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February 2014

STEEL CONSTRUCTIONModern

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MODERN STEEL CONSTRUCTION (Volume 54, Number 2) 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 MSC logos are registered trademarks of AISC.

February 2014

ON THE COVER: At the base of the tallest building in the U.S., p. 26. (Photo: WSP Cantor Seinuk)

steelwise 17 Tips to Take Your Team to the Top

BY MATTHEW D. BRADY, P.E., AND CLIFF SCHWINGER, P.E.

There are countless ways to improve constructability on your next project. Here are 50 of them.

business issues 24 Up to Speed on LEED

BY JOHN CROSS, P.E., LEED APWhat you need to know about the new version of the ubiquitous green building rating system.

26 Rising to the TopBY AHMAD RAHIMIAN, S.E., P.E., PH.D.,

AND YORAM EILON, P.E. The most highly anticipated American skyscraper in recent history, One World Trade Center comes together in the context of past tragedy, present demands and future expectations for tall buildings.

32 Building up the FortBY ROBERT WAYNE STOCKS, P.E.,

ZACHARY KATES, P.E., AND KEVIN MACLEOD

The new Army hospital at Fort Benning is the U.S. Army Corps of Engineers’ first-ever design-build hospital project.

40 Quick ThinkingBY WILLIAM KILLEEN, P.E. Emergency steel spans reopen an Interstate river crossing shortly after a bridge collapse.

44 Keep on Rolling BY GEOFF WEISENBERGERAn inside look at a modern, high-tech steelmaking operation.

52 Stability Matters BY LAWRENCE G. GRIFFIS, P.E., AND

DONALD W. WHITE, PH.D. A new AISC publication offers guidance on the three options for stability analysis and design.

56 To Toronto BY TASHA WEISS Canada’s largest city is set to host this year’s NASCC: The Steel Conference.

columns

features

departments 6 Editor’s notE 9 stEEl intErchangE 12 stEEl quiz

60 nEws & EvEnts66 structurally sound

resources 64 markEtplacE 65 EmploymEnt

in every issue

44

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Editorial Offices1 e. Wacker dr., Suite 700Chicago, il 60601312.670.2400 tel312.896.9022 fax

Editorial Contactseditor & PubliSherScott l. [email protected]

Senior editorgeoff [email protected]

aSSiStant editortasha [email protected]

direCtor of PubliShingareti [email protected]

graPhiC deSignerkristin [email protected]

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

EVER SINCE WE ANNOUNCED THAT THE 2014 NASCC: THE STEEL CONFERENCE WAS GOING TO BE HELD IN TORONTO AT THE END OF MARCH, I STARTED HEARING COMMENTS WORRYING ABOUT THE WEATHER. amazingly, a lot of these complaints were from my same friends who boast about how the end of March is a great time to visit Chicago; the cool days make walking around downtown a pleasure, etc.

As most of my friends know, my wife is from Toronto, so I’ve had daily weather reports from that city for more than 20 years. And typically the weather is just about the same as Chicago’s—plus or minus a degree or two.

If you’ve never visited Toronto, buy your ticket now. Not only will you have the opportunity to attend the year’s best conference, but you’ll also get to see one of the top cities in North America. Because of the quality of the restaurants, and because we recognize that many attendees will have never visited Toronto before, this year we’re reserving Thursday as a free night for you to explore the city. (If you want a sampling of activities, start with www.seetorontonow.com. And if you need more suggestions, drop me an email!)

If you’ve previously attended a Steel Conference, you know what to expect. More than 100 technical sessions (structural engineering, fabrication, bridges and more). There’s a huge exhibition hall with more than 200 companies. And, of course, there are more than 3,500 professionals in attendance (engineers, fabricators, detailers, erectors, educators, transportation officials, contractors and everyone else involved in the design or construction of steel-framed buildings and bridges).

SCOTT MELNICKeditor

If you have a smartphone, you can download the free NASCC app at either the Apple App store or the Google Play store. The app allows you to browse the schedule and make your own calendar of sessions to attend. You can start with a session on BIMsteel, welding inspection or floor vibrations on joist-framed floors. You can check out the session on stability bracing or effective BRBF design. You can learn about direct analysis, torsion and k-factors. You can attend stability sessions, bridge sessions or technology sessions. Attendees can earn 18.5 PDHs. Make sure you visit www.aisc.org/nascc to check out all the sessions and to register.

I hope to see you in Toronto, March 26-28! Bring an umbrella (just to be safe), and don’t forget to pack your walking shoes too.

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Modern STEEL ConStruCtion 9

Thermal CuttingWe are purchasing a plasma table for our fabrication facil-ity. Is plasma permitted to be used to create holes for bolts and anchor rods?

Thermally cut holes for bolted connections in buildings are explicitly allowed in the AISC Specification. See Section M2.5, which states:

“Bolt holes shall comply with the provisions of the RCSC Specification for Structural Joints Using High-Strength Bolts, hereafter referred to as the RCSC Specification, Section 3.3 except that thermally cut holes are permitted with a surface roughness profile not exceeding 1,000 μin. (25 μm) as defined in ASME B46.1. Gouges shall not exceed a depth of 1⁄16 in. (2 mm). Water jet cut holes are also permitted.”The glossary to the Specification then defines “thermally

cut” as being “cut with gas, plasma or laser” (see page 16.1-liv of the 2010 AISC Specification).

So, assuming that the plasma equipment in question can produce holes of the necessary quality, it is permitted—and indeed plasma equipment is becoming extremely common due to the efficiencies they can provide.

You may also find Section M2.2 of the AISC Specification to be useful, as it discusses thermal cutting for purposes other than bolt holes (the Commentary to Chapter M is also useful in a general sense). The above applies to buildings and building-like structures.

Note: If you are working on bridges, then thermally cut holes may be prohibited by the owner.

Martin Anderson

Group A & B Bolts The tables in the 14th Edition of the AISC Steel Construc-tion Manual refer to Group A and Group B bolts. What is the definition of Group A and Group B bolts?

This terminology is pursuant to Section J3.1 of the 2010 AISC Specification, and the groups correspond to material strength.

Per J3.1, Group A is composed of those materials that have a tensile strength similar to ASTM A325, and includes ASTM A325/A325M, F1852, A354 Grade BC and A449. Group B is composed of those materials that have a tensile strength similar to ASTM A490, and is composed of ASTM A490/A490M, F2280 and A354 Grade BD.

Section J3.1 itself can be found on page 16.1-118, with some relevant Commentary on the matter starting on page 16.1-400.

This change was made to simplify references to those strength groups (for example, when discussing connections it is convenient to distinguish between Group A and Group B as they have different strengths; it similarly simplifies discussions of minimum bolt pretension).

Martin Anderson

Stability Design and the ELMIn AISC 360 Table C-C1.1 “Comparison of Basic Stabil-ity Requirements with Specific Provisions,” in reference to the effective length method, it states, regarding basic requirements (3), (4) and (5): “All these effects are con-sidered by using KL from a sidesway buckling analysis in the member strength.” Can you explain how using KLaddresses each of these items? In addition, on a current project, I noticed that the K-factor from an eigenvalue buckling analysis is almost equal to that given by the alignment charts. Does this mean that an eigenvalue anal-ysis considers basic requirements (3), (4) and (5)?

First, the k-factor you get from an eigenvalue analysis is an elastic k-factor, so it does not account for any inelastic effects (4), it is not able to account for out-of-straightness (3) and it does not address uncertainty (5). Now, let me go through the six items that Table C-C1.1 says are addressed by using kLfrom a sidesway buckling analysis:

1) Member imperfections on structure response. You must do a second-order analysis in each method. This is the P-δ or “member effect” and its influence on the sway effect. Eigenvalue does not do this.

2) Member imperfections on structure strength. The column strength equations in AISC 360 Chapter E are based on initial out-of-straightness of the member, thus there is nothing more for the engineer to do in either method.

3) Effect of stiffness reduction on response. In determining the effective length factor you must take stiffness reduction into account. You can do this with the stiffness reduction factor when using the alignment chart. This has been in the AISC Manual for a very long time. Eigenvalue does not do this.

4) Effect of stiffness reduction on strength. In determining strength, inelastic buckling is already taken into account in the column strength equations in AISC 360 Chapter E. There is nothing more for the engineer to do.

5) Effect of uncertainty on response. This already is taken into consideration in the stiffness reduction factor for effective length. Eigenvalue does not do this.

6) Effect of uncertainty on strength. This is already accounted for the resistance or safety factors.

The fact that your eigenvalue solutions closely match the alignment chart is likely because your model matches the assumptions used in developing the chart. I find it hard to believe this is always the case for your structures as we almost always violate some of these assumptions—gravity-only columns, inelastic behavior, all columns buckling at same time, etc.

Heath Mitchell, S.E., P.E. (with assistance from Louis F. Geschwindner, P.E., Ph.D.)

steel interchange

If you’ve ever asked yourself “Why?” about something related to structural steel design or construction, Modern Steel Construction’s

monthly Steel Interchange column is for you! Send your questions or comments to [email protected].

10 february 2014

Special Inspection I cannot seem to find the Special Inspection tables for structural steel in the 2012 International Building Code. Where are they located?

Those tables are no longer in the IBC. They are now located as chapters within the relevant AISC standards. For special inspection of structural steel other than seismic lateral force resisting systems, 2012 IBC Section 1705.2.1 states:

“1705.2.1 Structural steel. Special inspection for structural steel shall be in accordance with the quality assurance inspection requirements of AISC 360.”

You will find these special inspection (QA) requirements in AISC 360 Chapter N. For special inspection of seismic lateral force resisting systems, 2012 IBC Section 1705.11.1 states:

“1705.11.1 Structural steel. Special inspection for structural steel shall be in accordance with the quality assurance requirements of AISC 341.

Exception: Special inspections of structural steel in structures assigned to Seismic Design Category C that are not specifically detailed for seismic resistance, with a response modification coefficient, R, of 3 or less, excluding cantilever column systems.”

You will find these special inspection requirements in AISC 341 Chapter J. These are in addition to the special inspection requirements in AISC 360-10 Chapter N.

All AISC specifications noted above are available as free downloads at www.aisc.org/epubs.

Heath Mitchell, S.E., P.E.

Capacity of Existing WeldsI am trying to determine the capacity of existing welds. Can I do this using NDT methods?

No. There are no nondestructive testing methods that can be used to determine the strength of the weld metal or the base metal. To determine the strength you generally have to break something.

NDT is used to determine the quality and geometric characteristics of welds. If the weld is a CJP groove weld, then ultrasonic testing or radiographic testing could be used to investigate the quality of the weld. These methods could also be used to determine if a groove weld is a PJP groove weld rather than a CJP groove weld. However, the quality of a PJP groove weld or fillet weld generally cannot be easily or accurately determined through these tests. The size of a fillet weld can be easily determined through visual inspection. Visual inspection can also reveal any issues at or near the surface of the weld.

Appendix 5 Section 5.2.5 of the AISC Specification (a free download at www.aisc.org/2010spec) states:

“Where structural performance is dependent on existing welded connections, representative samples

of weld metal shall be obtained. Chemical analysis and mechanical tests shall be made to characterize the weld metal. A determination shall be made of the magnitude and consequences of imperfections. If the requirements of AWS D1.1/D1.1M are not met, the engineer of record shall determine if remedial actions are required.”

The tests described are destructive tests. You must take “representative samples of weld metal” and physically test them.

Larry S. Muir, P.E.

Filling Weld Access Holes If weld access holes are required to be filled, how should this be accomplished? Is filling them with weld metal appropriate?

In the June 2009 issue of MSC (www.modernsteel.com), the article “In the Moment” by Victor Shneur offers the following advice:

“Do not fill weld access holes with weld material for cosmetic or corrosion-protection reasons. In addition to the cost, it creates undesirable triaxial stresses. Using mastic materials is preferable to welding.”Weld access holes exist not only to facilitate welding, but

also to limit the “undesirable triaxial stresses,” Shneur explains. The only pros to filling weld access holes are likely to be based in cosmetic or aesthetic reasons. The cons to filling them with weld metal include changes in the assumed stress distribution, increased cost and the cracking that weld access holes are used, in some applications, to prevent. Also, when filling by welding, unless done using a qualified procedure shown to develop the strength of the base metal, the resulting strength and behavior of the material within the filled hole may be dubious.

Larry S. Muir, P.E.

steel interchange

larry Muir is director of technical assistance and Martin anderson is solutions center specialist at aiSC. heath Mitchell is a consultant to aiSC.

Steel interchange is a forum to exchange useful and practical professional ideas and information on all phases of steel building and bridge construction. opinions and suggestions are welcome on any subject covered in this magazine.

the opinions expressed in Steel interchange do not necessarily represent an official position of the american institute of Steel Construction and have not been reviewed. it is recognized that the design of structures is within the scope and expertise of a competent licensed structural engineer, architect or other licensed professional for the application of principles to a particular structure.

if you have a question or problem that your fellow readers might help you solve, please forward it to us. at the same time, feel free to respond to any of the questions that you have read here. Contact Steel interchange via aiSC’s Steel Solutions Center:

1 e Wacker dr., Ste. 700, Chicago, il 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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The answers to this month’s Steel Quiz can be found in AISC Design Guide 27 as well as on the AISC and Modern Steel Construction websites (www.aisc.org and www.modernsteel.com). And for more on DG 27, see “A New Guide for Stainless” in the December 2013 issue.

1 how much does the coefficient of thermal expansion for austenitic stainless steel differ from that for carbon steel?

a) 10% higherb) 20% lowerc) 30% higherd) 40% lower

turn to Page 14 for anSWerS

2 true or false: Stainless steels for structural applications are generally austenitic.

3 true or false: When welding stainless steel, the welder does not need to be qualified to weld stainless if they are qualified to weld carbon steel.

4 the properties of cast stainless steels differ from their rolled versions. for example, austenitic stainless steel castings may be slightly _________.a) deformedb) blue in colorc) Magnetic

5 true or false: there is not a specific welding code for welding carbon steel to stainless steel.

6 the “l” designation in the material (such as 304l, 316l, etc.) stands for ___________. a) low-carbonb) lite (contains less nickel)c) less ductiled) low-chromium

7 true or false: When designing with stainless steels, the material test report yield and tensile strengths are used.

8 true or false: austenitic stainless steels can exhibit high-impact toughness.

9 P last ic ana lys is of f rames i s __________ stainless steel.a) not applicable tob) applicable to

10true or false: even stainless steels may be subject to various forms of corrosion under certain circumstances.

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anSWerSsteel quiz1 c) the coefficient of thermal expansion for austenitic

stainless steels is about 30% higher than that for carbon steel. Where carbon steel and austenitic stainless steel are used together, the effects of differential thermal expansion coefficients should be considered in design.

2 true. Structural applications that use stainless steel require a combination of good strength, corrosion resistance, formability (this includes the ability to make tighter bends), field and shop weldability and elongation. the austenitic stainless steels provide these combined qualities.

3 false. Stainless weld metals run differently than carbon or low-alloy steel weld metals. the welder should be qualified by welding using a stainless wire of the same f number that they will use in production. aWS d1.6 provides qualification information for both the welder and the welding procedure.

