STRUCTURE magazine | January 2014

January 2014 Concrete

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FEATURES Concrete “Paint” Arrests Cofferdam Corrosion at Submarine Pier

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By Brian Robinson, P.E.

Often, steel sheet pile walls are incorporated as part of cost-effective waterfront earth-retaining structures. Many of these walls are subjected to a host of environmental factors that accelerate corrosion. Cellular sheet pile cofferdams are particularly difficult to repair because of the lack of redundancy in the tensioned cell walls. This article highlights a unique method to repair a cellular cofferdam using a reinforced concrete facing installed over the aging sheet piling.

Geopolymer Precast Floor Panels

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By Rod Bligh, B.Eng, MSc, CPEng, and Tom Glasby, B.Eng (Civil), MBT, MIEAust, CPEng

Early in the design process, the structural engineering team explored the potential for the incorporation of structural timber. Timber-Concrete Composite (TCC) floors were of interest and TCC was proposed as a potential floor system that combined the benefits of timber framing with the acoustic, fire separation and wearing properties of concrete. It was at this stage that the strong potential for use of geopolymer concrete in the system was identified.

46 Special Section

Foundation Sector Grounded in Optimism for New Year

By Larry Kahaner

We have heard it before, but next year could be shaping up to be strong for the building business. What appears to be driving the industry are a growing economy, new offerings that are attracting clients, and a general optimism among those companies who have survived the lean years of the building slowdown.

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A Joint Publication of NCSEA | CASE | SEI

43 InSights ASTM A1085

By Kim Olson, P.E.

Transforming the Fan Experience

58 Structural Forum Velocity of Learning Revisited

By Tom Glardon, P.E.

THE

COVER

The Pennoni Philadelphia Structural Division investigated and developed repair bid documents for an existing, three-level, 1,200space precast concrete parking garage during the last quarter of 2012. Part 3 of the series of articles, page 20, conveys conclusions regarding the feasibility of repairing the garage in order to extend its service life.

January 2014 Concrete

51 Spotlight

By John M. Hann, P.E.

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

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STRUCTURE magazine

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January 2014

CONTENTS January 2014

COLUMNS 7 Editorial The “Ins” and “Outs” of the Software Black Box

By Andrew Rauch, CASE Chair

9 InFocus Risk and Virtue Ethics

By Jon A. Schmidt, P.E., SECB

10 Structural Forensics Untreated Submerged Timber Pile Foundations – Part 2

By Giuliana Zelada-Tumialan, P.E., William Konicki, P.E., Philip Westover, P.E. and Milan Vatovec, Ph.D., P.E.

16 Historic Structures Deconstructing Bridge 92297

By Ryan Salmon, EIT and Meghan Elliott, P.E.

20 Structural Rehabilitation Prescription for Repair – Part 3

By D. Matthew Stuart, P.E., S.E., SECB and Ross E. Stuart, P.E., S.E.

23 Construction Issues Welding Reinforcing Steel

By John Hlinka, P.E.

34 Professional Issues Opposition to Structural Licensure

By Timothy M. Gilbert, P.E., S.E., SECB

36 Structural Testing Lateral Loads Generated by Occupants on Exterior Decks

By Brian J. Parsons, Donald A. Bender, P.E., J. Daniel Dolan, P.E. and Frank E. Woeste, P.E.

40 Engineer’s Notebook Concrete Column Design

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

IN EVERY ISSUE 8 Advertiser Index 44 Resource Guide (Anchor Updates) 52 NCSEA News 54 SEI Structural Columns 56 CASE in Point

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Editorial

The “Ins” and “Outs” of new trends, new techniques and current industry issues the Software Black Box

By Andrew Rauch, CASE Chair

L

The question we must ask ourselves is how much of our design skill and interpretation do we want to delegate to software companies?

ast spring, I had the opportunity to attend one of the several terrific presentations that were part of the CASE Risk Management Convocation at the 2013 Structures Congress. This session was presented by James Parker and Pedro Sifre of Simpson, Gumpertz, and Heger, and I thank them for allowing me to present a portion of it to a wider audience.

The use of design software is in integral part of the structural engineering design process. None of us can imagine what our profession would be like without it. At the same time, it presents challenges and concerns to those who are responsible for the operation of an engineering firm. The attendees at this session discussed some of those challenges, including staff skills and training, the black box aspects of software, documentation of software results, and the delegation of design and code interpretation to software companies.

Are we training our staff to use software appropriately? Are we giving up an opportunity for young engineers to develop skills needed to conceive and implement structural designs by allowing them to extensively use software for design? As a young engineer, I learned design through repetition, reading code requirements and applying them in preparing calculations. (How many of you eventually memorized the member properties of some of the common beam sizes?) I began to understand what the expected results should be prior to performing the calculations. Today’s engineers need and use very different skills. They need to learn how to use software effectively, to learn how to properly build a structural model, and to learn how to make their design model interface with building information models. When and how do they develop a “feel” for the structure and intuition about a design that tells them if their design is reasonable?

The situation may arise where an engineer is using software to design a system they may not have previously designed. The software is able to provide design results for that structure, but has the engineer developed the skills to determine if the design results are correct or reasonable? Does the engineer have the skills necessary to approximate the design to verify the software results?

Obviously, in this situation, the engineer needs a significant amount of oversight.

Structural engineering software can also be a black box.

How often have you heard the explanation “that’s what the output said” in response to a question about a design result? How does the program handle design conditions such as unbraced length, cracked STRUCTURAL member stiffness, or the algoENGINEERING rithm for selecting the number INSTITUTE of shear studs on a composite beam? Often, the manual a member benefit

structurE

®

provides little information to help the engineer determine what process the software is using. Are we deferring code interpretation and some of our quality assurance to the software provider?

Documentation of design is another issue. Have you ever been looking for design information to answer a question and found no written calculations? You try to find a result from the software, only to find several versions of the model with no clear indication of which one is the most current or what the different models signify.

Young engineers will sometimes use the “brute force” method of design, using the computer to run multiple iterations. When it comes time to provide written documentation, suddenly there are pages and pages of calculation for a design problem that could have been designed much more simply. Are the requirements for computer analysis and design documentation procedures a part of your office policies and procedures?

The final question posed at this session asked how the profession should react. Should one (or all) of the structural engineering organizations provide reviews and vetting of software? Should we leave software verification to the purchasers and users, and let market forces drive software quality? Should the structural engineering organizations work with authorities having jurisdiction to demand certification or verification of software? While it would be nice to have third-party software verification, that is a Herculean task for structural engineering organizations that are run primarily by volunteers. For now, the consensus of those in attendance was to let market forces drive the quality.

The question we must ask ourselves is how much of our design skill and interpretation do we want to delegate to software companies? To our knowledge, there are no standards or requirements for software producers to check and verify their software. Writers of software codes are not required to be licensed to work under the direction of a licensed engineer. Our experience has been that every software program we have purchased or licensed has had some kind of error or bug that caused it not to work properly. How are we as individuals and as a profession going to react?▪

STRUCTURE magazine

Andrew Rauch is a principal with BKBM Engineers in Minneapolis, MN and is responsible for overseeing their quality assurance and risk management programs. He is the current chair of the CASE Executive Committee. He can be reached at arauch@bkbm.com.

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January 2014

Advertiser index

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Integrated Engineering Software, Inc..... 33 ITW Red Head ..................................... 29 KPFF Consulting Engineers .................... 8 NCEES ................................................. 41 NCSEA ................................................. 13 Pile Dynamics, Inc. ............................... 49 Polyguard Products, Inc......................... 50 Powers Fasteners, Inc. .............................. 2 QuakeWrap ........................................... 17

Editorial Board Chair

Chuck Minor Dick Railton

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

Brian W. Miller

CBI Consulting, Inc., Boston, MA

Eastern Sales Western Sales 847-854-1666 951-587-2982 sales@STRUCTUREmag.org

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Mark W. Holmberg, P.E.

Evans Mountzouris, P.E.

Heath & Lineback Engineers, Inc., Marietta, GA

The DiSalvo Ericson Group, Ridgefield, CT

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

KPFF Consulting Engineers, Seattle, WA

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

Khatri International Inc., Pasadena, CA

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

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

Brian J. Leshko, P.E.

John “Buddy” Showalter, P.E.

John A. Mercer, P.E.

Amy Trygestad, P.E.

BergerABAM, Vancouver, WA

CCFSS, Rolla, MO

American Wood Council, Leesburg, VA

HDR Engineering, Inc., Pittsburgh, PA Mercer Engineering, PC, Minot, ND

Chase Engineering, LLC, New Prague, MN

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AdvErtising Account MAnAgEr Interactive Sales Associates

Jon A. Schmidt, P.E., SECB

Craig E. Barnes, P.E., SECB

RISA Technologies ................................ 60 S-Frame Software, Inc. ............................ 4 Simpson Strong-Tie......................... 25, 39 The Soc. of Naval Arch. & Marine Eng. 44 Structural Engineers, Inc. ...................... 24 StructurePoint ....................................... 42 Struware, Inc. ........................................ 35 Subsurface Constructors, Inc. ................ 45 USP Structural Connectors ................... 11

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STRUCTURE® (Volume 21, Number 1). ISSN 1536-4283.

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January 2014

inFocus

new trends, new techniques and current industry issues Risk and Virtue Ethics

By Jon A. Schmidt, P.E., SECB

I

have previously (and repeatedly) cited a paper by philosophers Allison Ross and Nafsika Athanassoulis that highlights the risktaking nature of engineering practice and draws out some of the associated ethical implications. In two additional papers (“A Virtue Ethical Account of Making Decisions About Risk,” Journal of Risk Research, Vol. 13, No. 2, March 2010, pp. 217-230; “Risk and Virtue Ethics,” chapter 33 in Handbook of Risk Theory, Springer, 2012), the same authors discuss risk in a more general sense and argue convincingly that virtue ethics provides the most adequate approach for dealing with it.

Ross and Athanassoulis concede that “it would be convenient if there was a formula for making good and right decisions about whether, when, and what to risk.” This is essentially what the dominant modern ethical theories purport to offer: definitive guidance derived from universal principles, such as assumed duties and obligations (deontology) or assessment of anticipated outcomes (consequentialism). By contrast, virtue ethics recognizes that any truly substantive ethical inquiry will lead to “a complex, varied, and imprecise answer that cannot be captured in an overriding rule.”

When it comes to risk, Ross and Athanassoulis raise specific objections to consequentialism. Evaluations based only on what ultimately happens ignore the contributions of luck; for example, “avoiding the consequences of one’s recklessness does not make one any less responsible for it.” The alternative of assigning probabilities is problematic at best, and the corresponding utilitarian calculation often “clashes with our sense of fairness with respect to the equitable distributions of the burdens of risk taking.” Furthermore, it “does not allow room for differentiating between the bearers of risks and benefits,” who may not be the same parties.

Virtue ethics shifts the focus from individual actions to patterns of behavior – “choices that people make, those choices that are reaffirmed over time, and those choices that express their deeply held values and beliefs.” It is thus concerned primarily with someone’s long-term attitude toward risk, especially with respect to the potential impacts on the well-being of others. The central concept is character, defined

by Athanassoulis as “the set of stable, permanent, and well-entrenched dispositions to act in particular ways.” These dispositions qualify as virtues when they enable and incline someone “to respond well to whatever situation is encountered.”

The circumstances of greatest interest to Athanassoulis and Ross are those in which a person – say, an engineer – must intentionally make “choices that involve risk to others”; i.e., when all of the following conditions hold: • The person is deliberating whether to take a certain action.

• The person cannot guarantee the outcome of that action; there are multiple possibilities, one or more of which would affect others.

• The person is able to estimate (at least roughly) the likelihood of various outcomes.

• Some outcomes are desired, while others are unwanted (by the person and/or others).

• The person perceives the prospect of a positive outcome as outweighing the danger of a negative one.

STRUCTURE magazine

According to virtue ethics, the last item is crucial and cannot simply be the product of a straightforward cost-benefit analysis. Instead, it requires “a state in which the faculties of perception, motivation, thought, and reason seamlessly interact” to discern the relevant contextual features and properly take them into account – i.e., the exercise of practical judgment or phronesis. Since what subsequently transpires may not be entirely within the person’s control, what matters from an ethical standpoint is the quality of the decision at the time when it is made.

In other words, risk-taking is a good decision whenever it is based on defensible grounds, regardless of the actual results. Athanassoulis and Ross suggest that this criterion is usually satisfied whenever someone has “a clear and accurate view of the situation” and produces “a proportionate, rational response.” The underlying motives – fear, desire for pleasure, etc. – are not necessarily good or bad in themselves; what is important morally is “how, when and why we are moved” by them.

Nevertheless, Ross and Athanassoulis acknowledge a prominent place for emotions in the whole process: “Decisions about risk that proceed from a good character involve emotional responses, which are integral to firm and stable dispositions to virtue … The person of practical wisdom is someone who has the appropriate emotions, to the right degree at the right time.” Such sentiments may seem out of place in an engineering magazine; after all, engineers generally view themselves – and are widely viewed by others – as paragons of unbiased analysis and dispassionate design. But is this an accurate picture? And if so, should it be?

The framework that I have proposed for applying virtue ethics to engineering practice identifies not only objectivity and honesty as moral virtues of engineering, but also care. Is it possible for engineers to exhibit genuine care for the people who will be affected by their work while not experiencing any feelings toward them whatsoever? Can we be completely indifferent and still “hold paramount the safety, health, and welfare of the public” as stipulated by the most fundamental canon in our codes of ethics? Instead, perhaps emotions should play a more explicit role in our decision-making about risk.

In summary, according to Athanassoulis and Ross, “a decision to risk is a complex decision which involves the bringing together of personal reasons for acting, moral reasons for acting and a whole range of facts … Good judgements require phronesis and sensitivity and these are skills that are acquired and internalised through a process of observation and emulation of good exemplars, practice and reflection.” As engineers, we are routinely confronted with such decisions; are we going about them in the right way and preparing ourselves accordingly?▪ Jon A. Schmidt, P.E., SECB (chair@STRUCTUREmag.org), is an associate structural engineer at Burns & McDonnell in Kansas City, Missouri. He chairs the STRUCTURE magazine Editorial Board and the SEI Engineering Philosophy Committee, and shares occasional thoughts at twitter.com/JonAlanSchmidt.

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January 2014

Structural ForenSicS investigating structures and their components

A

s discussed previously in Untreated Submerged Timber Pile Foundations – Part 1 (STRUCTURE® magazine, December 2013), deterioration of pile tops exposed above groundwater levels is a wellknown problem. It is less known that submerged portions of timber piles can also deteriorate with time, albeit at a slower rate, due to bacterial attack. This may become critical when considering underpinning methods aimed at extending service life of structures supported on timber piles.

Historically, timber-pile supported structures have been underpinned by the cut-and-post method, where the top portion of the timber piles is cut and replaced with concrete posts or concreteencased steel posts. Although the cut-and-post method appears to be relatively straight forward and simple to execute, it remains an expensive undertaking due to accessibility issues, required temporary shoring and bracing, dewatering, and labor costs. Klaassen (2008-1) reports that, in the Netherlands, foundation replacement or repair sometimes involves up to 50% of the total renovation costs for a structure.

The authors’ experience in the Boston, Massachusetts area indicates cut-and-post underpinning of a typical downtown row house costs approximately $200,000 to $250,000. Bacterial attack in the remaining, submerged portion of the timber piles, however, may limit the effectiveness of the cut-and-post method, as well as the estimated remaining service life of the piles.

Untreated Submerged Timber Pile Foundations Part 2: Estimating Remaining Service Life

By Giuliana Zelada-Tumialan, P.E., William Konicki, P.E., Philip Westover, P.E. and Milan Vatovec, Ph.D., P.E. Giuliana Zelada-Tumialan, P.E., is Senior Project Manager at Simpson, Gumpertz & Heger, Inc., Giuliana may be reached atgazelada@sgh.com.

Remaining Service Life The aim of any foundation remediation/repair design is similar to that of new foundation

design: its design and execution must be able to (1) safely sustain all likely applied loads without failure (i.e. without overloading beyond the strength capacity of the foundation system), and (2) remain serviceable for the required use of the structure (e.g. without excessive settlement) during its intended service life. Hence, one of the greatest challenges in pile foundation remediation/repair design, and a key item for its success, is performing a reliable assessment of the current in-situ foundation’s material properties and loading history, after years in service and exposure to the surrounding natural environment. This forms the basis for the estimation of the remaining service life of the foundation system, if it is to be re-used.

The estimated remaining service life of any foundation system is governed by the determined minimum structural capacity (dependent on material properties and level of deterioration), the geotechnical capacity (dependent on soil properties and soil-structure interaction), and the magnitude of expected movements (e.g. settlement) compared to the allowable movements that a structure can sustain.

Determining Remaining Structural Capacity Based on the review of published literature and on relevant experience, the following approach is proposed to determine the remaining structural capacity of continuously submerged timber piles: Step 1 – Estimate the applied compressive stress acting on the timber pile cross-section versus time, considering the reduction in available load-bearing pile cross-section due to continued bacterial decay penetration. For spruce and pine piles, an estimated rate of advance of severe degradation of 0.0051 inch/year and 0.0098 inch/year,

William Konicki, P.E., is Senior Principal at Simpson, Gumpertz & Heger, Inc. William may be reached at wpkonicki@sgh.com.

Philip Westover, P.E., is a Staff Consultant at Simpson, Gumpertz & Heger, Inc. Philip may be reached at plwestover@sgh.com.

Milan Vatovec, Ph.D., P.E., is Senior Principal at Simpson, Gumpertz & Heger, Inc. Milan may be reached at mvatovec@sgh.com.

Figure 1: Decrease in timber pile compressive strength with in-service age (Base figure from Van Kuilen, 2007).

10 January 2014

would be expected that more than 90% of the applied load is resisted by the stiffer and stronger heartwood.

Step 2 – Estimate timber pile compressive strength versus time by using the reduction in compressive strength due to aging/ duration of loading for heartwood shown in Figure 1. This assumes that all of the remaining pile section (based on probing to measure the depth to sound wood), including any small amount of sapwood present, can be represented by the reduced average compressive strength for heartwood.

Step 3 – Determine estimated remaining structural service life of submerged timber piles by determining the time (from present) at which the demand-to-capacity (D/C) ratio for the various timber pile diameters considered (i.e. the ratio of applied compressive stress to the remaining compressive strength) is equal to the desired factor of safety level.

Alternatively, the designer may choose to use a target minimum allowable percent loss in pile cross-section to determine the remaining structural service life of the submerged timber pile. continued on next page

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respectively, can be used (Klaassen 2009). The following considerations should be included: • Current measured penetration of severe bacterial deterioration (based on probing to determine depth to sound wood) to be used as the starting point from which future reductions in pile cross-section will occur.

• Determine the taper of the timber pile for estimation of the pile tip diameter based on pile top diameter. Timber piles in many cases tend to derive their capacity by end bearing on a suitable soil stratum; therefore, the critical pile section is located at or near the pile tip. The rate of severe bacterial degradation should be applied uniformly over the entire pile length.

• The rate of bacterial attack decreases significantly beyond the heartwood-sapwood interface in spruce and pine piles. Therefore, for these species at least, it is reasonable to assume that for the most typical required service life of structures (i.e. 100 years or less), only the sapwood will deteriorate significantly and no further reduction in pile cross-section due to bacterial decay is expected once the sapwood thickness has been expended. The determination of the sapwood/heartwood boundary requires microscopic examination for heartwood signs, and for bacterial invasion and deterioration at different depths within the pile; this can be subjectively influenced by the examiner’s experience.

Without detailed microscopic observations, the depth to the heartwood/sapwood boundary can only be roughly estimated from obvious color changes in the wood, or based on publications like The Wood Handbook (USDA, 2010) or the Textbook of Wood Technology (McGraw-Hill, 1980).

