A Joint Publication of NCSEA | CASE | SEI
STRUCTURE
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March 2012 Seismic SEI Structures Congress Chicago, Illinois March 29 – 31
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FEATURES New Brunswick Gateway Transit Village
34
By J. Benjamin Alper, P.E., Cawsie Jijina, P.E., SECB and Fortunato Orlando, P.E.
Design and construction of the New Brunswick Gateway Transit Village posed significant challenges. For the majority of the structural work on a given project, the structural design is fully specified directly in the construction documents. However, there are often portions of the project that are intended to be designed by other structural engineers and most often for supplementary items. What happens and where do the lines of responsibility lie when these elements play not just a primary role but a critical role in the overall structure?
Structural Design Ingenuity
38
By Alvin P. Tabar, P.E.
Phase 1 of the Loyola Science Center (LSC) is equipped with the latest technologies and provides distinctive spaces for teaching, learning, and research. Given the high level of environmental control required by sophisticated scientific equipment, structural and foundation designs have become increasingly complicated, while the characteristics of the supporting soil had limited scope for manipulation.
DEPARTMENTS 49 InSights
License Engineers and Certify Disciplines
By Mark Nowak and W. Lee Shoemaker, P.E., Ph.D.
By Timothy A. Lynch, P.E.
Top Risk Management Questions Facing Design Firms Today By G. Daniel Bradshaw
52 Great Achievements Nabih Youssef
By Richard G. Weingardt, P.E.
59 Spotlight Portland’s Shriners Hospital
A Joint Publication of NCSEA | CASE | SEI
STRUCTURE
7 Editorial Why Attend a Technical Committee Meeting at the Structures 2012 Congress?
By Professor Dennis R. Mertz, Ph.D., P.E.
9 InFocus The Nature of Competence
By Jon A. Schmidt, P.E., SECB
10 Structural Performance What’s Happened to Seismic Isolation of Buildings in the U.S.? By Andrew Taylor, Ph.D., S.E. and Ian Aiken, Ph.D., P.E.
15 Codes and Standards Chapter 13 or Chapter 15?
By Dain M. Hammerschmidt, P.E. and Nicholas D. Robinson, P.E.
21 Structural Design
By Vitaly B. Feygin, P.E.
26 Practical Solutions Perforated Masonry Walls
30 Building Blocks
IN EVERY ISSUE 6 Advertiser Index 6 Noteworthy 54 Resource Guide (Software Updates) 60 NCSEA News 62 SEI Structural Columns 64 CASE in Point
THE
COVER
By John Hillman, P.E., S.E.
40 Structural Practices A Soil Improvement Primer By Carrie Johnson, P.E.
44 Technology Role of BIM in Infrastructure Seismic Retrofits By Terry D. Bennett
Holes in CFS Cross Sections
The natural rubber bearing and steel damper seismic isolation system of the Ishinomaki Red Cross Hospital experienced maximum movements of approximately 9.8 inches (25 cm) in the Great Tohoku Earthquake of March 11, 2011. Seismic damage prevention in the United States is the focus of the article that appears on page 10. Courtesy of SIE, Inc. STRUCTURE magazine
Hybrid-Composite Beam Technology
46 Just the FAQs
®
By Chris Thompson, P.E., S.E. and N. Jacob Stept, P.E., S.E.
March 2012 Seismic
COLUMNS
By David T. Biggs, P.E., S.E.
51 Business Practices
ON
March 2012
Seismic Design of Pile-to-Pile Cap Connections in Flexible Pier Structures
66 Structural Forum
Trends in Cold-Formed Steel
CONTENTS
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March 2012
Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.
Advertiser index
PleAse suPPort these Advertisers
Aegis Metal Framing ............................. 50 American Concrete Institute ................. 14 Atlas Copco Construction & Mining .... 33 Bentley Systems, Inc. ............................... 8 Clark Dietrich Building Systems ........... 48 Computers & Structures, Inc. ............... 68 Concrete Masonry Assoc. of CA & NV. 27 CSC, Inc. .............................................. 11 CTS Cement Manufacturing Corp........ 23 DBM Contractors, Inc. ......................... 41 Devco.................................................... 55
Noteworthy
Fyfe ....................................................... 19 Geopier Foundation Company.............. 25 Halfen, Inc. ............................................. 4 Hohmann & Barnard, Inc. .................... 29 Integrated Engineering Software, Inc..... 42 ITW TrusSteel ....................................... 31 KPFF Consulting Engineers .................. 41 NCEES ................................................. 43 Polyguard Products, Inc......................... 47 Powers Fasteners, Inc. .............................. 2 RISA Technologies ................................ 67
SidePlate Systems, Inc. .......................... 37 Simpson Strong-Tie............................... 17 StrucSoft Solutions, Ltd. ......................... 3 StructurePoint ....................................... 57 Struware, Inc. ........................................ 24 Subsurface Constructors, Inc. ................ 58 Taylor Devices, Inc. ............................... 13 USP Structural Connectors ................... 20
Advertising Account MAnAger Interactive Sales Associates
news and information
New in 2012 – Structural Engineers Volunteer Roster for Disaster Response Over 250 volunteers already signed up NCSEA is pleased to announce the development of a web-based database to make it easier to contact structural engineers for assessments following a disaster. Please click on the link on the NCSEA home page (www.ncsea.com) to add your name and pertinent information to this system, so that you can receive timely updates regarding training, SEER program developments, and deployment opportunities, following natural and man-made disasters.
Chuck Minor
Dick Railton
Eastern Sales 847-854-1666
Western Sales 951-587-2982
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editoriAL stAFF Executive Editor Jeanne Vogelzang, JD, CAE
execdir@ncsea.com
Editor
Christine M. Sloat, P.E.
publisher@STRUCTUREmag.org
Associate Editor Graphic Designer
About the NCSEA SEER Committee After the terrorist events of September 11th 2001, it became obvious that a disaster of previously unthinkable magnitudes was possible. The unprecedented need for structural engineering technical assistance in these situations mandates a level of preparedness to ensure the most immediate, efficient, and effective response in possible future disasters.
editorial Board Chair
Jon A. Schmidt, P.E., SECB
Craig E. Barnes, P.E., SECB
Brian W. Miller
Richard Hess, S.E., SECB
Mike C. Mota, Ph.D., P.E.
Hess Engineering Inc., Los Alamitos, CA
Mark W. Holmberg, P.E.
Heath & Lineback Engineers, Inc., Marietta, GA
Roger A. LaBoube, Ph.D., P.E.
CRSI, Williamstown, NJ
Evans Mountzouris, P.E.
The DiSalvo Ericson Group, Ridgefield, CT
Greg Schindler, P.E., S.E.
KPFF Consulting Engineers, Seattle, WA
Brian J. Leshko, P.E.
Stephen P. Schneider, Ph.D., P.E., S.E.
John A. Mercer, P.E.
John “Buddy” Showalter, P.E.
Mercer Engineering, PC, Minot, ND
William Radig
webmaster@STRUCTUREmag.org
STRUCTURE® (Volume 19, Number 3). ISSN 1536-4283. Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $65/yr domestic; $35/yr student; $90/yr Canada; $125/yr foreign. For change of address or duplicate copies, contact your member organization(s). Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board.
reproduced in whole or in part without the written permission of the publisher.
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STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be
Burns & McDonnell, Kansas City, MO chair@structuremag.org
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March 2012
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editorial
Why Attend a Technical Committee new trends, new techniques and current industry issues Meeting at the Structures 2012 Congress? By Professor Dennis R. Mertz, Ph.D., P.E.
L
Structures Congresses, specialty conferences, provide articles for journals, manuals of practice, committee reports and more.” Attendance and participation in a technical committee meeting during your stay at the Structures Congress provides you with access to the technical, educational, and professional issues needed to advance and succeed in your area of practice. The technical committee meetings highlight the newest developments in research and practice in their areas of expertise as the committee agendas feature up-to-the minute topics, not issues based upon abstract and paper submissions from months ago. More importantly, the SEI is looking for the participation of all of the members to enhance the activities of their technical committees and the Institute in general. You can contribute to these activities through attendance, participation and perhaps ultimately membership in one of these technical committees. Committee participation not only enhances your perspective, skills and expertise, but you can enhance the committee’s activities by bringing your unique insights and experiences to the committee. In recent years, technical committee members have developed several committee reports and manuals of practice on subjects such as concrete transmission poles, tension fabric structures, and structural identification of constructed systems. In addition, committee members contribute to the development of a wide range of TAD Special Projects. Currently there are special projects on performance-based design for fire loads, composite structures, and regional design forums to help create a generational dialogue between experienced structural engineering professionals and younger members. These projects would not have reached fruition without the help of dedicated committee members who volunteer their time. So, when you come to the Structures Congress, why not select a technical committee of interest to you and plan to attend their meeting. A list of technical committees, subcommittees and task committees with their mission statements and chairs is included on the TAD page of the SEI website (www.asce.org/SEI). The schedule of technical committee meetings can be found in the Structures 2012 Congress final program. This schedule is also available on the SEI (www.asce.org/SEI) and Structures 2012 Congress (www.structurescongress.org) websites. Attend a technical committee meeting at the Structures Congress, improve yourself and improve the Institute.▪
a member benefit
structure
®
ater this month, over 1000 structural engineers will gather in Chicago for the Structures 2012 Congress, March 29-31, 2012 at the Fairmont Chicago, Millennium Park. Few cities have a richer variety of structural engineering achievements than Chicago. From the staggering high-rise buildings to the network of bridges and other infrastructure, this year’s Structures Congress attendees will be surrounded by inspiration. The technical program will feature eleven tracks of technical sessions with current insights about buildings, bridges, and non-building structures from structural engineering leaders. In addition, attendees can enjoy multiple networking opportunities, well-respected keynote speakers, the ability to earn up to 25.5 PDHs, and a comprehensive exhibit hall. Do you know that most of the Structural Engineering Institute’s (SEI) Technical Administrative Division (TAD) technical committees meet during the annual Structures Congress? One of the unique elements of the Structures Congress is the breadth and number of technical committee meetings that occur concurrently. This gives attendees the opportunity to sample some of the initiatives that committees will be working on during the coming year. In addition to the various tracks of familiar technical sessions full of interesting presentations, the SEI technical committees meet to conduct their business. The purpose of the TAD is to “advance the science of structural design by increasing the knowledge of the physical properties of engineering materials, developing methods of analysis, studying the relative merits of various types of structures and methods of fabricating, and disseminating knowledge relating to this division of the engineering profession.” In order to accomplish this purpose, the executive committee of the TAD oversees more than sixty technical committees, subcommittees and task committees under nine technical administrative committees (TAC): Analysis and Computation; Bridges; Concrete and Masonry Structures; Dynamic Effects; Metals; Performance of Structures; Special Design Issues; Life-Cycle Performance, Safety, Reliability and Risk of Structural Systems; and Wood. Many of these committees meet during the Structures Congress, and most of their meetings are open to Congress attendees. Why would you wish to attend one of these meetings, you ask. You can see the inner workings of the TAD and its committees by attending a committee meeting, and you can contribute to these efforts. The STRUCTURAL committees “develop technical ENGINEERING INSTITUTE publications, technical sessions for conferences including future
STRUCTURE magazine
Professor Dennis R Mertz, Ph.D., P.E. is the Director of the Center for Innovative Bridge Engineering at the University of Delaware. Professor Mertz is currently a member of the SEI Board of Governors and as such a member of Executive Committee of the SEI Technical Activities Division. He also serves on both the Structures Congresses committee and the Structures Congress National Technical Program committee.
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March 2012
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inFocus
new trends, new techniques and current industry issues The Nature of Competence By Jon A. Schmidt, P.E., SECB
T
he purpose of engineering licensure is to verify that anyone who may legally accept responsible charge of an engineering assignment has demonstrated at least minimal competence in the relevant discipline. But what constitutes competence? And what degree of competence is an appropriate threshold? The fact that we are concerned with competence reflects how engineering is as much an art as a science, requiring knowledge-how as well as knowledge-that (“Engineering as Knowledge-How,” November 2011). In other words, engineering involves the exercise of skill, not just awareness of facts and techniques. It is therefore useful to consider how people develop skills in order to gain a better understanding of what it means to be competent and what it takes for someone to become competent. Philosopher Hubert Dreyfus and his brother Stuart, an industrial engineer, proposed a popular model of skill acquisition in conjunction with their work on the (in)feasibility of artificial intelligence (“What Computers Can’t Do,” November 2009). Using a phenomenological approach, they studied “unstructured” problem areas that (like engineering) “contain a potentially unlimited number of possibly relevant facts and features” and identified five distinct stages in their 1986 book, Mind over Machine: The Power of Human Intuition and Expertise in the Era of the Computer, and subsequent writings: 1) The novice complies with strict rules based on context-free features of the task environment. 2) The advanced beginner recognizes situational aspects of the task environment and follows maxims to adjust his or her actions accordingly. 3) The competent performer does not try to account for all discrete elements of the task environment, but instead selects a plan, goal, or perspective for establishing which of them are relevant and which may be safely ignored. 4) The proficient performer no longer reflects on the task environment as a detached observer, but sees what needs to be done without having to evaluate multiple options, and then chooses how to go about doing it. 5) The expert intuitively perceives both what needs to be done and how to do it, making especially subtle and refined discriminations in a variety of task environments that are sufficiently similar to those previously encountered. The higher levels can only be attained through extensive experience and are characterized by less rational deliberation and greater emotional involvement. As Dreyfus and Dreyfus put it, “When things are proceeding normally, experts don’t solve problems and don’t make decisions; they do what normally works.” A standard example is driving a car. The novice shifts gears based strictly on speed as conveyed by the instrument panel, while the advanced beginner also pays attention to less obvious cues like engine sounds. The competent driver, aware of multiple factors, may determine that he is going too fast, and then must decide what to do about it; while the proficient driver senses that he is going too fast. Finally, “The expert driver becomes one with his car, and he experiences himself simply as driving, rather than as driving a car.”
STRUCTURE magazine
The Dreyfus model is consistent with Billy Koen’s thesis that the universal method for all aspects of human existence is the use of heuristics (“The Engineering Method,” March 2006; “Heuristics and Judgment,” May 2006). Initially we learn explicit rules and maxims, and over time we develop conscious and unconscious ways of decomposing and solving problems based on what has and has not worked for us. These are not necessarily procedures that we can communicate in words; they have become integral to who we are and how we operate, as long as we remain within the domains in which we are genuinely competent. This is an important constraint to acknowledge. Even experts inevitably revert to the behavior characteristic of novices and advanced beginners when confronted with unfamiliar circumstances. They must fall back on rules and maxims, because they lack the kind or amount of experience that would enable them to discern the appropriate course of action on their own. How does the Dreyfus model apply to engineering? Formal education primarily imparts rules for the novice, like calculating the maximum moment on a simply supported, uniformly loaded beam as wL2/8. An engineer intern becomes an advanced beginner during the first few years of a career by picking up on maxims such as “least weight does not equal least cost” and their implications. Competence is achieved when an engineer is capable of employing independent judgment to focus on what really matters and converge relatively quickly on a viable solution. Although it may be an accident of terminology, this appears to be where the bar is currently set for licensure. In particular, it is important to recognize that the law does not require engineers to be experts. Instead, courts have established a reasonable “standard of care” by which professional conduct is judged against how a typical practitioner would ordinarily perform in similar situations. In fact, those who call themselves “experts” may find themselves held to a higher standard – one that is not covered by their liability insurance. That said, is competence – as defined by Dreyfus and Dreyfus – really sufficient to protect the safety, health, and welfare of the public? Given the complexity and life safety ramifications of structural engineering, perhaps the minimum qualification for those who are authorized to practice it should not be mere competence, but proficiency. The new NCEES Structural examination appears to reflect this sentiment. It is 16 hours long, and half of the problems are in essay format, while all of the other NCEES PE exams are only eight hours long and consist entirely of multiple-choice questions. If passing those tests legitimately establishes that someone is competent, then it seems fair to say that passing the more rigorous Structural exam establishes that someone is proficient.▪ Jon A. Schmidt, P.E., SECB (chair@STRUCTUREmag.org), is an associate structural engineer at Burns & McDonnell in Kansas City, Missouri, and chairs the STRUCTURE magazine Editorial Board. An abridged version of this text appeared in the November 28, 2011 issue of Engineering News-Record.
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March 2012
Structural Performance performance issues relative to extreme events
The seismically-isolated Ishinomaki Red Cross Hospital, about 75 miles (120 km) from the epicenter of the M9.0 Great Tohoku Earthquake of March 11, 2011, was undamaged, and fully-operational throughout and after the earthquake and subsequent tsunami. Courtesy of SIE, Inc.
S
eismic isolation is the strategy of placing a structure on a flexible foundation to effectively decouple earthquake ground motions from the motion of the building. It is a technically elegant solution to the challenging problem of minimizing or even eliminating earthquake damage in buildings. Yet, despite the substantial benefits offered by seismic isolation and its availability since the mid 1980s, while other countries have readily embraced the technology, the United States has been slow to adopt seismic isolation. In the United States there are only about 125 seismically isolated buildings, whereas in Japan there are more than 6500 and a similar number of bridges. In China there are estimated to be several hundred buildings. After a promising start in the mid-1980s, today seismic isolation of buildings in the U.S. has nearly ground to a halt: presently, only about four or five seismically-isolated buildings are constructed each year. Why have building owners in the U.S. apparently ignored the most effective means available for protecting their investments from earthquake damage? There is no single reason, but rather a host of factors. In this article we explore these factors, and make suggestions for removing some of the barriers to the implementation of seismic isolation in the United States. The concept of seismic isolation is not new. More than one hundred years ago, in 1885, the Englishman John Milne designed and constructed a seismic isolation system for a building in Tokyo that incorporated ball bearings and dished cast iron plates (Naeim and Kelly, 1999). The first use of rubber for a seismic isolation system was in 1969, when a school in Skopje, Macedonia was constructed on unreinforced rubber blocks. The first modern-era
What’s Happened to Seismic Isolation of Buildings in the U.S.? By Andrew Taylor, Ph.D., S.E. and Ian Aiken, Ph.D., P.E.
Andrew Taylor, Ph.D., S.E. is an Associate with KPFF Consulting Engineers (Seattle, WA). Andy may be contacted at andrew.taylor@kpff.com. Ian Aiken, Ph.D., P.E. is a Principal at Seismic Isolation Engineering, Inc. (Emeryville, CA). Ian may be contacted at ida@siecorp.com.
The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.
10 March 2012
seismically-isolated building was a government building in Wellington, New Zealand, constructed in 1981, which used laminated steel and rubber bearings. These bearings contained a lead core that dissipates energy through plastic deformation during an earthquake, a system that since has become one of the most widely used in the world. Seismic isolation was first introduced to the United States in 1985 with the construction of the Foothill Communities Law and Justice Center, in Rancho Cucamonga, California. This 170,000 square foot facility also uses laminated rubber bearings, called high-damping rubber bearings, with a specially formulated rubber compound to provide the energy dissipation properties to the system. Also developed in the United States in the mid-1980s was a sliding seismic isolation system known as the Friction Pendulum System, which has a sliding surface in the shape of a spherical dish and a low-friction articulated slider to provide an elongated natural period for the supported structure. The first application of this system was the seismic retrofit of a wood frame apartment building in San Francisco that was damaged by the 1989 Loma Prieta earthquake. The first design provisions for seismic isolation, the Tentative Seismic Isolation Design Requirements by the Structural Engineers Association of Northern California, were published in 1986. These evolved into the first formal building code provisions for seismic isolation in the 1991 Uniform Building Code (UBC) and are now embodied in the International Building Code (IBC), through reference to ASCE/SEI 7, and exist in similar form for seismic isolation retrofit in ASCE/SEI 41. Thus, by the early 1990s, it appeared that seismic isolation was poised to take off in the United States as the earthquake protection system of choice, particularly for critical facilities such as hospitals, police and fire stations, and emergency operations centers, high-value
buildings such as museums and data centers, and socially important buildings such as historic city halls. By the late 1990s, though, there were only about 50 seismically-isolated buildings in the U.S., of both new and retrofit construction. This hardly represented the “revolution” in seismic protection technology envisioned by early advocates of seismic isolation; on average, between 1985 and 1997 only about three seismically-isolated building projects were completed each year. In Japan, at the time of the Great Hanshin (Kobe) Earthquake on January 17, 1995, about 85 seismicallyisolated buildings had been approved for construction. By the year 2000, there were about 600 (Aiken, et al, 2000). Through the following decade, thousands more seismically-isolated structures were constructed in Japan. What has accounted for the slow pace of adoption of seismic isolation in the United States? While there certainly are technical challenges to the implementation of seismic isolation, these challenges have mainly been overcome. Today the barriers to implementation in the U.S. are not primarily technical, but rather economic, cultural and regulatory.
Economic Barriers With few exceptions, building construction in the U.S. is driven by “first-cost” considerations rather than “life-cycle” or “risk management” cost-benefit considerations. When the primary objective of a building project is to keep the initial cost of construction to a minimum, then seismic isolation does not make economic sense. The cost of seismic isolation varies, and the actual costs are a function of the building configuration, total floor area, and seismic design performance objectives. For a typical medium-size data center or laboratory building, a rough estimate of the cost of seismic isolation is 5 to 15 percent of the cost of the structural framing system (note that this is not the total project cost; depending on the type of facility, seismic isolation often amounts to only a few percent of the total project cost). When it comes to consideration of seismic isolation, this added cost almost always ends up being a “deal breaker”; why would a building owner add 5 to 15 percent to the structural cost of their project with no clear economic incentive? Why would a developer add seismic isolation as a “feature” when the cost of isolation might make their project un-competitive?
