt for the Delegate Engineer to perform the work. Again, I believe most Mason Contractors know the Engineers in their area that are worthy of this role; if not, a simple contact with TMS can open the door to many qualified choices.

Then, as with cold-formed metal framing, there would be a transition period to overcome inertia. There would be a period of ‘duplicate effort.’ Engineers will continue to provide masonry design in their documents, and Mason Contractors will need to push back, request the necessary design data from the Engineer, and submit an alternate Delegated Design with their shop drawings. There will be resistance at first (we all hate change). But as with the cold-formed metal framing industry, I believe everyone will eventually see the advantages of delegating masonry design, and the masonry industry will be better off.

Paradigm Shift

It’s time for a fundamental change. There are firms out there that know how to design masonry; they stay current with the latest advancements in the industry, like Masonry IQ and Direct Design, and they have the experience necessary to detail a masonry system that is efficient for masons and costcompetitive. Let’s get masonry design and detailing into the hands of those that do it the right way. Let’s get them on every job as Delegate Engineers. Perhaps this paradigm shift seems too daunting…

So, I will offer this quote that my father taught me; it was the motto of the US Army Corps of Engineers during WWII: “The difficult we do immediately, the impossible takes a little longer.” ■

MAY 2023 21
Jamie Davis, BAE, PE is the President of Ryan Biggs|Clark Davis Engineering & Surveying, DPC and can be reached at (jdavis@ryanbiggs.com) Repository: U.S. Navy Seabee Museum, Collections Department, Port Hueneme, CA 93043, www.history.nawv.mil/museums/seabee museum.htm

mass TIMBER

Buckling Restrained Braces In Mass Timber Projects: Three Case Studies

For high-seismic regions, force-resisting systems are necessary.

Mass timber construction has experienced a significant increase in adoption in recent years due to its architectural appeal and sustainable nature. As its use has spread into regions of high seismicity, the need for reliable and economic seismic force-resisting systems compatible with this type of construction has arisen. Lateral systems incorporating Buckling Restrained Braces (BRBs) complement the desirable benefits of mass timber, and several methods have been developed for their incorporation in mass timber buildings. Three of these methods will be highlighted: a timber/steel hybrid system which collects lateral forces over large areas and concentrates them into steel BRBFs that are able to handle the relatively high resulting forces; a timber BRBF system which resists the lateral forces on a more local level but which must develop the BRB demands into timber members, rather than steel; and a novel timber shear wall system utilizing vertically-oriented BRBs as hold downs at the base of the wall. Each system has its advantages for certain building configurations and will be illustrated through completed projects.

BRB In Mass Timber/Steel Hybrid System: San Mateo County Office Building 3 (SOM)

County Office Building 3 (COB3) is a new government center for San Mateo County in California. The 5-story building totals 208,000 square feet and utilizes a mass timber/steel hybrid system with a conventional BRBF lateral system. It will be the nation’s first net-zero energy civic mass timber building.

The building was designed in conformance with the 2018 International Building Code (IBC) with State of California Amendments (CBC 2019) and is classified as a Type IV HT (Heavy Timber) construction per fire-resistance rating requirements of 2019 CBC Table 601.

The new county office building, characterized by its H-shaped plan, is designed with an open-floor office concept in mind, with large open structural spans and a completely exposed timber structure. The building is located not only in a high seismic region (Seismic Design Category D), but also in a site prone to liquefaction, necessitating the need for a robust lateral

force-resisting system. Due to the required long spans, the structural lateral force-resisting system is concentrated from the main timber structure into 4 ‘cores’ of the building consisting of conventional steel buckling-restrained braced frames (BRBF). These elements are shown in Figure 1.

Due to the high seismic loads of a large floor plate relative to the available size of the steel frames, as well as current code restrictions in the use of timber shear walls in California, a BRB system was utilized to take advantage of the high Response Modification Coefficient, R, as given in ASCE 7. The COB3 structure consists of a traditional timber/steel hybrid design with the BRBs in frames consisting of steel columns and composite steel beams (the steel ‘cores’ of the building). In contrast, the timber structure consists of glulam columns and beams with a CLT floor system. Lateral loads in the timber structure are transferred between CLT floor plate panels using plywood splines which splice each adjacent panel together, allowing the transfer of in-plane loads. In addition to the splines, steel drag members are utilized throughout the floor plates to act as chords and collectors. Chord and collector members are connected

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Figure 2. Steel BRBF and Timber Construction, COB3. Photo Courtesy of Cesar Rubio Photography Figure 1. Plan View of COB3 Timber/Steel BRBF Hybrid Structure

via screws to the top faces of CLT panels. Collector members are then welded directly to the core steel columns to transfer axial loads into the braces, while CLT panels, which rest directly on the steel beams of the core, are connected via screws to transfer shear forces. These elements are indicated in Figure 1, and a view of the overall structure is shown in Figure 2.

With the steel cores of the building situated at the reentrant corners of the H-shaped building, the timber structure cantilevers more than 60ft in plan. As CLT systems tend to deflect significantly due to a combination of panel shear and bending, steel connector slip and plywood spline slip, the design criteria for the drift at the core was limited to 0.7%, allowing for an additional 1.3% drift in the cantilevered floor plate and thus remain under the code limited 2% total drift at the edge of the building. During the analysis of the BRB system, it was found that the braces, when sized for strength, did not need to be altered significantly to satisfy the more restrictive drift design criteria. This is made possible by the significant difference between R (8.0) and the deflection modification factor, Cd (5.0).

BRB In Mass Timber Frame: Terminus at District 56 (Aspect Engineers)

Terminus is an example of a mass timber structure with a novel lateral force-resisting system using BRBs entirely within timber frames. The Terminus project, a 5-story office building in Victoria, British Columbia, Canada, completed in 2021, presented an opportunity to explore a range of lateral force-resisting system options to find one that was best suited for the structure, the architecture, and the extremely high seismic demands of Vancouver Island.

The building is home to the head office of the project’s developer, Design Build Services (DBS), who sought a clean and modern mass timber look combined with resilient seismic performance. The high seismic demand of the region, with a short period 5% damped spectral acceleration of 1.32g, had the design team searching for a lateral system that was suitable for a mass timber project, namely that it was highly ductile, cost-effective, and still celebrated the exposed mass timber. Ultimately the team landed on using BRBs within timber frames, a combination that had not previously been built in North America and one that united the best of BRB with the best of mass timber. Housing BRBs in a glulam frame meant a refined and uniform architectural language of timber throughout the building and streamlined construction without sacrificing performance. A view of a typical frame can be seen in Figure 3.

The design and detailing of this novel system required careful consideration of the forces, the system's true performance, and the exposed structure's visual nature. One of the challenges was ensuring that the timber frame would not provide any rigidity or restraint that would limit the energy dissipation capabilities of the BRBs. In short: how to ensure the frame connections behaved as true pins and could accommodate the building drift. The design started with engineering first principles and good timber detailing practice: detailing the timber connections with numerous mild steel tight-fit pins. The ductile connection failure mode of the pins yielding would allow the joint to have some natural flexibility. The team further provided slotted holes in the steel plates so the connection assemblies would not be restrained and aligned the work points of all members to limit eccentricity introduced into the connection. These details can be seen in Figure 4. By a stroke of serendipity, researchers

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Figure 3. Timber BRBF in the Terminus Project, Vancouver, BC. Photo Courtesy of Dasha Armstrong Figure 4. Timber BRBF Connection Details

at the University of Canterbury studying BRB-timber structures had built and tested full-scale models of BRBs in glulam frames. The researchers demonstrated that a frame connected with bolted or pinned connectors could be approximated as a pinned frame that allowed the BRB to undergo the deformations necessary for the expected ductility.

A second challenge the designers faced was resolving the high seismic forces within the timber frame elements. The connection forces, which included an overstrength factor of around 2, drove an increase in frame member sizes and connection complexity. Two strategies helped to keep the timber connection forces in check: (1) The columns, which were under significant axial forces, were continuous over three stories to minimize splices, leaving only a single massive column connection at the base to be detailed, and (2) a steel tie element was concealed between the CLT deck and the raised access floor. In addition to these strategies, frame locations were chosen to keep the BRB sizes at a minimum, allowing the connections to be designed for the smallest force

possible.

With the biggest technical challenges addressed, collaboration between the design team, the timber fabricator, and the BRB supplier proceeded smoothly, and installation was comparatively simple. Connecting the BRBs to knife plates that were pre-installed into the timber elements kept the BRB erection straightforward. Ultimately, this building represents the possibilities for mass timber with nonconventional material and system combinations.

BRB As a Holdown for Mass Timber Shear Walls: Catalyst Building and Oregon State University Test Specimen (KPFF)

An innovative application of BRBs in a mass timber lateral force-resisting system is their use as hold-downs for mass timber shear walls. This timbersteel hybrid configuration utilizes each of the materials to their greatest benefit; namely, it takes advantage of mass timber panels for their stiffness and strength but relatively low ductility and BRBs for their stable cyclic behavior and force-limiting capability. The stiff mass timber walls limit story drifts but, with the inclusion of BRBs as hold-downs, can still be designed for relatively high ductility (e.g., a response modification coefficient, R, of 6 to 8). Since the maximum force exerted by a BRB hold-down in an overstrength condition can be reliably estimated, capacity-design principles can be straightforwardly applied to check the BRB-to-wall and BRBto-substructure connections as well as the mass timber wall itself to preclude brittle failure modes.

Currently, mass timber shear walls with BRB hold-downs are not prescriptively permitted for seismic regions in ASCE/SEI 7, as referenced by the International Building Code. As such, current projects must pursue performance-based seismic design. However, the equivalent lateral force and modal response spectrum procedures using a response modification coefficient, R, have been shown to produce designs that are likely to satisfy the requirements of performance-based design and nonlinear analysis. Engineers pursuing this system can therefore be confident that their preliminary/ proportioning designs will hold up to more sophisticated analysis later in the performance-based design process.

Two examples of mass timber shear walls with BRB hold-downs are the Catalyst building in Spokane, WA, and a 3-story building test specimen which, as of this writing, is being cyclically tested in Oregon State University’s laboratory. Catalyst is a five-story, 150,000ft² mixed-use education and office building completed in 2020, which uses a combination of planar and core-configured cross-laminated timber (CLT) shear walls. At each end of the planar

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Figure 5. Mass Timber Shear Wall with BRB Hold-Downs at Catalyst in Spokane, WA. Inset shows threaded bars epoxied into a mass timber panel for a BRB-to-wall connection. Figure 6. Mass Timber Shear Wall with BRB Hold-Downs in 3-Story Building Test Specimen at Oregon State University. Inset shows a U-shaped steel bracket for a BRB-to-wall connection (Inset photo shown prior to floor erection).

walls and each corner of the core walls, vertically oriented BRBs connect the CLT walls to the substructure below. See Figure 5. More information on Catalyst’s seismic force-resisting system can be found in a paper presented at the 2021 World Conference on Timber Engineering by Zimmerman et al. The 3-story building specimen being tested at Oregon State University also uses vertically oriented BRBs, but they are instead connected to mass plywood panel (MPP) walls. This work has been summarized in a paper presented at the 12th National Conference on Earthquake Engineering by Araujo et al. Testing of this 3-story building specimen saw the shear walls successfully undergo cyclic demands of up to 4% story drift. See Figure 6, which shows the shear wall and connection detail used in this testing. While quite similar, Catalyst and the 3-story building test specimen have a few notable differences. In Catalyst, mass timber walls bear on the substructure over their full length; in the 3-story building test specimen, they pivot about a central bearing area. In the former configuration, the BRBs experience larger tension than compression displacements (i.e., wall panels rock about their toe), whereas, in the latter, similar tension and compression displacements occur (i.e., wall panels pivot about their center). Additionally, Catalyst and the 3-story building test specimen utilize different BRB-to-wall connection details. At Catalyst, threaded bars are epoxied into the edge of the CLT panels above with embedment depths exceeding 2’-6” in order to produce an aesthetically concealed connection. In the 3-story building test specimen, a U-shaped steel bracket is used with 45-degree fully-threaded screws installed into the face of the MPP walls above. These connection methods are shown in the insets of Figures 5 & 6. These two examples present only some of the design and detailing flexibility available when using mass timber shear walls with BRB hold-downs. Other configurations are expected as this system sees continued development and application. For example, research is currently underway at the University of British Columbia (UBC) and the University of Northern British Columbia (UNBC), where BRBs are connected with glued-in rods into the side of CLT panels. The utility of BRB hold-downs for tall timber design was shown by Tesfamariam in the 2022 Council on Tall Buildings and Urban Habitat Journal.

