STRUCTURE magazine | June 2013 by structuremag

June 2013 Tall Buildings/High Rise

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE ®

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FEATURES San Diego Central Library

CONTENTS June 2013

By Sean Fleming, Jean Libby, P.E. and Paul Endres, S.E.

The San Diego Central Library encloses 504,000 square feet on its nine above-ground floors. The project presents multiple unique challenges in its many unique structural frame components. Prevalent among them are the cast-inplace architectural concrete frame beams and columns, exposed concrete waffle slabs, and the iconic steel and aluminum dome structure.

Diagrid on Display

By Daniel Riemann, P.E. and Jason Black, P.E., S.E.

The recently completed Federal Center South Building 1202 is a state-of-the-art office building resulting from architectural, structural, and construction innovation and collaboration. One of the key features that makes Building 1202 so innovative is the use of a diagrid system at the exterior wall of the structure.

John Jay College Expansion

By Jason Stone, P.E.

The CUNY John Jay College School of Criminal Justice Expansion Project is a new 625,000-square foot academic building in Midtown Manhattan. The project presented numerous and significant site challenges. In response to one such challenge, a shallow Amtrak tunnel that cuts through a corner of the site, the John Jay structural system is distinguished by a grid of rooftop trusses which hang the perimeter of eight floors below.

COLUMNS 7 Editorial On the Importance of Collaboration

By Edward M. DePaola, P.E., SECB

10 Guest Column The Proper Role of the Geotechnical Engineer

By Victor R. Donald, P.E.

12 Structural Testing Investigating Masonry Structures Andrew E. Geister, P.E.

16 Building Blocks Height and Area Considerations for Commercial Wood Buildings By Paul D. Coats, P.E. and Dennis Richardson, P.E.

21 Engineer’s Notebook Wood Design

By Jerod G. Johnson, Ph.D., S.E.

23 Structural Performance Seismic Modeling of an Irregular Water Treatment Structure By Louis Scatena, P.E.

26 Historic Structures Newburyport Bridge

STRUCTURE

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

THE

COVER

A Joint Publication of NCSEA | CASE | SEI

The newly built San Diego Central Library presents multiple distinctive challenges in its many unique structural frame components. The project encloses 504,000 square feet on its nine above-ground floors and includes reader seating for 1,200 persons, 407 computer stations, 22 wifi-enabled study rooms, and more. The project is featured on page 30.

June 2013 Tall Buildings/High Rise

IN EVERY ISSUE 8 Advertiser Index 8 Letter to the Editor 48 Resource Guide (Tall Buildings) 50 Noteworthy 52 NCSEA News 54 SEI Structural Columns 56 CASE in Point

44 CASE Business Practices Tools for Protecting the Bottom Line By Mark Erdman, P.E.

46 Great Achievements William LeMessurier

By Robert Hossli and Ronald Flucker, P.E.

51 Spotlight The Twisting Regent Emirates Pearl Hotel

By Ahmed Osman, P.E., M.Eng and Whitney Morris

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

DEPARTMENTS

June 2013

58 Structural Forum Black, White, and Gray

By Greg Cuetara, P.E., S.E.

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Editorial

On the Importance of Collaboration

new trends,M.new techniques and current By Edward DePaola, P.E., SECB, F.SEI industry issues A member of the SEI Board of Governors, representing SEI’s Codes and Standards Division

eople often say that the whole is greater than sum of its parts, and that is the case when professional organizations collaborate to accomplish more than the sum of their individual efforts. As you’ve read in these pages (and elsewhere) for many years, there are multiple organizations that represent engineers in one form or another. Specifically, for structural engineers, the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE), the National Council of Structural Engineers Associations (NCSEA), the Council of American Structural Engineers (CASE) and the Structural Engineering Certification Board (SECB), each represent structural engineers. These organizations have always shared the following goals: • To advance and serve the structural engineering profession; • To promote the profession to the public and within the profession itself. Now they have embraced the idea of collaboration to improve the level of practice by speaking with one, strong voice to promote structural engineering licensing throughout the United States. Protecting the public’s right to safe, sustainable and cost effective buildings, bridges and other structures is the primary responsibility of the structural engineering profession. Licensure of structural engineers to document their competency is crucial to ensuring that structures are properly designed. At this time, however, only 11 states (IL, HI, CA, NV, OR, UT, WA, AZ, ID, NE, NM) have structural engineer licensing acts. In the other 39 states, SECB Certification is the only option for recognition as a structural engineer. SEI and SECB firmly believe that SECB certification of structural engineers is an excellent interim step on the path towards structural licensure in all jurisdictions. Similarly, the Model Law Structural Engineer (MLSE) designation recently instituted through the National Council of Examiners for Engineering and Surveying (NCEES) can provide an intermediary step, but it is not an adequate substitute for structural licensure. SEI and SECB, in conjunction with NCSEA and CASE, are the voice of structural engineers and are providing guidance to state legislatures and licensing boards on matters related to SE licensure. The Structural Engineering Certification Board (SECB) is an independent, autonomous professional organization created to ensure that structural engineers have the credentials and experience they need to protect the public health and safety, and to work safely and productively in their profession. The criteria for certification by SECB include rigorous requirements for primary structural engineering education, continued structural practice, and ongoing professional development. In order to maintain certification, structural engineers must participate in extensive continuing education. SECB continues to hone these requirements with the goal of developing an effective model that can be used to make continuing education mandatory and uniform in all states. The SECB criteria parallel those of the Model Law Structural Engineer designation offered by NCEES, but establish more rigorous standards for education, practice, and professional development. SECB’s criteria for certification can serve as the qualifications required for SE licensure throughout the United States. The mission of the Structural Engineering Institute (SEI) is “to advance and serve the structural engineering profession,” which includes state licensure. In October 1999, the SEI Board of Governors passed the following resolution: STRUCTURE magazine

Coming together is a beginning, staying together is progress, and working together is success. – Henry Ford The Structural Engineering Institute (SEI) supports separate licensing of structural engineers. SEI will support and encourage activities to achieve this goal in each state and other jurisdictions. In January 2010, the SEI Board of Governors adopted SEI Policy Statement 101 on Structural Engineering Licensure: The Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE) supports Structural Engineering licensure. It encourages Professional Engineers practicing structural engineering to further obtain a Structural Engineer license in jurisdictions that have any form of Structural Engineering license by complying with the jurisdiction’s specified requirements for education, experience and examination, and by meeting continuing education requisites to maintain this license. SEI also encourages jurisdictions to license Structural Engineers as a post-PE (Professional Engineer) credential, and to include in their new legislation an equitable transitioning clause for engineers currently practicing structural engineering. In most states, SECB Certification is the only credential available, it is currently the only de facto standard, and it is a way to distinguish structural engineers from the other engineering professions. Recent changes to the NCEES examination process have triggered some changes in the Certification Application. For this reason, SECB has enacted an open enrollment period for licensed professional engineers practicing structural engineering to attain certification based upon experience and education. The license and/or registration must have been awarded on or before July 1, 2005 and must remain valid continuously through the time of application. The open enrollment period began January 1, 2013. In addition, SECB application fees have been temporarily reduced for SEI members and NCSEA members to encourage more practicing structural engineers to obtain SECB certification. For more information, see the SECB website. As professional engineers, we have a responsibility to set demanding requirements for our peers to ensure that our industry operates with the highest quality standards possible. We are confident that SECB’s rigorous core curriculum and continuing education requirements will raise the bar for our profession. And, we are confident that the ultimate goal of this collaboration – to transform the SECB certification program into the basis for structural engineering licensure – will be accomplished. Both SEI and NCSEA have active licensing committees that will work together to more effectively pursue structural engineering licensing. Once a mandatory, uniform SE licensure program is adopted throughout the country, state legislatures and state licensing boards will look to our organizations for guidance and advice on licensing issues. Together we will raise the bar for structural engineers to improve education requirements, licensure and continuing education. Structural engineers will be reenergized to promote and support structural engineering licensure. It is clear that the result of our collaboration will be greater than the sum of any individual efforts, and we are excited about enhancing and improving our profession.▪

June 2013

Advertiser index

PleAse suPPort these Advertisers

Canadian Wood Council ....................... 20 Computers & Structures, Inc. ............... 60 CSC, Inc. .............................................. 27 CTS Cement Manufacturing Corp........ 37 DBM Contractors, Inc. ......................... 36 Enercalc, Inc. .......................................... 3 Engineering International, Inc............... 18 ESAB Welding and Cutting Products ...... 9 Foundation Performance Association..... 17

Fyfe ....................................................... 19 Gerdau .................................................. 29 GT Strudl ............................................. 22 ICC....................................................... 43 Independence Tube Corporation ............. 6 Integrated Engineering Software, Inc..... 45 ITW TrusSteel & BCG Hardware ... 25, 33 ITW Red Head ..................................... 39 KPFF Consulting Engineers .................. 38

editorial Board Chair

Burns & McDonnell, Kansas City, MO chair@structuremag.org

Brian W. Miller

CBI Consulting, Inc., Boston, MA

Mark W. Holmberg, P.E.

Evans Mountzouris, P.E.

The DiSalvo Ericson Group, Ridgefield, CT

Dilip Khatri, Ph.D., S.E.

Greg Schindler, P.E., S.E.

Khatri International Inc., Pasadena, CA

KPFF Consulting Engineers, Seattle, WA

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

Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA

Brian J. Leshko, P.E.

John “Buddy” Showalter, P.E.

John A. Mercer, P.E.

Amy Trygestad, P.E.

HDR Engineering, Inc., Pittsburgh, PA

Mercer Engineering, PC, Minot, ND

Chuck Minor

Dick Railton

Eastern Sales 847-854-1666

Western Sales 951-587-2982

sales@STRUCTUREmag.org

Davis, CA

Heath & Lineback Engineers, Inc., Marietta, GA

CCFSS, Rolla, MO

Advertising Account MAnAger Interactive Sales Associates

Jon A. Schmidt, P.E., SECB

Craig E. Barnes, P.E., SECB

NCEES ................................................. 47 New Millennium Building Systems ....... 11 Powers Fasteners, Inc. .............................. 2 RISA Technologies ................................ 59 S-Frame Software, Inc. ............................ 4 Simpson Strong-Tie......................... 15, 35 Soilstructure.com .................................. 49 Strand 7/Beaufort Analysis, Inc. ............ 50 Struware, Inc. ........................................ 42

American Wood Council, Leesburg, VA

Chase Engineering, LLC, New Prague, MN

Letter to the Editor

editoriAL stAFF Executive Editor Jeanne Vogelzang, JD, CAE

execdir@ncsea.com

Editor

Christine M. Sloat, P.E.

publisher@STRUCTUREmag.org

Associate Editor Graphic Designer Web Developer

After reading Lara K. Schubert’s series of articles on the role of gender in structural engineering in the February and April issues of STRUCTURE magazine, I find myself in complete disagreement with the author. Neither earthquakes nor hurricanes nor gravity care about gender and, regardless of the sex of the engineer, clocks stubbornly refuse to tick more slowly as deadlines approach. There is an old axiom that correlation does not imply causation. A proclivity towards analytical thinking and the use of logic are common traits among engineers not because the majority are males, but because these traits are critical to success in engineering. The use of logic to solve problems is what draws many, both male and female, to the profession in the first place. If a larger percentage of men than women either naturally possess these traits or wish to further cultivate them through their career, it should be irrelevant. Women greatly outnumber men in both nursing and elementary education, but this does not provide evidence of discrimination against male nurses or elementary school teachers. Qualities that lead to enjoyment and success in these fields, such as being nurturing, are found more often in women, and in a free society people will naturally be drawn towards careers that match their interests and skill sets. It is the nature of the profession not the gender of the professionals that shape the culture. The key for a well functioning society should be that analytical women and nurturing men can and often do find success in engineering and nursing, respectively. I also found the two anecdotes of gender discrimination from the sciences (physics and neurobiology) as evidence against structural engineers to be misleading. Besides coming from professions not in the field of engineering, both examples came from an academic setting, whereas the vast majority of structural engineers work in industry. An ‘old boys club’ is more likely to be found in academia, where tenure exists, than in a highly competitive industry made even more so by the last economic downturn. Discriminating for any superfluous reason will cost structural engineering firms both talent and business. In this way, the free market is able to punish bad actors and help suppress discrimination in a way not possible in academia. James Lintz P.E., LEED AP STRUCTURE magazine

June 2013

Nikki Alger

publisher@STRUCTUREmag.org

Rob Fullmer

graphics@STRUCTUREmag.org

William Radig

webmaster@STRUCTUREmag.org

STRUCTURE® (Volume 20, Number 6). 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 $65/yr domestic; $35/yr student; $90/yr Canada; $125/yr foreign. For change of address or duplicate copies, contact your member organization(s). 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

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Guest Column dedicated to the dissemination of information from other organizations

s a practicing geotechnical engineer for over 30 years, I would like to thank Mr. Gerd Hartung, P.E., S.E. and Mr. Richard Anderson, P.E. for their insightful article entitled The RFP for the Geotechnical Report as presented in the March 2013 issue of STRUCTURE magazine. Their specific and relevant advice regarding how to procure the services of geotechnical engineers is beneficial to us all. The structural engineering community is wellknown as a strong advocate for the selection of geotechnical services based upon quality and understanding of the project and project area, and that article is another example of their commitment to the use of geotechnical engineers as significant contributors to the overall success of every project. Structural and geotechnical engineers must forge a team to create a successful design, as the article states. When I encounter a prospective client who considers geotechnical engineers to be a “testing laboratory” and chooses to hire based on the lowest price instead of selecting a capable and knowledgeable professional, I respond with a three-word declaration: “You deserve better.” It is a simple, yet significant statement. The fees of the geotechnical consultant are usually less than a fraction of one percent of the construction costs, yet their test results and opinions have an impact on the project budget that is orders of magnitude greater. Going with the cheapest provider for this critical investigation and design work ultimately places undue burden on the structural engineer to interpret the geotechnical data, select design parameters, consider site preparation and foundation options, etc. Along those lines, the structural engineer should not dictate the scope of the field and laboratory segments of the geotechnical engineer’s work, or exclude the geotechnical engineer from the process of foundation system selection. Our profession has grown immensely in the development of technologically enhanced ways to conduct a site characterization program using geophysical and/or in-situ test methods, typically complementing the traditional soil boring as a means of understanding the subsurface conditions. Geotechnical engineers also develop, understand and promote innovations in ground improvement, intermediate foundations and advancements in deep foundations to save owners millions of dollars. Today’s technology makes active collaboration with the geotechnical engineer simple, which minimizes the potential for miscommunication

The Proper Role of the Geotechnical Engineer By Victor R. Donald, P.E.

Victor R. Donald, P.E. (vrdonald@terracon.com), is a senior principal, senior vice president, and National Director of Geotechnical Services for Terracon in Olathe, Kansas.

10 June 2013

…the structural engineer has a unique appreciation of the benefit that a capable geotechnical engineer brings to the design team. that can result from a single point of delivery report and overly conservative designs. There are two types of foundation failures. The first is obvious – structures move, slopes fail, walls tilt, floors distort, walls crack, etc. This failure type gets significant attention. The second could be more prevalent, but it goes completely undetected. It is the foundation that costs at least twice and perhaps up to ten times more than necessary, all because the design team lacked the active participation of an innovative and capable geotechnical engineer knowledgeable of recent advancements in the profession. The design-build (D-B) environment is a good example of geotechnical engineers providing valuable participation on the design team. D-B projects include the geotechnical engineer in the design process in order to render a proposal for the project that offers the best value. In my experience, D-B projects allow for vigorous and highly collaborative interaction of all disciplines, with the winning proposal often resulting in an innovative solution. If the need for active participation by the geotechnical engineer is that obvious in D-B projects where best overall value wins, why do geotechnical engineers struggle to participate as design professionals in the traditional design-bid-build environment? As the referenced article implies, the structural engineer has a unique appreciation of the benefit that a capable geotechnical engineer brings to the design team. My request to the structural engineering community is to “help us help you.” By continuing to convey this message to your clients, you can assist us in becoming more influential in the design process and eliminating the burden of insufficient geotechnical engineering that must be borne by someone – usually the structural engineer.▪

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Structural teSting issues and advances related to structural testing

n a STRUCTURE® article published earlier this year, the author discussed some of the components of a nondestructive evaluation (NDE) program for existing masonry structures, and what types of information could be obtained through such methods. This article aims to elaborate on the procedures and techniques used to investigate existing masonry structures and diagnose potential issues.

Flatjack Tests From a structural design standpoint, some of the most important properties of existing masonry include strength, stiffness, and in situ stress. Flatjack testing methods are some of the most valuable tools available for measuring masonry resistance to loads as well as the existing stress that the masonry is currently experiencing. First, it’s important to distinguish the type of test to be specified, as the information provided by each test method is different. ASTM C1196, Standard Test Method for In Situ Compressive Stress Within Solid Unit Masonry Estimated Using Flatjack Measurements, provides a procedure for measuring the existing state of vertical compressive stress within an unreinforced solid masonry wall. This information is of particular use when supplemental supports are designed for areas where plans call for portions of existing masonry walls to be removed. The results of this method have also been used to verify analytical models, complicated load paths, and flexural bending moments across a wall section. In this test, a single stress-relieving horizontal slot is cut in a masonry bed joint in the area the information is desired. A series of gauge points placed above and below the slot help to precisely measure the vertical distance that the masonry drops after cutting. A single Flatjack is inserted into the slot and pressurized at increasing increments while the distance between gauge points is measured, until the original distance between gage points is

Investigating Masonry Structures Nondestructive and Minimally Invasive Techniques Andrew E. Geister, P.E.

Andrew Geister, P.E., is an engineer with Atkinson-Noland & Associates, Inc., specializing in masonry investigation through nondestructive, in-situ, and laboratory material testing. He is also a member of multiple committees in The Masonry Society. Andrew can be reached at ageister@ana-usa.com.

Figure 1: Single flatjack test used to determine masonry in situ stress.

