STRUCTURE magazine - April 2018 by structuremag

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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April 2018 Concrete Inside: John Anson Ford Amphitheatre, Los Angeles

Clark University Alumni & Student Engagement Center by Architerra with Odeh Engineers

LeMessurier Calls on Tekla Structural Designer for Complex Projects Interoperability and Time Saving Tools

Tekla Structural Designer was developed specifically to maximize collaboration with other project parties, including technicians, fabricators and architects. Its unique functionality enables engineers to integrate the physical design model seamlessly with Tekla Structures or Autodesk Revit, and to round-trip without compromising vital design data. “We’re able to import geometry from Revit, design in Tekla Structural Designer and export that information for import back into Revit. If an architect makes geometry updates or changes a slab edge, we’ll send those changes back into Tekla Structural Designer, rerun the analysis and design, and push updated design information back into Revit.”

Tekla Structural Design at Work: The Hub on Causeway

For over 55 years, LeMessurier has provided structural engineering services to architects, owners, contractors, developers and artists. Led by the example of legendary structural engineer and founder William LeMessurier, LeMessurier provides the expertise for some of the world’s most elegant and sophisticated designs while remaining true to the enduring laws of science and engineering. Known for pushing the envelope of the latest technologies and even inventing new ones, LeMessurier engineers solutions responsive to their clients’ visions and reflective of their experience. An early adopter of technology to improve their designs and workflow, LeMessurier put its own talent to work in the eighties to develop a software solution that did not exist commercially at the time. Their early application adopted the concept of Building Information Modeling (BIM) long before it emerged decades later. While LeMessurier’s proprietary tool had evolved over three decades into a powerhouse of capability, the decision to evaluate commercial structural design tools was predicated on the looming effort required to modernize its software to leverage emerging platforms, support normalized data structure integration and keep up with code changes. After a lengthy and thorough comparison of commercial tools that would “fill the shoes” and stack up to the company’s proprietary tool, LeMessurier chose Tekla Structural Designer for its rich capabilities that addressed all of their workflow needs. According to Derek Barnes, Associate at LeMessurier, ” Tekla Structural Designer offered the most features and the best integration of all the products we tested. They also offered us the ability to work closely with their development group to ensure we were getting the most out of the software.”

One Model for Structural Analysis & Design

From Schematic Design through Construction Documents, Tekla Structural Designer allows LeMessurier engineers to work from one single model for structural analysis and design, improving efficiency, workflow, and ultimately saving time. “Our engineers are working more efficiently because they don’t need to switch between multiple software packages for concrete and steel design. Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product,” said Barnes. LeMessurier engineers use Tekla Structural Designer to create physical, information-rich models that contain the intelligence they need to automate the design of significant portions of their structures and efficiently manage project changes. TRANSFORMING THE WAY THE WORLD WORKS

“Tekla Structural Designer has streamlined our design process,” said Craig Blanchet, P.E., Vice President of LeMessurier. “Because some of our engineers are no longer doubling as software developers, it allows us to focus their talents on leveraging the features of the software to our advantage. Had we not chosen to adopt Tekla Structural Designer, we would have needed to bring on new staff to update and maintain our in-house software. So Tekla Structural Designer is not just saving us time on projects, it is also saving us overhead.

Efficient, Accurate Loading and Analysis

Tekla Structural Designer automatically generates an underlying and highly sophisticated analytical model from the physical model, allowing LeMessurier engineers to focus more on design than on analytical model management. Regardless of a model’s size or complexity, Tekla Structural Designer’s analytical engine accurately computes forces and displacements for use in design and the assessment of building performance.

“Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product.”

Positioning a large scale mixed-use development next to an active arena, a below grade parking garage, and an interstate highway, and bridging it over two active subway tunnels makes planning, phasing and engineering paramount. Currently under construction, The Hub on Causeway Project will be the final piece in the puzzle that is the site of the original Boston Garden. Despite being new to the software, LeMessurier decided to use Tekla Structural Designer for significant portions of the project. “Relying on a new program for such a big project was obviously a risk for us, but with the potential for time savings and other efficiencies, we jumped right in with Tekla Structural Designer. It forced us to get familiar the software very quickly.” “Tekla Structural Designer allowed us to design the bulk of Phase 1 in a single model,” said Barnes. The project incorporates both concrete flat slabs and composite concrete and steel floor framing. “Tekla Structural Designer has the ability to calculate effective widths based on the physical model which is a big time saver,” said Barnes. “On this project, the integration with Revit, along with the composite steel design features enabled us to work more efficiently. Adding the ability to do concrete design in the same model was a bonus because we had both construction types in the same building.” “Tekla Structural Designer helped this project run more efficiently, and in the end it was a positive experience,” said Blanchet.

“Tekla Structural Designer gives us multiple analysis sets to pull from, which gives us lots of control. Most programs don’t have the capability to do FE and grillage chase-down. For the design of beam supported concrete slabs, Tekla Structural Designer allows us to separate the slab stiffness from the beam stiffness, so if we choose to we can design the beams without considering the influence of the slab. In the same model we can use a separate analysis set to review the floor system with the beams and slab engaged,” said Barnes. Barnes also shared similar benefits with concrete column design. “Tekla Structural Designer does grillage take-downs floor-by-floor, finds the reactions and applies them to the next floor. This allows us to view column results both for the 3-dimensional effects of the structure as a whole and from the more traditional floor-by-floor load take-down point of view. Doing both has always required significant manual intervention, but Tekla Structural Designer puts it all in one place.” “We reduce the possibility for human error because with Tekla Structural Designer less user input is required,” said Barnes. “Tekla Structural Designer automatically computes many of the design parameters, such as column unbraced lengths. The assumptions made by the software are typically correct, but we can easily review and override them when necessary.”

“Tekla Structural Designer provided the best fit for our workflow compared to other commercially available software.”

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CONTENTS

Cover Feature

26 A WORLD-CLASS MAKEOVER By Russell Kehl, S.E., Melineh Zomorrodian, S.E., and Maria Mohammed, P.E. The renovation and expansion of the John Anson Ford Amphitheater nestled in the Hollywood Hills included the transformation of the historic theater and construction of the new Ford Terrace building, all within the current boundaries of the site.

Feature 22 A NEW TREND IN MULTISTORY OFFICE CONSTRUCTION By James M. Williams, P.E., C.E., S.E., AIA Tilt-up construction has evolved to include multi-story, class “A” office buildings. Unlike warehouse buildings with little or no windows, the Entrata Building was designed to maximize the amount of glazing so interior spaces could have floor to ceiling windows.

Columns and Departments EDITORIAL

STRUCTURAL PERFORMANCE

7 The Business of Structural Engineering

18 Blast Design By Nabil A. Rahman, Ph.D., P.E.

By Corey M. Matsuoka, P.E.

BUSINESS PRACTICES

38 Mentoring in the Workplace By Jennifer Anderson

and Casey O'Laughlin, P.E. SPOTLIGHT

STRUCTURAL DESIGN

43 The Bay Area Metro Center

HISTORIC STRUCTURES

9 Design of Reinforced Concrete Diaphragms for Wind

By Leslie Zerbe, P.E.

30 Niagara-Clifton Steel Arch Bridge

By David A. Fanella, Ph.D., S.E., P.E.,

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

and Michael Mota, Ph.D., P.E., SECB

STRUCTURAL FORUM

50 Trust Me; I am An Engineer By Alan Kirkpatrick, P.E.

LEGAL PERSPECTIVES

STRUCTURAL PRACTICES

34 State Statutes – Part 3

12 Mass Concreting

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

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

STRUCTURAL SUSTAINABILITY

36 Capturing Points for Whole Building LCA in LEED v4

OUTSIDE THE BOX

14 Designing Destruction By Sean K. Hallet, P.E., Patxi Uriz, Ph.D.,

By Frances Yang, S.E.

P.E., and Morgan Griffith, P.E

IN EVERY ISSUE 8 Advertiser Index 40 Resource Guide – Engineered Wood Products 44 NCSEA News 46 SEI Structural Columns 48 CASE in Point

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, the Publisher, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

STRUCTURE magazine

April 2018

Editorial The Business of Structural Engineering By Corey M. Matsuoka, P.E., Chair CASE Executive Committee

hey do not teach business skills at the College of Engineering. At least they did not teach them at UCLA when I went there in the early 90s. They did a pretty good job of teaching me about things like pre-stressed concrete, AISC steel design, and shear/moment diagrams, but they did not go into things like liability and claims, how to transition from a project manager to a firm leader, and they definitely did not tell me that I could have a duty to defend someone even if no fault had been established. If they did, it might have been enough to scare me away from becoming a structural engineer. It is too late now to change professions, but the good news is that there are organizations like CASE to help. CASE, the Council of American Structural Engineers, is a coalition of the American Council of Engineering Companies (ACEC) and offers structural engineers the opportunity to further develop their businesses through shared business practices, advice to reduce professional liability exposure, and tactics to increase profitability. We do this through developing guidelines and contracts that outline best practices, along with extensive risk management tools designed to keep liability in check. We also sponsor seminars and workshops that present best business practices while providing the opportunity to share ideas and information with structural engineering peers from around the nation. One critical topic to the business of structural engineering is California’s successful passing of a new law (S.B. 496) blocking immediate duty-todefend requirements for design professionals in private-sector and most public-sector contracts. The law limits design professionals’ defense obligation (and that of their carriers) to the comparative fault of the design professional. Previously, this protection only was mandated by law to contracts between local public agencies and design professionals. For some historical background of why this new law is so important, we should look at a couple of cases trialed in California. The first is the case of Crawford v. Weather Shield Mfg. Inc. (2008). In this case, the California Supreme Court held that the contractual duty-to-defend was immediate even when not explicitly specified in the contract. As a result, the subcontractor was ordered to pay all of the general contractor’s attorney’s fees and costs, even though the jury ruled the subcontractor to be fault free. The second case, UDC v. CH2M Hill (2010) made it clear that the holding in the Crawford case concerning an immediate duty-to-defend extended to design professionals

STRUCTURE magazine

as well. In the end, a jury found CH2M Hill to be fault free, but the design professional was still ordered to pay all of its client’s attorney’s fees and cost. What makes these cases even scarier is that the provision of immediate duty-to-defend is an uninsurable risk for design professionals under their professional liability policies. To say it another way, a design professional who enters into a contract with this clause could be required to pay for a client’s attorney’s fees and costs without the help of insurance, even if the design professional was ultimately found to be fault free by a court of law. This is because, generally speaking, professional liability covers the professional negligence of parties and does not cover any additional liabilities assumed by agreeing to bad contract terms. With S.B. 496, private or local agency contracts that attempt to include an immediate duty-todefend clause will be unenforceable. This means that if a matter is litigated, and the design professional is determined to be 25% at fault, then the law requires that the professional would be responsible for only 25% of the attorney’s fees and costs of the party seeking contractual indemnity. Even better, since the 25% is determined to be tied to the design professional’s negligence, this cost now becomes insurable. If you want to hear more about the immediate duty-to-defend clause or learn more about running your business more efficiently while reducing your risk, join us for our Business of Structural Engineering Workshop. For more detailed information about the workshop, look for our ad in this month’s issue, contact Heather Talbert at htalbert@acec.org, or visit www.acec.org/education/seminars.▪

Information on S.B. 496 was based on the article by Justin Witzmann and Brian Stewart, “California Duty to Defend Rests on Fault,” which appeared in the Professional Times magazine, summer 2017 issue. Corey M. Matsuoka is the Executive Vice-President of SSFM International, Inc., in Honolulu, Hawaii. He is the chair of the CASE Executive Committee. He can be reached at cmatsuoka@ssfm.com.

April 2018

ADVERTISER INDEX

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Anthony Forest Products, Co. ..................31 American Concrete Institute ....................37 CASE .......................................................29 Cast Connex ..............................................2 CTP Inc. .................................................28 Dlubal Software, Inc. .................................4 Fyfe. .........................................................35 Hohmann & Barnard, Inc. .......................40 ICC..........................................................21 Integrity Software, Inc. ...............................8 Kinemetrics ..............................................23

KPFF .......................................................11 Larsen Products Corp. .............................41 Lindapter .................................................33 Precast/Prestressed Concrete Institute .......39 RISA Technologies ...................................52 Simpson Strong-Tie............................17, 25 StructurePoint ............................................6 Trimble ......................................................3 USG Corporation ...................................51 Weyerhaeuser ...........................................42 Woodworks ..............................................53

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April 2018, Volume 25, Number 4 ISSN 1536-4283. Publications Agreement No. 40675118. STRUCTURE® is owned and published by the National Council of Structural Engineers Associations with a known office of publication of 645 N. Michigan Ave, Suite 540, Chicago, Illinois 60611. Structure is published in cooperation with CASE and SEI monthly. The publication is distributed as a benefit of membership to members of NCSEA, CASE and SEI; the non-member subscription rate is $65/yr domestic; $35/yr student; $90/yr Canada; $60/yr Canadian student; $125/yr foreign; $90/yr foreign student. Application to Mail at Periodical Postage Prices is Pending at Chicago and at additional Mailing offices. POSTMASTER: Send address changes to: STRUCTURE, 645 N. Michigan Ave, Suite 540, Chicago, Illinois, 60611. For members of NCSEA, SEI and CASE, email subscriptions@structuremag.org with address changes. Note that if you do not notify your member organization, your address will revert back with their next database submittal. Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, the Publisher, or the STRUCTURE Editorial Board. STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

n addition to supporting gravity loads, floor • Bounding analysis, which considers results and roof systems in typical reinforced concrete based on upper- and lower-bound in-plane buildings act as diaphragms which transfer the stiffnesses of the diaphragm; lateral forces to shear walls, frames, or other • Finite element model; and elements that make up the lateral force resisting • Strut-and-tie model in accordance with ACI system (LFRS). A three-dimensional analysis 318 Section 23.2. that considers the relative rigidities of the diaFor reinforced concrete buildings with typical phragm and the elements of the LFRS provides span lengths and without diaphragm irregularities the most accurate distribution of the forces in (such as large openings or significant changes in these components. A more straightforward diaphragm stiffness in adjoining stories), the rigid analysis is possible when assumptions are made diaphragm model is commonly used to deterconcerning the rigidity of a diaphragm. mine approximate force distributions within a Cast-in-place, reinforced concrete slabs of typi- diaphragm. In this method, a diaphragm is modcal proportions and span lengths can usually be eled as a horizontal rigid beam that is supported considered rigid diaphragms, which means that by springs which represent the lateral stiffness of the lateral forces are transferred to the elements of the members in the LFRS. The roof and floor the LFRS in proportion to their relative rigidities. systems act as the web of the beam, which resists In systems that contain beams or ribs – like in the design shear forces that are uniform through wide-module, two-way joist and grillage systems the depth of the diaphragm. The boundaries of the – the elements below the slab help stiffen the diaphragm act as the flanges diaphragm even further. which resist the flexural tension According to the American Concrete Institute’s and compression design forces. ACI 318, Section 12.3, diaphragms must have Illustrated in Figure 1 is a sufficient thickness so that all applicable strength diaphragm with an LFRS and serviceability requirements are satisfied. consisting of structural walls Usually, the thickness of a floor or roof system and collector elements. The is determined first based on the strength and lateral force is transferred through the web of the serviceability requirements pertaining to grav- diaphragm to the walls, which act as supports ity loads. That thickness is typically sufficient for the diaphragm. Because the wall on the left to satisfy corresponding requirements for the does not extend the full depth of the diaphragm, combined factored load effects (gravity plus collector elements are needed to collect the shear lateral) on the diaphragm. from the diaphragm and to transfer it to the wall. In the case of gravity loads, many methods are The diaphragm boundaries that are perpendicular available that can be used to determine the fac- to the seismic lateral (commonly referred to as tored load effects, including the approximate chords) resist the tension and compression flexmethods in ACI 318 for one-way and two-way ural forces that are induced in the diaphragm. systems. For the most part, these methods are Boundary reinforcement is concentrated along the relatively simple to use and give very reasonable edges of the diaphragm to resist the tensile forces. results. In contrast, the distribution of in-plane For diaphragms with openings, forces develop in forces due to wind effects in diaphragms is com- the sub-diaphragms at the top and bottom of the plex. However, because a cast-in-place reinforced opening and collector elements on each side of the concrete system behaves more like a single, mono- opening are required to transfer the diaphragm lithic element compared to other types of systems, shear into the sub-diaphragms (Figure 2, page 10). simplified analysis methods can continued on next page be used to determine in-plane force distributions; these methods give results that compare well to those from more sophisticated procedures. In-plane design bending moments, shear forces, and axial forces in a diaphragm are permitted to be calculated by the methods in ACI 318 Section 12.4.2.4: • Rigid diaphragm model in cases where the diaphragm can be idealized as rigid; • Flexible diaphragm model in cases where the diaphragm can be idealized as flexible; Figure 1. Diaphragm force distribution.

