STRUCTURE magazine | August 2013

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

August 2013 Steel

RESULTS FROM THE 2013 STRUCTURAL ENGINEERING EDUCATION SURVEY

SO SPE SE FT CI C WA AL TI R O E N

POWERS’ PURE110+ EPOXY ADHESIVE ANCHOR SYSTEM

(1:1 RATIO)

WHY DO WE CALL IT 110+?

• Adhesive anchors are now included in the International Building Code • All adhesive anchor systems are required to be tested at 110˚F for sustained loading, known as “creep” • Pure110+™ has passed creep testing and is also approved for both cracked + uncracked concrete and seismic loads • Pure 110+ is the only approved epoxy that has the same bond strength at high temperature (110˚F ) as it does at room temperature So when you’re looking for an adhesive with great bond strength, creep resistance and that is code listed, remember the number 110+!

NEW!

Pure110+ is now available and in stock for immediate shipment!

Powers Fasteners, Inc. www.powers.com 2 Powers Lane P: (914) 235-6300 Brewster, NY 10509 F: (914) 576-6483

For over three decades engineers have relied on ENERCALC’s industry leading software to perform structural design and analysis for low to mid-rise buildings.

• Software for rapid creation of calculations for components of low to mid-rise buildings • Covers virtually all design & analysis tasks in steel, wood, concrete, masonry, load generation and frame analysis • Latest IBC, ACI, ASCE, AISC, NDS and CBC code provisions incorporated • Flexible licensing, automatic web updates, superb support, created by experienced engineers • Celebrating 30 years and 8,000+ users

ENERCALC

• Improved continuously to suit user’s needs

Did you know?

Our most recent addition is the Wood Shear Wall module.

The Individual Full-Height Wall Segment method from the NDS Special Design Provisions for Wind & Seismic is provided. It allows a wide variety of loading options applied to multistory walls and permits openings to be defined within the walls. It incorporates the full NDS database of the sheathing options and allows access to the Wood Reference Design Values database for the framing members. Results include sheathing fastening requirements with applicable adjustments for aspect ratio, compression and tension checks for chord members, forces for anchorage selection, and footing reinforcing requirements.

ENERCALC 800.424.2252 | www.enercalc.com | info@enercalc.com Evaluation Software: www.enercalc.com/demo

Features Sutter Health Eden Medical Center

32

By Mohammad Aliaari, Ph.D., S.E. and Edwin Najarian, S.E., P.E. SHEMC is a new, state-of-the-art, 230,000 square foot replacement hospital with 130 acute care beds and a 36-bed universal care service. For the 1st time in the U.S., an 11-party Integrated Project Delivery team co-signed an Integrated Form of Agreement contract, requiring them to work collaboratively in a shared risk, shared reward environment.

Columns 7 Editorial

By Thomas A. DiBlasi, P.E., SECB

10 Structural Design

By Robin Sham, Ph.D., C.Eng The Padma Bridge is a landmark structure and one of the longest river crossings in the world. At the Padma River site in Bangladesh, engineers used state-of-the-art technology and innovative disaster prevention and mitigation solutions to tackle some severe challenges.

Mass Transit at Phoenix Airport

38

August 2013

2013 NCSEA Annual Conference

Padma Bridge

36

CONTENTS

By David A. Burrows, P.E. and John A. Lobo, P.E., S.E. Stage 1 of the PHX Sky Train, a 5-mile long automated transit system exclusively serving the Phoenix Sky Harbor International Airport, consists of approximately 2 miles of guideway, of which over 1.5 miles is elevated.

Steel Deck Diaphragm Design 101

By Kurt Voigt, P.E.

14 Codes and Standards Update: Cold-Formed Steel Design 2012

By Helen Chen Ph.D, P.E., Roger L. Brockenbrough, P.E. and Richard B. Haws, P.E.

18 Structural Practices Prerequisites When Designing for Hot-Dip Galvanizing

By Philip G. Rahrig

22 InSights

SoNo Ice House

42

By Bruce D. Richardson, P.E., Nils V. Ericson III, P.E. and Chris T. O’Brien, P.E. The renovation of an obsolete manufacturing facility into a state-ofthe-art ice hockey development center presented challenges that required creativity, teamwork, and owner commitment.

Educating Future Structural Engineers

46

The Education Committee of the National Society of Structural Engineers Associations is pleased to present the 2013 survey of schools and colleges throughout the United States.

53 Special Section on

the

Economic Upturn for Building Industry

By Larry Kahaner As the economy improves and more construction projects are started, software developers are providing new products and services, as well as updating current offerings.

In every Issue

Cover

The first stage of the PHX Sky Train™, a 5-mile long automated transit system exclusively serving the Phoenix Sky Harbor International Airport. The two mile long first stage opened to the public on April 8, 2013, the next stage will open in early 2015 and the final stage is expected in 2020. The project is featured on page 38.

8 Advertiser Index 60 Resource Guide (Software) 68 NCSEA News 70 SEI Structural Columns 72 CASE in Point

STRUCTURE magazine

5

August 2013

Beating Chaos and Achieving Profits in BIM with LOD 350

By Will Ikerd, P.E.

24 Building Blocks Cold-Formed Steel Applications

By Winston E. Kile, P.E., S.E.

28 Historic Structures Piscataqua Bridge

By Frank Griggs, Jr., P.E.

Departments 45 Engineer’s Notebook Gravity Controls Over Seismic?

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

67 Spotlight BC Place Revitalization

By Karen A. Lynch, P.E.

74 Structural Forum Engineers Shouldn’t Think Too Fast

By William M. Bulleit, Ph.D., P.E.

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement

by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board.

Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

Remember This Ad? ITCOursAd.qxd

9/5/06

9:04 PM

Page 1

When We Built Our Plant In e Decatur, Alabama We Used Th y.

Finest Materials In The Industr

Ours.

Decatur facility

the same. Our We believe our customers deserve d from 100% of tube products supplie

is constructed with virtually plants. Now, with three locations our Chicago and Marseilles, Illinois e of production capacity, we welcom and over 1,000,000 square feet needs. tube the opportunity to secure all your industry’s most popular size Independence Tube features the tubing (plus corresponding range—2” square to 10” square to .625”. Our rolling schedule, .125” from walls with les) rectang that your order will be unsurpassed in the industry, assures ng ndence Tube’s customer shoppi delivered when promised. Indepe to a host of services. You have you links M BE.CO network, ITCTU les. schedu rolling and ry, access to bundle charts, tube invento

open orders and test You can release loads, download customer secure portal. results—all from your personal, ’t sell our customers At Independence Tube, we wouldn es. Come and experience ourselv use ’t wouldn we g anythin a world of possibilities. us at 800-376-6000 For further information please call dependencetube.com. and visit our website at www.in

Well, we did it again…

CH ICAG O, I L

MARSEI LLES, I L

DECAT U R , A L

…because our customers continue to deserve the best in tube quality, service and delivery.

In rebuilding the Decatur facility and mills, we figured now was the time to take our product line to the next level–bigger and better than ever before.

Our state-of-the-art facility can now produce Rounds to 14" OD and 16" OD with walls up to .625". This gives us a total Rounds range of 1.66" OD to 16" OD. In addition we will offer A500 ITC50 Pipe Sizes and A252 Pipe Piling sizes as well. Remember, Independence Tube offers the Industry’s most popular size ranges in square, rectangle, and round tube sizes.

We did it again, in no small way, with our employees’, customers’ and suppliers’ mutual respect and dedication.

1-800-376-6000 • www.independencetube.com Celebrating 40 Years of Quality Tube Products

Editorial

2013 NCSEA Annual Conference new trends, new techniques and current industry issues The Gathering for the Practicing Structural Engineer

By Thomas A. DiBlasi, P.E., SECB, Past President, NCSEA

T

he 21st Annual NCSEA Conference will be held in Atlanta from September 18-21. In keeping with tradition, this conference caters to the practicing structural engineer: The goal is to provide an outstanding educational opportunity filled with practice ideas and techniques that you can apply when you return to your office.

The formal program kicks off on the morning of Thursday, September 19, with a keynote address delivered by William (Bill) Baker of Skidmore, Owings & Merrill. The designer of an array of skyscrapers, including the world’s tallest building, the Burj Khalifa, Bill Baker will speak about The Philosophy of Design: The Structural Engineer’s Role in Creating Architecture. Following the keynote address, Jon Schmidt will discuss the ins and outs of the Department of Defense’s Minimum Antiterrorism Standards for Buildings, a must-know guideline for anyone involved with the structural design of military facilities. This will be followed up

by Bob Pekelnicky’s overview of ASCE 41-13, Seismic Evaluation and Retrofit of Existing Buildings, the new basis for seismic assessments and upgrades that will be invoked by the 2015 International Existing Building Code.

Thursday afternoon will offer dual tracks. Harry Gleich will delve into the provisions of ACI 550, Guide to Emulating Castin-Place Detailing for Seismic Design of Precast Concrete Structures.

Concurrently, Terry Malone will deliver The Analysis of Offset Diaphragms and Shear Walls which will include discussion of “The Visual Shear Transfer Method”, a simple method of depicting the direction of shears acting through a diaphragm. Next, Dr. William Thornton will discuss steel connections, The Last Bastion of Rational Design, which will provide the fundamental basis for connection design and will differentiate between analysis assumptions and reality, as well as provide an overview of the Lower Bound Theorem of Limit Analysis. Concurrently, Sam Rubenzer will present Load Generators: What exactly is my software doing?, which will compare and contrast the wind load and seismic load generation features of the major commercial structural engineering software packages, including RISA, RAM., ETABS, Fastrak, and STAAD, and will provide more insight into what building code provisions are, and are not, considered in the generation of the loads.

Thursday afternoon wraps up with some lessons learned. John Tawresey will present The Structural Curtainwall, which will focus on the structural performance criteria of curtainwall systems using examples of actual projects, as well as clarify and classify curtainwall structural criteria contained in the building codes, industry standards, and architects’ typical specifications. Concurrently, Greg Greenlee will deliver a case study of the underpinning and micropile foundations used at the renovation of the Northrop Auditorium at the University of Minnesota. In this project, the shell of an iconic 1929 structure was maintained, while an aggressive interior renovation was undertaken that included lowering the base floor elevation and enhancing the column loading capacities,

STRUCTURE magazine

permitting the transformation of an underutilized theater into a world-class performance facility.

On Friday morning, there will be Vendor Presentations from 8 a.m. to 10 a.m. Technical sessions will resume after the morning break with Dr. Donald White’s presentation of Practical Design of Complex Stability Bracing Configurations, introducing a more general approach to allow the application of the fundamental concepts and requirements of AISC Appendix 6 to more complex bracing scenarios not currently captured by the design equations.

On Friday afternoon, you can look forward to a two-part presentation on the book everyone has been waiting for, NCSEA’s newest publication, Guide to Design of Serviceability of Building Systems, delivered by lead author Dr. Kurt Swensson. This presentation will provide practical information for structural engineers to evaluate the serviceability performance of buildings pursuant to the requirements of the building code. It also tackles many of the “gray areas” that are noticeably absent from the building code.

In addition to the outstanding technical presentations, the conference has much more to offer. On Wednesday, you are invited to sit in on one or more of the many committee meetings that will be taking place throughout the day; and, on Wednesday afternoon, there will be a complimentary short-course tutorial by Dr. Leroy Emkin: The AISC Direct Analysis Method. The Direct Analysis Method is currently the most rational analytical procedure to account for structural stability of steel-frame structures, and it serves as the basis for the 2005 and 2010 AISC Steel Design Specifications. A detailed discussion and demonstration of the step-by-step process for performing the Direct Analysis Method by computer, combined with a discussion of the impact of such a process on structural engineering workflow, will be presented.

Conference social events include a Wednesday evening reception hosted by the Structural Engineering Certification Board (SECB), a Thursday evening Exhibitor Reception, and a Friday evening reception and Awards Banquet, highlighted by the presentation of the NCSEA Excellence in Structural Engineering Awards and honoring engineers who have made outstanding contributions to the structural engineering profession.

The annual meeting of NCSEA’s 43 member organizations is an open meeting and will be held on Friday from 8:00 a.m. to 10:00 a.m.

(Member Organization reports) and on Saturday from 8:00 a.m. to noon. Scholarships and registration discounts are again available to Young Members (defined as age 35 or younger), and a Young Members Group Reception is slated for Wednesday evening.

I trust you will agree that this line-up of technical presentations coupled with all the other activities of the conference make this an event that you, the practicing structural engineer, cannot afford to miss! In addition, you will have the chance to mingle with the leaders of the structural engineering profession. For more information and to register, please visit NCSEA Conferences and Institutes at www.ncsea.com. I look forward to seeing you in Atlanta!▪

7

August 2013

Advertiser index

PleAse suPPort these Advertisers

ASC Steel Deck ..................................... 44 Canadian Wood Council ....................... 59 Cast Connex ......................................... 51 Clark Dietrich Building Systems ............. 9 Computers & Structures, Inc. ............... 76 Concrete Reinforcing Steel Institute ...... 11 CSC Inc. ............................................... 55 Design Data .......................................... 52 ENERCALC, Inc. ................................... 3 Engineering International, Inc............... 16 Foundation Performance Association..... 26 Fyfe ....................................................... 23 Gerdau .................................................. 41

GT STRUDL........................................ 57 Hilti North America .............................. 61 Integrated Engineering Software, Inc..... 56 Independence Tube Corporation ............. 6 ITW TrusSteel & BCG Hardware ... 21, 29 KPFF Consulting Engineers .................. 50 MPS Civil Products............................... 35 NCEES ................................................. 43 NCSEA ................................................. 13 Nemetschek Scia ................................... 63 New Millennium Building Systems ....... 31 Nucor Vulcraft Group ........................... 27 Powers Fasteners, Inc. .............................. 2

Editorial Board Chair

RISA Technologies ................................ 75 S-Frame Software, Inc. ............................ 4 SidePlate Systems, Inc. .......................... 66 Simpson Strong-Tie............................... 25 Soil & Materials Engineers, Inc. .............. 8 Star Seismic ........................................... 45 Structural Engineers, Inc. ...................... 17 StructurePoint ....................................... 65 Struware, Inc. ........................................ 12

AdvErtising Account MAnAgEr Interactive Sales Associates Chuck Minor

Dick Railton

Eastern Sales 847-854-1666

Western Sales 951-587-2982

Jon A. Schmidt, P.E., SECB

sales@STRUCTUREmag.org

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

Craig E. Barnes, P.E., SECB

Brian W. Miller

Mark W. Holmberg, P.E.

Evans Mountzouris, P.E.

CBI Consulting, Inc., Boston, MA

Davis, CA

Heath & Lineback Engineers, Inc., Marietta, GA

The DiSalvo Ericson Group, Ridgefield, CT

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

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

Khatri International Inc., Pasadena, CA

KPFF Consulting Engineers, Seattle, WA

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

Stephen P. Schneider, Ph.D., P.E., S.E.

Brian J. Leshko, P.E.

John “Buddy” Showalter, P.E.

John A. Mercer, P.E.

Amy Trygestad, P.E.

CCFSS, Rolla, MO

HDR Engineering, Inc., Pittsburgh, PA

Mercer Engineering, PC, Minot, ND

BergerABAM, Vancouver, WA

American Wood Council, Leesburg, VA

Executive Editor Jeanne Vogelzang, JD, CAE

execdir@ncsea.com

Editor

Christine M. Sloat, P.E.

publisher@STRUCTUREmag.org

Associate Editor Graphic Designer Web Developer

Nikki Alger

publisher@STRUCTUREmag.org

Rob Fullmer

graphics@STRUCTUREmag.org

William Radig

webmaster@STRUCTUREmag.org

Chase Engineering, LLC, New Prague, MN

Senior Project Engineer

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

EditoriAL stAFF

Seeking experienced Senior Project Engineer to lead, manage and provide consulting engineering services for building envelope projects.

Other requirements: BS or MS in Civil/Structural Engineering and professional licensure preferred.

10+ years related experience in evaluating, analyzing and specifying building enclosure technology for both new facilities and existing structures requiring restoration/repair.

Experience with masonry and other building envelope systems: curtain walls/windows, air/ moisture barriers, flashing, waterproofing, and sealants.

Experience using WUFI moisture migration modeling.

Maintaining and developing clients and a passion for solving clients’ problems.

Strong verbal and written communication skills.

Ability to work in teams and desire to mentor and lead others.

Passion for learning, conducting research, and for fixing problems with existing structures.

Ability to travel to meet project and client needs.

SME offers excellent opportunities for professional advancement in a flexible work environment. For more information, please visit SME’s website at: www.sme-usa.com. SME is an Equal Opportunity Employer. Send resume, including cover letter and salary requirements, to the attention of Larry Chute, PE at: chute@sme-usa.com.

STRUCTURE magazine

8

August 2013

STRUCTURE® (Volume 20, Number 8). ISSN 1536-4283.

Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $65/yr domestic; $35/yr student; $90/yr Canada; $125/yr foreign. For change of address or duplicate copies, contact your member organization(s). Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board.

STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be

reproduced in whole or in part without the written permission of the publisher.

Celebrating

years

1993-2013

C3 Ink, Publishers

A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 P-608-524-1397 F-608-524-4432 publisher@STRUCTUREmag.org Visit STRUCTURE magazine

on-line at Visit STRUCTURE magazine on-line at www.structuremag.org www.structuremag.org Visit STRUCTURE magazine online at

www.structuremag.org

STOP FIRE IN ITS TRACKS.

[ M A K E T H A T O U R T R A C K S. ]

© 2013 ClarkDietrich Building Systems

BLAZEFRAME ®    . As a strong cold-formed steel head-of-wall system, it integrates the protection fire code demands, plus sound-dampening performance. BlazeFrame features a factory-metered strip of intumescent material that expands up to 35 times its original size when temperatures reach 375° F. By applying this safety measure under precisely controlled manufacturing conditions, we’re offering you a better way to stop flames, smoke and fumes with innovation and integrity. STRONGER THAN STEEL. SM

Interior Framing ∙ Exterior Framing ∙ Interior Finishing ∙ Clips/Connectors ∙ Metal Lath/Accessories∙ Engineering

clarkdietrich.com

Structural DeSign design issues for structural engineers

Figure 1: In its most basic form, a diaphragm behaves as if it were a short, deep beam.

Steel Deck Diaphragm Design 101

By Kurt Voigt, P.E.

Kurt Voigt, P.E., is an Engineering Manager at New Millennium Building Systems.

He can be reached at kurt.voigt@newmill.com.

Steel roof and floor deck diaphragm design requires careful attention to load paths, stiffness variations, fastener types, and regional preferences…

S

hear diaphragms are commonly used in buildings as a means of transmitting lateral loads. In building design, these loads are typically caused by wind and seismic events, although earth and water can exert lateral forces as well. Steel deck, plywood, and concrete are all common materials utilized in diaphragm applications. In its most basic form, i.e. a rectangular, uninterrupted plane, a diaphragm behaves primarily as if it were a short, deep beam (Figure 1). Using this basic concept, the diaphragm shear forces can be determined and generally the same principles applied even with the introduction of roof openings or irregular building geometry.

Let’s start with the roof framing plan in Figure 2. We’ll use the same basic layout and service level wind pressure as shown in Figure 1, with the addition of (8) skylight openings in the roof. The openings reduce the diaphragm stiffness in the same manner that a beam web opening would reduce the beam stiffness at the location of the Figure 1 opening. We’ll need to ensure adequate fastening and transfer elements are provided to resist and transfer the design shear, including the distributed shear around the openings.

For this example, we are only going to consider wind in the direction shown, assuming half of the net pressure shown is windward on AC and half is leeward on BD. Constructing the shear diagram (V) in Figure 3, using the free-body diagram of Figure 1, shows us the maximum shear exists at the ends of the building, along AB and CD. The Figure 2 average shear (S) in the diaphragm is

10 August 2013

determined by dividing the shear by the length of the diaphragm at the location in question. The maximum average shear (Smax) in this example occurs both at the ends of the building, as well as in the deck panels and fasteners just to the right of the roof framing along AB (where average shear length is reduced due to openings), where Smax = 0.292 kips per linear foot (klf ). Using the Steel Deck Institute (SDI) Diaphragm Design Manual, Third Edition, we can determine the required deck fastening. Using 5/8-inch puddle welds for attaching deck to supports and #10 sidelap screws, we find the nominal shear strength in the table for 0.0295-inch thick WR deck is 0.740 klf using a 36/4 (12-inch o.c.) support fastener pattern and (4) sidelap screws per span (15-inch o.c.). For ASD design, the wind factor of safety is 2.35, yielding an allowable shear force of 0.315 klf. This allowable shear force considers fastener strength and panel distortion around the fasteners; however, an additional check for stability must be made to ensure global buckling of the panel will not occur. The allowable buckling shear from the SDI table is 0.660 klf, so buckling will not occur.

Shear around Openings The next step is to determine the shear around the openings. Since the building, opening locations, and loading are all symmetrical, we’ll look only at the (2) openings nearest the left end of the building (abcd and opening directly below). The (2) openings at the opposite end of

Figure 2: Skylight openings reduce diaphragm stiffness in the same manner beam web openings do.

of the building will be the same, and the (4) openings near the interior will have different shear, but would be calculated using the same principles. From the average shear diagram (S) in Figure 3, we know the shear on the AB side of the openings is 0.219 klf and the opposite side is 0.201 klf. To determine the shear along the other (2) sides of each opening, we need to look at the rectangular deck areas directly above and below each opening. By constructing free-body

Figure 3: Shear around openings is determined based on forces diagrams of the and moments above and below each opening. areas in question, we can sum forces and moments around the area perimeters. right side shear force is 0.267 klf x 30 ft.

Looking at the top 6-foot 3-inch wide x = 8.01 k (downward). Summing moments 30-foot long area, with base ac, we need about point (a) yields a shear force along to ensure the forces around the perimeter the top (building perimeter above opening) of that area are in equilibrium (Figure 4 , of (8.01 k x 6.25 ft. + 0.175 klf x (6.25 page 12). We know from the S diagram in ft.)2 / 2) / 30 ft. = 1.78 k (leftward). Then, Figure 3 the left side shear force is 0.292 summing forces in the horizontal direction klf x 30 ft. = 8.76 kips (k) (upward) and yields an equal and opposite force of 1.78 ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org

Take Your Place In The CRSI Honors RECOGNIZING INNOVATION in the Design and Construction of Reinforced Concrete Buildings by creating value in any of several ways: – Collaborative Design – Lean Building Methods – Uniquely Inspiring Spaces – Planned Use Adaptability – Material or Systems Efficiency – Whole-Life Sustainability – Structural Resilience

ACKNOWLEDGING THE LEADERS at Every Stage that Drive Great Outcomes for Building Users: – Building Owners – Program Managers – Design Architects – Structural Engineers – Construction Managers – General Contractors – Construction Industries

Submittals will be accepted online from July 1, 2013 to November 1, 2013 Unlimited submittals per firm, entirely free to CRSI member organizations

HONORS

Presented by

2013

FOR FAST & EASY SUBMITTAL DETAILS VISIT

13070_CRSI_Honors_Structure_half_page_ad_2013.indd 1

STRUCTURE magazine

11

August 2013

honors.crsi.org TODAY! 6/10/13 12:17 PM

ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org

k (rightward) along ac. This force must be transferred into the adjacent diaphragm areas (½ into each) immediately to the left and right of the opening. Since this force is in addition to the existing diaphragm shear in those areas, care must be taken to provide sufficient transfer length into those areas to prevent crippling of the deck at the associated corners of the opening. Using A653 SS grade 33 steel, the allowable strength of an arc spot weld can be determined by the equation 2.2tFu(d-t)/Ω = 2.2(0.0295 in.)(45 ksi)(0.625 in.–0.0295 in.)/(2.35) = 0.740k. The required number of fasteners to distribute the additional shear into adjacent diaphragms is (1.78 k)/(2 sides)/(0.740k/ weld) = 1.2 welds per side, rounded up to 2.

Since the diaphragm in the area in question is capable of resisting a maximum allowable shear of 0.315 klf, we should ensure that the transfer length provided into adjacent diaphragm areas is sufficient to limit the average total shear to 0.315 klf. To the left of the opening, the diaphragm is required to resist 0.219 klf due to applied loads, so the additional shear we’re introducing should not exceed 0.315 klf – 0.219 klf = 0.096 klf.

The minimum transfer length or connection length can be determined by dividing the additional shear by the maximum additional shear calculated in previous step, (1.78 k)/(2 sides)/(0.096 klf ) = 9.27 feet.

Since this length exceeds the roof framing spacing, we’ll need to provide a transfer element, i.e. channel, angle, tube, etc., in line with ac that extends (2) spaces out to each side, upon which (2) 5/8-inch puddle welds should be placed approximately 4 feet 6 inches and 9 feet from a and c. Practically speaking in this example, since only (2) additional welds are required on each side, the deck could accommodate an additional weld at each of the (2) supports adjacent to a and c, in lieu of providing an additional

transfer element. Moving on to the 6-foot 3-inch x 30-foot diaphragm area between the (2) leftmost openings, by inspection, the additional shears along bd will be similar to those calculated previously, since the area is the same size and shears are similar.