12 June 2013

Figure 2: Flatjack deformability testing to measure masonry elastic modulus and estimate compressive strength.

restored (Figure 1). The Flatjack pressure required to restore the original masonry position generally corresponds to the in situ stress, after the necessary calibration and area factors are applied. ASTM C1197, Standard Test Method for In Situ Measurement of Masonry Deformability Properties Using the Flatjack Method, provides a means for measuring masonry stiffness and estimating masonry compressive strength, which are often the most important masonry properties in design and retrofit. In this test, two horizontal slots are cut with five courses of masonry between them. Both Flatjacks are pressurized together while monitoring the surface strain of the masonry between them (Figure 2); the result is a compressive strength test within the wall that produces a stress-strain curve (Figure 3 ). In order for the test to be effective, the Flatjacks must react against masonry which is rigid enough that only the masonry between the Flatjacks deforms during the test. Generally, this is not a problem below the test location as long as the test is not performed directly above an opening, since most walls are supported by foundations that won’t deflect during the test. Ensuring that enough dead load is present on the masonry above the test location can be more difficult, especially for single story buildings or test locations near the roof. Without enough overburden pressure, the upper Flatjack can actually lift the portion of the wall above it, limiting the maximum applied pressure to the test area. Masonry shear strength is measured by ASTM C1531, Standard Test Methods for In Situ Measurement of Masonry Mortar Joint Shear Strength Index. In this test, mortar is cleared from

Deformability Test #1 1000

Stress (psi)

800

600

400

Figure 4: Masonry shear strength testing using a specially-sized flatjack.

200

0 0.0000

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

Strain (in/in) Figure 3: Masonry stress-strain curve generated by flatjack deformability testing.

both head joints of a single unit. A single Flatjack, specially sized to match the brick end, is then inserted into one of the empty head joints, while instrumentation such as a dial gauge is used to measure displacement across the other. The Flatjack pressure is slowly increased until it causes the masonry unit to move toward the empty head joint (Figure 4 ). The pressure required to induce movement is recorded and used to calculate the mortar joint shear strength index. Unlike the Flatjack deformability test, having a minimal amount of dead load above the shear test is advantageous. Because normal stress contributes to the bed joint shear resistance, this normal stress must be estimated and then subtracted from the measured joint shear strength using the procedure described in the International Existing Building Code. One way to reduce the effect of normal stress on the shear test is to perform the test below an opening or near the top of the wall.

Surface Penetrating Radar The use of Surface Penetrating Radar (SPR) for masonry investigation does not follow a standardized procedure, but rather depends on the interpretation and experience of the user. In the right hands, SPR can be most useful in locating embedded objects such as metal reinforcing or conduit, locating bond courses, and assessing the extent of anomalies, voids, or ungrouted cells. The equipment often consists of a handheld or wheeled antenna, processor, and output screen. The antenna transmits microwave energy and then collects the reflected signal as it bounces back.

What the user sees on the screen is the result of this energy being reflected back at various times, which relate to depths of different materials. Metals, for example, are highly reflective to radar energy and thus SPR is very effective at locating reinforcing bars and other metal objects within masonry walls (Figure 5 ). Air, on the other hand, is not particularly reflective to radar energy. Since almost none of the transmitted energy is reflected back by these empty spaces, an experienced user will be able to differentiate between air and solid material. Therefore SPR can be used to locate cracks, voided areas, or hollow masonry cells. SPR is most effective on walls that are dry because wet areas are highly attenuative to microwave energy, thus reducing its effective penetration depth and limiting the information available to the user. Since the exterior face of a masonry wall tends to dry out before the internal portion does, significant moisture can still be present inside the wall even if the outer surface appears dry. It may be necessary to wait for an extended amount of time for masonry walls to dry after a severe weather event before performing SPR observations, depending on local climates. A moisture meter should always be used to confirm conditions if moisture is suspected.

Infrared Thermography Masonry’s thermal mass and thermal transfer properties make infrared thermography (IRT) an ideal method for investigating potential anomalies. The cost of infrared equipment has decreased in recent years, while quality has continued to improve. As it relates to

STRUCTURE magazine

June 2013

Figure 5: Surface Penetrating Radar output image showing masonry wall thickness and reinforcing bars.

masonry investigation, IRT is most useful in locating temperature differences at specific areas, which can indicate the possibility of internal anomalies. One such anomaly is the potential for excess moisture and leaks. The temperature difference between wet masonry and dry masonry, due to evaporative and other effects, will produce distinctive appearances between the two when viewed using infrared equipment. Larger air voids, such as those left by unfilled cells, can also be detected using IRT (Figure 6 , page 14). For IRT to work effectively on masonry structures, however, there needs to be a large enough temperature difference between the building and the surrounding air. This is usually best achieved in early morning or late evening, when the air temperature is changing. In the morning, the sun begins to warm the masonry while the grouted cells stay cool. In the evening, the opposite occurs; empty cells, voids, and wet areas become cool while the stored heat from the day remains in the wall. IRT also works well when there is at least a 30° temperature difference between interior and exterior wall surfaces.

Borescope Images observed via fiber optic borescope are a useful way to view concealed conditions without removing or damaging large portions of the wall. A small borehole, usually less

Figure 6: Infrared Thermography image used to quickly distinguish between grouted and hollow cells in concrete masonry construction.

Figure 7: Borescope view of a masonry wall cavity and veneer anchors.

Figure 8: Borescope image of a crack forming on the back face of a veneer panel.

than the thickness of a mortar joint, is the only opening needed to insert the probe. A borescope can be used to view the condition of connectors (Figure 7 ), cracks or deterioration on the back faces of units (Figure 8), and excess mortar within wall cavities.

may be adjusted based on local weather data. Water loss into the wall surface is recorded for a minimum of 4 hours, and any observed water penetration to the opposite wall face is reported. Spray tests can also be performed to gain understanding of wall leakage potential, especially around windows, following AAMA 501.2, Quality Assurance and Diagnostic Water Leakage Field Check of Installed Storefronts, Curtain Walls, and Sloped Glazing Systems. This test uses a specially sized nozzle and a prescribed pressure of 30-35 pounds per square inch (psi). If leaks are discovered during the test, specific components are then sealed off to determine the moisture entry paths. A direct evaluation of wall drainage and water collection systems may be performed using ASTM C 1715, Standard Test Method for Evaluation of Water Leakage Performance of Masonry Wall Drainage Systems. In this test, a series of tubes deliver water directly to the drainage cavity and the ability of the system to collect and redirect water to the exterior is observed.

direct electrical connection first needs to be made with the reinforcing steel, which is often accomplished by drilling or chipping the masonry to expose a small portion of the bar and attaching a clamp. This also requires that the reinforcing be located prior to performing the corrosion potential measurements. The electrical potential of the reinforcing metal is measured against a copper-copper sulfate reference electrode with a voltmeter. Measurements are made along the reinforcing by placing the electrode on the pre-wetted masonry surface and recording the potential difference displayed by the voltmeter at regular intervals. Corrosion potentials more negative than -0.35 V indicate a high probability of active corrosion at that location. Measurements can only be made at reinforcing with an electrical connection to the location that is clamped to the voltmeter; so, in masonry, this usually means along a bond beam or a vertically reinforced cell.

Pachometer

The proper selection and use of NDE methods are a valuable, and in some cases necessary, approach to determine properties required for design or use of existing masonry structures. In historic construction, destructive probes may not be allowed or must be kept to a minimum. In new construction, NDE has been used as a form of quality control to verify project requirements are met, especially for placement of grout, reinforcing bars, and veneer anchors. The nondestructive and minimally invasive diagnostic techniques described here allow effective evaluation of existing masonry structures without excessive damage and expensive sample removal. Finally, NDE methods provide the design engineer with confidence that material properties and conditions are known, and confident engineers provide the most cost-effective solutions for repairs or retrofit.▪

Pulse Velocity Pulse velocity testing following ASTM C597, Standard Test Method for Pulse Velocity Through Concrete, has been successfully used to evaluate masonry structures for cracks, deterioration, and construction quality. The equipment operates by sending a pulse of mechanical energy through the face of the masonry, and measures the length of time to receive the signal on the opposite face or on the other side of a suspected discontinuity such as a crack. Differences in velocity between known intact areas and possible deterioration can confirm these suspicions, and a decrease in velocity at the same location over time could indicate worsening conditions. Evaluation of energy loss (attenuation) and frequency characteristics provides additional information on the internal quality of the masonry.

Water Penetration Identifying moisture paths and water penetration through masonry walls, or evaluating water repellent surface treatments, are accomplished through the use of a spray chamber as described by ASTM C1601, Field Determination of Water Penetration of Masonry Wall Surfaces. The test method is performed using a 12-square-foot chamber attached to the wall, which allows the user to apply a prescribed water flow and pressure to the wall surface. The chamber has to be sealed to the wall surface so that no leakage occurs from the chamber during the test. Typical conditions of this test include a water flow of 3.4 gallons per square foot per hour at 10 pounds per square foot (psf ) air pressure, but these

Location of metal objects such as veneer ties and joint reinforcing within masonry walls may also be facilitated through the use of an eddy current pachometer. If reinforcement size is known, the pachometer is also useful for estimating the depth of masonry cover. The pachometer is especially useful for locating smaller metal objects such as anchors and veneer ties, which are difficult to locate using SPR due to their smaller reflection surface.

Corrosion Potentials Metal reinforcement corrosion potentials, also referred to as half-cell potentials, are evaluated using ASTM C876, Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete. A

STRUCTURE magazine

June 2013

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The Union Square condominium project was able to achieve seven levels of residential use with a density of 143 units per acre.

Wood buildings have economic, aesthetic, green, and structural attributes that make them a good choice for commercial buildings. However, perceived barriers have made designers reluctant to choose wood for large buildings, like building code limitations and the challenge to meet structural capacities. Fortunately, codes are shifting to accommodate new technology that, in turn, is permitting wood structures of sizes and heights heretofore unthinkable.

Height and Area Considerations for Commercial Wood Buildings By Paul D. Coats, P.E., C.B.O. and Dennis Richardson, P.E., C.B.O.

Paul D. Coats, P.E., C.B.O. (pcoats@awc.org), is Southeast Regional Manager and Dennis Richardson, P.E., C.B.O. (drichardson@awc.org), is Southwest Regional Manager for the American Wood Council’s Codes and Standards group.

Fewer Size and Use Limits Since the inception of the International Building Code (IBC), wood frame commercial structures have enjoyed larger building sizes inherited from the upper limits of each of the legacy building codes. Although certain uses and occupancies retain traditional size restrictions, limits for many low-rise buildings are nearly gone, given area increases permitted for sprinkler systems and open space around the building perimeter. In the IBC, one and two-story business and mercantile buildings can be unlimited in area when sprinklered and at least 60 feet of open space is provided on all sides of the building. Currently, even single-story assembly occupancies of Type IV (Heavy Timber) or Type III construction (typically wood frame with noncombustible or fire retardant treated wood exterior walls) are permitted to be unlimited in area under fairly standard conditions. It has been suggested that building size limits are unnecessary if compartmentalization is provided

16 June 2013

Case Study Project: Union Square Condominiums Location: San Diego, CA Architect: Togawa Smith Martin, Inc. Engineer: Edmond Babayan and Associates Size: 263 condominium units Completion Date: 2005 Architects for the Union Square condominium project in San Diego made use of code provisions to increase the height of the project by adding two levels for residential use. First, utilizing IBC Section 505, designers added a mezzanine, which increased the number of wood-frame levels to six. Second, since the project was not located in a retail neighborhood, the Type IA concrete level at grade was designed to incorporate residential “stoop units,” each with access to the street. The building was thus able to achieve seven levels of residential use with a density of 143 units per acre. to address fire resistance. An appendix in the NFPA 5000 Building Construction and Safety Code provides an alternate approach to construction types based on compartmentalization with fire resistance rated construction rather than the traditional building size limits.

Height Considerations The IBC has for some time permitted wood buildings to be nearly as tall as structural design considerations will allow them to be. The use of fire retardant treated wood (FRTW) in exterior walls, permitted by the IBC in Type III and Type IV Heavy Timber construction, enables

buildings entirely of wood to expand beyond low-rise into the mid-rise market. Type IIIA buildings (two hour exterior walls, either noncombustible or FRTW, and one-hour light frame interior structure) can go 85 feet above grade in a sprinklered building. Business occupancies could be six stories; mercantile, apartments, and condominiums can be five stories of wood frame construction, with one or more additional stories if they take advantage of special occupancy provisions for pedestal buildings. However, code height limits are often not the determining factor in choice of materials – there are engineering considerations for taller structures such as structural performance and detailing for wood shrinkage. In recent years, wood has taken a giant leap toward becoming a preferred structural choice for tall buildings with the introduction of Cross Laminated Timber (CLT). The IBC and NFPA 5000 have already changed to allow for the use of CLT.

Recent Code Changes Accommodating Greater Heights

Project: Promega GMP Facility Location: Fitchburg, WI Building design: Uihlein-Wilson Architects; EwingCole; Archemy Consulting CLT Engineer: Equilibrium Consulting Inc. Size: 260,000 square feet Completion Date: October 2012 Building codes are flexible enough to accommodate new materials, and it is common for building projects to require – and be granted – alternate methods approval for designs not in the code that can be justified on a case-by-case basis. Such was the case for the new Promega biotechnology production facility, which features an innovative mix of glulam and CLT. Building department approval was achieved through use of the newly completed ANSI/APA PRG 320-2011 Standard for Performance-Rated Cross-Laminated Timber. “The design team discussed the standard with building officials early in the process,” says Kris Spickler of StructurLam Products Ltd. “Engineering information was then submitted under the “alternate designs” section of the code. IBC Section 104.11 states that ‘An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of the code.’ Local building officials accepted both the ANSI/APA standard and the design.” Most of the new Promega facility will be dedicated to manufacturing with committed (fixed) production lines and flexible manufacturing areas. It will also feature a customer experience center for employees and guests that will include spaces for training, laboratory demonstrations, conferences, an exercise and fitness center, and dining. can be located in the podium itself. This follows a change to the 2006 IBC (appeared in the 2009 IBC) which had expanded the possibilities for occupancies in the podium from S-2 parking only to include B, M, and R occupancies. • Minimum sizes for Structural Composite Lumber (SCL) will be included in descriptions for Type IV Construction next to glulam, enabling the incorporation of large dimension SCL members in Type IV buildings without special approval. continued on next page

STRUCTURE magazine

June 2013

The 260,000-square-foot Promega biotechnology production facility, completed in October 2012, is dedicated to manufacturing with committed (fixed) production lines and flexible manufacturing areas.

The Promega biotechnology production facility features an innovative mix of glued laminated timber and cross laminated timber.

Building codes are flexible enough to accommodate new materials and it is common for building projects to require – and be granted – alternate methods approval for designs not in the code that can be justified on a case-by-case basis.

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Sometimes referred to as “plywood on steroids,” CLT typically consists of three, five, or seven layers of solid wood, kiln-dried and layered as perpendicular laminations bonded with adhesives to create full-depth solid wood wall and floor panels up to 12 feet by 60 feet. In the most recent code change cycle, CLT was given a place in IBC Type IV construction provisions, and a new product standard, ANSI/APA PRG 320-2011 Standard for Performance-Rated CrossLaminated Timber was referenced. Leading wood organizations have collaborated to publish a new CLT Handbook which can be downloaded at www.masstimber.com. A building constructed entirely of CLT is intriguing, but other changes in the 2015 IBC may also affect the choice of wood in tall hybrid buildings, including: • The 2015 code will permit wood to “top” multi-story Type I concrete or pedestal “podiums.” Currently, special podium building provisions limit Type I construction to a single story. The code currently allows multiple separate buildings over the top of a Type I podium. • Occupancy restrictions for the lower levels of special Type I “podium” buildings are eliminated in the 2015 code so that any occupancy permitted by the code except Hazardous (H)

Case Study

Structural “Brainstorming” with CLT CLT is formed of laminated nominal 2x wood members with alternating layers in perpendicular directions. It forms a robust structural billet that can be well adapted for walls (similar to tilt-ups) or prefab floor and roof slabs. One published concept for a thirty-story high rise using CLT and other building materials in a hybrid framing system involves the use of the strong column (or wall), weak beam approach. The Case for Tall Wood Buildings by Michael C Green and J. Eric Karsh can be downloaded here: www.woodsolutions.com.au/Blog/the-case-for-tall-wood-buildings. This system utilizes high aspect ratio CLT wall piers (or columns) connected to specially detailed steel link beams for energy absorption and ductility. A similar system using ductile connections to wood link beams may also be effective for energy absorption, and could be a very robust system. The weak link in such wood frame systems has been crushing of wood perpendicular-to-grain at the column/beam joints. However, CLT has the unique advantage of providing parallel-to-grain bearing in two directions, thus the ability to minimize this problem. One of the many challenges facing the broad acceptance of CLT in the U.S. is the lack of codified seismic design provisions. The International Building Code references ASCE 7 Minimum Design Loads for Buildings and Other Structures, which provides comprehensive requirements for seismic design. For example, Section 12.2.1 of ASCE 7 provides guidance on the selection of Response Modification Coefficients, R, for various Seismic Force-Resisting Systems (SFRS). CLT is not a recognized system in ASCE 7 Table 12.2-1; therefore, designers must rely on other provisions of the standard. ASCE 7 Section 12.2.1 states “SFRS not contained in Table 12.2-1 are permitted provided analytical and test data are submitted to the authority having jurisdiction for approval that establish their dynamic characteristics and demonstrates their lateral force resistance.” Until an R is recognized in ASCE 7, expected compliance pathways for CLT designs include performance-based design procedures described in ASCE 7, or demonstrating equivalence to an existing ASCE 7 system. Guidance for such evaluations can be derived directly from ASCE 7-10, FEMA P695, and FEMA P795 Quantification of Building Seismic Performance Factors: Component Equivalency Methodology.

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• Fire resistance rating requirements for building elements and structural members bracing exterior walls will be simplified to preclude code interpretations that currently result in substantially increased requirements for fire resistance rating of interior elements. Taken together, these code developments will make it easier for design teams to take

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advantage of current building height limits. Here are some potential design concepts that previously may have been more difficult from a code standpoint: • Heavy timber or Type IIIA light frame apartment buildings over heavy timber open parking garages has been allowed by the IBC for years, but now SCL and CLT will be permitted in Type IV parking podiums. This would allow an 85 foot tall, six story structure with five stories of apartment over one story of open parking. • CLT will be a possible solution for future fire wall construction; a CLT wall assembly with gypsum recently exceeded three-hours in a fire resistance test (see NGC Testing Services Test Report WP-1950 dated October 15, 2012). Currently, buildings can be subdivided by fire walls to create separate buildings for code purposes, but fire walls built out of combustible framing materials are limited to type V construction. The impressive three hour performance of a CLT test wall may now allow code

STRUCTURE magazine

June 2013

officials to consider approval of CLT as a fire wall in Type III and Type IV Heavy Timber construction. This means one CLT open parking garage podium structure could potentially support multiple wood frame residential buildings, each remaining within required area limits. • With removal of the one story limit and expansion of use and occupancy designations in buildings with a Type I podium, a variety of uses, including high occupancy assembly (with the associated taller story configuration), could be located in one area of the podium with two or more lowerheight stories of parking adjacent in the perimeter areas of the podium to fill in the remainder of the site.

