STRUCTURE magazine | February 2015 by structuremag

February 2015 Steel/Cold-Formed Steel

A Joint Publication of NCSEA | CASE | SEI

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editorial

7 Where We Go depends on Where We aim

ProFessional issues

32 rainbows only Come after rain

By Barry Arnold, S.E., SECB

By Ellen (Chuan-Hua) Kuo, P.E.

lessons learned

struCtural rehaBilitation

9 unintentional Corrosion by structural design By Julie Mark Cohen, Ph.D., P.E., SECB

44 divine design: renovating and Preserving historic houses of Worship – Part 3 By Nathaniel B. Smith, P.E. and

enGineer’s noteBook

13 Built-up Cold-Formed steel Compression Member design By Roger LaBoube, Ph.D., P.E. Code uPdates

17 Changes to the 2015 Wood Frame Construction Manual By John “Buddy” Showalter, P.E., Peter Mazikins, P.Eng and Michelle Kam-Biron, S.E., P.E. struCtural desiGn

20 Why it’s Good to be a lightweight

Milan Vatovec, P.E., Ph.D.

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

February 2015

insiGhts

48 Bollman truss at harper’s Ferry

52 integral Crystalline Waterproofing

Bethel Park By Jacob Bice, Ph.D., P.E. and Dilip Choudhuri, P.E. In 2005, a fire gutted the interior of this historic structure, collapsing the interior framing and roof, leaving only the exterior masonry walls in place. The structure sat exposed and abandoned until 2009, when the City of Houston purchased the property to convert the former church into a community park. Read about testing of the remaining structural components and development of strengthening solutions.

eduCation issues

55 leading the Charge By Uchenna T. E. Okoye, P.E. and Eric Borchers, S.E.

Guest ColuMn

sPotliGht

By Kerri Olsen

Feature

By Alireza Biparva, M.A.Sc.

By Peter Debney, BEng(Hons), CEng

24 the nisd difference

STRUCTURE

historiC struCtures

59 krishna P. singh Center for nanotechnology By Brian Falconer, P.E., S.E., SECB

struCtural liCensure

26 100 Years of structural engineering licensure By Gregg E. Brandow, Ph.D., P.E., S.E.

struCtural ForuM

66 is structural engineering education sustainable? By Lawrence C. Bank, Ph.D., P.E.

struCtural testinG

28 inside the Bridge inspection toolbox By Roger Roberts, Ph.D. On the cover The historic Bethel Baptist Church was destroyed after a fire gutted the interior in 2005 and severely damaged its masonry walls. The design team cocreated an amazing community park from the ashes of the fire-damaged structure and successfully restored aspects of its original historic splendor. Walter P Moore conducted a comprehensive investigation, in-situ testing, and developed a repair protocol that strengthened the walls in place. See feature article on page 34. Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

STRUCTURE magazine

Feature

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February 2015

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Editorial

Where We Go Depends On Where We Aim new trends, new techniques and current industry issues By Barry Arnold, S.E., SECB

nprecedented challenges face the structural engineering profession in the years to come. Threats from foreign competition, opposition to structural licensure, dwindling profits, decline in ethics, and increased risk and expectations are at our doorstep now. It has become obvious that trying to maintain the status quo will only result in a decline in the relevance of the profession. An idiom states that there are three types of people: Those that are in the loop, those that are out of the loop, and those that don’t know there is a loop. As licensed professionals, it is imperative that we be ‘in the loop’, actively engaged in advocating for our profession, and working to forge a meaningful future for all present and future structural engineers. There are three ways to approach the future: We can actively plan and contribute to make the future we want a reality, we can sit idle and wait and see what happens or, when the future arrives, we can see what happens and adjust. The first option requires that we plan and build the future we want, not unlike the planning, calculating, and construction that goes into building a structure. The second and third options require no planning, no effort, and no consideration for the profession or the public. To position itself to meet and address the present and future concerns of the structural engineering profession, NCSEA has taken the initiative to create a four-phase strategic planning process.

2-day Strategic Planning Session. The input by the SEAs provided a valuable resource of relevant information considered significant by the SEAs.

Phase 3 – Develop a Mission and Vision Statement Based on the SEAs’ input, NCSEA created new Mission and Vision Statements which better reflect the purpose and intent of the organization. NCSEA’s new Mission Statement: NCSEA advances the practice of structural engineering by representing and strengthening its Member Organizations. NCSEA’s new Vision Statement: The National Council of Structural Engineers Associations will be recognized as the leading advocate for the practice of structural engineering.

Phase 4 – Form Focus Groups Four focus groups were formed to undertake the following tasks and make recommendations to help NCSEA meet its mission and vision statements: (i) Evaluation of NCSEA’s Organizational Structure, (ii) Examination of the current NCSEA–MO delegate model and evaluation of the ways it can be modified and improved, (iii) Exploration of new ways to improve MO communication between all components of the organization, including Board, Staff, Committees, and Member Organizations, and (iv) Assessment of NCSEA’s financial sustainability, including evaluation of both opportunities for additional revenue streams and threats to current revenue streams. NCSEA’s Strategic Plan is an on-going process, based on feedback from the SEAs. And because great organizations do more than just collect feedback, NCSEA is putting the ideas, hopes, and dreams of the MOs into the strategic plan by addressing their concerns. NCSEA needs to be strong and aimed in the right direction as it advocates for the profession. It also needs to be nimble so it can easily adjust to changes in our world and provide additional emphasis in areas needing critical attention. NCSEA exists for the SEAs, and the SEAs exist for their members. Their members, the structural engineers, exist to protect the public. We are all in this together. We all need to be in the loop and actively engaged in this important process. NCSEA should aim high and set goals that will ultimately improve the structural engineering profession and benefit the public. NCSEA’s aim must be true, so that the structural engineering profession will remain relevant and vibrant as it faces the challenges ahead.▪

Phase 1 – Determine Whom You Serve Marcus Buckingham declared in his book, The One Thing You Need To Know, that the key to long term success is to know whom you serve. Knowing why your organization exists, who your clients are, and what they want, is crucial to your long-term success. After much thoughtful discussion, it was determined that NCSEA exists to represent and support the Structural Engineering Associations (SEAs) in their effort to improve the profession and protect the public.

a member benefit

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Phase 2 – Collect Data

STRUCTURAL ENGINEERING INSTITUTE

With clarity on whom NCSEA serves, NCSEA sent a 3-question survey to the leadership of the SEAs, asking them: First, what are the three most significant problems facing your member organization? Second, what are the three things you believe NCSEA is doing well? Third, what could NCSEA do to improve its support of your SEA? Seventy-five percent of the SEAs participated, providing a total of 291 responses, which were reviewed by the 34 participants attending NCSEA’s STRUCTURE magazine

Barry Arnold, S.E., SECB (barrya@arwengineers.com), is a Vice President at ARW Engineers in Ogden, Utah. He is a Past President of the Structural Engineers Association of Utah (SEAU), serves as the SEAU Delegate to NCSEA, and is the NCSEA President and a member of the NCSEA Licensing Committee.

February 2015

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PROJECT UPDATE: Since Pennoni issued the report for this facility and submitted the article for publication, the Property Manager and Owner for Industry City reacted quickly to the recommendations by immediately reroofing all of the buildings that had not already been reroofed at the time of the investigation. The Property Manager also retained Pennoni to design the structural systems associated with mechanical and electrical upgrades located on the roofs of the facility, and to peer-review a new adaptive reuse project, in order to ensure that these efforts would benefit from the firm’s previous involvement with and knowledge of the facility. The actions of the Property Manager serve to illustrate the proper approach to the ongoing use and renovation of a vital historic facility.

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EDITORIAL STAFF Executive Editor Jeanne Vogelzang, JD, CAE execdir@ncsea.com Editor Christine M. Sloat, P.E. publisher@STRUCTUREmag.org Associate Editor Nikki Alger publisher@STRUCTUREmag.org Graphic Designer Rob Fullmer graphics@STRUCTUREmag.org Web Developer William Radig webmaster@STRUCTUREmag.org

EDITORIAL BOARD Chair Jon A. Schmidt, P.E., SECB Burns & McDonnell, Kansas City, MO chair@structuremag.org Craig E. Barnes, P.E., SECB CBI Consulting, Inc., Boston, MA John A. Dal Pino, S.E. Degenkolb Engineers, San Francisco, CA Mark W. Holmberg, P.E. Heath & Lineback Engineers, Inc., Marietta, GA

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STRUCTURE magazine

February 2015

Brian J. Leshko, P.E. HDR Engineering, Inc., Pittsburgh, PA Brian W. Miller Davis, CA Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT Greg Schindler, P.E., S.E. KPFF Consulting Engineers, Seattle, WA Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA Amy Trygestad, P.E. Chase Engineering, LLC, New Prague, MN C3 Ink, Publishers A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 Phone 608-524-1397 Fax 608-524-4432 publisher@structuremag.org February 2015, Volume 22, Number 2 ISSN 1536-4283. Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student. For change of address or duplicate copies, contact your member organization(s) or email subscriptions@STRUCTUREmag.org. 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, C3 Ink, 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.

“Put away your swords. They will get rusty in the dew.”

– Othello, Act 1, Scene 2, by William Shakespeare, circa 1603

orrosion has been a problem since the beginning of the Iron Age, circa 1200 BC. Before the Industrial Revolution, corrosion was recognized and respected in hand-produced objects, such as weapons. After the advent of machinery that was used to fabricate metal alloys for structural framing members and components exposed to the elements, corrosion found new targets. The metal alloys include but are not limited to wrought iron, cast iron, hot-rolled steel, and stainless steel. Corrosion of metals is caused by either a chemical reaction or electrification, in which the base metal is changed and eaten away. An example of chemical interaction is the oxidation of iron in the presence of water by an electrolytic process to form iron oxide (i.e., rust). An example of electrification is a rapid-transit system, in which stray direct currents (DC) can corrode rails and nearby metallic infrastructure components, such as buried pipelines and cables. Corrosion has eight unique forms, which are more or less interrelated. These include the following in no particular order: (1) uniform or general attack, (2) galvanic or two-metal corrosion, (3) crevice corrosion, (4) pitting, (5) intergranular corrosion, (6) selected leaching or parting, (7) erosion corrosion, and (8) stress corrosion. Today, rusted vehicles no longer litter the landscape. From this, casual observers and perhaps some structural engineers may not realize that these vehicles have been recycled, and that technological advancements have ameliorated nearly all rust in modern-day vehicles. Some may also conclude that rust and various types of corrosion are no longer of concern, because they see essentially no rust in the landscapes; but rust and corrosion in general have by no means disappeared. Corrosion, although touted as “a natural but controllable process,” is an ultra-expensive nemesis of steel and reinforced concrete structures. In 1998, direct corrosion costs were approximately $276 billion or 3.1% of the GDP. The costs included but were not limited to utilities, drinking water and sewer systems, gas distribution, waterways and ports, and highway bridges. A recent publication stated, “In the 15 years that have passed since the [NACE] study was released, inflation has driven both the direct and indirect costs of corrosion over $500 billion annually, totaling over $1 trillion in 2013 … At 6.2% of GDP, corrosion is one of the largest single expenses in the US economy yet it rarely receives the attention it requires. Corrosion costs money and lives, resulting in dangerous failures and increased charges for everything from utilities to transportation and more.”

This article presents two examples of corrosion that were unintentional byproducts of structural designs. The first example, electric power transmission towers constructed from weathering steel, describes uniform or general attack corrosion. The second example, stress corrosion with hydrogen embrittlement, entails the design of a cofferdam and its waler bolts.

Lessons Learned problems and solutions encountered by practicing structural engineers

Example 1 Aesthetics versus Durability: Premature Use of Weathering Steel The stage for the first example – a corrosion problem, specifically the formation of rust within structural joints – was set circa 1965-1966, when structural engineers began selecting weathering steel for bolted structural members, typically angles, in electric power transmission towers. Weathering steel is a highstrength, low-alloy steel that forms a tightlyadhering “patina” during its initial exposure to moisture and oxygen. The patina, an oxide film of corrosion by-products, formed early on between bolted plate elements of the angles and continued to grow as “pack-out” rust. This rust, which decreased the cross-sectional area of the bolted members, forced bolted plate elements apart. On some occasions, bolts have fractured from excessive axial tensile stress. When the transmission towers were designed, no guidelines existed for bolting weathering steel structural members that were exposed to the elements. After corrosion was observed, design guidelines were developed and published. They provided information for bolt spacing, edge distance, and clamping forces to minimize the possibility of formation of “pack-out” rust between bolted plate elements, such as angles. Transmission towers that were adversely affected still exist and/or are being replaced in at least Virginia and New York.

Unintentional Corrosion by Structural Design By Julie Mark Cohen, Ph.D., P.E., SECB

Julie Mark Cohen, Ph.D., P.E., SECB (jmcohen@jmcohenpe.com), is a consulting structural and forensic engineer and published fiction writer in Latham, New York. This article constitutes a small part of her research, entitled Structural Engineers: Constraints on Design Decisions and Subsequent, Costly Failures 1950-2014.

Example 2 Caveat Emptor: Misuse of ASTM A722 A second example is the result of U.S. manufacturers misusing an ASTM standard. This problem has gone unrecognized by structural engineers, even though failures have occurred. Specifics of nearly all of these failures are not in the public domain. This example is presented by using a

STRUCTURE magazine

The online version of this article contains several detailed references. Please visit www.STRUCTUREmag.org.

fictitious scenario of the design of a marine structure, specifically a cofferdam. However, the impetus for misuse is factual, and the risk of subsequent failures is real. Design of a Fictitious Cofferdam Elliot Buyer is a 40-year-old structural engineer who earned a bachelor’s degree in civil engineering and a one-year project master’s degree, both with honors, and easily passed the FE, PE, and SE exams. He works in the century-old, well-respected firm, Clev-R Structural Engineers. In February 2014, Elliot procured a project from an international corporation to replace a 71-year-old, 650-foot-long cofferdam in the local ocean harbor. He felt comfortable working single-handedly, because he had designed dozens of large, complicated retaining walls in highly saturated soils, none of which had ever shown signs of distress. Recalling that Clev-R worked on another cofferdam project in the early 1990s, Elliot searched his office’s library. He ignored an unlabeled manila folder with a plastic-laminated article entitled “Atoms Villain in Culvert Collapse” that discussed the failure of A490 bolts. The failure was attributed to hydrogen embrittlement, “a phenomenon occasionally experienced in metallurgy but never before known to have occurred in highway culvert construction.” The article stated that the following three factors must be simultaneously present for hydrogen embrittlement to occur: stress, susceptibility, and a wet environment. Next to the manila folder, Elliot found a sheet pile design manual published by United States Steel. Near the manual, he discovered a binder, labeled Supplements to the Sheet Pile Design Manual, that was initialed by RC III. The binder included examples of waler designs with top and bottom channels stitched together, soil gravity loads on walers, and approximate analyses for continuous walers. He also discovered calculations for a smaller cofferdam’s waler bolts and tie-back rods using ASTM A325 material. In addition, he observed that the waler bolts were designed for axial tension plus bending, “just in case the walers rotate downward.” Elliot quickly realized that he would need high-strength steel for the waler bolts and tie-back rods. He searched the internet and learned that U.S. manufacturers were selling ASTM A722 threaded rods with the option of hot-dip galvanizing. He prepared a thorough, well-documented calculation package and requested an in-house peer review from a more seasoned colleague, Denis L’Accord. Denis spent two days

reviewing Elliot’s work, but had no comments, not even minor ones. The construction of the new cofferdam commenced in mid-summer and was completed in late fall 2014. A barely measurable out-ofplumbness was introduced into the sheet piles, but Elliot was confident that it was within acceptable levels and that the conservative waler bolt design was more than adequate. Cofferdam Failure At dawn on New Year’s Day, January 2015, the cofferdam failed: the sheet piles tilted toward the ocean, and the soil sank behind them. By 10 a.m., Elliot, Denis, and Roger Clevstone III (RC III), grandson of the founding principal, were poring over Elliot’s calculations, construction documents, reports by an independent inspector, and photographs taken during construction. The manufacturers’ catalogs sat at the bottom of a stack at the end of the conference room table. The men were mystified. Preparation of Deposition Questions The client, a private corporation, hired Quinn Santiago, Esq., an attorney who was wellknown for winning lawsuits on failing to meet the standard of care. In his thirty years of litigation, he had seen dozens of highlytrained professionals who did not realize that they lacked the knowledge to make informed design decisions. In turn, Quinn hired Abigail Sorrel, a consulting structural and forensic engineer, who was well-respected for what others called a “multi-disciplinary” approach to problemsolving. She fought against this designation, contending that any knowledge needed to solve a particular discipline’s problem is requisite to that discipline. The reports from three independent metallurgists were telling. From these findings, Abigail organized information with which she would assist Quinn in developing questions for the depositions of Elliot and Denis. Her preliminary list included the following items: 1. Metallurgists’ consensus: Hydrogen embrittlement and fracture of waler bolts. 2. Ocean cofferdam. Salt water environment. 3. 150-ksi steel, hot-dip galvanized, threaded bolts and rods. 4. U.S. manufacturers selling ASTM A722, hot-dip galvanized threaded rods and bolts. 5. Neither RCSC (2009) nor AISC (2010) specify ASTM A722 as a material to be used for structural fasteners.

STRUCTURE magazine

February 2015

6. An article in a steel industry publication about specifying proper materials (Anderson and Carter 2012) does not mention ASTM A722 for structural fasteners. However, one of the authors (Anderson 2011) previously stated, “To properly use an unlisted material, one must evaluate its various characteristics in relation to the contemplated uses for it ...” 7. ASTM A722/A722M: Standard Specification for Uncoated High-Strength Steel Bars for Prestressing Concrete. a. Originally approved in 1975. b.Dimensions given for Type I (plain) bars and Type II (deformed) bars. No threaded rods. c. Finished bars shall have a minimum ultimate tensile strength of 150 ksi. d. Minimum yield strength given for Type I and II bars as a percentage of ultimate strength. e. Minimum elongation is given for Type I and II bars, which is much smaller than for RCSC- and AISCaccepted A490 steel. f. Also, AASHTO M 275M/M 275 (same title). 8. ASTM A143/A143M: Standard Practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel Products and Procedure for Detecting Embrittlement. a. Originally approved in 1932. b.“In practice, hydrogen embrittlement of galvanized steel is usually of concern only if the steel exceeds approximately 150 ksi in ultimate tensile strength, or if it has been severely cold worked prior to pickling.” 9. ASTM F2329: Standard Specification for Zinc Coating, Hot-Dip, Requirements for Application to Carbon and Alloy Steel Bolts, Screws, Washers, Nuts, and Special Threaded Fasteners a. Originally approved in 2005. b.“For high strength fasteners (having a specified minimum product hardness of 33HRC), there is a risk of internal hydrogen embrittlement.” 10. Before Elliot’s design, Caltrans issued the following amendments to the AASHTO LRFD: “...ASTM A722 bars shall not be galvanized” and “Galvanization of ... ASTM A722 bars is not permitted due to hydrogen embrittlement.” Abigail also noted that sheet pile, waler bolt, and tie-back designs followed the

state-of-practice. However, overstrength (a higher factor of safety) and redundancy were not considered. She noted that, even if they had been considered, they were unlikely to have been helpful, since all of the waler bolts were equally susceptible to two interdependent cracking phenomena, tensile stress corrosion in salt water and hydrogen embrittlement.

Structural Engineers, Their Knowledge Base and Design Decisions

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Concluding Remarks Confucius said, “To know what you know and what you do not know, that is true knowledge.” In the first example, design criteria were not developed before a new material, weathering steel, was used for bolted structures exposed to the elements. In the second example, the knowledge base had been well-developed, but was not recognized by structural engineers. Clearly, the (fictitious) cofferdam failure described above could have been prevented if Elliot and his colleagues had taken a moment to look up the title of ASTM A722 and read the words “uncoated,” “bars,” and “prestressing,” which should have raised a red flag. Unfortunately, across the U.S., structural engineers are specifying hot-dip galvanized, threaded rods that are sold by manufacturers as compliant with ASTM A722 for cofferdams, underground pipes, bridge components, and other structures whose steel components are exposed to salt water environments. The intention of this article is to leave the readers with three questions: 1) How does a structural engineer recognize when his/her knowledge base is insufficient? 2) When should a structural engineer employ the services of a collaborator, such as a materials engineer? 3) What, if anything, should be done, and by whom, to ensure that structural engineers possess an adequate knowledge base to develop designs that provide reliable, predictable, and durable performance?▪

STRUCTURE magazine

February 2015

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Structural engineers hail from two different professional traditions. First, for centuries, civil engineers who worked on military and public works projects required the services of specialists who would later be known as “structural engineers.” Second, since the mid-1880s when architects relinquished their responsibilities for structural design, they have required the services of structural engineers who specialized in building projects. Regardless of the project type, for well over a century, structural engineers have been providing specialized technical services not strictly through their own profession, but under the broad umbrella of the civil engineering profession. In part as a result of this history, the undergraduate and graduate educations of these engineering specialists, mentoring in practice, licensure, and continuing education for licensure are not without their flaws and deficiencies. In the United States, ABET (2014) provides requirements for baccalaureate engineering education. Although civil engineering has been a long-established and accredited undergraduate major, structural engineering has never been recognized as a separate degree program. Structural engineering courses are offered as a “technical area” within civil engineering curricula. ABET’s requirements do not require solving problems that deal with microscopic behaviors of steel (e.g., fracture and corrosion). Senior-level capstone courses rarely, if ever, include collaboration with seniors studying materials engineering. From this, civil engineering students may receive the impression that such consultation with materials engineers is not necessary once they are practicing. Structural engineers who receive oneor two-year master’s degrees in structural engineering are also at a disadvantage. One-year curricula tend to focus solely on structural engineering, often with a project in collaboration with civil and/

or geotechnical engineers. Thesis-based two-year curricula rarely allow a structural engineering graduate student to enroll in a materials engineering course. The curricula for doctoral students are almost always as narrowly focused as those for two-year master’s degrees. Licensure for professional engineers and, where applicable, for structural engineers, as well as SECB certification, do not require that applicants and exam-takers possess any level of knowledge about corrosion of steel, or even an awareness of relevant ASTM standards. Continuing education courses reflect licensure. Consequently, structural engineers are asked to solve practical problems for which their educational and practical backgrounds may be inadequate. They may not be properly aware of their limitations.

