STRUCTURE magazine | December 2016

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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December 2016 Soils & Foundations Inside: San Francisco International Airport

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CONTENTS Columns/Departments EDITORIAL

7 Realizing a Vision for the Future of Structural Engineering

By John L. Carrato, P.E., S.E. CONSTRUCTION ISSUES

10 Cutting 100 Feet into Manhattan Bedrock

By Theodore von Rosenvinge, P.E. and David Pell, E.I.T

Cover Feature

26 NCSEA Excellence in Structural Engineering Awards

STRUCTURAL PRACTICES

15 Ground Improvement – The Eccentricity Matters

By Sompandh Wanant, P.E. and

The winners of the 2016 NCSEA Excellence in Structural Engineering Awards program were announced at NCSEA’s Structural Engineering Summit in Orlando in September. The program annually honors the best examples of structural ingenuity from around the world. STRUCTURE magazine is pleased to provide overviews of these unique projects.

Mekonnen Z. Gebresillasie, P.E. STRUCTURAL DESIGN

18 Common Misunderstandings with Geotechnical Work

Features

INSIGHTS

40 The Virtual Toolbelt

By Trent Parkhill, P.E.

By Elizabeth Angel and Daniel Shirkey BUILDING BLOCKS

22 Structural Challenge Facing the Wireless Communications Industry

CASE BUSINESS PRACTICES

42 Do You Know the Standard of Care?

By Mo Ehsani, Ph.D., P.E., S.E. and

By John A. Dal Pino, S.E. and

Ryan J. Rimmele, P.E., S.E.

Kirk Haverland, P.E., SECB

STRUCTURAL ANALYSIS

STRUCTURAL FORUM

38 Fatigue Analysis of Concrete Structures

By Dilip Khatri, Ph.D., S.E.

50 Structural Engineers and...

Energy Codes?

By Jim D’Aloisio, P.E., SECB

On the cover Walter P Moore was named a 2016 Outstanding Project Award winner in the NCSEA Excellence in Structural Engineering Awards program for the new SFO Air Traffic Control Tower. The 220-foot-tall tower is surrounded by an integrated three-story FAA office building with blastresistant walls. See page 26 for an overview of all of this year’s winners.

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.

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34 Challenging Foundation Built in the Heart of New York City

By Douglas P. Gonzalez, P.E. and Joseph L. Yamin, P.E. Locating and designing this 21-story state-of-the-art hospital building on a congested urban site in Manhattan proved challenging, especially for foundations and ground level construction.

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Editorial

Realizing a Vision for the Future of new trends, new techniques and current industry issues Structural Engineering

By John L. Carrato, P.E., S.E., F.SEI, F.ASCE

• Stakeholder workshop to ensure high-quality structural engineering continuing education • Scholarships for 10 Young Professionals to participate at the Structures Congress Engaging young members in our profession and SEI will go a long way toward realizing our Vision for the Future. Read about SEI Young Professional Scholarship recipient Fernando Martinez’ experience at the 2016 Congress: “The benefits of participating at the Congress are many: comprehensive exposure to structural engineering design topics that are relevant to current practice and technology, exposure to research areas that will advance structural engineering design and construction/material technology, exposure to topics related to professional licensure and project management, and an incredible networking opportunity with leading professionals from around the world. The Meet the Leaders event provided a casual setting for students and young professionals to interact with top senior engineers about the skills needed for a successful career. My overall experience at the 2016 Congress was outstanding, and I plan to participate in future SEI Structures Congresses.”

Through his experience and connection at Congress, Fernando is now actively engaged in efforts with the new SEI Global Activities Division.

Fernando Martinez receiving his SEI Young Professional Scholarship certificate from SEI President David Odeh and SEI Director Laura Champion.

A

s the SEI Futures Fund starts its fourth year, we are very excited about our progress to realize the Vision for the Future of Structural Engineering initiatives. Through leadership and innovation, the Futures Fund can revolutionize the future of structural engineering. It has been instrumental in helping start many of these initiatives, efforts that are possible only through your generous gifts of support.

While we have had a great start, our Vision is ambitious and our goal is to develop a culture of giving throughout SEI and the profession to enable these efforts. The SEI Board of Governors recommends annual minimum leadership giving levels of $500 for Board members, $250 for Executive Committee members, $100 for Committee chairs, and $50 for Committee members. Your work and dedication as a volunteer member significantly increases SEI’s ability to advance the art, science, and practice of structural engineering. An additional way to support our Vision and the profession is to make a contribution. If everyone gives, we can take even greater strides to realize our Vision for the Future.

The four strategic areas the Futures Fund supports are: • Invest in the future of the profession • Promote student interest in structural engineering • Support younger member involvement in SEI activities • Enhance opportunities for professional development Following a successful year of contributions, the Futures Fund Board of Directors has provided $64,000 for the 2017 fiscal year to support the following strategic initiatives – all of which are strongly in line with the Vision for the Future: • SEI Global Activities initiatives to grow SEI’s global presence through resource workshops, an international practice guide, and increasing international sessions at the Structures Congress • Funding for a new SEI Student Structural Engineering Competition and support for five student teams to compete at the Structures Congress

STRUCTURE magazine

Celebrating the Future of Structural Engineering The support we are receiving from our colleague, Ashraf Habibullah and CSI, by hosting Celebrating the Future of SE events at the Congress is tremendous. Those of you who were at the celebration in Phoenix last February had an incredible time in support of the Vision and the Futures Fund. You are invited to another special dinner reception, hosted by Ashraf, April 7, 2017, at the Structures Congress in Denver.

Join us for a fun evening of inspiration and entertainment in celebration of structural engineering; register at www.structurescongress.org.

We also have a unique gift match opportunity – give now through December 31 and your gift to the Futures Fund will be doubled by Ashraf, up to $25,000. Your gift in its entirety benefits the SEI Futures Fund, free of any administrative burden. The Futures Fund partners with the ASCE Foundation, a 501(c)(3) tax-exempt organization.

Your contribution is tax-deductible to the full extent of the law, and an acknowledgment and receipt will be provided.

