STRUCTURE magazine | December 2013

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A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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NCSEA EXCELLENCE IN

December 2013 Soils & Foundations

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Brian W. Miller

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Mark W. Holmberg, P.E.

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RISA Technologies ................................ 43 Simpson Strong-Tie............................... 29 Structural Engineers, Inc. ...................... 19 StructurePoint ....................................... 12 Struware ................................................ 34 Williams Form Engineering .................. 20

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STRUCTURE® (Volume 20, Number 12). ISSN 1536-4283.

Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student. For change of address or duplicate copies, contact your member organization(s).Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board.

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CONTENTS

FEATURES

December 2013

COLUMNS 7 Editorial SEI Young Professional Scholarship to Attend Structures Congress

By Dennis R. Mertz, Ph.D., P.E.

9 Structural Forensics Untreated Submerged Timber Pile Foundations

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

13 Construction Issues The Complexities of a Simple Line

By John H. Hart, P.E.

16 Structural Design Correlation between Soil Bearing Capacity and Modulus of Subgrade Reaction

By Apurba Tribedi

30 InSights What if Concrete Can Be Made Ductile?

22 NCSEA Excellence in Structural Engineering Awards

By Victor C. Li, Ph.D.

The NCSEA Excellence in Structural Engineering Awards program annually honors the best examples of structural ingenuity from around the world. The winners of the 2013 program were announced at the NCSEA annual meeting in October. Read about the structural solutions developed for these unique projects, and join NCSEA in congratulating these exceptional winners. ®

Development Length

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

Simplicity

STRUCTURAL ENGINEERING AWARDS

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

32 Engineer’s Notebook

42 Structural Forum

NCSEA EXCELLENCE IN

December 2013 Soils & Foundations

DEPARTMENTS

ON

THE

COVER

By Robert H. Lyon, P.E.

130 th Street and Torrence Avenue Railroad Truss Bridge in Chicago, Illinois. The transport and roll-in of this massive steel truss was a design and construction feat for Alfred Benesch & Company and the City of Chicago. See NCSEA Excellence in Structural Engineering Awards on page 25.

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

by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

STRUCTURE magazine

5

December 2013

IN EVERY ISSUE 4 Advertiser Index 34 Resource Guide (Earth Retention) 36 NCSEA News 38 SEI Structural Columns 40 CASE in Point

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©2013 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.

editorial

SEI Young Professional Scholarship to new trends, new techniques and current industry issues Attend Structures Congress Dennis R. Mertz, Ph.D., P.E., F.SEI, M.ASCE and shall follow ASCE reimbursement policy.

If you have previously received an SEI Young Professional Scholarship to attend Structures Congress, you are no longer eligible. Full time students are not eligible for this scholarship.

How do you apply? An online application, to be submitted by Friday, December 13, 2013, can be found at www.asce.org/sei. Your application package must include the following: • your resume or curriculum vitae (1-2 pages), • two narrative statements (described on the application form), and • an essay (also described on the application form).

Applicants must select which tier level(s) they want to be considered for, and must be willing to attend Structures Congress no matter which award they receive. Selection of multiple tiers will not affect consideration for the higher tier awards. All expenses incurred beyond those covered by the scholarship are the responsibility of the awardee. Awardees will be recognized at the Young Professional Mixer Thursday, April 3, 2014 at Structures Congress. The awards consist of the following: • Two Tier 1 Awards: complimentary Structures Congress registration, travel reimbursement (economy domestic travel with 14 day advance purchase) and lodging reimbursement (up to $135/night for three nights), • Three Tier 2 Awards: complimentary Structures Congress registration and $500 travel reimbursement, and • Five Tier 3 Awards: complimentary Structures Congress registration.

To prepare your application, view the full application in advance and allow sufficient time to prepare all required materials before you fill out and submit the application online. Once you submit the online form, you will receive a confirmation response and a copy of the completed form via email for your records.

If chosen, what is expected of you? Awardees are expected to attend Structures Congress in its entirety, and at least one SEI committee meeting in addition to the SEI Young Professionals Committee meeting. Upon conclusion of the conference, awardees are required to submit a 1-2 page narrative providing feedback on Structures Congress and testimony on the benefits of attending. Scholarship reimbursements are contingent upon submission of this document.

Do you want to see the big picture? A recent recipient says, “My immersion amongst a wide range of voices and perspectives of the structural engineering community at the SEI congress in Pittsburgh helped me better understand my current place in our exciting profession and enabled me to envision my potential fit, future involvement, and importance as an individual within the bigger picture.”

Remember: Submit your application online by Friday, December 13, 2013. Awardees will be notified by January 24, 2014.▪

Young Professionals Scholarship winners jump-start their careers at the Structures Congress.

F

or many decades, Structures Congress has been bringing together a national, international and diverse community of structural engineers to advance the practice within buildings, bridges, and non-building structures. Over the years, this annual event attracts more than 1,200 attendees from practice, academia, government, industry, and allied fields and has grown to become the premier event for all structural engineering professionals.

Structures Congress 2014 is in Boston on April 3-5.

Would you like to participate in the congress, but cannot get your employer to send you and cannot afford it yourself? Are you a young professional? If so, here is a wonderful opportunity for you.

SEI is committed to the future of structural engineering and offers a Young Professional Scholarship to attend Structures Congress. This scholarship provides motivated young professionals in structural engineering (and related fields) the opportunity to attend Structures Congress 2014 in Boston. Many young professionals have found Structures Congress to be a career-changing and energizing experience, opening up networking opportunities and expanding horizons to new and emerging trends.

Do you want to further develop your career? A past scholarship recipient says, “Without this support, I would probably not have been able to attend and would have missed out on a great careerdevelopment opportunity.”

How about getting more involved with SEI? Another recipient states, “Participating in the conference has driven me to become more involved in SEI and other professional organizations, has inspired me to take a leadership position in my local SEI chapter, and has given me the confidence to achieve my professional goals.”

Do you need networking opportunities? Another scholarship recipient says, “The main benefit I found of attending the Structures Congress was the connections I made with both peers and experienced industry leaders.”

How about getting more active in our industry? This recipient says, “Attending the Structural Congress gave me the courage to become more involved and more active in the industry.”

Are you eligible? Young professionals (35 years or younger) in both industry and academia who are looking to become more involved with the Structural Engineering Institute (SEI) of ASCE are eligible for this scholarship. Scholarships are limited to one time only per recipient STRUCTURE magazine

Dennis R Mertz, Ph.D., P.E., F.SEI, M.ASCE, is the Director of the Center for Innovative Bridge Engineering at the University of Delaware. Professor Mertz is currently a member of the SEI Board of Governors and, as such, a member of Executive Committee of the SEI Technical Activities Division. He has also served on both the Structures Congresses committee and the Structures Congress National Technical Program committee.

7

December 2013

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T

he use of untreated timber piles as foundation support in Europe and the U.S became more wide-spread at the end of the 19th century and beginning th of the 20 century, when industrialization led to the rapid expansion of urban areas. Their use was common in regions with natural soft soils, or where urban-fill was used for land development, such as in the northeastern U.S. Thousands of historic structures across Europe and the U.S. currently remain supported on untreated timber piles; their continued use and maintenance costs highly depend on the condition of the piles after tens or hundreds of years of in-ground service.

Early on, it was recognized that untreated timber piles needed to be submerged to provide anoxic (i.e. little to no oxygen) conditions, which was thought to prevent pile deterioration due to wood-destroying fungi and/or soft rot attack.

Therefore, the installation of untreated timber piles typically required the pile cutoff to be below the lowest expected in-service groundwater level.

Unfortunately, urban development resulting from the industrial revolution brought with it underground construction; and as a consequence, groundwater levels became lowered due to longterm construction dewatering, new underground structures acting as obstructions to groundwater flow, and leaks into poorly sealed basements and underground utilities. The lowered groundwater levels resulted in exposure of the timber pile tops to oxygen, leading to significant pile-top deterioration due to fungal attack, and ultimately, significant settlement of the structures.

The typical foundation repair method for deteriorated untreated timber piles is cut-and-post underpinning; an access pit is excavated along the length of the foundation and the tops of the timber piles are exposed, removed, and replaced with new structural elements, e.g. concrete posts or concrete-encased steel posts.

It took until the 1970s to identify that biodeterioration of timber piles can also be caused by bacteria (Boutelje et. al. 1968, Klaassen 2008-1).

And it was not until recently that more comprehensive studies performed in Europe, specifically the BAC-POLES scientific project funded by the European Commission in 2001 (Klaassen 2005), have been able to quantify the rate of bacterial attack and of related degradation of the submerged wood strength.

This article, Part 1 of a 2-Part series, provides a summary of the state of knowledge on bacterial biodeterioration on submerged and untreated timber piles, as well as a discussion on the impacts of time and deterioration on the in-service compressive strength of the piles. A method for performing qualitative assessment of the likely effectiveness and durability of cut-and-post underpinning remediation of untreated timber-pile supported structures will be proposed in Part 2.

Biodegradation of Untreated Submerged Timber Piles Until recently, bacterial attack on submerged wood was the least understood biodeterioration mechanism. The European BAC-POLES research project, which investigated causes and patterns of bacterial decay in timber piles in the early 2000s, as well as subsequent research performed primarily in the Netherlands, have shed much needed light on the nature of bacterial deterioration mechanisms. It is now thought that bacterial decay of timber piles occurs always, at all sites and in all conditions, although the rate and degree of attack may vary depending on site specific conditions The following list is a summary of the most salient results and conclusions in the literature, relative to bacterial attack of submerged timber piles, reached to date: • Bacterial wood degradation can occur under a wide range of conditions due to the variety of bacteria species, each with its own optimal environmental settings (Klaassen 2008-1, Nilson et. al. 2008).

• In addition to low levels of oxygen, wooddegrading bacteria also appear to thrive best in environments with low levels of nitrogen (Huisman et. al. 2008).

• Bacterial wood degradation occurs uniformly along the entire pile length (pile lengths of up to about 46 feet were included in the BAC-POLES study).

Thus, in terms of assessment of bacterial degradation, the condition of the pile tops is representative of the entire pile (Klaassen 2008-1).

• Slight cell wall deterioration due to bacterial attack results in no major loss of compressive strength (Klaassen 20081). On the other hand, severe cell wall deterioration due to bacterial attack results in softening of the wood, significantly reducing the compressive strength of the wood in the affected areas and, thus, the effective available load-bearing pile cross-section.

