STRUCTURE magazine - February 2021

STRUCTURE NCSEA | CASE | SEI

FEBRUARY 2021

CFS/STEEL

INSIDE: Johns Hopkins Laboratory Historic Metals in Renovations Galvanized Connections Modern Wood Fasteners

CONNECT ELEGANTLY

Stylish. Sophisticated. Deliberate.

The newly renovated Baraboo High School’s updated design focuses on transformative and collaborative spaces and draws influence from its surrounding vista. The building’s exterior features expansive curtainwall and a large cantilevered roof canopy supported

by HSS members fitted with Cast Connex® Architectural Tapers™ and Universal Pin Connectors™ at both ends. The result: a slender, transcendental, and thoughtful expression for exterior HSS connections.

Baraboo High School, WI Designed by Eppstein Uhen Architects Structural Engineer Pierce Engineers Photography by C&N Photography

The CAST CONNEX® Architectural Taper™ (ART) + Universal Pin Connector™ (UPC) is a creative connection detail for circular hollow structural section (HSS)/Pipe members achieved by combining two standardized Cast Connex off-the-shelf connectors.

Efficient Cast Connex ART+UPCs enable efficient connections when used in compression members where loading allows a small pin connection relative to the size of the member.

Sophisticated Used together, the ART+UPC provide an elegant aesthetic form that reduces the visual mass of both the connected member and the connection joint itself.

Hollow Structural Section Elevated • Available in sizes to fit a range of HSS members • Pre-engineered: two simple welds are all it takes • Designed specifically for AESS conditions making them easy for fabricators to work with • Stainless-steel hardware included (UPC)

ARCHITECTURAL TAPER™ + UNIVERSAL PIN CONNECTOR™ www.castconnex.com

innova�ve components for inspired designs

www.iesweb.com Discover the VisualAnalysis CFS advantages: iesweb.com/cfs

ADVERTISER INDEX

Please support these advertisers

STRUCTURE

American Concrete Institute

MAPEI Corp

Anthony Forest Products Co

NCSEA

sales@STRUCTUREmag.org

ASDIP Structural Software

New Millennium Building Systems

Cast Connex

New Millennium Building Systems Full Page

Director for Sales, Marketing & Business Development

Clark Dietrich

Nucor Tubular Products

ENERCALC

NCEES

Integrated Engineering Software, Inc.

RISA

EDITORIAL STAFF

Simpson Strong-Tie

Executive Editor Alfred Spada

KPFF

®

MARKETING & ADVERTISING SALES

Jose E. Mendoza, P.E. Tel: 312-649-4600 ext. 210 jose.mendoza@STRUCTUREmag.org

aspada@ncsea.com

HERE or THERE.

Publisher Christine M. Sloat, P.E. csloat@STRUCTUREmag.org Associate Publisher Nikki Alger nalger@STRUCTUREmag.org

Creative Director Tara Smith graphics@STRUCTUREmag.org

EDITORIAL BOARD Chair John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA chair@STRUCTUREmag.org Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT Erin Conaway, P.E. AISC, Littleton, CO

HARNESS THE POWER OF

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

STRUCTURE’s audience.

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

For full details contact sales@STRUCTUREmag.org.

Emily B. Lorenz, P.E. Chicago, IL Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY

Excellence in Structural Engineering The Emerald • Seattle • WA

Seattle

Los Angeles

St. Louis

Tacoma Lacey Portland

Long Beach Irvine San Diego

Chicago Louisville Washington, DC

Eugene

Boise

New York

Sacramento San Francisco

Salt Lake City Des Moines

www.kpff.com KPFF is an Equal Opportunity Employer.

STRUCTURE magazine

TOGETHER WE BUILD SOLUTIONS

ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

Jason McCool, P.E. Robbins Engineering Consultants, Little Rock, AR Brian W. Miller Davis, CA Evans Mountzouris, P.E. The DiSalvo Engineering Group, Danbury, CT John “Buddy” Showalter, P.E. International Code Council, Washington, DC Eytan Solomon, P.E., LEED AP Silman, New York, NY Jeannette M. Torrents, P.E., S.E., LEED AP JVA, Inc., Boulder, CO

STRUCTURE ® magazine (ISSN 1536 4283) is published monthly

by The National Council of Structural Engineers Associations (a nonprofit Association), 20 N. Wacker Drive, Suite 750, Chicago, IL 60606 312.649.4600. Application to Mail at Periodicals Postage Prices is Pending at Chicago, IL and additional mailing offices. STRUCTURE magazine, Volume 28, Number 2, © 2021 by The National Council of Structural Engineers Associations, all rights reserved. Subscription services, back issues and subscription information tel: 312-649-4600, or write to STRUCTURE magazine Circulation, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606.The publication is distributed to members of The National Council of Structural Engineers Associations through a resolution to its bylaws, and to members of CASE and SEI paid by each organization as nominal price subscription for its members as a benefit of their membership.

Yearly Subscription in USA $75; $40 For Students; Canada $90; $60 for Canadian Students; Foreign $135, $90 for foreign students. Editorial Office: Send editorial mail to: STRUCTURE magazine, Attn: Editorial, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606. POSTMASTER: Send Address changes to STRUCTURE magazine, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606.

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

Contents FEBRUARY 2021

Cover Feature

STRUCTURE AS A STATEMENT OF PURPOSE

By John Roach, P.E.

For Building 201 at the Johns Hopkins University Applied Physics Laboratory, a two-way concrete flat slab was selected for the structural system of both the laboratory and office wings. At the east wing, multi-bay conference rooms, closely spaced stair and mechanical shafts, and a two-story auditorium made reinforced concrete construction impractical. Instead, a steel frame structure is used throughout this five-story section of the building.

Columns and Departments 7 Editorial The Challenge of Virtual Collaboration

By David Horos, P.E., S.E.

8 Structural Renovations Encountering Historic Metals

in Renovations

By Ciro Cuono, P.E., and Christopher Ribeiro, E.I.T.

24 Education Issues Bringing Real-World Experience

into the Classroom

By Mark Kanonik, P.E.

26 Business Practices How to Recession-Proof

Your Engineering Career

By Stephanie Slocum, P.E.,

in collaboration with SEI’s Business Practices Committee

12 Building

Blocks Structural Connections for Hot-Dip Galvanizing By Alana Fossa and Thomas J. Langill, Ph.D.

14 Structural Connections Modern Wood Fasteners

– Part 2

By Alex Salenikovich, Eng, Ph.D., and David Moses, P.E., Ph.D.

22 Historic Structures Tariffville Bridge Disaster

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

February 2021 Bonus Content

34 Structural Forum Lessons for Young Engineers

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

In Every Issue Advertiser Index NCSEA News SEI Update CASE in Point Additional Content Available Only at – STRUCTUREmag.org

Feature Revisiting Lessons Learned from the Nicoll Highway Collapse Spotlight ICE Block I

By Hee Yang Ng, MIStructE, C.Eng, P.E.

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.

F E B R U A R Y 2 0 21

EDITORIAL The Challenge of Virtual Collaboration

By David Horos, P.E., S.E., LEED AP

W

hen I was a kid in the 70s, there was a children’s TV show looking toward the post-pandemic world, which called Zoom. I wouldn’t say I liked it too much, and it didn’t will likely include a new, hybrid model that consists of the best last too long. It was reintroduced in the 90s and, again, didn’t stick. For (and hopefully not the worst) of both the in-person and at-home worlds. understandable reasons, I suppose, this past year has had me thinking We all recognize some benefits of this new digital environment. Some about that show and how little I suspected the word zoom would of us have participated in virtual site visits, which, while not as good reenter my life in such a big way. A series of new software to install, as in-person, are likely better than no visit at all and certainly more learn, and make sure they are compatible with my hardware. The accessible with limited travel budgets. The requirement to go virtual need to run many programs (Zoom, Hangout, Teams, Webex, Goto, with conferences, dinner meetings, and seminars has been met with Bluejeans, Connect) interchangeably depending on hosts. And a series new opportunities for participation, with a larger audience pool not of terms introduced into our vocabulary (zoom fatigue, zoom etiquette, defined by geography. And our ability to attract speakers from afar virtual background, etc.). And now common phrases, “Can you see was made easier with virtual events. my screen,” “Can you make me the cohost,” and “Can you turn on On the other hand, we work in a very collaborative profession. Our your cameras so we can see designs are improved by interactions with our you?” The current question colleagues. And while we are still collaborain my mind is, where will this tive virtually, we may be losing something lead us moving forward? by missing out on spontaneous face-to-face Interestingly, Zoom was interactions. Are the online tools available formed as a company in 2011 for collaboration sufficient to replace tried and was worth $1 billion by and true approaches like sitting around a 2017, well before its most table with our colleagues to review designs? recent growth. Some savvy Or to collectively review drawings pinned folks anticipated changes in up on conference room walls? Engineers the world and how we do value networking at conferences, which is business before the pandemic. not fully replicated in the Were we all destined to evolve virtual environment.

The requirement to go virtual ... has been met to our current arrangement, How do we best take advanwith new opportunities for participation, with a and the adoption of Zoom tage of the medium? More was just accelerated? Or was this a professional setups – better larger audience pool not defined by geography. technology that would never have cameras, lighting, and microdeveloped without the pandemic? We may never know, and it may not phones. We are all in show business now, hopefully with less makeup! matter. Zoom and its cousins are indispensable now. A bigger question We have better electronic collaboration tools like surveys, virtual might be whether it, unlike the TV show, remains for the long term. whiteboards, and more, all of which will require learning and becomIt is great that collaboration technology already existed when we ing comfortable. We must learn to provide virtual access to in-person needed it. But how do we adapt to make the best use of the technol- meetings while ensuring that those attending virtually have the same ogy when it is no longer necessary? Collaboration technology opens opportunity to see, hear, and participate. opportunities in the way we practice and team up professionally. Less The challenge will be to blend these new approaches with prior business travel. More working from home without the commuting practices once we are past the pandemic while also mitigating the time. Less need for office space, meaning less overhead? Less face-to- potential downsides to remoteness. What is the right amount of time face interaction? We worry about extensive screen time for our kids to be in an office compared to working remotely? That answer will and a resulting lack of social skills. Will our technical communication depend on circumstances, and it will take time to strike the right skills and ability to collaborate suffer over time? What will we prefer, balance for different circumstances. phones or digital meeting spaces; does it matter? How about sharing As we approach both the one-year anniversary of the first lockdowns and messages live with large groups of people from far-distant regions, an the widespread availability of a COVID-19 vaccine, let us take the time to ability that was not readily known or used regularly. reflect on our ability as a profession to react and adapt to quickly changing And for those who design buildings, how will it affect our business circumstances. And to commit to taking the best of those adaptations prospects and projects? Will we be coordinating new “zoom rooms” in forward with us in our practices and our work serving the profession. offices and residences? Will the need for more flexible living and working I am very excited about the possibilities moving forward. Technology spaces require changes to our designs? Will there be a need for more has helped us advance throughout history, and this abrupt crash rehab/retrofit work? And will the ability to work from home result in course in virtual business has accelerated the current cycle decreased demand for new office buildings and other project types? of innovation even more. Harnessing that technology will Sooooo many questions to consider, and I certainly will not venture be key. Zoom on!■ to offer many answers. I will suggest that while there were initial David Horos is a Director in the Structural Engineering Studio at Skidmore, concerns, our profession showed we could survive and arguably thrive Owings & Merrill and a member of the NCSEA Board of Directors. in a fully remote environment. We were able to adapt and are now STRUCTURE magazine

FEB R U A R Y 2 021

structural RENOVATION

Encountering Historic Metals in Renovations

By Ciro Cuono, P.E., and Christopher Ribeiro, E.I.T.

S

tructural steel has been a dominant building material for more than 100 years. Although steel is not considered a particularly remarkable material

today, Vaclav Smil’s book, Still the Iron Age, illustrates how important iron and steel have been and continue to be in industrialized societies. For a structural engineer working on historic renovations and adaptive reuse of pre-war buildings, working knowledge of the history, development, and metallurgy of structural metals is necessary for the engineer to be effective and efficient.

Figure 1. A sample of a wrought-iron beam flange.

The three primary ferrous metals used in building construction from create various shapes; it has good compressive strength and low tensile approximately the 1850s to the 1920s were cast iron, wrought iron, strength. Wrought iron is a more malleable or workable (hence the and structural steel. All three materials are man-made metals (alloys) name “wrought”) alloy of iron with low carbon content and good whose primary ingredient is iron. The industrial revolution of the 18th tensile and compressive strengths. Both metals were used in early buildand 19th centuries brought iron making technology to an advanced ing structures, particularly industrial buildings in England, to replace state where cast iron and then wrought iron could be mass-produced and span farther than the heaviest timbers available. Steel, which is and used, first in transportation and then building projects. also an alloy of iron with low carbon content and other elements such Iron technology was used and developed predominantly in Europe, as manganese, silicon, sulfur, and phosphorus, eventually replaced China, the Middle East, and India. The basic process consisted of cast iron and wrought iron. Steel was known and available in limited smelting mined iron ore (naturally occurring deposits of iron-rich quantities in the early 1800s and became commercially available after minerals) and forging iron bars from the resulting “bloom” or sponge- Henry Bessemer developed an efficient process for producing steel, like mass of iron, separating the resulting slag and impurities. Smelting which he patented in 1856. This process, called the Bessemer process, was done in a furnace known as a bloomery, consisting of a chamber was improved by others and eventually replaced by the open-hearth or pit with masonry walls and an exhaust stack. The fuel typically process. Cast iron was used predominately in the early to mid-1800s for consisted of charcoaled wood or coal, which had a dual purpose of structural members and eventually relegated to columns and decorative creating heat and providing carbon. When the carbon combined with uses due to its high compressive strength but brittle nature. Wrought pure iron, the process created the first ferrous metals like wrought iron. iron was used in the latter half of the 1800s and replaced cast iron for The introduction of air or oxygen via bellows and pipes, called tuyeres, flexural members due to its superior tensile properties. was added to increase the heat within the furnace. Early development By the late 1800s, structural steel began to take over the market for was limited by the availability of fuel and the ability to achieve high structural metals and was stronger than wrought iron, both in tensile temperatures. However, the technology slowly advanced and came and compressive properties. In the building industry, particularly from to fruition with the industrial revolution, the Chicago School of Architecture, tradifirst in England and then in other parts tional heavy masonry buildings began to of Europe and the United States. The grow taller and introduce interior skeletal bloomery was eventually replaced by a framing, first with cast-iron columns and blast furnace – blast referring to a blast of wrought-iron beams and eventually with air (oxygen) and coke as a fuel instead of full skeletal steel framing. The “Chicago charcoal. Coke was a fuel made from bituSchool of Architecture” was a style of archiminous coal that was first heated to reduce tecture that came out of Chicago in the water content and impurities – a process late 1800s and early 1900s. The architects, called “coking.” The resulting coke burned engineers, and builders, experiencing a better and had a higher carbon content. building boom due to market forces and This advanced technology produced metal the rebuilding from the aftermath of the in liquid form at the bottom of the furnace, 1871 Great Chicago Fire, began to experiknown as “pig iron.” The term came from ment with new materials and techniques. the collected metal shapes of molds and This was the beginning of the common bars that resembled a litter of pigs. Pig skeletal frame type of construction. The iron is basically a cast iron or alloy of iron steel manufacturing industry grew, and each with high carbon content. Wrought iron, steel producer used their own formulations, cast iron, and, eventually, steel were made resulting in the finished product’s variability. by further refining pig iron.