structural

DESIGN

design issues for structural engineers

Design of Reinforced Concrete Diaphragms for Wind

STRUCTURE magazine

April 2018

By David A. Fanella, Ph.D., S.E., P.E., F.ACI, F.ASCE, and Michael Mota, Ph.D., P.E., SECB, F.ASCE, F.ACI, F.SEI

David A. Fanella is Senior Director of Engineering at the Concrete Reinforcing Steel Institute and can be reached at dfanella@crsi.org. Michael Mota is Vice President of Engineering at the Concrete Reinforcing Steel Institute and can be reached at mmota@crsi.org.

reactions in the springs. The distributed load is trapezoidal, which is depicted in Figure 3 for a diaphragm without a significant opening. The loads w1 and w2 at each end can be obtained by using the equations for force equilibrium and moment equilibrium, and then solving these two equations for the two Figure 2. Force distribution in a diaphragm with an opening. unknowns w1 and w2: (w1 + w2)(l1 + 12 + l3) = R + R + R = V For buildings subjected to wind, it is A B C 2 assumed that the wind pressures acting w1 over a tributary story height are uniformly ( 2 + w2)(l1 + 12 + l3)2 = distributed at that level over the width of 3 the building that is perpendicular to the R l + R (l + 1 ) + RC (l1 + 12 + l3 ) A 1 B 1 2 wind pressures. The resultant wind force

acts through the geometric center of the building at that level. In the usual case where the resultant wind force does not act through the center of rigidity (either due to geometry or minimum eccentricity requirements in the governing building code), a floor will translate and rotate. The members of the LFRS will be subjected to direct shear forces plus shear forces due to the torsional moment generated by the eccentricity. An equivalent distributed load on the diaphragm can be obtained based on the

Once w1 and w2 have been determined, shear and moment diagrams can be obtained (Figure 3). The moment diagram is used in determining the required chord reinforcement near the edges of the diaphragm. The compression and tension forces in the chords caused by flexure due to the wind forces can be obtained from the following equation: Cu = Tu = Mu,max d where d is the perpendicular distance between the chord forces, which is commonly taken as

95 percent of the total depth of the diaphragm in the direction of analysis. Tension forces govern, so the required area of chord reinforcement, As, can be determined from the following equation: As > Tu Ď&#x2020; fy where Ď&#x2020; = 0.9. Chord reinforcement must be provided in addition to any other required reinforcement, such as flexural reinforcement. In the case of roof and floor systems without perimeter beams, the chord reinforcing bars are typically concentrated near the edge of the slab and are tied to either the top or bottom flexural reinforcement. Chord reinforcement must also be located around large openings and must be properly developed within the slab. The shear diagram is used in (1) checking the design shear strength of the diaphragm, (2) designing the connections of the diaphragm to the vertical elements of the LFRS, and (3) determining the axial compressive and tensile forces in any collectors. The in-plane shear force per unit length is assumed to be uniform along the depth of the diaphragm when the rigid diaphragm method of analysis is used. Referring to the diaphragm in Figure 3, the maximum in-plane shear force per unit length, in this case, occurs along the right side of the diaphragm and is equal to Vu,max /L, which must be less than or equal to

Figure 4. Determination of dowel reinforcement in a diaphragm.

Figure 3. Rigid diaphragm model.

STRUCTURE magazine

April 2018

Figure 5. Unit shear forces, net shear forces, and collector forces in a diaphragm.

the in-plane design shear strength per unit length given by ACI 318 Equation (12.5.3.3):

φ Vn = φ Acv (2λ√fć + ρt fy )

φ Vn = φ μAvf fy ≥Vu = RB /L

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where φ = 0.75 and Vn is determined in accordance with the shear-friction provisions of ACI 318 Section 22.9.4.2. The coefficient of friction, μ, depends on the contact surface condition of the concrete, and Avf is the area of reinforcement that crosses the shear plane, which in this case is a construction joint. The following equation can be used to determine the required area of the dowel bars Avf for shear transfer: Avf > RB /L φ fy μ For hardened concrete that is clean, free of laitance, and not intentionally roughened, μ = 0.6 for normalweight concrete in the typical case where the slab and wall are cast at different times.

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In this equation, Acv is equal to the gross area of the diaphragm (thickness times a one-foot unit length) and ρt is the distributed reinforcement in the diaphragm that is oriented in the direction of analysis (that is, parallel to the in-plane shear). It is conservative to assume that ρt is equal to zero when calculating φ Vn. Even when this conservative approach is used, shear strength requirements are commonly satisfied. As noted previously, one of the primary roles of a diaphragm is to transfer wind forces to the elements of the LFRS. In typical castin-place reinforced concrete construction, this is accomplished by shear transfer reinforcement, which usually consists of dowel bars. Consider the diaphragm in Figure 4. Adjacent to wall B, the uniform shear force in the diaphragm is equal to RB /L, which is the same unit shear force in the wall. The strength requirement for shear transfer between the diaphragm and wall B is:

The shear transfer between the diaphragm and wall A in Figure 4 depends on the width of the collector elements. Where the width of the collectors is equal to the thickness of the wall, all the tension and compression forces from the collector are transferred directly into the boundary of the wall, and Avf is determined using the above equation based on the uniform shear along the length of the wall (which is equal to RA/L2). If the collector elements are wider than the wall, Avf must be determined using the uniform shear along the wall length plus a portion of the total collector force. For shear transfer between the diaphragm and the collector elements at wall A, using

μ = 1.4 to determine Avf is warranted because the diaphragm and collectors are usually cast monolithically. The dowel reinforcement must be fully developed for tension into the wall and the diaphragm (see Section 1-1 in Figure 4). The reinforcing bars must extend at least the tension development length, ld, determined in accordance with ACI 318 Section 25.4.2, past the inside face of the wall and past the underside of the slab. The dowel bars must also be designed for any out-of-plane wind forces that act on the wall. The axial forces in the collector elements at wall A in Figure 4 are determined by summing the areas in the net shear force diagram given in Figure 5. The collectors must be designed for this factored axial force (tension and compression) and any factored gravity loads tributary to the collector. Additional information on the design and detailing of reinforced concrete diaphragms and collectors can be found in the CRSI publication Design and Detailing of Low-Rise Reinforced Concrete Buildings.▪

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STRUCTURE magazine

April 2018

structural

PRACTICES practical knowledge beyond the textbook

here are many issues that arise when one places mass concrete, specifically as it relates to reinforced concrete elements in buildings. These elements, which most typically include reinforced mat foundations, pile caps, footings, piers, and transfer elements, differ from other reinforced structures such as dams and retaining walls due to high stresses, quantities of steel reinforcement, and the use of high strength concrete. Mass concrete element placement in buildings, therefore, presents unique challenges.

Mass Concrete: When It Applies

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

J. Benjamin Alper is an Associate at Severud Associates and serves as the Quality Control Officer for Severud Associates’ inspection services. He can be reached at jalper@severud.com.

Cawsie Jijina is a Principal at Severud Associates and serves as the Deputy Technical Director for Severud Associates’ inspection services. He can be reached at cjijina@severud.com.

Review the following publications for additional information, considerations, and approaches for mass concreting. ACI 207.1 – Guide to Mass Concreting ACI 207.2 – Report on Thermal and Volume Change Effect on Cracking of Mass Concrete ACI 207.4 – Cooling and Insulating Systems for Mass Concrete

The definition of mass concrete per the American Concrete Institute (ACI) is “any volume of concrete with dimensions large enough to require that measures be taken to cope with generation of heat from hydration of the cement and attendant volume change to minimize cracking” (ACI 116R and ACI 301). Although no specific thickness is given, a member thickness of three feet is often used as the threshold dimension for when mass concreting procedures are to be set in motion. Note that there may be circumstances where members with a thickness less than three feet will call for mass concreting procedures. The final determination as to whether mass concreting procedures should be followed is at the discretion of the Structural Engineer of Record (SER).

ACI 207

Goals of Mass Concreting The ACI definition of mass concrete names heat generated within the member due to the heat of hydration as a core concern. It is this heat, if not controlled, that can have detrimental effects on the concrete element. These could include cracking, delayed ettringite formation (DEF), and other issues. Another core concern with mass concreting is the potential formation of cold joints in the element. This is a problem more common to building structures as the use of higher strength concretes will rapidly accelerate the setting time of the concrete.

Temperatures ACI 301 provides two recommended temperature limits: a) The maximum concrete temperature shall not exceed 160 degrees Fahrenheit during curing, and b) The maximum temperature differential between the center and surface of placement shall not exceed 35 degrees Fahrenheit. These limits are in place to avoid delayed ettringite formation (DEF) which can cause cracking and reduce concrete strength. Although these temperature limits may not seem significant, they can often be difficult to achieve, especially the restriction on the temperature differential. Beginning concrete placement with a lower initial concrete temperature is recommended to keep the concrete from reaching upper-temperature limits. Typical methods to keep concrete temperatures low include the introduction of crushed ice to the mix in lieu of some of the mixing water and the use of precooled aggregate. For times when the ambient temperatures are high, it may

The ACI Committee 207 provides several reports for guidance in the use of mass concrete. ACI 207.1, Guide to Mass Concrete, is the primary resource for guidance in the use of mass concrete for structural building elements. Most of the data and concerns related to the use of mass concrete were formulated from lessons learned during the United States golden era of dam construction. It was during the construction of these massive structures more than one hundred years ago that issues related to the placement of mass concrete began to emerge. During dam construction, the strengths of concrete required were low (typically under 5,000 psi) compared to the requirements for strength of current building elements, where concrete strengths can exceed 10,000 psi. Although many of the recommendations from ACI 207 may be useful for these types of structures, other recommendations from ACI 207 may not be practical for building elements. Nighttime foundation mat placement with multiple points of placement. STRUCTURE magazine

12 April 2018

Completion of mat placement; insulation and tarps being placed.

be necessary to post-cool the concrete via embedded cooling coils. Other than when insulation is used, the use of curing water on the slab is essential to prevent water loss and assist in the curing operation. In a normal concrete element, a temperature gradient is created between the interior, where the heat of hydration is trapped, and the exterior surface of the concrete that is transferring heat to the atmosphere. In colder weather, insulation is added to the top of the slab to maintain the thermal temperature gradient and prevent the top from cooling more rapidly than the core. Trying to maintain this same 35-degree differential when the interior of the concrete is “insulated” with several feet of concrete above and below it, zones that are also generating heat, is difficult when the exterior of the concrete is exposed to colder atmospheric temperatures, even with the use of insulating blankets. Note that the 35-degree limit is a general recommendation to prevent deterioration of the concrete due to the separation of concrete layers, but it is often at the discretion of the Engineer of Record whether higher temperature differentials may be tolerated.

Mix Designs Many recommended changes to the concrete mix for mass concreting reduce or slow the heat of hydration to limit temperature change and thereby lower the amount of crack formation. It is critical to reduce the quantity of cement in the mix. The replacement of cement with slag and fly ash (and now ground glass pozzolans) can help maintain required strengths. The use of larger aggregates can also help; however, this can often be difficult as the congestion of steel reinforcement and the method of concrete placement may restrict the aggregate sizes. Admixtures used for air entrainment, water reduction, set time, and shrinkage reduction, strength, and durability can be adjusted to slow or reduce the heat of hydration.

Thermocouple and wiring installed with mat slab.

Monitoring Concrete Temperatures The monitoring of concrete temperatures in mass concreting is commonly achieved through the use of thermocouples. These sensors are buried within the structural element prior to the concrete placement operation. Often, the SER generates a three dimensional grid that allows the temperature gradient to be plotted throughout the cross-sectional area of the element. The sensors report the temperature within the element and enable the engineer to verify that the temperatures have remained within the desired range from the initial concrete placement until final concrete curing operations are complete. When temperatures approach the limits of the desired range, changes can be made to the curing procedures, such as the addition or removal of insulating layers to balance the temperatures.

Cold Joints A cold joint forms when concrete already placed within the element begins to set even as subsequent layers of concrete are still being placed on top of it. The formation of a cold joint negates the monolithic properties that are always desired and, unlike a planned and formed construction joint, it is typically haphazard in its locations and is horizontal or on a slope. The failure plane created within the structural element is often hard to document, as it usually happens in the middle of the concrete placement when operations are the most hectic. Avoiding cold joints takes prior planning. During a pre-placement meeting before the start of mass concreting operations, it is important to plan and discuss the order of concrete placement and the number of placement points. The order in which the concrete is intended to be placed should be strategic to avoid leaving specific areas for extended periods where concrete can start to

STRUCTURE magazine

April 2018

set prior to additional concrete being placed next to it. Maximizing the number of points of placement keeps concrete flowing as much as possible. The pre-placement meeting may reveal that, due to site restrictions, the formation of a cold joint in an element is highly probable. The SER may need to consider the addition of strategically placed construction joints within the structural element to minimize the risk of a cold joint forming, and provide for the reliable transfer of forces. The use of a retarding admixture or a set delaying admixture is important to prolong the workability period of concrete and can help control temperatures. A typical procedure is to start the early concrete trucks with the maximum recommended quantity of admixture and then slowly taper off the admixture during concrete placement. Tapering the admixture during placement helps keep the concrete workable and also supports constructability for the contractor. The added fluidity of the concrete late in the placement increases the pressure head on the formwork system. Additionally, for most elements, laborers must remain on site until finishing and curing procedures are completed. If the retarding admixture is used in its full dosage until the end of the placement, the staff needs to wait on site for many additional hours beyond the pour until they can walk on the concrete and begin finishing/curing. Tapering the quantity of the admixture allows for more efficient staffing. A licensed structural engineer or an ACI certified technician observing the placement is recommended to help prevent the formation of cold joints. The engineer, in concert with the contractor, can use observations to make strategic real-time changes to the pour sequencing. The contractor can come back with a small amount of concrete to refresh an area that is starting to set and potentially form a cold joint. The pour can then continue. Unfortunately, even with the best planning, things can go wrong – a pump breaks, the concrete delivery is delayed, and so forth. It is critical that someone on site, typically the inspector or engineer, record and document the location of any cold joints that form. This allows the Engineer of Record to more accurately evaluate the impact to the structure and provide the most efficient remediation, if one is required.

Conclusion This article describes general approaches to address some of the mass concreting concerns that are particularly relevant to building structural systems. Several ACI publications are available for more information.▪

OUTSIDE

the box highlighting the out-of-theordinary within the realm of structural engineering

Designing Destruction An Investigation into Demolition of Complex Structures By Sean K. Hallet, P.E., Patxi Uriz, Ph.D., P.E., and Morgan Griffith, P.E.

