Modern Steel Construction - September 2014

September 2014

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MODERN STEEL CONSTRUCTION (Volume 54, Number 9) 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.

September 2014

ON THE COVER: Marquez Hall brings a modern motif to the Colorado School of Mines in Golden, Colo., p. 22. (Photo: Nic Lehoux)

business issues 17 I’m Sorry...You Were Saying?

BY ANNE SCARLETTThoughts on adjusting your sales approach toward prospective clients with short attention spans.

columns

22 Thinning OutBY CHRISTOPHER O’HARA, P.E.,

AND JULIAN LINEHAM, P.E.Slender steel elements and expanded cantilevers define the structural system of a new building for the Colorado School of Mines.

28 Staying AfloatBY MCKAY M. PARRISH, S.E.A new convenience store keeps its head above water with an innovative structural steel framing system.

33 National TreasureBY LUCA COVIStructural renovations brace an iconic museum for the future.

41 Time TestedBY JENNIFER MCCONNELL, PH.D.,

DENNIS R. MERTZ, PH.D., AND HARRY W. SHENTON, III, PH.D.

A look at the performance of the national uncoated weathering steel bridge inventory.

46 Justice is ServedBY JASON STONEA criminal justice school blends the new with the old in an urban expansion project.

52 Piece by PieceBY MICHAEL P. CULMO, P.E.Span-by-span bridge construction, using modular steel bridge elements, can serve as a viable and economical bridge-building alternative.

56 Crossing the DelawareBY JIM TALBOTA steel truss, at the site of one of the first bridges over the Delaware River, is still standing after numerous floods and more than 100 years of life.

features

departments 6 EDITOR’S NOTE9 STEEL INTERCHANGE

12 STEEL QUIZ 60 NEWS & EVENTS 66 STRUCTURALLY SOUND

resources 64 MARKETPLACE 65 EMPLOYMENT

in every issue

22

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6 SEPTEMBER 2014

Since the section began more than two decades ago, every reader survey we’ve done ranks it as number one. Originally, the col-umn featured questions sent in by our readers, which were then answered in later editions by other readers. Staff response was sometimes to answer questions, but more often to simply vet the answers provided by readers. With the creation of the AISC Steel Solutions Center, however, the column morphed into a section where almost all of the answers were staff-generated. And today, most of the questions aren’t sent directly to the magazine; rather, the questions are taken from those submitted to the Solutions Center. Each week the AISC Steel Solutions Center responds to nearly 200 questions (that’s more than 125,000 inquiries since the SSC opened its doors in 2001). Despite this, hardly a day goes by where I don’t see a question about structural steel posed elsewhere. I’m always amazed when someone asks about the Code

of Standard Practice or has a question about composite beams and they don’t simply email [email protected]. You’ll usually get a response within one business day—and best of all, it’s free. The SSC is just one of AISC’s free re-sources. While it’s often difficult to navigate, there’s a boatful of freebies on the AISC web-site (www.aisc.org), including all of the speci-fications and codes published by AISC. The best place to start is by clicking on “ePubs and FreePubs.” Everyone can download design

examples, the shapes database, the latest issue of Engineering Journal and a lot more. We’re even converting some items that used to be available for a fee, into free resources. For example, this fall we’re planning on releasing the AISC Detailer Education Program as a free online course. We’ve also posted videos of almost every NASCC: The Steel Conference since 2008. Simply visit www.aisc.org/2008nascconline or substitute any other year for 2008 in the URL, and you can access more than 750 hours of educational video on everything from steel joists to moment connections. For those of you who are AISC members (and really, the cost is so nominal I’m always surprised when I encounter someone in the steel industry who isn’t), the freebies are even larger. Members can download copies of all of the Steel Design Guides and every article from every issue of Engineering Journal (plus they receive substantial discounts you get on continuing education and printed publications). But whether or not you’re a member, the AISC SSC is free. So if you have a question, know that AISC has an answer.

Editorial Offices1 E. Wacker Dr., Suite 700Chicago, IL 60601312.670.2400 tel

Editorial ContactsEDITOR & PUBLISHERScott L. [email protected]

SENIOR EDITORGeoff [email protected]

ASSISTANT EDITORTasha [email protected]

DIRECTOR OF PUBLISHINGAreti [email protected]

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AISC OfficersCHAIRJeffrey E. Dave, P.E.

VICE CHAIRJames G. Thompson

SECRETARY & GENERAL COUNSELDavid B. Ratterman

PRESIDENTRoger E. Ferch, P.E.

VICE PRESIDENT AND CHIEF STRUCTURAL ENGINEERCharles J. Carter, S.E., P.E., Ph.D.

VICE PRESIDENTJacques Cattan

VICE PRESIDENTJohn P. Cross, P.E.

VICE PRESIDENTScott L. Melnick

Advertising ContactAccount ManagerLouis Gurthet231.228.2274 tel231.228.7759 [email protected]

For advertising information, contact Louis Gurthet or visit www.modernsteel.com

Address Changes and Subscription Concerns312.670.5444 tel312.893.2253 [email protected]

ReprintsBetsy WhiteThe Reprint Outsource, [email protected]

editor’s note

SCOTT MELNICKEDITOR

WHAT’S YOUR FAVORITE SECTION IN MODERN STEEL CONSTRUCTION? Unless you’re one of my kids, odds are it’s Steel Interchange.

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Weld DesignationWhat do the “U” and "a" indicate in the prequalified weld type B-U4a?

The U indicates that the weld can be used with material of unlimited thickness, as opposed to an L, which would indicate that the weld is only appropriate within a range of thicknesses. AWS D1.1 states: “The lower case letters—e.g., a, b, c, etc.—are used to differentiate between joints that would otherwise have the same joint designation.” In this case there are two prequalified butt welds (B) using a single-bevel groove (4) with no limitation on thickness (U) listed in AWS D1.1. One of the listed welds uses backing (a) and the other does not (b). The “a” in your designation, “B-U4a”, indicates that backing is used.

Larry S. Muir, P.E.

Mixed Hole Sizes in Slip-Critical ConnectionsWe have designed slip-critical connections with standard holes. When the structure was erected, a few of the bolts could not be installed due to mislocated holes. Can we make the mislocated holes oversized and leave the others as standard holes? Does the strength of the connection need to be reduced due to the oversized holes?

There is nothing in the RCSC or AISC Specifications that discusses the mixing of standard and oversized holes in a slip-critical connection, so you will have to rely on your own judgment. I will provide some comments that might assist you in this process.

It is not uncommon to see slip-critical connections with oversized holes that contain a couple of standard holes to help maintain the intended geometry during erection, so the mixing of hole types is relatively common. In such cases, the entire group is designed using oversized holes, while also incorporating a couple of standard holes; this leads to a more conservative design strength. Your situation is also not uncommon, since things do not always fit the way we would like in the field. Some engineers would tend to design the entire group using the values for oversized holes, although this is likely not necessary. Though the strength provided in the Specification is less for connections with oversized holes, there is no loss of pretension or slip resistance due to the oversized holes. The lower nominal load is due to a higher factor of safety (reliability) to account for the consequences of slip. This is discussed in the Commentary to Section J3.8.

Since most of the holes in your connection are standard holes, the amount of slip that could occur prior to the bolts going into bearing would likely be small, and the higher factor of safety against slip likely is not warranted.

Carlo Lini, P.E.

DTIs Used For Preinstallation VerificationCan tension indicator washers be used in lieu of a Skidmore Wilhelm tension calibrator to perform pre-installation verification?

The answer to your question is yes, unless you are tensioning the bolts using turn-of-nut installation. This is covered in the commentary to Section 7.1 in the 2009 RCSC Specification (a free download at www.boltcouncil.org), which states:

Direct tension indicators (DTIs) may be used as tension calibrators, except in the case of turn-of-nut installation. This method is especially useful for, but not restricted to, bolts that are too short to fit into a hydraulic tension calibrator. The DTIs to be used for verification testing must first have the average gap determined for the specific level of pretension required by Table 7.1, measured to the nearest 0.001 in. This is termed the “calibrated gap.” Such measurements should be made for each lot of DTIs being used for verification testing, termed the “verification lot”…This technique cannot be used for the turn-of-nut method because the deformation of the DTI consumes a portion of the turns provided. For turn-of-nut pre-installation verification of bolts too short to fit into a hydraulic calibration device, installing the fastener assembly in a solid plate with the proper size hole and applying the required turns is adequate. No verification is required for achieved pretension to meet Table 7.1.

Carlo Lini, P.E.

Square-Cut Sloping BeamsThere are large wide-flange beams that slope with the roof pitch of ¼ in. per foot. In some instances they connect to girders and in other instances they connect to HSS col-umns. Can the beams be cut square leaving a varying dis-tance from the end of the beam to the face of the support?

Especially for heavy shapes, cutting the member square is easier than making a bevel cut. The decision on whether to bevel-cut the beam or to bevel the connection material is usually based on economics. As the bevel increases, the eccentricity on the connection increases, potentially adding to the connection cost and overriding any benefit of square-cutting the beam. In your case, the bevel adds only about ¾ in. to the usual setback; therefore, standard shear end connections likely can be used for the strength calculations. In this case, square-cutting the beam will be preferred by most fabricators, and this is acceptable from an engineering standpoint.

Bo Dowswell, P.E., Ph.D.

steel interchange

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 [email protected].

10 SEPTEMBER 2014

Special Inspection Waivers for ErectorsWe are an erector. Once AISC Certified, do we become self-inspecting as erectors?

The decision to waive third-party inspection, or Special Inspection, is the responsibility of the building official (authority having jurisdiction). As an erector, you are always responsible for the QC inspections outlined in Chapter N of the AISC Specification. The waiver of Special Inspection at the fabrication shop has become commonplace over the years, while the concept of waiver of Special Inspection at the job site is quite new (2010).

The bottom line is that Special Inspection will be required unless the building official decides otherwise. The IBC does provide the mechanism that the Building Official can use to waive Special Inspection for an approved contractor in Chapter 17, Section 1704.2.5.2.

Keith Landwehr

Special Inspections and Small ProjectsThe 2012 IBC has recently been adopted by our local government, and inspections in accordance with Chapter N of the AISC Specification are now required. I am cur-rently working on a small renovation project that did not even require the design of a lateral force resisting system. The inspections required by Chapter N seem excessive for this small project. Must all of these inspections always be performed?

IBC generally requires special inspections through reference to AISC Chapter N. However, there are at least a couple of provisions that would allow the authority having jurisdiction to waive the requirements. Waivers are often granted for approved contractors in accordance with IBC Chapter 17, Section 1704.2.5.2 (AISC Certified contractors, for example). There are also provisions in IBC that do not require special inspections for "work of a minor nature." Chapter N states that the QA shall be performed “when required by the authority having jurisdiction (AHJ), applicable building code (ABC), purchaser, owner, or engineer of record (EOR).” It does not independently mandate inspections.

Larry S. Muir, P.E.

Comparing AISC 360 Chapter J and Appendix 3 RequirementsI have four rods, threaded on one end, supporting a stair platform. The unthreaded end of the rod is welded to the upper support and the other end passes through an HSS, and a nut is installed. The AISC Specification seems to provide conflicting requirements related to the design of these rods. Table J3.2 provides a nominal tensile strength of 0.75Fu. However, Tables A-3.1 of Appendix 3 states that the threshold stress is limited to 7 ksi. Appendix 3 also bases the stress calculation on net tensile area while Chapter J neglects the reduction in area due to the

threads. When I design the rods for my 5.3-kip load using these provisions of Chapter J and Appendix 3, I get very different results. It seems that Appendix 3 would always govern, so why must the Chapter J checks be performed?

First, both Chapter J and Appendix 3 account for the reduction in area due to the threads. However, they take different approaches. Equation J3-1 refers to Table J3.2 for the nominal tensile strength. Table J3.2 provides a nominal strength of 0.75Fu. The 0.75 coefficient accounts for the reduction in area due to the threads. This is explained in the Commentary, which states: “The factor of 0.75 included in this equation accounts for the approximate ratio of the effective tension area of the threaded portion of the bolt to the area of the shank of the bolt for common sizes.”

Table J3.2 also states that the threaded rods shall conform to Section A3.5, which states: “Threads on anchor rods and threaded rods shall conform to the Unified Standard Series of ASME B18.2.6 and shall have Class 2A tolerances.” When used with the designated threads and the applicable safety factors, the 0.75 assumption provides an adequate estimate of the net tensile area, though the actual ratio of net tension area to nominal area will vary somewhat with diameter. Appendix 3 uses a more precise calculation of the net tension area.