The shear would be slightly less, since the applied load component is not present at the top or bottom of the area.

Transfer of Lateral Loads

Designing and specifying diaphragms to transfer lateral loads is a fairly involved process, becoming more complicated when openings and irregular geometry are introduced. There are many elements to be considered, including the interaction of the various structural components with varying stiffness. How the load travels from one part of the structure to another is highly dependent upon the stiffness of the components, the fasteners chosen, and the connection details in the areas where the forces are intended to transfer from one component to another. Careful consideration of the load path is critical in maintaining an economical, constructable diaphragm system.

Drag struts and collector elements are often framed in the direction of the shear load, in order to progressively collect the load and distribute it into the structural framing system.

In cases similar to the previous example, where the lateral load is being resisted by a horizontal diaphragm, a means of transferring the force from the diaphragm above to the structure below must be provided.

Suppose the roof framing at 6-foot 3-inch o.c. in the example (Figure 2, page 11) is an open web steel joist system, where the ends of the joists along walls AC and BD are bearing on a ledger angle on precast walls. When the wind is blowing on walls AB and CD, there must be a path for the shear in the diaphragm above the joists to transfer out into walls AC and AD. This may be accomplished in many ways; one of those would be via a deck bearing angle atop the joist ends adjacent to the wall, into the StruWare, Inc joist seats, into the ledger angle, and then Structural Engineering Software into the wall; another being more direct via a deck bearing angle that is attached to the wall The easiest to use software for calculating with sufficient fastening to directly transfer wind, seismic, snow and other loadings for the shear from the bearing angle and into IBC, ASCE7, and all state codes based on the wall; another would be to install channel these codes ($195.00). members or HSS tubing to the ledger angle CMU or Tilt-up Concrete Walls with & between the joist seats, such that the top of without openings ($75.00). the tubing is at the same elevation as top of Floor Vibration for Steel Bms & Joists ($75.00). joists, and would provide deck edge support and a method for shear transfer into the Concrete beams with torsion ($45.00). ledger angle (eliminating the shear on the joist seats which have limited capacity for Demos at: www.struware.com shear transfer), and into the wall.

STRUCTURE magazine

12

August 2013

Figure 4: Forces around the perimeter of an opening must be brought into equilibrium.

Regional Preferences So many choices – how do you choose? The answer lies in regional preferences, contractors and costs. Some erectors may prefer one method over another, and precast wall manufacturers will have preferences and associated costs as well. Steel joist seats have a fairly limited rollover shear capacity of around 2.5 kips service load at 21/2 inches deep. Thus, it is important whenever possible to provide an alternate means of shear transfer, such as the aforementioned channel or tube members, when shear loads begin to exceed the standard seat capacity. It is critical to provide adequate load paths, and for project teams to communicate with affected trades to determine the best option for the project. Similarly, deck fastening preferences vary regionally, and even vary among erectors within the same region. Diaphragm loads in the western U.S. are generally considerably larger than those present in the midwest. As such, a particular deck fastening and transfer system that typically works well in the western U.S. may be very uncommon, and/or unnecessary, in the midwest. Again, communication among the project team is important.

In summary, the next time you design a project with a diaphragm system, be sure to give careful consideration to ALL the details, from load paths, to stiffness variations, to fastener types, and regional preferences. The SDI Diaphragm Design Manual, Third Edition is an excellent design reference every engineer should utilize if designing with steel deck diaphragms. The manual includes pertinent design information, considerations, fastener information, deck shear capacity tables, and a plethora of highly relevant design examples, stepping you through all the intricate details and covering nearly any scenario you may run across.▪

NCSEA Structural Engineering Exam Live Online Review Pass the Structural Exam with Confidence!

This course is designed by the National Council of Structural Engineers Associations (NCSEA), Kaplan Engineering Education, and leading structural engineers from across the industry.

Online Course Dates: Vertical: July 27–28, 2013 Lateral: August 24–25, 2013

Course Fee* $1199

Vertical or Lateral Only $749 Course available with or without learning system

This targeted review includes:

Group pricing available

• Over 28 hours of instruction • Instructor Blog

(As low as $425 per person)

• Classes archived for 24/7 playback

Register today!

Instructors: • Tim Mays, Ph.D., P.E.

• John Lommler, Ph.D., P.E.

• Ravi Kanitkar, S.E.

• Donald R. Scott, S.E.

• Jennifer Butler, P.E.

• Russell Brown, Ph.D., P.E.

• Joe Miller, Ph.D., P.E.

• Larry Novak, SE, FACI, LEED® AP BD+C

MRKT-10253

• Rafael Sabelli, S.E.

877.884.0828 www.kaplanaecengineering.com/LiveReview

*Students repeating the SE Review Course are eligible for 50% discount. Call for details.

Codes and standards updates and discussions related to codes and standards

t R1

R2

Figure 2: Effective width at edge stiffener.

Figure 1: Corner radius.

A

merican Iron and Steel Institute (AISI) cold-formed steel design and construction standards are developed and maintained by the AISI Committee on Specifications for the Design of Cold-Formed Steel Structural Members and the AISI Committee on Framing Standards. The operation of both Committees follow the “Essential Requirements: Due process requirements for American National Standards” established by American National Standards Institute. All the standards developed by the Committees go through ANSI conducted public review and approval processes to become American National Standards (ANS). All AISI standards published in 2007 were either reaffirmed as the ANS or published as a new edition in 2012. A complete list of AISI standards and their status is given in Table 1.

This article provides an overview of major technical changes and additions that were included in the AISI standards and supplements published in 2012.

1) Technical Changes and Additions in AISI S100, North American Specification for the Design of Cold-Formed Steel Structural Members, 2012 Edition a) Section A2, Material. To facilitate the selection of appropriate steel grades, in the 2012 edition, the list of applicable steels has been grouped by their minimum elongation requirements over a two-inch (50-mm) gage length: the specified minimum elongation of 10 percent or greater, 3 percent to less than 10 percent, and less than 3 percent.

The permitted uses and restrictions are then specified for each of the groups.

For example, the steels with a specified minimum elongation of 10 percent or greater can be used without restriction as long as the steels meet the requirements specified in Section A2.3.1. Steels with elongation from 3 percent to 10 percent can be used with reduced yield stress and tensile strength as specified in Section A2.3.2. Steels with specified minimum less than 3 percent may be

Update: Cold-Formed Steel Design 2012

By Helen Chen Ph.D, P.E., LEED AP-BD+C, Roger L. Brockenbrough, P.E. and Richard B. Haws, P.E.

14 August 2013

used in multiple web configurations such as roofing, siding and floor decking provided the adjustments specified in Section A2.3.3 are met. Additionally, a new material standard ASTM A1063/ A1063M, Standard Specification for Steel Sheet, Twin Roll Cast, Zinc-coated (Galvanized) by the Hot-Dip Process, was added in 2012. b) Section B1.3, Corner Radius-toThickness Ratios. Research indicated that the provisions in Chapter B may become unconservative when predicting the effective width if the corner radiusto-thickness ratio, R/t, is larger than 10 (Figure 1). Thus, the effective width equations in Chapter B are restricted to R/t less than or equal to 10. However, the design engineer may use crosssections having radius-to-thickness ratios greater than 10 by using a rational engineering analysis method such as the Direct Strength Method or a prescriptive method applicable for 10 < R/t ≤ 20 that is provided in AISI S100 Commentary Section B1.3. c) Section B2.5, Uniformly Compressed Elements Restrained by Intermittent Connections. This section is used to determine the effective widths for elements, such as cellular decks, that are restrained by intermittent connections (Figure 2). The added provisions will enable increased moment capacities for some cellular deck profiles. d) Section C3.6, Combined Bending and Torsional Loading. This section takes into consideration the torsional effect for singly or doubly symmetric section members subjected to bending and torsional loading by applying a reduction factor, R, to the nominal flexural strength determined based on initial yielding. The reduction factor, R, was revised in 2012: R=

fbending_max ≤ 1 Eq. (1) fbending + ftorsion

where fbending_max = Bending stress at extreme fiber, taken on the same side of the neutral axis as fbending, fbending = Bending stress at location in cross-section where

combined bending and torsion stress is maximum, ftorsion = Torsional warping stress at location in cross-section where combined bending and torsion stress is maximum. Eq. (1) enables one to accommodate situations where the maximum stress due to combined bending and torsional warping occurs at the tip of a flange stiffener, and at web-flange or flange-lip junctions. e) Section D3.3, Bracing of Axially Loaded Compression Members. The

revised provisions should produce a more reliable and economic design of bracing to a compression member because the brace force and stiffness are now calculated based on the axial load in the column. The required brace force and stiffness can also be determined using the frame analysis that takes into consideration second-order effects (i.e., considering both P- and P-∆ effects).

f ) Section E3, Bolted Connections.

Provisions are added to determine the strength of bolted connections for slotted or oversized holes. The slotted or oversized hole sizes are defined in AISI Table E3a. The bearing strength, Pn, without consideration of bolt hole deformation can be determined from: Pn = C mf d t Fu

Eq. (2)

where C = Coefficient determined in accordance with AISI S100 Table

Table 1: AISI Standards Status.

Designation

Title

AISI S100-12

North American Specification for the Design of Cold-Formed Steel Structural Members, 2012 Edition

AISI S110-07w/S1-09 (2012)

Standard for Seismic Design of Cold-Formed Steel Structural Systems-Special Bolted Moment Frames with Supplement 1, 2007 Edition (Reaffirmed 2012)

AISI S200-12

North American Standard for Cold-Formed Steel Framing – General Provisions, 2012 Edition

AISI S201-12

North American Standard for Cold-Formed Steel Framing – Product Data, 2012 Edition

AISI S202-11

Code of Standard Practice for Cold-Formed Steel Structural Framing, 2011 Edition

AISI S210-07w/S1 (2012)

North American Standard for Cold-Formed Steel Framing – Floor and Roof System Design with Supplement 1, 2007 Edition (Reaffirmed 2012)

AISI S211-07 (2012)

North American Cold-Formed Steel Framing – Wall Stud Design, 2007 Edition (Reaffirmed 2012)

AISI S212-07 (2012)

North American Cold-Formed Steel Framing – Header Design, 2007 Edition (Reaffirmed 2012)

AISI S213-07 w/S1-09 (2012)

North American Standard for Cold-Formed Steel Framing – Lateral Design with Supplement 1, 2007 Edition (Reaffirmed 2012)

AISI S214-12

North American Standard for Cold-Formed Steel Framing – Truss Design, 2012 Edition

AISI S220-11

North American Cold-Formed Steel Framing – Nonstructural Members, 2011 Edition

AISI S230-07 w/S3 (2012)

North American Cold-Formed Steel Framing – Prescriptive Method with Supplement 3 (Reaffirmed 2012)

AISI S901-08

Rotational-Lateral Stiffness Test Method for Beam-to-Panel Assemblies, 2008 Edition

AISI S902-08

Stub-Column Test Method for Effective Area of Cold-Formed Steel Columns, 2008 Edition

AISI S903-08

Standard Methods for Determination of Uniform and Local Ductility, 2008 Edition

AISI S904-08

Standard Test Methods for Determining the Tensile and Shear Strength of Screws, 2008 Edition

AISI S905-08 w/S1-11

Test Methods for Mechanically Fastened Cold-Formed Steel Connections with Supplement 1, 2008 Edition

AISI S906-08

Standard Procedures for Panel and Anchor Structural Tests, 2008 Edition

AISI S907-08

Test Standard for Cantilever Test Method for Cold-Formed Steel Diaphragm, 2008 Edition

AISI S908-08

Base Test Method for Purlins Supporting a Standing Seam Roof System, 2008 Edition

AISI S909-08

Standard Test Method for Determining the Web Crippling Strength of Cold-Formed Steel Beams, 2008 Edition

AISI S910-08

Test Method for Distortional Buckling of Cold-Formed Steel Hat Shaped Compression Members, 2008 Edition

AISI S911-08

Method for Flexural Testing Cold-Formed Steel Hat Shaped Beams, 2008 Edition

AISI S912-08

Test Procedure for Determining a Strength Value for a Roof Panel-to-Purlin-to-Anchorage Device Connection, 2008 Edition

AISI S913-08

Test Standard for Hold-Downs Attached to Cold-Formed Steel Structural Framing, 2008 Edition

AISI S914-08

Test Standard for Joist Connectors Attached to Cold-Formed Steel Structural Framing, 2008 Edition STRUCTURE magazine

15

August 2013

E3.3.1-1; mf = Modification factor for type of bearing connection determined according to AISI S100 Table E3.3.1-2; d = Nominal bolt diameter; t = Uncoated sheet thickness; and Fu = Tensile strength of sheet as defined in AISI S100 Section A2.1 or A2.2. g) Section E3.4, Shear and Tension in Bolts. The nominal tensile and shear strengths of bolts were updated to be consistent with the values in the AISC Specification. h) Section E4.5, Combined Shear and Tension. This section now includes three combined shear and tension checks for screw connections: combined shear and pull-over, combined shear and pull-out, and screw combined shear and tension, where combined shear and pull-out and combined shear and tension are newly added: For combined shear and pull-out: T 1.15 Q + ≤ Pns Pnot Ω

For ASD Eq. (3)

and Qu Tu + ≤ 1.15φ For LRFD Eq. (4) Pns Pnot

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

where Q, Qu, and T, Tu = Shear and tension forces, respectively, determined in accordance with ASD or LRFD load combinations; Pns = Nominal shear strength of sheet per fastener = 4.2(t32d)1/2Fu2; and Pnot = Nominal pull-out strength of sheet per fastener = 0.85tcdFu2; Ω = Safety factor = 2.55; φ = Resistance factor = 0.60; t2 =Thickness of member not in contact with crew head or washer, Fu2 = Yield stress of t2; d = Nominal diameter of screw; and tc = Lesser of

230

Structural Design Spreadsheets

www.Engineering-International.com • Wind Analysis for Tornado and Hurricane Based on 2012 IBC Section 423 & FEMA 361/320.

AISI S100 Table E3.3.1-1 Bearing Factor, C

Connections with standard holes Thickness of connected part, t, in. (mm)

Ratio of fastener diameter to member thickness, d/t

0.024 ≤ t < 0.1875 (0.61 ≤ t < 4.76)

d/t < 10

3.0

d/t < 7

3.0

10 ≤ d/t ≤ 22

4 – 0.1(d/t)

7 ≤ d/t ≤ 18

1+14/(d/t)

d/t > 22

1.8

d/t > 18

1.8

Type of Bearing Connection

mf

Single Shear and Outside Sheets of Double Shear Connection using Standard Holes with Washers under both Bolt Head and Nut

1.00

Single Shear and Outside Sheets of Double Shear Connection using Standard Holes without Washers under both Bolt Head and Nut, or with only One Washer

0.75

Single Shear and Outside Sheets of Double Shear Connection using Oversized or Short-Slotted Holes Parallel to the Applied Load without Washers under both Bolt Head and Nut, or with only One Washer

0.70

Single Shear and Outside Sheets of Double Shear Connection using ShortSlotted Holes Perpendicular to the Applied Load without Washers under both Bolt Head and Nut, or with only One Washer

0.55

Inside Sheet of Double Shear Connection using Standard Holes with or without Washers

1.33

Inside Sheet of Double Shear Connection using Oversized or Short-Slotted Holes Parallel to the Applied Load with or without Washers

1.10

Inside Sheet of Double Shear Connection using Short-Slotted Holes Perpendicular to the Applied Load with or without Washers

0.90

Note: Oversized or short-slotted holes within the lap of lapped or nested Z-members as defined in AISI S100 Section E3 are permitted to be considered as standard holes.

depth of penetration and thickness of t2. The equations are applicable with the following requirements satisfied: (1) 0.0297 in. ≤ t2 ≤ 0.0724 in., (2) No. 8, 10, 12, or 14 self-drilling screws with or without washers, (3) Fu2 ≤ 121 ksi, and (4) 1.0 ≤ Fu/Fy ≤ 1.62.

For screw combined shear and tension:

Tu Vu + ≤ 1.3φ Pts Pss

Coupon for Package: $120 off Code: ASCE 7-2010

C

AISI S100 Table E3.3.1-2 Modification Factor, mf, for Type of Bearing Connection

For ASD

and

• Moment Connection Design for Beam to Weak Axis Column Based on AISC 360-10.

C

Ratio of fastener diameter to member thickness, d/t

Note: Oversized or short-slotted holes within the lap of lapped or nested Z-members as defined in AISI Section E3 are permitted to be considered as standard holes.

V T 1.3 + ≤ Pts Pss Ω

• Mitigate Lateral Drift for Cantilever Column using Post-Tensioning.

Connections with oversized or short-slotted holes

For LRFD

where Pts = Nominal tension strength of screw as reported by manufacturer or determined by independent

STRUCTURE magazine

16

August 2013

laboratory testing; Pss = Nominal shear strength of screw as reported by manufacturer or determined by independent laboratory testing; Ω = Safety factor = 3.0; and φ = Resistance factor = 0.5. i) Section E5, Power Actuated Fasteners.

Comprehensive design equations were adopted for the design of connections using power actuated fasteners.

Although the design equations address potential limit states such as shearing of the sheet or the connector, tension pull-over of the sheet or tension pull-out of the fastener, manufacturer’s published design values are still permitted. j) Appendix 1, Design of Cold-Formed Steel Structural Members Using the Direct Strength Methods. By using

A/S/ S230, Supplement 3, Table A1-3 Conversion of ASCE 7 Basic Wind Speeds to AISI S230 Basic Wind Speeds (mph) 1

1

ASCE 7-10 Basic Wind Speed

110

115

126

139

152

164

177

190

AISI S230 Basic Wind Speed

85

90

100

110

120

130

140

150

ASCE 7 permits linear interpolation between the contours of the basic wind speed maps.

software, Appendix 1 provides a rational engineering analysis approach for determining strengths of cold-formed steel members. Provisions were added for members with holes, web shear strength and inelastic reserve capacity.

2) Technical Changes in AISI S20012, North American Standard for Cold-Formed Steel Framing-General Provisions, and AISI S201-12, North American Standard for Cold-Formed Steel Framing-Product Data These two standards were reorganized as part of a code synchronization effort to eliminate duplications and redundancy, as well as to clear any ambiguities among AISI and ASTM standards, and building codes.

Specific areas considered include: material thickness, physical dimensions and tolerance, mechanical properties, coatings-corrosion resistance, and labeling requirements.

Another major reorganization was due to the development of a new AISI S220, North American Standard for Cold-Formed Steel Framing – Nonstructural Members. The design provisions related to nonstructural members were moved from AISI S200 and AISI S201 to AISI S220. Consequently, AISI S200 and AISI S201 are written for structural members, while AISI S220 is specifically for nonstructural members.

4) Technical Changes to AISI S211, North American Standard for Cold-Formed Steel Framing – Wall Stud Design Supplement 1 to AISI S211 includes updates of the referenced standards, and deletions of the provisions related to nonstructural members.

Helen Chen, Ph.D, P.E., LEED AP-BD+C, is manager of the Construction Standards Development of the American Iron and Steel Institute. She is directly involved in the development and update of AISI construction standards. Helen may be reached at hchen@steel.org.

6) AISI S220, North American Standard for Cold-Formed Steel FramingNonstructural Members Roger L. Brockenbrough, P.E., is President To help clearly delineate and eliminate of R. L. Brockenbrough & Assoc., confusion between the requirements for Chairman of the AISI Committee on cold-formed steel structural members and Specifications for the Design of Coldnonstructural members, AISI S220 was develFormed Steel Structural Members, oped in 2011 specifically for the design and Emeritus Member of the AISC Committee installation of cold-formed steel nonstructural on Specifications, and a member of members in buildings. AISI S220 should be ASTM. He is the editor of two current able to eliminate the confusing industry refMcGraw-Hill texts: Structural Steel erence to “equivalent” or “EQ” sections if Designer’s Handbook and Highway all nonstructural profiles are designed and Engineering Handbook. Roger may be designated in accordance with AISI S220. reached at rogerlbrock@msn.com.

In addition, AISI S220 clarified the definition of nonstructural member as “A member Richard B. Haws, P.E., is manager of in a steel-framed system that is not a part Nucor Building Systems, Chairman of of the gravity load resisting system, lateral AISI Committee on Framing Standards force resisting system or building envelope.” and Vice Chairman of AISI Committee Examples of a nonstructural members include, on Specifications for the Design of Coldbut are not limited to, members in a steel Formed Steel Structural Members. Richard framed system which is limited to a transverse may be reached at rick.haws@nucor.com. (out-of-plane) load of not more than 10 lb/ ft2, a superimposed axial load, exclusive of sheathing materials, of not more than 100 lb/ft, or a superimposed load of not more NEW VERSION RELEASED than 200 pounds. The strength of the nonstructural members may be determined by either non-composite or composite design Software to Analyze Floors for Annoying Vibrations approach. The non-composite assembly • Calculations follow AISC Design Guide 11 Procedures design approach utilizes the design provi• Analyze for Walking and Rhythmic Activities sions of AISI S100 but with adjusted safety • Check floors supporting sensitive equipment and resistance factors, ΩN = 0.9Ω; and φN • Graphic displays of output = 1.1φ; where Ω, φ = Safety and resis• Data bases included tance factors from relevant section of AISI • Expert advice in real time S100; and ΩN, φN = Corresponding safety and resistance factors for nonstructural Demo version at FloorVibe.com members. The non-composite assembly Structural Engineers, Inc. design approach can also be done via testtmmurray@floorvibe.com ing and, with the test results, evaluated

STRUCTURE magazine

FLOORVIBE v2.10

17

August 2013

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

3) Technical Changes in AISI S214, North American Standard for ColdFormed Steel Framing – Truss Design The major change for this standard is related to the provisions of truss responsibilities.

Those provisions were extracted from AISI S202, Code of Standard Practice for ColdFormed Steel Structural Framing, and added to AISI S214.

5) Technical Changes to AISI S230, Standard for Cold-Formed Steel Framing – Prescriptive Method for One and Two Family Dwellings With the introduction of ASCE 7-10, an equivalent wind load table was added in Supplement 3 that converts ASCE 7-10 basic wind speeds to AISI S230 basic wind speeds.

in accordance with AISI S100 Chapter F but with a target reliability index, β0 = 1.6.

For composite assembly design approach is generally accomplished by testing and, with the test results, evaluated in accordance with AISI S100 Chapter F. Detailed discussion on nonstructural design and installation can be found from a separate paper, Design of Nonstructural Members in Accordance with AISI S220, by R. A. LaBoube, et al (February 2013, STRUCTURE magazine).▪

Structural PracticeS practical knowledge beyond the textbook Three steps in the hot-dip galvanizing process.

H

ot-dip galvanizing provides a cathodic, barrier, and zinc patina protection of structural steel from corrosion. Structural steel put through the hot-dip galvanizing process goes through a series of chemical cleaning steps leading up to the final step of being completely immersed in an 830° F bath of molten zinc. The heat effect on the steel, the viscosity properties of the cleaning solutions and zinc, and the resultant metallic zinc coating, requires certain design parameters be met to ensure the steel after galvanizing performs precisely as the engineer intends it to.

Prerequisites When Designing for Hot-Dip Galvanizing

By Philip G. Rahrig

The Process

Philip G. Rahrig is the Executive Director of the American Galvanizers Association, working in all facets of market development.

He is responsible for worldwide coordination of objectives with international organizations with common industry interests.

He may be reached at prahrig@galvanizeit.org.

Batch, or after-fabrication hot-dip galvanizing is a factory-controlled process whereby mild or highstrength steel is progressively cleaned in caustic, acid (hydrochloric or sulfuric) and flux solutions prior to immediate immersion in a bath of 830° F, molten zinc. In the molten zinc, a coating on the steel develops as a result of a metallurgical reaction. The coating consists of four layers, three of which are zinc-iron alloy, and the fourth is a top layer of pure zinc. As a result of this reaction, a tightly adherent, abrasion resistant coating is formed. In fact, the three zinc-iron alloy layers are all harder than the steel itself and have a bond to the steel of approximately 3600 psi, making for a tough coating, difficult to damage during erection and exposure to harsh wear and tear. Typical coatings on structural steel will be in excess of 4 mils, but can vary based on the thickness and type of steel. Unlike most coatings where a thickness is specified, the galvanizer must provide a minimum coating thicknesses depending on which coating specification is used.

and isolates the substrate steel it is protecting from any electrolyte solutions (water, dew, rain, salt water), one of the requirements for electrochemical corrosion of steel. Zinc is anodic to steel, i.e. zinc exposed to air will sacrificially corrode before any of the substrate steel it is protecting will rust. This includes when scratches and gouges occur during the erection phase.

