Modern steel construction october 2015 by beerolercasre

Modern STEEL CONSTRUCTION

October 2015

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October 2015 columns

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in every issue departments 6 EDITOR’S NOTE 9 STEEL INTERCHANGE 12 STEEL QUIZ 60 NEWS & EVENTS 66 STRUCTURALLY SOUND resources 64 MARKETPLACE 65 EMPLOYMENT

features 22

Collaboration Computes BY ROBERT K. OTANI, P.E., AND JOHN BARRY, P.E. Named for computing’s best-known couple, Cornell’s new computer science facility brings together several departments into one centralized location.

Park View BY REZA FARIMANI, P.E., MICHAEL J. SQUARZINI, P.E., AND STEPHANIE WATERMAN The desire to optimize views of the New York Public Library’s back yard drove the structural system for a new Manhattan high-rise.

The Elevated Cube BY MARK SARKISIAN, S.E., P.E., ERIC LONG, S.E., P.E., ANDREW KREBS, S.E., P.E., AND ALESSANDRO BEGHINI, S.E., P.E. An 11-story cube of shimmering glass will soon float over the streets of downtown Los Angeles—and it isn’t a Hollywood special effect.

BY MICHAEL C. GRYNIUK, P.E. Boston College’s newest residence hall brings the school’s two campuses together in a modern, geometric space.

UL Design Considerations

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Top Heavy BY MARCO SHMERYKOWSKY, P.E., AND ANDREW STEINKUEHLER A simple skylight retrofit in a Manhattan high-rise becomes a complete roof overhaul.

Campus Connector

BY CHARLES J. CARTER, S.E., P.E., PH.D., FARID ALFAWAKHIRI, P.ENG., PH.D., AND LARRY S. MUIR, P.E. Using UL Designs for fire protection with today’s structural steel design codes. BY JOHNN P. JUDD, P.E., PH.D., AND FINLEY A. CHARNEY, P.E., PH.D. Exploring new collapse prevention systems for seismic events.

ON THE COVER: Gates Hall strikes a pose on Cornell University’s campus, p. 22 (Photo: Matthew Carbone) MODERN STEEL CONSTRUCTION (Volume 55, Number 10) ISSN (print) 0026-8445: ISSN (online) 1945-0737. Published monthly by the American Institute of Steel Construction (AISC), One E. Wacker Dr., Suite 700, Chicago, IL 60601. Subscriptions: Within the U.S.—single issues $6.00; 1 year, $44. Outside the U.S. (Canada and Mexico)—single issues $9.00; 1 year $88. Periodicals postage paid at Chicago, IL and at additional mailing offices. Postmaster: Please send address changes to MODERN STEEL CONSTRUCTION, One East Wacker Dr., Suite 700, Chicago, IL 60601. DISCLAIMER: AISC does not approve, disapprove, or guarantee the validity or accuracy of any data, claim, or opinion appearing under a byline or obtained or quoted from an acknowledged source. Opinions are those of the writers and AISC is not responsible for any statement made or opinions expressed in MODERN STEEL CONSTRUCTION. All rights reserved. Materials may not be reproduced without written permission, except for noncommercial educational purposes where fewer than 25 photocopies are being reproduced. The AISC and Modern Steel logos are registered trademarks of AISC.

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Structural Steel Fabrication Steel Plate & Sheet Metal Fabrication Miscellaneous Metals Machining Rolling & Forming Services Cutting Services Industrial Coatings Industrial & Electrical Contracting Crane Rental & Trucking Services Heat-Bending Services (AISC Certiﬁed for Major Steel Bridge Fabrication)

editor’s note Editorial Offices One E. Wacker Dr., Suite 700 Chicago, IL 60601 312.670.2400 tel

Editorial Contacts EDITOR & PUBLISHER Scott L. Melnick 312.670.8314 melnick@modernsteel.com SENIOR EDITOR Geoff Weisenberger 312.670.8316 weisenberger@modernsteel.com

FAMILY GET-TOGETHERS ARE ALWAYS FUN, BUT WHEN POLITICS IS THE SUBJECT DU JOUR THE ENTERTAINMENT VALUE IS RATCHETED WAY UP. My oldest child is a complete political junkie and my extended family runs the gamut from far left to far right; we have a couple who are prone to believe just about any conspiracy theory, and my youngest son simply views the whole thing as entertainment and voices support for whoever stirs the pot the most. F o r t h o s e o f u s i n t h e d e s i g n LEED Gold certification (or an equivalent community and construction industry, this “green” certification)? election cycle is important as much more Some candidates talk the talk about than simple entertainment, but I rarely strengthening American manufacturing. hear any candidates discussing the issues But as Ludwig Mies van der Rohe critical to us. famously said, “God is in the details,” and For example, we do hear some unfortunately, details seem to be in short platitudes about the need for a strong supply these days. What should be done infrastructure, but we don’t hear a about currency manipulation? Are new discussion about how to pay for a new anti-dumping provisions needed? How will transportation bill. Are candidates in favor we handle labor shortages brought about of a gas tax hike (one of the most common by a reduced workforce if undocumented proposals to pay for a new highway bill)? (but employed) immigrants are deported? And we don’t often hear any discussion What about structural engineers who are about past expenditures, such as the here on H1-B visas? American Recovery and Reinvestment Act, Modern Steel is putting together a which had an emphasis on “shovel-ready” questionnaire for the 2016 presidential projects rather than long-term solutions. candidates. We’d love the hear your ideas As a result, less than 15% of the more on any issues that we should be asking than $800 billion dollars was spent on new about. If there’s an issue on which you’d infrastructure assets. Was it a success and like to know a candidate’s position, drop should it be repeated if we experience a me an email at melnick@aisc.org. similar downturn in the future? There are general comments about global warming and the environment, but details are lacking. For example, what level of reduction (if any) of greenhouse SCOTT MELNICK gas emissions should be mandated by EDITOR 2030? Should all federal projects require

ASSISTANT EDITOR Tasha Weiss 312.670.5439 weiss@modernsteel.com DIRECTOR OF PUBLICATIONS Keith A. Grubb, S.E., P.E. 312.670.8318 grubb@modernsteel.com PRODUCTION COORDINATOR Megan Johnston-Spencer 312.670.5427 johnstonspencer@modernsteel.com GRAPHIC DESIGN MANAGER Kristin Hall 312.670.8313 hall@modernsteel.com

AISC Officers CHAIR Jeffrey E. Dave, P.E. VICE CHAIR James G. Thompson SECRETARY & GENERAL COUNSEL David B. Ratterman PRESIDENT Roger E. Ferch, P.E. VICE PRESIDENT AND CHIEF STRUCTURAL ENGINEER Charles J. Carter, S.E., P.E., Ph.D. VICE PRESIDENT Jacques Cattan VICE PRESIDENT John P. Cross, P.E. VICE PRESIDENT Scott L. Melnick

Advertising Contact Account Manager Louis Gurthet 231.228.2274 tel 231.228.7759 fax gurthet@modernsteel.com For advertising information, contact Louis Gurthet or visit www.modernsteel.com

Address Changes and Subscription Concerns 312.670.5444 tel 312.893.2253 fax admin@modernsteel.com

Reprints Betsy White The Reprint Outsource, Inc. 717.394.7350 bwhite@reprintoutsource.com

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If you’ve ever asked yourself “Why?” about something related to structural steel design or construction, Modern Steel’s monthly Steel Interchange is for you! Send your questions or comments to solutions@aisc.org.

Corrosion Resistance and Shear Connections The April 2015 Modern Steel article “Considering Corrosion” by Steven A. Sebastian (www.modernsteel.com) includes several options for shear connections in Figure 4. Among these is a field-welded, single-plate shear connection. The recommended design procedure in the AISC Manual is: “The plate must be welded to the support on both sides of the plate and bolted to the supported member.” Is a field-welded, single-plate shear connection acceptable? Is rotational ductility a concern? There is often not a perfect engineering solution for a given situation. Often the pros and cons of a condition must be weighed to determine the best—or at least an acceptable—solution. For typical beam-end conditions, engineers should probably adhere to the design procedures in Part 10 of the Manual. However, special circumstances may sometimes dictate other approaches. The author presents just such a case, where corrosion resistance is a primary concern. The trade-off is acknowledged in the article when it is stated that “The option at the top [of Figure 4] is simple and flexible and has sufficient strength for most applications. However, it is the most susceptible to corrosion…” If having a simple and flexible connection is the primary consideration, then a connection from Part 10 of the Manual should be chosen. As corrosion resistance becomes a bigger consideration, the engineer may have to move down the list of the connections perhaps making trade-offs in economy and behavior along the way. There is nothing in the AISC Specification that would prohibit the use of an all-welded connection. The Specification requirements are provided in Sections B3.6a and J1.2. Both of these sections address the need for rotational ductility. The AISC Manual design procedures for shear tabs are intended to address the need to accommodate simple beam end rotations. A de facto standard for this rotation has become 0.03 radians, which is a very large demand. If the end rotation is significantly less than this, then it makes sense that the detailing recommendations in the Manual could be relaxed. Conditions where minimal end rotation are expected might include: lightly loaded beams, short beams, beams governed by deflection (not strength), struts primarily resisting axial loads and beams with concentrated loads applied close to the end. The design procedure for conventional single-plate connections in Part 10 of the Manual assumes all of the end rotation is accommodated through plowing of the bolts, which obviously would not occur if the connection were welded. There are however other mechanisms that could be used to accommodate the end rotation. For instance, for the case of a connection to a beam web with no beam present on the other side, as is shown in Figure 4 of

steel interchange

the article, the simple beam end rotation could be accommodated through weak-axis flexure of the web of the support. Another mechanism that can be used to accommodate simple beam end rotations is flexure of the plate. This method is used primarily for extended tabs but there is no reason it could not be applied to a conventional single plate shear connection as well. When applying strong-axis flexural yielding to an all-welded conventional tab, I tend to have concerns about the relatively small distance that might exist between the welds at the supported beam and the welds at the face of the support. For this reason I have typically tried to use only the vertical weld at the end of the plate or if horizontal top and bottom welds are used hold them back somewhat to provide a larger length over which the tab plate can yield. Holding back the weld would reduce the effectiveness of the detail relative to corrosion, so again the engineer must weigh the options carefully. The all-around weld may be okay in some instances where the rotational demand is low or other mechanisms are able to accommodate the rotation. It should be noted that there are many tradeoffs inherent in the article. Opting for a field-welded detail over a field-bolted detail will likely incur additional costs relative to the erection, but as is stated, “The economic impact of shutdowns, repairs and maintenance may be of greater concern than the lowest initial capital cost.” Another issue is the use of seal welds. Seal welds may conflict with Specification requirements and will certainly affect the flow of loads through the structure. Section 3.13.3 of AISC Design Guide 21: Welded Connections—A Primer for Engineers (a free download for members from www.aisc.org/dg) provides a good discussion on this topic. Obviously, not all of these considerations can be fully addressed in a single article, so the article must be taken in context. Its primary focus is corrosion protection. As always, the engineer must consider a multitude of factors during the design process. Larry S. Muir, P.E.

Composite Collectors I am using equations from AISC Specification Section I3 to determine the spacing of shear studs to transfer collector forces in a concrete-filled steel deck diaphragm. ACI 318-11 Appendix D recommends using φ = 0.75 for cast-in headed studs with supplemental reinforcing, but I do not see anything specified in Specification Section I.3. Can the ACI φ-factor be used to design the shear stud in accordance with Specification Section I.3? No. The provisions in ACI should not be intermixed with the AISC provisions for composite members except where the AISC provisions specifically reference ACI. The AISC Modern STEEL CONSTRUCTION

steel interchange provisions have evolved over the last couple decades based on research, which is not reflected in the ACI provisions. AISC Specification Section I.3 does not specify a φ for headed studs. The studs are simply a component of the composite beam system, and the equations have been developed such that φ equals 0.9 for flexural bending of the composite beam. For other composite members (not beams), the appropriate φ for the shear connectors is defined in Section I8.3. I do not know whether you are designing the collector beam as a composite beam or a non-composite beam relative to the gravity load combination, and that can impact how you design the collector. The December 2008 article “Under Foot” (www.modernsteel.com) discusses collector beams in composite slabs that you may want to review, particularly if your collector beam is also a composite beam. Since this article was published, there has been some additional investigation into shear connector behavior, which pertains to non-composite beams used as collectors. When loads are applied to the floor system after the slab concrete has hardened, the floor beams will deflect. When a beam deflects, shear forces are induced at the interface between the steel section and the concrete section as the slab will try to “slip” along this plane. The shear connectors restrain this slip behavior and transfer force between the steel and concrete sections. If your beam is designed noncomposite, you still need to consider these shear loads on the studs due to the slip which may reduce the strength of the shear connectors available for the lateral load condition. For a simple span beam, the “slip” demand will be greatest at the beam ends. Therefore, it follows that studs located near the beam ends will be subject to higher shear forces due to the beam deflection than studs located at mid-span. If you are designing your beam as non-composite and only adding a few studs for horizontal load transfer, it may be best to locate the studs near mid-span where the slip demand is least. Shear connectors on non-composite beams do not know they are not supposed to behave like shear connectors for composite beams. If you are going to distribute studs along the entire length of the beam, then you should ensure you have enough studs installed for the beam to act as a composite member or there is a possibility the studs at the beam ends subject to the greatest slip demand will be overloaded and fracture. This is why the above article recommends installing enough studs to develop a minimum of 25% of the members composite beam capacity. Susan Burmeister, P.E.

