STRUCTURE magazine | April 2014 by structuremag

April 2014 Concrete

A Joint Publication of NCSEA | CASE | SEI

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Features Optimizing Light and Space in the Big City

By J. Benjamin Alper, P.E., S.E., Mohamed Arafa, Ph.D., P.E. and Steven Najarian, P.E., SECB

At eight stories high and comprised of reinforced concrete flat plate construction (concrete slab without beams), the residential building at 653 Tenth Avenue in New York City boasts distinct features that make this building more than the average ‘flat plate’, including a column free corner with cantilevers of up to 20 feet long. Maintaining desired light and site line parameters, and accommodating a nonuniform window pattern, without the use of corner columns on the south side of the building, forced the structural engineers to think outside the box.

The Hadley Overpass Project

April 2014

Columns 7 Editorial Are Special Inspections a Code Provision or Aren’t They? By Andrew Rauch

10 Structural Testing In-Situ Load Testing of Concrete Structures

By Gustavo Tumialan, Ph.D., P.E., Nestore Galati, Ph.D., P.E. and Antonio Nanni, Ph.D., P.E.

14 Structural Economics Right-sizing Under-slab Insulation By Joe Pasma, P.E.

By Matt Yerkey, P.E.

CONTENTS

Route 8 over the little Hoosick River and B&M Railroad (a.k.a. The Hadley Overpass) in North Adams, MA involves replacement and repair of the various super- and substructures that make up the roughly 800-foot-long bridge. A fair number of tasks were specified as delegated design to allow the contractor and construction engineer to develop the best means and methods.

16 Structural Design

The Rise and Demise of Egypt’s Largest Pyramids

20 Structural Rehabilitation

By Peter James

Read how one structural engineer’s efforts at rehabilitation of historic structures in Egypt led to an alternative theory as to how the pyramids were originally constructed.

Departments 9 Noteworthy Thomas Edward Abel In Memoriam

49 Great Acheivements Michel Bakhoum

By Seif El Rashidi

51 InSights AISI BIM Initiative By Joe Cipra

53 Legal Perspectives The Public Duty Doctrine

By Gail S. Kelley, P.E., Esq.

59 Spotlight One World Trade Center

By Dr. Rahimian, P.E., S.E. and Yoram Eilon, P.E.

By Songtao Liao, Ph.D., P.E., Benjamin Pimentel, P.E., Danny Jadeja, P.E. and Sunghwa Han, P.E., S.E.

Prescription for Repair – Part 4

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

25 Structural Failures Design Deficiencies in Edge Barrier Walls in Parking Structures By Mohammad Iqbal, D.Sc., P.E., S.E., Esq.

28 Structural Sustainability

66 Structural Forum Training the Structural Engineer – Part 1 By Stan R. Caldwell, P.E., SECB

In every Issue 8 Advertiser Index 56 Resource Guide (Engineered Wood Products) 60 NCSEA News 62 SEI Structural Columns 64 CASE in Point Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

STRUCTURE magazine

Accommodation to Reinforced Concrete High-Rise Building Deformations and Movements

April 2014

What’s New in LEED v4 for Structural Engineers

By Christine A. Subasic, P.E.

32 Engineer’s Notebook Slender Reinforced Concrete Walls By Jerod G. Johnson, Ph.D, S.E.

46 Construction Issues Pour Strips and Constructability By Mary Bordner Tanck

on the Cover Standing at 1,776 feet (541 m), One WTC is the tallest building in the country. One World Trade Center serves as a national monument as well as a tribute to the “freedoms” emanating from the Declaration of Independence adopted by the United States of America in the year 1776. See Spotlight article on page 59.

Editorial

Are Special Inspections a Code Provision new trends, new techniques and current industry issues or Aren’t They? By Andrew Rauch, CASE Chair

magine for a moment that the building official for one of your projects decided that they were not going to enforce the code provisions for fire protection or the provisions for exiting requirements. How do you think the project architect would react? Or, if the building official decided that a certain structural design provision could be ignored. Would you protest that the safety and welfare of the public was going to be jeopardized? How then is it that this is allowed to happen for special inspection provisions? First, a little background may be helpful. In the 1970s and early 1980s, there were a number of notable structural failures such as Kemper Arena, the Hartford Coliseum, a building in Cocoa Beach Florida, and the Kansas City Hyatt. As a result, the House of Representatives did what every good government body would do; they held hearings into the issue. The report issued as a result of those hearings, House Report 98-621 issued in 1984, identified the absence of the SER on the project site as a significant contributing factor in avoiding future failures. It recommended that provision be made to have the structural engineer of record be present at the project site during the construction of principal structural components. Specifically, the report stated “Professional organizations…should make every effort to ensure that provisions are written into building codes and adopted in the public forum which make the on-site presence of the structural engineer mandatory during the construction of structural components on public facilities.” Although special inspection provisions first appeared in the UBC in 1961, these provisions were not well defined and were largely ignored. After the House Report special inspection provisions were further developed in the national building codes. In 1988, the Uniform Building Code (UBC) was modified to make it the responsibility of project professionals to include special inspection requirements in the contract documents, and added the provision that special inspections could also be provided by the engineer of record as the owner’s agent. With these requirements, design professionals were required to specify that something be done, but were given no tools with which they could assist with enforcement and implementation of those provisions. To assist, several state structural engineering associations developed guidelines to help professionals and building officials specify and enforce those provisions. Fast forward to today. How are things different? At the recent CASE winter meeting, we took a simple poll of those present and asked questions about the special inspection process. The STRUCTURAL ENGINEERING questions addressed were: INSTITUTE • In what states or regions do you practice?

…has this model achieved the original goal of having the structural engineer at the site more often? … does this model improve quality and better serve the public good?

a member benefit

structurE

• Describe the enforcement of special inspections in your area of practice. • Who typically performs these inspections? • How would you characterize the quality of these inspections? Those in attendance well represented engineering practice around the country, with slightly stronger representation from the east and west coasts than from the mid-west and south. Over half responded with spotty enforcement, primarily better in metro areas than rural areas. 15% of the respondents indicated that the provisions were not enforced at all. Often, the structural engineer is construed as being an impediment to the project for either requiring the inspections or insisting that they be done properly. In general, special inspections are being performed by testing agencies who perform the work 85% of the time. The remainder is being provided by certified inspectors or licensed engineers. Over half of the respondents felt that the quality of these inspections were generally poor, with incorrect installation of critical items frequently being missed. Only 20% felt the quality was good, with the remainder responding that quality was average or variable. Generally, the west coast had more consistent enforcement and better quality. There, the work was done by certified inspectors rather than testing agencies. While this is likely not a scientific sampling, it probably is a reasonable representation of the state of affairs. This writer is personally familiar with instances where the special inspector has made errors in their work, including significant ones such as allowing retaining wall reinforcing to be placed over 5 inches out of position and directing the contractor to move the lower layer of top beam reinforcing to the beam mid-depth. If this truly is the current state of affairs, has this model achieved the original goal of having the structural engineer at the site more often? More importantly, does this model improve quality and better serve the public good? I understand the business and risk management implications of engineering firms trying to provide special inspection services. But, as an engineering profession, is this current state the way we want things to be? If we do not think the status quo is acceptable, what are we as individual firms and as a profession going to do about it? Changing current practices will take a consistent message and significant education of building officials, our clients, and building owners.▪

STRUCTURE magazine

Andrew Rauch is a principal with BKBM Engineers in Minneapolis, MN. He is the current chair of the CASE Executive Committee. He can be reached at arauch@bkbm.com.

April 2014

Advertiser index

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American Wood Council, Leesburg, VA

STRUCTURE® magazine, the author’s bio was inadvertently cut off. The bio should have started with – Monique Head, Ph.D., is an Assistant Professor in the Department of Civil Engineering at Morgan State University, Baltimore, MD. The online version of this article has been corrected.

PROJECT ENGINEER / STRUCTURAL GROUP Jenike & Johanson, the world’s leading firm in engineering, consulting, and technology for bulk solids handling, is looking for a civil/ structural engineer (PE or able to obtain) with 5 to 10 years industrial design experience in steel, reinforced concrete, and aluminum structures. As a member of the structural group, the successful candidate will design new silos, perform silo inspections, troubleshoot structural problems with existing silos and design retrofits. The position involves limited travel to meet with clients and conduct inspections. Familiarity with ACI, ASCE, AISC and AWS Codes and Standards expected, as well as basic knowledge of drafting software (AutoCAD and SolidWorks) and structural analysis design software (RISA, Compress, ANSYS, etc.) FEA experience is a plus. Knowledge of bulk solids handling operations including silo structure behavior is desirable but not essential. Candidate must be comfortable dealing with clients and possess excellent communication and report writing skills. We offer a competitive salary commensurate with experience as well as a comprehensive benefit package. Submit resumes to: employment12@jenike.com STRUCTURE magazine

April 2014

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ERRATUM: In the Structural Performance article in the March 2014 issue of

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Interactive Sales Associates

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S-Frame Software, Inc. ............................ 4 Simpson Strong-Tie......................... 15, 27 StrucSoft Solutions, Ltd. ....................... 50 Structural Engineers, Inc. ...................... 30 Structural Technologies ......................... 54 Struware, Inc. ........................................ 17 Subsurface Constructors, Inc. ................ 19 Soc. of Naval Arch. & Marine Eng. ....... 29 USP Structural Connectors ................... 33 Wood Advisory Services, Inc. ................ 56

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NOTEWORTHY

news and information

Thomas Edward Abel Renaissance Engineer NCSEA Board Member Thomas (Tom) Abel, P.E., SECB, President and Engineer at Abel Engineering Inc., of Kalispell, MT, passed away on Saturday, March 1st of heart failure. Tom attended the University of Minnesota where he received his B.A. in Mathematics, then went on to become a teacher. Years later, Tom and his father co-founded a general construction company and, subsequently, a pool and spa company. After nearly twenty years of construction work with his dad, Tom completed a B.S. in Engineering from Montana State University and started Abel Engineering. Tom served on the NCSEA Advocacy and Publications Committees and was elected to the NCSEA Board of Directors in September of 2013. He was also a current director, former President, Vice President and NCSEA Delegate of the Structural Engineers Association of Montana; and he was a former president of the Montana Society of Engineers. Whatever Tom did, he felt compelled to put in the extra

effort and take on leadership roles. At NCSEA’s January Board meeting in San Francisco, Tom volunteered to, as he put it, “honcho” the charge for putting together a publication consisting of general topics for young engineers, asking Board members and other professional engineers to help him write five pages on each of a variety of topics. He had a passion for promoting engineering to students and, for the past ten years, taught an evening class at the local junior college in engineering graphics. His advice was practical, as well as technical. Not long ago, he wrote: Another thing that is difficult to teach in a seminar is how to hang out in your local tavern and have a string of good jokes. Good for getting leads on new jobs too. At our Joint Engineer’s Conference last week, I sat at the motel bar listening to a young engineer talk about his work designing power switching stations. Soon his boss came to the table and we ordered

more Hefeweizens. We eventually got around to what I did for a living. After an hour or so, they looked at each other and then to me and asked if I would be interested in designing 70 foot high H frame structures for hanging power transmission lines… Tom was a leader in other areas as well. He served twice as the Commodore and Vice Commodore of North Flathead Yacht Club, served as Vice President and newsletter editor of the Glacier Street Rod Association, and was a frequent volunteer at the Flathead Lutheran Bible Camp. Tom is survived by his mother, wife Sherry, children, and grandchildren and, being the Renaissance Engineer that he was, will also be sorely missed by his fellow national and state board members and engineers, students, sailors, hot rod enthusiasts, church members, friends, and local tavern acquaintances.

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STRUCTURE magazine

April 2014

Structural teSting issues and advances related to structural testing

hile it is usually possible to demonstrate the safety of an existing structure through calculations based on general accepted engineering principles, this is not always the case. Sometimes there are structures for which calculations alone may not be sufficient to demonstrate fitness for intended occupancy or use. In such situations, in-situ load testing can provide valuable information about the performance of existing structures, and can take advantage of beneficial structural behavior not readily apparent with conventional computational methods. The primary goal of load testing is to demonstrate the safety of a structure. Load tests do not determine the design strength or load-carrying limit. In general, load tests can be used to determine the ability of a structure to support additional loads, to establish the safety of structures with design or construction deficiencies or structures with damage or deterioration, to validate design approaches for and effectiveness of strengthening schemes, to gain knowledge on the behavior of a structure by accounting on the beneficial effects of “hidden” load paths, and to supplement, validate or “tune-up” analytical work aimed at understanding the behavior of a structure. Part 1 of this two-part article discusses the rationale and objectives of in-situ load testing within structural evaluations of concrete structures, and presents methods for load application and instrumentation. Part 2 presents the load test procedures prescribed by the American Concrete Institute (ACI), and describes case studies that illustrate the use of in-situ load testing as a valuable tool in structural investigations.

In-Situ Load Testing of Concrete Structures Part 1: Rationale, Objectives, and Execution By Gustavo Tumialan, Ph.D., P.E., Nestore Galati, Ph.D., P.E. and Antonio Nanni, Ph.D., P.E. Gustavo Tumialan, Ph.D., P.E., is Senior Project Manager at Simpson, Gumpertz & Heger, Inc. Gustavo may be reached at gtumialan@sgh.com. Nestore Galati, Ph.D., P.E., is Senior Design Engineer at Structural Technologies (A Structural Group Inc. Company). Nestore may be reached at ngalati@structuraltec.net. Antonio Nanni, Ph.D., P.E., is Chair of the Department of Civil, Architectural & Environmental Engineering at the University of Miami. Antonio may be reached at nanni@miami.edu.

Load Testing in the Evaluation of a Structure The objectives of any structural evaluation are to establish the existing condition of the structure, identify issues affecting the structural performance, and develop and implement any remedial actions required. Very often, the evaluation of an existing structure requires performing structural analysis to investigate the ability of the structure and components to resist the load demands prescribed by the governing building code. Frequently, the evaluation of existing structures requires a field condition appraisal to determine the condition of the structure. The information collected in the field is used to supplement the structural analysis conducted to establish the adequacy of the structure or components of the structure in question. However, in some situations, the results of the structural analysis may

10 April 2014

Figure 1. Load test of precast concrete planks with drums filled with water.

not be conclusive and a high level of confidence in the results cannot be achieved. In situations like these, in-situ load testing may be required to gain further knowledge about the behavior of the structure to conclusively establish its adequacy. Load test programs can be expensive and, as such, they should only be used when analytical resources have been exhausted and when there is high confidence that the results of the load test can help with answering questions about the structural behavior not evident from other analyses.

The Load Test Program Generally, a load test program involves performing the tasks described below. Definition of Load Test Objectives The engineer should clearly define the load test objectives. The objectives, benefits and risks associated with the load test program should be clear to all the parties involved (i.e. owners and building officials). Load tests typically have the following objectives: • Demonstrate that the structure or structural element can safely resist the design loads with an adequate factor of safety against failure, and • Demonstrate that the service loads do not cause deflections or crack widths that exceed industry standard limits, or preset values established for operation of a given structure. Selection of Test Elements Constraints due to site access, implementation cost, execution time, etc. require that the number of test areas or test elements is limited. Therefore, the portion of the structure or structural elements selected for testing need to be representative of similar areas or elements of the structure so that the load test results can be extrapolated to other areas. The selection process requires an exhaustive review by the engineer of the existing conditions, which may include evaluating parameters such as: • Representative geometry (as-built cross sections and spans, and reinforcement)

• Representative distress (cracking patterns, deterioration, deflections, etc.) • Representative Demand-Capacity ratios Development of the Load Test Protocol The load test protocol includes the loading procedures and the means to evaluate the performance of the structure during the load test and at completion of the load test. The load test protocol has two components that are dependent on each other: the loading procedure and the acceptance criteria. The loading procedure describes how the structure will be loaded: load steps required to reach the ultimate test load magnitude, duration of each load step, loading and unloading requirements, hold period for the test load magnitude, etc. The acceptance criteria describe the parameters to evaluate the performance and acceptability of the structure. These parameters can be qualitative or quantitative. Qualitative parameters are those that can be assessed visually, including formation of new cracks, widening of existing cracks, or other damage caused by the applied loads. Quantitative parameters are those that can be physically measured and can include deflections, strains, angles of slope, and crack widths. The ACI Committees 318 and 437 prescribe two protocols for load testing of concrete structures: Monotonic Load Testing and Cyclic Load Testing. These protocols will be briefly described in Part 2.

Figure 2. Push-down method.

may behave during the load test, and serve as a check to assess if the structure is undergoing excessive distress during the test. For instance, test deflections much larger than the analytical deflections may indicate that the structure is being damaged by the test loads, which may warrant halting the test. The post-load test analyses, performed with a better understanding of the actual behavior of the structure, allow establishing the safety of the structure or determining a lower load rating, in case the acceptance criteria was not met. Preparation of a Safety Plan

The applied test load should replicate the effects of the design load conditions (typically uniform loads). Dead weights such as sand bags, water in containers, or mechanical apparatus such as hydraulic jacks can be used to load structural elements. The selection of the load application method depends on load test objectives, site conditions, time constraints, equipment availability, etc. In general, the use of either dead loads or hydraulic jacks requires the engineer performing a detailed structural analysis to determine the appropriate test load layout and the load test setup to apply those loads. Various types of load application methods used for in-situ load testing are described later.

An important consideration when undertaking a load test is the safety of the personnel involved in the test, and of the building occupants that may be in areas adjacent to the test area. Test loads are typically higher than the service loads on the structure; therefore, there is a possibility of failure of the element or structure during a load test. Structural failure can result in collapse of the tested element which can compromise adjacent structural elements. Also, since test loads create large stresses in the structure, there is a risk for falling hazards such as pieces of concrete spalled from the structure, or for flying hazards such as strained pieces of the test apparatus. Safety measures typically include the installation of shoring towers to prevent collapse of the structure in case of failure. There should be a gap between shoring and the test structure to allow the structure to deflect freely. The gap dimension should be selected based on the expected deflections obtained from the structural analysis. Thus, this gap should not be too large to preclude excessive deformation

Structural Analysis Any load test requires performing structural analysis before and after the load test. The pre-load test analyses are typically done to estimate the test loads and to determine the load layout. These preliminary analyses also provide information on how the structure

STRUCTURE magazine

April 2014

Methods of Load Application and Instrumentation Loading using Water and Dead Weights Dead weights or water can be used to load structural elements. Because of the relatively low specific weight of water, the use of containers (drums or cylinders) or reservoirs (pools) filled with water is typically feasible when the test loads do not exceed 200 psf. Figure 1 shows a load test using drums filled with water. The containers should be free of damage to prevent leakage, and stable when loaded to prevent flooding of the test area if a container breaks or tips over. A typical constraint for the use of water is the need for drainage near the test areas to dispose the water once the load test is completed.

238

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Selection of Load Application Method

in case of failure, nor too small to prevent restraint when the structure deflects during the load test.

Figure 3. Pull-down method.

Figure 4. Closed-loop method.