Individual companies developed allowCast iron is an alloy of iron, with a Figure 2. Excerpt from a 1930s framing plan showing beam able load tables for products made in the high carbon content, cast into molds to sizes and typical floor construction. late 1800s and early 1900s. In 1900, the STRUCTURE magazine

American Society of Testing Materials (ASTM) developed standards for conditions, or, in some lucky instances, rolls of original drawings structural steel such as ASTM A9, Specification for Steel for Buildings. tucked away in a corner (Figure 2). A detailed survey of the framing These standards defined minimum requirements for the steel materials is then conducted. A keen eye can pick up clues like a “Pencoyd” or used in these applications, bringing uniformity to the varying standards “Carnegie” stamp on the side of an old beam (Figure 3, page 10). published by the individual producers of the time. In 1939, the A9 Back in the office, the wealth of information in engineering literature standard for buildings was consolidated into ASTM A7 (the bridge can be used to determine allowable stresses, locate old load tables, standard up to that point), and the two standards remained combined and determine the limits and design methodologies at the time of until 1960, when the ASTM A36 standard was issued. This standard construction. Sources like the American Institute of Steel Construction INFO SPECS became the dominant standard for steel buildings until the 1990s. (AISC) Design Guide 15, Rehabilitation and Retrofit, and the AISC File Name: 20-1246 Structure Mag_March_System Solutions Flat Size: In 1921, the American Institute of Steel Construction (AISC) was PR: Engineering Journal Field Welding to Existing Steel Structures by David Finished Size: 5” × 7.5” XXXX MKT: 20-1246 founded to bring consistency to the design and construction standards Designer: Ricker,Georgina First Morra Quarter/1988, are invaluableBleed: resources for determining Yes Amount: .125” Email: gmorra@mapei.com 114 4 E. Newpor t Center Dr. for structural steel used in building construction, the February properties of structural steel.

Colors: 4/0 Other sources like Date: 6, 2020 and 12:20weldability PM D e e r f i e l dand B e a the c h , Ffirst L 3 3AISC 442 Standard Specification for Structural Steel forN OBuildings Parker’s, the T E : C O L O R S followed V I E W E D O N -in S C R1923.

E E N A R E I N TKidder ENDED FOR V I S U A L R E Architects’ F E R E N C E O N L Yand A N D Builder’s M A Y N O T M A Handbook, T C H T H E F I N A L Pnow R I N T E in D PR O D U public C T.

Metallurgical Differences

Field and Laboratory Investigations Investigating old buildings is like reading a detective novel. Much the way a detective first visits a crime scene, makes field observations and notes, collects forensic evidence, and conducts laboratory testing, an engineer performs the same tasks on existing framing conditions.

The first step is an initial walkthrough to determine the existing structure’s general layout and get the lay of the land.

Interviews with building superintendents can yield valuable information on previous renovations or descriptions of hidden

MAPEI: Your single-source provider

from restoration to protection System solutions for bridge restoration

Overhead Repair Solutions

Column Repair Solutions

Bridge Deck Solutions

ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

Cast iron contained a larger percentage of carbon (2% to 4%) and was produced by melting pig iron mixed with scrap metal in a “cupola” furnace. Though easily cast, it was brittle and not malleable. On the other hand, wrought iron is almost pure iron with a very slight amount of carbon (0.2% to 0.35%). It was manufactured by melting pig iron in a puddling furnace where many impurities from the pig iron were removed. The resulting product was an iron alloy with a glass-like fibrous slag that is malleable and has good tensile properties and good corrosion resistance.

The distribution of the slag fibers resulted in tensile strength and ductility higher in the longitudinal or rolling direction (Figure 1). By the early 1900s, steel completely replaced cast iron and wrought iron for structural framing. It is an alloy of iron with a carbon content of less than 2% (mild structural steel has a carbon content more in the magnitude of 0.3% to 0.6%).

It has a crystalline grain structure on a microscopic level, is ductile, and, unlike wrought iron, is more susceptible to corrosion. However, the relatively low carbon content and small amounts of other elements give it great strength and ductility.

MAPEI offers a full spectrum of products for concrete restoration, below-grade waterproofing and structural strengthening. Globally, MAPEI’s system solutions have been utilized for bridges, highways, parking garages, stadiums, buildings and other structures.

Visit www.mapei.us for details on all MAPEI products.

MAPEI USA

20-1246 Structure Mag_March_System Solutions.indd 1

F E B2/6/20 R U A12:20 R Y PM 2 021

Figure 3. Existing beam from a 1920s building with a “Pencoyd” stamp from the Pencoyd Iron Works.

Figure 4. A typical beam to cast iron column detail.

Note beams bear on cast lugs. From Kidder/Parker Architects’ and Builders’ Handbook.

domain, provide original load tables, historical details, and guidance on older systems’ methodologies. Knowledge of typical historical details can help in a field survey as well. For example, cast-iron columns often had integral cast seats or lugs for supporting timber, wrought iron, or steel beams (Figure 4). Knowledge of this detail makes it easy to spot cast-iron columns. Drilling holes in the cast iron to ascertain its thickness can allow for a capacity calculation from original load tables and formulas based on the column’s height.

Ultimately, laboratory testing of samples from the metal will provide the most definitive proof of older metals’ metallurgy and weldability.

Some quick “sanity” checks are also useful for comparative and validation purposes. For example, if one knows the initial loading and size of a beam and then back calculates the actual stresses, a low level of stress of say 8 to 10 kips per square inch (ksi) would indicate the metal is most likely wrought iron, rather than structural steel which would most likely be 16 to 18 ksi. Additionally, if one found an I-beam of unknown material but had, say, a 1-inch-thick flange for a 10-inchdeep beam, one could deduce that the beam is likely wrought iron since no 10-inch-deep steel beams had flanges that thick.

Laboratory testing is the best method for definitively determining the material, its weldability, and its yield strength. Specimens removed from the field at innocuous locations, such as the flange at the end of a simply supported beam, can be sent to a metallurgist for laboratory testing. Ricker provides guidance on this and determines the equivalent carbon content for steel weldability (Figure 5). Steel, with lower carbon, particularly after the 1920s, is generally very weldable. Cast

Chemical Carbon Manganese Silicon Chromium Molybdenum Vanadium Nickel Copper Boron

Sample 1 0.230 0.540 0.010 0.010 0.010 0.010 0.040 0.030 0.001

Carbon Equivalent Pcm

0.33 0.27

Phosphorus Sulfur

0.022 0.056

Figure 5. Sample from a laboratory analysis showing the results of a chemical analysis of a steel beam from ca. 1910.

iron and wrought iron (though weldable) are not reliable for welding purposes. It is generally recommended to strengthen and connect to those members by mechanical means. Another test, inherently qualitative, is the inexpensive spark test. A specimen is brought into contact with a grinding wheel, and the resulting stream of sparks observed can confirm the presence of carbon (Figure 6). Pure iron (e.g., wrought iron) results in smooth spurts of sparks, whereas the carbon in steel produces forked sparks; the more significant the carbon content, the more numerous the forks.

Repairs, Alterations, and Renovations Historic metals are typically encountered when repairing, altering, and renovating historic buildings. A common repair scenario involves strengthening due to rusting or corrosion. Corrosion, an electrochemical reaction (oxidation and reduction) that results in the expansion of iron alloys, particularly steel, causes sectional loss of members.

The reaction requires water, and thus, unprotected or inadequately protected metal is highly susceptible to corrosion.

Strengthening techniques of existing metal structures can be accomplished by shortening the span of the existing members, adding new structural members, replacing the existing structural members, post-tensioning (external prestressing) the existing members, and/or enlarging the structural member’s section by welding new reinforcing steel or by introducing composite action.

In adaptive reuse of older structures, new performance requirements often compel the addition of reinforcing material to increase loadcarrying capacity, to restore areas eroded by corrosion, to strengthen fire-weakened members, or perhaps alter the appearance of a member by changing its shape for aesthetic reasons.

In Conclusion Identifying the material through visual inspections, confirming details and original design methodology via consulting original texts and older codes, and confirming yield strengths and weldability via laboratory testing are the tools needed for successfully dealing with historic metals.■

Figure 6. Diagram of sparks showing branching and forking. Part A shows wrought iron, and Parts B through E shows various irons or steels. The presence of carbon is relative to the branching or forking of the sparks. From Iron and Steel by Erik Oberg and Franklin Day Jones, 1918.

STRUCTURE magazine

Ciro Cuono is the founding Principal of Cuono Engineering PLLC, White Plains, NY, and is a past Assistant Adjunct Professor of structural engineering at The Bernard and Anne Spitzer School of Architecture at the City College of NY. (ccuono@cuonoengineering.com) Christopher Ribeiro is Project Manager at Cuono Engineering PLLC.

Help your clients combat corrosion.

Stainless-steel fasteners for everything nature’s got.

No matter what projects you’re designing, we have the stainless-steel fasteners to help resist corrosion caused by moisture, salt, chemicals and countless other factors. From structural and wood screws to nails, our stainless-steel fasteners offer unmatched quality and performance. Protect every job — in every climate — with Type 304, 305 or 316 grade stainless-steel fasteners from Simpson Strong-Tie. To learn more, visit go.strongtie.com/ssfasteners or call (800) 999-5099.

© 2021 Simpson

Strong-Tie Company Inc. SSFAST20S

building BLOCKS Structural Connections for Hot-Dip Galvanizing

By Alana Fossa and Thomas J. Langill, Ph.D.

R

eliable connections in structural steel matched pair. This ensures that, when used in the assemblies must accompany superior corfield, the bolt and nut combination can give the rosion protection. Hot-dip galvanized (HDG) proper structural connection without any galling coatings produce maintenance-free corrosion of the bolt with its soft zinc coating on the threads. protection for many years. The structural conExposure of the bolt and nut combination to nections must provide equivalent corrosion environmental conditions hardens the outer zinc protection as well as structural integrity to layer and improves the ability of the two parts to ensure maintenance-free performance. A solid form a solid connection. structural connection is ensured by providing corrosion protection for the bolt and nut Slip Critical Connections connection and providing clearance for the HDG coating special treatment of the nut. A Although the hot-dip galvanized coating does not critical factor in structural connections is the affect design strength considerations for bearing slip factor for the faying surfaces. This article type connections, the design of slip critical condiscusses recent changes made by AASHTO to nections is affected by the slip coefficient of the Figure 1. Bolt and nut cross-section. the design parameters for HDG faying surfaces hot-dip galvanized faying surfaces. Traditionally, and the increased clearance holes for connections using bolts with industry standards denote newly hot-dip galvanized steel has a lower a diameter above 1 inch. mean slip coefficient (μ = 0.30) than blast cleaned bare steel (μ = 0.50) or bare steel painted with Class B coatings (μ = 0.50). As a result, design freedom and cost can be affected when specifying hot-dip HDG Fasteners galvanizing for corrosion protection. More bolts, holes, and joints HDG fasteners are coated in accordance with ASTM A153/A153M, are required in the design of high-strength structural connections.

Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware. Applying Class B zinc-rich paints (ZRP) over HDG faying surfaces This specification ensures that the corrosion protection of the bolt, can significantly increase the slip coefficient and provide a greater washer, and nut are in sync with the coating of the structural steel variety of coating options to the specifier/designer without affecting that is to be connected. The hot-dip galvanizing process is an inter- long-term corrosion protection. Recent slip factor and tension creep diffusional mixing of iron and zinc, forming a multilayer coating on testing performed by the American Galvanizers Association (AGA) the steel hardware's surface. The iron and zinc diffusion creates inter- indicates higher slip coefficients (μ = 0.45 or μ = 0.50) can be achieved metallic layers that form perpendicular to the steel surface and give by applying Class B zinc-rich paints to hot-dip galvanized faying a uniform coating on all steel surfaces. When galvanizing structural surfaces which have been prepared with a chemical pre-treatment/ bolts, zinc metal builds up in the bolt's threads, making it difficult conversion coating. Based on these findings, the 8th edition of the to thread a nut onto the bolt. The common practice for avoiding this AASHTO Load Resistance Factor (LRFD) Bridge Design Specification issue is to spin the container of bolts in a centrifuge or spin-a-batch includes updated class definitions to include any blast-cleaned surfaces system to reduce the excess zinc in the threads. coated with zinc-rich paints (Class D, μ = 0.45).