• The velocity of bacterial decay is variable between wood species and is generally slow, ranging between almost 0 to more than 1 mm/year (0.04 inch/year). Based on a database that included about 1000 spruce piles and 1000 pine piles with a service life ranging between 80 to 200 years, the rate of initial advancement of bacterial invasion before significant wood strength loss occurs is about 0.5 mm/year (0.02 inch/year) in pine, whereas in spruce it ranges between 0.1 to 0.5 mm/year (0.004 to 0.02 inch/

STRUCTURE magazine

Structural ForenSicS investigating structures and their components

Untreated Submerged Timber Pile Foundations

9

Part 1: Understanding Biodegradation and Compressive Strength

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.

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.

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

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

year). Once bacterial invasion is well established, the rate of deterioration increases; the average rate of severe bacterial attack causing significant wood strength loss was calculated to be about 0.25 mm/year (0.01 inch/year) in pine piles, and about 0.13 mm/ year (0.005 inch/year) in spruce piles (Klaassen 2009).

• The advancement of bacterial decay occurs inwards, starting from the pile perimeter. For spruce and pine piles with an in-service age of 650 years or less, the rate of bacterial attack decreases significantly at the heartwood-sapwood interface. Bacterial degradation of the heartwood was only observed in oak piles about 2000 years old; the degree of deterioration in the heartwood varied from moderate at the heartwood-sapwood interface to weak near the pith (Klaassen 2009).

• Wood species with more permeable tissue structures (e.g. alder, poplar, and the sapwood of pine and oak) are more susceptible to bacterial decay than those with less permeable tissue structures (e.g. spruce and the heartwood of pine and oak). More permeable tissue structures, i.e. wood species with larger open cross-field pits, allow more flow of water and therefore transport of wood-degrading bacteria in the water stream across the pile cross-section (Figure 1). In the presence of pressure gradients between the tops and bottoms of piles (i.e. the bottom and top of the piles are embedded in different soil layers with different groundwater levels), water flow and transport of wood-degrading bacteria is facilitated along the length of the piles (Klaassen 2008-2).

The authors’ observations, and observations by others, regarding a large number of piles exposed

234

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Figure 1: Deteriorated timber pile cross-section.

over most of their length confirm that bacterial decay occurs over the entire pile length. In addition, microscopic evaluations on spruce timber pile samples from one of the authors’ projects in the northeastern U.S. (for which historic records on timber-pile condition assessments are available), indicate the following: • Slight to no cell wall deterioration combined with the presence of bacteria was observed at depths ranging from 0.25 to 4 inches (6 to 100 mm) for piles with 67 to 117 years in service.

The calculated average rate of advance of bacterial invasion is 0.41 mm/year (0.016 inch/year).

• Severe cell wall deterioration with significant strength loss was observed in the outer 0.5 to 0.75 inches (13 to 19 mm) for piles with 103 years to 117 years in service. The calculated average rate of advance of severe degradation is 0.13 mm/year (0.005 inch/year).

Therefore, the behavior of microbial decay under submerged conditions in the U.S. appears to be similar to that observed by others in European piles of the same species and of equal or greater age.

Compressive Strength of In-Service Timber Piles Current design standards for new timber pile foundations (ASTM D245-06 and ASTM D2899-03) reference and use the allowable compressive strength of timber piles, rather than the ultimate compressive strength (strength at failure). The design strengths are based on, but are lower than, the representative ultimate compressive strength obtained from testing of clear, straight-grained, green wood samples. The ultimate compressive strength value is multiplied by a series of adjustment coefficients that are meant to account for a safety factor, duration of load (DOL) effects, grade/quality of wood, pile group effects, test

STRUCTURE magazine

10

December 2013

sample size, variability, and potential defects in the wood. Of all these factors, the most significant in terms of reduction in compressive strength is the DOL factor, which imposes approximately a 40% reduction in the compressive strength for permanent (constant) loads (ASTM D245-06). The DOL factor accounts for the laboratory-testing proven effects of duration of the applied load on the strength properties – the longer the wood is subjected to a constant load, the lower its strength. This is due to unrecoverable microdamage that takes place during the period the pile is loaded. Although the use of all these adjustment factors for design purposes is prudent and necessary, their use for evaluation of existing conditions is likely conservative.

Other than reductions in strength due to the DOL factor, current design standards assume no reduction in the compressive strength of wood due to aging effects, (provided no biodeterioration is present). This is reportedly based on strength tests of old timbers, 100 or more years old, which showed no appreciable deterioration of the wood’s strength or stiffness due to age alone (ASTM D245-06). Klaassen (2008-1) reached a similar conclusion when comparing the compressive strength of foundation piles that had been in use for more than 80 years (and suffered no bacterial or other degradation) with compressive strength of samples obtained from freshly sawn timbers.

Van Kuilen (2007), however, concluded that the compressive strength of submerged timber decreases with time. He presented results of compressive strength tests performed on clear wood samples obtained from submerged untreated European pine, spruce, larch, oak and alder piles with varying in-ground service ages (between 70 and 640 years). The results are presented as the ratio of the measured compressive strength (parallel to the grain) of the aged wood to the average strength of new wood in a wet condition, versus the time in service in the ground below the groundwater level (Figure 2). Van Kuilen further determined that the residual strength of the timber piles appears to be governed by the amount of heartwood in the cross-section (based on the results of tests on full pile cross-sections), and provided bestfit lines for estimating the decrease in timber pile compressive strength of the heartwood and sapwood as a function of time in service and under load. Van Kuilen did not elaborate on the cause of strength reduction with time beyond indicating that the magnitude of applied load (i.e. accumulation of mechanical damage under sustained loading) and the degree of decay likely play a role.

To validate the use of Van Kuilen’s curve for estimating the decrease in compressive strength

of the short-term ultimate wood strength, creep deflection levels off and additional deflection does not occur. As the applied stress levels increase to more than 55% of the short-term ultimate wood strength, creep continues indefinitely and ultimately results in failure. Thus, a pile loaded to 10% of its ultimate short term test capacity is likely to experience less damage under sustained loading than a pile loaded to 50% of its ultimate short term test capacity. For example, in large historic structures, where the number of in-place timber piles sometimes exceeds the minimum number of piles required to support the applied loads by design, the piles can be expected to have experienced a low level of sustained applied loads and hence less “aging/DOL” effects.

Figure 2: Decrease in timber pile compressive strength with in-service age (Base figure from Van Kuilen, 2007).

ultimate strength values are applicable for short-term loading only. Therefore, it appears that Van Kuilen’s curves reflect the decrease in compressive strength of submerged, undeteriorated heartwood due to aging under prolonged continuous loading (i.e. DOL).

The spread in the values of compressive strength parallel-to-the-grain obtained at various service ages could be related to variations in the level of applied compressive stress on the piles. Microscopic mechanical damage to timber piles under sustained loading, however, becomes less significant if the piles are loaded to a smaller fraction of their capacity. Hoyle and Woeste (1989) report that when the applied stress is at less than 55%

The authors’ experiences confirm that bacterial attack in the submerged portion of the timber piles can play an important role in limiting the estimated remaining service life of pile-supported structures, even after cut-andpost underpinning has been performed. Given the magnitude of involved costs, the presence and impact of bacterial attack may ultimately govern the choice of the underpinning method to be used. The current understanding of the rates of deterioration, loss of strength and loss of stiffness of wood with time is still developing. However, there is sufficient information available to allow for a qualitative assessment of the likely effectiveness and durability of cut-and-post underpinning remediation of untreated timber-pile supported structures.▪

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of heartwood, the author’s calculated strength ratios (i.e. ratio of measured compressive strength of aged pile to the expected compressive strength of a new pile) for full timber pile cross-sections and clear wood samples obtained from piles exposed at various projects throughout northern U.S. All full-timber pile samples considered were eastern spruce; clear wood samples considered were eastern spruce, red pine, and elm. The in-service age of the samples ranged from 67 to 137 years.

Only non-deteriorated heartwood samples were included in this evaluation.

For comparison with Van Kuilen’s curve, the expected average clear wood ultimate compressive strengths parallel-to-the-grain of 2650, 3280, and 3780 psi (18.2, 22.6, and 26 MPa) were used for spruce, pine, and elm piles respectively. These values were obtained from published average strength values for each wood species grown in the U.S. and Canada, as provided in Tables 2 and 3 of ASTM D-2555-06. Figure 2 shows a plot of the calculated strength ratios superimposed on Van Kuilen’s graph. In general, the data is reasonably centered and distributed around the best-fit line for decrease in compressive strength of submerged untreated pile heartwood proposed by Van Kuilen.

The laboratory compressive strength testing of samples obtained from existing timber piles includes the effects of any micro-damage, i.e. duration of load effects, that has taken place during the period the pile has been in service.

Conversely, the laboratory compressive strength testing of samples from freshlysawn timbers do not, and the published

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ConstruCtion issues discussion of construction issues and techniques

Soil nail wall construction.

W

hen a line is drawn on paper, what does it mean?

Retaining walls are usually drafted as a simple line on plans by the architect or engineer, with little direction other than a note: “Retaining wall design and construction by others.”

But retaining walls are more than just a simple line. A range of decisions face the design and construction team when planning solutions for grade separations with a retaining wall. Understanding these decisions and accurately communicating them to the client, as well as to each other, is essential for engineers, particularly as the use of retaining walls in construction continues to grow.

As usable or “good” sites become scarcer, retaining walls are often the only option for optimizing tight sites with hard-to-meet space requirements or significant slopes.

In short, that simple line can make or break a project. The key to designing and constructing a successful retaining wall – and avoiding a “situation” – is careful consideration in the initial design phases, including (1) the type of system to use, and (2) the contractual approach to design and construction.

type of wall that is best suited for a particular site. Choosing the wrong type of wall may not provide sufficient restraint, may be impractical to construct, and may cause instability in the existing geotechnical conditions.

A decision has to be made at the beginning of design: Is the site better suited for top-down construction or bottom-up construction? Topdown construction is appropriate for sites that need to be excavated to achieve final grade, while the bottom-up approach applies to sites that need to be filled. Technologies for topdown construction include soil nail walls, secant drilled shafts, and soldier pile walls, while technologies for bottom-up construction include mechanically stabilized earth (MSE) walls, conventional gravity walls, and gabion walls. Each of these technologies has unique applications that are dependent on the site layout, the height of wall, soil conditions, the presence of nearby structures, underground utilities, and the intended use of the areas near the top and bottom of the wall.

Too often, the wrong wall type is selected for a site, which results in two retaining walls Type of System being constructed where only one is needed.