4 c) Magnetic. austenite is soft, ductile and nonmagnetic, while ferrite is harder, less ductile and magnetic. austenitic stainless steel castings may contain higher levels of ferrite than rolled products, increasing magnetism. the additional ferrite also contributes to increased strength, increased resistance to stress corrosion cracking, less severe consequences of intergranular corrosion, and increased resistance to cracking during welding and casting (see www.stainlessfoundry.com/magnetic.asp).

5 true. Welding carbon steel to carbon steel has one set of requirements, which are covered by the aWS d1.1 welding code. Welding stainless steel to stainless steel has a separate set of requirements, which are covered in the aWS d1.6 welding code. no aWS document covers the mixing of products directly; however, there is some discussion of this topic in the Commentary to aWS d1.6.

6 a) the “l” in the designation indicates a low-carbon version with reduced risk of sensitization (of chromium carbide precipitation) and of intergranular corrosion in heat affected zones of welds.

7 false. it is recommended that the specified minimum yield stress, Fy, and the specified minimum tensile strength, Fu , be taken as the minimum values specified in the relevant aStM standard, just as with carbon steels.

8 true: even at low temperatures, austenitic stainless steels behave well. often, they are used for cryogenic applications and can demonstrate impact toughness well above 74 ft-lb (100 j) at –320 °f (–196 °C).

9 a) Plastic analysis of frames is not applicable to stainless steel due to a lack of research in this area.

10 true. however, good design and proper stainless steel selection provides suitable performance.

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WE HEAR THE WORD “CONSTRUCTABILITY” all the time—but what does it mean?

Simply put, constructability is the ease with which a struc-ture can be built. Constructable designs are more economical structures because they provide options and fl exibility before work has progressed and the die is cast.

The concept of constructability includes four main principles:➤ Simplicity = Economy➤ Least weight does not always = Least cost➤ Fewer pieces = Greater economy➤ Effi cient connection design = Reduced cost

Since the best, most constructable solutions for a project often depend on local construction practices and contractor preferences, the recommendations of the construction team—including the fabricator and erector—can improve effi ciency and economy and add value to your project early on and along the way. Below are 50 tips, seperated by category, that can enhance the construcability of your next project. (Note: These tips are from the seminar “50 Tips for Designing Constructable and Economical Steel Buildings,” presented at the 2011 and 2013 NASCC: The Steel Conference.)

ConnectionsTip 1: Design connections per the requirements of the

building code and AISC 360 (and AISC 341 if it is applicable). Tip 2: If delegating connection design work to an engineer

working for the fabricator, do so properly with Option 3 in Sec-tion 3.1.2 in AISC 303-10, the AISC Code of Standard Practice.

Tip 3: And also, show the reactions, moments and axial forc-es from Tip 1 when using Tip 2.

Tip 4: Provide load combinations and directions of reac-tions, moments and forces (Figure 1) at joints so the engineer

doing connection design can satisfy statics (always a plus!). Tip 5: Provide suffi cient information on the drawings to

minimize uncertainty among bidders. Section 3 in the AISC Code of Standard Practice lists the typical information needed to get responsive and comparable bids.

Tip 6: Understand that fabricator preferences differ regard-ing preferred connection details; some like shear tabs, others like all-bolted single or double angles, etc.

Tip 7: Don’t delegate design of reinforcing around beam web openings. Ei-ther eliminate the need for it or specify it on the design draw-ings. See AISC Design Guide 2: Steel and Com-posite Beams with Web Openings for more guidance (Figure 2).

Tip 8: Don’t del-egate design of plate girder welds (Figure 3).

Tip 9: Think about how the connections will be confi gured and detailed, even when using Option 3 in the AISC Code of Standard Practice.

TIPS TO TAKE YOUR TEAM TO THE TOPby MattheW d. brady, P.e., and Cliff SChWinger, P.e.

steelwiseThere are countless ways to improve

constructability on your next project.

Here are 50 of them.

Matt Brady ([email protected]) is aiSC’s upper Midwest regional engineer. Cliff Schwinger ([email protected]) is a vice president with the harman group.figure 1: diagram 1 is typical for gravity;

diagram 2 is excessive if it isn’t a real loading condition.

stiffeners

doubler plate

➤

do not delegate design of plate girder welds. (how does the fabricator know what the shear fl ow is?)

also, do not make these welds CjP welds. Size for actual required strength; fi llet welds usually work.

fabriCator to reinforCe WebS at oPeningS Where

reQuired to deVeloP Shear in beaM

figure 2

figure 3

➤

➤

18 february 2014

steelwise

Tip 10: Verify that framing can be installed (Figure 4). Talk to a fabricator—they’ll be happy you asked!

Tip 11: Use one-sided shear connections (like single-angle and single-plate connections) to simplify field work, unless they can’t provide the required strength.

Tip 12: Avoid full-depth stiffeners where possible. Eliminate them, and if they’re unavoidable, consider if they can be de-tailed to avoid fitting the stiffener (see Figure 5).

BoltingTip 13: Allow the use of bearing bolt strength values where

slip-critical values are not required in the AISC and RCSC Specifications.

Tip 14: Permit the use of any diameter and type of bolt, but avoid mixing grades in the same diameter.

Tip 15: Permit the use of short-slotted holes, especially in shear connections with the load transverse to the slot.

Tip 16: Remember that all slip-critical bolted connections are pretensioned, but not all pretensioned bolts need to be slip-critical. AISC 360-10, Section J1.10 has a list of connections where pretensioned bolts (or welds) are required, but these are not slip-critical.

WeldingTip 17: Use fillet welds sized for required strength whenever

possible. Overwelding increases volume and cost proportion-ally to the square of the weld size!

Tip 18: Avoid specifying arbitrary CJP groove welds and all-around fillet welds unless they are needed to achieve the required strength.

Tip 19: Favor fillet welds over groove welds.

Tip 20: Strive to configure connection details with a flat or horizontal welding position.

Tip 21: Favor a longer 5⁄16-in. (or smaller) fillet weld over larger fillet welds; 5⁄16 in. is the largest fillet weld size that can be made in one pass. Multi-pass welds are three to four times more expensive than single-pass welds.

ColumnsTip 22: Use the deepest practical column; especially avoid

W8 and smaller columns with connections to the web (Figure 6).

Tip 23: Size columns to eliminate the need for stiffeners, especially for the trapped double-angle connection illustrated in Figure 7, which cannot be installed.

Tip 24: Where column stiffeners can’t be avoided, make the opposing beams the same depth, and consider the effect of the stiffeners on beams framing in the perpendicular direction.

Tip 25: Orient columns to minimize skewed connections (Figure 8 ).

figure 4: framing geometry may present installation challenges.➤

do not extend stiffeners full-depth without reason

figure 5

➤

tranSfer girder beaM oVer ColuMn

Single- or double-angle connection may fit but must be welded to beam web; avoid W8s with web connections

bolt stagger

not needed

for W14s

Stagger bolts for W10s & W12s

W14 W12 W10 W8(difficult; not recommended)

figure 6

➤

➤ figure 7

Possible connections to column web—all more expensive than a standard full-depth connection

May not be able to install beam (depending on what’s happening at the other end)

May have web shear problems due to large cope on bottom

inefficient skewed connections to column web

3 skewed connections1 square connection

3 square connections1 skewed connection

➤

BUILD TOWARD THE SKY WHILE DRIVING CONSTRUCTION COSTS DOWN

For more information: Toll Free 800.475.2077 | Tel 949.305.7889 | sideplate.com

NEW FIELD-BOLTED SIDEPLATE® MOMENT CONNECTIONSidePlate designs use less steel tonnage than conventional ones, and now, by eliminating all field welding, our new bolted connection reduces field labor and delivers even lower construction costs on projects governed by wind or low seismic (R=3). Not to mention our engineers provide responsive assistance and customer service at no charge to the design team. Visit SidePlate.com to find out what we can save on your next project.

20 february 2014

steelwise

Tip 26: Simplify base plates and anchor rod details (Figure 9).

BeamsTip 27: Watch

out for connection interference where beams are slightly offset from columns (Figure 10). Change the details or determine that the geometry can work before showing this on the design drawings; again, ask a fabricator, and they’ll be glad you did.

Tip 28: Increase beam depth to avoid web reinforcing (Fig-ure 11).

Tip 29: Size members to have sufficient strength at the net section. This usually can be accomplished by limiting the re-quired strength to 75% of the gross section strength when the connection details are not known during member selection (Figure 12 ).

Hollow Structural Sections (HSS)Tip 30: Favor round HSS or steel pipe columns over square/

rectangular HSS when there are skewed connections (Figure 13).

Tip 31: Configure HSS framing to simplify connections (Figure 14 ).

Smallest base plate, but...➤ different anchor rod pattern

for every base plate➤ unsymmetrical anchor rod

pattern➤ fractional anchor rod spacing

(based on base plate size)

largest base plates, but...➤ Square plates➤ doubly symmetric anchor

rod pattern and fewer different anchor rod patterns

➤ easier to build

1¾”

1¾”

rod SPaCing

e.W.Square plates; square anchor rod patterns

Space anchor rods based on column size, not base plate dimensions.

figure 9: keep column base plates and anchor rod patterns square.➤

Connection interference

as shown on framing

plan

figure 10➤

Web reinforcing plate

use deeper beam to eliminate web

reinforcing plate

W14

W18

➤ figure 11

Possible situations requiring web reinforcing:➤ large copes with

heavy reactions➤ high beams

framing to low girders

➤ Skewed beams with long copes

angle if required to prevent web buckling

(if web reinforcing is required, a less expensive solution may be

to use a deeper beam)

➤

Max. recommended stress ratio at gross section

required strength

usable strength= 0.75 (max.)=

➤

figure 13➤

squaresquare

square

square skewed

skewed

end plate

Shim

Cope

hSS

double-angle

connectionno! yeS

no!yeS

Single plate shear conn.

thru-plate single-plate shear conn. (not necessary)

➤


steelwise

Vertical BracingTip 32: Orient columns square to the framing plan when

they are part of a braced frame (Figure 15).

Tip 33: Select efficient diagonal braces: single-angles (good for small loads), double-angles (efficient connections), HSS (highest brace strength per pound of steel), W-shapes (con-nections can be more intricate than other brace types, Figure 16). When properly selected with good connection details, any brace type can be economical.

Tip 34: Configure slopes of diagonal braces between 35 and 55 degrees (Figures 17 and 18).

Moment ConnectionsTip 35: Orient columns in moment frames for strong-axis

bending (Figure 19 ).

Tip 36: Strong-axis beam-to-column moment connections are generally less complex than weak-axis beam-to-column mo-ment connections (Figure 20).

Tip 37: Consider making girders continuous through col-umns at heavy moment-connected girders to simplify flow of moment through columns (Figure 21). Ask the fabricator, since the gain needs to outweigh the difference in construction to make this tip viable.

braced frame

Strive for connections to column flanges in braced frames

braced frame

avoid skewed connections to column in braced frames

hSS brace W shape braceSingle-angle or double angle brace

5⁄16

figure 15

figure 16

➤

➤

braces with shallow slopes can have

difficult connections

inefficient connections at braces

with shallow slopes

the closer braces are to 45°, the more compact the connections will be

figure 17

figure 18

➤➤

➤

efficient moment frame (all columns bending about strong axis)

inefficient columns at each end (bending about weak axis)

Where column orientation cannot be changed, consider eliminating weak-axis column moment connections.Weak-axis column moment connection details are often more complex than strong-axis column moment connection details

for 14”×14” W14 ColuMnS Ix ⁄ Iy > 2.5

heavy girder

beaM-to-ColuMn flange MoMent

ConneCtion

beaM-to-ColuMn Web MoMent ConneCtion

Size columns to eliminate

need for stiffeners

extended single-plate shear connection

all bolted shear connections

note: if columns were upsized to control drift, they may already be large enough to eliminate the need for stiffeners fitted t&b

flange plates

figure 20

figure 21: Where girder moments are big and column moments are small, consider running girders continuous through columns.

➤

➤

22 february 2014

Tip 38: Run cantilevered roof beams over the tops of col-umns (Figure 22).

Tip 39: Avoid skewed beam-to-column moment connec-tions (Figure 23).

Tip 40: Beams with flange-bolted moment connections must have sufficiently wide flanges to install bolts (Figure 24). Many light beams do not have wide enough flanges!

FramingTip 41: Frame members with very large reactions square to

columns—preferably to the flanges (Figure 25 ).

Tip 42: Configure framing so that no more than one beam frames to any one side of a column (Figures 26 and 27).

Tip 43: Head off steeply skewed connections (Figure 28 ).

Tip 44: Configure framing to minimize skewed connections (Figure 29 ).

steelwise

figure 22: note: if roof framing slopes, coordinate so there’s not a kink in the beam at the column.

yeS! no!

Cantilever Cantilever

➤

Min. gage for installation of 7⁄8”Ø bolts through flanges

3½”

figure 23: difficult to detail.

figure 24: Min. recommended flange width to install bolts through flange = 6”. (don’t forget to check net section.)

➤➤

➤

non-standard bent plate connection

flange interference

Weld connections to beam webs (to avoid bolt interference)

big cope; check web buckling

Web reinforcing, if required

do not do this!

figure 26

figure 27

➤➤

➤

Steep skewed connections can be a problem with,➤ Small beams (long copes realitive to depth)➤ big beams with large reactions

Steep skewed connection

add header beam

More constructable connection (smaller skew, smaller cope)

long cope; possible need for web reinforcing; difficult to install bolts in web of supported beam

Problem Solution

Square Connection

Skewed Connection

Skewed Connections@ e.e.

➤

double angle Conn. w/ ½“ thk. angleS & 10 roWS of 7⁄8”Ø a490n boltS

1” Pl. w/ (20)-1”Ø a490n boltS

CjP Weldfillet WeldSno WeldS

W36×150, Vu=490k

1” Pl. (aStM a572, gr 50) w/ (40)-1”Ø a490n boltS


Tip 45: Configure framing to minimize the number of beams (Figure 30 ).

Tip 46: Maximize slab span to minimize the number of beams (Figure 31).

Tip 47: Minimize the “gingerbread”— extra small pieces of steel (Figure 32).

Miscellaneous topics Tip 48: Avoid torsion in W shapes.Tip 49: Use R=3 and the associated basic

seismic design without AISC 341 require-ments, when possible.

Tip 50: Use camber intelligently. It often is more economical to design stiffer floors without camber.

steelwise

turning deck eliminates these small beams

Remember: The more choices the fabricator, erector and connection design engineer have available to them—and the earlier in the process they are able to provide in-put—the more likely they are to provide better solutions. Engage them early and they’ll help enhance your project’s constructability and success. ■

Want more constructability and economy tips? You can view the related SteelDay 2012 webinar for free (and receive free CEUs or PDHs) at www.aisc.org/50tips. You can also view the related 2013 NASCC presentation at www.aisc.org/50tipsmedia. And Cliff Schwinger will be presenting sessions at this year’s NASCC: The Steel Conference, March 26-28 in Toronto, as well. Visit www.aisc.org/nascc to register and find out more about the show.

