STRUCTURE magazine | September 2015 by structuremag

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

September 2015 Concrete Special Section

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editorial

7 PBd: a Component in the Future of Structural engineering By Stephen S. Szoke, P.E. iNFoCuS

11 representation and reality

STRUCTURE

gueSt ColuMN

34 BiM-M Symposium: generation 1

September 2015

By Daniel Zechmeister, P.E. StruCtural PerForMaNCe

38 the Most Common errors in Seismic design

By Jon A. Schmidt, P.E., SECB

By Thomas F. Heausler, P.E., S.E.

teChNologY

iNSightS

12 Modern limit analysis tools for reinforced Concrete Slabs By Angus Ramsay, M.Eng, Ph.D., C.Eng, Edward Maunder, Ph.D. and Matthew Gilbert, Ph.D., C.Eng StruCtural deSigN

16 What is a Masonry “Flush Pilaster”? By David L. Pierson, S.E. hiStoriC StruCtureS

18 the Niagara Cantilever Bridge By Frank Griggs, Jr., D. Eng., P.E. BuildiNg BloCkS

23 Proper Procedures and Protocol for interception grouting By Brent Anderson, P.E. StruCtural rehaBilitatioN

26 divine design: renovating and Preserving historic houses of Worship, Part 4 By Nathaniel B. Smith, P.E. and Milan Vatovec, P.E., Ph.D. CodeS aNd StaNdardS

30 Changes in adhesive anchor System approvals

Feature

58 Creating Clarity and Scoping Profits in BiM with lod 350

NCSea 2015 Summit Special Section

By Will Ikerd, P.E. eNgiNeer’S NoteBook

60 Moment-Curvature and Nonlinearity By Jerod G. Johnson, Ph.D., S.E. CaSe BuSiNeSS PraCtiCeS

63 Strategic Planning: a Comprehensive approach By Dilip Choudhuri, P.E.

The National Council of Structural Engineers Associations will host its 2015 Structural Engineering Summit at the Red Rock Resort in Las Vegas, NV, on September 30th through October 3rd. Read about the Summit, the extensive program and vendor information in the Special Summit Section… and plan to attend this exciting event!

Feature

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eduCatioN iSSueS

69 Structural education deficiencies

By Sunghwa Han, P.E., S.E. The behavior of structurally-linked multiple tower structures is largely affected by the effectiveness of the rigid links made between the towers. Depending on the interactive dynamic behavior of the adjacent building parts with one another, a separation joint may be considered. Read how engineers resolved numerous issues associated with separation gaps.

By Kevin Dong, P.E., S.E. SPotlight

75 Newport Beach Civic Center and Park By Janice Mochizuki, P.E., John Worley, S.E. and

Joseph Collins, S.E.

Feature

StruCtural ForuM

82 a “Plug” for Power line Structures By David C. Gelder, P.E.

By Richard T. Morgan, P.E.

On the cover Las Vegas CityCenter Block A, structural engineering by Thornton Tomasetti and architectural design by Pelli Clarke Pelli Architects, is the crown jewel of the 76-acre CityCenter development on the Las Vegas Strip. The development is the largest, most complex private construction project completed in the United States to date. Photo courtesy of Thornton Tomasetti. Join NCSEA at the Red Rock Resort in Las Vegas, September 30th through October 3rd (see page 42). 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

a Need for Speed By Ramon Gilsanz, P.E., S.E., Philip Murray, P.E., Gary Steficek, P.E. and Petr Vancura The fundamental principle that drives the need for speed in construction is economic, a major factor for owners. How do you approach fast-paced construction within a dense urban environment? Read how three projects in New York City illustrate the use of flat plate concrete systems, instant communication and in-the-field coordination to speed up the construction process.

iN everY iSSue 8 Advertiser Index 71 Resource Guide (Anchoring) 76 NCSEA News 78 SEI Structural Columns 80 CASE in Point

September 2015

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ACI 318-14: Reorganized for Design

The American Concrete Institute has recently published the newest edition of ACI 318, “Building Code Requirements for Structural Concrete (ACI 318-14).” This edition represents the first major change in Code organization in over 40 years and has been completely reorganized from a designer’s perspective. This seminar will help you get acquainted with the new organization and various technical changes to the code as quickly as possible and demonstrate how you can ensure that your design fully complies with the new code.

To learn more about ACI seminars and to register, visit www.concreteseminars.org Pittsburgh, PA—September 10, 2015 Raleigh, NC—September 15, 2015 Chicago, IL—September 17, 2015 New Brunswick, NJ—September 22, 2015 Minneapolis, MN—September 24, 2015 Albany, NY—September 29, 2015 ACI Headquarters—Farmington Hills, MI— September 30, 2015 Des Moines, IA—October 1, 2015

Portland, OR—October 6, 2015 Baltimore, MD—October 8, 2015 Little Rock, AR—October 9, 2015 Houston, TX—October 13, 2015 Tampa, FL—October 15, 2015 St. Louis, MO—October 20, 2015 Cincinnatti, OH—October 22, 2015 Indianapolis, IN—October 27, 2015 Savannah, GA—October 29, 2015

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Editorial

PBD: A Component in the Future of new trends, new techniques and current industry issues Structural Engineering By Stephen S. Szoke, P.E., F.SEI, F.ASCE, F.ACI

erformance-Based Design (PBD) has been practiced throughout history, dating back to the Code of Hammurabi, circa 1750 BCE. Today, the three most common applications of performance based design are: • Use of innovative engineering technologies or products; • Enhancement of project performance based on specific needs of the owners, such as design for special risk assessments like extreme loading conditions; and • Economy, where more affordable design and construction options can demonstrate compliance with the intent of the building code. Although PBD is already permitted in building codes, perhaps it is too infrequently practiced. Most building codes are based on the International Code Council International Building Code (IBC) which includes alternative means and methods to allow the use of materials, design techniques, or construction methods not specifically prescribed by the code. Many jurisdictions also adopt the International Code Council Performance Code (ICCPC) which permits innovation and deviations from the prescriptive criteria while maintaining the intent of the building code. The intent of the ICCPC is: “To provide appropriate health, safety, welfare, and social and economic value, while promoting innovative, flexible and responsive solutions that optimize the expenditure and consumption of resources.” Today, the trend in structural engineering, often driven by the potential for litigation, is to exclusively follow the prescriptive design criteria for loads based on Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7) combined with prescriptive load resistance criteria as provided in documents like the American Concrete Institute’s Building Code Requirements for Structural Concrete; American Institute of Steel Construction’s Steel Design Manual; and American Wood Council’s ASD/LRFD Manual for Engineered Wood Construction. However, an unintended consequence of these prescriptive criteria is the ability to generate designs compliant with both load and resistance criteria via computer models. This method of structural design, while it may still require a stamp by an engineer, limits the freedoms related to innovation and creativity in structural design. The development of strategies and mechanisms to expand the acceptance of PBD tend to better reflect the interests of clients and jurisdictions while elevating structural engineers as design professionals. A new opportunity to increase use of PBD may be to encourage acceptance of emerging philosophies related to design and construction solutions that are associated with “enhanced resilience” or “community resilience.” The National Institute for Standards and Technology is in the final development stages of the Community Resilience Planning Guide which proposes new concepts for codes and standards related to the design of building and other infrastructure components. Another strategy could be related to transparency of consequences to owners and communities should a disaster occur. This might be in the form of multiple performance levels within each risk category to better allow owners and communities to select the appropriate performance levels. The National Institute of Building Sciences Building Seismic Safety Council is considering a menu of performance levels in lieu of single performance levels for respective risk classifications. This would differ from the current approach, where the standards development process dictates the acceptable performance level, such as 10% failure for the STRUCTURE magazine

seismic design of most buildings, those classified in risk category II. This new approach may extend the role of the structural engineer in planning to help improve community resilience, the ability to rebound after disasters, seismic or otherwise. To address historical and current applications of PBD and the role of PBD in future, the SEI Board of Governors has established a committee, not to develop criteria for PBD, but to investigate the role of PBD in the future of structural engineering. Their charge is to champion the trend toward performance-based design. This aligns with several aspects of SEI’s A Vision for the Future of Structural Engineering and Structural Engineers: A case for change: “…The drive to develop codes and specifications has led to the outcome that many of the tasks previously done by structural engineers could be and have been automated… …we must curb our tendency to codify our design decisions and leave those decisions in the province of qualified structural engineers. If we mandate how a structure must perform, but leave freedom to how the engineer provides that performance, we open the possibilities for amazing solutions to presently unsolvable problems.” “One avenue for change that has emerged in recent years is the notion of performance-based design… … performance-based design would increase the importance of sound engineering judgment in the design process, rely on better technical knowledge, require the use of more sophisticated technology in problem solving, result in more efficient structures, and place the structural engineer in a better position to drive technological change.” The new PBD committee met during the 2015 Structures Congress. Many aspects and implications of PBD will be visited during the process of developing recommendations, including: development of a series of enabling documents to compliment current design criteria, possibly similar to Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41); use PBD to serve as the documents in the public domain moving prescriptive compliance criteria to other documents maintained by standards developers; defining professional liability as a standard of care; and use of shelter-in-place performance levels for significant natural disasters. This effort, while invaluable, is a complex, multi-faceted and long-term project for the advancement of structural engineering as a profession.▪ Stephen S. Szoke, P.E., F.SEI, F.ASCE, F.ACI, is the Senior Director of Codes and Standards for the Portland Cement Association. He serves on SEI’s Codes and Standards Division Executive Committee and represents the division on the SEI Board of Governors. He serves as the board liaison for the newly formed board level committee on performance based design. He may be contacted at sszoke@cement.org. The National Institute for Standards and Technology Community Resilience Planning Guide can be found at www.nist.gov/el/building_materials/resilience/guide.cfm, last visited July 2015.

September 2015

Advertiser index

PlEaSE SUPPoRT ThESE advERTiSERS

American Concrete Institute ............. 6, 21 Applied Science International, LLC....... 83 Bentley Systems, Inc. ............................. 10 CADRE Analytic .................................. 71 California Polytechnic State University .... 8 Construction Specialties ........................ 15 CTP, Inc................................................ 29 CTS Cement Manufacturing Corp........ 25 Decon USA, Inc. ................................... 64 Ecospan Composite Floor System ......... 61 Enercalc, Inc. .......................................... 3 Fyfe ....................................................... 19 Geopier Foundation Company.............. 50 Halfen USA, Inc. .................................. 70 Hardy Frame ......................................... 53 Hohmann & Barnard, Inc. .................... 13 ICC – Evaluation Service ...................... 74 Integrated Engineering Software, Inc..... 67 Integrity Software, Inc. .......................... 49

ITT Enidine, Inc. .................................. 57 JVA Inc. ................................................ 32 KPFF Consulting Engineers .................... 8 Legacy Building Solutions ..................... 37 LNA Solutions ...................................... 59 MAPEI Corp......................................... 62 Powers Fasteners, Inc. .............................. 2 QuakeWrap ........................................... 39 RISA Technologies ................................ 84 S-Frame Software, Inc. ............................ 4 Simpson Strong-Tie........................... 9, 33 SEA of Illinois ....................................... 68 Structural Engineers, Inc. ...................... 20 StructurePoint ....................................... 22 Struware, Inc. ........................................ 36 Tekla ..................................................... 72 USG Corporation ................................. 41 V2 Composites, Inc............................... 55

STRUCTURE

Advertising Account MAnAger InteractIve SaleS aSSocIateS sales@Structuremag.org Eastern Sales chuck Minor 847-854-1666 Western Sales Jerry Preston 480-396-9585

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

ARCHITECTURAL ENGINEERING The Department of Architectural Engineering at Cal Poly, San Luis Obispo, California is seeking applications for a full-time, academic year tenure track position for the teaching of structural analysis, design, and construction of buildings. Starting date is September 15, 2016. For details, qualifications, and to complete a required online faculty application, please visit WWW.CALPOLYJOBS.ORG and search for Requisition #103762. Review of application will begin October 15, 2015. Applications received after this date may be considered. EEO.

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 Dilip Khatri, Ph.D., S.e. Khatri International Inc., Pasadena, ca roger a. laBoube, Ph.D., P.e. ccFSS, rolla, Mo Brian J. leshko, P.e. HDr engineering, Inc., Pittsburgh, Pa Brian W. Miller Davis, ca

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Mike Mota, Ph.D., P.e. crSI, Williamstown, nJ 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 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

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STRUCTURE magazine

September 2015

September 2015, Volume 22, Number 9 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.

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inFocus

Representation new trends, new techniques and and current Reality industry issues By Jon A. Schmidt, P.E., SECB

epresentation is intrinsic to human life and engineering practice. We communicate with other people throughout the design and construction process by means of words, diagrams, and sketches. We create mental and computational models of materials, loads, and the arrangement of members. We develop building information models (BIM), drawings, and specifications to indicate how the various pieces and parts are to be assembled into the finished structure. The intent of these representations is to capture the relevant characteristics of reality, which may overlap but are not identical in each case. The engineer has to ascertain what those are, and then incorporate appropriate assumptions and simplifications accordingly. Two common strategies are abstraction, which involves neglecting certain aspects of reality in order to gain a better understanding of the remaining aspects; and idealization, which involves replacing a complicated and/or complex aspect of reality with a simplified version. This entails that representations are always less than 100% accurate, raising the question of how they relate to reality – the domain of semiotics, the study of signs and signification (or semiosis). Conventional theories are dyadic, emphasizing two components: the signifier and the signified; the relationship between them is essentially arbitrary. The limitations of this conceptualization have become evident with the emergence of deconstruction and other aspects of postmodernism, in that it effectively precludes objective meaning. An alternative was developed by American scientist and philosopher Charles Sanders Peirce (pronounced “purse”) in the late 19th and early 20th centuries. He founded what eventually came to be known as pragmatism, but was unhappy with the direction that it ultimately took in the more popular work of others – most notably William James and John Dewey – so he coined the name pragmaticism for his own approach, saying that this term was “ugly enough to be safe from kidnappers.” Peirce’s theory – which he preferred to call semeiotic – is triadic, emphasizing three relations: among the sign itself (or representamen), that which it signifies (object), and the effect that is produced (interpretant), which comes about by a habit of interpretation. Peirce aligned these elements with the three fundamental categories that he identified in both our encounter with the world (phenomenology or phaneroscopy) and the underlying nature of reality (metaphysics); he simply called them Firstness, Secondness, and Thirdness. Firstness is quality, feeling, possibility, spontaneity, vagueness; Secondness is difference, reaction, actuality, persistence, particularity; Thirdness is mediation, purpose, regularity, order, generality. For example, an icon relates to its object through some kind of resemblance (Firstness), an index due to a physical or other direct connection (Secondness), and a symbol by means of a convention or rule (Thirdness). A painting is an icon, a fingerprint is an index, and a word is a symbol. For Peirce, then, representation is reality: “…all this universe is perfused with signs, if it is not composed exclusively of signs.” Furthermore, all thought consists of signs, and inquiry is the deliberate and collaborative endeavor to process them in a way that results in genuine knowledge via three basic modes of inference: abduction (or retroduction), the formulation of a hypothesis or “guess,” often in response to a surprising event; deduction, the explication of what STRUCTURE magazine

else would be the case if that explanation is correct; and induction (or adduction), the examination of whether those consequences ever fail to materialize. This “logic of inquiry” applies most directly to science, but it also serves as a “logic of ingenuity” in engineering practice. Abduction constitutes the creative process that leads to the selection of one preliminary solution out of multiple potential options (“Engineering as Willing,” March 2010). Deduction corresponds to the deterministic analyses that indicate the expected behavior of that design, given certain presuppositions. Induction operates over time as an engineer learns from experience – i.e., gets better at abduction – developing competence, proficiency, and eventually expertise (“The Nature of Competence,” March 2012). Both inquiry and ingenuity thus employ signs to make that which is indeterminate more determinate, although never fully determinate. The only complete sign is the entirety of reality itself, which consists of continuous systems of relations, rather than discrete substances; hence its persistent complexity (“Complicated + Complex = Wicked,” July 2015). Truth is the final interpretant – the opinion on which an infinite community would converge after an indefinite investigation. In the meantime, we must always acknowledge the fallibility of our current understanding (“The Virtues of Ignorance,” May 2015). Uncertainty in representation is constrained by reality, but not eliminated entirely. Note that determination occurs primarily as discovery in science (conforming representation to reality) vs. decision in engineering (conforming reality to representation). This distinction was important to Peirce, because while he was a persistent advocate of grounding science firmly in reason, he was equally adamant that practical matters should be governed primarily by instinct and sentiment. When it comes to “topics of vital importance,” judgment must rely on one’s existing beliefs, which are nothing more or less than established habits of thought and action – much like virtues in Aristotelian ethics (“Virtuous Engineering,” September 2013). This column barely scratches the surface of Peirce’s wide-ranging and often idiosyncratic ideas. He never managed to write a single book – something that (so far) I have in common with him – but produced many thousands of pages of articles and manuscripts, leaving the bulk of them in draft or otherwise unfinished form. The Peirce Edition Project (www.iupui.edu/~peirce/) has compiled and published key selections from his philosophical writings in The Essential Peirce (two volumes, 1992 and 1998). Helpful introductory and summary material is available in The Fate of Meaning (1989) and Charles Peirce’s Guess at the Riddle (1994) by John K. Sheriff, The Continuity of Peirce’s Thought (1998) by Kelly A. Parker, and Peirce’s Theory of Signs (2007) by T. L. Short.▪

Jon A. Schmidt, P.E., SECB (chair@STRUCTUREmag.org), is an associate structural engineer at Burns & McDonnell in Kansas City, Missouri. He chairs the STRUCTURE magazine Editorial Board and the SEI Engineering Philosophy Committee, and shares occasional thoughts at twitter.com/JonAlanSchmidt. September 2015

Technology information and updates on the impact of technology on structural engineering

t a recent workshop, organized by the University of Sheffield in association with LimitState and held at the IStructE Headquarters in London, the authors of this article presented new computational tools for the limit analysis of reinforced concrete (RC) slabs. The workshop was attended by practising engineers from different fields, including those involved with the design of RC slabs and those with an interest in the assessment of existing RC slabs for changing service loads. The computational tools presented align closely with the traditional methods of designing and assessing RC slabs. The traditional method for assessing slabs has been Johansen’s yield line technique which, as an upper-bound method, relies for its accuracy on the ability of the engineer to postulate a realistic collapse mechanism. LimitState:SLAB uses the discontinuity layout optimisation (DLO) method, robustly and efficiently computerising the yield line technique, automatically identifying collapse mechanisms that have corresponding collapse loads very close to theoretical solutions (typically within 1%). In contrast, the traditional method for designing slabs has been Hillerborg’s strip method, which, as a lower-bound method, provides a set of equilibrium moment fields that may be used to size and position the reinforcement. Ramsay Maunder Associate’s (RMA) equilibrium finite element software, RMA:EFE, robustly and efficiently automates this approach to provide a complete equilibrium moment field (which includes torsional moments) with a corresponding collapse load very close to the theoretical solution. When used together, LimitState:SLAB and RMA:EFE lead to accurate plasticity solutions (typically within 1 or 2% of each other) that completely define the limit solution in terms of collapse mechanism (LimitState:SLAB) and moment fields (RMA:EFE). The efficiency of these solutions can be measured in the time taken to solve, typically no more than a few seconds.

Modern Limit Analysis Tools for Reinforced Concrete Slabs By Angus Ramsay, M.Eng, Ph.D., C.Eng, FIMechE, Edward Maunder, MA, DIC, Ph.D., FIStructE and Matthew Gilbert, B.Eng, Ph.D., C.Eng, MICE, M.ASCE,

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

Modern limit analysis tools such as RMA:EFE and LimitState:SLAB, when used in combination, provide the practicing engineer with a way of verifying the solutions (and of ensuring simulation governance), i.e. the engineer can sleep soundly at night knowing that the collapse load has been predicted with good accuracy (since when lower and upper bound solutions agree, the true solution has been found). In the absence of a verified solution, the engineer using the yield line method needs to rely on his or her good judgment to determine a realistic collapse mechanism. The engineer might also be tempted to rely on anecdotal evidence that inherent membrane action within the slab will increase capacity beyond that derived by consideration of flexural strength alone, and/or advice offered by professional bodies that, for example, yield line solutions are generally no more than 10% above the true value [1]. Neither of these, of course, would stand up to a great deal of scrutiny without further verification or validation work. In a recent article [2], a solution to a problem published by the first author in 1997, [3], was presented and used to demonstrate how yield line computations have developed over the last 20 years. Although the original published result was not intended as an exact solution, it now turns out, using modern limit analysis tools, that the collapse load was 40% above the theoretical value! While it is clear that experienced engineers might not have accepted the solution provided in the original publication, it is considered to be useful to less experienced engineers working in this field to document an example where the yield line method has produced an extremely unsafe result. The problem is defined as the Landing Slab Problem and automated methods using meshes of triangular elements together with geometric optimisation are used to demonstrate the state-of-art from the 1990s.

The Landing Slab Problem This problem involves a reinforced concrete landing slab typical of the type found in the stairways of modern buildings. It is a two-way slab in that significant moments are developed in both directions. The slab is simply supported on three adjacent

Figure 1. Landing slab problem.

12 September 2015

sides, and the reinforcement at the top and bottom of the slab provides equal isotropic moment capacity (m). The slab is loaded with a uniform distributed load (q) (the loading arrows are placed at the centre of the corresponding slab portion) as shown in Figure 1, and has a unit load to strength ratio (q/m).

The Automated Yield Line Technique

(a)

(b)

Figure 2. Results from the 1997 Research ( λ = 5.86). a) Mesh; b) Yield line pattern.

In the 1997 work, the mesh shown in Figure 2 was used. This led to the collapse mechanism shown with blue lines, representing element edges where the moment has reached the sagging capacity of the slab and with the symbol λ representing the load factor. An analysis of a more refined mesh in 2011 produced the following results shown in Figure 3. This result indicates that the 1997 solution was not correct – the yield lines, while emanating from the corners of the slab, do not terminate at slab corners. This sort of yield line pattern, which now involves red lines where the hogging capacity of the slab has been reached, appears to provide a qualitatively reasonable representation of the way in which the slab might crack. continued on next page

(a)

(b)

Figure 3. Results from the 2011 Research ( λ = 5.47). a) Mesh; b) Yield line pattern.

(a)

(b)

Figure 4. Results for a coarse unstructured mesh from EFE ( λ = 4.38). a) Mesh; b) Yield line pattern. ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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Figure 6. RMA:EFE Solution of 2014 using 2484 elements ( λ=4.20).

Figure 5. DLO Solution of 2014 using 4000 nodes ( λ = 4.21).

Geometric optimization of the mechanism indicated by the 2011 research is shown in Figure 4 (page 13).

Modern Limit Analysis Tools – LimitState:SLAB The results produced by the DLO-based software LimitState:SLAB [4] are in the form of yield line patterns with the same convention as already described for color and thickness of the yield lines (Figure 5). Note however that whereas the yield lines in Figures 2, 3 and 4 were based on moments, those in Figure 5 are based on rotation (hence the red lines on the supported boundary in Figure 5). This yield line pattern is similar to the geometrically optimized pattern of Figure 4 in terms of the dominant yield lines. However it shows additional yield lines that point to a more complicated collapse mechanism for the slab, with more distributed yielding than suggested in Figure 4. The load factor from the DLO method is 4% lower than that of the geometrically optimized solution already presented.

Modern Limit Analysis Tools – RMA:EFE RMA’s software tool (RMA:EFE) [5] provides a solution to this problem in terms of equilibrium moment fields. A method of demonstrating that these fields do not violate the yield criteria is to consider the utilization ratio. The utilization ratio, which compares the moment field with the moment capacity or yield moment, can be calculated at points in the model as the degree to which the local moment field can be scaled up before it causes yielding. Such a plot is shown for the landing slab in Figure 6, where the contour colors range from zero (blue–unutilized) to unity (red – fully utilized). The regions where the material is fully utilized correspond well with the yield line pattern of Figure 5.

With upper-bound (LimitState:SLAB) and lower-bound (RMA:EFE) solutions to this problem available, the theoretically exact collapse load can be predicted within very tight bounds: 4.20 ≤ λ ≤ 4.21 The load factors are within 1% of each other and thus give an extremely accurate prediction of the theoretically exact value. Erring on the side of safety and using the lower-bound load factor in the calculation shows that the published result of 1997 was 40% too high!

Practical Conclusions This brief article has shown how limit analysis, particularly the yield line technique, has developed over the last 20 years, and has led to modern computational tools for the practicing engineer that are able to bound the theoretical solution to very close tolerances thereby providing strong simulation governance in the design/assessment of reinforced concrete slabs. There is now no need to rely on rules of thumb, such as the ‘10% rule’, or arguments that any over-estimate of capacity through a coarse yield line analysis will implicitly be accounted for by membrane action (which for a given slab may in reality not be present). Also noted in the recent workshop, elastic techniques are increasingly being used in the design of new RC slabs but, as a result, reinforcement over columns becomes significantly greater than indicated to be required when using a limit analysis based approach. The availability of efficient and robust software for predicting the collapse load of reinforced concrete flat slabs now means that one of the original outcomes of the European Concrete Building Project, to encourage engineers to design slabs based on limit analysis techniques [6], can now safely be realized and applied with

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September 2015

confidence to both conventional and more complicated and novel slab configurations. RMA and LimitState encourage engineers practicing in this field to get involved by using and driving the future development of these software tools for their own commercial advantage.▪ Angus Ramsay, M.Eng, Ph.D., C.Eng, FIMechE, is the owner of Ramsay Maunder Associates, an engineering consultancy based in the UK. He is a member of the NAFEMS Education & Training Working Group and acts as an Independent Technical Editor to the NAFEMS Benchmark Challenge. He can be contacted at angus_ramsay@ramsay-maunder.co.uk. Edward Maunder, MA, DIC, Ph.D., FIStructE, is a consultant to Ramsay Maunder Associates and an honorary Fellow of the University of Exeter in the UK. He is a member of the Academic Qualifications Panel of the Institution of Structural Engineers. He acts a reviewer for several international journals, such as the International Journal for Numerical Methods in Engineering, Computers and Structures, and Engineering Structures. He can be contacted at e.a.w.maunder@exeter.co.uk. Matthew Gilbert, BEng, Ph.D., C.Eng, MICE, M.ASCE, is Professor and Director of Research in the Department of Civil and Structural Engineering at the University of Sheffield, UK. He is also the Managing Director of LimitState Ltd, a software company set up to make numerical methods developed in the University available to a wide audience. He can be contacted at m.gilbert@sheffield.ac.uk. A similar article was published in Concrete Magazine (July 2015). Content is reprinted with permission.

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Structural DeSign design issues for structural engineers

tructural engineers have a peculiar vocabulary, when you think about it. What we call “stress” is not much like what psychologists call “stress”. What we call “strain” is not what the spectators think about when watching a weight lifting match. And when we ask what the moment is, a confused general public thinks that in our own strange way we are asking what time it is. What we call something must be understood within the context of what we are talking about; it must be clearly defined. This is particularly important when we get into the writing of a legally binding document. If we mean to mandate something, we need to be clear on what it is that we are mandating.