When a life-cycle cost evaluation is performed, considering the full expected life span of a building and assuming the occurrence of a code-based design-level earthquake event during that life span, a far different conclusion is reached. For such an event, a seismically-isolated building can be expected to experience essentially no damage, a far different outcome than for an ordinary building. Furthermore, in the event of a design-level, or even beyond-design-level earthquake, most isolated facilities can be expected to remain fully functional, eliminating losses caused by down-time, lost production, lost data, and lost building contents. An impressive example of this is the fully-operational performance of the Ishinomaki Red Cross Hospital in the M9.0 Great Tohoku Earthquake of March 11, 2011, dramatically demonstrated in this publicly available video: www.youtube.com/watch?v=Pc1ZO7YwcWc. Viewed in such a light, seismic isolation almost always shows itself to be economically worthwhile. Seismic isolation would become more economically attractive to building owners if property insurers recognized the benefits of isolation in reducing earthquake damage. To date, however, insurers have
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Overall view of the isolation basement of the Ishinomaki Red Cross Hospital. The isolation system comprises about 100 natural rubber bearings and U-shaped steel dampers. (Photo: SIE, Inc.)
been unwilling to grant premium benefits for seismically-isolated buildings. Whereas insurers routinely offer premium discounts for protection measures such as fire-resistant construction, fire and theft alarms, hurricane resistant windows, and other building features that reduces potential losses, to date they have been unwilling to recognize the benefits of seismic isolation. If insurers were to provide premium incentives to building owners to use advanced protective measures such as seismic isolation, they would help to encourage the use of the technology in the same way that they have encouraged the use of fire-resistant construction.
Cultural Barriers In the United States earthquakes tend to be viewed as regional hazards, affecting mainly “seismically active” areas such as California, Nevada, Oregon, Washington State, and Alaska. Anyone familiar with seismic hazards in the United States, however, knows that significant seismic hazards actually exist throughout much of the country. Still, the general perception is that earthquakes are not a national problem, but a localized one. In other countries, such as Japan, New Zealand, and Italy, earthquakes are recognized as a threat to the safety and economic well-being of the entire nation. In these countries there is a heightened awareness of earthquake hazards and therefore a willingness to spend resources to mitigate earthquake damage through implementation of seismic isolation.
In the United States there is little interest in devoting time and money to prepare for earthquake events that are viewed (often incorrectly) as having only a small probability of occurrence during the life of a structure. When it is proposed to building developers that they may want to consider designing their building for a seismic performance level above the code-mandated minimum, the authors are consistently met with a blank stare: “Why would I want to do that? Doesn’t the building code make my building earthquake-proof?” When it is explained that the building code provides only a minimum level of safety, and that additional design and construction costs are required to provide improved seismic performance, the typical response is “Let’s just go with the code.” It is human nature to believe that bad things will happen to “the other guy”, and in a country the size of the United States, it is even easier to imagine that earthquake damage will happen to someone else in some other place. In other countries, where earthquake hazards exist throughout the nation, it is not as easy to rationalize away the threat of earthquakes. This cultural difference in the perception of seismic hazards, and the willingness to pay for improved seismic performance, applies not only to developers of commercial buildings, but also to individual home owners. Various estimates have that anywhere from 150,000 to 250,000 people live in seismically-isolated buildings in Japan, and these people have all paid a “premium” to do so. For a typical large condominium building in Japan, the accepted additional cost for seismic isolation
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is on the order of the price of a small car, about $15,000 or about 5 percent more than a condominium without isolation. In contrast, the number of people in the U.S. who live in isolated buildings is about two dozen. Countries such as Turkey, Chile and Italy are now experiencing a dramatic upswing in the adoption of seismic isolation for both critical (hospitals, emergency operations centers) and non-essential “commercial” applications (such as multi-unit residential structures). Why? In these countries, recent large earthquakes have caused profound economic and lossof-life disasters. Seismic isolation has been recognized as the best technology to protect core components of society’s infrastructure. It is also interesting to note that in Turkey seismic isolation devices must be imported, due to the lack of local manufacturers, which means the costs to implement seismic isolation are even higher than in the U.S. Even so, this cost premium is not proving to be an impediment to the use of the technology.
Regulatory Barriers Regulatory impediments to the acceptance and implementation of seismic isolation persist today. Numerous experimental and analytical research programs in the 1980s at many prominent research laboratories worldwide conclusively verified the effectiveness of seismic isolation, and established a strong technical basis for practical design. Building code provisions for seismic isolation, originally established in the 1991 UBC, have systematically evolved since then. It cannot, however, be said that code requirements have been improved in ways to facilitate more straight-forward and widespread use of the technology. In Japan, the 2000 revision of the Building Standard Law, the national building code, incorporated new provisions for seismically-isolated buildings that allowed for response spectrum, rather than time-history analyses, along with other simplified design requirements for certain types of isolated structures. These provisions are now used for the design of about one-third of all isolated buildings in Japan. Whilst a number of efforts have been made over time to codify simplified procedures for seismic isolation design in U.S. codes, none have ever been adopted. Instead, seismic isolation design codes have become increasingly complex, and therefore less intuitive and more difficult to use. In the U.S., the codified performance basis for seismically-isolated structures is higher than that for ordinary structures; that is, the
playing field is not level. Clearly, the analysis and design of a seismically isolated building presents greater technical challenges than for an ordinary building, but the building codes place significantly higher requirements on both the seismic performance expectations and on the level of technical review required of the designer. Building owners often do not understand that these additional requirements exist, or why they lead to increased construction costs and design fees. Seismic isolation is a mature technology with a 30-year track record of successful implementation. It’s time that onerous code requirements for complex analysis, multi-party peer review, and full preliminary prototype testing of isolation bearings on every project be reduced, as they lead to superfluous costs and schedule delays that inhibit the adoption of seismic isolation.
Summary
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In short, the authors believe that the following actions would increase the adoption of seismic isolation of buildings in the U.S.: • Move away from sole considerations of “first cost” when planning building projects, and give fuller consideration to building life-cycle costs. This is one of the bases of the “green building” movement, where potential increases in first costs are accepted to achieve long-term sustainability objectives. • Property insurers should be encouraged to recognize the benefits of seismic isolation (and other enhanced seismic protection technologies) in preventing earthquake damage. If reduced insurance premiums were factored into the life-cycle costs of seismically-isolated buildings, the technology would become more economically attractive. • The design team (engineers, architects, and planners) should not be afraid to promote seismic isolation as a means to reduce or eliminate seismic hazards, increase reliability, and lower total life-cycle costs. While seismic isolation is still a somewhat unusual approach to earthquake protection in the U.S., it has been widely accepted in other countries
to the point that elsewhere seismic Readers are invited to submit their own isolation design and construction are thoughts on why the U.S. has been slow to considered routine. adopt seismic isolation, while other countries • Regulatory barriers to seismic have more readily adopted the technology isolation should be reduced. In (isolationfeedback@live.com). The authors particular, better simplified methods are particularly interested to hear from those for seismic isolation design should of you who have promoted, but not managed be implemented in building codes, to implement, seismic isolation for a project. and requirements for peer review These ideas will be collected and will form the and project-specific prototype testing basis of a follow up article in a future issue of TAY24253 BraceYrslfStrctrMag.qxd 9/3/09 10:09 AM magazine.▪ Page 1 should be streamlined. STRUCTURE
T
he proper use and application of ASCE 7 seismic provisions for industrial structures (ASCE 7-05 Chapters 13 and 15) can be difficult to determine due to the complexity and individuality of these structures. Engineers are often left questioning how to properly apply the code to their unique situation. The objective of this article is to increase understanding of the code’s application pertaining to industrial structures, and help clarify the use of ASCE 7-05 generated loads for nonbuilding structures and nonstructural components. With a stronger understanding, structural engineers can stay focused on what they do best, smart designs that are safe and economical. Within this article several examples of commonly encountered design scenarios are presented, giving special emphasis to code application in industrial structures. The examples and associated commentary describe potential misapplications of code provisions pertaining to industrial structures. Procedures and flow charts are provided that are intended to provide engineers with a better understanding of how to use ASCE 7-05 generating loads, as defined within Chapter 13 and 15.
Classification One of the first challenges facing engineers designing industrial structures is determining if an item is classified as a nonbuilding structure or a nonstructural component. This is an important first step to help establish which load generation method, as prescribed in ASCE 7-05 Chapter 13 or Chapter 15, is needed. ASCE 7-05 is not always straightforward but as a rule of thumb; if an item is self supporting (i.e. sits directly on its foundation) it is a nonbuilding structure, whereas most other items in industrial facilities are components. An article published in the July 2008 issue of STRUCTURE® magazine (Bachman, Dowty. (2008, July) Is It a Nonstructural Component or a Nonbuilding Structure?) did a thorough comparison of nonstructural components and nonbuilding structures and is a suggested read. Also recommended is the ASCE publication (ASCE Task Committee on Seismic Evaluation and Design of Petrochemical Facilities. (2011) Guidelines for Seismic Evaluation and Design of Petrochemical Facilities, Second Edition). Both of these publications provide valuable information, which can be related to most industrial designs. The following are some examples of nonbuilding structures and nonstructural components commonly seen in industrial applications. Nonbuilding Structures: • Pipe Racks • Large Field Erected Tanks • Self Supporting Silos
• Chimneys • Cooling Towers • Large Fans • Large Pumps Nonstructural Components: • Piping • Large Ductwork • Suspended Boilers • Supported Turbines • Supported Tanks In general, these associations are typical but not always completely accurate. The use of nonbuilding structures similar to buildings to support other nonbuilding structures is common in industrial structures. To improve accuracy, the engineer needs to have a firm understanding of the physical makeup, construction and support of the industrial structure he/she is classifying. To achieve this understanding, the engineer may need to engage in important research and coordination with equipment vendors to better understand the structural behavior of the item being evaluated. This understanding can then be used to determine the three most important variables needed when classifying a structure accurately; relative weight, stiffness, and fundamental period. Sections 13.1.5 and 15.3 provide guidance for determining which path forward to take, once structural characteristics are understood. According to Sec. 15.3, three scenarios are possible (see the flowchart in Figure 1, page 16). The following are descriptions of these three potential scenarios: WNB = Weight of the supported nonbuilding structure WS = Weight of the supporting structure TNB = Fundamental period of the supported nonbuilding structure
Codes and standards updates and discussions related to codes and standards
Chapter 13 or Chapter 15?
Scenario 1 WNB ≤ 0.25(WNB + WS) The supported nonbuilding structure should be designed as a component using the provisions of ASCE 7-05 Chapter 13. The supporting structure should be designed as a nonbuilding structure similar to buildings using the provisions of ASCE 7-05 Chapter 15. The supported nonbuilding structure should be treated as an additional mass for the design of the supporting structure. Scenario 2 WNB > 0.25(WNB + WS), TNB ≤ 0.06s The supported nonbuilding structure should be designed as a component using the provisions of ASCE 7-05 Chapter 13 with the following modifications: Rp=R taken from the appropriate entry in table 15.4-2 and ap=1. The supporting structure should be designed as a nonbuilding
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Are You Using the Wrong Loads? By Dain M. Hammerschmidt, P.E. and Nicholas D. Robinson, P.E.
Dain M. Hammerschmidt, P.E. (dain.hammerschmidt@kiewit.com), is a Lead Engineer and Nicholas D. Robinson, P.E. (nicholas.robinson@kiewit.com), is a Staff Engineer at Kiewit Power Engineers Co. in Lenexa, Kansas.
structure similar to buildings using the provisions of ASCE 7-05 Chapter 15. The supported nonbuilding structure should be treated as an additional mass for the design of the supporting structure. It should be noted that TNB ≤ 0.06s is very rarely achieved given that the effect of support flexibility (such as floor beam deflections) must be included in the determination of TNB. Scenario 3 WNB > 0.25(WNB + WS), TNB ≥ 0.06s The supported nonbuilding structure and the supporting structure should be analyzed as a single composite structure. This combined analysis should accurately capture the mass distribution and stiffness of both the supported nonbuilding structure and the supporting structure. Both the supported nonbuilding structure and the supporting structure should be designed for the forces determined in the combined analysis in accordance with ASCE 7-05 Chapter 15. The R value used should be the lesser value of the supported structure or the supporting structure. Please note that for non building structures that have significantly different full and empty weights, the case that maximizes the weight of the non building structure should be used to determine the applicable scenario. Once the engineer has accurately classified the structure, and determined which portion of the code is applicable, execution of load generation can begin. The following are summarized procedures for Chapter 13 and Chapter 15, as outlined within ASCE 7-05.
Chapter 13 Procedures The ASCE 7-05 Chapter 13 procedure to determine seismic loading on nonstructural components is a method that is independent of the supporting structure, with most parameters contained within the chapter. The procedure described herein will be limited to the typical case used for mechanical and electrical components. The procedure consists of the following steps: 1) Evaluate the applicability of section 13.1.5. 2) Determine component factor Ip as defined in 13.1.3. 3) Determine the appropriate seismic coefficients Rp and ap, per table 13.6-1.
Figure 1: Design Flowchart for Nonstructural Components and Nonbuilding Structures in Industrial Facilities (ASCE 7-05).
4) Where a modal analysis is used, see equation and associated parameters 13.3.4. 5) Determine the component operating weight Wp per section 13.3. 6) The period can be determined using 13.6.1 but this value is not a direct variable needed for load generation. 7) The component design forces (Fp) should be determined per section 13.3.1 using the associated boundary limits. ASCE 7-05 Sec. 13.6 contains several design provisions for specific nonstructural components. While beyond the scope of this article, these provisions should always be checked. Section 13.4 instructs that the force Fp be used to design the component and its attachments. It is important to note that forces determined in accordance with Chapter 13 should not be used to design the supporting structure (Figure 2, page 18). It is common for equipment vendors to provide earthquake loads calculated in accordance with Chapter 13. These loads can
sometimes be misinterpreted as supporting structure design loads, which is not the case. Chapter 13 loads should be used to design the equipment and its attachment to the supporting structure. In most cases, for commercial type buildings these loads are conservative (in some cases extremely conservative). In industrial structures, however, it is common to use low R factors (1.5 or 1) selected from table 15.4-1 in order to avoid special detailing requirements. This decision can result in loads that are calculated using Chapter 13, which are not conservative when used to design the supporting structure.
Chapter 15 Procedures Most support structures and certain pieces of equipment in industrial structures are considered “Nonbuilding Structures” by ASCE 7-05. Seismic design of nonbuilding structures is governed by Chapter 15 of ASCE 7-05. Chapter 15 divides nonbuilding structures into two primary groups, those continued on page 18
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March 2012
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Figure 2: Steel Braced Frame Design Example.
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Figure 2: Steel Braced Frame Design Example.
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Figure 2: Steel Braced Frame Design Example.
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Figure 2: Steel Braced Frame Design Example.
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in which the Chapter 13 component loads are much greater than the supporting structure design loads. The second example uses a small R factor and highlights the less common situation in which the reverse is true. These examples highlight a potential misunderstanding that can occur when the ASCE 7 code is not accurately applied to a common industrial design scenario. Even though the seismic variables are accurately
STRUCTURE magazine
defined and calculated, the method chosen will yield substantially different results. The provided commentary, external references, flowchart, and examples have been assembled in an attempt to raise awareness in those engineers who face similar design challenges on industrial projects. Tooled with an increased awareness, future industrial projects can be designed with greater safety, smarter framing, and fewer material quantities.▪
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structures similar to buildings and those not similar to buildings. This article will focus on nonbuilding structures similar to buildings. The ASCE 7-05 Chapter 15 procedure to determine seismic loading on nonbuilding structures similar to buildings is very similar to that for buildings. In general, the procedure consists of the following steps: 1) Select a structural system from either table 15.4-1 or table 12.21. Determine the following variables: R, Ω0, and Cd. 2) Determine I from table 11.5-1 3) Determine the effective seismic weight in accordance with ASCE 7-05 Sec. 12.7.2. This weight should include any components or nonbuilding structures supported by the structure under consideration. The use of the full or empty weight should be in agreement with the gravity loads in the same combination (i.e. if the contents of a tank are not included in the gravity loads of a combination they should not be included in the seismic weight and vice versa). 4) Determine the period of the structure using one of the procedures outlined in Sec. 15.4.4. It is not acceptable to use the approximate fundamental period for a nonbuilding structure. 5) Determine Cs from the procedure outlined in ASCE 7-05 Sec. 12.8.1.1. 6) Determine the base shear V using Eq. 12.8-1. 7) Distribute the base shear per ASCE 7-05 Sec. 12.8.3. ASCE 7-05 Sec. 15.5 contains several design provisions for specific nonbuilding structures. While beyond the scope of this article, these provisions should always be checked. To better reinforce the goals of this article, a typical industrial scenario has been included that demonstrates the divergence that can occur between Chapter 13 and Chapter 15 load generation. The examples shown in Figure 2 illustrate scenario 2, discussed earlier. Both examples consist of a steel braced frame supporting a large ash hopper. The first example uses a large R factor and highlights the common situation
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D
iver inspections in the aftermath of the 1985 Kobe and 2010 Haiti earthquakes uncovered an unexpected discovery. In many locations, piles were completely or partially separated from the pile caps. In some areas, pile sockets were ripped off the pile cap. While such behavior was not anticipated, thorough review of the forces generated at the pile-to-pile cap interface indicated that, on many occasions, connection ductility was grossly overestimated. Current design practice utilizes an assumption, introduced by J.W. Gaythwaite, that the piles in a pile bent have a fixity point some distance (D) below the mud-line, equal to half the critical length. This is determined from a lateral pile deflection analysis based on the Winkler spring soil model. Gaythwaite produced two equations for calculating the depth between the mud-line and the assumed point of fixity: • For granular soils, D=1.8 (EI/nh)0.2 (Equation 1) • For consolidated clay, D=1.4 (EI/ks)0.25 (Equation 2) Where, E = modulus of elasticity of pile material; I = moment of inertia of the pile cross-section; nh = horizontal subgrade modulus for granular soils, which varies with depth; and ks = modulus of subgrade reaction for clay. Gaythwaite emphasized that Equations 1 and 2 apply only if the total pile embedment length exceeds 3D. However, his assumption is only partially correct. What Gaythwaite has identified is nothing more than the zero-deflection point whose partial fixity is represented by a rotational spring with a stiffness defined as follows: kr = M/ (Equation 3) Where, M = flexural moment at zero-deflection point; and = slope of the elastic curve at zerodeflection point. To produce a partial fixity support condition, the pile embedment length should be sufficient to develop at least two zero-slope points within the soil medium. The arbitrary 3D embedment length introduced by Gaythwaite sometimes falls short of that requirement. G.P. Tsinker suggested another model utilizing non-linear springs for pile soil supports; however, such springs utilizing P-y curves were only recently introduced into some finite element analysis software packages. Linear Winkler springs traditionally used for pile bent analysis frequently place the zero-deflection point significantly higher on the piles, underestimating soil crushing. Obviously, the use of non-linear soil springs increases the complexity of the pile bent analysis. However, non-linear soil supports better predict forces at the pile-to-pile cap interface.
Understandably, the complexity of the analytical procedure greatly affects design price. Nevertheless, deficient assumptions often impact the ultimate price of the product, adding the cost of remedial repairs required in the aftermath of a destructive event. Oversimplification of design assumptions frequently delivers an inferior product to the client.
Fundamentals of Seismic Forces There are two basic types of seismic waves: body waves and surface waves. Body waves travel along rays extended from the earthquake’s epicenter, deep under the earth surface, to the surface of the earth. They have two independent wave components: • P-waves, called primary longitudinal waves or “compression waves.” These travel in compression motions with speeds approaching 16,000 ft/sec in solid rock. • S-waves, called secondary waves or “shear waves.” These travel along the same ray path as compression waves but cause sinusoidal ground displacements perpendicular to the direction of wave propagation. The speed of S-waves is about 50-60% of the speed of P-waves in the same soil medium. Similar to body waves, surface waves have two independent components: Rayleigh waves and Love waves. Once surface waves are activated by body waves, they become independent, propagating along the earth’s surface. • Rayleigh waves travel as ripples with a speed comparable to that of S-body waves. Their behavior is similar to that of waves on the surface of water, creating vertical rolling motions in the direction of propagation. Soil particles in a Rayleigh wave move on an elliptical trajectory in a direction opposite to wave propagation. Rayleigh waves have a low frequency, but long duration, and comparatively small initial amplitude. However, the effects of the Rayleigh waves can be compared to those of tsunami waves during their final stage, when they are gaining amplitude in shallow waters. In some geotechnical conditions, surface waves are just as devastating, quickly gaining amplitude within very short distances, depending on the reflective and absorptive characteristics of the underlying soil medium. continued on next page
STRUCTURE magazine
Structural DeSign design issues for structural engineers
Seismic Design of Pile-to-Pile Cap Connections in Flexible Pier Structures
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By Vitaly B. Feygin, P.E. Dedicated to my mentor and friend R.J. Mancini, P.E.
Vitaly B. Feygin, P.E., is a principal structural engineer with Marine and Industrial Consultants, with offices in Baltimore and Tampa. He is the author of two patents related to sea walls, composite cofferdams, bridge fenders and port structures. He may be reached at (vfeygin.mic@gmail.com).