➤ fewer beams➤ fewer connections➤ fewer crane picks

20’

40’

30’

30’

benefits

➤ fewer pieces➤ less steel weight (usually)➤ fewer connections➤ fewer crane picks➤ More tributary area

per beam = greater ll reduction

➤ More mass per beam = less vibration

➤ thicker slab = greater composite beam Mn

(1½” deCk + 3½” l.W. ConCrete) (3” deCk + 3½” l.W. ConCrete)

6½” Slab5” Slab

6’-0” 10’-0”

➤

figure 31

figure 32

➤➤

24 february 2014

LEED WAS NEVER INTENDED to remain static but rather evolve over time—and evolve it has yet again.

Version 4 of the U.S. Green Building Council’s rating sys-tem (which stands for Leadership in Energy and Environmen-tal Design) is now a reality, approved by ballot in late spring of 2013 and announced to be open for the registration of new projects at USGBC’s Greenbuild conference in Philadelphia this past November.

In an attempt to push building performance levels to a higher level, LEED V4 represents a major change from ear-lier versions of the rating system. In no section are the credit changes more dramatic than the one focusing on building materials. Whether these changes were well thought through, appropriate and based on a good analytical foundation was cer-tainly much debated. But the fact is that LEED V4 is now a reality and the design and construction community is in the process of adapting to this new world.

LEED is not intended to exist in a vacuum as the only green building standard or rating system available for project owners. USGBC’s stated strategy is to encourage the adoption of green building codes and standards, such as the International Green Building Code and ASHRAE 189.1, by state and local jurisdic-tions to define a baseline for sustainable construction. The LEED program will then sit on top of this baseline, recogniz-ing projects that go above and beyond building code require-ments. The combination of this strategy and the more complex and stringent credit requirements in LEED V4 will probably result in a decrease in projects seeking LEED certification but also an increase in the sustainable performance of the overall inventory of new buildings.

Many of the nuances relative to the implementation of LEED V4, as it relates to materials used in building projects,

are yet to be worked out in practice. Below are a series of ques-tions related to LEED V4 that merit immediate attention by designers, fabricators and constructors.

Does LEED V4 immediately replace prior versions of LEED? No, projects can continue to be registered under LEED 2009 until June 1, 2015, and based on previous transi-tions between LEED versions those projects will then prob-ably have until mid-2021 to complete construction and apply for actual LEED certification. This means that the existing requirements for recycled content and regional material docu-mentation will continue to be in use for another seven years. For an overview of how these credits are addressed by the use of structural steel, see “A Green Roadmap” (MSC 02/13).

Does LEED V4 encourage the use of life-cycle assess-ments (LCAs) to select framing systems? Yes, the only way that new construction can gain any credit points under the MR credit for “Building Life-Cycle Impact Reduction” is either through the use of a large percentage of reused or salvaged materials or to conduct a life-cycle assessment of the project’s structure and enclosure, comparing the structure to a similar

“baseline” building. To gain three credit points the LCA must demonstrate a 10% improvement of the selected building in three of six environmental impact categories (one of which must be global warming potential) and no degradation of greater than 5% in the remaining three categories.

Are the data, expertise and technology required for LCAs available to support this level of analysis? No, the world of LCAs is a return to the Wild West. A limited number of LCA experts exist that understand the boundaries and cal-culation methodologies behind the various material data sets and are trained to use assessment tools that require the actual modeling of the entire construction process rather than an esti-mation of average impacts.

A variety of estimating programs for comparing the environ-mental impacts of competing framing systems have entered the marketplace in the last few years. The intention of these tools is to allow a design professional not trained in life-cycle assess-ment to perform these comparisons. The problem with them is twofold. First, relative to the environmental impact data, many assumptions are being made with respect to the environmen-tal impacts of various materials and construction operations. These assumptions include the boundary definitions for the equivalent comparison of data and underlying methodologies for determining the LCAs for individual products and materials. In addition, no distinction is made between different sources of (or process for making) the same product; rather industry aver-ages are used for material impacts. Secondly and of even greater

UP TO SPEED ON LEED

by john CroSS, P.e., leed aP

business issuesWhat you need to know about the new version of

the ubiquitous green building rating system.

John Cross is an aiSC vice president. you can reach him at [email protected].


concern is the determination of the quantities of materials used in each of the two framing scenarios. The quantities being used in these tools are based on rough parametric estimates rather than on preliminary design quantities. The parametric estimates are based on simple assemblies and limit the opportu-nity of the design professional to improve the efficiency of the structural system before the LCA comparison is made.

The AISC Steel Solutions Center routinely develops con-ceptual solutions for structural steel-framed projects using structural design software. While these conceptual solutions are one step before an actual preliminary design, they have been found to be typically within 10% of the final steel quantities for a project—a range that is appropriate for use in a LCA esti-mate. A random sample of 100 structural steel-framed projects for which conceptual solutions had been performed were ana-lyzed using one of the more prevalent environmental impact estimators. The difference between the quantities generated by the estimator and the quantities determined in the conceptual solution were significant, ranging from an 80% overstatement of steel quantities to a 40% understatement (see Figure 1). It is impossible to make a meaningful comparison of environmen-tal impacts to the required level of 10% improvement or 5% degradation if the variation of the material quantities can be as great as plus 80% or minus 40%.

The bottom line is that for a meaningful comparison of the environmental impacts of two building structures, it is neces-sary to engage the expertise of two trained professionals. An LCA expert who understands the background and limitations of the data sets being used in developing the comparison and a structural engineer who can create preliminary design models for the two alternatives from which material quantities can be extracted; see “And the Winner is…” (MSC 08/10) for an LCA study comparing two alternative building designs.

What’s all this talk about “transparency?” Transparency is a key concept in LEED V4. Three credits address transpar-ency in three different areas: transparency in the reporting of environmental impacts, transparency in reporting the sourcing of raw materials and transparency in the disclosure of material ingredients. To meet the requirements of these sections a mini-mum of 20 products used in the building project must have this information available. In each of the three credits, a point can also be earned for making a selection between similar products based on the information that has been disclosed.

Environmental impacts will be reported on a product basis through the use of an environmental product declaration (EPD). EPDs can be issued for the product at any stage of the product’s

life cycle and on either an industry average or individual prod-uct manufacturer basis. For example, there will be an industry average EPD for hot-rolled structural steel sections from cradle-to-mill gate and the individual mills producing hot-rolled struc-tural steel may also opt to create a producer-specific EPD for hot-rolled structural steel. In addition, an industry average EPD for fabricated hot-rolled structural steel from cradle-to fabricator gate will also be produced using fabrication industry data col-lected in a survey to be conducted over the next several months.

Responsible sourcing documentation can be either self-declared manufacturer reports of product sourcing practices (if self-declared, the product only gets half credit) or third-party verified reports relative to the supply chain of the project. In addition, a separate credit is available based on the sum of a number of single attribute factors including recycled content of all the materials in the project exceeding 25% of the cost of project materials (however, the overall contribution of struc-ture and enclosure materials is limited to 30% of the compliant building materials).

The disclosure of material ingredients will most likely take the form of a health product declaration (HPD) or material data sheets that list all of the ingredients of the product down to 1,000 parts per million. This data is product-specific and can-not be presented as an industry average. An additional point of credit is available for use of materials in the project exceeding 25% of the cost of the overall project materials, whose material ingredient disclosures are third-party verified and do not con-tain any chemicals with health-related issues.

This seems pretty complex; is the structural steel industry ready to provide this documentation? The struc-tural steel industry will continue to provide the documentation of recycled content and regional sourcing required by LEED 2009 and is committed to providing environmental impact doc-umentation required by LEED V4 on an industry average basis by mid-2014. Individual producers are working on developing the documentation required for responsible sourcing and mate-rial ingredients. As the transition to LEED V4 will be occur-ring over the next several years, this should meet the ongoing requirements of any building project.

Will LEED V4 result in more sustainable buildings? Any rating system like LEED cannot guarantee that it will result in more sustainable buildings. A rating system only focuses on limited discrete aspects of the building’s design and construc-tion. It is when design and construction professionals work together, using their expertise to optimize their designs and activities from both an economic and sustainable perspective, that the actual building becomes a more sustainable structure. LEED V4 can provide incentives, perspective and market push to help accomplish those goals, but in the end it is the expertise, collaboration and common sense of the design and construc-tion professionals and the guidance of the project owner that will result in a sustainable structure.

Where can I get additional help in understanding the requirements of LEED V4? MSC will continue to publish articles exploring the requirements of LEED V4. In addition, AISC regional engineers are available to discuss issues—and give presentations—regarding the sustainable characteristics of structural steel and the requirements of LEED V4, and the Steel Solutions Center is happy to answer questions regarding this new version of LEED. ■

80.0

60.0

40.0

20.0

0.0

-20.0

-40.0

-60.0

-80.0

% v

aria

tion

from

con

cep

tual

mod

el

figure 1: Variation (by percentage) between lCa estimator and conceptual solution material estimate, by project.

➤

26 february 2014

FOR SOME WHO VISITED the massive hole that was left in Lower Manhattan and the nation’s heart following the events of September 11, 2001, it was likely difficult to imagine that the area would eventually be the home of the nation’s tall-est building. For others, there may have never been any doubt that it would.

For more than 12 years, however you thought the redevelop-ment of Ground Zero would happen, its largest, most symbolic and most prominent piece is now in place.

One World Trade Center (1WTC), the tallest of four high-rises planned as part of the Ground Zero reconstruction master plan for lower Manhattan, was officially declared by the Coun-cil on Tall Buildings and Urban Habitat (CTBUH) to be the tallest building in North America; it will likely be the third-tallest building in the world upon completion.

In keeping with Daniel Libeskind’s master plan, the overall height of the tower from the ground level to the top of the spire reaches 1,776 ft, in reference to the year of the nation’s founding, though the main roof is designed to have the same height as the original WTC towers (1,368 ft). The addition of a 408-ft-tall spire rising from the main roof (mounted atop a

reinforced concrete mat directly supported by the tower’s con-crete core) brings the tower to its symbolic full height, and a multilayer circular lattice ring atop the main roof, which pro-vides support for the spire, allegorically recalls the torch held by the Statue of Liberty.

A New StandardThe symbolic and high-profile nature of the building cre-

ated a wide range of challenges and opportunities, and the structural considerations were equally immense. The collapse of the Twin Towers in 2001 created a major debate in engi-neering communities worldwide with respect to the appropri-ate lessons to be learned from the consequences of the attack and the need for mitigation strategies to be implemented for future high-rise buildings. The design team, faced with numer-ous and unique challenges—paramount among them being security issues—was expected to meet or exceed future codes and standards that had not yet been published. We were also keenly aware that the design of this tower would perhaps set a standard for future tall buildings, inspiring us to think beyond the conventional techniques of tall building design.

The most highly anticipated

American skyscraper in recent history,

One World Trade Center comes

together in the context of past tragedy,

present demands and future

expectations for tall buildings.

by ahmad rahimian, S.e., P.e., Ph.d., and yoram eilon, P.e.

rising to the ToP

Modern STEEL ConSTruCTion 27

➤

1WTC’s program includes 3 million sq. ft of new construction above ground and 500,000 sq. ft of subterranean space. The tower consists of 71 levels of office space, eight levels of MEP space, a 50-ft-tall lobby, tenant amenity spaces, a two-level observation deck at the 1,269-ft point, a “sky” restaurant, parking, retail space and access to public transportation networks. The tower structure extends 70 ft below grade passing through four subterranean lev-els where some of its structural components required reposition-ing to clear the PATH train tracks that cross the building at the lowest basement level. All of this space is framed with approxi-mately 45,000 tons of structural steel in total.

The building footprint above grade level starts with a 205-ft square plan. The office levels start 190 ft above grade, stacked over four levels of mechanical space above the main lobby. The four corners of the tower are gradually “cut away,” sloping gently from the first office level inward until, at the roof, the floor plan

The overall height of the tower (including the spire) is 1,776 ft, though the main roof will have the same height as the original WTC towers (1,368 ft).

Ahmad Rahimian ([email protected]) is director of building structures and Yoram Eilon (yoram.eilon@ wspgroup.com) is vice president of building structures, both with WSP Cantor Seinuk.

➤ 1WTC’s program includes 3 mil-lion sq. ft of new construction above ground and 500,000 sq. ft of subterranean space.

➤ The framing system uses approximately 45,000 tons of structural steel.

WSP Cantor Seinuk

dimensions again square off at 145 ft on a side, now rotated 45° from the base quadrangle. The elevation is transformed into eight tall isosceles triangles forming an elongated square antiprism frustum. At mid-height of the tower, the floor plan forms an equilateral octagon. The tapering of the building geometry not only accommodates the project’s gross area requirement but also creates an aerodynamic shape that reduces the wind effect on the tower. Since tall building design in New York is usually governed by wind load, the tower shape has an innate positive effect on the building performance under wind loading.

On the Right PATHThe tower’s foundation and below-

grade structure are founded on Manhattan bedrock using spread and strip footings with bearing capacities of 60 tons per sq. ft or better. Due to space constraints such as the proximity of the existing train lines, it was necessary to excavate deeper into the rock at select locations in order to achieve a higher bearing capacity of up to 114 tons per sq. ft. Rock anchors/tie downs extending 80 ft into the rock were installed to resist the overturning effect from extreme wind events.

PATH commuter trains run through the western portion of the “Bathtub” (an excavation down to the bedrock, surround-ed by slurry walls, that was built to keep water out of the subterranean levels of the original WTC). As it was essential to keep the PATH trains operational during the construction process, the constructability strategies became a primary consideration in the design of the below-grade structure. Temporary structural steel framing was in-troduced and integrated into the structure, bridging over the train tracks, and perma-nent and temporary steel framing was used for temporary support of the slab while some of the tower columns were trans-ferred away from the train tracks.

The tower stability system, although en-hanced by the below-grade structure, was

➤a completed rendering of 1 WTC (far left) and other buildings at the Ground Zero site in lower manhattan, at night...

➤

28 february 2014

...and during the day. 1 WTC’s elevation is transformed into eight tall isosceles triangles forming an elongated square antiprism frustum.

Silverstein Properties

Silverstein Properties


designed to be self-sufficient. The tower structure is comprised of a “hybrid” sys-tem combining a robust concrete core sur-rounded by steel floor framing and with a perimeter ductile steel moment frame. The reinforced concrete core wall system at the center of the tower acts as the main spine of the tower, providing support for gravity loads as well as resistance to wind and seis-mic forces. The core is approximately square in footprint with a depth of about 110 ft at the base—large enough to be its own build-ing; it houses mechanical rooms and all means of egress. The walls are connected to each other over the access openings using steel wide-flange link beams developed into the concrete shear walls. A ductile perimeter moment frame system is introduced for re-dundancy and to further enhance the over-all building performance under lateral wind and seismic loads. The perimeter moment frame wraps around all vertical and sloped perimeters, forming a “tube” system.

The tower’s antiprism geometry cre-ates unique structural conditions along its height, which necessitated the design and fabrication of special nodal elements using relatively large plating with signifi-cant capacity for load transfer. For further enhancement of the lateral load resisting system, the concrete core at the upper mechanical levels is connected to the pe-rimeter columns via a series of multilevel outrigger trusses, composed of built-up box sections, in both orthogonal directions. Taken together, the perimeter and core sys-tems make 1WTC safer than either system could make it on its own, thanks to the re-dundancy they provide to one another.

