STRUCTURE magazine | February 2022

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FEBRUARY 2022

Steel/CFS INSIDE: Nashville Airport Canopy 3-Sided Box Diaphragm Madison Avenue Hotel Restoration Seismic Retrofit of the Printery

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Contents FEBRUARY 2022

Columns and Departments 7 Editorial Supporting Our Future Leaders Through a Trying Transition

46 Business Practices Hiring and Retention Tips for 2022

By Brian Petruzzi, P.E.

By Mike “Batman” Cohen

Cover Feature

ELEVATING THE BNA® VISION

By Terry Palmer, P.E., Tom Meyer, P.E., S.E., and Kevin Kuntz, P.E., S.E.

The centerpiece of the Nashville International Airport’s project is a curvilinear “airwave” roof canopy. Amazingly, the roof’s unique, mildly rippled form is created with just two curvilinear “spine trusses” that carry the entire roof.

The canopy roof and IAF addition are interconnected as a single, homogeneous structure and stabilized by a moment-frame lateral system. Cover photos courtesy of Matt Good (www.mattshootsforgood.com).

Features RESTORING A CENTURY-OLD BUILDING

By Lauren Feinstein, P.E., Jordan Weinstein, P.E., and Kevin Poulin, Ph.D., P.E.

8

Codes and Standards

48

2021 IBC Significant Structural Changes – Part 4

Legal Perspectives Contracts 101

By Gail S. Kelley, P.E., Esq.

By Sandra Hyde, P.E., and John “Buddy” Showalter, P.E.

49

VR in Engineering, Architecture, and Construction

12 Structural Performance FRP Column Retrofit for Mt. Zion Housing – Part 2

By Abby Enscoe, P.E., et al.

16 Structural Design Ground Snow Loads for ASCE 7-22

By Marc Maguire, Ph.D., et al.

20

InFocus

A Call for More Voices!

InSights

The existing seventeen-story Madison Avenue Hotel has a transitional masonry superstructure, a historic hybrid system comprised of a steel skeleton embedded in the exterior brick masonry walls. During construction, the undocumented structural history of the building was discovered, leading to an unexpected scope of strengthening and repair.

By Rune Vandli

51

Spotlight

The First Unitarian Society Meeting House 58

Structural Forum

Calling on Structural Engineers to Design for Sustainability

SEISMIC RETROFIT OF THE ATASCADERO PRINTERY

By Jillian van Enckevort, S.E.

The Printery was damaged in December 2003, when the San Simeon Earthquake shook the central California coast.

The retrofit focused on: in-plane shear capacity, the outof-plane bending capacity, anchorage of the walls to the roof/floor, and weak flexible horizontal diaphragms.

By Jay Arehart, Ph.D.

By John A. Dal Pino, S.E

22

By Jim Lintz, P.E., S.E.

42

RESILIENT MILITARY HOUSING

Structural Components

Tackling the 3-Sided Box Diaphragm: One Engineer’s Perspective

Historic Structures

Tacoma Narrows Bridge Failure 1940 – Part 1

By Frank Griggs, Jr., D.Eng, P.E.

By Anantha Chittur, P.E., S.E., and Frank K. Humay, Ph.D., S.E.

In Every Issue Advertiser Index Resource Guide – Bridge NCSEA News SEI Update CASE in Point

The design for the Bachelor Enlisted Quarters project overcame several challenges. The foundation solution supported the structure on shallow concrete foundations bearing on vibratory stone columns. A hybrid approach was used for the slab-on-grade as an alternative to a slab fully supported on stone columns or structural fill. And much more…

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.

FEBRUARY 2022

EDITORIAL Supporting Our Future Leaders Through a Trying Transition

By Brian Petruzzi, P.E.

W

hile the effect of the Covid pandemic on today’s workforce will be written about for years, one segment of this workforce that I have seen affected directly is recent college graduates.

The first hurdle for young engineers graduating during the pandemic is finding a job. According to Pew Research, college graduates entering the workforce in 2020 (compared to 2019) were less likely to be employed and represented a smaller percentage of NCSEA’s New Graduate Education Initiative is producing an interactive resource to provide young the overall workforce. For those securing internships, engineers on-the-job answers at their fingertips. surveys from the National Association of Colleges and Employers show that nearly half of all internships during the panSix years ago, I wrote an editorial for STRUCTURE about my demic were remote. This makes it challenging to replicate the social first NCSEA Summit experience. I discussed the importance of building community outside the office and the Summit’s role in engagement that helps students bridge to the professional world.

Think back to when you started your first job. You were immediately empowering young engineers. As remote work challenges how shown your desk and introduced to the people in the office. Although I young engineers build their professional community, we must did not remember anyone’s name from my first day, these people would double down on industry efforts to connect young engineers. soon form my inner circle – the start of my professional community. Support your local YMGs. Find opportunities (when it’s safe) I spent more time with this community than my friends, resulting in to send young engineers to conferences. We must provide young a transfer of knowledge ranging from how to clear the printer when engineers with a community of like-minded professionals with it jammed to how to review my first steel connection submittal. whom they can engage.

Young professionals are torn about their professional experiences The New Graduate Education Initiative was launched in 2019 when during the pandemic. When I talk to people on my team, they value NCSEA redeveloped its five-year Strategic Plan and included a goal the flexibility and quality of life provided by remote work. However, to develop a new approach to educating recent graduates. We are not they do not have established networks or professional communities. trying to replace comprehensive technical content already available This can often result in greater isolation from their teams, making like webinars or textbooks. Instead, how do you create an e-learning them feel less informed than older colleagues. environment where new graduate engineers can learn enough to Where should the next generation of structural engineers turn for understand what resources they need to leverage and what questions their answers for the last two years and the foreseeable future? Who to ask? And how can you do this so content is easily accessible and is providing them the context? How are we ensuring that their com- ranges from a few minutes to a few hours, depending on what is munity for support and stability is as strong at home as in the office? needed at that moment?

The answers include a variety of different resources – some virtual When we started the initiative, we did not know that the pandemic and some in-person – probably achieving varying levels of success. would inhibit a new graduate engineer from walking over to their Unfortunately, I have witnessed first-hand how this vulnerable seg- colleague’s desk to ask about control joints in masonry structures. ment of the workforce is not receiving the same degree of support I However, the application and need remain the same. The strugdid. In fact, on more than one occasion, I have addressed concerns gle to support young engineers has been a growing problem in the that they may be missing out on career opportunities. professional world long before the pandemic. While NCSEA’s webSo, what can you do? First, reach out to a young engineer and connect based e-learning modules will not replace human mentoring, this with them. Then, create a forum where you can connect personally New Graduate Education Tool is meant to deliver young engineers and sustain the forum over time (months to years). Remote work answers when they need them. The first module on masonry is close has stripped away the human aspects of the job, and if we hope to to completion, and future modules for materials such as wood are replicate any of the office cultures in a remote environment, we need being ramped up. to create ample space for genuine human engagement.

As structural engineers, we must ensure that every structure has a This leads to two NCSEA Initiatives focused on young engineers – stable foundation. The future foundation of our profession is the the Young Member Group Support Committee (YMGSC) and the young engineers currently transitioning to the workforce.

New Graduate Education Initiative.

The time is now to ensure that the foundation has the supThe YMGSC was established in 2012 to assist the state SEAs in port, resources, and community it needs to succeed.■ embracing young engineers as they transition from student to proBrian Petruzzi is a member of the NCSEA Board of Directors, a former fessional life. This committee has grown to drive engagement across Chair of the NCSEA Young Member Group Support Committee, and a NCSEA initiatives while building the future leaders of our profession.

Founding Member and Past-Chair of the Structural Engineers Association Results are most prevalent in the content developed specifically for of Metropolitan Washington Young Member Group. young engineers at the NCSEA Summit.

STRUCTURE magazine

FEBRUARY 2022

7

CODES and STANDARDS 2021 IBC Significant Structural Changes Part 4: Concrete and Steel (Chapters 19 and 22)

By Sandra Hyde, P.E., and John “Buddy” Showalter, P.E.

T

his five-part series discusses significant structural changes to the 2021 International Building Code (IBC) by the International Code Council (ICC). Part 4 includes an overview of changes to Chapter 19 on concrete and Chapter 22 on steel. Only a portion of the total number of code changes to these chapters are discussed in this article. More information on the code changes discussed here can be found in the 2021 Significant Changes to the International Building Code, available from ICC (Figure 1).

IBC Chapters 19 and 22 provide minimum accepted practices for designing and constructing buildings and structural components using concrete and steel, respectively. The following modifications were approved for the 2021 IBC. New text is shown in underline format with a brief description of the change’s significance.

Figure 1. 2021 Significant Changes to the IBC.

Concrete Design and Construction The American Concrete Institute’s ACI 318, Building Code Requirements for Structural Concrete, has been updated to the 2019 edition (Figure 2) and includes changes addressing deep foundations, materials, and seismic design.

1901.2 Plain and reinforced concrete. Structural concrete shall be designed and constructed in accordance with the requirements of this chapter and ACI 318 as amended in Section 1905 of this code.

Figure 2. ACI 318-19 is referenced in the 2021 IBC.

Chapter 35 318-19: Building Code Requirements for Structural Concrete & Commentary Change Significance: ACI 318 includes requirements for the design and construction of structural concrete necessary to ensure public health and safety. The 2019 edition is now referenced, with changes that respond to new developments in materials, structural systems, and seismic design. Not only have the structural design provisions changed, but materials’ advancement and placement techniques are also addressed, resulting in procedural changes of interest to both manufacturers and contractors.

Structural Concrete Tolerances

Figure 3. ACI 117 and ACI ITG-7 are referenced in the 2021 IBC.

8 STRUCTURE magazine

American Concrete Institute standards ACI 117-10, Specification for Tolerances for Concrete Construction and Materials, and ACI ITG-7-09, Specification for Tolerances for Precast Concrete, have been added to the IBC by reference to provide acceptable tolerances for concrete construction (Figure 3).

1901.7 Tolerances for structural concrete. Where not indicated in construction documents, structural tolerances for concrete structural elements shall be in accordance with this section.

1901.7.1 Cast-in-place concrete tolerances.

Structural tolerances for cast-in-place concrete structural elements shall be in accordance with ACI 117.

Exceptions: 1. Group R-3 detached one- or two-family dwellings are not required to comply with this section.

2. Shotcrete is not required to comply with this section.

1901.7.2 Precast concrete tolerances. Structural tolerances for precast concrete structural elements shall be in accordance with ACI ITG-7.

Exception: Group R-3 detached one- or two-family dwellings are not required to comply with this section.

Chapter 35 ACI 117-10: Specification for Tolerances for Concrete Construction and Materials ACI ITG-7-09: Specification for Tolerances for Precast Concrete Change Significance: Two standards are now referenced for allowable tolerances of structural concrete elements when such tolerances have not been indicated in construction documents, providing building departments, designers, contractors, and special inspectors with information necessary for concrete design and construction within appropriate tolerances.

ACI 117 designates standard tolerances for concrete construction.

Applicable to exposed concrete and architectural concrete, tolerances in the specification are for typical concrete construction and construction procedures. Materials that interface with or connect to concrete elements may have tolerance requirements that are not compatible with those contained in ACI 117. Care should be taken to verify that concrete tolerances work with steel or wood tolerances of each structural assembly. This specification does not apply to precast concrete or shotcrete.

Figure 4. Welded Unreinforced Flange-Welded Web (WUF-W) connection.

Courtesy of American Institute of Steel Construction.

ACI ITG-7 provides standard tolerances for precast concrete construction, deals with dimensional tolerances for precast concrete members used in building construction, and addresses erection tolerances for individual members. Engineers may also specify projectspecific requirements in the contract documents rather than using the provisions of ACI ITG-7.

As a best practice, a series of preconstruction tolerance coordination meetings should be scheduled and held before the commencement of concrete work. The contractor, subcontractors, material suppliers, and other key parties should all attend. At the meeting, all should be given an opportunity to identify any tolerance questions and conflicts applicable to the work with materials, prefabricated elements, and work to be assembled or installed in the field by the contractor. continued on next page

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accordance with AISC 360, and need not be designed and detailed in accordance with AISC 341.

2205.2.1.2 Seismic Design Category D, E or F. Structures assigned to Seismic Design Category D, E or F shall be designed and detailed in accordance with AISC 341, except as permitted in ASCE 7, Table 15.4-1. Beam-to-column moment connections in special moment frames and intermediate moment frames shall be prequalified in accordance with AISC 341 Section K1, qualified by testing in accordance with AISC 341 Section K2, or shall be prequalified in accordance with AISC 358.

Change Significance: Supplements to AISC 358 are now produced more frequently than new editions of AISC 341, with the net effect of not recognizing newer steel proviFigure 5. Bolted Flange Plate (BFP) connection. Courtesy of American Institute of Steel Construction. sions in the code which leads to confusion among building officials, registered design professionals, and manufacturers regarding Seismic Steel Moment Frame prequalified connections. The most up-to-date standard is accomPrequalified Connections modated by directly referencing AISC 358 in the IBC. AISC 358 AISC 358, Prequalified Connections for Special and Intermediate Steel is just one approach for designing structural steel connections Moment Frames for Seismic Applications, includes requirements for for seismic loads. Section K1 or K2 of AISC 341 may also be design, detailing, fabrication, and quality control of tested connections used. Section K1 offers minimum requirements for the process for use with intermediate and special moment frames. In the past, of prequalifying a beam-to-column connection used in a special AISC 358 was directly referenced in AISC 341, Seismic Provisions for or intermediate moment frame. The intent is to allow the use of Structural Steel Buildings, which is referenced in the IBC. Applicable a few connection configurations tested to the point where typical provisions of AISC 358 are now referenced in the 2021 IBC. performance is understood for a narrow set of construction tolerNotably, in the 2021 IBC, beam-column moment connections in ances. Both Section K1 and AISC 358 are based on the premise of a Seismic Design Category B and C buildings are now required to be pre-tested connection for a moment frame. Section K2 of AISC 341, prequalified where the response modification coefficient exception addressing testing requirements for both beam-to-column moment is not applied. frame connections and link-to-column braced frame connections, 2205.2.1.1 Seismic Design Category includes a simplified list of requirements B or C. Structures assigned to Seismic that can be used to create a specific beamDesign Category B or C shall be of any column connection test protocol. construction permitted in Section 2205.

Examples of prequalified moment frame Where a response modification coefconnections are a welded unreinforced ficient, R, in accordance with ASCE 7, flange-welded web (WUF-W) connection Table 12.2-1, is used for the design of (Figure 4, page 9) and a bolted flange plate structures assigned to Seismic Design (BFP) connection (Figure 5). Each structural Category B or C, the structures shall steel connection ties a beam to a column. be designed and detailed in accordance with the requirements of AISC 341.

Cantilevered Steel Beam-to-column moment connecStorage Racks tions in special moment frames and intermediate moment frames shall be Requirements for cantilevered steel storage prequalified in accordance with AISC racks and their anchorage qualification con341 Section K1, qualified by testing in tinue to be clarified (Figure 6 ). accordance with AISC 341 Section K2, 2209.3 Certification. For rack storage or shall be prequalified in accordance structures that are 8 feet in height or with AISC 358. greater to the top load level and assigned Exception: The response modification to Seismic Design Category D, E, or coefficient, R, designated for “Steel F at completion of the storage rack systems not specifically detailed for installation, a certificate of compliance seismic resistance, excluding cantileshall be submitted to the owner or the ver column systems” in ASCE 7, owner’s authorized agent stating that the Table 12.2-1, shall be permitted for work was performed in accordance with Figure 6. Cantilevered steel storage racks. systems designed and detailed in approved construction documents.

10 STRUCTURE magazine

202 Definitions: STORAGE RACKS, STEEL. Cold-formed or hot-rolled steel structural members which are formed into steel storage racks, including pallet storage racks, movable-shelf racks, rack-supported systems, automated storage and retrieval systems (stacker racks), push-back racks, pallet-flow racks, case-flow racks, pick modules, and rack-supported platforms. Other types of racks, such as drive-in or drive-through racks, cantilever racks, portable racks, or racks made of materials other than steel, are not considered storage racks for the purpose of this code.

STORAGE RACKS, STEEL CANTILEVERED. A framework or assemblage comprised of cold-formed or hot-rolled steel structural members, primarily in the form of vertical columns, extended bases, horizontal arms projecting from the faces of the columns, and longitudinal (down-aisle) bracing between columns. There may be shelf beams between the arms, depending on the products being stored; this definition does not include other types of racks such as pallet storage racks, drive-in racks, drive-through racks, or racks made of materials other than steel.

Change Significance: The design of components utilized in steel storage racks is based on minimum thicknesses and minimum yield strength. Storage rack systems can be complex, and their fabrication and installation must comply with approved drawings.

Installation and anchorage of storage racks in high seismic regions require special inspection. In addition, a certificate of compliance is to be provided to the building official stating that the rack was fabricated and installed to meet the requirements in the approved construction documents.

The addition of a steel cantilevered storage rack definition acknowledges that this common type of storage rack has different load and design requirements than a standard steel storage rack. The definition for steel cantilevered storage racks is consistent with that found in ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Section 11.2 and states explicitly that the racks will be made of structural steel, that the arms cantilever, and that the definition does not apply to other types of steel storage racks.

Conclusion Structural engineers responsible for steel and concrete design should be aware of significant structural changes in the 2021 IBC. First, the latest ACI 318 standard is referenced along with references to ACI provisions for concrete construction tolerances. Second, AISC 358 is now directly referenced for design of structural steel connections for seismic loads. Finally, the addition of a steel cantilevered storage rack definition acknowledges that this common type of storage rack has different load and design requirements than a standard steel storage rack.■ Parts 1 through 3 of this series ran in STRUCTURE November 2021 (Loads), December 2021 (Foundations), and January 2022 (Special Inspections), respectively.

Sandra Hyde (shyde@iccsafe.org) is Managing Director, and John “Buddy” Showalter (bshowalter@iccsafe.org) is Senior Staff Engineer, both with ICC’s Product Development Group.

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structural PERFORMANCE FRP Column Retrofit for Mt. Zion Housing Part 2

By Abby Enscoe, P.E., Marc Steyer, S.E., Aniket Borwankar, Mike Wesson, S.E., Ph.D., Lawrence Burkett, Joe Maffei, S.E., Ph.D., and Rachel Cohen, P.E.

A

recent seismic retrofit project provided an opportunity to test an interior concrete column retrofit with a three-sided, fiber-reinforced polymer (FRP) wrap with FRP through-anchors on the fourth side. The testing demonstrated the effectiveness of this application, which could be applied to columns or beams with deficient shear strength in situations where site conditions prevent access to one side of the member. Please refer to Part 1 (STRUCTURE, January 2022) for additional testing information.

