STRUCTURE magazine | January 2012

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

Special Section: Anchors, Piers, Foundations

January 2012 Concrete

NCSEA Winter Institute New Orleans, Louisiana February 10 –11

and Underground Construction

SEISMIC ACTIVITY IS NOT JUST A WEST COAST PHENOMENON

Don’t Take A Risk With Mother Nature Natural disasters have been in the news lately. Both here in the U.S., and abroad, Mother Nature has been reminding us that earthquakes are not just a “ring of fire” occurrence but can happen anywhere, anytime.

That’s why in the United States our building codes have been updated to take into account earthquakes, hurricanes, tornados and other seismic activity.

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Five Reasons to Choose Wood for Your Next Project Wood provides more value—in terms of its beauty, design flexibility and environmental attributes—for less cost than other major building materials, all while meeting fire, safety and other code requirements.

1. Wood costs less – In addition to lower material costs, wood building systems typically cost less to install than other materials. Wood construction is fast, and wood’s relative light weight reduces the need for foundation capacity and associated costs.

2. Wood structures meet code – The International Building Code recognizes wood’s safety and structural performance capabilities and allows its use in a wide range of building types—from multi-story condominiums and offices to schools, restaurants, malls and arenas.

3. Wood performs well in earthquakes and high winds – Because wood-frame buildings are lighter and have more repetition and ductility than structures built with other materials, they are very effective at resisting lateral and uplift forces.

4. Wood is versatile and adaptable – Wood’s design flexibility lends itself both to traditional and innovative uses. With the exception of major members that are made to spec off site, wood can be adapted in the field, allowing quick solutions if changes are required. Wood is also well suited to additions and retrofits, and wood systems can be dismantled with relative ease and the materials used elsewhere.

5. Using wood helps reduce your environmental impact – Wood is the only major building material that grows naturally and is renewable. Life cycle assessment studies also show that wood buildings have less embodied energy than structures made from steel or concrete, are responsible for less air and water pollution, and have a lighter carbon footprint.

Photos: Top - Mid-rise wood building, VanDorpe Chou Associates, Inset - Rosa Parks Elementary School, Benjamin Benschneider

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FEATURES Innovative Reinforcing Gives Old Structure New ‘Light’

26

By B. Keith Brenner, P.E.

Maine Health was faced with adapting an existing 89,000 square foot building to house all of its corporate and administrative operations, currently scattered about the city of Portland, Maine. Architects and engineers were challenged with how to adapt the outdated 1946 concrete structure to a modern facility for all its employees.

31 Special Section

Anchors, Piers, Foundations and Underground Construction

By Larry Kahaner

In a still weak economy, some foundation companies are exploiting recent trends and events to improve their bottom line.

ASCE 7-10 Wind Provisions and Effects on Wood Design and Construction

By Mo Ehsani, Ph.D., P.E., S.E., Majid Farahani, P.E. and Eric Raatz, P.E.

By Philip Line, P.E. and William L. Coulbourne, P.E.

39 Education Issues

50 Structural Forum

Resolution of Deficiencies in Engineering Education

A Young Professional’s Perspective on Structural Licensing

By Greg Cuetara, P.E., S.E.

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

ON Special Section: Anchors, Piers, Foundations

January 2012 Concrete

and Underground Construction

THE

COVER

After the dream of a new building fell through, Maine Health was challenged with how to adapt an existing 1946 concrete structure to a modern facility. This project demonstrates the ability to use contemporary products to revitalize outdated structures.

See more about this project in the feature article on page 26.

Have you noticed those weird square graphics on some of the articles in this issue of STRUCTURE? Beginning with the January 2012 issue, STRUCTURE now includes QR codes with articles, linking to their online PDF. To scan a QR code, you need to download a free code reader application to your phone. So, the next time you read a great article in STRUCTURE, scan the code, then email the link to your colleagues! And, if an advertisement strikes your interest, there may be a quick link available in a QR Code on the ad.

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

7 Editorial My Company’s COOP is in the Cloud

By John A. Mercer, P.E., SECB

9 InFocus The Structure of Reason

By Jon A. Schmidt, P.E., SECB

10 Construction Issues Internal Curing

By Jason Weiss, Dale Bentz, Anton Schindler, P.E. and Pietro Lura

By John “Buddy” Showalter, P.E., Bradford K. Douglas, P.E., Philip Line, P.E. and Peter Mazikins, P.Eng

20 InSights Model Energy Code Development

By Kenneth E. Bland, P.E. and Dennis L. Pitts

23 Structural Forensics Unstable Shelves Put the Shake in Shakespeare

By Betsy Wilkinson, P.E., S.E. and Alberta Comer

®

By Kevin Dong, P.E., S.E.

COLUMNS

2012 NDS Changes

40 Code Updates

Repair of Columns with FRP Laminates

January 2012

14 Codes and Standards

DEPARTMENTS 35 Product Watch

CONTENTS

5

January 2012

28 Structural Practices Concrete Specifications Education

By Renee Doktorczyk

IN EVERY ISSUE 8 Advertiser Index 43 Resource Guide (Anchor Updates) 44 NCSEA News 46 SEI Structural Columns 48 CASE in Point

Envelope Connections and Compatibility AIA/CES module for Enclosures and Cladding¹ says: 1

“A continuous air barrier…… must seamlessly connect to the lowest slab on grade, foundation, and roof. This requires compatible materials and close coordination among the trades.”

2

“Of the many different connection points, one that requires the most careful detailing and is most often subject to failure, is the interface between the air/moisture membrane and window openings, curtain walls, or storefront framing edges.”

1. Enclosures and Cladding AIA/CES Module, www.BDCnetwork.com/EnclosuresAndCladding

AIR BARRIER

Polyguard has compiled a comprehensive book, Integrated Building Envelope™ Handbook – Connections with Exterior Wall Assemblies. This handbook (available to the design community at www.polyguardproducts.com/aat) describes the all important tie-in connections using isometric drawings and installation text.

WALL SYSTEMS

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DRAINAGE

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It’s not just about good air barriers and flashings. It’s about compatible, inexpensive, easy to install and single source end dams, cants, corner boots, corner flashing kits, drips, counters, thru wall and pan flashings, flared termination strips, horizontal and pan weeps, bottom and top vents, rain screens and pressure equalizing rain screens. AND it’s about clear and simple drawings, details, and instructions.

Work with Polyguard.

We’re the ones with the connections.

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Editorial

My new trends, Company’s new techniques and COOP current industry is in issuesthe Cloud John A. Mercer, P.E., SECB

S

ubsequent to September 11, 2001, I initiated an effort to create high security data centers in North Dakota. There are many variables that need consideration in site selection. One of these is seismic risk. For a 99.999% uptime facility, every opportunity to minimize a risk variable becomes important. The Seismic Risk Map to the right illustrates the strength of North Dakota.

I learned that many of the major data centers around the country were, and still may be, located on or near seismic faults. The thing about a seismic event is that you cannot escape the impact of the devastation of support infrastructure that is brought about regionally. Utilities, power, and other inputs to keep a data center and its operations and operators going isn’t as easy as having a diesel power unit kick-in when the grid power source is interrupted. There are other dimensions to the problem.

I made several trips to Washington D.C. to meet with my congressional delegation, resulting in a meeting with the CIO of the Treasury Department. She graciously received me and spent about an hour and a half visiting with me about the project. She stated…

“I’m in the bull’s eye” referring to the Treasury Department’s office building that is located one block away from the White House.

Treasury’s information assets were being relocated as we spoke.

In our conversations, “Continuity of Operations” came up a lot.

She mentioned that there were sights outside of the beltline that had been prepared for staff to retreat to in order to keep the government operational. All of this was predicated on the chance that there would be a devastating natural or man-made event. Well, terrorists had taken their shot, and then hurricane season intermittently impacted the D.C. area over the next few years. What is going to happen when a seismic event hits the Canary Islands and the Tsunami hits the east coast?

As a result of my efforts, I am probably more knowledgeable about computer networks and the operations of such enterprises than the average structural engineer. The journey was fun to follow, as I got to use the creative side of my brain to both understand the IT world as well as to develop criteria for a high security sight. I wasn’t alone in this effort, as I had selected qualified fellow ACEC firms in a virtual design team with credentials necessary to catch the imagination of government agencies and private sector organizations.

Fast forwarding, today my office has a powerful RAID 5 server collecting all of our business management data and integrates with the accounting system. It actually makes the capturing time and expenses for billing projects a fun process.

Recently, I added the Cloud to our internal network. I now see that the Cloud has opened many more opportunities for me as a small firm. With the advent of the Web App, I can record my time and expenses wherever I go provided WiFi is available. I’m no longer tied to the desktop to do data entry into the business management and accounting system. Effectively, I can do it in real time. In reality, I have the best of both worlds.

One of the greater benefits is that I now have a remote backup of my business management system, off sight, in the Cloud.

Currently not quite as robust a system as the desktop, the web based system has solved one of my internal office issues of backing up the data. Not only does my server have a RAID 5 data

STRUCTURE magazine

Courtesy of W. Gene Corley, 2001.

storage configuration for the SQL database, it has a state of the art removable internal cartridge drive that I can physically take with me, when I remember it. The problem is that when you wear all of the hats, it is often difficult to remember to exchange the cartridge drives and take them with you.

You may have attended seminars where the speaker discusses the Work Flow Process to get the timecard information into the accounting department so it can be input into the system and the Project Managers can have a timely report on their several projects. I sat in multiple seminars on how to make the Project Managers more effective. Too often they just don’t get reports soon enough to make a difference.

It is my observation that the Cloud may be a possible answer to correct or solve this issue for most firms. Today each employee can input time and expenses from their laptops, smart phones and tablets with a WiFi connection. Synced up to the main database, the Cloud data will allow the Project Manager to check a job’s status daily. With new project delivery systems being implemented, it will be imperative that a more robust approach to collecting and processing the data will be necessary to keep the business process going. Ongoing training will also be necessary to get employees to keep their time and expenses entered into the system.

So what does this have to do with COOP? Well, in the situation of a disaster in my office, I feel more confortable that I will be able to sit in Starbuck’s and have a latte while I continue my services using my laptop, tablet, or smart phone to conduct necessary business activities.

Disaster is all around us waiting to happen. Are you prepared?▪ 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

January 2012

Advertiser index

PleAse suPPort these Advertisers

Bentley Systems, Inc. ............................. 19 Computers & Structures, Inc. ............... 52 CTS Cement Manufacturing Corp........ 41

IRVINE INSTITUTE OF TECHNOLOGY C.V. Chelapati, Ph.D., P.E., F.ASCE

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Fyfe ....................................................... 25 Geopier Foundation Company.............. 33 Halfen USA, LLC ................................. 22 Hayward Baker, Inc. .............................. 34 Hohmann & Barnard, Inc. .................... 38 Integrated Engineering Software, Inc..... 43 Irvine Institute of Technology.................. 8 ITW Red Head ..................................... 42 KPFF Consulting Engineers .................. 32 LiteSteel Technologies ........................... 29 NCSEA ................................................. 11

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.

CBI Consulting, Inc., Boston, MA

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

BergerABAM, Vancouver, WA

American Wood Council, Leesburg, VA

Faculty Position in Structural Engineering

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

Advertising Account MAnAger 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

Interactive Sales Associates

5/10/2011 P.E., 2:33:39SECB PM Jon A. Schmidt,

ertisement.indd 1

Pile Dynamics, Inc. ............................... 31 Polyguard Products, Inc........................... 6 Powers Fasteners, Inc. .............................. 2 QuakeWrap, Inc. ................................... 37 RISA Technologies ................................ 51 Simpson Strong-Tie............................... 17 StrucSoft Solutions, Ltd. ......................... 3 Struware, Inc. ........................................ 15 Subsurface Constructors, Inc. ................ 30 Univeristy of Notre Dame ....................... 8 Wood Products Council .......................... 4

The Department of Civil Engineering and Geological Sciences at the University of Notre Dame (cegeos.nd.edu) invites applications for a full-time tenure-track or tenured position in structural engineering to complement the existing faculty. Qualified candidates at all levels (assistant, associate, or full professor) will be considered, with hiring rank and tenure status commensurate with academic accomplishments.

The successful candidate must hold a doctoral degree in an appropriate field and must demonstrate potential for high quality research and teaching. The existing faculty has significant strength in natural hazard risk mitigation and sustainable civil infrastructure. In accordance with these strength areas, the department is seeking an outstanding faculty member with a research focus on, but not limited to: infrastructure systems, high-performance and sustainable civil structures, reliability and performance of structures under extreme loading, innovative materials, computational mechanics, and foundation-structure interaction. Candidates for the position should be qualified to teach civil engineering courses, with a strong commitment to teaching excellence at both the undergraduate and graduate levels. The successful faculty candidate is expected to develop and sustain an externally funded research program and publish in leading scholarly journals. Applications should be submitted online at struct.nd.edu as a single PDF with cover letter, detailed CV, statements of research and teaching, and names and contact information for three references. Review of applications will start immediately and continue until the position is filled. The University of Notre Dame is committed to diversity in education and employment, and women and members of underrepresented minority groups are strongly encouraged to apply.

The University also supports the needs of dual career couples and has a Dual Career Assistance Program in place to assist relocating spouses and significant others with their job search.

Inquiries related to this search can be directed to Dr. Yahya Kurama at struct@nd.edu.

STRUCTURE magazine

8

January 2012

editoriAL stAFF Executive Editor Jeanne Vogelzang, JD, CAE

execdir@ncsea.com

Editor

Christine M. Sloat, P.E.

publisher@STRUCTUREmag.org

Associate Editor Graphic Designer Web Developer

Nikki Alger

publisher@STRUCTUREmag.org

Rob Fullmer

graphics@STRUCTUREmag.org

William Radig

webmaster@STRUCTUREmag.org

STRUCTURE® (Volume 19, Number 1). 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

reproduced in whole or in part without the written permission of the publisher.

National Council of Structural Engineers Associations www.ncsea.com

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A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 P-608-524-1397 F-608-524-4432 publisher@STRUCTUREmag.org

Visit STRUCTURE magazine magazine on-line at Visit STRUCTURE online Visit STRUCTURE magazine on-line at at www.structuremag.org www.structuremag.org www.structuremag.org

inFocus

new trends, new techniques and current industry issues The Structure of Reason

By Jon A. Schmidt, P.E., SECB

A

braham Lincoln is widely regarded as one of the most eloquent and persuasive speakers in American history.

What was the secret of his success?

Many scholars over the last 150 years have sought to answer this question. It was not some kind of special training; in fact, he was almost entirely self-educated, having received only a year (at most) of formal schooling. It was certainly not his style of delivery or any unusual charisma that he possessed; on the contrary, firsthand observers typically characterized his appearance and manner as somewhat awkward, and his voice as high-pitched and even unpleasant.

A new book, Abraham Lincoln and the Structure of Reason (New York: Savas Beatie, 2010), purports to unlock this mystery. The authors – David Hirsch, an Iowa attorney, and Dan Van Haften, an Illinois engineer who also has degrees in mathematics – posit that Lincoln ingeniously adapted the classical format of a geometrical demonstration to language. They cite what he once told a friend: “At last I said to myself, ‘Lincoln, you can never make a lawyer if you do not know what “demonstrate” means,’ and so I worked until I could give any proposition of the six books of Euclid at sight.”

Hirsch and Van Haften quote a commentary on Euclid by Proclus, a fifth-century Greek philosopher, to define the six elements of a proposition: 1) The enunciation states what is given and what is being sought from it.

2) The exposition takes separately what is given and prepares it in advance for use in the investigation.

3) The specification takes separately the thing that is sought and makes clear precisely what it is.

4) The construction adds what is lacking in the given for finding what is sought.

5) The proof draws the proposed inference by reasoning scientifically from the propositions that have been admitted.

6) The conclusion reverts to the enunciation, confirming what has been proved.

They then identify eight principles for transferring Euclid’s approach: 1) The elements of a proposition build sequentially.

2) Although one may work to make both the learning process and demonstrations as short as possible, they abide no shortcuts.

3) Axioms must be clearly understood.

4) Many steps are small, but all are necessary; none can be skipped.

5) The fewer the steps, the more elegant the demonstration.

6) Although many steps are simple, occasionally dramatic or creative steps must be made.

7) Each step must be precisely stated so that the demonstration is understandable and correct.

8) When the conclusion of a proposition is stated, the demonstration is complete, and further words generally are counterproductive.