Learn more about the Futures Fund and give at www.asce.org/SEIFuturesFund. Your support is greatly appreciated!▪ John Carrato is President and CEO of Alfred Benesch & Company in Chicago, Chair of the SEI Futures Fund Board, and serves on the SEI Board of Governors. For more information, contact Jen Ilchishin at jilchishin@asce.org.

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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 John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA

Erratum In the November issue of STRUCTURE, the last name of Sarv Nayyar was misspelled in a caption in NCSEA News on p. 69. STRUCTURE apologizes for this error.

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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 December 2016, Volume 23, Number 12 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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ConstruCtion issues discussion of construction issues and techniques

E

xtending New York City Subway lines requires deep excavations in a congested urban environment while protecting adjacent facilities. The 100-foot-deep Metropolitan Transportation Authority (MTA) No. 7 Line Station excavation, through soil and rock between West 34th and 35th Streets, was no exception.

MTA 7 Line Extension A 1.5-mile extension of the No. 7 Flushing Subway Line in the Borough of Manhattan, New York City, from its previous terminus at Times Square, was recently constructed. The project was constructed for the MTA and extended south and west to a new 34th Street, Hudson Yards Station (Figure 1).

This improvement grants more accessibility to the area, including the Hudson Yards Redevelopment Project and the Jacob K. Javits Convention Center.

Future plans will consider tunnel extensions west under the Hudson River to New Jersey.

The excavation of a West 34th Street cavern marked the start of construction in December 2007. The construction of the tunnels began in June 2008 with the use of tunnel boring machines. The No. 7 Line extension was opened to the public on September 13, 2015.

Elevations provided in this article are relative to New York City Transit Authority Datum at 97.347 feet below USGS mean sea level (NGVD 1929).

Cutting 100 Feet into Manhattan Bedrock

By Theodore von Rosenvinge, P.E., D. GE, F.ASCE and David Pell, E.I.T

Excavation for the 35th Street Access Theodore von Rosenvinge is a Geotechnical Engineer, Co-founder and President of GeoDesign, Inc. He can be reached at ted.von@geodesign.net.

The Hudson Yards Station (Figure 2) consists of three floors: an upper mezzanine, lower

Figure 1. Location plan with No. 7 Line in view.

mezzanine, and a platform level, with the platform level situated 125 feet below street level.

Access is provided from 34th Street with secondary access at 35th Street.

The focus of this article is the “Site P” portion of the 34th Street Station which provides the secondary access from 35th Street. Site P is located across from the Jacob Javits Center between 34th and 35th Streets and 10th and 11th Avenues. The Site P design and construction required soil and rock excavation to depths of over 100 feet into the rock adjacent to an Amtrak right of way (ROW) below.

The unique aspects of the support of excavation (SOE) work included requirements for phased excavation to tie into other 7 Line contract work in the extremely congested urban area. This involved concurrent de-tensioning of existing tie-back systems supporting site access to the Amtrak tunnel.

Contractor John P. Picone (JPP) was awarded construction of the Site P Station Entrance for the station in September 2012. JPP performed the excavation for the facility in two phases, Phase I and Phase II (Figure 3). Phase I consisted of a temporary SOE system for both soil and rock for the upper mezzanine station entrance. Phase II was

David Pell is a Project Engineer at GeoDesign, Inc. He can be reached at dpell@geodesign.net.

Figure 2. Composite plan showing the No. 7 Line and Site P.

10 December 2016

Figure 3. Plan view.

Figure 5. A typical section of the SOE.

more complex as it required the installation of another temporary SOE for the excavation of soil and support of vertical rock faces for the descent into the ground to connect with an existing “Shaft P.” Shaft P had been previously excavated to connect the Phase I & II excavations to the 34th Street Cavern and No. 7 Line tunnels, while also providing access to the cavern area during its construction.

The ground-surface, street-level elevation is at approximately 128 to 130 feet (Figure 4). Phase II required excavation to depths ranging from approximately 40 to 95 feet below the ground surface to connect to the existing Shaft P. The rock was excavated on a slope to facilitate escalator access construction from track level to ground surface. The temporary SOE supported up to 35 feet of

soil overburden down to the top of bedrock between the existing Phase 1 and Shaft P sites.

Soil and Bedrock Conditions Geotechnical data reports were prepared for the site by MTA geotechnical consultants in advance of construction. Borings found about 10 to 35 feet of overburden soils consisting largely of urban fill over glacial till/ decomposed rock before encountering the bedrock surface. The reports indicated massive granite (granodiorite, diorite, granite) and schist (mica schist, biotite-hornblende schist, gneissic schist) rock groups constituting the majority of the rock. Discontinuities in the rock, including fractures and multiple joint sets, were found in both rock groups. Joints are fractures in the rock mass where there has

been little or no movement, and a joint set is a group of joints of similar parallel orientation in space. The strike and dip orientation of the rock discontinuities were also measured during excavation.

Groundwater was found during design phase borings at about elevation +101 feet.

Challenges The phased construction presented several design challenges. The existing SOE wall between Phase I and Phase II had to be integrated into the new Phase II SOE, and the existing western SOE wall at Shaft P had to be partially removed to build the SOE necessary for the excavation. The installation of the north and south walls of the Phase II SOE also had to be tied into both the existing Shaft P and Phase I SOE. As excavation proceeded through the upper soils, SOE soldier piles driven through the soil to the top of rock were exposed. As the rock was excavated and exposed below the pile tips, additional rock support and pile toe pins were added at some locations to maintain pile bearing during excavation. Pile toe pins consisted of #14 reinforcing bars grouted into 5-foot deep by 2½-inch diameter rock sockets.

Construction Solutions Excavation was completed primarily with the use of excavators through soil overburden and then switched to controlled blasting and line drilling when rock was encountered. Blasting operations were controlled to limit vibrations below specified maximums.

The Phase II SOE (Figures 5 and 6, page 12) consisted of tied-back soldier piles and lagging.

The depth was based on the depth to rock, ranging from approximately 18 to 37 feet. Soldier

Figure 4. Elevation view of the Phase II SOE.

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Figure 6. A view of the Northwest corner (towards the Javits Center) of the Phase II Soil SOE.

Figure 7. A view from the bottom of Shaft P (looking west) showing the tunnel access.