Engineers have several different options for the An example is when a design incorporates a design and construction of retaining walls. At pres- bottom-up wall that requires excavation into an ent, retaining walls can be built out of traditional existing slope. In order to provide the restraint materials such as concrete and steel reinforcement, required, such as a heel for concrete walls or or from new technological materials such as geo- geosynthetic length for MSE walls, a nearly synthetics and lightweight concrete. Furthermore, vertical slope must be excavated behind these in the last twenty years, pre-manufactured retain- elements. This requires an additional top-down ing wall systems have become available that offer construction wall behind the proposed wall. If reasonable factors of safety while providing multiple the designer is aware of all the retaining wall aesthetic facing options. Typically, several condi- technologies, one top-down wall could be utitions from the geotechnical, structural, civil, and lized in this situation, resulting in a substantial construction perspectives have a bearing on the decrease in cost to the owner. continued on next page STRUCTURE magazine 13

The Complexities of a Simple Line Considerations for Retaining Wall Projects

By John H. Hart, P.E., D.GE.

John H. Hart, P.E., D.GE. (JHart@ctlthompson.com), is a practicing engineer at CTL|Thompson in Denver, Colorado. Specializing in the fields of deep foundations, earth retention design, and landslide/ stability analysis, Hart has led a broad spectrum of projects.

Contractual Approach to Design Top-down or bottom-up retaining walls have advantages and disadvantages that are specific to the site and situation. But who or what determines which retaining wall system is the most appropriate, considering cost, resistance and constructability?

There are generally two approaches to design and construction: the traditional approach, where an engineer designs the system and the contractor builds it; and the performancespecified approach, where the engineer provides the basic criteria such as length, height, and location, and the contractor designs and builds the wall with engineering support, either in-house or subcontracted.

Traditional Design Approach In the traditional approach, the contractor constructs the wall in accordance with the plans and specifications developed by the engineer. The owner hires an engineer to design a retaining wall, and the engineer provides plans and specifications for contractors to use in preparing competitive bids.

If the features at the site and limitations of construction equipment are not fully understood, the proposed construction may not be achievable. In

addition, if an engineer is well-versed in only one engineering discipline, then aspects from other points of view may be overlooked.

Undeveloped properties may have unique slopes or geotechnical issues that are yet undiscovered. This can lead to a difficult situation – especially if it is the contractor that recognizes the problem once the team is in the field.

Soil conditions may not be uniform, slopes may be steeper than expected, or the design may not be adequate for the overall loads.

If the contractor must make these decisions in the field, it may lead to change orders, which in turn lead to extra costs for the owner.

Furthermore, if the designer is not in the field with the wall builder, there may be less communication, which sets up the engineer as an adversary and lessens the likelihood for success. Lastly, the wall built by the low bidder may not be the most aesthetically pleasing.

On the other hand, there are real benefits to be derived from the traditional approach. For one thing, all of the contractors are bidding on the same design, which the engineer presumably designed in full compliance with the governing codes. This results in economical construction because it is streamlined and consistent – if the designer understands all engineering aspects of the retaining wall. It also puts the contractors in competition from a bidding perspective. In

Design/Build Earth Retention Foundation Support Slope Stabilization Ground Improvement Dewatering

addition, the owner should be assured that a functioning final product will be produced.

Performance-Specified Design Approach Another option for designing and building a retaining structure is the performancespecified wall. In this approach, the design team provides basic criteria, such as desired wall length, height, etc. and the contractor, with engineering support, designs and builds the wall. In this scenario, an in-house engineer or engineering consultant subcontracted to the contractor designs the wall considering the basic criteria provided by the design team. The contractor’s engineer decides which specific system should be constructed and designs that system accordingly. Furthermore, the contractor’s engineer selects facing for the proposed wall, which may be block, something that matches the natural environment, or sculptured shotcrete, which looks like natural rock.

There are several advantages to this approach: It could result in a lower cost to the owner because it allows the engineering to be more innovative, enabling the designer to be more aggressive, potentially offering more expertise as it relates to specific conditions and wall types. This approach also lays the groundwork for better communication between the engineer and contractor, so modifications can be made on the fly.

There are drawbacks as well. The performance of the wall may suffer because quality control and quality assurance is left in the contractor’s hands from both a design and construction perspective. Furthermore, the design may only be able to incorporate wall systems that the contractor can build and not truly evaluate different wall systems that may be appropriate for the site.

An example would be when the engineer who is working for the contractor designs an MSE wall to be built by an MSE wall contractor; a soil nail wall system might have been more appropriate for the site, but the contractor does not have the equipment to build it. Finally, with innovation in design, codes may be pushed to the farthest extent, which may result in deficiency in overall long-term performance of the wall.

Conclusion

800-562-8460 WWW.DBMCONTRACTORS.COM Donald B. Murphy Contractors, Inc.

STRUCTURE magazine

14

December 2013

There are numerous approaches to design and many types of retaining systems, each with specialized applications that can be used to retain soil and/or provide stability to slopes. Understanding what is involved in each design approach, how the system is constructed, and under what conditions they are constructed is imperative to successful and economical design and construction.▪

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Structural DeSign design issues for structural engineers

P

robably the most widely used value in a soil report is soil bearing capacity. The obvious reason is that basic examples given in most text books almost always use bearing capacity to calculate the plan dimension of a footing.

Because of simplicity and ease of use, this method is still the fundamental soil parameter for foundation design. However, that simplicity assumes the footing will behave as a rigid body. That particular assumption works well in practice for small and single column footings. But for large and multi column foundations, most engineers prefer flexible analysis.

Manual computation of flexible analysis could be challenging and, in almost all cases, software programs such as STAAD, SAFE, GT STRUDL etc. are used. However, these computer programs often ask for an input called “modulus of subgrade reaction”. Many engineers are not familiar with this term and often try to compare it with bearing capacity.

As more and more engineers will use software to design foundations, it is essential for engineers to have a fundamental understanding of this soil parameter.

Is there any relationship between bearing capacity and modulus of subgrade reaction?

Correlation between Soil Bearing Capacity and Modulus of Subgrade Reaction

By Apurba Tribedi

Apurba Tribedi is a Senior Product Manager at Bentley. He is one of the core developers of the STAAD. Pro program and currently manages the STAAD Foundation product. He may be reached at apurba.tribedi@bentley.com.

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

of the measured value and could be mistaken as a density unit or a volumetric measurement.

Mathematically, the coefficient of subgrade reaction is expressed as: Ks = p/s

(Eqn 1)

where p = contact pressure intensity and s = soil settlement As Terzaghi mentioned, proper estimation of contact pressure for a flexible foundation could be very cumbersome, so it is assumed that Ks remains constant for the entire footing. In other words, the ratio between pressure and settlement at all locations of a footing will remain constant. So the displacement diagram of a footing with a load at center will have a dishing effect. A point at the center of the footing will experience the highest displacement. Displacement reduces as it moves away from the center. Figure 1a shows a simple slab-on-grade foundation. It was modeled and analyzed in STAAD Foundation as “Mat”, which is a flexible foundation; the soil was defined using coefficient of subgrade reaction. For this exercise, the software default value for the modulus of subgrade reaction was used. The displacement diagram shows a dishing effect as discussed earlier. Figure 1b shows the soil pressure contour. It is also obvious that the pressure intensity at the center is maximum and reduces as the elements

Modulus of Subgrade Reaction (Ks) This term is measured and expressed as load intensity per unit of displacement. For the English unit system, it is often expressed in kip/in2/in; in the SI system it is expressed as kN/m2/m. Some express this term in kip/in3 (or kN/m3) which can be misleading. Numerically, kip/in3 is correct but does not properly represent the physical significance

Figure 1b: Soil pressure contour.

Figure 1a: Deflection diagram and soil pressure contour.

16 December 2013

Table 1: Soil pressure, node displacement and their ratio.

Node number

Soil pressure (p) (kN/m2)

1 (top-left corner) 41

Node displacement () (mm)

Ratio (p/) (kN/m2/m)

58.38282

5.377

10858

61.94684

5.70524

10858

51

65.56358

6.03834

10858

61

69.19262

6.37257

10858

71

72.64874

6.69087

10858

81 (middle)

75.31719

6.93664

10858

Figure 2: Selected points to compare base pressure, deflection and ratio.

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(or node coordinates) move away from the center. So, it could be assumed that the ratio of pressure intensity and settlement is constant.

Consider some of the numbers from the same example. Soil pressure, corresponding displacement and the ratio are listed in Table 1. The points are represented on a diagonal to illustrate the variation of pressure and displacement as the points move away from the center to the most distant point in the corner of the rectangular footing. Figure 2 shows the points on the mat slab.

This is hardly a surprise as, by definition, the modulus of subgrade reaction (Ks) is a constant for the entire footing and the program used Ks as its soil property. It is also important to note that the software default Ks value (10858 kN/m2/m) was exactly the same as the constant ratio calculated in Table 1.

Base pressure was calculated from the support reaction. One might think that the ratio of support reaction and corresponding displacement will also be a constant. As shown in Table 2 ( page 18 ), the ratios are not constant for all values. How is the Ks value used inside the program and how is the base pressure calculated?

Tributary Area Often an assumption is made to calculate how much area of a plate can be attributed to a node or, in other words, the influence of each node on the surface area of a plate. It depends on the shape of the plate. For a perfect square or rectangular plate, each node will influence exactly ¼ of the plate surface area (Figure 3a, page 18 ). But for a generalized quadrilateral, the best practice would be to calculate the center of the mass of the plate and STRUCTURE magazine

17

December 2013

Figure 3: Node tributary area.

Figure 4: Tributary area of selected nodes.

then draw lines from that center point to the middle points of each side. In Figure 3b, the shaded area represents the influence surface area of the corresponding node.

Spring Support Constant The above described tributary area calculation is the key procedure used internally by the commercial software to calculate the linear spring constant. The program first calculates the tributary area for each node of the footing and then multiplies the modulus of subgrade reaction by the corresponding tributary area for each node to get the linear spring constant at each node.

Kyi = Ks x Tai

(Eqn 2)

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where Kyi is the spring constant at ith node Tai is the influence area of ith node Ks is the modulus of subgrade reaction For a concrete foundation analysis, those springs have to be defined as compressiononly, as concrete is assumed not to carry any tensile force. The base pressure is calculated at each support node by dividing the support

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reaction with the corresponding node tributary area. If we look at the above example, Node 1 has a much smaller tributary area than the rest of the nodes. It can also be noted that all other nodes have same tributary area. This explains Table 2, as it shows the ratio for Node 1 is different than other nodes. Figure 4 shows the tributary area for different nodes. Node 1 has a tributary area which is 25% of Node 81. Table 3 is an extension of Tables 1 and 2 and shows how constant ratio is achieved for all nodes.