Disposal of water can be arduous. Pumps and hoses can be used to convey the water to distant drains but the unloading process may significantly slow down. Materials with higher specific weights such as sand, bricks, steel plates, etc. can be used when the test loads are higher. These materials are typically placed in pallets, which facilitates their handling and application in a controlled manner. A constraint for the selection of dead weights is the ability of the test area and adjacent areas to adequately resist the loads caused by the equipment, typically forklifts, used to convey the loading material to the test area. Concentrated loads caused by the front axle of a loaded forklift can be significant and can have detrimental effects on the structure. Loading using Hydraulic Jacks When using hydraulic jacks, an adequate reaction must be provided by the existing structure and/or steel elements specially manufactured for the load test. The elements (new or existing) should have sufficient strength and stiffness to allow application of the test loads without adversely affecting the outcome of the load test. The selection of load application method using hydraulics depends on the test load magnitudes, geometry of the

Figure 5. Strain gauge to measure strain in CFRP laminate and LVDT to measure crack growth.

structure, and field constraints. Common methods are briefly described below. • Push-down test method: One or more hydraulic jacks with extensions or appropriate supports are used to react against the structure above to create downward concentrated forces on the test element (push down). Figure 2 (page 11) shows an overall schematic of this test method. • Pull-down test method: The hydraulic jack applies the loads using a reaction on existing elements below such as columns or beams, or micro piles driven in the soil or dead weights to effectively pull down the test element. Figure 3 shows an overall schematic of this test method. • Closed-loop test method: Using a self-reacting load condition within the test component, this method does not require resistance of external reactions. Figure 4 shows hydraulic jacks applying the load simultaneously to two elements by reacting against an existing beam supporting the test elements.

Measuring Equipment and Data Recording In order to obtain good and reliable results, the instrumentation to monitor the response of the structure during the load test should be carefully selected. When using electronic devices, all the data is typically collected with an automated data acquisition system to monitor the response of the structure during the load test. However, when using dead weights, water or dial gauges, data can also be manually recorded at the completion of each load step. Load cells are typically used to monitor the load applied by hydraulic jacks. Load cells

STRUCTURE magazine

April 2014

come in a variety of shapes, sizes, and capacities. Pressure transducers can also be used to measure fluid pressures in the hydraulic system, which can be calibrated and correlated to applied loads. Dead weights are typically weighed using scales prior to loading. When using water, water meters can be used to measure the amount of water introduced in the containers. During load tests, movement and strains are measured at different sections of interest in the test element. Thus, deflections are commonly measured using linear variable differential transducers (LVDT) or dial gauges. Electrical resistance strain gauges are commonly used to measure strains. Strain gauges are bonded to the surface of the material for which the strain will be measured. Inclinometers are also used to measure the rotation or slope of a test element, which can later be correlated to deflections. LVDT’s placed across cracks can also be used to continuously measure crack growth (Figure 5 ). Optical comparators are also a useful device which is typically used to record cracks after each load step. In general, the accuracy of the measuring devices should be, as a minimum, 5% of the maximum value to be measured. Therefore, the engineer conducting the load test should always make preliminary calculations of the values to be measured in order to determine the appropriate instrumentation. Part 2 of this article, scheduled for an upcoming issue, will disuss how the principles of load testing have been implemented.▪ The authors would like to thank NCSEA and the International Code Council for the use of these graphics, which first appeared in the book, Inspection, Testing, and Monitoring of Buildings and Bridges, Chapter 8. They are reprinted with permission.

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Structural EconomicS cost benefits, value engineering, economic analysis, life cycle costing and more...

common, simplifying assumption used for specifying polystyrene insulation under concrete slabs results in material costs that are significantly higher than necessary. Using a design equation based on a more rigorous analysis of the design conditions can help avoid over-engineering the insulation and save thousands of dollars on the project. Rigid foam insulations, such as expanded polystyrene (EPS), have been used successfully under concrete slabs for more than 40 years. Such insulation helps reduce heat loss to the ground in residences, cold storage units, warehouses and other commercial, institutional and industrial structures. The problem is that designers often do not adequately account for how the concrete slab and underlying subgrade interact. Many designers assume that a concentrated load applied to the slab transfers to the rigid foam subgrade through a triangular load path. This assumption, while not necessarily incorrect, can be very conservative. Concrete slabs distribute loads in a more even fashion, which means that the insulation does not need as high a compressive resistance compared to the typical simplified approach. A more accurate approach to this problem is to use the Modulus of Subgrade Reaction (K) to determine the slab’s deflection and the resultant stress applied to the elastic insulation subgrade. The pressure beneath a given slab under a load can be determined using the following formula, found in the Theory of Plates on Elastic Foundations, as described by Timoshenko and Woinowsky-Krieger: Pressure on the subgrade = (P/8)√(K/D) Where: • P = concentrated load on concrete slab in pounds • K = Subgrade reaction modulus of total EPS insulation in pounds per cubic inch (k/t) • k = Stiffness of one inch of EPS insulation in pounds per square inch • t = EPS insulation thickness in inches • D = Eh3 / 12(1-u2) • E = Modulus of elasticity of concrete in pounds per square inch (57000√ f'c ) • f'c = specified concrete compressive strength in pounds per square inch • h = Thickness of concrete slab in inches • u = Poisson’s ratio for concrete (0.15) An example illustrates the significant difference in the calculated results. Take the case of a warehouse with a 6-inch-thick, 2,500-psi concrete slab on 2 inches of EPS insulation with a rated stiffness of 360 psi for one inch. Forklifts to be used in the building impart 8,000 pounds of force at the wheel, which has a 6-inch by 10-inch tire footprint on the slab. If the designer assumes that this load distributes at a 45-degree angle through the slab, the 8,000 pounds ends up

Right-sizing Under-slab Insulation Applying the Theory of Plates on Elastic Foundations to Save Material Costs By Joe Pasma, P.E.

Joe Pasma, P.E., is the Technical Manager for Insulfoam. He can be reached at joe.pasma@insulfoam.com.

14 April 2014

EPS insulation in an under-slab application. Courtesy of Insulfoam.

distributed over approximately 396 square inches [(6 + 6 + 6)(6 + 10 + 6)] of the insulation’s surface, for an average pressure of 20.2 psi. Taking into account the fact that concrete slabs distribute loads more evenly, using the Modulus of Subgrade Reaction method, the pressure on the insulation is actually much lower – approximately 1.85 psi. Since EPS insulation rated for 1.85 psi costs about 50% less than other rigid foam insulations rated for the much higher value of 20.2 psi, using the more precise method reduces insulation costs substantially. In fact, the 20.2 psi value is beyond the elastic range of the EPS material, and long-term creep effects must be taken into account when using that design approach. With: P = 8000 pounds, h = 6 inches, f'c = 2,500 psi, E = 57,000√ 2,500 = 2,850,000 psi, u = 0.15, k = 360 psi for 1-inch EPS K = 360 psi / 2 inches = 180 pci D = Eh3/12(1-u2) = 2,850,000 (6)3/12(1–(0.15)2) = 52,480,818 lb-in Pressure on EPS = (P/8)√(K/D) = 8000/8 √(180 / 52,480,818) = 1.85 psi. The k value can be found by consulting the insulation manufacturer. One EPS insulation brand available throughout the U.S. has k values ranging from 360 to 1860 psi for one inch of insulation thickness. The specific value depends on the product type selected. Note that increasing the thickness of EPS insulation decreases the overall subgrade modulus. Using the above method to determine the pressure that a slab transfers to the subgrade allows for proper specification of rigid foam insulation and avoids over-engineering the insulation for compressive strength. In the example application discussed in this article, the simplifying assumption of triangular load transfer through a concrete slab results in a compressive force on the insulation 11 times higher than the result from the more rigorous (but not much more complicated) analysis. Specifying higher compressive resistance insulation than necessary not only is overly conservative for the given design, it also does not improve the insulation’s thermal performance, and the cost to the project is excessive and unnecessary. It is a lose-lose scenario.▪

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Structural DeSign design issues for structural engineers

uring their service life, high-rise buildings and the associated nonstructural components endure various movements and deformations. Although the deformations and movements are not life threatening, inappropriate design of buildings and associated nonstructural components could induce expensive economic consequences in the long-run and, in order to ensure proper building behavior of the superstructures and the attached nonstructural elements, should not be ignored. In this article the possible deformations and movements of reinforced concrete high-rise buildings and the accommodation of the affected components are discussed.

Common Deformations and Movements Common, inevitable building movements and deformations include: differential column shortening, lateral story drift, building racking, slab and beam deflection, thermal deformation and building dynamic vibration, etc.

Accommodation to Reinforced Concrete HighRise Building Deformations and Movements By Songtao Liao, Ph.D., P.E., M. ASCE, Benjamin Pimentel, P.E., Danny Jadeja, M.S., P.E. and Sunghwa Han, M.S., P.E., S.E., LEED AP

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

Differential Column Shortening under Gravity Loads

When subjected to gravity loads, vertical reinforced concrete structural members, such as columns and shear walls, experience short-term and long-term shortening that is zero at the base and accumulates to be the maximum at the roof level. Magnitudes are dependent on concrete mix, gravity stress levels, construction sequences, loading histories, volume-to-surface ratios and ambient relative humidity, etc. Short-term column shortening is primarily a result of elastic deformation, while long-term shortening is the resultant of concrete creep and shrinkage. For reinforced concrete high-rise buildings, the long-term column shortening can be as high as 1/8 inch per floor (for a 10-foot story height building), and the cumulative differential column shortening causes floors to tilt. In order to reduce differential column shortening, it is a good practice during the design stage to ensure that the layout of vertical members is balanced so that the vertical members experience gravity-induced axial stresses as equal as possible. For example, in order to minimize the differential shortening between shear walls and columns, it is desirable to locate columns away from shear walls so that more gravity loads will be distributed to shear walls – thus resulting in smaller gravity-induced axial stress differences between columns and shear walls.

16 April 2014

Differential column shortening should be estimated by considering the effects of actual concrete mix, environment, construction sequence, etc. Although accurately evaluating column shortening is a very challenging task due to uncertainties of material parameters, environment, and gravity load redistribution, the method presented in the America Concrete Institute’s Guide for Modeling and Calculating Shrinkage and Creep in Hardened Concrete (ACI 209) can reasonably estimate column shortening if reliable material parameters are given. According to ASCE 7-2010, the load combination for long-term column shortening estimation can be used as D+0.5L, in which D is service dead load and L is service live load. Slab and Beam Deflections Due to Gravity Loads Well-established procedure, including maximum permissible criteria for reinforced concrete slab and beam deflection computation, is specified in ACI 318 (Building Code Requirements for Structural Concrete, 2011). The load combination for short-term effect deflection check is D+L, and for long-term effect is D+0.5L (Minimum Design Loads for Buildings and Other Structures, ASCE-7, 2010). It is also a general practice to use Finite-Element Analysis software to check floor deflections (especially for two-way flat slabs) based on actual reinforcing layout and reasonably assumed material parameters. When one checks floor system deflections, it is necessary to estimate floor slab edge deflections for cladding system installation, especially for large prefabricated concrete/stone panel facade system. For interior partitions, allowance is needed for differential deflection between two adjacent floors after the installation of interior partitions. There have been numerous examples where these joints have not been appropriately installed, particularly on tall slender buildings, which results in “creaking” complained by tenants because of rubbing joints as the buildings move under wind loading. The long-term deflections of girders, which pick up floors above, are particularly important and the deflection acceptance criteria should be more stringent than code-allowed values. Absolute long-term deflection limit values for the girders are recommended to control associated deflection of floors above, instead of satisfying the codeallowable deflection-over-span ratio alone. In many cases, cambers are specified in construction documents to ensure level slabs and minimum slab infill. Since there are many uncertainties in long-term deflection estimation, a camber may be set as one-half of the computed total long-term deflections including the immediate deflections, as building owners and contractors prefer that the cambers are sized to accommodate only immediate deflection and a portion of the

long-term deflection. It is also worth noting that cambers less than ¼ inch tend to be ignored by concrete contractors because the value is within construction tolerance and error range. Building Drift and Associated Racking Due to Lateral Loads

Temperature-induced Deformation Expansion/contraction of building members and facade systems due to temperature variation can induce large internal forces if they are constrained. Brittle façade systems, which are sensitive to thermal movements, tend

Building Dynamic Vibrations There are two main types of dynamic vibration issues in building service life: wind-induced building acceleration and floor vibration. Both may cause resident discomfort depending on tenants’ sensitivity to the motions, and can be reduced to a reasonable limit through wellplanned structural design by adjusting building stiffness, mass and damping (for instance, introducing supplementary damping systems). Although floor vibration usually needs to be checked for light structures such as steel framed floor systems, long span cast-in-place reinforced concrete floor systems could vibrate uncomfortably as well when subjected to gymnastic exercise or mechanical equipments vibration. A simple guideline was suggested to identify potential vibration problem by checking natural frequency of floor systems. However, controlling the floor fundamental frequency alone may result in uneconomic design of long-span reinforced concrete floor systems. To limit the long span reinforced concrete floor vibrations, structural stiffness, mass and damping should all be considered, and floor Finite Element dynamic analysis is recommended with realistic boundary conditions and reasonably assumed damping ratio at the design stage. Peak accelerations and peak torsional velocities at the topmost occupied floor of a high-rise building under wind loading should be checked to avoid excessive resident discomfort. Approximate estimation formula was given in National Building Code of Canada (NBCC); however, in many cases wind tunnel testing companies are hired to estimate the peak accelerations based on wind tunnel test results from scaled building models. In addition to building stiffness, mass distribution, damping and building geometry can be adjusted to reduce the peak accelerations and peak torsional velocities.

STRUCTURE magazine

April 2014

Affected Components and Measures to Accommodate Building Movements Because of inevitable building deformations and movements, the structure itself and the associated nonstructural components must be appropriately designed in order to ensure proper serviceability performance. Floor Elevation Correction Building floor elevation “loss” and floor tilting are expected due to the differential column shortening and should be addressed. During the construction process, the concrete sub-contractor should adjust formworks to the prescribed slab elevations in construction documents to level out the to-be-constructed floor, and compensate for the immediate shortening and a portion of long-term shortening of vertical members. The concrete sub-contractor should monitor floor elevations from a fixed base to make sure that reinforced concrete vertical structural members are shortening in an orderly fashion. In the long run, the magnitude of column shortening for a 10-foot story height residential building can be as high as 1/8 inch per floor, which accumulate to be largest at building’s roof level. Usually, the long-term absolute floor elevation “loss” is ignored as long as appropriate soft joints or connections are provided for other nonstructural components. When the long-term absolute floor elevations must be maintained, it is suggested to specify lumped elevation corrections every several floors. In this case, façade fabrication and installation should also be adjusted accordingly. Façade System Façade systems are inherently sensitive to building movements; therefore, great care and

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Transient lateral loads acting on buildings induce not only horizontal story drifts but also temporary shortening and elongation of vertical members. As a result, transient dynamic racking of the building is to be expected during the service life of buildings. Allowances for building cladding systems and interior partitions should be provided to accommodate the transient story drift and dynamic racking motions under both wind loads and seismic loads. Allowable seismic story drift criteria are given in ASCE 7 and vary with seismic risk category and the seismic force resisting structural system types (ASCE 7-2010). The building seismic design story drift is computed first by using the prescribed seismic design load through elastic analysis, and then adjusted with deflection multiplication factor Cd and seismic importance factor Ie. This nonlinear seismic story drift is compared with the relative seismic glass fallout limit (∆fallout), which is determined with the dynamic test method recommended by the American Architectural Manufacturers Association (AAMA). Different from the seismic story drift requirements, the building story drift ratio limit for wind design is not explicitly specified in building codes and is usually taken as 1/600 ~ 1/400 based on decades of design practice. Depending on the sensitivity of nonstructural elements to building lateral story drift, the lateral design loads for wind story drift check can be chosen as 10-year, 50-year and 100-year return periods respectively. The choice of return period should be governed by local code requirements and design engineer’s judgment. If 10-year return period design loads are used, the story drift ratio limit should be more stringent than the conventional drift criteria when the cladding systems are same. It is a typical design practice that 50-year return period wind design loads are used for story drift check, along with the commonly used inter-story drift ratio limit 1/400 for high-rise buildings.

to experience larger temperature oscillation and expansion joints (soft joints) should be provided. For roof parapets, relief joints are recommended to control the location of cracks because the parapets are usually exposed to weather and experience extreme temperature variation during the building’s service life cycle. In large scale cast-in-place reinforced concrete podium areas or mat foundation slabs, where the concrete floor expansion and contraction are restrained by structural elements such as foundation walls, control strips should be provided for cracking control.

good communication between the structural engineer and the façade designer is needed to avoid unexpected façade damage in the building’s service life (e.g. connection failure, non-uniformities and irregularities of joints, misalignment of faces and panel fallout), especially when the façade system is composed of large prefabricated concrete/stone panels, or includes panels of dissimilar materials. Prior to cladding installation, a new survey should be taken from a fixed base at the ground floor to establish new benchmarks to divide the available soft joints equally between the existing typical floor levels. Additional long-term building deformations and transient movements will continue to occur after the façade installation. Because long-term deformation and deflection are time-dependent, it is important for the designer to be informed as to when and how the façade system will be installed, in order to prescribe recommended joint sizes. To reduce the façade joint size, the installation of the façade system may need to be arranged to a later construction stage so that a larger portion of the long-term deflection and deformation can occur before installation. After installation of the façade system, the soft joint or adjusting device for prefabricated cladding system should accommodate the following items for both vertical and horizontal joints: Vertical joint: • Story drift due to wind design loads (50-year return period) • Thermal expansion/contraction of the façade system between expansion joints Horizontal joint: • Future additional long-term column shortening of exterior columns • Immediate deflection due to live load and long-term deflections due to sustained loads at the exterior edges of floor slabs • Thermal expansion/contraction of the façade system between expansion joints • Elastic column elongation and shortening due to wind design loads (50-year return period) Nominal joint size for a façade system should be equal to (or greater than) the sum of the calculated relative movements and the maximum tolerance permitted for abutting façade elements: Width of joint = total movement + total tolerance When wind loading acts on façades, the panels may tend to bow in (or out) and could touch supporting backup members. Large size glass panels could collide with the adjacent

supporting structures; therefore, enough separation distance should be provided between the façade and the adjacent supporting members as well. Besides interstory drift due to wind design loads, the structural engineer should provide seismic inter-story drifts (with nonlinear effect) for the cladding design engineer to check the glass fallout limit (∆fallout ) which is dependent on glass types and glazing details (AAMA). Vertical Transportation Due to the long-term shortening of vertical structural members and possible thermal movements, special attention is required to ensure proper behavior of the vertical transportation system and associated electrical vertical pipes. For example, elevator guide rails are tied back to the reinforced concrete superstructure and tend to move downward as the long-term shortening builds up over time. Allowance should be provided between elevator guide rails to accommodate the long-term movements (as mentioned before, about 1/8 inch each floor on average). The elevator stop locations may need to be adjusted as the building undergoes long-term creep and shrinkage. Vertical Piping Vertical piping should be supported vertically in between their expansion joints at one level only, and guided laterally at other levels as necessary. Expansion details and clearance above and below the piping to accommodate long-term shortening must be provided: the expansion joint should allow for long-term shortening of 1/8 inch per floor on average. Additional clearance will be required if the piping is located adjacent to the periphery of buildings, where building racking and temperature variation will induce extra movements for the piping. Horizontal pipe branches which are off vertical piping support, and distant from that support, such as sprinkler piping and gas lines, must be allowed to move freely up and down with respect to the adjacent floors. The allowance should be increased accordingly if long-term relative floor deflection will affect the horizontal pipes. Extra sloping of horizontal drain pipelines is required in order to accommodate the future reduction in slope due to differential shortening among building vertical members. Interior Partitions For interior partitions or nonstructural walls, allowance should also be provided for

STRUCTURE magazine

April 2014

differential deflection between two adjacent floors after the installation of interior partitions. If allowance is not large enough to compensate the floor deflection occurring after installation, “creaking” resulting from rubbing partitions will be heard. To make it worse, non-load bearing partitions could inadvertently become load bearing walls causing the partition walls to fail or develop a change of load path. As mentioned earlier, floor deflection is time-dependent so allowance can be relaxed if the installation of partitions is arranged to a later construction stage. Usually, the permissible allowance is generally not less than the clear span between supports divided by 360.