Masonry Pilaster Definition In the latest version of The Masonry Society’s 2013 MSJC Provisions, or the Masonry Building Code (TMS 402/602), there are certain provisions that apply specifically to the design of masonry pilasters. However, the writers of the code have not yet included a definition for pilaster. So, should we be allowed to impose our own (or Webster’s) definition onto the code? It seems that would be wrong, since the writers of the code obviously had in mind structural members with certain characteristics that were intended to be governed by the specific pilaster provisions. Although the original authors of the pilaster provisions did not include a definition, they did give us clues as to what characteristics they envisioned for pilasters. First we can look at the illustrations in the commentary. Note that in figure CC-5.4-1, titled “Typical pilasters”, all of the illustrations show projections from either one or both faces of the wall. We can also look at the provisions to see what they require. The table of contents for Chapter 5 refers us to Section 5.4 for pilaster provisions. Section 5.4 points us to sections 5.1.1.2.1 through 5.1.1.2.5. Interestingly, section 5.1.1.2 is called “Design of wall intersections”. So, we can assume that they intended that a pilaster would look something like that shown in the figures, and it would have similarities with the characteristics of intersecting walls. Reading the provisions of 5.1.1.2, we find references to a flange that is different than the web of the section. That is the similarity between intersecting walls and pilasters, and is shown by the projections in the illustrations. A pilaster has a web that projects from the flange(s). Engineers on the west coast (the author included, although few would define Utah as “the west coast”) often forget that the provisions of TMS 402/602 apply to both reinforced and

What is a Masonry “Flush Pilaster”? By David L. Pierson, S.E.

David L. Pierson, S.E., is a principal at ARW Engineers in Ogden, Utah. He teaches Masonry Design at Utah State University and is also the current vice-chairman of the TMS 402/602 committee.

unreinforced masonry. Section 5.4 is written to be generally applicable to both reinforced and unreinforced masonry. This clarifies the geometry even further. In unreinforced masonry, any geometry of a pilaster that did not have projections from the wall would be completely impossible to differentiate from a partially grouted wall.

Flush Pilasters When confronted with this, many engineers may ask “But wait – what about those ‘Flush Pilasters’ I’ve been designing for years?” In fact, in the 2008 edition of TMS 402/602, the figure that illustrates pilasters actually included a sketch showing a “hidden” (or “flush”) pilaster. Dr. Richard Bennett, current Chairman of the TMS 402/602 Committee and a member of the Committee when this was changed, shared some of the history as to why the figure was changed. The illustration for the “Hidden Pilaster” was removed from TMS 402/602 in the 2011 edition. This was done in response to a public comment that correctly noted that a hidden pilaster and a partially grouted wall are essentially indistinguishable. Yet the code allowed for a different compression width to be utilized for a pilaster (even a hidden pilaster) than it allowed for bars in grouted cells of walls. This was obviously not appropriate. It was wrong for the code to provide different requirements applicable to the same element. Dr. Bennett shared the exact language from the rationale of the ballot item that deleted that illustration: “In response to public comment 51a, the commentary is changed to remove references to hidden pilasters. Note that this does not preclude the construction shown in Figure 2.1-5(c). Rather it just removes the problem with the conflict pointed out in the public comment relative to the compression width of the bar. This ballot item does not address adding a definition of pilasters to Section 1.6 (public comments 51a and 69). This non-life safety issue will be taken up as new business in the 2013 cycle.” So, the response to those engineers who still want to design “Flush Pilasters” would be … You may call the strengthened portions of walls whatever you’d like; however, since the Pilaster provisions in the code are applicable to a member that doesn’t have a Flush geometric profile, those members are not Pilasters within the language of TMS 402/602. But, as was noted in the rationale of the ballot item quoted above, just because they are not technically “Pilasters” within the definition of TMS 402/602 does not, in any way, mean that

16 September 2015

they cannot be designed and constructed in accordance with this code. It must be clearly understood that those elements always could be and still can be designed and constructed in accordance with the code provisions.

The next question is this – What should be used for “b”, the width of the compression flange? There are a few options. For illustration we will check it three different ways: First, assume b = 16 inches, the width of the element. This is the minimum value that could be used. With b = 16 inches, 2/kj = 6.16 Design Example and npj = 0.0726. The masonry stress controls Take, for instance, the common occurrence the design, with a corresponding np = 0.109. of what might be termed “Flush Pilasters” So, p = A s /bd = 0.0067, and the required A s in sound wall systems that are built along = 0.97 square inches of steel. many roadways. To be technically accurate, Now, check it with b = 72 inches, the maxicall these Strengthened Sections. Typical mum value allowed in section 5.1.2. For this construction might be a 12-inch thick condition, 2/kj = 27.7 and npj = 0.016. Now CMU, with Strengthened Sections occur- steel stress controls the design, with np = ring between 12 feet and 24 feet apart. The 0.017. Thus, p = 0.00106, and A s = 0.68 Strengthened Section is likely16 inches wide, square inches of steel. with reinforcing on each face (to get a maxiSo, if we were very conservative we could use mum “d”) and cantilevers from a concrete pier b = 16 inches. Masonry stress would control or grade beam. The portion of wall between the design, and we would use (1) #9 or (2) these Strengthened Sections is supported ver- #7 bars, each face. By not utilizing a larger tically continuously, but spans horizontally b, I am not being as efficient with the steel. between the Strengthened Sections to resist If we use b = 72 inches, we are using the out-of-plane loads. maximum b allowed in section 5.1.2. Steel Below is one possible way to design these stress governs the design, so the steel is being elements using the Allowable Stress Design used to full efficiency. We would use (1) #8 Provisions. This solution utilizes a method or (2) #6 bars, each face. found in the Reinforced Masonry Engineering Finally, if we use b = 20 inches, which is just Handbook published by MIA (The Masonry 2 inches each side of the section, then np = Institute of America). It is called the Universal 0.064, and A s = 0.72 square inches. This is Elastic Flexural Design Technique. essentially the same answer as using b = 72 Given: inches. The reason for this is that at b = 20 • Wind Pressure per ASCE 7-10 = 30 inches, steel stress now governs the design. psf, Load Combination is 0.6W + D Once this happens, using a larger value for • Construction: 12-inch CMU, 12 feet “b” makes very little difference in the answer. high, with 16-inch wide Strengthened Some engineers might argue that if we use Sections spaced every 12 feet. (2) bars in this “Strengthened Section”, then • f´m = 2000 psi, Medium Weight section 5.1.2 would technically limit b to Block, and Grade 60 reinforcing, so 16 inches (8 inches per bar), based on the Fs = 32000 psi “center-to-center bar spacing” requirement. • Use bars each face, so “d” = 9 inches The author would argue that, since we could • The modular ratio n = 29,000,000 / have used just one bar and only used two Em = 16.1. bars because it makes construction simpler, The Design Loads on the Strengthened we should be allowed to assume that, for this Section for this load combination are: situation, the “center-to-center bar spacing” • Dead Load (self weight of element only) should be considered as the spacing of the = 165 plf x 12 feet = 2000 pounds Strengthened Sections. This is a case where • Wind Load = 18 psf x 12-foot spacing engineering judgment must be allowed to = 216 plf be exercised. The design moment on the section is 216 In either case, the wall would then be x 122 / 2, or 15,550 lb-ft (187,000 lb-in). designed to span horizontally between these (Note: some engineers may wish to reduce this elements, probably with (2) horizontal bars moment by the resisting moment provided by in bond beams at 48 inches on-center. the dead load of the element. By choosing not Whatever you want to call these, this conto, the author is perhaps a bit conservative) struction always has been and continues to The allowable Fb in the masonry due to be allowed. These elements could also be flexure is 0.45* f´m, or 900 psi. This must be designed using other design methodologies, reduced by the axial compression stress due based either on Allowable Stress Design or on to the weight of the element, which is 11 psi. Strength Design. Results would be similar, if So, use Fb = 900 – 11 = 889 psi for flexural not identical. design (see code section 8.3.4.2.2). STRUCTURE magazine

September 2015

Prescriptive Provisions Beyond section 5.4, the only other significant provisions related to pilaster design are found in 7.4.3.2.5., where additional requirements are imposed if the pilaster is supporting a discontinuous stiff element. Note that ties are required in pilasters only if: 1) the pilaster is supporting a discontinuous element as noted in 7.4.3.2.5, or if 2) the designer is relying on the steel to support compression loads (in which case the element essentially becomes a column), or if 3) the shear stress is so high that ties are needed to resist shear (which is theoretically possible but nearly impossible in practice). There is a caveat to this entire discussion. It applies to pilasters and strengthened sections of walls in reinforced masonry walls that are laterally supported at floors and/or a roof. Regardless of whether or not such “pilasters” are projecting or are flush, the design engineer should recognize that the provisions of ASCE 7 section 12.11.2.2.7 must apply. In other words, although ASCE 7 does not include a definition for pilaster, common sense indicates that for reinforced masonry, whether or not the strengthened section is projecting from the face of the wall, it is, for the purposes of this section of ASCE 7, a pilaster. It is possible that in the next edition of TMS 402/602, (anticipated to be the 2016 edition), additional definition will be given to clarify what a pilaster is and what it is not. If so, this will be simply a clarification, so that engineers do not have to wade through the provisions in order to determine if what they are designing is a “Pilaster”. It will not change the fact that strengthened sections of reinforced walls can still be designed and constructed, no matter what they are called. Finally, the next time you are trying to determine the limit on how much reinforcing you can put into that masonry wall you are designing, remember that ρmax has a very different meaning to you than it does to a spectator at the Harvard-Yale Regatta.▪ Although Mr. Pierson is affiliated with TMS because of his position on the TMS 402/602 committee, this article represents only his opinions. This should not be construed as an official position statement from TMS.

Historic structures significant structures of the past Schneider’s Plan for Niagara Bridge.

he Niagara River gorge had long separated the United States from Canada. It varied in depth up to 239 feet and in width generally between 800 and 1,000 feet between the Falls and Lewiston. Around 1836, suspension bridges were proposed by Francis Hall at Lewiston-Queenston and just above the falls. Charles B. Stuart, in 1845, then working on the location of the Great Western Railway in Canada, was looking for a way to connect his line with the Rochester and Niagara Falls branch of the New York Central. He proposed to span the gorge with a suspension bridge just above the Whirlpool. Many thought his idea foolhardy, as the only suspension bridges in the United States, other than some Finley bridges left over from the early part of the century, were Charles Ellet’s Fairmount Bridge over the Schuylkill River built in 1842 and John A. Roebling’s suspension aqueduct built across the Allegheny River in 1845. Stuart sent a circular letter to “a number of the leading Engineers of America and Europe, asking their opinion of the undertaking.” Of those who responded, only four thought the project feasible. Stuart wrote, “Charles Ellet, Jr., John A. Roebling, Samuel Keefer and Edward Serrell, alone favored the project...” Ellet’s proposal was accepted, with modifications, for the sum of $190,000. The span would be 800 feet with a deck width of 28 feet. The deck would have two carriage ways, two footways and one railway track in the center of the floor. Ellet started by building a 9-foot wide temporary bridge but, after charging tolls for people to cross, he had a falling out with the Company in 1849. John A. Roebling took over the project in 1850, offering to build the bridge for $180,000 and to subscribe to $20,000 in stock in the bridge company. He changed his original design from a single deck structure to a double deck structure, with the railway on the top level and carriage and footways on the lower deck. Work would not commence on the Niagara project until 1852, with Roebling providing all engineering services including design as well as construction supervision. His company

The Niagara Cantilever Bridge 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.

also supplied a significant amount of wire to be used in the bridge. He completed his 822-foot span double deck bridge in 1855. A one-track railroad ran on the upper deck (22 feet wide), and pedestrians and carriages passed on the lower deck (15 feet wide). In 1874, T. C. Clarke, of Clark & Reeves Company and later Phoenix Bridge and Union Bridge Companies, was asked by the manager of the Western Railway of Canada to “report on the best mode of construction, necessary time required, and cost of a double track iron bridge.” He recommended, “a braced arch, hinged in the center and at the springing. The clear span was 430 feet, and the height or versed sine 175 feet. The arches were to have been erected by corbelling out as was done at St. Louis.” In 1882, the Michigan Central Railroad was ready to build its own bridge at a site near the suspension bridge. On October 13 they requested Charles Conrad (C. C.) Schneider to submit a proposal. They wanted “an estimate for a double-track railroad bridge of 900 feet clear span, for the purpose of ascertaining the probable cost of bridging the Niagara below the Falls, near the Railroad Suspension Bridge, intimating that a braced arch reaching from cliff to cliff might be the proper design for the proposed structure.” Schneider had also been given the design for an iron bridge over the Fraser River, which flowed southerly into Puget Sound just north of the United States border. The Fraser River was a fast flowing stream which precluded the placement of falseworks in the river bed. Schneider, based upon his previous exposure to the Blackwell’s Island Bridge competition and Smith’s success at High Bridge, decided to build a bridge using a cantilever technique. He completed the design of the 525-foot span, located 125 feet above the river, in the spring of 1882. The directors of the line decided to have the iron rolled and fabricated in England, a result of Prime Minister MacDonald’s tariff program that made United States iron and steel excessively priced. Canada had not as yet developed its own iron and steel industry to any significant degree. Due to the slowness of the delivery of the Fraser River Bridge iron (it reportedly took almost six months for the ship carrying the iron

18 September 2015

Layout of span and reactions, showing suspended span.

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to Canada to make it across the Atlantic), it would not be completed until 1887 or four years after the Niagara Bridge. It lasted until 1910 when it was taken down and re-erected, one of the beauties of a pin-connected structure, across a chasm, appropriately called the Niagara Ravine, on a branch of the Canadian Pacific near Victoria, B. C. Upon receiving more exact topographic information at Niagara, Schneider “decided that the cantilever plan would be most feasible and economical for this location...” He submitted his completed design to the Central Bridge Works of Buffalo, New York. They in turn submitted a tender to the Niagara Bridge Company that was accepted by the Board of Directors on April 11, 1883. Based upon better survey and boring information, he modified his pier locations which changed the span lengths of the cantilever. He also decided to use wrought iron primarily, with some steel. He chose to use Squire Whipple’s double intersection pattern (STRUCTURE magazine, May 2015), for his anchor and cantilever spans that George Morison, his mentor, used on his Missouri River Bridges and C. S. Smith used on his earlier cantilevers. On the short suspended span he, used a single intersection truss. He wanted to have his piers of iron just as Smith had done at the High Bridge, but he decided to bring his iron work up parallel, in a direction perpendicular to the axis of the bridge. In order to make the structure determinant, he omitted the diagonals in panel BC; it is evident that no other strains can be transmitted between B and C than moments, the points of support being practically reduced to 2, and the shearing strain in panel BC becoming 0. Schneider took great care in insuring that all the iron and steel, particularly the steel, met the specifications. In accordance with his experience “with steel for structural purposes which had

STRUCTURE magazine

September 2015

Niagara Cantilever.

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to be made according to a specification, there have always been considerable delays, and this case was no exception to the rule. The records of the tests will show that the steel which has been accepted was of a good uniform quality.” With his design complete and quality of material acceptable, the fabrication of the structure took place in the yards of the Central Bridge Company. The erection technique worked out by Central Bridge Company and Schneider became the pattern that would be followed on many cantilevers in the future. They began by building the anchor spans from falsework resting on the rock banks and the towers by travelers off of the anchor span. The travelers worked outward on each cantilever arm until they reached the end of the cantilever span. The suspended span was 120 feet long, and the maximum reach of each traveler was 40 feet. Schneider did not want the traveler to go beyond the end of the cantilever span, as he did not want to overload the span or the anchorage. This left 40 feet of suspended span which could not be erected by the travelers. He handled this by placing wooden beams across the 40-foot gap and erecting the rest of the truss by hand methods. The speed at which the bridge was erected was as impressive. Schneider wrote: The first metal of the cantilever shore arm on the American side was placed Software and ConSulting

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Traveler and erection sequence, showing falsework and traveler.

on the falseworks on September 25 th, and erection completed on October 15 th. The erection of the cantilever shore arm on the Canadian side was commenced on October 8 th, and finished on October 22 nd. The traveler on the American side was completed on October 25 th, and erection of the river arm commenced on October 28 th. The traveler on the Canadian side was completed on October 31 st, and erection of the river arm commenced on November 4 th. The last connection was made on November 22 nd, at 11:55 A. M. The travelers and falsework were removed and the first track laid on December 6. The formal opening and testing took place on December 20, 1883. The bridge contained almost 4.5 million pounds of iron and steel, with about 70 percent of it being wrought iron. What Schneider and Central Bridge had done was to erect a new style bridge using new techniques, over 900 feet long and 230 feet over the Niagara River, in less than two months. The entire Niagara project, which started with foundation work on April 15, took only slightly more than eight months to complete. The bid price for the entire project was $680,000. In 1900, or seventeen years after construction, the bridge was reinforced without material interruption of traffic by the addition of a new center truss midway between the original trusses and supported on a new tower trestle and anchorage pier on each bank. “The new superstructure has the same

STRUCTURE magazine

September 2015

general outline and dimensions as the old one, and the details correspond so far as possible to those of the old members...It was decided to strengthen the bridge, not so much because it is unsafe under present loads but because the near future will evidently see trains and engines much heavier than are now being run across the bridge and heavier than was thought entirely safe for the original structure. The new truss is intended to be 50 percent stronger than either of the old trusses...In order to insure perfect safety against any uplifting of the anchorages, anchorage pits are being sunk about 25 feet under the end piers and the anchorage made there for the new truss in addition to the weight of the old pier...The material for the work is being furnished by the Detroit Bridge & Iron Works for plans made under my supervision [Benjamin Douglas, bridge engineer for the Michigan Central)...and the erecting is being done by the regular erecting gang. “ C. C. Schneider’s brainchild was reinforced without any apparent involvement by its creator. Schneider was still active in 1900 as Vice President in charge of Engineering for the newly formed American Bridge Company, located in New York City. The bridge was taken out of service and demolished in 1925 after having a useful life of over forty years. It was replaced by a steel arch bridge located between Schneider’s Bridge and Roebling’s Suspension Bridge (which was replaced with an arch by Leffert L. Buck in 1897).▪

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Fundamentals of Hardened Concrete Monolithic concrete with a compressive strength in excess of 3500 pounds per square inch (psi) is watertight, except at any irregularities in the structural element. Typical locations where irregularities occur include overhead decks, floors, and walls that have cracks, honeycombs, joints, mechanical/electrical penetrations, and form-tie supports. Hairline cracks in excess of 1/1000 of an inch (i.e. 1 mil) commonly leak water if subject to hydrostatic pressure. Water leakage rate and volume, or quantity, is related to pressure and crack width.

updates and information on structural materials

Concrete Cracking When concrete is freshly cast, its temperature is often between 60º and 90º F. Depending on the in-situ form, materials, temperature, environmental conditions, and composition of the mix design, concrete hydration may generate significant additional heat. Thermal expansion of the semi-plastic structural element will occur and, depending upon local restraint, may cause micro-cracking. Depending on local restraints, minute small cracks (defects within the cement/aggregate matrix typically so small they can’t be seen by the naked eye) develop externally and internally. After the forms are removed, the concrete continues to shrink from both cooling and loss of water. This process varies with environmental conditions and may create cracks capable of water leakage within hours of form removal, and within days after wet curing. For most structural elements less than 14 inches thick, it takes about 5 years for shrinkage to subside. In this time, the cracks initiated by thermal contraction become much larger. These cracks, depending on reinforcing, sectional dimensions, mix design, and restraint conditions, can be as large as 5 to 50 mils. If subjected to water under hydrostatic pressure, serious leakage will occur. Ingredients for Corrosion Corrosion in reinforced concrete requires three basic ingredients; oxygen, water, and an electrolyte medium. Fundamental to corrosion mitigation is minimizing at least one of these three basic ingredients. Issues from Leakage One of the biggest concerns with water leakage in heavily reinforced concrete is that the time for the onset of corrosion is shortened. It is well understood that if you eliminate oxygen and water from the immediate environment around reinforcing steel, corrosion is generally minimal and essentially mitigated. When through-element cracks

Monolithic concrete with a compressive strength in excess of 3500 PSI is watertight, except at any irregularities.

occur from outside to inside face, allowing air or dissolved oxygen in the water to interact with the steel, all three of the critical items are now available for corrosion to occur. In addition to corrosion, water leakage can bring salt and various stray minerals that can exacerbate other issues within the concrete, e.g., sulfate attacks. External issues with water leakage are many – ice buildup, slip problems, treatment of contaminated water, and potential mold issues.

Proper Procedures and Protocol for Interception Grouting By Brent Anderson, P.E.

Fundamentals of Interception Grouting Directional Drilling The objective of interception grouting is to make the concrete element monolithic. This can be achieved by pressure injecting a resinous material through one or both concrete element faces (surface mounted ports), or by drilling at a 45-degree offset to the defect and injecting into the defect in the center third of the concrete element section (interception grouting). The importance of drilling into the center of the concrete element is that, during grouting, the resinous material should flow equally to the inside and outside face of the concrete section in a uniform manner. If drilling into the interior third of the section, grout flow will not extend to the exterior. Drilling into the outer third of the section will unlikely allow grout migration to the interior. By proper placement of drill holes, grout flow will intersect from bottom-to-top or side-to-side with a relatively high degree of reliability. Long-term

STRUCTURE magazine

Brent Anderson, P.E., is the Moisture Control Solutions Team Leader at Structural Technologies. He serves on ACI 332 Residential Concrete and previously served on ACI 515 Protective Coatings for Concrete. Brent can be reached at banderson@structuraltec.com.

Typical water leakage paths.

grouting solutions intercept the defect in the center; short-term solutions allow shallow drill depth holes. In addition to crack interception at the concrete element’s center third, most quality contractors alternate directional drilling on each side. Drill Hole Spacing Generally, the rule of thumb is that drill hole spacing should be one half to two-thirds the concrete element thickness. This allows an overlap of about 20 to 30 percent between drill holes. Drill hole spacing up to the width of wall element can be done if cracks are relatively large – i.e. 50 to 100 mils wide. Interior and/or exterior steel can influence the drilling angle based on its density and location. Angles of 30º to 60º are not uncommon provided that interception drilling is done in the wall center. Because cracks vary in direction, drilling should be 20 to 25 percent deeper for interception grouting than what the typical calculations dictate. Drill hole diameter is not critical and can be left to contractor preference. Cleaning Just as important as intercepting the crack at the element midsection is cleaning the drill hole of debris prior to setting any ports. Injection drill holes should be blown out with high pressure air and then flushed thoroughly with a water jet. Some contractors even push and flush a wire bristle brush down the drill hole and scrub the area of intersection to remove surface debris. Crack Flushing The next important aspect is to put a port on the surface and flush the crack. Flushing the crack is important for two reasons: 1) To push out any mineral deposits (clay, silt) that may have accumulated in the crack, and 2) If water is pumped and does not make it to the surface of the concrete, grout will not make it through either.

These are often questions as to whether or not some kind of acidic material (e.g., phosphoric or muriatic) should be used. Generally, it is an acceptable approach, but it should come with some safety precautions and the use of proper personal protective equipment to keep acid away from the face. Acid washing the drill hole and the crack improves the bond ability of any type of resin that is injected into the crack later. If the crack has debris and mineral deposits, the effectiveness of the grout will not be as monolithic as needed, and secondary or minor leakage could still occur. Pressure Interception grouting should be done in a way that the internal hydraulic pressures of the grout never exceed the tensile strength of the concrete. The tensile strength of concrete is 10% of the compressive strength. Most concrete that interception grouting will be performed on will have a tensile strength of 300 to 500 psi. It is recommended not to use pumping grout pressures in excess of 500 psi. In so doing, the concrete surface may spall where the drill holes exist and/ or the pressure may hydraulically fracture the concrete and create additional cracks. A word of caution, use of high viscosity resins may lead to internal damage of the concrete. High viscosity resinous materials are not as user friendly as low viscosity injection materials. For comparison, water has a viscosity of one centipoise – so grouts that have values of 50 to 300 centipoises means that they are 50 to 300 times more viscous than water. It is not uncommon for contractors who do not have a good understanding of viscosity and crack width to use resinous grouts with 300 upwards to 500 centipoises and pressures up to 3000 psi to accomplish placing resinous material within the crack. Grout Delivery There are three types of delivery systems generally utilized: small hand operated pumps,

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September 2015

It is important to intercept the crack at the center third so that the resinous material flows equally to the inside and outside face of the concrete section.

small electric operated pumps, and high volume air driven or piston driven pumps. Most hand and small electric driven pumps are for single component resins. The larger piston pumps can be used for 1-3 components. Small electric pumps require minimal maintenance. However, after several uses the pumps are discarded and new ones are purchased. Others prefer to buy the large piston drive, both single and multi-ratio. What’s important is that these pumps have a capacity of ¼ gallon per minute and have pressure capabilities up to 750 psi. Injection Packers There are basically three types of injection packers – button head, grease zerk, and ball valve quick connect. The advantage of the grease zerk packers is that they are inexpensive and can be discarded after one use. Button head packers are similar and usually discarded after one use. The ball valve quick connect packers are more expensive, but can be reused multiple times. Another advantage of the ball valve is that you can open and close the valve to monitor water or grout flow. Button head and ball valve quick connect packers generally do not restrict grout flow and increase pump gauge pressure during application. Disadvantages of zerk packers are that they cannot be opened and closed to monitor grout movement and they are very restrictive to grout flow, requiring about 100 to 200 psi gauge pressure just to move most grouts through them.

Causes of Premature Grout Failure There are 4 basic causes of premature grout failure:

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FA S T ER STRONGER MORE DURABLE To achieve the right mixing ratio of water to grout, a multi-ratio pump should be used.

Most quality contractors alternate directional drilling on each side.

Conclusion It is important for engineers and contractors alike to remember that the grout viscosity needs to match up with the crack width, and the grout chemical resistance needs to match the exposure. The most successful grouting contractors have a good knowledge of chemical resistance and have good field experience in developing techniques that allow them to get low viscosity grouts to migrate deeply within finely cracked concrete.▪

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1) Improper drilling and delivery It is not uncommon for contractors to drill directly into the crack or too close to the surface. By doing this, a seal is created that is 1/3 to ½ of the crack depth and water under hydrostatic pressure is still within the concrete element. Very little flexural movement causes leakage to recur. 2) Inadequate mixing ratio of water to grout during application Most contractors are taught by manufacturers that pre-wetting the crack prior to urethane grout injection is all that is needed to activate the material. This would likely be the case of the wall 4 to 6-inches or less in thickness. Wall and floor sections greater than 12 inches would not fit the criteria however, and a multi-ratio pump for injecting water reactive urethane grouts should be used. Some contractors prefer to use two small electric pumps – one to inject urethane, one to inject water – and then rotate a few strokes of water to several strokes of grout thinking they are getting good cross-polymerization of water to urethane. While this may seem a viable solution because the first grout that comes to the surface appears to be fully reacted, it is very common to have areas of water deprived urethane grout within cracks and other defects. When these conditions are subjected to high temperatures in the environment (in excess of 100 to140º Fahrenheit), it is common to see a brown, unreacted urethane resin extrude from the cracks anywhere from 2 months to 2 years after the initial grouting. This urethane resinous material has now contaminated the crack for future injection. Many

contractors have found that the only viable way to seal cracks with unreactive grouts is the backside grouting method. 3) Excessive wall movement Excessive movement is most prevalent when the concrete is subject to outdoor temperatures – i.e. exterior tanks, retaining walls, exposed foundations, etc. Most resins have some degree of flexibility. It is not uncommon that during warm to cold cycles, a 5 mil crack will open to a 10 mil crack. Most resinous grouts, even though they are called flexible, cannot sustain repeated opening and closing of the crack and will fail. Grout adhesion to the substrate may fail during expansion and contraction of the crack if surface contaminants on the grout sidewall are prevalent. 4) Chemical attack Chemical attack is very common in the industrial environment, and this type of issue usually takes several years to work its way through the grout matrix. Residue hydrocarbons within water will commonly attack many of the grout formulations. This is exacerbated if chemical attack and thermal expansion/contraction are occurring simultaneously.