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uilt-up cold-formed steel compression members are commonly used as shear wall chord members, and at openings of doors and windows (stud packs) to resist the additional load transferred from an opening header. The provisions in North American Specification for the Design of Cold-Formed Steel Structural Members, AISI S100 Section D1.2 are limited to concentrically loaded compression members composed of two shapes joined together at discrete points along the axis of the member. Thus, the AISI S100 provisions are limited to either an I-shaped cross section or a box-shaped cross section. Today there are various assumptions employed when designing the stud packs. An often employed assumption by inexperienced cold-formed steel design engineers is that each stud in a stud pack has the same tributary area as a typical wall stud. What this assumption consists of is adding studs to the stud pack equal to the number of studs displaced by an opening. Thus, the stud pack is not engineered but, in fact, is simply assembled to provide an equal number of studs as if the opening did not occur. This assumption can be both uneconomical and can result in poor framing designs as illustrated by Figure 1.

Figure 1.

Another questionable assumption made by inexperienced cold-formed steel design engineers is that the axial load is shared equally to each individual member of the stud pack, and each member’s strength is based on the behavior as a discrete member. Making this assumption can lead to a suspect load path or an uneconomical, design as any synergy of the individual stud pack members is not accounted for in the design. The following discussion introduces design concepts and practical considerations for built-up member design, for which AISI S100 and AISI framing standards, AISI S211 North American Standard for Cold-Formed Steel Framing – Wall Stud Design have specific design provisions.

Design Methodology Built-up compression members interconnected at discrete points have a reduced shear rigidity which reduces the buckling stress of the member. To reflect the reduced shear rigidity, AISI S100 Section D1.2 requires the use of a modified slenderness ratio, (KL/r)m as follows:

where

( ) √( ) ( ) KL r

KL a + r o ri

(KL/r)o = Overall slenderness ratio of entire section about built-up member axis a = Intermediate fastener or spot weld spacing ri = Minimum radius of gyration of full unreduced cross-sectional area of an individual shape (single C-section) in a built-up member Note, the modified slenderness ratio is only applied to the buckling axis that requires the interconnecting fasteners to transfer shear. For an I-shaped section, this means the (KL/r)y axis is the slenderness ratio to be modified. The (KL/r)x axis is not modified. When applying the modified slenderness ratio, the following additional the fastener strength [resistance] and spacing shall be satisfied: 1) The intermediate fastener or spot weld spacing, a, is limited such that a/ri does not exceed one-half the governing slenderness ratio of the built-up member. 2) The ends of a built-up compression member are connected by a weld having a length not less than the maximum width of the member, or by connectors spaced longitudinally not more than 4 diameters apart for a distance equal to 1.5 times the maximum width of the member. 3) The intermediate fastener(s) or weld(s) at any longitudinal member tie location are capable of transmitting required strength [factored forces] in any direction of 2.5 percent of the available axial strength [factored resistance] of the built-up member. AISI S211 requires that if the above criteria are not met, the design strength of the built-up member shall be taken as the sum of the individual members of the built-up section. AISI S100 Section D1.2 imposes stringent connection requirements for the ends of built-up members (requirement 2 above). However, based on research, the following provision has been adopted for the next edition of the AISI framing standards which will combine the current framing standards into one document, North American Standard for ColdFormed Steel Structural Framing AISI S240: Exception: Where a built-up axial load bearing section comprised of two studs oriented backto-back forming an I-shaped cross-section is properly seated in a track in accordance with the requirements of Section C3.4.3, and the top and bottom end bearing detail of the studs consists of full support by steel or concrete

STRUCTURE magazine

EnginEEr’s notEbook aids for the structural engineer’s toolbox

Built-Up Cold-Formed Steel Compression Member Design

By Roger LaBoube, Ph.D., P.E.

Roger LaBoube, Ph.D, P.E. (laboube@mst.edu), is Curator’s Teaching Professor Emeritus of Civil Engineering and Director of the Wei-Wen Yu Center for Cold-Formed Steel Structures at the Missouri University of Technology. Roger is active in several professional organizations and societies, including the American Iron and Steel Institute’s Committee on Specifications and Committee on Framing Standards. He also serves on STRUCTURE’s Editorial Board.

components with adequate strength and stiffness to preclude differential end slip of the built-up studs, the compliance with the end connection provisions of AISI S100 Section D1.2(b) is not required. The current framing standards are a free download from www.aisistandards.org.

Example Problem Studs – back to back Reinforcing track (no shear connection top and bottom)

Figure 2.

A typical 9-foot jamb stud as shown consisting of two 600S162-54 (50 ksi) sections interconnected by two self-drilling screws 24 inches on center in the web (Figure 2). The track section is not considered to be a structural member to resist axial loads, but is needed to create a closure for the opening at the door or window. Weak axis bracing (in the plane of the wall) is provided at 4-foot intervals.

A design consideration is the spacing of the web connectors which will influence both load capacity and economics as summarized: “a” (inches) 24 18 12

“Pa” (kips) 13.85 14.50 14.99

The design engineer should carefully consider if the increased load will provide the most economical design solution because of the added labor expense of providing screws at a closer spacing. When creating built-up sections, orientation of the individual members should be considered. For example, if two 600S16254 (50 ksi) sections were oriented in a box configuration (Figure 3), with the toe-to-toe welds spaced 24 inches on center, the available strength, Pa, is 16.92 kips vs 13.85 kips for the I-section configuration. Furthermore, the I-section configuration requires the additional track section for the jamb closure. Studs – toe to toe

Lx = 9 ft, Ly = Lt = 4 ft Properties: Single 600S162-54, ry = 0.5699 inch

Figure 3.

Double 600S162-54, rx = 2.2677 inches, ry = 0.7042, a = 24 inches (center to center spacing of web fasteners) KL/r for the y-axis,

( ) √( ) ( ) KL r

KL a + r o ri

= [(48/0.7042)2 + (24/0.5699)2 ]0.5 = 80.12 KL/r for the x-axis, (KL/r)x = (9 x 12)/2.2677 = 47.63 The y-axis slenderness ratio controls the axial capacity. π2E Fe = = 45.35 ksi (KL/r)2 λc =

√

Fy = 1.05 Fe

For λc ≤ 1.5 2

Fn (0.658λ c )Fy = 31.52 ksi The effective area, Ae, is computed at f = Fn, Ae = 0.7010 square inches Pn = Fn Ae = 31.52 ksi x 0.7010 in2 = 24.93 kips Available Strength, Pa = Pn/Ω = 24.93 kips/ 1.80 = 13.85 kips

Check the following additional the fastener and spacing requirements: 1) The intermediate fastener or spot weld spacing, a, is limited such that a/ri does not exceed one-half the governing slenderness ratio of the built-up member. a/ri = 24/0.5699 = 42.11 0.5(KL/r) = 0.5 (80.12) = 40.06 Although the a/ri is 5% larger than onehalf the governing slenderness ratio of the built-up member, the 24-inch spacing is deemed to be acceptable. This criteria is to ensure that the individual member will not buckle prior to overall buckling of the built-up member. The additional track section, as well as sheathing attached to both flanges of the individual member, will enhance its buckling strength. 2) The ends of a built-up compression member are connected by a weld having a length not less than the maximum width of the member, or by connectors spaced longitudinally not more than 4 diameters apart for a distance equal to 1.5 times the maximum width of the member. The built-up member will be properly seated in track sections top

STRUCTURE magazine

February 2015

and bottom, thus by utilizing the provision of AISI S240, additional fasteners are not required. 3) The intermediate fastener(s) or weld(s) at any longitudinal member tie location are capable of transmitting required strength [factored forces] in any direction of 2.5 percent of the available axial strength [factored resistance] of the built-up member. Using No. 12 self-drilling screws, the nominal shear capacity of a screw is 1.29 kips. The available strength of a screw is 1.29 kips/3.0 = 0.86 kips per screw. Where 3.0 is the safety factor. 2.5% x 13.85 kips = 0.35 kips < 0.86 kips, Okay!

Practical Considerations Specific design methodology for two members interconnected is presented here, but in many cases more than two members are used to create a stud pack. The following are design thoughts offered by several experienced coldformed steel design engineers: • The design varies from job-to-job based on the contractor preference and politics (e.g. on some union jobs, the cold-formed steel contractor can’t install HSS thicker than 1/8-inch – iron worker vs carpenter unions). • Where we see a pair of 97-mil, S200 or bigger studs, our firm starts thinking HSS. The cost of buying two (2) heavy studs and then welding them together seldom makes sense when compared to buying a tube. • Our firm is not a big fan of triple or more built-ups both due to cost and, in the case of jamb stud packs, the notion that equal load-sharing is questionable for the studs away from the opening. • Our firm limits studs to a maximum of three (3) in a stud pack because of concern that equal load sharing does not occur as well as the economics of fabricating the stud pack. Our firm uses a light-weight welded I-section whenever three (3) studs are not adequate. Also, we do not change the thickness of the stud in the panel to create a stud pack. If the panel consisted of 6-inch 54 mil studs, we limited the stud pack to three 6-inch 54 mil studs; we did not up the thickness of the column studs. Giving consideration to load path and fabrication costs can help cold-formed steel design engineers to develop the most efficient coldformed steel wall framing assembly.▪

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Code Updates code developments and announcements

Figure 1. 2015 WFCM in 2015 IBC/IRC.

he 2015 Edition of the Wood Frame Construction Manual (WFCM) for One- and Two-Family Dwellings (ANSI/ AWC WFCM-2015) was approved on October 10, 2014 as an ANSI American National Standard (Figure 1). The 2015 WFCM was developed by the American Wood Council’s (AWC) Wood Design Standards Committee and is referenced in the 2015 International Residential Code (IRC) and 2015 International Building Code (IBC). Primary changes to the 2015 WFCM are listed here and are subsequently covered in more detail: • Tabulated spans for lumber framing members now reflect changes to design values for visual grades of Southern Pine as referenced in the 2015 National Design Specification® (NDS®) for Wood Construction Supplement: Design Values for Wood Construction. • New tables provide prescriptive wood-frame solutions for rafters and ceiling joists in response to new live load deflection limits for ceilings using flexible finishes (including gypsum wallboard) or brittle finishes (including plaster and stucco) as adopted in the 2015 IRC. • Header spans revised to reflect L/240 live load deflection limits for members supporting only a roof and ceiling as shown in IRC and IBC tables. The WFCM includes prescriptive and engineered design provisions for wood wall, floor, and roof systems and their connections. A range of structural elements are covered, including sawn lumber, structural glued laminated timber, wood structural sheathing, I-joists, and trusses.

ASCE 7-10 Load Provisions Tabulated engineered and prescriptive design provisions in WFCM Chapters 2 and 3, respectively, are based on the following loads from ASCE 7-10 Minimum Design Loads for Buildings and Other Structures (Figure 2): • 0-70 psf ground snow loads

Figure 2. ASCE 7-10 wind, seismic, and snow loads used.

• 110-195 mph 700-year return period 3-second gust basic wind speeds • Seismic Design Categories A-D Additional information concerning changes to snow, wind, and seismic loads in ASCE 7-10 compared to ASCE 7-05 is discussed in a paper titled 2012 WFCM Changes (STRUCTURE® magazine, August 2014).

Changes to the 2015 Wood Frame Construction Manual

Lumber Framing Spans Tabulated spans for lumber framing members now reflect changes to design values referenced in the 2015 National Design Specification® for Wood Construction Supplement: Design Values for Wood Construction. Notably, the 2015 NDS Supplement incorporates new design values for visually-graded Southern Pine. The American Lumber Standard Committee (ALSC) Board of Review approved changes to these design values for all grades and all sizes of visuallygraded Southern Pine and Mixed Southern Pine lumber, with a recommended effective date of June 1, 2013.

Rafters and Ceiling Joists with Brittle Finishes Tables for ceiling joist spans/capacities, rafter spans/capacities, and hip and valley beam capacity requirements have been revised to clarify the live load deflection basis of these deflection criteria, and to associate live load deflection limits to cases with “no ceiling attached” and ceilings with “flexible finishes” and “brittle finishes.” Tables are added to address deflection criteria of L/ΔLL=360 for brittle finishes (Figure 3, page 18). Flexible finishes are denoted as “(including gypsum board)” and brittle finishes are denoted as “(including plaster and stucco).” continued on next page

STRUCTURE magazine

By John “Buddy” Showalter, P.E., Peter Mazikins, P.Eng and Michelle Kam-Biron, S.E., P.E.

John “Buddy” Showalter, P.E. is Vice President of Technology Transfer, Peter Mazikins, P.Eng is Senior Manager of Engineering Standards, and Michelle KamBiron, S.E., P.E. is Director of Education with the American Wood Council. Contact Mr. Showalter (bshowalter@awc.org) with questions.

The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

Header Spans Supporting Roof and Ceiling Roof header span tables have been revised to be based on L/ΔLL=240 instead of L/ΔLL=360. The L/ΔLL=240 deflection limit basis is consistent with deflection limits for members supporting roofs and ceilings as shown in IRC Table R802.5.1 and IBC Table 2308.7.2 for rafters with ceilings attached to rafters and IRC Table R802.4 and IBC Table 2308.7.2 for ceiling joists, respectively.

Applicability to Non-Residential Structures New language in IBC 2309 allows for use of the WFCM for non-residential structures within its scoping limitations: (IBC) 2309.1 Wood Frame Construction Manual. Structural design in accordance with the AWC WFCM shall be permitted for buildings assigned to Risk Category I or II subject to the limitations of Section 1.1.3 of the AWC WFCM and the load assumptions contained therein. Structural elements beyond these limitations shall be designed in accordance with accepted engineering practice. WFCM 1.1.3 references Table 1 Applicability Limitations (Figure 4) which outlines building dimensions and load assumptions. While WFCM provisions are intended primarily for detached one-and two-family dwellings due to the floor live load assumption associated with those occupancies, many of the WFCM provisions for specific geographic wind, seismic, and snow loads may be applicable for other buildings. For example, wind provisions for sizing of roof sheathing, wall sheathing, fastening schedules, uplift straps, shear anchorage, shear wall lengths, and wall studs for out of plane wind loads are included in the WFCM and are applicable for other use groups within the load limitations of the WFCM tables. Similarly, roof rafter size and spacing for heavy snow, and shear wall lengths and anchorage for seismic, are applicable within the load limitations of the WFCM tables. Examples of non-residential applications include single-story wood structures or top stories in mixed use structures in Risk Categories I or II. Applications outside the scope of the WFCM tabulated requirements, such as floor joist design for floor live loads greater than 40 psf and design of supporting gravity elements for the additional floor live load is beyond the applicability of the WFCM and must be designed in accordance with accepted engineering practice. This parallels the approach taken in Section R301.1.3 of the IRC, which permits unconventional elements of one and two-family dwellings to be designed per the IBC.

WFCM Availability The 2015 WFCM is currently available for purchase in electronic format (PDF) only. Once the WFCM Commentary is updated (which is to be included with the WFCM) printed copies will be available for purchase. Once the WFCM Commentary is complete, those who purchased

Figure 3. Excerpt from 2015 WFCM Table 3.25B2 for common lumber ceiling joist spans.

STRUCTURE magazine

February 2015

electronic versions of the 2015 WFCM will receive the WFCM Commentary in electronic format at no additional charge.

Conclusion With more governmental focus placed on “community resiliency,” design tools such as the Wood-Frame Construction Manual become more relevant. The Manual equips designers with engineered construction methods that result in buildings better able to withstand damage, and protect occupants should disaster strike. Since the WFCM was first published in 1995, AWC has been providing a solution for design of wood-frame structures to resist natural disasters. Each successive edition of the standard continues to provide solutions to more severe events as required by building codes. The 2015 WFCM represents the state-of-the-art for design of one- and two-family dwellings for high wind, high seismic, and high snow loads. Its reference in the 2015 IBC and 2015 IRC will allow for its use in those jurisdictions adopting the latest building code. However, building oﬃcials often accept designs prepared in accordance with newer reference standards even if the latest building code has not been adopted in their jurisdiction. IBC 104.11 and IRC R104.11 for alternate materials and design provides the authority having jurisdiction with that leeway.▪

Figure 4. Reproduction of 2015 WFCM Table 1 Applicability Limitations.

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STRUCTURE magazine

February 2015

Structural DeSign design issues for structural engineers

raditional structures are linear, stiff, restricted, heavy, and inefficient; lightweight structures, on the other hand – whether in fabric, cable, timber, concrete or stone – are nonlinear, long-spanning, flexible, highly efficient, and environmentally friendly. This series shows how, when form follows force as well as function, the result is a structure that soars. The first article was published in the November 2014 issue of STRUCTURE®. This second article looks at compression structures and form-finding techniques for getting the optimum structural form. It will also look at the important step of optimizing the geometry for lightweight structures.

Compression Structures

Why It’s Good to be a Lightweight Compression and Form Finding By Peter Debney, BEng(Hons), CEng, MIStructE

Peter Debney, BEng(Hons), CEng, MIStructE, is a Chartered Structural Engineer and software specialist with experience specializing in computing applications. He is an application specialist for Oasys (www.oasys-software.com), concentrating on structural and crowd simulation software.

Compression-only structures take the familiar form of walls, arches, shells and grid shells. Unlike tension-only structures that deflect to balance the loads, compression-only structures do not have this luxury, as any movement increases the risk of buckling. This is a major risk for masonry structures, as they have little or no bending capacity other than that provided by the compression thrust. For the Gothic cathedrals of old, the soaring columns needed stabilizing with flying buttresses (Figure 1). Compare this to the Sagrada Familia cathedral by the Catalonian architect/engineer Antonio Gaudí. Here the columns are angled so as to take the loads in direct compression and thus avoid the horizontal reactions that would necessitate buttressing. The end result is something much more natural-looking (Figure 2).

Arches The overall forms may be the same, but the compression structure tends to be much thicker than the tension structure because it also has to resist buckling; or to put it another way, tension structures are in a stable equilibrium, but compression structures are in an unstable equilibrium. This

Figure 2. Sagrada Familia.

Figure 1. Westminster Abbey.

means that if the compression structure deflects too much, it will snap, while a tension structure will adjust itself instead. In a masonry structure, where the tension capacity is minimal, buckling is prevented by keeping the line of thrust – which is the moment divided by the axial load – in the middle third of the element, thus ensuring that no part is in tension. Some masonry design guides, such as The Stone Skeleton by Jacques Heyman (1995), say that in certain circumstances the structure is fine as long as the thrust line remains within the overall section. This implies that there is considerable tension or cracking in the section, but it remains stable. The medieval builders ensured that this would happen by increasing the axial load on the buttresses by means of sculptures and pinnacles; ornamentation can be functional! (Figure 3) Reinforced concrete or steel structures on the other hand can resist this with their innate tension capacity. While flexible tension structures can readjust themselves to maintain equilibrium with the loads, masonry has much less scope to do this, but more than is commonly realized. Arches can remain stable even after the joints open as the line of arching action moves, as long as things do not move too much (Figure 4). Note that while the arch is uncracked, the centroid of resistance remains in the middle of the arch and it behaves in a linear fashion. Once it cracks, the centroid of resistance moves to the other side of the line of thrust – assuming

Figure 3. ©J E Gordon, Structures, or Why Things Don’t Fall Down (1978).

20 February 2015

Figure 5. 1939 Cement Hall.

Figure 4. Thrust lines and collapse mechanism for a masonry arch (Heyman 1995).

a reasonably high stiffness – which actively resists that thrust. This illustrates a feature of many nonlinear systems; they are self-stabilizing as long as the perturbation is within certain limits.

Shells Incredibly thin arches and shells are achievable when they are geometrically optimised, such as Robert Maillart’s 1939 Cement Hall from the Zurich National Exhibition. The door openings on the bridge indicate both the scale and the thinness of this reinforced concrete shell (Figure 5).

When the shell is constructed from a grillage or lattice, often of timber, then it is referred to as a gridshell. The nature of these structures enables very organic forms to be produced; a well-known example being the Mannheim World Garden Exhibition building (Figure 6).