Figure 8. Typical rock bolts and mesh below the SOE.

piles were driven to the top of rock with toepins installed at the pile tips for toe restraint as excavation progressed. Tie-backs were preloaded strand anchors drilled and grouted into bedrock.

Wales were seated on diagonally cut HP pile sections that were welded to the soldier piles to anchor the exposed end of the tieback.

Two gravity retaining wall structures were constructed to support portions of the Phase I SOE while providing a means for removal

of a portion of the existing west wall of the Phase I SOE and commencement of the Phase II SOE. Rock bolts and shotcrete bracing the eastern Shaft P rock wall were removed. The SOE between the Phase II excavation and Shaft P was partially demolished to allow connection of the north and south walls of the Phase II and Shaft P SOE’s, and the ultimate connection to the tunnel (Figure 7).

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Rock support design required field mapping of the rock structure and the joint sets. Field mapping results were compared and coupled with the design-phase rock core information provided by the MTA. The data was used in rock mechanics analyses for final design and layout of the rock bolting construction.

The design also incorporated the sequencing requirements for the removal of rock with the installation of reinforcement at the exposed rock faces. Eight-foot, minimum-depth rock dowels and mesh were installed into the rock in a typical six-foot by six-foot pattern. Typical rock bolts and mesh installed below the SOE are shown in Figure 8.

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The shallow bedrock and phased construction required a real-time-design approach to address excavation techniques, support of rock faces, and integration of existing SOE’s. This method involved assessment of actual soil and bedrock conditions including field mapping of rock structure as the excavation progressed to expose actual conditions. Field data was analyzed for the final design of rock bolting to stabilize the faces of the deep bedrock cut, protect adjacent construction, and permit construction of the subway station in a heavily congested urban location.▪

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I

n Ground Improvement for Building Support

by Damian R. Siebert, P.E. and Steven R. Kraemer, P.E. (STRUCTURE, July 2015), we learn more about issues surrounding the ground improvement (GI) for a building support system (stone columns, aggregate piers placed under reinforced concrete footing). It is an intermediate foundation system, i.e. the system between shallow spread footings and deep pile foundation systems. Although the system has been around in Europe since the 1930s and in the U.S. about a decade later, it remains mostly in the hands of the specialty contractor’s foundation engineers.

Siebert and Kraemer state the following in their article: As applications of GI are being pushed to new limits, the need for deep understanding of installation conditions, behavior, and adequate quality assurance becomes more critical. The adequacy of GI in bearing capacity applications cannot be assumed simply because of its successful legacy for settlement control. In such challenging applications, the Engineer(s)-ofRecord (EOR) and project team must ensure that the GI provides comparable bearing capacity, settlement control, resiliency during earthquake and other loading conditions, quality assurance and overall performance as other “conventional” foundation systems. Experience is proving that this is easier said than done.

In practice, the GI specialty contractor engineer provides the Structural Engineer of Record (SER) with the equivalent uniform bearing capacity to size the footings for the building foundation walls and columns. When asked the overall Factor of Safety of the system, the answer cannot be obtained consistently. Instead, the GI specialty contractor engineer stresses that, for design adequacy, it is critical to know the traditional maximum acceptable settlement and the maximum differential settlement between columns. The SER’s only foundation design involvement for most projects is to review and approve the GI foundation system shop drawings (size of footings and locations of the

Figure 1.

piers, general construction/installation notes, and specifications, etc.) prior to installation.

The design concept of the GI foundation system for building support is to combine the bearing capacity of all piers and compressed soil under the footing and convert this total bearing capacity into the equivalent uniform bearing capacity for conventional spread footing design. Figure 1 shows typical single-, 2-, 3-, and 4-pier footing layouts under the square or rectangular concrete footing. The number of piers used under the footing can be as many as practically needed.

On a typical project, the GI foundation engineer evaluates the type of soil, determines the proposed improvement (diameter and length/depth of the aggregate piers), and calculates the stress modulus (stress per unit settlement) of the pier and the soil surrounding the pier. Kp is the stress modulus of the Pier and Ks is for the soil. The ratio Rs = Kp / Ks is obtained for use in determining the equivalent bearing capacity. The Rs values between 8 and 14 are normally used in practice, although a value as high as 40 is possible.

Having reviewed these GI foundation system shop drawings in the past, and more recently as a structural engineer or plan reviewer, the authors found that the geometrical layout of the 3-pier footing shown on some of the contractor’s shop drawings has substantial eccentricity. The footing, therefore, might not be adequate for the design intent (Figure 2a, page 16). Figure 2b (page 16) shows a correct layout of the piers in the 3-pier footing. The three piers should be installed in an equilateral triangle to each other, and the centroid of the piers and the soil under the footing coincide with the centerline of the footing (column center lines). For convenience in determining the centroid of the AP/soil matrix (3 piers and the soil surrounding the piers under the footing), one can write:

Structural PracticeS

Total capacity, P = (Rs-1) (3) (Ap) qs + (a) (b) qs

Mekonnen Z. Gebresillasie is a Geotechnical and Structural Engineer in the Building/Structural Section, Division of Building Plan Review, Department of Permitting, Inspections and Enforcement, Prince George’s County, Maryland. He may be reached at mzgebresillasie@co.pg.md.us.

practical knowledge beyond the textbook

Ground Improvement – The Eccentricity Matters

Where Ap is the area of the aggregate pier, qs is the soil pressure under the footing, and a and b are the footing dimensions. The centroid of the above two terms, as well as the total force, can be easily found.

Another concern that deserves the attention of the SER and the GI foundation engineer is the eccentricity of the single- and 2-pier footings. No matter how skilled the installer is, there will have to be some eccentricity when installing the piers. The single- and 2-pier footings are very sensitive to the eccentricity loading, and their capacity is substantially reduced when subjected to even a small eccentricity. continued on next page

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By Sompandh Wanant, P.E., M.ASCE and Mekonnen Z. Gebresillasie, P.E. Sompandh Wanant is Building/ Structural Section Supervisor in the Division of Building Plan Review, Department of Permitting, Inspections and Enforcement, Prince George’s County, Maryland. He may be reached at swanant@co.pg.md.us.

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

the remaining area is a function of “X”. By taking moments about the line of zero stress, we find the distance X equals 16.80 inches, and the total force equals 51,140 pounds. We can conclude that the capacity is reduced from the ideal of 96,000 pounds to 51,140 pounds, or reduced to 53.3 % of the ideal.