What about Concerns for Fire? Fire has always been a concern for combustible construction, and the use of wood in taller buildings will need adequate protection. A key concept for codes is fire resistance, which is not necessarily related to the combustibility of a material. Fire resistance is a performance metric and, for wood structures, it is typically achieved by protecting exposed wood with gypsum board or over-sizing the exposed wood structural elements to provide for sustained load-bearing capacity even while the member chars. The methodology is contained in the American Wood Council’s referenced design standard for wood construction, the National Design Specification® (NDS®) for Wood Construction. There is an acceptance by most fire professionals that heavy timbers and largedimension engineered products provide a known level of performance in fire conditions. This explains the larger building sizes permitted for Type IV construction, even over the unprotected Type IIB (noncombustible, unprotected) construction type. CLT will undoubtedly prove to be an exceptional performer for fire resistance (as the abovementioned test indicated). As wood buildings become taller, there will be higher expectations that finished wood buildings perform under fire conditions like tall buildings of noncombustible construction types. Occupant life safety is first addressed through early fire detection and notification, followed by active fire suppression and adequate means of egress, which are well covered in the IBC. Interior wall and ceiling finish requirements are no

different for CLT buildings and are based on the function of the particular space. Concealed spaces, while not permitted in a Type IV building, are permitted to be constructed with FRTW in certain locations within Type I and II construction. Concealed spaces in CLT construction, where otherwise not permitted, will need to be approved by the code official as an alternate method when adequately protected with noncombustible materials or fire sprinkler systems. Studies have already begun to determine if the current combination of fire resistance, flamespread protection, life safety systems, and fire suppression systems required for high rise buildings make the combustibility of the structural frame inconsequential in the big picture. Fire protection during construction is critical for combustible-frame

structures and this is an area where codes may likely need to be improved.

Conclusion New technology is dramatically increasing the potential for large commercial wood structures, and building codes are shifting to accommodate. In Europe, more so than the U.S., environmental concerns and incentives have resulted in a shift to wood for tall buildings that, until recently, would have been of other materials. There are notable

high rise CLT buildings in other countries, and interest has been high in North America as a result. Although the 2015 IBC is not yet available for purchase or adoption, it is already influencing these trends. The codes are paying less attention to combustibility of the frame and more attention to life safety and fire resistance, which is appropriate. The negatives of wood for large buildings are disappearing, as required levels of structural and fire performance in all environmental conditions are being emphasized.▪

Exterior Walls in Type III Construction

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The historic definitions for Type III and IV in the IBC require noncombustible exterior walls of 2-hour fire resistive rating. Traditionally, Type III construction described industrial buildings of masonry exterior walls and interior of heavy timber or wood frame. Often located in crowded urban sites, the protection afforded by masonry walls was a valuable asset in mitigating conflagration. Since Type III buildings are now permitted to have fire retardant treated wood (FRTW) exterior walls, there are some “disconnects” in the code in regard to the interface of exterior walls with interior structure, and code provisions which originally assumed masonry exterior walls may be the focus of varying interpretations in typical platform construction, since the floor assembly “interrupts” and supports the exterior wall at each floor level. Code officials handle this in a variety of ways, but usually a practical approach is to require solid wood blocking in all floor cavities that extend within the plane of the exterior wall. The char rate of solid wood substantiates such an approach, since solid wood of three inches in thickness would provide approximately two hours of fire resistance.

STRUCTURE magazine

June 2013

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f your office and its culture are consistent with most structural design firms, you probably embraced the load and resistance factor design (LRFD) approach for reinforced concrete years or even decades ago. For many, working stress design for concrete is a totally foreign concept, while LRFD ‘strength’ design is what you probably learned in school and practice to this day. In recent years, the push to LRFD has been embraced by many for the design of steel and masonry systems. While allowable stress design (ASD) methods are still acceptable, the perception is that the majority of engineers use LRFD for concrete, masonry and steel systems. This brings us to wood. ASD has been the basis for engineering wood systems for decades. Textbooks, codes and even the design values listed in technical catalogs of proprietary fasteners and hardware reflect the ASD approach. However, provisions for LRFD design in wood have gradually become more predominant, and it may be only a matter of time before ASD methods are relegated to appendices while LRFD becomes the primary basis of design. The adoption of LRFD methods for wood has a history not unlike its concrete, masonry and steel counterparts. The 2005 version of the National Design Specification® (NDS®) for Wood Construction lists adjustment factors and other values enabling the use of LRFD with the strength design load combinations of ASCE 7. Interestingly enough, the LRFD adjustment factors are listed as the last tables in the last appendix of NDS 2005. Elsewhere, references to LRFD can be found in the “Applicability of Adjustment Factors…” within the main body of the code (e.g., Table 4.3.1). Aside from this, NDS 2005 does little to embrace the LRFD methodology. On the other hand, NDS 2012 has made a major LRFD leap by placing the LRFD adjustment factors in Chapter 2 (page 12). Times are changing, and little by little the LRFD approach is becoming more mainstream for wood design. Breyer’s Design of Wood Structures has been a premier text for wood design for many years. The most current (sixth) edition has been re-titled Design of Wood Structures ASD/LRFD. At nearly double the size of earlier editions, this text contains side-by-side instruction, examples, and theory of both ASD and LRFD methods for wood design. NDS 2012 lists the LRFD adjustment factors (KF), resistance factors (φ) and time effect factors (l) in both the body of the code and the appendices. However, NDS 2012 is still structured in a manner reflecting ASD theory; the listed design values (e.g., Fb, Fc, Fv, etc.) all reflect allowable stresses. Even so, it should be noted that this information is the product of decades of research in the development of LRFD methods for wood. As an example, consider a simple (single) 2x8 purlin. Once we agree that moisture, temperature, flat use, incision, and repetitive use factors are

not applicable (each having a value of 1.0) and that the beam is laterally supported (CL =1.0), the adjusted design value for bending (following ASD methods) is calculated as: F 'b = FbCDCF For this, the load duration factor (CD) is predicated by the shortest duration load for a particular combination and the size factor (CF) is taken from Table 4A of the NDS code (1.2 for this example). Now consider the same scenario, but follow the LRFD approach. In accordance with the NDS provisions, the adjusted value for bending becomes:

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F 'b = FbCF K F φb l While the similarities are apparent, you may notice that the CD factor has been removed and replaced by the l factor, which accounts for the time effect associated with each of the load combinations for strength design. As you might expect, the value for l is smaller for sustained loads and larger for transient loads. The value ranges from 0.6 to 1.25 depending on the load combination and the nature of load (e.g., impact live loads vs. storage live loads). The φb factor is not unlike that used for steel and concrete, having a value of 0.85, while the KF factor reflects a significant adjustment having a value of 2.54 for the bending design herein discussed. This is the primary variable for adapting the long-held ASD approach to the LRFD approach. Size factor (CF) and primary design value (Fb) remain unchanged between the ASD and LRFD methods. Now consider the same 2x8 member and assume #2 DF-L. From NDS, this has Fb = 900 psi. If the controlling load is D+L, the CD factor is 1.0 and the adjusted design value for allowable stress becomes F 'b = 1,080 psi … quite simple. If we are using LRFD, the value for l is 0.8 (assuming normal occupancy) and the adjusted nominal design value becomes F 'b = 1,865 psi. Comparison of design values shows a general consistency to the comparison of the ASD (1.0D + 1.0L) and LRFD (1.2D + 1.6L) load combinations, depending on the ratio of live load to dead load. Hence, LRFD yields similar if not identical sizes of wood members as ASD, at least for this example. However, there are still challenges with making the LRFD leap, such as determining how to adapt all of the ‘allowable’ design values listed in catalogs of fastening hardware, engineered wood products and software. Admittedly, LRFD requires a few more variables, a little more calculation and perhaps a bit more effort, but it is a step toward a unified (and arguably more reliable) design approach for the four primary materials of construction. Whether you or your office should embrace LRFD for wood is still a matter of choice, but may eventually become only a matter of time.▪

STRUCTURE magazine

Wood Design

Making the LRFD Leap By Jerod G. Johnson, Ph.D., S.E.

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 SEAU Newsletter (March 2012). It is reprinted with permission

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Figure 1: Water treatment complex – overall view.

his article summarizes the author’s experience in developing a structural model to analyze and design a structure for the Victor Valley (California) Wastewater Reclamation Authority that is approximately 50 feet wide by 300 feet long. Because the structure has significant horizontal and vertical irregularities, and is in a high seismic area of southern California, design codes specified three methods of analysis: (A) Modal Response Spectrum Analysis (MRSA) for structures with horizontal irregularities; (B) Tank Hydrodynamics for water basins; and (C) Equivalent Lateral Force (ELF) for regular structures. The three processintegrated areas are separated from each other by expansion joints and are shown in Figure 1, in which some roof and wall segments are removed to display internal components. Overall design of the facility was completed by the office of Carollo Engineers, Inc. in Phoenix, Arizona.

main roof diaphragm. Bearing walls are 12-inch masonry units that are integrally colored and partially treated with a stucco finish. For details of the author’s method of modeling composite diaphragms, foundation soil springs, and ‘cracked’ masonry, as well as the ELF method of analysis, refer to Modeling and Analysis of a Masonry Building on Piling (March 2013, STRUCTURE magazine). The first step was to create a computer model and use it to determine the seismic base shear of the structure in accordance with the ELF of ASCE 7 paragraph 12.8, with a response modification factor R=5.0, importance factor I=1.25, and Site Class D. The resulting value was 245 kips. In accordance with ASCE 7 table 12.6-1 for Seismic Design Category D with horizontal

Seismic Modeling of an Irregular Water Treatment Structure

Area A – Main Building The main floor of the building is at grade, but the roof is divided into three different levels in order to lower each level as much as possible and minimize the visual impact of the complex on the surrounding residential neighborhood. One roof is approximately 20 feet above grade, a second is 18 feet-8 inches above, and the third is approximately 16 feet high. On each roof is an elevated tile mansard that surrounds several units of HVAC equipment. The tile is supported by metal deck over small steel trusses that are bolted to the concrete topping of a 5½-inch deep composite steel deck, which forms the

Figure 2: Roof diaphragm in-plane shear stress.

STRUCTURE magazine

By Louis Scatena, P.E.

Louis Scatena, P.E., is a senior structural engineer with Carollo Engineers, Inc. He can be reached at LScatena@carollo.com.

Figure 3: Wall in-plane shear stress at roofs separated 32-inch vertically.

Figure 4: Partial view of area B baffle walls and walkways.

irregularities and paragraph 12.7.3, the next step required performing MRSA in the north-south and east-west directions. Eighty modes produced more than 90% mass participation in each of the principal directions. The redundancy factor was 1.0 to check drift and torsional irregularities. Dividing modal response parameters by R/I (i.e., 4.0), multiplying calculated displacements by Cd/I (i.e., 2.8), and combining the various modes using the Complete Quadratic Combination (CQC) method resulted in base shears of 124 kips in the north-south direction and 156 kips in the east-west direction. The next MRSA included application of a load factor to scale the design base shear up to 100% of the ELF base shear. Since California Building Code Section 1615A.1.8 only applies to schools and hospitals, the final design was based on 85% of the calculated stresses. Displacing certain concentrated load masses associated with equipment in a direction orthogonal to that of the earthquake satisfied the code requirement for accidental torsion. Although not required by ASCE 7 paragraph 12.9.5, the accidental torsion was amplified in both directions. This conservative addition is intended to help preserve the integrity of the architectural wall finishes and stucco, which also includes fiber reinforcement. Combining the results of north-south (Z-direction) and east-west (X-direction) modeling using the relationship of 1.0X and 0.30Z (and vice versa) produced the critical design wall and diaphragm forces. The redundancy factor in the second MRSA was 1.3, based on ASCE 7 paragraph 12.3.4.2 and the configuration of the masonry shear walls. Design of collectors, such as the beams and columns under discontinuous shear walls at the ground floor, included an overstrength factor of 2.5. Figure 2 (page 23)

methodology of ASCE 7-05. The estimated wave sloshing height in the north-south direction due to seismic hydrodynamic loading is 1 foot, and freeboard is approximately 3 feet. In the east-west direction, sloshing height is 4 feet and an uplift resistance of 60 psf has been specified on the covers. The consequences of the impulsive and sloshing effects of the liquid, the impulsive effect of the walls, and the static and dynamic effects of the soil generated pressures for four load cases that were incorporated into the model: (1) backfilling operations during construction with equipment surcharge; (2) unbackfilled during construction and filled for the leak test; (3) backfilled and empty during a seismic event; and (4) unbackfilled and full during a seismic event. Figures 4, 5 and 6 suggests the benefits of the model for accurately determining the effects of walkways and interior baffle walls on the overall design. The analysis model included the basin mat, walls, and walkways under the pre-determined pressures for the four load cases. Figure 5 represents the vertical bending in the wall for Load Case 2, confirming the influence of the walkways in developing a large positive moment near the center of the wall and reducing the negative moment at the base (note sore spot at upper

represents the area A high roof diaphragm shear stress, which the model shows concentrated at the center of elements, for the roof on the right side of area A. However, some modeling references (e.g., NEHRP Seismic Design Tech Brief #5) recommend distributing the concentration over a larger deck cross-section based on the ductility of the steel deck with reinforced concrete topping. Modeling with smaller finite elements is another alternative to produce a finer distribution of visible stresses. Figure 3 represents the shear stresses in the wall supporting two roofs that are at moderately different levels.

Area B – Aeration Basins The basins are approximately 20 feet deep and the concrete walkways are a few feet above surrounding grade. Fiberglass deck panels span the basins between the walkways. Interior baffle walls are without walkways and serve as process weirs. For a partial rendering of the basins, see Figure 4. An initial analysis using proprietary software summarized the trapezoidal static, hydrostatic, and hydrodynamic pressures of the soil and liquid on the basin walls, in accordance with the linear distribution

Figure 5: Vertical bending on exterior basin wall in Figure 4 (walkway at top).

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June 2013

left due to interior wall). Figure 6 represents the horizontal bending in the walkways for the same load case, and suggests the influence of the (hidden) interior baffle walls.

Area C – Secondary Building The main floor of the secondary building is at grade, and its main roof is approximately 14 feet above grade. The basement houses a series of process pumps, while the ground floor supports an electrical equipment room. The main roof supports HVAC equipment surrounded by a mansard. The analysis model included the foundation mat, bearing walls, and composite steel deck diaphragm using the same methodology as previously stated. The ELF method for a regular structure produced the base shear and seismic stresses.

Conclusion The author is interested in learning how other structural engineers are modeling earthquake loads and stresses, and meeting the ever-growing complexity of seismic code requirements. Readers are encouraged to contact the author to share alternate methods. The author also wishes to thank the

Figure 6: Horizontal bending on walkways.

Orange County, California, office of Carollo Engineers for its thorough review of the seismic design of this project, which resulted in numerous improvements. One important example was the design of the ‘knee brace’ ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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June 2013

that interconnects each beam purlin (collector) at the vertical irregularity between two adjacent roofs, thereby significantly reducing ‘out-of-plane’ stresses in the top wall panel between those two roof levels.▪

Historic structures significant structures of the past

Newburyport – Essex-Merrimack Bridge 1792, Newburyport on the right looking easterly.

his is the first in a series of articles on the historic bridges of the United States. It will include those bridges the writer believes were the most significant structures since 1793 built in wood, iron and steel. Up to then, most bridges built in the country were wooden pile and stringer bridges built in much the same manner as Caesar did when crossing the Rhine centuries before. It remained for Timothy Palmer, a local architect and house wright, to build the first long span truss bridge in the country across the Merrimack River in Massachusetts. In 1790, Newburyport was a major port city, ranking 13th in population in the country, and was homeport to a large number of ships, brigantines, schooners and sloops. Several rope ferries crossed the Merrimack River in the area. The tolls from the ferries made them very attractive sources of revenue for their operators. Even though tides, seasons, and weather could make the journey across the river dangerous at times, ferries had met the needs of the traveling public. In 1791, a group of local leaders proposed a bridge across the river at a point just upstream from the town where an island split the river into two channels. A formal petition was submitted to the Massachusetts legislature on June 1, 1791 asking for a charter to build the bridge. The petition stated “That a bridge across Merrimack River from a place called the Pines in Newbury in the county of Essex to Deer Island, so called, and from the said Island to Salisbury in said County would in the opinion of your petitioners very greatly subserve the public interest and convenience by affording a safe, prompt and agreeable conveyance to carriages, teams and travelers at all seasons of the year, and at all times of tide, whereas great dangers are incurred and great delays often suffered by the present mode of passing in Boats.” The act of incorporation was approved by the legislature on February 24, 1792 and was signed by Governor John Hancock with the signature identical to his Declaration of Independence signature 16 years earlier. The tolls were in part,

Newburyport 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.