Summary

Buckling-restrained braces can effectively serve as elements of seismic force-resisting systems for mass timber structures. Successful projects have been completed using BRBs as hold-downs for mass timber shear walls, in fully timber frames, and in conventional steel frames within larger mass timber structures. In the San Mateo County Office Building

3 project, conventional steel bucklingrestrained braced frames were integrated into an otherwise mass timber structure allowing for large open spaces and accommodating a high seismic mass and significant re-entrant corners. In the Terminus project, BRBs were used in frames with timber beams and columns, allowing for an aesthetic architectural appeal that highlighted the mass timber structure and BRBs. The Catalyst project coupled the inherent stiffness and strength of mass timber shear walls with the ductility and stable cyclic behavior of BRBs to create a novel system which, in the testing of a 3-story building, withstood story drifts up to 4%.

Many other structures, completed and in progress, have used combinations of these systems, or others incorporating BRBs, to create reliable lateral force-resisting systems for mass timber structures.

Acknowledgements

The authors would like to acknowledge the assistance of the following individuals:

Mark Sarkisian, Eric Long, Peter Lee, David Shook with Skidmore, Owings & Merrill

Anne Monnier and Jack McCutcheon with KPFF Consulting Engineers

Mehrdad Jahangiri, Brendan Fitzgerald, Jackson Pelling with Aspect Structural Engineers

Dr. Arijit Sinha, Dr. Andre Barbosa, Dr. Tu Ho, and Gustavo Orozco of Oregon State University and Dr. Barbara Simpson and Gustavo Araújo of Stanford University (formerly of Oregon State University) Dr. Solomon Tesfamariam of the University of British Columbia (UBC) and Dr. Thomas Tannert of the University of Northern British Columbia (UNBC)■

Brandt Saxey, S.E., LEED AP (brandt.saxey@corebrace.com) is Technical Director at CoreBrace in West Jordan, UT where he is responsible for the research and development of Buckling-Restrained Braces.

Alex Zha, P.E., (alex.zha@som.com) is a Senior Structural Engineer with the San Francisco, CA office of Skidmore, Owings & Merrill.

Ilana Danzig, P.E., S.E., P.Eng, Struct. Eng., M.Eng (ilana@ aspectengineers.com) is a structural engineer in Vancouver, BC, Canada, licensed in British Columbia as well as many US states. With experience in all materials, her focus is mass timber design and detailing, and she works on mass timber projects throughout North America either as engineer of record or design assist engineer.

Reid Zimmerman, P.E., S.E. (reid.zimmerman@kpff.com) is the Technical Director at KPFF in Portland, OR and has focused his career on translating mass timber research into practice.

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Selling Your Engineering Business

Maximizing value for your firm requires careful planning, expert advisors and a complete understanding of all potential obstacles.

Selling your business is a life-changing event. You go from working more than forty hours a week, including many or most nights and weekends, to not working or working part-time. Selling your business at maximum value, should you choose to, protects your legacy and ensures that your employees continue to have jobs. Successfully selling a business, whether to a group of your current employees (an internal sale) or a third party (an external sale), should be planned and implemented over many years. Developing realistic expectations concerning the sales process, how long it takes, the expenses involved, the value of the business, and transferring the business will almost certainly require the assistance of an advisor(s) and attorneys.

This article mainly targets the seller, but there is always a buyer. Many engineers starting in the profession never dream of owning their own company. But as their careers develop, many engineers start to consider investing in the firm they work for, buying a part of it if the owner makes an offer, or buying it individually or in a group, so there is still much valuable information to be learned.

What Are You Selling?

A buyer is purchasing the future cash flow of the business. Unfortunately, no one knows how much money the company will generate in the future. Therefore, potential buyers look at key indicators that provide insight. For example, there is a strong correlation between future cash flow, the company’s past cash flow, the number of employees, and the employee’s skill level (measured by experience, professional licensure, status in the industry, etc.). Buyers like to see employees across all age brackets, not top-heavy with senior engineers with shorter remaining careers or bottomheavy with many inexperienced engineers. Employees with a breadth of experience capable of performing multiple tasks or working in multiple engineering fields are more valuable than employees with only one skill.

Another key indicator of future cash flow is the company’s current clients. Repeat clients are more valuable than single-project clients since it is expensive to develop new clients. Clients referred from a center of influence (COI) are highly valued if the COI makes consistent referrals. A COI could be a large government entity or a senior management group in a corporation. Commercial, institutional, and government clients are more valuable than individual customers who might require services only once. The pipeline of signed contracts for future work (backlog) is also essential as buyers focus on future work, which indicates future cash flow. In a typical

consulting practice, six months of signed contracts is a healthy pipeline; however, this could vary depending on the nature of the clients and types of projects. For example, some engineering firms working on large institutional projects (hospitals) or large multi-year government contracts (federal or state Indefinite Delivery/Indefinite Quantity (IDIQ) types) have large and lengthy backlogs. Buyers also look at the report of outstanding proposals and try to determine the amount of additional potential revenue.

The history of past projects is the foundation for the company’s name and reputation in the marketplace. The better the history, the better the reputation, and the easier it will be for the new owner to maintain existing clients, obtain future work from them, and leverage past work for new contacts and projects. A company with consistent and increasing sales is considered to have a strong position in the marketplace and can be more valuable than an equivalent-sized but more static company. Profit margins are also a key factor. A company that prices its services at a lower price (therefore assumed to make less profit per unit of staff time) is less desirable than a company that prices its services at a premium price. In a competitive marketplace, a premium price is almost always associated with a superior service offering, niche market, or skill that clients highly value. The percentage of sales wins compared to sales losses also indicates the company’s position and reputation strength. The seller can increase the value of the business by collecting this information over several recent years so it can be shared with potential buyers.

Another key factor in the valuation is the owner’s involvement in

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business PRACTICES
Selling your business at maximum value, should you choose to, protects your legacy and ensures that your employees continue to have jobs.

the business. While it is understood that the owner is highly involved in almost all aspects of a small business, there is a difference between involvement and total control or micro-managing. For example, an owner thinking of and planning for a future external sale should encourage employees to be the primary contact for some clients, make the board of directors and sales presentations, network with clients, and generally operate and market the business. The goal is to have the face of the company be more than that of a single person. Involving the staff in non-technical activities benefits an internal sale because the buyers will clearly understand the potential benefits of ownership.

A significant risk to an external buyer is that key employees may leave after the sale or after the sale is announced. Key employees generate substantial revenue in a well-run and valuable business by running projects, capturing new clients, and maintaining existing client relationships. The buyer will want to retain these employees. Providing retention bonuses is a common solution to decrease the risk of employee turnover. This barrier also increases the cost for another company to poach the employees or for the key employees to leave to start their own company. The owner contemplating or planning for a sale increases the value of the business by always maintaining positive relationships with the staff to mitigate the risk. Disgruntled or indifferent employees are not valuable to a buyer.

Buying a Business – The Buyer’s Perspective

Potential buyers of engineering businesses typically consist of other engineering companies, key company employees, and third-party individuals. Each buyer has different motivations and interests. Therefore, the owner contemplating a sale needs to ensure that each potential buyer type sees maximum value.

Existing companies or third-party individuals may buy a business as a strategic plan to gain a solid foothold in a new market or add new services in a market they currently serve. This immediately results in acquiring additional customers, employees, and a pipeline of future work.

For small businesses, the most likely buyer is frequently an employee or employee group. They are familiar with the business and see its value. They are familiar with the clients, employees, systems and processes, and culture. Using federal Small Business Administration (SBA) financing, the employee’s down payment may be as little as 10% of the purchase price.

Selling to an internal group can be more complicated than selling to outsiders. Although paid for their work, existing employees will generally believe they played a critical role in establishing the company as it currently exists and in its past successes. They might seek a significant discount over what an outsider might pay and use the leverage of leaving to obtain the discount they seek. Sellers need to face the reality that setting up a new engineering business is relatively inexpensive (renting office space or working from home today, buying computers and a phone system, etc.) compared to a business with significant amounts of plant and equipment or physical inventory. The key internal employee group is in a position to poach themselves and the key client relationships they have helped develop over the years. To avoid this showdown, a seller wishing to sell internally should develop a long-term ownership transition process that involves many individuals. The seller can end up with a much-diminished sales value by waiting too long.

How Much Is Your Company Worth?

Business value is a range as opposed to an exact value. The science of business value is calculating the cash flow. The most common standard is EBITDA (Earnings Before Interest, Taxes, Depreciation, and Amortization). However, the Seller’s Discretionary Cash Flow (SDCF) is used for smaller businesses because an owner can pull money from the business in many ways. The cash flow is multiplied by a factor to determine the estimated value, or a series of future cash flows can be discounted to the present to determine the present value. The art is in determining the factor to be applied or the discounting interest rate to be used, depending on the method used. Businesses with more revenue, income, and cash flow demand a larger factor. A simplistic rule of thumb is that the value of an engineering business ranges between 40% and 80% of gross sales. If the discounted cash flow method is used, the art is developing an appropriate risk-adjusted discounting rate and accounting for future revenue growth opportunities. Small differences in assumptions can have a significant impact on the calculated value.

The Sales Process and Beyond

The sales process requires a team of experienced advisors who sell professional service businesses. Your deal team members are your spouse, your accountant, a business transaction attorney, a financial advisor, and an M&A (mergers and acquisitions) advisor. The following description provides an overview of an external sale,

MAY 2023 27
A buyer is purchasing the future cash flow of the business.

but many of the same steps are taken for an internal sale.

The pre-planning phase is when the M&A advisor values your business and writes a Confidential Business Review (CBR). The CBR provides:

• An overview of your business and services,

• the history of the company,

• the services provided,

• types of clients, and

• a detailed discussion of the financial performance.

The pre-planning phase is also when you should prepare for the buyer’s due diligence (audit). Potential problems can be corrected or mitigated at this stage without time pressure. For example, if a buyer receives requested documents within a day, the buyer gains confidence in the seller and business. Conversely, the buyer loses confidence if it takes too much time to receive the document.

The M&A advisor markets your business in a manner that attracts the interest of prospective buyers without revealing sufficient information to allow your business to be identified. Confidentiality is of utmost importance because your clients may choose to shop around if they know your business is for sale. In addition, your employees may choose to control their destiny and leave during a time of uncertainty.

The M&A advisor pre-screens all prospective buyers and requires them to sign a confidentiality and non-disclosure agreement before they learn the name of your business. Then the M&A advisor provides the CBR to the prospective buyer.

A buyer/seller interview follows this. The buyer is seeking to learn more about the business. The seller will assess if they trust the prospective buyer with their business. Both parties evaluate whether they can work with the other party. The seller is selling the business they created, so there is a greater sense of attachment than if they were selling something with less personal investment.

Afterward, the buyer may request more sensitive information such as tax returns, pipeline reports, accounts receivable aging,

payroll register, etc. This allows the buyer to understand the business better, which helps the buyer to make a reasonable offer. At this stage, the seller is more comfortable with the prospective buyer and is willing to release the information.

This is followed by the buyer making a non-binding written offer. The purpose is to outline the transaction sufficiently to ensure a meeting of the minds. Critical aspects of the offer should include the purchase price, when the payments will be made, and what is included and excluded from the purchase. For example, engineering businesses typically require the seller to work for the new owner for a certain period and achieve certain financial metrics to ensure a smooth transition between employees and clients. This should be included in the offer.

The attorneys formalize the offer in a legally binding purchase and sales agreement. While the purchase and sales agreement is being negotiated, the buyer should apply for bank financing if needed.

The bank’s involvement provides extra assurance to buyers as their interests align. In addition, the seller benefits from the bank’s participation by receiving more or all of the sale proceeds at closing. The closing is when the papers are signed and the business is transferred to the new owner.