Allowable Settlement Bearing capacity is the measurement of the soil pressure a soil can safely bear. In other words, bearing capacity is the pressure which soil can withstand before it fails. The two most important soil failure criteria are: • Shear failure • Maximum allowable settlement Among many factors, foundation width (B) can influence failure criteria. Normally, shear failure governs for smaller foundations and settlement failure governs bigger foundations.

Table 4 is a typical example which shows the relationship among different foundation sizes and failure criteria.

To estimate settlement failure, an allowable settlement value is assumed (normally 25 mm or 1 inch). When soil settles more than the

allowable value, the soil fails. So, even for a bearing capacity calculation, an allowable soil settlement is used and structural engineers should be aware of that value while designing a footing. The allowable soil settlement value is typically an integral part of any soil report.

Why Use the Modulus of Subgrade Reaction It was previously stated that to design a flexible mat foundation, the modulus of subgrade reaction is used instead of bearing capacity of soil. But why? The answer lies in the underlying assumptions of how a foundation might behave.

Foundations can be rigid or flexible. Bearing capacity is used to design rigid foundations, but subgrade reaction is used for flexible foundations. The very assumption of a rigid foundation is that “the distribution of the subgrade reaction p over the base of the foundation must be planar, because a rigid foundation remains plane when it settles.”

Consider a simply supported beam loaded at its center, as shown in the Figure 5a. By statics, we can obtain R1 = P/2 and R2 = P/2. If the same beam is loaded eccentrically, the reaction can be calculated as shown in Figure 5b.

The same concept is extended for rigid foundation design. But instead of the end supports, the whole foundation is supported.

Table 2: Support reaction and displacement.

Node number

Support Reaction(P) (kN)

1 (top-left corner) 41

Node displacement () (mm)

Ratio (P/) (kN/m)

1.313609

5.377

244.3

5.575193

5.70524

977.2

51

5.900749

6.03834

977.2

61

6.227366

6.37257

977.2

71

6.538362

6.69087

977.2

81 (middle)

6.778522

6.93664

977.2

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December 2013

Table 3: Reaction, base pressure, displacement, Ks constant.

Node number

Support Reaction(P) (kN)

Influence area (m2)

Base Pressure (p) (kN/m2)

Displacement () (mm)

Ratio (p/) (kN/m2/m)

1 (top-left corner)

1.313609

.0225

58.38282

5.377

10858

41

5.575193

.09

61.94684

5.70524

10858

51

5.900749

.09

65.56358

6.03834

10858

61

6.227366

.09

69.19262

6.37257

10858

71

6.538362

.09

72.64874

6.69087

10858

81 (middle)

6.778522

.09

75.31719

6.93664

10858

Figure 5: Reactions for a simply supported beam.

on. As many authors have concluded, a rigid foundation can be safely designed using bearing capacity, as in most cases this method yields more conservative results.

P = 1/2L(R1 + R2 )

a flexible foundation cannot have linear subgrade reaction. Rather, it depends on the compressibility of the foundation as well as the structural rigidity. A flexible foundation is subjected to internal bending and relative displacements between two slab points. The greater the structural rigidity, the less the relative displacement. The author tested the case with very high rigidity of the slab elements, resulting in a nearly planar surface after the application of the load. Similarly, the greater

(Eqn 3)

P x a = 1/6B 2R1 + 1/3B 2R2

(Eqn 4)

But a mat foundation is often designed as a flexible foundation as it can be large in size and there may be many load application points and other complexities, including holes and grade beams. Widespread availability of FEA software contributes to this trend. But, unlike rigid foundations,

Table 4: Final allowable bearing capacity for allowable settlement = 25 mm and a given embedment depth.

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It is also assumed that the relative stiffness of the concrete slab is much higher than the soil stiffness. So, the slab is assumed to remain planar even after the application of load.

Figure 6a shows a footing loaded at the center. From a rigid wide beam analogy, P = R x L. Similarly, for an eccentrically loaded footing, the reaction will vary linearly from one end to the other as shown in Figure 6c.

Equations 3 and 4 can be solved to find end reactions. But none of the equations contain modulus of subgrade reaction (Ks). So, the “distribution of subgrade reaction on the base of a rigid footing is independent of the degree of compressibility of the subgrade” it is resting

Figure 6: Sub grade reactions for an isolated footing.

the modulus of subgrade reaction, the less the pressure distribution. In other words, a higher Ks value will absorb more pressure at the load application point. Hence, the modulus of subgrade reaction, which is the function of soil settlement and the external pressure,is used for flexible foundation design.

Correlations The most common – and probably the safest – answer to the question of correlation between bearing capacity and the modulus of subgrade reaction is that there is no correlation. But there should be one, as both are the measurements of soil capacities and any of these two parameters can be used to design a regular foundation.

Again, the definition of Ks is the pressure per unit settlement. In other words, soil capacity to withstand pressure for a given displacement. From earlier discussions, it is also clear that even bearing capacity has an allowable settlement. It is therefore tempting to conclude that the modulus of subgrade reaction is the bearing capacity per unit settlement.

This conclusion is very similar to the equation presented by Bowles.

SI: Ks = 40(SF )qa kN/m3

(Eqn 5)

FPS: Ks = 12(SF )qa k/ft 3

(Eqn 6)

where SF = Safety factor and qa is the allowable bearing capacity.

In Equations 5 and 6, the allowable bearing capacity is first converted to ultimate bearing capacity by multiplying with a safety factor.

The author assumed one inch or 25 mm settlement. The final equation is then formulated dividing the ultimate bearing capacity by the assumed settlement.

The more generic form of the equation can be written as: Iqa Ks = stress/displacement (Eqn 7)  where I = Safety factor qa is the allowable bearing capacity  is the allowable soil settlement These equations clearly indicate that the appropriate safety factor must be used, and the Ks value can be better compared with ultimate bearing capacity rather than the allowable bearing capacity. The safety factor can vary depending on projects and geotechnical engineers. The other important factor is the assumed allowable settlement for the calculated bearing capacity.

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STRUCTURE magazine

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December 2013

Similarly, it is to be noted that the base pressure values reported by FEA analysis cannot be directly compared with the bearing capacity.

Maximum base pressure should be multiplied by the safety factor and then compared with the allowable bearing capacity of the soil.

However the above mentioned equations have limitations. They can be applied to footings where settlement failure governs, but cannot be related to footings where shear failure occurs before reaching the allowable settlement limit. So, engineers must exercise caution before using these equations.

Conclusion The correlation between bearing capacity and modulus of subgrade reaction is at best an estimation. It can be used for estimation, but a Ks value determined by a plate load test should always be used if available or should be requested whenever possible. However, the above discussion gives insight into these values and helps engineers to understand the physical significance of modulus of subgrade reaction. And, as always, structural engineers should consult a geotechnical engineer professional prior to finalizing soil stiffness and bearing values.▪

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GINEERS

O NS

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OCIATI

NATIONAL

ASS

RAL

EN

COUNCIL

NCSEA

National Council of Structural Engineers Associations

Excellence in Structural Engineering NCSEA 16th Annual Awards Program

A

t their annual meeting in Atlanta, GA on September 20, NCSEA announced the winners of the 2013 Excellence in Structural Engineering Awards. This awards program annually highlights some of the best examples of structural ingenuity throughout the world. Awards are divided into eight categories: four building categories which are separated based on construction cost, bridge or transportation structures, international structures, forensic-renovation-retrofit-rehabilitation structures and an “other” category which encompasses all types of non-building or bridge structures. In each category, up to three award winners were named with one project named the Outstanding Project. All structures must have been completed, or substantially completed, within the past three calendar years.

The 2013 Awards Committee was chaired by Carrie Johnson (Wallace Engineering, Tulsa OK). Ms. Johnson noted: “We had a really great group of judges from the Structural Engineers Association of Illinois this year, and some truly outstanding projects. They had the task of evaluating a huge variety of projects, including projects from twentythree different states and several different countries. The judges did an outstanding job of analyzing each entry. They indicated that they had an interesting time reading about the creative ways structural engineers resolve unique and challenging problems. Seeing the entries each year continues to make me proud to be a structural engineer.”

Please join STRUCTURE® magazine and NCSEA in congratulating all of the winners. More in-depth articles on several of the 2013 winners will appear in the Spotlight Department of the magazine over the course of the 2014 editorial year.

STRUCTURE magazine

2013 Panel of Judges The judging was held Thursday, July 18, 2013 at the NCSEA offices in Chicago, IL. The 2013 awards jury included the following individuals from the Structural Engineers Association of Illinois:

22

Bill Bast, P.E., S.E., SECB Thornton Tomasetti Brian Dekker, P.E., S.E. Sound Structures, Inc. Soliman Khudeira, P.E., S.E. Chicago Department of Transportation Terry McDonnell, P.E., S.E. EXP US Services Chris Rockey, P.E., S.E. Rockey Structures, LLC David Weihing, P.E., S.E., LEEP AP Thornton Tomasetti Michael Wysockey, Ph.D., P.E. Thatcher Foundations John Zils, P.E., S.E., SECB Skidmore, Owings & Merrill LLP Deborah Zroka, P.E., S.E. Zroka Engineering

December 2013

CATEGORY

Outstanding Project

1

New BuildiNgs

Tracy Aviary Visitors Center Salt Lake City, UT Dunn Associates, Inc.

Photos courtesy of alanblakely.com.

uNder

The Tracy Aviary is completely transforming its physical landscape and exhibits to renew its position as one of Salt Lake’s prized assets.

A new Visitors Center was needed to act as a focal point for families and patrons as they entered the grounds. The center incorporates new entry facilities, multipurpose areas, a gift shop, and office space for Aviary staff. One of the buildings most notable features is the custom metal façade that forms the skin. A light, airy exterior incorporates an abstract pattern that suggests a tree canopy and branches, while evoking a sense of motion.

$10 M illioN

CATEGORY

2

Outstanding Project

New BuildiNgs

Lee Hall III, Clemson University School of Architecture Clemson, SC Skidmore, Owings & Merrill LLP Lee Hall III is a 55,000-square-foot addition to Clemson University’s College of Architecture, Arts and Humanities in South Carolina. The building houses academic programs in architecture, art and planning, faculty offices and student work-space.

Conceived as “a building that teaches,” Lee Hall III encourages informal learning through observation of its ultra-energy efficient design and exposed functional and structural systems, including a curving, warped roof with no curved steel used in the building’s frame.