Finally, the authors provide some additional guidelines for those who wish to emulate Lincoln’s method: • Enunciation – begin by reciting relevant, assumed, noncontroversial facts.

STRUCTURE magazine

• Exposition – present key, high-level background information.

• Specification – make a clear affirmative statement of the proposition to be proved.

• Construction – marshal the evidence that the investigation has produced.

• Proof – lay out a straightforward case, avoiding argumentative language until this stage.

• Conclusion – restate what is proved concisely and forcefully.

The book contains an extensive collection of Lincoln’s speeches and writings, which Hirsch and Van Haften have “demarcated” – that is, subdivided into the six elements of a proposition. These include not only famous examples like “A House Divided,” the Gettysburg Address (www.thestructureofreason.com/the-gettysburg-address/ the-gettysburg-address-demarcated), and the Second Inaugural, but also lesser-known works and numerous letters. The authors thus provide compelling illustrations showing that this was indeed Lincoln’s own methodology, whether he was explicitly conscious of it or not.

Abraham Lincoln “found out what ‘demonstrate’ meant” from Euclid and cleverly applied that knowledge to achieve an unparalleled clarity of expression that more than compensated for his perceived lack of rhetorical gifts. He was eloquent and persuasive because the structure of his presentations closely matched the structure of reason.▪

The Reasoning of Structural Engineers?

As I have written previously (“Engineering as Willing,” March 2010), I believe that engineering is more intentional than rational, since it routinely involves selecting a way forward from among multiple options when there is no one “right” answer. Even so, I see parallels between the Euclidean elements of a proposition and what William Addis calls a design procedure (“The Nature of Theory and Design,” May 2009). For the enunciation, exposition, and specification, the client requirements, applicable codes and standards, and time and cost constraints constitute the given, and the completed project is what is being sought. The construction is the engineer’s artful development of a suitable model, and the proof is the deterministic analysis showing that the structure will provide adequate strength and serviceability (justification). The conclusion is what is conveyed in the contract documents (description).

Join the Conversation The SEI Engineering Philosophy Committee is meeting and sponsoring a session on “Demarcating the Profession: Where Should We Draw the Line?” at the 2012 Structures Congress in Chicago. For more information, please contact the author.

Jon A. Schmidt, P.E., SECB (chair@STRUCTUREmag.org), is an associate structural engineer at Burns & McDonnell in Kansas City, Missouri, and chairs the STRUCTURE magazine Editorial Board. The text of this column is intended to manifest the six elements of a proposition in the proper sequence; it is left as an exercise for the reader to demarcate it accordingly.

9

January 2012

Prewetted LWA External water

discussion of construction issues and techniques

Water penetration

ConstruCtion issues

Normal Aggregate

Conventional (External) Water Curing

Cured Zone

Internal Curing with Prewetted Lightweight Aggregate (LWA)

Figure 1: Comparison of external (conventional) and internal curing using pre-wetted lightweight aggregate (LWA) (*Note that in practice the prewetted lightweight aggregates are placed sufficiently close to enable the cured zones to overlap allowing the entire paste to be cured)

Internal Curing Constructing More Robust Concrete

By Jason Weiss, Dale Bentz, Anton Schindler, P.E. and Pietro Lura

I

t is often said that there are two types of concrete: concrete that has cracked and concrete that is going to crack. Unfortunately, this is true all too frequently. Many of these unwanted cracks develop shortly after the concrete is placed and, in addition to being unsightly, can contribute to reduced long-term durability. This cracking may be attributed to the fact that, unlike many other materials that are prepared in factories under relatively well controlled conditions, a large proportion of concrete is cast on site under a wide range of climatic conditions (wind, temperature, relative humidity). This article reviews some promising research that is reengineering conventional concrete mixtures to make them more robust, (defined by Webster’s Dictionary as capable of performing without failure under a wide range of site conditions) for field construction.

The Importance of Concrete Curing

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

To begin, remember that concrete is a nonhomogeneous material consisting of aggregate in a cement paste matrix. While the cement paste is initially a fluid suspension, it reacts (hydrates) over time causing it to solidify, thus binding (gluing) the aggregates together. If water is lost from the paste due to evaporation at early ages, there are two main consequences. First, the hydration reaction will slow and ultimately stop, which limits strength development and produces a more permeable material when compared with a

sample that did not lose water. Second, the loss of water causes concrete to shrink and, if restrained, the concrete develops stresses that may lead to cracking. Conventional concrete construction relies on curing to reduce the potential for water loss. Some conventional approaches add water to the concrete surface (i.e., water ponding or misting) which can be absorbed (Figure 1), while other approaches focus on minimizing moisture loss (evaporation retarders, curing compounds, or plastic sheeting). Differences between providing additional water and preventing moisture loss become increasingly important for lower water-to-cement ratio (high-performance concretes), since they self-desiccate (loss of water in the concrete due to hydration which is similar to the effect of drying) as a result of hydration causing a (autogenous) shrinkage even without external moisture loss.

While curing is commonly specified in concrete construction, it is an additional step that is all too often overlooked or done inadequately. Further, when long curing times are specified, the construction process can be slowed substantially. This may be the case, for example, when large volumes of supplementary cementitious materials (SCMs) are used. As a result, research has focused on determining whether curing can be changed from an external process to something that happens inside the concrete mixture. This new approach is called internal curing.

What is Internal Curing?

Internal curing has been defined by the American Concrete Institute (ACI) as “supplying water continued on page 12

10 January 2012

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Figure 2: The relationship between the amount of internal curing provided (amount of LWA) and the age of cracking.

Figure 3: A plot of stress development in restrained concrete at early ages for conventional and internally cured concrete.

throughout a freshly placed cementitious mixture using reservoirs, via pre-wetted lightweight aggregates, that readily release water as needed for hydration or to replace moisture lost through evaporation or self-desiccation”. While lightweight aggregate is discussed in this article and is the most common method used as a water reservoir, researchers throughout the world are also investigating the use of superabsorbent polymers and natural fibers. Differences between conventional (external) curing and internal curing are shown in Figure 1. While external curing water is applied at the surface and its depth of penetration is influenced by the quality of the concrete, internal curing enables the water to be distributed more equally throughout the cross section.

While designing concrete specifically to provide internal curing is relatively new, the concept of lightweight aggregate improving the hydration of the cement paste was observed in the 1950s by Paul Klieger. Research on intentionally using lightweight aggregate for internal curing began to take shape in the late 1990s when a variety of research groups, primarily in Europe, began actively investigating whether mixtures could be designed with internal curing by using pre-wetted lightweight aggregates. Design procedures were then developed that enabled both the spatial distribution and amount of pre-wetted lightweight aggregate to be computed (Bentz et al. 2005).

A review of the details on many of these developments can be found in the RILEM 2007, and Bentz and Weiss 2011. Internal curing is becoming a mature technology, and its use is increasing since it provides great opportunities for a robust concrete construction. Some benefits of internal curing as it relates to reducing the potential for cracking are described in the following section.

Plastic Shrinkage Cracking Concrete can be susceptible to cracking (frequently called plastic shrinkage cracking) at the time of placement, if the evaporation rate is high (i.e., dry windy days). To understand how internal curing helps reduce the likelihood of plastic shrinkage cracking, it is important to review the key basic concepts associated with plastic shrinkage of concrete. Immediately after placement, the concrete system is in a fluid state and the aggregate and cement particles tend to settle due to gravity, simultaneously allowing pore fluid (water) to appear at the surface. This is commonly observed in practice as “bleed water.” This thin layer of bleed water covers the surface of the concrete and evaporates at a relatively constant rate, provided

STRUCTURE magazine

the environmental exposure conditions remain relatively constant.

After some time, the rate of settlement dramatically reduces as the particles contact each other. In conventional concrete, the stresses will rise relatively dramatically during this period. In internally cured concrete, however, the pre-wetted LWA will provide water on demand to replenish the water evaporating from the surface of the concrete. This keeps the pores within the hydrating cement paste fluid filled and thus helps to reduce or even eliminate the capillary stress, minimizing the likelihood of cracking. While the use of water-filled LWA is beneficial in reducing the potential for plastic shrinkage cracking and reducing the width of any cracks that do develop, it should be noted that any water consumed in this phase will not be available later to reduce autogenous and/ or drying shrinkage.

Thermal, Autogenous, and Drying Shrinkage Cracking Internal curing has the ability to reduce autogenous (sealed curing) shrinkage or to delay drying shrinkage (provided water has not been lost during the plastic shrinkage phase). By reducing the shrinkage, internal curing enables unwanted cracking to be delayed or eliminated.

Figure 2 (after Schlitter et al. 2010) shows an example of how the age of cracking can be delayed or prevented when internal curing is used (i.e., volume of pre-wetted LWA is used). As the volume of prewetted LWA increases (i.e., the internal curing provided), the age of cracking is delayed, until an asymptote appears to be reached when sufficient LWA has been added.

By reducing the autogenous and drying shrinkage, internally cured concrete can also provide concrete with the ability to undergo greater temperature variations before cracking. Figure 3 shows a comparison of the stress that builds up in a concrete mixture when shrinkage is restrained as compared with the tensile strength of that concrete. The stress that can be applied to the concrete from mechanical or thermal loading is the difference between the stress and the strength (called the reserve capacity, which is shown by the green arrows). Schlitter et al. (2010) quantified the importance of increasing the reserve capacity by showing that no cracking occurred in internally cured specimens during the first 72 hours, even when the temperature was reduced by as much as 32°C (58° F), while the equivalent plain specimens cracked when the temperature was reduced by only 10°C to 12°C (18° to 22° F).

This shows a substantial increase in the potential early-age robustness

12

January 2012

of the conventional concrete, the conventionally and internally cured concrete had equivalent strengths at approximately 10 days, while after 3 months, the internally cured concrete was 20% stronger than the conventional concrete. Rapid chloride permeability testing showed that the internally cured concrete had a 10% lower charge passed at 28 days and nearly 40% lower charge passed after 3 months. There is also evidence that internal curing reduces curling since it provides a more uniform moisture distribution throughout the concrete section.

It was also notable that cracks developed in the conventional deck after the first few months of service, while at the time of this article (nearly one year after placement), the internally cured concrete has no visible cracking. While cracking can occur in bridges for a variety of reasons, the lack of visible cracking in the internally cured deck is consistent with the reduction in the concrete’s autogenous and drying shrinkage.

Concrete Stress (MPa)

3

Tension 2 1 0

Conventional Concrete Internally Cured Concrete

-1

Compression

-2 0

24

48

72

Age of Concrete (h)

96

120

Figure 4: A plot of stress development in simulated bridge decks for conventional and internally cured concrete.

Implications on Practices and Sustainable Mixtures

of materials made using internal curing with respect to thermal shock (form removal), cooling, or diurnal temperature changes.

Byard and Schindler (2010) simulated the impact of partially internal cured concrete mixtures on the performance of a typical bridge deck that may be cast in the fall season in the southeastern parts of the US. The temperature of the specimens was controlled to simulate the concrete temperature history of each specific mixture as it would develop in an 8-inch (200-mm) thick bridge deck (Figure 4). It was noted that internal curing of the concretes delays the occurrence of cracking at early ages in bridge deck concrete applications when compared to the normal weight control concrete. This improvement in cracking behavior is attributed to the increase in tensile strength and decrease in modulus of elasticity and autogenous shrinkage of the internally cured concretes when compared to their normalweight counterparts.

Field Observations Internal curing has shown benefits in the field as well. Villarreal and Crocker (2007) reported results from field studies conducted in 2005 using internal curing in a large railway transit yard in Texas. Their report showed that internal curing increased the 28-day compressive strength by at least 15%, eliminated plastic shrinkage cracking, and eliminated drying shrinkage cracking. It was also noted that the reduction in concrete unit weight reduced fuel requirements and equipment wear. Since 2007, several informal crack surveys have been conducted at the railway transit yard, with only two or three cracks found (one of these being where a construction joint was inadvertently omitted). In 2006, internal curing was employed for a continuously reinforced concrete pavement by Friggle and Reeves (2008). A crack survey indicated “an overwhelming reduction in the number of cracks (21 vs. 52 in a comparable section of normal concrete) and a significant reduction in the measured width of the cracks”. More recently, two bridges were constructed in Indiana with a 4-inch (100-mm) topping slab. The first bridge used a conventional INDOT Class C mixture while the second bridge used a concrete mixture modified to provide internal curing. A year after construction, some preliminary observations have been made. First, the finishers found the concrete easy to work and finish, reporting no differences from conventional concrete. Second, while the one-day strength of the internally cured concrete was approximately 10% less than that

STRUCTURE magazine

Internal curing may also provide sustainability benefits. Replacing cement with supplementary cementitious materials (SCMs i.e., fly ash, slag) is suggested as a way to use substantially less clinker, resulting in a lower carbon footprint for in-place concrete. SCMs take longer to hydrate, thereby requiring water to be present for a longer time.

While research has shown improved long term durability performance, recent work has shown that internal curing is particularly well suited to be used in mixtures with larger volumes of SCMs. Internal curing enables the SCMs in these mixtures to react for a longer time, since the higher water content needed to support the reaction of the SCMs can be maintained.

While there are many benefits associated with internal curing, one needs to remember that these materials require quality control assessment at the plant to insure proper aggregate prewetting and often have a relatively small increase in costs associated with materials purchase, handling, and prewetting. The authors are not recommending that contractors stop providing conventional (external) curing that minimizes the evaporation of water. Rather, experience indicates that internal curing provides the construction community with a new approach for producing concrete that is more robust during the often variable construction phase. As a result, by using internal curing it may be possible to greatly reduce the risk of unwanted cracking.▪

13

Jason Weiss (wjweiss@purdue.edu), is a Professor of Civil Engineering at Purdue University.

Dale Bentz (dale.bentz@nist.gov), is a Chemical Engineer at the National Institute of Standards and Technology (NIST).

Anton Schindler, P.E. (schinak@auburn.edu), is an Associate Professor and HRC Director in the Department of Civil Engineering at Auburn University. He is the current chair of ACI 231 Concrete Properties at Early Ages and received ACI’s Wason Medal for concrete materials research in 2006 and 2011.

Pietro Lura (pietro.lura@empa.ch), is the Head of the Concrete and Construction Chemistry Laboratory at EMPA, Swiss Federal Laboratories for Materials Science and Technology, and Professor, ETH Zurich, Institute For Building Materials.

January 2012

Codes and standards updates and discussions related to codes and standards

This article is the first of two that outlines changes for wood design in the 2012 building codes. This article focuses on the 2012 NDS, while Part 2 will outline other updated standards and code modifications.

T

he 2005 Edition of the National Design Specification® (NDS®) for Wood Construction (ANSI/AF&PA NDS-2005) was recently updated.

The updated standard, designated ANSI/AWC NDS-2012, was approved as an ANSI American National Standard on August 15, 2011 (Figure 1).

The 2012 NDS was developed by the American Wood Council’s (AWC) Wood Design Standards Committee and is referenced in the 2012 International Building Code (IBC).

Primary changes to the 2012 NDS are listed here. Major issues are subsequently covered in more detail.

• Revised load and resistance factor design (LRFD) Format Conversion Factors (KF) to provide numeric values of KF rather than equations •Incorporated LRFD KF factors and resistance factors (φ) into NDS Chapter 2 and all material-specific chapters • Incorporated a new equation for intermediate calculation of members subjected to bending in combination with axial compression with or without edgewise bending • Removed sections on specification of glued laminated timber (glulam) and deflection • Added two glulam adjustment factors: stress interaction factor and shear reduction factor • Clarified applicability of existing glulam provisions for curved members, doubletapered and tapered straight beam members, and notching • For poles and piles: updated design values per ASTM D 2899, moved design values to the NDS Design Value Supplement, and revised several adjustment factors • Revised I-Joist beam stability factor to be more consistent with NDS Chapter 3 • Removed grade and construction factor for wood structural panels and clarified panel size factor applicability • Referenced ANSI/TPI standard for design of assemblies utilizing metal connector plates • Revised connection provisions and table headings and footers for consistency • Clarified provisions for dowel bearing strength of wood structural panels for fastener diameters less than or equal to ¼ inch • Added provisions for post-frame ring shank nails • Clarified how connection tip length is used for lateral load calculations

2012 NDS Changes

By John “Buddy” Showalter, P.E., Bradford K. Douglas, P.E., Philip Line, P.E. and Peter Mazikins, P.Eng

John “Buddy” Showalter, P.E. is Vice President of Technology Transfer, Bradford K. Douglas, P.E. is Vice President of Engineering, Philip Line, P.E. is Director of Structural Engineering, and Peter Mazikins is Senior Manager of Engineering Standards with the American Wood Council. Contact Mr. Showalter (bshowalter@awc.org) with questions.