Project Background

Seismic Deficiencies The structure has seismic deficiencies typical of a concrete building from the 1960s. The original gravity system has limited ductility capacity to withstand lateral deformation. The interior columns lack closely spaced ties over most of the column height. They are governed by non-ductile shear failure, as assessed

by ASCE 41-17, Seismic Evaluation and Retrofit of Existing Buildings. The seveninch-thick floor slabs have no bottom reinforcement that extends through the columns and thus are susceptible to punching shear failure under lateral seismic displacement of the building.

Exterior columns are captured by deep spandrel beams at all levels, creating a short-column effect.

The University of California, San Francisco’s (UCSF) Mount Zion Housing is a concrete apartment building constructed in 1968, with seven stories above grade plus a basement.

Seismic Evaluation The floor plan above grade is T-shaped Criteria and Methods and comprises approximately 14,000 square feet at each level. Rectangular Figure 11. UCSF Mount Zion Housing building before retrofitting The retrofit design follows the requirecast-in-place concrete columns support Courtesy of Gelfand Partners Architects. ments of the California Building Code post-tensioned concrete floor slabs. Fulland the ASCE 41-17 standard. The retheight concrete structural walls, located at the building’s corners and rofit targets performance objectives of Collapse Prevention under around a central core, serve as the lateral-force-resisting elements. the BSE-C (975-year return period) earthquake level and Life Safety The apartment building was donated to UCSF; the retrofitted build- under the BSE-R (225-year) level. As is typical, the first of these two ing will serve as faculty and staff housing at the Mount Zion campus. objectives governs the retrofit design.

Figure 12. Typical floor plan showing retrofit measures.

12 STRUCTURE magazine

Tipping Structural Engineers is the project’s structural engineer of record (SEOR). Consistent with UCSF seismic policy, they employed a nonlinear response-history analysis (NLRHA) for the seismic evaluation and retrofit design. The analysis model was built using the CSI Perform 3-D software and includes the concrete shear walls, basement walls, floor diaphragms and collector elements, and vertical soil springs at the foundation. The nonlinear actions that are modeled include wall flexure and axial behavior (using vertical fiber elements), existing wall shear behavior, collector yield (elastic perfectly-plastic), and soil springs (tri-linear). Actions intended to remain elastic include new wall shear behavior and diaphragm shear. The analysis was carried out using expected material properties for concrete and reinforcement.

Interior Columns A column tree sub-model was built in Perform 3-D and constrained for lateral displacement to the primary analysis model to determine shear deformation demands for the interior columns. Nonlinear static (pushover) loads were applied to the center of mass at each level to impose the building’s displaced Figure 13. Three-sided FRP column wrap, with FRP through-anchors parallel to the fourth side. shape onto the column tree. The floor slabs and columns were modeled as frame members with moment hinges. to allow for high compression strain often requires a jacket with an Comparing the results of this analysis to a hand calculation for shear elliptical cross-section to provide confinement. The space between demand based on probable slab moment confirmed that the model the column and jacket is filled with grout. However, if the principal provided a conservative demand. The existing columns had only deficiency is shear strength, testing has shown the effectiveness of half of the required shear capacity (based on ASCE 41-17) needed slightly rounding the concrete corners and applying FRP directly to to withstand the expected seismic displacements. the perimeter of the square or rectangular column. The fibers of the FRP (either carbon or glass fibers) are horizontal-only to provide shear strength without directly increasing flexural strength.

Seismic Retrofit Measures

Retrofit measures were applied to the exterior of the building and interior columns to address the seismic deficiencies (Figure 11 and Figure 12).

At the exterior, a concrete exoskeleton was designed to be constructed against the face of the pier-and-spandrel façade. The exoskeleton included four new or thickened planar structural walls, columns constructed against each existing exterior column, and collector beams constructed against the spandrels. The structural walls reduce the story drift demand and improve the building’s deformation profile over its height. The exterior columns provide a backup load path for gravity load at the vulnerable captured columns. The collectors tie the vertical elements to the existing floor diaphragms.

The interior retrofit uses steel brackets attached to the tops of interior columns to support the slab above to mitigate the consequences of punching shear failure under lateral displacement of the building.

Additionally, FRP wrapping is used at interior columns to prevent column shear failure under seismic deformation.

FRP Wrap at Interior Columns In the U.S., seismic evaluation and retrofit practice prior to the late 1990s emphasized adding strength and stiffness to the seismic-forceresisting system of buildings and often did not adequately address the vulnerability of gravity columns.

Current retrofit practice for concrete buildings now focuses on protecting gravity columns from brittle failure, which can occur under the lateral deformation demand imposed by earthquake ground motions.

Wrapping or “jacketing” of concrete columns using fiber-reinforced polymer (FRP) or steel is now commonly a part of concrete building retrofitting. Retrofitting a square or rectangular column section

Three-Sided FRP Wrap At most of the interior columns in the project, FRP wrap could be applied around the entire column perimeter (all four faces). However, existing interferences at nearly 30% of the interior columns prevented use of a full four-sided wrap, driving the need for a three-sided option.

UCSF, the SEOR, and the peer reviewers agreed that the designer of a three-sided FRP wrap would have to provide testing validation of the structural effectiveness of the proposed detail. This was a requirement of the construction documents.

The FRP subcontractor selected Simpson Strong-Tie as the FRP supplier and designer; Simpson was responsible for providing test results to meet the performance requirements.

Simpson proposed a solution using FRP through-anchors in place of the fourth side of wrapping (Figure 13). Such through-anchors are used in other FRP wrapping applications, such as for long narrow columns.

Another FRP supplier and designer, Aegion/Fyfe, has also tested a three-sided FRP wrap using an approach that includes through-anchors.

Column Testing Program The purpose of the test program was to determine the effectiveness of a three-sided FRP wrap in preventing a shear failure. The testing was carried out at Simpson Strong-Tie’s Tyrell Gilb Research Laboratory in Stockton, CA. The test was of a column similar to the interior columns of the buildings that were to receive the proposed three-sided FRP wrap. The control column design, test setup, test procedures, and displacement loading protocols were documented in detail in Part 1 of this series (STRUCTURE, January 2022). continued on next page

FEBRUARY 2022

13

Test Specimens The testing included one control column (Figure 14 ), i.e., a column without retrofitting, and two identical specimens of a column with the three-sided FRP retrofit.

After the specimens were cast and cured, two were placed in an upright position. The three-sided FRP wrap was then installed under conditions that represented the field conditions, including a sheet of oriented strand board that blocked access to the fourth side in a manner similar to the field conditions (Figures 15a and 15b).

The FRP testing and quality control measures required for the field installation were also applied to the laboratory specimens.

Test Setup and Procedures The columns were tested under imposed lateral displacement, with fixed-fixed end conditions. A cyclic-static history of lateral displacement was applied to the specimens. Axial load was not applied.

The control column was tested first. The second test was of one of the retrofitted columns tested perpendicular to the through-anchors.

The third test was of the other retrofitted column, tested parallel to the through-anchors.

Successful Test Definition Before testing, the SEOR and peer reviewer agreed that, for the retrofit to be judged effective, it had to, as a minimum: • Prevent a shear failure of the column that would otherwise occur by increasing shear strength to an extent such that flexural yielding governs the nonlinear behavior, and • Improve the deformation capacity of the column so that it achieves a story drift ratio for the building that meets the Collapse Prevention requirements of the California Building Code for state-owned buildings.

a)

b)

Figure 14. Test column. The central portion represents the column between floor slabs of the building.

The success criteria had to be met for each plan direction of testing.

For this building, the target story drift for the second criterion was 0.037. This was based on the lateral story drift demand from the nonlinear response history analysis, taking the worst story and worst of 11 records for BSE-C ground motions.

c)

d)

Figure 15. a) Installation of three-sided FRP wrap, including drilled holes that receive the FRP through-anchors. The holes are countersunk in a trumpet shape at the column; b) Installation of the FRP through-anchors, showing the splaying of the carbon fibers of the anchors onto the first layer of FRP wrap; c) Retrofitted column tested parallel to through-anchors, shown after reaching a peak lateral story drift ratio of 5.5% to the left followed by 11% to the right; d) Retrofitted column tested perpendicular to throughanchors, shown after reaching a peak lateral story drift ratio of 5.5% to the left followed by 11% to the right.

14 STRUCTURE magazine

Figure 16. Force versus displacement hysteresis output for the retrofitted column tested parallel to the through-anchors.

Figure 17. Force versus displacement hysteresis output for the retrofitted column tested perpendicular to the through-anchors.

Test Results

Findings and Conclusions

The control column failed in the behavior mode predicted: shear failure in diagonal tension in the mid-height region of the column that had a tie spacing of 12.8 inches. The shear demand at failure was 40 kips. The previous article discussed the control column test results and implications in detail. The testing of the retrofitted columns demonstrated the effectiveness of the three-sided FRP wrap. The retrofit met the criteria for success defined prior to the test.

The testing showed the effectiveness of the three-sided FRP wrap configured with through-anchors near the unwrapped side. The retrofit prevented shear failure and substantially increased the column’s ability to undergo large lateral deformations. However, for columns with heavy longitudinal reinforcement and/or high axial load, cover concrete may be prone to spalling on the unwrapped side.■

Prevention of Shear Failure The retrofit prevented the shear failure that occurred in the control column by increasing shear strength and enabling flexural yielding to govern the nonlinear behavior (Figures 15c and 15d ).

Having prevented shear failure, peak load occurred based on ductile flexural behavior, although the column with loading perpendicular to through-anchors exhibited reduced capacity from spalling of the cover concrete.

Peak lateral strength increased from 40 kips for the control (unretrofitted) column to between 52 and 60 kips for the retrofitted columns, for which shear failure did not occur (33% and 54% of additional lateral strength).

Deformation Capacity The retrofitted columns showed the ability to displace beyond a story drift ratio of 0.05 without substantial damage that would create a risk of collapse. Furthermore, the column suffered no strength degradation for loading parallel to through-anchors even up to a story drift ratio of 0.11 (Figure 16 ).

Spalling occurred on the unwrapped face as the cover concrete was subjected to high compression strains for the column with loading perpendicular to through-anchors. The spalling of the cover concrete reduced the effective section depth for flexure. As a result, the lateral strength of the column reduced from its peak strength of 52 kips to a strength of 37 kips, which it maintained without further degradation up to the maximum story drift ratio of 0.11 (Figure 17).

This was a success, given that retrofit was designed for shear strength and not confinement against high compression strain. The momentcurvature analyses show that compression strains would not have been as high for columns with less longitudinal reinforcement, and spalling would have been less likely.

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

Abby Enscoe is an Associate at Tipping Structural Engineers, located in Berkeley, CA (a.enscoe@tippingstructural.com).

Marc Steyer is a Principal at Tipping Structural Engineers, located in Berkeley, CA (m.steyer@tippingstructural.com).

Aniket Borwankar is the Senior Development Manager for Composite Strengthening Systems at Simpson Strong-Tie in Pleasanton, CA (aborwankar@strongtie.com).

Mike Wesson is the Engineering Manager for Tyrell Gilb Research Laboratory at Simpson Strong-Tie in Stockton, CA (mwesson@strongtie.com).

Lawrence Burkett is a Senior Structural Designer at Maffei Structural Engineering, located in San Francisco, CA (lawrence@maffei-structure.com).

Joe Maffei is the Founding Principal of Maffei Structural Engineering, located in San Francisco, CA (joe@maffei-structure.com).

Rachel Cohen is a Structural Engineer and Educator practicing out of Oakland, CA (rae.eng.co@gmail.com).

Project Team Owner: UCSF Structural Engineer: Tipping Structural Engineers Architect: Gelfand Partners Architects Seismic Peer Review and Structural Plan Check: Maffei Structural Engineering, Estructure, and the UCSF Seismic Review Committee, consultants to UCSF Building Permit Services.

Contractor: Webcor Subcontractor for FRP: FD Thomas Structural Specialties Design of FRP and Laboratory Testing: Simpson Strong-Tie Testing Compliance: TEI FEBRUARY 2022

15

structural DESIGN Ground Snow Loads for ASCE 7-22 What Has Changed and Why?

By Marc Maguire, Ph.D., Brennan Bean, Ph.D., James Harris, P.E., Ph.D., NAE, Abbie Liel, Ph.D., P.E., and Scott Russell, S.E., P.E., P.Eng

T

he new ASCE 7-22, Minimum Design Loads for Buildings and Other Structures, ground snow load maps target uniform reliability rather than a uniform hazard (Bean et al., 2021). Previously, the ASCE 7 snow loads used a uniform-hazard 50-year mean recurrence interval (MRI) with a 1.6 load factor. These loads resulted in non-uniform reliability for structures across the country. The site-specific ground snow load determination is no longer tied to a uniform hazard (i.e., X-year recurrence interval) but to the safety or reliability levels stipulated in Chapter 1 of ASCE 7. The new strength level loads are used with a load factor of 1.0, as shown in Equation 1, and were selected to create uniform reliability across the country. These loads are mapped in the new ASCE 7-22 Chapter 7 in the online Hazard Tool and additionally reduced the number of case study regions by 90%. φRn = 1.2Dn + 1.0Sn (Eqn. 1) In Equation 1, φ is the resistance factor; Rn is the nominal resistance; Dn is the nominal dead load; and Sn is the nominal roof snow load.

Snow loading has significant site-to-site variability, both in mean, coefficient of variation, and shape of the statistical distribution of measurements.

The earlier 1.6 safety factor, introduced by Ellingwood et al. (1980), bridged the gap between the largest expected snow load during the service life of the structure (i.e., 50-years) and loads that achieve safety objectives. The factor was derived by considering the average behavior of ground snow load probability distributions at eight locations across the country. This is a rational and computationally feasible approach for estimating design snow loads but averaging necessarily overestimates design snow loads in some regions and underestimates them in others. Fortunately, modern computational power and contemporary weather station data can estimate site-specific, reliability-targeted design snow loads.

Figure 1. Histograms, fitted distributions, and factored loads for select cities.

16 STRUCTURE magazine

Reliability Targeted Loads ASCE 7-22 Chapter 1 expresses safety as a reliability index of 3.0 for ductile limit states in Risk Category II structures, corresponding to an annual probability of failure of 3 × 10-5, which results in an approximate mean failure interval of 30,000 years. Such a low probability of failure is difficult to contextualize for any single building and outside the range of personal experiences. A different perspective on the 30,000-year interval is that, out of perhaps 10,000 communities in the U.S., one would not want to see failures due to snow overload in more than about one of those 10,000 communities every three years.

This low failure rate requires the extrapolation of the statistical distributions describing all ASCE 7 considered hazards (snow, wind, etc.) to events that exceed those observed in the period of record (which is well under 150 years and, in many cases, under 50 years). The resistance factor and the inherent conservatism in design procedures deliver part of the safety. Still, most of the margin must be based on the source with the highest statistical variability, which in this case is the snow load.

Bean et al. (2021) conducted a site-specific reliability analysis to determine ground snow loads, considering both the uncertainty in the snow load and the structural resistance. The targeted resistance member was the flexural yielding (0.9ZxFy) of a steel W-shape using new A992 steel statistical models (Bartlett et al., 2003).

This resistance was combined with a flat roof condition and a nominal dead load of 15 psf to be consistent with common roof construction. The authors also developed a unified depth-to-weight conversion (effective density) that converts ground snow depth to load, based on winter temperature, winter precipitation, and distance to coastlines, allowing data from stations that measure

Figure 2. Illustration of the increase in reliability-targeted ground snow loads (RTL) due to increases in the coefficient of variation (COV) of the ground snow load distribution while the mean remains constant. These increases are associated with a reduction in the mean recurrence interval (MRI) of the nominal ground snow load, as indicated by the increasing area under the orange curve to the right of the dashed line.

Changing Loads

in the upper Midwest or others in Northern New England that regularly receive moderately high snow loads may see loads decrease in ASCE 7-22. This is because there is a smaller relative difference

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depth, but not ground snow load, to be incorporated into the analysis. Site-specific snow load measurements were fit with a three-parameter Generalized Extreme Value distribution. This distribution can model symmetric (e.g., normal) or right-skewed (e.g., lognormal, extreme) data, capturing the climatic variability in snow load patterns across the country. Uncertainties were propagated through the assessment using Monte Carlo simulation, the outcome of which is a load at each site that achieves the targeted low probability of failure. The reliability-targeted loads were assessed at nearly 8,000 snow measurement locations in the U.S.; loads at other locations were determined from a mapping algorithm developed by the authors of Bean et al. (2021).

Calculations were performed for each risk category and associated target reliability index, β, thus eliminating the need for separate snow importance factors. Careful examination of the values from the four maps for each Risk Category shows that the ratio of load between risk categories is not constant; the ratio depends upon the site-specific climate, as represented in historical data for snow accumulation. This fact illustrates why using a single load factor of 1.6 applied to 50-year MRI loads results in inconsistent levels of safety.

More than 40 years of additional snow load data, covering a larger area of the country, made it possible to perform site-specific reliability analyses and significantly reduce Case Study regions in the west. The Case Study regions have been reduced by more than 90% from what they were in ASCE 7-10 and 7-16, prior to the adoption of state-specific studies into the standard.

Figure 1 presents local snow load histograms, and the resulting distribution fits for Minneapolis, Boston, and Baltimore. Figure 1 multiplies the ASCE 7-16 ground snow loads (black dashed lines) by 1.6 to make them directly comparable to the ASCE 7-22 Risk Category II ground snow load loads (red dotted lines). Notice that Boston, Minneapolis, and Baltimore all have very similar maximum measured loads, even though Minneapolis typically receives more snow than Baltimore or Boston. Generally, cities like Minneapolis FEBRUARY 2022

17

Baltimore, Maryland cost comparison for metal building, comparing ASCE 7-16 and the proposed reliability- targeted load.

Metal Building Structure

Weight Impact

Building Cost Impact

Total Cost Impact

70 feet (w) x 125 feet (l) x 15 feet (h) 2:12

+6.5%

+4.5%

+0.8%

200 feet (w) x 550 feet (l) x 18 feet (h) 3:12

+8.7%

+6.4%

+0.9%

between the typical annual maximum load and the extreme annual maximum load.

In contrast, mid-latitude locations (Baltimore, Chicago, Denver, Portland, etc.) needed a larger design load (relative to the 50-year MRI) than other parts of the country to achieve reliability targets.

These places all tend to see intermittent snowmelt throughout the snow season but also have recorded annual peak loads from substantial accumulations of snow in very short periods. In short, these locations typically did not receive large snow accumulations, but they all have the potential for extreme snow accumulations under the right extreme conditions.

The potential for extreme deviation from typical behavior drives the reliability-targeted loads. For example, Minneapolis receives substantially less winter (Dec – Feb) precipitation than Baltimore on average (2.9 vs.