After the closing, a primary component of selling the business is informing your former employees and clients that you sold the business. A good way to inform your employees is during a breakfast meeting the day after the closing. Immediately after informing your former employees, introduce the new owner. First, the new owner should assure the employees that they still have a job. Then, the new owner should meet with each employee individually.

The seller should rank clients: A, B, and C. Then, the former and new owner should conduct in-person joint visits with the A-level clients, in-person, Zoom meetings with the B-level clients, and phone calls with the C-level clients. We suggest multiple joint meetings to ensure a strong bond before the new owner meets with a client alone.

When selling your business, be flexible. The seller should not take a hard stand on any issue until or unless it is required. An open mind and controlling your emotions can make a huge difference. Selling a business in actual calendar days and hours invested in the process is time-consuming.

Conclusion

Your business has value because of its name, reputation, book of business, skilled employees, and ability to generate money in the future. However, the owner should be a part of the business and not the business. Therefore, a team of capable, experienced advisors is needed to help you sell your business.■

STRUCTURE magazine 28
Allen Business Advisors (www.AllenBusinessAdvisors.com) specializes in selling engineering businesses. John Allen is the Managing Partner and a former Commercial Loan Officer. He can be reached at John@ AllenBusinessAdvisors.com.Washington, D.C.
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An Example of Sustainability Using Timber

The Iconic and Symbolic County Office Building

Decarbonization must rapidly advance to avert further changes to our environment. As a signatory of SE 2050, Skidmore, Owings & Merrill (SOM) has committed to bringing meaningful carbon reductions to a wide spectrum of buildings. The use of mass timber in many buildings can be cost-effective when combined with the building’s architectural design and programmatic needs. The added benefits of carbon sequestration, reduced finishes, and biophilic aesthetics were all developed for the new County Office Building 3 (COB3) for the County of San Mateo in Northern California. The COB3 building will redefine the San Mateo County Government Center with an iconic, forward-looking design that reflects the values of the community. With a mass timber/CLT structural system, ultra-low carbon footprint, and net zero energy goal, the design sets a new standard for sustainable, generational, civic buildings beyond the Bay Area. The 5-story mass timber building totaling 208,000 square feet is located in downtown Redwood City and surrounded by existing county buildings, including the San Mateo Superior Court. The building configuration features a north

and south public plaza linked by a transparent building lobby creating a connection between the downtown Redwood City Theater District and the San Mateo County buildings. The building houses the main public functions at the ground level, including the Board of Supervisors Chamber.

The project is being developed by the Project Development Unit, with SOM as the architect and structural engineer and Truebeck Construction as the general contractor. Scheduled for completion in late 2023, with the goal of both net-zero energy and a significantly reduced embodied carbon footprint, SOM’s structural engineering design team responded to the challenges of the nation’s first net-zero energy mass timber civic building.

To reduce the embodied carbon footprint of a building, the starting point should be the structure, as it is the largest contributor. While using mass timber instead of a steel or concrete structure yields significant savings in the embodied carbon of any project, additional savings through engineering design and close collaboration with architecture and other trades can be had.

STRUCTURE magazine 32
By Mark Sarkisian, Eric Long, Benton Johnson, Peter Lee, David Shook, and Alex Zha

Building Structural Systems

Designed in conformance with the 2018 International Building Code (IBC) with State of California Amendments (CBC 2019), the civic building is assigned to Category II per occupancy load limits of 2019 CBC Table 1604.5. The structure is classified as a Type IV HT (Heavy Timber) construction per fire-resistance rating requirements of CBC 2019 Table 601. The building is located not only in a high seismic region, with a seismic design category D, but also in a region highly susceptible to liquefaction with a seismic site class F.

COB3 is characterized by its H-shaped layout with the gravity system consisting of glue-laminated (glulam) timber beams and columns with a cross-laminated timber (CLT) floor system. The overall plan dimensions of the building are typically 280 by 195 feet.

Distinctly, glulam beams are utilized only in a single direction: a pair of glulam beams, each measuring 8¾-inch by 25½-inch, span 35-foot and 30-foot bays. The long spans were achievable with relatively shallow beam depths by having beams continuous over the center supporting column.

All glulam columns are of consistent width perpendicular to the beam spans to allow for a continuous beam configuration with the beams running past the side faces of the rectangular columns. A unique connection system is utilized to secure the glulam beams at column supports while also acting as the splice connection for the columns. Having a repeatable dual-purpose connection system, combined with off-site fabrication, allowed for an efficient erection schedule by reducing the number of crane picks required on-site as well as reducing the overall steel material quantities. Only simple screw-type connections are needed on-site, in pre-drilled holes, to secure the structural elements. As part of the HT classification, all timber connections are hidden from view with a nominal layer of timber for fire protection.

Because timber beams only exist in one direction, the 6 7/8-inchthick 5-ply CLT slab system acts predominantly as a one-way spanning system spanning the 20-foot bays. Therefore, no additional spandrel beam is required around the perimeter of the building. CLT panels are nominally 8 feet - 6 inches wide, and 40 feet long. The length of the panels provides a double span condition over the center supports,

MAY 2023 33
County Office Building 3 (COB3) is set to be the nation's first net-zero energy mass timber civic building.

reducing the deflection of the panels, which is critical to achieving the large span-to-depth ratio of the panel.

The composition of the CLT was optimized for cost and performance. The CLT outer plies comprise a strong Structural Select Grade of Douglas Fir, while the inner three layers are of a weaker but stiff Coast Sitka Spruce. This composition allowed the exposed CLT layers to match the similarly exposed glulam beams and columns while providing the strength required of the panel. The weaker but stiff inner CLT plies significantly reduced the panels’ costs while providing the required stiffness to limit deflection and floor vibrations, often an issue in longspan timber buildings.

The structure consists of four separate cores located at the reentrant corners of the building. The cores are supported between W14 columns with floors comprised of composite steel beams. The composite steel-slab system generally consists of 4½-inch normal-weight concrete fill over 3-inch metal deck. The cores also provide the lateral forceresisting system for the building. Buckling-Restrained-Braced Frames (BRBF) are provided on all four sides of each core. Forces are developed into the BRBF system through the CLT diaphragm. CLT panels are spliced together using plywood splines and screw connectors, allowing in-plane shear transfer. Panels are also connected to each other and to the steel cores through steel straps and screws forming chords and collectors, creating a load path, designed to mitigate potential liquefaction effects, into the braced frames.

The deep foundation system consists of 18-inch-diameter auger cast-in-place displacement piles that support pile caps that resist superstructure gravity and lateral load reactions at the base of the building. A total of 300 piles extend 75 feet into the soil below. Grade beams

STRUCTURE magazine 34
Glulam columns, beams and CLT floors form a spandrel free perimeter. Photo courtesy of Cesar Rubio Photography. The glulam column, beam and project specific 5-layer CLT system was optimized for cost and performance. Photo courtesy of Cesar Rubio Photography.

interconnect pile caps with a 10-inch pile-supported suspended slab on grade at the first-floor level.

Net Zero Energy and Embodied Carbon

The COB3 design team focused on passive design strategies. With narrow floor plates, a balance between daylighting and solar heat gain to lower the lighting power density could be achieved. This also enabled the configuration of the floorplates to allow natural ventilation for night cooling to reduce loads. The design optimized the active systems, tailoring the mechanical equipment to its use, leveraging efficient hydronic fan coil units at the perimeter and VAV air distribution at the interior core spaces. The interior design strategically places the engineering systems within centrally located cores to minimize distribution distances for the most effective services. The exterior windows have automated window shades that reduce solar heat gain and reduce glare. Once the design loads were reduced, the energy required to operate the building was offset by on-site renewable energy generated by photovoltaics on the project’s roof and the roof of the nearby parking garage, making it a net-zero operational energy building.

In addition to being net-zero operational energy, the project has reduced its embodied carbon by 70% primarily by using advanced structural technologies, including Cross Laminated Timber slabs, with Glued Laminated Timber beams and columns.

Optimal bays and column spacings considering

MAY 2023 35
Steel strapping form the diaphragm chords creating a load path between CLT panels. Photo courtesy of Cesar Rubio Photography. Long spans for open office setting achievable with continuous glulam beam configuration. Photo courtesy of Cesar Rubio Photography.

modules based on office spaces, the layout of mechanical systems, fire sprinklers, and lighting, among other items, all in conjunction with the quantity, size, and thicknesses of glulam beams and CLT required for each configuration, were considered. In addition, the pieces and connections could be priced in real-time with the contractor’s help. The solution was ultimately to reduce the number of beams and have them run in only one direction, leading to a reduced number of pieces and connections, creating an efficient bay size that works well with the office layouts.

By running beams continuously over supports, long spans could be achieved with relatively shallow beams, saving overall timber quantities compared to traditional post-and-beam timber framing systems. In addition, by running the beams in only one direction, a more efficient ceiling/floor structure is achieved by integrating the MEP distribution parallel with the beam direction, which reduces the typical floorto-floor height and the overall building

STRUCTURE magazine 36
Embodied carbon comparison of COB3 with sequestration with baseline structure archetypes. The timber erection chases the steel core construction around the building. Photo courtesy of Cesar Rubio Photography.

height. Subsequently, with a reduced floor-to-floor height, the overall enclosure volume could be significantly reduced, saving further on the embodied carbon.

Setting an example of sustainability for the district, the new County Office Building will be an iconic and symbolic addition to Redwood City’s built environment. The material selection, structural optimization, and collaborative approach achieve enhanced performance, reduced embodied carbon impacts, net-zero energy, and a LEED Platinum rating.■

Project Team

Owner/Developer: San Mateo Project Development Unit, Redwood City, CA

Structural Engineer and Architect: Skidmore, Owings & Merrill, San Francisco, CA

General Contractor/Concrete: Truebeck Construction, San Mateo, CA

Timber Contractor: Western Wood Structures, Tualatin, OR Steel Contractor: Olson & Co. Steel, San Leandro, CA

All authors are with Skidmore, Owings & Merrill. They can be reached as follows:

Mark Sarkisian, P.E., S.E., Partner (mark.sarkisian@som.com)

Eric Long, P.E., S.E., Partner (eric.long@som.com)

Benton Johnson, P.E., S.E., Principal (benton.johnson@som.com)

Peter Lee, P.E., S.E., Associate Principal (peter.lee@som.com)

David Shook, P.E., Associate Principal (david.shook@som.com)

Alex Zha, P.E., Senior Structural Engineer (alex.zha@som.com)

MAY 2023 37
The continuous glulam beams and columns are supported by a dual-purpose steel connection system. Photo courtesy of Cesar Rubio Photography. ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

TMS 402 Appendix D: GFRP-Reinforced Masonry

Updates to the Building Code Requirements for Masonry Structures.

The 2022 TMS 402 Building Code Requirements for Masonry

Structures added Appendix D for glass fiber reinforced polymer (GFRP) reinforced masonry. GFRP reinforcement is non-corrosive, non-conductive, and not thermally conductive, so there is no thermal bridging. Due to these properties, GFRP reinforcement is advantageous in the masonry near electromagnetic equipment, such as MRI rooms in hospitals and masonry walls near high-voltage cables and transformers in substations. Other applications include walls exposed to severe environments, such as in coastal construction, seawalls, and chemical plants. The lightweight nature of the GFRP bar, being one-fourth the steel weight, allows for production efficiencies for the contractor and health and safety benefits to workers.

Scope

TMS 402 Appendix D is for solid, straight, and bent GFRP bars used as internal reinforcement in grouted concrete or clay masonry. Appendix D only applies to the design of masonry walls that do not support axial compressive, allowable stress-level loads of more than 200 lb/linear ft (2919 N/m) in addition to their weight, and lintels within such walls. In other words, Appendix D provides provisions for non-load-bearing partition walls and retaining walls. In addition, GFRP-reinforced walls are limited to non-participating walls in Seismic Design Category C or less. As additional research becomes available, the goal is to expand Appendix D and remove some current restrictions.