The bolt-to-nut connection has multiple layers of galvanized coating in the connection. The nut for a galvanized connection is coated Revised Surface Condition Classes as a blank before the threads are produced in the nut to reduce the and Slip Coefficients potential for coating layers to interfere with the nut travel on the bolt threads. The concern with this practice is providing corrosion AASHTO’s Technical Committee for Structural Steel Design (T14) protection for the threads inside the nut. recently passed changes to Section 6 (Steel Structures) of the LRFD Figure 1 shows a nut and bolt combination with the nut threads document, and the revised language appears in the new 8th revision. being uncoated and the bolt threads having a galvanized coating. The The revised language of Section 6 reflects the need within the industry bolt threads provide corrosion protection to the nut threads. The use to re-define the available surface condition classes and associated values of nuts that have been threaded after coating allows the nut threads for slip coefficients used to calculate the nominal slip resistance of a to be standard tolerances, whereas, if the threads inside the nut were high-strength bolt in slip-critical connections. Class definitions within coated, the threads would have to be produced to an oversized toler- Article C6.13.2.8 were updated to revise the class for hot-dip galvanized ance. Another advantage of using the nuts with threads produced after faying surfaces, and include options for metalized faying surfaces and coating is that threads are clear of extra coating. If the nut threads were blast-cleaned surfaces coated with zinc-rich paints (Table 1): produced before coating, then the nuts' interior threads would be more Class A: Unpainted clean mill scale and blast-cleaned surfaces difficult to clean of excess zinc coating. The cleanliness of the threads with Class A coatings. The value for a Class A surface condition is is essential to the connection of the bolt and nut, giving the joint reduced from 0.33 to 0.30 to better align with the value provided the proper tension when tightened. When using high strength bolts in the latest Research Council on Structural Connections’ (RCSC) in structural connections, the bolt and the nut are typically sold as a specification corresponding to the median of available historical data.

STRUCTURE magazine

Class B: Unpainted blast-cleaned surfaces to SSPC-SP 6 or better, blast-cleaned surfaces with Class B coatings, or unsealed (pure zinc or 85/15 zinc/aluminum) thermal-sprayed coatings with a thickness less than or equal to 16 mils. Unsealed thermal-spray coatings were not previously addressed by the specification, but are now included within Class B based on recent research data.

Class C: Hot-dip galvanized surfaces. Based on recent industry research, the value for a Class C surface condition is reduced from 0.33 to 0.30, and subsequent treatment (wire brushing) of the galvanized surface is no longer required.

Class D: Blast-cleaned surfaces with Class D coatings. Added to increase the options for zinc-rich coatings over any blast cleaned surface (including HDG).

Eventually, specifications related to structural connections used in other industries may be similarly revised. Slip critical testing on different HDG surfaces indicates that wire brushing of the HDG faying surface is no longer required as the brushing can smooth the coating and reduce the slip factor.

For the FHWA/bridge customer, the revisions allow a greater variety of coating systems that can be used to design high strength slip critical connections. Specifically, it will become easier and more economical for the specifier to select hot-dip galvanizing and metalizing for corrosion protection. Although the slip coefficient for hot-dip galvanized surfaces is reduced from 0.33 to 0.30 in this revision, it is anticipated that the new value will have minimal impact on design. However, there is a potential for a small increase in the number of bolts used in connections with HDG fasteners.

Regardless, customers will benefit from the removal of additional labor previously required to roughen HDG faying surfaces. For the new Class D (μ = 0.45) surface condition, a slightly lower slip coefficient value is provided than for Class B (μ = 0.50). However, the value will not significantly impact the overall number of bolts required for most high-strength bolted connections. Therefore, the addition of Class D simply provides a greater variety of coating options to the specifier/designer, including the use of HDG surfaces with zinc-rich paints.

Class D Paint Materials The combination of HDG coating and paints containing zinc silicate can increase the design slip factor and provide a decrease in the number of bolts required for a slip critical connection. Two specific paint materials that have been tested for slip factor and creep properties when applied to HDG coatings are: • HDG & Sherwin-Williams Zinc Clad II Plus with a slip factor μ = 0.45 • HDG & PPG Dimetcote® 9/Sigmazinc™ 9 with a slip factor μ = 0.50.

The HDG surfaces were prepared for painting using a chemical surface treatment (Picklex® 20), and both of the above paint systems were brush-applied (no thinner used) and cured following cure schedules provided within each paint manufacturer’s technical data sheet.

These paints can be applied at the galvanizing facility.

Clearance Hole Sizing Because hot-dip galvanizing is a coating of corrosion-inhibiting, highly abrasion-resistant zinc on bare steel, the original steel becomes slightly thicker. When talking about tapped holes and fasteners, the increased thickness is an important design consideration. Previously, the thickness of hot-dip galvanizing left the specifier choosing between reaming out through-holes after

Table 1. Slip coefficients by class.

Surface Condition

Ks (Slip Coefficient)

Definition

Class A

• unpainted clean mill scale • blast-cleaned surfaces with Class A coatings

0.30

Class B

• unpainted blast-cleaned surfaces to SSPC-SP 6 or better • blast-cleaned surfaces with Class B coatings • unsealed (pure Zn or 85/15 Zn/Al) thermalsprayed coatings with a thickness ≤ 16 mils

0.50

Class C

• hot-dip galvanized surfaces (roughening by wire brushing no longer required)

0.30

Class D

• blast-cleaned surfaces (including HDG) painted with Class D coatings

0.45

hot-dip galvanizing or further reducing slip resistance by specifying oversized holes that would allow sufficient clearance for the bolt. As a result, design freedom and cost can be affected when specifying hot-dip galvanizing for corrosion protection as more bolts, holes, and joints are required.

Experience has shown clearance holes for slip-critical connections, which are ⅛-inch larger than the bolt diameter, are sufficient to accommodate the zinc coating on the bolt and inside face of the hole without reaming. As a result, ANSI/AISC 360 Specification for Structural Steel Buildings (2016) and AASHTO LRFD Bridge Design Specifications (8th Edition) include updated recommendations for clearance hole sizing. A summary of the changes is presented in Table 2 (online).

For a nominal bolt size, 1 inch or greater, these changes to nominal hole size result in increased slip resistance, a simplified design, and reduced cost for hot-dip galvanized slip-critical connections.

Per the revised nominal hole dimensions, oversized holes are no longer required for connections involving bolts sized 1 inch or greater. The standard hole is already sized ⅛ inch greater than the bolt diameter. For connections where the specified bolt size is less than 1 inch, the standard clearance hole size is only 1⁄16-inch larger than the nominal bolt diameter. Therefore, the clearance holes must be oversized an additional 1⁄16 inch (i.e., ⅛ inch added to the initial bolt diameter) to provide a clearance hole that will accommodate a galvanized bolt without the need of extra hole cleaning.

Conclusion The application of zinc-rich paints over hot-dip galvanizing can significantly increase the slip coefficient of hot-dip galvanized slip critical connections and provide a greater variety of coating options to the specifier/designer while providing durable and long-term corrosion protection. Available research and updates to industry specifications allow this method to be readily utilized for future projects. Also, specifying updated standard clearance hole sizes can be used to improve the slip resistance and cost of hot-dip galvanized slip critical connections utilizing certain bolt sizes.■ References and Table 2 are included in the PDF version of the article at STRUCTUREmag.org.

Alana Fossa is a Senior Corrosion Engineer of the American Galvanizers Association. (afossa@galvanizeit.org) Thomas J. Langill is a Technical Director of the American Galvanizers Association. (tlangill@galvanizeit.org) FEB R U A R Y 2 021

S AV E O V E R T I M E F O R OTHER PLANS.

Getting off-site starts with using the right materials on-site. ClarkDietrich helps you do your best work as efficiently as possible. From framing to finishing, ClarkDietrich products and services save time, material and labor, so you can get the job done right and go grab some peace of mind.

© 2020 ClarkDietrich

structural CONNECTIONS Modern Wood Fasteners The Key to Mass Timber Construction Part 2: Introduction to Glued-in Rods

By Alex Salenikovich, Eng, Ph.D., and David Moses, P.E., Ph.D.

T

his is the second part of the series of articles on modern wood fasteners. Part 1 (STRUCTURE,

August 2020) focussed on self-tapping screws (STS). Part 2 introduces the reader to glued-in rods (GIR) and the components making up these joints. Part 3 will summarize design guidelines for the GIR connections. Despite the interest among designers of mass timber construction, there is no official recognition in U.S. and Canadian design codes for GIR connections. This article sheds light on the

Figure 1. 85 m (280-foot) clear span frame in the Gremyachinsky mining and processing plant. Note that the center wall is not a vertical support. Courtesy of TSNIISK Kucherenko.

state of the art of this emerging technology. We caution the reader that this an area of development without code approvals in the U.S. and Canada – the content is provided as informational and not to be used for design.

As is the case for self-tapping screws, glued-in rod technology originates from Europe. Studies started in German-speaking countries and Scandinavia in the early 1970s, initially for repairing and reinforcing floor and roof structures. In the same period, pioneering research on inclined glued-in rods started in the USSR under the leadership of S.B. Turkovsky at the Central Research Institute of Building Construction (TsNIISK Kucherenko). In 1982, design rules for GIR connections were adopted in the Soviet timber design code and had remained active in the Russian building regulation. Using the Russian methodology, over a hundred projects of various sizes, with free spans up to 100 m (over 300 feet), have been completed in Russia (Figure 1).

By the end of the 20th century, glued-in rods had been studied worldwide, including Canada, New Zealand, Australia, and Japan. To date,

the basic rules for designing GIR joints have been adopted in timber design practice in Germany, Switzerland, Sweden, Italy, and New Zealand. Several proprietary systems have been approved in Europe for GIR joints. Attempts have been made to include the design rules for GIR joints in the international (CIB) and European (Eurocode 5) design codes, but no consensus has been reached yet.

The principles and applications of GIR joints are somewhat similar to those of self-tapping screws. Steel rods with profiled shanks (threaded or ribbed) are embedded deeply into timber. The rods are preferably loaded axially to provide superior stiffness and strength for transferring forces and/or moments at joints or reinforce timber near supports and in zones of high horizontal shear or tension perpendicular to the grain (Figure 2).

Depending on the design configuration, the load-bearing capacity of the joints may be governed by the pullout resistance of the bondline or by the resistance of the steel shank of the fastener. Therefore, a higher capacity may be achieved with fewer glued-in rods than with screws. Using milder steel rods of smaller diameters may be desirable to achieve ductile performance of the joints. With careful choice of diameter and spacing of the rods, highly efficient joints can be designed with minimum loss of stiffness and strength of the adjoining members, even for loads of 400 kN (90 kips), as illustrated in Figure 3.

Furthermore, the design resistance of timber members can be significantly enhanced with transverse Figure 2. Applications of inclined glued-in rods. a) connections of built-up members, b) members in tension, reinforcement against splitting and c) lifting lug anchorage, d) rigid knee joint, e) ridge connection, f) column fixed base reinforcement. Dashed shear. These are desirable features lines are GIR’s. Recreated from TsNIISK Kucherenko.

STRUCTURE magazine

for engineers and architects who want aesthetically pleasing, versatile, 3-D structures with benefits for long-span structures, high fire resistance, or protection against corrosion.

While STS may not often need pre-drilling and can be quickly and easily installed in-situ with minimum precautions (avoiding over-driving and breaking the screws), glued-in rods require carefully controlled fabrication procedures, normally in a factory setting.

As opposed to the STS, where the fastener’s threads are directly engaged in mechanical grip with wood, Figure 3. High-capacity GIR joint with 400 kN (90 kips) capacity using inclined GIR welded to steel the bond between the glued-in rod and wood is cre- flange plates. Transverse GIR is for joint reinforcement. Courtesy of TSNIISK Kucherenko. ated utilizing an adhesive that forms a composite system (Figure 4). Consequently, each rod’s pull-out resistance greatly to “starving” bondlines where the adhesive is poured into a “botdepends on the quality and durability of the bond between the rod tomless” hole and does not surround the rod properly. Therefore, and the adhesive, between the adhesive and the wood substrate, and, European approvals of GIR joints are only valid for the CLT made obviously, on the adhesive itself. of edge-glued and ungrooved laminations. There are also special Numerous studies have investigated various restrictions on positioning the rods within adhesives, bondline thickness and length, rod CLT laminations and the penetration length materials and diameters, wood grain orientathat must be followed until more research data tion, heat and moisture resistance, creep, etc. becomes available.

Phenol-Resorcinol-Formaldehyde (PRF) has Rods been found unsuitable for GIR applications because of significant shrinkage and brittleness.

Threaded rods of low and medium carbon steel Adhesives that have been approved for GIR are with yield strengths between 250 and 380 MPa two-component polyurethanes and epoxies.

(36 ksi to 55 ksi), such as ASTM 1554 Grades Epoxies provide stiffer bondlines, which may 36 and 55, are currently recommended. The or may not be advantageous for the GIR joint lower strength allows designers to rely on rod performance, given stiffness compatibility with yielding as the governing failure mode, which Figure 4. Glued-in rod composite system. the wood substrate. Considering that Young’s Courtesy of Raphaël Bouchard. provides more predictable resistance indepenmodulus of wood is 20 to 30 times higher dent of load duration effects. Furthermore, in along the grain than in transverse direction, the distribution of cases such as seismic design, where it is necessary to avoid brittle stresses along the bondline and resistance and long-term performance failures, the performance of GIR joints should be limited by yielddepend significantly on the angle of insertion of the rod and load- ing of the rods. To ensure that rod yielding governs the design, ing direction. Design and fabrication of GIR connections require extra bonded length is provided for capacity protection because the sound knowledge and understanding of materials involved in this maximum ultimate strength of the steel is higher and may control. composite system to avoid dramatic mistakes. Basic guidelines are Overstrength factors between 1.2 and 2.1 have been proposed in discussed below.

Design and Production Guidelines Glued-in rods can be used with glulam, LVL, CLT, and solid wood panels.

Applications in softwood glulam timber are the most frequent today. Since CLT panels have gained momentum worldwide, efficient and reliable connections are often sought, especially for multi-story buildings. The fabrication and performance of GIR joints in CLT is an area of current study underway at Laval University in Quebec City, Quebec. If CLT is produced without edge-gluing of laminations, which is predominantly the case in the U.S. and Canada, special measures to avoid leakage of adhesive in the gaps between laminations are needed. The leaks lead

ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

Materials

FEB R U A R Y 2 021

the literature. It is currently proposed that the Adhesives design capacity of the bondline should be at least 50% greater than the design capacity of the rods.