Summary During their service life, reinforced concrete buildings constantly experience deformations and movements. The common deformations and movements in reinforced concrete high-rise buildings include differential column shortening, lateral story drift, building racking, slab and beam deflection, thermal deformation and building dynamic vibration, etc. As long as the inevitable movements and deformation and the effects on associated structural and nonstructural elements are not ignored by engineers, impaired serviceability performance can be avoided by applying precautionary accommodation measures during both design and construction stages.▪

Songtao Liao, Ph.D., P.E., M. ASCE, is an associate at Rosenwasser/Grossman Consulting Engineers, P.C. Steven can be reached at stevenl@rgce.com. Benjamin Pimentel, P.E., is President and CEO of Rosenwasser/Grossman Consulting Engineers, P.C. He currently serves on the Board of Directors for the Structural Engineering Association of New York and the Concrete Industry Board of New York. Benjamin can be reached at bpimentel@rgce.com. Danny Jadeja, M.S., P.E., is a senior associate at Rosenwasser/Grossman Consulting Engineers, P.C. Danny can be reached at danny@rgce.com. Sunghwa Han, M.S., P.E., S.E., LEED AP, is a director of design at Rosenwasser/Grossman Consulting Engineers, P.C. Sunghwa can be reached at Sunghwa@rgce.com.

Structural rehabilitation renovation and restoration of existing structures

Figure 1. Beam soffit repair detail.

s a part of Pennoni Associates’s oncall contract with an existing client, the Philadelphia structural division investigated and developed repair bid documents for an existing, three-level, 1,200space precast concrete parking garage during the last quarter of 2012. Part 1 of this series (September 2013) described the existing structure and summarized observations and material testing results. Part 2 (November 2013) presented an analysis of those findings. Part 3 (January 2014) conveyed conclusions regarding the feasibility of repairing the garage in order to extend its service life. This article discusses the solution of temporarily stabilizing and ultimately replacing the garage. Given the limited remaining service-life, extent of damage to the girders, and lack of adequate and cost-effective long-term repair options, replacing the existing garage with a new parking facility on the same site was recommended. While this assessment was based on a “worst-case” scenario, it was strongly believed that the material testing evidence and observed deterioration warranted such significant action.

Prescription for Repair The Triage, Life Support and Subsequent Euthanasia of an Existing Precast Parking Garage – Part 4 By D. Matthew Stuart, P.E., S.E., F. ASCE, F.SEI, SECB, MgtEng and Ross E. Stuart, P.E., S.E.

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

Temporary Repairs In order to accommodate the time required for the funding, design and construction of a new garage to replace the current facility, the existing

Figure 2. Beam galvanic protection detail.

20 April 2014

garage required some repairs so that it could remain in service. Therefore, the following measures were recommended in order to extend the life of the structure another ten years: 1) Remove approximately two inches of existing concrete at the underside soffit of all level-three cast-in-place, posttensioned girders and precast, prestressed girders, and approximately 25% of the level-two precast, prestressed girders, for the full length of the beams in order to inspect the condition of the tendons and mild reinforcing. If no further repairs were required, replace the removed concrete with high-strength grout, otherwise repair the girder reinforcing as required (Figure 1). These repairs would restore full use of the third level for parking, albeit with limited service life, and were needed to provide an adequate substrate for item #2 below. 2) Install a passive galvanic protection system, such as Galvanode ASZ+ manufactured by Vector Corrosion Technologies, by coating the sides and bottoms of all cast-in-place, posttensioned and precast, prestressed girders with the repair product (Figure 2). A detailed discussion of the protection mechanism and installation of this type of product is available in the manufacturer’s literature. The passive galvanic system should limit the amount of future deterioration of the girders for an additional five years based on the recommendations of the manufacturer. 3) Due to the lengthy anticipated funding, design and construction timeline for a new garage – beyond the extended five-year service life provided by the passive galvanic system – it was also recommended the concrete girders be shored (Figure 3). The purpose of the proposed shoring posts, located at third points of all of the girders

Figure 3. Beam shoring elevation.

did not always align with the parking space striping modules. Because the intent of these recommendations was only to extend the service-life of the garage as much as was necessary to build a new replacement garage, limited non-intrusive repairs would also be required at prioritized locations in order to address only the most severe observed deficiencies. These included: a) Repairing major cracks in double tees, columns and stair/bridge components by routing and filling with an appropriate epoxy injection system to prevent moisture from entering the concrete.

b) Repairing major spalls in double tees, columns and stair/bridge components by saw-cutting around the perimeter of the identified spall or subsurface delamination, demolishing the existing deteriorated concrete within the saw-cut area down to sound material, cleaning and inspecting for cross-sectional loss at embedded reinforcing, and strengthening to replace any significant loss as required. Installing embedded, sacrificial, passive galvanic devices such as Galvashield XP, manufactured by Vector Corrosion Technologies; then patching and BRELSFORD WASHINGTON STATE UNIVERSITY VISITOR CENTER, PULLMAN, WA // PHOTO BY: BENJAMIN BENSCHNEIDER

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in the garage, was to reduce the stresses imposed on the beams due to transient loads, such as those from cars and snow. However, installation of the shoring would not reduce the existing residual dead load stresses, because it was impractical to jack the beams up at each shoring location in order to relieve the existing dead load. Implementing the shoring scenario reduces the imposed stresses on the beams by 25%, such that only 75% of the existing reinforcement needed to be available to resist the super-imposed loads. Therefore, it would be reasonable to allow for a 25% reduction in the amount of required reinforcement, due to corrosion, before the beams are considered to have reached the end of their practical service life. Using the worst-case deteriorated beams as the basis for analysis and a maximum existing loss of reinforcement of no more than 10% – one completely deteriorated strand out of a group of ten – results in a maximum anticipated remaining service-life of ten years. Based on the beams in the best condition – i.e., girders that did not currently exhibit any visually detectable deterioration – a remaining service-life of thirteen years may be expected. These calculations were based on the installation of items #1 and #2 above, as well as the shoring posts. An assumed corrosion rate of 100 µm/year (0.00394 inches/year) for carbon steel exposed to atmospheric conditions served as the basis for this increased service-life analysis. Although the remaining service-life calculations were conservative, it would be reasonable to expect the following scenario for the parking garage structure after the installation of the recommended repairs, galvanic protection system, and shoring: • 0 to 10 years: Ongoing maintenance program required to clean up isolated spall debris and repair isolated areas identified by annual engineering visual condition assessment. • 10 to 15 years: Isolated areas of the third, second and ground floors are progressively closed off as areas become unsafe to use. • 15+ years: Garage is condemned and considered unsafe to occupy . The shores would be located approximately 20 feet away from the supporting columns, and align with the end of the parking stall striping. In this way, the shoring posts would not affect the driving aisles; however, some parking spaces would be lost because the beam locations

finishing the repair area using highstrength cementitious repair materials. c) Perform yearly inspections of the garage for significant deterioration until the new garage is constructed. It should be noted that the recommended repair scheme was based on the only practical available options that would allow for an extension of the remaining service-life of the garage. Permanently shoring a structure is not an ideal solution and is therefore generally not preferred; however, in the case of this garage, it was necessary to maximize the remaining service life in order to provide enough time to construct a replacement garage. A new garage will be required because at the end of the remaining ten years of service-life, additional repairs will not be economical or feasible, and the lack of a parking garage would severely disrupt facility operations. Therefore, it was imperative that a new parking garage be constructed and ready for use no later than 2022. It is anticipated that the time required to complete the recommended repairs, including installation of the passive galvanic system and shoring posts, would be approximately 12 months. This is due to phasing the repair work in order to keep as much of the garage operational as possible. The estimated cost is $2.7 million.

Replacement Garage As part of the project, conceptual structural and parking arrangement drawings for a proposed new five-story, 2,050-space garage were developed (Figure 4 ). In addition to assisting with the determination of the estimated construction cost of about $54 million, these plans were to demonstrate the construction of a new garage was feasible at the proposed site location, which coincided with the location of the existing garage. Although the existing garage was framed using double tees of varying lengths that spanned parallel to the driving aisles, and consequently over a shorter distance than the girders, the proposed new garage was conventionally designed to allow for the double tees to clear span across the driving aisle and parking spaces. This would allow all of the double tees to be fabricated to the same length, with tapered flange edges similar to a pie piece. A more conventional approach to framing the garage avoided the end bearing problems that exist in the original structure. It also allowed the girders to span a much shorter distance and, in most cases, allowed the perimeter spandrels to function more efficiently as load-bearing members, rather than just panels (Figure 5 ).

STAIR TOWER, SEE DRAWING SP–105 FOR ADDITIONAL INFORMATION.

PEDESTRIAN BRIDGE TO MATCH EXISTING CONSTRUCTION

STAIR TOWER, SEE DRAWING SP–105 FOR ADDITIONAL INFORMATION.

STAIR TOWER AND ELEVATOR SEE DRAWING SP–105 FOR ADDITIONAL INFORMATION.

PEDESTRIAN BRIDGE TO MATCH EXISTING CONSTRUCTION

STAIR TOWER, SEE DRAWING SP–105 FOR ADDITIONAL INFORMATION.

12' WIDE x 34" DEEP DOUBLE TEE WITH 4" THICK “PRE-TOPPED” FLANGE (TYP.) 12' WIDE x 34" DEEP DOUBLE TEE WITH 4" THICK “PRE-TOPPED” FLANGE (TYP.)

12' WIDE x 34" DEEP DOUBLE TEE WITH 4" THICK “PRE-TOPPED” FLANGE (TYP.)

STAIR TOWER, SEE DRAWING SP–105 FOR ADDITIONAL INFORMATION.

Figure 4. New parking garage plan.

STRUCTURE magazine

April 2014

Figure 5. New parking garage spandrel detail.

The construction of the new garage was proposed to be accomplished in two phases. In the first phase, approximately 60% of the existing garage would be demolished, including foundations, and replaced to minimize the impact of the loss of parking on the facility. Additional temporary external ramps would be required to maintain access to all levels of the remaining garage during this first phase. In the second phase, the remaining garage and temporary ramps would be demolished and the balance of the new fivestory garage would be constructed, while the first phase of the completed garage would become operational. Since the majority of the new garage would be completed as a part of the first phase, including the internal access ramps, there would be no need for temporary ramps during the second phase. The size of the conceptual garage was determined based on previously completed feasibility studies that indicated a demand of 2,003 parking spaces for the current operations at the existing facility. Constructing the replacement garage in the same area and in a similar configuration as the existing garage made sense since the existing garage was ideally located to minimize walking distances to the adjacent building. In addition, there were limited areas elsewhere on the campus where a new large garage could be practically constructed. Although additional planning and design would be required to determine the actual size and location of the proposed and recommended new replacement garage, the final design of the garage was outside the scope of the initial effort. However, Pennoni was confident that the conceptual drawings were feasible, cost-effective, and an excellent starting point for the planning, design and funding of an actual replacement garage.▪

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any failures occur in concrete structures because of inadequate detailing of reinforcement in joints and connections. The failures of perimeter vehicular barriers in concrete parking structures offer grim examples where numerous parking patrons have died or have suffered bodily injuries as their vehicles plunged down to the street during the past several years. As an example, Figure 1 shows a cast-in-place concrete barrier wall failure and a subsequent car plunge. Here, the edge of the concrete slab serves as the base of wall and the barrier is termed a wall-slab system. The perimeter of parking structures and the edges of split ramps in the interior of parking structures are required to have barriers, restraints or guardrails to stop vehicles inside the structure from plunging down. As a general rule, an effective edge barrier should be able to resist a reasonably foreseeable impact loading during the structure’s lifetime. The model building codes prescribe a certain minimum impact load and require that design professionals use their judgment in determining the anticipated load. For example, the International Building Code (IBC) prescribes 10,000 pounds as a minimum ultimate horizontal impact force which all vehicular barrier systems must withstand. The test results show that concrete wall-slab barrier systems do not meet the IBC’s minimum threshold. Due to the design and detailing deficiencies, the barrier systems have failed prematurely, resulting in bodily injuries and fatalities. This article describes the nature of such deficiencies and offers measures that can be taken to remedy the situation.

Figure 1. Barrier wall failure and car plunges down.

Figure 1 shows a parking structure located in the City of Los Angeles, CA, where a moving vehicle came in contact with the cantilever barrier wall on its fourth floor. As a result, the wall-slab joint failed in brittle mode and the car plunged down to the street. Subsequently, the driver and sole occupant of the vehicle was fatally injured. Such incidents are not uncommon. Figure 1 shows that the barrier wall system failed at the joint between the vertical wall and horizontal slab, without any cracking or other visible damage to the wall as the result of the car impact. Apparently, the cantilever wall rotated about its base and collapsed because the concrete in the wall-slab joint ruptured in a brittle mode. It showed that the wall-slab joint is the weakest link in the barrier system. The issue is whether the barrier system was capable of resisting the code-prescribed 10,000 pound ultimate impact load. The evidence suggests that it does not have the capacity to resist the prescribed load. Rather, its capacity is about onefourth of the prescribed load. As such, the barrier system has a significant design deficiency.

Historical Background

investigating failures, along with their consequences and resolutions

Design Deficiencies in Edge Barrier Walls in Parking Structures

The wall-slab barrier design to resist vehicular impact load was first published in the Handbook of Concrete Engineering (Ed. Mark Fintel) in 1970s. The Handbook provided the design calculations and the rebar detailing for a 6-inch thick concrete cantilever wall to withstand the code-prescribed 10-kip loading (Figure 2, page 26 ). Figure 2 shows that the wall is singly-reinforced, with vertical reinforcement on its inner face only. An upturned rebar hook is used to connect the wall to the supporting slab which has approximately the same thickness as the wall. Apparently, it was assumed in the design that the wall-slab joint would transfer fully the bending moment and shear force from a vehicular impact at the wall to the underlying floor slab. The approach was adopted and embellished in the book: Parking Structures – Planning, Design, Construction, Maintenance & Repairs, (A. P. Chrest, et al.). Further, the ACI’s committee on Design and Construction of Durable Parking Structures (ACI-362) endorsed the barrier system and published it in its design guidelines. In summary, the wall-slab barrier design has been accepted widely, and hundreds of parking structures have been built using the approach and the rebar detailing. It is estimated that approximately one million linear feet of the wall-slab barrier system has been installed in North America. While design professionals have been using the wall-slab barrier system for over 40 years in parking structures, the system has received little

STRUCTURE magazine

Structural FailureS

By Mohammad Iqbal, D.Sc., P.E., S.E., Esq.

Mohammad Iqbal, D.Sc., P.E., S.E., Esq., is a licensed attorney in the state of Illinois. A fellow and life-time member of ASCE, he serves on several ACI and ASCE committees. Dr. Iqbal can be reached at mi@iqbalgroup.us.

18"

42"

1-1/8" cover 10k #4 @ 12"

Figure 2. Wall-slab barrier system.

or no scrutiny as to how the cantilever wall bending moment and shear are transferred to the floor slab. The assumption that the wall shear force and bending moment at the base of the wall are fully transferred to the slab through the joint region appears to have no basis. Apparently, the assumption was made without researching the wall-slab joint test results available. The literature search shows that over the last 70 years numerous experimental studies on behavior of the joint were conducted and the results were published by ACI and the American Society of Civil Engineers (ASCE). The studies have shown that the joint is inherently weak in transferring the bending moment and shear force from one member to the other, and that it should not be relied upon without verifying its efficiency through experimental work.

Joint Efficiency A joint is defined as the region between two connected members. It has been long recognized that joints are the regions where Bernoulli’s hypothesis of a plane cross-section remaining plane after bending is not satisfied due to sudden changes in geometry, bends,

Figure 3. Brittle mode failure of slab-wall type joint under opening moment.

cracking and stress concentration. Joints subjected to bending are divided into two types: opening type and closing type. The joint shown in Figure 2 is called an opening joint, as the bending moment causes flexural tension on the inside face of the joint. Experimental studies have shown that opening joints are seriously deficient with commonly-used rebar detailing. However, with proper detailing, the joint efficiency can be improved. The joint efficiency, ξ, of a two-member assembly can be expressed as: MA ξ= MB MA = Ultimate flexural capacity of the assembly M1 = Ultimate flexural capacity of member 1 M2 = Ultimate flexural capacity of member 2 MB = Lesser of M1 and M2 For a joint to fully transfer the load from one member to the other, its efficiency ξ should be at least 100%. In addition, the joint should show adequate ductility. The unreinforced joints have low efficiency, generally less than 30%. Since such joints fail in a brittle mode, their capacity is not relied upon at all and, therefore, should not be used.

Experimental Studies In 1943, Professor C. J. Posey, University of Iowa, conducted tests on opening joints and reported that the joints failed in a brittle failure at much lower levels than the members they were connecting. Since then, several studies have been published and they invariably reaffirmed that the opening joints with commonly-used details are seriously deficient in strength and fail in brittle mode with low efficiency. Figure 3 shows a photograph of a joint specimen tested by Professor P. K. Singh, Banarus Hindu University, India, in 1997. The specimen failed in a brittle mode at 22% of the design load. As Figure 3 shows, a triangular corner piece ruptured off the joint in a brittle mode. Once the piece broke off, the system lost most of its capacity. The secondary mode of failure observed was the crack formation at the inner joint and then dowels bending backward with little flexural resistance. This is the mode of failure noted in Figure 1 in which the cantilever wall is hanging off the floor with its dowels bending backward. The brittle failure offers little warning and is not allowed in modern reinforced concrete design. To improve the joint efficiency, the concrete in the joint region and the members should be bound or confined with straps, hoops and

STRUCTURE magazine

April 2014

Figure 4. Reinforcement pattern in joint for ξ =94%.

ties. Figure 4 shows a rebar configuration used in a joint assembly in which the efficiency, ξ, improved to 94%. Obviously, such rebar arrangement is not feasible for a 6-inch wall and slab joint such as shown in Figure 2.

Conclusion The incidents such as one shown in Figure 1 have demonstrated that the edge wall, upon impact, fails suddenly and swings open, letting the vehicle plunge down. The root cause of the sudden premature failure is the joint that does not have an adequate mechanism or load path to transfer the cantilever wall moment and shear to its supporting slab. This is a design deficiency. The test results over the last 70 years on such joints have predicted that the joints would fail in a brittle mode and their strength should not be relied upon without proper reinforcement. However, the profession did not heed the warning. To avoid any further loss of life, it is suggested that the wall-slab system should not be used in the parking structures as a vehicular barrier. The main reason for the call is that the slab is too thin to properly install the rebars required to confine the concrete in the joint region. Further, it is recommended that such barriers that are already in place in constructed facilities should be retrofitted. Concrete construction is versatile, as it offers several viable systems that can be used to resist vehicular impact and transfer the load to the structure efficiently. For example, installing a downturn beam or installing an upturned beam instead of the wall can help avoid the deficiency. Further, a singly-reinforced wall is inadequate to distribute the impact load or to resist shear properly. It is suggested to use a wall that is reinforced each way, each face and to justify rationally the impact load flow from the point of application to the underlying structure.▪

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Structural

SuStainability sustainability and preservation as they pertain to structural engineering

he new, fourth version of the U.S. Green Building Council’s Leadership in Energy and Environmental DesignTM Building Design and Construction (BD+C) New Construction and Major Renovations rating system (LEED® v4) contains numerous substantive changes, including a reorganization of the credit categories, a shifting of category point totals, new credits in every category, revisions of existing credits, and a totally revamped materials section. This article provides an overview of changes in LEED v4 most likely of interest to structural engineers. For specific credit information and criteria, and a copy of the LEED v4 rating systems and Reference Guide, readers are referred to the U.S. Green Building Council’s website at www.usgbc.org/leed/v4.