Material Properties

There are three key material properties of GFRP bars to be used as flexural reinforcement: tensile strength, modulus of elasticity, and tensile strain at ultimate. ASTM D7957, Standard Specification for Solid Round Glass Fiber Reinforced Polymer Bars for Concrete Reinforcement, provides minimum values for these material properties. Due to the linear nature of GFRP reinforcement, the tensile strain at the ultimate can be taken as the tensile strength divided by the modulus of elasticity. The minimum values from ASTM D7957 can be used for design when the GFRP bar manufacturer is unknown. However, many manufacturers make bars that significantly exceed the minimum values. The designer should select and consult with the manufacturer to determine the actual material properties of bars that will be specified for the project. Improvements in manufacturing and materials have resulted in second-generation GFRP bars with higher strength and higher stiffness. Using these GFRP bars can result in much more efficient designs. It is to be noted that a GFRP bar presents a linear elastic behavior to failure with Young’s modulus of about one-quarter that of steel. Additionally, its transverse properties are resin dominated and, for that, significantly lower than that of steel.

Development and Splice Length

The development length of GFRP bars in masonry is taken as the development length in ACI 440.11-22 Building Code Requirements for Structural Concrete Reinforced with Glass Fiber Reinforced Polymer (GFRP) Bars (2022). For steel reinforcement, the lap splice length is equal to the development length in TMS 402. For GFRP bars, the lap splice length is 1.3 times the development length to match ACI 440.11. Testing was performed to validate using the ACI 440.11 equation for masonry. The testing indicated that using the ACI 440.11 tends to be conservative for masonry; however, sufficient testing was not available for the committee to develop a new equation. Somewhat counterintuitively, development and splice lengths tend to be smaller in masonry than in concrete for the same compressive strength. This is due to the masonry grout having a smaller aggregate size and high slump, resulting in a better encasement and better bond to the reinforcement.

Flexural Strength

The flexural strength will either be controlled by the tensile strength of the GFRP reinforcement or the compressive strength of the masonry. Due to the high strength of the GFRP reinforcement, the section will often be controlled by the strength of the masonry.

When the masonry controls the strength, the stress in the GFRP reinforcement will be less than the design strength. Similar to an “overreinforced” steel reinforced section where the stress is below yield, the stress in the GFRP reinforcement can be obtained as the solution to a quadratic equation.

A key difference between steel reinforcement and GFRP bars is the failure mechanism of the reinforcement. Instead of yielding, GFRP bars fail in rupture before the masonry’s ultimate compressive strain is achieved for the case of “under-reinforced” sections. Therefore, the depth of the neutral axis is unknown at failure when the GFRP reinforcement controls the strength, and the assumption of an equivalent rectangular stress block is inappropriate. In lieu of a more detailed analysis, which can become quite complex, TMS 402 conservatively permits an equivalent compression stress block based on the depth to the neutral axis corresponding to the balanced condition.

While a masonry crushing failure mode can be predicted based on calculations, the member, as constructed, may not fail accordingly. For example, if the masonry strength is higher than specified, the member can fail due to GFRP rupture. For this reason, a compression-controlled section is defined as a section in which the strain in the GFRP reinforcement is 80% or less than the design strain at GFRP failure. The strength-reduction factor for sections controlled by the GFRP reinforcement, or tension-controlled sections, is 0.55. The strength-reduction factor for a compression-controlled section is 0.75. A linear transition region is used between tension and compression-controlled sections or

STRUCTURE magazine 38
code UPDATES

for a GFRP strain at the ultimate of between 80 and 100% of the design strain. Figure 1 shows the nominal moment strength and the design moment strength (strength-reduction factor times the nominal strength) for an 8-inch concrete masonry wall with centered reinforcement and a masonry compressive strength of 2,000 psi as a function of the area of reinforcement. The design strength for Grade 60 steel reinforcement is also shown for comparison.

Wall Deflections

The horizontal deflection of walls under allowable stress level loads is limited to 0.01 times the height of the wall. This deflection limit is 42% higher than the deflection limit for steel-reinforced masonry walls of 0.007 times the height of the wall. A wall loaded in this range returns to its original vertical position when the lateral load is removed. With GFRP reinforcement, the wall will remain elastic at much higher deflection levels than walls with steel reinforcement. GFRP-reinforced masonry walls have a lower stiffness than steel-reinforced walls. This leads to increased second-order, or P-delta, effects. The second-order moment can be 30-50% of the first-order moment with GFRP-reinforced walls. Using second-generation higher stiffness GFRP bars can result in a significant reduction in the second-order moment.

Shear Strength

Due to a lack of research on the shear strength of GFRP-reinforced masonry members with or without shear reinforcement, the contribution of GFRP shear reinforcement is not quantifiable at this time, and all shear is required to be taken by the masonry. The nominal shear strength due to the masonry of GFRP-reinforced masonry members is taken as one-half the nominal shear strength of masonry with conventionally reinforced masonry members. The 0.5 factor is due to GFRP-reinforced members typically having a smaller depth to the neutral axis than steel-reinforced members with equal areas of reinforcement due to the lower modulus of elasticity of GFRP reinforcement as compared to steel reinforcement. This reduces the depth of the compression region and increases crack widths, thereby reducing the amount of interlocking aggregate under compression. Also, the contribution of dowel action of longitudinal GFRP reinforcement has

yet to be determined. Shear rarely controls walls under out-of-plane loads, which primarily affects lintel design.

Lintels

Masonry has a lower masonry compressive strength parallel to the bed joint than perpendicular to the bed joint. This will affect lintel design when the strength is controlled by masonry. To account for this, a χ factor is used, with the masonry stress over the equivalent compression stress block being 0.80χf'm, where f'm is the specified compressive strength of the masonry (determined with the load perpendicular to the bed joint). The values of χ are taken from the Canadian Masonry Code (CSA S304.1-14). The value of χ is 0.5 when the grout is not horizontally continuous in the compression zone, and χ is 0.7 when the grout is continuous horizontally in the compression zone. An example of the grout not being horizontally continuous would be the compression zone constructed of standard stretcher units with full-height webs. Head joints break up the grout core. An example of the grout being continuous horizontally would be the compression zone constructed of knock-out bond beam blocks, allowing the grout to be continuous across head joints.

When the strength is controlled by the masonry, χ significantly impacts the strength. When the strength is controlled by the reinforcement (either steel or GFRP), the compressive strength of the masonry has minimal effect on the nominal moment strength because the depth of the neutral axis is minimized. Thus, χ has minimal impact and is not needed in the design.

Creep Rupture

Creep rupture or static fatigue is a phenomenon that occurs in GFRP bars when the bar suddenly ruptures after being subjected to constant tension over a given period. Creep rupture can control retaining walls, where the entire load is sustained. To avoid creep rupture of GFRP bars, the sustained stress under allowable stress level loads is limited by TMS 402 Section D.5 to 30% of the design tensile strength of the bar.

Conclusions

The addition of Appendix D to TMS 402 is a significant advancement for masonry and composite reinforcement. The TMS 402/602 code committee accomplished the goal of adding composite reinforcement to the code. There is still work to be done to remove some of the current restrictions and to take advantage of continued research and product development to make designs more efficient. This is a major priority of the 2028 code committee.■

Richard Bennett, Ph.D., PE, is a Civil and Environmental Engineering professor at the University of Tennessee. He is currently vice-chair of the TMS 402/602 Code Committee. (rmbennett@utk.edu)

Antonio Nanni, Ph.D., PE, is a Professor and the Chair of the Civil and Architectural Engineering Department at the University of Miami. For over 30 years, he has studied advanced composites and their application to concrete and masonry. (nanni@miami.edu)

MAY 2023 39
Figure 1. Design Moment Strength vs. Area of Reinforcement

outside the BOX

Mass Timber for 843 N. Spring Street

First use of CLT in the Los Angeles Area

843 N Spring Street is a multi-use creative office and retail/restaurant space and the first mass timber project with cross-laminated timber (CLT) to be constructed in the Los Angeles area. It was fundamental gaining acceptance of CLT as a viable structural material under City of Los Angeles Building Code, and is presented as a case study for the sustainable benefits of adaptive reuse integrated with lightweight structures.

Structural Anatomy and the Local Code

The structure extends 5 stories above the existing ground-level podium and is comprised of a hybrid steel frame and CLT gravity system with concrete topping required for the diaphragm. With floor-to-floor heights ranging from 13 to 20 feet, and a total height of 74 feet, the lateral system consists of a mere 4 bays of special concentrically braced frames (SCBF) in each direction above the podium, all of which transition to special reinforced concrete shearwalls (SRCSWs) below the podium. Level 2 was constructed as a Type 1-A suspended two-way concrete flat slab, functioning as a fire separation between the mixed construction types. Under the 2016 California Building Code (CBC), the above-grade hybrid mass timber

structure met the height and story limitations of Type III-B construction, allowing the beautiful CLT and steel framing to remain unprotected and on full display. In addition, the building sits on a sloped site across the street from the Chinatown LA metro station – the parking benefits afforded to transit oriented developments were crucial in the feasibility of this adaptive reuse project.

Adaptive Reuse

The adaptive reuse design maintained the existing concrete structure and masonry segments of the previous two-story commercial building occurring at L1 and below grade. The design intent called for the preservation and selected interventions to the existing slab-ongrade, foundation, concrete columns, basement walls, and L1 podium slab. The design provided the construction team with options for preserving the existing slab-on-grade and foundations by doweling in and encapsulating the existing foundations with a larger concrete area, where required, to account for increased loading of the new structure.

The new structure, framed with steel beams, steel columns and a thin concrete topping over a CLT deck, was integrated into the concrete podium by aligning the new column grid with

STRUCTURE magazine 40
Building elevation featuring the cantilevered CLT panels along W College St. Photo Courtesy of Paul Vu. View of the first CLT panel craned over and placed on the first above-grade level. Photo Courtesy of Jeremy Bitterman / JBSA.

the existing column grid, eliminating the need for deep transfer systems that would have compromised the existing below grade parking. The above-grade W14x steel columns aligned over the 14-inch diameter existing concrete columns that were strengthened to satisfy the increased demands. Strengthening involved exposure of the internal rebar cages and reconstruction of longer columns that were no wider than the existing to maintain the existing parking layouts. It was crucial to the feasibility of the project that the existing column widths be maintained, as any deviation would have resulted in fewer stalls than required by the local building code. In the end, parking requirements for this transit-oriented development were met with a combination of bike parking, parking stackers, and the existing stalls. Through preservation of the existing column grids and parking counts, we saved an entire additional level of parking slab, basement walls, thicker foundations, full demolition, and extensive excavation. This reduced project time, cost, and the environmental impact associated with wide-scale demolition and excavation.

The Architectural design intent called for the use of SCBF’s above grade, in lieu of extending the below grade SRCSWs up to the new floors. With new steel lateral systems introduced above-grade, which transitioned to new or enhanced special concrete shearwall systems below grade, careful attention was given to the connection between these respective systems to ensure adequate and redundant load paths were provided. The connection between the respective steel and concrete systems was achieved by extending the steel SCBF columns down an additional level and developing them into the new or existing concrete shearwalls below. Where the steel SCBF columns required development into the existing below grade walls, it was provided with welded reinforcing and a combination of welded and mechanical splices were made with the existing basement wall reinforcing. At the new walls below, SCBF columns were extended into boundary elements and developed with a combination of welded studs and welded spliced reinforcing bars. With the thoughtful placement and integration of the new SCBF systems over the existing basement walls, we were able to engage a significant amount of the existing walls and footings to control uplift and distribute foundation loads over a large area, thereby minimizing the required foundation sizes. The design intent for preserving the existing structural elements, including the existing basement

walls, concrete columns, and suspended concrete slab, saved approximately 1540 cubic yards of concrete.