Sean K. Hallet is the CEO, Founder, and Senior Forensic Engineer of Engineering Design International, Inc. (EDII). He can be reached at shallet@edii-us.com.

carcity of buildable land, aging infrastructure, and changes in urban environments create an increasing demand for the demolition of existing structures. Often, demolition is planned and executed by a demolition contractor relying on experience and judgment for techniques and sequencing. Appropriate for some types of structures, such as small residential buildings with large offsets from surrounding structures, demolition plans not prepared by an engineer may not be appropriate for larger and more complex structures, where the consequences of unforeseen structural behavior during demolition can be dramatic or even fatal. Just as the design of a complex structure requires careful consideration of structural engineering principles, the controlled demolition of a complex structure should include consideration of load paths, member capacities, the formation of structural mechanisms, and more. In fact, controlled demolition arguably requires an understanding of advanced structural engineering principles, such as non-linear geometric behavior and post-yield material behavior, due to the large displacements and high member demands inherent in many demolition techniques. This is particularly the case for demolition techniques where the structure is purposely weakened prior to demolition. The pre-weakened structure must remain stable for loads that are present before demolition to protect demolition workers, adjacent property, and the public. It is precisely for these reasons that a demolition plan prepared by an engineer,

competent in the field of structural deconstruction and controlled demolition, is appropriate for the demolition of a complex structure. When examining cases where a demolition plan is prepared by an engineer, the role of the engineer is different than that of an Engineer of Record (EOR) for traditional building design. Building codes provide clear guidance on design loads, safety factors, and a design or constructability review process for new construction; those codes provide little guidance for engineers planning a demolition. An EOR for new construction often limits his/ her role to that of the completed structure and excludes intermediate states of the building as construction proceeds. By contrast, the engineerâ&#x20AC;&#x2122;s primary role in demolition is often to consider intermediate deconstructive states as original load paths change throughout the controlled demolition process. Further, design and construction of new structures involve new materials with well-known properties. A structure scheduled for demolition is typically at or near the end of its useful life, leading to issues of archaic materials, degradation, fatigue, undocumented modifications, and the lack of original structural plans for guidance. Two more key distinctions between new construction and demolition are the relationship between the contractor and the engineer, and the checks-and-balances for their respective activities. Traditionally, in new construction, an EOR is hired to prepare the structural plans, and a contractor is hired to execute the plans. If the contractor wishes to deviate from the structural plans, a formal communication

Patxi Uriz has 11 years of experience in multi-disciplinary forensic analysis and consulting. He can be reached at patxi.uriz@rms.com. Morgan Griffith is an Engineer in the Buildings & Structures practice of Exponent, a multi-disciplinary engineering and scientific consulting firm. He can be reached at mgriffith@exponent.com.

Figure 1. Aerial view of power plant (boiler outlined). Courtesy of Pictometry.

STRUCTURE magazine

14 April 2018

because of the contractor’s traditional responsibility for means-and methods of construction. This can result in tragic consequences during demolition.

Case Study A steel boiler structure at a power plant had reached the end of its useful life and was scheduled for demolition (Figure 1). The structure consisted of eight stories of steel columns and beams suspending a 3-million-pound boiler assembly. Steel diagonal braces in each story provided lateral support. Due to the weight and complexity of Figure 2. a) As-designed: column stable until H-shaped support removal from mid-column notch; b) As-built: H-shaped the boiler assembly, it was support at lower column notch does not prevent closing of notches above. determined that the structure process is in place, such as a request for In many cases, an experienced demolition should first be toppled and the boiler disasseminformation (RFI). This process alerts the contractor is likely to understand potential bled from ground level. Proximity to operating EOR of the requested deviation and ensures hazards far better than a design professional power plant components ruled out explosive the EOR formerly reviews the request and with limited demolition expertise. Further, demolition. The demolition contractor hired either approves or denies the deviation. the demolition contractor is typically in a an engineer (required by that jurisdiction) to Both the engineering and construction contractual position to take prompt corrective develop a plan to pre-weaken the structure, phases include oversight, including plan measures via their control over demolition followed by mechanical toppling. check comments for the engineer’s work worker actions. Ten days before the incident, the engineer and special inspection for the contractor’s However, during the controlled demoli- submitted a plan to the demolition contractor work. To the contrary, demolition contrac- tion of a complex structure, the demolition for a “three-hinged pull” design, involving tors often hire the engineer. Due to limited sequence may result in local or global struc- the cutting of three “V” notches at selected regulations, communications are usually tural instabilities not apparent to a person first story columns and removal of selected less formal, even for significant changes. unfamiliar with load path, changes in the first story diagonal braces. The weakened colBuilding officials may have limited expertise load path, buckling, mechanism formation, umns would then be collapsed using cables in demolition and provide little oversight. and torsional instability. In those cases, attached to them, resulting in the toppling of Finally, due to the rapid nature of many an engineer familiar with the structure the remaining structure. A summary of the demolitions, there may be little time to and the demolition plan is best capable of demolition plan is as follows: consider the ramification of field changes identifying hazards associated with struc1) Removal of three of seven first story diagoto the demolition plan. tural instability during demolition. This nal elements; is particularly true when pre-weakening 2) V-notches cut near the top and bottom structures prior to demolition, which in three of the six first story wide-flange Engineer vs. is alluded to in the OSHA regulations columns; Competent Person (29 CFR 1926.859[g]): 3) Cut one notch near the middle of OSHA requirements related to demolitions, …During demolition, continuing inspections the aforementioned columns. Install intended to protect workers and not to by a competent person shall be made as the work H-shaped supports preventing middle regulate the role of an engineer, include progresses to detect hazards resulting from weaknotch closure, ensuring stability of the provisions that specify an “engineering ened or deteriorated floors, or walls, or loosened columns prior to toppling; survey” by a “competent person” prior to material. No employee shall be permitted to work 4) Attach cables to the weakened columns demolition. The definition of a competent where such hazards exist until they are corrected at mid-height and extend the cables to a person in OSHA regulations (29 CFR by shoring, bracing, or other effective means… location clear of the fall zone; and, 1926.32[f ]) is: Unfortunately, even in cases of demoli5) Remove the H-shaped notch supports and …one who is capable of identifying existing tions involving engineers, the engineer may fail the weakened columns by pulling on and predictable hazards in the surroundings or not have “authorization to take prompt the cables. This initiates toppling. working conditions which are unsanitary, haz- corrective measures to eliminate” hazards As implied by the demolition sequence, the ardous, or dangerous to employees, and who has associated with instability. This may be configuration of the V-notches and installaauthorization to take prompt corrective measures because of the engineer’s contractual rela- tion of the H-shaped supports was critical to eliminate them… tionship with the demolition contractor, or to the stability of the weakened structure. STRUCTURE magazine

April 2018

As shown in Figure 2a ( page 15 ) a notched column with H-shaped support maintains its stability by preventing the closure of the middle notch. The top and bottom notches are kinematically restrained and cannot rotate without corresponding closure of the middle notch. Removal of the H-shaped support allows lateral force, applied at the column mid-height, to result in high bending stresses at the remaining steel around all three notches. The steel yields, allowing the open notches to rotate closed, initiating a collapse mechanism. Prior to toppling, the H-shaped supports are necessary to prevent global instability associated with changes in load path through the weakened/notched columns. Mass eccentricities are inherent in the structure from existing loads and applied loads such as environmental loads (e.g., wind) and forces induced by the demolition crew. Shortly after receipt of the engineer’s plan, the demolition contractor began pre-weakening the structure. However, several field changes to the plan were made by the demolition contractor, including: • The removal of two additional first story diagonal braces (i.e., 5 of 7 were now removed); • The overcutting of notches in the columns beyond the dimensions specified by the engineer; • In lieu of H-shaped supports, steel cut from the column notches was re-purposed as “wedge supports.” • Installation of wedge supports at bottom notches rather than at mid-column notches. According to the demolition contractor, removal of the extra braces and the overcut “V” notches were performed to ensure that the structure was weakened sufficiently to be toppled with the cables. Ironically, the decision to place the supports at the bottom notches of the columns was due to worker safety concerns. The original plan required workers to use a lift to place mid-column H-supports; the contractor felt workers using the lift could not quickly evacuate the fall zone in the event of a premature collapse. The contractor elected to make the final cut at the base of the column. The decision to reuse steel cut from the column notches as supports was apparently made for the sake of convenience. The demolition contractor reported verbal approval for changes to the demolition plan from the engineer on the day of the demolition. However, no formal approval process was in place, and there is no evidence the engineer

performed additional calculations in support of the changes. Regardless, the engineer was on-site during the day of the incident and admitted to observing the changes. According to the engineer, he recognized safety concerns associated with the changes and instructed the demolition contractor to stop work just prior to the incident. The engineer’s warning was not heeded. The changes resulted in a weakened structure more vulnerable to premature collapse. However, moving the H-shaped/wedge supports to the bottom “V” notches significantly influenced the stability of the columns. As shown in Figure 2a, the placement of the H-shaped supports prevented rotation of the top and bottom notches. The configuration in Figure 2b is ineffective at preventing the middle and top notches from rotating closed and initiating the global collapse mechanism (regardless of the lower H-shaped support effectiveness). The modification from the original plan resulted in a global instability condition identifiable by simple engineering modeling, but not apparent to the demolition contractor. As the demolition crew continued to perform their final cuts moments before planned toppling, the unstable columns collapsed and the entire structure fell. One worker was killed, and two others were injured.

Engineering a Safer Demolition The construction industry in the U.S. has a long record of ever-increasing safety through worker education, procedural safeguards, codified design/construction practices, and oversight during the design/construction process. Engineers improve safety in new construction by anticipating possible loading conditions and designing the structure to behave in an acceptable manner subject to those conditions. There is broad acceptance of the need for this expertise in the construction of complex buildings. The case study demonstrates demolition of a complex structure requires similar expertise to ensure the structure behaves in an acceptable manner subject to demolition loading conditions. Most demolitions do not result in injuries or fatalities, but there are opportunities for safety improvements in the demolition industry, including: • Mandatory involvement of an engineer for the demolition of complex structures. A thorough understanding of structural engineering principles is key to identifying hazards associated with instability

STRUCTURE magazine

April 2018

during demolition. For some structures and demolition techniques, engineering licensure should be one qualification of the “competent person.” • More specific requirements for a demolition plan that address the following: What should be the qualifications of the preparer? If a building department lacks demolition expertise, who should review and approve the plan? What measures should a plan include to address the safety of surrounding structures and the public? Important questions such as these could prompt Statewide or nationwide consensus documents for demolitions. • Design load and safety factor requirements for pre-weakened structures. As illustrated by the case study, pre-weakening can result in premature collapse, presenting an extreme hazard to demolition workers. Guidance for engineers considering design loads and safety factors for structures in a weakened state could be codified, similar to ASCE-37 for temporary structures. • Demolition plan review and oversight by experienced individuals. Building departments that lack demolition expertise should seek it via peer review or third-party plan reviewers specifically competent in the decomposition of structures and controlled demolition processes. Proper oversight and the authority to stop work throughout the demolition process can significantly enhance safety. • Clarification of the relationship between the engineer and demolition contractor. Both the engineer and the contractor play a key role in a safe demolition. Similar to new construction, communication between the two could be enhanced by a more formal process. A system of written requests for plan modifications by the contractor, prompting engineering evaluation and approval by the engineer, could help identify hazards associated with those modifications. Finally, the engineer’s on-site presence should be required during safety-critical phases of the demolition, as defined by the engineer in the demolition plan, and the engineer should have the authority to stop work upon hazard identification.▪ The online version of this article contains references. Please visit www.STRUCTUREmag.org.

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PERFORMANCE performance issues relative to extreme events

Blast Design Exterior Non-Load Bearing Cold-Formed Steel Walls By Nabil A. Rahman, Ph.D., P.E., and Casey Oâ&#x20AC;&#x2122;Laughlin, P.E. Nabil A. Rahman is the Director of Engineering and R&D for The Steel Network, Inc. and a Principal at FDR Engineers in Durham, NC. He is the current chairman of ASCE-SEI Committee on Cold-Formed Steel Members. He serves as a member of the Committee on Specification and Committee on Framing of the American Iron and Steel Institute (AISI), and a member of ASCE Committee on Disproportionate Collapse. He can be reached at nabil@steelnetwork.com.

he DoD Unified Facilities Criteria (UFC) program developed documents to assist in determining the design basis threat and the desired level of protection of structures. Determining the level of protection to be achieved by a building against an explosive threat can be complicated and is based on analysis that considers variables such as the value of assets inside the building, likelihood of aggressor attack, aggressor tactics, and threat severity. An engineer designing for Antiterrorism (AT) must have an understanding of how to perform a blast analysis. The focus of this article is blast protection of exterior cold-formed steel framing (CFS) in the building envelope with controlled perimeters subject to air blast.

The Unified Facilities Criteria 4-010-01 Federally-funded research programs led to the creation of design manuals for blast-resistance, such as TM 5-1300 which has since been superseded by the 2008 UFC-340-02, Structures to Resist the Effects of Accidental Explosions, and UFC 4-010-01, DoD Minimum Antiterrorism Standards for Buildings, published in 2013. UFC 4-010-01 was created with the overarching goal of minimizing the likelihood of mass casualties from terrorist attacks against DoD personnel inside routinely occupied buildings. Though developed for DoD use, many private sector projects utilize the UFC 4-010-01. Current design guidance for blast loads is scarce, making the UFC 4-010-01 an extremely valuable document. The levels of protection described within UFC 4-010-01 are adequate to meet the goal of minimizing the likelihood of mass casualties. It establishes a foundation for additional protective

Casey Oâ&#x20AC;&#x2122;Laughlin is a Senior Research and Development Engineer in the Blast and Ballistics Research Group for Jacobs Technology at Tyndall AFB, FL. He can be reached at casey.olaughlin@jacobs.com.

Figure 1. Blast load end of stud connection.

STRUCTURE magazine

18 April 2018

measures in higher threat environments. When confronted with design basis threats (explosive weights) more severe than outlined by UFC 4-010-01, the designer should consult UFC 4-020-01. Most UFC documents can be downloaded for free from the Whole Building Design Guide website, www.wbdg.org. Unless adequate standoff distance can be provided, the UFC 4-010-01 applies to all DoD inhabited buildings, billeting, high occupancy family housing, and all DoD expeditionary and temporary structures. Existing buildings that do not meet prescribed standoff distances are required to meet the requirements set forth by UFC 4-010-01 when the building undergoes a renovation, modification, repair, or restoration that exceeds 50% of its replacement cost. When any of the above types of work are done to an existing facility, and the cost does not exceed 50% of the replacement cost of the building, the requirements of UFC 4-010-01 are merely a recommendation and not a requirement. Other types of work or types of structures that may trigger the requirements of UFC 4-010-01 are listed in section 1-8 of the document.

Standoff Distances Conventional construction standoff distances are outlined in Tables B-1 and B-2 in Standard 1 of UFC 4-010-01. Baseline explosive weights are outlined in Table B-1 as explosive weights I and II. Explosive weight I is physically too large to be carried by an individual and is assumed to be delivered by a vehicle. There is high confidence that the quantities of explosives given by explosive weight I would be detected during a vehicle search and the designer should understand that the standoff distance associated with a controlled perimeter is based on this case. Explosive weight

Windows, Skylights, and Louvers Standard 10 of UFC 4-010-01 deals with the design of window openings in exterior walls. The standard states that blast analysis (using explosive threats provided in Standard 1) should be performed for the supporting structural elements of windows and their connections at all standoff distances, even if the wall meets or exceeds the conventional construction standoff distance. Where a building is within a controlled perimeter, the applicable explosive weights shall be determined based on the standoff from the controlled perimeter. Louvers may not need to be treated as windows if they are designed to remain open at all times. The structural designer should consult with the design team and DoD authority for clarification.

Design Approaches Figure 2. Prescriptive wall design SSW1 (Edited from PDC TR-15-01).

II is representative of a hand placed explosive. Hand placed explosives cause significant localized damage, and the assumption is that there will be controls in place to prevent them from being brought into the building. Failure to meet specified minimum standoff distance will trigger a blast analysis per UFC 4-010-01. It is essential to understand that the standoff distances listed in Tables B-1 and B-2 are based on the analysis of details commonly associated with various types of construction. For cold-formed steel (CFS) stud walls, the reader should consult Table 2-3, Conventional Construction Parameters, to ensure that the structure in question falls within the ranges of properties listed. Any construction outside the ranges listed in Table 2-3 will trigger the need for a blast analysis. Also, note that UFC 4-010-01 address only Very Low and Low Levels of protection against explosive weights I and II. The US Protective Design Center

(PDC) Technical Report 10-02 should be consulted for higher levels of protection. Research, development, testing, and evaluation of CFS stud wall systems exposed to blast continue today. Research studies on standoff distances and performance of stud wall end connections, similar to the test shown in Figure 1, have facilitated the development of improved designs. A recent PDC Technical Report 15-01, Minimum Standoff Distance for Non-Load-Bearing Steel Stud In-Fill Walls, provides reduced prescriptive standoff distances and construction criteria. These data were developed from numerical analysis and validated with lab tests for in-fill sheathed walls with end connections to structural concrete detailed with additional anchorage, as shown in Figure 2. When using these prescriptive standoff values, designers should carefully review construction criteria and connection details to ensure compatibility with project application.

