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STRUCTURE Special Section: Seismic Products
July 2012 Wind
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CONTENTS
FEATURES New York Waterfronts
26
July 2012
By Cliff McMillan, P.E., C.Eng
Structural engineering plays a vital role in waterfront projects... construction efficiency, longevity and costeffectiveness all rely upon intelligent structural solutions. Piers and seawalls often consume a large proportion of a project’s initial budget, and repairs and maintenance can lead to significant costs down the road. For these reasons, close attention is paid to structural design on all waterfront work.
Seismic Products By Larry Kahaner
Those involved with seismic construction are seeing a marked optimism from their customers. Not only is there more confidence about the future, but the numbers seem to bear it out. Read how firms are updating and improving products and services to remain competitive.
By Kenton Lee, S.E. and Anna Dix, P.E.
58 Structural Forum
Ownership Transition
A Structural Engineer’s Manifesto for Growth
By Kevin R. Sido and Todd M. Young
By Erik Nelson, P.E., S.E.
July 2012 Wind
ON
THE
14 Historic Structures The Real Story – Structural Engineers and Architects of the Golden Gate Bridge By Reinhard Ludke, S.E.
18 Structural Performance Special Seismic and Blast Design
By Nabil A. Rahman, Ph.D., P.E. and Kurtis Kennedy, E.I.T
24 Professional Issues Structural Exam Study Aids
By Christine A. Subasic, P.E.
34 Structural Design Waterfront Crane Runways By Vitaly B. Feygin, P.E.
IN EVERY ISSUE
®
A Joint Publication of NCSEA | CASE | SEI
STRUCTURE
Special Section: Seismic Products
By Christopher Tilley, P.E.
By Jesus Orozco and Matt Barnard, P.E., S.E.
The Left Coast Lifter
49 CASE Business Practices
Why Current Module FrameBased Mounting Systems are Inadequate
Encouraging Potential Structural Engineers
51 Spotlight
By Anwar S. Ahmad, P.E.
10 Structural Testing
20 Guest Column
DEPARTMENTS The Road to Preserving Bridges
By John A. Mercer, P.E., SECB
By Jon A. Schmidt, P.E., SECB
The Joplin Tornado (May 2011) was one of Missouri’s most destructive natural disasters. The magnitude of devastation to the built environment was extreme, so the Structural Engineers Association of Kansas & Missouri (SEAKM) formed a committee to investigate the performance of structures affected by the tornado. Their observations and insights are presented here.
47 InSights
ACEC/CASE Scholarship Award Winner
Knowledge, Rationality, and Judgment
By Curtis Geise, P.E., S.E.
39 Special Section
7 Editorial
9 InFocus
Lessons Learned from the Joplin Tornado
30
COLUMNS
COVER
The Golden Gate Bridge in San Francisco, California was created and built 75 years ago, thanks to extraordinary Structural Engineers and visionary Architects. To celebrate this great achievement, Reinhard Ludke takes us through the history, trials and successes in this structure. Part 1 of this article appears on page 14 of this issue.
Publication of any article, image, or advertisement in STRUCTURE magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions. ®
STRUCTURE magazine
5
July 2012
8 Advertiser Index 52 NCSEA News 54 SEI Structural Columns 56 CASE in Point
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Editorial
new trends, new techniques and current industry issues ACEC/CASE Scholarship Award Winner By John A. Mercer, P.E., SECB
T
he American Council of Engineering Companies and the Council of American Structural Engineers awarded a scholarship to a well deserving young engineering student, Mr. Eric Grusenmeyer. After reading Mr. Grusenmeyer’s application, I was reminded of my early years in pursuit of the coveted title of P.E. behind my name. It is quite apparent from Mr. Grusenmeyer’s application that somewhere along the line in his limited experience of working for a consulting engineering firm, or albeit from his educational institution, that he has a great start in the “culture” for the responsibility of carrying out the duties of the structural engineering profession. “Engineers are bound to a code of ethics to provide for public health, safety, and well-being.” In case you are wondering, CULTURE is the first of 10 foundations in the CASE Risk Management program. Culture is an interface between the things we do, how we do them, and the spirit of the engineer and staff doing them. Some tasks are mundane, yet when put into proper perspective are necessary to complete the professional services that we provide our clients. The success or failure of a project is highly dependent on the firm’s culture and the combined spirits of the team members. When staff members realize they are only one cog in the wheel and work harmoniously with other team members, much can be accomplished. Each successful team member seeks recognition for a job well done, but can also bask in the satisfaction of another getting the credit. Mr. Grusenmeyer’s application alluded to the challenges consulting engineers face to reduce structure damage created by natural disasters and constructed with limited resources. How right he is. It seems to be human nature to overlook the quality and integrity of a project for the sake of a few percent of the total project price. Notice I didn’t say cost. I have been consulting for 30 years, and haven’t found a substitute for the job being done right. I know you will say that there are many ways to do things right, and you are correct. However, product or material substitutions based on price alone do not always provide the performance the client expects or the project demands. This is when things become problematic for the structural engineering firm depending on the wording of their contract agreement, the expectations of the client, and their relationship with their insurance company and legal counsel. I’m not sure that today’s legal climate is any better or worse than it was a decade ago, but there must certainly be an increase in the number of hungry litigators available to add STRUCTURAL to an engineering firm’s miseries. ENGINEERING INSTITUTE What resourceful imaginations they must have.
When staff members realize they are only one cog in the wheel and work harmoniously with other team members, much can be accomplished.
a member benefit
structurE
®
What would you rather be doing, designing a project, playing golf with a client, or spending your billable time and evenings building a case file for your legal counsel to defend you from a law suit? Sort of a no-brainer, wouldn’t you say? I have to say that CASE Guidelines for Practice, plus a good scope of work in a CASE Contract with your client, would give you an edge to be “on-in-three and two putting”. You see, when you know what’s coming, you can pre-empt it with your scope of services and a good set of terms and conditions in your contract. After a few years of mentoring by a seasoned structural engineer, Mr. Grusenmeyer will also be able to accomplish his intended career of pre-empting destruction of his firm by natural disasters by using CASE documents as a communication tool between his consulting firm and the firm’s clients. If, on the other hand, you happen to be encumbered with a pending law suit, did you use the CASE Tools to document your project? A submittals log would be one simple example, among many others, that could save a lot of your time and provide irrefutable evidence to protect you from allegations relating to the schedule and delivery of the project. What about the Toolkit’s checklists to use on the job site from the preparation in your office, to the tools and safety equipment to take with you, and the site observation report? Putting educated eyes on the site is just as important as checking lines and dimensions on paper. A properly prepared observation team can identify issues that could be job stoppers before they happen, as well as build good will and appreciation from a qualified contractor. Building a project is a TEAM sport. Engineers do it best on paper, and contractors get it done in the field. Mr. Grusenmeyer’s education will be just beginning once he receives his Master’s Degree. To be sure, another one of the CASE Risk Management’s 10 Foundations, Education, will help Eric along his way to become a properly educated consulting structural engineer. Good luck, Eric. We have many more natural disasters to prepare for, and CASE will be there to help you assist your firm along the way. ACEC/CASE is proud to be able to play a small role in your success.▪
STRUCTURE magazine
John A. Mercer, P.E., SECB (Engineer@minot.com), is the president of Mercer Engineering, PC, in Minot, North Dakota. He currently serves as Chair of the Council of American Structural Engineers (CASE) and is a CASE representative on STRUCTURE’s Editorial Board.
7
July 2012
Advertiser index
PleAse suPPort these Advertisers
AZZ Galvanizing .................................. 25 Bentley Systems, Inc. ............................... 4 Computers & Structures, Inc. ............... 60 Construction Specialties ........................ 29 CSC Inc. ................................................. 3 CTP Inc. ............................................... 37 CoreBrace, LLC .................................... 39 CTS Cement Manufacturing Corp........ 21 Dynamic Certification Lab., LLC .......... 42
Fyfe ....................................................... 40 Halfen, Inc. ........................................... 48 Hayward Baker, Inc. .............................. 41 Integrated Engineering Software, Inc..... 22 ITW Red Head ..................................... 50 JMC Steel Group .................................. 45 KPFF Consulting Engineers .................. 23 NCSEA ................................................. 13 Polyguard Products, Inc........................... 6
Editorial Board Chair
Burns & McDonnell, Kansas City, MO chair@structuremag.org
Craig E. Barnes, P.E., SECB
Brian W. Miller
Richard Hess, S.E., SECB
Mike C. Mota, Ph.D., P.E.
Mark W. Holmberg, P.E.
Evans Mountzouris, P.E.
Hess Engineering Inc., Los Alamitos, CA
CRSI, Williamstown, NJ
The DiSalvo Ericson Group, Ridgefield, CT
Roger A. LaBoube, Ph.D., P.E.
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.
HDR Engineering, Inc., Pittsburgh, PA
Mercer Engineering, PC, Minot, ND
Chuck Minor
Dick Railton
Eastern Sales 847-854-1666
Western Sales 951-587-2982
sales@STRUCTUREmag.org
Davis, CA
Heath & Lineback Engineers, Inc., Marietta, GA
CCFSS, Rolla, MO
AdvErtising Account MAnAgEr Interactive Sales Associates
Jon A. Schmidt, P.E., SECB
CBI Consulting, Inc., Boston, MA
Polytec GmbH ...................................... 11 Powers Fasteners, Inc. .............................. 2 RISA Technologies ................................ 59 Structural Engineers Assoc. of S. Cal. .... 44 SidePlate Systems, Inc. .......................... 43 Simpson Strong-Tie......................... 17, 33 Star Seismic ........................................... 46 Struware, Inc. ........................................ 15 Subsurface Constructors, Inc. ................ 38
BergerABAM, Vancouver, WA
American Wood Council, Leesburg, VA
2012 NCSEA Excellence in Structural Engineering Awards
Call for Entries
EditoriAL stAFF Executive Editor Jeanne Vogelzang, JD, CAE
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STRUCTURE® (Volume 19, Number 7). 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. STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be
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inFocus
Knowledge, Rationality, and Judgment new trends, new techniques and current industry issues By Jon A. Schmidt, P.E., SECB
I
have written previously about the distinction between knowledge that something is the case and knowledge how to do something (“Engineering as Knowledge-How,” November 2011). The ancient Greeks, Aristotle in particular, actually identified three different kinds of knowledge by further subdividing knowledge-how: • episteme (eh-pis-TEH-meh), which is the root of the words epistemic (of, or pertaining to, knowledge) and epistemology (the study of knowledge) and designates knowledge-that. • techne (TEKH-neh), which is the root of words like technique, technical, and technology and designates knowledge-how to achieve a predetermined outcome. • phronesis (FRO-neh-sis), which has not found its way into English at all and designates knowledge-how to behave in a manner that is contextually sensitive and appropriate. Each kind of knowledge pertains to a specific human activity: • theoria (theh-oh-REE-ah), which is contemplation or thinking. • poiesis (POY-eh-sis), which is production or making. • praxis (PRAK-sis), which is (inter)action or doing. As such, episteme, techne, and phronesis also correspond with certain forms of rationality and judgment. However, for the sake of clarity, I will refer to them going forward as theoretical knowledge, technical rationality, and practical judgment, respectively. I believe that these terms succinctly capture the most fundamental aspects of each category. Theoretical knowledge is propositional in nature and aims at eternal truth. It consists of conceptual beliefs that count as facts when possessed by a person of understanding, who is characterized as intelligent and makes decisions on the basis of evidence grounded in data. It applies primarily in the mental realm, resides in one’s memory, and is imparted to a student by means of instruction. Technical rationality is procedural in nature and aims at external success. It consists of instrumental abilities that count as proficiencies when possessed by a person of skill, who is characterized as competent and makes decisions on the basis of method grounded in rules. It applies primarily in the physical realm, resides in one’s habits, and is imparted to an apprentice by means of training. Practical judgment is personal in nature and aims at internal integrity. It consists of ethical dispositions that count as virtues when possessed by a person of wisdom, who is characterized as prudent and makes decisions on the basis of intuition grounded in experiences. It applies primarily in the social realm, resides in one’s conscience, and is imparted to a disciple by means of education. Many scholars have argued that today’s culture has largely collapsed theoretical knowledge and practical judgment into technical rationality, with the result that the latter is widely regarded as the only legitimate form of reasoning. One example is Irish philosopher of education Joseph Dunne, who made the case for this position and worked out some of its implications in his book, Back to the Rough Ground, published by the University of Notre Dame Press. The original hardcover edition (1993) had the subtitle “Phronesis” and “Techne” in Modern Philosophy and in Aristotle, but this was changed in the
STRUCTURE magazine
paperback version (1997) and all subsequent printings to Practical Judgment and the Lure of Technique. It might seem natural to associate theoretical knowledge with science and technical rationality with craft. However, as Dunne noted: productive know-how... is now brought into alignment with the new science, which therefore no longer retains the contemplative aspiration of the old theory. Henceforth the only type of knowledge that really counts... is precisely that which is given to us by science. Scientific information about the world contains technical imperatives: the formulae for the new technology and modes of production no longer reside in the rules of craftsmen but rather in the corroborated findings of scientists. And so the gulf which had separated theory and production for the Greeks is now eliminated. Likewise, practical judgment has largely been discredited. Again, in Dunne’s words: The extension of the technical form of rationality has been pursued on the basis of a claim to value-neutrality... An orientation to efficiency and economy in the organization of means, which is the core of technique, does not in fact, as is often claimed... stand ready to serve any set of values which is otherwise (non-rationally) decided upon. Rather, by a deeper, though unacknowledged, decision, this orientation is imposed on the organization of practical life as itself the only value − even though it is not conceived as a value at all but is granted a privileged status because of its seeming coincidence with the structure of rationality itself. One might expect the triumph of technical rationality and its “orientation to efficiency and economy” to elevate the status of engineering. On the contrary, Steven Goldman recognized that these trends have actually fostered the higher regard in which science is generally held in comparison with engineering (“The Principle of Insufficient Reason,” May 2008), as well as the tendency for the latter to be exploited by managers and clients to achieve their own objectives (“The Social Captivity of Engineering,” May 2010). In other words, the institutions that employ and retain engineers largely embrace technical rationality and are motivated by goods that are external to the practice of engineering (“Rethinking Engineering Ethics,” November 2010). It thus falls to the profession itself to identify and pursue its internal goods by cultivating the appropriate virtues (“Engineering Ethics as Virtue Ethics,” May 2011). In order to do so, we must recover the classical notion of praxis and its associated concept of phronesis in contrast with poiesis and techne. Dunne had more to say about this in a 2005 paper, which I will summarize in my next column.▪ Jon A. Schmidt, P.E., SECB (chair@STRUCTUREmag.org), is an associate structural engineer at Burns & McDonnell in Kansas City, Missouri. He chairs the STRUCTURE magazine Editorial Board and the SEI Engineering Philosophy Committee.
9
July 2012
Structural teSting issues and advances related to structural testing
A
s cost pressures grow with regard to mounting systems for solar arrays, manufacturers look to module frames as a means to augment, or even replace, mounting structures. Practically, this makes sense. Module frames and mounting structures have traditionally been designed independently, neither taking into account the strength and stiffness contribution the other makes to the overall structure. Ignoring this interaction equates to inefficient design and wasted material. Put another way, properly integrating the module frame into the mounting structure should lead to a decrease in materials and the cost of the overall mounting structure. A fundamental requirement for developing an integrated solution, however, is a clear understanding of the characteristics and magnitude of the environmental loads the structure must safely resist. Unfortunately, in the case of wind loads, especially those on arrays mounted on flat rooftops, not much is known. Very little peer-reviewed research has been published and the building codes, e.g. ASCE 7, are largely silent on this issue. With no clear standard, the industry is currently using a hodgepodge of approaches to estimate wind loads on these systems. These approaches include using a code based design methodology intended for roof surfaces or roof-mounted signs, relying on manufacturers’ wind-tunnel test results, or basing estimates on various computational fluid dynamic (CFD) simulations. These methods are fraught with potential problems and often result in widely different estimates of the wind loading. Over the last five years, SunLink has undertaken an extensive wind tunnel test program at the Boundary Layer Wind Tunnel Laboratory at the University of Western Ontario (BLWTL) aimed at understanding, in great detail, the magnitudes and characteristics of wind loads on flat-rooftop mounted solar arrays. SunLink has measured surface pressures on many different types of arrays on various building configurations (see www.sunlink.com for more about this test program) and developed design curves for each array tested that appropriately envelope the largest measured pressures. The test procedures used to develop these curves followed the same methodology that was used as the basis for the rooftop load design curves in the ASCE 7 standard. All of the test results show the same consistent phenomenon: The maximum pressures measured on small surface areas (e.g. 20 ft2 or one typical module) are much greater than the maximum average pressures measured on larger surface areas (e.g. 300 ft2 or 15 modules).
Why Current Module Frame-Based Mounting Systems are Inadequate The Challenge of Resisting High Localized Wind Loads By Christopher Tilley, P.E.
Christopher Tilley, P.E. is CEO of SunLink Corporation. Chris may be reached at ctilley@sunlink.com.
10 July 2012
This reflects a fundamental characteristic of wind loading on building components and equipment, which is reflected in the prescribed code-design methodology. For small tributary areas (e.g. one roof panel), higher pressures must be used for design than for larger tributary areas (e.g. the area supported by a roof joist). In the case of rooftop structures for photovoltaic (PV) modules, this means that the structure supporting one module must be designed to resist the pressure expected for the tributary area of one module, or approximately 20 square feet. An array-roof connection intended to support 20 modules should be designed to resist the load implied by the tributary area of these 20 modules, or 400 square feet. An appropriate mounting system design needs to demonstrate that both of these requirements are met. In the case of rooftop PV systems, a nearly universally accepted design objective is to reduce the number of connections into the roof, or to reduce the weight of the PV system if ballast is used in the place of connections to resist wind loads. One way to achieve this result is to design a support structure that is stiff and strong enough to transfer loads across larger effective areas of the system. By doing this, the lower design pressure coefficients associated with larger tributary areas can be used to determine ballast requirements. Without a stiff and strong structure that interconnects each module, this strategy doesn’t work, and sufficient ballast must be deployed at each module to resist the maximum pressures that can be experienced for the tributary area of one module (20 ft2). SunLink’s testing clearly shows that the building code level pressures experienced by areas of 20 square feet are greater than 15 psf, even in mild wind environments. This leads to the conclusion that unless sufficient capacity can be shown in the surrounding structure, each module needs to have more than 15 psf of ballast to safely remain on the roof during a code level wind event, even in mild wind zones. Very few, if any, flat roof mounting systems in use today are ballasted with more than 15 psf. The implication is, therefore, that the structure that interconnects modules is providing the incremental capacity needed to make up for the deficiency in ballast. Unfortunately, calculations of this type are not typically being performed or required by building officials. Based on the magnitude of the wind loads measured in testing and the ballast configurations typically observed in use, it appears doubtful that many of the systems being deployed can demonstrate sufficient structural capacity needed to meet code-level requirements. This is especially the case for mounting systems that rely heavily on the module frame for structural capacity. Consider the following rooftop PV example that illustrates the issue and the reason to draw this conclusion:
Just Point, Shoot and Measure! Figure 1: Drawing and model of system tested by SunLink. Figure 2: Panel + Shroud vertical area averaged net pressure coefficient constructed for use in ASCE 7 plotted vs. area.