14 January 2012

Figure 1: National Design Specification for Wood Construction, 2012 Edition.

• Addressed perpendicular to grain outer row distance for fasteners accounting for expected glulam shrinkage • Clarified provisions for applicability of split ring and shear plate connections in side grain and end grain; relocated provisions for edge distance, end distance, and spacing • Revised geometry factors for split rings and shear plates for reduced edge distance associated with glulam with faces as narrow as 3 and 5 inches • Revised timber rivet capacity equations to allow proper application of the load duration factor and LRFD conversion factors • Directly referenced Special Design Provisions for Wind and Seismic (SDPWS-08) and removed all other provisions in Chapter 14

LRFD In Section 2.3.5, reference to the Format Conversion Factor, KF, (LRFD only) is changed from Appendix N.3.1 to new Table 2.3.5. Similarly in Section 2.3.6, reference to Resistance Factors, φ, (LRFD only) is changed from Appendix N.3.2 to new Table 2.3.6 (Figure 2).

The values in Tables 2.3.5 and 2.3.6 are based on Tables N1 and N2, respectively, from Appendix N. Note that Table 2.3.5 (and revised Table N1) shows the numeric values of KF directly. These numeric values are used to estimate the LRFD reference resistances because use of a constant/φ equation format from ASTM D5457-10 Standard Specification for Computing Reference Resistance of Wood Based Materials and Structural Connections for Load and Resistance Factor Design has proven to be confusing. Table 2.3.5 includes a revised Format Conversion Factor for Fcperp (revised from

Figure 2: LRFD format conversion factors and resistance factors.

KF=2.08 to KF=1.67). This revision is necessary in order to be consistent with ASTM D5457-10.

Variables for the Format Conversion Factor, KF, and the Resistance Factor, φ, in the applicability tables of NDS chapters 4, 5, 6, 7, 8, 9 and 10 have been replaced with specific values from Table 2.3.5 and Table 2.3.6, respectively (Figure 3 for an example). Specifying language in NDS sections 2.3.5 and 2.3.6 has been revised, as has the specifying language in each of the material chapters to reflect this change.

Intermediate Calculation for Combined Bending and Compression

Structural Glued Laminated Timber Sections on specification of glued laminated timber (Section 5.1.4) and deflection (Section 5.4.3) were removed. Dry-use adhesives are not permitted in ANSI/AITC A190.1 Structural Glued Laminated Timber, removing the need to specify whether the glulam can be used in dry or wet service conditions.

The specification of stress requirements and design values were removed for consistency with other NDS product chapters which do not contain similar requirements. Deflection information was redundant to provisions elsewhere in the standard, including Section 3.5.

Provisions were added for two stress adjustment factors (Figure 3). The stress interaction factor (Section 5.3.9) was added consistent with provisions of the Timber Construction Manual (TCM) used to adjust bending stress in tapered bending members. The shear reduction factor (Section 5.3.10), previously appearing in footnotes to glulam design values in the NDS Design Value Supplement, has been specifically defined as an adjustment factor applicable for shear design of other than prismatic beams (e.g. notched members, curved members, tapered members, design for radial tension, and shear design at connections).

Applicability of existing provisions was clarified for curved members (Section 5.4.1) and provisions for double-tapered and tapered straight beam members (Section 5.4.2 and Section 5.4.4) were added in lieu of referencing the TCM (Section 5.4.1).

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Finally, notching provisions were clarified for glulam. Notches are not permitted on the top and bottom of the beam at the same location (Section 5.4.5).

Timber Poles and Piles NDS Chapter 6 has been updated to address changes to ASTM standards for developing and adjusting round timber pile and round construction pole design values. Changes are summarized as follows: • New design values for Table 6A “Untreated Round Timber Piles” and Table 6B “Untreated Round Construction Poles” were relocated from NDS Chapter 6 to the NDS Design Value Supplement (Figure 4).

• Section 6.3.5 “Untreated Factor” adjustment was changed to “Condition Treatment Factor” in recognition that new reference

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A new equation 3.9-4 was added for intermediate calculation of members subjected to flatwise bending in combination with axial compression with or without edgewise bending. When a flatwise bending load is checked with the third term of the stress interaction equation, axial and edgewise bending interactions in the denominator can become negative. Occurrence of a negative value indicates an overstress. However, use of this negative term in the stress interaction equation overlooks overstress in flatwise bending and incorrectly reduces the overall interaction. While a check for overstress due to bending is a limiting condition of member design for bending per 3.3.1 of the NDS, an explicit check needs to be provided to clarify limitations on flatwise bending in NDS stress interaction equations. Similar modifications were made for built-up columns in Chapter 15 (equations 15.4-2 and 15.4-4).

Figure 3: Adjustment factors for structural glued laminated timber.

Dowel-type Fasteners

Figure 4: Reference design values for timber poles and piles.

design values are now based on air dried condition.

• Section 6.3.9 “Critical Section” is changed to be consistent with changes to reference design values in ASTM D2899 Standard Practice for Establishing Allowable Stresses for Round Timber Piles.

• Section 6.3.11 “Single Pile Factor” adjustment was changed to “Load Sharing Factor” in recognition that new reference design values are now based on a single pile condition.

Prefabricated Wood I-Joists NDS 7.3.5 regarding I-Joist Beam Stability Factor, C L, was revised to be more consistent with provisions in Section 3.3.3 and to address confusion that currently exists with these provisions. A new section 7.3.5.1 was created that permits C L=1.0 when the compression flange of an I-joist is supported throughout its length to

prevent lateral displacement, consistent with the general requirements in 3.3.3.3.

Additionally, a new section 7.3.5.2 was added that provides a method for designing the compression flange as an unbraced or partially braced column when the compression flange is not braced throughout its length. These provisions are consistent with 3.3.3.4.

Wood Structural Panels The Grade and Construction Factor, CG, was removed from Section 9.3.4 and Table 9.3.1 as this factor is no longer used by the wood structural panel industry. The NDS Commentary will also be updated to remove reference to CG. Additional wording is provided in NDS 9.3.4 to better clarify under what conditions the panel size factor, Cs, is required.

NDS Commentary Table C9.3.4 “Panel Size Factor” is relocated and designated as NDS Table 9.3.4.

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Provisions throughout NDS Chapter 11 have been revised to clarify intent and to add charging text utilizing a consistent format. Design value tables were also revised to use consistent and more descriptive table headings and table footnotes.

For lateral design value tables where penetration is an issue, footnotes clarify penetration basis of tabulated values and applicability of penetration adjustment to the table values only. The addition of penetration assumptions in the table titles are intentionally redundant with similar information in table footnotes to more clearly identify the reference penetration used for tabulated values.

Provisions for dowel bearing strength for wood structural panels were clarified as being applicable to fastener diameters of less than or equal to ¼ inch (see 11.3.2.2) for consistency with supporting data.

Commentary will be developed to address available guidance for larger diameter fasteners.

Provisions were added for postframe ring shank nails manufactured in accordance with ASTM F1667 Standard Specification for Driven Fasteners: Nails, Spikes, and Staples.

A withdrawal design (Section 11.2.3.3) equation for post-frame ring shank nails, based on research conducted at the Forest Products Laboratory including a 20% adjustment to account for effects of galvanized coatings, was added. Lateral design value tables (Table 11S and 11T), based on application of yield limit equations to standard properties for post-frame ring shank nails as noted in table footnotes, were also added.

Provisions were added to clarify how tip length is addressed in determination of bearing length used for lateral load calculations (Section 11.3.4). New provisions to specifically address length of tapered tip are based on analysis of reduced bearing present as the fastener diameter tapers to a point at the tip, and the effect of tip length on lateral design values for small penetrations. Commentary will be developed to provide background for determination of new bearing length provisions for driven fasteners and the effect of tip length.

Continued on page 18

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Provisions were also added to address the maximum perpendicular to grain distance for outermost fasteners in glulam based on moisture content and fastener type (Section 11.5.1.3), taking into account the expected shrinkage of glulam.

assumed previously (e.g. edge distances of 1.5 and 2.5 inches rather than 1.75 and 2.75 inches). Reduced values of the geometry factor were based on a re-evaluation of the original research and will be provided as background in NDS Commentary.

Split Ring and Shear Plate Connectors

Timber Rivets

NDS Section 12.3.2 was revised to clarify applicability of provisions to connections in side grain. Provisions for edge distance, end distance, and spacing (Section 12.3.3, 12.3.4, and 12.3.5) were relocated in the following sections: • Section 12.3.2.1 combines requirements for geometry factors for parallel or perpendicular to grain loading (i.e. Section 12.3.3.1, 12.3.4.1, and 12.3.4.5).

• Section 12.3.2.2 clarifies requirements for connectors loaded at an angle to grain. Separate geometry factors for end and edge distance are to be calculated for the parallel and perpendicular components of the resistance. An equation and table for determining spacing requirements were added (Eq. 12.3-1 and Table 12.3.2.1).

Provisions were added to clarify applicability of requirements to connectors installed in end grain: • Section 12.3.3 was revised to clarify that a single geometry factor is determined and applied to parallel and perpendicular components of the resistance.

• Section 12.3.3.1(a) clarifies that end distance provisions do not apply to connectors installed in end grain.

• For connectors in sloping surface of end grain, loaded parallel or perpendicular to axis of cut (Section 12.3.3.1b and 12.3.3.1c), an equation approach was added for determination of the geometry factor for greater consistency with the method used for side grain connections when transitioning from 0 degrees to 90 degrees and to remove a step function.

• Provisions were added to clarify requirements for connectors in sloping surfaces of end grain, loaded other than parallel or perpendicular to the axis of cut (Section 12.3.3.1d).

Geometry factors were revised to account for reduced edge distance associated with glulam with faces as narrow as 3 and 5 inches rather than 3.5 and 5.5 inches

The constant in Equation 13.2-1 for parallel to grain reference timber rivet capacity, Pr, was changed from 280 to 188, and the constant in Equation 13.2-2 for perpendicular to grain reference timber rivet capacity, Qr, was changed from 160 to 108. To allow proper application of the load duration factor and LRFD conversion factors to timber rivet connections, including those conditions limited by rivet strength rather than wood strength, these constants have been reduced to be consistent with other NDS connection values. Average ultimate values of Pr and Qr have previously been divided by 3.36. Similarly, a correlating change was made in Chapter 10, Table 10.3.1 to remove footnote 4 which will permit application of the load duration factor when rivet capacity controls as well as when wood capacity controls.

The following sentence was added to Section 13.3.1: “The maximum distance perpendicular to grain between outermost rows of rivets shall be 12.” This change parallels requirements in the new Table 11.5.1F specifying maximum spacing between outer rows of dowel-type fasteners in glulam connections.

NDS Supplement The NDS Supplement incorporates several new species combinations and revisions to existing design values. Changes include: • Revision of Table 1A “Nominal and Minimum Dressed Sizes of Sawn Lumber” to reflect new sizes for Timbers per Voluntary Product Standard PS 20-10 American Softwood Lumber Standard • Reorganization of Table 1B “Section Properties of Standard Dressed Sawn Lumber” to better distinguish between dimension lumber, Posts and Timbers, and Beams and Stringers • Incorporation of new Coast Sitka Spruce and Yellow Cedar design values in Table 4A for dimension lumber • Revision of Northern Species bending and tension design values in Table 4A

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January 2012

• Clarification of size factor adjustments for visually graded timbers in Table 4D • Revision of Ponderosa Pine decking repetitive member design values in Table 4E • Table 4F for non-North American species was revised to incorporate new design values for Douglas-fir from France and Germany, and revised values for Norway Spruce and Scots Pine from the countries of Estonia, Latvia, and Lithuania • Revision of glulam design values in Tables 5A, 5A Expanded, and 5B. Primary changes are to shear parallel to grain design values • Addition of Tables 6A and 6B for Timber Poles and Piles

More Details A comprehensive table listing section by section changes to the NDS, including modifications to Appendix material, is available to download from the AWC website (www.awc.org). Navigate to the NDS page to locate the document.

Availability The 2012 NDS and 2012 NDS Supplement is currently available for purchase in electronic format (PDF) only. Once the NDS Commentary and other support documents to be included in the 2012 Wood Design Package (WDP) are updated, printed copies will be available for purchase. Check the AWC website (www.awc.org) for status updates on the 2012 WDP. Once the NDS Commentary and other support documents are complete, those who purchased electronic versions of the 2012 NDS and 2012 NDS Supplement will receive those documents in electronic format at no additional charge.

Conclusion The 2012 NDS represents the state-of-the-art for design of wood members and connections.

Its reference in the 2012 IBC will make it a required design methodology in those jurisdictions adopting the latest building code.

However, building officials are also apt to accept designs prepared in accordance with newer reference standards even if the latest building code has not been adopted in their jurisdiction. IBC 104.11 for alternate materials and design provides the authority having jurisdiction with that leeway.▪

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InSIghtS new trends, new techniques and current industry issues

Model Energy Code Development

By Kenneth E. Bland, P.E. and Dennis L. Pitts

Kenneth E. Bland, P.E. (kbland@ awc.org), is Vice President, Codes & Regulations and Dennis L. Pitts (dpitts@awc.org), is Central Regional Director for the American Wood Council.

This article is adapted from a similar article appearing in the Spring 2011 issue of Wood Design Focus and is reprinted with permission.

Figure 1: DOE summary for residential state energy code adoptions.

N

ot since the oil crisis of the 1970s has there been so much attention paid to finding ways to reduce US dependence on foreign oil. In particular, reducing energy to make buildings comfortable and functional has been the target of the US Department of Energy (DOE). It was Executive Order 13423, Strengthening Federal Environmental, Energy, and Transportation Management, signed by President Bush on January 24, 2007, that sparked DOE’s latest push into energy code development.

This article discusses the development of model energy codes and the legislative mandate for DOE to assure their implementation.

Department of Energy Authority DOE’s role in facilitating enactment of energy codes is established by the Energy Conservation and Production Act of 1976 as amended by the Energy Policy Act of 1992 (EPACT). EPACT, among other things, requires DOE to support adoption and enforcement of energy codes in the states.

Historically, DOE did not have many “hooks” to insist that states maintain a current model energy code. However, with passage of the American Recovery and Reinvestment Act of 2009 (ARRA), DOE has funding available for implementation of state codes, but only when states pledge to update to current standards.

20 January 2012

EPACT also created the Building Codes Assistance Project (BCAP) as a non-profit organization that advocates on behalf of DOE for adoption, implementation, and advancement of energy codes. BCAP also works with DOE, state energy offices, regional energy efficiency alliances, and various shareholders to educate states, municipalities, and the building community about the benefits of code adoption and enforcement.

Two National Model Energy Codes There are two national consensus standards that are regularly enacted for implementation of energy efficiency criteria in both new construction and renovation of existing buildings.

• International Energy Conservation Code (IECC), which is developed by the International Code Council (ICC), addresses all buildings, including low-rise residential.

• ASHRAE 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings, is developed by the American Society of Heating, Refrigeration, and Air-Conditioning Engineers. It addresses energy-efficient design in all but residences three stories or less in height.

Regardless of its official scope, 90.1 is considered to be a commercial buildingspecific document.

Both are developed and amended in open public forums through somewhat different consensus processes.

DOE Influence in the Process DOE has used Executive Order 13423, which was intended for government-owned buildings, as the basis for seeking improvement in the energy codes.

DOE’s goals for low-rise residential structures are based on the 2006 edition of the IECC. DOE’s intent for the 2009 code was buildings that would be 17% more energy efficient than those designed under the 2006, and for buildings under the 2012 IECC to be 30% more efficient than the 2006.

DOE’s plans for the 2015 edition call for a result that is 50% more efficient.

Similar increases in efficiency for ASHRAE 90.1 are envisioned and are contained in a 2007 Memorandum of Understanding (MOU) between DOE and ASHRAE. DOE’s goal is to increase the efficiency Figure 2: DOE summary for commercial energy code adoptions. of 90.1-2010 by 30% over that of 90.1-2004. An increase of 50% for the 2013 edition is planned.

As explained in a 2010 document on the their website, MultiGiven the amount of money available through DOE for funding of Year Program Plan – Building Regulatory Programs, one of DOE’s local and state energy-related projects, it’s not surprising that within ultimate goals for codes is for “… net-zero energy buildings the last several years DOE has become a major player in the field of (NZEB) to be cost-effective alternatives to traditional construction energy codes and standards. by 2025 which means that NZEB should be required in codes by about the same time.”