26 June 2013

• For each foot passenger two thirds of a penny. • For each horse and rider two pence. • For each horse and chaise chair and Sulkey seven pence. The bridge itself was described as follows: And be it further enacted by the authority aforesaid that the said bridge shall be at least thirty feet wide; that between Newbury & Deer Island there be an arch one hundred and sixty feet wide; that between Deer Island and Salisbury there be an arch one hundred & forty feet wide, a convenient draw or passage way for the passing and repassing of vessels at all times fifty feet wide with well constructed substantial and convenient piers on each side of the bridge & adjoining said draw sufficient for vessels to lie at securely; and also another arch fifty feet in width; and that the crown of the arch between Newbury and Deer Island be at the least forty feet high, and that each of the abutments thereof be twenty eight feet six inches high in the clear above common high water mark… By early April, the Directors evidently had many proposals consisting of drawings, models, and extensive descriptions of bridge styles. With a new, or enhanced, plan in hand, they decided that the original legislation was not acceptable and submitted proposed changes to the legislature. The revised act was passed on June 22, 1792, modifying the restrictions and limitations of the first act as regards height above high water mark, braces, etc. The legislature required that the bridge not impact negatively navigation on the river, and therefore set minimum vertical clearances and clear waterway distances between abutments and piers. The change evidently came about after Timothy Palmer was selected as chief engineer of the bridge. For this bridge and others, he has been called “the Nestor of American Bridge Builders.” The revised act stated in part, Sect. 3 And be it further enacted by the authority aforesaid, That the crown of the arch to be erected between Newbury and Deer Island may not be less than thirty-six feet high, and that each of the abutments

averaged 34 feet deep? His bridge, most likely based upon a 16th century Palladio design, would have the longest span of any in the country at the time. A genius has been defined as someone who sees what everyone has seen but thinks what no one has thought. This phrase applies to Timothy Palmer, who began his bridge building career with this bridge. Early illustrations of the longest span show it with 10 panels of approximately 16 feet with a panel height equal to the panel length yielding compression diagonals on approximately a 45-degree angle. Palmer used what has been called by some a trussed or braced arch as his supporting system with the deck resting on the lower chord. How the truss/arch worked depended greatly on how the members were connected Salisbury Truss then covered, post 1808, with lift span looking south at Deer Island. at the upper and lower chord and the stiffness of the lower chord. If the lower chords thereof may not be less than twenty-four The Massachusetts Magazine, May 1793, were very stiff, the structure would act more feet and a half high, above common high reported, “…this bridge was built, under the like a braced arch if they were built into the water mark; and that braces or shores prospect of advantages much less encouraging, abutments that prevented longitudinal movemay be placed from the abutments of than any which have been granted by the leg- ment of the ends of the members. If the lower the said arch, at four feet and an half islature to undertakings of a similar kind…” chords were less stiff, and not anchored to Tedan the abutment, the whole structure would act from common high water mark, to pass What made Palmer, who, although No d w a s20 up to the said arch, at not more than accomplished millwright and housepacwright, like a highly cambered truss with radial ked vailab 1more 3 le a wi d w f th exc ntension forty-eight feet distance, from the top had never built a bridge, think that henecould posts and compression diagonals. It is eat u iting of the said abutments; any thing in the design and build a bridge over 1,030 feet long,res believed that the latter case was true. said Act to the contrary notwithstanding. with one span of 160 feet, over water that continued on next page ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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The foundations for the superstructure were probably stone filled wooden cribs that were Palmer’s standard foundation, sometimes with wooden piling and sometimes without. In the language of the day, they were called “huge log piers which extended far below the water line to a firm foundation of either stone, hardpan or gravel.” To build the arched lower and upper chords, he used what Theodore Cooper in his fine 1889 paper on railroad bridges called “crooked pieces of timber, so that the fibre might run in the direction of the curves.” Palmer ordered trees with a natural bend in them to match the curvature of his chords. Some of these timbers, in his later bridges, were 16 x 18 inches in cross section and up to 50 feet long. As seen in the engraving of the bridge, he used struts off the piers extending out several panel points to help support his trusses as permitted by the modified Act of the Legislature. His spans, piers, and abutment lengths working from the northerly shore (the Salisbury shore) were 124 feet, 50 feet, 45 feet, 60 feet, 50 feet, a 40-foot draw structure, 50 feet, his arch of 113 feet, and 60 feet to the northerly shore of the island. The bridge then ran from the island 93 feet, his truss of 160 feet, and 185 feet on piers and deck beams to the Newburyport shore. Shortly after the opening of the bridge in 1793, The Massachusetts Magazine wrote, “The two large arches, one of which is superior to anything on the continent, were both invented by Mr. Timothy Palmer, an ingenious house wright of Newburyport, and appear to unite elegance, strength and firmness beyond the sanguine expectation.” In the book Olde Newbury, the author states, “The principles upon which it was constructed were novel and hitherto untested; but the beauty and strength of the structure, when completed, demonstrated their practical value and utility.” The bridge opened in December 1793, but the official opening ceremony was on July 4, 1794. What we know about some of the early wooden bridges in the country came from travelers who wrote about what they had seen on their trips around the country. Timothy Dwight, President of Yale University, wrote about the EssexMerrimack Bridge (he also wrote that the bridge was painted a brilliant white): Between Salisbury and Newbury the Merrimack is crossed on Essex Bridge…It consists of two divisions, separated by an island at a small distance from the southern shore. The division between the island and this shore consists principally of an

Templeman Chain Bridge 1810-1909.

arch, whose chord is one hundred and sixty feet, and whose vertex is forty feet about the high water mark…the whole length of Essex Bridge is one thousand and thirty feet, and its breadth thirtyfour. I have already mentioned that Mr. Timothy Palmer, of Newburyport, was the inventor of arched bridges in this country. As Mr. Palmer was educated to house building only and had never seen a structure of this nature, he certainly deserves not a little credit for the invention...The workmanship of the Essex Bridge is a handsome exhibition of neatness and strength.” Another description by John Drayton, who saw the bridge shortly after it opened, gives a little better description of the long span as follows: Two or three miles beyond Newburyport is a beautiful wooden bridge of one arch, thrown across the Merrimac River, whose length is one hundred and sixty feet; and whose height is forty feet above the level of high water. For beauty and strength, it has certainly no equal in America, and I doubt whether as a wooden bridge there be any to compare with it elsewhere. The strength of the bridge is much encreased above the common mode in use by pieces of timber placed upon it and shouldered into each other. They run upon the bridge in three lines, parallel with the length of the bridge and with each other, so as to make two distinct passageways for carriages. These braces are some feet in height, and are connected on the top by cross pieces affording sufficient room for carriages to pass underneath without

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inconvenience. It is said that the upper work has as great a tendency to support the weight of the bridge as the sleepers upon which it is built… Palmer, in a letter to Richard Peters in Philadelphia dated July 11, 1808, wrote, “Last summer, I rebuilt one of the Arches, the span of which is 113 feet and is on the same principle with your Bridge. With much persuasion, I obtained liberty to cover it. There were many doubts in the minds of the Stockholders as to its stability against strong winds.” This covered span survived until 1882. In the same letter, Palmer informed Peters that on “the 17th of June last there came on one of the most tremendous gales of wind ever known in this country…The reason of my being thus particular in this reason is Essex-Merrimack bridge stands nearly in the centre of the direction of this tempest; and stood like Mount Atlas amid the warring elements.” In 1810, John Templeman, using a variation of James Finley’s chain suspension bridge patent, built a chain suspension bridge to replace Palmer’s 160-foot truss. This span had been, in the words of the boatmen, a “menace to navigation.” By going with a 244-foot suspension span as contrasted to a 160-foot truss with abutments extending greatly into the river, it was possible to widen the southerly passage around Deer Island. This bridge, even though suffering a partial collapse in 1827, survived until 1909 when a look alike bridge was built in the same location. This bridge, recently restored in 2003, still serves local traffic across the Merrimack River. It is the oldest continually occupied, long span, bridge crossing (220 years) in the country dating from 1793.▪

Building dreams that inspire future generations. Gerdau is installing 6,650 tons of steel in San Diego’s New Central Library.

All across America, Gerdau helps build dreams. San Diego dreamed of a library with 3.8 million books. Every day, people will walk in curious and emerge inspired. www.gerdau.com/longsteel

San Diego Central Library A Composition of Dramatic Concrete and Steel Structures By Sean Fleming, LEED AP BD+C, Jean Libby, P.E. and Paul Endres, FAIA, S.E.

Figure 1: The San Diego Central Library in March 2013.

hen the newly built San Diego Central Library opens its doors in autumn 2013, it will be a landmark project for both the City of San Diego and the project’s design and construction teams alike. The project presents multiple unique challenges in its many unique structural frame components, most of which are architecturally expressed with minimal treatment. Prevalent among the structural design elements are the cast-in-place architectural concrete frame beams and columns, exposed concrete waffle slabs, and the iconic steel and aluminum dome structure that provides shade and acclimatizes the eighth floor main reading room. The project encloses 504,000 square feet on its nine above-ground floors and includes reader seating for 1,200 persons, 407 computer stations, 22 wifi-enabled study rooms, meeting rooms and gallery/ exhibition spaces. The site is also home to a new 350-seat community auditorium building. Two subterranean levels provide parking for 250 autos. The project targets a LEED Silver certification. Figure 1.

Special Moment Resisting Frame Selection of vertical and lateral load-resisting systems for the library is dictated in good part by the building’s use. Programmatic requirements for an open and versatile floor plan with natural daylighting, heavy live loads, and the necessity for perimeter retaining walls below grade lend to employment of a reinforced concrete special moment-resisting frame (SMRF) above grade and reinforced concrete shear walls below grade. Sizing and shapes of SMRF columns are dependent on their location in the structure and on architectural considerations. Moment frame columns occur at the perimeter of the ninth floor, trace down through the structure, and continue below grade to retain ductile detailing to the foundation level. Frame columns and frame beams STRUCTURE magazine

are also introduced along different lines as the footprint of the floors increases top-down. SMRF columns prevail at 75 inches (1.9 meters) square, but grow to as large as 72 x 92 inches (1.8 x 2.3 meters) in the reading room and east colonnade. Typical moment frame beams are upturned 5 feet (1.5 meters) deep by 27 inches (0.7 meters) wide. Locating the SMRF columns and beams along the perimeters of the floor plates allows the interior of the floors to be supported by smaller gravity columns, which supports the design intent of an open floor plan. Gravity columns are minimized to 34 inches (0.9 meters) square below grade and 30 inches (0.8 meters) square above grade. Figure 2.

Waffle Slabs The building is designed for a minimum live load of 150 pounds per square foot (psf ) at and above the ground level, with limited areas to receive compact shelving designed for 300 psf. The nearly 350,000 square feet of typical floors employ a 23-inch (0.6 meter) thick waffle slab with waffle voids spaced four feet (1.2 meters) on center. The decision for waffle slabs also accommodates the 32-foot (10-meter) wide column bays. The aesthetic of the waffles as viewed from below, as an exposed ceiling, is architecturally appealing and also possesses sound-attenuating properties. Strategic use of in-slab beams, combined with upturned frame beams at the floor plates’ edges, allows maximum daylighting of the interiors via clerestory glazing set between the upturned beams and waffle ceiling soffits. Typical floor to floor heights are 15 feet (4.6 meters).

Heat of Hydration Issues Heat of hydration was a very real concern, since many concrete frame elements are in excess of six feet square and the concrete gravity arch

June 2013

the vision of a quilted aesthetic, hundreds of concrete shop drawings were translated from the BIM model (Figure 2) to account for every plywood seam and tie-hole in all exposed columns, beams, edges of slabs, and walls as well as in custom structures such as the concrete gravity arch. Due to the complexity and non-repeating nature of the plywood patterns, an unusual step was needed: the creation of formwork fabrication and placing drawings. These drawings were provided to field crews to assist with prefabrication and production in placing formwork. For example, each column form incorporated the deliberately located random patterns into the fascia sheeting, each with wholly unique seam layouts, such that no two were alike. Since forms had to be reused throughout the structure, placing drawings included production notes to assist field crews with a pre-planned strategy to “mix-up” the stock of forms, or rotate column forms from their prior axial orientation, from one pour to the next to further give the allusion of random, non-repeating patterns in the concrete. The regular pattern of the ties, juxtaposed with the scattered seams of plywood sheeting, creates a unique craftsmen quality in the finish product.

Figure 2: All structural and architectural components were modeled, coordinated, and 4-D scheduled thru Revit, Vico, and Synchro. Courtesy of Turner Construction.

reaches dimensions of thirteen feet radially by six feet wide. Initial mock-ups using the specified cement resulted in internal curing temperatures exceeding 250 degrees F in the first 24 hours. This exceeded the maximum allowable internal curing temperature of 180 degrees – the upper threshold established for control of thermal cracking and ensuring the long-term durability of the concrete. Additional trial batches were ordered to test heat characteristics and compressive strengths of mixes utilizing alternate architectural grade cements. While the alternate trial batches continued, nine mockups were performed to test non-technical heat mitigation strategies. Non-technical controls included placing mass concrete elements as early as possible in the morning to take advantage of low ambient temperatures, batching concrete with chilled water or ice depending on the season, and limiting concrete deliveries to five cubic yards per truck for the largest components. The non-technical strategies were found to effectively maintain concrete consistency between lifts without the need to introduce water at the jobsite – critical to achieving uniformity of color in the finish product. A single mix design of 6,000 psi concrete using locally available Colton, California Type-I cement and a set-retarding admixture was selected, and is employed for all architectural concrete applications within the building.

Architectural Concrete Aesthetic The program calls for all above-grade concrete to be architectural ascast and fair-faced, utilizing a high albedo architectural grade cement and incorporating an ACI Class A finish. Chief among the preferences for the concrete aesthetic are a light colored matte finish, minimal appearance of forming hardware, and a custom pattern that calls for plywood to be cut to random sizes and oriented to create an organic “quilted” effect. Slight imperfections and offsets are desirable to create an aged appearance. The combined application of mass concreting issues and architectural concrete program requirements resulted in a series of fifteen mock-ups and other research and development efforts to test cement options, concrete mix designs, plywood types, tie design strategies, form releases, and rustication strips. Structural concrete and non-structural concrete components employ different treatments as a visual telling of their role in the building. Ties are located in structural elements at wide spacings on a static series of datums: 5-foot on center (o.c.) vertically and 4-foot o.c. horizontally. A tighter tie spacing ranging from 2-foot o.c. to 4-foot o.c. is applied to non-structural concrete depending on the application. To achieve STRUCTURE magazine

Energy Efficiency As-cast architectural concrete contributes to energy efficiency by minimizing capital costs compared to other building finish systems since surface treatments involve only minor touch-up. The reduced expense for finish systems also translates to reduced maintenance and life cycle costs for the Owner. End-user energy demand is reduced significantly by way of the structure’s concrete envelope and its inherent thermal mass, which reduces day-time cooling needs and evening warming of the interior spaces. Aluminum sunshades on south and east facing clerestory windows further mitigate daytime heat gain.

Concrete Gravity Arch An open feeling was desired at the library lobby, so a 64-foot (20meter) long by 46-foot (14-meter) tall concrete gravity arch (Figure 3) was designed from the ground level to the fourth floor, eliminating a column from the center of the lobby. Congestion of reinforcing steel at the two ends where the arch was to be supported by vertical columns proved a challenge. Couplers and headed bars were utilized here and in many other locations where congestion was problematic to constructability. continued on next page

Figure 3: A 64-foot long concrete gravity arch dominates the library’s main lobby.

June 2013

Figure 4: Interior of the 8 th floor reading room.

Dome

Reading Room A concrete roof suspended sixty feet (18 meters) above the eighth floor shelters the library’s 4,000 square foot reading room (Figure 3). Structural steel and clerestory glass supported by four 72-inch square concrete columns complete the room. The concrete columns, cruciform in plan, rise 62 feet to support intersecting concrete roof beams spanning 58 feet in either direction and the diamond-shaped concrete roof slab (Figure 4).

Special Events Room The Special Events Room roof cantilevers 10 feet from the 9th floor deck and is made up of a hybrid system of precast beams laced into a 6-inch cast-in-place concrete slab. The roof is supported by a single 72-inch x 48-inch inclined concrete column, which begins its rake nearly 90 feet below between the 4th & 5th floors (Figure 4). The flanks of the roof structure are supported in part by tubular steel mullions set prior to casting the roof slab (Figure 5).

Project Team Owner: City of San Diego Engineer of Record: Martin & Libby Structural Engineers – San Diego, CA Dome Engineer: Endrestudio Architecture & Engineering – Emeryville, CA Design Architect: Rob Wellington Quigley, FAIA – San Diego, CA Architect of Record: Tucker Sadler Architects – San Diego, CA General Contractor: Turner Construction – San Diego, CA Concrete Contractor: Morley Construction – San Diego, CA Dome Contractor: SME Steel – West Jordan, UT

STRUCTURE magazine

The dome, believed to be the largest steel post tensioned segmental dome in the world, is 140 feet (43 meters) in diameter and rises 221 feet (67 meters) above ground level to provide shade and acclimatize the reading room. It is constructed of more than 3,000 individual members of steel, weighing 285 tons, and clad in 1,500 perforated aluminum panels to shade the eighth floor reading room beneath it. The dome is made up of eight unique truss “ribs” that rise from base to apex in varying heights from 72 to 113 feet (22 to 34 meters) and eight unique “sail” structures located between the ribs. Sails are oriented in plan with a pinwheel configuration, an effect created by offsetting each of the sails’ vertical leading edges to the outside of the ribs while the sails’ trailing vertical edges are connected to the inside rib surfaces. Each of the sails has an external pipe grid that is spherical at the upper part of the dome; however, the spheres are tipped vertically and horizontally so the center of each sail does not coincide with the center of the dome. Unfurled, the largest sail is 123 feet by 53 feet (38 by 16 meters) wide and comprised of 175 members of tubular steel and 60 cable segments. Architecturally, the lower edges of the sails are desired to be as thin as possible. This is achieved through the use of a three-dimensional truss spanning diagonally from rib to rib, and appears visually as a six-inch (15 centimeter) edge thickness. To further reduce the mass of the sails, steel cables are introduced to minimize large members on the interior surfaces close to the glass of the reading room. The penultimate concept, with cables covering the outer and inner surface, was deemed too difficult to erect by the contractor. The final design, a saddle shaped cable net, was chosen because the removal of cables on the outer surface allowed the contractor to erect them by crane more easily. The sails were constructed on-site, two at a time, on large temporary platforms on the ground and lifted into place, one sail at a time. Due to the discontinuous circular form and its peaked pinnacle, the dome behaves as a series of intersecting three hinged arches, or “ribs”. At the base, each rib is supported on a large fixed pin that allows the rib structures to pivot or expand with changes in temperature or seismicity.

June 2013

Each of the eight large pins falls onto one corner of a fixed octagonal plan. The octagonal plan causes unequal geometry from rib to rib. The fixed pins of the rib supports fall onto varying elevations located atop shear walls, freestanding columns and, in one case, supported by three inclined converging columns. Two of the rib supports fall outside the building envelope and are built on special composite braces made up of concrete columns with tubular steel diagonals.