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Structural rehabilitation renovation and restoration of existing structures

his series of articles discusses a number of commonly encountered structural issues on renovation and restoration projects that focus on historic houses of worship, and provides guidance on ways to address them. Parts one, two, and three of this series dealt with foundations, wall systems, and roof framing in historic houses of worship. This article addresses interior architectural components and finishes. Architectural components and finishes are often the most visible and identifiable elements inside historic houses of worship. They define the ambiance and “feel” of the space, reflect the cultural and religious sense, and are often a testament to history and development of communities in which these structures were built. Given their effect and significance, a lot of thought should be placed on their appearance, performance, and serviceability. However, if designed or installed improperly, if exposed to severe or unplanned conditions, or if not regularly maintained and repaired, they may undergo accelerated deterioration and decay, or can be subject to distress that can cut their expected service life short. Therefore, when planning repair, renovation, or rehabilitation projects, understanding the basic material properties of common architectural components and finishes, addressing their potential vulnerabilities and exposure limitations, and considering structural support, compatibility, and constraint issues, is paramount.

Divine Design: Renovating and Preserving Historic Houses of Worship Part 4: Architectural Components and Finishes By Nathaniel B. Smith, P.E. and Milan Vatovec, P.E., Ph.D.

Wood Components and Finishes 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.

Wood is a natural building material known for its workability, high strength-to-weight ratio, and durability. Wood’s natural beauty is unequaled. Wood is also the only truly organic building product that is renewable and sustainable. As such, wood has successfully been used for centuries in a structural role and, perhaps more prominently, as a go-to material for architectural components and decorative finishes in houses of worship. Its ability to be milled and carved, and its ability to receive stains and paints, has made it a great option for finish work and flooring, and exposed structural and architectural members. Wood, however, can also be challenging to work with. It comes in many varieties (species), with each variety having its own unique characteristics. Sawn lumber can have natural-growth defects (e.g. knots, splits, excessive slope of grain). Wood properties can vary significantly even between pieces of lumber taken from the same tree. The makeup of the cell structure of the tree trunk causes sawn wood to be orthotropic; it behaves

differently in three principal orientations (directions), defined basically with respect to the configuration of a tree trunk. The orthotropic behavior comes into play in terms of strength and stiffness differences, resulting in a number of design and detailing consequences (e.g. never load wood in tension perpendicular to grain). It is also a large factor when it comes to physical properties, most notably orientation-dependent differences in shrinkage and swelling (dimensional-change reaction to moisture intake and release in response to environmental changes), durability, and, last but not least, appearance. Finally, wood is susceptible to attack by microorganisms, which requires special care and consideration both in design and in-service. Because of all this, optimal use of wood often depends on special knowledge that requires integration of material science, engineering, and familiarity with construction practices and detailing. When it comes to structural design, engineers tend to place high importance on the mechanical properties of wood components, which typically includes variability in properties, natural-growth characteristics, and orthotropic-behavior considerations. By and large, this is accounted for through established design processes (e.g. stress grades and associated design values, etc.). Vulnerability to biological attack and propensity to dimensional change in service are generally addressed through standard detailing. Often, however, issues that affect non-structural wood components in service, and particularly in historic structures, involve non-standard use or detailing, or are not within the domain of a structural engineer. In these situations, architects, builders, and other practitioners that design, fabricate, and install wood components and finishes are required to pay special attention to a number of additional parameters, often related to all phases in the “life” of the wood component: harvesting, milling, drying, conditioning, installation, environmental exposure, geometric and boundary constraints, type and duration of loads, etc. The most common problems with wood in service are related to deterioration from unanticipated exposure or to distress resulting from dimensional changes. Both of these problems are driven predominantly by exposure to and effects of moisture (either as humidity in air or as liquid water). In general, moisture is considered to be the number one contributor to problems with wood and its performance in service. While wood deterioration due to decay (a.k.a. rot) from moisture exposure is likely the greatest contributor to loss of wood material in service in the world, the implications of water exposure, the resulting change in properties, and ultimately the damage caused by fungal action will not be discussed in detail here; the focus of this article will be placed on dimensional stability and associated issues.

26 September 2015

Wood elements and components meant for interior use will typically be in what is considered a “dry” condition immediately before, during, and after installation; they would have undergone either an air or kiln-drying process before delivery. However, the actual moisture content of interior wood, while in general considered dry, will fluctuate, sometimes significantly, in wood’s attempt to be in equilibrium with its environment. As the temperature and relative humidity (RH) of air surrounding wood components fluctuate (seasonally or otherwise), the wood’s moisture content (MC) will fluctuate as well, albeit with some inherent lag. As the MC goes up or down, wood elements will swell or shrink, respectively. Even for interior use, the expected yearly MC swing of wood components could be on the order of 5% (especially in spaces where RH is not controlled), which, depending on wood species, can translate into approximately 1 to 2% of cross-grain shrinkage or swelling (Wood Handboook, Forest Product Laboratory, 2010, Tables 4-2 and 4-3). To further complicate things, cross grain movement is not uniform; expected movement in the tangential direction is approximately two times larger than in the radial direction (relative to orientation of tree rings). Therefore, the extent and uniformity of movement will depend on the orientation of the wood grain within the piece, which is dictated by where the piece was milled from the tree. Given all of the above, it is not surprising that dimensional compatibility and restraint problems are often encountered with wood in service. If not designed or installed properly, shrinkage will cause joints between adjacent pieces of wood to open, whereas expansion will make the joints tight, and, in extreme situations, buckling or other distress will ensue. The buckling problem is often most pronounced in wood floors that are exposed to high levels of moisture (e.g. leakage), floors that were installed too wet (or on the high end of the expected equilibrium spectrum), or are not detailed to allow for sufficient expansion without causing distress. Other types of architectural components or finishes may also be subject to restraint-related distress, if not detailed to allow movement. It is not uncommon to see infill boards or trim panels crack or otherwise become distressed because they were too “tightly” connected to their frames. Veneers and other thin elements may crack or be subject to localized buckling (waviness) when “married” to a substrate that does not undergo similar moisture-driven dimensional changes. Depending on the orientation of the grain, individual members not restrained against movement can also be subjected to distress.

Buckled wood flooring.

Cupping and twisting may occur even when wood undergoes small MC changes in service because of the difference in cumulative dimensional movement between the tangential and radial directions. Simply put, wood will move with moisture fluctuations, and it does not like to be constrained against that movement. If it is, problems that may be difficult or very expensive to address will likely occur. Ironically, engineers, who are typically not involved with design, detailing, or specifying nonstructural components and finishes, are often best equipped to deal with existing issues, or to predict (and therefore avoid) problems in-service related to wood material behavior. Tools and knowledge exist. Having foresight, and respecting wood behavior and its response to the design environment, is key. Similarly, proper detailing, especially if developing new, non-vetted systems, is paramount. Finally, acclimatization, selection, treatment (if any), and proper installation of wood components should all be carefully considered and incorporated into the specifications for renovation and remedial projects.

Plaster Finishes Plaster is one of the most common interior finishes found in historic houses of worship, with typical applications for wall and ceiling surfaces. Ornate, molded plaster finishes (trim, finials, florets, etc.) are often incorporated into the overall finish work. While plaster is a tried and true finish that has been used for centuries,

Splitting of infill panel in wood bench.

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it is not without its limitations. Plaster in its simplest form is a combination of hydraulic lime, sand, and water. Water reacts with the hydraulic lime, causing it to chemically bond to the sand particles creating a solid substance. The plaster stays in a “fluid” state for a limited time, allowing it to be applied by trowel to walls and ceilings, or it can be placed into molds to take specific shapes prior to solidifying. Plaster for walls and ceilings is typically applied in two layers. The base layer, often called a “brown coat,” contains relatively coarse sand particles and helps give the plaster its strength. The top coat, or “finish coat,” typically contains fine sands, which gives the top coat its smooth finish. Plaster can be applied directly to masonry or terra cotta, as the hydrated lime will bond with stone and clay particles within these materials. However, plaster for walls and ceilings is often supported by lathe, which is typically wood or metal mesh. Older construction typically features a wood-lathe substrate, which is a series of parallel wood strips about ¼ inch thick, 1 inch wide, spaced about ¼ inch to ½ inch apart. When the plaster is applied to the lathe, it is pushed through the spaces between the wood strips and tends to ooze over the backside, creating a plaster “key”. This “key” helps hold the plaster in place. A similar process occurs with metal lathe as the plaster oozes through the wire mesh. Plaster keys are a critical component of overhead plaster applications. Sufficient keying needs to be created to hold the ceiling in place. Lack of adequate keys can cause portions of the ceiling to become loose, to debond, and potentially fall. Plaster keys in ceilings can also break over the life of a building through the course of regular maintenance and alterations. Installation of new lighting or mechanical equipment from within attic spaces can often break keys, resulting in the potential for ceiling failures. Detecting failures or distress in plaster keys is often difficult and may require specialized access and equipment (e.g. minimally-destructive testing instruments such as boroscopes). continued on next page

Typical wood lathe plaster ceiling with broken keys and lathe from light fixture installation.

There are numerous available options to address broken keys. Several of the more common options include: • Remove and Replace: One option to address broken keys is to remove the affected portion of the plaster and replace it. This will certainly address the issue but can be cost prohibitive due to access and coordination constraints (scaffolding likely required). It can also be a time consuming process as the plaster needs to be removed, new plaster installed and allowed to dry, then sanded and painted to match the surrounding areas. Special blending of paint is needed to match the surrounding areas as well. Also, plaster on metal lathe will likely require new lathe to be installed, as salvaging the existing lathe may be difficult. • Additional Mechanical Support: The affected portions of the plaster can be reattached to wood lathe through mechanical means, such as screws. Screws with large plastic washers are typically installed through the plaster into the lathe or ceiling framing. This option also requires access from the underside of the ceiling to allow for placement of a skim coat of plaster over the fasteners to conceal them, followed by a fresh coat of paint. • Cover-board: In some circumstances, placing a new ceiling below the original and fastening it through the existing ceiling is a preferred option. Gypsum drywall, often used in this application, is placed on the underside of the existing plaster. With this option, care should be taken to ensure that the

new drywall sheets are supported by the ceiling framing and not the wood lathe. Wood lathe in historic structures is often fastened to the ceiling framing with cut nails (tapered nails cut from flat stock), which may withdraw under the additional load of the drywall. • Consolidation: Another option that seems to be gaining popularity, due to its minimally invasive nature, is a consolidation process. The process includes applying an acrylic resin to the backside of the plaster, typically from within attic spaces or through small holes drilled in the plaster. The resin permeates into the plaster and then cures to create a solid mass that is stronger than plain plaster. This process can reestablish keys, fill in small cracks, and strengthen the plaster. This process also has the benefit of having a minimal impact on the finished face of the plaster. Choosing the correct plaster remediation option depends on numerous factors, including the condition of the existing ceiling, ceiling framing, and architectural features of the ceiling. If the ceiling is of architectural significance, options that leave the existing ceiling in place should be explored first. While leaving a ceiling in place may be the ultimate goal, understanding the limitations of the plaster and support system is a critical step in order to make an informed decision. Structural engineers are often called upon to evaluate the plaster-ceiling support system to determine if it has adequate capacity to support additional ceiling loads (cover-board) or other

Plaster ceiling framing can be quite complex.

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architectural features (lighting, insulation, etc.), or in some cases partial removal to accommodate access. In other cases, these framing systems require evaluation to determine if their condition renders them inadequate to continue carrying the ceiling loads. Understanding the ceiling-framing layout is a key step in this process. The support framing for flat-ceiling systems is typically straightforward, with a series of parallel joists supporting the lathe and plaster; these systems are easy to assess and analyze for additional loads. However, many houses of worship are not flat and feature very intricate ceiling geometries, often with gothic arches. Despite the large level of redundancy, the framing for such ceilings is often independent from the main roof structure and can be much more difficult to analyze due to complex geometry, a multitude of components (with various stages of effectiveness or deterioration that may be difficult to quantify), unclear load paths, and lack of accessibility.

Non-Standard Components and Furnishings Many renovation projects in historic houses of worship call for installation of new furnishings, or components that need to be incorporated with and supported by the existing structure. These new components may be related to accessibility (new ADA ramps or elevators), improvement of mechanical systems (e.g. new chiller units), or could simply be related to aesthetic or other improvements (new organs, chandeliers, heavy furniture, statues, etc.). While structural engineers will often consider

the load associated with furnishings as part of the uniform live load, some of the proposed components can be quite heavy and may require special attention. For example, many religious furnishings and statues are made of solid stone, are quite heavy, and require proper support analysis and design. Often, the hardest part of determining how to support the new loads is actually determining what the load is. Some of the furnishings are old and do not come with established weights, so an estimate needs to be made. Sometimes, fairly detailed historical or material research is needed to gain a comfortable level of understanding of the component materials and geometry, and to be able to develop reasonable loads for use in design of the support components. Similar to other situations where structural modifications to the original structure are proposed, addition of heavy loads requires that the load path and all elements that may be affected along it be well understood. Given the likely absence of any structural drawings, this frequently requires a probing program where finishes are removed to expose the underlying structure. This process is not always straightforward and may require several iterations before full or sufficient understanding of the load path and the involved structural components is gained. In addition, material characteristics of

or alternate load paths that can be evaluated, including sistering, shortening the span, adding supplemental supports or cross section to the existing members, etc. If the loads are excessive, it may be easier to provide an alternate load path through installation of new members or systems, in lieu of reinforcing. The best option will depend on the specifics of the furnishings, the existing framing, and the ultimate needs of the owner. Economics and ease of installation, along with the needs of the surrounding programming space all need to be considered when making recommendations.

Non-standard furnishings require proper support.

all the involved structural components need to be understood. Historic buildings often feature a variety of structural framing materials including wood, timber, cast iron, and steel, and it is not unusual to see any combination of these within the load path. The material properties for each can be difficult to ascertain, and, if conservative estimates cannot yield effective design, sampling and subsequent laboratory testing may be required. If a deficiency in the load path is found, there are numerous options for strengthening ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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September 2015

Conclusion While not always considered to be in the wheelhouse (or even within the scope of services) of structural engineers, consideration of mechanical and other material properties of non-structural components in the design phases of historic renovation projects is critical. Regardless of whether the project revolves around design and installation of new systems or evaluation and retrofit of existing systems, special care aimed at understanding and anticipating the in-service behavior of architectural components and finishes is required of everyone involved.▪

Codes and standards updates and discussions related to codes and standards

rovisions for the design of cast-in-place and post-installed anchors were introduced into the American Concrete Institute (ACI) publication Building Code Requirements for Structural Concrete (ACI 318) in 2002 (ACI 318-02) via Appendix D – Anchoring to Concrete. Since ACI 318 is referenced in the International Building Code (IBC), these provisions are thereby incorporated into IBC Chapter 19 – CONCRETE. Cast-in-place headed bolts and headed studs are generic products that can be used directly with Appendix D provisions. However, post-installed anchors must be qualified for use with the provisions of Appendix D due to the inherent diversity of adhesive and mechanical anchor products. For example, hybrid adhesives have different performance and behavioral characteristics versus epoxy adhesives. Likewise, epoxy adhesives can vary widely in performance due to differences in their chemical makeup, and in their installation requirements. Given the wide array of post-installed anchor types and performance characteristics, ACI developed two standards to qualify these anchors for use with the Anchoring to Concrete provisions in the ACI 318 code. ACI 355.2 Qualification of Post-Installed Mechanical Anchors in Concrete was first printed in 2002. ACI 355.4 Qualification of Post-Installed Adhesive Anchors in Concrete was first printed in 2011. These standards serve as baseline provisions for two International Code Council Evaluation Service (ICC-ES) Acceptance Criteria: AC193 Acceptance Criteria for Mechanical Anchors in Concrete Elements (first printed 2002) and AC308 Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements (first printed in 2006). AC193 and AC308 contain programs to evaluate an anchor system for recognition under an IBC version adopted by a local jurisdiction. Design parameters and data from this evaluation are given in an ICC-ES Evaluation Service Report (ESR). Therefore, a post-installed anchor system evaluated per AC193 or AC308, having an ESR noting recognition under an IBC, can be designed using the Anchoring to Concrete provisions of the ACI 318 code. In January 2015, ESRs for adhesive anchor systems began to list compliance with the 2012 IBC. There are changes with respect to the information contained in these reports compared to reports having recognition under previous versions of the IBC. This article explains what changes have been implemented into 2012 IBC-compliant adhesive anchor ESRs, and how these changes affect adhesive anchor design.

Changes in Adhesive Anchor System Approvals By Richard T. Morgan, P.E.

Richard T. Morgan, P.E., is the Manager for Software and Literature in the Technical Marketing Department of Hilti North America. He is responsible for PROFIS Anchor and PROFIS Rebar software. He can be reached at richard.morgan@hilti.com.

Review of the ICC-ES Acceptance Criteria AC308 The primary test programs for evaluating adhesive anchor systems in cracked and uncracked concrete are given in its Tables 3.1, 3.2 and 3.3 in AC308. AC308 evaluation of adhesive anchor systems for design using threaded rods, internally threaded inserts and torque-controlled elements include various types of tests: • reference tests establish the baseline bond strength of the adhesive • reliability tests determine sensitivity to installation and load conditions • service condition tests evaluate concrete conditions during the service life of the anchor, establish minimum spacing and edge distance requirements, and evaluate performance in simulated seismic conditions. Adhesive anchor ESRs based on evaluation per AC308 were first issued in November 2007, for recognition under the 2006 IBC. As such, an adhesive anchor system could be evaluated per AC308 and designed with the Anchoring to Concrete provisions of ACI 318-05 Appendix D. However, since ACI 318-05 Appendix D did not include provisions for adhesive anchor systems, AC308 was a stand-alone document that included a section titled 3.3 Strength design – amendments to ACI 318, which also contained equations and parameters for calculating bond strength in tension and concrete pryout strength in shear. The 2006 IBC-compliant adhesive anchor ESRs likewise began including these AC308 equations and parameters via Section 4.0 DESIGN AND INSTALLATION. Therefore, even though the scope of ACI 318-05 Appendix D did not include adhesive anchor systems, adhesive anchor design using Appendix D provisions could be performed via an ESR having 2006 IBC recognition. Adhesive anchor ESRs having 2009 IBC recognition also included the AC308 bond strength equations and parameters via Section 4.0, thereby permitting design per ACI 318-08 Appendix D. The ACI 318-11 code now includes adhesive anchor systems in Appendix D as referenced in Part D.2.2 – Scope, and ACI 355.4 is referenced in Part D.2.3 (d) as the standard to qualify adhesive anchor systems for use with Appendix D provisions. Part D.5.5 – Bond strength of adhesive anchor in tension contains provisions for calculating nominal bond strength in tension. Part D.6.3 – Concrete pryout strength of anchor in shear contains provisions for calculating nominal pryout strength in shear.

30 September 2015

AC308 (original) projected distance parameter Scr,Na

ACI 318-11 Appendix D projected distance parameter CNa

τk,uncr

√ 1450

Scr,Na 2

τk,uncr = 1670 psi

CNa

Scr,Na = 20da

da = 0.75 in

CNa = 10da

τuncr

√ 1100

τuncr = 1670 psi

da = 0.75 in

CNa

Scr,Na 2

Scr,Na = (20)(0.75 in)(1670 psi/1450 psi)0.5

CNa = (10)(0.75 in)(1670 psi/1100 psi)0.5

Scr,Na 2

Scr,Na = one half the ciritical spacing 2 between two anchors

= 16 in

CNa

Scr,Na 2 = (16 in)/2 = 8 in

Figure 1. AC308 (original projected distance parameter).

Harmonization Between AC308 and ACI 355.4 With the development of ACI 355.4 in 2011 to qualify adhesive anchor systems, ACI 355.4 and AC308 needed to be harmonized because ACI 355.4 will now serve as the baseline for AC308. Recall that AC308 was developed as a stand-alone document prior to the existence of ACI 355.4. Since adhesive anchor systems receive IBC recognition in an ESR via testing per AC308, the original AC308 provisions needed to be modified to coincide with the new baseline provisions of ACI 355.4. The significance of this is that the inclusion of adhesive anchor qualification and design provisions into the ACI 318 code has resulted in bond strength equations no longer being necessary in either AC308, or in adhesive anchor ESRs. Beginning with 2012 IBC-compliant adhesive anchor ESRs (issued January 2015), bond strength equations are no longer included in the report because they are now given in ACI 318-11 Appendix D Part D.5.5. This means that adhesive anchor design under the 2009 IBC/ACI 318-08 or under the 2006 IBC/ACI 318-05 should also be performed using the equations of ACI 318-11 Appendix D Part D.5.5, because the original AC308 bond strength equations given in previous ESR versions are no longer presumed to be “code compliant”.

Comparisons between Previous Bond Strength Calculations ACI 355.4 “prescribes testing and evaluation requirements for post-installed adhesive anchor systems intended for use in concrete under the provisions of ACI 318.” It includes test programs for evaluating adhesive anchor systems in cracked and uncracked concrete. Similar to AC308, the test programs in ACI 355.4 cover various conditions:

CNa

Figure 2. ACI 318-11 Appendix D projected distance parameter.

• reference tests to establish the bond strength of the adhesive • reliability tests to determine sensitivity to installation and load conditions • service condition tests to evaluate possible concrete conditions during the service life of the anchor, establish minimum spacing and edge distance requirements, and evaluate performance in simulated seismic conditions. Although the ACI 355.4 test program is similar to the AC308 test program, it is important to note that ACI 318-11 Appendix D bond strength calculations, per the provisions given in Part D.5.5 Bond strength of adhesive anchor in tension, are based on parameters established in ACI 355.4. The D.5.5 calculation results will differ from bond strength calculations based on parameters previously established in AC308. The calculations for nominal bond strength per the original version of AC308, i.e. pre-ACI 355.4, used a parameter corresponding to the spacing between two adhesive anchors, scr,Na, and the equations for calculating nominal bond strength utilized either scr,Na or scr,Na /2. Nominal bond strength calculations in ACI 318-11 Appendix D are now based on a parameter corresponding to the projected distance from the center of an adhesive anchor to one side of the anchor, cNa, which does not equal the original AC308 value scr,Na /2. The value calculated for cNa is greater than that calculated for scr,Na /2. Figure 1 and Figure 2 illustrate why the original AC308 parameter scr,Na /2 differs from the new ACI 318-11 Appendix D parameter cNa. Looking at Figure 1, assume the characteristic bond stress (τk,uncr) equals 1670 pounds per square inch, and the anchor element consists of a ¾-inch diameter (da) threaded rod. The value for scr,Na calculated per the original AC308 Equation (D-16d) would equal 16 inches and the value calculated for scr,Na /2 would equal 8 inches. Looking at Figure 2, using the same values for τuncr and da, the value

STRUCTURE magazine

= 9.24 in

CNa = projected distance from the center of one anchor to one side of the anchor

September 2015

for cNa calculated per ACI 318-11 Equation (D-21) would equal 9.24 inches. Therefore, cNa is greater than scr,Na /2, which means ACI 318-11 Appendix D bond strength calculation results using cNa will differ from the original AC308 calculation results using scr,Na or scr,Na /2.

Adhesive Anchor Design Per ACI 318-11 Part D.5.5 Bond strength data published in 2012 IBC-compliant ESR tables titled BOND STRENGTH DESIGN INFORMATION is derived from adhesive anchor qualification testing per ACI 355.4/AC308, and is product-specific. This data is used to design the adhesive anchor system per the provisions of ACI 318-11 Part D.5.5. The parameter corresponding to the characteristic bond stress (τ) of an adhesive is a key parameter used in ACI 318-11 bond strength calculations. Values for τ given in the ESR bond strength tables are designated τk,cr for the characteristic bond stress of the adhesive in cracked concrete, and τk,uncr for the characteristic bond stress in uncracked concrete. Characteristic bond stress (τ) is used either directly or indirectly in the ACI 318-11 equations (D-21), (D-22) and (D-27) to calculate cNa, the basic bond strength Nba, and the critical edge distance cac, respectively. Another parameter relevant to the characteristic bond stress (τ) is the concrete temperature range. The ESR bond strength tables include a footnote that defines the concrete temperature ranges for which the adhesive has been tested. Temperatures corresponding to the “maximum short term” and “maximum long term” concrete temperatures for a given range are defined, and the characteristic bond stress (τ) values corresponding to these temperature ranges are given in the ESR bond strength tables. The concrete temperatures are defined in terms of “short term” and “long term”. Short term concrete temperatures are defined

3.2 Bond Strength Nag =

( AA ) Ψ Na

Na0

ec1,Na

Ψec2,Na Ψed,Na Ψcp,Na Nba

ACI 318-11 Eq. (D-19)

ɸNag ≥ Nua ANa = see ACI 318-11, Part D.5.5.1, Fig. RD.5.5.1(b) ANa0 = (2 cNa)2 τuncr cNa = 10 da 1100 1 e ≤ 1.0 Ψec,Na = 1+ N cNa ca,min ≤ 1.0 Ψed,Na = 0.7 + 0.3 cNa ca,min , cNa Ψcp,Na = MAX ≤ 1.0 cac cac Nba = λa – τk,c – αNsels – κbond – � – da – hef

√

(

Variables τk,c,uncr [psi] 1670 ec1,N [in.]

ACI 318-11 Table D.4.1.1 ACI 318-11 Eq. (D-20) ACI 318-11 Eq. (D-21)

) (

ACI 318-11 Eq. (D-23)

) )

ACI 318-11 Eq. (D-25) ACI 318-11 Eq. (D-27) ACI 318-11 Eq. (D-22)

da [in.]

hef [in.]

ca,min [in.]

τk,c [psi]

1.000 ec2,N [in.]

15.000 cac [in.]

6.000 κbond

805 λa

αN,sels

1.00

1.000

0.000 Calculations cNa [in.]

0.000

23.146

ANa [in.2]

ANa0 [in.2]

Ψed,Na

12.266 Ψec1,Na

1032.60 Ψec2,Na

601.80 Ψcp,Na

0.847 Nba [lb]

1.000 Results Nag [lb]

1.000

37935

ɸbond

ɸseismic

ɸnonductile

ɸNag [lb]

Nua [lb]

55115

0.650

0.750

0.400

10747

7450

Figure 3. PROFIS anchor bond strength calculations.

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as “temperatures that occur over brief intervals, e.g., as a result of diurnal cycling,” and long term concrete temperatures are defined as temperatures that are “roughly constant over significant periods of time.” The harmonization of AC308 with ACI 355.4 has resulted in some of the maximum short term temperature/maximum long term temperature values being increased. Characteristic bond stress (τ) values are correspondingly reduced as a result of these changes. ESRs that are 2012-compliant are the first ESRs to include these changes. Reference each ESR for changes specific to a particular adhesive anchor system. Adhesive anchor ESRs having 2012IBC compliance are used with the bond strength provisions of ACI 318-11 to design an anchorage in jurisdictions recognizing

IBC 2012/ACI 318-11. Adhesive anchor design in jurisdictions recognizing previous IBC/ACI 318 versions should also utilize the ACI 318-11 provisions in order to be presumed “code compliant” because (a) the original AC308 bond strength equations have been removed from the ESRs, and (b) bond strength equations for adhesive anchor design are now given in ACI 318-11 Appendix D. There has understandably been some confusion regarding the requirement, and feasibility, of using ACI 318-11 bond strength provisions to design adhesive anchors in jurisdictions that have not yet adopted IBC 2012/ACI 318-11. Since AC308 (compliance January 15, 2015) no longer contains equations for calculating bond strength, use of the original AC308 equations given in pre-2012 IBC compliant ESRs needs to be justified by the Engineer of Record (EOR). When an ESR is updated, the previous version is no longer used unless justified by the EOR. Therefore, in order to be presumed code compliant, adhesive anchor design in jurisdictions still recognizing IBC 2009/ACI 318-08, for example, should be performed using the most current (2012 IBC-compliant) ESR and the ACI 318-11 equations unless justified by the EOR. Pre-2012 IBC ESR bond strength equations conflict with ACI 318-11 bond strength equations. Therefore, use of the pre-2012 IBC ESR bond strength equations must be justified for use in lieu of the equations now given in ACI 318-11.