In Europe, several manufacturers obtained their own When the design resistance of the joint is governed National Technical Assessment (NTA) and European by the rods, the design is essentially a steel conTechnical Assessment (ETA) reports on adhesives nection familiar to most designers. Threaded rods for bonding steel rods into wood building materiare easily connected to other steel parts using nuts als using either two-component polyurethanes or (Figure 5). Alternatively, ribbed reinforcing steel bars epoxies. Typically included in these reports are basic (rebar) present a very economical option. In coninformation on the adhesive properties, installation struction joints, rebar can be welded to other steel instructions, and specific design parameters, such parts (as shown in Figure 3), with certain precautions as characteristic pull-out strength as a function of to avoid burning the wood. In welded joints, the the bondline thickness and length, recommended portion of the bonded length within 3 diameters of minimum spacing, and limits of the bonded-in the rod near the weld should be discounted because length of the rods. In all cases, the installation must of overheating. be executed by specially trained authorized personnel Rods with diameters from 8 mm (5⁄16 inch) to Figure 5. Concept of a glulam in a controlled environment.

30 mm (13⁄16 inch) have been tested in GIR con- portal frame connection using steel Joint assembly nections. The most practical range of diameters threaded glued-in rods with a steel is between 12.5 mm (½ inch) and 20 mm (¾ connector weldment to allow bolted Because of the very high stiffness of GIR joints, there inch). The bonded length considered in design with assembly onsite. Threaded rods is little redistribution of forces between the rods softwood timber products is between 10 and 30 must be glued in factory conditions. until they start yielding. Therefore, nuts should be times the nominal rod diameter. Smaller diameters Adapted by Raphaël Bouchard from tightened uniformly using a torque-limiting wrench and shorter rods are impractical and can be easily Buchanan and Fairweather (1993). to close any initial gaps in the joints during the replaced by screws. Longer rods may be used when installation and induce equal tensile forces in the necessary to avoid stress concentrations, but length does not nec- rods. A study conducted by R. Bouchard at Laval University showed essarily increase the joint’s resistance in softwood timber products that a torque of 75 N.m (55 lb.ft) is sufficient to achieve the desired (Figure 6 ). More work is required to develop design methods to effect. Overtightening (snug-tight installation) may be harmful to account for the broad range of bonded lengths. Note also that drill- the joint performance because overtightening may cause excessive ing deep and large holes requires dedicated equipment that most prestressing of the bond line. Prestressing is not recommended for producers do not possess. low carbon steel.

Hole Diameters

Quality Control (Q.C.)

Some earlier studies focused on holes with smaller diameters, sometimes smaller than the nominal diameter of the thread, aiming at mechanical locking of the threads with wood and economical use of adhesive. It has been established that the thickness of the bondline does not significantly affect the joint’s performance.

However, the oversize of the hole does affect the ease and accuracy of installation and the amount of adhesive used. Currently, recommended hole diameters are between 2 mm (1⁄16 inch) and 6 mm (¼ inch) larger than the rod diameter. Holes of smaller diameters are not recommended.

Thorough quality control is a key in the GIR technology, especially when the structure’s integrity relies upon high-capacity rigid joints.

As in any gluing process, the components’ surface preparation is of primary importance: the rods and holes in timber must be clean and dry, free of rust, grease, and dust. It is essential to avoid overheating the wood when drilling the holes.

The timing of the gluing operations and the ambient and surface temperature must be within limits imposed by the adhesive supplier. Any deviation from the prescribed procedures may compromise the bond’s quality and put the finished structure at risk of catastrophic failure.

Since the glued joints are hidden inside the wood, visual inspection is difficult. Unless elaborate (and expensive) NDT techniques are employed, the bond’s true quality remains uncertain. At a minimum, the quality of the cured adhesive should be tested for every batch during fabrication according to a Q.C. plan.■ References are included in the PDF version of the article at STRUCTUREmag.org.

Alex Salenikovich is a Professor of Timber Engineering at Laval University in Quebec. (alexander.salenikovich@sbf.ulaval.ca)

Figure 6. The approximate behavior of GIR showing axial yielding of rods with sufficient bonded length.

STRUCTURE magazine

David Moses is a Structural Engineer and owner of Moses Structural Engineers Inc. (dmoses@mosesstructures.com)

BUILD LONG LASTING STRUCTURES WITH POWER PRESERVED GLULAM®

STRONG, DURABLE,

SUSTAINABLE

POWER PRESERVED GLULAM® FEATURES • Manufactured with superior strength southern yellow pine MSR Lumber.

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

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

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

• 25-year warranty from the treater.

WWW.CANFOR.COM |

800.221.BEAM | W W W . A N T H O N Y F O R E S T. C O M

Anthony Forest Products is part of the Canfor Group of Companies ©

Anthony Forest Products Company, LLC

C

an a building’s structure enhance the human interactions that occur within and communicate its raison d'être to those outside its walls? These are the ideas that shaped the design of Building 201 at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, the nation’s largest University Affiliated Research Center. The result is an innovative structure that promotes collaboration and embraces the sense of the unknown inherent to revolutionary scientific research.

A Revolutionary Workplace for Scientific Discovery Building 201 serves as the flagship facility for the Research and Exploratory Development Department (REDD) at APL, a multidisciplinary group of researchers whose work in hard science, engineering, and advanced fabrication drives groundbreaking discoveries at the Laboratory. Innovation at REDD is powered by teams of scientists and engineers drawn from across a broad spectrum of disciplines. Consequently, promoting collaboration and physical connection throughout the 263,000-square-foot building was the primary design objective. Because REDD is mission-focused, its needs for specialized laboratories, manufacturing facilities, and offices are continually evolving. In response to these challenges, CannonDesign and APL created a building that promotes collaboration, provides for maximum future flexibility, and reflects the critical research that occurs within.

Supporting the Mission Steel framing provides the structure for the ornamental stairs and bridges that span across the skylit central atrium.

The structural design of Building 201 supports the core functions of scientific discovery, which depends on partnership, cross-disciplinary collaboration, and efficiency. Research and fabrication facilities occupy an L-shaped wing along the south and west sides of the

STRUCTURE AS A STATEMENT Johns Hopkins University Applied Physics Laboratory Building 201

The “flying” fourth floor, supported by concrete-filled HSS columns and cantilevered plate girders, is perched 45 feet above the entrance plaza.

STRUCTURE magazine

By John Roach, P.E.

building, while offices, dry labs, and conference rooms are housed in separate wings along the north and east. At the center of the complex is a five-story atrium, which connects each of these intertwined zones.

To accommodate constantly evolving research needs, laboratory and office spaces are based on the Universal Grid, a structural configuration consisting of 31.5-foot square bays that can be subdivided into 10.5-foot planning modules for nearly unlimited flexibility.

With a floor-to-floor height of 15 feet, a two-way concrete flat slab was selected for the structural system of both the laboratory and office wings, which maximized the available overhead space for the intense concentration of mechanical, electrical, and plumbing systems serving the area.

APL required that each floor’s long-term live load deflection not exceed L/480 and established stringent Vibration Criteria (VC) for all lab spaces. To meet these requirements, CannonDesign structural engineers used RAM Concept to design a 14-inch-thick reinforced concrete slab in both the laboratory and office wings, which allows the latter to be quickly converted into research space as future needs dictate. Vibration consultant Colin Gordon Associates (CGA) used proprietary finite element modeling software to validate the design

for both VC-A and VC-B performance, which correspond to acceleration limits of 2000 μ-in/s and 1000 μ-in/s, respectively.

At the east wing, multi-bay conference rooms, closely spaced stair and mechanical shafts, and a two-story auditorium made reinforced concrete construction impractical. Instead, a steel frame structure is used throughout this five-story section of the building, separated from the concrete portion by an expansion joint to accommodate differential movement. Three, five-foot-deep steel transfer girders, each weighing 20,000 pounds, span 60 feet across the auditorium. The design approach of varying the structural system according to programmatic requirements helped reduce costs and maximize constructability.

Bridging the Divide The heart of Building 201 is a five-story skylit atrium that links each part of the complex and emphasizes the role of structure in making unique connections between spaces and people. On each floor along the south side of the atrium, the two-way slab cantilevers 10 feet into the open volume, providing a path for circulation and a “gallery corridor” that offers views into the laboratory spaces. Seven bridges span the width of the atrium from the gallery corridor to the north wing to promote cross-disciplinary collaboration and encourage informal encounters.

Several structural challenges added complexity to the bridge design.

First, each bridge is skewed relative to the Universal Grid structure, resulting in spans that exceed 40 feet. Additionally, five ornamental stairs that connect the bridges to one another are oriented at severe angles, which adds complexity to their support conditions. Finally, the south end of each bridge begins at the tip of the cantilevered gallery corridor, while the north supports occur at a building expansion joint.

CannonDesign evaluated several alternatives for the bridge construction, including cast-in-place concrete, prestressed concrete, and steel

OF

Concrete and steel are interwoven throughout Building 201 to maximize each material’s structural efficiency.

to minimize the impact of differential deflections between floors and across the width of each bridge. The stair and footbridge provisions of the American Institute of Steel Construction’s (AISC) Design Guide 11, Vibrations of Steel Framed Structures Due to Human Activity, provided initial vibration design criteria, which was further refined by finite element analysis. Heavy W14 girders with a composite slab were used to satisfy these requirements while holding the structural depth to only 22 inches.

Telling a Story Through Structure Alluding to the transparency and objectivity that drives the process of scientific discovery, architecturally exposed structural steel and concrete are prominently featured throughout the building. At the atrium, these materials are intertwined with one another in the same way that individuals and building functions blend together in the same space. At the perimeter, five-story monolithic shear walls with a board-formed finish visually anchor this vast open space.

Self-consolidating concrete (SCC) was used in each wall to preserve the grain and texture of the wood formwork.

The defining feature of Building 201 is the “flying” fourth floor at the north wing. Here, the lower three floors of the structure end at an outdoor courtyard while the fourth level transitions from concrete to steel framing and continues another 150 feet. This upper floor is supported by seven, asymmetrically arranged, three-story columns that serve as a physical metaphor for the core mission of the REDD team at APL: bringing together diverse teams for one common purpose.

While the building’s interior embodies transparency through structural expression, the flying fourth floor serves as a counterpoint by instead emphasizing mystery. When viewed from below, the structure seems to float in space. The steel columns, which appear impossibly slender, are composite HSS sections filled with reinforced, 10,000 psi SCC to maintain a less than 50% demandcapacity ratio. The underside of the flying fourth floor features a mirror-like stainless steel surface. To someone looking up from the ground, the reflected columns appear to extend infinitely through the building itself.

Seven five-foot-deep steel plate girders span between the columns, concealed behind the mirrored surface. Weighing nearly 50,000 pounds, the girders cantilever up to 27 feet to the west and 15

pUrpOSe

framing. The limitations of cast-in-place concrete became evident early in the process due to the span-to-depth ratio that would have been required to limit deflection. Furthermore, site-cast concrete would have required the construction of multistory formwork and scaffolding, which was both impractical and detrimental to the construction schedule. The alternative of using site-cast prestressed concrete slabs would eliminate the challenges posed by deflection and formwork, but craning the 80,000-pound slabs into the center of the building was determined to be impractical. This left steel framing as the most viable alternative.

The cantilevered slab of the gallery corridor is interrupted by each bridge structure so that each span begins at the first interior line of columns. Each bridge girder bears in a shear wall pocket or on a W12x72 beam encased in concrete, rather than a structural concrete beam, to simplify the connections at this end and minimize structural depth. At the north expansion joint, each bridge girder bears on a polytetrafluoroethylene (PTFE) pad supported by a concrete corbel.

The design team used both RAM Structural System and RISA 3D to analyze the steel bridge and stair structures. Due to the complex configuration of the stairs and bridges and the location of the expansion joint, careful consideration of construction sequencing was necessary

FEB R U A R Y 2 021

feet to the north and south, enhancing the perception that the fourth floor is floating in space above the courtyard.

Their concealment, together with the mirrored surface above the columns, creates a skewed perspective of reality that alludes to REDD’s ethos: to see what everyone has seen and to think what no one has thought.

To capture the compound deflections of the multidirectional cantilever framing, the design team used RISA 3D to model and analyze the floor structure. Because this portion Highly textured, board-formed concrete of the structure lacks its own shear walls are prominently featured throughout the completed structure. lateral force-resisting system, both the steel framing and the composite slab diaphragm are designed to independently transfer wind and seismic loads into the north wing shear walls. Steel framing at the roof level is augmented by in-plane bracing, and spandrel beams serve as chord elements. These beams are encased within the SCC shear walls to provide load transfer, with headed studs welded to the steel engaging the vertical wall reinforcing.

Building for the Future APL Building 201 is a landmark facility that will accelerate discoveries by promoting collaboration within the scientific workplace. Therefore, it is fitting that close collaboration between its architects, engineers, and APL leadership drove this revolutionary design. Critical to this process and the successful completion of Building 201 is an appreciation that structure can shape human interaction and tell the story of a building and its purpose in subtle but important ways. In this way, Building 201 will provide APL with one more tool as it carries out its mission to solve the most complex technical, engineering, and scientific challenges facing the nation.■ John Roach is a Structural Engineer with the Buffalo office of CannonDesign. (jroach@cannondesign.com)

Project Team Owner: Johns Hopkins University Applied Physics Laboratory Structural Engineer: CannonDesign, Buffalo, NY Architect: CannonDesign Arlington, VA, and Chicago, IL Lab Planning: CannonDesign Arlington, VA, and Boston, MA MEP/FP Engineer: CannonDesign St. Louis, MO, and Buffalo, NY Vibration and Acoustical Consultant: Colin Gordon Associates, Brisbane, CA

ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

PROJECT GALLERY 250 inspiring photos from a range of applications newmill.com/gallery

Smarter school design

Photo credit: Project Frog, Inc.