Statewide Energy Two other pieces of rulemaking have increased DOE’s influence in the energy codes arena: the States Energy Program (SEP) and the Code Adoption American Recovery and Reinvestment Act of 2009 (ARRA). SEP It is fairly common knowledge, even within DOE, that codes are not provides federal assistance to states to share the costs of improved being adopted or enforced in a consistent manner. Across the United energy efficiency and establish renewable energy programs. SEP States many jurisdictions, both state and local, are just now adopting funds are applicable across a very broad range of construction, the 2009 IECC. A few states, with laws that make updating to the making DOE influential in energy-related decisions to be made by current edition of the IECC mandatory, will soon start the adoption state and local policy makers. SEP’s funding in energy efficiency process for the 2012 IECC. Otherwise, it is expected that states with and renewable energy projects within a state generates jobs in local no mandatory process will enforce the 2009 or an earlier edition of energy, manufacturing, retail, and home services industries. This the IECC for the foreseeable future. increases the tax base in the state and indirectly supports other jobs.

DOE’s website summarizes the status of code adoption within the SEP also funds preparations for natural disasters and recovery from United States. For residential code adoption, Figure 1 provides the those disasters. The flexibility of SEP allows states to also use the DOE overview as of April 2011. funding to develop new energy infrastructures that are resistant to The DOE summary for commercial energy codes, as of April of 2011, damage from natural disasters. shows somewhat similar adoption trends for ASHAE 90.1 (Figure 2).

ARRA provides financial benefits to improve energy efficiency as part of the Obama administrations’ $787 billion program intended Conclusion to stimulate the U.S. economy. This act provides SEP with $3.1 billion that can be used by states in the form of grants, and can Given the current awareness of energy conservation due to world geobe provided as direct funding not requiring matching funds from political situations and the relatively new field of sustainable building the states. Additionally, a DOE energy-related grant program design, it’s not surprising that there is a greater interest in energy codes was provided with $3.2 billion. States and local governments now than in the past. Important to designers is the change in players can obtain block grants to improve energy efficiency and install involved in code writing and adoption. Currently, there is a movement renewal energy systems. Nonprofits and governmental agencies to ratchet up code requirements to such an extent that practicality and may also use these grants. cost benefits appear to be ignored. Additionally, DOE’s influence in the BCAP, which receives funding from DOE, provides states with code arena steadily increases due to federal funding available to states and energy code advocacy assistance on behalf of DOE and coordinates local jurisdictions. DOE’s goals for future editions of the energy codes DOE technical assistance to the states. and standards promise even greater difficulty in complying with the codes using traditional materials and methods of design and construction.▪

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January 2012

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quiet day in August 2010. The Library Dean, Alberta Davis Comer, MLS Indiana University-Bloomington, was at a retreat when she received a call that book ranges had fallen. Relieved to find that no one had been seriously injured, the Dean left immediately for campus which was about 15 minutes away.

At the library, the Dean proceeded immediately to the second floor stacks where the ranges had fallen. There she found five ranges, each with 13 sections, collapsed and two more ranges precipitously leaning. Later it was determined that about 20,000 books were on the floor. The Dean called the Facilities Department and asked for their assistance in assessing the situation. Facilities responded immediately. After the General Construction Supervisor reviewed the situation, he determined that the area was unsafe for public or staff. Since each library floor is connected by 2 elevators and 4 stairwells, it was not practical to block off the entire floor. An electronic alert was broadcasted to campus that the Library was closing for the rest of that day and would also be closed the following day to allow time for safety measures to be put in place.

Cunningham Memorial Library (CML), built in 1973, has five floors. Three floors above ground and two below, the library holds about 1 million print items. Shelving, typical of libraries of this age, was erected without bracing, although top, lateral bracing was added a few years ago.

In 1989, twelve ranges of shelves, holding an estimated 20,000 books, collapsed in the Libraries Annex of Columbia University. Some of the books went through the window, falling three stories to the ground. The culprit in this mishap was determined to be the lack of laterally braced shelving. Many of the Annex books were fragile and about five thousand volumes were either lost or damaged (Gertz). The information available in the literature is mostly about earthquake-related damages and how to make library structures safer.

For example, an article in the Journal of Library Administration discusses non-structural earthquake hazards including “unsecured or unbraced library shelving, any library materials which are stored on shelves over 5 feet from the ground” (Beinhoff) and states: Probably, the only unique furnishing in the library which will not be fully addressed in a regular earthquake preparedness seminars (sic) and which needs to be examined by a trained professional is the library’s shelving.

Although the CML shelving collapse was not caused by an earthquake, it was still important to hire a professional to inspect all of the library shelving. A structural engineer was hired to determine the cause of the ranges falling at CML, and to appraise the current status of all library shelving.

An Engineering Perspective Upon arrival to Facilities Management for a regularly scheduled meeting, Betsy Wilkinson, P.E., S.E. of KIVA Structural Engineers, was informed that the university architect, Scott Tillman, AIA, wanted to make a detour to the CML building before continuing with their previous plans. This was the same morning that the ranges tipped over. Upon first inspection, it appeared that one range tipped, precipitating a domino effect of the adjacent ranges. The only thing that had stopped the chain of motion was the remaining bracing straining to give up as well. The library staff was in the process of removing the books that still pressed against the remaining upright ranges. The initial response was clear: “What caused this?” and “How do we prevent this from happening again?”

The answers to these questions are as important to Indiana State University’s CML as they are to any library. Ms. Wilkinson set about looking at sources of the instability that caused this specific event but felt it was important to also investigate other potential causes. For this she turned to the 2006 International Building Code (IBC), as well as the record drawings for the CML structure and the range manufacturer’s literature. There are three potential direct causes for an event such as this: asymmetric shelf loading, floor deflection, and seismic (earthquake) forces.

Each of these influences introduces a horizontal force that causes the ranges to tilt. The additive effect is the sum of all three influences. The largest of these forces is the seismic force, followed by shelf asymmetry and then floor deflection. Each cause has unique contributing factors.

Structural ForenSicS investigating structures and their components

Unstable Shelves Put the Shake in Shakespeare

Floor Deflection In general, a library structure is laid out with a repeating grid of columns. This facilitates the placement of ranges and aisles to maximize the space. The columns are often laid out in a square grid, or very close to square. The floor framing is often concrete or composite steel construction because these systems are cost effective for construction in repetitive framing patterns and have excellent sound and fire resistance qualities.

The shelf sections are considered movable at any future point in time, so would be classified by the building code as a live load. The code minimum live load capacity required for library floors is 150 pounds per square foot (psf ) (2006 IBC, Section 1607, Table 1607.1 and footnote b). This is a relatively high live load compared to the average building, but it is appropriate for a library due to the expected use of the floor space. continued on next page

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By Betsy Wilkinson, P.E., S.E. and Alberta Comer, MLS

Betsy Wilkinson, P.E., S.E. is a Principal and structural engineer with KIVA Structural Engineers.

She may be contacted at kivase@cs.com.

Alberta Comer, MLS is the Library Dean at Indiana State University. She may be contacted at alberta.comer@indstate.edu.

The online version of this article contains detailed references and resources. Visit www.STRUCTUREmag.org.

top of a 7-foot 6-inch tall shelf section relative to its base. If the shelves have partial asymmetry (a more balanced distribution of weight), then some fraction of this tilt will exist until complete symmetry of weight distribution is reached.

Seismic

Courtesy of Cunningham Memorial Library PR Unit.

The industry standard for book shelves requires them to hold up to 50 pounds of media per linear foot (plf ) of shelf space, or 50 pounds per cubic foot (pcf ) of shelf volume (Shelton). The expected maximum weight of a typical 3-foot wide shelf section that has seven shelves on each side is about 2,150 pounds when fully loaded.

In the CML building, the floor framing system used concrete columns on a 22 foot-6 inch square grid supporting concrete beams, joists and slab in a repeating pattern. This structure created a predictable pattern of floor deflection and rotation. In other words, for the CML, if a given shelf was precisely located where the floor slope calculated to be the greatest, then it could contribute a sideways deflection (tilt) of approximately 1/8 inch at the top of a 7-foot 6-inch tall shelf section relative to its base. These shelf sections are not located exactly to achieve this much tilt; however, some fraction of this much tilt will exist in each shelf section depending on their as-built locations relative to the building columns. Floor deflection is unavoidable because the structure has to deflect and rotate in order to support any load.

Shelf Asymmetry Shelf asymmetry is conceptually simple: too many books on just one side. As long as the shelf is always loaded symmetrically with identical weight distribution on each side, this effect can be avoided, right? This is not a realistic expectation for a working library.

Even if a shelf could be identically loaded on

both sides, it would become partially asymmetric as soon as a patron wanted to check out a book. Let’s assume that the shelves on one side are all loaded with books up to the industry standard (50 plf of shelf space), while the opposite side is empty. This is what would be considered complete asymmetry. The effect of this complete asymmetry will introduce a sideways deflection. The magnitude of this deflection depends on the strength of the vertical uprights, which is specific to the range manufacturer and is proprietary information.

Simply put, if one is choosing from two range manufacturers, Company A and Company B, their prices would be directly related to their material expenditures. Company A offers “excellent resistance to unbalanced loading” while Company B offers “economic use of materials, saving you money.” The vertical uprights for A would be strong and stiff with a small deflection when the shelf is asymmetrically loaded, but then how often does complete asymmetry occur in practice? Company B offers a monetary savings in exchange for vertical uprights that flex more when asymmetrically loaded. There are manufacturers that fall everywhere in between these two extremes, so this evaluation must be specific to the manufacturer that supplies a library with its system of ranges.

For the CML, Ms. Wilkinson took measurements of the vertical uprights and made conservative assumptions for the material strengths so that she could estimate the deflection to some reasonable degree of accuracy.

The resulting sideways deflection (tilt) was estimated to be approximately 3/4 inch at the

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January 2012

Imagine standing on a rug while several people on each side of the rug pull it back and forth. This is what happens during an earthquake. You must react to the motion with a compensating force in the direction of the motion in order to re-align your center of gravity with your feet. This is perhaps easier if you are standing with your feet apart and your arms out to brace you against impact with other objects. Now, imagine you have to stand with your feet together and your hands at your sides. Not so easy! This is how it is for the library ranges. They are tall and narrow and, without top bracing, would tip over when the “rug” is pulled.

This appears to have been the case at California State University in 1994 (CSU Northridge, 2/10/2011), where a 30-second earthquake eliminated the university’s library service for 25,000 students for a period of eight months, and restricted the full services for over four more years while new facilities could be built. On January 17, 1994, the Northridge Earthquake hit Los Angeles, California. No one was seriously injured because the university was on a break between semesters; however, 600,000 volumes were thrown off their shelves and had to be stored and reorganized. The lessons learned not only changed the structural engineering of steel connections, but also changed library standards for shelving.

The seismic force must be determined for a typical shelf section. The seismic force is directly related to the weight of the shelves plus the books. The seismic analysis revealed a need to establish a pattern of bolted bases and top bracing. Not every row required bolting because the top bracing helps deliver the forces to a bolted row. For every row that was bolted to the floor, up to four more rows of ranges could be braced to that bolted row to use it for support during an earthquake.

In addition, some of the bracing was bolted directly to building columns to eliminate some of the required floor bolting.

Cause of Collapse What caused the collapse at the CML building? On that August day there was no recorded earthquake of any significant

magnitude; however, the first two causes proved enough to make the difference. It was determined that a combination of two factors initiated the first shelf to fall over, which created a domino effect on the remaining shelves. At the time of the collapse, the books were being reorganized and re-shelved. In addition, some top braces were missing their bolts to the ranges. The shelf sections were also not bolted to the floor. It is believed that the initial row of shelves fell due to temporary shelving asymmetry and floor deflection.

When a top brace was removed, this released the top of that shelf allowing it to deflect and then become unstable.

concept, writing that if the bracing was installed before the early 1980s it might not meet today’s seismic code, and that more damage might be sustained by having improperly braced shelving than if there were no bracing. Beinhoff states: Getting trained professionals in to examine and recommend a method of properly securing and reinforcing library shelving is essential because only someone with engineering experience will be able to understand how library shelving will react to the different stresses caused by an earthquake….

In a 1996 article, author Guy Robertson, a Canadian librarian, reinforced this concept when he wrote that a shelving risk analysis may be needed, especially since libraries “move things to different locations, revise and reinstall.” Thus, the shelving system that was initially installed loses its integrity over time.

Although the literature may not reflect either the magnitude of the problem or the importance of the subject, having just witnessed such an incident has convinced these authors that libraries need to carefully assess their shelving situation.▪

Timing It Right

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Through the cooperation of Mr. Tillman and Facilities Management, KIVA Structural Engineers created contract documents for competitive bidding. The winning contractor, MSI Construction, was required to place the bolts and bracing system for all five levels of the library within the three weeks of Christmas break, so there would not be any interruption in student access to library materials while classes were in session. The noise and material storage would have otherwise proven to be an unacceptable imposition to library patrons.

Nick Roman with MSI Construction maintained contact with Ms. Wilkinson, who was to be on call as needed in order to clarify bolting and bracing requirements and minimize any delays. Various university staff, Alberta Comer (Library Dean), Debra Robinson (Library Assistant), Paula Huey (Library Assistant), and Scott Tillman (University Architect) were also on call when questions regarding costs, changes, or handling of books came up.

Mr. Roman’s crew of skilled laborers did an excellent job of installing the bolting and bracing system to support 9,030 linear feet of ranges, while maintaining their commitment to the schedule and budget.

Conclusion When a library suffers a shelving collapse, no matter the reason, it is important to consult a structural engineer. Such a proactive approach may prove beneficial, especially as libraries continue to age and building codes under which they were built become outdated. Beinhoff reinforces this STRUCTURE magazine

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January 2012

Final Opening.

Rough Opening.

Innovative Reinforcing Gives Old Structure New ‘Light’

By B. Keith Brenner, P.E.

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fter the dream of a new building fell through, Maine Health was faced with finding an existing building to house all of its corporate and administrative operations. Multiple offices, scattered about the city of Portland, Maine needed to be consolidated into one facility. A suitable 89,000 square foot building was obtained, and Harriman, architects and engineers located in Auburn, Maine, were challenged with how to adapt the outdated 1946 concrete structure to a modern facility for all its employees.

The building was originally constructed for Sears Roebuck Co. as a retail store in downtown Portland. There were very limited floor-tofloor heights and no windows. Although some small windows were added in the 1980s when it was converted to office space, the building was still a very uninviting place to work.

The three-story structure consisted of reinforced concrete two way slabs, with square concrete columns, capitals and drop panels. The bay spacing was typically 18 by 20 feet. This type of construction is very uncommon in the State of Maine, but it provided a very solid structure to work with.

A design concept was developed which involved cutting large openings at each floor level, including the roof. The size of the openings varied, with the largest being 86 by 17 feet. This would create a STRUCTURE magazine

three-story atrium allowing natural light into the floors below. The challenge structurally was to develop a way to reinforce the structure to accommodate these large openings. Several options were considered, including the addition of structural steel in key areas. The disadvantage of this option was that it would create a cumbersome matrix of steel beams surrounding the atrium at each floor level. There was also the difficulty of getting longer pieces of steel into the building given the limited size and location of openings. The steel framing would have visually reduced the spaces even more and was not the desired option architecturally. This is when the option of using CFRP (carbon fiber reinforced polymer) was considered. CFRP is used to reinforce/ rehabilitate existing structures that are currently deficient, or need alterations such as presented here. CFRP is often used for seismic retrofit of concrete structures in high seismic areas. The product is desirable from an architectural standpoint, as it is not visually detractive and consumes very little space.

The first task was to analyze the existing slabs to verify their capacity and to determine the effects of placing large openings at each level. Ram Concept from Bentley was used to aid in this analysis.

Fortunately, existing structural drawings were obtained to provide input such as reinforcing steel placement, concrete design strengths

26

January 2012

Carbon Fiber Install.

Reinforced Slab.

and design loads. Since the building was designed as a retail facility, it had greater design live loads than those required for office use. This helped in the end, as it reduced the amount of CFRP reinforcement that was required.