For 30 modules, the coefficient would be just above 2, giving a design pressure of 3.7 pounds. With a perfectly stiff and infinitely strong structure interconnecting 30 modules, a weight of 3.7 psf based on the module area (distributed appropriately) should be enough ballast for this system. With the same perfectly stiff and strong structure connecting nine modules, a weight of 7.1 psf in ballast should be enough to keep the system on the roof. Note that all of the calculations above represent unfactored 50 year loads. When designing the structure per ASCE 7, these wind loads would need to be factored by 1.6 and the weight would be reduced by 10% (i.e. the relevant load combination in ASCE 7 is 1.6W+0.9D). Calculation results can be seen in Table 1. To understand what these numbers mean for the structure of a real array, let’s look at the 3x3 group of modules within the dashed line in Figure 3 (page 12). Assuming that these 9 modules are ballasted to 5 psf, the design load for wind uplift on these modules would be 1240 pounds (11.4-5 * 0.9 = 6.9 psf; 6.9 psf * 20 ft2 * 9 modules). The connections between the three modules at the interface to the larger array need to be shown to have the capacity to resist the moment generated. If the 1240 pound load is assumed to be uniformly distributed, the
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Table 1.
Number of Modules
1
3
9
30
GCn value for tributary area
1.00
0.60
0.40
0.23
Design Pressure (psf )
17.8
10.6
7.1
3.7
Factored Design Pressure per ASCE 7 (i.e. * 1.6) (psf )
28.4
16.9
11.4
6.0
Ballast Weight Required Per ASCE Load Combination (/.9)
31.6
18.8
12.7
6.6
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July 2012
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A 12-module-by-12-module array of the system depicted in Figure 1 was tested in the BLWTL on a standard flat roof building. Pressures were measured on all surfaces at a frequency and duration consistent with the test method accepted by the ASCE 7 standard. Pressure taps on the top and bottom of each surface were summed to provide net pressures. The maximum net pressures measured for different contiguous areas of modules were then calculated from the measurements. A design envelop was created from this testing using the same methodology as used in the ASCE 7 Standard and is shown in Figure 2. As can be seen from the curve, for one module area, the GCn coefficient for this system is 1.0. Per the ASCE Code, this GCn value is multiplied by the basic velocity pressure, qh to provide the design pressure, p= GCn*qh. For a 35-foot high building in a 90 mph 3 second gust speed wind zone and with open terrain around it, the basic velocity pressure would be 17.8 psf per ASCE 7. The design pressure for one module would therefore be 17. 8 psf (17.8* 1.0). For three modules, the GCn coefficient would be 0.6. So the design pressure that should be used for three interconnected modules on the same building would be 10.6 psf (17.8 * 0.6). For nine interconnected modules on the same building, the design pressure would be approximately 7.1 psf (17.8 *.4).
Figure 3.
resulting moment around these connections is 8,680 ft-lbs (7ft * 1240). It is hard to imagine that the typical module frame can handle a 2900 ft-lb (8680/3) moment about one of its sides. Note that all of these calculations were based on a fairly benign wind environment. For higher wind zone regions, these numbers would be significantly larger. The numbers calculated for a 50-foot high building in a 120 mph wind zone and surrounded by open terrain can be seen in Table 2. The code-based design velocity pressure for this case would be 34.15 psf per ASCE 7. The design load on the 3x3 section of the array described above would therefore be 3,132 lbs (21. 9-5 * 0.9 = 17.4 psf; 17.4 psf * 20 ft2 * 9 modules). The resulting moment around the connections is now 21,924 ft-lbs (7ft * 3132), leaving each module frame to handle a 7,308 ft-lb moment about one of its sides (Figure 4).
Use of Deflectors and Shrouds Note that, for this example, test data for a system that has shrouds (deflectors) was used. While this type of system provides better aerodynamics and lower overall net pressure coefficients compared to an open system (i.e. one without shrouds), it has a very significant potential drawback. One of the key aerodynamic mechanisms that accounts for the reduced net pressure coefficients is the shrouding, which extends down close to the roof and prevents wind from impinging on the underside of the modules. The aerodynamics of this type of system can change dramatically if the shrouding lifts off the roof, even locally (e.g. over one or two
modules). As a result, shrouded systems need to have additional stiffness requirements when looking at the connections discussed above. Namely, not only does the frame connection need to have the strength to resist such a moment, it also needs to provide enough stiffness to keep the modules from rising even a few inches off the roof. SunLink has yet to see a module frame that can deliver this level of stiffness or strength.
The Importance of Proper Wind Tunnel Testing If rooftop PV systems really do need to be designed to this magnitude of load, why are so many companies and engineers standing behind systems that are clearly short of the mark? A good deal of the problem lies in the type of wind tunnel testing that is being performed and the way the results of this testing are being applied (See Rooftop Solar Arrays and Wind Loading: A Primer on Using Wind Tunnel Testing as a Basis for Code Compliant Design per ASCE 7, available at the SunLink website). To illustrate a typical example, “fly-away” testing is used to determine the wind speed at which a small array first moves (“fails”). A conclusion is then drawn that this array can be placed safely on a roof as long as the design wind speed is less than the measured “failure” wind speed. To draw this conclusion, however, the shape, location and size of the array needs to be the same as that which is tested and, more importantly, the strength and stiffness characteristics of the model need to be properly scaled to match those of the actual array. Because this type of testing needs to be done at scales of 1:20 or smaller, this type of fidelity in the model is nearly impossible to achieve (imagine getting the structural characteristics of a 1 inch module clamp accurately represented in 3 dimensions at 1:20 scale). The likely error is that the model will, with proper scaling, be stiffer than the actual fullscale array. For a 30-module array that is particularly stiff, array movement will first
Table 2.
Number of Modules
1
3
9
30
GCn value for tributary area
1.00
0.60
0.40
0.21
Design Pressure (psf )
34.2
20.5
13.7
7.2
Factored Design Pressure per ASCE 7 (i.e. * 1.6) (psf )
54.6
32.8
21.9
11.4
Ballast Weight Required Per ASCE Load Combination (/.9)
60.7
36.4
24.3
12.7
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Figure 4: 7,308 ft-lb capacity for each side of the module frame.
occur in testing at a speed that is commensurate with the GCn coefficient that corresponds to a tributary area of 30 modules. As can be seen by the above analysis, this yields a much lower number than what is seen over smaller tributary areas. The result is that the higher pressures associated with smaller tributary areas are hidden by the testing, and therefore ignored in design.
Conclusion Everyone in the solar industry is committed to the same goal – namely increasing the amount of clean, reliable, renewable energy produced in way that is both safe and cost effective. As the industry matures, we will need to create standards that assure the safety of these systems. SunLink’s research indicates that there is more work to be done in the area of wind loading.
Overview of SunLink’s R&D on Wind and Solar Arrays Over the last 5 years, SunLink has performed over 1000 test runs on more than 75 different array and building models. • Effect tilt angle: 2°, 5°, 10°, 15°, 20°, 30°, 35° systems have been tested. • Effect of height off the roof or ground: various tests from 0 to 4-foot clearance. • Effect of spacing between rows: various tests with spacing between 2 and 4 times the height. • Effect of set-backs from roof edge: various tests from very close to the edge to distances of nearly twice the building height from the side of building. • Effect of deflectors/shrouds: various deflector designs and configurations applied to the arrays. • Effect of roof height: from 24 to 72-foot buildings. • Effect of panel height (chord length) from 3 feet to 15 feet. • Effect of arrays on roof surface loads. • Effect of combinations of the above.▪
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Historic structures significant structures of the past
Golden Gate Bridge – 75th Anniversary. Courtesy of Reinhard Ludke.
W
ith many great achievements, the end result is the sum of the contributions made by all that participate. Neil Armstrong and Edwin “Buzz” Aldrin, the Apollo 11 astronauts that stepped on the moon on July 20, 1969, got there through the efforts of 1000s of engineers and scientists. Engineers worked behind the scenes for years developing and supporting the moon landing program, but only Armstrong and Aldrin receive the tribute and went down in history for this accomplishment. Joseph B. Strauss, visionary and promoter to span the Golden Gate, receives the credit as the Engineer of the Golden Gate Bridge. Mr. Strauss, owner of his own engineering firm, Strauss Engineering Corporation, in Chicago, Illinois, was appointed the Chief Engineer by the Golden Gate Bridge and Highway District Board of Directors on August 15, 1929. Joseph Strauss is the “statue” near the bridge toll plaza, and he receives the credit for spanning the gate. In 1916, more than four decades after railroad entrepreneur Charles Crocker proposed a bridge across the Golden Gate Strait, James H. Wilkins, a structural engineer and newspaper editor for the San Francisco Call Bulletin, suggested spanning the Gate. San Francisco City Engineer, Michael M. O’Shaughnessy, the lead engineer of the San Francisco Hetch Hetchy water system, contacted bridge engineers to consult with them about the feasibility and cost of bridging the Golden Gate. Most speculated that a bridge would cost over $100 million. Joseph Strauss, who had designed nearly 400 bridges, claimed it could be built for $25 to $30 million. This man, “Joseph Baermann Strauss was an undersized man with a Napoleonic ego, yearning for a career in the arts, with only the
The Real Story – Structural Engineers and Architects of the Golden Gate Bridge Part 1 By Reinhard Ludke, S.E.
Reinhard Ludke, S. E. is a Bridge Engineer, Principal Structural Engineer, for Creegan + D’Angelo Engineers, San Francisco, CA. He was the Past President of the Structural Engineers Association of Northern California, served as the Director and Secretary of the Structural Engineers Association of California, and was elected FELLOW of the Structural Engineers Association of California in 2010.
The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.
14 July 2012
most modest amount of formal engineering training…”, says John Van Der Zee. “Strauss was a strange, at times almost a self cancelling mixture of conflicting traits: promoter, mystic, tinkerer, dreamer, tenacious hustler, publicity seeker, and recluse. He was not a member of the American Society of Civil Engineers nor was he a graduate of a college of engineering.”
Strauss Hybrid Bridge Concept His answer to spanning the gate, Joseph Strauss imagined a hybrid concept for the span that included a steel truss bridge from the shore with cantilevered steel truss from the main towers. Two suspension cables would be attached at the ends of the top chord of the cantilever, with a stiff steel truss road deck suspended from the cables. Strauss submitted a design proposal for bridging the Golden Gate Strait to O’Shaughnessy in June 1921, with a cost estimate of $17 million. Strauss called his solution a symmetrical cantilever-suspension hybrid bridge. Once his design was made public by O’Shaughnessy in December 1922, the public voiced little opposition, even though the local press described it as ugly. In 1921, Strauss hired Charles A. Ellis, Professor of structure and bridge engineering at the University of Illinois, to head up his engineering staff in Chicago. Ellis joined Strauss
1921 Strauss Symmetrical Cantilever-Suspension Hybrid Bridge Concept.
Joseph B. Strauss
Bridge Engineer Charles A. Ellis
Bridge Consultant Leon S. Moisseiff
Bridge Architect Irving F. Morrow
1931 Suspension Bridge Elevation by Irving F. Morrow. Collection of the Golden Gate Bridge, Highway and Transportation District. Photo by Robert David.
Dear Sir: In accordance with your letter of acceptance of June 8, 1925, I present herewith to you a report on a comparative design for a suspension bridge with a single span stiffening truss based on identical specifications and prices as the cantilever-suspension type proposed by you for the Golden Gate Bridge at San Francisco and on which I made a report to you on July 27, 1925. Respectfully submitted, /s/ Leon Moisseiff This letter included the Report on Comparative Design of a Stiffened Suspension Bridge over the Golden Gate at San Francisco, California. The seven-page report describes an all wire cable bridge of the stiffened suspension type, consisting of two parallel wire cables spanned over two towers and anchored on each side into bedrock. The bridge had a span of 4,000 feet between towers and provided a clearance of 200 feet above the high tide water. Two 36-inch diameter main cables were described as 91 strands, made with 25,700 high strength wires, spaced 90 feet apart supporting the suspended steel roadway. Together, Moisseiff and Ellis explored a practical application of Moisseiff’s deflection theory of suspension bridges. They made their bridge design flexible enough to withstand the gales that often blew through the Golden Gate. The bridge would be lighter, longer, and narrower than any of its predecessors. Moisseiff believed that up to half the stress caused by winds could be absorbed in a suspension bridge by the bridge cables and suspender ropes, and transmitted to the bridge towers and abutments. If a bridge were designed to bend and sway with the winds, the suspended structure – the roadbed – would act as a counterweight and restore the bridge to equilibrium. At the time of his report, Moisseiff was working as a consultant on the design of the George Washington Bridge, New York
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City, and he was in close contact with O. H. Ammann, Chief Engineer, Port of New York Authority. Moisseiff’s design incorporates several key features of the George Washington Bridge design, including traffic live loads for long span suspension bridges, the allowable stresses, and anchorage of the cables in rock tunnels. The 1925 report suggests a bridge that is very similar to the one that was built. A continuous steel stiffening truss bridge deck is suspended from the main cables. The towers rise from piers constructed in the water. Each tower is constructed of multiple riveted steel plate cells that form two large columns. The two columns are braced together at multiple levels, into a transverse frame. Architectural features were added during the design to create the Art Deco style that was popular at the time. The 435-foot tall towers have a trapezoidal plan shape that tapers from 40 feet at the base to 20 feet top. Moisseiff estimated the suspension bridge construction cost as $19,400,000. Eventually Strauss would speak of these conceptual ideas, who’s technical engineering was beyond his capabilities, as if they were his own. continued on next page
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Engineering Corporation after a 14 year teaching career in Civil Engineering at the Universities of Michigan (1908 to 1912) and Illinois (1914 to 1921). The University of Illinois had the preeminent civil engineering faculty in the United States in first half of the 20th century. He had studied mathematics and structural engineering theory and authored a textbook, Essentials in the Theory of Framed Structures, which was a popular university textbook of that time. Ellis quickly advanced to Vice President at the Strauss company where he was in charge of all bridge engineering, design and construction supervision. The original September 1937 Report of the Chief Engineer did not include detailed information about the roles played by Ellis and by Leon S. Moisseiff, a New York bridge engineer, who was developing new mathematical methods for the analysis of suspension bridges. In Ellis, Joseph Strauss found the structural engineer he needed for his dream of a bridge across the Golden Gate. Unlike Strauss, Ellis had no inclination to seek fame. The pair was quite odd – the sly businessman and a academic and professor, who found satisfaction in completing complex mathematical analysis and engineering. Ellis and Moisseiff had a profound influence in the evolution of the final design for the Golden Gate Bridge. In 1925, Strauss had Ellis arrange for Leon S. Moisseiff, designer of New York’s Manhattan Bridge, to serve on a “Board of Consultants” for the bridge district. He reviewed Strauss’s plans for a cantilever-suspension hybrid bridge, and found them to be practical from an engineering standpoint and capable of being built within the estimated budget of $21 million. Moisseiff had some concern about the hybrid bridge design and asked Strauss to consider an alternate “all cable” design. Moisseiff noted this in his letter to Strauss dated November 15, 1925:
The suspension span concept did not immediately become the leading design for the bridge. As late as 1929, Strauss continued to campaign for a bridge using his original symmetrical cantilever-suspension hybrid design. On August 15, 1929, the Board appointed prominent engineers Leon Moisseiff and Othmar H. Ammann, and Professor Charles Derleth, Jr. of the University of California Engineering School at Berkeley, to serve as the Bridge District Advisory Board of Engineers alongside Chief Engineer Strauss. Strauss also appointed Charles Ellis to the Advisory Board of Engineers, serving as its Secretary. On August 27, 1929, the first meeting of the Board of Engineers took place. A year later, on August 27, 1930, Mr. Strauss submitted his Report of the Chief Engineer with Architectural Studies, Volume I, to the Board and made his presentation of a suspension span. The preliminary plans illustrated the distinctive shape of the main towers and the elevation of the suspended span that is very similar to what was eventually built, as proposed in Moisseiff’s 1925 report. Ellis signed all the design drawings, and he is included on the official letterhead of the Office of the Chief Engineer which lists the Officers and Engineers of the District, naming Charles A. Ellis as Designing Engineer. Mr. Strauss noted in his cover letter accompanying his report: The staff in charge of the detail work of the Golden Gate Bridge has been the staff of the Strauss Engineering Corporation of Chicago, under the immediate direction of Mr. Charles A. Ellis and with other heads of the Strauss staff advising … The work of the Company is directed by myself as President and Chief Engineer through two Engineering Vice Presidents; namely, Mr. Ellis, above referred to, and Mr. C. E. Paine, assisted by a large force of engineering specialists. Mr. Ellis has acted as Chief Assistant to myself on the Golden Gate bridge, and on other similar projects...while Mr. Paine has similarly acted as Chief Assistant on such projects as the Columbia Longview bridge... From Strauss’s original design of a symmetrical cantilever-suspension hybrid bridge to Moisseiff’s 1925 suspension bridge design, to the suspension span design presented to the Advisory Board of Engineers in August 1930, Ellis played a fundamental role in this design evolution. November 4, 1930, signaled the start of the final design for the Bridge and Strauss submitted an Outline of Engineering Procedure, for District General Manager Alan MacDonald’s approval.
