STRUCTURE magazine | April 2012 by structuremag

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

Special Section:

April 2012 Concrete

Steel Industry Reacts to New Customer Demands (page 43)

SEISMIC ACTIVITY IS NOT JUST A WEST COAST PHENOMENON

Don’t Take A Risk With Mother Nature Natural disasters have been in the news lately. Both here in the U.S., and abroad, Mother Nature has been reminding us that earthquakes are not just a “ring of fire” occurrence but can happen anywhere, anytime. That’s why in the United States our building codes have been updated to take into account earthquakes, hurricanes, tornados and other seismic activity. Powers is committed to providing products that meet the latest building code requirements and helping designers and engineers understand the importance of specifying code compliant anchors. To help assist the engineering community, Powers Register today for FREE has developed real-time anchor PDA2 software download at: www.powersdesignassist.com software which is now available in a FREE download ® and our 6th Edition Technical Manual, available through your local Powers representative

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Features UT’s New Hackerman Experimental Science Building Inspires Teamwork – Part 2

By Michael Brack, P.E.

The 294,000-square-foot Norman Hackerman Building replaces the old Experimental Sciences Building (ESB) on the campus of the University of Texas (UT) at Austin. Part 1 of this series provided general information about the project and discussed the structural system selection and schedule challenges. This article, Part 2, describes some of the additional challenges encountered and the innovative solutions that the design and construction team developed.

Condition Assessment and Repair – Part 1

By D. Matthew Stuart, P.E., S.E., F. ASCE, SECB

In the fall of 2010, a property management company requested a condition assessment of a large sub-grade parking garage and loading dock located in Center City, Philadelphia. Establishing the extent and cause of the deterioration and identifying appropriate repairs, required a thorough condition assessment of all of the sub-grade loading docks, parking areas and ramps, including visual observations as well as chain dragging of the exposed wear surfaces to determine the presence of sub-surface delaminations.

43 Special Section

Steel Companies Driven by Customer Demand By Larry Kahaner

Companies involved in the construction steel industry – fabricators, software developers and more – are meeting customer demand with new offerings and updates of current products and processes. Although cautiously optimistic, most companies are seeing an upturn in business.

Departments 55 From Experience By Dan Mazzei, P.E.

60 Education Issues Principles for Engineering Education – Part 1

By Eric M. Hines, Ph.D., P.E.

62 Great Achievements Job Abbot

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

Working Capital Management By Nic Perkin

67 Spotlight Bellezza e funzione By Aine Brazil, P.E.

74 Structural Forum A Structural Engineer’s Manifesto for Growth – Part 1 By Erik Nelson, P.E., S.E.

STRUCTURE magazine

April 2012

Columns 7 Editorial Are You MAD? By John A. Mercer, P.E., SECB

9 Building Blocks

The Promising Future of Middleweight Concrete By Kenneth B. Bondy, S.E.

14 Codes and Standards What’s So Fascinating About Fasteners? By Elyse G. Levy, S.E.

18 Structural Forensics

Evaluation of Timber Foundation Piling in Marine Applications By Bogdan Zmeu, P.E., S.E.

22 Guest Column

Creating Redundancy in Building Envelope Design By Scott Lockyear, P.E.

26 Structural Performance

Engineered Wood Products Exposed to Floodwaters By Adam Pittman, P.E.

29 Technology

Structurally Speaking By Leo Salce, Intl Assoc AIA

33 Structural Practices A Case Study

By Zeno Martin, P.E., S.E. and Eric Anderson, P.E., S.E.

In every Issue

64 Business Practices

Punching Shear in Thin Foundations

CONTENTS

April 2012

6 Advertiser Index 66 Resource Guide (Engineered Wood Products) 68 NCSEA News 70 SEI Structural Columns 72 CASE in Point 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.

ADVERTISER INDEX

PLEASE SUPPORT THESE ADVERTISERS

American Concrete Institute ................... 4 AZZ Galvanizing .................................. 65 Bentley Systems, Incorporated ................. 3 Canadian Wood Council ....................... 25 Cast ConneX......................................... 45 Computers & Structures, Inc. ............... 76 CSC, Inc. .............................................. 44 CTS Cement Manufacturing Corp........ 19 Devco.................................................... 51 ESAB Welding and Cutting Products .... 54 Fyfe ....................................................... 15 GT STRUDL........................................ 53

Halfen, Inc. ........................................... 17 The IAPMO Group............................... 63 Integrated Engineering Software, Inc..... 47 ITW Red Head ..................................... 59 ITW TrusSteel ....................................... 61 JMC Steel Group .................................. 50 KPFF .................................................... 66 New Millennium Building Systems ....... 49 Nucor Vulcraft Group ........................... 28 Polyguard Products, Inc......................... 32 Powers Fasteners, Inc. .............................. 2 RISA Technologies ................................ 75

editorial Board

S-Frame Software, LLC ......................... 46 SidePlate Systems, Inc. .......................... 42 Simpson Strong-Tie......................... 13, 21 StructurePoint ....................................... 37 Struware, Inc. ........................................ 10 SYNTHEON, Inc................................... 8 Taylor Devices, Inc. ............................... 11 Valmont Tubing .................................... 35 V&S Galvanizing, LLC ......................... 52

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Executive Editor Jeanne Vogelzang, JD, CAE

Evans Mountzouris, P.E.

Editor

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Davis, CA

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STRUCTURE® (Volume 19, Number 4). ISSN 1536-4283. Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $65/yr domestic; $35/yr student; $90/yr Canada; $125/yr foreign. For change of address or duplicate copies, contact your member organization(s). Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board. STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be

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THE

COVER

A Joint Publication of NCSEA | CASE | SEI

The Norman Hackerman Building is the new home for experimental sciences at The University of Texas at Austin. The 294,000 square foot facility houses numerous wet labs, imaging suites, neuroscience research, and teaching and administrative spaces. The building sets a new standard for design on the campus, and required creative engineering and massive amounts of teamwork to solve budget, schedule, design, and building performance challenges. Courtesy of Tom Bonner, 2011. See more about this project in the feature article on page 38.

April 2012 Concrete

STRUCTURE magazine

April 2012

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editorial

new trends, new techniques and current industry issues Are You MAD? By John A. Mercer, P.E., SECB

“Once a firm has established itself, it has the potential to make a difference in its community and market area.”

pring is just around the corner, a few short weeks away. Daylight savings time and longer days are already starting, leading us into another year of construction. Actually, in North Dakota construction occurs all year round, unlike the past. New technology has triumphed in breaking frost in the ground so that footing trenches can be dug and concrete can be placed to begin the construction of new buildings and structures. All of this is at a cost, but an oil boom in my part of the world is the motivation to proceed at any cost. A few weeks ago, CASE had its winter planning meeting in New Orleans. Thirty CASE committee members met to continue the development and improvement of the world class CASE Documents and Tools that are helping CASE firms use best business practices and manage the risk associated with the business of structural engineering. CASE Excom approved the addition of insurance liaisons to be embedded into CASE committees to add a new dimension of value and credibility to the CASE products. The practical side of managing risk will now be observed by professional liability insurance professionals that will not only see the difference that CASE member firms can make, but who will carry that message back to their insurance underwriters. CASE firms are MAD. Oh I don’t mean they are angry, CASE member firms are Making A Difference in their businesses and for their clients. Once a firm has established itself, it has the potential to make a difference in its community and market area. I believe that structural engineers are best equipped to envision the needs of a community based on their understanding of both design and construction. Certainly the young engineer in training, as it was referred to in my day, needs some experience under his or her belt, but it doesn’t take long for them to begin to see how the application of engineering knowledge and practice can be put to work to improve the lives of their fellow man. Subsequent to the CASE Winter Planning Meeting, NCSEA had its Winter Institute. What a breath of fresh air to hear about the breakwater project that the US Army Corps of Engineers was tasked to complete in record time after Hurricane Katrina. For those of you who were not able to attend, the Corps embedded STRUCTURAL themselves in the engineering ENGINEERING INSTITUTE design group in order to speed up the process for the design a member benefit

structure

build project for the breakwater. The project was designed and constructed in a three-year window, a record for the Corps in constructing a project of this scope and national importance. I can actually say that the Corps is MAD. Congratulations! Other topics presented included the ASCE 7-10 Wind Design provisions. In case you haven’t had an opportunity to implement them yet, we now have three wind maps, each based on a structure’s Category. The wind velocities on the maps vary from the past, and now have an Importance Factor incorporated into the Velocities. The new equations therefore don’t use the Importance Factor. This is a small change, but one that we can live with. Later, at the end of the presentation during Q&A, we heard that one day there will be two volumes of the ASCE 7 document. The preferred method for calculating the wind pressures will be in Volume 1, and all the alternate or simplified methods that can be used will be in Volume 2. I’ll let you guess which Method will be in Volume 1. The best news going forward is that the ASCE 7 may be going to a six year cycle after the ASCE 7-13 is published. [Now, after you’ve had a chance to catch your breath after an exhausting round of cheering, send a thank you note to the appropriate people on the ASCE 7 committee.] Many have survived the down economy of the past few years by making hard choices concerning their business practices, and most important of all about their employees. I think it is time for all structural engineers to take a hard look at both their technical skills and the business practices their firms have been using. One day soon, the economy will turn around, and you won’t have the time to bone up on your skills by attending seminars, or even webinars. You’ve always looked forward to receiving that paycheck, but what have you done lately to earn it? What a strange question, you say. Not so strange when you want to be giving the best service you can to your clients and your community. That means continuing education should be an important part of your culture, even if your client doesn’t appreciate its benefits. Certainly, you will. What have you been doing in your community lately? Are you MAD?▪

STRUCTURE magazine

John A. Mercer, P.E., SECB (Engineer@minot.com), is the president of Mercer Engineering, PC, in Minot, North Dakota. He currently serves as Chair of the Council of American Structural Engineers (CASE) and is a CASE representative on STRUCTURE’s Editorial Board.

April 2012

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Building Blocks

or several years in the early 2000s, as a senior member of ACI Committee 318, I chaired a 3-person Task Group whose mission was to improve and unify the provisions governing lightweight concrete in the ACI Building Code. Our recommendations were incorporated into the 2005 edition of the Code. I was not selected for the job because I had any particular expertise in the chemistry, properties, or production of lightweight concrete. I was primarily a taskmaster, nagging and prodding, making sure our work was responsive to the mission and completed on time. The heavy technical lifting was done by the other Task Group members, Calvin McCall and Tom Holm, who do know a lot about lightweight concrete. Nonetheless, because of my participation in this Task Group, and the generally favorable reviews our recommendations received from users of the code, I developed a mostly undeserved reputation for knowing a lot about lightweight concrete. That may explain why, in 2006, I was approached by a major chemical company and asked to review a new product they were developing. The product was a portland cement concrete made by supplementing a portion of normalweight coarse and fine aggregates with lightweight synthetic particles (LSP), resulting in a concrete with a substantially reduced unit weight (110-120 pcf ). The chemical company, at that time, considered this product to be “lightweight concrete”, thus retaining me for this work seemed reasonable. My assignment was to determine if and how the product conformed to the ACI Building Code (ACI 318-05 at the time), and to make recommendations for additional testing and research, which would assist in gaining general approval of the product

CU beads in concrete. Courtesy of Syntheon.

updates and information on structural materials

Elemix in a hand. Courtesy of Syntheon.

within the engineering and construction communities. The work sounded interesting and, because of my recent lightweight concrete code experience, I felt I could help them. I enthusiastically accepted the assignment and completed it with a final report in early 2007. My first conclusion was that the product was not, in fact, lightweight concrete. Since the product contains no lightweight aggregate, it could not be considered lightweight concrete in accordance with ACI 318 definitions. Thus, it must be considered normalweight concrete, albeit with a very low unit weight. The term “middleweight concrete” was coined to describe this novel material. Further, LSP would not qualify as an aggregate, even though it replaced aggregate. Under 318 definitions, it would, however, qualify as an admixture. Test results already completed at the time of my review showed that compressive and tensile strengths of middleweight concrete were similar to strengths developed with conventional normalweight concrete without LSP and with the same w/cm. However, I pointed out to my client that a normalweight concrete with a unit weight of 120 pcf would raise performance questions from engineers and building officials. Accordingly, I recommended additional testing in the areas of 1) bond and anchorage, and 2) shear. Finally, I recommended that the client obtain an ICC Evaluation Report from the ICC Evaluation Services for this product, which would demonstrate de facto conformance to ACI 318 and the International Building Code (IBC).

The Promising Future of Middleweight Concrete

continued on next page STRUCTURE magazine

By Kenneth B. Bondy, S.E.

Ken Bondy, S.E. is a consulting structural engineer specializing in the design, construction, and retrofit of concrete buildings. He is a senior member of the ACI Standard Building Code Committee (ACI 318), first joining the committee in 1973.

Tweezers holding a bead. Courtesy of Syntheon.

Shear and Bond Behavior

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Three years later, the client had accomplished everything I had recommended and more. Notably, they completed an extremely comprehensive testing program at North Carolina State University supervised by Dr. Paul Zia, a renowned researcher and an ACI colleague of mine. The NCSU work included testing to failure of 27 large-scale specimens addressing shear, bond, and anchorage of middleweight concrete members. They also obtained, from ICC Evaluation Services, an Acceptance Criteria report (AC408, Acceptance Criteria for Structural Concrete with Lightweight Synthetic Particles) and an ICC approval (ICC-ES Evaluation Report ESR 2574, September 1, 2009) available at www.icc-es.org. The results of the NCSU testing are particularly impressive. The testing focused on bond and shear behavior of concrete beams and slabs with LSP and normalweight coarse and fine aggregate at target unit weights of 120 and 130 pcf. The results of bond testing “…confirmed that the bond strength of beams containing [LSP] met the bond

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requirements specified by ACI 318-08.” A similar conclusion was reached based on shear testing: “In all cases the measured shear strength exceeded the predicted values using the equations of ACI 318-08….” A closer examination of the shear test results shows that Vc, the measured shear strength of the concrete (no contribution from web reinforcement) substantially exceeded ACI predicted values. For the 120 pcf mix design, the measured shear contribution of the concrete Vc exceeded the predicted value by 58% (measured/predicted=1.58). This is strikingly good behavior. One could argue that this can be explained by conservatism in the ACI shear equations; however, many other beam shear tests (on specimens without LSP) have shown measured/predicted Vc results with much smaller ratios, closer to 1.0. That strongly suggests that the LSP enhanced the concrete shear capacity to some significant degree in these tests. Another notable conclusion of the NCSU testing was that the ACI 318 “” modifier for lightweight concrete need not apply to middleweight concrete with LSP.

Middleweight with Heavyweight Savings Based on what I have learned in my involvement with this material, I believe that middleweight concrete could have

STRUCTURE magazine

April 2012

a major impact on concrete construction. A concrete with mechanical properties equal to or better than conventional normalweight concrete, but weighing 20% less is a big deal. Its use results in significant savings in reinforcing steel in all structural elements of a concrete building: the floor system, columns, walls and foundations. Secondary benefits of middleweight concrete include, among others: • Reduced structural beam depth, resulting in a greener, more sustainable building with: - Less volume to heat and cool - Less vertical height - Less raw materials used in the structure including structural materials, envelope, skin, plumbing, electrical, anything related to building height - Less impact on the community at construction (fewer raw material deliveries), during the life cycle (lower HVAC cost), and at demolition (less debris) - All the related cost and time savings • Improved fire resistance and freeze/ thaw durability. • Improved constructability including pumpability, placing, finishing, and reduced formwork loading. Based on current estimates for the cost of LSP, it appears that its use in the floor systems of cast-in-place concrete buildings can result in a net savings in the total cost of the

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structural frame of 2-4% with no downside, and some significant improvements in performance. Elaborating further on the economics of middleweight concrete, it has been my experience that the installed cost of reinforcement (prestressed and nonprestressed) represents about onethird of the total cost of a cast-in-place structural concrete frame. Forming and concrete contribute the remaining two thirds. If middleweight concrete (120 pcf ) replaces normalweight concrete in a structural frame, and superimposed dead load is negligible, the frame dead load is reduced by 20%. The frame reinforcement designed to resist seismic loads (shearwalls, SMRF, seismic foundation elements) will be reduced by the full 20%, since it is directly proportional to dead load. However, the reinforcement which is designed to resist gravity loads, will be reduced by a smaller percentage. For example, if a normalweight frame supports a factored dead load of 120 psf and factored live load of 80 psf, gravity load reinforcement is designed to resist 200 psf. If the dead load is reduced by 20% with the use of middleweight concrete, gravity reinforcement would be designed for 0.8x120+80=176 psf, and the net reduction in reinforcement would be (1-176/200)x100=12%. If we assume that the average reduction in reinforcement in typical frames in seismic areas is 15%, the total savings in the cost of the entire concrete frame, with the use of middleweight concrete, should be 0.15x0.33x100=5%, less the premium cost of concrete incorporating the LSP. For buildings designed for gravity and wind loads only (no seismic) the total savings in the cost of the frame should be 0.12x0.33x100=4%. In California, the midrange cost of a complete, well-designed structural frame in a multistory concrete building is about $25/

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Brace YourselfApril STRUCTURE TAY24253 magazine 2012Magazine October 2009 11 Ad Structure

Half-Page Island 5" x 7.5"

31”

5”

Trib = 20’-0”

ADL=5 psf LL= 40 psf 14”

Section sf; therefore, the resultant savings in reinforcing steel attributable to middleweight concrete is estimated to be $1.00 to $1.25/sf. This, of course, must be reduced by the premium for middleweight concrete with LSP, which, depending on geography and other factors such as required dosage, ranges between $20 and $28/cy for a 120 pcf mix. For buildings with an average floor system concrete thickness of 8 inches (0.025 cy/sf), the cost of LSP will range between $0.50 and $0.70/sf − substantially less than the savings in reinforcement and resulting in a significant net savings in the cost of the frame.

Post-Tensioned Parking Structure Example To further investigate the advantages of middleweight concrete in post-tensioned concrete buildings, something I do know about, I designed a representative bay of a commonly proportioned California parking structure with geometry, loading, and material properties shown in the Figure above. I designed the beam and slab first with normalweight concrete (150 pcf ) and then with middleweight concrete (120 pcf ). As might be expected,

sf), the premium cost for middleweight concrete with LSP would range between $0.42/sf and $0.59/ Cols 22”x22” Typ sf, and the net savings in the cost of the structural frame would be between $0.23/sf and $0.40/sf. This is reasonably consistent with ’ f c = 4,000 psi typ Flr-flr ht. 10’-0” typ the savings projected in the more general analysis above. For a 200,000 square foot park65’-0” 65’-0” ing structure (about 600 cars), depending on the premium cost of middleweight concrete with Elevation LSP ($20-$28/cy), the net savings would range between $46,000 and $80,000. With no structural there was a significant reduction in material downside, I don’t think anyone would turn that quantities between the two unit weights. I down. It should also be noted that the use of did a careful takeoff of the reinforcement in middleweight concrete with this geometry and the beams and slabs, and based on extensive loading would offer the possibility of reducing experience with parking structures, I esti- the beam depth to 30 inches, a 6-inch reducmated the reinforcing steel quantities in the tion in floor-to-floor height with no change in columns, walls and foundations. headroom. The savings in tendons would not Using current California unit prices for be as great; however, that might be offset by tendons and nonprestressed reinforcement, the savings in total vertical building height and the resulting savings ranges between $0.23 long-term sustainability advantages. and $0.40/sf, depending on the premium In summary, middleweight concrete made cost of the middleweight concrete with LSP. with lightweight synthetic particles has This is about 2% of the total estimated strength, serviceability, and durability propercost of the frame. In this type of fram- ties equivalent to or better than conventional ing, minimum requirements control most normalweight concrete and, based upon curof the nonprestressed reinforcing steel in rent unit prices for reinforcement and LSP, the beams and slabs; therefore, the weight its use results in a significant reduction in the savings is of no benefit there. However, cost of structural concrete frames.▪ the use of middleweight concrete offered substantial savings in the post-tensioning NCSU Testing Results, as mentioned in tendons and in the reinforcing steel in the this article, are: Use of Lightweight Synthetic columns, walls and foundations. Particles to Produce Concrete with Reduced The estimated quantities and unit prices I used Unit Weight, Technical Report No. RDfor this analysis are shown in the Table. The cost 09-05, Constructed Facilities Laboratory, savings in reinforcement, resulting from the Department of Civil, Construction and use of middleweight concrete, is estimated to Environmental Engineering, North be $0.82/sf. Since the average concrete thickCarolina State University, Raleigh, NC. ness of this typical bay is 6.8 inches (0.021 cy/

Savings in Reinforcement with Middleweight Concrete.