9.6 inches, from PRISM 2015), but Minneapolis almost always receives that precipitation as snow because of consistently colder temperatures. The reliability-targeted loads reflect what might happen if the mid-Atlantic received a series of super-heavy storms with unusually cold temperatures that prevent the snow from melting between storms. The chance that such an event happens in the lifetime of a building is small, but so is the probability of failure that ASCE 7 permits.

Many local jurisdictions such as Portland (SEAO 2013), Denver, and Baltimore (Baltimore County Building Code, 2015) had already superseded ASCE 7-16 loads with requirements that are like those in the new maps. DeBock et al. (2016) demonstrated the non-uniform reliability of the ASCE 7 snow loads in Colorado and introduced the concept of reliability targeted snow loads. Engineers and building officials in Colorado had long recognized the potential for extreme loads exceeding the published ASCE 7 values in Denver and the eastern plains of that state.

Cost Impact While a few locations had snow loads that changed drastically, most locations have an ASCE 7-22 factored flat roof load of 0.95 to 1.15 times the ASCE 7-16 factored flat roof load with an average ratio of 1.05.

One of the more significant changes in design Ground Snow Load values occurred in Baltimore, Maryland. In ASCE 7-16, pg is 25 psf (× 1.6 load factor). The reliability targeted (ASCE 7-22) value of pg for Risk Category II is 60 psf (× 1.0 load factor) for this location.

The change calculated to the roof Total Load (using a uniform roof dead load of 15 psf ) is an increase of 30%. Two buildings were analyzed for these loads (along with changes to the minimum roof snow load) to assess the cost on a snow-sensitive metal building, as shown in the Table. There is a about 1% total cost increase with the new loads vs. ASCE 7-16. However, Baltimore County had already superseded requirements presented in ASCE 7-16 by requiring a minimum roof snow load of 30 psf (or 48 psf factored roof load), exceeding the design roof snow load resulting from the reliability targeted load.

18 STRUCTURE magazine

Mean Recurrence Interval Past ASCE 7 uniform hazard snow loads defined a single recurrence interval for each load. However, the mean recurrence interval for the calculated design snow load in the reliability-targeted scenario is no longer constant because the shape of the snow load distribution changes to reflect site-specific climatic conditions. Figure 2 (page 17) illustrates this variation with vertical dashed lines showing the load that results in a reliability of 3.0 in each scenario. For this illustration only, the reliability analysis assumes the snow load and resistance follow normal probability distributions and ignores all other sources of variability (such as dead load).

In this simplified scenario, the reliability-targeted load increases as the coefficient of variation (COV) of the ground snow load distribution increases. This increase is associated with a reduction in the MRI, as indicated by the increasing area to the right of the black dashed line in the upper tail of the ground snow load (orange) distribution. When the COV of the ground snow load distribution gets larger, the variability of the resistance loses importance, and the MRI gets smaller. In short, if the annual variability of the hazard (i.e., snow load) changes relative to the variability of the resistance, the MRI of the design snow load must also change to maintain a constant probability of failure.

Final Thoughts The changes coming to the ASCE 7-22 ground snow loads dramatically reduce the number of case study regions, incorporate 40 years of additional data, and create a more uniform risk of failure across the U.S. Shifting away from uniform hazard to uniform risk-based snow loads should provide engineers and owners reassurance that their structures are designed for the anticipated level of safety and will reduce the need for local jurisdictions to supersede ASCE 7.

While changes in some locations may appear significant, the anticipated average total cost impact is minimal.■ Full references are included in the online PDF version of the article at STRUCTUREmag.org.

Marc Maguire is an Assistant Professor, Durham School of Architectural Engineering and Construction, University of Nebraska – Lincoln, Omaha, NE. Brennan Bean is an Assistant Professor, Department of Mathematics and Statistics, Utah State University, Logan, UT. James Harris is a Principal, J.R. Harris and Company, Denver, CO. Abbie Liel is a Professor Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, CO. Scott Russell is Manager – Group Technical Services, Nucor Steel, Norfolk, NE.

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19

INFOCUS A Call for More Voices!

By John A. Dal Pino, S.E.

D

uring my two-plus year tenure as the Editorial Board Chair and the several years before that as a Board member, STRUCTURE has received several proposed articles on three topics: 1) the experiences of engineers with many years in practice, 2) the current state of the industry and the inner workings of firms, and 3) the perceived unnecessary expansion of the building code and over-regulation. Of course, the same individuals did not necessarily write these articles. Still, if I were to do some research, I would expect to find that the authors have similar professional experience, job tenure, standing in their firms, firm ownership, and socio-economic situations. Not to generalize, but these engineers are likely to be older and in the middle or later parts of their careers.

We are also starting to see more article ideas from an entirely different engineering demographic, namely younger engineers.

This group is generally not satisfied with the status quo regarding professional relationships with their managers, engagement in the firm, pay and benefits, respect, and racial and gender diversity. The national and regional SE3 groups are outgrowths of this general dissatisfaction and represent the desire to be heard and effect change. In terms of the building code, they seem to embrace it and desire to expand it to address non-traditional issues like climate change. This runs counter to what the older group likely thinks.

I think any outspokenness by engineers (of all stripes) is great for our industry since we are all driven by the same genuine desire to make things better. Collectively, we see issues that need to be improved or solved, and rather than just accepting the status quo, we write and speak out about them. I am glad that STRUCTURE can serve as a platform for this dialogue.

Please excuse my generalizations, as there is some overlap between these groups. Some engineers certainly jump back and forth between groups depending on their personal situation or the specific issue. I find it a bit ironic that the general tone I see from the older engineers is advocacy for more independence, less regulation, and a love of being an engineer for the sake of engineering. In contrast, while unhappy with the status quo, younger engineers are not seeking to leave and start their own companies. Instead, they 20 STRUCTURE magazine

seem to want to work within their existing firms while fundamentally changing their firm’s systems.

This all seems a bit upside down to me, but maybe not. The older group grew up in the 1960s and 1970s, which saw the tail end of the Vietnam war protests and a general rejection of the establishment, i.e., the “man,” however defined, on several fronts. I suspect that the younger group was born in the late 1980s and early to mid-1990s. By then, the government had grown immensely in terms of influence and as a financial backstop, and seemed to be involved in everything. In the private sector, firms were getting bigger and bigger and had global control. There was no “fighting the tide.” The idea of working for a little, five-person company seemed crazy.

We at STRUCTURE are searching for a way to facilitate these contrasting dialogues. We would very much like to hear from you if you have an opinion to express. Many opinions drawn from the entire industry should better frame the issues and present possible solutions that will lead to further discussion.

To get this going, let me suggest some topics we believe are of interest to STRUCTURE’s readers. Then, please write and let us know if you want to author an article on these topics or another topic you feel strongly about.

1) The personal experiences of engineers. There is always a benefit in learning from the experiences of others, just like reading biographies. Some things stick, and some will not, but the engineers we hear from generally have long careers and can inspire others. We wish we would hear from more women because they undoubtedly have valuable experiences and perspectives to share.

Also, do not shy away from writing about technical issues or your projects.

Think of it as an easy way to build your personal brand or to advance within your firm by showcasing your work and your firm’s expertise.

2) The industry’s current state, the firm’s inner workings, professional relationships with managers, engagement in the firm, pay and benefits, respect, and racial and gender diversity in

the workplace. Just because it has been done before does not mean it is the best or only way. There is often a valid reason that should be understood before moving in another direction.

The industry developed in response to the world it was working within.

When the world changes, the best firms change accordingly, particularly if they want to retain staff.

3) The expansion of the building code and over-regulation. The objection to code expansion is likely a push against what is perceived as an undemocratic process. When the code was smaller and engineers were closer to the writing process, I suspect they perceived some influence over the process. Today, codes are written nationally, and the influence of any individual engineer is greatly diminished. This process riles the group from the 60s and 70s, and their stance is a general rejection of the establishment. But what about the viewpoint of younger engineers?

The easiest way to start the process is to submit a one- or two-paragraph abstract on STRUCTURE’s digital Author Intent form – an easy process. Visit STRUCTUREmag.org on the For Authors page. We hope to hear from you soon!■ John A. Dal Pino is a Principal with FTF Engineering located in San Francisco, California. He serves as the Chair of the STRUCTURE Editorial Board. (jdalpino@ftfengineering.com)

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structural COMPONENTS Tackling the 3-Sided Box Diaphragm: One Engineer’s Perspective

By Jim Lintz, P.E., S.E., LEED AP BD+C

M

any engineers consider rectangular structures with light gauge metal deck diaphragms unstable if they are laterally supported on only three sides. Given the standard assumption that light gauge metal deck diaphragms are completely flexible, this type of structure, often referred to as a 3-sided box, would be unstable. While this assumption is often useful for diaphragm design, it is not strictly true.

Light gauge metal deck diaphragms have stiffness, and 3-sided box structures are stable when designed properly. A design method for this type of diaphragm was introduced in the Steel Deck Institute’s Diaphragm Design Manual (DDM) 2nd Edition in 1995. Since then, many single-story structures have been designed using this method, demonstrating its validity.

Additional information can be found in the current DDM 4th Edition in Section 10, Example 7.

It is not uncommon for tilt-up and precast warehouses in low seismic regions (SDC A & B) to be designed with a rectangular diaphragm laterally supported on three sides when an expansion is added to an existing building or when an expansion joint is required due to the building length.

The following explanation and design example focuses on wind loads on a rectangular building with shear walls on three sides and no lateral force resisting system (LFRS) on the fourth. The fourth side is assumed covered, with no wind pressure acting on it.

Figure 1. 3-sided box diaphragm with a) traditional unit shear diagram and b) alternate unit shear diagram with diagonal tension/compression struts.

Windward/Leeward Shear Loads For lateral loads in the north/south direction (Figure 1), parallel to only one shear wall, the shear and moment in the roof can be calculated as if the roof were a fixed-free beam, fixed at the shear wall end and free at the opposite end. The shear wall parallel to the load resists the shear in the north/south direction, while the shear walls perpendicular to the load act as flanges to resist the moment. The LFRS’s perpendicular-to-the-wind load must form a couple to resist the moment to keep the structure in equilibrium and resist twisting and structural collapse. In addition, these shear walls must transmit the lateral load from the roof diaphragm to the foundation to complete the load path and stabilize the structure.

Inherent in this design approach is that the roof behaves as a rigid diaphragm. ASCE 7-16 Section 26.2 permits untopped steel decks to be idealized as rigid for wind design if the span-to-depth ratio is not greater than 2. Yet, Section 12.3 only allows concretefilled metal deck to be idealized as rigid for seismic design, forcing semi-rigid analysis of the deck. However, relative stiffnesses of the diaphragm and vertical lateral force resisting systems do not

22 STRUCTURE magazine

affect the total load distribution to any of the vertical LFRS. With restraints on only three sides, the only way for the system to maintain equilibrium is for the loads to be distributed as if it were a standard rigid diaphragm.

The shear diagram produced by this loading in the north/south direction is intuitive based on standard beam theory. Figure 2 shows the unit shear diagram for the loads given in the figure. The total load that must be resisted by the shear walls perpendicular-to-thewind load, to maintain equilibrium and resist the torsion on the structure, can be calculated by ensuring the sum of the moments on the structure equals zero. This can be done easily if the point about which the moments are calculated is chosen as corner A-1 or G-1.

The total load P in shear walls A and G can be calculated by dividing the moment at A-1 or G-1 by the depth of the roof. Figure 2 shows the calculation of this force where the load, P, at lines A and G must be in opposite directions to maintain equilibrium.

For the load, P, to accumulate in shear walls A and G, the load must be transferred from the diaphragm into the shear walls. It is often assumed that this is an additional shear load in the diaphragm that needs to be combined with the direct shear parallel with the wind load. However, this is not correct. The shear being

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transferred into the shear walls at lines A and G is the perpendicular component of the direct shear and is not additive.

To better understand this, consider the shear on a small square section of the roof diaphragm, as shown in Figure 1a.

For equilibrium to be maintained on this roof section, for both translation and rotation, a force couple must exist on both the left and right and top and bottom of the square. In Figure 1a, the component of the shear stress parallel with the load is represented as τy, and the component of the shear stress perpendicular to the load is represented as τx.

It is the τx shear stress that is transferred into the shear walls at A and G. Admittedly, considering small square sections of a diaphragm with stress couples and transforming that into the loads on a large roof is not intuitive. As evidence that the load transferred to shear walls A and G is a component of the direct shear and not additive, consider the following. First, take into account that the area under the shear diagram in Figure 2 equals P. Second, consider that the unit load transferred into shear walls Figure 2. Example 3-sided box structure with 50-foot square bays and windward/leeward loads.

A and G can be calculated by taking the change in moment in the diaphragm between two adjacent points wall; therefore, the total load P = 2Vm/2n = Vm/n, which equals and dividing that by the depth of the building (δM/δx)/d and that the moment at corners A-1 or G-1 divided by the roof depth as this will exactly equal the shear diagram in Figure 2. discussed above. Readers are encouraged to spend 15-20 minutes setting up a similar diaphragm in their preferred structural modeling software with various loading patterns. The results will demonstrate Shear as Tension/Compression Struts the structure’s stability, the shear in the diaphragm, and the load It may also be helpful to consider the shear in the diaphragm from transfer to the shear walls. another perspective. Shear, considered a set of perpendicular tension and compression stresses turned 45 degrees from the applied load, as Sidewall Shear Loads shown in Figure 1b, is equivalent to Figure 1a. Each resists the same amount of shear, and each has equilibrium maintained. There are, While the windward and leeward wind loads being transferred to however, two advantages of viewing the shear as shown in Figure 1b. shear walls A and G are not additive to the direct shear, there is Generally, it provides a clear illustration of why shear cracks in con- often additional shear load in this type of 3-sided box structure that crete form at 45 degrees to the applied load. Specifically, this case provides an easier way to visualize how shear can be transferred into a shear wall perpendicular to the applied load. If the diagonal tension and compression loads are enlarged from the small square of the roof diaphragm into macro-level x-braces throughout the roof, it provides an alternative method for viewing the roof shear, We are currently looking for: as illustrated in Figure 3 (page 24).

By setting up a model of the example building’s roof diaphragm • Structural Engineers with an x-brace in each bay, roller supports around the perimeter • Civil Engineers resisting translation parallel to the shear walls, and a shear load, • BIM Technicians V, at the free end, statics can be used to show how the shear • Construction Managers load is transferred into the shear walls. With n bays vertically • Steel Detailer and m bays horizontally, it also allows a quick calculation for the Please visit klaa.com/open-careers load, P, in shear walls A and G. Since the load in each diagonal for more information and to apply. member is V/(n√2), the horizontal component is V/2n. There G O L D E N | L O V E L A N D | C A R B O N D A L E | B U F FA L O are 2m diagonal members framing into each east/west shear

FEBRUARY 2022

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does need to be considered. When calculating the Main Wind Force Resisting System forces in the diaphragm of a traditional 4-sided structure, the sidewall wind forces often cancel each other out since they are equal in magnitude but act in opposite directions. However, for the 3-sided box shown in this example with no wall at line 8, there is no opposing sidewall wind force to counteract the sidewall wind at line 1. This sidewall wind pressure produces a shear diagram like a simply supported beam between the two parallel shear walls, as shown in Figure 4.

Combining Shear Loads The sidewall wind shear must be added to the windward and leeward wall wind shear to calculate the total shear load in the diaphragm at any location. At Line A, the combination of the shear loads is additive, while at line G, the shear loads are in opposing directions. The shear diagrams on small squares of deck shown in Figure 5 can help visualize the shear direction at various locations. The maximum shear occurs at corner A-1 and decreases when moving away from the corner in each direction. This combined shear load is checked against the diaphragm shear capacity to determine Figure 3. Tension/Compression strut diaphragm model. the adequacy of the design.

The wind may blow in any direction, so while corner A-1 may with this in mind. On large diaphragms, it is common to vary have the maximum shear one moment, corner G-1 may have the the deck gauge and connection patterns across the roof as the maximum shear the next. The diaphragm should be designed shear forces change.

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The sidewall wind pressure creates bending moment in the roof. This moment can be calculated by assuming the roof as a simply supported beam between shear walls. At the free end of the structure, this moment is generally designed to be resisted only by the members along line 8. The sidewall pressure-producing suction on the wall creates a compression chord force at line 8, which can be calculated as shown in Figure 4.

This force will typically either be resisted by the top chords of the joists along line 8 or by a continuous perimeter angle. If resisted by joist top chords, a tie plate or tie angles must be added between joists to transfer load from one joist to the next.

The tension force created by the moment in the diaphragm at line 1 will not build up in the perimeter angle along the wall as the compression force does in the perimeter angle/ joist top chords at line 8. At line 1, the chord force is transferred into the wall panels at each connection. Similarly, the chord force along lines A and G from the windward/leeward loads will

not build up in the perimeter angle along those lines but will be transferred to the shear walls with each connection.

Design Considerations While the ANSI/AWC wood code (Special Design Provisions for Wind and Seismic, SDPWS) places dimensional limits and L/W ratio limits on diaphragms of open-front structures, there are no such dimensional or L/W ratio code requirements on light gauge steel roof deck diaphragms. As a practical matter, it is generally advisable to limit the unit shear in the deck to that which 20-gauge deck can resist. Experience has shown that adding a line of braces or Figure 4. Example 3-sided box structure with sidewall wind loads. moment frames near the open end of the structure is generally less expensive than leaving that end the deflection between any two points can be calculated by the followx2 V without an LFRS when 18-gauge deck is required due to the cost of ing integration: ∫ x1 bG' dx, where V is the shear, b is the depth of the the heavier deck and additional deck connections. diaphragm, and G´ is the diaphragm shear stiffness. For a uniformly To ensure that all lateral deflection requirements are met, the deflec- loaded cantilevered diaphragm with a uniform depth and uniform tion of the diaphragm must also be checked. As noted in the DDM stiffness, the maximum deflection at the free end can be calculated qL2 4th Edition, a diaphragm with the dimensions shown in this example as ∆= 2bG' , where q is the uniform load and L is the length of the is controlled by shear deflection; therefore, flexural deflection is diaphragm. For this example, where the load is not uniform across ignored. Assuming uniform stress over the depth of the diaphragm, the entire length of the diaphragm, the deflection at the free end can be found by dividing the area under the unit shear curve shown in Figure 2 by G´. The equation for G´ can be found in the DDM 4th Edition and varies based on the deck type and gage, fastener type, and connection pattern.

Rectangular light gauge metal roof deck diaphragms with LFRS on three sides have been successfully designed and constructed using the design method described above for decades.

Efficient and safe designs can be implemented with a proper understanding of the shear in the roof diaphragm and how it is transferred to the shear walls.

Understanding this design approach provides engineers with another arrow in their quiver of design techniques and provides another way to meet client needs.■

Figure 5. Example 3-sided box structure total unit shear loads in diaphragm.

Jim Lintz is a Structural Engineer at LJB Inc. in Dayton, OH (jlintz@ljbinc.com).