Connection Design Forces The 9th Edition of the AISC Manual required connections to be designed for one-half the total uniform design load (UDL) shown in the allowable uniform load tables, if loads were not provided in the design documents. Is this still a requirement? No. The AISC Specification does not contain this requirement. The AISC Code of Standard Practice, which generally governs 10

OCTOBER 2015

trade practices for the fabrication and erection of structural steel, addresses the reporting of loads for connection design. Section 3.1.2 of the Code requires the engineer of record (EOR) to provide design loads when connections are to be selected or completed by the fabricator. Loads should not be assumed. If the contract documents do not provide sufficient information to determine the loads, then an RFI should be sent to the EOR requesting this information. AISC has never recommended the use of one-half UDL. The use of actual reactions has always been the preference. Older editions of the Manual stated: “For economical connections, the beam reactions should be shown on the contract drawings.” They went on to say, “If these reactions are not shown, connections must be selected to support one-half the total uniform load capacity… The effects of any concentrated loads must be taken into account.” There were several problems with this language. First, the Manual is not adopted into law through the building code and therefore cannot introduce requirements; it can only provide guidance related to requirements in the Specification or the Code. Second, though the use of one-half UDL is generally going to be conservative, it is not fool-proof. Third, stating that a detailer/fabricator (the parties presumably being addressed) must account for concentrated loads does not really resolve an issue where no loads are provided. In essence the detailer/fabricator would have to make engineering decisions about when the concentrated loads existed and when they were significant. However, only an engineer can make engineering decisions. The current language in the Code is a much better approach. The engineer is clearly responsible for providing the loads. The engineer can still choose to use one-half UDL criteria, but this is not the preferred or optimal method. Further discussion concerning the problems associated with the use of one-half UDL is provided on page 2-30 of the 14th Edition Manual. Carlo Lini

The complete collection of Steel Interchange questions and answers is available online. Find questions and answers related to just about any topic by using our full-text search capability. Visit Steel Interchange online at www.modernsteel.com.

Larry Muir is director of technical assistance and Carlo Lini is a staff engineer—technical assistance, both with AISC. Susan Burmeister is a consultant to AISC.

Steel Interchange is a forum to exchange useful and practical professional ideas and information on all phases of steel building and bridge construction. Opinions and suggestions are welcome on any subject covered in this magazine. The opinions expressed in Steel Interchange do not necessarily represent an official position of the American Institute of Steel Construction and have not been reviewed. It is recognized that the design of structures is within the scope and expertise of a competent licensed structural engineer, architect or other licensed professional for the application of principles to a particular structure. If you have a question or problem that your fellow readers might help you solve, please forward it to us. At the same time, feel free to respond to any of the questions that you have read here. Contact Steel Interchange via AISC’s Steel Solutions Center: 1 E Wacker Dr., Ste. 700, Chicago, IL 60601 tel: 866.ASK.AISC • fax: 312.803.4709 solutions@aisc.org

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steel quiz

This monthâ&#x20AC;&#x2122;s quiz is all about hollow structural sections (HSS). Consult AISC Design Guide 24: Hollow Structural Section Connections and the AISC Specification for more information.

1 True or False: When designing trusses

using HSS, AISC Design Guide 24 recommends that a designer should select a relatively stocky chord (or column) main member.

2 For the transfer of axial load, which of two details (a or b) is preferable per the recommendations given in AISC Design Guide 24?

HSS Truss Web Member

HSS Truss Chord

3 True or False: When designing an HSS truss, one should try to use gapped K-connections instead of overlapped connections.

4 The configuration shown here

illustrates a _________ (note that the arrows indicate the load distribution necessary for equilibrium). a. T-connection b. Y-connection c. K-connection d. Crossconnection e. a and b

5 True or False: It is possible for

branch members to transmit part of their load as K-connections and part of their loads as T-, Y- or crossconnections.

6 The preferred material specification for HSS is: a. ASTM A500 Gr. B b. ASTM A500 Gr. C c. ASTM A1085 d. ASTM A847

7 Use of ASTM A1085 provides the following benefit(s): a. Tighter material tolerances b. Maximum specified yield stress of 70 ksi c. Standard Charpy notch toughness requirement d. a and b e. All of the above

TURN TO PAGE 14 FOR ANSWERS 12

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steel quiz

ANSWERS

1 True. The static strength of nearly all HSS connections is

5 True. This is permitted in Section K2 of the AISC

enhanced by using stocky chord members. This choice will maximize connection strength and therefore facilitate connection design. Selecting thin HSS can make truss connection design a challenge.

Specification. When this is done, the adequacy of the connections is determined by interpolation on the proportion of the available strength of each in total.

2 a. AISC Design Guide 21 recommends that Bb < B â&#x20AC;&#x201C; 4t.

When this expression is met, fillet welding of the branch is usually possible, and difficult, expensive flare-groove welds (arising when Bb â&#x2030;&#x2C6; B) can be avoided. In addition to following this recommendation, a good connection design strategy is to make tb/t as low as possible and Bb/B as high as possible.

3 True. Gapped connections are easier and less expensive to fabricate than overlapped connections. This is particularly the case with round-to-round HSS welded connections, where branch member ends require complex profiling and the fit-up of members requires special attention.

4 d. Cross-connection. A cross-connection is defined as one where the punching load, Pr sin Î¸, is transmitted through the chord member and equilibrated by branch member(s) on the opposite side. See section K2 in the AISC Specification for definitions of T-, Y- and K-connections. T R A I N I N G

Ăˇ

F I E L D

S U P P O R T

6 b. ASTM A500 Gr. C. Note that this is a change from what is currently shown in Table 2-4 in the 14th Edition Manual and was recently highlighted in the Modern Steel article â&#x20AC;&#x153;Are You Properly Specifying Materials?â&#x20AC;? (February 2015), available at www.modernsteel.com.

7 e. All of the Above. Although ASTM A500 Gr. C is still more common in the marketplace, ASTM A1085 has some benefits that may help it to eventually become the preferred material. Tighter material tolerances means the 0.93 thickness reduction likely will not be required for A1085 material in the 2016 AISC Specification, leading to more economical and efficient designs. A maximum yield stress of 70 ksi will result in a lower expected yield strength and reduced capacity design requirements and column required strengths in seismic designs. A1085 provides a defined level of material toughness that makes HSS more suitable for use in dynamically loaded structures.

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dŚĞ 'ĞŵŝŶŝ ŝƐ Ă ĐŽŵƉůĞƚĞ ƌĂŶŐĞ ŽĨ ƉůĂƚĞ ĨĂďƌŝĐĂƟŽŶ ĐĞůůƐ ĨŽƌ ƚŚĞ ĚƌŝůůŝŶŐ͕ ƚĂƉƉŝŶŐ͕ ŵŝůůŝŶŐ͕ ŵĂƌŬŝŶŐ ĂŶĚ ƚŚĞƌŵĂů ĐƵƫŶŐ ŽĨ ĮŶŝƐŚĞĚ ƉĂƌƚƐ ŝŶĐůƵĚŝŶŐ ďĞǀĞůŝŶŐ ĨŽƌ ǁĞůĚ ƉƌĞƉ͘ dŚĞ 'ĞŵŝŶŝ͛Ɛ ƵŶŝƋƵĞ ƐƵď ĂǆŝƐ ǁŝƚŚ ĚƵĂů ƐƉŝŶĚůĞ ĐĂƉĂďŝůŝƚǇ ĚŽƵďůĞƐ ƚŚĞ ƉƌŽĚƵĐƟǀŝƚǇ ŽǀĞƌ ƐŝŶŐůĞ ƐƉŝŶĚůĞ ƐǇƐƚĞŵƐ ǁŝƚŚŽƵƚ Ă ƐƵď ĂǆŝƐ͘

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&ŝĐĞƉ ŽīĞƌƐ ĐŽŵƉůĞƚĞůǇ ŝŶƚĞŐƌĂƚĞĚ ƐǇƐƚĞŵƐ ǁŝƚŚ ĨƵůů ĂƵƚŽŵĂƟŽŶ ŽĨ ƚŚĞ ĞƋƵŝƉŵĞŶƚ ĂŶĚ ƚŚĞ ŵĂƚĞƌŝĂů ŚĂŶĚůŝŶŐ͘ EŽ ůŽŶŐĞƌ ĂƌĞ &ŝĐĞƉ ŽīĞƌƐ ĐŽŵƉůĞƚĞůǇ ŝŶƚĞŐƌĂƚĞĚ ƐǇƐƚĞŵƐ ǁŝƚŚ ĨƵůů ĂƵƚŽŵĂƟŽŶ ŽƉĞƌĂƚŽƌƐ ƟĞĚ ƚŽ ĞĂĐŚ ŵĂĐŚŝŶĞ ŝŶ Ă ƐǇƐƚĞŵ ĂƐ ƚŚĞ ĂƩĞŶĚĂŶƚ ŽĨ ƚŚĞ ĞƋƵŝƉŵĞŶƚ ĂŶĚ ƚŚĞ ŵĂƚĞƌŝĂů ŚĂŶĚůŝŶŐ͘ EŽ ůŽŶŐĞƌ ĂƌĞ ŵŽŶŝƚŽƌƐ ƚŚĞ ƚŽ ŵƵůƟͲƚĂƐŬŝŶŐ ŽƉĞƌĂƟŽŶƐ͘ :ŽďƐ Žƌ ŽƉĞƌĂƚŽƌƐ ƟĞĚ ĞĂĐŚ ŵĂĐŚŝŶĞ ƐǇƐƚĞŵ ŝŶ Ă ƐǇƐƚĞŵ ĂƐ ƚŚĞ ĂƩĞŶĚĂŶƚ ƐĞƋƵĞŶĐĞƐ ĂƌĞ ŵƵůƟͲƚĂƐŬŝŶŐ ĞǀĞŶ ƐŝŵƵůĂƚĞĚ ƉƌŝŽƌ ƚŽ ĨĂďƌŝĐĂƟŽŶ ƚŽ ĂĐŚŝĞǀĞ ŵŽŶŝƚŽƌƐ ƚŚĞ ƐǇƐƚĞŵ ŽƉĞƌĂƟŽŶƐ͘ :ŽďƐ Žƌ ƚŚĞ ŽƉƟŵƵŵ ƵƌŝŶŐ ŚĂŶĚƐͲŽī ƚŽ ŽƉĞƌĂƟŽŶ ƐĞƋƵĞŶĐĞƐ ĂƌĞ ƉƌŽĚƵĐƟǀŝƚǇ͘ ĞǀĞŶ ƐŝŵƵůĂƚĞĚ ƉƌŝŽƌ ƚŚĞ ƚŽ ĨĂďƌŝĐĂƟŽŶ ĂĐŚŝĞǀĞ ŽĨ ƚŚĞ ĐŽŵƉůĞƚĞ ƉƌŽĚƵĐƟǀŝƚǇ͘ ƐǇƐƚĞŵ͕ ƚŚĞ ƵƌŝŶŐ ĂĐƟǀŝƚǇ ƚŚĞ ĐĂŶ ďĞ ŐƌĂƉŚŝĐĂůůǇ ǀŝĞǁĞĚ ƚŚĞ ŽƉƟŵƵŵ ŚĂŶĚƐͲŽī ŽƉĞƌĂƟŽŶ ŽĨ ƌĞŵŽƚĞůǇ ĂŶĚ ƵƉůŽĂĚĞĚ ƚŽ ƚŚĞ ŵŽĚĞů ĨŽƌ ƚƌƵĞ ϰ ĐĂƉĂďŝůŝƚǇ͘ ƚŚĞ ĐŽŵƉůĞƚĞ ƐǇƐƚĞŵ͕ ƚŚĞ ĂĐƟǀŝƚǇ ĐĂŶ ďĞ ŐƌĂƉŚŝĐĂůůǇ ǀŝĞǁĞĚ ƌĞŵŽƚĞůǇ ĂŶĚ ƵƉůŽĂĚĞĚ ƚŽ ƚŚĞ ŵŽĚĞů ĨŽƌ ƚƌƵĞ ϰ ĐĂƉĂďŝůŝƚǇ͘

