STRUCTURE magazine | April 2015 by structuremag

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

April 2015 Concrete CASE Convocation and SEI Structures Congress April 23 – 25 Portland, Oregon

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• Support for IBC 2012 / CBC 2013 including referenced design standards • Fully revised load combination generation system • Proven modules for the analysis and design of key components common to most buildings • Wood Shear Wall module for individual full-height panels • Project Load Group Builder for developing and tracking design load components • 2D Frame analysis and design • Wind loads per ASCE 7-10 Chapter 27 and per IBC Alternate All-Heights method • Project Manager facilitates a “project approach” to developing and printing calc sets

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STRUCTURE

April 2015 28

Feature

rural Philippine Shelter Construction 34 editorial

7 Professional involvement By Andrew Rauch, P.E., S.E.

engineer’S noteBook

27 Concrete Beam Strength vs. Serviceability By Jerod G. Johnson, Ph.D., S.E.

By Gustavo Cortes, Ph.D, P.E. On November 8, 2013, super typhoon Haiyan, with Category 5 hurricane force winds, hit the Philippines in November of 2013. In the aftermath, shelter units were provided to the most vulnerable victims. Who would have thought that designing a 10- by 13-foot structure would present so many unique challenges, including anticipation of load conditions, availability of materials, and quality of materials received?

StruCtural rehaBilitation

9 Cinder Concrete Slab Construction

gueSt Column

36 a Brief history of atC…

By Ciro Cuono, P.E.

By Vicki Arbitrio, P.E., SECB

StruCtural deSign

hiStoriC StruCtureS

15 Vibration of reinforced Concrete Floor Systems

StruCtural ForenSiCS

18 Periodic inspection of retaining Walls

40 monongahela river Bridge By Frank Griggs, Jr., D. Eng., P.E. ProFeSSional iSSueS

46 Why they Stay… Why they leave…

Kyle Twitchell, P.E.

Feature

SPotlight Building BloCkS

By Eric Karsh, M.Eng, P.Eng, and Rebecca Holt

By Eric R. Ober, P.E., S.E. and Robert P. Antes Insufficient documentation of the existing construction in adaptive reuse projects challenges designers and contractors. In the case of the Parkway 301, hidden conditions overwhelmed all other structural challenges. The seven-story building, originally constructed in 1910 and vertically expanded in the early 1920s, was adapted to house residential apartments on the upper floors over renovated ground floor retail space.

By Robert Pekelnicky, S.E. and

By Dan Eschenasy, P.E.

22 overview of the Survey of international tall Wood Buildings

Feature

Parkway 301

By David A. Fanella, Ph.D., S.E., P.E. and Mike Mota, Ph.D., P.E.

Building a Strong Future

51 680 Folsom By Bill Janhunen, S.E.

By Jun Fei, P.E. The University of Kansas, School of Engineering’s Structural Testing Laboratory offers one of the most advanced structural testing facilities in higher education. The principal element of the facility consists of a strong floor and strong wall system constructed of cast-in-place concrete. The key engineering challenge of this project was the strong wall, which is a performance-driven, highly customized element.

and Gina Phelan StruCtural Forum

58 the role of engineers in transforming the global economy By Ashvin A. Shah, P.E.

On the cover The seven story E3 building in Berlin successfully demonstrates that a cost equivalent, high performing building with a mass timber structure is a strong alternative to other structural materials in mid-rise residential development. See more in the Building Blocks article on page 22. Architecture by Kaden Klingbeil, photo courtesy Bernd Borachrt. 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

in eVery iSSue 8 Advertiser Index 44 Resource Guide (Engineered Wood Products) 50 InBox 52 NCSEA News 54 SEI Structural Columns 56 CASE in Point

April 2015

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Editorial

Professional Involvement new trends, new techniques and current industry issues Service and Reward

By Andrew Rauch, P.E., S.E., LEED AP, CASE Chair

spring CASE Risk Management Convocation for the 2015 Structures Congress. It will kick off with the CASE Breakfast featuring an address by Sue Yoakmun on how our liabilities and responsibilities will change with changes in technology and project delivery methods. The convocation will feature four sessions. • In the first session, Brian Stewart will talk about how additional risks are creeping into our design contracts and we may not be aware of them. • The second session will feature a panel discussion on some of the non-technical risks faced by today’s structural engineering project managers and provide tools for addressing them. This will be a great session for those project managers, who are interested in learning more about the “softer” side of the profession. • Jeff Coleman, an attorney, structural engineer, and probably the only lawyer who is a Fellow of the American Concrete Institute will present at the third session. This session will feature case studies from actual litigation. From there, it will highlight the lessons learned from those projects and how you can use those lessons to protect your practice. • The fourth session will be a roundtable discussion which should be very valuable to practicing engineers, especially project managers. We are often forced to balance between the amount of effort to expend on a project and the amount of fee available to complete the work. This session will look at several situations encountered regularly, and offer guidance on how to strike that balance. The National Guidelines Committee has just published a commentary on the Code of Standard Practice for Steel Joists from the Steel Joist Institute. How many of you have taken the time to read this document that governs the design and procurement of structural elements we all use so often? The new publication from SJI contains some significant changes to how joists are designed. This commentary helps to understand those changes and highlights provisions in the Code of Standard Practice of which you may not be aware, but you should be. This document is available at www.acec.org/case/getting-involved/guidelines-committee/. In the first of these articles, almost two years ago, I urged you to get involved in a structural engineering organization for your own benefit and as a service to your profession. To close out my last article, I will repeat that encouragement. I continue to be amazed at the expertise, abilities, insights and commitment that I have seen from my structural engineering colleagues. You truly receive much more from involvement in your profession than it ever asks of you.▪

a member benefit

structurE

t is hard to believe, but this will be my last editorial as chair of CASE. This spring, I will turn the gavel over to the capable hands of Dave Mykins from Stroud Pence and Associates of Virginia Beach, Virginia. It has been a pleasure and an honor to serve both the structural engineering firms who are members of CASE and the structural engineering profession as a whole. I am pleased with what CASE has been able to accomplish these last two years, producing guidelines, contract forms, tools and programs that can be used to enhance the business practices and risk management efforts of structural engineering firms. For that, I must give credit to the hard-working members of CASE’s guidelines, contracts, toolkit, programs and membership committees, and to the extra efforts put forth by the chairs of those committees. CASE is one of six coalitions within ACEC. The other coalitions represent mechanical/electrical engineers, land surveyors, land development consultants, small firms and large firms. I have enjoyed being a part of the growth and collaboration among all of these coalitions as we share resources to enhance and improve business practices among the greater engineering community. That could not have been done without the capable assistance of Heather Talbert and Katie Goodman at ACEC, and I thank them for all that they do. I would like to highlight some of the more recent activity within the CASE committees. John DalPino, chair of the Guidelines Committee, recently authored a white paper on the engineering standard of care. It does not try to define the standard of care (to the disappointment of lawyers, and the relief of engineers and their insurers) but rather discusses how the standard of care evolved over the years, and how it differs from other forms of liability. It also offers insight on how the standard of care might evolve in the coming years. This white paper is available at: www.acec.org/case/news/publications/. The Contracts Committee is hard at work updating all of the CASE contract forms. This is a major undertaking, and is almost complete. Look for the updated versions of these contract forms to be available soon. Our surveys have consistently shown that these forms are some of our more heavily used products. These contract forms will be available at: www.acec.org/case/gettinginvolved/contracts-committee/. The Toolkit Committee has recently published a tool to help assess the risks associated with pursuing a given project. It takes you through the questions you should ask yourself about the client, the project, and your own capabilities before deciding to pursue and accept the project. This document is available STRUCTURAL at www.acec.org/case/gettingENGINEERING involved/toolkit-committee/. INSTITUTE The Programs Committee has been busy putting together the

STRUCTURE magazine

Andrew Rauch, P.E., S.E., LEED AP, 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 2015

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EDITORIAL BOARD Chair Jon A. Schmidt, P.E., SECB Burns & McDonnell, Kansas City, MO chair@structuremag.org Craig E. Barnes, P.E., SECB CBI Consulting, Inc., Boston, MA

ERRATUM The author of Understanding Seismic Design through a Musical Analogy (STRUCTURE, March 2015) would like to correct the acknowledgements at the end of the article. It should read: Special thanks to Verónica Cedillos, Dan Eschenasy and Ayse Hortacsu for their valuable insights on the subject.

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STRUCTURE magazine

April 2015

Amy Trygestad, P.E. Chase Engineering, LLC, New Prague, MN C3 Ink, Publishers A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 Phone 608-524-1397 Fax 608-524-4432 publisher@structuremag.org April 2015, Volume 22, Number 4 ISSN 1536-4283. Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student. For change of address or duplicate copies, contact your member organization(s) or email subscriptions@STRUCTUREmag.org. Note that if you do not notify your member organization, your address will revert back with their next database submittal. Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board. STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

he great fires of the 1800s in Chicago, New York, and elsewhere spurred a technology race to develop the best fireproof floor system. The years between the 1870s and 1940s represented a golden age of new technology in structural systems. Cast iron, wrought iron, structural steel and reinforced concrete framing systems, terra cotta arch construction, cinder concrete slabs, and many proprietary systems were introduced during this period. Although now known as “archaic” structural systems, as they are no longer used and have been replaced with modern methods and materials, these systems represent a large portion of our building stock. Of these varied archaic systems, cinder concrete slab construction became one of the most dominant structural slab systems used from the 1920s to the 1940s. This article explores the origin, history, design, performance and relevance today of cinder slab construction with focus primarily on use in New York City (NYC); however, it was used in many other parts of the country as well. Cinder concrete slab construction, also known as cinder arches, “goulash” construction, or even “short span arch construction”, was a type of reinforced concrete slab system consisting of low strength concrete which used cinders as an economic substitute for stone aggregate and draped wire mesh as reinforcement. Unlike stone aggregate concrete with reinforcing bars, these systems were not really “reinforced concrete” in the conventional sense but actually tensile structures encased in a light weight low strength concrete. This subtle but key concept can be the source of misunderstanding in dealing with these systems. The steel draped wire mesh acted as a tensile catenary system which carried all loads in tension between steel beams. The cinder concrete provided a walking service, transferring loads to the tension wires and acted as fireproofing protection for the steel wires. Although this type of system is no longer specified, it is very relevant to engineers and architects today, not only in NYC, but in other cities as well since many of our office buildings, residential buildings, school buildings, industrial buildings etc. are made with these types of floor systems. As a result, it is important to understand their origin, history, performance, strengths and weakness when planning renovations, and repairing defects and deterioration.

History and Origin Cinder arch construction developed as a result of economic and social forces. As the concrete industry began to develop in the United States (US) in the late 1800s and early 1900s, the key ingredients took shape to form this new type of construction.

Welded wire mesh was first patented in 1901. Although it had a variety of uses, its use took off in early concrete road construction. The early wire mesh was triangular and woven, and then rectangular in shape. From road construction it began to enter the building market where rolls of wire mesh could be easily shipped and rolled out on a job site. The “cinder” part refers to cinder and clinker, by products of coal generating plants, recycled and used to replace more expensive aggregates. The NYC empirical tables referred to “clean boiler cinders” and Anthracite or coal cinders. This incidentally provided good fire resistance which was validated in various tests. “Draped” mesh refers to wire mesh placed over the tops of steel floor beams and then draped down at the mid-span between the beams, thus creating the “catenary” or “hung chain” which provided optimal geometry for essentially a cable system in tension. The high load capacity, excellent fire proofing properties, light weight, and ease of construction (rolling out a wire mesh versus laying out reinforcing bars), made these floor systems the primary choice for many engineers and builders. By the 1930s, they seem to have replaced terra cotta arch construction and many other proprietary systems. It seems most of the testing and early uses in building construction occurred in NYC where many office and residential buildings built prior to World War II are still functioning quite well, the most famous of which is probably the Empire State Building.

Structural rehabilitation renovation and restoration of existing structures

Cinder Concrete Slab Construction By Ciro Cuono, P.E.

Testing, Analysis, and Design Many tests were conducted in NYC, over several years, as part of the technology race for fireproof floor systems. One such test was conducted by Professor Ira Woolen at Columbia University in conjunction with the City Building Bureau in 1907 and 1908. The test consisted of a fire, water, and load test of a cinder concrete slab with 5-foot and 8-foot spans and reinforced with triangular wire mesh. The cinder concrete contained “boiler cinders”. Specimens were load tested to a compressive strength of 1,000 (pounds per square inch (psi). The results of the testing were good, withstanding a four-hour fire at approximately 1,700 degrees Fahrenheit and sustaining a 600 psf dead load. Another significant test, in a series of many tests, was conducted in the summer of 1913 by Harold Perrine of Columbia University in Long Island City, NY. The test consisted of the construction of three types of floor systems; a cinder slab, a flat terra cotta arch, and a gypsum slab (also reinforced with welded wire mesh). The testing, funded by a

STRUCTURE magazine

Ciro Cuono, P.E., is a Principal at Cuono Engineering PLLC, a structural engineering firm located in Port Chester, N.Y., and is an assistant adjunct professor of structural engineering at the Bernard and Anne Spitzer School of architecture at The City College of NY. He may be reached at ccuono@cuonoengineering.com.

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

Allowable load The allowable load shall be determined by the following formula: w = 3CAs /L2 where: w = gross uniform load (psf) As = cross sectional area of main reinforcement (sq. in. per ft. of slab width) L = clear span between steel flanges in feet. (L shall not exceed ten feet in any case, and when the gross floor load exceeds two hundred psf shall not exceed eight feet) C = the following coefficient for steel having an ultimate strength of at least fifty-five thousand psi; 1. For lightweight aggregate concrete: a. twenty thousand when reinforcement is continuous. b. fourteen thousand when reinforcement is hooked or attached to one or both supports. (1) When the above formula is used the reinforcement shall be hooked or attached to one or both supports or be continuous. (2) If steel of an ultimate strength in excess of fifty five thousand psi is used, the above coefficient C may be increased in the ratio of the ultimate strength to fifty five thousand but at most by thirty percent.

Figure 1. Excerpt from the 1968 New York City Building code (27-610) showing an empirical formula for cinder slab construction (carried over from earlier versions of the code). Figure 3.

fireproofing company, was done to compare the fire resistivity of the three types of floor systems. Each was subjected to fire and test loading. The slabs were subjected to four hours of fire that was approximately 1,700 degrees Fahrenheit and then rapidly cooled with cold water, all the while carrying 150 pounds per square foot (psf) of pig iron. After 24 hours of cooling, the slabs were loaded with further weight. The cinder slab had the best overall performance, with minimal damage from the fire and supporting 600 psf with only ½ inch deflection. According to Frank Eugene Kidder, (a famous author of engineering handbooks in the early 1900s), some earlier tests conducted in 1902 had 4½-inch cinder slabs load tested to approximately 1,400 psf! The successful testing and market use led to a codification of cinder floor slabs in NYC. The building code contained empirical formulas for determining slab thickness and wire mesh areas for many years (Figure 1). These “empirical” formulas were essentially based on statics of a tensioned cable. The design became simply a matter of calculating a wire mesh area, or picking out the area from a load and span chart. The cinder concrete itself was essentially unimportant. If conducting a modern compression core test on one of these slabs, a good result would be in the range of 700 psi – a result woefully unacceptable for a slab that is conventionally reinforced.

Construction A typical cinder slab mix, often found on many old drawings, might be a 1:2:5 mix (1 part cement, 2 parts sand and 5 parts cinders) ranging in unit weight from 85 pounds per cubic foot (pcf ) to 110 pcf. Touching a sample piece of cinder slab in the field feels like a piece of pumice stone. This light weight resulted in a material savings for the steel frames and foundations, making it very appealing as a floor slab system. A typical slab was 4 inches to 5 inches thick, although 3½ inches thick can be found in many old buildings. Usually the top of the slab is at the beam elevation or just above it. The beams and slabs were then topped with a layer of loose cinder fill, which provided fireproofing to the top flanges. Within this fill layer were beveled wood sleepers, usually 16 inches on center. A hardwood floor could then be nailed to the sleepers. This fill layer was typically 2 inches to 2½ inches thick. At flat roofs, where

Figure 2.

STRUCTURE magazine

April 2015

pitch was required for drainage, the fill could be 6 inches to a 1 foot or more (Figure 2). The wire mesh was draped, as mentioned above, and hooked around the flange of the end or perimeter beams. The steel beams were encased in concrete for fireproofing. Typical spans ranged from 5 feet to 8 feet.