Concrete Unit Weight (pcf ) Item (psf )

150 (Normalweight)

120 (Middleweight)

Material Savings (psf )

Installed price ($/lb)

Cost Savings ($/sf )

Beam PT

0.31

0.21

0.10

$2.25

$0.23

Slab PT

0.28

0.23

0.05

$2.25

$0.11

Beam rebar

1.20

0.00

$0.80

$0.00

Slab rebar

1.10

0.00

$0.80

$0.00

Non-seismic columns & foundations

1.70

1.44

0.26

$0.80

$0.21

Seismic walls and foundations

1.70

1.36

0.34

$0.80

$0.27

Total

$0.82

STRUCTURE magazine

April 2012

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Codes and standards updates and discussions related to codes and standards

Years ago, in the early days of my career, if you had told me that fasteners could be fascinating, I would have thought you had a screw loose. (Yes, of course the pun was intended!) Today, I can’t think of another type of building component that comes in more varieties and performs more functions. It is difficult to imagine what buildings would be like without fasteners.

asteners used as structural building components include nails, screws and power-driven pins. These products are generally manufactured from steel wire and typically have diameters of 1/4 inch or less. They are used as repetitive elements and, unlike bolts and post-installed concrete anchors, fasteners are installed in one operation. The point of the fastener is driven through all of the connected materials, without the need for nuts or other components on the back side of the material. There are typically at least three zones of interest along the length of a fastener: the point or tip; the body or shank; and the head. The design of each of these zones can vary greatly depending upon the intended use of the fastener. While the 2009 International Building Code® (IBC) and 2009 International Residential Code® (IRC) address requirements for the use of traditional fasteners such as nails, the codes do not address all of the available types of fasteners and novel applications of these products. The code shows awareness of this by requiring the use of fasteners which comply with a named standard or with an approved design or alternate (e.g., Section D1 of AISI S200) and by generally allowing for alternate materials (IBC Section 104.11), but does not stipulate how to judge an alternate design. Fortunately, ICC Evaluation Service (ICC-ES) addresses suitability of alternate designs, ongoing quality control of structural fasteners, and innovations in fastener design. Fastener products are recognized in ICC-ES Evaluation Service Reports (ESRs), based on documents known as Acceptance Criteria (AC). These documents have been developed by ICC-ES in conjunction with industry experts and approved by the ICC-ES Evaluation Committee, which is comprised solely of code officials. These ACs are public documents available on the ICC-ES website. As manufacturers continue to develop new fastener designs and applications, these ACs will be revised and expanded, and new ACs may be developed. Currently, the ICC-ES ACs applicable to fastener evaluations are as follows: • Fasteners Power-driven into Concrete, Steel, and Masonry Elements (AC70) • Nails and Spikes (AC116) • Tapping Screw Fasteners (AC118) • Wood Screws Used in Horizontal Diaphragms, Vertical Shear Walls and Braced Walls (AC120)

What’s So Fascinating About Fasteners? By Elyse G. Levy, S.E.

Elyse Levy is a Senior Structural Engineer with ICC Evaluation Service, and leads the fastener work group. She may be reached by email at elevy@icc-es.org.

This article is intended to provide information about Fasteners and related ICC-ES acceptance criteria. It should not be construed as an endorsement or recommendation by ICC-ES®.

14 April 2012

It may be easy to lump all fasteners together, but each type of fastener has unique applications and capabilities. Courtesy of Thinkstock.

• Staples (AC201) • Power-driven Pins for Shear Wall Assemblies with Cold-formed Steel Framing and Wood Structural Panels (AC230) • Alternate Dowel Type Threaded Fasteners (AC233) • Corrosion-resistant Fasteners and Evaluation of Corrosion Effects of Wood Treatment Chemicals (AC257) • Power-driven Pins for Attaching Gypsum Board Materials to Cold-formed Steel Wall Framing (AC259) • Horizontal Diaphragms Consisting of Wood Structural Panel Sheathing Attached to Cold-formed Steel Framing (AC262)

Power-driven Fasteners Power-driven fasteners, sometimes referred to as power-driven pins or shotpins, are installed using tools which exert an extremely high force on the fastener either by igniting a charge of gunpowder (powder-actuated fasteners) or igniting a measure of compressed gas (gas-driven or gasactuated). Power-driven fasteners often resemble common nails, but are used to attach materials to base materials which are much harder and stronger than wood, including concrete, steel and masonry. To achieve this, the fasteners are typically case-hardened to a Rockwell C hardness of 50 or more. Since there is currently no national standard for these fasteners, they must be evaluated in accordance with AC70. Many different power-driven fasteners have been recognized in ICC-ES evaluation reports. Variations in shank design include straight, tapered or stepped shanks, which can be either smooth or knurled. Flat heads are sometimes

2209.1). AC118 also allows for connection capacities to be justified based on testing in accordance with AISI S905. One specialized use of a tapping screw that is already addressed in an ICC-ES Acceptance Criteria is that of constructing diaphragms consisting of wood structural panels attached to CFS framing. While the AISI S213 standard (referenced in IBC Section 2210.6) provides shear strength and deflection information for some of these diaphragms (those

Tapping Screws While power-driven fasteners are offered as alternates to tapping screws, the design of tapping screws continues to evolve. The tapping screws are evaluated under AC118, which provides manufacturers with an avenue for several different types of recognition. First, screws complying with all of the requirements of a code prescribed fastener standard, such as ASTM C 1513 or ASTM C 954, can be recognized as such. Secondly, if a screw design deviates from a prescribed standard, the design can be evaluated for use as an alternate to screws which comply with the prescribed standard. If a standard screw (or a recognized alternate) is intended for use in engineered connections, the shear and tension strengths of the screws must also be known. Since standards such as ASTM C 1513 do not go as far as establishing minimum screw strengths, ICC-ES ESRs recognize fastener shear and tension strengths based on independent laboratory testing. Using these strength values, connection capacities can then be determined in accordance with Section E4 of AISI S100 (referenced in IBC Section STRUCTURE magazine

constructed with the screws prescribed in Table D2-1), manufacturers may wish to justify diaphragm capacities for other screw sizes or proprietary designs of screws. AC262 provides the requirements for this type of evaluation.

Wood Screws Long before screws were developed to join pieces of steel, they were used to join pieces

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replaced with threaded portions to create power-driven studs. Various accessories can be factory affixed to the fasteners to create assemblies for special uses. Examples include ceiling clips, threaded rod hangers and a variety of washers. While AC70 is the basis for evaluating power-driven fasteners installed in steel with a thickness of 3/16 inch or more, power-driven pins are also recognized for uses involving cold-formed steel (CFS) framing, which are similar to the use of tapping screws. AC259 addresses requirements for justifying the transverse load capacity of power-driven fasteners used to attach gypsum board products to CFS wall framing. Power-driven fasteners used to construct shear walls comprised of wood structural panels fastened to CFS framing are evaluated under AC230. This criteria also includes requirements for establishing single-fastener connection capacities. Requirements for recognition of diaphragms comprised of wood structural panels fastened to CFS are provided in AC262. Together, AC230, AC259 and AC262 allow for broad recognition of power-driven fasteners used to attach sheathing materials to CFS framing.

April 2012

Fastener Criteria Matrix

Fastener Type Main Member/ Side Member/ Substrate Material Connected Element Material Intended Use / Type of Evaluation

Wood

Cold-Formed Steel (CFS)

Wood

Steel

Wood Structural Panels (WSP)

Screws

AC116 AC201

AC233

Corrosion resistance of fasteners used in treated wood AC257 AC257

AC257

Diaphragms of wood structural panels attached to wood framing

AC120

Shear walls with wood structural panels attached to wood framing

AC120

Braced wall panels with wood structural panels attached to wood framing

AC120

Steel side plate-to-wood connections AC116 AC201

AC233

Connections of wood structural panel to CFS

AC118

AC230

Diaphragms of wood structural panels attached to CFS

AC262

Shear walls with wood structural panels attached to CFS CFS

CFS

Powerdriven

Staples

Wood-to-wood connections

Nails

AC230

CFS-to-CFS connections

AC118

Gypsum board

Connections of gypsum board to CFS

AC118

Steel t ≥ 3/16"

Various

Connections of building materials to structural steel

AC70

Steel

WSP

Diaphragms of wood structural panels attached to structural steel framing

AC70

Concrete

Various

Connections of building materials to concrete & concrete filled steel deck

AC70

Masonry

Various

Connections of building materials to masonry

AC70

of wood together. As with many types of building products, the IBC and IRC address the most common type of wood screws, standardized in ANSI/ASME B18.6.1. However, many alternate screw designs are being developed to ease installation, to improve performance, and to address specialized connection needs, such as those needed for log construction. These alternate screw designs and applications are evaluated by ICC-ES in accordance with AC233. This criteria requires testing to determine reference lateral, pull-through and pullout capacities, as well as bending yield, tensile and shear strength of the fasteners. For screws which are expected to provide lateral capacity comparable to standard wood screws, the lateral connection capacities are calculated in accordance with the code, and confirmed by testing. For screws which are expected to perform better than the code-specified

standard wood screws, lateral connection capacities may be justified directly by testing. To date, at least seven ESRs have been issued based on evaluations performed in accordance with ICC-ES AC233, providing reference connection values for more than twenty unique wood screw designs. While wood screws have existed for a long time, use of wood screws to construct wood diaphragms and shear walls is not yet addressed by the building code. Manufacturers wishing to have their screws used in this manner must comply with the requirements of AC120 to justify substitution of the screws for the code-prescribed nails or to justify higher shear strengths.

Nails Nails may be the most prescribed type of fastener in the building code. Through

STRUCTURE magazine

April 2012

AC259

a combination of references to AF&PA National Design Specification for Wood (NDS), the direct incorporation of shear wall and diaphragm load tables, and direct prescription of the number and size of nails needed for particular connections, the IRC and Chapter 23 of the IBC address the broad use of common nails. Nails are required to comply with ASTM F 1667. While a myriad of nail types is covered by this standard, not all nails on the market conform to the shank geometries and bending yield strength prescriptions of ASTM F 1667. The ICC-ES AC116 exists to help nail manufacturers demonstrate that their commodity nails comply with ASTM F 1667 and to provide an opportunity to justify the use of proprietary nail designs, or uses of nails not addressed by the NDS. Visit the ICC-ES website, www.icc-es.org for more information.▪

Petr Vaclavek/shutterstock.de

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Structural ForenSicS investigating structures and their components

valuation of timber piling for “vintage” marine structures is a challenging task. Traditionally, timber piles have been widely used for supporting piers, wharves, seawalls, bridges and other structures. In a temperate marine environment, such as the New York harbor, and properly maintained, these structures have effectively supported waterfront infrastructures that are more than a century old. Like any other structure, over time, timber piles may undergo physical and material degradation due to a host of factors including wear-and-tear, freeze-thaw cycles, fungal rot, or marine borer attack. Consequently, for some of these structures the current capacity is less than the initial design capacity.

Attacking Organisms A marine borer attack can happen relatively quickly, and has the potential for sudden and significant degradation of the affected pile. Marine borers are small organisms that burrow into the wood for food and shelter. According to Aquatic & Wetland Structures, published by the Timber Piling Council, marine borers are more active in warm coastal waters, with the highest activity in Florida, the Gulf States, and California. The teredo, commonly referred to as shipworm, is a mollusk, a small invertebrate animal that is two to eight inches long and is active inside the sapwood of the pile, above the low-water level. Resulting internal

Evaluation of Timber Foundation Piling in Marine Applications Knowledge Based Computational Algorithms for Pile Evaluation Analysis By Bogdan Zmeu, P.E., S.E.

7" CONCRETE SLAB

Bogdan Zmeu, P.E., S.E. is a Consulting Engineer and helps with the design and the technical aspects on a variety of projects. Bogdan can be reached at Bogdan.Zmeu@hdrinc.com.

damage to the pile resembles a honeycombed structure. Another species, limnoria, attacks the timber from the outside, gradually reducing the pile diameter. Severe abrasion in combination with limnoria attack may rapidly reduce the pile cross-sectional area, leaving an hourglass shape with exposed heartwood at the center of the section (Figure 1).

Evaluation If not addressed, these deteriorations may lead to a downgraded load-carrying capacity, causing escalated repair costs, shutdowns, and eventual closure and loss of the facility. Preservation of the structure can be accomplished through implementation of repairs that restore structural integrity to damaged piles. To be effective, repairs should be based on engineering investigations comparable to the Level II or Level III inspection routines described in the Waterfront Inspection Guidelines Manual, by the New York City Economic Development Corporation (NYCEDC). Establishing the state of structural health for marine piling is crucial for medium- and long-term management of waterfront infrastructures, and for establishing and implementing rational decisions with regard to rehabilitation or replacement of these structures. Structural engineers are often called upon to evaluate marine piles for older piers, wharves, and seawalls. Assessing the load-carrying capacity of a damaged pile is a challenging task that requires knowledgeable professionals, reliable information, and state-of-the-art analysis. The evaluation begins with the most recent pile inspection report. Traditionally, inspection reports consist of various records including structure descriptions,

TOP OF PIER EL. +7.75'

6 X 12 TIMBER PILE CAP (TYP.) 3/4" BOLT WITH N.Y. DOCK DEPT. WASHERS (GALV.) (TYP.) 3' 7"

BRACING DOWN

4x10 WALE

5' 1"

0' 5"

BRACING UP

DETERIORATION OF PILE'S CROSS-SECTIONAL AREA t1' = 2-in ; t2' = 2.25-in

REMAINING PILE CROSS-SECTIONAL AREA d1' = 5-in ; d2' = 4-in

M.L.W. EL. -2.25'

See the online version of this article for additional content and a sample computer output calculation PDF. www.STRUCTUREmag.org

Figure 1: Typical pier.

18 April 2012

12" TIMBER PILE (TYP.)

TOP OF PIER EL. 307.0

FILL

CONCRETE PILE EXTENSION 1' 0"

SHEET PILE 1-7/8" TIE ROD (8'-0" CTRS.)

2' 0"

M.L.W. EL. 295.0

FILTER STONE

STAYLATHING EA. SIDE

3' 0"

2' 0" 4' 0"

3' 0" 4' 0"

5' 4"

RIP RAP DIKE

APPROX. FIRM BOTTOM AFTER DREDGING

M.L.W. EL. 263.0

photographs, probes, offsite laboratory test results, field notes, and sketches showing geometry and extent of deteriorations. Not all of this information is available in every situation. In particular, often the position of the deteriorated segment of the pile with respect to the butt end, or the data needed to calculate the end eccentricities about the principal axes of the cross section, is missing. In such cases the engineer can employ estimates of section losses based on the photographic record, especially for routine or rapid assessment inspections, when the scope of work does not call for repair design or for the change of use of the facility. However, establishing rational decisions regarding the rehabilitation or the replacement of large structures, or portions of these structures, requires carefully planned inspection routines that can detect internal and external defects, along with rigorous analysis for all the structures that are being evaluated.

Pile Capacity Methodologies The methodology for pile capacity evaluation that is presented here consists of two computational algorithms. The first algorithm is based on Equation 15.4-2, Wood Columns with Side Loads and Eccentricity, Special Loading Conditions, Section 15, National Design Specification® (NDS®) for Wood Construction (NDS-2005). This algorithm investigates the

local buckling criterion for the deteriorated section of the pile by determining the direct compression load that an eccentrically loaded column can sustain. The second algorithm involves second-order elastic analysis of the pile. This analysis includes the degradation effects by considering a “hinge”-type discontinuity in lieu of the actual geometric properties of the reduced cross-sectional area of the pile. Additional considerations include an initial horizontal translation at the location of the hinge. Due to the large volume of computations, both analyses are performed by a desktop computer. Pre- and post-processing automation routines are employed for data transfer between the database and the processing modules. Detailed descriptions for each routine and typical runtime output with pile capacity calculations for a 28-pile dataset are included in the online version of the article (www.STRUCTUREmag.org). The pile capacity analysis was used for typical foundation piling for a deep water pier and for a container wharf. Both are major waterfront structures similar to those encountered at port facilities throughout the United States. Typically, piers are open- or closed-type structures that extend perpendicular from the shore into navigable waters, with berthing on both sides. Wharfs are open-type marginal platforms that are parallel to the shoreline. Figure 1 illustrates the heavy horizontal structure for a typical high-level platform. The pier deck is a 7-inch thick concrete slab

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April 2012

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Figure 2: Typical wharf with low-level relieving platform.

Pile Stability Analysis

Axial Capacity for Deteriorated Pile 40000.000 35000.000

P vs. d1 (e1=10% of D; e2=5% of D)

30000.000

P vs. d1 (e1=1% of D; e2=1% of D)

70000 60000

P (lbs)

15000.000

40000 30000 20000

10000.000

d1- inch

Discussion of Results Pile capacity curves for eccentricities of 1% and 10% of pile diameter, as calculated with NDS Equation 15.4-2, are shown in Figure 3. This illustrates the capacity degradation rate as the eccentricity of the applied axial load increases. Loss of capacity is due to bending moments introduced at the ends of the deteriorated portion of the pile. For the 10% curve and d1= 6 inches, i.e. an equivalent square area

6.00

5.67

5.33

5.00

4.67

4.33

4.00

3.67

3.33

3.00

L/ l -Ratio

Figure 3: Allowable Bearing Capacity vs. Diameter (P vs. d1).

and is set on two 6x12 timber pile caps. The pile bents are typically 12 to 16 feet on center for the full length of the pier, which can reach 800 feet or more. Typical pile spacing is 4 to 6 feet on center for the full width of the pier. Figure 2 (page 19) illustrates typical wharf construction for a low-level relieving platform. This type of construction predates modern wharves, which are typically high-level platforms with reinforced concrete structures, by at least 45 years. The low-level relieving platform wharf is a massive, 6-foot thick horizontal structure. The platform is set on 8- by 5-foot pile grids to support a total service load of approximately 1,200 pounds per square foot. The top side is asphalt on gravel fill to withstand heavy container trucks. The bottom side is 1-foot thick reinforced concrete and is set directly on the pile extension structures as shown in Figure 2. The pile extensions are 22-inch (inside diameter) precast concrete pipes, filled with concrete and encasing the pile head over the top 2 feet of the pile. The minimum allowable capacity for these piles is 25 to 30 tons.

2.67

2.33

6.7

6.4

6.1

5.9

5.6

5.3

5.0

4.7

4.4

4.1

3.9

3.6

3.3

3.0

2.00

10000

5000.000

1.67

P-lbs

20000.000

0.000

P vs. L/l ( l = 4.5 ft.)

50000

25000.000

Figure 4: Allowable Bearing Capacity versus Pile Length Ratios (P vs. L/l).

of 5.091x5.091 inches, the bearing capacity is 16,300 pounds (see web version with computer output for pile W-1). For this case, the bearing capacity of the pile is approximately 33 percent of the initial design capacity of 25 tons. For the 1% curve and d1= 6 inches, the capacity is 28,000 pounds, or 56 percent of the initial design capacity. The pile capacity curve shown in Figure 4 illustrates the variation of P, the allowable bearing capacity, for increasing pile length ratios L/l for the pile dataset for which the strut length l = 4.5 feet. For a 22.5-foot pile with the length ratio L/l = 4, the allowable capacity is 11,800 pounds, or approximately 24 percent of the initial design capacity of 25 tons.

Final Considerations Based on Figure 2-7 in the NYCEDC Waterfront Inspection Guidelines Manual, the damage grade for advanced deteriorations is defined as a section loss of 25-50% of the undamaged cross-sectional area of the pile. Considering actual diameters d1=8.86 inches and d2=8.12 inches (i.e. an equivalent square area of 7.5x7.5 inches) which corresponds to a cross-sectional area that is half its original size, and extrapolating values for the 10% curve in Figure 3, the pile axial capacity is 43,000 pounds. This capacity is less than the initial pile design if a 25-ton pile is considered. Therefore, the pile classification is Severe Deterioration. By contrast, the NYCEDC classification is still Advanced Damage and unchanged, since the section loss is still 50 percent of

STRUCTURE magazine

April 2012

the original section. Hence, for piles with pronounced eccentricity at the damaged sections – end eccentricities of 10% of the nominal pile diameter or greater – the evaluation based strictly on loss of crosssectional area can over-rate the structure. A Sever Degradation can pass as the lesser Advanced Degradation when the length of the deteriorated segment of the pile, and its end eccentricities, are not accounted for by the evaluation algorithm.

Conclusion Structural analysis is a powerful method for the evaluation of deteriorated timber piling in older marine infrastructures. The power and versatility of the method is improved when multiple evaluation algorithms are used to determine the remaining capacity in a deteriorated structure. The dual algorithm approach presented here takes advantage of well researched code provisions such as NDS Equation 15.4-2, Section 15, Special Loading Conditions, and of traditional stability analysis for overall elastic buckling of column-type structures. Among notable features of this approach are: integral database that is periodically updated; consistency of evaluations; and, the opportunity to address large datasets by employing latest computer technology. For the most part, the analysis confirms the evaluation procedure recommended in the Waterfront Inspection Guidelines Manual. Exceptions are noted for the deteriorated pile sections displaying large eccentricities about the longitudinal axis of the pile.▪

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Guest Column dedicated to the dissemination of information from other organizations

Figure 1: Sloped roof and overhangs protect the building from moisture accumulation.

ood frame construction has been utilized for centuries and has resulted in many of the most beautiful and durable structures around the world. Examples include Chinese temples built in the 12th century and Norwegian Stave Churches dating back to the 1300s. The longevity of these structures has been achieved through the use of durable materials and protection from the elements. As modern day building construction evolves with an increased focus on energy efficiency, it is of continuing importance that we understand how buildings perform when exposed to moisture from rain and snow. This article covers the use of redundant water management strategies to protect buildings from moisture intrusion. Just like backing-up data on computers in case of a hard drive crash, a redundant building envelope can minimize damage in the case of sealant or caulking failures. This is important, since many sealant products used in commercial construction may only last two to five years depending on the exterior environment and product installation.

Creating Redundancy in Building Envelope Design By Scott Lockyear, P.E.

Scott Lockyear, P.E. is a Technical Director for the WoodWorks initiative which provides free support to design professionals that want to utilize wood in commercial structures. He may be reached at scott@woodworks.org.

Roof Systems

The online version of this article contains references. Please visit www.STRUCTUREmag.org.

One common technique is the use of pitched roof systems instead of flat roofs. In commercial construction, it is common for buildings to utilize flat roof systems with parapet walls. While these are ideal for providing partial concealment of roof top units and allow easy access for maintenance, they are also more susceptible to water ponding. Additionally, it is common in low-slope roof construction to omit overhangs, which increases the bulk water absorbed by the wall system. Overhangs and sloped roof systems, as shown in Figure 1, are effective tools to divert moisture away from buildings.

22 April 2012

In 1996, a report was commissioned by the Canadian Mortgage and Housing Corporation to study the impact of overhang length on moisture related wall issues. Results from the study (Figure 2) clearly show that, as overhang length decreases, the likelihood of moisture problems in the wall cavity increases. Based on these numbers, a 2-foot overhang may reduce the likelihood of moisture intrusion by over 50 percent in exterior walls. If moisture is diverted from the walls, it also follows that breaches in the building envelope are less of an issue. Another key element in diverting moisture away from walls is the use of a properly designed drainage system. One area where proper drainage is commonly overlooked is at the eaves where roofs and walls intersect. As shown in Figure 3, kickout flashing has been installed to guide roof runoff into the gutter without saturating wall cladding.