Lee Hall III was awarded a LEED Gold certification by the U.S. Green Building Council.

$10 M illioN to

$30 M illioN STRUCTURE magazine

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December 2013

CATEGORY

Outstanding Project

3

$30 M illioN

Federal Center South Building 1202 is the result of both the 2009 American Recovery and Reinvestment Act funding (ARRA), and the U.S. General Services Administration’s (GSA) Design Excellence program which was established to procure the nation’s best engineers and architects in order to achieve the most innovative and high performance design in federal government building projects.

With reuse and high energy-performance as part of both the GSA and ARRA requirements, the new 1202 building transforms a 4.6 acre brownfield site into a highly flexible and sustainable 209,000 SF regional headquarters for the U.S. Army Corps of Engineers (USACE) Northwest District.

New BuildiNgs

Federal Central South Building 1202 Seattle, WA KPFF Consulting Engineers

to

$100 M illioN

CATEGORY

4

Outstanding Project

New BuildiNgs

San Francisco Public Utilities Commission Headquarters San Francisco, CA Tipping Mar

over

$100 M illioN

The LEED Platinum SFPUC headquarters opened in June 2012, after a long saga of budget crises, value engineering, design, and redesign. The original base isolation system had given way to a cheaper system of steel moment frames with viscous dampers, yet costs were still $62 million too high. Tipping Mar designed a vertically post-tensioned concrete shear-wall system with composite link beams, delivering immediate-reoccupancy performance at a negligible premium over conventional design using the floorand-column grid set during DDs. The innovative link beams served as formwork and a shallower, more flexible beam that is easy to build.

Courtesy of Bruce Damonte (2012).

STRUCTURE magazine

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December 2013

CATEGORY

Outstanding Project

5

iNterNatioNal structures

La Plata Stadium La Plata, Argentina

Weidlinger Associates, Inc.

The elegant 53,000-seat La Plata Stadium is the quintessence of innovation. It is the first fabric-covered stadium in South America and the first anywhere to adapt the Tenstar™ tensegrity roof concept to a twin-peaked configuration. Based on a prize-winning concept developed by architect Roberto Ferreira, its unique dog-bone plan provides separate identities for two resident football teams. The dome’s unusual shape inspired the development of a new, complex construction method that permitted the roof rings to be lifted before being expanded to their full circumference. Unlike some tensile roof systems, La Plata’s does not rely on its fabric for stability.

over

$100 M illioN

Courtesy of Birdair, Inc.

CATEGORY

6

Outstanding Project

New Bridges & traNsportatioN structures

130 th Street and Torrence Avenue Railroad Truss Bridge Chicago, IL Alfred Benesch & Company Innovative Accelerated Bridge Construction (ABC) techniques used to assemble and transport a 394-foot-long, 4.7-million-pound steel railroad truss made history with what is believed to be the largest steel railroad truss rolled into place. Assembling the truss in a staging area kept construction separated from rail and vehicular traffic, improved safety during construction, and improved accessibility for quality checks. It took four months to assemble and paint the truss, which consists of over 25,000 steel pieces and 65,000 bolts. Four Self Propelled Modular Transporters (SPMTs), each equipped with 96 individually computer-controlled wheels, rolled the massive truss 800 feet to its permanent position.

Photos courtesy of Alfred Benesch & Company.

STRUCTURE magazine

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December 2013

CATEGORY

Outstanding Project

7 F oreNsic /r eNovatioN / retroFit/rehaBilitatioN structures

UC Berkeley California Memorial Stadium Seismic Upgrade Berkeley, CA Forell/Elsesser Engineers, Inc. UC Berkeley’s existing California Memorial Stadium sits directly over the active Hayward Fault. The original non-ductile concrete frame western stadium bowl has been seismically retrofitted and modernized with new seating bowl framing, a new press box, and the preservation/restoration of the historic perimeter concrete wall. The sections of the stadium positioned over the Hayward Fault have been designed to accommodate the predicted 6-feet of horizontal fault rupture displacement and 2-feet of vertical fault rupture displacement. The press box is a new 375-foot long steel structure which hovers above the west seating bowl on four rocking, post-tensioned core walls.

Courtesy of Tim Griffith.

CATEGORY

8

Outstanding Project

other structures

GIWW Sector Gate Monolith New Orleans, LA Ben C. Gerwick, Inc. The Sector Gate Monolith houses the primary gate east of New Orleans, which allows closure of the Gulf Intracoastal Waterway (GIWW) during storm surges. The monolith provides protection for a 100-year hurricane. It is 380 feet long by 160 feet wide, and 50 feet from top to pile cap. It has a 150-foot-wide by 42-foottall opening for navigation that can be closed in 30 minutes or less. It was built on weak soils, supported by 478 155-foot-long piles. It is part of the largest design-build infrastructure project in Army Corps of Engineers’ history.

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December 2013

Category 2 Award Winner

Category 4 Award Winners

Category 6 Award Winners

Cummins Parking Structure Columbus, IN American Structurepoint, Inc.

One World Trade Center New York, NY WSP

Gulf Intracoastal Waterway Floating Barge Gate New Orleans, LA Ben C. Gerwick, Inc.

A parking garage that is aesthetically pleasing and constructed at 60 percent of the national average is hard to achieve, but this was exactly what was accomplished with the Cumming Parking Structure in Columbus, Indiana.

Minimizing architectural treatments, and instead expressing the raw structure, drastically improved cost and appearance. The design-build project was completed in 11 months and features a massive installation of vertical green walls comprising 7,000 square feet of living, growing vines along two of the four sides of the 5-story parking garage.

With aggressive pricing, efficient geometry, streamlined architecture, and repeatability, the cost per space was drastically reduced.

One World Trade Center (1WTC), the tallest of the buildings planned as part of the Ground Zero reconstruction master plan, will also be the tallest building in the Western Hemisphere upon completion in 2013.

The overall height of the tower to the top of the spire reaches 1776 ft. (541m). 1WTC includes 3.0 million SF of new construction above ground and 500,000 SF of new subterranean levels.

The complex design and construction challenges of 1WTC were met through a relentless collaborative effort between numerous teams resolutely focused on creating an iconic tower reaffirming the preeminence of New York City.

Ben C. Gerwick, Inc. designed a reinforced concrete Floating Barge Gate to close a 150foot navigation channel as part of the $1 Billion Lake Borgne Hurricane Surge Barrier in New Orleans. Significant features include surge resistance to a top elevation of +26 feet, a top deck roadway (when closed), an FRP ballast system, 700 kip vessel impact walls, 2 ksf pressure hull, four 1,200 kip surge anchors, and 400 kip towing bollards. It has an estimated 100-year design life using a marine lightweight concrete mix (110 pcf wet), marine grade stainless steel embeds, and FRP embeds.

Category 3 Award Winner World Trade Center Memorial Pavilion New York, NY Buro Happold Consulting Engineers

Academic Building, John Jay College of Criminal Justice New York, NY Leslie Robertson Associates, Inc.

SkyDance Bridge Oklahoma City, OK SXL

Courtesy of Edward Hueber/Archphoto.

Courtesy of Hans Butzer.

Achieving a unique Snohetta design with limited structural support, constraints on all sides, security requirements, and complex geometry was an unprecedented, but successful challenge.

The World Trade Center Memorial Pavilion will welcome over 5 million visitors annually as they enter the subterranean galleries of the National September 11 Memorial and Museum. The structure is an intricate web of steel and glass showcasing two surviving tridents from the Twin Towers. The true complexity of the project remains hidden to visitors as the building is supported on only 12 points split between the PATH station and Memorial Museum below.

The Expansion Project at the CUNY John Jay College School of Criminal Justice is a 625,000-square foot academic building in Midtown Manhattan. The project consists of a 15-story tower on 11th Avenue and 4-story podium with a garden roof that connects to the College’s existing Haaren Hall on 10th Avenue, effectively consolidating the campus into one city block. The John Jay structural system is distinguished by a grid of rooftop trusses which hang the perimeter of eight of the floors below and create a dramatic column-free cafeteria space on the 5th floor with spectacular views of the Hudson River.

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December 2013

Oklahoma City’s landmark bridge, SkyDance Bridge, is a 380-foot-long pedestrian bridge and 197-foot-tall sculpture that spans I-40 south of downtown. The bridge’s soaring architecture was inspired by Oklahoma’s state bird, the scissortailed flycatcher. The unique geometry, stainless steel “feathers” and design constraints posed many structural engineering challenges. Due to its complexity, the bridge was modeled with two separate programs to verify results.

Planning began when Mayor Cornett announced an international competition to design a pedestrian bridge of “iconic status that reflect the cosmopolitan and vibrant qualities of Oklahoma City and serve as a symbol for the City.”

Category 7 Award Winners

Category 7 Award Winner

UC Berkeley’s Hearst Greek Theatre Berkeley, CA Tipping Mar

Hinman Building Renovation Atlanta, GA Uzun + Case Engineers, LLC

Not 100 yards from the Hayward Fault and built of unreinforced concrete, the Greek Theatre posed extremely serious life-safety dangers in a large seismic event. As a California landmark listed on the National Register of Historic Places, the required seismic retrofit and renovation could not alter its appearance. New strongback columns hidden in the colonnade’s cavities and founded on large concrete footings anchored by deeply drilled piers provided a solution. Reinforcement was installed in existing voids in the columns. A reinforced concrete yoke at the roof tied all the new reinforcement together. Glass-fiber reinforcing polymer was added to the back of the colonnade, strengthening and connecting the wall panels.

The 1939 historic Hinman Research Building was the first engineering research facility at Georgia Tech. A major restoration and adaptive reuse project which transformed the building into a design studio for the Georgia Tech College of Architecture was completed in 2010.

Program requirements for the College of Architecture necessitated the addition of 3,000 square feet of space within the existing building shell while preserving its historic character. These issues were artfully resolved by hanging a thin floor structure from the building’s existing bridge crane beams and addressing vibrations.

McCamish Pavilion Atlanta, GA KSI Structural Engineers

San Diego Main Library Dome San Diego, CA Endrestudio

Courtesy of Bob Hughes, Brilliance Photography.

The McCamish Pavilion project is the renovation of an arena originally constructed in 1956.

The original structure included a 50-foot tall, 270-foot diameter structural steel Schwedler dome over a cast-in-place concrete bowl.

Georgia Tech’s goal for the renovation was to improve the fan experience and bring the facility into compliance with current building codes.