(a)

Estimate of the Capacity The contact pressure between the footing and the pier is similar to the contact pressure between a circular footing and the soil underneath. Therefore, we can utilize the empirical formula from previously published resources.

Considering contact pressures under the footing independently, we find from the example:

(b)

Total capacity, P ≈ (Rs–1) qs x Ap/k + (4 x 4) qs = (10 – 1) x 1595 x 4.909 / 2.70 + 16 x 1595 = 26,100 + 25,520 = 51,620 lbs.

Where k is the value from the Table. In this instance, the estimate (51,620 pounds) happens to be, coincidentally, a very close approximation of the example solution. The more accurate and reliable value should always come from computation as illustrated in the design example.

Figure 2.

Conclusion

Example Determine the capacity of a single-pier footing having the centerline of the aggregate pier installed 6 inches away from the building column centerline (6 inches is the acceptable construction tolerance). The footing is 4 feet x 4 feet (12 inches thick), and the aggregate pier diameter is 30 inches (Figure 3). The stress ratio (Rs = 10, the given equivalent allowable bearing capacity) is 6,000 pounds per square foot.

Solution: If the aggregate pier were installed right at the center of the column, the capacity would be (4 x 4) x 6,000 = 96,000 pounds.

With the stress ratio, Rs =10, and bearing stress, qs as the stress of the soil under the footing, we have

When designing the aggregate pier single- and 2-pier footings, one must take into account the field-installed eccentricity loading on the pier(s).

As demonstrated in the example, the capacity is greatly reduced even when installed within the construction tolerance. The GI foundation engineer and the SER must be aware of this reduced capacity and adjust the design accordingly. The eccentricity for the 3-pier footing addressed in this article is from a contractor’s incorrect layout of the piers (Figure 2a) and can easily be fixed.

Figure 3.

Final Note The eccentricity issues of the pier(s) footings addressed in this article can certainly be detected and resolved during the design process or shop drawings review by the SER. Also, other technical and non-technical issues, as described by Siebert and Kraemer in their article, should be addressed as soon as possible. Perhaps a task force consisting of academics, representatives from the ground improvement foundation industry, geotechnical and structural engineering groups, and the model codes developing organizations such as the International Code Council (ICC) is needed.▪

Table of values (k) for determining pressure (q) under circular footing.*

(4 x 4) qs + (10 – 1) π (15/12)2 qs = 96,000 qs = 1,595 psf Since the eccentricity is outside the “kern” (the area at the center of the pier having a radius of ¼ of the pier radius, i.e. 15 ÷ 4 = 3.75 inches), we know that the footing is not likely to be fully effective. Therefore, let’s assume the footing has zero stress near the edge of the pier (see the stress distribution on Figure 3). To find the total resultant force under the footing, we subdivide the circular area of the pier into nine (9) strip areas as shown, and with the stress distribution associated with each area, the forces at each strip and under

* Adapted from “Foundation Design” by Teng, W.C. (1962)

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December 2016

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Structural DeSign design issues for structural engineers Figure 1. Geotechnical risk spectrum.

I

n his December 2015 editorial, the president of the Structural Engineering Institute of ASCE, David Odeh, suggested that the increasing complexity of design necessitated that structural engineers interact more with people in other disciplines. While great innovation can come from a better interaction between structural and geotechnical engineers, there is also a potential for tremendous savings for clients. A reduction in cost can come from simple but critical improvements in communication. This article provides some examples of how that communication can be improved and of frequent misunderstandings that can arise. These misunderstandings can both drive up project costs and increase risk.

Common Misunderstandings with Geotechnical Work …And How to Reduce Risk and Project Costs

By Trent Parkhill, P.E.

Common Misunderstandings Uncertainty and Risk Trent Parkhill is a Senior Principal Geotechnical Engineer and Senior Fellow at Kleinfelder in Salt Lake City, Utah. He can be reached at tparkhill@kleinfelder.com.

While owners are usually less aware, most structural engineers understand that there is considerable uncertainty in geotechnical work. This uncertainty is driven by variations in soils under the site, the fact that the geotechnical engineer develops their understanding of the soils by sampling only about 0.000015% of the soil under the site, and the very large coefficient of variation for the properties of the soils. The uncertainty caused by these factors means that there is not one correct, code-based answer, but rather a range of possible answers, each with a different associated risk.

This collection of possible answers ranges from one extreme where the solution could mean failure to another extreme where considerable money would be wasted on unnecessary site improvements or expensive foundation systems. Figure 1 depicts a range of owners and their aversion to risk. Some owners are willing to allow increases in structural and geotechnical costs to minimize risk (Owner A), and other owners want to reduce every possible cost and are willing to experience some structure distress/maintenance (Owner C).

In situations where the geotechnical engineer is working for a more sophisticated owner, there can be a conversation about the balance between cost and risk. However, on most projects, the geotechnical engineer is left to guess about the owner’s preferences to balance risk and costs.

Many owners and structural engineers may think that the variations in answers they get from geotechnical engineers on the same site are due to the level of conservatism of particular engineers.

However, most of the variation comes from a lack of direction from the owner establishing a preference between risk and cost. Moreover, when the geotechnical engineer has to guess about the owner’s tolerance for risk, the building costs usually go up.

Allowable Bearing Pressure The typical project design process involves conducting the geotechnical work, finalizing the position of the structure on the site, deciding on-site grading, and then starting the structural design work. As you can see in Figure 2, if the geotechnical engineer does not know what the site grades will be or whether or not the building will have a basement, the geotechnical engineer cannot know what soils the footings will bear on.

And, if the structural design has not started, the geotechnical engineer will not know the loads on the foundation system.

Frequently, when the analyses are conducted, the geotechnical engineer does not usually know what soils will be below the footings nor do they know the loads (and therefore the sizes of the footings).

This information is essential for calculating bearing capacity and settlement, and for selecting the

Figure 2. Unknown information at the time of geotechnical design.

18 December 2016

allowable bearing pressure. The geotechnical engineer must guess at these conditions and then hope that, if the guesses are incorrect, someone will contact them for revised bearing pressures. Since the geotechnical engineer is rarely contacted and asked to verify their original assumptions and, if needed, modify their report, they make conservative guesses which result in conservative allowable bearing pressures.