A Place of Inspiration and Learning The San Diego Central Library is poised to serve its community as a center of knowledge and learning through its planned 1.5 million volumes, internet access terminals, numerous literacy programs, staff, volunteers, and other contributors. The design and construction team believe it will also contribute to the city’s character as an iconic structure and landmark. The expressive and often dramatic applications of architectural concrete and steel discussed here are intended to inspire the minds of the library’s population, be they children or adults, students or working class, rich or poor.▪ Sean Fleming, LEED AP BD+C, is a Senior Project Manager at Morley Construction in San Diego, California. Sean may be reached at sfleming@morleybuilders.com. Jean M. Libby, P.E., is Principal and President of Martin & Libby Structural Engineers in San Diego, California. Jean may be reached at jlibby@libby-lei.com. Paul Endres, FAIA, S.E., is Principal and President of Endrestudio Architecture & Engineering in Emeryville, California. Paul may be reached at paul@endrestudio.com.

Figure 5: A 90-foot tall inclined column supports a hybrid cast-in-place and precast concrete roof deck at the 9 th floor.

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STRUCTURE magazine

June 2013

Diagrid on Display

Federal Center South Building 1202, the new headquarters for the United States Army Corps of Engineers in Seattle, Washington. Courtesy of Benjamin Benschneider.

Federal Center South Building 1202 By Daniel Riemann, P.E. and Jason Black, P.E., S.E. This is the second article highlighting the innovative design features of Federal Center South Building 1202. “A Worthy Wager: The Innovative Use of Composite Concrete & Timber Floors on Federal Center South” was featured in the April 2013 edition of STRUCTURE.

he recently completed Federal Center South Building 1202, serving as the Seattle District Headquarters for the United States Army Corps of Engineers (USACE), is a state-of-the-art office building resulting from architectural, structural, and construction innovation and collaboration. One of the key features that makes Building 1202 so innovative is the use of a diagrid system at the exterior wall of the structure. While the diagrid is a system used in many new buildings around the world, its use in Building 1202 represents a clever solution to meeting the specific

requirements of this design-build project. Utilizing this unique structural system strengthens the building while reducing material costs and shortening the construction schedule. Building 1202 was planned, designed, and constructed in less than two and a half years, and stayed within the original $65 million construction budget. In addition to being an effective solution to progressive collapse requirements, the diagrid played an important role during the competition phase of the design-build project and it was a significant part of the architectural expression and story of the building.

Canted building ends. Courtesy of Benjamin Benschneider.

STRUCTURE magazine

Diagrid Defined A diagrid system consists of sloping columns (diagonals) and spandrel beams (horizontals). The diagrid system for Building 1202 utilizes a 3-story module (full building height) with bolted connections between spandrels and diagonals. Effectively, the diagrid system is a multi-story truss with pin connections. This system creates an efficient and inherently redundant structure by carrying gravity loads to the foundation through multiple load paths.

Progressive Collapse Requirements As a U.S. General Services Administration (GSA) project, one of the primary requirements for Federal Center South Building 1202 was that the structure be designed to resist progressive collapse in the event of a terrorist attack. Progressive collapse is the uninhibited spread of an initial local failure to other elements of the structure, eventually resulting in the collapse of the entire structure or a disproportionately large part of it. Examples of progressive collapse include the collapse of the Alfred P. Murrah Federal Building in Oklahoma City, when localized structural damage caused by an explosion spread throughout the gravity load carrying system, eventually resulting in the collapse of a large portion of the building. Building 1202 is designed to the requirements outlined in UFC 4-023-03, Design of Buildings to Resist Progressive Collapse. The goal of this design document is to limit the number of casualties by ensuring that buildings have adequate inherent redundancy to continued on page 36

June 2013

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Method

Description

Tie Force

Structural elements are designed and detailed as catenary elements to transfer loads through tension to undamaged portions of the structure.

Alternate Path

Structural elements are designed and detailed to bridge over compromised portions of the structure.

Enhanced Resistance Shear and flexural capacity of exterior structural elements are increased to minimize the extent of initial damage.

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resist catastrophic damage due to unforeseeable events. The requirements for progressive collapse design provided in UFC 4-023-03 apply only to buildings which are three stories or taller. This three story requirement is based on a maximum casualty threshold set by the UFC and not the mechanics of progressive collapse. The level of progressive collapse design is based on the Occupancy Category (OC) and building function. Similar to the OC determined using the IBC, greater risk is associated with loss of structures of higher OC. This OC dictates which method of progressive collapse resistance is to be used in design. The three methods of progressive collapse resistance prescribed in UFC 4-023-03 are the Tie Force Method, Alternate Path Method, and Enhanced Resistance Method (see Table).

Traditionally, requirements for progressive collapse resistance have been met by utilizing moment frames or tie beams at the exterior of the building, or by increasing member sizes to provide enhanced resistance. However, for Building 1202, a diagrid was chosen as the primary collapse prevention system. The diagrid is supplemented by moment frames at the canted building ends. The diagrid system is an optimal solution for meeting collapse prevention requirements because it is essentially a multi-level truss, with the diagonal columns acting as the web members and the horizontal spandrels at each floor acting as the truss chords. The 3-story diagrid module used for Building 1202 creates a 3-story truss. Should any of the diagonal columns become damaged during an attack, the remaining portions of this truss can span over areas of localized structural damage.

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Typical bolted connection.

Diagrid Use as Potential Lateral Force Resistance System The sloped columns of the diagrid are representative of braces in a braced frame. For this reason, the diagrid system was initially explored for use as the lateral system of the building. However, there are drawbacks when utilizing the diagrid as the lateral system. A braced frame is designed to yield and dissipate energy during a seismic event. As the primary gravity load carrying system for the exterior of the building, the sloped columns could not be allowed to yield during a seismic event. Accordingly, the building code requires that systems acting as both the primary gravity and lateral force resisting systems be designed to remain elastic during a seismic event. Therefore, the response modification factor, R, is required to be in the range of 1.0 to 1.5 to achieve essentially elastic behavior. At the schematic stage, the diagrid for Building 1202 was analyzed and designed for seismic forces associated with this level of elasticity. For an R of 1.0, member sizes were reasonable, only slightly larger than those required for collapse prevention, and maximum drifts were within the code requirements. However, the number of bolts required for connections increased significantly when design overstrength factors were considered. Using bolted connections as much as possible was preferred by the contractor in order to maintain a rapid fabrication schedule and save costs associated with full penetration welds. The labor costs associated with the increased number of bolts that were required to allow the diagrid system to also meet the lateral system requirements effectively mitigated the cost advantage of having a dual system. Ultimately the decision was made to rely on concrete shearwalls at the stair cores as the lateral system for the building, thereby allowing both the lateral and gravity systems to be optimized both in terms of performance and cost.

DIAGRID APEX SPANDREL BEAM SLOPED COLUMN ROOF LEVEL

LEVEL 3

LEVEL 2

LEVEL 1 (GRADE)

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PILE FOUNDATION

Diagrid system.

CONSTRUCTION CEMENT

Diagrid erection.

Construction Savings

Material Savings

At the onset of the project, the team developed a progressive collapse resistance scheme utilizing moment frames, to compare to the diagrid scheme. This moment frame option consisted of 3-story moment frames at the building perimeter on a 22-foot bay module. From early studies, it was clear that the diagrid scheme provided the greater savings potential for the project in terms of foundations, materials, and fabrication. Foundations Building 1202 is located adjacent to the Duwamish River on extremely poor soils, requiring that the building be supported on driven steel pipe piles. These piles typically extend 150 to 170 feet below grade to reach a competent bearing layer. In the moment frame scheme, a single pile is required at each moment frame column, or every 22 feet. In contrast, the diagrid system utilizes a 44-foot bay module, meaning that pairs of sloped diagonal columns meet grade every 44-feet. Therefore, the moment frame scheme would have required twice as many piles at the perimeter of the building.

The diagrid system results in approximately 30% savings in steel tonnage as compared to a moment frame system. This savings is manifested largely in the spandrels, which become primarily tension/compression members when the diagonal columns become compromised. The spandrel beams in a traditional moment frame system need to resist much larger flexural demands in order to span over damaged columns, requiring larger, heavier spandrel sections.

ADVANCED TECHNOLOGY

Erection and Fabrication

• Great freeze thaw durability

Recognizing the old “time is money” axiom, KPFF worked with Sellen Construction to propose a simple “tilt-up” method for erecting the diagrids. In this sequence, pairs of sloped columns were fitted up while on the ground and welded together at the apex to form a triangular assembly, which was then tilted in to place. The horizontal spandrels were then flown in and bolted in to place. This sequence allowed the diagrids, and therefore the entire steel skeleton, to be erected in a relatively short amount of time. continued on next page

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June 2013

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Project Team Owner: General Services Administration (GSA) Tenant: United States Army Corps of Engineers (USACE) Seattle District Structural & Civil Engineer: KPFF Consulting Engineers Contractor: Sellen Construction Architect: ZGF Architects, LLP Funding: American Recovery and Reinvestment Act (ARRA) When compared to a moment frame, a diagrid system requires far fewer welded connections. For Building 1202, there are 19 apex connections where field welding is needed. Bolted connections are used at all other spandrel to diagonal column connections. By comparison, the moment frame scheme studied by the team would have required a total of 108 full penetration welds at all connections between spandrels and columns – more than five times as required for the diagrid system.

Architectural Expression

river-facing view as much as possible, to reiterate the Corps’ mission statement of “Building Strong”. The diagrid, by its very nature as a strong diagonal element that contrasts with the orthogonal lines of floors, walls, and windows, is a key element of this expression. The design team moduled the building so that the diagrid naturally ended with a backslope on the southwest corner and an outslope on the northwest corner as a counterpoint. These canted ends of the buildings create light filled office and conference room spaces with sweeping views of the Duwamish River. The diagrid is painted white throughout in

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USACE FEDERAL CENTER SOUTH BUILDING 1202 / PHOTO BY BENJAMIN BENSCHNEIDER

One of the key early design decisions by the project team was to have the structure of the building exposed to the western

Conference room at canted end. Courtesy of Benjamin Benschneider.

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June 2013

order to assist in diffusing both natural and artificial light inside the building, but also to be prominently visible through the exterior glazing. The stainless steel skin of the building is peeled back at the main entry to fully expose the diagrid, creating a formal entry portal. The diagrid scheme also allowed the building’s unique Oxbow form to be achieved, which drew inspiration from the historic meandering path of the Duwamish River adjacent to the site. Smooth transitions through the curved portions of the building are facilitated with the diagrid by utilizing a tangential variation at each floor line. This allows the exterior skin to easily transition through the corners of the U-shape, resulting in a smoother appearance. Although the use of sloping columns results in a small loss of floor area directly under the column, the diagrid creates unique and dynamic interior spaces.

Summary The diagrid represents an effective solution to progressive collapse requirements and helps create an iconic identity for Building 1202. The success of this designbuild project is a tribute to the early-on collaboration between the architect, engineer, and contractor.▪ Daniel Riemann, P.E., is a project engineer with KPFF Consulting Engineers in Seattle, W.A and was the lead designer for the diagrid system for Building 1202. Dan can be reached at Dan.Riemann@kpff.com. Jason P. Black, P.E., S.E., is a Structural Principal with KPFF Consulting Engineers in Seattle, W.A. Jason can be reached at Jason.Black@kpff.com.

John Jay College Expansion st

Transforming a 21 Century Urban College Campus New York, NY By Jason Stone, P.E.

he CUNY John Jay College School of Criminal Justice Expansion Project is a new 625,000-square foot academic building in Midtown Manhattan. The facility consists of a 15-story tower on 11th Avenue and a four-story podium with a garden roof that connects to the College’s existing Haaren Hall on 10th Avenue. Following significant growth in criminal justice interest over the last decade (partially in response to the attacks of September 11th) the new building was planned to accomplish a doubling of the existing facilities and unification of the campus into one city block – creating an academic city within a city. In explaining the design concept, Abadan Mustafa of SOM said, “Criminal justice is not something that should be hidden away. Glass makes the relationship to inside and outside clearer. It relates to our ideals of transparency and justice, the way justice is applied to everyone equally and openly.” The new facilities offer traditional college campus amenities including classrooms, offices, research laboratories, theaters, lounges, and flexible collaboration spaces. In addition, unique features specific for future investigators and law enforcement officers include a ballistics room, areas for chemical storage and analysis, mock trials, and an emergency control center simulation lab.

Site Challenges In response to a shallow Amtrak tunnel that cuts through a corner of the site, the John Jay structural system is distinguished by a grid of rooftop trusses which hang the perimeter of eight floors below. This

Construction over the tunnel was done at night and coordinated around the train schedule. Noise and vibration were controlled by isolating the tunnel enclosure from the tower structure.

STRUCTURE magazine

The 65,000-square-foot podium garden roof, known as ‘Jay Walk’ by the students, links the College’s existing Haaren Hall to the new tower on 11th Avenue and provides an oasis from the city below. Courtesy of SOM.

creates a dramatic column-free cafeteria space on the 5th floor, with views of the Hudson River for the full 195-foot width of the building. Two layers of structure were provided to effectively isolate the building from the train vibration and noise. The main building structure spanned over and behind the train tunnel, which was enclosed with a hollow core precast plank ceiling and concrete crash walls. At points of convergence, creative detailing was required to maintain the load path and necessary separation. Another challenge was accommodating the almost two-story change in grade between 10th and 11th Avenue. A second main entrance to the building occurs along 59th Street and negotiates this steep slope. To design for this condition, the perimeter columns – in an area that support heavy loads from the rooftop garden – were eliminated, and the entrance was pulled back to allow room for the necessary steps and ramps. Story-deep trusses were fit inside the walls of the 4th floor classrooms to efficiently accomplish the 40-foot cantilever out to the tip of a V-shaped tapering canopy. The interior architecture also responded to the sloped grade with a series of cascading staircases and escalators that complicated the structure, but allowed for fluid circulation to all parts of the campus. “The cascade replicates a miniature Manhattan, with the ‘travelers’ passing through different building functions and academic departments rather like the squares – Madison, Herald, and Times, among others – that bisect Broadway and function as independent nodes within the city,” Mustafa said. A large skylight

June 2013

With the temporary columns removed, the load path for the hanging structure is clear. The column-free fifth floor cafeteria offers great views of the Hudson River to the west.

Main entrance on 11th Avenue. Setbacks in the façade were an important aesthetic feature that also reduced the impact of the load on the shallow train tunnel below.

supported by architecturally-exposed narrow tube sections provides natural light into these main circulation areas and offers views into the space from the garden roof.

curtain wall at the transition floor between the conventionally framed and hung structure. To simplify the steel frame erection, the design accounted for temporary columns at the 5th floor around the tower perimeter and temporary angles bolted to the plate hangers above the 6th floor, to stiffen these elements during erection. This allowed the construction process to proceed similar to conventional construction, and maintain the project schedule. Once the truss assembly was finished, jacks at the temporary columns slowly lowered the building and engaged the trusses. At this point, the temporary columns and angles could be removed and concreting of the tower could begin. Calculating the required amount of vertical cambering for the perimeter steelwork in order to super-elevate each of the 26 hanger/column locations for the anticipated deflection during construction proved to be a challenge as well. Design estimates were based on the assumed construction schedule, estimated construction loads, and realistic modeling of the structural behavior. During construction, continuous surveying verified whether the perimeter was behaving as anticipated.

Hanging System Accommodating the necessary two layers of structure around the train tunnel mandated a practical limit to the weight that could be supported. After exploring numerous options, the hanging solution was favored by SOM and DASNY and adopted for numerous reasons, including assistance in achieving the series of distinguishing setbacks that frame the west façade’s main entrance along 11th Avenue. The hanging system was continued around the full perimeter to balance the weight, complete the column-free aesthetic, and take advantage of the thin plate hangers which could fit inside a standard partition wall instead of traditional column enclosures. To maintain efficiency, the hanging system was stopped where the structure over the tunnel could accommodate conventionally-framed floor weight. In coordination with the architect, the 5th floor was chosen for this transition, allowing the transparent column-free floor to align with the podium roof garden. The primary construction challenge involved achieving approximately level floors when the building opened, and a 2-inch stack joint in the STRUCTURE magazine

Truss construction supports the 26 perimeter hangers.

June 2013

Project Team Owner: Dormitory Authority of the State of New York Client Team: City University of New York John Jay College of Criminal Justice Design Consultants: LERA – Structural Engineers Skidmore Owings & Merrill – Design Architect Turner Construction – Cost Estimator & Construction Manager Jaros Baum & Bolles – MEP Engineers Langan Engineering – Civil/Geotechnical Consultant Shen Milsom & Wilke – Acoustic Consultant Scott Blackwell Page Architect–Higher Education Planning Contractors: Owen Steel – Structural Steel Fabrication Cornell & Company – Structural Steel Erector Enclos Corporation – Curtain Wall Designer Once shop drawings were available for the nonstructural elements, and there was a better understanding of the schedule, a full reanalysis was done incorporating what was being learned from the surveying. This reanalysis revealed that it was likely the perimeter would not come down as much as originally thought (one reason for this being the curtain wall was actually 30% lighter than assumed in design) and field adjustments were made to lower the steel frame prior to starting the truss erection. Based on the last survey data received, this adjustment proved effective as the perimeter settling and final stack joint were tracking closely with the predicted behavior and targeted final thickness.

Future Expansion

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While considered and subsequently ruled out during design, the College revisited the idea of future expansion during construction and decided this flexibility was important. The design team was asked to consider a design that allowed for an additional ten floors over the podium to raise this section to match the height of the new tower. At the time the decision was made, the podium structural steel

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Careful detailing at the train tunnel was required to isolate members supporting the precast tunnel enclosure from the main building structure.

was already mostly fabricated and the caisson foundations were actively being drilled in some of the affected areas. After quick discussions focused on limiting the financial, schedule, and design changes, the College chose to reinforce only the below grade areas and take advantage of a hanging structural system similar to the one used in the tower to limit the affected area to the interior core. Additional elevator pits with knock-out slabs were provided along with significantly reinforced foundations based on the anticipated future circulation and structural weight needs. Instead of increasing the column and vertical bracing member sizes for the expected future loads, the additional capacity is intended to come from a high strength composite concrete encasement, allowing the already fabricated vertical members to still be used.

than those that could be tolerated in the ceiling package. The alternative solution, which saved both material and depth, was to separate the problematic excitation from the sensitive equipment, adding an isolation joint in the floor between the labs and the adjacent main circulation corridor. In addition to efficient uses of material, the project specifications were written to be environmentally sensitive. The building did not officially submit to USGBC, but LEED certification requirements were pursued wherever feasible. Fly ash and silica fume were substituted for up to 30% of the cement in the concrete. The reinforcing and structural steel were also sourced from mills regionally close to NYC and produced from over 90% recycled content.