A new octagonal seating bowl for better sight lines, a new upper deck seating area utilizing innovative materials and design and construction techniques, a new concourse addition, and a discrete lateral force resisting system were added to the facility. In addition, numerous miscellaneous repairs to address existing design and construction deficiencies were performed.

Category 8 Award Winner

A 140-foot diameter post-tensioned steelleaved dome serves as the beacon for San Diego’s ten-story, $185 million downtown main library. Conceptual designs of the dome spanned eight years and explored six different circumferential and segmented options. The final scheme resulted in eight intersecting post-tensioned, three dimensional, moonshaped truss elements with a saddle-shaped cable net on each. Adjacent to the dome, the vertical stair tower forms a strong structural core that anchors the two wings of the building. Thrusting outward and upward from this anchor are projecting triangulated arms that catch a few of the dome rib bases. The computer model of the dome enlisted over 6000 “tension only” members and required programs written specifically for post-processing filtering.

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December 2013

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InSIghtS new trends, new techniques and current industry issues

T

he most important concrete property in the ACI 318 Building Code is compressive strength. This reflects the notion of using concrete as a strong material against compressive stress in structural members. Tensile forces are expected to be carried by prestressing or reinforcing steel. These fundamental structural design concepts of putting concrete in compression and steel in tension have largely worked very well.

In recent years, the increasing attention to the need for structural resiliency and environmental sustainability has shed new light on the limitations of concrete material. There are plenty of visual examples of fracture failure of reinforced concrete members during major earthquakes, for example. It is also known that the durability of concrete structures is often compromised by the presence of cracks while exposed to an aggressive environment.

The high carbon and energy footprints of civil infrastructure are closely linked to the need for repeated repairs during its service life.

What if concrete can be made ductile?

A ductile concrete can result in high structural load capacity, even though high structural strength is more commonly associated with high material strength.

For structural members whose capacity is limited by brittle fracture failure of concrete, the governing parameter is tensile ductility, not the compressive strength. As an example, S. Billington at Stanford University conducted a comparative test of a shear panel using a normal concrete of 7,250 psi compressive strength and a ductile concrete of 5,950 psi compressive strength. The ductile concrete panel yielded a higher structural shear capacity of 12,590 lbf compared to 8,540 lbf for the normal concrete panel. This illustrates that structural capacity does not always correlate with material compressive strength. Apart from enhancing load capacity, ductility of concrete also embeds damage tolerance, and therefore resiliency, into structures.

While concrete structural durability is often associated with concrete impermeability, there is evidence that a densely packed concrete does not always translate into structural durability.

As example, P.K. Mehta of UC Berkeley examined the durability of concrete bridge decks and concluded that those built with high strength, densely packed concrete have, in recent years, demonstrated a lower service life than their predecessors using lower strength concrete. The underlying cause of the discrepancy in durability expectations is that the lower permeability

What if Concrete Can Be Made Ductile?

Victor C. Li, Ph.D., FASCE, FASME, FWIF, FACI

Victor Li, Ph.D., FASCE, FASME, FWIF, FACI, is the E. Benjamin Wylie Collegiate Professor at the University of Michigan, Ann Arbor. He may be reached at vcli@umich.edu.

Figure 1: Ductile SHCC under bending.

concrete is measured in the laboratory without load application, whereas the field permeability of concrete structures under load is dominated by the presence of cracks. Hence, material durability (impermeability) does not always translate into structural durability. Instead, a ductile concrete can suppress cracking with wide crack width and lend itself to supporting structural durability.

A ductile concrete, with substantially higher tensile ductility compared to normal concrete, can contribute to higher structural resiliency and environmental sustainability, the latter by virtue of the need for less frequent repairs.

The technology to making concrete ductile, with tensile strain capacity several orders of magnitude higher than normal concrete, has been realized in recent years. This class of concrete, often known as strain-hardening cementitious composites (SHCC), exhibits a tensile stress-strain curve with a shape that resembles that of a ductile metal, while maintaining a compressive strength of that of a normal to high strength concrete. While still expensive, the material has found its way into full-scale structural applications in several countries and especially in Japan. The Japan Society of Civil Engineers has published a design recommendation on SHCC to fill the gap left by standard concrete structural design codes that emphasize mainly the compressive strength of concrete. In the popular press, SHCC has often been called “Bendable Concrete” due to its ability to undergo large

30 December 2013

(a)

(b)

Figure 2: (a) Previous design with super-frame; (b) New design with SHCC coupling beams.

Courtesy of T. Kanda, Kajima Corporation, Japan.

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December 2013

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flexural deformation even without steel reinforcement (Figure 1).

Figure 2 illustrates the change in building design with the introduction of this new SHCC technology, utilized in high-rise construction project in Japan. In the design without SHCC (Figure 2a), the building self-centers under seismic loading by means of two pairs of super-frames that bracket the whole building in two perpendicular directions. Each super-frame is constructed of two huge columns that rise from the building foundation to the top of the building, and connected through dampers at the ends of an enormous sky beam. The 9-footdeep beam is difficult to hoist to the top of the building, requiring fabrication at the building top. In the SHCC design (Figure 2b), the super-frames were eliminated and replaced with four SHCC precast coupling beams to connect the core walls on each floor. The damage tolerant SHCC coupling beams are expected to undergo large shear deformation in a ductile mode with high energy-absorption capability.

In 2005, the Michigan Department of Transportation conducted a demonstration project on a new type of jointless bridge deck. The conventional expansion joint was replaced by a 9 inch thick SHCC link-slab, measuring 16.5 feet x 60.75 feet. The link-slab connects the adjacent normal concrete bridge deck and accommodates temperatureinduced expansion and contraction of the underlying steel girders, acting as an invisible joint. The design requirements called for a tensile strain capacity of 2% in the link-slab material, a value not achievable with standard concrete of any compressive strength.

Other recent use of SHCC includes repair applications, such as the rehabilitation of the Mitaka Dam and the repair of the Hida tunnel lining in Japan.

While the applications in transportation, building, water and energy infrastructures appear widely different, the primary feature of SHCC is its ability to meet tensile deformation and durability demands.

Ductile concrete can serve as a new material technology that contributes to enhancing civil infrastructure resiliency and sustainability. Although current application of the material remains limited, the advantages of ductile concrete will likely broaden its adoption in coming years when a supply chain of this new class of concrete is established globally.▪

EnginEEr’s notEbook

aids for the structural engineer’s toolbox

Development Length More Complexity or Saving Grace?

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

F

or most of us, the provisions for development length and lap splices of reinforcing steel are taken from ACI 318-11, Table 12.2.2. From this, we can surmise that basic development lengths (l d ) follow the form: ld =

( 251 , 201 , 503 , or 403 ) f Ψ√fΨ' λ d y

t

e

b

c

where fy and f 'c represent steel yield and concrete compressive strengths, respectively; d b represents bar diameter; Ψt and Ψe represent bar location and coating factors; and λ accounts for the use of lightweight concrete.

As we examine this relationship and the associated variables, we may find that some simplifications are in order based on rational assumptions. If bars are not epoxy-coated and concrete is normal weight, we can immediately eliminate two variables (Ψe and λ), giving them a default value of 1.0. Furthermore, we can eliminate two of the four fractional coefficients listed (3/50 and 3/40) when we confirm that minimum thresholds of bar spacing and cover are established. As a result, the expression for development length may summarily be reduced to the following: ld =

( 251 , or 201 ) √ff Ψ' y

t

db

c

If we further assume that the material properties ( fy and f 'c ) are constant, the only differentiators become the fraction coefficient (which is basically the size factor) and whether more than 12 inches of fresh concrete is cast below the bar (Ψt ). With this as a basis, the development of standard schedules, details and embedment length versus bar diameter relationships become fairly trivial.

This might even be the basis of standard lap splice length schedules used by your office.

However, the simplicity introduced within this discussion does come with a price – a conservative design.

Perhaps you have been a party to the following scenario, or something akin to it: You get a call from a contractor planning to place a large volume of concrete the next day. Final inspection of rebar placement has occurred and the inspector has found, due to some unknown error, that the lap splices

on a particular size bar in the bottom a mat foundation are short by 6 inches. The contractor is asking for advice. Do you: a) instruct him to cancel his concrete pour until the problem can be fixed? b) allow him to continue as planned, but add more bars (excess reinforcement) at the lap splice that will effectively lap with each of the bars in question? c) tell him that he can proceed if he splices the bars with mechanical couplers? d) allow him to proceed without changes, since your design was conservative?

Certainly any of these options might be pursued, but the first three are not likely to be favored by the contractor and may be injurious to the good working relationship that you have been striving to foster with him for many years. He would be happy with option D initially, but upon further consideration may wonder how much money is being wasted on the project due to your conservative design.

Is there another alternative?

ACI 318 allows for a rational and simple solution. While the provisions of ACI 318 section 12.2.3 are secondary to the aforementioned section 12.2.2, fundamental research led to the development of the following empirical relationship (ACI 318, Equation 12-1): ld =

(

))

3 fy Ψt Ψe Ψs λ db 40 √f 'c c b + K tr db

(

While this equation has considerable similarity to the equations of ACI 318 section 12.2.2, it also includes a distinct difference: the (c b + K tr )/db term offers the potential for explicitly including the benefits of other factors that contribute to development length, specifically bar cover/spacing (c b ) and transverse reinforcement index (K tr ). As such, the results of this calculation offer a less conservative result for development length, but with increased complexity of the calculation itself. For this equation, ACI recognizes that, in virtually all cases, the (c b +K tr )/db value is at least 1.5. Hence, simply substituting this value offers a conservative result that is reflected in the relationships of ACI 318 section 12.2.2. The positive of this is

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December 2013

a simple design; the negative is a conservative design. (As a side note, one wonders if ACI 318 Appendix D might someday offer a similarly simple but conservative approach.

We can only hope!)

Consider our contractor’s dilemma. If the bar in question is an uncoated #6 bottom bar, with a yield strength of 60 ksi in normal weight concrete ( f 'c = 4,000 psi), ACI 318 section 12.2.2 would yield a basic development length (and Class A lap splice length) of 29 inches. Following ACI 318 section 12.2.3, if the bars are spaced at 12-inch on center or greater, and even if there is no transverse reinforcement intersecting the bars in question, the (c b + K tr )/db value becomes 4.5, which must be truncated to the maximum permissible value of 2.5. The basic development length (and Class A lap splice length) then becomes just over 17 inches – a reduction of over 40%. Hence the saving grace for our contractor in trouble, by qualification, becomes option D. The only drawback is that this calculation requires more consideration and engineering input, the likes of which are probably not practical in every case.