FLEX 12 ZŽďŽƟĐ ^ƚƌƵĐƚƵƌĂů ^ƚĞĞů &ĂďƌŝĐĂƟŽŶ ^ǇƐƚĞŵ

dŚĞ &Z ZŽďŽƟĐ ƵƫŶŐ ^ǇƐƚĞŵ ĨƌŽŵ &ŝĐĞƉ ŽƌƉŽƌĂƟŽŶ ŝŶĐŽƌƉŽƌĂƚĞƐ Ă ĐŽŵŵĞƌĐŝĂů ƌŽďŽƚ ǁŝƚŚ ĂŶ y ʹ z ƉŽƐŝƟŽŶŝŶŐ ƐǇƐƚĞŵ ĨŽƌ ĞǆƉĂŶĚĞĚ ĐĂƉĂďŝůŝƚǇ ĂŶĚ ƌĂŶŐĞ͘ dŚĞ &Z ͕ ǁŝƚŚ Ă ůĂƐĞƌͲƐĐĂŶŶŝŶŐ ĐĂŵĞƌĂ͕ ĂĐŚŝĞǀĞƐ ƉƌŽĐĞƐƐ ƟŵĞƐ ƚŚĂƚ ǁĞƌĞ ƉƌĞǀŝŽƵƐůǇ ŝŵƉŽƐƐŝďůĞ ƚŽ ƌĞĂůŝǌĞ͘ dŚŝƐ ĞůŝŵŝŶĂƚĞƐ ƚŚĞ ŶĞĞĚ ĂŶĚ ƟŵĞ ůŽƐƚ ĨŽƌ ŵĞĐŚĂŶŝĐĂů ƉƌŽďŝŶŐ ƚŽ ĮŶĚ ƚŚĞ ƌĞůĂƟǀĞ ƐƵƌĨĂĐĞƐ͘ dŚĞ ƌŽďŽƚ ĂůƐŽ ĨĞĂƚƵƌĞƐ ĂŶ ĂƵƚŽŵĂƟĐ ƚŽŽů ĐŚĂŶŐĞƌ ƚŚĂƚ ĞŶĂďůĞƐ ďŽƚŚ ƉůĂƐŵĂ ĂŶĚ ŽǆǇͲĨƵĞů ĐƵƫŶŐ ŽĨ ƚŚĞ ƐĂŵĞ ƉĂƌƚ ĂƐ ĐŚĂŶŐŝŶŐ ĨƌŽŵ ŽŶĞ ƚŽƌĐŚ ƚŽ ƚŚĞ ŶĞǆƚ ŝƐ ũƵƐƚ ϭͲϮ ƐĞĐŽŶĚƐ͘

&ŝĐĞƉ ŝƐ ƚŚĞ ƚƌƵĞ ŵĂƌŬĞƚ ƐŚĂƌĞ ĂŶĚ ƚĞĐŚŶŽůŽŐǇ ůĞĂĚĞƌ ŝŶ ƚŚĞ ƉƌŽĚƵĐƟŽŶ ŽĨ ƐǇƐƚĞŵƐ ĨŽƌ ƚŚĞ ĨĂďƌŝĐĂƟŽŶ ŽĨ ƐƚƌƵĐƚƵƌĂů ƐƚĞĞů ĂŶĚ ƉůĂƚĞ͘ ƵƌƌĞŶƚůǇ͕ &ŝĐĞƉ ŚĂƐ ƐǇƐƚĞŵƐ ŝŶƐƚĂůůĞĚ ŝŶ ŶĞĂƌůǇ ϵϬ ĐŽƵŶƚƌŝĞƐ ŐůŽďĂůůǇ ƚŚĂƚ ĂƌĞ ƐĞƌǀŝĐĞĚ ďǇ ϭϯ &ŝĐĞƉ ǁŽƌůĚǁŝĚĞ ĐŽŵƉĂŶŝĞƐ͘

&ŝĐĞƉ ŽƌƉŽƌĂƟŽŶ ϮϯϬϭ /ŶĚƵƐƚƌǇ ŽƵƌƚ ͻ &ŽƌĞƐƚ ,ŝůů͕ DĂƌǇůĂŶĚ ϮϭϬϱϬ WŚŽŶĞ ;ϰϭϬͿ ϱϴϴͲϱϴϬϬ ͻ &Ăǆ ;ϰϭϬͿ ϱϴϴͲϱϵϬϬ ǁǁǁ͘ĮĐĞƉĐŽƌƉ͘ĐŽŵ

business issues Eight tips to boost the fun factor.

ARE YOU HAVING FUN AT WORK? BY ANNE SCARLETT

“I NEED TO HAVE MORE FUN AT WORK!” Outwardly exude positivity. (It will eventually shift I hear this sentiment often—whether from a partner in an inward.) When you feel disenchanted (with your company, engineering firm, or a head of compliance at an accounting firm, your business unit or your immediate work), you must monior an adjunct professor. The desire to truly enjoy one’s work tor your verbal and non-verbal expressions. For every gripe, engulfs us all, regardless of salaries, titles or degrees. why not also share at least two positive things—whether they So, is one of your perpetual resolutions to inject fun and be complimenting your direct report, or giving a shout out for humor into your business development efforts (and into work an existing client. Offering up kudos helps create a respectful, in general)? positive vibe. Positivity, in turn, is uplifting and fun. Some firms—namely the hot, Gravitate towards (or emuyoung, tech-savvy organizations— late) colleagues that are havmake a concerted effort to weave fun ing fun. Depending upon your Who in your company is into their physical and cultural work firm size, you may have options environment. Advertising agency for observing others. Who is havhaving fun? Is it a group dynamic ing fun? Is it a group dynamic or mcgarrybowen clearly works hard and plays even harder; their fun is evoked by key individuals? What’s or evoked by key individuals? loaded with clever pranks, parties their secret sauce? If you feel comand unique extracurricular activities. fortable, ask them directly what it Chicago-based Groupon, another is that makes them experience such What’s their secret sauce? example, is a pleasure to tour. Abunjoy at work. Otherwise, feel free dant laughter rings through their to be silently observant and see if open office environment. Oversized there’s anything you can borrow headshots—almost caricature in nature—hover above each per- from their “fun playbook.” son’s workstation. Small teams gather in the ‘forest’ or other Laugh. Just laugh. I used to have a boss that would say he playfully designed areas in their workspace and hold quirky enjoyed making me laugh (I have a goofy laugh, apparently!). contests that require creativity and brainwork. Even the morn- If people around me aren’t making me laugh, then I turn to ing commute is fun for Groupon employees, as it culminates other sources for quick amusement: New Yorker cartoons, Key with a ride on their dedicated “Party Elevator,” complete with & Peele sketches, even The “Ultimate Dog Tease” video, which music and dancing. While I’m sure these “fun firms” have their gets me every time! Children may laugh hundreds of times a own issues, stresses, and conflicts, they certainly do their part to day. What’s your daily dose of laughter? Levity matters, and it encourage an element of fun into their work! can honestly change your entire outlook on your work. Many AEC firms also work to boost their own esprit de Lighten up. In addition to genuinely smiling and laughing, corps. Senior leadership, together with human resources and it’s helpful to be less intense. I’m intense by nature. Intensity the business development team, often brainstorm ideas to keep can be an asset when things need to get done, and done well. staff engaged and productive. Our industry recognizes that happy employees equals productive employees which in turn equals loyal, long-lasting employees. Perhaps most important, Anne Scarlett is president of we know that fun-filled employees will often jive with clients. Scarlett Consulting, a Chicagobased company specializing in (Hey, clients want to have fun, too!) All of this is a given. But perhaps some of those company- AEC-speciﬁc strategic marketing driven efforts are too campy or contrived for your taste. No plans, marketing audits and problem. It’s a matter of figuring out your own definition of coaching. She is also on the “fun” and how you can make it happen. So let’s focus on the adjunct faculty of Columbia micro-level things that you can do for yourself to make sure College of Chicago and DePaul you have more fun as a business developer, working through University. She can be contacted through her website, your sales process and beyond. www.annescarlett.com. Modern STEEL CONSTRUCTION

business issues But the intensity can be off-putting to those with a less intense demeanor. I learned this the hard way, in the classroom. My undergraduates have taught me that thereâ&#x20AC;&#x2122;s a fine line between intensity equating to motivational and energetic, versus intensity equating to scary and overpowering. I have adjusted, so that I only dial up the intensity regarding topmost priorities. Get stuff done! When you are stuck and you look back and ask, â&#x20AC;&#x153;What in the world did I get done today?â&#x20AC;? it might bring you down. For me, I have more fun at work when Iâ&#x20AC;&#x2122;m accomplishing and producing. Think about when you move a sales prospect one step closer to a signed contract. Or you finally wrap up your strategic business development planning for the year. Or you hire someone new. These things feel good. Find your go-to goof. Whether your style of humor is dry and subtle, slapstick and silly or somewhere in between, thereâ&#x20AC;&#x2122;s likely someone in your firm (or else in your professional network) that shares your humor. It doesnâ&#x20AC;&#x2122;t matter if itâ&#x20AC;&#x2122;s someone you work with directly or not, but it does help if they work within your firm (for context). Locate that person and have frequent touch points with them to get a laugh. Shake it off (Ă la Taylor Swift). When you take bad news hard, itâ&#x20AC;&#x2122;s a challenge to have fun. Losing a client to a competitor is hands down one of the worst feelings in the business devel-

oper role. But thereâ&#x20AC;&#x2122;s also internal politics, budget cuts, leadership inconsistencies and an array of other things that could be fodder for moping at work. For me, I use a lot of shake-it-off self-talk. My message typically revolves around the fact that I did the very best I could to impact a positive outcome. Or Iâ&#x20AC;&#x2122;ll reflect on something crappy that happened in the past and then note how we were able to get through it. Shake it up: Sometimes, we discover that even when we are doing wellâ&#x20AC;&#x201D;attaining our business development goals, collecting kudos during reviews, being on track for a promotionâ&#x20AC;&#x201D;something is off. Perhaps your work process is redundant, lacking the excitement that comes with fresh new challenges. It becomes same-same-same rather than the oft-used term â&#x20AC;&#x153;same-same, but different.â&#x20AC;? In the business developerâ&#x20AC;&#x2122;s role, locating new challenges is fairly easy. Your firm is likely to support an interest in additional, different twists to your internal responsibilities or a newfound commitment to external activities such as professional organizationsâ&#x20AC;&#x201D;particularly if your efforts will strengthen your position with the prospective clients. Figuring out ways to have fun at work is worthy of your attention and should be revisited more than once a year! Itâ&#x20AC;&#x2122;s an endless processâ&#x20AC;&#x201D;but one that makes all the difference for life â&#x2013; balance and success.

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Collaboration

COMPUTES Named for computing’s best-known couple, Cornell’s new computer science facility brings together several departments into one centralized location.

BY ROBERT K. OTANI, P.E., AND JOHN BARRY, P.E.

THE C IN CIS typically stands for “computing,” but in the

Robert K. Otani (rotani@thorntontomasetti.com) is a principal with Thornton Tomasetti’s CORE studio and John Barry (jbarry@ thorntontomasetti.com) is an associate with Thornton Tomasetti.

OCTOBER 2015

case of Cornell University’s new Bill and Melinda Gates Hall, it could also stand for “centralized” or “collaborative.” The new 100,000-sq.-ft building sits in the middle of the renowned Ithaca, N.Y., campus and was designed to foster collaboration between the academic departments of the university’s computing and information science (CIS) unit, home to the computer science, information science and statistics departments. Cornell’s goal was to create an innovative academic structure for its world-class CIS faculty and students, who have ties to departments across the university. The new four-story building houses classrooms, collaborative spaces, faculty offices and an auditorium. Circulation starts at the voluminous and curved atrium at the entrance, which extends up to a linear skylight. The fully glazed atrium, through its transparency, creates a visual connection between the collabora-

The new 100,000-sq.-ft Bill and Melinda Gates Hall sits in the middle of Cornell’s renowned campus.

➤ Matthew Carbone

➤ ➤

Matthew Carbone

The building’s curtain wall consists of sloped and vertical glazing with integrated thermally broken brackets that support perforated, folded stainless steel shading panels.

Thornton Tomasetti

tive spaces, interconnecting stairs and the 60-ft-long cantilever extending to the south at the upper floor levels. Hanging Out Gates Hall’s structural system consists of composite steel floor framing with concentrically braced steel cores for the lateral system and drilled shaft foundations and footings bearing on rock. It uses a total of 759 tons of structural steel in the form of 1,703 members. Concentrically braced frames with HSS members were used to simplify the enclosure wall details that needed to be built around the diagonal bracing. The bracing connections were field bolted, and the gusset plates were welded at fabricator Schenectady Steel’s shop. The site grade on the transverse (north-south) section of the building has a substantial elevation differential, which required intermittent shear walls in the lower mechanical levels to resist

the net earth pressures acting on the structure’s north side. The challenges from an erection/logistics standpoint were largely based on the limited space available for the crane and delivery of large truss sections. Shoring was required for the large cantilever truss to the south, and the entire second floor cantilevers 10 ft to the north and south, providing both an open east/west pedestrian passageway at the ground level and shading for offices and the auditorium at the lower level. The high-performance building is accentuated by the southfacing cantilevered truss, which allows the third-floor collaborative lounge and work spaces to extend far beyond the building base while acting as a visual gateway to the south campus. The truss consisted of W24 members, which also supported the floors. Since the diagonals were exposed, architect Morphosis called for HSS members without gusset plates, so welded connections were employed for the bracing. Modern STEEL CONSTRUCTION

On the west, a perforated metal scrim provides shading and partially shields the views of the full-height truss, and the 60-foot cantilever overlooks the David F. Hoy baseball field to the southeast. In plan, the cantilevered floor tapers south, framing a view of that part of the campus and the engineering quad. At the floor level of the cantilever is a glass floor that provides an overhead view of the pedestrian activity at the entrance. To accomplish the open views to the southeast, the eastern portion of the cantilever was only framed with large girders at the third and fourth floors. The imbalance of vertical stiffness necessitated careful façade glazing detailing to accommodate the inherent rotation of the cantilevered slabs, as well as a rigorous diaphragm analysis (using SAP2000) to account for the in-plane shear forces from gravity, wind and seismic forces acting on the cantilevered portal.