STEEL BUILDING SYSTEMS SOLVE YOUR TOP 5 CHALLENGES Steel joists and a combination of roof and floor deck systems create versatile open spaces, promote health and safety, control acoustics and elevate aesthetics while providing sustainable solutions. Bring greater knowledge to the design, construction and performance of your next education project.

GET THE TOP 5 GUIDE [ newmill.com/education CONTROL ACOUSTICS Manage acoustics with composite floor deck newmill.com/nrc

STRUCTURE magazine

historic STRUCTURES Tariffville Bridge Disaster

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

T

he Connecticut Western Railroad was chartered on June 25, 1868, to run from Hartford, Connecticut to the New York State line at Salisbury, where it was

planned to connect with the Dutchess & Columbia Railroad in New York State near Millerton, NY. It would then connect to the New York & Harlem Extension railroad running northerly out of New York City towards Albany, NY. It was completed on December 21, 1871, with many of its bridges being wood and iron Howe Trusses, even though many railroads had adopted iron bridges by this date. Tariffville was a small town west of Hartford and located in a bend in the Farmington River that generally flowed eastward into the Connecticut River.

Tariffville Bridge disaster.

The Railroad Commissioners described the bridge as: behind it, and the baggage car still further back in the river. The three “The structure was a through bridge of two similar spans, of the ordinary passenger cars on the east span were also forced into the opening by the Howe truss pattern, each span 163 feet in length between extreme panel momentum of the train behind them, the first one being turned to a points, and some ten feet above the water of the river… The bridge, position nearly at right angles with the bridge, and the second and third built in 1870… uncovered and unpainted. Its diagonal braces, top and left with their forward ends in the river and their rear platforms against bottom chords, were of yellow pine, and vertical suspension rods of the center pier. The remaining six cars of the train were uninjured.” wrought iron. Each span consisted of 16 panels of 10 feet 2 inches each, The Hartford Courant described the collapse more emotionally or in all a few inches less than 163 feet. Height between chords, 20 feet. as follows, Upper chord composed of two pieces 6 x 11 inches, and two pieces 7 x “The first locomotive had cleared the west span, and entered upon 11 inches, lower chord two pieces 6 x 14 inches, and two pieces 7 x 14 the trestlework, when the entire span gave way, breaking off immeinches. Main braces, two to each panel, 9 x11 inches; counter braces, one diately east of the heavy stone pier in the center of the river. As the to each panel, 7 x 8 inches. Floor beams, 6 x 12 inches, 14 feet in the structure gave way, the first locomotive was hurled violently over, and clear between chords. One track stringer 10 x 11 inches under each rail.” embedding itself in the ground was completely wrecked. The other The Commissioner’s description went on to detail the sizes and engine and the baggage car went down with the wreck in an upright locations of the suspension rods. Sizes ranged from 1¼ inches to 17⁄8 position, and the side of the heavy truss fell over upon them. The inches. None of the rods had enlarged or upset ends, but the cutting first passenger car was whirled around and sank to the bottom of the of threads in the rods reduced diameters by ¼ inch or more. river, lying nearly in a parallel direction with the stream. The second On January 14, 1878, about seven passenger car went down end foremost years after the bridge opened, a train upon the first car, smashing the larger consisting of two locomotives and eight portion of it into kindling wood, the It is clear that different people passenger cars running westerly from rear end of the car resting upon the Hartford and ½ mile west of Tariffville bridge. The next car occupied a similar placed the blame for the collapse Station started to cross the bridge at a position but swerved more to the left on the railroad company, the speed estimated at six to eight miles per and therefore did not rest upon the car bridge designers and builders, the hour. The locomotives and cars passed in front of it. over the easterly span safely, and the None of the remaining coaches left the maintenance and inspection corps, forward engine just reached the western track. The crash produced by the fall, a derailment, and more. abutment, “when suddenly a snapping and the cries of the wounded and dying, was heard and a sense of sinking experispeedily brought assistance, but the firstenced by those in charge of the engines comers worked at a great disadvantage. and baggage cars and by the occupants of the forward passenger cars. The cars had broken through the ice, which rendered it difficult to Then a fearful crash and fall of the bridge carrying with it engine approach near enough to reach the passengers. But all worked with a will.” tender, baggage, and three passenger cars causing the death of thirteen As was usual in these cases, a Coroner’s Jury was convened and they persons and wounding and injuring many others.” visited the site between January 22nd and February 12th. “A large The Annual Report of the Railroad Commissioners of Connecticut number of witnesses were examined, not only of persons on the described the crash as, “Both the trusses of the west span, with the two train, or who were connected with the railroad but also of experts locomotives and baggage car thereon, immediately fell together towards and scientific men, bridge-builders, civil and mechanical engineers, the south, the forward locomotive being overturned and leaving its ash- from various parts of the country in this and adjoining states.” They, 8 pan on the abutment, the second locomotive landing on the ground just out of 12 jurors, concluded the following, as taken from their report.

STRUCTURE magazine

1) We are of the opinion that no blame or censure can be justly charged upon the conductor of the fated train, or any of those associated with and aiding him in running it, but on the contrary have before us the most abundant evidence of the constant carefulness and watchful solicitude of Conductor Elmo, Superintendent Jones, and their subordinates on the eventful night.

2) We have not the least evidence to lend us to believe that the bridge had been tampered with for the purpose of wrecking the train, or for any other purpose.

3) We have not sufficient evidence to lead us to believe that there was any derailment, either of engines or cars, but, on the contrary, all were moving along smoothly when a sudden crash of the bridge was heard and felt, with a simultaneous sense of sinking.

4) We are of the opinion that placing an additional engine on the track in advance of the train, or the uniting and running two engines together, when deemed necessary, is not at all censurable, but that, in the language of a witness of large experience and intelligence, ‘Any bridge that would not carry two locomotives ought not to carry one.’

5) We are of the opinion that if the materials of the bridge at the time of its construction were of suitable quality, quantity, and proportion to fulfill all of its requirements, they had at the time of the disaster become deteriorated; that the iron suspension rods, from being overstrained or from some other cause, had lost their tension and sustaining power; that the timber of the chords from many years exposure to the action of the elements without covering or paint, had become weakened by decay to such an extent as to render the bridge unsafe and unfit for the purpose for which it was constructed; and that the disaster was occasioned by the heavy train passing over a bridge thus rendered dangerously weak and defective.

6) We, therefore, find that the responsibility of this sad disaster largely rests upon the directors of the Connecticut Western Railroad Company and that they are deserving of censure for allowing the use of a bridge for railroad purposes after its materials had become defective to the point of danger, and for permitting so many years to pass without covering, strengthening, and preparing the same in such a manner as not to jeopardize human life.

“In conclusion…it is time to take a new departure; that in their construction the eternal principles of nature’s laws should not be violated; and that in their management all from the highest official to the lowest operative, should at times be held to a strict accountability.

Upon the directors especially rests a weight of responsibility which they cannot shake off; they have assumed duties which they cannot shirk. These duties are not fully discharged by attending only to the financial affairs of the company. …To them is committed the most sacred of all trusts – the freight of human life! For its safe transportation, they should be held accountable; and this disaster should remind them that eternal vigilance is the price of safety.”

The other four non-majority jurors concluded, “In our opinion, from the evidence, the bridge at the time of the disaster was in a safe condition for the passage of trains, whether consisting of one or more engines. And we further believe that the same was constructed upon thorough scientific principles, and we do not believe that it had become deteriorated by exposure to the elements sufficient to weaken the same to a point of danger. We also believe by the numerous tests of the iron that it is of good quality and that the same had not been overstrained sufficiently to cause any weakening or danger therefrom. We have had sufficient evidence to believe that there was a derailment of some portion of the train, and if so, by falling upon the timbers of the bridge, or coming in contact with the side of the same, would in either case, in our opinion, cause a severe shock, sufficient to cause the structure to fall.”

The Railroad Commissioners concluded, after writing a lengthy report on the bridge and its failure,

“The principal lesson, therefore, taught by the Tariffville disaster is the necessity of larger suspension rods than those heretofore used in most of the wooden railroad bridges of the State. If, in that bridge, the broken rods had been one-quarter inch larger in diameter with upset ends, their area and efficiency would have been nearly doubled, their liability to breakage correspondingly diminished, and their strength nearer the standard recommended by the best engineers. They were, however, fully equal in size and strength to the general average of rods used on other similar bridges in the State. At the time of the accident, this Board was not empowered by law to order any changes of construction to increase the safety of bridges or other railroad structures, but simply “to recommend from time to time the adoption of such measures and regulations as they may deem conducive to the public safety and interest.”

Mansfield Merriman, a well-known professor of civil engineering at Yale and Lehigh, concluded in a letter to the Courant, “In short, the designers of this bridge violated mathematical calculation and engineering precedent; to save the money which a few pounds of iron would have cost, human lives were daily put in danger. Wooden bridges are usually covered to protect them from the action of the rain, ice, and snow; but this was left exposed for six years until the upper chord became rotten enough to give way under a fraction of the strain which it was intended to support, and no steps were taken to repair it.

Not even the iron rods were painted. To save the money which repairs would have cost, the lives of passengers were daily risked. It was not properly inspected by a commission which has examined it every year since its erection on behalf of the State. An efficient inspection would have discovered the defective tie-rods six years ago; an effective inspection would not have allowed it to remain exposed to the action of the weather for six successive years; an intelligent inspection would have detected and repaired the rotten timbers. For the lack of such inspection, human lives were lost. The immediate responsibility for the accident must fall upon the officers of the railroad company, not for running two locomotives over the bridge, but for building such a structure and neglecting to keep it in repair. But the State of Connecticut is also responsible for sanctioning, as it has done annually by its railroad commissioners, the use of such an ill-proportioned and unsound bridge.”

It is clear that different people placed the blame for the collapse on the railroad company, the bridge designers and builders, the maintenance and inspection corps, a derailment, and more. The New York Times in its August 17, 1878 issue wrote, under a headline – A BRIDGE DISASTER EXPLAINED, “At the time of the inquest it was held that, if the car was off the track, the engineers and passengers would have noticed it, but with the experience of Satan’s Kingdom [a local name for the area] it is now firmly believed that the car derailed on the Tariffville wooden bridge and the wheels striking the weak timbers let the span down. This exploded the theory that the bridge had been tampered with, which was prevalent at the time of the accident.”

Despite this failure, the Howe Truss was still used on many railroads and roadways around the country well into the 20th century. Like the iron bridge builders, the builders of most of the Howe Trusses adopted the upsetting of threaded tension bars such that the cross-sectional area of the bars at the root of the threads was equal to or greater than the cross-section of the main bar.

The Western Connecticut Railroad went bankrupt in 1880 after it settled with families of the 13 victims for an amount varying from $200-$600 per person. The lesson learned is the importance of inspection of wooden bridges.■ Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19 t h Century cast and wrought iron bridges. He is now an Independent Consulting Engineer. (fgriggsjr@twc.com) FEBRUARY 2021

education ISSUES Bringing Real-World Experience into the Classroom

By Mark Kanonik, P.E., F.ASCE

In

2019, the American Society of Civil Engineers (ASCE) published the Civil Engineering Body of Knowledge (CEBOK, 3rd ed.), which “defines the set of knowledge, skills, and attitudes necessary for entry into the practice of civil engineering at the professional level.” ASCE acknowledges that the “fulfillment of the CEBOK must include both formal education and mentored experience.” Indeed, the CEBOK lists 21 desired outcomes, although 14 cannot be achieved without mentored experience after or separate from formal classroom experience. In 2019, ASCE also hosted the Education Summit: Mapping the Future of Civil Engineering Education. In the proceedings published in August 2020, the Summit listed four objectives of future engineering education; Objective 2 is to “Elevate professional skills to a truly equal footing with technical skills.”

Employers expect graduates to correctly perform the calculations necessary to design beams and columns, and footings. Still, many employers feel that recent graduates lack the ability to apply these calculations to real-world problems where the general solution is not obvious.

Today’s economic reality is that employers expect recent graduates to be immediately billable and productive workers who can effectively apply the theoretical knowledge gained in the classroom to the projects on their desks.

The author recently conducted an unscientific review of 96 open faculty positions posted on the ASCE website and noted that only two required licensure for appointment. However, eight stated that licensure was “preferred.”

Another recent and unscientific review of the first 10 civil engineering programs in New York State listed by Google showed that only 10 of 212 faculty are licensed, as reported on their respective college’s website. It is disappointing that more faculty are known by the author to be licensed even though their respective college websites do not acknowledge this. Why does the “engineering education system” place such little value in the licensure of its faculty when students are so strongly encouraged to become licensed after graduation?

The author acknowledges that requiring all faculty to be licensed or even to have experience outside of academia is unrealistic. Perhaps a reasonable middle-ground is to employ adjuncts in the classroom. Most students study structural engineering because they want to improve the built environment. They long to STRUCTURE magazine

see how the abstract concepts learned in the classroom can be applied to actual projects with all of their unexpected complications. Often, it is the adjunct who is most apt to bring that project experience into the classroom. Many

“

It has been said that a picture is worth a thousand words, but a visit to a construction site is worth a thousand pictures in a PowerPoint presentation.

adjuncts have years of meaningful experience, and they view teaching as one way to “give back” to the profession. They bring the experience that students want but that many faculty cannot provide. Adjuncts cannot and should not replace full-time faculty, but adjuncts can and do complement full-time faculty by bridging the gap between academics and experience.

Most structural engineering classwork is very matter-of-fact. Often homework problems are structured to guide students to a particular answer, such as the lightest-weight beam to support a given load. But structural engineers design buildings (and other complex structures, too), which are more than just a collection of individual elements. And there is rarely, if ever, one and only one correct answer to any real-world engineering problem. Computer programs are incredibly sophisticated, allowing structural engineers to design buildings that could not have been conceived a generation earlier. But these same computer programs cannot conceptualize. They cannot locate the columns in a building, and they cannot determine if the building should be framed in steel or concrete or some other material. Such conceptual thinking is typically gained through years of experience.

Still, conceptual thinking can also be taught, most effectively by an adjunct who interacts with the architects who design buildings and the contractors who build them. Nearly all civil engineering programs culminate in a designintensive capstone project, in which the students work on projects meant to simulate professional

practice. What better opportunity to engage an adjunct who can demonstrate what actual professional practice entails?