What You Should Know The spirit of a LEED project is that of a collaborative nature, encouraging dialogue between design disciplines, contractors and the owner. Thus, structural engineers are encouraged to become familiar with the whole of LEED, as well as those credits they are most likely to work with directly. While this article is intended primarily for structural engineers, it cannot provide detail on all of the changes in LEED v4. For a look at other changes, particularly in the area of building products, see LEED v4 – New Categories and Credit Shake Up Ways of Contributing, in a 2014 issue of SMART/dynamics of masonry magazine (www.dynamicsofmasonry.com).

What’s New in LEED v4 for Structural Engineers By Christine A. Subasic, P.E., LEED AP

Christine A. Subasic, P.E., LEED AP, is a consulting architectural engineer and owner of C. CALLISTA SUBASIC in Raleigh, NC. She can be reached at CSubasicPE@aol.com.

New Organization LEED v4 boasts 9 distinct categories in which projects can earn points toward certification. A new category, Integrative Process, was added. In addition, the credits related to the building site

1 6 4 16

and location are split into two separate categories in LEED v4, Sustainable Sites (SS) and a new category, Location and Transportation (LT). Those credits related to site development, rain water management, and heat island effect are found in the SS category, and those related to site selection, density, and transit land in the LT category. However, the total number of available points has remained constant at 110 points, and the certification levels remained unchanged. The Figure shows the points allocated to each category with the new categories in green. Structural and civil engineers should pay particular attention to the Materials and Resources, Sustainable Sites, and Location and Transportation categories. The new category, Integrative Process, focuses on achieving “synergies across disciplines and building systems” through collaborative efforts across disciplines. This credit requires preliminary analysis in the areas of energy and water use, including site conditions, massing and orientation of the building, and the building envelope – all areas where the structural engineer can provide valuable input. Location and Transportation Sustainable Sites

Water Efficiency Energy and Atmosphere

Materials and Resources Indoor Environmental Quality Innovation

11 33

28 April 2014

Regional Priority Integrative Process

LEED v4 point distribution by category.

Changes in Sustainable Sites Category Sustainable Sites includes a new credit on Site Assessment whose goal is to encourage early analysis of the site to inform design. Issues such as topography, hydrology, climate and soils are among the issues to be addressed. This category also had numerous smaller changes to existing credits such as renaming the Storm Water Management credit to Rainwater Management, and combining the Heat Island credits for roof and non-roof surfaces into one credit with slightly revised criteria. Sustainable Sites is a category where the civil/structural engineer will want to closely review the new requirements. Comparison of materials and resources credits in LEED v4 versus LEED 2009.

The Energy and Atmosphere (EA) category has a new prerequisite for building-level energy metering and two new credits, one for advanced metering and one for demand response programs. Perhaps the most significant change, though, is that the minimum energy standard is now the 2010 edition of ASHRAE 90.1. The change from the 2007 to the 2010 version represents a nearly 20% savings in overall building energy use according to the U.S. Department of Energy. EA credit 1: Optimizing Energy Performance has been adjusted to reflect the more stringent base standard. Structural engineers involved with wall systems would benefit from understanding these changes.

Changes in Materials and Resources (MR) Category / Building Products

STRUCTURE magazine

April 2014

RCHITECTS LA

RINE ENG MA I

The limit on the contribution of structure and enclosure materials toward meeting the minimum criteria for the Building Product Disclosure and Optimization credits (MR credits 2, 3 and 4) is another important change in LEED v4. Structure and enclosure materials may not contribute toward more than 30% of the value of compliant building products for some options within these credits. This does not mean that such products cannot be used in higher amounts, but only that they are

MR Credit 1, Building Life-Cycle Impact Reduction, incorporates the former Building Reuse and Material Reuse credits and gives more weight (points) to reuse of whole buildings than the previous versions of LEED. Options 1, 2 and 3 focus respectively on reuse of historic buildings, abandoned or blighted buildings, and other building and material reuse, and are worth up to 5 points. Option 4 awards 3 points for new construction that meets whole building life cycle assessment (LCA) criteria that includes a reduction in global warming potential. LCA gives a bigger picture than looking only at single-attribute criteria (i.e. recycled content) and considers the full life of a product, which is a good thing; however, databases for LCA for building products are not robust, nor up-to-date in some cases. continued on next page e rat bo nce a l l e co peri p ex velo de end att rn lea are sh eet m n joi

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You Can’t Meet the Requirements with the Structural Frame Alone

Think More about Building Renovation and Reuse

Structural systems fall under the broad category of building products, and when it comes to building products, LEED has changed dramatically. In LEED v4 the focus has shifted from “green” attributes of products (recycled content, bio-based content, certified wood, and regional sourcing) to product disclosure. In fact, six of 13 available points in the Materials and Resources (MR) category relate to building product disclosure in the form of environmental product declarations (EPD), supply chain reporting, material ingredient reporting and the like. The Table shows the old and new MR credits side by side.

A significant change related to building products is the elimination of the regional materials credit. While LEED 2009 included a credit that awarded points for materials and products that were extracted, harvested and manufactured within a 500 mile radius of the project site, this is no longer a stand-alone credit in LEED v4. According to USGBC responses to public comment during the LEED v4 development process, the former regional materials credit did not necessarily achieve the desired environmental benefits, and so the decision was made to focus on the benefits of supporting the local economy. As a result, regional sourcing now applies to products that are extracted, manufactured and purchased within 100 miles of the project site. This attribute is used only as a multiplier within the Building Product Disclosure and Optimization credits (MR credits 2, 3 and 4).

limited to 30% of the total by cost when doing the calculations.

ETY OF NAV A CI O

Say Goodbye to the 500 Mile Radius

• THE ERS S NE

Changes in Energy and Atmosphere Category

EPD is the New Buzzword MR Credit 2, Building Product Disclosure and Optimization – Environmental Product Declarations, is a new credit in LEED v4. This credit has two options, worth one point each. Option 1: Environmental Product Declaration (EPD) requires use of products with publicly available LCA or EPD. Products are valued differently depending upon the type of declaration, with product-specific Type III EPD having the highest value. Option 2: Multi-attribute Optimization awards one point for selection of third party certified products with environmental impacts below industry average for 50%, by cost, of the total value of permanently installed products in the project. Regional weighting and structure/enclosure limits apply to this option, and the calculation can be somewhat complex. Though development of LCA and EPD requires significant investment from product manufacturers, availability of LCA and EPD for building products continues to grow. Several common structural and enclosure products have, or are working on, LCA and EPD for their products.

Resources LEED v4 puts a focus on product transparency of building products. Understanding the differences between life cycle inventories (LCI), life cycle assessment (LCA), product category rules (PCR), and environmental product declarations (EPD) is vital to navigating the terrain. For those wishing to learn more about the requirements in LEED v4, product disclosure, life cycle assessment and other topics mentioned in this article, the following list provides a starting point for further reading. LEED v4 • LEED v4 rating system and credits – browse by rating system: www.usgbc.org/leed/v4 • LEED v4 User Guide (June 2013), www.usgbc.org/resources/leed-v4-user-guide • White paper: LEED v4 Ushering in the Era of Tansparency and Disclosure by PE International, www.pe-international.com/international/resources/whitepapers/detail/ whitepaper-leed-v4/ Product Disclosures • Cradle to Cradle Certified Product Standard, www.c2ccertified.org/ • GreenScreenTM for Safer Chemicals (“GreenScreen”), www.cleanproduction.org/Greenscreen.v1-2.php • Health Product Declaration, HPD Collaborative, www.hpdcollaborative.org Life Cycle Assessment, Environmental Product Declarations • ASTM International article on environmental product declarations, www.astm.org/sn/features/environmental-product-declarations-nd12.html • U.S. EPA website on life cycle assessment, www.epa.gov/nrmrl/std/lca/lca.html

Do You Know Where That Came From? MR Credit 3, Building Product Disclosure and Optimization – Sourcing of Raw Materials, rewards reporting of raw material sourcing practices. Option 1: Raw Material Source and Extraction Reporting requires use of a specified number of products sourced from manufacturers that have publicly released a report from their raw material suppliers. Like MR Credit 2, products are valued differently depending upon the type of report. Third-party verified corporate sustainability reports are counted at their full value. Self-declared reports are valued at half. Option 2: Leadership Extraction Practices requires use of a minimum dollar value of products that meet criteria for recycled Software and ConSulting

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content, bio-based materials, certified wood and material reuse, similar to the criteria found in LEED 2009. This option also includes extended producer responsibility. Regional weighting and structure/enclosure limits also apply. Do You Know What’s In That? MR Credit 4, Building Product Disclosure and Optimization – Material Ingredients, has three options that require documentation of the raw material ingredients for building products. Several chemical and ingredient screening programs are listed as compliance paths including the GreenScreenTM for Safer Chemicals, Cradle to Cradle certification, and the Health Product Declaration (for more information, see Resources). Option 1 in MR Credit 4, Material Ingredient Reporting, focuses on reporting of material ingredients and requires use of a specific number of products meeting the listed criteria. Option 2, Material Ingredient Optimization, awards points for selection of products meeting material ingredient certification criteria for at least 25%, by cost of the total value of products in the project. Option 3, Product Manufacturer Supply Chain Optimization, requires selection of materials that, among other things, have a third-party verified supply chain. Regional weightings and structure/

STRUCTURE magazine

April 2014

enclosure limits apply to both Options 2 and 3 of MR Credit 4. The First “R” is Reduce New in LEED v4 is Option 2 in MR Credit 5, Construction and Demolition Waste Management. Option 2, Reduction of Total Waste Material, awards 2 points if the project does not generate more than 2.5 lbs of construction waste per suare-foot of the building’s floor area. This recognition of the value of minimizing waste in products and packaging is long overdue. Option 1, Waste Diversion, now includes a requirement that diversion must include three material streams and 50% diversion for 1 point, or four material streams and 75% diversion for 2 points.

Putting it into Action As you evaluate product choices on LEED projects, the new LEED v4 requires a paradigm shift from thinking focused on product attributes to consideration of life cycle, product disclosure and waste avoidance, all in the context of collaboration with other design disciplines and input from the contractor and owner. The structural engineer can be a valuable contributor to this process, particularly if educated on the details of commonly-used structural systems and building products.▪

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

imit states design – also known as ultimate strength design or load and resistance factor design (LRFD) – is largely supplanting the traditional methods of allowable stress design for most structural materials. Perhaps you are seasoned enough to remember the days when working stress design of reinforced concrete was the norm, and limit states design was a fairly new concept. However, for most of us, limit states design has always been the norm, though some remnants of working stress design have endured. For instance, when the deflection of a concrete beam comes into question, we revert to methods drawn from the working stress design theory. Why is this necessary? The answer is simple and grounded in the basic theory of limit states design. When evaluating a “strength” limit state – e.g., flexural design of a reinforced concrete beam – we are considering the ultimate failure state of the member. We know that the likelihood of a sufficiently designed member ever reaching this failure state is extremely small and that, if it does happen, the member will fail “in a certain way” so that its behavior is controlled, manipulated and even predictable; ductile is another descriptor that comes to mind. Calculation of deflections at the ultimate limit state is not pragmatic and probably not realistic, since even the best tools at our disposal cannot reliably predict deflections (strains) that occur in concrete as it is being crushed. More to the point, this is such an extreme condition that it does not reflect a serviceability (deflection) limit state. We are simply satisfied in assuming that concrete begins to crush at a compressive strain of 0.003 and that we can approximate its average stress over the whole of the compression zone as 85% of f 'c. This is why we must revert to working stress methods to check deflections – we are looking to calculate the anticipated deflections under realistic (un-factored) loads that probably do not push the member anywhere near yielding of steel, let alone (if we have designed it correctly) crushing of concrete. The need for both limit states design methods and working stress design methods in reinforced concrete is perhaps most evident if we look at slender walls as addressed by the American Concrete Institute’s ACI 318-11, section 14.8. The slenderness of the element not only exacerbates bending loads due to the P-delta effect, but also potentially causes appreciable out-of-plane deflections. The first part of this section is, in essence, a check to ensure that factored flexural loads (Mu) do not exceed flexural capacities (fMn) as expressed in equation 14-3. The fMn calculation is trivial, but the factored moment (Mu) becomes a little more challenging as it must account for the P-delta

Slender Reinforced Concrete Walls The Merging of Design Philosophies By Jerod G. Johnson, Ph.D, S.E.

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

32 April 2014

effect. Required within this approach is the outof-plane deflection (Δu) at the wall mid-height for the load combination in question. Fortunately, ACI 318-11 prescribes the equations for this, which include several variables for which calculations are relatively straightforward. Consider Δu , the theoretical displacement of the wall at mid-height under the ultimate load (Mu ); note that this is not the displacement considering realistic service loads. Solving equation 14-5 for Δu and equation 14-4 for Mu typically requires at least a few iterations; for example, the first attempt could assume zero deflection. Conveniently, equation 14-6 provides direct calculation of Mu, implicitly accounting for the P-delta effect. Interestingly, this approach uses cracked section properties, a rational (and probably conservative) presumption since we are applying ultimate loads that will likely produce stresses beyond the concrete modulus of rupture. Note that ACI 318-11 section 14.8.3 does not prescribe a maximum limit for this (ultimate) displacement. Moving on, ACI 318-11 section 14.8.4 prescribes a maximum out-of-plane deflection Δs due to service loads of lc /150. The ACI procedure for this calculation accounts for several factors. Chief among them is whether the anticipated rupture (tensile) stress of the concrete has been exceeded. Obviously, if the rupture stress is not surpassed, the wall effectively acts as a homogeneous material and deflections will probably not be excessive. On the other hand, if the rupture stress is surpassed, then the wall cracks, the reinforcement tensile mechanism mobilizes, and cracked section properties (e.g., moment of inertia) become significantly altered such that the out-of-plane deflections become relatively high. Whether the concrete remains uncracked is thus an important serviceability issue – one that we do not even consider when we look at strength design. ACI 318 section 14.8.4 prescribes an ‘iteration of deflections’ approach for determining the balanced condition of applied loads, P-delta effects and out-of-plane deflection. Why this procedure? The answer is simple: out-of-plane deflections are dependent upon moments, and moments are dependent on out-of-plane deflections. In other words, a stable, nontrivial solution to a differential equation comes into the picture. Rather than forcing us to crack open the “Advanced Engineering Mathematics” textbook, ACI 318 allows us to use a numerical procedure (iterative calculations) until we find a solution that converges.

presumes that it has cracked. For this example, the serviceability analysis shows a peak moment of 2.7 kip-ft/ft, while the cracking moment for this wall, based on the modulus of rupture, is 5.06 kip-ft/ft. Hence, the wall does not crack and essentially maintains its gross section properties and relatively high stiffness. Interestingly, the cracked moment of inertia for the strength analysis is only 34.7 in4/ft, whereas the gross moment of inertia is 512 in4/ft. Considering this, coupled to the concept that the procedure for strength design presumes that the wall is cracked, it should not

be surprising to see such a large difference in deflections between the strength design and serviceability design approaches. Closer corollaries in behavior between strength analysis and serviceability analysis can be observed in elements with relatively high loads such as jamb columns, which are more likely to crack under service loads.▪ A similar article was published in the Structural Engineers Association-Utah (SEAU) Monthly Newsletter (January 2013). Content is reprinted with permission.

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Most engineers will be inclined to implement this process using a spreadsheet, although when considering only one load combination, most solutions converge quickly and can be obtained by hand. However, once you start considering multiple load combinations and the ubiquitous trial-and-error design scenarios, automating the process becomes very attractive. Interestingly, a direct solution is available, not unlike the strength design process; but it becomes a challenge if we are on the threshold of cracking, since the equations are dramatically changed between the uncracked and cracked states. Hence, the procedure inherently requires that we consider whether the wall has cracked within each iteration, and we use different equations for peak out-of plane displacement accordingly. Consider an example: An 8-inch thick concrete wall (f 'c = 4,000 psi) spans vertically 24 feet. One curtain of vertical bars is at the center of the wall with #5 @ 12 inches (assume effective depth d = 4 inches). Over a 1-foot wide design segment, unfactored loads include 1.6 kips of dead load and 0.5 kips of snow load, both at an eccentricity of 7 inches with respect to the wall centerline, plus a 30 psf outward wind load. Based on ACI 318-11 load combination 9-4 (1.2D + 1.0W + 0.5S), the wall is satisfactory, with Mu = 4.19 kip-ft/ft < fMn = 6.21 kip-ft/ft. This calculation utilizes the effective area of steel drawn from the compressive axial load, the cracked moment of inertia, and other provisions of ACI 318-11 section 14.8. The calculated ultimate deflection of the wall at mid-height is approximately 4.6 inches. Now consider serviceability and a correlating service load combination from ASCE 7-10 section 2.4: D + 0.6W, where W is taken as the same 30 psf wind load indicated previously. Following the procedure from ACI 318-11 section 14.8, the calculation for deflection appropriately incorporating the P-delta effect requires the iteration of deflections approach unless you are certain that the wall does not crack, in which case a direct solution can be found similar to the strength analysis. It turns out that the deflection is about 0.10 inches, a far cry from the 4.6 inches determined from the earlier strength calculation. Why the major disparity? It stands to reason that the strength analysis and the serviceability analysis should yield different results, but by a factor of nearly 50? What are we missing? The answer is simple and was alluded to earlier: the serviceability analysis considers whether the wall has cracked, whereas the strength analysis

Optimizing Light and Space in the Big city

By J. Benjamin Alper, P.E., S.E., Mohamed Arafa, Ph.D., P.E. and Steven Najarian, P.E., SECB

t eight stories high and comprised of reinforced concrete flat plate construction (concrete slab without beams), the residential building at 653 Tenth Avenue in New York City boasts distinct features that make this building more than the average ‘flat plate’. These include a column free corner with cantilevers of up to 20 feet long and a large amount of exposed reinforced concrete structure, both of which were achieved with a structural slab of no more than 8 inches thick on the interior of the space.

Figure 1. Overall view of the building – South East corner. Courtesy of Eduard Hueber/archphoto.