The surrounding zinc corrodes first before any steel corrosion takes place. The corrosion rate of zinc in most atmospheres is very low, meaning the hot-dip galvanized coating will cathodically protect the steel underneath from corrosion for 75 years, and often more. In the zinc corrosion process, the zinc coating progressively forms a patina of zinc oxide, zinc hydroxide, and finally zinc carbonate. The carbonate film is tightly bound to the zinc underneath, very passive, i.e. slow to react with corrosive elements in the air, and is not water soluble.

Galvanizing Implications for Design Approximately 3.4 million tons of structural and miscellaneous steel is hot-dip galvanized each year in North America. Certain characteristics of the process and resultant zinc coating require some well-thought out planning and consideration by structural engineers. (See Hotdip Galvanizing for Corrosion Protection – A Specifiers Guide, 2006, American Galvanizers

How Zinc Protects Steel The zinc coating is metallic in nature and thus impervious to moisture. It serves as a barrier

18 August 2013

Utility poles just seconds after removal from the molten zinc bath.

Keyhole method of draining zinc from a pole during removal from the molten zinc of the hot-dip galvanizing process.

Photomicrograph of the typical hot-dip galvanized steel coating.

Association or Design Guide – The Design of Products to be Hot-Dip Galvanized after Fabrication, 2012, American Galvanizers Association, for more information) Viscosity Steel designs must provide venting and drainage outlets on the parts to be hot-dip galvanized. In the cleaning process of steel to be hot-dip galvanized, the fluids can penetrate between overlapped steel surfaces unless they are seal-welded. Because the viscosity of molten zinc is low compared to the cleaning solutions, it does not penetrate into the overlap areas. The temperature of the molten zinc is 830° F and creates a virtual high pressure enclosure in the overlapped areas, one which can explode, destroy the fabrication, and cause serious injury to the galvanizing personnel in the plant.

Vent/Drain Holes When immersing welded round, square, and rectangular hollow structural sections (HSS) with closed ends in molten zinc, there must be holes somewhere near both ends to allow air to escape out the top and molten zinc to

enter in the bottom. Otherwise, the air pressure doesn’t allow the zinc to flow throughout the inside of the piece, and consequently no zinc coating forms on the inside where most corrosion begins.

Welds All welded areas must be clean and free of slag prior to arriving at the galvanizer’s plant. The cleaning solutions do not remove the slag and the result is uncoated steel.

Coating Thickness and Bolted Connections

Example illustration of vent and drain hole location.

Tapped through-holes must be re-tapped oversize after galvanizing when used in conjunction with galvanized bolts, because the bolt shaft is slightly larger in diameter due to the addition of zinc coating to the bolt threads. Oversizing holes according to American Institute of Steel Construction (AISC) guidelines is usually sufficient to account for the zinc coating’s thickness.

Bolts are completely galvanized, but internal threads in holes or nuts must be tapped oversize after galvanizing to accommodate the increased diameter of the bolts. And, although the re-tapping or chasing cause a bare steel condition on the female thread, the zinc on the bolt threads protects both components from corrosion.

When galvanized bolts are used in conjunction with galvanized and faying structural members, the surface must be roughened or coated with a zinc-silicate paint to achieve a 0.5 coefficient of friction. Exact procedures for this roughening are currently being developed by the American Galvanizers Association. No special preparation of galvanized surfaces is required for bearing connections.

significant changes in the mechanical properties of the structural steels or welds commonly used throughout the world. The galvanized substrate is chemically and metallurgically equivalent to the uncoated steel.

Embrittlement Structural steel severely cold-worked (punched, notched, sheared, or bent sharply) is susceptible to strain-age embrittlement.

This embrittlement is relatively slow to occur in ambient temperatures, but may be immediately evident after exposure to the elevated temperature of the galvanizing bath.

Precautions such as selecting steel with carbon content less than 0.25%, bending with a radii of at least 3X the section thickness, and more are detailed in ASTM A143, Safeguarding Against Embrittlement of Hot-Dip Galvanized

Mechanical Properties

Vent and drain holes on fabricated tubing.

According to studies by the BNF Metals Technology Centre in the UK (as well as numerous other national and international studies), hot-dip galvanizing produces no STRUCTURE magazine

19

August 2013

Hot-dip galvanized bolts used on connection of structural members.

Communication among...

Design Engineer/ Architect

Distortion Some fabricated assemblies, and even asymmetric shapes such as channels, may distort at galvanizing temperature as a result of relieving stressed induced during the steel production and/or fabrication operations. Keys to minimizing distortion include using symmetric rolled sections, parts of equal or similar thickness (so the heating/cooling gradient in the 830° F zinc bath is nearly the same), and large bend radii. For a complete list of tips refer to ASTM A384, Safeguarding against Warpage and Distortion During Hot-Dip Galvanizing of Steel Assemblies.

Overshadowing those improvements is the fact that the steel chemistry is the overwhelming determinant of both coating thickness and aesthetics. Besides iron in steel, which reacts with zinc to form the coating, there are trace elements of silicon (Si) and phosphorous (P). Steels containing Si and P outside recommended ranges are known as reactive steel, and may produce a coating of almost entirely zinc-iron alloy layers. Such coatings tend to be thicker than normal, infrequently making edge areas susceptible to flaking when impacted by tie-down chains during transport or when jarred by contact with other steel during loading/unloading and erection, and tend to be matte gray in appearance.

Reactive steels are still galvanized on a regular basis, and it is important to note differences in appearance have no effect on the corrosion protection afforded by the galvanized coating.

Specifications The predominant hot-dip galvanizing specification in North America is ASTM A123, Standard Specification for Zinc (HotDip Galvanized) Coatings on Iron and Steel Products and covers coating thickness requirements for various steel section thickness, sampling, and inspection procedures. ASTM

Appearance Galvanizers make regular process modifications to improve coating thickness consistency and appearance, all the while adhering to the requirements of the ASTM specifications.

Variation in coating appearance.

DeltaPort Expansion Project – Vancouver, BC.

STRUCTURE magazine

Galvanizer

...from the project’s inception to its completion, can optimize turnaround times, minimize costs, and ensure superior quality hot-dip galvanized steel.

Special designs can minimize distortion when fabrications comprised of dissimilar thickness are required.

Structural Steel Products and Procedure for Detecting Embrittlement.

When galvanized steels of ultimate tensile strength of 150 ksi (1050MPa) are used in design, grit-blasting instead of acid-pickling should be specified. The steel can then be flash-pickle cleaned for just a few minutes instead of 45 to 60 minutes. This minimizes the introduction of gaseous hydrogen which becomes trapped in the grain boundaries during the pickling process. Too much hydrogen in high-strength steels causes a change from ductile to brittle steel, aka hydrogen embrittlement of the steel.

Fabricator/ Detailer

20

August 2013

A153, Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware, is the complementary specification for bolts, nuts, and other connection types.

Within these standards is the understanding that certain design details are required and it is critical there is an open line of communication between the structural engineer, fabricator, and galvanizer. This communication loop helps eliminate costly pitfalls and helps ensure everyone’s expectations are met.

Sustainability Zinc and steel are 100% recyclable.

Approximately 95% of all structural steel is produced from recycled steel and 30% of all zinc produced comes from recycled sources.

The rate for zinc would be much higher if material would be available. The fact is most galvanized steel is in use for 70 years or more.

More importantly, the reclamation rate for zinc is 80%, i.e. of all zinc available for recycling, 80% is recycled.

Zinc is a naturally occurring metal, the 27th most prevalent in the earth’s crust. It is used in myriad consumer products from vitamin supplements and cold remedies to sunscreens, baby ointments, tires, and coins.

Zinc is required for all organisms to live and reproduce. But, by far the largest use of zinc is to protect metal from corrosion via its application in the hot-dip galvanizing process.

Sustainability measurement is rapidly progressing to encompass the complete stream for any product from raw material to final use. For hot-dip galvanized steel this means measuring the energy consumed and emissions generated from the mining of zinc and steel, smelting, and application on steel to the recycling phase and back to raw material. The emphasis of the galvanizing industry is that no maintenance of galvanized steel is necessary for 70 years or more. This means the environmental impact is almost exclusively confined to the production phase. This is unlike most other coatings, which require periodic and frequent maintenance throughout their service life.

The only environmental impact during the use-phase results when the zinc coating corrodes over many decades and makes its way back into water and soil from which it was mined. When the zinc coating is exposed to air and goes through the natural wet and dry cycles of weather events (rain, snow, fog), it oxidizes and very slowly, often 75 years or more, makes its way into streams, rivers,

oceans, and lakes. These compounds (zinc oxide, zinc hydroxide, zinc carbonate) are added to the existing background level of zinc in the water, but only on a very temporary basis. The zinc level does not accumulate in water due to the interactions between zinc and the various water quality constituents present in natural waters. The suspended solids in water (minerals and coarse organic material) decrease the total zinc due to settling and are incorporated into the sediment. Over time, the system maintains a consistent ambient zinc concentration in the water column and sediment because there is a constant supply of new sources of suspended solids in the flowing water. These new sources remove and bury the zinc in a continuous cycle. Even if there are multiple sources of zinc, the dilution factor and suspended solids removal is such that the natural background level of zinc is relatively unchanged approximately 2500 feet downstream from each zinc source, and even closer for bodies of water with very large volumes such as oceans.

This addition of zinc to the water environment does not cause the background level of zinc to exceed the criterion level, defined by the U.S. Federal Clean Water Act, as the amount of zinc in water causing toxicity to aquatic organisms.

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

STRUCTURE magazine

21

August 2013

Bergen County, New Jersey Hot-dip Galvanized Short-Span Bridge.

Summary The hot-dip galvanizing process is unique in that it economically protects valuable structural steel from corrosion, but it requires some special design considerations in order to deliver the precise requirements specified by the structural engineer. When the structural engineer understands the governing specifications for hot-dip galvanizing and is in constructive communication with the architect, fabricator, and galvanizer, all expectations are met. And, the use of galvanized steel assures that sustainability has been integrated into the final project.▪

InSIghtS new trends, new techniques and current industry issues A structural column base plate member at LOD 100 through 400.

P

oorly defined structural engineering contract scopes rob engineers of time, profit, and – most importantly – the personal satisfaction of their profession. Building Information Modeling (BIM) can improve this challenge if addressed proactively, or compound the difficulties if ignored. The construction industry has reached a point where the use of BIM is not self-explanatory: it could be used to create 2D shop drawings, coordinate trades, or estimate cost. Since BIM came into existence, the industry has lacked a vocabulary for communicating the Level of Development (LOD) between parties. The BIM Forum™ Level of Development (LOD) Specification (http://bimforum.org/LOD/) is an industry-changing reference that enables structural engineers to clarify their scope with BIM, providing the solution to this paramount problem of vague BIM scope definition.

Previous to this development, many model element authors were unaware of expectations upon entering a project. The LOD Specification now gives a way to define the scope of detail and input minimums for each particular component of the design. It is simply a collection of definitions describing input and information requirements, and graphic/model examples of the different levels of development for building elements. The document does not outline the necessary levels of development for different steps in the construction process, leaving these determinations for each project team. Instead, it gives a common vocabulary for use between parties on a project team.

Beating Chaos and Achieving Profits in BIM with LOD 350

By Will Ikerd, P.E., CWI, LEED AP

Will Ikerd, P.E., CWI, LEED AP, is principal at IKERD Consulting. Mr. Ikerd currently co-chairs both the Designers Forum of the AGC’s national BIM Forum and the Structural Engineering Institute’s national BIM Committee. Additionally, he co-chairs the AGC BIM Forum – AIA workgroup on Structural LOD. He may be contacted at structures@IKERD.com.

LOD Definitions in Terms of Model Elements • LOD 100 – The Model Element may be graphically represented in the Model with a symbol or other generic representation, but

22 August 2013

It is important to note that there is no LOD of an entire model; the model is a mixture of different elements within different LODs. Source: BIM Forum™ Level of Development Specification – Draft 2013 does not satisfy the requirements for LOD 200. Information related to the Model Element (i.e. cost per square foot, tonnage of HVAC, etc.) can be derived from other Model Elements.

• LOD 200 – The Model Element is graphically represented within the Model as a generic system, object, or assembly with approximate quantities, size, shape, location, and orientation. Non-graphic information may also be attached to the Model Element.

• LOD 300 – The Model Element is graphically represented within the Model as a specific system, object or assembly in terms of quantity, size, shape, location, and orientation. Non-graphic information may also be attached to the Model Element.

• LOD 350 – The Model Element is graphically represented within the Model as a specific system, object, or assembly in terms of quantity, size, shape, orientation, and interfaces with other building systems.

Non-graphic information may also be attached to the Model Element.

• LOD 400 – The Model Element is graphically represented within the Model as a specific system, object or assembly in terms of size, shape, location, quantity, and orientation with detailing, fabrication, assembly, and installation information. Nongraphic information may also be attached to the Model Element.

• LOD 500 – The Model Element is a field verified representation in terms of size, shape, location, quantity, and orientation.

Non-graphic information may also be attached to the Model Elements.

Shortcomings and Adjustments

STRUCTURE magazine

lines. This creates the risk of failing to discover that the line will not fit below the structure and above the ceiling if the lines are not modeled at LOD 300 (with slopes). The structural engineer may then be forced to consider adding web openings in their beams or redesigning shallower beams, losing time and profit.

Profit is vital in the business of any profession; structural engineering with BIM is no different. LOD 350 is a key to beating chaos in the design to construction process and aiding structural engineers in the opportunity to find profits in clearly defined project BIM scopes.▪

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

For permit drawings, which will be required for the foreseeable future on building projects, elements are typically only modeled to LOD 300. However, for full trade coordination, higher LOD is required, short of fabrication LOD. For this reason, the author proposed LOD 350 for bridging the gap between element development at permit drawings and fabrication level. LOD 300 does not include the information necessary for full cross trade coordination, while LOD 400 requires information that may not yet be available.

LOD 300 represents model elements traditionally shown in the plan view of a set of construction documents. This would include main structural members, with information such as specific location and type. Construction Documents made from the LOD 300 model are accompanied by 2D information: general notes, typical details, specific details and specifications to define higher level information not typically shown in 1/8-inch scale plans or modeled for permit drawings. For coordination, model elements with an LOD of 350 represent information generally shown with typical details in construction drawings. This information requires tradeknowledgeable input to model accurately.

Most main structural member elements are at LOD 300. However, structural engineers must be mindful that LOD 300 requires elements to be in the correct location. For example, although the 2D plans may appear to be correct, sloping roof members that are modeled flat are not at LOD 300. Also, design-level open web bar joists at LOD 300 are not acceptable for trade coordination with MEP, as they do not have the specific manufacturer’s web profiles to detect conflicts. Other areas of misunderstanding are structural elements shared with architecture, such as tilt walls, slabs and load bearing masonry walls. Situations such as this make a compelling case for using LOD 350 as an important step between specific assemblies and detailed assemblies for coordination with manufacturer’s specific content. The structural engineer’s scope should address who is responsible for modeling items such as floor depressions, openings, top of wall heights of parapets, etc.

As more projects require detailed 3D coordination, the need for accurate MEP models will become even clearer to lower the risk of the entire designer team. There is little value in above-ceiling coordination in taking the architectural and structural model elements to LOD 300 (specific in the actual

orientation) if MEP model elements are only at LOD 200 (generic in approximate location).

Structural engineers should consider adding additional services in their contracts for manual MEP coordination review if the MEP model elements are not to LOD 300. This represents the added time the structural engineer will have to invest in the project during construction administration to deal with changes in the MEP due to lack of model definition (and MEP design). For instance, all gravity plumbing lines must slope for these elements to be at LOD 300, whereas many MEP design models do not slope these

23

August 2013

Building Blocks updates and information on structural materials

Figure 1: Roof and wall framing.

C

old-formed steel can be utilized in a variety of construction applications because of its versatility. This article describes two applications where one is likely to find cold-formed steel being utilized. The Cold-Formed Steel Engineers Institute (CFSEI) gave the two projects described below an Award of Merit for Design Excellence at the CFSEI EXPO in Orlando, Florida in May, 2012.

Cold-Formed Steel Applications

By Winston E. Kile, P.E., S.E.

Self-Storage Facilities

Winston E. Kile, P.E., S.E., is the President of Structuneering Inc. He has served as Chairman of the Cold-Formed Steel Engineers Institute and is a member of several subcommittees of the AISI Committee on Specifications for the Design of Cold-Formed Steel Structural Members. He can be reached at edkile@structuneering.com.

The self-storage industry has matured from small, one story structures to large multi-story architecturally designed facilities in major urban areas. Self-storage buildings have become part of American folklore; a fictional character in John Grisham’s “The Summons” temporarily stored $1,000,000 cash inside Unit 37A at Chaney SelfStorage in Charlottesville, VA. Deer Park Storage is a 62,600 square foot fourstory self-storage building located in Babylon, NY on Long Island. The building contains 578 storage units and a business center. This facility earned a LEED Silver Certificate from the U.S. Green Building Council. The storage building is thought to be the first self-storage facility to earn this distinction in the United States.

It is known to be the first self-storage facility to achieve this status on Long Island. Figures 1 and 2 show the project during construction and after completion.

Each floor of this building is constructed primarily of load-bearing cold-formed steel stud walls.

The bottom floor of the building is a basement.

Each floor is designed to support an ASCE 7 light storage floor live load of 125 psf. Each coldformed steel post in the basement is designed to support a total gravity load of 13,400 pounds.

The building was designed to resist 115 mph winds. The building was assigned a Seismic Design

24 August 2013

Figure 2: Deer Park Storage in Babylon, NY.

Category C. Twenty-five percent of the self-storage live load at each floor level has been considered as part of the effective seismic weight. No damage was sustained during Hurricane Sandy.

The roof panels are 24 mil (24 gage) cold-formed steel standing seam panels. Each floor consists of 47 mil (18 gage) composite cold-formed steel deck supporting four inches of concrete. Portions of the exterior wall are constructed with composite insulation board, which consists of two inch thick foam insulation sandwiched between cold-formed steel panels on both the exterior and interior surfaces. The interior partition walls between storage units consist of either 14 mil (29 gage) or 18 mil (26 gage) cold-formed corrugated panels that function as shear walls to resist lateral loads. The roof top HVAC framing and the exterior canopies are constructed with cold-formed steel.

The roof panels are supported by 60 mil coldformed steel zee purlins. The load bearing walls consist of either 60 mil or 105 mil cold-formed steel cee posts braced by cold-formed steel partition panels and 48 mil cold-formed steel J-shaped sections. The top and bottom track members at the load bearing walls are cold-formed steel sections. The lobby and retail areas of the building have two story high ceilings with structural steel and cold-formed steel intermixed.

The Deer Park Storage project was developed by the Deer Park Storage Partners, LLC in conjunction with the Marcus Organization.

Anthony Garrett, AIA, of Bilow Garrett continued on page 26

Easier to bridge – inside

and out

DBC

SUBH

Reduce installed cost and increase productivity with the Simpson Strong-Tie® DBC and SUBH bridging connectors. A single screw holds the connector to the channel, reducing the installed cost over conventional connections that require four screws. The SUBH wall-stud connector fits snug over 1½" U-channel and is the only code-listed bridging connector. The DBC is the first and only connector load rated for drywall studs and smaller ¾" U-channel.

The SUBH and DBC have been extensively lab tested as a system, ensuring that tabulated design values reflect stud web depth and thickness. To learn more, call (800) 999-5099 or visit www.strongtie.com/cfs.

DBC and SUBH

© 2013

Simpson Strong-Tie Company Inc. DBCSUBH13

Figure 3: Cold-formed steel for roof retrofit at MacDill AFB in Tampa, FL.

Architects and Planners provided the architectural design and Bruce Goldman, P.E., was the project engineer of record.

Ashwin Mupparapu, P.E., of Structuneering Inc. provided the structural engineering design calculations for both the coldformed steel and structural steel framing.

The steel for this building was provided and erected by Rib-Roof Metal Systems.

Roof Retrofits

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

Retrofit roofs are a practical and innovative use of cold-formed steel construction for the renovation of flat roof areas. A retrofit roof is very similar to a one-story self-storage facility minus the interior partition panels.

A cold-formed steel retrofit roof provides a variety of functions and advantages: • Provides a maintenance free permanent solution metal roof to eliminate roof leaks resulting from standing water on flat composite or built-up or membrane roofs.

• Lowers the life-cycle cost of roof maintenance.

Foundation Performance Association (FPA) ENGINEERS - Need CEU’s??

The FPA hosts monthly events with interesting presentations that provide you CEU’s. FPA also sponsors the publication of technical papers and research material. FPA is great for networking and low-cost CEU’s.

Membership $96/yr ≈ $8/CEU

Figure 4: Roof retrofit at MacDill AFB.

• Provides a pleasing architectural upgrade with pitched metal roof panels in an array of finishes and eave/fascia treatments.

• A twenty year warranty is provided for the finish of the new roof panels.

• Insulation can be added in the new attic to improve energy consumption efficiency.

• Hides unsightly roof top mechanical units.

• Provides roof overhangs above entry areas.

A new retrofit roof was installed on Building 53 at MacDill AFB in Tampa, Florida as part of a renovation project for this building. The covered roof area is approximately 20,000 square feet. Figures 3 and 4 show the retrofit roof during construction.

Approximately one-half of the existing flat roof at Building 53 consists of structural steel framing with open web steel joists at 48 inches on-center (OC). The other half of the existing flat roof consists of wood framing with 2x roof joists at 16 inches OC. Approximately 4000 square feet of the original roof was elevated four feet above the surrounding roof.

The new roof consists entirely of coldformed steel: • The roof panels are 24 mil (24 gage) cold-formed standing-seam metal panels. The roof panels were formed on-site with the use of portable roof forming equipment. The panels were rolled to the exact length required for each panel run to eliminate any splices between the ridge and eave. The panels contain a patented vinyl weatherseal strip at the seams. The panels have been tested for UL-1897 and ASTM E-1592 wind uplift and UL fire resistance.

www.foundationperformance.org

STRUCTURE magazine

26

August 2013

Also, the panels have received Florida Building Code approval.

• The roof panels are supported by a 30 mil (22 gage) cold-formed steel Type 1.5F metal deck.

• The metal deck is supported by 60 mil cold-formed steel rafters spaced according to the wind uplift roof zones.

• The rafters are supported by 60 mil cold-formed steel posts at a maximum spacing of five foot on center in both directions.

• The posts are supported by either the existing steel joists or by 60 mil cold-formed steel base support zees.

The base support zees are provided to distribute the roof loads across the existing steel and wood joists.

• Cold-formed steel trusses constructed of 60 mil C-sections were installed above a new entryway.

The new retrofit roof for this project is designed to resist 130 mph winds. The structural engineering design of the coldformed steel retrofit system was provided

by Laerta Mushi Campbell, MSCE, of Structuneering Inc. Berridge Manufacturing Company provided the cold-formed steel material for this retrofit project. Bobby Marks, Jr. of Berridge Manufacturing prepared the cold-formed steel drawings.

The overall renovation project was designed

by GLE Facilities and Environmental Consultants of Tampa, Florida. Derek Weaver, RA, NCARB, LEED AP was the project architect. Heather Tank, P.E. was the engineer-of-record. Danner Construction was the General Contractor for this project. The cold-formed steel was installed by Morrell Architectural Systems.▪

What do you do when you’ve been in the lead for 67 years? Widen the gap.

Vulcraft’s Detailing Center demonstrates our strong committment to innovation.

Today’s building landscape is radically different from when we began in 1946, but our commitment to being on the forefront of technological development has never changed. Vulcraft is built on a constant drive to innovate.

From precision engineered joists to first-in-class joist applied technology, Vulcraft continues to leverage technology to create solutions that work for our customers.

Vulcraft’s innovations today will be the industry standards for tomorrow.

Vulcraft’s technological leadership is centered on providing forward-thinking solutions for our customers; solutions that make our customers’ jobs easier and more accurate, solutions like NuBIM™-Joist Plug-in for Tekla Structures, the NuBIM™ Vulcraft Add-In for Revit® Software and Tekla and SDS2 BIM detailing software. These programs,

and others like them, satisfy our customer’s need to find better ways to build in an increasingly competitive marketplace.

In an industry that demands solutions to complex problems, Vulcraft delivers the technology that gets it done.

Introducing advanced software is just one way Vulcraft is leading our industry into the next age of innovation. See what else we’re doing to leverage technology and create meaningful solutions for your business.

Leveraging Technology. Creating Solutions. www.vulcraft.com

Autodesk and Revit are registered trademarks or trademarks of Autodesk, Inc., and/or its subsidiaries and/or affiliates in the USA and/or other countries.

Historic structures significant structures of the past

Piscataqua Bridge

By Frank Griggs, Jr., Dist.

M. ASCE, D. Eng., P.E., P.L.S.

Dr. Griggs specializes in the restoration of historic bridges, having restored many 19th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an independent Consulting Engineer.