Analysis Masonry can behave differently from other engineering materials, such as steel and concrete. It is both orthotropic and nonlinear with little tensile capacity, but finite element analysis can be very useful if employed with care.

Figure 6. Mannheim World Garden Exhibition. Courtesy of Arup.

Like all nonlinear analyses, one must remember to evaluate all load combinations together. Masonry often resists imposed loads with its selfweight, so the dead load increases the moment capacity by reducing or negating the induced tension. Also, due to its tendency to crack, the load paths through a masonry structure can vary with the applied loads and support conditions. continued on next page

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STRUCTURE magazine

February 2015

12/23/14 3:50 PM

Figure 7 Analysis stage: 2 : fixed Scale: 1:10.31 Moment, Myy: 1.000 kNm/pic.cm Torce Lines, -ve thrust (at structure scale) Case: A4 : Analysis Case 1 [1]

z y

Figure 7. Circular arch.

Figure 9. GSA model of Westminster Abbey.

Form Finding

Figure 8. Flip-Flap arch analysis.

Consider an arch. Here one might model one-dimensional (1D) beam elements to carry the load, then use the combination of the bending moments and axial loads to check that the eccentricity is within limits. Some programs include this calculation in the post-processor, possibly described as Thrust or Torce lines. If the Torce line remains within the middle third of the section, then no tension is induced (Figure 7 ). One can improve the behavior of the arch through geometric optimization, also known as form-finding, which will be discussed below. Like many nonlinear structures, the load path through cracked masonry will change with the load and movement. One can model this within an arch by using twodimensional (2D) elements and what are known as “flip-flap” joints – compressiononly strut elements – in the arrangement shown in (Figure 8). Like all masonry analyses, it is important to model the support stiffness accurately, as this has a major effect on the end result. For more complex models, such as a crosssection through Westminster Abbey (Figure 9), you can use a full 2D mesh to analyze the lines of principal force, shown here in green for compression and red for tension. This analysis assumes that the masonry is uncracked, so is only suitable if the stresses remain low. You can get a good idea of the line of thrust from the flows of compression lines, as well as locations of likely cracking (Figure 10).

Physical models are still incredibly useful, at least for the initial design, as they are very quick to give results in a form that is tangible. The author has personally found physical models especially useful for tensegrity structures. Physical models have the limitation, though, that they are difficult to take measurements off and very poor for quantitative analysis. The good news is that there are now a number of computational methods available to determine the geometry such that the model can be analyzed. Note that these methods are called “form-finding,” as they are searching for the optimum form, not calculating it; this means that they can sometimes get lost on their journey, and might need guiding to the desired result. A close look reveals that the Sagrada Familia (Figure 2) is essentially the same as that of Cement Hall, which is the form of a parabola, the ideal shape for an arch under uniform load. This shape was determined in the 17th century by Robert Hooke, who realized that the perfect arch exactly mirrors the catenary shape of a hanging chain. Gaudi made use of this phenomenon when designing his cathedrals (Figure 11). He determined the overall form by modeling the columns and arches with chains and superimposed loads with weights (Figure 12). Frei Otto used physical models for the Munich Olympic structures prior to numerical analysis. Another famous example is the gridshell for the Mannheim World Garden Exhibition by Ted Happold and Ian Liddell while they were at Arup, prior to their forming of Buro Happold. Creating a model for form-finding requires first establishing the boundary conditions, which are the fixed points, as well as any fabric edges, which need either a flexible pretensioned cable or solid member to pull them

STRUCTURE magazine

February 2015

Figure 10. Thrust lines from FEA principal stresses.

taut. The engineer must also decide on the form-finding properties and loads that will push or pull the model into shape. These will vary depending on the selected form-finding method; some might be calculated, and some be an initial guess.

Force Density Form-Finding Force Density is one of the earliest and quickest of the numerical form-finding methods, but it is a little abstract. A 2D element’s area is set proportional to its stress, and a bar element’s length is set proportional to its force. This means that a longer element will have a reduced force density, and vice-versa (Figure 13). The end result should not only be a balanced geometry, but also a set of forces that may need to be scaled to the desired pretension values.

Figure 11. Colònia Güell Crypt.

Figure 12. Antonio Gaudi’s hanging chain.

Force Density is a quick way to get results, but it may require some experimentation to get the desired form. It is quite good for cable nets, but not as good for fabric structures as there cannot be different prestresses in the two orthogonal directions, restricting the forms that can be achieved.

Soap Film Form-Finding The Soap Film method of form-finding replicates the minimum surface inclinations of soap bubbles, by replacing the 1D bars and 2D fabric elements with elements that have a constant stress but zero stiffness. Conceptually, this is similar to soap bubbles edged by elastic bands. Because there is no stiffness in the system, apart from restraint points and beam elements, the nodes are free to move anywhere and so can possibly get in a muddle. This requires the addition of form-finding elements

called Spacers that are there just to ensure that the nodes are equally spaced out. While the method requires more work than Force Density, the major advantage of Soap Film is that it specifies the target prestresses rather than the more arbitrary force per length or area, and thus provides a more logical control over the final form, as well as probably resulting in a structure with less material. Another advantage of Soap Film over Force Density when using certain form-finding programs is that one can specify different warp and fill (weft) prestresses, which is extremely useful for conic fabric structures, as they generally need a relatively higher radial prestress, and can be beneficial for other forms as well.

Normal Properties Form-Finding Normal Properties form-finding literally uses the normal properties of the elements. This means changing the structural geometry to the deflected shape, rather than just determining how the given structure will deflect, with the possible option of locking in the resulting forces and distortions. This means that it is both an excellent method for form-finding

Figure 13. Force Density form-finding.

grid shells, replicating a hanging chain physical model, and for determining locked-in stresses from construction sequencing. As an example, Buro Happold’s London 2012 Olympic Main Stadium design used Normal Properties form-finding to analyse the locked-in construction stresses in the compression ring, and then Soap Film formfinding for the roof cables and infill fabrics.

Conclusion Compression structures may not be the most obvious candidates for lightweight options, but whether tensile or compressive, lightweight structures can soar over space to create iconic and efficient buildings. It is just a matter of getting the shape right.▪

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STRUCTURE magazine

February 2015

Guest Column dedicated to the dissemination of information from other organizations

esigners, fabricators and other industry partners tend to believe that the shop detail drawings are all created the same. What is often not understood is that the manner by which the steel detailers conduct their work, and how their information is presented on the shop detail and erection drawings, are what create the difference between shop detail drawings which are easy to use and encourage correct fabrication as opposed to those which do neither. There is a faulty idea in the industry that how the fabrication information is presented on the shop drawings does not matter, as long as the information is correct. It is like saying we don’t care how the car runs as long as it gets us to where we are going. The truth is that the shop detail and erection drawings are a key element to steel fabrication and steel installation. Shop drawing development, level of completion and detail presentation is paramount to the success of every project.

The NISD Difference By Kerri Olsen

Kerri Olsen is the Marketing Chair of the NISD. She may be contacted at kerriolsen@steeladvice.com. The NISD may be contacted at www.nisd.org.

Industry Professionals are Unaware

Steel detailers and steel fabricators with years of practice may not know about correct shop detail and erection drawing production and presentation because they have never been exposed to the difference themselves. Often, these same steel detailers and fabricators blame other sources as the cause of problems, and thus, the cycle is never broken. This lack of understanding by both steel fabricators and steel detailers can cause problems for reviewers in verifying that the shop drawings follow the original intent of the design drawings. Failure to follow industry standards for shop drawing presentation may cause parts to be fabricated and installed incorrectly, even though the information shown on the drawings may be correct.

Presentation Matters The manner by which the fabrication information is presented in the shop detail and erection drawings determines the flow of the work for all who use them. Properly developed shop detail and erection drawings promote efficiency for the designers, the shop fabricator and the field erector, which in turn creates confidence in their accuracy. Problematic shop detail and erection drawings are often a result of the steel detailer’s focus on the steel fabricator’s wants and needs only. Thus, the information shown will sometimes be confusing to others, and may not be complete and accurate upon the first approval submittal.

24 February 2015

Common Approval Submittal Problems Sending out shop detail drawings for approval prior to checking and not ready for fabrication is a common industry problem. This is a practice often caused by the general contractor pressuring the fabricator to get shop drawings out faster. But, in fact, it slows down the shop detail drawing development and approval process altogether. Further, this practice may prevent the production of subsequent drawing submittals while the first batch is being completed and checked. The contractor’s pressure on the steel fabricator to produce speedy detail drawing approval submittals induces the steel fabricator to then force the detailer to submit the shop detail drawings for approval unchecked and possibly incomplete. The steel detailer, with the incomplete and unchecked drawings out for approval, will then return to complete the drawing development for those same sheets. Upon receipt of the engineers’ review comments, the questions, answers and verifications will be incorporated. The steel detailer has now developed the drawings to three completion levels. The fourth completion level will be the checking and then the fifth level will be the final scrub for approval verification. Forced submittals of partial and incomplete steel shop detail drawings by the general contractors and steel fabricators intent upon getting quick approval, actually slows down the shop detail drawing production, and is in strong contrast to the NISD suggested practice.

The Designer’s Problem The designers are the first to notice the level of shop detail drawing development while they struggle during the approval process to see how the application of their design intent has been presented. The steel detailer’s questions and verification requests will be included on the detail drawings, with the expectation of answers from the designers on the return approval. Multiple drawing approval submittals will be required. Shop fabrication delays may result, erectors may be delayed by fabrication errors and then production schedules are pushed out. This inefficient process can continue until the last refabricated piece of steel has been placed. This is the normal process for many and it does not have to be so. The National Institute for Steel Detailers (NISD) was born out of the need for a better way to produce steel shop drawings. The NISD continues to support the construction industry by promoting the proper method of shop detail drawing development and production. The NISD Industry standard publication provides information and encourages sound project management procedures conducive to successful projects.

The NISD Mission Statement

The Supporting Business Practice

detail views are correct and consistent, eliminating confusion for the reviewers, fabricators and erectors. NISD members and NISD Certified steel detailers are encouraged to perform every job with an emphasis on accuracy, clarity in presentation, consistency in format, and endeavor to never waiver from that commitment. That is the NISD Difference – using quality procedures and certified detailers. Such a standard will always increase speed and efficiency for all who use NISD produced shop detail and erection drawings.▪

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The following paragraph is the mission statement at the center of the entry web page for The National Institute of Steel Detailing: Founded in 1969, The National Institute of Steel Detailing or NISD is an organization which fosters a professional approach to doing business as a steel detailer in the construction industry. The mission of the group is to create a better understanding of the importance of steel detailing services, by advocating improved quality, education and certification. What does this statement mean to NISD member detailers? What about to those who are not members? Let’s break this down by parts and review what is meant by each sentence. “The National Institute of Steel Detailing or NISD is an organization which fosters a professional approach to doing business as a steel detailer.” The goal of the NISD is to encourage and support steel detailers, their fabrication partners and other trades people by promoting a professional approach to steel detailing. This is achieved through the active execution of the other half of the mission statement. ‘The mission of the group is to create a better understanding of the importance of steel detailing services, by advocating improved quality, education and certification.’ The NISD provides guideline documentation, in both CD format and written materials, which is information on providing a professional approach to steel detailing for their members. These training CDs, guides and informational materials all focus on the best business practices for creating complete and accurate shop detail drawings following industry standard procedures. Advanced steel detailers working on structural steel buildings and bridges may be NISD tested and certified. NISD members and certified steel detailers are sought out by designers and steel fabricators wanting complete and accurate steel shop fabrication and erection drawings.

detail drawings are developed and produced using a careful review, and correct application of the design drawings together with only essential RFI requests. Shop detail drawings are not submitted for approval until the shop detail development is complete and the drawings have been checked and are fabrication ready. In most cases, shop detail and erection drawing presentation is provided in a manner that promotes ease of review using cross reference details and notes leading back to the design drawings as appropriate. Section cuts and

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The business practice promoted by the NISD, NISD members and NISD certified detailers provides a much more rigorous process regarding shop detail drawing approval submittals. Steel shop

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Structural licenSure issues related to the regulation of structural engineering practice

Chicago skyline at sunrise. Courtesy of Daniel Schwen.

rowing up with a father who was a structural engineer, I learned at an early age about the impressive buildings in Los Angeles that he was responsible for engineering, but never put much thought into his professional title, “S.E.” Following in his footsteps, I quickly learned the academic requirements, and soon after completed the examination and experience that it took to put “S.E.” after my own name. The phrase, “protecting the public,” and the challenges of designing structures to withstand “nature’s fury,” especially earthquakes in California, put the responsibility that goes with holding the title of “Structural Engineer” into perspective. My structural engineering practice began as a kid when I would lay a wooden plank over the wash to serve as a bridge. Fortunately, the public did not use my bridges, because sometimes they would fail. Nobody said that I had to be licensed to engineer my bridge. The same problem occurred in Wyoming back in 1907, when water and irrigation required engineering, and anybody could provide such services. From this unruly situation came the first state law to regulate the practice of engineering. Today, every state has statutes that “protect the public” by regulating the practice of engineering in the built environment and the use of the title of “Professional Engineer” (P.E.). As I look back and look forward, I realize that I am part of a profession that is well established in some states, in desperate need of recognition in other states, and embraces licensure that varies significantly from state to state.

100 Years of Structural Engineering Licensure Looking Back, Looking Forward By Gregg E. Brandow, Ph.D., P.E., S.E.

Gregg E. Brandow, Ph.D., P.E., S.E. (brandow@usc.edu), is Professor of Engineering Practice at the University of Southern California in Los Angeles. He is also a Principal at Brandow & Nastar, Inc. Structural Engineers.

Looking Back The history of structural engineering dates back to at least the time of the Egyptian pyramids, where structural form and stable construction were planned and achieved. For the next 4,000 years, engineers built large and impressive structures without beam theory, Euler’s equation or the computer software that we have today. The 20 th-century structural engineer became equipped with new tools, such as moment distribution, and

26 February 2015

began to refine more elegant and taller buildings and longer bridges. Illinois Structural Engineers’ Act of 1915 The first efforts to regulate the practice of structural engineers started in 1908 when the Western Society of Engineers began negotiations with the Illinois branch of the American Institute of Architects and the Illinois Society of Architects to support and establish a state building code and provide a licensing law for structural engineers. The architects had been successful in creating the 1897 Architectural Act in Illinois, which gave them the exclusive right to design and supervise building construction. However, in 1913, efforts to establish a state building code failed to gain enough support. Architects’ support for engineering laws waned, and it took another two years of bitter debate before passage of the new Structural Engineers’ Act in 1915. The motivation to regulate the practice of structural engineering in Illinois was the rapid growth of downtown Chicago, which resulted in the construction of “skyscrapers” like the world had never seen before. These taller, more complex and higher-occupancy buildings drew the attention of the state legislature, which saw a need to regulate the profession responsible for designing them. As the late Gene Corley related to me, the legislature was compelled to keep “the fools and rascals from building unsafe structures.” As we begin 2015, we celebrate 100 years of structural engineering licensure that began with the first Structural Engineers Act in Illinois. The skyline of Chicago is a testament to the accomplishment of structural engineers over that century. California Title Authority of 1931 In California, the cities of San Francisco and Los Angeles were growing and developing their own skylines, and the structural engineering profession was faced with the additional challenges of building on ground that was susceptible to violent shaking. The great 1906 San Francisco Earthquake and the 1925 Santa Barbara Earthquake were very destructive. Civil engineers managed to get a Civil Engineering Registration Law passed in the California legislature in 1929, but structural engineers were unsuccessful in achieving a separate practice act.

They tried to gain the support of architects, but in 1931 amended the Civil Engineering Registration Law to include regulation of the title of “Structural Engineer” or “S.E.” without restricting any class of buildings to the exclusive purview of those authorized to use it. The 1933 Long Beach Earthquake caused widespread damage to, and the collapse of, many masonry school buildings throughout Southern California. If this earthquake had occurred during school hours, it could have resulted in an unimaginable loss of life. The legislature passed the Riley Act, which required seismic design, and the Field Act, which required that school buildings be engineered by licensed Structural Engineers. Years later, hospitals were added. Even without the legislative requirement, the vast majority of California’s significant structures are designed today by a licensed Structural Engineer. Progress in enacting legislation recognizing and regulating structural engineers in other states has been slow. Only a handful have structural engineering practice restrictions within the P.E. practice acts, while a few have separate structural engineering practice acts, and a few more have structural engineering title restrictions. NCEES Model Law Structural Engineer

NCEES 16-Hour Structural Engineering Exam The SEERTF recognized the need for a single national exam with the adoption of the International Building Code (IBC) in all states. The SEERTF convinced NCEES to develop a new exam based on the new IBC, which replaced the three previous national building codes that had been adopted in various states. A subsequent NCEES task force developed a test plan and exam format, and created and implemented a new NCEES 16-hour exam that all states agreed would be the standard for minimum competency for structural engineering licensure. All states that recognize structural engineers adopted this new exam, and most of the other states allow engineers to take this exam. SELC Unites Structural Engineers The Structural Engineering Licensure Coalition (SELC, www.selicensure.org) was created in 2012 to be a single voice for structural engineers to advocate the advancement of structural engineering licensure. According to its position statement, its goal is protection of the public through the implementation of minimum standards for the practice of structural engineering in every jurisdiction by enacting the national minimum standards (MLSE) and using the minimal competency 16-hour NCEES SE exam with a consistent licensure format in each state. The SELC is a coalition of SEI, NCSEA, the Structural Engineering Certification Board (SECB) and CASE. The SELC recognizes that the missing piece of the puzzle is to establish a structural engineering licensure format – practice restriction, title restriction or partial practice restriction – that can be adopted by NCEES as a standard and a guide for states to use.

Looking Forward If the structural engineering profession wants to be recognized nationally and have consistent licensure requirements across the states, we need to build support both inside our profession and among those who have

STRUCTURE magazine

February 2014

historically been opposed to our efforts. The next 100 years of structural engineering licensure will depend upon our efforts. Recent successes occurred in two states, Utah and Washington, where legislation was passed for partial structural engineering practice acts with the restriction that “significant structures” can only be designed by licensed Structural Engineers. In both of these states, provisions for transitioning Professional Engineers currently practicing structural design into the new S.E. license without having to take another exam was an important aspect of gaining wide support. Other states are currently undertaking similar efforts. With 100 years of history and a lot of passion, the structural engineering profession needs to recognize that we are part of a larger community of Professional Engineers in many disciplines, all as dedicated as we are to the protection of the public. We must keep this in mind as we work with NCEES to develop a consistent structural engineering licensure format, especially when interacting with organizations like the National Society for Professional Engineers (NSPE), which for many years was opposed to our efforts because of their concern about fracturing the wider engineering profession. We need to convince them and others that we all have the same goals of protecting the public, and that establishing a uniform S.E. licensure program across the country will enhance the public’s recognition of all engineers, whether they call themselves Structural Engineers or Professional Engineers. I can now design a bridge across a wash or a high-rise building, and the public, seeing a “S.E.” after my name, will be confident that I meet the minimum qualifications to be a Structural Engineer. Let us continue as a profession to promote structural engineering licensure for our second 100 years.▪

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In 2001, the National Council for Examiners for Engineering and Surveying (NCEES, www.ncees.org), which is the organization of state licensing boards for engineers and land surveyors, established the Structural Engineering Examination/Recognition Task Force (SEERTF) to address issues regarding structural engineering licensure. The NCEES President, Ted Fairfield from California, saw this national effort as a way to enhance public recognition of structural engineering and to standardize the requirements for professional practice. The national structural engineering organizations – SEI, NCSEA, and CASE – and NCEES have all recognized that structural engineering lacks national recognition, uniformity of requirements, and a means to facilitate comity and mobility. In addition, the NCEES national two-day competency exam for structural engineers was not used uniformly – for example, some states used only the first day – and the states of California, Oregon and Washington used different additional examinations. I served as chair for the SEERTF, and we recognized that no uniformity existed in the states that recognized structural engineers. In response, the SEERTF created the Model Law Structural Engineer (MLSE),

a standard for experience, education and examination requirements. To facilitate comity and mobility, NCEES established a Records Program for MLSEs. Structural engineers can now establish MLSE records with NCEES, and this information can be used to apply for comity in states that recognize structural engineers.

Structural teSting issues and advances related to structural testing

Figure 1. NDT testing procedure, called hammer sounding, using an acoustical representation to identify areas of delamination.

A Inside the Bridge Inspection Toolbox Ground Penetrating Radar Yields Benefits By Roger Roberts, Ph.D.