Column Free Corners Maintaining prime views and ample daylight was extremely important to the architectural design of this building. No less important was maintaining the desired visual impact of the façade, namely, a non-uniform window pattern. Herein lay a conflict for the buildings designers. Maintaining the desired parameters for light and site lines would not permit the introduction of a corner column to the space at the south-east and the south-west corners of the building. Even an architecturally exposed round column or small column would have had drastic impacts on the site lines. Making matters worse, the typical corner window arrangement utilized in this building consists of an L-shaped window, with the long leg of the L measuring approximately fifteen to twenty feet and the shorter leg measuring approximately seven feet. Moreover, the non-uniform window pattern of the façade required that the orientation of the longer window be on alternating sides from floor to floor. As such, the introduction of a column anywhere within twenty feet of the corner in the east-west direction or fifteen feet of the corner in the north-south direction would compromise these views (Figures 1 and 2). Numerous solutions were investigated to avoid the introduction of the corner column. Deep cantilevered beams upset into the exterior wall were considered, but the locations of the HVAC units in the exterior restricted the depth of the cantilevers to sixteen inches – far too shallow of a beam to cantilever up to twenty feet. The use of a much thicker slab without beams was considered as well. However, STRUCTURE magazine

Figure 2. Rendering showing the structural frame of the vierendeel truss. Courtesy of Cannon Design.

the impact on the floor to ceiling heights would have negatively impacted the usage of the space. Even if either of these options had been architecturally feasible, trying to maintain the deflection requirements (considering instantaneous deflection along with long term deflections) would have been extremely difficult. After much review and discussion, the introduction of a Vierendeel truss frame within the exterior envelope was suggested for its

April 2014

Figure 3. Unfolded elevation of the Vierendeel truss.

consistency with the irregularity of the façade and its windows, as well as cost effectiveness in supporting the long cantilever. A Vierendeel truss is a frame that utilizes the bending of vertical members and the horizontal chord members with rigid connections. This is in contrast to a standard truss which relies on axial forces in diagonal members to transfer loads. While a typical truss has minimum bending in its elements, the Vierendeel truss has significant bending. Although this results in a relatively low stiffness, it still remains far stiffer than a simple cantilever without this frame action. A shallow eighteen inch deep beam by sixteen inches wide was introduced around the perimeter. The portion of the span (approximately eight and a half feet) nearest the corner was achieved with a simple cantilever, while the portion of the span (up to about thirteen feet) closest to the column utilized the Vierendeel. The Vierendeel panel had an effective depth of approximately ten feet (the story height), making it extremely stiff and keeping the deflection at the tip to a minimum. In addition, the Vierendeel truss cantilevered in two directions, interlocking at the corner (Figure 3). This results in the entire corner of the building moving together from floor to floor, thereby reducing the differential deflections. Since the floors are all locked together in one system, deflections for live load could be considered utilizing a reduced live load since the system supports a far larger tributary area than just one floor. While using Vierendeel trusses is relatively common, using them in this manner is far more unusual. As such, basic modeling of the system was necessary to verify its feasibility. After initial modeling, it was clear that the use of the Vierendeel truss was feasible and would result in relatively small deflections at the corners. Controlling the deflections in the corner was important not only for the comfort of residents, but also for the initial erection of the façade. Special attention was paid to the concern of long term deflection (primarily creep) by way of additional compression steel added to the frame elements in bending. The Vierendeel frame was reliant on several floors working together. The design of these corners required additional inquiry into the staging and construction sequences of the building. This necessitated specific instructions related to shoring these members, so that the shoring designed by the contractor properly met the design concept. To ensure proper fit up of the façade, minor cambering of the corner of the frame was placed such that the façade installation could start with a frame that began as straight as possible. The construction of a concrete Vierendeel truss was no more difficult than standard concrete construction. The beams/chords and verticals are formed the same as conventional beams or columns. While the construction details of these elements needed to be more descript in several areas (such as development lengths, tie locations, clear covers, joint confinement, etc.), it resulted in minimal extra work for the contractor (Figure 4 ). This resulted in little additional cost due to the introduction of the frame. continued on next page STRUCTURE magazine

Figure 4. The Vierendeel truss under construction. Courtesy of Jesse Cooper, Severud Associates.

Figure 5. Exterior view of the relaxation garden with the building and the architecturally exposed concrete wall in the background. Courtesy of Eduard Hueber/archphoto.

April 2014

Gaining Key Space with Architecturally Exposed Concrete It was imperative that the building footprint be kept as small as possible. Any additional space required for the building footprint would have taken away from key amenities, such as the relaxation garden at the west end of the site (Figure 5, page 35 ). The architect desired the unrefined look of exposed concrete to help create the calming effects of the exterior space. Exterior walls of exposed concrete cast over ship lapped old lumber were used to create visually pleasing elements. To tie the visual into the interior spaces, an exposed concrete finish was selected for the central core areas of the floors. In addition to achieving the specified look, this helped reduce the overall thickness of the walls, thereby optimizing the space. After many meetings, discussions, and trials, a rough finished exposed concrete was selected. By utilizing a rough finish, many of the more costly requirements typically associated with architecturally exposed concrete were eliminated (special forms, ties, etc). This brought the cost of the exposed walls well below that of typical architecturally exposed concrete while still maintaining the desired architectural intent. Where exposed concrete was desired for the exposed underside of the floor slab, similar economy was desired. By simply adjusting the concrete mix with admixtures to make the concrete more flowable, the floor slabs could be cast with standard formwork, but create a rough architecturally exposed concrete with little additional cost.

first glance can pose situations which necessitate creative solutions. The best solutions are often those that reapply commonly used principles in innovative ways. In the case of the residential building at 653 Tenth Avenue, the solutions described herein allowed the architects to maximally achieve their visual intent while providing an economic and functional design solution.▪

Conclusion As engineers, we approach every building with new ideas and a fresh outlook. Even buildings which may appear to be ‘cookie-cutter’ on

J. Benjamin Alper, P.E., S.E., is an Associate at Severud Associates. He can be reached at JAlper@severud.com. Mohamed Arafa, Ph.D., P.E., is an Associate at Severud Associates. He can be reached at MArafa@severud.com. Steven Najarian, P.E., SECB, is a Principal at Severud Associates. He can be reached at SNajarian@severud.com. The author would like to note the contributions of Jesse Cooper, Gustavo Amaris and Cawsie Jijina, P.E., SECB, to this article.

Project Team Structural Engineer: Severud Associates Consulting Engineers Owners: WAF Munich Architects and MEP Engineers: Cannon Design Owner’s Representative: Levien and Company Site/Civil/Geotech: Langan Engineering General Contractor: Dynatec Contracting, Inc.

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April 2014

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The

hadley Overpass prOjecT Taking the “Stress” out of Bridge Repairs

By Matt Yerkey, P.E. Figure 1. Skewed truss span elevation.

oute 8 over the little Hoosick River and B&M Railroad (a.k.a. The Hadley Overpass) in North Adams, MA has been undergoing a major rehabilitation. Ryan-Biggs Associates, P.C. is the structural engineering firm working as the construction engineer for the contractor, J.H. Maxymillian Inc. The approximately $30 million, multi-staged project involves replacement and repair of the various super- and substructures that make up the roughly 800-foot-long bridge, which spans over several parking lots, a river, and a railroad. While much of the work was called out in the contract documents via the owner’s design consultant, a fair number of tasks (structural lifting, substructure shoring, active truss member replacements, etc.) were specified as delegated design to allow the contractor and construction engineer to develop the best means and methods. This article explains some of the means and methods designed by the construction engineer. The bridge, owned by Massachusetts DOT, was constructed circa 1946 and consists of 15 substructures, 11 multi-girder spans, and one signature skewed through truss (Figure 1) spanning 160 feet. The project involved a triple-staged traffic pattern utilizing approximately two-thirds of the bridge width to continue carrying vehicles, while one-third was removed and replaced in stages until the full width of the bridge was replaced. For the multi-girder spans, the deck and existing

girders were replaced. For the truss span, the deck was replaced while the superstructure was repaired and retrofitted. Conventional engineering was required for several facets of the project. The superstructures for spans 7, 8, and 9 were shored with steel moment frames founded on cast-in-place concrete footings (Figure 2). In addition, existing substructures were shored during concrete repairs using towers, and the construction engineer designed utility supports to span unbraced from pier to pier, designed temporary lateral-bracing systems to permit existing truss bottom lateral-bracing retrofits (Figure 3), and developed procedures for the systematic replacement of the existing truss end sway frames. The main trusses were also lifted and shored so that each bearing (520-kip design lifting load) could be removed and replaced. The project also involved some more “fun” (unconventional) engineering tasks with regards to the truss span; in particular, the main truss bottom chord detensioning. The main trusses span 160 feet between bearings and are spaced 45 feet apart, carrying three lanes of traffic, two outboard sidewalks, and a bank of utilities. The two main trusses are interconnected with floor trusses spaced 16 feet on center at each main truss panel point. The main trusses are heavily skewed such that one end of a floor truss is supported at mid-span of one main truss, while the other is at the bearing of the other one (Figure 4 ). The floor trusses span 45 feet between main trusses – or

Figure 2. Span 9 shoring via steel moment frames.

Figure 3. Bottom lateral retrofit shoring.

STRUCTURE magazine

April 2014

Figure 4. Schematic truss span plan.

36 feet, 27 feet, 18 feet, and 9 feet where they span from main truss to the bridge seat at the skewed portions of the superstructure – and are approximately 9 feet 6 inches deep. Analysis was complicated given the large skew of the bridge, as well as the number of load cases and combinations. The construction engineer used RISA-3D software to envelope the forces given the staged deck strips (on or off), temporary concrete barrier locations, live load (far side and/or near side), sidewalk (on or off), under-bridge suspended platform (on or off), wind load (on or off, to the east or to the west), etc. Needless to say, the main truss bottom chord is not a single 160foot long piece from bearing to bearing, but rather is made up of five 32-foot pieces with four splices. The splice plates had experienced a fair amount of deterioration over the years and were noted by the design consultant to be replaced. With nearly 1,000 kips of tension going through the bottom chord at mid-span, it was not just a matter of taking out the splice plates and replacing them. Engineering and construction issues to be addressed included: a) What would hold the truss together without the splice plates? b) What would the force distribution be in the chord after the project if the plates for a given splice were replaced one at a time? The solution was to detension the bottom chord (i.e., bring it to a state of near zero stress) so that the splice plates at a particular panel point could be replaced simultaneously and, once retensioned, share the load equally. Since the panel points in question contained a main truss diagonal, the average chord force was used as the detensioning force. One side of the joint would still have a residual amount of tension, while the other side would have a small amount of induced compression. This was deemed acceptable by the owner and design consultant since all were in agreement that attempting to resolve the main truss diagonal forces to get the bottom chord force to true zero would have been even trickier. The goal of the temporary detensioning component design was to develop a system that could be reused at multiple locations, but was still efficient considering that the bottom chord forces varied from around 600 kips to about 1,000 kips. This was accomplished by designing a single setup for about 340 kips and using multiple setups for the incrementally higher loaded areas of the bottom chord. At the highly loaded panel points, three setups were used (1,020 kips total capacity) on each side, while at the lighter loaded panels points, only two setups were used (680 kips STRUCTURE magazine

Figure 5. Vertical transfer plate as detailed.

Figure 6. Vertical transfer plate as constructed.

April 2014

Figure 7. Transfer plates and channels.

Figure 8. Hydraulic rams and threaded rods.

total capacity). The multi-setup system also proved advantageous for connecting the vertical load transfer plates to the existing main truss bottom chord. The smaller the vertical transfer plates, the easier it was to find symmetric locations on either side of the panel point to install the vertical transfer plate while avoiding the existing bottom chord top and bottom stay plates. In addition, the owner wanted as few new holes in the existing bottom chord as practical for the connection of these temporary components to the existing bottom chord; therefore, existing rivets were removed and replaced with high-strength bolts. All of the existing rivet spacings were field-measured so that the bulk of the components

could be shop-fabricated. The vertical transfer plates served as thrust points against which the hydraulic rams could ultimately pull (Figures 5 and 6, page 39). Upper and lower horizontal transfer channels were installed at each vertical transfer plate, which projected both above and below the bottom chord. The horizontal transfer channels projected both to the inboard and outboard of the existing main truss bottom chord. This would keep the threaded tie rods out away from the panel point, giving the contractor room to remove and replace the splice plates. In addition, the horizontal transfer channels at the first, second, and third setups projected progressively longer

Photo Courtesy of Sacramento International Airport

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3/5/2014 8:41:09 AM

Figure 9. Truss elevation before ram pressurization; red fully tensioned, blue near zero.

Figure 10. Truss elevation after ram pressurization; red fully tensioned, blue near zero.

so that the threaded tie rods could pass by those from the preceding setup. Ultimately, each transfer channel was connected to its sister on the opposite side of the panel point with 2-inch-diameter, 150-ksi threaded rod (Figures 7 and 8). There were four threaded rods per setup: upper outboard, upper inboard, lower outboard, and lower inboard. Four 60-ton hollowcylinder rams “stretched” each of the threaded rods to specific pressures depending on the panel point being worked. Hydraulic manifolds ensured uniform pressure distribution. Tensioning of the rods compressed the bottom chord, thus counteracting the existing axial tension force, and in turn bringing the existing main truss bottom chord to a near zero state of stress at the panel point (see Figures 9 and 10 for before and after ram pressurization). Before, during, and after hydraulic pressure application, various points were benchmarked and monitored for both horizontal and vertical movement using high-tech lasers and, as a low-tech (yet highly effective) back-up, stretched thin piano wire. The existing trusses appeared to be stiffer than the 3D computer model suggested, with all movements and measurements at the lower ends of the anticipated ranges. For best monitoring practices, hydraulic pressure application occurred at about 4:00 am, with the bridge temporarily closed to traffic so that moving live loads would not affect the load transfer or the anticipated measurements. After hydraulic pressurization, the rams were mechanically locked off and the contractor could remove and replace all of the splice STRUCTURE magazine

plates at the panel being worked. Each panel point required about 10,000 pounds of temporary steel to replace about 200 pounds of permanent splice plates. After retensioning the system, the owner had confidence that the splice plates had equal known amounts of stress, which made future analysis of the truss less “stressful.” There are a few more phases of work remaining, but the project is expected to be completed in 2014. With direct communication and a collaborative effort among all team members, the Hadley Overpass project has “overpassed” the expectations of those involved in this interesting bridge rehabilitation.▪

Matt Yerkey, P.E. (myerkey@ryanbiggs.com), is a Principal Associate with Ryan-Biggs Associates, P.C. and works in the corporate office in Clifton Park, NY.

Project Team Construction Engineer: Ryan-Biggs Associates, P.C., Clifton Park, NY Contractor: J.H. Maxymillian Inc., Pittsfield, MA Owner: Massachusetts Department of Transportation Design Consultant: The Louis Berger Group

April 2014

The Rise and demise of

egypT’s LaRgesT pyRamids A Builder’s View by Peter James

y love of Egypt and my first contact with Egyptian construction started in 1994 when I was asked to provide a scheme to strengthen parts of historic Cairo after the devastating earthquake in 1992. This initial contract was to work with the state-owned Arab Contractors to strengthen the Al Ghory Mosque, which had been extensively damaged. It was at that time that I was able to visit the Giza Plateau to see the pyramids. My first view of the Great Pyramid was in the early evening when I got out of my vehicle at a local hotel. I was expecting to see a pyramid, but I was not prepared for the scale and size of the monument that was in deep shadow at that time of the day, almost obliterating half the sky. Like many other visitors, the first question that inevitably came to my mind was: ‘How could people with primitive tools build these fantastic monuments in such a short time?’ At that time, I did not take any professional interest in the construction of the pyramids, but I did feel a great deal of respect for the constructors. Although we have been fascinated with how the ancient Egyptians built these incredible monuments, there is still a lot of discussion and mystery surrounding the actual method. The Step Pyramid of Djoser,

which is 62 meters (203 feet) high, was the first high-rise structure that the ancient Egyptians built; previously, their structures were no more than 10 meters (33 feet) tall. How did the ancient Egyptians manage to construct the Step Pyramid, having never before erected a structure anywhere near that size? My professional interest in the construction of the pyramids was initially sparked by observations that I made during Cintec’s work restoring the ceiling of the burial chamber of the Step Pyramid. We were called in to restore the ceiling, which was collapsing due to the failure of the timber beam that the ancient Egyptians had used to hold the ceiling stones in place (Figure 1). Our unique Waterwall airbags supported the dangerous hanging stones temporarily, and our patented anchors permanently secured them (Figure 2). While in the burial chamber, I noticed that although we were drilling holes that were 4 meters (13 feet) in length, we never actually drilled through stones that were more than 40 centimeters (16 inches) wide. This appeared to be a direct contradiction of the common belief that the enormous stones on the outside were the same all the way through the pyramid. In some cases, the fill was a great deal smaller. It was

Figure 2. Cintec Waterwall airbags supporting ceiling of Step Pyramid. Figure 1. The burial chamber of the Step Pyramid.

STRUCTURE magazine

April 2014

this observation that prompted me to question the accepted theories that attempt to explain how the pyramids were built. Having worked in the construction industry for 54 years, I began to analyze these theories from a practical builder’s perspective. I put myself in the mind of an ancient Egyptian builder faced with limited tools and little experience of large-scale construction. The main problem that I found with the existing theories was that, from a builder’s perspective, they made the process more difficult than it needed to be. Why would the Egyptians haul huge stones from a long distance away unless it was absolutely necessary? The internal core and filling would never be seen, so why fill it with quarried blocks that took time and presumably money to extract and transport to the site? The logistical problems were already enormous – coordinating all the elements from quarrying, transport, scaffolding, design, setting out and manpower requirements. Figure 3. Diagram demonstrating the three layers of the pyramid.

A Progression of Knowledge Cintec has undertaken restoration work in both the Red and Step Pyramids in Egypt, and during this work I have observed the progression of the ancient Egyptians’ knowledge of construction techniques. With every pyramid they built, they became more skilled and corrected previous design defects. One such example is their use of corbelling to create openings in the pyramid for the burial chamber. At the Step Pyramid, the builders attempted to create an opening for the chamber by using large timber beams. However, the timber buckled and failed, causing stones to fall. It was this failure that Cintec was brought in to correct. When the ancient Egyptians moved on to create the burial chamber ceiling in the next two pyramids, the Meidum and Bent Pyramids, they attempted to use a corbelling

technique to overcome the failure of the timber beams. Both of these pyramids have unusual shapes; the Bent Pyramid’s top section sits at a slightly different angle to the main body, giving the structure its ‘bent’ appearance, while the Meidum Pyramid has the appearance of a truncated box sticking out of the ground, rather than the even slopes of the later pyramids. Corbelling stone and masonry is now a well-known technique in construction. However, the ancient Egyptians were newly using it when building the pyramids. Therefore in both the Meidum and Bent Pyramids, the builders exceeded the overhang needed for the corbel arch to support the weight. This resulted in the burial chamber being squeezed together, and it is this mistake which I believe is the

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April 2014

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Figure 4. Stylized diagram of the first stage of construction.

cause of both pyramids’ unusual shapes. The builders rectified it in the construction of the next pyramid, the Red (or North) Pyramid, which is a perfect example of the correct use of corbelling and has a true pyramid shape.

How Were the Pyramids Actually Built?

to conceal. The inner core was used to create internal ramps, which enabled the Egyptians to build the pyramid from the inside out (Figures 4 and 5). The ramps were started at the mid-point of the pyramid and would zigzag across its full internal width, matching the height of the middle-core stones as the pyramid was built. The small number of heavy middle core blocks could have been raised on these internal ramps and positioned at the perimeter of the pyramid. As most of the inner fill stones were much smaller, they could have been easily handled by men and animals. The ramps would get steeper as the pyramid grew in height, but they would not exceed the normal angle used to calculate the external ramp gradient. The ramps could have had small palm tree trunks partly embedded into them as a mechanism to slide the heavier core blocks on wooden sledges. As the pyramid reached the apex, more reliance on scaffolding would have been necessary to top out the structure. The final layer is the outer cladding, which would have been added last and used by the ancient Egyptians to smooth the outer appearance of the pyramid and ensure its ‘true’ pyramid shape using additional stones or tufla grout, like the final icing on a cake. Some people have been skeptical of any theory involving the use of scaffolding, as they argue that the ancient Egyptians would not have had access to enough timber. My method requires only a small amount of scaffolding in order to attach the outer cladding, and the same scaffolding could have been moved around the pyramid as they worked. In recent restoration work on the pyramids, traditional timber lashed together has been used as scaffolding (Figure 6), which demonstrates that it clearly would have been possible to use scaffolding to construct them in the first place.