Balconies Balconies can provide the same protection as roof overhangs, provided detailing is designed and constructed properly. Unfortunately, this protection may be negated if moisture is allowed to drain toward the building. Additionally, balconies are inherently more susceptible to moisture-related issues given their exposure to the elements along with relatively complex detailing requirements for flashing and connections. One of the most common ways to protect balconies is with the use of membrane assemblies which divert moisture away from both the balconies and other exterior elements. These membranes commonly use plastic or elastomeric systems to provide protection. When these systems have a tear or are improperly detailed for drainage, underlying structural components can be readily wetted allowing for decay, rust, or spalling depending on the materials being utilized. To highlight how common failures are in waterproof membranes, some condominium homeowner associations (HOA) have language in their agreements transferring liability for moisture intrusion to the owner (see sidebar).

SAMPLE HOA VERBIAGE BALCONIES–All of the condominium balconies are coated with a waterproof membrane, which if properly cared for, will withstand the elements for many years. If you see a puncture in the balcony floor or if you see a water stain on the ceiling beneath a balcony, let our Property Manager know immediately. The following rules apply to all second floor balconies: A. Potted plants must be on raised bases/plant stands with water catch basins (this allows air to circulate underneath); no plants may be placed directly on the balcony floor (over time, trapped water will damage the balcony surface) B. Objects with sharp feet are not allowed on the balcony. Residents will be held responsible for any damage to the waterproof balcony floor/membrane that results from puncture(s) they cause. Puncturing of membranes may occur when balcony handrails and posts or other items are improperly connected over lightweight concrete. Moisture may also circumvent the membrane protection entirely when proper detailing is not provided. This includes prematurely ending the membrane protection at the top of the deck edge, which leads to moisture exposure of the perimeter framing. When this occurs with untreated wood, decay as shown in Figure 4 is likely.

% of Surveyed Buildings with Wall Performance Issues

Effect of Overhang Length on Wall Performance 100 80 60 40 20 0

< 1'

1'–2'

> 2'

Overhang Length (ft)

Figure 2: Effect of overhang length on wall performance.

Redundancy Unfortunately, failures in membrane design and installations do occur, which creates a potential need for redundancy in the envelope design. Use of preservative treated wood components can provide this redundancy in exterior balconies. The concept of redundancy can also be used on breezeways where concrete toppings may act as a sponge for moisture. Figure 5 is an extreme case, given that the protective membrane was completely omitted leading to premature failure. While the use of preservative treated wood will not prevent rusting of metal connectors and mold growth, it will protect structural members of the breezeway until the building envelope breach can be identified and repaired. Given the inherent

Figure 3: Kickout flashing.

risk of membrane failures, the situation in Figure 5 could have occurred even with the membrane in place. If a redundant approach including the use of preservative treated wood is utilized, the designer should contact the plastic membrane and/or preservative wood manufacturer to ensure that chemical reactions will not occur between the plastic and the wood treatment.

Wall Systems Even if overhangs and balcony areas are designed to divert moisture away, wall systems still need to provide protection from moisture intrusion. This is even more relevant in multi-story wood frame structures where

Figure 4: Decay at balcony edge where inadequate drainage provided led to decay.

STRUCTURE magazine

Figure 5: Breezeway with no plastic membrane installed.

April 2012

Figure 6: Reverse flashing at window.

Figure 7: Untreated wood beam with exposed end grain.

shrinkage of wood coupled with cladding (e.g., brick) expansion may put additional stresses on caulking and mortar intended to minimize moisture intrusion. Many articles have been written about shrinkage characteristics of wood along with expansion of brick. The Brick Institute of America’s Technical Note 18A contains provisions for calculating expansion of brick, and the Wood Handbook published by the USDA Forest Products Laboratory has provisions for calculating shrinkage of wood. This should be a consideration when designing expansion joints of the building envelope. With regard to wall systems, there is a litany of envelope choices available. Barrier systems are one option, with a long track record of success in existing European structures with thick stone walls that can dissipate moisture. One common barrier system is an exterior insulating finish system (EIFS). In these modern day wall systems where excess material is minimized, water may not dissipate if there is a building envelope failure which leads to moisture intrusion. In relatively simple wall systems with few penetrations, these systems may perform quite well. Penetrations in the building envelope may result from windows, plumbing, or other systems critical to overall building performance. Proper design and installation techniques can be found in ASTM E2112–07 Standard Practice for Installation of Exterior Windows, Doors and Skylights. During installation, it is critical that common mistakes are avoided such as reverse flashing as shown in Figure 6. As the number of penetrations increases, the probability of moisture intrusion past the barrier system also increases. This is due to the fact that caulking is relied upon to protect around these openings. Highdensity residential construction exterior

walls often have multiple penetrations from windows and balconies. This has been identified as a concern in section 1408.1.1 of the 2009 International Building Code (IBC) where a drainage plane behind the EIFS in commercial buildings is required for residential occupancy. This was not required in previous versions of the IBC, leading to significant field issues. Another option for building envelopes is drainage wall systems, which include brick veneer, cast stone, or EIFS with drainage. In drainage wall systems, the cladding provides a first layer of protection as well as a secondary drainage plane. With this strategy, small failures are less likely to cause issues; however, these systems do have a higher initial cost and do cost more to repair if there is an issue with installation. Additional considerations for drainage wall systems include proper application of weather barriers, and provision of a drainage plane gap between the wall and cladding along with a mechanism for water to exit such as weep holes in brick facades.

Untreated Wood Another strategy is the use of untreated wood in semi-exposed applications. While untreated wood may perform well in exterior applications in certain climates, for the most part it needs to be protected to avoid significant weathering and/or decay. The easiest way to prevent issues with decay in exterior environments is to utilize decay-resistant or preservative treated wood in accordance with Chapter 23 of the IBC. In some instances, for aesthetics, it may be desirable to utilize untreated wood at the building exterior where it is designed for minimal exposure to moisture. Section 2304.11.5

STRUCTURE magazine

April 2012

of the IBC provides guidance on the use of untreated wood and indicates that a roof, eave, overhang, or other covering, to prevent moisture or water accumulation on the surface or at joints between members, is required unless the building is located in a geographical area where moisture is not a concern. One application where untreated wood is often used is rafter overhangs. When detailed properly, an untreated wood overhang may withstand many seasons of rain and snow. However, of particular concern is exposure of wood end grain to moisture. Trees inherently allow easy moisture transport along the grain. In a living tree, water absorbs through its roots and travels up the tree trunk to the limbs and leaves. When trees are cut into timbers, this same mechanism exists, allowing end grain to be more susceptible to uptake of moisture in exterior applications. When designing wood rafters, it is desirable to seal the end grain and situate the beams within the roof system to minimize exposure to wind-driven rain and draining water. When this does not occur, decay may result as shown in Figure 7. Exposed untreated wood may be utilized, provided it does not exceed moisture content of between 16 and 19 percent. Fortunately, wood in unexposed applications will have moisture content much lower than this unless a building envelope design failure occurs.

Conclusion Before embarking on a wood frame design, it is important to consider materials and techniques which will lead to a redundant building envelope. Many internet resources are available for design and construction. When questions relating to wood frame construction arise, a useful resource is the WoodWorks website (www.woodworks.org). By clicking “search other wood associations,” the WoodWorks search engine will guide you to resources from most of the wood industry associations in North America. By utilizing available design resources coupled with a redundant approach to the building envelope, it is possible to design and construct woodframe structures that will stand for centuries to come.▪ This article was previously published in the December issue of Wood Design Focus. It is reprinted with permission.

Design Office 9 IBC 2009 and SDPWS 2008 compliant Shearwalls: • Shear wall deflection and story drift • Deflection derived stiffness for force distribution • Hold-down design using editable database Sizer: • Full control over bearing and span lengths • Supporting member bearing design • Full, clear or design spans • Multiple beams and columns in one workspace • Integration with Autodesk Revit® (optional)

Complete list of features and Demo at woodworks-software.com “You can buy more sophisticated wood engineering software, but ... it’s expensive, takes considerable time to model your structure, and is usually overkill for what engineers need for the design of most wood structure projects. WoodWorks® Design Office doesn’t have the most advanced graphics or the latest interface style, but its component-based operation is intuitive, quick and easy to use, inexpensive, and is produced by the same wood experts that contribute to the development of Canadian and American wood design standards. While our non-profit organization’s budget means we need to continue to focus on only our niche of wood design, we are capitalizing on the stengths of other software packages like Autodesk’s Revit® Structure to help give you the level of sophistication of fully modelled structures by creating a bi-directional integration with this leading BIM software. A Revit/Sizer link is now available as a separate purchase.” Robert Jonkman, P.Eng, Manager, Structural Engineering and WoodWorks Software, Canadian Wood Council

www.woodworks-software.com

800-844-1275

Structural Performance performance issues relative to extreme events

here have been a number of significant flooding events in recent years, ranging from the Nashville flood in May 2010 to Hurricane Irene in August 2011. Floods are one of the leading natural disasters in the United States. Average annual U.S. flood losses for each of the past 10 years (2001-2010) exceeded $2.7 billion (National Flood Insurance Program). Fortunately, engineered wood products can be considered relatively durable when temporarily exposed to floodwaters. Many of the losses involving engineered wood products can be reduced if proper measures are taken.

Dry It Out If a building or home is flooded, it is imperative to get the structure dried out as soon as possible. This is necessary to prevent mold growth and fungal decay – the latter can lead to permanent strength loss (Kirby, Wiggins). After floodwaters have receded, any standing water in a basement or crawl space should be removed. Any insulation, gypsum board, carpet and padding, or other interior finish materials that are wet should be removed. Ceramic tile floors should also be removed, as concrete topping or backer boards used underneath ceramic tiles often retain moisture. This will speed up the drying process and allow for visual inspection of the structure. Fans and dehumidifiers should be used when possible to circulate air. As stated by APA in a publication on assessing flood damage, “Depending on conditions, the drying process can take from a week or two to several months.” While the building is being dried out, temporary shoring of any wood products may be necessary to prevent permanent set, especially for primary support members that are heavily loaded. Engineered wood products should be dried out to a moisture content less than 16%, returning it to the assumed “dry use” conditions, as specified in Section 8.1.4 of the 2005 National Design Specification® (NDS®) for Wood Construction. While not a structural concern, any mold on wood should be cleaned by a detergent and water solution, as recommended by the EPA, or a 1 cup bleach per 1 gallon water solution as recommended by the CDC. The CDC also recommends that large mold infestations should be addressed by a professional who has experience with cleaning mold in buildings and homes. A moisture meter will be necessary to determine if wood members are properly dried. A handheld electrical resistance meter with pins is the most common type of moisture meter used in the field. For engineered wood products, the pins of the meter should be put in the wide face

Engineered Wood Products Exposed to Floodwaters By Adam Pittman, P.E.

Adam Pittman, P.E. is an engineer with the engineered wood products division of Weyerhaeuser. He may be reached at adam.pittman@weyerhaeuser.com.

The online version of this article contains references. Please visit www.STRUCTUREmag.org.

26 April 2012

Moisture meter with pins inserted into bottom of I-joist.

of the beam or panel. They should be inserted parallel to the grain. It should be noted that the resins in engineered wood products affect the electrical resistance and often cause readings to be higher than the actual moisture content. Rather than attempting to account for this potential difference, it is recommended that the moisture meter output be used directly with knowledge that it may be slightly conservative.

Adhesives in Engineered Wood Products Engineered wood products are manufactured by taking a tree apart, removing inconsistencies inherent in the lumber, and putting its fibers back together to take full advantage of its natural strengths. This results in high-quality products that have higher allowable design properties, and more dimensional stability than sawn lumber. Examples of engineered wood products include I-joists, structural composite lumber, oriented strand board (OSB), and plywood. Structural composite lumber (SCL) products include laminated veneer lumber (LVL), parallel strand lumber (PSL), and laminated strand lumber (LSL). One of the most common concerns about engineered wood products exposed to extreme moisture conditions such as flooding is whether the adhesive bond will be compromised, leading to delamination of individual wood veneers or strands. Engineered wood products use adhesives that are rated for exterior use, although this use category is intended for temporary moisture exposure during construction, not long-term exposure. Structural composite lumber and I-joists use adhesives adhering to ASTM D 2559 requirements while plywood and OSB meet the Exposure 1 classification required in the U.S. Department of Commerce PS-1 and PS-2 standards, respectively. The most common adhesives used to manufacture engineered wood products are phenol formaldehyde (PF), phenol resorcinol formaldehyde (PRF) and diphenylmethane diisocyanate (MDI). During the manufacturing process, bonding is caused by a chemical reaction in the adhesive. In that reaction, the adhesive becomes

SCL Dimensional Change at Different Moisture Exposures.

% Thickness (Width) Swell Product Wet Recovery (>30% MC) from Wet LSL 18% 9% LVL 6-8% 3-4% PSL 10-15% 5-8%

% Depth Swell Wet (>30% MC) 1% 4-6% 5-6%

% Length Swell

Recovery from Wet 0.3% 1-1.5% 2-2.5%

Wet Recovery (>30% MC) from Wet Negligible Negligible Negligible

1) From ‘as manufactured’ dimensions and moisture content. 2) ‘Wet’ assumes MC > 30% throughout the cross-section. Partially wetted product will exhibit lower percentage swell than shown in this table. 3) ‘Recovery from wet’ assumes original manufactured moisture content. chemically inert. Once the reaction is complete, the adhesives are more resistant to moisture than the wood and there is no concern over the adhesives breaking down and causing delamination.

Strength and Dimensional Stability Most wood strength properties decrease as moisture content increases beyond dry use conditions, until fiber saturation (roughly 30% moisture content) is reached. Beyond fiber saturation, these properties remain relatively constant. The NDS provides guidance for reducing design values in wet use applications. When temporarily wet wood members are dried back to normal equilibrium moisture content (< 16%), it is typical to assume no change in allowable strength properties, though a small loss may occur in relative ultimate strength due to wetting. Elevated moisture contents can also affect the stiffness and creep performance of wood members. Creep is an increase in deflection that occurs over time under sustained load or exposure to moisture; this increase is typically only applied to dead load deflection because the live load applied is considered too transient to produce creep. Raising the moisture content from dry in-service conditions to fiber saturation decreases stiffness up to 25%, thereby causing an additional deflection of about one-third more than calculated. For this reason, it is good practice to temporarily shore primary support members and joists supporting offset bearing walls until the wood members are dried. Moisture content for sawn lumber at time of fabrication varies from 15% to more than 20% depending on whether it is kiln-dried or shipped green. Equilibrium moisture content for wood in buildings typically ranges from 6 to 15%, depending on the building location, climate, and season. This is why sawn lumber

typically shrinks as it equilibrates to the inservice moisture content of the structure. Conversely, engineered wood products are typically manufactured at a moisture content of 5 to 7%. If wood products are exposed to flooding, the moisture content will likely be elevated to more than 15%, which could result in substantial swelling. Thus, it is important to give consideration to potential dimensional stability issues. SCL products swell more in the thickness direction than the depth direction, because this is the orientation of pressing during the manufacturing process. After significant exposure to moisture, a SCL beam can be expected to shrink back to approximately half of its swollen dimension upon redrying, also known as springback. For example, a 3½-inch x 16-inch PSL beam that has swollen to 16½ inches can be expected to shrink back to 16¼ inches when it is properly redried to its original manufactured moisture content. An example of dimensional changes SCL products experience when exposed to varying moisture contents is shown in the Table. I-joists will follow the same general rules as SCL products in regards to swelling, including springback when the joists are properly redried. If I-joists are submerged or exposed to moisture for extended periods of time, the webflange connection should be closely inspected to ensure that the web has not swollen and split the flange or been otherwise compromised.

Panel Products OSB and plywood panels exposed to flooding will likely experience swelling along the panel edges. After drying, the swollen edges can typically be sanded down to maintain a flat floor surface. If panels become very saturated, they may expand and buckle along the panel edges. APA’s publication on assessing water damage after a flood is an excellent reference for OSB and plywood panels. In particular, they provide two ways to remedy panel buckling. One option

STRUCTURE magazine

April 2012

Depth

Width

is to run a circular saw (set to the panel thickness) along the panel joints. This is called “kerfing,” and will help relieve the pressure that causes buckling. If tongue-and-groove edges are cut, they must be blocked from underneath or a layer of underlayment must be installed over the top with underlayment joints offset from subfloor joints. However, kerfing and drying may not completely remedy buckling. The other option involves blocking under buckled portions of the floor to push panels flat again. Depending on the degree of flood damage, it may be necessary to add a second layer of sheathing or to replace panels to ensure subfloor integrity. If hardwood flooring is to be installed over flooded OSB or plywood panels, it is critical that panels be allowed to dry. The National Wood Flooring Association® (NWFA) Installation Guidelines state that the moisture content of properly acclimated solid strip flooring less than 3 inches wide should be within 4% of the subfloor moisture content at time of installation. For 3 inches or wider solid flooring, that difference should not exceed 2%. High moisture content in hardwood flooring or subfloor panels can lead to poor fastener retention, which is one of the most common causes of “popping” with hardwood floors.

Conclusion Taking appropriate measures may lessen the impact of flood damage on sawn lumber and engineered wood components in a structure. In all cases of flood damage, it is recommended that an engineer or design professional with knowledge of wood products and engineered wood products assess the unique conditions of each structure and provide specific recommendations for remediation and/or replacement procedures. In many cases, the engineered wood product manufacturer can provide guidance to the design professional on how to evaluate their specific products.▪

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oday, Building Information Modeling (BIM), the process of creating virtual information-rich three-dimensional models of a building or structure, is being leveraged in some capacity at every stage of the project delivery process, from design to construction to operations and maintenance. This is a far cry from where we were 10 years ago. Extraordinary advancements in technology and processes have not only made BIM possible, but effectively necessitated its use in many projects today. Much of the reason for this movement can be attributed to the fact that the benefits of BIM, from improved visualization and model analysis to increased coordination and reduced project costs, are being realized in one shape or form by all the key players, structural engineers included. Adoption has progressed significantly in recent years, albeit largely due to the proliferation of more requests to have BIM models as the project deliverable. The ability to propose on more projects and potentially win more business are powerful motivators for any firm to get BIMready and become more marketable. However, beyond being able to answer more RFPs, the structural industry is lagging behind some of its counterparts in the other design industry segments, such as architectural and MEP engineering. The reason for this is that, in most projects, creating drawings and using a BIM model for coordination are still the primary uses for BIM software by structural engineers; documentation is not dependent on analysis links or the other disciplines’ models.

Challenges for Structural Work A particular challenge for structural engineers that impacts their rate of adoption is the ability to effectively integrate structural analysis design into

the BIM process. Most firms still start their design in an analysis software package such as RAM, RISA, or ETABS and then bring in the architect’s 2D CAD drawings to produce an analytical model. The problem with this workflow is that unless you can link that model into a BIM environment, that’s where it ends. As a result, many “BIMready” firms end up creating an entire second model that is completely disconnected from the analytical one. Over the last few years, interoperability between software tools has improved, but it’s still not perfect. Among some of the most commonly reported complaints are issues with missing or shifted elements when importing BIM models into the analytical tool. This may be due to the fact that the program does not support that particular element or the model element was in the wrong type format, wrong position, or not connected. Any number of reasons could be to blame. Another issue related to this is that a lot of engineers find that is not practical to go back and forth between BIM and analytical software more than once. This is due to the level of effort needed to simplify geometry in order to properly run the analysis, or the mapping involved for interpreting the elements. Also, there is a cascading effect of changes in the model where the analytical results have been already used in the design of many other elements. That is why it’s important to really understand the limitations of the analysis links and to develop an internal best practice modeling workflow. Yet, despite some of these issues, many structural engineering firms have already discovered that the benefits of BIM can far outweigh the challenges. continued on next page

STRUCTURE magazine

Structurally Speaking

A Practical Approach to Implementing BIM By Leo Salce, Intl Assoc AIA, LEED AP

Leo Salcé is an architect and consultant with Microdesk. He specializes in Building Information Modeling (BIM) technology implementation in architecture and engineering firms, both nationally and internationally. Leo may be contacted at lsalce@microdesk.com.

Benefits of BIM

Getting There

While it is commonly held that BIM costs more, many of these perceived costs are relative and based on a wide range of factors. For instance the project’s scale and complexity, the firm’s BIM workflow, its ability to efficiently produce several structural what-if scenarios, and its process to track and update changes efficiently, to name a few. Firms can realize greater efficiencies by decreasing the need to spend an engineer’s time on tedious re-work of the design and coordination of changes, and instead focus on true engineering and problemsolving tasks. This is made possible thanks to a reduction in the errors introduced by design changes. Errors are always a possibility whenever changes are made, and are practically a given when the changes are complex and accompanied by the stress and rush associated with the late stages of a project. A true bi-link associated model reflects changes made to elements across the model, thereby reducing the margin for error. The engineer still has a labor-intensive role during the BIM modeling process, but being able to visualize, isolate, section, and filter areas or elements in the structure in 3D allows for more direct problem solving. BIM can also improve coordination between trades. Clash detection and monitoring of key elements can reduce non-discretionary change orders that would otherwise come up. However, none of the above will matter if there is not a change in ones attitude towards a change in the usual process.