It also has to be recognized that Chapter J and Appendix 3 are quite different requirements and apply to different conditions. The strength calculated using Chapter J should be compared to the total load on the hanger. The strength calculated using Appendix 3 only applies to the portion of the load causing fatigue. So, first you must determine if fatigue must be considered for your condition. If it must, then the net tensile stress area should be calculated as shown in Equation A-3-9. However, the 7 ksi is not compared to the total load, but rather only to the stress range. For example, the dead load of stair platform will contribute to the total load but will not contribute to the stress range. Only cyclic loads will contribute to the stress range.

Larry S. Muir, P.E.

steel interchange

Larry Muir is director of technical assistance and Carlo Lini is staff engineer–technical assistance, both with AISC. Bo Dowswell and Keith Landwehr are consultants 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 60601tel: 866.ASK.AISC • fax: [email protected]

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.

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1 For the beam shown in Figure 1, calculate the Cb value. Lateral bracing is provided at the support points only.

2 Assuming the length L in Figure 2 is long enough that lateral-torsional buckling controls, which of the following is true about the flexural strength of beam segments A? It is:

a) Equal to the flexural strength of segment B b) Greater than the flexural strength of segment B c) Less than the flexural strength of segment B

3 Given: From AISC Manual Table 3-6, the Lp value for a W18×35 beam is equal to 4.31 ft. The beam below has an unbraced length of 6 ft. True or False: The nominal flexural strength of the beam will be less than Mp = FyZx.

4 True or False: Cb values are routinely useful in the design of HSS used as beams.

This month’s Steel Quiz looks at the use of design tables in the AISC Steel Construction Manual. steel quiz

TURN TO PAGE 14 FOR ANSWERS

Figure 11.5k/ft

Lb = 30'-0"

P

L/3 L/3 L/3

P

(A) (A)(B)

Braced at Load PointsFigure 2

P

6'-0"

Braced at Load Points

6'-0" 6'-0" 6'-0"

P P

W18×35

Figure 3

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14 SEPTEMBER 2014

ANSWERSsteel quiz1 Use Specification Equation (F1-1) to determine Cb.

Note that this Cb value, and many others for common cases, are provided in AISC Manual Table 3-1.

2 b) Greater than the flexural strength of segment B. The Cb value for segments A is greater than that for segment B. Given that LTB controls the design, this is true because all other variables in AISC Specification Equation F2-2 are constant. The Cb value for each segment is shown in Figure 4 below and can be determined via the User Note in Section F1, where Cb = 1.0 for the case of equal end moments of opposite sign (uniform moment) and Cb = 1.67 when one end moment equals zero. Also, see AISC Manual Table 3-1.

3 False. Per AISC Specification Equation F2-2, the nominal flexural strength is equal to the plastic bending moment, Mp = FyZx (because of the effect of Cb). Per AISC Manual Table 3-6, Lp = 4.31ft and Lr = 12.3ft. Per AISC Manual Table 3-1, Cb = 1.11 for the two interior segments (the outer segments have a higher value of Cb). Per Table 1-1, Sx = 57.6 in.3, Zx = 66.5 in.3

Mp = FyZx = 50 ksi × 66.5in.3 = 3,330 kip – in.

=3,380 kip – in. ≤ 3,330 kip – in. =3,330 kip – in.

Therefore, the design is controlled by yielding and Mn=Mp.Note that AISC Specification Commentary Figure C-F1.2 clearly illustrates the effect Cb can have on the nominal flexural strength, Mn.

4 False. HSS beams are generally not sensitive to lateral-torsional buckling—because their torsional strength and stiffness are so high—and so their strength is governed by the yield or local buckling strength of the member. Therefore, Cb rarely impacts the design of an HSS beam.

Figure 4

M

Lb Lb Lb

1.67 1.671

w × x2

MA = MC = (L–x) = (30ft – 7.5ft) =1.5kip – ft × 7.5ft2

12.5Mmax

2.5Mmax+3MA+4MB+3MCCb = = =1.1412.5 × 169

6.5 × 169+6 × 127

w × L2 8

Mmax = MB = = = 169 kip – ft1.5kip – ft × 30ft2

8

127kip – ft

[ ] = 1.11 3,330 – (3,330 – 0.7 × 50 × 57.6) ≤6 – 4.31

12.3 – 4.31( )Mn = Cb Mp– (Mp – 0.7FySx) ≤ Mp

Lb – Lp

Lr – Lp( )[ ]

3,330kip – in.

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RECENTLY, MY FIRM RECEIVED A QUERY from a “hot prospect” through our website. Based on a series of initial conversations, I deduced that the prospect had a notably short attention span.

According to Archives of General Psychiatry and the WebMD article “ADHD in the Workplace” (by Laura J. Martin, MD), 4.4% of working adults have been formally diagnosed with ADHD, which accounts for an estimated 10-12 million profes-sionals in the American workplace. I’m not a physician and I’m certainly not diagnosing this prospect with ADHD, but merely stressing the point that short attention spans of varying degrees abound.

At any rate, in crafting my sales strategy, it made sense to adjust my approach in order to best accommodate this prospect. I decided to research adult ADHD-like symptoms. My goal was to formulate best practices around selling (and relationship building) toward professionals fitting this profile.

After conducting my research, I concluded that there was an opportunity to modify my “typical” selling approach. After all, savvy sales professionals aim to make their client look good (and feel good) in their professional role. So, I made some adjustments, with the intention of both maximizing their posi-tive skill sets and assisting in areas they might find challenging.

The first step is to leverage the potential strengths often found in professionals who exhibit ADHD-like behaviors—or at the very least, short attention spans. Those behaviors include the following:

Creative: People with ADHD-like behavior often propose ideas that may or may not seem relevant. To handle that, prepare a mini “parking lot” during the meeting. At the onset of your meeting, walk the prospect through your proposed agenda (you do prepare a meeting agenda, don’t you?) to confirm agreement. Then, let the prospect know that you’ll set aside a blank piece of paper for recording any “ideas or topics worthy of exploration at a different time.” This tactic is very useful in group meetings and can also help capture spin-off ideas, thoughts and com-ments. Later, one attendee takes responsibility for determining (or delegating) next steps for each.

In short: Explain and use the parking lot practice with appli-cable clients to record extraneous ideas.

Talkative/communicative: A forthright person is a sales per-son’s dream, right? Indeed, this behavior may enable you to learn about the prospect’s goals and challenges with minimal probing efforts. That said, you may need to maintain meeting focus on

the intended topics by succinctly summarizing them (even par-roting back their words) throughout the entire conversation.

In short: Offer mini oral summaries as you move forward in the meeting.

Curious: Perhaps one of the most beautiful things about some-one with ADHD symptoms is their innate sense of curiosity. They may ask something like “How can this be done better?” If you are new to the prospect, then the “What’s better?” attitude can work in your favor, and you will follow your personal approach toward demonstrating value and differentiating your services.

If you are an incumbent but looking to grow your business with an existing client who exhibits these behaviors, then you must realize this question may be top-of-mind for your client. How might you nip their “feeling” in the bud by either a) brain-storming together about how to handle a future project or b) walking them through the post-project outcomes to demon-strate that it was done well? How might you underscore that your firm remains the best fit for their needs?

In short: Remain acutely aware of the “What’s the next big thing?” or “What’s better?” questions. Proactively address it during conversations with the prospect or client.

On the flip side, be aware of potential challenges that pro-fessionals with symptoms of ADHD face. Do your best to help them overcome them during your sales process and beyond. Some of those challenges include:

Short attention span: As you always do while selling, take good care to engage with enthusiasm, energy and warmth. Don’t muddle your message with detail. Keep everything con-cise and be ready to switch on a dime if their eyes glaze over or they seem restless. When offering something new, highly stimulating or intriguing, then you may be able to capture—

I’M SORRY…YOU WERE SAYING?BY ANNE SCARLETT

business issuesThoughts on adjusting your sales

approach toward prospective clients

with short attention spans.

Anne Scarlett is president of Scarlett Consulting, a Chicago-based company specializing in AEC-specific strategic marketing plans, marketing audits and coaching. She is also on the adjunct faculty of Columbia College of Chicago and DePaul University. She can be contacted through her website, www.annescarlett.com.

18 SEPTEMBER 2014

business issues

and hold—their attention. Continually ask yourself if there’s a way you can reshape your message so that it feels exciting and new to them.

In short: Deliver with energy, omit the details and empha-size what’s “new.”

Diffi culty staying on track and sticking to time commit-ments: If you want to make sure the meeting starts on time, make it easy by going to them. Meet in their offi ces, if pos-sible. Once you’ve launched the meeting, try visibly checking off items on the agenda as you go through them. This will give everyone a sense of progress and accomplishment throughout the meeting.

In short: Give the overall sense that things are moving along.Fidgety, often wants to

move around: Business devel-opers within the AEC industry love when a prospect wants to experience our projects fi rst-hand through a site visit. This might be just the type of per-son who would be willing to trek to the site for a tour. (Ide-ally, you will provide trans-port.) Try offering this early in your sales cycle.

In short: Arrange a site visit, suggest a walk-and-talk after your meetings or take a “stretch our legs” coffee break.

Frustrated with their lack of focus: It can be maddening for an adult to strive for career success while tackling their ADHD symptoms. Whenever possible during your sales pro-cess, try to subtly demonstrate empathy. Examples might be

“Wouldn’t you know it? I completely spaced out at a meeting I had last week.” Or “Boy, I sure am having trouble getting through my action items list for this project.” Whatever you can (honestly) share about yourself that gives them the sense that they are not alone will be appreciated. After all, many of us experience these symptoms. (A personal example: It took me a long time to write this piece; I have acquiesced to many distractions).

In short: Relate to them by sharing your own relevant challenges.

Experience challenges when reviewing detailed written work: Streamline any written documentation, and present con-tent in bullet format. Tighten the language in your fee propos-als and, if at all possible, orally walk through them through the proposal.

In short: Keep. It. Short.Disorganized: Since these folks are often “organization-

ally challenged,” make sure any experiences they have with

you appear well organized. Ideally, they will associate you with organization.

To do this in a sales meeting, start off by helping them get organized by providing a brief list of what they should bring to the meeting. This can be done in your email confi rma-tion. Perhaps they need to bring a calendar, business cards, other colleagues, specifi c documentation about their poten-tial project, budget numbers, etc. Also, be very organized yourself when you are conducting the meeting. Present your materials in an even more organized manner than you might otherwise. (One example: Put materials about their project in a three-ring binder with labeled tabs. This radiates a level of competency, and a “we can handle this for you” spirit.)

In short: Demonstrate your own über-organized skills.

Procrastinate: As with any prospective client, you always want to agree upon a “next step.” In these cases, you may want to reiterate scheduled steps/com-mitments more than once (i.e., orally during the meeting, recap at the close of the meeting and in a follow-up email). Also, try to keep the next steps as close together as possible. While this

is certainly a goal in every sales process, there might be ways to shave off a day here or a day there to help the procrastinator to feel the sense of urgency that he/she might actually thrive within.

In short: Strive to keep the process tight. Express emotion that may seem intense, short-fused

or irrational for the workplace. Help guide them back to a rational, calm and professional state of mind (but try not to squelch any positive passion or personal investment). Suggest win-win alternatives whenever possible. If the discussion is going south with no signs of immediate recovery, then pro-pose a break for 15 minutes before reconvening. This might be more likely to happen if you are up-selling to an existing client rather than working through the sales process with a prospective client.

In short: Aim for win-win; demonstrate a calm, professional demeanor; suggest a break.

These are the adjustments that I’ve used with the prospec-tive client I mentioned earlier. So far, I have managed to get to know her better through a series of fairly successful “touches.” I feel optimistic about turning her company into a client.

To reiterate, I am a complete novice when it comes to adult ADHD. If any of you readers have advice and comments from your experiences in similar situations, I would enthusiastically welcome your feedback. ■

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22 SEPTEMBER 2014

Slender steel elements and expanded cantilevers

define the structural system of a new building for the Colorado School of Mines.

BUILDINGS CAN EXHIBIT not only progress and expansion, but also a shift in focus.