Performance The performance of cinder slabs is rather amazing when one considers some of the inherent weaknesses of their design. The demonstrated analytical and historical strength of steel cables is well documented. As an essentially pure tensile structure, there seems to be a robust capacity for overloading. However, the small diameters of the cables or mesh result in a small robustness once there is the susceptibility to corrosion. Roof slabs and slabs near plumbing lines or below wet areas of construction (for example a restaurant kitchen floor) are

common sources of leaks. The author has personally observed the underside of slabs that were subjected to long term corrosive environments, resulting in severely spalled slabs. From the floor one may observe the exposed mesh with an obvious rust color; however, upon close inspection one may find the wires severely corroded, snapped, or even completely disintegrated leaving behind a streak of rusting that almost looks like a partially corroded wire (Figure 3). One can only wonder how a condition like this has not resulted in a collapse. Perhaps a combination of redistributions at adjacent more fully intact areas, conservative loading requirements, friction, and other “ignorance factors” has prevented more disastrous results. To this author’s knowledge, there is no significant documented major failure of these types of floor systems. The ductility of steel mesh and the obvious signs of spalling have perhaps helped as well, as these signs of impending disaster usually signal a building owner to call in an engineer and provide some type of repair.

absorbed by the cinder concrete and can stay there for years, slowly corroding the wire mesh. The combination of the cinder aggregates and water can react to create sulfuric acid which, along with poor resistivity of the cinder concrete, can lead to severe corrosion. The expansion from corroding wire mesh can crack and spall the underside of cinder slabs. Often a small spall is noticed and upon a few “whacks” of a sounding hammer, the entire underside can quickly spall off leaving the rusting wire mesh completely exposed. Caliper

measurements can be used to recalculate a remaining capacity, assuming further corrosion is arrested. However, this can be impractical since conditions can vary greatly even in a few bays; thus, a few spot measurements may not give a reliable result. An overhead repair mortar could be applied to patch the underside of a spalled slab; however, this cosmetic repair will not restore any lost capacity. New low profile steel beams (such as channels, angles, or tubes) can be installed below a defunct slab

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Since cinder concrete arches are no longer used, it would seem an “archaic” structure. In NYC, however, they are so ubiquitous that a working knowledge of their design and construction is a prerequisite to engaging in renovation work. The usual issues have to do with either planned renovations, where loading changes and opening or closing of stair, mechanical or elevator shafts occur (Figure 4 , page 12), or repairs due to rusting and corrosion. Their long history of good use and tremendous load capacity from testing generally makes analysis fairly easy. Armed with a tape measure and a caliper, an engineer can take a few spot field measurements of the wire size and spacing and, in conjunction with the empirical formulas from decades ago, quickly arrive at a safe loading capacity. Reframing openings can be tricky, since loss of anchorage or continuity of the mesh could theoretically relax the mesh. Many engineers often require contractors to tack weld any exposed mesh to the steel beams, especially adjacent to newly cut slabs. Repairs are more complicated. Cinder concrete is extremely porous and lightweight. Water from leaks, from old steam lines, or roofs and parapets gets STRUCTURE magazine

April 2015

Figure 4.

to reduce the span in lieu of a total demolition and replacement. On a roof, where the loose fill may be quite thick, this fill can be removed and replaced with a new modern reinforced concrete slab spanning between the tops of the existing steel beams, thus abandoning the old slab in place and using it as form work only. The creative engineer can find ways of working around a deteriorated slab. Understanding the limits of cinder slab construction is important to this process. Another issue in modern renovations is hanging ceilings and mechanical units. Cinder concrete is notoriously unreliable with epoxy and mechanical anchors in tension. The original ceilings were often hung with wire that was hooked into an exposed portion of the slab wire mesh. Regular spots of chipped out concrete, exposing the wire mesh, can provide opportunities for easy field measurements. Load testing of anchors for light loads like a gypsum ceiling (say for 4 to 5 times the load) can be used; however, conditions could vary over short distances, making this method somewhat unreliable. The more conservative approach is to hang off the original steel beams, especially for anything heavier than a ceiling.

advantage of the loose cinder fill atop the structural slab to gain valuable space for new structure. As mentioned, the fill layer on roof slabs (of apartment buildings with flat roofs) was often quite thick; six inches to twelve inches was not uncommon. The removal of 10 inches of loose cinder fill is equivalent to almost 50 pounds per square foot (psf ) of dead load. Removal of this dead load could be used to justify new additional dead and live loads, such as pavers for a roof deck. This “load balancing method” is quite convenient, especially if analysis of

Renovation and Repair Examples One example of a renovation of cinder slabs that has been successful is to take

Figure 5.

STRUCTURE magazine

April 2015

the existing framing cannot be done due to lack of original drawings and the inability to make destructive probes of the framing. Pitfalls to this method include the lack of an actual engineering analysis (what if the original framing was undersized?) or overestimation of the actual weight as the loose fill could be lighter than historic load tables may indicate. Also, consideration has to be given to fireproofing, as the top flanges of the steel beams were often fireproofed by the loose cinder. A repair example, also at a roof slab, involved the removal of the loose fill to create a newer stronger conventional reinforced concrete slab that spans between the new beams. This is a convenient methodology where the existing slab is deteriorated. Rather than complete demolition and replacement (which could be more costly, and expose the interior to increased risk from temporary instabilities and the elements), the loose fill could be removed and then a new slab poured atop a thin layer of rigid insulation (to prevent bonding) (Figure 5). In an extreme case, where the existing slab was severely corroded, steel plates could be hung from the new slab to “lock-in” the old slab or prevent localized pieces from falling onto the occupants below. In summary, the dominance of cinder slab systems from the 1920s to the 1940s and their continued successful performance in so many buildings today, despite some pitfalls that have been mostly related to corrosion issues, is a testament to their strength and versatility.▪

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t is generally perceived that vibration is not an issue for reinforced concrete floor systems. Because of the inherent mass and stiffness of such systems, this perception is generally true. However, there can be situations where the effects of vibration are one of the main design issues that need to be addressed. In this general overview, simplified methods are provided that can be used in a preliminary analysis to determine approximate fundamental vibration characteristics, which can help in choosing a suitable floor system for a given set of conditions.

Acceptance Criteria for Human Comfort Human response to floor vibration is very complex. The magnitude of the motion and what a person is doing are two of the factors that have an impact on perception and acceptability. Floor systems that can “dampen out” the effects of vibration in a relatively short period of time are likely to be perceived as less annoying than those systems that cannot dampen vibration as quickly. Many criteria have been proposed through the years related to vibration and human comfort. To date, no universally accepted criteria exist. A discussion on walking and rhythmic excitation follows. Vibrations can be caused by a person or persons walking on a floor system. Depending on a number of factors, this vibration can be annoying, or worse, for the people that are occupying the area affected by the vibration. Recommended acceleration limits for human comfort due to specific human activities were developed by the International Standards Organization and have been successfully implemented in a wide variety of situations (ISO 2631-2). This standard provides limits for different occupancies in terms of root-mean-square acceleration as a multiple of a baseline curve. For vibrations due to walking to be acceptable, the peak acceleration of the floor system should be less than or equal to the recommended acceleration for a particular occupancy. The natural frequency (fn), the effective weight, and the inherent damping of the floor system are all related to peak acceleration. It is common to find that the acceptance criterion for walking is satisfied for all types of reinforced concrete floor systems, including flat plates. The same conclusion is not necessarily true for reinforced concrete floor systems subjected to rhythmic excitations. Activities in health clubs, gymnasiums, and dance halls, to name a few, can produce significant vibrations. Because the dynamic forces and accompanying vibration associated with rhythmic activities is generally large, it is usually not practical to mitigate

vibration by increasing the mass or damping of the system. The acceptance criterion for rhythmic excitations is satisfied when fn is greater than the frequency of the highest harmonic that can cause resonant vibration. While the acceptance criterion for walking excitations is easily satisfied for a flat plate system, it is unlikely that the appropriate criterion will be satisfied when the flat plate is subjected to aerobics or jumping. In such cases, it would probably be more economical to use a twoway joist (waffle) system or a grillage system, the latter of which consists of evenly spaced concrete beams in two orthogonal directions. For less demanding activities such as dancing, a concert, or a sporting event, a wide-module joist or a voided slab system can usually be utilized (a voided slab system is similar to a flat plate, except it contains regularly-spaced voids that are created using hollow recycled plastic void formers; see Mota 2010 for more information).

Acceptance Criteria for Sensitive Equipment

design issues for structural engineers

Vibration of Reinforced Concrete Floor Systems

Manufacturers of sensitive equipment will generally provide vibration acceptance criteria for their equipment. The limits are usually given as a vibrational velocity, which has the units of micro-inches per second. The criterion for sensitive equipment is satisfied when the expected maximum velocity, which is a function of the walking pace of the occupant or occupants near the equipment, is less than or equal to the limiting value given by the manufacturer. The smaller the limiting value, the more challenging it is to satisfy the acceptance criteria. In the preliminary design stage, the equipment is usually known only in general terms and no information on the specific model or type is available. In such cases, generic acceptance criteria can be utilized to arrive at a suitable floor system. This system can be subsequently checked once specific information on the equipment becomes available. The type of reinforced concrete floor system to use when supporting sensitive equipment depends for the most part on the limiting value of the vibrational velocity and the bay sizes. For example, a flat plate system supporting computer equipment, which has a relatively large vibrational velocity limit, may work for slow and moderate walking paces but may not work for a fast walking pace. It is unlikely that a flat plate would satisfy the criteria for a facility where eye surgery is performed, except possibly for a slow walking pace. Two-way joist or grillage reinforced concrete systems are typically

STRUCTURE magazine

Structural DeSign

By David A. Fanella, Ph.D., S.E., P.E. and Mike Mota, Ph.D., P.E. David A. Fanella, Ph.D., S.E., P.E., F.ASCE, F.ACI, is a Principal at TGRWA, Inc., a consulting structural engineering firm in Chicago, IL. David is a member of a number of ACI Committees and serves as an Associate Member of ASCE Committee 7, Minimum Design Loads for Buildings and Other Structures. He may be reached at dfanella@tgrwa.com. Mike Mota, Ph.D., P.E., F.ASCE, F.ACI, is the Vice President of Engineering for the Concrete Reinforcing Steel Institute (CRSI). Mike is an active member of several ACI and ASCE committees, Member of ACI 318 and 318 sub B and sub R, Chair of ACI Committee 314 on Simplified Design of Concrete Buildings, serves on the Board of Directors of the Concrete Industry Board of New York City/ NYC ACI Chapter and is a past member of the editorial board of STRUCTURE magazine. He may be reached at mmota@crsi.org.

utilized to support equipment where the spans are long and/or the vibrational velocity limits are small.

Approximate equations for natural frequency of reinforced concrete floor systems.

System Wide-module Joist

Vibration Characteristics Stiffness, damping, and natural frequency are parameters that are needed in the vibration analysis of any reinforced concrete floor system. The following recommendations and approximate procedures can be utilized in the preliminary design stage to quickly ascertain the types of floor systems that are best suited to satisfy the required vibration criteria. Stiffness. The stiffness of the floor system has a direct effect on natural frequency: the greater the stiffness of the floor, the greater the natural frequency, which translates to a likely decrease in adverse effects caused by vibration. For typical reinforced concrete floor systems of usual proportions, the major component of the deflection of the system is due to flexure. Thus, only the flexural stiffness of the floor EcIe needs to be considered. The quantity Ec is the modulus of elasticity of the concrete. Because the strains in the concrete are small when subjected to dynamic loading, it is appropriate to use a value of Ec that is 20 to 30 percent larger than the codeprescribed value. The term Ie is the effective moment of inertia. It is recommended to include the effects of cracking when initially determining the stiffness of a non-prestressed floor system because the natural frequency may be overestimated if it is not considered. A more refined cracking analysis can always be performed later, if desired. Damping. Damping is a measure of how quickly vibration will subside and eventually stop. It is greatly dependent on the nonstructural items that are supported on the floor, such as people, partitions, file cabinets, bookshelves, and furniture, to name a few. The amount of damping is usually expressed as a percentage of critical damping and is commonly referred to as the damping ratio. A damping ratio of 0.02 is recommended for floors with few nonstructural components (like electronic offices), while a ratio of 0.05 can be used where full-height partitions are present between floors (ATC 1999). A value of 0.03 is commonly used for office spaces with partial height partitions. Additional information on how to choose an appropriate damping ratio can be found in Hewitt and Murray, 2004. Natural frequency. Natural frequency is a measure of how the floor system will respond to the sources that can cause vibration, and is related to how occupants will perceive

Natural Frequency 3.54 √(Δj + Δg) Δj = instantaneous mid-span deflection of the joists Δg = instantaneous mid-span deflection of the girders

fn =

[

]

[

]

½ 2 k1Ec h3 fn = k2λ12 2 2πℓ 1 12γ(1 – v ) k1 = Ie /Ig 1.9 for c1 ≤ 24 in. k2 = 2.1 for c1 > 24 in. c1 = column dimension h = thickness of slab ℓ1 = longer of the two center-to-center span lengths of the plate panel ℓ2 = shorter of the two center-to-center span lengths of the plate panel γ = mass per unit area of the plate v = Poisson’s ratio ℓ1/ℓ2 λ21 1.0 7.12 1.5 8.92 2.0 9.29 ½ 2 k1Ec h e3 fij = λij 2 2πℓ 1 12γ(1 – v 2) k1 = Ie /Ig he = equivalent slab thickness ℓ1 = longer of the two center-to-center span lengths of the panel γ = mass per unit area of the plate v = Poisson’s ratio ℓ 2 λ2ij = π2 i 2 + j 2 1 ℓ2 i,j = mode indices

{

Flat Plate and Voided Slab Systems

Two-way Joist

[

( )]

[

]

½ xy f 11 = π½ D4x + D4y + 2D 2 2 2γ ℓ 1 ℓ 2 ℓ 1 ℓ 2 3 Dx = Dy = k1Ec h s 2 + k1Ec Ir 12(1 – v ) s

k1Ec h s3 12(1 – v 2) k1 = Ie /Ig hs = slab thickness Ir = moment of inertia of rib s = center-to-center spacing of ribs ℓ1 = longer of the two center-to-center span lengths of the plate panel ℓ2 = shorter of the two center-to-center span lengths of the plate panel γ = mass per unit area of the plate v = Poisson’s ratio Dxy =

Grillage

such vibrations. Numerous resources and methods are available to determine this property. It is usually convenient to obtain this and other vibration characteristics from a commercial computer program. Like all software, it is very important to understand the methodologies that are used to calculate this parameter. The equations in the Table give approximate values of the natural frequency for various reinforced concrete floor systems. They have been developed using fundamental principles

STRUCTURE magazine

April 2015

of dynamics. More information on their use, including worked-out design examples for commonly used reinforced concrete floor systems, can be found in the Design Guide for Vibrations of Reinforced Concrete Floor Systems (Fanella and Mota, 2014).▪ The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

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Structural ForenSicS investigating structures and their components

n the wake of a major retaining wall collapse, the New York City Department of Buildings (DOB) examined the condition of numerous retaining walls within the city’s boundaries and concluded there was a need for a regulation mandating periodic condition assessment of retaining walls. This article presents the ensuing local law that became effective in 2014. While several federal and state highway authorities require such inspections, this is the first such law enacted by a large municipality. It was developed based upon local experiences with periodic Figure 1. Collapsed retaining wall at Castle Village. condition assessments and concerns with the city’s high pedestrian and vehicular densities. DOT). Taken together, the findings demonUsually the introduction of such laws requir- strated the need for a proactive program. ing a new particular type of periodic condition It was not the particular causes of the May 2005 assessment induces some engineers and firms to collapse, but the findings revealed by the rapid specialize in such inspections. inspections that led the Board of Inquiry report to recommend: “The Department of Buildings should propose legislation to require owners to engage Accident a New York State licensed architect or engineer to On May 12, 2005, a 200- perform periodic inspection of retaining walls that foot section of a 65-foot high front a public way.” retaining wall collapsed over In conjunction with the American Society of a major New York City high- Civil Engineers (ASCE) Metropolitan Section, way (Figure 1). At that time, a city program of the Department organized meetings with leading surveying arterial retaining walls was already in local consulting engineering specialists – civil, place, but it covered only retaining walls under structural and geotechnical. The discussions the purview of city and state transportation agen- included the methods and findings of the inspeccies. The collapsed retaining wall was an 80 year tions, the classifications of retaining walls, and the old, privately owned, rubble wall. development of the most appropriate program to New York City has over 2,000 retaining walls, safeguard the public. most of which are owned by various governmental transportation and park authorities. This accident Local Law brought into focus the existence of a number of retaining walls that are inside private lot lines The DOB drafted a proposed rule to address and, as such, are privately owned. The New York the concerns of the Board of Inquiry. Following City Building Code had provisions that placed public hearings, a rule mandating periodic the responsibility for wall maintenance on private condition assessments of retaining walls was owners, but it did not set specific mandates for adopted in 2013, i.e. the Rules of the City of professional reporting on their condition. New York (RCNY) 103-09. It covers all pubTo analyze the causes of the accident, a Board licly or privately owned retaining walls within of Inquiry was established by the DOB. The the city limits that front a right of way and are Department also proceeded to survey the taller than ten feet. Basement walls and vault condition of privately owned retaining walls. walls that are part of a building, underground Using an ad-hoc inspection methodology for structures and swimming pools are exempt. rapid assessment, a large number of walls were As recommended by the Board of Inquiry, the evaluated. The rapid inspections revealed many rule uses as a model the New York City façade conditions that required maintenance or repair inspection local law. It lists the requirements (Figures 2, 3 and 4 , page 20). Several walls for wall specific assessment programs and report had to be immediately stabilized. It became content. The law defines and allows only four clear that the stock of retaining walls, mostly categories for evaluation – “Safe”, “Safe with dating from the first half of the 20th century, Maintenance and Repair”, “Safe with Repair was showing signs of aging and neglect. Poor and Engineering Monitor”, and “Potentially conditions also had been identified in a previ- Unsafe”. A registered professional engineer with ous survey of arterial retaining walls performed three years of specific experience is deemed by Gandhi Engineering, on behalf of the New qualified to perform the inspection and make York City Department of Transportation (NYC all technical evaluations.