Option D may thus be demonstrated and qualified, as shown here, as the best approach; but a little tact may be required to help the contractor understand the lengths you undertook to qualify the situation as it stands.

Furthermore, ACI 318 section 12.2.5 allows for reduction of development length and lap splice in direct proportion to the amount of excess reinforcement provided. Owing to the discreteness of bar sizes, excess reinforcement can usually be quantified such that embedment and lap splicing requirements can be rationally adjusted accordingly.▪ 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, 2005).

It is reprinted with permission.

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Speciality Contractors Hayward Baker Inc. Phone: 800-456-6548 Email: info@HaywardBaker.com Web: www.HaywardBaker.com Product: Retaining Walls Description: Temporary or permanent excavation support and slope stabilization, and remediation of existing walls. Anchors, gabion systems, micropile slide stabilization system, secant or tangent piles, sheet piles, soil mix walls, soil nailing, sculpted shotcrete, and soldier piles and lagging.

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STRUCTURE magazine

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December 2013

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EN

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1993-2013

NCSEA News

News form the National Council of Structural Engineers Associations

Celebrating

COUNCI L

NCSEA to Debut New Webinar Subscription Option NCSEA member engineers attending highly-regarded NCSEA webinars for continuing education now have a new option. Beginning January 1, NCSEA NCSEA Webinar Subscription will offer a Webinar Subscription. For $750, an individual will have access $750 per year for unlimited to all live webinars over the course of one year. Availability of a minimum of NCSEA live webinars ten webinars will be guaranteed, and up to 24 webinars may be offered in the course of a year. The subscription option does not apply to the list of NCSEA recorded webinars, and it is open only to NCSEA members, i.e., members of NCSEA Member Organizations.

Each webinar includes speaker slides, notes, and one free PDH certificate. If others watch the webinar with the subscriber and wish to obtain a certificate, they may purchase a certificate for $30 within one week of completing the webinar. After one week additional certificates will not be available.

NCSEA webinars will be offered voice-over-internet. Voice over telephone can be made available at an additional cost.

To take advantage of this new subscription, NCSEA members can access a webinar subscription form at www.ncsea.com.

The subscription will begin on the 1st of the month in which you enroll.

Barnes, Hamburger Retire from Long-time Committee Chairmanships At the NCSEA Annual Conference in Atlanta, two long-time chairs of NCSEA committees retired from their chairmanships. Craig Barnes and Ron Hamburger were recognized for their support and commitment to NCSEA and their respective committees.

Craig Barnes, a member of SEAMASS, has chaired the Basic Education Committee since its inception in 1999. During that time, the committee worked to determine and promote the core curriculum that should be offered to, and required of, structural engineering students. The committee’s yearly surveys of the engineering curricula of colleges and universities are published in STRUCTURE magazine each year. Brent Perkins, a member of SEAKM, is now the chair of the NCSEA Basic Education Committee.

NCSEA Webinars January 23, 2014 The Performance Basis of ASCE 7-10 Ron Hamburger This webinar will describe the risk basis for ASCE 7-10 and the procedures that can be used to implement performance-based design under the standard. In addition, the basis for the new risk-based seismic maps will be described, and the innovations proposed for ASCE 7-16 will be briefly addressed.

January 28, 2014 Prying Action in the AISC Manual of Steel Construction – Historical Development & Current Usage Dr. William Thornton This webinar will present the development of the current method which, for a given load, results in the least required material, or for a given material configuration, will provide the maximum design strength. More information on the webinars can be found at www.ncsea.com.

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.

STRUCTURE magazine

36

Ron Hamburger, a member of SEAOC, is stepping down as chair of the NCSEA Code Advisory Committee (CAC) after eight years.

As chair, he directed the six separate subcommittees of the CAC, all of which are structured to work with Model Code and Standards issues and activities and the charge of generating and responding to code changes over many code cycles. Tom DiBlasi is now chair of the Code Advisory Committee.

NCSEA thanks Craig and Ron for their committee work on behalf of the association and the structural engineering field.

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Vertical January 18 & 19 Lateral March 8 & 9

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Join other engineers in preparing by taking NCSEA’s Structural Engineering Exam Review Course live online!

Register at www.ncsea.com

December 2013

Course playback available 24/7— study anytime!

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. This two-day Forum will feature top-notch speakers and thought leaders. Sessions include:

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

Steven J. Isaacs, P.E., Associate AIA, is the Division Manager of FMI Corporation with 40 years of experience. He assists firms in overall organization and management, strategic long term planning, financial controls, project performance and profitability, negotiation, ownership transition, joint ventures and partnering.

Jennifer Morrow has more than 20 years of experience working in Alternative Dispute Resolution (ADR). She is the Executive Director of Commercial Services at ADR 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 including complex, multi-party case management.

Baby Boomers Delay Retirements – Career Bottleneck at the Top – Steven Isaacs

Professionals enjoy and count on on their work, salaries, and benefits, and are less willing or able to retire. Determine how your firm can still create visible and achievable pathways to leadership in order to retain and develop high-potential staff.

Ownership Transition Case Studies

How does a firm transition ownership through multiple generations? When do you offer stock and to whom? What is the criteria for ownership? How will it be valued and who will approve the new shareholders? Learn about and participate in discussions by the leaders of three engineering firms that have confronted these issues and more: Robert L. Miller Associates & Sound Structures, Inc. “S” Corporation 1 shareholder, 7 total staff Sole proprietorship in 1984.

Incorporated following asset sale in 2013.

Brian Dekker, President PCS Structural Solutions “C” Corporation 13 shareholders, 40 total staff Incorporated in 1969.

Brian Phair, CEO DCI Engineers “S” Corporation 15 shareholders, 185 total staff Incorporated in 1988.

Mark Aden, President

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

– 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? Learn from this experienced attorney how to structure a solid defense.

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.

Take Your Seat at the Table

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NATIONAL Celebrating

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GINEERS

OCIATI

Discuss and develop new strategies, and learn what other principals are doing and thinking.

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Register at www.ncsea.com

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

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

News from the National Council of Structural Engineers Associations

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

STRUCTU

Thursday

NCSEA News

Winter Leadership Forum

COUNCI L years

1993-2013

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

New Bridges Calendar Available from ASCE Bridges 2014 offers spectacular images of bridges from the United States and around the world. As always, this calendar celebrates the unique blend of technology and art that is the hallmark of great engineering. For 2014, the calendar also celebrates great photography! Every photo in the calendar was selected from entries to ASCE’s first-ever Bridges Photo Contest.

Order calendars and view photos on the ASCE website at: www.asce.org/calendar.

This year’s calendar includes twice as many bridges as in previous years. The technical or historical significance of each bridge is described, and winners of the photo contest are identified.

With exceptional photographic detail, this collection of distinguished bridges celebrates the form, function, and style central to excellence in civil and structural engineering. Bridges 2014 is a full-size wall calendar, with plenty of room to jot down daily activities and appointments.

Photograph by Ekaterina Evdokimova.

Promote Your Business All Year Long!

Print your company name and logo across the full 12-inch width at the bottom of customized Bridges 2014 calendars. Your brand and message will be in front of your clients and colleagues every day. For more information, visit “imprint calendars” on the calendar webpage.

SEI Sustaining Organization Membership Now Available SEI Sustaining Organization Membership is an exciting new opportunity for organizations to demonstrate their commitment to excellence in structural engineering year-round, and support the mission and objectives of SEI. An organization can choose SEI Sustaining Organization Membership at one of two annual membership levels to show its support of SEI, and receive benefits of increasing visibility and exposure in the structural engineering community directly to more than 20,000 SEI members and at SEI conferences, through the SEI website www.asce.org/SEI, SEI Update e-newsletter, and STRUCTURE magazine.

Review the SEI Sustaining Organization Membership Details and Benefits and join now at www.asce.org/ SEI-Sustaining-Org-Membership for 2014, and start receiving benefits for the rest of 2013 FREE. Join by December 31 to take full advantage of 2014 benefits and be included in plans at Structures Congress April 3-5, 2014 in Boston, where SEI Sustaining Organization Members will be recognized for their support of SEI. If you have questions, contact Suzanne Fisher at sfisher@asce.org or 703-295-6195.

SEI Sustaining Organization Members who choose to exhibit at SEI conferences receive preferred booth placement in the Exhibit Hall and increased networking opportunities through recognition in the program guide and exhibit space.

To learn about exhibiting at Structures Congress 2014, contact Sean Scully at sscully@asce.org, 703-295-6154, or visit http://content.asce.org/conferences/structures2014/.

Earn your PDHs/CEUs by December 31, 2013 for your License Renewal and Save 25% On ASCE’s On-Demand Seminars On-Demand Learning is a comprehensive, proven, and convenient way to earn PDHs/CEUs toward your license renewal.

To save 25% on ASCE’s On-Demand Seminars, register at www.asce.org/On-Demand-Learning by December 31, 2013 and use Promo Code STRUC25. Please note that this offer is not valid in combination with any other discounts, nor can it be applied to Course Sets or P.E./F.E. Review Courses.

Attention Undergraduate Student Structures Congress Scholarship Teams And Faculty Advisors Opportunity For Younger Members Participate in the 2014 SEI Student Structural Design Competition

For Members 35 And Younger Applications Due December 13

Innovative projects demonstrating excellence in structural engineering are invited for submission. Awards include an opportunity to present finalist designs at Structures Congress 2014 in Boston, MA, April 3 – 5, 2014, cash prizes, and complimentary registration for Structures Congress (up to three student registrations and one full registration for the faculty advisor). Entries are due January 3, 2014 for design projects completed in 2013.

For more information and to apply, visit the SEI website at www.asce.org/SEI.

SEI is committed to the future of structural engineering and offers a scholarship for Young Professionals (age 35 and under) to attend the Structures Congress, April 3 – 5, 2014 in Boston.

Many young professionals have found Structures Congress to be a career-changing and energizing experience, opening up networking opportunities and expanding horizons to new and emerging trends. Visit the SEI website at www.asce.org/SEI for details and to apply online.

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Boston, Massachusetts, April 3–5, 2014 Make your plans to attend the Structures Congress 2014 in Boston, April 3-5, 2014. More than 1,200 structural engineering professionals are expected to attend.

Earn up to 18.5 professional development hours (PDHs).

Register now for the best rates, early bird registration available until February 12, 2014.