The allowable bearing pressures could often be increased if the geotechnical engineer would be allowed to revisit their assumptions and analyses after site grading, footings loads, and footing elevations are available.

Subgrade Modulus

Figure 3. Subgrade modulus zone of influence.

Dynamic Lateral Earth Pressure

Allowable Settlement and What Settlement Matters?

The “allowable settlement” for a structure is one of the most significant areas of misunderstanding between geotechnical and structural engineers, and the lack of conversation about this subject can result in large, unnecessary project costs. In particular, in localities where there are significant thicknesses of soft clays or earthquake prone areas with soil liquefaction settlements, the allowable and maximum settlement is critical. Ideally “allowable settlement” should not be expressed to the owner until the structural and geotechnical engineer have an opportunity to talk. While it might be tempting to say “the allowable settlement is 1 inch” when asked what settlement a structure can tolerate, this is likely a very conservative number which could result in very large building and ground improvement costs.

In areas where seismic accelerations can be large, structural engineers say they appear to get differing recommendations regarding the lateral dynamic earth pressure for foundation or retaining wall design, and that sometimes they find it almost impossible to produce a reasonable design. Given the changes in design methodologies and misunderstandings about dynamic lateral earth pressures, it is not surprising that differences exist in the recommendations made by the geotechnical engineer. In the past, the dynamic earth pressure was expressed as an inverted triangular distribution. Recent research has concluded that the actual distribution is more likely a curved distribution, low on the top and low on the bottom (Figure 4). The current state of practice in most regions is to simplify this curved distribution to a uniform distribution, with a resultant load acting half way up the

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Subgrade modulus values are sometimes misunderstood or incorrect. The most common misunderstanding occurs when the geotechnical report does not make it clear whether the value reported is for a 1- x 1-foot plate (k1x1) or a value already scaled for the size of the mat/combined footing. If the report does not say the modulus value is for a 1x1 plate, the geotechnical engineer should be contacted to provide clarification.

Incorrect subgrade modulus values are sometimes developed because of insufficient information or geotechnical scope. When there is little information available on the proposed structure, and no scope to interact with the structural engineer, most geotechnical engineers will select a modulus value from a table based on the properties of the soil layer anticipated to be immediately below the foundation system (e.g. the “Sand & Gravel” unit in Figure 3). This works if the soil type does not change in the “zone of influence” below the foundation element. However, to design the mat shown in Figure 3, the soils that determine the actual modulus experienced by the mat are the soils to a depth equal to about twice the width of the mat. The easiest way to evaluate subgrade modulus, in this case, is to calculate settlement below the mat (elastic and consolidation settlements) and then create an initial modulus by dividing the load by that settlement.

This value can be further refined by comparing the structural engineer’s calculated deformation with the estimated settlement, and then iterating between the structural and geotechnical analyses if there is a significant difference in deformation. Leaving out the interaction between the structural and geotechnical engineer, in this case, results in wrong estimates of the mat’s settlement/deflection and incorrect reinforcing.

If the scope allows time for the geotechnical and structural engineer to discuss settlement, the settlement can be broken into components based on when they will occur (e.g. before the façade is placed, before construction is completed, after construction).

Moreover, with this level of refinement, the geotechnical engineer may be able to reduce foundation and ground improvement costs on some projects.

The possible effects of various amounts of settlement on structural performance and costs is an important topic that the structural and geotechnical engineer must discuss with the owner.

wall. Having the resultant half way down the wall, rather than 1/3 of the way down, can lead to more practical wall designs.

If it is not clear from the geotechnical report which methodology was used, the structural engineer should contact the geotechnical engineer for clarification.

How Structural Design Can Be Improved Given the examples provided above, geotechnical and structural engineers can improve the cost effectiveness of the design and reduce risk by: 1) More interaction between the geotechnical and structural engineer after the structural engineer has reviewed the geotechnical report and started design work. During this conversation, the structural engineer should: • Talk through their understanding of the geotechnical recommendations.

• Explain what has been done or will be done concerning site grading, basements, building location, and footing bearing elevations.

• Provide the magnitude of the loads on the footings.

• Break out the live loads between persistent and transient loads so that transient live loads do not drive the design.

• Explain the range of footing sizes that will be used with the allowable bearing pressure provided in the geotechnical report.

• For combined footings or a mat that uses a subgrade modulus, give the geotechnical engineer the elevation and size of the mat/footing, and ask if the subgrade modulus is applicable or needs to be modified.

• Request that the geotechnical engineer checks their recommended bearing pressures to see if the bearing pressure can be increased now that they have actual loads and know what soils the footings will bear on.

If the geotechnical engineer does not have work scope to revisit the project, speak with the owner and request that they provide the geotechnical engineer with additional scope. Explain to the owner that, with additional, critical information, it is likely that either project costs will go down or that the risk of serious problems with the building will be identified and resolved. The author’s experience in Utah would suggest that, knowing actual loads and knowing the soils that the footings will bear on, a revised bearing pressure will likely cost less than

$500 and will typically reduce the cost of footings by $15K to $35K (from 40,000 square-foot to 100,000 square-foot structures), perhaps more.

2) Suggest that the owner includes the following stages in the geotechnical work scope: • Initial geotechnical design.

• Discussion/meeting with the structural engineer after the building is Figure 4. Dynamic lateral earth pressures. set in location and elevation, and the loads are available, so that this information 5) Get the geotechnical design firm can be passed on to the geotechnical involved during construction so that engineer and alternate foundation surprises can be minimized and resolved systems can be considered. quickly and inexpensively.

• Geotechnical revisions: either 6) Help fight the commoditization of an addendum letter or revised geotechnical work. As a structural engigeotechnical report neer, this may not seem like your battle.