Dr. Griggs can be reached at fgriggs@nycap.rr.com.

T

he Piscataqua Bridge across the Great Bay of the Piscataqua River is located six miles west of Portsmouth, New Hampshire, and was built in 1794 with a span of 244 feet. It was the longest span bridge in the United States when it opened, holding that record until Lewis Wernwag built his Colossus Bridge across the Schuylkill River north of Philadelphia in 1812 with a span of 340 feet. Timothy Palmer had built bridges across the Merrimack River in Massachusetts, and was a pioneer in long span wooden truss bridge design and construction when he was called to build the most difficult part of the Piscataqua Bridge.

Palmer’s first bridge was the Essex–Merrimack Bridge, west of Newburyport across the Merrimack River, that opened in 1792 (June 2013 issue of STRUCTURE magazine). That bridge was followed by a bridge at Andover (now Lawrence) Massachusetts across the same river in 1793. The bridge was built “to open a communication between Portsmouth and the interior of the state, and to divert its trade from Boston, Newburyport, and Portland, by which it has hitherto been engrossed. This bridge lies in a direct course to the heart of the state; and a turnpike road was originally intended to be opened from it to Concord on the Merrimack, and thence to the Connecticut River.”

The Turnpike had been started in 1791 to connect Concord, the capital, with tidewater at Durham, New Hampshire. The users of the turnpike found, however, that a direct land route to tidewater at Portsmouth would be most advantageous and urged the construction of a bridge across the Great Bay connecting Durham with Newington.

The initial petition to the legislature was submitted in December 1792 for authorization to build a toll bridge, and a survey made of the crossing and the results were published in the Portsmouth Herald on June 4, 1793 as follows: From Fox point to Ram Island, 600 feet at high water, depth from 50 to 54 feet.

From Ram island to Goat Island, 330 feet at high water, depth from 42 to 44 feet.

From Goat island to Tuttle point on Durham side, 888 feet at high water, depth from 42 to 44 feet.

Length on the water 1818 feet.

Breadth Ram island 50 feet.

Breadth Goat island 390 feet.

Whole length of bridge 2258 feet.

28 August 2013

The existence of Goat Island in the middle of the Bay cut down on the amount of bridging required. In addition, a roadway system of sorts was in place as Furber’s Ferry was in service across the Bay. The state legislature granted a charter for the bridge to the Proprietors of Piscataqua Bridge on June 20, 1793 for an “Act to incorporate certain persons for the purpose of building a bridge over Piscataqua River between Bloody Point and Furber’s Ferry so called and for supporting the same.” The act also indicated that “a draw or Hoist, over some one of the channels shall be constructed of such width as the Judges of the Supreme Court of Judicature shall direct, previous to the erection of said Bridge, not exceeding forty feet, so that vessels may freely pass and repass through the same.

Shortly after receiving the charter, the Proprietors began purchasing the property at both ends of the bridge and Palmer was formally selected in mid 1793. He gave them the design for the long trussed span; they started ordering materials for the bridge in November 1793 based upon his design. Major Zenas Whiting of Norwich, Connecticut was selected to build the trestle approach structures and the required draw span.

The Whiting Bridge was a trestle structure on each end at the sides of the river and the Great Arch, Palmers 244-foot span, was over the main channel. The trestle’s were “…supported by piles, five of which were strongly framed and braced together and driven into the bottom of the river bed; string pieces were laid from one set of piles to another, and on them the planks or flooring was secured.” On the Durham side, Whiting built a small draw span for high masted boats.

Notices in the New Hampshire Gazette on November 30 and December 11 described the wood that the Proprietors would need to build the entire bridge, including the long arch. Since the plans are missing and presumed lost in the fire at the offices of the bridge company, the materials ordered taken in conjunction with other Palmer Bridges give an idea of the size and placement of his members in the bridge. Robert Gilmor, who visited the bridge in 1797, made a sketch of Palmer’s prominently featured arch.

The December 14, 1793 issue of the New Hampshire Gazette listed the timber required for the arches. It included 1,535 pieces of pine timber from 15 feet to 50 feet in length, and ranging in size from 3 inches by 5 inches to 14 inches by 18 inches. Ninety-four of these pine timbers, intended for use in the wooden arch of the bridge, were to be 50 feet long and 14 inches x 18 inches with a 20-inch curve or sweep over the 50 feet. In other words he, wanted 50-foot long 14 x 18 pine timbers with a natural bend in them.

Palmer designed his “great arch” with three sets of arches over a total width of 38 feet; each of these arches were different than his previous bridges as he added a third intermediate member of the structure to carry the floor, rather than resting the floor on the bottom chord. In the words of a local historian, “the arch is composed of three tiers of girders, the lower one is sixteen feet from the chord, and twenty feet from the water at high tide. The second tier supports the planking on which the road passes, which is on a larger circle to facilitate the travelling. The upper tier answers the purpose of railing. There are three sets of these girders, one on each side, and one in the middle of the bridge, which are so braced and framed together, as to make them whole strong and firm.” In other words, the lower

20'

4' 24'

Deck

Top Chord (Railing) Roadway

16' 4'

40-50'

arch was the bottom chord of his truss, the upper arch was the top chord of his arch and the middle arch carried the floor to the truss.

The span was almost 30% longer than his longest previous bridge.

As with most wooden bridges of the time, the timbers would be cut and drilled to plan and erected off site to assure the proper fit of all members. The trusses would then be dismantled and transported to the bridge site and re-erected on falsework. After all the connections were finished, the falsework would be dropped and the truss/arch would stand-alone.

Work started on April 1, 1794 and the bridge was completed on November 25 of the same year. Palmer built massive falsework on which to build his trusses in the 50-foot deep and rapidly moving water. From a constructability ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

STRUCTURE magazine

29

August 2013

~ 450'± Lower Chord R = Upper Chord R ~ = 610'±

standpoint, the falsework must have been as difficult to erect as the bridge. The main reason, other than depth of the water, was the 7-8 foot tidal range in the Bay. Palmer would later state, “he had, at the Piscataway Bridge, erected an arch of 244 feet; but he repeatedly declared that, whatever might be suggested by theorists, he would not advise, nor would he ever again attempt extending an arch, even to our distance, (Permanent Bridge) where such heavy transportation was constant proceeding.”

The December 9, 1794 issue of the Portsmouth Gazette gave information on the bridge; its length was given as 2,362 feet, and width 38 feet. The article described the trestles as being built “on piles from fifty-three to sixty-five feet, driven into the bed of the river by ‘large hammers’ of oak timbers, braced and framed

on a new and improved plan.” The bridge construction used 3,000 tons of oak timber, 2,000 tons of pine, 80,000 feet of 4-inch plank; 20 tons of iron; and 8,000 tons of stone. Enos Whiting of Norwich, Connecticut is credited with superintending the pile work, and also with constructing “a draw for the passage of shipping, which moves across in a horizontal direction, instead of being raised on hinges, but it is feared this expected improvement will not answer the purpose.”

Adams wrote “hundreds of people came long distances to cross and view the great enterprise that so auspiciously opened a new era in business. The Architect was Timothy Palmer of Newburyport, and the success of his work earned for him a great reputation.

The entire bridge, [including the trestle spans and draw spans] cost $65,974.34, a large sum for those days.”

It is clear that Palmer’s top chord on this bridge was only at railing height, and that the deck was close to the top chord and some distance (16 feet) above the bottom chord. This was the first time he changed his normal method of bracing the top chords overhead. He determined that a deeper truss was required for the longer span and that it became more difficult to have overhead cross braces, even if connected with ships knees, to provide sufficient lateral bracing. By having the deck near the top chord, it is possible to cross brace the trusses below the deck down to the lower chord.

The bridge sparked a great deal of interest in the few international journals and books dealing with engineering subjects in the late 18th and early 19th century. The first written description of the bridge was in the Dictionary of Arts, Sciences and Miscellaneous Literature in its Supplement printed in Philadelphia in 1803: …a wooden bridge erected in North America, in which this simple notion of Grubenhamm’s is mightily improved.

The span of the arch was said to exceed 250 feet, and its rise exceedingly small.

The description we got is very general, but sufficient, we think, to make it perfectly intelligible. In… are supposed to be three beams of the arch. They consist of logs of timber of small lengths, supposed of 10 or 12 feet, such as can be found of a curvature suited to its place in the arch without trimming it across the grain.

Each beam is double, consisting of two logs applied to each other side to side, and breaking joint, as the workmen term it.

They are kept together by wedges and keys driven through them at short intervals…

Thomas Pope, in his 1811 A Treatise on Bridge Architecture, wrote that the “part which engages the attention of travelers is an arc nearly in the centre of the river, uniting two islands, over water forty-six feet deep. This stupendous arc of two hundred and fortyfour feet on the chord, is allowed to be a masterly piece of architecture, planned and built by the ingenious Mr. Timothy Palmer of Newburyport…”

Since the original plans for the bridge have been lost in a fire at the company offices in Portsmouth, it is necessary to rely on the observations of travelers, and later writers, who were not engineers or builders but who had actually seen the bridge and crossed it, to understand the design and construction of the bridge and the impact it had on users.

Timothy Dwight crossed the bridge in the fall of 1795, and described it as follows: …This structure stands in a region which gives it every advantage to make a striking impression on the mind…we came suddenly upon the bridge, an enormous structure, twenty-six hundred feet in length, of an interesting figure, finished with great beauty and elegance, new, white, and brilliant.

There are at this place two islands in the river; one, next to the southern shore, an oblong narrow rock: the other of sufficient extent for the site of house, garden, and some other enclosure…The whole scene had the appearance of enchantment, and in Arabia might not unnaturally have been attributed to the hand of a genie...Piscataqua bridge is formed of three sections; two of them horizontally, the third arched…The arch like the Haverhill Bridge [built in the following year] is triple, but no part of the work is overhead. The chord is 244 feet; and the versed sine, nine feet and ten inches. This arch is the largest in the United States, contains more than seventy tons of timber, and was framed with such exactness that not a single stick was taken out after it had been once put in its place. The whole length of planking is 2,244 feet. The abutments make up the remaining 356 feet and the island already mentioned…This is by far the most interesting structure of the kind which I have ever seen. Like the face in a well-contrived portrait, it is surrounded by such objects as leave the eye to rest on the principal one, and the mind to see but a single impression.

Fletcher and Snow described the bridge as follows: Its length was 244 feet, the rise was 27 feet 4 inches and the depth of framework of the arch, 18 feet 3 inches. There were three concentric ribs the middle one

STRUCTURE magazine

30

August 2013

carrying the floor of the bridge. The ribs were made from crooked timbers, so that the fibers were nearly in the direction of the curves, and they were connected by pieces of hard and incompressible wood, with wedges, driven between. The ribs were mortised to receive these connecting pieces and wedges, thus keeping an equal and parallel distance between them. Each rib was formed of two pieces, about 15 feet long, laid side by side in such a manner as to break joints. Their ends all abutted with square joints against each other, and were neither scarfed nor mortised. The two pieces of timber being held together by transverse keys and joints. All the timbers were admirably jointed and freely exposed to the action of the air. Any piece might be removed for replacement without injury to the remainder of the structure.

It, primarily the deck portion, was rebuilt in 1803 when a lottery was held to cover the reconstruction. It was unusual that a wooden bridge would have to be rebuilt in only 7 years, but exisiting uncovered in a New Hampshire coastal environment could have accounted for significant decay of some of its members. The tolls were not sufficient to cover expenses, and the bridge was never a financial success.

In 1818, Cyrus Frink, who had completed most of the earlier repairs, replaced the arch with “an entire new bridge, according to a wooden plan by him exhibited to the directors.” The reconstruction, including the new arch, was to be completed between June 4th and September 15th without obstructing or impeding the passengers. What his plan was, and how he replaced the main span while not cutting off traffic, is not clear.

Whatever he did, it resulted in the removal of Palmer’s span.

Frink’s bridge gave way on March 18, 1830 and, after being rebuilt, gave way again in 1854 and was not repaired. An ice jam on February 18, 1855 took the remainder of the bridge out. By that time, traffic had decreased significantly due to competition from the railroad that had opened between Boston and Portland, Maine, and the bridge was not rebuilt.

This bridge was the most written about of any bridge in the country until Palmer’s Schuylkill River Permanent Bridge in 1805.

Its 244-foot span was 84 feet longer in span than the Newburyport Bridge and incorporated an entirely unique framing plan, one that he, in part, was to use in his later bridges across the Schuylkill and Delaware Rivers.▪

Stack the deck

Assure the success of your building projects New Millennium is your source for reliable nationwide steel decking supply: 14 profiles of roof, floor and composite floor deck – plus steel joists and FreeSpan™ castellated and cellular beams.

FREE steel decking catalog: www.newmill.com/steeldeck

Sutter Health Eden Medical Center Structural Engineer’s Active Role in an IPD Project with Lean and BIM Components

By Mohammad Aliaari, Ph.D., S.E. and Edwin Najarian, S.E., P.E.

T

he Sutter Health Eden Medical Center (SHEMC) project in Castro Valley, California, set a new standard for structural engineers to play an active and significant role in a successful Integrated Project Delivery (IPD) project, enhanced with Lean practices and Building Information Modeling (BIM) technologies. SHEMC is a new, state-of-the-art, 230,000 square foot replacement hospital with 130 acute care beds and a 36-bed universal care service. The vision of the project was to create

Figure 1: Sutter Health Eden Medical Center (SHEMC) Project. Courtesy of Sutter Health, DPR Construction.

a landmark medical center that combines quality medical care, outstanding physicians and staff, and advanced technology to provide the best care for the community. The project consisted of a 7-story hospital building with a 4-story tower on top of a 3-story podium, a new central utilities plant and several new canopies (Figure 1 and 2).

The design and construction cost was $230 million.

IPD Collaboration and Lean Practice

Figure 2: Sutter Health Eden Medical Center (SHEMC) Project. Courtesy of Sutter Health, Devenney Group, Christopher Skow Photography.

STRUCTURE magazine

For the 1st time in the U.S., an 11-party IPD team including the owner, architect, structural engineer, design teams, general contractor and selected trade subcontractors, all co-signed an Integrated Form of Agreement (IFOA) contract, requiring them to work collaboratively, extensively use 3D BIM technologies, and implement lean practice, in a shared risk, shared reward environment, to design and deliver this hospital project within a 30% accelerated schedule and aggressive budget targets. Based on a study by the owner, there were potential high schedule and cost risks under a conventional design-bid-build process for this project. Some key strategies that were implemented to achieve the IPD objectives included: use of Value Stream Mapping to map the workflow; allocation of adequate early time and resources to plan the design process prior to design itself; bi-weekly 2-day team meetings (big room meetings) for design coordination; extensive use of BIM technologies with direct digital exchange capabilities (model based estimation, automated fabrication, scheduling, etc.); and, real time broad access to all project information through a web-based software. Extensive pool planning sessions were utilized during big room meetings for both design and construction phases throughout entire project duration. Arrangements were made for the inspector of record (IOR) of the project to be present in early project meetings. This allowed his voice and ideas to be heard ahead of time to minimizing potential comments and slowdowns during construction. Typically, IORs join the project long after approvals and at the start of construction.

32

August 2013

IPD Project Team Owner: Sutter Health Structural Engineer: TTG (TMAD Taylor & Gaines) Architect: Devenney Group General Contractor: DPR Construction Other design teams and trade subcontractors

Structural System and Main Challenges The project site is 0.5 miles from the active Hayward fault with Seismic Design Category F. Being an essential facility under California Office of Statewide Health Planning and Development (OSHPD) jurisdiction, results in a seismic importance factor of I=1.5. These factors led to the highest seismic design requirements in both California and the U.S. It was a challenging task for the structural engineer to design a structural Figure 3: Top: Isometric view of 3D structural analysis and design model. Courtesy of TTG system under the restricted requirements, meet the (TMAD Taylor & Gaines). inter-story drift limitations, and at the same time maintain the architectural intent and design. Several schemes were The foundation system consists of nearly 600, 60-foot deep, drilled investigated for an optimum system and, ultimately, a lateral friction cast-in-place piles (CIDH) with 75 ksi rebar. system combining Special Reinforced Concrete Shear Walls for The exterior of the building is a very complex skin interface the podium and Special Concentric Braced Frames (SCBF) for of glass curtain wall, precast CCAPP, precast GFRC, and metal the tower was selected. The tower floor plan is very irregularly panels. The analysis of interaction between the structure and skin shaped and lateral resisting brace frames are distributed mostly was a very challenging task. Design of geometrically complicated along the perimeter of the structure and around the elevator canopies and a 125-foot tall signature spire were among the other cores, where architectural design allowed. This provides a very challenges for the structural engineer. The building spire is designed robust and balanced distribution of the lateral system to control with all pipe elements and connected to five cantilevered beams the torsional and lateral movements (Figure 3). All braced frames with double end plate connections, which required very high fabare supported on shear walls in the podium level, with columns rication accuracy (Figure 4 ). There was an early aggressive project continuing to the foundation. The shear walls were designed using deadline to obtain a partial fund contingent on OSHPD approval concrete compressive strength of 7,000 psi. TTG, the structural of the structural design package, which put tremendous pressure engineer, performed extensive soil-structure interaction model- on the structural engineering team. The structural engineer had ing and analyses to provide a justified and lighter design for this to complete the structural design and obtain approval in advance, hospital project. A study by the project geotechnical consultant while the other design disciplines were still in early design phases provided required information for soil modeling and parameters. with target approval dates of at least one year ahead.

Incremental Review and Structural Plan Checking Process

Figure 4: Photos of installation of signature 125-foot tall spire element with double end plate connections. Courtesy of Sutter Health, DPR Construction.

STRUCTURE magazine

33

This project is one of the earliest projects in California using OSHPD’s incremental phase review process to accelerate the permitting process. The project was submitted in five different increments, including; primary structural system, site, building exterior, building interior, and medical equipment. Each increment consisted of several segments or phases. The design team had to completely transform from the traditional design workflow of schematic design (SD), design development (DD), and detailed construction documents (CD), and create a new workflow and process to allow the start of early construction along with a simultaneous design progress and intense 3D model-based design coordination. A 3rd party structural engineering firm was assigned

by OSHPD for structural plan checking of the project.

The structural engineer worked very closely with the

August 2013

plan checking team through a detailed and delicate process, in which the review comments and responses were communicated in a weekly manner until all the comments were resolved and approval for the structural package was obtained on time.

3D Review of Structural Shop Drawings This project is one of the 1st projects where the structural engineer reviewed shop drawings in full 3D format. The 3D review of structural steel shop drawings was conducted through direct exchange of TEKLA models between the structural engineer and the steel contractor in 22 different segments. The structural engineer worked with Herrick, the steel fabricator, to customize TEKLA for a more streamlined review process. At any point in time, the structural engineer Figure 5: Full 3D BIM-Based design, and construction modeling and coordination. was working on the review of new segments Courtesy of TTG (TMAD Taylor & Gaines). while back checking prior segments, sequentially. In addition, rebar installation shop drawings were also generated in 3D TEKLA models and reviewed in 8 different concrete pours. This allowed for a detailed constructability review by the structural engineer, In Conclusion general contractor, and rebar detailer. The 3D review process eliminated st SHEMC was the 1 full IPD, 11-Party IFOA project in the US and traditional methods of providing and mailing thousands of hard prints, also one of the earliest OSHPD incrementally reviewed projects. The resulting in savings in both project cost and in time. project was very successful. TTG, the structural engineer, played a significant role, utilizing advanced and innovative technologies to BIM-Based Design and Clash Detection overcome challenges and contribute to the success of the project: • All of the IPD goals were met or exceeded.

Extensive virtual design and building modeling efforts were utilized.

• Project delivered ahead of schedule, even with 30% fast Various 3D design models, along with 3D shop drawings models, track schedule. were reviewed and clashed using Navisworks in a multi-disciplinary • Project delivered on-budget, even with aggressive budget targets. fashion (Figure 5). This process allowed the structural engineer and • The structural engineer produced fully coordinated and contractors to better understand the contact between the various constructible drawings and 3D models. structural and non-structural elements, and permitted resolving issues • Steel delivered 6 months ahead of schedule with over $1 and conflicts ahead of time (Figure 6 ). Typically, these types of issues million in savings, returned to owner by steel contractor due to would not be identified and resolved until progress of construction, active collaboration between the structural engineer and steel resulting in costly field repairs and delays. contractor and IPD team in review of 3D shop drawing.

• Construction change orders & RFIs for structure were under 15% of estimates for comparable hospital projects in California.

• The project has won numerous design and construction awards.

• The project has been twice on cover page of Engineering News-Record (ENR) (September 2011 and May 2009 issues).▪ Mohammad Aliaari, Ph.D, S.E., is a Senior Associate, Structural Project Manager at TTG Office in Pasadena, CA. He can be reached at maliaari@ttgcorp.com.

Edwin Najarian, S.E., P.E., is a Principal, Structural Vice President at TTG Office in Pasadena, CA. He can be reached at enajarian@ttgcorp.com.

Figure 6: 3D Multi-disciplinary clash detection review using Navisworks model.

Courtesy of TTG (TMAD Taylor & Gaines).

STRUCTURE magazine

34

August 2013

Padma Bridge Design for Severe Earthquake and Deep Riverbed Scour

By Robin Sham, Ph.D., C.Eng, FICE Padma Bridge – a 6.15km long, combined rail-road river crossing.

O

ne of the greatest challenges to long-span bridge engineering is the forces of nature. Recent catastrophic events around the world reinforce the fact that nature can be destructive to infrastructure. At the Padma Bridge site in Bangladesh, AECOM used state-of-the-art technology and innovative disaster prevention and mitigation solutions to tackle some severe challenges.

At 6.15 kilometers (3.8 miles) in length, the Padma Bridge is a landmark structure and one of the longest river crossings in the world.

The Padma River is the third largest river in the world, and has the largest volume of sediment transport.

During monsoon seasons, the Padma River becomes fast flowing and is susceptible to deep scour, requiring deep-pile foundations for bridge stability. The Padma Bridge site is also in an area of considerable seismic activity, resulting in significant earthquake forces being exerted on the bridge. This combination, together with other forces of nature, posed a unique challenge.

The multipurpose Padma Bridge detailed design project has been successfully completed. AECOM developed alternative concrete deck forms, including an extradosed concrete truss bridge, a concrete girder bridge and a steel truss bridge. In all cases, a two-level structure was chosen, having significant advantages over a single level structure.

These included segregated highway and railway envelopes to offer enhanced safety, improved operation, inspection, maintenance, and emergency evacuation procedures, as well as efficient provisions for utilities. With the railway in the lower deck, the structural depth beneath the railway is reduced, allowing the lengths of the railway approach viaducts for tie-in at the north and south banks to be minimized. With a two-level structure the construction cost is reduced, making the structure more efficient.

Analytical models were developed for each of the bridge forms to determine member sizes and, in particular, the weight of the superstructure. The steel truss bridge was found to be the most efficient with the lightest deck. Further details of this option were developed to determine the optimum span length. Total deck weight and foundation loads were compared for span lengths of 120 meters, 150 meters and 180 meters (394 feet, 492 feet and 591 feet, respectively). From this data, a construction cost was estimated for each span length with the optimum span being 150 meters. In conclusion, the most economic and appropriate form for the bridge was found to be the steel truss bridge with a concrete top slab acting compositely.

STRUCTURE magazine

The multipurpose bridge also has many utilities built into it, including a gas pipeline, telecommunications and a high-voltage power transmission line. Additionally, it has emergency access points in order to facilitate evacuation of a train on the lower deck.

A detailed study of seismic hazard at the site was performed to determine suitable seismic parameters for use in the design. Two levels of seismic hazard were adopted: Operating Level Earthquake and Contingency Level Earthquake. Operating Level Earthquake has a return period of 100 years with a 65 percent probability of being exceeded during that period. Contingency Level Earthquake has a return period of 475 years with a 20 percent probability of being exceeded during a 100-year bridge life period. Any damage sustained from such an earthquake would be easily detectable and capable of repair without demolition or component replacement.

In conjunction with these investigations, AECOM carried out further analysis to determine the optimum foundation design, and two pile types were investigated; large diameter (3 meter; 10 feet) raking steel tubular piles and large diameter cast-in-situ concrete bored piles. Raking piles were more efficient in resisting lateral loads resulting from earthquake motions. This type of load is resisted as axial force in the steel piles, while the lateral load is resisted by the flexural capacity of the piles for the concrete bored piles. The very large bending moments generated by a seismic event dictated that insufficient flexural capacity could be created by reinforcement alone, and a permanent steel casing would be

36

Raking steel tubular piles are very effective in withstanding large lateral forces. Some 60 meters (197 feet) of pile is unsupported due to riverbed scour.

August 2013

A three-dimensional global model for a 6-span bridge module.