Other Features

Conclusion

The 65,000-square-foot terrace atop the podium serves as a new, outdoor gathering place for students and faculty. The planted green roof is landscaped with large grassy zones, full-sized trees, and decked outdoor dining areas which the students immediately embraced and nicknamed “Jay Walk”. To preserve the dramatic views from the large collaboration areas in the tower of the Hudson River and this garden roof, the hanger spacing was increased to nearly 50-feet at the middle of both the east and west faces for the hung tower floors. These long span conditions created a problem in the laboratories on the 6th, 7th, and 8th floors, where strict vibration criteria needed to be met. Stiffening the floor to control the expected excitations resulted in deeper and heavier members

The John Jay College Expansion project exceeded the expectations of owner and client, giving the students and faculty a new stateof-the-art home to be proud of, along with providing the College flexibility to adapt to whatever the future holds. The project success was due primarily to the collaborative efforts and superior skill of the design and construction team – in particular SOM, Turner, Owen Steel, and Cornell & Company – who also exceeded every expectation in realizing this special structural system.▪

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June 2013

Jason B. Stone, P.E., is a Senior Associate at Leslie E. Robertson Associates (LERA) and an Associate Adjunct Professor of Architecture at Columbia University. Jason can be reached at Jason.Stone@lera.com.

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CASE BuSinESS PrACtiCES

business issues

Tools for Protecting the Bottom Line By Mark Erdman, P.E.

any engineering companies are experiencing financial challenges that place an even greater emphasis on the bottom line than normal. Even when times are good, business is brisk, and projects seem to be coming through the door with little effort, it can become easy to lose focus on best business practices, even those that directly affect the bottom line. Two of the latest tools released by the Council of American Structural Engineers (CASE) Toolkit Committee address aspects of firm management that have a significant impact on every engineering firm’s financial position, specifically professional liability premiums and the development of appropriate fees for engineering services.

Tool No. 2-5 An article recently published by the Insurance Journal (March 19, 2013) shows that, for the second consecutive year, “the insurance market for architects and engineers continued its firming trend…as a number of leading insurance companies providing specialized coverage again achieved moderate price increases”. The article also states that the majority of insurers expect to seek premium increases in the range of 4% to 8% this year, despite the overall number of claims remaining flat. The focus of Risk Management Foundation #2 is to employ preventative techniques to assist design professional firms with maintaining sound risk prevention processes within the company. The committee has recently issued Tool #2-5: Insurance Management: Minimize your Professional Liability Premium. One of the primary strategic goals of the CASE Toolkit committee is to bring tangible value to member firms through increased recognition by the insurance industry, in particular professional liability insurance. This recognition can be used to decrease liability insurance costs, overall number of claims, and the severity of the claims filed. Professional liability insurance premiums are one of the largest overhead expenses for structural engineering firms. The pricing for the insurance varies significantly depending on the insurance company, so it is hard to

argue against making every effort to obtain the best combination of coverage, premium, and value. Ironically, the insurance applications themselves leave very little space to provide details of the firm’s practice that could positively impact the premium; it is as though the lack of space to fully describe the firm’s practice is out of proportion to the importance and expense of the coverage that is provided. The application is the best and arguably only opportunity to demonstrate to the insurance company the details of your company and what differentiates it from others. Tool #2-5 was designed as a guide to help the design consultant provide the information needed to get the best insurance premium. The tool was developed primarily with feedback provided by brokers and underwriters serving in the A/E community. They were asked: What supplemental information would you like to see incorporated into the typical application? What would you need to see in order to justify a reduction in premium? Structural engineers are often times called upon to make decisions with incomplete information. SEs make reasonable assumptions, and call upon experience and expertise, and incorporate conservatism in order to compensate for a lack of information. Insurance underwriters are no

STRUCTURE magazine

June 2013

different. You have to actively demonstrate that your firm is serious about avoiding claims, and is a good risk. Like many aspects of managing a business, it is all about communication; they do not know unless you tell them. The more they are able to remove some of the layers of uncertainty and conservatism from their evaluation, the easier it is to justify a reduced premium. The implementation of Tool #2-5 may not only reduce your company’s liability premium, it might also reduce the overall number and severity of insurance claims for the industry as a whole.

Tool No. 7-2 Risk Management Foundation #7 pertains to Compensation, with a focus on preparing and negotiating fees that promote quality work resulting in successful projects that are profitable for the firm. The Committee’s latest tool #7-2 Fee Development provides an outline for consultants to answer the question: How do we determine the fee for a project? Determining an appropriate fee for a project is a mixture of both art and science, and there is no better substitute for experience when it comes to figuring out the art component of a fee. The science component is easier to quantify and justify with available information, and therefore is the

focus of the tool. This tool is currently under review by American Council of Engineering Companies (ACEC) and will be available upon completion of the review. Any attempt to determine the fee for a project should begin with a thorough examination of the scope of work. Itemizing the scope of work is the simplest and most direct way to project what resources will be required to perform the work, and the costs of those resources relate directly to the fee. Nailing down the scope can be diﬃcult on larger projects with lengthy and complex schedules. One of the goals of the tool is to take uncertainties and turn them into quantifiable scope items by asking the right questions, analyzing historical data, and making reasonable assumptions. What are the Client’s expectations for meetings? What is the Client’s expectation for the firm’s involvement during the preliminary approval phases? Are these variables effectively communicated in the proposal and reflected in the fee? Another crucial element of fee development, and potentially the most important of all elements, is the assessment of risk. This assessment should include both design related and business related risks. No project is risk-free, and the list of potential risk

factors for a given project can seemingly be endless. A central point of the tool is to put the requisite thought into identifying potential risk factors so that the client understands the value and benefit brought to the project by the consulting engineer. Incorporating the risk factors into the fee development process reiterates to the owner that acceptance of increased risk warrants increased reward. Historical data should be analyzed and referred to as part of fee development, both with respect to the Client, and also within the design firm. With regards to the Client it’s important to look back and dig for trends in important factors such as payment timeliness, scope creep, and the overall experience of working together. That information should be used in combination with an analysis of the firm’s database of past performance on similar projects. Fee development should consider the fees on past projects, a comparison of the scope of work to the new project, and a review of the performance on the past projects. Every project is unique. However, past performance can be a valuable indicator of future performance if applied appropriately.

Conclusion Professional Liability Insurance premiums are on the rise, putting additional strain on bottom lines that may already be stretched thin. At the same time, fee development remains a challenging yet essential part of the structural engineering practice. Both situations can be effectively managed by understanding the perspective of the audience, understanding the risks involved, effectively communicating your firms qualifications.▪ Mark Erdman, P.E., is an Associate Principal at the Baltimore, MD oﬃce of Structura, Inc. Mark has been serving as a member on the CASE Toolkit Committee since 2011. He can be reached at merdman@structura-inc.com. The goal of The Council of American Structural Engineers (CASE) is to promote excellence in structural engineering business practices and risk management. The tools presented in this article were developed by CASE members who volunteer their time and expertise to advance the structural engineering profession.

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June 2013

Great achievements

notable structural engineers

William LeMessurier Educator and Innovative Engineer By Robert Hossli, RA, NCARB and Ronald Flucker, P.E.

he story of William LeMessurier’s engineering accomplishments was featured in the September 2012 issue of STRUCTURE magazine. The author, Richard G. Weingardt, quoted William Theon, a long-time personal friend and professional partner: “Bill loved teaching as much as engineering and was always at his best with an audience.” This is a chapter in Bill’s productive life not covered in Mr. Weingardt’s article – a time when he was working with students on collaborative projects, often sponsored by industry. During the early 1960s, Bill lectured at the Massachusetts Institute of Technology (MIT) and was a key member of project teams that involved graduate students from the architectural and engineering departments. He wanted to give those students a chance to try out their theoretical training on real-life architectural and engineering problems, and let them receive financial benefits from corporate grants. Bill played a major role in one particular project sponsored by the Applied Research Laboratory (ARL) of The United States Steel Corporation (USS). By 1960, the flat-slab concrete structural system had, for several reasons, virtually eliminated structural steel as a competitive material in high-rise residential construction. Concerned with this, USS charged the ARL with developing innovative ideas that might help regain a share of that market. Bob Hossli, an ARL research consultant and recent graduate of MIT, had been impressed with the team headed by architect Marvin Goody and engineer Albert Dietz that designed and tested

Figure 1: Early schematic of the staggered truss framing system.

Figure 2: Embassy Suites (now Conrad) Hotel in New York City.

the glass fiber reinforced polyester shells of the Monsanto-sponsored “House of the Future.” With this in mind, he suggested that MIT submit a proposal for an interdisciplinary research project to develop an economically competitive structural steel frame solution for high-rise residential buildings. This proposal was accepted, with Bill LeMessurier as the engineer and Marvin Goody as the architect on the team. Several meetings took place without much progress. Then, as LeMessurier told it, one night, when he could not fall asleep, he had a “eureka” moment. Quoting from the USS Technical Report, Staggered Truss Framing Systems for High-Rise Buildings, he envisioned a “… system … of story-high trusses spanning transversely between columns at the exterior of the building and arranged in a staggered pattern. The floor system acts as a diaphragm, transferring lateral loads in the short direction to the trusses. Lateral loads are thereby resisted by truss diagonals and are transferred into direct loads in the columns. Therefore, the columns receive no bending moments in the transverse direction. Columns can thus be oriented so that the strong axis is available to help resist bending due to longitudinal wind forces. “The interior of the building is column free, and clear spaces are defined and

STRUCTURE magazine

June 2013

limited only by intersecting floor and truss planes. Trusses are typically penetrated by one rectangular opening to provide a corridor space. However, other openings can be provided in the truss to allow for door opening if required by the architectural room arrangement.” (Figure 1) Bill presented the idea to the MIT team, which accepted it heartily as the answer to the sponsor’s charge. In January 1967, the MIT team developed and presented to USS a thorough report about the system, how to design the structure, how to lay out various configurations for occupancy, and how to construct it. Upon review by ARL and USS’s Construction Marketing Department, in which Ron Flucker worked, it was judged to be immensely successful. The system would be extremely cost-competitive and adaptable to many floor layouts, could be built to the same height limitations as flat-slab concrete, and utilized rolled steel shapes as the principal structural elements. USS also recognized that the idea was patentable, but decided that it would be more in its best interests, and those of its structural steel fabricator customers, to keep the concept in the public domain. The American Institute of Steel Construction (AISC) got wind of the concept through its Boston Regional Engineer and invited LeMessurier to present a paper describing the

system at its June 1966 annual Engineering Convention in Boston. As a result of this early exposure, the firm of Bakke & Kopp, Inc. of Minneapolis decided to use the system for the frame of a local housing authority’s seventeenstory high-rise apartment building for the elderly, which was constructed in 1968. U. S. Steel then began promoting the system and it caught on. Although no accurate count exists, it is estimated that some one hundred buildings (or more) have been constructed using the system, including one designed by LeMessurier’s firm, the Lafayette Place Hotel in Boston. While most buildings have been modest in size, typically 10 to 20 stories (Figures 2 and 3 ), some have bordered on monumental like the 30-story Resorts International Hotel in Atlantic City, which has withstood several hurricanes. Bill LeMessurier’s “eureka” moment has resulted in a successful concept for high-rise steel framing. Perhaps more important to him was the learning experience provided for five graduate student assistants in the MIT Civil Engineering and Architectural Departments. The authors wish to recognize the assistance of Tabitha Stine of AISC in researching this article and providing the accompanying images. All graphics courtesy of AISC.▪

Figure 3: Boston Convention Center Hotel.

Robert Hossli, RA, NCARB (bhossli@providencepoint.org), is a retired architectural development engineer who worked for US Steel, Westinghouse, Reynolds Metals, Armarlite Division of Anaconda Aluminum, H. H. Robertson, and Centria and was a member of ASTM and AAMA Standards Committees. Ronald Flucker, P.E. (rlflucker@verizon.net), is a retired structural engineer who worked for ALCOA, US Steel, AISC, and J&M Turner in areas of structural research, product and engineering development, and promotion for structural steel.

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STRUCTURE magazine

June 2013

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Phone: 800-449-5033 Email: clint@digitalcanal.com Web: www.digitalcanal.com Product: VersaFrame Description: VersaFrame has the key features needed to “get the job done” without becoming overly complex. Includes steel design (AISC 13th) and concrete design (ACI 2011). Try it free at the website.

Phone: 949-951-5815 Email: info@risatech.com Web: www.risa.com Product: RISAFloor Description: RISAFloor and RISA-3D form an unrivaled building analysis and design package. Modeling has never been easier whether you’re doing a graphical layout, importing a BIM model (from Autodesk Revit Structure), or prefer spreadsheets. Full code checks and optimization for six different material types makes RISA your first choice in buildings.

GT STRUDL Phone: 404-894-2260 Email: casec@ce.gatech.edu Web: www.gtstrudl.gatech.edu Product: GT STRUDL Description: Offers linear and nonlinear static and dynamic analysis features including response spectrum, transient and pushover analyses, plastic hinges, discrete dampers, base isolation, and nonlinear connections. Auxiliary GT STRUDL features available for the Base Plate Module and GT64M MultiProcessor Solver.

Integrated Engineering Software Phone: 406-586-8988 Email: info@iesweb.com Web: www.iesweb.com Product: VisualAnalysis Description: A great tool for tall building design including area loads, streamlined design features, and a “stay out of your way” attitude. Tall buildings are more than just a “total model” and VisualAnalysis is excellent for all kinds of investigations and analysis.

S-FRAME Software Inc. Phone: 203-421-4800 Email: info@s-frame.com Web: www.s-frame.com Product: S-FRAME® Analysis and Design Description: An easy-to-use structural modeling, analysis and design environment for tall buildings, bridges, frames, trusses, industrial buildings, plate/shell structures, and cable structures for seismic analysis, staged construction, slab design, Direct Analysis Method, linear and nonlinear static and time history analyses, moving load analysis, buckling load evaluation and more. Product: S-CONCRETE Design Description: Use S-CONCRETE to analyze and design reinforced concrete columns, beams and wall sections in an interactive design environment. The powerful analysis capabilities are coupled with an intuitive, interface with optional auto-design capabilities and comprehensive international standards. Auto-design single sections or batch process thousands of designs in one run.

Nemetschek Scia Phone: 877-808-7242 Email: info@scia-online.com Web: www.nemetschek-scia.com Product: Scia Engineer Description: Looking to migrate to, or improve your 3D design workflows? Scia Engineer links structural modeling, analysis, design, drawings, and reports in ONE program. Design to multiple codes. Tackle larger projects with advanced non-linear and dynamic analysis. Plug into BIM with IFC support, and bidirectional links to Revit, Tekla, and others.

POSTEN Engineering Systems Phone: 510-275-4750 Email: sales@postensoft.com Web: www.postensoft.com Product: POSTEN Multistory Description: The most eﬃcient & comprehensive post-tensioned concrete software in the world that not only automatically designs the tendons, drapes, as well as columns, but also produces highly eﬃcient, cost saving, sustainable designs with automatic documentation of material savings for LEED. No guessing, no fiddling, no time wasting.

All Resource Guides and Updates for the 2013 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

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June 2013

Firms Leslie E. Robertson Associates, R.L.L.P. Phone: 212-750-9000 Email: sawteen.see@lera.com Web: www.lera.com Product: Structural Engineering Description: A120-person M/WBE firm providing structural engineering services to architects, owners, contractors, and developers. Established in 1923, we have designed numerous landmark projects, both nationally and internationally. Our long tradition of innovative design together with our advances in technology has brought LERA to the forefront of the engineering profession.

The Masonry Society Phone: 303-939-9700 Email: info@masonrysociety.org Web: www.masonrysociety.org Product: Publications Description: A non-profit professional organization of volunteers, dedicated to the advancement of masonry knowledge. Through our Members, information & opinions about all aspects of masonry are discussed & debated. The resulting information is disseminated to provide guidance to the masonry industry on aspects of design, construction, & repair.

Walter P Moore and Associates

Decon® USA Inc.

Powers Fasteners

Phone: 404-898-9620 Email: tsanti@walterpmoore.com Web: www.walterpmoore.com Product: Innovative Engineering Description: WPM provides innovative engineering solutions to buildings of all types, all over the world.

Phone: 866-332-6687 Email: frank@decon.ca Web: www.deconusa.com 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 also being increasingly used to reinforce against bursting stresses in banded post-tension anchor zones.

Phone: 985-807-6666 Email: jack.zenor@sbdinc.com Web: www.powers.com Product: Concrete Anchoring Description: FREE – Anchor Design Software – Powers Design Assist. Helps tall Building designers deal with the complexity of ACI 318 Appendix D. Powers Fasteners now has 23 Product Code Compliance ICC ES Reports! Visit our website to download the software.

WSP USA Phone: 212-687-9888 Email: contact.structures@wspgroup.com/us Web: www.wspgroup.com/usa Product: Structural Engineering Description: The High Rise Center of Excellence within WSP’s global consultancy. Services include high and low rise building design, peer review and value engineering, forensic engineering structural investigations, building renovations and alterations, blast resistant design, construction inspection, 3D visualization, building information modeling (BIM) and steel detailing.

Suppliers Construction Specialties, Inc. Phone: 800-526-6930 Email: sgaskill@c-sgroup.com Web: www.c-sgroup.com Product: Blast Louvers Description: Blast protection, air movement and rain defense rolled into one. Government buildings, VA hospitals, computer centers and power plants are particularly vulnerable to explosive threats. C/S has developed six Blast Resistant models designed to withstand blasts up to 8 PSI and capable of meeting government requirements. Product: Expansion Joint Covers Description: Provides a covered transition across the expansion or movement joint openings of a building, which remains unaffected by the relative movement of the two surfaces on either side of the joint. These covers can be extremely large and complex on base isolated-buildings in seismic hotbeds.

