STRUCTURE magazine | January 2017

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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January 2017 Concrete Inside: Zurich North America Headquarters

SPECIAL SECTION

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CONTENTS Columns/Departments EDITORIAL

7 The Ever-Changing Face of Communication

Cover Feature

By David W. Mykins, P.E.

26 Raising the Bar

INFOCUS

By Patrick Ragan, S.E. and James Swanson, S.E., P.E. The large size of the Zurich North American Headquarters is not its most unique feature. The building is comprised of three long rectangular bars, with the uppermost bar sitting on top of, and spanning between, the two lowermost bars.

9 Your Mileage May Vary

By Barry Arnold, P.E., S.E., SECB STRUCTURAL SYSTEMS

10 5-over-2 Podium Design – Part 1

By Terry Malone, P.E., S.E.

LEGAL PERSPECTIVES

ENGINEER’S NOTEBOOK

14 How Full Can Concrete Trucks be when Driving on Slabs-on-Grade?

By Rafik R. Gerges, P.Eng, Ph.D., S.E., SECB and Harsh K. Nisar

44 Understanding Indemnification Clauses

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

46 BIM and Structural Engineering

By Desirée P. Mackey, S.E., P.E.

STRUCTURAL ANALYSIS

18 Effective Stiffness for Modeling Reinforced Concrete Structures

SPOTLIGHT

51 Tour de Force for San Francisco International Airport

By John-Michael Wong, Ph.D., S.E., Angie Sommer, S.E., Katy Briggs, S.E. and Cenk Ergin, P.E.

By Rafael Sabelli, S.E., Joe Maffei, S.E., Ph.D.,

BUILDING BLOCKS

Lawrence Burkett

Susendar Muthukumar P.E., Ph.D. and

22 Mass Timber: Knowing Your Options

By Robert Jackson, E.I.T., Tanya Luthi, P.E. and Ian Boyle, P.Eng., Struct.Eng, P.E., S.E. PRODUCT WATCH

STRUCTURAL FORUM

58 Wood Products and Resilience of the Built Environment

By Kenneth Bland, P.E.

32 Roof Penetration Framing

By Bob Hasulak PROFESSIONAL ISSUES

34 What Structural Engineers Need to Know about Resilience

By Erica C. Fischer, Ph.D., P.E., Megan Stringer, P.E. and Christopher Horiuchi, P.E.

IN EVERY ISSUE 8 Advertiser Index 38 Noteworthy 43 Resource Guide (Anchor Updates) 52 NCSEA News 54 SEI Structural Columns 56 CASE in Point

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

STRUCTURE magazine

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January 2017

Features 30 The Wharf 525 Water Washington, DC

By Bill Wilde and Joe Wilkum The use of prefabricated cold-formed steel systems as the primary structure are perfectly demonstrated in the 525 Water project, a mid-rise condominium building. Over 9,000 linear feet of wall framing including complex curves and angles was prefabricated off-site for the project.

40 Foundation Companies Close 2016 Strong and Optimistic

By Larry Kahaner 2017 should bode well for foundation companies, particularly those that answer the call from structural engineers for cost-effective, high performance innovations for ground improvement, software, shallow footings to deep foundations, and more.

On the cover The cover photo shows a view from level 10 of the upper bar atrium of the new Zurich North America Headquarters. Read more in the feature article on page 26.

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Editorial

The Ever-Changing Face of Communication new trends, new techniques and current industry issues Taking Control of Business Expectations

By David W. Mykins, P.E., Chair CASE Executive Committee

J

ust the other day I was talking with a client and said, “I will fax that to you in a few minutes.” That might have been one of the first “senior moments” of my life, or at least the first I remember.

I caught the mistake right away, and we both had a chuckle about how far technology has come in the course of our careers. However, the incident got me thinking about our use of technology.

In my career, I have seen our profession go from using calculators to computers, from hand drafting to BIM modeling, from telephone calls to emails, and from tape measures to laser scanners. These innovative technological advances have allowed us to examine, analyze, design and draw some of the most sophisticated and complex structures in history. They have increased the speed of our communication and the accuracy of our work, but these new sophisticated tools require new training and new quality control reviews to ensure the safety of the structures we design.

A short search through the archives of STRUCTURE magazine will produce a number of articles on the use of computers and software in design. In fact, in 2007 there was an article or editorial on this issue almost every month. There were even a couple of folks who predicted a crisis that would result in the collapse of structures. However, some authors provided very thorough examinations of the pitfalls of blind reliance on computer results, and practical suggestions for education and training to avoid getting into trouble. I believe that a decade later, while we still need to be vigilant in our use of technology for design, we also need to be aware of how we use technology in other aspects of our business.

Our entry-level engineers have never known a time without personal computers, and some even seem to have been born with a cell phone in their hands. They can text faster with two thumbs than I can type with two hands. Because of this, they are unafraid to adopt and use new technology. However, just as they need to be taught how to use structural analysis software properly, they must also be shown how to use technology for business communication.

According to a recent report by The Radicati Group, Inc., the average business email account receives 90 emails per day and sends 33 emails. This is the way we communicate most of the important information in our day to day work. With so much traffic coming in and out of our mailboxes, it seems appropriate that we devote some time to considering how it should be used. This topic may already be addressed in the company’s employee handbook, but should be dusted off once in a while and re-emphasized to ensure that users remain vigilant.

One of the best rules for email use was summed up by an attorney who said, “Don’t say anything in an email that you do not want to see blown up and shown on a big screen in a public courtroom.” With that in mind, we should be careful to make sure that our messages always remain respectful, professional, and factual. Also, because it is sometimes difficult to interpret the intended tone of a written message, it is a good idea to avoid using sarcasm in your communication.

If you follow these simple rules, you may never have to worry about an accidental “reply all” response.

STRUCTURE magazine

No discussion of electronic communication would be complete without including text messaging. Most of our younger engineers and their client counterparts are using text messages as the primary form of social communication; for some, it is becoming an increasingly common means of business communication. Because texting is more informal by nature, those who regularly use it can be tempted to include comments in their messages that they would never put in a written letter or email, which can be very risky if problems develop on a project and these communications become part of the record.

For this reason, some firms prohibit the use of text messages for business communication.

Finally, what about social media? Almost every firm has a Facebook presence, and may also have Instagram, LinkedIn, Twitter, Snapchat or some other social media account. There should be clear guidelines on who can post to the company’s social media accounts and what types of messages are appropriate. And, there also should be policies that address which work-related material is acceptable to share on an employee’s personal account. The purpose of these rules is not to limit anyone’s free speech, of course, but rather to protect against improper sharing of confidential information.

There are lots of excellent references that address the proper use of electronic communication and social media. The topic is covered in several of the CASE National Practice Guidelines and Tools that are available to our member firms free of charge. Take a few minutes to review the policies in your office and see if they need updating, and ensure that you are using these tools correctly. Feel free to email me or, if you want to go old school, send me a fax with your questions or comments.▪ David W. Mykins is the President and CEO of Stroud, Pence & Associates, a regional structural engineering firm headquartered in Virginia Beach, VA. He is the current Chair of the CASE Executive Committee. He can be reached at dmykins@stroudpence.com.

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January 2017

ADVERTISER INDEX

PLEASE SUPPORT THESE ADVERTISERS

American Concrete Institute ................... 4 BASF..................................................... 38 Cast ConneX........................................... 2 Dlubal Software, Inc. ............................ 45 Geopier Foundation Company.............. 41 Halfen USA, Inc. .................................. 29 Hayward Baker, Inc. .............................. 39 Integrated Engineering Software, Inc..... 33 Integrity Software, Inc. ............................ 8 KPFF Consulting Engineers .................. 19 Legacy Building Solutions ..................... 13 NCEES ................................................. 47

Powers Fasteners, Inc. ............................ 59 Professional Publications Inc. (PPI) ....... 50 Rhino Carbon Filter .............................. 21 RISA Technologies ................................ 60 Simpson Strong-Tie............................... 17 Structural Engineering Inst. of ASCE .... 37 Structural Technologies ......................... 25 StructurePoint ......................................... 6 Struware, Inc. ........................................ 49 Subsurface Constructors, Inc. ................ 42 Super Stud Building Products, Inc......... 35 Trimble ................................................... 3

ADVERTISE IN PRINT and ONLINE Visit our website to see what advertising opportunities are right for you! www.STRUCTUREmag.org

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ADVERTISING ACCOUNT MANAGER INTERACTIVE SALES ASSOCIATES sales@STRUCTUREmag.org Eastern Sales Chuck Minor 847-854-1666 Western Sales Jerry Preston 480-396-9585

EDITORIAL STAFF Executive Editor Alfred Spada aspada@ncsea.com Editor Christine M. Sloat, P.E. publisher@STRUCTUREmag.org Associate Editor Nikki Alger publisher@STRUCTUREmag.org Graphic Designer Rob Fullmer graphics@STRUCTUREmag.org Web Developer William Radig webmaster@STRUCTUREmag.org

EDITORIAL BOARD Chair Barry K. Arnold, P.E., S.E., SECB ARW Engineers, Ogden, UT chair@structuremag.org Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT Erin Conaway, P.E. SidePlate Systems, Phoenix, AZ John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA

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

Linda M. Kaplan, P.E. TRC, Pittsburgh, PA Dilip Khatri, Ph.D., S.E. Khatri International Inc., Pasadena, CA

Important news for Bentley Users

Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY Brian W. Miller Davis, CA Mike Mota, Ph.D., P.E. CRSI, Williamstown, NJ

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January 2017

Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT Greg Schindler, P.E., S.E. KPFF Consulting Engineers, Seattle, WA Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA C3 Ink, Publishers A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 Phone 608-524-1397 Fax 608-524-4432 publisher@structuremag.org January 2017, Volume 24, 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 $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student.

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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.

InFocus

Your Mileage May Vary new trends, new techniques and current industry issues

Are You Taking Full Advantage of CEU Opportunities?

By Barry Arnold, P.E., S.E., SECB

A

re you investing in your future or wasting your time and money on CEUs? CEUs are an investment in your future and, like all significant purchases, should be taken seriously.

At eighteen, I was ready to make an investment in my future by buying a reliable, affordable, and economical car, so I headed to the used car lot. Among the numerous options in color, age, make, mileage, and models, I found a car that fit my budget, appeared road worthy and, according to the Dealer’s Data Sheet, got high gas mileage. I was in heaven.

Within two weeks I was stranded on the roadside twice and had to pay for major repairs. It also became apparent that the only way the car was going to achieve the advertised mileage was if it was freefalling or being towed, so I returned to the dealer to complain.

The salesperson pointed out the fine print on the bottom of the Data Sheet which read: Your mileage may vary. He followed up with, “You get what you pay for.” My money was spent, and I did not get what I needed. I was in misery.

Adages like “Your Mileage May Vary” (YMMV) and “You Get What You Pay For” (YGWYPF) are subcategories of Caveat Emptor (Latin for “Let the buyer beware”) that are more than just witty sayings and apply to more than just purchasing used cars.

A college education was my next big purchase, and the phrases YMMV and YGWYPF were in the forefront as I thoroughly researched various universities. I considered location, convenience, cost, professor credentials, and the college’s emphasis (teaching, research, etc.). Because college would be the foundation of my career, I was determined to get the biggest return on my investment and make the best choice.

After securing my degree, I came to realize that college was not, and could not be, the end of my education. I realized that I had not only a chance but a responsibility to continue my education by earning Continuing Education Units (CEUs or PDHs), which give me an opportunity to not only refine and improve my engineering skills but to achieve greater success. Self-Development Guru Brian Tracy pointed out that, “Those people who develop the ability to continuously acquire new and better forms of knowledge that they can apply to their work and to their lives will be the movers and shakers in our society for the indefinite future.” CEUs provided the opportunity to acquire new and better forms of knowledge.

Beyond the personal gains an engineer may receive through continuing education, CEUs are important to the profession and the safety of the public. They offer opportunities to learn about new procedures, materials, and techniques. CEUs help engineers stay up-to-date with current code requirements. Ultimately, CEUs are an investment in your future and, therefore, should be taken seriously. Although some states accept almost any CEUs to retain a professional engineering license, it is important to maximize the return on your investment of time and money by participating in CEU programs that will build on your college education and fill gaps where additional training is

STRUCTURE magazine

needed to open doors to new opportunities. As Benjamin Franklin said: “An investment in knowledge pays the best interest.”

YMMV and YGWYPF apply to our investment in CEUs. CEUs require an investment of your time and your money – both of which are non-refundable – so it is important not to get caught in the YMMV and YGWYPF trap. The easiest way to avoid the trap is to have a plan.

I recently spoke to a group of engineers and suggested a 4-step process for securing the most from CEU opportunities: 1) Determine where it hurts. What problems are you currently facing? What challenges are preventing you from achieving your highest potential? Determine your weak points and address them by obtaining CEUs in relevant technical or non-technical courses, such as business development, marketing, networking, human resources, writing, accounting, or team management. Be open to new learning opportunities.

2) Consider before you buy. Not all CEU programs are created equal. Some are true educational opportunities filled with valuable content while others merely give you something to do for an hour.

Look for providers with a proven record of offering quality programs.

3) Be prepared, be present. Request the instructor’s slides/notes before the presentation, so you will know what the course will cover and you can prepare questions. You paid to participate in the event.

You know where it hurts. Now ask your questions and get answers.

Be actively engaged in the educational experience.

4) Have a retention plan. The information you acquired is of little value if you do not remember it. Research indicates that you will only remember 50% of a 10-minute presentation immediately after you hear it. By the next day, you will lose 75% of the information.

Within a week you will only remember 10% of what you learned.

The best way to receive long-term benefit from a presentation is to review the related written material early and often.

If you feel like you are not receiving the mileage you should out of your career, or that your career has stalled and left you stranded on the side of the road while your competition and colleagues pass you by, I recommend reevaluating your continuing education vehicle. Engage in programs that will provide a return on your investment. Carefully consider available CEU options and strengthen your long-term success by investing in educational opportunities that will benefit your career and protect the public. What are your thoughts? Would you like to share your ideas? The discussion continues at www.STRUCTUREmag.org.▪ Barry Arnold (barrya@arwengineers.com) is a Vice President at ARW Engineers in Ogden, Utah. He chairs the STRUCTURE magazine Editorial Board and is the Past President of NCSEA and a member of the NCSEA Structural Licensure Committee.

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Structural SyStemS discussion and advances related to structural and component systems

N

ationwide, there has been an increase in the demand for multi-story mixed-use and multi-residential structures. Common configurations include up to five stories of residential use over retail, commercial, office, and parking occupancies, similar in configuration to the building shown in Figure 1. Podium designs are one way to maximize the number of stories, increase unit density, and lower construction costs. This article covers important design considerations and traditional approaches related to the design of a five-story wood-framed structure over a two-story concrete or masonry podium.

The 2012 and 2015 editions of the International Building Code (IBC) allow a maximum building height above grade of 75 feet using Type IIIB construction and 85 feet for Type IIIA if NFPA13 sprinklers are used. However, they only allow up to five stories for Types IIIA or IIIB structures under those same conditions. Structural provisions in the American Society of Civil Engineers’ Minimum Design Loads for Buildings and Other Structures (ASCE 7) limit the maximum height of wood structural panelsheathed shear walls to 65 feet above the base of the seismic force-resisting system (SFRS) in Seismic Design Categories (SDC) D, E, or F. In order to gain additional stories, increase building area, and stay within the allowable building and seismic system heights, the IBC and ASCE 7 each have provisions which enable podium designs.

IBC 2015 Section 510.2 allows an upper portion of any construction type to be built over a lower portion where the two portions are treated as separate and distinct structures. This is for purposes of

5-over-2 Podium Design Part 1: Path to Code Acceptance

By Terry Malone, P.E., S.E.

determining the allowable area limitation, continuity of firewalls, type of construction, and number of stories. This allowance only applies when: • The building portions are separated by a horizontal assembly with a minimum 3-hour fire resistance rating, • The building below is of Type IA construction and is protected throughout with NFPA13 sprinklers, • Shafts, stairways, ramps, and escalator enclosures penetrating the horizontal assembly have a 2-hour fire resistance rating, and • The maximum building height measured in feet above grade is not exceeded.

In versions of the IBC up to and including 2012, the lower portion of the construction described by these provisions, commonly referred to as the podium, can be no more than one story above the grade plane. However, the 2015 IBC allows multiple story podiums. This allows two stories of podium with five stories of wood framing above to meet the 85-foot maximum building height limitation and also meet the 65-foot SFRS height limit. For buildings designed in jurisdictions enforcing codes preceding the 2015 IBC, this would require an alternate means and methods request approval by the Authority Having Jurisdiction (AHJ). However, knowing that this allowance is provided in the 2015 edition often eliminates the AHJ’s concerns.

Example floor plan configurations typically encountered in mid-rise multifamily construction are shown in Figure 2. These plans are frequently rectangular in shape with or without exterior shear walls, or they can have multiple horizontal offsets and wings. The lateral force resisting system for the flexible upper portion is typically built with wood-framed shear walls sheathed with wood

Terry Malone is a Senior Technical Director of Architectural and Engineering Solutions at WoodWorks. He is the author of The Analysis of Irregular Shaped Structures: Diaphragms and Shear Walls, published by McGraw-Hill and ICC. He may be reached at terrym@woodworks.org.

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

Figure 1. Typical mid-rise five stories of wood framing over the two-story concrete podium.

10 January 2017

Blocking used to fasten wall board and reduce vertical shrinkage

Typical Unit

Ext. SW Typical

Open Front

Ext. SW Typical

Joists or trusses

Open Front & Non-open Front Floor Plan w/ and w/o offsets

Semi-Balloon Framing

Figure 2. Typical floor plans for mid-rise multifamily construction.

structural panels (WSP). Many, if not all, of the walls separating the dwelling units are used as interior shear walls in the transverse direction. Lateral forces in the longitudinal direction are typically resisted by the exterior walls and corridor walls. If a rigid diaphragm analysis is warranted, the transverse walls would also act to resist torsional forces.

Designers of these buildings should avoid having more than one SFRS in the flexible upper portion. ASCE 7-10 Section 12.2.3 notes that, when combining different seismic-force-resisting systems in the same direction, the most stringent applicable structural system limitations of ASCE 7-10 Table 12.2-1 shall apply. For example, lightframed shear walls with WSP sheathing have a response modification coefficient of R=6.5.

Combining light-framed shear walls sheathed with other materials (e.g. gypsum wallboard) having a response modification coefficient of R=2 would require the WSP walls to be designed for forces in excess of three times greater (6.5/2) than if only WSP walls are used. Similar force modifications for wind demands do not apply.

Framing systems for gravity loads in the upper portion commonly consist of loadbearing wood-framed wall configurations as shown in Figure 3. Semi-balloon framing can be used to reduce vertical shrinkage.

This system utilizes top flange joist hangers to support the floor framing off the bearing walls. Considerations with this system include the eccentric gravity load effects on the wall studs caused by top flange joist hangers. This must be accounted for in the design and can in some cases increase the size of the studs. Another consideration is the detailing and added framing challenge of placing the interior wall sheathing between or behind the joist hangers. Several connector manufacturers now have joist hangers that are

Rim joist

Top flange hanger

Corridor Walls Non-Open Front

Corridor Walls

Transverse SW Typical

Transverse SW Typical

Concrete topping Typical Unit

unique for this type of installation, which simplifies the process. The other option is to use platform framing, which is easier to install, reduces stud heights, takes less time to install, and can eliminate the joist hanger and costs associated with semi-balloon framing. However, this method of framing has an increased potential for vertical shrinkage.

Proper detailing for either framing system can address this issue.

Two-Stage Seismic Analysis Structurally, ASCE 7-10 Section 12.2.3.2 provides a two-stage analysis procedure that can be beneficial for seismic design of podium projects. The procedure treats the flexible upper and rigid lower portions of the structure as two distinct structures, thereby simplifying the seismic design process. Only the weight of the flexible upper portion has to be considered in its design, not the entire weight of both portions. The two-stage analysis also allows the seismic base of the upper portion to be the top of the lower portion. This allows measuring the maximum SFRS height for a wood structural panel-sheathed shear wall system, in SDC D through F of 65 feet, from the top of the podium. The requirements for a two-stage analysis are: a) The stiffness of the lower section is ten times the stiffness of the upper section. b) The period of the entire structure is not more than 1.1 times the period of the upper portion considered as a separate structure supported at the transition from the upper to lower portions. c) The upper portion is designed as a separate structure using the appropriate R and redundancy factor, ρ. d) The lower portion is designed as a separate structure using the appropriate R and ρ. The reactions

STRUCTURE magazine

Platform Framing

Figure 3. Typical framing details for load-bearing wood-framed walls.