Materials and Construction Methods

Whenever possible, the team seized on opportunities to reduce the demolition of the existing structure and use it to the design’s advantage in resisting the new and additional loading demand. The lightweight nature of the CLT floors was crucial in allowing the design team to provide an option to avoid demolition of the existing foundations and opt for enlarging the existing foundations to meet the new load demands. Although CLT was listed as a building material in the building code at the time of design, it was not considered a viable diaphragm to resist lateral loads in Los Angeles due to the lack of official standardized in-place shear values. However, its use was functional for the gravity system and disproportionally contributed to the overall unique aesthetic beauty of the building. With 14-foot cantilevers rising out of the building structure along its wings, the astounding beauty of the CLT panels from the bottom of College Street is unparalleled. As previously indicated, in addition to the warm aesthetic that the CLT deck produced, this type of floor construction allowed for a lighter structure in general. This secured the architectural intent of round HSS braces for the SCBF frames for which the team was striving. Any significant increase in the seismic mass, which would have easily been exceeded with either a steel or concrete framed system, would have forced the use of either rectangular HSS or Wide-Flange braces, neither of which was a viable option for completely exposed structural steel. The lightweight nature of the structure was directly correlated with preventing the required widespread demolition of the existing foundations and the excavation associated with new, deeper foundations. Had the structure been any heavier, the existing foundations would have failed in shear and forced the design team to demolish nearly the entire existing building. The lightweight properties of a CLT deck framed with steel beams also contributed to smaller concrete and steel column sizes. An 8% decrease in seismic mass compared to a traditional building led to an 11% decrease in steel frame quantity.

MAY 2023 41
Detail depicting chipped existing concrete column and the intended new concrete column pour encapsulating the existing rebar cage CLT panels sequentially placed and bolted into the primary steel frame. Photo Courtesy of Jeremy Bitterman / JBSA.

Sustainability and Carbon Sequestration

From a pure sustainability standpoint, the use of CLT was quite compelling. The carbon sequestration from the CLT decks used from Level 2 to the Roof equated to about 930,000 kilograms of carbon dioxide equivalent (kg C02-e) throughout the intended lifetime of the building. The average recycled content for steel manufactured in the United States is about 93% for hot-rolled structural shapes. The use of Wide-Flange beams and columns throughout contributed to 86% of the steel on the project being produced through electric arc furnace process (EAF), as opposed to its more polluting counterpart, basic oxygen furnace (BOF) process. Due to the Type III-B construction designation, the building could fully expose its steel and CLT framing, significantly reducing the embodied carbon associated with architectural finishes and fireproofing. Many aspects of the design came together to contribute to the building’s lower-than-average global warming potential (GWP):

• The use of CLT allowed for a relatively light structure when compared to conventional steel or concrete structures with similar bay sizes;

• Reuse of the bottom section of the building saved more than 31% of the total amount of concrete in the building;

• Reusing the existing concrete elements and strategically using the local parking code requirements prevented the project site’s widespread demolition and extensive excavation.

These seemingly small but meticulously coordinated design items all made significant contributions to reducing the embodied carbon of the building when compared to a standard office building. The design intent for reusing the existing elements alone accounted for approximately

480,000 kg CO2-e in global warming potential (GWP) savings. In addition, preserving much of the existing structure and preventing demolition and broad excavation led to an additional savings of 330,000 kg CO2-e. Finally, the material savings associated with the prevention of an additional parking level accounted for approximately 360,000 kg CO2-e. These GWP savings, combined with the aforementioned carbon sequestration from the CLT panels, led to eliminating approximately 2,100,000 kg CO2-e from being released into the atmosphere. This would be the equivalent of the building occupants emitting no commuting transportation emissions for the first 12 years of the building’s operations.

Conclusion

SUPERIOR SEISMIC PERFORMANCE

The 843 N Spring Street project provided a stepping stone for the CLT and adaptive reuse space in the Los Angeles market. The author’s firm is humbled to have taken part in such an iconic structure in historic Chinatown. It was foundational in providing a pathway for other buildings in the Los Angeles area to use CLT for both the gravity and lateral system. It further embodies a more sustainable way of looking at building design through the use of more sustainable materials, lighter materials, and the reuse of existing structural elements. All involved will be excited to see this building come to completion and open in the near future.■

Rachelle Habchi, MS, PE is a project engineer at Glotman Simpson US Inc. and can be reached at (rhabchi@ glotmansimpson.com).

Chris Smith, MS, SE is a Partner with Glotman Simpson US Inc. and can be reached at (csmith@glotmansimpson.com)

STRUCTURE magazine 42
Finalized glazing and fin system on display showcasing the view of the North-East corner of the structure. Photo Courtesy of Kevin Lee of LEVER Architecture. Photo courtesy of Design Build Services and Dasha Armstrong
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REHABILITATION

Repairing and Modernizing Masonry Cavity Walls

Unintended Consequences

Many brick-clad buildings constructed from the 1950s through the 1970s employ an early version of cavity wall construction that looks like contemporary veneer wall construction from the outside but has different structural behavior. Repairs and modifications to such cavity walls that are seemingly cosmetic or undertaken to improve envelope performance can change the wall’s load path and impact its ability to resist lateral loads. Owners, contractors, and design professionals should be able to recognize cavity wall construction, understand when potential repairs or modifications warrant structural evaluation, and design and implement structural strengthening when required.

Construction and Structural Behavior

Original Design and Construction

Early cavity walls, as defined in this article, comprise an unreinforced concrete masonry (CMU) interior wythe (commonly 4 in. thick, and sometimes 6 in. or 8 in. thick), an air gap, and a brick masonry exterior wythe (Figure 1). The two wythes are tied with horizontal wire reinforcement embedded in the masonry bed joints. Early cavity walls typically were designed using empirical span-to-thickness ratio requirements that considered a combination of the brick thickness and the CMU thickness, prescribed minimum masonry material properties, and prescribed the gage and spacing of the wire reinforcement that joined the wythes.

Early cavity walls were often constructed with brick relieving angles at every story; however, horizontal expansion joints below the angles were typically narrow, if they existed at all. While architectural standards at the time called for narrow open joints below the relieving angles, brick masonry was often installed directly in contact with the angle or with mortar in the joint. Connections of the CMU wythe to the building

frame were designed to include reinforcing dowels, dovetail anchor assemblies, or simply mortared bed joints, though in practice, such connections were sometimes omitted entirely during construction. If any connections of brick wythes to the building structure were provided, they usually consisted of mortar joints to relieving angles at each floor.

Early cavity walls generally lack continuous air, water, vapor, and thermal barriers. The limited enclosure elements that are incorporated primarily consider only water management within the wall cavity and commonly include elements such as through-wall flashings and weeps at brick relieving angles and window heads.

Structural Behavior

Unlike modern brick veneer construction, in

STRUCTURE magazine 44
structural
Figure 1. Schematic wall section of common early cavity wall construction. Figure 2. Spalled brick above steel relieving angle (behind horizontal sealant joint) where the horizontal joint width is inadequate.

which the brick is typically idealized as purely a cladding element that transfers all lateral forces to a lateral-load-resisting backup wall, the brick and CMU wythes of cavity wall construction resist out-of-plane lateral loads as a combined assembly. The embedded horizontal joint reinforcement ties the brick and CMU wythes to each other and distributes load between them but is not typically stiff enough to create fully composite flexural behavior of the wall assembly, the proportion of lateral load resisted by each wythe depends on its relative stiffness. At the ends of the wall span, early cavity walls were intended to transfer shear to the base building frame through the CMU wythe, but the actual load path varies depending on each wythe’s method of attachment to the building.

Common Problems and Repairs

Cavity walls subject to exposure-related deterioration may exhibit conditions that require more than simply in-kind mortar joint repointing and localized brick repair or replacement. Three commonly encountered conditions include brick masonry distress caused by restraint of volume change; corrosion of embedded horizontal joint reinforcement; and inadequate envelope performance given modern expectations.

Distress Caused by Restraint of Volume Change

Symptoms of restraint-induced stresses that may trigger an evaluation include cracks, spalls, and bulges in the exposed brick wythe (Figure 2). Brick is at its driest state immediately after manufacturing and takes on moisture over its lifetime. This absorption results in irreversible brick growth. Brick also changes volume cyclically as it expands and contracts with temperature change. When the brick grows without sufficient horizontal expansion joints to accommodate the growth, the building structure restrains the brick expansion. Early cavity wall systems containing narrow horizontal expansion joints (by design) or no horizontal expansion joints (due to poor construction) are not able to accommodate brick growth. One common repair strategy to reduce the likelihood of worsening distress due to restrained brick expansion is to introduce an expansion joint below relieving angles with sufficient joint width to accommodate the movement (Figure 3).

Corroded Horizontal Joint Reinforcement

Symptoms of corroded horizontal joint reinforcement include cracked or spalled brick mortar joints and corrosion staining on the face of the wall. Corrosion occurs in the presence of moisture and oxygen, and cavity walls that manage water poorly are susceptible to it. Corrosion product (rust) has a larger volume than the original, stable base metal, and the increase in volume induces stresses in the mortar joints that can lead to the cracks and mortar spalls. If allowed to progress long enough, the corrosion can lead to section loss, compromising the integrity of the joint reinforcement. Depending on the extent and severity of corrosion-related deterioration, common repair approaches include localized or widespread brick removal to repair or replace corroded reinforcement.

Envelope Performance Issues

Although often initially spurred by observations of brick distress to assess their building’s exterior walls, once they begin investigating,

MAY 2023 45
Figure 3. Examples of introducing horizontal expansion joints below relieving angles for projects that involve strengthening of the backup wall.

building owners may become aware of other envelope performance issues associated with cavity wall construction. Common problems include leakage to the interior, ineffective water management within the wall cavity (e.g., water dwells within the cavity), missing or deficient flashings, and occupant comfort issues brought on by lack of an air barrier or poor thermal performance and humidity control.

Leakage and water management issues can sometimes be mitigated through modifications made local to brick relieving angles and windows, which typically require removal and replacement of brick above and/or below the angle or window and installation of new flashing and/or weeps. In other cases the scope may expand to include full removal and replacement of the brick wythe. Examples include when moisture-related deterioration of interior building components advances; more reliable moisture mitigation is desired; or a new air barrier and insulation are desired for improved code compliance, energy efficiency, or occupant comfort. It is impractical, however, to salvage horizontal joint reinforcement and still provide a reliable air/water barrier while implementing such intrusive modifications. Therefore, in these circumstances, the existing joint reinforcement typically is cut at the CMU face and replaced with post-installed brick veneer ties (Figure 4).

Structural Effects of Modifications

Common approaches used to address the restraint-of-volume distress, corroded horizontal joint reinforcement, and envelope performance issues described above can have unintended structural implications. Whether the modifications to the cavity wall are local to relieving angles (e.g., cutting in new horizontal expansion joints) or wholesale in nature (e.g., removing and replacing the entire brick wythe and cutting the joint reinforcement), the designer must review and understand the potential structural consequences of these modifications. Below, two types of modifications are described which can affect the cavity wall’s load path and its structural capacity.

Horizontal Expansion Joints Below Relieving Angles

Adequately sized horizontal expansion joints are important for the long-term durability of masonry walls. However, introducing these joints into walls that previously lacked them alters the load path of the wall. Compressive stresses in the existing brick that develop in the absence of an adequately sized expansion joint reduce the net flexural tension on mortar joints when the wall is subjected to out-of-plane lateral load. Releasing the precompression by introducing a horizontal expansion joint increases the net flexural tensile stress in the wall when it is loaded out of plane. Empirical cavity walls, especially those with horizontal through-cracks or non-compliant spanto-thickness ratios, might rely on this precompression to resist lateral loads. Precompression also affects the capacity of masonry wall connections to the base building structure by increasing frictional resistance. Releasing the precompression alters the load path through which lateral-load induced shear forces are transmitted to the base building.

Cutting Horizontal Joint Reinforcement

Cutting existing embedded horizontal joint reinforcement at the exterior face of the CMU wythe and replacing it with conventional brick ties to address corroded reinforcement or to accommodate new wall waterproofing, air barrier, and insulation in the cavity makes the existing wall noncompliant with empirical requirements for cavity walls. Post-installed brick ties fastened to the face of the CMU behave differently than joint reinforcement embedded in the CMU wythe, which impacts the load-sharing behavior between the brick and CMU wythes. Therefore, cutting the embedded joint reinforcement alters the original design intent and the in-situ structural behavior of the wall.

Evaluation and Analysis

Building Code Triggers for Structural Evaluation

Most codes used by local jurisdictions (state, county, or city) adopt, in whole or in part, the International Building Code (IBC) and, by reference, the International Existing Building Code (IEBC).