This document details the bridge engineering staff organization as follows: Computation of Stresses and the preparation of stress sheets is assigned to the Computation Division under the direction of M. Charles A. Ellis of the Strauss Staff. General Plans: Preparation of the general plans and checking of the contractor’s working plans is assigned to the Plans Division under the direction of Mr. Clifford E. Paine of the Strauss Staff. Specifications, Contract and Proposal Forms: The specifications, contract and proposal forms are assigned to the Computation Division under the direction of Mr. Ellis, reviewed by Mr. Paine of the Plans Division. Lateral forces, from the wind and earthquake, were a major analysis, design and engineering challenge of the time. The engineer had to determine the wind force, the forces in the cable and deck and towers, and the lateral movement. In the 1920s, complex manual calculus mathematics computation was required to solve for multiple unknown variables. Ellis was the engineer who understood the new theories and spent many hours of his own labor to complete the analysis and “design every stick of steel on that bridge”, according to his record at Purdue University. Construction of bridge tower foundations in the deep water and swift currents of the gate also required innovative engineering and construction. Engineers calculate predictable static forces and designed their structures with strength, stiffness, and stability to support those forces. They had to also consider forces that change over time, temperature, traffic, and wind which added complexity to their calculations. Charles Ellis and Leon Moisseiff calculated forces for the Golden Gate Bridge with only a slide rule and a manual adding machine. Ellis worked for months solving equations and designing the structural members of the bridge. Over 75 years ago, the bridge design and structural calculations provided by Charles Ellis and Leon Moisseiff persuaded Strauss to abandon his own design in favor of a suspension bridge, which is celebrated in 2012. The Golden Gate Bridge, Report of the Chief Engineer, September 1937, written by Mr. Strauss, provides no details on the transition from his originally proposed symmetrical cantilever-suspension hybrid bridge to the Moisseiff inspired suspension span design that was eventually built, and simply states on page 37:
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Eberson’s Bridge Tower Sketch. Golden Gate Bridge, Elevation study of tower, ca. 1930. Pencil on vellum. Courtesy of The Architectural Archives, University of Pennsylvania by the gift of Drew Eberson, 1984.
“... In the interval which had elapsed any advantages possessed by the cantileversuspension type bridge had practically disappeared and on recommendation of the Chief Engineer, the cantilever-suspension type was abandoned in favor of the simple suspension type.” The timing of the change from the original Strauss proposal to a suspension bridge design is not exactly known, but it had to have been accomplished sometime between Mr. Moisseiff’s report of November 15, 1925, and the August 27, 1929, meeting of the Board of Engineers. An upcoming issue of STRUCTURE® will continue this Golden Gate Bridge structure engineering history and the contributions of Charles Ellis, Leon Moisseiff and Irving Morrow.▪
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Structural Performance performance issues relative to extreme events
E
nd connections of cold-formed steel (CFS) framing are major components of the structural system. Evaluation of connection strength for design purposes is mostly done through laboratory tests to obtain the ASD strength and the LRFD strength. For special seismic and blast design, other levels of design strength are needed by the engineer – primarily the nominal strength. Some design codes even allow the use of an increased nominal strength or an increased expected strength. A Static Increase Factor (SIF) and a Dynamic Increase Factor (DIF) can be applied to the nominal and expected strength, respectively, to attain greater strength of the connection for special design purposes. This article provides a summary of the strength demand for CFS connections in special seismic and blast design, and how engineers can calculate the different levels of strength from the connection test data.
Seismic Design
Special Seismic and Blast Design Cold-Formed Steel Connection Strength By Nabil A. Rahman, Ph.D., P.E. and Kurtis Kennedy, E.I.T
Nabil A. Rahman, Ph.D., P.E. directs the R&D projects of The Steel Network, Inc. in Durham, NC. He can be reached at nabil@steelnetwork.com. Kurtis Kennedy, E.I.T is Technical support engineer with The Steel Network, Inc. He can be reached at kkennedy@steelnetwork.com.
Special seismic design requirements are mandated in AISI S213-07 North American Standard for Cold-Formed Steel Framing – Lateral Design, Section C1.1 “Seismic Requirements”, which are applicable to the design of CFS shear walls or systems using diagonal strap bracing that resists wind, seismic, or other in-plane lateral loads. Section C1.1 further directs the designer to Section C5, the “Special Seismic Requirements” section, if the Response Modification Coefficient (R) of the shear wall system is greater than 3 or the Seismic Design Category of the structure is D through F. Section C5 contains the provisions allowing nominal strength of material to be used in the design of members and/or connections. Section C5.1, “Shear Walls”, and Section C5.2, “Diagonal Strap Bracing”, present the provisions for design of connections, chord studs and anchorage, and foundations when using a shear wall or diagonal strap bracing lateral force resistance systems. Section C5.2.2.2 states:
All members in the load path and uplift and shear anchorage thereto from the diagonal strap bracing member to the foundation shall have the nominal strength to resist the expected yield strength AgRyFy, of the diagonal strap bracing member(s), except the nominal strength need not exceed the following, as applicable: (a) In the United States and Mexico: Amplified seismic load. (b) In Canada: Maximum anticipated seismic loads calculated with RdRo= 1.0.
Blast Design Standard 10 of the new 2012 Department of Defense UFC 4-010-01 DoD Minimum Antiterrorism Standards for Buildings, outlines the design of window and skylight systems under blast pressure loading. Provisions are given for a static or dynamic method of analysis and design for window and skylight opening framing and connections. Section B-3.1 allows the use of nominal strength when performing a static analysis of structural elements which support windows and skylights. These elements include jamb, header, and sill members along with connections between them and connections to the primary structure. The code states: “Use strength design with load factors of 1.0 and strength reduction factors of 1.0 for all methods of analysis referenced herein.” The UFC design code provides an alternative design method utilizing the dynamic material properties of the window glazing, framing members, connections, and supporting structural elements. Section B-3.1.1 “Dynamic Analysis” states: Any of the glazing, framing members, connections, and supporting structural elements may be designed using dynamic analysis to prove the window or skylight systems will provide performance equivalent to or better than the hazard rating associated with the applicable level of protection as indicated in Table 2-1. Dynamic analysis guidance is presented in PDC TR 10-02. The design loading for dynamic analyses will be the appropriate pressures and impulses from the applicable explosive weights
Table 1: Static and dynamic increase factors for cold-formed steel.
Static Increase Factor (SIF) or Average Strength Factor (ASF)
Dynamic Increase Factor (DIF) Bending/ Shear
Tension/ Compression
ASCE/SEI Standard 59-11
1.1
1.1
1.1
ASCE Design of Blast-Resistant Buildings in Petrochemical Facilities (2010)
1.21
1.1
1.1
UFC 3-340-02 (2008)
1.21
1.1
1.1
18 July 2012
at the actual standoff distances at which the windows are sited. The design loading will be applied over the areas tributary to the element being analyzed. The dynamic method of analysis and design of framing members incorporates strength increase factors that enhance the nominal and expected strength of materials. A Static Increase Factor (SIF) can be applied to the nominal strength of a material, while a Dynamic Increase Factor (DIF) can be applied to the expected strength of a material. Note that the Static Increase Factor (SIF) is sometimes called the Average Strength Factor (ASF). Documents such as the UFC 3-340-02 Structures to Resist the Effects of Accidental Explosions, the ASCE Publication Design of Blast-Resistant Buildings in Petrochemical Facilities, and the ASCE/SEI Standard 59-11 Blast Protection of Buildings describe Static and Dynamic Increase Factors and the uses of each. Since the nominal strength is typically taken as the lower bound minimum yield strength of the material, the Static Increase Factor (SIF) is applied to the nominal strength to account for higher yield strength of installed components than minimum specified yield strength values. The resulting value is the “Expected Strength”. Beyond the use of this expected strength level, ASCE and the UFC code states that the Dynamic Increase Factor (DIF) is to be applied to the expected strength to account for strain rate effects from a rapid blast loading. The resulting value is the “Dynamic Strength”. Table 1 shows suggested increase factors to be used for CFS design as recommended by the ASCE publications and the DoD UFC 3-340-02.
How to Determine the Connection Design Strength? Figure 1 shows two examples of CFS curtain wall framing connections. CFS connections are usually tested according to AISI Test Standard S905-08 Test Methods for Mechanically Fastened Cold-Formed Steel Connections or ICC-ES AC261 Acceptance Criteria for Connectors Used with Cold-Formed Steel Structural Members. A connection is typically tested to failure, and the load obtained from the test is considered the “Ultimate Strength” of the connection. Chapter F of the AISI S100-07 specification permits the calculation of the LRFD strength of the connection as the ultimate strength of the test multiplied by a calculated test resistance factor
(a)
(b)
Figure 1: Cold-formed steel curtain wall framing connection; (a)sliding connection (b) fixed connection.
(φt). The test resistance factor (φt) is typically less than the strength resistance factor (φ) from the main specification. To determine the nominal strength of the connection for use in seismic or blast design, it is recommended to use the factor φ rather than φt and apply it to the LRFD strength. Selection of the appropriate φ from AISI S100-07 should depend on the observed mode of failure of the connection during the test. Once the nominal strength of the connection is determined, its expected strength and dynamic strength can be calculated using the appropriate SIF and DIF as explained above. Figure 2 is a diagram depicting the various levels of connection strength and the factor relationship between them.
Dynamic Strength DIF
Ultimate Strength
Expected Strength SIF
Nominal Strength (Lower bound strength) Spec. Resistance Factor (φ)
Test Resistance Factor (φt )
LRFD Strength
Figure 2: Strength relationship diagram.
Sample Calculations The VertiClip® SL600 connector (Figure 1a) is used at the top of the curtain wall to connect CFS studs to the floor slab or beam, and to provide a sliding connection to isolate the wall from the vertical deflection of the floor system. The connector was tested under load in the out-of-plane horizontal direction. The observed modes of failure of the connector were bending then rupture: Test ultimate strength Calculated φt using Chapter F of the AISI S100-07 LRFD strength = 4250 x 0.633 Appropriate φ from AISI S100-07, Section C3.1 Nominal strength = 2690 / 0.9 Expected strength = 2990 x 1.21 Dynamic strength = 3620 x 1.1
= 4250 lbs = 0.633 = 2690 lbs = 0.9 = 2990 lbs = 3620 lbs = 3980 lbs
This data is applicable to the connector only. Attachment of the connector to stud framing and to the floor should be evaluated in a similar way. Also, it should be noted that engineers tend to use the ultimate strength of the connector as a measure of its dynamic strength. This example shows that this assumption is reasonable (difference about 7%) but un-conservative at the same time.▪
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Guest Column dedicated to the dissemination of information from other organizations
A
s structural engineers, we are one part of a design and construction industry that provides great service to our communities. Ironically though, it seems that many of our youth do not know about or dream of joining any one of the many rich and rewarding careers available, whether as an architect, structural engineer, construction manager, electrician, mason, plumber, etc. It appears that many of our youth aspire to become doctors, lawyers, athletes, video game designers, singers or the latest reality TV star, just to name a few. But there are also young men and women whose only hope is to avoid the traps of gang life and crime that surrounds them in their neighborhoods. As a child, I dreamt of being a train engineer, operating one of the thundering locomotives of the Santa Fe Railway that rolled through my hometown. In middle school, I was convinced that I wanted to be an architect after reading a book on Frank Lloyd Wright. While in high school, a very influential and memorable teacher inspired me to pursue chemistry and teaching after I took her challenging but very engaging AP chemistry course. This changed my career plans considerably. A year later, I entered the University of California, Davis committed to becoming a university professor in chemistry. It was only through good fortune that I became friends with a group of engineering majors and eventually pursued a civil engineering degree, then went on to earn a Master of Science in Structural Engineering from the University of Illinois at Urbana-Champaign. The fundamentals of my story are not unique. Many of us considered different careers when we were growing up, then something happened along the way that launched us into a career where we have the privilege of designing structures and making a lasting contribution to our
Encouraging Potential Structural Engineers By Jesus Orozco and Matt Barnard, P.E., S.E.
Jesus Orozco joined ACE in 2007 and joined Degenkolb in 2008 as a senior in high school. He is currently attending Santa Monica College and plans to transfer to Cal Poly San Luis Obispo and major in civil engineering with a focus in structural engineering. Jesus can be reached at jorozco@degenkolb.com. Matt Barnard, P.E., S.E. joined Degenkolb in 2001. His experience includes structural analysis, seismic evaluation and structural design, retrofit design of existing structures, and new building design. Matt can be reached at mbarnard@degenkolb.com.
20 July 2012
communities. As a group, we cannot wait to see if future generations will be similarly inspired to pursue a career in structural engineering. We must be proactive and be that spark ignites passion in someone, and inspires them to join us in making a difference in our communities by being structural engineers. It is critical that new talent enter the structural engineering field and the design and construction industry behind us. It is absolutely relevant to us all. Young men and women are needed to carry on the proud tradition of the structural engineering community, designing the infrastructure and the buildings that house our society and provide sanctuary against the powerful forces of nature. Likewise, young men and women are needed to define the architecture and build these structures. Fortunately, the ACE Mentoring Program gives each of us a way to inspire youth to learn about and pursue careers in the construction industry and structural engineering. ACE (Architecture, Construction and Engineering) is a unique partnership among industry professionals who work together to attract young people to design and construction-related professions. Architects, interior designers, landscape architects, mechanical, structural, electrical, environmental and civil engineers, construction managers, college and university representatives and other professionals from related corporations and professional organizations are all involved. Started in 1994 in New York and then formed as a not-for-profit organization in 2002, ACE has
I have personally expanded my involvement and I’m now serving my fifth year on the Los Angeles Metro Area Affiliate’s Board of Directors, and my second year on the regional council appropriately named the California Council. The Los Angeles Metro Area Affiliate covers both Los Angeles County and Orange County, with fifteen active teams and the goal to dramatically increase our number of teams in the next few couple of years. To complement the regular slate of team meetings, our program includes the All-Schools Event where we have a yearly pasta building contest on the campus of Sci-Arc, a Trades Day where the students are treated to a day of hands-on activities under the supervision of the instructors of a local training center, and the End-of-Year Presentation Event where each team presents their project and scholarships are awarded. The California Council is a collection of representatives of each Affiliate in the state and will be offering our second annual ACE Summer Camp on the campus of Long Beach State July 15th through July 22nd. The reason for Degenkolb’s involvement in ACE goes way beyond the extensive networking opportunities in our relationship-driven industry and the public speaking opportunities it offers participating mentors. If you can capture the attention of thirty teenagers in the late afternoon on a school night, even with the smell of freshly delivered pizza and the competition of cell phones chimes announcing the latest text message from their friends, then you know you are in good shape for your next client meeting. The reason to be involved is Jesus Orozco and all of the young men and woman like him who have been involved in ACE. Jesus was a
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July 2012
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a presence in more than two hundred cities in America – from New York to Los Angeles, Seattle to Miami, Chicago to Dallas, even Honolulu – and is still growing. Thanks to the dedication of ACE’s mentors and staff, and the support of local schools, more than 60,000 students, many who are economically challenged, have had an opportunity to explore the design and construction industry. ACE consists of a collection of small mentor/ student teams organized into Affiliates that cover different portions of the country. While the national organization provides a general direction and infrastructure for the entire program, each Affiliate operates relatively independently with control of their own operations and aspirations. Over the course of the school year, each mentor team gives the participating high school students on their team an introduction into the different facets of the design and construction industry through construction site visits, office visits, a project and other activities. All three aspects of ACE – architecture, construction, and engineering – are highlighted at various points during the year. The meetings are typically every other week in the late afternoon after school. There is no set curriculum, only general guidelines for the mentors to consider when developing their program for the year. There is no cost to the students to participate in the program, except for their time and effort. Degenkolb Engineers, the nation’s oldest seismic engineering firm, is an active contributor to the ACE Mentoring Program from Seattle down the West Coast to San Diego. Their Los Angeles office became involved in 2005 when they were invited by the construction firm Charles Pankow Builders, Ltd. to give a presentation to the ACE team at Roosevelt High School about what is a structural engineering. The very next year, Degenkolb were taking on the leadership of the ACE team at Belmont High school. The Belmont team has now evolved into the Downtown Los Angeles Team, with 20 to 40 students each year from up to four different local high schools. The Los Angeles offices of Degenkolb Engineers, the architecture firm Perkins+Will, and general contractor Swinerton Builders form the current Downtown Los Angeles mentor team.
A Student’s Perspective By Jesus Orozco Former ACE Student & Staff Assistant at Degenkolb Engineers
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young man that I met when the Downtown LA team first appeared on the campus of Los Angeles School of Global Studies. We have been blessed to watch this young man grow from being an unfocused high school student into a committed college student realizing his potential and a valued member of the Degenkolb family. First joining us as an office assistant, Jesus has progressed until now he is indispensible to the success of our office. His story is best told in his own words. Jesus is why I am involved in ACE. Rarely is there something that is truly a win for all involved. ACE is one of those special things where the students, the schools, the design and construction industry as a whole, and
I come from a community where it is perfectly normal to stop attending school, have a child at an early age, and where joining a gang seems to make sense. I fortunately have both of my parents present and supportive, but there are many cases where the only support comes from the streets. I know these people that cause police sirens to go off. I played on the monkey bars with people that now flood drugs into the streets; I knew them in their innocence. I return to this neighborhood every night, still unable to help. There are so many ways to go down the wrong path. When I first heard about the ACE Mentoring Program at my school, I knew it would be something I definitely wanted to be a part of. At the first meeting, Matt was talking about the overview of the program; meeting with professionals, going to job sites, participating in various competitions between schools and many other activities. When it was over, some of my friends and I grabbed applications on our way out. We talked about the program all day. Turning in that application was the best decision I have ever made in my life. Every Wednesday afternoon for the two years I was in the program, I would gather up my teammates after school and head down to our meetings. My favorite project was designing a train system that ran between all of the schools that were part of the Los Angeles ACE team. On my part of the project, we had the train dive into the side of a hill. (Since our project’s budget was as big as our imagination, we had no problem making it work!) This project may have been hypothetical, but it was not so far-fetched. Each and every team member could potentially become an architect, engineer, or contractor. We may be the designers and construction team behind the structures of tomorrow. It didn’t take long to realize that the construction industry was not only where I wanted to be, but where I needed to be. I now know that I can make a difference in this industry. Many times during my trips back home from meetings or from my job at Degenkolb today, I’ve seen many of my friends who are stuck in a hole that they may never escape. Some of them even knew about ACE but didn’t take advantage of the opportunities it offered. Quite a few of them still ask if I’m still working with Degenkolb. When I respond that I am, the usual response I get is: “I wonder where I would have been if I would have taken it more seriously.” Because of ACE and meeting Matt, I have now been with Degenkolb Engineers going on four years. I started as an office assistant before I graduated high school and now am a staff assistant and parttime drafter. I contributed to various projects, including a hospital which I used to pass every day on my way to school. That is the best part of this industry: seeing projects you have worked on being erected. There is still much to learn in this industry and there are many seats to be filled. My personal goal now is to one day become a mentor myself and do the best I can to make sure other students have the same great experiences and opportunities I had. It really is life changing.