Table 1. Static and dynamic increase factors for cold-formed steel members.

Cold-Formed Steel

Static Increase Factor (SIF)

ASCE/SEI 59-11 Blast Protection of Buildings

1.1

ASCE Design of Blast-Resistant Buildings in Petrochemical Facilities (2010)

1.21

UFC 3-340-02 (2008)

1.21

STRUCTURE magazine

Standard 10 of UFC 4-010-01 provides two design approaches to size the supporting structural elements of exterior window openings subjected to blast loads. Static Design Approach The static design approach is a direct, simplified method to determine the required moment and shear strengths of the jamb, header, and sill that frame the opening. However, this approach is only allowed if the conventional standoff distance to the wall is met and it can only be used for punched openings. A punched opening is bound by a header, a sill, and two jambs, and has faĂ§ade material on all four sides. In the static design approach, a tributary area increase factor (C) is calculated as: a C = trib â&#x2030;Ľ1.0 awall

where awall is the tributary area for the typical conventional wall section (the typical stud), and atrib is the combined tributary area for the supported window and wall section. The required Dynamic Increase Factor (DIF) moment and shear strengths are calculated as: Bending/ Tension/ MSSE = C.MCW Shear Compression VSSE = C.VCW where MSSE and VSSE are the 1.1 1.1 required moment and shear strength of the supporting jamb, header, or sill, while MCW and VCW 1.1 1.1 are the moment and shear strength of the conventional wall stud section. The static approach is limited 1.1 1.1 to punched openings since it uses

April 2018

Figure 3a. Top slip track with no mechanical attachment.

Figure 3b. Top slip connector with mechanical attachment.

Figure 3c. Top slip track with mechanical attachment.

the tributary area of the typical wall stud to calculate the factor C. The end connections of the supporting structural element shall be designed for a load equal to the increased member shear capacity (VSSE).

to the element’s minimum yield strength. The SIF accounts for the difference between the specified minimum and expected actual yield strength, while the DIF accounts for high strain rate effects when the element is loaded dynamically. The recommended SIF and DIF values for cold-formed steel are summarized in Table 1 (page 19 ). In order to accept or reject the results of the SDOF analysis, response criteria should be defined. PDC-TR 06-08, SDOF Structural Response Limits, gives the response criteria limits in the form of maximum ductility ratio (μ) and maximum support rotation (θ). Table 2, which is part of PDC-TR 06-08 Table 4-6, shows the maximum allowed μ and θ for steel studs with various end connection conditions. Notice that the response criteria limits are dependent on the allowed damage level of the element. The damage level is a function of the Level of Protection (LOP) assigned to the structure, and whether the element is primary, secondary, or non-structural. For example, a gravity load-bearing element is a primary element while a curtain wall lateral load bearing element is a secondary element. The relationship between the LOP and element damage level is given in PDC-TR 06-08 Table 3-2. The

response criteria limits in Table 2 are relatively stringent due to the limited capacity and ductility of conventional CFS framing systems in addition to limited test data. Exterior CFS studs and opening jambs are categorized as top slip track stud walls if a single or double slip track detail is used to attach the stud or the jamb, at their top ends, to the structure (Figure 3a). This connection detail does not provide a direct mechanical attachment between the stud and the top track; therefore, it is assigned a relatively low ductility ratio. However, exterior CFS studs and jambs can be categorized as studs connected top & bottom if a slip connector or a slip track detail is used to attach the stud or the jamb at their top end to the structure, as shown in Figures 3b and 3c. This provides mechanical attachment between the stud and the top track and, therefore, it is assigned a higher ductility ratio. The same ductility ratio can be used for exterior CFS by-pass studs and jambs if the member spans across at least three supports. The PDC offers an Excel-based tool to design structural components with applied dynamic loading using the SDOF approach. The tool is called Single-degree-of-freedom

Dynamic Design Approach Typical CFS stud walls and the supporting structural elements of a window opening can be designed for the appropriate blast pressure, impulse, and duration using dynamic analysis. The design loads are determined from the applicable explosive weight at the actual standoff distance and should be applied over the areas tributary to the element being analyzed. A simple dynamic approach recommended by the UFC is the single-degree-of-freedom (SDOF) analysis. In the SDOF, the structural element is modeled as an equivalent mass-spring system. The mass and dynamic load of the equivalent system are based on the structural element mass and blast load, respectively. The spring stiffness and yield load are the flexural stiffness and out-of-plane flexural capacity of the structural element, respectively. The flexural capacity includes the effects of the Static Increase Factor (SIF) and the Dynamic Increase Factor (DIF) applied

Table 2. Flexural response limits for cold-formed steel (From Table 4-6 in PDC-TR 06-08).

B1 Superficial Damage

Member

Steel Studs

B2 Moderate Damage

B3 Heavy Damage

B4 Hazardous Failure

Top slip track stud walls

0.5

0.8

0.9

Studs connected top & bottom

0.5

Stud ends anchored to develop full tensile membrane capacity

0.5

STRUCTURE magazine

April 2018

Summary This article introduces antiterrorism design requirements and various analysis processes for exterior CFS stud walls. The UFC 4-010-01 provides measures to establish a required level of protection against terrorist attacks for all DoD buildings. Conventional construction parameters and conventional construction standoff distances for CFS stud walls are established in UFC 4-010-01. Exterior CFS walls meeting the requirements for conventional construction parameters and standoff distances do not require blast analysis. However, blast analysis should be performed for the supporting framing elements of windows and their connections, at all standoff distances. For a numerical design example illustrating the detailed blast analysis and design of a CFS exterior non-load bearing wall and the Jamb member of a punched window opening, refer to Cold-Formed Steel Engineers Institute TN S100-16, www.cfsei.org. It shows that the dynamic design approach for CFS stud walls is more economical and is, therefore, recommended over the static design approach.▪

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18-15103_premACC_Structure_Mag_Ad_2thirds_Update_FINAL.indd STRUCTURE magazine 21 April 2018

18-15103

2/27/2018 12:12:54 PM

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Blast Effects Design Spreadsheet (SBEDS) and is available online at www.pdc.usace.army.mil/software/sbeds after obtaining approved access. The top and bottom connections of wall studs and window jambs are designed for the peak reaction of the member. Note that, if the resulting ductility ratio (µ) of the member is less than 1.0, the member did not reach its yield limit in flexure and it is, therefore, permissible to reduce the design peak reaction by the value of the ductility ratio. Connector and fastener strength are conservatively recommended to be calculated based on their nominal resistance and appropriate code strength reduction factors (φ). The connection design shall account for all potential failure modes for the given connection type and base material. Regardless of whether the static or dynamic design approach is used, the reaction forces from the CFS studs or window jambs do not have to be carried through the horizontal bracing system or floor diaphragm as long as the mass of the building can dissipate these reactions before they are transferred to the foundation. However, if the stud wall does not have a direct path to a bracing system or a diaphragm, then a path needs to be created for the reaction until it is dissipated into a massive element.

A New Trend

in Multi-Story Office Construction

“Tall-Tilts” Tilt-Up Construction Elevated to Class A Office Buildings By James M. Williams, P.E., C.E., S.E., AIA, LEED AP

The Entrata Building is the first 4-story, tilt-up, class “A” office building in Utah, and one of a few nationally.

ilt-up construction is typically associated with non-descriptive, natural light and takes advantage of the surrounding views. The “big-box” warehouses and is considered “cheap construction” glazing-to-wall ratio matches or exceeds class A office space requireby many. When a structural engineer is asked to select a struc- ments. Spandrel glass is used architecturally to conceal portions of tural system for a new multi-story office building, tilt-up concrete the tilt-up panels where desired for aesthetics. probably doesn’t make the list of options. Tilt-up concrete construction The tilt-up concrete panels support gravity loads as well as resist today, however, is not the tilt-up construction of past generations. both in-plane and out-of-plane lateral loads due to wind and seismic Tilt-up construction has evolved from warehouse buildings to large forces. Since most tilt-up wall panels in these applications are slender, retail centers, schools, places of worship, and now…multi-story, jambs at the wall openings and the orthogonal wall adjacent to the class “A” office buildings. This trend has gone almost unnoticed openings must contribute to the stability and structural capacity of due to contemporary architectural designs and finishes and creative the tilt-up component. This contribution is often neglected but is structural solutions; the public probably isn’t aware these buildings critical in the design of tilt-up wall panels. Section 11.8, “Alternative are constructed of tilt-up concrete. There are numerous design and construction resources available through the American Concrete Institute (ACI) and the Tilt-up Concrete Association regarding tilt-up construction. Some of these publications include; ACI 551.2R-15 Design Guide for Tilt-Up Concrete Panels, ACI 318-14 Building Code Requirements for Structural Concrete, 550.2R-13 Design Guide for Connections in Precast Jointed Systems, and Engineering Tilt-UP published by the Tilt-Up Concrete Association. The Portland Cement Association (PCA) also publishes, PCA Notes on ACI 318-15 Building Code Requirements for Structural Concrete with Design Applications. The Precast/Prestressed Concrete Institute (PCI) publishes the PCI Design Handbook, 7 th Edition and PCI Design of Connections of Precast Concrete. These publications provide a lot of useful information, but none of them fully address the design of multi-story tilt-up concrete buildings. The Entrata Building is a new four-story, 106,000-squarefoot, class A office building constructed using tilt-up concrete. Unlike warehouse buildings with little or no windows, this building was designed to maximize the amount The Entrata Building is the first tilt-up building in Utah to be braced to the exterior of glazing so that interior spaces could have floor-to-ceiling during construction, using temporary bracing attached to temporary helical piers instead windows. This design feature provides an abundance of of the conventional deadmen. STRUCTURE magazine

April 2018

Typical jamb and header reinforcing and additional diagonal bars at inside corners.

method for out-of-plane slender wall analysis,” of ACI 318-14 should be considered in the design. Also, slender wall sections must consider the reduced wall thickness due to the effect of any reveals or thin brick or form liners that may be used. Additional information regarding the design of slender walls is provided in ACI 551.2R-15 Design Guide for Tilt-Up Concrete Panels. Design examples are provided in the appendix. Keep in mind that, when designing connections, each load combination and path must be considered since nearly all connections are part of the gravity, the in-plane, and the out-of-plane load-resistance of the system. Most structural failures occur in the connections and are due to load combinations (as well as the direction the loads are acting) that are often not properly considered. The 60-foot-tall wall panels of the Entrata Building were constructed on the ground and lifted into place. The building shell was erected in only 10 days without the need for any exterior scaffolding. Tilt-up walls are often braced to the interior of the building and the brace is temporarily connected to the slab-ongrade. This bracing method generally works for construction up to three-stories but, when erecting taller tilt-up walls, the panel needs exterior bracing. Historically, exterior bracing requires connection to deadmen or piles. The Entrata is the first tilt-up building in Utah using exterior braces during construction, attaching braces to temporary helical piers. Typically, interior structural steel members are not placed until after the walls have been erected. To expedite this project, however, a portion of the structural steel building core was erected prior to the wall panels to meet the owner’s aggressive construction schedule. For small-footprint, 4-story buildings and taller, there is typically not enough available space on the floor to cast all wall panels. Therefore, temporary waste-slabs are needed for casting. Waste slabs are a “means and methods” of construction, are usually 4- to 6-inch-thick concrete

and are unreinforced. For this project, all the walls were cast on waste slabs, allowing the structural steel to start erection while reinforcing steel for wall panels were still being tied. Generally, structural steel arrives at the site about the same time, or shortly after, walls are being erected. However, in this case, early steel erection was able to help expedite the construction schedule. The waste slabs were later crushed on-site and used as recycled roadway base. The 60-foot-tall wall panels are only 11.25 inches thick, having a height-to-thickness ratio of 64. ACI 551.2R-15, Section 7.1, suggests a minimum thickness of h/50 for a single-layer of reinforcing steel, and h/65 for walls with reinforcement at each face. A 6,000-psi concrete was required to satisfy in-plane shear wall forces, in conjunction

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Concrete tilt-up wall panel with various form liners and reveals. Innovative brick systems were also used to cast thin brick into some of the tilt-up wall panels.

April 2018

hooked ends in walls and lintel beams, or the bars needed to extend through jambs with vertical reinforcing and boundary members encased on closely spaced ties. To eliminate some of the reinforcing congestion in lintel beam and jamb interfaces, standard hooked ends were replaced with Headed Reinforcing steel, which is new to tilt-up construction. This greatly facilitated rebar and concrete placement, reducing weight, and helped to reduce the overall schedule. Buildings can often be longer in one direction than in the other. For tilt-up construction like Entrata, wall panels can easily be designed to resist all lateral loads in the longitudinal direction while the interior, steel braced frames resist loads in the transverse. However, this experience suggests that 4-story tilt-up buildings are posPanel drawings for a portion of the tilt-up walls, showing openings, spandrel glass locations, form sible without any interior braced frames, where liners, reveals, and embedment plates for connections. the perimeter wall system resists all of the lateral with the required reinforcing steel. While thicker walls with lower loads in both orthogonal directions. This can reduce the construcconcrete strength are sometimes specified, this results in heavy wall tion schedule even more, resulting in more substantial cost savings. panels. Thinner walls reduce the weight of the panels, help facilitate Usually, the design of a multi-story tilt-up concrete building requires lifting, and reduce crane costs, which can be substantial. A minimum the use of multiple software packages to provide a complete engineercompressive strength of 4,000 psi is recommended for durability. ing design and increase productivity. ENERCALC, Tilt-Werks®, or Construction sequencing is essential since the wall panels experience other structural engineering programs can be used to design the condifferent load and bracing conditions throughout the erection process. crete elements for gravity loads, or specialized MathCad worksheets While most tilt-up wall panels are initially designed as slender, walls can provide control in design, especially for the slender wall evaluation. in their final state, braced at each floor and roof, may no longer act as Ram® Steel can be used for the interior steel framing, Ram Structural slender. An analysis must consider sustained environmental loading System for the lateral analysis, and then Ram Concrete can be used as well as construction considerations. to evaluate all shear walls. Typically, a specialty engineer hired by the manufacturer provides One advantage to tilt-up is exterior wall panel surfaces also act as the the lifting inserts and bracing calculations, which are reviewed by the architectural finish and can have a variety of textures created through the design professional. Design calculations should consider the geometry use of multiple form-liners, reveals, plain concrete surfaces, and thin-brick. of each panel, the recessed areas, reinforcing steel (as specified by the All of these finishes are cast into the tilt-up panels and are integral with project engineer plus any additional needed for lifting), the size and each panel. For this building, the exterior concrete surfaces are painted. location of lifting inserts, panel weight, other embeds, all bracing Other finish options include natural concrete, exposed aggregates, colored requirements, and all lifting requirements. For the Entrata Building, concrete, and effects using sandblasting. The building shell of this building the reinforcing steel required for the design of gravity and lateral loads significantly reduces the need for future maintenance. was also adequate for lifting the panels; no additional reinforcing Although the Entrata building is the first 4-story tilt-up building steel was required. Buildings that are 3-stories or less often require in Utah, there are other tilt-up office buildings in other parts of the additional reinforcing steel for lifting. country which are 5 and even 6 stories in height. These are accomThe weight of each 4-story wall panel is approximately 150,000 plished by constructing a 4-story structure and then stacking a single pounds, but such panels can weigh as much as 200,000 pounds. Larger or two-story panel on top of the 4-story structure. The upper levels loads may require a larger crane, which can add significant costs. In are braced internally to the 4-story structure. some states, wall panels are erected by steel erectors, while in other states The new trend of multi-story office building construction will conthe general contractor, or a tilt-up sub-contractor, erects the panels. tinue to expand as engineers, architects, and owners become more Since all the connections are achieved using embedment plates, con- familiar with tilt-up construction and the endless possibilities that nection eccentricity and computed demands must also be considered exist. Tilt-up construction is coming of age and can be a cost-effective in the design. In a multi-story building, the floor diaphragms brace solution for multi-story buildings. the walls, and properly designed connections can help resist the The Entrata building is the recipient of 2017 Excellence in Concrete additional bending due to the eccentric load. Award, the 2017 TCA Tilt-Up Achievement Award, the Once in place and depending on how they were detailed, the tilt- 2017 ENR Regional Best Projects award, and the Utah up wall panel, or portions, may act as a beam, deep lintel, column, Construction and Design Magazine’s Publishers Pick, jamb, wall pier, shear wall, moment frame, or some combination. Most Outstanding Building Award.▪ The design of these panels and components are addressed in ACI 318-14, while Chapter 18 addresses special detailing needed for James M. Williams is President of AE URBIA aka J.M. Williams and structures in regions of high seismicity. Coupling beam requirements Associates, Inc., a Utah based architectural and structural engineering firm. can typically be avoided by applying section 18.10.7.1 or 18.10.7.3, He has served as the President of SEAU and has also served on the Board but that behavior must be consistent with the analytical modeling. and Executive Board of Directors for the TCA for 7 years. James is currently The Entrata Building is located in an area of high wind and seismic, on the AIA’s Codes and Standards Committee. thus requiring special detailing. Horizontal bars needed to have STRUCTURE magazine

April 2018

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Renovating a Hidden Treasure

By Russell Kehl, S.E., Melineh Zomorrodian, S.E., and Maria Mohammed, P.E.