Marquez Hall, a new 87,000-sq.-ft facility for the Petroleum Engi-neering Department at the Colorado School of Mines in Golden, Colo., was designed to reflect the country’s energy shift from petroleum to renewables. The building, designed by the Seattle office of Bohlin Cywinski Jackson in partnership with Denver-based Anderson Mason Dale Architects, reinforces the school’s vision for the future by looking to the user, the campus and community to achieve an aesthetic reflec-tive of the school’s nationally recognized engineering programs and in-novative applied science research. The structural steel framing system, featuring long cantilevers and architecturally exposed steel, was chosen to help achieve a dynamic vision for the building and address the basic structural need of supporting gravity and lateral loads (total steel used, including miscellaneous, was 773 tons). Vibration requirements for the laboratories contained within also required a high degree of sensitivity.

Thinning OUT

BY CHRISTOPHER O’HARA, P.E., AND JULIAN LINEHAM, P.E.

Christopher O’Hara ([email protected]) is a cofounder, principal and façade director, and Julian Lineham ([email protected]) is a cofounder and principal, both with Studio NYL Structural Engineers in Boulder, Colo.


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Steel fins in the lobby.

The west elevation of Marquez Hall.

Box girder-to-column construction.

Two overriding themes can be found throughout the design of the building’s structure: the varied use of cantilevers (for vi-sual effect in some areas and to develop efficiencies of mate-rial and cost savings in others) and the use of slender elements throughout the primary structure and cladding systems.

In terms of layout, two parallel, linear programmatic bars, as well as a wing to the southeast, allow users to easily understand and navigate the facility’s varied program of public, semi-public and private spaces. Functionally, the building forms one edge of the pedestrian walkway that connects the campus’ two main quadrangles, thus opening its interior spaces to the area’s ex-traordinary Front Range mountain views. Its L-shaped plan di-vides the building into two bars while defining a new courtyard featuring custom seating to encourage interaction. The north-ern bar houses a combination of graduate and undergraduate laboratories, a 4D visualization classroom and a drilling simula-

tor room. The southern bar holds offices and laboratory sup-port spaces, and the southeastern wing includes a lecture hall as well as four levels of smart classrooms and seminar rooms.

CantileversOn the southeastern wing, full-story cantilevered trusses

take their cues from staggered truss concepts and are recon-figured to create a cost-effective 20-ft cantilever for the third and fourth levels. Diagonal ties applied in the cavity inside the solid walls—similar to a cable-stayed bridge—suspend the building’s extension over the campus quad below. While this feature provides refuge for people entering and exiting the building and a sense of closure to the end of the quad, the driv-ing force for this design move was cost savings, as providing ad-ditional foundations and traditional columns would have been more expensive than the diagonal framing. Additionally, the

Nic Lehoux

Nic Lehoux

Kari Rogne

building is supported on deep-drilled pier foundations because of the area’s poor soils, and the structure of the surrounding floor plates is arranged to bear on the backspan of the story-high trusses, thus eliminating the possibility of a net uplift on columns and foundations.

The laboratories of the northern wing, separated from campus offices by a primary circulation corridor, have been designed to strict laboratory vibration criteria through the use of steel composite beams and gird-ers. The structural framing is oriented to minimize footfall-induced and corridor vibrations from being transmitted into the laboratories. Beams within the labo-ratory run north-south, while the remain-ing beams span east-west, parallel to and independent of the laboratories’ girders. The girders feature a double-cantilevered design to help maintain deflection criteria in the presence of shallower beams that permit significant mechanical duct runs to cross the girder line.

SlendernessAlong the south façade of the northern

bar is the building’s primary entry point from the quad. Because the design team was not satisfied with the cost and finish quality of intumescent paint for application on the heavily loaded south-side columns, a solution beyond a fireproofed, wrapped column was pursued. This lead the team to investigate and discover fire-rated compos-ite columns (as per Appendix 4 of ANSI/AISC 360-05), allowing the architects to use a high-quality Tnemec paint, eliminate column covers and avoid a costly solution known for its inferior finish.

The use of slender steel elements was most notable in areas outside of the primary structure. While plate stringer stairs are quite common and are used throughout Marquez Hall, the feature stair joining the west lobby with the laboratory and office bars of the building took it a step further. Here the balustrade and stringer are all one element with ½-in.-thick by 48-in.-deep plates spanning more than 40 ft. Fabricator Zimkor used software to locate the center of gravity so it could design and locate lifting lugs that could be rigged to lift the stair at its installed pitch. Shipping bracing incorporated in the lifting lugs braced the

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Tekla models of the structure.

24 SEPTEMBER 2014

LVTA


stair sides to avoid bending them during hoisting. The balustrades around the stair opening are constructed using ½-in.-thick plates cantilevered from the floor structure. The steel was left natural with a simple oiled finish (and sealed) to make it clear that all of the slender elements are indeed raw steel.

Slender CantileversThe main feature of the building, the

west lobby, is at the end of the northern wing. It serves as a focal point and assem-bly space for entertaining potential donors. This transparent exhibition and lobby space marks a potent position on the cam-pus’s main thoroughfare and serves as the building’s main entrance. Since the lobby is primarily glass, a long roof extension was required to shade it from the region’s plen-tiful sunlight. To solve this from a struc-tural standpoint, glazed glass walls hang from a 60-ft cantilevered roof via a pair of tapered box girders that extend out from the east side of the lobby.

Because the at-grade perspectives do not permit an angle sufficient to see the roof’s slope, the tapered girders main-tain a flat bottom flange with a sloped top flange to create the illusion of a thin structure. To help maintain the cantilever, the building’s mass is oriented to bear on a story-high truss at the end of the canti-lever’s backspan. This significant mass acts as ballast for Colorado’s snow loads, and the harsh 116-mph wind speeds prevalent along Colorado’s Rocky Mountain Front Range. The girders and their supporting columns vary in depth from 24-in. at the tip to 84 in. deep at the column girder intersection, and 12-in.-deep steel beams spring from them to extend the cantilever a bit further. Finally, the perimeter gutter system truncates down to just 6 in. using angle ribs with gage thickness plate to form the gutter.

To achieve the architect’s goal of a trans-parent façade while maintaining a respon-sible budget, a structural steel fin system was used to support the façade. The fins replace the traditional aluminum mullion and steel wind girt system that would typi-cally be required for this 30-ft span under the building’s wind loads. By hanging the system and directly mounting the double-insulated glass panels to the structure, the

➤The west façade of the lobby.

Nic Lehoux

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fins are essentially prestressed to feel as though they are in ten-sion. The system does not have any horizontal steel members. The localized load due to seismic loading on the weak axis of the fin is resisted using the glass panels as “shear walls.” The

fins vary in depth but are only ½ in. thick. Structural steel bear-ing plates extend from the fins to eliminate the need for costly point-fixed glazing solutions, and the glass adheres to the fins laterally with structural silicone.

➤ Steel sunshades on the south end of the building.

➤ Looking in at the steel fins.➤ The facility uses 773 tons of steel in all.

Nic LehouxZimkor

St. Louis Screw & Bolt2000 Access Blvd Madison, IL 62060

Phone: 800-237-7059 Fax: 314-389-7510Email: [email protected]

Web: www.stlouisscrewbolt.com

Nic Lehoux


Getting it DoneThe Marquez Hall project required an extremely aggressive

schedule, which would not have been possible without close inte-gration of the design and construction teams. Revit models were confi gured with tight tolerances for cuts on exposed elements, and 3D connection elements, where critical to the design intent, were exported to the fabricator and lead detailer through an .ifc format for inclusion in the Tekla model. With an accurate Revit model, direct import into Tekla was possible, which saved critical time and decreased the possibility of misinterpretation, allowing the detailing team to meet the tight schedule.

The construction team proactively conducted meetings on-site with the design team to prereview shop drawings, discuss erection strategies for the intricate elements of the west lobby and perform coordination reviews with other trades, such as HVAC, through general contractor Adolphson and Peterson Construction’s Navisworks model. Due to the size and weight of the box girders, fi eld splices and erection were a challenge, thus two shoring towers were erected and all splices were ar-ranged with temporary bolt splices to facilitate fi eld welds. As the system was primarily governed by defl ection, all welds were confi gured to use only fi llet and partial penetration welds, and precise splice locations were determined by truck-ing limitations. The street layout in this area of the campus is quite tight, so the team needed to verify that the chosen box girder fi eld splice locations would yield shipping lengths that wouldn’t cause turning problems (and Zimkor also needed to

verify that it had the hoisting capacity to lift each shipping piece in the shop).

Whether it was an exposed feature such as sunshades, fa-çade fi ns, stairs or fi re-rated columns, or hidden elements such as the story-high trusses of the southeastern wing/bar or tapered box girders of the west lobby, the agile capabilities of structural steel—along with the design and construction team’s ingenuity—created a beautiful building that not only expands the school’s capabilities, but also signals progress in terms of energy use. ■

General ContractorAdolphson and Peterson, Aurora, Colo.

Design ArchitectBohlin Cywinski Jackson, Seattle

Architect of RecordAnderson Mason Dale, Denver

Structural EngineerStudio NYL Structural Engineers, Boulder, Colo.

Steel Team

FabricatorZimkor, Littleton, Colo. (AISC Member/AISC Certifi ed Fabricator)

DetailerLehigh Valley Technical Associates, Northampton, Pa. (AISC Member)

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28 SEPTEMBER 2014

A new convenience store

keeps its head above water with an innovative structural steel framing system.

HEADING DOWN to the corner store for a gallon of milk is a bit of a different experience at Lake Powell’s Wahweap Marina.

That’s because the store floats. Situated between the marina’s docks and houseboats, the 6,655-sq.-ft building—which houses the Wahweap Marina Store, a restaurant and office space—is supported by a 10,144-sq.-ft floating platform. The structure is topped with a 1,425-sq.-ft covered deck on the second floor that allows visitors to relax and drink in their surroundings.

The facility has been designed to accommodate the constant-ly changing water level of the lake (Wahweap Marina is located toward the south end of the lake, just south of the Arizona-Utah border near the beginning of the Grand Canyon). The floata-tion portion of the structure consists of wide-flange and HSS

McKay Parrish ([email protected]) is a project structural engineer with ARW Engineers.

Staying AFLOATBY MCKAY M. PARRISH, S.E.

beams that are designed as a truss system to evenly distribute loads throughout the platform. This “T” shaped floatation system is approximately 8 ft deep in the middle section and 5 ft deep in the side sections. The side walls and bottom of the floatation’s structural hull are covered with ¼-in. and 5∕16-in. steel plates and angles, and the top of the flotation structure consists of a sloping 7½-in. suspended concrete slab on metal deck. The lower section of the hull houses all of the mechani-cal equipment and also doubles as a storage room. The upper structure consists of exposed HSS beams and battered columns that project away from the building and provide the lower deck with shade. The upper patio area is constructed with a 4½-in. suspended concrete slab on metal deck with a covered steel roof

system above, and wood-sheathed steel stud shear walls provide lateral resistance for wind and wave loads.

The battered columns consist of HSS8×8×3∕16 sections that extend from the lower deck to the upper canopy roof. The architectural design pushed for an exposed structure, so the HSS8×8 columns around the perimeter of the building are off-set from the exterior shear walls to show off these beams and columns. The four columns supporting the upper deck and roof canopy are designed as cantilevered columns that are braced at the low roof; they cantilever to the high roof to avoid the use of bracing that could have obstructed views from the upper deck. All roof framing members consists of exposed HSS beams that range in size from HSS12×4 members to HSS16×8 members.

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The 6,655-sq.-ft building houses the Wahweap Marina Store, a restaurant and office space.

The floatation portion of the structure consists of wide-flange beams and HSS that are designed as a truss system to evenly distribute loads through-out the platform.

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Aramark Aramark

Aramark

Aramark

Most of the lower hull float framing consists of continuous W8×18 or W8×24 beams that are full-pen welded at the joints. The traditional and Vierendeel truss configurations used in the hull consist of W8 beams that form the top and bottom chords, with HSS4×4 and HSS5×5 posts at approximately 8 ft on center and matching diagonal HSS members where needed. The truss systems occur at approximately 6 ft on center and are designed to align directly beneath the column locations so that the truss system can be used to evenly distribute the structures loads.