This progression of knowledge shows that the ancient Egyptian builders were pragmatists, and as such would have always built in the simplest and most efficient way they knew how. As stated earlier, I have found many of the existing theories on how the pyramids were built to be overly complicated and sometimes entirely impractical. I believe that they instead employed much simpler and therefore more viable methods than many current theories propose. It is my opinion that the pyramids were constructed using internal ramps, combined with some additional scaffolding, and not with enormous external ramps, a theory currently favored by many archaeologists. I believe that the pyramids consist of three different layers (Figure 3, page 43). First is the middle core that is visible on every pyramid after the Bent Pyramid. I predict that this layer is only three blocks wide, with the blocks diminishing in size as they near the apex. This layer was used by the Egyptian builders to retain the core filling and would have been a key to connect the outer cladding. The step design of the pyramid meant that the builders were able to connect the cladding to the pyramid while still supporting the weight of the cladding blocks. From my observations of the burial chamber of the Step Pyramid, I believe that the infill and central core of the pyramid primarily consist of much smaller stones, and any other larger blocks that the builders wanted Figure 5. Stylized diagram of the second stage of construction. STRUCTURE magazine

April 2014

Like many other visitors, the first question that inevitably came to my mind was: ‘How could people with primitive tools build these fantastic monuments in such a short time?’ Conclusions I acknowledge that these are only my theories and not facts. However, there is a way to prove my theory of the layers of the pyramid, and I volunteer to carry out this work at no charge to the Egyptian Antiquities. We could diamond drill 100-millimeter (4-inch) core holes into the pyramid at varying heights to a depth of 30 meters (100 feet) and provide a drilling log of all the contents of the bored hole to establish the true nature of the fill. The drilling would be done with the latest dry drilling techniques to prevent damage to the pyramid, and the core would be plugged and filled to match the external appearance. The short period of intensive construction by an ancient civilization who managed to build these wonderful monuments was remarkable. One can only admire the great ingenuity and effort that was required

Figure 6. Scaffolding in use on the Step Pyramid.

by a team of specialist builders, who from the very start showed great ingenuity and the ability to adapt, overcome problems, and learn from their mistakes.▪ Peter James (peterjames@cintec.co.uk), is the Managing Director of Cintec International in Newport, South Wales, United Kingdom. He has worked on projects across the globe, strengthening and restoring historically significant structures from Windsor Castle to the parliament buildings in Canada.

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STRUCTURE magazine

April 2014

ConstruCtion issues discussion of construction issues and techniques

Pour Strips and Constructability By Mary Bordner Tanck

Mary Bordner Tanck is an engineer at Bordner Engineering Services. She currently serves on ACI Committee 347, Formwork for Concrete. Mary can be reached at marybtanck@gmail.com.

n constructing a concrete building with a strip has been poured back does not necessarily large foot print and/or post-tensioning, it is mean backshores can be removed once they have often necessary to have pour strips. A pour been loaded. Another example is if the structure is strip, also known as a closure strip, is a sec- 9 stories and the pour strip is in the same bay for tion of concrete slab left open to control shrinkage all nine levels, the lowest level cannot be removed and elastic shortening; it can also be utilized to until the 9th level is cast and cured. If the construcprovide access for stressing of post-tensioning tion sequence averages one floor per week that tendons. Pour strips are usually left open for 30 puts the stripping operations out a minimum of to 60 days to allow for the initial shrinkage and nine weeks, plus the 30 to 60 days the pour strip elastic shortening, and then filled with concrete is required to remain open. This could mean that after that time to complete slab continuity. While other trades will not be able to access the lower a pour strip is not an inherently difficult obstacle levels for a minimum of 10 extra weeks. to overcome, it often gets pushed aside as the Additionally, if there is any delay on a pour at any different subcontractors and suppliers involved level of backshores, it is possible that a floor above on a project hesitate to take responsibility for it. will be poured before all the pour strips have been If the job is awarded late in the schedule, a lack placed and backshores stripped. The reshoring of planning can paint the reshoring designer into designer needs to carefully consider these types a corner, and adversely affect the construction of situations and communicate closely with the schedule. This article provides the reader with contractor with regards to scheduling, as that is a helpful advice for handling a pour strip from a critical path item. Once a backshore plan has been reshoring designer’s point of view. developed and construction has begun, it is difficult First, it is important to define to add backshoring for additional floors. While it the problem. Often, pour can be done, some backshores are preloaded; it is strips are designed to be fairly difficult to add backshores to take a similar load narrow; approximately 3 feet and to anticipate how the loads will redistribute. to 5 feet wide. This can leave A better option is to widen the pour strip and very large slab cantilevers on balance the backspan so that the large cantilevers either side of the pour strip. If will support their self-weight. This will allow the backspan is not designed to support the canti- the floor to be stripped and reshored without lever, the primary shoring cannot be stripped and, when applied to slabs in multi-story construction, loads from the levels above will accumulate. Thus, the formwork designer and contractor are faced with a backshoring situation. All effected bays will be closed off to other trades until the pour strips are placed and cured. In taller buildings, it is likely that shoring will be so tight in these areas that materials cannot be moved across the floor through these bays. This is a particular problem in urban areas where the building edge may be close to the property line and there is not adequate access around the building perimeter for material movement (Figure 1). Sometimes, in a multi-story building, the pour strip will not extend through every level and may only be present at lower (larger) levels. In these cases, it is tempting to assume that the backshoring will only be required to carry the floors that have a pour strip. There are many situations that would make that assumption incorrect. The backshoring needs to be stripped from the upper-most level and then down to the lowest level. Therefore, just because the lowest level of pour Figure 1. Backspan is not balanced and cantilevers are not self-supporting.

46 April 2014

Figure 2. Backspan is balanced to support cantilevers but no superimposed design live load.

accumulating several floors of dead load. Reshores will extend to slab on grade, as there is no live load capacity in the floors to resist pour loads. Once the formwork under the cantilevers is stripped, then reshores are installed to carry construction loads from upper levels. Having reshores extend to the slab on grade in these areas may limit access in the affected bays, but likely will not close them off entirely. With careful planning, it is often possible for the reshore designer to provide access points through the reshoring to allow other trades to move from one side of the building to another. Please note, if the engineer designs the backspan in this manner, it is imperative to strip the backspan before stripping the cantilevers in order to eliminate the risk of large tip deflections (Figure 2). The best option for the construction schedule is for the contractor to ask the Engineer of Record to widen the pour strip and balance the post-tensioning forces so that there are short cantilever slabs that will support their

Figure 3. Backspan is balanced to support cantilevers plus design live load.

self-weight and some live load. This allows the reshoring designer to design the area as he/she does any other reshored area. Other trades will have full access to the floors below. While it is possible to design these cantilevers to support some superimposed live load, it is often not as much as the typical bays; therefore, the reshoring designer should take extra care to only utilize the slab capacity that is actually there. Again, the backspan should be stripped before stripping the cantilevers (Figure 3). If it is not possible for the pour strip to be widened, then the Engineer of Record has the option of staggering them in different bays at different levels. This is especially effective if the schedule is such that lower floors are poured and have live load capacity to support the cantilever and construction loads from levels above. Using this option, the schedule can often be worked so that the reshores only need to support the loads from one or two poured floors instead of stacking several above each other.

STRUCTURE magazine

April 2014

With a little planning, pour strips need not be a major headache for anyone involved on a project. Once a project is awarded to a general contractor, he/she should sit down with the design team and discuss pour strips. The main questions to ask are: 1) Are the cantilevers on either side of the pour strip self-supporting? 2) If so, will they support any superimposed live load? 3) If not, would the Engineer of Record consider widening the pour strip and balancing the backspan so that the cantilevers will carry their self-weight and, ideally, some superimposed live load? Once these questions have been addressed, the reshoring designer can get involved and construction can commence in an organized fashion without any surprises creeping up on the owner, the contractor, or the other trades as construction progresses.▪

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Michel Bakhoum Pioneer of the Built Infrastructure of Africa’s Most Populous Nation By Seif El Rashidi

Bakhoum and his business partner Ahmed Moharram, a steel specialist, a key place in designing and delivering Egypt’s largest construction projects. Many of them reflect a nation grappling with the crippling demands of a soaring population, burgeoning traﬃc, and limited space. Like all companies, Bakhoum’s, established in 1950, started small. However, he was soon involved in designing the structural elements of a new bridge being constructed across the Nile in Cairo, and it was this that established his reputation as the preeminent concrete engineer in the region. Several larger projects in the Gulf – such as the runways for Kuwait Airport and a major cement factory in Saudi Arabia – made the firm regionally significant and led to its rebranding as Arab Consulting Engineers. Bakhoum’s expertise was essential for a region eager to leap ahead, and for which good infrastructure – especially in the form of bridges, high rises, and large public facilities – was critical. Bakhoum’s knowledge of concrete, coupled with Moharram’s comparable expertise in steel, made them an ideal combination. They first rose to prominence at a time when Middle Eastern countries were redefining their identities as modern nations, for which

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national-scale projects were essential. In Egypt, for example, Cairo’s International Stadium, its International Fair Ground, and the tunnel connecting mainland Egypt to the Sinai under the Suez Canal were all designed by Michel Bakhoum. Moharram-Bakhoum. Despite the scale of his endeavors, former oﬃce members and students remember Bakhoum as somebody who was quiet, hardworking and very competent in his field, and it was this that led to his professional success. He was also an excellent educator, and tens of thousands of engineers are estimated to have been taught by him over the twenty-year period during which he lectured at Cairo University. A former student and later staff member in his oﬃce, Fikry Garas, subsequently became head of Research and Development at Taylor Woodrow, one of Europe’s largest engineering firms. He recalls: “Professor Bakhoum was remarkable as a teacher because, as an international leader in his field, he was up-to-date with all the relevant technological

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A K E E S A F E T Y C O M PA N Y

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hink of Egypt, and three monumental engineering endeavors immediately come to mind: the pyramids – timeless, iconic, pioneering. But arguably more critical to the survival of this nation of almost 90 million people is the infrastructure of its modern capital, Cairo, home to a massive 20% of the country’s population and host to several million commuters daily. Herein lies the legacy of Michel Bakhoum, master of prestressed concrete, born in the small northern Egyptian town of Tahta in 1913; Cairo- and then US-educated; boundary-pusher, practitioner, and educator. Few engineers can claim to have designed structures that form the daily lifeline of a nation as Bakhoum did. To his credit lie the Sixth of October and May 15th flyovers (elevated freeways) in Cairo, literally, the arteries which enable one of world’s densest and most traﬃc-ridden cities to function. In the late 1960s, at the time of the construction of the first phase of the 6th of October flyover, Greater Cairo’s population had doubled from 3 million in the late 1940s, and the need for large-scale infrastructure solutions as a response to changing demographics was urgent. Today, running for over 20 kilometers (12.5 miles), “6th of October” (as its users call it) is the longest flyover in Africa. Thanks to the pyramids, it is unlikely that 6th of October would be voted as Cairo’s most beautiful landmark, but few of its 500,000 daily users would question its importance as the city’s lifeline. As many have experienced, it takes just a small obstruction to the flow of traﬃc to bring the city to a standstill. Bakhoum initially studied at Cairo University’s Faculty of Engineering (then Fouad I University), obtaining a bachelor’s degree in 1936, a master’s degree in 1942, and a doctorate in 1945 – just the second to be granted by that department. He then went on to complete a second PhD at the University of Illinois and further studies at Columbia University. It was his specialization in the use of prestressed concrete, as well as his international involvement in the development of the material, that earned

6 th of October Bridge.

6 th of October Bridge at night.

advancements around the world in a speciality which was then very new, and so brought valuable professional experience into the lecture hall. He was a soft-spoken man who looked you straight in the eye and explained everything in great detail, but did so with clarity and simplicity so that everything became comprehensible. Nonetheless, just to make sure, he would pause to check that everyone had understood what he had said before proceeding.” It is perhaps testament to his skills as a teacher that his own students went on to great things themselves. Apart from Garas,

Bakhoum’s protégés include the current Head of the Department of Structural Engineering at the University of California, San Diego; the former head of Civil Engineering at the University of Urbana Illinois; the former Dean of the Faculty of Engineering at Cairo University; and the former Dean of Cairo University – currently the Governor of Giza, Egypt – to name but a few. Although Michel Bakhoum passed away in 1981, the firm he co-established over 60 years ago still continues to flourish, with Ahmed Moharram still at its head, supported by members of both the Moharram and Bakhoum families, along with a staff ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

STRUCTURE magazine

April 2014

of over 800. The legacy of national projects continues. The Egyptian Ministry of Foreign Affairs Building and Cairo’s newest flyovers are some of the firm’s more recent landmarks, and in the near future, the Grand Egyptian Museum, currently under construction, will be another iconic project under their belt. Further afield, recent projects in places as disparate as Bangladesh, Chad and Mali all owe something to Egypt’s quiet concrete king.▪ Seif El Rashidi is the Coordinator of the Durham World Heritage Site in the United Kingdom. Seif may be reached at seif.el-rashidi@dur.ac.uk.

new trends, new techniques and current industry issues

InSIghtS

AISI BIM Initiative Steel Joists and Deck Summary By Joe Cipra

Sample of LOD 300 provided by specifying professional.

s Building Information Modeling (BIM) continues to progress through the steel design and construction industry, showcasing its many benefits to the building project and its owners, demand for BIM information continues to increase. However, with a wide gamut of methods still being utilized for sharing job information, from the standard 2D contract drawings to 3D model sharing on cloud sites, there was invevitably going to be confusion among those specifying what information they wanted to be incorporated into their BIM and who should be responsible to provide that information. The Steel Joist Institute (SJI) and Steel Deck Institute (SDI) have been working over the past year to address and educate the steel design and construction community on what SJI and SDI member groups are doing to comply with the ever evolving BIM process. Although most member companies are handling this education on their own, both the SJI and the SDI felt that providing standard “BIM Guidance” with regards to their specific products and their manufacturers role in providing information about steel joist and deck products would benefit the industry and alleviate confusion. In August 2013, the Associated General Contractors (AGC) through the BIMForum group attempted to relieve some of this confusion as well. And so, the 2013 Level of Development Specification (LOD) was released. With permission from the American Institute of Architects (AIA), the BIMForum modeled

Sample of LOD 350 provided by joist and/or deck manufacturer.

their framework around the AIA’s Digital Practice documents. The BIMForum group felt it was important to provide a distinction for a model used during construction coordination. The current AIA LOD 300 was geared more toward specification information, with too little information to actually begin trade coordination, and LOD 400, which was a fully designed handover type model which would rarely ocurr until items were already being fabricated, was thus not very valuable to increase trade coordination ahead of construction. The result was an LOD 350, which is unique to the ACG’s LOD document and provided the construction professionals more specific information to enable better coordination. The BIMForum Level of Development Specification provides easy to read tables defining what should be required at various levels for many different structural systems, including floor framing with steel joists and floor deck. With the release of the BIMForum’s 2013 Level of Development Specification in August, the SJI and SDI felt they had a base framework by which to define their respective capabilities and still maintain cohesiveness with industry needs. The SJI and SDI “BIM Guidance”, as it has been titled during the initial working process, is being developed to assist owners, contractors, erectors, fabricators, and specifying professionals with Building Information Modeling guidance regarding the use of steel joists and steel deck through an SJI or SDI member manufacturer. The SJI and SDI have modeled their comments and included

STRUCTURE magazine

April 2014

reference to the AGC’s Level of Development (LOD) Specification document, paying special attention to LOD350 which the SJI and SDI believe is the information they will be expected to incorporate into the models for coordination. The SJI and SDI have also incorporated common items of note that should be considered when using steel joists or steel deck in a 3D model based on current design and manufacturing processes. With draft documents now complete and in review, both the SJI and SDI are working through their respective committees to release the documents in the coming months as position statements added to their respective websites. The SJI and SDI member groups realize that BIM and its requirements will continue to evolve and, therefore, the SJI and SDI must continue to work with groups such as the AGC, AISI, AISC, and the National Institute of Building Sciences to provide input and maintain a cohesive working relationship with the steel construction community. The SJI and SDI also intend to monitor the trends and practices for BIM required of their members being put forth by owners, architects and engineers.▪ Joe Cipra leads the SJI and SDI BIM Task Group and is also involved in AISI BIM efforts as well as the AISC-Technology Integration committee. Joe is currently leading BIM Development within NucorVulcraft’s New Product and Market Development group. Joe can be contacted at joe.cipra@nucor.com.

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discussion of legal issues of interest to structural engineers

LegaL PersPectives

The Public Duty Doctrine: What it Means to an A/E By Gail S. Kelley, P.E., Esq.

ore than one A/E has been in the uncomfortable position of having a structure that he or she designed fail an inspection due to a code-related design defect. The immediate reaction, in printable form, is often “How were the plans approved if they didn’t comply with the building code? That’s negligence on the part of the building department.” While this reaction is understandable, it doesn’t provide much support for the A/E when explaining the situation to the owner. In order for an injured individual (in this case the A/E) to say that another party’s negligence was responsible for the injury, the other party had to owe the individual a duty and the injury had to result from a breach of that duty. For the A/E to hold the plan reviewer responsible for not finding an error, the plan reviewer had to have a duty to find all the errors in every drawing. From a practical standpoint, this is not possible. Within the amount of time allotted to review a set of plans, there is no way the reviewer can flip back and forth between dozens of drawings and make sure everything is coordinated. In most cases, there would be no point. At the time plans are submitted for permits, certain design decisions may not have been made, and some dimensions may have been intentionally left off or approximated. Furthermore, from a legal standpoint, the courts in many states would hold that the plan reviewer does not owe the A/E any duty to find errors in the plans. Plans are reviewed for compliance with the building code for the same reason that building codes are adopted – to ensure the safety and protection of the public at large. Because the duty to find errors in the plans is owed to the general public rather than any particular individual, many states would find the A/E has no basis for a claim. This holding – that a private individual cannot A legal doctrine is a framework that provides guidance on how a ruling should be made in specific circumstances. Often a doctrine develops when a judge, in explaining why he or she decided a case in a particular way, outlines a process that can be applied to similar cases. When enough courts use the process, it becomes the defacto method of deciding these cases.

bring a negligence claim when the duty that was breached is owed to the general public–is known as the “public duty doctrine”.

Sovereign Immunity The public duty doctrine is sometimes referred to as “sovereign immunity” and while the two legal arguments are related, they are not the same. Sovereign immunity (“the King can do no wrong”) dates back to 13th century England. Since the King’s will was the law, if the King did something, it was inherently legal. The King could not be sued in the King’s Court because the Court’s authority was subordinate to the King. This concept was inherited by the newlyindependent American colonies, along with the rest of the English legal system, but was translated to mean that neither the federal nor state governments could be sued unless they expressly agreed to the lawsuit. Cities, counties, and other political subdivisions of the states were granted government immunity, which was essentially the same thing. The rationale was not that the government could do no wrong, but that allowing a lawsuit for breach of a government duty would expose the government to unlimited liability, the costs of which would have to be borne by taxpayers. The immunity was not absolute however. Most, if not all states, distinguish between so-called propriety functions, which were not granted immunity, and governmental or discretionary functions, which were granted immunity. Although the distinctions are a little fuzzy, proprietary functions are generally those that can be performed by a private entity. An example of a proprietary function is the government acting as a landlord by providing public housing. The government is held to the same standard as a private landlord and can be sued if its failure to properly maintain a public housing development causes an injury. In contrast, governmental functions are those that can only be done by the government and are done for the benefit of the general public. Plan review and building inspection are examples of governmental (discretionary) functions. Building officials must typically exercise some degree of discretion in performing their work, i.e., there may be no clear law on whether something is acceptable or how

STRUCTURE magazine

April 2014

something should be done. In addition, the government, in determining how to spend public money, must often exercise discretion in whether, or to what degree, to provide a service. Governmental immunity protects both the government and the government official when a problem arises. The benefit of hindsight might suggest that things should have been done differently; however, it is generally felt that the public interest is not served by such second-guessing.

Tort Claims Acts Under sovereign and governmental immunity, if an individual was injured by the government or a government employee, the only way the individual could get compensation was to persuade the legislature to pass a special law authorizing such compensation. Eventually, this system proved too much of a legislative burden and too susceptible to corruption; starting in the 1940s, the federal government and many of the states passed Tort Claims Acts. While these acts vary from state to state, they generally create exceptions to governmental immunity that allow an individual to bring a negligence (tort) claim in certain situations. The California Tort Claims Acts of 1963 and the New Jersey Tort Claims Act of 1972 are typical of these acts.