Defying GravityThe floor system within the concrete

core zone is a formed cast-in-place con-crete beam and flat slab system, while the floor area outside the core is concrete on composite metal deck supported on steel beams and connected via shear connec-tors. The column-free floor system spans between the core and the perimeter steel moment frame (with a maximum span of 47 ft) for construction efficiency and maxi-mum flexibility of tenant use.

One of the most common approaches to hybrid construction is having the concrete core constructed using jump-forms or slip-forms, independent of and ahead of the steel framing. Subsequently, steel framing is constructed around the advancing constructed core. In New

York City, however, this approach has generally not been available to the construction community until recently. The construction is sequenced by first erecting an all-steel framing system throughout the floor, both inside and outside of the core, preceding the concrete core construction; the steel framing within the core is primarily an erection system that is embedded in the concrete core walls. The

construction of the structure was staged in four highly orchestrated sequences of steel framing, metal deck and concrete outside the core, concrete core shear wall and concrete floor construction inside the core. A wide-flange ring beam is introduced at the outer face of the core in order to maintain a temporary gap between the floor system and the core wall allowing for the raising of the forms. The total

30 february 2014

lag for the entire sequences is about eight to 12 floors. The construction sequencing was a critical aspect of the structure’s design as it would affect the connection approach and details between various elements, especially at the interface between the concrete core walls and adjacent areas. It would also affect the nature of axial shortening of the tower as well as the method of computation and the construction compensation. Axial shortening becomes more important in hybrid structures due to the differing natures of the materials’ behavior, such as the shortening of steel and concrete as a result of elastic, creep and shrinkage effects over time.

Axial shortening studies were performed to identify the an-ticipated deformation of the concrete core wall and perimeter steel framing during and following construction. The elastic shortening of the steel erection columns at the core before en-casement had to be carefully considered. The goal was that at the end of construction the floors would be leveled and po-sitioned at the theoretical elevations. In order to compensate for the shortening, the contractor could adjust the elevations of perimeter steel columns and center concrete walls by super-elevating them to differing degrees. For the structural steel this could be achieved by either fabricating the columns longer than the theoretical, shimming in the field during erection or a com-bination of both.

Correct CodeFrom the onset, one of the main challenges was the selection

of appropriate codes and standards for the design of the structure. The latest edition of the New York City Building Code at the time, which was based on the 1968 code with amendments, was used as the primary design code in combination with the Port Authority’s design guidelines. However, acknowledging that it was essential to design this building with the most advanced standard available at the time, the IBC 2003 structural provisions were adopted with re-spect to wind and seismic loading (and were selected knowing they would be the basis for the new version of New York City Building Code). With respect to structural integrity, hardening and structural redundancy, the U.S. Government Standards such as GSA, DOD and FEMA were used as references for further enhancements. In addition, the latest edition of AISC and ACI codes, standards and specifications were adopted, particularly those regarding ductile design of the moment frame connections.

Wind Tunnel TestingThe structure has been designed for wind load requirements

of IBC 2003, taking into consideration New York’s local wind conditions. In addition, a series of wind tunnel tests were per-formed to ascertain a more accurate measurement of wind load-ing and wind response of the tower with respect to hurricane

➤ The building is now officially the tallest in north america.

➤ The structural system at the base of the tower.

WSP Cantor Seinuk


wind load effects and human comfort criteria. High-frequency force balance (HFFB) and aeroelastic tests were performed at the Rowan Williams Davies & Irwin wind tunnel facilities at different stages of the design; the aerodynamic and aeroelas-tic effects of the spire were also considered. Wind tunnel tests were performed, including the surroundings effect, in view of the likelihood that Towers 2, 3 and 4 may or may not be com-pleted at the time of 1WTC’s completion. The acceleration re-sults at the highest occupied level meets the criteria of human comfort for office buildings, and the structure is also designed for wind storms with 1,000-year return periods, per IBC 2003.

As of December 2013, construction of 1WTC was complete, though it isn’t scheduled to open until later this year. The tower incorporates numerous innovative engineering solutions, some of which were presented here. If we could to go back and change anything, it would be the circumstances under which we were invited to engineer this symbolic building. That said, the design and construction of this project is the result of a relentless collaborative effort between numerous design and construction teams over a period of several years with a resolute focus on the goal of creating an iconic tower reaffirming the preeminence of Lower Manhattan and the resiliency of the country’s spirit and ingenuity. ■

OwnerPort authority of new york and new Jersey

Owner’s RepresentativeSTV Construction, new york

ArchitectSkidmore, owings and merrill, new york

Structural EngineerWSP Cantor Seinuk, new yorkSbP, new york (Spire)

Construction ManagerTishman Construction Company, new york

Steel TeamFabricatorsmrP, llC, South Plainfield, n.J. (aiSC member/aiSC Certified fabricator)banker Steel Company, llC, lynchburg, Va., (aiSC member/aiSC Certified fabricator)

Detailersdowco Consultants, ltd., mississauga, ontario, and Surrey, british Columbia (aiSC member)automated Steel detailing associates, ltd., Toronto (aiSC member)

➤ The building is designed for wind storms with 1,000-year return periods, per ibC 2003.

WSP Cantor Seinuk WSP Cantor Seinuk

The new Army hospital at Fort Benning is the

U.S. Army Corps of Engineers’ first-ever design-build hospital project.

by roberT Wayne SToCkS, P.e., ZaChary kaTeS, P.e., and keVin maCleod

buildinG up the fort

32 february 2014

Thornton Tomasetti


BRAC MEANS SOMETHING DIFFERENT for every military installation.

Under the Base Realignment and Closure program, facili-ties are generally downsized, consolidated or demolished alto-gether. In some cases, however, the program mandates new or replacement facilities.

The U.S. Army base at Fort Benning, on the outskirts of Columbus, Ga., is one of these cases and is currently under-going major redevelopment. A critical part of this realignment includes replacement of the aging Martin Army Community Hospital, which originally opened in 1958. Since April 2011, a team led by Turner Construction Company has been construct-ing the new Martin Army Community Hospital, the U.S. Army Corps of Engineer’s first-ever design-build hospital project.

The 745,000-sq.-ft facility, which is seeking LEED Silver certification, was designed by a joint venture between architects Ellerbe Becket (now AECOM) and RLF. It features a 70-bed hospital with two attached clinic buildings, which are separated by a four-story, column-free concourse that serves as the pri-mary entrance to the facility.

Structuring the CampusThe project is located on a challenging 50-acre site that

slopes 230 vertical ft from front to back. The site layout was designed to “communicate” with the surrounding wooded ar-eas with the intent of improving the patient experience. The hospital building is eight stories high and is set into the sloping site, with two floors located below grade and exposed to daylight on the downhill side. The lower levels of the hospital support diagnostic space and are separated from the upper floor patient rooms by an interstitial mechanical level housing the hospi-tal’s air-handling equipment.

The structural floor framing system of the hospital consists of composite steel deck supported by wide-flange steel W16 beams, W24 girders and W14 columns with a

typical 32-ft by 32-ft bay size and a typical floor-to-floor height of 16 ft. Lateral forces for the hospital are resisted by steel mo-ment frames that are located at the building’s perimeter and with one interior line in each direction. The moment frames transition to steel braced frames at the lower two levels to match the stiffness of the concrete basement walls and to par-ticipate in resisting the unbalanced earth pressure, as well as wind and seismic loads. The clinic buildings are of similar steel construction to the hospital, and the lateral system for the clin-ics consists of perimeter steel braced frames.

The grand concourse is structurally independent and is sand-wiched between the hospital and clinic buildings. It functions as the main entrance to the entire facility, welcoming occupants into a four-story, high-bay space surrounded by a glass curtain wall and views of nearby Upatoi Creek. The triangular-shaped roof area includes steel roof deck supported by steel beams and girders, and the column-free space is made possible by two long-span tension rod trusses—the longest being 75 ft—located in the clerestory be-tween the high and low roofs. The truss diagonals consist of double 1¼-in. tension rods in one direction and single 1¾-in. tension rods in the opposite direction. Steel wide-flange columns surrounding the high bay space support a grid of HSS girts that provide lateral support to the glass curtain wall. The lateral system was carefully integrated with the architecture of the space and includes braced frames hidden in elevator shafts, exposed tension rod bracing in the panoramic glass wall and wide-flange columns that cantilever above a low roof diaphragm.

➤a four-story, column-free con-course that serves as the primary entrance to the facility.

Topping out the building.

Robert Wayne Stocks ([email protected]) is a managing principal, Zachary Kates ([email protected]) is a vice president and Kevin Macleod ([email protected]) is a senior engineer, all with Thornton Tomasetti’s Washington, d.C. office.

➤

Thornton Tomasetti

The Design-Build PursuitThe team participated in several full-day

design charettes attended by all disciplines, where design concepts were studied for cost and constructability. Having all of the major stakeholders present at the charettes improved collaboration and focus and al-lowed decisions to be made quickly, with everyone understanding the driving forces behind the decisions. For example, the team prioritized flexibility of space in the hospital building and quickly determined that pe-rimeter steel moment frames, in lieu of steel braced frames, would meet that goal. Schuff Steel, the fabricator, was on board from the beginning of the pursuit and offered great direction into the availability and selection of steel materials and steel-related detailing. Repetitive design details such as exterior wall attachments, steel connection types and slab edge support conditions were chosen to align with Schuff’s fabrication and erection preferences.

“The collaboration and active participa-tion of the designers and the builders in these early charettes made the difference,” said Martin Miller, project executive for Turner. “The collaboration allowed the team to study, discuss and decide on de-sign concepts in days what would normal-ly take months.”

To accurately capture steel costs, Thorn-ton Tomasetti (TT) created preliminary de-sign models using RAM Structural System and transmitted them directly to Schuff Steel for tonnage determinations. TT provided estimates of additional tonnage required for project-specific requirements, such as steel framing premiums at vibration-sensitive areas supporting medical equipment or ad-ditional framing needed to support major piping runs. Preliminary tonnage estimates for the steel frame were found to be within a few percent of the actual steel frame tonnage.

In addition, the design met the strict re-quirements of the request for proposal au-thored by the Corps of Engineers, includ-ing the referenced International Building Code, Savannah District Design Manual and Department of Defense “Unified Facilities Criteria.” Overall, the pursuit phase was a two-month effort.

➤a truss for the concourse.

➤ a rendering of the concourse framing.

The councourse separates the 70-bed hospital and two attached clinic buildings.

➤

34 february 2014

Thor

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Chicago Metal Rolled Products Saved Their CustomerMore Than 80,000 lbs. of 12 Sq. Tubing.

Early involvement in the University of Phoenix Stadium (2007 IDEAS2 National Award Winner) allowed Chicago Metal Rolled Products to save their customer time and money when curving 402 tons of 12 x 12 x 5

8

and 12 x 12 x 12 tubing to radiuses from 1000 to 1200 feet for the roof trusses.

Using advanced technology, Chicago Metal curved 52 feet of distortion-free arc from stock only 54 feet long. With traditional curving methods, 6 to 10 feet of each tube would be lost to scrap. Chicago Metal’s solutions also substantially reduced freight charges.

Always meeting the fabricator’s schedule, the company received 213 pieces of tubing from mills, stored it clean and dry, and then curved and shipped it over the course of five months.

According to the project manager and subcontract administration manager, this project “went almost flawlessly despite its complexity and challenging schedule.” A tribute to the teamwork of the roller, the fabricator and the erector.

Model SharingFrom day one, Turner was committed

to a building information modeling (BIM) approach for the project, which minimized conflicts during construction and reduced requests for information and costly field work. The design team produced work us-ing Revit and traded coordination models on a weekly basis, and the structural Revit models were transferred to Schuff as the basis for the Tekla fabrication models. The fabrication models were then combined with the architectural and mechanical mod-els by Turner’s in-house modeling group to create one comprehensive BIM model. This model was used to coordinate the location of work in the field, perform clash detection and help resolve system interferences.

“The steel frame became the base layer for the development of the architectural model, providing excellent coordination of the en-tire exterior shell,” said Miller. “The interior details were then added as design progressed. In retrospect, the biggest coordination prob-lems in the field were with construction elements that did not get put into the BIM model during the accelerated proposal devel-opment period, such as precast panel bracing.”

Consistent with Turner’s commitment to BIM, TT and Schuff employed an innova-tive use of the 3D Tekla fabrication model by performing in-model review of the steel shop drawings. Specifically, a model-based shop drawing review was performed wherein steel elements were approved directly in the model. Because hard-copy shop drawings were a required submittal by the Corps of Engineers, shop drawings in PDF format were linked to each steel piece and accessible directly through the model. Shop drawing markups were made using a PDF writer, and the submittal, model and shop drawings were returned electronically. This allowed a more efficient and higher-quality review process for TT, as repetitive elements were grouped and reviewed together. More complex, high-ly detailed connections were viewed in 3D, clearly showing the relationship to adjacent connecting members. The process resulted in a faster approval process and a reduction in re-detailing efforts, which subsequently led to a reduction in fabrication time and field work.

➤ a bird’s-eye view of the new facility.


➤ Truss installation.

The triangular-shaped roof area includes steel roof deck supported by steel beams and girders, and the column-free space is made possible by two long-span tension rod trusses.

➤

TurnerTurner

Thornton Tomasetti

36 february 2014

TT’s Construction Support Services group in Kansas City was employed directly by Schuff to perform all steel connection design on the project. This allowed the connection designers to communicate directly with the structural engineers to resolve questions quickly, avoiding the cumbersome RFI process; con-fi rming RFIs replaced the traditional approach of ineffi cient sequential communication. The construction support team was able to help identify and resolve areas where complicated and expensive connections could be avoided or simplifi ed, and working as an integrated team saved time and ultimately pro-duced an effi cient and coordinated end product.

Designing For the UnthinkableThe hospital, clinics and concourse comply with Department

of Defense requirements of the Anti-Terrorism Force Protection (ATFP) Directorate and resistance against progressive collapse, with the goal of minimizing occupant fatalities during a terror-ist attack. Blast consultant Weidlinger Associates determined the blast loading on the structure and provided reactions at critical steel connections. Resistance against blast loads is mainly pro-vided by the exterior precast concrete panels and glazing on the clinic and hospital buildings, while the blast loads on the con-course are supported entirely by the steel frame. The blast-rated curtain wall is supported by a grid of 12-in. by 8-in. HSS girts tied to the perimeter wide-fl ange columns. These columns span from the ground level to the roof diaphragm, a vertical distance of up to 60 ft, and horizontal truss members were introduced into the roof diaphragm to ensure that the concourse roof will distribute blast loads to the lateral frames.

The goal of the progressive collapse requirements is to pre-vent an uncontrolled collapse of a large portion of the structure in the event of removal or damage of a local structural element. Horizontal and vertical tension ties extending the full height and width of the buildings were detailed into each steel frame to allow the structure to bridge over damaged areas without disproportionate collapse. Tension forces were considered in all connection and element designs along each tie, and the steel moment frames for the hospital also provide a high degree of redundancy to help mitigate any progressive collapse conditions.