• Although the deteriorated sapwood has some measurable compressive strength, it seems prudent to ignore its contribution to the timber pile strength capacity. Measured values of elastic modulus for specimens of deteriorated sapwood obtained from piles (from previous projects) indicate that the ratio of elastic moduli between deteriorated sapwood and sound heartwood is in the range of 0.1 or less. Therefore, it

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Pile Service Load (P) = 20 kips 3000

Estimated Future Settlements

Applied Compressive Stress:

Once cut-and-post underpinning is performed (i.e. no inelastic settlement due to softening of pile tops), and assuming no change in the level of 2500 7-inch diam. pile butt applied loads or in soil or groundwater properties, the only viable mechanism for future settlement is 8-inch diam. pile butt 2000 elastic compression of the remaining submerged 9-inch diam. pile butt timber pile sections. This can be due to potential softening as a result of aging/creep, and decay 1500 10-inch diam. pile butt (i.e. a decrease in the Young’s modulus, E) of the timber piles. The National Design Specification® 11-inch diam. pile butt 1000 (NDS®) for Wood Construction (2005) recommends a creep factor of 2 for wet wood, i.e. the 12-inch diam. pile butt E value should be decreased by 50% under long500 term permanent loads. Current design standards Estimated Average Heartwood do not provide recommendations for further Ultimate Compressive Strength 0 reductions in E values due to decay.

Time to 50% Pile Tip Cross0 100 200 300 400 500 A review of limited data available from compresSection Loss Time (in years from 2009) sive-strength testing of timber pile samples from Figure 2: Sample plots of applied compressive stress and estimated heartwood various projects throughout northern U.S. (with compressive strength vs. time. in-service ages ranging from about 100 years to 137 years) indicates that there may be an ongoing Figure 2 shows a sample plot of the calculated reduced heartwood reduction in E values with time, similar to that of compressive strength compressive strength with time (Step 2), superimposed on plots of values. However, the data spread is too broad and the breadth of time the applied compressive stress curves developed for various timber periods too limited to be able to more accurately and reliably infer a pile diameters as bacterial decay penetrates to the heartwood/sapwood rate of degradation of the E value with time. boundary for a service load of 20 kips (Step 1). The intersection of the Assuming a 50% loss of cross-section in the timber piles, a pile length time under load dependent ultimate heartwood compressive strength of about 10.5 feet, and using an E value of 1.2 x 106 psi for spruce curve and the applied compressive stress curves defines the expected (average published E value for fresh spruce from ASTM D2555-06), remaining pile service life for each pile diameter at the expected load the added submerged pile settlement under sustained loads varies from combination, with no factor of safety included. Figure 2 was developed less than 0.04 inches (for a service load of 50 kips combined with a for spruce piles with an in-service age of 109 years, 2-inch sapwood continued on page 14 thickness, and measured severe bacterial attack penetration of about 0.75 inches at time zero. The plot of applied compressive stress is 600 2609 shown in relation to the pile butt (pile top) diameter, rather than the critical pile section (i.e. pile tip) used to calculate the applied stresses for ease of use during investigations where, typically, just the pile tops 500 2509 are exposed. Figure 2 also shows the time for 50% loss of original pile cross-section for reference.

400 2409 Figure 3 shows plots of the estimated remaining service life for each timber pile butt (top) diameter and different levels of applied service load calculated similarly to Figure 2, and considering a D/C ratio of 300 2309 1.0 (i.e. no factor of safety is included). Since Figure 2 only considers time up to 500 years, the curves in Figure 3 level off at 500 years.

Evaluation of Remaining Geotechnical Capacity The Table (page 14) summarizes the results of load testing on five timber piles from separate areas of a single project site in downtown Boston.

Two of these piles were extracted after the load tests were performed.

Results of the pile load tests indicate no apparent adverse impact of timber pile deterioration on the geotechnical bearing capacity of the piles. Area 1-1, which showed a larger penetration depth of severe deterioration (with 75% or more loss of pile cross-section), performed stiffer and had a higher measured unit end bearing capacity than the Area 1-2 pile which showed less deterioration (about 34% loss of pile cross-section). However, the data evaluated in this analysis is too limited to draw more in-depth conclusions regarding the impact of deterioration on the geotechnical capacity of the submerged timber piles.

STRUCTURE magazine

200

2209

100

2109

0

4

6 8 10 Pile Butt (Top) Diameter (in.)

12

Remaining Structural Service Life (Year)

Remaining Structural Service Life (Beyond 2009, in years)

Compressive Stress (psi)

6-inch diam. pile butt

2009

P = Applied Service Load (per pile): P = 10 k

P = 20 k

P = 30 k

P = 40 k

Figure 3: Sample plots of estimated remaining structural service life of submerged timber piles.

12

January 2014

P = 50 k

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Summary of pile load tests.

Load Test

Pile Tip Diam (inches)

Max. Applied Load (Kips)

Max. Measured Pile Top, Total Settlement (inches)

Inferred Ultimate Unit End Bearing Capacity (ksf (1))

Theoretical Ultimate Unit End Bearing Capacity (ksf (2))

Area 1 – 1

7 (3)

70

0.56

224.5

220

Area 1 – 2

9

70

0.63

113.2

190

Area 2 – 1

6.5

(4)

40

0.57

130

130

Area 2 – 2

6

(5)

50

0.24

N/A

170

Area 2 – 3

8 (5)

60

0.71

114.5

110

(1) (2) (3) (4) (5)

(5)

Based on Davisson’s Offset Criteria.

Based on Meyerhoff’s method for driven piles in sand (Meyerhoff 1976).

Severe to moderate soft rot/bacteria deterioration penetrating about 1.5 to 2 inches into the pile at the pile tip.

Severe soft rot/bacteria deterioration penetrating about 0.75 inches into the pile at the pile tip.

Estimated based on pile taper. Condition of pile tip not known. Microscopy on upper pile sections indicate none to slight bacterial erosion in outer 0.5 inches.

12-inch pile diameter), to about 0.2 inches (for a service load of 50 kips and a 6-inch pile diameter). Even if it is assumed that, over time, the E value has degraded to about 50% of its original value throughout the pile length, the added submerged pile settlement under sustained loads for the same assumed conditions remains low, varying from about 0.1 inches to 0.4 inches. If the applied loads are sufficiently high, longer pile lengths could result in settlements greater than 0.5 inches.

Based on the calculation case described above, added settlement solely due to pile elastic compression will likely not exceed 0.5 inches over the remaining service life of timber piles. However, detailed settlement calculations, taking into account actual pile diameters, pile lengths, measured pile properties and applied load magnitudes, must always be performed. Although most structures can experience differential settlements on the order of 0.5 inches without resulting in much structural distress, the foundation remediation designer will have to take into consideration the present condition of the structure. If the structure is fragile and has already undergone significant settlements, even small added settlements could have an adverse impact on its serviceability.

Conclusions • The remaining service life of in-service timber piles appears to be controlled by the structural capacity of the timber piles, rather than their geotechnical capacity. Evaluation of a more significant amount of data is necessary for confirmation of this postulate.

• Measured rates of bacterial deterioration indicate that, for piles with 100 to 140 years of in-service age

and with diameters of 6 inches or less, bacterial decay may have advanced sufficiently that little to no remaining service life is anticipated. For relatively small applied service loads (around 10 kips per pile and no factor of safety included), pile diameters of 7 inches or greater are likely have a remaining service life of 100 years or greater from present time. For larger applied loads (on the order of 40 to 50 kips per pile), pile diameters of 10 inches or greater would be required to attain the same remaining service life expectancy (100 years or more).

• Once tops of piles are replaced and the new pile cutoffs remain submerged (e.g. cut-and-post underpinning is performed), settlements due to pile elastic compression over the remaining service life of the timber piles will likely not exceed 0.5 inches.

The analysis used herein to estimate remaining service life of submerged timber piles is based on average conditions (i.e. average measured strength and/or modulus values).

Although measured strength and modulus data is well distributed around the average values used, there is still a 50% probability that the actual values may be lower or higher than the ones used. In addition, other than limiting the depth of penetration of bacterial decay to include only the thickness of the sapwood of submerged piles, it is possible that local building codes may require foundation remediation/repairs be performed once a certain percentage of the original pile capacity has been lost. For the smaller-diameter timber piles, this would likely result in smaller remaining service life expectancies than those indicated above.

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January 2014

Final Thoughts Further research remains to be performed regarding the impact of bacterial attack on submerged timber pile structures, especially any potential reduction of the pile’s geotechnical capacity.

There is also continued concern that soft-rot deterioration could still occur even with groundwater levels maintained above the top of the untreated pile cutoff. Recent research indicates that soft-rot attack may be supported even in submerged conditions, if the dissolved oxygen content in the groundwater is above a threshold value of 2 ppm (Klaassen 2005). Given that potable water is often used for recharging groundwater levels near timber piles to maintain submersion, and this could lead to an increase in dissolved oxygen levels in the groundwater, further research is required to confirm this potential deterioration mechanism.

Development of a large database of U.S. historic building stocks supported on untreated timber piles, similar to that currently in existence for some European countries, would be of significant value in evaluating current conditions and required foundation remediation/repair options. Based on the European studies on bacterial decay, existing untreated submerged small-diameter timber piles with more than about 100 years in service (which represents a significant percentage of the existing untreated timber pile stock in the U.S.) are likely to be reaching a level of bacterial attack at which there is little to no remaining service life. For these structures, significant structural settlement, with the consequent building distress, may start developing within a relatively short-time from present.▪ The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

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Historic structures significant structures of the past

Figure 1: Bridge No. 92297 shortly before demolition. Photograph by Daniel R. Pratt, courtesy of MN Historical Society Archives.

T

wo days of expected work turned into a week; one equipment breakdown cascaded into another; a 30-minute delay became 24 hours. A documentation project that was scheduled to happen in June did not begin until September.

The challenges of keeping a bridge demolition project on schedule are not unique, but the requirement for historical documentation of a 1912 reinforced concrete bridge by historians and engineers added another layer of complexity to a highway widening project. However, this documentation effort ultimately provided interesting information about the early development of reinforced concrete flat slab design.

The historians’ involvement was prompted by a routine set of circumstances. The structure in question, Bridge No. 92297 – enumerated as part of a statewide inventory of highway bridges – was being demolished in order to facilitate a joint Minnesota Department of Transportation (MnDOT) and Federal Highway Administration (FHWA) project to reconstruct and widen a section of the adjacent Interstate Highway I-35E in St. Paul. The FHWA provided federal dollars, which triggered the process known as a “Section 106 review.” Passed in 1966, the National Historic Preservation Act (NHPA) created the National Register of Historic Places and requires all federal agencies to take historic resources “into account” when funding, permitting, or licensing undertakings. Section 106 of the NHPA describes a process of planning for preservation in advance of construction.

For this project, MnDOT retained Summit Envirosolutions, Inc. as the cultural resource consultant to complete the initial portion of the Section 106 review: identifying historic or potentially historic resources by researching properties and structures in the area that would be affected by the highway expansion. Through this process,

Deconstructing Bridge 92297 From Destruction Comes Knowledge

By Ryan Salmon, EIT and Meghan Elliott, P.E., Associate AIA

Ryan Salmon, EIT (salmon@ pvnworks.com), is a project associate and Meghan Elliott, P.E., Associate AIA (elliott@pvnworks. com), is the founder and owner at Preservation Design Works, LLC, a historic preservation consulting and project management firm in Minneapolis, Minnesota.

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

16 January 2014

the consultants determined that Bridge No. 92297 was historically significant. In instances when a federally funded project affects a historic resource, the project agency must work with the State Historic Preservation Office (SHPO) to determine how best to mitigate the impact.

Options can range from major changes, such as re-routing a proposed road, to documenting the historic structure prior to demolition, as was the case with Bridge No. 92297. The pending demolition of the bridge presented a unique opportunity to investigate the steel reinforcement concealed within the structure. The team conducting the sequenced research, documentation and demolition included Summit Envirosolutions, Preservation Design Works (PVN), a photographer, MnDOT engineers, and the contractor.

Bridge No. 92297 was a monolithic, single-span, reinforced concrete flat slab deck with vertical abutments supported on reinforced concrete strip footings, constructed in 1912 (Figure 1). It was oriented on a 35-degree skew, measured 49 feet in total length, and had a clear span of 41 feet with a 60-foot-wide deck. Without any background about its history, the bridge would have appeared rather unremarkable. However, research on the bridge revealed that it was an innovative design for its time. Its documentation shed more light on the work of the bridge’s designer, and also created a record available for future study.

C.A.P. Turner and the Flat Slab Claude Allen Porter (C.A.P.) Turner, a Minneapolisbased structural engineer, was a pioneer in the development of the reinforced concrete flat slab and designed bridge No. 92297. According to several articles by Dario Gasparini, Turner was born in Lincoln, Rhode Island in 1869, and graduated from Lehigh University in 1890. He subsequently worked for various bridge companies until 1901, when he began his own consulting firm with the Minneapolis, St. Paul and Sault Ste. Marie Railroad (the “Soo Line”) as a principal client (Gasparini, 2002). As Turner progressed in

Figure 2: Excerpt of C.A.P. Turner’s U.S. Patent 1,002,945: “Short-Span Flat-Slab Bridge,” filed October 1, 1909. Although the deck reinforcement of Bridge No. 92297 did not resemble the design in this patent, the profile of the deck, abutments, and footings, as well as the abutment reinforcement bears a striking resemblance. Digitized by Google Patents.

his career, he expanded his practice to the design of buildings, including the first one in Minneapolis with reinforced concrete floors and columns in 1904. His major breakthrough in concrete design would be realized two years later: in 1906, Turner designed his first building with the “mushroom” system of flat slab floors, the Johnson-Bovey building in Minneapolis (now demolished).

In the next few years, implementation of Turner’s proprietary flat slab floor system grew at a furious pace. His design consisted of floors with four-way reinforcement supported directly on reinforced concrete columns, each with a distinctive flared capital. Between 1906 and 1910, Turner claimed that buildings constructed with his system were “rapidly approaching a thousand acres of floor” (Turner, 1910; 7-12). This growth can be attributed in part to his extensive publication of designs and load test results for his flooring system in nationally prominent engineering journals, which proved their reliability and cost-effectiveness. However, a series of patent lawsuits and countersuits beginning in 1911 resulted in a dramatic downturn in the use of Turner’s flat slab system. Nevertheless, he substantially contributed to the acceptance of reinforced concrete flat slab technology

among practicing engineers (Gasparini, et al., 2001; 17-21).

In addition to implementing his system in buildings, Turner designed several reinforced concrete flat slab bridges, most as adaptations of his mushroom floor system. To date, all known flat slab bridges in the Twin Cities designed by Turner have been demolished. The bridge decks were often designed with four-way reinforcement similar to his floors, with longitudinal, transverse, and diagonal steel. With the exception of a tunnel originally located not far from the area studied for this project, Turner’s published examples of flat slab bridges did not bear much resemblance to Bridge No. 92297 (Gasparini, et al., 2001; 12-27). However, Turner held a number of related patents for both floor systems and bridges, one of which bears a striking resemblance to Bridge No. 92297, particularly the configuration of the abutment reinforcement (Figure 2).

Copies of construction drawings and plans dating to the erection of the bridge, as well as correspondence between the Soo Line railroad engineers and the city of Saint Paul engineers, revealed some insights into the bridge’s design and also raised questions. Although the discovery of original drawings was fortuitous – and rare for a structure of this age – the copies

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STRUCTURE - January 2014 HP-H-4C.indd 1

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were of poor quality and only partially legible (Figure 3 ). Of the six sheets in the set, one was stamped with “CAP Turner Consulting Engineer” in the title block, while the “Chief Engineers Office” of the railroad was stamped on the remaining sheets. The date of the sheet stamped with Turner’s firm was illegible, but several of the sheets stamped by the railroad engineers were clearly dated to 1912. The correspondence between engineers indicates that plans were originally drawn for the bridge in 1908, and then were revised in 1912 because the earlier plans did not meet the standards of Figure 3: Original construction drawing of plan and elevation of Bridge No. 92297. the 1907 city ordinance. Summit Envirosolutions postulated that the drawing considered an ideal method of research, the sheet stamped by Turner was part of the removal of this 1912 bridge presented an original 1908 set, and the remaining sheets opportunity to gain additional knowledge were a revision of Turner’s design made by of early flat slab bridge design. the railroad’s engineers.

Interpretation of the original drawings Deconstruction and was also hampered by their poor legibilDocumentation ity and a lack of corresponding notes or engineering calculations. This was com- Bridge No. 92297 was documented to pounded by the fact that changes had Minnesota Historic Property Record obviously been made to the bridge after (MHPR) standards. MHPR is a modified its construction, such as the replacement version of the national standard Historic of the railing and the installation of a new American Engineering Record (HAER) topping slab, which complicated efforts to program. The HAER program documents differentiate original and more recently nationally significant historic mechanical added features. Despite these difficulties, and engineering structures and sites; the comparison with observed conditions, the extensive collection is digitized and available original drawings, and Turner’s patent for to the public on the Library of Congress weba similar bridge design, led to the con- site (www.loc.gov/pictures/collection/hh/). clusion that the structural design of the Both programs maintain documentation of bridge can be substantially attributed to historic resources, and have a target archival C.A.P Turner. life of 500 years. The MHPR materials for The complications that the team expe- Bridge No. 92297 included a report with rienced in reading the Bridge No. 92297 a written description, large format photodrawings are actually typical obstacles to graphs, and measured drawings of selected understanding historic engineering struc- areas of the bridge highlighting its design tures. Any engineer asked to retrofit an older and construction. building can relate to the frustration of not Deconstructing and documenting a historic being able to locate the original engineering bridge requires time, care and coordination design drawings; while architectural draw- that is not required with standard demoliings are often kept as much for their visual tion and removal (Figure 4). Determining appeal as their content, engineering drawings the configuration of reinforcement for comare often inadvertently lost, or even inten- parison to the original construction drawings tionally destroyed for insurance and liability required investigative openings in areas that reasons. Likewise, details of the construction would expose representative samples of reinmethods and sequence may never have been forcement in the bridge deck, abutments and recorded, but rather negotiated in the field footings. Maintaining stability of the bridge by a contractor or builder. Finally, the struc- to allow for safe access after its partial demoture itself is often concealed, limiting the lition, as well as to expose sections of the ability to measure and record the structural abutments and footings, required an extensive elements. While deconstruction is not often amount of earthwork.

STRUCTURE magazine

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January 2014

A two-stage demolition process accommodated the documentation process. Backhoes equipped with hydraulic jackhammers removed concrete in selected areas of the bridge to expose reinforcement. Fill placed below the bridge stabilized the abutment walls during the exposure and removal of the deck. Two full-depth openings in the bridge deck – one near the middle, and another along the edge and the adjoining transition into the top of the abutment – facilitated its documentation before complete demolition.

Next came excavating soil on both sides of the abutment to the top of the footing, then removing concrete from the selected area to expose the underlying reinforcement. The investigation team took measurements and photographs all along the way.

This investigative process was hampered by poor accessibility of the machinery, especially after demolition of the bridge began to compromise its ability to support heavy loads. There were several equipment breakdowns, and the existing concrete was stronger than expected in some locations. These issues created unforeseen delays that impacted the demolition schedule.

Despite the slower than expected progress of the work, careful operation resulted in exposure of the majority of the reinforcement with minimal changes to its as-built configuration.

The destructive nature of the work resulted in some deformation or breakage of the reinforcement being recorded. In these cases, carefully exposing adjacent sections made it possible to document the typical configuration of reinforcement as originally placed.

The plan and profile of reinforcement was generally congruent with the original construction drawings from 1912, with the exception of minor details and extra reinforcement along the fillet corner in the deck-to-abutment transition. The skewed geometry of Bridge No. 92297 was not well-suited to Turner’s patented short-span bridge design, but the two layers of slab reinforcement in the bridge were similar to the configuration of diagonal reinforcement in Turner’s patent. One layer of slab reinforcement was placed parallel to the span of the bridge, and the other layer was placed perpendicular to the abutment walls.

Some transverse reinforcement was present, which correlated with the patent, but it was so widely spaced – over five feet on center – that its intended purpose was likely just to support the draped geometry of the two primary layers of slab reinforcement. The profile of the

Figure 4: Careful demolition of the bridge revealed the reinforcement, facilitating its documentation in selected areas.

slab and abutment reinforcement correlated closely with the design illustrated in Turner’s patent. Because of the geometry of the bridge span, the flat slab of Bridge No. 92297 more closely resembled a one-way structural system, rather than the four-way systems found in Turner’s published designs.