Periodic Inspection of Retaining Walls By Dan Eschenasy, P.E., F.SEI

Dan Eschenasy, P.E., F.SEI, is the New York City Buildings Department Chief Structural Engineer. He is a member of the ASCE Structural Assessment of Buildings Committee.

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

18 April 2015

Figure 2. Cracked and leaning retaining wall brick veneer.

The requirement to inspect only retaining walls fronting public right of ways is similar to the text of the façade inspection Local Law 10 of 1980. (As an aside, this local law was later expanded in 1998 by Local Law 11 to include all sides of a building). As a consequence of the city’s extreme pedestrian and vehicular traffic densities, the ratings focus on the urgency to protect and to mitigate. The rating categories do not allow for differentiation based upon severity or extent of deterioration. The condition assessments are required to occur on a five year cycle, with the reporting staggered by boroughs. The first phase is now in progress. It is expected that, aside from providing a higher level of safety, this first cycle of reporting will help increase the accuracy of the inventory of walls and help establish a solid baseline for future cycles. A potential complication is the fact that many retaining walls extend over several lots and, as a result, the responsibility for maintenance and repair is shared by different owners. If these adjoining owners chose different professionals to assess, the repair recommendations may differ and may create the need for conflict resolution.

The experience gained with the façade condition inspection Local Law 10 provided a strong basis for formulating the retaining wall inspection program. Deterioration of a retaining wall’s face, similar to the deterioration of a building’s façade, may be the result of extended exposure to adverse weather conditions. Many symptomatic conditions indicating potential hazards – delamination of concrete, corroded reinforcement, missing mortar or cracking of stone units, etc. – are

common to both facades and retaining walls. This is especially true when the face of the retaining wall is only an architectural veneer of thin stone or brick. The façade local law had demonstrated that a five year cycle of inspection is effective for observing advances in material weathering and such periodicity was thus maintained. Even in the absence of original drawings or design criteria, an inspector can discern most changes from the façade’s original architectural aspects – deviations from vertical or horizontal positions, separations or gaps in the continuity of the envelope, unexpected departures from symmetry, etc. Such elementary observations might not be indications of disrepair when examining some types of retaining walls. Verticality, a benchmark for façade reliability, is not necessarily a given for retaining walls as they might have originally been built with a batter. Not all masonry retaining walls have regular coursing. Dry retaining walls might have been originally built with gaps between stones. Many, if not most, of the structural features ensuring the safety and serviceability of a retaining wall are not visible from the outside, e.g., condition of tensile reinforcement in concrete walls, condition of soil anchors, condition of fill to allow water drainage, depth of embedment of foundation base, and thickness of wall stem. Because inspections of retaining walls, especially older ones, have to overcome a high level of uncertainty, the law makes clear that this assessment cannot be merely visual. “The methods used to assess the retaining wall in question must permit a complete condition assessment of the wall, including, but not limited to, selective probes, cores and measurements of wall dimensions, including, but not limited to, thickness.” Collectively, these, together with other

STRUCTURE magazine

April 2015

reporting provisions (e.g. providing wall sections), insure that a baseline for future inspections is created. Facades and retaining walls have different functional purposes, and the mitigation of their potential failures is usually different. A distressed façade condition might reveal the potential risk that some of its constitutive elements will fail and fall. In the vast majority of cases, the public can be safeguarded by the installation of temporary protection, typically a sidewalk shed that will be in place until the condition is remedied. Some distressed conditions of retaining walls may indicate the potential of failures that could include the collapse of large wall segments together with the retained soil. The forces in play are such that simple interventions, such as the installation of sidewalk sheds, might not be sufficient to safeguard the public. As a consequence, the category “Safe with Repair and Engineering Monitor” was introduced to designate the cases where “a retaining wall is found at the time of assessment to be safe but requires repair within the next five years to correct minor to severe deficiencies in order to

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Correlation with Façade Local Law

Figure 3. Leaning segment of retaining wall.

minimize or delay further wall deterioration and to remain safe.” This rating applies to walls that require repairs and provides a differentiation from walls that require only maintenance work. The completion of the repairs indicated in conjunction with this evaluation has to be certified by the inspecting engineer and cannot be postponed to a subsequent cycle. The rating also can be applied to walls that are deemed safe at the time of the inspection, but have some features that require the inspector “to regularly monitor and/or investigate further the retaining wall to determine the nature or cause of observed distresses and what action may be required.” This monitoring needs to be performed by the responsible engineer following a clearly detailed plan. The stability of the walls in this category has to be demonstrated by an analysis which reports a factor of safety.

Other Programs of Condition Assessment

Figure 4. Severe crack in stone retaining wall.

About the same time that the RCNY 103-09 was being developed in New York City, the Federal Highway Administration and the National Park Service were collaborating to launch a Retaining Wall Inventory and Condition Assessment Program (WIP). Compared with the RCNY 103-09, the WIP program uses a wider definition of retaining walls as it also includes structures such as culverts, slope revetments and sea walls. This procedure uses a numerical condition rating system from 1 to 10 for the wall elements and a separate Wall Performance rating that refers to the overall functionality of the entire wall and the relational performance of different components. The numerical systems can be interpreted as “Excellent” (rating 9 or 10), “Good”, “Fair”, “Poor”, and “Critical” ratings. The WIP manual provides specific and systematic instructions for what elements to observe, together with a summary guidance on grading. The final rating is based upon the aggregation of the various element and wall ratings, including the reliability of observations. The “appropriate wall action” is decided based on considerations that involve the final rating, the consequences of wall failure, the reliability of engineering of the original design and the need for additional investigations. The possible outcomes are (in order of importance): “No Action”, “Monitor”, “Maintenance”, “Repair Elements”, “Replace Elements” and “Replace Wall”. The “Critical” rating indicates a high severity of distress and is an indication that the “wall is in imminent danger of falling catastrophically, requiring… the roadway be closed.” The WIP recommends an inspection

cycle of ten years maximum. Shorter cycles should be used for some particular wall types or for walls that have lower prior ratings. An example of a slightly different inspection program is the Gandhi arterial highway retaining wall condition assessment program that started in 1999. Prepared for a transportation authority (NYC DOT), the program was derived from this authority’s long experience of periodic road and bridge inspections. It uses ratings from 1 to 7, as recommended in the New York State Department of Transportation (NYS DOT) Bridge Inspection Manual section for retaining walls that adjoin abutments. The inspectors are expected to evaluate general stability indicators, wall elements (e.g. exposed faces, weep-holes) and structural deterioration. The numerical condition rating is translated into “Poor”, “Fair”, “Good” and “Very Good” categories. These four categories represent an indication of the need and urgency of repairs. The “Poor” condition rating is intended for walls requiring close monitoring or immediate action, and triggers a detailed evaluation. Some of the experience gained with this program was used in the creation of RCNY 103-09, which in turn influenced later NYC DOT inspection methodology. The WIP and the Gandhi programs require reporting that is for the benefit of governmental agencies with the purpose to maintain public safety, and also to budget and schedule repair or replacement construction work. These reporting methods, employing numerical ratings, have a large number of evaluation categories and thus allow for a more refined

STRUCTURE magazine

April 2015

classification. The RCNY 103-09 relies on evaluations made by engineering practitioners that are experienced in the use of industry standards. The RCNY 103-09 is intended for various types of owners, including private property owners who might not have a technical background and, as a consequence, provides categories that are expressed in terms that make clear when an owner’s property poses potential risks to the public and when it is in need of repair. Due to the extraordinary traffic density in New York City, any potential risk to the public needs to be abated, irrespective of the severity or extent of the deterioration. As a consequence, the RCNY 103-09 incorporates within the category “Safe with Repair and Engineering Monitor” conditions that reflect concerns regarding wall stability as well as face deterioration. The RCNY 103-09 also gives a higher consideration to potential changes in loading conditions, especially those resulting from rapid water accumulation, a factor associated with several wall collapses. The RCNY 103-09 requires the assessment of the adequacy of the entire water management system around walls, and not only the proper functioning of weepholes. An interesting review of various other retaining wall inspection programs can be found in National Cooperative Highway Research Program (NCHRP) Project 20-07, Task 259. In essence, the RCNY 103-09 is focused on the urgency of action to protect the public while the WIP and the other similar programs include detailed prescriptions of the methodology of condition assessment.

Conclusions The fact that during the past fifteen years several programs of systematic inspection of retaining walls have been developed indicates that various authorities have recognized a new domain of public protection. It will take several cycles to determine the advantages of each program and what adjustments or improvements these programs may need. It is quite likely that, in time, these programs will influence each other. The New York City 1980 law, requiring periodic inspections of facades, led some engineers to develop specific expertise and to form companies offering these specific services. Several other cities have followed New York City’s example and have enacted similar façade inspection ordinances. One can expect the New York City retaining wall inspection law will have similar effects as more jurisdictions realize the potential risk posed by an aging stock of retaining walls.▪

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Building Blocks updates and information on structural materials

esigners dedicated to restoring ecosystems and enhancing social conditions through the built environment know that wood can contribute significantly to this aspiration. Although timber used as structural elements in taller buildings is not a new concept, it has been largely abandoned as a solution in favor of other materials. Projects around the world are demonstrating the potential of engineered, mass timber products as structural elements for tall buildings, and wood is re-emerging as a viable and beneficial option. Learning from the experiences of early adopters in the industry is essential for building capacity, credibility and market acceptance for tall wood buildings. In the fall of 2013, the Survey of International Tall Wood Buildings (the Survey) was conducted with the goal of collecting lessons and experiences from built projects. The aim is to share this information with potential North American project stakeholders to help simplify processes, increase comfort, and potentially lower the risk of designing tall wood structures, ultimately broadening the uptake of wood systems used in tall construction. The Survey included ten completed projects around the world (see Table), and focused on gathering lessons and experiences from four stakeholder groups: Owners/Developers, Design Teams, Construction Teams and Authorities Having Jurisdiction (AHJ). The Survey methodology included a short, online questionnaire followed by a more in-depth, in-person or telephone interview.

Overview of the Survey of International Tall Wood Buildings By Eric Karsh, M.Eng, P.Eng, StructEng, MIStructE and Rebecca Holt, M.Urb, LEED AP BD+C, ND Eric Karsh, M.Eng, P.Eng, StructEng, MIStructE, is a founding principal of Equilibrium Consulting Inc., a structural engineering consulting firm located in Vancouver, BC. Eric is co-author of the Tall Wood report, and was senior technical advisor for the Survey of International Tall Wood Buildings. He can be reached at ekarsh@eqcanada.com. Rebecca Holt, M.Urb, LEED AP BD+C, ND is a Senior Sustainable Building Advisor and researcher with Perkins+Will’s Research team. Rebecca was the lead researcher and primary author of the Survey of International Tall Wood Buildings. She can be reached at rebecca.holt@perkinswill.com.

Project Name

Location

Cenni di Cambiamento. Architecture by ROSSIPRODI ASSOCIATI srl. Courtesy of Riccardo Ronchi.

Researchers also conducted site visits for nine of the ten surveyed projects. This work offered a unique opportunity not only to learn from specific project experiences, but to cross reference results, aggregate information, and identify trends. The work focused on discovering the rationale for pursuing structural wood solutions and lessons about design processes, construction processes, approvals, and unique aspects associated with delivering a tall wood project. What follows are a few highlights of the results describing the range of design solutions applied across the surveyed projects, followed by best practices for navigating approvals.

Building Type

Stories

Wood Construction Type

Completion Date

Berlin, Germany

Commercial/ Residential

Post and Beam

2008

Vaxjo, Sweden

Residential

Panelized

2009

Bridport House

London, England

Residential

Panelized

2010

3XGRÜN

Berlin, Germany

Residential

Combination Panels/ Post and Beam

2011

Holz8 (H8)

Bad Aibling, Germany

Commercial/ Residential

Panelized

2011

Forté

Melbourne, Australia

Commercial/ Residential

Panelized

2012

University of British Columbia Earth Sciences Building

Vancouver, Canada

Institutional

Combination Panels/ Post and Beam

2012

LifeCycle Tower One

Dornbirn, Austria

Commercial

Combination Panels/ Post and Beam

2012

Zurich, Switzerland

Commercial

Post and Beam

2013

Milan, Italy

Commercial/ Residential

Panelized

2013

E3 Limnologen

Tamedia Cenni di Cambiamento

22 April 2015

CONSTRUCTION CEMENT

FA S T ER STRONGER MORE DURABLE 3000 PSI IN 1 HOUR 3XGRÜN. Architecture by Atelier PK, Roedig Schop Architekten and Rozynski Sturm. Courtesy of Stefan Mueller.

All panel systems are generally favored for residential construction, while a combination of post and beam and floor panels is favored for institutional and commercial space – likely because post/ beam offers a more open floor plan that can be reconfigured easily. Panels provide a more compartmentalized layout, well suited for residential. Where a combination of structural systems and materials were applied (concrete, steel, glass, mass timber), complexity and the overlapping of trades impacted the schedule. Designers indicated that detailing interfaces between

Holz8 (H8). Architecture by SHANKULA Architekten. Courtesy Huber & Sohn.

materials was exceptionally time consuming, owing in part to the variation in tolerances between materials. Simplified solutions and approaches were pursued to mitigate this effort. Among the projects surveyed, lateral stability is achieved through either a concrete core or Cross Laminated Timber load bearing walls, some reinforced with steel tie-down rods. The Earth Sciences Building with exposed, ductile heavy timber chevron bracing, is the only exception. Connection solutions are unique in almost all project examples, although solutions appear to be evolving and focusing quickly. Early projects struggled with complex steel connections between wood elements as well as wood-concrete connections. More recent buildings focused on simplifying design details to better support modular prefabrication, assembly, and building configuration. Pure timber connection strategies also vary and appear to be evolving quickly. Each surveyed project has a unique solution to avoid compression perpendicular to grain at horizontal joints; however, self-tapping, angled screws appear to be emerging as an economical and reliable strategy to secure joints, along with steel plates as a tie down method. Team members for projects that used concrete cores all emphasized that use of precast concrete panels accelerates the construction schedule and maintains a dry site. Of the projects that used cast-in-place concrete for the core, almost all of the schedule savings afforded by other prefabricated components were lost due to long curing time. continued on next page

STRUCTURE magazine

April 2015

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Design Solutions

Envelope: Moisture Protection and Durability Generally, design teams did not perceive moisture as a major risk. In all cases, any exposed structural wood elements were either inside the building envelope, protected by an overhang or, in the case of cantilevered panels, exposed only on the underside. In two cases, moisture sensors were installed to monitor envelope performance as part of ongoing operational research projects.

Fire Protection Fire protection strategies varied depending on authority requirements, and a range of solutions were implemented across participant projects. In all cases, fire testing was conducted in collaboration with research institutions or other industry partnerships. Strategies included oversizing timber elements (where required) to include a char layer, in addition to encapsulating timber with gypsum to some degree. Sprinkler systems and intumescent paint applied to exposed timber were also common fire protection strategies, although not consistently required or applied across projects. Most projects chose not to install wood cladding on the exterior, and opted for non-combustible façades; where wood façades are used, fire protection strategies were more challenging and complex. Generally, designers indicated that solid timber products supported good fire protection given that open spaces in wall assemblies were limited or eliminated.

Best Practices for Navigating Approvals Navigating the approvals process is identified as one of the most significant challenges with advancing mass timber systems for tall buildings. Of the projects included in the Survey, none of the local jurisdictions explicitly recognized mass timber systems in building codes, and all facilitated some form of ‘Alternate Solutions’ process. Every participant project experienced a different approvals process based on existing codes, degree of market acceptance for mass timber as material for taller buildings, and varying regulatory policy, but they all emphasized the importance of collaborating with authorities early to establish methods of compliance and methods of testing. Of the ten participant projects, only one approval pathway was already established (3XGRÜN), owing to the E3 project completed a few years earlier in the same

UBC Earth Sciences Building. Architecture by Perkins+Will. Courtesy of Martin Tessler.

jurisdiction. All other projects were the first to overcome code barriers and challenges successfully. Participants identified three important strategies: • Start educating the authority when you start educating yourself. Share information, expertise and engage local authorities by inviting them into the discourse, providing them with credible industry resources, and engaging them in research. • Establish an acceptable method of compliance as early as possible with the AHJ, to allow the team to plan for testing and account for extra time associated with creating a new path to approvals. • Plan for on-site inspections by the authority during construction. The Survey results confirm that where authorities were able to visually inspect assemblies and observe construction process and quality, their level of comfort increased and sense of risk decreased. In some cases, authorities deemed multiple fire protection strategies redundant and allowed a revised, less onerous approach.

Tamedia. Architecture by Shigeru Ban Architects. Didier Boy de la Tour.