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from the upper portion are determined from the analysis of the upper portion amplified by the ratio of the R/ρ of the upper portion over the R/ρ of the lower portion. This ratio is not less than 1.0. e) The upper portion is analyzed with the equivalent lateral force or modal response spectrum procedure, and the lower portion is analyzed with the equivalent lateral force procedure.

Some confusion exists regarding the required amplification of forces that are transferred from the flexible upper portion into the podium slab.

The amplification factor in ASCE 7-10 Section 12.2.3.2 (d), when used, applies to only the seismic component of the reaction forces, not the entire reaction-included gravity loads.

Gravity framing (e.g. beam, post-tensioned slabs, columns) supporting a discontinuous shear wall is designed for over-strength where required by ASCE 7-10 Section 12.3.3.3.

Connection requirements to the podium slab are shown in Figure 4 (page 12).

Diaphragm Design Distribution of forces to the vertical resisting elements are based on analysis methods where the diaphragm is modeled as follows: • Idealized as flexible – The distribution is based on tributary area. In common multi-family shear wall layouts, this can under-estimate forces distributed to corridor walls and over-estimate forces distributed to exterior walls with a similar impact on diaphragm forces being delivered to the walls.

• Idealized as rigid – The distribution is based on relative lateral stiffnesses of vertical-resisting elements of the story below. This more conservatively distributes lateral forces to corridor

Wall element, hold downs and connections are designed for std. ld.

Comb.

Vr

Collector

SW4

Connections are designed for std. ld. Comb.

Wall element designed for std. ld. Comb.

V2

Support beam/collector Support column

SW5 Seismic reactions from the flexible upper portion shall be amplified by the ratio

Concrete Podium slab

Conc. wall

Concrete Conc. beam wall > 1.0 Elements supporting discontinuous walls or frames require over-strength factor per Section 12.3.3.3 for connections • Collector embedded into slab • Columns (does not apply to • Podium slabs gravity reactions).

• beam ASCE 7-10 Sections 2.3 or 2.4-Standard load combinations ASCE 7-10 Section 12.4.3-Over-strength factor load combinations

Figure 4. Discontinuous shear wall at podium slab.

VRf

H3

T3

Wall displacement 3rd Flr. SW

C3

Semi-balloon framing

Rod coupler

Overturning

Shrinkage Comp.

Brg. Pl.

V3rd Resistance

and transverse walls and allows easier determination of building drift, but can over-estimate torsional drift and underestimate forces distributed to exterior walls, including diaphragm forces.

• Modeled as semi-rigid – The diaphragm is not idealized as rigid or flexible.

Shear is distributed to the verticalresisting elements based on the relative stiffnesses of the diaphragm and the vertical-resisting elements, accounting for both shear and flexural deformations. In lieu of a semi-rigid diaphragm analysis, it is permitted in the American Wood Council’s Special Design Provisions for Wind and Seismic (SDPWS) 2015 Section 4.2.5 to use an enveloped analysis, analyzing for both flexible and rigid conditions and taking the largest forces.

Current practice for light-frame construction commonly assumes that wood diaphragms are flexible for the purpose of distributing horizontal forces to shear walls. ASCE 7-10 Section 12.3.1.1 (c) allows diaphragms in light-frame structures to be idealized as flexible when 1½ inches or less of non-structural topping, such as concrete or a similar material, is placed over WSP diaphragms, and each line of vertical elements of the SFRS complies with the allowable story drift of ASCE 7-10 Table 12.12-1. Using the flexible diaphragm assumption would allow distribution of diaphragm forces to shear walls to be based on tributary area. In 1999, the Structural Engineers Association of California Code and Seismology Committees recommended that relative flexibility requirements outlined in ASCE 7 Section 12.3.1 be considered for wood framed diaphragms.

12.3.1 Diaphragm Flexibility The structural analysis shall consider the relative stiffnesses of the diaphragms and of the vertical elements of the seismic forceresisting system. Unless a diaphragm can be idealized as either flexible or rigid in accordance with Sections 12.3.1.1, 12.3.1.2 or 12.3.1.3, the structural analysis shall explicitly include consideration of the stiffness of the diaphragm (i.e. semi-rigid modeling assumption).

Even though diaphragms may be idealized as flexible, it is sometimes good engineering judgment to consider other flexibility conditions. Currently, some designers only perform a flexible diaphragm analysis and some a rigid diaphragm analysis, but a few use semi-rigid modeling (enveloping). On that basis, some confusion and lack of consistency exist regarding which type of diaphragm analysis should be employed for a given project. Verifying the

Crushing H2

T2

2nd Flr. SW

C2

Compression blocking

V2nd

Shear wall Deflection (Typ.) Shear wall boundary elements

Tension Side

Rim joist

H1 Discrete hold down system

T1

Platform framing

1st Flr. SW

∑M

C1

Compression Side

Continuous tie rod system w/ shrinkage compensating devices

Figure 5. Typical shear wall components and summation of lateral forces.

diaphragm flexibility is becoming increasingly more important given trends toward larger openings in exterior shear walls, shorter wall lengths, and a greater number of wood frame stories over the podium.

Shear Wall Design Traditionally, shear walls are designed from floor to floor, assuming that they are pinned

STRUCTURE magazine

12

January 2017

at the top and bottom at each floor, and the out-of-plane stiffness of the floor framing is rigid. The sum of the lateral forces from the walls above is transferred to the walls below as shown in Figure 5. Overturning forces are typically determined by dividing the sum of the moment applied at the top of the wall by the distance between the center of the tension anchoring device and the centroid of the compression boundary members. These

3 Δ sw = 8vh + vh + hΔ a EAb 1000Ga b

not account for multi-story shear wall effects on structures having more than three stories.

New studies and discussions are taking place to consider including the effects of wall bending and rotation of the walls acting together as a unit, as will be discussed in Part 2 of this article.

Conclusion Mid-rise structures using podium designs provide many opportunities for cost-effective, higher-density construction. It has

SDPWS Eq. 4.3-1

For SDPWS Equation 4.3-1, the first term represents the bending deflection resulting from the lateral forces applied at the top of the wall. The second term accounts for shear deflection and nail slip. The last term accounts for rigid wall rotation. Wall rotation for shear walls typically includes the consideration of rod elongation, anchor slip, and the crushing effects at the bearing plate and wall plates. Traditional methods of calculating wall deflection using the three- or four-part deflection equation do STRUCTURE magazine

become increasingly important to consider the relative stiffness of diaphragms and shear walls, and the effects of multi-story shear walls as buildings become taller and more complex in shape. Research, full-scale testing, and performance-based studies continue to evolve, which impact both changes to the building code and guidelines for engineers. Recognized, comprehensive guidelines and design examples providing in-depth coverage are available, demonstrating traditional methods of analyzing mid-rise and podium designs.▪

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

overturning forces are cumulative to the foundation. Traditional shear walls must comply with the allowable height-to-width, (h/b), aspect ratios of the 2015 SDPWS, which can be found in Section 4.3.4 and Table 4.3.4.

Where the aspect ratio is greater than 2:1, the nominal shear capacity must be adjusted to account for the reduced unit shear capacity in high aspect ratio walls due to the loss of stiffness as the aspect ratio increases. This can significantly affect multi-story shear wall stiffness and capacity.

Two types of anchoring systems can be used as shown in Figure 5, discrete hold downs and continuous tie-rod anchoring systems. Continuous tie-rod systems with shrinkage-compensating devices are becoming the preferred method of anchoring for multiple narrow stacked shear walls because they account for vertical shrinkage at each floor level and provide better control over story drift. It is recommended that bearing plates, rod couplers and shrinkage-compensating devices be installed at each floor to provide a more efficient system and reduce story drift. As overturning forces develop, the bearing plates at the tension boundary members act to resist these forces causing bearing perpendicular-to-grain stresses and crushing at the bearing plate, sole plate, and top plates of the wall. The number of boundary studs on the compression side of the wall are often controlled by these stresses.

Varying rod diameters help reduce rod elongation and wall rotation and produce a more efficient and cost-effective system.

Shear wall deflections and story drifts are determined floor to floor. Traditional shear wall deflection is determined by calculation using the familiar three-part deflection SDPWS Equation 4.3-1, the four- part deflection SDPWS Equation C4.3.2-1 or equation 23-2 found in the 2015 IBC for stapled shear walls.

13

January 2017

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

I

n typical tilt-up construction, the slab-ongrade is the working surface for the lifespan of the building. Certain situations, such as otherwise inaccessible panel casting beds, demand the use of the slab as a path of access for construction vehicles like concrete trucks.

These trucks, when full, can exert high loads and pose a risk to the slab’s serviceability. An acceptable compromise involves filling the truck only partially when driving over the slab-ongrade. The extent to off-load the truck depends on various parameters including slab, soil, and vehicle properties.

For large-scale warehouses and distribution centers, tilt-up construction is the preferred option from a cast-and-schedule standpoint. These buildings tend to have multiple repeatable elements and connections, so all stages of a given project tend to roll at a brisk pace. Typically, once the footings are poured, the slab-on-grade is cast.

The slab is used as a casting bed for wall panels, which form the shell of the building. Once the panels are poured, they are tilted up using cranes and placed into their positions around the building perimeter with temporary braces. The roof is erected and connected to the wall panels to complete the structure.

Most contractors plan the pouring of the wall panels in such a way that all the panels can be poured, albeit in stages, from outside the building.

However, special conditions arise from time-totime, limiting accessibility. The access to wall panel casts might be blocked due to a variety of reasons, such as closeness to the property line or unforgiving soil. In these cases, the slab is used as an access path to pour panels. The slab is typically designed for a uniform load, rack point load, and forklift load addressing service conditions. Such a design may not always accommodate

How Full Can Concrete Trucks be when Driving on Slabs-on-Grade?

By Rafik R. Gerges, P.Eng, Ph.D., S.E., SECB, LEED AP, BSCP and Harsh K. Nisar, MSCE

Rafik R. Gerges is a Principal at HSA & Associates, Inc., La Mirada, California. Dr. Gerges can be reached at rgerges@hsaassociates.com.

Harsh K. Nisar is a Senior Structural Designer at HSA & Associates, Inc., La Mirada, California. He can be reached at harsh@hsaassociates.com.

Figure 1. A typical concrete truck.

14 January 2017

a full concrete truck. Each concrete panel can require 30 cubic yards of concrete, depending on the building dimensions and project location.

A panel pour of 500 cubic yards is not uncommon, for which multiple truckloads are required.

Depending on the slab capacity to take this wheel load, a truck can be partially off-loaded to have minimal effect on the serviceability performance of the slab.

A balance between what the slab can support without visible cracking versus the number of trucks needed to complete a given pour is required.

American Concrete Institute Approach The slab-on-grade is modeled as a plate supported on a continuous area spring. The plate is acted upon by a load distributed over a small area representing a wheel. The design goal is to keep the slab uncracked under the action of wheel loads Most recognized methods are based on Westergaard’s solutions. These equations assume that the plate dimensions are sufficiently large to avoid edge effects due to the load. The critical location of the wheel for design is in the interior of a slab. To avoid the creation of any free edges under wheel loads, and to help against the effects of curling, sufficient smooth dowels should be provided at all edges and corners, which is the current practice. A factor of safety is employed against the modulus of rupture of concrete for additional assurance.

ACI 360R-10, Guide to Design of Slabs-on-Grade, suggests the following methods for determining the thickness of a concrete slab-on-grade under wheel loads. i. Portland Cement Association Method (PCA): published by PCA in Concrete Floors on Ground (2001) ii. Wire Reinforcement Institute Method (WRI): published by WRI in Design Procedures for Industrial Slabs (1973)

420 400 380 360

Concrete Modulus x 10 6 (psi)

C hart 1

C hart 2

340

3

0

10

0

0

30

0

0

50

70

0

40

11 10

220

5 7. 2

200

5 2.

20

240

215

9

280 260

10

10

15

0

20

12

300

30 20

40

13

50

Effective Subgrade Modulus k (pci)

Unit Moment/1000 lb wheel, lb-in.per in

00

320

14

75

4

0 0 0 20 15 10

5

180

8

160 7 140

5 360

6

120

5 100

3

4

5

6

8

10

20

D/k x 10

5

40

30

50 60

80 100

200

300

0

5

10

(in ) 4

15

12

2

5 7. 2

1

25

30

Chart 3

C hart 4 100

50

0

7000

Additional Unit Moment, lb-in. per in

10000 9000 8000

40

0

6000 5000

30

0

4000

334

3000

Influence of other loaded wheel

80

60

20

0

10

0

50

40

10

20

20

0

0 290

20

4

5

1500

2.5

7.2

2000

52

0 10

50

60

70

80

84

40

52

Maximum Slab Bending Moment (ft-lb/ft)

20

Equivalent Loaded Diameter, (in)

90

100

110

120

Distance between centers of load wheels, (in)

1000 900

50

800 700 600 500

4

5

6

7

400

7

8

9

10

11

12

13

14

15

16

17

18

Slab Thickness, (in)

Figure 2. WRI method.

Both of these methods are based on limiting the tension on the bottom of the slab resulting from the applied wheel loads. The ACI guide offers design charts for both of these methods which call for similar inputs and yield similar results. A third method using Corps of Engineers’ Charts is also suggested by the guide. This approach has a far broader scope in terms of accounting for cumulative passes by different kinds of trucks over the slab’s life, but it is not developed to accommodate the precise inputs and the particular outputs this article aims to present.

The Concrete Truck A typical fully loaded truck exerts 66,000 pounds on the slab, 28,000 pounds on each of its rear axles. An empty truck weighs 27,000 pounds. Each additional cubic yard of concrete adds 4,000 pounds. The distance between the front and rear axles is typically around 20 feet. The rear axles are separated by around 4.5 feet and, on each axle, wheels are separated by around 8.5 feet in plan view.

The rear axles govern design, considering the share of load they carry and their proximity to each other. As will be shown in the design

STRUCTURE magazine

15

January 2017

charts, the proximate wheels have a considerable effect on the slab’s design. The typical tire pressure is 120 psi.

Slab-On-Grade and Soil Properties On most industrial warehouses and distribution centers, 4,000 psi concrete is used for slabs. The slab thickness is 6 to 7 inches for smaller scale structures and 7 to 8 inches for larger ones. The crucial property is the modulus of rupture. The ACI design guide suggests using 9√fc times a safety factor. Based on ACI-360 recommendations, a factor-ofsafety of 1.7 has been used in the analysis. A

Additional Unit Moment from proximate wheels from Chart 3

Target Maximum Slab Bending Moment from Chart 4

14 40 13 30

30 40

12

25

Effective Contact Area (in2)

10

9 10 9

Slab Thickness (in)

50 0 20

0

15

11

10

Wheel Spacing (in)

80 120

Stress per 1000-lb Axle Loads, (psi)

60

22

20

Target Maximum Slab Bending Moment per wheel

Target (D/k)0 from Chart 1

For Assumed Point Wheel Load Pwheel Iteration = i

(D/k)i

8

8 7

Positive Increment to Pwheel

7

7

6

(D/k)i = (D/k)0 Yes

Pwheel

No

6

5

i=1 (D/k)1 = (D/k)i

4

5

3 50

100

i=2 (D/k)2 = (D/k)i

200

Subgrade Modulus k (pci)

Figure 4. PCA method.

higher factor-of-safety of 2 may be utilized for additional assurance depending on the engineer’s judgment.

Geotechnical recommendations typically include the value of the modulus of subgrade reaction. Soils that are highly compressible, and have low strength, have lower subgrade modulus (around 100pci) while moderately stronger soils have a higher design subgrade modulus (around 200pci).

Yes

Negative Increment to Pwheel

No i>2 (D/k)i > (D/k)0

Yes Positive Increment to Pwheel

(D/k)2 > (D/k)1

No Yes

i>2 (D/k)i < (D/k)0

No

Figure 3. WRI method flowchart.

Design Methods

Results

Conclusions

The WRI method goes through a series of design charts to estimate the design slab thickness for a given wheel load (Figure 2, page 15). These charts were used in the reverse direction for the purpose of this analysis. Instead of computing an allowable slab thickness for a target wheel load, the allowable wheel load for a given slab thickness and subgrade modulus needed to be calculated. The calculation is tricky as the process now becomes non-linear. One has to satisfy multiple conditions with the chosen inputs. The trick lies in beginning with the inputs that are not affected by the output, and eliminating them. Refer to Figure 3 for the algorithm.

The PCA method simplifies the process, using only one design chart. To estimate the slab thickness, this method uses rupture stress per 1,000 pounds of axle load, the wheel spacing, and the area of contact. It does not have an approach to account for the presence of a proximate heavy axle. An amplification factor on the axle load is used to ensure the inputs are consistent. This amplification factor can be the same as the ratio of the additional unit moment to unit moment obtained from WRI.

A consistent safety factor has been used for both methods. The Table presents a summary of the results for typical slab thicknesses and subgrade moduli. The result in question is the amount of off-loading necessary for a typical truck. It can be seen that both methods yield comparable results for the given inputs. An 8-inch thick slab is almost always fine for a fully loaded concrete truck. A 7-inch slab can allow for around 60 to 80% of a full truck, whereas a 6-inch thick slab can only allow for 25 to 35% of a full truck.

Driving concrete trucks on slabs should not be the contractor’s first choice but rather considered with great caution after all other options are exhausted. While the study relies on values of modulus of subgrade reaction, certified pads may have soft spots. If it happens that trucks drive over those spots, the slab will be damaged. In the authors’ experience, some of this damage may not appear for years after construction. Additionally, possible slab surface damage from rocks, mud, and debris, should be considered and planned for before allowing trucks to go on the slab.▪

Table showing change per truck.

Factor of Safety Method

ACI 360R10

Ringo & Anderson

Used

WRI PCA

2 1.7

3 2

1.7 1.7

Average Average (% Full Truck)

STRUCTURE magazine

16

Change in Cubic Yards of Concrete per Truck Slab Thickness = 6in Slab Thickness = 7in Slab Thickness = 8in Subgrade Modulus (k) 100 (pci)

150 (pci)

200 (pci)

100 (pci)

150 (pci)

200 (pci)

100 (pci)

150 (pci)

200 (pci)

-7.0 -7.3 -7.1 26%

-6.7 -6.7 -6.7 30%

-6.4 -6.1 -6.3 35%

-4.1 -3.5 -3.8 61%

-2.6 -2.3 -2.5 74%

-1.7 -1.5 -1.6 83%

-0.3 -0.6 -0.4 95%

FULL FULL FULL FULL

FULL FULL FULL FULL

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Structural analySiS discussing problems, solutions, idiosyncrasies, and applications of various analysis methods

S

eismic building design has typically been based on results from conventional linear analysis techniques. This type of analysis is a challenge for the design of reinforced concrete because the material is composite and displays nonlinear behavior that is dictated by the complex interaction between its components – the reinforcing steel and the concrete matrix. Simplifying the behavior of reinforced concrete components, so they can be modeled using a linear-elastic analysis approach, is vital to our ability to effectively design reinforced concrete structures.

Modeling of concrete structural elements using linear analysis to extract a reasonable structural response typically involves modifying the stiffness of concrete structural elements. However, this method presents its challenges, including the following: • Effective stiffness is a function of the applied loading and detailing of the component. Reinforced concrete components behave differently under different loading conditions (e.g. tension, compression, flexure), as well as different rates of loading (impact, short term, long term).

• Applying stiffness modifiers can be an iterative process since the assumed stiffness of reinforced concrete elements in a structural analysis model influences the dynamic characteristics of the structure, which, in turn, changes the results of the analysis and the effective stiffness.

• Schedule demands pressure engineers to simplify the design process further, leading to only one stiffness modifier per element type applied to many analytical elements.