Considering its age, Bridge No. 92297 was in remarkably good structural condition and continued to perform as intended by carrying heavy vehicular traffic even into the start of demolition. Despite the somewhat deteriorated condition of the bridge, including concrete spalling and substantial graffiti, its continued use had demonstrated that the early design was not only adequate for the

streetcar loads at the time of construction, but also remained suited for the loading demands imposed by modern traffic.

Conclusion Researching the history of engineering has unique and persistent challenges: structural details are concealed, drawings are often not available, and the field is relatively new compared to the more established scholarship of architectural history. However, programs such as the MHPR and HAER provide a framework for expanding this field of study.

When demolition of a resource is unavoidable, documentation can partially mitigate its

loss by recording and allowing for the future study of its features. Understanding the history of a profession can provide a valuable perspective on how its common practices and philosophy have evolved.

Likewise, engineers seeking to preserve or rehabilitate existing structures can benefit from studying previously documented and demolished examples for the insights that they provide into design and construction. Bridge No. 92297 offered a unique opportunity to document the details of the steel reinforcement in a historic reinforced concrete structure, a task that is – for obvious reasons – generally infeasible for such structures that are to remain intact.▪

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STRUCTURE magazine COLORS

JOB#

19

FILE NAME

January 2014 OK as is

Structural rehabilitation renovation and restoration of existing structures

A

s a part of Pennoni’s on-call contract with an existing client, the Philadelphia structural division investigated and developed repair bid documents for an existing, three-level, 1,200-space precast concrete parking garage during the last quarter of 2012.

Part 1 of this series (September 2013) described the existing structure and summarized Pennoni’s observations and material testing results. Part 2 (November 2013) presented an analysis of those findings. This article conveys Pennoni’s conclusions regarding the feasibility of repairing the garage in order to extend its service life.

The third level precast, prestressed inverted “T” concrete girders that supported the 16-inch deep double tees were in extremely poor condition.

The corresponding second level girders were also in poor condition due to high chloride content, and several locations exhibited large subsurface delaminations. The cast-in-place, post-tensioned concrete inverted “T” girders that supported the conventional 24-inch-deep precast double tees were generally in fair condition due to limited deterioration at isolated areas. In addition, the extremely high chloride content of all of the concrete, in conjunction with ongoing carbonization, was expected to cause deterioration to accelerate in the near future.

Material testing indicated that the existing concrete in the garage girders had a chloride content that was significantly greater (25 times) than the limit recommended by ACI for prestressed structures in a moist environment that are exposed to chlorides in the form of either admixtures or deicing salts (0.06%). None of the previous testing performed in 2002 or 2005 included chloride testing from the beams, therefore the previous reports failed to reveal the true nature of the current rapid demise of the garage. Extrapolating the results of carbonization analysis indicated that the depth of carbonization would reach the embedded reinforcing in approximately two to three years. Significant repairs would be required within that time to prevent permanent damage to the embedded reinforcing.

Prescription for Repair The Triage, Life Support and Subsequent Euthanasia of an Existing Precast Parking Garage – Part 3

By D. Matthew Stuart, P.E., S.E., F.ASCE, F.SEI, SECB, MgtEng and Ross E. Stuart, P.E., S.E.

D. Matthew Stuart, P.E., S.E., F.ASCE, F.SEI, SECB, MgtEng (MStuart@Pennoni.com), is the Structural Division Manager at Pennoni Associates Inc. in Philadelphia, Pennsylvania.

Ross E. Stuart, P.E., S.E. (RStuart@Pennoni.com), is a project engineer at Pennoni Associates in Philadelphia, Pennsylvania.

Service Life Analysis Pennoni determined that the practical remaining operational service life of the existing parking structure was approximately two years. This was commensurate with the large spalls and severely corroded reinforcing, observed during the site visit, at the girders associated with the barricaded portion of the third level. In addition, the service life calculations were considered representative of the remaining portions of the garage, which indicated that some if not all of the other third floor girders would also begin to corrode in the same fashion within the next two years, and the second level would follow shortly thereafter.

20 January 2014

From an engineering perspective, the service life of a structure is considered to be over when the extent of deterioration renders the facility inoperable due to impending hazards to public safety, and remediation is required in the form of complete repair or replacement. Therefore, the end of a structure’s service life does not mean that it is in a state of imminent collapse, but instead implies that the structure can no longer safely function or support minimum loads as required by the building code.

In the case of this particular garage, vehicles and pedestrians would no longer be able to use the entire garage for parking, similar to the current partial loss of service at the third level. Pennoni estimated that, within the next two years, the garage would have to be progressively closed as additional areas became unsafe, until eventually the entire facility would be completely out of operation. The eventual and unavoidable loss of use of the entire garage by the current occupants would therefore have a direct impact on the practical everyday operations of the facility in the very near future.

Typically, a garage constructed with precast concrete components should have a useful lifespan of 40 to 50 years before significant repairs would be required. In this case, the actual service life of the garage in the absence of any remediation will be approximately one-half of this duration.

The shortened lifespan of the garage is directly attributable to the use of chloride-containing admixtures in the main girders.

Feasibility of Repairs It is clear from the results of the condition assessment, material testing and investigation that the primary source of the internal reinforcing and concrete deterioration in the garage was the presence of excessive chlorides in the concrete in conjunction with continued exposure to deicing salts. In addition, it was anticipated that further carbonization of the concrete would cause additional deterioration of the structure. Therefore, any solutions involving the repair and restoration of the garage to extend its service life would have to address the presence of the high chloride content.

Typically, a chloride extraction process, such as Norcure by Vector Corrosion Technologies, or an active galvanic protection system, such as Ebonex or Vectrode TiTape by Vector Corrosion Technologies, could be used to reduce or remove the chloride ion content or arrest the current rate of deterioration in conjunction with conventional concrete repairs. However, the presence of the high-strength prestressing steel precluded the use of chloride extraction processes or active galvanic protection systems due to the potential for hydrogen embrittlement of the strands, as described

by State-of-the-Art Report: Criteria for Cathodic Protection of Prestressed Concrete Structures, published by NACE International – The Corrosion

H2O

Society. Damage to the internal prestressing steel due to hydrogen embrittlement would clearly further increase the degradation of the structure.

Pennoni performed additional research as part of an exhaustive effort to verify that there were no other practical long-term repair methods of lowering the extremely high chloride content besides the types of systems mentioned above. This led to a state-of-the-art technology, known as nanoparticle treatment, which is intended to address the corrosion of internal reinforcing of distressed prestressed concrete beams. ACI Materials Journal Technical Paper 109-M60, “Corrosion Mitigation in Reinforced Concrete Beams via Nanoparticle Treatment” (Kunal et al.), contains a thorough discussion of this process, which is not commercially available at this time.

Based on the results of the referenced ACI study, the potentials during and after the nanoparticle treatment were as negative as -1200 millivolts (mV). However, the threshold for hydrogen embrittlement in high-strength prestressing reinforcement is around -1060 mV (or more positive if the concrete pH is lower than 13). Therefore, even this new technology is not applicable for the repair of the garage. As a result, Pennoni was confident that no viable options existed for effectively reducing the chloride content in the existing girders to an acceptable level that would allow for a conventional repair. In addition, the presence of high-strength bonded reinforcing tendons would make conventional repairs very difficult and time-consuming because of the need to de-tension and then re-tension any strands impacted by deterioration as a part of the overall remediation process.

Furthermore, conventional concrete repairs, in the absence of chloride extraction or an active or passive galvanic protection system, would result in the accelerated deterioration of the remaining existing concrete due to the interruption of the incipient anode effect (see Figure). The incipient anode effect is a phenomenon by which steel corroding under the influence of chloride contamination dissolves, causing the formation of iron “ions” (tiny charged particles of iron). Simultaneously, electrons are released that flow along the bar and react with both air and oxygen at some point remote from the corrosion location.

The corroding areas are therefore supplying electrons to surrounding areas of steel, effectively providing localized cathodic protection to the adjacent steel. If the corroding area is removed and a repair patch is installed, without dealing with chloride contamination in adjacent areas, the natural cathodic

O2

H2O

O2

CI-

H2O

OH-

O2

OHFe(OH)

e-

Fe++

Fe++

CATHODE

ANODE

protection system is disabled. As a result, new corrosion cells rapidly occur on either side of the repair, resulting in accelerated premature failure of the surrounding concrete.

STRUCTURE magazine

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January 2014

eCATHODE

Part 4 will appear in a future issue and discuss recommendations for the temporary stabilization and ultimate replacement of the garage.▪

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O

n a recent chemical plant project for which the author was the Engineer of Record, an electrical contractor, contrary to contract specifications, manually arc welded electrical grounding conductors to reinforcing steel for a pipe rack foundation.

The electrician explained that the National Electric Code (NEC) allows welding to concrete encased reinforcing steel, and he frequently does so in lieu of independent electrical ground rods which were specified on this project. Paragraph 250.52 (A) (3) Concrete-Encased Electrode of the NEC does permit welding to reinforcing steel.

However, NEC does not reference AWS D1.4/ D1.4M Structural Welding Code-Reinforcing Steel or provide any guidance to the special rules, regulations, and procedures prescribed by AWS D1.4/ D1.4M. If AWS D1.4 is not followed for manual arc welding reinforcing steel, the structural integrity of reinforced concrete may be jeopardized.

Unfortunately, this particular contractor did not conform to D1.4 and the reinforcing steel was encased in concrete before a visual inspection could be conducted.

This article covers AWS requirements for welding reinforcing steel in reinforced concrete applications. It summarizes the main themes of the various sections as they pertain to welding reinforcing steel and contains guidelines for working with the body of rules and procedures for structural welding of reinforcing steel to reinforcing steel, welding reinforcing steel to structural steel, and welding reinforcing steel to electrical grounding electrodes. Implications to improve future projects are also addressed.

Fusion welds in shop fabrication of reinforcing steel and CADWELDs are outside the scope of this article. Electric resistance welds found in the fabrication process of welded-wire reinforcement are conducted by computer controlled welding machines within a controlled environment. A combination of pressure and heat generated by electric impulses fuse intersecting wires together.

Shop personnel are never engaged in the actual welding process and no filler material or other foreign matter is introduced. CADWELDs do not apply because the steel-filled coupling sleeve of a CADWELD is a mechanical splice in which molten metal interlocks the grooves inside the sleeve with the deformations on the reinforcing bar.

Weldability of reinforcing steel and compatibility of welding procedures need to be considered and closely supervised when manual arc welding of reinforcing steel is required. Weldability is determined by the chemical composition of steel and described by the Carbon Equivalent (CE) number. Carbon is the primary hardening element in steel. Hardness and tensile strength are inversely related to ductility and weldability.

As carbon content increases up to 0.85%, so does hardness and tensile strength. As carbon

content decreases, ductility and weldability increases. CE is an empirical value in weight percentages, related to the combined effects of different alloying elements used in making carbon steel, of an equivalent amount of carbon. This value can be calculated using a mathematical equation. The lower the CE value the higher the weldability of the material. The welding Code provides two expressions for calculating CE. The first expression (Equation 1) only considers the elements carbon and manganese, and is to be used for all bars other than ASTM A706 material. A second more comprehensive equation (Equation 2 ) is given for ASTM A706 and considers carbon, manganese, copper, nickel, chromium, molybdenum, and vanadium content. Chemical composition is obtained through certified mill test reports or independent chemical analysis.

Chemical composition varies for each production run, so it is important to obtain the analysis that matches the specific material to be welded.

Once the CE number is calculated, the minimum preheat and interpass temperature is determined from Table 5.2 of the Code. If material test reports are unavailable and chemical composition is not known, which is particularly common in alterations and building additions of existing structures, the Code prescribes the highest preheat and interpass temperature for desired reinforcing bar size: 300° F (150° C) for number 6 bars and smaller, and 500° F (260° C) for number 7 bars and larger. If the chemical composition for ASTM A706 is not known or obtained, then preheat and interpass requirements are somewhat relaxed; no preheat is required for number 6 bars and smaller, 50° F (10° C) for number 7 to number 11 bars, and 200° F (90° C) for number 14 and larger.

As with all welding, when the material is below 32° F (0° C), the Code prescribes the material to be preheated to at least 70° F (20° C), and maintained during the welding process.

ConstruCtion issues discussion of construction issues and techniques

Welding Reinforcing Steel AWS D1.4/D1.4M:2011

By John Hlinka, P.E.

John Hlinka, P.E., is Senior Project Manager/Structural Engineer at QualEx Engineering in Paducah, Kentucky. He can be contacted at jhlinka@qualex.com.

CE = %C + %Mn/6 (Equation 1) CE = %C + %Mn/6 + %Cu/40 + % Ni/20 + %Cr/10–%MO/50–%V/10 (Equation 2) Standard specifications for low-alloy steel ASTM A706 limit chemical composition and CE to enhance weldability. However, it is permissible to weld other base metals, such as ASTM A615, which is commonly used in reinforced concrete, as long as the appropriate weld procedure specification (WPS) is followed and correct filler weld metal is used. Many other permissible base metals are listed under paragraph 1.3.1 of the Code. High strength reinforcing steel such as ASTM A615 material is susceptible to cracking when not adequately

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

Sample Material Comparison Table

Material Grade

Chemical Analysis (Percent)

Preheat Temp. °F (°C)

Rebar Size

C

ASTM A615

#7

0.39

1.00 0.018 0.037 0.21 0.39 0.20 0.13 0.038 0.00 0.00 0.56

200 (90)

ASTM A706

#7

0.28

1.18 0.028 0.028 0.17 0.29 0.19 0.09

50 (10)

Mn

P

S

Si

Cu

Cr

Ni

Mo

0.02

Cb

V

CE

0.00 0.24 0.48

Sample mill test report data with calculated CE numbers and minimum preheat and interpass temperatures from Table 5.2 of AWS D1.4.

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preheated. Welding of ASTM A615 material should be approached with caution, since no specific provisions have been included to enhance its weldability. The Table compares chemical composition, CE, and preheat temperatures for sample ASTM A615 and ASTM A706 materials. As shown, the preheat requirements are lower for A706 than A615 material. A lower carbon percentage and the addition of molybdenum and vanadium contribute to a lower CE number for A706. Bar size also is considered in determination of preheat temperature. The smaller the bar size, generally, the smaller the preheat temperature. With all rebar welding, allow bars to cool naturally. Never accelerate cooling; accelerated cooling will change the metallurgy of the reinforcing steel.

Sections 2 and 3 of the Code provide allowable stresses and structural details, respectively. A wide range of details are provided, including Direct Butt Joints, Indirect Butt Joints, Lap Joints, and Interconnection of Precast Members. The effects of eccentricity should be considered when designing Lap Joints, if external restraint is not provided.

AWS D1.4 does not provide details for welding reinforcing steel to electrical grounding conductors. If unavoidable, the author suggests using the CADWELD method to attach the grounding conductor to an ASTM A36 plate and then using the AWS Lap Joint detail to attach the plate to the reinforcing Software and ConSulting

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steel, or CADWELD the conductor directly to the reinforcing steel. Other mechanical type attachments provided by NEC are preferable to manual arc welding.

Section 4 of the Code addresses workmanship in regards to preparation of base metal, joint assembly, distortion, and quality.

Welding of bars which cross and welding within two bar diameters from the points of tangency for the radius of bent bars are not permitted. Cross bar welding can lead to local embrittlement of reinforcing steel.

When welding on bars that are already embedded in concrete, allowances must be made for thermal expansion of the steel to prevent spalling or cracking of concrete or destruction of the bond between the concrete and steel. Acceptable and unacceptable fillet and grove weld profiles are illustrated in Section 4 of the Code.

Section 5 of the Code discusses welding technique. Technique includes selection of filler metal, minimum preheat and interpass temperatures, welding environment, arc strikes, cleaning, progression of welding, coated base metal, and welding electrodes.

Allowed welding processes include shielded metal arc welding (SMAW), gas metal arc welding (GMAW), or flux cored arc welding (FCAW). Other processes maybe used when approved by the Engineer of Record. Special storage conditions are required for low-hydrogen electrodes. Low-hydrogen electrodes must be purchased in hermetically sealed containers or must be baked prior to use.

Selection of correct welding electrodes which are compatible with base metal material is critical. An incorrect choice may lead to micro cracking in the heat affected zone, which may lead to joint failure. Generally speaking, tack welds are prohibited unless they conform to all design and control requirements of D1.4.

Tack welding can create a metallurgical notch effect and weaken a bar at the weld.

Sections 6 and 7 of the Code pertain to welder qualifications and inspections, respectively. All structural welding must be performed by qualified welders. WPS qualification by testing must include

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January 2014

specific joint type and size to be welded.

Inspectors must also be qualified. Acceptable qualifications include AWS certification, Canadian Welding Bureau certification, or an Engineer/Technician trained or experienced in metal fabrication, inspection, testing, and who is competent to perform inspection work. It is not unusual for the Engineer of Record to request evidence of welder qualifications prior to starting a project. Annex A of the Code includes the following sample forms for informational purposes: Procedure Qualification Record (PQR), Welding Procedure Specification (WPS), and Welder Qualification Test Record.

Conclusion Welding of reinforcing steel should be approached with caution to prevent cracking of base metal and potentially jeopardizing the integrity of a reinforced concrete foundation or structure. AWS D1.4/D1.4M covers the design, workmanship, technique, qualification, and inspection requirements for welding reinforcing steel in most reinforced concrete applications.

NEC paragraph 250.52 (A) (3) allows welding of electrical conductors to reinforcing steel without reference to AWS D1.4/D1.4M. Electrical contractors can potentially damage the structural integrity of reinforced concrete foundations if the requirements of AWS D1.4 are not followed. Proposed Tentative Interim Amendments (TIAs) were submitted to the NFPA Standards Council on August 6, 2013.

Hopefully, the NFPA Standards Council will adopt these amendments.

In the case presented at the beginning of this article, the minimum amount of reinforcing steel required by ACI 318 provided greater than two times the strength needed for design loads. Therefore, if the integrity of one reinforcing bar was reduced, the foundation would still be structurally adequate.

The author suggests that a note be added to future concrete drawings that specifically prohibit welding of electrical conductors to reinforcing steel without the approval of the Engineer of Record.▪

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Concrete “Paint” Arrests Cofferdam Corrosion at Submarine Pier

By Brian Robinson, P.E.

E

ach year, the American Society of Civil Engineers (ASCE) publishes a Report Card for America’s Infrastructure. Their rating system uses familiar academic grading (A through F) to report on the condition of America’s aging infrastructure. Last year, America’s infrastructure received a D+, indicating deteriorating infrastructure. Included in this report are waterfront structures, which are vitally important. According to ASCE, America has over 3,700 maratime terminals serving as commerce and transportation hubs.

Often, steel sheet pile walls are incorporated as part of cost-effective waterfront earth-retaining structures for these harbors. Many of these walls are subjected to salt-water exposure, tidal fluctuations, and a host of other environmental factors that accelerate corrosion. Even if the coatings are maintained and a cathodic protection system is employed, the corrosion near the waterline eventually necessitates expensive repairs and, often, replacement of the structure. Cellular sheet pile cofferdams are particularly difficult to repair because of the lack of redundancy in the tensioned cell walls. This article highlights a unique method to repair a cellular cofferdam using a reinforced concrete facing installed over the aging sheet piling.

Existing Structure Configuration The submarine pier is located in the Hood Canal waterway in Washington State’s Puget Sound region. Considered a vital natural resource, Hood Canal provides vessel passage and is home to many aquatic species, some of which are fished for human consumption.

The triangular shaped pier, accessible from land by two pile-supported trestles serves as a vessel docking-surface on two sides and a dry dock is integrated into the third side of the triangle (Figure 1). The concrete deck supports gantry cranes, mooring hardware, and a number of buildings. Most of the deck is supported by concrete piles, but portions are supported by a cofferdam that surrounds the dry dock structure. The cofferdam is formed by a series of circular interlocking steel sheet pile cells that form the outer perimeter of the dry dock structure. These sheet piles were vibrated or driven into the underlying seabed, and

Figure 2: Existing failing cofferdam coating.

STRUCTURE magazine

Figure 1: Submarine pier aerial view. Courtesy of the U.S. Geological Survey.

each cell was backfilled to form a cylindrical earth retaining structure.