3) On projects where conditions are dif- However, as engineers, we all have an oblificult, or there is a sophisticated owner, gation to work toward efficient designs. engage the owner and geotechnical engineer When a structure performs poorly, we in a conversation about uncertainty/risk/ are all drawn into the ensuing dispute. costs so the design meets both the mini- And the structural engineer is uniquely mum code requirements and the owner’s positioned to explain to the owner how desired level of risk. the recommendations in the geotechnical 4) Be careful when telling the owner what report impact the cost of the structure, to expect for geotechnical issues and design and why they should invest in more and based on experiences on a nearby project. Soil better geotechnical work. conditions can vary. Moreover, generalizations Making these changes to interactions with of the anticipated soil conditions can make it the geotechnical engineer and how the geodifficult for an owner to accept differences in technical work is performed will both reduce soil conditions on their site that may impact project costs and reduce the risk of failure or the structure design. poor performance.▪

Why Was the Geotechnical Scope Insufficient on My Project?

Geotechnical work scopes on projects have continued to shrink over the last three decades, such that owners pay less for the geotechnical work but far more for their structures because of the resulting recommendations.

This problem is driven by clients who think that they need “a Geotech report” versus recommendations that will produce the lowest cost project at a desired level of risk. This lack of understanding on the part of clients forces geotechnical firms to reduce their proposed scope to make sure they get the project and stay in business.

As an example of how much has changed, test boring spacing has continually increased over the last 35 years. In Utah, geotechnical firms are doing 10% to 15% of the number of borings that were done in the early 1980s, and the borings continue to be done to lesser depths. This decrease in information increases risks as well as structure and site costs.

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Building Blocks updates and information on structural materials

T

he wireless communications industry that, in the hours immediately following a large has experienced exponential growth in earthquake, wireless communication is in high recent years. Not only is the number of demand and the system must be designed to customers increasing, but the amount survive such an event. For example, Los Angeles of information being transmitted through these recently introduced an ordinance requiring all networks is also increasing. Whereas a decade telecommunication towers to be upgraded to ago we used our mobile phones strictly for voice survive the impending “big” earthquake. transmission, the introduction of the smartphone has increased the demand on the networks and Case Study the supporting infrastructure.

In response to this growth, and as we migrate This case study presents the first known application from 3G to 4G and beyond, wireless compa- of an innovative FRP solution to strengthening a nies, such as AT&T, Sprint, and Verizon, must structurally deficient tapered prestressed concrete provide additional equipment on the towers telecommunication tower. The successful complethey lease. These wireless companies lease towers tion of this project has led to the identification for from businesses like Crown Castle, American retrofit in the immediate future of approximately Tower, or others. Each entity owns and main- fifty similar concrete poles. tains approximately 40,000 towers in the U.S. The structure is a 75-foot long hollow precast Occasionally, installing additional equipment on concrete pole located in Tehachapi, California existing towers results in overstressed structures. (Figure 6, page 24 ). The bottom 15 feet of the Towers or poles that were originally installed pole is directly embedded in the soil, leaving the some twenty years ago are remaining 60 feet above ground. The outside often located in congested diameter of the pole ranges from 31.59 inches areas where obtaining per- at 15 feet elevation to 15.39 inches at 60 feet mits for installation of new elevation. The thickness of the tube tapers from towers is very difficult and 3.4 to 2.5 inches, respectively. Reinforcing steel time-consuming. is comprised of twelve ½-inch diameter 270k Prestressed concrete poles seven-wire strands uniformly placed around the are typically designed for a circumference. The design compressive strength single carrier based on the of concrete was 9500 psi. code requirements at the time of design. Future The pole was analyzed for all dead and live load antenna additions or code changes may lead to the effects, including lateral loads from wind and structure not having sufficient capacity. Options earthquake. The controlling design moments are for reinforcing theses structure are limited and shown in Figure 1. The original capacity of the may not be cost effective. pole at the base was about 420 kip-ft. The capacity A typical structural upgrade to steel monopole had to be increased by nearly 50% at the base to towers is to bolt flat plate steel sections onto the safely resist currently anticipated loads. Detailed pole for additional reinforcement. This solution analysis of the structure demonstrated both comis not feasible on a concrete pole, as there is no pressive and tensile stresses in the pole exceeded economical way to attach the steel to the pole the allowable limits under the new loads. The through bolting or welding. Another option is to new design also provides enough reserve capacuse guy wires. However, this is impractical since it ity to accommodate future additional demands requires additional land and ongoing maintenance on the tower. and inspection. A third option is to add a steel lattice structure to Moment vs. Height wrap around the existing tower, 70 which may not be economical as 60 it leads to building a new structure and foundation. Moreover, 50 obtaining permits and meetNew Demand ing local zoning requirements 40 Original Capacity may prohibit such repairs. A New Capacity 30 fourth option involves the use of Fiber Reinforced Polymer 20 (FRP) as described in the case study below.

10 In parallel with this need for strengthening, there is a grow0 0 100 200 300 400 500 600 700 800 900 ing interest in the western Moment - k-ft United States to upgrade these towers seismically. It is obvious Figure 1. Demand and capacity of the pole at various elevations.

A New FRP Solution for Strengthening Concrete Telecommunication Towers

By Mo Ehsani, Ph.D., P.E., S.E. and Ryan J. Rimmele, P.E., S.E.

Dr. Mo Ehsani is President of QuakeWrap, Inc., and Centennial Professor Emeritus of Civil Engineering at the University of Arizona. He can be reached at mo@quakewrap.com.

Ryan J. Rimmele is a Project Lead at Tower Engineering Professionals in Raleigh, NC. He can be contacted at rrimmele@tepgroup.net.

Height - ft

Structural Challenge Facing the Wireless Communications Industry

22 December 2016

Figure 2. Elevation of the pole for the retrofit scheme using FRP.

The FRP Alternative

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STRUCTURE magazine

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Figure 3. Carbon and glass FRP fabric applied to the lower 35 feet of the pole.

press that applies heat and pressure, resulting in 4-foot wide rolls with a thickness as little as 0.01 inch. The relatively large width and small thickness of the laminates make their manufacturing unique and challenging. The thin laminates can be easily cut (Figure 4, page 24) and wrapped around a column of any shape or size, in the field, to create a stay-in-place form that can be filled with grout or resin. continued on next page

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Fiber Reinforced Polymer (FRP) products have high tensile strength and can easily address the shortcomings of the pole. However, the compressive strength of FRP is lower than its tensile strength.

In most retrofit projects, it is not uncommon to ignore the compressive strength of the FRP. This meant that conventional concrete or grout had to be added to the pole to increase the pole thickness and thereby reduce the compressive stresses below the allowable limits.