➤ ➤

Crucial Cladding Knowing that the façade design was one of the most important elements of the

The building uses a total of 759 tons of structural steel in the form of 1,703 members.

Thornton Tomasetti

OCTOBER 2015

project, both architecturally and for environmental performance, structural engineer Thornton Tomasetti’s structural and façade teams worked very closely with Morphosis and the design assist façade contractors (W&W Glass and Erie Architectural Products USA) to ensure that building movements and tolerances were fully coordinated. The building’s curtain wall consists of sloped and vertical glazing with integrated thermally broken brackets that support perforated, folded stainless steel shading panels. The entire façade system is supported by the cantilevered structural system, which required differential movements and glass-to-metal façade interfaces to be carefully detailed and designed. The original design required a thermally broken shroud around the metal bracket that supported the shading panels at the aluminum mullion interface, as well as a specified U-value (heat transfer rate) for the assembly. The façade contractor, Zahner, performed a thermal analysis and chose stainless steel, which has lower conductivity than aluminum or carbon steel, for the support bracket. The thermal

➤

Matthew Carbone

A 60-foot cantilever overlooks the David F. Hoy baseball field to the southeast. Morphosis Architects

Modern STEEL CONSTRUCTION

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Steel framing allowed for a lightweight building that minimized foundation loads.

break also included a stainless steel insert to the mullion, which allowed the mullion assembly to exceed the performance criteria of the specified U-value. In some instances, the structural design was modified specifically to adhere to the stringent tolerances of the façade systems and interfaces of single-span glazing elements with multi-span glazing elements. The design team collaborated with Zahner in 3D building information models (BIM) to coordinate the various façade systems and structural interfaces. At both the exterior and interior atrium spandrel conditions, extensive detailing and system coordination was undertaken to integrate the glazing systems, curtain wall and brise soleil perforated skin. Thornton Tomasetti

➤

The building is accentuated by the south-facing cantilevered truss.

Thor

nton

Green Space The sustainable features at Gates Hall demonstrate Cornell University’s commitment to environmentally conscious policies. As the structural engineer and façade consultants, Thornton Tomasetti used high-efficiency glass façades and skylights throughout the building to allow for maximum daylight, as well as occupancy sensors and high-efficiency lighting. The perforated solar shading panels on the façade reduce glare and cooling loads during the summer. The university uses lake source cooling to run its central chilled water system on campus. This method, in addition to other efficient mechanical systems such as radiant flooring and active and passive chilled beams, is expected to lead to a 30% reduction in energy usage at Gates Hall compared to a comparable typical academic building. In addition, the use of structural steel and composite steel framing allowed for a lightweight building, minimizing the foundation loads (Thornton Tomasetti estimates that a concrete-framed building with the same column grid would have been at least 50% heavier than the steel building given the complexity of the building superstructure) and overall embodied energy, which was tracked and implemented using the firm’s custom embodied energy/carbon parametric analyzer called GreenSpace.

setti

a Tom

Thornton Tomasetti

At both the exterior and interior atrium spandrel conditions, extensive detailing was undertaken to integrate the glazing systems, curtain wall and brise soleil perforated skin. Modern STEEL CONSTRUCTION

➤

details both in terms of constructability and overall economy. This iterative and collaborative effort ensured that the façade cost and long-term performance met or exceeded the estimated façade budget and project design criteria and goals, respectively. The integrated engineering approach of both façade and structural design allowed the project team to address any proposed changes quickly and efficiently, and the project schedule was reduced by nearly a year from the original schedule established in the RFP. The building opened last year, adding a new component of modern, high-tech flare to the historic campus. ■

A model of the scrim system.

Owner Cornell University

Morphosis Architects

The building’s envelope has many interfaces of both façade materials and systems in elevation and section, re-entrant corners and the many cantilevered conditions. To facilitate the building movements with the tight façade detailing tolerances, the structural design team created specific movement drawings in plan, section and elevation of the dead load, live load, wind and seismic movements to convey our understanding of the façade system’s gravity loading points and wind-only connection points. These macro-scale views of the behavior of the structural system allowed the façade team to fine-tune and optimize the façade

OCTOBER 2015

General Contractor Welliver Architect Morphosis Architects Structural Engineer Thornton Tomasetti, Inc. Steel Team Steel Fabricator and Erector Schenectady Steel Co., Inc. Steel Detailer Lehigh Valley Technical Associates, Inc.

Changing how you think about your project

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The desire to optimize views of the New York Public Libraryâ&#x20AC;&#x2122;s back yard drove the structural system for a new Manhattan high-rise.

Park

VIEW

BY REZA FARIMANI, P.E., MICHAEL J. SQUARZINI, P.E., AND STEPHANIE WATERMAN

A NEW SKYSCRAPER is rising kitty-corner to Bryant Park, an expanse of green that serves as the back yard of the main branch of the New York Public Library. Given the location across Avenue of the Americas from the southwest corner of the park, the owners of the 30-story office building, known as 7 Bryant Park, wanted to maximize views of the green space for its occupants.

Off-Center Core The structural framing for the 475-ft-tall, 471,000-sq.-ft tower is comprised of a hybrid system consisting of perimeter steel framing and a concrete core, and steel floor framing created a column-free office space between core and perimeter columns. For this project, the view dictated the structural system. To maximize park views to the east, the core is offset to the

Reza Farimani (rfarimani@ thorntontomasetti.com) is a vice president, Michael J. Squarzini (msquarzini@thorntontomasetti. com) is managing principal and Stephanie Waterman (swaterman@ thorntontomasetti.com) is an engineer, all with Thornton Tomasetti.

SEPTEMBER 2015

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The northeast corner of the building.

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The building is oriented to optimize its views of Bryant Square Park. Bolted connection assemblies.

west side of the floor plate, and all floors above grade have a view of the park. The design includes office levels above grade plus a mechanical penthouse, retail spaces and a lobby at the ground floor and two floors below grade for amenities and MEP spaces. The upper levels were typically designed for office occupancy, though a few upper floors are designed for higher live loads should future occupancies require additional loading capacity. The typical floor framing system consists of wide-flange steel beams and girders with a composite concrete slab on metal deck. At the podium levels, the floor beams span 62 ft from the core to the spandrel girders. Embed plates were provided in the shear walls to support the steel floor beams framing to the walls. At level 10, the east façade sets back and exposes an outdoor terrace. To keep the columnfree space above this level, 5-ft-deep built-up

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Thornton Tomasetti

Below-grade framing. The building is adjacent and connects to a subway station.

Thornton Tomasetti

Modern STEEL CONSTRUCTION

At the podium levels, the floor beams span 62 ft from the core to the spandrel girders.

The 471,000-sq.-ft building is 30 stories high.

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Thornton Tomasetti

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Thornton Tomasetti

Looking down at the Avenue of the Americas.

transfer girders were designed to transfer 20 floors above this level. One of the iconic aspects of this project is the curtain wall at northeast corner facing Bryant Park, which slopes to create an hourglass-shaped façade. To create this form, four sloping columns (ranging from W14x132 at the roof to W14x550 at the base of the building) at the northeast corner of the building—two sloping columns above level 10 and two below level 10—were used, and all of these columns induce lateral kicks at level 10. To transfer these kicks to the core, steel horizontal bracing was introduced at the level 10 diaphragm that had the maximum diaphragm forces. The core was designed to provide lateral and torsional resistance and stiffness of the building for wind and seismic forces. The core, consisting of shear wall in the orthogonal direction, also transfers the gravity loads of the structure and its own weight, which helps reduce the uplift forces. The 2-ft-thick concrete core wall was constructed using a jumped form system ahead of the steel-framed floors. The concrete was poured eight levels above the steel erection. Staged analysis was performed to predict the core deformation during the construction and lifespan, and the results of this analysis, along with periodic surveying, were used for erection of the steel and curtain wall within specification tolerances.

made of two long cantilevered steel plate girders off the second level-framing; both girders were tapered to satisfy the architectural cladding shape. The wide-flange “spokes” of the canopy were also tapered for architectural cladding, and the connecting members are HSS. The exposed quarter of the disc uses curved members while the cladded portion employs straight members with curved plates attached. Two challenges of erecting such a large disc lay in the construction sequences and tolerances. The contractor, Turner, opted to erect the disc after completion of structure, which varied from the original design’s construction sequence. Originally, the disc was to be erected at the same time as the second-floor steel. To accommodate this change, a new analysis was performed to include the deflection at the second level caused by the weight of the second-floor slab as well as the column shortening due to the load of 30 stories above. Connections of the disc to the base structure were modified to accommodate the construction sequence. Additionally, by erecting the disc later, the curtain wall at the second level was installed; therefore, staging analysis with deflection prediction of the cantilevers from the second level had to be completed.

Flying Saucer A striking entrance canopy at the northeast corner of the building resembles a flying disc and is located directly below the hourglass façade. The disc is 48 ft in diameter and cantilevers 51 ft off the second-level spandrel beams. A quarter of the disc is exposed steel and detailed as architecturally exposed structural steel (AESS). The disc is

Down Under The site is bordered by 40th Street to the north, the Sixth Avenue subway line to the east, 39th Street to the south and the Springs Mills Building to the west. There is a subway stop at the corner of 39 Street and 6th Avenue, and a new tunnel was constructed to connect this station to the building through lower level 1. The subgrade condition includes two types of rock capac-

SEPTEMBER 2015

The tower is comprised of perimeter steel framing and a concrete core.

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To maximize park views to the east, the core is set to the west side of the floor plan.

Thornton Tomasetti

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Thornton Tomasetti

The “flying saucer” canopy at the main entrance.

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The conic shape of the curtain wall at northeast corner facing Bryant Park slopes to create an hourglass-shaped façade.

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The entrance canopy disc is 48 ft in diameter and cantilevers 51 ft from the second-level spandrel beams.

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To keep the column-free space above level 10, 5-ft-deep built-up transfer girders were designed to transfer 20 floors above this level.

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Photos this page: Thornton Tomasetti

Divider beams between the elevator shafts.

ity: 40 tsf and 20 tsf. Therefore, spread footings were typically adequate to be used as the foundation. One challenge of the substructure was the proximity of the existing subway tunnel to the building property line along the east border of the project. The foundations along the east side of the building required drilled mini-pile supports that extend below and bear on the Sixth Avenue subway influence line. The basement excavation and foundation supports were coordinated such that underpinning of the adjacent building foundation was not required. To avoid underpinning, the adjacent building foundation (a tangent pile system) was used on northwest site of the lot, and the core is supported on a mat foundation with tension tie-downs as required. Fabricator and erector W&W|AFCO Steel performed the steel detailing and also designed the secondary framing connections for the project, while Thornton Tomasetti designed the main connections and modeled them in Tekla. Since electronic submission of construction documents in BIM form is not yet industry standard, traditional PDF drawings were also submitted. The Tekla model was translated through in-house software to a Revit Model, which was used for design team coordination. Both the Revit and Tekla models were used in BIM 34

SEPTEMBER 2015

360 Glue by Turner for contract administration coordination between the subcontractors. The building’s core and shell were completed earlier this year, and the framing system uses approximately 3,500 tons of steel. Bank of China took ownership of the building in April, and fit-out is currently in the design phase. ■ Owner Bank of China Developer Hines General Contractor Turner Construction Company Architect Pei Cobb Freed and Partner Architects, LLP Structural Engineer Thornton Tomasetti Steel Fabricator, Erector and Detailer W&W|AFCO Steel

An 11-story cube of shimmering glass will soon float over the streets of downtown Los Angeles—and it isn’t a Hollywood special effect.

The Elevated

CUBE

BY MARK SARKISIAN, S.E., P.E., ERIC LONG, S.E., P.E., ANDREW KREBS, S.E., P.E., AND ALESSANDRO BEGHINI, S.E., P.E.

Mark Sarkisian is a partner, Eric Long is associate director, Andrew Krebs is an associate and Alessandro Beghini is an associate, all with Skidmore, Owings and Merrill, LLP, in San Francisco.

OCTOBER 2015

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The 633,000-sq.-ft facility, scheduled to open next July, appears to float over its surroundings in downtown L.A. thanks to a lack of ground-level perimeter columns.

Skidmore, Owings & Merrill, LLP

Clark Construction Group

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A cross-section view of the building’s framing.

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Skidmore, Owings & Merrill, LLP

A temporary shoring column being removed.