Medical EquipmentThe vibration-sensitive medical equipment was carefully co-

ordinated early to help mitigate its impact on the steel frame; these units are not only heavy but also have strict defl ection and vibration requirements. In a typical bay for the hospital, the fl oor system consists of 4.5 in. of normal-weight concrete on a 3-in. composite metal deck and is supported by W16×31 beams and W24×55 girders. For the typical MRI bay, the fl oor system was increased to 6 in. of normal-weight concrete on 3-in. compos-ite metal deck to minimize sound transmission. In addition, the beams and girders were increased to W30×124 and W30×191, re-spectively, to stiffen the fl oor system and control vibration.

The design-build team members on the Fort Benning Mar-tin Army Community Hospital were true partners during the design and construction of this project. The 3D BIM approach allowed full integration of the systems and is driving the on-time delivery of this fast-track project to the base.

“Without the entire team’s active participation and the use of BIM, we could not have achieved the successful design and construction in the 1,200 calendar days allowed in the RFP,” said Miller. “The results have been extraordinary. I can’t imag-ine building another project in the future without the full use of BIM and the active collaboration of the design and construc-tion professionals.” ■

Ownerfort benning/army Corps of engineers, Savannah district

Design-Build ContractorTurner Construction Company

Architectellerbe becket (now aeCom), arlington, Va., and rlf, orlando, fla.

Structural Engineer and Steel DetailerThornton Tomasetti, inc., Washington, d.C., and kansas City, mo.

Steel Fabricator and Erector Schuff Steel – atlantic, inc., orlando (aiSC member/aiSC Certifi ed fabricator)

➤ The truss diagonals consisted of double 1¼-in. tension rods in one direction and single 1¾-in. tension rods in the opposite direction. Steel wide-flange columns surrounding the high bay space support a grid of hSS girts that provide lateral support to the glass curtain wall.

Thornton Tomasetti

Turner

There’s always a solution in steel.

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Emergency steel spans reopen

an Interstate river crossing shortly after a bridge collapse.

by William killeen, P.e.

IT WAS THE THURSDAY EVENING before Memorial Day week-end of 2013 when the unthinkable happened.

As western Washington commuters headed home and vacationers got underway via Interstate 5 about 60 miles north of Seattle, a southbound truck hauling an oversized load shifted to the right as it crossed the Skagit River Bridge, causing the load to strike the overhead parts of the bridge. Within moments, the damaged north span of the bridge collapsed, carry-ing with it numerous vehicles and their drivers and passengers into the river below. Fortunately, the accident did not result in any loss of life, but Washington State Department of Transportation (WSDOT) now had to find a quick and safe solution for resolving a connectivity disaster with significant negative financial implications in the making.

I-5 is the main interstate highway on the West Coast of the U.S., stretch-ing from Canada to Mexico and connecting several major cities, including Vancouver, Seattle, Portland, Sacramento, Los Angeles and San Diego. The commercial and passenger traffic that this critical transportation ar-tery carries on a daily basis is enormous. The I-5 Skagit River Bridge has four main spans of 160 ft each and is part of the primary route connecting Vancouver and Seattle, with an estimated 71,000 vehicles crossing the steel through-truss bridge every day. Its collapse created a transportation night-mare with immediate financial impact; a nearby Costco alone reported a loss of $1 million in one day as a result of the collapse.

QuiCk Thinking

40 february 2014

William Killeen ([email protected]) is president and Ceo of acrow bridge.

➤ The north span of the Skagit river bridge, following the collision.

WSdoT


Crisis AvertedClearly, a solution needed to be developed and commis-

sioned as quickly as possible to stem the losses in business and tax revenues as well as the disruption to daily life and its wide-spread consequences. Different options were considered for the reopening of the river crossing, and in the end, WSDOT se-lected a bridging solution of prefabricated modular steel, which could be mobilized and assembled with great speed while pro-viding the strength and durability demanded.

WSDOT awarded Atkinson Construction the emergency con-struction contract two days after the incident, and Acrow Bridge, a fabricator of modular bridges, became part of the team charged with engineering a rapid solution for bridge replacement. Acrow supplied two modular, prefabricated steel panel bridges. Each bridge weighed 180 tons, with clear spans of 160 ft and road widths of 24 ft, to replace the damaged section of the bridge. Modular steel orthotropic deck sections, which were overlaid with asphalt, were used for the roadway, and heavy-duty crash barriers were installed on each side for driver safety.

Acrow bridges are all-steel bridges composed of smaller compo-nents that pin and bolt together. All of the bridge components are available on a COTS (components off the shelf) basis and can be rapidly mobilized. With all components prefabricated and requir-ing no field welding, the bridges can be rolled into position with or without the use of sophisticated equipment, including a crane. This became an important factor in the Skagit River Bridge installation, as no suitable crane was available at the time for a lift-in of the spans. A crane-assisted launch was also not possible, as the existing multi-

span through truss was an obstruction. The only workable approach for putting the emergency bridges into place was by rolling each bridge across the gap in full cantilever, balancing each span like a large playground seesaw, without the use of a crane.

To facilitate the installation, the bridge pedestals were de-signed to allow for the sliding of the bridges sideways on Hil-man rollers, which was necessary because the existing through truss was 8 ft narrower than our structures. Once the pedestals were in place, the first bridge (northbound lanes) was rolled into place, jacked down onto the rollers, moved eastward, can-tilevered over the bridge pedestals and positioned out of the way to make room for the second bridge (southbound lanes). The second bridge was jacked down and positioned on perma-nent bridge bearings, 6 in. from the first bridge, and the deck was then situated and asphalted.

Speed and ServiceWe coordinated our response to the emergency through our

local office and depot in Camas, Wash. When we first learned of the collapse, we made the decision to send eight truckloads of Acrow prefabricated bridge steel to the project site that would be used to construct the bridge spans—even though a contract to supply the bridges had not yet been awarded—as we thought it would be best to have everything in place for quick assembly.

We also deployed field technicians to work side by side with the WSDOT and Atkinson Construction team. The techni-cians were a critical element in our ability to deliver a bridg-ing solution within a very tight time frame, working closely

Temporary spans were erected, and the bridge reopened only 23 days after the collapse.Vince Streano, Steano/havens

Vince Streano, Steano/havens

➤erection of the temporary spans.

➤

42 february 2014

with our engineers at our corporate head-quarters in New Jersey and the engineers at Atkinson. Everyone worked around the clock to assemble the emergency bridg-es and roll them out across the Skagit River. The highway bridge was formally reopened in June, only 23 days after the collapse of the damaged span. The Acrow spans were in place until mid-September when the permanent spans were installed via a roll-out/roll-in method. The Acrow bridge was then disassembled and shipped to the company’s storage yard in Washing-ton. Later in the year, almost all of these components were shipped to California as part of a planned detour bridge. ■

Owner and Structural EngineerWashington State department of Transportation

General Contractoratkinson Construction of renton, Wash.

Steel Fabricator and Detaileracrow Corporation of america, Parsippany, n.J. (aiSC member)

Two 160-ft spans, weighting 180 tons each, were installed via hilman rollers.

➤

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LATE LAST YEAR, Nucor-Yamato Steel’s (NYS) mill in Blytheville, Ark., reached a signifi cant milestone: a quarter-century of operation.

Since opening in 1988, it has produced an estimated 48 million tons of structural steel—all of it via the electric arc furnace (EAF) pro-cess. The short version is that the mill makes new steel products out of old steel products, melting down scrap and casting it into new wide-fl ange and other shapes. The long version is much more interesting.

The Right MixIt all starts with scrap—lots of scrap. Thanks to the mill’s strategic

positioning on the Mississippi River, the majority of scrap arrives via barge and is typically sourced from within a 500-mile radius. (Blytheville is about an hour north of Memphis, Tenn., and the site was chosen for its central U.S. location, access to the river, reliable local electrical grid, regional scrap supply and proximity to a good transportation network of

An inside look at a modern, high-tech steelmaking operation.

STory and PhoToS by Geoff WeiSenberGer

keep on rollinG

Geoff Weisenberger ([email protected]) is Modern Steel ’s senior editor.

➤

railroads and highways.) A specialized crane, which looks like a giant claw, plucks the scrap from the barge and loads it into trucks.

All inbound scrap is run through a monitor, which basically looks like a yellow steel archway, that tests the scrap load for radioactive materials. In rare cases of detection, material that contains traces of radioactivity is moved to a confi nement area before being hauled away. (Sometimes the trace amount of radiation is emitted by steel from demolished industrial facilities where radioactive processes were once used; in those cases the sus-pect scrap is segregated for further evaluation by trained radiation technicians.)

The scrap is then transported to the

caption


➤ Steel on its way from rolling to fi nal cutting.

Slag being dumped from a ladle, after being emptied at the caster, into a slag pot.

Graphite electrodes melt the steel at temperatures approaching 3,000 °f in the electric arc furnace. in this picture, the roof is swung open while the scrap bucket is emptied into the furnace.

➤

➤

appropriate pile. The mill uses several different types of scrap, based on content and density, each with a certain percentage of iron and other residual elements: nickel, chromium, copper, tin, etc. For example, one type is composed of steel that was most recently used as structural steel, another type has the same chemical makeup but has already been shredded and yet another is composed of scrap that wasn’t formerly structural elements but still has a high iron (ferrous) content (cars, appliances, roadside recycling, etc.). There is also a

designation for “home scrap” that has been recycled from the steelmaking process at the facility.

The Blytheville facility has two rolling mills, which specialize in different products. Mill 1 focuses on wide-flange, angles (up to L10), S-sections (up to S24), channels (up to C18), H-piles and sheet piles. Mill 2, which opened in 1993, primarily produces heavy wide-flange sections and H-piles (up to HP16 and HP18). The range of W-shapes produced at the Blytheville facility is W6×15 to W14×730

➤ Casting the steel. Two molten steel streams are fed into molds. Granulated powder is also continuously fed into the molds so that the steel doesn’t stick—much like greasing a pan.

46 february 2014

➤

molten steel is fed directly into the caster from the ladle. it is at this point that it takes on its “dog bone” profile.

➤

Scrap is dropped into the electric arc furnance from a charg-ing bucket, which has a hatch at the bottom.

(with regard to foot-weight) and up to W44×335 (with regard to section depth).

While the EAFs are in the same building, the rolling mills are located in two different buildings on the facility’s 850 acres, approximately 45 acres of which is under roof. Most of the facil-ity runs 24-7, with four crews on a “four-on, four-off” schedule (meaning four 12-hour days in a row followed by four days off).

Steelmaking via the EAF process is much like baking, and you can think of each scrap type as a specific ingredient and the various scrap piles as the pantry. For the most part, each product uses the same scrap recipe or blend (that is, a measured tonnage of each scrap type, loaded into the scrap buckets). Once the bucket is load-ed, the scrap is dumped into one of the mill’s two EAFs, where it will be melted down at temperatures approaching 3,000 °F. Each batch is called a “heat” and the scrap mix is added to the furnace in two buckets or “charges.” The first charge, typically 90 to 95 tons, is melted, then the second charge of 40 to 45 tons is added and melted; the variation in tonnage depends on the scrap density. In addition to the scrap, lime is added for flux, as is charge carbon as an additional heat source; at this facility, charge carbon is also substituted with shredded tires. Each heat takes approximately

35 minutes and there are typically 36 heats per furnace per day; a good yield from a heat is 120 tons of molten steel.

Observing the melting process is a powerful experience, akin to being close to a volcano while it’s erupting—a lot of noise, a lot of smoke and an intensity that you can feel throughout your body, especially when standing on a metal catwalk several stories above the ground. The furnace is lined with refractory bricks, which keeps the furnace itself from melting, and the melting is performed by three 24-in.-diameter graphite elec-trodes that are lowered through the roof of the furnace. When the electrodes first hit the steel, there’s a loud pop followed by a continuous rumbling. Once the heat is completed, the furnace is “tapped” and the molten steel, which looks like lava, is ex-tracted for the next step in the process. Slag, materials that rise to the surface, is skimmed from the top and separated—much like skimming the cream at a dairy—and sold, typically as road aggregate. A vacuum or “bag house” above the furnace removes emissions, and the particulates are sent to a recycling facility.

Next, the molten steel is transported via giant ladles to the ladle metallurgy furnace (LMF). Here, the steel is reheated, using elec-trodes similar to the EAF, deoxidized, desulfurized and further re-


➤beam blanks after being cut by the oxygen torch.

➤

Two circular saws (approximately 84 in. in diameter) perform the final cutting.

➤ Steel exiting the breakdown mill (left) and being rolled in the universal rougher/edger mill (right).

➤ after going through all three sets of rollers, each one further forming the shape, steel is ready for final cutting.

48 february 2014

fined with the addition of various other alloys to bring it to the perfect mix before it is cast. It is at this stage that the chemistry is adjusted to create a specific end product. For example, too many alloys for a light product will cause the mechanical properties to be too high for the specification, while too few alloys for a heavier product will cause the me-chanical properties to be too low for the specification. Basi-cally, the chemistry is fine-tuned to specific, tight, internal specifications within a general specification such as ASTM A992 or ASTM A588.

“Without this step, it would be like a cake without flour,” says Jim Schoen, one of the plant’s metallurgists.

“Basically, the steel would be of little use because it could not meet the intended properties without deoxidation, desulfurization and alloying.”

At the LMF, an operator takes a sample of the steel, which cools into a small shape resembling a lollipop, and tests it with an optical emission spectrometer.

“This machine tells you the chemical composition of the sample,” explains Schoen. “Sometimes the LMF op-erators achieve the procedural aim for the end product with the first addition.”

If not, the proper proportions of specified alloys are further added until the perfect mix is achieved.

Casting CallAt this point, the ladle is transported to the caster, where

the steel will be cast into long shapes called beam blanks or “dog bones”—as this is what the cross section resembles—which will then be cut and rolled into finished products. As the liquid steel flows out from a ceramic gate in the ladle bottom, it is guided into the caster in perfect strands. Granulated powder, which is designed to melt at a specific temperature for NYS products, is continuously fed into the bottomless caster mold so that the solidified steel shell that forms along the mold wall doesn’t stick to it—much like greasing a pan. The emergence from the caster is where the steel first begins to take on the look of a finished product—a cast beam with a web and two flanges (in the case NYS’ main products, W- and HP-shapes). However, there are a few products produced at rolling Mill 1 that come from a

“bloom” with a rectangular cross section. At this point, the steel needs to be cut, as it emerges

from the caster in lengths of up to 40 ft. Still orange-hot, the dog bones are cut with an oxygen torch, then cooled slightly with water so magnets can move them to storage if they are not going to be taken directly to the rolling mill. All water used at the plant is pulled from wells and is recirculated as many times as possi-ble through a closed-loop system, then treated before being released. The mill is working toward zero dis-charge into the local groundwater and sewage systems and is currently using some of its treated, nutrient-rich discharge to irrigate adjacent farmland.

➤

Scrap is separated into multiple types. a consistent “recipe” of steel from the various piles is used to create the products.

➤most scrap arrives at the facility via barge. from here it is transferred, via trucks, to the proper scrap pile to await melting.

➤nucor-yamato’s riverfront property provides fertile ground for grazing cattle owned by nearby farms.


While steel is tracked through the facility from the very beginning, it is at this point where each beam blank or bloom, while still at the caster torch tables, receives a physical tag. The time frame from scrap melting to cutting is around two hours: 35 minutes for the heat in the EAF, 10 minutes or so in transit, 40 minutes in the LMF and 40 minutes for the casting operation.