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students’ after school hours, including family life, work, athletics and other academic commitments. Even with these challenges, the program continues to grow. There is no better reward than the personal satisfaction of seeing a young man or woman discover a passion for our industry and embark on a path that will help them realize their potential to better of our communities and our industry. If you are looking to make a difference, consider becoming involved in your local ACE affiliate. If you are not sure of whom to contact, visit the ACE national website at www.acementor.org and you can find the location and contact info for the Affiliate local to you.▪
often occur after school but still within typical working hours, making it challenging for mentors to balance work commitments and participation in the program. • Keeping the students engaged for the duration of the program is difficult as there is extensive competition for the
STRUCTURE magazine
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the individuals serving as mentors all benefit immensely. And this benefit is clearly demonstrated by the numerous success stories. The ACE Mentoring Program was even recognized with the nation’s highest award for mentoring when the program was honored with a 2010 Presidential Award for Excellence in Science, Mathematics, and Engineering Mentoring. I would be remiss if we did not acknowledge the challenges that the ACE program faces. The following are just a few of the challenges that we have experienced: • Always a challenge even in good times, ACE is dependent on fundraising that often consists of donations from design and construction industry firms, many of which have been hit hard by the current economic environment. • ACE is challenged by the critical need for an on-campus champion for schools participating in the program, whether in the faculty or administration. The ACE teams often struggle without champions promoting the program on the school campus, securing transportation and resources given the challenges faced in school budgets, and committing to chaperon the students during the after-school activities. • Having a deep and diverse bench of mentors is critical for the success of the program, but there are intense pressures on the availability of the professionals serving as mentors. The meetings
This article consists solely of the opinions of the authors and was written independent of the ACE Mentor Program. Thank you to Terry Dooley who founded the program in Los Angeles; his passion for ACE drives us forward. Thanks to Jesus Orozco for sharing his story, Mark Day of John A. Martin & Associates for photographs, and Ryan Mangindaan of Verten Media for photographs.
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Professional issues issues affecting the structural engineering profession
Passing the New Structural Exam–You Too Can Do It after Turning 40 by Thomas A. Grogan, Jr., P.E., S.E., which appeared in the September 2011 issue of STRUCTURE®, detailed an excellent strategy for preparing to pass the new SE exam. This article provides further information on the SE exam and some of the tools available to help you study. These tools can also be used to prepare for the PE Civil: Structural exam.
questions, even if you have to guess, as unanswered questions count as wrong answers. The morning breadth problems may include both building and bridge problems. Each of the afternoon depth modules requires examinees to complete 3 or 4 problems in either the area of buildings or bridges. The amount of time available for each problem depends on the module chosen. The breakdown of the depth problems is shown in the Table.
The SE Exam Beginning in April 2011, the SE exam was reorganized into a 16-hour exam spread over a Friday and Saturday. The Friday component focuses on Vertical Forces, and Saturday focuses on Lateral Forces. Both days are broken into 4-hour sections, with the morning covering breadth problems in a multiple choice format and the afternoon containing a choice of essay (work out) problems. Examinees must choose between either Buildings or Bridges for both of the afternoon modules, and the two cannot be combined. In this way a single area of practice (buildings or bridges) is evaluated in depth. Each of the morning breadth modules contain a total of 40 multiple choice questions that must be completed in a 4 hour time period. This provides an average of 6 minutes to complete each problem. It is important to answer all of these
Structural Exam Study Aids The Key to Your Success By Christine A. Subasic, P.E., LEED AP
The PE Exam The PE Civil: Structural exam follows a similar format but is only an 8-hour exam. It is composed of a 4-hour morning breadth module and a 4-hour afternoon depth module. However, for the PE Civil: Structural exam, both modules are multiple-choice format, with an average of 6 minutes to complete each problem. In addition, the Structural depth module can include both building and bridge problems.
Choose Your Study Aids So what is the best way to prepare? There are many types of study aids available to choose from. A brief (unscientific) survey of some recent examinees indicated that sample multiple-choice problems and solutions was the most helpful type of study aid, followed by other solved problems. Several publishers produce study aids with multiple-choice problems, including NCEES,
SE Exam Afternoon Depth Problems.
Vertical Depth Component
Lateral Depth Component
Buildings Module
Four 1-hour problems in each of Four 1-hour problems in each of the following areas: the following areas: • Steel structure • Steel structure • Concrete structure • Concrete structure • Wood structure • Wood and/or masonry structure • Masonry structure • General analysis (e.g., existing At least one problem includes a structures, secondary structures, multistory building, and at least nonbuilding structures, and/or one problem includes a foundation. computer verification) At least two problems include seismic content at Seismic Design Category D and above, and at least one problem includes wind content of at least 110 mph. Problems may include a multistory building and may include a foundation.
Bridges Module
Two 1-hour problems and one 2-hour Two 1-hour problems and one 2-hour problem, in the following areas: problem in the following areas: • Columns (1 hour) • Concrete superstructure (1 hour) • Footings (1 hour) • Other elements of bridges (e.g., • General analysis (i.e., seismic culverts, abutments, retaining walls) (1 hour) and/or wind) (2 hours) • Steel superstructure (2 hours)
Christine A. Subasic, P.E., LEED AP is a consulting architectural engineer in Raleigh, NC, specializing in sustainable design and masonry. She is also the author of “SixMinute Solutions for the Civil PE Exam Structural Problems” and “Six-Minute Solutions for the Structural I PE Exam Problems,” and co-author of “The Masonry Designers’ Guide.” She can be reached at CSubasicPE@aol.com.
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Professional Publications Inc., and others. The study aids identified as most helpful by those surveyed are described below, but are in no way the only options available. One popular option is the Six-Minute Solutions series published by Professional Publications Inc. This series gets its name from the average of 6 minutes that you have for each of the multiple-choice questions on the exam. These books contain 80 to 100 multiple choice questions like those encountered on the exam and detailed,
step-by-step solutions. The problems cover most of the topics included in the NCEES exam specifications, and wrong answers are based on mistakes that are easy to make. Another option is the NCEES sample exam study materials, published for both the SE exam and the PE exams. These guides contain sample exam questions and solutions in the exact format they appear on the actual exams. Kaplan also publishes a series of review books, sample problems, as well as online tools to aid in studying for the SE and PE exams. Though not mentioned by the survey respondents, there are a number of other online resources available, which can easily be found with an online search for “PE exam study”. Options include webinars as well as self-paced online study aids. In many cases, you have a choice of a complete exam preparation package covering all topics likely to be found on the exam, or choosing only select topics that you feel you need the most review. For example, many state and national engineering associations offer webinars on specific topics covered in the PE/SE Exams. There are several websites that offer online study aids for specific subject areas.
Practice, Practice, Practice and Plan for the Test The key to successful preparation is practice solving problems – lots of them. Or as one survey respondant said, “Work as many practice problems as you can.” Recent examinees also had the following advice to offer: “Manage your time during the exam! You must bring a watch to manage time. Time seems to go by very quickly during the exam.” “Tab out your books so you can quickly find the appropriate information. When you think you have worked enough sample questions, work more. Create a binder with useful reference material and organize it by subject (e.g. concrete, wood, steel).” “Cover all the topics in proportion to the expected questions on the test; mark your references for quick access.” With so many choices available, everyone should be able to find something that works for them. The secret to success is doing the work, regardless of which tools you choose. Allow yourself plenty of time to prepare. It’s real work, but the benefits are real as well. Good Luck!▪
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July 2012
OK as is
OK with changes
New York Waterfronts
Structural Engineering Challenges
By Cliff McMillan, P.E., C.Eng A look at the completed waterfront project.
W
ith 500 miles of shoreline, New York’s waterfront is the largest of any city in the world. After decades of neglect, the waterfront has again become a place of intense interest for government and civic organizations. With the 1992 New York City Comprehensive Waterfront Plan and 2001’s Vision 2020: New York City Comprehensive Waterfront Plan, the city government took stock of the needs and opportunities of the waterfront and laid out plans to transform it for the benefit of all New Yorkers. Arup has been involved in this process for over a decade, with six discrete waterfront projects covering almost nine miles in total, including Hudson River Park, the East River Waterfront, Teardrop Park, Pier A in Manhattan, and Hunter’s Point in Queens. Structural engineering plays a vital role in waterfront projects in supporting clients and design teams to achieve durable and cost-effective results. Construction efficiency, longevity and cost-effectiveness all rely upon intelligent structural solutions that take into account a project’s full lifecycle. Structural elements such as piers and seawalls often consume a large proportion of a project’s initial budget, and repairs and maintenance can lead to significant costs down the road.
Figure 1: Hybrid steel concrete pile. The design adopted a hybrid steel and concrete pile to manage the poor soils above the rock. Courtesy of Hudson River Park Trust.
STRUCTURE magazine
For these reasons, close attention is paid to structural design on all waterfront work, with particular challenges arising in relation to longevity, pier design, materials selection, and flooding.
Longevity The harsh marine environment of Manhattan’s waterfronts – with their damp, salty atmosphere, intense solar exposure, constant cycles of wetting and drying due to splashing and tide range, and damage caused by skateboarders and vandals – can lead to the untimely deterioration of even the hardiest materials. These factors are considered at a particular site to develop a design that avoids the need for maintenance as much as possible. In targeting a 50-year lifespan or more for all park structures and permanent exterior elements, sustainable, durable materials matched to the particular demands of their setting are all considered.
Pier Design Meeting the goal of a 50-year lifespan represents a particular challenge for pier design due to the forces they have to resist and the extent of their exposure to corrosive elements. Piers have to be designed for a wide range of structural loads, including 1) self-weight, 2) dead loads due to the make-up to achieve surface treatments and soil for planting and trees, 3) live loads arising from the planned activities on the pier, and 4) lateral loads from wind, seismic effects, currents, ice and possible vessel mooring forces and impacts. All these have to be considered in relation to the particular circumstances and to provide flexibility for possible future changes – for instance, the type of vessels likely to be moored in the future, or the depth of soil needed to accommodate possible tree layouts. Geological conditions along New York’s shoreline and rivers can be variable over short distances and are often unfavorable for foundations, thereby presenting major challenges. New York City river silts, sands and clays vary greatly in composition and depth. At some points around Manhattan, rock begins at riverbed level; at others, such as several of the Hudson River Park piers, piles had to be driven to over 300 feet below the surface. Seismic considerations then become a
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significant factor. Providing sufficient lateral support to the piles, and the depth of water and poor material below the pier deck before such lateral support is achieved, can become a dominant factor in the design. At Hudson River Park, the very long piles founded on rock at up to 350 feet deep and the poor soils above the rock, presented a particular challenge. The design adopted used a hybrid steel and concrete pile. For the upper approximately 70 feet – through the water and weakest soils – pile stiffness, bending strength and corrosion resistance are most critical. A high quality 24-inch-square precast, prestressed concrete pile section was used. Cast in a controlled environment and tensioned to minimize cracks provides high strength and durability. Below that, corrosion and bending resistance are not a critical issue, and the loads in the pile are primarily axial. There, a steel HP section, up to more than 200 feet long, transfers the load to the rock. The connections between the concrete and the steel section, and between successive steel sections, were designed to ensure simple construction in the field (Figure 1). This hybrid pile was less expensive than an all-concrete pile; by minimizing the concrete, its weight was reduced substantially, which was beneficial during the lifting and splicing process, and costs were saved. It was felt that the high-quality concrete section in the vulnerable upper zone provided better corrosion resistance and durability than corrosion-protected structural steel. To provide further protection, the concrete specification was designed to prevent reinforcement corrosion, usually caused by chloride ion inward migration. A concrete blend suited to preventing this phenomenon was selected, and epoxy-coated rebar was used for all reinforced concrete structures, as epoxy stops moisture and chlorides from corroding the steel. Another issue with pier design is the form of superstructure construction and how to accommodate the form needed by the landscape design, program design and also the often extensive utilities and services required on the pier – water, electricity, gas, fire and waste disposal. Because of the constraints of over-water construction, the most cost-effective structure usually employs a rectangular pile grid and a flat or uniformly sloping deck. This facilitates the use of precast concrete pile caps and longitudinal beams with precast concrete slabs spanning between the pile caps. The build-up above the pier deck to create the surface shaping, necessary for the landscape design program and to accommodate services and utilities, can then be achieved in a number of ways. To reduce dead loads, styrene foam and lightweight fill were used on the Hudson River Park pier to create the shaping. The services were accommodated within the void above the structural deck (Figure 2).
Figure 3: The installation of new concrete pile caps over the new precast concrete piles. Pile caps are elevated to avoid contact with river water. Courtesy of Hudson River Park Trust.
To drain the space above the deck, and avoid saturation and damage to plants and utilities when the tide rises, non-return valves were provided at the underside of the structure to allow any water to drain out when the tide is low but to prevent inflow when the tide is high. On Pier 15 at East River Waterfront, a utility trench runs the length of the pier within the structure to accommodate the utilities that serve the buildings out on the pier and provide maintenance access. For this two-level pier, the structural columns supporting the upper deck are located to coincide with the piles below. These designs minimize interaction between the structure and the harsh water environment to the fullest extent possible. Pile caps, for example, are elevated so as to typically avoid contact with river water (Figure 3). Often new piers are built over or among the remains of the timber piles from previous piers. This means careful mapping of the old piles to minimize conflicts when the new piles are driven. Some of the old piles can be retained to provide a visual connection to the history of the park, as well as a habitat for fish, wildfowl, and other marine life. Sometimes new over-water esplanade areas are constructed on existing but deteriorated platforms. This requires careful study of the existing conditions, and the load capacity and state of deterioration of the existing piles and structure. Often strengthening of the existing structures becomes necessary.
Materials Selection
Figure 2: Plate at the bottom of the concrete which connects to the steel section. The connections use a simple detail to facilitate construction in the field. Courtesy of Hudson River Park Trust.
STRUCTURE magazine
A key objective throughout the design was to ensure low maintenance and operational costs, partly through the choice of sustainable, durable materials. Common structural and non-structural elements that require consideration are: railings, paving, lighting, benches and other outside furniture. For instance, for the extensive length of railing on the Hudson River Park pier, Grade 317 stainless steel was selected to improve corrosion resistance. Even with this material, a coating of Adsil, a commercial coating product, proved necessary to minimize “tea-staining” in the harsh, salty environment. FieldTurf grass, a synthetic grass that is designed to mimic real grass, was selected to provide a maintenancefree surface for sports fields and picnic areas on piers. For timber rails and benches, selected tropical hardwood Ipe, farmed from forests
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Figure 5: East River Pier 15 deck had to be raised to the flood elevation to accommodate the small pavilions below the code requirement of the FEMA flood elevation. Courtesy of Arup.
certified to meet sustainability requirements, were specified. For the esplanade, granite and blue stone paving were selected. Where structural steel is used for marine structures, such as pier piles or floating structures, several methods of corrosion prevention were considered. Some piles were coated with glass flake epoxy. Others were covered in fiberglass jackets and epoxy. Cathodic protection has been used for protection on projects, but this has limitations in the splash zone, and is considered by some clients to be a maintenance burden because of the need for an electric current (Figure 4).
Flooding Resilience An important factor in the design of the piers and esplanades is the flood elevation under the 100-year Federal Emergency Management Agency (FEMA) extreme flood conditions. This would involve overtopping of existing piers and esplanades around Manhattan, sometimes to the extent of 3 feet. The typical finished esplanade elevation is fixed in relation to the historic bulkhead elevations, as well as the finished grades utilized in the reconstruction of the roads such as Route 9A which runs along the Hudson River waterfront. As a result, the esplanade elevation at Hudson River Park and East River Waterfront is set generally around three feet below the FEMA 100-year flood level. By this approach, buildings on the esplanade or piers would generally be subject to occasional flooding in extreme circumstances.
This means that the park buildings would either have to be raised to meet the code stipulated FEMA requirement, or be designed to withstand flooding and be “drip dry” after flooding. All electrical and mechanical equipment and critical services are elevated to above the 100-year flood level. For the East River Waterfront, it became necessary to obtain a variance through the Board of Standards and Appeals in order to build small pavilions below the code requirement of the FEMA flood elevation. This variation was granted specifically for the unusual headroom constraints under the existing Franklin Delano Roosevelt Drive. The elevation of the East River Pier 15 deck had to be raised to the flood elevation to accommodate the small buildings (Figure 5).
Creating a Legacy for New York City Until the 90s the city of New York turned its back on its waterfront. Hudson River Park, East River Waterfront, and other recent developments mark a dramatic shift in attitude towards the water and waterfront amenity. Mayor Michael Bloomberg and his administration’s strong commitment to the issue, along with public demand for waterfront access, and the extent of the shoreline, present countless opportunities for the city. While the 500 miles of New York City waterfront pose a tremendous opportunity, they also create a tremendous design challenge. The waterfront is not an infinite resource; it is often narrow and fragmented and is subject to competing interests such as marine habitat preservation, public demand for amenity, and commercial demand for prime locations. They also present a range of engineering challenges, including dealing with an aggressive, salt-laden physical environment that makes material selection critical for providing durability, resisting aging and deterioration, and satisfying regulatory and permitting requirements. The waterfronts referred to above have responded to these special challenges with unique solutions that demonstrate success in improving quality of life and also in expanding our expectations of what waterfront spaces can become.▪ Cliff McMillan, P.E., C.Eng, is a Principal in Arup’s New York office. He has been deeply involved with several Manhattan waterfront projects over the past 11 years, including leading Arup’s multi-disciplinary design coordination and management services since 2001 on the entire five miles of Hudson River Park and on the design of East River Waterfront. He may be reached at Cliff.McMillan@arup.com.
Figure 4: Corrosion of steel piles in intertidal splash zone, without protection. (Instead of showing cathodic protection, this photo shows what happens when the pile is not protected.) Courtesy of Hudson River Park Trust.
STRUCTURE magazine
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July 2012
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Lessons Learned from the
Joplin Tornado By Curtis Geise, P.E., S.E.
Non-residential building remains standing despite major damage.
T
he Joplin Tornado of May 2011 was one of the most destructive natural disasters ever to hit the state of Missouri. There were more than 160 deaths, 1,100 injuries and $3 billion in damages. The physical and psychological impact will not soon be forgotten. In consideration of the magnitude of devastation to the built environment, the Structural Engineers Association of Kansas & Missouri (SEAKM), a Member Organization of NCSEA, formed a committee to investigate the performance of structures affected by the tornado, whether directly or indirectly. This article offers some of the committee’s observations and recommendations, which are based on site reconnaissance and other information. The committee’s full report will be posted on SEAKM’s website (www.seakm.com). In general, structures designed in accordance with building codes, such as those published by the International Code Council (ICC), are not required to resist tornado wind effects. Tornado wind speeds vary greatly and may exceed 200 mph, as was the case with the Joplin Tornado. The International Building Code (IBC) 2006 establishes a baseline of 90 mph as the basic wind speed for this area of the country. Observations of wood structures indicated the main area of vulnerability is maintaining a strong load path through connections. Overall, the wood structures reviewed were of an older generation of construction materials and methods and performed poorly. The few newer commercial buildings included in the committee’s study performed better. Typically, wood structures have an inherit redundancy within the framing system, with multiple interior walls intersecting and connected to the outer structural frame; but today, with larger open spaces, this redundancy is reduced significantly and the prescriptive connections techniques in codes may no longer be appropriate. Pre-engineered metal buildings are typically designed and constructed to provide column-free spaces. The pre-engineered building that the committee investigated suffered damage to the envelope, even though it was not directly in the path of the tornado. The damaged areas appear to be consistent with overpressures that are beyond the codespecified wind loads. Fortunately, main structural frames remained stable and did not collapse. STRUCTURE magazine
Mapping of the Joplin Tornado EF Rating. Courtesy of the United States Department of Commerce, National Weather Service, Central Region Headquarters, Kansas City, MO.