The 2018 IEBC includes the following relevant definitions: Repairs are the “reconstruction, replacement or renewal of any part of an existing building for the purpose of its maintenance or to correct damage.” Alterations are “any construction or renovation to an existing structure other than a repair or addition.”

Modifications like the introduction of new horizontal expansion joints below relieving angles and the cutting of embedded horizontal joint reinforcement change the structural behavior of the cavity wall and should be classified as “alterations.” For “alterations,” the IEBC requires lateral-load-resisting elements

STRUCTURE magazine 46
Figure 4. Example of in-progress re-clad. Existing horizontal joint reinforcement was cut to allow installation of new air and water barrier; new adjustable brick ties were later installed to support replacement brick.

that experience a stress increase of more than 10% due to the alteration to be analyzed for their ability to resist current code loads, and strengthened if needed.

Structural Analysis of Modified Wall

Unless the designer can demonstrate that the modifications to the cavity wall – adding new expansion joints beneath the relieving angles and/or cutting the existing horizontal joint reinforcement –result in a stress increase on each of the wall elements of no more than 10%, they must analyze the modified wall for its ability to resist current code loads.

Unreinforced CMU used in the construction of early cavity walls is typically 8 in. thick or less and frequently lacks positive anchorage to the building structure. Designers should analyze the existing wall assembly in its proposed modified configuration against current code-prescribed lateral loads using estimates of material properties published in standards contemporary to the time of original construction. If the analysis finds that the modified wall is unable to resist current code loads and there is a strong desire to avoid strengthening work, it may be possible to justify higher material properties than those published in contemporary standards with a testing program. However, such a program can itself be costly to design and execute and does not guarantee results that would eliminate or substantially reduce the need for wall strengthening.

Wall Strengthening Approaches

When the proposed modified wall is unable to resist code-prescribed loads as required by IEBC, the following strengthening approaches are available, among others:

• Fiber Reinforced Polymer Strips – Install fiber reinforced polymer (FRP) strips to strengthen the existing CMU wythe. FRP will be required on both the interior and exterior faces of the CMU to resist out-of-plane loads in opposing directions. If existing top- and/or bottom-of-wall connections also require strengthening, provide new attachments between the wall and the building structure. Where new attachment details include post-installed fasteners, designers should keep in mind that commonly used fastener design tables and design-assist software are calibrated to modern material properties and workmanship; requiring in-situ tests to demonstrate fastener strengths in existing material substrates is prudent for validating assumed design values.

• Internal Reinforcing Bars – Reinforce existing CMU by cutting cells open, installing vertical reinforcing bars, and grouting newly reinforced cells solid (Figure 5). Work can be performed from either the interior or exterior of the building. New reinforcing bars may connect directly to the base building structure, or separate top- and/or bottom-of-wall attachments may be added where needed, as described in the FRP strengthening approach above.

• Cold Formed Metal Framed Backup Wall – Install a new interior cold formed metal framed (CFMF) backup wall to strengthen or entirely bypass the existing cavity wall. The supplemental wall must be sufficiently stiff relative to the cavity wall and adequately connected to the existing CMU to receive out-of-plane lateral loads. Designing the CFMF wall with at least an L/600 deflection limit will limit masonry

cracking as out-of-plane loads transfer between the walls. The new backup wall can be attached at its top and bottom to the existing building structure similarly to modern backup walls in veneer wall assemblies. In this approach, the new wall installed against the interior face of the CMU will reduce the occupiable floor space somewhat, but the end result is a functionally new backup wall that can be constructed using methods familiar to most contractors.

• Wall Replacement or Overcladding – If a strengthening approach is not preferred, the existing cavity wall can be demolished and replaced with a new exterior wall assembly, or it can be abandoned in place behind a new overclad wall. Both approaches offer the opportunity for the owner and design team to fully re-envision the exterior wall from an aesthetic and envelope performance perspective, if desired, but they require a comprehensive review of the existing building structure and foundations for their ability to support the new exterior wall. The relative merits of the various strengthening and replacement strategies will likely include considerations outside of the designers’ control. For example, project budget and available funding, buildingor owner-driven limitations on access (interior vs. exterior) or working hours, tolerance for noise and disruption, and material availability can impact decision-making on the preferred approach.

Summary

Repairing and modernizing masonry-clad buildings that employ early cavity wall construction may be more complicated than it first appears. Designers, contractors, and owners must appreciate that seemingly non-structural improvements can affect the cavity wall’s structural behavior and ability to resist out-of-plane loads. When structural strengthening of the cavity wall is needed to support a repair or modernization project, the best approach will account not only for structural requirements but also for the owner’s non-structural priorities and constraints.■

Trey Dondrea is a Senior Consulting Engineer at Simpson Gumpertz & Heger in Washington, D.C. (aldondrea@sgh.com).

Emily Appelbaum is an Associate Principal at Simpson Gumpertz & Heger in Washington, D.C. (epappelbaum@sgh.com).

R. Scott Silvester is a Principal at Simpson Gumpertz & Heger in Washington, D.C. (rssilvester@sgh.com).

MAY 2023 47
Figure 5. In-progress installation of reinforcement into existing CMU.

historical STRUCTURES

19th Century Mississippi River Bridges #6

Quincy Bridge, Illinois/Missouri 1868

The Quincy Bridge Company was incorporated in Illinois in 1853 and in Missouri in 1866 as part of a general act regulating the construction of roads and bridges. It was to connect Quincy, Illinois with West Quincy, Missouri. On July 25, 1866 Congress passed a bill approving construction of the bridge. This was part of a larger bill “to authorize the construction of certain bridges, and to establish them as Postroads” and was for bridges over the Mississippi and Missouri Rivers. Section 1 stated,

Be it enacted by the Senate and House of Representatives of the United States of America, in Congress assembled:

SECTION 1. That it shall be lawful for any person or persons, company or corporation, having authority from the States of Illinois and Missouri for such purpose, to build a bridge across the Mississippi River at Quincy, Illinois…

Section 2 went on to state that if it was to be a draw bridge it should have a clearance on each side of the draw pier of 160’ and that the two adjacent spans should be of 250’ long. It also required all spans to be a minimum of 10’ above high water. If it was to be a high, continuous span it should have a 50’ clearance over the high water mark with spans no less than 250’ with one span over the main channel of 300’.

In November 1866 the bridge companies in Illinois and Missouri were merged under the name “Quincy Railroad Bridge Company.” Thomas C. Clarke was named Chief Engineer. He began work immediately surveying the previously proposed sites and in late November recommended the upper site. James Joy, Managing Director and Warren Colburn, Consulting engineer for the bridge company, however, had many ideas of their own as to how the bridge should be built. They instructed Clarke that the bridge should be iron, built at the low level with a swing and there should be no temporary wood work (trestling). Clarke and the bridge management decided to “draw up general specifications and solicit tenders from bridge builders of known ability, in conformity with these specifications.” On March 1, 1867 Clarke completed the design and sent out his request for proposals. In other words, he set the span lengths, width of

the superstructure, and the material to be used. The specifications consisted of four requirements.

1.The fixed spans to be built of cast and wrought iron, the draw span of wrought iron only. Both to be of the best and toughest quality and to be subject to rigid inspection during manufacture.

2.Max. rolling load 2,500 lbs. per lineal foot, which, with weight of

STRUCTURE magazine 48
Swing and main spans, Quincy Bridge – 15 spans to right of swing Image taken along axis of bridge

bridge, shall not cause a tensile strain of over 10,000 lbs. per square inch on the ties and lower chords, or 7,500 lbs. on pins, or a compressive strain on upper chords or posts of which the factor of safety shall not be less than five.

3.Workmanship to be of best quality.

4.After testing with full load, bridges shall return to original camber.

Thirteen tenders were submitted for bowstring trusses, Bollman and Fink trusses, Triangular girders (Double intersection Warren trusses), Howe trusses and Quadrangular girders (Double intersection Whipple’s). Clarke recommended the Quadrangular truss “with pin and screw connections.” He also wrote as to material, “my own choice has always been to build bridges wholly of wroughtiron. Cast-iron upper chords may be perfectly sound, but we have no means of knowing that. No inspection can detect hidden flaws in a casting. If they are of rolled form, we use a material in which the process of manufacture will reveal flaws.” He selected the proposal of the Detroit Bridge and Iron Works, the same firm that built the Clinton Bridge west spans, with cast iron upper chords, wrought iron diagonals and posts. It was also building the Burlington Bridge (STRUCTURE April 2023) at the time. The Detroit Bridge and Iron Works had recently taken control of the firm run by Charles Kellogg who opened his firm in 1857. Kellogg initially took control of construction of the bridge working with Clarke. Shortly after he left to start his own company in Buffalo, New York and new management took over. The bridge was divided into three parts. The fixed spans were quadrangular girders with cast iron upper chords, Phoenix section rolled posts, and bottom chords composed of open links with pin connections. The main draw was a quadrangular truss (Whipple) with both chords of rolled channel beams latticed together. The contract was signed on May 6, 1867. The length of bridge over the main channel was 3,250’ consisting of a 362’ swing bridge, and 16 fixed spans with three being 200’ and two being 250’ with the other 11 being 157’ each. The first stone of the foundation was laid September 25, 1867 and the last stone August 5, 1868.

In addition it had a bridge across Quincy Bay consisting of a 190’ Bollman Truss swing bridge and 4 fixed, Bollman Deck Trusses plus a short masonry approach span at each end. These were also built by the Detroit Bridge & Iron Company. The bridge was fabricated and erected between December 1867 and November 1868.

Quality control was stressed and “every piece of wrought iron in the ties, links, bolts, &.c., was tested in a hydraulic press up to 23,600 pounds to the square inch, and struck with a hammer, while under tension, before being used in the bridge.” The bridge was test loaded by a select panel of prominent engineers on November 7, 1868 by placing a 300,000# load both static and moving at speeds of 10 to 16 miles per hour. The deflection on one of the 250’ spans was 2.433”. On one of the 257’ spans it was only 1.374”. Both of these were close to the predicted deflection for those loads.

Clarke estimated the cost of the main bridge at $1,150,625 with the superstructure at $475,000 and the foundations at $400,000. The total cost of the Bay Bridge was $165,000 and the total cost of the entire project $1,500,000. Clarke wrote a complete bridge description that was published by Van Nostrand’s in 1869. A review in Van Nostrand’s Eclectic Engineering Magazine ended with “The Quincy Railroad Bridge is a carefully finished structure, and with all its magnitude presents a graceful and attractive appearance.” Clarke finished his description of the bridge with, “I hope this brief description may incite other engineers to put their experience on record, so that it can be accessible to the profession. If so, I shall consider that my labor has not been wasted.”

It was replaced in 1899 with the original piers being re-used. After the Burlington Bridge (which has opened a few months before), it was the second bridge across the Mississippi to be built entirely in iron.■

MAY 2023 49
Quincy Bridge 1868, 250’ span in foreground Bay Bridge of Bollman Trusses 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@twc.com).

Board of Directors Transition

Announcing Officers & Directors for 2023-24

NCSEA is pleased to announce the new Board of Directors for 2023-2024. Ryan Kersting (SEAOC), Buehler Engineering, Inc., will serve as President replacing David Horos (SEAOI), Skidmore, Owings & Merrill, who will transition to Past President for one year before exiting the board. Christopher Cerino (SEAoNY), STV, Inc., was named Vice-President, Jami Lorenz (SEAMT), DCI Engineers, remains as Secretary, and Brian Petruzzi (SEA-MW), Meta, was named Treasurer. Two new directors have been welcomed to the Board: Angelina Stasulis (SEAOG), Shear Structural and Cervente Sudduth (SEAKM), DuBois Consultants, Inc.

President: Ryan Kersting, S.E. (SEAOC)

Vice President: Christopher Cerino, P.E. (SEAoNY)

Secretary Jami Lorenz, S.E. (SEAMT)

Treasurer: Brian Petruzzi, P.E. (SEA-MW)

Past President David Horos, P.E., S.E. (SEAOI)

Director Jeannette Torrents, P.E., S.E. (SEAC)

Director Ken O'Dell, S.E. (SEAOC)

Director Angelina Stasulis, P.E., S.E. (SEAOG)

Director

Cervente D. Sudduth, P.E. (SEAKM)

NCSEA News STRUCTURE magazine 50 follow @NCSEA on social media for the latest news & events!