For firms contemplating making the transition to BIM, the big questions are what are the next steps and how do I get there? There are numerous theories on how to best go about implementing BIM in a firm, but there is no single cookie-cutter implementation approach. No two firms are alike. Therefore, your BIM implementation plan must address the firm’s own unique business and processes. The first thing your firm needs is executive sponsorship to ensure there is real commitment to the Better coordination between trades. move, plus a clear vision of what the organization’s goals are and an awareness • List the types of analysis tools to of the impacts a major transition will have on be used by the organization to compliment the above the organization, from processes to staffing to • Develop a company template with technology needs. When moving to BIM, it all of your standards is important to remember that it is more than • Outline a staffing plan that clearly a lateral move; it is a change in process, too. defines the roles of engineers and Firms doing this on their own tend to suffer drafters, as well as organizational from painful lessons learned, so having your structure relative to the types of process assessed by a professional consultant projects you’ll be doing is recommended. • Define an internal and external With this framework in place, you can then communication system set yourself to the task of defining a well • Create a training and support plan thought-out implementation plan. Outlined 2. Select the Right Software below are the common steps: Determine what BIM software(s) will 1. Define the Organizational best address your organization’s needs, Framework from one to all of the following tasks: Create a modeling plan that outlines the • Model Creation roles and responsibilities for everyone • Model Integration involved, from what will be modeled to • Clash Detection/Model Mediation who has ownership of what, by doing • Model Sequencing the following: • Model Quantity Takeoff

Steel tonnage design options.

STRUCTURE magazine

April 2012

• Collaborative Project Management Most Structural firms will only require model creation software, but this depends on the company’s current processes. It is important to note that BIM software is NOT structural analysis software, and although powerful, you will still require other structural analysis tools. At this stage, you must also ensure IT and hardware are able to meet the software requirements in order to allow for a smooth transition and avoid frustrations. Also consider a server strategy for accessing the BIM model from multiple office locations. The success of the implementation will be based on doing an early assessment of the company’s current workflow and state of technology to better provide a clear and complete roadmap. 3. Create a Project Deployment Plan When rolling out your new tools and processes, it is often best to identify an initial pilot project and define: • Specific project goals and objectives • Clear internal and external collaboration plans • A document management workflow • A BIM management workflow • Construction Management, Cost Management, Project Closeout workflows, if required.

Ensuring Implementation Success Additional words of advice to help you prepare for a successful implementation would include the following tips: • Do not cut corners in your implementation just to save money. Taking measures such as cutting project support and shadowing from an experienced consultant during the pilot project, or cutting training days because you already have staff in the firm who know Revit and can help the rest of the team, can be a fatal mistake in your implementation. Investing up front will save you down the road. • Don’t skip on defining a workflow strategy. This will ensure the clean exchange of models between your

architect, consultants, and your firm. Also be sure to have a standard folder structure where the users would locate the latest and greatest models. • Invest on advancing internal skills. Having someone within the firm who is savvy in tasks like custom content creation, for those projects that require complex modeling, is priceless. Invest in people who will serve as your internal gurus in the long-term after implementation is complete • Develop an Internal BIM User group. Having lunch and learn discussions for internal BIM processes, techniques and enhancements in the BIM software improves users’ knowledge and opens communication.

Common Obstacles Knowledge is power. Being aware of these common pain points is the first step to entering into BIM implementation with eyes wide open and understanding potential issues that you should prepare for. Training: • Lack of time to learn the software • Steep learning curve • No clearly defined modeling requirements and staff responsibilities (drafting and engineering tasks are no longer separated) Coordination: • Defining who owns all the BIM model elements • Difficulties in format conversions between platforms • BIM requires structural engineers to know a lot about the model very early, often before they even have the information. For instance, beam sizes are needed in order to draw framing even before they are designed. • Liability if the BIM model is sent to a fabricator Documentation: • Drafting tools in BIM not yet as well developed as in CAD • Conversion of CAD to BIM standards is time consuming • BIM cannot produce drawings as quickly as CAD • Annotation more difficult in BIM than in CAD • Last minute changes in 2D CAD are easier than in 3D BIM

STRUCTURE magazine

April 2012

• Manual editing required for unwanted graphics Design: • Issues with linking analytical software to the BIM model • Lack of confidence in the accuracy of the links • Underestimating the level of effort involved in design/modeling. BIM models appear further developed than the actual design may be. These issues and common perceptions emphasize the need for professional consulting and a well thought-out implementation plan to address or avoid obstacles before they get in the way.

BIM is the Future In 2012, BIM will continue to transform the industry, with more structural and architectural firms recognizing the same opportunities, benefits and values. As the industry continues to educate itself on advanced technologies such as BIM, firms will see the need to increase collaboration among all project participants. More companies, in turn, will focus on forging new relationships fused by common workflows and technologies in order to operate under a more holistic approach that better serves the bottom line. According to a recent McGraw Hill SmartMarket report, the use of BIM by structural engineers is expected to double in the next few years. So the question is not if you should consider implementing BIM, but when are you going to. When moving to BIM, again, it is important to remember that it is more than a lateral move; it is a change in process too. Understanding the necessary steps involved when making the transition, and making the appropriate investments in consulting and technology, are crucial for a successful transition. Don’t view the transition to BIM as a necessary evil. Rather, approach this transformation in our industry with an open mind. In seeking new approaches and new tools to solve common project challenges, we can increase efficiency, improve the quality of work, and advance the design process overall. That’s when we can really start to see how BIM means better business.▪

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ood shrinks perpendicular to grain as it loses moisture, a well known phenomenon. Shrinkage magnitudes depend on the size of wood members, grain orientation, and moisture content. For typical conventional light-frame wood floor construction with solid sawn lumber, framing shrinkage due to wood drying can be on the order of 0.25 inch to 0.5 inch or more per floor. Engineered wood products are manufactured relatively dry compared to solid sawn lumber, and as a result have less shrinkage potential compared to solid sawn lumber framing. In addition to shrinkage, settling occurs as construction gaps between stacked wall components (studs, plates, floor sheathing, etc.) close over time. The magnitude of gapping settlement for light-frame wood construction is not

Wood-framed wall, typ. Engineered wood I-joists, typ.

Walkway deck

Steel tube column, typ.

Figure 1: Section of wood framed wall system showing deck framing with steel deck support columns.

well documented, but one study (Commins, STRUCTURE magazine, August 2007) found that light gauge steel framing had settlement of around 0.125 inch per floor. Settlement of conventional light-frame wood construction is assumed to be of similar magnitude. The amount of shrinkage and settling varies depending on initial moisture contents, species, and sizes of wood components used. In addition, other effects may play a role in building shortening. Compression of materials due to vertical gravity load also occurs, but typically this is of a lower magnitude than shrinkage and gapping effects and is considered negligible for this discussion. The gapping settlement described herein refers to that within the stacked wall framing components, and not to foundation settlement. Differential foundation settlement is also beyond the scope of discussion in this paper, but should be considered when applicable. Building codes require that shrinkage analysis be completed, for buildings three stories or greater in height, that shows shrinkage will not have any adverse effects (e.g. 2009 International Building Code (IBC) Section 2304.3.3). This type of evaluation should include adverse effects to drainage caused by deck back-slopes (toward building walls) resulting from framing shrinkage; however, such application is not explicitly named in the building codes and may be overlooked. Historically, decks have been required to slope, for drain purposes, ¼ inch per foot (2%) minimum (e.g. 1997 Uniform Building Code (UBC) Section 1402.3). Explicit requirements for deck drainage no longer exist in the IBC. Now, the 2009 IBC, Chapter 15 Section 1507, contains provisions for roof decks where the slope requirements are dependent on type of covering; however, a 2% minimum slope is still required for a number of different coverings. Further, IBC Section 1405.4 requires flashing to be installed to prevent moisture from entering walls or to redirect it to the exterior, with Section 1405.4.1 specifying that locations in which moisture can accumulate should be avoided, implying drainage should be directed away from building walls. This article examines a case study of multistory wood frame shrinkage and settlement causing exterior waterproof decks to slope back toward the exterior wall. In this case, the deck is supported on one side by a ledger at the wall framing rim board and by exterior steel columns on the other side (Figure 1). The steel column supports did not have the same shrinkage and settlement over time as the wall framing and, as a result, the differential led to back-sloping exterior decks. These backsloping decks concentrated rain runoff toward the wall and deck ledger area. Significant decay

STRUCTURE magazine

Structural PracticeS practical knowledge beyond the textbook

A Case Study

Multistory Wood Frame Shrinkage Effects on Exterior Deck Drainage By Zeno Martin, P.E., S.E. and Eric Anderson, P.E., S.E.

Zeno Martin, P.E., S.E. is a Senior Associate in the Seattle, Washington office of Wiss, Janney, Elstner Associates, Inc. and can be reached at zmartin@wje.com. Eric Anderson, P.E., S.E. is a Senior Associate in the Portland, Oregon annex office of Wiss, Janney, Elstner Associates, Inc. and can be reached at eanderson@wje.com.

The online version of this article contains references. Please visit www.STRUCTUREmag.org.

Figure 2: Deck ledger attached to the inner wood framed wall and outer steel posts. (Note: Project is under construction in photo.)

Figure 3: Deck framing supported by steel posts adjacent to the wood framed building wall creating a “fixed” deck condition. (Note: Project is under construction in photo.)

damage to the wood framed walls occurred when the detailing of the weather-resistive barrier and flashings could not resist the magnitude of resultant drainage to the wall from the deck. Flashing design defects were also at issue. However, the objective of this article is to raise awareness of the back-slope drainage problem, present the magnitudes of shrinkage and settlement observed, and to offer recommendations on how to prevent deck back-slope conditions from developing.

significant decay damage to the wood framed building walls. Moisture intrusion problems were manifested only a few years after construction was completed. Five years after construction was completed, comprehensive deck slope measurements were made of the top surface of the exterior walkway decks. Table

Case Study This multifamily residential building and deck has four stories of vertically stacked walls constructed of dimension lumber stud framing. Engineered wood I-joists were used for floor framing. A tube steel ledger was attached to the rim joist at the wood framed building wall for support of the exterior deck framing (Figure 2). Steel columns supported the outer edge of the deck. In some locations, deck support was also provided by steel columns on the inner deck edge (Figure 3). The building was constructed in the Willamette Valley in Oregon. The project consisted of multiple buildings constructed similarly, with exterior walkway decks surrounding the main entry perimeter areas (approximately 2/3 of the perimeter face parking areas). Deck back-slopes were observed to concentrate rain water toward the wall and deck ledger area, exacerbating water infiltration and leading to

1 summarizes results of deck slope measurements. Approximately half of the deck areas were constructed in accordance with Figures 1 and 2, where the deck ledger was attached to the rim joist such that the deck could rotate relatively freely toward the wall – a so-called “free” condition in Table 1. The other half of the decks were constructed

Table 1: Summary of Measured Deck Slopes.

Summary of Deck Slopes for: Free Ledger Condition Fixed Ledger Condition

Deck Slope (%)

Story

Measured Locations

Average

Minimum

Maximum

-2.38

-0.70

-2.50

-1.22

-0.50

-2.20

-0.81

-0.20

-1.60

-0.26

0.70

-0.90

-0.19

1.00

-1.10

-0.27

1.20

-1.60

Note: Negative slopes drain to building wall, positive slopes drain away from building wall.

Table 2: Summary of Difference between Free and Fixed Deck Slopes and Apparent Resultant Shrinkage.

Story

Apparent(2) Δ Deck Slope(1) average (%) Cumulative Shrinkage (in.) Story Shrinkage (in.)

2.11

1.14

0.58

1.03

0.56

0.26

0.55

0.30

(1) Difference between free and fixed measurements. (2) Assuming the measured fixed condition represents initial free condition.

STRUCTURE magazine

April 2012

Wood Posts The building in this case study was constructed with steel posts to provide outer edge deck support. The resultant shrinkage differential may have appeared more predictably obvious as a result. However, similar behavior has been observed by the authors for a multistory building constructed with exterior entry decks supported on wood posts at the outer edge (Figure 5, page 36). In the latter case, there was no observed resultant sheathing or framing damage, but ponding or accumulation of water on the decks near the wall was evident. Wood shrinkage parallel to grain is approximately 25 to 50 times less than shrinkage

perpendicular to grain. Thus, parallel to grain shrinkage is often considered negligible in comparison to perpendicular to grain shrinkage. In this respect, exterior wood deck post supports will not have the same shrinkage or settlement potential as a wood framed wall assembly with stacked sill and plate components (Figure 5). This type of exterior deck construction, therefore, may also require measures to avoid back-slopes induced by shrinkage differential problems. Conclusions The combination of shrinkage and settlement (i.e., compression of framing “gaps”)

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where the ledger was supported by a steel post adjacent to the building wall restricting inward deck rotation (Figure 3) – a so-called “fixed” condition in Table 1. The fixed deck areas with a steel support at the ledger serve as a control, in comparison to the free condition where the deck can more freely rotate at the ledger to rim joist connection. The fixed condition supports the deck such that settlement and shrinkage of wood framing has minimal influence on deck rotation. For the purpose of estimating shrinkage and settlement of wood framing, the fixed deck areas were assumed to represent the as-built slope of the decks and construction tolerances assumed to average out. Using these assumptions, Table 2 summarizes the difference between free and fixed deck slopes and the resultant apparent shrinkage of exterior building walls estimated by comparing these two conditions. The building’s wood shear wall system was constructed using shrinkage compensating devices at the overturning hold down locations. These devices ensure that the shear wall hold down system remains tight even after wood shrinkage or settlement occurs. In this case, the shrinkage take-up devices were found to be extended (Figure 4, page 36) confirming that shrinkage and settlement had occurred, assuming the take-up devices were originally installed tight. Unlike the shear walls, the exterior decks had no provision to ensure that proper drainage slope was maintained in the event wood frame shrinkage and settlement developed. In this instance, resultant deck back-sloping led to significant damage to the wood framed walls related to concentrated moisture intrusion at the deck attachment locations (Figure 4). A couple of other influential factors affecting the measured slope values should also be noted. Heavy rains reportedly occurred during original construction on this project, during the framing phase before building envelope enclosure. These conditions could have increased the moisture content of the framing (assuming no efforts were made at framing dry-out before envelope close-in), effectively increasing subsequent drying shrinkage. Also, resultant decay damage was severe and it is possible that a portion of the measured shrinkage and settlement was due to crushing of decayed wood material. These highlight some of the practical variables that influence the measured phenomena. These and other specific project details should be considered when interpreting these results toward broader application.

Figure 4: Typical shear wall hold down shrinkage take up device extended (arrow).

was estimated to average 0.38 inch per floor for the case study described. The observed magnitude of shrinkage and settlement corresponds reasonably well to the “conservative” recommendation of 0.36 inch per floor for this type of building per Commins (2007). As described, heavy rains during initial construction and resultant wood decay from moisture intrusion induced by deck back-slopes may have contributed to the relatively high magnitude of shrinkage and settlement observed in this case study. Another similar case examined by the authors (Figure 5) measured only approximately 0.125 to 0.20 inch of combined shrinkage and settlement per floor. Exterior decks supported by multistory wood framed walls on their inner edge and exterior vertical posts (or walls) on the outer edge are prone to shrinkage differentials that can create a back-sloping condition. In stacked multistory construction, the effect of shrinkage is cumulative, and the magnitudes can become significant even for three or four story construction. While this phenomenon is not new, the authors have seen little attention paid to the matter in industry literature with respect to mitigating this effect and its potential to cause accumulated puddling and resultant damage.

Recommendations Designers should be aware that multistory wood framed walls supporting exterior decks are prone to shrinkage and settlement differentials that can create a back-sloping condition and potential moisture intrusion problems. It is recommended that a reasonable magnitude of shrinkage and settlement be anticipated

Figure 5: Wood post deck support columns.

and accommodated in the design of the deck framing system and/or drainage detailing. If preemptive sloping to account for shrinkage and settlement is not specified to ensure resultant drainage is maintained after framing shrinkage has occurred, then the designer should consider provisions for deck slope adjustability and/or drainage near the deck to wall interface to avoid potential moisture intrusion problems into exterior walls. Settlement and Shrinkage Magnitudes The magnitude of shrinkage and settlement depends on a number of variables but, for common conventional light-frame wood construction, the following values are recommended for design: • 0.25 inch per floor with engineered wood I-joist and solid sawn lumber wall framing when products are installed and kept relatively dry (at or below 19% moisture content) during construction • 0.375 to 0.5 inch per floor with engineered wood I-joist and solid sawn lumber wall framing when products are installed and/or allowed to get relatively wet (above 19% moisture content) during construction • 0.5 inch to 1.0 inch per floor with solid sawn joists depending on moisture contents of products during construction These recommended design shrinkage and settlement values are similar to those reported by Commins (2007) and represent a somewhat conservative, but not unrealistic, condition as shown by this case study.

STRUCTURE magazine

April 2012

Design for Adjustment To maintain desired deck slopes after shrinkage and settlement has occurred, provisions could be made to install an adjustable post or post base. These provisions would need to accommodate cumulative settlement at each story. Alternatively, a leveling bolt adjustment could be installed at the deck to exterior post attachment, or at the deck to building connection at each level. Caution would be necessary to ensure these structural adjustments would not damage the building or flashing details while adjustments are made. Design for Drainage Alternatively, provisions could be made to gap the deck near the building wall to allow for drainage. APA – The Engineered Wood Association provides details for a gapped ledger design when attaching the ledger to a solid sawn rim joist (this detail is not recommended for engineered rim joists). Alternatively, the deck membrane, or surface, can be gapped near the building wall to allow for drainage. In this approach, the ledger would be flashed. In either design, drainage is allowed to occur near the deck to wall interface, and flashing would be necessary to protect key connection details and direct ponding moisture to a gutter.▪

This article was previously published in Wood Design Focus, Fall 2010. It is reprinted with permission.

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UT’s New Hackerman Experimental Science Building Inspires Teamwork Part 2

By Michael Brack, P.E.

The 300-foot-long colonnade required special attention to detail to relieve thermal expansion/contraction stresses. Courtesy of Tom Bonner, 2011.

he 300,000-square-foot Norman Hackerman Building replaces the old Experimental Sciences Building (ESB) on the campus of the University of Texas (UT) at Austin. Part 1, in the September 2011 issue of STRUCTURE® provided general information about the project and discussed the structural system selection and schedule challenges. This article describes some of the additional challenges encountered and the innovative solutions that the design and construction team developed. Key team members include CO Architects, Taniguchi Architects, The Beck Group and Datum Gojer Engineers.

Site Challenges A 40-foot-deep hole was required – 20 feet deeper than the original ESB basement – to sink the new building into the ground. This strategy allowed UT to maximize its use of the site without building a structure so tall that it would overwhelm the site and surrounding campus scale. Of particular concern related to the large, deep hole was the adjacency of several buildings and utilities, most critically the Nano-Science Technology (NST) building directly to the north. The NST had been designed and built a few years before as the first step in replacing the old ESB. The decision to build the new Hackerman building right up against the NST, combined with the decision to sink the new building as deep as possible, created the risk of undermining the seven-story tall NST. The new excavation would be 4 to 10 feet deeper than the skin friction zone of the NST piers, and 2 to 4 feet deeper than the bottoms of the NST piers. Datum Gojer worked together with The Beck Group to develop a sequence of excavation and underpinning to keep the NST stable. The excavation for Hackerman was taken down to a level equal to the top of the skin friction zone of the piers. Next, a low-overhead drill rig was used to install deeper 30-inch-diameter underpinning piers on either side of each existing pier. This solution STRUCTURE magazine

The 40-foot-deep excavation for the new NHB was surrounded by buildings and campus roads. Courtesy of The Beck Group.

was helped greatly by the fact that a deep basement wall exists along the south face of the NST, allowing vertical loads from columns above to be redistributed without retrofitting the building superstructure. After the underpinning piers were installed, excavation was allowed to continue as deep as needed for the new building. During the demolition, excavation, and underpinning operations, vibration sensors were set up in adjacent buildings to monitor construction-induced vibrations in these critical facilities. The sensors would send an alarm to the contractor’s cell phones when the threshold levels were breached, and construction activity would be modified or deferred to a less sensitive time.

Basement and Earth Pressure Challenges Some of the mechanical systems were strategically located in the windowless basement. The space was double height to accommodate two levels of mechanical space separated by a catwalk. This meant that the basement columns (with the heaviest loads) had 26-foot unbraced lengths, compared to 14-foot in the rest of the building. The double-story height of the deep basement, along with the need for an expansion joint near the middle of the long building, created a very large bracing force requirement at the first elevated level, due to lateral earth pressures. The delivery of this large force through the basement walls, into the floor framing and back into the perpendicular basement walls, was tracked carefully to ensure an adequate design and load path. The slab reinforcing was increased to provide more diaphragm shear strength, and girders were checked for combined compression plus bending, with axial forces derived from the earth pressures.

April 2012

The detail includes stiffened steel angle haunches connected to embed in the column. The precast shelves rest on shims on the haunches for erection. On top of the precast shelf is either a welded connection (fixed condition) or a bolted connection with slotted holes (slip condition). Shelf angle collars were installed directly above the precast shelves, to support the masonry wraps around the columns at the slip side. These final details were carefully developed among the architectural, structural and construction team, including the masonry subcontractor, to ensure constructability and tolerance. The design and layout of the random masonry pilasters was an iterative effort of teamwork and close coordination between the architect and structural engineer.

Other Challenges

Detail of the “slip” and “fixed” support conditions for the precast shelves. A shelf angle attached to the column allows the masonry to float above the slip side. Courtesy of Datum Engineers.

The bottoms of the deepest walls were trenched and socketed 3 feet into rock to keep the large lateral forces from buckling the basement floor slab.