Among the options considered, the use of FRP offered the most viable solution (Figure 2). The repair technique offered the flexibility to easily change the strength of the pole along the height.

Tension reinforcement for the pole was provided by bonding unidirectional carbon fabrics to the exterior surface of the pole. The carbon fabric used for this project was supplied in 24-inch-wide rolls and had a tensile strength of over 6 kips per inch of width of the fabric. The fabric can be cut into narrower bands for ease of installation without any adverse effect on its strength.

Based on the analysis, 3 layers of carbon fabric saturated with epoxy were required on the lower 20 feet of the pole. Only 2 layers were required between 20 and 35 feet. Elevations above 35 feet required no strengthening. The sudden change in capacity of the retrofitted pole at these elevations, shown in Figure 1, is due to the change in the number of layers of carbon fabric. For confinement, and to eliminate any interference with the antennae signals, 2-foot wide bands of a unidirectional glass fabric saturated with epoxy were wrapped in the hoop direction over all of the carbon fabric for elevations 0 to 35 feet (Figure 3).

The additional tensile reinforcement resulted in the concrete in the walls of the pole to exceed acceptable compression limits.

Therefore, the pole wall thickness had to be increased by 1.5 inches between elevations of 5 to 35 feet to achieve the allowable compressive stresses. Placing a 1.5-inch thick concrete over the tapering pole presented a challenging construction issue. Use of prefabricated steel or wood formwork would have added significant cost to the project.

A special FRP laminate was developed during two decades of R&D that offered an economical solution for this problem. PileMedic® laminates are made by saturating rolls of fabric with resin and running them through a special

December 2016

Table of material properties of FRP laminate.

Unidirectional Carbon

Biaxial Carbon

Biaxial Glass I

Biaxial Glass II

0.026

0.026

0.026

0.010

Tensile Strength, ksi

156

101

62

49

Tensile Modulus, ksi

13,800

7,150

3,500

3,200

Tensile Strength, ksi

9

64

60

49

Tensile Modulus, ksi

1,190

2,940

3,650

3,200

Thickness, in.

Longitudinal Direction:

Transverse Direction:

The properties of these laminates are listed in the Table. Depending on their composition, the laminates offer exceptional tensile strength in the longitudinal direction, or in the longitudinal and transverse directions. For this project, the biaxial glass laminate with a thickness of 0.026 inches was used. For the region between 5 and 35 feet, the 4-foot wide laminates were coated with an epoxy paste and wrapped around the pole to create a two-ply shell. Temporary 1½-inch thick spacers, such as a PVC pipe, can be attached to the pole surface to facilitate the wrapping of the laminates with the necessary standoff distance. By overlapping the 4-foot wide laminates by 4 inches, a long shell was created, in the field, that covered the pole at the necessary elevation.

A structural shell created in this fashion provides the equivalent of No. 4 Gr. 40 ties at a spacing of 2½-inches on-center. The shell also provides tensile reinforcement equivalent to No. 4 Gr. 40 steel reinforcing bars distributed at 2½-inches on-center around the pole. For this project, these contributions were ignored.

The selection of glass over carbon laminates was based on the electrical insulating properties of the former. At this stage, the shell is not bonded to the pole. An expansive non-shrink grout with a compressive strength of 6000 psi was used to fill the 1.5-inch thick annular space between the jacket and the pole.

At the base of the pole, a new 9-foot x15foot x1.5-foot concrete mat foundation was installed. The rectangular shape was required to fit within the tight footprint of the tower compound. The new foundation reinforces the existing direct embed pole through load sharing. The forces were proportioned to each foundation element based on the relative member stiffness and soil stiffness. The concrete mat also terminates the FRP. Fifteen No. 8 hooked dowels, extended four feet above grade, transfer the forces from the FRP into the mat foundation. These bars were placed to accommodate the access port for cables entering the core of the tower (Figure 5). The FRP fabric in that region was coated with a layer of sand for improved bond and transfer of stresses.

A shell with an outside diameter of 38.5 inches was created at the lower 5 feet, corresponding to a 5-inch thick annular space. As can be seen in Figure 1, this resulted in a very conservative design near the base of the pole.

Figure 4. PileMedic laminates being cut to size on the job site before it is wrapped around the pole.

Field Installation The strengthening solution presented herein takes approximately 4 days to install. The lightweight laminates eliminate the need for any heavy equipment and all work can be accomplished using scaffolding (Figure 6). The finished laminates are coated with a UV-resistant coating. Many cables and appurtenances that were near or attached to the pole were moved slightly to accommodate the FRP and concrete placement. These were eventually relocated back to their original positions (Figures 5 and 6). This design approach allows the pole to remain fully operational during the repair, with little change in the appearance and size of the pole.

Over thirty monopoles were reinforced in the greater Los Angeles basin in 2015. Many more such repairs have been identified for completion in 2016 and beyond. The FRP design provides an economical solution to reinforcing concrete poles not available just a short time ago. The FRP solution is a vital part in accommodating the increasing demands of the rapidly growing wireless communication industry. A video showing the field installation of such monopole towers is available online and can be viewed at http://goo.gl/L7pxJb▪

Figure 5. Foundation and the steel dowels at the base of the pole.

Acknowledgements The products and the strengthening technique described in this article are protected by U.S. Patent Nos. 8,650,831 and 9,376,782 and several other U.S. and international pending patent applications. The tower and foundation design was performed by Tower Engineering Professionals, Raleigh, NC, in conjunction with QuakeWrap Inc., Tucson, AZ. Field installation of this project was conducted by FRP Construction, LLC, Tucson, AZ.

STRUCTURE magazine

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December 2016

Figure 6. Painted pole at the conclusion of the project.

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NCSEA 19 th Annual Awards Program

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he National Council of Structural Engineers Associations (NCSEA) is pleased to announce the winners of the 2016 Excellence in Structural Engineering Awards. The top projects were announced on the evening of September 16th during the Awards Program at NCSEA’s Structural Engineering Summit in Orlando. Presented annually since 1998, awards highlight work from the best and brightest in our profession.