STRUCTURE magazine

September 2015

Other anchor calculations, such as seismic calculations, will be based on the IBC/ACI 318 code version currently adopted by the jurisdiction because there is nothing in the 2012 IBC-compliant ESRs that conflicts with these code versions. Figure 3 shows calculations performed with Hilti PROFIS Anchor software using the data given in ESR-3187 (revised January 2015) for the HIT-HY 200 adhesive anchor system. Design using the seismic provisions of ACI 318-08 Part D.3.3.6 was selected. Besides the 0.75 seismic factor defined in ACI 318-08 Part D.3.3.3, Part D.3.3.6 requires an additional factor to be applied to non-ductile design strengths. The 0.75 seismic factor is shown below as φseismic, and the D.3.3.6 non-ductile factor is shown as φnonductile. Note that the calculations for nominal bond strength (Nag) are based on ACI 318-11 Part D.5.5, but the seismic calculations are based on ACI 318-08 Part D.3.3.3 and Part D.3.3.6. Therefore, the design strength calculations (φNag) performed per ACI 318-08 Appendix D seismic provisions, and the nominal bond strength calculations (Nag) performed per ACI 318-11 Part D.5.5 are presumed to be “code compliant”.

Summary ACI 318-11 Appendix D now includes provisions for calculating the nominal bond strength of adhesive anchor systems in Part D.5.5. Prior to ACI 318-11, adhesive anchor systems were not within the scope of Appendix D; however, ICC-ES developed the acceptance criteria AC308 to qualify adhesive anchor systems for recognition under the IBC, and to design adhesive anchor systems with the provisions of Appendix D. The original AC308 included provisions for calculating nominal bond strength since no provisions were available in Appendix D. With the development of ACI 318-11 Part D.5.5, ACI developed a test standard, ACI 355.4, to qualify adhesive anchor systems for use with Appendix D provisions. AC308 has been harmonized with ACI 355.4, resulting in the only provisions recognized under the IBC for calculating bond strength being given in ACI 318-11 Appendix D. Revised bond strength calculations are now based on the projected distance from an anchor instead of the spacing between anchors. Characteristic bond strength values have also been revised per the changes in maximum short term/ maximum long term temperature ranges. Adhesive anchor design for pre-2012 IBC jurisdictions should use the provisions of ACI 318-11 Appendix D to be presumed “code compliant” unless justified by the Engineer of Record.▪

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Guest Column dedicated to the dissemination of information from other organizations

n April 9-10, 2015 the Building Information for Modeling Masonry (BIM-M) Initiative held their first Symposium in St. Louis, MO at the St. Louis Masonry Center. Since the beginning, the initiative has been following its mission statement: To unify the masonry industry and all supporting industries through the development and implementation of BIM for masonry software to facilitate smoother workflows and collaboration across all disciplines from owner, architect, engineer, manufacturer, mason, contractor, construction manager, and maintenance professionals. While the BIM-M Initiative has been progressing for over two years, many structural engineers may not have been aware of this major effort. This article provides some of the highlights of BIM-M and the symposium, and their relevance to structural engineers. It is important to remember that the term BIM represents both an object (a model), and a process (modeling). Why BIM-Masonry? To give masonry an opportunity to compete with other building materials while simultaneously improving the industry. The BIM-M Initiative began in 2012 and represents the masonry industry in the United States and parts of Canada. The Symposium opened by welcoming the many architects, structural engineers, manufacturers, contractors, suppliers, supporters, and guests. The audience learned that Phase II (Development) based on the original roadmap has been completed. Phase II contained four projects; 1) Masonry Unit Model (MUD) Definition, 2) Masonry BIM Benchmark, 3) Masonry Wall Model Definition, and 4) BIM-M Contractor

BIM-M Symposium: Generation 1 By Daniel Zechmeister, P.E.

Daniel Zechmeister, P.E., is the Executive Director of the Masonry Institute of Michigan and a member of the Executive Committee of BIM-M representing The Masonry Society. He is active in ASTM and the Masonry Standards Joint Committee, which is responsible for the TMS 402 code and the TMS 602 specification. He can be reached at dan@mim-online.org.

Input. BIM-M also announced that an updated Roadmap, a report for developing and deploying BIM for masonry, has now been posted on the website (www.bimformasonry.org). The proposed timeline for Phases III and IV begins now and will run until the end of 2017 with the completion of Generation 1. What is Generation 1 BIM-M? Generation 1 is defined as the conceptual termination of the BIM-M Initiative’s initial efforts to make masonry more accessible to architects, structural engineers, masons, contractors, manufacturers, and owners using BIM. Some aspirations for what Generation 1 will include are: • Masonry unit database accessible to all BIM users. • Masonry wall definitions for Level of Development (LOD) with standard details. • BIM software upgrades that achieve LOD 350 or greater for design (Figure1). • BIM software that allows contractors to achieve LOD 400 or greater for construction purposes, and can detect clashes with specific masonry features (bond beams, grouted cells, shelf angles, etc.) • BIM software upgrades that will operate with other masonry specific software. • New and/or improved design tools (software upgrades, add-ins, plugs-ins) that provide for modularity, early project pricing, and masonry detailing.

Masonry Unit Model Definition Over the course of the last two years, the BIM-M Masonry Unit Working Group, led by Jeff Elder, SE, Interstate Brick, HC Muddox and Western States Clay Products developed a spreadsheet to represent the majority of data parameters and specification information to be used by BIM

Figure 1. LOD 350 for design.

34 September 2015

software developers for the design, purchasing, shop drawing and sustainability of clay, CMU and cast stone. This data set was based upon geometric and material attributes provided by numerous manufacturers. The physical properties entity includes attributes for both mechanical properties and thermal properties of masonry units, including; weight, density, compressive strength, modulus of elasticity, modulus of rigidity, shrinkage coefficient, coefficient of thermal expansion, and creep coefficient. For structural engineers, this means there will be on-line access to geometrical and material properties for modeling masonry in BIM software as well as for analytical programs that interact with BIM.

BIM-M Benchmark The original intent of the BIM Benchmark project was to focus on software capabilities and to understand the role of software in the masonry industry at all project phases. The Phase II project, led by Russell Gentry, PE, Project Manager, Digital Building Laboratory, Georgia Institute of Technology, extended this scope to focus not only on software but also on BIM processes, that is, how masonry stakeholders use BIM or other tools. The primary goal was to develop a vision for “future state” processes that can take advantage of the Generation 1 BIM-M software. The original proposal called for the analysis of three project types: brick/CMU, structural masonry, and complex masonry. Georgia Tech, along with the University of Pennsylvania, completed nine building case studies of various building types. The Benchmark Project focused on three areas: Task 1 – Framework Development Task 2 – Process Documentation Task 3 – Process Model Evaluation For structural engineers, this will lead to better interaction between analytical programs and BIM modeling during design and construction.

Masonry Wall Model Definition

Figure 2. Cover of 2014 LOD Specification.

to track individual masonry units in an entire building. Therefore, the masonry BIM data structure must include the definition of wall types, and must provide the means to map these wall types onto regular and irregular regions on wall surfaces. The working group discussed and suggested a level of development (LOD) of 350 for architects and structural engineers. Also, one of the four new tasks for Phase III is to develop and publish a Best Practices Guide for Modeling of Masonry using Autodesk Revit in cooperation with The Masonry Society (TMS). The Guide has a three-fold purpose, including: 1) informing users on how current BIM tools may be used to model masonry, 2) to define what collaboration and modeling tools are lacking, and 3) to create a wish-list of modeling tools that would be helpful to the industry. Structural engineers will have more efficient modeling tools that will carry over into the analytic programs.

BIM-M Contractor Input

This project is at the core of masonry BIM and is managed by Jamie Davis, PE of Ryan Biggs/Clark Davis through the TMS BIM Committee. Because masonry BIM is a computational model of masonry construction, and masonry walls are the fundamental assembly in masonry construction, it is critical that the data representation of the masonry wall support all of the functionality that is envisioned for BIM-M. Currently, it is simply not computationally practical for BIM software

It has been clearly determined that mason contractors and masons will benefit from BIM-M. In this project, BIM-M proposes that mason contractors explore in greater detail the potential benefits of BIM, and document their current work processes and their use of software in current practice. Input from general contractors will be solicited as well, to identify areas where general contractors desire interaction with masonry construction in their BIM models – for example, in coordination of masonry with structural,

STRUCTURE magazine

September 2015

mechanical and other building systems for clash detection. The keynote speaker was Will Ikerd II, PE, from Ikerd Associates, Dallas, TX. He also represents the BIM Forum and chairs the SEI BIM Committee. He began his presentation by stating BIM is about giving a “common vocabulary”. Will discussed the various levels of development (LODs). He pointed out that, in 2008, an AIA document for the first time defined LODs. In giving his opinion, he described the LODs simplistically as: • LOD 100 – symbolic • LOD 200 – approximate • LOD 300 – specific • LOD 350 – detailed (interfaces with other building systems) • LOD 400 – detailing and fabrication Will announced to the audience that the Level of Development (LOD) Specification is a reference that enables practitioners in the AEC Industry to specify and articulate with a high level of clarity the content and reliability of Building Information Models (BIMs) at various stages in the design and construction process. Shown on the cover of the 2014 LOD Specification are the various LODs for masonry (Figure 2). The specification is a free download from store.bimforum.org. Two specific presentations came from BIM-M consultants who are providing modeling tips and tricks for masonry, which will be released later this year as Best Practices Guide. BIM-M has tasked them with demonstrating the modeling of masonry using current software and recommending future improvements.

Best Practices #1 Presenters from the architecture and engineering firm Integrus Architecture from Seattle, WA included Mike Adams, BIM Manager; Morgan Weise, EIT; and Clint Bailey, AIA showed some features of what they will be contributing to the Best Practices Guide. The most common masonry elements in BIM are walls which are always modeled in three-dimensions. However, many masonry details are presently handled in two-dimensions. The current strategy for creating drawings is to take the three-dimensional model and slice it to reveal the information that is desired. Integrus demonstrated the three-dimensional detailing function. Because these views are live or three-dimensional, any changes that are made in them affect the rest of the model. For example, BIM software typically includes a number of pre-made families including openings with arched tops. In the BIM-M project, Integrus used three-dimensional

Figure 3. Three-dimensionally reinforced wall.

Figure 4. CMU wall in structural model and remaining wall layers in architectural model.

sweeps (model elements) to represent stone sills, lintels, and quoining. Another example dealt with representing reinforcement in models. The current advantages of two-dimensional reinforcement are detail line, components or groups; fast to make changes; and easy to export details from project to project. The current disadvantages are an absence of embedded information (no clash, no scheduling and no tagging), everything fits and no warnings as things move. Integrus noted that the current advantages of modeling reinforcement in three-dimensions are improved coordination, accurate schedules, tagging, and correct warnings when things are moved. The current disadvantages are longer modeling time, all walls are treated equal and an enlarged model file size (Figure 3).

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Best Practices #2 The second BIM-M consultant was Shawn Zirbes, Cad Technology Center (CTC) from Minneapolis, MN. Shawn used the BIM Forum LOD 2014 Level of Development Specification and displayed the BIM-M for Masonry LOD examples for levels 300, 350 and 400. Shawn showed a structural model of the Brick Office Building with brick on CMU backup on a portion, and brick with metal stud backup on the remaining portion. The model was then split into an exterior shell model and an interior model. For both the brick with block backup wall and brick with metal stud backup wall, Shawn presented the LOD 300 with a plan and section view, respectively. He then displayed LOD 350 for the block (CMU) backup showing the grouted cells where the CMU wall is placed in a structural model and the remaining wall layers (brick veneer, wall ties and drainage panel, rigid insulation, and air barrier) are modeled as individual wall types in an architectural model (Figure 4). With respect to the LOD 350 for metal stud backup, all wall layers (brick veneer, wall ties, rigid insulation, air barrier, sheathing, metal studs and gypsum board) are modeled as individual wall types in an architectural model. Anchor type placement was shown for both systems in plan and sectional view. Brick patterns were developed as model hatch patterns showing running bond (primary), stacked bond and

STRUCTURE magazine

September 2015

Flemish bond. This allows for architects and structural engineers to check modularity in their designs.

Contractor Software for Use by Engineers Bill Pacetti and Bill Pacetti, Jr., from Tradesmen’s Software, Inc., Morris, IL, presented their software. This software was developed for mason contractors but has features that could be valuable to architects and structural engineers including cost estimating, evaluating aesthetics by varying units, checking dimensions for modularity of units, and more.

BIM-M and Structural Software In Phase III, BIM-M will start a new project associated with structural engineering. In an attempt to improve modeling techniques and interoperability of analytical software with BIM authoring tools, consultants will be selected to examine various software packages and their use with BIM packages. Structural engineers interested in being considered for this work should contact BIM-M through its website. While this article has provided an overview, free downloads of videos, presentations and reports for BIM-M are available from the website also.▪

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Structural Performance performance issues relative to extreme events

his article identifies common errors that structural engineers make when performing seismic design and calculations. The intent is to help engineers avoid those errors and misapplications. This article is written in checklist format such that an engineer can verify adequate self-knowledge, as well as review the work of others on a project. It is based upon the 2012 International Building Code (IBC), the American Society of Civil Engineers’ ASCE/SEI 7-10, the American Concrete Institute’s ACI 318-11, the American Institute of Steel Construction’s AISC 360-10, AISC 341-10, and other current standards. For ease of identification, referenced sections are noted in brackets and refer to ASCE/SEI 7-10 section numbers, unless otherwise noted.

diaphragms, walls, etc. However, in addition to those specifics, the engineer is required to provide a continuous load path for all inertial forces from their origin to the foundation. Such load paths must conform to the relative stiffness and strength of the elements that exist in the structure. See [12.1.3].

1) Seismic Design Category A

4) R Factor

When in seismic design category (SDC) A, it is not necessary to use any of the provisions of Chapter 12. Instead, the general structural integrity provisions of Section 1.4 apply. Note that these provisions include some loads that may often be erroneously neglected. The required lateral forces include 1% of dead load, 5% of dead plus live load for beam (axial load) connections, and 20% of wall weight for wall connections. Non-structural components in SDC A are exempt from seismic design requirements. See [1.4], [11.4.1], and [11.7].

The response modification coefficient, R, is part of a concept where an elastic design may be performed, but with due consideration of the overstrength and ductility inherent in the lateral force resisting system. In order to ensure reliability, many requirements are triggered with each R factor. The “R” Tables, [Table 12.2-1] and [Table 15.4-1, 2], list the corresponding detailing requirements. The “strings attached” can be extremely significant, especially for concrete structures that fall under ACI 318-11 Chapter 21 and steel structures with R greater than 3 (AISC 341 Seismic).

The Most Common Errors in Seismic Design … & How to Avoid Them By Thomas F. Heausler, P.E., S.E.

2) Importance Factor

Thomas F. Heausler, P.E., S.E. (TFHSE@aol.com), has 33 years of experience in structural and seismic engineering and has been a voting member of ASCE/SEI 7 Seismic Provisions since 2006. He provides seismic expertise and senior review to engineering firms for building and industrial projects.

The importance factor is based upon the risk category and the associated life safety, hazard or essential nature of the structure. Both [Table 1.5-1] and [IBC Table 1604.5] should be reviewed. A typical building can sometimes evolve into an Ie equal to 1.25 or 1.5 when occupancy or use expands. Examples include relatively small churches (expanding to an occupancy greater than 300) or a building where hazardous materials are stored. It should be noted that for building design, Ie = 1.0, 1.25, or 1.5; but for non-structural components, Ip = 1.0 or 1.5 only [13.1.3], such that Ip may not equal Ie, and in some instances Ip may be less than Ie. See [11.5.1] and [Table 1.5-2]. 3) Continuous Load Path ASCE/SEI 7-10 has very specific provisions for many elements such as collectors, connections,

… a checklist to verify self-knowledge as well as check the work of others on a project.

5) Irregularity Triggers [Table 12.3-1] and [Table 12.3-2] describe various horizontal and vertical irregularities, respectively, which trigger specific provisions. Each referenced section must be reviewed. Triggered provisions include modal analysis, three-dimensional analysis, redundancy factor, force amplification, torsion amplification, and collector force increases. See [12.3.2.1] and [12.3.2.2]. 6) Overstrength – Ωo The variable Ωo is an amplification factor applied to the forces in certain elements in the seismic load path. It is required so as to prevent a weak link from occurring prior to the full energy dissipation and ductility potential of the primary lateral-force-resisting system. For example, in a steel braced frame, in order for the diagonal brace to yield and dissipate energy in a controlled and reliable manner, all other portions of the load path (e.g., connections,

When you select an R factor from the Table, you are obliged to implement the associated “strings attached.” 38 September 2015

bolts, welds, gusset plates, anchor bolts, columns and collectors) need to be stronger than the maximum anticipated strength or force in the brace. Therefore, Ωo amplification and load combinations are specifically triggered for those elements, in the sections mentioned below and in Material Standards such as AISC 341-10 and ACI 318-11. For example, AISC 341-10 states that anchor bolt forces must be amplified by Ω o, which is typically 2.0 or greater. This applies to all steel buildings where R is greater than 3, unless you can prove otherwise via an advanced and rigorous analysis. See [12.4], [12.2.5.2], [12.10.2.1], [12.3.3.3], [12.13.6.5], and [AISC 341 when R>3, ACI Chapter 21, Appendix D, etc.]. 7) Redundancy – Rho Rho is a factor that penalizes structures that do not have redundancy. Rho is equal to either 1.0 or 1.3. Rho is equal to 1.0 for SDC B and C, for drift calculations, non-structural component forces, collectors, Ωo load combinations, and diaphragms. See [12.3.4]. 8) Vertical Seismic Load Effect – Ev [12.4.2.2] requires that a vertical load effect equal to 0.2 SDs be applied to dead load. It is applied as a dead load factor adjustment and

…anchor bolt forces shall be multiplied by Ωo, which is typically 2.0 or greater. may act downward or upward. It is at the strength design level, so it may be multiplied by 0.7 for allowable stress design (ASD). The values of Ie, Ip, Rho and R are not applied to Ev.

SDC D, E, and F be considered with 100% of forces in one direction plus 30% in the other. It should be noted that IEEE 693 (Electrical Equipment) applies orthogonal effects to all elements, including corner anchor bolts.

9) Load Combinations and Allowable Stress Design – 0.7 E

11) Effective Seismic Weight

For ASD load combinations [12.4.2.3], [12.4.2] shall be used in lieu of [2.3.2] and [2.4.1]. Earthquake forces are at strength level, so for the ASD combinations, use 0.7 E. The 0.7 E applies to non-structural component forces (Fp). See [13.3.1]. 10) Orthogonal Effects Earthquake forces must be calculated for each of the two primary orthogonal directions. In order to consider the effects of earthquake forces at some angle other than those two directions, “orthogonal effects” must be considered. [12.5] requires that irregular buildings in SDC C and corner columns in

[12.7.2] defines the effective seismic weight, W. Except for as mentioned below, live load is not included in the inertial force; however, the seismic force is later combined with dead and live loads in the load combinations. [12.7.2] stipulates that W must include the following masses: 25% of storage live load, partition load of 10 psf [4.3.2], industrial operating weight and unbalanced conditions, 20% of snow if greater than 30 psf, and weight of roof gardens. 12) Distribute Base Shear over Height Once the base shear, V, is calculated, it must be distributed over the height of the structure. For a one-story building, all of the base shear would be applied at the roof. For multi-story

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STRUCTURE - September 2015 - HP-H-4C.indd 1

STRUCTURE magazine

September 2015

6/10/2015 6:37:49 PM

structures, the base shear must be distributed to each floor, not only in proportion to each floor’s mass, but also in proportion to the distance of the floor from the base. A triangular distribution of force results for regular multi-story buildings. For distributed-mass structures like stacks and masonry fences, the centroid of the load should result at 2/3 of the height above the base, not at ½ the height or at the center of gravity. See [12.8.3]. 13) Modal Response Spectrum Analysis When a structure has significant vertical or horizontal irregularities, the equation [12.812] (triangular force distribution) becomes inaccurate, and therefore a modal response spectrum analysis is required. See [12.6], [Table 12.6-1] and [12.9]. The purpose is not to refine the magnitude of the base shear, but to perform the following more accurately: 1) Distribute base shear over height. 2) Quantify horizontal torsional effects. 3) Account for higher mode effects. Note that the “NP” entry in [Table 12.6-1] includes many common irregularities, including horizontal type 1a, 1b and vertical type 1a, 1b, 2 and 3, and thus a modal analysis is triggered for those structures. 14) Accidental Torsion In addition to inherent torsion, accidental torsion must be applied. This is to prevent weak torsional resisting arrangements, as well as account for unexpected distribution of live load and unexpected stiffness of structural and non-structural elements. This provision applies to non-building structures, as well as buildings. For torsionally irregular buildings, amplification of the accidental torsion may be required as per [12.8.4.3]. See [12.8.4.2]. 15) Drift Check Results from the elastic analysis must be amplified by Cd to render expected deflections. Note that Cd is a very large value, typically a factor of about 4 or 5. The drift is then divided by Ie, because the allowable drifts are organized into a table that considers risk category. One should be careful when using ASD load combinations not to apply the 0.7E to drift calculations. See [12.8.6], [12.12], and [Table 12.12-1]. 16) Diaphragm Forces Forces at lower floor diaphragms may be higher than those used for the lateral force resisting system [Equation 12.8-12]. This is due to higher mode effects (i.e., modes higher than the first mode) where the lower floors may be accelerating higher than calculated. Note that Fpx minimums of [Equation

12.10-2] often govern for the lower floors. See [12.10.1.1]. 17) Non-structural Components Non-structural components may also experience higher local accelerations due to higher mode effects, as well as amplification of the force within the non-structural element itself. See [Equation 13.3.1]. Industrial structures often feature very large forces. It is unlikely that the forces on two different floors would occur at the same point in time. Therefore, one method of accounting for the forces in a computer model is to evaluate two conditions. 1) Run a load case with the weight of the equipment included in the seismic weight of the floor and the base shear, V, distributed over the height as per [Equation 12.8-12]. 2) Run a load case with only the nonstructural component force for one piece of equipment, so as to verify an adequate load path to the vertical system and/or foundation. Note that it is necessary to apply Ev to load combinations with nonstructural component forces. The factor Ωo does not apply to such load combinations, except in some ACI 318-11 Appendix D calculations. Note also that when non-structural components get very large – i.e., 25% or more of total structure mass – then [15.3] provisions apply. For these heavy components, the stiffness and design coefficients of both the component and the primary structure must be considered together in a computer model. 18) Wall Design Connections to wall panels made of concrete and concrete masonry units (CMU) have performed poorly in past earthquakes. The equations of [12.11.1] and [12.11.2.1] should be implemented, as well as ACI 318-11 Appendix D for anchorage. 19) Foundation Ties Foundation ties are required as per [12.13.6.2] in order to ensure that the foundation system acts as an integral unit, not permitting one column or wall to move appreciably relative to another. This applies to pile caps in SDC C, D,E and F, and spread footings for SDC E and F. 20) Reduction of Foundation Overturning [12.13.4] allows for a reduction of the bearing pressures at the soil-foundation interface.

STRUCTURE magazine

September 2015

Forces may be reduced by 25% in recognition that the first mode triangular force distribution will likely not occur without higher mode effects occurring and negating the direction of the first mode, resulting in reduced maximum overturning moments. 21) Errata The ASCE/SEI 7-10 and IBC 2012 websites have the latest errata for those documents. Significant entries due to typographical mistakes or unintended consequences of revisions are corrected in the errata. 22) IBC Overrides IBC 2012 contains amendments to ASCE/ SEI 7-10. See [IBC 1613], [IBC 1613.5], and [IBC Chapters 18 through 23]. ASCE/ SEI 7 is on a six-year update cycle, and IBC is on a three-year cycle. Technical changes to IBC often have to be approved well before the issue date. Inevitably, coordination between ASCE 7, IBC and referenced material standards (e.g. ACI, AISC, etc.) often occur through errata, supplements or IBC-published amendments. It is essential to check for these changes periodically. Individual state and local governments may also adopt amendments that affect projects located within their jurisdiction. 23) ASCE/SEI 7-10 Third Printing It is recommended that the user make use of the ASCE/SEI 7-10 Expanded Seismic Commentary, which provides 135 pages of valuable background information. It is incorporated in the third printing of ASCE/ SEI 7-10 only. For those who own a first or second printing, you may download a PDF file of the commentary for free from the ASCE website. This Commentary was developed by the National Earthquake Hazard Reduction Program/Building Seismic Safety Council/Provisions Update Committee (NEHRP/BSSC/PUC) and describes the reasons for the individual provisions of ASCE/SEI 7-10.

Conclusion A concerted effort to avoid errors is essential. Errors can be minimized by applying knowledge and experience. This article is intended to assist in that effort. The above listing of common errors was developed by the author during frequent reviews of other engineers’ work. It is based upon the author’s experience and should not be construed as a consensus document prepared or endorsed by the ASCE/SEI 7-10 or NCSEA Seismic Committees.▪

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Take Your Practice to New Heights at the 2015 Structural Engineering Summit

National Council of Structural Engineers Associations

September 30 – October 3rd Red Rock Resort Las Vegas, NV th

STAY CONNECTED BY USING THE HASHTAG #NCSEASummit

Wednesday, September 30 8:00 – 5:00 8:00 – 12:00 5:30 – 6:30 6:30 – 8:30

evacuation refuge structures, based on the new ASCE 7-6 chapter Tsunami Loads & Effects. Gary Chock is Chair of the ASCE 7 Tsunami Loads and Effects Subcommittee that in 2015 completed the ﬁrst national standard for tsunami-resistant design for the upcoming 2016 edition of the ASCE 7 Standard.

Committee Meetings NCSEA Board of Directors Meeting Young Engineer Reception SECB Reception

B.) Effective Communication: Tips for Improving Your Skills

Thursday, October 1 7:00 8:00

Delegate Interaction Meeting Welcome & Introduction

Kirsten Zeydel, S.E., President, ZO Consulting and Annie Kao, P.E., Field Engineer, Simpson Strong-Tie

8:15 – 9:30 Keynote STRUCTURAL ENGINEERING: The Profession, The Grandeur, and The Glory Ashraf Habibullah, S.E., President & CEO, Computers & Structures, Inc.

Ashraf brings into focus the invaluable socio-economic contributions of structural engineering by recognizing its unmatched impact on humanity. He will highlight the ways in which the intellect and talent of structural engineers have literally saved hundreds of millions of lives, spared us from death and destruction, and preserved and protected progress and property. Ashraf Habibullah is a registered Civil and Structural Engineer who founded CSI in 1975 and has led the development of CSI’s products, including SAP2000 and ETABS, for the last four decades. CSI’s software is used by thousands of engineering ﬁrms in over 160 countries.

9:45 – 11:00 Basis for ASCE 7 Seismic Design Maps

ASCE 7-10 and IC-2012 introduced the concept of risk-adjusted Maximum Considered Earthquake (MCE-R) shaking derived to produce a 1% chance in 50 years that buildings will experience earthquake-induced collapse. As compared with older MCE deﬁnitions, this resulted in reduction of design ground motions in much of the U.S. while assuring design risk comparable to that already accepted in the Western U.S. The basis for this change and its signiﬁcance are presented. NCSEA Past President and Past Code Advisory Committee chair, Ron Hamburger, is Senior Principal with Simpson Gumpertz and Heger in San Francisco and the current chair of the ASCE-7 Committee. He is presently chairing a joint USGS-BSSC planning committee, formalizing plans to develop a new generation of seismic risk maps for the building codes.