Skidmore, Owings & Merrill, LLP

THE CONCEPT OF “FLOATING” isn’t typical of courthouses. The norm for such facilities is to project authority while staying rooted in the foundations of justice. But the new United States Courthouse in Los Angeles, currently under construction, takes a different approach. Developed in close collaboration with the Clark Construction Group, the design concept for the 633,000-sq.-ft facility, scheduled to open next July, is based on a novel idea of elevating the building above a large civic plaza by removing all vulnerable ground-level perimeter columns and supporting the entire structure on hardened-concrete shear wall cores. Since none of the perimeter columns extend to the ground level, the exterior loads are support by a frame designed for redundancy around the entire building perimeter. The open plaza area provides greater standoff (an additional 33 ft) from the Modern STEEL CONSTRUCTION

Optimization Iterations

Skidmore, Owings & Merrill, LLP

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Overlay of Optimal Michell Truss

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The top row illustrates several iterations of a topology optimization study. Based on the results, it is possible to infer an optimal truss geometry (bottom right). There is a resemblance of the optimization results with the optimal layout proposed by Michell for the problem of a single point load supported by a simply supported truss in a half space (bottom left). The nearly complete truss.

neighboring streets and allows the cube to stand clear as an object. The core assemblies are designed to act as organizing elements for stairs and mechanical rooms and correspond directly to the organization of the floor layout. These cores provided excellent opportunities to support the building and provide lateral stiffness from the foundations through the entire height. The shear wall cores are linked with 16 steel buckling restrained braces (half with a capacity of 2,000 kips and half with 1,500 kips), manufactured by CoreBrace, to not only provide greater lateral load resistance but also provide greater long-term resiliency, given that the braces can be replaced if required following a major seismic event. The core elements also provide support for a three-dimensional steel truss system at the roof level that supports the vertical loads beyond the cores. This allows the outer 33 ft of the building to be supported from the truss above and also lets the cubic massing appear as a singular form, hovering above the plaza. The trusses are designed with a innovative concept that is based on optimization principles. The final geometric form is similar to a bicycle wheel and resulted in material savings of over 15% when compared to the most efficient conventional trusses. The Structural System The approximately 240-ft-tall courthouse, which contains 24 courtrooms and 32 judges’ chambers, is square in plan, with dimensions of 222 ft by 222 ft, and the typical floor-to-floor height is 20 ft. The lateral system consists of four primary reinforced concrete shear wall cores, with additional shear walls in the north-south direction. The shear walls use vertical W12x40 to W12x87 sections in the boundary zones as longitudinal reinforcement, which allowed the steel framed floors to be erected ahead of concrete pouring during construction. The shear wall cores extend from foundation to roof and are interconnected with ductile reinforced 38

Final Truss with Optimized Overlay

OCTOBER 2015

Clark Construction Group

coupling beams at openings required for doorways and corridors. The gravity framing system consists typically of conventional 3-in. metal deck topped with 3¼-in.-thick lightweight concrete supported by conventional steel wide-flange beams. The steel floor framing members span to the steel columns embedded in the concrete shear walls within the center portion of the building and to steel columns at the perimeter of the building. These perimeter steel columns, 24 in all, are suspended from 12 onestory-deep structural steel trusses at the roof, one at each end of each truss. The truss system is comprised of wide-flange sections and cantilevers from the internal reinforced concrete shear walls out to the perimeter steel columns. The roof trusses extend through the interior of the plan and act as coupling elements between the reinforced concrete shear walls, and BRBs are used for the diagonal truss members between shear walls. Herrick provided 24 42-in.-diameter by 48-ft-long temporary steel columns, which were used in compression to assist in construction and were removed upon completion of superstructure construction. These were located on top of the basement slab, penetrated through the Level 1 concrete podium slab and extended up to the underside of each perimeter column, which began at Level 2. Each corner of the building is completely column-free, with a cantilever of more than 30 ft in each direction. These cantilevered corners were accomplished using a “layered” cantilevered beam framing approach that was used to control displacements

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Column-free cantilevered corner framing.

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Skidmore, Owings & Merrill, LLP

The linking truss: induced double curvature deformation (left) and inﬂuence in weak axis (X) drift (right).

Skidmore, Owings & Merrill, LLP

while minimizing the steel needed. Temporary angles were used during steel erection to support the cantilever corners to hold the steel at the proper elevation until the final moment welds could be made. The Bicycle Wheel One of the project’s most significant design challenges involved the gravity loads from the perimeter columns needing to be carried back to the reinforced concrete core elements through a steel roof truss system. The overall depth and configuration of the roof truss members was critical to optimizing the steel weight given the strength and deflection requirements. The roof truss member configuration was inspired by the results of the topology optimization and evaluated for efficiency using Maxwell’s Theorem of Load Paths. This theorem is at the foundation of Michell’s early 20th century work on frames of least weight, also known as Michell trusses. These truss systems represent the stiffest layouts for the least amount of material in a continuum and were chosen for the roof trusses on the courthouse due to the high floor-to-floor elevations, as well as for their ability to coordinate well with the MEP layout. (See the previous page for an illustration of the iterations that led to the final truss design.)

Skidmore, Owings & Merrill, LLP

Story Elevation (ft)

Story Drift Ratio Under Seismic Action

DRIFT Y NO BRBs

DRIFT X NO BRBs

DRIFT X WITH BRBs

CODE LIMIT

Another challenge was the interface between the truss steel and the reinforcing steel inside of the core walls, in terms of fitting everything inside the walls and working around the large member sizes. Tekla was used to model the steel and Altair HyperWorks was used to model the rebar, which assisted with identifying areas where they clashed and the subsequent finalization of the reinforcing steel details. The Linking Trusses Yet another challenge was that the layouts of the shear wall core elements were best suited as rectangles given the organization of the floor program. This led to a “weak” direction and a “strong” direction. In the weak direction (north-south), behavior was identified that exceeded the allowable story drift. But rather than a conventional optimization process of increasing wall thicknesses, the idea to use the roof truss as a “mega” coupling beam at the top story was explored and incorporated in the design. The introduction of linking diagonals produced a change in the lateral mode of deformation in the weak direction, from the single curvature cantilever typical of shear wall buildings to a double curvature mode of deformation more typical of an outrigger system. With the coupled system, lateral drifts were satisModern STEEL CONSTRUCTION

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Skidmore, Owings & Merrill, LLP

A BRB-to-column connection drawing.

factory and contained slightly over 1.0%, and as a consequence, the structure became strength-controlled rather than stiffnesscontrolled. Fabricator Herrick Steel assisted SOM in the final detailing of the truss connections and node joint configuration, providing iterative comments in working sessions to provide the most economical and efficient joints. BRBs were the most efficient elements for the coupling system. As they are not intended to be the main energy dissipating mechanism, the linking braces are designed to remain essentially elastic under the elastic demands produced for the design earthquake. The BRBs were erected in sequence with the structural steel framing. However, only the top pin in each BRB was installed at that time. To ensure that minimal dead loads were carried by the BRBs, the hole for the bottom pin was bored through the gusset plate in the field, and all welding was completed after the concrete was completed through the roof level.

moval process; SOM provided the design parameters and expected deflections while Herrick and steel erection consultant Hassett Engineering developed the temporary column sizes, support connections, jacking scheme and temporary column removal plan. The transfer of compression in the temporary shoring columns was facilitated by a jacking system in the basement, which allowed for the removal of 2 in. of steel shims from under the temporary shoring columns. Nonlinear staged construction analyses were performed using ETABS 2013, and deflections at critical stages were tabulated. Relative elastic deflection between the perimeter columns and the core walls was studied at each level in combination with creep and shrinkage analyses. Corrections in floor elevations at the perimeter locations were determined for construction, with the perimeter cantilever poured to thickness, and the slab between the core walls poured to design elevation. ■ Owner United States General Services Administration

From Compression to Tension In order to shorten the construction schedule, a bottom-up procedure was followed by temporarily shoring the perimeter columns until the roof truss was built; more than 400 chevron braces were installed and removed as the concrete floors were poured. Building the reinforced concrete walls from ground to roof first, then erecting the roof trusses, erecting the floor framing below and pouring the slab on metal decks would have more than doubled the schedule for the superstructure and increased the cost of construction beyond feasibility. Early collaboration between SOM, Clark Construction Group, Herrick and the concrete contractor was critical to the success of this sequencing and the development of the re-

Design-Build Contractor Clark Construction Group

OCTOBER 2015

Architect and Structural Engineer Skidmore, Owings and Merrill, LLP Erection Consultant Hassett Engineering Steel Team Fabricator and Erector The Herrick Corporation (AISC Member/Certiﬁed) Detailer SNC Engineering, Inc.

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A simple skylight retrofit in a Manhattan high-rise becomes a complete roof overhaul.

TOP Heavy BY MARCO SHMERYKOWSKY, P.E., AND ANDREW STEINKUEHLER

IF YOU HAD TO sum this high-rise alteration project up to someone outside of the AEC industry, you’d tell them it was a basic skylight installation. If you were trying to impress your industry friends, maybe you’d add that the project took place in a centuryold, 18-story office building on Fifth Avenue in Manhattan. But most historic high-rises are constantly being altered or renovated, whether for a new tenant or an owner looking to make their building more appealing to potential renters. And anyway, it’s just a skylight installation. You put in a 25-ft by 8-ft skylight, make a few structural modifications here and there to increase architectural head room and available floor space, and you’ve got a much more appealing location for potential tenants. Easy, right? Actually, no. The project ended up needing an entirely new structural support system, and the design team at Shmerykowsky Consulting Engineers was also tasked with increasing the head room below existing roof trusses and maximizing overall floor space—a difficult task considering that the simplest way to do the former (posting down to the floor below) would get in the way of accomplishing the latter. Not so simple after all. 42

OCTOBER 2015

Existing Space The project took place on the building’s 18th floor, below the roof level. The central roof structure consists of a standard pitched roof with the main ridge spanning in the east-west direction, and the “hips” of the roof are located on the east and west ends of the main ridge. The structure consists of a metal roof deck spanning between W8 purlins, and the purlins for the main roof span between two roughly 39-ft-long trusses supported on building columns; the original trusses had a depth of 6 ft at mid-span. The roof hips connect to the main ridge purlins approximately 7 ft away from the main trusses, and the support for this connection point is created by the cantilevering of the ridge beam past trusses. At some point during the life of the building, three dormers were added to the original sloped roof area. The original structure consisted of cinder-crete slabs, shallow beams and posts down to the floor below, and the main framing bay between building columns was approximately 26 ft wide. Within each of these bays, the original purlins were located 8 ft, 9 in. on center.

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The central roof structure consists of a standard pitched roof with the main ridge spanning in the east-west direction, and the “hips” of the roof are located on the east and west ends of the main ridge. The structure consists of a metal roof deck spanning between W8 purlins, and the purlins for the main roof span between two roughly 39-ft-long trusses supported on building columns; the original trusses had a depth of 6 ft at mid-span.

Making Space Now for the fun stuff! Shmerykowsky was tasked with maximizing floor space on the 18th floor, and the designers felt that they could accomplish this by creating more column-/post-free open space along the floor’s south side. The aforementioned dormers had increased the headroom along the south side of the floor when they were originally installed, but the previous alteration left the supporting posts in place. After examining the existing purlin members in the field, the team determined that the members were too shallow to support roof loads while simultaneously covering the distance between the base of the roof and the roof ridge in a single span. Field investigation revealed that there was an additional existing post at the purlin’s mid-span buried within a concrete masonry unit (CMU) wall running the perimeter of the floor. Since the new framing for the new dormer roofs was bearing on the existing purlins, a two-part modification was required. First, a

Marco Shmerykowsky is a principal and Andrew Steinkuehler is a drafter and marketing assistant, both with Shmerykowsky Consulting Engineers. You can contact the authors via their ﬁrm’s website, www.sce-engineers.com.

Modern STEEL CONSTRUCTION

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new girder was installed in each dormer bay spanning between building columns. Next, a new “horizontal” purlin was installed parallel to the roof deck between the mid-span post and the new east-west girder. All of this work required that the existing roof structure was temporarily shored so that the existing purlins could be removed and the new steel could be added. Once the new steel was installed, the new load path essentially replicated the original load path. With goal one—opening up additional floor space—achieved, the team now had to figure out a way to increase headroom. We opted to replace each existing truss with two shallower trusses on either side. Each of these trusses spanned 39 ft, 3 in., with a depth of 5 ft at mid-span, and were constructed with HSS6×3 chords and HSS3×3 vertical and diagonal members. These truss pairs would be supported on brackets attached to the sides of the existing columns.

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At some point during the life of the building, three dormers were added to the original sloped roof area. The original structure consisted of cinder-crete slabs, shallow beams and posts down to the floor below, and the main framing bay between building columns was approximately 26 ft wide. Within each of these bays, the original purlins were located 8 ft, 9 in. on center.

The skylight also required an additional support structure that would work as an independent framing system and would be located above the roof deck surface. A box frame constructed of HSS12×8 and HSS12×4 members was developed by the engineers and arranged so that the new frame would bear on a total of eight support posts, which were coordinated with the roof purlins below.

The structural design also had to account for the fact that new tenants in the space might choose to treat the new trusses as architecturally exposed structural steel (AESS) rather than cladding it or installing a drop ceiling. The team felt that hollow structural sections (HSS) would lend the new trusses a cleaner, more aesthetically-pleasing profile (a truss made up of angles would need to be connected via bolted connections, which would both decrease available headroom and lack the streamlined look of a welded HSS truss). The installation process posed its own challenges. Luckily, the top floor was unoccupied and a freight elevator made removing existing steel and bringing up new members possible. As the new trusses were being installed, the design team had to be sure to prevent deflections in the existing roof structure. Therefore, the contractor was instructed to preload the trusses by jacking both ends of each truss pair for a predeterModern STEEL CONSTRUCTION

An exterior view of the 25-ft by 8-ft skylight.