Roger Roberts, Ph.D., is a Senior Software Engineer for Geophysical Survey Systems, Inc. (GSSI). Roger’s specialty is using ground penetrating radar for transportation infrastructure applications.

ccording to the American Society of Civil Engineers (ASCE), approximately 25 percent of the nation’s bridges remain structurally deficient or functionally obsolete. The 2013 edition of ASCE’s Report Card for America’s Infrastructure warns that more than two hundred million trips are taken daily across deficient bridges in the nation’s largest metropolitan regions. One in nine of the nation’s bridges are rated as structurally deficient, and the average age of the nation’s 607,380 bridges is currently 42 years – many around the country are sixty to eighty years old. The report states, “The challenge for federal, state, and local governments is to increase bridge investments by $8 billion annually to address the identified $76 billion in needs for deficient bridges across the United States.” Bridge inspection is of fundamental importance in meeting that challenge. For bridges that were built in the 1960s, which have been deteriorating or been repaired throughout the years, how do responsible authorities prioritize which need to be repaired and which need to be replaced? How do they know which can wait until next year? How do they arrive at appropriate budgets? The answers lie in understanding and selecting the right combination of bridge inspection tools, which can provide information relative to the condition assessment of the bridge structures.

from state to state – and different states tend to have particular biases and preferences. Some states are progressive, using the latest technology or combination of technologies. Many states see the benefits of NDT methods as a way to reduce the amount of work that is required, and as a way of ensuring condition assessment data is most accurate. Here is a quick overview of the pros and cons of the key inspection techniques engineers have in their toolbox. Acoustical techniques are typically performed using a chain drag or a hammer, where the human ear discerns changes in the sound or pitch made by the chain or hammer being moved over the surface. The goal is to detect delamination, which refers to the separation of a coating from a substrate or the splitting of a structure into layers. Delamination in bridge decks is caused by the corrosion of reinforcing steel bar (rebar) and/or freezing and thawing. Delamination can often only be detected by nondestructive tests, including hammer sounding or chain dragging. The advantage of acoustical methods is that they are inexpensive and easy to do with limited training. Typically, the worker will locate areas of deterioration just by the change in tone and will mark the extents of the area with spray paint; the areas are then recorded later by another employee who will take a photograph or lay out a grid to map them. The technique is basically designed to get “real time” answers to delamination locations.

Range of Bridge Inspection Tools

The online version of this article contains detailed references. Please visit www.STRUCTUREmag.com.

Inspection methods are usually divided between destructive methods, like coring and chipping, and non-destructive testing (NDT) methods – those that evaluate the properties of a material, component, or system without causing damage. There is a wide array of bridge inspection tools used around the country. Options can be used alone or in combination. The preferred techniques vary

28 February 2015

Figure 2. Simplified diagram of how ground penetrating radar technology works.

Figure 3. Data collection using GPR.

STRUCTURE magazine

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The drawbacks to the method include the fact that it does not work on bridges with asphalt overlays (built-in boundary layer), and that different users may provide different delamination maps due to hearing biases. Outside noise, for example, traffic, can affect the results. It is not possible to get 100 percent repeatable results with different people conducting the inspections. Also, the technique only produces a map of existing delamination, which occurs after the rebar is significantly corroded. Deterioration that has not yet led to delamination is not mapped, rendering the technique inappropriate for planning more proactive repairs. Half-cell potential – This is a method of assessing rebar corrosion by measuring the voltage between the rebar in the concrete and a reference electrode placed on the surface of the concrete. The advantage of this approach is that it is more sensitive to rebar corrosion than acoustical sounding, so it can detect corrosion before it has progressed to the point where it has caused delamination. Unfortunately, this method also cannot be performed on bridges with asphalt overlays, as bare concrete is required. In addition, the method requires closing down the bridge deck, which can have a negative effect on traffic. It also requires quite a bit of time to complete, as discrete measurements are obtained on a grid pattern. This method is probably best used when you already know the bridge deck requires repairs, and you are trying to determine where repairs are needed and what kind of repair is necessary. It can help determine if you need to totally remove the deck or do in-place cut and patch repairs. Infrared – This method relies on changes in infrared radiation from the surface of concrete that are indicative of delamination. The method can be performed quickly and with a moving vehicle, minimizing bridge downtime and maximizing human safety. However, it requires that data be obtained at specific times when there is a large thermal gradient between the bridge temperature and the ambient temperature. Once again, this method cannot be performed on bridges with asphalt overlays. Visual inspection – This “low tech” method calls for surface mapping cracks, spalling, and potholes on bridge decks that can be seen with the naked eye. It is a straightforward approach that allows inspectors to map areas that are in immediate need of repair. The down side is that it is not possible to obtain a condition assessment of the interior of the concrete. Visual inspection is also the least efficient maintenance method, since it addresses problems only after they have resulted in damage and cost the most to repair. It is analogous to a leaky roof or water pipe

February 2015

Figure 4. GPR software denoting areas of concrete deterioration.

– it is best to repair the roof or pipe before the leaking water ruins everything around it. Ground-penetrating radar (GPR) – GPR uses radar pulses to image the subsurface. This NDT method uses electromagnetic radiation in the microwave band (UHF/VHF frequencies) of the radio spectrum, and detects the reflected signals from subsurface structures. GPR can be used in rock, soil, ice, fresh water, pavements and structures. The reflected signals are used to detect objects, changes in material, voids and cracks. GPR is used for assessing the quality and uniformity of an asphalt or concrete highway surface, and detecting deterioration on bridge decks. The two most common types of GPR for bridge surface measurement are groundcoupled and air-launched. Ground-coupled systems rely on an antenna that is placed very close to the roadway/surface while airlaunched systems use directional antennas aimed at the surface from a height of 12-20 inches. Ground-coupled antennas have a reputation of being less prone to radio frequency interference (RFI) from cell towers and TV broadcasting, but typically operate at very slow speeds that are below normal highway minimums. Air-launched antennas, even when travelling at 65 mph, are located at a safe distance from the surface. There are a number of advantages of GPR technology for bridge inspection, and the method is particularly well-suited to prioritizing for budgeting purposes. Whereas acoustical methods are very subjective, GPR data is quantitative. Noise does not affect radar technology. Coring and chipping – Even if NDT methods are used, a certain amount of coring (drilling a hole to view the concrete and rebar condition) and chipping (actually chip the cover away to be able to view the rebar) may be required to justify the deterioration that was mapped using NDT techniques. Corroborating results of NDT methods with coring/chipping increases confidence levels. Cores can also be obtained to measure the mechanical properties of the concrete – the compressive and shear strength, as well as the chemical properties of the concrete – chloride ion content and presence of alkali-silica reaction (in conjunction with petrographic

examination). All this is useful information beyond what the NDT methods provide. Of course, aside from being destructive, there is a relatively higher cost factor associated with each core, so the goal is to minimize the number of cores required to give the owner assurance that the results are correct.

Using GPR for Bridge Inspection As noted, GPR can be an excellent tool and is used for condition assessment, concrete cover, and concrete inspection. Typically, a cart-based system is used, in which data is collected at a walking pace (or a vehicle traveling about 5 miles per hour). The equipment will include the antenna and a controller. The radar technology looks for weakness in the returning radar signal from the reinforcing steel; the weaker the signal, the more deteriorated the concrete. The technology can show the location and depth of rebar, tie bars, and dowel bars. Figure 3 (page 29) shows the system being used in the field on a bridge deck. Condition assessment can be performed using both air-launched horn antennas and ground-coupled antennas. The groundcoupled antennas provide better horizontal resolution, which is sufficient to enable imaging of individual rebar in the top mat, typically not possible with horn antennas. This is one of the major reasons why groundcoupled antennas provide higher quality data than air-launched antennas. Ground-coupled antennas are used to collect densely spaced measurements along lines that are oriented so they cross over the top rebar in the upper mat at right angles (or close to a right angle if the rebar are skewed). The amplitude of the radar wave reflection from each rebar is recorded versus its location on the bridge. Relative changes in the rebar reflection amplitudes are typically indicative of the condition of the rebar and/or the concrete cover above. For maximum accuracy, rebar reflections arriving from rebar positioned at different depths may need to be corrected, depending on the depth difference. This can be tricky as variation in concrete moisture can lead to the illusion of depth variation. Also,

STRUCTURE magazine

February 2015

there are rules of thumb for choosing the relative change in rebar reflection, which is indicative of deterioration that requires maintenance. Often the GPR practitioner will map surface defects and map the corrosion evident from staining on the underside of the bridge deck to help fine-tune the deterioration threshold value. GPR can also be used for quality assurance/ quality control (“QA/QC”) of the concrete cover on new bridge decks to determine whether the depth of the rebar meet the proper specifications. Concrete cover measurements are most often obtained during QA of the bridge deck after it has been poured to ensure the top rebar mat is at the depth range specified in the bridge plans. The measurements involve collecting data with a ground-coupled antenna along one or more profile lines to record the arrival time of the rebar reflections. Then, a core is drilled at one of the rebar locations to measure the rebar depth. This is input into the processing software, which calculates the radar wave velocity. This information is then used to obtain the depths of the rebar. This is a straightforward procedure that provides a very accurate measure of rebar depth. The user should select a rebar near the beginning or end of the profile line for the calibration core to ensure that the rebar depth can be matched up with the same rebar that generated the reflection detected in the GPR data. One example of GPR technology used around the country is the BridgeScan™ system, a structured approach to collecting, processing and interpreting GPR data for bridge deck condition assessment, developed by GSSI. The procedure provides a map of rebar reflection amplitudes. As shown in Figure 4, the areas with the lowest rebar reflection amplitudes (yellows and reds) correspond to portions of the bridge deck containing the most distress in terms of concrete deterioration and/or rebar corrosion. ASTM standard D 6087 is used to assess the range of reflection amplitudes that correspond to expected bridge maintenance. Assessment of the maintenance requirements indicated by the GPR data is augmented by visual inspection and other accessory condition information, such as previous maintenance records.

Inspecting the Future Bridge inspection techniques and equipment have come a long way, and the development of improved GPR technology has enhanced inspection results substantially. GPR is gradually becoming a mainstream application in the toolbox of methods used to evaluate bridge conditions.▪

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Professional issues issues affecting the structural engineering profession

orming a Young Members Group (YMG) has altered my professional vision and influenced the lives of many others. In 2010, shortly after attaining my master’s degree, I joined the Structural Engineers Association of Massachusetts (SEAMASS) and have been actively involved ever since. However, I soon noticed that there were hardly any young registered members or event attendees. Observing other young professionals in my network, I noticed that young engineers lacked a cohesive network of resources which we could use to seek answers to entry level questions (which some find difficult to ask at work), and have our opinions and concerns addressed through an established avenue. In 2012, Sofia Zamora and I took the initiative to establish a Young Members Group of SEAMASS, with the goal of supporting young engineers in the Massachusetts structural engineering community, particularly in aiding their transitions from school to professional life. Establishing a new group was quite a challenge, but not nearly as difficult as justifying the importance of the YMG to the local structural engineering community. We found that this initial position was somewhat common among other NCSEA state affiliates. I am sure that there remain some who believe that a YMG cannot contribute as much to the profession as senior members, and it is my goal to change their minds. As the SEAMASS YMG continued to thrive, members of the SEAMASS Board applauded our efforts and achievements, and began to embrace the germination of a reciprocal relationship. Upon receiving proposals from the YMG, SEAMASS has been investing in us, allowing us to explore different group activities, host creative topics that are geared toward young professionals, and build a vibrant community for the future. SEAMASS YMG creates avenues for young members to grow in areas outside of the customary technical presentation setting. We want to further prepare young engineers for their careers in many aspects in addition to technical knowledge. SEAMASS YMG provides hands-on learning experiences, such as touring facility plants and construction sites, training programs and study groups, community outreach opportunities, as well as soft-skills building. Many of the young engineers that come to YMG events to network and learn in a more casual environment ultimately become a part of the team, further benefiting the member organization (MO). Not only does the member organization benefit from the increased number of members and a great contribution of novel ideas from the YMG, but also senior board members of the MO

Rainbows Only Come After Rain The Importance of a Young Members Group By Ellen (Chuan-Hua) Kuo, P.E., LEED AP BD+C

Ellen (Chuan-Hua) Kuo, P.E., LEED AP BD+C, is a structural engineer with Symmes Maini & McKee Associates in Cambridge, Massachusetts. She is Co-Founder of SEAMASS YMG and the Resource Guide Administrator of NCSEA YMG Support Committee. She may be reached at ekuo@smma.com.

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receive new perspectives and creative concepts that inspire them to reevaluate the longstanding status quo and organizational approach. Society is often resistant to change, and some organizations may be hesitant to implement new plans – in this case, a new committee group. In the start-up stage, there are hurdles that must be overcome by both the established senior members and the joining young members. Convincing others to believe in us and to fight this uphill battle can be difficult. That said, we, both senior and junior members, must be resilient and perseverant if we wish to build something truly significant.

A Reciprocal Relationship (Mentorship) I believe that a reciprocal relationship is just one of many advantages created from establishing and maintaining a YMG. In the structural engineering context, reciprocal relationships allow young engineers to apprise senior engineers of the latest industry trends and new methods, while senior engineers continue to foster the professional development of young engineers in the traditional mentorship mold. In order to properly implement reciprocal mentorship, we must first ask ourselves, “How is the industry different today from what it was in the past?” The college curriculum for the LRFD generation varies considerably from the curriculum of the ASD generation 20 years ago, when those who are now the experienced, senior engineers received their educations. Many experienced engineers adopted the rule-of-thumb methods that they learned from their own mentors and practice with formulas from old codes, shortening design times while staying adequately conservative. However, methods that were once commonly used are no longer efficient today, or applicable to modern structural shapes and the constantly changing codes. Reciprocal mentoring would help to bridge the knowledge gap between generations of engineers, allowing both parties to increase their knowledge base. Younger engineers could brief the experienced engineers on the latest design technology options and industry trends, while simultaneously learning to ply their trade from the more experienced minds. This relationship would lead senior engineers to consider more factors (such as unforeseen software constraints and limited resources) when they estimate project budgets and required hours. Consequently, accurate projections would increase the efficiency and competitiveness of their work. In return, young members will receive lessons learned from individual senior engineers and collective structural knowledge within the MO.

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The focus of nurturing a young community, which is oftentimes undervalued or overlooked, is the key to a better future. It is very important for experienced engineers to be aware of the frustration that exists in the industry today – acknowledging the dynamic role of today’s young engineers and the importance of their roles in the structural community. Planting the YMG seed is one solution to sustain the growth of engineers, to increase competency and competitiveness in the industry, to develop leadership and management skills early, and to learn what it takes to create and complete a job. Young members should no longer be thought of as just individuals taking up seats in the structural community; rather, they should be thought of as individuals with extensive, growing networks who exchange information and cultivate one another to be future leaders. At the 2014 NCSEA conference held in New Orleans, the regular attendees must have noticed an obvious change in the NCSEA community. There were 10 times more young professionals attending the conference compared to just two short years ago. In addition, the NCSEA Young Members Group Support Committee was in charge of one of this year's conference sessions, deliberating challenges that the industry is facing, recommending strategies to mitigate them, and working together to solve problems. Great things take time and energy to bring to fruition. With support and guidance from the community, this LRFD generation will soon be capable of assessing, creating, and forecasting new solutions and opportunities for development of a greater community, and to further improve the practice and the standard of this profession. By planting the seeds now to germinate tomorrow’s success, we ask you to help us grow the YMG network, so that those who are following in your footsteps can receive some of the advantages that you can only wish you had. The successful launch of the Young Members Group of SEAMASS was due in large part to the resources and guidance offered by the NCSEA Young Members Group Start-Up (Resource) Guide. The 2014 version of the NCSEA YMG Resource Guide, compiled by Heather Anesta (heather.anesta@stantec.com) and Ellen Kuo (ekuo@smma.com), can be found at www.ncsea.com/resources/documents. We look forward to hearing your feedback and suggestions about the Young Members Group!▪

Restoration of Historic Fire-Damaged Masonry Walls

By Jacob Bice, Ph.D., P.E. and Dilip Choudhuri, P.E.

Figure 1.

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Figure 2.

Figure 3.

ethel Missionary Baptist Church was founded in the nineteenth century by Reverend Jack Yates, an early leader of Houston’s African American community. Located in Freedmen’s Town, a post-Civil War Houston neighborhood founded by freed slaves, the church was the first constructed by former slaves, with the earliest portion constructed in the 1890s. The first two church buildings were destroyed, and in 1923 a third single story church building was erected. In 1950, second and third stories were added. The sanctuary was designed by James M. Thomas, a prominent architect of African American churches. In January 2005, a fire gutted the interior of the historic structure, collapsing the interior framing and roof, leaving only the exterior masonry walls in place. The structure sat exposed and abandoned until 2009, when the City of Houston purchased the property to convert the former church into a community park (Figure 2). The remaining walls consist of two distinct constructions. The 1923 single story is a reinforced concrete frame in-filled with structural clay tile with a brick veneer. These walls were present at the base of the east, west, and south walls. In 1950, when the second and third stories were added, the north wall of the building was re-clad with a concrete masonry unit (CMU) and brick cavity wall system, and the new north façade was increased to a height of 50 feet. The CMU and brick cavity walls were also constructed on top of the existing 1923 walls on the east, west, and south elevations during the 1950 renovation.

Determining Basis for Design The biggest challenge in any restoration project is developing information about unknown conditions. Once the walls were stabilized, a comprehensive visual condition assessment was performed to document the distress conditions for repair and understand the wall construction. Given the fire-damaged state of these walls, understanding the appropriate masonry strength to use in design was fundamental. A combination of flat-jack tests and unit compressive strength tests were utilized to determine the masonry material capacities needed for design. Flat jack testing is a nondestructive technique where masonry compressive and shear strengths are evaluated in-situ. When measuring compressive strengths, the test consists of routing out a horizontal mortar joint to allow a calibrated steel bladder to be inserted into the joint. For shear strength tests, a vertical joint is tested. Linear variable differential transformers (LVDTs) are mounted to wall surface and the bladder then “inflated” hydraulically (Figure 4). The hydraulic pressure and displacements are measured and a stress-strain relationship is developed. The laboratory testing data showed that the historic brick had a compressive strength of 1,600 psi. The modern brick in the building had a compressive strength of 2,000 psi, which is consistent with the minimum compression strength for Grade S-I, S-II bricks, while

Before Restoration, Protection Walter P Moore of Houston, Texas, was initially retained to provide nondestructive testing services to evaluate the conditions of the existing masonry walls and develop strengthening solutions as necessary. However, once an initial site visit was conducted, the first challenge of the project became evident; access into the site to evaluate the masonry walls was nearly impossible due to the collapsed framing and debris that still remained from the 2005 fire, and a large crack in the 50-foot tall brick veneer running from the base of the wall to the top was visible at the northeast corner of the building (Figure 3). The deteriorating façade immediately adjacent to the pedestrian sidewalk posed a potential risk to public safety. Before any assessment could be performed, the engineering team made recommendations to the City to immediately close the street to traffic and temporarily brace the existing walls. Emergency shoring and bracing was designed and installed within a 24-hour period to protect the public and the structure. STRUCTURE magazine

Figure 4.

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Grade N-1 and N-2 bricks commonly used in modern construction have a minimum compressive strength of 3,000 psi. In historic preservations, the designer always has to specify materials that conform to, or are as close as possible to, those used in the original construction. For this project, it was anticipated that repointing deteriorated mortar joints would be necessary, so a mortar analysis was performed. Three mortar samples were excised from the structure and analyzed by acid digestion of the binder and sieve analysis of the aggregate in accordance with ASTM C136. This analysis determined the starting proportions for the mortar specified in the design documents should be 1: 1¼: 5½ (Portland cement : lime : aggregate). In addition, the color and gradation of the mortar aggregate were determined, which allowed the contractor to closely match the original mortar properties and aesthetics (Figure 5).

Wall Strengthening in Plain Sight The engineering assessment program determined that the CMU back-up walls and structural clay tiles were in poor condition as a result of the fire, resulting in a dangerous condition. Significant cracking was evident throughout the back-up wall system, and large portions of the wall were unreinforced, including the 50-foot tall north wall. At several locations, the brick ties that anchor the brick veneer to the back-up wall, installed during the 1950 construction, had corroded and failed. Failure was likely prior to the fire and was due to the age of the building, but resulted in veneer that was separating from the back-up. In keeping with the historic nature of the walls, a strengthening solution had to be designed that would not alter the existing aesthetics and

Figure 5.

would minimize the extent of replacement in the building veneer. To accomplish this objective, the design team proposed a galvanized steel frame that would visually recall the original gabled roof lines of the church, with new metal panels and poly-resin glass panels installed in the existing windows and door openings (Figure 1, page 34). The existing walls would have to be strengthened to span between the girts of the new frame for the loads imposed by the 110-mph hurricane wind speeds required by the building code (IBC 2006 modified with City of Houston amendments). This design requirement alone would be challenging enough for a heavily damaged masonry structure. However, because the walls themselves would be exposed and without interior finishes, strengthening would need to be “hidden in plain sight” to community park patrons while not visibly altering the appearance of the walls. The design team developed a repair solution that consisted of strengthening of the back-up wall and pinning the existing brick veneer to the strengthened back-up. With this strengthening accomplished, a ferrocement finish was

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February 2015

applied that provided additional strengthening and added to a clean appearance for the interior of the park. At the base of the walls in the 1923 construction, a new, reinforced CMU back-up wall was constructed to “sandwich” the existing structural clay tile in-fill; removing this infill could have potentially compromised portions of the wall supported above it. Stainless steel helical anchors were then driven through the existing veneer, the existing structural clay tile, and into the new back-up wall beyond. In the 1950 construction, the existing CMU back-up walls were reinforced by removing the interior shell of the CMU and grouting in new vertical reinforcing bars doweled into the existing grade beams. Large cracks in the existing CMU back-up were reinforced by routing out the horizontal grout and installing stainless steel helical ties across the crack. Once this crack reinforcement was installed, the grout line was re-pointed and the crack itself was then grouted. Cracks through the exterior brick were also treated in this manner, and the brick veneer then pinned using helical anchors back to the strengthened back-up wall. A ferrocement coating was then applied to provide lateral reinforcement to the CMU back-up wall and provide a uniform finish to the interior of the park walls (Figure 6 ). Galvanized welded wire reinforcement was pinned to the interior faces of the walls, and a 2-inch thick shotcrete coating was applied. At window openings and the tops of the walls, the ferrocement coating was extended around the edges of the openings to provide clean and aesthetically pleasing terminations. The ferrocement was given a drag finish for a relatively smooth wall surface that resembled a stucco wall finish. A cream colored elastomeric finish coating was specified by the design team to brighten the interior finish and contrast against the new multicolored fenestrations.