11:00 – 12:00 Building Rating, Retrofit Ordinances, and Community Resilience

A.) Wood & Cold-Formed Light Steel Frame Construction – Deficiency in IBC Special Inspections The session will compare light frame construction inspection requirements to other structural systems, identify the areas of deﬁciency in the Code, and present strategies to address these deﬁciencies. Kirk Harman is President and Managing Principal of The Harman Group, headquartered in Philadelphia, PA. He served for 10 years as Chairman of the NCSEA Code Advisory Committee’s sub-committee on Special Inspections.

B.) Find the Lost Dollars: 6 Steps to Improve Profits June Jewell, CPA, AEC Business Solutions

Learn to get the most from people, processes and technology to gain a competitive edge. June Jewell will show you how to improve your firm’s performance and prepare the firm’s future leaders to successfully take the reins. June Jewell is a speaker and business management consultant to the A&E industry, and author of Find The Lost Dollars: 6 Steps to Increase Profits in Architecture, Engineering, and Environmental Firms.

Concurrent Sessions 4:00 – 5:00

Panel from Structural Engineers Association of California Moderator: Ryan A. Kersting, S.E., Associate Principal Buehler & Buehler Structural Engineers, Inc.

A.) Changes to Wind Loading in ASCE 7-16 Don Scott, S.E., PCS Structural Solutions

The panel will discuss building rating systems, performance based design, renewed efforts for retroﬁt ordinances, and emerging concepts of community resilience that have launched a wave of discussions, innovations, and political involvement by California’s structural engineering community.

Concurrent Sessions 1:00 – 2:15 A.) The ASCE 7-16 Tsunami Loads Design Standard The session will provide an overview of the technical basis and methodology for tsunami-resilient design of critical and essential facilities, taller building structures and tsunami

STRUCTURE magazine

Concurrent Sessions 2:45 – 3:45

Kirk Harman, P.E., S.E., SECB, President, The Harman Group

Ron Hamburger, P.E., S.E., SECB, Senior Principal, Simpson Gumpertz & Heger

Gary Chock, S.E., President, Martin & Chock

Instant communication – email, Facebook, LinkedIn, Twitter, Snapchat, and more – doesn’t mean that we are communicating effectively. You will hear concrete tips to improve your written, verbal, and non-verbal communication skills. Kirsten Zeydel has over 15 years of experience leading over 200 projects and is the President of ZO Consulting, Inc. located in Orange, CA. ZO Consulting specializes in cold-formed steel and evaluating/coordinating exterior facades . Annie Kao is a ﬁeld engineer for Simpson Strong-Tie, where she connects with and educates engineers, architects, building ofﬁcials, and contractors on design and product solutions for wood, concrete, steel, and masonry construction in the Southwest region of the U.S.

This session will identify signiﬁcant changes to the wind load provisions of ASCE 7-16 and the rationale for these changes. These include new wind speed maps, changes to component and cladding pressure coefﬁcients, expanded commentary on tornado design, and more.

Don Scott has been a member of the ASCE 7 Wind Load Committee since 1996 and currently serves as chair, shaping future IBC provisions for wind design. He is also a member of the ASCE 7 General Provisions committee and the ASCE 7 Steering Committee, Chairman of the NCSEA Wind Committee and Past-Chair of the SEAW Wind Load Committee.

B.) BIM and Structural Engineering Desiree Mackey, P.E., S.E., BIM Manager, Martin/Martin

What is the future of Building Information Modeling (BIM) in structural engineering? This session will cover the processes, collaboration, and coordination with clients and other project participants, with an open forum for questions. Desirée (Dezi) Mackey is the BIM Manager at Martin/Martin, Inc., in Denver. Dezi has been using Revit for most of her career, and she is extremely active in the BIM community as a regular speaker at conferences, co-founder of the Rocky Mountain Building Information Society, and Chair of SEAC’s BIM Committee.

Welcome Reception on Trade Show Floor (Red) Rock ‘n’ Bowl with NCSEA

6:30 – 8:30 8:30 – 11:30

Friday, October 2 8:00 – 10:00 8:00 – 10:00

Member Organization Reports Vendor Product Presentations

Cliff Schwinger is a Vice President and Quality Assurance Manager at The Harman Group. He serves on the AISC Manuals Committee and has over 30 years of experience designing building structures.

Concurrent Sessions 2:45 – 3:45 A.) Concrete & CMU Elements in Bending + Compression John Tawresey, S.E, retired, KPFF Consulting Engineers

John Tawresey will present the applied mechanics equations for cracked elements subject to bending plus compression in a form more understandable for the practicing engineer and will then relate these to the latest masonry and concrete code requirements. JohnTawresey is a past president of The Masonry Society, past president of the Structural Engineers Risk Management Council (SERMC), past chair of the SERMC Claims Committee, past president of SEI and current member of the ASCE 7 Main Committee and TMS 402/602 Main Committee.

B.) The Decline of Engineering Judgment Jon Schmidt, P.E., SECB, Associate Structural Engineer, Burns & McDonnell

Concurrent Sessions 10:15 – 11:30 A.) Lateral Design of Buildings with Sloped Diaphragms Steven Call, P.E., S.E., Call Engineering

Buildings constructed with slope roof diaphragms are often designed as if they had a flat roof diaphragm. The significant differences between the lateral designs of sloped vs. flat diaphragms will be presented, including the proper diaphragm depth, the effect on the wall-todiaphragm connection, and the effect on the design of shear walls with a sloped connection to the diaphragm. Steven Call has over 25 years of experience in structural design of buildings, including 17 years as the president of Call Engineering, and is an instructor on design and analysis of diaphragms for Boise State University.

Modern society increasingly embraces theoretical knowledge and technical rationality – i.e., science and technology – while downplaying practical judgment. For structural engineers, this is especially evident in the constantly growing size and complexity of the codes and standards. Jon Schmidt will discuss the implications, unintended consequences, and potential alternatives. Jon Schmidt is an associate structural engineer at Burns & McDonnell. He chairs the editorial board for STRUCTURE magazine and authors a bimonthly “InFocus” column in which he often explores the relationship between philosophy and engineering.

Concurrent Sessions 4:00 – 5:00 A.) Creative Problem Solving for Repairing Wood Structures

B.) Working with Multiple Generations Panel Discussion with the NCSEA Young Member Group Support Committee Moderator: Emily Guglielmo, S.E., Associate, Martin/Martin Inc.

Structural engineering ﬁrms ﬁnd themselves managing four generations of employees, while working to attract, train and retain staff. This session will explore differences and similarities between generations, ways to leverage their uniqueness, and suggestions for successful integration of a multigenerational workplace.

Kimberlee McKitish, P.E., Nutec Group

Kimberlee McKitish will showcase four mini-case studies with creative solutions to wood repair issues. The case studies will look at the problems encountered, alternative repair options, and the thought process that led to the chosen solutions. Kim McKitish is a structural engineer with NuTec Design Associates, Inc. A licensed professional engineer, her area of expertise is in the design, repair, and reuse of manufacturing and industrial buildings.

B.) Business Ownership Transfer Craig Barnes, P.E., SECB, Founding Principal, CBI Consulting

Concurrent Sessions 1:00 – 2:30 A.) Lateral Analysis: Right Way/Wrong Way with Software Sam Rubenzer, P.E., S.E., Structural Engineer, FORSE Consulting

Lateral load requirements and corresponding analysis methods continue to increase. Sam Rubenzer will discuss the key points in lateral analysis when using different software, and will guide engineers regarding what is right and what is wrong in modeling loads. Sam Rubenzer founded FORSE Consulting in 2010 and has been assisting other structural engineers with, and comparing the attributes of, an assortment of structural engineering design software.

B.) Quality Assurance for Structural Engineering Firms

Craig Barnes and a likeminded structural engineer started CBI Consulting Inc. in 1984. In 2002 he designed and implemented a detailed buyout transition program with two of his long-term employees, to enable them to continue operations of what is now a multidiscipline engineering consulting firm. This presentation will be of benefit to attendees looking toward, or involved in, ownership transfer. Craig Barnes worked for a structural engineering firm, an architectural firm, and a national multi-disciplined consulting firm before joining with a fellow engineer to start and grow a new firm to an engineering architectural company with 35 employees.

6:00 – 7:00 7:00 – 10:00

Cliff Schwinger, P.E., SECB, Vice President & Quality Assurance Manager, The Harman Group

BIM modeling, sophisticated analysis and design software, increasingly complex building codes and young engineers taking on more responsibility earlier in their careers, all emphasize the need for a formal inhouse Quality Assurance program. This seminar reviews the components of a model Quality Assurance program, as well as the methodologies for performing in-house Quality Assurance reviews.

STRUCTURE magazine

Awards Reception (formal attire encouraged, but not required) NCSEA Banquet & Awards Presentation, featuring the NCSEA Excellence in Structural Engineering Awards and the NCSEA Special Awards (see pages 76 – 77 for honorees)

Saturday, October 3 8:00 – 12:00 12:30 – 2:00

NCSEA Annual Business Meeting NCSEA Board of Directors Meeting

September 2015

Take Your Practice to New Heights at the 2015 Structural Engineering Summit Trade Show Hours: Thursday, October 1st – 10 a.m. to 3:30 p.m. & 6:30 to 8:30 p.m. Friday, October 2nd – 7 a.m. to 12 p.m.

(###) Booth number

Denotes NCSEA membership

(138) AISC

(114) Simpson Strong Tie

(135) Alpine ITW

(106) Star Seismic

www.aisc.org

www.strongtie.com

www.trussteel.com

www.starseismic.net

www.concrete.org/

www.sdi.org/

www.armadillonvinc.com

www.steeljoist.org

www.atlastube.com

www.steeltubeinstitue.org

www.azzgalv.com

www.strand7.com

www.bekaert.com/building

www.cscworld.com

www.herculesbolt.com

www.usg.com

www.castconnex.com

www.valmonttubing.com

www.corebrace.com

www.vector-corrosion.com

www.dlubal.com

www.nucor.com/products/products/matrix/

www.euclidchemical.com

www.vulcraft.com

www.fabreeka.com

www.vulcanmaterials.com

(120) Steel Deck Institue

(143) American Concrete Institute

(119) Steel Joist Institute

(134) Armatherm (armadillo)

(140) Steel Tube Institute

(126) Atlas Tube

(144) Strand7 PTY LTD

(125) AZZ Galvanizing

(149) TEKLA/CSC Inc

(108) Bekaert

(141) USG

(146) Blind Bolt

(131) Valmont Tubing

(129) Cast Connex Corporation

(130) Vector Corrosion Technologies

(137) CoreBrace Buckling Restrained Braces

(136a) Verco Decking, A Nucor Co.

(117) Dlubal Software, Inc

(136b) Vulcraft-Nucor

(128) Euclid Chemical

(139) Vulcan Materials Company

(127) Fabreeka International INC (123) Fyfe Co./Fibrwrap Construction

Please visit www.ncsea.com for the most current list of exhibitors.

www.fyfeco.com

(115) Geopier Foundation Company/TENSAR www.geopier.com

Reserved

(122) Hilti

www.us.hilti.com/engineering

100

101

102

Available

103

104

105

106

107

(133) Holcim Inc www.holcim.us

113

112

111

110

109

108

114

115

116

117

118

119

(121) Lindapter

125

124

123

122

121

120

(118)Meadow Burke LLC

126

127

128

129

130

131

(116) Independence Tube Corporation www.independencetube.com

(124) ITW Red Head, Ramset and Buildex www.itwredhead.com

www.lindapterusa.com

133

Entrance

www.meadowburke.com

132

(107) MiTek, USP Connectors, Hardy Frame www.mitekbuilderproducts.com

141

(132) Nemetschek Scia

140 134

www.nemetschek-scia.com

149

(147) New Millennium Building Systems

148

147

146

142

139

www.NEWMILL.com

135

(142) Powers Fasteners www.powers.com

(148) RISA

www.risa.com

143

138

144

137

136a

(145) Side Plate Systems www.sideplate.com

145

STRUCTURE magazine

September 2015

136b BAR

National Council of Structural Engineers Associations

September 30th to October 3rd

Red Rock Resort Las Vegas, NV

Sponsors NCSEA extends its appreciation to the sponsors of the NCSEA Annual Conference. Platinum

Gold

Copper

Registration

Contributing

Full conference registration includes:

AZZ Galvanizing Services

• 17 educational sessions & resources on 2 tracks, geared toward the practicing structural engineer • Wednesday evening receptions • Thursday’s Gala Opening Reception • All breakfasts, lunches & refreshment breaks • Access to the NCSEA Trade Show • The NCSEA Awards Banquet, featuring the Excellence in Structural Engineering Awards and NCSEA Special Awards

Conference Hotel

The Red Rock Resort is located just 10 miles from the Las Vegas strip. Enjoy 4-diamond accommodations, the unmatched combination of comfort, extravagance and value for just $180/night + the discounted resort fee of $15. Reserve your room online at www.ncsea.com to take advantage of the group rate. Please contact NCSEA if you have trouble securing a room.

Transportation to Hotel

There will be plenty of opportunities to network with structural engineers from across the country at the sessions and these special events:

The hotel is accessible by shuttle from the McCarran Airport. The complimentary shuttle is included in your $15 resort fee.

• Young Engineer Reception • SECB Reception • NCSEA Red Rock ‘n Bowl Event on Thursday

More than just a conference hotel!

Whether you like gambling, entertainment, shopping or outdoor activities, the Red Rock area of Las Vegas has you covered! The host hotel, Red Rock Resort & Casino, features restaurants, lounges, a movie theatre and bowling alley, and a walkway to Downtown Summerlin, with shops, dining and entertainment options. If you want to check out The Strip, the hotel has a shuttle to take you there. If you prefer outdoor options, a high desert wonderland is located just minutes from the hotel.

Special Offers!

Engineers 35 years of age or younger pay only $250 for complete registration, which also includes special Young Engineer activities. First-Time Attendees to the NCSEA Annual Conference pay only $600.

STRUCTURE magazine

Reservation information is available at www.ncsea.com.

September 2015

606

West 57th street,

New York

Design of Structurally-linked Multiple Tower Structures By Sunghwa Han, P.E., S.E., LEED AP

he behavior of structurally-linked multiple tower structures is largely affected by the effectiveness of the rigid links made between towers at the bases or at the tops. These links have a strong influence on the distribution of wind and earthquake loads. Depending on the interactive dynamic behavior of the adjacent building parts with one another, a separation may or may not be needed. If the links are rigid enough, then two linked towers can be considered to be one integral structure. But if the links cannot be made strong enough, one might consider placing a separation joint.

Project Description The project consists of a shared base with two levels below grade and two residential towers (1.2 million square feet of gross building area holding 1,028 apartments): a 42-story tall tower on the east and a 17-story tall tower on the west side of the site. The two towers are connected by a shared podium below the 7th floor, and the podium footprint is enlarged below the 2nd floor. These two towers are structurally separate above the 7th floor. However, the occupants of the two towers require access between the two at every floor. Therefore, there is a separate, 10-story tall, 7-foot wide and 30-foot long cast-in-place concrete “bridge” structure (the west bridge) between two towers. This bridge structure will provide a continuous means of egress for each floor of the 17-story west tower. STRUCTURE magazine

Figure 1. Building perspective (south elevation).

The 42-story east tower is comprised of three sections (Figure 1). Two towers emanate from the 2nd floor, and each rises up to the 28th floor on the east side of the site. On top of these two towers, there is an additional 13-story tall building section rigidly connecting the two towers above the 28th floor. The two eastern towers are 30 feet apart below the 28th floor and have another seven-foot wide

September 2015

Figure 2. Site plan.

and 14-inch thick concrete slab pedestrian corridor-bridge (the east bridge) connecting them at every floor from the 3rd floor to the 28th floor. The corridor bridges are fixed to one tower but rest on sliding bearing pads on the other tower. This allows the two eastern towers to sway independently of one another from the 3rd floor to the 28th floor. The ground level gently slopes down to the west in the site. Thus, a portion of the ground floor is exposed above grade at the southwest corner of the site. Top of rock elevation gradually slopes to the west, but drops drastically at the northwest corner of the site. Spread footings or excavated piers resting on an allowable bearing capacity of 40 tons per square foot (tsf ) bedrock was recommended in the eastern portion of the site. The site is surrounded by the existing low-rise buildings ranging in height from three to seven stories tall. Most of the existing buildings are planned to be underpinned except the relatively newer buildings at the west end of the site. These buildings were found to be supported by caissons. The structure will also have caissons in this western portion of the site, where the top of rock elevation is low.

Structural System of Towers A combination of cast-in-place concrete (CIP) shear walls and 10-inch thick flat plates supported by CIP columns and shear walls is utilized to resist gravity loads, wind loads and earthquake loads. Some of the tower columns need to be transferred to accommodate a variation in the architectural layouts. The main elevator core located in the middle of the site (one of two eastern towers – Figure 2) provides vertical transportation for occupants of other towers. This main core is constructed with concrete shear walls. It is the primary source of the overall building stiffness, resisting the lateral loads and reducing the calculated displacements of the east tower. The seismic load resisting system of the buildings is defined to be a “Shear wall-Frame Interactive System with Ordinary Moment Frames and Ordinary Reinforced Concrete Shear walls” per the New York City Building Code (NYCBC) 2008. This system allows utilizing frame elements as a part of the seismic load resisting system for a building with a seismic design category B rating. It was beneficial to consider contribution of frames in the seismic load resisting system to reduce the calculated building displacements. STRUCTURE magazine

Structural System of Two Bridges and Separation Joints Originally, both bridges (west and east) were designed as a concrete slab pedestrian corridor-bridge fixed to one tower and supported on a sliding connection resting on the other tower at every floor. The lateral displacements of each tower were calculated, and the largest relative displacement was used to determine the distance of the separation joint for these elements shared by the adjacent towers. The displacements due to wind loads were calculated using the results from the wind tunnel test performed by Rowan Williams Davies & Irwin Inc. (RWDI). The elastic displacements due to the seismic loads were also calculated based on the elastic dynamic analysis (response spectrum analysis). These calculated displacements were magnified using the deflection amplification factor of Cd = 5 for Shear Wall-Frame Interactive System to compute the inelastic maximum displacements as per ASCE 7. These calculated inelastic maximum displacements were significantly larger than the displacements due to the wind loads. The required distance of separation joints was calculated to be 2 inches at the sliding connection of the east bridge and approximately 9 inches at the sliding connection of the west bridge, assuming two towers can be moving in opposite directions at the same time. The 2 inches of movement can be easily accommodated, but the 9 inches seismic separation requirement became a critical issue to the cladding design.

Code Requirements for Building Separation The building code allows the use of alternate methods to compute the distance of separation gaps which generally produce preferable results. When considering a seismic separation at the lot line, it is acceptable to set back structure from the property line by 1 inch for every 50 feet in height according to the NYCBC 2008 for structures assigned to seismic design category A, B or C (the project building is assigned to Seismic Design Category B). This section of the code may be applied to separate structures, assuming that the provided separation is sufficient enough to avoid significant damage to the adjoining structures.

continued on next page September 2015

The design team has adopted a more advanced analysis method (Nonlinear Response History Analysis – NLRHA) to ensure the sufficient separation gap between adjacent structures. The structural system of the west bridge was modified to become a separate ten story tall structure consisting of a 14-inch thick flat plate and four corner columns supported by the transfer beams at the 7th floor. This independently supported west bridge structure, with separation gaps at both ends, would be able to accommodate larger differential movements of two adjacent towers than the previously considered system (a flat plate supported on a sliding connection at one end). A 6-inch seismic gap (magnified by less than Cd) is tentatively provided at both ends of the west bridge. This will allow 3½ inches of movement of the buildings, after the compressible material in the gap joints is fully compressed. This net 3½ inches of separation has been verified through the recent NLRHA.

Period Range of Interest (0.72 sec – 5.4 sec)

Spectral Acceleration (g)

0.1

0.01

Development of Ground Motion Time Histories Initially, the site-specific seismic design spectra were developed for design of the structures. For NLRHA, three sets of ground motion time histories consisting of two horizontal components were provided by Amec Foster Wheeler, Environment & Infrastructure, Inc. Three sets of seed time history (1999 Chi-Chi Earthquake) were selected. Then, these time histories were scaled to match their response spectra with the site-specific design response spectrum as per Section 16.1.3.2 of ASCE 7-10 Chapter 16. This design spectrum (Figure 3) represents the Maximum Considered Earthquake (MCE) with a mean recurrence interval of 2475 years (2% probability of exceedance in 50 years).

606 West 57th Street Target Average of SRSS GRN180 GRN270 KAU078N KAU078W TAP078N TAP078W

0.001 0.01

0.1

Period (Sec)

Figure 3. Comparison of response spectra and 3 sets of scaled time histories prepared by Amec.

Estimating Required Seismic Separation The Nonlinear Time History Analyses were performed using Perform 3D, a commercial analysis software which considers material nonlinearity. The analysis model on Perform 3D includes the cellar floor excluding foundation walls. The flat plates were modelled as slab-beam elements with an effective width reduced from a full panel width as recommended in ASCE 41. Stiffness of slab-beam elements and columns was further reduced in consideration of nonlinear behavior of structural members. Shear walls were modelled using fiber sections, and link beams are modelled using beam elements with an inelastic hinge at both ends of the link beams.

Figure 4. Wind load cases maximizing differential loading between towers.

Wind Loads on Structurally Linked Structures

SUBSTRUCTURE 1

In general, for a typical single tower, the wind tunnel testing results are combined with the local climate data and the dynamic properties of the structure to generate the design wind loads. Wind loads are provided in the form of static point loads applied at each floor, along with the multiple load cases representing loading that imposes the maximum effect on the structural members. Each set of wind loads is represented by the corresponding load combination factors for each component (X, Y and Torsion) which are applied simultaneously to the tower to determine the internal forces acting in each member of the lateral load resisting system. For buildings with rigid links or shared components, additional loading scenarios must be considered. Load cases maximizing their effects on each tower will be separately generated first. When the foundation, podium or the linked portions such as a bridge between STRUCTURE magazine

SUBSTRUCTURE 3

SUBSTRUCTURE 4

SUBSTRUCTURE 2

Figure 5. Multi-blocks (substructures) approach used in wind tunnel study.

September 2015

Figure 6. Sample displacement time history (at top of the west tower in E-W direction).

towers are involved, additional simultaneous loading conditions maximizing differential loading between linked towers can be generated. These load cases (Figure 4) were used to design the two bridges and the 29th floor slab, which is the lowest rigid link of the top 13-story tall section spanning the two towers rising up to the 28th floor in the east tower. The differential movements of the adjacent towers were calculated using these load cases, and compared with the maximum calculated displacements for the seismic loads to finalize the distance of separation gaps. For an appropriate analysis of the wind tunnel data and accurate assessment of wind-induced responses, the entire building was “divided” into five blocks or “sub-structures” as shown in Figure 5 and presented in the RWDI’s wind study report. Diaphragms assigned in the analysis model, using ETABS®, are matched with this substructure configuration.

Currently, the foundation is under construction and the super-structure is scheduled to be completed by 2017. Danny Jadeja, P.E., Senior Associate, was the project manager and Ben Pimentel, P.E., President, was the engineer of record.▪ Sunghwa Han, P.E., S.E., LEED AP, is a senior associate at Rosenwasser/Grossman Consulting Engineers, P.C. and in charge of conceptual structural design and analyses, including a nonlinear response history analysis. She can be reached by email at sunghwa@rgce.com.

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Owner: TF Cornerstone Inc. Structural Engineer: Rosenwasser/Grossman Consulting Engineers, P.C. Design Architect: Arquitectonica Architect of Record: SLCE Architects, LLP Geo-technical Engineering Consultant: RA Consultants LLC Geo-seismic Engineering Consultant: Amec Foster Wheeler, Environment & Infrastructures, Inc. Wind Engineering Consultant: Rowan Williams Davies & Irwin Inc. (RWDI)

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The site is approximately 550 feet in the east-west direction by 200 feet in the north-south direction. The base of the towers is designed as one single structure without any expansion joint. In order to minimize shrinkage cracks, one 4-foot wide control strip is placed between the west tower and the east tower in the podium floors. It is located at approximately 2/3 of the building length in east-west direction (Figure 2).

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A Need for Speed

Coordinating Fast PaCed Urban ConstrUCtion By Ramon Gilsanz, P.E., S.E., F.SEI, Phil Murray, P.E., Gary Steficek, P.E. and Petr Vancura

Figure 1. Avalon West Chelsea. View from High Line Park.

ast-paced construction within a dense urban environment like New York City has several distinctive rationales, approaches, constraints, and requirements that necessitate careful coordination. The fundamental principle that drives the need for speed in construction is economic. The sooner a new building is completed and put into operation, the lower are the carried financing costs and the sooner the project can recapture generated revenue streams. There are numerous approaches and structural systems that can speed up the construction process. This article focuses on characteristics of flat plate concrete systems which, when floor plates are repetitious and identical, can achieve fast superstructure builds by using a 2-day concrete placement cycle. However, in tight urban locations, spatial constraints for staging, installation, material, and labor, as well as complexity of architectural/design coordination, can potentially interrupt the cycle and cause delays. Instant communication and in-the-field coordination are keys to maintaining the fast paced schedule and to minimizing mistakes. The structural engineer needs to be fully immersed in the day-to-day construction process to ensure successful and timely completion of the project. Three projects in New York City are presented to illustrate coordination issues that are particular to this type of construction: Avalon West Chelsea, 41-42 24th Street (aka “QLIC”), and 150 Charles Street. These developments are primarily multi-family residential, but also feature street-level retail, at- and below-grade parking, and amenity features at upper levels including planted green roofs and terraces. Both Avalon West Chelsea and QLIC are rental buildings that required high-speed construction. In contrast, 150 Charles Street is a luxury condominium development.

Avalon West Chelsea Avalon West Chelsea is a recently completed 588,000 square-foot “L-shaped” building located in the prime Chelsea Arts District of STRUCTURE magazine

Manhattan (Figure 1). Programmatically, this building consists of two distinct components: a 31-story tower featuring 309 luxury apartments, and a 14-story mid-rise that extends from the tower at the west to the elevated rail structure, now known as High Line Park, at the east, housing 405 units geared toward a younger demographic. The LEED Silver certified property also includes 142 affordable housing units, roof-top terraces, green roofs, rear yards, a fitness center, lounge areas, a 140-car parking garage, and retail space at street level.

QLIC QLIC, a 400,000 square-foot development at Queens Plaza North in Long Island City, is nearly complete (Figure 2). The 21-story tower holds 421 rental units, double-height retail at grade and parking for 120 cars below grade. The building’s 28,000 square feet of amenity space includes a rooftop pool, cabanas, a roof deck with an open-air theater and barbecue, a landscaped courtyard with a fire pit, media lounge, game room, fitness center, and other amenities on an accessible terrace.

150 Charles Street This 300,000 square-foot, 16-story luxury residential development in Manhattan’s West Village consists of 98 condominium units (Figure 3). The project incorporates the façade structure of an existing 4-story warehouse for the lower podium floors. Above, two corner towers flank a mid-block volume and each floor steps back, forming a cascade of terraces toward the Hudson River. The superstructure accommodates high gravity loads due to precast façade assemblies as well as 40,000 square feet of landscaped courtyards, green-roofs and planted terraces with up to five feet of soil cover. The building’s total landscaped area is equivalent to the combined areas of four small neighboring parks. continued on next page

September 2015

Figure 2. QLIC – architect’s rendering.