Pre-conference seminars include: • Post-Disaster Safety Evaluations, in Cooperation with California Office of Emergency Services (CALOES) and Applied Technology Council • Design of Sustainable Thermal Breaks

Keynote Address by Boston Luminaries on: • Urban Impacts Beyond Structural Engineering • Our Needs and Challenges of Drawing Young Students into Engineering Careers The full program of technical sessions can be viewed on the Congress website. A full 12 track technical program will be presented on current topics and research in structural engineering. Tracks include the CASE Spring Management Convocation, codes and standards, natural disaster mitigation, structural optimization and monitoring, and emerging trends in bridges.

To learn more and to register, visit the Structures Congress website at www.structurescongress.org.

Get Involved in Your Local SEI Chapter

Structural Columns

Registration Now Open for Structures Congress 2014

Mohawk Hudson Chapter

Nebraska Structural Technical Group The ASCE Nebraska Section’s Structural Technical Group hosted a joint dinner meeting in association with the Structural Engineers Association of Nebraska (SEAON) and the Annual Structural Conference on September 19, 2013. After enjoying some great BBQ, the group of over 40 attendees listened to a presentation by Andrew Johnson, PE, about the SAC Federal Credit Union Headquarters under construction in Papillion, NE. He discussed the architecturally exposed concrete walls, large cantilevered steel trusses, a custom AESS “floating” staircase, and a four-story hardwood glued-laminated façade. The 33rd Annual Structural Conference was held the following day.

The full day conference was well attended with about 225 participants. Two $2,500 fellowships were awarded to University of Nebraska students, Kurt Thomsen and Nicole Jaber, who are pursuing advanced structural engineering degrees.

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

STRUCTURE magazine

Virginia Tech Chapter The SEI Graduate Student Chapter at Virginia Tech (SEI-VT) has been very busy to start off the 2013 academic year, with multiple events already held and more planned for the future.

Three invited speakers have already held seminars for our graduate students, and a fall break trip is planned in conjunction with the undergraduate ASCE chapter.

Join your local SEI Chapter or Structural Technical Groups (STG) to connect with colleagues, take advantage of local opportunities for lifelong learning, and advance structural engineering in your area.

If there is not an SEI Chapter or STG in your area, talk with your ASCE Section/Branch leaders about the simple steps to form an SEI Chapter.

Some of the benefits of forming an SEI Chapter include: • Connect with other SEI local groups through quarterly conference calls and annual conference • Use of SEI Chapter logo branding • SEI Chapter announcements published at www.asce.org/SEI and in SEI Update • One free ASCE webinar (to $299 value) sponsored by the SEI Endowment Fund • Funding for one representative to attend the Annual SEI Local Leadership Conference to learn about new SEI initiatives, share best practices, participate in leadership training, and earn PDHs. • SEI outreach supplies available upon request Visit the SEI website at www.asce.org/SEI for more information on how to connect with your local group or to form a new SEI Chapter.

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December 2013

The Newsletter of the Structural Engineering Institute of ASCE

The Mohawk Hudson Chapter held their Third Annual Structures Day October 16, 2013 in Albany. The program included three presentations, the First Annual Structural Engineering Awards, and the installation of officers for 2013-2014. Attendees are saying “… an outstanding program again this year” and “…the projects were very interesting and educational.”

The Newsletter of the Council of American Structural Engineers

CASE in Point

CASE Toolbox Foundation 4 – Communication Communicate to Match Expectations with Perceptions

Foundation 5 – Education Educate all of the Players in the Process Tool 5-1 (Revised 2013): A Guide to the Practice of Structural Engineering

Tool 4-1: Status Template Report This tool provides an organized plan for keeping your clients informed and happy. This report is intended to be sent to your Client, the Owner and any other stakeholder whom you would like to keep informed about the project status.

Tool 4-2: Project Kick-Off Meeting Agenda Effective communication is one of the keys to successful risk management. Often times we place a significant amount of effort and care into communication with our clients, owners and external stakeholders. With all that effort, it’s easy to take for granted communication with our internal stakeholders — the structural design team. If a project is not started correctly, there is a good chance that the project will not be executed correctly either. Tool 4-2 is designed to help the Structural Engineer communicate the information that is vital to the success of the structural design team and start the project off correctly.

Tool 4-3: Sample Correspondence Guidelines The intent of CASE Tool 4-3 is to make it faster and easier to access correspondence with appropriate verbiage addressing some commonly encountered situations that can increase your risk. The sample correspondence contained within this tool is intended to be sent to the Client, Owner, Sub-consultant, Building Official, Employee, etc., in order to keep them informed about a certain facet of a project or their employment.

Tool 4-4: Phone Conversation Log Poor communication is frequently listed among the top reasons for lawsuits and claims. It is the intent of this tool to make it faster and easier to record and document phone conversations.

Tool 4-5: Project Communication Matrix This tool is to provide an easy to use and efficient way to (1) establish and maintain project-specific communication standards, and (2) document key project-specific deadlines and program/coordination decisions that can be communicated to a client or team member for verification.

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

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

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

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

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

December 2013

CASE held its biannual convocation alongside ACEC’s Fall Conference on Monday, October 28th in Scottsdale, AZ. CASE kicked off the day with a session lead by Sue Yoakum of Donovan Hatem on what are the legal aspects associated with going forward with the use of BIM; what are the risks and liabilities, if any, with the use of BIM; any recent lawsuits relating to the use of BIM and if yes, how to avoid BIM risks. A panel consisting of Brian Stewart (Collins, Collins, Muir + Stewart), Tom Bongi (Caitlin) and Atha Forsberg (Marsh) identified some of the most dangerous exposures facing the design community today and some suggestions on how to work through these problems so that firms do not risk losing it all through bad contracts and poor risk management. Finally, Michael Strogoff (Strogoff

Consulting) talked about recruiting people with appropriate risk management attitudes, screening which projects to pursue, negotiating effective contract terms (even when the contracting party insists that contract terms cannot be changed), managing client expectations, and improving quality control programs.

CASE would like to thank all of its presenters for a great convocation!

CASE’s Spring Convocation will be held April 4, 2014 in conjunction with SEI’s Structures Congress in Boston, MA. Stay tuned to next month’s feature for more information and programming.

Donate to the CASE Scholarship Fund!

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.

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 February 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.

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 STRUCTURE magazine

helps SFC direct the 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.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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CASE is a part of the American Council of Engineering Companies

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,

CASE in Point

Great Turnout, Programming at CASE Convocation

Structural Forum

opinions on topics of current importance to structural engineers

Simplicity

By Robert H. Lyon, P.E.

M

ost of us would agree that simplicity is an admirable characteristic of design. Indeed, simplicity has historically been considered a virtue. This article considers the question of simplicity in structural engineering practice. It concludes by critiquing the advancement of the profession in the area of design specifications.

I distinctly remember two things about my first week as a practicing bridge engineer fresh out of college. The first was the awe I had of an experienced designer’s ability to see simplicity in complicated details. The second was the reaction of a colleague as he watched me perform my first design. I started with a blank sheet of paper, and methodically worked my way through the code equations, until I had enough information to proportion and detail a sign support structure. What my colleague said at that time has stayed with me: always draw your finished product first, and then merely confirm your solution by the code equations. How simple!

More recently, I have been reading about some of the great structural engineers in history – the elegance and simplicity of Gustave Eiffel’s famous tower and less well-known railroad bridges, and Robert Maillart’s ability to justify the design of his deck-stiffened arch on only a page and a half of paper.

Simplicity of design returned to my mind.

I am not the first.

Blaise Pascal said in one of his letters, “I have made this longer than usual because I have not had time to make it shorter.” Antoine de Saint-Exupery said, “A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away.” The grandfather of structural mechanics, Isaac Newton, said, “Truth is ever to be found in the simplicity, and not in the multiplicity and confusion of things.” To prevent any confusion about where he stood on this issue, Newton also said, “Nature is pleased with simplicity. And nature is no dummy.”

Newton was no dummy, either. Another pretty good designer, Leonardo da Vinci, said, “Simplicity is the ultimate sophistication”.

There seems to be a natural tendency that prompts us to find unnecessarily complicated answers to simple problems.

In what direction is our practice heading – towards greater simplicity, or greater complexity? There seems to be a natural tendency that prompts us to find unnecessarily complicated answers to simple problems. As a result, there seems to be a need for greater clarity – greater simplicity – in our profession today.

Perhaps there is a link with the amount of information available to us now, such that we more easily feel overwhelmed and confused.

Since I am a bridge engineer, consider as an example the AASHTO LRFD Specifications.

Twenty-five years ago, the objectives of developing a new bridge specification included being technically state-of-the-art, as comprehensive as possible, yet readable and easy to use.

How did we do? Experienced designers have always lamented the fact that young engineers have the tendency to follow code equations blindly, without having a solid sense of what they represent. Interestingly enough, inexperienced engineers are now recognizing the same thing. Read this excerpt from an online forum (www.eng-tips.com/viewthread. cfm?qid=207593), written by a young engineer giving counsel to another young engineer who was contemplating a switch from building to bridge engineering: “I am pretty young and made the switch from bridge to building in very short time, but here is what I disliked about bridge work. AASHTO LRFD Manual is a beast.

Have you ever seen it? It’s huge. There’s no way possible to get a firm grasp on the equations in the steel section. Each equation has about 10 different variables that need to be determined from other longer, iterative equations. Long story short: you will flip through the whole steel section just to successfully complete one equation.

Basically, as I was once told by someone with the DOT: you better have some good

computer programs if you want to use this code. For a young engineer, I hated being so heavily reliant on computers to do my analysis for a bunch of code equations that it was hard to get a good physical grasp of.”

How sad. I remember being astonished by the speed with which AASHTO adopted the LRFD Specifications. It is certainly true that any change will prompt at least some opposition from experienced designers. I am willing to acknowledge that perhaps I am just a stodgy old designer who does not properly appreciate the comprehensive, state-of-the-art advancements of the new code. But I am sure that we have lost simplicity.

Given that structural engineering is still “the art of molding materials we do not really understand into shapes we cannot really analyze, so as to withstand forces we cannot really assess” (Jon A. Schmidt, “The Definition of Structural Engineering,” January 2009), does it warrant a system complexity that is predicated on establishing mathematically uniform probabilities of failure?

Have we struck the appropriate balance between comprehensiveness and ease of use? I think not. The time is right for a pilot research project to restore a greater degree of simplicity in our design specifications. The goal of the project would be to reduce multiplicity and confusion, to simplify the complicated, and to do the hard work of shortening the specifications such that there is nothing left to take away.▪ Robert H. Lyon, P.E. (blyon@ku.edu), is a Professor of Practice in the Civil, Environmental and Architectural Engineering Department at the University of Kansas and a structural engineer at HNTB in Kansas City, Missouri.

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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