October 2017, renovated John Anson Ford Amphitheatre.

n 2012, Structural Focus and the project team led by renowned preservation architect Brenda Levin embarked on the renovation and expansion of the historic John Anson Ford Amphitheatre nestled in the Hollywood Hills above Los Angeles. The project included the renovation of the historic theater and construction of the new Ford Terrace building, all within the current boundaries of the site. The topography and the historic nature of the project presented unique structural challenges for the team. Tucked in a canyon in the Cahuenga Pass, the historic amphitheater is embedded in the steep slope of the hills around the site. Originally

Figure 1. The theater reconstruction out of reinforced concrete (1931). Courtesy of the Los Angeles Public Library Photo Collection.

STRUCTURE magazine

built as a wood framed structure in 1920 and destroyed by a brush fire in 1929, the Ford Amphitheatre was reconstructed out of reinforced concrete in 1931 (Figure 1). As the theatre structure aged, it became evident that improvements were needed. At the beginning of the renovation project, the team spent many hours on site trying to understand how the existing building structure fit within the site topography. The first challenge was understanding the existing building layout and structure since no original structural drawings were available. The lack of existing drawings meant the steel reinforcing in the concrete elements remained a mystery. The analysis of all existing concrete structural elements was a challenge throughout the project. The canyon hillside is the backdrop for the amphitheater stage where a series of stepped stone retaining walls behind the stage were failing. It became clear that rebuilding the retaining walls was necessary. A significant amount of time was spent working with the contractor to come up with a design and layout that could be built on the hillside, as the retaining walls needed to step down towards the stage following the steep slope of the canyon. Coordinating access to transport construction materials and heavy machinery required outside-the-box thinking. The final solution used a large crane to lift construction materials and machinery from the staging area over the existing concrete stage tower onto the canyon hillside where the retaining walls were being constructed (Figure 2). The original stage was not centered on the amphitheater seating area. The design team was tasked with rebuilding a new stage that was centered and could house a lift connecting the split-level stage. Also, a portion of the subterranean area below the original stage was not usable due to the sloping canyon hillside that tucked under the stage slab. By reconstructing the stage, additional square footage was captured below. This created new back-of-house space for the April 2018

performers. The new reinforced concrete stage was constructed with to support lighting fixtures, banners, two 3,000-pound speakers (one concrete retaining walls around the perimeter (Figure 3 ). The new stage at each end), and other theatrical equipment. The truss is supported retaining walls resist surcharge loads from the existing stage-left and on new HSS 20x20 columns connected to the towers for lateral stage-right towers and the newly constructed hillside retaining walls. support. Locating the new supporting columns adjacent and inside Several potholes were dug adjacent to the existing concrete towers required the existing structure to discover the coordination with the design team to size and depth of existing footings to limit the impact on the interior space determine the surcharge loading from of the towers and the historic characthe structure. teristics of the amphitheater. To improve the experience of both The new Ford Terrace building is performers and audiences, the team tucked into the canyon hillside and also designed a new sound wall and constructed on the north side of the control booth behind the amphiamphitheater with a seismic joint theater, along with multiple new between the existing historic buildlighting towers located on either ing and the new structure (Figure 5, side of the stage and the seating area page 28). A new stair and elevator (Figure 4 ). The twenty-five-foot tall tower between the amphitheater and sound wall improved the acoustics the new structure provides access to of the venue and shielded the theater Figure 2. Construction of new stepped retaining walls behind the both buildings. The three-story buildfrom Hollywood Freeway noise. Early stage. Courtesy of Levin & Associates Architects. ing includes a loading dock at the in the design process, the decision bottom with direct access to the stage, was made to work with a design/build a terrace with a concession stand at the contractor to design the aluminum second level, and office space at the sound wall. By using aluminum, the third level. The roof houses mechanical weight of the sound wall was reduced units for both the amphitheater and significantly. However, the large wall the Ford Terrace building (Figure 5). area and narrow depth created subA mechanical screen wraps around the stantial overturning forces due to roof to hide the equipment. wind and seismic loads. Structural Similar to the new stage retaining Focus designed a new structural walls, lateral soil pressure from the steel support system for the sound hillside was accounted for during the wall while coordinating with the calculation of structural loads on the Texas-based design-build engineer. Ford Terrace building. The new buildThe new frames support the sound ing was designed to be structurally wall over the existing twelve-foot-tall Figure 3. Construction of the new reinforced concrete stage. Courtesy independent from the existing amphihistoric concrete wall behind the seat- of Levin & Associates Architects. theater, but there are several locations ing area. Support columns penetrate where the two buildings touch and through the amphitheater concrete isolation joints were required. This slab and extend into the space below. included a slide bearing joint at an Locations of the new sound wall supexterior stair and a joint between port columns above and below the adjacent retaining walls. The acceleramphitheater were coordinated to ated project schedule required careful avoid disrupting the existing concoordination between the depth of crete framing below. Without original the new building footings and the building drawings and with a limited new stair and elevator tower to avoid exploratory investigation, assumpshoring and surcharge loading on the tions were made about the layout amphitheater retaining walls. Also, of the existing building foundations vertical clearance requirements for during the design phase. This led to truck access to the loading dock more coordination and modifications located below the terrace slab required during construction. that the location of the concrete colFigure 4. New sound wall and control booth behind the amphitheater. There were several complexities assoumns that support the terrace slab, ciated with the design of the new lighting towers. In addition to and the depth of the terrace slab beams, be limited and established catwalk lighting towers on either side of the new stage, cantilevered very early in the design. lighting towers were added on the right and the left side of the The existing and the new structures are also connected by a new amphitheater seating area (Figure 4 ). The forty-five-foot-tall towers underground tunnel between the area below the stage and the new added significant foundation reactions to the complex hillside foun- building loading dock. Careful coordination with the contractor was dation system. The house-left tower required the construction of a required to build the tunnel because it passed under an existing hisnew retaining wall below the amphitheater to resist surcharge loads. toric wall that dictated shoring and protection during the excavation A new proscenium truss spans sixty-five feet over the stage between process. The new tunnel walls and lid were designed for the surcharge the two existing concrete towers on either side (Figure 4 ). It is used loads from the existing structure above. continued on next page

STRUCTURE magazine

April 2018

Figure 5. The new Ford Terrace building on the north side of the amphitheater. Courtesy of Tom Bonner Photography.

Figure 6. Renovated John Anson Ford Amphitheatre.

The team collaborated to solve challenging constraints and deliver a successful project. “We have had the pleasure of working with Brenda on several historic renovation and preservation projects,” stated Structural Focus Principal Russell Kehl, S.E. “Brenda is amazing at collaborating with her project team to solve challenging constraints and deliver a wonderful project that will be enjoyed by many generations to come.” In July 2017, the Ford re-opened as a state-ofthe-art performance venue and cultural meeting place (Figure 6 ). In a recent interview with The Planning Report, Brenda Levin stated, “The Ford Theatres, for the first time in its 86-year history, has the capacity to be a competitor with any of the great venues in Los Angeles.”▪

Russell Kehl, S.E., is a Principal at Structural Focus. Russell is a member of the Structural Engineers Association of Southern California and the American Society of Civil Engineers. He can be reached at rkehl@structuralfocus.com. Melineh Zomorrodian, S.E., is a Project Engineer at Structural Focus. Melineh is a member of the Structural Engineers Association of Southern California. She can be reached at mzomorrodian@structuralfocus.com. Maria Mohammed, P.E., is a Design Engineer at Structural Focus. She co-chairs the Structural Engineers Association of Southern California Younger Members Committee. She can be reached at mmohammed@structuralfocus.com.

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STRUCTURE magazine

April 2018

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STRUCTURES significant structures of the past

ver the years, Leffert Buck (STRUCTURE, December 2010) replaced some of the wires, added anchorages, replaced the wood and iron suspended span, and finally changed the masonry towers with iron in Roebling’s Niagra Suspension Bridge (STRUCTURE, June 2016). The bridge, with its single track, outlived its usefulness by the early 1890s. Buck received the commission to build a new two-track bridge on the same alignment without interrupting traffic. His assistant in the calculations and his resident Engineer was Richard S. Buck, graduate from Rensselaer in 1887. The two Bucks would have an association lasting twenty years. Buck had to choose between a three-hinged arch, similar to his earlier Driving Park Bridge in Rochester, a two-hinged arch, or a hingeless arch. In actuality, he only considered the first two types, asking himself “which is preferable, ease of calculation and adjustment, inconsiderable temperature stresses, and greater vibration, or greater rigidity with increased temperature stresses and difficulty of adjustment?” Once he had chosen his number of hinges, he had to decide how he would brace his arch. Three methods were used in the past. They were the solid-rib, similar to the Washington Bridge in New York City; the bracedrib, similar to the Eads Bridge in St. Louis; or the spandrel braced bridge, similar to his Driving Park Bridge. Having had the experience of Driving Park, he chose the two-hinged spandrel-braced arch, primarily for its greater rigidity.

Replacement Arch for Roebling’s Niagara Suspension Bridge By Frank Griggs, Jr., Dist. M.ASCE, D.Eng., P.E., P.L.S.

Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an Independent Consulting Engineer. Dr. Griggs can be reached at fgriggsjr@twc.com.

Deck cross section (built up around suspended span).

STRUCTURE magazine

30 April 2018

Having selected his arch type, how could he build it without interrupting traffic on the suspension bridge? It was clear that he could not hang the new arch from the existing bridge without overloading it, making it inadequate to carry the required railroad traffic. He contemplated transporting material using a cableway supported on the existing bridge towers similar to the method he had used on the Verrugas Viaduct in Peru, but he determined the cost of the plant would be excessive. He decided to use Roebling’s bridge only for worker access and to carry members to their location on a track running on a cantilever off of the lower deck on each side. The members would then be lifted into place by a traveler, initially running on the falsework and later on the top chords of the new arch. The arch would be built as a cantilever with no erection loading being placed on the suspension bridge. Since the new bridge would be wider than the old, the two arches would be erected outside of the existing suspension bridge structure. Placement of the cross bracing between the arches, which were directly under the existing bridge, required careful handling of the members with block and tackles anchored to the underside of the top chord. Drift pins or bolts secured all connections during erection. Most of the field riveting was done after the arch was closed. The steel was fabricated and erected by the Pennsylvania Steel Company with John V. W. Reynders, another Rensselaer graduate, as chief engineer. Pennsylvania Steel was an up-and-coming company and, with this project, they earned a reputation which they would build upon in

Toggle plan.

Erection under Roebling Suspension Bridge.

the rest of the century and the early part of the 20th century. Since the two-hinged arch is statically indeterminate, Buck based his design upon work by Clerk Maxwell. Maxwell had developed an equation based upon the deformation of any member of the arch under unit values of the horizontal and vertical components of one of the reactions. His member sizes were designed utilizing the analysis technique contained in Professor Greene’s book on Arches. He determined the load in each member under a unit value horizontal

reaction and a unit value vertical reaction and then determined their contribution to the horizontal reaction, summing these effects to obtain the total horizontal reaction. He started his analysis by assuming all the member sizes were identical, thus simplifying his calculation for the initial horizontal reactions. Once these values were known, the arch became statically determinate and forces in the members could be found under design loading. These forces would lead to new member sizes. This was an iterative process, requiring an estimated member size to

start the process, and was extremely time consuming and laborious. Since Buck decided to build the bridge utilizing the cantilever technique, he would have to design each member to carry its erection loading as well as its service loading. This, of course, increased the amount of calculation required. Buck, however, decided to not rely entirely on these calculations. “The lower chords at the middle point were lighter than the speaker [Buck] liked to have them, and the middle portion of the top chords was very heavy;

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Buck Bridge.

consequently, he increased the middle portion of the bottom chord by one-half the difference between the three-hinged and the two-hinged arch.” He further said, “for which he is not sorry.” His skewback foundations were begun in 1895. He notched the foundations into the rock on the side of the gorge and built the masonry, with some concrete, directly on the rock. He then set his steel skewback on the masonry, anchoring it down with six 2½-inch-diameter bolts. Unlike any bridge prior to this, Buck decided to use a roller assembly rather than a pin to connect the structure to the skewback. He used this method because this type of bearing “reduces frictional resistance much as a ball-bearing does, and was adopted to avoid the use of an excessively large pin, with which movement is rather doubtful of realization.” Buck built falsework out from the banks to support the approach spans and traveler tracks. The top chords of the approach spans were strengthened to provide tension members that would be utilized to support the cantilevered segments of the arch during construction. Buck designed and built a unique toggle device and anchorage. A short segment of falsework was erected under the arch near the skewbacks to commence the construction of the arch. Once the arch reached this point, a diagonal was dropped down from the ends of the anchor bars to support the first portion of the arch. This cable, of course, in addition to placing loading in the anchor bars, also placed loading on the end vertical of the spandrel bracing. This member was therefore significantly larger than it needed to be to carry its service loadings. Once the end vertical and first diagonal was erected, the end post was inclined a specified amount towards the shore using the toggle. The next vertical and first top chord member were placed and pinned

to the anchor chains. The traveler then moved off of the falsework onto the top chords of the arch, and the next panel erected and tied back. This process was repeated six more times from both ends of the bridge until the arches met in the middle. He decided not to plane the ends of his center segments until the ends of the arch approached one another (with each arch six panels out). At this time, he measured the distance between the two ends of the converging arches. Due to atmospheric conditions, he did not trust the accuracy of this measurement and decided to plane the ends to plan. As the pieces were put in place, “the closure at the middle was anticipated with considerable interest and anxiety. The absence of the center hinge rendered great accuracy in laying out the work necessary, in order to secure proper closure and distribution of load between the top chord and the rib.” He anticipated that if “the stresses in a two-hinged arch were carefully calculated through all the members when the dead load alone was on, and the shortening of members in compression and the lengthening of members in tension accurately worked out, and the increase or decrease in the length of each as indicated by these calculations made; the top chords being in tension and the lower chords in compression in erection, the top chords would naturally meet first when the bridge came together.” This, however, did not happen. When the final pieces were placed, there was a gap of 8 inches at the bottom chords since the arches were drawn back to erect the arches above their final position. They then slackened all the toggles and, to their surprise, the bottom chords met first, leaving an approximate gap of ½ inch in the top chord. They had planned on the top chord carrying about 350 tons in this state and, with the gap, it obviously was carrying no load. They then removed some of the drift