Additional sheet pile arcs connect each cell. In total, the dry dock uses 20, 75-foot diameter cells connected by 19 arcs in a U-shaped pattern that forms three sides of the dry dock structure. The fourth side is open to accept vessels and configured to accept a caisson (gate) that closes the dry dock off from the surrounding water. The internal cast-in-place concrete dry dock walls envelope portions of the cofferdam cells and arcs. However, at the outer perimeter, the sheet pile walls are fully exposed to the marine environment above and below the water line.

Field Observations The first step in developing a comprehensive design strategy was to perform field investigations of the existing pile condition. From boat- and deck-based observations, the design team documented the condition of each exposed sheet pile face and noted special conditions that would need to be considered through the design process. The existing coatings were in a state of failure at most locations (Figure 2). The facility was equipped with an active cathodic protection system that consisted of anodes suspended from cantilevered beams extending over the cofferdam face. It is important to note that this type of cathodic protection system is fully effective only below the low water line, with reduced effectiveness in the tidal zone. The field observations also illuminated a number of construction constraints that would have otherwise been difficult to discern from a review of the design documents alone. The most surprising and important constraint was the restricted conditions under the deck. As shown in Figure 3, some existing concrete piles were less than 1 foot from the sheet pile face.

The number and proximity of existing concrete piles would present a substantial access and construction challenge for under-pier work.

Additionally, the design team observed a number of deck-based and water-based operations associated with the day-to-day function of the pier that would present a construction staging and sequencing challenge for the contractor.

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January 2014

Figure 3: Existing concrete piers in close proximity to the cofferdam wall face.

Figure 4: Pre-fabricated welded headed stud rails. Courtesy of Seaward Marine.

Corrosion Mitigation Selection and Design Considerations The owner considered a number of coating systems to mitigate further sheet pile corrosion: a high performance marine coating, thermal spray aluminum, copper-nickel cladding, and a concrete facing. Due to the considerable durability and low life-cycle cost, the owner chose a concrete facing extending from the top of the cofferdams to two-feet below Mean Lower Low Water as the preferred repair alternative. The owner called for a concrete service life of at least 50 years. Considering the cofferdam pile structure appeared to be performing well and did not exhibit excessive corrosion, the concrete facing would not be structural, but rather would provide an overlay to passivate and protect the steel cofferdam.

The concrete facing would present a number of different technical design challenges, but most of them would be related to one central issue: crack control. In this case, the design team had two related tools for controlling concrete cracking: rebar configuration and concrete specification.

Rebar Configuration The design team considered that, during drying shrinkage, the formation of a crack requires a point or line of restraint. In this case, the vertical interlock joints between the sheet piles provided that restraint.

Each interlock has two nested knuckles that protrude from the face of each sheet by about an inch. This protrusion is the line of restraint where an assumed crack might form. Table 4.1 of ACI 224R indicates a reasonable crack width for seawater spray is 0.006 inches, so this was adopted as the target crack width for the facing. Assuming the crack would form vertically, in-line with the knuckles, the primary reinforcement would be horizontal. Using minimum reinforcement, the resulting calculated crack width was 0.003 inches.

Concrete Specification The basis of the concrete design was the owner’s specification for marine concrete with special considerations added for shrinkage control. Considering the non-structural nature of the facing, the concrete would not need to develop especially high compressive strength. This was advantageous because it presented the opportunity to lower the cement content in the mix, which would lower the water content, thereby minimizing shrinkage-induced cracks. This was accomplished by limiting the specified 90-day strength to a range of 3500 pounds STRUCTURE magazine

per square inch (psi) to 4000 psi. Additionally, the mix incorporated a maximum water/cement ratio of 0.38 and a provision for rapid strength gain with age combined with a low shrinkage requirement.

To assure maximum durability in this sea water environment, the concrete mix was proportioned to maximize its resistance to the penetration of chloride ions with a limit of less than or equal to 1000 coulombs at 56 days. The mix was also developed to limit the drying shrinkage to a maximum of 0.03% at 28 days.

Special additives were also required in the concrete. Much of the concrete casting was to be done underwater by divers in a bottom-up pumping operation. Due to the strict environmental requirements for working in the Hood Canal, anti-washout additives were required to prevent concrete paste leakage. Also, due to the long travel time and delays getting through the base, a set retarder was used.

Design for Constructability The contractor would face a myriad of technical and operational challenges during construction of the facing. The following is a partial list of these challenges: • Under-pier access was substantially restricted due to the close spacing of existing concrete piling.

• The curvature of the wall face would present a formwork challenge.

• The contractor needed to minimize interruption of pier operations. This would restrict construction laydown space and vehicle access. Additionally, the contractor would have to schedule activities around all pier operations.

• The construction crew and concrete deliveries would have to pass through checkpoints.

• The large distance between the jobsite and the nearest concrete batch plant would make the efficient delivery of concrete even more critical, as the mix is intended to have rapid strength gain as part of the shrinkage control strategy.

• The tidal fluctuation is as much as 11 feet, so the work schedule would have to consider tidal conditions.

• Due to the presence of protected aquatic species, in-water work was restricted to a 7-month period, called a “fish window”, starting in July.

The operational nature of these restrictions made mitigating them by design difficult. Some modest mitigating design strategies included provisions to make construction of the panels as flexible as possible,

27

January 2014

like simple rebar layout and coordinating the weldedheaded-stud (WHS) spacing and rebar spacing to minimize the amount of additional rebar. Prior to construction, the designers and contractor also conducted a constructability meeting to review the design.

This resulted in a number of adjustments: • Welded headed studs were pre-fabricated on steel bars, which were then fillet welded to the sheet pile face (Figure 4, page 27). Considering the large number of WHS’s on project, this would save substantial time by minimizing layout and welding time in the field, some of which had to be done under water by divers.

• To more easily accommodate the in-water Figure 6: Completed cell and arc facing. Courtesy of Seaward Marine. construction restriction, the contractor implemented a horizontal cold joint, which broke the and under-pier work. Cores were taken of the test wall segment to facing into “uppers” and “lowers.” This would allow the measure specific gravity, chloride ion penetration resistance, voids, contractor to pour the “lowers” when in-water construction and compressive strength. Additionally, it was an opportunity to was allowed and could continue construction above-water evaluate the cracking at specific concrete ages. Figure 6 shows a typion the “uppers” between the fish windows. Figure 5 shows cal cell and arc with completed “uppers” and “lowers.” The test wall a completed “upper” in an under-pier condition. The only was a success and remained as a permanent part of the facing. After changes required to accommodate this configuration were a the test wall was approved by the owner, the contractor constructed minor modification to the welded headed stud layout at the the project faster than expected, allowing it to be finished ahead of cold joint and the implementation of epoxy-coated vertical schedule. During the last on-site observation, the facing appeared bars, at the joint locations only. to be performing very well and very few cracks have formed. As you might expect, the owner is very pleased with this outcome.

Test program and Completion Since the construction of the facing panels would be so difficult, contract documents included provisions for a test wall segment. This would mitigate risk in two ways. One, it would give the contractor the opportunity to refine the construction process while including provisions in the budget to re-construct the wall if necessary. Two, it would give the owner and designers the opportunity to inspect the wall and adjust the design if necessary. The test wall segment would be constructed with the intent to remain as the first section of the wall if all tests and inspections were acceptable. The wall segment was located to capture a representative collection of all the different existing conditions, including one cell, one arc, the cell-arc joint,

Conclusion This project demonstrated the successful use of what amounts to a thick coat of “paint” made of high-tech concrete to repair an aging sheet pile cofferdam located at a very challenging site. While more expensive to install than other coatings, this solution is estimated to offer the greatest long-term durability and lowest lifecycle cost. Additionally, this solution was installed with relatively little impact to the facility operations.

With America’s infrastructure, including over 300 harbors, in a deteriorating state (remember that D+?), having cost-effective and flexible strategies to mitigate corrosion while minimizing day-to-day facility operations is imperative. If you find yourself faced with a replace or repair scenario on a quay wall or cofferdam, consider using a concrete facing to extend the structure’s life. After going through this project, I’d give the strategy an A.▪ Brian Robinson, P.E., is a Project Engineer in the structural group at KPFF Consulting Engineers in Seattle. He specializes in excavation shoring and was a design engineer on the cofferdam repair project. Brian may be reached at brian.robinson@kpff.com.

Project Team

Figure 5: Completed “upper” facing under the pier. Courtesy of Seaward Marine.

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28

Owner: US Navy Structural Engineers: KPFF Consulting Engineers, Seattle, WA Cathodic Protection Engineers: Norton Corrosion, Woodinville, WA General Contractor: Seaward Marine, Chesapeake, VA January 2014

GEOPOLYMER PRECAST FLOOR PANELS Sustainable Concrete for Australia’s Global Change Institute

By Rod Bligh, B.Eng, MSc, CPEng, FIEAust and Tom Glasby B.Eng (Civil), MBT, MIEAust, CPEng, RPEQ

Figure 2: Panel soffit with ceiling service panel installed. Courtesy of Angus Martin.

T

he Global Change Institute (GCI) is an Australian organization within The University of Queensland (UQ) that researches global sustainability issues including resource security, ecosystem health, population growth and climate change (Figure 1). The design of its new $32 million (AUD) building by project architects, HASSELL and structural and façade engineers, Bligh Tanner, was to be an exemplar project benchmarked using the Green Building Council of Australia’s Green Star rating (at 6 Star Green Star level), as well achieving an Australian-first Living Building Challenge compliance. The Living Building Challenge is an international rating system based in North America that explores a broader basis of sustainability, assessing the seven performance areas of site, water, energy, health, materials, equity and beauty. Further design parameters set for the project were zero net carbon emission for building operation, carbon neutral with carbon offset.

Design process Early in the design, the structural engineering team explored the potential for the incorporation of structural timber. The work at the University of Technology, Sydney, developing and testing

Figure 1: Completed Global Change Institute building. Courtesy of Angus Martin.

STRUCTURE magazine

Figure 3: Global Change Institute – vaulted panel soffit.

Timber-Concrete Composite (TCC) floors, was of interest and was proposed as a potential floor system that combined the benefits of timber framing with the acoustic, fire separation and wearing properties of concrete (Figure 2). It was at this stage that the strong potential for use of geopolymer concrete in the system was identified, as the structural topping would be working at low stress and precasting of the TCC panels would enable quality control in a factory environment. Use of precast was also recognized as advantageous considering the very limited site.

The design of the passive and low energy thermal control systems was developing at the same stage, and was pushing the floor systems toward high thermal mass with active heat exchange by the pumping of air or water through a concrete slab system. The next logical iteration of the design was to precast geopolymer concrete floor panels with incorporated hydronic pipes coils. To maximize the effectiveness of the radiant heat transfer from the concrete, the soffit needed to be exposed with maximum surface area. This then led to the development of vaulted soffit panels, which were both visually appealing, of high thermal efficiency and reflected light down onto functional spaces (Figure 3). Suspended ceiling panels contained lighting, communication technology and sprinklers.

Various forms of the 11-meter-span (36-foot) panels were explored, which allowed for air distribution in a plenum/services void above

30

January 2014

Figure 4: Support at the panel end during the full-scale test.

Figure 5: Full scale load test at precast factory.

the panels. The exposed concrete frame, which supports the precast geopolymer concrete panels, was designed to incorporate the air distribution system, which supplies the plenum.

Bligh Tanner made contact with Wagners who were developing a geopolymer concrete product branded Earth Friendly Concrete (EFC). Wagners had undertaken some preliminary testing at the time to produce an initial summary engineering report that would ultimately lead to further verification testing for compliance with AS3600 (Australian Standard for Concrete Structures). Although the use of geopolymer was so novel that it would not gain any additional Green Star points in the Material category, The University of Queensland, as the client, understood the significance of the innovation which went beyond Green Star rating. Wagners were asked to fast track the reporting and testing, with a critical cut off date for the interim research report to be indicating whether or not the use of geopolymer concrete on the project was viable. The Green Star submission, which is currently being assessed, includes two Innovation points for the use of the geopolymer concrete on the basis of being a world-first innovation and exceeding the Green Star benchmarks. A positive interim report was delivered during the design period. The only issue identified as a potential concern relative to normal concrete was carbonation resistance; however, this was not considered to be of significance in this case as it was for internal use only. Subsequent testing has shown that rate of carbonation for the mix design adopted is similar to normal concrete incorporating blended cement. At this point, the project consultants accepted geopolymer concrete as the preferred option for the precast floor beams used in the three suspended floors.

An additional concern was the ability to supply the geopolymer concrete to the precast fabricator, and also for the precast fabricator, to be willing to take on the risk of working with a new product. The design team and Wagners worked closely with Precast Concrete to ensure that the process was feasible. Bligh Tanner stipulated that a full-scale load test (up to maximum working load) could be undertaken on a panel to confirm the strength and deflection were as predicted. This was considered prudent given the world-first application of modern geopolymer concrete for suspended construction.

the building. The specification for the geopolymer concrete in these beams relied on: • Testing key material properties referenced in AS3600.

• Independent engineering verification that the tested results showed structural performance properties equivalent to the design basis for design reinforced concrete dicated in AS3600.

All tests were undertaken by Wagners Technical services, in some cases using external laboratories (Figure 4 ). The results were independently assessed by Dr James Aldred of AECOM, who Wagners commissioned to provide the independent certification on the geopolymer concrete.

Test samples, with the exception of creep and the fire and load tests, were cast and made from geopolymer concrete used during the supply phase of the project. The relevant Australian Standard test method was used in all cases. Creep was assessed via full scale prestressed beams which were made in 2010 and were monitored under load via the use of internal vibrating wire strain gauges. A fire test was conducted at the CSIRO fire testing station at North Ryde, Sydney prior to the start of the project.

The first floor beam panel produced served as the prototype to be load tested. Figure 5 shows that the measured deflection under an equally distributed 10 ton load was 2.85 mm (0.10 inches), slightly less than the predicted 3mm using an uncracked section analysis.

The testing program revealed a number of beneficial properties of the geopolymer concrete compared to normal GP based concrete, most notably: • Half the typical 56 day drying shrinkage, at an average value of 320 microstrains • 30% higher flexural tensile strength than a comparison standard concrete • Extremely low heat of reaction These properties would indicate that an improved level of performance would be achieved in a range of typical structural applications.

Compliance Testing Geopolymer concrete was included in the design for the 33 precast floor beams (320m3 ≈ 419 c.y.) that formed three suspended floors in STRUCTURE magazine

Practical Aspects Apart from the design and specification details, the geopolymer concrete was required to meet all of the usual handling requirements involved in batching and delivering concrete. Based on several years of EFC supply to a range of external projects and trials, Wagners were able to demonstrate that the geopolymer concrete could be handled and finished similarly to normal concrete. In the case of filling and compacting precast moulds, the methods are the same

31

January 2014

Figure 7: EFC geopolymer concrete being vibrated into the beam molds, at Precast Concrete Pty Ltd factory, Brisbane.

Figure 6: Proto-Type EFC geopolymer beam load test.

(Figure 6 ). Loads can be batched with all ingredients except the activating chemicals and transported for up to 12 hours to a remote destination in a completely dormant non-reactive state. At the destination, the chemicals are added in a dry powder form directly into the Agitator bowl and mixed on site.

While EFC can be produced in normal concrete batching facilities, it is a requirement that GP cement does not contaminate the mix because it causes rapid setting, particularly at higher temperatures.

If weigh bins and the like are shared with normal concrete production in a batch plant, then it is possible that the fines of GP cement dust will enter the EFC geopolymer mix in enough quantity to cause variable set times.

Another beneficial aspect of geopolymer concrete is its natural off-white finish, is considered a desirable architectural feature. The finished precast geopolymer beams were installed into the building structure during the period of August to October 2012 (Figure 7 ).

Following installation, the precast geopolymer beams were sealed.

Several patch trials were carried out to ensure compatibility between the geopolymer concrete and proprietary sealers.

may have quite different structural properties. The proprietary geopolymer concrete used in the Global Change Institute building proved to be fully compliant with the structural performance parameters that AS3600 is based on.

The use of geopolymer concrete in the multi-storey Global Change Institute building provides an example of how a medium sized engineering consultancy went about assessing a new technology’s ‘fit for purpose’ suitability. It is hoped that this example may provide a path for others to explore new and innovative approaches to structures that improve the sustainability of our built environment. In association with a range of other sustainability innovations utilized in this building, the geopolymer concrete floor beams help to make the Global Change Institute building an outward expression of its inner purpose.▪

Conclusion Geopolymer concrete has now moved beyond an emerging technology into the space of a structural concrete that can be designed and used in structures and other applications, as long as the necessary verification and testing is undertaken. The term geopolymer is very broad and encompasses a range of different concretes which

Rod Bligh, B.Eng, MSc, CPEng, FIEAust, is a founding director of Bligh Tanner in Australia. Rod may be reached at rod.bligh@blightanner.com.au.

Tom Glasby B.Eng (Civil), MBT, MIEAust, CPEng, RPEQ, is a professional engineer and manager in the construction materials group at Wagners. Tom may be reached at tom.glasby@wagner.com.au.

A similar article was presented at the Concrete 2013 Conference, October 2013 in Queensland, Australia. It was also used as a reference document for media releases and other media articles.

Concrete finishing in the precast factory. Courtesy of Wagners.

STRUCTURE magazine

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January 2014

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Professional issues issues affecting the structural engineering profession

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upport for structural licensure led NCSEA, SECB, ASCE-SEI and ACEC’s CASE to form the Structural Engineering Licensure Coalition (SELC). While SELC serves to provide a common voice in support of structural licensure, there are engineers and organizations that oppose structural licensure. This article examines the reasons for such opposition.

Structural engineers’ efforts serve to protect the public with safe designs. Every day, millions of people work in, live in or travel on the buildings and bridges that we design and rely on the power plants, industrial facilities and numerous other structures that have been built from structural plans. The NCSEA and ASCE Codes of Ethics place protection of the public as their highest priority. ASCE’s first canon states: Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable development in the performance of their professional duties.

Along with a professional obligation to protect the public, engineers are expected to prepare designs under the responsible charge of an engineer who has demonstrated the necessary qualifications.

Training and studies provide engineers with powerful tools, useful to serve clients and society. Like other professions where special knowledge and skills come to bear, the public has an interest in regulating who may use these tools In parallel with the growth of our society and scientific understanding of physical phenomena, the performance expectations of structures have increased. This is manifest in the complexity and size of the building codes. As we learn more about structural performance, we amend or revise the codes accordingly. As an example, consider how the provisions related to roof anchorage have changed in response to undesirable performance in storms. Also consider the code changes related to steel moment frames following earthquake investigations. In both instances, increased knowledge led to increased complexity of design requirements in service of the public interest.

In 1907, to protect the public, as well as land rights and water rights, Wyoming became the first state to license engineers. By 1950, all of the states and the District of Columbia had licensing rules or laws. Now, engineering licensure has become integral to building in our society.

Illinois first licensed structural engineers in 1915, followed by California in 1931. Currently, fifteen states hold the practice of structural engineering significant enough to have specific licensing provisions for the discipline. Seven – California, Hawaii, Illinois, Nevada, Oregon, Utah and Washington – require a licensed structural

Opposition to Structural Licensure

By Timothy M. Gilbert, P.E., S.E., SECB

Timothy M. Gilbert, P.E., S.E., SECB (TGilbert.PE@gmail.com), is a Project Specialist with Timken in Canton, Ohio. He is also a member of the NCSEA Structural Licensure Committee, and a Director and the Licensure Committee Chair for the Structural Engineers Association of Ohio (SEAoO).

34 January 2014

engineer for the design of all or certain structures. Idaho and Nebraska limit the use of the “structural engineer” title. Arizona, Louisiana, New Mexico, Oklahoma, Texas and Vermont designate structural engineers in their state rosters.

Structural engineering licensure is now recognized by NCEES, a federation of the state licensing boards. The ANSI-accredited Model Law Structural Engineer (MLSE) standard provides the recommended criteria for structural licensure. The MLSE is a guide framework that may be used in the individual jurisdictions.

The concept of structural licensure and imposing limitations on who may practice structural engineering has opponents with reasoned perspectives on the issue. This article considers these opponents and the grounds for their resistance.