With the openings cut, the computer model revealed that relatively few areas were deficient. Additional reinforcing would be required at the adjacent column line for negative moments above the column capitals. This was welcome news for the contractor, since it meant that the CFRP strips could be applied to the top of the existing slab as opposed to having to work overhead on the bottom of the slab. This good fortune was short lived however, as it was discovered that there was a 3-inch un-bonded topping on the structural slab. This topping was removed in the reinforced areas prior to applying the CFRP strips.

The product used for the reinforcing was Sika Carbodur®, manufactured by Sika Corporation. The CFRP strips were 0.047-inch (1.2mm) thick and approximately 4 inches wide. The material is lightweight, easy to work with and has a design tensile strength of 4.06x105 psi.

Existing Construction.

Software, provided by SIKA Corp. was used to help determine the amount of CFRP strips required at each column location. The contractor, Consigli Construction of Portland, Maine, was trained by SIKA to apply the products. The 15-foot long strips were adhered to the slab using SIKADUR 30 epoxy, after pull tests confirmed that there was adequate bond strength of the concrete surface.

Once all of the CFRP strips were applied and properly cured, cutting of the concrete slabs began at the lowest level. 8- by 5-foot sections were saw cut and lowered to the basement level. Control points, placed on the bottom of the slab, were monitored with surveying equipment during the removal to verify the slabs behavior after the redistribution of stresses. The actual deformations, measured in the adjacent bays, compared well with the predicted amounts. Removal operations continued upward until the last piece of concrete was removed at the roof.

For the first time in the building’s history, natural light was provided to all levels of the concrete structure. The openings were staggered at each level to maximize the light penetration and to create interest.

The use of the CFRP strips was the key to making this a very successful project that was completed under a compressed 14-month schedule. It also demonstrates the ability to use contemporary products to revitalize outdated structures.▪ B. Keith Brenner, P.E. is a Senior Structural Engineer and Associate at Harriman Architects and Engineers in Auburn, Maine. He can be reached at kbrenner@harriman.com.

Framing Plan.

STRUCTURE magazine

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January 2012

Structural PracticeS practical knowledge beyond the textbook

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here appear to be two schools of thought on cast-in-place concrete specifications. The first school likes to separate the cast-in-place concrete into three separate master specification sections; 031000 – Concrete Forming and Accessories, 032000 – Concrete Reinforcing, and 033000 – Cast-in-Place Concrete. The second school likes to keep the entire section together (as distributed by many master specification libraries) named 033000 – Cast-in-Place Concrete. Both schools have the ability to produce clear, correct, concise, and complete specifications. Both schools could benefit from some additional educational opportunities as summarized by the following two hypothetical educational courses.

Concrete Specifications 101 As the course number implies, this course covers the basics of concrete specifying: 1) What version of MasterFormat (or another guideline) is to be used?

2) Is the project attempting to attain LEED certification?

3) What is the format for the specifications?

4) Is the terminology consistent between the specifications and the drawings?

Will the project be written to conform to the 2010 version of MasterFormat, or the 1995 version?

MasterFormat, produced by the Construction Specifications Institute, is the numbering system used in the construction industry to organize specifications, cost estimating documents, product data, and even architectural libraries. An easy way to tell the difference between the two versions is by the length of the section number: the 2010 version uses six digits, while the 1995 version used only five.

Is LEED a factor in the scope of the project?

LEED, Leadership in Energy and Environmental Design, is a process of certifying a project to varying levels of environmental friendliness. The rating system was developed by the U.S. Green Building Council. The process not only affects the drawings, but also the specifications. If it is determined that the project will attempt to obtain one of the levels of LEED certification, asking for and using the LEED scorecard during the development of the specifications is important.

Like drawings, specifications also need to follow a specific format. Format items to be requested and incorporated into a specification include, but are not limited to font, header and footer requirements, margins, and watermarks (if any).

Concrete Specifications Education

By Renee Doktorczyk, AIA, CCS, CSI, SCIP

Renee Doktorczyk, AIA, CCS, CSI, SCIP is an architectural specifier and the president of ArchiTech Consulting, Inc. in Mount Prospect, Illinois. She can be reached at rdoktorczyk@architechspec.com.

28 January 2012

Consistent terminology is required for a well coordinated set of documents. The specifications will call out a vapor retarder. However, many times, a more proprietary term will show up on the drawings. For example, instead of the term vapor retarder, the term Stego WrapTM may be used. The use of proprietary terminology on the drawings does not easily allow for other manufacturers to bid on a project. Changing the term to its non-proprietary version allows the specifications to determine the manufacturers that will be allowed to bid. If help is needed for a correct non-proprietary term, contact the project’s architectural specifier.

Concrete Specifications 201 This course covers advanced cast-in-place concrete specifying, including topics on editing manufacturer lists, below grade vapor retarders, floor and slab treatments, liquid floor treatments, and concrete finishing.

One of the often overlooked, but easy editing tasks is to edit the list of manufacturers for every product included in the specifications. Many structural engineers leave the entire list as it was distributed in master specification in the project specification. It is well known that if there are seventeen different manufacturers listed for a curing and sealing compound that not all manufacturers’ products will have an equal quality level. It is up to the structural engineer to select the products. If there is truly no manufacturer preference, only that the product complies with the indicated ASTM standards, then delete the entire list of manufacturers.

The days of throwing a sheet of visqueen below the rebar prior to a concrete pour are over. Below grade vapor retarders have become more sophisticated. The floor finishes installed over concrete slabs on grade have become less tolerable of moisture migration through the concrete slab. As a result, the structural engineer and the architect need to coordinate not only what vapor retarder is being used, but where it is being specified. Some architectural specifiers have moved to specifying the below grade vapor retarders in the Division 7 sections with the waterproofing, damp proofing, or air barrier products in an effort to have single responsibility for the building envelope moisture control. Since many manufacturers produce vapor retarders, waterproofing, and air barriers, architects like to have one manufacturer for all of these products because of transition details and compatibility issues. As a result, structural engineers need to verify whether or not the vapor retarder will be included in the cast-in-place concrete section and what type of vapor retarder is required, especially if there is a specific product required.

Many structural engineers leave floor and slab treatments in the cast-in-place concrete specifications. Many architects don’t even know what these product entail, let alone require them on their projects. Floor and slab treatments include slip-resistive emery aggregate finish, slip-resistive aluminum granule finish, metallic dry-shake floor hardener, pigmented and unpigmented mineral dry-shake floor hardener. In this instance, it is better to take the floor and slab treatments out of the specification. There are projects requiring some of these products, but the majority of projects do not. Regardless of whether or not the floor and slab treatments are required in a project, the question needs to be asked of the architect. In addition, if none are required, be sure to delete the products out of Part 2 and the installation out of Part 3.

Similar to floor and slab treatments, many times all of the liquid floor treatment products are kept in a section. These products are used more frequently than the floor and slab treatments, but not frequently enough to err on the side of leaving them in the specification. More often than not, the structural engineer should err on the side of automatically removing the products and adding them

back in if truly required. The penetrating liquid floor treatment product included in the master specification section is intended to be a hardener and densifier for high traffic floors (think warehouses and distribution facilities).

However, when architects say they want a clear concrete floor sealer, they usually mean a second coat of curing and sealing compound, not a true concrete floor sealer. Liquid floor treatment products also include treatment for polished concrete floor surfaces. Polished concrete flooring for the most part is still in the kindergarten phase. The products included in the cast-in-place concrete floor system are not for the architecturally finished polished concrete flooring system. They are geared more toward the warehouses and distribution centers. Architectural polished concrete floor systems are covered in a separate section that will include the densifiers, the penetrating sealer, and sheen of the finish, and the amount of the aggregate to be exposed. Again, if a polished concrete flooring system is desired, verify with the architect whether it is to be specified in the cast-in-place concrete section.

Concrete finishing expectations of the architect always requires coordination. Architects always want the best finish, but the budget

rarely allows it. Out of all of the finishes that can be left in the cast-in-place concrete section for formed surfaces, the one most frequently kept is the smooth rubbed finish.

Floor slab finish expectations also need to be coordinated with the architect, especially in regards to floor flatness and floor levelness.

Verify whether the architect wants to pay the contractor to form a flat floor, or if cement based hydraulic underlayment will be specified to achieve the desired floor flatness and levelness if tighter tolerances are required for a specific project. If there is a specific finish required for a project, confirm whether a mockup is required for the finish. As budgets are being cut and architects are adapting to the change by accepting concrete as it is cast, more architects are requiring mockups for the cast-in-place concrete for review and verification of the accepted finishes during the construction period.

The two cast-in-place concrete specification courses mentioned above have the ability to improve the caliber of the castin-place concrete specifications for a project.

Better specifications can translate into fewer requests for information and a smoother running project.▪

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STRUCTURE magazine

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January 2012

10/5/11 3:16 PM

FOUNDATION Foundation Companies Taking Advantage of Current Events and Trends

Bids Now More Realistic

By Larry Kahaner

I

n a still weak economy, some foundation companies are exploitFitzPatrick also notes that the recession has skewed project estiing recent trends and events to improve their bottom line. mates that are just now beginning to unwind. “Four years ago, For example, Subsurface Constructors, Inc. in St. Louis estimates were provided during the design stage before the recession (www.subsurfaceconstructors.com) is capitalizing on the had hit. When projects actually came up to bid, there was so much ‘going green’ movement by improving soil beneath wind turbine competition that it drove prices down to unrealistic levels. Now, installations. “People don’t think about the wind turbine industry in estimates have become more realistic but budgets are still being general, or about ground improvement in particular, because they squeezed, so there are a lot of owners looking for cost savings on think it’s only one pole,” says Lyle Simonton, Director of Business projects. We’re helping our clients save money but making sure Development. “People don’t realize that there’s a lot of stress on wind that estimates are realistic.” (See ad on page 33.) turbine bases. They sit on a huge mass of concrete, a big pedestal that you don’t see because it’s all below ground, and sometimes that soil im Hussin, Director at Hayward Baker Inc. headquartered needs improvement.” in Odenton, Maryland (www.haywardbaker.com) also has A typical wind turbine pedestal sinks beneath the surface at an angle noticed the price dislocation of estimates and is using it to their for about ten feet and can be about 65 feet wide at the bottom, says advantage. “Although the overall U.S. construction market Simonton. “That’s what we’re supporting on stone columns.” remains tight, we have seen a slight improvement in our margins.

He notes that his company has been expanding away from their We have accomplished this with clients who, in addition to requirMidwest home turf. “We have switched from being predominantly ing a fair price, see value in our ability to recognize, communicate a St. Louis area, deep-foundation contractor into more of a and control risk. Many of these clients have experienced the false national ground improvement contractor over the last five years as economy of working with contractors who priced the work at desa result of the economy driving us in that direction. There aren’t perately low levels, stumbled while performing and then sought to as many deep foundation opportunities as we used to see locally, recover their losses through claims.... A lot of customers who went so we have had to adjust and chase the work a lot further out. We for the lowest price realize now that it wasn’t a bargain at all.” He have been successful doing so.” As for the overall market, Simonton sees the private sector coming back a bit, but Wave Equation Analysis of Piles there still is a lot of public work. “We’ve been doing a huge amount of transRun GRLWEAP to: portation work in Indiana, Oklahoma, Wisconsin and Illinois.”

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B

rendan FitzPatrick, Director – North America for Geopier Foundation Company in Mooresville, North Carolina (www.geopier.com), says that his company is helping SEs deal with earthquakes in areas that had not previously experienced them. “The earthquake that occurred in August, 2011 near Mineral Springs, Virginia, has provoked lots of discussion about seismic codes. We’re seeing a greater focus, a greater emphasis on liquefaction mitigation solutions and designs for seismic events after this rare East Coast quake.”

“

The biggest question out there is: ‘what is the federal government going to do next?’ There’s just so much that needs to be done in the transportation system, and also in the dams and levees sector.

says that during the worst part of the downturn, Hayward Baker was able to charge reasonable fees, in part, because they understood risk. Some firms downplayed risk and got themselves into financial trouble, he adds.

Like others, Hussin says that public projects are still the strongest source of work but that Congress’s inaction on some funding matters is injecting uncertainty into the marketplace. “The biggest question out there is: ‘what is the federal government going to do next?’ There’s just so much that needs to be done in the transportation system, and also in the dams and levees sector.” Currently, the company is working on the Thornton Composite reservoir in Chicago, and just completed the Wolf Creek Dam in Kentucky. (See ad on page 34.)

P

the integrity of drilled shafts in a way that’s different and more economically advantageous, says Beim. “The traditional, current way of testing drilled shafts to see if they’re adequate or not is by doing crosshole sonic logging. Crosshole is a very good test, but it has two disadvantages: One is you have to wait for the concrete to cure in order to perform the test, so you’re waiting a week or so. The second is that you don’t really see the entire cross-section of the drilled shaft.

You can’t see everything that is on the outside of the reinforcement cage.” TIP remedies this by measuring the heat generated by the curing concrete which gives a more complete picture. “Because the data is taken while the concrete is curing, you’re doing the test 24 to 48 hours after construction of the foundation element and getting answers right away so you can move on with the building process much faster…We see a lot potential in this product.” (See ad on page 31.)

Economic pressures in 2011 continue to force companies to re-think markets, processes, reasonable fee structures, products and more. With continued uncertainty in global and U.S. economics, success appears to come from an ability to be nimble and adapt businesses to these events and emerging trends.▪

Hayward City Hall, Hayward, CA

ile Dynamics (www.pile.com), and its sister company GRL Engineers in Cleveland, is helping foundation companies increase profits with a product that can cut testing time and give a fuller reading of any flaws, according to Gina Beim, senior consulting engineer – marketing. The Thermal Integrity Profiler or TIP, now in post-beta testing in about 25 projects, investigates

”

ADVERTISING OPPORTUNITIES

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STRUCTURE® magazine is planning several additional SPECIAL

ADVERTORIALS in 2012.

To discuss advertising opportunities, please contact our ad sales representatives:

CHUCK MINOR Phone: 847-854-1666

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STRUCTURE magazine

32

January 2012

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Product Watch

Repair of Columns with FRP Laminates

By Mo Ehsani, Ph.D., P.E., S.E., Majid Farahani, P.E. and Eric Raatz, P.E.

L

oss of load-carrying capacity in columns and piles in bridges is a major concern worldwide. In coastal regions, the dry-wet cycles lead to corrosion of reinforcing steel in concrete piles and bridge piers. In cold climates, the use of deicing chemicals results in corrosion of steel. Figure 1 shows one of many such cases in Chicago where reinforced concrete columns are severely weakened by corrosion and steel trusses have been added to carry the load. Similarly, in industrial facilities such as mines, aggressive chemicals cause premature corrosion of steel columns.

Thousands of wooden utility poles weakened by infestation break each year during hurricanes and tornados. Many old bridges are supported on timber piles. Due to recent successes in cleaning the waterways, marine borers have returned and the timber piles are deteriorating at alarming rates.

These scenarios all require efficient techniques for in-situ repair and retrofit. The ideal solution will not only replace the loss in strength due to decaying materials, but should create a stronger and more durable structural element.

The concept of repair and retrofit of structures with FRP was first introduced by the principal author in the late 1980s (Ehsani and Saadatmanesh, 1990). In the ensuing years, the same researchers received the first grant awarded by the NSF to study retrofit of bridge piers with Fiber Reinforced Polymer (FRP) products (Saadatmanesh et al. 1996).

That study, and many others that were conducted worldwide in the following years, have undeniably demonstrated the effectiveness of FRP in strengthening deteriorated columns. A large number of columns in buildings and bridges have been retrofitted with this technique worldwide.

All those studies and field applications use the wet layup technique, whereby fabrics of carbon or glass are saturated with resin in the field and wrapped around the column. However, there are several shortcomings with that technique. The flexibility of the fabric requires that the surface of the host structure be repaired to a smooth surface before the fabric can be wrapped onto the column. This prolongs the repair time. Similarly, the flexible fabric cannot

Figure 1: Corrosion-damaged concrete piles in Chicago being assisted with steel trusses.

be bonded to wooden piles that have an uneven surface. The wet layup is also useless for repair of steel column shapes.

FRP Laminate To overcome the above shortcomings, a new form of FRP laminate has been developed (Ehsani, 2010). During the manufacturing process, one or more layers of carbon or glass fabric are saturated with resin and subjected to heat and pressure to construct pre-cured laminate sheets as thin as 0.01 inches. The precision required to produce such a thin laminate was one that was finally achieved after an extended R&D process.

The laminates are 4 to 5 feet wide and are supplied in rolls as long as 300 feet. The tensile strength of these laminates ranges between 60,000 and 155,000 psi depending on the number of layers of fabrics and the orientation of the fibers.