STRUCTURE magazine

April 2018

pins and bolts, allowing the joints to close which reduced the gap to ¼ inch. To close this gap, they built a new toggle that “was improvised largely from material on the ground.” They calculated that the ends would have to be separated by 1 inch to place a load of 350 tons in the top member. Turning “but one nut, the toggle was compressed on both sides and with a given pull on the wrench, and a careful estimate of friction, the required pressure could be very closely obtained.” They then inserted a 1-inch-thick shim with the same cross-section of the top chord and released the toggle, thus placing the desired loading in the top chord. With this step complete, they finished riveting the arch using a 70-ton pneumatic riveting machine operated by a compressor plant located on the American side. They then began construction of the deck structures and the transfer of load from the suspension bridge to the arch bridge, all the time maintaining traffic on the bridge. The new lower floor structure was placed to pick up the bottoms of the existing trusswork and the existing lower deck. The suspenders and stay cables were then cut, transferring the entire load of the Roebling bridge to the Buck bridge. The main cables were then removed by cutting the wrapping wire with axes, and by cutting the strands from their shoes and dropping one strand at a time. The upper floor was then placed following a technique similar to that done by Buck when he replaced the wood and iron suspended structure of Roebling with all iron in the 1880s. “The same track alignment was preserved, and the same rails and ties were used temporarily after the new floor beams and stringers were in place.” They replaced two panels per day in the two-hour windows in which they had to work. The towers were then removed and the plate girder approaches installed. Over time, the tracks were replaced as they went to the two-track configuration. Buck designed the bridge to carry 10,000 pounds per running foot, but he could not find any locomotives that would place this loading on the bridge. He, therefore, tested the bridge under 6,500 pounds per running foot by making up two test trains. “Each train consisted of two heavy Lehigh pushers, four of the heaviest Grand Trunk locomotives at hand, and nine coal cars...some load was put on the lower deck, chiefly on the end spans.” Under this loading, the maximum deflection was 13⁄16 inch. Differences at the quarter points, due to the test trains being at a quarter point, was less than 1¼ inch. His brothers in the bridge-building field acknowledged Buck’s triumph. Gustav Lindenthal wrote that, “the use of riveted

connections in the Niagara Bridge is a remarkable deviation from American practice; but that it was a proper choice cannot be questioned, and it is the more creditable to the engineer as the temptation to use pin connections, for greater ease of erection, was one not easily ignored.” He did not like the rollers at the skewbacks, writing that they “will hardly find imitators.” J. M. Moncrieff, an English engineer, wrote, “the engineer, and all concerned in the work, are to be congratulated on the successful completion of so handsome a structure under difficult conditions of erection.” Henry Tyrrell, in his History of Bridge Engineering, wrote, “the opening of the Niagara Railroad Arch marked a new period in American bridge design. The remarkable example of modern engineering was completed in 1896 at the cost of $500,000.” Erection on the bridge started September 17, 1896, and it was tested on July 29, 1897. The bridge was completed on August 27, 1897. It was, with its 550-foot span, the longest railroad bridge in the world for three years, having replaced the Roebling Bridge which held the record prior to this time. Within five years, its span was exceeded by the Forth Bridge, the Lansdowne Bridge, the Red Rock

Bridge, and the Memphis Bridge. All were cantilevers designed for railroad traffic only. It remained the longest railroad arch bridge for many more years. With this bridge complete, Buck would, after 21 years, finish his work on rehabilitating and replacing Roebling’s Bridge. The existing bridge is truly Buck’s creation and has served as a model for subsequent railroad arch bridges. The bridge was opened with a three-day, international celebration, September 23 to 25, 1897, sponsored by the Grand Trunk Railway. The Niagara Falls Gazette wrote, “today Niagara Falls is celebrating the achievement of one of the greatest engineering feats of the day – the completion of the new railway suspension bridge, connecting Canada and this country with one of the most magnificent structures of the world.” The actual opening took place on September 23 at 1:30PM when, to the accompaniment of four bands, the mayors of both Niagara Falls’ “met in the center of the bridge, and there, standing upon a massive steel link connecting two of the greatest nations of the earth, each grasped the hand of the other in a hearty and sincere grip...” The press

could not say enough good about the bridge and in this account called it “one of the most miraculous mechanical and engineering works of man.” There were no speeches “because it would have been impossible to find any place where the crowds could be accommodated, and the management of the celebration had decided that there will be no public speaking.” The Bridge was rehabilitated in 1919 by Charles Evan Fowler, who wrote a lengthy article in the Transactions of the American Society of Civil Engineers. In discussing Fowler’s article, F. E. Schmidt concluded, “taken as a whole, the facts developed in Mr. Fowler’s investigation and throughout the subsequent revision of the structure, constitute a most gratifying testimonial to the excellence of the design embodied in the original bridge. It does not seem to be extravagant to say that the design was a generation ahead of its time.” The bridge still stands after 120 years of serving railroad and vehicular traffic. It is the oldest structure spanning the river and has fully lived up to the claim of the Engineering News at its opening that it is, “capable of serving the purpose, barring injury by corrosion, a hundred years from now as it is today.”▪

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April 2018

LegaL PersPectives

discussion of legal issues of interest to structural engineers

State Statutes Governing Law and Forum Selection Provisions: Part 3 By Gail S. Kelley, P.E., Esq.

art 1 and 2 of this series (STRUCTURE, February and March 2018) provided an overview of both governing law provisions and forum and venue selection provisions. A governing law provision, also referred to as a choice of law provision, specifies that the law of a designated jurisdiction will govern disputes arising out of the agreement, regardless of where the dispute is adjudicated. Forum and venue selection provisions specify the location of the adjudication. A forum selection provision indicates the state where the adjudication is to take place; a venue selection provision indicates the actual location of the court. For a case in state court, the venue would be a county; for a case in federal court, the venue would be a district. This final article in the series takes a closer look at the some of the state statutes that may override provisions that the parties have agreed to in their contracts, as well as issues related to governing law provisions.

What Provisions Apply to Design Agreements? It is not always clear whether a statute that sets the governing law or forum for a construction project applies to an agreement for engineering services. Statutes regarding construction often reflect the lobbying efforts of subcontractor associations. As a result, a strict interpretation of the wording of a statute might lead to the assumption that the statute only applies to construction contractors and subcontractors. Nevertheless, when courts interpret these statutes, they tend to look at the intent of the statute, rather than the wording. For example, Cal. Civ. Proc. Code § 410.42 prohibits enforcement of a provision in a contract between a contractor and a subcontractor with its principal offices in California if the provision requires the subcontractor to litigate a dispute with the contractor in another state, provided the dispute arises out of a construction project performed in California. In Vita Planning and Landscape Architects, Inc. v. HKS Architects, Inc., 240 Cal.App.4th 763 (2015), the California Court of Appeals interpreted the word

“contractor” as used in Cal. Civ. Proc. Code § 410.42 to include architects and other design professionals. The court found that Vita was unquestionably a “subcontractor” because it was awarded a portion of HKS’s contract with the Owner and it did not have a direct contractual relationship with the Owner. The court was not persuaded by HKS’s contention that section 410.42 did not apply because HKS was an architect rather than a general contractor. Several of the statutes in the tables provided in Part 1 and 2 of this series indicate that they apply to any contract for an improvement to the property. This is also the language found in the mechanic’s lien laws of many states; it is generally considered to apply to design agreements unless there is a specific limitation. As an example of such a limitation, the Florida venue statute appears to apply only to those contracts where the engineers are working pursuant to a design-build contract. Any venue provision in a contract for improvement to real property which requires legal action involving a resident contractor, subcontractor, sub-subcontractor, or materialman, as defined in part I of chapter 713, to be brought outside this state is void as a matter of public policy. Part 1 of Chapter 713 (713.01 (8)) of the Florida code states that the term contractor “includes an architect, landscape architect, or engineer who improves real property pursuant to a design-build contract ...” When a statute specifically includes certain entities, it is generally held to exclude those not listed; thus the Florida venue selection statute does not appear to apply to engineers unless they are working pursuant to a design-build contract. In contrast, the New Mexico code (Stat. Ann. § 57-28A-1) explicitly defines a construction contract to include engineering services: § 57-28A-1 C. As used in this section, “construction contract” means a public, private, foreign or domestic contract or agreement relating to construction, alteration, repair or maintenance of any real property in New Mexico and includes agreements for architectural services, demolition, design services,

STRUCTURE magazine

April 2018

development, engineering services, excavation or other improvement to real property, including buildings, shafts, wells and structures, whether on, above or under real property. However, if a statute simply refers to either “the construction contract” or the “contractor” without specifically referencing the engineer, and there is no court case interpreting the statute, a party trying to invoke the statute to cover a design agreement may find that the other party challenges its applicability. The California court’s holding in the Vita case can be cited in cases involving the law of other states, but it is not binding precedent in such cases. Statutes may also be specifically limited by subject matter. For example, 73 Pa. Stat Ann. §514 states that “a contract subject to the laws of another state or requiring that any litigation, arbitration or other dispute resolution process on the contract occur in another state, shall be unenforceable.” However, in the case Stivason v. Timberline Post and Beam, 947 A.2d 1279 (Pa. Super. Ct. 2008), the Pennsylvania Superior Court found that because the code section was part of the Pennsylvania Contractor and Subcontractor Payment Act, a forum selection provision that required lawsuits to be filed in Ohio was enforceable even though the project was in Pennsylvania, because the dispute at issue did not involve payment.

Enforceability of Governing Law Provisions When there is no applicable statute with respect to governing law to the contrary, courts will generally enforce a governing law provision in a contract, provided there is some relationship between the transaction and the

law that would govern, and there is no overriding public policy concern. Donaldson v. Fluor Engineers, Inc., 169 Ill. App.3d 759 (1988) is an example of when a court refused to enforce the governing law provision in a contract due to a public policy concern. This case involved an employee of one of Fluor’s subcontractors who was injured while working on a project in Illinois. The injured employee sued Fluor in an Illinois court, and Fluor brought a third-party suit against the subcontractor for indemnification. The contract between Flour and the subcontractor stated that California law would govern; under California law at that time, the subcontractor would be required to indemnify Fluor for Fluor’s own negligence, provided Fluor’s negligence was not the sole cause of the injury. However, under Illinois’ anti-indemnity statute, an agreement to indemnify another person from that person’s own negligence is void as against public policy and wholly unenforceable. Even though the contract specified that California law governed, the Illinois court refused to enforce the governing law provision because California law would allow enforcement of the indemnification provision, whereas Illinois law would not.

and case law (cases that have interpreted the statutes and cases that have interpreted contractual language). It should be noted, however, that determining whether a statute applies to a particular design agreement will often require research into the relevant case law, preferably by an attorney with expertise in the laws of the state where the project is being constructed. Disclaimer: The information in this article is for educational purposes only and is not legal advice. Readers should not act or refrain from acting based on this article without seeking

An analysis of the merits and disadvantages of selecting a particular state’s law as the governing law for a design agreement would require research into the applicable statutes, cases that have interpreted the statutes, and cases that have interpreted contractual language. A state’s anti-indemnity statute might be one consideration. Other considerations might include whether design professionals are covered under the state’s mechanics’ lien law; the statute of limitations/statute of repose for bringing claims for design defects; whether a certification of merit is required for a negligence claim against an engineer; whether the state’s interpretation of the “economic loss doctrine” would allow an entity that was not in contractual privity with the engineer to bring a tort claim for economic damages; and whether an engineer can be held personally liable for an allegedly defective design.

Conclusion This series of articles has provided an overview of the governing law and forum/venue selection provisions that are often found in design agreements. The series also reviewed the state law relevant to these provisions, where “state law” includes both statutes STRUCTURE magazine

Gail S. Kelley is a LEED AP as well as a professional engineer and licensed attorney in Maryland and the District of Columbia. Her practice focuses on reviewing and negotiating design agreements for architects and engineers. She is the author of Construction Law: An Introduction for Engineers, Architects, and Contractors, published by Wiley & Sons. Ms. Kelley can be reached at gail.kelley.esq@gmail.com.

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Choice of Governing Law

appropriate legal or other professional advice as to their particular circumstances.▪

April 2018

Structural SuStainability

sustainability and preservation as they pertain to structural engineering

Capturing Points for Whole Building LCA in LEED v4 By Frances Yang, S.E., LEED AP

tructural engineers have an unprecedented Whole Building Life Cycle Assessment, serves as The second part describes specific strategies opportunity to contribute to green building a pre-standard for use by the project team to for the reference building a structural engineer certification. Within the green building practice, define and model the structural system within may choose to employ for reducing life cycle the U.S. Green Building Council’s (USGBC) the “reference building design,” as required by impacts on a project, including: Leadership in Energy and Environmental green building standards and rating systems • Structural Material Quantity Reduction Design (LEED) rating system has set a precedent when performing comparative WBLCA. Not • Structure as Finish for green building standards and codes such as to be confused with WBLCA primers, the • Performance-Based Design for Material the IgCC, ICC 700, CALGreen and ASHRAE scope of the document is limited to: Damage Reduction 189.1. The latest version of LEED v4, released • Definition of the “reference building design.” • Using Alternate Structural Systems in 2012, awards a total of 3 points for perform• Design and construction choices within • Low-cement Concrete ing whole building life-cycle assessment and the influence of the structural engineer. • Sourcing Salvaged Materials specifically limits the assessment to structure • Discussion of the approach to con• Design for Deconstruction and enclosure to encourage participation structing the reference building design • Contributing to Operational Energy from structural engineers. The LCA Working influenced by choice of the structural Savings Group of the SEI Sustainability Committee has system and materials. These strategies are not inclusive of all possible found that approximately 50% strategies but, instead, they are of the embodied impacts from the strategies the authors deemed structure and enclosure typically most common or effective and This situation could fail to come from structure. Thus, also most relevant to the role of structural engineers have an enorthe structural engineer. encourage the meaningful mous opportunity to contribute WBLCA is a relatively new contribution structural engineers to attaining the environmental application of life cycle assessimpact reductions prescribed in ment (LCA). Because LCA has might make towards reducing green building rating systems and primarily been used for massreal environmental impacts standards, when compared to a produced products, applying “reference building.” the principals and method to of our building structures. The LEED v4 credit requires buildings – which are for the showing a 10% improvement most part one-off creations – in environmental impacts comhas some challenges. While pared to a “reference building,” using whole This guide does not discuss the process of this guide addresses some of these chalbuilding life-cycle assessment (WBLCA) tools conducting a WBLCA or compare the stan- lenges, the authors acknowledge that the that are now readily available. This is compa- dards and rating systems prescribing the use guidance offered is preliminary and will rable to the performance options in the other of WBLCA, as it assumes the user possesses continue to improve as the field of WBLCA green building standards, and the approach some basic knowledge of life cycle assess- grows and matures with its users, as well is similar to using energy modeling to dem- ment for whole buildings. If the user needs as through feedback directed to the SEI onstrate energy performance improvements. to establish these fundamentals, appendices Sustainability Committee. However, existing standards and guides do not of the guide provide several go-to resources, This guide represents a milestone in strucprovide enough specifics about the structural including descriptions of the most popular tural sustainability and, through ASCE’s system and materials within the “reference WBLCA and LCA tools. support, structural engineers can now more building,” which could allow designers to The crux of the guide is reflected in its readily embrace the call from green building construct an unrealistic reference and unfair two-part organization. The first part sets programs to have a more active and meaningreward in the rating systems. out the fundamental concepts to support a ful role in reducing environmental impacts This situation could fail to encourage the defensible reference building. Much of this of our built environment.▪ meaningful contribution structural engineers centers around using the structural design Frances Yang is a structures and materials might make towards reducing real environ- criteria to define the “functional unit,” sustainability specialist in the San Francisco mental impacts of our building structures. to ensure apples-to-apples comparisons office of Arup and leads the Materials Skills Thus, the Structural Engineering Institute’s while recognizing special cases when the Network and the Structural Sustainability Task Sustainability Committee, with support from design criteria should be allowed to differ Force for Arup’s Americas region. She has an ASCE Special Project grant, is working to between the reference and proposed buildserved as vice-chair of the MR TAG of USGBC, chair of the ASCE/SEI LCA working group, produce a guide to bridge the gap and ensure ing designs. This first part also offers three contributes to the Carbon Leadership Forum, a nominal level of integrity in comparing logical options to use as starting points: a AIA Materials Knowledge Working Group, structural designs using WBLCA. similar existing building, an earlier iteraand was the principal investigator for the ASCE The guide, titled Guide to Definition of the tion of the structural system for the same Special Project described in this article. Reference Building Structure and Strategies in building, and a building archetype. STRUCTURE magazine

April 2018

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Business Practices

business issues

Mentoring in the Workplace By Jennifer Anderson

ut of all the training and development programs to choose from, mentoring can have the most significant impact on the careers of everyone involved. Be it a junior engineer fresh out of college or a senior engineer with 20 years of working experience, mentoring makes a difference. Unfortunately, very few companies have an official mentoring program available; it is an area that is often overlooked.