Structural steel and concrete framed buildings performed better in resisting the extreme wind effects of the tornado, although not without damage. St. John’s Hospital and its Medical Office Buildings sustained damage, but the structural frames remained stable. The buildings’ envelope materials were severely damaged, with most of the destruction caused by the ballasted roof systems used throughout the complex. Essential facilities should consider a comprehensive tornado preparedness plan when considering the layout of the facility and the respective infrastructure requirements. Emergency generators, electrical switch gear, mechanical systems and the structures that support them require consideration of the implications of windborne debris. Reports indicate that cars impacted the backup generator building for the hospital during the tornado, which rendered the facility inoperable. Hard wall structures are a building type that is constructed to be very efficient in the use of materials, while providing the most building square footage for the minimum amount of cost. These buildings are commonly described as “big box stores.” A few such buildings experienced a near-direct hit by the tornado. The high wind speeds caused significant damage, including roof deck connection failure, leading to the failure of several structural framing members and, in some cases, almost total collapse of the hard wall system. The roof deck diaphragms of buildings have a propensity to fail first when tornado winds impose high uplift on the structure. This was most evident in hard wall buildings that the committee reviewed where roof framing was light and material usage was efficient. Roof
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deck diaphragms are an essential building component that typically does not incorporate a redundant load path; once it fails, other structural members will likely fail, as seen in both of the hard wall structures investigated. It is understood that tornados are an extreme loading event, with a low probability of occurrence, but it is also evident that society is impacted by these events. As professionals, structural engineers need to lead in determining if and when enhancements to the building codes are warranted. We understand that most buildings do not need to be designed to the maximum wind speeds of a tornado to provide life safety, but we need to be prudent and consider these potential events to some extent.
Summary of Recommendations The intent of the following recommendations is to increase life safety for occupants and overall building integrity and robustness when impacted by tornado type St. John’s Hospital damage; note the ballasted roof, lightweight concrete and glazed curtain wall destruction. winds. However, it should be understood that a structure built in accordance with them will not be “tornado proof.” 1) Implement statewide building code legislation in all allowing it to occur within the connection. Connection failures are 50 states. often sudden and catastrophic, whereas member failures tend to be The public has the opportunity to enhance the built environment more ductile and may not result in a catastrophic failure. The Engineer by passing legislation requiring compliance with an appropriate of Record or joist manufacturer should design the connection based building code. Such legislation is currently being considered in the on the strength of the most critical component of the joist or joist state of Missouri, and at least fifteen other states have already enacted girder assembly, such as top chord shear or end diagonal compressuch a provision. This legislation should enable local jurisdictions sive capacity. to enforce the statewide building code and include funding for this 5) Develop code requirements for greater robustness or enforcement. Studies have shown that a building code provides a safer redundancy in hard wall buildings. These may be in the built environment for all. form of specifying: a defined base moment; a maximum 2) Determine if the use of mechanical deck connections for length of continuous wall prior to a full-height lateralsteel metal deck thicknesses of 22-gauge or less should load-resisting member, wall or frame; or a system of be mandatory. continuous cross-ties. The roof diaphragm is essential to the overall integrity of a building’s One of the buildings impacted by the Joplin Tornado experienced structural system. Inspections by several groups have revealed failures a near-total collapse of the tilt-up wall panel system except at the of the decking metal around supposedly sound arc-spot (puddle) loading dock area, where the base of the panel was well below grade welds. Today, steel deck manufacturers and their governing bodies such that it behaved as a cantilever. Details could be designed and do not recommend welding of side laps for 22 gage decks. It seems provided that would offer a fixed or partially restrained base condition. apparent that this may need to be considered for typical fastening of Alternatively, if a lateral bracing element, such as a perpendicular wall the deck to the supporting structure. or steel brace, is placed to restrain the wall system at some prescribed 3) Design roof deck fasteners considering simultaneous uplift length, the potential for failure of a significant portion of the wall tension and diaphragm shear and reflecting the different system is greatly reduced. factors of safety in accordance with the [Steel Deck Institute Building codes should also include requirements for more robust Diaphragm Design Manual], Third Edition. continuous ties across the roof diaphragm so as to preserve walls when Steel deck manufacturers’ data typically does not consider tension the diaphragm fails. Wind force levels could correspond to EF-0 or and shear simultaneously, and at times will provide notes regarding EF-1 and allowable stresses could be ultimate, with a factor of safety the different factors of safety for wind and seismic. Inspection of equal to 1.0. This would allow significant damage, but minimize the damaged structures indicates that uplift in the field of the roof may propensity for collapse of the hard wall system. have been much higher than traditional loading patterns currently 6) Require a storm shelter, or at a minimum an area of refuge, indicate. This is likely due to the large atmospheric pressure drop in in retail stores, manufacturing buildings and similar the vortex of a tornado. There is little or no available research into types of structures with a certain number of occupants, the wind patterns on a structure during a tornado, but designing the for employees and customers that may be inside during a fastening of the diaphragm system for an amplified wind pressure tornado event. load capacity in both shear and uplift seems appropriate. According to published accounts, lives were saved in one hard wall 4) Require a specific design for open web steel joist building because store employees and patrons were able to shelter connections to primary framing members and joist girders. themselves in an employee break room. Although not specifically In many instances, connections between joists and joist girders designed as a storm shelter, the inherit robustness and redundancy in and between joist girders and building columns are standard details the framing of the room provided sufficient protection for the occuprovided by the joist supplier. These details need to reflect the design pants who took refuge there. Design could be based on the principles practice of forcing any failure into the member itself, rather than of ICC-500, ICC/NSSA Standard for the Design and Construction of STRUCTURE magazine
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July 2012
Devastation near the center of the path of the EF-5 Joplin Tornado.
Storm Shelters, and FEMA 361, Design and Construction Guidance for Community Safe Rooms. 7) Require storm shelters designed in accordance with ICC500 and FEMA 361 for all elementary, middle and high schools, as well as other critical facilities, such as police and fire stations, emergency preparedness centers of control and other post-disaster structures including hospitals. Society relies on the public school system to protect their children while they are being educated, and expects critical facilities and infrastructure to withstand extreme loadings. The tornado that struck Joplin provides sufficient evidence that schools need to consider alternative measures for offering security during these times of violent weather. It is very fortunate that, at the time of the tornado, the schools were empty. It is unfortunate that some of the critical facilities were unusable after the event. 8) Require essential buildings to have impact-resistant glazing systems and door units, similar to those required in hurricane-prone regions. The winds of the Joplin Tornado caused significant damage to envelope materials of several important buildings, including the St. John’s Hospital complex. The hospital facilities may have been able to treat some of the injured had these items not catastrophically failed. Critical structures should conform to the same practices required in regions where windborne debris is a concern during a hurricane. 9) Prohibit the use of ballasted roofs in all construction. During high wind events, both hurricanes and tornadoes, loose roof ballast is ineffective at preventing roof blow-off. In fact, roof ballast often becomes airborne debris that typically destroys glazing systems and exterior finishes and may directly injure people. Many hurricane-prone regions of the country have enforced codes restricting or eliminating their use. 10) Research the concept of implementing similar design considerations for wind load distribution to diaphragms, drag struts and chord attachments in high-risk tornado areas that are currently codified for seismic lateral force distribution. Enhanced design requirements for diaphragms, drag struts and chord development will lead to more robust connections of the diaphragm to the bearing walls and to other lateral-force-resisting system elements. The research should consider all aspects. 11) Enhance inspection requirements for big box structures. Adopt provisions similar to those in the Florida Building Code, which requires a “threshold inspection” for all structures over a certain size. 12) Review and update prescriptive practices for wood construction to ensure a robust load path through connections, from roof to foundation. STRUCTURE magazine
Connections in wood with nailing procedures as outlined in prescriptive guidelines should be reviewed, for both the International Residential Code (IRC) and the IBC. Several studies indicate that simple, low-cost modifications can achieve significant robustness in the load path; for example, metal plate connections for roof trusses, top plates and sill plates. 13) Place renewed emphasis on special inspections, with improvements for wood framed buildings, including residential. As design and construction professionals, we should review our past practices and determine ways to enhance them to serve the public better. In the wake of a disaster, there tends to be a renewed effort in inspections and other requirements for design and construction. Several cities around the country have developed their own special inspection manuals that typically are more stringent than a recognized building code. 14) Encourage installation of tornado shelters in existing buildings. There are several available pre-manufactured storm shelters that satisfy FEMA 320, Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business. The guidelines offer simple and economical methods to designing and constructing residential structures. This document, along with others regarding tornado preparedness, is available at www.fema.gov. 15) Study the impacts to design and construction practices if codes required the design of buildings for EF-1 or EF-2 tornados in tornado-prone areas. It seems appropriate to consider the design of structures for a higher level of wind pressures, based on the current observed wind speeds through the Enhanced Fujita Scale Rating System. However, we must realize that these wind speeds are estimated from observed damage and not measured directly. 16) Study tornados further in an effort to develop appropriate code design equations. The current equations consider straight-line winds, which are significantly different from winds near the vortex of a tornado, where uplift forces are considerably higher and turbulence occurs. Tornados are one of nature’s most elusive adversaries to the built environment. Although modern technology has enabled the prediction of potential tornadoes and their possible paths, it is still a struggle to record wind speeds and develop structural design methodologies based on actual conditions. This is an opportunity for design professionals, the construction industry, government agencies and the general public to learn from these devastating events and react to these recommendations. Readers are encouraged to conduct further research by reading other Joplin reports that have been or will be issued by the National Institute for Standards and Technology (NIST), Federal Emergency Management Administration (FEMA), and National Oceanic and Atmospheric Administration (NOAA), along with reports regarding the Tuscaloosa, Alabama tornado and Enhanced Fujita (EF) Scale developed by Texas Tech University (TTU) in cooperation with the National Weather Service (NWS) in 2004, www.spc.noaa.gov/efscale/ef-ttu.pdf.▪
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Curtis Geise, P.E., S.E. (CGeise@HNTB.com), is a structural engineer at HNTB Corporation in Kansas City, Missouri. He is a past president of the SEAKM Kansas City Chapter and chaired the SEAKM committee that studied the aftermath of the Joplin Tornado.
July 2012
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Structural DeSign design issues for structural engineers
M
odern container terminals are designed with two main functions in mind: to provide a loading/ unloading area for ship containers and to support lifting devices that can move loads from one location to another. Design of the supporting structure for crane operation is an intricate task that affects other components of a modern pier. Engineers designing a crane runway should take into account possible future changes in the crane load rating, the potential addition of another crane, a future extension of the crane runway, the accidental ramming of the crane against the crane stops, an extreme range of loads and/or a high incidence of maximum loads. In general, a waterfront crane runway is designed as a beam on an elastic foundation, where piles are treated as elastic springs. In recent years, there were some attempts made to design crane girders using the Strut-and-Tie Model (STM) methodology. Utilization of STM for the design of waterfront crane girders may have questionable benefits requiring a separate discussion. This article will concentrate on simple design issues that are often neglected and are typically investigated only after the destruction of expensive property.
Waterfront Crane Runways Common Omissions and Practical Solutions By Vitaly B. Feygin, 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.
Design of Crane Stops Frequently, design of the crane stop is treated without due respect. Many engineers use salvaged crane stops, relocating them in a new position along the crane runway. Such decisions can become very costly mistakes. Crane stops are controlled by boundary conditions identified in the energy equation and the tipping force equation (Figure 1). The crane stop should be designed for the larger of the two forces.
Figure 1: Free body diagram for crane tipping force equation.
Energy Equation Kinetic energy of the crane at full rated speed must be equal to the energy dissipated by a spring or plunger in the crane stop device. WV2/2g = P
Where W = total weight of the crane excluding the lifted load, V = rated speed of the crane, g = acceleration due to gravity, = length of spring or plunger travel required to stop the crane (usually about 0.25 ft), and P = force of impact. Tipping Force Equation aW = Ph
(Equation 2)
Where W = crane dead weight, a = horizontal distance from the crane tipping point to the crane’s center of gravity (C.G.), and h = vertical distance from the point of impact to C.G. of the crane. Example Energy Equation: W = 2,400 kip, V = 2.5 ft/sec, = 0.25 ft, P = 2,400*2.52 / (2*32.2*0.25) = 931 kip/per two stops or 465 kip per stop
Figure 2: Crane stop detail (not recomended for heavy cranes).
34 July 2012
(Equation 1)
Moment resistance provided by the diagonal tension rods: M'r = 576*0.574*4.0 +576*0.819*2.17 = 2,346 ft-kip Shear resistance provided by the diagonal tension rods: V'r = N*= 576*0.819*0.7= 330 kip ΔMr = 3,168 – 2,346 = 822 ft-kip ΔVr = 792 – 330 = 462 kip fv = 462/(2 *3*2.4) = 32 ksi / bolt < vFv = 0.75*0.4*Fu = 0.75*0.4*150 = 45 ksi The tension on the bolt group is: 822 = 2*T*4.0+2*T*2.58/4.0+2*T*1.17/4.0 T = 83.3 kip F'nt = 1.3Fnt – Fnt*fv/(Fnv) = 1.3*0.75*150 – 0 .75*150*32/45 = 66.25 ksi < Fnt =.75*150 = 112.5 ksi T/Ab = 83.3 / 2.4 = 34.71 ksi < F'nt = 0.75*66.25 = 49.7 ksi. While the detail shown in Figure 2 fails at a load well below the required limit, the detail shown in Figure 3 has significant extra capacity.
Figure 3: Alternate crane stop detail.
The Tipping Force Equation: W = 2,400 kip, a = 44 ft, h = 80 ft, P = 2,400*44/80 = 1,320 kip/per two stops or 660 kip per stop In ideal conditions, the force of crane impact is shared equally between two crane stops. However, in the real world, crane frames are skewed. The force of the crane impact is almost never shared equally by both crane stops. Therefore, prudent design would require each crane stop to be designed for an impact force that is 20% higher than the force calculated from an assumption of equal force distribution; i.e., 60% of the total impact force. Consider a commonly used crane stop detail (Figure 2). The force of the crane impact is an ultimate load and should be treated as such. Shear force on the bolt group, V = 0.6*1,320 = 792 kip Moment, M = 792 kip*4 ft = 3,170 kip-ft The detail shown in Figure 2 uses two 2½-inch-diameter bolts and four 1¼-inch-diameter bolts for tension and shear. Without an oversized hole in the base plate, shear force will be shared proportionally to the shear stiffness AbG of each bolt. Therefore, two 2½-inch (Ab = 4.91in2) bolts will resist twice the force resisted by four 1¼-inch bolts (Ab = 1.22 in2). fv = 792*0.66 / (2*4.91) = 53.20 ksi/bolt > vFv = 0.75*0.4*Fu = 0.75*0.4*150 = 45 ksi–@ 2½-inch bolts (Table J3.2, AISC 13) fv = 792*0.33 / (4*1.22) = 53.55 ksi/bolt > vFv = 0.75*0.4*Fu = 0.75*0.4*150 = 45 ksi–@ 1¼-inch bolts Tension on the bolt group. 3,168 = 2*T*3.5+2*T*2.25/3.5+2*T*1/3.5 T = 358 kip Combined Tension and Shear in Bearing Type Connection F'nt = 1.3Fnt – Fnt*fv/(Fnv) (F-la J3-3a, AISC 13) This formula is losing physical meaning since fv exceeds vFv T/Ab =358/4.91 = 72.91 ksi (Front Bolts are greatly overstressed.) 0.64T/Ab = 229/1.22 = 188 ksi (Middle Bolts are greatly overstressed.) 0.285T/Ab = 102/1.22 = 84 ksi (Exterior Bolts are greatly overstressed.) Now consider a modified connection (Figure 3). The force of the impact is taken into horizontal and vertical components of diagonal tension rods, (with the balance of force resisted by the base plate anchor bolts). For this connection, use all 1¾-inch-diameter rods (Ab = 2.40 in2). Two diagonal rods running at a 55 degree angle to horizontal will be post-tensioned to 0.8fpu = 0.8*150*2*2.4 = 576 kip.
Design of Stowage Devices Both tie-downs and stow pins should be designed for hurricane wind force only; these devices are not intended for seismic events, which are unpredictable in time such that it is impossible to stow a crane in advance. It should be remembered that the wind force can be acting at an angle to the crane, which makes it difficult to determine the actual percentage of the force acting on each of four tie-downs. However, each of the two stow pins should be designed for 50% of the total force. Tie-downs There are two general schemes for tie-down design: • Case 1: Tie-down device is symmetrical to the centerline of the rail (Figure 4). • Case 2: Tie-down device is placed on one side of rail (Figure 5, page 36). In both cases, tie-downs create torsional moment in addition to shear and flexure. Even though it is minimal in Case 1, torsional moment should always be included in the analysis of the crane girder to pile cap connection detail, and into the analysis of the girder’s lateral reinforcement. Tie-downs should be placed as close to the pile cap as practical. In that instance, all shear caused by torsional moment will be concentrated at one end of the crane beam. Additional shear force can be easily addressed by special longitudinal reinforcement placed on the vertical faces of the crane beam and spliced within the pile cap closure pour. Another important issue that is frequently neglected during design of the tie-down device is prying action. The analysis shown in Figure 6 (page 36) explains how the force acting on the tie-down rod can be
Figure 4: Symmetrical tie-down detail.
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July 2012
Figure 5: One sided tie-down detail.