STRUCTURE magazine

April 2015

Conclusions The Survey results highlight that a range of design and construction techniques can be successful, and that they are still evolving to respond to the varied code requirements, market demands and expectations, climates and regulatory conditions, and lessons learned from earlier projects. To build more momentum and support for built examples in North America and around the world, a clear lesson from the Survey is that a deeply integrated and collaborative process between all design disciplines, fabricators, research institutions and regulatory bodies is essential. The breadth of design considerations necessitates a greater blending of professional roles across teams working on tall wood buildings; for instance, structural engineers must be concerned with acoustics, vibration, fire, and aesthetic performance of exposed structural building elements, where these issues are not typically integral to design considerations of more established structural systems. Working closely with other design disciplines, fabricators, researchers, and authorities at all project stages will be essential to advancing successful examples of tall buildings with solid timber structural elements. Forestry Innovation Investment (FII) and the Binational Softwood Lumber Council (BSLC) engaged Perkins+Will, with Equilibrium Consulting Inc., to conduct the Survey. For more details and to access the Summary Report for the Survey of International Tall Wood Buildings, please visit www.rethinkwood.com/tall-wood-survey.▪ Disclaimer: The Summary Report was developed by a third party and is not funded by reThink Wood or the Softwood Lumber Board.

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εcu

c d

εt

C N.A.

N.A.

T = Asfy

Figure 1. Strain and stress diagrams for concrete beam for strength design.

C = 0.85f ’c(ab)

c/3

ngineers largely appreciate the differences afforded between allowable stress design (ASD) and ultimate strength design (LRFD) methods, and we generally follow the prescribed protocol for each procedure without much trouble. However, even though the ASD approach has been largely supplanted by LRFD, certain occasions require that we revisit the old ASD theory for reinforced concrete (or masonry). As such, it is appropriate that we recognize the subtle and not-so-subtle differences between the two. Strength design for reinforced concrete has been the norm for many years. Its basic premise is that we design for a specific failure mechanism in the element and ensure that it is ductile. We commonly assume (among other things) that reinforcement yields and concrete crushes, preferably in that order. With this concept in mind, we can readily apply yield and crushing stresses to the steel and concrete, respectively, and develop overall capacity boundaries and limitations. We also apply load and strength reduction (φ) factors to the design to ensure that the likelihood of breaching said boundaries and limitations is acceptably small. The current strength design methods are a far cry from the previous working stress design approaches used for reinforced concrete. We no longer need to calculate depths to neutral axes based on transformed sections, nor do we need to use the parallel axis theorem to calculate a cracked moment of inertia. However, these traditional design approaches must still be examined as we look at serviceability. The actual failure mechanism of the member is an extreme condition that is not easily adapted to ordinary serviceability conditions. Hence, strength design methods are not well-suited to addressing serviceability issues, since the goal of the latter is not to predict how much deformation will occur in steel as it actually yields or in concrete as it is actually being crushed. Working stress design methods typically use the same load combinations for strength and serviceability, but we must often develop two concurrent combinations, one set for strength design and another for serviceability, when using contemporary methods. A potential error in the design of reinforced concrete is to mismatch design values and/or section properties between strength and serviceability design methods. An example of this is the depth to the neutral axis of a reinforced concrete beam,

Figure 2. Serviceability stress diagram.

often assigned the variable c. For strength design, this occurs where the strain is zero when assuming a positive (compressive) strain of 0.003 (εcu) for the concrete on the top side, the net tensile strain (εt) in the rebar at the bottom side, and linear variation between them. The value of c is calculated by using similar triangles. The stress diagram to complement this is then easily derived from the assumed concrete crushing capacity and reinforcing steel yield strength, as shown in Figure 1. For serviceability design, strain may not necessarily be a consideration, but the stress diagram is taken as that shown in Figure 2. This would apply to both a serviceability limit state, for calculating cracked and effective section properties, and the maximum working stresses in the concrete and reinforcement, used to assess strength in the older methodology. For this diagram, the relationships are derived using transformed sections and assuming elastic behavior. As an example, consider a 12-inch wide by 18-inch deep concrete beam (f'c = 4,000 psi) reinforced with three #6 bars (fy = 60,000 psi). Assuming that the span exceeds the limitations of table 9.5(a) in ACI 318-11, the strength design must be accompanied by a check for serviceability (deflection). For strength design, the depth to the neutral axis (c) is 2.28 inches. For serviceability, the depth to the neutral axis is nearly double this, at 4.51 inches. Hence, for valid design, the engineer must be cognizant of which limit state is under consideration (strength or serviceability). In addition, the correct application of equations must accompany the method being used. Derived values between the approaches must never be interchanged. Interestingly, leading textbooks often assign the variable c as the depth to the neutral axis regardless of design consideration (strength vs. serviceability), hence the potential for confusion. In actuality, the behaviors reflected in the compared numerical models of the flexural mechanism are vastly different, one corresponding to the ultimate flexural failure of the member, the other to the stresses that may develop under normal service loading. One addresses behavior as the flexural strength threshold is breached, the other behavior that affects the comfort of the occupants that it supports.▪

STRUCTURE magazine

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

Concrete Beam Strength vs. Serviceability

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.

Rural Philippine Shelter Construction

Structural Engineering Challenges By Gustavo Cortes, Ph.D, P.E.

ho would have thought that designing a 10-foot (3 meter) by 13-foot (4 meter) structure would present so many unique challenges? The structure, a single family shelter, seemed very straightforward at first; however, a field visit to Leyte Island in the Philippines proved otherwise. The task was to develop structural drawings for a shelter unit that is being provided to the most vulnerable victims of super typhoon Haiyan. Nearly 1,080 units are to be built by July 2015. This article presents some of the challenges encountered, including anticipation of load conditions, availability of materials, and quality of materials received. On November 8, 2013, super typhoon Haiyan hit the Philippines, devastating the Visayan Islands in Central Philippines, particularly the islands of Samar and Leyte. The super typhoon, locally known as Yolanda, had winds exceeding 190 mph (300 km/hr), making it equivalent to a hurricane Category 5 on the Saffir–Simpson hurricane wind scale. The strong winds and rain brought flash floods, landslides and immense destruction. This mega storm killed more than 6,200 people, damaged 1.1 million homes, and left some 4.1 million people displaced (USAID, 2014). Several non-governmental organizations (NGOs) mobilized personnel to help restore the community. Medair, a Swiss based NGO, rapidly responded to the humanitarian crisis by reaching out to remote and rural communities that had not received assistance. Medair found almost total devastation in the Dulag municipality, 19 miles (30 km) south of Tacloban. The typhoon had damaged or destroyed 9,004 houses (81% of all homes); leaving approximately 44,000 people, out of a population of 53,883, displaced from their homes (Medair, 2013). Medair’s shelter construction project is now underway. After an assessment of the needs and the living habits of the local population, architects from Medair rapidly developed a prototype shelter. Figure 1 shows elevation views of the structure in its first phase. Initially, the unit is enclosed by means of a tarp, allowing for immediate occupation and future expansion. This initial phase provides 129 square feet (12 square meters) of living area; however, the owners could increase its size to 301 square feet (28 square meters) as their income allows. This can be accomplished by adding two rooms, one on each side of the house. Once the main concept was developed, the structural design started. Fundamental principles of design for high-seismic and high-wind loads were followed. Many aspects of the design and construction had unique challenges. These are discussed next with the intention of helping the readers understand challenges encountered when designing relief structures in undeveloped regions.

Figure 1. Shelter elevation views.

considered. First, because of potential flood exposure in many locations, the floors were not on the ground as initially thought; instead they were attached to columns. What was really worrying was the fact that, given the approximate 13-foot clear height of the roof ridge, and the floors often being placed at around mid-height of the columns, a two-story house was basically created. This produced a significant deviation from the original design, increasing the load on the columns. Secondly, with regard to seismic loads, what was initially thought to be a lightweight structure with insignificant mass, coming mostly from roof dead loads, now became a structure with a mass at the elevated floor location as well. Another unique aspect of the loading conditions was created by the enclosure used for exterior walls. The initial phase included the distribution of a tarp to be placed around the shelter to provide protection against wind and rain. Accordingly, the lateral-force resisting system was designed to withstand the forces generated by the wind pressures acting on the membrane. Several houses visited, however, had not used the provided membrane and were instead using a locally produced thin fabric called Amakan. This fabric is made by weaving bamboo strips at 90 degree angles (Figure 2). These fabrics have large gaps between the bamboo strips, which allow for wind to flow through the shelter. This membrane is also very likely to let water enter the shelter even during moderate winds. Under high wind pressures, the Amakan fabric will possibly fail, allowing wind to flow through the

Anticipation of Load Conditions Several complications arose when determining the design loads for the shelters. First, the National Structural Code of the Philippines: NSCP Volume 1 (ASEP, 2002), was used to determine the design wind loads. These were compared to ASCE 7 (ASCE, 2010) and results were very similar. The unique challenge here was to obtain the NSCP and to learn how to implement it. Once the design was nearly completed, a visit to similar relief shelters built in the region revealed two new issues that had not been STRUCTURE magazine

Figure 2. Amakan fabric used for siding.

April 2015

Adjusted strength values.

Strength Value No. 1 Radiata Pine Southern Pine % (LRFD) Framing (psi)1 No. 2 (psi)2 difference F*bn

928

2591

94.5

F*tn

371

1426

117.4

F*vn

353

302

15.6

F*cn

1392

2851

68.8

Design values account for a strength reduction factor (φ) of 0.8 for timbers and a duration of load factor (k1) of 0.8 for medium duration loads (live load). Note that base values are given in LRFD format. These values are based on New Zealand’s design code (NZS, 1993).

Figure 3. Local coco lumber supply.

2 Design values account for the corresponding format conversion factor (KF), resistance factor (φ), and assume a time effect factor ( λ ) of 0.8 for the load combination of 1.2D + 1.6L (occupancy).

shelter, reducing wind pressure on the main lateral-force resisting system but increasing the pressure at roofing elements. The solution, if all the scenarios are to be considered, is to design the lateral-force resisting system for the maximum loads coming from the full wind pressure, when the structure is enclosed, while the roof should be designed to withstand uplift from an open structure.

of No. 2 Southern Pine for a 2x4 section. Note how the difference can exceed 100%. Although this point may seem obvious, verifying other designers’ calculations for overseas shelters, on two different occasions, revealed the use of design properties from a typical USA species group/grade even though the wood used was a local wood with significantly different properties.

Availability of Materials

Quality of Materials Received

Coco lumber is a natural resource widely available in the Philippines. It is extensively used for housing construction in rural areas because of its availability and relative low cost. An extensive amount of coco trees fell during super typhoon Haiyan, increasing the supply of this inexpensive material. Figure 3 shows a typical coco lumber supplier found by the side of a major road in Tacloban. However, coco lumber requires careful processing and strict quality control for it to serve as structural lumber. Untreated coco lumber exposed to weather is very susceptible to fungi and termites, which can destroy the hard portion of the trunk in less than 2-3 years and the soft portion in just a few months (Arancon, 2009). Although treatment would increase its life span, treated coco lumber was not readily available in the region. Furthermore, available coco lumber from local supplies varied greatly in dimensions and density. Much of it was cut using chainsaws, resulting in uneven pieces of lumber. Given the uncertainty of the quality of the coco lumber found, it was not used for structural elements. However, in order to promote the local economy, coco lumber was specified for non-structural elements that will not be directly exposed to the weather. It is important to aid the local economy as much as possible without compromising the structural integrity of the shelters. The construction managers consulted several suppliers in the region and decided to import treated No. 1 Grade Radiata Pine framing from New Zealand. This wood species is not included in the National Design Specification® (NDS®) for Wood Construction (AWC, 2012), normally used for design of wood structures in the United States. Thus, the New Zealand timber construction standard, NZS 3603 (1993) had to be consulted to find the design strength of these species. Upon inspection, it was found that the strength value given does not include the same adjustment factors as the US design specification. Thus, these strength values could not be applied directly in the NDS member strength equations. Instead, strength values were adjusted according to New Zealand’s design standard. It would be erroneous to assume the properties of the lumber used, based on a typical grade of species group normally found in the USA. As an illustration, the Table compares the adjusted strength values, ignoring stability, for No. 1 Radiata Pine framing with those

Another challenge was to obtain materials with the requested quality. Often the material received was substandard. One example is the requested marine plywood, which ended up being regular interior plywood whose product name was marine plywood. Another example is the wire used to tie purlins to rafters, which corroded in a short time after installation because the galvanization was inadequate. To complicate things further, nails provided did not follow the same dimensions as those in the United States, but they were instead a little shorter. For example, a 16D common wire nail in the US has a 3½ inch length. In the Philippines, nails provided were often only 3 inches long. This was solved by specifying the required length and diameter of the nails.

STRUCTURE magazine

Conclusion The intentions of this article are to share the experience encountered when designing a transitional shelter in an undeveloped region of the Philippines, and to raise awareness for future relief projects. It is crucial for a design team to research and anticipate many of these challenges before finalizing the design phase, in order to better serve these communities. An early site visit is necessary since it can potentially reveal any challenges and possible solutions to those challenges. This relief effort is currently underway with 1,080 units to be built by July 2015. The aspects discussed in this article were taken into account, and included in the construction plans and documentation currently used by the construction crews. This project is a great example of how the structural engineering profession can help underserved communities.▪

Gustavo Cortes, Ph.D, P.E., is an Assistant Professor of Civil Engineering at LeTourneau University. He may be reached at GustavoCortes@letu.edu. The online version of this article contains detailed references. Please visit www.STRUCTUREman.org. April 2015

Parkway 301 P

Adaptive Reuse of the Shenandoah Building

By Eric R. Ober, P.E., S.E. and Robert P. Antes

arkway 301, formerly the Shenandoah Building, is a transitional masonry structure located in the Downtown Historic District in Roanoke, Virginia. The seven-story building, originally constructed in 1910 and vertically expanded in the early 1920s, had office occupancy over ground floor retail since its opening. Recently, the building was adapted to house ninety residential apartments on the upper floors over renovated ground floor retail space. Insufficient documentation of the existing construction in adaptive reuse projects challenges designers and contractors. In the case of the Parkway 301, hidden conditions overwhelmed all other structural challenges of the project.

Project Background Roanoke is located in the southwest portion of Virginia and is the state’s eighth largest city. Its population grew substantially in the first half of the twentieth century. A number of the buildings of this time period in the Downtown Historic District remain standing and have undergone renovation in recent years. Parkway 301 is among the most recent (Figure 1). The building was initially constructed in 1910 as a rectangular three-story reinforced concrete office building over a one-story basement. The footprint is approximately 120 by 95 feet. In the early 1920s, the Shenandoah Life Insurance Company

purchased the building and commissioned a four-story steel-framed vertical expansion with a U-shaped plan opening to the south (Figure 2). The west, north, and east wings surround a central light well which occupies a footprint of 40 by 40 feet. Exterior masonry walls are primarily composed of brick and terra cotta, and infilled tight to the concrete and structural steel frame. This type of wall construction was common in buildings of the early 1900s, where designers intended to maximize the usable interior space and relied on the erroneous assumption that masonry construction was effective waterproofing for the embedded structural framing.

Project Description The building remained largely unaltered until purchased by Chapman Enterprises Inc. in 2012. Chapman retained the project architect, Baskervill, to design an adaptive reuse of the building to include ninety residential apartments on the upper six floors over ground floor retail space. Baskervill engaged Simpson Gumpertz & Heger Inc. to provide structural engineering services for the project. The major structural components of the renovation initially included a new full height interior egress stair (basement to seventh floor), reconstruction of the interior lobby slab inside the building to meet ADA requirements, lowering portions of the basement slab to create adequate headroom for tenant amenity use, and demolition of portions of the third and fourth floors to extend the light well into the original 1910 construction to accommodate additional apartment units. Field Investigation Figure 2. Parkway 301 (then The Shenandoah Building) during 1920s vertical expansion.

STRUCTURE magazine

Drawings for the building were non-existent. The existing building construction was extensively investigated while still partially occupied.

April 2015

Figure 3. Draped mesh slabs and steel-lumber joists at upper levels.

Readily-visible components were measured and hidden structural members were probed at representative locations. Due to the age of the existing structural steel, weldability could not be presumed by default. Samples were retrieved from columns and beams and tested with the finding that the steel is consistent with ASTM A36 in terms of metallurgy and thus easily weldable. The 1910 construction is framed with one-way composition slabs (reinforced concrete ribs between clay tile fills) spanning between reinforced concrete beams and columns. The 1920s vertical addition has steel columns stacked over the existing concrete columns below, with the exception of three columns. Three upturned east-westspanning transfer girders at the fourth floor carried the loads of the three offset columns above to the existing concrete columns below. The girders, encased in brick, penetrated the building envelope into the light well such that each girder was located on the interior and partially on the exterior. The presence of some unusual structural assemblies complicated structural analysis of the existing framing. Concrete slabs and beams at the 1910 construction are reinforced with Kahn bars, developed by Julius Khan and patented in 1892. These bars were rolled in various sizes with a diamond-shaped center and horizontal projecting flat plate wings. The projecting plates were cut free from the core in a regular pattern and bent upwards at 45 degrees so that the bars served as both flexural and shear reinforcement. At the 1920s construction, draped mesh concrete slabs are supported by steel-lumber joists at close spacing, which span between structural steel girders. The name is a misnomer as there is no “lumber” in these joists. They are composed of back-to-back cold-bent C-shaped steel sections (similar to modern cold-formed steel studs) and were introduced to be a component of light framed floor systems economical in situations where wood joists were traditionally employed (Figure 3). Asbestos-laden materials hindered completion of all of the desired probes (including those at the existing upturned transfer girders). With no visually apparent signs of structural damage or excessive deflection, further probing was deferred to the construction phase.

comprised of angles and plates. Where the girders penetrated the building envelope near midspan, long-term water infiltration substantially corroded the steel resulting in areas of full section loss of the web and partial section loss of flanges (Figure 5). Along the south side, the soffit of each of the concrete spandrel beams across the width of the light well and into the adjacent bays had severe spalling and moderate reinforcement corrosion. Steel lintel angles over the punched window Figure 4. Severely cracked concrete openings in the south wall were beam at north side light well. severely corroded.