News from the National Council of Structural Engineers Associations

Submit Your Project for a Structural Engineering Excellence (SEE) Award!

NCSEA's Structural Engineering Excellence (SEE) Awards highlight structural engineering ingenuity throughout the world and incredible achievements in the profession. Projects are judged on innovative design, engineering achievement, and creativity. Structural engineers and structural engineering firms are encouraged to enter their projects to highlight their successes and accomplishments. The awards are presented in the following categories:

• New Buildings < $30 Million

• New Buildings $30 Million to $80 Million

• New Buildings $80 Million to $200 Million

• New Buildings Over $200 Million

• New Bridges or Transportation Structures

• Forensic/Renovation/Retrofit/Rehabilitation Structures < $20 Million

• Forensic/Renovation/Retrofit/Rehabilitation Structures > $20 Million

• Other Structures

Visit https://www.weseeaboveandbeyond.com/see-awards to submit your project.

Entries are due on Tuesday, June 5, 2023. The winners will be honored at NCSEA's Structural Engineering Summit November 7-10 in Anaheim, in STRUCTURE magazine, in a professionally produced video on the NCSEA website, and in a special webinar series the following spring/summer.

2023 NCSEA Special Awards | Call for Nominations

The Special Awards are presented annually to NCSEA members who have displayed outstanding service, exceptional dedication, and notable commitment to the association and the structural engineering profession. These include the NCSEA Service Award, the Robert Cornforth Award, the Susan M. Frey NCSEA Educator Award, the James Delahay Award, and the recently added Susan Ann “Susie” Jorgensen Presidential Leadership Award. Nominations for the Special Awards are due on June 5, 2023. Click this link to nominate a colleague http://www.ncsea.com/awards/specialawards/

NCSEA Webinars

May 2, 2023

May 11, 2023

Visit

Concrete Ductile Coupled Walls and Seismic Design of Concrete Walls: SEAOC Seismic Design Manual Volume III, Examples 1 & 2

Reinforced

New Buildings $30 Million to $80 Million: Idaho Central Credit Union Arena

May 17 & 18, 2023

California Office of Emergency Services (CalOES) Safety Assessment Program

This California Office of Emergency Services (CalOES) Safety Assessment Program (SAP), presented by NCSEA, is based on ATC-20/45 methodologies and forms. This SAP training course provides engineers, architects and code-enforcement professionals with the basic skills required to perform safety assessments of structures following disasters. Licensed design professionals and certified building officials will be eligible for SAP Evaluator certification and credentials following completion of this program and submission of required documentation.

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

MAY 2023 51
latest news on upcoming webinars and other virtual events. Courses award 1.0 -1.5 hours of Diamond Review-approved continuing education after completing
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SEI Update

ASCE Committee Techsession: Introduction to Structural Fire Engineering

Join us for Introduction to Structural Fire Engineering, Thursday, May 18, 3:00pm ET younger member leaders, Xia Yan, Michael Drury, Nan Hua, and Julie Liu, of the SEI Fire Protection Committee.

The program will introduce concepts and provide design resources. Highlights include fire effects, and prescriptive and performance based design for steel, concrete and timber structures. Young structural engineering professionals are encouraged to participate. Participants will earn 1.5 PDHs and have live Q/A with speakers.

Learn more and register at www.asce.org/education-and-events

Get involved in SEI Committees to advance your career and the profession

Applications from Young Professionals are especially encouraged:

• Digital Design Committee - joint SEI-CASE effort that includes practitioners from engineering firms of all sizes. Our mission is to explore and share the benefits and risks of digital design tools to improve the business and practice of engineering. We present at conferences, have published articles, and are working on a collection of “what you need to know” white papers on topics that directly impact practicing engineers: BIM Execution Plans, Reality Capture, and project QAQC. www.seibim.org

• SE Licensure Committee - furthers the mission of SEI relating to licensing, regulatory issues, and professional development activities for structural engineers. Our desired outcome is to enact legislation for SE licensure requirements in all jurisdictions by creating a plan for working proactively with local engineers, stakeholders, and engineering organizations, and developing resources such as statistical data, white papers, case studies, etc. to support the efforts of local structural engineers. The committee represents SEI at the Structural Engineering Licensure Coalition (SELC) www.selicensure.org to further our vision.

• Mentoring Committee - working to increase participation in ASCE Mentor Match, raise awareness of specific aspects of mentoring, i.e. mentors provide guidance, advice, feedback, and support to the mentee, serving variously as role models, teachers, counselors, advisors, sponsors, advocates, and allies, depending on the specific goals and objectives agreed by the mentor and the mentee. We welcome any looking to give back, at any stage in your career!

SEI Committees need you – learn more and apply to an SEI committee today www.asce.org/SEICommittees !

Mission: To advance structural engineering education, facilitate professional growth opportunities, and promote networking with industry experts ensuring a smooth transition from college to career.

Learn more about local SEI Chapters www.asce.org/SEIlocal

submit errata, contact

STRUCTURE magazine 52
Welcome to the new SEI Graduate Student Chapter, University of New Haven SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI. To
sei@asce.org. Errata

Congrats to SEI Futures Fund Young Professional Scholarship Recipients to Structures Congress

May 3-6 in New Orleans

Stefanie Rae Arizabal, Oakland CA

Ana Paula Bernardo, Sarasota, FL

Sujit Bhandari, Corvalis, OR

Autumn Buesking, Davenport, IA

Judian Duran, Tampa, FL

Emily Durcan, Neconset, NY

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David Fratamico, Springfield, PA

Meriton Gollopeni, Baltimore, MD

Robert Gunter, Washington, DC

Evan Jordan, Seattle, WA

Maha Kenawy, Menlo Park, CA

Tony Kulesa, Overland Park, KS

Ignace Mugabo, Little Rock, AR

Polly Murray, Anchorage, AK

Shima Rajaei Dehkordi, Melrose, MA

Ishwarya Srikanth, Acton, Canada

Ann Sychterz, Champaign, IL

Hasan Tariq, Norfolk, VA

Megan Vandervort, Emeryville, CA

Haifeng Wang, Pullman, WA

Song Wang, W. Hartford, CT

THANK YOU, DONORS, who have given January - March!

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Hiring for SEI Senior Technical Manager – see details at

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Robin A. Kemper & Family

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Norma Jean Mattei, Ph.D., P.E., F.SEI, F.ASCE, Pres.17.ASCE

Andre Newinski, S.E., A.M.ASCE

Lawrence C. Novak, S.E., F.SEI, M.ASCE

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Donald R. Scott, P.E., S.E., F.SEI, F.ASCE

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

Stephanie L. Slocum, P.E., M.ASCE

Thomas W. Smith, III, CAE, ENV SP, F.ASCE

J. Greg Soules, Ph.D., P.E., P.Eng, S.E., F.SEI, F.ASCE

W. Henryk Staniewski, P.E., P.Eng, M.ASCE

Stephen S. Szoke, P.E., F.SEI, F.ASCE

John G. Tawresey, P.E., F.SEI, Dist.M.ASCE

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Anonymous

As a donor to the SEI Futures Fund, you are supporting the future of structural engineering, promoting student interest, aiding younger-member involvement, and ensuring opportunities for professional development.

Help us maximize the full impact of the CSI match opportunity and give a gift today!

MAY 2023 53 News of the Structural Engineering Institute of ASCE
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Are You Looking for a Professional Development Opportunity?

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?

The Structural Coalition at ACEC has several committees that meet regularly to develop documents that help guide engineers in their business practice. The Contracts Committee is responsible for developing and maintaining contracts to assist practicing engineers with risk management.

The Contracts Committee is actively looking for a new member. 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!

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.

Check out some of the CASE Contract Documents developed by the Contracts Committee…

• CASE #1 – An Agreement for the Provision of Limited Professional Services. This is a sample agreement for small projects or investigations of limited scope and time duration. It contains the essentials of a good agreement including scope of services, fee arrangement and terms and conditions.

• CASE #2 – An Agreement Between Client and Structural Engineer of Record for Prof. Svs. This agreement form may be used when the client, e.g. owner, contractor developer, etc., wishes to retain the Structural Engineer of Record directly. The contract contains an easy to understand matrix of services that will simplify the “what’s included and what’s not” questions in negotiations with a prospective client. This agreement may also be used with a client who is an architect when the architect-owner agreement is not an AIA agreement.

• CASE #9 – An Agreement Between Structural Engineer of Record and Consulting Design Professional for Service. The Structural Engineer of Record, when serving in the role of Prime Design Professional or as a Consultant, may find it necessary to retain the services of a sub-consultant or architect. This agreement provides a form that outlines the services and requirements in a matrix so that the services of the sub-consultant may be readily defined and understood.

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!

STRUCTURE magazine 54
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Upcoming Events

2023 Annual Convention and Legislative Summit

June 11-14, 2023

Grand Hyatt Washington, Washington DC

A new Congress. A new Speaker. A House and Senate with razor thin margins. Heated debates on hot-button issues with outsized impact on our industry and its future.

That’s the backdrop for ACEC’s Annual Convention & Legislative Summit, scheduled for June 11 – 14 in Washington, DC downtown at the Grand Hyatt just steps from Capitol Hill.

Join your peers for this three-day event and leave armed with the political intelligence and added insight you need to make informed decisions about your strategic priorities in a changing economy. From the continued implications of IIJA implementation to the ongoing debate surrounding immigration reform and beyond, the business of the 118th Congress is the business of our firms.

The post-pandemic legislative and regulatory landscape is ripe with opportunity for our industry. ACEC is here to help you seize those opportunities and navigate through a changed – and charged – political environment.

The Annual Convention and Legislative Summit will offer the high value speakers you expect from ACEC’s marquee advocacy event including former New Jersey Governor Chris Christie, and Borge Brende, president of the World Economic Forum. The event will also offer attendees a full schedule of educational sessions and networking opportunities to learn, share and connect with your peers.

Most important, Capitol Hill has fully reopened with the lifting of COVID restrictions. That means, our in-person grassroots advocacy program will be back in full force as engineers from across the country take to the Hill to advocate for our industry.

We have the capacity to create a world changed for the better – and we’re excited to work together to get there. See you in June!

MAY 2023 55 News of the Coalition of American Structural Engineers
Now more than ever we need to support the upcoming generation of the workforce. Give to the CASE Scholarship today! • Stay Current on Industry Opportunities and Challenges • Reconnect Face-to-Face with Peers and Partners • Get the PDHs you Need • Meet with Vendor Partners
https://www.acec.org/conferences/2023-annual-convention

structural SPECIFICATIONS

Robust Lumber Specifications on Construction Documents

It is more important than ever due to the increase in grade-marked products entering the U.S.

Registered design professionals (RDPs) typically specify in their construction documents the assumed lumber grade, moisture content, and species or species combination of the dimension lumber (2-4 inches thick) used in their design work. For example, in the materials section of the construction documents, a note might state:

All wall and floor framing shall be (minimum) No.2 S-DRY Douglas Fir. Roof framing shall be pre-manufactured wood trusses.

This article aims to explain the practical importance of a more robust lumber specification and why it is more important than before due to additional grade-marked products entering the U.S. from other countries over the past 20 years. Further, North American grading agencies are also grade-marking lumber with multiple species or species combinations. As a result, a simple layman’s description may no longer clearly communicate to other parties what products and associated design values were assumed and used by the RDP in their design.

Background

RDPs rely on the Supplement to the National Design Specification® (NDS®) for Wood Construction: Design Values for Wood Construction (NDS Supplement) for the lumber design values assumed for their designs. The 1991 and 1997 NDS Supplement had three tables for dimension lumber:

• Table 4A Base Design Values for Visually Graded Dimension Lumber (all except Southern Pine)

• Table 4B Base Design Values for Visually Graded Southern Pine

Dimension Lumber

• Table 4C Design Values for Mechanically

Graded Dimension Lumber

For the lumber species or species combinations referenced in Tables 4A, 4B, and 4C, base design values are associated with a typical lumber specification. For example, for any species or species combination and grade, the tabulated design values in the 1997 NDS Supplement are as follows:

Fb = tabulated bending design value, psi

Fc = tabulated compression parallel to grain design value, psi, and E = tabulated modulus of elasticity, psi.