Figure 6.

While this strengthening ensured that the historic walls would stand through the hurricanes that are possible in the Houston area, a number of other details were required to enhance the appearance of the park and preserve key architectural elements of the walls. Cast stone panels installed in the north wall required patches to repair spalls and restore these panels. Existing lintels over door and window openings in the 1923 construction were removed and replaced since corrosion of the original lintels had resulted in rust-jacking and cracking. Once construction began, it became evident that each wall opening varied from the next. Each new fenestration required special detailing to connect to the existing walls. To anchor the new window and door panels, structural clay tile had to be removed between the new CMU

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back-up wall and the existing brick veneer. Helical anchors were then installed between the brick and the CMU back-up, and the cavity filled as a part of the ferrocement construction. This provided a solid substrate into which anchors for the new panels could be installed. Coordination between the City, the design team and the contractor was a fundamental component to successfully delivering this project. Mock-ups of the ferrocement installation, coatings, and window terminations were constructed at key milestones in the project. These mock-ups allowed the design team and the Owner to meet, and review with the Contractor, issues related to aesthetics and constructability before getting approval by the Owner and design team. In addition, routine field observations by the design team throughout construction identified unknown conditions and developed alternate repairs and details as needed. All told, the construction lasted just over one year, with the ribbon cutting for the new park on December 15, 2013. The completed Bethel Park features concrete and brick walkways, installation of an artificial turf interior courtyard, and site amenities including raised fountains, seat walls, benches, lighting, fencing, landscaping and irrigation. A particular highlight of the park is the historic education panels mounted throughout the space.

Conclusion

Figure 7.

Severely damaged by fire, abandoned, but not forgotten by its community and congregation, Bethel Park preserves an important part of Texas and African-American history. Preserving heavily damaged, unreinforced masonry walls, protecting the public safety, and creating a new community space in which the original church walls were integrated were significant challenges for the design team. The unique strengthening techniques made it possible to have exposed masonry walls that contribute to the overall park aesthetic (Figures 7 and 8). The total project cost with property acquisition, bracing, design and park development was $4.7 million. The cost of strengthening the structure was $2.1 million, about half the total construction cost.▪ Jacob Bice, Ph.D., P.E., is a Senior Associate and Senior Project Manager in Walter P Moore Diagnostics Group. Dr. Bice conducts structural health monitoring and nondestructive evaluations such as GPR, impact echo, impulse response, UPV and half-cell corrosion potential on existing structures. Jacob can be reached at jbice@walterpmoore.com. Dilip Choudhuri, P.E., is a President and CEO of Walter P Moore Diagnostics. Dilip can be reached at dchoudhuri@walterpmoore.com.

Project Team Owner: City of Houston – Parks Department, Houston, TX Structural Engineer for Masonry Wall Repairs: Walter P Moore, Houston, TX Structural Engineer for Structural Steel Framing: Henderson + Rogers, Inc., Houston, TX Architect of Record: PGAL, Houston, TX General Contractor: JE Dunn, Houston, TX Masonry Subcontractor: United Restoration & Preservation, Houston, TX Landscape Architect: White Oak Studios, Houston, TX

Figure 8.

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One solution to strengthen such buildings is the Simpson Strong-Tie® Strong Frame ® special moment frame. Its patented Yield-Link™ structural fuses are designed to bear the brunt of lateral forces during an earthquake, isolating damage within the frame and keeping the structural integrity of the beams and columns intact. “The structural fuses connect the beams to the columns. These fuses are designed to stretch and yield when the beam twists against the column, rather than the beam itself, and because of this the beams can be designed without bracing. This allows the Strong Frame to become a part of the wood building and perform in the way it’s supposed to,” said Steve Pryor, S.E., International Director of Building Systems at Simpson Strong-Tie. “It’s also the only commercially-available frame that bolts together and has the type of ductile capacity that can work inside of a wood-frame building.”

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CFS Transforms Octagonal Structure into Elliptical Curve

Figure 1. Pinnacle Bank Arena rendering.

Pinnacle Bank Arena, Lincoln, Nebraska By Jeffrey Kreinke, P.E., S.E., Karl Scherzer, P.E. and Jamie John, E.I.T.

hrough the use of cold formed steel (CFS) framing, the corners of a rigid polygonal concrete structure can be smoothed and transformed into the gentle curve of an ellipse, enlivening the architect’s vision and creating a landmark structure in an up-and-coming neighborhood.

Project Overview Constructed as part of Lincoln’s West Haymarket Redevelopment Project, the new Pinnacle Bank Arena was completed August 2013. The 470,400 square foot multi-use event complex will not only serve as the new host for the University of Nebraska’s men’s and women’s basketball games, but also as a venue for year-round entertainment. Concerts, touring acts, and family productions will utilize the arena’s three public concourses and seating capacity for up to 15,900 guests. The new indoor arena is a seven level concrete structure wrapped in a metal panel and glass curtain wall façade. The inner, octagonal concrete super structure is enclosed by cold formed steel framing, which transforms the outer shape into a tri-radial ellipse. The facility combines “space-frame” panelized walls at the upper collar section with “stick-framed” walls at the lower collar area. Adjacent CFS framing with long span sloping walls were also “stick built” due to size and site constraints. STRUCTURE magazine

Figure 2. Typical CAD wall section showing “Space Frame” at upper collar.

February 2015

Project Challenges/Solutions Various architectural design considerations, structural requirements, and construction obstacles had to be addressed throughout the cold formed steel design process to keep the project on schedule and on budget: • Tri-Radial Elliptical Façade • Panelized Space Frames • Special Construction Loading Requirements • Sloping Wall Studs • Staggered Openings at Bypass Wall Conditions • Connection Requirements • Large Duct Opening within Space Frame Panels The use of cold formed steel space frames was determined to be the best method to accommodate the changing radius of the elliptical façade and to address the sloping exterior at the upper collar. Each frame was modeled and analyzed at its maximum and minimum offset distance (from the building super structure) using RISA 3D. Various load cases and load combinations were applied to the space frames per ASCE 7-05. Special construction loading considerations were necessary for this project due to the volume of cold formed steel framing required, the duration of time to install and enclose the building, and the limited access to the exterior cold formed steel façade throughout construction. During the construction process, the building would only be partially enclosed for a substantial period of time, making it necessary to engineer the space frames to withstand the higher wind loads associated with this type of exposure. Each space frame was designed to support temporary construction platforms located on the horizontal frame members. The platforms were necessary to provide access to the outside of the wall studs until the exterior was completed. The frames were designed to be constructed into wall panels and lifted into place by crane (Figure 4 ). As a result, the space frame panels had to be analyzed with reactions at the crane “pick points,” in addition to the standard reactions at building supports. Another construction complication was the large offsets between the concrete super structure and the outside face of the exterior wall studs. Each space frame panel was 50 feet tall by 12 feet wide with offsets varying in depth from 6 feet to 20 feet. Frames were spaced at 16 inches on center throughout, with of a variety of stud depths and thicknesses depending upon location (Figure 2). The lower building collar has portions of curved, sloping walls that bypass the structure. Within these walls, staggered windows of different lengths and elevations require this section to be stick framed in a more traditional manner, in lieu of panelization. Engineering the framing around each of these window openings is difficult since the windows are positioned in locations that do not allow the jamb studs to run continuous from top to bottom; jambs are often interrupted by another window opening above or below (Figure 3). To accurately engineer the headers, jambs, and sills at these misaligned openings requires intricate load trace calculations. Large concentrated loads on headers and sills from adjacent jamb reactions caused the opening framing to be heavier than typical when compared to openings in a stacked configuration. The building’s super structure was engineered to laterally support the exterior building façade; however, all gravity loads needed to be transferred and relieved at the main concourse level. The cold formed steel space frame construction at the upper collar allows for the transfer of gravity loads through trussed sloping members down to the base connection without gravity loading intermediate levels. For both the space frame panels at the upper collar and the STRUCTURE magazine

Figure 3. Staggered stick-framed openings at the west building elevation.

Figure 4. Installed CFS wall panel.

stick framed walls at the lower collar, the bypass connections to the super structure are made with vertical slide clip connections at all levels above the main concourse (Figure 2). The vertical slide clip (VSC) connections allow each level to deflect independently under gravity loading without any vertical load transfer to the attached framing. The large facility requires systems of an equal scale to meet its high electrical, mechanical and plumbing demands. To avoid possible conflicts with various systems’ piping and ductwork, BIM software was used during the design phase to coordinate CFS framing with the building systems and provide clash detection prior to installation. This extra measure enabled multiple disciplines to work together and provide solutions in the early stages of the project,

February 2015

Figure 5. BIM rendering of Pinnacle Bank Arena upper seating bowl.

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preventing delays during the construction phase. One specific item discovered using BIM was interference between the space frames and a large ventilation duct in the upper seating bowl of the arena (Figure 5). This discovery resulted in the addition of structural steel during the design phase, to allow for CFS space frame attachment around the ducts, avoiding potential costly field modifications during construction. The unique and complex layout of the arena also had an impact on the construction methods used. The space frame wall panels were constructed on a “jig table” during the day, and lifted into place by crane in the evening. A concrete slab was poured on-site to create a jig table large enough to layout four panels at one time (Figure 6 ). Each panel was constructed of ten individual frames, which were tied together with cold rolled channel to create

Figure 6. “Jig Table” used for on-site panel construction.

space frame wall panels. The panels were lifted by a crane via engineered pick points, clipped to the super structure and lapped on to previously installed vertical stud framing. A total of 96 space frame wall panels were required to complete the construction of the structure’s upper collar.

Conclusion The ideal combination of construction materials, along with coordination of multiple disciplines, ensured the Pinnacle Bank Arena was successfully completed on time. The use of innovative design concepts and construction practices were valuable in addressing a challenging building design and keeping the project on schedule. The CFS framing was utilized to accommodate the ever-changing slopes of the exterior metal wall panels and the tri-radial curve of the building’s footprint. Its lightweight characteristic allowed contractors to more easily build and transport large CFS wall assemblies, lending favorably to wall panelization. As demonstrated during construction of the Pinnacle Bank Arena, specialized and complex panel framing can be constructed in a controlled environment, then lifted, and connected to the structure. Benefits of the panelized construction method include increased quality assurance, decreased production time, and overall project safety. Innovative designs often require engineers and contractors to utilize building materials in new ways, reinforcing the

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February 2015

importance of proper material selection. When selecting building construction materials, consideration should be given not only to achieving the desired building aesthetics, but also to project constructability.▪ Jeffrey Kreinke, P.E., S.E., is a project manager and structural engineer at Excel Engineering, Inc. in Fond du Lac, WI. He served as the principal cold formed steel engineer for the Pinnacle Bank Arena. He can be reached at jeff.k@excelengineer.com. Karl Scherzer, P.E., is a principal and structural engineer at Excel Engineering, Inc. in Fond du Lac, WI. He can be reached at karl.s@excelengineer.com. Jamie John, E.I.T., is a senior technician at Excel Engineering, Inc. in Fond du Lac, WI. She can be reached at jamie.j@excelengineer.com.

Project Team: Owner: PC Sports Structural Engineer of Record: Buro Happold Consulting Engineers PC Architect of Record: DLR Group Construction Manager: Mortenson Construction Specialty Structural EOR for CFS Framing: Excel Engineering, Inc. Wall Panel Fabricator/CFS Framing Contractor: Falewitch Construction Services, Inc.

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Structural rehabilitation renovation and restoration of existing structures

his series of articles discusses some of the commonly encountered structural issues during the renovation and restoration of historic buildings of this type, and provides guidance on ways to address them. Parts one and two of this series focused on foundation and wall systems, respectively. This part focuses on roof structures.

General Description of Typical Timber Roof Systems One of the most common types of structural roof systems found in historic houses of worship in the United States is the heavy timber truss, which has been used to frame and support the roofs of these structures for centuries. Over time, many different truss geometries and configurations have evolved and were successfully used: king post, queen post, scissor trusses, hammer beam, as well as a number of various combinations involving trusses and other heavy timber frames. While the trusses are typically the main structural support for the roof, the remainder of the roof system is typically constructed of wood decking supported by a system of wood rafters and purlins that span between or parallel to the trusses. Heavy timber roof trusses typically bear directly on the exterior masonry walls, and will either span clear from wall to wall, or rely on interior columns to provide intermediate support.

Divine Design: Renovating and Preserving Historic Houses of Worship Part 3: Roof Structures By Nathaniel B. Smith, P.E. and Milan Vatovec, P.E., Ph.D.

Joints and Connections Nathaniel B. Smith, P.E., is a Senior Project Manager at Simpson Gumpertz & Heger’s office in New York City. He can be reached at nbsmith@sgh.com. Dr. Milan Vatovec is a Senior Principal at Simpson Gumpertz & Heger Inc. He can be reached at mvatovec@sgh.com.

The type and configuration of connections found in timber structures are numerous and can vary significantly depending on the age of the structure. In older structures, they may include mortise and tenon joints, shear keys, bolted connections (with or without external steel hardware), or a number or other combinations of the above. Newer timber trusses, post World War I, may also feature shear plate or split-ring connectors. Regardless of their type, due to lack of redundancy and ductility, or their often concealed nature and susceptibility to deterioration and/or distress, truss connections are usually the structural weak link in timber-framed roof systems. Several typical issues encountered in practice are described below. Timbers were typically green (moisture content greater than 19%) when originally installed. As they dried in service, the associated shrinkage may have caused the joints to loosen or open with time. Typical truss maintenance should therefore include inspection and occasional tightening of the bolted connections, aimed at maintaining their serviceability and effectiveness.

44 February 2015

Heavy timber roof framing.

Unfortunately, this level of inspection and maintenance is commonly overlooked, or not continuously performed, and may ultimately lead to ineffective load transfer through the connections, excessive truss deflections, or redistribution of loads to other members causing overstresses. As heavy timbers dry and shrink, checks and other drying defects may also form. Checks are commonly mistaken for structural cracks, and are automatically assumed to be detrimental to the timbers. Checking is a normal part of the drying process, and, unless severe, it may not drastically affect the capacity of the timber elements. In fact, modern design practices account for the presence of checks, and design reduction factors have been established to account for this phenomenon. Nonetheless, checks and splits, especially when they extend through the entire cross-section of the member, will affect member’s flexural capacity and should be evaluated on a case by case basis. If a significant reduction in member capacity is suspected, various reinforcement options are available to restore the needed capacity (installation of straps, dowels, sister members, plates, etc.). More critical, however, is the potential presence of checks or splits near member ends, where connections are expected to transfer internal forces through the structure. Many localized joint failures and slippages, and sometimes roof-structure collapses, initiate at the checks or splits, where the dowel-bearing strength of the bolts can be significantly compromised (especially if the joint configuration features insufficient bolt end distance). Gusset plates, external tie rods, or other joint-reinforcement details are available as joint strengthening options. In some cases, slipped (open) joints need to be closed (tightened) and the resulting excessive truss deflection “removed” prior to installing the permanent strengthening detail. This can be accomplished

by pulling the members back together using a system of come-a-longs, pulleys, or by shoring and jacking the truss upward. However, great care needs to be taken during this process to prevent damage to the timbers or to other portions of the structure. This work should only be performed by an experienced contractor working with an engineer knowledgeable in heavy-timber truss behavior. Closing a single joint on a truss may require manipulating the adjacent trusses, and a good understanding of the load paths and the expected behavior of the structure is paramount. Careful monitoring of movements needs to be performed to verify that the structure is behaving as intended. In general, special expertise and knowledge of wood behavior is needed to differentiate between normal checking and severe cracking that could pose a serious structural concern. Consulting with a wood-science expert can help to determine what, if any, repair or strengthening work may be needed. Proper assessment of the issue at hand may significantly reduce the amount of needed remedial work.

Fungal Deterioration

Opening of joint due to shrinkage.

and probing inspections alone are often not enough to fully assess the remaining strength of the member, appropriate experience with timber structures and associated ability to holistically and realistically assess the effects of decay is often key in such situations. After safety is assessed and addressed, the next step should be to determine the source of moisture and if it is still active. Repairing deteriorated timber (the symptom) without addressing the moisture source (the underlying cause) will not be effective; further deterioration after repairs are made can be expected. Only once the moisture issue is addressed and further exposure eliminated (through appropriate waterproofing detailing or treatment), remedial or strengthening solutions (discussed in subsequent sections) will be effective. continued on next page

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Moisture is probably the single most detrimental factor affecting wood structural members. Moisture-related deterioration of wood typically begins to occur when the moisture content of the wood exceeds 20%. This level of moisture, which provides sufficient resources for woodattacking fungal hyphae (rot) to stay active and cause wood-cell material destruction, can be achieved by leakage, or by repeated wetting and drying in service. As discussed in Part 2 of this series, ends of timber elements (e.g. roof trusses) bearing in pockets in masonry walls are typically the most vulnerable to the effects of moisture absorbed by the masonry. To compound the issue, bearing ends of the roof-structure timbers are typically in the vicinity of the roof gutters; any associated leakage or masonry saturation could further contribute to deterioration of the roof-structure timbers. Wood is generally a very ductile material that behaves well under loading; however, decay significantly affects the cell structure of the wood, which causes a loss in strength and ductility. Significant deterioration can cause timbers to fail suddenly, in a brittle manner, without undergoing large displacements or giving early warning before the ensuing collapse. Also, because of the lack of redundancy in timber trusses and roof framing, failure of even one member can have catastrophic

consequences, including partial or full collapse of the roof structure. Periodic inspections of roof framing need to be performed to locate and address areas of potential deterioration before they become a significant hazard. Wood-educated inspectors should have the ability to recognize tell-tale signs associated with fungal decay and insect attack, although it is less common in roof structures. This is especially important in situations where the most vulnerable portions of timber members are concealed (e.g. by masonry), and where the exposed portion of the member does not exhibit any apparent or visual signs of deterioration. However, if the concealed member end is wet, chances are that the decay process is on-going, and even the apparently healthy-looking exposed wood may already have lost a portion of its strength due to decay. Often inspections must rely on considering secondary effects of deterioration (e.g. staining of masonry), minute characteristics of timber grain appearance, or even sampling and subsequent microscopic laboratory investigation. If deterioration is found, some level of repair or strengthening is typically required. Shoring may be required as well if deterioration or its effects are deemed to significantly affect members’ abilities to support loads. Because visual

Fungal deterioration at truss bearing.

Truss reinforcement.

Renovation Effects Renovations of these types of structures often include a decision to insulate the ceiling above the worship space to help reduce costs associated with heating and cooling. While adding insulation may help the energy efficiency of the building (if installed properly), it may also result in unintended consequences on the performance of the roof structure. The majority of historic houses of worship were not constructed with a significant heating or cooling source. Often, the only heat source may have been a single wood or coalfired stove. In northern climates, any heat generated within the building would eventually escape through the ceiling and roof, and help melt any snow accumulation on the roof; intended or not, this can help keep the roof snow loads fairly minimal. The addition of insulation, however, effectively traps the heat within the worship space and prevents it from reaching the roof; the exterior roof surface remains cold, potentially allowing snow build-up and increasing the snow load. If not anticipated and addressed, the increase in snow load can cause overstressing of timber members and connections, unanticipated deflections, or in some cases even partial or full collapse of the roof structure. If adding insulation to the ceiling of a house of worship is being considered, consult with a structural engineer experienced with timber framing and an engineer experienced in building science to develop appropriate details. Renovations may also include changing the roofing type (e.g. from asphalt shingles to slate tiles). The slate tiles and any associated waterproofing will significantly increase the load on the roof structure, which then needs to be carefully evaluated to determine if any roof members or connections need to be reinforced. Similarly, different roofing materials may provide for different resistance against snow sliding

(and can result in unintended snow accumulation), also requiring consideration.