Colonnade Among the interesting aspects of the design, both architecturally and structurally, is the two-story colonnade which wraps around most of the south and east façade, forming deep porches and two-story lobby spaces. The colonnade serves to humanize the scale of the building, and prevent the visual monotony that can happen in a large rectangular building with a strong module. Architecturally, the colonnade appears to be a random assortment of solids and voids formed by masonry pilasters. A 14-inch-deep precast concrete shelf provides a horizontal boundary between the upper and lower parts of the colonnade, allowing the random pilaster pattern to alternate above and below it. Cast-in-place architectural concrete was considered for the shelves, but would have created a construction sequence problem, and was considered to be less reliable from an appearance standpoint, in addition to being more expensive. The precast shelves fit with the design concept of a masonry colonnade. The colonnade creates double-height columns up to 39½ feet tall (two 16-foot stories plus a 7½-foot drop at the east end of the first floor to work with the sloping site). Because the architect desired slender columns, these columns were made rectangular (24 x 29 inches) with the narrow edge facing out, and the architect worked them into the apparently random pattern of the masonry pilasters. Because the colonnade and precast shelves are exposed to the elements on the south face of the building, there was concern about the expansion and contraction that would occur with 100-degree temperature changes over the course of a year. Specifically, the concern was that the buildup of thermal contraction forces over the 300-foot length could cause a brittle pull-out failure of the connections of the precast shelves to the columns. To prevent this, a plan was devised to provide for slip along the longitudinal axis of the precast shelves, at every other bay. STRUCTURE magazine

Although the Hackerman building is very large and regular, there were many opportunities for challenges throughout the project. These included: • A concrete staircase that appears to spiral up through the building. The stair engages each floor on the south end, as well as a shear wall in the northeast corner and an intermediate beam in the northwest corner. • A massive 15,000 square foot solar water heater array on the roof of the penthouse. The array required its own grillage of steel tube framing to suspend it above the roof to provide access for future roofing maintenance during the life of the building. • A light shade canopy around the top of the building, which cantilevers up to 24 feet in each direction at the corner of the building. • A series of concrete beams that are offset 2 feet vertically at midspan to create room for a massive 48- x 144-inch lab exhaust air duct. The 2-foot offset creates a complicated knuckle joint which required an intense layout of reinforcing to work with the change in direction of forces in the rebar. • 48- x 60-inch post-tensioned transfer girders spanning 48 feet to carry 5 levels of building above the first-floor auditorium. • This was one of the structural firm’s first Revit projects (started in 2006). They learned a great deal during the project; however it went relatively smoothly thanks in part to the fact that the client, CO Architects, had produced two similar large lab projects like this one before.

Conclusion Many projects have unique challenges, some more monumental than others. But the most rewarding thing is tackling those challenges together as a team. This project was a huge success because of the teamwork among the owner, architects, engineers, and construction manager, and their willingness to collaborate on solutions.▪

Michael Brack, P.E. is President of Datum Engineers, Inc., a Texasbased structural engineering firm. Credit for this fantastic project is rightfully shared with his in-house team of Jeremy Klahorst, P.E., Igor Teplitskiy, P.E., Emily Cleland, and Kelly Thibodeaux, as well as the good people of CO Architects, Taniguchi Architects, The Beck Group, and The University of Texas. Michael can be reached at michaelb@datumengineers.com.

April 2012

Condition Assessment and Repair An Existing Composite Concrete Slab and Steel Beam Framed Parking Structure Part 1 By D. Matthew Stuart, P.E., S.E., F. ASCE, SECB

n the fall of 2010, a property management company retained Pennoni Associates Inc. to conduct a condition assessment of a large sub-grade parking garage and loading dock located in Center City, Philadelphia. The garage included only two levels of parking beneath two adjacent high-rise oﬃce towers; however, the overall footprint of the parking facility involved an entire city block, for a total of over 500 parking spaces. The upper parking and loading dock area consisted of varying thicknesses of a reinforced normal weight and lightweight concrete slab supported by galvanized composite metal deck, which in turn was supported by composite steel wide flange beams. The lower level of the garage was a concrete slab on grade. Constructed during the 1980s, the structure was exhibiting signs of significant deterioration of the wearing surface and the supporting composite metal deck. Establishing the extent and cause of the deterioration, and identifying appropriate repairs, required a thorough condition assessment of all of the sub-grade loading docks, parking areas and ramps, including visual observations as well as chain dragging of the exposed wear surfaces to determine the presence of sub-surface delaminations. The assessment also involved obtaining core samples for conducting petrographic analysis of the existing concrete and independently testing it for the presence of carbonation and chloride content. Additional cores exposed a number of headed steel studs associated with the composite steel beams to facilitate detection of any deterioration.

Typical Surface Spalling and Cracking.

Observations and Material Testing The condition assessment revealed isolated but widespread and significant concrete surface cracking, spalling and sub-surface delamination. In addition, the majority of the framed areas of the sub-grade parking facility exhibited widespread, significant deterioration of the galvanized composite metal deck. Deterioration was also occurring at the exposed structural support steel associated

Typical Composite Metal Deck Corrosion.

Composite Concrete Slab and Galvanized Metal Deck Summary Table.

Location

Concrete Slab Thickness above the Metal Deck

Galvanized Composite Metal Deck Depth

Total Slab and Deck Thickness

West of Grid Line 11 (Lightweight Concrete) Parking Garage

3¼ inches

2 inches

5¼ inches

Loading Dock

6 inches

2 inches

8 inches

East of Grid Line 11 (Normal weight Concrete) Parking Garage

4½ inches

2 inches

6½ inches

Loading Dock

6 inches

2 inches

8 inches

STRUCTURE magazine

April 2012

Deteriorated Headed Stud.

Concrete Core Location Plan.

with the expansion joints and trench drains. One interesting facet of the investigation was that very little of the concrete wear surface deterioration occurred directly above an area of corroded metal deck below. This became evident from overlaying plans of the two damage types. A total of six concrete core samples of the slab, four in the parking and ramp areas and two in the loading dock area, were obtained for the purposes of conducting a petrographic analysis of the concrete. X-rays of the slab at the proposed core locations, which were all at or in the immediate vicinity of exposed deteriorated metal deck, assured that no electrical conduits or significant internal reinforcement would be damaged during the coring operation. Core sample #5 came from an area of the driving aisle that had been painted, while core samples #1 and #2 came from an area of the driving aisle that had been coated with an epoxy topping. The petrographic analysis indicated that the concrete was airentrained (except at core sample #1), included natural sand fine aggregate and manufactured expanded clay lightweight coarse aggregate (except at core sample #4), and exhibited moderately hard paste, very few unhydrated particles, a good paste-to-coarseaggregate ratio, no ettringite deposits in the water voids, and no micro-cracking. Drilled powder samples were obtained from the upper one inch of the exposed wear surface adjacent to each core location except #5, which came from the bottom one inch of the core sample that had been in direct contact with deteriorated metal deck. Watersoluble chloride tests of the powder samples indicated that the chloride content, per mass of concrete, was as high as 0.503% (#2) in the upper wear surface and as high as 0.171% (#5) at the bottom of the concrete slab. The average chloride content of the surface samples (#1 through #4 and # 6) was approximately 0.27%. As a result of the chloride content tests, additional cores from the concrete slab were obtained in order to assess the condition of the

STRUCTURE magazine

Carbonation Test Results at a Concrete Core Sample.

headed studs associated with the composite steel beams. X-rays of the slab at the proposed core locations again assured that no electrical conduits would be damaged during the procedure and indicated the specific location of the headed studs. A total of four headed studs were exposed for visual observation in the vicinity of two of the original test cores (#2 and #5) and near other areas of deteriorated metal deck. A core was also removed at a stud located directly below an area of the slab that exhibited surface spalling. Field tests for the presence of carbonation in the exposed concrete located within wear surface spalls adjacent to the core sample locations using phenolphthalein were positive for the presence of carbonated concrete. Additional carbonation tests confirmed the presence of carbonated concrete in the upper 1/8 inch of the wear surface of core samples #2 and #5.▪

D. Matthew Stuart, P.E., S.E., F. ASCE, SECB (MStuart@Pennoni.com), is the Structural Division Manager at Pennoni Associates Inc. in Philadelphia, Pennsylvania. He has 35 years of experience as a practicing structural engineer and is actively licensed in 21 states.

Part 2 of this article will appear in a future issue of STRUCTURE magazine, and will present a discussion and assessment of the observations and material testing described above. Part 3 will address the resulting repairs.

April 2012

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Steel Companies Driven by Customer Demands By Larry Kahaner

ruce Bates, Founder and President of RISA Technologies, LLC. (www.risatech.com) in Foothill Ranch, California, sums up what fabricators, suppliers and those involved with steel-related software are saying: “I think the general consensus is that we’ve hit bottom. We’ve started recovering, but nobody’s really where they want to be. Things seems to be generally improving at a slow pace.” Amid this slow and steady climb, steel-related companies continue to roll out new products and services and improve current offerings. “Our newest product is one we released last year as part of our RISAConnection program, says Bates. “What’s new about it are our releases of the core products, namely RISA-3D and RISAFloor. We’ll include full integration with RISAConnection. In other words, you’ll be able to specify connections inside of RISA-3D and RISAFloor. RISAConnection will do the detailing and design code compliance calculations, etc., and pass that information back into either RISA-3D or RISAFloor. It’s coming out this month [March].” He says that the new products are the result of customer demand. “I like to say that I haven’t had an original idea in ten years. I just do what my clients tell me to do and that seems to work out. Everything we do is driven by our customers.” (See ad on page 75; visit Booth #721 at the NASCC.) enry Gallart, President of SidePlate Systems, Inc. (www.sideplate.com) located in Laguna Hills, California, offers specialized steel connection designs for moment frames that are constructed of standard steel plates and fillet welds. “Because SidePlate is much stiffer than conventional moment connections, lighter beams and columns–and often fewer lateral connections–can be used to achieve the required structural performance,” says Gallart. “We are structural engineers, and our services include design assistance to the engineers of record, calculations and drawings for the SidePlate connections on the project, and construction phase services to verify conformance with our drawings.” On current improvements, Gallart says: “The connection plates and fillet welds sizes are lighter and smaller than before, and we changed the construction method from shop-welded beam stubs and a fieldwelded CJP link beam construction method to a full-length beam with four horizontal position fillet welds. These changes resulted in up to a 50 percent reduction in shop labor than before, eliminated all CJP welding and all UT inspections, and opened up markets beyond just seismic and progressive collapse. Another big change is that our license fee is now typically paid by the steel fabricator, so

STRUCTURE magazine

engineers get all of our design assistance, drawings, and calculations for free.” The company is excited about the growth in wind power, he says. “Like most companies, we are constantly trying to increase efficiency and improve our services. Refining the SidePlate geometry, making it easier and cheaper to fabricate and erect, and making it easier to specify have always been a priority. These recent changes were essential in order for SidePlate to be able to save money in the ‘wind world.’ We’re very excited about what SidePlate offers today, and the feedback from engineers and fabricators, not to mention the company’s growth, tells us we’re doing something right.” (Visit Booth #408 at the NASCC.) t Toronto-based Cast Connex Corporation (www.castconnex.com), CEO Carlos de Oliveira says his company offers both ‘offthe-shelf ’ connection solutions and custom cast components for a large range of steel connection solutions. These include Cast ConneX Universal Pin Connectors which are aesthetic, clevis-type end fittings for round HSS and pipe members that are intended for use in Architecturally Exposed Structural Steel (AESS); Cast ConneX High-Strength Connectors which are brace-end connectors for use in Special and Ordinary Concentrically Braced Frames (SCBF/OCBF) situated in seismically active zones; and Cast ConneX Scorpion Yielding Brace System, a highly ductile yielding brace system for use in braced frames in high-demand seismic zones or for the retrofit of deficient building structures. “Our Universal Pin Connectors range in sizes to fit round HSS and pipe from 4 inches in diameter up to 16 inches in diameter. Each size of connector has been designed to provide sleek, streamlined, organically-curving geometry from all viewing angles and are suitable for all thicknesses of HSS or pipe in their respective diameters,” says de Oliveira. “No longer does it require a fabricator with extensive experience in AESS to produce elegant connections. Using Cast ConneX Universal Pin Connectors, all that is required between the UPC and the tube is a simple

April 2012

groove weld to provide an ultra-smooth finished appearance sufficient to please the most demanding architect or owner. Each Universal Pin Connector is supplied with the appropriately sized carbon-steel pin and stainless steel, electro-polished washers, cap plates and set screws to dramatically set off the connection.” What’s the biggest complaint de Oliveira hears from customers during these challenging economic times? “They wish they had known about our products earlier.” (Visit Booth #511 at the NASCC.) or customers of CSC, Inc. (www.cscworld.com), trying times are being dealt with by investment in the right tools. “The general feeling is that while the business climate is improving, it is still important to invest in productivity tools to be competitive enough to win the work that is available,” says Vice President Stuart Broome. The company has over 35 years experience in developing its structural calculation software Tedds, and its steel building design software, Fastrak. “We recently launched a brand new BIM integration tool, CSC Integrator, which provides seamless integration between Fastrak models and Autodesk Revit Structure,” Broome says. “Ultimately we specialize in developing code-based structural design solutions. This means that rather than adding design post processors on to a frame analysis program, we build our software from the ground up around the requirements of a design code, such as AISC360 in the case of Fastrak.” CSC has recently formed a new strategic business relationship with Autodesk’s Architecture, Engineering and Construction (AEC) Division. As part of this new relationship, CSC and Autodesk will continued on page 47

Cast ConneX ® Universal Pin Connectors™ employed at both ends of the architecturally exposed, inclined steel columns supporting a roof overhang at the New Jersey Air National Guard Operations and Training Facility, Egg Harbor, NJ. Courtesy of Carlos de Oliveira, Cast Connex Corporation.

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April 2012

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provide customers with integrated solutions that support more effiStylianou adds: “In 2011, we also released a new product, S-PAD, cient structural engineering workflow for BIM, says Broome. (Visit specifically for the small consulting engineering. S-PAD is a standBooth #209 at the NASCC.) alone steel design program which has the same design code coverage ustomers of IES, Inc. (www.iesweb.com) in Bozeman, and optimization capabilities as S-STEEL but with a low entry level Montana are also investing in tools that keep them com- pricing.” (Visit Booth #620 at the NASCC.) petitive, says Engineer and Developer Terry Kubat. “The s a nationwide supplier of Flexible to the Finish steel joists economic hardships from the last few years have hit our clients very and metal decking, serving non-residential steel construchard. We have seen many firms go out of business or split up. But tion, New Millennium Building Systems in Butler, Indiana the good news is that engineering firms are investing in technology in (www.newmill.com) considers manufacturing flexibility as their anticipation of the turn-around, and former customers are contacting competitive advantage, according to General Manager Art Ullom. IES from their new offices and others are upgrading for the first time “Based on this advantage, our value proposition to the structural steel in three or four years. The bottom line is that the money is flowing marketplace is that we are together building a better steel experience. significantly more than it was in 2009 or 2010.” We’re helping our customers recognize the joist and metal decking VisualAnalysis 9.0 is the company’s newest release of its flagship discipline for what it is – vital to the development of the structural product. “This general-purpose design tool is faster, easier, more stable steel package, which in turn impacts the cost performance of the and more accurate than any prior version. Our long-term customers total project.” are praising the continued improvements that help them save time Ullom notes that the cost side is getting the most attention in today’s and solve tougher problems,” says Kubat. “VisualAnalysis 9.0 is now economy. “This is good for us, because while the price of our joists still undergoing a strict validation process that automatically checks the matters to construction decision makers, their expectations for value accuracy of analysis, and design checks against nearly 1000 ‘test cases’ delivery have increased. Construction leaders are more interested now prior to every single update. This is just one way IES is improving in the impact a joist and metal deck partner can bring to a project by quality in our tools.” way of better-engineered and better-planned cost avoidance – colKubat echoes others who rely on customer feedback to improve their laboration that will greatly benefit a project owner.” products. “Computer hardware, software, and customer expectations Castellated and cellular beams are a relatively new offering for the never stand still. Our products must be nimble enough to meet the company, and they recently opened a plant in Ohio that is dedicated demands of the latest BIM and mobile revolutions that are taking to the engineering and production of those products. “This is a place. IES is simply listening to customer requests in our efforts to add features or products.” nother person listening to customer desires is Marinos Stylianou, CEO of S-Frame Software (www.s-frame.com) in Guilford, Connecticut. “Our customers Structural Software Designed for Your Success demand incremental improvements to our current products in terms of new features that allow them to tackle new classes of problems and improved connectivity with BIM and automation that increases their productivity,” he says. “To this end, the latest enhancements of S-FRAME R10 focus particularly on supporting the trend of building codes and engineering practice towards more advanced forms of dynamic analysis, especially for seismic loading. A parallel trend is towards larger and more complex models, due to more prevalent • Sketch, Generate, Import or Copy & • Easy to Learn and Use use of ‘shell’ finite elements (FEs) and the Paste Models and Loads • Analyze “Just about Anything!” influence of BIM. Such models present • Professional, Customizable Reports • Design: Steel, Wood, Concrete, challenges both in terms of organiza• Building Code Support: IBC, ASCE 7, etc. Aluminum, and Cold-Formed tion and processing. To assist our users, S-FRAME R10 includes enhanced autoVisit www.iesweb.com IES, Inc matic meshing algorithms and processing 519 E Babcock St. power by leveraging the potential of the Download Your Free Bozeman, MT 59715 800-707-0816 30-day Trial Today new 64-bit operating systems and multiinfo@iesweb.com core processors.”

April 2012

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“The construction sector is still pretty soft, but we’re seeing some movement. . . The recovery is definitely going on, but it’s slow and steady. We’re not going to see a boom any time soon, but there’s activity out there, and it’s good activity. We’re not seeing a lot of projects that aren’t real, like in the past where we saw a lot of speculative work.” product that offers architects and engineers an alternative structural approach that supports an open and esthetic design with long-span applications, and often with cost advantages,” Ullom says. (Visit Booth #809 at the NASCC.) t JMC Steel Group (www.jmcsteelgroup.com) in Chicago (its two divisions are Atlas Tube and Wheatland Tube), structural engineer Brad Fletcher says that the company’s goal is to advance the marketplace and further the growth of hollow structural sections. “We can now offer what we refer to as ‘jumbo hollow structural sections.’ These are larger than what is currently made here in North America. These are made offshore in Japan, and we are the exclusive distributor. We currently have the largest size range in the industry and this expands our range even further.” The Jumbo HSS sizes range from 18-inch square to 22-inch square and up to .875inch wall thickness. “Obviously, in long span situations it’s going be much more efficient with higher strength-to-weight ratios. There’s less surface area, so if you’re looking at coatings, fireproofing, there’s less to apply to the member.” He adds: “The connections for hollow structural sections have become simpler, and there’s definitely more information available about them in the marketplace. In the past, the connections were a little bit of a mystery. Now, people are very comfortable with them.” As for business, Fletcher notes: “The construction sector is still pretty soft, but we’re seeing some movement. We’ve got a pretty good order book. The recovery is definitely going on, but it’s slow and steady. We’re not going to see a boom any time soon, but there’s activity out there and it’s good activity. We’re not seeing a lot of projects that aren’t real, like in the past where we saw a lot of speculative work.” (See ad on page 50. Visit Booth #330 at the NASCC.) ast October, Computers & Structures, Inc. (www.csiberkeley.com) rolled out a product called CSI Bridge which was part of SAP 2000, according to Rob Tovani, Director of Verification, Validation and Training. “We pulled out the bridge module and made it a stand-alone program called CSI Bridge. It’s actually been very popular, especially in this economy, because infrastructure and transportation has been a pretty hot sector. We have been pretty busy with that product.” He says that SEs like the standalone module. “The criteria has changed for designing bridges, and it has forced engineers to use full

STRUCTURE magazine

three-dimensional analysis tools. In the past, they could get away with something a little less rigorous.” Tovani says that the bridge program and the global economy have helped the company get through the current tough financial environment. “Business has been pretty good actually. I think a big part of it is the CSI Bridge program and the fact that we sell throughout the world. We’re finding increased sales in India, for instance, and that helps the bottom line.” The other helpful factor is a substantial overhaul of their ETABS program. “It’s going to be released soon and we’re very excited about it.” He adds that CSI has recently became ISO compliant. “Everything we do, from design to support, has been improved by going through the ISO process.” (See ad on page 76.) &S Galvanizing (www.hotdipgalvanizing.com), headquartered in Columbus, Ohio, has been in business for over 100 years in Europe and 30 years in the United States, says Terry Wolfe, National VP Marketing & Sales. “We are a hot dip galvanizing company and our main job is to protect steel from corrosion. We offer value-added services that you will not find at all galvanizing companies. For example, we can do small items like bolts and fasteners, and we also have some of the largest galvanizing kettles in the country and can do structural steel beams up to 88 feet. We offer our exclusive COLORZINQ system of wet paint or powder coat over galvanizing. We have our own trucks and tractor trailers, and offer just-in-time delivery with no surcharges or fees. We are ISO certified and have a NACE Level 3 inspector working with us and for the customer.” Wolfe says they are offering a new galvanizing system from their parent company Hill & Smith Holding . “ZONEGUARD is a steel barrier system that is all hot dip galvanized and can be purchased or leased. In many cases, customers can have up to 750 feet to a job site, per truck, in 24 hours. This compares to days of waiting for only 100 feet per truck with a standard concrete barrier. This product complements the many highway and bridge projects with which we are involved.” As for the overall view of the economy, Wolfe says, “Some areas are slower coming out of the slump, but we are hearing positive responses in an industry that has seen saw so many lows in the past three years.” (See ad on page 52. Visit Booth #915 at the NASCC.) ob Madsen, President of Devco, Software, Inc. (www.devcosoftware.com) in Corvallis, Oregon, sees improvement, too. “Generally our customers are optimistic. continued on page 51

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and everything else–and the Passport is an example of that. We also have another program called the Enterprise License Subscription, which basically takes that Passport model and extends it to absolutely everything that Bentley makes.” Roberts says that both of these programs are unique in the industry. “Users really appreciate that approach to accessing particular software technology so that they don’t have to worry about ‘If I buy it now to use it on this project, and I don’t need it for another six months, is it worth paying for?’ That’s not even a question anymore because it’s in the Passport.” In October, Bentley released Structural Synchronizer View, that allows engineers to explore 3D structural models created with Structural Synchronizer V8 from anywhere using an iPad, iPhone or iPod Touch. Says Roberts: “You can navigate as you would on an iPad, interrogate the data, answer questions. It’s a free app.” (See ad on page 3; visit Booth #321 at the NASCC.) eroy Emkin, Founder and Co-Director of the CASE Center in Atlanta (www.gtstrudl.gatech.edu), says that GT STRUDL – its Structural Design & Analysis software programs for Architectural, Engineering-Construction (AEC), CAE/CAD, utilities, offshore, industrial, nuclear and civil works – continues to be the product of choice for the nuclear industry with civil engineering structures. “We can handle, for example, models on the order of 40,000 joints, which is not that great, but 40,000 joints and you have to complete 7,000 modes to do earthquake analysis is mindboggling.” He says that the mega-computing power offered by GTSTRUDL