This may be significantly inaccurate for a number of reasons, including: o Analysis models can be very sensitive to the stiffness of a single element, (e.g. backstay effects due to at-grade concrete diaphragms or stiff podium structures in a tall building). o Certain types of elements may have varying stiffnesses due to loading and location. For example, a multi-story column in a tall building will have a higher stiffness at the base compared to the roof. o The design may warrant the consideration of multiple ground motion return periods, such as a service-level earthquake and a Maximum Considered Event (MCE) earthquake, each with a unique set of stiffness properties.

This article aids the structural engineer by providing a summary of the range of stiffness

Effective Stiffness for Modeling Reinforced Concrete Structures A Literature Review

By John-Michael Wong, Ph.D., S.E., Angie Sommer, S.E., Katy Briggs, S.E., and Cenk Ergin, P.E. Seismology Concrete Subcommittee of the Structural Engineers Association of Northern California (SEAONC)

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

18 January 2016

modifiers recommended by domestic and international publications for a variety of building components. A literature review of codes, standards, and research articles is provided, along with a brief summary of the key assumptions made in each document. Effective stiffness parameters for flexural and shear stiffness are summarized in the Table for easy comparison.

Domestic Codes A summary of a variety of documents, which were published domestically and are typically used by structural engineers in the United States, is included below. Note that the recommendations provided in each document correlate to specific return periods or hazard events, or specific levels of applied loading. Some recommendations are independent of loading.

ACI 318, Building Code Requirements for Structural Concrete ACI 318-11 is referenced by the 2012 International Building Code (IBC). Sections 8.8.1 through 8.8.3 provide guidelines for effective stiffness values to be used to determine deflections under lateral loading. In general, 50% of the stiffness based on gross section properties can be utilized for any element, or stiffness can be calculated in accordance with Section 10.10.4.1. ACI 318-14 contains similar recommendations for stiffness modifiers reformatted in Section 6.6.3.

Section 10.10.4, Elastic Second Order Analysis, provides both a table of effective stiffness values independent of load level and equations to derive stiffness based on loading and member properties. Commentary Section R10.10.4.1 explains that these recommendations are based on a series of frame tests and analyses, and include an allowance for the variability of computed deflections (MacGregor and Hage, 1977).

ASCE/SEI 41-13, Seismic Evaluation and Retrofit of Existing Buildings Table 10-5 of ASCE 41-13 provides effective stiffness values to be used with linear procedures.

Section 10.3.1.2.1 states that these may be used instead of computing the secant value to the yield point of the component, which is independent of the force level applied to the component.

ASCE 41 differentiates between columns with an axial load greater or less than 0.1*Ag*f'c and refers to Elwood and Eberhard (2009) for further guidance regarding calculation of the effective stiffness of reinforced concrete columns.

Future editions of ASCE 41 will use ACI 369 as the source document for concrete buildings.

The next revision, ACI 369-17, is anticipated to be published with ASCE 41-17 and will include improved stiffness provisions based on current research.

Figure 1- Property Modifiers for Modeling of Concrete Buildings Figureof1-stiffness Property Modifiersfor formodeling Modelingconcrete of Concrete Buildings Table assumptions structures.

Elements Elements Conventional Beams (L/H > 4) Beams Beams

Conventional Beams (L/H > 4)

ACI 318-11 10.10.4.1

0.35Ig

0.30Ig

n/a

1.00Ig

Columns Columns--Pu Pu≥≤0.5Agf'c 0.3Agf'c Columns - Pu ≤ 0.3Agf'c

Columns - Pu ≤ 0.1Agf'c

Columns - Pu ≤ 0.1Agf'c

n/a

Walls Walls (4) (4)

Walls - cracked

Walls - cracked

Walls - shear

Walls - shear

Conventional flat plates and flat

Conventional flat plates and flat slabs slabs

Slabs Slabs

Notes Notes

n/a

0.70Ig

0.70Ig

0.70Ig

0.70Ig

0.30Ig

0.30Ig

Columns - tension

Walls - uncracked

LATBSDC Servicability

FEMA 356

0.50Ig

0.35Ig

0.70Ig

0.50Ig

0.70Ig

0.70Ig

0.35Ig

0.35Ig

n/a

n/a

n/a

n/a

n/a

n/a

0.50Ig

0.50Ig n/a

n/a

0.75Ig

0.50Ig

0.75Ig

0.50Ig

0.40EcAw (10

0.40EcAw (10

0.25Ig See 10.4.4.2 0.25Ig

See 10.4.4.2

0.35Ig

1.00Ig 1.00Ig

n/a

Columns - tension

Walls - uncracked

LATBSDC MCE-Level

0.50Ig

1.00Ig

Prestressed Beams (L/H > 4)

Columns - Pu ≥ 0.5Agf'c

Columns

0.30Ig

0.35Ig

Coupling Beams (L/H ≤ 4)

Columns

PEER TBI

NZS 3101: Part 2:2006

2:2006

0.40Ig (rectangular)

0.70Ig (rectangular)

Paulay &

Priestly, Calvi &

0.40Ig

0.17Ig-0.44Ig

Guidelines LATBSDC Non Linear Ultimate Limit State Servicability Limit CSA A23.3-14 EuroCode TS 500-2000 Priestley NZS 3101: Part ACI 318-11 & Wind Table 6-5 Kowalsky (2007) Models LATBSDC (fy=300Mpa) State (µ=3) (1992) ACI 318-14 Table 10-5 PEER Service TBI MCE-Level 2:2006 2:2006 Paulay & Priestly, 10.10.4.1 (2014) FEMA 356 NZS 3101: Part & (2014) Servicability 6.6.3.1.1 ASCE 41-13 Guidelines Level Non Linear Ultimate Limit State Servicability (Note Limit 3) CSA A23.3-14 EuroCode TS 500-2000 Priestley KowalskyCalvi & Wind Table 6-5 (2007) Table 10-5 Models (fy=300Mpa) State (µ=3) (1992) ACI 318-14 Service (2014) (2014) (Note 3) 6.6.3.1.1 Level

Prestressed Beams (L/H > 4)

Coupling Beams (L/H ≤ 4)

ASCE 41-13

Property Modifier for Modeling Elements Property Modifier for Modeling Elements NZS 3101: Part

n/a

n/a

0.50Ig 0.50Ig

Post tensioned tensionedflat flatplates platesand and Post flatslabs slabs flat

n/an/a

See 10.4.4.2 See 10.4.4.2

In-planeShear Shear In-plane

n/an/a

n/an/a

n/a n/a

(5)(5)

(2) (2)

(2) (2)

n/a

n/a

n/a

0.20Ig

0.20Ig

0.70Ig

0.70Ig n/a n/a

0.30Ig

0.30Ig

0.90Ig

0.90Ig

n/a

n/a

n/a

1.00Ec (1)

1.00Ec (1) n/a

0.70Ig

0.50Ag

n/a

n/a n/a

0.75Ig

0.75Ig

1.00Ag

0.35Ig (T and L 0.70Ig 0.60Ig (T and L 0.40Ig (rectangular) beams) (rectangular) beams) 0.50Ig 0.35Ig (T and L 0.60Ig (T and L beams) 0.35Ig beams) 1.00Ig n/a n/a 0.35Ig 0.50Ig 1.00Ig n/a n/a n/a

0.60Ig (diagonally n/a reinforced) 0.60Ig (diagonally

0.70Ig

0.70Ig

0.50Ig

0.50Ig

0.80Ig

0.80Ig

0.50Ig

0.50Ig

n/a

0.50Ag

1.00Ag

n/a

0.25Ig 0.25Ig

0.50Ig 0.50Ig

n/a

n/a

0.25Ag 0.80Ag 0.80Ag 0.25Ag

n/a

n/a

reinforced) 0.80Ig

0.80Ig0.55Ig 0.55Ig0.40Ig 0.40Ig n/a n/a

n/a

0.80Ig 0.70Ig 0.70Ig n/a

0.32Ig-0.48Ig

n/a

n/a

n/a

n/a

n/a

n/a

n/a

(2) (2)

n/a

n/a

n/a

n/a

n/a

n/a

(3)

(3)

n/a

n/a

0.80Ig (Note 6)

0.70Ig

0.7Ig 0.35Ig n/a

0.70Ig

0.50Ig

0.40Ig n/a

0.35Ig

(9) 0.40Ig - 0.80Ig 0.50Ig 0.40Ig - 0.80Ig (Note 6) (Note 6)

0.50Ig

n/a

n/a

n/a n/a

Notes Notes (1)Non-linear Non-linear fiber elements cracking of of concrete because the the concrete fibers havehave zero zero tension stiffness.

(1) elementsautomatically automaticallyaccount accountforfor cracking concrete because concrete fibers tension stiffness.

(2)Elastic Elastic modulus modulus may material strengths.

(2) may be be computed computedusing usingexpected expected material strengths.

(3) µ is ductility capacity.

(3) µ is ductility capacity.

(4)Wall Wall stiffness stiffness is is intended (4) intendedfor forin-plane in-planewall wallbehavior. behavior.

(5)ACI ACI 318-11 318-11 Section Section 8.8 permits thethe assumption of 0.50Ig for all under factored laterallateral load analysis.

(5) 8.8 (ACI (ACI318-14, 318-14,Section Section6.6) 6.6) permits assumption of 0.50Ig forelements all elements under factored load analysis.

(6) TS 500-2000 specifies the use of 0.4Ig for Pu/Ac/f'c < 0.1 and the use of 0.8Ig for Pu/Ac/f'c > 0.4; interpolate for all values in between 0.1 and 0.4.

(6) TS 500-2000 specifies the use of 0.4Ig for Pu/Ac/f'c < 0.1 and the use of 0.8Ig for Pu/Ac/f'c > 0.4; interpolate for all values in between 0.1 and 0.4.

(7) T and L beams should use recommended values of 0.35 Ig. For columns, categories are P = 0.2 f'c Ag and P = -0.05 f'c Ag (7) T and L beams should use recommended values of 0.35 Ig. For columns, categories are P = 0.2 f'c Ag and P = -0.05 f'c Ag (8) Shear stifness properties are unmodified unless specifically noted otherwise.

(8) Shear stifness properties are unmodified unless specifically noted otherwise.

(9) Effective stiffness per equation. See reference for more information.

(9) Effective stiffness per equation. See reference for more information.

(10) Note that G = 0.4*I, so ASCE 41-13 is recommending that a modifier of 1.0 be used for the shear stiffness of concrete shear walls; that is, they recommmend no reduction in shear stiffness.

(10) Note that G = 0.4*I, so ASCE 41-13 is recommending that a modifier of 1.0 be used for the shear stiffness of concrete shear walls; that is, they recommmend no reduction in shear stiffness.

n/a

n/a

n/a

(9)

(9)

n/a

n/a

0.80Ig 0.60Ig

0.12Ig-0.86Ig

0.12Ig-0.86Ig (9)

n/a

n/a

n/a n/a

n/a (9)

0.50Ig

0.25Ig 0.25Ig 0.50Ig n/a

0.80Ig

0.80Ig (Note 6) 0.50Ig 0.60Ig 0.40Ig

0.7Ig

0.50Ig

0.17Ig-0.44Ig

0.40Ig

0.40Ig

(9)

0.50Ig-0.70Ig

0.50Ig-0.70Ig

n/a

0.50Ig

0.75Ig

1.00Ig 1.00Ig 0.80Ig

n/a

0.32Ig-0.48Ig n/a

0.75Ig

0.40Ig

(9)

n/a

n/a

0.20Ig-0.30Ig

0.20Ig-0.30Ig

(9)

n/a

n/a

n/a

n/a (9)

(9)

n/a n/a

n/a

n/a

n/a

n/a

n/a n/a

n/a n/a

n/a n/a

n/a

0.50Ig

(7)

(7)

Definitions Definitions Ig = GrossIg moment of moment inertia of inertia = Gross L = Clear span of coupling beam L = Clear span of coupling beam H = HeightHof=coupling beam Height of coupling beam Pu = Factored load axial load Pu =axial Factored Ag = Ac = Ag Gross (uncracked) area = Ac = Gross (uncracked) area f'c = Compressive strength of concrete f'c = Compressive strength of concrete Ec = Modulus of elasticity of concrete Ec = Modulus of elasticity of concrete fy = Yield stress of reinforcing steel fy = Yield stress of reinforcing steel MPa = Megapascals MPa = Megapascals Aw = Horizontal area

Aw = Horizontal area

PEER Tall Buildings Initiative

Los Angeles Tall Buildings Structural Design Council (LATBSDC) Manual Section 2.5 requires structural models to incorporate realistic estimates of stiffness

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Guidelines for Performance-Based Seismic Design of Tall Buildings, also referred to as the Tall Buildings Initiative (TBI), is a consensus document that presents a recommended alternative to the prescriptive procedures for the seismic design of buildings taller than 160 feet. Whereas prescriptive requirements suggest a dual system, the alternative procedures in TBI allow for the use of shear-wall-only structures.

While much of the PEER TBI document focuses on nonlinear analysis for larger earthquakes, the provisions of this document also give a set of recommendations for effective component stiffness values to use in a linear-elastic model subjected to a service-level earthquake (minimum return period of 43 years or 50% probability of exceedance in 30 years). The provisions of this document are meant to apply only to relatively slender structures with long fundamental vibration periods, and with significant mass participation and lateral response in higher modes of vibration.

Long Beach Pasadena Irvine San Diego Boise St. Louis Chicago New York

KPFF is an Equal Opportunity Employer. www.kpff.com

The Ardea Portland, OR

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and strength considering the anticipated level of excitation and damage. In lieu of a detailed analysis, the effective reinforced concrete stiffness properties given in Table 3 of that document may be used. This table provides separate values for MCE-level seismic event nonlinear models as opposed to serviceability seismic events and wind loads.

A serviceability seismic event is defined to have 50% probability of exceedance in 30 years; the MCE-level event is equivalent to the MCER of ASCE 7-10, which has a 2% probability of exceedance in 50 years.

Commentary Section C.3.2.4 also states that stiffness properties may be derived from test data or from Moehle et al. (2008).

International Codes and Other References A summary of a variety of documents published outside of the United States, is included below. Note that the recommendations provided in each document correlate to specific return periods or hazard events, or specific levels of applied loading, and some recommendations are independent of loading.

New Zealand Standard NZS 3101: Part 2 (2006 Edition) states that effective stiffness in concrete members is influenced by the amount and distribution of reinforcement, the extent of cracking, tensile strength of the concrete, and initial conditions in the member before structural actions are applied.

To simplify the complex analysis that would be required to address these factors, the standard lists recommended effective stiffnesses for different members, similar to U.S. codes.

However, the level of loading used in NZS 3101 differs from U.S. codes. The ultimate limit state earthquake for a typical structure (importance level 2) is based on a 10% probability of exceedance in 50 years for a structure with a 50-year design life. The ultimate limit state earthquake for a structure with an importance level of 4 is based on a 2% probability of exceedance in 50 years.

The serviceability limit state earthquake for all structures is based on an annual probability of exceedance equal to one in 25 for a structure with a 50-year design life.

Canadian Standards Association Design of Concrete Structures CSA A23.4-14 provides recommended stiffness modification factors in Section 10.14.1.2.

These factors are provided to determine the first-order lateral story deflections based on an elastic analysis. The Canadian Standards

are based on an earthquake with a 2% probability of exceedance in 50 years.

European Codes According to Eurocode 8 (EN1998-3), the elastic stiffness of the bilinear force-deformation relation in reinforced concrete elements should correspond to that of cracked sections and the initiation of yielding of the reinforcement. Unless a more accurate analysis of the cracked elements is performed, this standard recommends that the elastic flexural and shear stiffness properties of concrete elements are taken as 50% of the corresponding stiffness of the uncracked element.

Part 3 of Eurocode 8 provides an equation based on moment-to-shear ratio and yield rotation, which can be used for determination of a more accurate effective stiffness. Both ultimate level and serviceability level loads are addressed in Eurocode 8 for linear and nonlinear analysis.

Turkish Standard Turkish TS 500-2000 refers to the Turkish Earthquake Code (2007), which states that uncracked properties shall be used for components when performing certain types of analyses. However, stiffness modifiers for cracked section properties may be utilized for beams framing into walls in their own plane and for coupling beams of coupled structural walls when performing these types of analyses. Cracked section properties must be used for the analysis of existing structures.

Cracked section properties may also be used when performing advanced analyses.

Paulay and Priestley (1992), Seismic Design of Reinforced Concrete and Masonry Buildings Paulay and Priestley provide recommendations for stiffness modifiers for cracked concrete frame members and shear walls. In their discussion of stiffness modifiers for frame members, they emphasize the inherent approximation in the use of stiffness modifiers.

Recommendations for frame stiffness are provided in Table 4.1 (Pauley and Priestley).

The authors note that the column stiffness should be a function of the axial load, with the permanent gravity load taken as 1.1 times the dead load plus the axial load resulting from seismic overturning effects. For the analysis of concrete wall structures, the authors recommend the use of component-specific equations to determine their effective stiffness.

Priestley, Calvi, and Kowalsky (2007), Displacement-Based Seismic Design Priestley, Calvi, and Kowalsky conclude that the stiffness of a member is related

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to its strength, and that yield curvature is independent of strength. Because of the strength-stiffness relationship, they recommend that engineers performing force-based analyses should always treat the assignment of stiffness modifiers as an iterative process.

This reference provides ranges of stiffness modifiers based on different member strengths for various reinforced concrete elements, all of which correspond to displacement-based seismic design. However, the authors assume that these recommendations can be used for force-based seismic design as long as an iterative process is used.

Conclusion As shown in the Table (page 19) and discussed above, different standards and codes provide varying guidelines for modifying the stiffness of reinforced concrete elements.

When performing a structural analysis, it is useful to review multiple codes and standards to determine the effective stiffnesses of elements. The information derived from multiple sources may reveal a more accurate method of analysis for the particular structure the designer is currently assessing. Because the effective stiffnesses of reinforced concrete elements can have significant effects on the results of structural analysis, it is prudent for the designer to understand the appropriate modification factors and, in some cases, run multiple analyses using upper- and lowerbound stiffness modification factors.▪ John-Michael Wong, Ph.D., S.E., is an Associate at KPFF in San Francisco, California. He has served on the SEAONC Concrete Subcommittee since 2014 and can be reached at john-michael.wong@kpff.com.

Angie Sommer, S.E., is an Associate at ZFA Structural Engineers in San Francisco, California. She has served on the SEAONC Concrete Subcommittee since 2014 and can be contacted at angiesommer@gmail.com.

Katy Briggs, S.E., is a Principal at BASE Design in San Francisco, California. She is the current chair of the SEAONC Concrete Subcommittee and the vice-chair of the SEAONC Seismology Committee. She can be reached at katy@basedesigninc.com.

Cenk Ergin, P.E., is a Senior Design Engineer at Gilbane in Concord, California. He is past chair of the SEAONC Concrete Subcommittee. He can be contacted at cergin@gilbaneco.com.

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Building Blocks updates and information on structural materials

Figure 1. Mass timber panelized products.

M

ass timber building systems are becoming more popular throughout North America as creative and cost-effective alternatives to concrete and steel construction. While post and beam timber frame buildings have been around for centuries, new panelized products have begun to change the way we build with wood.

The term ‘wood construction’ is often associated with light wood frame, a tried and tested method of creating buildings from dimensional lumber and sheathing. Mass timber, however, is a fundamentally different type of construction. Light wood framed buildings are typically erected on site, while mass timber buildings are usually prefabricated as a kit-of-parts which can be erected quickly and smoothly.

The intent of this article is to introduce practicing engineers to mass timber panel products available in the North American marketplace and to highlight some key considerations unique to each.

Mass Timber: Knowing Your Options

By Robert Jackson, E.I.T., Tanya Luthi, P.E., and Ian Boyle, P.Eng., Struct.Eng, P.E., S.E.,

Robert Jackson is a Project Engineer at Fast+Epp Structural Engineers. He can be reached at rjackson@fastepp.com.

Tanya Luthi is an Associate at Fast+Epp Structural Engineers.

She can be reached at tluthi@fastepp.com.

Ian Boyle is a Principal at Fast+Epp Structural Engineers. He can be reached at iboyle@fastepp.com.