Unlike the wet layup system, the laminates are stiff enough to stand on their own (Figure 2). In the field, an appropriate length of the laminate is cut and wrapped around the deteriorated column to create a structural shell that is not bonded to the host column. A thin layer of epoxy is brushed over the overlapping portion of the laminate to create a two- or three-ply shell in the field – similar to a sonotube. The annular space between the shell and the host column is filled with resin or grout to make the host column and the shell work compositely.

Advantages of the New System

Figure 2: Carbon and glass FRP laminates.

STRUCTURE magazine

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January 2012

FRP laminates offer several advantages over conventional methods and materials used for repair of columns and piles. In the field, the laminates are usually wrapped two times and epoxy is applied in the overlapping portion to create a seamless shell around the column.

From a structural behavior point of view, the combination of high tensile strength of the laminates and the creation of a seamless shell results in a tube that offers very high confining pressure for the grout and

Figure 3: Repair of steel poles at TEP substations: original repair concept; corroded pole; filling the pole with grout; reinforcing steel welded to base plate; applying epoxy to the laminate, wrapping it around the pole and holding it with straps while grout is placed; finished and painted jacket.

the pile. The magnitude of this confining pressure depends on the strength of the laminates and the number of plies that are incorporated in forming the shell in the field. For example, if a concrete pile constructed with 4000 psi concrete is encased in a laminate jacket that offers a confining pressure of 600 psi, the confinement results in a rise of concrete compressive strength from 4000 psi to 6600 psi.

In the wet layup FRP systems, it is customary to prepare coupons (witness panel) of the installed fabrics each day. These coupons are later shipped to a qualified laboratory for strength verification. However, by the time the results become available, the project is most likely completed, making any remedial measures difficult to implement. In contrast, the laminates can be tested in advance and any substandard roll can be rejected.

From a construction point of view, the laminates can be made into endless geometrical shells in the field; this eliminates time and expense of ordering customized jackets in advance and speeds the repair process.

Similarly, shipping and storage costs are reduced. The light-weight laminates require no heavy equipment for handling, and the entire repair kit and necessary tools fit on a typical pickup truck. This eliminates traffic controls and, in most situations, reduces labor, equipment, and associated delays and expenses.

FRP laminates also serve as a moisture barrier, protecting the grout and the host column from future deterioration. Even in cases where reinforcing steel is placed within the annular

space, there is no need to provide substantial concrete cover for the reinforcing bars. This, combined with the ability to build the jacket to any size in the field allows construction of snug-fitting jackets that minimize the volume of grout needed for repair.

In certain applications, for example when a concrete or wooden pile is embedded in soil, the repair can be completed with no open cut trenches. The shell is first created above ground and is free to slide up and down along the height of the pile. Next, high pressure water or an air jet is used to remove a 1-inch ring of soil adjacent to the pile. Then the shell is lowered along the pile into its final position and the annular space is filled with resin or grout.

Similarly, in repair of underwater piles, it is possible to construct the jacket on the portion of the pile above the waterline and gradually lower the jacket into the water as it is being constructed. Moisture insensitive epoxies are used in such applications to allow curing of the epoxy in water. Such repairs can eliminate the use of costly divers and result in significant cost savings.

FRP laminates are non-metallic and will not corrode. They offer a long service life with little maintenance. The laminates are ideal for repair of deteriorated concrete or wooden piles and utility poles. In such applications, it is best to inject a low viscosity resin in the annular space. The resin can be pressurized to penetrate into the voids and crevices of the concrete or wood for enhanced structural performance and elimination of decay from the environment and insects.

STRUCTURE magazine

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January 2012

Field Application There are several different structure types within Tucson Electric Power Company (TEP) substations that are typically constructed with galvanized 10- x10-inch hollow steel tubes (HSS). Due to improper drainage, moisture from rainwater is trapped inside the tubes and causes significant corrosion near the base of the structures. Figure 3 shows a typical HSS where the corroding steel has been scraped off and removed from the inside face of the pole. Earlier attempts to remedy the problem called for steel plates that were externally bolted to the lower 3-feet of the structures (Figure 3). However, these repairs would hide the corroded portion of the structures from view and inspection, while the corrosion process continued inside the poles.

Rather than replace the structures, use of the FRP system enabled the structures to be repaired in place and resulted in continuing system reliability. With proper oversight of safety personnel, the structures could be repaired without need for a costly outage.

The repair of the poles with laminates was aimed at strengthening the lower 3 feet of the structures. An access port about 3 inches in diameter was cut at an elevation of 33 inches from the base. All loose rust was removed from inside the structure and the openings were temporarily sealed with plywood and clamps. A non-shrink high-strength grout was mixed and pumped into the structure from the access port. Four No. 5 U-shaped reinforcing bars were welded to the base plate; these bars were primarily for enhanced flexural capacity of the structure.

Figure 4: The I-70/I-270 interchanges in St. Louis, MO where 49 corroded bridge piling were recently repaired with FRP laminates.

rating of this bridge to poor (National Bridge Inspection rating of 4 on a 9 point scale).

This meant these bridges were considered Structurally Deficient due to the number of piling with significant section loss (Figure 4).

The repairs were completed in just two weeks, improving all four bridges to a Satisfactory Condition Rating (NBI rating of 6). All of this was affordable enough to be funded with the region’s operations budget, and repairs took place on one of the busiest highways in Missouri without causing any delays or distractions to the traveling public.

FRP laminates have been used on other projects, including the repair of underwater concrete piles in a condominium building in Miami, FL. They are currently being considered for repair of timber bridge piles and utility poles. The numerous applications attest to the unique features of this product.▪

STRUCTURE magazine

Mo Ehsani, Ph.D., P.E., S.E. is Professor Emeritus of Civil Engineering at the University of Arizona and President of QuakeWrap, Inc., Tucson, AZ. He may be reached at Mo@QuakeWrap.com.

Majid Farahani, P.E. is Civil/ Transmission Engineering and Standards Supervisor at Tucson Electric Power Company, Tucson, AZ. He may be reached at MFarahani@TEP.com.

Eric Raatz, P.E. is Civil/Transmission Engineer at Tucson Electric Power Company. He may be reached at ERaatz@TEP.com.

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

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Due to its dielectric properties, a glass laminate with tensile strength of 62000 psi and thickness of 0.026 inch was used. A 3-foot wide x 8.5-foot long piece of laminate was used for each structure. A special two-component epoxy was mixed in the field and applied to an approximately 5-foot long section of the laminate. The mixed epoxy has a paste-like consistency and is applied with a trowel to a thickness of 20-30 mil. The laminate is then wrapped loosely around the structure to create a two-ply shell. The 8.5-foot length of the laminate allows creation of a two-ply 15-inch diameter shell with 8 inches of overlap beyond the starting point.

At this stage, before the epoxy cures, ratchet straps must be used to hold the shell in the desired shape. A 1-inch diameter PVC pipe was installed to make sure no rain water will accumulate inside the structure. The bottom edge of the jacket was sealed with tape atop the base plate.

Grout was placed into the shell form.

Consolidation of the grout was completed with a small vibrator and the top of the grout was finished with a trowel. Before the grout sets, the hydrostatic pressure from the grout pushes the inner layer of the jacket outward against the outer layer and forces the two plies of the laminate to be tightly pressed against each other.

After several hours, the ratchet straps were removed and the exterior of the shell was painted. All of these repairs were performed while the substation remained fully operational.

A similar approach was used to repair 49 steel H piling in four bridges at the intersection of I-70 and I-270 in St. Louis, MO (Ehsani and Croarkin, 2011). Routine inspections had resulted in lowering the substructure condition

37

January 2012

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core requirements and lifelong learning for structural engineers

Education issuEs

Resolution of Deficiencies in Engineering Education

By Kevin Dong, P.E., S.E.

T

his is the second article in the Engineering Education series, focused on education requirements and lifelong learning for structural engineers. The series provides suggested selfteaching course content outlines for Structural Steel, Reinforced Concrete, and Timber and Masonry prepared by the Basic Education Committee of NCSEA. The author has prepared the Concrete Design curriculum outline in this article for those needing guidance in selecting a course that will help them become a more rounded structural engineer.

Concrete Design Course Content • Mechanics and assumptions of reinforce concrete design ° Whitney stress block ° Reinforcement ratios and the balanced condition ° Cracked section properties • Gravity load resisting systems ° Column design • Premise of design equations • Un-braced length, slenderness ratio, and second order effects • Ties and cross ties to achieve confinement • Reinforcement ratios and limits • Deformation compatibility and ACI Chapter 21 requirements Beam/one-way slab design ° • Limit states, such as tension control, and its relationship to the steel ratio • Tee-beams • Shear design • Deflection and serviceability limits ° Cracked section properties, creep, and compression reinforcement Beam-column elements ° • Combined stresses – P vs. M diagram ° Compression controlled, balance point, and tension controlled regions • Second order effects and slenderness ° Basic connection principles • Development length, splices, and hooks • Lateral load resisting systems ° Understand the failure mechanisms and required detailing to ensure the failure mechanism can be formed.

The system proposed for study: special concrete walls

° Special Concrete Walls • Statics and basic wall thickness considerations • Web reinforcement – “code” level and capacity level • Shear friction at construction/ pour joints • Boundary elements • Amplified loads per ASCE 7versus designing for flexural yielding • Computer analysis and modeling to “match” proposed design philosophy and wall detailing Diaphragms ° • Diaphragm shear • Drags and chords • Amplified loads and capacity-based design • Deformation compatibility • Foundations ° Shallow footings • Design of a simple pad footing for beam shear, punching shear, and flexure. Plus introduction of simplified design methods • Constructability considerations and construction sequencing ° Shear wall footing • Applicable load cases • Overturning and bearing • Stress distribution when axial and moment are considered • Potential failure mechanisms or critical sections for shear and bending • Transverse reinforcement and strong band concept • Construction Documentation ° General Notes • Relation to project specifications • Content and purpose of general note sheets ° Framing Plans and “industry standards” for notation • Line weights, line types, hatching, dimensioning, text work • Information required to build, such as openings, dimensioning, and misc. framing members for items such as a roof screen ° Frame elevations • Walls – detail references, framing members intersecting walls, and considerations for splice locations,

STRUCTURE magazine

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January 2012

mechanical couplers, boundary zones, and starter dowels ° Detailing • Load path and detailing for typical gravity elements: slabon-grade, pad footings, beam to girder (reinforcement layering), beam to columns (reinforcement congestion), and column schedules • Load path and detailing for diaphragms and shear walls: collectors and tension reinforcement, boundary zones, wall sections at base, floor, and roof • The bread and butter of the industry, but again, academia does not adequately cover this topic and this is integral to design and ultimately building performance • Elective Topics – not necessary to achieve the goal of life long learning, but helpful to integrate into practice ° Two-way slab design: flat slabs and plates • Direct design method • Equivalent frame method • Drop panels/shear panels • Moment frames ° Strong column – weak beam concept • Beam shear and column moment • Joint shear The full Basic Education for Structural Engineers program containing curriculum, course content and desired outcomes can be viewed at the STRUCTURE website, www.STRUCTUREmag.org. (see the “Education” pages) Structural steel curriculum was discussed in the June 2011 issue of STRUCTURE. The third and final article in this series will address Timber and Masonry design. Kevin Dong and the Basic Education Committee of NCSEA welcome your comments.▪ Kevin Dong, P.E., S.E. is a professor in the Architectural Engineering Department at California Polytechnic State University and a member of the NCSEA Basic Education Committee. He may be contacted at kdong@calpoly.edu.

Code Updates

code developments and announcements

ASCE 7-10 Wind Provisions and Effects on Wood Design and Construction

By Philip Line, P.E. and William L. Coulbourne, P.E., M. ASCE

T

he major change for wind design in ASCE 7-10, Minimum Design Loads for Buildings and Other Structures, is often broadly described as the introduction of new wind speed maps (referred to as ultimate wind speed maps in the 2012 International Building Code (IBC)). Several coordinated changes include: • revised load factors for wind in allowable stress design (ASD), and load and resistance factor design (LRFD) load combinations; • removal of the Occupancy Factor for wind due to new wind speed maps that vary by Risk Category (analogous to Occupancy Category); • reinstating applicability of Exposure D in hurricane prone regions; • revised wind speed triggers for definition of hurricane prone region and wind-borne debris region; and, • revised pressure values for minimum design loads.

Comparison of Design Velocity Pressure The net effect of changes to mapped wind speeds and wind load factors on the calculated design velocity pressure can be significant in some locations, as shown in Table 1.

Locations outside of the hurricane prone region, excluding special wind regions, can be generally represented by a ratio of approximately 1.0, as shown for Dallas, TX. An expected outcome, due to the uniform hazard basis of the new maps, is Figure 1: Application of minimum wind loads. that design pressures for Exposure C locations in the hurricane prone low-rise buildings designed in accordance region (Boston, Virginia Beach, and Miami) with the envelop procedure for low-rise are smaller under ASCE 7-10. Assuming buildings. For comparison, the minimum Exposure D, which is applicable in hur- design pressure of 10 psf, applicable for ricane prone regions per ASCE 7-10, an both walls and roofs under ASCE 7-05, approximate 10 percent increase in design when factored for LRFD is equal to 16 psf pressure is observed for Boston, MA and an (i.e. 10 psf x 1.6 = 16 psf ). approximate 16 percent decrease in design pressure is observed for Virginia Beach, VA.

Wind Speed Triggers

Minimum Design Wind Loads Minimum wind load provisions of ASCE 7-10 for design of main wind force resisting systems (MWFRS), under the directional procedure and envelop procedure, have also been revised to specify a minimum 16 psf wall pressure and a minimum roof pressure of 8 psf projected onto a vertical plane (Figure 1). And, it is now less likely to be the controlling minimum design wind load, particularly for some building configurations in lower wind speed regions and for

Changes to mapped wind speeds are also coordinated with revision of several windspeed “trigger” values, such as the definition of hurricane prone regions (Figure 2). The revised wind speed trigger in ASCE 7-10 for hurricane prone regions (i.e. 115 mph) represents an algebraic conversion of the wind speed trigger in ASCE 7-05. Revised wind speed triggers for wind-borne debris regions and glazed opening protection have also changed, and do not follow the same conversion and exclusive linkage to wind speed maps for Risk Category II.

Table 1: Comparison of design velocity pressures using ASCE 7-10 and ASCE 7-05 (33-foot mean roof height).

ASCE 7-10

ASCE 7-05

Ratio

Risk Category

Design Wind Speed (MPH)

[A] Exp C Velocity Pressure (psf )

[B] Exp D Velocity Pressure (psf )

Design Wind Speed (MPH)

[C] Exp C Velocity Pressure (psf )

[A]/[C]

[B]/[C]

Boston, MA

II

128

35.7

42.1

105

38.4

0.93

1.10

Va Beach, VA

II

122

32.4

38.2

114

45.2

0.72

0.84

Miami, FL

II

170

62.9

74.2

146

74.2

0.85

1.00

Dallas, TX

II

115

28.8

-

90

28.2

1.02

-

Boston, MA

III, IV

140

42.6

50.3

105

44.1

0.97

1.14

Va Beach, VA

III, IV

132

37.9

44.7

114

52.0

0.73

0.86

Miami, FL

III, IV

181

71.3

84.1

146

85.3

0.84

0.99

Dallas, TX

III, IV

120

31.3

-

90

32.4

0.97

-

Location

STRUCTURE magazine

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January 2012

Figure 2: Illustration of hurricane prone regions (FEMA P-804).

Summary

IBC adopts ASCE 7-10 provisions for wind design by reference, and incorporates ASCE 7-10 wind speed maps. A conversion of mapped wind speed to an ASD basis (i.e. Vasd per 2012 IBC is calculated as Vasd = Vult x 0.61/2) is added to the IBC to coordinate with previously established IBC wind speed triggers. For wood construction, the conversion is necessary for use of tables covering attachment of wood structural panels for wind, wind applicability limit for conventional light-frame construction, and wind uplift connector requirements in Section 2308. Within the 2012 International Residential Code (IRC), new maps illustrate ASD-based wind speeds. The IRC format of the wind speed map eliminates the need for conversion of the mapped value as is done in the IBC; however, the contour lines do not directly align with those in ASCE 7-10 maps incorporated in the IBC. The 2012 Wood Frame Construction Manual (WFCM) for One- and Two-Family Dwellings includes ASCE 7-10 Risk Category II wind speed maps, tabulated requirements for wind speeds ranging from 110 mph to 195 mph for both Exposures B and C, and a conversion table to adjust tabular values for Exposure D. The removal of the occupancy factor adjustment to wind loads in ASCE 7-10 will generally limit ease of applicability of WFCM load tables to other occupancy categories. Prior WFCM load tables were based on occupancy Category II, and were easily adjusted by the occupancy factor.