Opposition Opponents of structural licensure may contend that the current system of professional engineering licensure provides adequate regulation of the profession and protection for the public. Four basic arguments are commonly made in support of this view: 1) the lack of structural failures shows the adequacy of the current system; 2) structural licensure is unnecessary, since engineers are already required to practice only within their areas of competence; 3) regulation of the engineering profession is best implemented when the practice is not segregated into various disciplines; and 4) structural licensure would place undue restrictions on the practice of engineering. These points do not encompass all positions held by opponents; for example, in some cases opposition is based on the specific circumstances within a jurisdiction, a situation that is outside the scope of this article.

The first point in opposition, citing a lack of structural failures, may be viewed as a request for evidence. Engineers’ professional practice is based on scientific principles supported by evidence, and it is rational to expect evidence in support of any engineering-related proposition. This point of view is commonly expressed by individuals who oppose structural licensure. By logical extension, one might consider this point of view as a reluctant opposition.

Implicit in the request for evidence is a willingness to consider its possible veracity and relevance.

Specific structural failures attributable to those who would not practice under a regime of structural licensure would answer the question: “Where are the failures?” Unfortunately for society, the true cause of a structural failure may never be known.

In his book, Beyond Failure, Dr. Norbert J. Delatte examines several structural failures. The 1987 L’Ambiance Plaza collapse during construction led to the death of 28 workers. Legal settlements by the affected parties closed the investigation before a definitive cause could be established. The engineering lessons which could have come from this failure

ACEC – American Council of Engineering Companies ASCE – American Society of Civil Engineers CASE – Council of American Structural Engineers NCSEA – National Council of Structural Engineers Associations NSPE – National Society of Professional Engineers SECB – Structural Engineering Certification Board SEI – Structural Engineering Institute by one regulatory agency in each jurisdiction offering generic licensure to all engineers.

NSPE is a prominent proponent of this perspective, and has officially endorsed it in Position Statement No. 1737 – Licensure and Qualifications for Practice. The following is included within this document: Professional engineering licensure is the only qualification for engineering practice.

NSPE and its state societies will actively oppose attempts to enact any local, state, or federal legislation or rule that would mandate certification in lieu of or beyond licensure as a legal requirement for the performance of engineering services.

NSPE members have offered the medical profession as a guide for licensing professionals in a highly varied field. Doctors may practice in a specific specialty or as a generalist. The state licenses the practice of medicine, and specialists are recognized by nongovernmental certification boards. The American Board of Medical Specialties coordinates with several medical boards to certify specialists.

NSPE members have suggested that ASCE and other professional engineering organizations could perform the same function.

Part of the NSPE position is a perception that structural licensure proponents seek a completely separate regulatory system.

Proponents of structural licensure bear some responsibility in helping to create this perception. In past discussions, the term “separate” was frequently used in relation to structural licensure. However, in general, structural licensure proponents believe that the current licensing boards are adequate agencies to administer structural licensure as part of their existing engineering licensing responsibilities.

The fourth point of opposition relates to structural licensure’s effect on business. Some view the process to become a licensed structural engineer as an obstruction to fair business practices. More ardent opponents with this perspective view the structural licensure movement as an attempt to limit competition and artificially increase fees. This viewpoint

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inherently includes a contention that current regulations are sufficient, and it may frequently be linked to one or more of the other three points of objection.

Supporters of structural licensure recognize that all forms of licensure affect business, both by limiting who may participate and by providing buyers with confidence in the quality of the marketplace. Structural licensure would have the same effect by restricting practice to qualified individuals. Supporters also favor a transition process, often called “grandfathering,” that would allow current practitioners to continue and ensure that new practitioners meet higher standards of qualification.

As noted earlier, the four points considered here do not address all grounds for opposition.

However, common sources of opposition are based on the number of known failures, our profession’s ethical obligations, a perspective for regulating engineers, or possible effects on business practices. Each jurisdiction that considers structural licensure will encounter opponents with alternate perspectives.

Understanding these objections and opening a dialog with opponents is a crucial step toward structural licensure. Actions taken in support of structural licensure are more likely to have positive results when there is better understanding of the opposition and recognition of their interests. As Ben Franklin said, “Would you persuade, speak of interest, not of reason.”▪

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are clouded by its incomplete examination. It is worth considering whether it is possible to know where the failures are.

Opposition to structural licensure based on an absence of evidence does have possible limitations. It indirectly contends that an absence of evidence about structural failures is evidence in support of current regulations.

Proponents of this perspective might be insulated from witnessing the effects of poor design impacts on the public, and draw the conclusion that no change is needed.

Two points can be offered for consideration relative to this perspective. One is that many structures have not been subjected to designlevel loads. Potentially deficient designs might perform acceptably under common conditions, yet fail when called upon to provide the performance needed under code-level events, such as a major windstorm or earthquake.

Second, a structural failure might not become public knowledge, and waiting for a failure to happen subjects the public to potential risk.

The second basis for opposition correctly notes the ethical constraints on all professional engineers. Most jurisdictions require that engineers practice only within their areas of competence, and engineering codes of ethics also recognize similar obligations. This implicitly recognizes that engineering is a diverse practice, and practitioners are unlikely to be competent in all fields of engineering. Inherent in this thought is the idea that it is reasonable to assume that we are the best judges of our own abilities. Opponents citing this point frequently note that these ethical obligations preclude a need for structural licensure.

A corollary of this perspective is that opposition helps prevent an unwarranted growth of governmental regulation and governmental expenditures. From this perspective, structural licensure is a redundancy given the ethical restriction already established.

Cornell University research has shown that individuals may not be fully able to assess their lack of competence in fields without obvious objective standards. This has come to be known as the Dunning-Kruger effect. Proponents of structural licensure also recognize the diversity in engineering practice and cite this in support of their view. Jurisdictions with partial practice restrictions codify the concept by establishing a threshold for the involvement of a licensed structural engineer. Structural licensure proponents contend that this reduces the chance that significant structures are designed by professionals who inadvertently overestimate their own capability.

The third common point in opposition makes a case that the profession is best served

Structural teSting issues and advances related to structural testing

T

he safety of exterior elevated decks, balconies and porches is an important national issue due to numerous documented structural collapses that have resulted in serious injuries and, in some cases, deaths (Shutt 2011; Legacy Services 2010). The problem is not confined to residential construction, as decks are also popular in commercial structures. Due to larger occupancies, the stakes are even higher in commercial construction as evidenced by deck collapses in Polson, MT casino with 52 injured in 2004 and a Miami, FL sports bar with 24 injured in 2013. Engineered design has been hampered by knowledge gaps on structural loads – especially lateral loads. This information is vital for registered design professionals to create safe and efficient engineered designs for decks, porches and balconies.

Vertical loads on decks, such as occupancy and snow, are straightforward to calculate using the provisions of the 2012 International Building Code (IBC) and ASCE/SEI 7-10 Minimum Design Loads for Building and Other Structures (ASCE 2010); however, determining lateral loads on decks is more challenging. Wind and seismic loads can be calculated using the provisions of ASCE 7-10.

Lyman et al. (2013a; 2013b) demonstrated the ASCE 7-10 methodology for wind and seismic loads through example calculations for a 12 x 12 foot deck. They found that while wind loads generally control over seismic, the wind loads would not pose much of a design challenge except for hurricane and special wind regions. Of course, the results of the analyses would vary for decks with different sizes and aspect ratios.

The building codes and ASCE 7-10 are silent on the subject of lateral loads due to occupant movement, with the exception of grandstands, bleachers, and stadium seating. This article describes laboratory experiments on full-size decks with two types of occupant loadings: cyclic side-sway and impulse (run and jump stop). Results indicate that lateral loading from occupants will often exceed the worst-case loads from either wind or seismic. The key point being that occupant loading can occur on any deck, anywhere.

Preliminary research at Washington State University revealed that forces generated by occupants are significant, and in many cases greater than wind or seismic forces. The objective of this study was to quantify lateral loads caused by dynamic actions from the occupants.

Two deck configurations and two dynamic load cases were investigated: • Deck Configuration 1: Deck boards oriented parallel to the ledger

Lateral Loads Generated by Occupants on Exterior Decks

By Brian J. Parsons, Donald A. Bender, P.E., J. Daniel Dolan, P.E. and Frank E. Woeste, P.E.

Brian J. Parsons, former graduate student, Civil and Environmental Engineering.

Donald A. Bender, P.E., Director, Composite Materials & Engineering Center, and Weyerhaeuser Professor, Civil and Environmental Engineering, Washington State University, Pullman, WA. Donald may be reached at bender@wsu.edu.

J. Daniel Dolan, P.E., Professor, Civil and Environmental Engineering, Washington State University. Daniel may be reached at jddolan@wsu.edu.

Frank E. Woeste, P.E., Professor Emeritus, Virginia Tech University. Frank may be reached at fwoeste@vt.edu.

The online version contains detailed references. Please visit www.STRUCTUREmag.org.

36 January 2014

• Deck Configuration 2: Deck boards oriented 45 degrees to the ledger • Load Case 1: Cyclic • Load Case 2: Impulse It was expected that the two deck board orientations would result in dramatically different stiffnesses in the lateral loading plane since according to the ANSI/AF&PA Special Design Provisions for Wind and Seismic (AWC 2008), diaphragms and shear walls sheathed with diagonally oriented boards compared to horizontal boards results in a four-fold increase in stiffness. The two dynamic load cases were chosen to represent the types of occupant behavior that might result in the greatest lateral loads. The full details of the research reported herein can be found in Parsons et al. (2013b).

Background The 2009 (IBC) and the ASCE/SEI 7-10 are silent on the subject of lateral loads from occupants, with one exception. Table 4-1 in ASCE 7-10 gives gravity loads for reviewing stands, grandstands and bleachers, along with Footnote k which stipulates lateral loads of “… 24 lbs per linear feet of seat applied in the direction parallel to each row of seats…”. Footnote k was based on empirical research by Homan et al. (1932) where the lateral forces caused by the movement of a group of people on a simulated grandstand were studied. The lateral load provision in Footnote k is a convenient benchmark for comparing the deck loads reported in this article. For example, assuming each row of bleacher seats is approximately 2 feet apart, this lateral load provision would be equivalent to 12 psf of plan area.

Materials Both deck floor configurations were 12 feet square using similar materials, with the orientation of deck boards being the only factor that differed.

Decks were built according to Design for Code Acceptance 6 (DCA 6) (AWC, 2010), which is based on the 2009 International Residential Code (IRC). The deck ledger was constructed of 2x12 lumber; joists were 2x10, spaced 16 inches on center; and deck boards were 2x6, installed with no gapping. Deck boards were not gapped due to their high moisture content at time of installation.

All lumber was incised and pressure preservative treated (PPT), with a grade of No. 2 and Better, and species grouping of Hem-fir. The PPT formulation was Alkaline Copper Quaternary Type D (ACQ-D) with a retention level of 0.40 pcf.

The hangers used to connect the deck joists to the ledger were Simpson Strong-Tie Model No. LU210, which use 20-gauge steel and 16 fasteners; 10 into the header and 6 into the joist. This hanger was selected because the fastener pattern

(all fasteners installed perpendicular to the member faces) performed well when joists were loaded in tension (pulling away from the hanger). The manufacturer’s joist hanger that was recommended for corrosive environments had a double-shear (toe-nail) type fastening pattern for attaching to the joists, which did not perform well in preliminary tests when the joists were loaded in withdrawal from the hanger. Of course, before any connection hardware is used in an actual deck, the appropriate corrosion protection must be satisfied.

The joist hanger manufacturer permits their hangers to be installed with either nails or screws as specified in their technical literature. Screws were used with the joist hangers to meet the provisions of the model building codes. IRC-2009 Section R507.1 and IBC-2009 1604.8.3 both state that the deck attachment to an exterior wall shall not be accomplished by nails subject to withdrawal.

These provisions have been widely interpreted as applying to the deck ledger attachment; however, these provisions also should apply to deck joist hanger attachment to the deck ledger to complete the lateral load path from the deck to house. The joist hanger screws were #9 (0.131 inch diameter, 1½-inch long) Simpson Strong-Tie Structural-Connector Screws (Model No. SD9112). These screws have a Class 55 2006 IRC-compliant mechanical galvanized coating to mitigate corrosion due to the preservative chemicals in the lumber and wet use conditions. The deck boards were attached to the top of each joist with two 3-inch #8 wood screws rated for outdoor use.

Test Methods Standard test methods are not available for occupant-induced lateral loading, so two testing protocols were developed to represent worst-case conditions. Each person participating in the study was weighed, allowing occupant density evaluations of 10, 20, 30, and 40 psf. A conservative assumption was

made that other than the attachment at the ledger, the deck substructure would provide negligible lateral resistance; therefore, the deck was supported on rollers as shown in Figures 1 and 2 ( page 38 ). In reality, many decks have some degree of lateral support provided by stairs, braces or other configurations that provide resistance to lateral movement. Lateral stiffness of decks differs substantially when loaded parallel versus perpendicular to the ledger; hence, loadings in both directions were conducted for all cases.

The first load case was an impulse. For this type of loading, the occupants were instructed to start at one end of the deck and run and jump, in unison, towards the opposite side of the deck. Impulse loading was conducted with an occupant density of 10 psf to allow occupants ample room to run and jump.

The second load case was cyclic, in which the occupants were instructed to sway, in unison, following visual and audible cues, back and forth at an approximate frequency of 1 Hz. All impulse and cyclic tests were performed with motion parallel and perpendicular to the deck ledger. Forces were recorded at the two corners where the deck was anchored to the laboratory floor with steel brackets (simulating the building). In an actual building, the load path would differ from this test set-up since deck ledger boards are typically connected to the house along the entire length. The rationale for attaching the deck at two discrete points was to obtain a conservative (high) load estimate by attracting all load to the two attachment points. Load path from the deck into the house floor diaphragm was investigated in a separate study reported in a paper by Parsons et al. (2013a).

Results & Discussion Results of this study were reported as equivalent uniform lateral surface tractions in psf generated by occupant actions. These values were determined by dividing the total force

Table 1: Forces generated by occupants from impulse loading.

Occupant Load Deck Board Level, (psf ) Orientation to Ledger

Total Force, (lbs)

Uniform Lateral Load, (psf )

Impulse loading perpendicular to ledger 10

Parallel

384

2.7

10

45 Degrees

443

3.1

Impulse loading parallel to ledger 10

Parallel

428

3.0

10

45 Degrees (East)

1,297

9.0

10

45 Degrees (West)

1,351

9.4

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Figure 1: Impulse loading caused by occupants leaping/stopping in unison.

generated by the surface area of the deck floor.

Loads in this form can easily be applied to decks of any size for design purposes. For the perpendicular to ledger load cases, the total force was taken as the sum of the two load cells. For the parallel to ledger load cases, the total force was taken as two times the maximum load cell value by applying basic equilibrium principles.

Impulse Loading Forces generated for both deck configurations are shown in Table 1 for the perpendicular and the parallel to ledger load cases. All tests were recorded with high-definition video and retained by the authors. A sample still shot from the video can be seen in Figure 1 for the impulse loading.

Perpendicular to ledger: Impulse loads were similar for both decking configurations since deck stiffness was primarily controlled by axial stiffness of the joists rather than the decking orientation. The stiffness of the deck resulted in many short duration pulses as each person landed, but was not flexible enough to allow the pulses to accumulate into one large force.

Parallel to ledger: When impulse loading was directed parallel to the deck ledger, as shown in Figure 1, decking orientation controlled the stiffness of the system.

Table 1 shows that the less stiff deck (with decking oriented parallel to the ledger) experienced lower loads as the pulse duration was relatively long at impact, and the occupants velocities were reduced by the deck movement as the occupants pushed off to accelerate. The greatest loads were observed for diagonal decking. Apparently this scenario “hit the sweet spot” of a deck with just enough flexibility to allow the individual impacts to act additively in a long enough time interval. In any case, the maximum traction load of 9.4 psf was less than the value of 12.1 psf for cyclic loading.

Cyclic Loading Figure 2 shows a sample still shot from the video for the cyclic side-sway motion. continued on next page

The highest lateral load observed in all tests was 12.1 psf, as shown in Table 2. In this case, deck boards were oriented parallel to the deck ledger, resulting in a very flexible deck that swayed back and forth approximately 7 inches each way at a frequency of approximately 1 Hz. These large displacements caused significant inertial forces from the mass of the deck and also allowed the occupants to “feel” the deck movement, making it easier for them to synchronize their movements. As displacements of the deck reached maximum values of approximately 7 inches, the occupants started pivoting their hips (like downhill skiers) with the deck while leaving their upper body nearly motionless. At this point, it could be argued that the majority of the force generated is coming from deck inertial forces rather than from the occupants. This would imply that if lateral sway/acceleration of a deck is adequately restrained, these inertial forces could be reduced or eliminated. For example, when the cyclic motion was perpendicular to the deck ledger (the stiffest orientation), the maximum traction load was 4.5 psf. In summary, it could be argued for design that 12 psf would provide a reasonable upper estimate of lateral loads from occupants for flexible decks.

Conclusions When deck boards were oriented parallel to the ledger and occupant loading was applied

Figure 2: Cyclic loading caused by occupants swaying side-to-side in unison.

parallel to the ledger, large side-to-side displacements were observed when a cyclic action was performed by the occupants. These large displacements produced significant inertial forces with a maximum equivalent uniform lateral surface traction load of 12.1 psf. When cyclic actions were perpendicular to the ledger (i.e. the stiffest lateral direction), it was difficult for the occupants to synchronize their movements and the resulting maximum uniform surface traction load was 4.5 psf. The maximum recorded impulse load resulted in a uniform lateral surface traction load of 9.4 psf as compared to 12.1 psf.

A design lateral load of 12 psf of plan area is recommended, which conservatively includes inertial forces from a flexible deck.

Table 2: Forces generated by occupants from cyclic loading.

Occupant Load Level, (psf )

Deck Board Orientation to Ledger

Total Force, (lbs)

Uniform Lateral Load, (psf )

Cyclic loading perpendicular to ledger (stiffest direction) 10

Parallel

224

1.6

10

45 Degrees

226

1.6

20

Parallel

398

2.8

20

45 Degrees

543

3.8

30

Parallel

411

2.9

30

45 Degrees

482

3.3

40

Parallel

651

4.5

40

45 Degrees

502

3.5

Cyclic loading parallel to ledger 10

Parallel

320

2.2

10

45 Degrees

567

3.9

20

Parallel

983

6.8

20

45 Degrees

862

6.0

30

Parallel

1,431

9.9

30

45 Degrees

995

6.9

40

Parallel

1,747

12.1

40

45 Degrees

1,020

7.1

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The 12 psf observed in the laboratory is similar to the lateral load specified in Table 4-1, Footnote k (ASCE/SEI 7-2010) for reviewing stands, grandstands and bleachers, which call for 24 lb/linear feet of seating (assuming seats are 2 feet apart, the resulting load would also be 12 psf ). One surprising outcome of this research is that measured lateral loads from occupancy exceeded the calculated worst-case lateral loads from wind or seismic events (Lyman and Bender, 2013; Lyman et al., 2013). Furthermore, extreme occupant loading can occur anywhere in the US, while extreme wind and seismic events are limited to smaller geographic regions.

The testing protocol and conclusions reported herein are based on the assumption that the proposed deck or porch sub-structure has no auxiliary lateral support to resist occupant loading. The design professional is encouraged to include lateral support structures to resist all or part of the lateral loads produced by occupant loads (as well as other design loads such as wind or seismic).

It should be noted that the weak link in the load path might be the fasteners used in the joist hangers. Test assemblies were fabricated with screws to prevent premature withdrawal of nails in the joist hangers. The first step in any lateral load analysis, when required, should be to address the lateral design capacity of the joist connections (hangers) as nails would likely not be adequate in resisting lateral loads produced by occupants.▪ Acknowledgement: Donation of construction hardware from Simpson Strong-Tie is gratefully acknowledged.

This article, which originally appeared in Wood Design Focus, contains minor edits and additions and is used with permission.

Wood Design Focus is a quarterly publication available through the Forest Products Society at www.forestprod.org.

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EnginEEr’s notEbook aids for the structural engineer’s toolbox

O

ften a summary refresher helps keep us grounded in the fundamentals of elements that we commonly design. Owing to many requests from peers, this article is provided as a summary of the steps that may be taken for the development of a typical reinforced concrete column interaction diagram.