Launching a BuildingAs the structural engineer, ARW Engineers’ role went be-

yond the typical goal of providing practical and economic structural solutions to satisfy the owner’s and architect’s overall vision for the project. They were also tasked with providing so-lutions for including fluctuating water levels, determining con-struction sequencing of the float system with launching and bal-lasting restrictions, designing deeper hull sections in the lower float structure for better accessibility to storage and mechanical units and integrating exposed beams with cantilevered decks.

Typical building projects begin with geotechnical reports and foundations designed to mitigate any potential settlement in the structure. But the Wahweap Marina Store is anything but typical. Instead of ordering geotechnical reports and determin-ing seismic loads, the project team and owner focused on work-ing together to determine how they could best move the build-ing during construction so it could be launched into the water.

One unique aspect of this building system is the trusses in the hull section. Unlike structures built on soil with indepen-dent footings supporting individual columns, the truss mem-bers were designed to carry multiple columns and act together with adjacent trusses to distribute loads evenly over the built-up plates below; this allowed the localized “settlement” beneath each individual column to be minimized. The structure is de-signed to accommodate a fluctuation in the storage dead loads and live loads each day; as buoyancy pressure beneath the truss system increases as water depth increases, the pressure used to analyze the truss system changes as well. The upper level build-ings loads are not equally distributed over the structural float, and this requires a ballasting system to keep the building from tipping toward the entrance where the structure is heaviest due to the second-level framing.

The decision of how the floatation platform and upper structure would be built and launched played a vital role in this process. The marina is located in a remote part of Lake Powell that is surrounded by cliffs. The boat launch ramps are the only access to the waterfront, and clogging up the boat ramps during the summer months was not an option. Consequently, differ-ent methods of constructing the floatation system off-site were discussed and after reviewing the additional time and material required to construct the float in sections, it was decided that a portion of the parking lot and one of the ramps would be dedicated to the accelerated construction of the facility during the winter.

30 SEPTEMBER 2014

➤ The store floats on Lake Powell’s Wahweap Marina in northern Arizona, near the eastern end of the Grand Canyon.

➤This “T” shaped floatation system is approximately 8 ft deep in the middle section and 5 ft deep in the side sections. The side walls and bottom of the floatation’s structural hull is covered with ¼-in. and 5∕16-in. steel plates and angles.

ARW Engineers


Once the steel-encased floatation system was built and launched, the middle 8-ft-deep storage section was so buoy-ant without the steel and concrete structure above that it liter-ally supported the side sections and suspended them above the water. The contractor was directed to fill the deeper float sec-tion with water so that the suspended W-2 deck and concrete topping could be poured without causing damage to the truss members. The suspended concrete floor was poured in such a way that the structure did not lean or cause torsion in the structural members.

The new store is located at the same site as the original fa-cility, which was constructed in the early 1960s and had expe-rienced a number of additions and renovations over its 50-year life (it contained little or no storage space, had deficient me-chanical systems and only had a small convenience store, hence the replacement). The construction process undertaken with the new structure allowed the majority of the new facility to be constructed away from the site and then moved into place after the existing building was disconnected from the docks and removed. This allowed for the ongoing service to the marina visitors with minimal disruption.

Previous, similar projects with this client had incorporated the use of long cylindrical tanks that can be filled with water (as needed) to buoy up and/or ballast the floatation system—simi-lar to what is used on a pontoon boat. Any piping beneath these structures is exposed to severe weather conditions and erosion.

For this project, the owner requested that a mechanical room and storage room be placed beneath the structure and that all of the ducts and piping be placed within this space. They also required approximately 28 in. of freeboard between the water and the top of the deck to allow for neighboring docks to be attached at similar levels and to allow boats to pull up to the walkway. Creating too deep of a storage area would pro-duce too much buoyancy, making it difficult to tie the platform into surrounding structures. Innovative approaches were used in the design of the deeper storage section so that the forces were transferred throughout the structure to increase its stiff-ness and meet the required buoyancy objectives. The T-shaped section was designed to mitigate any warping or twisting of the platform with the changing loads.

The project, which uses approximately 300 tons of (float-ing) structural steel, opened for business in time for the 2013 high season. ■

OwnerAramark, Wahweap Marina

General ContractorLake Powell Construction, Page, Ariz.

ArchitectVCBO Architects, Salt Lake City

Structural EngineerARW Engineers, Ogden, Utah

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The facility has been designed to accommodate the constantly changing water level of Lake Powell; it is supported by a 10,144-sq.-ft floating platform.

VCBO Architects

Aramark

Aramark

Vulcraft Group joists were used to assemble an inventive design for the Golden Gate Pavilion in honor of the

Bridge’s 75th Anniversary. “The Golden Gate Bridge has been hailed as one of the modern wonders of the world.

Its visitor center deserves the latest technology and innovation.” said Louis Lozano, Vulcraft’s Northern California

District Sales Manager.

Working with design team, Project Frog, it was determined that Vulcraft’s LH series joists with their open web

aspect were the right choice. These special profi le joists are designed to reach longer spans while supporting

large loads.

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Vulcraft’s joists play a vital aesthetic role in the design and architecture of the Golden Gate Pavilion.


Structural renovations brace an iconic

museum for the future.

THE SMITHSONIAN INSTITUTION’S Arts and Indus-tries Building is widely known as the fi rst U.S. National Museum.

The dream of the Smithsonian’s fi rst curator, Spencer Ful-lerton Baird, it was designed by architecture fi rm Adolf Cluss and Paul Schulze and fi rst opened its doors in 1881. In recent years, renovations became necessary thanks to roofi ng, HVAC and plumbing leaks, which led to structural renovation as well. Exterior enclosure and structural improvements to the 102,200-sq.-ft structure were completed early this year at a to-tal construction cost of roughly $44 million.

As with any National Historic Landmark, there is a delicate balance in preserving a structure’s historical elements while also revitalizing the building to meet the needs of the present day. Using prior knowledge of the original construction time frame, the architects were able to successfully depict an over-whelming majority of elements, despite the fact that many were hidden in three to fi ve wythes of masonry.

The design team performed an extensive amount of existing condition surveys, which was an integral fi rst step in completing the roof replacement and in kind, the repair/replacement of the struc-tural framing. The existing lead-coated copper and slate roofi ng was

replaced with 20-gauge stainless steel and new slate to match the existing patterns, and the new roofi ng system weighed considerably more than the existing one. The new structure needed to not only support the additional weight of the new roofi ng system, but also improve seismic, wind, blast and snow load performance.

National TREASURE BY LUCA COVI

Pete

r C

rane

Luca Covi ([email protected]) is business development manager with Grunley and served as senior project manager for the Arts and Industries Building renovation.

➤ The building first opened in 1881.

34 SEPTEMBER 2014

The building is laid out as four quads around a central rotunda. Each quad consists of six individual structures (hall, court, transition, range, entrance/tower and pavilion) that were systematically demol-ished and rebuilt using modern steel components while matching the fabric of the original design. Each quad was unique in terms of dimension and geometrical configuration, a condition that required each area to be field checked for correct dimensions and elevations; in some cases, 3D sketches were drawn by hand in the field. Our team took this information and loaded it into SDS/2 to develop fab-rication and erection drawings, and the field checking and modeling exercise totaled in excess of 3,000 labor hours.

The four quads were integral to one another and required sig-nificant in-house engineering to ensure proper fit-out of new and existing structural members between quads. Each quad consisted of approximately 2,200 pieces of steel weighing approximately 125 tons per quad, 15,000 pieces of hardware (A325 and A490 TC structural bolts with nuts and washers of various diameters and lengths, as well as 2,400 Hilti epoxy anchors of various sizes) and 26,000 sq. ft of decking. A portion of the existing iron structure was reused, requir-ing significant remediation to meet the new structural requirements.

Installation of the new structural framing began on the rotunda roof, then the team moved into the southwest quad hall structure and continued in a clockwise fashion around the building, finish-ing with the topping out of the roof structure replacement. The

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Installation of the new structural framing began on the rotunda roof, then moved into the southwest quad hall and continued in a clockwise fashion around the building.

Exterior enclosure and structural improvements to the 102,200-sq.-ft Smithsonian Institution’s Arts and Industries Building were completed early this year.

The four quads were integral to one another and required significant in-house engineering to ensure proper fit-out of new and existing structural members between quads. Each quad consisted of approximately 2,200 pieces of steel weighing approximately 125 tons per quad.

Phot

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top

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Feeh

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final enhancements were made to existing trusses in the southeast range portion. Each truss was at a different elevation and the required improve-ments had to be made on a per-truss basis to al-low the roof system to be installed properly.

One key strategy to the success of this project, and a great example of innovation, was the use of temporary scaffold decks. The scaffold decks pro-vided the necessary work platform, acted as tem-porary roofing and provided lateral bracing of the exterior walls. In lieu of trying to find a way to keep water from entering the building, our team devel-oped a plan to purposefully route the water inside. To accomplish this, we built scaffolding platforms just below the existing roof levels with knee walls and waterproofed them to the existing walls. To maintain consistent temperature and humidity levels between the inside and outside of the walls,

Installation of the new structural framing began on the rotunda roof, then moved into the southwest quad hall and continued in a clockwise fashion around the building.

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36 SEPTEMBER 2014

The building is laid out as four quads around a central rotunda. Each quad consists of six individual struc-tures (hall, court, transition, range, entrance/tower and pavilion) that were systematically demolished and rebuilt using new steel components.

➤

➤

Christopher Feehely

Peter Crane

we installed vents in the knee walls. On the scaffold decks, we installed an ethylene pro-pylene diene monomer (EPDM) layer and floor drains. To protect the EPDM roofing (since the scaffold decks were the main work platform) we covered the entire surface with horse mats. Although rubber horse mats are normally used for lining stables, we found them to be perfect for our application as well, and we have been able to reuse almost every single mat on other projects. This system al-lowed the ironworkers to perform elevated work at what felt like ground level.


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Each truss was at a different elevation and the required improvements had to be made on a per-truss basis to allow the roof system to be installed properly.

The new structure needed to not only support the additional weight of the roof-ing system, but also improve seismic, wind, blast and snow load performance.

Christopher Feehely

Christopher Feehely

Christopher Feehely

Christopher Feehely

38 SEPTEMBER 2014

To enhance productivity, Grunley established a work sequence that flowed from the highest roof elevation to the lowest elevation, while simulta-neously progressing clockwise around the build-ing. The installation of each level of roofing was followed by window installation. This productive sequence reduced the risk of damage to the new windows, limiting the need to work off of the new-ly installed roof and ensuring safety for workers by reducing overhead activities. A tower crane was erected in the southeast quadrant and was able to reach 90% of the roof structure. Since staging was limited and all material deliveries had to be stra-tegically scheduled, the tower crane provided effi-cient material handling capabilities with the ability to reach all three staging and unloading areas. ■

General ContractorGrunley Construction Company, Inc., Rockville, Md.

ArchitectsEnnead Architects, LLP, New York, and SmithGroupJJR, Washington, D.C.

Structural EngineerMcMullan and Associates, Reston, Va.

Steel Fabricator, Erector and DetailerSuperior Iron Works, Inc., Sterling, Va. (AISC Member/AISC Certified Fabricator/Advanced Certified Steel Erector)

The building is widely known as the first U.S. National Museum.

Peter Crane

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Phone 205-791-2011

Fax 205-791-0500 E-mail: [email protected]

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A look at the performance of the

national uncoated weathering steel bridge inventory.

ALL RESEARCH TAKES PLACE in a lab—of sorts.For uncoated weathering steel (UWS) bridges, that lab is

out in the open, exposed to the elements, in various types of environments across the country.

UWS bridges have now seen domestic use for nearly a half-century, an appropriate time frame for assessing their long-term performance. Such an assessment has been the focus of recent research, “Evaluation of Unpainted Weathering-Steel Highway-Bridge Performance,” conducted at the University of Delaware’s Center for Innovative Bridge Engineering in part-nership with the Federal Highway Administration’s (FHWA) Long Term Bridge Performance Program (LTBPP) and Rut-gers University. Specifically, UWS performance has been as-sessed through surveying the varied experiences of 52 US transportation agencies as well as through compiling a national database of UWS bridges and performing a data analysis on the condition of these bridges. In total, the performance of nearly 10,000 structures has been quantified as a result of these efforts.

Qualitative PerformanceThrough a survey facilitated by the organizational structure

of FHWA’s LTBPP—which has “state coordinators” in each state, Puerto Rico and the District of Columbia—data has been compiled regarding owners’ perceptions on the performance of UWS. Respondents were asked to “briefly describe your gen-eral perception of the overall performance of unpainted weath-ering steel in highway bridges within your agency.”