Model building codes and standards that rely on the new wind design approach in ASCE 7-10 include the 2012 IRC, the 2012 IBC, and the 2012 WFCM. Each of these documents addresses implementation of ASCE 7-10 in a different manner. This will likely create confusion for the users of these documents, as they reconcile new wind speed basis of ASCE 7-10 maps and different formats of the maps appearing in the 2012 IRC and 2012 IBC. For wood construction in accordance with the WFCM, the Risk Category II wind speed map is incorporated into the standard directly as it appears in ASCE 7-10 and tabulated requirements will be associated with ASCE 7-10 mapped wind speeds.▪ Philip Line, P.E. is the Director, Structural Engineering, American Wood Council. He may be reached at pline@awc.org.

William Coulbourne, P.E., M. ASCE is the Director, Wind and Flood Hazard Mitigation, Applied Technology Council.

He may be reached at bcoulbourne@atcouncil.org.

This article is based on a more comprehensive paper outlining additional details on changes to wind load provisions in ASCE 7-10. The longer, more comprehensive version has been posted online at STRUCTURE’s website, www.STRUCTUREmag.org.

STRUCTURE magazine

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January 2012

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Coordination with Codes and Standards

ANCHOR UPDATES

news and information from anchor companies American Concrete Institute

Hilti North America

Powers Fasteners

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Description: The American Concrete Institute (ACI) and Concrete Reinforcing Steel Institute (CRSI) have recently launched the new Adhesive Anchor Installer Certification program. This certification is now a requirement in ACI 318, Building Code Requirements for Structural Concrete.

Phone: 800-879-8000 Web: www.us.hilti.com Product: PROFIS Anchor Software Anchor Solutions Description: Hilti leads the way in educating and supporting engineers and installers with more than 1600 field engineers and account managers. Through installer training programs, PROFIS Anchor Software and code approved anchor solutions, Hilti helps to ensure the right anchor and the proper installation on the jobsite.

Phone: 985-807-6666 Web: www.powers.com Product: Construction Fasteners Description: FREE – anchor design software – POWERS DESIGN ASSIST (PDA). Download from the Powers website. Will help designers deal with ACI 318 APPENDIX S. NEW…16 new anchor/fastener Code Compliance ICC-ES Reports!

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Phone: 202-463-2766 Web: www.awc.org Product: 2008 Special Design Provisions for Wind and Seismic Description: Standard with Commentary, covers materials, design, and construction of wood members, fasteners, and assemblies to resist wind and seismic forces.

Phone: 800-707-0816 Web: www.iesweb.com Product: IES VisualAnchor Description: A FREE web application that calculates shear and tension capacity of a rectangular group of concrete anchors. Visit the website to start using VisualAnchor for FREE today.

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Phone: 203-805-0574 Web: www.bentley.com Product: RAM Connection V8i Description: Used for the design of a wide variety of steel connections, including column and gusset base plates per AISC 360-05. Anchor bolts are also designed per ACI 318-08 Appendix D. Base plates supporting a single column or a column with braces can be designed.

Phone: 219-878-1427 Web: www.ctpanchors.com Product: CTP Stitch-Tie Description: Helical reanchoring system for reattaching masonry walls.

Phone: 949-951-5815 Web: www.risa.com Product: RISABase Description: Uses an automated finite element solution to provide exact bearing pressures, plate stresses, and anchor bolt pull out capacities, eliminating the guess work of hand methods. Define bi-axial loads and eccentric column locations. Choose from several connection types and specify custom bolt locations.

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Phone: 630-694-4780 Web: www.itwredhead.com Product: Overhead Trubolt+ Description: The only U.S. manufactured complete overhead anchoring system for rod hanging. This product is ICC-ES listed (2427) and achieves high performance values using shallow embedments.

All Resource Guides and Updates for the 2012 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. STRUCTURE® magazine is not responsible for errors.

Construction Tie Products

RISA Technologies

Phone: 925-560-9000 Web: www.strongtie.com Product: Strong-Bolt™ 2 Wedge Anchors Description: This line of wedge anchors includes the only code-listed, 3⁄8-inch diameter anchor for both 3¼-inch-thick concrete and concrete on metal deck.

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Halfen Anchoring Systems Phone: 210-658-4671 Web: www.HalfenUSA.com Product: HALFEN Description: Adjustable anchoring systems for façade and structural connections. Cast-in channels and T-bolts with high load capacity for curtain wall, precast, masonry, elevator, balcony, and other applications. Anchors for dynamic loads and with 3-dimension adjustability are available in galvanized carbon steel or stainless steel.

Hayward Baker Inc. Phone: 800-456-6548 Web: www.HaywardBaker.com Product: Anchors Description: Hayward Baker provides permanent, temporary, and removable ground and rock anchors for support of excavations, permanent resistance of hydrostatic uplift forces on bottom slabs, and resistance of wind-induced uplift forces. Provides a full range of geotechnical construction services.

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STRUCTURE magazine

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Phone: 866-332-6687 Web: www.deconusa.com Product: Studrails® and Jordahl Anchor Channels Description: Studrails is a North American standard for punching shear enhancement at slab-column connections. Produced to specifications of ASTM A1044, ACI 318-08, and ICC-ES 2494; used to reinforce against bursting stresses in banded posttension anchor zones. Jordahl anchor channels are embedded in concrete and used to securely transfer high loads. Their main application is for flexible connections of glazing panels to high-rise buildings.

NCSEA 2012 Winter Institute

NCSEA News

News form the National Council of Structural Engineers Associations

Hotel Monteleone, New Orleans, Louisiana February 10 -11, 2012

Soft Soil – Water and Wind Friday/Saturday lectures, along with a Friday afternoon tour of the Inner Harbor Navigation Canal (IHNC) and Lake Borgne Surge Barrier.

Friday, February 10

8.0 Professional Development Hours

8:00 a.m. – 8:10 a.m. – Introduction of Topic 8:10 a.m. – 9:10 a.m. – Overview: Inner Harbor Navigation Canal (IHNC) and the Lake Borgne Surge Barrier The centerpiece of the New Orleans Hurricane and Storm Damage Risk Reduction System (HSDRRS), the Inner Harbor Navigation Canal (IHNC)–Lake Borgne Surge Barrier, is designed to reduce risk for some of southeast Louisiana’s most vulnerable areas (New Orleans East, metro New Orleans, Gentilly, Ninth Ward and St. Bernard Parish) from storm surge generated in Lake Borgne and the Gulf of Mexico during a 100-year event. Nearly two miles long and 26 feet high, it is the largest design-build civil works project in the history of the Corps.

Angela DeSoto Duncan, P.E., is the Director for Civil Works, TetraTech INCA Engineers. She recently joined INCA after a 24-yr career with the Corps of Engineers. She was the Corps Design Lead for the IHNC-Lake Borgne Barrier and was responsible for Corps design oversight of the project.

9:10 a.m. – 10:10 a.m. – Geotechnical Engineering and Test Pile Program, Lake Borgne Hurricane Surge Barrier The Lake Borgne Hurricane Surge Barrier comprised the installation of a 1.8-mile long barrier wall, three navigational structures, and two floodwall transitions to existing hurricane protection. This presentation describes the subsurface investigation, pile load tests, and geotechnical decisions that were necessary to support the aggressive schedule for the installation of the barrier wall piles. The barrier wall is comprised of vertical 66-in. diameter concrete cylindrical piles and 36-in. diameter steel pipe driven on batters.

William Gwyn, P.E., the Geotechnical Engineer of Record, is the President of Eustis Engineering, a geotechnical engineering and materials testing firm that specializes in the soft deltaic and alluvial soils that typify southeastern Louisiana.

10:30 a.m. – 11:15 a.m. – Structural Design of Gates The IHNC Lake Borgne Surge Barrier is constructed near the confluence of the Gulf Intracoastal Waterway (GIWW) and the Mississippi River Gulf Outlet (MRGO), a natural funnel indentified as an area of critical vulnerability in the Hurricane and Storm Damage Risk Reduction System (HSDRRS). The design consists of two 150-foot-wide flood control gates at GIWW (a buoyant sector gate and a concrete barge swing gate), a 56-foot-wide vertical lift gate with vehicular bridge at Bayou Bienvenue, and complete floodwall closure of the MRGO. The gates are closed in advance of a hurricane, providing surge protection with a watertight barrier to elevation EI 26.0. The IHNC sector gate is a fully buoyant steel gate designed to be closed in advance of hurricane landfall and can be operated with up to 10 feet of differential head.

Dale Miller, P.E., S.E., the Project Engineer of Record, is currently serving as one of the PIANC U.S. Commissioners and managing the design of the IHNC Lake Borgne Surge Barrier Project in New Orleans, including two miles of innovative floodwall and three major navigation gates.

11:15 a.m. – 12:00 p.m. – IHNC–Overcoming Construction Challenges In April of 2008 the U.S. Army Corps of Engineers awarded their largest ever design-build civil works contract to Shaw Engineering and Infrastructure Inc. (Shaw E&I, Inc.) for the engineering, procurement and construction of the IHNC HSDRRS. This presentation will address the challenges and lessons-learned for the construction of this non-traditional one-of-a-kind civil works project.

Charles M. Hess, Vice President of Operations for Shaw E&I, Inc., and Shaw’s FEMA Account manager, was responsible for all aspects of Shaw’s FEMA Individual Assistance – Technical Assistance Indefinite Delivery/Indefinite Quantity (ID/IQ) contract.

12:00 p.m – 1:00 p.m. – LUNCH 1:00 p.m. – 1:45 p.m. – Moderated Discussions and Video Highlights Enroute to the IHNC 1:45 p.m. – 4:30 p.m. – Tour–Inner Harbor Navigation Canal (IHNC) and the Lake Borgne Surge Barrier 6:30 p.m. – 7:30 p.m. – RECEPTION

Register at www.ncsea.com.

Cost: $350 for one day, or $595 for both days. Price includes breakfast, lunch, breaks, and Friday reception.

Accommodations: Reserve your room at the Hotel Monteleone by January 17, 2012, and pay the reduced rate of $165 per night.

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January 2012

7.25 Professional Development Hours

8:00 a.m. – 9:15 a.m. – ASCE 7-10 Wind Loading and Design This session includes coverage of revised wind speed maps and a building classification system based on risk of a natural hazard to the building or contents instead of occupancy, as used in the past. It will focus on the analytical (directional) method for determining wind pressures, including wind pressure determination for both the Main Wind Force Resisting System (MWFRS) and Components and Cladding (C&C).

William L.Coulbourne, P.E., holds Certifications in Structural Engineering and Building Inspection Engineering and is a national expert in wind and flood mitigation. He has been involved in FEMA Mitigation Assessment Teams for over 15 years, including every major hurricane and flood disaster since 1995.

9:15 a.m. – 10:30 a.m. – Design Aspects of Fluid-Containing Walls, Soil-Retaining Walls and Flood Walls on Soft Soils This presentation will review some of the design and construction aspects to be accounted for in layout, jointing and construction of three types of reinforced concrete walls for fluid-containing structures, soil-retaining structures and hydrodynamic flood walls founded on soft soils. Design examples of each type of wall will be reviewed, illustrating the design differences and foundation considerations required by structural engineers, along with an application to a replacement flood wall system for the HSDRRS. Mike Sheridan, P.E., SECB, is the Lead Structural Engineer for the Memphis District of the U.S. Army Corps of Engineers and has 26 years of private and public structural engineering experience.

12:00 p.m. – 1:00 p.m. – LUNCH and presentation by Dennis Boehme, Hayward Baker 1:00 p.m. – 2:00 p.m. – Foundations in Soft and Challenging Soils When designing foundations in soft soils, there are three options: Use the soft soil directly, improve the soil, or use deep foundations. This talk will focus on ground improvement and deep foundations, describing the different techniques available and giving guidance for their use.

Mike Wysockey, P.E., Ph.D., is the President of Thatcher Engineering, a specialty subcontractor working in design-build earth retention, pile driving, drilled foundations, and marine construction. His publications range from shore erosion, to the effect of local soil conditions on earthquake motions, to the capacity of deep foundations.

2:00 p .m. – 3:00 p.m. – Design of Piles and Piers for Lateral Loads Design of deep foundations for lateral loads will be discussed in two parts, battered piles and plumb piles, with the majority of the presentation focusing on vertical piles, outlining design procedures, and case histories.

Mike Wysockey, see 1:00 p.m. session.

3:15 p.m. – 4:15 p.m. Hurricane and Tornado Shelter Design This session will provide technical information important to consider when designing shelters for use in either tornados or high wind events such as hurricanes. The wind load provisions of ASCE 7-10 Minimum Design Loads for Buildings and Other Structures, the ICC-500 Storm Shelter Standard, and FEMA 361, Design and Construction Guidance for Community Safe Rooms, form the basis for this presentation.

William L Coulbourne, see 8:00 a.m. session.

NCSEA/Kaplan Structural Engineering Exam Review Course Prepare for exam day success with this SE exam review course designed by the National Council of Structural Engineers Associations (NCSEA), Kaplan Engineering Education, and leading structural engineers from across the profession.

January 21-22: Vertical Forces Review February 25-26: Lateral Forces Review Visit www.ncsea.com and follow the “Hot Topics” link for the NCSEA/Kaplan SE Exam Review Course, to register and for more information on the course and the instructors.

Upcoming NCSEA Webinars

January 10, 2012: Rehabilitation of Timber Structures – Paul Gilham January 24, 2012: Reorganization of the ACI 318 Building Code – Randall W. Poston, Ph.D., P.E., S.E. These courses will award 1.5 hours of continuing education. The times will be 10:00 am Pacific, 11:00 am Mountain, 12:00 pm Central, and 1:00 pm Eastern. Approved in All 50 States.

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January 2012

News from the National Council of Structural Engineers Associations

10:45 a.m. – 12:00 a.m. – Building Design for Coastal Flooding Improved foundation performance is one significant contribution to reducing losses from severe coastal events and helping communities recover faster. This session will present information on how to identify all coastal hazards, including the effect of scour and erosion on the flood loads and foundation design. An example of a coastal foundation design will be included.

William L. Coulbourne, see 8:00 a.m. session.

NCSEA News

Saturday, February 11

Structures 2012 Congress Technical Sessions Thursday, March 29, 2012 The Newsletter of the Structural Engineering Institute of ASCE

Track 8:00 AM – 9:30 AM

Blast

Seismic

New and Innovative Materials for Blast Protection

10:00 AM – Predicting Blast Loads Associated with Complex 11:30 AM

Buildings 1

Buildings 2

Business 1

Seismic Design of Midrise Cold-Formed Steel Framing Systems

Chicago’s Leadership in Tall Buildings

Floor Vibration Serviceability

Can Alternative Delivery Method Help the Engineering Community?