Structural Systems The structural systems of the three buildings consist of reinforced cast-in-place concrete flat plates, which is the most common slab structural system for high-rise residential construction in New York City (Figure 4). Compared to other structural systems, flat-plate construction maximizes usable floor-to-ceiling space (no beams or suspended ceilings) and also provides flexibility in the architectural layout of interiors since columns are not constrained to gridlines. This type of construction affords both lower costs and, depending on the uniformity of design, faster erection. Concrete construction is also

inherently fireproof and, with sufficient slab thickness, is minimally susceptible to vibration and noise transmission between floors. At Avalon West Chelsea, floor slabs are supported by almost 200 columns that range from one story to thirty-one stories, and seven shear wall configurations around two vertical cores. QLIC employs 120 columns and four cores. Despite its smaller size, 150 Charles Street has over 300 columns, though few of these extend the full height of the building. Columns are transferred from level to level, because each floor has a distinct architectural layout (Figure 5, page 54). For contrast: 1) QLIC included 10 column sizes and 4 transfers, 2) Avalon West Chelsea had 14 column sizes and approximately 20 transfers, primarily at the 13th floor connection between the tower and the mid-rise, and 3) 150 Charles included 41 various column sizes and 250 transfers, whereby columns substantially changed location, size/shape, or orientation between floors. Shear walls are located around building cores that house elevator shafts and egress stairs to provide a structural and fireproof enclosure of these spaces and to minimize the architectural impact of the walls. The 8-inch slabs used at each of these buildings accommodate multiple in-slab mechanical and plumbing services, as well as electrical conduits. The smaller-footprint repetitious upper floors of Avalon West Chelsea and QLIC were erected using one concrete pour on a two-day cycle (see below for explanation), whereas the larger lower levels required several pours. At 150 Charles, due to the irregular and constantly changing floor layouts, slab elevation steps, and the larger quantity of column sizes (requiring differently sized formwork), concrete placement took 16 days on average per floor. At QLIC, the locations of construction

Figure 3. 150 Charles Street – architect’s rendering.

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September 2015

joints between the two or three pours at the 27,000 square-foot horseshoe-shaped lower eight floors were assessed and determined in the field by the inspector-engineer. In-house Special Inspections therefore served to expedite this coordination in the field. At Avalon West Chelsea, however, the 575-foot-long floor slabs of the lower 14 floors demanded an advanced construction sequence analysis to understand changes in temperature and shrinkage of concrete. The structural design thus enabled a four-part pour sequence without the need for any expansion joints. All three projects incorporated crack-control reinforcing at column exteriors, shear wall corners, and re-entrant corners.

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Coordination During superstructure erection of highrise buildings, materials and equipment must be lifted to the top level using a tower crane, which all trades share. If a delay in delivery or staging prevents a component’s lift, placement crews must improvise using materials that are available

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The tower portions of Avalon West Chelsea (above the 14th floor) and QLIC (above the 16th floor) were built using a 2-day cycle whereby an entire floor slab is poured every two days (Figure 6 ). The maximum feasible floor size that can achieve a 2-day cycle is around 20,000 square feet, with floor plates around 65 feet wide. This dimension is typical of multifamily rental buildings organized around double-loaded corridors, and was the case for both buildings. Only a skilled labor force, experienced with this method of construction, can execute the cycle because it requires a specific sequence of tasks before crews can proceed to subsequent floors. These tasks include installation of: deck slab formwork, bottom mats, MEP duct/conduit/ pipe & blockouts, top mats, concrete for deck slab, column/shear wall formwork, reinforcing steel, and concrete for columns/shear walls. Therefore, a setback of any single step of the process can potentially “domino” into a delay of an entire work day. With the advent of computer aided analysis and design, buildings are more complex, less repetitive, and less conservative than they were in the 1950s, when this technique was developed. Highperformance buildings today also hold many more systems and services, so there are more trades and more congestion on the construction site. As a result, buildings with a 2-day cycle today are more challenging than they were half a century ago.

on the deck, rather than wait for subsequent lifts. The engineer must be available to assess if each ad hoc substitution is structurally acceptable. Moreover, at dense urban construction sites that have limited space for staging and storage, contractors may request temporary slab openings in order to reposition materials and equipment, or achieve clearance for installation. These logistics are not included on construction documents and are typically decided in the field. In the event that the designed slab reinforcement gets displaced as a result, the structural engineer is on-hand to coordinate its relocation. Coordination of mechanical, electrical and plumbing (MEP) trades typically occurs during shop drawing review, and layouts of these systems remain schematic until finalization of construction documents. MEP subcontractors often respond to field conditions

Figure 4. Flat plate concrete construction at QLIC.

by proposing amendments to sizes or locations of slab penetrations, which may impact the structural design. Such substitutions require the structural engineer’s review to confirm that the integrity of the slab is not compromised.

Foundations The foundation of QLIC is a combination of spread footings and a 3-foot mat foundation over rocky geology. The columns and shear walls at Avalon West Chelsea are supported by more than 1,000 piles within a 67,000 square-foot site containing varying rock and soil conditions. Here, the underlying rock stratum was found to be so shallow in about one-third of the site that the piles were too short to achieve substantial lateral resistance capacity. However, the remaining piles were able to provide sufficient lateral resistance to eliminate the need for footings or additional foundation elements. A foundation slab ties all the piles together. As the floor slabs are designed without an expansion joint, the structure engages all the piles jointly. The stiffness of the slab without expansion joints enables the 14-story mid-rise structure to laterally support the tower.

Envelope Avalon West Chelsea employs a standard masonry/curtain wall façade. The building envelope system of QLIC, however, is comprised of STRUCTURE magazine

Figure 5. Column transfer at 150 Charles. This transfer occurs at the slab edge and uses a concrete beam segment. Transfers at slab interior employ beams or thicker slab sections.

September 2015

prefabricated metal-stud-reinforced panels with thin brick veneer. These components were assembled on Long Island along with windows fabricated in Buffalo, and then shipped to the construction site in Queens. These panels with pre-installed windows were lifted and attached to the building using a crane. While the price of this system is comparable to traditional masonry façade systems, utilizing prefabricated panels saved roughly 20% of the time required to enclose the building. The combination of using the pre-assembled façade panels and just-in-time shipping (a delivery method whereby material arrives to the site at the time it is to be installed) resulted in multiple benefits for the design and construction team. By assembling the panels in the shop, the working conditions and consistent temperatures allowed for higher Figure 6. Avalon West Chelsea. Tower (at right) is on a 2-day cycle, with staging on mid-rise roof deck. quality water- and air-tightness, improving the energy efficiency of the building. Just-in-time delivery allowed Having both structural and building envelope teams in-house the Contractor to minimize staging and storage space while efficiently allowed communication of structural requirements internally, withenclosing the building. out the need for time-consuming Request For Information (RFI) While 150 Charles also used pre-fabricated panel components (in processes through the architect, thus enabling speedy communication this case pre-cast concrete with brick exterior), the entire building and coordination of interacting structural and envelope systems. featured additional façade systems including masonry cavity walls, Another aspect that facilitated coordination at QLIC was the use of curtain walls, window walls, stone cladding & storefront assemblies. Building Information Modeling (BIM), whereby all trades (strucIn most locations, the 13-inch precast panels are at least as thick as tural, mechanical, electrical, etc.) could be coordinated within a single the building frame to which they are attached (Figure 7, page 56).

Uniformity

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Uniformity of design and repetition of structural elements enables efficiency of construction, which in turn results in economies of scale. This approach allows installation crews to maintain consistent work processes and reuse formwork, rather than needing to adjust for each individual location. This speeds-up erection. At Avalon West Chelsea and QLIC, approximately 80% of the columns have the same cross section and reinforcing. At Avalon West Chelsea, 80% of pile caps are also typical. The varying areas of the floor plates and architectural amenity features at 150 Charles required a different interior layout for every floor, as well as numerous slab elevation changes at each level. This provided opportunities for innovative solutions to structural challenges associated with shifting and rotating columns between the floors through slab transfers. While the structural design responds to the architectural requirements to achieve real estate marketing objectives, such a design is not conducive to sustaining a 2-day cycle. The complexity and variety of floor layouts result in lathers relocating their staging at each level. The work space is further congested by MEP trades that also deal with offsetting mechanical shafts and plumbing risers at each floor.

Team Interconnectedness The structural engineer’s continuous presence in the field allows for quick responses to coordination issues. Since Gilsanz Murray Steficek (GMS), the project’s Structural Engineer, also served as special inspector of concrete and steel at each project, the engineer-inspector was often on-site. A direct line of communication between the construction team and the design team allowed challenges to be immediately resolved with the contractor, trades and other design team members, as needed. STRUCTURE magazine

September 2015

digital 3D model during design development and pre-construction. Few unanticipated conditions remained in the design by the time the first shovel hit the ground.

Economics The speed of construction translates directly to cost of the project. New York City construction projects with the scale and complexity of Avalon West Chelsea typically employ approximately 150 union workers on a given day of superstructure erection. According to local prevailing wages, this project would incur a cost of over $100,000 for a delay of a single day for labor alone. This does not include other costs associated with remobilization or equipment rentals. At the same time, the owner continues to maintain high-interest construction loans and his receipt of operating revenues is also delayed. As a result, field changes after concrete placement, such as demolition/removal/re-placement of concrete, or fiber-reinforced polymer applications for topical reinforcement or modification/repairs, while expensive, tend to be more economical to both contractor and developer as opposed to stalling the construction cycle for design coordination. The impact of construction speed upon a project’s overall economics, however, depends largely on the type of asset that is being developed. Avalon West Chelsea and QLIC are both rental apartment buildings. Other types of buildings, such as residential condominiums, follow a different economic formula focused on the apartment buyer. The target market with high sales prices demands diversity of unique units and amenity-rich architecture which cannot be easily systematized into repetitive workflows. Unlike rental buildings, where tenants constantly change, condominium building design is driven by the ability to sell the apartments. 150 Charles sold out with asking prices ranging from $3-$35 million (or approximately $3,200 per square foot). In comparison, Avalon West Chelsea currently rents at around $78 per square foot per year. This translates to a property value of approximately $312 per gross square foot, as assessed by the New York City Department of Finance. (Note that this incorporates the building’s operating expenses). Despite the structural design challenges at 150 Charles, the added costs of longer construction duration are absorbed by the condominium project since returns on investment are realized immediately upon completion and sale of the units, whereas rental revenue streams are distributed over the course of a building’s operation.

Summary Not all projects rely on speed to maintain profitability. Those that do, achieve efficiencies through uniformity of design, systematized construction methods, and the engineer’s engagement during construction. Moreover, when members of the design and construction teams have direct mutual access to information through all phases of project design, preconstruction and construction, coordination conflicts during erection can be immediately resolved.▪

Team: Avalon West Chelsea Owner/Developer: AvalonBay Communities Structural Engineer: Gilsanz Murray Steficek Architect: SLCE Architects Geotechnical Engineer: Mueser Rutledge MEP Engineer: MG Engineering Construction: AvalonBay Communities Concrete: SBF Construction Team: QLIC Owner/Developer: World Wide Group Structural Engineer: Gilsanz Murray Steficek Architect: Perkins Eastman Geotechnical Engineer: Langan Engineering MEP Engineer: MG Engineering Construction: Lettire Construction Corp. Concrete: RNC Construction Team: 150 Charles Street Owner/Developer: Witkoff Group Structural Engineer: Gilsanz Murray Steficek Architect: Cook + Fox Architects Geotechnical Engineer: RA Consultants MEP Engineer: Flack+Kurtz Construction: Plaza Construction Concrete: Navillus

Ramon Gilsanz, P.E., S.E., F.SEI, is founding partner of Gilsanz Murray Steficek and project manager for Avalon West Chelsea. He currently serves as Chair of the New York City Department of Buildings’ Structural Technical Committee and Chair of the American Council of Engineering Companies of New York Metropolitan Section Structural Code Committee. Ramon can be reached at ramon.gilsanz@gmsllp.com. Phil Murray, P.E., is founding partner of Gilsanz Murray Steficek and project manager for QLIC. Phil can be reached at phillip.murray@gmsllp.com. Gary Steficek, P.E., is founding partner of Gilsanz Murray Steficek and project manager for 150 Charles Street. Gary can be reached at gary.steficek@gmsllp.com. Petr Vancura is Director of Communications at Gilsanz Murray Steficek and has experience in construction management, real estate development and urban planning. Petr can be reached at petr.vancura@gmsllp.com. Figure 7. 13-inch precast façade panel at 150 Charles Street.

STRUCTURE magazine

September 2015

InSIghtS

new trends, new techniques and current industry issues

Creating Clarity and Scoping Profits in BIM with LOD 350 By Will Ikerd, P.E., CM-BIM, LEED AP

learly defined structural engineering contract scopes save engineers time, profit, and – most importantly – the personal satisfaction of their profession. Building Information Modeling (BIM) can improve this scope clarity if addressed proactively, or compound the difficulties in achieving clarity if ignored. The construction industry has reached a point where the use of BIM is not self-explanatory: it could be used to create 2D shop drawings, coordinate trades, or estimate cost. Since BIM came into existence, the industry has lacked a vocabulary for communicating the Level of Development (LOD) between parties. The BIM Forum™ Level of Development (LOD) Specification 2015 (BIMforum.org/ LOD) is an industry-changing reference that enables structural engineers to clarify their scope with BIM, providing the solution to this paramount problem of vague BIM scope definition. Previous to this development, many model element authors were unaware of expectations upon entering a project. The LOD Specification now provides a way to define the scope of detail and input minimums for each particular component of the design. It is simply a collection of definitions describing input and information requirements and graphic/model examples of the different levels of development for building elements. The document does not outline the necessary levels of development for different steps in the construction process, leaving these determinations for each project team. Instead, it gives a common vocabulary for use between parties on a project team. It is important to note that the document is now in its 3rd edition, with the 2015 version released for public comment. Key aspects of the document are its support and input from the national BIM Masonry (BIMforMasonry.org), Steel Joist Institute (SteelJoist.org), Steel Deck Institute (SDI.org), ACI (Concrete.org), and the National Institute of Steel Detailers (NISD.org). LOD definitions in terms of model elements* (emphasis added): • LOD 100 The Model Element may be graphically represented in the Model with a symbol or other generic representation, but does not satisfy

A masonry wall element progression shown from LOD 200 through 400. Copyright, BIM Forum (BIMforum.org/LOD) & IKERD Consulting (IKERD.com) 2015.

the requirements for LOD 200. Information related to the Model Element (i.e. cost per square foot, tonnage of HVAC, etc.) can be derived from other Model Elements. • LOD 200 The Model Element is graphically represented within the Model as a generic system, object, or assembly with approximate quantities, size, shape, location, and orientation. Non-graphic information may also be attached to the Model Element. • LOD 300 The Model Element is graphically represented within the Model as a specific system, object or assembly in terms of quantity, size, shape, location, and orientation. Non-graphic information may also be attached to the Model Element. • LOD 350 The Model Element is graphically represented within the Model as a specific system, object, or assembly in terms of quantity, size, shape, orientation, and interfaces with other building systems. Non-graphic information may also be attached to the Model Element. • LOD 400 The Model Element is graphically represented within the Model as a specific system, object or assembly in terms of size, shape, location, quantity, and orientation with detailing, fabrication, assembly, and installation information. Nongraphic information may also be attached to the Model Element.

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September 2015

It is important to note that there is no LOD of an entire model; the model is a mixture of different elements within different LODs. For permit drawings, which will be required for the foreseeable future on building projects, elements are typically only modeled to LOD 300. However, for full trade coordination, higher LOD is required, short of fabrication LOD. For this reason, the author proposed LOD 350 for bridging the gap between element development at permit drawings and fabrication level. LOD 300 does not include the information necessary for full cross trade coordination, while LOD 400 requires information that may not yet be available. LOD 300 represents model elements traditionally shown in the plan view of a set of construction documents. This would include main structural members with information such as specific location and type. Construction Documents made from the LOD 300 model are accompanied by 2D information: general notes, typical details, specific details and specifications to define higher level information not typically shown in 1/8-inch scale plans or modeled for permit drawings. For coordination, model elements with an LOD of 350 represent information generally shown with typical details in construction drawings. This information requires trade-knowledgeable input to model accurately. Most main structural member elements are at LOD 300. However, structural engineers must be mindful that LOD 300 requires elements to be in the

correct location. For example, although the 2D plans may appear to be correct, sloping roof members that are modeled flat are not at LOD 300. Also, design-level open web bar joists at LOD 300 are not acceptable for trade coordination with MEP, as they do not have the specific manufacturer’s web profiles to detect conflicts. Other areas of misunderstanding are structural elements shared with architecture, such as tilt walls, slabs and load bearing masonry walls. A masonry wall element, for example, is shown in the progression from LOD 200 through 400 (see the accompanying graphic). Note that most structural design models would only take the wall elements to LOD 300 to create sealed 2D construction permit drawings. The wall at LOD 300 would specifically identify the masonry system, and would reference typical details and project specifications for higher levels of development details. This higher LOD information, such as but not limited to jam conditions, bond beams, grouted cells, dowel locations, and joints, would not appear until LOD 350 and higher. These higher LOD aspects would typically be modeled as part of the construction side submittal process. LOD 400 masonry modeling is currently found on more progressive BIM projects

in limited areas of building as part of virtual mockups for water proofing review at key building transition areas. Situations such as this make a compelling case for using LOD 350 as an important step between specific assemblies and detailed assemblies for coordination with manufacturer’s specific content. The structural engineer’s scope should address who is responsible for modeling such information at higher LOD, as owner and lead designers begin requesting higher LOD model elements. As more projects require detailed 3D coordination, the need for accurate MEP models will become even clearer to lower the risk of the entire design team (A & E). There is little value in above ceiling coordination in taking the architectural and structural model elements to LOD 300 (specific in the actual orientation) if MEP model elements are only at LOD 200 (generic in approximate location). Structural engineers should consider adding additional services in their contracts for manual MEP coordination review if the MEP model elements are not to LOD 300. This represents the added time the structural engineer will have to invest in the project during construction administration to deal with changes in the MEP due to lack of model definition (and MEP design). For

instance, all gravity plumbing lines must slope for these elements to be at LOD 300, whereas many MEP design models do not slope these lines. This creates the risk of failing to discover that the line will not fit below the structure and above the ceiling if the lines are not modeled at LOD 300 (with slopes). The structural engineer may then be forced to consider adding web openings in their beams or redesigning shallower beams, losing time and profit. Profit is vital in the business of any profession; structural engineering with BIM is no different. Clearly defined scopes in BIM and LOD 350 is a key to creating clarity in the design-to-construction process and aiding structural engineers in the opportunity to find profits in clearly defined project BIM scopes.▪ Will Ikerd, P.E., CM-BIM, LEED AP, is a principal at IKERD. He currently co-chairs both the Designers Forum of the AGC’s national BIM Forum and the Structural Engineering Institute’s national BIM Committee. Additionally, he co-chairs the AGC BIM Forum – AIA workgroup on Structural LOD. He may be contacted at info@IKERD.com.

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EnginEEr’s notEbook

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Moment-Curvature and Nonlinearity A Fundamental Discussion By Jerod G. Johnson, Ph.D., S.E.

early every day in our careers as structural engineers, we consider the following equations: Mn = As fy(d-a/2), Mn = Fy Z x

Readers will no doubt recognize these as the nominal flexural strengths utilized in beam designs for reinforced concrete and steel, also known as (among other things) the flexural limit state. While there are variations reflecting unbraced lengths, the presence of compression reinforcement, axial loads and other considerations, these are the fundamental relationships. What exactly does this mean? Structural engineers understand that the capacities represented by these equations do not correspond to the loads that we actually expect the members to see during a typical service condition. Rather, these are the approximate magnitudes of loads that the members would experience in the unlikely event that they are pressed toward ultimate failure. This will hopefully never occur for members that are part of the ‘gravity’ system. Likewise, this will hopefully not occur for a large but rare transient event in members that are part of the ‘lateral’ system. Either way, the fundamental objective is to ensure that designs have φMn greater than Mu, the maximum flexural factored load effect. Now consider the ‘middle ground’ in this scenario – the flexural behavior that occurs between zero load and a condition where Mu equals Mn. Doing so offers a glimpse of basic nonlinear behavior and the formation of flexural mechanisms that hopefully reflect stable and ductile performance. For the concrete beam scenario, at a load equal to Mn it is assumed that the reinforcement has yielded in tension following the idealized elastic-to-plastic relationship, with a constant stress equal to yield stress (fy) with a strain somewhere beyond the yield strain of approximately 0.00207 (for Grade 60 bars). It is also assumed that the concrete acting in compression has reached a strain of 0.003 and that at this point, it is theoretically being crushed at its extreme compressive surface. To understand what has happened in the beam while reaching this point requires developing a series of calculations reflecting various levels of reinforcement strain, from zero all the way

Moment vs. curvature relationship for reinforced concrete beam.

up to the net tensile strain (εt) which occurs at a theoretical load of Mn. For each one of these calculations, it is possible to develop resultant forces based on relative strains in the tension steel and the concrete compression zone, and a momentcouple relationship based on the distance between the resultant forces. This relationship is relatively simple, since we know from statics that the resultants of tension and compression must always be equal in magnitude and opposite in direction. While many theories have led to the development of models reflecting the distribution of stress in the concrete compression zone, assuming a uniform compression zone as prescribed by ACI 318 is valid and greatly simplifies the calculation, enabling the a/2 portion of the equation previously shown. For each series of calculations, the curvature value is simply taken as the strain in flexural reinforcement divided by its distance from the theoretical neutral axis. Plotting the values of Mn and curvature yields a load-deformation (curvature) relationship, an example of which is shown in the Figure. Among the interesting things observable in this figure is that nominal moment capacity is nearly reached at the point where the tensile reinforcement first yields – long before the member reaches is ultimate capable curvature at Mn. What does this mean in a practical sense? Observe that the nominal flexural strength is approximately 240 kip-ft and that this particular member reached this capacity at a curvature just beyond 0.0002/in. However, the member was able to sustain this load to a curvature nearly five times this value, thereby demonstrating the ductile behavior toward which the codes are geared. This exercise demonstrates that failure of this member would be preceded by deformations

STRUCTURE magazine

September 2015

likely to present a serviceability issue, thus giving occupants warning of trouble. As an interesting exercise, consider increasing the area of reinforcement to the balanced or over-reinforced condition. The results will demonstrate a smaller ratio of maximum capable curvature vs. yield curvature, which grows ever smaller as the amount of reinforcement increases. This demonstrates the pitfall of simply adding reinforcement to improve strength. It is also worthwhile to consider seismic response. The Figure demonstrates the potential for favorable hysteretic behavior as the area under the curve is proportional to the energy release occurring through each cycle of flexural load and rotation. If the reinforced concrete is detailed correctly, this is a favorable, stable and controlled method for dissipating energy during an earthquake, thereby preventing it from becoming manifest elsewhere. The same holds true for steel beams, provided that they are appropriately sized and detailed to promote fundamental material nonlinearity, as opposed to other forms of ‘macro’ nonlinearity such as global or local buckling. Observations of the projected theoretical behavior of mechanisms such as this are worthwhile. They offer a glimpse into the basis for code provisions that we often take for granted.▪ Jerod G. Johnson, Ph.D., S.E. (jjohnson@reaveley.com), is a principal with Reaveley Engineers + Associates in Salt Lake City, Utah. A similar article was published in the Structural Engineers Association-Utah (SEAU) Monthly Newsletter (September 2011). Content is reprinted with permission.

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business issues

CASE BuSinESS PrACtiCES

Strategic Planning: A Comprehensive Approach By Dilip Choudhuri, P.E.

ost high-performing firms that are successful over the long term are those which truly embrace strategic planning. If you have been part of a strategic planning process in your firm and are still skeptical about the importance of such a process, you should revisit the goals of your firm’s last two strategic planning sessions and assess how your firm has changed as a result. You will likely be amazed! Walter P Moore has been in business for 84 years; its latest comprehensive strategic plan was developed in 2012 and is currently being implemented. The firm has the benefit of the historical perspective of the last five strategic plans that outlined its trajectory and validated the importance of building upon previous strategies. Walter P Moore’s successful strategic planning under the author’s leadership is the basis for this article.

people “outside the room” should be engaged for various efforts, increasing engagement and buy-in. Deciding on an Approach There are many approaches that can be used for comprehensive strategic planning. For example, you could chose to conduct a vision-based, goal-based, issue-based, or scenario-based planning session. Some of the most widely used books which should be read prior to deciding on a strategic planning approach include The Balanced Scorecard by Kaplan and Norton, Blue Ocean Strategy by Kim and Mauborgne, and Good to Great by Collins. Each approach has its special nuance and benefit. However, whichever approach is ultimately chosen, the successful implementation of the resulting initiatives requires a strong commitment from the core strategic planning team. Hiring a Facilitator

Planning Framework Getting Started Ideally you want to start the process by having the firm’s senior leadership team agree on the need for a new strategic plan. This should be followed by hiring the strategic planning consultant, providing the selected consultant with necessary firm background and deciding on two important facets of the proposed strategic planning work – (i) the ideal number of core team members and (ii) the methodology for the strategic planning session. You want to have the largest number of people in the room that the facilitator is comfortable including, without any adverse effects on sessions for the chosen strategic planning approach. This will afford you greater flexibility on the issue of being inclusive with team members from across the firm who are at different stages of their professional career. Selection of the core group should be well thought out and incorporate new leaders within the firm as well as senior leadership for a balanced perspective. Preferably, these core strategic planning team members are either principals or senior project managers. Consistent communication firm-wide about the ongoing process can build excitement, especially among those not actively involved in the planning sessions. These

Working with an expert facilitator knowledgeable about your selected approach, and one who is intimately familiar with firms in the A/E/C space, is critical. Indeed, most successful strategic planning efforts require firms to hire an outside specialty consultant to facilitate the process. The external facilitator, by virtue of being an outsider, has tremendous freedom of expression and inquiry, and can maintain objectivity, which is understandably difficult to do from an insider perspective. At Walter P Moore, the external facilitator who was selected used The Balanced Scorecard approach to guide five strategic planning sessions that spanned a 12-month period for the 2012 strategic planning. The session was a goal-based strategic planning session which was tested for alignment with the firm’s overall vision. The core strategic planning group of twenty-two leaders met for two days for each of the five sessions. These meetings were held within Walter P Moore’s facilities, which made it efficient from a logistics point of view and also signaled to others in the office that the firm’s leaders were planning the future of the firm in plain view. When working in your own facilities, it is even more important to stay focused and observe the ground rules. There were always assignments between the sessions for the entire group of twenty-two. The facilitator was very successful in making

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September 2015

Culture and strategy are intertwined.

sure that the conversations at these sessions were not dominated by a few of the most outspoken in the room.

Assessing Firm Culture For strategic initiatives to be successful, a supportive cultural environment is a must. It is critically important to seek the answer to “How are things done within the firm?” Personal mastery guru David Aitken of the Aitken Leadership Group says, “Any good strategy is going to depend on culture to support it. So culture and strategy become synergistic, part of a system diagram.” Hence, knowing the cultural predisposition of your firm is an important first step in a successful strategic planning process. Conducting a cultural scan at the early stages of the strategic planning process is also a great way to engage all members of your firm. Typically, your strategic planning consultant will need to depend on a specialized personal mastery expert to develop the parameters of a cultural scan and then interpret the findings. There are well-established ways in which organizational behavior experts collect valuable qualitative data through employee surveys with respect to the cultural aspects of a given firm. At Walter P Moore, all employees responded to a confidential survey that helped develop the cultural scan for the firm. From the data, the firm recognized the collective wisdom of how employees viewed what made Walter P Moore successful in the past, how things get done, and how they envisioned the firm’s future – very valuable insight for all involved. It was also recognized that, as a firm, organic growth continued on page 65

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was preferred over growth through mergers and acquisitions because it allows maintenance and reinforcement of its culture across the firm. Walter P Moore has made just four acquisitions in its history, so an acquisition is rare. Culture is important; hence, the firm is much more deliberate about determining the cultural fit in the due diligence process as it approaches any acquisition opportunities for growth.