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Business has been improving steadily and we’ve seen that reflected in the sales of our programs.” The company offers software for the design of cold-formed steel framing members, specifically cee’s, zee’s and channel shapes. “All of our software is designed by engineers for engineers, so the input and output is intuitive with an appropriate level of input and output for the type of problem being solved. The newest version of our software includes the latest code requirements. There have been significant changes in the cold-formed steel codes recently, so it is important for engineers to be up to date,” says Madsen. He explains that previous versions of the cold-formed steel codes did not require calculation of distortional buckling strength of cee and zee shapes. Current codes do. “If engineers are unaware of these new requirements, then their designs could be non code-compliant,” says Madsen, who adds: “The best thing about our software is that we probably use it ourselves more than anybody else. We are design engineers first and we develop software to meet certain needs in our work.” an Spackman, Product Develop Manager for Cored Wires U.S. at The ESAB Group, Inc. in Hanover, Pennsylvania (www.esabna.com), says that with the continuing shortage of skilled welders the company keeps rolling out new products to help mitigate this problem. “Our Atom Arc Acclaim line is a low-hydrogen stick welder designed to help less experienced welders pass their test, weld easier, get up to speed quicker and help owners become more profitable,” he says. Another area of growth is in seismic certified products. “We have a line of products that are seismic certified with the D1.8 seismic supplement welding code. These are primarily flux-cored wires, but also include submerged arc wires and flux combinations.” These seismic products have been under continuous development since 2010, and the company will soon introduce a catalog for ‘demand critical seismic certified products’ which will include an introduction to seismic codes, certified products, data sheets and test results. “We’ve noticed that customers are asking for seismic products even though they are not in a seismically active area,” says Spackman. “Some areas are putting in seismic requirements regardless of their geographic area.” (See ad on page 54. Visit Booth #615 at the NASCC.) t Bentley Systems, Incorporated (www.bentley.com), Huw Roberts, Global Marketing Director – Building and Structural, says that their Structural Passport offering continues to be well received by customers who can buy the software they need and not be forced to buy what they don’t need. “One of the things that we’ve recognized at Bentley is that about 70 percent of our users are in a continuous subscription relationship with us. That’s great for us and them because you’re always getting support and updates and latest and greatest

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April 2012

is being spurred by increasing rigorous standards. “The profession is moving in a direction now which requires engineers to perform not only the geometric analysis. Engineers are making a horrible mistake if they think that they can get an acceptable solution in any way other than a rigorous nominee of second-order analysis. All the approximate methods are just totally unreliable, except in the most academic of problems – and I don’t know many engineers who are solving academic problems.” The company plans to soon introduce its new GT STRUDL version 32, which Emkin says will offer significant improvements in the base plate analysis and design feature of GT STRUDL. “In heavy industries, especially power and nuclear, there could be tens of thousands of base plate analyses that have to be done. All of them require non-linear analysis. All of them require automatic meshing at the base plate and the steel shapes connected to the plate. There’s some significant improvements being added to our base plate processor in version 32.” “We’re getting a lot of action and a lot of demands in connection with companies involved in nuclear. It’s looking good from our perspective. One of the things I’m seeing, especially as a result of what occurred at the Fukushima nuclear power plant, is a tightening of standards and an interest in extreme high quality engineering,” says Emkin. (Visit Booth #126 at the NASCC.) ▪

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how did you do that?

From ExpEriEncE

Punching Shear in Thin Foundations By Dan Mazzei, P.E.

n 2010, Wallace Engineering (Tulsa, OK) was asked to perform the structural engineering for a 137,000 square foot, single story commercial building in Puerto Rico. Load conditions at this site are a combination of the 145 mph winds found in Florida, California level seismic loads, soft site class E soils found in the Carolina coastal areas, and a minimum live load of 40 psf for low slope roofs. The structure was a steel bearing frame, supported laterally by precast shear walls on shallow spread and strip footings, with a polished concrete slab interior floor surface. Additionally, the geotechnical engineer had limited footing bearing depths to a maximum of 18 inches below grade. This maximum restriction was based on the geotechnical engineer’s assumption that a certain thickness of engineered fill was required to span over a layer of soft soils below the building’s footprint. Understanding the more costly engineering and detailing that would be required to accommodate this limit, Wallace Engineering first attempted to persuade the geotechnical engineer to reconsider his conclusions. Initial attempts were unsuccessful in getting the recommendations changed, and the analysis and design began. Additionally, the owner required that the interior floor be a crack-free polished concrete slab, which limited the top of footing elevation to 6 inches below finished floor and provided only 12 inches of depth for the footing. The maximum ultimate gravity load was 220 kips. Normally, a spread footing could be made as wide and thick as required to support this level of ultimate load. However, the maximum bearing depth restriction prevented the use of a thicker footing. Instead, the footing was reinforced so that it could support the shear requirements detailed in ACI 318-08 11.11.2.1 and ACI 318-08 11.11.1.2, as well as the tension forces from wind uplift loads illustrated in ASCE 7-05 Figure 6-6. The procedure used to satisfy the design requirements of the footing was as follows: A. Check base plate to support the ultimate gravity load. B. Check punching shear capacity of the thin footing per ACI 318 15.5. C. Determine increased punching shear capacity from raising concrete compressive strength. D. Use flexural theory to size a rigid base plate that would justify increasing the loaded area on the footing from half the distance between the face of the column and the edge of the base plate, per ACI 318 15.4.2.C, to the full width of the base plate. E. Design a reinforced shear head, per ACI 318 11.12.3, within the footing to distribute the gravity loads sufficiently throughout the footing to further increase the effective punching shear capacity. Then, verify the flexural capacity of the portion of the footing surrounding the shear head, per ACI 318 15.4, for the ultimate gravity load. (Note: This solution permits the use of a typical steel base plate) Once the shear head and footing are properly designed for gravity loads, the footing must then be checked for both global uplift and also flexure (again per ACI 318 15.4) due to its size. Lastly, the anchor bolt

group at the column must be sized, and the reinforcing ties properly arranged and considered to prevent ACI 318 Appendix D pullout. Items A-E are explained in more detail below. Also, it should be noted that, to set up the rigid base plate calculation, the base plate bearing calculation is described in detail. This may seem redundant but is useful in fully understanding the concepts used during the later bending check. A. Check bearing capacity of base-plate to support the ultimate gravity load: • Pultimate = 220 kips (after live load reduction per IBC 1607.11.2.1) • f 'c = concrete compressive strength = 3500 psi • A1 = width and length of square base plate (Figure 1, page 56) • A2 = area of concrete below plate (Wallace Engineering uses this size unless smaller) = (24 in.)(24 in.) = 576 in.2 • Base plate supports HSS 8x8 column and has (4) anchor bolts with 1½-inch clear from the edge of the base plate to centerline of bolt. • Per equation J8-2 of AISC 13th Edition, the limit state of concrete crushing is: Pp = (0.85f 'cA1)(A2/A1)1/2 < 1.7f 'cA1 Where 0.85f 'cA1 = Bearing strength on concrete per ACI 318 10.14.1 when the supporting area is not wider than the base plate. (A2/A1)1/2 = Permitted increase when the loaded area of concrete is wider on all sides of base plate because the loaded area is confined by surrounding concrete (again, the total increase must be < 2 per ACI 318) 1.7f 'cA1 = Upper limit so that increase from (A2/A1)1/2 is less than 2, per ACI 318 (i.e. (2)(.85) = 1.7) In the absence of code provision, conservatively use  = .6 per AISC Section J8, but could use  = .65 per ACI 318 9.3.2.4. Since A2 = 576 square inches, we can solve for A1 and take advantage of the concrete below the base plate being confined by the concrete outside the base plate’s footprint (i.e. (A2/A1)1/2 < 2 translates into the upper limit of (1.7)(.85f 'c)(A1)). Therefore, A1 equals the greater of the following: A1 = (1/576 in.2)[(220 kips/((0.6)(.85)(3.5 ksi))]2 = 26.4 in.2 A1 = 220 kips/[(0.6)(1.7)(3.5 ksi)] = 61.2 in.2 The required base plate width for concrete bearing is simply the square root of A1, or 7.85 inches. However, since the columns are HSS 8x8s and a 1½-inch clear spacing will be specified between the center-line of the anchor bolt and the edge of the base plate, the base plate size will be increased to 14x14 inches (see Figure 1). Therefore, actual area under the base plate is A1 = (14 in.)(14 in.) = 196 square inches. The area of concrete support below the base plate is still A2 = 576 square inches. continued on next page

STRUCTURE magazine

April 2012

Figure 1: Bearing plate check.

Therefore, the capacity of the selected base plate for concrete crushing is Pp = (.6)(0.85)(3.5 ksi)(196 in.2)(576 in.2/196 in.2)1/2 = 599.8kips > 220 kips ⇐ OK for Concrete Crushing Since the assumed HSS 8x8 base plate width of 14x14 inches is acceptable with respect to concrete crushing, the bending capacity of the plate must be checked. The base plate width (B) = 14 inches and the base plate length (N) = 14 inches. With the base plate’s bending plane being near the face of the column, and considering the portion of the base plate beyond the face of the column as cantilevered out some length beyond that point, the maximum cantilever length is the greater of m, n and n´:

Per 13th Edition AISC part 14 and Figure 1, for a square HSS shape m = n = [N – (0.95)(column width)]/2 = [14 in. – (0.95) (8 in.)]/2 = 3.2 in.

Therefore, to satisfy initial bearing requirements, a 7/8-inch thick base plate is required. This same theory is defined in Part 14 of the 13th Edition of AISC and will also be used to size the rigid base plate. As shown in Figure 2, with the applicable ACI 318 references, the punching shear capacity is shown to be:  for shear = 0.75 per ACI 318 9.3.2.3 (Note: the lower  value due to increased dependence on concrete quality for shear strength) c for normal weight concrete = 1.0  Vc = (0.75)(4)(1.0)(3500 psi)1/2(19 in.)(4 sides)(8 in.) (1 kip/1000lbs) = 107.9 kips < 220 kips ⇐ No Good For Punching Shear

This must be compared to a cantilevered length based on yield line theory, also referred to as n´. (Note: n´ will not control when the base plate is this much larger than the supported column, but the check is included for reference) n´ = [(overall column depth)(column flange width)]1/2/4 = [(8 in.)(8 in.)]1/2/4 = 2 in. s = 2(X)1/2/(1+(1-X)1/2) ≤ 1 X = [(4)(overall column depth)(column flange width)/(overall column depth + column flange width)2](Pu/Pp) s could be conservatively taken as 1, however solving for X and then for s: X = [(4)(8 in.)(8 in.)/(8 in. + 8 in.)2] (220 kips/599.8 kips) = 0.37 s = (2)(0.37)1/2/(1+(1-0.37)1/2) = .68 sn´ = (0.68)(2) = 1.36 in. For flexure design, the longest cantilever length controls. In this case, that is m = n = 3.2 inches. Viewing the cantilevered plate as a uniformly loaded 1-inch wide strip, the maximum moment is near the face of the column and the load on the plate is w = (P/Aeff)(1 in.). Therefore, the maximum moment at the support of a cantilever, wl2/2 can be expressed as (1 in)(Pu/Aeff)(l2)/2. Since the plastic section modulus, Z = tplate2/4 and the nominal moment, Mn = Mp = (Fy)(Z), the expressions are combined and the equation for tplate is derived as follows:  = 0.9 for flexure tp = (max. cantilevered length) [(2)(Pu/Aeff)(1/.9Fy)]1/2 tp = 3.2 in[(2)(220 kips/(196 in2)(1/(.9)(36 ksi)]1/2 = .84 in.

STRUCTURE magazine

Figure 2: Punching shear.

April 2012

Figure 3: Rigid base plate calculation.

Since soft soils were an issue for this site, and since the design bearing pressure was 1500 psf, soil pressure offset was disregarded in the punching shear calculations. With that said, at this point one would normally simply increase the thickness of the footing until the punching shear check was satisfied. If that had been an option on this project, increasing the depth of the footing by 6 inches to a total depth of 18 inches would have provided a punching shear capacity equal to Vc = 248.5 kips > 220 kips, flexural capacity would have been verified per ACI 318 15.4 and the footings would be acceptable. A thicker footing in this case is the preferable and more cost effective solution. However, due to the maximum bearing depth constraints, deeper footings were not an option. Therefore, an alternative was necessary. C. The increased capacity from a higher compressive strength concrete, although minor due to the tensile nature of shear failure, is still worth checking. Using f 'c = 5000 psi. along with the procedure shown above provides another 21 kips of capacity: Vc = (0.75)(4)(1.0)(5000 psi)1/2(19 in.)(4 sides)(8 in.)(1 kip/1000 lbs) = 128.9 kips << 220 kips ⇐ No Good For Punching Shear D. To further increase the punching shear capacity, a rigid base plate can be sized by holding the deflection of the previously defined cantilever to L/600. The assumption being that such a rigid plate could distribute its load over its entire foot-print (in lieu of just up to half the distance from its edge to the face of the column) and engage enough of the concrete footing to achieve the necessary critical shear area. Per Figure 3, this resulted in a 25-inch x 25-inch x 2-in-thick base plate. However, with the top of footing only 6 inches below finish floor, the top of the anchor bolts penetrate significantly into the previously mentioned interior of the polished concrete slab. This penetration increased the potential for unattractive cracks in the polished slab. Therefore, to utilize more typically sized column base plates, the

STRUCTURE magazine

Figure 4: Shear head reinforcement.

decision was made to add a shear head within the footing to distribute the punching shear forces over a wide enough area so that the thin footing could handle the applied ultimate load. E. Design Shear Head per ACI 318 11.11.3. As noted in the rigid base plate calculations, the required critical shear area length, bo, is just under 130 inches. Therefore, any shear head installed inside the footing must be able to distribute Pu out to this line. If the shear head is considered a reinforced concrete beam within the footing that extends from where Pu is applied to the edge of the critical shear area, the following results: • Assume the beam within the footing to be as wide as the critical shear area, then the cross-section of the beam is 32.5 inches x 12 inches • Assume the beam has #3 shear ties at 4 inches OC each way the full length of the beam, and assume it has (4) #6 bars each way top and bottom for flexural reinforcement. • Per ACI 318 11.1.1 total shear capacity is Vn = Vsteel + Vconcrete • Per ACI 318 11.11.3, shear reinforcement is permitted since the calculated d of 8 inches exceeds both 6 inches and (16) (bar diameter). • Per ACI 318 11.4.7.2 and Figure 4, the shear capacity of steel, Vs = AsFyd/s  = reduction factor per ACI 318 9.3.2.3 = .75 for shear As= area of shear reinforcement = (0.11 in.2)(9 verticals) = 0.99 in.2 Fy = shear reinforcement yield strength = 60 ksi d = depth from top of concrete to top of bottom reinforcing steel reinforcement = 8 inches s = spacing of shear reinforcement along shear failure plane = 4 inches continued on next page

April 2012

Figure 5: Shear head flexure check.

Per Figure 4, the #3 ties are spaced at 4 inches OC each way so that (9) verticals crossed the punching shear failure plane. Their hook lengths were sized per ACI 318 7.1.3.a as (6)(db) = (6)(3/8 in.) = 2.25 inches. Ties were spaced at this interval within the entire shear head so that they would both cross the shear failure plane and also fully engage the bottom steel. Full engagement of the bottom steel is necessary to prevent anchor bolt pullout in uplift, per ACI 318 Appendix D. Vs = (0.75)(0.99in.2)(8 in.)(60 ksi)/(4 in.) = 89.1 kips • Per ACI 318 11.2.1.1 the shear capacity of the concrete, Vc = 2(f 'c)1/2(b)(d)  = reduction factor per ACI 318 9.3.2.3 = .75 for shear f 'c = compressive strength of concrete = 5000 psi b = width of concrete beam, in inches d = depth from top of concrete to top of bottom reinforcing steel reinforcement = 8 inches Vc = (0.75)(5000)1/2(32.5 in.)(8 in.) = 27.6 kips Therefore Vn = Vs + Vc = 89.1 kips + 27.6 kips = 116.7 kips on one side of the critical shear plane. However, the beam crosses the plane at four locations; therefore, the shear capacity of the shear head = (4)(116.7 kips) = 466 kips >> 220 kips ⇐ OK At Shear Head For Punching Shear • Per ACI 318 Chapter 10 and Figure 5, the flexural capacity of the shear head beam (within the footing) = Mn = AsFyd(1-.59Fy/f 'c)

STRUCTURE magazine

 = reduction factor per ACI 318 9.3.2.1 = .9 for flexure bo = 130 inches and therefore beam cantilever length = (130in/4)/2 = 16.25 inches As = area of tensile reinforcement = bd  = the balanced steel ratio (between pmax and pmin per ACI 318 10.3.3 and ACI 10.5.2) = As/bd = (4)(.44 in2)/(32.5 in.)(8 in.) = 0.0067 Fy = steel reinforcement yield strength = 60 ksi f 'c = compressive strength of concrete = 5000 psi b = width of concrete beam, in inches d = depth from bottom of concrete to bottom reinforcing steel = 10.25 in. Therefore, the flexural strength of the beam within the footing resolves to Mn = Fybd2 [1-(0.59)()(Fy)/(f 'c)] Therefore, Mn = (0.9)(0.0067)(60 ksi)(32.5 in.)(10.25 in.)2(1/12)[1-(.59)(0.0067)(60 ksi)/(5 ksi)] = 78.2 kip-ft The required moment at the shear head = 71.2 kip-ft, calculated per Figure 5. Since the moment capacity of the beam in the shear head = 78.2 kip-ft >> 71.2 kip-ft ⇐ OK At Shear Head For Flexure Since the shear head (or beam within the footing) checks out for shear and for bending, the entire footing’s flexural capacity must be checked per ACI 318 15.4. This last check requires that reinforcing steel be added or that the shear head size be increased. Once that is accomplished, the footing can support an ultimate load of Pu = 220 kips. Once the footing is designed for gravity loads (per the above procedure) and soil bearing capacity, the uplift forces must be accounted for. Using wind load pressures from 145 mph winds per ASCE 7-05 Figure 6-6, base plate thickness is determined based on the yield moment of the base plates per 13th Edition AISC, anchor bolt pullout is checked against ultimate uplift forces per ACI 318 Append D and finally, per ACI 318 13.2.1, the extra large footings must be designed with sufficient flexural strength to ensure the entire footing is engaged to resist the maximum applied uplift. Lastly, the footings must be tied together per the requirements in International Building Code (IBC) Chapter 18 for seismic design category D structures built on site class E soils. In the end Wallace Engineering convinced the owner to pay the geotechnical engineer to perform an additional analysis of the building pad and to verify its ability to support deeper footings. After the new analysis was completed, the geotechnical engineer revised his recommendations to permit a maximum bearing depth of 30 inches. Per the calculations above, this allowed the footing to be made sufficiently deep to pass the bearing, punching shear, flexure, and uplift checks. Therefore, a workable solution was developed to solve the original problem, and the shear heads were not required.▪

Dan Mazzei, P.E. is an Associate at Wallace Engineering, headquartered in Tulsa, Oklahoma. He is a former U.S. Army officer, a member of the American Concrete Institute, and a member of the Oklahoma Structural Engineers Association. Dan can be reached at dmazzei@wallacesc.com.

April 2012

www.itwredhead.com 800.899.7890

Education issuEs

core requirements and lifelong learning for structural engineers

Principles for Engineering Education Part 1 By Eric M. Hines, Ph.D., P.E. Since 2002, the National Council of Structural Engineers Associations’ (NCSEA) Basic Education Committee has been working to improve the practice of structural engineering through improvements in basic education and a variety of other initiatives. The education process has changed significantly over the years and continues to evolve. A classroom-friendly approach to instruction is being introduced here in a three-part series by Eric Hines. As a professor at Tufts University and a practicing professional engineer, he is uniquely able to see the perspectives of both the academic institution and the workplace. Parts 2 and 3 of this series of articles will be included in upcoming issues of STRUCTURE®.

s a practitioner and educator, I was invited to discuss ideas for improving the “technical and practical quality of education for structural engineering students.” To this end, I would like to introduce four principles which I think can help accomplish this NCSEA goal. While I agree that engineering students today are in danger of missing fundamental technical knowledge that was common a generation ago, I think that the roots of this problem are human and not technical. Solving the problem therefore requires recourse to human principles: 1) Theory and practice are indivisible. 2) Engineering is a creative discipline. 3) Drawing is the language of the engineer. 4) There is more than one way to model every problem. These principles are no doubt familiar to many engineers. As I understand them more clearly through my experiences and discussions with colleagues, I communicate them more explicitly to my students.

Principle 1: Theory and practice are indivisible. There is only one real world. Theory attempts to make sense of it. Practice attempts to assume responsibility for it. Engineers’ technical quality shines brightest when they recognize the limits of theory, and design so that these limits become irrelevant. I first learned this from Professor David Billington at Princeton University through his lectures on the great works of structural engineering and his book The Tower and the Bridge. A review of historical literature suggests that the distinction between theory and practice developed as a matter of convenience. Unfortunately, this distinction became

pervasive during the 20th century and led to the misconception that professional activity amounts to the mere application of scientific knowledge. Scientific Culture and the Making of the Industrial West, by Margaret Jacob, discusses how the natural integration of theory and practice in 18th century England stimulated the industrial revolution in advance of other countries by more than a generation. As the industrial revolution grew in scope and complexity, well meaning attempts to divide responsibility between the creation and application of technical knowledge resulted in the now common distinction between theory and practice. Considering professional knowledge in general, Donald Schön argues in The Reflective Practitioner that this distinction was canonized in American higher education at the end of the 19th century during the founding of American professional schools. These authors help us to understand the assumptions on which our current approach to professional education is based. If the American medical profession struggles with the epistemology of the modern research university, then how much greater is the challenge to engineering, which was not part of this initial professionalization inside the American university? Professionals recognize that problems need to be framed before they can be solved. We recognize that a given problem may be both framed and solved in a multitude of ways. To call this “practical” is to completely misunderstand the intellectual depth required for good judgment. Judgment in structural engineering requires mastery of our discipline. Things that are “practical” are important pedagogically only insofar as they call this mastery to account. For this reason, I often remind my students that the purpose of a design course is to motivate and challenge their fundamental understanding of structural behavior. I have

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April 2012

come to this conclusion over time, as I have learned that even students who get good grades don’t understand structures very well. Theory is valuable–but only insofar as it is understood, and only insofar as it describes reality. Theory is the foundation of professional practice, but practice is the discipline of theory.