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Restoring a Century-Old Building The NH Collection New York Madison Avenue Hotel Renovation

By Lauren Feinstein, P.E., Jordan Weinstein, P.E., and Kevin Poulin, Ph.D., P.E.

T

he newly renovated NH Collection New York Madison Avenue Hotel, located at 22 East 38th Street in Midtown Manhattan, is housed in the former Renaissance Revival-style Fraternities Club Building constructed in 1923. The seventeenstory building is approximately 125 feet wide by 100 feet long by 220 feet tall and has multiple setback roofs. The NH Hotel Group, SA (NH) hired Simpson Gumpertz & Heger, Inc. (SGH) as the Engineer of Record, and HLW International, LLP (HLW) as the Architect of Record, to modernize and transform the hotel. The work included creating two double-height lobbies, updating the facilities, and modernizing the guest rooms.

These upgrades required strengthening and repairing the existing structure. NH engaged Newgrange Construction (Newgrange) as the contractor for the renovation.

Without the benefit of design drawings from the original construction, SGH investigated and documented the existing building structure – a transitional masonry superstructure (a historic hybrid system comprised of a steel skeleton embedded in the exterior brick masonry walls) with draped-mesh, cinderconcrete floor slabs. Since the hotel remained open during the investigation phase, surveying the existing conditions could not disturb the guests or affect the architectural finishes. As a first step, Langan Engineering, Environmental, Surveying, Landscape Architecture, and Geology, DPC (Langan) was retained to survey the columns and perimeter masonry walls, and SGH performed localized ground-penetrating-radar (GPR) surveys to locate existing steel beams. SGH also used a comparative-loading analysis, where possible, to eliminate the need for additional probes and subsequent analysis of the structure. SGH strategically documented probes at a limited number of back-of-house locations to obtain representative steel column sizes and beam sizes for analysis. They targeted areas critical to the design and planned to verify the remaining structure during construction.

As the contractor removed interior finishes during construction, SGH discovered the undocumented structural history of the building and encountered a series of unforeseen conditions.

For example, despite assumptions about uniform floor plans, the beam layouts varied substantially throughout the building, leading the project team to address an unexpected scope of strengthening and repair, in addition to several redesigns, during construction. continued on page 28

26 STRUCTURE magazine

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Figure 1. Draped-mesh cinder-concrete slab strengthening details at floor penetrations

The original structural scope of work for the transformation consisted of redirecting lateral loads around two new double-height lobbies, designing an interior steel-framed glass vestibule, and adding rooftop dunnage to support a new generator, screen wall, and mechanical units.

The scope of work also consisted of framing slotted slab openings at new MEP penetrations at all floors and infilling existing double-height spaces with new steel framing and concrete-on-metal-deck slabs to increase the usable floor space.

SGH considered several issues for new openings in the drapedmesh cinder-concrete floor slab. The existing floor system typically consisted of a 3-inch-thick non-structural cinder fill with a 1-inch cement topping slab over a 4-inch-thick structural cinder-concrete slab with draped, steel-wire mesh that spanned one-way between encased steel beams. The draped steel mesh supports the slabs via catenary action. The 1968 New York City Building Code (NYCBC) governs modifications to archaic structural systems used on this project and specifically addresses openings and penetrations in this type of floor system. According to the 1968 NYCBC, a single opening greater than 18 inches or multiple openings totaling over 18 inches in any 10-foot width or span of slab must be framed. As the creation of new floor openings comprised a large portion of the structural

scope, SGH proposed two options (topside and underside) for slab strengthening (Figure 1). Both details satisfied the architect’s strict head-height criteria and avoided increasing the floor load enough to trigger additional beam strengthening. The cinder fill was removed locally and replaced with a thin slab on deck that spanned to shallow HSS beams for the topside repair option. This system bypassed the existing slab and was supported entirely on the existing steel floor framing. For the underside repair option, the existing slab spanned as plain concrete between flat channels tight to the underside of the slab spaced at 2 feet on-center.

Additionally, the 1968 NYCBC quantifies that when the mesh is continuous over steel beams at both ends (i.e., middle spans), the slab has approximately 40% more capacity than an equally reinforced end span. For new openings exceeding the above threshold for opening size, SGH reanalyzed cinder-concrete slabs in bays adjacent to the bay of the opening, as end spans due to the discontinuity in the mesh, and designed strengthening, as required. For strengthening adjacent bays, SGH designed a flat channel at the midspan of the bay. While SGH initially intended to use these details for new floor openings, the details were also applicable when the contractor discovered numerous, closely spaced large floor openings from prior renovations that required

Figure 2a. Section loss at corroded cellar steel beams

Figure 2b. Cellar slab deterioration

28 STRUCTURE magazine

Figure 3. Cellar column temporary bracing.

the strengthening plates to avoid temporary shoring of the columns; the contractor locally cut the flanges of the existing beams at the connections to the columns and installed slotted strengthening plates around the beam webs. The contractor demolished the slab and floor beams only after installing all column strengthening.

In addition to strengthening the columns, SGH redirected the lateral loads around the new large openings in the second-floor diaphragm. The original lateral-load-resisting system consisted of semi-rigid moment connections and masonry shear walls. SGH designed WTs to be installed below the existing slabs to redirect the lateral loads around the openings and back to a continuous line of columns. At the exterior of the building, where the demolition for the double-height space would disconnect columns from the diaphragm, SGH retrofitted the existing connections to create a new moment frame to resist the redirected lateral loads. At this moment frame, SGH designed single-sided channel strengthening for the existing double-height columns as the exterior faces of the columns were not accessible. The demolished second-floor framing had supported a large, cantilevered marquee over the entryway.

SGH strengthened the existing spandrel supporting the marquee with a welded plate between the existing spandrel flanges, creating a closed section that could resist torsion loads from the cantilevered marquee. As this beam was also part of the new moment frame, SGH designed its connections to the columns to resist the torsion loads, in addition to transferring the moments.

This renovation preserved the beauty of the Fraternities Club Building’s early years, boasting its restored ornamental brick-andsandstone facade, Romanesque arches, red tile roofs, and copper-clad octagonal cupolas. At the completion of the structural upgrades and interior overhaul, The NH Collection New York Madison Avenue Hotel opened to guests in May 2021. The upscale hotel features 288 new guest rooms, an onsite gym, a bar, and two spacious lobbies.■

support. This unforeseen condition accounted for approximately half of the floor strengthening.

Another unforeseen condition, concealed by ceiling finishes, was extensive corrosion and deterioration in the cellar floor. Maintenance staff informed the project team that steam pipes leaked for decades in the cellar and subcellar. This triggered a thorough investigation of the cellar structure to assess its condition. As shown in Figure 2a, some of the steel beams had nearly complete section loss. As shown in Figure 2b, all that remained of the wire mesh in deteriorated sections of the slab was rust staining on the concrete. After the contractor installed temporary shoring, SGH visually surveyed the underside of the cellar slab, looking for spalled or cracked concrete, and requested that the contractor sound these areas to locate additional delamination within the slab. SGH also identified steel beams with cracked concrete encasements that indicated expansive pressure from corrosion. SGH directed the contractor to remove the encasements and grind the corrosion All authors are with Simpson Gumpertz & Heger, Inc. to bare metal at these beams. SGH then measured and documented Lauren Feinstein is a Consulting Engineer (lpfeinstein@sgh.com). the remaining cross-sections and determined whether strengthening was necessary. This survey led to the removal and replacement of Jordan Weinstein is a Consulting Engineer (jcweinstein@sgh.com). approximately half of the cellar slab and framing, in addition to some Kevin Poulin is a Principal (kcpoulin@sgh.com). local strengthening of corroded steel columns.

Seven perimeter columns relied on the deteriorated portion of the cellar floor structure for bracing.

For temporary bracing prior to slab removal, SGH designed a new grid of horizontal, inclined, and skewed steel braces, just above the existing cellar floor (Figure 3), which connected the affected columns to the remaining floor diaphragm, avoiding obstacles such as slab steps and floor openings. In addition, SGH designed replacement beams and slabs and worked closely with the contractor to sequence piecewise beam and slab demolition and replacement to ensure that the existing columns were continually braced during reconstruction.

As part of the architectural transformation, HLW designed two large floor openings, the larger of which was 55 feet long by 35 feet wide in the second-floor slab, to create a spacious double-height lobby for the hotel (Figure 4 ). Several floor beams needed to be removed to create this space, resulting in seven columns becoming unbraced in one or both directions. SGH designed plate reinforcing for these columns to strengthen them for their newly doubled unbraced lengths. SGH sequenced the installation of Figure 4. New spacious double-height lobby.

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Nashville International Airport’s Inspirational Terminal Lobby and IAF Expansion Project Rise to Meet Soaring Passenger Demands

By Terry Palmer, P.E., Tom Meyer, P.E., S.E., and Kevin Kuntz, P.E., S.E. Concept rendering of the curvilinear roof and entry at Nashville International Airport . Courtesy of Corgan.

S

o much of Nashville, Tennessee, is defined by the inspired and creative music of the famed Music City. So when the airlines approached Nashville International Airport® (or BNA, as it is also known) with requests to expand their facilities to meet ever-increasing numbers of domestic and international passengers, it was clear the project would need to embody its city’s energy and character.

It was a tall order. Overall, the BNA Vision includes a new Terminal Lobby and International Arrivals Facility (IAF), parking garages, an airport hotel, expanded Concourse D, and a central utility plant.

The plans also called for more gates, ticket counters, and spaces for dining and shopping experiences to better serve passengers and airport personnel. At its centerpiece: a curvilinear “airwave” roof canopy that would inspire and awe.

Moreover, the airport had to remain open, safe, and inviting to passengers throughout construction; the project scope and schedule were

The BNA Vision with the iconic airwave roof canopy. Courtesy of Corgan.

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daunting; and the BNA Vision, when completed, would so thoroughly revamp the airport that visitors would be hard-pressed to find any signs of the old terminal.

Yet competition soared when the Metropolitan Nashville Airport Authority (MNAA) shared early renderings and videos of the BNA Terminal Lobby and IAF Expansion project’s design. It seemed that nearly everyone in the airport design and construction industry wanted to design and build the new terminal.

A Design that Captures the Spirit of Flight With multiple projects planned at once, MNAA needed a unifying experience so each project would work well with the overall campus texture and architecture. As such, Joel Efrussy and Ross Payton, Senior Associate and Principal, respectively, at Corgan led a series of stakeholder workshops and community outreach meetings, which revealed wonderful insights regarding the features and design themes that should be captured and reflected – including Cumberland Forest’s natural beauty, Music City’s unique culture, and Nashville’s diverse and vibrant people and neighborhoods.

Many of these elements are expressed in the Terminal Lobby’s iconic and conspicuous airwave roof canopy, which draws in cascading natural light and visually connects the pedestrian bridge entry to the airfield.

“Corgan brought a number of canopy styles and options, but we felt the curvilinear form best represented the spirit of flight,” explained Robert Ramsey, BNA’s Senior Vice President and Chief Operating Officer.

The roof canopy’s initial structural design was well-thoughtout and included in the bridging documents offered to prospective design/build teams. The initial structural concept developed by Rao Patri, Principal at the structural

design firm of Logan Patri in Nashville, was supported on several existing building columns to keep the roof lightweight. The concept also employed a new, braced-frame, lateral design in lieu of the existing moment-frame structure of the original terminal.

To transform the airwave canopy roof concept renderings into an actual structural design, Magnusson Klemencic Associates (MKA) collaborated with Hensel Phelps and Fentress Architects during the RFQ phase to generate creative ideas that would add value, reduce costs, and shorten construction schedules. Early images of the new BNA Terminal Lobby motivated the design/build team to figure out how they could make an already excellent design concept even better.

• As a bonus, the existing roof could temporarily serve as a work platform for crews to install ducts and pipes within the new roof without requiring construction lifts, resulting in faster and safer installation.

• Finally, raising the roof enhanced views and allowed natural light to cascade into the terminal, reminiscent of sunshine filtering through the Cumberland Forest trees.

Amazing Views and Spatial Openness Meeting with Neal Terrell and Scott Shelby, Project Development Director and Operations Manager, respectively, at Hensel Phelps to prepare to respond to the Request For Qualifications (RFQ), Terry Palmer, Senior Principal at MKA, floated the idea of raising the new canopy roof a few feet from where the concept roof was envisioned. Upon sketching The Terminal Lobby’s iconic airwave roof canopy draws in cascading natural light and openness. Courtesy of Corgan. this idea, the team discovered some amazing design revelations: “Most importantly, modifying the airwave canopy structural concept • The existing terminal roof could stay in place until the new allowed for a much more elegant design that truly resulted in a form roof was built and weather tight, thus avoiding huge issues that was inspired and driven by function,” added Corey Ochsner, an with weather protection within the existing terminal throughAssociate Principal and Project Manager at Fentress Architects. “By out construction. removing almost all of the interior columns, we were able to capture • By providing a clear-span roof structure over the existing teramazing views and spatial openness.” minal and roadway, the project team could avoid strengthening the roadway and terminal structure entirely, thereby saving The “Bones” of Innovative Design time and money. More importantly, this would allow the airport to remain open and operational throughout construction.

To better understand what gives the airwave roof canopy its singular • The project team could eliminate all the proposed braced and iconic form, it is important to look at the structure’s “bones” – frames and interior columns within the existing terminal particularly its trusses and column placements. building, thereby achieving tremendous openness and unobAs the project team studied the roof geometry, it was evident that structed views. the conceptual design form was created with true radial arcs and

The new terminal roof was lifted a few feet to span over the existing occupied terminal and roadway – offering tremendous structural, architectural, and construction benefits.

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At Nashville International Airport, the new roof’s unique, mildly rippled form is created with just two curvilinear spine trusses. Courtesy of Aerial Innovations Southeast.

tangents to ease fabrication. As the structural design advanced, a decision was made to minimize, as much as possible, the number of curved members to reduce fabrication costs.

Amazingly, the roof ’s unique, mildly rippled form is created with just two curvilinear “spine trusses” that carry the entire roof. In a true collaboration, MKA, Fentress Architects, Corgan, and MNAA worked together to slightly adjust the roof ’s profile to accommodate deeper spine trusses and sharpen the roof ’s edges to achieve a knifeedge, wing-tip aesthetic.

To achieve schedule goals and cost savings, the project team utilized straight, secondary trusses to frame between the two spine trusses, resulting in a roof profile that softly curves. Further, the roof trusses were preassembled at the fabrication plant, shipped to the site, and erected with minimal field assembly.

The project team avoided weaving braced frames down and through the Terminal Building, with visual openness being so vital.

Instead, the canopy roof and IAF addition are interconnected as a single, homogeneous, 660-foot-long structure with a maximum span of 180 feet and stabilized by a moment-frame lateral system.

By avoiding joints in the roof, stability during steel erection was far easier to achieve. Moreover, the potential for leaky building joints was eliminated.

Meanwhile, column placement was very surgical. The canopy roof ’s support columns and moment frames, located on the landside over the roadway and new Parking Plaza, had to be installed several months ahead of the canopy roof itself. Working closely with Brad Miller, Callie Hepler, and Don Shoop at Hensel Phelps, the team identified two “sweet spots” where cruciform columns could be placed directly through the roof of the existing terminal without hitting the huge glass façade, and with just enough room to continue operating the rental car counters in the lower level.

Similarly, MKA and Hensel Phelps collaborated with Messer Construction’s Parking Plaza team to identify where columns could be placed within their new elevator towers just days before foundations were built. To accommodate this column placement, two plate girders spanning 100 feet were utilized to maintain the continuity of the spine trusses. The plate girders were built using Grade 65 plates and were tapered – ten feet, three inches deep at the peak, and eight feet deep at the ends – to mimic the profile of the straight secondary trusses.

32 STRUCTURE magazine

The canopy roof itself was erected in three discrete phases, which were closely coordinated with the fabricator and the erector so that roofing, skylights, clerestory glazing, piping, and other elements could be installed early to shorten the overall construction schedule. In addition, as mentioned, the subcontractors took full advantage of the existing roof, using it as a work platform to install ducts and pipes without erecting scaffolding or employing lifts.

BNA: A Great Story of Collaboration What began as a need to expand and improve the Nashville International Airport evolved into a tremendous story of many dedicated people working closely together and united by the desire to contribute and make the BNA Vision even better than hoped.

In a sense, what began as a passion for building something extraordinary in Nashville has turned into a great story of collaboration. Like a co-written song, the talents and abilities of many people contributed to a vision that will resonate for many years to come. Most visitors will not know the “hows and the whys” of the airport’s design and construction, but they will definitely know they are in Nashville, Tennessee!■ All authors are with Magnusson Klemencic Associates.

Terry Palmer is a Senior Principal (tpalmer@mka.com).

Tom Meyer is a Principal (tmeyer@mka.com).

Kevin Kuntz is a Senior Design Engineer (kkuntz@mka.com).

Project Team Master Architect – BNA Vision: Corgan Lead Structural Design: Magnusson Klemencic Associates Design/Build Lead: Hensel Phelps Architect of Record: Fentress Architect Associate Architect: TM Partners Substructure Design: Logan Patri Mechanical/Electrical Design: IC Thomasson Associates

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Figure 1. Rendering. Courtesy of Ravatt Albrecht & Associates.

Seismic Retrofit of the Atascadero Printery

By Jillian van Enckevort, S.E.

O

n December 22nd, 2003, the San Simeon Earthquake shook the of wood rafters spaced at 2 feet on-center, trussed with 1x bottom central California coast damaging two historic unreinforced chords and webs with the hips supported on a steel truss at each end. masonry buildings in downtown Atascadero. One of those buildings The single-story portions have hipped roofs framed with long-span was The Printery, constructed in 1915 to house E.G. Lewis’ (the steel trusses and wood rafters between. Currently, the buildings are Founder of the Colony of Atascadero) printing operation. Since the topped with metal roofing over straight sheathing, though there is a earthquake, the building has been abandoned and has suffered from reference to a mission tile roof in the as-built drawings.

In 2000, the building was nominated for the National Register of vandalism over the years. In 2016, FTF Engineering was introduced to a non-profit looking to purchase the building to transform it into Historic Places and was officially added in 2004. The prominent a community arts building (Figure 1). The non-profit, operating historical features of the building include the Italian Renaissance terra as The Printery Foundation, was able to secure ownership of the building from a public auction in 2017.

The building was designed by Bliss and Faville Architects out of San Francisco and Engineer M.C. Couchot out of Oakland. The main portion of the building is a rectangular-shaped 2-story structure with a partial basement. At the rear is an original single-story room that housed the printing press and another single-story annex, constructed later, used as a gymnasium for a boy’s home tenant (Figure 2). The foundation, basement, and second floor are of concrete construction with ½-inch-square smooth bar reinforcing with unreinforced brick masonry bearing walls. The first story walls are 4-wytheswide, and the second story walls are 3-wythes.