Figure 6: (left) Tie-down detail. (right) Free body diagram.
greatly underestimated. There have been multiple occasions when tiedown bolts were snapped and expensive cranes were destroyed. Stow Pins Stow pins should be designed for shear forces. The most commonly used stow pin detail is shown in Figure 7, and a suggested stow pin detail is shown in Figure 8. The following example explains common omissions in the design of stowage elements. Example For the design of tie-down devices and stow pins, the engineer should know the maximum forces that will develop on these devices. Formulas provided by ASCE 7-05 can be used for preliminary analysis. However, the magnitude of these forces has been proven to be underestimated when investigated in wind tunnel tests. Therefore, actual forces should be based on wind tunnel test results. The design of stowage devices has frequently been treated without due respect. The results of inadequate designs in these seemingly secondary devices have proven to be catastrophic. In the following example, we will use a more realistic design approach and actual forces provided by a crane manufacturer. Tie-down force = 440 kip per corner Wind force perpendicular to rail = 530 kip Wind force parallel to crane rail = 485 kip
Similarly, the net section of the sole plate should be checked against the flexural stress. The outlined procedure is reasonably conservative. Depending on plate thickness, the parameter “a” might shift towards the anchor bolt. Some engineers prefer to use “0.66a” rather than “a” when calculating heel reaction C. Such an assumption may be excessively conservative. The ratio (a/b) = 0.75 can be used for rational design of the tie-down device. Stow Pin The stow pin pocket should be designed for V = 530 kip. Consider two stow pin details: a commonly used detail (Figure 7) and a modified detail (Figure 8). To understand the principles at work in any embedded vertical elements, we must view them as short piles in a very stiff medium. It is obvious that the elastic foundation reaction under the pipe sleeve is considerably higher than the sum of elastic foundation reactions under all studs. Therefore, before the load can even reach the stud, it will crush the concrete. The bearing stress at the top of the concrete is: fp = 530/(2*8*4) = 8.28 ksi. The dynamic load will certainly crush the top 4 to 6 inches of concrete,
Tie-down Device (Figure 6) It is highly advisable to use sleeves and through bolts for tie-down anchorage. Tie-down bolts work for tension only, and they can be easily replaced if subjected to excessive corrosion. If the pullout force P = 440 kips, with a = 3.0 inches and b = 4.188 inches, then the reaction force on each side of the tie-down center line will be: C = 0.5*440*2.094/3.0=153 kip. The force on the each bolt will be: Treq = (0.5*P+C)/2 = (0.5*440+153)/2 = 186 kip. Therefore, each tie-down should be anchored with four 1¾-inch-diameter anchor rods: Tprov = *0.75Fu*Ab = 0.75*0.75*2.66*150 = 224 kip. The original tie-down detail specified 1¼-inch-diamter threaded rods, a clear indication that prying action was not considered in the design. This is a dangerous omission. It is impractical to design a tie-down device without considering prying action. The sole plate thickness for such a device would be unreasonably thick. The thickness of a sole plate should be checked for flexural stress and deflection. Based on the diagram shown in Figure 6, = (0.5P*(0.5b)3/3EI)*2 = P*b3/24EI < 0.063 in. The designer should use net section moment of inertia for the deflection analysis. STRUCTURE magazine
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Figure 7: Commonly used stow pin detail (not recomended for heavy wind load).
July 2012
does not have efficient reinforcement to deal with short stiff pile rotation. The unintended consequence of this stow pin detail is additional shear and tension force on the tie-down. Analysis of both stowage devices clearly indicates the possibility of a crane progressive collapse. The alternate approach (Figure 8), treating the sleeve as a long pile in a stiff medium, shows a 6-inch-diameter x 40-inch-long pipe with concentric 12-inch-diamter x 12-inch-long sleeve at the top of the device. Analysis of the stow pin device shows an Elastic Foundation Reaction at the top of the sleeve, EFR = 35.5 k/in. That EFR translates into a concrete bearing pressure = 35.5/12 = 2.96 ksi < 0.85*f 'c = .85*5 = 4.25 ksi Comparison of the two stow pin details clearly indicates the deficiency of the commonly used solution. It should be noted that failure of only one out of six stow elements (stow pins or tie-downs) can lead to progressive collapse of the whole system, and the loss of a multi-million dollar piece of equipment. Figure 8: Alternate stow pin detail.
Load Combinations
and the sleeve will try to rotate as an infinitely stiff short pile. The slip circle surface formed by such a failure will intersect one stirrup, possibly two if they are placed close enough to confine the ruptured surface. Assume that slip surface intersects two legs of #5 stirrups in a direction parallel to the crane girder. The shear capacity provided by #5 bars can be estimated using the shear-friction formula. Assume a 20-degree shear plane surface. The angle between the slip surface and the rebar is = 90 – 20 =70 degrees. Vn = 0.85*4*0.31*60(1.4*sin70+cos70) = 105 kip < 485/2 = 242 kip. However, the direction perpendicular to the crane rail is the most critical one. That direction has a higher force, 530/2 = 265 kip, and
Suggested Load Combinations and impact allowance were discussed in a previous series of articles, Rational Approach to Design and Analysis of Piers and Marginal Wharves, in STRUCTURE® magazine (May, November, and December 2011). These articles are available in the online archives at www.STRUCTUREmag.org.
Conclusion Each aspect of a crane runway should be treated with the same respect and diligence as major crane runway components. Disaster frequently results from the failure of secondary elements.▪
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STRUCTURE magazine
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July 2012
Seismic Construction Showing Signs of Improvement By Larry Kahaner
Public Projects Still Strong; Private Projects Growing
F
STRUCTURE magazine
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July 2012
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or the first time since the economic downturn began, Individual firms are continually updating and improving prodthose involved with seismic construction are seeing a ucts and services to remain competitive. According to Corebrace’s marked optimism from their customers. Companies are Saxey, the company began testing BRBs in 2001 with the goal of not only sanguine about the future, but the numbers are providing the best performing brace on the market. “We thrive bearing this out. “We are seeing a significant increase in the use on difficult projects where additional lead time is not an option. of BRBs in the marketplace,” says Brandt Saxey, Chief Engineer at We offer BRBs with every connection option available on the West Jordan, Utah-based CoreBrace, LLC (www.corebrace.com). market, including pinned, welded, and bolted connections.” He “We are also seeing a general upward trend in the construction says they recently tested braces specifically designed for bridge industry as a whole, though perhaps not as significant as the BRB- applications which included some braces fabricated out of standard specific increase. While the availability of project funding remains a constant concern, it seems that it may be loosening up somewhat.” Lyle Simonton, Director of Business Development at Subsurface Constructors (www.subsurfaceconstructors.com) in St. Louis, Missouri concurs. “Most people I speak with feel much better about the construction climate this year than in the past year or two. The B U C K L I N G R E S T R A I N E D B R A C E S quantity of projects that we’re bidding and the type of projects that we’re doing is also an indicator that more private projects are being developed compared to the past couple of years.” While companies are seeing a bump in private construction, public work remains strong. “Fyfe Company has seen an uptick in the number of inquiries over WWW.COREBRACE.COM 801.280.0701 the last 12 months, which signals an increase in the number of construction ✔ Bolted, Pinned, and Welded Connections— projects. This indicates growth in the Fully Qualified and Exceeding AISC 341 Requirements existing structure renovation market and an increase in construction spending. ✔ Real-Time Engineering Assistance We also see great potential in govern✔ Non-linear Modelling Design Guides ment sector work in the next 12 to 24 ✔ Maximum QA/QC and Scheduling Control months,” says Aura Joyce, Marketing Communications Manager of Aegion ✔ Integration with RAM Structural System and REVIT Corporation (www.aegion.com), Fyfe’s ✔ New! “Near Fault Effect” Testing parent company.
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steel, galvanized steel, and stainless steel. “Each of these different material types produced a unique set of brace performance data, but each can be fit for any project type.” They also tested braces designed specifically for retrofit use which are installed in two separate pieces, with a splice in the middle, allowing them to be fit-up in tight spaces where the use of a traditional brace would be impossible. “These recently tested braces underwent some of the most rigorous testing we have ever performed – far exceeding
the AISC-341 code requirements. Our ongoing R&D program allows us to continually provide the most state-of-the-art performance levels and keep our fabrication processes as economical as possible,” Saxey adds. Subsurface Constructors stays competitive by offering full service geotechnical contracting along with services not available from others, says Simonton. “We are one of the very few companies to offer both the full range of deep foundations and earth retention, and in addition serve as a design-build contractor for vibro-ground improvement solutions nationwide.” He adds: “Our ground improvement division, although no longer new, continues to grow in our abilities to be competitive in all industries and geographic locations. We have designed and constructed vibro- ground improvement for hundreds of structures of all sizes. Regarding seismic construction, we have seen an increase in using this type of ground improvement to prevent liquefaction in granular soils and/or provide reinforcement to weak soils that could be susceptible to liquefaction induced settlement.” The Fyfe Company, along with their construction arm, Fibrwrap Construction, were purchased last year and are now part of Aegion Corporation. Recent developments include a specialized FRP system for gypsum walls, a double-thick FRP product and a new low-profile UL-approved fire resistant finish system for projects which require a fireproofing product. Says Joyce, “The Tyfo CFP system is the new fire-resistant finish system which can provide a 1, 2, 3 and 4 hour UL-rated thickness, which is used in conjunction with the Tyfo Fibrwrap system. By far, Tyfo CFP is one of the lowest profile fireproofing systems available for FRP with a total thickness of ⅞ of an inch at 4 hours.” At Hayward Baker, Inc. (www.haywardbaker.com), headquartered in Odenton, Maryland, Director James Hussin says that the company’s newest technique is the TRD Wall method which constructs high quality soil mix walls in situ without the need for excavation required by other methods. “It also constructs a continuous wall that eliminates the risk of discontinuities or leaks that can occur continued on page 42
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July 2012
when overlapping columns or panel construction methods are used.” His company is seeing a steady increase in work, but the recent downturn has caused unique problems for some contractors. “General contractors have experienced the pain of hiring inexperienced subs offering unrealistically low prices only to be hit with performance problems and claims. They now have come to understand the value of an experienced sub who can identify the risks associated with our business and avoid surprises during the work,” says Hussin. Recent earthquake activity has caused an increase in inquiries, especially from areas that are usually not considered seismic zones, according to Joe LaBrie, managing partner of Dynamic Certifi cation Laboratory (www.shaketest.com) in Arcadia, California. LaBrie will be president of the Structural Engineers Association of Southern California starting July 1 st. DCL performs seismic simulations for the purpose of certification of equipment for use in Category IV and other critical buildings. “Hospital buildings in California make up the lion’s share of where that demand is coming from right now,” LaBrie notes, but DCL is experiencing interest from the East Coast following the recent earthquake activity in Virginia. “The Eastern United States has the New Madrid Fault and you’ve got other areas of the country that also have active seismic areas. Consequently, the design community, the building owners and the construction community are taking
it very seriously and encouraging the science, the engineering and the measures necessary to improve the reliability and the safety of structures and their contents.” Says LaBrie: “DCL provides full service from shake table testing and the preparation work associated with that to the structural engineering involved along with the processing through the regulatory entities… We’re the only laboratory that I’m aware of that is owned and operated by a licensed structural engineer who also has IAS accreditation and a 30-year background in the design of hospitals.” He encourages people to attend the annual Buildings at Risk Summit (www.seaosc.org) that will take place on October 11 in Southern California (venue not yet decided). (See ad on page 44.) Henry Gallart, President of SidePlate (www.sideplate.com) in Laguna Hills, California says his company just executed some tests of its products at UC-San Diego. “We tested some short-span W36 x 150 beams, which have a high compactness ratio that, with the new SidePlate frame configuration and the U-shaped slotted cover plates, allowed this system to go to levels never before recorded on such a beam,” he says. “We were able to obtain two complete cycles at six percent rotation, where the requirements for testing a special moment frame are one cycle at four percent. It was very exciting.” Gallart says that the data collected in these tests helps feed the market that is seeking performance-based design. “With continued on page 44
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July 2012
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performance-based design, you can take advantage, or take more advantage, of the added ductility that one system may provide over another.” As for business, Gallart notes: “The bigger government projects are definitely reducing in number, compared to, say, three to five years ago. And the commercial markets seem to be growing a little bit, which is surprising to many, including us.” He describes his company’s business as continuing to grow at an “incredible pace,” adding, “things are going really well.” Robert Pyle, Director of Technical Marketing at Star Seismic (www.starseismic.net) of Park City, Utah tells a similar story. “Business has been really good for us. We’ve got a lot of work. Last year was our most successful year and I think we’re going to do better this year. As far as people I talk to, engineers and general contractors, I am hearing that things are picking up. People are getting busy again. We’re finally starting to see work come out of the private sector which has been dead for four years or so.” The company manufactures buckling-restrained braces and provides full engineering services. “We actually design all of the braces and gusset plates for clients. We do not charge any fees for these services, and we watch the project from conception until the braces are actually erected and filled,” says Pyle. “If any issues come up, whether it’s engineering concerns, questions about fabrication or erection, we stick with the job and with the client… If there is
Individual firms are continually updating and improving products and services to remain competitive. any problem, whatever it might be, we will fly to the job site and help resolve any issues.” Pyle adds: “What has carried us the last couple of years has been primarily schools, hospitals, and government-type facilities, but we’re starting to see it expand out. One of our most recent jobs was to provide the braces for a casino on an Indian reservation in California. We’ve got a big private project going in Arizona and another one coming up in Oregon, so companies are starting to move forward. We are seeing much more private work.” (See ad on page 46.) At JMC Steel Group (www.jmcsteelgroup.com) in Chicago, (its two divisions are Atlas Tube and Wheatland Tube), Sales Engineer Brad Fletcher says that the advantages of hollow structural section over a built up section is its cost effectiveness. “As an industry, we are moving forward or trying to respond to all research, including continued on page 46
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seismic, in trying to create better products.” He has some advice The company offers a free trial of Tedds on its website. Next month, for SEs planning to use hollow structural sections. “They continue the company will release its new integrator with improved functionalto be readily available and the size range that’s out there is quite ity for integrating design models with Revit Structure, Broome says. large and quite flexible, especially coming from our company. “We continually add new features to help our clients work efficiently. One word of caution is that it’s important for engineers to check BIM is increasingly becoming common practice, and it’s the availability of sections before they specify them. There are vital we offer our clients a cutting edge BIM solution some sizes that are actually listed in the steel manual that aren’t so that they can increase their productivity, win more necessarily produced anymore, or not produced on a regular basis. work and be more profitable.” (See ad on page 3.)▪ It’s a wise investment of engineer’s time to make sure that sections they’re considering are readily available, whether it be through distributors or from the mills.” Also looking out for engineers is STRUCTURE® magazine is planning several additional Software maker Chicago-based CSC, Inc. SPECIAL ADVERTORIALS in 2012 and 2013. (www.cscworld.com), which develops structural software and provides technical support To discuss advertising opportunities, please contact to SEs in the United States. “We’re a global our ad sales representatives: company with over 35 years’ experience of developing our structural calculation software, CHUCK MINOR DICK RAILTON Tedds, and our steel building design softPhone: 847-854-1666 Phone: 951-587-2982 ware, Fastrak & CSC’s Integrator,” says Vice President Stuart Broome. CSC’s Integrator is Sales@STRUCTUREmag.org a free tool for synchronizing Fastrak and Revit structure models back and forth.
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new trends, new techniques and current industry issues
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The Road to Preserving Bridges By Anwar S. Ahmad, P.E.
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tate departments of transportation and other bridge owners are faced with significant challenges in addressing the Nation’s highway bridge preservation and replacement needs. According to the National Bridge Inventory, more than 30% of the 600,000 highway bridges nationwide have exceeded their 50 year design life and are in need of repairs and or replacement; more than 25% are classified as structurally deficient or functionally obsolete. This issue is exacerbated by an increase in travel demands, shortfalls in funding, and increasing costs of labor and materials. As a result, it is more imperative now than ever before that cost effective bridge preservation strategies are adopted by the bridge community. The American Association of State Highway and Transportation Officials (AASHTO) defines bridge preservation as “actions or strategies that prevent, delay or reduce deterioration of bridges or bridge elements, restore the function of existing bridges, keep bridges in good condition and extend their life.” Preservation actions may be preventive or condition-driven. Typically, the term “bridge preservation” is associated with existing bridges. However, bridge preservation actions and strategies should be considered during all phases of a bridge’s life, from the initial planning through design, construction, and its service life until the bridge is decommissioned. Considering preservation throughout these stages is essential to maximize the service life and minimize the overall lifetime cost of the bridge. The Federal Highway Administration’s (FHWA) Bridge Preservation Guide (FHWAHIF-11042) contains some common bridge related definitions, commentaries and examples that can assist bridge owners in developing and implementing a systematic preventive maintenance (SPM) program, which is a major component of bridge preservation. The key steps of an effective SPM program include:
Establishing Goals & Measures As with any effective bridge management program, an SPM program should have objectives and measurable goals. This is a key step in the development of a successful program as it serves as a compass for the journey ahead and a mirror that reflects past performance.
Some of the items that are generally considered during this step include: • Current condition of the bridge inventory; • Historical condition and funding trends; • Available resources; and • Customer & stakeholder input.
Identifying SPM Activities This involves the selection of proven and cost effective treatments and activities. Generally, preventive maintenance activities can be classified under two categories: 1) Condition based activities, such as sealing or replacing leaking deck expansion joint material, painting structural steel elements, installation of scour countermeasures, performing electro chemical extractions on heavily chloride contaminated concrete deck, etc.; and, 2) Cyclical activities, such as bridge cleaning, lubricating bearing devices, sealing and waterproofing bridge decks, etc. Some of the items that are generally considered during this step include: • Activities that will facilitate achievement of goals; • Establishing condition thresholds for bridge elements, components, or entire bridge. For example, bridges in overall fair to good condition; • Bridge material types; and • Cyclical and condition-based activities.
Determining Investment Levels This involves estimating the cost of the work needed to achieve the established program goals. Some of the items that are generally considered during this step include: • Data currency for bridge condition and unit costs; • Adequacy and sustainability of funding levels to achieve desired goal(s); and • Balancing investment levels for preservation and replacement needs.
Selecting & Prioritizing Work Efforts This involves selecting and prioritizing qualified projects based on the established program’s parameters. Factors such as traffic volumes, detour lengths, risks, safety, etc. can be considered when developing a prioritization scheme.
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Developing & Executing Work Plans This involves the development and execution of short and long term plans based on established goals and objectives. Key factors that are typically considered during this stage include: • Availability of funding; • Resources (in-house vs. outsourcing); • Environmental restrictions; • Work zone traffic restrictions; and • Past plan delivery performance. Preservation activities often cost much less than major reconstruction or replacement activities. Delaying or forgoing warranted preservation treatments will result in worsening condition and can escalate the feasible treatment or activity from preservation to replacement. The latter will result in extensive work and higher cost. A viable alternative is timely and effective bridge preservation of sound bridges to assure their structural integrity and extend their useful life before they require replacement. As bridge stewards and owners, we need to become more strategic in our approach to managing our bridge programs, and embrace the concept of bridge preservation as an integral component of the overall management of our bridge assets. Investing wisely in timely preventive maintenance reduces high costs for future major repairs and replacements. Implementing an effective bridge preservation program calls for appropriate tools and resources. Optimum results are achieved by applying the appropriate treatments/strategies at the appropriate time.▪ Anwar S. Ahmad, P.E. is a Senior Bridge Preservation Engineer with FHWA’s Office of Infrastructure in Washington, DC. Mr. Ahmad is actively involved in various committees, including AASHTO TSP.2 Bridge Preservation Regional Partnerships, AASHTO Subcommittee on Structures and Bridges, AASHTO Subcommittee on Maintenance, and Transportation Research Board Structural Maintenance Committee. He is currently serving as the co-chair for the FHWA Bridge Preservation Expert Task Group and is the author of the Bridge Preservation Guide, FHWA Publication Number FHWA-HIF-11-042. He may be reached at Anwar.Ahmad@dot.gov.