The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.
A brief review of the nature of seismic forces indicates that, at any given time during an earthquake, a point on the earth’s surface is constantly moving in all six degrees of freedom. Therefore, accounting for forces restricting pile head movement in all six degrees of freedom is important for the successful design of ductile pile-to-pile cap connections.
Analytical Procedure for Pile Bent Analysis
Figure 1: Forces acting on the pile head at any time during seismic event.
• Love waves cause horizontal shifts perpendicular to the direction of wave propagation. They have the highest amplitude. Frequently, a direct surface wave can create a reflective wave traveling in the opposite direction. Superposition of two harmonic waves depends on the relative phase of each wave. Superposition of two waves traveling in opposite directions can create a local standing wave with amplitude equal to the sum of two individual wave amplitudes. Such a phenomenon is based on soil medium reflection and transmission characteristics. The sign of the reflected wave depends on the reflection boundaries of the soil medium. Prediction of the phases of direct and reflected waves is a demanding and nearly impossible task. However, engineers cannot ignore the possibility of a standing wave. Destruction of the port waterfront facilities in the aftermath of the 2010 Haiti earthquake strongly suggests the presence of standing waves during that seismic event.
Equations 1 and 2 provide a first trial approximation of the zero-deflection point. A more exact location can be determined by a finite element analysis of the pile bent. In some software packages, pile lateral supports can be modeled as non-linear springs from soil P-y curves. Locating the zero-deflection point along the pile embedment length allows a designer to establish an effective pile length. Pile unsupported length is taken as the length between the pile cap and the zero-deflection point. Since piles are slender compression elements experiencing a combination of compression, shear and flexural forces, the pile slenderness ratio as described by Equation 4 carries great importance: = keLu/r (Equation 4) Where, ke = effective column length; Lu = pile unsupported length; and r = least radius of gyration of the pile cross section. The design value for ke can be determined from Jackson-Moreland alignment charts, utilizing the relative rotational stiffness at both ends of the pile. Rotational stiffness at the pile-to-pile cap connection can be easily established, while rotational stiffness at the zero-deflection point is provided by Equation 3. The slenderness ratio is used for preliminary sizing of piles in the pile bent and should be kept below 100.
Design for Seismic Event Determining base shear acting on the pile head provides a value for the magnitude of the force in one direction only. Chapter 12.5 of ASCE 7-05 recommends the design of foundation components for 100% of the dynamic forces in one direction acting simultaneously with 30% of the forces in the perpendicular direction. Structures should be analyzed in both major directions, and pile connections should satisfy the most critical case. Pile-to-pile cap connections experience forces in all six degrees of freedom. While there is clarity among designers as to how
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determine the Mx, Mz, Vx, Vz, and Vy components (Figure 1), ASCE 7-05, AASHTO and IBC are silent on the planar torsional component My. It would be prudent to assume pile torsional fixity at the pile-to-pile cap interface, with torsional force applied at the level of the zero-deflection point. Depending on the pile length, piles are characterized as short, intermediate or long by Equation 5: K =L/(EI/fv)1/5 (Equation 5) Where, L = pile embedment length; E = modulus of elasticity of shaft material; I = moment of inertia of the “beam”; and fv = modulus of subgrade reaction of the soil medium. Piles with K > 4 are classified as long piles. In long piles, the so-called “partial fixity point” is the first zero-deflection point along the pile embedment length developing at least two zero-slope points. Such fixity is described by the rotational spring of Equation 3 (see page 21). Some traditional designs based on full fixity at the zero-deflection point greatly underestimate flexural moment at the pile-to-pile cap interface. That was likely one of the reasons why some connections failed during extreme seismic events. An additional factor was something that is often completely ignored by pier designers. Unfortunately, all applicable codes are silent on the effect of Love waves on the pile-to-pile cap connections. The Love component of the surface wave can twist the structure in plan. Therefore, pending further research, the following torsional force at the pile-to-pile cap interface is suggested: My = 0.125VBS*(n*S)2*y*dp/Ip (Equation 6) Where, VBS = base shear acting on the pile bent, disregarding reduction due to ductility of the lateral force resisting system; S = spacing between the pile bents (deck span); n = number of deck spans within ½ of the Love wave length; y = the distance between the c.g. of the bent and extreme pile of the bent; dp = pile diameter; and Ip = polar moment of inertia of the piles in (n-1) pile bents.
Review of Pile-to-Pile Cap Connection Details There have been several attempts made to solve the problem of pile-to-pile cap connection failures. The recent work of M. Teguh, C.F. Duffield, et al. indicates that current
into the closure pour of the pile cap. A portion of the dowel cage is embedded into the pile cap sleeve. Dowels are confined by 3/8-inch-diameter spiral whose pitch is debatable. There are arguments in favor of a 6-inch spiral pitch in a “short rigid pile” stub and arguments in favor of a reduced value, but there is no evidence that pitch of the spiral is a significant factor influencing ductility. Something that is a factor is the ductility of the pile socket confinement. In connections where this becomes a critical element, the designer is urged to use closely spaced Ω-shaped stirrups as shown in the Type 3 connection (Figure 2c). The effect of Ω-shaped stirrups is explained below. Type 2: Regular connection between steel pipe pile and pile cap (Figure 2b). This detail shows an arrangement very similar to that of Type 1. Type 3: Improved pile connection detail for zones with strong seismic activity and connections subject to high seismic effects (Figure 2c). Forces acting on the pile head are shown in the diagram in Figure 1. To understand the design requirements for pile head connections, the designer should review all mechanisms restricting pile head movement in all six degrees of freedom.
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continued on next page
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international design practice results in joint details with congested steel reinforcement, while formation of the plastic hinge in the pile remains a serious risk. The paper rightfully states that “lack of careful detailing and poor confinement of core concrete” were at the root of the problem, pointing to inelastic damage that occurred at the pile cap interface during recent catastrophic seismic events. Current design practice does not provide designers with a tool to perform accurate analysis of a pile-to-pile cap connection’s physical behavior during an earthquake. The following details provide engineers with a simple and yet reliable tool for the design of a ductile pile-to-pile cap connection. This connection should be treated as a “short pile” embedded into a very stiff medium (reinforced concrete). Figures 2a, 2b and 2c explain the concept of pile-to-pile cap connection design by reviewing several types of such details. Note that development of a plastic hinge at the pile-to-pile cap interface does not typically result in failure of the structure; that only occurs when a plastic hinge develops within the pile socket of the pile cap. Type 1: Connection between precast pile and pile cap (Figure 2a). This detail shows rebar dowels grouted into special sleeves within the precast pile. Dowels are anchored
Figure 3: Force and deflection diagrams.
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A pile dowel cage confined by a spiral is viewed as a “short rigid pile” in a very stiff medium. Analysis is simplified by the fact that the P-y curve for concrete is a well-known parameter. The designer can easily establish upper boundaries for an elastic foundation reaction curve using maximum passive pressure along the “pile” length as a limiting value. Ω-shaped stirrups can significantly increase the effective width of the elastic foundation, increasing the pile cap’s shear capacity. Coupled Ω-shaped stirrups provide effective anchorage of the sleeve into the compression zone of concrete. The effective width of the unreinforced sleeve elastic foundation, beff, tends to be equal to the sleeve diameter dslv. The effective width of the reinforced sleeve elastic foundation is defined as: beff = dslv + b–2d' (Equation 7) Where, dslv = sleeve diameter; b = width of the pile cap; and d' = concrete cover.
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To model a short stiff pile correctly, the designer should select the minimum pile stiffness allowing a straight deflection line, or a slope curve with nearly constant slope along the pile length. Figure 3 shows shear, V; moment, M; elastic foundation reaction, EFR; deflection and slope diagrams of the “short pile” in one direction. Similar forces are acting in the orthogonal direction. For “short pile” analysis, forces from both directions should be combined as vectors. Based on that analysis, the designer should check dowel reinforcement for a combination of direct tension, flexural, shear and torsional forces; bearing stress on the concrete confining the pile socket; deflection of the socket; slope of the short pile within the socket; and flexural moment developed in the “short rigid pile”. It is important to remind designers that all tension forces caused by flexure should be algebraically combined with tension forces caused by shear and torsion. A connection can be considered satisfactory if all conditions listed below are satisfied: • The combined stress in any dowel or pipe section of the “short pile” does not exceed the yield stress of the steel; • The bearing stress under the “short pile” effective width footprint does not exceed the bearing capacity of the concrete (EFR / beff); • The crushing of concrete inside of the socket does not exceed 1/16inch (“short rigid pile” deflection); • The slope of the “short pile” is described by nearly straight line; and • The flexural moment developed in the “short rigid pile” can be resisted by the short pile flexural
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reinforcement (Type 1 and Type 2 connections), or a short pile pipe section (Type 3 connection). Analysis of Type 1 and Type 2 connection details can explain pile embedment reinforcement shear failure at pile-to-pile cap interfaces during seismic events similar to the 1995 Kobe and 2010 Haiti earthquakes. The Type 3 detail provides a better alternative and addresses another reported failure mechanism – rupture of the pile socket. Ductility of the concrete confining the pile socket becomes a serious issue in regions with high seismic activity. Since a seismic wave has a composite multispectral and multidirectional nature, it is easy to imagine a simultaneous downward force and lateral force acting at the pile-to-pile cap interface, normal to the pile bent frame. Such a force combination can rip off the pile socket from the pile cap. Failures of that nature were observed in the aftermath of the Kobe and Haiti earthquakes. Placement of closely spaced Ω-shaped stirrups significantly improves the ductility of the socket detail. The size and spacing of Ω-shaped stirrups should be based on forces normal to the pile bent, and a vertical force equivalent to the gravity force tributary to one pile. The shear plan for that failure mode should be taken at the vertical boundaries of beff. Ω-shaped stirrups can be used in Type 1 and Type 2 connections as well. While the additional cost of such an improvement is minor, the benefits of such a modification are difficult to ignore.
Summary Many pile-to-pile cap connection failures in seismically active regions could have been prevented with proper design and detailing. A great deal of research on that subject was done by several groups of engineers and researchers. However, recent failures of pile-to-pile cap connections indicate that previously suggested models were somewhat inadequate. Solutions suggested by this article provide a simple and yet reliable model for analytical investigation of the pile-topile cap details. It is evident that moment connection details of Type 1 and Type 2 are viable solutions for regions with low seismic activity and in connections exposed to moderate seismic forces. Connections designed for high seismic forces require the “short pile approach” and the more ductile Type 3 detail.▪
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Practical SolutionS solutions for the practicing structural engineer
In Part 1 of this series of articles (STRUCTURE magazine, May 2011), we discussed the load distribution for out-of-plane loads on perforated walls and performed the calculations for an example. In Part 2, we transition into the use of commercially available software and then solve the same example for comparison of the methods.
Wall Element Analysis There are several software products that design masonry elements. One is the National Concrete Masonry Association (NCMA) Structural Masonry Design System, Masonry 4.1. It is possible to obtain a design for the solid wall and the pier. This program analyzes walls for out-of-plane and in-plane effects, columns, and lintels. The wall portion of the program does not allow for parapets for outof-plane lateral loads; however, the weight of the parapet can be included as an added vertical load at the top of the wall. The same masonry properties were used for both methods, except that the program calculated the wall weight. For the solid wall, the results are given in Table 1 along with the results of the hand calculations (See Perforated Masonry Walls, Part 1). The software was directed to evaluate the 48-inch grout spacing using #5 bars. It did not produce its own design. The software is primarily being used as an analysis tool. Both methods require a trial and error procedure of assuming the grout and reinforcement
Perforated Masonry Walls Part 2: Wall Design Software By David T. Biggs, P.E., S.E.
spacing, and then analyzing the wall. The results are iterated until the allowable stresses are met. This is repetitious and tedious by hand, but faster using the program. For the software, the key is understanding the limitations of the program and staying within these limits. The size of the parapet in this example was not significant to affect the results. The program does not directly design piers adjacent to openings. Piers have to be treated as an equivalent 1-foot width of a wall. The engineer must determine the loads on the pier and factor them to represent an average load per foot of width for the pier. Thus, it is not surprising that the hand calculations and this software provide similar results, because the software is simply using the hand-calculated loadings to analyze the strip of wall. The only significant difference is attributed to the effects of the parapet reducing the moment in the hand calculations. Based upon the hand calculations, the design loads are P= 2986 pounds / 3.33-foot pier = 897 pounds per foot, and M = 10,406 foot-pounds / 3.33-foot pier = 3,124 foot-pounds per foot = 37,488 inch-pounds per foot. These loads must be input for the specific load combination to be checked. Using these values in the program, the
Table 1: Out-of-plane results for a solid strip of wall.
Method David T. Biggs, P.E., S.E. is with Biggs Consulting Engineering, a structural engineering firm in New York. He specializes in the design, evaluation, and restoration of masonry structures, forensic engineering, and the development of new masonry products. He is a Distinguished Member of ASCE and an Honorary Member of The Masonry Society. David can be reached at biggsconsulting.att.net.
Modified and reprinted with permission from The Story Pole, volume 39 number 4, 2008.
Hand NCMA
Wall weight (psf )
Maximum Design axial load at moment maximum moment (ft-lbs) (lbs) = 0.6D
Location of maximum Reinforcement moment from the foundation (ft)
63
946
355
7.93
#5 @ 48 inches
62.4
957
337
8.48
#5 @ 48 inches
Figure 8: Strip of solid wall.
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Figure 9: Wall model.
results come out to #4 @ 8 inches on center. The program can only accommodate 8-inch increments for reinforcement spacing. For a 3-foot, 4-inch pier, the total steel would be 5–#4 which is approximately equivalent to 3–#5 determined by hand. The software removes the tedious repetitive calculations that are required by hand; however, for piers, every load combination must be generated by hand to use the software.
Figure 10: Loading combinations.
Finite Element-Based Design There are several software products that analyze shells using finite element analysis. While there are drawbacks, the technology for masonry is improving. RAM Elements (formerly RAM Advanse) from Bentley is one program that has incorporated a masonry design module. It allows a wall segment to be designed with openings. The wall analysis is based upon linear elastic shells. Figure 11: Lateral load distribution at openings. First assuming a solid wall (no openings), the design loads obtained from the software for 0.6D + W are axial load 320 pounds per foot (at mid height) and M= 938 foot-pounds per foot (Figure 8). The wall weight is equal to 58.5 psf. The reinforcement generated is #5@48. All values are comparable to the hand and element software. Figure 9 shows the model of our wall using v9.5.1 of the software. The input allows for selection of partial or full grouting, bar size selection, masonry strength, and more. Loading cases and combinations can be input or generated. Figure 10 shows the 0.6D +W combination used throughout this article. This software designs the entire wall, not just one element at a time. It does not distribute the wall loads at openings In this re unless the engineer makes that choice in tion fi the configuration. When set, the distribuconstruc ood frame w e th , tion is as shown in Figure 11. photo n completely has bee d, while the For the wall element being considered, destroye asonry base m Figure 12 (page 28) shows the segmenconcrete ins intact. tation created by the program. Extra rema strips were added on the left side of the personnel door and on the right side of Concrete masonry is safe. It does not burn, melt, or warp. Buildings made with concrete masonry are fire, weather, earthquake, flood, and mold resistant. the overhead door, in the event that we wanted to look specifically at the jambs. FIND OUT WHY YOU SHOULD CHOOSE CONCRETE MASONRY FOR YOUR NEXT PROJECT AT Segments 3, 9, and 15 between the doors represent the pier under discussion. continued on next page
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Figure 13: Finite element results. Figure 12: Wall segmentation.
Figure 15: Wall detailing.
Figure 14: Pier loading.
Figure 13 shows the finite element results for the out-of-plane bending moment in the wall. The dark-blue area of the pier has the highest stress. Figure 14 shows the axial load and moment diagrams for the pier for the 0.6D + W load combination. The program produces a design axial load of 2.87 k, a moment of 7.6 ft-kips, and reinforcement of 3–#5. The wall is grouted at 16 to 32 inches on center. Note that the shell analysis produces a Figure 16: Design criteria. lower design moment than was determined Table 2: Out-of-plane results for a solid strip of wall. by hand. Since this is a two-way analysis, Method Wall Maximum Design axial load some of the moment was distributed to the weight moment at maximum stiffer end segments. Figure 15 shows the (psf ) (ft-lbs) moment wall detailing with reinforcement for the (lbs) = 0.6D entire wall including the pier. The program uses an equivalent thickness Hand 63 946 355 method to determine an equivalent weight of 66.5 psf. It also gives several options for NCMA 62.4 957 337 sizing the reinforcement. The engineer can control either the bar size or the bar spacFinite 58.5 938 320 ing. This example was developed using the element criteria shown in Figure 16.
Location of Reinforcement maximum moment from the foundation (ft) 7.93
#5 @ 48 inches
8.48
#5 @ 48 inches
8.0
#5 @ 48 inches
Table 3: Out-of-plane results for a wall pier for the perforated wall.
Summary For the solid wall, the three methods described give comparable results (Table 2). For the perforated wall, the load distribution varies between the methods but the reinforcement results are the same (Table 3). Perforated walls are a challenge, but using some of the developing software, the design time can be shortened.▪
Method
Maximum moment (ft-lbs)
Design axial load at maximum moment (lbs) = 0.6D
Reinforcement
Grout
Hand
10,406
2,986
3 - #5
Solid pier
NCMA
10,406
2,986
3 - #5
Solid pier
Finite Element
7,557
2,870
3 - #5
Partial grouting
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Hybrid-Composite Beam Technology A Cost-Effective, Safe and Sustainable Bridge Construction Method By John Hillman, P.E., S.E.
John R. Hillman, P.E., S.E. is a Senior Associate with Teng & Associates, Inc. in Chicago and is also Founder and President of HC Bridge Company, LLC. Mr. Hillman holds three patents for the unique bridge technology known as the Hybrid-Composite Beam (HCB). His work on the development of the HCB has brought worldwide recognition and, most recently, Mr. Hillman was honored with the 2010 Engineering News Record – Award of Excellence.
R
emote country roads were once the only location for small single-span composite bridges. With the limitations in span lengths and the load carrying capacities of early fiber reinforced polymer (FRP) bridges, this was the logical and safe place to start. Eventually composite bridge technology would advance and technology would allow the use of composite materials in larger bridge structures. Today composite materials are used safely and costeffectively on a variety of bridges throughout the United States. This new technology, Hybrid-Composite Beam (HCB), is an emerging structural technology that utilizes concrete, steel and fiber reinforced polymer in an embodiment that exploits the inherent advantages of each of these materials. The HCB combines the strength and stiffness of conventional concrete and steel with the lightweight and corrosion-resistant advantages of advanced composite materials. The concept of the HCB was originally conceived in 1996. Over the course of the next ten years, substantial progress was made under the High Speed Rail-Ideas Deserving Exploratory Analysis program (HSR-IDEA) of the Transportation Research Board (TRB). The concept started out of academic curiosity, with just a few hand calculations attempting to predict the behavior of this unusual structural member.
Goals of the HCB Throughout the development of the HCB, the goal was to develop a revolutionary bridge
30 March 2012
system that exploits the inherent benefits of FRP materials, but at the same time is compatible with the types of conventional structures in terms of design as well as construction. The result is a new alternative for rebuilding the world’s infrastructure with state-of-the-art structures having the following characteristics: • Lightweight – 1/10 the weight of concrete and 1/3 the weight of steel. • Safer – Internal redundancy and serviceability design result in capacities that greatly exceed code requirements. Reduced mass and resilient, energy absorbing materials offer excellent resistance and elastic response to seismic forces. • Reduced Carbon Footprint – Beams use 80% less cement, one of the largest contributors to the carbon footprint. They also require 75 to 80% fewer trucks for shipping, and smaller cranes for erection and reduced emissions. • Congestion Relief – Lighter, modular bridge system allows for Accelerated Bridge Construction and reduced traffic congestion during construction. • Sustainability – No painting, rusting, cracking, spalling or alkali-silica reactions (ASR) results in a sustainable technology that provides for projected 100+ Year Service Life.
HCB Fabrication and Construction To fabricate the Hybrid Composite Beam system, the FRP box beam is laid-up in a mold with the tension reinforcement in place. Lightweight foam is used to hold the shape of the arched conduit during fabrication. The
FRP box beam is then infused with resin and removed from the mold. This lightweight beam is shipped to the bridge site, where it can be installed without the use of heavy cranes or lifting equipment. Accidents and injuries related to cranes have become more frequent in recent years. Because the HCB is a substantially lighter weight structural member (1/10 that of prestressed concrete), significantly smaller cranes can be used for installation. In most cases, the beams can be safely set with 30-50 ton cranes instead of 150-300 ton cranes. This provides a much safer working environment. Once in place, Portland cement concrete is pumped into the arched conduit and is allowed to cure while the concrete fluid load is fully supported by the FRP box beam. Once cured, the concrete arch acts as the compression portion of the beam that is equilibrated by the steel tension reinforcement. Although typically filled in-place, the concrete arches and deck slabs of the HCB may also be precast prior to erection, resulting in an entirely prefabricated bridge element. Although this construction methodology reduces the lightweight advantage of the technology, it also demonstrates the flexibility to accommodate accelerated bridge construction. Using these construction techniques, a bridge
superstructure could literally be installed and put in service within the same day, resulting in substantial congestion relief.