Seismic Design and Analysis: General Topics

Tribute to Clyde Baker’s Impact on Chicago High Rise Building Foundations

Integrating Environmental and Seismic Performance Metrics

Trial Designs and Building Code Issues

Threat Environments

12:00 PM – 1:45 PM Opening Plenary Luncheon and Awards Program 2:00 PM – 3:30 PM

Blast Effects on Infrastructure

Innovative Seismic Solutions I

Healthcare and Research Facilities

Achieving Design Build success with Early Involvement of Specialty Contractors and a Collaborative, Model Driven Process

2011 Masonry Code & Specification Update

4:00 PM – 5:30 PM

Collapse Resistance of Steel Frame Structures: Connection Behavior, Slab Effects, and Robustness Assessment

Innovative Seismic Solutions II

Advances in Full-Scale Monitoring of Tall Structures

Sustainability and Steel

Evaluation and Analysis of Existing Masonry Structures

5:30 PM – 6:30 PM Young Professionals Mixer 6:30 PM – 8:00 PM SEI and PCI Welcome Reception in Exhibit Hall (Sponsored By PCI)

Friday March 30, 2012 7:00 AM – 8:15 AM CASE Breakfast Track 8:30 AM – 10:00 AM

Blast

Seismic

The New ASCE/ SEI Standard for Blast Resistant Design

10:30 AM – Blast Resistant Structures in the Petrochemical 12:00 PM

Buildings 1

Buildings 2

CASE

Achieving Economy and Seismic Safety in LowDuctility Steel Buildings

The History of Chicago’s Highrise Structures

2011 Tornado Season: Lessons in Building Design for Structural Engineers

Profitability Killers and How to Avoid Them

Seismic Base Isolation and Damping

Chicago Sports Stadiums

SEI Reconnaisase Report on the Christchurch Earthquake

Key Financial Indicators to Look for When Running a Structural Firm

Industry

Structural Columns

12:00 PM – 1:30 PM Buffet Lunch in Exhibit Hall 1:30 PM – 3:00 PM

Multi-Hazard Robustness Assessment Building Structural Systems

From Hazard to Design – A Case Study of the Benefit on Nonlinear Response History Analysis in Practice

Wind Loads on Super-Tall Towers

Preliminary Study of the Damage Caused by the 2011 Tohoku Earthquake

Making the Transition from Project Manager to Principal – Panel Discussion

3:30 PM – 5:00 PM

Design Concepts for Progressive Collapse Mitigation

What the Future Holds: ASCE 41-13 – Seismic Evaluation and Upgrade of Existing Buildings

Human Perception of Motion in Wind-excited Tall Buildings

Performance of Structures in the Canterbury New Zealand Earthquakes

Succeeding at Ownership & Leadership Transition During Uncertain Times

6:00 PM – 9:00 PM Chicago! Mid America Club Reception (Sponsored by Alfred Benesch and Co. and Thornton Tomasetti, Inc.)

Saturday March 31, 2012 Track

Blast

Seismic

Buildings 1

8:00 AM – 9:30 AM

Blast Resistant Curtainwall

Design Considerations for Timber Buildings

Design and Construction Planning of Iconic Tall Buildings with Current Technologies and Global Perspective

Steel Connection Design

Sustainable Structural Engineering-Gaining Greater Benefits to Communities in Developing Nations

10:00 AM – Historic Structures: Balancing Blast Protection 11:30 AM

Reducing Seismic Risk for Soft-Story Woodframe Buildings

Design and Construction Planning of Iconic Tall Buildings with Current Technologies and Global Perspective – Part 2

Innovative Solutions to Challenging Stability Design Problems

Sustainability and the Structural Engineer: The First World ChallengeTEJH Synopsis

& Aesthetics

Buildings 2

Sustainability

12:00 PM – 1:45 PM Closing Plenary Luncheon and Business Meeting

2:00 PM – 6:00 PM

Post Conference Seminars

For more information about the Structures 2012 Congress, including Registration and Housing STRUCTURE magazine

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January 2012

Non-Building Structures

20th A&C

Bridge Practice

Bridge Research and Implementation

PCI

Special Topics

Wind Loads on Solar Collectors Systems and Rooftops

Recent Innovations and Application of Passive Seismic Control I

ABC’s of Rapid Construction

Seismic Effects I

Diaphragm Seismic Design Methodologies – Part 1

How Digital Databases are Changing the Ways in which Engineers Do Research and Write Codes

Advances in Analysis and Design of Wind Energy Structures

Recent Innovations and Application of Passive Seismic Control II

Emerging Trends in Rail Bridges

Seismic Effects II

Diaphragm Seismic Design Methodologies – Part 2

Finite Element Analysis of Nuclear Structures

Student Structural Design Competition

Opening Plenary Luncheon and Awards Program Evaluation and Retrofit of Petrochemical Strucutres and Pipelines

New Directions in Damage Detection Using Structural Health Monitoring

Transit Rail and Movable Bridges

Seismic Effects III

Concrete Structures Behavior in Recent Seismic Events

Tunnel and Underground Structures: Second Avenue Subway Project, New York

Selected Issues in Analysis and Computation

Movable Bridges

Experimental Investigation of the Seismic Performance of Horizontally Curved Bridges

Concrete Blast Resistant/ Life-Cycle Performance Disproportionate of Structural Systems Collapse Design under Multiple Hazards

Young Professionals Mixer SEI and PCI Welcome Reception in Exhibit Hall (Sponsored By PCI)

Non-Building Structures

20th A&C

Seismic Response of Nonstructural Systems in the Tests at E-Defense

Optimal Design Using Advanced Computational Methods

Aesthetics and Special Criteria for Pedestrian Bridge Designs

Finite Element Analysis Techniques for Fatigue and Fracture Evaluation and Design

The Typical Claim Against a Structural Engineer – Panel Discussion

Topics in Structural Engineering Education and Research

Design, Analysis and Testing of Nonstructural Components

Benchmark Cases of Optimum Structural Design

Pedestrian Bridge Vibration

IDOT Ongoing and Recently Completed Research, Development and Implementation Efforts

The Case of the Sagging Floors

International Buildings

Midwest DOT Bridges

Design of Concrete Bridges with Innovative Materials

Demarcating the Profession: Where Should We Draw the Line?

Design of Timber Buildings: General Considerations

Bridge Practice

Bridge Research and Implementation

Business 2

Special Topics

Buffet Lunch in Exhibit Hall Seismic Testing, Analysis, Qualification, and Performance-based Design for Raised-access Floors and Equipment

Advances in Hybrid Simulation

NB230 – Miscellaneous Topics on Nonbuilding Structures/Nonstructural

Calibration and Validation of Concrete Models

Structural Collapse Due to Snow: 2010-11 Winter

Chicago! Mid America Club Reception (Sponsored by Alfred Benesch and Co. and Thornton Tomasetti, Inc.)

Non-Building Structures

20th A&C

Bridge Practice

Bridge Research and Implementation

Business 2

Special Topics

Design of Unique and Unusual NonBuiliding Structures

Evaluation and Design of New and Existing Buildings Against Disproportionate Collapse

International Bridges

Implementation of Structural Health Monitoring in Management and Inspection of Bridges

Lessons Learned from the Recession and Where Do We Go from Here

Retrofit of Concrete

Unique Structures

Recent Advancements in Collapse Assessment of Structures Under Earthquakes

Cabled Stayed Bridges

Construction and Special Topics

Creative, Collaborative, and Communicative: Perspectives on Developing a Future Generation of Engineering Leaders

Forensic Engineering

Closing Plenary Luncheon and Business Meeting

To view the interactive Technical Program, including all presenters and abstracts, on the SEI Website, visit www.structurescongress.org

Post Conference Seminars

visit our website at www.structurescongress.org.

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January 2012

The Newsletter of the Structural Engineering Institute of ASCE

CASE Breakfast

Structural Columns

March 29 -31, 2012 – Fairmont Chicago, Millennium Park, Chicago, Illinois

CASE in Point

The Newsletter of the Council of American Structural Engineers

Donate To The CASE Scholarship Fund!

The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at minimum, in an ABET-accredited engineering program.

We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates.

One way to enhance the ability of students in pursuing their dreams to become professional engineers is to offer incentives in educational support.

In addition, the CASE scholarship offers an excellent opportunity for your firm to recommend eligible candidates for our scholarship. If your firm already has a scholarship program, remember that potential candidates can also apply for the CASE Scholarship or any other ACEC scholarship currently available.

Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for tax deduction and you don’t have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

CASE Announces the Release of Two NEW Products!

CASE 9-2: Quality Assurance Plan Elements Essential for Quality Client Service High-quality client service – from project initiation through construction completion – is critical to achieving project success and maintaining key client relationships. Elements essential for quality service include: • Client and project ownership by the individuals responsible for the project.

• Continual staff education, including both leadership and technical skill development.

• Firm-wide standard of care.

• Quality control process with a complete communication loop.

• Written Quality Assurance Plan.

As part of the Ten Foundations of Risk Management, CASE Tool 9-2: Quality Assurance Plan provides guidance to the structural engineering professional for developing a comprehensive, detailed Quality Assurance Plan suitable for their firm. A well-developed and implemented Quality Assurance Plan ensures consistent high-quality service on all projects, and includes: 1) Quality Control Review 2) Firm-wide Standards 3) Construction Quality Assurance The quality control review may consist of three elements: Design (Jury) Review, Engineering Review and Construction Document Review. Comprehensive firm-wide standards (consisting of design/analysis standards, documentation standards and construction administration standards) enable staff to gain historical firm-wide benefits while providing resources to ensure the design and documentation are clear, concise, accurate and consistent.

Construction quality assurance is an important element of the quality assurance plan since it is the final step in the process.

Developed by the CASE Toolkit Committee, this tool is available at www.booksforengineers.com.

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CASE Document 7-2011 Commentary on AIA Document A295–2008 “General Conditions of the Contract for Integrated Project Delivery” The American Institute of Architects (AIA) has developed a family of documents intended for use when the Integrated Project Delivery method is used. These documents are entirely new, not updates of existing documents. The Integrated Project Delivery approach is a collaborative process involving all participants through all phases of the Project. The AIA documents assume that the primary parties in Integrated Project Delivery are the Owner, Architect, and Contractor, and the Agreements are written in that manner. Another document prepared by the AIA is titled Integrated Project Delivery: A Guide, which provides the principles and techniques of Integrated Project Delivery from the AIA perspective, and appears to be the basis for the provisions of AIA Document 295-2008. The SER should read and become familiar with AIA Integrated Project Delivery: A Guide before entering into an Agreement for an IPD project.

CASE Document 7-2011 provides assistance to the Structural Engineer of Record (SER) when entering into an agreement with an Architect when the project delivery approach is Integrated Project Delivery.

Developed by the CASE Contract Committee, this commentary is available at www.booksforengineers.com.

January 2012

The Council of American Structural Engineers (CASE) is a national association of structural engineering firms. CASE provides a forum for action to improve the business of structural engineering through implementation of best practices, reduced professional liability exposure and increased profitability. Our mission is to improve the practice of structural engineering by providing business practice resources, improving quality, and enhancing management practices to reduce the frequency and severity of claims. Our vision is to be the leading provider of risk management and business practice education, and information for use in the structural engineering practice.

Your membership gets you free access to contracts covering various situations, as well as access to guidance on AIA documents,

free national guidelines for the Structural Engineer of Record designed to help corporate and municipal clients understand the scope of services structural engineers do and do not provide, free access to tools which are designed to keep you up to date on how much risk your firm is taking on and how to reduce that risk, biannual CASE convocations dedicated to Best Practice structural engineering, bi-monthly Business Practice and Risk Management Newsletter, AND free downloads of all CASE documents 24/7.

For more information go to www.acec.org/case or contact Heather Talbert at htalbert@acec.org. You must be an ACEC member to join CASE. You can follow ACEC Coalitions on Twitter – @ACECCoalitions.

If you would like more information on the items below, please contact Ed Bajer, ebajer@acec.org.

Responsibility after Being Value Engineered

Asked to Certify Something Beyond Control

If a design is value-engineered, is the original design invalidated? The engineer that value-engineered the project still has an obligation to perform to the prevailing standard of care and, generally, would be required to seal any modifications but probably only the modifications. The original engineer is not released from liability for errors and omissions in the original design by the revision, but would not have responsibility for the revisions unless they reviewed and approved them. With properly worded language, the VE engineer can limit his/her liability to only their revisions.

Many public entities are issuing contracts that require the retained engineer to provide “certifications” that go well beyond the engineer’s scope of work and beyond the engineer’s experience or knowledge. Some states have statutory language that says the use of “certify” or “certification” constitutes a professional opinion and does not amount to a warranty or guarantee, express or implied. Some state Boards have language that the engineer should decline to sign or seal any document that relates to matters beyond their technical competence or their scope of services.

Authority to Stop Work

Contract Language: Comply With All Codes, Standards and Regulations

Some contract documents allow the Engineer to stop work that may become defective, even though the same documents may expressly state safety procedures are the domain of the contractor. Some firms disclaim the right to stop work under any circumstances. However, if the engineer “assumes” control of site safety through their actions, they may lose any immunity granted to them and severely impact their insurance coverage.

There should be no question of what to do in the case of imminent danger. The consequences for failure to take action prior to an accident are far greater than when accused of entering into the domain of the contractor’s safety responsibilities.

STRUCTURE magazine

This is common language in many contracts. The problem is with “all”. Thousands of laws and regulations are on the books.

They change frequently and are open to interpretation. In some cases, they conflict with one another. As a professional you are already required to comply with codes and laws, and if you don’t it’s negligence per se. If you can, delete this clause from your contract and delineate your obligation in your scope of services.

If you can’t delete the clause, try to delete the word “all” or put in a finite date when this responsibility ends.

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January 2012

CASE is a part of the American Council of Engineering Companies

CASE Business Practice Corner

CASE in Point

JOIN CASE!

Structural Forum

opinions on topics of current importance to structural engineers

A Young Professional’s Perspective on Structural Licensing

By Greg Cuetara, P.E., S.E.

T

he professional engineer (PE) exam format and content have changed significantly in the past 30 to 40 years, as have the education and experience that engineers receive prior to taking the exam. 30 years ago, engineers did hand calculations for everything and had a good feel for answers that were outside the norm. Today, computers rule our world, and the “feel” of engineering is not as evident. Structures have become more complicated, as have building code provisions, which look more like theory than anything that would be used in practical applications.

The Civil PE exam encompasses many different fields of study, including environmental, water treatment, transportation, geotechnical, and structural. The Civil PE exam has questions in the morning that include all areas of civil engineering, and in the afternoon the examinee chooses a concentration and answers more detailed questions. The Civil PE exam covers many different topics, which means that no single one can be covered in much detail.

Consequently, the Civil PE exam does not sufficiently test examinees on the kinds of challenges that practicing structural engineers face on a daily basis.

The NCEES former Structural I exam was very fast-paced and required quick thinking and knowledge of all current codes and standards. It consisted of 80 multiple-choice problems that candidates had to complete in eight hours, so time was a critical factor. The best way to prepare for this test was to know the basic concepts of structural engineering and do as many practice problems as possible.

The former NCEES Structural II exam required more knowledge but provided more time to dissect each problem into its components. It consisted of four essay-type problems, two in the morning and two in the afternoon, requiring candidates to write out solutions with comments, rather than selecting answers from among the choices given. Knowing where to

“As structural engineers, we save lives.”

– Barry Arnold find every formula in the code was the key to passing this exam, especially the provisions related to seismic principles.

In 2011, the National Council of Examiners for Engineering and Surveying (NCEES) made some important revisions to the exam.

There are no longer separate Structural I and Structural II exams. In fact, the original Structural I exam was never meant to be a stand-alone PE exam; rather, it was intended to be passed in conjunction with the Structural II exam. With this in mind, there is now a single two-day exam that covers all of the material on the older Structural I and Structural II exams, along with additional high wind and seismic content. The format for each day includes 40 multiple-choice questions in the morning and four essay-type problems in the afternoon.

There are laws and rules in every state regarding the practice of engineering. It is important to understand the specific licensing requirements of the jurisdictions in which you intend to practice. Most of them do not distinguish structural engineering from other disciplines, whereas others consider it to be a post-PE credential and require 16 hours of structural engineering exams after you become a PE. It would be safe to say that passing the Civil PE exam and then the new two-day Structural exam will allow you to practice structural engineering in almost every state. Again, the Civil PE exam alone does not effectively test structural engineers; 16 hours of structural exams should be required.

I attended my first NCSEA Annual Conference in 2008 in Cleveland, where I heard Barry Arnold speak about separate

structural engineering licensure. His first words were, “As structural engineers, we save lives.” This statement made me stop and think about why I want to be a structural engineer, and you should do the same.

We all have our reasons, and mine is exactly what Barry said – I want to save lives. As a result, I am in favor of anything that will “raise the bar” for our profession.

Many people think that the exams exist primarily to weed people out of the engineering profession. The truth is that the exams are in place to test our knowledge and skills – to verify that we have the capability to keep people safe. More education, more experience, and more exams help us to provide better service to our clients and safer structures on which everyone can rely.

Personally, I have sat through a total of 39 hours of engineering exams – including the FE, Civil PE, Structural I and II, Canadian Ethics, and California Seismic and Surveying – and right now I would not have it any other way. Times are changing; engineering has changed and is currently changing, and we need to keep up for the sake of the safety, health, and welfare of the public.▪ Greg Cuetara P.E., S.E. is a Senior Structural Engineer with the Power group of Stantec Consulting Inc. in Scarborough, Maine. He is the current president of the Structural Engineers Association of Maine (SEAM), serves as the SEAM Delegate to NCSEA, and is a member of the NCSEA Licensing Committee. He can be reached at greg.cuetara@stantec.com.

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

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