The methodology outlined below reflects the provisions of ACI 318, but Figure 1: Superimposed series of strain diagrams. it is not the only viable method. In fact, ACI 318 does not explicitly require an interaction diagram for column design. However, The result is a strain for each and every bar in the most structural engineers understand that such a column as it correlates to the level of strain that tool is the most convenient form of expressing the was arbitrarily assigned to the layer of reinforcenominal axial and flexural capacities, as well as the ment opposite the compression surface. This also best tool for helping us know how axial loads and helps us know where the theoretical neutral axis bending loads influence and affect one another. for the column is for this strain condition, which Assume, just for the sake of argument, that the occurs where the aforementioned line intersects factored load effect for the design of a tied con- the vertical axis of the strain diagram. Once the crete column is a trivial strain levels and the neutral axis are known, the matter, and that we have design may proceed to the next step. the results for Mu and

By Hooke’s Law, stress is equal to strain Pu. The next step that we multiplied by the material’s elastic modulus. might follow would be Multiplying the strain for each layer of reinforceto examine a generated ment by 29,000 ksi yields the corresponding interaction diagram and see whether our inter- stress. This must be truncated to the yield stress active load (represented by Mu and Pu) falls within for any results lying outside of the elastic range the capacity boundary of our trial column. of behavior for the reinforcement (typically 60 Let us further assume that we do not have the ksi). For the concrete acting in compression, the benefit of an interaction diagram and thus are depth of the compression zone is related to the ‘starting from scratch’. You may recall that an neutral axis by the β1 value, which is a function interaction diagram for a reinforced concrete of f 'c and ranges from 0.65 to 0.85 (0.85 for f 'c of column may be developed by examining a 4000 psi or less). The stress in the concrete has series of strain conditions at one surface of the a default value of 0.85f 'c and is assumed to be column. These strain conditions are arbitrary, and distributed uniformly over the entire compresare selected on the basis of providing the most sion region. Figure 2 illustrates the relationship descriptive capacity boundary that can conve- between the strain and stress diagrams for one niently be determined. At the opposing surface, iteration of interaction diagram development. an ultimate concrete compressive strain of 0.003 Once the stress in each layer of reinforcement is assigned. This is meant to represent the strain in is known, as well as the dimensions of the the concrete at ultimate compressive failure and is concrete compressive stress region, the resulassigned this value regardless of concrete strength. tant forces in each are calculated simply by Figure 1 illustrates the establishment of the fixed multiplying the stresses by the respective areas.

0.003 strain value at the compression edge while Summing the result yields a total force Pn, the layer of reinforcement at the opposite surface the nominal axial capacity of the column as it is subject to a series of strain conditions.

The series of strains (tensile and compressive) are then assigned to the layer of reinforcement opposite the concrete compressive failure surface. For any one particular level of strain that we have arbitrarily assigned, we can follow ACI 318 criteria and connect the two opposing points of strain on a diagram with a straight line, thus assuming that the strain is distributed linearly across with column width. This makes for simple calculation of the strain in the remaining layers of reinforcement, using the simple formulas for similar triangles that we learned in high Figure 2: Assumed strain and stress diagrams for school math. reinforced concrete.

Concrete Column Design Back to the Basics

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

Jerod G. Johnson, Ph.D., S.E. (jjohnson@reaveley.com), is a principal with Reaveley Engineers + Associates in Salt Lake City, Utah.

A similar article was published in the Structural Engineers Association-Utah (SEAU) Monthly Newsletter (April 2007).

It is reprinted with permission.

40 January 2014

correlates to this level of strain. Multiplying these same forces by their relative distances from the centroid of the gross column section and summing the result yields the nominal moment capacity Mn. The final step for this one iteration of design is to determine the strength reduction factor that is appropriate for the level of strain under consideration. This is a function of the net tensile strain arbitrarily assigned earlier; it has a value of 0.9 for net tensile strains of 0.005 or more and a value of 0.65 for net tensile strains of 0.002 or less. Intermediate values are linearly interpolated. The strength reduction factor is then multiplied by each of the Mn and Pn values calculated previously to determine the resulting φMn and φPn that define this one point on the interaction diagram.

The entire process is repeated several times, with varying levels of strain assigned to produce a series of points that define the interaction diagram boundary. Figure 1 depicts the superimposed strain conditions as recommended by prominent textbook authors. For each level of strain, the calculations described herein are repeated. For each level of strain, a corresponding point on an interaction diagram can be determined. Interconnecting the points results in the interaction diagram (potentially similar to Figure 3) on which we

can plot Mu, Pu and assess whether the column is sufficient.

In summary, the steps for developing a concrete column interaction diagram are: 1) Assign an arbitrary level of strain to the layer of reinforcement opposite the compressive surface and calculate the depth to the neutral axis (c), the depth of the compression stress zone (a), and the level of strain in the remaining layers of reinforcement (using Figure 3: Typical interaction diagram. linear interpolation, similar triangles, etc.). nominal axial capacity (Pn). Multiply 2) Using the ultimate compressive these same forces by their distances stress in the concrete (0.85f 'c ) and from the center of the section and the dimensions of the compression add the results to yield the nominal stress zone, calculate the resultant flexural capacity (Mn). Determine compressive force in the concrete. the strength reduction factor and Using the strains in each layer of multiply it by Mn , Pn . Plot the point reinforcement, calculate the stresses φMn, φPn on the interaction diagram. and the resultant forces in each layer 4) Repeat steps 1-3 at least a dozen by multiplying the stress in each layer times, with strain values typically by the area in each layer. ranging from 0.5 to -6, to create 3) Add the resultant concrete force enough points to draw the and the forces in all of the layers interaction curve. Then, simply of reinforcement to determine the connect the points.▪ ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

STRUCTURE magazine

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January 2014

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STR_7-13

new trends, new techniques and current industry issues

InSIghtS

ASTM A1085 An Update to a Classic Material Specification

By Kim Olson, P.E.

A

STM A500 has been the preferred material specification in the United States for cold formed, welded carbon steel hollow structural sections (HSS) since the late 1970s. In April of 2013, a new material specification, ASTM A1085, was released for steel tubes used in structural applications.

The development of A1085 took approximately six years and was led by the American Institute of Steel Construction’s (AISC’s) HSS Marketing Committee. The goal of the Committee, which also included HSS producers, was to improve the efficiency and performance of the HSS members in three main areas: material, seismic design and bridge design.

Traditionally, ASTM A500 allowed for a wall thickness tolerance of -10% of the value specified. Hence, manufacturers have produced tubes with a design thickness of up to 10% less than the nominal thickness required by the standard. This reduction in material led to recommendations made jointly between AISC and the Steel Tube Institute (STI), leading to provisions (AISC 2010 Specification for Structural Steel Buildings ANSI/AISC 36010, Section B4.2) requiring a reduction in the nominal thickness of all HSS members by 7% for all HSS section calculations. In comparison, A1085 tightens the wall thickness tolerance to -5% and adds a new mass tolerance of -3.5%. These tighter restrictions better align HSS tolerances with other structural members and eliminate the need for the 0.93 factor in calculations. Obviously, these improvements result in more efficient designs when utilizing HSS. Designers are aware A500 includes four distinct grades of steel for different HSS section shapes, each having different yield and tensile strengths. A1085 greatly simplifies these values for the designer. The specification has one grade and one yield strength (of 50 ksi) for all HSS shapes. This value represents an increase over A500 Grade B, offering another potential savings.

Bending a flat plate of steel into a square or rectangle shape requires careful attention to the radius of the corners. Too tight of a bend

could lead to cracking, which often is not visible until a weld is made along the corner of the member and is subjected to extreme heat. A500 lists a maximum corner radius but does not limit the minimum radius bend, whereas A1085 specifies both a minimum and maximum for the reasons listed above.

For material that is less than 0.4-inch thick, the corner radius is permitted to be between 1.6t and 3.0t. For material greater than 0.4inch thick, the lower bound of the corner radius is 1.8t. Most domestic manufacturers produce tubes with a corner radius of 2t so there will be little difference in the workable flat face of a tube.

A common application of HSS members is in a braced frame to resist seismic load. HSS sections are often utilized as the bracing element due to their efficiency in carrying both tension and compression loads. This efficiency has come at a price when designing a building with a resistance factor (R) of greater than 3. The seismic provisions of AISC 360 require an engineer to focus on the actual capacity of a member in order to control the failure mechanism of the lateral force resisting system. To realize the actual capacity of a steel brace, a designer must multiply the specified yield strength by an overstrength factor (R y) to account for inherent overstrength in steel members. R y for A500 is 1.4, while R y for A992 is 1.1. Clearly, the larger Ry results in a nearly 30% increase in force the designer must account for. The high R y for A500 is due to the high variability in acceptable yield strength of tubes. A1085 specifies an upper bound on the yield strength of 70 ksi. In time, this upper bound limit will logically lead to better predictability of the material strength, a lower R y factor, and more economical seismic designs utilizing HSS members.

Historically, HSS members have not been used frequently in pedestrian and vehicular

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bridges, but the demand to utilize these architecturally pleasing shapes in transportation structures has increased. According to the American Association of State Highway and Transportation Officials (AASHTO), sufficient fracture toughness is a requirement for primary bridge members. Accordingly, A1085 includes a Charpy V-notch test requirement of 25 ft-lb at 40°F. This corresponds to an AASHTO Temperature Zone 2, which is applicable throughout the majority of the United States. If more stringent requirements must be met, A1085 carries a supplement that may be specified. Hence, A1085 allows for the usage of HSS shapes in the transportation field by meeting the requirements of AASHTO. A1085 is already an option for designers when selecting a material to use for design in software packages. STI has been in contact with most major design software companies to better educate them on the intricacies and advantages of new specification. RISA, SCIA Engineer, RAM Structural System and RAM Elements all will include the new material and section properties in their updates to be released in the near future, with other software packages to follow. AISC has surveyed domestic manufacturers on A1085 production and the results of that survey are available on the AISC website (www.aisc.org/hss) along with section properties and column load tables for A1085. Further, the new section properties are also available on STI’s website (www.steeltubeinstitute.org/hss/ tech-brochures), and any questions on A1085 may be submitted in the Contact section to be answered by STI’s Technical Consultants.▪ Kim Olson, P.E., is a structural engineer at FORSE Consulting and serves as a technical advisor to the HSS Committee of the Steel Tube Institute. Kim may be reached at kim@forseconsulting.com.

ANCHOR UPDATES

news and information from anchor companies

Bentley Systems, Inc.

HALFEN USA

Cintec Reinforcement Systems

Heckmann Building Products, Inc.

Phone: 610-458-1491 Email: francisco.diego@bentley.com Web: www.bentley.com/structural Product: RAM Connection Description: The software includes base plates for almost any kind of column support. Choose between uniaxial or biaxial analysis, design the base plate per AISC 360-05 (additional seismic check per AISC 341-05 included), design the anchor bolts per ACI 318 Appendix D in seconds.

Phone: 800-363-6066 Email: solutions@cintec.com Web: www.cintec.com Product: Cintec Reiforcement Anchors Description: The patented Cintec anchoring system is straightforward: injecting a proprietary cementitious fluid grout into an anchor surrounded by a fabric sock, which has already been placed in an oversized drilled hole. The system’s ingenuity lies in its versatility. Cintec designers can customize it to any specification.

Devco Software, Inc.

Phone: 541-426-5713 Email: rob@devcosoftware.com Web: www.devcosoftware.com Product: LGBEAMER v8 Description: Analyze and design cold-formed cee, channel and zee sections. Uniform, concentrated, partial span and axial loads. Single and multi-member designs. 2007 NASPEC (2009 IBC) compliant.

Pro-Tools include shearwalls, framed openings, X-braces, joists and rafters.

Grip-Tite Mfg. Co., LLC

Phone: 515-462-1313 Email: nfarkas@griptite.com Web: www.griptite.com Product: Anchors and Piles Description: Grip-Tite provides a complete line of anchors and piles for general construction and retrofit applications. This includes Push Piers, Helical Piles and Anchors and Wall Anchor retention systems.

Grip-Tite has been continually manufacturing highquality anchoring products since 1921.

Phone: 800-423-9140 Email: pschmidt@halfenusa.com Web: www.halfenusa.com Product: Anchor Channels Description: Halfen is a global leader in design and manufacturing of anchor systems for concrete. Hot rolled anchor channels for edge or top of slab transfer high loads while also providing field adjustability.

Custom anchors are available for special corners and thin slab conditions.

Phone: 800-621-4140 Email: david@heckmannanchors.com Web: www.heckmannanchors.com Product: Pos-I-Tie® ThermalClip™ Description: This new break-through in masonry construction adds thermal-break technology to all of the advantages of the Original Pos-I-Tie Veneer Anchoring System! The ThermalClip decreases thermal transfer and has over 100 times less conductivity than metals such as steel. The snap-on design provides for easy installation.

Hilti, Inc.

Phone: 800-879-8000 Email: us-sales@hilti.com Web: www.us.hilti.com Product: Hilti HIT-HY 200 Adhesive Anchor System Description: The industry’s most revolutionary system to date. Inadequately cleaning holes during installation can reduce the performance of conventional adhesive anchor systems. Hilti Safe Set™ Technology eliminates this almost entirely, and improves reliability and productivity because no manual hole cleaning is required to obtain optimum performance.

Hubbell Power Systems, Inc. – CHANCE

Phone: 855-477-2121 Email: civilconstruction@hubbell.com Web: www.abchance.com Product: Helical Anchors Description: A helical anchor/pile is a segmented deep foundation system with helical bearing plates welded to a central steel shaft. Load is transferred from the shaft to the soil through these bearing plates.

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&

• THE ERS S NE

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Phone: 800-707-0816 Email: sales@iesweb.com Web: www.iesweb.com Product: IES VisualAnalysis Description: VisualAnalysis offers ACI Anchor Design checks with the base plate design feature included in VAConnect. Use VisualAnalysis for a wide variety of analysis and design projects. It is simple, productive and versatile.

Kelken Construction Systems

Phone: 732-416-6730 Email: dick@kelken.com Web: www.kelken.com Product: Keligrout Anchor Systems Description: Structural high strength polyester anchoring system.

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Powers Fasteners

Phone: 985-807-6666 Email: jack.zenor@sbdinc.com Web: www.powers.com Product: Anchoring Systems Description: ICC Listed/IBC Compliant Anchoring Systems: Powers-Stud+ SD1/SD2 carbon steel wedge anchors; Powers-Stud+ SD4/SD6 304/316 stainless wedge anchors; Powers-Stud SD5 galvanized carbon steel wedge anchors; Pure 110+ adhesive anchoring (meets high temperature performance requirements in IBC 2012).

Simpson Strong-Tie

Phone: 925-560-9000 Email: web@strongtie.com Web: www.strongtie.com Product: Anchor Products Description: Wide range of code-listed and general purpose anchoring, fastening, and repair products for concrete and masonry applications. Design software, adhesives, mechanical anchors, gas and powderactuated tools and fasteners, carbide drill bits, and repair, protection and strengthening products offer innovative solutions for infrastructure, commercial, industrial and residential construction.

Standards Design Group, Inc.

Phone: 800-366-5585 Email: info@standardsdesign.com Web: www.standardsdesign.com Product: Window Glass Design 5 Description: WGD5 performs all required calculations to design window glass according to ASTM E 1300-09. WGD5 also performs window glass design using ASTM E 1300 02/03/04, ASTM E 1300-98/00 and ASTM E 1300-94. GANA endorses WGD5 as best tool available in designing window glass to resist wind and long-term loadings.

Strand7 Pty Ltd

Phone: 252-504-2282 Email: anne@beaufort-analysis.com Web: www.strand7.com Product: Strand7 Description: An advanced FEA system used worldwide by engineers for a wide range of structural analysis applications. It comprises preprocessing, a complete set of solvers and post processing. It includes a range of material models suitable for the analysis of soil allowing for simulations of the complete soil/structure system.

Timberlinx

Phone: 877-900-3111 Email: timberlinx@rogers.com Web: www.timberlinx.com Product: Timberlinx Description: A connection tube, inserted equally in both members of the joint and linked by two expanding cross pins. Wood/wood, wood/concrete, wood/steel connectors.

All Resource Guides and Updates for the 2014 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. STRUCTURE® magazine is not responsible for errors.

FOUNDATIONS Foundation Sector Grounded in Optimism for New Year

By Larry Kahaner 2014 is shaping up to be a strong year, according to those working in the foundations sector. “We probably have more backlog going into a winter of a new year than I can remember,” says Lyle Simonton, Director of Business Development at Subsurface Constructors, Inc. (www.subsurfaceconstructors.com), St. Louis, Missouri. “We’re not seeing that winter slowdown that we’ve sometimes seen in the past.

Rather than have a seasonal lull, we have a lot of work carrying on into the first months of the year.”

Jim Hussin, Director at Hayward Baker, Inc. (www.haywardbaker.com) in Tampa, Florida agrees. “There has been a steady increase in work in the past few years to where, when combined with our acquisitions, we are now back to record sales volumes.”

What appears to be driving the industry are a growing economy, new offerings that are attracting business, and a general optimism among those companies who have survived the lean years of the building slowdown. One sign of improvement is companies that recently

relied heavily on government work are now seeing increases in private work. Says Kord Wissmann, President of Davidsonville, North Carolina-based Geopier Foundation Company (www.geopier.com), “Like the rest of the construction industry, we have seen a rebound in residential (multi-family) developments along with the light commercial and retail projects that follow.” He also credits increasing worldwide awareness of seismic risks for interest in companies like Geopier that engage in soil mitigation. The company specializes in providing a wide variety of cost-effective ground improvement solutions to support load ranges on any project, Wissmann says.

“Recent innovations including the Geopier Armorpact system, provide structural engineers with the tools to support higher loads with increased allowable bearing pressures in very soft cohesive soils.

The Geopier Densipact system affords allowable bearing pressures of up to 14,000 psf in granular soils. All of these systems are geared to save time and money for foundation construction.”

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

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Wissmann adds: “Historically, the industry has focused on liquefaction mitigation using soil densification techniques. This remains the case on many projects. There is also a growing trend towards the use of more cost-effective approaches by reducing liquefaction triggering while simultaneously addressing dynamic settlement – particularly differential settlement. Geopier uses many of its systems, for example, its Impact pier technology, to reduce liquefaction-induced settlements while providing cost-effective foundation support.” (See ad on page 48.)

Hayward Baker’s Hussin notes that soil mixing is a relatively new product offering. The process improves weak soils by mechanically mixing them with a cementitious binder, and it continues to gain popularity. “The binder can be added as a slurry for dryer soft soils or as a dry powder to very wet soft soils. To construct columns, a powerful drill advances drill steel with radial mixing paddles located near the bottom of the drill string. The binder is pumped through the drill steel to the tool as it advances, and additional soil mixing is achieved as the tool is withdrawn. To perform mass soil mixing, or mass stabilization, a horizontal axis rotary mixing tool is located at the end of a track hoe arm. The technique has been used to strengthen soft soils at sites of planned buildings, storage tanks and embankments,” he says. One impetus for soil mitigation, according to Hussin, is an increase of soft soil sites, particularly port facilities. Recently, the company acquired Geo-Foundations, a full-service geotechnical construction firm operating out of Toronto, Ontario. “This demonstrates Hayward Baker’s commitment to the Canadian market, especially when combined with our parent company Keller’s recent acquisition of the assets of North American Energy Partners’ piling division, known as North American Caisson (NAC). The company

has been renamed Keller Foundations Ltd.,” says Hussin, “and it operates throughout Canada.”

Simonton says that Subsurface continues to build on its capacity to perform ground improvement work all over the country. “We have created some new equipment to support that endeavor, and it’s led to work even further away from our traditional Midwestern base,” he says. “We’re doing a lot of work in the Northeast, the New England area… we’ve just seen a lot of development, commercial and otherwise, all over the U.S. but in the Northeast in particular. I think a lot of people assume that we’re a smaller, Midwestern company, that there’s no way we could cost-effectively travel to the Northeast and be competitive. And yet, we’ve done about four or five Boston and New England-area projects in the last year or two.”

At CTS Cement Mfg. Corp. (www.ctscement.com) in Cypress, California, Marketing Director Janet Ong Zimmerman also says that business is improving. “Things are better than last year and slowly going in the right direction… We are seeing a gradual, yet steady, recovery in the commercial, industrial and non-residential markets.”