Roof framing in the two-story section consists Figure 2. Existing floor plan.

34 STRUCTURE magazine

cotta ornamentation on the exterior of the building and the original Ralph Holmes tapestry murals and marble tile in the central lobby. The building required a seismic retrofit and, because of the historical status of the building, FTF Engineering and Ravatt Albrecht & Associates were able to use the 2019 California Historic Building Code (CHBC) to guide the analysis and retrofit. The retrofit focused on the four items of typical unreinforced masonry buildings known to result in the most damage and loss of life in major earthquakes: in-plane shear capacity of the brick, the out-ofplane bending capacity of the brick, anchorage of the walls to the roof/ floor, and weak flexible horizontal diaphragms. The CHBC references Appendix Chapter A1 of the 2013 California Existing Building Code (CEBC). For historic structures, the ideal retrofit minimizes the intervention, maximizes the strength of the existing elements, and adds new elements in specific locations where necessary.

Simpson engineering staff. Simpson then determines the thickness of the cement plaster and the number of layers of carbon fiber grid reinforcement needed to make up for the deficiency. They also provide supplemental calculations and drawings to accompany the SEOR’s design package. For The Printery, the code requires a minimum seismic design lateral force of V = 0.75SDSW/R, with an R = 1.5 for ordinary plain masonry shear walls and a cap of 0.4W for Risk Category III and IV buildings per exception 4 of section 8-706.1 (2019 CHBC). With an SDS of 0.777, the cap of 0.4W controlled the retrofit base shear value.

For example, the wall piers at either end of the building were analyzed using equations Va = vmA/1.5 (equation A1-20; 2013 CEBC) for shear capacity and Vr = 0.9PDD/H (equation A1-21; 2013 CEBC) for rocking shear capacity.

The wall piers were found to be controlled by rocking shear with a capacity of 7,315 pounds at the second floor and 10,523 pounds at the first floor. The demand on In-Plane Strengthening these panels were 14,665 pounds Initial retrofit concepts provided and 25,157 pounds, respectively, by the consultants hired by the city requiring a 1-inch-thick layer of after the earthquake included the cement plaster and two layers of addition of narrow shotcrete panels Figure 3. Cracking at the southwest corner. reinforcement in the second story at the corners of the building to serve as new lateral load resisting and 1.5 inches of cement plaster and four layers of reinforcement elements replacing the strength of the original walls. During the in the first story. The existing URM walls had sufficient capacity schematic design phase, FTF explored this option but determined to resist the seismic demand in other locations with longer shear that collecting the load and dragging it out to the corners of the panels. Still, a single layer of fabric reinforcement with 1 inch of building would be problematic with the current wood-framed roof cement plaster was specified to help control the cracking of the to 3-wythe brick wall connection. Shotcrete panels would also add brick during a seismic event. a substantial amount of mass to the structure, impede on the interior square footage, and concentrate the lateral overturning forces Out-of-Plane Strengthening resulting in the need to strengthen the existing foundation. With an existing brick shear strength of 100 psi, based on testing and Supplemental bracing must be provided where the wall height-toequation A1-4 (2013 CEBC), the team instead decided to explore thickness ratios do not meet the requirements of Table A1-B (2013 the option of strengthening the masonry exterior walls to improve CECB). The ratios vary based on whether the building has qualifying their in-plane shear strength. The best option was to team up with cross-walls (partitions) or not. The Printery contains large open-span Simpson Strong-Tie to utilize their Fabric Reinforced Cementitious spaces where cross-walls do not exist; therefore, the limits are 13 for Matrix (FRCM, ESR-3506). The FRCM product was chosen over the one-story building, 15 for the first story of the two-story buildFRP because it is better suited to the unevenness of the brick sur- ing, and 9 for the second story. Analysis revealed that the upper story face and results in a finished plaster surface that matches what was required bracing. HSS steel strong backs tied into the floor and roof historically in the interior of portions of the structure. The product diaphragms with epoxy anchor connections to the brick wall were will be installed on the interior faces of the walls to avoid disrup- used to brace the wall out-of-plane. The design lateral force is per tion of the historic exterior. Heli-Ties will be drilled through the A110.1 and meets the spacing/deflection requirements of section interior wythe of brick at a depth to reach the exterior wythe and a A113.5.2 (2013 CEBC). spacing of three feet horizontally and four feet vertically to tie the wythes together. The ties will be staggered vertically to support a Out-of-Plane Wall Anchorage diamond-shaped section of the brick wall.

The design process for the use of the FRCM product includes One of the most noticeable deficiencies of the existing building after determining the demand and the capacity of the individual unre- the earthquake was the inadequacy of the anchorage between the inforced masonry wall piers and providing this information to the walls and the roof. The walls showed signs of pulling away from the FEBRUARY 2022

35

Figure 4. Wall-to-roof strengthening detail.

roof in numerous locations and have since been shored to prevent further movement and possible collapse. In the years since the San Simeon earthquake, the crack at the southeast corner of the building appeared to be worsening (Figure 3, page 35 ). In addition to adding shoring, a mason was hired to reconstruct the interior wythes of brick to restore the wall’s structural integrity.

The typical roof-to-wall framing condition in the building has the roof rafters sitting on top of the URM walls with a 2x6 wood plate at the top of the wall. In the one-story portion of the building, the rafters are supported by trusses made up of steel angles spaced approximately 12 feet on-center. The trusses are set into and bear directly on the brick walls with short anchor bolts with limited lateral strength. Beneath each of the trusses is a section of brick wall bulging outward, signifying that the walls were pulling away from the roof during the earthquake. As part of the seismic retrofit, HSS posts have been added underneath any large point loads to help prevent roof collapse if the brick is damaged. The upper roof of the two-story section consists of rafters spaced at 2 feet on-center, trussed with 1x webs, and a built-up 1x bottom chord spliced at approximate third points.

Per the CEBC, it is recommended that the walls be anchored to the roof system at a spacing no greater than six feet on-center, and the preferred method of attachment is to use a through bolt with an anchor plate on the exterior face of the wall. However, since this method would have caused a great deal of disruption to the terra cotta detail on the exterior of the historic building, it was not an option. Instead, a system consisting of epoxy anchors at a spacing of two to three feet on-center was used to reduce the design force per anchor while still significantly improving the expected performance in a seismic event. In most cases, a steel angle was designed to span continuously underneath the existing rafters/trusses with steel angle side plates extending up to tie into the rafters and transfer the outof-plane forces into the diaphragm. These details aim to simplify construction and reduce field welding wherever possible (Figure 4 ).

36 STRUCTURE magazine

Diaphragm Strengthening The diaphragm is the “glue” that holds all of the other pieces of the retrofit together; it transfers the loads from the out-of-plane anchors and strong backs out to the newly strengthened shear walls. Per the CEBC Table A1-D, Strength of Existing Building Materials, the existing straight sheathed diaphragms are adequate for 300 plf but, with the heavy weight of the building, it was determined that the minimum diaphragm force was 323 plf and a maximum of 686 plf. Since the metal roofs are at the point of needing replacement, ½-inch plywood overlay will be used to strengthen the diaphragms with nail spacing and patterns varying based on the required capacities. The plywood will be applied directly over the 1¼-inch sheathing, and 16-penny nails have been specified to achieve the required penetration. As an alternative, FTF provided an option for a diaphragm screw since the age of the wood framing can make it difficult for nails to penetrate the hardened wood.

Summary While the deficiencies of most URM buildings are similar, the details of the retrofits are all very unique to the individual buildings. The Atascadero Printery building had its own set of challenges, including the irregular geometry, the historic nature of the project, and working with a nonprofit tasked with raising money to save the building. The first two items were solved with engineering and teaming with companies like Simpson Strong-Tie. The last led FTF to use creativity to design connections that do not require skilled tradespeople, permitting as much volunteer labor as possible to achieve the retrofit and stay involved in the organization’s fund-raising efforts. If you are interested in supporting the project and saving a piece of history, please see https://atascaderoprintery.org.■ Jillian van Enckevort is a Principal of FTF Engineering and manages the San Luis Obispo office (jvane@ftfengineering.com).

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Resilient

MILITARY HOUSING

By Anantha Chittur, P.E., S.E., and Frank K. Humay, Ph.D., S.E.

T

Figure 1. Building configurations.

his Bachelor Enlisted Quarters (BEQ) project is a $60 million multi-story housing complex for enlisted military personnel. In addition to sleeping rooms, the facility includes an entry vestibule, quarterdeck, multi-purpose rooms, classrooms, laundry areas, and other support spaces. The T-shaped building results from multiple studies that considered site orientation and access, parking layout, view planes for future expansion, and more (Figure 1).

The project was a competitive design-build procurement based on a Request For Proposal (RFP). The general contractor, design-build subcontractors, and A-E Team were involved in intensive pre-design sessions to explore various design solutions and associated costs.

Pricing documents with sufficient detail to budget the project were developed as a basis for the final bid.

Building Description The building measures 380 feet in the north-south direction with an 80-foot extension in the east-west direction. The six-story building is 71 feet tall with an exterior consisting of face brick with reinforced concrete masonry backing and a hipped standing seam roof supported on cold-formed steel trusses bearing on the concrete roof slab (Figure 2).

Level 1 consists of a spacious centrally located quarterdeck, multipurpose rooms, and other administrative spaces.

A total of 308 dormitory units are distributed along double-loaded corridors, maximizing daylight and views from the living quarters.

Each unit has operable windows, which are punched openings in the exterior wall. Vertical circulation is provided through two centrally located passenger elevators, a freight elevator, and exit stairs located at the ends of the corridors.

The design is in accordance with the 2015 International Building Code (IBC) and other applicable Department of Defense (DoD) Unified Facilities Criteria (UFC). This Risk Category II building is designed for a wind speed of 115 mph and a seismic design category B.

Primary Structural Systems

Figure 2. Building rendering.

38 STRUCTURE magazine

Three different structural systems were evaluated: steel framing with composite deck, precast concrete with hollow-core planks, and a castin-place concrete structure. The steel solution increased building floor-to-floor heights, added fireproofing requirements, increased MEP distribution costs, and introduced uncertainties in steel costs due to new tariffs. In addition, the precast system proved difficult to meet the progressive collapse requirements. The cast-in-place system was selected because it provided the greatest flexibility, lowered the building height, reduced MEP distribution costs, and insulated the schedule from supply chain delays.

The floor and roof framing consists of conventionally reinforced two-way cast-in-place concrete

Figure 3. Rammed aggregate pier foundation with hybrid slab-on-ground.

slabs that are 8.5 inches in thickness with spans in the range of 18 to 27 feet. The exterior columns are inset from the perimeter, creating cantilever end spans. Interior columns consist of wall columns in the demising walls and rectangular columns. Column location and configuration was chosen to create a feeling of openness in the living quarters.

The lateral force-resisting system consists of ordinary reinforced concrete masonry shear walls with a modular layout on the perimeter and supplemental interior ordinary reinforced concrete and masonry shear walls. In addition to providing a highly redundant lateral force-resisting system, multiple hazards are addressed by the exterior masonry walls. DoD UFC criteria mandated blast-resistant construction. Progressive collapse avoidance was also considered in the design due to the building’s height. Rigid diaphragms are used to transfer lateral loads.

Foundation System This project is constructed on a site left vacant by the demolition of an existing building. As a result, the site contained uncontrolled fill materials and building demolition debris (e.g., pieces of concrete, brick, wood, etc.). It was not suitable to support a six-story building without remediation. The RFP recommended compaction grouting to improve the site. After a careful evaluation by the design-build team, it was determined that compaction grouting was not viable, and several alternatives were assessed. Another alternative involved the removal of 6 feet of existing soil and replacement with structural fill, but this option was rejected due to significant added cost and impacts to the project schedule.

The final solution supported the structure on shallow concrete foundations bearing on vibratory stone columns (also known as rammed aggregate piers). In addition to its suitability for this site, the strength and stiffness of the piers can be reliably quantified using modulus load tests. The stone columns are typically 2 feet in diameter and extend 8 to 17 feet below the uncontrolled fill material.

Hybrid Slab-on-Ground The slab-on-ground also involved an unconventional approach. A hybrid approach with selective soil replacement was used as an alternative to a slab either fully supported on stone columns or structural fill (Figure 3). Compacted structural fill is placed over the footprint of the foundations (supported on stone columns) to act as “rigid” supports, reducing the slab clear span. The slabs have isolation joints around the columns and were analyzed as conventionally reinforced two-way slabs supported on springs representing different moduli of subgrade reaction (150 pci at the foundation and 10 pci for the native soil). Studies were performed to ensure that the maximum live load settlement is less than ¼ inch. The hybrid approach resulted in a thinner slab (7.5 inches) with reduced reinforcement compared to a conventional structural slab-on-ground.

Building Resiliency and Hardening Considerations DoD buildings are designed with enhanced life safety provisions per the Unified Facilities Criteria requirements, available on the Whole Building Design Guide website (www.wbdg.org). This facility was designed for blast resistance and progressive collapse avoidance (i.e., disproportionate collapse). Design requirements for blast resistance are project-specific and vary for each project.

Facilities with at least three inhabited stories are designed to prevent disproportionate collapse caused by a loss of structural support in accordance with UFC 4-023-03 Design of Buildings to Avoid Progressive Collapse. Multiple design methods are prescribed in that document, and the applicability is determined based on the risk category of the facility. Due to the framing and geometry of this project, the alternate path method was used, which requires the design to consider the removal of individual vertical load-supporting elements around the perimeter of the building and provide a viable alternate load path. continued on next page

FEBRUARY 2022

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Figure 4. Masonry construction using MULE.

Several structural schemes were evaluated, including perimeter columns with uniform spandrel beams on each floor or a single transfer girder at the roof. The layout of the rooms of the building constrained the location and spacing of the columns. Due to the modular design of the building, removing an exterior column effectively doubled the span length of the beams. Removing outside corner columns created a two-way cantilevered beam condition. Due to architectural constraints, the beam sizes required to support these design options were too large and costly. The final solution developed by the structural design team addressed architectural functionality, minimized material costs, and helped shorten the construction schedule by insetting the perimeter columns and relying on Vierendeel truss action of the masonry walls.

Multi-Functional Masonry Wall The building’s exterior is constructed with reinforced concrete masonry that also provides resistance to lateral wind and seismic forces. In the original design, the masonry wall also supported the edge of the concrete slabs. However, this required that the masonry wall and concrete

Figure 5. Progressive collapse avoidance analysis.

40 STRUCTURE magazine

frame be constructed concurrently, which would have increased construction time and cost. Concrete columns, inset from the exterior walls, were added so that the construction of the concrete frame was independent of the masonry. Material Unit Lift Enhancers (MULEs), along with jumbo masonry blocks, 8-inch by 32-inch and 74 pounds in weight, were used to increase productivity and safety (Figure 4).

The exterior masonry wall enhances the redundancy of vertical load paths in the building. If a portion of the exterior masonry wall is removed, the loads from the unsupported walls above are redistributed to adjacent wall segments through Vierendeel truss action. Reinforced masonry bond beams at headers, sills, and floor levels and the window jambs are designed for the resultant axial, flexure, and shear forces.

Smooth dowels at masonry control joints permit horizontal movement due to temperature and shrinkage while allowing vertical shear load transfer (Figure 5).

The masonry walls are built outboard of the concrete slabs but connected to them to transfer in-plane and out-of-plane loads. The connections allow the masonry to deflect vertically without imposing additional loads on the cantilever slab when a section of the wall is removed. Detailed deflection analyses were performed to verify the slab deflection at the cantilevered slab edges, and, where necessary, the formwork was cambered. The two-way slabs performed well with minimal unanticipated deflections.

Conclusions The structural design for the project overcame several challenges through close collaboration between the various design team members and the client. The team continually improved the design when opportunities arose, and constant effective communication and timely decision-making were critical in the fast-track delivery of this building, a functional, efficient, and resilient home for our military for many decades to come.■ Anantha Chittur is Senior Associate at BASE and is based in its Chicago office (achittur@baseengr.com).

Frank K. Humay is Vice President at BASE and is based in its Honolulu office (fkh@baseengr.com).

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historic STRUCTURES Tacoma Narrows Bridge Failure 1940 Galloping Gertie, Part 1

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

T

he collapse of the Tacoma Narrows Bridge is one of the most well-known of all bridge failures as its collapse was caught on film. The film was and still is viewed in many introductory physics classes.

Planning for the bridge started in 1929, just before the Great Depression, when proponents of the bridge, including the Tacoma Chamber of Commerce, pushed for its construction. It was to cross an arm of Puget Sound, the Tacoma Narrows Strait in the State of Washington connecting Tacoma with Gig Harbor.

In 1929, D. B. Steinman proposed a suspension bridge followed in 1931 by a cantilever bridge by the Tacoma City Engineer. In 1932, a local engineer formed the Tacoma Bridge Company that hoped to raise at least $3.5 million to construct a Narrows suspension bridge.

The Corps of Engineers approved his plan, but the Reconstruction Finance Administration (RFA) would later propose a cantilever bridge as preferable. In the late 1930s, the Washington State Legislature created the Washington Toll Bridge Authority to finance and operate bridges Tacoma Narrows Bridge on opening day. in the State, including the Tacoma Narrows.

It should be understood that, by this time, New York City had built the Brooklyn Bridge in 1883, the Washington Bridge, when he virtually eliminated all deck trussing, Williamsburg Bridge in 1903, the Manhattan Bridge in 1909, and relying on the weight of the cable only for roadway stiffness. The the George Washington Bridge in 1931. Also, for the record, the Williamsburg Bridge by Leffert L. Buck, with its 40-foot-deep stiffenWheeling Bridge by Charles Ellet, Jr. (1849), the Lewiston-Queenston ing truss, was the last major bridge to be built using the elastic method Bridge (1851) by Edward W. Serrell, and the Niagara Clifton Bridge first proposed by William M. Rankine. Finally, on the Golden Gate (1899) by Leffert L. Buck had all been destroyed by the action of Bridge, Joseph B. Strauss and Charles Ellis, with Leon Moisseiff, used winds. These failures were well documented in the literature of the day. a stiffening truss of a far lesser depth than the shorter Williamsburg Significant changes in suspension Bridge. Moisseiff also applied it to the bridge design occurred between 1903 Bronx Whitestone Bridge across the and 1909, incorporating the Austrian East River in New York City, built Josef Melan's deflection theory. between 1936 and 1939.