Development of the Public Duty Doctrine In contrast to sovereign immunity, the public duty doctrine is an American invention and can be traced back to the 1856 Supreme Court case South v. Maryland (59 U.S. 396). A Mr. Pottle sued the county sheriff (Mr. South) for not arresting a gang of workmen who were essentially holding Pottle hostage because they were owed money. The Court ruled that the sheriff’s duty was to the public, not to Pottle; thus, failure to provide Pottle with police protection did not give him grounds for a lawsuit. Initially, this ruling was only applied in cases where law enforcement personnel were sued for failing to prevent a crime or injury. It was subsequently extended to other emergency personnel such as firemen, ambulance EMTs, and 911 operators who were sued for failing to correctly diagnose or understand the

significance of a problem, or for providing incorrect information. After the Tort Claims Acts were passed, the public duty doctrine became widely used as a defense any time the government was sued because of the allegedly negligent behavior of a government employee.

Application of the Public Duty Doctrine to Construction

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In the context of construction, most claims of government negligence are for negligent inspection, alleging that the inspectors failed to notice a violation. In a Minnesota lawsuit brought against the city for personal injuries and death after a motel fire, the injured parties alleged that the city was negligent in allowing the motel to be remodeled in violation of the city’s building code; Hoffert v. Owatonna Inn Towne Motel, Inc., 293 Minn. 220 (1972). The trial court dismissed the complaint; the dismissal was affirmed by the Minnesota Supreme Court who noted that building codes, permits, and inspections were designed to protect the public and were not meant to be an insurance policy by which the city guaranteed that every building was built in compliance with the building and zoning codes. The court further noted that the fee charged for a building permit was to offset the expenses incurred in promoting the public interest; it was not an insurance premium that made the city liable for defective construction.

Criticism of the Public Duty Doctrine The public duty doctrine has been widely criticized because, to a large extent, it negates the effect of the Tort Claims Acts. While the injured party can bring a claim against the government, it is extremely difficult to prevail on the claim. A number of states, including Arizona, Colorado, Florida, Iowa, Massachusetts, Nebraska, New Hampshire, New Mexico, North Dakota, Ohio, Oregon, Vermont, and Wyoming, have rejected the doctrine and do not allow it to be used as a defense against claims of government negligence. Other states have limited its application. Michigan and North Carolina, for example, have declined to expand the doctrine beyond cases alleging failure to provide police protection from the criminal acts of a third party. In the Michigan Supreme Court’s

view, the fact that a government employee owes general duties to the public does not logically preclude the imposition of a private, individual duty as these duties are not mutually exclusive; Beaudrie v. Henderson, 465 Mich. 124 (2001).

Differences between the States

States that do follow the public duty doctrine have all created exceptions. For an A/E who is concerned that some aspect of a design might not comply with the code, the most important exception is the “special relationship” exception. Under this exception, if the individual has a special relationship with the government official, different from that of the general public, the government will have a duty to the individual. Most building departments will allow an A/E to schedule an interview to review a detail before the plans are submitted for permits. When a detail has been explicitly approved by the building department, it will be hard for an inspector to insist that it does not meet code. Legally, a special relationship would have been created by the direct contact between the building official and the A/E, the explicit assurance of compliance, and the detrimental reliance by the A/E on the assurance.

Conclusion Even in those states that don’t follow the public duty doctrine, it is unlikely that the building department would be held liable for the extra costs that are sure to arise when a design error is not found until construction. An A/E who is concerned about some aspect of a design should schedule an appointment with the building department to review the detail in question. To avoid misunderstandings, the A/E should circulate an email summarizing his or her understanding of the meeting to those in attendance, and ask for any corrections. If there are no corrections, a second email can state that the A/E is proceeding with the detail as discussed. However, the A/E should realize that the approval will generally just be for the detail that was discussed; if there are any changes, the detail will probably need to be re-approved.▪ Gail S. Kelley, P.E., Esq., is a LEED Accredited Professional as well as a licensed attorney in Maryland and the District of Columbia. She is the author of Construction Law: An Introduction for Engineers, Architect, and Contractors, published in 2012 by John Wiley & Sons. Ms. Kelley can be reached at Gail.Kelley.Esq@gmail.com.

Disclaimer: The information and statements contained in this article are for information purposes only and are not legal or other professional advice. Readers should not act or refrain from acting based on this article without seeking appropriate legal or other professional advice as to their particular circumstances. This article contains general information and may not reflect current legal developments, verdicts or settlements; it does not create an attorney-client relationship.

STRUCTURE magazine

April 2014

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The difference in state laws has meant that the holdings in very similar cases have often been completely opposite. In a North Dakota case, Ficek v. Morken, 685 N.W.2d 98 (2004), homeowners sued both their builder and the city after discovering that their house was built on uncontrolled fill with foundations that did not extend below the frost depth. The resulting differential settlement made the house unsafe to live in. The North Dakota Supreme Court agreed with the homeowners that the city had a duty to properly inspect construction and that it had breached this duty by approving the foundation. In contrast, in a Washington State case, Williams v. Thurston County, 997 P.2d 377 (2000), a contractor who was concerned about the foundation subcontractor’s work talked to the building inspector and was assured that the foundation had been approved. During the next phase of construction, a second inspector found numerous defects in the foundation and work was stopped until repairs were made. Although the first inspector was subsequently fired, the Washington Court of Appeals found that the questions asked by the contractor were not specific enough to create a special relationship, and thus the County did not owe the homeowner any duty to find the defects before the contractor began the next phase of the work. In another Washington State case that alleged the County was negligent in issuing a permit, Taylor v. Stevens County, 759 P.2d 447 (1988), the court held that the duty to ensure that buildings comply with county and municipal building codes rests with the individual builders, developers and permit applicants, not the local government. The court noted that issuance of a building permit does not imply that the plans submitted are in compliance with all applicable codes; likewise periodic inspections do not imply that the construction is in compliance with all applicable codes. Under this holding, building permits and code inspections only authorize construction to proceed; they do not guarantee compliance with all provisions of all applicable codes.

The Special Relationship Exception

ENGINEERED WOOD PRODUCTS GUIDE a definitive listing of wood product manufacturers and their product lines Simpson Strong-Tie ®

Associations American Wood Council

Phone: 202-463-2766 Email: info@awc.org Web: www.awc.org Product: Design Proceedures for Engineered Wood Products Description: Design proceedures for I-joists, glued laminated timber and structural composite lumber.

Connectors

StructurePoint

Hardy Frames

Phone: 800-754-3030 Email: dlopp@mii.com Web: www.hardyframe.com Product: Hardy Frame Panels, Brace Frames and Special Moment Frames Description: Hardy Frames manufacture and provide the leading prefabricated Shear Wall Systems for resisting lateral loads in narrow wall sections. Our Special Moment Frame is structural steel with SidePlate® moment connections now included in the Standard AISC 358 and the first pre-assembled Moment Frame in the industry.

Laminated Concepts Inc.

Phone: 607-562-8110 Email: frank@lamcon.com Web: www.lamcon.com Product: Vehicular Bridges Description: Glued laminated timber vehicular bridge structures. Short or long span.

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

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

Phone: 925-560-9000 Email: web@strongtie.com Web: www.strongtie.com Product: Simpson Strong-Tie® ITS I-Joist Hanger Description: The ITS I-joist hanger sets a new standard for engineered wood top flange hangers. It installs faster and uses fewer nails than any other EWP top flange hanger. The new Strong-Grip™ seat and Funnel Flange™ features allow standard joist installation without requiring joist nails resulting in the lowest installed cost.

Wood Advisory Services, Inc.

“The Wood Experts” Consultants in the Engineering Use of Wood & Wood-Base Composite Materials in Buildings & Structures • Product Evaluation & Failure Analysis • In-situ Evaluation of Wood Structures • Wood Deterioration Assessment • Mechanical & Physical Testing • Non-Destructive Evaluation • Expert Witness Services

www.woodadvisory.com 845-677-3091

Phone: 847-966-4357 Email: info@structurepoint.org Web: www.StructurePoint.org Product: Concrete Design Software Programs Description: spMats – Analysis & design of reinforced concrete foundations, combined footings or slabs on grade. spColumn – Design & investigation of rectangular, round & irregularly shaped concrete column sections.

Timberlinx

Phone: 877-900-3111 Email: timberlinx@rogers.com Web: www.timberlinx.com Product: Timberlinx Description: A simple, concealed and adjustable fastening system for joining wood to wood, wood to concrete, and wood to steel.

Engineered Lumber Anthony Forest Products Company

Phone: 870-862-3414 Email: info@anthonyforest.com Web: www.anthonyforest.com Product: Power Preserved Glulam® (PPG) Description: 2400Fb – 1.8E – 300Fv SYP glulam industrial grade; Pressure treated with Hoover CopGuard® or Cop-8®; Balanced lay-up & zero camber; No top or bottom; As environmentally safe as untreated wood; Above ground use for beams and ground contact for the columns. Product: PRG® (Power Rated Glulam) Description: I-Joist compatible depths; Full 3½- and 5½-inch widths; Balanced lay-up with no camber makes PRG® a natural choice for simple, multi and cantilever span applications; Easy one piece installation; Individually wrapped and surfaced sealed; Available in lengths up to 60 feet.

Bentley Systems

Phone: 800-BENTLEY Email: structural@bentley.com Web: www.bentley.com Product: RAM Elements V8i Description: RAM Elements V8i provides quick, reliable tools for specific structural tasks. RAM Elements V8i is the only structural engineering software system that offers finite element analysis plus stand-alone or integrated design tools all in one low-cost, easy-to-use package.

STRUCTURE magazine

April 2014

Weyerhaeuser

Phone: 888-453-8358 Email: wood@weyerhaeuser.com Web: www.woodbywy.com Product: Parallam® PSL Description: Trus Joist® Parallam PSL is engineered to support heavy loads and span long distances, making it an ideal option for creating spacious open floor plans and potentially eliminating columns or supports. The beams and columns are consistently straight and strong, and resist bowing, twisting, and shrinking.

Wheeler

Phone: 800-328-3986 Email: info@wheeler-con.com Web: www.wheeler-con.com Product: Panel-Lam Description: Engineered wood bridge kits for vehicular and recreation applications.

Wood Structural Panels RISA Technologies

Phone: 949-951-5815 Email: info@risa.com Web: www.risa.com Product: RISAFloor Description: RISAFloor and RISA-3D form the premiere software package for wood design. Create 3D models of your entire structure and get full design of wood walls (with and without openings), flexible wood diaphragms, dimension lumber, glulams, parallams, LVL’s, joists and more. Custom databases for species, hold-downs-and panel nailing offer total flexibility.

Simpson Strong-Tie

Phone: 925-560-9000 Email: web@strongtie.com Web: www.strongtie.com Product: Simpson Strong-Tie Strong-Wall® SB Description: A prefabricated wood shearwall that provides enhanced design flexibility and greater lateralforce-resistance performance. In areas susceptible to seismic activity or high winds, it provides structural support comparable to steel shearwalls in narrow panel widths. It installs easily to support two-story structures, garage portals and large openings.

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MOUNTING TECHNOLOGY

Anchor Channels

“Get used to being ahead – with JORDAHL® anchor channels.“ Elisabeth Smith, Development Engineer at JORDAHL

1913

– First anchor channel manufacturer.

2013

– First IAPMO uniform ES anchor channel product evaluation. – First anchor channel design software based on IBC and IRC building codes.

JORDAHL® anchor channels for structural connections For more than 100 years JORDAHL® anchor channels and T-bolts have guaranteed the reliable anchoring of loads to concrete. Providing simple and fast installation, the JORDAHL system provides easy location adjustment for structural concrete connections without the time consuming hassle of welding or drilling. Hot rolled channel proles provide high capacity and reduce in-built stresses allowing high dynamic load capability. This enables their ability to accommodate both high and rapidly uctuating loads over millions of cycles without metal fatigue. Just the sort of anchoring reliability needed for your project.

DECON USA INC. 103 East Napa Street, Suite B Sonoma, CA 95476 Tel (866) 332-6687 www.deconusa.com

With reliable performance veried by IAPMO Uniform ES Report #0293 and City of Los Angeles Research Report RR25797-T, JORDAHL® anchor channels are easy to design according to IBC, IRC, ACI 318 Appendix D, and ICC-ES AC 232, using our innovative JORDAHL® EXPERT software. The software can be downloaded for free from our website. Our team oﬀers unequalled customer service and technical experience. We would be pleased to oﬀer you additional assistance, and look forward to working with you.

award winners and outstanding projects

Spotlight

One World Trade Center By Dr. Rahimian, P.E., S.E., F. ASCE and Yoram Eilon, P.E. WSP was an Award Winner for the One World Trade Center project in the 2013 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings over $100M).

tanding at 1,776 feet (541 m), One WTC is the tallest building in the country. One World Trade Center serves as a national monument as well as a tribute to the “freedoms” emanating from the Declaration of Independence adopted by the United States of America in the year 1776. One WTC rises from a footprint that, at 200 feet by 200 feet, is the same size as those of the original Twin Towers. With its main roof at 1368 feet (417m) above ground, it is designed to reach the same height as the original towers. The addition of a 408 feet (124m) tall spire rising from the main roof completes the tower as it soars to its symbolic height. One World Trade Center’s program includes 3 million square feet of new construction above ground and 500,000 square feet of construction of subterranean levels. The tower consists of 71 levels of office space and eight levels of MEP space. It also includes a 50-foot high lobby, tenant amenity spaces, a two-level observation deck at 1,242 feet (379m) above ground, a “sky” restaurant, parking, retail facilities and access to public transportation networks. It provides a world-class model of life safety and security, energy efficiency and environmental sustainability. The tower structure is composed of a “hybrid” system combining a robust concrete core with a perimeter ductile steel moment frame. The reinforced concrete core wall system at the center of the tower acts as the main spine of the tower, providing support for gravitational loads as well as resistance to wind and seismic forces. The core is approximately square in footprint with a depth of about 110 feet at the base, large enough to be its own building. It houses mechanical rooms and all means of egress. The core structure is compartmentalized with additional interior shear walls in orthogonal directions. The core wall thickness varies along the height of the tower. The concrete strength ranges from 14,000 psi to 8,000 psi for foundation, columns and tower core walls, and 8,600 psi to 4,000 psi for slabs. The walls are interconnected over the core access openings using steel link beams embedded into the concrete walls.

The floor system within the concrete core zone is a cast-in-place concrete beam and flat slab system. The floor area outside the core is concrete on composite metal deck supported on steel beams and connected via shear connectors. The column-free floor system spans between the core and the perimeter steel moment frame for construction efficiency and maximum flexibility of tenant use. The tower height and its slenderness imposed stringent demands on the overall strength and stiffness of the structure. In order to meet those demands in an economical way, high strength concrete of up to 14,000 psi was utilized. Previously, the highest concrete compressive strength used in New York City was 12,000 psi. The key factor to successful and consistent results in such demanding concrete mixes is the quality control and tight monitoring of its mix components, as well as the use of local materials that are readily available. In addition, the high strength concrete used for the thick concrete walls, defined as mass concrete, required a particular concrete mix to meet the most stringent of demands. This was accomplished by limiting the Portland cement content in the mixes, substituting ice for mix water, and shifting pour schedules to cooler parts of the day. Radio Frequency Identification Devices (RFID) data-loggers were imbedded in the concrete to measure internal concrete temperature, heat of hydration, and maturity of the newly constructed walls. This facilitated early formwork removal, helping to shorten the construction cycle. Excessive heat of hydration during the curing process would expose the concrete to Delayed Ettringite Formation (DEF), and produce thermal cracking, which could result in reduced concrete compressive strength and modulus of elasticity. A concrete mix design test program, in collaboration with the Port Authority Materials Division, Engineer of Record and the concrete producers, was established to create the appropriate mix designs. Self-Consolidating Concrete (SCC) was used for all concrete requiring strengths greater than 8,000 psi. Due to the high density of reinforcing steel at the base of the building, most of the (SCC) mixes were consolidated with internal and external vibrators.

STRUCTURE magazine

April 2014

All mixes contained supplemental cementitious materials, fly ash, and granulated ground blast furnace slag cement and silica fume, as required. The use of these materials substantially contributed to the building’s United States Building Council LEED Gold rating. Due to the height and slenderness of the structure, the mix proportions for the core were designed for creep, shrinkage and Modulus of Elasticity. Paying careful attention to the coarse aggregate, type and volume were critical in order to obtain a Modulus of Elasticity in excess of 7 million pounds per square inch. As of February 2014, construction of One WTC structure is complete. The One World Trade Center tower incorporates numerous innovative engineering solutions, some of which were presented here. If we could to go back and change anything, it would be the circumstances under which we were invited to engineer this symbolic building. That said, the design and construction of this project is the result of a relentless collaborative effort between numerous design and construction teams over a period of several years, with a resolute focus on the goal of creating an iconic tower reaffirming the preeminence of New York City.▪ Dr. Ahmad Rahimian, P.E., S.E., F. ASCE, is Director of Building Structures at WSP USA. Yoram Eilon, P.E., is Senior Vice President of Building Structures at WSP USA. For additional information about this project refer to the article The Rise of One World Trade Center which appeared in the November 2012 issue of STRUCTURE® magazine.

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NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

2014 NCSEA Membership

NCSEA recognizes and thanks its Partnering Organizations and the following companies, organizations, Partnering Organizations and structural engineering firms for CASE SEI (Structural Engineering Institute of ASCE) their Associate, Affiliate and Sustaining memberships in 2013-2014. For Washington, DC Reston, VA information on becoming an Associate, Affiliate or Sustaining member, contact Associate Members Susan Cross at 312-649-4600, ext. AISC Five Star Products 204, or email scross@ncsea.com.

American Wood Council

Insurance Institute for Business & Home Safety

Schuff Steel Company

International Code Council

Simpson Strong-Tie

Metal Building Manufacturers Assn.

Steel Tube Institute

AZZ Galvanizing

Design Data

OTERA USA, Inc.

Bekaert

Hilti, Inc.

Powers Fasteners

Blind Bolt

Independence Tube Corporation

Red Seat Software

Cast Connex Corporation

ITW Commercial Construction North America

RISA Technologies

Bentley Systems, Inc. Fabreeka International

Affiliate Members

Cold-Formed Steel Engineers Institute Construction Tie Products, Inc. CSC, Inc.

Lindapter USA

SidePlate Systems, Inc.

Nemetschek Scia New Millenium Building Systems

DECON USA

SE Solutions, LLC

Steel Joist Institute Strand7

Sustaining Members ARW Engineers Ogden, UT

Degenkolb Engineers San Francisco, CA

Ruby & Associates, Inc. Farmington Hills, MI

Ballinger Philadelphia, PA

DiBlasi Associates, P.C. Monroe, CT

Simpson Gumpertz & Heger Inc. San Francisco, CA

Barter & Associates Mobile, AL

Dominick R. Pilla Associates Nyack, NY

Sound Structures, Inc. Rolling Meadows, IL

Bennett & Pless, Inc. Atlanta, GA

Dunbar, Milby, Williams, Pittman & Vaughan Richmond, VA

Structural Engineers Group, Inc. Jacksonville, FL

Blackwell Structural Engineers Toronto, Ontario Burns & McDonnell Kansas City, MO

Gilsanz Murray Steficek New York, NY

Cartwright Engineers Logan, UT Construction Technology Laboratories Skokie, IL Cowen Associates Consulting Structural Engineers Natick, MA Criser Troutman Tanner Consulting Engineers Wilmington, NC DCI Engineers Seattle, WA

Engineering Solutions, LLC Oklahoma City, OK

Holmes Culley San Francisco, CA

Martin/Martin, Inc. Lakewood, CO Omega Structural Engineers, PLLC Newbury, NH R & S Tavares Associates San Diego, CA

TGRWA, LLC Chicago, IL The Harman Group, Inc. King of Prussia, PA The Haskell Company Jacksonville, FL

LBYD, Inc. Birmingham, AL

STRUCTURE magazine

STV, Inc. New York, NY

April 2014

Thornton Tomasetti Chicago, IL United Structural Systems Ltd., Inc. Lancaster, KY Wheaton & Sprague Engineering, Inc. Stow, OH

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National Council Council of Structural Structural Engineers Associations

2014

NCSEA EXCELLENCE IN STRUCTURAL ENGINEERING AWARDS

Call for Entries The NCSEA Excellence in Structural Engineering Awards annually highlights some of the best examples of structural engineering ingenuity throughout the world. Structural engineers and structural engineering firms are encouraged to enter this year’s program. Projects will be judged on innovative design, engineering achievement and creativity.