The Timber Advantage There are several advantages to mass timber building systems, with the first being construction speed. On mass timber projects, it is possible to see the superstructure completed 25% faster than a steel, concrete, or light wood frame counterpart. Almost invariably, reducing time on site reduces construction costs. Fully coordinated shop and erection drawings can create a smooth and efficient flow on site, where small and large pre-fabricated elements can be installed within a matter of days.

Additionally, mass timber project sites typically require only 10% of the number of trucks to service them when compared to a concrete alternative. As most of these projects use large, prefabricated timber panels for the decking

22 January 2017

system, the labor required on the active deck can be reduced to 25% of that of a concrete alternative. With all of these factors working together, site noise is significantly reduced thereby reducing the impact on the local community.

Aside from these construction phase advantages, mass timber can be an important part of the building industry’s larger narrative about sustainability, which has evolved into a fundamental market force. Structural engineers play a significant role in shaping the built environment – from creating architecturally expressive structural designs to choosing the materials used in those design. Timber is a renewable resource and should be considered in new building designs for its low embodied energy and carbon-storing abilities. It is also a beautiful material; leaving it exposed creates an opportunity to express the structure as part of the architecture.

Common Panelized Products Several mass timber panelized products are being used as alternatives to concrete, steel, light wood frame, and masonry buildings throughout North America and Europe. Figure 1 (left to right, and top to bottom) shows the following: • Nail-Laminated Timber (NLT) • Glued-Laminated Timber (GLT) • Cross-Laminated Timber (CLT) • Laminated Strand Lumber (LSL) • Laminated Veneer Lumber (LVL) • Timber-Concrete Composites (TCC) Nail-Laminated Timber (NLT) NLT floor, roof, and wall panels have been in use since the early 1900s. These panels are typically comprised of Spruce-Pine-Fir or Douglas Fir 2X lumber stock, stood on edge and nailed together side by side. However, any wood species could be used for the lamination stock. Plywood is used to sheathe the panels, providing in-plane stiffness and shear resistance for lateral diaphragm loads. The panels can be fabricated in a shop

Figure 2. Mountain Equipment Co-Op Head Office. Courtesy of Ed White.

environment or they can be nailed together on-site by any reputable carpenter.

Robust moisture protection during fabrication and erection is a must for NLT panels, as they are susceptible to swelling perpendicular to the grain. To mitigate these potential swelling issues, a 2X lamination should be left out every 20 feet and installed back in after the panels have acclimatized.

NLT is a non-standardized one-way panel system. Standards for the base material exist in the form of typical dimensional lumber grading rules.

Typical Panel Dimensions: • Thicknesses: 2.5 to 11.5 inches • Lengths: 8, 10, 12, 16 feet • Max Width (Prefabricated): 4 feet Where spans exceed 16 feet, interlocking finger-jointed lumber may be used or a staggered butt-jointed pattern may be specified.

However, these longer panels tend to be less cost-effective when compared to simple span panels less than 16 feet. Additionally, a fluted profile can be created to help with acoustics and the visual appearance of the material (for example, alternating 2X4s with 2X6s in one panel).

A recent project which used NLT panels in the floor and roof systems is the Mountain Equipment Co-op Head Office in Vancouver, BC, Canada (Figure 2). Panels were prefabricated in 4-foot widths and 40-foot lengths using butt-jointed laminations.

Figure 3. Kin Centre Complex. Courtesy of JS Photography.

provide a fluted soffit, which can help with acoustics and give a unique visual appearance.

GLT panels also require robust moisture protection during erection, as they are susceptible to swelling perpendicular to the grain. One way to mitigate these potential swelling issues is to add a ¼-inch gap between each 2-foot panel, leaving room for expansion and contraction throughout the construction phase and the first few drying seasons.

GLT is a standardized one-way panel system, covered by the American National Standards Institute (ANSI) A190.1-2012 Standard for Glued Laminated Timber.

Typical Panel Dimensions: • Thicknesses: 3.125 to 8.5 inches • Max Lengths: 40 to 60 feet depending on supplier • Typical Spans: 15 to 30 feet • Max Widths: 2 feet, or increments of 1½ inches A recent project which used GLT panels as the secondary roof framing is the Kin Centre Complex in Prince George, BC, Canada (Figure 3).

Cross-Laminated Timber (CLT) CLT panels were developed in Europe in the early 1990s and are now considered to be the

most versatile and robust product for use in mass timber buildings. CLT can be used for floor, roof, and wall panels. CLT panels are comprised of 2X stock that is laminated together in an alternating crosswise pattern, similar to plywood veneers. Typical species used in CLT are SprucePine-Fir, Douglas Fir, or Black Spruce. Due to CLT’s cross laminations, the panels afford significant in-plane shear capacity and can be used as diaphragms or shear walls in building lateral systems. In these cases, panel-to-panel joints need to be carefully detailed for in-plane shear transfer. However, current U.S. building codes and material standards do not recognize the use of CLT in a lateral capacity. Special provisions may be negotiated with the authority having jurisdiction.

CLT panels are currently produced to APA standards at only a few fabrication plants in North America, but many more plants exist in Europe. In-plane panel dimensions are quite stable due to the cross laminations, but the thickness of the panels remains susceptible to swelling and shrinkage. For buildings that load CLT perpendicular to grain over multiple stories, it is important to consider the shrinkage and compression that can occur through the depth of the panel as they accumulate over the height of the building. continued on next page

Glued-Laminated Timber (GLT) GLT floor and roof panels are similar to glued-laminated timber or “glulam” beams laid on their sides, with the lamination lines running vertically. Typical species used in glulam are Spruce-Pine-Fir, Douglas Fir, Black Spruce, Alaskan Cedar, or Port Orford Cedar.

Similar to NLT, plywood is used to stitch the panels together and to act as a diaphragm.

The panels can be produced by any glulam supplier and shipped to site as a pre-fabricated product. Some glulam suppliers are able to

Figure 4. UBC Brock Commons Student Residence rendering. Courtesy of UBC and Acton Ostry Architects.

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Figure 5. Guildford Recreation Centre.

CLT is a standardized product that is often used in a one-way decking capacity.

However, it can also be used as a two-way bending member. In North America, the product is covered by The Engineered Wood Association’s (APA) PRG 320 Standard for Performance-Rated Cross-Laminated Timber.

Typical Panel Dimensions: • Thicknesses: 4.125 inches (3-ply) to 12.375 inches (9-ply) – Many more thicknesses/layups are available depending on supplier • Max Lengths: 30 to 60 feet depending on supplier • Typical Spans: 10 to 35 feet • Max Widths: 8 and 10 feet depending on supplier. Wider panels are available from European suppliers Currently, an 18-story student residence building is being constructed as a CLT hybrid in Vancouver at the University of British Columbia (Figure 4, page 23). The building has 16 floors of two-way, 5-ply CLT panels on glulam columns. There are no beams in this building, creating a flat, point-supported surface for easy service distribution, analogous to concrete flat plate construction.

Laminated Strand Lumber (LSL) LSL panels are a one-way system made from flaked wood strands that have a lengthto-thickness ratio of approximately 150.

Combined with adhesive, the strands are oriented and formed into a large mat or billet and pressed together. Typically, the billets are ripped into smaller beams and rim boards for light wood frame construction, but they can also be left in their larger panel form.

Aspen is used as the fiber of choice for LSL panels by most of the larger North

American suppliers. Plywood is typically used to sheathe the panels, providing inplane stiffness and shear resistance for lateral diaphragm loads. Although there is some in-plane member stiffness due to the semirandom orientation of the flakes, it is not recommended nor recognized by the material standards for diaphragm applications.

In-plane panel dimensions are stable due to the fiber orientation. However, as with CLT, the thickness of the panels remains susceptible to swelling and shrinkage.

Typical Panel Dimensions: • Thicknesses: 1.5 and 3.5 inches • Max Length: 64 feet • Typical Spans: 10 to 20 feet • Max Width: 4 feet Although mass timber products are often used for floor and roof panels, the larger scale of LSL billets offers unique opportunities to machine large structural components out of a single piece, minimizing connections. The recently completed Guildford Recreation Centre in Surrey, BC, used machined LSL billets to create the webs in prefabricated roof trusses spanning 90 feet (Figure 5).

Laminated Veneer Lumber (LVL) LVL panels are a one-way system comprised of glued plywood veneers stacked in parallel, essentially a thicker, single-direction plywood.

Typically, the billets are ripped into smaller beams for light wood frame construction but, similar to LSL, they can also be left in their larger panel form.

Douglas Fir is used as the veneer in LVL panels. Many suppliers in North America can supply LVL beams and billets. Plywood is typically used to sheathe the panels, providing in-plane stiffness for lateral diaphragm loads.

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It is not recommended to use LVL panels in diaphragm applications, as the product is not cross-laminated.

Similar to LSL, the in-plane panel dimensions are stable; however, the thickness of the panels remains susceptible to swelling and shrinkage.

Some Canadian and European suppliers also laminate LVL beams on edge into panels, which exposes the end and edge grain of the veneers rather than the face grain in a typical exposed LVL billet. This technique gives a clean, visual aesthetic and can be used to produce a larger range of thicknesses.

Typical Panel Dimensions – LVL Billet: • Thicknesses: 1.75 and 3.5 inches • Max Length: 66 feet • Typical Spans: 10 to 20 feet • Max Width: 4 feet Typical Panel Dimensions – Secondary LVL: • Thicknesses: 3.125 to 11.5 inches • Max Length: 60 feet • Typical Spans: 10 to 40 feet • Max Width: 4 feet Timber-Concrete Composites (TCC) Timber-concrete composite panels consist of a thicker layer of concrete on the top side and a mass timber panel on the bottom side. The concrete acts as a compression element while the timber acts as the tension element, giving flexural stiffness. There are several ways to engineer the connection between the concrete and timber, generating the required shear flow. They range from glued-in perforated steel plates to fully threaded screws installed at an angle.

TCC floor systems are very efficient and can achieve high span-to-depth ratios. The depth of the concrete topping also allows for electrical conduits and in-floor heating lines to be hidden inside the floor system. Any of the mass timber panels previously mentioned can work as the tension lamination in a TCC floor system.

Typically, the concrete is cast on-site directly on top of the timber panels, connecting them together. However, precast versions of the concrete compression element are possible by installing proprietary screw sleeves within the concrete. Additionally, timber-concrete composite T-beams are possible with wood beams rather than a wood panel.

Building Codes + Material Standards All of the products listed above are covered in the International Building Code (IBC 2015). Projects falling into construction types III, IV (Heavy Timber), and V are

Conclusion A broad variety of mass timber products is available in today’s market, suitable for many project types in the North American building industry. Knowing your product options is critical when starting to design a mass timber building system. With this introductory information, engineers should be able to make informed design decisions regarding each product.

Mass timber construction has been in use in Europe for decades, with great success.

This style of construction continues to grow in popularity in North America. As engineers, we have the opportunity to play a significant role in shaping and promoting this type of construction. With mass timber, architecturally expressive and sustainable structures can be created, adding value to your client’s project.▪

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the likely candidates for a mass timber alternative. Depending on the occupancy classification, the permitted height for these construction types can be up to 85 feet.

Although Type I and II construction are limited to non-combustible materials, mass timber roofs are permitted. Additionally, there are taller mass timber projects in New York and Oregon, which are negotiating jurisdictional approvals with the local building authorities.

All of the products are covered in the National Design Specification (NDS 2015) for timber design. NLT, GLT, and CLT can be designed in accordance with Chapters 4, 5, and 10 respectively. LSL, LVL, and Secondary LVL should be designed in accordance with Chapter 8. Reference values are not provided for LSL or LVL in NDS 2015, as they are unique to each supplier’s APA product reports.

It is possible to calculate individual CLT panel capacities with the Kreuzinger shear analogy method. However, NDS 2015 also requires that the resistance values be taken from the individual supplier’s APA product reports and then further modified with the Chapter 10 factors.

Under current U.S. codes and material standards, all of the mass timber panel products require plywood sheathing for in-plane diaphragm stiffness and shear resistance. The use of CLT without plywood is indeed a viable solution but must be negotiated with the authority having jurisdiction. Plywood diaphragms on mass timber panels can be considered as “fully blocked” when detailing with the NDS 2015 Special Design Provisions for Wind and Seismic (SDPWS).

RAISING THE BAR

Courtesy of James Steinkamp Photography.

By Patrick Ragan, S.E., and James Swanson, S.E., P.E.

T

he 783,800-square-foot Zurich North America Headquarters is the largest build-to-suit office project completed in the Chicago area in the last 15 years, but this striking addition to the I-90 corridor in Schaumburg is not just notable for its size. The unique building form is comprised of the three long rectangular bars shown in Figure 1. The east and west lower bars rise six stories from the ground, while the five-story upper bar sits on top of – and spans between – the two lower bars.

A Building and a Bridge The dramatic 180-foot main span and the two 60-foot cantilever spans on each end are made possible by two steel trusses at the exterior faces of the upper bar and a third truss centrally located in the interior.

Usually, a requirement to transfer five levels of office loading over such long spans would be an arduous task associated with a significant cost premium. In this case, however, loads from the upper bar are not carried by a one-story or two-story transfer truss. Instead, the main structure of the entire upper bar is a truss. By replacing vertical columns with truss diagonals throughout the entire five-story upper bar office space, the full 68-foot height of the space becomes structural depth for the truss, allowing chord axial forces to be minimized.

Additional efficiency is achieved by making the truss continuous over its supports, and ideally proportioning the cantilever spans to balance forces and deflections in the main span. These effects further reduce chord axial forces and result in deflections which are approximately equal at the main span and the cantilevers.

Although the depth and continuity of the trusses make them inherently stiff, and therefore not prone to large deflections, the trusses were fabricated and erected with slight cambers to mitigate concerns about floor levelness. By super-elevating initial panel point elevations by up to one inch, the initial truss deflection due to dead load was effectively eliminated. Meanwhile, live load deflections are less than ¾-inch at both the main span and the cantilevers.

Figure 1. Plan diagram.

Figure 2. Typical main truss elevation.

Truss Design The design of the truss chords was governed by the axial truss forces acting in combination with significant bending moments, since the chords also act as 60-foot continuous W36 steel girders supporting the conventional 45-foot composite steel framing. A series of large truss chord penetrations (40 inches wide x 22 inches high) were carefully coordinated to allow mechanical services to fit within the standard 13-foot-six-inch floor-tofloor heights without compromising the ceiling height.

While coordination of the deep truss chords with mechanical services was a challenge, coordination of the truss diagonals with the STRUCTURE magazine

Figure 3. Construction of five-story upper bar. Courtesy of Goettsch Partners.

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Figure 4. Typical truss diagonal-to-chord node. The force in the compression diagonal (left) is transferred primarily through bearing.

Courtesy of Ruby Associates.

Figure 5. Typical elevation of primary north-south-braced frames.

interior office space was less so. As the centerpiece to the most iconic component of the project, the trusses are featured and celebrated by the architecture rather than hidden behind partition walls.

Early in the design phase, the design team worked closely with the contractor’s connection engineer to develop economical splices and compact connections at the truss nodes. The typical truss diagonalto-chord node (Figure 4) was shop-welded and delivered to the site in one piece with the chord, with bolted diagonal splices accommodated on both sides of the node. Where possible, bolt quantities were reduced by taking advantage of bearing, such as in compression diagonals which were not subject to load reversals.

Braced Frames With a roof height of 152 feet, the building will not be confused with the tallest high-rise office buildings found in downtown Chicago. Still, the 480-foot wide wind sail of the upper bar, in combination with the Exposure C wind loads blowing off the expressway from the south, creates substantial overturning forces that required creativity in the layout of the two braced frame cores which stabilize each end of the upper bar.

The typical elevation of the primary north-south braced frames is shown in Figure 5. It was critical to take advantage of the large gravity loads present in the columns supporting the main trusses to minimize foundation tensions. However, the trusses are laid out on a 45-foot module, while the extent of the braced frames was limited to the 29-foot-8-inch width of the elevator core. Outrigger braces were provided directly beneath the upper bar at the Level 6 mechanical level at each of the four brace lines to engage the truss support columns and their beneficial gravity loads.

In addition to reducing the uplift forces, the extra depth of the structural system, combined with the high axial stiffness of the large truss support columns, ensured that lateral drifts could be controlled with a minimal steel weight premium beyond what was required for strength.

Open Spaces Four large atrium spaces give the interior a dramatic feel befitting the project, and a series of feature staircases connect the various levels served by the atriums. The longest, shown in Figure 6, spans 40 feet STRUCTURE magazine

Figure 6. Upper bar atrium with long-span steel staircase connecting levels 9, 10, and 11. Courtesy of Goettsch Partners.

between Level 9 and a 17-foot cantilever landing at Level 10, and another 50 feet between the Level 10 landing and Level 11.

Given the susceptibility of long-span staircases to vibration, a series of dynamic analyses were undertaken to predict the vertical accelerations at mid-span of the stair under the worst case of a rapidly descending individual. Since the dynamic response of a long-span stair is a highly nonlinear problem, it is possible for a moderate increase in stiffness to result in dramatically improved behavior. In this case, the initial stair design based on strength and deflection was stiffened by optimizing the steel stringer profile, with a 3-inch increase in depth and a modest increase in steel weight. This reduced the estimated stair accelerations under the controlling case by more than a factor of 3 (Figure 8, page 28) compared to the initial design.

Challenging Soil Conditions Ground conditions at the site consisted of significant regions of soft fill and organic clays, particularly on the south end of the site where, as shown in Figure 10 (page 28), a large pond had previously existed.

To mitigate differential settlements during and after construction, an innovative “preloading” program was undertaken in which approximately 20 feet of soil from the adjacent parking garage excavation was

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Figure 8. Vertical acceleration at mid-span of staircase versus step frequency of a descending individual.

Figure 7. Atrium staircase primary mode of vibration.

piled on top of the entire building area of the site. Over the course of 60 days, the weight of the additional fill, in conjunction with 20 to 35-foot long vertical “wick drains” arranged in a 5-foot triangular grid pattern, accelerated the consolidation and settlement of the soft organic material. Upwards of three feet of settlement was observed during the preloading phase; additional settlement after construction is anticipated to be limited to approximately one inch.

Had the preloading program not been implemented, a significant portion of the settlement would have occurred after construction.

Also, a suspended slab system would have been required in the basement rather than the traditional slab-on-grade which was ultimately used. Moreover, the continuous flight auger (CFA) piles used for the deep foundation system would have been subjected to “down-drag” forces – essentially negative skin friction – as the surrounding soils consolidated. The resulting reduced capacities would have required significantly more piles and associated expense.

Notably, the preloading and drainage program also mitigated the susceptibility of the soils to liquefaction under seismic loads, allowing the seismic site classification to be reduced from F to D. This corresponds to a considerable reduction in seismic forces and detailing requirements, and eliminated the need to perform a site-specific seismic response analysis.

Figure 9. View from level 10 of the upper bar atrium. Courtesy of James Steinkamp Photography.

Conclusion A careful integration of structure – in particular, the three structural steel trusses of the suspended upper bar – allowed this iconic piece of architecture to stand apart from its peers in the suburban office building landscape. After opening in October 2016 to rave reviews from occupants and critics alike, it is clear that the Zurich North America Headquarters has quite literally raised the bar for the suburban office building.▪

Project Team

Figure 10. The extent of the old pond encompasses the majority of the building footprint.

Owner: SFG Schaumburg 1, LLC Structural Engineer: Halvorson and Partners, a WSP | Parsons Brinckerhoff Company Occupant: Zurich North America Developer/Design-Builder: Clayco Architect: Goettsch Partners Geotechnical Engineer: GEI Consultants STRUCTURE magazine

Patrick Ragan, S.E. (pragan@hpse.com) is a Senior Engineer with Halvorson and Partners, a WSP | Parsons Brinckerhoff Company in Chicago.

James Swanson, S.E., P.E. (jswanson@hpse.com) is a Senior Vice President with Halvorson and Partners.