Design Methodology Although the HCB contains materials that are generally new to most practicing structural engineers, with a basic understanding of the mechanics of Bernoulli-Euler beam theory and a working knowledge of standard bridge design codes, it is not difficult to assess the load carrying capacity of the HCB. In fact most design codes, including the American Association of State Highway and Transportation Officials (AASHTO) and the American Railway Engineering and Maintenance-of-Way Association (AREMA), are compartmentalized and allow the engineer a fair amount of flexibility in assessing how forces are resisted by a structure. Further, the applied loads as well as the load and resistance factors can easily be rationalized for assessing the response and structural capacity of the HCB. The bending capacity of an HCB is calculated using strain compatibility and force equilibrium in the same manner as a reinforced concrete beam. The major difference is the additional contributions from the FRP
Fragmentary perspective of the hybrid-composite beam.
box. Alternatively, one can generally get an approximate answer within 5 to 10% of the exact answer simply by taking the compression force in the concrete, i.e. the slab and arch, and equilibrating it to a tension force in the steel tension reinforcing in the bottom flange. In other words, the nominal moment capacity of the section is as shown in Equation 1 (page 32). Validation of the approximate solution can be found by using the rigorous strain compatibility and force equilibrium
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calculations, and setting the areas of the various FRP components to zero. ФMn=C(d-a/2) (Equation 1) Where: C = fc'ab (the compression force in Whitney’s equivalent stress block) d = the distance from the centerline of the steel reinforcement to the top of the beam a = the depth of concrete in compression In quantifying the shear resistance of the HCB, the first component is to establish the thrust in the arch at a given section and discretize this force into horizontal and vertical components. The vertical component can then be deducted from the gross shear on the section, as this is being resisted by the arch. The remaining shear is then resisted primarily by the FRP webs, but also by the thin concrete web above the arch. This results in a hybrid resistance to the shear forces in the beam. There are also some other interesting facets of the shear behavior that very much emulate a reinforced or prestressed concrete beam. For example, when the loads are applied to the structure to produce maximum shear effects, e.g. adjacent to a support, the majority of the shear is resisted strictly through the arching action similar to the strut and tie behavior. There are inherent benefits to public safety resulting from the structural behavior of the HCB. Since design is usually governed by satisfying live load deflections, the HCB consistently exemplifies significant reserve capacity for strength. In fact there is enough redundancy in the HCB that, in many cases where the bridge deck was completely deteriorated, the HCB would still have sufficient capacity to carry all of the factored design loads applied to the bridge. Laboratory tests have consistently confirmed bending and shear strength capacities well beyond the code specified factored demand.
Out of the Laboratory Development of the design methodology, manufacturing process and structural validation was a long and arduous process that encompassed over a decade of sheer perseverance. In 2007, the first real demonstration of a HCB Bridge took place on the test track at the Transportation Technology Center, Inc. (TTCI) in Pueblo, CO. Not only was this the first application of an HCB Bridge, but it was also the first installation of an FRP railroad bridge anywhere in the world. The first installation of an HCB highway bridge began with the construction of the High Road Bridge in Illinois. This bridge
comprises a 57-foot single span bridge that carries two lanes of traffic over Long Run Creek. The superstructure is comprised of six 42-inch deep by 20-inch wide HCBs supporting a conventional 8-inch thick reinforced concrete deck with an out-toout dimension of 43 feet and a curb-to-curb width of 40 feet. The HCBs are spaced at 7-feet 4-inch centers. The bridge’s six beams, each 58 feet long, weighed less than 4,000 pounds, so all six beams could be shipped on one truck. Had these been precast concrete beams, it would have required six trucks instead of one. The contractor was also able to erect the beams with a 30 ton utility crane instead of a 150 to 200 ton crane. Another milestone in HCB technology took place in the summer of 2011 with the completion of the Knickerbocker Bridge in Boothbay, Maine, which constitutes the longest composite bridge constructed to date anywhere in the world. In order to comply with the hydraulic criteria for the new Knickerbocker Bridge, the HCBs were designed to match the recommended 33-inch deep box beams in order to maintain the required vertical underclearance. Also, similar to the proposed precast box-beam bridge, the HCB framing system was limited to two 60-foot end spans and six 70-foot interior spans resulting in an 8-span bridge with a total length of 540 feet. The beams were also made continuous for live load with negative moment reinforcing steel cast over the piers in the 7-inch concrete topping slab. Another advantage of the lightweight nature of the beams was that it allowed the contractor to ship the beams across the existing timber trestle that was posted with load restrictions. In general, the HCBs were erected at a rate of approximatey 16 beams per day. After setting the first four spans of the bridge, the contractor placed the concrete for the arches in the HCB units. By simply placing a hopper with a steel tube into the tops of the beams, it was possible to fill each beam in approximately ten minutes. Once the beams were filled, the contractor began placing reinforcing for the deck pour. Scupper details, screed rails and reinforcing details were no different than those for a comparable precast concrete bridge. The first half of the deck was cast in October 2010. After working through the winter to complete the remaining piers, the contractor completed installation of the second half of the HCB superstructure in April 2011. The bridge was officially opened to traffic on June 11, 2011. When all was said and done, the cost of the HCBs for the Knickerbocker
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Bridge was no more than it would have been for a conventional bridge, making this one of the first composite bridges to be economically viable on a first cost basis.
HCB in the Show Me State In June 2009, the Missouri Department of Transportation (MoDOT) let a single Design-Build contract to replace 554 small bridges located in rural areas throughout the State of Missouri. When completed in 2012, the Safe & Sound Bridge Improvement Program will have replaced the 554 deteriorating bridges that are no longer cost effective to maintain, as well as 248 bridge rehabilitation projects. KTU Constructors, a joint venture consisting of Kiewit Western Co., United Contractors, Inc. and Traylor Bros., Inc., proposed using standard precast concrete box beam and voided slab construction on a majority of the bridges in the program. However, as part of a Highways for Life Award from the Federal Highway Administration (FHWA), MoDOT plans to use HCBs in place of the precast concrete box beams on three of the replacement bridges. This is a first time use of the HCB system in Missouri. The first of the three bridges is Bridge B0439 that carries MO 76 over Beaver Creek, just outside of Jackson Mill. This bridge comprises a three-span structure with typical spans of 60 feet and an overall length of 180 feet, and was opened to traffic in November 2011. The remaining two bridges will be constructed in the first half of 2012, including Bridge B0410 carrying MO 97 over Sons Creek. This bridge, with a single span of 106 feet founded on integral abutments, will establish yet another milestone in span length for HCBs. The cross-section itself is comprised of three, 60-inch deep, double-webbed HCB boxes that only weigh 9 tons each.
The Future The significance of the success of these bridges will hopefully pave the way for additional advancements in composite bridge construction. Currently additional bridge installations are slated in Maryland, Virginia, Utah and West Virginia, to name a few. With economies of scale and further advances in fabrication automation, it is now possible, with the HCB, to make sustainable structures using advanced composites a mainstream component for reconstruction of the world’s deteriorating infrastructure.▪
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New Brunswick Gateway Transit Village Integration of Diverse Structural Systems and Design Delegation in a Mixed Use Space By J. Benjamin Alper, P.E., Cawsie Jijina, P.E., SECB and Fortunato Orlando, P.E.
T
he New Brunswick Gateway Transit Village (NBGTV) is situated adjacent to the commuter rail train station in New Brunswick, NJ. At 300+ feet tall, NBGTV is currently the tallest building in the city. The building consists of 632,000 square feet of mixed used space which includes parking, retail, office and residential uses. The podium structure of the building consists of a precast parking garage, with areas of concrete and metal deck on structural steel framing wrapping around the garage. Rising above the ten story podium is a fourteen story precast plank on structural steel framed residential tower. All of this is supported by deep continuous cast-in-place concrete footings.
The Problem At Hand The parking consultant required 24-foot and 36-foot spacing between the support walls of the garage to optimize the parking spaces and the available width of precast double tees. Upstairs in the residential tower, the architects demanded a grid that completely ignored the supporting grid below. Utilizing 10-inch thick pre-cast pre-stressed concrete plank as the floor slab system, Severud Associates, as the project’s Structural Engineer of Record (SER), was able to span up to 36 feet between supports thereby aligning the column lines of the residential tower with the garage support walls below. As a clear drive aisle was required in the garage structure, a series of 9-foot deep steel transfer trusses were designed to transfer the loads from the residential tower’s interior columns to the exterior columns and shear walls located between the parking spaces. As the majority of the steel residential tower rests above the precast garage, the precast garage walls provide support for both the gravity and the lateral forces from the steel framed tower above. While it is standard practice for the precast fabricator to design all the precast structural elements themselves, with a complicated structure such as this, the division of design responsibilities needed to be set. Direction was requested from the construction manager to determine the elements whose design would be delegated to the precast manufacturer and the elements to be designed directly by the SER. It was Severud’s preference to design the precast concrete support walls themselves and provide complete design documents for the precast concrete contractor to adhere to. The remainder of the elements (typically gravity walls and double tees) would then be in the domain of the precast contractor. However, the construction manager during the design development phase requested that the design be left completely open and flexible. It was their opinion that allowing the precast fabricator full flexibility in the design would result in a more economical bid. This, in effect, required that the gravity and lateral systems in the lower half of the building, a building that essentially was not only a structure unto itself but also supported the building above it, be done as a delegated design.
Overall View of Building.
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Deep Cast-In-Place Footings and Tie Beams to Resist Overturning at the Base of the Precast Walls.
Delegated Design For the majority of the structural work on a given project, the structural design is fully specified directly in the construction documents. However, there are often portions of the project that are intended to be designed by other structural engineers. Typically, these other engineers are hired either by the general contractor, a fabricator or a sub-contractor. These delegated designs can include elements of the façade, steel connections, open web joists, precast elements and/or miscellaneous metals such as stairs. The main purpose of these delegated designs is to allow fabricators to utilize materials, member sizes and connection types that are most economical for their particular shop. It is important for the SER to properly define the parameters of the delegated design elements in the construction documents and supervise their design and construction throughout the project. In most projects, these delegated designs are done for supplementary items. However, what happens and where do the lines of responsibility lie when these elements play not just a primary role but a critical role in the overall structure? The NBGTV is a project that illustrates some of the challenges faced by Severud Associates in their capacity as the overall project’s SER and design team when the delegated design items include critical elements of the lateral and gravity structural systems. In order to maintain overall structural integrity for the entire building, Severud demanded and retained complete control of the overall design, the right to review, approve and/or reject any aspects of the garage design, and the right to modify component design and connections, all with the express understanding that the process was to be a collaborative effort with the engineers retained by the precast concrete manufacturer. As the lateral elements in the garage would be designed by the precast fabricator’s engineer, Severud prepared an early bid set of drawings and specifications for the precast concrete portion of the work. This would allow the chosen precast manufacturer to join the design team earlier in the design process and deliver the foundation loads necessary to allow for the design of the foundation system prior to the final bid. This time sequence required Severud to make certain base assumptions about the garage structure in the early stages to determine the support locations and approximate relative stiffnesses of the various structural elements. The bid documents would include information and the locations of all the load vectors from the structure above as applied to the top of the precast walls below. As the transfer trusses STRUCTURE magazine
transfer both lateral and gravity loads, information about dead, live, wind and seismic forces, along with the required eccentricities for both wind and seismic load cases was placed on the bid documents. In addition to resisting the provided loading, deflection and rotational boundaries for the tops of the precast concrete walls were provided to ensure that the movements at the top of the tower would stay within acceptable serviceability levels. All of these parameters forced the bidding fabricators to conduct a preliminary structural design during the bid phase and in effect helped ‘weed out’ precast contractors who lacked the engineering capabilities to complete the project. While the garage itself is only ten stories, the overall structure still stands at twenty four stories tall, requiring the precast walls to resist the forces for the full lateral and gravity loads of the twenty four story building.
Design and Coordination The precast concrete portion of the building was awarded to High Concrete. Immediately after the contract award, weekly meetings were
Precast Garage Supports both Lateral and Gravity forces from the Steel Structure.
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Steel Column and Brace Supported by Precast Garage Wall.
conducted with the entire design team which included members from the precast manufacturer’s engineers, Severud, as the overall Structural Engineer of Record, the Building Architect, the Garage Designer, the Owner and the General Contractor. In addition, Erection of Steel Residential Tower over Precast Garage. other trades including the steel fabricator, the steel detailer, and the erector would often attend the meetings. These be challenging in even the most basic of designs. Trying to delegate meetings were very necessary since the design was an iterative process essential elements of a lateral system can be even more onerous. At the between the SER and the precast fabricator. Changes to the lateral end of the project, one can look back and see that the final product walls in the garage below would result in changed stiffness values at is due not only due to the ground work laid out by the SER, but by the base of the residential tower, redistributing the loads within the the efforts of all involved stake holders.▪ steel tower structure above. At each step of the parking garage design, Severud would recheck the original base design to ensure that the The author would like to note the contributions of Dr. Mohamed load distribution in the residential tower structure did not change. Arafa, P.E., Fianna Ouyang, P.E., Justin Lawson, Stephanie Connections between the steel tower and precast structure were DeCruz, P.E. and Gustavo Amaris to this article. developed by Severud, along with detailed drawings of the embedded connector elements. It was imperative to Severud that these connections provide a high level of detailing to ensure complete coordination J. Benjamin Alper, P.E. is an Associate at Severud Associates. He can between the steel and precast fabricators. be reached at JAlper@severud.com. The final design by High Concrete relied on twenty four-inch thick Cawsie Jijina, P.E., S.E.C.B. is a Principal at Severud Associates. shear walls constructed with 10,000 psi concrete and with up to forty He can be reached at CJijina@severud.com. four #11 reinforcing bars on each end. These high strength, densely reinforced walls reduced field labor by concentrating the load in a Fortunato Orlando, P.E. is an Associate Principal lesser number of walls instead of requiring additional field connecat Severud Associates. He can be reached at tions to engage additional structural elements, thereby yielding a more FOrlando@severud.com. economical design for the precast concrete contractor. While these twenty four-inch thick shear walls were sufficient in most areas, there were areas where the initially assumed design could not be replicated. Project Team In these select areas, cast-in-place concrete placement strips were added to allow the precast concrete walls to engage the adjacent walls. Structural Engineer of Record: Severud Associates Consulting While the final design used different member sizes and materials than Engineers the starting assumptions made by Severud, the global load path and Owners: load distribution remained the same throughout the design process, Somerset Development Partner since the locations of the load resisting elements, as coordinated by New Brunswick Development Corp. (DEVCO) the design team prior to precast concrete bid, remained constant New Brunswick Parking Authority throughout the process. Architect of Record: Meltzer Mandl Architects Designer: EEKR Conclusion Parking Garage Consultant: Tim Haahs and Associates General Contractor: AJD Construction, Leonardo, NJ It is a common misconception that delegated design is the ‘easy way Precast Contractor and Designer: High Concrete Group, out’ or an effort by the SER to pass the responsibility for a portion Denver, PA of the design onto the sub-contractors. Delegating that design can Steel Fabricator: SteelFab, South Carolina, Georgia often be far more burdensome for the SER than designing the strucand North Carolina tural elements themselves. Preparing concise documents which fully Steel Erector: Shamrock, Keyport, NJ explain the parameters of the overall design, the required constraints Steel Detailer: Prodraft, Chesapeake, VA and the lower and upper performance boundaries of the elements can STRUCTURE magazine
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Structural Design Ingenuity
A Critical Component for a Sophisticated Science Building University of Scranton – Loyola Science Center By Alvin P. Tabar, P.E.
I
n fall 2011, Phase 1 of the Loyola Science Center (LSC) at The University of Scranton in Scranton, Pennsylvania, opened its doors, transforming the university’s science, technology, engineering, and mathematics (STEM) learning environment. The new 150,000-gross-square-foot facility is equipped with the latest technologies to support STEM pedagogy, and provides distinctive spaces for teaching, learning, and research within and across disciplines. Given the high level of environmental control required by sophisticated scientific equipment, structural and foundation designs have become increasingly complicated, while the characteristics of the supporting soil have only limited scope for manipulation. Providing a safe and efficient interface between science facilities and the soil media therefore requires structural engineering ingenuity. For the LSC, these design complexities were exacerbated by existing site conditions, where abandoned coal mines below the site and nearby railroad traffic presented extraordinary challenges.
Abandoned Coal Mines The City of Scranton, known today as the home of the fictional DunderMifflin paper company in the NBC sitcom, The Office, was once the center of Pennsylvania’s anthracite coal mining industry. When oil and natural gas replaced anthracite coal as a preferred energy source, the downfall of the mining industry in Northern Pennsylvania left a city scarred by abandoned coal mines. As soon as buildings started rising above and around these abandoned mines, ground subsidence became a widespread problem as the pillar supports for the roofs and overlying surfaces of abandoned mines began to fail. While such failures are no longer a common occurrence – thanks to the state and federal flushing projects or backfilling efforts that stabilized the ground surface in the late 1970s – underground voids are still present in some areas. Site soil exploration performed by the geotechnical engineering consultant revealed deep underground voids within 100 feet below ground of the proposed LSC, and determined that a potentially 20-foot wide sink hole could develop anywhere beneath the new structure. During early design phases, engineers considered three viable foundation systems to mitigate possible structural failure due to mine subsidence: • Caissons or conventional spread footings with interconnected grade beams. STRUCTURE magazine
• Conventional spread footings after site modifications through grouting of underground voids. • Mat slab foundation system. For the LSC, mat slab proved to be most appropriate alternative because of its simplicity, more rapid pace of construction, and the relatively inexpensive cost estimated to be fifty percent less than that of the caisson option.
Mat Slab Foundation System Every structural problem has a solution, but sometimes the solution to one problem creates its own challenges. Such was the case with the mat slab foundation system for the LSC Project. Mat slab is relatively simple to design using the finite element method (FEM) adopted in most structural concrete design programs like SAFE by Computers & Structures, Inc., which is utilized in the design or RAM Concept by Bentley and a number of other commercially available structural analysis and design software. For a complicated site such as that of the LSC Project, the challenge is in manipulating the supporting natural soil media to achieve the desired engineering properties for a safe and efficient building support. This solution requires a high degree of ingenuity and “engineering judgment” or instinct on the part of the structural engineer. For the LSC Project, the mat slab foundation mitigated the potential for structural failure due to ground subsidence by acting as a transfer slab bearing on the stable ground left behind around the depression. At the same time, however, it takes up space for under-slab ducts, plumbing, and other services that in conventional foundation construction could otherwise have been easily located between spread footings or pile caps. To make room for these elements, the top of mat slab needed to be dropped three feet below the ground-floor slab. The shallow top of bedrock at this site required rock excavation in some areas, which increased the risk of weakening the roof of the abandoned mines. Another concern was the subsequent irregularity in the substrata due to the variability of the topography of the top bedrock found in the site, which caused some portions of the mat slab to sit on bedrock and the rest on native soil. Resolving this challenge required a more complex structural analysis, necessitating the use of multiple flexibility coefficients or modulus of sub-grade reactions. To maintain a homogeneous subsoil layer throughout the entire mat slab, modification to the existing site soil
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condition was required. One option was removing the natural soil portion of the site and infilling cavities with lean mass concrete. This option can provide additional stiffness to the overlying surfaces of the abandoned mines, reducing the risk of ground subsidence, but it requires significant amounts of concrete and the associated cost is considerably high. The alternative was to further undercut the existing substrata, including the bedrock, and backfilling with select structural fill materials up to the desired founding level. While the latter option further increases the required rock excavation and could weaken the roof of the abandoned mines, increasing the risk of ground subsidence, the structural fill layer separating the mat slab from the bedrock serves a double purpose. It not only creates a homogeneous subsoil layer for the mat slab to bear on, it can also produce foundation coupling loss or partial reflection of vibration energy at the interface between the bedrock and the layer of fill materials due to impedance mismatch (different material properties). Foundation coupling loss is essential to mitigating the effect of the other structural issue in the project, “ground-borne train vibration” from nearby railroad traffic. Adopting the latter site modification option in the LSC project contributed to reducing construction cost by avoiding otherwise costly special vertical vibration mitigation.