On a RollOnce ready for rolling, the beam blanks are placed in

reheat furnaces, which can handle up to 32 blanks at a time depending on the size. Reheating typically takes two hours and brings the steel up to around 2,400 °F. The tracking tags are burned off during the reheating process and new ones are added back on after rolling and cutting (steel is tracked continuously via computers throughout the mill).

When it’s heated back to the proper temperature and is once again orange-hot, the steel goes through three sets of rollers, each one further forming the steel until it becomes a usable member, ready for fabrication.

“Think of it as rolling out batter or pulling taffy,” Schoen says.

The first set, the breakdown rolls, shapes the beam blank to the approximate section depth and flange width. The number of passes through this set varies by product; the steel we witness today will become HP16x121 and takes 11 passes, mov-ing through the breakdown rolls forward and back a total of 11 times, then advancing to the universal rougher/edger mill after the 11th pass.

This second set of rollers further works the beam blank to the desired flange width and section depth. It is also at this point that temperature is controlled to achieve yield strength as well as CVN (Charpy V-notch) properties; 15 passes are required for this particular product.

The third and final set of rolls, the universal finish-ing mill, determines the final dimensions and requires just one pass.

Rolls need to be substituted based on the product requirements, maintenance needs and production schedule. They can be changed in about 45 minutes and can withstand thousands of production hours before being replaced. The company is currently building a robotic roller storage rack, adjacent to one of the mill buildings, which will increase the efficiency of rebuilding stands and replacing rolls.

Following rolling, the steel is cut to length via mas-sive circular saws that send out a shower of sparks (old saw blades are turned into home scrap and eventually new steel products). Samples are cut periodically to check the dimensions of the product. Additionally, samples are cut to be tested for strength and other properties, at frequencies

➤ after cooling, beam blanks are often stored outside before they are ready to be reheated and rolled into shape.

➤ following cutting, beam blanks are cooled with water.

➤ now final products, steel members cool before they are stored outside and eventually shipped to customers.

50 february 2014

A Bigger FurnaceThe two-charge method of adding scrap to the eaf is

dictated by having to melt down the first charge in order to make room for the second one; if the scrap was piled up past the top edge of the furnace, the lid wouldn’t fit on. a good compromise, it would seem, would involve only having to use one charge while getting the same yield as the two-charge system. but how to do this?

in a nutshell: make the furnace larger. and that’s just what nucor-yamato is in the process of doing. The upgrade in-volves a new gantry system, scrap bucket, lower shell, spray-cooled upper shell and spray-cooled roof. The benefits will be a safer working environment, lower operating costs and improved shop logistics.

The modifications to eaf 2 are expected to be completed this spring, and modifications to eaf 1 are planned to be completed a year later.

➤

one of the many “pulpits” throughout the mill, com-mand centers from which operators can monitor their processes.

➤

➤

Specialized grapple cranes are used for transferring scrap.

Proprietary software provides real-time data from every operation in the facility.

Cutting a beam blank via oxygen torches. ➤


determined by the specifications. The testing NYS performs on its steel could warrant an entire other article, but includes tensile, yield, elongation and CVN properties, when ordered.

Maintaining ControlWhile the steelmaking process involves a lot of what could

be considered massive hardware, it is monitored and con-trolled by proprietary software that gives operators through-out the mill and offices precise, up-to-the-minute information on each step. Sitting at Schoen’s desk, we can see the location, temperature and other vital statistics for every steel member currently being produced at the mill.

At each process, there is a “pulpit” or enclosed area where mill personnel can monitor their operation—a cool, enclosed oasis of sorts amidst the high temperatures and heavy industrial goings-on of the mill. This network of command centers is the nerve center of the mill, providing a bird’s-eye view of the action and housing con-trol equipment and multiple monitors; there are cameras throughout the mill that provide operators an up-close look at what’s happening. Some of the pulpits, especially the one for the oxygen cutting opera-

tion, resemble the bridge on the Starship Enterprise, complete with captain’s chair. And captain is an apt descriptor.

“Operators ‘own’ their departments,” says Schoen. “The de-cisions and discoveries they make in their areas can make their processes more efficient, which will lead to better efficiency and innovation for the facility and company as a whole.”

One example of innovation is NYS’ use of “smart start” tech-nology on the four locomotives that transport steel off-site, which has significantly reduced fuel consumption and emissions. Another innovation involves diapers. NYS found that it could use an ab-sorbent dust (which might normally be landfilled) from a diaper manufacturer in the region to help solidify some of the sludge that accumulates in the mill’s water treatment vessels.

All of this monitoring, testing, control, ownership and innova-tion leads to a precision-made—and safely made—final product, ready to ship to one of the mill’s hundreds of customers (for wide-flange steel, this typically means a steel service center or structural steel fabricator). The facility can currently produce 2.4 million tons of steel per year—and is ready to take on another quarter-century of service. ■

a “lollipop” sample from the ladle metallurgy furnace follow-ing testing via the optical emission spectrometer.

➤it goes with the territory.

➤

52 February 2014

The following is a brief outline of what is included in the guide:➤ Chapter 1: Introduction

• Purpose of the guide and how to use it• Overview of stability analysis and design methods• The concept of notional loads

➤ Chapter 2: Effective Length Method (ELM)➤ Chapter 3: Direct Analysis Method (DM)➤ Chapter 4: First-Order Analysis Method (FOM)➤ Chapter 5: Related Topics

• Application to seismic design• Common pitfalls and errors in stability analysis

and design➤ Appendix A: Basic Principles of Stability➤ Appendix B: Development of the First-Order Analysis

Method➤ Appendix C: Modeling Out-of-Plumbness for Taller

Building Structures➤ Appendix D: Practical Benchmarking and Application of

Second-Order Analysis Software➤ Appendix E: Bracing Requirements for Columns and

Frames Using Second-Order Analysis• Types of column bracing• A summary of design recommendations for stability

bracing problems using the new DM• Solution to practical column and frame bracing

problems found in practice

Analyzing Analysis MethodsThe primary purposes of the new guide are to discuss the ap-

plication of each of the above three methods and to introduce the DM to practicing engineers. Some of the most attractive features of the new DM are that there is no need to calculate K factors; internal forces are represented more accurately at the ultimate limit state; and it applies in a logical and consistent manner for all types of steel frames, including braced frames, moment frames and combined framing systems.

The concept of notional loads is also presented—including the role these loads play in the DM—as is the concept of

With neW design resources come new ways of doing things.

When the 2005 AISC Specification for Structural Steel Build-ings was published, it offered three methods for stability design, including a powerful new approach: the direct analysis method (DM). The DM is a practical alternative to the more traditional effective length method (ELM), which has been the primary basis of stability considerations in earlier editions of the AISC Specification and continues to be permitted. A streamlined de-sign procedure called the first-order analysis method (FOM), which is based upon the DM with a number of conservative simplifications, was also introduced.

And now practicing engineers, students and teachers have a new resource for stability analysis and design of steel buildings that incorporates these three methods: Design Guide 28—Stability Design of Steel Buildings. While the guide was primarily written around the 2005 Specification, it includes notes throughout to explain simplifications and improvements that were incorporated into the stability design provisions in the 2010 Specification.

A new AISC publication offers guidance on the three options

for stability analysis and design.

by Lawrence G. GriFFis, P.e., and donaLd w. white, Ph.d.

Lawrence g. griffis is a senior consultant with walter P Moore, and can be reached at [email protected]. donald W. White is a professor at the Georgia institute of technology and can be reached at [email protected].

stability Matters

Modern steeL construction 53

➤

stiffness reduction at the ultimate load state due to residual stresses in members and other effects. Since stability is an inherently nonlinear problem, the guide explains why all second-order analyses must be carried out at the ultimate strength load level, even when the allowable stress design method is used. In addition, many of the provisions contained in Chapter C of the 2010 Specification (Design for Stability) are explained in detail.

Practical design office problems are presented as well, demonstrating the use of each of the three methods and comparing the answers solved by each method for the same problem. The DM is permitted and now explicitly referenced in Chapter C of the 2010 Specification, and its procedural de-tails are further described in Chapter C Commentary. As explained in Chapter C and in the new guide, the DM is required as the only acceptable method in cases where the second-order effects due to sidesway are significant. Appen-dix 7 of the 2010 Specification (Alternate Methods of Design for Stability) contains the ELM and the FOM approaches, and each has its own dedicated chapter, with example prob-lems, in the new guide.

In addition to covering the three stability methods and em-phasizing the DM, the guide does several other things as well, including:

➤ Discussing the requirements for overall stability design in the 2005 and 2010 Specifications, as well as in the International Building Code and ASCE/SEI 7—Mini-mum Design Loads for Buildings and Other Structures

➤ Describing the traditional ELM and updating designers on new conditions placed on its use

➤ Introducing the FOM and explaining when this method can be advantageous

➤ Discussing application of stability methods to seismic design

➤ Highlighting common pitfalls and errors in stability analysis and design

➤ Providing an overview of basic principles of stability analysis and design for practical steel structures

➤ Providing guidance on benchmarking of second-order analysis software

➤ Illustrating how the DM can be applied to provide streamlined and efficient solutions for the assessment of column stability bracing

Applicable AppendicesAppendix A of the new guide contains practical tips about

the different aspects of stability of steel structures. It begins with a definition of stability and describes factors that influ-ence frame stability, such as second-order effects, geometric imperfections and fabrication/erection tolerances. Three simple stability models (see Figure 1) are described in detail and help illustrate many of the practical aspects of stability encountered in everyday practice, such as P-Δ and P-δ effects and when each should be considered; the effect of out-of-plumbness and how to account for it; and the effect of lean-ing columns on stability and second-order effects. In addition, an extensive discussion about the often perplexing effective length factor, K, is included for those designers accustomed to the ELM approach; many designers struggle with how to determine the effective length factor K for some of the more

Figure 1. simple models demonstrating various principles of stability.

Model cMoment Frame

Lg

elg

elg

elc

PmPg

rigid Linkh

L c

Leaningcolumn

Model bbraced Frame

elc

Leaningcolumn

h rigid Link

Pg Pb

βb

Model aMoment Frame

PmPg

rigid Linkh

Leaningcolumn

elcL c

54 February 2014

➤

common but complicated cases found in practice (see Figure 2). One of the most compelling reasons for using the new DM approach, as stated earlier, is that the method uses an effective length factor K=1.

Additionally, a section on the beam-column interaction equations found in Chapter H of the Specifi cation is includ-ed in Appendix A, as is a discussion on out-of-plumbness effects.

For designers considering new soft-ware programs that proclaim to account for second-order P-Δ and P-δ effects as required by the AISC Specifi cation, Ap-pendix D provides guidance on deter-mining whether second-order effects are considered with suffi cient accuracy to meet specifi cation requirements as defi ned in Chapter C. Practical guide-lines are also given to assist designers in accurately modeling for second-order effects given potential limitations in the software being evaluated, such as not di-rectly modeling P-δ effects in members.

Figure 2. Finding the effective length factor K can be complicated.

common but complicated cases found in practice (see Figure 2). One of the most compelling reasons for using the new DM approach, as stated earlier, is that the method uses an effective length factor

column interaction equations found in Chapter H of the ed in Appendix A, as is a discussion on out-of-plumbness effects.

ware programs that proclaim to account for second-order required by the AISC pendix D provides guidance on deter-mining whether second-order effects are considered with suffi cient accuracy to meet specifi cation requirements as defi ned in Chapter C. Practical guide-lines are also given to assist designers in

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One of the new and potentially most useful topics covered in the guide is that of bracing requirements for columns and frames. While the Specifi cation’s Appendix 6—Stability Brac-ing for Columns and Beams provides relatively simple practi-cal equations for beam and column bracing, many designers struggle with determining the appropriate bracing classifi ca-tion (relative, nodal, lean-on or continuous) for their problem. The new guide’s Appendix E—Bracing Requirements for Col-umns and Frames Using Second Order Analysis explains the various types of bracing and provides a detailed step-by-step approach to using a second-order analysis with the principles of the DM to solve perplexing and complex column bracing requirements. This approach is permitted in Appendix 6 of the

Specifi cation and is a powerful tool in solving complex bracing problems more accurately. (A few of the guide’s sample brac-ing problems, which are solved using second-order analysis and DM, are shown in Figure 3.)

Whether you seek to better understand your favorite meth-od of stability design, are looking to understand basic principles of stability effects in steel building structures or simply want to learn how to use a second-order analysis approach for solving complex bracing problems, Design Guide 28 is a new powerful reference for your design offi ce library. ■

AISC members can download Design Guide 28—Stability Design of Steel Buildings as a free PDF at www.aisc.org/epubs.

Figure 3. solving bracing problems using a second-order analysis/dM approach.

➤ a) core bracing of multi-story exterior columns in a high-rise building.

b) combination of nodal and relative bracing.

c) Long-span roof truss bracing (plan view).

➤

➤

at The Steel Conference examining the lessons learned from the earthquake and the latest developments in seismic design. The special sessions kick off on Wednesday with presentations on what happened in Northridge and the subsequent development of the SAC Steel Project (an initiative formed to investigate the damage to welded steel moment frame buildings and develop repair techniques and new design approaches to minimize damage in future earthquakes). The presentations in this series include:

➤ The SAC Steel Project Steve Mahin, University of California-Berkeley➤ The Moment Connection Details We Left Behind (and Why)

Mike Engelhardt, University of Texas at Austin➤ The Changes to Design Practice

Tom Sabol, Englekirk and Sabol➤ Revisiting W1a Indications

Duane Miller, The Lincoln Electric Company➤ The Changes that Resulted in Fabrication and Erection

Robert Hazleton, The Herrick Corporation➤ Japan’s Experience in Kobe

Masayoshi Nakashima, Kyoto University➤ The Changes that Resulted in Research

Chia-Ming Uang, University of California at San Diego➤ AISC 341 Then and Now

Jim Malley, Degenkolb Associates➤ AISC 358: Prequalified Moment Connections

Ron Hamburger, Simpson, Gumpertz & Heger➤ Changes in Materials and Inspection Tom Schlafly, AISC➤ Column Base and Splice Details

Amit Kanvinde, University of California, Davis➤ Conventional Braced Frames

Charles Roeder, University of Washington➤ Buckling-Restrained Braced Frames

Rafael Sabelli, Walter P Moore➤ Shear Walls

Michel Bruneau, State University of New York at Buffalo ➤ Systems that Mix Steel and Concrete (Beyond Composite

Design) Jerry Hajjar, Northeastern University➤ System Reliability

Greg Deierlein, Stanford University➤ ASCE 41

John Hooper, Magnusson Klemencic Associates

Canada’s largest city is set to host

this year’s NASCC: The Steel Conference.

BY TASHA WEISS

FOR THE FIRST TIME in nearly a decade, NASCC: The Steel Conference is heading north of the border.

This year’s show will take place in Toronto, March 26-28, at the Metro Toronto Convention Centre; Montreal hosted The Steel Conference in 2005.

Each year, NASCC puts the latest in structural steel design and construction on display, and last year’s show in St. Louis was the largest one yet, boasting an all-time record of 3,748 attendees. The Toronto show promises massive educational and networking offerings, with more than 100 technical sessions. The exhibit hall will be filled with 200 companies featuring cutting-edge technologies and products, ranging from the latest structural software to state-of-the-art fabrication equipment. The show also incorporates a special new series of seismic sessions, Northridge—20 Years Later, as well as the World Steel Bridge Symposium (WSBS), the Technology in Steel Construction Conference (TSCC) and the Structural Stability Research Council’s Annual Stability Conference (SSRC).