An additional lumber property for the design of fasteners (such as nails, screws, bolts) and connectors, Specific Gravity (G), was tabulated for all species combinations in Table 8A of the 1997 NDS.

In the 2001 edition of the NDS Supplement, a new Table 4F was added to facilitate the design process when specifying visually graded dimension lumber from other than North American countries (historically, U.S. and Canada):

Table 4F. Base Design Values for Non-North American Visually Graded Dimension Lumber (2”-4” thick)

With one exception, the species names included in the new Table 4F differed from U.S. species. Thus, the potential for a miscommunication of what was used and specified by the RDP was minuscule. By the time of publication of the 2018 NDS Supplement, the number of Non-North American species and species combinations had increased and included species and species combinations with a different grade-mark format comprising multiple lumber products (https://awc.org/wp-content/uploads/2022/02/AWC-2018NDSSupplement-Updates-Errata_22-2-25.pdf). The traditional grade mark applies to one lumber product that includes a single specie or a species combination. For example, the No.2 KD-HT S-P-F grade mark shown in Figure 1 represents one species combination comprised of eight individual species -- Alpine Fir, Balsam Fir, Black Spruce, Engelmann Spruce, Jack Pine, Lodgepole Pine, Red Spruce, and White Spruce. Reference design values for the Spruce-Pine-Fir (S-P-F) combination are given in the 2018 NDS Supplement, Table 4A.

F

t = tabulated tension parallel to grain design value, psi

F

v = tabulated shear parallel to grain design value, psi

F

cT = tabulated compression perpendicular to grain design value, psi

As shown in the recently developed Table 4G of an Addendum to the 2018 NDS Supplement (link above), a new grade mark format can include two or more products from two or more countries. For example, a grade mark representing the species combination Spruce-Pine-Fir from Canada (S-P-F) and Spruce-Pine-Fir from the U.S. (SPFS) is shown in Figure 2. The design values that apply to this grade mark can be found in the 2018 NDS Supplement Addendum Table 4G. Another grade mark example representing three products from Austria, Romania, and Ukraine is shown in Figure 3. The design values that apply to this grade mark can also be found in the 2018 NDS Supplement Addendum Table 4G.

STRUCTURE magazine 56
Figure 1. Grade mark example of a single species combination Spruce-Pine-Fir processed in Canada under the National Lumber Grades Authority (NLGA) grading rules.

Codes and Standards

For the International Residential Code (IRC) and International Building Code (IBC), traditional lumber species or species combinations and newer sources are listed in the NDS Supplement’s applicable version (Tables 4A, 4B, 4C, 4F, and 4G). In addition, they are required to be manufactured following American Softwood Lumber Standard PS 20 and the grading rules of an approved lumber rules-writing agency. PS 20 (http://alsc.org/uploaded/PS%2020-20%20Revsion%201%20 October%202021.pdf) is the referenced standard for lumber in both the IRC and IBC.

For lumber products grade marked with multiple species or species combinations (as demonstrated in Figures 2-3), the reference design values are governed by the new NDS Supplement Table 4G. Due to the way the design values were derived for products included in Table 4G, the tabulated design values are at least as conservative as the design values for products included in Tables 4A, 4B, 4C, and 4F. Since imported lumber is manufactured and graded under that same product standard, grading rules, and supervisory agencies as U.S. lumber, RDPs and regulatory agencies should be comfortable using and recognizing the additional new resource of structural dimension lumber (2-4 inches thick, 2 inches & wider) included in Table 4G.

In summary, the common specification format used in construction documents, such as “All framing lumber shall be No. 2 Southern Pine (or Douglas Fir)”, does not have sufficient detail to differentiate between design values for the traditional U.S. and Canadian lumber products versus imported species or species combination products that are now available. The additional supply of lumber from countries other than the U.S. and Canada motivates rethinking how RDPs can clearly specify dimension lumber in their structural construction documents.

Robust Lumber Specifications

A robust lumber specification should document the lumber grades, species or species combinations, and associated design values used in the structural design. In addition, the specification should include sufficient detail whereby the description incorporates a single set of design values published in the applicable edition of the NDS Supplement as referenced by the relevant building code for the project.

For dimension lumber, the elements of a robust specification are grade, maximum moisture content, and species, species combination, or multiple species or species combinations directly linked to a set of reference design values given in the NDS Supplement edition as referenced by the applicable building code for the project.

Accurate Specifications Matter

The most compelling reason for an accurate and robust specification is that a vague specification can “open the door” to performance issues in-service stemming from the use of materials that have structural design values lower than those used for design. Vague specifications can also impact the design and construction work of others. The following examples point to the need and value of accurate and robust specifications of minimum lumber properties assumed by the RDP.

Wind Uplift Connectors

Fastener and connector design values are based on specific gravity (G), a very important strength variable. For the case of a roof-truss-to-wall wind uplift connection, the published allowable uplift capacity for a specific connector is tabulated for species specific gravity (G) which assumes that both the truss and wall framing are the same species. In many cases, the specific gravity of the wall framing is less than the specific gravity of the truss chords; thus, the lower value of the wall framing must be used for the truss-to-wall connection design.

When a truss manufacturer designs and supplies roof trusses and uplift connectors only, the connector designs would typically be based on the specific gravity of the truss chords. As truss-to-wall connections are the responsibility of the RDP per Chapter 2 of the National Design Standard for Metal Plate Connected Wood Trusses (TPI 1-2014), it is incumbent on the RDP to specify without ambiguity and communicate in the Construction Documents the design values assumed for the wall framing (studs and plates) that includes the specific gravity value.

Referring to Table 1, the block labeled DF/SP Allowable Loads “…are for Douglas Fir-Larch under continuously dry conditions. Allowable loads for other species or conditions must be adjusted according to the code.” Additional instructions for designers indicate the following: “For connections involving members with different specific gravities, use the allowable load corresponding to the lowest specific gravity in the connection unless noted otherwise.”

MAY 2023 57
Table 1. Hurricane Tie design values (excerpted from Simpson Strong-Tie webpage: (https://www.strongtie.com/seismicandhurricaneties_strapsandties/h25a_htie/p/h25a#LoadTables). Figure 2. Grade mark example representing two species combinations, Spruce-Pine-Fir and Spruce-Pine-Fir (South), manufactured in North America. Reference design values are given in the NDS Supplement’s new Table 4G. Figure 3. Grade mark for No.2 Austrian Spruce, Norway Spruce, and Scots Pine imported (I) from Austria, Romania, and Ukraine, kiln-dried (KD) and heat treated (HT).

Douglas Fir-Larch specific gravity is 0.50; thus, the DF/SP block applies to species with G ≥ 0.50. Likewise, the block labeled SPF/HF Allowable Loads applies to species having a G ≥ 0.42.

Potential Uplift Design Deficiencies

What is the potential design error if a wall framing design is based on Spruce-Pine-Fir (Figure 1) and a truss manufacturer supplies Southern Pine (SP) roof trusses (G=0.55) that include truss-to-wall connectors based on SP? The connector design capacity could be as much as 12% less (from Table 1: 615/700) than what is required by the specified wind uplift load on the truss design drawings using the H2.5A uplift connector as an example. Hurricane Ian is a recent reminder of the structural importance of wind load connection design, especially in coastal areas with higher wind load requirements.

The actual wall framing lumber could potentially have a specific gravity as low as 0.35. However, assuming the wall framing has a G< 0.42 and the uplift connectors are designed based on SP lumber, the design deficiency would be even greater. Since connector design tables for lumber with specific gravity values less than 0.42 are not typical, engineering analysis would be needed to evaluate the uplift connectors in this scenario.

RDPs are encouraged to expand their typical design notes to include the minimum design values for both the trusses and the wall framing. For example, consider the following format:

• Roof and floor trusses shall be minimum 2x4 KD19 No. 2 Southern Pine, with minimum reference design values of: Fb/1100, Ft/675, Fc/140, Fc-perp/565, E/1,4000,000 and G/0.55.

• Wall-framing shall be minimum 2x4 No. 2 Spruce-Pine-Fir with minimum reference design values of: Fb/875, Ft/450, Fc/1150, Fc-perp/425, E/1,400,000 and G/0.42.

This specification format should alert the truss manufacturer to the fact that the truss uplift connection package must be designed based on Fc-perp equal to 425 psi and G equal to 0.42. By successfully transmitting the wall-framing criteria to the general contractor and truss manufacturer, truss uplift connections can be properly designed by the truss manufacturer using the properties of the specified wall framing.

Shear Wall Design

Nominal unit shear capacities for wood-frame shear walls (and woodframed diaphragms) are published in Chapter 4 of the Special Design Provisions for Wind and Seismic (SDPWS) standard. Tabulated values assume that lumber G ≥ 0.50. For species groupings with G < 0.50, the nominal unit shear capacities must be reduced using a Specific Gravity Adjustment Factor (SGAF):

SGAF = [1 – (0.5 – G)] ≤ 1.0.

Where G is the published specific gravity value for the wall framing lumber. To demonstrate the impact of G on shear wall capacity, consider an example where the wall framing specification on the construction documents is the following:

“Wall framing lumber and plates shall be (minimum) No. 2 S-DRY DFL”

Referring to the 2018 NDS Supplement, Table 4A, the G for Douglas Fir-Larch (DFL) is 0.50. Since G is not less than 0.50, the SGAF would not be required for DFL lumber. However, how would the design values be affected by the inadvertent use of lumber

having a G less than the 0.50 shown on the construction documents? Assume the lumber used for the wall framing had a grade stamp that listed multiple species or species combinations (e.g., Douglas Fir, Hem-Fir & Spruce-Pine-Fir from North America).

In this case, the design values would not be taken from the DFL species combination in NDS Supplement Table 4A; rather, design values would be found in NDS Supplement Table 4G, where G= 0.42. Using the SGAF adjustment equation for the reduced G:

SGAF = [1 – (0.5 – 0.42)] = 0.92

resulting in an 8% reduction in unit shear design capacity. This type of error can be mitigated using a more robust lumber specification such as the following:

• All wall framing shall be minimum 2x4 No.2 KD19 Douglas FirLarch with minimum reference design values of: Fb/900, Ft/575, Fc/1350, Fc-perp/625, E/1,600,000 and G/0.50.

Wall Studs Resisting Wind

Responding to this issue, the Pacific Lumber Inspection Bureau published a wall stud design guide for different wall heights and wind loads titled Technical Report No. 5 Maximum Allowable Stud Length Tables for European Species and Countries in High Wind Regions (https://www.plib.org/staging/wp-content/ uploads/2021/05/TR-5-Max-Stud-Length-Tables-for-EuropeanSpecies-1.pdf). The document includes allowable stud heights for 2x4 to 2x8 studs and ultimate wind speeds of 90-195 mph.

Conclusion

The customary specification of structural lumber used for decades is no longer sufficient for engineered wood construction. Over the last two decades, the volume of foreign dimension lumber (2-4 inches thick, 2 inches and wider) available has dramatically increased. Additionally, North American grading agencies are also grade-marking lumber with multiple species or species combinations. Using two hypothetical design cases, roof truss uplift connector design and shear wall design, the structural impact of the lumber used in construction with lower than assumed design values was demonstrated. Since other designers are typically involved in designing a typical wood-frame construction project, it falls on the RDP to reliably communicate what reference design values were used for their work when the validity of the design work of others is affected by their framing lumber specification. One format for a more robust lumber specification for wood trusses and wall framing is offered. Further, additional steps or documentation are encouraged to advise the owner, general contractor, truss manufacturer, and framing contractor of the specific framing lumber requirements.■

Don Bender, P.E., Ph.D., is a Professor Emeritus of Civil Engineering at Washington State University. (bender@wsu.edu)

John “Buddy” Showalter, P.E., M.ASCE, is a senior staff engineer with the International Code Council’s product development group. (bshowalter@ iccsafe.org)

STRUCTURE magazine 58
Frank Woeste, P.E., Ph.D., is a Professor Emeritus and Adjunct Professor of Sustainable Biomaterials at Virginia Tech. (fwoeste@vt.edu)

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