The company manufactures Rapid Set fast-setting hydraulic cement and Type K shrinkage compensating cement. “Rapid Set exceeds 3000 psi in one hour, which means you can make structural repairs and rehabilitation, and return the concrete to full use in just one hour,” Zimmerman says. She would like SEs to know about Rapid Set Flooring Products that “offer a complete way to repair, resurface and renew interior and exterior floors.”

She adds: “Products include TRU Self Leveling for polished overlays and toppings, LevelFlor for self-leveling underlayment, acrylic and epoxy primers, Skim Coat for patching and skim coating, and repair mortars.”

In addition, the company is touting Rapid Set Corrosion Inhibitor which continued on page 49

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

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We help you fix bad ground.

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Sand. Clay. Fill. Organics. Liquefaction. Slides.

geopier iS ground iMproVeMenT™ EnGInEErEd SOLUTIOnS FOr Virtually all soil types & groundwater conditions Work with engineers worldwide to solve your ground improvement challenges. For more information call 800-371-7470, e-mail info@geopier.com or visit geopier.com.

©2014 Geopier Foundation Company, Inc. The Geopier® technology and brand names are protected under U.S. patents and trademarks listed at www.geopier.com/patents and other trademark applications and patents pending. Other foreign patents, patent applications, trademark registrations, and trademark applications also exist.

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provides triple-protection against corrosion. “It increases corrosion resisaggregates that is used at any thickness from 1½ to 24 inches. tance when used in areas susceptible to corrosion and chloride. It repels It delivers 20-30 minutes of working time. water, thereby preventing an unsightly appearance to concrete. It reduces Owens notes that he’s seeing an interest in turning plain, grey conchloride permeability, thereby increasing the life expectancy of metals, crete into attractive surfaces. “With this growing interest in designer steel and rebar,” Zimmerman says. (See ad on page 3.) concrete, we’ve introduced a new suite of advanced formula concrete John Somers, Vice President of Sales/General Manager at Polyguard décor products including stains, sealers, coatings and cleaners.

Products (www.polyguardproducts.com), Architectural Division On the testing side of the foundations sector, Senior Consulting in Ennis, Texas announced that his company is celebrating its 60th Engineer, Marketing Director Gina Beim of Pile Dynamics, Inc. anniversary. “Our Architectural Division provides high quality water- (www.pile.com) of Cleveland, Ohio, says that her company has witproofing membranes for both pre and post pour concrete applications nessed an ‘explosion’ of popularity of the Thermal Integrity Profile (TIP). as well as drainage boards, thru wall flashings and the best sealants “The interest in evaluating the shape of drilled foundations using TIP and transition products in the industry. In addition we manufacture with either data collection method – thermal probes or thermal wire a complete line of fluid applied air barrier and waterproofings.” cables – is increasing, and the industry recognizes that. The TIP received He says that for some SEs, Polyguard may be a new name but their two innovation awards in 2013 – one from the Deep Foundations products, such as Underseal and 650, are likely to be familiar. “In institute and the prestigious NOVA Award for Innovation from CURT/ 2013, we launched a new balcony product called Balconyguard. This CIF (Construction Innovation Forum). In 2013 some testers branched is a membrane product and system specifically designed for balcony out to try the thermal profiling on jet grouting columns, soil nails and applications. We also introduced a series of pre-fabricated boot prod- micropiles. It’s exciting to see these new applications tried out, and PDI ucts for waterproofing around columns and penetrations. They save thinks most of them will open new markets for the TIP.” time and are easy to install,” Somers says.

The company also increased the number of options available for its “The boots were a result of customer requests. Job-site fabricated Pile Integrity Tester. “That’s PDI’s instrument for pulse echo testing boots are time consuming and cumbersome, particularly in harsh job of concrete foundations. The PIT, as it’s known, now comes in two site and poor weather conditions. Having the boots prefabricated in sizes (some people favor a compact size, others prefer a larger screen advance saves time, and results in a high quality job in the end,” says to visualize results), with either wireless or traditional (cabled) sensors, Somers. (See ad on page 50.) and with either one or two channels of data acquisition.”

Another company celebrating longevity is The QUIKRETE PDI hasn’t stopped there, Beim says. “We have developed another device, Companies (www.quikrete.com) of Alpharetta, Georgia, says Frank an instrument for independent inspectors of ACIP / CFA piling jobs. It Owens, Vice President Marketing. “We were founded nearly 75 years streamlines and standardizes the entire process of recording the installation, ago, and we manufacture more than 200 professional-grade products something that inspectors still tend to do with pencil and paper. PDI will including mortar mixes, cements, concrete repair products, stucco, start marketing it to inspectors soon,” she says. Speaking about 2014, Beim waterproofing, tile setting, blacktop products, floor underlayments, predicts that the U.S. market will remain steady. “Outside the U.S., some sand and aggregates from more than 100 facilities in the U.S., Canada, countries are seeing increased interest in foundation quality control, either Puerto Rico and South America.” just as a natural evolution of construction practices or because new codes Owens says that the company has a state-of-the-art technical center have been enacted that require or incentivize deep foundation testing. where research and development is constantly driving product enhance- One example is Sweden, which now requires pile driving ments. “Our FastSet line, which features five products designed for monitoring in virtually all construction sites. Brazil requires rapid strength gain while providing contractors with adequate time a significant amount of pile load testing, too. PDI’s reprefor mixing, pouring and finishing projects, is a great example of sentatives are, therefore, cautiously optimistic,” says Beim.▪ QUIKRETE product innovation.”

He also wants SEs to know about three FastSet products that are designed specifiThermal Integrity Profiler cally with engineering job requirements The Heat Is On. in mind.

• QUIKRETE FastSet Repair Mortar Shape, quality, cage alignment uses a special low-sag formula and concrete cover of drilled to make vertical and overhead shafts. Shape and quality of structural repairs to any concrete, jet grouting columns. masonry or stucco surface. It Winner of the 2013 CIF/CURT NOVA delivers 20-30 minutes of working Award for Data acquisition with Probes Innovation time and allows sculpting of the or Thermal Wire® cables. material during placement.

Winner of • QUIKRETE FastSet Non-Shrink TIP: test fast and soon after the DFI 2013 C. William Grout is designed for structural Bermingham casting, so construction can Award for concrete repairs from ¼ to 24 Innovation move on. inches deep, and can be mixed to a plastic, flowable or fluid consistency. It delivers 30 minutes of working time.

• QUIKRETE FastSet Concrete Mix is a blend of cement with www.foundations.cc www.pile.com/tip engineering@foundations.cc sales@pile.com specifically graded fine and coarse

Innovation based. Employee owned. Expect more.

Polyguard celebrates our 60th year in business this year! For years on thousands of projects across the U.S. and globally, Polyguard’s high quality engineered products have been protecting structures from Moisture and Air intrusion.

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contractors protect their projects. Polyguard’s below grade waterproofing product line includes membranes intended for both pre and post concrete pour applications and our Air Barrier products have passed NFPA 285 test protocols. When your project calls for protection think of Polyguard first! “ Moisture and Air Stop with us!”

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award winners and outstanding projects

Spotlight

Transforming the Fan Experience A New Arena for the Yellow Jackets

By John M. Hann, P.E., LEED AP KSi/Structural Engineers was an Award Winner for the McCamish Pavilion project in the 2013 NCSEA Annual Excellence in Structural Engineering awards program (Category – Forensic/Renovation/Retrofit/Rehabilitation Structures).

T

he McCamish Pavilion is the home of the Georgia Tech Yellow Jacket basketball program and has been a part of the Georgia Tech Community since 1956. The original facility included a 50-foot tall, 270-foot diameter, 32 rib structural steel Schwedler dome over a 25 foot deep, cast-in-place, circular concrete bowl. Several renovations and additions have been performed over the life of the facility.

Georgia Tech’s goal for this renovation was simply to improve the fan experience in the arena. Desired improvements included better sight lines, increased seating row depth from front to back, a circulation concourse open to the court, modern audio visual equipment including a center hung scoreboard, an improved HVAC system, an enlarged circulation concourse and compliance with current building codes.

To improve sight lines and address seating row depth issues, a new octagonal seating bowl design was developed. The original bowl was demolished and a new cast-in-place concrete bowl installed at grade. The new octagonal bowl design eliminated approximately 2,000 seats. To replace these lost seats, a new upper deck was installed within the existing Schwedler dome. The upper deck utilizes elevated flooring supported on structural steel raker beams which are in turn supported on curved structural steel struts.

Traditional materials for elevated arena seating floors include precast concrete and folded steel plate, but neither of these materials was optimal due to the capacity of the existing structure. The precast concrete option was simply too heavy and overstressed the existing steel dome ribs. The layout of the upper deck made it desirable to span the upper deck riser system from existing rib to existing rib, on the order of 25 feet. Folded steel plate could not span this far without the addition of significant secondary framing. A new material, the Sandwich Plate System, SPS, was investigated and selected for the flooring system.

This composite flooring system was originally developed for the offshore and shipbuilding

industry. The SPS system includes two ¼-inch steel plates at the top and bottom of the assembly infilled with a polymer resin layer on the order of 1-inch thick. The McCamish Pavilion installation is the first onshore use of the SPS material in the western hemisphere.

The SPS system cannot be field cut or welded; it has to fit perfectly the first time.

Innovative point cloud technology was used in the design, fabrication and installation of the upper deck structural steel and SPS. A three dimensional map of the upper deck was developed by inserting a laser scanned point cloud survey of the existing steel into the 3D BIM model of the new structural steel components. All of the structural steel and SPS components were fabricated from this model. The method was so precise that all pieces fit without shimming, trimming or other modification upon installation.

The raker beams supporting the SPS are attached to the existing Schwedler dome for lateral stability, and balanced on curved struts to limit the gravity load introduced to the existing framing. New foundation systems to support the struts were also challenging.

The location of the facility over an abandoned landfill, and thrust loads from the new upper deck, required the use of battered deep foundations. These deep foundations were installed from the sloped side of the existing bowl underneath the existing steel ribs, resulting in a low headroom condition on a working platform sloped at 30 degrees. Because of the installation conditions, steel pipe micro piles were utilized for this application.

The addition of the other fan amenities also posed structural challenges for the project. The audio visual, lighting, and HVAC components all added significant load to the Schwedler dome. A three dimensional analytical model of the facility was developed to study the effects of added loads from new audio, visual, lighting and HVAC components. The added load significantly overstressed the existing building ribs. To

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mitigate the effects, connections of existing secondary roof members were modified to resist increased tension loads, converting the secondary members into tension rings. In the review of the existing documentation, it became evident the existing facility had no discrete lateral load resisting system. To bring the existing structure into compliance with the current building code, a new lateral load resisting system within the existing dome structure was required. New structural steel V brace frames were selected because they were the least intrusive applicable system. The new frames were “woven” through existing steel, changing the planar angle of the brace at each level to reduce impacts to seating counts and sight lines.

To limit lateral bracing locations, supporting the need for unobstructed site lines, all lateral loads were transferred from the new circulation concourse to the dome bracing through the use of roof diaphragms and collector elements. Conversely, the amount of gravity load the new concourse framing transferred to the existing structure had to be limited to avoid overstressed conditions in the existing dome ribs. The layout of the concourse framing was developed to achieve these goals.

The look and feel of the arena was completely changed by the renovation, transforming an aging facility from the 1950s into a twentyfirst century arena. The renovation would not have been possible without the innovative structural materials, assemblies, and construction techniques developed by the project team.▪ John M. Hann, P.E., LEED AP, is a Principal at KSi/Structural Engineers in Atlanta, GA. John can be reached at jhann@ksise.com.

President’s Message

GINEERS

ASS O NS

STRUCTU

OCIATI

RAL

EN

COUNCI L

NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

Keeping Up

Last week, I was preparing to give a presentation on snow load design. In order to support one of the points I wanted to include, I was doing some research on how much the codes have changed over the past 15-20 years. Looking at this really made me stop and think. We understand so much more today about how drifting affects snow loads and about the amount of snow we should design our structures to support; and this is just one example of the myriad of changes that we as structural engineers have to keep up with, in order to provide our clients with safe structures. We must understand the codes, keep up with changes, and understand how materials perform. This highlights how important it is to make sure that all engineers who are practicing structural engineering are qualified to do so and are keeping up with the changes. NCSEA supports the following three efforts that I feel speak directly to this need and serve to raise the bar in our profession.

The first is an ongoing effort by NCSEA’s Basic Education committee to determine and promote the core curriculum that should be offered to, and required of, structural engineering students. Integral parts of this committee’s mission include working with the Structural Engineering Certification Board (SECB) to achieve a common objective, working with educational institutions on curriculum content, and working with practitioner employers to ease students from the academic environment into the workplace. Although the committee has been successful in determining which universities offer the recommended coursework, a number of universities claim they are unable to do so. Most universities are being pushed to provide more economical degrees, which typically means requiring fewer hours, rather than adding to their programs.

Recognizing this, the focus of the committee has turned to

NCSEA Webinars January 23, 2014 ASCE 7-10 Ron Hamburger, S.E., SECB January 28, 2014 Prying Action in the AISC Manual of Steel Construction – Historical Development & Current Usage Dr. William Thornton, P.E. February 6, 2014 Understanding ASCE-7 Requirements for Seismic Design of Nonstructural Components Maryann Phipps, S.E. These courses will award 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program.

Time: 10:00 AM Pacific, 11:00 AM Mountain, 12:00 PM Central, 1:00 PM Eastern. Register at www.ncsea.com.

NEW! Webinar Subscription Option!

NCSEA is offering a Webinar Subscription Plan. For an annual fee of $750, an individual can access all NCSEA live webinars over a one-year period. This option is only open to NCSEA members, i.e., members of NCSEA MO’s. Enrollment form available at www.ncsea.com.

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providing a framework for individuals to take courses outside of the traditional setting and to recognizing those individuals who do so. This is an important endeavor and a joint effort with SECB and NCSEA’s Young Member Group Support Committee. I look forward to seeing what their efforts produce.

Second is an ongoing effort to promote Structural Licensure.

All fields of engineering have become increasingly complex and specialized over time, but none more so than structural engineering. In addition, structural engineering has a unique responsibility to provide structures that protect the safety, health, and welfare of the public. Unfortunately, it is not uncommon for clients to retain an engineer who is not qualified to provide the services required, whether the client realizes it or not. Yet, of the 55 jurisdictions in the United States, only 12 of them have a Structural Engineering Title or Practice Act. Illinois recognized this as far back as 1915, but other jurisdictions have been slow getting on board. The mission of the Structural Licensure committee reads “The NCSEA Structural Licensure Committee works with the Member Organizations to influence states to adopt consistent licensing laws and rules in the interest of public safety, especially relating to the licensure of structural engineers”. Over the last year, NCSEA joined with SEI, CASE, and SECB to form the Structural Engineering Licensure Coalition (SELC), so that these four organizations can speak with one voice and combine their efforts in this endeavor.

I am hopeful that we will have a new structural licensing act in several states over the next few years.

The third effort involves required continuing education.

NCEES has advocated for uniform laws regarding continuing education for many years. At this time, 40 states require continuing education, indicating that this concept has been embraced by the licensing boards in most of the country. Although the requirements vary, the most common requirement matches the NCEES recommendation of fifteen hours per year, which calculates to only 75 minutes per month. Opportunities for good continuing education are plentiful. Most of NCSEA’s member organizations offer monthly meetings that include a continuing education offering. Also, quite a few of the member organizations have day-long conferences with continuing education presentations. This is an excellent way to meet with colleagues and engage in discussion about our practice. For those unable to attend local meetings or interested in topics not offered locally, NCSEA offers webinars each month that have been thoughtfully discussed and reviewed for content by NCSEA’s Continuing Education committee. The NCSEA conference each Fall also offers two full days of continuing education opportunities.

I would be remiss if I didn’t say that I’m also very excited about the upcoming Winter Leadership Forum (WLF), focusing on tools for business success, which is another critical aspect of our practices. The WLF format includes roundtable discussions that really give attendees a chance to learn from and about each other; and the location, in Napa, California on March 20-21, should only add to that opportunity.

Carrie Johnson, S.E., SECB, is the NCSEA President for 2014 and is a Principal at Wallace Engineering in Tulsa, Oklahoma.

She can be reached at cjohnson@wallacesc.com.

January 2014

March 20 – 21, 2014 The Meritage Resort & Spa, Napa, California The second NCSEA Winter Leadership Forum will gather together structural engineering principals and leaders in an energetic and engaging environment, focused on key strategic issues vital to firm survival and success. Sessions include:

Get the Value You Deserve Without Ruining the Relationship – Steven Isaacs

This interactive session includes a new approach to negotiations and will offer a variety of field-tested ways to get the value and compensation you deserve, from current and future clients.

Leadership is a Full-Contact Sport: Dealing with Conflict in the Workplace

– Jennifer Morrow This session will focus on effectively dealing with conflict in the workplace and beyond.

Jennifer Morrow is the Executive Director of Commercial Services at ADR (Alternative Dispute Resolution) Systems of America, LLC, and consults with law firms and companies on the effective use of mediation, arbitration and all types of dispute resolution processes.

Baby Boomers Delay Retirements: Career Bottleneck at the Top

Managing the Cost of Conflict: Mediation, Arbitration or Litigation?

– Steven Isaacs Professionals enjoy and count on on their work, salaries, and benefits, and, especially today, are less willing or able to retire. Determine how your firm should react to retain talented employees.

Ownership Transition Case Studies

How does a firm transition ownership?

Leaders of three engineering firms that have confronted these issues will tell how they did it.

Robert L. Miller Associates & Sound Structures, Inc. Brian Dekker, President 7 staff PCS Structural Solutions Brian Phair, CEO 40 staff

DCI Engineers Mark Aden, President 185 staff

– Jennifer Morrow and Kevin Sido This session will explore the full spectrum of dispute resolution processes available and provide tools for evaluating when to use which process. Learn the nomenclature, know your options and make more informed decisions to minimize the impact on your time, your business and your reputation.

You’ve Been Sued – Now What?

What Engineers Need to Know to Structure Their Defense – Kevin Sido Realizing that claims will inevitably be filed against Structural Engineers regardless of merit, what should the Structural Engineer do when the summons is served and in the months that follow?

Kevin Sido, attorney, is a senior partner in the Chicago office of Hinshaw & Culbertson LLC. He has represented design professionals for more than 38 years, is an author and speaker on construction law issues, and is the editor of Architects and Engineers Liability, Claims Against Design Professionals.

Bart Miller, P.E. Principal Walter P Moore

While in college, engineers typically have no courses in business management and typically learn management skills by trial and error while on the job.

The 2013 Winter Leadership Forum was a great experience providing useful fundamental management insights for individuals running an engineering office or thinking of starting their own firms.

The structural engineering profession is evolving, just as are business management practices. I highly recommend the Winter Leadership Forum to anyone to help keep them abreast of currently developing management practices.

Michael Cochran, S.E., SECB Associate Principal Weidlinger Associates Inc.

Take Your Seat at the Table Discuss and develop new strategies, and learn what other principals are doing and thinking.

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January 2014

O NS

NATIONAL

OCIATI

Register at www.ncsea.com

Major Corporate Platinum Sponsor:

ASS

The Winter Leadership Forum will take place at the beautiful Meritage Resort & Spa in Napa, California. The Resort is centrally located in idyllic Wine Country at the southern tip of Napa Valley and has an evening shuttle for guest transportation to Downtown Napa’s restaurants and tasting rooms.

STRUCTURE magazine

News from the National Council of Structural Engineers Associations

Steven Isaacs, P.E., Division Manager, FMI Corporation, assists firms in strategic planning, financial controls, project performance/ profitability, negotiation, ownership transition, joint ventures and partnering.

Last year I gained some valuable insights into how to differentiate our firm from our competitors in a challenging economy. The speakers provided fresh and practical lessons that I have applied throughout this year in real project pursuits. I found the Winter Leadership Forum very relevant and I look forward to attending again in the future.