Response The contractor halted construction while the newly exposed existing conditions were evaluated by the structural engineer. Each of the conditions was determined to require repair intervention. The need for temporary shoring was unclear since there was no visually apparent deflection of the structure; however, the steel girders were believed to be marginally stable based on the extent of corrosion damage. The structural engineer undertook a series of structural analyses to evaluate the effects of measured steel girder corrosion on building temporary stability, including consideration of potential alternative load paths (such as Vierendeel frame behavior of the supported structure above). No structurally adequate load path was identified. Temporary shoring of the structure supported by the transfer girders was installed to maintain building stability while permanent repair options were contemplated. After the building was shored, the contractor resumed construction in unaffected areas.

Repairs The concentration of structural deterioration challenged the designers and contractors to work together to develop the most efficient approaches to resolving and repairing the damage. At the north side of the light well, there was adequate headroom to enable

Discovery While non-structural demolition was underway, the general contractor uncovered significant hidden structural damage around the perimeter of the light well at the fourth floor. At the north side, two concrete beams, carrying heavy masonry walls and spanning the width of the light well, were found to have wide full width diagonal cracks at their supports (Figure 4 ). Along the west side, the upturned transfer girders were uncovered and found to be riveted built-up steel sections STRUCTURE magazine

Figure 5. Severe deterioration of steel transfer girder.

April 2015

installation of new steel beams below both of the damaged concrete beams. The south spandrel beam damage was the result of poor construction quality (inadequate reinforcement cover) but had not resulted in significant steel section loss for the Kahn bars. Conventional concrete repairs were implemented. The most serious structural concerns were with the three steel transfer girders. The range of steel girder repair options considered included repair in place, elimination of the transfer by adding new columns to new foundations, and replacement of the transfer girders inside the enclosed portions of the building. Repair in place was eliminated from consideration early. The original ill-conceived design concept of penetrating the building envelope could not be easily made more reliable. Extending new columns to new foundations was technically feasible but architecturally unacceptable in the first floor retail space. Thus the last option, new transfer girders inside the building, was implemented. At Parkway 301, substantial clear headroom was available below the second floor to accommodate the new girders. The final repair design consists of new structural steel transfer girders spanning directly below and parallel to the original transfer girders above, maintaining the original gravity load path to the foundations. Work included the following: • Erecting a pair of parallel wide flange girders below each transfer girder above. • Adding steel sections and post-installed anchors around the existing columns to receive the new girders. • Adding new columns to extend the transferred columns down to the new transfer girders. • Modifying the existing transfer girders to retain the interior portions (intimately anchored with the existing steel columns above) and eliminate those portions outside the building envelope.

• Partially pre-loading the new girders by hydraulically jacking prior to releasing the shores. Construction schedule was a significant consideration in the overall approach to the repairs. These repairs had to be completed before other schedule-intensive work, such as structural demolition at the light well, could be implemented. Project funding hinged on meeting occupancy goals established at the conceptualization of the project. The contractor worked with the design team to develop expedient details and, ultimately, the repairs were completed in a timely fashion to allow the overall project to meet critical deadlines.

Lessons Learned Hidden structural deterioration is commonly uncovered in renovation or adaptive reuse projects. In the case of Parkway 301, visual observations alone would have misled the design team into the erroneous assumption that “all is well”. Diligent investigation of existing conditions, regardless of the availability of drawings and often including destructive probing of representative hidden conditions, is always recommended. The success of the Parkway 301 project is a testament to the hard work of all parties involved and a team approach to achieving the Owner’s vision.▪ Eric R. Ober, P.E., S.E., is a Senior Project Manager at Simpson Gumpertz & Heger’s Washington DC office. Eric can be reached at erober@sgh.com. Robert P. Antes is a Staff II-Structures at Simpson Gumpertz & Heger’s Washington DC office and serves as the Project Engineer on all types of repair and rehabilitation projects. Robert can be reached at rpantes@sgh.com.

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Figure 6. Test area with overhead cranes.

ith an eye toward innovation and student collaboration, the University of Kansas (KU) School of Engineering wanted to significantly expand its scope of structural research. Opened in 2014, the Structural Testing Laboratory (Figure 1), located on the KU West Campus in Lawrence, is laying the groundwork for future innovation and offers one of the most advanced structural testing facilities in higher education. The 26,000-square-foot building is equipped with state-of-the-art instruments to accommodate full-scale systems and components and provide workshop spaces for student design and competition projects, as well as fabrication and machine shops.

Figure 1. Structural Testing Laboratory – KU West Campus.

STRUCTURE magazine

The principal element of the facility consists of a strong floor and strong wall system (Figure 2) constructed of cast-in-place concrete with a specified strength of 5,000 psi at 28 days. The strong floor, which provides 7,000 square feet of test area, is a 3-foot-thick slab supported by basement walls. A heavily reinforced mat slab (Figure 3) was designed as the foundation to support the strong wall and strong floor system. As a result, the strong floor, basement walls, and mat foundation slab form a four-cell box girder that is 15 feet deep, 48 feet wide and 145 feet long. To secure test specimens, the strong floor has vertical through-slab tie-down holes (anchor points) spaced at 3 feet on center in both directions (Figure 4), each tie designed for an allowable vertical load of 100,000 pounds in tension or compression. The 40-foot-tall strong wall – also called a reaction wall – is 4 feet thick and located at the east end of the strong floor, backed by 8-foot-deep buttresses spaced every 12 feet. Self-consolidating concrete and ASTM A416 Grade 270 post-tensioning tendons were used for both the wall and the buttresses (Figure 5), and the vertical reinforcing bars are ASTM A615 Grade 75. The strong wall is perforated with horizontal tie-down holes (anchor points), on the same grid as the strong floor, for the wall-mounted hydraulic actuators to apply lateral forces to the test specimens. The strong wall has an “L-shaped” profile, with two equal legs, to provide versatility for bi-directional testing. Each leg of the wall has a reaction area that is 36 feet long by 40 feet tall. The strong wall design provides an allowable lateral testing force of 880,000 pounds at each leg simultaneously, and thus an overall allowable lateral testing force of 1.76 million pounds. The strong floor and strong wall test area is equipped with two 20-ton capacity overhead cranes (Figure 6 ) to handle large and/or heavy test specimens, as well as hydraulic actuators and other equipment inside the laboratory.

April 2015

Figure 2. Strong floor and strong wall ISO. Courtesy of Burns & McDonnell.

Figure 3. Concrete mat foundation.

The key engineering challenge of the project was the strong wall, which is a performance-driven, highly customized element. From the design perspective, at the very earliest stage of the project, the structural team had numerous meetings with the end-user groups including the Dean of the School of Engineering, professors, researchers, and graduate students. It was critical to learn from these groups their expectations, needs, and intentions regarding the strong wall. Information from these meetings set the design goals for the structural team to achieve in a constructible and economical way. Because of the tremendous test forces to be placed on the strong wall, the design team and KU were concerned about potential cracking in the concrete surface. To address this concern, the design team performed concrete stress analysis utilizing computer software to determine the magnitude of the calculated stresses under various load combinations that were representative of different tests that could be performed. This identified “hot spots,” where the calculated tensile stress was greater than the allowable value. The next challenge presented to the structural engineer was how to reduce the high tensile stresses in a constructible manner. The solution was to place post-tensioning tendons in the vertical direction of the wall to introduce compressive forces. Once the design was complete, the strong wall also presented challenges from the construction perspective. The design criteria required a high-level concrete surface finish to satisfy both aesthetic and performance requirements. After further discussions with the construction contractor, the Kansas City office of Turner Construction, the team decided to utilize self-consolidating concrete for the wall. To ensure

Figure 4. Strong floor with tie-down sleeves.

achievement of the desired concrete finishes and structural qualities, Turner built a large-scale mock-up of the strong wall on the site and then cut it open to determine how the self-consolidating concrete had performed. The results passed inspections with flying colors. Turner also developed a robust system of formwork that was adequate to hold the fresh concrete in place. The $14.5-million facility has opened to positive reviews on campus. Research commitments are building, and KU’s structural labs will be fully committed by the time of this article’s publication according to Michael Branicky, the Dean of KU School of Engineering.▪ Jun Fei, P.E. (jfei@burnsmcd.com), is a senior structural engineer in the Global Facilities Group at Burns & McDonnell in Kansas City, Missouri.

Project Team Owner: The University of Kansas Structural Engineer of Record: Burns & McDonnell Prime Contract Holder: Treanor Arch. Architect of Record: Burns & McDonnell Construction Contractor: Turner Construction Company, Kansas City Figure 5. Strong wall.

STRUCTURE magazine

April 2015

Guest Column dedicated to the dissemination of information from other organizations

ATC products funded by the Henry J. Degenkolb Memorial Endowment Fund.

The Council The Applied Technology Council (ATC) was created by practicing professionals with the intent of serving the evolving needs of engineering practice. Begun in 1971 after the San Fernando earthquake demonstrated the need for improved hazard mitigation strategies and seismic design standards, the founders came up with the novel idea to pay engineers and researchers to develop these technologies instead of relying on volunteer labor. ATC became a nonprofit, tax-exempt corporation in 1973. Since its inception, ATC has engaged the services of highly qualified expert consultants in design practice, building regulation, academia and other specialty areas, to “review research, decide what is useful, and convert it to a format readily useable by the practicing engineer,” in the words of its first two Executive Directors, Ronald Mayes and Roland Sharpe. ATC’s mission is to develop and promote state-of-the-art, user-friendly engineering resources and applications used in mitigating the effects of natural and other hazards on the built environment. ATC also identifies and encourages needed research and develops consensus opinions on structural engineering issues in a nonproprietary format. ATC thereby fulfills a unique role in funded information transfer. ATC is guided by a Board of Directors consisting of representatives appointed by the American Society of Civil Engineers’ Structural Engineering Institute (ASCE-SEI), the National Council of Structural Engineers Associations (NCSEA), the Structural Engineers Association of California (SEAOC), the Structural Engineers Association of New York (SEAoNY), the Western States Council of Structural Engineers Associations (WSCSEA), and four at-large representatives concerned with the practice of structural engineering. The Board members are balanced between practicing and academic experts with a wide knowledge of

A Brief History of ATC… By Vicki Arbitrio, P.E., SECB, F.SEI

Vicki Arbitrio, P.E., SECB, F.SEI, is the Vice President of ATC and an Associate Partner at Gilsanz Murray Steficek in New York. She can be reached at vickiarbitrio@gmsllp.com.

The online version of this article (www.STRUCTUREmag.org) includes in-depth listings of ATC Council Directors (past and present) and ATC Projects and Reports.

36 April 2015

different hazards: earthquakes, wind storms, floods, fires and tsunamis. Project management and administration for all ATC projects are carried out by ATC’s technical staff, led by the Executive Director. Because the technical development work is conducted by a wide range of highly qualified consulting professionals, including individuals from academia, research, and professional practice, each project benefits from experience which would not be available from any single organization. Funding for ATC projects is obtained from government agencies such as the Federal Emergency Management Agency (FEMA) and the National Institute of Standards and Technology (NIST), state agencies such as the State of California, local municipalities such as the City of San Francisco, and from the private sector in the form of taxdeductible contributions. In 1989, ATC established the Henry J. Degenkolb Memorial Endowment Fund, named in honor of a dedicated international leader in structural and earthquake engineering. The ATC Endowment Fund supports projects of critical importance to structural engineering design practice, but for which funds are not available from traditional funding sources. In 2015, ATC will take over management of the James Merriam Delahay Foundation, named in honor of a leader known nationwide for his work on wind codes and standards. The ATC Board of Directors would like the ATC Endowment Fund to support at least one significant project annually. Most recently, the ATC Endowment Fund has contributed funding to the development of the following (for a complete list, please visit the ATC website): ATC-20-1 Bhutan, Field Manual: Postearthquake Safety Evaluation of Buildings (2014) ATC Windspeed by Location website, http://windspeed.atcouncil.org/ (2011) ATC Design Guide 2, Basic Wind Engineering for Low-Rise Buildings (2009)

The covers of Landmark publications.

ATC-20-1, Field Manual: Postearthquake Safety Evaluation of Buildings, Second Edition (2005) ATC-45, Field Manual: Safety Evaluation of Buildings after Windstorms and Floods (2004)

Extraordinary Impacts Reviewing ATC’s history and products, it is difficult to imagine building without this knowledge. ATC-3-06, Tentative Provisions for the Development of Seismic Regulations for Buildings (1982), was funded by the National Science Foundation (NSF) and the National Bureau of Standards (NBS), with amendments funded by the Federal Emergency Management Agency (FEMA). The provisions served as the basis for the seismic provisions of the 1988 and subsequent issues of the Uniform Building Code and the National Earthquake Hazards Reduction Program (NEHRP) Recommended Provisions for the Development of Seismic Regulation for New Buildings. In 1987, ATC-14, Evaluating the Seismic Resistance of Existing Buildings, was published with funding from NSF. This document provided standardized checklist procedures for evaluating seismic deficiencies in existing buildings, and has evolved into the standard, ASCE31-03, Seismic Evaluation of Existing Buildings. The ATC-20 family of documents, including ATC-20-1 Field Manual: PostEarthquake Safety Evaluation of Buildings, provides procedures, criteria, and forms to enable structural engineers, building inspectors, and other qualified personnel to determine if an earthquake-damaged structure can be safely occupied. These documents, funded by the California Governor’s Office of Emergency Services (OES) and the California Office of Statewide Health Planning and Development (OPHPD), were initially published in 1989, two weeks prior to the Loma Prieta earthquake, and were used by the City of San Francisco to post buildings following the earthquake. ATC-45, Field Manual: Safety Evaluation of Buildings After Wind Storms and Floods,

published in 2004, is modeled after ATC20-1 to provide guidelines and procedures to evaluate buildings damaged by wind storms or floods. Upon publication, this document was immediately deployed in inspections performed following Hurricanes Katrina and Rita in 2005. The SAC Joint Venture, a partnership between the Structural Engineers Association of California (SEAOC), ATC, and the California Universities for Research in Earthquake Engineering, (CUREe), was funded by FEMA and the California OES to investigate the failure of welded connections in numerous steel moment-frame buildings after the 1994 Northridge earthquake. In 2000, the SAC Joint Venture produced the FEMA 350 through FEMA 353 series of reports, along with supporting technical and background documentation, that changed the practice of steel design and construction across the country. FEMA P-58, Seismic Performance Assessment of Buildings, Methodology and Implementation (2012), was funded by FEMA. This more than 10-year work effort on the ATC-58 series of projects developed a next-generation system for seismic performance assessment

of individual buildings that accounts for uncertainty in our ability to accurately predict response, and communicates performance in ways that better relate to the decision-making needs of stakeholders. A three volume set was produced that described the methodology, as well as the development of basic building information, response quantities, fragilities and consequence data which are used as inputs. The work included data for most common structural systems and building occupancies, and developed an electronic Performance Assessment Calculation Tool (PACT) for performing the probabilistic computations and calculating the accumulation of losses in terms of repair costs, repair times, casualties, and unsafe placarding.

Extraordinary People ATC’s remarkable contributions to our industry have been overseen for the last 34 years by ATC Executive Director, Christopher Rojahn. Chris became ATC’s third Executive Director in 1981, following Ronald Mayes and Roland Sharpe. Over the years, Chris has nurtured a very talented team of technical personnel, project managers, editors, document production specialists, and administrative staff who have assisted him in running ATC projects and producing ATC reports. Having spent more than 40 years in the field of structural engineering, he has served in leadership roles on a wide range of research and development (R&D) projects, and has served as Principal Investigator/ Project Manager/Senior Advisor on more than 60 major technical projects. He has been at the helm of the organization and

ATC staff and Board of Directors touring Cardinals Stadium in Arizona.