Strengthening In some cases, strengthening of the truss members may be necessary due to alterations (addition of insulation, HVAC equipment, change of roofing type, etc.), or to address existing distress or deterioration of the timbers. Strengthening can often be accomplished by reinforcing the existing members with additional wood framing, steel plates, or channels. The reinforcing is commonly attached to the existing timbers using through bolts or lag screws. To arrive at an effective strengthening solution, compatibility of displacements, load sharing, or any geometric or other constraints introduced to the existing structure need to be carefully examined. Also, if temporary removal of truss elements is needed, shoring, load transfer sequencing, and temporary lateral bracing of often tall and slender masonry walls need to be considered. Finally, if any change in the overall truss behavior is introduced (e.g. when tie rods are added to prevent further spreading of scissor trusses), all members and their connections along the load path should be examined to determine if they are adequate to resist the new loads (in some cases compression members become tensile members, etc.). Since the dead loads from the roof are already being supported by the existing truss framing, the reinforcing is typically designed to only support the live loads (snow, wind, seismic) and any new dead loads (HVAC equipment, catwalks, lighting, etc.). If the existing structural dead loads need to also be carried by the reinforcing (e.g. due to the amount of overstress or due to deterioration), the existing dead loads will need to be taken out of the system by a combination of jacking, temporary shoring, and other methods.

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February 2015

Relieving timber trusses of the existing dead loads is a significant undertaking. Shoring and lifting of roof trusses from below can be quite intensive and in some cases even cost prohibitive due to large ceiling heights (40 feet or more) and potentially large reaction loads associated with truss lifting. Shoring systems will need to be designed by an experienced professional to verify that the shoring can support the intended loads, and will remain stable. The actual jacking of the loads out of the trusses (and into the new, supplemental members such as tie-rods) can be very involved, and may result in unwanted damages if not carefully performed and monitored. Similar to closing slipped truss joints, an experienced engineer and contractor are needed to perform this work to determine the appropriate jacking loads, jack locations, and to monitor the trusses for movement to help to avoid unwanted damages.

Closure Trusses and other timber frames have been successfully used to support roof systems in houses of worship for centuries, and, with proper maintenance and repairs, they should continue to serve as reliable and effective roof framing systems for years to come. Proper understanding of the material behavior, structural characteristics, and system limitations is needed to enable designers and builders to develop effective remedial or strengthening solutions in historic restoration or renovation projects. While ultimately aimed at addressing the changing needs of the congregation, careful consideration and good implementation of available restoration options can also extend the remaining useful service life of these important buildings. Future articles will include review of material and structural performance of architectural components in houses of worship (e.g. wood floors, trim, plaster ceilings, roofing, finishes, etc.).▪

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Historic structures significant structures of the past

he Bollman Truss was the first widely adopted cast and wrought iron railroad bridge in the United States. It was designed and patented by Wendel Bollman (STRUCTURE, February 2006) on January 6, 1852 after he built several on the B&O Railroad. Richard Osborne built an earlier iron bridge in 1845 on the Reading Railroad at Manayunk, a portion of which is now on display at the Smithsonian Institution in Washington. It consisted of three cast iron trusses with wrought iron verticals. James Milholland also built a 50-foot long wrought iron riveted girder bridge for the Baltimore & Susquehanna Railroad at Bolton Station in Baltimore in 1846. As Bollman’s patent application drawing shows, it could be built either as deck or a through truss. As in the Whipple Bridge (STRUCTURE, December 2014), all compression members were of cast iron and all tension members of wrought iron. He called his top compression chord a “stretcher” that could be built of iron or wood. If of iron, he recommended hollow tubes. His cast iron verticals, struts, which had different shapes for the deck or through versions, had a “shoe” at the bottom under which an eyebolt projected to pick up diagonal wrought iron bars that ran from the bottom of the strut up to each end of the stretcher. In addition, he had cross bracing in each panel to retain the geometry of his truss. He wrote in his patent application,

Bollman Truss at Harper’s Ferry By Frank Griggs, Jr., Dist. M. ASCE, D. Eng., P.E., P.L.S.

Dr. Griggs specializes in the restoration of historic bridges, having restored many 19th 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 fgriggs@nycap.rr.com.

“This bridge has the advantage of great strength and perfect security, with very little weight of metal; all the forces can be calculated with absolute certainty, and without

Bollman Patent No. 8,624.

48 February 2015

complicating the problem; and the structure is so simple, that all the wrought iron work can be executed by the commonest blacksmith. The bridge has been thoroughly tested, and fully proves the correctness of the principles upon which it is based.” In other words, it was just the opposite of Whipple’s truss that used a lower chord tension member to keep the thrust of the arches from spreading the ends, in that he used top chord compression member to keep the tension ties from pulling the end of the truss inwards. Knowing Whipple’s method of determining the force in each member, he could size them efficiently. Whipple, however, in his book, determined that the most efficient angle for any tie in a truss was 45°; Bollman, especially in long trusses, had some very flat angles on his ties, thus reducing their efficiency. Bollman began his bridge building career as a carpenter on the B&O Railroad in 1837, working on Benjamin Latrobe’s and Lewis Wernwag’s Harper’s Ferry Bridge (STRUCTURE, August 2014). By 1840, Bollman was named by Latrobe to be “Master of Road” that placed him in charge of all bridges on the line. Some time late in the 1840s, Wendell looked into the design of an iron bridge. Trussed beams had been utilized for years but usually consisted of one beam, one vertical post and a wrought iron bar dropping from the ends of the beam down under the post. This system created a simple truss. Bollman extended this system by adding several posts to a top stretcher with asymmetric rods supporting the posts. Robert Vogel, in his fine paper on Bollman, wrote, “he was perhaps the most successful of the latter class [self taught]... He may be said to be a true representative of the transitional period between intuitive and

The wrought-iron requires little workmanship, the rods from the centre to abutments having but an eye at one and a screw at the other end, with a weld or two between according to length. The long counter-rods have two knuckles and one swivel for adjustment of strain and convenience in welding, as well as in raising the whole. The cast-iron stretcher is octagonal without, circular within, and averages one inch of metal. It is cast in lengths according to the length of panel, and

jointed in the simplest manner; at one end of each length is a tenon, at the other a socket. The latter is bored out, and the tenon and its shoulder turned off in a lathe to fit the socket; thus, when thoroughly joined, to form one continuous pipe between abutments. The ends of the sections of cylinders, inserted to those contiguous, are slightly rounded, to allow a small angular movement without risk of joint fracture… continued on next page

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exact engineering Actually, his designing was a composite of the two methods. While making consistent use of mathematical analysis, he was at the same time more or less dependent upon empirical methods. For years, B&O employees told stories of his [Bollman’s] sessions in the tin shop of the railroad’s main repair facility at Mount Clair in Baltimore, where he built models of bridges from scraps of metal and then tested them to destruction to locate weaknesses. It seems most likely, however, that the empirical studies were used solely as checks against the mathematical.” Bollman built his first bridge, The Little Patuxent Bridge, near Laurel, Maryland in 1850 and replaced the Winchester & Potomac 124-foot span of the Harper’s Ferry Bridge in 1851. In 1852, he built his third bridge at Bladensburg, Maryland over the Anacostia River. Many others followed in the 1850s and 1860s, but this article will primarily discuss the Harper’s Ferry Bridge across the Potomac River. The B&O Railroad and the Winchester & Potomac Railroad built their covered wooden bridge directly across the Potomac River in 1837. Several years later, the B&O built a “Wye” span to continue its line to the west. In 1850, they decided to upgrade the westerly span, sometimes called the Washington Branch, and chose to utilize the Bollman design, as the Little Patuxent Bridge had proved satisfactory. It was a through span to match the existing wooden spans. They built three masonry towers, rather than cast iron towers, on the end pier and the westerly abutment to support the span. Bollman wrote a pamphlet on this span entitled, Iron suspension and trussed bridge as constructed for the Baltimore and Ohio Rail Road Co. at Harper’s Ferry, and on the Washington branch of this road. That was published by John Murphy and Company in Baltimore and dated 1852. Bridge engineers used pamphlets in those days as a means of advertising their designs and showing their cost effectiveness. In his pamphlet Bollman wrote, “This bridge was erected in 1852, from the designs of Wendel Bollman, C.E., Inspector of Repairs, Baltimore and Ohio Railway. The span is 124 feet between abutments. The length of castiron in stretcher, 128 feet. The weight of cast-iron in the R. R. truss, 65,137 lb.; of wrought-iron, 33,627 lb.; making a total weight of cast and wrought iron, 98,664 lb.

Harper’s Ferry Bridge post 1868 from Maryland side, C&O Canal in foreground. Courtesy of HAER.

This system, perfect in itself, is additionally connected by diagonal rods in each panel; also by light hollow castings, acting as struts. The diagonal side rods might be safely dispensed with, for the peculiar merit of the truss is its perfect independence of such provision. They are therefore used as a safeguard only in case of the fracture of any of the principal suspension rods. By this combination of cast and wrought iron, the former is in a state of compression, the latter in that of tension, – the proper condition of the two metals. It unites the principles of the suspension and of the truss bridges. Each bar performs its own part in supporting the load in proportion to its distance from the abutment; so that the entire series of suspending rods transmits the same tension to the points of support as would be equally transmitted from thence to the centre of bridge…” And after presenting his method of analysis he concluded, “This bridge, it will be seen, is composed of seven independent trusses, which transfer the weight concentrated on each floor beam directly to the abutments, without aid from any other connection; and not from panel to panel, as in general use… In case of fire, the floor may be entirely consumed without any injury to the side truss… In an experiment undertaken to prove the rigidity of this structure, three first-class tonnage engines, with three tenders, were first carefully weighed, and then run upon the bridge, at the same time nearly covering its whole length, and weighing in the aggregate 273,5501b. or 136 1850/2000 tons nett, being over a ton for each foot in length of the bridge. From this test it was found, according to gauges properly set and reliable in their

Bollman Bridge, Savage, Maryland. Courtesy of HAER.

action, that the load did not cover the entire length of bridge by about 13 feet, yet the excess of weight in the middle, and at a speed of about eight miles per hour, produced no greater deflection than 13/8 inch at the centre post, and 9/16 inch at the first post from abutment.” Squire Whipple didn’t like it, writing in the American Railroad Journal that it was, “a sort of mongrel bridge, something between a Suspension Bridge and a truss bridge and partaking in a measure of the character and qualities of both...” He had discussed a similar idea in his 1847 book but concluded, “it was fully and conclusively demonstrated, that the main principle and idea involved was utterly worthless, as it regarded Truss bridges. Not meaning that a safe and useful bridge cannot be made in this way; but that it can only be done at a much greater expense than is required to make an equally safe and useful bridge, on other plans and principles.” It was, he wrote, “A mere fossil of one of Whipple’s discarded principles.” Herman Haupt, however, who headed a committee to report on the bridge, wrote, “the bridge constructed by Wendel Bollman possesses every essential requisite of an efficient structure, and that no arrangement of parts in general use can be considered superior to it, or promising more satisfactory results.” The bridge remained with a single iron span and 7 wooden spans until June 14, 1861. when General Joseph Johnston blew up and burned the wooden spans as he evacuated Harper’s Ferry early in the civil war. The only thing remaining was the Bollman Truss and the piers. The military then built a pontoon bridge for their use and the B&O built a wooden trestle for their purpose. In July and August 1862, the B&O replaced some of the trestlework with two Bollman spans. Shortly after, the reb’s burned the bridge again when retreating from the battle of Antietam on September 18, 1861. The B&O then built three Bollman spans in September and November 1862. On July 20, 1863, the

STRUCTURE magazine

February 2015

Bollman Truss, cast iron columns and top chord, wrought iron diagonals. Courtesy of HAER.

Yankees burned the bridge when Lee was invading the north on the way to Gettysburg. The bridge was rebuilt and in July 1864 General Jubal Early burned it after his failed invasion of the north that was stopped outside of Washington after a battle at the Monacacy River. After the War in 1868, the bridge was entirely rebuilt with Bollman iron trusses. The Winchester Span was documented by the National Park Service’s Historic American Engineering Record (HAER) (WVA, 19, HAER, 28) based upon iron retrieved from the river after the 1936 flood that washed away the entire bridge, and early drawings by Bollman. Bollman trusses were used on many B&O bridges, as well as approach spans in two major Mississippi River crossings at Quincy, Illinois and Bellaire, Ohio and at Clinton, Iowa as a swing bridge. The only surviving Bollman Bridge is at Savage Station in Maryland across the Little Patuxent River. It was originally built in 1869 for the B&O and moved to its existing site in 1887 and is used only for pedestrians. It was documented by HAER in 1985. Bollman’s plan was widely used as a cast and wrought iron railroad bridge between 1850 and 1870, especially on the B&O Railroad, but was generally replaced starting in the late 1870s by Fink and Whipple Iron Double Intersection Trusses that made a more efficient use of the iron.▪

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Integral Crystalline Waterproofing The Future of Concrete Durability By Alireza Biparva, M.A.Sc., LEED Associate

n a building landscape where the expected lifespan of a structure is longer than usual, the durability of the materials that encompass the structure become more critical. Sustainability is key for any structures viability in today’s construction world, which means new technologies are of great value to not only the project teams, but also the environment. Concrete is currently the most used humanmade material in the world, used twice as much as all other materials combined. Concrete is used so much because it has a relative low cost, is versatile, has unique engineering properties and its ingredients are widely available. This often makes concrete more attractive to the construction industry than other materials like steel or wood. Moreover, a key advantage to concrete is that it can be molded or formed into virtually any shape when freshly mixed and, when hardened, becomes a strong and durable material capable of a long lifespan. In most instances, deterioration of concrete is due to a lack of adequate durability, rather than deficient strength. Concrete structures can become unserviceable due to gradual weakening arising from concrete deterioration and steel corrosion. Reducing concrete deterioration by increasing its durability has become a challenging problem facing the industry. In most every case of concrete degradation, the root cause of the issue is the presence of moisture or water within the concrete. The ingress of deleterious substances into concrete takes place through the pore system in the concrete matrix, or through microcracks. In order to effectively ensure a concrete structure’s durability, which leads to a longer lifespan and a more sustainable building, the concrete must first be effectively waterproofed.

Surface Applied Membranes As is the case in business, there are often several options to choose from; concrete waterproofing is no different. One of the options available on the market is an external surface-applied membrane. The membrane is installed after concrete has hardened to prevent the ingress of water into basements, foundations, walls, and roofs. However,

surface applied waterproofing membranes do have limitations: • are at risk to puncture damage; • application takes time and is labor intensive; • lifespan of the membrane is usually less than desired structure life; and • is difficult to repair since it can be inaccessible and hard to locate the failed area. External membrane failure can occur in a number of different situations, most as a result of design errors, installation mistakes, or material limitations and defects. This is why simplifying the process by making the concrete itself serve as the waterproofing barrier can prove valuable for a project.

Integral Crystalline Waterproofing Integral Crystalline Waterproofing (ICW) prevents the movement of water through the concrete by plugging or blocking the natural pores, capillaries and micro cracks, thereby making concrete its own waterproofing barrier. This stands in contrast to more conventional means of waterproofing, which usually involves applying a coating or membrane to the concrete surface. The process is sometimes also attempted through densification of the concrete. The ICW method of concrete waterproofing has been proven effective through successful use in virtually every country in the world.

The Science ICW technology is based on principles that are very similar to the processes that occur during concrete hydration. When ICW products are added or applied to concrete, crystalline chemicals facilitate a reaction that causes long, narrow crystals to form, filling the pores, capillaries and hairline cracks of the concrete mass. As long as moisture remains present, crystals continue to grow throughout the concrete. Once the concrete has dried, the crystalline chemicals sit dormant until another dose of water (such as through a new crack) causes the chemical reaction known as crystallization to begin again.

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February 2015

When reacting with water and cement, an ICW creates millions of needle-like crystals that block the ingress of water. Courtesy of Kryton International Inc.

The ability to reactivate in the presence of water gives crystalline-treated concrete the ability to improve self-sealing. When cracks form due to drying shrinkage, settling, seismic activity, etc., water entering through them causes new crystals to form and grow, blocking and filling the cracks. Improving the self-sealing ability of concrete is one of crystalline technology’s most unique and useful features, and can help to dramatically reduce the long-term maintenance and repair costs of a concrete structure.

Main Benefits of ICW ICW contributes many beneficial properties to a given project, including: • Continual Protection – One of the unique traits of an ICW admixture is its ability to improve the self-sealing ability of concrete. Due to the potency of the crystalline chemicals, only a small portion is required to facilitate a large amount of crystal growth. The chemicals lay dormant so when future cracks occur, triggering new crystal growth that seals the crack; • Easy To Apply – ICW comes in a powder form and is conveniently and easily added to new concrete at the time of batching, either in a ready-mix truck or at the plant. The chemicals create a powerful water barrier, which leaves no need for any surface applied product at the jobsite; • Sustainable & Reliable – ICW is a permanent solution to concrete waterproofing needs. It is impervious to physical damage or deterioration, and can reduce shrinkage cracking. It’s non-toxic, safe for use in portable water and contains no volatile organic compounds (VOCs); and

Concrete pores with ICW. Using an ICW improves the matrix of a concrete mix, blocking the flow of moisture. Courtesy of the University of Seoul.

• Saves time & Money – The use of an ICW admixture can accelerate a project’s schedule by eliminating the need for a traditional surface applied membrane. Backfilling can begin right after concrete has set, lowering the cost of labor and materials. ICW can also be used with structural shotcrete.

Where Can ICW Be Used ICW systems have been used in a wide variety of concrete structures across the world. The most common applications include: • Below-grade foundations, parking garages, elevator pits, basements; • Bridges & dams; • Tunnels & pipelines; • Water containment & Aquatic facilities; and • Marine Structures. ICW has proven to be most effective in areas exposed to high-hydrostatic pressure, such as is found in below-grade foundations and water containment tanks.

What ICW to use?

These products are suitable for damproofing or above grade water repellency, but not suitable for below grade waterproofing applications. An ideal concrete waterproofing system should: • Reduce the permeability; • Reduce the chance of cracking; and • Improve Self-Sealing ability. Furthermore, the concrete waterproofing industry redefined their terminology a short time ago. In fact, American Concrete Institute’s (ACI) 212.3R-10 Report on Chemical Admixture document devoted Chapter 15 to Permeability Reducing Admixtures that outlines PRAH and PRAN classifications. Permeability Reducing Admixture – Hydrostatic Conditions or PRAH products are sufficiently able to resist water under hydrostatic pressure penetration and are suitable for watertight construction. Conversely, damproofing admixtures are now referred to as Permeability Reducing Admixture – Non-Hydrostatic Conditions or PRAN. PRAN admixtures reduce water absorption by repellent chemicals (soap, oils) or partial pore blocking (densifiers). These admixtures are not suitable for concrete exposed to water under pressure and cannot protect in the presence of hydrostatic pressure. Waterproofing against hydrostatic pressure is an important distinction that sets PRAHs apart from PRANs. Also, select a crystalline waterproofing supplier who can demonstrate a repeated history of long term success. The manufacturer should offer a long term warranty and have the company history to back it. The manufacturer should be able to provide accredited third party test results and have achieved industry recognized certifications for product quality and performance. Most importantly, because of the ongoing value of close technical support, be sure to select a product from a manufacturer who has demonstrated the willingness and ability to

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February 2015

provide on-site service and support for major projects anywhere in the world.

Conclusion Integral Crystalline Waterproofing is the future of concrete waterproofing worldwide. With sustainable building practices increasing in importance, and the lifespan of a structure intrinsically connected to this movement, a reliable waterproofing solution that will last for the intended life of the concrete structures becomes very important.▪ Alireza Biparva, M.A.Sc., LEED Associate, is research and development manager/concrete specialist at Kryton International Inc. Alireza oversees several research projects focusing primarily on concrete permeability studies and the development of innovative products and testing methods for the concrete waterproofing and construction industries. He can be reached at alireza@kryton.com. The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

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A number of companies offer integral waterproofing products for new and existing concrete structures. These products have different chemistries and, more importantly, different levels of performance. When selecting Integral Crystalline Waterproofing products, it is important not to confuse them with: • Hydrophobic or water repellent products; such as, water repellent soaps, fatty acids (stearates), mineral oils etc.; • Finely divided solids known as densifiers intended to “take up space” and densify the concrete; and • Products based on silicates, clays, bentonite, silica or polymers; these offer temporary waterproofing at best.

Concrete pores without ICW. Courtesy of the University of Seoul.

Are you taking the SE exam in April 2015?

Make sure you have the latest design standards before exam day. The latest design standards are used to develop and score the SE exam. Download the list, which is effective beginning with the April 2015 exam, at ncees.org/SE_exam. Study for the SE exam using the NCEES Structural Practice Exam, available at ncees.org/PracticeExams. It’s the only practice exam that’s created by the same experts who develop the actual exam.

core requirements and lifelong learning for structural engineers

Education issuEs

Leading the Charge By Uchenna T. E. Okoye, P.E., LEED AP and Eric Borchers, S.E.

o you remember what inspired you to become a structural engineer? Did you love building blocks and toy construction sets when you were little? Maybe you had a relative who was an engineer or an architect. Maybe you loved problem solving, or you just wanted to build big things. However you managed to get involved with this profession of ours, we remain a relatively small and unique selection of the general population. Our profession is typically not very well known or en vogue, but it has a strong impact on the lives of countless people. It is up to each of us to grow our profession by helping to mold the next generation of engineers and leaders within the industry. Without a strong corps of professionals volunteering to teach the next generation, it is possible that we may inadvertently stifle innovation, suppress fees, and by extension, wages, and reduce the talent pool due to attrition and lack of leadership. Volunteering in schools is a great way to have a positive impact on students’ lives and improve the long-term well-being of our profession. Many engineers are already part of outreach programs that seek to introduce students to structural engineering in fun and meaningful ways. You too can make a difference in as little as a single classroom session by using the High School Outreach Program provided by the National Council of Structural Engineering Associations (NCSEA). Engineers Alliance for the Arts (EAA) and the Architecture Construction Engineering (ACE) Mentor Program feature the opportunity for students to learn about the engineering and design process over a longer in-depth program. All of these programs serve as catalysts for us to get involved in raising the next generation of engineers at varying levels of personal commitment.