RAL

Friday

STRUCTU

Thursday

NCSEA News

Winter Leadership Forum

COUNCI L

Structures Congress 2014 Technical Sessions Thursday April 3, 2014

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Track

STeel TopicS

Building caSe STudieS

SeiSmic

diSproporTionaTe collapSe

BridgeS –

BridgeS –

currenT pracTice

emerging TrendS

Track Chair

Cynthia Duncan

Brian McElhatten

Mustafa Mahamid

Shalva Marjanishvili

Bruce Peterson

Cheng Lok “Caleb” Hing

8:00 AM – 9:30 AM

ST100 New AISC Design Guides: 26-Design of Blast Resistant Structures and 28-Stability Design of Steel Buildings

BB100 Integrated Design of Tall Buildings

SE100 Seismic Design in New England

DC100 Disproportionate Collapse Resistance of Floor Systems

BP100 Expediting Project Delivery in the MassDOT Accelerated Bridge Program

BT100 Dynamic Effects

10:00 AM – 11:30 AM

ST110 Steel Connection Innovations

BB110 The Boston School of Tall Buildings

SE110 Low-Ductility Braced Frames in Moderate Seismic Regions

DC110 Multi-Hazard Robustness Assessment of Building Structural Systems

BP110 The MassDOT Accelerated Bridge Program

BT110 Seismic Effects

2:00 PM – 3:30 PM

ST120 Steel Braced Frame Innovations

BB120 Museum Projects in Boston

SE120 Practical Considerations for Implementation of Self-Centering Seismic Systems

DC120 Designing for Robustness to Resist Disproportionate Collapse

BP120 Bridge Design

BT120 Blast Protection for Bridges

4:00 PM – 5:30 PM

ST130 Cold-Formed Steel Design: Advances through IndustryAcademic Collaboration

BB130 Impact of Boston Geology on Foundation Development

SE130 Seismic Analysis in Regions of Moderate Seismicity

DC130 International Disproportionate Collapse Design Requirements and Research

BP130 Construction and Performance

BT130 Damage Detection and Evaluation

Friday April 4, 2014 7:00 AM – 8:15 AM CASE Breakfast Track

Special Building TopicS

maSonry and Wood TopicS

codeS and STandardS

BlaST and impacT

BridgeS –

BridgeS –

currenT pracTice

emerging TrendS

Track Chair

Cynthia Duncan

Brian McElhatten

William Jacobs, V

Shalva Marjanishvili

Bruce Peterson

Cheng Lok “Caleb” Hing

8:30 AM – 10:00 AM

BD200 Structural System Innovations

MW200 Design and Construction of Masonry – A Look towards New Requirements and Recommendations

CO200 The State of Design Loads – A discussion of changes in the new ASCE 7, ASCE 24, & ASCE 37

BL200 Boston Marathon Bombing and West Fertilizer Explosion

BP200 Rehabilitation of Historic Bridges

BT200 Case Studies of Sensing for Structural Health Monitoring: Bridges

10:30 AM – 12:00 PM

BD210 Vibration Serviceability

MW210 Evaluation and Repair of Masonry

CO210 Using the New ASCE 41 – Seismic Evaluation and Retrofit of Existing Buildings

BL210 Blast Load Predictions

BP210 Recent Advances in Bridge Inspection Practices

BT210 Steel Orthotropic Bridge Decks – Recent Developments and Implementation

1:30 PM – 3:00 PM

BD220 Optimization in Tall Buildings

MW220 Timber Structures and Bridges

CO220 The 2014 NEHRP Recommended Seismic Provisions – An Overview

BL220 Blast Environment and Hazard Predictions

BP220 Bridge Evaluation

BT220 Evaluation and Assessment of Bridges Subject to Fire

3:30 PM – 5:00 PM

BD230 Composite Construction

MW230 Investigation and Repair of Existing Wood and Timber Framed Buildings

CO230 Snow Loads and Rain Loads – What’s New and Different

BL230 Blast Protection: From R&D to Design/ Retrofit

BP230 Rehabilitation and Strengthening

BT230 Next-Generation Multihazard Resilient Bridge Systems

Saturday April 5, 2014 Track

concreTe TopicS

Wood TopicS

progreSSive collapSe

BlaST and impacT

BridgeS –

BridgeS –

currenT pracTice

emerging TrendS

Track Chair

Mustafa Mahamid

Brian McElhatten

William Jacobs, V

Shalva Marjanishvili

Bruce Peterson

Cheng Lok “Caleb” Hing

8:30 AM – 10:00 AM

CT300 Modeling Shear and Bond in PCC

WW300 Experimental and Modeling Studies on Wood Frame Buildings

PC300 Disproportionate Collapse Considerations

BL300 Analysis Methods for Blast Loads

BP300 Designing Concrete Bridges for Increased Durability and Resiliency

BT300 High-Performance Materials

10:30 AM – 12:00 PM

CT310 Concrete: Code Revisions and Innovations

WW310 Application of Wood Frame Research to Design Practice

PC310 Design and Detailing of Bearing Wall Systems to Resist Disproportionate Collapse

BL310 Exterior Envelope

BP310 Vehicle Impact and Barriers

BT310 Recent Developments in Improving the Fatigue Life of Infrastructure

For more information about the Structures Congress 2014, including Registration and Housing, visit our website at www.structurescongress.org.

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January 2014

STrucTural opTimizaTion and moniToring

non Building and Special STrucTureS

naTural diSaSTer miTigaTion

emerging TrendS in STrucTural eng. educaTion

www.structurescongress.org

profeSSional pracTice

SuSTainaBle BuSineSS

Colby Swan

J. Gregory Soules

John F. Silva

Paul Mlakar

John Tawresey

Jeremy Isenberg

SM100 Integration of Construction Practice into Structural Optimization

NB100 Design of Thermal Power Generating Facilities

ND100 Modeling Coastal Hazards

ED100 Emerging Trends in Education

PP100 Codes After Failures: Changes in Structural Codes and Standards

SB100 Exploding the Myth – Successful International Working is not just the Preserve of the Largest Businesses

SM110 Advanced Sensing for Infrastructure Monitoring

NB110 Design and Analysis of Power Plants

ND110 Hurricane Risk Assessment and Mitigation

ED110 New Direction in Structural Eng. Education

PP110 Professional Practice Topics

SB110 The International Market: The Opportunities and the Challenges

SM120 Case Studies of Sensing for Structural Health Monitoring: Other Structures

NB120 Design and Analysis of Tanks and Silos

ND120 Advancing MultiHazard Analysis to Improve Emergency Response

ED120 Student Structural Design Competition

PP120 Practicing Engineers Trial Design Problems

SB120 How to Leverage Various Alternative Delivery Methods to Solve our Infrastructure Problem in US

SM130 Instrumentation for Monitoring and Assessment of Structures

NB130 Modular Design of Petrochemical Structures

ND130 Modeling Earthquake Risk and Damage

ED130 Classical Methods of Analysis – The Art and Feel of Structural Engineering – Work & Energy Methods of Analysis

PP130 The Structural Engineering License Exam-1

SB130 The Philosophy of Sustainability

career developmenT

applied BuSineSS mechanicS

Structural Columns

April 3– 5, 2014 – Boston, Massachusetts

CASE Breakfast non STrucTural componenTS

naTural diSaSTer miTigaTion

caSe

Colby Swan

John F. Silva

John F. Silva

Paul Mlakar

John Tawresey

Jeremy Isenberg

RR200 Panel Discussion: From LRFD to Risk-based Design and Beyond

NS200 Analytical Modeling of Nonstructural Components for Seismic Loading

ND200 Lessons Learned from Recent Tornadoes

CD200 The Cycle of a Structural Engineering Career: Learning and Leading

AB200 How Technology is Changing our Business

CS200 Mobile Technology for the Field

RR210 Incorporating Life-Cycle Concepts into Structural Design and Assessment

NS210 Experimental Investigations of Nonstructural Components for Seismic Loading

ND210 Extreme Load Design: Tornado-Generated Missile Protection

CD210 Life in Academia, Life in the Profession

AB210 Productivity Tools for the Structural Engineer

CS210 Developing an Internal Culture to Manage a Firm’s Risk

RR220 Operationalizing Risk-informed Decisions for Sustainable and Resilient Civil Infrastructure

NS220 Wind Loads on Solar Panels

ND220 ASCE Response to Natural Disasters – Hurricane Sandy and Moore, OK Tornado

CD220 Mentoring and the Young Professional

AB220 The Case of Inadequate Factors of Safety – What Engineers Should Know

CS220 SE Agreements and Lessons Learned

RR230 Applications of Resilience Design Concepts in Structures

NS230 Access Granted: Design and Evaluation of Exterior Building Maintenance Equipment

ND230 Addressing Tornados and Hurricanes

CD230 Changing the Paradigm for Engineering Ethics

AB230 Meet the Press

CS230 Key Components to Starting Your Own Successful Engineering Practice

duraBiliTy and maTerialS

non Building and Special STrucTureS

innovaTionS in STrucTural TeSTing

naTural diSaSTer miTigaTion

applied BuSineSS mechanicS

fire

Colby Swan

J. Gregory Soules

John F. Silva

Paul Mlakar

John Tawresey

Cynthia Duncan

DM300 Understanding Steel Corrosion in Civil Infrastructure

NB300 Offshore Wind in the Northeast

ND300 Security, Resiliency, and Sustainability

IT300 Seismic Experiments for Structures with Ratedependent Behavior

AB300 SEI BPC-Financial Monitoring

FF300 Multi-Hazard Design of Structures Considering Earthquake and Fire

DM310 Novel Structural Materials

NB310 Design and Analysis of Wind Turbine Support Towers

ND310 Resilient and Sustainable Structures and Infrastructures

IT310 Innovative Structures Testing Concepts

AB310 Structural Deficiencies and Failure Investigations

FF310 Innovations and Advances in Test Methods for Structural-Fire Safety

To view the interactive Technical Program, including all presenters and abstracts visit www.structurescongress.org STRUCTURE magazine

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January 2014

The Newsletter of the Structural Engineering Institute of ASCE

riSk reSilience and reliaBiliTy

Updated in 2013 – CASE 962-D

CASE in Point

The Newsletter of the Council of American Structural Engineers

A Guideline Addressing Coordination and Completeness of Structural Construction Documents The guidelines presented in this document will assist not only the structural engineer of record (SER) but also everyone involved with building design and construction in improving the process by which the owner is provided with a successfully completed project. Their intent is to help the practicing structural engineer understand the importance of preparing coordinated and complete construction documents, and to provide guidance and direction toward achieving that goal.

These guidelines focus on the degree of completeness required in the structural construction documents (“Documents”) to achieve a “successfully completed project,” and on the communication and coordination required to reach that goal. They do not attempt to encompass the details of engineering design; rather, they provide a framework for the SER to develop a quality management process.

**New for 2013 was a top to bottom comprehensive update that incorporated important added insights on coordination and completeness, including issues involving BIM and alternative project delivery.** This update is available for purchase at www.booksforengineers.com.

CASE Risk Management Convocation in Boston The CASE Risk Management Convocation will be held in conjunction with the Structures Congress at the Sheraton Boston Hotel and Hynes Convention Center in Boston, MA, April 3-5, 2014. For more information and updates go to www.seinstitute.org.

The following CASE Convocation sessions are scheduled to take place on Friday, April 4:

7:00 AM – 8:15 AM

CASE Breakfast: The Storms are Coming, the Storms are Coming: The Need for a Revolution in Engineering Approaches to Climate and Disaster Risk Stephen Long, The Nature Conservancy

1:30 PM – 3:00 PM

SE Agreements and Lessons Learned Speaker – Steven Schaefer, Schaefer Associates

3:30 PM – 5:00 PM

Key Components to Starting Your Own Successful Engineering Practice – Panel Discussion Moderator – Chris Poland, Degenkolb Engineers

8:30 AM–10:00 AM

Mobile Technology for the Field Speaker – Theron Peacock, Woods Peacock

10:30 AM – 12 Noon

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

Developing an Internal Culture to Managing a Firm’s Risks Speaker – Michael Strogoff, Strogoff Consulting

Creating a Culture of Accountability within a Small Firm The new normal is here, and even firms thriving in growing markets have been forced to adjust strategies as large or out of town competitors sweep in. For most firms, the competitive advantage lies not in a better plan, but in a much murkier area of organizational life: culture. Industry professionals are increasingly asked to do more with less, both resources and people. A/E firm leaders need employees to step up. But they know that accountability is an attitude, and it can’t be forced.

This will be the main topic of discussion when ACEC’s Small Firm Council (SFC) holds its annual Winter Meeting Feb. 7-8, 2014, in New Orleans, LA. Facilitator Geordie Aitken of Aitken Leadership Group will lead a two-day discussion and exploration of how accountability – the personal “ownership” employees demonstrate in their work – is developed.

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This program will offer ways for firms to achieve competitive advantage and explore how to build a culture of accountability by recognizing and reinforcing industry best practices.

SFC was established to protect and promote the interests of the smaller firms within ACEC. Its winter meeting provides an exclusive forum for small firm principals to attend seminars, network with peers, address key issues affecting their firms, and learn and share ideas. Attendees provide valuable input that helps SFC direct a business and legislative agenda for the coming year. To register for the SFC Winter Meeting, please visit www.acec.org/coalitions.

For questions regarding the Small Firm Council Winter Meeting or ACEC’s Coalitions, please contact Heather Talbert, 202-682-4377 or htalbert@acec.org.

January 2014

Plan to be Claims Free Tool 3-1: A Risk Management Program Planning Structure (Updated in 2013) This tool is designed to help a Firm Principal design a Risk Management Program for his or her firm. The tool consists of a grid template that will help focus one’s thoughts on where risk may arise in various aspects of their engineering practice, and how to mitigate those risks. Once the risk factor is identified, then a policy and procedure for how to respond to that risk is developed. This tool contains 10 sample risk factors with accompanying policies and procedures to illustrate how one might get started. The tool is designed to insert custom risks and policies and tailor it to individual firms.

Firms are provided a simple to use and easy to manipulate spreadsheet-based tool for predicting the staff that will be necessary to complete both “booked” and “potential” projects. The spreadsheet can be further utilized to track historical staffing demand to assist with future staffing and revenue projections.

ACEC Business Insights Upcoming ACEC Online Seminars

Ownership Transition 2.0 February 5, 2014; 1:30 pm to 3:00 pm Eastern Learn how to establish value, design an ownership transition program, choose appropriate transfer mechanisms, and identify leaders. For more information and to register: www.acec.org/education/eventDetails.cfm?eventID=1512

Are You Fighting Fires Instead of Managing Your Employees – 2014 February 11, 2014; 1:30 pm to 3:00 pm Eastern Proper delegation techniques will get you out of the firefighting syndrome. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1515

Enabling Social Collaboration and Engagement in the Workplace February 26, 2014; 1:30 pm to 3:00 pm Eastern Social collaboration allows for one common space for individuals to get together, share ideas, share tasks, manage tasks, share files, share calendars and collaborate with the entire group to move your project to completion. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1521 STRUCTURE magazine

This tool lists website links that contain information that could be useful for a Structural Engineer. A brief description of the website is also included. For example, there is information about doing business across state lines, information regarding the responsibility of the Engineer of Record for each state, links to each State’s Licensing Board, etc.

Tool 3-4: Project Work Plan Templates Preparing and maintaining a proper Project Work Plan is a fundamental responsibility of a project manager. Work Plans document project delivery strategies and communicate them to the team members. Project Managers will use this template to create a project Work Plan that will be stored with the project documents.

All of these tools and more are available at www.booksforengineers.com.

Donate to the CASE Scholarship Fund!

The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success.

The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at minimum, in an ABET-accredited engineering program.

We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates. One way to enhance the ability of students in pursuing their dreams to become professional engineers is to offer incentives in educational support.

In addition, the CASE scholarship offers an excellent opportunity for your firm to recommend eligible candidates for our scholarship. If your firm already has a scholarship program, remember that potential candidates can also apply for the CASE Scholarship or any other ACEC scholarship currently available.

Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for tax deduction and you don’t have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

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January 2014

CASE is a part of the American Council of Engineering Companies

Tool 3-2: Staffing and Revenue Projection

Tool 3-3: Website Resource Tool

CASE in Point

Foundation 3 – Planning

Structural Forum

opinions on topics of current importance to structural engineers

Velocity of Learning Revisited

By Tom Glardon, P.E.

I

read eagerly the Structural Forum column in the July 2013 issue, Increasing the Velocity of Knowledge, by Gene Frodsham, MS, S.E. As a professional educator and professional engineer, I hoped that he had insights that I could use. I am constantly faced with clientele that ask me to teach them the same material faster – always faster. Do not teach me cost estimating in five days; teach it to me in five hours. Do not take four hours to teach me basic timber design; show me in four minutes. So I need a way to increase the velocity of knowledge. Indeed, he had good ideas to propose.

However, I need to temper these good ideas with a cold dose of reality. The human operating system, regardless of the beliefs of popular culture and the amazing digital effects that are now routine, is still working on version 1.0. The 10-year-olds of today have the same brain capacity that our founding fathers had.

We certainly have different tools available to us, and we have been trained to learn through different media, but we constantly face the fact that the human mind processes cognitive learning in certain ways.

According to the most common model (Bloom’s Taxonomy), knowledge and (to some degree) comprehension learning are fairly well-supported by our digital tools, from automated systems to modeling software to Internet knowledge bases. Mr. Frodsham and his virtual environments seem to focus at this level; note his title: “Increasing the Velocity of Knowledge.” Throughout the article, he has great ideas on how to make knowledge – or, perhaps more appropriately, information – more accessible and more mobile for engineers. These are excellent points! We need to better prepare our engineers for constantly evolving sciences and environment by making them more information-proficient.

However, returning to our cognitive learning model, analysis and synthesis learning is much more difficult to teach and inevitably takes time. I can lecture to achieve knowledge, but to achieve analysis and synthesis takes exercises, case studies, research, and projects – and not just one exposure, but

The skill set of the engineer is to explore the real world and to determine how to apply the tools that we have learned. multiple exposures in a variety of scenarios and environments. Analysis in the cognitive model involves examining and breaking a complex problem into its parts to determine the elements, relationships and organization.

Synthesis involves such skills as hypothesis, design, organization, planning, and experiment based on a set of abstract relations. These are not skills that you can explain to someone and they simply repeat; students must practice, experience, and develop them.

This skill set is the definition of an engineer: when faced with a real-world situation, we can break it into its elements to determine how we can solve it using our wide variety of tools. From this analysis, we then hypothesize, potentially test it, and then design and plan the solution. I joke in my structural classes that our undergraduate degrees teach students how to distribute arrows pointing at a beam on a teeter-totter and a rolling pin.

I then show the students a building and ask them to tell me where they should be putting the arrows and where they might find a teeter-totter or a rolling pin. The skill set of the engineer is to explore the real world and to determine how to apply the tools that we have learned.

In this cognitive process, the digital tools are simply tools. It does not matter if we use software or a slide rule, I need the engineer to be able to solve problems. I do not need an engineer to be able to load data into a computer program and produce a result; I need the engineer to determine what the problem is and then decide which computer program to use. I recall a project of mine in which the consultant team faced an apparently failed floor fastening system. The five seasoned professional engineers were not standing around scratching their heads over how to use modeling software. Instead, they were deliberating

over what the problem was (analysis) and what the possible solutions were (synthesis).

From that point on, the technical design was simply running the numbers.

Regarding the move toward a bachelor’s degree plus 30 hours for future professional engineers, I am not sure what Mr. Frodsham’s point is. I do not see us being able to make it an associate’s degree plus 15 YouTube videos.

The issue is that the BS, as important as it is, only provides the beginning of any professional engineer’s skill set. We must set standards for proficiency, and education credit is one such standard. Mr. Frodsham appears to agree that we need to set high standards, but his thought appears to be that engineers can attain the necessary ‘knowledge’ through non-traditional methods.

I applaud Mr. Frodsham’s concepts of how to “digitize” our learning environment. I encourage him to become an educator and help us get there! I want to work with him! The profession can certainly gain efficiencies in this direction. We are in a world where I do not need to be in a university laboratory to learn how to design timber connections. There are many high-quality, big-name master’s degree programs out there that prove every day that I do not need to sit in a lecture hall to learn the material. But to suggest that students can learn the higher-level skills needed as engineers faster … I would challenge proponents of that assertion to prove it. Grand visions … but show me the money.▪ Tom Glardon, P.E., is an instructor at The Civil Engineer School of the Air Force Institute of Technology at Wright-Patterson Air Force Base near Dayton, Ohio. He can be reached at thomas.glardon@afit.edu.

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

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