Attendees will learn about the new direct analysis method and the Code of Standard Practice, as well as explore the practical aspects of designing for torsion and what really matters in weld inspection. Some sessions are aimed at engineers while others are of greater interest to fabricators and others in the steel supply chain. How-ever, all attendees are welcome to attend any session.

A complete list of sessions is provided in the 2014 Advance Program, available online at www.aisc.org/nascc.

Seismic SessionsTwenty years ago the Northridge Earthquake shook California,

and the results surprised designers throughout the U.S. AISC will present a special series of sessions, Northridge—20 Years Later,

To

56 FEBRUARY 2014

Tasha Weiss ([email protected]) is Modern Steel’s assistant editor.


Building BridgesHeld every other year in conjunction with The Steel Con-

ference, the World Steel Bridge Symposium (WSBS) brings together bridge design engineers, construction professionals, academics, transportation officials, fabricators, erectors and constructors to discuss and learn state-of-the-art practices for enhancing steel bridge design, fabrication and construction techniques.

“The National Steel Bridge Alliance (NSBA) is very excited to colocate WSBS with The Steel Conference in Toronto,” said Brian Raff, NSBA’s marketing director. “This year’s Symposium features the greatest number of presentations in its history—more than 50 specialized sessions on all aspects of steel bridge design and construction. It also marks the greatest number of international presentations, truly highlighting the ‘World’ in the World Steel Bridge Symposium.”

You’ll find sessions on coatings, accelerated construction technologies and prefabricated bridge elements and systems, as well as others that focus on steel’s long life, low maintenance cost, quick erection and environmentally sound attributes. The three days of sessions are co-sponsored by the International Association for Bridge and Structural Engineering. View all WSBS sessions and learn more about exhibiting opportunities at www.steelbridges.org/wsbs.

talking technologyFor the third year in a row, NASCC will deliver a glimpse

into the future of technology in the steel construction industry with the TSCC. This special track features nine sessions that focus on advanced technology use throughout the steel con-struction industry.

Opening the TSCC are two Wednesday afternoon sessions: “BIMsteel: AISC’s Interoperability Initiatives for the Structural Steel Industry” and “Structural Engineers and AISC: Remov-ing the Reasons Why not to Share the BIM.” The former will explore AISC’s current BIMsteel initiatives for the industry, in-cluding automating steel fabrication, progress in material pro-curement, developing robust data exchanges between structural engineers and detailers and moving to a model-based review

process. The latter examines the structural engineer’s pivotal role in the digital delivery of steel buildings and how AISC can support them in the BIM-enabled process.

The remaining TSCC sessions on Thursday and Friday will range from “BIM, A Cost vs. Benefit Study for the Detailer and Fabricator” to “Beyond Drawings: How the Evolution of BIM will Integrate Models and Shape the Future of the Review Pro-cess” and “Expanded Use of Laser Scanning Structural Steel.”

From classrooms to careersSpeaking of those at the forefront of using progressive

technology, dozens of college students are expected to join the conference for the fourth annual Students Connecting with In-dustry Sessions (SCIS).

The half-day program, sponsored by the AISC Education Foundation and organized in cooperation with SE Solutions, will begin with a Thursday morning expert-led session about the role of the engineer in project design and making the tran-sition from student to practicing engineer.

“The Steel Conference epitomizes the vibrancy of the steel construction industry with its mix of designers, con-tractors, producers and academics,” said Nancy Gavlin, AISC’s director of education. “Our programs make students an integral part of the experience. With the assistance of SCIS, students moderate sessions, have one-on-one interac-tion with leaders in the steel construction industry, explore

scoping out sculpturessteelday 2013 not only gathered more than 10,000 people nationwide to learn about the structural steel industry, but also encouraged participation from aisc full and associate members to show what they can do creatively with steel.

Fourteen sculptures were entered into this year’s steelday sculpture competi-tion for a chance to be one of five finalists to have their creation on display at the steel conference in toronto. there, the ultimate winner will be chosen by attendees! the finalists were chosen via aisc’s Facebook page where fans were able to view photos of the sculptures and vote for their favorites. the top five finalists headed to toronto are:

➤ Memories of steel➤ Lunch atop a skyscraper ➤ Get a Grip➤ reflecting the high way➤ steve the robot you can view photos all of this year’s entrants, including the finalists, at

steelday’s Facebook page at www.facebook.com/Aiscdotorg (in the “steel sculpture competition Voting 2013” photo album).

Last year’s steelday sculpture competition winner: “steel Life-cycle” by bruce helmreich of Michelmann steel company.

➤

58 February 2014

Back to schoolThose who have been in the working

world for a while are also able to learn something new, whether it’s a highly technical issue or a business-related strategy.

This year’s keynote speaker is Neil Pasricha, author of The Book of Awesome, a #1 international bestseller. His lecture,

“1,000 Awesome Things,” will touch upon his project of posting one awesome thing every weekday for 1,000 consecutive weekdays—and he’ll teach you how to bring awesome principles to life in your organization.

Another, more technically oriented pre-sentation, the T.R. Higgins Award Lecture,

“Statics, Strength, Ductility, and the Uni-form Force Method,” will be presented by Larry S. Muir.

Muir is the 2014 recipient of AISC’s T.R. Higgins Award for his paper “Design-ing Compact Gussets with the Uniform Force Method,” published in the first quar-ter 2008 issue of AISC’s Engineering Jour-nal. Muir recently became AISC’s director of technical assistance.

“I am so very pleased that Larry is the recipient of the Higgins Award,” said Charlie Carter, AISC’s vice president and chief structural engineer. “His pa-per is very meaningful; it simplifies gus-set design by the uniform force method and allows the use of even more compact gusset plates than the original method. Larry is a very accomplished and deserv-ing recipient.”

registration tipsThe registration fee as of February 1

is $400, but be sure to register as early as possible; the rate increases $10 every week until the conference opens.

This single registration fee gains you entry to all technical sessions, the exhibi-tion hall, the keynote address and the T.R. Higgins Award Lecture. It also includes admission to all Structural Stability Re-search Council, Technology in Steel Con-struction Conference and World Steel Bridge Symposium sessions. The main conference offers up to 18.5 PDHs; at-tendees of short courses can earn an ad-ditional 4 PDHs for a total of 22.5 PDHs. Visit www.aisc.org/nascc to register or view the advance program.

See you in Toronto (and don’t forget your passport)! ■

the exhibit hall, attend lectures and participate in social events. This year we are very happy that the Canadian Institute of Steel Construction will be joining AISC in sponsoring student participation in the conference.”

The program will continue with a tour of the exhibit hall and con-clude with the “Direct Connect Stu-dent Career and Mentoring Session,” which is an opportunity for students to converse one-on-one with indus-try experts and representatives from

more than 30 companies. “SICS provided me a great platform to de-velop my network,” commented one student from last year’s program. An-other praised the program for “devel-oping experiences that are impossible to obtain from just being in the class-room.”

Students who are AISC members (membership is available for free to qual-ified students) receive free admission to The Steel Conference, including the SCIS program.

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TORONTO ON-TARIOCanada

MARCH26–28

WORLD STEEL BRIDGE SYMPOSIUM

• 3,700 design and construction professionals

• 100+ educational seminars • 200+ exhibitors

To view the advance program, visit www.steelbridges.org

The Premier Event for EVERYONE INVOLVED

IN THE DESIGN AND CONSTRUCTION of Steel-Framed Bridges and Buildings

Including NASCC: THE STEEL CONFERENCE, the Technology in Steel Construction Conference, and the Annual Stability Conference.

Register early!Registration fee increases $10 each week.

IABSE

60 February 2014

news

People and Firmsin MeMoriAM

William M. heenan, Jr., Former President of sri, dies • Lincoln electric (an aisc

m e m b e r ) h a s a c q u i r e d an ownership interest in Bur l i ng ton Automat ion corporation, a designer and manufacturer of 3d robotic plasma cutting systems based in hamilton, ontario. (terms of the transaction were not disclosed.) in separate news, Lincoln electric announced that it has entered into a definitive agreement to acquire robolution gmbh, a provider of robotic arc welding systems based outside of Frankfurt, Germany.

• Anthony naccarato, P.e., has been promoted to president of Philadelphia-based structural engineering firm o’donnell & naccarato. he succeeds nick cinalli, P.e., who served as pres ident since 2003 and will remain a principal and active member of the f i rm’s e x e c u t i v e l e a d e r s h i p team.

• V ic to r techno log ies , a provider of solut ions for cutt ing, gas contro l and specialty welding equipment, recently opened its west Lebanon des ign center. dedicated to innovation in plasma cutting and arc welding technologies, the 50,000-sq.-ft facility employs approximately 75 people.

• tekla has released tekla BiMsight 1.9, the latest version of its free software tool for building information modeling (biM) project coordination. the tool now supports sketchup models to improve the design coordination process and biM collaboration.

William M. Heenan, Jr., former president of the Steel Recycling Institute (SRI) and 2013 recipient of the Steel Market De-velopment Institute’s (SMDI) Lifetime Achievement Award, died this past De-cember at the age of 65.

Thomas J. Gibson, president and CEO of the American Iron and Steel In-stitute (AISI), of which SRI and SMDI are both business units, issued the fol-lowing statement earlier this month on Heenan’s death:

“On behalf of the AISI family and our member companies, we were deeply sad-dened to hear of Bill’s passing. Bill was a tireless and devoted leader in the steel in-dustry, building SRI from the ground up and establishing steel as the world’s most recycled material. We are forever grate-ful for the lasting impact Bill had on our industry and send our deepest sympathy to his family.”

Lawrence W. Kavanagh, president of SMDI and longtime colleague of Heen-an’s, said, “Beyond work, Bill was a gen-erous and devoted family man. He set an example for all of us by crediting every success he had to his family.”

Heenan, who had retired in recent years to Daufuskie Island, S.C., was presi-

dent of SRI from 1990-2010. Prior to join-ing SRI, he was general manager of tin mill products for the United States Steel Corp., a position to which he was appointed in 1988. He was a lifetime board member of the National Recycling Coalition, served as a board member of Keep America Beau-tiful, Inc., and was co-chairperson of Keep Pennsylvania Beautiful.

Heenan is survived by Barbara, his wife of 43 years; two sons, Sean and Bri-an; and a daughter, Becky.

ProJects

First B2 Modules hoistedThe first steel-framed modular units of Brooklyn’s B2 tower—planned to be the tallest modular building in the world when it’s completed late this year—were recently hoisted into place.

The building schedule called for the placement of three adjacent “mods,” which together will compose a single apartment. The mods were built by union labor af-filiated with the New York Building and Construction Trade Council. Mods are built fully assembled, including kitchens, bathrooms and appliances, then trucked to the construction site and hoisted by crane and bolted into place.

At 32 stories, B2 will be the world’s tall-est modular building and is one of 15 build-ings planned at the $4.9 billion, 22-acre Atlantic Yards site. The structure will be comprised of 4,000 sq. ft of retail space as

well as 362 residential units of which almost 50% will be designated as affordable hous-ing for low-to-middle-income residents.

Banker Steel (an AISC member/AISC certified fabricator), the steel fabricator for the project, expanded one if its Lynchburg, Va., facilities earlier this year by an additional 45,000 sq. ft to create a purpose-built work-shop solely dedicated to the fabrication of these modules. It is estimated that B2 will weigh almost half as much as a traditional steel building, cost 30% less to build and take significantly less time to complete, according to Banker Steel. In addition to requiring less labor, material and erection time, this process is expected to be safer, cause minimal disrup-tion to the surrounding neighborhoods dur-ing construction and be environmentally friendly—estimated to reduce construction site waste by as much as 90%.

Modern STEEL CONSTRUCTION 61

news

The AISC Board of Directors elected a new chair and vice chair this fall dur-ing its Annual Meeting of the Mem-bers of the Institute in Cape Elizabeth, Maine. Jeffrey E. Dave, P.E., president and CEO of Dave Steel Company, Inc., Asheville, N.C., succeeds William B. Bourne III, president and CEO of Universal Steel, Inc., Lithonia, Ga., as chair of the 27-member board. James G. Thompson, CEO of Palmer Steel Sup-plies, Inc., McAllen, Texas, is the board’s new vice chair. Both positions carry a two-year term.

“As past chair, I am very excited about the future of AISC,” said Bourne. “The Board has chosen two exceptional peo-ple to lead our industry over the next four years. Our next chair, Jeff Dave, is a proven volunteer, an AISC board member since 2003 and a successful businessman. He has led his company, Dave Steel, for more than 20 years and is an important part of the Virginia Carolinas Structural Steel Fabricators Association. Jeff will have great backup with vice chair Jim Thompson. Jim has also successfully led his company, Palmer Steel Supplies, for more than 20 years and has served as a board member since 2007. Congratula-tions and thank you to both Jeff Dave and Jim Thompson.”

Dave has worked in all areas of the steel fabrication business since 1985. During the past 20 years, he’s played an instrumental role in the timing and imple-mentation of significant process and tech-nology changes at AISC-member fabrica-tor Dave Steel Company, which has AISC Certified facilities in Asheville, N.C., and Chesnee, S.C., and an engineering office in Cincinnati. He was COO of the com-pany from 1992 to 2004, and since then has served as president and CEO.

“Our industry will continue to expe-rience quick advancements in the op-portunities to use models throughout the design and fabrication processes,” commented Dave on his new position. “As we push the edge of this technology and its use on steel construction projects, it will be very important for all to exer-cise due diligence in transitioning from research to case studies to normal use

and implementation on projects. One of my goals during my tenure as Chair is to make sure this transition process occurs in a manner that assures that we continue to achieve our mission of increasing the market share of steel by making struc-tural steel the material of choice on con-struction projects.”

Dave graduated from North Carolina State University with a bachelor’s degree in civil engineering. In his early career he worked for several years at Newport News Shipbuilding in Newport News, Va. He also worked for a structural en-gineering firm on a contract at Langley Air Force Base in Hampton, Va., and an engineering firm in Raleigh, N.C. He’s remained very active with various indus-try boards and associations as well as sev-eral local community boards. Since 1989 he’s served on the Board of Directors of the Virginia Carolinas Structural Steel Fabricators Association, including a term as president. He joined the AISC Board in 2003 and has served for three years as chair of the Certification Committee as well as a two-year term as vice chair. Dave’s grandfather, Joseph Dave, served on the AISC Board from 1959-1965, as well as his uncle, Bernard Dave, from 1970 to 1976.

Thompson has more than 30 years of experience in steel fabrication and erection. His expertise includes sales,

estimating, production management, operations management and adminis-tration management. He joined Palmer Steel Supplies, an AISC-member fab-ricator and AISC Certified fabricator, as a management trainee and promptly ascended to general manager in 1975. That same year he was promoted to vice president, and in 1984 he achieved the position of president. He currently serves as CEO, after passing on the presidency of the company to his son, Palmer, who is now the third genera-tion of family management.