High School Outreach Program One way to get involved in helping to ensure the longevity of structural engineering, and to give back to the community, is to participate in a High School Outreach Program within your local NCSEA member organization (MO). This program is a simple, fun way for design professionals to engage with students and teachers and, in the process, demystify structural engineering

EAA finalists display their bridges prior to lead testing. Courtesy of EAA.

and the architecture, engineering, construction (AEC) industry in general. The High School Outreach program is defined by a 1 to 1½ hour workshop put on by design professionals in local schools during the school day. The workshop is generally composed of two parts. The first part is a short but comprehensive presentation on structural engineering and the AEC industry. The presentation may be customized to emphasize engineering challenges typical to the area, e.g. earthquakes in California, large snow drifts in Montana, or hurricanes in Florida. The second part is a hands-on activity used to strengthen the students’ understanding of some of the structural engineering principles detailed in the presentation. This is usually the fun part. Example activities include gum-drop and toothpick towers, and chocolate chip pudding concrete. The High School Outreach Program is perfectly suited to be created and sustained by a volunteering committee within your MO. However, the program excels when a champion is found to actively recruit schools with willing teachers, and to organize the volunteers. Young Members Groups in several states have taken on the task of implementing this program with great success, and many MO’s have adapted the same basic program for both high school students and middle school students. The recent article in the August 2014 issue of STRUCTURE by Barnes and Dos Santos describes one adaptation for the middle school level.

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February 2015

The High School Outreach program represents a relatively short-term program that can reach multitudes of students and communities with the strength of its volunteer core. Start one of your own, or contact your local MO about getting involved. NCSEA has even created a guide available on the resources page of their website. The High School Outreach Start-Up Guide includes a sample presentation and a step-by-step rubric for building a base of schools interested in the program. This guide is available for download at www.ncsea.com/resources/documents/.

Engineers Alliance for the Arts Another extraordinary way to engage younger members of the community is through the Engineers Alliance for the Arts (EAA) organization. EAA was founded in 2000 by several San Francisco Bay Area structural engineers to introduce engineering concepts specifically to visual and performing arts students. This organization seeks to bridge the gap between art-and-architecture and structural engineering, thereby aiding in the development of well–rounded, unique minds capable of understanding the world through both an engineering and artistic framework. The flagship program within the organization is called the Student Impact Project, in which volunteer engineers teach in a classroom once per week for ten weeks. Volunteers are equipped with a curriculum that has been developed by the EAA

Boston area students race against the clock to build the tallest tower during a High School Outreach program workshop.

curriculum committee and is approved by several school districts in California. The curriculum begins with general engineering concepts, but students quickly dive deeper into specific structural systems as they build and test prototype girder, arch, and suspension bridges. Along the way, students also learn about efficiency, scale, sustainability, and presentation skills. The program culminates with a final project – a physical scale model bridge and presentation that represents each student team’s entry into a realistic design competition based on a specific scenario. A final competition is held in which students must present their bridge to a group of design professions and sell their idea as the best. Projects are judged based on several factors including structural efficiency, aesthetics, and student presentation. The program is held in such high regard that there is a long wait list for teachers at multiple schools around the San Francisco Bay Area. EAA has recently expanded to other U.S. cities due to overwhelming demand for programs like this from schools, teachers, students, and structural engineering professionals alike. As a 10-week program, volunteers make strong connections with the students, but without the commitment of a full school year. It does take a few hours out of your workday, but working with students in local schools and teaching them the fundamentals of engineering is a rewarding experience. Finally, by volunteering for this program you get to ensure the future of our profession while also meeting other design professionals from your area. Please do not hesitate to start or participate in an EAA program near you. Visit EAA’s website, www.eaabayarea.org, for an overview of the organization and contact EAA Executive Director Kelly Bitzer at eaa@eaabayarea.org for opportunities to participate in your region.

Science and craft combine as an EAA bridge begins to take form. Courtesy of EAA.

ACE Mentor Program The ACE Mentor Program was founded by Charles Thornton in 1994 in New York City, and it has grown into a national program that every year mentors over 8,000 high school students who are interested in Architecture, Construction and Engineering. ACE Teams consist of 20-25 students and industry mentors that represent the project owner (client), the design disciplines (architecture, civil, structural, mechanical, electrical, and plumbing), and construction managers. Over the course of a school year, ACE teams develop a design project that covers all disciplines, and most teams construct a model of their design project. At the end of the season, each team gives a presentation explaining their design to other teams, family members, teachers, prospective mentors, and ACE Board Members and company principals. The ACE Mentor Program has active Affiliates in most states that each comprise multiple teams. Each team meets after school for 2 hours, either weekly or bi-weekly, from October through May. Many teams have company sponsors which provide funds for model materials and refreshments at team meetings. In addition to developing a project, teams take field trips to construction sites or construction trade apprenticeship facilities. Finally, many ACE Affiliates offer college scholarships for promising graduates of the program who go on to study architecture, construction, or engineering. If you are interested in volunteering, find a local ACE Affiliate at the ACE Mentor Program Website, www.acementor.org.

Find Your Fit and Fund Your Find These options, which represent a range of opportunities and time commitments, have

STRUCTURE magazine

February 2015

each been successfully used by many design professionals to inspire and develop some of the bright young engineers in firms throughout the country today. However, they are by no means exhaustive. If you have a particularly ambitious venture, note that NCSEA has recently launched a grant program whereby interested members can apply for funds to advance the profession through research, outreach, or other creative means. Any program that can help introduce developing minds to the profession certainly deserves consideration for such a grant, whether you wish to begin a brand new program or expand upon any of the opportunities mentioned in this article. The grant application can be found at the NCSEA website: www.ncsea.com/resources/documents/. Applications are due on February 15, 2015, and grants will be awarded on March 15, 2015. The actions of engineers like you are what will lead our profession to new heights. By volunteering your time and expertise, you will become the leader that directs our profession and new leaders for decades to come. You have more power than you realize. Take action. Get involved. You will not regret it. It may even be more fun than running calculations.▪ Uchenna T. E. Okoye, P.E., LEED AP, is an independent professional engineer based in San Francisco currently working with Arup Americas. Uchenna is a member of the NCSEA Basic Education Committee. Uchenna may be reached at uokoye@gmail.com. Eric Borchers, S.E., is a senior structural engineer with Arup in San Francisco. Eric is a member of the NCSEA Basic Education Committee. Eric may be reached at eric.borchers@arup.com.

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Bridge resource guide Bentley Systems

Phone: 919-609-7614 Email: barbara.day@bentley.com Web: www.bentley.com Product: LEAP Bridge Steel Description: Comprehensive 3D steel bridge design and rating program; offers advanced physical 3D bridge modeling, design, analysis and load rating of everyday steel bridges, following AASHTO LRFD standards. Intuitive user interface and workflow enables rapid modeling, design and analysis of steel girder bridges. Product: LEAP Bridge Enterprise Description: A powerful modeling and analysis solution for small to medium-sized concrete bridges of all types. Comprehensive bridge information modeling (BrIM) system; geometric modeling, substructure, and superstructure analysis and design, and load rating in a single environment.

CTS Cement Manufacturing Corporation Phone: 800-929-3030 Email: jong@ctscement.com Web: www.ctscement.com Product: Rapid Set® Low-P™ Cement and Type-K Shrinkage-Compensating Cement Description: With Low-P cement, get better quality, lasting performance and an in-place cost less than Portland cement concrete. Type-K ShrinkageCompensating cement used in over 800 bridge decks with reduced permeability, excellent durability, virtually no cracks and increased concrete life cycle.

Fabreeka International, Inc.

Phone: 781-341-3655 Email: pgoulart@fabreeka.com Web: www.fabreeka.com Product: Bearing Pad & Slide Bearing Description: Fabric reinforced, elastomeric bearing pad. Used to compensate for construction irregularities, such as rotation and non-parallel load bearing surfaces. Can also be provided with a Teflon® surface for use in expansion and slide bearings.

a definitive listing of major bridge professionals and suppliers

LNA Solutions, A Kee Safety Company

Phone: 888-724-2323 Email: tdoran@lnasolutions.com Web: www.lnasolutions.com Product: BeamClamp Description: Beam and girder clamps that connect steel to steel without welding or drilling. BoxBolt blind anchor bolts certified to ICC-ESR 3217 for HSS connections. FastFit universal kits to clamp steel to steel. Fasteners to secure open steel gratings or solid steel plate flooring.

Nemetschek Scia

Phone: 443-542-0638 Email: dmonaghan@scia-online.com Web: www.nemetschek-scia.com Product: Nemetschek Scia Engineer Description: Links structural modeling, analysis, design, drawings, and reports in ONE program. Design to multiple codes. Bi-directional links to Revit, Tekla, and others.

POSTEN Engineering Systems

Phone: 510-275-4750 Email: sales@postensoft.com Web: www.postensoft.com Product: POSTEN Multistory X Description: Designs Tendons and Rebar for Multistory Buildings. Includes design of Moment Frames, Seismic & Wind, Columns, Torsion, and sustainable design (with LEED documentation).

S-FRAME Software

Phone: 203-421-4800 Email: info@s-frame.com Web: www.s-frame.com Product: S-FOUNDATION Description: Complete foundation management solution. Run as a stand-alone application, or utilize S-FRAME Analysis’ 2-way integration links for a detailed soil-structure interaction study. Automatically manages the meshed foundation model and includes powerful BIM links.

Simpson Strong-Tie

Phone: 800-999-5099 Email: web@strongtie.com Web: www.strongtie.com Product: Simpson Strong-Tie® FX-70® Structural Repair and Protection System Description: Steel pipe and H-piles deteriorate over time. The FX-70 system makes in-place repair of piles possible and practical. By eliminating the need to dewater repair sites or take structures out of service, FX-70 drastically reduces the overall cost of restoring deteriorating or damaged structures.

Strand7 Pty Ltd

Phone: 252-504-2282 Email: anne@beaufort-analysis.com Web: www.strand7.com Product: Strand7 Description: Structural analysis applications including preprocessing, solvers (linear and nonlinear static and dynamic capabilities) and postprocessing. Staged construction, a Moving Load module and quasi-static solver for shrinkage and creep/relaxation problems.

Western Wood Structures, Inc.

Phone: 800-547-5411 Email: jagidius@westernwoodstructures.com Web: www.westernwoodstructures.com Product: Timber Bridges Description: Design and construction of vehicular, pedestrian, golf course, park and residential bridges, using the highest quality, pressure-treated, glulam timber.

Williams Form Engineering Corp. Phone: 616-866-0815 Email: williams@williamsform.com Web: www.williamsform.com Product: Post Tensioning All-thread-bar Description: Pre-stressing/post tensioning 150 KSI All-Thread-Bars are high tensile steel bars available in seven diameters from 1 to 3 inches with guaranteed tensile strengths to 969 kips.

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STRUCTURE magazine

February 2015

award winners and outstanding projects

Spotlight

Krishna P. Singh Center for Nanotechnology University of Pennsylvania, Philadelphia, Pennsylvania By Brian Falconer, P.E., S.E., SECB

Courtesy of Albert Večerka/Esto.

Severud Associates Consulting Engineers, PC was an Award Winner for the Krishna P. Singh Center for Nanotechnology – University of Pennsylvania project in the 2014 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings $30M to $100M).

s a leader in the emerging field of nanotechnology, the University of Pennsylvania has opened a ninetytwo million dollar research and educational center that will enable researchers from different disciplines to transcend traditional boundaries of engineering, medicine, and the sciences. Weiss/Manfredi designed this cuttingedge building with Severud Associates, a New York City-based structural engineering firm. A number of innovative structural design solutions were used to create the functional and aesthetic features of the architecturally complex Krishna P. Singh Center for Nanotechnology. The seventy eight thousand square-foot facility ascends as a spiral to its highest elevation ending at the forum, a meeting space that cantilevers 68 feet over the quad and the building’s most complex structural design feature. The forum will be used for lectures, meetings, and receptions that may include activities such as dancing, making strength and vibration of the floor under dynamic human loading the controlling structural design criteria for this space. The vibration of the floor beams and the overall rhythmic vibration of the room are controlled by the stiffness of the trusses, the lateral restraint of the braced frame, and the caisson foundations. Vertical loads are carried by the two triangular cantilevering trusses with hangers to pick up the floor below, and horizontal loads are carried by the cantilevering metal deck diaphragm at the roof and concrete on metal deck diaphragm at the floor. The sensitivity of nanotechnology research, which requires complete isolation from surrounding elements such as vibration, electromagnetic interference, and UV light waves, posed another significant design challenge. Strict vibration tolerances had to be observed in order to create a suitable environment for researchers’ labs, so the building is setback a considerable distance from the street and the elevator cores of surrounding buildings. As the most sensitive of all the equipment, the

transmission electron microscope (TEM) is housed in a completely isolated, six-sided box construction protected by a three-foot concrete plinth tied into bedrock and an internal floating concrete slab on gravel. This design isolates the TEM from both vibration and under-slab drainage. In contrast, the clean room bays and chase have 52-foot free span beams overhead, which create a column free space for maximum flexibility. The general labs are stacked on framed floors. The 34-foot floor beams used in the general labs make the space flexible and also enhance the vibration performance enough to exceed the articulated design criteria. Another challenge to constructing the labs below grade was the groundwater table, located only eight feet below grade. To address this issue, a water-tight, concrete structural tub was employed to resist the hydrostatic pressure of the groundwater. The galleria and the monumental stair are two additional structural features requiring creative design approaches. The galleria’s stepping façade – designed as a prefabricated module system to expedite fabrication and installation – has a sloping roof on the south side which slices through the curtain wall plane in two directions. A horizontal truss diaphragm is employed at the sloping roof plane to resist the horizontal wind loads on the curtain wall. The south side of the horizontal truss is supported by steel columns on the foundation wall. The north side of the horizontal truss is more structurally dynamic; it is supported by cantilevered beams with hanging columns that suspend the truss from above. The hangers and columns are all architecturally exposed structural steel (AESS). In order to match the construction tolerances of the AESS, slip connections are provided where the hangers meet the upper roof steel. The lower roof between the hangers and the columns is constructed with AESS tolerances.

STRUCTURE magazine

February 2015

The monumental stair is unusual because it is a 55-foot long free span stair stringer supported by a twenty-four-inch deep, twenty-foot long cantilever. Though deflection and strength were considerations, similar to the forum, vibration parameters controlled the design. Five twenty-four-inch deep wide flange steel members frame the ten-foot wide stair. The team sought to seamlessly integrate the architecture and structure together into a cohesive whole, both aesthetically and functionally. Highly visible public areas such as the galleria, forum, and monumental stairs embody some of the most challenging design elements with major structural components that are strategically concealed. The more private laboratory spaces including the characterization, clean room bays, and general labs had the most stringent structural performance requirements, including column free spans and strict vibration criteria. Early in the design process, architects developed a three dimensional digital model of the building, which the structural engineers used to generate a three dimensional structural model for analysis and framing. SAP 2000 was used to perform dynamic modeling for the vibration analysis of the cantilever. The structurally innovative Center for Nanotechnology brings together researchers from both the School of Arts and Sciences and the School of Engineering and Applied Sciences, offering them spaces to interact and share their knowledge about different disciplines.▪ Brian Falconer, P.E., S.E., SECB, is a Principal in the firm Severud Associates. He participates in multiple committees of the Structural Engineering Institute and the Structural Engineers Association of New York. Brian can be reached at bfalconer@severud.com.

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NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

2015 NCSEA Membership Partnering Organizations CASE

SEI (Structural Engineering Institute of ASCE)

Associate Members AISC

Insurance Institute for Business & Home Safety

American Wood Council

International Code Council

Bentley Systems, Inc.

NCSEA recognizes and thanks its Partnering Organizations and the following companies, organizations, and structural engineering firms for their Associate, Affiliate and Sustaining memberships in 2014-2015. For information on becoming an Associate, Affiliate or Sustaining member, contact Susan Cross at 312.649.4600, ext. 204, or email scross@ncsea.com. A listing of all of these members, including contact information, can be found at www.ncsea.com/members/more/.

Metal Building Manufacturers Assn.

Simpson Strong-Tie

Schuff Steel Company

Steel Tube Institute

AZZ Galvanizing

Fibrwrap Construction, L.P.

New Millenium Building Systems

Bekaert

Headed Reinforcement Corp. (HRC)

Powers Fasteners

Blind Bolt

Hilti, Inc.

Red Seat Software

Cast Connex Corporation

Independence Tube Corporation

RISA Technologies

Cold-Formed Steel Engineers Institute

ITW Commercial Construction North America

SE Solutions, LLC

Fabreeka International Five Star Products

Affiliate Members

Construction Tie Products, Inc. CSC, Inc.

Lindapter USA

Steel Joist Institute

Microsol

DECON USA

Strand7

Nemetschek Scia

Design Data

SidePlate Systems, Inc.

Tekla

Sustaining Members ARW Engineers

DiBlasi Associates, P.C.

Martin/Martin, Inc.

Ballinger

Dominick R. Pilla Associates

Omega Structural Engineers, PLLC

Barter & Associates

DrJ Engineering

R & S Tavares Associates

Bennett & Pless, Inc.

Dunbar, Milby, Williams, Pittman & Vaughan

Ruby & Associates, Inc.

Blackwell Structural Engineers Burns & McDonnell Cartwright Engineers Cowen Assoc. Consulting Structural Engineers Criser Troutman Tanner Consulting Engineers

Engineering Solutions, LLC Gilsanz Murray Steficek The Harman Group, Inc. The Haskell Company Holmes Culley

Simpson Gumpertz & Heger Inc. Sound Structures, Inc. Structural Engineers Group, Inc. STV, Inc. TGRWA, LLC Thornton Tomasetti

Kevcor

United Structural Systems Ltd., Inc.

CTL Group

Krech Ojard & Associates

DCI Engineers

LBYD, Inc.

Wallace Engineering Structural Consultants

Degenkolb Engineers

Mainland Engineering Consultants

Wheaton & Sprague Engineering, Inc.

STRUCTURE magazine

February 2015

3 Reasons to Sign Up for the NCSEA Webinar Subscription Plan

Plan your 2015 continuing education hours with NCSEA’s new Webinar Subscription Plan. For just $750, you can receive unlimited live NCSEA webinars for one year. The subscription plan is open only to NCSEA members – members of NCSEA Member Organizations and NCSEA Sustaining, Associate and Affiliate members, and membership status will be verified. It includes live NCSEA webinars only and has a guarantee that a minimum of ten webinars, and up to 24, will be offered. A subscription plan can be started at any time. The one-year plan begins on the first day of the month in which the subscription application is received. Each webinar includes speaker slides, notes, and one free PDH certificate. If others watch the webinar with the subscriber and wish to obtain a certificate, they may purchase a certificate for $30 within two weeks of completing the webinar. After two weeks, additional certificates will not be available. NCSEA has a proven track record, having offered webinars since 2006, and structural engineers who sign up for this plan will receive excellent, and abundant, continuing education.

1. A flat rate of $750 gives you access to all live NCSEA webinars over the course of one year. If you attend just 10, your cost is $75 per webinar, a savings of over 70%! 2. NCSEA online webinars are targeted, quality programs, led by experts and leaders in structural engineering, all from the comfort of your own computer. All webinars are NCSEA Diamond approved for 1.5 PDH hours. 3. It’s a member-only benefit of belonging to NCSEA – only our members can take advantage of this terrific plan! Sign up today at www.ncsea.com!

The NCSEA SE Exam Review Course, offered by NCSEA in conjunction with Kaplan Engineering, will be held in February and March. The Vertical Course is scheduled for February 8–9, and the Lateral Course will held March 8–9. The National Council of Examiners for Engineering and Surveying (NCEES) recently released a code change, so the review courses are being updated for the April 17–18, 2015 SE exam. This targeted review assists engineers in preparing for the SE Exam and includes: Over 28 hours of instruction with an emphasis on building design: • Including sessions on exam strategy and bridge design • Key topics of structural code • Efficient analytical methods • New material in the 16-hour Structural exam • Typical exam questions • Problem solving techniques • Exam day skills • 24/7 playback within a 6 month period - study anytime There are significant discounts available for groups taking the course. Log on to www.ncsea.com under Education, for more information and to register for the course.