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Eco-friendly HALFEN HIT connections are designed to help maintain comfortable interior temperatures while reducing energy use. Efficient Integral polystyrene insulation and the selective use of stainless steel components almost eliminates thermal transfer between the balcony and the floor slab. This reduces heat loss through the structure, and reduces the possibility of interior condensation and mold growth.
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business issues
CASE BuSinESS PrACtiCES
Ownership Transition Passing the Torch without Getting Burned By Kevin R. Sido and Todd M. Young
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tructural engineering and other design firms depend upon their professionals for survival. The loss of even one owner can lead to turmoil at the least and dissolution of the firm at the worst. Proactive succession planning can help firms fend off those worst-case scenarios. In the process, succession planning can help senior owners realize that they won’t want (or be able) to work forever, and that they need a buyout from the younger engineers just as much as the younger engineers look forward to their turn at ownership and management.
Are You Ripe for Ownership Planning? Every closely held firm can benefit from ownership transition planning. But if your firm has any of the following attributes, you could be particularly ripe for the process: • Ownership is concentrated in a sub-set of professionals at the firm, especially individuals of a similar age. • Younger professionals have expressed a desire for ownership and participation in firm governance/strategic planning. • Certain equity owners have expressed a wish to reduce workload and/or focus on non-revenue-producing activities (mentoring, strategy, life-balance, etc.). • Firm management has realized a need to provide incentives to a sub-set of non-owner professionals, to encourage them to develop business on their own.
Risks in Succession Events Like most complex endeavors, ownership transition events are not without risk. There are management risks (Are we promoting and giving ownership to the right people, and are we reducing ownership interests of the right people, too?). There are also business risks (Will the clients have concerns when they learn of the shifts in ownership?). And there are financial issues to consider (If the succession model involves having the firm repurchase equity from certain owners, will the firm be able to afford the repurchase price?). Regulatory risks also arise. State regulations on the practice of engineering may specify how the firm can be named, owned and
managed, often requiring all or a percentage of the current owners, directors or managers to be licensed professionals. Firms must prepare succession plans with an eye on continued compliance with licensure rules.
Employment Law Risks An important source of risk in ownership transition involves employment laws. Succession planning involves making distinctions between senior owners and younger professionals, and those distinctions often involve reducing ownership in the senior group and increasing it in the junior group. Federal and state employment laws generally take a dim view of treating older people less favorably than younger ones for age-related reasons. Thus, a critical piece of any succession plan is an analysis of employment law concerns. Many professional firms have an explicitly age-based succession plan hard-wired into their operating documents (such as a Shareholders Agreement or Bylaws). Those plans often require equity owners to sell back their equity in the firm at a specified time, determined in relation to the owner’s age. Recent case law and EEOC administrative proceedings have raised the possibility that some of these provisions constitute age discrimination, exposing firms that have those provisions to liability. Even if these provisions are drafted to apply only to professionals who are equity owners of the firm, they may still expose the firm to damage claims and challenges to the enforceability of the provisions. Happily, there are creative solutions that can provide the desired incentives while staying on the right side of the employment laws.
Whom to Involve? In creating an ownership transition plan, it is essential to assemble the right team of professionals. The firm’s attorney and tax accountant are key players. Outside lenders, valuation firms and succession planning consultants can provide assistance as well. Estate planners for the affected professionals will have important guidance to share also. We sometimes add (only half jokingly) that it can be useful to include a psychotherapist in the planning process. Everyone involved in succession planning needs to be aware of the complex and powerful emotions that affect
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every participant. Senior professionals who have defined themselves through their roles at the firm may struggle to let go. Younger professionals may have difficulty tempering enthusiasm and eagerness with realism about the pace at which their mentors can embrace this change. And everyone will need to understand the art of compromise.
Creative Succession Planning Firms have a range of options in creating succession plans. One set of solutions involves creating a “senior professional” status, and endowing that with enough favorable attributes to make it appealing to the senior owners. Another option is to create a formalized “buy-in” program by which the directors of the firm offer selected mid-level professionals the opportunity to buy equity in the firm as part of the annual review process. In all cases, counsel and management should analyze the terms of the firm’s existing organizational documents (Articles of Incorporation, Bylaws, Shareholders “Buy-Sell” Agreements, etc.) to determine what changes must be made to create the succession incentives.
Conclusion Ownership planning, not unlike designing a complex structure, calls for awareness of many variables, of both law and business. Growing and mentoring a new crop of professionals so that they are ready and able to become equity owners, while maintaining harmony with existing owners as they await their eventual retirement and buy-out, calls for constant and careful attention. But the results of careful planning are clearly worth the effort: insuring that the success of the firm benefits existing owners and their future successors.▪ Kevin R. Sido is a Senior Partner in the Chicago office of the national law firm of Hinshaw & Culbertson LLP. He has represented engineers and architects in litigation and transactional matters, and can be reached at ksido@hinshawlaw.com. Todd M. Young is the Chair of the Commercial Transactions Group at Hinshaw’s Chicago office. He assists architecture and engineering firms and others with business succession planning, mergers and acquisitions, financing transactions and general issues of corporate governance, and can be reached at tyoung@hinshawlaw.com.
www.itwredhead.com 800.899.7890
award winners and outstanding projects
Spotlight
The Left Coast Lifter By Kenton Lee, S.E. and Anna Dix, P.E. Liftech Consultants was an Outstanding Award winner for the Left Coast Lifter project in the 2011 NCSEA Annual Excellence in Structural Engineering Awards Program (Category – Other Structures).
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he Left Coast Lifter floating crane was delivered to Oakland, California, in 2009 to aid in the erection of the new eastern span of the San Francisco-Oakland Bay Bridge. The new bridge incorporates the largest single tower self-anchored suspension span (SAS) in the world, which, by nature, requires special construction considerations. Since the bridge deck provides the anchorage for the main cables, the deck needs to be temporarily supported by falsework while the cables are installed. This is different from a conventional suspension span, where the deck can be suspended from the main cables during erection. The Left Coast Lifter was procured by the contractors for the SAS, American Bridge/ Fluor Daniel Joint Venture (ABF), specifically to lift and place the falsework, the deck, and portions of the tower in the bay. The Left Coast Lifter components were fabricated in different parts of the world. The 100-foot wide by 400-foot long barge was fabricated by US Barge LLC in the United States. The crane and barge floats were fabricated by Shanghai Zhenhua Heavy Industries Co., Ltd. (ZPMC) in Shanghai, China. The crane was mounted onto the barge in Shanghai. Liftech Consultants Inc. (LCI) provided structural engineering consulting services to ABF for the crane structure, including technical specifications, design, and fabrication review assistance. The crane structure design was a collaborative effort by ZPMC, LCI, and ABF, with ZPMC as the design-build contractor. The approximate total project construction cost was US$50 million.
Operation The 328-foot shear leg boom is a welded tubular truss structure with a capacity of 3.75 million pounds (1700 metric tons) at 65° and an operating angle range from 19° to 65°. The boom design allows a 66-foot boom tip section to be removed to reduce the length to 262 feet. The truss is shaped like an “A” in plan view to efficiently resist the barge listing and rolling forces.
The boom heel imposes large vertical and longitudinal loads on the barge. To minimize the local reinforcement in the barge, large structures were used to distribute the loads: massive 30-foot long shear stops (longitudinal thrust) and an equally massive 15-foot long boom carriage (vertical loads). To achieve uniform bearing over the entire length, the surface of the carriage was machined to match the bearing rail surface. The Left Coast Lifter is towed by tugboat from the port to the operating location and is positioned more precisely with the barge’s computer-controlled anchor and spud system. Three floats are attached to each side of the barge for stability during large lifts. These six floats are connected to the barge by upper and lower connections that resist a tensioncompression couple. The float design criteria required that the floats be easy to install and remove on the water. To address this, a guidance system was designed to help align the floats with the barge. Once the floats are guided into the lower connection, the float is attached to the barge deck at the upper connection using two 2.95-inch diameter pins. Another design challenge was that, in an accident, the lower connection to the barge may tear a hole in the side of the barge, so replaceable ductile links were designed to yield and limit the force imposed on the side of the barge.
Transportation The crane is designed to fold up for a 32.8foot vertical clearance while navigating US waterways. The boom heel can slide back on rollers (“skid”) from the stern toward mid-ship so the boom tip can rest on a barge-mounted stand. This substantially reduces the voyage loads on the boom during transportation.
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The A-frame can also be lowered onto the barge deck to clear 32.8 feet for travel in US waterways. Tension and relaxation of the topping lift and jacks control the A-frame raising and lowering. In order to lower the A-frame, the backstays were designed to fold like links in a chain. To skid the boom heel, the boom tip is lowered to a stand mounted on an auxiliary barge. The stand has a spherical bearing to allow for differential list and roll between the crane barge and the auxiliary barge. Then, the boom heel carriage is unlocked from the operating position and rolled on Hilman rollers along a 197-foot track. Winches pull the structure toward mid-ship. At the stowed position, the carriage is locked again by bolting it to a pedestal. Finally, the boom tip is hoisted, to separate it from the auxiliary barge, and lowered onto the boom stand on the main barge. Early in the design, a skidding system using Teflon and stainless steel bridge bearings was considered instead of the rollers, but it could not provide an acceptable level of reliability since the track is very long. The rollers were much more suitable due to their relative insensitivity to slight imperfections in the track. Another design consideration was level of the tracks. During skidding, the load on each of the two boom heels is approximately 44,000 pounds (200 metric tons). Uneven tracks could potentially overload one of the 10 vertically loaded Hilman rollers on each boom heel. To equalize the load, Fabreeka elastomeric pads were installed above each roller.▪ Kenton Lee, S.E. is a principal and Anna Dix, P.E. is an associate at Liftech Consultants Inc.
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News form the National Council of Structural Engineers Associations
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NCSEA Code Advisory Committee Report Ronald O. Hamburger, S.E., SECB, Chair, NCSEA Code Advisory Committee
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he Code Advisory Committee is composed of 6 subcommittees: General, Existing Buildings, Seismic, Quality Assurance, Wind, and Evaluation Services, and an executive committee, composed of the chairs of each of the subcommittees, including Ed Huston (General), David Bonowitz (Existing Buildings), Kevin Moore (Seismic), Kirk Harman (Quality Assurance), Don Scott (Wind), Bill Warren (Evaluation Services), and this author. In a general sense, the Code Advisory Committee’s charge is to improve the building codes to assure safe, economical and reliable construction. However, building codes today consist of no single document but, rather, a complex suite of documents including the model codes themselves (there are several), the ANSI consensus standards the codes adopt by reference, and a series of evaluation service reports that identify the code conformance of proprietary products of different types. The committee’s specific activities include: 1) Monitoring the status of the building codes, their referenced standards, and evaluation service approvals, to assure that our “codes” are providing safe and economical structures, and to not place undue burden on structural engineers either through unfair apportionment of professional responsibility/liability, or through imposition of unclear, conflicting, or hardto-implement requirements. 2) Suggesting to the standards committees, through advocacy, proposals intended to address our membership’s concerns. 3) Providing public comment to the standards associated with revisions that are not in our members’ interests. 4) Development and submittal of code change proposals to the ICC, to address issues of concern. 5) Monitoring code change proposals submitted by others, to assure that these do not violate the principles indicated in 1 above. 6) Attending the ICC code hearings and advocating for (submitting argument against) proposals consistent with the goals indicated in item 1 above. 7) Partnering with the ICC-ES to improve the technical adequacy of their evaluation of acceptance criteria and product reports. 8) Providing public comment on acceptance criteria proposals, through the public hearing process, as appropriate, to accomplish the goals in item 1 above. A brief summary of our activities follows: Building Codes ICC is in the process of developing its 2015 series of model building codes. It does this in 2 groups, over a period of 3 years. Group A changes include technical changes to structural design criteria. Group B changes include administrative adoption of updated structural standards. Presently, we are in the middle of the cycle for Group A changes. Proposal submittals were due in January 2012 and ICC held public hearings in Dallas during the month of May to review and vote upon proposals submitted. In recent years, and in accordance with NCSEA policy, most technical structural engineering provisions have been moved out of the building codes and become adopted STRUCTURE magazine
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by reference to national standards, such as ASCE 7, ACI 318, and so forth. As a result, there has been little direct submittal activity by our Seismic and Wind Subcommittees, as technical criteria under the purview of these committees is mostly contained in the reference standards. The Existing Buildings, General Requirements, and Quality Assurance Subcommittees, however, have been quite active, as the requirements in these areas remain within the body of the building codes. The Existing Buildings Subcommittee submitted 30 separate proposals, heard by the ICC’s General and Structural Committees, dealing with such topics as when an existing building must be structurally evaluated or upgraded, as well as the detailed technical requirements of certain evaluation and upgrade means. The requirements for existing buildings are embodied in both the International Building Code (IBC) and International Existing Building Code (IEBC). A major focus of this cycle was the reference of ASCE’s newly reorganized ASCE 31/41 standard, not yet complete, by both the IBC and IEBC. The General Requirements Subcommittee submitted 11 separate proposals to the Structural Committee, addressing requirements associated with roof-mounted, photo-voltaic cells, snow loads, allowable deflections, public assembly classification, crane wheel loads, excavation and stockpiling of earth adjacent to construction, conventional wood construction, and coordination of the risk categories in ASCE 7, with the occupancy categories specified by the building codes. The Quality Assurance Subcommittee submitted 4 proposals, clarifying definitions associated with Quality Assurance requirements for structural observation and load testing of structures. The Seismic Subcommittee submitted 1 proposal associated with anchorage to concrete and clarifying miscoordination of references to ACI 318 Appendix D. Following submittal of proposals, our subcommittees reviewed a total of 445 proposals with potential structural content submitted by others and provided public comment on many of these. This is a major effort by our delegates, lasting several weeks, and is one of NCSEA’s most publicly visible activities. A major part of this effort is coordination between the subcommittees, to make sure that one of our subcommittees does not speak contrary to the position of another of our subcommittees. Our delegates to the code hearings work with their subcommittees and the other subcommittees to develop consensus positions on each proposal. However, the code hearings often involve last-minute, smokefilled room deals between advocates of various proposals, as well as floor modifications made during the hearings. Effective action in this environment requires not only detailed technical knowledge, but also political sensitivity and superior communication skills. Evaluation Services The Evaluation Services Subcommittee has been engaged in two principal activities. One of these consists of participation in an ICC-ES task force, developing acceptance criteria for proprietary, lateral force resisting elements (substitute shear walls such as Simpson Strong Wall, Hardy Frame, etc.) when installed in multi-story configurations or on flexible bases. The second consists of participation with ICC-ES on a task force to review the Simpson Strong Frame submittal for qualification as a Special Steel Moment Resisting Frame. July 2012
Standards Liaisons The CAC maintains active liaisons with the ASCE 7, ASCE 31/41, AISC Committee on Specifications, Masonry Joint Standards, and ACI 318 committees. The most significant activities this year include: • ASCE 7 – initiating the cycle to produce the 2016 edition of the standard. This will include splitting the standard into 2 volumes. Volume 1 will be the basic standard, applicable to all construction and for all loadings. Volume 2, sometimes referred to as “ASCE 7-light”, will contain one simplified procedure for each of the most common loadings, applicable to regular,
low and mid-rise construction in regions of modest environmental hazards. This is a major attempt at simplification of the codes. • ASCE 31/41 – nearing completion of a major effort to combine the two former standards ASCE 31 and ASCE 41 into a single, coordinated standard. Three of our Existing Building Subcommittee members are voting members on the ASCE committee. • ACI 318 – undergoing major reorganization for the 2014 edition. • AISC 341 – The seismic committee of AISC is attempting to pull much of the “how-to” information out of the code and place it in commentary or reference to manuals and texts, while leaving the standard as a “what is required” document. This is also an attempt at code simplification.
NCSEA News
In addition, the Evaluation Services Committee monitors proposals for Acceptance Criteria submitted by others, and provides testimony as appropriate at three hearings per year.
NCSEA 2012 Conference in St. Louis, October 3-6, 2012
Free Wednesday events: All day, visit and sit in on ICC-ES Evaluation Committee meetings. AZZ Tour from 11:30 a.m. – 1:30 p.m., including transportation and lunch: Experience a State of the Art Hot Dip Galvanizing Plant and see how steel is inspected, cleaned, fluxed and then Hot Dip Galvanized. St Louis Plant capacities: Kettle 7' wide x 10' deep x 51' long, 60,000 lb. lifting capacity, parts up to 62' long (depending on height). Ten Vendor Presentations from 1:30 – 5:30 p.m., including software and non-software vendors. Refreshments provided. SECB Reception from 6:30 – 8:30 p.m. Enjoy drinks and hors d’oeuvres, compliments of SECB, and learn more about the program from SECB members and Board members.
Register at www.ncsea.com, and note two special offers for Young Members of local SEA’s (age 35 and younger):
News from the National Council of Structural Engineers Associations
Two full days of continuing education, business meeting on Saturday, exhibits, exhibitor reception on Thursday night, Awards Banquet on Friday night. That almost sums it up, but then there are also several free events going on Wednesday, October 3, in addition to the NCSEA Committee meetings. Come early and enjoy the following:
• NCSEA is offering a 25% discount on registration for all Young Members • NCSEA is awarding at least two fully paid conference registrations to highly motivated Young Members who submit a 1-2 page essay about “How can forming a Young Member Group in my local SEA benefit my career?” Please submit your essay to execdir@ncsea.com by August 1. Essays will be judged by a panel of NCSEA Board members, and winners will be announced by August 10, to allow sufficient time to book economical travel to the conference. Use this opportunity to encourage your young members to take advantage of these new discounts and this year’s reasonable hotel prices ($102/night), to learn what NCSEA is all about and to network with some of the well-known and highly-experienced structural engineers in the profession!