CTS Cement Manufacturing

Product: Rapid Set® Cement Products Description: Use Rapid Set cement products for concrete repairs, restoration and new construction, and achieve high durability, fast strength gain and structural or drive-on strength in one-hour.

Ecospan Composite Floor System Phone: 770-296-4097 Email: rbullens@vulcraft-al.com Web: www.ecospan-usa.com Product: Composite Floor System Description: An innovative, simple, effective and economical method of providing open web structural components for elevated floor construction while incorporating benefits of lightweight composite design. UL fire rating, G561, for 1, 2 and 3 hours and a STC sound rating of 57.

New Millennium Building Systems Phone: 260-868-6000 Email: kevin.disinger@newmill.com Web: www.newmill.com Product: Steel joists, metal decking, castellated beams, BIM design, Flex-Joist Description: New Millennium engineers and manufactures standard steel joists, architecturally unique steel joists, steel decking, and FreeSpan castellated beams for wide-span bay designs. A leader in BIM-based steel joist design; recently introduced the Flex-Joist Gravity Overload Safety System, for early warning in the event of roof overloads.

Pile Dynamics, Inc. Phone: 216-831-6131 Email: www.info@pile.com Web: www.pile.com/pdi Product: QC systems for foundations of Tall Bulidings Description: World leader in Deep Foundations QA/QC system brands: Pile Driving Analyzer® and CAPWAP® (Dynamic Load Testing/Pile Driving Monitoring), Pile Integrity Tester, Thermal Integrity Profiler, PIR (Automated Monitoring Equipment for augercast/CFA piles), Cross-Hole Analyzer (CSL), GRLWEAP (wave equation analysis of piles), SPT Analyzer, E-Saximeter (driving logs), more.

STRUCTURE magazine

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Simpson Strong-Tie® Phone: 925-560-9000 Email: web@strongtie.com Web: www.strongtie.com Product: Strong Frame® Special Moment Frame Description: The new code-listed Strong Frame special moment frame is a unique lateral system solution for new construction and soft-story retrofit. With patented Yield-Link™ structural fuse technology, the links bear the brunt of lateral forces during a seismic event, keeping the structural integrity of the beams and columns intact.

Vulcraft/Verco Group Phone: 402-844-2570 Email: mike.klug@nucor.com Web: www.vulcraft.com Product: Steel Decking Description: Used in many applications, but is particularly well suited to roofing and flooring. Vulcraft/ Verco group manufactures many different types of deck, including roof deck, floor deck, composite floor deck and cellular deck. A full line of deck accessories, such as end closure and pour stop, is also available. Product: Steel Joist and Joist Girders Description: Open web-steel joists and joist girders are an engineered, truss-like construction component used to support loads over short and long spans. Steel joists and joist girders provide an economical system for supporting floors and roofs. Vulcraft joists and joist girders are designed/manufactored in accordance with the Steel Joist Institute.

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Product: Anchor Channels Description: Decon USA is the 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.

Noteworthy

news and information

Susan M. Frey An Engineer’s Engineer

usan (Sue) M. Frey, P.E., S.E., passed away on Sunday, May 12, 2013 at her home. Sue received her B.S. and M.S. from Purdue University, graduating in 1977. Later that year, she was hired as a structural engineer at CH2M HILL in Corvallis, OR, where she spent her entire career designing everything from concrete water storage reservoirs and wastewater treatment plants to performing arts centers. Sue was known as a tremendous mentor, both for junior staff and for advanced technical excellence across the firm, through her role as Structural Engineering Global Technology Leader. Sue served on the Civil Engineering Advisory Council at Purdue for many years. Purdue University awarded her the Civil Engineering Alumni Achievement Award in 2005. In 2010, she won the CH2M HILL CEO Excellence Award in the category of respect. She also contributed her time to many national and international professional societies, helping to advance the improvement and refinement of building codes and design practices through The Masonry Society, The Masonry Standards Joint Committee, The Structural Engineers Association of Oregon (President 1997 – 1998), the American Concrete Institute, The American Waterworks Association, and the National Council of Structural Engineers Associations (NCSEA). She was an adjunct professor for Design of Masonry Structures at Oregon State University, and was a masonry seminar and webinar instructor for the Northwest Concrete Masonry

Association. Recently, she was appointed by the Governor to the Oregon State Board of Examiners of Engineering and Land Surveying as a board member. Sue was also honored with a Special Merit for Lifetime Achievement Award from the Structural Engineers Association of Oregon (SEAO). She was the SEAO delegate to NCSEA, was very active on the NCSEA Licensure Committee and taught the Masonry portion of the NCSEA Structural Examination Review Course. Sue is survived by her husband of 33 years, Rich, and her two children, Jamie and Patrick. Sue served her profession as few do and made countless friends in the process. She was an inspiration to all that she met, constantly being upbeat and courageous during her 10 year battle with cancer. She was an engineer’s engineer. She will be sorely missed by her family, her countless friends and the structural engineering profession to which she gave so much. Donations in Sue’s memory may be made to the Good Samaritan Hospital Foundation Survivorship Fund, 3600 NW Samaritan Drive, Corvallis, OR 97330, or the Susan M. Frey Civil Engineering Scholarship Fund, Purdue University, 403 West Wood Street, West Lafayette, IN 47907-2007 (check should include note “for the Susan M. Frey Civil Engineering Scholarship Fund.”). Online condolences may be sent to: www.mchenryfuneralhome.com.

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STRUCTURE magazine

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June 2013

award winners and outstanding projects

Spotlight

The Twisting Regent Emirates Pearl Hotel By Ahmed Osman, P.E., M.Eng and Whitney Morris, LEED AP UAE DeSimone Consulting Engineers was an Outstanding Award Winner for the Regent Emirate Pearl Hotel project in the 2012 NCSEA Annual Excellence in Structural Engineering awards program (Category – International Structures over $100M).

he iconic Regent Emirates Pearl development will rise and twist 255 meters (840 feet) above its calm turquoise ocean front, claiming its spot in the Abu Dhabi skyline. The mixed-use AED 1.0B ($287M) complex is located amidst palaces and high profile skyscrapers on the Corniche Street of Abu Dhabi in the United Arab Emirates. The vast plot area of 13,600 square meters (146,500 square feet) provides top rate views of Capital City, private islands and yachts along with the luxurious Emirates Palace. The Pearl’s signature feature is the 45-story twisting elliptical floor plan, and columns which contains 60 luxury serviced apartments occupying levels 1 thru 10 and a 5-star hotel with 437 keys including presidential and royal suites occupying levels 11 thru Roof. The expansive podium area includes five levels of restaurants, retail areas, spas, swimming pools, a gym and more, with another 5 levels of underground parking. The total project build up area includes 55 stories and 130,600 square meters (1.4 million square feet). The main structural challenge was to appropriately model, analyze and design the complicated twisting shape of the tower. The perimeter tower columns are inclined 7 degrees vertically and “shift” 48 centimeters (19 inches) each level in the circumferential direction, with a total of 21.60 meters (70.8 feet) from bottom to top. In plan, each floor rotates 0.56 degrees each level with a total of 25 degrees of total rotation from Level 1 to the Roof. The sloping columns cause the building to rotate at each level, therefore inducing a torsional force in the elliptical concrete core wall, with the force accumulating over the height of the building. DeSimone carefully studied and analyzed the effects of the torsional force, and formulated a structurally innovative solution to relieve the torsion from the core. The perimeter tower columns were strategically located to transfer at Level 27 and Level 1 in order the help relieve the torsion from the core. The inclined concrete tower column transfers were designed to reverse the twist

by transferring the column gravity loading directly into the core wall in the opposite direction of the torsional force, and therefore reversing the force in the core wall. The tower columns and transfers played a two part structural role in the stability of the building. The first role, as described above, is to help alleviate the twist on the core wall; the second is to act as part of the lateral force resisting system as an outrigger to help the core wall resist the lateral loads. The perimeter tower columns range from 400 x 1600 millimeters (16 x 63 inches) at the top to 600 x 1600 millimeters (24 x 63 inches) at Level 1. From Podium Roof to the raft, the tower columns transfer to 1325-millimeter (53-inch) diameter, circular. The structural gravity framing system of the typical tower floors is composed of Post Tensioned slabs supported by concrete perimeter columns and a central elliptical core wall. The 27 centimeter (10.5 inch) PT-concrete C50 (7,200 psi) flat plate slabs span more than 10.5 meters (35.0 feet) from the core wall to the perimeter tower columns. The flat plate design reduced the construction time significantly. This structural system concentrated the gravity loads into the core wall, to help reduce the reinforcing of the core wall due to wind and seismic forces. Also, this system helps minimize the load to the 16 perimeter tower columns that transfers at Level 1 to 1325-millimeter (53-inch) diameter, circular. Since the slab and core wall are elliptical in plan, a slip form was key to the success of the speed of construction and the project as a whole. This factor, and many other strategic components, helped with the delivery of the project below budget and construction schedule. The Podium Levels consists of a cast-in-place concrete slab and beam gravity system. The Architect’s façade requirements at the Lobby Level prevented the Podium Level North and South perimeter columns to continue past Podium 1. In order to facilitate the Architect’s needs, another unique and innovative structural solution was provided. Steel hangers from Podium 1 to 3 were designed and

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June 2013

installed as an attractive structural solution. The hangers are supported by a deep Post Tension beam at the Podium Roof where clear height was not a major issue. The project also has 5 underground parking levels to accommodate the 679 parking spaces required by Abu Dhabi’s DOT. The 20.0-meter (66-foot) deep excavation was unearthed and sealed off using a temporary reinforced concrete diaphragm wall with tie-backs. Since Abu Dhabi is an island with the average water level at ground level, excavating that deep below the surface creates extremely high hydrostatic forces. The diaphragm system provided a water-free environment to apply extensive water proofing and to build the permanent foundation walls. The foundations walls have an average thickness of 375 millimeters (15 inches) and were designed to resist soil and tremendous water pressure.▪ Ahmed Osman, P.E., M.Eng, is a Managing Principal with DeSimone Consulting Engineers, Abu Dhabi, UAE. Whitney Morris, LEED AP, has been working for DeSimone for the past 6 years in both the San Francisco and Abu Dhabi offices. Last year Whitney was awarded the Young Engineer of the Year for 2012 from Big Project-Middle East.

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NCSEA News

News form the National Council of Structural Engineers Associations

Celebrating

Professionalism and Structural Licensing Barry Arnold’s presentation at the Ohio SEA (SEAoO) Annual Conference, Ethics: A Practical Guide for the Practicing Engineer, reminded us that a profession carries several distinguishing characteristics and it is more than an occupation. Although there is some variation in the exact definitions, most generally agree a profession’s characteristics include the following: • A core body of knowledge; • Academic programs which teach the body of knowledge; • Practitioners with autonomy in the application of the body of knowledge; • Ethical rules of conduct that constrain practitioners; and • Licensing laws or rules limiting who may practice. Structural engineering meets the first four of these criteria and, with licensing of engineers, it partially meets the last. Divinity, law and medicine represent the earliest professions. Pharmacy, accounting, teaching, engineering and others entered the professional ranks over time. Establishment of structural licensure in all jurisdictions would provide structural engineering with official stature due to both the public and its practitioners. A typical structural engineer invests many years in training and education. Frequently, this starts before college with advanced high school classes as preparation for the rigors of university. Exams are commonly used to establish whether a student meets the necessary standards to begin college. The rigors of college entrance are evidence of the body of knowledge. The study of engineering at the college level presents prospective engineers with a challenging curriculum. It includes the core arts, as well as history and communication courses which all students tackle, and adds intensive mathematics and science courses. College’s structured environment provides the framework to teach how basic problems are solved with the application of scientific principles. All of a student’s earlier coursework culminates in the last academic semesters, which focus efforts into a specialized field of engineering. These focused courses are where structural engineers learn the principles of analysis, building materials and building systems from the building blocks of earlier work. University engineering programs convey the profession’s core body of knowledge. Several engineering societies recognized the significance of the college curriculum and founded what is now the Accreditation Board for Engineering and Technology (ABET) to help ensure the quality of the programs. This body accredits college engineering programs. ABET accreditation is widely recognized as the standard necessary to establish an academic program’s qualification and provides verification of the institution’s qualification to convey the material. The wide array of problems faced by structural engineers makes predefined solutions impractical, and it fosters the growth of new technologies and innovations of existing methods. A direct result of the wide array of possible solutions is that a large degree of autonomy is necessary to serve our clients. Upon entering the workforce, engineers learn various methods of applying the core body of knowledge under the guidance of more seasoned professionals. This guidance provides training in the application of knowledge and develops the independent thought process crucial to successfully using the autonomy available to engineers. Structural engineers use this autonomy regularly. An engineer might decide whether a building should be built from concrete masonry block or framed by cold formed steel, whether a STRUCTURE magazine

It is clear that engineering meets the criteria of a profession. Establishment of structural licensure would provide the last step for structural engineering to take its place among the great professions of our society. concrete frame or structural steel frame is more economical or, on a smaller scale, whether to use 10 penny or 8 penny nails in a joint. Independence in the application of engineering principles is evident in daily activities and necessary to effectively address the various factors influencing design. Our codes and standards are rarely so prescriptive that the engineer has no options. Engineering autonomy is balanced by ethical obligations. The special knowledge held by engineers, combined with a wide degree of freedom in how it is applied, give structural engineers a great responsibility. In Ohio, and most jurisdictions, engineers are bound by the state’s rules of ethical conduct. Further, members of societies such as ASCE or NSPE have ethical codes of conduct. These ethical frameworks have common features: to consider public safety as the highest priority, to be truthful, to perform only in areas of expertise, to be faithful agents for clients and to continue development throughout our career. Structural engineers face these ethical obligations daily. Without a second thought, thousands of people regularly depend on the fact that a structural engineer’s work will perform, that the bridge will carry them home to their family, that their office will be there to host a critical sales meeting, that the high school stadium bleachers will let them cheer on their children, and much more. Structural engineers truly have to have high ethical standards. Each jurisdiction’s regulatory body limits who may practice engineering through a rigorous licensing process. The process includes consideration of education, training, experience, referrals and no less than two examinations. Ohio, like many other jurisdictions, offers examinations in 24 disciplines or variations of engineering discipline. Structural disciplines are considered in two distinct exams: the single day CivilStructural exam and the 16 hour Structural exam. SEAoO joins ASCE-SEI, NCSEA, SECB and CASE in advocating the establishment of structural licensure. Timothy M. Gilbert, P.E., S.E., SECB (TGIlbert.PE@gmail.com) is a Principal Quality Engineer with Louis Perry & Associates, Inc. in Wadsworth, Ohio. He is also a Director and Licensure Committee chair for the Structural Engineers Association of Ohio (SEAoO). This article was previously published in the March 2013 issue of the SEAoO newsletter.

In Memoriam: Sue Frey NCSEA mourns the passing of Sue Frey, P.E., S.E., principal structural engineer, CH2M HILL, and adjunct professor/ instructor at Oregon State University. Sue was an active member of NCSEA and SEAO, and served on NCSEA’s Licensing and Continuing Education Committees. She was also an instructor for the SE Review Course, and a past presenter of NCSEA webinars and NCSEA Annual Conferences. She will be sorely missed. June 2013

News from the National Council of Structural Engineers Associations

• Keynote: The Philosophy of Design: The Structural Engineer’s Role in Creating New Architecture by Bill Baker, P.E., SECB, F.ASCE, FIStructE, Structural & Civil Engineering Partner, Skidmore, Owings & Merrill • Serviceability presentation based on NCSEA publication Guide to the Design for Serviceability: In Accordance with IBC 2012 and ASCE/SEI 7-10 by author Kurt Swensson, Ph.D., P.E., LEED®AP, Principal, KSI Engineers • ACI 550 session by Harry Gleisch, Vice President of Engineering, Metromont Corporation, and Chairman of Joint ACI-ASCE 550, Precast Concrete Structures • Connections: The Last Bastion of Rational Design by Bill Thornton, Corporate Consultant, Cives Corporation • ASCE 41 session • Practical Design of Complex Stability Bracing Configurations by Donald White, Ph.D., School of Civil and Environmental Engineering, Georgia Tech • DoD Minimum Antiterrorism Standards for Buildings by Jon Schmidt, P.E., SECB, M.ASCE, Associate Structural Engineer, Burns & McDonnell

• The Analysis of Offset Diaphragms and Shear Walls by R. Terry Malone, P.E., S.E., Senior Technical Director, WoodWorks–Architectural & Engineering solutions • Load Generators: What Exactly is My Software Doing by Kim Olson, FORSE Consulting • University of Minnesota Northrop Auditorium Renovation: Underpinning & Micropile Foundation Case Study by Greg Greenlee, Principal, Engineering Partners International • The Structural Curtainwall by John Tawresey, S.E., KPFF Consulting Engineers

NCSEA News

Technical and management sessions on structural engineering:

The Annual Conference will also include: • Social events that facilitate networking with fellow structural engineers; • [New] reception for Young Member attendees; • SECB reception and information on changes to application requirements; • A trade show featuring the best in structural engineering products and services. Check www.ncsea.com for continually updated information on Annual Conference educational sessions, events, and registration information.

Current NCSEA Annual Conference Sponsors: Bronze

Silver

June NCSEA Webinars

Rebuilding the World Trade Center required the use of several hundred thousand yards of concrete. This course will explain what field tests should be performed on delivered concrete to have some assurance that the high-strength will be achieved.

June 27, 2013 Building Design for Tornadoes Bill Coulbourne, P.E.

June 14, 2013 Training for Post-Disaster Assessment Jim Barnes

This webinar provides information gathered in investigations into the Tuscaloosa, AL and Joplin, MO 2011 tornadoes, which are leading the ASCE 7 Wind Load Task Committee to include new commentary in ASCE on designing buildings to resist the effects of tornado winds.

This California Emergency Management Agency (CalEMA) Safety Assessment Program (SAP) is one of only two postdisaster assessment programs that will be compliant with the requirements of the forthcoming Federal Resource Typing Standards for engineer emergency responders.

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

The program consists of three webinar segments available over one day’s time. Cost: $500 – Per Connection. Several people may attend for one connection fee.