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mined amount. Once the new truss pairs were preloaded and connected, the original trusses were removed. Finally, to engage the new truss sets as a single structural unit, connecting members were added at each panel point between the trusses.

The structural team decided to support the roof hips with new ridge beams that would span between existing building columns, which were conveniently located at the center of each roof hip’s base as well as at the center of each exterior truss.

A New Opening Then there was the skylight itself. The primary challenge in creating the new skylight opening stemmed from the fact that the roof hips were supported by cantilevered purlins. Before the skylight opening could be cut, a new support structure for the roof hips would need to be in place. For a number of reasons, particularly the need to maximize available floor space, the new support structure could not introduce any new posts or columns. That meant that the new structure would have been fully integrated into the existing roof steel. After careful consideration, the structural team decided to support the roof hips with new ridge beams. These ridge beams would span between existing building columns that were conveniently located at the center of each roof hip’s base as well as at the center of each exterior truss; the new beams were simply supported. The skylight also required an additional support structure that would work as an independent framing system and would be located above the roof deck surface. A box frame constructed of HSS12×8 and HSS12×4 members was developed by the engineers and arranged so that the new frame would bear on a total of eight support posts, which were coordinated with the roof purlins below. Small spans of deck there originally spanned to the ridge purlins were re-supported by ledge angles as required. The project resulted in a handsome new space, complete with new AESS trusses and more room and sunlight for the build■ ing’s tenants. General Contractor Henry Restoration, Ltd. Architect Janko Rasic Architecture Structural Engineer Shmerykowsky Consulting Engineers

OCTOBER 2015

CAMPUS Connector BY MICHAEL C. GRYNIUK, P.E.

All images this spread: EYP

Boston College’s newest residence hall brings the school’s two campuses together in a modern, geometric space. THE 2150 COMMONWEALTH Avenue residence hall will bring Boston College students together in more ways than one. Situated on the corner of Commonwealth Avenue and St. Thomas More Rd. in Brighton, Mass., the new residence hall will be ideally positioned as a gateway between the school’s Chestnut Hill and Brighton campuses. A large portion will be located adjacent to Commonwealth Ave., the main transportation corridor through both campuses, giving the building a significant presence from every direction. The facility will house 490 beds in apartment-style rooms, seminar spaces, music practice rooms and University Health Services. To provide space for the new facility, the school demolished an existing structure containing administrative offices. The façade is composed of glass, brick and ashlar granite and is highlighted by pointed roof features and all-glass corner study lounges intended to glow at night. 48

OCTOBER 2015

Building Bars The five-story building is relatively large in plan and the project architect, EYP, Inc., broke it into three distinct, structurally independent geometric portions called bars—east, north and south. Each bar contains residential units on each side of a central corridor as well as a combination of lounges and meeting spaces for study and collaboration. The northeast corner of the building includes distinct double-height spaces and more common areas for meeting and circulation. To further break up the bars into distinct pieces, a connecting “gasket” was strategically placed and clad with a glass curtain wall from the ground to the roof and offers views on each side of this central connector. Specific residential units have bay spaces that project out from the main plane of the building facade and offer 180° views. Although a number of structural systems were considered during the conceptual design phase, steel was chosen because

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The five-story building is broken up into three structurally independent portions.

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BC’s newest building will house 490 beds in apartment-style rooms, seminar spaces, music practice rooms and the University Health Services Center. To provide space for the new facility, the school demolished an existing structure containing administrative offices.

it offered the most flexibility in the face of certain constraints; initial studies of CMU block and plank and concrete flat plate construction proved to have limitations that did not suit this project. One area in particular was the signature double-height spaces that were offset vertically at every other level of the northeast corner. The offset nature and inconsistent shape of the floor openings would have made it nearly impossible to align solid bearing walls to support the openings. In addition, since all of the mechanicals were fed vertically from the mechanical attic, a significant number of slab openings would have been required. Framing the openings with steel, on the other hand, was relatively straightforward. To work with the tight floor-tofloor requirements of the project, the use of lightweight concrete deck composite with steel floor beams and cambered beams allowed us to limit the typical floor framing to W14 beams for 35-ft spans. Where beams conflicted with mechanical ducts, beam-web penetrations were installed— and since they were coordinated ahead of time, all these penetrations were shop fabricated, thus keeping the rela-

tive cost low. And by keeping the typical floor framing to W14s, a constant ceiling height was achieved without the need to add soffits around framing. Finally, the relatively light nature of the steel framing enabled us to keep the seismic forces and impact to the foundations at a minimum.

Michael Gryniuk (mgryniuk@ lemessurier.com) is an associate with LeMessurier in Boston.

Modern STEEL CONSTRUCTION

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A significant number of columns from the typical residential units above did not align with allowable locations below and required further coordination and study with the architect. This led to the need for four column transfers, all on W14 beams, to work with the tight floor-to-floor requirements.

LeMessurier

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The residential unit layout for the building consistently located the beds on back-to-back demising walls along the exterior walls, which severely limited the locations of the columns along the outer column lines to spans on the order of 29 ft.

Columnar Concerns Another structural challenge throughout the project was locating interior and exterior columns. The total out-to-out dimension between exterior column lines is 57 ft, 4 in., which, given the tight floor-to-floor requirements and the need for lateral bracing elements in the longitudinal direction, required at least one line of interior columns. The decision on the column number and arrangement was driven by both the interior architecture of the room and door layout as well as an effort to limit the number of pieces and foundation elements required. The door arrangement of the apartment-style rooms is relatively inconsistent throughout and is exclusively offset from doors on the other side of the corridor. As such, a decision was made to use one side of the corridor as the column line and coordinate the bracing elements between door elements. The exterior column locations presented another challenge with the residential rooms. The residential unit layout for the building consistently located the beds on back-to-back demising walls along the exterior walls, which severely limited the locations of the columns along the outer column lines to spans 50

OCTOBER 2015

on the order of 29 ft. Normally, that column span is modest, but the façade system of brick and granite was relatively heavy and sensitive to floor movements under live loads, thus requiring relatively robust W14 beams. This situation was the leading factor in the decision to locate a brick relief at each floor instead of the fairly typical scheme of having a relief at every two floors. A Different Plan A significant amount of coordination was required at the University Health Services area, which is located at the lowest level of the south bar and whose floor plan is completely different from that of the residential units above. Thus, a significant number of columns from the typical residential units above did not align with allowable locations below and required further coordination and study with the architect. This led to the need for four column transfers, all on W14 beams, to work with the tight floor-to-floor requirements. The lateral force resisting system is made of concentrically braced frames one each side of the corridor linked together with a moment frame. Linking the two frames together allowed

➤

One of pointed roof sections on paper and in the field.

➤ LeMessurier

LeMessurier

➤

Some of the residential units have bay spaces that project out from the main plane of the building façade and offer 180° views. LeMessurier

LeMessurier

the unbraced corridor space to become part of the lateral system, using compact W14 beams, and increased the overturning capacity. The approach was to first lay out the bracing assuming that each bar was a separate building, then link them together through the diaphragm. The architecture was such that several columns were not aligned from one spandrel to the other, so in some cases the link beam was skewed to maintain the additional lateral capacity. Early on in the project, the thought was to eliminate expansion joints as they added complex architectural joint details, which came with the need for long-term maintenance of the joint itself. In conjunction with that was the fact that decks on the northeast corner have a number of large openings that vary in size and location at each of the five levels. As such, the team designed the north bar and the south bar to stabilize the northeast corner of the east bar. Additional slab diaphragm steel was included in the concrete deck to ensure adequate shear transfer as well as mitigate any cracking due to building movements. Speaking of movement, move-in is scheduled for next summer and BC’s newest residence hall will open in time for the

2016 academic year and provide the school with more and bet■ ter residential space for the next group of students. Owner Boston College Construction Manager Bond Brothers Architect EYP, Inc. Structural Engineer LeMessurier

Modern STEEL CONSTRUCTION

UL Design Considerations Using UL Designs for fire protection with today’s steel design codes. BY CHARLES J. CARTER, S.E., P.E., PH.D., FARID ALFAWAKHIRI, P.ENG., PH.D., AND LARRY S. MUIR, P.E.

RECENTLY, AISC AND AISI received several inquiries related to Monokote Fireproofing Bulletins that representatives of W.R. Grace are distributing. The bulletins in question concern load restrictions on structural steel beams in Underwriters Laboratories (UL) Designs. The prevailing sentiment in these inquiries seems to be that nobody understands what these bulletins mean, nor do they know what they need to do as a result of them. UL usually tests their assemblies using beams that are loaded to the full design flexural strength of the beam used in the test. Before 2005—and even after that, depending upon the wishes of their client—UL often has used 1989 ASD (or earlier) design criteria to determine the beam test loading. Because modern structural steel design criteria recognize higher flexural strength, beams designed using LRFD or post-2005 ASD equations for beam design may experience higher loads than those assumed in some UL test assemblies, unless something other than flexural strength (deflection, for example) controls the design. This difference is the crux of the issue when discussing load restrictions related to UL Designs for beams. UL Canada has implemented load restrictions for several years. In the U.S., however, the confusion occurs primarily because UL has not provided clear load restriction guidelines applicable to the U.S. marketplace. The recent W.R. Grace bulletins do not seem to provide clear guidelines either—they just state that the Canadian load restrictions now apply to UL Designs in the U.S. Unfortunately, this is not a solution. Rather than settling the matter and bringing clarity, the W.R. Grace bulletins have been distributed in the absence of appropriate UL guidelines, thereby adding confusion. Neither the bulletins nor the UL guidelines provide any solution or clarification as to how to apply load restrictions in the U.S. This article attempts to clarify the matter and provide solutions. 52

OCTOBER 2015

Some Background UL fire-resistance tests and the resulting UL Designs usually are sponsored by the manufacturers of proprietary fire protection materials, such as spray-applied fire-resistive materials (SFRM) and intumescent coatings. AISC and the steel industry usually have no involvement in the development of these UL Designs and the associated tests. Ultimately, UL and the sponsors of the UL Designs determine the structural loads used in the associated fire-resistance tests. While they follow the AISC Specification to determine the test loads, they do not always use the latest edition of the Specification and they do not always update their designs for the higher loads permitted by modern structural design codes and standards. Recognizing this, AISC and the American Iron and Steel Institute (AISI) have been working with UL to facilitate the update of UL Designs. In addition to conducting tests at modern load levels to create new UL Designs using current design methods, AISC and AISI also funded a series of UL beam tests with varying levels of beam loading. We did the latter so that UL would have the data they need to update existing old UL Designs to current loading levels. Our test program at UL is ongoing. Some results have already been made available in UL Design No. D982, which was publicized previously in Modern Steel (see “Restrained or Unrestrained?” in the September 2013 issue at www.modernsteel.com). Although this reference is more focused on clarifying the restrained vs. unrestrained confusion, the article is an applicable reference for the load restriction question because we used modern loading calculations that work for both LRFD and ASD. There are other UL Designs that are based upon modern loading levels. More on that later, but first…

Photos: Farid Alfawakhiri

How Can You Tell If Your UL Design Is Old or Modern? UL provides subtle distinctions in the language that introduces each UL design. Generally, for older designs, the language used is: “This design was evaluated using a load design method other than the Limit States Design Method (e.g., Working Stress Design Method). For jurisdictions employing the Limit States Design Method, such as Canada, a load restriction factor shall be used—See Guide BXUV or BXUV7.” Generally, for modern designs the language used is: “Loading Determined by Allowable Stress Design Method or Load and Resistance Factor Design Method published by the American Institute of Steel Construction, or in accordance with the relevant Limit State Design provisions of Part 4 of the National Building Code of Canada.” Variations on the above statements do occur in some UL De-

signs. Nonetheless, as one example, a specifier would know that our UL Design No. D982 is “modern” because it is prefaced by the modern language indicating loads were calculated using modern methods. The UL Guides BXUV or BXUV7 referenced in the language for older designs are related to ANSI/UL 263 and CAN/ ULC-S101M, respectively. Both documents address load restriction, but do so using only terms consistent with Canadian codes and design methodologies; “Limit States Design” is Canadian terminology for LRFD. Thus, this language relates primarily to the Canadian marketplace, avoids the terms common in the U.S. marketplace and is not tied to any specific edition of the Specification. It also remains unclear how the listed load restriction factors were derived. As a result, we are unsure whether the load restriction factors of 0.88 listed for the “non-composite steel beam” and 0.71 listed for the “composite steel beam” are appropriate in the context of U.S. standards.

Charles J. Carter (carter@aisc.org) is a vice president and chief structural engineer with AISC. Farid Alfawakhiri (falfawakhiri@steel.org) is senior engineer, Construction Codes and Standards, with the American Iron and Steel Institute. Larry S. Muir (muir@aisc.org) is director of technical assistance with AISC’s Steel Solutions Center.