NCSEA Webinars David G. Pollock was recently appointed the Coughlin Distinguished Professor of Structural Engineering in the Civil & Environmental Engineering Department at Washington State University (WSU). Prior to joining the faculty at WSU, Dave was the Director of Engineering for the American Wood Council (AWC) of the American Forest & Paper Association (formerly the National Forest Products Association). He is a co-author (along with Don Breyer, Ken Fridley, and Kelly Cobeen) of the Design of Wood Structures textbook published by McGraw-Hill, and he is a licensed P.E. in Virginia.
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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. Time: 10:00 AM Pacific, 11:00 AM Register at www.ncsea.com. Mountain, 12:00 PM Central, 1:00 PM Eastern.
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Hear David Pollock on July 24 and July 31 July 24: Design Provisions for Lumber & Glulam Beams based on the 2012 NDS This webinar will address the design of wood bending members for moment, shear, bearing, deflection, and long-term creep using either the allowable stress design (ASD) methodology or the load and resistance factor design (LRFD) methodology. July 31: Design of Bolted Connections using the 2012 NDS This webinar addresses the design and behavior of bolted timber connections, as modeled by yield limit equations in the 2012 National Design Specification for Wood Construction (NDS).
COUNCI L
SEI Election Announcement
Structural Columns
The Newsletter of the Structural Engineering Institute of ASCE
Deadline: July 31, 2012 There are ten Governor positions on the SEI Board of Governors: two representatives from each of the four Divisions (Business & Professional, Codes & Standards, Local Activities, and Technical Activities), one appointed by the ASCE Board of Direction, and the most immediate and available Past President of the SEI Board. The representatives from the Divisions each serve a four-year term. This year SEI is conducting an election for a Business & Professional Activities Division (BPAD) and a Codes & Standards Activities Division (CSAD) representative on the Board of Governors. The BPAD and CSAD Executive Committees have nominated David Odeh and Stephen S. Szoke as their respective candidates. In accordance with the SEI Bylaws, each ballot provides a space for a write-in vote. If you are a member of ASCE/SEI please complete and mail the ballots to the address provided. Either vote for the named candidate or provide a write-in candidate. Because we must confirm SEI/ASCE membership, ONLY SIGNED BALLOTS WILL BE ACCEPTED. DEADLINE JULY 31, 2012. David J. Odeh, P.E., SECB, M. ASCE is vice president and principal at Odeh Engineers, Inc. In this position, he is responsible for a wide variety of building structural design projects. His recent work includes a new 21-story Residence Hall for the Massachusetts College of Art and Design in Boston, MA; the structural restoration of the 1681 Old Ship Meeting House in Hingham, MA (among the oldest existing wood frame churches in North America); and a new large scale fire test center for Factory Mutual Research in West Glocester, RI. Since 2001, David has also been on the adjunct faculty of the Brown University School of Engineering, and regularly speaks at professional conferences. He has published articles in STRUCTURE magazine (2006), ASCE Natural Hazards Review (2002), and conference proceedings from the SEI Structures Congress (2005). He recently edited and contributed to a white paper on Building Information Modeling published by CASE (2011). Full Name:
David has served as the co-chair of the ASCE-SEI Building Information Modeling Committee since 2009, and has served on the SEI Business and Professional Activities Division Executive Committee since 2010. He also serves on the Existing Buildings/ Structural Retrofit Subcommittee of NCSEA’s Code Advisory Committee. David was a founding board member and former president of the Structural Engineers Association of Rhode Island. David received a BS in Civil Engineering from Brown University (1992) and an MS in Structural Engineering, Mechanics, and Materials from the University of California at Berkeley (1993). Stephen S. Szoke, P.E., FACI, IOM, LEED/AP, M. ASCE is Director of Codes and Standards for the Portland Cement Association. He graduated with a Bachelor’s of Science Degree in Civil Engineering from Lehigh University. He is licensed as a professional engineer in Virginia and the District of Columbia, Fellow of the American Concrete Institute, and US Green Building Institute Leadership in Energy and Environmental Design Accredited Professional. Steve has been a corresponding member of the SEI CSAD Executive committee since 2001. He is active in the International Code Council code development process and serves on the Industry Advisory Committee. His broad experience includes activities related to the advancement of structural, fire, structural-fire, energy conservation, sustainability, and enhanced resilience concepts. His experience as a leader includes having directed market development programs for the masonry industries, Executive Director of the Southeast Cement Shippers Association, and Past-Chair and Honorary Member of the Sustainable Building Industry Council. Steve participated in the organization efforts of the National Institute of Building Sciences High Performance Building Council and is active on the Multi-Hazard Mitigation Council. He continues leadership roles in ASTM International, American Concrete Institute, and The Masonry Society and holds an Institute for Organization Management certificate from U.S. Chamber of Commerce.
_____________________________________Member’s ASCE/SEI ID No:________________
(Please print)
Date:______________ Signature: _______________________________________________________________
Return postmarked no later than July 31, 2012 to: SEI Board Election, 1801 Alexander Bell Dr., Reston VA 20191.
Business and Professional Activities Division SEI 2012 Board of Governors Election
q David J. Odeh q Write-in vote:_______________________________
Official Ballot
Codes and Standards Activities Division
q Stephen S. Szoke q Write-in vote:_______________________________
STRUCTURE magazine
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The SEI Technical Activities Division Executive Committee awarded the 2012 O.H. Ammann Research Fellowship in Structural Engineering to Ms. Megan McCullough, a Ph.D. student in the Department of Civil & Environmental Engineering at the University of Notre Dame. The fellowship was awarded for her research entitled Data-Driven Models: From Data to Knowledge for Multi-Hazard Engineering.
ATC & SEI Advances in Hurricane Engineering Conference Learning from Our Past
Registration Now Open Miami, Florida
October 24-26, 2012
The O. H. Ammann Research Fellowship in Structural Engineering is awarded annually to a member of ASCE or SEI for the purpose of encouraging the creation of new knowledge in the field of structural design and construction. All members or applicants for membership are eligible. Applicants will submit a description of their research, an essay about why they chose to become a structural engineer, and their academic transcripts. This fellowship award is at least $5,000 and can be up to $10,000. The deadline for 2013 Ammann applications is November 1, 2012. For more information and to download an application visit http://content.seinstitute.org/inside/ammann.html.
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.
ASCE 7 Committee
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.
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. 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 ETS conference website at http://content.asce.org/conferences/ets2012/index.html.
Registration will open in July To see the Technical Program visit the conference website at http://content.asce.org/conferences/ets2012/program.html In-Depth Technical Sessions will be presented by leading industry experts on topics including Aesthetic Design Principles; STRUCTURE magazine
Call for Proposals for the 2016 Edition Deadline extended to December 31, 2012 The Structural Engineering Institute (SEI) of ASCE is currently accepting proposals to modify the 2010 edition of ASCE 7, Minimum Design Loads for Buildings and Other Structures Standards Committee to prepare the 2016 revision cycle of the standard. Interested parties may download the proposal form from the SEI Website at www.asce.org/SEI. The committee will accept proposals until December 31, 2012. For additional information please contact Jennifer Goupil, SEI Director, at jgoupil@asce.org.
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The Newsletter of the Structural Engineering Institute of ASCE
This is the first hurricane conference to focus exclusively on topics of interest to professionals who design, engineer, regulate and build projects in hurricane affected regions. This event will bring together practitioners, educators, federal and state government officials, students, and business leaders from across the nation and around the world. Hurricane engineering has evolved since Hurricane Andrew wreaked havoc on South Florida and Louisiana nearly 20 years ago. Andrew taught us much about how these powerful storms affect our built environment. Much has changed in building codes, standards and products designed to resist the effects from strong hurricanes, and much more needs to be improved upon. Visit the conference website at www.atc-sei.org for more information and to view the technical program.
Structural Columns
2012 Ammann Fellowship Winner and Call for Nominations
Two New Tools from CASE
CASE in Point
The Newsletter of the Council of American Structural Engineers
Tool 4-5: Project Communication Matrix and Coordination Log Poor communication is frequently cited among the top reasons for deteriorated client relationships and claims. It is the intent of the Project Communication Matrix and Coordination Log tool to make it easier to maintain consistent project communication standards, and to document and communicate project coordination decisions. This Excel-based tool, which is easily adaptable for each individual firm’s needs, provides an easy to use and efficient way to (1) establish and maintain project-specific communication standards, and (2) document key project-specific deadlines and program/coordination decisions that can be communicated to a client or team member for verification.
Tool 5-4: Negotiation Talking Points
This tool provides an outline of items to consider during fee negotiations for private sector and for public sector projects. The tool offers suggestions of what to do and what not to do in different sets of circumstances, and provides reminders of ethical and professional obligations that must be kept in mind during these negotiations. CASE Tool 4-5 and 5-4 are available at www.booksforengineers.com.
Legislative Update The Disaster and Emergency Response Protection Act of 2012 Ready to be Introduced in the 112th Congress Protecting public health and the lives and property of unfortunate victims of disasters and emergencies is at the heart of structural engineering. Structural Engineers design structures that are disaster resilient and, after a disaster, work quickly to determine their condition and usability. It is in the national interest to encourage design and construction professionals to respond, since government institutions do not have sufficient resources. Unfortunately, 9/11 and Katrina have taught us that there can be unfortunate and unearned liability in the mere fact that we responded. The lawsuits that followed those events effectively told the experts to stay home. ACEC stepped in to help at the request of CASE and the member firms that were affected by the lack of liability protection. Working with a diverse group of potential responders and legal counsels, ACEC’s Government Affairs group drafted the Disaster and Emergency Response Protection Act of 2012 and is currently working to secure congressional sponsors. The bill recognizes the needs and provides the necessary legal protection against enterprise-threatening liability and costs. With this protection, entities with the know-how will step up and help federal authorities respond to disasters and emergencies. This is not a Good Samaritan Bill; rather it covers all consulting work done for pay as well as pro-bono during the emergency period. The legislation recognizes that design professionals who are working in challenging conditions, with limited information and under tight time constraints because lives hang in the balance, play a vital role in disaster and emergency response and recovery STRUCTURE magazine
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efforts. They assess the safety of buildings and other structures that police officers, firefighters, and other rescue workers must enter. They determine the soundness of levees, bridges, and other components of our national infrastructure upon which thousands of lives depend. They also guide the mitigation of conditions that threaten life and property. The Disaster and Emergency Response Protection Act of 2012 as drafted would extend legal protection to qualified architectural and engineering firms. The bill would: • Create an exclusive federal cause of action for claims of death, injury or business or property loss proximately resulting from the deployment of architectural or engineering technology or services during responses to or recovery from declared federal disasters or emergencies; • Include all actions taken within the area of practice expertise of the participant; • Provide legal immunity to registered architects or licensed engineers and their firms as long there was no fraud or willful misconduct; • Require engineers and architects to be properly licensed in a state or territory in order to be eligible for legal protection, meeting all of the educational requirements to receive and maintain a license and passing all licensure examinations; • Require firms responding to disasters or emergencies to carry liability insurance. The full text of the draft legislation is available from ACEC’s Katharine Mottley (kmottley@acec.org). Your comments on the draft language and support of the bill when introduced are welcome and encouraged. July 2012
CASE Convocation at the ACEC Fall Conference On October 14-17, 2012, ACEC is holding its Fall Conference in Boca Raton, FL. CASE will be holding its convocation on Monday, October 15th. Sessions will include: Seismic Assessment Repair and Design: Washington Monument and National Cathedral, Daniel J. LeMieux & Eric Sohn, Wiss, Janney, Elstner Associates, Inc., Project Risk Management Plans, Stephen Cox, GHD, and Risk Management Essentials for Structural Engineers, Randy Lewis, CPCU, XL Group.
You can follow ACEC Coalitions on Twitter – @ACECCoalitions.
LinkedIn is a great virtual resource for networking, education, and now, connecting with CASE. Join the CASE LinkedIn Group today! www.linkedin.com.
CASE Announces the 2012 CASE Scholarship Winner Since 2009, the CASE Scholarship has helped engineering students make positive steps towards a bright future in structural engineering. The CASE Scholarship, administered by the ACEC College of Fellows, is awarded to a student pursuing a Master’s degree in Structural Engineering. CASE strives to attract the best and brightest to the structural engineering profession and educational support is the best way we can ensure the future of our profession. The 2012 winner, Eric Grusenmeyer, will graduate in December with a combined M.S./B.S. in Architectural Engineering with a Structural Emphasis from Kansas State University.
CASE Business Practice Corner If you would like more information on the items below, please contact Ed Bajer, ebajer@acec.org.
The Project May Not Be Risky but the Contract Could Be Some DOT’s are considering requiring project professional liability policies for larger projects. They use a list of cost and complexity factors, with each risk being assigned a dollar value, and give a project a risk rank. Agencies are subject to economic conditions like everyone else, and requiring these policies could be a factor in limiting the number of projects they take on. Also, known professional limits could increase unreasonable damage demands. There are many ways to determine risk, address it in the contract, and have adequate insurance limits.
Small Bank Financing Despite the current credit crisis in the U.S., there appears to be plenty of cash available to business borrowers. Small banks particularly see this time as an opportunity to wrest some STRUCTURE magazine
business from larger institutions that are currently saddled with problem loans and limiting their lending activity. However, even from small banks you can expect more scrutiny and a return to lending practices as they were before the liberal loan era. Also expect the terms to be tighter with more collateral required.
What I Meant to Say in the Contract was… Clients will sometimes contend that the contract was supposed to say something that it did not say. It is a longstanding principle of contract law that a written agreement supersedes all prior oral agreements or understandings. You and your client should review the final agreement to assure it says what you meant it to say and contains all your intentions as to your services. Contracts should contain an “integration” clause that says, in effect, the agreement is final and complete and supersedes all previous written or oral communications.
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CASE is a part of the American Council of Engineering Companies
CASE is on LinkedIn
ACEC’s program will include: • CEO Insights on Firm Growth and Profitability • Industry Economic Update – Where is the Movement for 2013? • Tour of the Everglades and learn about the Federal Government Restoration Project • The Annual ACEC PAC Golf Tournament For more information, go to www.acec.org.
CASE in Point
SAVE THE DATE
Structural Forum
opinions on topics of current importance to structural engineers
A Structural Engineer’s Manifesto for Growth Part 4
By Erik Nelson, P.E., S.E.
T
The most important part of my day as an engineer is lying in bed for about 20 minutes or so after slowly and naturally waking up from sleep. Not only do I lay out my work day, I literally solve engineering problems in my head. I can view the entire project, rotate it in my mind, find problems with the design, prioritize where I need to focus, and improve the design. I can think better because part of my subconscious is still present consciously; it has not yet scurried to the back of my brain. I am grateful for projects that last more than one day because I will be able to sort them out in the morning. Try not to finish deadlines at 7 p.m., finish them at 7 a.m. the next day. In Gorden Glegg’s The Design of Design, we find the following: History tells us that artists in various fields from music to mathematics, their key inspiration came suddenly and unexpectedly and never when they were working at it... Concentration and then relaxation is the common pattern behind most creative thinking. So, make sure that you have time for reflection (not “working”) and it will be the best work you did that day.
just wandered in there themselves and somebody had handed them a wrench. There was no identification with the job. No saying “I am a mechanic.” What Pirsig is suggesting is that this guy was not a mechanic, he was an idiot. We have among us plenty of idiots, too; plenty of spectators who follow procedures or are slaves to the status quo, non-thinkers. But engineers, like mechanics, are not spectators. Engineers actively engage projects to reveal solutions to problems or yield new ideas. Matthew Crawford, in the terrific book Shop Class Is Soulcraft, describes the difference between an expert mechanic and an idiot: The forensic perceptual expertise of the engine builder is active in the sense that he knows what he is looking for. But with the idiot we see the result of a premature conceit of knowledge. An engineer, like a master mechanic, is selfreflective and constantly aware of the possibility of making a mistake. Before taking a hammer to the problem, the engineer reflects and asks questions regarding the design solution; questions such as, “Is this the best solution of all the possibilities?” or “Am I correct in assuming that this can be treated this way?” Since problems in engineering are rarely simple or straightforward, it takes a high level of self-reflection, teamwork, and attentiveness. Since our mistakes live as long as we do, it also takes great deal of humility. The best of us recognize that these mistakes are lifelong reminders that we are at times idiots, too, just like everyone else. So we need to succeed in reducing idiocy by being attentive and by participating actively in every project.
19: Succeed in Reducing Idiocy
20: Worry is OK
Robert Pirsig complained about a bad motorcycle mechanic when writing Zen and the Art of Motorcycle Maintenance. After dropping off his bike at a shop, the mechanic immediately misdiagnosed the problem. He started pounding the engine head with a chisel, breaking off two of the cooling fins. This made the problem worse. Pirsig later thought to himself: Why did they butcher it so? They sat down to do a job and they performed like chimpanzees. Nothing personal in it ... they were uninvolved. They were like spectators. You had the feeling they had
Worrying about your design will make you better. You will be better able to prioritize which parts of the project need more attention. James Gordon, in his book Structures, writes: When you have got as far as working drawings, if the structure you propose to have made is an important one, the next thing to do, and a very right and proper
his is the fourth and final installment of what I am calling my manifesto, which presents some of my thoughts about our profession and how we can grow as individual designers. For steps 1-17, please see Parts 1-3 in the April, May and June issues of STRUCTURE®.
18: Throw Away Your Alarm Clock
thing, is to worry about it like blazes. . . it is confidence that causes accidents and worry that prevents them.
21: Draw 1 to 1 Scale Drawing on a one-to-one scale will help you make a better design decision on a particular component of a project. Try drawing a 6×6 wood post on paper with the joist hanger, or 4x4x5/16 steel framing angle with bolts to scale. See if the bolts will fit and get into the code on bolt length (shank, threads, tension control bolt tips, etc.).
22: Buy Samples of Typical Structural Components Go to the nearest hardware store and buy stuff to have in your office while you design on the computer. Having the material in your hand is the best way to proportion members later on the computer. Visit my blog for some recommendations of samples (rebar, CMU, wood, etc.). Display these proudly in the office for all engineers to see. These real components are vital to being able to make informed structural design decisions.
23: Build Physical Models The computer will never replace the importance of a physical model out of cardboard, balsa wood, paper, glue, etc. Architects build these all the time; we should, too.
Conclusion As I stated at the very beginning, this manifesto will always be a work in progress. There will be more ideas on how to grow as individual designers and as engineering communities. My blog (www.structuresworkshop.com/blog) contains more clarification and images for each of the steps. Please visit and provide feedback so that I can improve them, or provide new suggestions of what I can add.▪ Erik Anders Nelson, P.E., S.E. (ean@structuresworkshop.com), is owner of Structures Workshop, Inc. in Providence, RI. He teaches one class per semester at the Rhode Island School of Design and Massachusetts Institute of Technology.
Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C 3 Ink, or the ® STRUCTURE magazine Editorial Board.
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