Four Basic Steps to Strategic Planning

Steps for strategic planning.

Expecting linearity in the strategic planning process is unrealistic. The overall process is highly non-linear; hence, having a high level of comfort and trust in the selected facilitator is of utmost importance. The facilitator must guide the sessions while retaining the flexibility to modify the direction of the sessions to elicit open dialogue concerning the four basic steps to strategic planning – Current State Analysis, Desired Future State, Understanding of Barriers, and Development of a Strategic Plan. These steps do not necessarily occur in sequence. Rod Hoffman, CEO of S&H Consulting, a strategic planning firm, likes to use The Balanced Scorecard as a framework for strategic planning sessions. Hoffman says, “Strategic planning is about connecting the dots so that everyone can see the picture.” A comprehensive strategic planning exercise typically requires multiple sessions over multiple days. The benefit of having the core team attend all of these sessions is the continuity component, and the team building that happens through group exercises during the sessions and informal conversations outside of the sessions. 1.0 Current State Analysis Context for the current state analysis is established by restating the vision, mission, and core values, and by sharing the updated firm-wide cultural scan with the core strategic planning group. It is critical for any strategic planning exercise to do a deep dive into the current state of the firm, and the current internal environment as perceived by the internal core team, members of the firm, and clients of the firm. To understand the current state of the firm, a basic Strengths, Weaknesses, Opportunities, Threats (SWOT) analysis should be conducted by the core team. In addition, key production leaders who may not be part of the core strategic planning group can be surveyed for additional SWOT data points. A select group of the firm’s clients can be surveyed, via a series of prepared questions, on their thoughts on Social, Technological,

Environmental, Economic, and Political trends affecting their industry (STEEP analysis) in the next five years. These client response data sets can then be aggregated to enhance the current state analysis. This is yet another example of where others can be engaged who may not be part of the core strategic planning group to improve the overall process. The core strategic team can then be engaged to see what trends are working in the firm’s advantage (also known as tailwinds) and those that are working against the firm (headwinds). During the strategic planning process at Walter P Moore, the firm confidentially turned to about 40 trusted clients across market sectors to provide answers for the STEEP analysis. These were very useful client touches in that they educated the firm about their client’s business realities in their specific sector while showing Walter P Moore’s interest in them. The data collected was sorted by the various categories to understand the impact of these client-specific realities. Some created opportunities and some required the strategic direction as a firm to be altered. 2.0 Desired Future State This desired future state analysis should not be limited to business growth opportunities, but should also examine internal and cultural aspects of the firm’s future. This goes back to the central idea that business strategic growth is very much intertwined with culture. The growth opportunities can be categorized as those that can be achieved through an increase in market share, change of portfolio, and through acquisition of new lines or divesting from a current line of business. There are many exercises that can be developed by the facilitator to have a dialogue within the core group about these topics, and also engage the group members in smaller working groups with a report out process. In Walter P Moore’s 2012 strategic planning process, the core team of twenty-two leaders each had five votes to endorse various growth and cultural strategies that were the result of the planning work. In addition, the full corporate Board of Directors had an

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September 2015

opportunity to vote on each of the stated growth and internal/cultural initiatives. This was another way to formally get the board as a group to review selected initiatives and provide their wisdom with respect to prioritization of the strategic initiatives. The votes from the Board of Directors were weighted and then tabulated in addition to those of the core strategic planning group. Corporate boards tend to like to weigh in on strategic initiatives because they, as a group, do have strategic thinkers who have taken on the responsibility. It is also much easier for the board to support the CEO when they are implementing the strategy, because they are familiar with it and have provided a voice to the plan. Walter P Moore’s core team settled on thirteen initiatives – seven growth initiatives and six internal/cultural initiatives. 3.0 Understanding of Barriers This phase of strategic planning builds on the current state analysis described in Step 1 and the desired future state analysis described in Step 2. There is clearly a need to have an open and robust discussion about the culture of the firm and the current state of the external barriers that impact the attainment of the desired future state. If you have a large core strategic planning team (20-24 people), you can use group work and a voting process to continue engagement and maintain focus. This phase of planning provides insight into potential cultural initiatives needed for success, and can test the durability of your core practice areas. Such informative insights into the firm likely would not have been discovered without having gone through this comprehensive process. 4.0 Development of a Strategic Plan Potential growth and cultural strategies should be voted on by the core group and the Board of Directors of the organization. Each strategy should be associated with a weighting system to allow ranking by levels of importance. The development of the final strategic plan requires the core team to consider three horizons or time-frames of growth. Horizon 1 includes strategies that affect the core business and are

things that need to be addressed immediately. Horizon 2 contains those strategies that need to be addressed in three to five years and are about building emerging practice areas. Horizon 3 strategies are those that are very ‘blue-sky’ growth opportunities achievable further out – five years plus into the future. In general, there should be more initiatives in Horizons 1 and 2 than in Horizon 3. Stair-step to growth – starting a new practice while limiting risk.

Strategic Implementation Once a strategic direction is identified, the final step and bigger task is to develop a preliminary schedule of implementation for each strategic initiative adopted. Once implementation plans are developed, they should be reviewed by the Board or a subset of the Board for acceptance and authorization. The strategies for Horizon 2 or 3 require better risk management since they are considered relatively uncharted territory compared to the core business strategies. The CEO should create a detailed communication plan to share the strategic direction with firm members who were external to the process. He or she should regularly communicate updates of the strategic plan’s implementation as items are completed or revised. This keeps the strategic plan front and center for the entire firm. One can consider a stair-step implementation process for those initiatives in Horizon 2 and 3. The first step is to conduct small-scale experiments of a service or practice area, followed by a validation of the service or practice area – is it profitable? Is it something that fits our firm well? Once the service or practice area is validated, one can replicate and then scale the practice area within the firm. Think carefully about key performance indicators for each of the strategies being implemented. As it is said, “what cannot be measured cannot be improved.” Once a firm-wide implementation plan is developed, individual business units or groups within a firm need to develop complementary implementation plans that are shorter-term and co-exist with firm-wide strategic direction. Walter P Moore’s 2012 plan outlined several strategic growth initiatives that were specific to select individual business units (business unit = a group of complementary practice areas with service offerings). It was then the responsibility of each business unit to develop the strategic implementation plans for the growth initiative. The implementation plan was then reviewed by a review committee consisting of members from across the firm. Seventy-five percent of the review committee membership consisted of people within the business unit for the specific growth initiative and the remainder from outside the business unit. In 2014, a Strategy

Council was created as part of the organizational structure which is chaired by the CEO and has the business unit leaders from each operating group and two additional members that are appointed by the CEO. The Strategy Council meets on a quarterly basis to focus on the strategic agenda of the firm. The implementation plans are subsequently submitted to the Strategy Council and the Board of Directors for formal authorization and approval.

Achieving Results Team members within high-performing firms will want to see results of the strategic planning process. Results primarily depend on solid execution of the strategic plan. The old project management adage that you have to “plan the work and then work the plan” is true for strategic initiatives, too. In a multi-discipline firm, the number of concurrent strategic initiatives can be numerous and overwhelming. It may be acceptable to have multiple growth and internal/cultural strategic initiatives, as long as the implementation team

5 Key Takeaways 1) Use an external facilitator familiar with the A/E/C industry for your strategic planning. 2) Conduct a cultural scan of your entire firm and try to communicate the importance of the survey for a high response rate. 3) A long-range view of the strategic planning process is important. This allows you to make sure that you focus on the progress and not worry about small delays that are bound to occur. 4) Communicate the final strategic plan widely with your entire team. Strategic implementation happens both from the top down and the bottom up. 5) Devote ample time to developing actionable implementation plans. The goals of the implementation plans should be revisited at least quarterly to ensure their achievement.

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September 2015

members are selected from across the organization and also across various practice areas of the firm. There are many reasons for this: implementers bring passion to their initiative of choice (ask for volunteers for some initiatives), they bring subject matter expertise, their service to the firm should be linked to their personal action plans and annual performance goals. When leaders stop going to the same ‘four’ people for all strategic implementation needs, you have the unintended and beneficial consequence of getting broad based buy-in for the implementation of the strategic plan. For a multidiscipline firm or firms in multiple geographies, it becomes vital to energize some of the non-core practice areas or emerging offices that have the potential to blossom in the near future.

Conclusion A comprehensive strategic planning process requires a huge commitment of resources for any professional services firm, but yields incredible benefits. Having the entire senior leadership team support the effort, without any questions, is critical since the strategic planning process will intrude on your firm’s immediate needs and other tasks that are critically important today. A comprehensive strategic planning and implementation process is akin to a marathon rather than a sprint. To succeed, we must maintain collective focus on the critically important initiatives for the three horizons – short, medium and long-term. Walter P Moore implemented a new organizational structure as a direct result of one of the strategic planning initiatives from the firm’s 2012 Strategic Plan. Operating under a new organizational paradigm for the firm for just over a year now, Walter P Moore has successfully deployed a flat, responsive organizational structure to address the challenges of a changing marketplace and client needs.▪ Dilip Choudhuri, P.E., is President and CEO of Walter P Moore. Dilip can be reached at dchoudhuri@walterpmoore.com and followed on Twitter @dilipC66.

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Structural Education Deficiencies Timber and Masonry By Kevin Dong, P.E., S.E. on behalf of the Basic Education Committee

ne of the concerns of professionals in the structural engineering community is the limited exposure to timber and masonry design for graduating civil/structural engineering majors. A majority of smaller scale structures are constructed using timber/ masonry separately or a combination of these materials; yet most civil/structural engineering curriculums emphasize steel and concrete as building materials and provide less of a focus on timber and masonry design. Additionally, the timber industry has evolved beyond the typical traditional stick-framed construction Suggested Timber/Masonry Module One 1) Wood Buildings and Design Criteria using allowable stress design (ASD) 2) Properties of Wood & Lumber Grades 3) Beam & Joist Design – Sawn Lumber, Glued Laminated Timber, Manufactured Lumber 4) Stud & Column Design – Axial members (buckling versus crushing) and combined axial and bending 5) Shear Wall Design – Segmented and perforated wall concepts. Calculations for segmented wall method only 6) Diaphragm Design – Sheathing, chords and collectors for flexible diaphragms 7) Connector capacity – Behavior and capacity of nails and bolts 8) Masonry Buildings and the history of masonry as a building material, ASD versus LRFD 9) Construct-ability, sequencing, and terminology for masonry construction, material strengths and lab testing 10) Beam Design (LRFD) – flexural model, failure modes, shear requirements, deflections using cracked section properties 11) Column/Pilaster Design – role of longitudinal and transverse, pure axial and combined axial and bending 12) Shear Wall design – in-plane design for shear, flexure, and introduction of the axial-moment relationship 13) Wall Design – out of plane design, including second order effects

to a more advanced and innovative building material, and many students will be unprepared to design buildings without this as part of their curriculum. As noted in prior STRUCTURE® articles, the National Council of Structural Engineers Associations (NCSEA) promotes a varied curriculum that includes a balance of analysis, design, and other technical skills. Timber and masonry design are an integral part of the recommended curriculum. And although NCSEA believes timber and masonry should each be provided as its own course, a timber/masonry material design curriculum can be organized into two modules: element design and building systems design. In the first module, the basics are introduced, such as: the properties of a given material, advantages and limitations of a given building material, design of beams (flexural), columns (axial and combined axial and bending), shear walls or structural panels, and diaphragms Suggested Timber/Masonry Module Two 1) Building configuration 2) IBC load requirements (gravity and lateral) 3) Selection of roof and floor systems 4) Preliminary design process 5) Structural design computations using allowable stress design (ASD) for timber and LRFD for masonry, then develop working drawings (notes, plans, elevations, details) for structural systems including: a. floor framing – sawn lumber, I joists, manufactured lumber, glulams, etc. b. roof framing – sheathing, stick framing, prefab trusses, tiebacks/ anchorage etc. c. wall framing – sheathing, studs, posts, headers, masonry, trim requirements at openings etc. d. shear walls – sheathing/block selection, chords, connections, segmented, perforated (optional) for plywood and masonry, etc. e. diaphragms – sheathing, chords, collectors, sub-diaphragms, cross-ties, flexible vs. rigid, cantilever, etc. 6) Configuration & design of connections

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(where applicable). The second module links the use of building codes and standards, such as the International Building Code, American Concrete Institute’s Building Code Requirements for Structural Concrete, American Institute of Steel Construction’s Specification for Structural Steel Buildings, American Wood Council’s National Design Specification for Wood Construction, and Masonry Standards Joint Committee’s Building Code Requirements for Masonry Structures, with structural analysis to design small scale (and regular) buildings. The curriculum includes developing a framing system for both lateral and vertical loading to emphasize the concept of load path and to gain exposure to building irregularities in structural systems. Then there is determining the gravity and lateral loads to establish loading and design criteria, followed with designing beams, columns, structural panels, diaphragms, collectors, and connectors to resist gravity and lateral load requirements. Finally, there is the development of structural drawings (plans and connection details) to connect analytical work to the communication tool used for construction. The last step exposes students to a critical part of design, but also to constructability and building sequencing. Together, Module One and Module Two encompass the NCSEA Core Curriculum suggestions for Timber and Masonry. It’s envisioned that the first module is either a combined timber/masonry course, as currently offered at some institutions, or as two separate timber and masonry courses. Schools limited by a variety of constraints can implement Module One to expose students to both materials. Module One is sufficiently intense to provide a student with a basic understanding of both materials so that self-teaching can raise the student to a higher level of understanding. In either scenario, 60 (semester) lecture hours are proposed to introduce the basics of material design for wood and masonry. The second module would include the design of a regular building with the two materials, and a comparative study of using either masonry or wood as the lateral load resisting elements, such as shear walls. Although this module may be more demanding, 60 lecture or contact hours are foreseen as a minimum to cover the recommended material.▪

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ANCHORING GUIDE American Wood Council

Phone: 202-463-2766 Email: lbalsavage@awc.org Web: www.awc.org Product: Special Design Provisions for Wind and Seismic standard Description: Provides criteria for proportioning, designing, and detailing engineered wood systems, members, and connections in lateral force resisting systems. Allowable stress design (ASD) or load and resistance factor design (LRFD). Nominal shear capacities of diaphragms and shear walls are provided for reference assemblies.

Bentley Systems

Phone: 800-236-8539 Email: structural@bentley.com Web: www.bentley.com/ Product: RAM Connection Description: Perform analysis and design of virtually any connection type, verify connections in seconds, all with comprehensive calculations, including seismic compliance. Increase productivity to optimize workflows. Full integration of 3D design models, including the ability to customize the application with your preferences.

Construction Tie Products

Phone: 219-878-1427 Email: steve@ctpanchors.com Web: www.ctpanchors.com Product: Stitch-Tie Description: Stainless steel helical anchors for masonry crack repair (6mm) and masonry anchors (8mm & 10mm) for re-attaching existing brick veneers to masonry, wood, concrete, tile and steel stud. Replicates missing wall ties, but stronger and stiffer. Installs easily and is concealed when completed.

Decon® USA Inc.

Phone: 866-332-6687 Email: frank@deconusa.com Web: www.deconusa.com Product: Anchor Channels Description: Exclusive representative of Jordahl in North America. Hot rolled Anchor Channels are embedded in concrete and used to securely transfer high loads. Their main application is for flexible connections of glazing panels to high-rise buildings. Anchor Channels with welded-on rebar or corner pieces are available. Product: Studrails® Description: The North American standard for punching shear enhancement at slab-column connections. Studrails are produced to the specifications of ASTM A1044, ACI 318-08, AND ICC ES 2494. Decon Studrails are increasingly used to reinforce against bursting stresses in banded posttension anchor zones. All Resource Guide forms for the 2015 & 2016 Editorial Calendar are now available on the website, www.STRUCTUREmag.org.

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Gripple Inc.

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Product: Powers Submittal Generator (PSG) Description: PSG is a submittal and substitution online tool that helps contractors create submittal packages in just minutes. In only a few simple steps users can include all applicable code reports and technical details. Contact us for a free demonstration.

Phone: 630-952-2113 Email: e.balsamo@gripple.com Web: www.gripple.com Product: Anchor Hanger Kits for Suspended Services Description: Cable hanger kits suspend mechanical & electrical services like HVAC, lighting, conduit racks, and cable basket. Spider Kit is a cast-in-place concrete insert hanger kit that’s ready-to-use, has a safe working load of up to 200 lbs, and includes a Spider insert, cable hanger, and a Gripple fastener.

Phone: 800-423-9140 Email: info@halfenusa.com Web: www.halfenusa.com Product: HALFEN HCW Curtain Wall System Description: Designed to anchor curtain wall façade elements quickly, securely, and economically to the main structure. Offers various configurations for ‘top of slab’ and ‘edge of slab’ applications. Utilized to ensure quick, efficient, and adjustable connections to account for on-site conditions and engineered to resist any load combination (horizontal, vertical, and longitudinal) as required by the project. Product: HALFEN HSD-LD Lockable Dowel System Description: For temporary movement joints, commonly found in post-tensioned concrete slabs. Dowels allow initial shrinkage of the concrete to take place and are then locked in position with a mechanical plate and a controlled amount of epoxy resin. The locked dowels continue to transfer shear, but pervert further movement. Product: HALFEN HGB Handrail Anchor Channels Description: HALFEN HGB Anchor Channels for handrail connections enable safe anchoring of railing posts to the edge of thin concrete slabs. These Anchor Channels allow strong connections to the edge of concrete slabs as thin as 4 inches (100mm).

Hardy Frame

Phone: 800-754-3030 Email: dlopp@mii.com Web: www.hardyframe.com Product: Hardy Frame Shear Walls Description: Hardy Frame now offers pre-engineered anchorage solutions that drastically reduce large pad footings that can be associated with pre-fabricated Shear Wall Panels; standard details are available for inclusion with plan submittals.

IES, Inc.

Phone: 800-707-0816 Email: sales@iesweb.com Web: www.iesweb.com Product: IES VisualAnalysis Description: VisualAnalysis offers ACI Anchor Design checks with the base plate design feature included in VAConnect. Use VisualAnalysis for a wide variety of analysis and design projects. It is simple, productive and versatile.

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September 2015

Phone: 845-230-7533 Email: Mark.Ziegler@sbdinc.com Web: www.powers.com Product: Powers Design Assist (PDA) Description: Anchor design software provides calculations in accordance with ACI 318-11 and CSA A23.3 for mechanical, adhesive and cast-in place anchors. Includes seismic provisions and concrete-filled metal deck profiles. Download or update to version 2.3 for free today to take advantage of the most current code standards.

RISA Technologies

Phone: 949-951-5815 Email: amberf@risa.com Web: www.risa.com Product: RISABase Description: Uses an automated finite element solution to provide exact bearing pressures, plate stresses, and anchor bolt pull out capacities, eliminating the guess work of hand methods. Define bi-axial loads and eccentric column locations. Choose from several connection types and specify custom bolt locations.

S-FRAME Software Inc.

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

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CADRE Pro 6 for Windows Solves virtually any type of structure for internal loads, stresses, displacements, and natural modes. Easy to use modeling tools including import from CAD. Much more than just FEA. Provides complete structural validation with advanced features for stability, buckling, vibration, shock and seismic analyses.

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ANCHORING GUIDE Product: S-CONCRETE Description: Easily view instantaneous results as you optimize and design reinforced concrete walls, beams and columns. Automate workflow by checking thousands of concrete section designs in one run. With comprehensive ACI 31811 code support plus additional design codes, S-CONCRETE produces detailed reports that include clause references, intermediate results and diagrams.

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Standards Design Group

Phone: 806-792-5086 Email: info@standardsdesign.com Web: www.standardsdesign.com Product: Wind Loads on Structures 4 Description: Performs computations in ASCE 7-98, 02 or 05, Section 6 and ASCE 7-10, Chapters 26-31 computes wind loads by analytical method rather than the simplified method, provides basic wind speeds from a built-in version of the wind speed, allows the user to enter wind speed. Has numerous specialty calculators.

Phone: 800-999-5099 Email: web@strongtie.com Web: www.strongtie.com Product: Adhesive Piston Plug Delivery System Description: Offers an easy-to-use means to dispense adhesive into drilled holes for threaded rod and rebar dowel installations at overhead, upwardly inclined and horizontal orientations. The matched balance design between the piston plug and drilled hole virtually eliminates the formation of voids and air pockets during adhesive dispensing.

Strand7 Pty Ltd

Product: Titen HD® Screw Anchor Description: The patented, high-strength Titen HD screw anchor for concrete and masonry offers optimum performance in both cracked and uncracked concrete, as required by the 2012 IBC for postinstalled anchors. Newly redesigned, this anchor now features optimized thread geometry and is available in ¼-inch diameter.

Tekla, Inc.

Phone: 252-504-2282 Email: anne@beaufort-analysis.com Web: www.strand7.com Product: Strand7 Description: An advanced FEA system used worldwide by engineers for a wide range of structural analysis applications. It comprises preprocessing, a complete set of solvers and post processing. It includes a range of material models suitable for the analysis of soil allowing for simulations of the complete soil/structure system.

Phone: 770-426-5101 Email: kristine.plemmons@tekla.com Web: www.tekla.com Product: Tedds Description: Automating your everyday structural designs, Tedds’ broad library includes anchor bolt design per ACI 318 Appendix D. The calculation includes comprehensive checks for tensile and shear failure of anchors and is available as part of a free trial of the website.

Product: Tekla Structural Designer Description: Revolutionary software that provides the power to analyze and design steel and concrete buildings efficiently and profitably. Physical, information-rich models contain all the intelligence needed to fully automate the design and document your project, including all end force reactions communicated with two-way BIM integration, comprehensive reports and drawings. Product: Tekla Structures Description: An Open BIM modeling software that can model all types of anchors required to create a 100% constructible 3D model. Anchors can either be created inside the software or imported directly from vendors that have 3D CAD files of their products.

Williams Form Engineering Corp.

Phone: 616-866-0815 Email: williams@williamsform.com Web: www.williamsform.com Product: Anchor Systems Description: Providing threaded steel bars and accessories for rock anchors, soil anchors, high capacity concrete anchors, micro piles, tie rods, tie backs, strand anchors, hollow bar anchors, post tensioning systems, and concrete forming hardware systems in the construction industry for over 90 years.

All Resource Guide forms for the 2015 & 2016 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

2015 Annual Trade Show in Print The definitive buyers’ guide for the practicing structural engineer Get your submissions in soon for this year’s issue! Visit www.STRUCTUREmag.org. STRUCTURE magazine

September 2015

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award winners and outstanding projects

Spotlight

Newport Beach Civic Center and Park Inspiring Community through Holistic Design By Janice Mochizuki, P.E., LEEP AP, John Worley, S.E., LEED AP and Joseph Collins, S.E. Arup was an Outstanding Award Winner for the Newport Beach Civic Center and Park project in the 2014 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings over $100M).

spiring to create a civic center that would bring the community together, the coastal city of Newport Beach, California chose to position the new development in the geographic and cultural center of the expanded population. Newport Beach’s old city hall, built in 1948, was no longer positioned to serve the needs of the community. The team of architects from Bohlin Cywinski Jackson (BCJ) aimed to provide a civic center that would be an inspiring place for the community to converge and to provide a transparent civic institution. Contributing and collaborating on this design vision was PWP Landscape Architecture and the Arup multidisciplinary team from the San Francisco office consisting of structural, mechanical, electrical, plumbing, and civil engineering, as well as lighting, sustainability, and telecommunications consulting services. C.W. Driver was the general contractor. The Newport Beach Civic Center and Park is positioned on a narrow, 20 acre plot of land partially inhabited by protected wetlands and flanked by three major roads. The project consists of a new city hall, community room, council chambers, parking garage, parkland, 4 pedestrian bridges, and an addition to an existing library. Straddling the wetlands are three modest pedestrian bridges amongst the 14 acres of park land and picnic areas. The two separate parcels of the site are connected with a sightline compatible, low-profile pedestrian bridge spanning 150 feet over a main thoroughfare, San Miguel Drive. The San Miguel Bridge has a 52-foot observation platform that provides views of the Santa Catalina Islands. It was created by cantilevering steel supports off of the concrete shear wall elevator tower and perching the main bridge girders on those supports to allow for longitudinal movement. The 17,000 square-foot addition to the existing Central Library, which was located adjacent to the site, was built to serve the high demand for reading room space and the need for a children’s area and high-tech media center. Over the new grand library

entrance, a dramatic 50-foot cantilever faces the civic center and provides covered exterior spaces that can be used as an Courtesy of David Wakely. entertainment stage. A pair of built-up king post roof trusses with lighting) were carefully routed through web tension cables provides a column free space openings in the wave roof beams to achieve in the 150 seat council chambers. The special a clean look while exposing the structural concentric brace frame building has a curved steel. The shape and directional placement of and canted wall that provides support for the the roofs allows for ideal placement of future iconic Polytetrafluoroethylene (PTFE) backlit solar panels. exterior “sail”. The building is stabilized against wind and Located between the council chambers and seismic loads by buckling restrained braced the city hall is a double-height, 4,500 square- frames (BRB). Due to the discontinuity of the foot community. It is a continuation of the city roof diaphragm resulting from the repeating hall’s architectural expression with large sliding- wave roof layout, each 20-foot wave roof bay door facades that allow for the room to open functions as its own local diaphragm. Two up to the park and sheltered outdoor spaces. horizontal lines of pinned-ended, round HSS The 89,000 square-foot city hall building collectors pick up the lateral force from the is a two-story architecturally exposed struc- wave roofs to deliver it to the BRBs located tural steel (AESS) building clad with a glass in the cores and the ends of the building. curtain wall, envisioned by BCJ as an expresThe aesthetic of the pinned-ended, round sion to the public of a transparent structure HSS members is carried throughout the and civic institution. Wave roofs, one of project. Double-height exterior axial-only colthe most multi-functional design elements umns that support the overhanging wave roofs of the project, top the second floor of the are round HSS members with a pinned base city hall and pay homage to the marine sur- connection. The exposed BRBs, provided by roundings. North facing operable clerestory CoreBrace, have meticulously crafted pinnedwindows that are equipped with automated ends and a round HSS casing with a custom motorized dampers provide natural ventila- made collar to conceal the cruciform core. tion and lighting. Wide flange beams were Through holistic decisions and collaboration sculpted into their double radiused form by of the entire project team from design through SME Steel. The higher elevation side of the construction, the Civic Center earned a wave sits on top of a vierendeel truss created LEED Gold Certification while creating a from commonly available wide flange chords place for the community to enjoy.▪ and vertical members. By using the vierendeel truss layout, the window elements and Janice Mochizuki, P.E., LEEP AP lighting fixtures are nicely nestled within the (janice.mochizuki@arup.com), is a structure. The wave roofs extend beyond the Senior Engineer in Arup’s structural buildings curtain wall facades to create sunshade for the group. John Worley, S.E., LEED AP building and exterior spaces surrounding the (john.worley@arup.com), is a Principal structure. A result of implementing a raised in the structural buildings group. Joseph floor system, and early design coordination Collins, S.E. (joseph.collins@arup.com), between Arup and BCJ, was concealing many is an Associate in the structural buildings of the distribution services. The few required group. All three are located in Arup’s San overhead services (fire sprinklers and overhead Francisco office.