STRUCTURE magazine

April 2015

Chris Rojahn and spouse Stephanie King in Vancouver, BC for the 13 th World Conference on Earthquake Engineering, August 2004.

overseen the production of every landmark ATC document produced to date. Chris has also served as ATC’s Ambassador, working to expand ATC’s reputation at home and abroad. ATC has written papers for World Conferences on Earthquake Engineering in Lisbon 2012, Beijing 2008, Vancouver 2004, Auckland 2000, Acapulco 1996, Madrid 1992, Tokyo-Kyoto 1988, and San Francisco 1984. ATC has held bi-annual workshops sponsored in conjunction with the Japan Structural Consultants Association (JSCA) to develop policy recommendations for improved engineering practice. The 2014 Workshop was the 15th in a series that started in 1984, and was focused on community resilience following typhoons, hurricanes, earthquakes, and other disasters, based on the current state-ofpractice, innovative engineering solutions, and new and emerging technologies. ATC has teamed with the Structural Engineering Institute of ASCE on a series of hazard-mitigation conferences. In 2009, ATC and SEI co-sponsored a conference on Improving the Seismic Performance of Existing Buildings and Other Structures in San Francisco and in 2012, they co-sponsored a conference on Advances in Hurricane Engineering: Learning from our Past in Miami. A second ATC-SEI Conference on Improving the Seismic Performance of Existing Buildings and Other Structures is planned to take place in San Francisco December 10-12, 2015. This conference will provide a forum for the presentation and exchange of new information on seismic evaluation and seismic retrofit of existing buildings, including case studies, new discoveries, innovative use of new technologies and

materials, implementation issues, needed improvements to existing standards and methods, and socio-economic issues. Visit www.atc-sei.org for more details. Under Chris’s leadership, ATC has successfully expanded its focus to encourage needed research on structural engineering issues involving high wind and flood hazard events, including hurricanes and tornadoes. Chris and ATC have built international relationships, teaming with Japanese, Chilean, Dutch, British and Bhutanese structural engineers to share knowledge and document ideas for additional research. Chris has accomplished this work by bringing together an extraordinary staff with diverse expertise, including Tom McLane as Director of Business Development and William L. Coulbourne, Director, Wind and Flood Hazard Mitigation, now both retired.

Chris Rojahn began his career as a deck officer for USGS.

STRUCTURE magazine

April 2015

Current staff includes Jon A. Heintz, Director of Projects, Ayse Hortacsu, Associate Director of Projects, Bernadette Hadnagy, Operations Manager, and Amber Houchen, Administrative, Marketing, and Publications Specialist. In the fall of 2014, ATC hired new talent: Anna Olsen began working as Research Applications Manager, and Veronica Cedillos joined the team as a second Associate Director of Projects. In January of 2015, Scott D. Schiff joined the staff as Director of Projects, and will be located on the East Coast. In May 2015, Chris will become Director Emeritus and Jon Heintz will step into the Executive Director role. Jon joined ATC in 2005, after many years as a practicing structural engineer and more than 25 years of experience in earthquake engineering practice and research, natural hazard mitigation, seismic evaluation and strengthening, advanced analysis methods, and strategic planning on structural engineering research needs at the national level.

The Future Over the last 40 years, ATC has achieved an unmatched success in developing and implementing diverse seismic mitigation strategies. Products like ATC-20 will endure for many generations to come to mitigate against losses for people around the world. And more recently, ATC has completed successful projects to improve engineering practice for making structures resistant to wind, flood, and blast, as well as providing practical guidance for service conditions such as floors vibration response. ATC will continue its current practice of bringing together the brightest minds and the latest research to solve engineering challenges, implement hazard mitigation, and improve community resilience in the Unites States. The ATC family includes incredibly talented and generous members, including staff, consultants, and clients, all striving to improve the structural engineering profession. The Board of Directors would like to take this opportunity to thank the dedicated staff, and particularly Chris Rojahn, for their tireless efforts to make the Applied Technology Council synonymous with excellence. For additional information about the history of ATC, or to read more about current projects, please see the online version of this article, review The Structural Design of Tall and Special Buildings (Vol 14, Number 3, September 2005, Editor Gary C. Hart, published by Wiley), or visit the Applied Technology Council website, www.atcouncil.org/. Both of the latter were primary sources for this article.▪

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Historic structures significant structures of the past

fter the success of Wendell Bollman’s truss at Harpers Ferry and elsewhere, Benjamin Latrobe encouraged Albert Fink to design a longer span iron bridge that he could use on his major river crossings between Harpers Ferry and the Ohio River. Fink (STRUCTURE, May 2006), after obtaining his engineering degree in Germany, immigrated to the United States in late spring 1849. He went to work on the B&O Railroad working with Wendel Bollman (STRUCTURE, February 2006) and Latrobe. Fink, after reviewing Bollman’s bridge, believed he could improve on that design. His first effort for a cast and wrought iron bridge was similar in appearance and details to Bollman’s. He prepared his drawings, and he and Latrobe decided to enter it into a design competition held in Boston. He wrote in his diary, “The competition is over. We who have brought designs were handsomely entertained. I did not win. Latrobe has taken my defeat greatly to heart. I was surprised when he told me politics influenced the decision.” Hungerford, in his history of the B&O, wrote a description of Fink’s design method: “The rule of thumb methods that were used in the creation of so many early iron and wooden bridges were hardly to be trusted in the making of an all iron one. So Fink would go to work with pieces of tin and wires, building up trusses in miniature, testing strains and stresses carefully upon these, and from such experiments making his deduction and formulas for the construction of full sized spans.” Based upon this work, Latrobe gave him the project of building a three span bridge across the Monongahela at Fairmont, Virginia (later West Virginia) in 1852. He thought, as did Fink, that Fink’s plan was better suited than Bollman’s for longer spans, and he adopted it for sites requiring such spans. This was Fink’s first bridge and it was

Monongahela River Bridge By Frank Griggs, Jr., Dist. M. ASCE, D. Eng., P.E., P.L.S.

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

Monongahela Bridge 1852 – 1863. Courtesy of HAER.

40 April 2015

Monongahela Bridge 1865 – 1887, note skew. Courtesy of HAER.

the longest span iron bridge in the United States at that time, surpassing Bollman’s span length of 124 feet by 65%. A four span wooden trestle was built first, to aid in construction and to serve as a temporary crossing. Construction on the masonry piers began in 1850 but was not finished until the end of 1851. Fink’s plan, which may have preceded Bollman’s according to a family biography, consisted of three 205-foot long pinned spans with cast iron upper chords, verticals, lower chord and towers, and wrought iron diagonals and bracing. Many of the details were similar to Bollman’s, since they were both built at the B&O shops. The main difference between Bollman’s and Fink’s trusses was that all of Fink’s long paired diagonals were of equal length. The bridge was 16 feet wide for a single track, had a depth of 20 feet and was built on a skew. It opened in 1852. When building it he wrote home to Germany telling his fiancée Mimi, “I am in complete charge of the building of our bridge across the Monongahela River, a project which will cost $120,000…I cannot help but think often of my colleagues in Germany who

On May 9, 1854, Fink received patent #10,887 for a Truss Bridge. It was for both a deck truss and a through truss like he built over the Monongahela River. He claimed, “I do not claim as new, the manner in which the central post is supported; nor do I claim the combination of a series of triangular bracings, in such a manner, that one system of triangles is supported by and dependent on the other, merely, as I am aware that this has been done before, both in trusses for bridges and

roofs. But what I do claim as of my own invention, and as different from any other method of bracing and strengthening bridge trusses heretofore known, is – The method of combining the different systems of triangular bracings, above described, so that a weight coming on one of the systems of the truss, is not only transferred over one or more other systems, before it is carried back to the abutments; but the foot of the post in each triangle, being unconnected with

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are still sitting with their feet under a desk waiting for some opening…” The difference between a Bollman and Fink Truss was covered in a newspaper article in the Republic and Times newspaper of Buffalo, New York. They wrote, “Mr. Bollman’s plan is entirely different in principle from that of the iron bridge over the canal, near the Erie Depot. This bridge is the Bollman plan. The tension rods are of unequal length, so that for the same expansion there is a different increase in the lengths of the rods sustaining the same point, causing the longer rods to become very loose. This is not the case with the Fink patent – the one selected by Mr. Latrobe. In this bridge, the tension rods are of equal length and, expanding and contracting together, they are kept in proper adjustment at all times. The manner of joining the supporting rods to the uprights upon the piers is also entirely different. This connection is so arranged in the Fink patent that the whole bridge truss is allowed to move freely, thus preventing the strains to which the injurious effects of expansion and contraction are attributable. These two circumstances are sufficient to make up the difference between a very good and a very bad bridge; and we therefore warn all not to confound the two.” In other words, the Fink is the good truss and the Bollman the very bad truss.

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the tension rods of the other triangular bracings, can settle vertically, as well as move to the side; so that the tension rods of each system of the triangular bracings will be strained equally, when the bridge settles under a superincumbent weight. This would not be the case, if the foot of the post in the 2d system of triangular bracings rested on the tension chord of the post, in the first system, as heretofore used; and herein consists my improvement, for which I ask Letters Patent.” He also noted “the sinking of a portion of the truss by a superincumbent weight, or by changes in the condition of the material used in construction from the effect of temperature, will not cause the several parts of the truss to deviate from their mutual adjustments…” The “first system” he is referring to is the Bollman Truss, which had been patented two years earlier and was being built on the eastern segment of the B&O. After its opening in 1852, it lasted until 1863 when it was burned by the Confederates during the Civil War. It was replaced with a wooden trestle that lasted until 1865 when two spans were replaced with Fink Trusses. In 1868, the third span was replaced. The trusses were similar to the original, but the new towers were built in an Italianate design. The bridge was replaced in 1887 and again in 1912 when steel Warren Trusses were used. At the time of its construction, it was the longest iron bridge built in the United States with a total length of 615 feet. It, along with Bollman’s, led to a greater trust in the use of iron for railroad bridges. For total length it was only exceeded by Robert Stephenson’s Tubular Bridge in Wales. It received worldwide recognition after

Rio Chili Bridge. Courtesy of Mark Yashinsky.

its construction. It was never adopted overseas or by other American bridge builders, with the notable exception of C. Shaler Smith and the Baltimore Bridge Company. Fink left the B&O in 1857 to work on the Louisville and Nashville (L&N) railroad. One of his first efforts was the construction of the Green River Bridge near Mammoth Kentucky. It was a five span deck bridge with the three middle spans being 208 feet and the two outer spans 181 feet. The deck level was 115 feet above the water level in the river. The bridge opened in 1859, but during the Civil War the Confederates blew up the two southerly spans. After the Civil War, the wooden High Bridge over the Appomattox River was rebuilt in 1869 with 21 Fink deck trusses at an elevation of up to 160 feet. His largest bridge was his Louisville, Kentucky Bridge over the Ohio River that opened in 1870. It was the longest bridge (5,250 feet) in the world at the time. It consisted of 25 conventional Fink deck trusses with spans ranging from 50 feet to 245 feet - 5 inches, and two major long-span through trusses of

Monongahela Bridge from a French Publication.

STRUCTURE magazine

April 2015

370 feet and 400 feet, plus a side mounted swing span over the Louisville and Portland Canal. His and Bollman’s trusses were generally built between the early 1850s up until the post Civil War period, when Whipple Double Intersection Trusses in cast and wrought iron, and later steel, became the standard railroad trusses until the end of the century. Only two of Fink’s bridges survive in the United States. The first was constructed in approximately 1870 as a railroad bridge and converted to vehicular use in 1893. The truss was moved to a park in Lynchburg, Virginia in 1985, where it is now used as a footbridge. It was designated as a National Historic Civil Engineering Landmark in 1985. A 108-foot single span through truss was originally built by the Smith & Latrobe Company in 1869 as one of three spans to cross the Tuscarawas River at Canal Dover, Ohio. Smith was a protégé of Albert Fink, working with him on the L&N Railroad. It utilized Phoenix wrought iron compression members and cast iron junction blocks, and was a modified Fink Truss, lacking four verticals. It was replaced with a new bridge in 1905 and moved to Zoarville Station, Ohio, where it was abandoned in place in 1940. It was restored and rebuilt at this site across the Conotton River in 2007. There it serves as a bicycle and pedestrian path that connects with the Ohio and Erie Towpath Trail. One Fink truss remains in Arequipa, Peru crossing Rio Chili. It originally carried a railroad, but now carries a single line of automobile traffic. Mark Yashinsky, a California Bridge Engineer, indicates that the locals say the bridge was built by Gustav Eiffel, which is unlikely. The Baltimore Bridge Company was building bridges like the Verrugas Viaduct in Peru at the time. It was erected by Leffert L. Buck, so it is likely that the entire Arequipa Viaduct was built by the Baltimore Bridge Company. The towers are supported by Phoenix Columns, and the truss compression members are also Phoenix shapes.▪

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Professional issues

issues affecting the structural engineering profession

Why They Stay… Why They Leave… A Look at Preserving the Future of Structural Engineering By Robert Pekelnicky, S.E and Kyle Twitchell, P.E., M.ASCE, with the SEI Young Professionals Committee “If you like solving puzzles, this is a profession you can enjoy doing it and be paid for it. You build things that last a century. Much more rewarding than practice of Medicine and Law. And you can do this way past retirement and keep enjoying it.” “Stay out of this career. Too many long hours, high stress and nobody cares... My wife hates me, and my kids don’t know me. Nobody should have to work this much in life. If it paid a lot of money, that’s one thing... but it doesn’t. If you’re considering structural engineering... you’re a bright individual... use your brain to do something else.”

ould you believe that these two statements came from people who share the same profession? Have you found yourself saying one of these things? Have you found yourself saying both of those things? Hopefully, if you’re reading this right now, you’re more aligned with the former statement than the latter. Now think about someone you know, maybe a classmate or a former colleague… someone who started out as a structural engineer only to one day decide they were leaving the profession. Most of us can think of one or two people that we’ve known over the years whose departure was a true loss to the profession. So why did they leave? Could something have been done different to prevent them from leaving? These questions inspired the SEI Young Professionals Committee to look into the question of “why people stay” and “why people leave” as part of a series of topics on enhancing the future of structural engineering. To do this, a survey was mass emailed to people in the profession with the caveat to pass this along to their colleagues – both

current and former. The survey questions were combined with another survey on diversity within the profession. In total, 741 people responded. Of those, 107 (14%) identified as not being practicing structural engineers. The survey included demographic data, in terms of where they worked, how long they’ve worked, level of education, and what type of work they did. The survey was then divided, with questions for those who were still in the profession and those who had left. At the end of the survey there was an option to provide additional written comments. All of the quotations interspersed throughout this article are directly from the survey.

View of the Profession “…the stress and demands of the job in today’s environment have increased considerably over the span of my career due to the requirements for tighter schedules and faster production combined with a fee structure that has basically remained unchanged for years.” “The profession is becoming more of a commodity service. Another issue is that

college graduates now are much less prepared to be productive, proficient engineers than they were 20 or 25 years ago.” These statements represent two common themes voiced in publications and at conferences. Therefore, a reasonable place to look for why people are leaving the profession would lie in their perception of what they did. The survey asked responders for their opinion and the results were interesting. Responders, practicing and formerly practicing, said that they believe the profession has lost stature as opposed to gaining stature by a margin of 2:1. However, an equal number of responders said they believed that the stature has not changed. With a significant number of survey respondents indicating they felt the profession had lost stature, it was interesting to note the number of people who indicated they were satisfied with their current job. In the survey, only about 5% of the responders who were currently structural engineers indicated they were dissatisfied with their career. That is in stark contrast to the 80% who indicated they were satisfied or very satisfied with the profession.

Structural engineer’s satisfaction with their careers.

STRUCTURE magazine

April 2015

Reason for leaving the field of structial engineering.

Why They Leave

commenter summed things up rather well with the following, “I love the technical aspects of our field and the satisfaction of seeing something I designed built. However, the business practices within the field are extremely frustrating. I have had many friends leave the profession to pursue other professions where they work the same amount but make much more money. I worry that we have

a long term issue with attracting, compensating, and retaining talent. I believe a key problem is that many of the people running firms have little to no business training. We lament that we can’t make money, yet when it comes time to negotiate a fee we don’t think about how much effort we will have to expend and the scope, but instead use a number that we think will get us the job. We also have contracts with

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Examining the data on why people choose to leave the profession did not reveal any specific, overarching reason. The “Why They Leave” graphic highlights the most significant reasons identified by respondents. The numbers add to greater than 100% because some people identified more than one reason for why they chose to leave. The most significant reason people choose to leave is that they lose interest. Surprisingly, being discriminated against is a very close second. A perception of lack of growth opportunities and financial pressures were the next two items which contributed to people leaving. The loss of interest or perceived lack of growth opportunities were tough to determine if they could have been prevented. On the one hand, every firm has its share of repetitive tasks and it can be easy for someone to get burnt out. However, it was clear from some of the survey’s written responses that many people felt like they were doing the same thing over and over, often at greater than 40 hours, without the recognition they felt they deserved. The following quotation harshly, but truthfully, describes one responder’s feelings. “My job as a Structural Engineer has been much more conservative than I originally thought it would be. It feels like working in a retail job; responsibilities seem more tied to term than ability, and people seem afraid to give responsibility to young people. I believe this to be very consistent with other professions of high responsibility, but with a much lower long term salary potential.” Regarding the financial reasons, so much has been written about this and talked about at professional conferences that an entire book could be written about it. However, one

Years out of the profession with statement of returning to the profession.

poorly defined scope that lead to “scope creep” and doing work for free. Yet we then wonder why we lose money. Also, there is a willingness within the field to ‘buy work’. We also are not trained to communicate. This leads to difficulty in communicating the value we bring to owner which then leads to selections based solely on fee. While technical training is key to engineering education, we are professionals – not technicians. Most engineers eventually (and sometimes quickly) rise to a level where we are managing younger engineers, marketing our services, and negotiating contracts. However, we receive very little training in those areas.” The fact that feeling discriminated against was the reason for almost 30% of the people leaving the profession was surprising, and frankly shocking. With a profession that has a significant underrepresentation of women and minorities (Liel, STRUCTURE® magazine, October 2014), this is an issue that should be looked at in more detail. Several of the reasons people left the profession were outside of their control, such as moving, family issues, or being part of a staff reduction. However, the numbers who indicated that was the reason they left was small compared to those who lost interest, felt discriminated, didn’t see growth or wanted more money. The survey indicated that most people who leave the profession do so within the first five years of beginning work, with almost one quarter leaving within their first year. With so many people leaving the profession so early, a natural question arose of whether they could come back into the profession. Of those surveyed, less than 30% indicated they would return. The numbers remained somewhat constant up to those who had been out of the profession for more than 10 years. It is noteworthy that there is a possibility for people to return; however,

Job satisfaction with no mentors.