Melan’s main breakthrough was the The first design for the Tacoma understanding that the deck and the Narrows Bridge by the Washington Moisseiff believed that its cables act together to carry vertical Toll Bridge Authority was by Clark loading and that, as the span length Eldridge, an engineer for the state. It stiffness depended on structural increased with greater dead loads, the was a conventional suspension bridge weight and proportion and that need for a stiffening truss was reduced with a 25-foot-deep stiffening truss on greatly. Leon Moisseiff, then working either side of the roadway to resist the he “could reduce truss depth for the City of New York, translated strong Narrows winds. He estimated Melan’s work and applied it to the the cost of the bridge at $11,000,000. without adversely affecting design of the Manhattan Bridge with Its main span was 2,600 feet with side its 1,590-foot span and 25-foot-deep spans of 1,300 feet and a sag of 260 bridge stiffness.” stiffening truss. Next, O. H. Amman feet. The Director of the Washington applied it to the design of the George State Highway Department took the

42 STRUCTURE magazine

design to the Public Works Administration (PWA) and, by most built to this time. Moisseiff’s design was by far the longest, thinaccounts, they determined the $11 million was excessive and urged nest, and narrowest suspension bridge ever built and contributed the state to contact Leon Moisseiff and the firm of Moran & Proctor to its sleek appearance. The 2,800-foot suspended span made it for a cheaper design, which they did. J. J. Madigan, the head of the the third-longest suspension bridge in the world after the George PWA, later wrote, “In no instance did this Administration nominate Washington and the Golden Gate Bridge, both of which Moisseiff or express any preference for any particular individual, group, or was involved in as a consultant. firm.” Eldridge later wrote, Moisseiff and Moran and Proctor “assoMoisseiff believed that its stiffness depended on structural weight and ciated themselves to secure the commission to design the Tacoma proportion and that he “could reduce truss depth without adversely bridge. They went to Washington, called on the Public Works affecting bridge stiffness.” He carried this theory further by postulatAdministration, and informed them that they could design a structure ing that the use of shallower stiffening trusses naturally led to plate here that could be built for not more than $7,000,000. So, when Mr. girders, which he believed offered “many structural advantages for Murrow appeared asking for $11,000,000, our estimate, he was told connections and fabrication” and “presented a simple and good $7,000,000 was all they would approve.

They suggested that he confer with Mr. Moisseiff and Moran and Proctor. This he did, ending up employing them to direct a new design.” What really happened is unknown, but Eldridge was likely closer to the truth.

In June 1938, President Roosevelt approved a grant for about $2.8 million and a loan of $3,300,000. After the bids were received, this was increased to a total of $6,400,000. The loan was to be paid back from tolls.

Moisseiff, after reviewing Eldridge’s design, proposed a suspension structure with 1,100-foot side spans, a 2,800-foot main span, and a sag of 232 feet. Its road deck measured 26 feet curb-to-curb.

In addition, it had 5-foot sidewalks, the same as Eldridge. He wrote, “To approach the problem from another angle, the stiffening trusses may prac• Concrete Repair Mortars tically be omitted, and the desired • Corrosion Protection • Construction Grouts rigidity can be obtained by other means, • Waterproofing shortening of side spans and reduction • Sealants and Joint Fillers in sag ratio…” and “…To stiffen the • Coatings and Sealers bridge vertically as well as transversely, • Epoxy Adhesives the main span has been increased to • Decorative Toppings 2,800 feet, and the side spans reduced • Cure and Seals to 1,100 feet.” This resulted in a sag • Densifiers ratio of 1/12.2, flatter than any sus• Structural Strengthening Products pension bridge in the United States.

His towers soared 425 feet above the piers and were battered, 50 feet at their bases tapering to 39 feet at their top. He Your single-source provider for restoration, also made them the same height while strengthening and corrosion protection Eldridge had his at different heights. He designed it with an 8-foot-deep plate MAPEI offers a full range of products for concrete restoration, waterproofing girder serving in place of Eldridge’s and structural strengthening. Globally, MAPEI’s system solutions have been deep trusses, thus saving a great deal utilized for such structures as bridges, highways, parking garages, stadiums of steel. The cables were spaced 39 feet and high-rises. center-to-center. With its narrow width Visit www.mapei.us for details on all MAPEI products. (roadway 26 feet and two sidewalks of 4 feet 9 inches) and span of 2,800 feet, it resulted in a depth to span length ratio of 1:350. Up to this time, the greatest value of this measure was 1:84. The width of the deck-to-span ratio of 1:72 was also the narrowest of any bridge

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43

appearance and [were] easy to maintain.” Finally, he believed “that with reference to its span length, the super-structure design is techcables had the ability to control and supply stiffness to a suspension nically sound. It is probably technically sound notwithstanding its bridge. By flattening the catenary of the cables to a modified parabola, narrowness, but there are several reasons why it would be of material he could increase the rigidity of the bridge’s polygon, again reducing advantage if the bridge could be widened at a reasonable increase in the stiffening girder’s depth.” the cost, and therefore, I recommend that serious consideration be Lacey Murrow had three engineers review Moisseiff’s design, and given to the possible increase in the width of this structure before the they reported, on August 31, 1938, in part, contract is let or work begun.” From these reports, it seems as if both “We have examined the superstructure design as to its general fea- the Board and Condon were giving Moisseiff the benefit of any doubt tures. Time has not permitted the checking of stresses in the cables given his status as a designer of suspension bridges. However, it should and stiffening trusses. In this regard, we have full confidence in Mr. be pointed out that this was the first suspension bridge for which he Moisseiff and consider him to be among was the Chief Structural Engineer. He the highest authorities in suspension was a consultant to the Chief Engineer bridge design. on the Manhattan, George Washington, It might seem to those who are not and Golden Gate, etc. experienced in suspension bridge design The Bridge Authority, with the advice that the proposed 2,800-foot span with a of the Panel and Condon, adopted all of It became a sort distance between stiffening trusses of 39 Moisseiff’s design changes over the objecof thrill ride as motorists feet and a corresponding width of span tion of Eldridge, who believed they were ratio of 72, being without precedent, is buying a bridge on the cheap. He later drove across it to experience somewhat excessive. In our opinion, this wrote, “The men who held the pursefeature of the design should give no constrings were the whip-crackers on the the longitudinal rippling cern. The development of the deflection entire project. We had a tried-and-true theory of suspension bridge design in conventional bridge design. We were told motion of the deck... recent years for both vertical and lateral we couldn’t have the necessary money deflections has proven beyond doubt without using plans furnished by an that the matter of width ratio is limeastern firm of engineers, chosen by the ited not by structural stress but only by money-lenders…But in order to obtain the amount of lateral deflection in the government money, we had to do as we wind, which can be realized without were told.” discomfort or fear to the driver of an automobile over the bridge…

Contractors on the bridge were the Pacific Bridge Company of San In a long narrow bridge, the matter of side deflection thus becomes Francisco, with the Bethlehem Steel Company furnishing and erecta function of not width only but of both width between stiffening ing the steel and spinning the wire cables. The contractors noticed trusses and dead load cable stress, with the dead load cable stress that the span would move considerably in the wind when placing the playing more and more a part as the width and sag ratios increase. deck, but Moisseiff assured them that it was not a problem. David In other words, a suspension bridge with a lesser distance between L. Glenn, the Public Works Administration (PWA) field engineer, stiffening trusses and a low sag ratio may be just as stiff laterally as would not sign off on the acceptance of the bridge due to what he one with a greater width between stiffening trusses and a greater called faults in design, but he was over-ruled, and the PWA and the sag ratio. In the proposed design, the dead load stress in the cables Washington State Toll Bridge approved of the bridge. It opened with is approximately 6/7 of the total stress. This large dead load stress is a grand celebration on July 4, 1940, and everyone associated with the accomplished by decreasing the sag ratio of the cable. A sag ratio of project praised its slender, gossamer-like structure. l/l2 has been used, while the general practice in wider bridges is to The bridge, however, continued to exhibit vertical movements, use between 1/7 and 1/10… galloping, and it became a sort of thrill ride as motorists drove The same reasoning applies to stiffening truss depth. Here again, across it to experience the longitudinal rippling motion of the deck, the low sag ratio of the cables with the greater total dead load stress with many noting that oncoming automobiles appeared to vanish makes the cable more difficult to distort and, in consequence, reduces behind hills as the waves moved through the structure. As a result, the bending moments and shears in the stiffening truss. This feature it received the nickname “Galloping Gertie,” which did not please of stiffening truss design is strikingly demonstrated in the George the Washington Toll Bridge Authority who worried about its moveWashington Bridge, where no stiffening truss is used. It may be said ments. They requested Frederick B. Farquharson of the University that the necessity of a stiffening truss and its depth and moments of of Washington engineering department to prepare a study of vertical inertia depend largely upon the ratio of dead to live load and cable oscillations in the bridge’s deck, hoping to discover a means to reduce sag. The greater the ratio of dead to live becomes, and the lower the the movements. He experimented with a 54-foot-long model of the sag ratio, the less the necessity of the stiffening truss… bridge in a wind tunnel to determine its behavior under various wind We believe that the present span could be materially increased if speeds and directions. In May 1940, they installed hydraulic buffers it were necessary, keeping the same width without any detrimental between the deck and the towers to dampen longitudinal motion to effect. In consequence, we have no concern as to the general features show they were doing something. This was based upon work being of the proposed design of the superstructure.” done on the Bronx Whitestone Bridge in New York City that had T. L. Condon also reviewed the plans and wrote, “With regard to 11-foot-deep plate girders for deck stiffening. Diagonal cable ties conthe super-structure, I do not pretend to be qualified to analyze and necting the suspension cables to the stiffening girders were also placed check the design of the long-span suspension bridge…I, therefore, on the main span with the hope of also minimizing the movements. feel that, with the exception of the unusual narrowness of this bridge But despite these measures, the structure continued to undulate in a

44 STRUCTURE magazine

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vertical motion with moderate amplitudes under both modest and the outer surfaces of the girders and had ordered the steel to impleheavy winds. The WTBA contacted Moisseiff, who told them he ment the recommendation in early November. Unfortunately, they had experienced similar, but smaller, movements on his Deer Island never had a chance to modify the girders as the bridge collapsed on Bridge (with D. B. Steinman) in Maine and his Bronx-Whitestone November 7, 1940.

Bridge (with O. H. Ammann) in New York City. Apparently, he had An upcoming issue will include more on the failure and no suggestions on how to minimize the movements. the subsequent investigation.■ After talking to Eldridge, a newspaper article reported, “There is nothing unusual about the antics of the Narrows span, Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having Eldridge states, although those of this bridge are aggravated by its slenrestored many 19 t h Century cast and wrought iron bridges. He is now an der proportions necessitated by shortage of funds with which to build Independent Consulting Engineer (fgriggsjr@twc.com). it. The Narrows span is narrower in proportion to its length than any bridge in the world, and at the same time, the girders, which would be expected to stiffen it, are shallower than those of any similar structure. The Whitestone Bridge, recently completed in New York, has as much bounce as the Narrows bridge, according to reports but, instead of publicizing it, New Yorkers have done everything they could to keep it quiet.

There is nothing dangerous about the STICK TO THE performance, which in no way affects the M O S T I M P O R TA NT strength or safety of the Narrows span, SCHEDULE. Mr. Eldridge states. Aside from affording YO U R S . a basis for tall tales of the span’s cavorting, the bridge’s bouncing is having no real effect whatever. Motion in the span deck is caused by the center span being swung out of line by a puff of air. This draws the tops of the towers together, lifting the two outside spans; as the center span swings back, the shore end spans drop, starting the wave motion, which is further aggravated by swinging of the center span. As the center span is designed to raise and lower 10 feet or more, due to changes in temperature, the four-foot hop of the bounce does not put any strain on it, which the design does not take care of with a large factor of safety.”

After completing preliminary wind tunnel tests, Professor Farquharson suggested several modifications be made to the structure to possibly cure its susceptibility to wind movements. They had already placed tie-down cables in the side-spans, attaching them to concrete anchorages, but they snapped during the first windstorm. He recommended the streamlining of the plate girder’s shape with “a rounded out-rigger type buffer Extra steps. More parts and pieces. Skilled labor issues. They all along the side of the bridge to prevent add up to one thing: less of doing what you really love. But with the wind from hitting the flat side of the bridge full force,” believing, correctly, ClarkDietrich, time and innovation work in your favor. Our framing that its large flat surfaces contributed to and finishing systems speed up and simplify installation. Because the oscillating movements. He also sugyou’ve got better plans waiting. gested drilling a series of holes along the plate girders to let the wind pass through © 2021 ClarkDietrich them. They accepted the recommendation to add the rounded out-riggers to

FEBRUARY 2022

45

business PRACTICES Hiring and Retention Tips for 2022

By Mike “Batman” Cohen

A

s we move into 2022, we all understand that things have changed for everyone, everywhere. And just as our personal and professional lives have changed, so must our approach to hiring and retention.

Authenticity Let’s first define authenticity for the sake of this discussion. Webster’s dictionary defines it as true to one’s own personality, spirit, or character.

What does this have to do with hiring talent in 2022? Everything.

We are living in a world where communication is primarily digital, and the job market is the hottest we have seen in almost 15 years.

The days of talking about the company’s culture, the family-like organization, and cool ping pong tables and foosball are gone. That is not what is essential to most job-seekers today. Over-used terms like good culture or family-like have no meaning in today’s environment. What does ring true? Knowing the people that the candidate will be working with; truly knowing. Not the professional version of someone, but the actual, true-to-form, human behind the job title.

Who you are as a person outside of work is now just as important as who you are in the workspace. The days of “keep your home life at home” are gone. Embrace who you are and what you bring to your organization. Remember, you work at the company, meaning that you make up a piece of the corporate culture. Be yourself. Let the candidate be themselves. And both of you decide whether it makes sense to commit to one another.

Humans vs. Skillsets

Hire humans, not resumes. Discover who they are, not just what they have done.

Self-Complexity Theory The third tip for 2022 revolves around a psychological study called the Self-Complexity Theory. The self-complexity theory says that we all have multiple aspects to our self-representation, or how we view ourselves in our own minds. Those aspects include context-dependent social roles, activities, goals, and relationships.

(Visit https://bit.ly/3G6Pv6U for more information.)

The general idea is that, as technology and social media increase, the world becomes smaller. Not just externally, but internally as well, which means that the areas of our lives that used to be distinctly separate (“work-life at work, home-life at home,” etc.) are now all a part of the same cosmosphere. As we continue to evolve socially and professionally, we must allow people to blend the different aspects of their lives. It is okay to share something difficult you are going through in your personal life with your colleagues. Relating to authenticity (above), we need people to be true to themselves and act with integrity, compassion, and empathy. The only way to do that is to realize we are the same person at work, with our families, and with our friends. No need to be different people.

Next, it is important to define to what degree you hire humans, skillsets, or a combination of the two. Many of us are used to hiring people because of their skills. It makes sense on the surface, right?

Yes, it does, but only on the surface.

Find ways to connect with your candidates on a human or personal level – of course, they need to know how to do the job, but what do you think has a more significant impact on your organization: someone who needs a little training on the skills involved in the job, or someone who Working From Home and Work Schedule does not fit in or feel at home? You can usually train people to do a job; you cannot train people to feel like part of a team, as in belonging and While exclusive from one another, the following two tips do go connecting to the group. A great attitude that hand-in-hand. They are working from home promotes synergy in a team always has more and what a work schedule looks like. Let’s Building Work Relationships: impact than someone who has good skills. A touch on the big one first–working from https://bit.ly/3eW7ocu positive attitude, team player, and generally home. Between the pandemic affecting How to Build Relationships: enjoyable person can make everyone more people’s ability to work in an office and https://indeedhi.re/338onWu productive and efficient. A skillful employee the new year (2022), it is time to let go of will add their skills to the production. the mantra that we have to be face-to-face.

Good Relationships: Ask yourself, “out of 100%, how important If you think that being face-to-face helps https://bit.ly/3pWYtOp is the candidate’s skill set versus their ability build camaraderie and relationships with Cultivate Better Work Relationships: to join as an integral part of your culture?” If each other, there is a lot of information https://bit.ly/3G4pQfd someone adding to your culture is important out there to the contrary (see the sidebar Effective Work Relationships: at all to you or the organization, then answer for a few resources). https://bit.ly/3JKJlvn a follow-up question, “what are you doing in If you think that face-to-face is better your interview process to assess this?” Hire for collaboration, again – nope. Here are Good Coworker Relationships: humans, not resumes. Discover who they are, two quick tests to drive this home for your https://tek.io/3eXVEX9 not just what they have done. organization.

46 STRUCTURE magazine

First Test – the Data

Ready for this? Crazy idea here…. Ask your employees what they want.

They are the ones you worry about collaborating with, so ask them.

Easy tip: Unless you have a job that requires you to be on-site for something (medical research, chemical engineering, construction, etc.), let people work from home if they want to.

As far as the work schedule goes – keep it simple. The idea of 40 hours a week is dead. It is an irrelevant number. Why not 42 hours?

Why not 37 hours? Because 8 hours is ⅓ of the 24 hours in a day and we should be working ⅓ of the workweek? And why the 9:00 to 5:00 routine? This is where we are heading (some readers will not like this but take a deep breath because you do not have a choice) – how many hours people work and the specific hours when they are working do NOT matter.

People have a job. They have things to do. They have to get their job done. And they have to attend meetings when it is necessary.

Everything else is moot. Expectations: #1 – be in the meetings you need to attend, and #2 – get your job done when it is due.

Let people work when they need/want to, and you will get more and higher quality work from all of your colleagues.

Metrics

Mike “Batman” Cohen is the Founder of Wayne Technologies and Paired Talent, recruiting solutions providers. Mike is a nationally recognized key-note speaker, contributing author, webinar host, and industry thought leader.

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Join the Unengineering Firm GI EN UN

Metrics is a big one, so pay attention. As leaders, it is vitally important to keep track of Key Performance Indicators (KPIs) to understand the pulse of the state of your business/team. It is also essential to hold your team accountable to particular metrics as leaders. However, these things should not be the same. While KPIs are a metric, they are treated differently for this conversation. Just as we still call a square a square, not a rectangle (yes, they are the same, but we still refer to them differently), there is a reason for that.

KPIs – get the pulse of where things are at with your business.

Are you on target to hit your goals? What numbers are not on target? What part of the pipeline is struggling? All super important, but none tells the story of WHY these particular indicators are happening. It is like an EKG monitor; the monitor rapidly speeding up tells you there is a problem, but not what is wrong.

Super important to monitor the EKG, but when you see it start to increase rapidly, it does not tell you what you have to do to fix it; it just tells you where you need to look. That is also true for KPIs. Metrics are the controllable, tactical facets of the jobs you can hold your colleagues/employees to.

A quick tip: most metrics have the word “versus” or a percentage sign in them. Metrics should talk about the efficacy/efficiency of the work being done, not the quantity. Great example: The author is a recruiter. Many companies look at a recruiter’s performance and

hold them to “metrics” like Messages Sent, Candidate Submissions, or Interviews Set Up. Seems pretty reasonable on the surface, but those are KPIs, not metrics. How do we know? Because if Recruiter A sent 200 messages this week and Recruiter B sent 50 messages this week – which is better? Naturally, you would want to say Recruiter A, right? But what if Recruiter A had a 10% response rate, and Recruiter B had a 50% response rate? (20 responses versus 25 responses, respectively). Who is doing better? Recruiter B would be, in this example, because they received more responses with fewer messages (more output with less input).