A structure-free field soil interaction model.

required to enhance the capacity down to 10 meters (33 feet) below the riverbed level, which for a 100-year scour event would be -61m PWD. It would also be necessary to have more than fifteen 3-meter (10 feet) diameter vertical concrete piles, compared to eight raking steel tubular piles. The large number of piles increased the weight of the pile cap and also the local scour. All of these factors had an adverse effect on the cost and constructability of the foundations, therefore the preferred solution was recommended as being the raking steel tubular piles.

The behavior of the bridge is complex due to its height, which is 120 meters (394 feet) when the effects of scour are taken into consideration, and the large mass of the superstructure, pile caps and piles. A three-dimensional non-linear time history dynamic analysis, using a modified Penzien model, was adopted. It was divided into two parts, the structure and the free field soil. The interactions between the structure and the free field were simulated by lateral spring links. In order to determine the equivalent shear modulus and effective damping ratio between each layer of the soil, free field analysis was carried out beforehand using the Shake analysis program. Subsequently, a threedimensional dynamic analysis was carried out using the equivalent shear modulus and effective damping as input data.

Ground motions were applied to the model to simulate the earthquake case, and loads were generated in the piles and substructure accordingly. Although other load combinations were considered, such as ship impact and wind, these effects were not found to be critical for the substructure, and the seismic load combination dictated the design.

A further model was developed to investigate the global behavior of the bridge. The bridge is divided into six span modules, each span 150 meters (492 feet) long, so the global analysis model examined an individual six span module and applied different levels of scour at each pier. A scour hole may form around an individual pier, or around two or more piers. The global model looked at various combinations in order to determine the critical axial, shear and bending loads on the foundations of any particular pier.

Initial studies of the bridge were based on the deck being supported by traditional sliding bearings, with the point of fixity being the central pier of the six-span module. To avoid the fixed pier being heavily loaded during a seismic event by a longitudinal translation, shock transmission units were proposed at the free piers to ensure even load distribution between the piers. But under this system, the loads applied to the piers were still large; therefore, as part of the value engineering process, AECOM considered alternative forms of articulation.

The original seismic design strategy was to dissipate seismic energy through plastic hinges at the bottom of the piers. Further design optimization identified the benefits of seismic isolation, which allows the structure to behave elastically without damage. The application of seismic isolation has reduced the number of piles, the size of the pile caps and the size of the steel superstructure, resulting in a more cost effective design. Seismic isolation bearings have been used worldwide to mitigate seismic response by isolating structures from seismic input. They can accommodate thermal movements with minimum resistance, but will engage under seismic excitations. In this strategy, all primary structural members remain elastic without any damage or plastic hinging.

Isolation bearings contain three key elements: one to provide rigidity under service loads and lateral flexibility beyond service loads, one to provide self-centering capability, and one to provide energy dissipation. These key elements have to be properly designed and fine-tuned to achieve optimal seismic behavior.

Analyses indicate that seismic forces can be greatly reduced by replacing conventional pot bearings with isolation bearings. Friction pendulum bearings utilize the characteristics of a pendulum to lengthen the natural period of the isolated structure so as to reduce the input of earthquake forces. The damping effect due to the sliding mechanism also helps mitigate earthquake response. Since earthquake induced displacements occur primarily in the bearings, lateral loads and shaking movements transmitted to the structure are greatly reduced.

The reduced seismic loading generated at the top of the bridge piers significantly reduces pile loads. With the conventional scheme of bearings and shock-transmission units, eight raking steel piles were required for each pier; with seismic isolation this was reduced to six, leading to a savings in foundation costs of more than 20 percent.

AECOM then further developed the design with the inclusion of seismic isolation. The impact of the seismic isolation scheme is not limited to the substructure; the reduced seismic loading leads to reduction in section sizes for truss members, with an overall saving in truss steelwork of greater than 6 percent.▪ Robin Sham, Ph.D., C.Eng, FICE, is Global Long Span and Specialty Bridges Director of AECOM. In 2011, he was conferred the highly prestigious Fellowship of the City and Guilds of London Institute for his “outstanding contribution to the field of civil engineering”. Dr. Sham may be reached at robin.sham@aecom.com.

Principles of seismic isolation for Padma Bridge.

STRUCTURE magazine

37

August 2013

Mass Transit at Phoenix Airport

By David A. Burrows, P.E., LEED AP BD+C and John A. Lobo, P.E., S.E.

PHX Sky Train headed east over the Taxiway R Crossing, Terminal 4 and the control tower in the background. Courtesy of Bob Perzel.

O

n April 8, 2013, Phoenix Sky Harbor International Airport opened the first stage of the PHX Sky Train™, a 5-mile long automated transit system exclusively serving the Airport. Expected to carry 2.5 million passengers a year, the system provides a dedicated, streamlined, safe, convenient, and more sustainable transportation link between airport terminals, parking lots, rental car center and regional lightrail transit facilities, and reduces congestion around the airport terminals. This is no small feat given that Sky Harbor is one of the ten busiest airports in the country.

Known as one of the largest economic engines in the state of Arizona, Sky Harbor currently serves over 40 million people a year and has grown steadily throughout its 75 year history. Since the development of its newest terminal in the late 1980s, the Airport has contemplated building a transit system to deal with traffic congestion due to increasing passenger demand and aging ground transportation infrastructure. Without the Sky Train, projections show that quality of service and future Airport growth would be crippled by gridlock on the Airport’s roadways.

Planning efforts resulted in a 5-mile long corridor for the Sky Train in three stages to spread overall funding requirements. Currently operating, Stage 1 consists of approximately 2 miles of guideway, of

Figure 1: PHX Sky Train route map. Courtesy of Phoenix Aviation Department.

which over 1.5 miles is elevated, to connect three stations: a Metro light-rail stop; a major airport parking facility; and Terminal 4, the largest airport terminal. Stage 1A, which is now under construction, builds a new station at Terminal 3, approximately ¾ mile of guideway and a walkway to connect the Stage 1 facilities and Terminal 2. The final stage is in conceptual design and will provide future connections to the rental car center and another major airport parking lot (Figure 1).

Transit System Planning

Figure 2: Map showing the location of the Maintenance and Storage Facility (MSF) and SR-153. Courtesy of Gannett Fleming, Inc.

STRUCTURE magazine

Constructing a dedicated transit system within an operating airport is costly and will unavoidably impact existing facilities and operations. However, the Phoenix Aviation Department determined that long-term benefits outweighed the short-term cost and potential disruptions. Projections for Sky Harbor showed that an automated transit system would be the best way to increase landside capacity and avoid restricting future airport growth. To maximize benefits, planning considered long-term development of the Airport, opportunities for transit oriented development, strategies to maximize ridership on the system, and repurposing an adjacent underutilized freeway.

• Station siting – providing connections at the airport terminals, parking facilities, rental car center and the regional light rail system, stations are located to serve passengers as well as airport and airline employees and other support staff.

When fully operational, the Sky Train will eliminate existing

38

August 2013

44th Street Station. Courtesy of Bob Perzel.

airport bus operations. Stations are sited and programmed to accommodate future parking garages, support facilities and potential private development to increase ridership.

• Accommodation for future stations – segments along the alignment are designed to accommodate future stations for additional airport parking and terminal facilities needed for long-term growth.

• Provide drop-off /pick-up away from terminal core areas – to relieve congested terminal curbs, designated nonterminal stations will accommodate buses, vans, shuttles, passenger vehicles, etc. This will create convenient passenger drop-off and pick-up areas that are a short Sky Train ride away from terminals.

• Repurpose an existing freeway – without a good connection to the surrounding regional freeway system, a section of freeway located just east of the Airport, SR 153, had historically been underutilized. The project uses a portion of the corridor to carry the Train at-grade, creating a very cost effective solution to what would otherwise have been a costly below grade alignment through a runway protection zone. The remainder of SR 153 was modified to a typical city street where it still has ample capacity to carry traffic flows (Figure 2). This freeway corridor reconfiguration is estimated to have saved the project approximately $30,000,000.

construction schedules overlapped by 2 years in an overall construction schedule of 3.5 years; and, to allow design to stay just ahead of construction, 31 separate design packages were issued. Building Information Modeling (BIM) was used by all design disciplines for vertical structures, and shared with the contractor to avoid conflicts and quickly resolve those that did occur.

The single most fundamental element to mitigating construction impacts to all airport patrons, tenants, airlines, and operations was developing and communicating a well planned construction plan, gaining buy-in by stakeholders, and executing it as scheduled. It was essential that the airport continue to provide for the needs of airport users even through the most demanding construction operations.

Therefore, a thorough outreach to multiple stakeholders was critically important. Key stakeholders extensively involved in the project were: Airport Operations, Airport Facilities & Services, the Airlines, Federal Aviation Administration, Valley METRO Rail and the Union Pacific Railroad.

Some of the challenges mitigated by advanced planning and stakeholder communication included: • Restricting heavy construction activities around Terminal 4 to nights in order to minimize effects of noise, dust and congestion from construction traffic on passengers.

Planning to Build in an Operating Airport Sky Train infrastructure design required careful consideration of construction impacts on airport operations and facilities, as construction requirements drove many key design decisions. An integrated design and construction approach was used to help ensure that the project was built on-time and on-budget. At the 30% design level, a Construction Manager at Risk (CMAR) contractor was brought onto the team. The use of CMAR allowed early confirmation of construction schedule and budget, value engineering to be integrated into design, constructability issues and operational impacts to be mitigated during the design phase, and design tailored to the contractor’s preferred construction approach.

A fast-track delivery of construction documents was necessary to minimize overall project schedule and risk associated with inflation and fluctuating material costs. In order to accomplish this, design and STRUCTURE magazine

PHX Sky Train adjacent to Sky Harbor Blvd. East of the Terminal 4 Station.

Courtesy of Bob Perzel.

39

August 2013

A US Airways jet passes beneath the Taxiway R Crossing with the PHX Sky Train overhead. Courtesy of City of Phoenix Aviation Department.

• Keeping the pedestrian bridge between concourses open while constructing the Terminal 4 Station and guideway directly above them.

• Minimizing the number of concourse gates that were closed during any given period. The Sky Train team worked closely with the affected airlines to minimize gate closures and scheduled work so that closures could be staggered, especially during peak travel seasons.

• One of the security checkpoints directly below the Terminal 4 Station was scheduled for expansion shortly before Sky Train construction. By working closely with the Airport and Checkpoint design team, the support columns of the Station in the area were constructed during the checkpoint widening work, thereby eliminating a future disruption.

• Sky Train’s pedestrian bridge link to the Valley Metro Light Rail system crosses above the Light Rail’s overhead catenary power lines. To avoid future disruption of Light Rail service, completion of the pedestrian bridge had to be advanced ahead of the December 2008 start of Metro Light Rail operations, several months ahead of breaking ground on Sky Train construction.

In January, 2013, the PHX Sky Train facilities achieved Gold certification from the U.S. Green Building Council (USGBC) under the Leadership in Energy and Environmental Design (LEED) for New Construction Version 2.2. Supporting LEED’s priority to reduce greenhouse gas emissions, operation of the Sky Train alone will relieve terminal roadway and curb congestion and will result in approximately 20,000 fewer vehicles per day at Sky Harbor, thereby reducing CO2 emissions by nearly 6,000 tons annually and ensuring that the airport’s Figure 3: LEED scorecard for PHX Sky Train Stage 1.

Source: U.S. Green Building Council.

LEED Facts for New Construction (v2.2) Certification awarded Jan 2013 44

Sustainable sites

5/14

Water efficiency

3/5

Energy & atmosphere

10/17

Material & resources

7/13

Indoor environmental quality Innovation

roadways flow freely. Efficiencies that were built into the Sky Train project, as documented by the LEED process, are expected to save the City over $10 million dollars in the first 20 years of operation.

Initially, only the Sky Train stations were planned to be LEED certified. However, during the design process, a campus approach, whereby stations and guideway would be rated together, was chosen as the best option. This change was motivated primarily because the East Economy Lot station was changed from an enclosed to an open-air structure. While the latter consumes less energy, the baseline against which energy reduction would be measured was reset to an open-air structure. Although the first transportation project to be evaluated using a campus approach, it allowed credits to be computed as an aggregate for the guideway and stations, rather than by each individual station. The campus approach proved to be advantageous, allowing a score of 44 out of 69 possible credits, as seen in the details of Figure 3.

Stage 1 Grand Opening

Creating a LEED Certified System

Gold

Interior of the bridge over Sky Harbor Blvd leading to the Terminal 4 Station.

Courtesy of Bob Perzel.

With about 300 elected officials, business leaders and other invited guests in attendance, on April 8th of this year, the PHX Sky Train made its debut run from the 44th Street Station to Terminal 4. The automated, electric train’s smooth and seemingly effortless ride stands in sharp contrast to the monumental effort that went into building it. Constructing nearly two miles of guideway at one of the busiest airports in the country without disrupting flights, halting traffic, or going over budget, is a huge achievement for the City, the contractors and the design professionals involved.

Challenges such as making the world’s first crossing of an active taxiway, fitting the Terminal 4 Station around an existing pedestrian bridge and concourses, and weaving a narrow path between two multistory parking garages, were overcome with collaboration, cooperation and perseverance. The end result is that the Sky Train has transformed the Airport’s landside transportation system. Growing from a two terminal airfield serving 3 million people annually just four decades ago to a three terminal international airport serving 40 million passengers last year, completion of the Sky Train will position Sky Harbor to continue providing highquality service well into the future.▪ David A. Burrows, P.E., LEED AP BD+C, is a senior structural engineer at Gannett Fleming, Phoenix, Arizona. He was the lead engineer for the design of the Taxiway R crossing. David can be reached at dburrows@gfnet.com.

John A. Lobo, P.E., S.E., is a bridge engineer at Gannett Fleming, Phoenix, Arizona. He was a member of the Sky Train fixed facilities design team for 10 years. John can be reached at jlobo@gfnet.com.

14/15 5/5 STRUCTURE magazine

40

August 2013

A roadway that connects dreams to success.

Gerdau has shipped more than 19,000 tons of steel to Tampa’s I-4 Connector Project.

All across America, Gerdau helps build dreams.

Tampa’s I-4 Connector will improve movement of people and goods, as well as remove truck traffic from one of only two National Historic Districts in Florida. www.gerdau.com/longsteel

SoNo Ice House Time for a Change

By Bruce D. Richardson, P.E., Nils V. Ericson III, P.E., LEED AP and Chris T. O’Brien, P.E. Figure 2: Clear-span trusses.

T

he renovation of an obsolete manufacturing facility into a state-of-the-art ice hockey development center presented challenges that required creativity, teamwork, and an owner committed to following a lifelong dream in order to keep the project on schedule and under budget.

Ryan Hughes, the owner and operator of North American Hockey School and manager of North American Rink Management, had the vision to utilize the former manufacturing building’s high bay clearance and wide open interior spaces to create a state-of-the-art hockey facility that featured two indoor hockey rinks. He needed to get the project started quickly and be in operation in time for the start of the season for the Connecticut Oilers of the Empire Junior Hockey League, the first local hockey team in Norwalk, CT in over 50 years.

Ryan enlisted the help of Claris Construction Inc., a Design-Build contractor from Newtown, CT and The Di Salvo Ericson Group, Structural Engineers, Inc. from Ridgefield, CT. After the initial walk-through of the cavernous space in July 2011, it was apparent that the building had some obstacles to overcome before conversion into a hockey facility would be completed. The one-story industrial building had served as a manufacturing plant for Nash Engineering from the time it was constructed in the 1960s until they moved out in 1995. The building’s configuration was well-suited for a manufacturing plant; it included tall interior clearance, 45 feet high at the roof peak, and widely spaced interior columns. The roof framing system consisted of sloping steel rafters supporting zee-purlins. Despite the tall clearance and wide column spacing, many of the interior columns would conflict with the layout of the hockey rinks and would need to be removed. In addition, a temporary sound studio had just moved into a portion of the building to begin the filming of a major motion picture, and the noise sensitive filming operations would prevent any construction activity on the site for several months.

Using historical documents of the original construction, The Di Salvo Ericson Group modeled the existing roof framing system and developed a method of removing the interior columns that conflicted with the hockey rink locations. The column removal would be accomplished by creating trusses out of the existing sloping steel rafters by introducing new horizontal steel bottom chords and sloping steel web members between the rafter ends. The new truss configuration would STRUCTURE magazine

clear span over the new hockey rink locations and be supported on new steel columns and footings at each end. Furthermore, the new column-truss frame would be rigidly connected to upgrade the renovated facility to current Connecticut State Building Code wind and seismic requirements. The upper portion of the existing steel columns would be incorporated into the new truss configuration and, after the construction of the trusses was completed, the lower portion of the columns would be removed (Figure 1).

Claris Construction, Inc. prepared a final layout of the new hockey facility within the existing building that indicated the removal or relocation of twelve (12) interior columns. Also, a new two level mezzanine would be required to provide additional space for a training gym, locker rooms, and a snack bar.

Prior to the final design and fabrication of the clear span trusses, field measurements and documentation of the existing steel rafters and columns were required to provide an accurate basis for the final design model and for the fabrication drawings. This responsibility was assumed by the steel fabricator, Engineered Building Products, of Bloomfield, CT, and was undertaken immediately following the completion of the motion picture filming and the removal of the sound stage sets. Interestingly, the results

42

Figure 1: Roof truss solution.

August 2013

of the field measurements showed that the existing steel framing was out of plumb by a few inches at the peak of the roof, parallel to the ridge, and required that the new columns at the ends of the trussed rafters be offset from the existing columns on the exterior wall by the same amount.

The structural engineers used the field measurements to prepare a final design model with RAM Structural System and Visual Analysis to analyze and design the new structural steel elements of the clear-span roof trusses. The final design included the analysis and strengthening of the existing sloping steel rafters to support the additional compression force that would be introduced after the truss construction was completed and the columns were removed. The field measurements were also used for the preparation of the structural details of the new truss connections, and allowed for including provisions to accommodate the field variations in the location of the steel members and for the out-of-plumb steel framing.

The unique approach to the roof framing alterations allowed the building to remain enclosed and intact during the renovation, and the new horizontal bottom chord of the trusses allowed ample headroom for the hockey activities. In addition, by leaving the existing columns in place until after the construction of the trusses was completed, the requirement to temporarily shore the building was eliminated, allowing unrestricted access to the work area so that the installation of the footings at the new column locations could start immediately. This feature turned out to be extremely beneficial to the project schedule. During the early part of the project, as the excavations for the new column footings began, several buried foundations were uncovered that were not anticipated and that were not reflected in the historical documents. As a result, the design and construction of many of the new foundations was delayed in order to address the unique condition of these specific footing locations. The project completion would have been delayed significantly if the new foundation work had not benefited from the early start.

Once the foundations were completed, the steel roof truss framing was installed relatively quickly and the tight project schedule was maintained while transforming the forty year old industrial building into a modern sports facility (Figure 2).

Claris Construction, Inc. and The Di Salvo Ericson Group approached the project with the understanding that the solution to the column removal needed to address the short time schedule, the limited access to the space at the start of the schedule, and the need to keep the project within budget. The unique solution to create trusses out of the existing sloping rafters was a simple idea that made maximum re-use of the existing structure, and took advantage of the existing high bay clearance and the relatively low headroom required for hockey. The execution of the solution was complicated by the need to implement the work in a short time period while adapting to the various geometries and hidden surprises provided by the existing conditions.▪ Bruce D. Richardson, P.E., is a Principal with The Di Salvo Ericson Group in Ridgefield, CT. Bruce may be reached at bruce@tdeg.com.

Nils V. Ericson III, P.E., LEED AP, is a Project Manager with The Di Salvo Ericson Group in Ridgefield, CT. Nils may be reached at nils@tdeg.com.

Chris T. O’Brien, P.E., is a Senior Project Engineer with The Di Salvo Ericson Group in Ridgefield, CT. Chris may be reached at chris@tdeg.com.

The project was awarded a 2013 ACEC/CT Engineering Excellence Award.

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

STRUCTURE magazine

43

August 2013

SHEAR VALUE

At ASC Steel Deck, providing our customers with shear value is what we do best.

36/7/4 Attachment Pattern with DeltaGrip® Side Seam Attachment With 30% fewer attachments to supports, 36/7/4 provides the highest diaphragm shear value at the lowest installation cost in the market.

ASC Steel Deck is a Full Product Line Deck Manufacturer.

We deliver a line of quality structural, floor and roof deck that has been fully tested for commercial construction.

Form Deck • B-36 • N-32 • 2W-36 • 3W-36 • Deep Deck • Nestable • Cellular

Visit us online at www.ascsd.com or call 800.726.2727

aids for the structural engineer’s toolbox

ENGINEER’S NOTEBOOK

Gravity Controls Over Seismic?

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

W

idth/thickness ratios for members resisting both gravity and seismic loads are generally thought to be controlled by seismic criteria. This only makes sense, since the transient loads due to an earthquake typically impose demands far above and beyond those associated with simple gravity service conditions. Is it likely that gravity considerations would ever be more restrictive than seismic considerations?

If you answered ‘no’ to this question, you would be right – it is not likely. Nevertheless, there is a minority of conditions for which the converse is true and gravity criteria control over seismic criteria for a given shape. Section E7 of AISC 360-05 in the 13th Edition of the Steel Construction Manual requires adjustment to certain design parameters for slender compression elements. Here, the reduction factor Q is defined and has the effect of reducing the critical buckling stress (Fcr). Where does this adjustment become manifest?

Consider a W14x43 column in either a single-story braced frame or at the top level of a multi-story braced frame. This section supports both gravity and seismic loads. The ratio of the height to the web thickness (h/tw) for this section is 37.4. Per Table B4.1, the limiting slenderness ratio ( λr) for the web of this element is 1.49(E/ Fy)0.5 or 35.9. Hence, this column is slender and subject to the provisions of Section B4.

By contrast, depending on the magnitude of the axial force in the column, AISC 341-05 in the First Edition of the Seismic Design Manual would define this shape as seismically compact if the slenderness ratio of 37.4 is less than 3.14(E/ Fy)0.5(1-1.54Ca). AISC 341-10 in the Second Edition of the AISC Seismic Design Manual has a somewhat different equation, but the point still applies. Among other criteria, Section E7 of AISC 360-05 requires that design strengths be reduced by the Q factor, and that section properties be calculated based on ‘effective’ section dimensions. Though tedious, these calculations may validate the use of this column for

its intended application in the braced frame.

It is noteworthy that many of the commercially available and commonly used structural design software applications do not perform this particular slenderness check; it must always be verified by hand.

Again, the shapes for which the standard AISC 360-05 criteria for compactness may be more stringent than those in AISC 341-05 are among the minority. Eliminating these shapes from one’s design database is not likely to cause dramatic changes in the cost or performance of the resulting structures. As an alternative to the column example, the next size up (W14x48) does not suffer from the same ‘slenderness’ classification and will certainly result in lower demand/capacity ratios for the given scenario. Such measures should be judged on a case-by-case basis.▪ Jerod G. Johnson, Ph.D., S.E. (jjohnson@reaveley.com), is a principal with Reaveley Engineers + Associates in Salt Lake City, Utah.

A similar article was published in the SEAU Monthly Newsletter (November, 2006). It is reprinted with permission.

ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

Buckling Restrained Braces are in our DNA Call: 435.940.9222 www.starseismic.net ss_structure_aug2013_final.indd 1

STRUCTURE magazine

45

August 2013

5/29/13 10:25 AM

Educating Future Structural Engineers

T

he National Society of Structural Engineers Associations (NCSEA) is pleased to present the 2013 survey of schools and colleges throughout the United States. The schools surveyed offer educational opportunities for students desiring to become professional civil/structural engineers. NCSEA has sponsored the survey since 2002. Curriculum on which the survey is based is primarily that which practicing engineers have determined as appropriate for structural engineering students working to obtain recognition as a structural engineer in the workplace. Although the emphasis of the National Council of Structural Engineers Associations is on those structural engineers in the vertical and horizontal construction aspects of the industry, structural engineers have prominent roles in other related fields such as the airframe industry and industrial machine design.

For those following the progress of structural engineering education in the United States, it has long been recognized that the emphasis and focus of curriculum, and curriculum content, is constantly under review. Readers of STRUCTURE, NCSEA’s monthly STRUCTURAL CONNECTION publication, and attendees at the NCSEA annual conference and Institutes have observed the ebb and flow of the process. Since the 2010 survey, NCSEA has gathered opinions from structural engineers and instructors regarding: • Offering a single course split in Masonry and Timber • Expanding the core curriculum to include non-traditional structural materials such as aluminum and cold formed steel • Accepting the substitution of computers as an educational tool to improve the student’s understanding of structural function, in lieu of Matrix Methods • Changing the two concrete courses to be two core requirements for Cast-In-Place Concrete or reducing the demands within Concrete 1 and retaining Concrete 2 for PreStress Post-Tensioning.

STRUCTURE magazine

For the current proposed curricula and past survey results, visit www.structuremag.org/EducationSurveys.aspx.