Job satisfaction with at least one mentor.

no respondents indicated they had left the profession and returned. This is significant. Our profession does not lend itself to people making a mid-career change into it. Any mid-career change would involve significant coursework at the undergraduate level and possibly a master’s degree.

Mentorship is key to retention. You are never too young to take on a mentee. The effects of mentorship are apparent and appear to lead to significant increases in job satisfaction and retention. If you don’t feel you can find one within your oganization, look to local and national professional socieities. Many respondants replied that they found a greater degree of engagement and mentorship through their involvement in a professional organization. It appears from the survey that the we need to take more steps toward ending discrimination. The fact that almost 30% of those who left cited feeling discrimiated against is alarming and unacceptable. Examine your organization’s culture and why people have left. Is this something that needs additional attention within your company? Lastly, inspire someone in your company or your professional organization to feel like this person… “[Structural Engineering] is a rewarding profession where you see tangible results for your work with the construction of something. You can feel fulfilled in your day and have meaning to your work life this way.”▪

A Case for Mentorship “I think the availability of a mentor is important to the development of an engineer in any field. It is something I wish I had sought more.” One bright spot within the survey was the very apparent positive influence of mentorship. The two pie charts on mentorship show satisfaction ratings for those who did not identify as having any mentor versus those who did. Satisfaction increases from around 70% to almost 90%. More importantly, dissatisfaction drops from 9% to 2%. Considering the two most significant reasons people left were losing interest and feeling discriminated against, mentorship appears to be a significant way to address those issues. Anecdotally, it seems that having a mentor can go a long way toward keeping someone engaged and feeling their contributions are meaningful. It also appeared that a mentor could help one to address discrimination within their organization. Thus, the importance of mentorship cannot be understated in improving retention rates.

Conclusions & Actions

Length of time in the profession.

Now that the economy is starting to recover and job opportunities are becoming more prevalent, think about what your firm can do about retaining the people you’d like to retain. What can be done to keep your people engaged? STRUCTURE magazine

April 2015

Robert Pekelnicky, S.E., is a Principal with Degenkolb Engineers in San Francisco and is the founding chair of the SEI YP Committee. He can be reached at rpekelnicky@degenkolb.com. Kyle Twitchell, P.E., M. ASCE, is a Senior Engineer with Robert Silman Associates in New York, NY and is a member of the ASCE YP and SEI YP Committee. He can be reached at twitchell@silman.com. All graphics courtesy of ASCE.

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Bookcase

book reviews and news

A Guide to Managing Engineering and Architectural Design Services Contracts

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

What Every Project Manager Needs to Know (John M. Lowe, Jr., P.E.) Review by Keith M. Bouchard, P.E., Structural Engineer, CBI Consulting, Inc.

Review by Michael S. Teller, AIA, Principal CBI Consulting, Inc.

This book is intended to provide a primer for young engineers on the important aspects of design services contracts. It also introduces the importance of creating and maintaining a culture of professional liability awareness within a design office to minimize the risk of a claim. The book is concisely written and broken into five sections: An introduction, a brief description of the basic elements of a design services contract, common issues with implementing the contract, requirements during bidding and construction, and a summary and recommendations section. Young engineers rarely have any formal instruction on the subject of contracts and liability, and this book provides a useful introduction to these topics. Too often these lessons are learned “the hard way” through claims and disputes. Gaining a basic understanding of the principles of design service contracts before one takes on the responsibility of project management can be invaluable, and this book covers all the basic concepts. This reader was hoping to see more real-world case studies and “horror stories”; however, the text is to the point and well worth the couple hour read for a young professional entering the world of project management.

This is about our practice first and greatly assists in the area of Contracts. This could be called a “Pocket” Guide, it is easy enough to carry around – also implying it is important to do so. It could certainly be longer. I would add “and” between “Services and Contracts,” because it is about practice and contracts. The bullet point format makes it very easy to read. I would suggest giving “pearls of wisdom” after each set of recommendations and a different graphic look to emphasize the importance of the message. All the suggestions are sound and correct. I wish I had been required to read this book early in my career. However, until you have experienced all the reasons you need to adhere to these guidelines, I can imagine a young professional would not be able to grasp their importance. That’s why I suggest that each of the chapters could benefit from a story to illustrate the cause and effects that would compel the reader to implement each bullet point. I have learned most of the things in this book over my 36 years of practice. Every professional would benefit from reading this book early in their careers and yearly as a refresher. Face it, this book will make your life easier and keep you out of trouble. I learned several things I’m going to implement in my office – specifically in our contracts.

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Review by Russell F. Conn, Esq., Conn, Kavanaugh, Rosenthal, Peisch & Ford, LLP This is a very readable and straight-forward primer that covers many of the basic contractual and legal issues confronted by a design professional. Above all, it emphasizes the importance of careful, concise, and timely communications as the hallmark of a good professional relationship. It further provides the newly minted architect and engineer with basic liability principles and cautions – “do’s and don’ts,” if you will – in the principal areas of exposure. This includes standards of care, ownership of design documents (or “deliverables), limitations of liability and disclaimers, indemnification obligations and perils, and dispute resolution, and how those principles intersect with professional liability insurance. On a more fundamental level, the guide also alerts the young design professional to the basic importance of getting paid. The book is noteworthy in several of its omissions that might be addressed in an expanded second edition. This would include a discussion of the role of AIA documents and their standard provisions, the importance of codes, and job safety and liability issues. Nonetheless, it is a good and simple “read” – 76 pages or about a 90 minute commitment – for any new design professional. Mr. Conn regularly represents design professionals in all aspects of their practice.▪

award winners and outstanding projects

Spotlight

680 Folsom Ancient Meets Modern Ingenuity in an Unprecedented Seismic Solution By Bill Janhunen, S.E., LEED AP and Gina Phelan Tipping Structural Engineers was an Outstanding Award Winner for the 680 Folsom Street project in the 2014 NCSEA Annual Excellence in Structural Engineering awards program (Category – Forensic/Renovation/Retrofit/Rehabilitation Structures).

he transformation of 680 Folsom – an uninspiring steel-momentframed building originally completed in 1963 – into desirable office space is an Ugly Duckling story with a commercial-development fairy-tale ending. The building, formerly owned and occupied by Pacific Bell until 2007, stood empty and obsolete in San Francisco’s South-of-Market neighborhood, an area otherwise buzzing with redevelopment. The developer saw an opportunity to attract coveted tech clients by upgrading the 12-story, concrete-clad, asbestos-filled “Class C” building to 14 stories with a “Class A” rating. Successfully doing so necessitated a complete overhaul – upgrading the structure’s seismic performance, replacing the drab precast skin with a sleek glass curtain wall, and expanding the space vertically and horizontally. Like many projects at the time, 680 Folsom’s ambitious rehabilitation fell victim to the Great Recession, which forced a hold in 2008 and a value-engineering redesign in 2010. However, by February 2011, even before construction had started, 85 percent (420,000 square feet of the building) had already been leased. In a quest to design a cost-efficient seismic retrofit scheme that would meet the budget and performance criteria set by the developer, Steven Tipping of Tipping Structural Engineers (formerly Tipping Mar) reached centuries back and an ocean away to medieval Japan for design inspiration. The result? A unique isolative lateral system, unprecedented in modern engineering, that proved valuable to the owner, architect, and general contractor. The novel design solution was inspired by the structure of the ancient Japanese pagoda. In this architectural tradition, dating as far back as the seventh century, an entire tree trunk (or shinbashira) forms a central spine that rests in a stone well, the well providing a pivot point for the trunk. Wooden brackets loosely connect each of the pagoda’s floors to the spine. During a large earthquake, the shinbashira acts as a mode shaper; it pivots freely in its stone well and dictates a more uniform displacement at all floors, allowing

seismic forces to dissipate along the full height of the structure, which then returns to plumb. How was all this accomplished? A combination of good “bones,” creative thinking, and performance-based design set things in motion. Constructed as a bolted-flange moment space frame, 680 Folsom possessed some exceptionally good structural qualities that the design team could use. The original seismic system employed moment connections at every column-girder connection, providing a very redundant system. In addition, the boltedflange connections gave the structure a high degree of ductility and rotation capacity. (The building, however, did not meet the global drift requirement of a new structure.) During a 2010 value-engineering redesign, the original seismic retrofit solution consisting of two I-shaped core walls gave way to a new study exploring the possibility of a modern shinbashira: a single, rocking 30-foot-square concrete core located in the center of the building, where the elevator shafts are housed. The preliminary findings from the study proved promising and showed that the existing moment frames, when forced by the core to displace uniformly, possessed the redundancy and ductility to resist lateral forces. The engineers then focused on detailing the base of the new modeshaping core to act as a pin-base connection. A number of connection details were explored but were jettisoned in favor of a single friction pendulum bearing that would support the base of the concrete core. This base connection has a number of structural benefits: it isolates the core’s 232-foot, 8-million-pound gravity load to one location during a seismic event; provides a virtual pivot point for the core at the stiff first floor; and, does not require any overturning moment capacity at the foundation level. In this modern shinbashira, the friction pendulum is analogous to the stone well. For this detail to work, however, the 30-foot square core had to be sculpted down to rest on the bearing’s 5-foot by 5-foot steel housing. A deep concrete beam, or “sacrum,” measuring 12 feet deep by 12 feet wide, was designed to span over the friction isolator and transfer all of the

STRUCTURE magazine

April 2015

gravity loads from the concrete core into the friction bearing. The bearing, stabilized in its cast-steel housing, measures 3.5 feet in diameter and slides freely in its bowl-shaped base, much in the same way that the shinbashira is free to rotate in its stone well. The entire structural assembly is founded on a relatively shallow, 15-foot wide by 15-foot long by 7-foot deep pile cap foundation system; 30 micropile elements provide the gravity support. The single rocking core harnesses the strength of the existing moment frame by forcing yielding throughout the frame’s height, thereby redistributing seismic deformations throughout the structure. In addition, horizontally placed buckling restrained brace (BRB) elements – analogous to the wooden brackets that loosely join a pagoda’s floors to the shinbashira – link the floors to the core and limits load transfer between the systems. In summary, Tipping’s modern shinbashira greatly benefited the owner, architect, and builder by providing 680 Folsom with a building performance that was tuned to match the 1.7 percent (DBE) drift limit of the new curtain wall, chopping ten weeks off the construction schedule, saving $4 million on a $110-million project, lowering earthquake-insurance premiums, allowing greater architectural freedom, and increasing leaseable space. When it was complete, Jones Lang LaSalle’s International Director David Churton referred to the rehabilitation of 680 Folsom as “the ultimate repositioning and renovation in San Francisco history.”▪ Bill Janhunen, S.E., LEED AP, serves as Senior Project Engineer at Tipping Structural Engineers. Gina Phelan is an Associate and serves as Strategic Development Director at Tipping Structural Engineers.

GINEERS

ASS

NCSEA NCSEA EXCELLENCE EXCELLENCE IN IN STRUCTURAL STRUCTURAL ENGINEERING ENGINEERING AWARDS AWARDS

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News form the National Council of Structural Engineers Associations

NATIONAL

CallCall forfor Entries Entries The NCSEA The NCSEA Excellence Excellence in Structural in Structural Engineering Engineering AwardsAwards annually annually highlights highlights some ofsome the best of the examples best examples of of structural structural engineering engineering ingenuity ingenuity throughout throughout the world. the world. Structural Structural engineers engineers and structural and structural engineering engineering firms are firms are encouraged encouraged to entertothis enter year’s thisprogram. year’s program. ProjectsProjects will be will be judged judged on innovative on innovative design,design, engineering engineering achievement achievement and creativity. and creativity. Up to three Up toawards three awards will be will presented be presented in eightincategories: eight categories: • • • • • • • •

New • Buildings New Buildings Under Under $10M $10M New • Buildings New Buildings $10M to $10M $30M to $30M New • Buildings New Buildings $30M to $30M $100M to $100M New • Buildings New Buildings Over $100M Over $100M International • International Structures Structures New • Bridges/Transportation New Bridges/Transportation Structures Structures Renovation/Retrofit • Renovation/Retrofit Structures Structures Other • Structures Other Structures

EligibleEligible projectsprojects must bemust substantially be substantially complete complete betweenbetween JanuaryJanuary 1, 20121,and 2012 December and December 31, 2014. 31,Entries 2014. Entries are dueare due Monday, Monday, July 20,July 2015. 20, 2015.

NCSEA News

AwardsAwards will bewill presented be presented in September in September at the at NCSEA the NCSEA Structural Structural Engineering Engineering SummitSummit in Las in Vegas. Las Vegas. Winning Winning projectsprojects will be will featured be featured in future in issues futureof issues STRUCTURE of STRUCTURE magazine. magazine. For award For award program program rules, project rules, project eligibility eligibility and entry and entry forms, forms, see theseeCall the for CallEntries for Entries on theon the NCSEANCSEA websitewebsite at www.ncsea.com. at www.ncsea.com.

STRUCTURE magazine

April 2015

NCSEA has launched a new online member portal where NCSEA members (members of NCSEA Member Organizations, Associate, Affiliate and Sustaining members) can access their information, register for all NCSEA events and programs, and access member-only resources and files. All Member Organization members recently received a letter from NCSEA with log-in information for accessing the portal from links on the NCSEA website. NCSEA Delegates will be able to see delegate-specific information and interact with Delegates in other Member

Organizations. Members of NCSEA committees will also be able to see committee-specific information in their records. Many of the reports, resources and manuals that have been available from the NCSEA website will now be member-only resources, including NCSEA committee reports and information, technical documents, and manuals and guides such as the SEER Manual, High School Outreach Manual, and Young Member Group Start-Up Guide. In addition, the electronic version of STRUCTURE magazine is now available for viewing by subscribers and NCSEA/SEI/CASE members only.

MO Meetings Now Featured on NCSEA Website

NCSEA News

NCSEA Launches New Online Member Portal

News from the National Council of Structural Engineers Associations

NCSEA Member Organizations will have another way to promote their events and programs online. The NCSEA website home page has been revised to highlight MO events. MO events can be added to the NCSEA calendar, by clicking on the calendar on the home page and submitting the event using the form provided. Events will be reviewed by NCSEA staff and posted to the website. Each posting will include a link to the MO event webpage, and the two most current events will appear on the NCSEA home page.

NCSEA Webinars April 14, 2015

May 5, 2015

Quick Methods for Quality Assurance Reviews The presentation will focus on completeness and coordination requirements for structural drawings and strategies for assuring the correctness of structural calculations. Edward Westerman, P.E., S.E., Principal and Director of Structural Engineering with Clark Nexsen, Inc.

Practical Design of Structures for Blast Effects: Structural Elements Part 2 of this updated three-part webinar series will address inherent uncertainties and common assumptions and dynamic and equivalent static analysis using SDOF models. Jon A. Schmidt, P.E., SECB, BSCP, Associate Structural Engineer and the Director of Antiterrorism Services at Burns & McDonnell

STRUCTURE magazine

April 2015

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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, Flex-Plan, and Yearly Subscription. Visit www.ncsea.com for more information or call 312-649-4600.

NATIONAL

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Diamond Reviewed

Practical Design of Structures for Blast Effects: Glazing Systems Part 3 of this updated three-part webinar series will address static analysis using equivalent wind pressures and dynamic analysis using specialized software. Jon A. Schmidt, P.E., SECB, BSCP, Associate Structural Engineer and the Director of Antiterrorism Services at Burns & McDonnell

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May 12, 2015

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Practical Design of Structures for Blast Effects: Design Criteria Part 1 of this updated three-part webinar series will address ASCE/SEI 59-11 Standard for Blast Protection of Buildings and risk assessment principles and methodologies from DoD and DHS/ FEMA including helpful resources and tools, as well as detailed design examples. Jon A. Schmidt, P.E., SECB, BSCP, Associate Structural Engineer and the Director of Antiterrorism Services at Burns & McDonnell

STRUCTU

April 28, 2015

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Registration Now Open for Structures Congress 2015

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

New ideas. New practices. New science. New resources. New colleagues. April 23 – 25, 2015, Portland, Oregon Congress Highlights: • 120 informative technical sessions • Earn up to 15 PDHs • The Council of American Structural Engineers (CASE) Spring Risk Management Convocation • Two renowned keynote speakers in the Opening & Closing Plenary Sessions: Tad McGeer, Ph.D., Founder & President, Aerovel Corporation, and Avery Louise Bang, CEO, Bridges to Prosperity • Student and Young Professional opportunities Saturday Special Opportunities: • Preparing for the Future of Structural Engineering: Interactive Session led by Donald Dusenberry, P.E., F.SEI, F.ASCE; SEI President • Portland by Bike Tour • From Streetcar to Aerial Tram Tour Visit the congress website at www.structurescongress.org for more information and to register.