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January 2017

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The Wharf 525 Water Washington, DC

By Bill Wilde and Joe Wilkum

T

he Wharf development is transforming Washington DC’s storied Southwest quadrant by creating a mile-long waterfront neighborhood that includes retail, residential, hospitality, offices and cultural complexes as well as a public park and piers. 525 Water is a 107-unit condominium building in Washington, D.C. and the first residential project to be constructed in The Wharf. The 525 Water project is located in the lower right area of the development shown in Figure 1. Featuring views of the Potomac River and fronting a new 3.5-acre Waterfront Park (Figure 2), these new condominiums extend five stories above grade and contain over 105,000 square feet. The building is primarily a square shape, with a curved southern exposure matching the radius of the streetscape (Figure 3). Its courtyard offers landscaped scenery and natural lighting for residents of the interior units. Other amenities include a club room, private rooftop, balconies, green roof, and a two-story garage substructure. Final punch list items were completed in July 2016 with a construction cost of $30 M. The project consisted primarily of load-bearing cold-formed steel framing (Figure 4). The load-bearing wall panels support concrete over Hambro joists for levels three and above. Over 9,000 linear feet of wall framing containing complex curves and angles was prefabricated off-site by FrameCo, Inc. On May 5, 2015, the first of over 1,040 panels was placed on the second floor. In just three months, the structure was topped out with its final pour at the roof. Although masonry elevator and stair shafts were included in the building design, cold-formed X-braces stabilize the building above the second level.

The garage and first-level structure were constructed with concrete columns supporting reinforced two-way concrete slabs. The first story exterior wall is infill curtain wall fabricated with cold-formed steel framing and deflection track at the top of the wall. These curtain walls were installed after much of the second story was already in place The exterior facade is composed primarily of brick, metal panels, and glass. In some locations, the cold-formed steel framing was required to support the vertical as well as the lateral loads imposed by the brick veneer.

A prominent feature of the exterior is the tower occurring at the building’s southwest corner, (Figure 2) which contains floor-to-ceiling glazing supported by miscellaneous cold-formed shapes and structural steel.

The benefit of cold-formed prefabricated panels on this project is best exemplified by the beam pockets that were required to achieve a positive load path (Figure 5). With over 100 steel beams at the fifth level, Excel Engineering, Inc coordinated beam depth, width, and bearing locations so that appropriately sized cold-formed posts STRUCTURE magazine

Figure 1. Overview of the project area.

Figure 2. Rendering of The Wharf area.

Figure 3. 525 Water at the Wharf.

could be provided. The posts were capable of supporting each beam while still allowing adequate space for the field crew to make their connections. This avoided costly delays associated with traditional ironwork. Adding to the complexity, more than 550 MEP (mechanical, electrical and plumbing services) sleeves penetrated each level. Excel coordinated every stud location to avoid interference and enable a much faster installation of the wall panels.

Shear walls are an integral part of many projects, and this project was no different. Aligning the shear wall posts floor-to-floor, in particular through concrete, is difficult and required Excel to work with FrameCo on a creative solution. Taller cold-formed shear wall posts with cap plates were designed and supplied within each panel (Figure 6). The panel above contained slots in its bottom track at

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Figure 4. Typical story framing.

Figure 5. Typical framing with beam pockets.

these posts, enabling the field crew to properly align the shear wall post and directly weld each assembly together. Due to the nature of the project, some shear walls were not able to be shipped full-length.

Therefore, Excel created an overlap detail (Figure 7) to maintain continuity across the splice between shear wall panels. This involved welding a plate that extended past the end of one panel so it could be fastened to the adjacent panel once set in the field.

Due to an aggressive construction schedule, Excel Engineering, Inc. developed an innovative process to communicate new information among team members quickly. Requests for Information (RFIs) were submitted well before the engineering was completed, and a level of importance was assigned to each request so the design team could address time-sensitive issues first.

Excel also provided a level of accelerated service by handling complex aspects directly with the project design team. This coordination process alerted the design team of potential issues, allowing them to be resolved before they could create delays. For instance, in-depth coordination with the stair fabricator was required for beam design at the fifth-level stair openings. By anticipating the need and addressing it upfront, Excel was able to produce accurate wall panel elevation drawings quickly.

Combining attention to detail with innovative design, Excel and FrameCo demonstrated that prefabricated cold-formed steel systems can work perfectly as the primary structure for any mid-rise building. 525 Water was recently recognized by the ColdFormed Steel Engineers Institute with a 2016 CFSEI Design Excellence Award for its’ innovative use of cold-formed steel.▪

Figure 6. Typical shear wall post cap plate detail.

Bill Wilde is a cold-formed load bearing and wall panel specialist in the industry. He may be reached at bill.w@excelengineer.com.

Joe Wilkum is a Project Manager at Excel. He is experienced with curtainwall design, although load bearing design is his specialty. He may be reached at joe.w@excelengineer.com.

Project Team Owner: RWP, LLC Engineer of Record for Structural Work: Ehlert Bryan Architect of Record: SK&I Architectural Design Group, LLC Cold-Formed Steel Specialty Engineer: Excel Engineering, Inc. Cold-Formed Steel Specialty Contractor: FrameCo, Inc. General Contractor: Balfour Beatty Construction STRUCTURE magazine

Figure 7. Typical shear wall horizontal splice.

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Product Watch

updates on emerging technologies, products and services

Roof Penetration Framing Creative Ways to Outsmart an Unpredictable Steel Market

By Bob Hasulak

M

any factors impact the choice of steel construction in the U.S. How can a structural engineer stay nimble and creative in utilizing steel construction? Here are a few tips regarding the market, considering roof penetration framing as an example.

Roof penetrations at mechanical openings are traditionally constructed of structural steel framing, such as L4x4x1/4 angles welded between existing beams or joists. Recently, preengineered products have entered the market as an alternative to welded steel framing. One manufacturer, QuickFrames USA, LLC, provides a bolt-on, adjustable frame where no field welding or cutting is required. Another manufacturer, Chicago Clamp, provides end connections for traditionally cut steel framing that eliminate the need for welding.

Use Historical Insights to Plan Ahead When working alongside a design-build firm in the planning of a new structure, you must consider all aspects of design and durability.

Maybe you have experienced a time when an uptick in steel prices has caused your distributor to hike its costs, or perhaps a lack of steel availability has halted the building’s progress.

Pay attention to predictions put out by market analysts. Most recently in 2016, some U.S. manufacturers have seen a 20% increase in the price of steel.

A structural engineer might consider a concrete framing system when steel prices rise or when a potential vendor proposes less-thanideal rates. Don’t forget that, according to AISC, the “cost differential of structural steel and concrete framing systems has remained relatively constant with a five percent savings gained by selecting structural steel.” When steel prices rise, the cost of other building materials often experience an increase as well, so it is important to look at the greater context.

Review previous jobs with which you have been personally involved. Consider any delays you have seen as a result of changes with steel, and the significance of the impact on your work.

If you see a pattern – or even a single instance –in which your work suffered, take note. Then you can start to flesh out the likelihood of a similar

situation and make changes to specifications, details, or suppliers to avoid it.

For example, consider difficulties in the detailing process such as a lack of mechanical coordination that required multiple resubmissions. Choosing pre-engineered adjustable products can reduce the need for detailing and custom fabrication during construction.

Manufacturers of pre-engineered products can provide stock supply rated for maximum loads, and some even provide site-specific engineering that is included within the cost of the product.

Be Strategic when Specifying Products One of the most common ways that steel could impact your work is through its role in the products you specify. Ask vendors hard questions like what they would do if steel prices happened to surge during the lifecycle of the job, and whether or not they have a significant store of steel and other necessary materials. Typically, a manufacturer may hold a one month supply. If you understand a vendor’s approach to potential roadblocks and upsets, you can then decide upon the best-prepared supplier – and create a plan if anything goes awry. Be sure you do not dismiss steel products entirely if one vendor does not answer all your questions thoroughly.

Other vendors might be able to.

Remain Open to Innovation Structural engineering is an enduring field.

This speaks to the importance of the career, but it can also be the reason that some practitioners get stuck in a comfort zone. If someone has done something a certain way for 20 years and knows that his company has done the same thing for 50 years before that, it is unlikely that he or she will want to change practices.

However, this can be a big problem as stagnancy can harm your progress and your profits.

For roof penetrations, many structural engineers stick to the traditional method of welded angle frames since it is historically what their client expects. However, new adjustable roof penetration frames can offer flexibility at a slight savings on new construction, where

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traditionally welded frames could be hoisted into place, and can be nearly 50% cheaper compared to welding frames into an existing structure. The installation time can be as little as ¼ of the time spent to field weld frames in place.

Just as technology becomes more efficient and refined over the years, the same is happening with construction products if you look for them.

Consider Tangential Implications The costs of using steel in construction rarely (if ever) are limited to the raw material itself.

Ancillary elements to take into account include the costs of associated labor, the impact steel might have on the project’s level of risk, and what long-term costs may be down the road, especially regarding maintenance.

For example, welding is a highly specialized skill and the expense of the necessary labor can be significant. Welding also requires special inspection to ensure the welds are adequate, which adds to time and cost. Furthermore, the potential risk is increased with welding due to the presence of hazardous flames and fumes. OSHA reports that fatal injuries occur in four of every 1,000 workers over a lifetime from welding, cutting, and brazing.

New roof penetration products that require no field welding or cutting could save direct and indirect costs.

Steel is usually a solid material to choose, thanks to its durability and longevity, but it can also be susceptible to damage. The most common type of damage in steel structures is moisture damage. The good news is that proper precautions upfront, like choosing the appropriate protective coatings, can reduce the likelihood of corrosion. Pre-engineered roof frames are constructed of light gauge framing and are galvanized or painted for protection.

Conventional frames are typically painted, but must be touched up in the field after welding.

So if the availability and price of steel can make a big difference on your job site directly, plan ahead, be strategic in your specifications, seek out innovation whenever possible, and look at how steel factors into the bigger picture.▪ Bob Hasulak is the Director of Operations for QuickFrames USA, LLC, the only bolt-on, adjustable, pre-engineered roof opening frames for commercial buildings. Contact Bob by visiting www.quickframes.us.

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Professional issues

issues affecting the structural engineering profession

What Structural Engineers Need to Know about Resilience

By Erica C. Fischer, Ph.D., P.E., Megan Stringer, P.E., LEED AP BD+C, and Christopher Horiuchi, P.E., LEED AP BD+C

I

n 2016, many organizations launched resiliency initiatives making “resilience” the new buzzword. In the building and infrastructure industry, resilience is defined in many ways. In 2014, the ASCE/ SEI Sustainability Committee defined resilience as the ability to suffer less damage and recover more quickly from adverse events. These adverse events are not only external shocks in the form of natural or man-made disasters (hurricanes, floods, earthquakes, etc.), but also economic, social, political, and cultural adverse events that could damage the framework of a community. Today, this also includes the effects of climate change and the resulting rapid increase in the frequency of external shocks.

President Barack Obama has made resilience a priority in the past year with two events hosted at the White House. The White House Summit on Earthquake Early Warning Systems was a full-day publically broadcast event that discussed the benefits of earthquake early warning systems on hazard mitigation and disaster resilience. The second event was the White House Conference on Resilient Building Codes. This event included the Obama administration announcing public and private sector efforts to increase community resilience through building codes.

LEED offers three resilience pilot credits for project teams that plan and design for potential disasters in the project area. This includes pre-planning and site investigation, designing to resist the potential disasters, and designing a structure to be habitable after the disaster.

These credits shift disaster resilience from disaster recovery to disaster risk mitigation.

States and cities are developing resilience plans to assess their current infrastructure and prioritize future planning. In 2014, New York City developed OneNYC, a resilience plan that addresses flood mitigation along New York City’s 520 miles of coastline. Figure 1 shows the Battery Park Underpass in New York City after Hurricane Sandy. Motivated by the extreme effects of Hurricane Sandy in 2012, this plan also addresses how to mitigate flooding for the 400,000 residents of New York City that live in a 100-year floodplain. The City of Boston has also addressed the effect of sea level rise. A Climate Change Adaptation Plan was developed by the city and includes flood hazard maps that account for sea level

rise, and climate preparedness and community engagement. In 2014, the city of New Orleans also developed a resilience strategy. This plan addresses flood mitigation through the use of innovative methodologies such as parks and green streets to protect the city’s population and economy. Both New York City and New Orleans received grant money from the HUD National Disaster Resilience Competition to implement many of their resilience strategies.

These will have direct implications on the work that civil and structural engineers are performing in the regions. Other areas of the country have also developed resiliency plans, including the city of San Francisco and the states of Washington and Oregon.

How will these initiatives affect structural engineers, their jobs, and their projects? The Disaster Resilience Working Group of the ASCE/SEI Sustainability Committee has researched some of the organizations within the building construction community that are addressing resilience. This article identifies these organizations, along with their resilience goals and how these goals will affect structural engineers.

Legislation Cities within the state of California have been actively working to increase their seismic resilience. Wiss, Janney, Elstner Associates, Inc. (WJE) developed a website to track seismic ordinances within California. This website (www.seismicordinances.com) provides upgrade requirements and relevant deadlines. In April 2013, the city of San Francisco adopted an ordinance that required the mandatory seismic retrofit of wood-frame soft-story buildings (buildings with a weaker first floor that are prone to collapse in an earthquake). As a result of this ordinance, around 4300 buildings were surveyed and 2800 were identified by engineers to have a soft story. All of the affected building owners were notified in September 2013 and required to have submitted forms demonstrating that their building was evaluated by a licensed professional engineer by September 2014.

There was a 99% compliance with this step of the ordinance. Those building owners that did not comply had their building placarded with a Notice of Violation. The next phase of the ordinance, for those buildings affected, is to submit a permit application with plans for

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Figure 1. Battery Park Underpass in New York City after Hurricane Sandy. Courtesy of FEMA.

a seismic retrofit. Once the permit application is submitted, the building owner has one year to complete the retrofit. All retrofits must be completed by 2020.

In October 2015, the city of Los Angeles adopted an ordinance that requires the mandatory seismic retrofit of wood-frame soft-first-story buildings, similar to the ordinance in San Francisco, and an ordinance that requires the retrofit of nonductile concrete buildings. These ordinances affect over 15,000 buildings.

The cities of Portland and Seattle have developed interactive maps to locate all of their unreinforced masonry buildings (URM). Both cities are currently working on developing legislation for URM ordinances mandating retrofits of URM buildings.

The City of New York has prepared a Climate Change Adaptation Task Force that has developed climate predictions for New York City through 2100. The City has also produced a document, Retrofitting Buildings for Flood Risk (NYC Planning, 2014), and updated the New York City Building Code to include increased risk of flooding.

Organizations Promoting Resilience Resilience can be addressed at different scales: on an individual building basis or a community basis. The following section describes organizations and tools addressing building resilience and community resilience.

The Rockefeller Foundation 100 Resilient Cities is a program developed by the Rockefeller Foundation. This initiative is challenging cities around the world to make

resilience a priority. 100 Resilient Cities not only considers the progress cities have made to decrease the long-term impacts of external shocks (hurricanes, earthquakes, floods, etc.), but also the day-to-day stresses a city experiences on its social, economic, cultural, and political framework. Cities are required to apply for the distinction by developing a resilience strategy or plan. Those cities chosen to be part of the 100 Resilient Cities receive monetary and logistical support to establish a Resilience Officer for the city. Figure 2 shows the locations of the 100 Resilient City participants in North America.

NIST Community Resilience Program NIST addresses natural and man-made disasters having catastrophic impacts on the building stock of a community (NIST, 2015). Today’s communities are constructed with many interdependencies within the built environment.

Previous earthquakes have demonstrated that buildings in a community can have an effect on functionality after an earthquake. There is a potential that, if one building is not functional, there is a global impact to the community’s ability to operate after a disaster. NIST has developed a program that allows communities to examine the vulnerabilities in the interdependencies of the built environment.

Figure 2. Map of 100 Resilient Cities Participants in North America.

based on a 10-year FEMA study which provides a performance prediction based on building-specific analysis. The results from a FEMA P-58 analysis are Losses (in dollars), Fatalities & Injuries, Repair Time & Tagging, and Environmental Impacts. The methodology involves a probabilistic approach using a Monte Carlo simulation. Probabilistic variables including ground motions, structural responses, content damage fragility curves, and loss curves are run through various simulations to provide confidence levels for certain outcomes. The Performance Assessment Calculation Tool (PACT) is the companion software to FEMA P-58.

Resilient Design Institute (RDI)

USRC Rating System

The Resilient Design Institute is a web-based application that hosts case studies, strategies, and principles of resilient design. The website aims to be a resource for individuals, organizations, and communities that would like to incorporate hazard mitigation and resilience into their designs. This website addresses both man-made and natural disasters. RDI also provides consulting services for project teams.

The United States Resiliency Council is a non-profit organization which implements a rating system for the earthquake performance of buildings. It aims to provide a universal rating system akin to LEED ratings for sustainability. As of now, the rating system is limited to earthquakes, but the goal of the council is to expand the rating systems into additional disasters in the future. The city of Los Angeles has already adopted this rating system to improve the performance of its buildings. continued on next page

FEMA P-58 FEMA P-58: Seismic Performance Assessment of Buildings (FEMA, 2012) is a document ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org

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Arup REDi Arup’s Resilience-Based Earthquake Design Initiative (REDi) is both a framework for designing resilient buildings as well as a rating system which qualifies the level of resilience.

This rating system focuses on planning for three different levels of resilience: Building Resilience (structural system), Organizational Resilience (disaster planning), and Ambient Resilience (adjacent buildings and other site hazards). The REDi rating system also requires a loss assessment using PACT. REDi ratings are classified as Platinum, Gold, and Silver. The building must be shown to meet certain performance objectives for Downtime, Direct Financial Loss, and Occupant Safety to meet any of the ratings.

SP3 The Seismic Performance Prediction Program (SP3) is an online, cloud-based tool developed

by Haselton Baker Risk Group. It serves as an interface to use the FEMA P-58 methodology and can also calculate probable maximum loss (PML), an Arup REDi rating, and a USRC rating. The tool provides a more streamlined way to implement the FEMA P-58 methodology by providing soil and hazard curves and content estimates pre-packaged in the tool.

EA Tool The Environment Assessment Tool™ (EA Tool) is a life cycle analysis tool developed by Skidmore, Owings & Merrill LLP to estimate the equivalent carbon emissions of a structure.

Calculated embodied carbon quantities consider contributions from materials and construction including material extraction, transportation, construction waste, and equipment operations.

Furthermore, the tool provides a link between sustainability and resilience by estimating the embodied carbon associated with repairs related to seismic damage and the potential for full demolition and replacement of a severely damaged structure. Probable seismic damage is based on HAZUS fragility curves and can account for increased performance for enhanced seismic systems. The EA Tool is intended to be used by architects, engineers and building owners to help inform early design decisions and provide a costbenefit analysis of enhanced seismic systems.

Resilience Insight Tool BuroHappold’s Resilience Insight Tool is an online tool that evaluates the resilience of an entire city. It provides a framework to assess a city’s capability against different shocks/stresses including natural hazards, epidemics, and attacks. Based on a series of inputs, the tool provides an assessment of the

vulnerability and adaptive capacity of a city in terms of the effects on Society & Community, Governance & Economy, and Environment & Infrastructure (BuroHappold, 2016).

U.S. Climate Resiliency Toolkit The U.S. Climate Resilience Toolkit (NOAA, 2016) provides multiple scientific tools and information to assist people and entities that would like to manage their climate-related risks and improve their resilience to extreme events. This site is developed for citizens, communities, businesses, city planners, and policy advocates. The site includes many different modules: a five-step process to plan, initiate, and manage a project that is resilient to climate-related events; real-world case studies that have been successfully implemented by communities and businesses; climate data organized in maps, interactive tools, charts, and more; and federally-developed training programs. The U.S. Climate Resilience Toolkit was developed in response to President Barack Obama’s Climate Action Plan and Executive Order to help the nation prepare for climaterelated changes and impacts.

Conclusions Modern-day cities are approaching disaster mitigation from a holistic perspective that includes the performance of the built environment during a natural or man-made disaster. Cities and regions are assessing their infrastructure for long-term resilience. These assessments and recommendations can have an impact on the extreme loading demands structural engineers use to evaluate buildings, in addition to the priorities of a region. For example, the cities of Boston, New York, and New Orleans have updated coastal flooding hazard maps to incorporate the effects of climate change and sea level rise. The City of New York has updated the New York City Building Code to incorporate these changes.

The tools presented in this article aim to help engineers design for long-term resilience in a manner consistent with city, state, and countries resilient plans.