Ground-Borne Train-Induced Vibration Along with the coal mining industry in Scranton came the railroad business that transported coal to ports in larger cities for eventual distribution around the country. While the last mine in Scranton closed down in the mid 1960s, the railroad track that lies less than 100 feet from the new Loyola Science Center is still in use. Today it transports not coal but tourists from the nearby Steamtown National Historic Site, as well as carloads of goods transported throughout the Delaware-Lackawanna Line. These historic steam trains and freight trains were potential sources of ground-borne vibration disturbances to the new science building. There is yet no generally accepted, comprehensive model for predicting train-induced structural vibrations inside a building. Structural engineers must therefore rely on partially empirical techniques for predicting the transmission and propagation of vibration from a railroad traffic source as it enters into the building base or foundation, as it proliferates through the building structure, and as it is finally transmitted into the receivers (i.e. vibration-sensitive equipments and occupants). Normally, the level of vibration in the foundations is lower than that in the surrounding ground due to the foundation coupling loss that occurs as vibration is transmitted from the ground into a building. For mat slab bearing on bedrock, the coupling loss may only be very minor or nil. Since concrete is just as dense as rock, the concrete and bedrock therefore have the same mechanical impedance properties (no material mismatch). The foundation design for the new LSC therefore ensures that the mat slab bears on a different intermediate soil media and not directly on the bedrock, since the separation created by the layer of structural fill materials between the mat slab and the bedrock produces impedance mismatch and would result in foundation coupling loss. The physical size and mass of the building, and the characteristics of its foundation, also contribute to the level of attenuation of ground-borne vibration inside a building. A mid-value of -6 VdB coupling loss was assumed in the prediction process for the LSC Project. Vibration can be expressed in linear (µ in/sec) or logarithmic amplitude scales. Ground-borne vibration is normally expressed in a logarithmic scale VdB (vibration velocity level in decibel). In this scaling, any increase in level of 6 VdB represents a doubling of amplitude regardless of the initial level. Therefore, the aforementioned value -6 VdB due to assumed coupling loss basically implies that ground-borne vibration is reduced by half as it enters into the foundation of the new LSC. Vibration amplification due to STRUCTURE magazine
Mat Slab Foundation Construction.
excitation by the floor’s own natural frequency was also considered in the predictions and assumed to be +12 VdB. In like manner, this change represents an amplification factor of 4. Losses also occur with the transfer of vibration from floor to floor due to structural damping and geometrical spreading. In the predictions, -2 VdB floor-to-floor attenuation was assumed. All in all, a net change in ground-borne vibration level of +4 VdB was assumed in the predictions due to foundation coupling loss, resonance of floors, and floor-to-floor attenuations. Pre-construction measurements of on-site ground-borne vibrations were taken over an approximately 24-hour period in two spots, at both ground level and bedrock, that border vibration-sensitive areas in the building. As expected, vibrations nearer to railroad traffic were higher than those farther away, since ground naturally attenuates vibration as it moves further away from the source. The maximum measured train-induced vibrations on the bedrock were 1,050 µ in/s (65.4 VdB) and 460 µ in/s (58.3 VdB) at the nearest and farthest locations respectively. With the predicted net change in vibration level of +4VdB, the anticipated most severe train-induced vibrations at the above-grade floors would be 69.4 VdB, equivalent to approximately 1660 µ in/s. At the ground level, the measured vibrations were 1,500 µ in/s at the nearest location and 500 µ in/s at the farthest location. These would be the expected trained-induced vibrations at the underside of the slab on grade for buildings with conventional foundations. In the mat slab-supported LSC, whose mat slab foundation encompasses the entire building footprint, ground-borne vibration transmission into the ground-floor slabs are minimized, making the ground floor ideal for program spaces with highly sensitive equipments or occupants.
Conclusion The use of a mat slab foundation system mitigates the risk of the structural failure of the new LSC due to potential ground subsidence. Project structural engineers predicted that mat slab bearing on a different intermediate soil media that separated the foundation from bedrock could result in foundation coupling loss and improve the vertical vibration mitigation. Observed train-induced vibration levels inside the completed building support predictions and confirmed compliance to the design goal: moderately sensitive equipments, such as microscopes at magnifications up to 400X and analytical balances, can generally be used without disturbance within the laboratory spaces of the new Loyola Science Center. The laboratory spaces in the building can also accommodate highly sensitive equipment in vibration isolation systems.▪
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Alvin P. Tabar, P.E. is a Senior Associate with EYP Architecture & Engineering, structural engineers for this project. He can be reached at atabar@eypae.com.
March 2012
Structural PracticeS practical knowledge beyond the textbook
B
ecause increased development has led to the need to use marginal sites, and because many types of soils can be modified so that they are a viable support material for many types of structures, soil improvement (also called ground modification) has become an important consideration for many project types. The goal of soil improvement is typically to allow the development to be constructed on a shallow foundation system. In cases where the alternatives are to remove and replace soils, surcharge the site or install settlement plates and wait for an extended period of time, or extend deeper foundations through the relatively weak soil layers to a suitable bearing layer, soil improvement is often an economical option. The costs of the different methods, and the soils for which they are most effective, vary greatly. The intent of this article is to highlight the basic merits of each system. There are a number of soil improvement methods available, and the list continues to expand as building owners push to build on land that was previously deemed undesirable. The common names for many of these methods have been trademarked, which makes comparing the different options difficult. The following explains what each technique involves, what improvements can be expected, and what type of soil it is best for improving.
A Soil Improvement Primer By Carrie Johnson, P.E.
Categories
Carrie Johnson, P.E. is a principal at Wallace Engineering Structural Consultants, Inc. with offices in Tulsa, OK, Kansas City, MO, Oklahoma City, OK, and Castle Rock, CO. She can be reached at cjohnson@wallacesc.com.
Each technique for improving soils can be categorized as one of the following: 1) Soil Stabilization – mixing soil with cementitious materials. 2) Compaction – applying mechanical energy. 3) Consolidation – preloading the soil. 4) Grouting – pressure injecting grout into the soils. 5) Soil reinforcement – adding a stronger material.
Selection Although the recommendation for foundation type and soil improvement methods typically falls into the geotechnical engineer’s area of expertise, it is important for the structural engineer to be aware of what those recommendations mean, recognize the cost implications, and ask questions accordingly. Typically, the structural engineer provides the geotechnical engineer with information about the anticipated loading to the foundation, the expected framing systems, and the settlement criteria. The geotechnical engineer then makes recommendations for the foundation system, and the structural engineer utilizes those recommendations to provide a final design. Communication during this process is essential to ensure that all of the appropriate options are being
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considered. The selection of the best method will depend on a number of factors, including: 1) Type and degree of modification required – to improve settlement, slope stability, bearing capacity, etc. 2) Area, depth, and total volume of soil requiring improvement. 3) In-situ soil type and its initial properties. 4) Availability of equipment, materials, and experienced contractors. 5) Time available. 6) Cost. 7) Environmental constraints, including effects of adjacent structures. 8) Accessibility.
Dry Soil Mixing Dry soil mixing, sometimes referred to as lime stabilization, improves the characteristics of soils with high moisture content (>40%) – such as clays, peats, and other weak soils – using a dry cementitious material as a binder. The process involves using a mixing tool to blend the dry cement with the soft, wet soil and is often very cost-effective. The dry binder utilizes the moisture inherent in the wet soils during the hydration reaction. Binder types include lime, cement, a lime-cement mixture, or a mixture of slag and cement. The typical dosage is approximately 10% by weight of soil. The dosage amounts vary and should be identified in a laboratory and then verified on-site during installation, because results in the field will likely deviate from the laboratory ideal. Both shallow and deep applications are common. With shallow applications, a mass mixing technique is utilized, involving a mixing tool mounted on a machine with low pressure tracks. Deep applications are done in columns of soil with a soil mixing tool. The tool is rotated into the ground, a binder is injected, and then the tool is rotated at high speed during withdrawal to mix the binder with the soil. With dry soil mixing, you can expect to increase bearing capacity, decrease settlement, mitigate liquefaction during earthquakes, and increase shear stability to improve slope stability.
Wet Soil Mixing The process for wet soil mixing is similar to that for dry soil mixing, except that a water-cement slurry is used instead of dry cement. In very wet soils, the wet soil method can result in columns that are not as strong; however, it provides stronger columns in dryer soils. Wet soil mixing is typically more expensive than dry soil mixing. Wet soil mixing is also an effective method to form ground water barriers, to stabilize contaminants, or as a chemical treatment for soils with undesirable chemical properties. It is most suitable for soft or loose soils with a lower moisture content than those where dry soil mixing is effective.
With wet soil mixing, you can expect to increase bearing capacity, decrease settlement, mitigate liquefaction during earthquakes, and increase shear stability to improve slope stability.
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Dynamic compaction is the dropping of a heavy mass onto the ground surface to densify the soils below. The weights used are typically on the order of 10 to 25 tons at heights between 30 and 100 feet. Testing of this method has shown that it can impact soils at depths of over 100 feet. The underlying concept is that by imposing a loading onto the soil that is higher than will be imposed by the proposed construction, the soil will be over-consolidated, thereby minimizing any future settlement. Dynamic compaction is done with a number of passes in a grid pattern. The spacing of the grid, as well as the number of passes, must be verified during installation. With dynamic compaction, the biggest impact is on settlement, since it collapses any voids. It can also be utilized to prevent soil liquefaction during earthquakes and to increase the density of fills in land reclamation sites. Dynamic compaction is most suitable for sands with less than 5% fines. It can also be effective on sands with up to 12% fines, but success depends on clay content, grain shape and size, and the water table. It is not recommended for sands with over 12% fines or for clays.
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Dynamic replacement is similar to dynamic compaction. In this method, stone or suitable granular fill is driven and compacted into the ground using high energy pounders to form large–diameter dense columns to reinforce the soil. This method is often referred to as stone columns. Cohesive, mixed and layered soils generally do not densify easily when subjected to vibration alone. With dynamic replacement, these columns of crushed stone are intended to increase bearing capacity, but the designer needs to be aware of the variation in soil conditions between the dense columns and the less dense in-situ soil. The design should include a layer of soil to transition between these two conditions, or a foundation system that effectively spans between them. Dynamic replacement can effectively reduce foundation settlements, increase bearing capacity, mitigate soil liquefaction
during earthquakes, and increase the shear strength of the soil to improve slope stability. Dynamic replacement is most suitable for sands with less than 12% fines, but vibro-compaction (discussed below) or dynamic compaction may be more cost-effective for sands with less than 5% fines. It can also be effective on silty soils or clays. It is not recommended for sensitive soils that lose strength when vibrated.
Vibro-Compaction Another similar method is vibro-compaction, which is typically used to densify clean, cohesionless soils. This method uses probe-type vibrators hung from cranes or mounted on piling equipment to densify granular soils to depths over 100 feet. The action of the vibrator, usually accompanied by water jetting, reduces the inter-granular forces between the soil particles, allowing them to move into a denser configuration, typically achieving a relative density of 70 to 85%. Vibro-compaction can effectively increase bearing capacity, mitigate soil liquefaction during earthquakes, densify soils, and reduce foundation settlements. Vibro-compaction is most suitable for sands with less than 5% fines. It can also be effective on sands with up to 12% fines, but success depends on clay content, grain shape and size,
and the water table. Is not recommended for sands with over 12% fines or for clays.
Compaction Grouting Compaction grouting is a technique that displaces and densifies loose granular soils, and stabilizes subsurface voids or sinkholes, by injecting a slow-flowing grout mixture into the soil. The method involves extending a pipe to the maximum injection depth and then injecting grout as the pipe is slowly extracted. This method is effective where there is a potential for sinkholes, or any type of underlying void that could form a depression, or sag, at the surface. The most common causes of subsidence are aquifer system compaction, drainage of organic soils, underground mining, sinkholes, and permafrost. Compaction grouting can also be used as a remedial measure for an existing structure that has experienced settlement. It is effective in treating both foundation systems and slabs on grade. Compaction grouting can effectively reduce foundation settlements, increase bearing capacity, and mitigate soil liquefaction during earthquakes. Compaction grouting is effective on almost any type of soil and can be used to treat existing sinkholes or to reduce the potential in sinkhole-prone areas.
Injection Systems Injection stabilization is used to reduce heave on expansive clays, using pressure injection of various types of fluids to reduce the shrink/ swell potential of the in-situ soils. This method is also referred to as chemical injection and is used to change the expansion/ contraction cycles of the soil. It uses a unit that drives injection pipes beneath either an existing structure or a new building pad. A solution is then injected in the soil. Common injection systems include lime, potassium, water, and electrochemical pressure.
Rapid Impact Compaction Rapid impact compaction is a technique that densifies shallow, loose granular soils using a hydraulic hammer struck repeatedly by an impact plate. The energy is transferred through the plate to the soils and the particles are rearranged into a denser configuration. The impact is typically applied in a grid pattern, and the spacing is determined by the underlying soils and the proposed configuration and loading of the structure. Rapid impact compaction is used to reduce settlement, increase bearing capacity, increase density and stiffness of the soils. Rapid impact compaction is most effective on loose granular soils, where the depth of the loose soils is relatively shallow and there are denser underlying soils.
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The price tag on these systems can vary tremendously, both between methods and between installers. Competitive bidding on the basis of a well-defined specification for how the system is expected to perform is recommended. The specification should also include a proper Quality Assurance and Quality Control program to ensure that all equipment used is fully instrumented and monitored, and that testing is done to verify the results in the field. Since some of these techniques are highly specialized, it is appropriate to require evidence that the installer has successfully performed the method a number of times previously.▪
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Technology information and updates on the impact of technology on structural engineering
M
any of the challenges and opportunities that define the early years of the 21st century are most visible in cities, where a growing proportion of the world’s population now lives. The complexities of cities today mean that the demands on infrastructure change and expand constantly. City managers have a responsibility to ensure that their physical and technological attributes support the changing needs of their citizens – and they must do so under all types of pressures. These pressures range from the strains of rapid urbanization to addressing the potential for loss of life and economic destruction from the approximately 18 major earthquakes (7.0 magnitude and above) that occur worldwide each year. The recent earthquakes in Chile, Haiti and Japan attest to the stark differences between structures that were designed or retrofitted to handle large earthquakes and those that were not. While much is reported about buildings, the infrastructure component of cities must be taken into account as well. We need new holistic perspectives on cities. In order to develop infrastructure strategically, economically, sustainably and with added seismic resiliency, the right tools are required. Ideally, these tools can help users to transition to a more integrated approach and assessment, where they can visualize, simulate and analyze infrastructure designs long before construction to meet the ever-changing demands. Some of these tools exist today.
Role of BIM in Infrastructure Seismic Retrofits By Terry D. Bennett, LS, LPF, MRICS, LEED AP
Terry D. Bennett, LS, LPF, MRICS, LEED AP is the senior industry program manager for civil engineering and planning at Autodesk. He is responsible for setting the company’s future vision and strategy for technology serving the planning, surveying and civil engineering industries, as well as cultivating and sustaining the firm’s relationships with strategic industry leaders and associations.
Critical Components A city’s basic physical systems – including roads and utilities – are essential to the health of its economy. Currently, there is a worldwide focus on the need for stronger, safer infrastructure. Transportation systems (including highways, railroads, airports and harbors) and utilities (such as gas, electric, water and wastewater) represent critical components. Any disruption to these systems causes an immediate ripple effect. In the event of an emergency, transportation systems in particular are vital. They facilitate mobility for search and rescue and medical teams to get the injured to hospitals; provide access to repair and restore critical utilities, such as power and water; and enable movement of provisions, including food and water. During a natural disaster such as an earthquake, it is imperative that transportation systems remain operational or be restored as soon as possible.
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Past events have shown that earthquake damage to highway components (e.g., bridges, roadways, tunnels and retaining walls) can severely disrupt traffic flow and negatively impact the short- and long-term economy of a region, as well as hinder post-earthquake emergency response and recovery activities.
Seismic Retrofitting: The Role of Building Information Modeling In the past, seismic retrofit was done in order to achieve a specific public safety objective, but engineering solutions were often limited by economic and political considerations. However, with the development of Performance-Based Earthquake Engineering (PBEE), performancelevel objectives are now recognized. Although there is no such thing as an earthquake-proof infrastructure, through appropriate visualization, simulations and analysis procedures, the effects of future infrastructure challenges – including seismic events – can be mitigated. This is where Building Information Modeling (BIM) can play an important role. BIM is an intelligent model–based process for gaining greater insight to accelerate better planning, design, construction and management of infrastructure systems, economically and with less environmental impact. BIM design tools provide a new approach, and can help rehabilitate and retrofit aging transportation and urban infrastructure projects. BIM helps users create highly detailed 3D structural models of roads, railways, bridge tunnels and utilities to enable public, government, engineering, construction and business communities to better understand the task holistically and plan alternatives. In addition, the BIM process can help identify, diagnose and even predict problems that city infrastructures might experience in the future by simulating such seismic events and their impacts. BIM can aid designers and contractors by enabling modeling, analysis and collaboration at any point in the project lifecycle, including existing conditions under stress. Once the future design parameters are known, a BIM process can aid in the creation of alternatives that address them while helping to identify the most economical and time-efficient approach to construction. Two excellent examples of these concepts can be seen in online videos related to the Alaskan Way Viaduct project in Seattle. To view these videos, visit the STRUCTURE website – www.STRUCTUREmag.org/relatedvideo.aspx.
Alaskan Way Viaduct Seattle. BIM enables designers to address one of the biggest challenges, to develop a series of design alternatives that are very different from each other, yet all seismically safe and fiscally responsible replacement structures for the viaduct. Courtesy of Parsons Brinkerhoff.
BIM: Getting Started To transition from an existing paper or 2D process to BIM, especially for infrastructure retrofits, it is best to start at the beginning. Most of our infrastructure today has outdated or nonexistent plans, and few have complete and up-to-date existing condition surveys. This lack of baseline information makes it difficult to predict future performance throughout the life of existing infrastructure structural assets, especially when a retrofit project involves evaluating and comparing proposals from various companies to determine which has the best chance for seismic resiliency. Traditionally, the solution was laboriously to create drawings in 2D form and use them as the basis for an engineered seismic analysis. While these drawings include all of the needed information for submission to the local authority and are used by the contractor for installation or by the inspector for conformance review, creating as-builts by hand is not efficient given the volume of infrastructure that needs to be addressed for seismic retrofits worldwide, let alone the myriad of inputs required today for project approval. Fortunately, new technologies make this once overwhelming prospect more manageable. Over the past few years, terrestrial and mobile laser scanning as well as aerial Light Detection and Ranging (LIDAR) have facilitated fast, accurate and precise data capture of existing infrastructure assets. The point clouds produced from these scans can be combined with 3D modeling software and a BIM workflow to create rich hybrid data sources, providing an as-built model of existing infrastructure that enables designers to work within the 3D environment to evaluate design alternatives.
Presidio Parkway Project Road Seismic Retrofit. Preliminary design of new tunnels and entrance to the golden gate bridge. Courtesy of Parsons Brinkerhoff.
For example, the point cloud that results from capturing road, bridge or other structure geometry and characteristics through laser scanning can be used to create a model for use in a BIM process in order to visualize and simulate the performance, appearance and cost of renovations. This allows a designer to explore design alternatives, associated structural performance analyses, seismic audits, and cost and schedule visualizations, thus enabling better decision-making by project stakeholders. The power to have part of the point cloud turned into a model in the areas of critical design, while leaving the rest unchanged, provides the best of both worlds. The 3D digital model can include data components that represent infrastructure elements such as materials, weight, loading resistance, and other physical properties that contribute to seismic performance, as well as cost or schedule parameters. With BIM, users can then more accurately analyze and assess the performance of individual components, and evaluate, compare, and rank the environmental and financial impact of proposed renovations for an entire system. With a deeper understanding of the relative performance of the infrastructure portfolio, stakeholders can prioritize an overall infrastructure modernization program, and focus on those projects that have the greatest impact or are of the most critical nature. Traditional methods are time-consuming and often inaccurate, which can lead to unacceptable scheduling delays and budget overages. Besides helping design and construction professionals retrofit based on accurate existing conditions, the combination of advanced capture technology with the ability to visualize, simulate and analyze in 3D helps provide owners with a tool for the future. Scanning at the completion of the project produces an asbuilt deliverable for the owner. This base-line
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can be used in operations and maintenance over time to see if any movement or other degradation takes place by simply scanning again and comparing the two models. This allows detection of issues long before they would be apparent from visual inspection, and can make mitigation more cost effective. BIM can improve project management, helping save money. It enables the inclusion of the whole community and administrative stakeholders at local, regional and national levels. Any nation’s growth and economic prosperity is dependent on the adequacy and resiliency of its transportation and utility infrastructure in times of crisis. Through very detailed 3D visualization, simulation and analysis, BIM helps users to forecast future infrastructure requirements for cities and to address concerns.
Future Infrastructure Design Laser scanning combined with BIM requires a rethinking of traditional methods, yet there are plenty of success stories. It is clear that the speed, accuracy and efficiency of these tools are turning what was once an unmanageable task into a process that is both more accurate and efficient, and that helps to reduce our impact on the environment while improving the quality of the spaces in which we live and work The challenges and opportunities that define the early part of the 21st century involve cities and their supporting infrastructures. With advances in technology, BIM now enables engineers working on seismic and other retrofits to balance safety, resiliency and cost requirements. This integrated approach also means that city managers can establish more collaborative solutions to plan for the city’s future, and deliver more resilient infrastructure that meets the needs of an ever-changing landscape.▪
A
Just the FAQs
lthough cold-formed steel wall studs and joists are manufactured with prepunched holes, the trades often modify or create a new hole (Figure 1). The following are two related questions pertaining to the size of a hole that may be drilled, punched or cut into the cross section of a cold-formed steel stud or joist.
questions we made up about... Cold-Formed Steel
Question: I have a question regarding the installation of non-structural steel studs. Is there a limitation on the size hole that can be cut into the web of a 35/8-inch, 20 ga. metal stud?
Answer Thank you for your question. Section 2210 of the International Building Code (IBC) references AISI Standard for Cold-Formed Steel Framing– General Provisions (S200) which in turn references ASTM C754 Standard Specification for Installation of Steel Framing Members to Receive Screw-Attached Gypsum Panel Products for installation of nonstructural framing. Table 2508.1 of the IBC also references this standard. ASTM C754 does not explicitly give a limitation on the size of holes; nor does ASTM C645 Standard Specification for Nonstructural Steel Framing Members. However, for the design of members, AISI North American Specification for the Design of Cold-Formed Steel Structural Members (S100) provides guidance on the size of holes that may be considered when checking member capacity. S100 is referenced in section 2209 of the IBC. Section B2.4 of S100 puts the following limits on C-sections with holes under a stress gradient (i.e. flexural members): • Holes may be no more than 70% of the web depth • Hole spacing must be at least 18 inches • Circular holes must be 6 inches or smaller • Holes should be centered at mid-depth of the web • Non-circular holes must not have sharp corners: the tightest radius of a corner must be at least twice the thickness of the steel. If a hole exceeds these limitations, that does not mean that the member is inadequate, but it must be evaluated by testing rather than using the parameters in section B2.4.