And, for the first time, the 2013 survey sought to determine school interest in a student version of the structural certification available to registered engineers (SECB certification); 76% of responding schools expressed interest in the program.

Change follows discussion, and systematized discussion results in consensus. This same process established NCSEA’s proposed curriculum over 10 years ago, and it is the process that will lead to modifications in the current curriculum, adjustments in school and college programs, and changes in the mindset of practitioners.

Parents as well as students use the survey to help plan for the future.

Readers of this article and participants in the survey are effective in maintaining its relevance.

NCSEA is considering making the survey timelier by conducting a web based survey every year for two years, followed by a detailed interactive response survey from schools every 3rd year. We hope you enjoy reading the 2013 survey, studying the curriculum, and commenting on both.

46

NCSEA and its Education Committee would like to receive your thoughts on the current state of the proposed curricula and the latest survey results. Please send your comments to NCSEA.Education@structuremag.org.

August 2013

Full Curricula The following is a list of schools/universities who responded directly to the 2013 survey AND who have indicated that they provide the full curricula as proposed by the NCSEA Education Committee.

University Arizona State University Auburn University Clemson University California Polytechnic State University California State University, Fresno Colorado State University Colorado State University – Fort Collins* Columbia University in the City of New York* Kansas State University Michigan Technological University Milwaukee School of Engineering Missouri University of Science and Technology* Montana State University New Jersey Institute of Technology New Mexico State University

University of Southern California University of Texas at Austin University of the Pacific University of Washington University of Wisconsin-Madison University of Wisconsin-Milwaukee University of Wyoming

North Carolina State University Oregon State University Rose-Hulman Institute of Technology Sacramento State* Texas A&M University University of Alabama University of Arkansas* University of Detroit Mercy* University of Florida University of Kansas University of Maine* University of Minnesota University of Nevada Las Vegas The University of New Hampshire University of North Carolina at Charlotte

* The schools/universities who did not responded directly to the 2013 survey, yet do list courses which comprise the full curricula (as determined by a review of the school’s website).





 



















































 













































Technical Writing

 



Foundation Mechanics / Soils

Dynamic Behavior and Design



Masonry Behavior and Design



Timber Behavior and Design



Concrete Behavior and Design 2

Steel Behavior and Design 1



Concrete Behavior and Design 1

Matrix Methods

Bucknell University City College of New York Cleveland State University Colorado School of Mines Gonzaga University Hofstra University Idaho State University Illinois Institute of Technology Lawrence Technological University

Analysis 2

University

Analysis 1

The following is a list of schools/universities who responded directly to the 2013 survey but who have indicated that they do not provide the full curricula as proposed by the NCSEA Education Committee. The Table indicates which courses are, or are not, offered.

Steel Behavior and Design 2

Partial Curricula



 















table continued on next page

STRUCTURE magazine

47

August 2013

Steel Behavior and Design 1

Steel Behavior and Design 2

Concrete Behavior and Design 1

Concrete Behavior and Design 2

Dynamic Behavior and Design

Foundation Mechanics / Soils

Technical Writing

































Saint Martin’s University



San Francisco State University



Santa Clara University South Dakota State University Stevens Institute of Technology The University of Akron Tufts University University of Alaska Anchorage University of California at Davis University of California, San Diego University of Colorado University of Dayton University of Evansville University of Hartford University of Houston University of Idaho University of Kentucky University of Miami-Coral Gables University of Michigan University of Mississippi

 



 























































  



 

































































 

























































































































































































 





 

STRUCTURE magazine



 

Masonry Behavior and Design

Matrix Methods

Analysis 1

Lehigh University Marquette University Midlands Technical College Northeastern University Northern Arizona University Ohio Northern University Ohio State University Ohio University Oklahoma State University Old Dominion University Owens Community College (Design Technologies) Owens Community College (Architectural Engineering Technology) Point Park University Rensselaer Polytechnic Institute Rutgers University

University

Timber Behavior and Design

Analysis 2 

Schools/universities who have indicated that they do not provide the full curricula as proposed by the NCSEA Education Committee, continued.



 





 



































 

























 























































































48

August 2013





























Technical Writing



Foundation Mechanics / Soils



Masonry Behavior and Design

Concrete Behavior and Design 2



Timber Behavior and Design

Concrete Behavior and Design 1



Dynamic Behavior and Design



Steel Behavior and Design 2



Steel Behavior and Design 1

University of New Mexico University of North Dakota University of Oklahoma University of South Alabama University of Toledo Valparaiso University Virginia Tech Worcester Polytechnic Institute

Matrix Methods

University

Analysis 2

Analysis 1

Schools/universities who have indicated that they do not provide the full curricula as proposed by the NCSEA Education Committee, continued.

























 





































































 







The following is a list of schools/universities who did not responded directly to the 2013 survey, and do not list the full range of courses which comprise the full curricula (as determined by a review of the school’s website).

Alabama A&M Arkansas State University Berkeley University of California Blue Mountain Community College Bradley University Brigham Young University Broome Community College Brown University Cal State Long Beach Cal State University - Northridge California Tech California State University - Fullerton California State University - Los Angeles Carnegie Mellon University Case Western Reserve University Catholic University of America Central Connecticut State University Central Piedmont Community College Christian Brother University Cincinnati Technical College The Citadel City University of New York Clarkson University College of San Mateo Cornell University CSU Chico District of Columbia University Drexel University Fairleigh- Dickinson University Fairmont State University

Florida Institute of Technology Georgia Institute of Technology George Washington University Georgia Southern University Horry-Georgetown Technical College Howard University

Iowa State University Johns Hopkins University Lakeland Community College Lamar University Louisiana State University continued on next page

Suggested Course/Curricula Semester Credit Hours Suggested

Course Analysis 1 Analysis 2 Matrix Methods Steel Behavior and Design 1 Steel Behavior and Design 2 Concrete Behavior and Design 1 Concrete Behavior and Design 2 Timber Behavior and Design Masonry Behavior and Design Dynamic Behavior and Design Foundation Mechanics / Soils Technical Writing

STRUCTURE magazine

49

August 2013

3 3 3 3 3 3 3 3 3 3 3 3

Comments

Including code application Including code application Including code application Including code application

Schools/universities who do not list the full range of courses which comprise the full curricula, continued.

ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org

PHOTO BY: DAVID WAKELY

Louisiana Tech University Loyola Marymount University Manhattan College Massachusetts Institute of Technology Merrimack College Metropolitan State College Miami University Michigan State University Middlesex County College Mississippi State University Missouri Western State University Morgan State University Murray State University Nassau Community College North Carolina A&T State University North Dakota State University Northwestern University Norwich University Oregon Institute of Technology Penn State Pennsylvania State University- Dunmore Polytechnic Institute of New York University Portland State University Prairie View A&M University Pratt Institute

University at Buffalo, The State University of New York University of Akron Princeton University University of Alabama - Birmingham Purdue University University of Alabama - Huntsville Rice University University of Alaska Fairbanks Roger Williams University The University of Arizona Rowan University University of California, Los Angeles San Diego State University University of Central Florida San José State University University of Cincinnati Sandhills Community College University of Colorado Seattle University University of Connecticut South Carolina State University University of Delaware Southern Illinois University University of District of Columbia Southern Methodist University University of Hawaii Southern Polytechnic State University University of Hawaii Manoa Stanford University University of Illinois at Chicago Swarthmore College University of Illinois at Urbana-Champaign Syracuse University The University of Iowa Temple University University of Louisville Tennessee State University University of Maryland Tennessee Tech University University of Massachusetts Amherst Texas A & M University University of Massachusetts Dartmouth Texas Tech University University of Massachusetts Lowell Tulane University University of Memphis United States Air Force Academy University of Missouri United States Coast Guard Academy University of Nebraska Omaha United States Military Academy - West Point University of Nebraska-Lincoln University of Nevada, Reno The University of New Orleans University of Notre Dame AIA San Francisco University of Oregon Chapter Integrated University of Pennsylvania University of Pittsburgh Project Delivery Award University of Pittsburgh Johnstown The University of Rhode Island University of South Carolina University of Southern Indiana University of Tennessee - Knoxville University of Tennessee - Martin The University of Texas at Arlington University of Texas at El Paso The University of Utah University of Virginia University of Wisconsin - Platteville Utah State University Vanderbilt University Villanova University Virginia Military Institute Walla Walla University PALO ALTO MEDICAL FOUNDATION Washington State University Wayne State University Seattle • Tacoma • Lacey • Portland • Eugene • Sacramento • Wentworth Institute of Technology San Francisco • Walnut Creek • Los Angeles • Long Beach • West Virginia University Institute of Technology Pasadena • Irvine • San Diego • Boise • Phoenix • St. Louis • Western Kentucky University Chicago • New York Widener University Youngstown State University

STRUCTURE magazine

50

August 2013

introDucing the

HOW/2

MODEL APPROVAL using sDs/2

series by sDs/2

hybriD moDel approval

using sDs/2 viewer

The free SDS/2 Viewer can be used as a supplemental tool to more easily verify drawings. From the model, engineers can view information during the approval process, like connection design calculations, material information, member status and more.

full moDel approval

using sDs/2 approval

SDS/2 Approval supports the full model approval method by allowing communications like sketches, addendums and RFIs as well as status updates to be stored and exchanged via the model.

“It is easier to find pieces in the model, easier to catalog them using status display, and easier to track their progress through the shop drawing process. It also allows a more comprehensive review by seeing each piece in 3D, to scale, and interacting with connecting pieces.”

JOHn J. TRAcy

McNamara/Salvia Inc., Consulting Engineers

lite moDel approval

LEARn MORE Design Data supports and participates in AISC’s initiative to educate engineers, detailers and fabricators on the benefits of model-based approval. Join us at one of the AISC Model Review and Approval Seminars to learn more about how you can verify the drawings and the model through the model approval process.

using sDs/2 approval

Engineers can improve upon the hybrid method by receiving submittals via the model. Once received, engineers use their version of the model to approve, reject or note changes to be made, and can transmit that information via tools provided

by SDS/2 Approval.

800.443.0782 sds2.com | info@sds2.com

Special Section

Engineering Software

Economic Upturn for Building Industry Software Companies Address Construction Rise with Innovations, Interoperability, Better Graphics and Mobile Apps

By Larry Kahaner

A

s the economy improves and more construction projects get underway, software developers are meeting the increasing number of projects with new products and services, as well as updating current offerings. Software companies are also responding to the needs and interests of their customers: a need to continue to run lean and interests in interoperability, more sophisticated graphics, flexibility and mobile apps.

“There’s a lot more work out there,” says Amber Freund, Director of Marketing for RISA Technologies, LLC (www.risatech.com) in Foothill Ranch, California. “People are still working pretty lean.

Even companies that had been slow are now getting more work; they haven’t really increased their staff – a lot of them – or at least not proportionately to the work. Some of our customers are expanding, so we are getting people calling us for new licenses because they have new projects. People who have been out of maintenance because they couldn’t afford to pay for their software are now renewing because they have projects to justify it.” (See ad on page 75.)

Notes Randall Corson, Structural Engineer at Computers & Structures, Inc. (CSi) (www.csiberkely.com) headquartered in Berkeley, California: “For us, the transportation sector continues to be a significant source of business domestically, and we are seeing an increase in the use of building design software in certain regions of the country. Internationally, portions of the Far East are still very active.” (See ad on page 76.)

“From my conversations with people in the industry, things are turning in the right direction,” says Michele Arnett, Marketing Manager of Lincoln, Nebraska-based Design Data (www.sds2.com). “There are areas that are doing better than others, but the worst of the economic downturn appears to be behind us.”

At RISA, Freund says that they just released their first version of RISA-Tekla Link which links RISAConnection with Tekla Structures.

“Tekla Structures does all of the scale detailing, but they have never been able to do any of the connection design. This link allows users to design connections in their Tekla Structures model using RISAConnection. We’ve had really positive feedback on it. The Tekla users are thrilled, because they now have a complete package. And it’s been good for us because it gets RISAConnection to a market that we typically wouldn’t touch.” She adds: “We do structural engineers.

They [TEKLA] do detailers and navigators. So it’s been nice to get STRUCTURE magazine

into that market. All of a sudden, they [TEKLA users] don’t have to learn a new software. They’re doing everything within Tekla Structures, since they’re basically using RISAConnection to design it.”

As for trends, Freund notes: “Definitely, I think it’s interoperability.

Everybody’s talking about BIM – and has been for a while. I think you’re going to see more implementation of that. I think the trend over the next five years is going to be that people are going to start using it more. With that, it’s going to require the software to change a bit, too.”

To meet its customer needs, CSi recently released the latest in their ETABS product line, ETABS 2013. “It’s an innovative and revolutionary integrated software package for the structural analysis and design of buildings,” says Corson. “From design conception through the production of schematic drawings, ETABS 2013 assimilates every aspect of the engineering design process. A 64-bit solver allows for extremely large and complex models to be rapidly analyzed, and supports nonlinear modeling. Design of steel and concrete frames, composite beams and columns, joists, shear walls, connections and base plates is seamlessly integrated with the analysis.”

He adds that the latest offering from CSi for bridge engineers is CSiBridge V15. “This software allows for quick and easy design and retrofitting of steel and concrete bridges. The parametric modeler allows for rapid generation of complex bridge models using terms familiar to bridge engineers such as layout lines, spans, bearing, abutments and bents.” Corson is proud of the company’s quality management system. “Computers and Structures, Inc. is one of the few structural engineering software companies that has implemented a verifiable quality management system to ensure that customer expectations and industry requirements are not only met, but exceeded. CSi is ISO 9001 compliant as certified by Det Norske Veritas, an independent agency accredited by the International Organization for Standardization. CSi’s quality management system covers processes and procedures for all of our software.”

Design Data’s Arnett would like SEs to know about two newer products that will benefit them. “SDS/2 Approval is an in-model review tool that allows engineers to improve their shop drawing review process by taking advantage of today’s technology. With SDS/2 Approval, engineers can view the shop drawings alongside the 3D model, streamlining the process by eliminating time consuming searches through 2D information,” she says. “Using the detailer’s 3D

53

August 2013

Special Section Engineering Software

model, SEs gain the ability to see the steel they are reviewing in the context of its actual location in the structure, reducing ambiguity as they review the detailer’s submittals. In addition, electronic approval is a ‘green’ process, eliminating the need to store stacks and stacks of paper drawings as well as reducing printing and paper costs. Instead, the model is archived and storage space becomes digital rather than physical. Learning to implement the electronic approval process is straightforward and free.”

“We have seen a trend in the software industry as a whole in the demand for mobile apps. In response, we’ve released our SDS/2 Mobile Status app for Android and iOS, including interfaces for both phones and tablets. It shares the same status update technology that is in SDS/2 Approval, allowing updates to be sent via email to the detailer’s model from any location,” Arnett says.

Another product from Design Data is a connection design add-in for Revit Structure called SDS/2 Connect. “This tool allows engineers to access the connection design that has long been associated with SDS/2 products inside their native Revit model. With SDS/2 Connect, SEs can design and apply connections to the model, allowing them to see the materials, bolts and connection design calculations without ever leaving Revit Structure. As an added benefit, SDS/2 Connect includes model round-tripping tools to send the Revit Structure design model downstream to the fabricator and receive model updates back into Revit Structure, getting users closer to the as-fabricated product,” Arnett says. A free 30-day trial of SDS/2 Connect is available at www.sds2connect.com.

SEs and others can also get a free trial for Tedds, a structural calculations software (www.cscworld.com/Try/Tedds), from Chicago-based CSC, Inc (www.cscworld.com). “We have just launched our latest version: Tedds 2013,” says Vice President Stuart Broome. “It’s up to twice as fast as its predecessor and includes a new, fully integrated 2D frame analysis application as well as many new and enhanced calculations to both U.S. and Canadian design codes. Tedds 2013 is also compatible with Microsoft Word 2013.” Broome says that the new release enables engineers to access a range of analysis options within Tedds, avoiding the need to use separate analysis software. “Engineers can analyze frames such as trusses, cranked beams and portal frames, then create a single-project document including calculations, notes and sketches.

The primary benefit of Tedds is increased productivity, but many of our clients value the detailed and transparent output which Tedds produces.”

CSC also offers Fastrak, a steel building design software, alongside CSC’s Integrator (a free tool for synchronizing Fastrak and Revit Structure models back and forth). Broome notes, “It is a physical object-based modelling solution which automates the requirements of AISC360 and ASCE7.” He says the main reasons clients use Fastrak are: the ability to model and automate the design of composite floors and complex roof structures/trusses in one model and in one interface; the ability to model and automatically design gravity and lateral systems in one model and in one interface; and, the ability to synchronize a design model with a Revit model and pass information in both directions as many times as required in a manageable way.

The company also offers CSC’s Integrator which is available as part of Fastrak. This free software enables structural engineers to synchronize models between Autodesk Revit Structure and Fastrak. Adds Broome: STRUCTURE magazine

“It is an industry-leading solution making two-way integration with Revit Structure easy, highlighting any amendment made during the synchronization process, thus enabling engineers to react to changes quickly and reduce the risk of errors.”

Michael Brooks, President of ENERCALC, Inc. (www.enercalc.com) of Corona del Mar, California, would like SEs to know that their Structural Engineering Library is not just a collection of over 50 design modules. “It is a calculation preparation program where the engineer builds calculation packages that include Excel, Word, PDF, and Scanned materials in addition to the calculation modules we provide. ENERCALC has been in business for a very long time and we’ve had a number of products released. From the original Lotus 1-2-3 templates to the current sophisticated Windows program. We want SEs to be sure to check out our latest software packages, as things are continually being improved.”

Brooks is seeing a strong recovery for his company. “Last year was a 20 percent jump over 2011, and 2013 shows a 25 percent to-date increase. Because we see the early trends in design office activity, it’s obvious that the construction industry is in a recovery stage.” As for seeing other trends, he says: “Software is becoming more transparent across devices, so we are seeing more cloud-based data storage and software delivery. ENERCALC offered our first web based ‘thin client’ software over 10 years ago. We were too early…but we’re developing a full web platform to cater to the swelling demands of our clients for work-anywhere and data-anywhere.” (See ad on page 3.)

According to Marinos Stylianou, CEO of S-Frame Software (www.s-frame.com) in Guilford, Connecticut there are four key trends that he sees in software: interoperability, ease of use, integration and the ability to easily automate repetitive tasks. “Ideally, clients want a ‘single-glass’ model for their software/tools. They can’t afford to move back and forth between dissimilar products and technologies.

Integration is key not only at the designer or engineering level, but at the entire business level of the company and its partners. With each new release of our product suite, we strive to offer our clients tangible improvements in all four key areas.”

S-Frame recently released R11 of their Structural Office Suite. “All our existing products saw feature additions, enhancements and bug fixes,” says Stylianou. “In addition, we released a collaboration and validation tool called S-VIEW, which is included within S-FRAME Analysis. Our Interoperability with BIM and CAD systems was expanded via brand new bi-directional links with Tekla and Revit.

The DXF translator was also completely rewritten and modified to handle increased customer needs. S-FRAME Software will release an entirely new product called S-FOUNDATION this summer to expand our leading presence in the concrete analysis and design arena.”

Stylianou sums up his company’s goal by saying: “Industry trends and demands motivate our team to provide the best state of the art technology, while providing an enjoyable and simple user experience.

The ability to communicate between our products and with 3rd party and in-house products is another driver being requested by our clients. Clients are seeing a refresh in their business that requires faster concepts, better designs, all at a reasonable cost. Our solutions aim to address all three of these points.” (See ad on page 4.) continued on page 56

54

August 2013

Introducing Tedds 2013, the next evolution in structural software.

With Tedds 2013 you can now analyze frames, use a broad library of calculations, create high quality, transparent documentation, and even write your own calculations.

You can:

Go online to request your free Tedds trial

You will:

Use a broad library of calculations

Save time & increase profit

Write your own calculations Work within Microsoft Word

Reduce calculation errors

Improve consistency

Analyze frames

Reduce overheads

Produce transparent output

Enhance QA processes

Archive documents electronically

Thousands of engineers choose CSC software “I have been using Tedds for nearly 12 years. Tedds calculations are logical, concise and easy to follow.

Tedds is the best friend an engineer could have.”

R. Dean Morris, President, CEO Morris Engineering, Inc.

Evolutionary software. Revolutionary service.

877 710 2053 (Toll Free) www.cscworld.com

Delivering:

#cscworldglobal

Special Section Engineering Software

At IES, Inc. (www.iesweb.com) in Bozeman, Montana, Engineer and Developer Terry Kubat says that the company provides everyday tools for analysis and design projects. To his customers he says: “Your success is based on working efficiently to get your job done, so our programs stay out of your way to let you do what you need to do. We stand behind our tools with free technical support, free web-based training, and reasonable pricing.”

IES continues to upgrade their products, says Kubat. “VisualAnalysis 10.0 is the newest release of our flagship product. Our long-term customers are praising the continued improvements that help them save time and solve tougher problems. Coming this fall are design specification updates to stay current with IBC changes.”

Kubat adds: “Customers are starting to move to new machines and upgrade Windows and so we are working hard to ‘retool’ our software to leverage all of the capabilities that were not available in Windows XP, or as easy to leverage on that platform. Things like parallel processing, multiple-threading and the like are going on behind the scenes to make our products significantly faster… IES has always been a democracy, with customers leading the evolution of our tools: our job is simply to listen and respond.”

The company offers free trials. “You may test our products, fullyfunctional and fully-supported without ever having to deal with a

sales-person, because we don’t have any. Nearly 30 percent of those who try an IES product buy it within a few months,” says Kubat.

Reaching a specific market niche is the aim of Leroy Emkin, Founder and Co-Director of the Computer Aided Structural Engineering Center (GT STRUDL) at CASE Center (www.gtstrudl.gatech.edu) in Atlanta. “[Our customers are] companies involved in the analysis and design of nuclear, fossil fuel power and nuclear defense industry safety-critical structures, general process and plant design industry structures, offshore oil & gas exploration structures, offshore wind farm structures, cable supported structures, sport stadiums, complex long-span bridge structures, hi-rise commercial buildings, etc.,” he says. Emkin would like SEs to know about a product developed by one of the GT STRUDL Distributors located in Athens, Greece. “3DR Engineering has developed a new and powerful GUI interface to GT STRUDL called ATLAS, which takes full advantage of AutoCAD’s powerful 3D graphical modeling features. ATLAS is a highly powerful GUI to GT STRUDL that is easy to learn and easy to use by any structural engineer familiar with AutoCAD. ATLAS performs automatic modeling of structural frameworks and finite element meshes.”

Also going for a niche approach to software is the Canadian Wood Council (CWC) (www.cwc.ca), a national, non-profit association, continued on page 58

ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org

Structural Software Designed for Your Success • Easy to Learn and Use • Analyze “Just about Anything” • Design: Steel, Wood, Concrete, Aluminum, and Cold-Formed • Friendly, responsive support

www.iesweb.com Free 30-Day Trial

IES, Inc. | 519 E Babcock St. Bozeman MT 59715 800-707-0816 | info@iesweb.com

STRUCTURE magazine

56

August 2013

GT STRUDL

7

Structural Analysis & Design Software

Engineers who Demand Quality and Performance Choose GT STRUDL

Base Plate Module

Georgia Tech - CASE Center www.gtstrudl.gatech.edu casec@ce.gatech.edu 404-894-2260

Special Section Engineering Software

located in Ottawa, Ontario, representing manufacturers of Canadian wood products used in construction. Robert J. Jonkman, Manager, Structural Engineering for WoodWorks, their software product, says CWC’s main priority is to ensure that “building professionals such as engineers, architects, and other design professionals have the needed information in hand to specify and use wood products in a safe, secure, and code-compliant manner. One way we do this is through our wood engineering software, WoodWorks.” Separate Canadian and US versions of WoodWorks software are available. For the U.S. version, compatible with the IBC, NDS, SDPWS, and ASCE7, CWC works closely with the American Wood Council (AWC) to ensure consistency in technical interpretations, according to Jonkman.

“The US version of WoodWorks has been updated to conform to the 2012 IBC, the 2012 NDS, and the 2010 ASCE-7. New features have been added as well,” he says. These include: Shearwalls: • shear walls with inadequate capacity to resist the lateral loads are now automatically highlighted, making them easy to identify • .PDF files can now be imported as a template to lay out the structure Sizer: • the fire design procedure from NDS Chapter 16 is now included • revised southern pine values are included in the database • steel beams are now included as a design option in the latest Canadian version of the software Connections: • the connections software has been upgraded to a fresh format that is significantly more efficient to use WoodWorks software can be purchased as a full suite called Design Office, which includes Sizer, Shearwalls, Connections, editable database, a PDF version of the NDS and SDPWS (US) or CSA O86 (Canada), and free technical support for the current version. Sizer can also be purchased separately.A free download is available to test the software.