A terrific new student outreach tool is now available from NCSEA. The ‘Make Your Mark’ poster, produced by the NCSEA Students & Teachers Advocacy committee, along with the Structural Engineering Institute, can be used to encourage students to pursue a career in structural engineering. Limited quantities of the poster are available to NCSEA Member Organizations and MO members. Contact Joyce VanWieren, joyce@ncsea.com, with the quantity you would like and the shipping information. Electronic versions of the poster, along with other resources to promote structural engineering to students, can be found on the NCSEA website under the Resources tab, including a sample Outreach Presentation and a new High School Outreach Start-Up Guide.

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These courses will award 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program. Time: 10:00 AM Pacific, 11:00 AM Mountain, 12:00 PM Central, 1:00 PM Eastern.

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Chris Poland, S.E.

More detailed information on the webinars and a registration link can be found at www.ncsea.com. EN

February 26, 2015 The Structural Engineer’s Role in Building Community Resilience

Michelle Kam-Biron, P.E., S.E., SECB, M.ASCE

Duane K. Miller, Sc.D., P.E.

March 31, 2015 AWC’s 2015 Special Design Provisions for Wind and Seismic – Overview and Changes from Previous Editions

February 10, 2015 Practical Solutions to Frequently Asked Welding Questions

News from the National Council of Structural Engineers Associations

SE Exam Review Course set for February and March

‘Make Your Mark’ Poster Available

NCSEA Webinars

NCSEA News

Subscription Plan Offers Unlimited Live NCSEA Webinars

COUNCI L

Structures Congress 2015 Technical Sessions

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Thursday April 23, 2015 Track

Bridge research

Bridge PracTice

BlasT and imPacT

emerging Technologies

Trends in educaTion

Building codes and sTandards

Track Chair

Bruce Peterson

Cheng Lok Hing

Shalva Marjanishvili

Colby Swan

Sam Kiger

Mustafa Mahamid

8:00 AM – 9:30 AM

Bridge Loads

Bridge Assessment and Health Monitoring

Computational Analysis for Blast Loads

Advances in Sustainable Structural Materials

The Art and Feel of Structural Engineering – Part 2: Classical Methods of Analysis

The State of Design Loads – a Discussion of ASCE 7-10 Seismic and Proposed Tsunami Loads

10:00 AM – 11:30 AM

Bridge Analysis

Tsunami Structure Interaction

Validating the Performance of Structural Protection Against Explosive and NonExplosive Threats

Experimental Testing with High-Performance Materials

Innovations in Educating Structural Engineers and Architects

What is Next for ASCE 7 and ASCE 37?

2:00 PM – 3:30 PM

Bridge Design

Innovative Bridge Systems, Analysis Techniques and Construction Methodologies

Overview of Updates to “Structures to Resist Effects of Accidental Explosions” UFC 3-340-02, Change 1

Emerging Concepts for Damage-Limiting Seismic Concrete Building Systems

Engineering Education: Innovative Methods for Preparing the 21st Century Structural Engineer

New Performance-Based Standards for Structures Subject to Fire

4:00 PM – 5:30 PM

Bridge Replacement and Rehabilitation

Application of Remotely Operated Devices in Assessment of Bridges

Behavior of Damaged Structures

Seismic Centering for Enhanced Resilience

Structural Optimization: From Research/Practice to Structural Engineering Education

Verification, Refinements and Background on Codes and Loadings

Friday April 24, 2015 Track

Bridge PracTice

Bridge research

disProPorTionaTe collaPse

emerging Technologies

concreTe comPosiTe and cold-formed

sTrucTural sTeel

Track Chair

Taka Kimura

Dennis Mertz

Robert Smilowitz

Colby Swan

Sarah Vaughan Cook

Mustafa Mahamid

8:30 AM – 10:00 AM

Behind the Scenes: Design and Construction of the World’s Longest Floating Bridge

Bridge Seismic Design

Case Studies of Disproportionate Collapse Analysis

Performance Based Design of Structures: Evolution, State-ofthe-art, and State-of-Practice

Assessing Risk, Developing Strategies, and Improving Understanding of Older Concrete Buildings

Innovative Structural Steel Seismic-Resisting Systems

10:30 AM – 12:00 PM

New Bridges in Portland

Bridge Seismic Analysis

Recent Research on Resistance to Disproportionate Collapse

Performance-Based Eng. Approaches for Mitigation of Single and Multiple Hazards

Concrete Expectations

Advances in Understanding of Steel Connections

1:30 PM – 3:00 PM

Historic Bridge Rehabilitation in the Pacific Northwest

Innovative Low Damage Bridge Systems for Accelerated Construction in Seismic Regions

Progressive Collapse

Corrosion and Structural Degradation

The Art and Science of Composite Construction

Advances and Applications in the SSRC Guide to Stability Design Criteria for Metal Structures

3:30 PM – 5:00 PM

Oregon Bridge Seismic Retrofit Program

Accelerated Bridge Construction

The Philosophy Behind the SEI Disproportionate Collapse Mitigation Standard

Bridge Corrosion and Deterioration

Empowering Next Generation Sustainable System Design in Cold-Formed Steel Framed Buildings

The New AISC Design Guide 29: Vertical Bracing Connections – Analysis and Design

Saturday April 25, 2015 Track

Bridge PracTice

Bridge research

BlasT

emerging Technologies

Wind and flood loading

Wind ToPics

Track Chair

Taka Kimura

Dennis Mertz

Shalva Marjanishvili

Colby Swan

Brian McElhatten

Mustafa Mahamid

8:00 AM – 9:30 AM

Timber Bridges – Design and Performance Issues

Bridge Innovative Solutions

Blast Protection of Bridges

Measurement, Identification, and Assessment of Structural Performance

The State of Design Loads – a Discussion of ASCE 7-10 Wind and Flood Loads and ASCE 24 Flood Resistant Design

Computational and Physical Modeling of Non-Synoptic Winds (Thunderstorms)

10:00 AM – 11:30 AM

Case Studies: Results of Practical Sensing, Identification, and Monitoring Projects

Bridge Foundations and Soil Interaction

Security FaÇades

Fire Resilience of Bridge Structures: Evaluation and Design

Modeling, Understanding, and Designing for Wind Effects

Wind Loading on Multi-Layered Building Envelope and Roofing Systems

Register early and save. For more information including registration and housing, visit our website at www.structurescongress.org. STRUCTURE magazine

February 2015

Building case sTudies

Wood ToPics

Tall Buildings and analysis ToPics

www.structurescongress.org

Business and Professional PracTice

naTural disasTer and resilience

non Building sTrucTures & non sTrucTural comPonenTs

Brian McElhatten

Paul Mlakar

John Tawresey

John Silva

Greg Soules

Seismic Design of Building Structures in the Pacific Northwest

Pacific Northwest Timber Topics

Optimization in Tall Buildings

Career Paths for Young Professionals and Students

Preparing for Natural Disasters

Innovative Special Structures: Art in Engineering Design

Portland’s South Waterfront Redevelopment

Technology Advances and Potential Opportunities for Wood Structures

Tall Building Systems

ATC-115. Integrating High Strength Reinforcing Bar into ACI 318 Bldg. Code; Bringing ACI 318 Bldg. Code into the 21st Century

The Oregon Resilience Plan – From Legislation to Action Plan

Advancing Design Approaches for Wind Energy Structures

Forensic Case Studies and Considerations

Design Practice and Serviceability Concerns for CLT

Analysis and Design Considerations and Techniques

Understanding the Alternative Deliveries: Discussion of Design/Build and P3 through Case Study

Building Community Resilience Using Performance-Based Engineering – Part 1

Structural Design of Renewable Energy Systems

The Art of Steel Building Design

Seismic Response of Timber Buildings

Challenging Issues in NonLinear Seismic Analysis – A Panel Discussion

Evolving Subjects for the Structural Engineer

Building Community Resilience Using Performance-Based Engineering – Part 2

Wind Loads on Solar Panels

case sPring risk managemenT convocaTion

Business and Professional PracTice

Building case sTudies

Building ToPics

naTural disasTer and resilience

non Building sTrucTures and non sTrucTural comPonenTs

Mark Waggoner

Brian McElhatten

Paul Mlakar

John Tawresey

John Silva

Greg Soules

Steel, Art and Society

Vibrations Serviceability

Addressing Hidden Risks in Today’s Design Contracts

How the Future of Structural Engineering Sees the Future of Structural Engineering

Structure and Infrastructure Resilience: Can It Be Quantified?

Design Considerations for Structures Crossing or Close to Fault-Rupture Zones

Building Case Studies

Advances in Composite Beams, Floors, and Diaphragms

How to Succeed Without Risking it All!

Advancing Structural Eng. through Better Integration of Practice, Education, and Research

Resilient Design Using Performance-Based Eng. and Advanced Information Technologies

Foundations for Nonbuilding Structures

Challenges and Complexity of Air-Rights Structures

Reduction of Carbon Emissions from Building Structures

Lessons Learned from Structural Cases in Litigation

I am a Structural Engineer – Now What?

Risk-Based Methods in Structural Design and Evaluation: Current Practices and Perspectives

Performance of Ceiling Systems

Innovative Building Systems, Analysis Techniques and Construction Methodologies

Innovative Technologies for Sustainable Tall Buildings

SE Practice for Quality and Profitability

Ethics in Structural Engineering – Design and Construction Inspection

Challenges and Solutions Towards Risk-Based Structural and Infrastructure Performance Assessment and Decision Support

Curtain Walls

Building case sTudies

masonry ToPics

exPanding The sTrucT. engineer’s role in socieTy

Business and Professional PracTice

naTural disasTer and resilience

non Building sTrucTures and non sTrucTural comPonenTs

Mark Waggoner

Brian McElhatten

John Tawresey

John Silva

Greg Soules

Design and Aesthetics of Non-Traditional Structural Materials

New Techniques and Trends for Seismic Design and Retrofit of Masonry

The Role of Structural Engineers in Sustainable Development and Poverty Reduction

Structural Engineering Licensure for the Next 100 Years

Performance-Based Design for Extreme Events

Analysis and Testing of Nonstructural Components

Evaluation and Retrofit of Low-Ductility Steel Braced Frames

Masonry Quality Assurance – Inspection and Testing Requirements and Recommendations

The Inherent Conflicts of Litigation and Engineering

Introduction to a New SEI/ ASCE Standard for Load and Resistance Factored Design

Fire Following Earthquake: A Sequential Hazard Approach

Floors and Partitions

View the interactive Technical Program, including all presenters and abstracts at www.structurescongress.org STRUCTURE magazine

February 2015

The Newsletter of the Structural Engineering Institute of ASCE

Mark Waggoner

Structural Columns

April 23– 25, 2015 – Portland, Oregon

CASE in Point

The Newsletter of the Council of American Structural Engineers

Donate to the CASE Scholarship Fund! The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at minimum, in an ABET-accredited engineering program. We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates. One way to enhance the ability of students in pursuing their dreams to become professional engineers is to offer incentives in educational support.

In addition, the CASE scholarship offers an excellent opportunity for your firm to recommend eligible candidates. If your firm already has a scholarship program, remember that potential candidates can also apply for the CASE Scholarship or any other ACEC scholarship currently available. Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for tax deduction and you don’t have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

CASE Risk Management Tools Available Foundation 1: Culture

Foundation 2: Prevention & Proactivity

Tool 1-1: Create a Culture for Managing Risks and Reducing Claims The most comprehensive CASE tool provides sample templates and presentations that aid in creating a culture of risk management throughout the firm. This tool was updated in 2013 to include: • Revised PowerPoint presentations, scripts, and sample statements that allow users to modify for their own use. • Case studies that highlight best practices and procedures to manage liability and limit risk.

Tool 2-1: A Risk Evaluation Checklist Don’t overlook anything! A sample itemized list of things you should look for when evaluating a prospective project.

Create a Culture of Managing Risks & Preventing Claims

Tool 1-2: Developing a Culture of Quality This tool was developed to identify ways to drive quality into a firm’s culture. It is recognized that every firm will develop its own approach to developing a culture of quality, but following these 10 key areas offer a substantial starting point. The tool includes a white paper and customizable PowerPoint presentation to facilitate overall discussion. All of these tools and more are available at www.booksforengineers.com.

Tool 2-2: Interview Guide Getting “the right people on the bus” is one of the most important things we can do to mitigate risk management and yet we never learn about interviewing skills in school. The tool will help your firm conduct higher quality interviews and standardize the process among all your staff. Tool 2-3: Employee Evaluation Templates This tool is intended to assist the structural engineering office in the task of evaluating employee performance. The evaluations provide a method to assess employee performance and serve as an integral part of the company’s risk management program. Tool 2-4: Project Risk Management Plan This plan will walk you through the methodology for managing your project risks, along with a few common project risks and templates on how to record and track them. Tool 2-5: Insurance Management: Minimize Your Professional Liability Premium This tool is designed as a guide to help you provide critical additional information to the underwriter to differentiate your firm from the pack.

Follow ACEC Coalitions on Twitter – @ACECCoalitions. STRUCTURE magazine

Act with Preventative Techniques, Don’t Just React.

February 2015

WANTED

The CASE Guidelines Committee has developed a white paper on Standard of Care now available for free on the CASE website: www.acec.org/case/news/publications/. Many engineers are licensed and practice in many states; what is customary in one, may not be so in another. Codes and standards are becoming more standardized and national in nature, meaning more uniformity and perhaps a higher level of engineering skills across the country. Gone may be the days when an engineer can really say that “we don’t do that around here.” Having a good understanding of your legal responsibilities is more important than ever!

If you’re looking for ways to expand and strengthen your business skillset, look no further than serving on one (or more!) CASE Committees. Join us to sharpen your leadership skills – promote your talent and expertise – to help guide CASE programs, services, and publications.

ACEC Business Insights ACEC’s highly regarded Business of Design Consulting course is a unique playbook for building leadership and managing your firm at the most effective levels. The 3½-day agenda is taught by an experienced faculty of industry practitioners and highlights current strategies for a wide array of critical, need-to-know business topics that will keep your business thriving despite a churning business environment. Topics include how to manage change and build success in performance management, strategic planning and growth, finance, leadership, ownership transition, contracts and risk management, marketing, and more! For more information and to register for the course, www.acec.org/calendar/calendar-seminar/business-of-designconsulting-dallas-2015/.

We have a committee ready for your service: • Risk Management Toolkit Committee: Develops and maintains documents such as business practices manuals and policies for engineers under CASE’s Ten Foundations for Risk Management.

Expectations and Requirements To apply, you should • be a current member of the Council of American Structural Engineers (CASE) • be able to attend the groups’ two face-to-face meetings per year: August, February (hotel, travel reimbursable) • be available to engage with the working group via email and conference call • have some specific experience and/or expertise to contribute to the group Please submit the following information to htalbert@acec.org • Letter of interest • Brief bio (no more than 2 paragraphs) Thank you for your interest in contributing to your professional association!

CASE Risk Management Convocation in Portland, OR The CASE Risk Management Convocation will be held in conjunction with the Structures Congress at the Doubletree by Hilton Downtown Hotel and Oregon Convention Center in Portland, OR, April 23-25, 2015. For more information and updates go to www.seinstitute.org.

The following CASE Convocation sessions are scheduled to take place on Friday, April 24: 7:00 AM – 8:15 AM CASE Breakfast: The Future of Structural Engineering Sue Yoakum, Donovan Hatem 8:30 AM–10:00 AM Addressing Hidden Risks in Today’s Design Contracts Speakers – Rob Hughes, Ames & Gough; Brian Stewart, Collins, Collins, Muir & Stewart 10:30 AM – 12 Noon How to Succeed Without Risking It All! Moderator – John DalPino, Degenkolb Engineers 1:30 PM – 3:00 PM Lessons Learned From Structural Cases in Litigation Speaker – Jeffrey Coleman, The Coleman Law Firm 3:30 PM – 5:00 PM SE Practice for Quality and Profitability – Panel Discussion

STRUCTURE magazine

February 2015

CASE is a part of the American Council of Engineering Companies

Best Management Strategies in Business of Design Consulting Course March 18 – 21, 2015 Dallas, TX

Engineers to Lead, Direct, and Get Involved with CASE Committees!

CASE in Point

NEW!! Standard of Care White Paper

Structural Forum

opinions on topics of current importance to structural engineers

Is Structural Engineering Education Sustainable? By Lawrence C. Bank, Ph.D., P.E.

ithin the broad field of civil engineering, structural engineers have perhaps been among the slowest to embrace and adopt the concepts of sustainability in the built environment. Many sit by with mounting frustration as architects, other types of engineers, and urban planners have defined “green” agendas for their disciplines, and successfully embraced and marketed them. The reasons for this, which are perhaps understandable, can be traced to the way in which structural engineers are educated, as well as to the fact that it has been difficult to identify an appropriate vision for incorporating sustainability principles into our practice. In order to define the appropriate vision for the future of our profession, we need to understand how sustainability emerged from the environmental movement, where it currently is in terms of global development, and how structural engineers can restructure and develop opportunities in this new sustainable world. According to the Department of Labor, there are approximately 258,000 civil engineers in the United States today. The total memberships of NCSEA, CASE, and SEI suggest that about 40,000 are structural engineers, and most of those have a license to practice civil engineering as a Professional Engineer (PE). A few states require an additional license to practice as a Structural Engineer (SE). SEI’s report on A Vision for the Future of Structural Engineering and Structural Engineers: A Case for Change suggests that there is considerable angst in the SE community regarding the future. The structural engineering curriculum typically consists of courses in engineering mechanics and linear structural analysis. These are often taught using textbooks first published in the 1960s (or earlier) and are based on the theory of structures from the late 18th century to the early 20th century. There is usually only one course in materials. Design of steel and concrete structures is taught from textbooks from the 1950s and is based on the AISC and ACI codes, respectively. The emphasis is on framed multi-story buildings and short-span bridges. Other commonly used materials may

or may not be covered. There is some exposure to computer codes, but very little use of the design features of these codes. The master’s degree typically covers more of the same, except in somewhat greater detail (e.g., nonlinearity, seismic design, more classical mechanics) and perhaps an independent study or thesis. The doctorate is researchbased and typically deals with advanced topics of the same type (steel and concrete frames) in great depth and of little immediate value to the practicing engineer. In 1987, sustainable development was defined by committee in the United Nations (UN) Brundtland Report, Our Common Future, as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” Less known is the latter part of the definition that “contains within it two key concepts: the concept of ‘needs’, in particular the essential needs of the world’s poor, to which overriding priority should be given; and the idea of limitations imposed by the state of technology and social organization on the environment’s ability to meet present and future needs.” Since then, sustainable development and sustainability science have proceeded along two distinct paths – one focused on the first key concept, sometimes referred to as the “brown agenda,” including population, pollution, public health, poverty, and property rights; and the other focused on the second key concept, sometimes referred to as the “green agenda,” including the Triple-Bottom-Line, P3, and LEED. Today these two streams are expressed in the UN’s Millennium Development Goals (MDG) and Intergovernmental Panel on Climate Change (IPCC) reports. In the US, sustainability in structural engineering has focused primarily on the second key concept and has worked toward the green agenda. On the materials side, this has typically been manifested in life-cycle assessment (LCA) and embodied energy; decreasing greenhouse gas emissions, primarily from cement production; and using recycled materials, primarily steel. On the structural side, the main effort has been the optimization of framing systems to use less material.

Neither of these approaches is likely to contribute significantly to sustainable development. The embodied energy in materials is a small fraction of the energy consumed over a building’s lifetime, which in turn is only a small fraction of the commercial value of the property, not to mention the income and health costs of the building occupants. The cost of the structural system in a building is perhaps 15% of the initial construction cost, so optimization is unlikely to yield great sustainability benefits. In addition, there has been significant consolidation in consulting firms over the last two decades, leading to less need for specialized designers for what are now “routine” multi-story building frames. One vision for a sustainable future for structural engineering is to align our teaching, research, and practice with the first key concept of sustainable development; i.e., reorient our curricula to focus on the knowledge and skills needed to address the needs for safe and resilient infrastructure and housing for the three billion people earning less than five US dollars per day, many living in informal and even illegal settlements. It is disgraceful that we as structural engineers do not yet know how to provide meaningful input to solve these human catastrophes that are a direct function of the built environment. Such a focus will, of course, require a significant reprioritization and rethinking of every part of the curriculum. It will require courses in social sciences, environmental sciences, geography, world cultures, and economics. However, it will bring back to the profession – and especially to students – a sense of mission and purpose, akin to those now studying environmental engineering and sustainability sciences of various types. It will make us relevant again.▪ Lawrence C. Bank, Ph.D., P.E. (lbank2@ccny.cuny.edu), is a professor in the Department of Civil Engineering at the City College of New York. This article is based on the 2014 Landis Lecture in Structural Engineering at the University of Pittsburgh.

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, C 3 Ink, or the STRUCTURE® magazine Editorial Board. STRUCTURE magazine

February 2015

STRUCTURE magazine | February 2015

Articles inside

is structural engineering education sustainable?

leading the Charge

integral Crystalline Waterproofing

Bollman truss at harper’s Ferry

divine design: renovating

100 Years of structural engineering licensure

rainbows only Come after rain

inside the Bridge inspection toolbox

the nisd difference

Why it’s Good to be a lightweight

Changes to the 2015 Wood Frame Construction Manual

Built-up Cold-Formed steel Compression Member design

unintentional Corrosion by structural design