The organizations and toolkits discussed within this article each present different approaches to resilience, and allow structural engineers to be a part of the movement. This is by no means a comprehensive list of organizations and tools. It is critical to remember that resilience is not only applicable to seismic hazards. In fact, the LEED sustainability metric has expanded its resilience pilot credits to include floods, hurricanes, and wildfires. The northeastern U.S. is still recovering from Hurricane Sandy. Building owners are considering the

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future impacts of climate change and natural disasters on their buildings. Most recently, the Whitney Museum of Art building in southern Manhattan was constructed considering flooding due to storm surge.

As structural engineers, we have a responsibility to help protect cities from a variety of disasters and aim to continually improve our communities. As natural disasters become more frequent and larger in magnitude, cities observe the capacity of their infrastructure and their ability to recover first-hand. In the U.S., every dollar spent on pre-disaster hazard mitigation results in four dollars in future benefits for a community (ASCE/ SEI Sustainability Committee, 2014). In the past ten years, the damage due to increasing amounts of rainfall and increasing temperature around the world has totaled over US$1.4 trillion (Michell, 2016). Natural disasters and the effects of climate change are causing large economic burdens for cities around the world.

Cities within the U.S. are developing resilience strategies for pre-disaster mitigation to take advantage of that statistic, and reduce post-disaster recovery costs and the effects of the disasters in their communities. These resilience strategies will have a direct impact on structural engineers’ work and the direction of the building codes.▪ Erica C. Fischer is a Design Engineer at Degenkolb Engineers in Seattle, Washington. She is an active member of the ASCE/SEI Sustainability Committee serving as the Chair of the Disaster Resilience Working Group and a member of the Steering Committee. Erica can be reached at efischer@degenkolb.com.

Megan Stringer is a Senior Engineer in Holmes Structures’ San Francisco office. She is an active member of the sustainable design community and serves as chair of the SEAOC Sustainable Design Committee and is on the steering committee of ASCE SEI’s Sustainability Committee. Megan can be reached at mstringer@holmesstructures.com.

Christopher Horiuchi is a Project Engineer with Skidmore, Owings & Merrill LLP in San Francisco, CA. He is a member of the ASCE/SEI Sustainability Committee and its Disaster Resilience Working Group. He can be reached at christopher.horiuchi@som.com.

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

Structural Engineering Institute of ASCE

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| April 6–8, 2017

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NOTEWORTHY

news and information

Roger LaBoube Retires from the STRUCTURE Editorial Board After serving for five years on the STRUCTURE magazine Editorial Board as the steel industry representative, Roger A. LaBoube, Ph.D., P.E., is retiring. Roger is the Curator’s Distinguished Teaching Professor Emeritus of Civil Engineering and Director of the Wei-Wen Yu Center for ColdFormed Steel Structures at the Missouri University of Science & Technology (formerly University of Missouri-Rolla).

Dr. LaBoube has an extensive background in the design and behavior of cold-formed steel structures. His research and design activities include: cold-formed steel beams, panels, trusses, headers, wall studs as well as bolt, weld, and screw connections. Roger is active in several professional organizations and societies.

Barry Arnold, P.E., S.E., SECB, Chair of the STRUCTURE magazine Editorial Board, had this to say about Rogers’s Departure: “Roger has served faithfully and diligently on the Editorial Board since February 2011. Even after Roger announced he would step down from the Board in December, he continues to find content for the magazine and to work with authors on developing articles.

Roger’s dedication and commitment to our publication and the profession are commendable, and he will be missed.” Regarding his tenure on the Board, Roger commented, “I have enjoyed the opportunity to serve on the Board and work with highly professional

individuals. I look forward to continuing to contribute content to the magazine.”

Erin Conaway, P.E., LEED AP, will replace Mr. LaBoube as a Steel Industry representative. Ms. Conaway is a Regional Engineer for SidePlate Systems, Inc. based in Phoenix, AZ and provides support for design and construction professionals utilizing SidePlate connection technology in the Southwestern U.S. She is a graduate of the Oklahoma State University Architectural Engineering (Structures) program in Stillwater, OK. On a national level, Erin also serves as SidePlate’s Industry Specialist, involved with the development and implementation of initiatives focused specifically on construction clientele.

Previously, Erin was the Intermountain West Regional Engineer for the American Institute of Steel Construction (AISC). Barry Arnold said this about Ms. Conaway’s appointment to the Editorial Board: “I am pleased to welcome Erin Conaway to the Editorial Board.

She is an experienced author, and editor and has a great passion and enthusiasm for writing and working on the Board. She was highly recommended by her peers, so I have no doubt that she will be a productive addition to the team.”

Please join STRUCTURE magazine in congratulating Roger LaBoube on his service and welcoming Erin Conaway to the team.

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

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Foundation Companies Close 2016

Strong and Optimistic

By Larry Kahaner

C

ompanies involved in foundations are reaping the benefits of new techniques and methods that allow building on land that was once deemed unbuildable.

For instance, at Geopier Foundation Company, Inc. (www.geopier.com), Director of Business Development Matt Caskey points to their GeoConcrete Column (GCC) system which offers a cost-effective solution to support heavy applied loads, and control settlement at sites with weak and compressible cohesive and organic soils overlying dense soils or rock. The system provides this reinforcement by matching high modulus elements with the low modulus soil to control settlements. GCCs are installed through a patented displacement process by driving a hollow mandrel to the design depth while simultaneously pumping concrete. The process forms an enlarged concrete base to develop resistance efficiently. GeoConcrete Columns are only rammed at the base. Following the creation of the bottom bulb, the mandrel is extracted while continually pumping concrete under pressure. The GCCs then support engineered footing pads and high-bearing-pressure shallow footings or mat foundations to provide settlement control. GeoConcrete Columns are an effective replacement for deep foundations including driven piles, drilled shafts or auger cast-in-place piles, or time-consuming surcharging.

Caskey says, “Through continued research and development, Geopier has expanded its system capabilities to ensure high performance and reliability while providing value compared to deep foundation alternatives. Geopier’s design-build engineering support and sitespecific modulus testing, combined with the experience of providing settlement control for thousands of projects, provide an unmatched level of ground improvement options for virtually any soil type and groundwater condition across many applications. Geopier rigid inclusions are high-stiffness elements constructed of cement treated aggregate, grouted aggregate, or plain concrete and are used to transfer loads through weak soils, such as soft clays and organics, down to a suitable bearing stratum.”

STRUCTURE magazine

He adds: “We are expanding our technologies, and continuing to explore and test new ground improvement techniques that will continue to grow the intermediate foundation market. We also continue to hire new employees ranging from additional regional engineers, engineers to assist in our design center, a director of business development and more office help. We also continue to update our marketing efforts. We are becoming much more active regionally, as well as promoting ourselves through social channels such as LinkedIn and YouTube.”

At RISA Technologies (www.risa.com), CEO Amber Freund notes that RISAFoundation v9 was recently released and includes masonry retaining wall design. “Structural engineers who used RISAFoundation to design concrete retaining walls in the past wanted the ability to switch between masonry and concrete for their designs. This new feature allows them the flexibility of evaluating the best material solution for their project,” Freund says.

She says that the company is seeing a growth trend in commercial and residential markets. “Slow and steady seems to be the pattern.”

Freund concludes: “Engineers are increasingly turning to software to evaluate different material and design choices. This is becoming more of a necessity as projects become so fast paced.” (See ad on page 60.)

Last year was an exciting year for Subsurface Constructors (www.subsurfaceconstructors.com), according to Lyle Simonton, Director of Business Development. “Not only did we turn 110 years old, but we were able to stay extremely busy in all three of our major services areas – deep foundations, ground improvement, and earth retention. We continue to see structural engineers seek out more cost-effective ways to support structures in soft soils, which often results in designing foundations supported by aggregate pier ground improvement. Subsurface Constructors completed over 75 such projects nationwide in 2016, including small retail projects, such as Dollar General Stores, to large educational and medical facilities like the Post-Acute Rehab Hospital in Corpus Christi, Texas.”

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January 2017

Simonton notes that structural engineers seem to be leaning more heavily on specialty geotechnical contractors in project development efforts with respect to preliminary design, budgeting, and specification writing. “As one of the few companies to provide both deep foundation and aggregate pier ground improvement, Subsurface Constructors helps structural engineers determine the most economical approach for foundation support.”

“In 2016, Subsurface Constructors saw an increase in ground improvement work in the Northeastern United States as a result of their new office in the Boston area,” Simonton adds. “With so much of the development in this region taking place in old urban fills and very soft existing soil, aggregate piers and grouted columns are often the go-to ground improvement solutions for structural support.” (See ad on page 42.)

Hayward Baker’s Director of Business Development (www.haywardbaker.com), Jeff Hill, says that his company is doing more earthquake drains. “It is a more cost-effective means to mitigate liquefiable slopes than some of the traditional improvement methods. We also make a push for rigid inclusions. We believe that it is a good improvement technique when soils are too soft to use aggregate piers but the structure doesn’t dictate a traditional GIVE YOUR STRUCTURE STABILIT Y deep foundation.”

Hill says: “There’s been a lot more emphasis in the last couple of years on Work with Geopier’s geotechnical engineers to solve your ground real-time monitoring, and using real-time improvement challenges. Submit your project specifications to monitoring parameters for structural receive a customized feasibility assessment and preliminary cost movement, vibration, settlement, poor estimate at geopier.com/feasibilityrequest. water pressure, and things like that. It is all generated on a computer. We can 800-371-7470 make a three-dimensional map of the geopier.com structure as we’re doing our work. For info@geopier.com example, we can map an adjacent structure to monitor and protect it from the work that we’re doing concurrently.”

As for trends, Hill sees more competition. “We are seeing some of our techniques become mature and He concludes: “The segment continues to grow and I think that it’s frankly more commoditized. We’re also starting to see more people because there is a wider acceptance of specialty techniques. We routinely enter the specialty foundation business, and a lot of them are not get calls from structural engineers because an owner is saying ‘you need experienced with the techniques. We’re noticing some construction to consider aggregate piers’ or something of that nature integrity issues that we didn’t see ten or fifteen years ago because which, ten years ago, we didn’t see. Business is excellent. It there were just a few people doing this work, and they had a lot of is growing. We’re having a very good year at Hayward Baker experience.” pretty much across the country. (See ad on page 39.) ▪

GEOPIER GROUND IMPROVEMENT CONTROLS STRUCTURE SETTLEMENT

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LegaL PersPectives

discussion of legal issues of interest to structural engineers

Understanding Indemnification Clauses

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

W

hen design professionals review proposed contracts with their risk management consultants, they are invariably told that they should look closely at provisions that could create uninsurable risk and negotiate better language. One issue that often arises is the language of the indemnification clause. The reason for this is simple – indemnification clauses can shift significant risks to the design professional, and these risks may not be insurable.

The Purpose of an Indemnification Clause The purpose of an indemnification clause is to shift risk from one party to another.

One party (the Indemnitor) agrees to financially protect the other party or parties (the Indemnitees) against specified claims and expenses. This can include both reimbursing an Indemnitee for the amounts it has had to pay on account of the specified claims, or paying these amounts in place of the Indemnitee. Often, a service provider such as a design professional is asked to indemnify its client for claims and expenses arising from the work that the service provider has undertaken for the client. On its face, the concept seems reasonable in that the party performing the services should bear the risks for its negligent performance. In practice, owners may try to shift risk that is beyond the control of the design professional or that extends beyond negligence-based liability.

Indemnification Clauses in Design Contracts While it is not unreasonable for owners to require indemnification from the design professional, they sometimes try to obtain the protection they are seeking with language that is completely inappropriate.

One reason for this is that many design contracts are based on the AIA agreements and, historically, the AIA agreements have not included an obligation for the designer to indemnify the owner. As a result, owners who want to require indemnification from the design professional often just copy the indemnification provision from the construction contract.

There are significant differences between how contractors and design professionals handle risk, however: • Contractors tend to be less risk‐ averse. This may be partly due to the personalities of the individuals involved but is also due to the risk/reward trade‐ off. Contractors may take projects that are significantly larger or different from their previous projects because of the financial incentives. Design professionals do not have the same “upside” potential in their projects and therefore shouldn’t be required to assume the same level of risk.

• A contractor’s work involves following a set of plans and specifications to create the building or structure. While contractors are almost always required to provide warranties and guarantees, design professionals are not required to guarantee their work. Like doctors and lawyers, they are judged by the professional skill and care ordinarily provided by firms practicing in the same or similar locality under the same or similar circumstances.

• The liabilities that a contractor is required to provide indemnification for are covered under its Commercial General Liability (CGL) policy. Typical CGL policies provide much broader coverage than professional liability policies for liabilities assumed in a contract.

Coverage Under a Professional Liability Policy It is helpful to review the basics of professional liability insurance to understand why indemnification clauses can create issues for design professionals: • Coverage is only granted for the insured’s negligent acts, errors or omissions in the rendering of, or failing to render, professional services.

• Contractual assumption of liability is excluded, except for “liability that would have attached in the absence of the contract.” In the absence of a contract stating otherwise, the design professional would only be liable for its own negligence. If a design professional agrees to indemnify its client for claims

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not caused by its negligence, there will be no coverage under its professional liability policy.

Indemnification Clauses Can Create Uninsurable Risk Even beyond the issue that the indemnification clause may be based on language written for contractors is the reality that some owners simply want to transfer as much risk as they can to other parties, rather than allocating the risk fairly. The following is an example of a clause creating uninsurable risk for the design professional: Consultant shall indemnify, defend and hold harmless the Client, the Client’s employees, directors, officers, agents, representatives, and lenders from and against any and all liability and expenses including, but not limited to, attorney’s fees that occurred, in whole or in part, as a result of the Consultant’s acts, errors or omissions.

Suggested revisions to this wording: • Delete the word “defend.” This is the most significant issue. While professional liability insurance covers defense when a claim is filed against the insured, it does not cover defense of an indemnified party.

An agreement to defend means the design professional will be paying the costs of defense from the moment a claim is made, even if it is ultimately determined that the design professional was not negligent. Thus, the design professional will agree to

•

•

•

•

•

liability that goes beyond “liability that would have attached in the absence of the contract.”

Delete “agents, representatives.” The terms “agents” and “representatives” are extremely broad. The client should identify the specific entities it wants indemnified by either name or function.

Delete “any and all.” The wording “any and all” implies indemnification of claims that may not relate to negligence.

Insert “negligent” before “acts, errors or omissions.” For the indemnification obligation to be insurable, it must be based on the insured’s negligence.

Insert “where recoverable under applicable law on account of negligence” after attorney’s fees. Not all states allow a plaintiff to recover its legal costs in a negligence claim as a matter of law. Attorney’s fees will generally not be covered under a professional liability policy unless entitlement is provided by state law.

Replace “in whole or in part” with “to the extent caused by.” The words “in whole or in part” makes the design professional liable for the entire amount of the claim, even

if it was only partly responsible.

Professional liability insurance policies only cover the insured for its share of the liability.

The revised version of this indemnification provision (with inserted text in bold type) would be as follows: Consultant shall indemnify, defend and hold harmless the Client, and the Client’s employees, directors, officers, agents, representatives, and lenders from and against any and all liability and expenses arising from third-party claims, including attorney’s fees where recoverable under applicable law on account of negligence, that occurred in whole or in part, as a result of to the extent caused by the Consultant’s negligent acts, errors or omissions.

The final version would read: Consultant shall indemnify and hold harmless the Client, and the Client’s employees, directors, officers, and lenders from and against liabilities and expenses arising from third-party claims, including attorney’s fees where recoverable under applicable law on account of negligence, to the extent caused by the Consultant’s negligent acts, errors or omissions.

Conclusion Indemnification clauses are a fact of life for design professionals, and they may find it necessary to make a “business decision” to proceed even with poor contract wording.

While ideally a design professional will be able to negotiate a fair allocation of risk, at the very least it should be aware that a contract holds the potential for uninsurable exposure.▪ Gail S. Kelley is a LEED AP, as well as a professional engineer and licensed attorney in Maryland and the District of Columbia. Her practice focuses on reviewing and negotiating design agreements for architects and engineers.

She is the author of Construction Law: An Introduction for Engineers, Architects, and Contractors, published

by Wiley & Sons. Ms. Kelley can be reached at Gail.Kelley.Esq@gmail.com.

Disclaimer: The information in this article is for educational purposes only and is not legal advice. Readers should not act or refrain from acting based on this article without seeking appropriate legal or other professional advice as to their particular circumstances.

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Business issues

new trends, new techniques and current industry issues

BIM and Structural Engineering The Industry Now and in the Future

By Desirée P. Mackey, S.E., P.E., C.E., LEED AP BD+C

B

uilding Information Modeling (BIM) has moved the structural engineering industry to a time where changes and improvements have become constant.

Structural engineers are continually adapting and improving, and the development plateau is nowhere in sight. The first big step was to adopt a three-dimensional (3D) software, such as Revit or Tekla. Switching software was a huge jump, and some structural engineers are still figuring out how to operate within that new tool.

Throughout the industry there are varying BIM workflows – multi-disciplinary coordination in 3D is common, clash detection and construction sequencing also occur, and even some fully connected models are being created and offered as a construction deliverable.

Like any other new process or technology, BIM has swept through the industry at varying speeds and levels, and it will continue to evolve.

As with any other industry shift, there were early adopters and skeptics, but momentum picked up and what was once rare and new is now commonplace. This is where the structural engineering industry sits with the adoption of BIM. BIM is widespread, to whatever level, and there is still some resistance from those who are more comfortable with “how we have always done it,” but BIM is here to stay.

With BIM now a permanent part of the structural engineering workflow, the question is not if structural engineers will be doing BIM, but what is the next step? It is important that structural engineers objectively observe the landscape and take proactive and deliberate steps to incorporate BIM into structural workflows. With BIM coming onto the scene mostly as a project or client requirement, structural engineers have been somewhat reactive in their BIM adoption. This approach limits choices and autonomy in maintaining sound process and workflows. Thus, looking ahead to collectively move toward the next step as an industry will allow structural engineers to leverage the BIM process in ways that are beneficial both internally and to the project as a whole.

What is BIM? Although BIM has been in our collective vocabulary for some time now, the definition is under-defined or defined differently from

one firm to another and even from one project to another. BIM seems to be many things, perhaps a lot of different things, but what is it to the structural sector of the industry? The Structural Engineers Association of Colorado (SEAC) BIM Committee surveyed structural engineers in the Colorado region to determine what BIM means to them. The following is a sample of some of the varied responses: BIM is a design tool but is really separated from the actual construction documents…

Figure 1. Coordination issue made obvious by the use of BIM.

BIM is used to produce traditional paper drawings, but no one actually constructs anything from the model. The paper drawings are still what matters.

In its truest, most idealized form, BIM should be part of a project from conception to demolition. BIM should be utilized by all stakeholders in a project, and the information should be shared from one project participant to another with an eventual goal of being passed onto the owner for facilities management. If only some parties utilize BIM, or if those parties do not share the information, the benefits are lost.

A project has a life cycle with each stakeholder. During this time, a stakeholder can add value to the project and utilize BIM for internal benefit, for the benefit of other stakeholders, and for the benefit of the project in general. Idealized BIM would include as many project participants as possible, with the ultimate downstream stakeholder being the owner. This suggests that the level of BIM utilized by a project should be dictated by the client/owner.

As BIM evolves and advances, it begins to include analysis and the incorporation of the results of those analyses into the project, resulting in information that can be widely utilized. BIM seems to blur the line between design and coordination. This is perhaps the root of some struggles. Idealized BIM forces stakeholders to expand, or at least change the definition of their scope, responsibilities, analysis, and design for a more generalized goal of a coordinated project.

BIM removes the discrete intervals of designing and coordinating, and instead causes more continuous design while coordinating procedures. Although favorable for the project, this is different and difficult to define, and therefore harder for some to adapt.

Regardless of the official definition of BIM, it can be classified as a disruptive innovation.

[BIM is] 3D modeling.

[BIM is] a database that contains data that describes the physical aspects of the building.

[BIM] is modeling the actual information that it takes to understand and build a building.

[BIM is] a tool to consolidate and manage building component information.

[BIM means that] components/elements contain information beyond geometry.

BIM is a process of creating a building through a virtual model distributed with metadata that is then utilized and harvested throughout the project duration by the team, and is potentially passed on to the owner for their use.