StructurePoint, LLC (www.structurepoint.org) in Chicago, Illinois was formerly the Engineering Software Group of the Portland Cement Association, and is a dedicated team of engineering professionals committed to excellence, continuous improvement, and service, according to Marketing Director Heather Johnson. “We provide civil and structural engineers with the software and technical resources they need for designing concrete buildings and structures. StructurePoint is a convenient single point of access to the vast resources and knowledge base of the entire cement and concrete industry including library services, training, R&D, publications, building codes, specialty engineering services, concrete material and testing, concrete repair, codes and standards consulting.”

StructurePoint’s primary focus and passion is concrete structures. “We are watching closely every code change and amendment relevant to concrete design. We are also behind the scenes looking for important upcoming changes to make concrete design simpler, faster, and more accurate. This way we do it once and well, so that every engineer can benefit and sleep better at night knowing that at least his concrete design is optimal, economical, safe and code compliant,” Johnson says. “In spColumn v4.81, StructurePoint has further refined slender column design provisions to meet stringent new requirements of ACI-318.”

STRUCTURE magazine

Business has been improving, says Johnson. “Companies of all sizes and geographies have been increasingly more upbeat about business opportunities, and cement shipments have been growing steadily indicating more construction spending. Amongst our users, geotechnical engineers have been exceptionally active responding to exploding opportunities in oil, gas and petrochemical projects. These opportunities continue to drive additional demand of our spMats and spBeam program for foundations in industrial facilities and infrastructure construction.” (See ad on page 65.)

Better graphics are always of interest at Simpson Strong-Tie (www.simpsonanchors.com) which, in 2009, purchased a state-ofthe-art 3D visualization company so they could provide competitive sales and design programs for their customers. “We continue to invest in this technology and see further integration of 3D visualization applications in our industry in the coming years,” says Paul McEntee, Engineering R&D Manager. The Pleasanton, California company recently released its new Anchor Designer professional design software to comply with ACI 318, ETAG and CSA code requirements.

The software features a fully interactive 3D graphical user interface with intuitive navigation and real-time design. “Anchor Designer enables structural engineers to satisfy the strength design provisions of ACI 318 Appendix D, CAN/CSA A23.3 Annex D, ETAG 001 Annex C or EOTA TR029 design methodologies. The software quickly and accurately analyzes an existing design or suggests anchorage solutions based upon user-defined design elements in cracked and uncracked concrete conditions. The software replaces Anchor Selector for ACI 318 and Anchor Selector for ETAG software, and is compatible with design files created with those programs,” says McEntee. To download the new Anchor Designer software, go to www.simpson.com/anchordesigner. (See ad on page 25.)

At Nemetschek Scia (www.scia-online.com), Dan Monaghan, North American Managing Director, based in Columbia, Maryland notes that they just released a new version of its flagship structural design software, Scia Engineer 2013. “Scia Engineer 2013 is part of a new breed of integrated structural design software that is helping engineers plug analysis and design into today’s 3D workflows. Scia Engineer is the only analysis and design program that integrates Structural BIM Modeling with advanced FEA analysis, design, drawings, and calculation reports, in one design environment,” Monaghan says. “It handles any combination of materials, free-form geometry, multiple design codes, and all types of analysis, from simple beam check (1D), to single plate (2D), to whole structure (3D), to detailed analysis of how structures will perform over time (4D). And, with bi-directional links with Revit Structure, Tekla Structures, and certified support for IFC 2.X3, Scia Engineer makes it easy for structural engineers to participate with others in today’s BIM process.”

Monaghan sees a trend among BIM users. “We’re seeing a recognition from experienced BIM firms that there isn’t one software product or even software vendor that can cover the various needs of all the stakeholders involved in the design, construction and management process. Firms are recognizing that the, ‘ONE BIG BIM model’ concept is not possible or even practical. Today, ‘working collaboratively in a model based workflow’ means creating and coordinating many continued on page 60

58

August 2013

Design wood structures effectively, economically and with ease!

Design Office

SIZER Gravity Design

SHEARWALLS Lateral Design

CONNECTIONS Fasteners

O86

Engineering design in wood

2x4

DATABASE EDITOR

PDF

Adobe

WOOD STANDARDS

(US version)

PDF

Adobe

WOOD STANDARD (CDN version)

Download a Free Demo at woodworks-software.com

AMERICAN WOOD COUNCIL

US Design Office 10 - Now Available!

NDS 2012, IBC 2012 and ASCE 07-10 compliant

www.woodworks-software.com

Canadian Design Office 8 CSA O86-09 compliant

800-844-1275

Special Section Engineering Software

expertise covers the areas of adhesive and mechanical anchoring, measuring, powder actuated fastening, drilling and demolition, diamond coring and cutting, firestopping, screw fastening, strut and hanger systems. We offer software for anchor design (PROFIS Anchor) and steel diaphragm deck design (PROFIS DF).” She adds: “PROFIS Anchor software now includes the innovative new Hilti product known as HIT- HY 200 Adhesive Anchoring System. The HIT-HY 200 System eliminates the traditional blow-brush-blow method of cleaning anchor holes. Therefore, when the complete HIT-HY 200 System is used, no manual hole cleaning is required to obtain optimum anchor performance. Calculations with the provisions of ACI 318 Appendix D can be performed for this product.”

Biggs says that the PROFIS Anchor portfolio now includes the provisions of ACI 318-11 Appendix D. “This is the latest addition to the portfolio, which also includes provisions for ACI 318-08 Appendix D, ACI 349-01 Appendix B, CSA A23.3-04 Annex D, ETAG design and Allowable Stress Design.”

Biggs concludes: “Many of our customers are using Building Information Modeling during both the design and construction phases of the project. To support this strong trend of BIM usage, Hilti has developed a comprehensive library of BIM/ CAD objects for our products including anchors, fasteners, firestop and strut. In the long term, Hilti expects further integration of design analysis software into BIM.”▪

ADAPT-PT_RC Strip Design

ADAPT Corporation Phone: 650-306-2400 Email: info@adaptsoft.com Web: www.adaptsoft.com

ADAPT-Builder Edge Floor Pro MAT SOG ADAPT-ABI 4D Construction Phase Analysis

X X

X

X

X

X

X

X

X

X

wood

steel

MAsonry

lIght gAuge steel

generAl/ pAckAges/suItes

FoundAtIons/ retAInIng wAlls

concrete

S o f t wa r e

cAd

name

BusIness/productIvIty

com pany

BIM

Not listed? Visit www.STRUCTUREmag.org/guides.aspx and submit your information for upcoming guides! Listings are provided as a courtesy.

STRUCTURE magazine is not responsible for errors.

BuIldIng coMponents

SOFTWARE GUIDE

A software guide for Structural Engineers

BrIdges

smaller federated BIM models created by different stake holders using different software, i.e. software that works best for their part of the BIM process. From this, new BIM model servers, or cloud BIM services, are becoming more important as a way to assemble, manage, view and report on the various models being created for a BIM project. “ He adds: “A big problem for engineers is how to efficiently plug analysis and design into today’s BIM workflows. While direct links to Structural BIM programs are great, the links can be fragile, difficult to work with, and do not support every material or geometry. Scia Engineer 2013 compliments our direct link workflows with certified support for the IFC BIM exchange format. IFC is a vendor neutral BIM exchange format developed by the AEC software industry under buildingSMART International (www.buildingsmart.org/organization).

The IFC file format provides the AEC industry a robust way to exchange models amongst the various BIM software programs used in today’s design, engineering, construction and facilities management process. By providing certified support for IFC, Scia Engineer 2013 makes it easy for engineers to leverage models from designers into engineering analysis, and pass back to optimized structural designs for model coordination or documentation.” (See ad on page 63.)

“In the past twenty-four months, Hilti has launched almost sixty new products which have contributed to us seeing growth in all parts of our business,” says Carla Biggs, head of Public Relations for Hilti Corporation (www.hilti.com) headquartered in Liechtenstein. “Hilti

X

American Wood Council Phone: 202-463-2766 Email: info@awc.org Web: www.awc.org

X

AWC Online Connection Calculator

Bentley Systems Phone: 610-529-6629 Email: Dave.eckrote@bentley.com Web: www.bentley.com

STAAD

X

LEAP Bridge Steel

X

X

X

X

X

X X

X

RAM

X X

X

X

X

X

X

X

Concrete Masonry Association of CA and NV (CMACN) Phone: 916-722-1700 Email: info@cmacn.org Web: www.cmacn.org

x

CMD09

ConSteel Solutions Ltd. Phone: 36-30-9676742 Email: schell@consteel.hu Web: www.consteelsoftware.com

x

StabLAB

continued on page 62 STRUCTURE magazine

60

August 2013

HIT-HY 200 Adhesive Anchoring System

One giant leap.

Introducing the world’s first non-cleaning adhesive anchoring system.

Once in a blue moon something comes along with the power to change the way we work. The HIT-HY 200 Adhesive Anchoring System featuring Safe Set™ Technology does just that. This innovative, new system eliminates an important and load-critical step of the installation process: manually cleaning the hole before injection of the adhesive. It's one small step in the construction process and a giant leap forward in reliability.

For HIT-HY 200 technical data and more information about Safe Set™ Technology and how it works, visit www.us.hilti.com/HY200.

Hilti. Outperform. Outlast.

Hilti, Inc. (U.S.) 1-800-879-8000 www.us.hilti.com/HY200 • Hilti (Canada) Corp. 1-800-363-4458 www.hilti.ca/HY200

wood

steel

MAsonry

lIght gAuge steel

x

generAl/ pAckAges/suItes

SDS/2 Connect

FoundAtIons/ retAInIng wAlls

x

concrete

Fastrak

cAd

S o f t wa r e

BusIness/productIvIty

name

BrIdges

com pany

BIM

Not listed? Visit www.STRUCTUREmag.org/guides.aspx and submit your information for upcoming guides! Listings are provided as a courtesy.

STRUCTURE magazine is not responsible for errors.

BuIldIng coMponents

SOFTWARE GUIDE

A software guide for Structural Engineers

CSC

Phone: 877-710-2053 Email: sales@cscworld.com Web: www.cscworld.com

x

x

x

Design Data

Phone: 402-441-4000 Email: marnett@sds2.com Web: www.sds2connect.com

x

Devco Software, Inc. Phone: 541-426-5713 Email: rob@devcosoftware.com Web: www.devcosoftware.com

ENERCALC, INC. Phone: 800-424-2252 Email: info@enercalc.com Web: www.enercalc.com

x

LGBEAMER v8

ENERCALC

x

Structural Engineering Library V6

x

x

x

x

x

x

x

x

x

x

Evolution1 Phone: 206-455-1978 Email: duane@envirobeam.com Web: www.envirobeam.com

x

Envirobeam

Georgia Tech – CASE Center Phone: 404-894-2260 Email: joan.incrocci@ce.gatech.edu Web: www.gtstrudl.gatech.edu

x

GT STRUDL

x

x

x

x

x

x

Hilti, Inc.

Phone: 800-879-8000 Email: us-sales@hilti.com Web: www.us.hilti.com

Hilti PROFIS Anchor, PROFIS DF

x

VisualAnalysis

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

Integrated Engineering Software Phone: 406-586-8988 Email: sales@iesweb.com Web: www.iesweb.com

x

LARSA, Inc. Phone: 800-LARSA-01 Email: info@larsa4d.com Web: www.Larsa4D.com

x

LARSA 4D

x

Leigh & OKane

Phone: 816-444-3144 Email: rokane@leok.com Web: www.leok.com

RWallHD

x

x

x

x

Nemetschek Scia

Phone: 877-808-7242 Email: info@scia-online.com Web: www.nemetschek-scia.com

x

Scia Engineer 2013

x

x

x

x

x

Opti-Mate, Inc. Phone: 610-530-9031 Email: optimate@enter.net Web: www.opti-mate.com

x

Engineering Software

x

x

Powers Fasteners

Phone: 985-807-6666 Email: jack.zenor@sbdinc.com Web: www.powers.com

Powers Design Assist Software 2.0

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

x

RISA Technologies Phone: 949-951-5815 Email: info@risatech.com Web: www.risa.com

RISAFloor

continued on page 64 STRUCTURE magazine

62

August 2013

ADVERTISEMENT

Plugging Analysis Plugging Analysisand andDesign Design into Your 3D Workflow

W

ITH new processes like BIM (Building Information Modeling) and new project delivery methods like IPD (Integrated Project being asked to participate in collaborative, modelMigrating to these new processes can be made easier with software designed to support them— software like Scia Engineer from Nemetschek.

Scia Engineer is a new breed of integrated structural design software that goes beyond

Scia Engineer, update our model, run a quick analysis, and give them enough information to continue moving forward. I don’t think we would have been able to do this with any of the other Another advantage of Scia Engineer is its extensive functionality. Analysis and design is becoming more rigorous, and owners are looking for highly optimized structures to minimize materials, construction time, and costs. Being

Go Beyond Analysis Explore. Optimize. Collaborate.

ability to handle complex analysis tasks is a

Modeling is an essential requirement for any 3D project timelines compressed, modeling needs Engineers need to be able to keep up with the modern designs coming from architects and contractors who push the limits of new materials and methods.

“A unique feature of Scia Engineer is its modeling capabilities,” says Mark Flamer, M.I. FEA (Finite Element Analysis) modeling tool. freeform modeling capabilities make it easy for me to work up designs in 3D and keep pace with my architect’s avant-garde designs. And, its parametric object technology has allowed me to automate routine and repetitive work. I can quickly work up and test design concepts. an accurate structural model in Scia Engineer or link my design to another modeling program for coordination and documentation.”

With support for open standards like IFC 2x3 and direct links to a number of BIM software programs like Autodesk Revit® Structure & Tekla® Structures, Scia Engineer makes it easier for engineers to reuse models created by others advantage when working in a collaborative “For the new National Music Centre project in Calgary, Canada, the architect made frequent and sometimes dramatic changes,” says Andrea Hektor, KPFF Portland. “We needed to be able to give them a quick thumbs up or thumbs down on their revised designs. With Scia Engineer it updated models. We would import them into

“With support for non-linear, multi-material design and multiple codes, I’ve avoided having to invest in disparate analysis programs,” says Michael Ajomale, Principal, Design Depictions Structural Engineering, P.C. “Reducing the number of analysis programs we manage saves on maintenance costs and makes it less expensive to train new employees. Most importantly, it reduces the risks that come with manually coordinating multiple analysis models. For occasions when I need to go outside Scia Engineer, I appreciate its ability to integrate my Excel™ checks and its XML support.”

“More in tune with the “Eye-opening” “Extremely impressed”

Growing with Technology their usual projects, and take on work wherever as well as go beyond buildings,” says Flamer.

“While our expertise is in commercial, we just completed a bridge project and are ready to take He added: “I evaluated the usual list of structural analysis programs, and there isn’t another program in the market like it. Scia Engineer is the only program I found that multi-material design, and lets me easily reuse and share 3D models. For us, Scia Engineer was a logical choice.”

For information, call 1.877.808.Scia (7242) or visit www.nemetschek-engineering.com Daniel Monaghan is the U.S. Managing Director of Nemetschek Scia, developers of leading software products for AEC software industry. He can be reached at dmonaghan@scia-online.com

Read the AECbytes Review

http://nemetschek-scia.com/review

Scia Engineer is a new breed of integrated structural design software that goes beyond

and simple FEA analysis. Recycle and leverage models created by others into analysis. Centralize your design tasks with static, dynamic, and advanced nonlinear analysis, plus mult-material design in ONE program.

Call to request your FREE trial today at (877) 808-7242.

www.nemetschek-scia.com

Phone: 203-421-4800 Email: info@s-frame.com Web: www.s-frame.com

S-CONCRETE Design

Simpson Strong-Tie®

Anchor Designer™

x

wood

steel

MAsonry

lIght gAuge steel

generAl/ pAckAges/suItes

FoundAtIons/ retAInIng wAlls

x x

Structural Office R11

Phone: 925-560-9000 Email: web@strongtie.com Web: www.strongtie.com

concrete

x

S-STEEL Design

S-FRAME Software Inc.

cAd

S o f t wa r e

BusIness/productIvIty

name

BrIdges

com pany

BIM

Not listed? Visit www.STRUCTUREmag.org/guides.aspx and submit your information for upcoming guides! Listings are provided as a courtesy.

STRUCTURE magazine is not responsible for errors.

BuIldIng coMponents

SOFTWARE GUIDE

A software guide for Structural Engineers

x

x

x x

x

x

Holdown Selector Web App

x

Rafter Hanger Slope and Skew Online Calculator

x

Strand7 Pty Ltd. Phone: 252-504-2282 Email: anne@beaufort-analysis.com Web: www.strand7.com

x

Strand7

x

x

x

x

x

x

x

x

x

x

StrucSoft Solutions Phone: 514-731-0008 Email: info@strucsoftsolutions.com Web: www.strucsoftsolutions.com

MWF – Metal Wood Framer

x

x

Structural Engineers, Inc. Phone: 540-731-3330 Email: tmmurray@floorvibe.com Web: www.FloorVibe.com

FLOORVIBE

x

FloorVibe v2.10

x

StructurePoint

Phone: 847-966-4357 Email: info@structurepoint.org Web: www.StructurePoint.org

Concrete Design Software

Struware, LLC

CMU or Tilt-up Walls

Phone: 904-302-6724 Email: email@struware.com Web: www.struware.com

x

x

x

x

x

x

x

x

x x

Struware Code Search

Tekla, Inc. Phone: 877-835-5265 Email: info.us@tekla.com Web: www.tekla.com/us

x

Tekla Structures

x

x

USP Structural Connectors Phone: 952-898-8772 Email: bashwell@mii.com Web: www.uspconnectors.com

x

USP Specifier

x

x

WoodWorks Software

Phone: 800-844-1275 Email: sales@woodworks-software.com Web: www.woodworks-software.com

x

Design Office Suite

2013 Trade Show in Print

Double your exposure…

Advertisers in the annual Trade Show

The definitive buyers’ resource for the practicing structural engineer…

in Print receive a free ½-page ad

Your best option for exposure to targeted buyers

with the purchase of a ½-page

The only comprehensive resource guide targeted to the structural

ad, or a free full-page ad with

engineering community. The Trade Show in Print is delivered to

the purchase of a full-page ad.

over 32,000 practicing structural engineers every October, and is

Contact us by September 2, 2013!

seen on the STRUCTURE magazine website by as many as 300,000 people per month! See what we mean at www.STRUCTUREmag.org.

Chuck Minor, Eastern Ad Sales 847-854-1666

sales@STRUCTUREmag.org

STRUCTURE magazine

64

August 2013

Dick Railton, Western Ad Sales 951-587-2982

Work quickly.

Work simply.

Work accurately.

StructurePoint’s Productivity Suite of powerful software tools for reinforced concrete analysis & design

Finite element analysis & design of reinforced, precast ICF & tilt-up concrete walls

Analysis, design & investigation of reinforced concrete beams & one-way slab systems

Design & investigation of rectangular, round & irregularly shaped concrete column sections

Analysis, design & investigation of reinforced concrete beams & slab systems

Finite element analysis & design of reinforced concrete foundations, combined footings or slabs on grade

StructurePoint’s suite of productivity tools are so easy to learn and simple to use that you’ll be able to start saving time and money almost immediately. And when you use StructurePoint software, you’re also taking advantage of the Portland Cement Association’s more than 90 years of experience, expertise, and technical support in concrete design and construction.

Visit StructurePoint.org to download your trial copy of our software products.

For more information on licensing and pricing options please call 847.966.4357 or e-mail info@StructurePoint.org.

STR_7-13

award winners and outstanding projects

Spotlight

BC Place Revitalization

By Karen A. Lynch, P.E. Geiger Gossen Campbell Engineers, PC was an Outstanding Award Winner for the BC Place Revitalization project in the 2012 NCSEA Annual Excellence in Structural Engineering awards program (Category – Forensic/Renovation/Retrofit/Rehabilitation Structures).

BC Place, the first domed stadium in Canada, opened in 1983 in Vancouver, BC. The stadium sat on the north shore of False Creek amidst stacks of lumber, with barges and log booms moored along the shore.

Over the following decades, BC Place, while hosting sports, trade shows, and entertainment events, was a catalyst that transformed the eastern False Creek basin into a vibrant mixed-use urban area.

The original roof of BC Place was an air-supported PTFE-coated (polytetrafluoroethylene) fiberglass membrane supported by a concrete perimeter compression ring on the 54 frames of the superstructure. In early 2007, while Vancouver was planning for the 2010 Winter Olympic Games, the air-supported roof deflated in a snow event. Although it was certain that they would host the Olympic Games, PavCo, the stadium’s owner, had to make a decision regarding the future of the aging stadium: demolish and rebuild, relocate, or renovate. They chose a complete, top-down revitalization of the stadium.

In revitalizing the stadium, PavCo sought to strengthen the spectator experience, reignite public excitement for the facility, and enhance its position in the entertainment marketplace while reinforcing the presence of the building in the city-scape that had grown up around it. Coupled with these goals was a desire to minimize loss of use of the stadium and the displacement of the anchor sports tenant, the Canadian Football League’s BC Lions.

Replacement of the aging air-supported roof with a new iconic roof structure was a priority from the inception. Due to continued facility use and physical site constraints, the design team decided to support the new roof on the existing compression ring of the air-supported roof. This presented significant challenges. The mass of the original air-supported roof was almost negligible and, because of the use of a snow-melt system, it had been designed to support a reduced snow load. Additionally, the Building Code had changed since the stadium was designed; therefore, the gravity and seismic loads on the new roof were significantly more than on the

original. The new 40,000 square meter (430,556 square foot) roof is designed to support nominally 7,000Mg of snow (the 1 in 100 year snow load) on clear spans of 227 x 186 meters (745 x 610 feet).

The roof, designed by Geiger Engineers and Schlaich Bergermann in response to these challenges, is a spatial cable truss clad with three different tensioned membrane systems. Thirtysix steel perimeter masts rise 47.5 meters (155.8 feet) above the original roof’s concrete ringbeam. The masts support a radial cable truss, post-tensioned within a new steel compression ring. The upper radial suspension cables support the roof via hanger cables. The masts are supported on guided slide and rotation bearings on a reinforced concrete transfer girder in the channel cross-section of the original roof’s precast concrete compression ring. The girder was necessary to transfer load from the 36 roof masts to the original building superstructure.

Seismic demand was mitigated by exploiting the distinctly different dynamic characteristics of the new roof and its supporting superstructure. The new roof contributes only 10% to the stadium seismic design base shear.

Seismic and wind loads are transmitted from four eccentrically braced frames of the roof through articulated link elements to buckling inhibited braces at the tops of the shear walls in the base structure.

The fixed portion of the roof is a PTFEcoated fiberglass tensioned membrane, the same generic material of the original air-supported roof. The roof membrane is supported on steel tube tied-arch purlins carried by the primary cable truss.

The center 7,500 square meters (80,729 square feet) of the roof is retractable.

Supported on carriages that slide on the lower radial cables, the retractable roof is a pneumatic tensile structure of fluoropolymer coated woven PTFE fabric and high-strength polymer belts. The space between two layers is pressurized to create cushions that span

STRUCTURE magazine

67

August 2013

between the radial cables. Pressure in the cushions is automatically modulated in response to roof load. The roof is opened by evacuating the cushions and contracting the membrane into the center gondola of the roof above the new center-hung video scoreboard.

The new roof system incorporates integral building services for lighting, sound, and natural ventilation. The cable truss roof supports 320 Mg at the center node; including the center node connection (126 tonnes [139 tons] with cable connection fittings), the retractable roof receptacle, and the center hung video board and its hoist. Suspended catwalks support new event and house lighting, radiant heating, and broadband wireless transmitting antennae. New sound system speaker arrays are supported directly from the roof cables.

The steel and cables of the primary structure are prominently featured on the exterior of the building envelope allowing for a light airy interior. Below the roof eave is a 12.5-meter (41 foot) clearstory façade clad in ETFE (Ethylene tetrafluoroethylene) membrane; a clear fluorocarbon film. This is the first use of this material in Canada. Its use was in keeping with the light-weight design concept that dramatically increases the natural lighting in the building.

The revitalized stadium is more than satisfying the needs of its owners and tenants.

BC Place is once again a state-of-the-art venue holding its own amongst new facilities which cost more than twice the cost of this renovation.▪ Karen A. Lynch, P.E., is a Principal of Geiger Engineer and was the Project Manager of the new roof design for Geiger Engineers, in association with Schlaich Bergermann and Partner LP. Karen can be reached at kal@geigerengineers.com.

EN

GINEERS

O NS

STRUCTU

OCIATI

RAL

ASS

NATIONAL

years

1993-2013

News form the National Council of Structural Engineers Associations

Celebrating

COUNCI L

NCSEA Offers Short Courses on New Serviceability Book In conjunction with the release of the NCSEA publication Guide to the Design of Building Systems for Serviceability in Accordance with the 2012 IBC and ASCE/SEI 7-10, NCSEA is offering an associated course on the new guide. The course provides an overview of the book material and includes approximately 25 percent new material, not included in the publication, to help the engineer better understand the fundamental theory behind the practical example problems, and often verify approaches with hand calculations and simple computer modeling results.