If that is too confusing or in the weeds, look at it this way: KPIs are used to see how much is being done and if little is being done to hit targets. Metrics are used to see why those numbers are not being hit and if they can be optimized. KPIs tell you where to look. Metrics tell you the story.

If you hold people accountable to KPIs, they will work hard enough to hit the numbers, but never harder because there is no reason to.

Take the idea of someone being paid hourly. What is their motivation if they can do a 40-hour job in 20 hours? If they do it in 20 hours, they get paid half as much! So they want to take up the time and do the minimum required of them because there is no other incentive.

If you hold people accountable to metrics, their goal becomes to work as smart as possible to reduce the amount of work they have to do to generate the output they need to get. Once they optimize the efficiency, incentivizing them to “work harder” becomes straightforward.

Hopefully, this helps give some perspective on where professional industries worldwide are heading as we progress technologically and socially together into the future.■

AN

Second Test – The People

Ask your employees what they want. They are the ones you worry about collaborating with, so ask them.

WH AT ’S

How much productivity did you lose between 2020 and 2021 as it relates to collaboration?

There are only 3 answers: 1) Based on “X” data, we lost “Y” productivity.

2) We did not lose any productivity based on “X” data (either remained flat or increased productivity).

3) Or, probably for many companies/readers: We have no data, but we have always worked face-to-face, so we should keep doing that because we know it works. Not to be “that guy,” but with that logic, we would still be looking for ways to make horses faster. You ride your horse. I will drive my car.

Let’s see who gets there first.

FEBRUARY 2022

47

legal PERSPECTIVES Contracts 101

By Gail S. Kelley, P.E., Esq.

W

hile previous articles in STRUCTURE have looked at specific contract provisions – for example, the Waiver of Consequential Damages in the November 2021 issue – this article discusses contracts in general.

Rights and Obligations What is a contract? While the answer seems obvious, having a specific definition in mind is helpful when reviewing contracts. A good definition is: “A contract is a statement of the parties’ rights and obligations.” Rights and obligations are typically framed as promises and are often reciprocal. For example, the Owner’s obligation to pay the Engineer creates a reciprocal right for the Engineer to be paid.

In a professional services contract, there are two main promises – a service provider such as the Engineer promises to provide the services, and the Owner promises to pay for the services.

There will be several other promises, however.

These typically include promises concerning the quality of the services, the timing of the services, the timing of the payment, and the Engineer’s obligation to comply with applicable laws. The word promise is seldom if ever used, however. Instead, promises are generally stated with the word shall or must.

Rights can be implied. For example, saying “The Owner shall pay the Engineer within thirty (30) days of receiving an invoice” creates an implied right for the Engineer to be paid within thirty days. Rights can also be explicitly stated, for example: “The Owner shall have the right to audit records for Reimbursable Expenses and any services provided on a time and materials basis.”

Rights are also sometimes established using will or may. Although there is some disagreement about the meaning of these words, will and may are typically used to provide information or create a right without implying any obligation. For example, “The Owner may hire additional consultants for the Project.”

Contract Versus Agreement Legally, a contract is the same as an agreement.

They both refer to a statement of the parties’ rights and obligations. While contract might seem to imply something more definite than agreement, the words are interchangeable. In the A/E/C industry, there is a tendency to refer to agreements with design professionals and other consultants as agreements, and 48 STRUCTURE magazine

agreements with the Contractor and other construction professionals as contracts, but the distinction is simply to help keep the various agreements on the project clear. A prime consultant’s agreements with its subconsultants are generally referred to as subcontracts, although they can also be referred to as subconsultancy agreements.

Defined Terms A/E/C contracts typically make liberal use of defined terms. A defined term is simply a capitalized term that replaces a word or group of words. Sometimes contracts have a definitions section, but often terms are just defined the first time they are used by putting them in quotes and parentheses. For example, “This agreement (“Agreement”) is entered into effective the 12th of August, 2021 (the “Effective Date”) between Lakeshore Holdings, Inc. (“Owner”) and Grey Engineers, LLP (“Engineer”).” Any references in the agreement to the capitalized words Agreement or Owner or Engineer or Effective Date will mean these defined terms.

Other terms that are commonly defined are the Standard of Care and the Services.

Recitals and Preambles Contracts sometimes start with a preamble, recitals, or both. A preamble is a paragraph that typically identifies the parties and the project. Recitals are clauses that begin with “Whereas” and generally indicate the parties’ desire to enter into the contract. For example, “Whereas Owner desires to engage a design professional for the work of this contract.”

Often the recitals or preamble will be followed by a statement such as “For good and valuable consideration the parties thus agree…” This is followed by the actual contract terms. There is some disagreement over whether the recitals and preamble are part of the contract, but generally recitals and preambles just provide information about the project without creating any rights or obligations. If a recital contains important information such as a reference to a letter of intent, the agreement may start with: “The recitals above are incorporated into this agreement as if they are specifically stated herein.” This makes it clear that the recitals are part of the contract. However, even without such a statement, it is generally understood that, by signing the agreement, the parties have agreed that the information in the recitals or preamble is correct.

Proposals versus Contracts Often, an Owner or Prime Consultant will ask the Engineer for a proposal to provide certain services. The Engineer generally prepares a proposal and attaches its standard terms and conditions. If the Owner or Prime signs the proposal, it becomes the contract. However, the Owner or Prime may send the Engineer its standard contract form, which usually includes an entire agreement clause. While the wording of this clause can vary, it will typically say something like, “This Contract constitutes the entire agreement between the parties and supersedes and cancels all other prior agreements including, but not limited to, any proposals or oral agreements. Engineer’s proposal is attached for scope and fee only; all other terms are expressly rejected.” This means that provisions such as payment terms, limitation of liability, or waiver of consequential damages in the Engineer’s proposal will not be included in the contract unless they are explicitly stated. If the parties are signing anything other than the Engineer’s proposal, the Engineer should closely review the terms and conditions to ensure that the agreement includes appropriate risk management provisions.

Conclusion Reviewing a lengthy Owner-drafted contract can be a daunting undertaking, and it helps to keep the above basic principles in mind.

If there is something in a contract that you do not understand or does not seem to make sense, you should strike it out or ask for clarification. Often contracts are copied from other projects and have terms that are incorrect or not applicable. Having a knowledgeable A/E/C attorney review the contract with you can be an invaluable part of your risk management practices.

The author thanks Marc Gallagher of Langan Engineering for his assistance in reviewing this article. ■ Gail S. Kelley is licensed attorney in Massachusetts, Maryland and D.C. She is the author of “Construction Law: An Introduction for Engineers, Architects, and Contractors” (gail.kelley.esq@gmail.com).

FEBRUARY 2022

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INSIGHTS VR in Engineering, Architecture, and Construction

By Rune Vandli

O

ver the last few years, Virtual Reality (VR) has moved from a gimmick to a valuable tool in the construction industry.

Studies show that a large and unnecessary part of a construction budget is typically allocated towards fixing mistakes made during planning and execution or correcting bad solutions after work is completed. The root cause of this is a lack of clear communication among stakeholders. The cost of fixing completed work becomes more expensive late in the project. Too often, it results in either high costs or sub-optimal solutions for the end-user. A large percentage of these issues can be prevented with clear and understandable communication early in the project.

Building Information Modelling, BIM, has been increasing communication and collaboration in design for years. The problem is that BIM has been primarily available to design professionals. In fact, the Connected Construction survey by Autodesk showed that leaders and decision-makers in the owner, developer, and end-user roles are least likely to use digital tools and BIM for making decisions.

Virtual Reality VR is a tool available to communicate BIM clearly to everyone involved in the project and make sure they fully understand the challenges the project is facing. This makes it a large part of the solution for communication between BIM experts and inexperienced stakeholders and decision makers. VR is the tool to democratize BIM for everyone, not just design professionals and specialists.

The Value of VR Everyone involved in the project has different potential benefits that can be extracted through VR implementation.

Reduced Decision-Making Time Using VR gives decision-makers a 1:1 scale experience of the project and proposed solution. This gives them the full context and enables them to understand the challenges and proposed solutions with additional clarity.

For example, critical areas may need testing to find the optimal solution; bring the team STRUCTURE magazine

VR is a tool available to communicate BIM clearly to everyone involved in the project...

into those areas virtually to show and discuss multiple solutions.

Data gathered from major nursing-home and hospital projects show that VR achieves a 90% reduced decision-making time.

Test Groups and End-User Satisfaction Building owners and end-users experience increased satisfaction through being able to follow the process earlier, closer, and more frequently in a way they can fully understand.

VR clearly communicates the proposed solutions and requires no prior knowledge of BIM or floor plans to participate.

Bringing advisors and test groups, such as wheelchair users, into the design review makes accessibility an integral part of the design and not an afterthought. Simply complying with accessibility regulations does not necessarily mean the solution is the most practical.

In the healthcare industry, doctors and nurses can review treatment and operation rooms to ensure that the size and equipment layouts are functional and that sightlines from the outside are acceptable.

Life safety engineers and construction safety managers can review a virtual building to plan for scaffolding, tie-offs, and access.

Reduced Travel VR has the benefit of being 100% remote, making it easy for geographically spread teams. During pandemics and lock-downs, VR is a communication enabler. A recent

PricewaterhouseCoopers UK study showed that, on average, 60% of meetings could be digital, reducing the time and cost spent on the road. This time can be used productively and bring added value to the project.

Communication can also be enabled between contractors in the field and the office's design professionals and decision makers. As a result, the carbon footprint is reduced accordingly.

Critical Success Factors As with any new technology or process, a handful of factors determine success or failure. VR is no different. Implementation should include: • Define clear, narrow, and measurable goals for what to achieve by using VR. • Anchor these goals within the leadership of the organization and the project team.

• Establish a process required to reach these goals. VR providers are eager to help you do this, so take advantage.

• Commit the time and resources required to reach the goals.

• Tracking is key! Track the successes closely, evaluate the findings, and adjust along the way.

• Industrialize – Document the successes and processes to repeat them in current and future projects.■ Rune Vandli is a Virtual Reality Specialist at Vrex (rune@vixel.no).

FEBRUARY 2022

49

BRIDGE resource guide Adhesives Technologies Corporation

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EPOTHANE T3 is a low-modulus, epoxy urethane skid-resistant overlay. V65 HI-MOD, V120 LOWMOD, and V200 HI-MOD: a suite of healer/sealers with varying viscosities and moduli to extend the life of decks and roadways. ATC is a Meridian Adhesives Group Company.

ASDIP Structural Software

Phone: 407-284-9202 Email: support@asdipsoft.com Web: www.asdipsoft.com Product: ASDIP RETAIN Description: Advanced software for quick and efficient design of cantilever, restrained, counterfort, and sheet pile retaining walls. See immediate results with calculations and reports of load combinations per the latest IBC/ASCE 7 and AASHTO. Includes 4 intuitive modules to help you design and verify structural members in no time.

Cast Connex

Phone: 888-681-8786 Email: info@castconnex.com Web: www.castconnex.com Product: Standardized Cast Steel Connectors and Custom Cast Steel Connectors Description: The industry leader in the architectural and structural use of cast steel components in the design and construction of building and bridge structures. Our products include pre-engineered connectors that simplify the design and enhance the performance of structures. We also offer design-build services for custom cast steel notes and components.

Phone: 646-732-7774 Email: info@lusas.com Web: www.lusas.com Product: LUSAS Bridge Description: Use to analyze, design, and assess all types of bridge structures and investigate soil/structure interaction effects. Recent releases have extended the engineer’s workflow from analysis into steel and RC frame design and improved prestress, concrete modeling, and vehicle and rail loading capabilities.

Phone: 510-649-2200 Email: sales@csiamerica.com Web: www.csiamerica.com Product: CSiBridge Description: Offers a single user interface to perform modeling, analysis, design, scheduling, load rating, and reporting of bridge structures. The ease with which these tasks can be accomplished makes CSiBridge the most versatile and productive software program available on the market today.

Dlubal Software, Inc.

Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM Description: Capable of linear, non-linear, static, and dynamic analysis, RFEM is complete with moving load generation (AASHTO library), influence lines, cable form-finding, parametric modeling, and multi-material design considerations. This FEA software is seamless in the design and analysis of pedestrian and highway cablestayed, suspension, arch, and beam bridge structures.

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ENERCALC

Phone: 800-424-2252 Email: info@enercalc.com Web: https://enercalc.com Product: ENERCALC Structural Engineering Library (SEL) Description: Major ENERCALC improvements for 2022 include the addition of ENERCALC 3D FEM and RetainPro modules to installed ENERCALC software. New FEM-powered Steel Base Plate and Flitch Plated Wood Beam modules.

No more hand-calculated Z values! Coming soon – ENERCALC for Revit – use the familiar calculation power of ENERCALC within Revit.

New Millennium Building Systems

Phone: 260-969-3500 Email: gerald.arvay@newmill.com Web: www.newmill.com Product: Bridge-Dek® Description: Bridge-Dek is a high-strength, galvanized bridge deck forming system for new construction and rehabilitation.

Trimble

Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Tekla Structures Description: Software for steel, concrete, wood, and composite bridge structures. Automation of fabrication and 4-D product management.

Extensive range of steel profiles, including elliptical and tubular, and individual connection details with welds and bolts. Automate drawings and reports from constructible 3-D models.

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Listings are provided as a courtesy, STRUCTURE is not responsible for errors.

SPOTLIGHT The First Unitarian Society Meeting House Creative Solutions for a National Historic Landmark

N

estled between university housing and hospitals in Madison, WI, is a building that, even among equals, distinguishes itself as a monument to architecture. A National Historic Landmark, the First Unitarian Society Meeting House was designed by Frank Lloyd Wright and completed in 1951. The building’s auditorium is supported by centerhinged wood trusses spanning up to 76 feet near the entrance, down to 12 feet at the building’s iconic prow. Trusses bear on stone piers and walls. Wright restricted himself to using 2×4s and occasionally 2×6s. The contractor later commented that Wright wanted to “build that church with toothpicks,” a statement that would become apparent over the next 60 years.

Within 10 years, the longest spanning truss (“truss J”) had settled noticeably. In 1961, a 1-inch-diameter steel cable was added to tie the bottom ends of truss J together. Though the concept was sound, the cable attached to the side of the truss and the 9-inch eccentricity forced the truss out of plane as it settled further.

Pierce Engineers (PE) studied the auditorium structure, historical documents, and past repairs to recognize the underlying issues.

Nonlinear FE modeling of the entire structure indicated that Wright’s structure was severely under-designed even when compared against decreased and more realistic roof loads. The structure’s stability, though fragile, pointed to the load-sharing ability and redundancy in the structural system. For example, roof sheathing stresses in the FE model suggested their heavy involvement in load-sharing, likely due to construction sequence. Trusses were constructed before the load-bearing stone and were supported by wood shoring until the roof sheathing and stonework were completed. This sequence engaged the purlin/ sheathing along truss top chords, contributing to truss strength and stiffness.

The simplest solution to address truss settlement would have been to add a new steel truss. However, removing a portion of the roof to install a new truss was rejected due to concerns of disrupting the roof sheathing’s contribution to load-carrying capacity.

Removing a portion of the ceiling to raise the truss into place was not an option since the auditorium needed to be functional during repairs. Only a 30- x 48-inch opening in the ceiling was available, and work needed STRUCTURE magazine

Pierce Engineers was an Award Winner for the First Unitarian Society Meeting House project in the 2020 NCSEA Annual Excellence in Structural Engineering Awards Program in the Category – Forensic/Renovation/Retrofit/Rehabilitation Structures under $20M.

to be completed in a dry attic with wood framing and old insulation, so fire concerns limited welding. With these limits, PE proposed assembling a cold-formed steel (CFS) and structural steel hybrid truss that would be assembled in the attic. Members could be passed through the ceiling opening and were light enough to carry with no special equipment.

This new truss (“truss J1”) was placed 4 feet from truss J and spanned roughly 5 feet.

Typical chords were (2)600S350-68 (placed back-to-back) with webs ranging from 400S250-68 to 600S300-97. Typical panel point connections consisted of #12 screws with 10GA gusset plates (¼-inch-thick Gr. 50 steel at chord splices). The client requested that one panel in the truss be left open to walk through, so some truss chords were HSS6x4x¼ due to moments from a missing web diagonal.

It is common to support existing framing with shore posts, install new members, and then release shoring to shift the load onto new framing. In this case, roof sheathing was essentially being used as a compression flange for the trusses. PE had concerns about reversing member/connection loading that had been in a state of fragile equilibrium by ‘jacking up’ the structure. Therefore, PE designed a pretensioning mechanism to transfer the load into truss J1. A 1-inch-diameter threaded rod was installed on the bottom chord at midspan, and

a nut on the rod was tightened with an impact wrench that shortened the bottom chord. This lifted the truss and engaged the roof purlins without the need for jacking. Pretensioning also had the critical benefit of tightening truss connections. By analyzing several upper and lower bounds of stiffness, a pretension force of 18,400 pounds was selected based on the amount of load needed to shift away from truss J while keeping in mind that too much upward movement could damage roofing. FE modeling suggested that this amount of force would result in a maximum net upward movement of 3⁄16 inch at midspan. Though pretension force could be estimated by a “turn-of-thenut” method, movement/pretension needed to be closely monitored during the operation to avoid damaging the structure. Therefore, PE installed two strain gauges on the threaded rod that were monitored during the pretension process. Torquing was terminated at the desired force, and the pretension mechanism was welded in its final position. Upward movement during pretensioning matched calculated values without damaging the existing structure.

The site and logistic constraints and the structural challenges of a landmark structure required unique and creative solutions.

The pretensioned hybrid CFS truss was able to maneuver these constraints while keeping one of Wright’s most famous buildings functional during a major repair.■ FEBRUARY 2022

51

NCSEA

NCSEA News

National Council of Structural Engineers Associations

Congratulations to the 2021 Young Member Scholarship Winners and Young Member Group Finalists Each year, NCSEA awards Young Member scholarships for the NCSEA Structural Engineering Summit. We are pleased to announce the 14 winning young engineers. Their essay responses to the competition question – “What is your opinion about the public’s perception of structural engineers?” – are available at www.ncsea.com/awards.

NCSEA also awards the Young Member Group of the Year award at the Structural Engineering Summit. This award recognizes Young Member Groups that are providing a benefit to their young members, member organizations, and communities. The winning Young Member Group will be announced at the Summit and will receive an additional $2,500 for their Young Member Group to use for future activities.

A round of applause for the finalists for the Young Member Group of the Year: Minnesota Structural Engineers Association, Structural Engineers Association of New York, and Structural Engineers Association of North Carolina.