BIM is a drawing methodology where the production cost is burdened onto the unappreciated design team, whereas the benefits are reaped by the contractor who takes all the credit.

There is confusion in the structural engineering industry between what is BIM and what is simply modeling in three dimensions. In many ways, a three-dimensional model is not BIM unless that model has embedded, useful information. With that in mind, parts of the BIM process do not need to be three dimensional, and likely are not. While a three-dimensional model offers a way to convey design intent more clearly and is an excellent tool in the BIM process, it is not BIM in and of itself.

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A professor at Harvard University, Clayton Christensen, coined this term. A disruptive innovation transforms an existing market by disrupting that market and displacing the previous technology. BIM certainly falls under this category.

Why is BIM Important to Structural Engineers Now? Structural engineers have accepted most of the obvious benefits of BIM. It is often a project requirement so, regardless of specific benefits, structural engineers are participating.

The more obvious benefits, such as enhanced and earlier coordination, are relatively well understood. An example of a coordination issue is shown in Figure 1.

There is also some level of acceptance that modeling in three dimensions, with components that contain some amount of embedded data, is inherently favorable and more efficient than the traditional twodimensional approach.

Engineers also seem to understand that, if all members of a project team utilize information modeling, significant collaboration is immediately available. Beyond the simple act of combining models to visualize the interaction between disciplines, models from other

Figure 2. In-model review to address a request for information (RFI).

project team members can be incorporated and used by the other disciplines.

Why should/could BIM be important to Structural Engineers now and in the future?

Those on the leading edge of BIM would argue that the BIM process is robust and, regardless of the level at which it is currently being utilized, has significant potential to be beneficial for those who participate.

Beyond the already utilized coordination and collaboration opportunities, there are other underutilized benefits of the BIM process that could be leveraged now or in the future. One such benefit is material takeoffs. Engineers spend lots of time creating accurate models, so accurate take-offs are often just a few clicks away. This information could be utilized in the design process

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Figure 4. Drones are building a block structure.

Figure 3. Robot laying a brick wall.

and could serve as a helpful Quality Assurance (QA)/Quality Control (QC) tool.

While this is likely regarded as a benefit for contractors and/or fabricators, sharing design models downstream can also benefit the design team by obtaining more rapidly produced and more accurate bids.

Furthermore, if providing these models would mean more streamlined construction translating into shortened construction schedules, could that also offer an opportunity for designers to negotiate more time for design? Alternatively, could designers potentially negotiate additional fees for providing these benefits? If the flow of information and models is considered to go back upstream from the contractor to the design team, in-model review processes could also offer some efficiencies, some of which are illustrated in Figure 2 (page 47 ). Presumably few engineers would claim that reviewing hundreds of sheets of steel shop drawings is a quick or enjoyable process, so reviewing this information in a three-dimensional format could offer a benefit.

As structural engineers invest in creating accurate information models, it is important to remember that there is an extensive amount of information embedded in the model that often goes unused. The general approach tends to be to create the model for coordination and some document creation, but then to also create documents in a two-dimensional manner without utilizing the model, thus entering information a second time. Often two-dimensional plans and details are still created using “intelligent” components, which causes more embedded data to go unused because after drawing with these data-rich elements, the engineer then uses “dumb text” to convey information. Using the embedded data, either within the 3D or the two-dimensional (2D) elements, is an additional opportunity to expand on the potential benefits and efficiencies of the BIM process.

models for collaboration among the design team, but little beyond that.

• Advanced BIM: Both the design team and the contractor work in BIM, which offers a more advanced level of coordination. The projects that dabble in this level of BIM likely have each firm authoring their own model, while achieving a higher level of collaboration.

• Innovative BIM: Models change hands between the design and construction teams, and then potentially the owner.

Integrated Project Delivery (IPD) projects, as well as projects where models are moved downstream for use in fabrication, construction, facilities management, etc., would qualify as this more innovative level of BIM.

Where is the Industry Headed?

The utilization of the BIM process will move more toward “innovative solutions.” However, as it does, there are several more potential applications that may seem far-fetched but are conceivable (may even be happening now), and could be commonplace in the future.

The following examples are achieved by extracting data from an information model and utilizing that data to build a structure in an innovative and efficient manner, potentially more accurately than traditional building methods. Figure 3 shows a mechanical arm that is laying a brick wall. Figure 4 shows drones that are building a structure, one block at a time. Finally, Figure 5 shows a concrete castle that a contractor 3D printed in his own backyard.

Where is the Industry Now? Utilization of BIM exists on many levels: • Basic BIM: Two-dimensional approach only – BIM software utilized to create only 2D documents but no model. This approach could still involve some utilization of data, so it can still be categorized as BIM, but it is likely challenging to realize benefits.

• Lonely BIM: A term adopted by the BIM industry to describe the case where one firm works in a BIM software and creates an information model but does not share it with any other firm. This provides some internal benefits to that one firm but forgoes all potential coordination, collaboration, and downstream benefits.

• Collaborative BIM: This is where most of the industry operates today. Everyone is working within a BIM software, sharing STRUCTURE magazine

Figure 5. 3D printed concrete castle.

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These examples probably seem far-fetched, or even futuristic, but are they? Could derivatives of these sorts of processes start showing up on projects? If or when they do, the information models created by design and construction teams will become even more important than they are now.

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What is the Next Step?

Idealistic theories aside, BIM continues to increase in importance in the building industry. The question becomes, what is the next step to advancing BIM for structural engineers?

Optimistically speaking, somewhere down the BIM road, building information models and analytical models will be fully integrated or perhaps even one in the same. This is the most obvious shift that will impact the structural engineering industry. With each release of the various software packages, interoperability improves. The time spent creating, modifying, updating, and managing two independent models is a significant line item in a project budget, so there is much to be gained as these two modeling efforts merge.

However, this is not necessarily something that structural engineers can control; this is dependent upon future advancements in technology.

Looking at what structural engineers can conFigure 6. 2D detail and information derived from an information model instead of being recreated. trol, the next step is more likely finding ways to improve upon internal workflows. This could be achieved by more completely and more efficiently utilizing the to advance BIM is the new competitive advantage – structural data embedded in the information models that are already being engineers should not be reactionary, but rather proactive in taking created. By removing the unintelligence of a simple drawing and that next step, if for no other reason than to have input instead of replacing it with layers of metadata, information about a structure allowing that decision to be fully controlled by other parties. The can be exchanged more efficiently and accurately across the entire sooner structural engineers embrace this technology shift, believe in design and construction team. Utilizing this metadata is key in it, and commit to collaborating fully with the other project particitaking the next step with BIM. As an example, much of the content pants, the sooner immense benefits will be realized both internally shown in Figure 6 is usually recreated content using “dumb lines and for the project.▪ and text”; however, Figure 6 was instead derived directly from the information model that had been created anyway. There are Acknowledgments efficiencies to be gained here.

Much of the content of this article was derived from discussions among the SEAC BIM Committee. I would like to offer sincere thanks to the Conclusion following committee members for participating in those conversations BIM used to be a competitive advantage but has evolved to become over the past several years. a requirement to even participate in a project. Taking the next step Jeremy Crandall, P.E. – Structural Consultants David Weaver, P.E. – Mold Tek Jedidiah Williamson, P.E. – Martin/Martin John Brunner, P.E. – JVA Demos at www.struware.com Neal Bohnen, P.E. – SA Miro Wind, Seismic, Snow, etc. Struware’s Code Search program calculates these and other loadings for all codes based on the IBC or ASCE7 in just minutes (see online video). Also calculates wind loads on rooftop equipment, signs, walls, chimneys, trussed towers, tanks and more. ($195.00).

Desirée Mackey is Senior Project Engineer and BIM Manager at Martin/Martin in Denver, Colorado. Desirée is extremely active in the BIM community as a regular speaker at many conferences, as co-founder of the Rocky Mountain Building Information Society, as the Chair of the Structural Engineers Association of Colorado’s BIM Committee, as the Program Manager for the RTC (Revit Technology Conference) North America Committee, and a past Vice President and board member for the AUGI (Autodesk Users Group International).

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award winners and outstanding projects

Spotlight

Tour de Force for San Francisco International Airport Performance-Based Design of the New Air Traffic Control Tower

By Rafael Sabelli, S.E., Joe Maffei, S.E., Ph.D., Susendar Muthukumar P.E., Ph.D., and Lawrence Burkett Walter P Moore was an Outstanding Award Winner for its Air Traffic Control Tower and Integrated Facilities Building project in the 2016 NCSEA Annual Excellence in Structural Engineering Awards Program in the Category – New Buildings over $100M.

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an Francisco International Airport has a prominent new landmark: a 220-foottall air traffic control tower with the latest aviation technology and stateof-the-art structural engineering. The iconic tower rises at the public doorstep of the airport between the main roadway, the active airfield, and Terminals 1 and 2.

Beneath the tower’s brushed aluminum cladding, a vertically post-tensioned cylindrical core of cast-in-place concrete resists extreme earthquakes and wind-induced vibration. The flared upper structure and control cab, framed in steel, cantilever up and out from the core. The base of the tower is surrounded by a three-story, 50,000 square foot building housing Federal Aviation Administration (FAA) offices and connecting corridors for passengers walking between terminals. The non-secure corridor features a 35-foot-tall glass ceiling providing a colorful view of the LED-lit tower. The base building has concrete walls and steel gravity framing designed to resist blast threats from the nearby roadways and the non-secure pedestrian corridor. A performance-based seismic design methodology was adopted early in the process, allowing flexibility in the choice of structural system and reliable and customized performance objectives.

Located 2.5 miles from the San Andreas Fault, the control tower is designed to remain fully operational at the Design Earthquake level, and to provide safe exiting and no collapse at the Maximum Considered Earthquake level. A nonlinear response-history analysis was used from the beginning of design. Earthquake ground motions were selected and scaled to account for soil nonlinearity and pile effects on site response.

The vertically post-tensioned core is designed to re-center after earthquake deformation. The base building buttresses the tower with four horizontal buckling-restrained braces that provide a force-limiting backstay. The backstay efficiently distributes and resists overturning without overloading the roof diaphragm of the base building. The design reduced foundation costs and facilitated fast construction, with the slip-formed tower quickly rising without needing to wait for the base building construction.

The project demonstrates the feasibility of constructing damage-resistant, self-centering structural systems economically and efficiently.

The flared shape and the offset control cab address new FAA requirements to place additional electronic equipment near the control cab. The cab is column-free for 220 degrees of its perimeter allowing unobstructed views of runways and taxiways for controllers, the first with this configuration. Tuned mass dampers near the cab reduce wind accelerations that could cause discomfort to occupants.

Located on reclaimed wetlands, the site has extremely soft soil. Piles extend 125 feet deep to reach bearing in the Franciscan bedrock. Since the noise and vibration of driven piles were incompatible with ongoing operations in the adjacent passenger terminals, the building is founded on a seven-foot-thick mat supported on auger pressure-grouted piles. Excavation volume was minimized in the foundation design to reduce the costly disposal of contaminated soils. The piles are detailed with spiral ties over their full length to accommodate concentrated lateral deformation imposed by the interaction of soil layers under strong ground shaking.

The project was completed on schedule and budget. Solar panels, eco-friendly mechanical systems, and sustainable materials were used to achieve a LEED Gold certification. The project is the first use of performance-based seismic design by the FAA, and the first designbuild control tower. According to SFIA Deputy Director of Design and Construction, Geoffrey Neumayr, “We were very pleased with the skill and ingenuity that Walter P Moore brought to the task of creating this amazing structure. They were able to convince the FAA to deviate from their traditional prescriptive structural design to a performance-based design, which allowed for the post-tensioning. They showed a strong personal commitment to the success of our project.

Their responsiveness during construction and their overall focus on constructability and cost were major factors in our ability to complete our project within budget”.

The new tower has been well received by the public and has been the recipient of acclaim in

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the architectural press. News stories about the project have touted not just the iconic form of the tower but its innovative engineering and enhanced seismic performance criteria. San Francisco Chronicle architecture critic John King wrote: “No Bay Area building shows the engineered reality of today’s architectural scene – or rather, keeps it under wraps – quite like the new flight control tower at San Francisco International Airport. The first impression is effortless, a flared silver beacon topped by a glass swirl within which the controllers do their job. What we don’t see is the work behind the lyrical flourish: a concrete spine rising from a concrete mat 7 feet thick, concealed by the aluminum skin and topped by 75,000 pounds of steel weights calibrated to thwart high winds and earthquakes. With all these requirements, it’s easy to imagine a brawny tower hulking over SFO, rather than the curvy cone sliding up into the sky. The efficiency with which the tall structure fits into the tight site is a tribute to the engineering firms involved: Walter P Moore, Rutherford+Chekene and Maffei Structural Engineering.”▪ Rafael Sabelli is a Principal and Director of Seismic Design at Walter P Moore.

Joe Maffei founded Maffei Structural Engineering in 2013.

Susendar Muthukumar is a Senior Engineer and Senior Associate with the Research & Development Group of Walter P Moore.

Lawrence Burkett is a Senior Structural Designer at Maffei Structural Engineering.

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NCSEA News

News form the National Council of Structural Engineers Associations

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NCSEA Provides Resources for Your Local Structural Engineering Association Thomas Grogan Jr., P.E., S.E., F.ASCE, NCSEA President The saying, “all politics are local,” resurfaces every election season as candidates are seen creating opinion polls to establish their position on the key issues. In the Structural Engineering Community, a similar refrain can be made that “all structural engineering is local and Structural Engineering Association (SEA)-based.”

Your local SEA is the go-to organization for your structural engineering needs. It helps provide for a key part of your professional licensure, continuing education requirements, and networking opportunities with other like-minded engineers. That is why NCSEA’s mission, as the national organization for structural engineers, is to help strengthen those local state-level SEAs (NCSEA’s Member Organizations or MOs), because the stronger they are, the greater the resources to which you have access.

In NCSEA’s pursuit to strengthen the state SEAs, we have established resources to assist with: • licensure questions; • young member group development and growth within your SEA; • speakers for continuing education; • best practices across SEAs (for annual conferences, dues, web-based learning, etc.)

• networking (face-to-face and web-based) across SEAs; • committee interaction from SEA to national and among SEAs; • grants for SEA project funding; • scholarships for young members to attend national events.

An example of this state-to-state interaction, supported through NCSEA, is the information shared about Florida’s drive to create a structural engineering license. The Florida Structural Engineering Association (FSEA) moved a bill all the way to the Governor’s desk before it was vetoed. While Florida wasn’t successful in its efforts, NCSEA provided a forum for FSEA to present its lessons learned on the path to licensure so other SEAs could learn from it. Based on the response FSEA has received since that presentation, the information was deemed extremely valuable.

Another example of the power of the national-local coordination is the NCSEA Structural Engineering Emergency Response (SEER) Committee. At a national level, this committee is working to further develop and enhance its 2nd Responder Roster (pictured on the right), a comprehensive database of structural engineers across the U.S. with post-disaster training interested in assisting with post-disaster condition assessments

of structures. This database will be a critical tool for state-level SEER committees if their state is impacted by a disaster. They will need to look for help beyond their state for 2nd responders to support the assessment and recovery efforts.

This national support for local initiatives defines the relationship between NCSEA and the state SEAs. In addition, NCSEA itself is a Thomas Grogan, resource for you. Your relationship NCSEA President with your SEA establishes your relationship with NCSEA. As a national organization, NCSEA can also be a source of information to you on topics like continuing education, licensure and networking. NCSEA is an association with fulltime staff ready to be utilized as a resource to the volunteers and part-time employees of your local association.

A final example of the support NCSEA provides to the volunteer leaders of your local SEA are the monthly MO Communication Webinars. These webinars are provided at no cost and focus on providing practical tools that your local SEA can use to operate more effectively. A recent webinar focused on best practices for continuing education, including discussions on webinars, annual conferences and on-demand learning. Attendees were pleased with the value of that webinar.

As a practicing structural engineer, you have two great resources at your fingertips – your local SEA and NCSEA. Take advantage of them to help you professionally because they exist to support you.

The efforts of the NCSEA SEER Committee to support local SEA SEER committees defines the working relationship between NCSEA and the state SEAs.

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January 2017

As 2017 begins, the time to plan your continuing education for the coming year is now. NCSEA offers several opportunities for advancement and learning, but it doesn’t stop there! Our State SEA Member Organizations also offer many events and meetings to fulfill educational needs.

Webinar Series: Structural Seismic Design Manuals

Continued Education on Continuing Education

NCSEA SE Review Course

CalOES Safety Program

On December 7 th, NCSEA held a webinar with three of its Member Organizations to examine the successes and lessons learned while planning or implementing in-person events, conferences, webinars and digital education technology. Tim Gilbert of SEAoO (Structural Engineers Association of Ohio) stressed the importance of organization while planning their most successful program which is their local Annual Conference.

Stephanie Crain from SEAOI discussed Illinois’s vast educational offerings (from online learning to in-person sessions) and the tools they use to keep driving attendance. Carisa Ramming with OSEA boasted about Oklahoma’s semi-annual Conferences that receive almost 50% of their membership in attendance.

NCSEA Education Director, Jan Diepstra, finished the webinar with an overview of what educational resources we offer to the public and to our members. The slides from the December 7 th meeting can be found in the NCSEA Member Portal.

News from the National Council of Structural Engineers Associations

The California Office of Emergency Services (CalOES) Safety Assessment Program (SAP), presented by NCSEA, is highly regarded as a standard throughout the country for engineer emergency responders.

The training has been reviewed and approved by the Federal Emergency Management Agency’s Office of Domestic Preparedness.

Based on ATC-20/45 methodologies and documentation, the SAP training course provides engineers, architects and code-enforcement professionals with the basic skills required to perform safety assessments of structures following disasters.

Licensed design professionals and certified building officials will be eligible for SAP Evaluator certification and credentials following completion of this program and submission of required documentation.

The next course offered by NCSEA is March 24, 2017.

Registration can be found on www.ncsea.com.

This series of webinars will feature an in-depth look at design examples from the newly published 2015 IBC Structural/Seismic Design Manual (SSDM) Volumes 1, 2 and 3. This will be your opportunity to hear directly from contributing authors of the example problems as they share their significant expertise and experience in the design area and underlying building code provisions of the new 2015 International Building Code (IBC). These unique sessions, hosted by SEAOC and supported by NCSEA, are sure to be useful to experienced and new engineers alike.

All webinars will be held on consecutive Thursdays in January and February 2017 from 11:00 a.m. to 12:30 p.m. PST with time for a Q&A at the end of each session. PDHs are available for attending the live webinars and recorded versions will be available afterwards through the SEAOC bookstore.

• Jan. 19: Tilt-up Building Design Example • Jan. 26: Concrete Shear Walls & Concrete Coupling Beams Design Examples • Feb 2: Pile Foundations & FEMA P-1051 Design of Piles for Lateral Spreading Design Examples For more information visit www.seaoc.org.

NCSEA News

2017 Education

Twice yearly, NCSEA offers the Structural Engineering Exam Online Review Course in both lateral and vertical concentrations.

The purpose of the course is to prepare attendees for exam day success by providing efficient analytical methods, problem solving techniques, key topics of structural code, and typical exam questions. This newly designed program will feature insight from leading structural engineers from across the industry. Registration for the Spring and Fall classes will be announced soon.

NCSEA Webinar Subscription Plans Available only to NCSEA and SEA members, these plans offer a flat fee for 12 months of webinars: • Live & Recorded Webinar Subscription - $995 • Live Webinar Subscription - $750

More information on www.ncsea.com February 21, 2017

NCSEA Webinars

Designing for Hot-Dip Galvanizing Alana Hochstein, EIT

January 17, 2017

Masonry Movement Joints Pat Conway, AIA

March 9, 2017

February 7, 2017

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The Most Common Errors in Seismic Design & How to Avoid Them Tom Heausler, P.E.,S.E.

More detailed information on the webinars and a registration link can be found at www.ncsea.com.Subscriptions that include both live and recorded webinars are available for NCSEA members! A library of over 150 Recorded Webinars is now available online 24/7/365. Webinars provide 1.5 hours of continuing education, approved for CE credit in all 50 states.

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Design of Connections for Wood Members using the NDS & TR12 Lori Koch, P.E.