He grew up in numerous locations in the U.S. and Europe, and in 1969 he graduated from Texas Christian Uni-versity (TCU) with a bachelor’s degree in mathematics. While at TCU, he was enrolled in the Reserve Officers’ Training Corps (ROTC) and was com-missioned a 2nd lieutenant in the U.S. Air Force after graduating. He imme-diately entered pilot training and, after 53 weeks, earned his wings. He served on active duty for the next four years as an instructor pilot in Mississippi and Texas. Following his departure from the USAF, he moved to McAllen, Tex-as, and began his career at Palmer Steel Supplies.

Thompson joined the AISC Board in 2007 and has also been active on several local community boards.

BOARD NEWS

AISC Board Elects New Chair and Vice Chair

Dave Thompson

62 February 2014

news

ProJects

rehabilitating the heaviest double-deck Lift Bridge

An unusual surge in public construction in October pushed total construction spending to its highest level since May 2009 despite a dip in both private residen-tial and nonresidential activity, according to an analysis of new Census Bureau data by the Associated General Contractors of America (AGC). Association officials urged lawmakers in Washington to make water and surface transportation invest-ment a top federal priority.

“Nearly every category of public con-struction increased in October, according to the preliminary Census figures, although for the first 10 months of 2013 combined, public spending continues to lag the 2012 year-to-date total,” said Ken Simonson, the association’s chief economist. “Meanwhile, residential spending slipped for the month but still showed strong year-to-date gains, and nonresidential spending remained stuck in neutral.”

Construction put in place in October totaled $908 billion, 0.8% higher than in September. But figures for August and July were revised down below levels that initially exceeded the current October es-timate. The total for the first 10 months of 2013 was 5.0% above the year-to-date

mark for the same months in 2012.Public construction spending jumped

3.9% for the month but trailed the 2012 year-to-date total by 2.8%. The two larg-est public components were mixed: high-way and street construction increased 0.6% in October and 0.3% year-to-date, while educational construction leaped 8.5% for the month but fell 8.5% year-to-date, Simonson said.

Private residential spending slid 0.6% for the month but still climbed 17% year-to-date. New single-family construction decreased 0.6% in October but soared 30% in the first 10 months of 2013 compared with 2012. New multifamily spending advanced 2.2% in October and 46% year-to-date.

Private nonresidential spending edged down 0.5% for the month and up 0.8% year-to-date, Simonson observed. The largest private nonresidential cat-egory, power—including oil and gas as well as electricity—plunged 5.7% and 5.8% over the two time periods. But the next three niches by size—manufactur-ing, commercial (retail, warehouse and farm) and office—rose for the month and year-to-date.

“Construction will likely display var-ied patterns in the next several months,” Simonson said. “Multi-family construc-tion will keep burgeoning but single-family homebuilding may stall. Private nonresidential spending should benefit from more power, energy and manufac-turing work. Public construction remains threatened.”

Association officials said Congress and the administration should keep public construction from returning to its recent slump by quickly completing water resources development legisla-tion that has already passed both the House and Senate, as well as passing a new surface transportation bill this year that funds repairs to deteriorating highway, bridge and transit infrastruc-ture. They added that any new trans-portation bill must include provisions to adequately fund the nearly depleted federal Highway Trust Fund.

“If Congress can act in a biparti-san way on transportation funding as it did on the water resources bill, it can avoid a cliff-like drop in highway spending,” said Stephen E. Sandherr, the association’s CEO.

MArKet neWs

construction spending spikes to Four-Year Peak

Bridge engineering firm Modjeski and Masters has been selected by the Michigan Department of Transportation (MDOT) for the rehabilitation design of the Portage Lake Lift Bridge, a 269-ft-long, 54-ft-wide steel lift bridge. The lift span, which can be raised up to 100 ft, features upper and lower decks capable of carrying a total of eight lanes of U.S. Highway 41 and M-26.

As part of the agreement, Modjeski and Masters will lead the steel replace-ment design as well as the electrical and mechanical design of the rehabilitation.

The project will focus primarily on the replacement of the wire ropes, a criti-cal hoisting mechanism. To successfully accomplish this, Modjeski and Masters engineers proposed that replacement take place during winter months when the bridge can be left in the fully lowered position, with traffic maintained on the

upper deck. This would also help to ac-commodate snowmobile traffic, which commonly uses the lower deck during the same season. The engineering team will also implement homeland security recommendations, provide structural re-pairs to the operator’s house and design upgrades to the barrier gates.

Preservation of this historic structure is a high priority for the state. The Por-tage Lake Lift Bridge was completed in 1959 and is the fourth bridge crossing to be built at the site (following two steel swing bridges as well as the original 1875 wooden swing bridge).

“The Portage Lake Lift is no doubt an iconic structure due to its sheer size, but also its history of connect-ing the two communities,” says Kevin Johns, P.E., project manager and mov-able bridge business unit leader with

Modjeski and Masters. “We’re very grateful to continue our long-term re-lationship with MDOT and are thrilled to help with the rehabilitation of this monumental bridge.”

The rehabilitation design is scheduled to be finished by the end of the summer, and construction will take place during the first half of 2015.

nathan h

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newsProJect neWs

high steel and hirschfeld to Fabricate steel for tappan Zee BridgeHigh Steel Structures, Inc. (an AISC/NSBA member and AISC Certified fab-ricator) of Lancaster, Pa., and Hirschfeld Industries (an AISC/NSBA member and AISC Certified fabricator), LLP of San Angelo, Texas, have each been awarded a contract to fabricate structural steel for the approach spans of New York’s new Tappan Zee Bridge. The project is the largest de-sign-build transportation project to date in the U.S. and one of the largest construction contracts in New York State history.

After proposals were submitted in mid-2012, the New York State Thruway Authority awarded a $3.142 billion con-tract to design and build the project to Tappan Zee Constructors (TZC), a con-sortium including Fluor Enterprises, Inc., American Bridge (an AISC/NSBA mem-ber and AISC Certified fabricator and Advanced Certified steel erector), Granite Construction Northeast, Inc., and Tray-lor Bros., Inc. (an AISC member erector). The design team working with Tappan Zee Constructors consists of HDR, Buck-land & Taylor, URS and GZA.

Shortly after the project was ad-vertised, High Steel Structures and Hirschfeld Industries teamed together to bid the project due to the massive size and scope of the steel production.

Fluor Enterprises is TZC’s lead con-tractor for sourcing the structural steel. The project was divided into two steel

packages: one for the approach steel, to-taling nearly 100,000 tons; and another for the main span cable stay steel, totaling approximately 10,000 tons. Each fabrica-tor will produce approximately half of the steel under separate contracts, and will provide portions of both the eastbound and westbound approach spans. The main span steel package has yet to be bid.

Steel deliveries are set to begin in October and will continue into the first quarter of 2017. High performance steel (HPS) plate is being employed in the de-sign. The primary material supplier for the project is ArcelorMittal USA.

“The award of the Tappan Zee struc-tural steel contract to the team of fabricators High Steel Structures, Inc. and Hirschfeld Industries, with material supply by Arcelor-Mittal USA, validates the fact that the Unit-ed States steel construction industry has the capacity, capability and collaborative spirit to meet our nation’s infrastructure needs,” stated AISC president, Roger Ferch.

“We answered our industry’s call for leadership,” Hirschfeld’s executive vice president, John O’Quinn, said. “Together we were able to provide the owner and design-build team with all the tangibles a project of this magnitude required, while mitigating their risks. The largest design-build bridge in U.S. history will utilize the two largest bridge fabricators in the U.S.; it just makes sense.”

High Steel president Brian LaBorde said, “We are looking for-ward to working on this historic proj-ect, which demonstrates that fabrica-tors in the U.S. have the capacity and capability to fabricate and deliver the massive quantity of structural steel re-quired for a project of this size—a win for Buy America.”

Located north of New York City, the new Tappan Zee Bridge will carry the Thruway, Interstate 87 and Interstate 287 over the Hudson River between South Nyack, N.Y., and Tarrytown, N.Y. According to the Thruway Authority, the first span of the new twin-span bridge is scheduled to open in 2016, and the new bridge should be complete in 2018. The bridge will be designed and constructed to last 100 years without major structural maintenance.

In separate news, High Industries, Inc., the holding company for High Steel Structures, recently announced the formation of High Structural Erectors, LLC, a new company that combines the field operations of High Steel Structures and High Concrete Group, LLC, and provides erection services to the infrastructure, com-mercial, institutional and industrial markets. The company began formal operations as a High Industries affili-ate in October.

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64 February 2014to advertise, call 231.228.2274 or e-mail [email protected].

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

Are you looking for software, products, or services for your next project?You can find it in Modern Steel Construction’s online product directory.

http://modernsteel.com/product_categories.php

If you’re a provider of software, products, or services and would like more information about being listed or enhancing your current listing,

contact Louis Gurthet at:

[email protected] or 231.228.2274

Visit steelTOOLS.orgJoin the conversation at AISC’s new

fi le-sharing, information-sharing website.

Here are just a few of the FREE resources now available:• More than 160 steelTOOLS utilities available for downloading• Discussion blogs where your can connect and share ideas with

your peers• Files posted by your peers in special interest libraries, including:

• A Pocket Reference to W Shapes by Depth, then Flange Width

• Welding Capacity Calculator• Moments, Shears and Reactions for Continuous Bridges • Video: Bridge Erection at the SeaTac Airport

Got Questions? Got Answers?

Participate with us at steelTOOLS.org.

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

“Like” AISC on Facebookfacebook.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]

LATE MODEL STRUCTURAL STEEL FABRICATING EQUIPMENT

Peddinghaus 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 #20654Voortman VB1050S Horizontal Straight Cut Band Saw, 20” x 44”, 135-400 SFPM, 2.64” Blade Height, 15 HP, 2007 #22645HEM DC-2038RB Double Column Horizontal Band Saw, 20” x 38”, 45-60 Deg. Miter, 2” Blade, 15 HP, 75-400 SFPM, 2006 #22215 LS Industries STRB-4848 Structural Steel Pass Through Blast Cabinet, (4) Wheels, 20 HP, 48” x 48”, Recovery Sys, Dust Collector, 2001 #23775

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

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].

marketplace

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 TaylorPROCOUNSEL

Toll free: 866-289-7833 or 214-741-3014Fax: 214-741-3019

[email protected]

Business Development Representative(s)

AISC is looking for seasoned business development professionals, preferably on the West Coast, to join our growing team of Business Development Representatives and help promote the use of structural steel to decision makers in the construction industry across the U.S. and show others the advantages of designing and building with steel.

Email your resume and cover letter (including salary requirements) to:[email protected]

NSBA Managing Director

AISC is looking for an accomplished executive to join our senior management team as the leader of our bridge division. The National Steel Bridge Alliance (NSBA) is the technical and marketing arm of the steel bridge community and is dedicated to increasing the market share of steel bridges.

The NSBA Managing Director will develop key relationships with bridge owners, government offi cials, designers and constructors, and will provide strategic leadership and direction for the NSBA team to implement programs and tactics to address all facets of marketing, government relations, and technical support for the steel bridge industry.

To apply, please email your resume and cover letter (including salary requirements) to: [email protected]

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

We are a niche recruiter that specializes in matching great structural engineers with unique opportunities that will help you utilize your talents and achieve your goals.• We are structural engineers by background and enjoy helping other

structural engineers find their “Dream Jobs.”• We have over 30 years of experience working with structural engineers. • We will save you time in your job search and provide additional

information and help during the process of finding a new job.• For Current Openings, please visit our website and select Hot Jobs. • Please call or e-mail Brian Quinn, P.E.

([email protected] or 616.546.9420) so we can learn more about your goals and interests. All inquiries are kept confidential.

SE Impact by SE Solutions, LLCwww.FindYourEngineer.com


Project ManagersWest 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 with 5 years’ experience and an experienced detailer with a minimum of 3 years’ experience with TEKLA software to join our team. West Coast Iron offers competitive salaries and a comprehensive benefi ts package.

Please send your resume to Enrique Rayon at [email protected]

Plant Manager Steel Stairs, Rails & Light Structural, Phoenix, Arizona

Successful, profi table, AISC Certifi ed Fabricator of steel stairs, rails & light structural seeks experienced Plant Manager to oversee the daily plant activities including but not limited to scheduling production, shipping, QC, supervision (8-25 employees), plant maintenance & safety. Ideal candidate minimum 10 years experience steel fabrication, strong organizational & communication skills. AWS-CWI Certifi cation plus. $60-$70K DOE. E-Verify. EOE. Contact [email protected] or fax (602) 774-1624. No calls.

Chief Estimator The Berlin Steel Construction Company,

an Employee Owned structural steel and miscellaneous metals fabricator-erector, located in Kensington, CT

is seeking experienced applicants for Chief Estimator.

The person who fi lls this position will be a seasoned structural and miscellaneous metals estimator with a proven track record of quantifying, material and shop and fi eld labor. This is a senior level position with one of the Northeast’s leading fabricators and erectors. In addition to being the chief estimator, this position will be directly involved with the improvement and implementation of a team oriented sales strategy that meets the goals of Berlin Steel.

Please forward resume to [email protected]. We are an AA/EOE.

66 February 2014

the LAFAYette coLLege Arts Plaza in Easton, Pa., brings the indoors outside. The $1.7-million, 7,000-sq.-ft space, designed by Spillman Farmer Architects, transforms a former auto-repair facility into a dynamic outdoor teaching space that responds to its natural environment and built con-text. Designed as an outdoor black box theater, the plaza hosts a wide variety of planned and spontaneous artistic endeavors, including performance art, visual art exhibits and small group musical performances.

“Unlike many urban developments, which are conceptual-ized as ‘infill’ of an existing context, the Arts Plaza is an urban ‘unfill’ project,” says Spillman Farmer design principal Joseph N. Biondo, AIA. “The existing building had solid walls that blocked the relationship between the site and the community. We removed these walls to create new types of connections in and around the site, bringing together the Easton community, the college, the natural environment, the streetscape and local history. These interactions encourage a focus on user experience, material richness, spatial transparency and sensory stimulation.”

At its core, the project is a distillation of the existing structure. The 29-ft-high facility’s concrete platform foundation and timber

frame, both salvaged and reused elements of the former building, are complemented by newly introduced masonry and steel. Inside the plaza, structural engineer Barry Isett and Associates calculated loads where the new steel armatures had to rest on the concrete floor, ensuring the structural integrity of the slab and the arched structure below. Tension rods were installed between the timbers to provide lateral stability for the existing structure, and the roof was removed to create an open trellis effect.

The project incorporates two cubic structural steel arma-tures, each draped with a veil of stainless steel mesh. The armatures, fabricated and erected by McGregor Industries, Inc., of Dunmore, Pa. (an AISC member/Certified fabricator/Advanced Certified Steel Erector), feature 32 tons of steel, mainly w8×28s structural steel members. These transparent, ghost-like structures complement the masonry monoliths and reflect the dimensions and rhythm of the windows of the adja-cent Williams Visual Arts Building. The delicate details of the steel mesh, carefully lit at night and adorned with climbing veg-etation, complete the forms and bring a natural softness to the hard-edged, industrial street front. This effect is reinforced in the winter, when ice and snow build up on the mesh. ■

structurally sound inside out

Photos by barry halkin Photography, courtesy of spillman Farmer architects

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