NCSEA News

Up to three awards will be presented in eight categories:

News from the National Council of Structural Engineers Associations

• New Buildings Under $10M • New Buildings $10M to $30M • New Buildings $30M to $100M • New Buildings Over $100M • International Structures • New Bridges/Transportation Structures • Renovation/Retrofit Structures • Other Structures Eligible projects must be substantially complete between January 1, 2011 and December 31, 2013. Entries are due Friday, July 11, 2014. Awards will be presented in September at the NCSEA Annual Meeting in New Orleans, Louisiana. Winning projects will be featured in future issues of STRUCTURE magazine. For award program rules, project eligibility and entry forms, see the Call for Entries on the NCSEA website at www.ncsea.com.

GINEERS

April 2014

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Diamond Reviewed

Non-CalOES courses 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. NCSEA offers three options for registrations to NCSEA webinars: ala carte, FlexPlan, and Yearly Subscription. Visit www.ncsea.com for more information or call 312-649-4600.

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May 8, 2014 Fire Protection for Steel Nestor R. Iwankiw, Ph.D., P.E., S.E., Senior Engineer, Hughes Associates, Inc.

May 22, 2014 Fire Resistance of Concrete, Masonry & Timber Nestor R. Iwankiw, Ph.D., P.E., S.E., Senior Engineer, Hughes Associates, Inc. EN

May 1, 2014 Designing Buildings for Tornadoes Bill Coulborne, P.E., Director of Wind & Flood Hazard Mitigation, Applied Technology Council

IN NT

April 24, 2014 Structural Fire Resistance – Overview, Codes & Standards Background Nestor R. Iwankiw, Ph.D., P.E., S.E., Senior Engineer, Hughes Associates, Inc.

May 16, 2014 CalOES Safety Assessment Program (full day webinar, not included in subscription plan) Jim Barnes, C.E., California Governor’s Office of Emergency Services

NCSEA Webinars

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Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

Two New Journals from ASCE and ASME The American Society of Civil Engineers and the American Society of Mechanical Engineers are pleased to present two new journals addressing risk and uncertainties in both the civil and mechanical engineering aspects of engineered systems. The two titles will share one expert editorial board focused on presenting state-of-the-art research and best practices for ensuring a full discussion on risk and uncertainty related issues. Part A will be published by ASCE, and Part B will be published by ASME and focus on mechanical engineering. The format will be online-only with a list cost of $256, and an ASCE membership price of $64. The editor is now inviting submissions to be considered for publication in the new journal. Visit the journal website

at: www.asce-asme-riskjournal.org/ for more information. Accepted topics include, but are not limited to: • Risk quantification based on hazard identification • Scenario development and rate quantification • Consequence assessment • Valuations, perception, and communication • Risk-informed decision-making • Uncertainty analysis and modeling • Other related areas Get Your FREE Trial Email ASCE at ascelibrary@asce.org with the subject line SUBSCRIBE to get your free 2014 subscription to the Journal.

Get Involved In Your Local SEI Chapter North Jersey Chapter

Become Involved in Local Activities

On February 6th, 2014, the North Jersey SEI Chapter met for their annual dinner seminar with a presentation on Cornell University’s Milstein Hall project. The speaker was Alastair C. Elliot, P.E., LEED AP, Chief Operating Officer at the New York City office of Robert Silman Associates, Structural Engineers. The building was designed using sustainable practices by the renowned architect Rem Koolhaas. Read more about this project on the SEI website at www.asce.org/SEI in the News section.

Maryland 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.

Download the all-new Civil Engineering Magazine App for Mobile Devices The SEI Maryland Chapter has announced the launch of their new website. The site includes calendars for ASCE-MD events such as the Annual Indoor Golf Tournament and the 100th Anniversary Gala; and also SEI Events such as general meetings, tours, and webinars geared towards structural engineers. The website incorporates many conveniences such as “one-click” event sign up, online payments, and “add to my calendar” options. Visit the chapter’s new website at http://ascemd.org/sei/ and learn more about recent activities. STRUCTURE magazine

Read Civil Engineering magazine on your smart device. You can read ASCE’s flagship magazine, and access past issues, whenever and wherever it’s convenient for you. Civil Engineering magazine also publishes exclusive news and feature content on the Web every week. Get the latest industry news from the office, home, or anywhere online. Apple users can get the new app via Apple’s iTunes store at https://itunes.apple.com/us/ app/civil-engineering-magazine/id494066575?mt=8. The app for Android users is available through the Android Market at: https://play.google.com/store/apps. April 2014

ASCE Roundup: The Civil Engineering Blog & News Network

2015 Structures Congress is scheduled for April 23-25 at the Portland, Oregon Convention Center. Schedule Changes: In response to attendee feedback all committee meetings will take place on Wednesday, April 22, 2015. This change will eliminate the schedule conflicts between committee meetings and technical sessions. 2016 Joint Congress with the GEO Institute will take place in February 2016. Dates and location are not finalized. Special Joint Event: The 2016 congress will feature a total of 15 concurrent tracks: 5 tracks will be on traditional GI topics, 5 tracks on traditional SEI topics, and 5 tracks on joint topics. In addition, we will be offering interactive poster presentations within these tracks. What this means for you? Start thinking about sessions that would be of interest to both Geotechnical and Structural Engineers and prepare your session proposals.

ASCE has condensed its blogs and ASCE News into a single, comprehensive blog and news network called ASCE Roundup. Now, instead of 6 separate blogs, we have one with multiple channels: • ASCE News – news about ASCE and its members • President’s Perspective – thoughts from ASCE Presidents • Promote the Profession [formerly Talk About Civil Engineering] – getting word out about civil engineers and civil engineering • Save America’s Infrastructure – calling attention to the importance of infrastructure • The Leadership Imperative [new] – why it’s important for engineers to be leaders (associated with Vision 2025 and the Raise the Bar initiative) • The Emerging Engineer [formerly Bridging the Gap] – getting your career started • Technical Notes [future] – focus on technical content related to ASCE products (webinars, conferences, publications) Visit the ASCE Roundup at http://blogs.asce.org/.

SE Licensure Roundtable Report

Save the Date Electrical Transmission and Substation Structures Conference 2015 Branson, Missouri September 27 – October 1, 2015

Caldwell Gives to the SEI Futures Fund Structures Congress 2015 Portland, Oregon, April 23–25, 2015

CALL FOR PROPOSALS Submit your abstract and/or full session proposal today for Structures Congress 2015. We are currently accepting proposals for complete sessions and abstracts for individual papers to be presented at Structures Congress 2015. The Congress provides a forum to advance the art, science, and practice of structural engineering. All proposals are due June 11, 2014. Visit the conference website for all the details www.structurescongress.org.

STRUCTURE magazine

In January 2014, Stan Caldwell and his wife, Jane, gave a leadership gift of $7,500 to the SEI Futures Fund. When asked why he supported the SEI Futures Fund so generously, Stan responded, “I believe in leading by example. I don’t know how I could credibly chair the SEI Futures Fund without making a meaningful gift, and doing so sooner rather than later. I also believe in the mission, and the heavy lifting needs to start now.” Learn more at www.asce.org/Foundation/Learn_More/ Spotlight_on_Philanthropy/. Invest in the future of structural engineering, visit the SEIFF website at www.asce.org/SEIFuturesFund/. Gifts are fully deductible for income tax purposes.

April 2014

The Newsletter of the Structural Engineering Institute of ASCE

On January 23, 2014, the Missouri Structural Licensure Coalition and its member organizations, SEI – St. Louis Chapter and the Structural Engineers of Kansas and Missouri, organized a Structural Engineering Licensure Roundtable at the Engineer’s Club in St. Louis that attracted a number of engineers in the St. Louis region. It was also an opportunity for many to present questions and hear from distinguished experts on the rationale behind this nationwide movement. Four distinguished panelists were the focus of the Roundtable and each provided a brief presentation on a different aspect of licensure before addressing questions from the moderator and the audience. Read the entire report on the SEI website at www.asce.org/SEI in the News section.

Structural Columns

Important Information about the 2015 and 2016 Structures Congresses

The Newsletter of the Council of American Structural Engineers

CASE in Point

Books for Engineers CASE 962-F – A Guideline Addressing the Bidding and Construction Administration Phases for the Structural Engineer

CASE 962-G – Guidelines for Performing Project Specific Peer Reviews on Structural Projects

This document has been developed to assist all the parties associated with bidding and construction administration phases of a project, with a primary emphasis on those issues associated with the structural engineer (SER). It is important that the design team remains proactive in communicating with the contractor and the owner after the construction documents have been issued. This communication during the construction phase, as well as during the pricing and bidding process, should have as its primary goal assistance, interpretation and documentation for the improvement of the constructed project. This is a guide to the SER’s roles after the construction documents have been issued for construction. It provides guidance on pre-bid and pre-construction activities through the completion of the project. The appendices contain tools and forms to assist the SER in applying this guide to their practice. The project construction delivery system (e.g., design/build, design/bid/build) and for whom the SER works (e.g., owner, architect, general contractor) will influence the approach and the process during the bidding and construction administration phases. It is important to understand that no single method can be defined to accommodate, and to be totally effective for, every construction situation and construction team makeup. Therefore, this guideline includes suggested approaches to the various components that can make up the bidding and construction administration phases.

Increasing complexity of structural design and code requirements, compressed schedules and financial pressures are among many factors that have prompted the greater frequency of peer review of structural engineering projects. The peer review of a project by a qualified third party is intended to result in an improved project with less risk to all parties involved, including the engineer, owner, and contractor. Many aspects of the peer review process are important to establish prior to the start of the review in order to ensure that the desired outcome is achieved. These items include the specific goals, scope and effort, the required documentation, the qualifications and independence of the peer reviewer, the process for the resolution of differences, the schedule and the fee. The intention of these guidelines is to increase awareness of such issues, assist in establishing a framework for the review and improve the process for all interested parties. These guidelines and more are available at www.booksforengineers.com.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

Shuster, Schieffer Lead Speaker Lineup at 2014 ACEC Convention Top political and economic analysts will highlight the ACEC Annual Convention in Washington D.C., April 27-30. Bob Schieffer, CBS News chief Washington correspondent and host of Face the Nation, will address Hyper-Partisan Politics and the National Agenda. In the Congressional Issues Briefing, House Transportation & Infrastructure Committee Chair Bill Shuster (R-PA) will update attendees on the status of critical infrastructure legislation, including the reauthorization of MAP-21. Former NSA and CIA Director General (Ret.) Michael Hayden will offer his insights on America’s New Security Threats. Martin Regalia, chief economist and senior vice president at the U.S. Chamber of Commerce, will provide a national economic forecast. STRUCTURE magazine

Former IRS Commissioner Mark Everson, who is vice chairman of alliantgroup, will discuss the impact of recent IRS rules on engineering firms. The Convention will also feature Capitol Hill visits; federal market opportunities; CEO roundtables; bottom-line focused educational sessions; the 48th Annual Engineering Excellence Awards Gala; and a “teaming fair” for large and small firms to pursue partnering opportunities. Go to www.acec.org/conferences/annual-14/ to register!

April 2014

How often are we asked for financial contributions to causes, personal and professional, and every one of them worthy of our support? Dozens, if my own mailbox is any indication. Rarely, though, do we get to put a name and face to the recipients who directly benefit from our support. That’s why I’m delighted to introduce you to the 2013 winner of the ACEC/CASE Scholarship Fund: Samantha Dupaquier will graduate this May from Auburn University with a Master’s degree in Civil/Structural Engineering. The CASE scholarship, administered by the ACEC College of Fellows, is awarded every year to a deserving student seeking a Bachelor’s degree, at minimum, in an ABET-accredited engineering program. Since 2009, the CASE Scholarship program has given $12,500 to engineering students to help pave their way to a bright future in structural engineering. As the Chairman

and a member of CASE, I encourage you, along with our fellow CASE members and our structural engineering colleagues, to support this popular and successful program. Your contribution today will help CASE and ACEC increase scholarship monies to promising students who need it most. This year, we hope to garner enough donations to award scholarships to two deserving students. You can send your tax-deductible contribution to: ACEC/CASE Scholarship Fund 1015 15th Street NW, 8th Floor Washington, DC 20005 Fax: 202-336-5332 This is an exceptional opportunity to encourage growth in the structural engineering profession, and ensure that the highest caliber of students become the future of our industry. Thank you in advance for your generosity and for participating in this vital project.

EJCDC Publishes Free Commentary on Engineering Contract Document Series The Engineers Joint Contract Documents Committee (EJCDC) has released a free-for-download 30-page commentary on the content and use of its Engineering Series (E-Series) documents. The E-Series consists of nine professional services agreements, each with a specific intended application; one document for engineering firms subcontracting non-professional services; and two special-purpose documents – a teaming agreement/joint venture document, and a peer review agreement. To download the commentary, www.acec.org/userfiles/file/ E-001_Engineering_Commentary.pdf.

Upcoming ACEC Online Seminars Got Business Intelligence?

The Art of Skillful Communications

Getting out of a Rut: How to Diversify Your Network to Expand Your Business

Beware the Risks Posed by Non-Standard Construction Contract Documents – Updated for 2014

May 1, 2014; 1:30 pm to 3:00 pm Eastern Used right, Business Intelligence can drive business decision-making that leads to improved performance. For more information and to register, www.acec.org/education/ eventDetails.cfm?eventID=1551.

May 7, 2014; 1:30 pm to 3:00 pm Eastern Build connections and maximize the benefits of today’s diverse marketplace by using the latest networking strategies. For more information and to register, www.acec.org/education/ eventDetails.cfm?eventID=1552. STRUCTURE magazine

May 13, 2014; 1:30 pm to 3:00 pm Eastern Learn techniques to improve your performance during difficult and adversarial conversations. For more information and to register, www.acec.org/education/eventDetails.cfm? eventID=1569.

May 21, 2014; 1:30 pm to 3:00 pm Eastern Learn how to reduce the risks of using non-standard construction contract documents. For more information and to register, www.acec.org/education/eventDetails.cfm?eventID=1553.

April 2014

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Structural Forum

opinions on topics of current importance to structural engineers

Training the Structural Engineer Part 1 By Stan R. Caldwell, P.E., SECB

tructural engineering education today is a real mess! The problem starts with the young students who are traditionally attracted to our profession. Almost without exception, they like math and science much more than other subjects. Many, if not most, are more comfortable interacting with other people through their computers and mobile devices than doing so in person. This left-brained, somewhat introverted group is the raw material that feeds the pipeline year after year. Thus, the stereotype begins early. Most structural engineering students initially pursue a BSCE degree. Unfortunately, the requirements to earn it have dropped precipitously, from nearly 150 hours in 1960 to an average of about 125 hours today. Over this period, civil engineering has grown into a very broad field with many areas of specialization and complexity. Academic departments understandably strive to expose their undergraduates to all areas of civil engineering. The result is a curriculum that now amounts to little more than an introduction to the field. It does not provide much breadth of knowledge beyond civil engineering. Even worse, it utterly fails to provide anything close to the depth of knowledge necessary to start a career in a specialty such as structural engineering. As an example, just a few years ago a summer intern arrived at my firm in May, having just received a BSCE from a leading civil engineering program. His area of emphasis was structural engineering; he had earned a 4.00 GPA; and, he planned to return to school in August and pursue a master’s degree. I initially gave him a very simple concrete design project. Two weeks later, after observing no progress, I sat down with him to discuss the apparent problem. It turned out that his formal education in concrete amounted to just six weeks of study abroad in Spain. He knew that “concreto” was gray and hardened with time, but little else. As a second example, I recently served on the visiting committee for an ABET-accredited civil engineering program. To my amazement, I discovered that it offered its undergraduates no concrete design courses whatsoever, and only one steel design course, which was optional.

For many years, structural engineering students have been urged to pursue a graduate degree. The master’s degree has been the “sweet spot” for entering the structural engineering profession for at least the past two decades. It typically requires 30 to 36 hours, and the majority of those are spent in a single specialty. Consequently, a structurallyfocused master’s degree typically provides the depth of knowledge needed to start a career in structural engineering. However, it provides little or no additional breadth of knowledge beyond that which was acquired as an undergraduate. This is truly unfortunate. Without a breadth of knowledge, and a bit of rightbrained thinking, young structural engineers are unlikely to emerge as future leaders. Most structural engineers spend their time designing beams, columns, frames, trusses, connections, and the like. They do not lead their project teams, their firms, their profession, or society. Preferring to avoid risk, and constantly reminded that failure is not an option, they seldom innovate. Instead, they believe that good design work “to the code” is their highest calling, and they derive considerable satisfaction when their designs become reality. Sadly, in twenty years or so, the majority of these engineers will likely be just as obsolete as telephone operators, bank tellers, and travel agents are today. Most of their work will have been replaced by automation, and much of the remainder will have been sent overseas to be done at lower cost. Without substantial change, it is likely that the profession of structural engineering will shrink dramatically. An SEI task committee recently completed a two-year study on the future of our profession. Their ground-breaking report, A Vision for the Future of Structural Engineering and Structural Engineers: A Case for Change, is available as a free download at www.asce.org/SEI. The committee concluded that there are two keys to success: Future structural engineers must become leaders and innovators. It is my view that most structural engineers today are neither. Bridging the gap will take time, and the process must start with education. A much more diverse group of young students must be

attracted to the profession. By that, I specifically mean diversity of thought, of personality, and of interests. Also, the antiquated notion of professional education at the undergraduate level must finally be abandoned. How can this possibly be achieved? One radical plan, which I have grown to support in concept, is sometimes referred to as “The Law School Model”. Under this plan, students will be encouraged to seek an undergraduate degree in any field that interests them. Beyond good grades, the only prerequisites will be math, physics, and chemistry. A degree in biology, political science, or psychology will be viewed just as highly as a degree in engineering. A year (not six weeks) of study abroad will be viewed as a plus. After graduation, those students pursuing careers in structural engineering will take entrance exams for their preferred structural engineering schools. Those schools will be similar to law schools in many respects. After two or three years of focused structural engineering study, starting with statics and ending with the latest cutting-edge technology, graduates will receive professional structural engineering degrees. If this plan works as intended, those graduates will be a diverse group of well-rounded individuals with the skills and attitudes necessary to lead and innovate in a very different world.▪ Stan R. Caldwell, P.E., SECB (www.stancaldwellpe.com), is a consulting structural engineer in Plano, Texas. He currently serves on the SEI Board of Governors, SEI Futures Fund Board of Directors, SECB Board of Directors, and SELC Steering Committee. The focus of this two-part article is on training the future structural engineer prior to licensure. Part 1 addresses training in the classroom and laboratory. Part 2, which will appear in a future issue, addresses training in and around the workplace.

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

April 2014

STRUCTURE magazine | April 2014

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