“Overall performance” was defined as performance away from problematic details such as leaking joints, details that trap moisture and debris, etc., because the reasons for inferior performance at the locations of problematic details is relatively well understood and theoretically easy to remedy with suffi-cient maintenance resources. Rather, a major goal of this survey was to reveal general information on the frequency and charac-teristics of structures suffering from accelerated corrosion over more widespread areas.

The responses to this question were categorized into the three distinct categories listed below, which emerged as the re-sults were reviewed:

➤ Entirely Positive (EP): No overall performance problems with UWS indicated.

➤ Mostly Positive (MP): A generally positive perception of UWS performance was indicated, but some drawbacks were also mentioned.

➤ Negative: A response indicating a negative perception of UWS performance.

Based on these definitions, Figure 1 (on fthe following page) shows the geographic distribution of the 50 responses to this ques-tion (agencies not reporting data for this question are filled with a dashed pattern). The map indicates that 96% of the respondents have a positive perception of the performance of UWS, including 29 of the 50 respondents (58%) being in the EP category. The 38% of respondents in the MP category reported issues typically associated with various specific environments or situations. These

TIME TestedBY JENNIFER MCCONNELL, PH.D., DENNIS R. MERTZ, PH.D., AND HARRY W. SHENTON, III, PH.D.

Jennifer Righman McConnell ([email protected]) is an associate professor, Dennis Mertz ([email protected]) is a professor and Harry W. Shenton, III ([email protected]) is a professor and department chair, all with the Department of Civil and Environmental Engineering at the University of Delaware.

42 SEPTEMBER 2014

➤

problematic environments were most often related to the use of deicing agents on underpass roadways. The only two states with a negative perception of UWS were Michigan and Alaska—nei-ther of which has constructed any UWS bridges since guidance on proper UWS maintenance (“Uncoated Weathering Steel in Structures Technical Advisory”) was published by FHWA in 1989. (Michigan’s newest UWS bridge was constructed in 1983 and all of four of Alaska’s UWS bridges were built in 1974 or 1975.)

Quantitative PerformanceA national UWS bridge database was created through co-

operation with 46 state coordinators and representatives from eight federal agencies who identified the UWS bridges within their inventory. As a relatively simple means to assess the per-formance of this extensive inventory of UWS bridges, the Na-tional Bridge Inventory (NBI) superstructure condition rating (SCR) of each structure was compiled. The SCR is an integer value from 0 to 9 that is meant to describe the overall condition of girders, cross-frames, bearings, etc., with 0 being the worst condition (failed) and 9 being the best condition (excellent). The rating takes several factors into consideration, including fatigue cracks and other visual signs of over-stressed members, damage resulting from vehicular impacts, missing bolts in struc-tural connections and corrosion. From the review of numerous inspection reports of specific structures, it has been observed

that the last of these (corrosion) is one of the more common causes of decreasing SCR. Thus, when reviewing these ratings for an extensive sample size of UWS bridges, the authors have shown that these ratings give a general quantitative indication of UWS performance.

The data summary shown in Figure 2 shows that on average UWS bridges perform quite well, with the most populated SCR being 8, which represents “very good” condition, and 50% of the total inventory of UWS bridges having either a SCR of 8 or 9. Furthermore, 95% of the UWS population has a rating of 6 or better, indicating “satisfactory” performance or better. Note that only 1% of the UWS population received a rating of 4 or less. Furthermore, the SCR values of 0 to 3 were not found to be a direct result of UWS or corrosion-related issues; instead, they were most commonly related to un-arrested fatigue cracks in the sample of bridges for which detailed information has been obtained. Figure 3 shows, perhaps unsurprisingly, that a clear factor affecting SCR is the age of the structures. Specifi-cally, a relatively linear decreasing trend in SCR with increasing age is observed, where the average SCR for bridges 10 years old and younger is 8.0 and is 6.5 for bridges 41 years old and older.

Comparative PerformanceThe significance of the above data increases when viewed

in context relative to other material types. Figure 4 shows the SCR versus age for UWS bridges in two representative agen-cies (one from an agency in the “entirely positive” category and the other from the “mostly positive” category based on the sur-vey results discussed above) plotted relative to the other steel (OS) bridges in these same agencies. As a simple means to aid in interpretation of and comparison between data sets, trend lines based on linear regression analysis of each data set are added to each of these data series.

In comparing the performance of the UWS and OS data sets, it is observed that in the entirely positive category, the performance trend of the UWS data set is similar to the per-formance trend of the OS data set, with UWS tracking slightly above. This difference is more pronounced for younger bridg-es, although even UWS bridges designed prior to the publica-tion of the FHWA UWS technical advisory outperform their OS counterparts. For the mostly positive performance category, it is also observed that the UWS bridges display similar per-formance relative to their OS counterparts. For these two data sets, the trend lines are very similar, with the UWS trend line being slightly superior to the OS trend line for ages between 1 and 25 years and the OS data set being slightly superior oth-erwise. However, this finding should be viewed in light of two facts. The first is that even though data is plotted here for ages 1 through 49, there are relatively few (only nine) bridges older than 35 years old, so data for these structures is not statistically

Favorable performance of a UWS overpass.

Entirely Positive

Mostly Positive

Negative

Figure 1. Owners’ perception of the performance of UWS bridges in their state.

➤


significant in light of the total number of bridges considered in this figure (12,000). The second is that it has been 25 years since the FHWA UWS techni-cal advisory was published. Thus, it is possible that design or maintenance practices implemented since that time would change these trend lines as the new-er bridges in this population age in the future.

Further WorkAs a result of the data presented herein, we

have concluded that UWS generally provides reliable performance in highway bridge applica-tions throughout the U.S. Specifically, as a result of the survey of bridge owners, it was found that 96% of the respondents have a positive perception of UWS performance within their inventory and that the remaining two agencies had not built any UWS bridges since 1983—which was, again, prior to the FHWA guidance on this topic being pub-lished in 1989. When reviewing the NBI ratings of the structures in the newly created national UWS bridge inventory, it was found that the superstruc-ture condition ratings of the majority of UWS bridges are classified as excellent or very good. While these tend to be newer UWS bridges, UWS

➤Figure 2. Distribution of UWS population by SCR.

Figure 3. Distribution of UWS population by age with corresponding SCR.

Figure 4. Superstructure condition rating vs. age, UWS vs. other steel bridges.

Num

ber

of U

WS

Brid

ges

Ave

rag

e SC

REP UWS

EP OS

MP UWS

MP OS

Linear (EP UWS)

Linear (EP OS)

Linear (MP UWS)

Linear (MP OS)

Sup

erst

ruct

ure

Con

diti

on R

atin

g

Age (years)

Num

ber

of U

WS

Brid

ges

SCR

➤

➤

44 SEPTEMBER 2014

bridges that have been in service for over 40 years were shown to be also generally performing well.

Furthermore, based on the fact that Figure 4 shows the average performance of UWS is on par with or better than the average performance of painted steel superstructures for the representative agencies evaluated here, we can con-clude that when choosing between these two corrosion-control strategies and considering the economic and environ-mental benefits of UWS bridges, UWS is a sound choice in many different en-vironments. That said, complementary research is recommended to more care-fully evaluate potential exceptions to this general statement.

One such research topic has been to analyze UWS performance as a function of climate (see “National Review on Use and Performance of Uncoated Weather-ing Steel Highway Bridges” in ASCE’s Journal of Bridge Engineering). This work revealed that UWS bridges generally performed well across all climate cat-egories and suggested that maintenance practices may be a more influential in-dicator of UWS performance than cli-mate; this latter hypothesis is of interest for future evaluation. Furthermore, the climate analysis to date has consisted of broadly categorizing bridges into re-gional climate categories. However, re-cent creation of a geographic informa-tion system (GIS) database combining the UWS inventory, climate data and atmospheric chemical concentrations now allows the specific climate condi-tions (e.g., monthly humidity values, an-nual snowfall and atmospheric chloride levels) of each UWS bridge to be known, which could reveal new insights on the effects of local climates.

Lastly, field work to more rigorously evaluate specific UWS bridges is also un-derway, along with a complementary effort to obtain as much information as possible from existing inspection reports of ad-ditional UWS bridges so that additional metrics beyond SCR, such as element-level condition state data and visual observations, can be considered. Through such efforts, guidance on expected UWS performance in representative realistic conditions can be obtained, which can ultimately lead to the development of UWS best practices and guidelines. ■

46 SEPTEMBER 2014

A criminal justice school blends the new with the old

in an urban expansion project.

THE YEAR FOLLOWING the attacks of September 11th ini-tiated a sudden boom in the popularity of criminal justice careers.

As the trend continued over the years, this led one of the country’s most highly esteemed criminal justice schools, the City University of New York’s (CUNY) John Jay College of Criminal Justice in Manhattan, to eventually expand its campus.

The result is a new 625,000-sq.-ft academic building, com-prised of a 15-story tower on 11th Avenue and a four-story po-dium with a garden roof that connects to the college's existing Haaren Hall, which dates back to the late 19th century, on 10th Avenue. The building doubles the existing facilities and unifies of the campus into one city block.

Justice is SERVEDBY JASON STONE

SOM


Abadan Mustafa of Skidmore Owings and Merrill, the proj-ect’s architect, explained the design concept thusly: “Criminal justice is not something that should be hidden away. Glass makes the relationship to inside and outside clearer. It relates to our ideals of transparency and justice, the way justice is ap-plied to everyone equally and openly."

The new facilities offer traditional college campus amenities in-cluding classrooms, offices, research laboratories, theaters, lounges and flexible collaboration spaces. In addition, unique features specif-ic to educating future investigators and law enforcement officers in-clude a ballistics room, areas for chemical storage and analysis, space for mock trials and an emergency control center simulation lab.

Over the TunnelThere are many challenges to construction in Manhattan,

not the least of which are the countless train tunnels below the streets, and a shallow Amtrak tunnel cuts through a corner of the project site. To effectively isolate the building from the train vibration and noise, two layers of structure were provided. The train tunnel was enclosed with a hollow core precast plank ceil-ing and concrete crash walls, and the main steel-framed build-ing structure spans over and behind these elements (the columns were mostly W14, with the largest being W14×665, and the beams were typically W14×22 that frame to W18 and W36 gird-ers at the long spans). At points of convergence, creative detailing was required to maintain the load path and necessary separation.

However, accommodating the almost two-story change in grade between 10th and 11th Avenues would pose a challenge, as would a second main entrance to the building that occurs along 59th Street and negotiates this steep slope. To design for these conditions, the perimeter columns, which are in an area that sup-ported heavy loads from the rooftop garden, were eliminated and the entrance was pulled back to allow room for the necessary steps and ramps. One-story-deep trusses were fit inside the walls of the fourth-floor classrooms to efficiently accomplish the 40-ft cantilever out to the tip of a V-shaped tapering canopy.

The interior architecture also responded to the sloped grade with a series of cascading staircases and escalators that compli-cated the structure but still facilitated circulation to all parts of the campus.

➤ A partial section view from 11th Avenue at the Amtrak tunnel (the structural system is highlighted).

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

Jason Stone ([email protected]) is a senior associate with LERA Consulting Structural Engineers.

Hung floors

Core columns

Perimeter hangers

Penthouse trusses (cantilevered from core)

Column-free5th floor cafeteria

Traditional framing

Amtrak tunnel

Temporary erection column

Support structure cantilevered over tunnel

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

“The cascade replicates a miniature Manhattan, with the ‘travelers’ passing through different building functions and academic departments rather like the squares—Madison, Herald and Times, among others—that bisect Broadway and function as independent nodes within the city,” said Mustafa. Additionally, a large skylight supported by narrow architecturally exposed narrow HSS20×4×½ provides natural light into these main circu-lation areas and offers views in from the garden roof.