“STRUCTURES CONGRESS is really exciting; it’s one of the only Conferences that brings together academics like myself and practicing engineers to work together to advance the profession.”

Marc Hoit, Ph.D., F.SEI, F.ASCE Vice Chancellor for IT & CIO, Profession of Civil Engineering, NC State University

Encourage Students with the ‘Make Your Mark’ Poster Include the Make your Mark poster to inspire encourage The joband of a structural engineer is both an art and science. students to pursue structural engineering as a career. This poster was produced by the National Council of Structural Engineers Associations (NCSEA) and SEI. Complimentary posters are available upon request to Suzanne Fisher at sfisher@asce.org. Be sure to include the number of posters you are requesting and where they should be sent. Visit the ASCE website at www.asce.org/pre-college_outreach/ for more Makeresources your mark by and visiting ideas for outreach with young students.

MAKE YOUR MARK GO THE DISTANCE

Structural engineers design the buildings where we live, work, go to school, and play, and the bridges we cross everyday. As buildings reach greater heights and bridges span further distances, structural engineers must design these structures with materials such as steel, concrete, masonry, and timber to resist all forces. These forces include gravity, earthquakes, hurricanes, explosions and much more. All of this is considered to create the architect and client’s vision while creating a safe place for the public.

www.ncsea.com and www.asce.org/SEI

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Local Activities SEI San Francisco Chapter

SEI WVU Graduate Student Chapter

The SEI San Francisco Chapter had its inaugural Meet & Greet on February 12th. More than a dozen structural engineers representing a variety of companies shared their ideas of what they envision the new local chapter can provide, and how they can contribute to its success. The Meet & Greet was informal and in a relaxed environment. Attendees enjoyed chats during happy hour at a local Oakland bar & restaurant. Now that the chapter has had this “kick off” event, they are eager to move forward with momentum. Anyone interested in joining this new local chapter can contact Ed Tometz at ethometz@stanfordalumni.org.

The SEI Graduate Student Chapter at West Virginia University recently elected a new executive committee for the 2015 calendar year. New positions for publicity and website administrator were created to enhance the chapters activities and outreach. The chapter participated in the Spring EngineeringFest, displaying glass and carbon fiber reinforced polymer composite products to freshman engineering students.

SEI St. Louis Chapter The St. Louis Chapter organized a tour of the Hillsdale Fabricators facility in St. Louis. Hillsdale is a steel fabricator for bridge and building components. About 23 members participated in the tour. Hillsdale did a good job answering a lot of questions about steel fabrication. Afterward, there was a happy hour at a nearby pub. STRUCTURE magazine

Get Involved in SEI Local Activities Join your local SEI Chapter, Graduate Student 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. Visit the SEI website at www.asce.org/SEI and look for Local Activities Division (LAD) Committees. April 2015

Committee on the Reform of Structural Engineering Education

Call to SEI Committee Chairs to Submit Proposals by June 1

Call for Participation

The SEI Futures Fund (SEIFF) invites proposals for new initiatives in line with Futures Fund SEIFF strategic areas that benefit the structural engineering profession and/or Investing in the Future of Our Profession SEI as a whole, and would not otherwise be funded out of SEI Division or operating funds. Review the SEIFF Case Statement and the Guidelines for FY2016 funding requests. If your SEI Division Executive Committee wishes to vet the proposal, plan to do so this spring to meet the June 1st final proposal submission deadline. See the SEI website at www.asce.org\SEI for more information.

How do we educate tomorrow’s leaders and innovators? The SEI Board of Governors has embarked on a mission with a bold vision to engage with key stakeholders from both academia and the profession to create new initiatives to transform university structural engineering programs. An approved board-level Committee on the Reform of Structural Engineering Education, chaired by Keith Hjelmsted, Ph.D., will examine how structural engineers are educated and explore innovative alternate models and methods. The committee is seeking interested stakeholders with broad experience who can focus on the unique challenges of structural engineering education. Please contact Jennifer Goupil at jgoupil@asce.org for more information and details on how to apply for the committee or become involved in the effort; applications accepted until May 30th.

Second ATC-SEI Conference on Improving the Seismic Performance of Existing Buildings and Other Structures December 10 – 12, 2015 Hyatt Regency San Francisco www.atc-sei.org/

Geotechnical & Structural Engineering Congress 2016

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

Save the Date February 14-17, 2016, Phoenix, AZ Connect | Collaborate | Build www.Geo-Structures.org

SEI Member Ron Hamburger Design Loads on Structures Elected to National Academy during Construction Standard ASCE/SEI 37-14 Just Published of Engineering Longtime SEI volunteer Ron Hamburger, S.E., SECB, F.SEI, has earned engineering’s highest honor, election to the National Academy of Engineering. Ron was recognized by the academy for his advances in seismic design principles and practices for buildings through research and development of codes and guidelines. He is a Senior Principal at Simpson Gumpertz & Hager in Waltham, Massachusetts, and was last year’s winner of SEI’s Walter P. Moore Award. STRUCTURE magazine

ASCE/SEI 37-14 describes the minimum design requirements for construction loads, load combinations, and load factors affecting buildings and other structures that are under construction. It addresses partially completed structures as well as temporary support and access structures used during construction. Visit the ASCE Bookstore at www.asce.org/bookstore/ to purchase this book and other structural publications.

April 2015

The Newsletter of the Structural Engineering Institute of ASCE

Save the Date

Structural Columns

SEI Futures Fund Seeks Strategic Initiative Proposals for Funding Consideration

CASE Risk Management Tools Available

CASE in Point

The Newsletter of the Council of American Structural Engineers

Foundation 3: Planning – Plan to be Claims Free Tool 3-1: A Risk Management Program Planning Structure This tool is designed to help a Firm Principal design a Risk Management Program for his or her firm. The tool consists of a grid template that will help focus one’s thoughts on where risk may arise in various aspects of engineering practice and how to mitigate those risks. Once the risk factor is identified, a policy and procedure for how to respond to that risk is developed. This tool contains 10 sample risk factors with accompanying policies and procedures to illustrate how one might get started. The tool is designed to insert custom risks and policies to tailor it to individual firms. Tool 3-2: Staffing and Revenue Projection Firms are provided a simple to use and easy to manipulate spreadsheet-based tool for predicting the staff that will be necessary to complete both “booked” and “potential” projects. The spreadsheet can be further utilized to track historical staffing demand to assist with future staffing and revenue projections. Tool 3-3: Website Resource Tool This tool lists website links that contain information that could be useful for a structural engineer. A brief description of the website is also included. For example, there is information about doing business across state lines, information regarding the responsibility of the Engineer of Record for each state, links to each State’s Licensing Board, etc. Tool 3-4: Project Work Plan Templates Preparing and maintaining a proper Project Work Plan is a fundamental responsibility of a project manager. Work Plans document project delivery strategies and communicate them to the team members. Project Managers will use this template to create a project Work Plan that will be stored with the project documents.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

Foundation 4: Communication – Communicate to Match Expectations with Perceptions Tool 4-1: Status Template Report This tool provides an organized plan for keeping your clients informed and happy. This project status report is intended to be sent to your client, the owner and any other stakeholder whom you would like to keep informed about the project status. Tool 4-2: Project Kick-Off Meeting Agenda Effective communication is one of the keys to successful risk management. Often times we place a significant amount of effort and care into communication with our clients, owners and external stakeholders. With all that effort, it’s easy to take for granted communication with our internal stakeholders – the structural design team. If a project is not started correctly, there is a good chance that the project will not be executed correctly either. Tool 4-2 is designed to help the Structural Engineer communicate the information that is vital to the success of the structural design team and start the project off correctly. Tool 4-3: Sample Correspondence Guidelines The intent of CASE Tool 4-3 is to make it faster and easier to access correspondence with appropriate verbiage addressing some commonly encountered situations that can increase your risk. The sample correspondence contained within this tool is intended to be sent to the client, owner, sub-consultant, building official, employee, etc., in order to keep them informed about a certain facet of a project or their employment. Tool 4-4: Phone Conversation Log Poor communication is frequently listed among the top reasons for lawsuits and claims. It is the intent of this tool to make it faster and easier to record and document phone conversations. Tool 4-5: Project Communication Matrix This tool is to provide an easy to use and efficient way to (1) establish and maintain project-specific communication standards, and (2) document key project-specific deadlines and program/coordination decisions that can be communicated to a client or team member for verification. All of these tools and more are available at www.booksforengineers.com.

NEW!! Commentary on the 2010 & 2015 Code of Standard Practice for Steel Joists

The CASE Guidelines Committee has developed a Commentary on the Code of Standard Practice for Steel Joists now available at www.acec.org/bookstore/. This commentary provides observations and analysis of the revisions and additions in both documents, and discusses specific aspects of the COSP that have a direct impact on the structural engineer’s practice of specifying steel joists. A familiarity and understanding of the entire SJI COSP is necessary to ensure the proper design and documentation of steel joists and Joist Girders. However, the discussion highlights sections of particular interest to the specifying structural engineer. STRUCTURE magazine

April 2015

Donate to the CASE Scholarship Fund! We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates. One way to enhance the ability of students in pursuing their dreams to become professional engineers is to offer incentives in educational support. The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at minimum, in an ABET-accredited engineering program. Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for tax deduction and you don’t have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate. STRUCTURE magazine

Membership Committee – Stacy Bartoletti (sbartoletti@degenkolb.com) • Researching potential dues level re-structuring • Preparing for membership recruitment campaign with CASE staff members, target date August 2015 Programs and Communications Committee – Michael Planer (mplaner@pesengineers.com) • Creating track of risk management sessions for 2016 ASCE/SEI Structures Congress • Creating track of risk management/business practice sessions for 2015 ACEC Fall Conference • Putting together the 2015/2016 editorial calendar for articles to STRUCTURE magazine from CASE Toolkit Committee – Brent White (brentw@arwengineers.com) • Updating the following current Tools: • Tool 4-3: Sample Correspondence Letters • Tool 10-1: Site Visit Cards • Working on the following new tools: • Tool 1-3: Sample Office Policies • Tool 8-3: Contract Clause Commentary • Tool 9-3: Deferred Submittals The CASE Summer Planning Meeting is scheduled for August 6 – 7 in Chicago. If you are interested in attending the meeting, or have any suggested topics for the committees to pursue, please contact CASE Executive Director Heather Talbert at htalbert@acec.org.

WANTED

Engineers to Lead, Direct, and Get Involved with CASE Committees! If you’re looking for ways to expand and strengthen your business skillset, look no further than serving on one (or more!) CASE Committees. Join us to sharpen your leadership skills – promote your talent and expertise – to help guide CASE programs, services, and publications. We have a committee ready for your service: • Risk Management Toolkit Committee: Develops and maintains documents such as business practices manuals and policies for engineers under CASE’s Ten Foundations for Risk Management. Expectations and Requirements To apply, you should • be a current member of the Council of American Structural Engineers (CASE) • be able to attend the groups’ two face-to-face meetings per year: August, February (hotel, travel reimbursable) • be available to engage with the working group via email and conference call • have some specific experience and/or expertise to contribute to the group Please submit the following information to htalbert@acec.org • Letter of interest • Brief bio (no more than 2 paragraphs) Thank you for your interest in contributing to your professional association!

April 2015

CASE is a part of the American Council of Engineering Companies

On February 5 – 6, the CASE Winter Planning Meeting took place in New Orleans, LA. CASE does two planning meetings a year to allow their committees to meet face to face and interact across all CASE activities. Over 30 CASE committee members and guests were in attendance, making this another well attended and productive meeting. During the meeting, break-out sessions were held by the CASE Contracts, Guidelines, Membership, Toolkit, and Programs & Communications Committees. Current initiatives include: Contracts Committee – Ed Schweiter (ews@ssastructural.com) • Currently working on revisions to the entire Contract Document library; available Summer, 2015 • Will be creating a “How to” sheet educating people on using the CASE Contract Documents Guidelines Committee – John Dal Pino (jdalpino@degenkolb.com) • Released the new Commentary on Code Of Standard Practice for Steel Joists (January, 2015) • Released a Standard of Care White Paper • Revising the following current Practice Guideline Documents: • CASE 962B – National Practice Guidelines for Specialty Structural Engineers • CASE 962-E – Self-Study Guide for the Performance of Site Visits During Construction • CASE 962-F – A Guideline Addressing the Bidding and Construction Administration Phases for the Structural Engineer • Guide to Special Inspections and Quality Assurance • Working on the following new documents: • Guideline on Project and Business Risk Management • Commentary on ASCE-7 Wind Design Provisions • Commentary on ASCE-7 Seismic Design Provisions

CASE in Point

CASE Winter Planning Meeting Update

Structural Forum

opinions on topics of current importance to structural engineers

The Role of Engineers in Transforming the Global Economy By Ashvin A. Shah, P.E.

he American political stalemate today between individual freedom and social equity is occurring in the context of increasing inequality in the domestic economy. However, the American economy is directly linked to and affected by the global economy ever since America emerged as the leader of the free world after two World Wars. The global economy, today serves well the 300 million Americans, along with perhaps another 700 million people; it does not serve well the remaining 6 billion people on the planet. In other words, the issues do not end at America’s borders; they are universal and demand a global approach. The debate needs to be focused on America’s role in transforming the global economy to become socially equitable and environmentally sustainable by a date certain. The vast majority of people in the global civil society lack adequate food, water, shelter, health, education, and security, to name a few social benefits that emerged from the 200-year-long technological revolution. These people need more of the individual freedom and social equity that Americans already have, but without the free-market fundamentalism of libertarians and the big-government safetynet ideas of the progressives. Freedom and equity go together in human affairs. When in harmony, both increase. When in conflict, both decrease. In my lifetime, I have seen Americans living with decreasing freedom and equity because these two values are in conflict in our politics. This also diminishes America’s role as the leader of the global economy. Refocusing politics to assume the challenges of this role will increase freedom and equity, not only in the American economy, but also in the global economy. Only America can provide leadership to make the global economy socially equitable and environmentally sustainable. Those living elsewhere simply do not have our two centuries of experience with the democratic evolution of constitutional government and equitable distribution of the social benefits of the technological revolution. Besides, there is now a third dimension beyond freedom and

equity making an impact: the natural environment, unable to provide virgin resources and unable to absorb wastes. Business as usual will not be able to create economic growth to provide well-being for everyone without reaching unacceptable levels of social and environmental impacts. A good example is China: In one generation, its economy has become the second largest, most inequitable, and most unsustainable in the world. Some say that we need to control population growth, which is true, but they advocate topdown measures that would not work in the long term; they fail to see the link established by demographers and sociologists that increasing freedom and equity together also leads to reduced population growth. Often this occurs in one or two generations, as we have seen for example in post-war Europe, Japan, Taiwan, and Korea. Scientists are aiming for a sustainable global economy for 9 billion people by 2050, but say nothing about social inequity. By joining the issues of equity and sustainability, we may actually be able to stabilize the population at 6 billion or fewer within that time frame – an easier path to a sustainable global economy. Exasperated by the present political stalemate, serious thinkers in American politics fear that constitutional government no longer works. Some are looking to the Declaration of Independence for remedies, whether more free markets or more government, adding to the stalemate. Only those professions that are directly involved in securing the wellbeing of Americans have the ability to take on the challenges to help the global economy become socially equitable and environmentally sustainable. These include medicine, engineering, education, law, and local and regional governments. Their goals should include decentralizing the economy and implementing the 10th Amendment of the Constitution to reduce the power of the federal government, increase the power of local governments, and increase both individual freedom and social equity. There are global political reasons why the federal government over the past one hundred

years has become so centralized. Chief among them is organization around high-energydensity fossil fuels. After the end of the Cold War, global political realities are rapidly changing, thanks in part to the information technology revolution that is actually helping to decentralize power around the world. Sources of low-energy-density energy may play as decisive a role in decentralizing the global economy in the 21st century as fossil-fuelsbased energy played in centralizing it around big corporations, big labor, big finance, big governments, and big national defense forces. The engineering (and architecture) profession has a compelling story to tell about how we have successfully avoided going to the federal government to regulate safety in buildings. There is no giant Department of Buildings in Washington, DC, or even in most state capitals. Buildings, even big buildings, are generally regulated at the local level, by small departments in each town or city who enforce a uniform building code developed within an open and democratic consensus process. This system evolved strictly in the American domestic politics arena, untouched by the events that tended to centralize power at the national level. This is a success story worth touting for the benefit of other professions. In summary, we need decentralization of science, engineering, and economics in America to function well at the local level, ultimately enhancing both individual freedom and social equity. Jon Schmidt’s work on engineering ethics stands out as exemplary in its systematic inquiry at the philosophical level of what needs to be done in changing the paradigm of engineering ethics. Now we need a similar effort at the engineering practice level to implement this new paradigm.▪ Ashvin A. Shah, P.E., is a professional engineer in Scarsdale, New York. He is involved in the topics of clean energy technologies, social equity, and environmental sustainability in the global economy. He can be reached at ashvinshah@aol.com

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 2015

STRUCTURE magazine | April 2015

Articles inside

Why they Stay Why they leave…

monongahela river Bridge

the role of engineers in transforming the global economy

Cinder Concrete Slab Construction

a Brief history of atC

Concrete Beam Strength vs. Serviceability

Periodic inspection of retaining Walls

Vibration of reinforced Concrete Floor Systems