Holes in CFS Cross Sections Answers provided by Don Allen, P.E., LEED A.P. who is Technical Director for the Cold-Formed Steel Engineers Institute (CFSEI), Steel Stud Manufacturers Association (SSMA), and Steel Framing Alliance (SFA); and Roger LaBoube, Ph.D., P.E. who is Curator’s Teaching Professor Emeritus of Civil Engineering, Director of the Wei-Wen Yu Center for Cold-Formed Steel Structures and Director of the Student Design and Experiential Learning Center at the Missouri University of Science & Technology (formerly University of MissouriRolla). Roger is active in several professional organizations and societies, including the American Iron and Steel Institute’s Committee on Specifications for the North American Specification for the Design of Cold-Formed Steel Structural Members and the AISI Committee on Framing Standards. He also serves on STRUCTURE’s Editorial Board.
Question: As you know, the IBC does not provide limitations to allowable holes, nor cutting and notching of steel studs and joists. Researching this, I have not had much luck. I am wondering if you may be able to provide your reference standards.
Answer Thank you for your question. The American Iron and Steel Institute (AISI) Standard for Cold-Formed
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Steel Framing–General Provisions (AISI S200) as well as the AISI Standard for Cold-Formed Steel Framing–Prescriptive Method for One and Two Family Dwellings (AISI S230) provide some guidance with respect to this. The Prescriptive Method does not permit holes within 10 inches of bearing or support locations, and provides a detail for patching holes. It also prohibits cuts or notches in flanges or return lips without an approved design. AISI S200 provides the following design information: E. MISCELLANEOUS E1 Utilities E1.1 Holes Holes shall comply with the requirements specified in Section B2.1. Penetrations of floor, wall and ceiling/roof assemblies which are required to have a fire resistance rating shall be protected in accordance with the applicable building code or in accordance with the requirements as stipulated by the authority having jurisdiction. B2.1 Web Holes Holes in webs of studs, joists and tracks shall be in conformance with an approved design, AISI S100 [CSA S136], or an approved design standard. Webs with holes not conforming to the above shall be reinforced or patched in accordance with an approved design or approved design standard. B2.2.1 Cutting and Patching All cutting of framing members shall be done by sawing, abrasive cutting, shearing, plasma cutting or other approved methods. Cutting or notching of structural members, including flanges and lips of joists, studs, headers, rafters, and ceiling joists, or the patching of those cuts shall not be permitted without an approved design or in accordance with an approved design standard. Section A4.5 of AISI S230 gives a method of hole patching, as well as limitations on the size of the hole. A4.5 Hole Patching Web holes violating the requirements of Section A4.4 shall be patched if the depth of the hole does not exceed 70% of the flat width of the web and the length of the hole measured along the web does not exceed 10 inches (254 mm) or the depth of the web, whichever is greater. The patch shall be a solid steel plate, stud section, or track section in accordance with Figures A4-3 or A4-4. The steel patch shall be of a minimum thickness as the receiving member and shall extend at least 1 inch (25.4 mm) beyond all edges of the hole. The steel patch shall be fastened to the web of the receiving member with No.8 screws spaced no greater than 1 inch (25.4 mm) center-to-center along the edges of the patch with minimum edge distance of ½ inch (12.7 mm). For engineering solutions to reinforce a hole in a cold-formed steel member, CFSEI Tech Note TN-G900-08 Design Methodology for Hole Reinforcement of Cold-Formed Steel Bending Members should be consulted.▪
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new trends, new techniques and current industry issues
InSIghtS
Trends in Cold-Formed Steel By Mark Nowak and W. Lee Shoemaker, P.E., Ph.D.
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old-formed steel (CFS) is widely used in conventional construction as well as in metal building systems. It continues to show promise, even with the overall size of the construction market shrinking during the latest economic turndown. More than ever, building owners and contractors are seeking buildings and materials that are cost-effective but also meet specific code requirements for non-combustible construction. Throw in the increasing demand for sustainable or “green” products, and CFS starts to make a lot of sense. In conventional construction, the interest is in structural use in buildings that traditionally have relied on heavier materials. This includes hotels, multi-family housing, dormitories and mixed-use buildings in the mid-rise markets from four stories to as many as nine stories. However, the healthcare field is also a growth market, with most of these buildings falling under the IBC’s use group I-2 that requires non-combustible construction for any building over one story. From the structural engineer’s perspective, the challenge is in expanding the number of designers experienced in taller CFS buildings. Fortunately, groups like the Cold-Formed Steel Engineers Institute (the technical institute of the Steel Framing Alliance) and the Hawaii Steel Framing Alliance are actively engaging their members in educational activities to expand the industry’s expertise for CFS mid-rise design.
Cold formed steel framing spanned up to 30 feet in this final assembly building for the largest radio telescope in the world, Atacama Desert, Chile.
For metal building system applications, CFS has traditionally been used for secondary members. This includes girts, purlins, wall cladding, and roofing. In the past, metal building systems were primarily used for “backstreet” buildings such as warehouses and manufacturing. Now they are often selected for “main street” buildings such as Cold formed steel framing used for the structural system on a midrise building in Seattle, WA. schools, offices, retail, etc. This reflects a decrease in the manufacturing sector, because of longer fasteners required to penas well as the emergence of more architectur- etrate thicker insulation. Condensation issues ally aesthetic solutions using metal buildings. must also be thoroughly addressed as tried and Although the traditional structural design true roof and wall assemblies are re-engineered challenges are part of the ongoing market to be more energy efficient. development, perhaps no other issue is Another trend that is on the horizon in impacting the state of the CFS industry as CFS design in the U.S. is the use of more much as sustainability. There is a growing efficient sections, utilizing more complex propush for increased energy efficiency and the files. This is being facilitated by an alternate use of Life Cycle Assessments (LCA) to evalu- design methodology in the AISI Specification ate building materials. called the Direct Strength Method. This perAlthough LCA is not really appropriate as mits the optimization of sections using more a tool to compare different building mate- stiffening elements in webs and flanges of CFS rials, that has not stopped its proponents members that can be easily incorporated in from trying to gain traction through dif- the roll forming process. A recent student ferent “green” programs and various codes competition sponsored by the University of and standards. It may be only a matter of North Texas utilized this design method and time before someone from the steel industry yielded some imaginative entries. That is the involved in a project’s design has to step advantage of this method – for any cross secup and become proficient at the practice of tion that you can imagine, you can determine LCA. The structural engineer may very well its critical elastic buckling load. be that professional. As we move forward and the economy recovThe latest energy codes will change the way ers, the CFS industry is well-positioned to buildings are designed. If the use of CFS is to expand. The structural engineering commucontinue to grow, no longer will it be accept- nity will be an important part of the process able for the structural engineer (or any of the along the way.▪ other designers in the process) to operate with a sole focus on the structure. More cooperaMark Nowak is Manager of Research of tive design among the different disciplines the Steel Framing Alliance in Washington, will be the norm. DC. SFA is a trade group representing For example, the structural capacity of some steel producers, manufacturers, suppliers, CFS members is based on testing that was and contractors. He can be reached at done with a certain amount of fiberglass mnowak@steelframing.org. insulation sandwiched between cladding W. Lee Shoemaker, P.E., Ph.D. and supporting elements. Energy codes are (lshoemaker@thomasamc.com), is the now requiring greater thermal efficiency, Director of Research and Engineering for the and therefore more insulation or different Metal Building Manufacturers Association types of insulation than previously assumed. in Cleveland, OH. MBMA is a trade This has to be considered, and will impact association that represents metal building both strength and serviceability. Deflections manufacturers and suppliers to that industry. and rotations of members may be increased
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“We originally specified steel rafters due to the complexity of the roof. However, Aegis cold formed trusses proved to be a more economical alternative.” Project Engineer, The Crossing, San Bruno
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business issues
Business Practices
Top Risk Management Questions Facing Design Firms Today By G. Daniel Bradshaw, CPCU
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s an insurance agent working with design firms every day, I get lots of questions regarding professional liability risks. Here is a listing in no particular order of the top professional liability questions I have been hearing from my clients and prospects, including my structural clients. It’s not a scientific poll, mind you, but a fair reflection of what’s on the minds of design firms when considering their professional risks.
Should I sign my client’s take-it-or-leave-it contract? This is a very difficult question to answer. First, the fact that a client would take such a stance should send up a red flag. Is this the type of entity or individual you want to do business with? But if it’s a project or client that is attractive to you from a business standpoint, a client-drafted contract is not necessarily a bad thing. The key is to ensure the contract does not contain onerous language you simply can’t accept. First of all, READ the contract – or have legal counsel do so. Highlight any language that you feel presents risks to your firm. Look for language that asks you to indemnify the client from risks that might otherwise logically belong with the client. For example, does it ask you to take responsibility for the client’s negligence or actions? Please be aware, if you agree to accept liabilities that would not be yours absent the contractual obligation, those liabilities will most likely NOT be insured! In the end, it comes down to a risk-versusreward business decision. You may be able to get a contract review from your insurance agent, but only you know whether you can live with the contract conditions.
Whatever happened to project insurance? Long ago and far, far away, most professional liability insurers offered a product called project-specific insurance. Generally, this type of insurance covered all of the design firms
working on a single project up to the policy’s dedicated limits. It was typically paid for by the project owner and the fees earned by the design firms did not count in the calculation of their own practice policies. Sounds great, right? Who could lose when project owners had guaranteed coverage up to their desired limits and the design firms avoided most if not all the cost? The insurance company, that’s who! These policies, for a variety of reasons, resulted in monumental losses for insurers. As claims and loss ratios hit the stratosphere, insurance companies pulled their products off the market and project policies went the way of the dinosaur. Actually, there are still a few insurers who may offer project policies under the right conditions, but prices are extremely high and policy conditions are not as attractive as before.
Will my clients really accept a limitation of liability (L of L) contract provision? You’ll never know until you try! The fact is many clients accept L of L contract provisions once the reasoning behind them is explained. The primary line of reasoning goes something like this: The client has the most to gain from a successfully completed project. The designer’s gain is limited to project fees minus expenses. So if the owner has the bulk of the reward, shouldn’t they also be willing to accept its fair share of risk? As a structural engineer, your client is often another designer who didn’t negotiate a limitation of liability clause with its client, the project owner. Regardless, you should discuss the importance of this clause and the benefits for you and them. The best L of L negotiation stance is to avoid a yes/no decision. Provide your client an option – you can either perform your services with unlimited liability for one fee, or you can lower that fee if the client is willing to accept the L of L. If clients balk at the amount, raise the limit. A cap at your available insurance limits rather than your fee, for example, is much better than no clause at all.
This material is provided for informational purposes only. Before taking any action that could have legal or other important consequences, confer with a qualified professional who can provide guidance that considers your own unique circumstances. STRUCTURE magazine
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How much will my professional liability insurance cost next year? That’s going to depend on a whole slew of factors. Your premiums will be based on your annual fees, your claims history, the types of projects you’ve worked on and whether you take advantage of cost-saving opportunities offered by your insurance company – such as completing loss prevention education programs or including prescribed risk management practices. All things being even, insurance premiums are currently pretty stable, but that may change. Be sure you consider the entire cost of professional liability protection, not just your annual policy premium. You might find an insurance agent or broker offering significantly reduced premiums. But if you end up with inferior policy coverage and inadequate claim service, support and advice, buying that cheap policy may turn out to be the most expensive decision you’ve ever made.
What is the best thing I can do to reduce my professional liability risks? That one is pretty easy – manage your client relations. Claims studies show that non-technical factors are the leading cause of claims, and topping the list are communication problems between designers and their clients. Stress within your firm the need to have open, honest and clear communications with your clients. Good communications go a long way to uncovering misunderstandings, omissions and errors at the earliest stage possible, before they require an expensive fix. Equally important, if you have a solid, open and trusting relationship with your clients, they are more willing to seek amicable solutions to any project upsets that arise, rather than immediately calling in their lawyers and threatening you with claims. When your client’s attitude is one of “how can we fix it?” rather than “how are you going to fix it?” you’ve won half the battle.▪ G. Daniel Bradshaw, CPCU is a professional liability specialist in Bountiful, Utah, and is Immediate Past President of the Professional Liability Agents Network (PLAN), an association of agencies and brokerages serving design firms in the U.S., Canada and Puerto Rico.
Great achievements
notable structural engineers
Nabih Youssef Pioneering Seismic Pacesetter By Richard G. Weingardt, P.E., Dist.M.ASCE, F.ACEC, D.Sc.h.c.
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ince its founding in 1989, Nabih Youssef Associates (NYA) has become an internationally recognized consulting firm providing specialized structural and earthquake engineering services for both new and existing buildings. As a leader in implementing state-of-the-art technologies, NYA’s contributions to the development of earthquake engineering codes and standards and performance-based design has made possible numerous elegant, cost-effective and leading-edge structures. The firm’s founder, Nabih Youssef, pioneered the concepts of performance-based design – refinement of the idea that buildings should move with earthquakes, not resist them – and of base isolation to protect structures seismically. Incorporating base isolation techniques into the design of the Cathedral of Our Lady of the Angels has given its structure a projected service life of 500 years. Youssef used innovative steel-plate shear walls, instead of thick concrete shear walls, to provide the lateral strength for the 55-story LA Live! Hotel and Residences Tower in downtown Los Angeles, the first high-rise building in the city to have such a system. It reduced the weight of the structure by 30 percent, shortened the project’s construction timeline and made available more window space. The thinner (⅛ inch) steel-plate shear walls also allowed for more rentable floor space – approximately 750 square feet extra per floor, and roughly 20,000 square feet total. Nabih was born on May 29, 1944 in Cairo, Egypt, to Fouad and Amira Youssef. He was the third child of five boys and one girl and grew up in an upper-middle-class family within an ethnically, religiously and linguistically diverse community, which he described as a “Mediterranean culture.” Nabih’s father, from a large family who were mostly owners of large farms, was educated in the American College and held a government position with the interior ministry. Following in the family tradition, Nabih attended French Catholic School. In his youth and early adulthood, he enjoyed
athletics and cultural activities, and was an active member of the YMCA as well as other sports and Nabih Youssef. leadership programs. His Courtesy of favorite subjects were his- NYA. tory, geography, engineering and science. He was 16 when he first decided on a career in engineering, influenced by the American space program. Initially, Nabih thought he wanted to be a scientist because of his fascination with aerospace and its promises. However, at Cairo University he encountered several renowned faculty members who were graduates of Cal-Tech, MIT, ITT, Cal-Berkley and Cambridge/Oxford. He shifted from aerospace to structural engineering and received a bachelor’s degree, with distinction, in 1967. After immigrating to the United States, he received a master’s degree from California State University (CSU) in Los Angeles and then a postgraduate Diploma in earthquake engineering from the University of California at Los Angeles (UCLA) in 1974. Nabih married Isis, a computer analyst, on April 28, 1974. They have three children, Michelle-Marie, John Paul and Christine-Marie. Michelle works in the field of education, John Paul is the founder and manager of Capital Creation Investments, and Christine is working on a master’s degree in social work at the University of Chicago with a focus on special needs children. Youssef started at Welton Becket in 1969. During his time there, he worked on such projects as the Hyatt Regency and Theme Tower in Dallas, Texas; the Moscow World Trade Center; the Washington, DC, Convention Center; and the 1975 redesign of Olive View Hospital, whose partial collapse during the 1971 San Fernando earthquake cemented his focus on seismic engineering. In 1982 he joined A.C. Martin Partners in Los Angeles, where he led its engineering division. He designed the Manu-Life Tower, Beverly Hills Civic Center, downtown Los Angeles YMCA and Home Savings Tower during this time. He then started his own firm in 1989.
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LA Live! Hotel and Residences. Not only modern in its architectural form, the hotel tower takes full advantage of a leading edge structural steel lateral force resisting system, comprised of unstiffened thin steel plate shear walls (SPSW), moment frames, Buckling Restrained Braces (BRB), mid-height outriggers and cap trusses. The design process exemplifies a successful collaboration of performance-based engineering and rigorous peer review by a panel of noted experts in each structural system type. The result minimizes the cost and construction schedule while maximizing the interior space available for architectural programming. Courtesy of NYA.
Significant projects in NYA’s bulging portfolio, in addition to the Cathedral of Our Lady and LA Live!, include the J. Paul Getty Villa Renovation in Malibu, California; Cleveland Museum of Art Expansion; Skirball Jewish Cultural Center; Dodger Stadium Renovations; Los Angeles Coliseum Renovations; UCSF Ray and Dagmar Dolby Regeneration Medicine Building; Los Angeles City Hall Base Isolation; Los Angeles Police Department Headquarters; Broad Museum; and the New Stanford Hospital. Youssef is registered civil and structural engineer in California, and is also licensed in Arizona, Hawaii, Nevada, New Jersey, New York, Ohio, Oklahoma, Oregon, Texas and Washington. He has been active in
a number of engineering organizations including the American Society of Civil Engineers (ASCE) and Structural Engineers Association of California (SEAoC). He is also a member of many industry-impacting engineering committees, most notably as the co-founder of the Los Angeles Tall Buildings Structural Design Council, a non-profit organization dedicated to advancement in research on tall buildings by means of an annual conference and scholarship program. A recognized expert in the field of seismic design and seismic safety, Youssef has served as chair of the City of Los Angeles Mayor’s Blue Ribbon Panel for Seismic Hazard Reduction, as a commissioner for Santa Monica Building and Safety, on the Governor’s California Buildings Standards Commission and as chair of the Seismic Safety Commission. He has evaluated the seismic hazard in LA’s existing inventory of older buildings and investigated numerous major earthquakes around the world including Managua, Nicaragua (1972); Tangshan, China (1976); Mexico City (1985); Loma Prieta (1989); Cairo, Egypt (1991); Kobe, Japan (1995); and Chile (2010). Youssef is a Fellow in the Institute for The Advancement of Engineering. He is a member of the California Club, Jonathan Club and Downtown Breakfast Club and is very active in his church, where he works with the youth through education, training programs, leadership camps and sports. He is a co-founder of the Coptic Educational Foundation, a non-profit organization that encourages children in the community to pursue their educational goals, and provides support and funding so that they can receive college degrees. He has served on the board of Marymount High School (which his daughters attended), Junior Blind and the LA Conservancy. In addition to his various publications and presentations, Youssef has taught at universities for more than 20 years. He has been a lecturer for key courses in structural design, preservation of historical structures and glass structures at the University of Southern California (USC) and the Southern California Institute of Architecture (SCI-ARC).He has also been involved in various industry and governmental panels, notably: • Congressional Office of Technology Assessment Advisory Panel
Our Lady of the Angels Cathedral. Although the building is essentially two stories, 150 feet tall, it has multiple roof diaphragm levels and shapes. The architectural features of the design (exposed concrete, tall slender walls, and an abundance of glass) placed exceptional demands on the structural design and construction. Designed as a place of refuge after major disasters for 500 years, the entire cathedral was base isolated, making it the heaviest building to ever be isolated. Response modification using different isolation; global finite element models and nonlinear time history analyses were performed to study the global response. For the concrete walls (BIAX), moment curvature analysis was performed to assess cracking at DBE displacement, and several different stress-strain models for concrete tension behavior were created. Courtesy of NYA.
• Vision 200 Committee (founder and chair) • Seismology Committee of SEAoC • Project Restore (past chair), a nonprofit organization dedicated to the restoration and revitalization of historic facilities in Los Angeles, such as City Hall Lindbergh Beacon and Hollyhock House, designed by Frank Lloyd Wright. Among Youssef ’s specialties are monocoque structures that are highly irregular, such as the Cathedral of Our Lady of the Angels and Broad Museum. Other examples are the Glendale MSB, Hines La Jolla, Brinderson Towers, 1100 Wilshire and Madame Tussauds, Hollywood. He also has much interest in structural glass design and has been involved in many projects featuring it, such as a glass staircase for the Apple Store in San Francisco, a large glass cantilever at the Cleveland Museum of Art and large glass panels at Claremont McKenna College. Youssef was the recipient of the 2010 AISC Designer Special Achievement Award, as well as a special AISC Presidents Award for
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Excellence in Structural Engineering for LA Live! He received the AIA Los Angeles Presidential Award in 2008, the USC Architectural Guild award for Outstanding Achievement, and the 2001 Cal State LA Distinguished Alumni Award. In 1999 he received the Egyptian American Organization’s Outstanding Achievement Award. Said Youssef, “The complete integration of art, science and technology is the point at which design excellence is achieved. This profession is about committing yourself wholly to your vision and living it through your clients, projects, associates and life’s opportunities.”▪ Richard G. Weingardt, P.E., Dist.M.ASCE, F.ACEC, D.Sc.h.c. (rweingardt@weingardt.com), is Chairman of Richard Weingardt Consultants, Inc. in Denver, Colorado. He is the author of ten books, including Circles in the Sky: The Life and Times of George Ferris and Engineering Legends. His latest book, Empire Man, is about Homer Balcom, structural engineer for the Empire State Building.