Principle 2: Engineering is a creative discipline. Engineers ought to understand their work as creative, even if it is not artistic. Creative work requires choices. If there is more than one way to do something, creativity comes into play. The creative process has three stages: 1) An idea is generated: and exists in the imagination only. 2) It is expressed in language: drawing, words, mathematics. 3) Only then can it be judged: through thought, feeling and discussion. The creative process becomes an artistic process when expression is intended to evoke an emotional response. Understood in this way, Engineering, Mathematics, the Arts, the Humanities and the Sciences need not vie for superiority. They are all creative endeavors, each with distinct intentions. In engineering terms, one might describe the stages of the creative process as highly non-linear and coupled. The generation, expression and judgment of many ideas proceeds iteratively and in parallel. Modes of expression may change over the life of an idea, people may alter their judgments, and the idea itself may evolve. Thus, in the context of teaching, high quality design problems are those that can be thought about rigorously and simply while requiring several choices to be made. Teaching the discipline of creativity also requires room for students to iterate on

their own designs, so educators must make hard choices to give up breadth in the interest of mastery. Understanding creativity as a process of choice-making frees it from the exclusive mystique surrounding modern art and invention. It also frees creativity from the assertion that novelty is required. If the creative process is misunderstood as consisting of its first two stages only (generation and expression), the result is a fundamental lack of rigor. When engineering students recognize that the rigors of judgment are as essential to creativity as the openness of generation and the energy of expression, they can learn to withhold judgment of an idea until it has been appropriately expressed. Inability to recognize the place of rigor within a larger process leads many engineering students to short circuit this process. They believe that ideas come into being fully formed, that they must solve each problem correctly on the first try, and that to offer spontaneous responses is to demonstrate stupidity. These prejudices rob students of their courage. Parts of the creative process can be taught, and parts of it cannot. The unteachable parts

may be understood in terms of inspiration, talent and wisdom. The teachable parts may be understood as the discipline of creativity: 1) Generation: it may not be possible to teach inspiration, but it is possible to share the development of one’s own ideas honestly and transparently. It is possible to tell the stories of real engineers and artists. 2) Expression: it may not be possible to endow talent, energy and committment, but educators can teach the use and meaning of fundamental languages such as drawing, words and mathematics. 3) Judgment: it may not be possible to teach wisdom, but it is possible to value it and to demonstrate it. The discipline of creativity accepts the necessity for iteration, and so requires engagement of the creative process with speed and courage. In this context “speed” is necessary to ensure that the expression of ideas is uninhibited and that judgments are disciplined. “Courage” is necessary to temper one’s fears of expressing a bad idea or facing a tough decision. Since most engineering projects are the work of ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org

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April 2012

more than one person, individuals need to be aware of interpersonal interactions that can either fuel or inhibit the creative process. We should not shy away from the potential discomfort these interactions present. In doing so, we miss opportunities. Understanding the principles of the creative process provides strength to see the process through.▪ Eric M. Hines, Ph.D., P.E. is a Principal at LeMessurier Consultants, Inc. and Professor of Practice, Department of Civil and Environmental Engineering, Tufts University. Dr. Hines specializes in the design and renovation of building structures, renewable energy infrastructure, and the seismic performance of bridges. In 2011 he received the Henry and Madeline Fischer Award, recognizing him as “Engineering’s Teacher of the Year” at Tufts; and in 2012 he received the Designer Special Achievement Award from the American Institute of Steel Construction. He can be reached at ehines@lemessurier.com.

Great achievements

notable structural engineers

Job Abbot

By Frank Griggs, Jr., Ph.D., P.E., P.L.S.

ob Abbott was born on August 23, 1845 in Andover, Massachusetts. He was the son of Nathan B. Abbott, one of the well-known Abbott families in the area. He attended local schools and then Phillips Andover Academy near his home. He then enrolled at the Lawrence Scientific School, Harvard University. It opened in 1847, as Harvard decided to provide a program in engineering and the physical sciences to go along with its historic law, divinity and medicine programs. Abbott Lawrence, its earlier benefactor, suggested that its faculty “number among its teachers men who have practiced and are practicing the arts they are called to teach. Let theory be proved by practical results.” Abbott graduated in 1864, near the end of the Civil War. Job worked briefly for Manchester Locomotive Works, one of the leading manufacturers of locomotives, in New Hampshire. He then went into civil engineering as an assistant engineer on the Long Island Rail Road, after which he went west and joined the Pittsburgh, Fort Wayne and Chicago Railroad. He was stationed in Canton, Ohio, where in 1866 he laid out part of the town practicing as a civil and mining engineer. He was then admitted to the Ohio bar, specializing in Patent Law. This experience brought him into contact with the Wrought Iron Bridge Company located in Canton, where he served on the Board of Directors for several years. The Wrought Iron Bridge company was one of many smaller bridge fabricators that sold what some have called catalog bridges to local governments. In 1872, he became vice-president and chief engineer of the Company, starting his long time involvement with bridges. Through his efforts, the company became one of the major builders of prefabricated bridges. The company produced catalogues, as early as 1872, that were used by local governments to choose the type of bridge they required. The firm was also active selling bridges in Ontario, Canada until 1879. At this time, Canada placed a 25 per cent tariff on imported fabricated ironwork and steelwork, and all American firms were unable to compete. Since Canada did not have its own bridge building industry, some Toronto and Montreal men organized the Toronto Bridge Company with the help of Abbott and the Wrought Iron Bridge Company. In 1880, Abbott was

Job Abbott 1845-1896. named president and chief engineer. His previous contacts with railway builders opened many doors and business improved greatly. He saw that the location of his fabricating Bridge, over 3,400 feet long linking Montreal plant and its distance from Montreal, where and the south shore. Abbott designed the St. many railroad company headquarters were John Bridge, which was built next to Edward located, put him at a disadvantage in com- Serrell’s suspension bridge that opened in peting for the huge number of bridges that 1853. It was an early example of cantilever would be needed. construction in Canada. Abbott and his colleagues decided to form The Lachine Rapids Bridge was designed by a new company with headquarters near C. Shaler Smith, but the details of fabrication Montreal and on September 23, 1882 a char- and erection were worked out by Abbott and ter was issued to Dominion Bridge Company his staff. Limited. The new company was permitted The company also built the Coteau Bridge to manufacture iron and steel, as well as to (a 17 span truss bridge with a 355-foot swing fabricate and erect bridges and structural span) across the St Lawrence River for the work throughout Canada; hence the name Canada Atlantic Railway, and the low level Dominion. Abbott became president and with swing span Grand Narrows Bridge chief engineer. English and Scottish investors at Iona, Nova Scotia for the Intercolonial purchased a large portion of the available Railway. While its specialty was railway stock with the understanding that the new bridges, primarily for the Canadian Pacific firm would purchase steel from their plants, Railroad which was replacing its wooden which were not required to pay the 25% duty. The new firm decided to locate its plant at Lachine, near Montreal. Two of its early important contracts were a cantilever bridge over the Reversing Falls at Saint John, New Brunswick and another cantilever, the Lachine Rapids St. John Cantilever (1885).

Lachine Rapids Bridge (1886).

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April 2012

trestle bridges, it also constructed many smaller bridges in towns and counties and steel framework for tall buildings. Abbott, being president and chief engineer, was largely responsible for the success of Dominion Bridge. He was also the main salesman and negotiated many contracts with major clients. Like many engineers of the time, he devoted himself exclusively to his profession, often to the detriment of his health. Between October 1887 and March 1888 he was away from his post due to health issues. In June 1890 he resigned as President of the company and returned to the United States, setting up an office in New York City and becoming chief engineer of the New York Rapid Transit Railway. He returned to bridge building as a consulting engineer for the Wheeling Bridge and Terminal Railway Company of West Virginia that was built to carry the Baltimore and Ohio Railroad across the Ohio River. He designed the bridge, sometimes called the Martin’s Ferry Bridge, located adjacent to Charles Ellet’s Wheeling Suspension Bridge that carried two tracks across the Ohio River. It opened in 1891 and served until 1982 when it was abandoned. It was demolished in 1993.

Abbott finished his career as chief engineer on the Bangor and Aroostock Railroad in Maine that ran from Brownsville north to Caribou. He designed 200 miles of road, as well as all the stations along the route. His health again declined, however, and he died in August 1896, just before his 51st birthday. The Andover Townsman wrote in his obituary that he was, “taken sick in March, 1895…but…manfully carried on Wheeling Railroad Bridge 1891. through his work in Maine and although suffering much, he never complained, of his time. He was inducted and only gave up in April last, on the insis- into the Canadian Business tence of his friends.” The Townsman also wrote, Hall of Fame in 1984.▪ “hardly more than in the prime of his life, Mr. Abbott’s best work seemed to be yet before him Dr. Griggs specializes in the restoration of and his death will come as a personal loss to historic bridges, having restored many 19 th a host of friends.” He is buried in the South Century cast and wrought iron bridges. Parish Church Cemetery in his hometown of He was formerly Director of Historic Andover, Massachusetts. He was one of the Bridge Programs for Clough, Harbour & th giants in 19 century bridge building. It was Associates LLP in Albany, NY, and is now an he, along with Edward Serrell, who brought independent Consulting Engineer. Dr. Griggs American methods in bridge building to can be reached at fgriggs@nycap.rr.com. Canada, building some of the greatest bridges ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org

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April 2012

Business Practices

business issues

Working Capital Management Understanding the Challenges and Exploring Solutions By Nic Perkin

espite the pressures of commoditization, outsourcing, and competition, the structural engineering industry has seen a swell in activity, thanks to new opportunities driven by private enterprise and the restructuring of the country’s infrastructure. For firms to pursue new projects, they may need to recruit qualified staff, invest in technology and expand operations–efforts that require sufficient working capital. Unfortunately, given the economy, many engineering firms are finding it harder than ever to get working capital on their terms using traditional methods. Working capital is defined as current assets minus current liabilities. In simpler terms, it’s the amount of cash a company has on hand, and is a measure of a company’s efficiency and short-term financial health. Positive working capital means the company has more assets (cash, accounts receivable and inventory) than liabilities, and, therefore, has the cash flow to fund operations or fuel growth. For structural engineering firms, this might mean the ability to take on a large project with little or no outside funding. Negative working capital results when liabilities outweigh assets and there is not enough cash on hand to run a business. In a prolonged negative working capital situation, some form of outside funding can be critical to survival.

Cash Flow a Top Concern? You’re Not Alone A recent survey conducted among executives at U.S. B2B companies found that working capital is a perpetual challenge for small and mid-sized businesses, including private structural engineering firms. Nearly two-thirds of survey respondents cited working capital as their #1 business challenge, edging out escalating costs and margin maintenance. Why is working capital such a concern? Because it is tricky to manage. CFOs at structural engineering firms are constantly juggling the demands of clients, who want to extend their payables as long as they can

Factoring

Asset-Based Lending

Bank Financing

Online Receivables Financing

Requires long-term contracts?

Yes

Yes (non-binding)

Requires all-asset liens and personal guarantees?

Yes

Often

Competitive, market-based pricing?

Yes

Facility fees and other hidden costs?

Yes

One-time registration fee & per trade fee

Funds available in less than 30 days?

Yes

Notifies your customers?

Yes

(60+ days), and pressing liabilities such as payroll and technology costs that require immediate payment. Unfortunately, the financing needed to overcome these working capital challenges has become increasingly difficult to secure. The economic downturn has caused most banks and financial institutions to tighten their lending standards. Other traditional financing sources, such as factoring companies and asset-based lenders, impose sizeable fees and require all-asset liens and personal guarantees, making them less attractive options for firms needing access to fast and affordable cash.

Traditional Financing Isn’t as Cheap as You Think Many business owners and finance executives consider bank financing a cheap and simple way to fund a business. However, bank financing often comes with hidden charges and penalties that most don’t factor into their costs. Some loans require a company to put up a down payment and pay sales tax on the loan in advance, which can be a significant upfront cost. Businesses can incur penalties for missing a payment, or for paying early, whether to alleviate their debt or to refinance. Add processing fees, documentation fees,

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April 2012

third-party fees, and government fees and taxes associated with loans and lines of credit, and the costs add up to far more than merely “principal plus interest.” Further, the cost of factoring, where a company sells or assigns its accounts receivable to a third party, can also carry a heavy price tag. The price paid for the receivables is discounted from their face amount to offset the risk that some of the receivables may be uncollectable. For example, suppose you have $100,000 in receivables. A factor will advance funds to you at a certain percentage of the total amount, often ranging from 75% to 80% (this is called the reserve), based on the quality of the receivable (your client) and your average days sales outstanding (time it takes your clients to pay). In addition, the factor typically charges interest on the advance plus a commission, and some factors have begun charging a fee to monitor an account and for use of their software. Another traditional financing option is asset-based lending. Asset-based lenders make secured loans against certain business assets – such as accounts receivable, equipment and inventory – which you offer as collateral. Though rates are often better than unsecured loans, asset-based lenders charge relatively high rates, and can legally seize assets if you miss payments.

Personal Guarantees Are Not Worth the Risk It’s also important to keep in mind that traditional financing can carry heavy restrictions and personal risk. To satisfy bank loan requirements, a business is usually required to put up a mix of collateral, including cash and hard assets such as property or equipment. Since the recession, many traditional lending options are now requiring some form of personal guarantees in order to approve (or at least consider) business loans. While it might seem a small concession for a loan, personal guarantees should be avoided. If you sign a personal guarantee and your business hits a rough patch, not only is the company on the line, but your personal assets are as well. You risk losing your house, your car, or your savings.

Online Receivables Financing Offers Flexibility In the changing economy, it’s important for engineering firms and their finance executives to examine innovative alternatives that in many cases are cheaper than traditional financing, and that carry fewer restrictions.

One such alternative is online receivables financing. This option allows you to sell your receivables in a real-time, online auction. Unlike other forms of receivables-based financing, online receivables financing allows you to sell invoices to multiple institutional investors, so you get the most competitive pricing. (Businesses get 99-98 cents on the dollar, on average, in as little as 24 hours.) There are no personal guarantees, all-asset liens, contracts or hidden costs, and there is no obligation to trade. While sometimes mistaken for factoring, online receivables financing relies on a completely different business model that offers companies flexibility and market-based pricing. With online receivables financing you are not required to monetize all of your invoices, but instead you choose when and at what price to sell individual invoices. If your firm needs sufficient capital to fund a new project, online receivables financing may be an ideal option.

The Bottom Line When all the fees, penalties and risk are added up, traditional financing is not necessarily the most inexpensive or worry-free option. In the

changing economy, it’s important for small and mid-sized companies to examine innovative alternatives that in many cases may be more advantageous and carry fewer restrictions.▪ Nic Perkin is co-founder and president of The Receivables Exchange, an online marketplace for sale and purchase of accounts receivable. He can be reached at nic@receivablesXchange.com.

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Engineered Lumber

Wood Products Council Phone: 866-966-3448 Email: info@woodwors.org Web: www.woodworks.org Description: WoodWorks provide resources that allow engineers, architects, general contactors, developers and others to build non-residential and multi-family structures out of wood more easily and at less cost.

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All Resource Guides and Updates for the 2012 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

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STRUCTURE magazine

April 2012

award winners and outstanding projects

Spotlight

Bellezza e funzione Design of New Government Seat Combines Beauty & Function By Aine Brazil, P.E., LEED AP Thornton Tomasetti provided structural design services through design development for the Lombardia Regional Government’s new headquarters complex in Milan, Italy, a project selected as one of the winners for the NCSEA 2011 Excellence in Structural Engineering Awards in the International Structures Over $100 Million category.

n 2004, an international competition was held for the design of the Lombardy Regional Government’s new seat and civic square in Milan, Italy. Located in northwestern Italy, Lombardia is the most populous region in Italy and its capital, Milan, is one of Italy’s most densely populated areas. The competition to design the new government seat and civic square required entrants to consider a visible symbolic and functional presence in their designs. Another factor that affected the site was the proximity to the Pirelli Tower, an existing icon in the local landscape. The final Pei Cobb Freed and Partners Architects LLP design was chosen from 10 finalists who were selected from a larger group of 98 applicants. Their winning design was inspired by the region’s interweaving mountain peaks, rivers and valleys. The open spaces created by the curved forms of the buildings encourage the community to gather, reinforcing themes of engagement and social interaction. Thornton Tomasetti provided structural design services through design development for the project Sited in the greater Garibaldi-Repubblica urban enhancement area, close to the heart of the city, its scale relates to the surrounding neighborhood, while the tower speaks to the Pirelli building and the city. Key design principles were: to create an urban passage that invites entry and is a significant destination; design a sequence of engaging spaces that promote social interaction; and add an emblematic vertical element that contributes to Milan’s skyline. This high-profile headquarters includes five nine-story wavelike buildings that total 1.05 million square feet (98,000 square meters), a 43-story tower that is 405,000 square feet (37,000 square meters), three parking/storage levels below grade and a plaza with an irregular footprint of 856 feet by 607 feet (261 meters by 185 meters). The major determining factors in the choice of structural materials and structural system for the project

were the curved building shapes and floor-tofloor heights. Construction began in December of 2006 and was completed in March 2011. The completed government buildings include general assembly spaces, offices and areas for social functions and public debates. A large enclosed piazza with a curved glass roof at the center of the site references Milan’s Galleria, and links to two secondary open spaces and a linear landscaped spine. The piazza roof is covered by a tubular lamellar (skewed grid) structure spanning 459 feet by 148 feet (140 meters by 45 meters) and is clad in an extremely light, innovative Ethylene Tetraflouroethylene pillow membrane system. The rim of the “eye” shaped roof structure is supported along the edges of the podium structures with slide bearings that accommodate building movement at expansion joints. The enclosure of the building is a highly innovative and efficient “climate wall” double layered glass curtainwall. The project also includes an open roof garden with trees and landscaping, enclosed by an approximately 50-foot (15-meter) tall wall of glass supported by vertical cantilevered tube steel vierendeel trusses with no overhead beams. Grand entrances to the piazza are created by open double height ground floor areas and multiple column transfers. The project is divided above grade into six building structures separated by expansion joints that accommodate thermal expansion and contraction. The maximum length of these structural units is approximately 361 feet (110 meters). Although in Italy expansion joints are commonly spaced more closely than 328 feet (100 meters), the architectural layout and the arrangement of the structural elements in these buildings facilitate the larger joint spacing. The 525-foot (160-meter), 43-story tower structure has an efficient concrete form even with the curves presented, which made finding economical solutions to structural requirements possible. The major elevator,

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April 2012

Palazzo Lombardia. Courtesy of Simon Hsu.

service and stair core is enclosed by cast-insitu concrete shear walls to create the lateral system for the building, to resist both wind and earthquake forces. The curvilinear form of the building makes a cast-in-situ concrete system an appropriate and cost-effective structural solution for both the low-rise buildings and the tower. Concrete is the local material of choice, and Italian building codes required office spaces to have access to direct light. Flat plate construction was possible because of the narrow building width, which addressed this constraint and eliminated the long spans that can make concrete an unsuitable material. The low-rise buildings follow a repetitive form, permitting multiple reuse of the formwork. Column formwork economy was provided by using uniform sizing and standard floor-to-floor heights. Once the project was passed on to the Italian design-build contractor Consorzio Torre, the construction team opted to substitute some of the cast-in-situ elements with precast elements in an effort to accelerate the schedule. This was most prevalent with the columns and flat plate slabs in the gravity system.▪ Aine Brazil, P.E., LEED AP is Vice Chairman of Thornton Tomasetti.