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NCSEA News

News form the National Council of Structural Engineers Associations

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The 2015 NCSEA Special Awards Honorees The following awards will be presented at the Awards Banquet on October 2 nd during the 2015 NCSEA Structural Engineering Summit in Las Vegas. For more information on the Annual Conference, see pages 42 – 45.

The James M. Delahay Award The James M. Delahay Award is presented at the recommendation of the NCSEA Code Advisory Committee to recognize outstanding individual contributions towards the development of building codes and standards. It is given in the spirit of its namesake, a person who made a long and lasting contribution to the code development process.

Donald R. Scott, S.E., F.SEI, F.ASCE Donald R. Scott is the Vice President and Director of Engineering at PCS Structural Solutions, a 50-person firm with offices in both Tacoma and Seattle, Washington. He has been a Principal of the firm since 1986 and has led many of the firm’s educational, commercial, institutional and private projects for new and renovated construction. Don is a civil and structural engineering graduate of the University of Idaho with civil and structural engineering licenses in Washington and seven other states. Don has authored many technical publications and has presented numerous seminars and NCSEA webinars on wind design throughout the country. He has been a member of the ASCE 7 Wind Load Committee since 1996, shaping future IBC provisions for wind design, and currently serves as Chairman. He is also a member of the ASCE 7 General Provisions committee, a member of the ASCE 7 Steering Committee, Chairman of the NCSEA Wind Committee, and a former Chair of the SEAW Wind Load Committee.

The NCSEA Service Award The NCSEA Service Award is presented to an individual or individuals who have worked for the betterment of NCSEA to a degree that is beyond the norm of volunteerism. It is given to someone who has made a clear and indisputable contribution to the organization and therefore to the profession.

Craig Barnes, P.E., SECB Craig Barnes founded CBI Consulting Inc. in 1984 and is licensed in 20 states. Craig helped establish the National Council of Structural Engineers Associations (NCSEA) in 1993, was President of NCSEA from 1995-1996, and received the NCSEA Robert Cornforth Award in 2005. He is a member of STRUCTURE Magazine’s Editorial Board, as well as a continuing contributor to the publication. Craig is a Past President of the Boston Association of Structural Engineers, as well as the Structural Engineers Association of Massachusetts. He chaired NCSEA’s Basic Education Committee for several years, where he was instrumental in creating a highly-recognized list of Basic Education requirements for students in the structural engineering field. Craig has provided consulting services for exhibits at Boston’s Museum of Fine Arts and their affiliates abroad, and he spent two weeks in Port-au-Prince following the catastrophic earthquake in 2010, reviewing and commenting on reports prepared by Haitian consultants to determine if buildings were safe for occupancy.

The Robert Cornforth Award This award is presented to an individual for exceptional dedication and exemplary service to a Member Organization and to the profession. Nominees are submitted to the NCSEA Board by the Member Organizations.

Carl Josephson, S.E., SECB Carl Josephson is a Principal Structural Engineer with Josephson-Werdowatz & Associates, a structural engineering firm located in San Diego, California with additional offices in Sacramento, Las Vegas, and Scottsdale. Carl is a licensed Professional or Structural Engineer in twelve states. He has served as Convention Chair, Director, and President of SEAOC. He is currently Chair of SEAOC’s Professional Licensing & Certification Committee and SEAOC’s recently reestablished Legislative Committee. He was elected to the SEAOC College of Fellows in 2007. He is a member of NCSEA’s Professional Licensing Committee and is a member of SEI’s Professional Activities Committee. In 2010, Carl was appointed by former Gov. Schwarzenegger as the SE member of the California Board for Professional Engineers, Land Surveyors and Geologists, (BPELSG), and he now serves as an Emeritus member of, and consultant to, BPELSG. He is active in the National Council of Examiners for Engineers and Surveyors (NCEES) and has served on their SE Exam Committee and Mobility Task Force. STRUCTURE magazine

September 2015

The Susan M. Frey NCSEA Educator Award is presented to an individual who has a genuine interest in, and extraordinary talent for, eﬀective instruction for practicing structural engineers. The award was established to honor the memory of Sue Frey, one of NCSEA’s finest instructors. Nominees are submitted to the NCSEA Board.

Emily Guglielmo, S.E. Emily Guglielmo is an Associate with Martin/Martin, Inc. and also serves as manager of the Northern California office. Emily is deeply committed to assisting structural engineers in solving real world engineering problems with simple, reasonable solutions. Toward that goal, she has served as a frequent lecturer for several Structural Engineering Associations on topics ranging from wind and seismic loads to serviceability design. Emily is a member of the ASCE 7 Seismic Committee and the NCSEA Publications Committee, and is a founding member and current Chair of the NCSEA Young Member Group Support Committee. Outside of the profession, Emily enjoys hiking and traveling with her husband and three children. Deeply honored by her receipt of the prestigious Sue Frey Educator Award, Emily’s goal is to contribute to Sue’s legacy through her educational eﬀorts.

NCSEA News

The Susan M. Frey NCSEA Educator Award

More information on the NCSEA Structural Engineering Summit can be found on pages 42 – 45.

NCSEA Awards Six Young Member Scholarships to Annual Conference Thomas Mendez, S.E. A Structural Engineer with Halvorson and Partners, Chicago, Illinois, Thomas is a member of the Structural Engineers Association of Illinois. Matthew McCarty, S.E., P.E. A Project Structural Engineer with Whitman, Requardt & Associates, Monrovia, Maryland, Matthew is a member of the Virginia Structural Engineers Council.

Matthew Ernst, E.I. A Structural Staﬀ Engineer with Engineering Ventures, PC, Burlington, Vermont, Matthew is a member of the Structural Engineers Association of Vermont.

Greg McCool, P.E. A Structural Engineer with Ericksen Roed & Associates, St. Paul, Minnesota, Greg is a member of the Minnesota Structural Engineers Association.

Yasmin Chaudhry A graduate student at Montana State University and an intern at Morrison-Maierle, Inc., Bozeman, Montana, Yasmin is a member of the Structural Engineers Association of Montana.

NCSEA Webinars

News from the National Council of Structural Engineers Associations

For the third year, NCSEA awarded Young Member Scholarships for the NCSEA Structural Engineering Summit. The scholarship competition was open to any current member of an NCSEA Member Organization who was under 36 years old. Applicants were asked to compose an essay or video answering one of three questions, as well as write a brief essay upon attending the Summit. Scholarships included Summit registration and a travel stipend. The winners of this year’s scholarships are:

Michelle Quinn, P.E. A Design Engineer with Ensign Engineering, Sandy, Utah, Michelle is a member of the Structural Engineers Association of Utah.

October 27, 2015

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Diamond Reviewed

Non-CalOES courses award 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program.

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

Observations & Reﬂections on the 2014 South Napa Earthquake Five speakers from Degenkolb Engineers: David Bonneville, S.E.; John Dal Pino, S.E.; Mahmoud Hachem, S.E.; Kirk Johnston, S.E., LEED AP; Roger Parra, S.E.

Calculating & Applying Design Wind Loads on Buildings Using the Envelope Procedure in ASCE 7 T. Eric Staﬀord, P.E., President, T. Eric Staﬀord & Associates

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October 22, 2015

November 3, 2015

What You Need to Know About the Seismic Peer Review Process Farzad Naeim, Ph.D., S.E., Esq., President, Farzad Naeim, Inc.

October 6, 2015

Significant Changes to the Wind Provisions of ASCE 7-10 T. Eric Stafford, P.E., President, T. Eric Stafford & Associates

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Second ATC-SEI Conference on Improving the Seismic Performance of Existing Buildings and Other Structures

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

December 10 – 12, 2015, San Francisco, California REGISTRATION NOW OPEN The ATC-SEI Conference on Improving the Seismic Performance of Existing Buildings and Other Structures is an opportunity for structural engineers, business owners, and users of ASCE seismic standards to learn the latest in seismic evaluation and rehabilitation. Earn up to 14 Professional Development Hours (PDHs) The conference technical program offers a wide variety of valuable sessions, including: • Seismic Resilience–Lessons from the Field • Performance-Based Seismic Evaluation of Reinforced Concrete Structures, in Conjunction with ASCE/SEI 41 • Innovative Approaches and Codes for Historic Structures • Performance Assessment of Tall Buildings • Recent Legal Developments Affecting Owners and Designers: Using Performance Targets to Manage Seismic Risk in the Legal Arena • Multiple case studies on Evaluation and Retrofit of Existing Buildings

Each day will begin with two compelling Keynote Speakers and will include multiple opportunities for networking with colleagues and leaders in the field. Don’t miss the Champions of Earthquake Resilience Awards Dinner benefiting the ATC Endowment Fund and the SEI Futures Fund. Visit the conference website at www.atc-sei.org for complete information and to register.

Young Professional Scholarship Forensic Engineering th Congress Apply for the SEI Young Professional (age 35 and younger) 7 Scholarship to the Geotechnical & Structural Engineering Congress, February 14 – 17, 2016, in Phoenix, Arizona. SEI is committed to the future of structural engineering and offers a scholarship for Young Professionals to participate and get involved at the annual Congress. Many find this event to be a career-changing and energizing experience, opening up networking opportunities and expanding horizons to new and emerging trends. Applications are on the SEI website at www.asce.org/ structural-engineering/sei-young-professionals-scholarshipapplication/ and are due November 2.

Registration Now Open

Advance to SEI Fellow

ASCE’S “Game Changers” Highlights Innovative Infrastructure

The SEI Fellow grade of membership recognizes accomplished SEI members as leaders and mentors in the structural engineering profession. The benefits of becoming an SEI Fellow include recognition via SEI communications and at the annual Structures Congress along with a distinctive SEI Fellow wall plaque and pin, and use of the F.SEI designation. SEI members who meet the SEI Fellow criteria are encouraged to submit application packages online by November 1 to advance to the SEI Fellow grade of membership and be recognized at the Geotechnical & Structural Engineering Congress, February 14–17, 2016 in Phoenix, Arizona. Visit the Fellows webpage at www.asce.org/structural-engineering/sei-fellows/ to learn more. STRUCTURE magazine

Registration is now open for the ASCE Forensic Engineering 7th Congress, November 15 – 18, 2015, in Miami, Florida. Learn alongside professionals who share the same challenges in their work to identify and address the root causes and consequences of design errors and construction defects. Register today at www.forensiccongress.org/.

Americans are all too aware of infrastructure challenges, yet many states and communities are finding and implementing innovative solutions that deserve wider recognition. ASCE recently released Infrastructure #GameChangers, a report and associated website identifying top trends in energy, freight, transportation, and water, and the ways they are transforming how infrastructure is designed, planned, and built. Explore more than 30 examples at http://ascegamechangers.org/.

September 2015

February 14 – 17, 2016, Phoenix, Arizona • Structural Wall Research: Recent Research & International Collaboration In addition several sessions explore topics that include both structural and geotechnical engineering. Joint sessions include: The Geo-Institute (G-I) and Structural Engineering Institute • Bridge Scour & Erosion: Th e Way Forward (SEI) of the American Society of Civil Engineers (ASCE) are • Novel Methods of Educating Geotechnical & Structural coming together to create this fi rst-of-its-kind event. By comEngineers bining the best of both Institutes’ annual conferences into one • Managing Risk in Geotechnical & Structural Analysis & unique conference, you will profit from unmatched networking Design opportunities with colleagues within and across disciplines. • Foundations for Specialized Structures With a large and varied technical program, the joint congress • Structural Design of Deep Foundations will offer structural engineers ample educational opportunities. These structural sessions include: Join the conversation: #GeoSEI2016 • Experimental & Analytical Investigation of Robustness Visit the Joint Congress website at www.Geo-Structures.org of Structures for complete information and to register. • Seismic Performance of Tall Buildings • Lifecycle Analysis & Carbon Calculation: Parts 1 & 2 • Alternative Approaches to Multi-Hazard Analysis & Design of Structures WITH SEI SUSTAINING ORGANIZATION MEMBERSHIP • Bridge Analysis • Analysis of Nonbuilding Structures

REGISTRATION NOW OPEN Connect | Collaborate | Build

REACH SEI MEMBERS

Errata SEI posts up-to-date errata information for our publications at www.asce.org/SEI. Click on “Publications” on our menu, and select “Errata.” If you have any errata that you would like to submit, please email it to Jon Esslinger at jesslinger@asce.org.

www.asce.org/SEI-Sustaining-Org-Membership

Electrical Transmission & Substation Structures Conference September 27 – October 1, 2015, Branson, Missouri REGISTRATION NOW OPEN Can you afford to wait until 2018? This is your last chance to register for the premier conference on transmission line and substation structures, and foundation construction issues. Don’t miss out on an excellent opportunity to network with professionals in your industry.

Grid Modernization – Technical Challenges & Innovative Solutions The conference will feature three days of technical sessions, four days of exhibits, a pre-conference workshop, and an exciting construction-oriented demonstration day that will offer many opportunities to share international knowledge on grid modernization from a structural and construction standpoint. Attendees will experience a unique setting in which to learn and network with peers, industry leaders, and knowledgeable suppliers. The conference features a compelling, single track program of sessions chaired by moderators that are leaders in the field: • Structural Analysis 1 – Mike Miller, P.E., M.ASCE • Special Design Considerations – Marlon Vogt, P.E., M.ASCE

STRUCTURE magazine

• Managing Aging Infrastructure – Gary Bowles, P.E., F.SEI, M.ASCE • Structural Analysis 2 – Robert Nickerson, P.E., F.SEI, M.ASCE • Case Studies – Frank Agnew, P.E., M.ASCE • Foundations – David Todd, P.E., M.ASCE • Substation Design Issues – Jerry Wong, P.E., F.SEI, M.ASCE • Construction Challenges – Dana Crissey, P.E., M.ASCE • Line Design – Wesley Oliphant, P.E., F.SEI, M.ASCE • Rerating and Upgrading – Tim Cashman, P.E., M.ASCE • Codes and Standards – Otto Lynch, P.E., F.SEI, M.ASCE • Conference Wrap up – Otto Lynch, P.E., F.SEI, M.ASCE The pre-conference workshop, Panel Discussion of Storm Hardening, Resiliency and Security Issues, gives attendees an additional educational opportunity. All the major companies in the industry will display their latest products and services in the exhibit hall, one of the highlights of the conference. The conference will close with a demonstration day offering participants unique opportunities to witness several overhead power line construction and supplier demonstrations in a single day. Earn up to 19 PDHs. Visit the conference website at www.etsconference.org for complete information and to register.

September 2015

The Newsletter of the Structural Engineering Institute of ASCE

Increase your exposure to more than 25,000 SEI members through www.asce.org/SEI, SEI Update e-newsletter, STRUCTURE magazine, and at SEI conferences year round.

Structural Columns

Geotechnical & Structural Engineering Congress 2016

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Risk Management Contracts Available CASE #1 An Agreement for the Provision of Limited Professional Services This is a sample agreement for small projects, or investigations of limited scope and time duration. It contains the essentials of a good agreement including scope of services, fee arrangement and terms and conditions. CASE #2 An Agreement between Client and Structural Engineer of Record for Professional Services This agreement form may be used when the client, e.g. owner, contractor developer, etc., wishes to retain the Structural Engineer of Record directly. The contract contains an easy to understand matrix of services that will simplify the “what’s included and what’s not” questions in negotiations with a prospective client. This agreement may also be used with a client who is an architect when the architect-owner agreement is not an AIA agreement. CASE #3 An Agreement between Structural Engineer of Record and Consulting Design Professional for Services The Structural Engineer of Record, when serving in the role of Prime Design Professional or as a Consultant, may find it necessary to retain the services of a sub-consultant or architect. This agreement provides a form that outlines the services and requirements, in a matrix so that the services of the subconsultant may be readily defined and understood. CASE #4 An Agreement between Owner and Structural Engineer for Special Inspection Services Special Inspection services provided by a Structural Engineer are normally contracted directly by the Owner of a project during the construction phase. This agreement has a Scope of Service that directly relates to the applicable code or industry standard requirements. The Structural Engineer of Record or another structural engineer providing these services may use this agreement. The language for coordinating laboratory testing work is also included within this agreement. CASE #5 An Agreement for Structural Peer Review Services A request to perform a peer review of another structural engineer’s design brings with it a different responsibility than that of the Structural Engineer of Record. The CASE #5 document

addresses the responsibilities and the limitations of performing a peer review. This service is typically performed for an Owner, but may be altered to provide peer review services to others. CASE #6 Commentary on AIA Document C141 Standard Form of Agreement between Architect and Consultant, 1997 Edition and AIA Document C142 Abbreviated Standard Form of Agreement between Architect and Consultant, 2009 Edition This document provides a form letter of agreement to be used with adoption by reference to AIA Document C401. This Agreement is intended for use when owner-architect agreement is an AIA B-series. A scope of services is included. The purpose of the commentary is to point out provisions that merit special attention. CASE #6A Commentary on AIA Document B-141 Standard Form of Agreement between Owner and Architect with Standard Form of Architect’s Services, 1997 Edition The purpose of this Commentary is to point out provisions which merit special attention, or which some have found to contain “pitfalls”. CASE #8 An Agreement between Client and Specialty Structural Engineer for Professional Services When structural engineering services are provided to a contractor or a sub-contractor for work to be included in a project where you are not the Structural Engineer of Record, but you are a specialty structural engineer. Your contractual relationship differs from the norm, and the typical contract forms will not suffice. The CASE #8 document is tailored to this particular situation. CASE #9 An Agreement between Structural Engineer of Record and Testing Laboratory The Structural Engineer of Record may be required to include testing services as a part of its agreement. If a testing laboratory must be subcontracted for this service, CASE # 9 may be used. It can also be altered for use between an Owner and a testing laboratory. You can purchase these and the other Risk Management Tools at www.acec.org/coalitions/coalition-publications/.

WANTED Engineers to Lead, Direct, and Get Involved with

CASE Committees!

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. 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. Please submit the following information to htalbert@acec.org: • Letter of interest • Brief bio (no more than 2 paragraphs) STRUCTURE magazine

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 partially reimbursed) • 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 Thank you for your interest in contributing to your professional association! September 2015

III. Membership Committee – Stacy Bartoletti (sbartoletti@degenkolb.com) • Preparing for membership recruitment campaign with CASE staff members, target date September 2015 • Working on educating CASE Members about new Community sites and how to use while updating new benefits of membership IV. Programs and Communications Committee – Nils Ericson (nericson@m2structural.com) • Confirmed/finalized sessions for 2016 ASCE/SEI Structures Congress • Working on sessions for 2016 AISC Conference and the ACEC Annual Convention • Putting together the 2015/2016 editorial calendar for articles to Structure Magazine from CASE V. Toolkit Committee – Brent White (brentw@arwengineers.com) • Finished updates on the following tools: • Tool 4-3: Sample Correspondence Letters • Tool 10-1: Site Visit Cards • Working on the following new tools: • Tool 1-3: Sample Office Policies • Tool 8-3: Contract Clause Commentary • Tool 10-3: Deferred Submittals • Committee will be surveying CASE membership on ideas for future tools and what would be helpful for their business and/or risk management plan The 2016 CASE Winter Planning Meeting is scheduled for February 11-12 in Phoenix, AZ. If you are interested in attending the meeting or have any suggested topics/ideas from a firm perspective for the committees to pursue, please contact Heather Talbert at htalbert@acec.org.

ACEC Fall Conference Features CASE Risk Management Convocation and More! October 13 – 17 ACEC is holding its Fall Conference at the You will not want to miss these additional important risk manWestin Copley Place, Boston, MA. CASE will be holding a agement sessions: convocation on Thursday, October 15. Sessions include: Managing Uncertainty and Expectations in Building Design and Construction 10:45am How to Reduce Your Risk on Alternative Clark Davis, Cameron MacAllister Group; Stephen Jones, Delivery Projects Dodge Data & Analytics Moderator: Beth Larkin: HNTB Building Resilient Infrastructure for Future Cities Speakers: Mary Conway, HNTB; George Wolf, Shook Terry Bennet, Autodesk Inc.; Donna Huey, Atkins Global; Hardy & Bacon; David Hatem, Donovan Hatem Marty Janowitz, Stantec 1:45pm Dead in the Water: A Case Study of Claims Missouri’s Peer Review Law–Should Your State Have One? Facing Civil Engineers Karen Erger, Lockton Companies Dan Buelow & Bob Stanton, Willis A/E How to Reduce Your Professional Liability Costs 3:30pm Non-Negotiable Contracts: What’s Plan B? Tim Corbett, SmartRisk Karen Erger & Bob Fogle, Lockton Co.; Eric Miller, The Conference also features: Ice Miller; Jennie Muscarella, Kenny, Shelton, Liptak, • General Session addresses by Pulitzer Prize-winning author Nowak LLP Doris Kearns-Goodwin; 2015 ACEC Distinguished 5:15pm ACEC/Coalition Meet and Greet Award of Merit Honoree Dr. Robert Ballard • CEO roundtables; For more information and to register go to www.acec.org/ • Exclusive CFO, CIO, Architect tracks; • Numerous ACEC coalition, council, and forum events; and conferences/fall-conference-2015/registration. • Earn up to 21PDHs STRUCTURE magazine

September 2015

CASE is a part of the American Council of Engineering Companies

On August 6-7, the CASE Winter Planning Meeting took place in Chicago, IL with over 30 CASE committee members and guests in attendance, making this a well-attended and productive meeting. Included in the planning meeting was a roundtable discussion lead by Stacy Bartoletti, Degenkolb Engineers and Brent White, ARW Engineers on Real Life Lessons Learned: Project Claims Impacting Structural Engineers. During the meeting, break-out sessions were held by the CASE Contracts, Guidelines, Membership, Toolkit, and Programs & Communications Committees. Listed below are the current CASE initiatives being developed by the committees: I. Contracts Committee – Ed Schweiter (ews@ssastructural.com) • Finished working on revisions to the entire CASE Contract Document library; release of updated Contract Library prior to ACEC Fall Conference • Will be creating a “How to” sheet educating people on using the CASE Contract Documents II. Guidelines Committee – John Dal Pino (jdalpino@degenkolb.com) • Finishing current revisions to the following Practice Guideline Documents: • CASE 962B – National Practice Guidelines for Specialty Structural Engineers • CASE 962-E – Self-Study Guide for the Performance of Site Visits During Construction • CASE 962-F – A Guideline Addressing the Bidding and Construction Administration Phases for the Structural Engineer • Guide to Special Inspections and Quality Assurance • Working on the following new documents: • Commentary on ASCE-7 Wind Design Provisions • Commentary on ASCE-7 Seismic Design Provisions

CASE in Point

CASE Summer Planning Meeting Update

Structural Forum

opinions on topics of current importance to structural engineers

A “Plug” for Power Line Structures By David C. Gelder, P.E.

ithin the structural community, there seems to be a lack of awareness, as well as a growing opportunity, regarding overhead electrical transmission and distribution structures. In the United States alone there are millions of miles of corridor consisting of aging single- and double-pole structures and lattice towers. These structures form an impressive network, supporting high and extra-high voltage wires (12 kV to 765 kV) and delivering power from generation facilities to customers located hundreds of miles away. This enormous infrastructure, known as the electric grid, is a critical system to society and constitutes a specialty market for structural engineers. I wish to “put in a plug” for power line structures to increase awareness and interest among fellow structural engineers. In 2011, when I graduated, it was still difficult to get an interview – let alone a job – with a structural firm. Given the slow job market, I pursued a master’s degree. The following year, I graduated and found employment, though not designing buildings as I had supposed, but rather designing transmission structures. Interestingly, five fellow graduate students found similar entry-level positions designing either transmission structures or wind turbines – all structures within energy sector markets. In retrospect, this hiring trend may not have been coincidence, but rather a lesson in diversification: the energy market showed signs of growth during the recession, while the commercial building market all but collapsed. I was both excited and curious about my first engineering job in this non-traditional field. After all, power lines are electrical systems, right? While they are indeed electrical systems, there is also a huge civil engineering component – as well as environmental, archeology, survey, construction, permitting, and other disciplines. It seems obvious now, but many fellow civil and structural engineers have yet to realize that we are more academically prepared than any other discipline to design transmission structures, including the poles, towers, wires, and foundations.

While considered an eyesore by many, these structures are undoubtedly critical to society. When properly designed, power lines provide an invaluable service to consumers; however, when defective or deteriorated, power lines may yield devastating consequences to the public – particularly during extreme weather and loading conditions. Transmission lines have failed in a variety of ways. In extreme cases, power lines have been blamed for igniting wildfires leading to loss of life, extensive loss of property, and environmental damage. Failure has also triggered power outages such as the infamous Northeast Blackout of 2003, which led to loss of life, water supply contamination, transportation system closures, and billions of dollars in negative economic impact. Not all failures pose equal risk, but clearly proper design of poles and towers of all voltages is critical to safeguard public health and safety. Transmission structures are typically designed to withstand ice accumulation, as well as extreme wind and temperature loading using at least 50-year recurrence intervals. Originally most wire systems were copper; now most modern wires are aluminum, including aluminum conductor steel-reinforced (ACSR) pulled to thousands of pounds of tension. They are designed to meet ground and wire-to-wire clearance requirements at all times in accordance with the Institute of Electrical and Electronics Engineers (IEEE) National Electrical Safety Code (NESC) and other codes. Loading is of course unique from buildings. For example, loads on a single-pole foundation may consist of relatively light axial load (10-30 kips) combined with heavy shear (50-100 kips) and heavy bending moment (1,000-3,000 kip-ft). Poles and towers have a relatively low seismic base shear; therefore, earthquake loads rarely govern the design. Some additional tools used by today’s practicing transmission engineers include modern nonlinear finite element software and Light Detection And Ranging (LiDAR) data, which are widely used in all aspects of design and analysis. ASCE/SEI

issues Standards 10 and 48 – for designing steel towers and poles, respectively – and hosts the triennial Electrical Transmission & Substation Conference (this year it will be held September 27 – October 1, 2015 in Branson, MO). On the business side, historically power lines were designed, built, and maintained for the most part in-house by electric utilities. Now, much of the design knowledge base and workforce has transferred to consulting firms, so many utilities rely on them to help complete projects. Large projects are often offered as engineer-procure-construct (EPC) contracts – similar to design-build contracts – while many smaller projects are simply awarded as part of a master service agreement (MSA). Due to the increasing demand for power, the aging infrastructure, and a retiring workforce, there is a growing need for transmission engineers. This poses an opportunity for structural engineers either individually or as a firm. For example, some structural engineers have chosen to pursue transmission engineering as a means of specialization. Additionally, some large civil engineering firms have chosen to offer power delivery services in order to diversify, though newcomers have found the market extremely difficult to penetrate. In summary, power line design can be an enjoyable and rewarding career path for structural engineers, and the power delivery market can be a means of diversification for their firms. The greater civil and structural engineering communities will benefit by recognizing and promoting these poles and towers as civil structures. Lastly, power line structures may be viewed by some as an eyesore, but for others, they represent an opportunity.▪ David C. Gelder, P.E. (DGelder@trcsolutions.com), is licensed as a professional engineer in the State of California and works as a Transmission Engineer for TRC in Salt Lake City, UT.

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

September 2015

STRUCTURE magazine | September 2015

Articles inside

a “Plug” for Power line Structures

Structural education deficiencies

Moment-Curvature and Nonlinearity

Creating Clarity and Scoping Profits in BiM

BiM-M Symposium

Proper Procedures and Protocol for interception grouting

divine design: renovating

the Niagara Cantilever Bridge

What is a Masonry “Flush Pilaster”?

Modern limit analysis tools for reinforced Concrete Slabs

representation and reality