For Junior Level Employees At the college level, academic professionals try to create an environment for learning. Most of us can look back on our college years with fond memories of educational experiences that helped us to grow and learn as we developed our knowledge of concepts. Upon graduation and entering the workforce, most junior level employees receive a dose of reality when they realize that the real world of the workplace is entirely different from an academic setting. As these people join your organization, having a mentoring program available to help them understand the nuances of becoming an engineer is important for a successful transition. There is much to be learned in the workplace that cannot be learned in the classroom or a textbook. If your organization has invested in hiring a junior engineer, it is well worth your time and effort to invest in helping them understand the trade in order to increase the likelihood they will become long-term contributors to the company. The reasons why mentoring junior engineers is important to your organization’s bottom line include: • If your company has a solid mentoring program, you can talk about it during the recruitment and interview process. This type of program is very attractive to Junior level engineers and will help your firm stand out from other hiring companies. • Mentoring helps to reduce turnover. Junior engineers will typically stay with their first firm for 3 to 4 years before going elsewhere. During those first few years, they are evaluating how managers are treating them. If they do not feel supported, their desire to stay may waiver. • Leveraging the knowledge of senior engineers will help junior engineers come up to speed more quickly. Time is money and

money is time, so take advantage of helping junior engineers come up to speed so that they can make a better impact on their assigned projects.

For Senior Level Employees As a senior engineer, the benefits of mentoring come more from being the mentor rather than the mentee. Think back to those people who made a difference by helping you develop into the engineer that you are today. Wouldn’t it feel great to know that you made an impact on the lives and careers of other engineers? • At a certain point in your career, gaining knowledge is no longer as important as sharing knowledge. Being in an environment where you can be a mentor can be personally satisfying. • Leveraging your experience and helping others get up to speed is invaluable to the firm because it will reduce lost time and lost wages, making your firm more profitable and productive. • Even mentoring people outside of your company pays dividends to your professional reputation and the reputation of your firm, and contributes to the structural engineering industry as a whole.

How to Start a Mentoring Program If your company does not yet have an organized mentoring program in place, here are key points to consider when starting one: • Mentee requests the mentoring. The best mentoring programs are driven by the mentees, not the mentors. If the mentee is forced to have a mentor, it may feel like another layer of supervision. On the other hand, if the mentee is shown the value of mentoring to their career, they will likely desire to participate in a helpful program. • Begin with the end in mind. As you begin a new mentoring program, be clear about what your goals are for establishing the program at your company. • Someone needs to take the helm. If anything is to succeed in a company, someone needs to sponsor it. Perhaps that is you? • Designate funding. Budgeting for a mentoring program does not require hundreds

STRUCTURE magazine

April 2018

of thousands of dollars; a small budget of $500-$1000 per person mentored is typically sufficient. The money can be used for occasional one-on-one lunches, purchasing books, and other activities to support mentorship. • Start small. In the beginning, start with a small group of people who want a successful mentoring program in the company – at a minimum start with three mentors and three mentees. Have this small group determine how the mentoring will look. Mentoring programs can vary from company to company, so allow the mentors and the mentees the flexibility to be creative about what will work for your company’s program and what will align with your company’s culture. • Trial period. Start with a six- or 12-month mentoring duration to see how the mentors and mentees do in this initial run. At the end of the trial period, bring together the mentors and mentees to have a collective conversation about the successes and challenges of the initial mentoring program. Review your original goals, determine what worked and did not work, then use the knowledge gained to move forward with the next phase of the mentoring program. If your company has a robust mentoring program in place, whether as a junior engineer or senior engineer, take full advantage of the opportunity and participate. If your company does not yet have a mentoring program established, do yourself and your firm a favor and help to get one started today.▪ Born into a family of engineers but focusing on the people side of engineering, Jennifer Anderson (www.CareerCoachJen.com) has nearly 20 years helping companies hire and retain the right talent. She may be reached at jen@careercoachjen.com.

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STRUCTURE magazine

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EnginEErEd Wood Products guidE a definitive listing of wood product manufacturers and their product lines Simpson Strong-Tie

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STRUCTURE magazine

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Spotlight

The Bay Area Metro Center Lightening the Impenetrable By Leslie Zerbe, P.E. Holmes Structures was an Outstanding Award winner for its Bay Area Metro Center project in the 2017 Annual Excellence in Structural Engineering Awards Program in the Category – Forensic/Renovation/Retrofit/Rehabilitation Structures over $20M.

he Bay Area Headquarters Authority (BAHA) is a sustainability-driven joint powers authority that was founded to connect regional agencies overseeing transportation, housing, land use, air quality, and climate change. BAHA sought to unite these agencies, previously dispersed across the San Francisco Bay Area, under one roof – the new Bay Area Metro Center. The headquarters repurposed a seemingly impenetrable building that stood eight stories tall and encompassed half of a city block. Since the existing structure provided more square footage than BAHA required, the remaining floors were allocated to revenuegenerating tenancies. The building was originally constructed in 1942 as a World War II-era military depot and later operated as regional U.S. Postal, Mint, and Treasury Services, and a forensic laboratory. At the start of the project, this substantial fortress was out of place, with its drab exterior and dark interior, in San Francisco’s burgeoning SoMa neighborhood – most of its floors were unoccupied for years. The design team had an appreciable challenge bringing this building into the 21st century regarding aesthetics, seismic performance, daily functionality, and

sustainability. The new Bay Area Metro Center celebrates the building’s history while embracing its contemporary context. Early retrofit concepts focused on conventional shear wall additions that required extensive foundation work, rather than leveraging the existing structure’s contributions. BAHA approached Holmes Structures (Holmes) for an alternative solution, concerned that the retrofit was consuming too much of the project’s limited budget. Holmes devised a retrofit solution that met BAHA’s budget and schedule requirements for rehabilitation. The first step was to “lighten” the structure. Since the building had ample square footage, there was no need to keep dark interior spaces that would be less desirable to prospective tenants. Holmes suggested carving out a vast seven-story atrium through the core of the building, which lightened its mass and interior spaces. Nestled between the San Andreas and Hayward fault lines, the existing structure did not meet BAHA’s required seismic performance level – but it was robust. Holmes implemented proprietary performance-based engineering software to model its expected performance in the event of a major earthquake, running a suite of time histories to evaluate the building under pre- and post-retrofit conditions. The non-linear analysis revealed that shotcrete overlays could work in parallel with the existing pier and spandrel system. It also showed that the existing stout end piers were subject to excessive damage and not improved by strengthening measures that also increased stiffness, so they were simply decoupled from the lateral system allowing rotation without high damage. The design solution focused on the building’s inherent strengths, efficiently augmenting the capacity of the existing materials. This philosophy extended to the foundations, where existing perimeter foundations were reused with limited and selective strengthening. A restrictive column grid limited the creation of large open spaces that the program required. Designing two large transfer walls enabled the removal of first floor columns, creating an open auditorium and multi-purpose spaces. On the

STRUCTURE magazine

April 2018

Beale Street façade, shotcrete overlays enhanced piers and spandrels to create a vierendeel truss, enabling the removal of a perimeter column. This modification created the dramatic new entry at 375 Beale Street (a nod to California’s Senate Bill 375 targeting a reduction in greenhouse gas emissions through transportation and land use practices). The bright, airy atrium lined with solar panels dramatically reduces lighting costs for the building’s core. Even the shotcrete overlays of the retrofit create deeper window sills, projecting natural light further into the interior. Upper levels include a roof terrace with views of the iconic Bay Bridge and a three-story tree well, both visible to the estimated 270,000 commuters using the bridge every day. The distinctive exposed wood accents were repurposed predominantly from local sources. During the retrofit, the neighboring Transbay Terminal underwent demolition and strips of its 40-foot long Douglas-fir piers now line the interior of the Metro Center. The feature stair, a delicate structure hung from a new atrium beam and tied seamlessly into to the slab edge, incorporates wood from bumper rails that once shielded the building’s walls from mail carts when it was a major postal center. The stair also provides direct connectivity between the agencies that once functioned miles apart. Holmes worked closely with the project team to transform this seemingly impenetrable building into an engaging LEED Gold workspace. These efforts, driven by a deep commitment to sustainability, saved the building from demolition and realized its potential as a leading-edge civic institution recognized for its innovative design.▪ Leslie Zerbe is a Senior Engineer at Holmes Structures in San Francisco with experience at Holmes Consulting in New Zealand. She can be reached at leslie.zerbe@holmesstructures.com.

Paper Folding

The Newest Trend in Engineering Design is an Age-Old Tradition

NCSEA News

News form the National Council of Structural Engineers Associations

Mark R. Morden, AIA, CCS, Associate Principal, Wiss, Janney, Elstner Associates, Inc. In late 2017 at Benaroya Hall in Seattle, the Structural Engineers Foundation of Washington (SEFW) held their annual Fall Forum. SEFW was founded in 2010 by leaders of the Structural Engineers Association of Washington (SEAW), who envisioned an organization that would elevate and advance the profession of structural engineering. SEFW is a charitable organization that serves in many capacities to fulfill this mission, like hosting public forums such as the one discussed here, producing and promoting educational materials that support structural engineering, and awarding scholarships on behalf of the Structural Engineers Association of Washington. SEFW Chair, Mark D’Amato, took a moment at the start of the Forum to identify some of SEFW’s endeavors for the year, including outreach with the SEAW Outreach Committee and the FilmWorks Initiative. The theme of this forum was Origami: Inspiration in Science, Design, and Structures. Three speakers were featured in the program: Robert D. Lang, Ph.D., origami artist, author, and consultant; Tina Hovsepian, AIA, professional architect/developer and founder of the non-profit Cardborigami; and Mark R. Morden, AIA, Associate Principal at Wiss, Janney, Elstner Associates, Inc. (WJE) in Seattle and local origami enthusiast. Each speaker brought a unique perspective on applications of origami to engineering and structures. Robert Lang, a former physicist and engineer, is now a full-time origami artist, author, and consultant on applying folding technology to aerospace and other engineering projects. His talk presented the math and structure of origami and how it has been applied to various types of technology. One example was using folding patterns to stow large solar arrays into a satellite’s limited payload for delivery into space. Other examples included efficient folding of car air bags, folded stents delivered through blood veins that unfold to open clogged arteries, assembly of micro-robotics, bulletproof barriers for police, furniture, building panels, and kitchen utensils. Robert aptly demonstrated the order and complexity of math and structure as it can be applied to something as basic as folding paper. He also shared his stunning folded art pieces as examples that math and structure can be beautiful. More about Robert and his works can be viewed on his website, www.langorigami.com. Tina Hovsepian is an architect and the founder and Board Chair of the non-profit Cardborgami organization. The organization is dedicated to using folding technology to provide disaster relief, homeless aid, and job creation. Tina developed a folded cardboard structure that can serve as temporary STRUCTURE magazine

relief shelter for victims of a natural disaster or those who are homeless. The shelter is a tube-shaped structure, roughly 7 or 8 feet long and 3 feet tall. The cardboard is pre-creased so it can be flattened for storage and portability. When extended, the folds in the cardboard provide the structure for the shelter. During the Fall Forum, Tina shared a video of the work her organization was doing including providing jobs assembling shelters for at-risk youths. Tina also engaged in a dialogue with the audience, answering questions about Cardborigami. Information about Cardborigami is available at www.cardborigami.org. Mark Morden is a forensic architect and Associate Principal at Wiss, Janney, Elstner Associates (WJE). He is also the founder of PAPER, a local Seattle origami group that has been meeting for over twenty years. Mark shared how folding technology has been incorporated into buildings and structures today, and ways in which applications of folding may be applied to the design and construction of future projects. Examples of current applications include folding sunshades enveloping towers in Dubai, fabric roofs that can be unfolded to cover the tops of sports arenas, and portable utility structures that are delivered to project sites and unfolded into much larger facilities. Other applications being studied included temporary bridges to be used in emergencies, folded tubes that could serve as structural members in buildings, and adjustable, acoustic ceilings made up of folding panels that can be repositioned to “tune” a concert hall for the specific music being played. Close to 300 people participated the event, which included a pre-function networking reception featuring origami art displays, hands-on origami examples, and a Cardborigami temporary shelter. The local origami group, PAPER – the Puget Area Paperfolding Enthusiasts Roundtable, contributed volunteers and origami examples to the reception. SEFW also wishes to extend a special thank you to the 43 local firms, 16 individual Friends of the Foundation, and 19 Cooperating Organizations that supported the Forum this year. All donated funds will go toward SEFW programs this upcoming year, including support of the SEAW Outreach Committee, SEAW Scholarship program, and more. To see the complete report of the SEFW Fall Forum please visit www.sefw.org. April 2018

The Structural Engineering Engagement and Equity (SE3) Committee is currently administering a nationwide survey of structural engineering professionals. This survey is designed to provide valuable information about our profession regarding demographics, compensation, satisfaction, and engagement. It will be one of the largest comprehensive nationwide surveys of structural engineering professionals to date, and we invite you to October 24–27, 2018 contribute to this project by completing the survey. This project began in 2015 when SEAONC (Structural Engineers Association of Northern California) funded a committee to study engagement and equity in the structural engineering profession. In 2016, Sheraton Grand this group administered their first national survey of over 2,100 structural engineering professionals. Findings from this study included insight into why engineers leave the profession, the importance of mentorship, and the existence of a nuanced gender pay gap. In mid-2017, an SE3 Committee was created at the national level through NCSEA with the primary goal of administering a similar nationwide study Chicago, IL of structural engineering professionals every two years. This biennial survey will focus on measuring engagement and equity with the goal of providing Register now on www.ncsea.com data and best practices to help engineers around the country improve our industry and help ensure that every structural engineering professional has a positive experience within our profession. Over the past seven months, we’ve been developing the 2018 version of this survey, and it is now live! We would love to have your input. If you’d like to participate, the link to the survey is available on our website at www.ncsea.com/committees/se3.

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NCSEA Webinars April 26, 2018 ASCE 7-16 Component and Cladding Wind Design This webinar will describe the new requirements in ASCE 7-16 for Component and Cladding design, including the revised higher roof pressure coefficients for gable and hip roofs. There will be examples with calculations to demonstrate the extent of the changes. There have been other structure types added to the standard, such as tanks and solar panels, that have associated C&C design requirements and these are also covered. Speaker: William L. Coulbourne, P.E. May 8, 2018 How the AISC 360-16 Chapter K Changes Affect HSS Design This webinar will provide the background for the changes to AISC 360-16 Chapter K, an overview of the updates, and illustrate that the differences are not as extreme as it appears at first glance. During the webinar, we will also work design examples and provide resources for engineers to continue to provide efficient HSS designs. Speaker: Kim Olson, P.E. Register at www.ncsea.com. Webinar time: 10:00 am Pacific, 11:00 am Mountain, 12:00 pm Central, 1:00 pm Eastern. Courses award 1.5 hours of continuing education after the completion of a quiz. Diamond Review approved in all 50 States.

STRUCTURE magazine

April 2018

News from the National Council of Structural Engineers Associations

Subscribe to Knowledge

The Newsletter of the Structural Engineering Institute of ASCE

Structural Columns

Structures Congress 2018

Join us for a great program of technical/professional learning, networking, and fun social events at Structures Congress in Ft. Worth, #structures18. Learn more and register at www.structurescongress.org.

Congratulations Structures Congress Scholarship Winners

Ten students and twenty young professionals (35 and younger) have been awarded scholarships to participate at Structures Congress. Check out the list at www.asce.org/SEI. Scholarships were made possible by the SEI Futures Fund in partnership with the ASCE Foundation.