Modern STEEL CONSTRUCTION

What Can You Do Now? There are at least two solutions that you can use today. First, you can use a UL (or adapted ULC) Design that is not load restricted. If it is desired to maintain the usual relationship where the architect is responsible for fire protection and the structural engineer has little to no involvement, this solution clearly is preferable. Several unrestricted UL and ULC Designs for beams are shown in Table 1. Table 1. Unrestricted UL and ULC Designs For W-Shape Beams

For Specialty Beam Products

UL Designs

G592, D798, D982, D985, N743, N852, N860 and S750

N858, N904, N905 and N906

ULC Designs

D501, F906, F912 and N815

O710, N900, N901 and N902

View these and other UL Designs at www.ul.com/ﬁrewizard.

Alternatively, you can use an older UL Design and choose to apply the UL load restriction factors (LRF) to ensure the bending moment due to gravity loads does not exceed: LRF ×

Mn for ASD, or 1.67

LRF × 0.9Mn for LRFD If you choose this option, you are essentially accepting a U.S. adaptation of the reduced loading levels in restricted ULC Designs. This assumes that the same restrictions ULC provides for Canada can be used in the U.S. despite difference between Canadian and U.S. codes. Note also that the second option is not as clean because it may require the structural engineer to do work beyond the normal scope of structural design services. Nonetheless, it is common for deflection and other serviceability criteria to already have limited the design moment, and this option can work without resulting in any design changes. What Else Can We Do? The answer to this question is not yet known. As of the time of writing of this article, AISC and AISI have a September meeting scheduled with UL. Updated information will be posted with this article at www.aisc.org/ULclarity. ■ 54

OCTOBER 2015

www.aisc.org/nightschool Class begins September 21, 2015

AISC

Night School Seismic Design Manual and Applications of the 2010 AISC Seismic Provisions Presented by Thomas A. Sabol, S.E., Ph.D.

Monday nights 7:00 p.m. Eastern Time (90 minutes each) This 8-session course will: • Explore the 2010 AISC Seismic Provisions and Second Edition Seismic Design Manual • Present key provisions and commonly misapplied provisions • Present selected examples from the Seismic Design Manual

There’s always a solution in steel. American Institute of Steel Construction One E Wacker Drive, Suite 700 Chicago, IL 60601 www.aisc.org 312.670.2400

Exploring new collapse prevention systems for seismic events.

Still STANDING BY JOHNN P. JUDD, P.E., PH.D., AND FINLEY A. CHARNEY, P.E., PH.D. S43MRI a SMCE a 1/1 Seattle 12% Boston 3.8%

1/1.5

New York 2.2% 1/2.5

1/4

1/6

1/10

1/15

1/40

1/63

1/100

San Francisco 18%

Charleston 0.5% Los Angeles 12%

â&#x17E;¤

1/25

Figure 1. Ratio of 43-year MRI spectral acceleration (Ss) compared to maximum considered earthquake (MCE) ground motion.

Johnn P. Judd (johnnjudd@gmail.com) is an assistant professor in the Department of Civil and Architectural Engineering at the University of Wyoming. Finley A. Charney (fcharney@vt.edu) is a professor in the Department of Civil and Environmental Engineering at Virginia Tech.

OCTOBER 2015

Memphis 1.7%

NOT ALL SEISMIC ZONES are created equal. Ground shaking and spectral acceleration conditions vary significantly between the central and eastern U.S. and the west (see Figure 1 for an example). Yet lateral force resisting systems tend to be designed in essentially the same manner throughout the country. However, the concept of designing lateral force resisting systems for regional differences in seismic accelerations is gaining some traction. A new kind of seismic force resisting system called a collapse prevention system (CPS) is being developed for implementation in the central and eastern U.S. The system consists of a collapse prevention mechanism working in tandem with the primary steel moment frame and engages the steel gravity framing system to delay or prevent collapse. Where enhanced performance is needed, the collapse prevention mechanism may be augmented with energy dissipation devices.

➤

Collapse risk less than 1% in 50 years Moment Frame (MF) MF+Gravity Frame (GF) MF+GF+Slack Cables (SC)

a. Two-story building

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Figure 3. Collapse safety of a steel moment-frame building employing collapse prevention system.

with a steel deck and concrete slab system are partially restrained and inherently have lateral stiffness and strength (Liu and Astaneh-Asl, 2000). In new construction, using slab steel can be a cost-effective way to increase strength, stiffness and robustness. The lateral strength in a typical shear tab connection is small compared to an equivalent fully restrained connection (on the order of 10% to 30%, for example), but it can be significant in the aggregate, depending on quantity of gravity connections in the building (Judd and Charney, 2015). The effect of gravity columns is also important. Continuous columns and columns with moment-resisting splice connections, for example, considerably reduce drift concentrations in steel moment frame buildings (Flores and Charney, 2014). A variety of designs can be considered for the collapse prevention mechanism. The simplest mechanism consists of a pair of slack cables or loose linkages (Figure 2a, previous page) that provide no significant increase in stiffness or resistance until the main building system deformation reaches some limit—e.g., 2% inter-story drift. At that point, the cable or linkage becomes taut and engages with the reserve strength in lateral and gravity framing to prevent or delay collapse. An important aspect of theses mechanisms is their size. The mechanism can be configured to be compact and unobtrusive and, in some cases, they could reasonably fit in the ceiling space. Since the compactness of the mechanisms limits their capacity, they would likely be distributed throughout the building.

b. Eight-story building

OCTOBER 2015

A more complex collapse prevention mechanism can be formed using a telescoping brace (Figure 2b, previous page). In this mechanism, two steel tubes telescope over each other and can elongate without resistance until a “stop” mechanism causes the brace to go into tension. The brace cannot carry compression. This type of telescoping brace is an adaptation of the hybrid passive energy dissipation device described in Marshall and Charney (2012). Of course, compared to the quantity of slack cables and loose linkages, fewer telescoping braces would be deployed in a building. Strength on Reserve We’ve put the system to the test (Judd and Charney, 2014), and preliminary results indicate that reserve lateral strength provided by the gravity framing is a significant factor in the success of the collapse prevention system. In most of the buildings we studied, the reserve lateral strength significantly reduced the probability of collapse. For example, CPS with half of the connections for gravity (shear tab) and half for lateral (directly welded flange steel moment frames not specifically detailed for seismic resistance, or R=3) passed the FEMA P-695 criteria (probability of collapse less than 10% given MCE ground motions) up to the minimum of Seismic Design Category (SDC) D. CPS using steel moment frames were adequate for many regions in the central and eastern U.S. (Figure 3), and improved collapse safety was predicted for CPS using special steel moment frames.

The CPS concept is equally relevant—and perhaps more attractive—for repairing and retrofitting existing buildings. An important advantage in using CPS for rehabilitation (compared to a traditional retrofit) is that collapse prevention mechanisms can be deployed into the gravity system and don’t need to be part of the main lateral load resisting system. A related advantage is that the CPS concept has less reliance on added deformation capacity, a key factor in older construction. Research is still in the early stages, and essential aspects related to the design and behavior of CPS need to be addressed before implementation. Looking forward to the next stage of our research, we are planning to flesh out the details on the proposed collapse prevention mechanisms and their connecting elements. We’ll investigate the demands imposed on the gravity framing (such as increased base shear forces) as well as conduct experimental testing of collapse prevention mechanisms. ■ The work described in this article was supported by the National Institute for Standards and Technology (NIST) under grant No. 60ANB10D107. References 1. Liu, J., and Astaneh-Asl, A., 2000. “Cyclic testing of simple connections including effects of slab.” Journal of Structural Engineering; Vol. 126, No. 1, pp. 32–39. 2. Judd J.P., Charney F.A. “Resilience of steel moment-frame buildings with reserve lateral strength.” Proceedings, 15th US-Japan Workshop on the Improvement of Structural Engineering and Resiliency 2015; December 3–5, Kohala Coast, Hawaii. 3. Flores F.X., Charney F.A, Lopez-Garcia D. “Influence of the gravity framing system on the collapse performance of special steel moment frames.” Journal of Constructional Steel Research 2014; Vol. 101, pp. 351–62. 4. Marshall J.D., Charney F.A. “Seismic response of steel frame structures with hybrid passive control systems.” Earthquake Engineering and Structural Dynamics 2012; Vol 41, No. 4, pp. 715–733. 5. Judd J.P., Charney F.A. “Seismic collapse prevention systems.” Proceedings, 10th National Conference on Earthquake Engineering (NCEE) 2014; July 21–25, Anchorage, Alaska.

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news CONTINUING EDUCATION

Achieve Higher Quality in High-Density Residential with AISC’s New CEU Course AISC is offering a new continuing education article, “Achieving Higher Quality in High-Density Residential: the Strengths of Structural Steel,” available at Architectural Record’s online Continuing Education Center and originally published in the August issue of Architectural Record. Designed for architects, the course covers how to maximize space, versatility and quality in mid-rise and high-rise apartments and condominiums using structural steel. After reading the article, you’ll be able to:

➤ Compare the advantages of structural

steel framing to other building materials ➤ Explore system concepts that allow the architect greater flexibility in programming and designing apartments and condominiums ➤ Determine economical design methods ➤ Analyze faster methods of construction by using structural steel framing You can also earn 1.00 HSW (Health, Safety and Welfare) credit by completing the online quiz. Go to tinyurl.com/ aiscarceu to read the CEU article and take the online quiz.

WELDING

New Edition of AWS Structural Steel Welding Code Now Available A revised edition of the American Welding Society’s Structural Welding Code—Steel (AWS D1.1/D1.1M:2015) is now available. The new edition, which supersedes the 2010 edition, spells out the requirements for design, procedure/performance qualification, fabrication, inspection and repair of steel structures made of tube, plate and structural shapes that are subject to either static or cyclic loading. In addition to editorial changes in the text and commentary, this edition in-

cludes a reorganization of tubular clauses, tables and figures previously located throughout the code into a new “Tubular Structures” clause. A corresponding new section of commentary is also included. This 646-page publication is the joint effort of the D1 Committee on Structural Welding and its D1Q Subcommittee on Steel. It is available for purchase in hard copy or pdf download at go.aws. org/2015D1. The price is $411 for AWS members and $548 for nonmembers.

BRIDGES

Purdue Releases New Bridge Inspection and Repair Guidance Purdue University has released a new report titled Fatigue and Fracture Library for the Inspection, Evaluation, and Repair of Vehicular Steel Bridges. This free document is intended to provide engineers and inspectors with technical guidance regarding evaluation, repair and retrofit procedures for both common as well as nonstandard, noncompliant or failed

People and Firms • Walter P Moore’s Board of Directors has elected senior principal Lee Slade, P.E., a 39-year veteran of the firm and a key member of the executive leadership team since 1993, as the structural engineering firm’s fourth Chairman of the Board. In his new role, Lee will work closely with new president and CEO Dilip Choudhuri, P.E., to continue to expand the firm’s service offerings and geographic reach. Former Chairman and CEO Ray Messer, P.E., will continue to play a key role at WPM, leading the firm’s strategic initiatives in the designb u i l d m a rket, and Lee will maintain his position as executive director of the firm’s largest operating group, Structures. Slade • Two veterans of structural and civil engineering firm JQ have relocated to support future growth of the firm. Thomas L. Scott, P.E., moved from the Fort Worth office to lead the Austin office as partner and principal, and Carlo N. Taddei, P.E., moved from Dallas to lead the Fort Worth office as principal.

details encountered on steel bridge structures. The report also contains supplemental videos that further illustrate certain topics, such as Charpy impact tests and dealing with brittle fracture. The document is available for free download as a PDF or e-book at docs.lib. purdue.edu/sbritereports/1/. Scott

OCTOBER 2015

Taddei

news SCHOLARSHIPS

AISC Student Members Win Tau Beta Pi Engineering Scholarship Four AISC student members have won a Tau Beta Pi scholarship for undergraduate study during the 2015-16 academic year. James A. Hillegas of the University of Akron, Ohio, Andrew J. Plucinsky of Rowan University, Glassboro, N.J., Timothy H. Sabins of the University of South Carolina, Columbia, and Seth W. Strelow of Valparaiso University, Ind., are among the 261 scholars selected by the engineering honor society from more than 800 applicants. Most scholarship winners will receive a cash award of $2,000 for their senior

year of engineering study, and a few will receive $1,000 for one semester. The society will award $513,000 in scholarships total. All Tau Beta Pi Scholarships are awarded on the competitive criteria of high scholarship, campus leadership and service, and

IN MEMORIAM

Safety Expert Henry Mykich Dies at 60 Henry J. Mykich, director of safety for the American Bridge Company in Coraopolis, Pa., passed away on August 22 of complications from lung surgery. He was 60 years old. Mykich was well respected in his field and served as American Bridge’s representative to the Ironworker Employers Association of Western Pennsylvania, Inc., the Iron Workers International and Ironworker Management Progressive Action Cooperative Trust (IMPACT) Safety Committee, the Steel Erection Negotiating Rule Making Committee (which developed the Fall Protection Standard for OSHA) and the Association Of Union Constructors (TAUC) Safety Committee.

promise of future contributions to the engineering profession. All scholars are members of Tau Beta Pi. View all of this year’s scholarship winners and learn more about the scholarship program at www.tbp.org/ scholarships.cfm.

A former member of the Pittsburgh Ski Club and an avid Pittsburgh Steelers, Penguins and Pirates fan, Mykich was a proud resident of Pittsburgh and was also a passionate reader, sharing his favorite books with family and friends. He is survived by his wife, Denise.