Structural engineers spend much of their time producing construction documents, yet little if any coursework is devoted to this.

This seems counter-intuitive since construction documents are part of a legally binding agreement with significant potential risks.

Rarely do buildings collapse because of a gross error, but many construction projects have become legal battlegrounds over inadequate drawings and specifications. Yet adjuncts, with their years of experience, know full well the importance of proper construction documents and can explain the subtle nuances that make a successful set of documents. Since calculations are not usually included with the construction documents, students must understand how abstract calculations become a physical building based on construction documents that they will ultimately develop.

Adjuncts are also likely to have close contacts within the industry outside of the classroom.

Students spend considerable time calculating the potential failure mechanisms of a bolted connection. However, nothing explains the actual working of that connection like going to a steel fabrication shop and seeing it in person. Learning the difference between mortar and grout is much easier when the students build a masonry wall with a trowel in hand. It has been said that a picture is worth a thousand words, but a visit to a construction site is worth a thousand pictures in a PowerPoint presentation.

Certainly, a thorough understanding of the subject matter is necessary to teach at the college level, but one does not need to be a worldrenowned expert to be an effective adjunct.

The primary requirement for being an adjunct is simply a willingness to teach. There is an investment in time and energy, particularly the first year, but the benefits far outweigh the costs.

The author’s sincere wish is that many readers become actively involved in educating the next generation of structural engineers. No less than the future of the profession of structural engineering is at stake.■ Mark Kanonik is the National Technical Director of Structural Engineering at EYP Architecture & Engineering, PC, in Albany, NY. He is also an Adjunct Faculty at Rensselaer Polytechnic Institute in Troy, NY. (mkanonik@eypae.com) F E B R U A R Y 2 0 21

DOING BUSINESS JUST GOT EASIER

NEW APP

NOW AVAILABLE Features include: - Submit quick quote requests - Calculate the weight of your material needs - Contact your sales representative Stay tuned...more features coming soon!

WWW.NUCORTUBULAR.COM

BUSINESS practices How to Recession-Proof Your Engineering Career

By Stephanie Slocum, P.E., in collaboration with SEI’s Business Practices Committee

T

here is a skillset that makes your engineering career “recession-resistant.” That skillset is basic business development and has proven value to ALL structural engineering firms. Yet, many engineers actively avoid learning it for a variety of reasons.

This article explores why engineers with this skillset have an advantage, why learning these skills is of increased urgency in uncertain economic times, and how engineers can improve their skills.

Engineers with business-development skills have more options and job security than those that do not. The AEC industry – and by extension structural engineering – is known for being cyclical. Engineers with technical expertise are in high demand in boom times. In economic downturns, Management makes tough choices to reduce staff to match projected reduced workloads. Engineers identified as having a long-term benefit to the firm have a leg-up when making these decisions.

As someone who recently turned 40, the author has experienced a completed cycle three times to date, beginning with the 1999 dot-com bust. Recently, the COVID-19 pandemic has created new economic uncertainty.

When the 2008 recession began, project managers with direct client relationships were asked to help bring in new business and take over business development responsibilities, while pure business development staff was dismissed. This concept is not new and is often referred to as the “Seller-Doer” model. The Society for Marketing and Professional Services (SMPS) defines the seller-doer model as: “…technical staff who are also responsible for billable hours, and, to some degree, for securing contracts or projects for their firms, either through repeat clients or fostering relationships with new clients.”

This model is prevalent throughout the industry, largely because clients are demanding it. It is estimated that 84% of engineering, 70% of architecture, and 66% of construction firms use this model. There is a proven financial benefit; firms using this model are more likely to be high-performing, averaging at least 14% greater operating profits on net revenue than other AEC firms (41 st Annual Deltek Clarity Architecture & Engineering Industry Study, Data collected 1.21.20-3.23.20).

History shows us that the seller-doer’s role increases during uncertain economic times and that candidates with these skill sets are more difficult to find than strictly technical STRUCTURE magazine

engineers. There is also a perception that employers can always find someone with technical expertise when work picks up again.

Although technology has dramatically increased the speed of some design aspects, it cannot rekindle a broken client relationship or nurture a new client relationship. As a result, engineers with business development skills have a significant advantage over those only comfortable sitting behind a computer during periods of economic uncertainly.

“

In times of economic uncertainties, a focus on business development and client relationships keeps the doors of engineering firms open.

Structural engineering leaders share how important this skillset is: “Engineers with great communication skills, a sense of the importance of teamwork, and good personal relationship skills are extremely important. These employees make every interaction with clients – day in, day out – a business development opportunity.

Engineering is a service business, and the best way to create repeat clients is to exceed their expectations on the level of service.” – Mary Kay Knight, P.E., Principal, Uzun+Case LLC “We try hard to encourage all of our team members to understand and to embrace the fact that every interaction is a sales call. The best client is a repeat client. That makes your best business developers the project managers in charge of making projects successful.

This means the ability to develop a genuine business relationship, to be seen as a trusted advisor, and partner.” – Scott Rosemann, P.E., COO, and Structural Engineering Director, Rosemann & Associates, P.C. It is never too early or late to learn business development skills. Primary functions of seller-doers include participating in client meetings and presentations, writing proposals, and participating in organizations that provide opportunities for client interaction.

Seller-doers may also author articles for client publications, attend networking events, or provide content for their firms’ websites.

Learning these skills takes time. But what if you are an engineer who knows they cannot afford to wait to start honing their business development skills?

“Get involved with local structural engineering associations and allied groups such as civil engineers, builders, contractors, and architects. Network with industry people, develop contacts, and nurture those relationships to last lifetime.” – Arpan B. Tailor, M.S., P.E., S.E., Arun, Inc. Do not wait to take action on business development. In times of economic uncertainties, a focus on business development and client relationships keeps the doors of engineering firms open. Many engineers have worked at multiple firms or have clients with whom they have lost touch. Now is the time to be transparent about the relationships you have developed and rekindle them if needed.

A quick email to a client you have not spoken to recently, with a focus on service first, is a great start.

As an individual engineer, you can reach out to those clients and demonstrate that you care about them as a person or share something valuable, like a link to a newly advertised project of interest. You can also talk to your employer about how best to leverage existing relationships.

If you are an employer, do not rely on your monthly client newsletter or business development staff to keep these relationships strong.

Empower the engineers who work directly with your clients on a daily basis to set aside time each week to focus on nurturing those relationships beyond the transactional. Not sure where to start? Ask them to send a personalized (preferably handwritten) note of gratitude to a client. Stress is currently high for everyone. A simple, thoughtful act helps your firm stand out when the number of available new projects dwindles.

This article is the author’s opinion and is a collaboration of the SEI Business Practices Committee, of which the author is the Chair. If you would like to learn more about this topic, please see this FREE video presentation at https://youtu.be/gZHLx3Zoy84.■ Stephanie Slocum is the Founder of Engineers Rising LLC. She presently chairs the SEI Business Practices Committee and serves on the SEI Board of Governors. (stephanie@engineersrising.com)

F E B R U A R Y 2 0 21

“An NCEES Record makes it fast, easy, and convenient to apply for additional P.E. licenses in other states.”

Alexander Zuendt, P.E. Zuendt Engineering Record holder since 2011

RECORDS Establishing an NCEES Record is the most efficient way to complete the licensure process in multiple states. Once established, an NCEES Record will include most—if not all—of the materials you need to apply for comity licensure in additional states and territories. If you are a Council Record holder, NCEES will electronically submit your materials directly to the state licensing board on your behalf each time you apply for a license. This saves time and simplifies the application process when you need to practice in multiple states.

Record no. 46864

Build your NCEES Record today. ncees.org/records

NCSEA NCSEA News

National Council of Structural Engineers Associations NCSEA Corporate Members

ASSOCIATE MEMBERS

Nationally recognized bodies that are associated with the practice of structural engineering, or companies who provide supplies or services to structural engineers.

AECDaily Corporation AISC American Wood Council Atlas Tube AZZ Galvanizing Services Blind Bolt Cantsink Cast Connex Corporation Chicago Clamp Company Commercial Metals Company Copper Creek Companies, Inc. CoreBrace DBM VirCon DeWALT Dlubal Software Inc. Fabreeka International, Inc. Fox Rothschild LLP Freyssinet, Inc. GIZA Steel

Graitec GRM Custom Products Headed Reinforcement Corporation Hilti, Inc. Hubbell Power Systems (CHANCE) International Code Council International Masonry Institute ITW Commercial Construction Jordahl USA Inc. Kinemetrics Lindapter USA LNA Solutions MeadowBurke Metal Building Manufacturers Assoc.

Mitek Builder Products National Ready Mixed Concrete Assoc.

Nelson Stud Welding New Millennium Building Systems Nucor

Peikko Pieresearch Post-Tensioning Institute PROSOCO/CTP RISA Technologies Schneider Structural Eng., Inc. SE Solutions, LLC SidePlate Systems, Inc. Simpson Strong-Tie SkyCiv Steel Deck Institute Steel Joist Institute Steel Tube Institute Taylor Devices Trimble USG Corporation - Structural Solutions Vector Corrosion Technologies Vitruvius Project

SUSTAINING MEMBERS

Structural engineering firms, firms that employ structural engineers, or individual professional engineers practicing structural engineering.

4x Engineering Allan Klein PA Consulting Engineer ARW Engineers ASC Engineers Inc Barter & Associates, Inc. Burns & McDonnell C.A. Pretzer Associates, Inc. Case Engineering, Inc. Collins Engineers, Inc. Cowen Associates Consulting Structural Engineers Criser Troutman Tanner Consulting Engineers CSA Engineering Davis Patrikios Criswell, Inc. Deems Structural Engineering Degenkolb Engineers DiBlasi Associates, P.C. Dominick R. Pilla Associates DrJ Engineering, LLC ECM

Engineering Solutions, LLC Gilsanz Murray Steficek Haines Structural Group Haskell Heyer Engineering Holmes Culley Holmes Structures HSI - Home Structural Inc. Ian Hoff Design IBI Group Engineering Services Inc. Indurkar Structural Engineers J Welch Engineering LLC James Andel, P.E. Joe DeReuil Associates JVC Engineering Krech Ojard & Associates Lance Engineering LLC Larson Engineering, Inc. LBYD, Inc. Mainland Engineering Consultants Corp Mainstay Engineering Group, Inc.

Morabito Consultants, Inc. Mortier Ang Engineers O'Donnell & Naccarato, Inc. Omega Structural Engineers, PLLC Ruby & Associates, Inc. Schaefer Schultz Burman Engineering, PLLC Simpson, Gumpertz & Heger Stability Engineering STV, Inc. TEG Engineering, LLC TGRWA, LLC The Harman Group, Inc. Thornton Tomasetti Virginia A&E, PLLC Wallace Engineering WDP & Associates Willo Engineering LLC

Learn more about NCSEA's Corporate Memberships by visiting www.ncsea.com.

STRUCTURE magazine

News from the National Council of Structural Engineers Associations Call for 2021 Structural Engineering Summit Abstracts The Structural Engineering Summit Committee is seeking presentations for the 2021 Summit in New York, NY, October 12–15, 2021. Ideal presentations are between 45 and 90 minutes and deliver pertinent and useful information that is specific to the practicing structural engineer, in both technical and non-technical tracks. Submissions on best-design practices, new codes and standards, recent projects, advanced analysis techniques, management, business practices, the future of the profession, and other topics that would be of interest to practicing structural engineers are desired.

Submit your abstract by April 2, 2021. Visit bit.ly/2021SESabstracts for more details.

Volunteer for an NCSEA Committee

NCSEA has a variety of committees that work to further the association’s mission to constantly improve the level of standard of practice of the structural engineering profession throughout the United States, and to provide an identifiable resource for those needing communication with the profession.

NCSEA SEA members may apply for committee positions throughout the year using the online Volunteer Application. Most committees admit new members on a rolling basis while others add members only once per year. Once submitted, the application will be reviewed to confirm Member Organization/SEA membership and then forwarded to the committee chair(s) for review. Please expect a response within 30 days.

Visit www.ncsea.com/committees to learn about NCSEA's Committees and to complete a volunteer application.

2021 Excellence in Structural Engineering Awards NCSEA's Excellence in Structural Engineering Awards annually highlights some of the best examples of structural engineering ingenuity throughout the world. Projects are judged on innovative design, engineering achievement, and creativity. Multiple winners are presented in eight categories with an outstanding winner chosen from each category. The winners will be honored at NCSEA's Structural Engineering Summit in New York this October.

The awards are presented in the following categories: • New Buildings under $30 Million • New Buildings $30 Million to $80 Million • New Buildings $80 Million to $200 Million • New Buildings over $200 Million • New Bridges or Transportation Structures • Forensic/Renovation/Retrofit/Rehabilitation Structures under $20 Million • Forensic/Renovation/Retrofit/Rehabilitation Structures over $20 Million • Other Structures Entries are due on July 13, 2021. Structural engineers and structural engineering firms are encouraged to enter. More information about the awards along with submission instructions can be found on www.ncsea.com.

NCSEA Webinars

Outstanding Project Winner in the New Buildings $80 to $200 Million Category: International Spy Musuem – Washington, DC, submitted by SK&A

Register by visiting www.ncsea.com.

February 9, 2021

February 16, 2021

March 4, 2021

90 Seismic Ideas in 90 Minutes

Wind Load Effects on Canopy Systems

Overview of Changes and Additions in ACI 318-19

James Malley, S.E.

Medapati Abhinav Reddy, E.I.T

Royce Floyd, Ph.D., S.E.

This presentation will provide a rapid-fire series of ideas for engineers to consider in the implementation of seismic designs of new steel buildings.

Wind is one of the most important considerations while designing the structures. This topic tries to explore the wind load on canopy systems and its effect on them. Design and detailing of wind components is also included.

Discussion of technical changes to design provisions in the 2019 edition of the ACI 318 Building Code Requirements for Structural Concrete and an overview of the reorganization for the 2014 edition that carried over into 2019.