The 4-hour NCSEA Diamond approved course can be provided as a stand-alone course or as part of an arranged program such as an NCSEA Member Organization meeting. All attendees receive one copy of the Guide, a $60 value. Sessions have

The James Merriam Delahay Foundation

NCSEA Webinars August 13, 2013

Checklist for Reviewing a Concrete Mix Design – There’s More to It Than you Think!

Kim Basham, Ph.D., P.E., KB Engineering Learn how to review a concrete mix design that’s been submitted by the concrete supplier and/or contractor. See how to use a checklist to organize your review and to ensure the concrete mix design complies with the project specifications, requirements of the building code and industry standards.

August 27, 2013

Specialty Structural Metals: Design and Detail Considerations Steve Huey, P.E., Wallace Engineering This webinar discusses metals other than carbon steel, which are used in buildings in a structural manner, and the special considerations to be addressed when they are used. These metal structures may be designed by the building engineer of record or by an engineer working for a specialty subcontractor.

ST RU

RS EE

GIN

CT UR

AL

The Importance of a Specification or General Structural Notes (GSN) Review David Flax, Euclid Chemical Company The guiding principles for writing specifications are Clear, Concise, Correct, Complete. As specifications and GSNs are aging without being reviewed and updated, they invariably move away from these four guiding principles. This webinar will focus on concrete related specifications and GSNs, but the principles are all the same.

EN

G UIN

TIO N CA

N NTI CO

ED U

NCSEA News

September 26, 2013

NCSEA

Diamond Reviewed

been scheduled for Member Organization meetings in Memphis, TN; Little Rock, AR; Tulsa, OK; and Oklahoma City, OK. The course instructor, Timothy Mays, Ph.D., PE, uses design examples given in the design guide and many of his own additions to illustrate recommended practices for building serviceability. Dr. Mays is President of SE/ES and an Associate Professor of Civil Engineering at The Citadel in Charleston, SC. He recently served as Executive Director of the Structural Engineers Associations of South Carolina and North Carolina, and currently serves as NCSEA Publications Committee Chairman. Registration information for scheduled courses is available at www.ncsea.com.

The publication will be available for purchase through the NCSEA website and the International Code Council by the end of July. NCSEA Member Organization members receive a discount on the publication price.

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

The James Merriam Delahay Foundation is a non-profit organization that was established to advance the field of structural engineering through education and scientific research.

Formation of the Foundation was initiated by the Structural Engineers Association of Alabama to honor the memory of Jim Delahay, who passed away suddenly in 2005, at only age 46, yet who was already known nationwide for his work on wind codes and standards. Management of the Foundation was recently transferred to James Delahay NCSEA, with the idea that it will soon be reinvigorated.

Plans for the Foundation include contributions from individuals and estates, which will fund a considerable number of meaningful scholarships for undergraduate, graduate and postgraduate students pursuing the study of structural engineering. The Foundation was formed to support the following activities: • Tuition scholarships for undergraduate and graduate students enrolled and in good standing in engineering programs, with specialization in structural engineering.

• Competitive awards to recognize outstanding scientific achievements in the field of structural engineering.

• Sponsorship of scientific research intended to aid in the advancement of structural engineering.

• Publication of reports, papers and books of special importance and significance to structural engineers.

Although the Foundation is likely to focus on scholarships, it has not ruled out the other activities listed above. The Foundation is an independent, charitable 501(c)(3) organization, meaning contributions to it will be tax-deductible within the limits prescribed by the applicable provisions of the tax law. For more information, please call the NCSEA office at 312-649-4600 or email NCSEA’s Executive Director at execdir@ncsea.com.

Mark your calendars!

The 2nd NCSEA Winter Leadership Forum will be held March 20 & 21, 2014, at the Meritage Resort & Spa in Napa, California. Check out the schedule of speakers at www.ncsea.com STRUCTURE magazine

68

August 2013

NCSEA News

Wednesday – September 18

Concurrent Sessions 8:00 – 5:00 Committee Meetings 8:00 – 11:45 Board of Directors Meeting 3:00 – 5:00 The AISC Direct Analysis Method Dr. Leroy Emkin 5:30 – 6:30 Young Members Group Reception 6:30 – 8:30 Structural Engineering Certification Board (SECB) Reception

Thursday – September 19

9:15 – 10:15 10:30 – noon 11:00 – 8:30pm noon – 1:00

Breakfast Welcome and Introduction Keynote Address: The Philosophy of Design: The Structural Engineer’s Role in Creating New Architecture Bill Baker, P.E., SECB, F.ASCE, FIStructE, Structural & Civil Engineering Partner, Skidmore, Owings & Merrill DoD Minimum Antiterrorism Standards for Buildings Jon Schmidt, P.E., SECB, M.ASCE, Burns & McDonnell ASCE 41-13: Seismic Evaluation and Retrofit of Existing Buildings Robert Pekelnicky, Degenkolb Engineers Trade Show open Lunch

News from the National Council of Structural Engineers Associations

7:00 – 8:00 8:00 – 8:15 8:15 – 9:15

Concurrent Sessions 1:00 – 2:15 A) ACI 550: Guide to Emulating Cast-in-Place Detailing for Seismic Design of Precast Concrete Structures Harry Gleich, P.E., FACI, FPCI, Chairman of ACI-ASCE 550, Metromont Corporation B) The Analysis of Offset Diaphragms and Shear walls Terry Malone, P.E., S.E., WoodWorks 2:45 – 3:45 A) Connections: The last Bastion of Rational Design Bill Thorton, Ph.D., P.E., NAE, Cives Corporation B) Load Generators: What Exactly is My Software Doing? Sam Rubenszer, FORSE Consulting 3:45 – 4:45 A) UMinn. Northrop Auditorium Renovation-Underpinning & Micropile Foundation Case Study Greg Greenlee, P.E., Engineering Partners International B) The Structural Curtainwall John Tawresey, S.E., KPFF Consulting Engineers 5:30 – 6:30 President’s Reception for Delegates 6:30 – 8:30 Welcome Reception with Exhibitors

Friday – September 20 7:00 – 8:00 8:00 – 10:00 8:00 – 10:00 10:30 – noon noon – 1:00 1:30 – 2:45 3:15 – 5:00 6:00 – 7:00 7:00 –10:00

Continental Breakfast Member Organization Reports Vendor Presentations Practical Design of Complex Stability Bracing Configurations Donald White, Ph.D., Georgia Tech Lunch (exhibits close at 1:00) NCSEA Serviceability Design Guide (Part 1) Kurt Swensson, Ph.D., P.E., LEED AP, KSI Engineers NCSEA Serviceability Design Guide (Part 2) Kurt Swensson Awards Reception Conference & Banquet and Awards presentation

7:00 – 8:00 8:00 – noon 12:30 – 2:00

Continental Breakfast Delegate Meeting & Committee Reports Board of Directors Meeting

hotel

registration open at

Saturday – September 21

www.ncsea.com

NCSEA Annual Conference Sponsors: Bronze:

EN

GINEERS

ASS OCIATI

RAL

Silver:

NATIONAL Celebrating

STRUCTURE magazine

69

August 2013

O NS

STRUCTU

Platinum:

COUNCI L years

1993-2013

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

2013 Ammann Fellowship Winners and Call for Nominations

Sarah Bobby

Erica Fischer

Eric Kjolsing

Teng Wu

In 2013, the SEI Technical Activities Division Executive Committee awarded four O.H. Ammann Research Fellowships in Structural Engineering. SEI received a record number of high-quality applications in 2013 and chose to give multiple awards.

This year’s winners are Sarah Bobby, Erica Fischer, Eric Kjolsing, and Teng Wu. See the SEI website at www.asce.org/SEI for more information about the winners and their research.

The O. H. Ammann Research Fellowship in Structural Engineering is awarded annually to a member or members of ASCE or SEI for the purpose of encouraging the creation of new knowledge in the field of structural design and construction. All members or applicants for membership are eligible. Applicants will submit a description of their research, an essay about why they chose to become a structural engineer, and their academic transcripts.

This fellowship award is at least $5,000 and can be up to $10,000. The deadline for 2014 Ammann applications is November 1, 2013.

For more information and to fill out the online application, visit the SEI website at: www.asce.org/SEI.

Prepare for the New California Building Code

Errata

Seismic Design with ASCE 7-10 The 2013 California Building Code goes into effect on January 1, 2014, with seismic requirements based on ASCE 7-10. Are you ready to start using the provisions of ASCE 7-10 for seismic design? ASCE Continuing Education is offering a day-long seminar that will cover the major changes in ASCE 7-10, and includes example problems. Three California locations are available: San Francisco on September 23, Los Angeles on September 26, & San Diego on September 27. For more information, visit the SEI website at: www.asce.org/SEI.

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

LOCAL ACTIVITIES New Student Chapter at the University of Texas at Arlington Welcome to the new SEI Graduate Student Chapter (GSC) at the University of Texas at Arlington, chaired by Istiaque Hasan and Faculty Advisor Dr. Nur Yazdani. The mission of SEI-UTA is to create a platform for the structural engineering graduate students at UT Arlington in order to facilitate knowledge sharing and professional networking among the students and the local/national structural engineering community.

SEI Dallas Chapter Welcome to the new SEI Dallas Chapter, chaired by James Brown. They will hold their kick-off meeting and elect officers in September. For more information, visit the chapter website at www.dallasasce.org/.

STRUCTURE magazine

70

North Jersey Chapter The SEI North Jersey Chapter organized a half-day seminar on the Impact of Hurricane Sandy on the Impact of Hurricane Sandy on the Infrastructure Systems – Recovery Efforts, on May 2, 2013 at New Jersey Institute of Technology (NJIT). There were three presentations about various impacts on roads, Port Authority facilities, and other critical facilities.

To get involved with the events and activities of your local SEI Chapter or Structural Technical Group (STG), visit http://content.seinstitute.org/committees/local.html. Local groups offer a variety of opportunities for professional development, student and community outreach, mentoring, scholarships, networking, and technical tours.

August 2013

Congratulations to the 2013 Winning Teams Cal Poly State University for their Engineering Hangar Project Second Place: Seattle University for their Structural Evaluation and Retrofit of a Steel Warehouse Project Third Place: Southern Illinois University Edwardsville for their Dalian Office Building Project Innovative projects demonstrating excellence in structural engineering are invited for submission.

A written submission is judged and three finalist teams are invited to present their designs at Structures Congress 2014 in Boston, MA, April 3–5, 2014. The finalist teams are First Place:

judged on an oral presentation during the conference and 1st, 2nd, and 3rd place awards are determined as a combination of the written submission and oral presentation. Awards include complimentary registration to the conference (up to three student registrations and one full registration for the faculty advisor) and cash prizes: First Place – $1,000, Second Place – $500, Third Place – $250.

For more information and to view the winning projects, visit www.asce.org/SEI.

SEI Election Announcement August 31, 2013 Deadline

Andrew W. Herrmann, P.E., SECB, F. SEI, F. ASCE has been active in SEI and ASCE for many years. He served on SEI’s Technical Activity Division’s Executive Committee and as chair of the Technical Administrative Committee on Bridges. He was also the Co-Chair of SEI’s 2005 Structures Congress in

New York City. For ASCE he served as ASCE 2012 President, president of the New York City Metropolitan Section, director of Region 1, and national treasurer. He served on the Advisory Council for the 2003 and 2005 Report Cards for America’s Infrastructure and chaired the council for the 2009 Report Card. Along with numerous other volunteer efforts, Herrmann has served as director of St. Mary’s Rehabilitation Center for Children, a member of AREMA’s-Committee 15, Steel Railroad Bridges, and Chairman Emeritus of Heavy Movable Structures. Herrmann received his bachelor’s degree in civil engineering from Valparaiso University, Indiana, and his master’s degree from the Polytechnic Institute of New York, now POLY-NYU. During his 38 years at Hardesty & Hanover, LLP, Herrmann has held many positions including structural detailer, structural engineer, project engineer, and associate engineer before becoming managing partner and then a principal.

Full Name: _____________________________________Member’s ASCE/SEI ID No:________________ (Please print) Date:______________ Signature: _______________________________________________________________

Return postmarked no later than August 31, 2013 to: SEI Board Election, 1801 Alexander Bell Dr., Reston VA 20191.

SEI 2013 Board of Governors Election Official Ballot

Technical Activities Division

q Andrew W. Herrmann q Write-in vote:_______________________________

STRUCTURE magazine

71

August 2013

The Newsletter of the Structural Engineering Institute of ASCE

There are ten Governor positions on the Structural Engineering Institute Board of Governors: two representatives from each of the four Divisions (Business and Professional, Codes and Standards, Local Activities, and Technical Activities), one appointed by the ASCE Board of Direction, and the most immediate and available Past President of the SEI Board. The representatives from the Divisions each serve a four-year term.

In accordance with the Structural Engineering Institute Bylaws, this year SEI is conducting an election for a Technical Activities Division representative on the Board of Governors. The TAD Executive Committee has nominated Andrew W. Herrmann as its candidate. In accordance with the SEI Bylaws, each ballot provides a space for a write-in vote. If you are a member of SEI, please complete and mail your ballot to the address provided.

Either vote for the named candidate OR provide a write-in candidate. Because we must confirm SEI membership, only signed ballots will be accepted.

Structural Columns

SEI Student Structural Design Competition

Important Tools Educate Your Engineers on Minimizing Risk Within Your Firm and Projects By Using These Tools:

CASE in Point

The Newsletter of the Council of American Structural Engineers

Tool 5-1: A Guide to the Practice of Structural Engineering Intended to teach structural engineers the business of being a consulting structural engineer and things they may not have learned in college. While the target audience for this tool is the young engineer with 0-3 years of experience, it also serves as a useful reminder for engineers of any age or experience. The Guide also contains a test at the end of the document to measure how much was learned and retained. Other sections deal with getting and starting projects, schematic design, design development, construction documents, third party review, contractor selection/ project pricing/delivery methods, construction administration, project accounting and billing, and professional ethics.

Tool 5-2: Milestone Checklist for Young Engineers The tool will help your engineers understand what engineering and leadership skills are required to become a competent engineer. It will also provide managers a tool to evaluate engineering staff.

Tool 5-3: Managing the Use of Computers and Software in the Structural Engineering Office Computers and engineering software are used in every structural engineering office. It is often a struggle to manage and supervise these tools. Software availability is in constant flux, software packages are continually updated and revised, and few software packages fully meet the needs of any office. This tool is intended to assist the structural engineering office in the task of managing computers and software.

Tool 5-4: Negotiation Talking Points This tool provides an outline of items for your consideration when you are in a situation in which you are pressured to agree to lower fees. The text is subdivided into situations that are commonly experienced in our profession. This document is purely advisory and designed to assist you in your individual negotiations and business practices.

You can purchase all CASE products at www.booksforengineers.com.

Upcoming ACEC Online Seminars Improving Alternative Delivery Projects from Cradle to Grave, September 5, 1:30-3:00 pm As alternative delivery methods become more popular, firms need to better understand how these processes work. In Improving Alternative Delivery Projects from Cradle to Grave, Renee Hoekstra of Rha will examine approaches such as scoping, value engineering, and partnering and demonstrate how to employ them on every project.

Your Clients Talked, We Listened: Top Ten Research Findings Every Firm Should Know, September 10, 1:30-3:00 pm In Your Clients Talked, We Listened: Top Ten Research Findings Every Firm Should Know, Ray Kogan and Cara Bobcheck of Kogan & Company present their findings from hundreds of one-on-one interviews with municipal, institutional, and private clients over the past ten years.

Forget (Almost) Everything You Know About Business Development, September 11, 1:30-3:00 pm Innovations in business development are changing the way engineering services are sold. In Forget (Almost) Everything You Know About Business Development, Ken Tichacek, founder/ principal, Think Like Your Clients, will introduce the power of these tools and discuss the new management/leadership issues that arise from their use.

For more information and to register, visit www.acec.org/education/.

STRUCTURE magazine

72

Strategic Decision-Making in Uncertain Times, September 24, 1:30-3:00 pm In Strategic Decision-Making in Uncertain Times, Mick Morrissey, principal of Morrissey Goodale, will show how to link and leverage the clarity of vision, commitment of leadership, competency of management, and capitalization to rank your strategic options and make the best decisions for your firm.

CASE Convocation at the ACEC Fall Conference October 27-30 ACEC is holding its Fall Conference in Scottsdale, AZ. CASE will be holding convocation on Monday, October 28th. Sessions will include: What’s Next, the Legal aspects of Building Information Modeling, Sue Yoakum, Donovan|Hatem LLP Practical Insurance Advice, Brian Stewart, Collins, Collins, Muir & Stewart, Tom Bongi, Caitlin, Atha Forsberg, Marsh Developing an Internal Culture to Manage a Firm’s Risks, Michael Strogoff, Strogoff Consulting ACEC’s program will include: • CEO Insights on working with private clients in commercial, industrial and energy markets • Panel on the Future of Transportation Funding • Desert Jeep Adventure • Play in the Annual ACEC PAC Golf Tournament August 2013

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

How Does a Certificate of Merit Work?

Residential Development Work There are many commentaries dissuading engineers to avoid residential development work, and scare stories to go along with them. Engineers can be left holding the bag for sympathetic third party plaintiffs. On the other hand, there are cases where residential work is a significant part of the practice. It has it challenges and you have to know what you are doing; however, there are established homebuilders that are sophisticated and know the business. Condos, however, may be a different animal.

Client and project selection are key.

Unless you plan to provide the actual inspection services, you should avoid the use of the word inspect in describing your basic role of observation. If the owner has it in the contract, delete it and insert observation. If that cannot be done, then carefully define the word in the definitions or scope of service sections so it clearly means observation. Clients have been known to use the word inspection when they really mean the normal level of contract administration. Inspections connote a more detailed examination and consequently more obligations than you bargained for. It could raise the standard of care and the liability implications can be huge.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

ACEC/CASE Members Named to ZweigWhite’s 2013 25 Best Civil Engineering Firms to Work For CASE Member Firms named to the Structural Engineering Firm category of the ZweigWhite 2013 25 Best Civil Engineering Firms to Work For include: ARW Engineers, Ogden, UT Structura, Inc., Rockville, MD Simpson Gumpertz & Heger; and Reaveley Engineers + Associates, Inc., Salt Lake City, UT

ACEC Business Insights ACEC’s Fall Conference Provides Leadership and Training for the A/E Industry’s Next Generation The Emerging Leaders Forum at the upcoming ACEC 2013 Fall Conference in Phoenix, October 27-30, will help to develop leadership and management skills in your firm’s “rising stars.”

Young professionals participating in the Forum gain valuable perspective on how politics, economics, and laws relate to the engineering industry. They will also develop relationships with engineering peers from around the country.

Emerging Leaders Forum participants receive a reduced Conference registration rate of $799, which includes the Forum sessions and all other Conference programming and events.

For more information and to register, www.acec.org/conferences/fall-13/index.cfm.

STRUCTURE magazine

Best Management Strategies in Business of Design Consulting Course September 18-21, 2013; Chicago, IL Acomprehensive 2013 update on the primary underpinnings of the successful A/E business, ACEC’s highly regarded Business of Design Consulting course is a unique playbook for building leadership and managing your firm at the most effective levels.

The 3½-day agenda is taught by an experienced faculty of industry practitioners and highlights current strategies for a wide array of critical, need-to-know business topics that will keep your business thriving despite a churning business environment; including, how to manage change and build success in performance management, strategic planning and growth, finance, leadership, ownership transition, contracts and risk management, marketing, and more!

For more information and to register for the course, www.acec.org/education/eventDetails.cfm?eventID=1473.

73

August 2013

CASE is a part of the American Council of Engineering Companies

A certificate of merit statute requires a plaintiff who intends to sue a design professional to consult with a third-party design professional to review the facts of the plaintiff’s claim and render an opinion regarding whether the claim is meritorious or not. One law that appears to work well is Arizona’s, which requires: 1) The expert’s qualifications to express an opinion on the licensed professional’s standard of care or liability for the claim.

2) The factual basis for each claim against a licensed professional.

3) The licensed professional’s acts, errors or omissions that the expert considers to be a violation of the applicable standard of care resulting in liability.

4) The manner in which the licensed professional’s acts, errors or omissions caused or contributed to the damages or other relief sought by the claimant.

Avoid Use of the Word “Inspect”

CASE in Point

CASE Business Practice Corner

Structural Forum

opinions on topics of current importance to structural engineers

Engineers Shouldn’t Think Too Fast

By William M. Bulleit, Ph.D., P.E.

E

ngineers use intuition in design, but intuition can lead us astray. Daniel Kahneman (Thinking, Fast and Slow, Farrar, Strauss, and Giroux, 2011) describes how humans have two thinking modes: System 1, where we think fast (intuition); and System 2, where we think slowly (analysis). Since humans over history have lived in dangerous environments, System 1 tends to take precedence if we do not consciously apply System 2. When the bushes move, it is better to run than to stand and think about running.

Those who ran often ran from nothing, but those who stopped to think about running eventually got eaten. Unless System 2 is consciously activated, System 1 will give an answer, and that answer will be accepted. Furthermore, since System 1 has worked so well for so long, we often are overconfident of our System 1 answers and do not activate System 2.

The following problem from Kahneman should allow you to see how System 1 works.

Read the problem below and let System 1, intuition, determine the answer. Then consciously shift to System 2 and solve it again.

A bat and ball cost $1.10.

The bat costs one dollar more than the ball.

How much does the ball cost?

Most of you got a System 1 answer of 10 cents, but, of course, the actual answer is 5 cents, as System 2 determined.

When facing any decision, you cannot turn off System 1. It gives an answer whether you request it or not. One way it obtains its answers is using heuristics, techniques that help solve problems that would otherwise be intractable. I will use the term engineering heuristics to distinguish them from the heuristics that System 1 employs. Engineers know that engineering heuristics have limits, and care must be taken when using them. Similar care needs to be taken when System 1 uses its heuristics. An understanding of some of these heuristics may allow you to spot when System 1 is making a decision that should be reassessed by System 2.

Unfortunately, though, if System 2 is otherwise engaged, it will tend to believe what System 1 says. System 2 invests only as much

effort as necessary; the easy thing to do is to allow System 1 to make the decision. The use of heuristics by System 1 causes biases in your thinking and the resulting decisions. The use of engineering heuristics is a more conscious operation than is the use of System 1 heuristics. When you use an engineering heuristic, you can examine it in light of the situation in which you plan to use it. That is not the case with System 1 heuristics.

Structural engineers get little feedback on their designs, in the sense that they experience few failures. Thus we can fall into the trap of thinking that everything we have done in the past was correct, and that our intuition is almost always right. This blinds us to errors that we might make by relying too much on System 1 and is referred to as confirmation bias. We all know that there may be errors in our designs, but that does not stop System 1 from telling you that the designs must be right, unless you take the time to use System 2. Another System 1 heuristic leads to the availability bias: you are inclined to believe that which is most available in your memory.

The design decisions that are most familiar to you are the most recent ones. If they all have been successful, you will tend to believe that what you did was correct.

Engineering heuristics are not valid over the entire range of problems to which they seem to apply. It is not always obvious where the limits lie, but we know to be cautious when we attempt to use engineering heuristics to solve problems that are new to us or push the state of the art. The heuristics used by System 1 are also most questionable when we have not had a lot of experience in comparable situations. Intuition is most dependable when it is grounded in a long history of making

similar decisions and receiving feedback, which requires a consistent environment.

As Kahneman says, “Remember this rule: Intuition cannot be trusted in the absence of stable regularities in the environment.”

System 1 will give you answers no matter what your experience. It may produce quick answers to difficult questions by substitution: the question answered is not the one intended, but the answer is reasonable enough to pass the limited review of System 2. Whether it is accurate or not depends on the situation.

Common sense would tell you not to do this, but intuition is not always constrained by common sense. The worst part of such an intuitive judgment is that you will be confident in your System 1 answer. To quote Kahneman again: “This is why subjective confidence is not a good diagnostic of accuracy: judgments that answer the wrong question can also be made with high confidence.”

Engineers are human and have innate abilities and limitations. One limitation relates to the two thinking modes that humans use: System 1, which thinks fast and is confident in its decisions; and System 2, which thinks slowly but is lazy and would rather let System 1 do the work. We as engineers use design processes that reduce the chance of errors, but the reduction of System 1 errors requires constant vigilance against its tendency to jump to conclusions and run from the moving bushes, rather than stopping to think.▪ William M. Bulleit, Ph.D., P.E. (wmbullei@mtu.edu), is a professor in the Department of Civil and Environmental Engineering at Michigan Tech in Houghton, Michigan.

Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C 3 Ink, or the STRUCTURE® magazine Editorial Board.

STRUCTURE magazine

74

August 2013