Software UpdateS ADAPT Corporation Phone: 650-306-2400 Email: info@adaptsoft.com Web: www.adaptsoft.com Product: ADAPT-Edge for Concrete Buildings Description: This new structural analysis software offers the only complete solution for the detailed analysis and design of concrete floors, foundations, and full building structures, eliminating the need to maintain separate slab and general purpose programs. Models RC or post-tensioned members. Supports BIM workflow through seamless integration with Revit Structure.
Bentley Systems Phone: 760-431-3610 Email: jason.reichel@bentley.com Web: www.bentley.com Product: RAM Structural System V8i Description: The RAM Structural System is a specialized engineering software tool for the complete analysis, design, and drafting of both steel and concrete buildings. It optimizes workflows through the creation of a single model by providing specialized design functions for buildings and by providing thorough documentation.
CADRE Analytic Phone: 425-392-4309 Email: cadresales@cadreanalytic.com Web: www.cadreanalytic.com Product: CADRE Pro Description: New version 6.5. Finite element application with advanced modeling tools. Designed by professional engineers as a practical tool for architectural, civil, mechanical and structural engineers. Solves beam and/or plate type structures for internal loads, stress, displacements, vibration modes, and natural frequencies. Advanced features for stability, shock and seismic loads.
CMC Steel Products Phone: 972-772-0769 Email: marketing@cmc.com Web: www.cmcsteelproducts.com Product: RAM SBeam CMC SMARTBEAM® Version 5.01 Description: RAM SBeam – CMC SMARTBEAM is a powerful and versatile program for the design of castellated and cellular steel beams. Using one of several design codes, RAM SBeam – CMC SMARTBEAM® can select the optimum SMARTBEAM size or check the adequacy of existing construction.
Computers & Structures, Inc. Phone: 510-649-2200 Email: info@csiberkeley.com Web: www.csiberkeley.com Product: CSiBridge Description: CSiBridge V15.2 features enhanced bridge design of prestressed concrete box girders and composite sections with precast I-girders and U-girders. Design includes the effect of both mild reinforcing and prestress
news and information from software vendors
tendons, and is current with the latest US, Eurocode, and International standards. Steel bridge design now includes new steel shapes.
Concrete Masonry Association of CA and NV (CMACN) Phone: 916-722-1700 Email: info@cmacn.org Web: www.cmacn.org Product: CMD09 Computer Program Description: Design of reinforced concrete or clay hollow unit masonry elements. Designs masonry elements in accordance with provisions of Ch. 21 of the 1997 UBC; 2001, 2007 or 2010 CBC; 2003, 2006 or 2009 IBC; and 1999, 2002, 2005 or 2008 Bldg. Code Requirements for Masonry Structures (TMS 402/ACI 530/ASCE 5) [MSJC].
CSC Inc. Phone: 877-710-2053 Email: sales@cscworld.com Web: www.cscworld.com Product: Fastrak Description: The essential design and drafting software for steel buildings. Design simple or complex steel buildings to US codes. Produce clear and concise documentation including drawings and calculations. Product: Revit Integrator Description: As an Autodesk Industry Partner, CSC launched Revit Integrator. This free, unique software enables structural engineers to synchronise models between Autodesk Revit Structure and CSC’s steel building design software, Fastrak. It is an industry leading solution making two-way integration with Revit Structure easy, highlighting amendments made during the synchronisation process. Product: TEDDS Description: Powerful software to automate your daily structural calculations. Access Tedds’ comprehensive library of automated structural and civil engineering calculations. Easily check your output with Tedds’ transparent calculations.
Design Data Phone: 402-441-4000 Email: marnett@sds2.com Web: www.sds2connect.com Product: SDS/2 Connect Description: SDS/2 Connect enables structural engineers using Autodesk® Revit ® Structure to intelligently design connections and produce detailed documentation on those connections. SDS/2 Connect is the only product that enables structural engineers to design and communicate connections based on their Revit Structure design model as an active part of the fabrication process.
All Resource Guides and Updates for the 2012 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.
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Devco Software, Inc. Phone: 541-426-5713 Email: rob@devcosoftware.com Web: www.devcosoftware.com Product: LGBEAMER v8 Description: Analyze and design cold-formed cee, channel and zee sections. Uniform, concentrated, partial span and axial loads. Single and multi-member designs. 2007 NASPEC (2009 IBC) compliant. ProTools include shearwalls, framed openings, X-braces, joists and rafters.
Digital Canal Phone: 800-449-5033 Email: clint@digitalcanal.com Web: www.digitalcanal.com Product: Wind Analysis Version 9 Description: Wind Analysis Version 9 makes implementing the new ASCE 7-10 standard simple and intuitive. The program has been reorganized to match ASCE’s new workflow and even includes context sensitive display of ASCE figures. Reports with unsurpassed detail can be generated in your choice of DOC, PDF and XLS format.
Dimensional Solutions, Inc. Phone: 281-497-5991 Email: Info@DimSoln.com Web: www.DimSoln.com Product: DimSoln Foundation Design Suite™ Description: Design Suite components are integrated, single program analysis/design tools that complete soil and pile-supported foundation design from concept to construction drawings to modeling in minutes. Learn how Foundation3D, Mat3D, DSAnchor, Combined3D and Shaft3D can give you significant time savings and increased productivity. Product: Foundation3D Description: Foundation designs for plant equipment supports have never been easier! Use Foundation3D to complete soil and pile supported foundation designs for exchangers, vessels, drums, towers, silos, pipe racks, and similar equipment. Experience significantly enhanced productivity by reducing your design, drawing and 3D modeling time by over 50%. Product: Mat3D Description: Mat3D completes soil and pile supported mat/pile cap designs supporting multiple load points, in an integrated environment that takes you from concept to construction in minutes. Enhance your productivity from input to construction drawings and 3D foundation modeling in popular CAD/modeling engines for industrial, commercial, petrochemical, transmission foundation design projects.
GT STRUDL Phone: 404-894-2260 Email: casec@ce.gatech.edu Web: www.gtstrudl.gatech.edu Product: GT STRUDL Description: GT STRUCDL Version 32 – Comprehensive linear and nonlinear static and dynamic analysis features for frame and finite element structures. Models plastic hinges,
news and information from software vendors geometric nonlinearities, discrete dampers, tension/compression only members and nonlinear connections. Steel Design including NEW Nuclear Codes and Reinforced Concrete Design. Base Plate Analysis and Multi-Processor Solvers available.
Software UpdateS
literally allows single story concrete masonry buildings to be designed in minutes considering all load combinations. Excellent graphics and fully detailed wall elevations generated.
Nemetschek Scia
Hilti, Inc. Phone: 800-879-8000 Email: us-sales@hilti.com Web: www.us.hilti.com Product: PROFIS Anchor and PROFIS DF Description: Hilti offers two design programs for structural engineers. PROFIS Anchor performs anchor design for cast-in-place and Hilti post-installed anchors using ACI 318, Appendix D provisions. PROFIS DF Diaphragm performs design calculations for steel deck roof and floor diaphragms using the SDI Diaphragm DesignManual, 3rd Edition provisions.
Phone: 877-808-7242 Email: usa@scia-online.com Web: www.scia-online.com Product: Scia Engineer Description: Scia Engineer links structural modeling, analysis modeling, design, drawings and reports in ONE program. Discover simple FEA analysis. Centralize design with static and advanced non-linear analysis and support for many U.S. and International codes. Freeform and parametric technology, and links to many popular 3D/BIM programs makes modeling fast and efficient.
IES, Inc.
Opti-Mate, Inc.
Phone: 800-707-0816 Email: sales@iesweb.com Web: www.iesweb.com Product: VisualAnalysis 9.0 Description: In version 9.0 of VisualAnalysis we have added over 30 new features and improvements. Topping the list of exciting new features are: Steel Warping Torsion Checks, Graphical Bracing Locations, CADLike Selection Box, Automatic Patterned Live Loads, Design Checks for Dynamic Response, Improved Concrete Slab Design, Significant Performance Improvements, and more!
Phone: 610-530-9031 Email: optimate@enter.net Web: www.opti-mate.com Product: Bridge Engineering Software Description: Software titles include Merlin Dash, Descus I and Descus II for curved girders, TRAP for trusses and SABRE sign bridges.
Pile Dynamics, Inc. Phone: 216-831-6131 Email: gina@pile.com Web: www.pile.com/pdi Product: GRLWEAP Description: GRLWEAP simulates pile driving, predicting driving stresses, hammer performance, bearing capacity versus net set per blow relationship, and total driving time. Allows selecting an adequate and economic hammer for the pile-soil condition. Based on Wave Equation Analysis. New: GRLWEAP Offshore Wave Version with special modeling features for offshore projects.
popIcon Software Phone: 415-875-7850 Email: communications@popiconsoftware.com Web: www.popiconsoftware.com Product: popIcon 2011 & 2012 Description: PopIcon Software improves productivity for both model building and documentation by giving users an easy interface that puts tools, tabs and icon families at your fingertips. Now available for Revit® Structure 2011 and Rivit Structure 2012. Try poplcon free for 14 days!
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LARSA, Inc.
ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org
Phone: 800-LARSA-01 Email: jhorner@larsa4d.com Web: www.Larsa4D.com Product: LARSA 4D Description: LARSA 4D analysis and design software addresses the specialized needs of cable-stay, suspension, curved, skewed, and other bridge forms, as well as structures requiring geometric nonlinearity or a staged analysis. Standard in leading firms for bridge design and construction analysis, LARSA 4D continues to lead innovation in analysis and support.
Losch Software, Ltd Phone: 323-592-3299 Email: edlosch@loscheng.com Web: www.LoschSoft.com Product: LECWall Description: Precast/Prestressed or Tilt-up Concrete Wall and Column Design Software.
National Concrete Masonry Association Phone: 703-713-1900 Email: dgraber@ncma.org Web: www.ncma.org Product: Direct Design Software Description: This new software based on The Masonry Society’s new consensus standard Direct Design Handbook (TMS 403-10),
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Software UpdateS POSTEN Engineering Systems Phone: 510-275-4750 Email: sales@postensoft.com Web: www.postensoft.com Product: POSTEN Multistory V9 Description: Now Available – V9 – With sophisticated post-tensioning algorithms, only POSTEN automatically & efficiently designs the Tendons and Rebar (no hours of fiddling with drapes). The only post-tensioned concrete software that includes design of Moment Frames, Seismic & Wind, Columns, Torsion, and Truly Sustainable Design (with automatic documentation for LEED).
Powers Fasteners Phone: 985-807-6666 Email: jzenor@powers.com Web: www.powers.com Product: Powers Design Assist Software Description: “Strength Design” software, for designing in accordance with the IBC and ACI 318 Appendix D. Results for both cast-in-place and postinstalled mechanical and adhesive anchoring systems.
RISA Technologies Phone: 949-951-5815 Email: info@risatech.com Web: www.risa.com Product: RISA-3D Description: RISA-3D designs and optimizes steel, concrete, masonry, wood, cold-formed steel and aluminum with a fast, intuitive interface. State of the art solvers, customizable reporting options and robust integration with other products such as RISAFloor, RISAFoundation and Revit Structure make RISA-3D the premier choice for general purpose structural analysis and design.
S-Frame Software Phone: 203-421-4800 Email: info@s-frame.com Web: www.s-frame.com Product: S-CONCRETE™ Description: Section analysis, design and detailing tool for reinforced concrete beams, columns and walls to multiple design codes (ACI, CSA, BS, UBC). Axial load-moment interaction and moment-curvature diagrams with pre-stressing strands. Earthquake resistant design and detailing including boundary elements for shear walls. Product: S-FRAME® Description: Easy-to-use structural modeling and analysis environment for frames, trusses, bridges, office and residential high-rises, industrial buildings, plate/shell structures, and cable structures for seismic analysis, staged construction, slab design, Direct Analysis Method, linear and nonlinear static and time history analyses, moving load analysis, buckling load evaluation and more.
news and information from software vendors
Product: S-PAD™ Description: Entry-level steel member design and optimization application. Simple spreadsheet-like interface to advanced code-checking capabilities and auto-design to multiple design codes (AISC, CSA, EU, BS) for strength and serviceability of columns, beams, and braces. No need to build a complete detailed model.
Standards Design Group Inc. Phone: 800-366-5585 Email: info@standardsdesign.com Web: www.standardsdesign.com Product: Wind Loads on Structures 4 Description: WLS4 performs all the wind load computations in ASCE 7-98, 02 or 05, Section 6 and ASCE 7-10, chapters 26-31. User can “build” structures within the system. It provides basic wind speeds from a built-in version of the wind speed map(s) or allows the user to enter a wind speed.
Strand7 Pty Ltd Phone: 252-504-2282 Email: anne@beaufort-analysis.com Web: www.strand7.com Product: Strand7 Description: Advanced, general purpose, FEA system used worldwide by engineers, designers, and analysts for a wide range of structural analysis applications. It comprises preprocessing, solvers (include linear and nonlinear static and dynamic capabilities...) and postprocessing. New features include staged construction, new solvers including quasi-static for shrinkage and creep/relaxation problems.
StrucSoft Solutions Phone: 514-731-0008 Email: info@strucsoftsolutions.com Web: www.strucsoftsolutions.com Product: MWF Floor Description: MWF Floor module is a Metal and Wood floor framing application that supports both Stick framing and panelizing work methods. The application also supports both Platform and Balloon framing methods.
Structural Soft, LLC Phone: 650-813-9500 Email: contact@structuralsoft.com Web: www.structuralsoft.com Product: BuildingWorx Description: BuildingWorx is the most comprehensive structural design software suite on the market for light frame wood buildings, both residential and light commercial. Receive free trial software at the website.
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StructurePoint Phone: 847-966-4357 Email: info@structurepoint.org Web: www.StructurePoint.org Product: Concrete Design Software Description: Upgraded to ACI 318-11, earlier PCA concrete design program suites provides updated code provisions and user features geared for productivity and speed in designing reinforced concrete buildings and structures.
Struware, LLC Phone: 904-302-6724 Email: email@struware.com Web: www.struware.com Product: Struware Code Search Description: Struware announces a new version of its Code Search program. The software has been updated to incorporate ASCE 7-10 and the 2012 IBC. The program will provide you with all pertinent wind, seismic, snow, live and dead loads in just minutes. Struware also offers other structural software. Demos at website.
Tekla Phone: 770-426-5105 Email: info.us@tekla.com Web: www.tekla.com Product: Tekla Structures Description: Structural engineers use Tekla to widen their role in building projects, increasing the value of structural engineering and ensuring the highestquality end results by moving from design-oriented to construction-oriented engineering.
Weyerhaeuser Phone: 888-453-8358 Email: wood@weyerhaeuser.com Web: www.woodbywy.com Product: Weyerhaeuser Javelin® Design Software Description: Weyerhaeuser has added more than 30 features to Javelin design software that simplify data input, expand design capabilities, and enable wider sharing of output results. The enhancements allow users to design wood structural frames even faster and more efficiently – specifying products and tracking vertical loads from ridge to foundation.
All Resource Guides and Updates for the 2012 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.
Work quickly. Work simply. Work accurately. StructurePoint’s Productivity Suite of powerful software tools for reinforced concrete analysis & design
Finite element analysis & design of reinforced, precast ICF & tilt-up concrete walls
Analysis, design & investigation of reinforced concrete beams & one-way slab systems
Design & investigation of rectangular, round & irregularly shaped concrete column sections
Analysis, design & investigation of reinforced concrete beams & slab systems
Finite element analysis & design of reinforced concrete foundations, combined footings or slabs on grade
StructurePoint’s suite of productivity tools are so easy to learn and simple to use that you’ll be able to start saving time and money almost immediately. And when you use StructurePoint software, you’re also taking advantage of the Portland Cement Association’s more than 90 years of experience, expertise, and technical support in concrete design and construction.
Visit StructurePoint.org to download your trial copy of our software products. For more information on licensing and pricing options please call 847.966.4357 or e-mail info@StructurePoint.org.
STR 6-09
award winners and outstanding projects
Portland’s Shriners Hospital
By Chris Thompson, P.E., S.E. and N. Jacob Stept, P.E., S.E.
S
ince 1924, Shriners Hospitals for Children™ has provided health care to children in the Pacific Northwest. The hospital’s mission is to provide no-cost treatment to children up to the age of 18 for orthopedic conditions, burns, spinal cord injuries, cleft lip and palate. In Portland, surgery, rehabilitation, and research are also conducted. Built in 1980, the Portland facility was overutilized, impacting their ability to provide care in the region. As the region experienced a growth in population, so did the need for care. The wait list for treatment was ever increasing, and the existing facility needed updating to address Code and regulatory requirements. In 2005, the Shriners retained a design team led by SRG Partnership, Inc. to study options for updating the aging facility located on Oregon Health & Science University’s Marquam Hill campus. Andersen Construction Company was retained by Shriners as the Construction Manager/General Contractor. Catena consulting engineers worked with the design and construction team to study several replacement options, including: relocating the hospital to another site; demolishing part or all of the existing hospital; and, renovating the existing hospital and constructing an adjacent facility. Several key factors drove the evaluation of the options including the synergistic relationship with OHSU, cost, schedule, and disruption to service. The team developed an innovative approach in a structural system for the expansion that spanned over an existing parking structure and maximized key project drivers. The application of structural transfer trusses integrated into the program of the hospital, and integration of Buckling Restrained Braces for resistance to lateral forces, made for a creative solution on a challenging and constrained site. The chosen option called for a 73,000 square foot, four-story addition housing surgery suites, patient rooms, laboratory, clinical, and support spaces. The addition was constructed adjacent to the existing hospital, over the existing parking structure. This option maintained the proximity to OHSU that allows the Shriners to collaborate with University doctors in providing care and conducting research. It also was the least cost solution – approximately 33% less cost than the next option. This option allowed for the shortest project schedule, saving six months. Given the expanding need for services,
Spotlight
Catena consulting engineers was an Outstanding Award Winner for the Shriners Hospital for Children project in the 2011 NCSEA Annual Excellence in Structural Engineering Awards Program (Category – New Buildings $30M to $100 M)
the Shriners could not afford disruption to operations. A clear benefit was that it provided the least disruption to service, allowing the Shriners to continue operations throughout the entire construction process.
Structural System The team investigated several structural systems for the expansion, and quickly arrived at a steel composite deck system for floor framing, with steel trusses that spanned over the existing parking structure supporting the expansion. Structural steel was chosen due to the irregular bay layout (a result of the constrained site) and constructing the expansion over the existing parking structure, which remained operational throughout most of the construction. Catena incorporated Buckling Restrained Braces (BRB) to resist the seismic loading and motions – the first project in the City of Portland to employ this emerging technology. The use of BRB in the structure helped to minimize the effects of the seismic ground motions at the site through the ability of BRB to dampen and absorb the energy of the ground motion. By using BRB, catena helped the owner to save approximately 10% of the seismic force resisting structure cost, including the supporting foundations.
Construction Challenges and Design Solutions Constructing the hospital on the constrained and steeply sloping site, over the existing parking structure, provided for a high level of project complexity. The supporting foundation wall on one side of the project was constructed in a gap between the hillside and parking structure that had a maximum width of 30 inches. The team devised a foundation system robust enough to withstand the building loads that could be constructed in this minimal space. The foundations employed were micro piles which extended to the underlying basalt strata. Modern hospitals demand high quality in the construction of the floors, with strict limits on the variations from level in the floor structure and on vibrations for highly sensitive equipment used by staff. Spanning over the existing garage added complexity to meeting these criteria. Additionally, the supporting trusses needed
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to be designed to accommodate a future threestory expansion. The trusses were designed to support the current expansion, and additional transfer trusses placed at the uppermost level of the future expansion are planned to help share loads between current and future building configurations. Predicting the truss deflections during construction was a key element. Truss deflections were estimated for a range of conditions, including variations in connection fixity. The trusses were cambered to minimize initial deflections based on deflection estimates. By working closely with the contractor on this aspect of the project, floor leveling to meet project specifications was minimized.
Exceeding Client/Owner’s Needs or Expectations Given the complexity of the project and site constraints, the team understood the potential for project cost overruns. Through a close collaboration of the team, owner, and contractor, coupled with the effective use of Building Information Modeling (BIM), the design and construction team was able to minimize the scope modifications during construction. The team exceeded the owner’s needs and project goals by bringing the project construction cost almost $2M under the established budget. The Shriners elected to utilize the savings to complete a badly needed exterior façade replacement of the existing hospital. Catena spent significant effort in the preliminary design of the structure, along with extensive field verification and constructability review with the contractor. The result was that the final cost of the completed structure came within 1% of the cost established in the budget.▪ Chris Thompson, P.E., S.E. is Managing Principal at catena consulting engineers. He served as Principal in Charge for the Shriners Hospital for Children Expansion and Renovation. He can be reached at chris@catenaengineers.com. N. Jacob Stept, P.E., S.E. is an Associate at catena consulting engineers. He served as Project Manager for the Shriners Hospital for Children Expansion and Renovation. He can be reached at jake@catenaengineers.com.