FSEA Palm Beaches Chapter Young Members Group Attracting Young Structural Engineers to their Local FSEA Chapter

NCSEA News

News form the National Council of Structural Engineers Associations

By Heather Anesta, E.I., M.S., LEED AP

f you are a PE who employs structural undergraduate interns and EI’s, then you have probably noticed that the past few years have affected your ability to hire, train, and groom your younger employees. The current economic crisis hit the structural industry especially hard, and although poor economic times call for greater efficiency, greater efficiency requires more training. Due to this conflict, many EI’s lost their jobs and many PE’s felt a break in the continual growth of their firm. A Young Members Group within your local NCSEA Member Organization (MO) could offer a way for firms to continue the employment and training of EI’s without impacting their budget. In fact, results from the past year in the FSEA Palm Beaches Chapter Young Members (YM) Group have shown that our EI’s provide greater efficiency at their engineering firms when they regularly attend the YM meetings. Learn together and from each other. If you are an EI or a PE who graduated college within the last 5+ years, you do not need a full article to understand the value of having a YM Group within your local MO. You have most likely already realized that the process of furthering your skills as a structural engineer without imposing on your boss’ time (and money) would be easier if you had company. A YM Group offers a venue for engineers early in their careers to lessen their individual load by forming a network with their peers. A difficult and stressful task for one could become enjoyable and more beneficial when tackled by a large group. I would highly recommend that you go to your local Chapter’s Board of Directors meeting and ask to start a YM Group with their help. EI’s have fallen into a training gap that few realize exist. While in school, universities cater to a student’s desire to become a structural engineer by teaching them the basics of mechanics and material strength, as well as the technical background associated with common design procedures. Later in their career, most MO’s and their underlying chapters cater to the Professional Engineer’s continuing education of new products and design techniques as well as professional concerns. In between these phases, the growth and development of a structural EI’s skills and experiences in a group setting have been left solely to their place of employment, which in times of economic downturns leaves EI’s pretty much fending for themselves. MO’s can expect to increase their membership base. I recommend that MO’s extend their operations to cover EI-based functions in order to include the full spectrum of the structural engineers’ career in our organization’s mission to further the structural profession. Visualizing the need for this extension is simple. When an established PE attends a dinner presentation on “Vertical Wall Sheathing”, the PE wants to know the cost, strength, and code compliance of the product. The EI, excited to learn and hoping for more pictures, wants to first and foremost know why the presenter is pronouncing “sheeting” incorrectly. This has nothing to do with the intelligence of the EI, merely their lack of experience. MO’s can utilize YM Groups to fill the gap between schooling and licensed practice, while subsequently filling the gap in their membership base. NCSEA MO’s should consider this as supply and demand; the more information they STRUCTURE magazine

supply, the greater the demand from the members, leading to more overall involvement. Prepare EI’s for better discussion of the topic at your next meeting. When the main chapter plans a meeting on “Vertical Wall Sheathing”, the YM Group carries out a meeting a week beforehand that reviews wood-framed wall design, definitions of terms, and the load path of forces, in order to acquaint the members with why and how vertical sheathing differs from conventional horizontal sheathing. These YM meetings prepare the EI not only to attend the Chapter meeting, but they also attract structural engineers to NCSEA MO’s at an earlier stage of their career. Having a YM Group will help an MO grow while ensuring that its budding structural engineers remain valuable despite economic downturns and shortfalls. The FSEA Palm Beaches Chapter YM Group, established in January 2011, created such a peer network for Structural Engineer Interns. This YM Group provides a venue for those EI’s to find and excel at work as well as for PE’s to find valuable employees, has established an FSEA Student Chapter at Florida Atlantic University, and has allowed its members to develop exponentially. The resulting and continued benefits of the group are outlined below: • A venue is provided for young structural engineers to meet, advise, network, and grow together. • A productive transition from the community of the University setting to the individuality and confidence of the licensed engineer is made possible. • Confidence and experience are infused among members. • More experienced EI’s and PE’s hone their design understanding and presentation skills as they instruct the younger EI’s and students. • Unemployed YM’s gain experience and knowledge that will give them an edge at their next job interview. • YM’s working in civil disciplines can maintain their structural connections and code knowledge while waiting for the economy to improve, and YM’s employed in structural engineering firms can grow in design knowledge while reducing the time required by their employers to teach such designs. • Members in all stages of their careers are able to take part in refreshing and interesting discussions and presentations, either as an attendee or a volunteer presenter. I highly encourage other MO’s to start YM groups of their own, and to promote it heavily to EI’s and PE’s. NCSEA will provide guidelines for starting a YM group upon request, and I am always available to anyone who has any questions or comments (h_anesta@me.com). April 2012

Soft Soil, Water and Wind — The pictures tell the story:

Saturday speaker Bill Coulbourne.

Friday reception.

Board Members take the tour in stride.

Saturday speaker/sponsor Dennis Boehm.

Seeing the Surge Barrier was no easy task.

Speaker Mike Wysockey with Bill Bast and Sarv Nayyar.

Saturday speaker Mike Sheridan.

The Seabrook Floodgate Complex.

NCSEA Webinars in April April 10: Special Inspection Observation & Testing

April 26: UFC 4-023-03 Design of Buildings to Resist Progressive Collapse

This presentation, given by Sue Frey, will review a project team’s contract document requirements under the 2006 or 2009 International Building Code (IBC) for Special Inspection, Professional Observation, and Testing.

This presentation, given by Ronald Hamburger, will review the procedures, from determination of a building’s risk category through selection of a design method for progressive collapse resistance, including application of each of the methods.

Sue Frey is a principal structural engineer serving as a designer, design manager, structural technical quality assurance reviewer, and multi-discipline team quality assurance manager on various types of projects during her 34 years with CH2M HILL. Ms. Frey is active in various code and standard committees, including masonry and prestressed concrete tanks, and teaches a masonry and building forces class annually at Oregon State University.

Ronald Hamburger was appointed to the joint FEMA/ASCE team that performed the initial investigation of the collapse of the WTC buildings and, later, participated in the more detailed studies performed by NIST. Mr. Hamburger chaired the NCSEA-sponsored joint ad hoc committee that developed the recent progressive collapse resistance requirements proposal adopted by the IBC and currently chairs the ASCE-7 General Requirements Subcommittee responsible for adoption of similar requirements in ASCE 7.

Cost: $225 for NCSEA members, $250 for SEI/CASE members, $275 for non-members, FlexPlan option still available. Several people may attend for one connection fee. 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program. Applicable for SECB recertification. No fee for continuing education certificates. Time: 10:00 AM Pacific, 11:00 AM Mountain, 12:00 PM Central, 1:00 PM Eastern. Miss a webinar that you wanted to see? Purchase the recording at www.ncsea.com. STRUCTURE magazine

April 2012

News from the National Council of Structural Engineers Associations

Friday morning speakers: Charlie Hess, Dale Miller, Angela DeSoto Duncan, and Bill Gwyn.

NCSEA News

NCSEA’s 2012 Winter Institute in New Orleans

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Call for Abstracts and Proposals The Structures 2013 Congress program will provide a forum to advance the art, science, and practice of Structural Engineering. We are currently accepting proposals for complete sessions and abstracts for individual papers to be presented during the Structures Congress. Abstract submissions should be 250 to 500 words describing what will be discussed in the presentation and identifying what the attendee will learn from your presentation. Include the abstract title, all authors, with names, credentials (P.E., Ph.D.), organization, correct e-mail address, and name of the presenter. Session proposals require a two step process. First you upload a 100-200 word session document describing what will be discussed during the 90 minute session, explain if this is a panel session or a traditional session with authors presenting papers. After the session document is loaded, each author will upload their papers to this existing session proposal. List all panel members or authors and paper titles, include name; credentials (P.E., Ph.D.), organization and working e-mail address. Tell us who the moderator is with e-mail address and if the session is sponsored by a committee or organization. Make sure to review the Author Guide on how to upload a full session proposal.

Attendance and registration are required for all presenters. Presentations will be selected from the open call, as well as by special invitation. Suggested Technical Paper Topics (full list of subtopics available on the Congress website) • Blast and Impact Loading and Response of Structures • Bridges and Transportation Structures • Buildings • Business and Professional Practice • Education • Non-Building and Special Structures • Nonstructural Systems and Components • Research Visit the SEI Website at www.asce.org/SEI for an author guide on how to upload a session proposal or abstract.

Key Dates All Abstract and Session Proposals due June 12, 2012 Notification of Acceptance September 18, 2012 All Final Papers due January 15, 2013 (extensions not possible) For more information about the Structures 2013 Congress and how to submit your abstract, visit www.asce.org/SEI.

Journal of Structural Engineering Special Issue Call for papers on Sustainability

The Journal of Structural Engineering is planning a special issue to highlight and document some of the recent advances in sustainability. Yahya C. Kurama, Ph.D., P.E., of the University of Notre Dame, and Arzhang Alimoradi, Ph.D., P.E., of Southern Methodist University will be the guest editors. The special issue will contribute to the general mission of the Journal of Structural Engineering by focusing on fundamental knowledge on the stateof-the-art and state-of-practice in structural design, analysis, behavior, and construction as related to sustainable building structures. Manuscripts that investigate the physical properties

of sustainable materials will demonstrate strong relevance to structural engineering through building or component design, analysis, and behavior. Papers that rigorously discuss real-world applications and case studies on reducing the environmental impacts of building structures through better engineering will be within the scope of the special issue. Deadline for submissions is April 30, 2012. Tentative publication date for the special issue is July 2013. Visit the JSE website for more information and details about how to submit your abstract: http://ascelibrary.org/sto/.

ASCE 7 Committee

SEI Logo Available for Local Groups and Committee Chairman

Call for Proposals for the 2016 Edition

ASCE Branding Toolkit

The Structural Engineering Institute (SEI) of ASCE is currently accepting proposals to modify the 2010 edition of ASCE 7, Minimum Design Loads for Buildings and Other Structures Standards Committee to prepare the 2016 revision cycle of the standard. Interested parties may download the proposal form from the SEI Website at www.asce.org/SEI. The committee will accept proposals until June 30, 2012. For additional information please contact Jennifer Goupil, SEI Director, at jgoupil@asce.org.

ASCE’s Collaborative Marketing Department has created a Branding Tool Kit website to help standardize branding across the Society. All institute logos, including SEI’s, were redesigned recently to include the ASCE shield. Please make sure that you use the most up-to-date ASCE and SEI logos when sending out correspondence, creating flyers, or marketing events. The Branding Tool Kit includes logos in black and white, color, horizontal, and vertical versions. The website will walk you through creating a login to access the toolkit. Visit the Branding Toolkit today at: www.ascebrandingtoolkit.com/pages/login.php.

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April 2012

New Publication Now Available Advanced Analysis in Steel Frame Design presents formal guidelines for the use of second-order inelastic analysis in the design and assessment of steel framing systems. This advanced analysis methodology focuses on the strength of the structural system as a whole, rather than design load levels producing first member failure. The report includes design rules, background and commentary regarding these rules, and benchmarks for columns and frames. It also provides specific recommendations regarding the rigor of the analysis, minimum modeling requirements, consideration of limit states, serviceability, and live load reduction, yet allows latitude for the judgment of the design engineer. 2012 | Soft cover | 56 pp. | ISBN 978-0-7844-1196-4 | Stock # 41196 | List $45 | ASCE Member $33.75 To order, visit the ASCE Publications website at: www.asce.org/bookstore.

New ASCE Structural Webinars Available SEI partners with ASCE Continuing Education to present quality live interactive webinars on useful topics in structural engineering. Date April 5, 2012 April 18, 2012 April 19, 2012 April 25, 2012 April 30, 2012 May 2, 2012 May 3, 2012 May 11, 2012

Instructor Bill Coulbourne Jennifer Laning Eric Stafford Bill Coulbourne Leighton Cochran Tom Williamson Bijan O. Aalami Scott Lockyear

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

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

SAVE THE DATE

ISEC-7

ATC & SEI Advances in Hurricane Engineering Conference Miami, Florida October 24-26, 2012 For more information visit the ATC & SEI Hurricane conference website at: www.atc-sei.org/.

2012 Electrical Transmission and Substation Structures Conference Columbus, Ohio November 4-8, 2012

For more information visit the ETS conference website at: http://content.asce.org/conferences/ets2012/index.html. STRUCTURE magazine

Call for papers The Seventh International Structural Engineering and Construction Conference (ISEC-7) has issued a call for papers. ISEC-7 will be held June 18-23, 2013 in Honolulu. Papers are sought for the following tracks: All branches of Architecture and Architectural Engineering, Coastal Engineering, Construction and Engineering Management, Construction Safety, Cost and Project Management, Education and Professional Ethics, Energy, Facilities and Asset Management, Geotechnical and Foundation Engineering, Housing, Infrastructure, Law and Dispute Resolution, Materials, Policies for Technology and National Development, Procurement, Quality, Risk Analysis and Disaster Management, Structures, Sustainability, Water and Air, and more. Abstract submissions are due by June 15, 2012. For more information visit the ISEC-7 website: http://isec-society.org/ISEC_07/index.htm.

April 2012

The Newsletter of the Structural Engineering Institute of ASCE

Several new webinars are available: Webinar Title Design of Buildings for Coastal Flooding The Five Most Common Errors Made During Bridge Inspections Significant Changes to the Wind Load Design Procedures of ASCE 7-10 Elevating Wood Framed Structures Wind Tunnel Testing for Wind Loads on Structures Connection Solutions for Wood Framed Structures Deflection Calculation of Concrete Floors – Immediate; Long-Term; Cracking Wind Design for Non-Residential Wood Structures

Structural Columns

Advanced Analysis in Steel Frame Design

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Member Firm Wins Grand Award Congratulations to CASE Member firm Magnusson Klemencic Associates of Seattle, Washington for winning a Grand Award for project Aqua at Lakeshore East and for being a finalist for the Grand Conceptor Award. The Grand Conceptor Award is given to the year’s most outstanding engineering achievement. The Winner will be announced at the Engineering Excellence Awards Gala during the ACEC Convention in Washington, D.C. on Tuesday, April 17, 2012. As described in their application for the award: The developer of Aqua wanted an aesthetically appealing, highly marketable, sustainable residential tower, so architect Jeanne Gang set out to create a one-of-a-kind “topographic tower” with direct sightlines to Chicago landmarks. Turning vision into reality required six major engineering achievements, most visibly the design of 78 individually unique curving floor plates with balconies that cantilever up to 12 feet and feature skinny 6-inch edges. Engineers also invented a new structural system, performed advanced wind engineering analysis on the 868-foot tower, utilized cutting-edge techniques to increase foundation efficiency, developed a method of molding 8 miles of concrete slab edges into delicate ripples, and digitally transformed the architect’s intent into construction reality. The technologies developed for Aqua (pending LEED Silver) will transform the next generation of buildings, with dramatic architectural options, increased occupant comfort, enhanced amenities, and community reconnectivity. Additionally, two CASE firms have been awarded 2012 Engineering Excellence Honor Awards. Walter P Moore of Houston, Texas was honored in the Structural Systems category for the KFC Yum! Center Louisville Arena, in Louisville, Kentucky. Also winning an Honor Award was the SSFM International/Moffatt & Nichols Joint Venture of Honolulu Hawaii for the Submarine Drive-In Magnetic Silencing Facility, Pearl Harbor, Hawaii. On behalf of CASE, congratulations to the Honor Award winners and best of luck to Magnusson Klemencic Associates on April 17th! For more information on the EEA Awards, visit www.acec.org/getinvolved/eea.cfm or contact Daisy Nappier at dnappier@acec.org.

Tool 2-4: Project Risk Management Plan CASE is announcing the newest tool under Foundation 2, Prevention and Proactivity, Tool 2-4: Project Risk Management Plan. Have you ever had something go wrong on your project and when looking back you say, “I should have thought of that!”? Well, here’s your chance to prove it. We all need to be thinking about what could go wrong on our projects, and what we need to do to prevent that from happening. With Tool 2-4, Project Risk Management Plan, you’ll walk through the methodology

STRUCTURE magazine

for managing your project risks, along with a few common project risks and templates on how to record and track them. It’s the tool that no project should live without. Developed by the CASE Toolkit Committee, this product is for sale at www.booksforengineers.com.

April 2012

Since its inception in 1995, the American Council of Engineering Companies’ prestigious Senior Executives Institute (SEI) has attracted public and private sector engineers and architects from firms of all sizes, locations and practice specialties. Executives–and up-and-coming executives – continue to be attracted by the Institute’s intense, highly interactive, energetic, exploratory, and challenging learning opportunities. In the course of five separate five-day sessions over an 18-month timeframe, participants acquire new high-level skills and insights that facilitate adaptability and foster innovative systems thinking to meet the challenges of a changed A/E/C business environment. The next SEI Class 18 meets in Washington, D.C. in September 2012 for its first session. Registration for remaining slots is available.

Executives with at least five years’ experience managing professional design programs, departments, or firms are invited to register for this unique leadership-building opportunity. As always, course size is limited, allowing faculty to give personal attention, feedback, and coaching to every participant about their skills in management, communications, and leadership. SEI graduates say that a major benefit of the SEI experience is the relationships they build with each other during the program. Participants learn that they are not alone in the challenges they face both personally and professionally, and every SEI class has graduated to an ongoing alumni group that meets to continue the lifelong learning process and provide support. For more information, visit www.acec.org/education/sei/ or contact Deirdre McKenna, 202-682-4328, or dmckenna@acec.org.

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

Local Preference The preference for hiring local firms appears to be spreading to procurements for professional services, despite that the requirement does not having any rational connection to the technical requirements of the project. More than a few states and municipalities have these preferences written into state law or municipal ordinance. Many businesses, including engineering firms, use this to their advantage by citing their local connections in their proposals. On the other hand, some states without local preference have asked firms to disclose whether the jurisdiction of their headquarters has a local preference with the inference of possibly using it against them. Here is an excerpt from a veto message on a local preference bill vetoed by then Gov. Schwarzenegger (CA) in 2010. Reciprocity statutes, enacted by at least 36 other states, would add a percentage to bids submitted by California businesses bidding on contracts with those states, making it difficult for California businesses to contract with other states. For these reasons, I am unable to sign this bill.

a non-compete agreement? Is it the responsibility of the person under the agreement or can the firm get dragged into it? When considering hiring someone under a non-compete ask to see a copy of it. Is it enforceable under your state law? Some courts look for ways not to enforce them because people have to be able to work. The decision may ride on how limited the opportunities are in a particular geographic area.

Substitutions An engineer should be entitled to presume that an item sold by a manufacturer based on their specifications does in fact meet the advertised standard (but this has not always been true). There are cases where the engineer has been held liable for failure to have new material tested. Where new materials or equipment are called for, the engineer should be sure that the producer knows how their product is to be used and, where practical, the producer’s representative should be present when it is used.

You can follow ACEC Coalitions on Twitter – @ACECCoalitions

Non-Compete It seems non-compete agreements are becoming more common. What to do when possibly hiring someone under

STRUCTURE magazine

April 2012

CASE is a part of the American Council of Engineering Companies

CASE Business Practice Corner

CASE in Point

A/E Industry’s Premier Leadership-Building Institute Filling Fast for September Class

Structural Forum

opinions on topics of current importance to structural engineers

A Structural Engineer’s Manifesto for Growth Part 1 By Erik Nelson, P.E., S.E.

his is the first installment of what I am calling my manifesto, which presents some of my thoughts about our profession and how we can grow as individual designers. Additional parts will appear in future issues of STRUCTURE®. I realize that some of what I say will come across as too simplistic or perhaps even misleading. It is meant to be read as a coherent whole, not piecemeal. My intent is not to provoke; it is to seek truth, to be clear, to translate what I do as an engineer, as an educator, and as a citizen and human being. In 20 years, I suspect that this is all going to sound pretty straightforward and bland. Finally, this manifesto will always be a work in progress – just like engineering.

1: Understand Structural Engineering Itself In order to grow, we need to understand who we are (see “What Is Structural Engineering Exactly?” in the February 2011 issue of STRUCTURE).

2: Embrace the Process Let the design process push and pull you constantly. It is healthy. Design is nonlinear. It goes backward as much as forward, and it curves around on itself. That is okay. If you have issues with that, this may not be the best profession for you–although there are engineers that successfully do only computer modeling or code research, so there is still hope.

3: Listen Be a better listener and collaborator. Architects (and other clients) will make you a better engineer, but you have to listen.

4: Become a Lifelong Learner Not because it is a goal, but because you want to maximize your well-being now. Engineering, like the good life, requires lifelong learning. Ask stupid questions often and pursue answers. Stupid questions are really smart. Who am I? What is engineering? What

is a weld, really? How can something turn from a liquid to a solid within a liquid (concrete underwater)? How come I don’t add that tension force I calculated to the pretension already within the bolt shank from tightening? If you are constantly thinking about these types of questions, you are in great shape.

5: Take Risks Designing big things requires risk-taking. Design of new and unique solutions to problems involves even more risk. Because engineering requires ingenuity, it requires risk. Be daring. We need to continue to be leaders in design and construction, and we need to take more active roles in pushing our projects forward, not getting pushed. As Lord Kelvin put it: “It’s no trick to get the answers when you have all the data. The trick is to get the answers when you only have half the data and half that is wrong and you don’t know which half.” In popular terminology, scientific applications or procedural calculations are about the “known knowns.” Design is much more about the “known unknowns.” Embracing this means embracing risk.

6: Accept Imperfection If there is no perfect solution, it follows that all solutions are imperfect. In other words, there is always a better solution than the one that you just submitted for construction. Every design has many compromises, such as code requirements, construction skill, material limitations, conservativeness on new construction techniques, possible errors of design, bad decisions early, etc. Get accustomed to that and own it. All designs are fallible. All designs can be improved. Guess what, the design that you submitted last week has numerous problems or design compromises, and that is okay. Learn and do better next time. Hopefully, you did not just lose a client; but that will happen, too. Take your imperfect project to a lower state of imperfection next time.

STRUCTURE magazine

April 2012

7: Forget About Goals Structural engineering is a process without a goal. Design constraints are not goals, they are ways to make decisions and move the project forward in the present. Engineering is an evolution from a concept to a built project. Let the final product be unknown during the design process. Understanding that design is inherently goalless is good for you. Design is means-driven, not ends-driven. It is about the present, not the future. Ask yourself often, “What am I doing right now? How am I improving the project now? Am I increasing my well-being, that of my team, and that of the project?” Engineering is about taking action to improve the quality of the object using experience-based judgment. If you have an end product first, that is less effective than if you live and work honestly in the present. When you take meaningful steps in the present, the next day the project will evolve to a higher level. This repeats itself day after day. The end product (building/structure) simply becomes. Let it become. Nurture the process. Be patient. The goal of achieving this or that building is useless. How could something unknown obligate us? I would submit that even known goals are useless; they are not only obvious, they are superfluous. Goals themselves are always good things for the person who has them, so I am not debating whether this or that goal is a worthy pursuit. Yearning for the vast and endless sea is fine as a goal, but the more immediate task is building the boat. Focus on the boat, not the sea. Let the design process produce the next evolution of the concept instead of trying to pin it down beforehand. Try to design the boat by asking what materials are available first, and keep proceeding. The built project, the boat itself in its final state, should not be known until it is done. Let the boat become, hop on board, and then the sea can be reached.▪ Erik Anders Nelson, P.E., S.E. (ean@structuresworkshop.com), is owner of Structures Workshop, Inc. in Providence, RI. He teaches one class per semester at the Rhode Island School of Design and Massachusetts Institute of Technology. Please visit and comment on his blog at www.structuresworkshop.com/blog.

STRUCTURE magazine | April 2012

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Editorial

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Technology

From Experience

Structural Performance