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

FEB R U A R Y 2 021

SEI Update Learning / Networking

SEI Virtual Events

www.asce.org/SEI/virtual-events • #SEILive Conversation with Leaders on Sustainability – Wednesday, February 3, 12:30 pm US ET • NEW – SEI Standards Series Join live, virtual sessions for exclusive interaction with expert ASCE/SEI Standard developers on state-of-the-market updates. Participants will learn about technical revisions and review a design example. Attendees are encouraged to join and participate in Live Q&A. Each session is LIVE and only available 1:00 – 2:30 pm US ET. March 18 – ASCE/SEI 43 May 20 – ASCE/SEI 49 July 15 – ASCE/SEI 72 September 16 – ASCE/SEI 59 November 18 – ASCE/SEI 8

Seismic Design Criteria for Structures, Systems, and Components in Nuclear Facilities Wind Tunnel Testing for Buildings and Other Structures Athletic Field Lighting Blast Protection of Buildings Specification for the Design of Cold-Formed Stainless Steel Structural Members

Individual session: Member $49, Nonmember $99. Student member: Free registration.

REGISTER NOW at https://cutt.ly/9hQDTEo

Structures Virtual

Save the Date – June 2-4, 2021 Join SEI and the global structural engineering community as we expand our reach to advance structural engineering practice! We are saddened to have had to cancel Structures Congress in-person in Seattle in March and look forward to hosting you for an online event June 2-4 on the latest advances and new interactive technical/professional learning.

To sponsor, contact Sean Scully sscully@asce.org www.structurescongress.org

#StructuresVirtual21

The must attend triennial conference on the analysis, design, construction, and maintenance of electrical transmission line and substation structures and their foundations. View Program, including: • Pre-Conference Workshop on using ASCE/SEI Standards and Manuals of Practice for reliability and resiliency of power delivery systems • Expert Technical Session Topics: Wildfires, Case Studies/Projects, Design/Analysis, Lattice Towers, Managing Aging Infrastructure, Substations, Loading, Foundations, Special Design Considerations, SEI/ASCE Overhead Line Loading Standard • Fun Golf Scramble with colleagues and friends sponsored by Power Line Systems • Student Scholarship to participate – To be announced Sponsor/Exhibit – Book your space to reach transmission line and substation professionals. Contact Sean Scully sscully@asce.org

www.etsconference.org • #ETSC21

Errata STRUCTURE magazine

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI-Errata.

If you would like to submit errata, contact Kelly Dooley at kdooley@asce.org.

News of the Structural Engineering Institute of ASCE Advancing the Profession

Share lessons from structural failures, near misses, and incidents in order to not repeat them. Submit and review reports at www.cross-us.org.

Get Involved with your Local SEI Chapter

Connect with colleagues, take advantage of lifelong technical/professional learning, and advance structural engineering in your area. www.asce.org/SEILocal

Joint CASE, NCSEA, and SEI Virtual Town Hall February 23: For the Betterment of the Structural Engineering Profession

On Tuesday, February 23, 2:30 – 4:00pm CST, the leadership from the three organizations will host a virtual Joint Town Hall event to discuss how the three organizations are progressing to fulfill the Joint Vision, with Q&A with participants.

See full info and sign up for free registration on page 21.

Participate in Engineers Week: INSPIRING WONDER February 21-27

• Celebrate how engineers make a difference • Increase public dialogue about the need for engineers • Bring engineering to life for kids, educators, and parents For promotional materials, activities, and guidance visit www.asce.org/event/2021/engineers-week.

Celebrating 25 years of SEI – Advancing and serving structural engineering SEI News Read the latest at www.asce.org/SEINews SEI Standards Visit www.asce.org/SEIStandards to view ASCE 7 development cycle FEB R U A R Y 2 021

CASE in Point 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. 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!

CASE has several tools available for firms to use to enhance their business development processes: CASE 962-F CASE 962-H CASE 976-A CASE 504 Tool 5-4 Tool 7-1 Tool 7-2 Tool 8-1 Tool 8-2

A Guideline Addressing the Bidding and Construction Administration Phases for the Structural Engineer National Practice Guideline on Project and Business Risk Management Commentary on Value-Based Compensation for Structural Engineers Proposal Preparation Spreadsheet

Negotiation Talking Points Client Evaluation Fee Development Contract Review Contract Clauses and Commentary

CASE Popular Guideline Updated!

CASE has released a comprehensive update to their popular guideline, CASE 962-D: Guideline Addressing Coordination and Completeness of Structural Construction Documents. The guideline will assist the structural engineer of record (SER) and everyone involved with building design and construction in improving the process by which the owner is provided with a successfully completed project. Their intent is to help the practicing structural engineer understand the importance of preparing coordinated and complete construction documents and to provide guidance and direction toward achieving that goal.

This guideline focuses on the degree of completeness required in the structural construction documents (Documents) to achieve a “successfully completed project” and the communication and coordination required to reach that goal. They do not attempt to encompass the details of engineering design; instead, they provide a framework for the SER to develop a quality management process.

Currently, the coordination and completeness of Documents vary substantially within the structural engineering profession and among the various professional disciplines comprising the design team. The SER’s goal should be meeting both the owner’s and the contractor’s needs by producing a complete and coordinated set of Documents. Owners and contractors generally understand that some changes will occur because they realize that no set of Documents is perfect. The SER must focus on completeness, coordination, constructability, and the reduction of errors to minimize potential changes.

An overall comprehensive update was done to the Guideline to keep with best business practices and current industry standards.

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

ACEC’S Coalitions Virtual Winter Meeting

Join ACEC Coalitions for its 2021 Winter Education Series February 24-26, and you can earn 5 PDH credits! The three-day program features education sessions covering cybersecurity, business tax implementation, and communication/documentation in a remote work environment; briefing on ACEC leadership activities; and an economic outlook briefing.

Registration is free to Coalition members and only $179 for ACEC members and $279 for non-members.

Go to https://education.acec.org/diweb/catalog/item?id=6190547 to check out the three-day agenda and to register.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

STRUCTURE magazine

News of the Coalition of American Structural Engineers DONATE to the CASE Scholarship Fund!

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.

Since 2009, the CASE Scholarship program has given $34,500 to help engineering students pave their way to a bright future in structural engineering.

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 the ability of students to pursue their dreams to become professional engineers is to offer incentives in educational support.

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 don’t have to be an ACEC member to donate!

Donate today at www.acecresearchinstitute.org/scholarships.

WANTED: Engineers to Lead, Direct, Engage with CASE Committees!

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 – Committee is responsible for developing and maintaining contracts to assist practicing engineers with risk management.

Guidelines – Committee will be responsible for developing and maintaining national guidelines of practice for structural engineers.

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

Toolkit – Committee will be 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 (mternieden@acec.org), subject line, CASE Committee: • 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!

FEB R U A R Y 2 021

structural FORUM Lessons for Young Engineers

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

That which we obtain too easily, we esteem too lightly.

-THOMAS PAINE

S

tructural engineering is a stressful profession, especially for young engineers. The construction industry is highly competitive regardless of your niche in it, and clients are always looking for designs to be maximally efficient and executed as quickly as possible.

Unfortunately, projects run even faster today than they did a decade ago, leaving less time for young engineers to learn how to produce quality work quickly and communicate effectively with their clients.

As a young engineer, your top concern is probably not efficiency or schedule, but rather doing your job competently and avoiding unpleasant consequences if you do not. It is not uncommon to make a simple mathematical error, make an invalid assumption or estimate, misinterpret a code section, or miss an important note that should have been added to the drawings. Consider these as learning experiences.

You will soon appreciate that there are many safeguards to ensure appropriate design solutions but remember that the best way to gain your colleagues’ trust and earn more responsibility is to produce consistently good work.

Review of your work through your company’s Quality Assurance/Quality Control (QA/QC) process is intended to catch invalid assumptions, improve the design solutions, and ensure code compliance. You will learn to welcome this oversight. Any issues that slip past the QA/QC process are likely to be spotted by detailers since they closely examine the project drawings as they produce shop drawings. Experienced contractors also often question designs if a size or spacing is out of the ordinary or if they think they have a better idea. At first, you may not welcome their comments and questions, but their ideas are often well-founded and result in a better product.

Fabricators and contractors may also make unintentional errors or omissions that could affect the structure. They could misinterpret the drawings, forget to put an embedded plate in a concrete wall, layout rebar incorrectly, make an unacceptable weld, etc. As a structural STRUCTURE magazine

engineer, you will be called upon to determine if what the contractor has done is acceptable or design a correction if it is not and do so as promptly as possible to not hold up construction. Again, another learning experience.

The stress that these everyday occurrences cause never completely goes away. However, the level of stress does get more tolerable.

The more projects you complete, the greater your understanding becomes, and the more your engineering judgment grows. And the more conversations you have with clients, the more comfortable these interactions become.

All of this helps. Unfortunately, there is just no substitute for spending time and gaining experience. Or maybe it is fortunate. After all, “That which we obtain too easily, we esteem too lightly.” – Thomas Paine There are things that you can do to lower your stress level. Review your work and bring questions to your supervisor or a colleague with more experience. This can be humbling, but it is also an excellent opportunity to learn.

Most people like to help others; it feels good to pass on knowledge, and explaining ideas to others helps build their understanding.

However, learning how to come up with answers on your own is part of growing as an engineer. Look for the answer in an old textbook, use an internet search engine, read a journal article. If you are like me, the complex problems that you have during the workday remain with you at night. Sometimes the cleverest solutions pop into your head out of the blue when you shower or climb into bed.

If your firm does not have checklists, create your own for calculations to be done and items to be on drawings – and use them.

Please do not view the checking of shop drawings as something you would like to delegate to others but as a way to confirm that everything is as it should be before construction begins. Pay close attention, and you will find the detailer’s mistakes and any design issues that slipped through previous reviews.

We are lucky to live at a time when, each year, our design tools become more powerful,

allowing us to create ever more sophisticated models. However, it is helpful to keep in mind mathematician George Box’s quip: “All models are wrong, but some are useful.” To improve efficiency and get the right answers, keep structural design models as simple as possible while still maintaining their usefulness. It generally takes a few years to develop the intuition for when a member is under- or over-sized, so it is even more important early in your career to understand what the software you are using can and cannot do, and to be intentional with the design assumptions inherent in the model. For example, if a steel beam connection is modeled as fixed, the drawings ought to have connections at the flanges, and if a concrete slab is necessary, do not model it as a flexible diaphragm.

In this author’s experience, it takes about four years to develop confidence in most daily tasks. I still had questions. I still have questions, but I realized around the time that I took the P.E. exam that requiring four years of experience before allowing someone to be professionally licensed is not just an arbitrary period. Four years really is a reasonable amount of time to develop acceptable competence.

So, strive to get better each day and find and learn from your mistakes. Take personal responsibility. Try to keep things in perspective and remain humble, and in doing so, you will be able to push through and overcome.

Structural engineering is an honorable profession that plays a valuable role in society.

When storms blow through, or earthquakes shake the ground, our communities rely on us and our expertise to keep them safe. It is, however, not an easy profession. All of us have had times when the job presented a real challenge, but it is a challenge worth pursuing. The rewards are significant.■ Jim Lintz is a Structural Engineer at LJB Inc. in Dayton, OH. (jlintz@ljbinc.com) F E B R U A R Y 2 0 21

ACI 212.3R-10

Access to ACI University Learning

Report on Chemical Admixtures for Concrete

Reported by ACI Committee 212

ACI Members receive free access to all ACI live webinars and 220+ on-demand courses.

• 12-month subscription available for nonmembers • Multi-user options available Visit www.concrete.org/aciuniversity to view all your access options

220+ On Demand Courses | Live Webinars | Multi-User Options | 55+ Different Topics

www.ACIUniversity.com

STRUCTURE FEB RUA RY 2021 |

Bonus Content

Revisiting Lessons Learned

from the Nicoll Highway Collapse

By Hee Yang Ng, MIStructE, C.Eng, P.E.

T

he Nicoll Highway excavation shoring construction collapse occurred in Singapore on April 20, 2004, around 3:30 pm.

The accident deeply impacted Singapore’s local construction

industry. Many regulations were tightened up through this incident, such as appointing qualified geotechnical engineers for deep excavation works and requiring authority submissions for temporary construction. The collapse resulted in four people killed and three injured. Several project parties were charged in court, and project completion was delayed.

Diaphragm walls with multiple levels of struts were often thought to be a robust earth-retaining wall system. How did such a system fail?

This article revisits some of the contributing causes of the earth-retaining structure collapse and highlights six essential lessons learned from the incident.

Project Details

Plan view of the collapse area.

STRUCTURE magazine

The collapse was located in the south-central part of Singapore island. The land transport agency of Singapore had wanted to build a circular metro line (Circle Line 1 Stage 1 – Contract C824) connecting the suburban areas of Singapore to the central business district in the downtown area. Excavation work for

a cut-and-cover tunnel was underway and had almost reached the base of the excavation when the collapse occurred.

The 20-meter-wide (approximately 65.6 feet) cut-and-cover tunnel had to be constructed by excavating to 33 meters (approximately 108.3 feet) below ground level. The ground consisted of deep layers of soft marine clay with very low shear strength (20 kPa to 40 kPa), which typically increased linearly with depth. 800-millimetersthick (approximately 2.6 feet) reinforced concrete diaphragm walls (D-walls) were used as earth-retaining structures, supported by 10 levels of steel struts, spaced at about 3 to 3.5 meters (approximately 9.8 to 11.5 feet) vertically. Two levels of Jet Grout Pile (JGP) near the base of the excavation were constructed to provide strength and stability to the soft soil as the base was being excavated. It is worth noting that such a deep excavation in adverse ground conditions would typically require a wall thickness of about 1500 millimeters (approximately 4.9 feet). That thickness is twice the size of the wall used in C824.

Modeling Undrained Behavior In designing a multi-stage excavation, the use of software is often required. Although, in many cases, the drained behavior of soil is critical for excavation works (due to unloading), undrained behavior is still relevant and appropriate for soil such as marine clay, which has very low permeability.

The software used to design the cut-and-cover tunnel for Nicoll Highway was Plaxis. When considering the undrained behavior of soil, the relevant strength parameters are total stress soil parameters.