STRUCTURES CONGRESS 2018 LIVE STREAM PROGRAM What’s W

structures congress 2018? Live stream seLect sessions from your home or office.

the next best thing to attending

Four select expert sessions available via live stream on Friday, April 20.

Register for 1- 4 sessions and earn up to 5.5 PDH’s in the comfort of your home or office. Must register by 5:00 p.m. US Eastern Time (ET) April 12, 2018. REGISTER TODAY Individual registration only. Registered attendees are eligible to receive PDH credit.

Session 1

Session 3

Conserving Ancient Sites from the Empire of Alexander the Great, David Biggs, Biggs Consulting Engineering

Case Studies - Buildings, Erleen Hatfield, BuroHappold Consulting Engineer, Hessam Kazemzadeh, RAD Urban, Daniel Wilcoxon, Arup, Owen Rosenboom, WJE

Session 2

Session 4

Performance-Based Engineering: State-of-the-art, state-of-practice, and future trends – 8 expert presenters including; Michele Barbato, LSU, Donald Dusenberry, SGH, Donald Scott, PCS Structural Solutions, David Shook, SOM and more…

Salesforce Tower: New Benchmarks in Seismic Performance, Ron Klemencic, MKA, Mike Valley, MKA, Kirk Ellison, Arup, Robert Hazleton, The Herrick Corporation

Made possible by the SEI Futures Fund in partnership with the ASCE Foundation.

All sessions take place in US Central Time (CT) Friday, April 20, 2018.

Read full session details on the website www.structurescongress.org/livestream

Membership

SEI Sustaining Organization Membership

Reach more than 30,000 SEI members year-round with SEI Sustaining Organization Membership. Show your support for SEI to advance and serve the structural engineering profession. Learn more and join today at www.asce.org/SEI-Sustaining-Org-Membership.

SEI Elite Sustaining Organization Members Join or Renew SEI/ASCE for innovative solutions and learning, to connect with leaders and colleagues, and enjoy member benefits such as SEI Member Update monthly e-news opportunities and resources – visit www.asce.org/myprofile or call ASCE Customer Service at 800-548-ASCE (2723). STRUCTURE magazine

April 2018

Review the SEI Annual Report 2017: Resilience 2017 was a year of many challenges, around the world and within our profession. As SEI members strive to advance and serve the profession, we build a more resilient future. Read more at www.asce.org/SEI.

ASCE Journal Special Collections

Learning / Networking

SEI/ASCE Live Webinars - Learn from the Experts April 9 April 13

Significant Changes to the Wind Load Provisions of ASCE 7-16 and Coordination with the 2015 IBC and 2015 IRC Deterioration and Repair of Concrete

Individual Certificate Fee Discontinued. Register at Mylearning.asce.org for these and much more.

SEI Online

Propose Changes to ASCE 7 The 2022 development cycle for ASCE 7 has begun and, like previous cycles, the committee will consider public proposals received prior to June 20. Proposals to revise ASCE 7 can be submitted anytime using the ASCE 7 Change Proposal Form. For this and more, including the ASCE 7 committee meeting schedule see www.asce.org/structural-engineering/asce-7-and-sei-standards.

Check out SEI News at www.asce.org/SEI Perspective from international experience: Engineers without Borders in Thailand

SEI is now on Twitter! Follow @ASCE_SEI and join the conversation to share what inspires you in structural engineering.

Errata

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI-Errata. If you would like to submit errata, contact Jon Esslinger at jesslinger@asce.org.

STRUCTURE magazine

April 2018

The Newsletter of the Structural Engineering Institute of ASCE

Journal of Structural Engineering: • Recent Advances in Assessment and Mitigation of Multiple Hazards • 60th Anniversary State-of-the-Art Papers • Recent Advances in Reinforced Concrete Walls Designed to Resist Seismic Loads Journal of Bridge Engineering: • Cable Structures in Bridge Engineering • Fatigue Design, Assessment, and Retrofit of Bridges Practice Periodical on Structural Design and Construction: • Construction Safety Journal of Performance of Constructed Facilities: • Civil Infrastructure: From Failure to Sustainability • Seismic Risk of Monumental Buildings: Outcomes of the Research Project RiSEM Journal of Management in Engineering: • Supply Chain Management in Megaprojects Submit a paper at ascelibrary.org/page/callforpapers.

Structural Columns

Advancing the Profession

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Practice Guidelines Currently Available CASE 962 – National Practice Guidelines for the Structural Engineer of Record (SER) The purpose of this document is to give firms and their employees a guide for establishing Consulting Structural Engineering Services and to provide a basis for dealing with Clients generally and negotiating Contracts in particular. Since the Structural Engineer of Record (SER) is normally a member of a multidiscipline design team, this document describes the relationships that customarily exist between the SER and the other team members, especially the team leader. Further, this Guideline promotes an enhanced Quality of Professional Consulting Structural Engineering Services while also providing a basis for negotiating a fair and reasonable compensation. Additionally, it provides a basis for Clients to better understand and determine the Scope of Services that the Structural Engineer of Record should be retained to provide. CASE 962-A – National Practice Guidelines for the Preparation of Structural Engineering Reports for Buildings The purpose of this document is to provide the structural engineer a guide for not only conducting conditional surveys, code reviews, special purpose investigations, and related reports for buildings but includes descriptions of the services to aid with the client risk management communication issues. This

Guideline is intended to promote and enhance the quality of engineering reports. CASE 962-B – National Practice Guidelines for Specialty Structural Engineers This document has been prepared to supplement CASE’s National Practice Guidelines for the Structural Engineer of Record by defining the concept of a specialty structural engineer and the interrelation between the specialty structural engineer and the Structural Engineer of Record. CASE encourages the concept of one Structural Engineer of Record for an entire project. However, for many if not most projects, there may be portions of the project that will be designed by different specialty structural engineers. The primary purpose of this document is to define the relationships between the SER and the SSE better, and to outline the usual duties and responsibilities related to specific trades. This is done for the benefit of the owners, the PDP, the SER, the SSE, and the other members of the construction team. The goal is to help create positive coordination and cooperation among the various parties. You can purchase these and the other CASE Risk Management Tools at www.acec.org/case/news/publications.

CASE Member Firms Win Engineering Excellence Grand, Honor Awards Congratulations go out to CASE Member firms Magnusson Klemenic Associates, Inc. and Simpson Gumpertz & Heger for winning Grand Awards. Magnusson Klemenic Associates, Inc.’s highlighted project, 150 North Riverside in Chicago, IL, and Simpson Gumpertz & Heger’s two projects: University of Massachusetts Design Building, in Amherst, MA, and Baha’i

Temple of South America in Santiago, Chile, are all finalists for the Grand Conceptor Award to be presented at the 51st Engineering Excellence Awards Gala being held during the ACEC Annual Convention. CASE Member Firm Clark Nexen won Honor Awards for their project, Davis Barracks, U.S. Military Academy, West Point, NY.

Construction Management at Risk, Second Edition ACEC’s Construction Management at Risk, Second Edition offers an updated look at the process and benefits of the Construction Management at Risk (CMAR) alternate project delivery method. Prepared by design professionals for design professionals, this handbook provides practical, hands-on information on how to use CMAR, with particular emphasis on the roles of the architect/engineer and the project owner. It also covers:

• Types of projects best suited to CMAR • The A/E and contractor selection processes • Methods of managing the project team for best results With examples of real projects that illustrate potential pitfalls for architects and engineers, and how you can use the CMAR process to better serve the needs of your clients, this book is an invaluable resources to anyone considering CMAR for their next project. Order your copy today at www.acec.org/bookstore.

Follow ACEC Coalitions on Twitter – @ACECCoalitions. STRUCTURE magazine

April 2018

June 7 – 8, 2018; Anaheim, CA An Intensive Workshop for Structural Engineering Firm Leaders & Project Managers Real-World Skills… Strategic Insights… Best Practices for Success Managing your structural engineering business for success requires technical know-how coupled with a broad awareness of today’s best business practices. Firm managers must know the rules of finance and how they work in the real world, and the ins and outs of managing people, risk, and resources, including: • Understanding Duty-to-Defend and How to Protect Your Firm • Avoiding Getting Burned by Electronic Communications • Driving Financial Performance Through Metrics • Navigating Your Way Through High-Risk Projects • Transitioning Project Managers to Firm Leaders

What Will Attendees Learn? Attendees will leave the event with best practices to assist your firm in: • Reducing claims • Increasing profitability • Improving quality • Enhancing management practices

Workshop Schedule Thursday, June 7 5:30 pm Workshop Dinner and Presentation Enhance Project Performance through Team Culture: California Pacific Medical Center (CPMC), Van Ness IPD Project Speakers: Stacy Bartoletti, President and CEO, and Jay Love, Senior Principal – Degenkolb Engineers Friday, June 8 6:45 am – 7:30 am Breakfast 7:30 am – 7:45 am Welcome Corey Matsuoka, SSFM International

STRUCTURE magazine

9:15 am – 10:30 am Did I Say That!? Electronic Communication, Retention, and Back-up in the Engineering Practice Karen Erger, Lockton Eric Singer, Ice Miller, LLP 10:45 am – 12 Noon Key Business Metrics Matt Fultz, Matheson Financial Advisors, Inc. 12:00 Noon – 1:30 pm Lunch 1:30 – 2:45 pm Projects with the Largest Losses and Claim Frequency Tim Corbett, SmartRisk Brian Stewart, Collins, Collins, Muir + Stewart 3:00 pm – 4:15 pm Transitioning Project Managers to Firm Leaders Howard Birnberg, Birnberg & Associates Get Full Program and Registration Details at http://bit.do/acec-case2018.

Thank You to Our Workshop Sponsors

Title Sponsor: CSI Workshop Partner: ACEC/CALIFORNIA Gold Patrons: ARW ENGINEERS DEGENKOLB ENGINEERS Seeking Workshop Patron Sponsors Be a patron sponsor and get additional registration slots! Interested in taking advantage of this special sponsorship, contact Heather Talbert for more information: htalbert@acec.org or 202-682-4377. Patron Sponsor (Gold – $2,000; Silver – $1,500, Bronze – $1,000) Sponsor the “Business of Structural Engineering” as a Patron of CASE • Listed on all materials and promotions • Listed on all signage • Gold – Three (3) Registrations • Silver – Two (2) Registrations • Bronze – One (1) Registration

April 2018

CASE is a part of the American Council of Engineering Companies

Contemporary Best Practices and Critical Operational Management Methods This workshop highlights strategies for a wide array of critical business topics that will keep your business thriving despite a churning business environment. Attendees will learn specific skills and techniques to help them manage change and build success in finance, leadership development, contracts, and risk. This workshop is presented by the Council of American Structural Engineers (CASE), the leading provider of business practice and risk management information for structural engineering firms. Structural engineering firms are not simply run on technical know-how – you cannot be successful without understanding the basics of the business world. The Business of Structural Engineering Workshop will share challenges facing today’s structural engineering firms and how to address them.

7:45 am – 9:00 am California Duty to Defend Reform (SB 496) Brett Stewart, XL Catlin Design Professional Michael Olson, Dealey, Renton & Associates

CASE in Point

The Business of Structural Engineering Workshop

Structural Forum

opinions on topics of current importance to structural engineers

Trust Me; I am An Engineer By Alan Kirkpatrick, P.E.

recent internet meme titled “Trust Me, I’m An Engineer” shows a photo of a severely-damaged concrete column. To remedy gaping vertically-oriented cracks, someone wrapped the column with kitchengrade cellophane. The caption reads, “Don’t worry; we’re safe – I fixed it.” Pretending Saran™ Wrap as reinforcing is humorous, but attempting to fix a serious problem with a clearly inadequate solution while asking for trust is the real irony. Engineers are asked to be resourceful, imaginative, and use “out-of-the-box” thinking to fill needs. However, before the number crunching begins, engineers must build trust and should always endeavor to earn that trust. Numbers can be argued definitively among peers, but meaningful trust takes time to develop with clients. Licensure helps engineers earn that trust. A singular, common definition for an engineer is not ubiquitous. Some states associate the terms engineer and professional engineer. In Oregon, for example, an engineer is defined to mean a licensed professional engineer, and a person practices engineering if that person implies through the use of a title that he or she is an engineer. So, in Oregon, if you claim you are an engineer, what you produce can be considered engineering work. Strangely, this distinction earned national attention for Mats Järlström, a Portland resident who immigrated to the United States from Sweden over 20 years ago and claims to be an electrical engineer. It started in 2013 when Järlström’s wife received an automatically-generated traffic ticket for running a red light. After studying the light timing and a vehicle’s critical stopping distance, Järlström determined that the yellow light illumination period was too short. Using his background, he developed an algorithm to correct the light timing formula and shared his findings in 2014 with the Oregon State Board of Examiners for Engineering and Land Surveying, or OSBEES, among others. After reviewing Järlström’s request, OSBEES noticed he was not a registered engineer in Oregon and cautioned him

against using the title engineer in publicized critiques of engineered systems. Järlström initially agreed but continued to promote his fix for the light timing system. When again, in 2015, he described himself as “an excellent engineer,” OSBEES opened a law enforcement case against Järlström and assessed a $500 penalty against him for the unlicensed practice of engineering. In its Final Order, OSBEES stated that Järlström violated Oregon’s statutes by “purporting to be authorized to practice engineering, including through the use of the ‘engineer’ title, and by providing an engineering analysis and critique of an engineered traffic signal formula, all to a public body.” The Järlström case has generated broad interest including that of the Portland news media, 60 Minutes, and even George Will. Partnering with the Institute for Justice, Järlström filed a federal civil rights lawsuit against OSBEES, contending violation of his civil rights. Järlström vowed to fight for free speech so that “no one should need a license to speak out when they’re concerned about how the government is operating, whether the topic has to do with taxes, trade policy, or traffic lights.” Eventually, he hopes that he, “along with the rest of Oregon, will soon be free to talk about technical subjects without risking running afoul of the law.” This suit, which recently settled in favor of Järlström, was a collision between Civil Rights and Licensure. The evolution of civil rights and engineering licensure is interesting. In a paper written by Liberty University’s Professor Paul Linden, he provides a rich history of engineering licensure in the U.S in which he describes pre-Civil War engineers as almost nonexistent, fewer than 2,000. They had little specialized education and practiced “mechanic arts.” After the war, as towns blossomed into cities, rural farmers became urban business owners, and science played leapfrog with inventions, engineering needs grew. By the late 19th century, engineers became more established because “as technology incorporated scientific principles, it gradually moved beyond the capabilities of

an artisan…whose limited understanding of science and physics could not keep pace.” By the early 20th century, with improved educational training and continued industrialization, the number of engineers increased to roughly 136,000. Professional societies, such as ASCE, ASME, AIME, and IEEE, began promoting engineering interests concurrent with trending state legislation to protect the rights of consumers. Linden writes, “Unlike inhabitants of rural areas, city dwellers often did not know the persons from whom they bought their goods or on whom they depended for important services.” These inhabitants had “no way of testing their suspicions of being cheated.” States, most notably Wyoming and Louisiana, took action and began enacting licensing laws as a way to shape a profession so deeply invested in the development of the nation. Illinois and Florida followed. Moreover, here the past becomes prologue: Linden contends that when it came to licensing and the governmental proof that an engineer could begin to be trusted, it is the engineers themselves who were “surprisingly ambivalent toward licensing, if not outright rejecting of it.” Engineers opposed to licensure? Yes. Licensure is not intended to restrict civil rights. It is intended to assure the public that those who are hired to create solutions have met minimum standards. Licensure starts the trust process. Whether there is a damaged column or a short yellow light, the public should always know that those who work on their behalf are not charlatans or imposters. Trust me; I am an engineer.▪ Alan Kirkpatrick is a Principal with Kirkpatrick Forest Curtis, PC in Oklahoma City, Oklahoma. He co-chairs the NCSEA Licensure Committee and is a member of the ASCE/SEI Structural Engineering Licensure Rationale Research Committee and the Structural Engineering Licensure Coalition (SELC). He may be reached at akirkpatrick@kfcengr.com.

Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, the Publisher, or the STRUCTURE® magazine Editorial Board. STRUCTURE magazine

April 2018

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