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June 11, 2013 Lessons Learned: Rebuilding the World Trade Center with HighStrength Concrete up to 14,000 psi Casimir Bognacki, P.E., FACI

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2013 Emerging Leaders Alliance Conference

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Interested in improving your leadership skills? Sponsorships available for ASCE members to attend 2013 Emerging Leaders Alliance conference ASCE, as a partner in the Emerging Leaders Alliance (ELA), will sponsor eight members to attend the 2013 ELA leadership conference. The conference provides rising leaders with tools to more effectively lead their organizations and serve our professional community. This program also allows you to network with engineers and scientists from other disciplines and earn PDHs. The workshop will take place on November 11-13, 2013 at the Hyatt Regency Reston in Reston, Virginia, USA. Interested ASCE members must apply for sponsorship online at http://tinyurl.com/cplhatd by July 1, 2013. For more information, visit www.emergingleadersalliance.org or contact professional@asce.org.

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 Paul Sgambati at psgambati@asce.org.

Structures Congress 2014 Call for Proposals Be part of the cutting-edge technical program of the Structures Congress 2014 in Boston, April 3-5, 2014. The Structural Engineering Institute is now accepting session and presentation proposals for the Structures Congress 2014.

Key Dates All Abstract and Session Proposals due June 12, 2013 Notification of Acceptance September 18, 2013 All Final Papers due December 18, 2013 (extensions not possible) Session proposals can take two forms: a traditional session with 4 papers presented, or a panel session with no papers and perhaps more audience interaction. In addition, you can submit individual abstracts that may be combined with others to form cohesive sessions. Topics will include but are not limited to: Bridges Buildings Seismic Wind and Flood Loads Sustainability Business and Professional Practice Blast and Impact Loading Nonbuilding and Special Structures Nonstructural Systems and Components Visit the Structures Congress 2014 website for more information and submission instructions at http://tinyurl.com/dxlgyr9.

Local Activities SEI East Central Florida One Day Seminar

New Student Chapter at WVU Welcome to the new SEI Graduate Student Chapter (GSC) at West Virginia University (WVU), chaired by Daniel Estep and Faculty Advisor Dr. Udaya Halabe. The SEI GSC at WVU is within the Department of Civil and Environmental Engineering (CEE). The mission of SEI-WVU is to promote graduate education in structural engineering, develop leadership skills, create professional development opportunities for current graduate students, and enhance networking with structural engineering professionals. By encouraging interaction between SEI student members and professional members, and providing opportunities for professional and educational development, SEI-WVU will facilitate a successful college-to-career transition, and encourage its members to engage in SEI activities both at WVU and at the national level throughout their professional career. STRUCTURE magazine

The SEI East Central Florida Branch of ASCE is pleased to invite you to participate in their Annual Structural Group One-Day Seminar, Friday, June 28, 2013 at the University of Central Florida. The seminar consists of a morning session from 8:30 a.m. to 11:30 a.m. and an afternoon session from 1:30 p.m. to 4:30 p.m. Keynote Speakers • Composite Design – Provisions and Applications: William P. Jacobs V, P.E., S.E. • Floor Vibrations – A Critical Serviceability Issue: Thomas Murray, Ph.D., P.E. Throughout the years, participation in the seminar has provided valuable exposure to both seminar sponsors and exhibitors, while providing a professional benefit to community and raising funds for engineering student scholarships. Contact Sameer Ambare, P.E. at sambare@hntb.com for more information and to register. To get involved with the events and activities of your local SEI Chapter or Structural Technical Group (STG), visit www.asce.org/SEI. Local groups offer a variety of opportunities for professional development, student and community outreach, mentoring, scholarships, networking, and technical tours. June 2013

Register now. This eleven-part, live webinar course references codes specified by NCEES for the exam, including effects of wind loads and seismic loads for both building and bridge structures. This course will refine your skills for the comprehensive, essay-like design questions. Or consider taking ASCE’s Live P.E. Review Courses and learn from experienced instructors during live webinars. You will benefit from immediate feedback and assistance from your instructors during the live webinars, and supplement your learning with free on-demand recordings of the sessions. With our guarantee, if you register as an individual and you do not pass your exam, provide us with proof of your exam results, and we will enroll you in the next course for free. To save $100, register at: www.asce.org/pereviewlive/ by July 1 using Promo Code EHPE13 – this savings applies to group and individual registrations.

myLearning ASCE Library Features Free Collection of Six Papers from Your New PDH Tracker and Personalized Hub for Continuing Education Past Structures Congresses

Manage your professional development and license renewal through ASCE’s new learning management system – myLearning. Track all your PDHs/CEUs, including those from other providers; obtain certificates of completion; take program-related exams; print or save transcripts of your professional development – all in one place! Make myLearning your personalized hub for continuing education and explore the comprehensive program catalog and track your PDHs. Visit the myLearning website at www.asce.org/mylearning/ and get started today.

New ASCE Structural Webinars Available SEI partners with ASCE Continuing Education to present quality live interactive webinars on useful topics in structural engineering. Several new webinars are available: Designing for Flood Loads Using ASCE 7 and ASCE 24

June 3, 2013

William L. Coulbourne

Structural Thermal Bridging in the Building Envelope

June 5, 2013

James A. D’Aloisio

Damping and Motion Control in Buildings and Bridges

June 7, 2013

Brian Breukelman

Movable Bridge Series – Details of Bascule Bridges

June 14, 2013

Andrew Herrmann

Philosophy of Structural Building Codes

June 17, 2013

Dave Adams

Introduction to the Seismic Design of Nonbuilding Structures to ASCE 7-10

June 26, 2013

Greg Soules

Vibration of Concrete Floors – Evaluation, Acceptance and Control

June 28, 2013

Bijan Aalami

The Five Pieces of Equipment Every Bridge Inspector Should Have

July 10, 2013

Lance Andrews

A General Overview of ASCE 7-10 Changes to Wind Load Provisions

July 15, 2013

Bill Coulbourne

Pier and Beam Foundation Design for Wind and Flood Loads

July 29, 2013

Bill Coulbourne

Significant Changes to the General Requirements for Determining Wind Loads of ASCE 7-10

July 31, 2013

Eric Stafford

Webinars are live interactive learning experiences. All you need is a computer with high-speed internet access and a phone. These events feature an expert speaker on practice-oriented technical and management topics relevant to civil engineers. Pay a single site fee and provide training for an unlimited number of engineers at that site for one low fee, and no cost or lost time for travel and lodging. ASCE’s experienced instructors

STRUCTURE magazine

deliver the training to your location, with minimal disruption in workflow – ideal for brown-bag lunch training. ASCE Webinars are completed in a short amount of time – generally 60 to 90 minutes – and staff can earn one or more PDHs for each Webinar. Visit the ASCE Continuing Education website for more details and to register: www.asce.org/conted.

June 2013

The Newsletter of the Structural Engineering Institute of ASCE

The ASCE Library has provided free access to a diverse collection of six papers presented at past Structures Congresses. The papers were selected by the National Technical Program Committee to provide examples of the type of topics presented and discussed at this annual event. Download the papers as a warm up to attending the 2013 congress or to help you formulate your 2014 session or abstract proposal. Free access to these papers will be available through July 31, 2013 at http://ascelibrary.org/page/ jsendh/structuresfeaturedproceedingspapers.

Structural Columns

Save $100 and Pass the S.E. Exam with ASCE-Guaranteed

Become a Confident Engineering Expert Witness

SAVE THE DATE

June 20 -21, 2013

The CASE Summer Planning Meeting is scheduled for August 6-7 in Chicago, IL. A new feature to this meeting will have CASE leaders facilitate a roundtable of discussion topics in the structural engineering field. If you are interested in attending the meeting or have any suggested topics for the roundtable, please contact CASE Executive Director Heather Talbert at htalbert@acec.org.

CASE in Point

The Newsletter of the Council of American Structural Engineers

If asked for your expert testimony today... Would you feel ready to take on these potentially lucrative assignments with a sense of purpose AND confidence? You could, can and will when you’ve had the proper preparation from professionals who’ve walked this walk before! Become a Confident Engineering Expert Witness will show you how to prepare and successfully provide expert testimony for discovery, depositions, courtroom, and related legal proceedings. • Earn new firm services revenue • Enhance your professional credentials • Expand personal and professional opportunities • Qualify for recognition as an Engineering Expert Witness Earn 11 PDHs and a Certificate of Completion Since 2009, this popular introductory program has been the top choice for professional engineers, architects, and surveyors. Take the training and watch how quickly you become the “goto” resource for your clients and their representatives. There’s never been a better time than now to begin! For more information, visit http://witness2013.acec.org or contact Ed Bajer, ebajer@acec.org.

CASE Summer Planning Meeting

CASE Announces the 2013 CASE Scholarship Winner Since 2009, the CASE Scholarship has helped engineering students make positive steps towards a bright future in structural engineering The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student pursuing a Master’s degree in Structural Engineering. CASE strives to attract the best and brightest to the structural engineering profession, and educational support is the best way we can ensure the future of our profession. The 2013 winner, Samantha Dupaquier, will graduate May 2014 with a Master’s Degree in Civil Engineering with a Structural Emphasis from Auburn University.

ACEC Business Insights ACEC’s 2013 Annual Convention and Legislative Summit On April 21-24, a record 1,400 ACEC members attended the ACEC Annual Convention in Washington, D.C., meeting with 300 Senators, Congressmen, and Capitol Hill staffers to urge passage of long-term transportation, water/wastewater infrastructure, and energy legislation. 600-plus attended the black-tie Engineering Excellence Awards Gala, which recognized 147 preeminent engineering achievements from throughout the world. The Kauffman Center for the Performing Arts in Kansas City, MO was honored with the 2013 Grand Conceptor Award on April 23rd. The engineering work for the Kauffman Center, which features an 1,800-seat opera hall and a 1,600-seat symphony hall enclosed in twin shells towering 16 stories, was done by New York-based Arup. The complex was designed by Moshe Safdie and built by J.E. Dunn Construction Co. The award citation referred to the facility as a “gleaming … architecturally intricate entertainment complex that features two acoustically tuned performance halls; a four-story, wide-angled glass wall front facade topped by slightly concave sloping roofs; and a pioneering tensile structural support system of encompassing high-strength interior rods. The result is an exciting new focal point for the region’s art and entertainment community, and a dazzling addition to the downtown Kansas City skyline.” ACEC’s Annual Convention also marks the induction of a new ACEC Executive Committee. Gregs Thomopulos, Chairman/ CEO of Stanley Consultants, Inc in Muscatine, IA., succeeded STRUCTURE magazine

Ted Williams as ACEC Chairman for 2013-2014 at the spring meeting of the ACEC Board of Directors. New members of the 2013-2014 Executive Committee are: Chairman-elect Richard Wells, Vice-President of Kleinfelder; Manish Kothari, President and CEO, Sheladia Associates; Chris Poland, Chairman and Senior Principal, Degenkolb Engineers; Clinton Robinson, Associate Vice President, Black and Veatch Corporation; ACEC/Michigan Executive Director Ronald Brenke is the new NAECE representative. June 2013

Fee Development Being adequately compensated for the effort and value added to a project by the structural engineer is an essential element of the consulting structural engineering practice. Developing fair, yet adequate, fees is always a challenge. Tool 7-2: Fee Development is intended to be used within a consulting firm to stimulate thought and consideration in the development of fees. Engineers in firms that may be experiencing new responsibilities as project engineers and project managers often ask the question – “How do we decide on fees?” This tool may be a useful primer for these employees, and lead

You can follow ACEC Coalitions on Twitter – @ACECCoalitions.

to further discussion with firm management on the firm’s fee development strategies. CASE has developed previous tools in the toolkit, as well as other documents, that can aid in the development of fees and compensation. Several of these tools will be referenced herein. The user of this tool is encouraged to become familiar with the other tools and documents available. Please see the following documents for more information: • CASE Document 504, Proposal Preparation Spreadsheet • CASE Document 976-A, Commentary on Value-Based Compensation for Structural Engineers • CASE Tool 2-1, Risk Evaluation Checklist • CASE Tool 5-4, Negotiation Talking Points • CASE Tool 7-1, Client Evaluation You can purchase all CASE products at www.booksforengineers.com.

If you would like more information on the items below, please contact Ed Bajer, ebajer@acec.org.

A recent case in New Jersey, Nicholas v. Mynster, barred the testimony of a doctor who was hospital-credentialed to treat the condition suffered by the plaintiff, finding that was not enough. Cases in the health care industry are even to the point of requiring a similar board-certified specialist in some instances. Can engineers be far behind? It has been argued that having equal credentials is not enough; the expertise must be in the same area. The list of experts on ACEC’s contractscentral.net does list the area of expertise of all its credentialed experts. The next expert witness program is June 20-21 in Chicago.

Patent Trolling These involve the use of scanner/copiers that scan a hard copy document into an electronic file and then transmit that file to someone else. Some firms have received letters saying that, if they are using this technology, they are infringing on someone’s STRUCTURE magazine

patent and must pay a license fee. Some believe the patents are not valid but no court decisions have as yet determined that. The situation is not settled on how to handle these circumstances. Other industries are involved as well. It is best keep up to speed on this issue and look for any cases that have been resolved. The Shield Act has been introduced in Congress. Author Rep. DeFazio says that his legislation “would force patent trolls to take financial responsibility for their frivolous lawsuits.”

What Do You Seal? The Practice Act or rules in most jurisdictions govern whether a seal is required and when it must be applied to professional documents. Some states will also define what they are. In some states, “as-builts” must be sealed, in others no. The term “as built” is not encouraged in favor of something like record drawings or marked up set of prints. Some follow the general rule of sealing only documents that the government requires to be sealed. NCARB (the National Council of Architectural Registration Boards) has a Model Handbook for Building Officials that offers answers to this question.

June 2013

CASE is a part of the American Council of Engineering Companies

CASE Business Practice Corner Experts Must Actually Be Experts

CASE in Point

New CASE Tool Now Available

Structural Forum

opinions on topics of current importance to structural engineers

Black, White, and Gray Ethics in Engineering By Greg Cuetara, P.E., S.E.

s engineers, we have a great deal of black and white in our world. We have been trained to define a problem and come up with a solution. Does a structure have the capacity we need, or not? How do the capacities compare to the imposed loads? We use “engineering judgment” grounded in our knowledge and experience to determine whether a structure is safe; but, even with this information, we are using defined skills. It can be difficult to see that there is also a lot of gray area in engineering. One such area is ethics. Essentially, ethics is doing what is right. To be ethical as engineers, we need to practice within our discipline, field of competence, and area of examination, which is why we are licensed in the first place. As our licensing rules state, we also have an ethical duty not only to ourselves, the engineering community, and the work that we produce, but also to protect the safety, health, and welfare of the public. In most jurisdictions, there is no differentiation between disciplines; each engineer has the obligation to practice only in the areas in which he or she is genuinely competent (structural, electrical, etc.). However, this arrangement is now being questioned by many in our industry. For example, NCSEA, CASE, and SEI all advocate specifically licensing structural engineers (SE) as distinct from other disciplines, either separately or as an additional credential beyond the professional engineer (PE) license. Building codes are changing so frequently that it is difficult for anyone not practicing solely in that discipline to keep up with them. In addition, the National Council of Examiners for Engineering and Surveying (NCEES) has determined that engineers should be tested specifically in their area of competence, which they have organized into 25 different exams. Some of these are generic in the morning and specific in the afternoon. NCEES has also determined

that a single 8-hour exam is not sufficient to test structural engineers and instead now offers a 16-hour structural exam. These exams do not cover every situation, but they are a means to evaluate engineers to verify that they have achieved a minimal level of competence. Some states and municipalities require peer reviews of an engineer’s work. As a result, I have had the opportunity to review other engineers’ drawings and projects, and at times this has tested my ethics. Recently, a set of documents from another engineer raised a number of red flags as I was looking through the drawings, calculations, and field notes. The existing conditions as noted did not make sense and did not match what was shown on the drawings, and my own initial calculations suggested problems with the design. I discussed my concerns with the engineer, and he simply blew them off. I was now in a position in which I had to defend what was right and the safety of the building’s occupants. I was fortunate enough to be able to take my concerns to the next level; fortunately, that person paid attention to my concerns, and everything was resolved. This situation, to me, was black and white – we did not have the option to disregard inconsistencies. When it comes to ethics, however, many people often assume that it is a gray area with no right or wrong answers. The other engineer was trying to please his client by taking shortcuts, putting his duty and responsibility aside. There are times when we as engineers push our limits and that is okay, as long as we are practicing within our area of legitimate competence as demonstrated by having been tested. Still, we have a duty as professionals to act in an ethical manner. Unfortunately, we sometimes lose sight of the big picture and get caught up in the weeds when we are working for our clients. They ask for the impossible and we believe that, in order to keep them happy,

we have to provide any design that they request. However, we are the trained professionals and need to make well-reasoned recommendations to our clients on what is required and appropriate. Ultimately, we need to remember that our “clients” are not only the people paying our immediate fees, but also the end users of our buildings, bridges, and other structures. We must always keep them in mind, especially in the (hopefully rare) circumstances in which we are forced to question what is right and what is wrong. We have a duty to the public, due to our education and experience, to protect our friends, family, and neighbors as best we can. While it is impossible to find and catch everything, when we see something that is not right, it is our responsibility to question and challenge why and determine what should be done to address it. In short, when it comes to engineering, we need to defend what is right. If you are ever put in a position that tests your ethics, you do have options. Many large companies have an ethics hotline that you can call to report the situation. If that is not an option, take it to your industry peers by notifying professional engineering licensing boards or building code officials. It is up to us as engineers to police ourselves and uphold the ethical responsibility that we have to the public, and it is a part of the job that we should take just as seriously as the designs that we produce.▪ Greg Cuetara, P.E., S.E. (greg.cuetara@stantec.com), is a senior structural engineer with the power group of Stantec Consulting Inc. in Scarborough, Maine. He is the current president of the Structural Engineers Association of Maine (SEAM), serves as the SEAM Delegate to NCSEA, and is a member of the NCSEA Licensing Committee.

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

June 2013

STRUCTURE magazine | June 2013

Articles inside

Structural Forum

Spotlight

Historic Structures

CASE Business Practices

Engineer’s Notebook

Guest Column

Building Blocks

Great Achievements

Structural Performance

Structural Testing