Updated Concrete Repair Code and Companion Guide Jay Paul, S.E.

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The Newsletter of the Structural Engineering Institute of ASCE

Structural Columns

Registration Now Open The Premiere Event for Structural Engineering Come for the innovative solutions and cutting-edge knowledge, leave with connections and resources to advance your career.

Register before February 15, 2017, to receive the best rates The Preliminary Program is available on the congress website at www.structurescongress.org.

WHO SHOULD ATTEND • Structural Engineers • Civil Engineers • Bridge Engineers • Business Owners • Researchers working in the structural engineering discipline • Professors/Academics • Students • Young Professionals • Users of ASCE 7, ASCE 41 and ASCE 24 • ASCE/SEI Members in the Pacific Northwest • Professional Engineers looking for additional PDH opportunities

Convention Hotel: Hyatt Regency Denver 650 15th Street Denver, CO 80202

Errata

Visit the congress website at www.structurescongress.org for more information and to register.

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

ASCE Live Webinars

ASCE Convention Call for Presentations Now Open Submissions Due January 25, 2017 The ASCE 2017 Technical Program Subcommittee is currently accepting proposals for presentations at the Convention, scheduled for October 8 – 11, 2017 in New Orleans, Louisiana. This is your opportunity to be part of this outstanding program.

Share your expertise, professional insights, and industry best practices by becoming a session presenter. Interact with the industry’s best and brightest civil engineers and engineering students while imparting your knowledge.

ASCE is seeking sessions on the following topics: • State of the Industry/Profession • Professional Development • Multidisciplinary Technical • Natural and Man-Made Disasters • Strategic Issues/Public Policy • Significant Projects • History & Heritage Visit the ASCE Convention website at for more information (http://2017.asceconvention.org) and to submit your session abstract.

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The Structures Congress offers 120 technical sessions on all aspects of the profession. Be inspired by the extraordinary keynote speakers, network with your colleagues, earn PDHs, and celebrate the future of structural engineering at the special Friday night reception.

We expect the convention hotel to sell out well in advance of the official cutoff day, so book your room now.

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ASCE recently lowered prices on webinars, making them an even better value. Webinars are convenient, low-cost, and an efficient training option. Login anywhere and interact with the instructor and other participants. Our webinars cover practical, targeted topics taught by experts in their field. Gain knowledge and earn PDHs. Members enjoy value pricing of $99 for 60- or 90-minute live webinar individual registrations. Group/site registration for members is $199 to $249.

Non-members rates are $129 to $159 for individual registrations.

Non-member group/site registration is $199 to $249 but requires a $30 non-member certificate fee per non-member individual.

Upcoming Structural Webinars: January 17, 2017 – Significant Changes to the Wind Load Provisions of ASCE 7-16 January 26, 2017 – Design Snow Loads for Solar Paneled Roofs February 7, 2017 – Changes to the Nonbuilding Structures Provisions in ASCE 7-16 February 15, 2017 – International Building Code Essentials for Wood Construction: Fire Protection Basics for Structural Engineers Visit the ASCE Continuing Education website for more titles and to register at www.asce.org/continuing-education/ live-webinars.

January 2017

Honoring a legacy in structural engineering and architecture Lehigh University is pleased to announce the dates and speakers for the 2017 Fazlur R. Khan Distinguished Lecture Series.

Friday, February 17, 2017 – 4:30 pm Eugen Brühwiler, Professor and Dr. Structural Engineer, Swiss Federal Institute of Technology Lausanne (EPFL), Lausanne, Switzerland Getting More Out of Existing Bridges Friday, March 31, 2017 – 4:30 pm Lawrence G. Griffis, Walter P. Moore and Associates, Inc., Austin, TX Design and Construction of Cowboys Stadium

Guided Online Courses on Seismic and Retrofit

The Fazlur R. Khan Distinguished Lecture Series has been initiated and organized by Dan M. Frangopol, the first holder of Lehigh’s Fazlur Rahman Khan Endowed Chair of Structural Engineering and Architecture. Presentations will be held on the Lehigh University campus in Bethlehem, PA. The Structural Engineering Institute-Lehigh Valley Chapter will be awarding 1 PDH credit for each lecture to eligible attendees. For additional information about the Fazlur R. Khan Distinguished Lecture Series, please visit www.lehigh.edu/frkseries.

PE Exam Courses Register now for P.E./S.E. Review Courses beginning February 2017! Taking the P.E. Civil, S.E., or Environmental Exam this Spring? ASCE’s Exam Review Courses take the guesswork out of your study plan and prepare you for exam day.

Qualified experts deliver interactive courses that will build your confidence for exam day. You will receive access to recorded webinars and reference materials. Group rates are available for 2 or more engineers preparing in the same location. www.asce.org/live_exam_reviews Recordings of these sessions will be available in February and March.

SEI Local Activities University of Illinois at Urbana-Champaign Graduate Student Chapter SEI welcomes the new SEI Graduate Student Chapter at the University of Illinois at Urbana-Champaign, chaired by Derek Kozak, S.M.ASCE, with Faculty Advisor Prof. Daniel Abrams, Ph.D., P.E., F.SEI, M.ASCE. The SEI GSC will be incorporated into the existing Structural Engineering Graduate Student Organization (SEGSO) which has various academic and professional activities planned, and more to be planned with the help of SEI resources. These activities include the existing annual Chicago Professional Weekend which exposes students to various professionals in Chicago and academic activities such as student research seminars which encourage the sharing of graduate student research with others and spreads knowledge of cutting edge structural engineering research. Professional seminars using SEI resources and connections are also planned. Learn more on the SEGSO website at http://segso.cee.illinois.edu.

Get Involved in Local SEI Activities Join your local SEI Chapter, Graduate Student Chapter (GSC), or Structural Technical Groups (STG) to connect with colleagues, take advantage of local opportunities for lifelong STRUCTURE magazine

learning, and advance structural engineering in your area. If there is not a SEI Chapter, GSC, or STG in your area, review the simple steps to form a SEI Chapter at www.asce.org/ structural-engineering/sei-local-groups.

Local Chapters serve member technical and professional needs.

SEI GSCs prepare students for a successful career transition.

SEI supports Chapters with opportunities to learn about new initiatives and best practices, and network with other leaders – including annual funded SEI Local Leader Conference, technical tour, and training. SEI Chapters receive Chapter logo/branding, complimentary webinar, and more.

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The Newsletter of the Structural Engineering Institute of ASCE

ASCE’s Guided Online Courses are back January 23, 2017.

Two courses in structural engineering are available: Earthquake Engineering for Structures, which premiered in April 2016 and explains the why and how of ASCE 7, and Seismic Evaluation and Retrofit of Existing Buildings, which is a new course and explains the differences between seismic evaluation and retrofit. Learn more at www.asce.org/continuing-education/ guided-online-courses.

Friday, April 21, 2017 – 4:30 pm Peter A. Weismantle, Director of Supertall Building Technology, Adrian Smith + Gordon Gill Architecture, Chicago, IL Architectural Technical Design of the New Generation of Supertall Buildings

Structural Columns

2017 Fazlur R. Khan Distinguished Lecture Series

CASE 2016 Bestsellers Now Available!!

CASE in Point

The Newsletter of the Council of American Structural Engineers

Contract Documents #1: An Agreement for the Provision of Limited Professional Services – This is a sample agreement for small projects or investigations of limited scope and time duration. It contains the essentials of a good agreement including the scope of services, fee arrangement, and terms and conditions. #2: An Agreement Between Client and Structural Engineer of Record for Professional Services – This agreement form may be used when the client, e.g. owner, contractor developer, etc., wishes to retain the Structural Engineer of Record directly. The contract contains an easy to understand matrix of services that will simplify the “what’s included and what’s not” questions in negotiations with a prospective client. This agreement may also be used with a client who is an architect when the architect-owner agreement is not an AIA agreement. #13: Prime Contract, An Agreement Between Owner and Structural Engineer for Professional Services – This Agreement is intended for the Structural Engineer to serve as the Prime Design Professional. It addresses projects which may require other engineering disciplines and architectural services which are more than incidental. Examples are parking garages, warehouses, light industrial buildings, sports facilities, and structural renovations. It should be distinguished from CASE # 2 which is to be used when the Structural Engineer of Record has an agreement with the Owner but does not serve as the Prime Design Professional.

This document is written to be compatible with CASE #3 which can be used by the Structural Engineer as Prime Design Professional to contract with consultants on the same project in conjunction with this agreement.

Guideline Documents 962: National Practice Guidelines for the Structural Engineer of Record (SER) – The purpose of this document is to give firms and their employees a guide for establishing Consulting Structural Engineering Services and to provide a basis for dealing with Clients generally, and negotiating Contracts in particular. Since the Structural Engineer of Record (SER) is normally a member of a multi-discipline design team, this document describes the relationships that customarily exist between the SER and the other team members, especially the team leader. Further, this Guideline promotes an enhanced Quality of Professional Consulting Structural Engineering Services while also providing a basis for negotiating a fair and reasonable compensation.

Additionally, it provides a basis for Clients to better understand and determine the Scope of Services that the Structural Engineer of Record should be retained to provide.

962-C: Guidelines for Int’l Building Code-Mandated Special Inspections and Tests and Quality Assurance – The Guideline is an update of the previous, 3rd Edition to bring it current with the requirements of the 2012 International Building Code. The Guideline describes the roles and responsibilities of the parties involved in the special inspection and testing process, how to prepare a special inspection and testing program, the necessary qualifications of the special STRUCTURE magazine

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inspectors, how to conduct the program, and who should pay for the special inspections and test. The Appendix contains sample forms for specifying special inspections and tests, and sample letters to be filed with code-enforcement agencies after the program is completed.

962-E: Self-Study Guide for the Performance of Site Visits During Construction – Co-authored by ten professional engineers on the CASE National Guidelines Committee, Guidelines for the Performance of Site Visits is a guide intended for the younger engineer but will be useful for engineers of all experience levels. Structural engineers know that site visits are critical construction phase services that help clarify and interpret the design for the contractor. Site visits are also opportunities to identify construction errors, defects, and design oversights that might otherwise go undetected.

Engineers should include adequate construction phase services as a part of their scope of services to ensure the design intent is properly implemented.

In 2016, the document was updated with key points to summarize each section, revisions to references and definitions, and details on current tools for conducting site visits.

A companion document is available and was also updated in 2016: CASE Tool 10-1: Site Visit Cards.

Toolkits 1-1: Create a Culture for Managing Risks and Preventing Claims – This tool includes a storyboard and role playing guide to involve your staff in the risk management discussion. It also includes sample commitment statements for your firm to buy into the process.

9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Documents – The CASE Tool Kit Committee has repackaged a previously released CASE document with upgrades and additions! A summary test and answer key have been added to the Appendix of the original document.

It is recommended that engineers read this Guideline and take the test at the end of the document. More experienced engineers should then sit down with the engineers to go over the various subjects and answer any questions. The CASE Drawing Review Checklist will be a valuable tool to take away from this experience and implement for regular office use.

A companion document is available: CASE 962-D – A Guideline Addressing Coordination and Completeness of Structural Construction Documents.

9-2: Quality Assurance Plan – High-quality client service – from project initiation through construction completion – is critical to both project success and maintaining key client relationships. Elements of ensuring 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. As part of the Ten Foundations of Risk Management, CASE Tool No. 9-2: Quality Assurance Plan guides the structural engineering professional in developing a comprehensive, detailed written Quality Assurance Plan suitable for their firm. continued January 2017

You can purchase these and other CASE products at www.acec.org/bookstore.

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 a minimum, in an ABET-accredited engineering program. Since 2009, the CASE Scholarship program has given $20,000+ to engineering students to help pave their way to a bright future in structural engineering.

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.

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 Risk Management Convocation in Denver, CO

CASE Winter Planning Meeting

April 7, 2017

February 17-18, 2017; San Diego, CA

The CASE Risk Management Convocation will be held in conjunction with the Structures Congress at the Hyatt Regency Denver and Colorado Convention Center in Denver, CO April 6 – 8, 2017. For more information and updates go to www.structurescongress.org.

The following CASE Convocation sessions are scheduled to take place on Friday, April 7: 8:00 am – 9:30 am

Contractual Risk Transfers for Professionals: Mastering Indemnity, Insurance and the Standard of Care Moderator/Speaker: Ryan J. Kohler, Collins, Collins, Muir + Stewart, LLP 10:00 am – 11:30 am Construction Administration as a Risk Management Tool Moderator / Speaker: Daniel T. Buelow, Willis Towers Watson 2:00 pm – 3:30 pm Projects with the Largest Losses and Claim Frequency Moderator: Mr. Timothy J. Corbett, SmartRisk Speaker: Brian Stewart, Esq., Collins, Collins, Muir + Stewart, LLP 4:00 pm – 5:30 pm Tackling Today’s Business Practice Challenges – A Structural Engineering Roundtable Moderator: David W. Mykins, P.E., Stroud Pence & Associates STRUCTURE magazine

The 2017 CASE Winter Planning Meeting is scheduled for February 17 – 18 in San Diego, CA. If you are interested in attending the meeting or have any suggested topics/ideas from a firm perspective for the committees to pursue, please contact Heather Talbert at htalbert@acec.org.

The meeting agenda is found below. One of the highlighted features of the meeting is a joint roundtable with the other ACEC Coalitions to work on projects/issues that cross various disciplines.

Friday, February 17 8:00 am to 12:00 pm CASE Executive Committee Meeting 12:00 pm to 1:30 pm Shared Lunch w/speaker 1:45 pm to 5:45 pm CASE General / Toolkit Committee Meeting CASE Contracts Committee Meeting CASE Guidelines Committee Meeting CASE Programs & Communications Committee Meeting 6:00 pm to 8:00 pm Joint Coalition Roundtable 8:30 am to 12:00 pm CASE Toolkit Committee CASE Contracts Committee Meeting CASE Guidelines Committee Meeting CASE Programs & Communications Committee Meeting 12:00 pm to 12:30 pm Wrap-up Meeting

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CASE is a part of the American Council of Engineering Companies

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

Donate to the CASE Scholarship Fund!

CASE in Point

10-1: Site Visit Cards – This tool provides sample cards for the people in your firm who make construction site visits.

These cards provide a brief list of tasks to perform as a part of making a site visit, such as: what to do before the site visit; what to take to the construction site; what to observe while at the site; and, what to do after completing the site visit. The sample cards include several types of structural construction, plus a general guide for all site visits.

As of 2016, Tool 10-1: Site Visit Cards has been expanded and updated. General information is now consolidated to one section or card, with the remaining cards dealing with specific materials or types of construction. Added sections include: Driven Piles, Auger Cast Piles; Post-Tensioned Concrete, Tilt-Up Concrete, and Cold-Formed Steel Framing.

A companion document is available and was also updated in 2016: CASE 962-E – Self-Study Guide for the Performance of Site Visits During Construction.

Structural Forum

opinions on topics of current importance to structural engineers

Wood Products and Resilience of the Built Environment

By Kenneth Bland, P.E.

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n recent years, the term “resilience” has become a buzzword used by interest groups to demonstrate how products fit into efforts to adapt the built environment to expected changes in weather patterns, increases in storm frequency, and other natural disasters. Historically, engineers have used the term to define the structural performance of buildings under extreme conditions, but today it is used by a much broader group of stakeholders that are interested in proper preparation, response, and recovery. As more interests try to define what resilience means to them, it highlights the need for a comprehensive discussion by the stakeholders. This article demonstrates a need for a standard definition of resilience and further describes how building codes and wood industry design standards work together to mitigate the consequences of natural disasters on structures.

The International Code Council (ICC), developers of a family of building related codes, has a keen interest in the national conversation to define resilience. In response to a growing number of interests pursuing a proprietary position with respect to a definition, ICC launched the Alliance for National and Community Resilience (ANCR), with the fitting acronym “anchor.” ANCR is just finding its way into the resilience discussion but, at a recent meeting, their spokesman expanded the conversation from how to better address natural disasters to a comprehensive understanding of how unexpected disruptions can impact all levels of society from the smallest neighborhood to the massive response of the federal government. This initiative by ICC and its partners in ANCR, including the American Wood Council (AWC), will hopefully make the resilience discussion about much more than preparing for and recovering from natural disasters.

Since publication of the first U.S. building codes in the late 19 th century, the updating of code provisions has relied on a mix of experience and science to improve the response of structures subject to natural hazards (e.g., wind, seismic, and flood). In most instances, these changes have resulted in more robust building design and construction, leading to overall better structural performance under extreme

events. More recently, as the severity and financial costs from natural disasters becomes an increasing burden to society, increased attention has been paid to enhancing life safety and property protection measures in new and existing structures. For example: • In tornado-prone regions, safe rooms are required in certain occupancies of new construction and incorporated voluntarily in others.

• In hurricane-prone regions, glazed openings in new buildings are required to be protected in special wind-borne debris regions.

• In seismic hazard regions, both mandatory and voluntary programs for the upgrade of existing seismicallyvulnerable structures have been implemented.

• In flood hazard regions, requirements for building elevations vary based on a building’s flood risk category and locally designated flood elevation requirements.

Model Codes and Resilient Construction Since there is not a common understanding or definition of the term “resilience,” some industries have seen this as an opportunity to propose self-serving definitions that favor one product over another. There is a need for a nationally-accepted definition that would permit performance-based design and construction of all building types and materials to be identified as “resilient.”

Fortunately, modern model building codes promulgated by the ICC and the National Fire Protection Association provide criteria that result in resilient design and construction of the built environment. Conversely, at present, no less than ten federal agencies have varying definitions and classifications of “resilience.”

These different interpretations can cause even greater confusion to designers, builders and those responsible for ensuring a safe building environment. Further, some building material interests are promoting a need for more restrictive code requirements that can only be achieved by their products. The 10 second sound bite that modern codes do not provide

for resilient construction should be left on the cutting room floor. There are ample tools to help designers and builders exceed code requirements if a greater level of resilience is sought, including resources provided by the wood products industry.

Agreeing that today’s minimum code requirements provide for resilient construction is an essential starting point to launch the conversation. Prescriptive requirements are the result of historical performance, professional judgment, and risk/benefit. With the code as the baseline, industry is positioned to develop and implement tools that provide added levels of performance. For the wood products industry, demonstrating that wood buildings are engineered for resilience is at the core of its message.

Building codes rely on wood design standards to provide the necessary guidance for designers to meet higher performance goals, which in turn provide greater resistance to loads. In some instances, the code mandates the use of these standards. In other cases, they are voluntary or provide an alternative.

For engineered design, loads associated with natural hazards, design criteria, and values of material resistance are prescribed by the codes and reference standards. These design requirements provide a baseline performance and level of risk of the built environment that represents a consensus of design professionals, producers, code officials, and general interest.

Careful consideration should be given when recommendations to enhance resilience are provided from other sources. The recommendations must be coordinated with those of the U.S. model building codes to avoid inadvertent weakening of building requirements. This inadvertent weakening could occur through novel resilience schemes that are based on non-standard loads or non-standard values of material resistance. In principle, increasing performance in one area of the code to enhance resiliency should not weaken a different area of the code.▪ Kenneth E. Bland is the Vice President of Codes & Regulations at the American Wood Council. He can be reached at kbland@awc.org.

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

STRUCTURE magazine

58

January 2017

Introducing

Screw-Bolt+

™

CODE LISTED ICC-ES ESR-3889

APPROVED FOR USE IN: • Concrete • Cracked Concrete

ESR-3889

INTEGRATED WASHER with serrations under the head secures the attachment

• Seismic & Wind Loads • Lightweight Concrete Over Metal Deck

IDENTIFYING MARK diameter, length and product marks embossed on head for easy identification

• Tested In Accordance With ACI 355.2 • Tested For Reliability Against Brittle Failure

STOCKED IN THESE DIAMETERS

1/4" 3/8" 1/2" 5/8" 3/4"

ENGINEERED STEEL designed to cut through hard concrete and maintain ductility

ALSO AVAILABLE IN ROD HANGER DESIGN

STANDARD BIT designed for ANSI carbide drill bits

DUST RELIEF THREAD PROFILE improves speed & reduces effort for faster installation

701 E. Joppa Road • Towson, MD 21286 • www.DeWALT.com • (800) 524-3244 • engineering@powers.com