Hanging SystemAccommodating the necessary two layers of structure around the train

tunnel mandated a practical limit to the weight that could be supported. After exploring numerous options, a hanging solution, distinguished by a grid of rooftop trusses that hang the perimeter of the eight floors below, was favored by SOM and the Dormitory Authority of the State of New York (DASNY) and was adopted for numerous reasons. One of these was achiev-ing the series of distinguishing setbacks that frame the west façade’s main entrance along 11th Avenue. The hanging system was continued around the full perimeter to balance the weight, complete the column-free aesthetic and take advantage of the thin plate hangers that could fit inside a standard partition wall instead of traditional column enclosures. The hanging sys-tem was stopped where the structure over the tunnel could accommodate conventionally framed floor weight to maintain efficiency. The fifth floor was chosen for this transition, allowing the transparent column-free floor to align with the podium roof garden, and providing views of the Hudson River for the full 195-ft width of the building.

The primary challenge was to achieve approximately level floors as well as a 2-in. stack joint in the curtain wall at the transition floor between the con-ventionally framed original building and the new hung structure. (The steel that frames between the hanging perimeter—increased for anticipated deflec-tion—and the down-to-the-ground supported core steel sloped upward until the temporary support columns at the sixth floor were distressed/removed.) To simplify the steel frame erection, the design accounted for temporary columns at the fifth floor around the tower perimeter and temporary angles bolted to the plate hangers above the sixth floor to stiffen these elements dur-ing erection. This allowed the construction process to proceed similarly to conventional construction and maintain the project schedule. Once the truss assembly was finished, jacks at the temporary columns slowly lowered the building and engaged the trusses. At this point, the temporary columns and angles could be removed and concreting of the tower could begin.

Calculating the required amount of vertical cambering of the steelwork (or how much to super-elevate the perimeter steel at each of the 26 hang-er/column locations to account for the anticipated deflection during con-struction) proved to be a challenge as well. Design estimates were based on the assumed construction schedule, estimated construction loads and real-istic modeling of the structural behavior. During construction, continuous surveying verified whether the perimeter was behaving as we anticipated. Once shop drawings were available for the nonstructural elements, a full reanalysis was done incorporating what was being learned from the sur-veying. This reanalysis revealed that it was likely the perimeter would not come down as much as originally thought (one reason being the curtain wall was 30% lighter than assumed in design) and field adjustments were made to lower the steel frame prior to starting the truss erection. Based on the last survey data received, this adjustment proved effective as the perim-

➤

➤

With the temporary columns removed, the load path for the hanging structure is clear.

➤

The rooftop truss hanging system supports the 26 perimeter hangers.

48 SEPTEMBER 2014

Eduard Hueber


eter settling and fi nal stack joint were tracking closely with the predicted behavior and targeted fi nal thickness.

Future ExpansionDuring the expansion, the college decided that fl exibility for future

generations was important. A design was considered that allowed for an additional ten fl oors over the podium to raise this section to the height of the new tower. When the decision was made, the podium structural steel was already mostly fabricated and the caisson foundations were actively being drilled in some of the affected areas.

It was then agreed upon to only reinforce the foundations up to the slab-on-ground and take advantage of a hanging structural system similar to the one used in the tower; this would reduce the affected area to the in-terior core and limit the fi nancial and schedule impacts as much as possible. Additional elevator pits with knock-out slabs were provided along with signifi cantly reinforced foundations, based on the anticipated future circu-lation and structural weight needs. Instead of increasing the column and vertical bracing member sizes for the expected future loads, the additional capacity is intended to come from a high-strength composite concrete en-casement, allowing the already fabricated vertical members to still be used.

Up on TopThe 65,000-sq.-ft roof terrace atop the podium serves as a new, out-

door gathering place for students and faculty. The planted green roof is

➤Construction over the Amtrak tunnel was done at night and coordinated around the train schedule. Noise and vibration were controlled by isolat-ing the tunnel enclosure from the tower structure.

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landscaped with large grassy zones, full-sized trees and decked outdoor dining areas, which students have immediately embraced and nicknamed “Jay Walk.”

To preserve the dramatic views, the hanger spacing was increased to nearly 50 ft at the middle of both the east and west faces for the hung tower floors. These long-span conditions created a problem for the laboratories on the sixth, seventh and eighth floors, where strict vibration criteria needed to be met; stiffening the floor resulted in deeper and heavier members than could be tolerated in the ceiling package. The solution, which saved material and depth in the floor members, was to remove the problematic excitation by adding an isolation joint in the floor between the labs and the adjacent main circulation corridor.

The John Jay College Expansion project exceeded the expectations of owner and client, giving the students and faculty a new state-of-the-art home they feel proud of, along with the flexibility to adapt to whatever the future holds. ■

OwnerDormitory Authority of the State of New York

Client Team City University of New YorkJohn Jay College of Criminal Justice

Construction ManagerTurner Construction, New York

ArchitectSkidmore Owings and Merrill, New York

Structural EngineerLeslie E. Robertson Associates (LERA) Consulting Structural Engineers, New York

Steel TeamFabricator and DetailerOwen Steel, Columbia, S.C. (AISC Member/AISC Certified Fabricator)

ErectorCornell and Company, Woodbury, N.J. (AISC Member/AISC Certified Erector)

➤

A cross section of the building. The 15-story, 625,000-sq.-ft facility sits atop a four-story podium and is connected to the college’s existing Haaren Hall.

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52 SEPTEMBER 2014

Span-by-span bridge construction, using modular steel bridge elements,

can serve as a viable and economical bridge-building alternative.

ACCELERATED BRIDGE CONSTRUCTION (ABC) has come a long way in the last 10 years.

And prefabricated, modular elements made with steel beams have been a big factor in making this happen, as they can be used to reduce the weight of the assemblies, thereby making crane installations more cost effective and viable.

Modular steel beam/deck elements generally consist of two or three steel beams with a composite concrete deck cast in the fabrication plant. They are erected quickly and joined with re-inforced concrete closure pours made with high-early-strength concrete; a bridge superstructure can be built in as little as two days using this technique.

One of the more successful examples of this method was the 93Fast14 project in Medford, Mass. (a 2012 NSBA Prize Bridge Awards winner), which involved replacing 41 spans on 14 bridges along Interstate 93. The 14 bridge superstructures were replaced during ten 55-hour weekend work periods. The use of structural steel for the beam elements made the project possible since crane capacities controlled many of the sites.

Span by SpanLet’s take a look at the two common ABC methods to design

and construct a multi-span bridge. The first is to detail multiple simple spans between supports, sometimes referred to as “span-by-span” construction. Conventional simple-span bridges re-quire expansion joints at each pier—historically a problematic feature of many bridges—as leaking joints, considered by many to be the most common cause of premature bridge deteriora-tion, lead to the corrosion of beam ends and deterioration of the substructures under the joints.

The second method for designing multi-span bridges is to use continuous-span beams, which do not require deck expan-sion joints at the interior supports, and require less structural steel for a given span arrangement.

Span-by-span beams are simply erected on the substruc-tures without the need for splicing and shoring towers. The problem with leaking deck joints has been addressed by de-signing these bridges to be either joint-less or continuous for live load by using simple concrete pours at interior supports to eliminate the need for deck expansion joints. Using span-by-span techniques for the superstructure can accelerate the process by eliminating the need for welded or bolted field splices in continuous girders. Beam erection can progress very rapidly as the modular units are inherently stable. Once set, the crane can release the beam without the need for any external bracing.

One method that has been developed to eliminate deck joints on simple-span bridges is “link slab” technology. A link slab is built by simply casting the slab continuously across the pier linking the two spans. The link slab is de-signed to accommodate the live load rotation of the girders without significant cracking. This is accomplished by de-bonding a portion of the deck near the support to form the link slab, which acts as a flexible beam. The recommended

Michael P. Culmo ([email protected]) is vice president of transportation and structures with CME Associates, Inc., in East Hartford, Conn.

Piece BY PieceBY MICHAEL P. CULMO, P.E.

caption

caption

length of de-bonding is 5% of the adjacent span on each side of the pier. Keep in mind that link slabs are not a form of continuity. The bending moments in the link slab are much less than typical negative bending moments in continuous girder bridges; therefore, the design of the girders is based on simple-span supports.

The bending moment in the link slab can be calculated us-ing a simple equation. Reinforcing can then be designed to re-sist the bending and control cracking. The bending stresses in link slabs are often less than the tension stresses that develop in continuous-span bridges. The same principals of crack control reinforcing design are applied to both.

Greater Effi ciencyWe are taught in engineering courses that continuous steel

girders are more effi cient than simple-span girders and that “least weight equals least cost.” In principle, these lessons are true. But in order understand the true effi ciency of steel bridge construction, the engineer needs to look at the total cost of the bridge, including the cost of connections, construction meth-ods and deck reinforcement. In order to study the effi ciency of span-by-span construction, we investigated the preliminary design of a hypothetical two-span bridge. The bridge selected is a typical expressway overpass with equal spans of 122 ft and fi ve girder lines.


➤ The 93Fast14 Project in Medford, Mass., demonstrated the viability of modular steel bridge construction by replacing 41 spans in ten 55-hour weekend work periods.

Bridge deck joints can be eliminated at piers through the use of “link slabs.”➤

M = 2 EI θ / L

θ = Girder end rotation L = De-bond lengthE = Modulus of elasticity of link slab I = Gross moment of inertia slab

De-bonding materialSlab de-bond zone

0.05 L0.05 L

CME Associates, Inc.

Two bridge types were studied for this structure: continu-ous girders and simple-supported girders. The NSBA computer program Simon was used to complete a preliminary design of the girders. (Simon is available for free at www.steelbridges.org and can be used to design efficient steel girders for sim-ple- and multiple-span bridges based on the AASHTO LRFD Bridge Design Specifications.)

The results of the preliminary design showed that the simple-span bridge required 30 more tons of steel at a cost of $70,000 more than the continuous-span option (based on construction costs in the Northeast). The remainder of the study was dedicated to investigating the total cost of the bridge in order to determine if other factors would offset the increased cost for the structural steel.

On such factor was splicing. The 122-ft-long simple-span girders can be shipped in one piece (without field splices), where the continuous girders would need at least one field splice. The study assumed that two field splices would be required for the bridge. It may be possible to build this bridge with one splice, but the length of the pieces would be more than what some permitting agencies would allow.

Another NSBA computer program, Splice, was used to de-sign the bolted splice for the continuous girder study bridge. This program can efficiently design a bolted field splice accord-ing to the requirements of the AASHTO LRFD Bridge Design

Specifications. The final design of the splice included 116 high-strength bolts, and the cost for fabrication and installation of the splice was estimated to be $5,800 per splice (again, based on typical regional construction costs). By eliminating the need for bolted field splices in the span-by-span bridge, an estimated cost savings of $58,000 could potentially be realized.

The Bridge Design Specifications require the use of longi-tudinal reinforcing steel in the negative moment region of

continuous girder bridges in order to control cracking due to composite dead load and live load moments. In general, the design of link slabs results in longitudinal reinforcing that is much less than that used in continuous girder bridges. In ad-dition, the link slab reinforcing steel need only be applied over the link slab zone, which is typically smaller than the negative moment region of a continuous girder. For the study bridges, the link slab design saved considerable reinforcing steel when compared to the continuous-span bridge, which equated to an approximate savings of $22,000.

Another avenue of potential cost savings with simple-span construction is erection. Many agencies require the use of shor-ing towers under bolted splices. Even if shoring towers are not used, the cranes are required to hold the girders until sufficient bolts are installed in the field splices, which is a less efficient process. The potential erection cost savings for the simple-span bridge was estimated to be approximately $30,000.

54 SEPTEMBER 2014

➤

➤

Typical two-span overpass bridge.

Continuous girder with bolted splices. Simple-span bridge with joint-less deck.

➤

➤ Bolted field splice designed using NSBA’s Splice program.


When it comes to bearings, simple-span construction requires two lines of bearings at the center pier, compared to one line of bearings in the continuous girder bridge. The simple-span bearings are small but there are more to fabricate and install, and the cost of the extra bearings was estimated to be approximately $1,500.

When the above items are account-ed for, an estimated net cost savings of $38,500 could be realized for the span-by-span bridge.

ItemNet Cost Savings

Structural Steel -$70,000

Bolted Splices $58,000

Additional Deck Reinforcing $22,000

Steel Erection Cost $30,000

Bearings -$1,500

Net Savings $38,500

Net cost savings for simple-span construction as compared to continuous bridge construction.

To recap: 1. Continuous-girder spans require less

structural steel and fewer bearings.2. The simple-span construction meth-

od may not need bolted fi eld splices, uses less additional deck reinforce-ment and may be less expensive to erect when compared to a continuous girder bridge.