Visit www.ncsea.com/awards to learn more about the scholarship program and Young Member Group of the Year award.

NCSEA thanks Computers & Structures, Inc (CSI) for their sponsorship of this year’s young member scholarships and travel stipends for representatives from the Young Member Group finalists. Their investment in the future of the engineering profession is much appreciated!

Cesar Castro

Jonathan Tavarez

Yue (Jessica) Chen

Tyler Hessler

Kyle Kucharski

Vincent Wenzel

Nisarg Mehta

Saura Jost

Chase Carpenter Young

Brian Richerson

John Morganstern

Neda Winograd

Lisa Hartley

Dorian Krausz

Call for Abstracts for the NEXT Structural Engineering Summit NCSEA is seeking abstracts for the 2022 Structural Engineering Summit, scheduled for November 2-4 in Chicago, Illinois. Sessions will be 45-60 minutes total and should deliver pertinent and useful information that is specific to the practicing structural engineer, in both technical and non-technical tracks. Potential submission topics include: • • • •

Best-design practices New codes and standards Recent project case studies Advanced analysis techniques

• • • •

Management and business practices Diversity and inclusion Resilience Sustainability

For more information and to submit your abstract, visit https://bit.ly/2022SummitAbstracts.

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

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News from the National Council of Structural Engineers Associations

Structural Engineering Summit Trade Show THE Place to Meet the Best Exhibitors in the Industry The NCSEA Structural Engineering Summit is in New York City, February 14-17, and online January 31-February 24. The Summit Trade Show (in both in-person and online formats) is THE place to network with knowledgeable product experts, engage with helpful industry resources, and discuss the latest software innovations!

NCSEA would like to recognize and thank exhibitors (in-person and virtual, as of 1/14/22) for supporting the NCSEA Structural Engineering Summit and serving as valued partners to the structural engineering community.

American Institute of Steel Construction (AISC) American Society of Civil Engineers (ASCE) American Welding Society (AWS) Atlas Tube Blind Bolt Cast Connex Chicago Clamp Concrete Reinforcing Steel Institute (CRSI) CoreBrace DBM Vircon DEWALT Dlubal Software DuraFuse Frames Engineers Alliance for the Arts Euclid Chemical Fabreeka Headed Reinforcement Corporation (HRC) IDEA StatiCa International Code Council (ICC) IronOrbit Keller

Lindapter LNA Lynch Mykins Master Builders Solutions MiTek New Millennium Nucor Peikko Post-Tensioning Institute (PTI) Qnect RISA Rothoblaas Simpson Strong-Tie SkyCiv SlipNOT Steel Deck Institute (SDI) Steel Joist Institute (SJI) Steel Tube Institute (STI) Taylor Devices Trimble

NCSEA Webinars February 8, 2022

THANK YOU TO OUR SPONSORS

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

021 IBC Significant Structural Changes – Part 1: Loads and Special Inspections

February 10, 2022 Seismic Connections Day 6: Concrete: Seismic Design of Special Shear Walls – Major Changes in ACI 318-19 February 22, 2022 Structural Engineering Considerations for Mid-Rise, Light Wood Frame Buildings March 10, 2022

2021 IBC Significant Structural Changes – Part 2: Foundations and Materials

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!

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

FEBRUARY 2022

53

SEI Update Learning / Networking

SEI Events

www.asce.org/SEIEvents The 2022 SEI Standards Series will preview ASCE 7-22 as a 5-part series that reviews the changes from ASCE 7-16. This unique program includes a dialogue between the leaders and experts who develop ASCE 7 and a detailed technical presentation on the specific changes and three main hazards – Seismic, Wind and Tornado, and Snow/Rain. In addition, information will be provided on the ASCE 7 Digital Products/ Hazard Tool. Attendees are encouraged to join the discussion for the extensive live Q&A portion of the session. 1.5 PDHs per session.

• February 10, 2022: ASCE 7-22 Overview & Changes (FREE) • May 12, 2022: ASCE 7-22 Seismic • June 9, 2022: ASCE 7-22 Wind & Tornado

• July 14, 2022: ASCE 7-22 Snow/Rain • September 8, 2022: How & Why to Use ASCE 7-22 in Your Practice

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

Join us at Structures Congress 2022 in Atlanta Keynote Speakers The Opening Keynote Lauren Gardner led the team that developed an online interactive COVID-19 dashboard, first released publicly on January 22, 2020, hosted by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. She will speak about the evolution of the dashboard, the challenges it faced, and how the data has been used to build prediction models and improve the general understanding of COVID-19.

Friday’s Keynote is Kate Simonen, the founding director of the Carbon Leadership Forum and Professor and Chair of the Department of Architecture at the University of Washington. Connecting significant Lauren Gardner professional experience in high-performance building design and technical expertise in environmental life cycle assessment, she works to spur collective action to bring net embodied carbon to zero through cutting-edge research, cross-sector collaboration, and the incubation of new approaches. Join Kate’s dynamic session and explore opportunities to be part of building climate-responsive solutions.

Kate Simonen Rounding out the conference, our Closing Keynote is Melodie Yashar, Director of Building Design and Building Performance at ICON. She will highlight ICON’s robotics, material optimization, and logistics of construction with its 3-D printing technologies and its ability to deliver affordable disaster relief and mainstream home construction projects. She will also discuss building performance, structural engineering, and achieving building code approvals for Melodie Yashar 3D-printed structures. View the program and register at www.structurescongress.org.

Electrical Transmission and Substation Structures Conference October 2- 6, 2022, Orlando

Apply for a student scholarship made possible by the SEI Futures Fund. Learn more at www.etsconference.org.

Future World Vision – Infrastructure Reimagined!

ASCE’s Future World Vision is an interactive, immersive experience exploring the built environment of 2070. Providing tangible visualizations and provocative scenarios, the Mega City 2070 digital platform allows engineers and stakeholders to craft a shared vision of the future they would like to see. Grounded in deep research reflective of the cutting edge of engineering practice, Future World Vision introduces a common vocabulary, rich storytelling, and multi-layered systems modeling to allow participants ASCE and the ASCE Foundation are dedicated to helping civil engineers conquer the of tomorrow. Together we can engineer a sustainable future. to immerse themselves in the future world. It also has a strong application in university challenges courses and student stimulation and engagement.

Take action now to help create solutions for tomorrow’s civil engineering Mega City 2070 will launch during Engineers Week 2022 via free download at futureworldvision.org. challenges today.

Errata 54 STRUCTURE magazine

Support Future World Vision with a gift to the ASCE Foundation. www.ascefoundation.org/future-world-vision-support

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

News of the Structural Engineering Institute of ASCE Advancing the Profession

Congratulations to the 2022 SEI Fellows F. George Abatt, Ph.D, P.E., F.SEI, F.ASCE Jamal A. Abdalla, Ph.D., P.E., F.SEI, F.ASCE Arzhang Alimoradi, Ph.D., P.E., S.E., F.SEI, M.ASCE Eyosias Beneberu, Ph.D., P.E., F.SEI, M.ASCE Rudraprasad Bhattacharyya, Ph.D., P.E., P.Eng, ENV SP, F.SEI, M.ASCE Lacey Goetz, P.E., F.SEI, M.ASCE Wael Hassan, Ph.D., P.E., S.E., F.SEI, M.ASCE Zhengyu Hu, P.E., P.Eng, S.E., C.Eng, F.SEI, M.ASCE Saif Hussain, P.E., S.E., LEED AP, F.SEI, M.ASCE Andrew Keaschall, P.E., S.E., F.SEI, M.ASCE Brian Kehoe, P.E., S.E., F.SEI, F.ASCE

John E. Kennelly, P.E., S.E., F.SEI, M.ASCE Mahendrakumar Madhavan, Ph.D., P.E., F.SEI, M.ASCE Michael Miller, P.E., P.Eng, F.SEI, F.ASCE Shiling Pei, Ph.D., P.E., F.SEI, M.ASCE Harold Sprague, P.E., F.SEI, F.ASCE Jeffrey Stapleton, P.E., S.E., F.SEI, M.ASCE Gene R. Stevens, P.E., S.E., F.SEI, M.ASCE David Todd, P.E., F.SEI, M.ASCE P.V. Vijay, Ph.D., P.E., F.SEI, F.ASCE Silky Wong, Ph.D., S.E., P.E., C.Eng MICE, LEED AP, F.SEI, M.ASCE Bill Zhang, Ph.D., P.E., S.E., LEED AP, F.SEI, M.ASCE

The SEI Fellow grade of membership recognizes accomplished SEI members as leaders and mentors in the structural engineering profession. Reach out to congratulate your peers, and encourage your member colleagues to apply to advance to SEI Fellow. SEI Fellow must be current SEI, actively involved, licensed P.E./S.E., 10 years responsible charge (typically post P.E.). Learn more and complete the application package at www.asce.org/SEIMembership.

SEI Online

New Publications www.asce.org

Access ASCE Disaster Response Resources Free through February

Includes tornado collection of curated ASCE journal content and Joplin, Missouri, Tornado of May 22, 2011: Structural Damage Survey and Case for Tornado-Resilient Building Codes. www.asce.org/topics/disaster-response

Visit the online tool for career tips and resources. collaborate.asce.org/careerbydesign

Follow SEI on Social Media: FEBRUARY 2022

55

CASE in Point CASE Tools and Resources Did you know? CASE has tools and practice guidelines to help firms deal with a wide variety of business scenarios that structural engineering firms face daily. So whether your firm needs to establish a new Quality Assurance program, update its Risk Management program, keep track of the skills engineers are learning at each level of experience, or need a sample contract document – CASE has the tools you need!

Is your firm looking for guidance when retaining a structural engineer or when a Structural Engineer is retaining an additional entity? Here is a list of tools that are available for download or purchase.

Agreements When Structural Engineer is Retained CASE Agreement #1 – An Agreement for the Provision of Limited Professional Services. This agreement is intended for small projects or investigations of limited scope and time duration.

CASE Agreement #2 – An Agreement Between Client and Structural Engineer of Record for Professional Services. This agreement is intended for use when the client, e.g., owner, contractor developer, etc., wishes to retain the Structural Engineer of Record directly. This agreement may also be used with a client who is an architect when the architect-owner agreement is not an AIA agreement.

CASE Agreement #3 – An Agreement between Owner and Structural Engineer as Prime Design Professional. This agreement is intended for use when the Structural Engineer serves as the Prime Design Professional.

CASE Agreement #4 – An Agreement between Client and Structural Engineer for Special Inspection Services. This agreement is intended for use when the Structural Engineer is hired directly by the Owner to provide Special Inspection services.

CASE Agreement #5 – An Agreement Between Client and Specialty Structural Engineer for Professional Services. This agreement is intended for use when the structural engineer is hired directly by a contractor or sub-contractor for work to be included in a project where you are not the Structural Engineer of Record.

CASE Agreement #6 – An Agreement Between Client and Structural Engineer for a Structural Condition Assessment. This agreement is intended for use when providing a structural condition assessment.

CASE Agreement #7 – An Agreement for Structural Peer Review Services. This agreement is intended for use when performing a peer review for an Owner or another entity and includes responsibilities and limitations.

CASE Agreement #8 – An Agreement Between Client and Structural Engineer for Forensic Engineering (Expert) Services. This agreement is intended for use when the engineer is engaged as a forensic expert, primarily when the Structural Engineer is engaged as an expert in resolving construction disputes. However, it can be adapted to other circumstances where the Structural Engineer is a qualified expert.

Agreements When Structural Engineer is Retaining Additional Entity CASE Agreement #9 – An Agreement Between Structural Engineer of Record and Design Professional for Services. This agreement is intended for use when the Structural Engineer of Record, serving in the role of Prime Design Professional or as a Consultant, retains the services of a sub-consultant or architect.

CASE Agreement #10 – An Agreement Between Structural Engineer of Record and Geotechnical Engineer of Record. This agreement is intended for use when the Structural Engineer of Record retains geotechnical engineering services. It can also be altered for use as an agreement between an Owner and the Geotechnical Engineer of Record.

CASE Agreement #11 – An Agreement Between Structural Engineer of Record and Testing Laboratory. This document is intended for use when the structural engineer retains testing services.

CASE Agreement #12 – An Agreement Between Structural Engineer of Record (SER) and Contractor for Transfer of Digital Data (Computer Aided Drafting (CAD) or Building Information Model (BIM)) Files. This document is intended for use to provide an agreement for the Structural Engineering of Record (SER) to use when transferring digital data (CAD or BIM) files to the contractor.

You can purchase these and other publications at www.acec.org/bookstore.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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News of the Coalition of American Structural Engineers Upcoming Events 2022 NASCC: The Steel Conference March 23-25, 2022, Denver, CO

CASE will sponsor a presentation on delegated design at the upcoming Steel Conference in Denver. The presentation, Delegated Design and the Engineer of Record, with speaker Bruce F. Brothersen, Research Engineer at Vulcraft-Nucor, reviews the roles and responsibilities between the Engineer of Record and specialty engineer or specific product engineer. Included is a review of the IBC for direction and key aspects to follow.

For registration information, go to www.aisc.org/aisc-events/2022-nascc-the-steel-conference.

ACEC Annual Convention and Legislative Summit May 22-25, 2022, Grand Hyatt, Washington, D.C.

ACEC sponsors two major national meetings each year: the Annual Convention and the Fall Conference.

National meetings provide attendees an opportunity to obtain information about issues that affect the industry through informative education, networking, and exhibits.

To register visit https://www.acec.org/conferences/annual-convention.

Support the Future of Our Industry We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates. One way to enhance students’ ability to pursue their dreams to become professional engineers is to offer incentives in educational support.

ACEC’s Coalition of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a master’s degree in structural engineering in an ABET-accredited engineering program.

Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for a tax deduction, and you do not have to be an ACEC member to donate!

Donate today at www.acecresearchinstitute.org/scholarships.

Get Involved!

If you are looking for ways to expand and strengthen your business skill set, look no further than serving on one (or more!) CASE Committees.

Join us to sharpen your leadership skills – promote your talent and expertise – to help guide CASE programs, services, and publications.

We currently have openings on all CASE Committees: Contracts – responsible for developing and maintaining contracts to assist practicing engineers with risk management.

Guidelines – responsible for developing and maintaining national practice guidelines for structural engineers.

Programs – responsible for developing program themes for conferences and sessions that enhance and highlight the structural engineering profession.

Toolkit – responsible for developing and maintaining the tools related to CASE’s Ten Foundations of Risk Management program.

To apply, your firm should: • Be a current member of ACEC • Be a member of the Coalition of American Structural Engineers (CASE), or be willing to join the Coalition • Be able to attend the groups’ regular face-to-face meetings each year: August, February (hotel, travel partially reimbursable) • Be available to engage with the committees via email and video/conference call • Have some specific experience and/or expertise to contribute to the group Please submit the following information to Michelle Kroeger, Coalitions Director (mkroeger@acecl.org): • Letter of interest indicating which committee • Brief bio (no more than a page) Thank you for your interest in contributing to advancing the structural engineering profession!

FEBRUARY 2022

57

structural FORUM Calling on Structural Engineers to Design for Sustainability

By Jay Arehart, Ph.D.

S

tructural engineers neglect a key tenet of their professional obligation to society – designing for sustainability. While the concept of sustainability spans the social, economic, and environmental domains (the so-called triple bottom line), immediate action in the environmental domain is required in the face of the climate crisis, specifically around greenhouse gas emissions. Anthropogenic greenhouse gas emissions (e.g., carbon dioxide and methane) are causing global temperatures to increase, resulting in increased frequency and severity of weather events, impacting infrastructure in the United States and worldwide. According to the Intergovernmental Panel on Climate Change (IPCC), all sectors, including buildings, must decarbonize (have net-zero carbon emissions) by 2050 to avoid a 1.5 degree C (2.7 degrees F) temperature rise.

However, today, the manufacturing of construction materials for buildings contributes to 11% of global greenhouse gas emissions.

Thus, to achieve a decarbonized built environment, structural engineers must consider strength and serviceability when designing structural systems and commit to mitigating their greenhouse gas emissions.

The structural engineering profession is home to some of the best problem solvers in the world. While the profession has been charged with ensuring the public’s safety, it is also responsible for designing breathtaking buildings and bridges. In both realms, structural engineers are the ones who have contributed creative solutions to increasingly complex design problems and have enabled concepts to come to life. However, despite the profession’s ingenuity and leading problemsolving abilities, the structural engineering community has only recently been engaged in developing solutions to the climate crisis.

Many structural engineers think that the sustainability of a building is best left to the architect or systems engineers on the design team – that the structural engineer’s role is to ensure the safety of the building. Yet, the recently updated Code of Ethics from the American Society of Civil Engineers states that engineers must “mitigate adverse societal, environmental, and economic effects” of infrastructure. Thus, as structural engineers, our ethical imperative is to reduce the

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greenhouse gas emissions of the structural systems we design.

Some may argue that structural engineers have no control over reducing the greenhouse gas emissions of their structural designs – that building codes and architectural geometry constrain their designs too much. However, instead of pushing away the responsibility, the structural engineering profession must become advocates for sustainable design and apply their creative problem-solving skills to reduce the greenhouse gas emissions of the structural system. While this is a paradigm shift for many surrounding the discussion of sustainable building design, it is a necessary one if we are to address the most complex and challenging issue of our generation – global climate change.

So, how should structural engineers address the greenhouse gas emissions of their structures? During the life of a building, greenhouse gas emissions can be categorized in two ways: embodied and operational.

Embodied emissions are those associated with the manufacturing, transportation, and disposal of construction products, while operational emissions are those associated with heating, cooling, and lighting a building.

For a high-performance building that achieves net-zero energy status, the annual operational greenhouse gas emissions are near zero, but the embodied emissions can be substantial.

Thus, structural engineers are well-positioned to bring buildings to absolute-zero carbon, that

is, net-zero greenhouse gas emissions over the lifecycle of the building.

Structural engineers can contribute to achieving absolute-zero carbon buildings through first tracking and measuring the embodied carbon of their structural systems and second, applying their problem-solving skills to reduce it. Just as loads are tracked through a structure, so should the embodied carbon. The SE 2050 Commitment is one place where structural engineers can commit to tracking and reporting the embodied carbon of the projects they work on, with the aim of reducing embodied emission of all structural systems to net-zero carbon by the year 2050.

As structural engineers, we must embrace that designing for sustainability is a core tenant of our profession – it is no longer enough to just design for strength and serviceability. Over the past century, the profession has been reshaped many times, and addressing embodied carbon is the next most pressing problem and shift for the profession. If we harness the problem-solving expertise of structural engineers, creative solutions will be developed and shared so that, collectively, we can contribute to realizing an absolute-zero carbon built environment.■ Jay Arehart is a teaching assistant professor of Architectural Engineering at the University of Colorado Boulder and teaches courses on sustainability in the built environment.

FEBRUARY 2022