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NCSEA News News form the National Council of Structural Engineers Associations
October 3- 6, 2 012 in St. Louis
Designing for Extreme Loads, IBC changes and updates, teasers on new NCSEA publications like the upcoming one on Serviceability, various states’ progress on obtaining Separate Licensing, Young Members Forums, the new Advocacy Committee video, software decisions – so much to talk about and, this year, there will be more time. Committees will meet on Wednesday, and software and other vendors will offer presentations. Thursday will be filled with continuing education, exhibitors, and the Exhibitors’ Welcome Reception. Friday will offer Member Organization Delegate updates on what state organizations are doing, as well as more continuing education
and the Awards Banquet. Saturday will be the NCSEA Business Meeting and a presentation, and open forum on, what NCSEA can do for its members (concluding early Saturday afternoon). The Hilton Frontenac has an excellent rate ($102) for meeting attendees who book their rooms before Tuesday, September 11; and, if you want to come earlier in the week, the ICC Evaluation Services Committee invites you to attend their open hearings. Transportation to and from the Lambert International Airport and the Metro Link will be complimentary, as will transportation to and from the Galleria Mall, the Anheuser-Busch Brewery, and the St. Louis Zoo. Register at www.ncsea.com.
NCSEA Committee Work
NCSEA News
NCSEA’s 20 th Annual Conference
NCSEA Basic Education Committee Members Participated in the Development of the Fundamentals of Engineering (FE) Exam Specification
Upcoming NCSEA Webinars March 1: Concrete with Little or No Shrinkage, Cracking and Curling
March 15: Mechanically Stabilized Earth Walls – Lessons Learned from Past Failures
This presentation will cover a great many topics that affect the shrinkage, cracking and curling of concrete. Typical concrete shrinks about 0.06%. In this presentation the emphasis for the concrete mix design will be on reducing the shrinkage to 0.04%, 0.02% or even 0.00% by the use of the proper coarse aggregate size and quantity, and by the use of shrinkage reducing & shrinkage compensating admixtures. Also covered: How to write a spec to achieve these low shrinkage percentages and what happens after the concrete is placed, including the use of an evaporation retarder, proper curing, joint layout, sawcutting, etc.
Dr. James Collin will review the basic components of MSE walls and the importance of overall site requirements in the long term performance of MSE walls. Following this review, Dr. Collin will discuss key lessons that he has learned as a result of over 100 forensic analyses of poorly performing MSE walls.
David Flax of The Euclid Chemical Company has a Civil Engineering Degree from RPI and over 35 years of experience as a field engineer, contractor, and researcher with the Corps of Engineers. He has earned his CDT and CCPR from CSI, has specialized in concrete, and is widely published. Mr. Flax is also a member of numerous national organization committees, including the “Guide Specifications Committee”.
Dr. James Collin has extensive practical experience, both as a specialty contractor and as a geotechnical consultant. One of his areas of expertise is earth retention systems. As a specialty contractor, Dr. Collin was responsible for the design and construction of temporary and permanent earth retention systems, including tieback retaining walls, soil nailing, slurry walls, tangent pile walls, and freeze walls. He has authored numerous articles on various aspects of MSE walls and was the Editor of the National Concrete Masonry Association Manual on the design of segmental retaining walls. As a geotechnical consultant, Dr.Collin has been involved with the design and construction of hundreds of reinforced soil slopes and geosynthetic reinforced retaining walls and has performed forensic evaluation of over 100 MSE wall failures.
Cost: $225 for NCSEA members, $250 for SEI/CASE members, $275 for non-members, FlexPlan option still available. Several people may attend for one connection fee. 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program. Applicable for SECB recertification. No fee for continuing education certificates. Time: 10:00 AM Pacific, 11:00 AM Mountain, 12:00 PM Central, 1:00 PM Eastern. Miss Register at www.ncsea.com. a webinar that you wanted to see? Purchase the recording at www.ncsea.com. STRUCTURE magazine
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News from the National Council of Structural Engineers Associations
Two representatives of the NCSEA Basic Education committee recently participated in the National Council of Examiners for Engineering and Surveying (NCEES) committee charged with the task of developing a new specification for the Fundamentals of Engineering (FE) exam. The main steps in the process of developing a new FE exam specification were developing, conducting, and reviewing the results of an FE exam content review survey. The purpose of the FE exam content review survey was to ensure that the questions on the FE examination accurately test the relevant areas of knowledge required to enter into an engineering internship. The FE exam content review survey included a list of over 150 topics as determined by the NCEES committee to be possible examination topics. Over 2800 volunteers responded to the FE exam content review survey that rated the importance of each topic.
2012 Structures Congress
Structural Columns
The Newsletter of the Structural Engineering Institute of ASCE
March 29-31, 2012 Chicago, Illinois Forge Connections in the Windy City
Last Chance To Register For The Structures 2012 Congress Don’t miss this opportunity to attend this year’s Structures Congress. Offerings this year include: • A wide variety of Pre- and Post Conference Seminars on current topics in structural engineering • Eleven Tracks of Technical Sessions • Outstanding Keynote Speakers • CASE 2012 Spring Risk Management Convocation • Student Program • Young Professionals Program • Thursday Night SEI and PCI Welcome Reception
• Friday Night Reception on the 80th floor of the Aon Building • Comprehensive Exhibit Hall • Many Opportunities to Network • Over Sixty Committee Meetings • And Much More For more information about the Structures 2012 Congress and to register, visit www.asce.org/SEI.
SEI Apparel Now Available SEI has created a new line of branded apparel, perfect for showing your pride in being a SEI member while attending conferences, networking events, on-site visits, and other casual occasions. The three-button polo shirts are stone-colored and are 65% polyester, 35% cotton featuring the SEI logo embroidered in three colors. A wide range of men’s and woman’s sizes are offered. The adjustable cap is also stone-colored and features SEI and ASCE embroidered in blue. These easy-to-wear items are offered on the SEI website at: www.asce.org/SEI.
Orthotropic Bridge Conferences Proceedings Now Available
SEI Logo Available for Local Groups and Committee Chairman
Recognizing this is a specialized area of bridge engineering, the Sacramento Section of the American Society of Civil Engineers (ASCE) sponsored the Orthotropic Bridge conferences so all engineers around the world can share their ideas, insights and projects. In 2004, the first Orthotropic Bridge Conference was held in Sacramento. It was a pioneering effort by California bridge engineers passionate about the application and future development of Orthotropic configuration for bridges. They recognized the value of offering other professionals in their field the opportunity to join and share their knowledge and experience. That first conference attracted representatives from 11 countries and received excellent comments from many who attended. In 2008, Sacramento Section of ASCE along with the approval of the US Federal Highways Administration (FHWA) conducted the 2nd International Orthotropic Bridge Conference. There had been many advances in research and many projects had been built in the intervening four years. It was a very informative and enriching conference. Proceedings from both the 2004 and 2008 International Orthotropic Bridge Conferences are now available. Visit the SEI Website at www.asce.org/SEI to download the order form and get your copy today!
ASCE’s Collaborative Marketing Department has created a Branding Tool Kit website to help standardize branding across the Society. All institute logos, including SEI’s, were redesigned recently to include the ASCE shield. Please make sure that you use the most up-to-date ASCE and SEI logos when sending out correspondence, creating flyers, or marketing events. The Branding Tool Kit includes logos in black and white, color, horizontal, and vertical versions. The website will walk you through creating a login to access the toolkit. Visit the Branding Toolkit today at: www.ascebrandingtoolkit.com/pages/login.php.
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Errata SEI posts up-to-date errata information for our publications at www.asce.org/SEI. Click on “Publications” on our menu, and select “Errata.” If you have any errata that you would like to submit, please email it to Paul Sgambati at psgambati@asce.org. March 2012
ATC & SEI Advances in Hurricane Engineering Conference Miami, Florida October 24-26, 2012 Much has changed in building codes and standards, and in products designed to resist the impacts from strong hurricanes; however, there is still a great deal to improve upon. As recently as six years ago, Hurricane Katrina hit the Gulf Coast eclipsing Hurricane Andrew as the nation’s worst natural disaster. The Conference Program will feature presentations on topics such as: • Wind Engineering • Coastal Flooding • Engineering for the Building Envelope • Low-Rise Buildings • High-Rise Buildings • Infrastructure • Meteorology and Oceanography • Risk Modeling and Forensic Engineering For more information visit the conference website at: www.atc-sei.org/.
2012 Electrical Transmission and Substation Structures Conference Columbus, Ohio – November 4-8, 2012
A new generation of utility engineers is overcoming unprecedented challenges to find Solutions to Building the Grid of Tomorrow. The Electrical Transmission and Substation Structures Conference is widely recognized as a one-of-a-kind conference that focuses specifically on transmission and substation structure issues to help utility engineers meet the daily challenges of today’s high-stakes energy environment. This must-attend event offers an ideal setting for learning and networking for utilities and suppliers. You won’t want to miss: • In-Depth Technical Sessions presented by leading industry experts on topics including Aesthetic Design Principles; Construction Challenges; Emerging Technologies; Foundations; Lifeline Reliability and Performance; Line and Substation Siting; Line Design, Re-rating and Upgrading; Extreme Loading Events; Managing Aging Infrastructure; Project Management; Regulatory Compliance; Structural Analysis and Design; Substation Design and Upgrading. STRUCTURE magazine
• A dynamic Pre-Conference Workshop on Design Criteria and Load Requirements for Transmission Line Structures. • Networking events where you can exchange ideas with colleagues from around the world. This year the Conference will feature a special 2012 Election Night Reception! • An Exhibit Hall packed with state-of-the-art products and services from leading industry suppliers. • Tours and demonstrations at American Electric Power’s transmission facilities where you can view EMF and Corona demonstrations, EHV hot-line maintenance, and hands-on substation operations all in the same day! Can You Afford to Wait? Held only every three years, if you miss the 2012 Conference, you’ll have to wait until 2015! Mark your calendars now and plan to attend this forum where transmission and substation engineers can share technical knowledge and explore emerging issues, while bringing new engineers up to speed on core issues. For more information visit the conference website at: http://content.asce.org/conferences/ets2012/index.html.
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The Newsletter of the Structural Engineering Institute of ASCE
Hurricane engineering has evolved since Hurricane Andrew wreaked havoc on South Florida and Louisiana nearly 20 years ago. One of the most devastating natural disasters in United States history, Andrew taught us much about how these powerful storms affect our built environment. The Applied Technology Council (ATC) and the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE) are teaming up to present the Advances in Hurricane Engineering Conference in Miami, October 24-26, 2012. This is the second joint conference of these two organizations in a growing partnership to benefit the engineering community regarding natural hazard issues. We invite you to join us in discussing how design practices are evolving to meet the building and infrastructure challenges presented by powerful hurricanes. This conference is being designed to define what we’ve learned, illustrate how these lessons have affected losses, and bridge the gap to identify what we still must learn.
Structural Columns
SAVE THE DATE
UPDATED for 2012
CASE in Point
The Newsletter of the Council of American Structural Engineers
CASE 962A: National Practice Guidelines for the Preparation of Structural Engineering Reports for Buildings Updated for 2012, CASE 962A gives firms who prepare structural engineering reports for condition assessments, load capacity, structural damage/failure investigations, building performance, and other special purpose investigations, a guide for preparing reports. Firms can also use the information contained in the Guidelines to establish and describe the scope of services to be performed, and to reach a contractual agreement with their client. The Guidelines are intended primarily for use in the preparation of reports for buildings. They address the services which are typically provided by the SE in preparing a report. Not every report will require all listed services and many
times a report will encompass other areas which may require additional expertise. CASE hopes these Guidelines will promote and enhance the quality of written engineering reports. Clearly written reports describing the engineer’s findings in a factual, truthful, and unbiased manner will not only serve the client better, but also will benefit the engineering profession through enhancement of its image. Developed by the CASE Guidelines Committee, the updated guideline is available at www.booksforengineers.com.
Save 20% in March on All CASE Products Looking for publications focused on structural engineering? Now is the time to purchase these valuable resources, written by structural engineers for structural engineers, at a 20% discount! CASE products are built on the years of combined experience and know-how of its members. CASE is dedicated to improving the quality of the structural engineering industry through enhanced business practices, decreased professional liability exposure and increased profitability. Take advantage of this discount and see your business improve its bottom line. The 20% discount has already been applied to the website – no coupon needed. Sale ends March 31, 2011. Go to www.booksforengineers.com to take advantage now!
CASE Meets in New Orleans On February 8-9, the CASE Winter Planning Meeting took place in conjunction with the NCSEA Winter Institute in New Orleans. 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, Toolkit, and Programs & Communications Committees. We are finalizing the schedule of new products being released in 2012/2013, plus reviewing current documents for scheduled revisions and finalized speakers/sessions for the ASCE/SEI Structures Congress this month, the ACEC Fall Conference in October in Boca Raton, and the 2013 ASCE/SEI Structures Congress scheduled for May in Pittsburgh. In addition, on February 9th, the CASE Executive Committee met and continued to refine the CASE Strategic Plan anticipating a final document by this summer. In tandem, they discussed movement on the strategic initiatives. The Executive Committee also discussed CASE’s relationship with other ACEC coalitions and CASE sister organizations. CASE wants to make these relationships as beneficial as possible to CASE members. In addition, they reviewed the newly redesigned CASE website which has become more user friendly, is an increased resource
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for members, and provides a better interface for member input and feedback. The CASE Summer Planning Meeting is tentatively scheduled for August 2012 in Chicago. If you are interested in learning more about the CASE committees or have any suggestions for them, please contact CASE Executive Director Heather Talbert at htalbert@acec.org.
March 2012
The Council of American Structural Engineers (CASE) is a national association of structural engineering firms. CASE provides a forum for action to improve the business of structural engineering through implementation of best practices, reduced professional liability exposure and increased profitability. Our mission is to improve the practice of structural engineering by providing business practice resources, improving quality, and enhancing management practices to reduce the frequency and severity of claims. Our vision is to be the leading provider of risk management and business practice education, and information for use in the structural engineering practice. Your membership gets you free access to contracts covering various situations, as well as access to guidance on AIA
documents, free national guidelines for the Structural Engineer of Record designed to help corporate and municipal clients understand the scope of services structural engineers do and do not provide, free access to tools which are designed to keep you up to date on how much risk your firm is taking on and how to reduce that risk, biannual CASE convocations dedicated to Best Practice structural engineering, AND free downloads of all CASE documents 24/7. For more information go to www.acec.org/case or contact Heather Talbert at htalbert@acec.org. You must be an ACEC member to join CASE. You can follow ACEC Coalitions on Twitter – @ACECCoalitions.
If you would like more information on the items below, please contact Ed Bajer, ebajer@acec.org.
Using Social Media
Using Innovative Material or Equipment
Firms should develop a social media policy that encourages the use of these new and emerging tools in innovative ways. The involvement of young minds is essential to the process. New employees have weathered the job market in the social media age; ask them how they did it. Some firms have a prescriptive policy of when and how to engage in social media. A more dynamic approach is recommended, tailored by your firm culture. Consider offering incentives for those coming up with new and innovative ways of using social media. The benefit to your firm can be great if you use the tools wisely.
An engineer should be entitled to presume that an item sold by a manufacturer based on their specifications does in fact meet the advertised standard (this has not always been true). There are cases where the engineer has been held liable for failure to have new material tested. Where new materials or equipment are called for, the engineer should be sure that the producer knows how his product is to be used and, where practical, the producer’s representative should be present when it is used.
Protecting Your Business Reputation Replacing a product or correcting a mistake as quickly as possible is good business and an obvious solution to a problem. Some “great” economists say there is a social responsibility with business ownership and business should be conducted in that context. You may take risks with your business decisions but not with your business reputation. By pursuing his own interest an individual frequently promotes that of the society more effectually than when he really intends to promote it. I have never known much good done by those who affected to trade for the public good. – Adam Smith, The Wealth of Nations STRUCTURE magazine
The Owner as Dispute Resolver Some public contracts state that, in the event of a dispute the owner will make a decision, and the owner’s decision is final and binding. There have been several cases nationally on the validity of such clauses. In summary, the courts will not enforce such clauses without judicial review. There is some indication that such a clause would not be enforceable where the decision maker has a direct financial interest in the project. In the court decision Steinberg v. Fleischer 706 S.W.2d 901: Clearly, it would be unjust to require plaintiffs to abide by such a contractual provision when secretly the “impartial judge” has a direct financial interest in the outcome of the project.
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Structural Forum
opinions on topics of current importance to structural engineers
License Engineers and Certify Disciplines By Timothy A. Lynch, P.E., M. ASCE-SEI
S
tating that licensure of structural engineers is necessary to protect the health, safety and welfare of the public is nothing short of professional arrogance. Advocates of the SE license initiative have been attempting to redefine competence; one might suspect the legal community is following suit. Competence is a basic, minimum level of achievement that is required, demonstrated and accepted as legal authority to practice the profession of engineering. One does not increase competence and one does not lose competence without fundamental personal changes, such as physical or mental health conditions, or unethical behavior. Fundamentally, an assertion that separate licensure is required to ensure competence is equivalent to a belief that significant structural engineering practitioners are incompetent, or unethical. The result is a self-created dilemma: a claim that our own ethics are insufficient to protect the public from ourselves. Simply requiring that Engineers pass another exam – be it multiple choice; essay; eight hours; or, sixteen – will not provide the public with adequate protection from failure. The title “structural engineer” is advertising. It denotes the discipline of engineering in which an individual practices. The motivation of advocates for separate licensure, as stated by Jon Schmidt in the September 2011 InFocus column, is a “conviction that such a step is necessary for” public safety. This is an overstatement that is detrimental to our profession. We are ethically bound to “perform services only in areas of [our] competence.” SE licensure is NOT necessary. It may be prudent as a certification; it may be a beneficial distinction to potential clients and licensees; but, it is not necessary. Certifications, such as that provided by the Structural Engineering Certification Board (SECB), or advanced degrees are equal and arguably superior assurance of professional development and expertise, more so than passing a single exam and issuance of a license. Claiming a governmental restriction on the practice will effectively increase public safety is naïve and potentially unethical in itself. To suggest that our discipline is more important than those who design processes for treatment of our drinking water or the safety measures incorporated in our
highways or any of the other health and welfare aspects of our lives is conceited. A separate, or subsequent, license is an economic restriction – generally as argued by John Mercer in his editorial in the July 2011 issue of STRUCTURE. Fundamentally, an initial shortage of structural engineers would tend to increase the market price. Unfortunately, the long run equilibrium would reduce the price as additional engineers seek the benefit. One could argue that supply would not be restricted if a “grandfathering” clause were included; however, one should carefully consider such a clause if one supports the “necessity” claim. It is unwise for our profession to promote reliance upon regulation as a judge of our competency. That is our job. The licensure exam is a final administrative step in the exhibition of the mastery of basic skills required to practice. To qualify for the exam, our individual competency must be judged by a registered design professional who accepts the intern engineer’s experience and abilities as representative, relevant and sufficient evidence of competence. Ongoing evaluation must be performed by ourselves, our peers and, ultimately, the legal system. Unfortunately, the SE exam will not prevent incompetence, mistakes or poor judgment. Recall statistics – we cannot design to protect against all possible events and we cannot prevent bad engineers. If practicing engineers have evidence demonstrating incompetence, they are ethically and legally bound to report that fact or, perhaps at least, to have a conversation with, enlighten and educate the subject individual. The implication of the SE initiative is that we are less capable than governmental authorities to judge individuals and enforce the requirements of professional practice. Lawyers, doctors and architects have correctly decided to retain their own control over those decisions. The form of the licensure examination is not why the “analogy breaks down” as Mr. Schmidt contends. It holds true when one considers the profession of engineering instead of the specialty of structures. In New York, in 1996 when I sat for the PE exam, there was no distinction of discipline. The licensed PE is limited by
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statute to practice only within the area of his or her competence. Certification beyond licensure, preferably by engineers instead of bureaucrats, makes more sense as a means for demonstrating competence in a discipline. Once licensed, competency should rarely be questioned. Sufficiency of experience and expertise along with continued ethical practice is the question. Further legislation to restrict the practice of engineering will simply put additional incendiary devices in the control of plaintiffs in courtrooms. There are currently more than enough laws on the books available to convict and punish those found responsible for failure, and those who are truly incompetent. We should be championing motivation for ethical practice. We should be arguing for economic incentives to support our discipline. Allowing market factors to regulate activity has been shown to be more effective than governmental controls. The liability alone – of practicing the discipline of structural engineering – should be sufficient to restrict the supply of practitioners. We need to educate our fellow professionals, corporate underwriters and public consumers with regard to the increased education and experience that is necessary for proper practice of this complex discipline. To limit engineering “competence” to only those tasks for which an engineer has demonstrated prior experience is contrary to continued development. If one can only do what one has done before, one will never accomplish anything new. As engineers, we have demonstrated the ability to analyze problems, to research requirements and constraints and to develop solutions. The successful completion of the SE examination demonstrates a superior level of discipline-specific technical expertise, but it is not sufficient or necessary for the protection of the public. Judgment as to the sufficiency of an engineer’s ability to design structures should not be made by government agencies. As engineers, we need to accept that responsibility as our own.▪ Timothy A. Lynch, P.E., M. ASCE-SEI (tim@talynch.com), is a consultant in the Hudson Valley region of New York.
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Windy City Reception March 29, 2012
7:30 to 9:30pm
The Structural Engineers Certification Board cordially invites attendees of the SEI Structures Congress to the SECB “Windy City” Reception Meet And Greet. This cocktail and dessert reception will be hosted by the SECB Board of Directors and held at the award winning offices of Gensler. Please join us for a spirited evening of discussion, innovation and structural engineering fellowship. Phone: 312-649-4600 E-mail: Joyce@ncsea.com
Complimentary transportation will be provided to and from The Fairmont Hotel and Gensler’s Chicago Loop Office every 30 minutes (walking distance about 1 mile). 11 East Madison Street, Suite 300