3. Least weight of structural steel does not always equate to least overall bridge cost.

4. By using link slab technology, sim-ple-span construction can be accom-plished with a joint-less deck that is durable.

5. Simply put, simple-span construc-tion is a valuable tool for accelerated bridge construction projects.

This study was limited in that only one bridge was investigated. Other bridge con-fi gurations will yield different results. In some cases, a continuous-girder bridge may have a lower overall bridge cost. The conclusion of the study is that simple-span construction should not be ignored due to concerns over the structural effi ciency of the girders alone. When total bridge costs are applied, this method can be competi-tive or even less expensive than conven-tional continuous-girder designs. ■

➤

56 SEPTEMBER 2014

CROSSING the Delaware BY JIM TALBOT

THE MOST FAMOUS CROSSING of the Delaware River happened in 1776, when America’s first president, George Washington, brought troops across the river in a surprise attack against Hessian Forces during the Amer-ican Revolutionary War.

Nearly 40 years later, in September 1814, a covered span followed suit and became the first bridge to cross the Delaware River that connected New Hope, Pa., and Lambertville, N.J., replacing Coryell's Ferry.

Designed by Lewis Wernwag, a German immigrant and pioneering bridge-builder, the wooden covered bridge was 32 ft wide and had two wagon lanes and two lanes for pedestrians. Flooding carried the bridge away in January of 1841, and another flood destroyed a second, similar bridge at this site in 1903.

From Wood to SteelThis led to the construction of a steel, pin-connected Pratt truss bridge in

1904, the New Hope-Lambertville Bridge. Lewis F. Shoemaker and Com-pany of Pottstown, Pa., built the bridge, listing R.G. Devlin as the engineer. The cost: $63,818.81.

Today, the bridge carries 14,000 vehicles across the Delaware River daily; roughly the same number of pedestrians cross the bridge on a single sum-mer weekend day. No other bridge across the Delaware sees this level of foot traffic. Tourists, residents, antique shoppers, bikers and others use the crossing to take advantage of the many attractions offered by the two com-munities on opposite banks.

The six-span bridge contains 962 tons of steel. Each nine-panel span measures 171 ft, and the bridge has a total length of about 1,050 ft and a roadway width of 20.3 ft. Vertical truss members measure 27 ft in height, and abutments date back to the original 1814 bridge. Pedestrians cross on a

Our nation’s rich past was built on immovable determination and innovation that found a highly visible expression in the construction of steel bridges. The Steel Centurions series offers a testament to notable accomplishments of prior generations and celebrates the durability and strength of steel by showcasing bridges more than 100 years old that are still in service today.

STEEL CENTURIONSSPANNING 100 YEARS

STEEL

CENTURIONS

A steel truss, at the site of one of the first bridges over the Delaware River,

is still standing after numerous floods and more than 100 years of life.


Jim Talbot is a freelance technical writer living in Ambler, Pa. You can reach him at [email protected].

cantilevered walkway along its southern downstream side. Addi-tionally, the bridge carries a pumped 8-in. sewer line to a treat-ment plant located in Lambertville.

For its first 15 years, tolls supported the bridge's operation and maintenance, but now tolls on other bridges across the Dela-ware support these activities, along with security. (The Delaware River Joint Toll Bridge Commission, created in 1934, owns and operates the bridge; the commission operates 20 Delaware River bridges in all.) The bridge carried U.S. Route 202 over the Dela-ware River until 1971, when the route was realigned to cross the river upstream on a new bridge; it now carries Route 179.

Surviving the FloodThe flood of August 1955—the greatest the Delaware River

had ever experienced—destroyed many of the structures cross-ing it. The New Hope-Lambertville Bridge was one of the rare survivors, though its No. 2 span was seriously damaged, forcing a closure for five weeks. In 2004, the bridge underwent an exten-sive $7.7 million rehabilitation project, coinciding with its 100th anniversary. This figure included preliminary and final design, public involvement, construction and oversight. It also funded a free shuttle service for pedestrians, which operated when the project closed the bridge to traffic on weekdays. On weekends,

➤

construction stopped and the bridge reopened to minimize economic impact to the two connected communities.

The centennial project replaced flooring systems, sidewalk and handrails. The walkway was widened from 6 ft to 8 ft and paneled with fiberglass. Other improvements included mis-cellaneous steel repairs, blast-cleaning, sewer line rehabilita-tion and modifications to safety and lighting. Painting crews added three coats of "bridge green" anticorrosive polyure-thane paint. The general contractor, J.D. Eckman, Inc., faced

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The New Hope-Lambertville Bridge opened in 1904 and currently carries 14,000 vehicles across the Delaware River daily. Each of the bridge's six spans measures 171 ft, and the total length is about 1,050 ft.Vertical truss members measure 27 ft in height, and abut-ments date back to the original 1814 bridge.

58 SEPTEMBER 2014

with a $10,000 per day reward or penalty, completed the project a week ahead of schedule.

As part of its security system, nine cameras on the bridge now feed images to the commission's com-mand center. Threats of � ood damage in 2005 and 2006 motivated the commission to install a radar-based level sensor to the side of the bridge that measures the river's height every 15 minutes and transmits the data via satellite to the National Weather Service and other entities. Biannual maintenance activity includes send-ing divers underwater to inspect for defects, cracks and scaling on the bridge's supports.

This past D-Day anniversary (June 6), mainte-nance crews hung banners at both ends to commemo-rate 200 years of bridge crossings over the Delaware River. The banners had images of the steel truss bridge as it appears today and the wooden bridge destroyed in the great � ood of 1903. In addition, a � lm cover-ing the bridge's history premiered in April: The New Hope-Lambertville Bridge, Connecting Two Towns, Span-ning Two Centuries. �

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The six-span bridge contains 962 tons of steel.

In 2004, the bridge underwent an extensive $7.7 million rehabilitation project, coinciding with its 100th anniversary.

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SteelDay® is an annualevent hosted by theAmerican Institute of Steel Construction,its members andpartners. Plan your SteelDay® visits andsee fi rst hand why it makes sense to buildwith structural steel.

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American Institute of Steel ConstructionOne East Wacker Drive, Suite 700Chicago, IL 60601

312.670.2400 www.aisc.org

There’s always a solution in steel.

SteelDay It’s coming... 9.19.2014www.SteelDay.org

60 SEPTEMBER 2014

news

People and Firms• Victor Technologies wi l l

award more than $30,000 in equipment and cash prizes as part of its 2014 “A Cut Above” student contest. The contest is open to students in cutting, welding and related programs at secondary and p o s t - s e c o n d a r y s c h o o l s . Entr ies are accepted now through October 31, with rules and entry forms available at www.victortechnologies.com/acutabove.

• Carney Engineering Group, a multi-discipline structural engineering firm serving the Mid-Atlantic region, has hired Eric Alwine as a structural project manager. His previous experiences include projects ranging from the $110 million renovation of a historical 23-building campus to building hotels and casinos in San Juan, Puerto Rico.

• Dexter + Chaney, provider of Spectrum Construction Software, has unveiled its new Project P lan Room mobile app, which al lows users to distribute construction documents, communicate data and relay project information in real time to employees’ and subcontractors’ mobile devices on the job site. (Visit www.dexterchaney.com.)

NSBA

Jeff Carlson Joins NSBA as Western Regional Director

STEELDAY

SteelDay Gears up with Chicago High-Rise TourAn 11-story, 157,000-sq.-ft steel residen-tial high-rise known as Circa 922 is cur-rently under construction just west of the Chicago Loop. It’s the first project in the city to be built using the Girder-Slab sys-tem, and AISC recently hosted a tour of the building, which drew more than 100 construction professionals.

The project site tour and presentation served as a “pre” SteelDay event, offer-ing a sneak peak at the dozens of events scheduled in Chicago and around the country on SteelDay. Set for Friday, Sep-tember 19, SteelDay is an annual event, sponsored by AISC and hosted by its members and partners, celebrating struc-tural steel. It offers events all over the country for AEC professionals, university faculty and students and the general pub-lic to get an inside look at how the struc-tural steel industry works to build Amer-ica. You can also keep up with SteelDay updates and discussions via AISC’s social media channels at www.facebook.com/AISCdotORG, www.twitter.com/aisc and www.youtube.com/AISCsteelTV.

The National Steel Bridge Alliance welcomes Jeff Carlson, P.E., as its Western Regional Director. Carlson is responsible for working with state DOTs, bridge design consultants and construction professionals in Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington and Wyoming, providing technical and project assistance and communicating the advantages that structural steel brings to bridge projects.

“Jeff’s background adds another dimension and a fresh perspective to the NSBA team,” said Bill McEleney, NSBA’s managing director. “His experience dealing directly with owners will surely be appreciated by our DOT colleagues as we work to better quantify the life-cycle advantages of steel bridges.”

Carlson brings more than a decade of project management and engineering

experience to NSBA. Most recently, he was a financial analyst and project manager for Omni Development Corporation in Denver, where he was responsible for managing real estate redevelopment projects, overseeing several construction professionals,

providing financial recommendations and developing budgets for presentations to the owner. Prior to that, he was a research analyst for Cornerstone Real Estate Advisors in Hartford, Conn. Before entering the real estate market, he worked for six years as a professional engineer and project manager for Martin/Martin Consulting

Engineers in Lakewood, Colo. Carlson lives in Englewood, Colo.,

and can be reached at 720.440.3011 or [email protected]. To view a map of NSBA staff’s territories, visit the NSBA website homepage (www.steel-bridges.org).

Go to www.aisc.org/seminars for more information.

$350 for Members, $600 for Member + Buddy

(Sign up two people and save $50 per registrant!)

The 2nd Edition Seismic Design Manual

will be available for purchase for $100

(a discount from $175 member price/ $350 non-member price)

The Louis F. Geschwindner Seminar

Seismic Design Manual and Application of the 2010 AISC Seismic Provisions

Written by Thomas A. Sabol, S.E., Ph.D. | 0.8 CEUs/8.0 PDHs

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FALL SEMINARS

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

St. Louis, MONew York, NYLexington, KYPittsburgh, PABatavia, NY Hosted by ASCE Buffalo Section Structures Committee

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62 SEPTEMBER 2014

news

Engineering Journal has replaced its digi-tal edition browser with a single down-loadable PDF file at www.aisc.org/ej. The current issue—third quarter 2014—will be available for download and view-ing until the next issue is posted.

Articles for the complete collection of EJ will remain available individually in the searchable archives. Downloads of current and past articles in PDF format are free to AISC members and ePubs subscribers. Non-AISC members may subscribe to EJ at the AISC bookstore.

The Q3 2014 of EJ is the second of two issues with a special focus on the “simple for dead load–continuous for live load” (SDCL) design concept. The premise behind the concept is that gird-ers erected as simple spans can be made to function under live load as continu-ous spans by providing continuity with a unique field connection. In addition to covering research, the issue highlights a successful SDCL bridge project from the engineer’s perspective.

Here are the Q3 articles:

➤ 2013-02 HSS Truss Connections with Three BranchesJeffrey A. Packer

Hollow structural section (HSS) three-branch (or KT) connections fre-quently occur in modified Warren trusses, but the design of these planar welded connections is beyond the scope of Chapter K of the 2010 AISC Specifi-

cation for Structural Steel Buildings. Such connections are also not covered by oth-er contemporary HSS design guides and standards. This paper reviews the many potential member and loading arrange-ments, for both gapped and overlapped KT connections, and offers some design guidance. A worked example for an over-lapped square HSS KT connection is then given, in both LRFD and ASD for-mats, in accordance with the 2010 AISC Specification for Structural Steel Buildings.

Keywords: Hollow structural sec-tions, trusses, connections, KT, welded joints, overlapping branches.

➤ 2012-25RField Application Case Studies and Long-Term Monitoring of Bridges Utilizing the Simple for Dead–Continuous for Live Bridge SystemAaron Yakel and Atorod Azizinamini

The performance of three bridges constructed using the SDCL bridge system for steel girders was monitored during and after construction to com-pare actual performance with predicted performance. The structure types were a box-girder bridge, an I-girder bridge and a box-girder bridge built using ac-celerated construction details. During construction, strains and deflections were monitored so that the degree of continuity over the pier could be deter-mined. The design concept assumes that a simply supported condition exists dur-ing casting of the concrete deck. How-ever, to provide lateral bracing, the con-crete diaphragm—or turndown—over the pier is cast and cured prior to casting the deck. As expected, encasement of the girders provides some continuity over the pier during casting of the deck. The degree of continuity over the pier can be reduced by lowering the height of the construction joint and through the use of crack-inducing details. Long-term monitoring of the structures showed the behavior to be consistent over time with no significant deviations from the predicted bridge behavior. During the initial time period of approximately 18 months, a slight overall change in strain values was observed in concrete ele-ments. The rate of change slowed dur-ing this period and eventually ceased. Subsequently, the response of the struc-ture has been consistent with only small seasonal fluctuations observed. These fluctuations are expected and are gener-ally attributable to changes in ambient temperature, relative humidity, incident solar radiation and ground freeze/thaw conditions.