John Correnti, EAF Innovator, Dies at 68 John Correnti, 68, CEO of Big River Steel and the driver behind a $1.3 billion steel mill project currently under construction in Arkansas, passed away on August 18. After beginning his career at U.S. Steel, he moved to Nucor Steel, where he helped usher in the era of electric arc furnaces and fostered other innovations while rising through the ranks to become first president and then CEO.

PROJECTS

PennFab Puts Amtrak Back on Track This past spring, Amtrak’s Northeast Regional train from Washington, D.C., to New York City derailed on the Northeast Corridor in Philadelphia. The disaster left eight dead, 200 injured and millions of Americans without their daily Amtrak service. Following the crash, the agency needed two new catenary portal structures, the tall steel structures that hold the overhead wires above rail lines, at

Frankford Junction to get its Northeast Corridor service operational again; each one requires about 15 tons of steel. Typically, they take at least six weeks to create. PennFab (an AISC Member and AISC Certified fabricator), based in Bensalem, Pa., just minutes away from the disaster, stepped up to build and erect the catenary structures in a mere 36 hours. “We knew hundreds of thousands

of people’s livelihoods are on those trains,” said Mike Mabin Sr., owner of PennFab. “We literally didn’t have a second to spare.” Read the story at www.philly.com. In addition, Peddinghaus (also an AISC Member) has created a video illustrating how PennFab worked to process the catenary structures needed for Amtrak to restore service. Watch the video at tinyurl.com/pennfabpedd. Modern STEEL CONSTRUCTION

news CONSTRUCTION MARKET

Construction Spending Grows at Fastest Pace Since 2006 Total U.S. construction spending in June recorded the highest year-over-year growth rate since 2006, according to the Associated General Contractors of America. However, AGC officials cautioned that those spending gains could be at risk unless all levels of government strengthen programs to develop the construction workforce. â&#x20AC;&#x153;Spending rose strongly in June from a year ago for all major construction categoriesâ&#x20AC;&#x201D;private nonresidential, residential and public,â&#x20AC;? said Ken Simonson, AGCâ&#x20AC;&#x2122;s chief economist. â&#x20AC;&#x153;Although the initial estimate for June showed minimal growth from May, totals for May and April were revised upward by large amounts.â&#x20AC;? Construction spending in June totaled $1.065 trillion at a seasonally adjusted annual rate, 12% higher than in June 2014, Simonson said. He noted that

the year-over-year growth rate was the strongest since March 2014, indicating a faster pace of construction spending overall. The June total was the highest level since July 2008 and was 0.1% higher than the May total following an upward revision of $28 billion in that figure. â&#x20AC;&#x153;Several of the private categories have risen especially fast,â&#x20AC;? Simonson added. â&#x20AC;&#x153;Whether they can keep growing depends in part on companies being able to find enough skilled workers, a problem many contractors are already facing.â&#x20AC;? He cited as areas for which worker shortages could be troublesome: the oneyear increases of 62% in manufacturing construction spending, 48% in amusement and recreation construction, 42% in lodging construction, 27% in private office construction and 24% in private multifamily construction.

â&#x20AC;&#x153;It is clear that construction is rebounding but the progress may stall unless there is a concerted effort at all levels of government to provide training to get new workers into high-paying construction careers,â&#x20AC;? commented Stephen E. Sandherr, the associationâ&#x20AC;&#x2122;s chief executive officer. â&#x20AC;&#x153;It would be a lost opportunity for the economy if firms canâ&#x20AC;&#x2122;t take advantage of growing demand for work because of a lack of qualified workers.â&#x20AC;? Association officials urge federal, state and local officials to implement the steps listed in the associationâ&#x20AC;&#x2122;s Workforce Development Plan. Those measures, which include expanding career and technical education opportunities, making it easier for firms to establish regional training programs and immigration reform, are designed to make it easier to recruit and prepare new construction workers.

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OCTOBER 2015

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WE INVITE YOU TO SUBMIT ENTRIES TO THE 2016

PRIZE BRIDGE COMPETITION SUBMISSION Requirements and entry form available at:

www.steelbridges.org/PrizeBridge DEADLINE FOR ENTRIES

DECEMBER 14, 2015 Winners will be notiﬁed shortly after judging and we will make a public announcement of the winners in Modern Steel Construction magazine. Designers of the winning Prize Bridge entries will be presented with plaques and honored during the World Steel Bridge Symposium. Owners of the winning Prize Bridge entries will be presented with plaques and honored at a dinner banquet during the 2016 AASHTO Subcommittee on Bridges and Structures.

ELIGIBILITY All award-winning bridges are built of fabricated structural steel and are located in the United States (deﬁned as the 50 states, the District of Columbia, and all U.S. territories.) Eligible bridges must have been completed and opened to trafﬁc between May 1, 2013 and September 30, 2015.

JUDGING CRITERIA An independent panel will judge entries on the following criteria: innovation, aesthetics, value, design and engineering solutions. Quality of submitted presentations, though not a criterion, is important. Entries may be judged in more than one category, but an entry can only receive one award.

AWARD CATEGORIES

Major Span – One or more spans greater than or equal to 400 ft. Long Span – Longest span equal to or greater than 250 ft but less than 400 ft. Medium Span – Longest span equal to or greater than 140 ft but less than 250 ft. Short Span – No single span greater than 140 ft. Movable Span Reconstructed – Having undergone major reconstruction, rehabilitation or widening NSBA will offer special recognition to one project that best exempliﬁes Accelerated Bridge Construction, and one project that best exempliﬁes a full range of Sustainable attributes.

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Contract Auditor Quality Management Company, LLC is seeking contractors to conduct audits for the AISC Certiﬁed Fabricator and AISC Certiﬁed Erector Programs. Contractors must have knowledge of quality management practices as well as knowledge of audit principles, practices and techniques and knowledge of the steel construction industry. If you are interested, please submit your statement of interest contractor@qmconline.org.

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Looking for something from an old issue of Modern Steel?

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LATE MODEL STRUCTURAL STEEL FABRICATING EQUIPMENT

AISC Continuing Education Seminars www.aisc.org/seminars 64

Ficep 2004 DTT CNC Drilling & Thermal Coping Line, 78-3/4” x 24” Max. Beam, 3-Drill, Ficep Arianna CNC Control, 2003 #20382 Controlled Automation ABL-100-B CNC Flat Bar Detail Line, 143 Ton Punch, 400 Ton Single Cut Shear, 40’ Infeed, 1999 #24216 Controlled Automation 2AT-175 CNC Plate Punch, 175 Ton, 30” x 60” Travel, 1-1/2” Max. Plate, PC CNC, 1996 #23503 Peddinghaus F1170B CNC Plate Punching Machine, 170 Ton, Ext Tables, Fagor CNC, 30” x 60” Trvl., Triple Gag Head, 2005 #19659 Peddinghaus FPB1500-3E CNC Plate Punch with Plasma, 177 Ton, Fagor 8025 CNC, 60” Max. Width, 1-1/4” Plate, 1999 #25161 Controlled Automation BT1-1433 CNC Oxy/Plasma Cutting System, 14’ x 33’, Oxy, (2) Hy-Def 200 Amp Plasma, 2002 #20654 Peddinghaus Ocean Avenger II 1000/1B CNC Beam Drill Line, 40” Max. Beam, 60’ Table, Siemens CNC, 2006 #25539 Visit www.PrestigeEquipment.com for our inventory & services Phone: 631.249.5566 | Fax: 631.249.9494 | sales@prestigeequipment.com To advertise, call 231.228.2274 or e-mail gurthet@modernsteel.com.

OCTOBER 2015

Search employment ads online at www.modernsteel.com.

Structural Engineers

Are you looking for a new and exciting opportunity in 2015? We are a niche recruiter that specializes in matching great structural engineers with unique opportunities that will help you utilize your talents and achieve your goals. • We are structural engineers by background and enjoy helping other structural engineers find their “Dream Jobs.” • We have over 30 years of experience working with structural engineers. • We will save you time in your job search and provide additional information and help during the process of finding a new job. • For Current Openings, please visit our website and select Hot Jobs. • Please call or e-mail Brian Quinn, P.E. (Brian.Quinn@FindYourEngineer.com or 616.546.9420) so we can learn more about your goals and interests. All inquiries are kept confidential. SE Impact by SE Solutions, LLC

www.FindYourEngineer.com

Advertise Your Job Openings in Modern Steel! Modern Steel employment ads also appear online!

www.modernsteel.com/jobs (Please note that these ads no longer appear at www.aisc.org.)

Contact: Lou Gurthet at 231.228.2274 or gurthet@modernsteel.com

“Like” AISC on Facebook facebook.com/AISCdotORG

Follow AISC on Twitter @AISC

employment RECRUITER IN STRUCTURAL MISCELLANEOUS STEEL FABRICATION ProCounsel, a member of AISC, can market your skills and achievements (without identifying you) to any city or state in the United States. We communicate with over 3,000 steel fabricators nationwide. The employer pays the employment fee and the interviewing and relocation expenses. If you’ve been thinking of making a change, now is the time to do it. Our target, for you, is the right job, in the right location, at the right money.

Buzz Taylor

PROCOUNSEL Toll free: 866-289-7833 or 214-741-3014 Fax: 214-741-3019 mailbox@procounsel.net

Visit steelTOOLS.org See what’s new at AISC’s revampedﬁle-sharing and Looking for something from an old issue of Modern Steel? information-sharing website. Here a few of the FREE resources now available: All of are the just issues from Modern Steel Construction’s • More than 160 steelTOOLS utilities available downloading first 50 years are now available as free PDFfordownloads • Filesatposted by your peers in special interest libraries, www.modernsteel.com/backissues. including: • A Pocket Reference to W Shapes by Depth, then Flange Width • Welding Capacity Calculator • Moments, Shears and Reactions for Continuous Bridges • Video: Bridge Erection at the SeaTac Airport Got Questions? Got Answers? Check out steelTOOLS.org.

Vice President of Finance & Administration The American Institute of Steel Construction (AISC) is looking for an experienced finance executive to join our Senior Management team and participate in the development of the strategic plans supporting our mission and goals. The Vice President of Finance and Administration reports to the President of AISC, and acts as lead spokesperson to the AISC Board of Directors for activities related to finance, business administration, and information systems. This role provides participative leadership, financial management, strategic management, and direct hands-on help for finance, accounting, information systems, facilities and risk management activities in support of AISC’s operations. To qualify, you must have a Bachelor’s degree in Finance, Accounting or Business Administration, MBA and/or CPA strongly preferred. Minimum 10 years of experience in a senior management role with responsibility for finance, accounting, facilities administration, and information systems. Please send resume, cover letter and salary expectations to hr@aisc.org for consideration. To advertise, call 231.228.2274 or e-mail gurthet@modernsteel.com.

DRAKE-WILLIAMS STEEL BUILDING VALUE NOW HIRING We are looking for Experienced Structural Steel, Estimators, Project Managers, Detailers, and Checkers. Drake-Williams Steel Offers a Comprehensive and Competitive Compensation and Benefit Plan, including but not limited to: • Employee Ownership • Quarterly Incentive Bonus • 401K • Company Paid Life and Disability Insurance • Open-Book Management • Health, Dental, and Vision Coverage To apply, go to http://www.dwsteel.com/career or send your resume to DWS_HR@DWSTEEL.COM Modern STEEL CONSTRUCTION

structurally sound

FULL HOUSE

Courtesy of Weidlinger Associates

EVER-EVOLVING LAS VEGAS

OCTOBER 2015

continues to pack ’em in. Its McCarran International Airport is now the sixth busiest in the U.S. and 15th busiest in the world. In order to keep up with the airport’s rapid increase in traffic—it currently serves nearly 40 million passengers annually—a new 350-ft air traffic control tower has been added. While the main shaft of the tower (designed by structural engineer Weidlinger Associates) was built with reinforced concrete, the upper third of the tower consists of a structural steel “bell” that houses sensitive equipment and critical support spaces, including the control cab for air traffic controllers. Site line requirements meant that only three strategically placed steel columns were permitted at the cab level. Steel beams cantilever from steel moment frames to satisfy the complex geometric requirements, support the cab roof and resist Vegas’ large earthquake and wind design loads. The moment frames transfer loads to braced frames, which are intricately placed to avoid conflicts with the extremely dense layout of cables, shafts, ducts and other specialized equipment in the floors below. Steel beams also support a tuned mass damper that minimizes windinduce vibrations and ensures that air traffic controllers are able to perform tasks comfortably. Since welds were not permitted in major structural elements, all critical connections are bolted and designed to ■ extremely tight tolerances.

AND

STRUCTURAL FABRICATORS

FORUM 2015 THE VENETIAN HOTEL, LAS VEGAS MONDAY, NOVEMBER 30

Looking to increase your odds of winning? Secure your spot at autodesk.com/fabforum

Like many others, you are already thinking about the future and how to increase your odds of winning. If you detail or fabricate structural steel and are interested to learn how Building Information Modeling will transform your business — then this event is for you. Our speaker line-up and technical classes will provide information you’ll ﬁnd hard to learn elsewhere.

MEP