For strength design, it is the undrained shear strength, cu. Designers may sometimes choose to input the value of undrained shear strength of a particular soil directly into the software. However, in Plaxis, the software allows the designer to model undrained behavior using effective stress parameters (i.e., using cohesion c´ and friction angle φ´). The advantage of this is that shear strength increase due to consolidation can be used in the design, resulting

Lateral soil pressure acting on D-wall panels causing joint to open up.

Section of the cut-and-cover tunnel.

in economies. C824 designers took advantage of this and modeled the undrained conditions using effective stress parameters in Plaxis.

However, the C824 project designers failed to recognize that such an increase in shear strength can be quantitatively wrong, especially for soft clay. In a p-q plot, it can be visualized that in an undrained loading using the Mohr-Coulomb (MC) model, the stress path moves vertically upwards. This means that the center of the Mohr circle (p-coordinate) remains the same, while the radius of the circle (q-coordinate) increases. Note that p and q are also average stress (stress components added together and divided by the number of components) and deviatoric stress (difference in major and minor principal stress), respectively.

In undrained loading, the load is taken entirely by the water in the soil, so there is no change in the soil’s effective stress. The load only increases the deviatoric stress (q-coordinate) as the Mohr circle becomes larger as loading increases. In reality, as the positive excess pore water pressure increases during undrained loading (i.e., pressure exerted on water), the stress path deviates to the left, resulting from a decrease in average effective stress (p-coordinate) because total stress = effective stress + pore pressure. As water exerts pressures in all directions, it is important

F E B R U A R Y 2 0 21 B O N U S C O N T E N T

(e.g., loose sand and soft clay), soil loss occurred due to these weak soils leaking through the utility gaps at areas where the interfacing gaps were not adequately secured. Also, the builder had difficulties installing continuous strutting. For C824, investigators suspected that the jet grout piles (JGP) were not carried out near utility areas (due to concerns of damage), and this could have severely impaired the effectiveness of the JGP in providing strength when acting like a strut and providing stability close to the base of the excavation.

Poor Strutting System

Poor strutting design and construction.

to appreciate that an increase in vertical stress in water will result in the same stress exerted horizontally.

The over-prediction of soil shear strength using effective stress parameters resulted in severe under-design. The forces and moment in the retaining walls were grossly underestimated, and deflections predicted were too optimistic. This resulted in an earth retaining system that was inadequately sized. Back analysis for C824 D-walls showed that the bending moments and deflections were underestimated by 50%.

Curved Diaphragm Walls The curved alignment on the metro line plan meant that the retaining walls had to follow this curvature. It should be noted that curved diaphragm walls posed many challenges for design and construction.

First, the usual 2-dimensional (2-D) plane strain analysis adopted for a section design would not capture the effects of curvature, which runs in the out-of-plane direction. Forces and moments in retaining walls, strut forces, and wall deflections might be increased or decreased due to the curvature.

When it comes to construction, it is not easy to construct a continuous waler due to the wall’s curvature. In C824, discontinuous walers at some locations resulted in weakness between adjacent diaphragm wall panels. As D-walls were constructed as discrete panels, wall joints opened up at weak locations due to the lateral soil pressure acting in a direction causing the walls to move inwards into the excavation. A robust and continuous tying waler needed to be constructed to provide a “tying effect” to prevent opening up of the wall joints, which the designers had overlooked.

There were many inadequacies in the design of the strutting system in C824. Due to the design-and-build nature of the contract, the contractor wanted a very lean design. The curved diaphragm walls and close vertical spacing of the struts (obstructing ease of construction) did not help. In C824, it was found that some walers were discontinuous. Some struts were installed without splays. There were also cases where struts were bearing directly onto D-wall panels without a waler. The waler’s fundamental purpose was to provide continuous line support to the retaining wall so that loads could be redistributed, and the effects of eccentricity could be mitigated.

When this was omitted, the effectiveness of the strutting support system was somewhat compromised.

Sway Stability of Open Stiffeners During construction, it was found that some of the plate stiffeners for the strut and waler connection had buckled. The contractor thought that this happened due to more load being transferred through the strut’s flanges, resulting in the plate stiffeners being inadequate. Unknown to the contractor, the inadequacy of the steel stiffener plates was due to an overestimate of the stiff bearing length of the waler resulting in under design of stiffeners.

The contractor then replaced the steel plates with C-channels, thinking that the “bigger” C channel sections would perform better as stiffeners. This proved to be a costly mistake, as it was one of the main contributing factors leading to the strutting system’s inadequacy.

The contractor did not realize that the C-channels acting as stiffeners had resulted in an “open” stiffening system. This means

Utility Crossings Existing underground utilities have to be protected from damage during excavation. Sometimes, utilities may be diverted away from the excavation area before construction commences, but this is not always possible. There will be occasions where project parties are required to contend with existing utilities in the way of the excavation activities. In C824, critical electrical cables (66kV) were in the way of the diaphragm walls. Utility gaps of 4 meters (approximately 13.1 feet) disrupted the continuity of the diaphragm walls. This created a zone of weakness in the diaphragm walls. In weak soils

STRUCTURE magazine

Replacing plate stiffeners with C-channel stiffeners.

that the “opening” created had an inherent weakness, a failure by sidesway. Sidesway failure mode is dangerous because of the after-peak brittle response. Once the system is overloaded beyond capacity, failure occurs suddenly and the load-carrying capacity decreases sharply.

Telltale Signs A large-scale infrastructure project such as C824 inevitably required a large team of project personnel for design and on-site during construction. Despite the large team of engineers, supervisors, client representatives, and contractors present on-site, none of the project parties realized that the numerous abnormal sightings were telltales signs of an impending collapse. Before the collapse, the lateral wall deflection was more than 400 millimeters (approximately 1.3 feet), which did not appear to be alarming to the project parties.

Furthermore, there were signs that the strutting system was under distress, manifested by stiffener plates buckling and kingposts deformed beyond vertical alignment.

The tragedy of the Nicoll Highway incident could have been avoided if project parties were aware of the dangers in deformed and distorted structural members and large wall and ground movements. In C824, the immense pressures of cost and time impelled the builder to take unnecessary risks, even to the extent of not stopping work in the face of warning signs, hoping to complete the work quickly so that the situation could turn around and stabilize. This mindset to rush work and complete the excavation and backfill to achieve safety is a dangerous fallacy. The more secure way would be to cease work and strengthen the weak areas to ensure safety and stability.

Comparison of Results It is sometimes useful to check computer output using simple rules of thumb. Designers can use apparent wall pressure diagrams where lateral pressure pa acting on the wall = γH(1-m4cu/(γH)) to estimate the strut load. Using m = 0.4, cu = 30 kPa, γ = 18 kN/m3, H = 33m, pa works out to be 0.9 γH = 535 kN/m2. Adding a surcharge of 20 kPa (assume Ka =1), the earth pressure becomes 555 kN/m2. Therefore, the estimated unfactored strut load is 555 multiplied by the spacing of 3.8 meters (largest tributary area near the base), giving 2100 kN/m.

Conceptual load-displacement curve showing sudden failure due to side-sway.

Sidesway failure mode of “open” stiffeners.

Designers should note that apparent earth pressures can only be used to estimate strut loads, not retaining wall forces.

To estimate retaining wall moments, designers can use Rankine’s earth pressure. Assuming active pressure is Kaσv and Ka = 1, with a surcharge of 20 kN/m2, maximum earth pressure is 33x18+20 = 620 kN/m2.

The maximum bending moment is 620x4.52/8 = 1600 kNm/m using maximum bending moment for a simply supported beam (wL2/8).

The factored moment becomes 1.5x1600 = 2400 kNm/m.

Using the above rule of thumb, designers must remember that these simplified methods cannot predict strut loads or wall forces with great accuracy, especially for a complex deep excavation project. It is only meant to give the designer a sense of the order of magnitude. This is because an actual excavation construction is a multi-stage process. Therefore, additional forces will be introduced during the intermediate stages of loading. Also, the stiffness and rigidity of the wall, struts, and soil interact with one another. Forces and moments get redistributed according to the soil and wall and strut movement. For example, a flexible wall bending moment would be very different from that of a rigid wall.

Therefore, software such as Plaxis is often required to analyze a complex deep excavation project.

Conclusions The safety of temporary construction might sometimes take a backseat because they are constructed only for a relatively short period to facilitate permanent construction. Parties are sometimes tempted to adopt lower safety standards for temporary works. However, this can be a costly mistake, especially for a large-scale project involving complex site conditions, as shown in the C824 incident. In Singapore, as a result of the C824 incident, temporary construction requires the same safety factors as permanent construction, and submission to authorities for approval of the design is required before work can commence on site.

Designers involved in complex geotechnical works need to understand soil behavior to use appropriate software and predict forces on retaining structures correctly, including the software’s assumptions and the limitations of the model and analysis results.

In addition to theoretical knowledge, experience is also critical to identify site-specific problems and avoid potential pitfalls.■ Hee Yang Ng is a Principal Engineer with a building control agency in the Asia-Pacific region.

F E B R U A R Y 2 0 21 B O N U S C O N T E N T

DECK DETAILS

LOAD TABLES

250 inspiring photos from a range of applications newmill.com/gallery

Access to over 3,400 DWG and PDF drawings newmill.com/dwg

Customizable steel deck and joist load tables newmill.com/loadtables

Photo credit: Project Frog, Inc.

PROJECT GALLERY

CONTROL ACOUSTICS Manage acoustics with composite floor deck newmill.com/nrc

MINIMIZE FLOOR DEPTH

Smarter school design

Dovetail deck provides thin-floor advantages newmill.com/multistory

STEEL BUILDING SYSTEMS SOLVE YOUR TOP 5 CHALLENGES Achieve superior designs while addressing the unique demands of the education market. Steel joists and a combination of roof and floor deck systems create versatile open spaces, promote health and safety, control acoustics and elevate aesthetics while providing sustainable solutions. Bring greater knowledge to the design, construction and performance of your next education project.

THE TOP 5 GUIDE [ GET newmill.com/education LIVE REMOTE LEARNING Earn credit as you gain knowledge newmill.com/courses

SPOTLIGHT ICE Block I

Seamlessly Blending Three Structural Materials

I

CE Block I in Sacramento, California, is the reincarnation of the historic Crystal ice manufacturing facility, which was destroyed by fire on the same site. The new structure is an elegant blend of architecture and structure.

The $26 million project hosts retail and restaurant tenants on the first floor with office tenants on the second through fourth floors. The exposed heavy timber structure for the upper floors honors the character of the original historic building. The fourthfloor mezzanine layout provides a 30-foot-tall volume with expansive views of downtown through the full glass curtainwall. The second floor includes post-tensioned concrete transfer girders to accommodate the basement parking layout. Exposed braced frames on the exterior of the north and south façades further serve to create an authentic expression of structure in harmony with architecture.

ICE Block I was one of the first projects in Northern California to utilize an exposed mass timber structure. The building blends three structural materials seamlessly and visibly: mass timber at the upper floors supported by a concrete podium at the second floor, combined with steel Buckling Restrained Braced Frames (BRBFs).

The glulam post and beam system of the upper levels intentionally leveraged cantilevered girders over the columns. This allowed a reduction in girder depth to make them commensurate with beam depths. The glulam beams connect to girders and columns with custom steel saddle hangers and column caps.

Solid sawn 3x decking with a non-structural concrete topping completes the floor system at the wood levels. The fourth floor is the crown jewel of the architectural expression.

With the north and south edge of the floor pulled back from the exterior wall to create a two-story volume, tenants experience a vertical connection to the mezzanine through the 30-foot-clear volume.

The concrete second floor is a one-way reinforced concrete slab supported by posttensioned girders. The girders serve as transfer elements to transition the column spacing of the wood levels to a grid appropriate for drive aisles in the basement parking level.

The second floor was chosen as the transfer level because there was ample height clearance above level 1 to accommodate the girders, STRUCTURE magazine

which allowed the basement garage level to be as shallow as possible to minimize excavation.

The BRBFs strategically exposed on the building’s exterior on the north and south sides express the structural elements as an architectural feature; this provided a unique engineering challenge to deliver the lateral forces to the frame.

The BRBF system transfers its forces to the concrete shear wall system of the basement walls at the first-floor level through large, embedded steel plates in the tops of the concrete columns.

The nearly identical east and west wings are connected by a sky bridge at the second through fourth floors, which is seismically isolated at one end. The first-floor exterior deck area is elevated 30 inches from the adjacent sidewalk grade to create a pedestrian area for retail and restaurant use.

The design of an exposed exterior braced frame system posed challenges. Early in the project, the architect was interested in utilizing the exterior brace system as a purely architectural element, even if that meant the real structural braces had to reside somewhere else.

Buehler, the structural design firm, took on the challenge to make the structural design also serve as the architectural expression, eliminating the need for a duplicate system. This was not a trivial undertaking; the structural diaphragm had to penetrate the curtainwall system in order to attach to the braced frame.

Waterproofing concerns were mitigated by providing a ‘box’ section for the curtainwall to join. The structural design also needed to account for the eccentricities of the diaphragm connections.

The fourth-floor mezzanine is pulled back from the exterior wall except in the two end bays. This complicated the seismic load path between the diaphragm and exterior braced frame. The diaphragm in the two end bays is strengthened by a horizontal, diagonal steel truss below the wood floor to address this.

ICE Block I was one of the first projects in Northern California to utilize an exposed mass timber structure.

Accommodating a full-length drive ramp into the basement parking level also presented challenges on this relatively small site. The response was to utilize the existing sloped alley behind the building as part of the ramping solution. This approach minimized the ramp length within the structure while simultaneously minimizing required clearance below the post-tensioned beam over the ramp.■ Buehler was an Outstanding Award Winner for the ICE Block I project in the 2020 Annual Excellence in Structural Engineering Awards Program in the Category – New Buildings under $30 Million.

Project Team Structural Design Firm: Buehler Architect: RMW Architecture General Contractor: Ascent Builders F E B R U A R Y 2 0 21 B O N U S C O N T E N T