Keywords: Steel bridges, steel gird-ers, SDCL, simple for dead load, con-tinuous for live load.

➤ 2012-26Experimental Investigation, Ap-plication and Monitoring of a Simple for Dead Load–Continu-ous for Live Load Connection for Accelerated Modular Steel Bridge Construction Saeed Javidi, Aaron Yakel and Atorod

Azizinamini

The inherently modular nature of the SDCL system makes it a natu-ral fit for the accelerated construction paradigm. A detail capable of connect-ing pre-topped girders over the middle supports is developed and described in this paper. To evaluate the performance of the proposed connection, a full-scale specimen was built and subjected to cyclic and ultimate load testing. The connection showed very little change during cyclic loading equivalent for 70 years of traffic. During the ultimate load test, the connection demonstrated large displacement ductility, reaching its ultimate capacity after complete yield-ing of the longitudinal reinforcement. After the successful experimental test, a field application bridge was constructed using a modular pre-topped steel box girder system, which allows much of the construction process to be performed prior to placing the girders. The bridge consisted of three pre-topped steel box units placed side by side and connect-ed using longitudinal joints between pre-topped units. The steel box gird-ers used 70-ksi high-performance steel in the bottom flange and 50-ksi steel in the top flanges and webs. The use of high-performance steel combined with the SDCL system allows eliminating the need for section transitions through the length of the structure and using constant cross-section throughout the length of the girders. Long-term moni-toring of the structure was performed and showed that the system worked as intended.

Keywords: Steel bridges, steel gird-ers, SDCL, simple for dead load, con-tinuous for live load.

ENGINEERING JOURNAL

New Format for EJ; Q3 Now Available


➤ 2013-03Existing Simple Steel Spans Made Continuous: A Retrofit Scheme for the I-476 Bridge over the Schuylkill RiverDaniel Griffith and John A. Milius

The rehabilitation of the SR 476 Bridge over the Schuylkill River near Philadelphia converted existing steel multi-girder simple spans into three- and four-span continuous units. Employing a design method typically used for construc-tion of new simple-span-made-continuous (SSMC) steel girder bridges, it is believed to be the first bridge rehabilitation project in Pennsylvania to use such a scheme. The rehabilitation design upgraded load capac-ity of the girders to meet current LRFD code requirements. The SSMC design, coupled with other deck joint elimination techniques, was able to reduce the com-bined number of deck joints on the north-

bound and southbound structures from 25 to 8. With nearly all previous steel dete-rioration occurring at deck joints, this sub-stantial reduction in deck joints will aid in extending the remaining life of the bridge. This paper will illustrate the construc-tion methods employed for conversion of the bridge from multiple simple spans to continuous spans. It will also provide detailed insight into the many design re-quirements for this structural conversion, from substructure retrofits and sequential bearing replacements to superstructure continuity and full-depth concrete dia-phragm details.

Keywords: Simple-span-made-con-tinuous (SSMC), bridge rehabilitation, modified fixity conditions, steel wedge plates, bolted steel splice plates, full-depth concrete diaphragm, staged con-struction, sequential bearing replace-ment, steel bolsters.

letter to the editor

Evolving InnovationWhile reading your July editori-al, I could not help but think of something I read in a book about Steve Jobs. He hated marketing studies. It was mentioned that if Henry Ford would have asked a focus group what they wanted, they would have said a faster horse. Jobs and Ford had the same idea. They invented something that the public did not even know they could not live without. Innovation and evolu-tion will continue. I think Girder-Slab fits into this category.

We need to look from the out-side into our operations, visualize the future and look back to where we are now.

—Daniel G. Fisher, Sr.

Managing Partner

Girder-Slab Technologies, LLC

marketplace Search employment ads online at www.modernsteel.com.

AISC Continuing Education Seminars

www.aisc.org/seminars.

“Like” AISC on Facebook

facebook.com/AISCdotORG

Follow AISC on Twitter

@AISC

Looking for something from an old issue of Modern Steel?

All of the issues from Modern Steel Construction’s first 50 years are now available as free PDF downloads

at www.modernsteel.com/backissues.

AISC QUALITY CERTIFICATIONIT WORKS... DON’T WAIT!

For fabrication or erection helpCall Jim Mooney

your Quality Certification Connection

JAMES M. MOONEY & ASSOCIATES941.223.4332 • [email protected]

Contract AuditorQuality Management Company, LLC is seeking contractors to conduct audits for the AISC Certifi ed Fabricator and AISC Certifi ed 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 [email protected].

64 SEPTEMBER 2014To advertise, call 231.228.2274 or e-mail [email protected].

Don Kidd or Steve Willems 670-779-1400

STRUCTURAL STEEL FACILITY AVAILABLE Turn Key Opportunity including Business, Real Estate &

Equipment * Approx. 150,000 SF under roof on 12 acres * Rail serviced * AISC certified w/paint endorsement * Located in SE PA w/close proximity to NY & Baltimore/ Washington metro areas

LATE MODEL STRUCTURAL STEEL FABRICATING EQUIPMENT

Ficep 2004 DTT CNC Drilling & Thermal Coping Line, 78-3/4” x 24” Max. Beam, 3-Drill, Ficep Arianna CNC Control, 2003 #20382Controlled Automation ABL-100-B CNC Flat Bar Detail Line, 143 Ton Punch, 400 Ton Single Cut Shear, 40’ Infeed, 1999 #24216Peddinghaus Ocean Avenger II 1000-1 CNC Beam Drill, Siemens 840D CNC, (1) Drill Head, 40” x 60’ Beam Capacity, 2004 #20877Peddinghaus BDL1250 CNC Beam Drill, 50” Max. Beam, (3) 10 HP Spindles, PC Ctrl (Upgrade 2005), 2000 #21739 Controlled Automation 2AT-175 CNC Plate Punch, 175 Ton, 30” x 60” Travel, 1-1/2” Max. Plate, PC CNC, 1996 #23503Peddinghaus F1170B CNC Plate Punching Machine, 170 Ton, Fagor CNC, 30” x 60” Trvl., Triple Gag Head, Ext. Tables, 2005 #19659Controlled Automation BT1-1433 CNC Oxy/Plasma Cutting System, 14’ x 33’, (1) Oxy, (2) Hy-Def 200 Amp Plasma, 2002 #20654Controlled Automation BFC-530 (5) Press CNC Beam Line, 36” Max. Beam, Hem Saw, Conveyor, 1998 #24261HEM DC-2038RB Double Column Horizontal Band Saw, 20” x 38”, 45-60 Deg. Miter, 2” Blade, 15 HP, 75-400 SFPM, 2006 #22215

Phone: 631.249.5566 | Fax: 631.249.9494 | [email protected] Visit www.PrestigeEquipment.com for our inventory & services

Looking for the latest information on AISC Certifi cation Programs?

Visit www.aisc.org/certificationEmail [email protected]

or call 312.670.7520

employment

To advertise, call 231.228.2274 or e-mail [email protected].

Search employment ads online at www.modernsteel.com.

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.

RECRUITER IN STRUCTURAL MISCELLANEOUS STEEL FABRICATION

Buzz Taylor

PROCOUNSELToll free: 866-289-7833 or 214-741-3014

Fax: 214-741-3019 [email protected]


Connection Design EngineerInternational Design Services is seeking a steel

connection design engineer for our St. Louis office.

Minimum 4 years of experience and the ability to obtain a PE license. Working

knowledge of Mathcad is preferred. Candidate will have experience managing

others and will be responsible for the production of an engineering team.

Candidate must also skillfully interact with the detailing team, fabricator, general

contractor and EOR. IDS offers a benefits package, competitive salary, and

relocation allowance. SE license is strongly preferred.

Please call 314-872-1791 or email your resume to [email protected].

Paxton & Vierling Steel (PVS), a steel fabricator established in 1885 and located in Omaha, Nebraska, is currently recruiting structural steel

estimators and detailers. PVS is an AISC and ISO certified steel fabricator who’s quality program is compliant with Canadian Weld Bureau and

NQA-1 (nuclear) requirements. PVS’ specialty is industrial and nuclear projects throughout North America.

For information on our company please visit www.PVSteelFab.com. Please send your resume to [email protected].

Project ManagerLenex Steel Company is currently seeking Project Managers to join our team in the Indianapolis and/or Chicago markets. The Project Manager has overall responsibility for managing projects from pre-award through completion and managing project engineers and field project managers. The ideal candidate has a degree in engineering or building construction

management with structural steel experience. Lenex Steel offers competitive salaries and a comprehensive benefits package.

Email resume to [email protected].

Lincoln Engineering Group is one of the fastest growing steel detailing firms in the country located in beautiful Chicago area. We currently have

immediate openings for experienced Project Managers and checkers.

Ideal candidate would have 5 years’ experience in Structural and Miscellaneous steel detailing and checking, as well as, knowledge of applicable codes. He/she should be a team leader with excellent

communication skills. Knowledge of CAD & 3D Software such as SDS/2 or Tekla, and Miscellaneous Steel Detailing is a plus but not a must!

We offer a competitive compensation and benefits package. May consider relocation allowance for the right candidate.

Please submit your Résumé to: [email protected] or Contact Salah Bassiouny at (630) 445-2111.

Structural Steel Detailing Project Managers

and Checkers

Estimators • Detailers • Project Managers

West Coast Iron, Inc. has specialized in the detailing, fabrication,

and erection of structural steel, stairs and miscellaneous metals for

some of Southern California’s most prominent and successful general

contractors for over 25 years. We are currently seeking Project

Managers & Estimators with 5 years’ experience in structural steel,

miscellaneous metals, and metal deck and experienced Detailers with

a minimum of 3 years’ experience with TEKLA software to join our

team. West Coast Iron offers competitive salaries and a comprehensive

benefits package.

Please send your resume to

[email protected]

Structural EngineersAre you looking for a new and exciting opportunity in 2014?

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66 SEPTEMBER 2014

A STUNNING MEMORIAL on the State Capitol grounds in Saint Paul honors the sacrifice of Minnesota firefighters killed in the line of duty. Designed by Leo A Daly, the memorial houses the Minnesota Firefighter Memorial Statue, previously on display at Minneapolis-Saint Paul International Airport.

A large steel monolith hovers above the statue, forming a pavilion, and a field of light steel columns supports its weight. The weathering steel of the monolith presents a rich patina, evolving in a slow process analogous to the rapid oxidation of fire. The organizing grid of 100 potential columns represents a century—10 decades by 10 years per decade. There are cur-rently 86 columns, recording the years in which Minnesota firefighters have died in the line of duty, and names of the fallen are inscribed on the columns. Over time, the assemblage will

accumulate additional inscriptions, and new columns will appear as future firefighter deaths occur in years not yet plotted.

The column-to-monolith connections contain a pipe-sleeve that joins the upper and lower faces of the monolith; this sleeve allows the column to support both surfaces and also joins the two surfaces. The slender columns were made stable by designing the base and the top connection to be fixed, and the foundation was designed as a mat slab to accommodate the nontraditional column layout; this further accommodated a fixed base plate connection with pretensioned bolts. The sleeved connection at the top of the column allows fixity in that it accommodates a spanning knife-plate. The plate’s short span, in conjunction with the sleeve’s engagement of both planes, was stiff in both bending and torsion. ■

structurally sound

IN THE LINE OF DUTY

Strong Structures Come From Strong Designs

© 2014 Bentley Systems, Incorporated. Bentley, the “B” Bentley logo, ProjectWise and MicroStation are either registered or unregistered trademarks or service marks of Bentley Systems, Incorporated or one of its direct or indirect wholly owned subsidiaries. Other brands and product names are trademarks of their respective owners.

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Visit www.bentley.com/Structural to learn more!

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Documents

Modern Steel Construction - September 2014