Recognition is given in seven categories, with one project in each category named the Outstanding Project. The categories for 2016 were as follows: • New Buildings under $10 Million • New Buildings $10 Million to $30 Million • New Buildings $30 Million to $100 Million • New Buildings over $100 Million • New Bridge and Transportation Structures • Forensic / Renovation / Retrofit / Rehabilitation Structures • Special Use Structures

Courtesy of Chris Broste

The 2016 Awards Committee was chaired by Carrie Johnson (Wallace Engineering Structural Consultants, Inc., Tulsa, OK). Ms. Johnson noted: “The quality of projects this year was outstanding. The number of entries and complexity of the projects presented continues to grow each year. Our judges for 2016 were from the Structural Engineers Association of Colorado, and they had the enormous task of evaluating some truly quality projects. They did an excellent job of thoroughly analyzing each entry and thoughtfully discussing which ones should receive the award.”

Please join NCSEA and STRUCTURE® magazine in congratulating all of the winners. More in-depth articles on several of the 2016 winners will appear in the Spotlight section of the magazine over the course of the 2017 editorial year. A list of the 2016 Judges can be found on page 32 of this article.

Category 1 New Buildings under $10 Million

OUTSTANDING PROJECT Pterodactyl Culver City, CA NAST Enterprises Corp.

The Pterodactyl is an office for a creative advertising agency atop a four-level parking garage in a complex of new and remodeled buildings located in Culver City, California. The building is formed by the intersection of nine rectangular boxes.

The boxes are one level above the garage’s top level, stacked either on top or adjacent to each other along the west edge of the garage roof. The nine boxes organize essential program elements connected by an interior, second-floor bridge and are supported on the steel column grid extended from the parking garage.

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December 2016

Category 2 New Buildings $10 Million to $30 Million

OUTSTANDING PROJECT 740 Heinz Avenue Berkeley, CA

Tipping Structural Engineers

The Buckling Restrained Brace Mast Frame system enhances seismic performance and offers better architectural compatibility at a lower cost than conventional BRB systems. Designed as a response to the disadvantages posed by conventional steel and BRB-only systems, the BRB mast-frame system consists of yielding BRBs in series, with a stiff, elastic vertical frame (the “mast”) designed to pivot about its base.

The mast redistributes loads between stories, producing a more uniform distribution of inter-story drift. This eliminates the possibility of inelastic weak-story mechanisms. 740 Heinz Avenue is a case study in the efficacy, cost efficiency, and replicability of BRB mast frames.

Category 3 New Buildings $30 Million to $100 Million

OUTSTANDING PROJECT Grandview Heights Aquatic Centre Surrey, British Columbia

Fast + Epp

Grandview Heights Aquatic Centre features an undulating roof structure with hanging timber “cables,” suspended between large concrete buttresses. While hanging systems have historically used steel cables, Fast + Epp took a novel approach, pioneering one of the firm’s most ambitious and daring designs in its 30-year history.

Engineers chose wood as a cost effective, structurally efficient and aesthetically pleasing alternative, cleverly balancing form and function. The resulting structure fulfills the client’s desire for an iconic building that will be a catalyst for civic growth and is believed to be the world’s most slender, long-span, timber catenary roof.

Courtesy of Ema Peter Photography

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December 2016

Courtesy of Ema Peter Photography

Category 4 New Buildings over $100 Million

OUTSTANDING PROJECT Air Traffic Control Tower and Integrated Facilities Building San Francisco, CA

Walter P Moore

Each day at San Francisco International Airport, air traffic controllers guide over 1,100 aircraft onto and off four runways. Just four kilometers from the San Andreas fault, the old control tower was temporarily shut down by the 1989 Loma Prieta earthquake. A new tower compliant with stringent design criteria for post-seismic operability was needed to meet airport and FAA expectations.

Optimally located and up-to-date with the latest earthquake standards, the tower incorporates a unique offset cab with a 220-degree unobstructed view of the runways. Completed in August 2015, the tower adds a modern architectural icon to the SFO campus.

Category 5 New Bridges or Transportation Structures

OUTSTANDING PROJECT Hastings Bridge Hastings, MN

Parsons

Minnesota’s Hastings Bridge, a 1,938-foot-long, free-standing tied-arch bridge, carries Trunk Highway 61 over the Mississippi River in a scenic recreation area.

It is the longest free-standing arch bridge in North America.

The bridge features a steel box arch rib with a post-tensioned concrete tie girder and a network hanger system, plus a load path redundant steel-grid floor. The 3,300-ton, 545-foot-long main span was erected on land, transferred onto barges using self-propelled modular transporters, guided downriver by tugboats, slid into position using a hydraulic skid system, and lifted 55 feet into place with strand jacks.

Courtesy of Rich La Salle

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December 2016

Category 6 Renovation / Rehabilitation

OUTSTANDING PROJECT Provo City Center Utah LDS Temple Provo, UT

Reaveley Engineers + Associates

The Provo Tabernacle was a historical treasure. The original building hosted U.S. presidents, musical performances, interfaith gatherings and community events.

It seated 1,500 and featured octagonal towers at all four corners, a high-pitched roof, and exquisite woodwork.

In December 2010, a four-alarm fire destroyed the unreinforced masonry building. The original wood floors and roof of the building were completely burned, and only the exterior walls remained. This 35,000-square-foot historic structure was converted into a modern 85,000-square-foot temple. A system was engineered to support and reinforce existing masonry walls while excavation took place, accommodating the addition of two new subgrade levels.

Category 7 Special Use Structures

OUTSTANDING PROJECT Façade System for the Petersen Automotive Museum Renovation Los Angeles, CA

Wallace Engineering – Structural Consultants, Inc.

The Petersen Automotive Museum is housed in a 1960s-era, cast-in-place concrete structure. The original exterior was reimagined by Kohn Pedersen Fox as a series of freeform stainless steel “ribbons” flowing over the structure, evoking the image of aerodynamic smoke trails over a car.

The ribbon elements are dual curved and follow no regular pattern. They are supported by elaborate treelike structures designed to resemble engine manifolds.

Moment-resisting connections, complicated thermal expansion issues, and highseismic anchorages posed additional structural concerns. Collaboration between the design team and the facade manufacturer resulted in a solution that satisfies both architectural vision and structural needs.

STRUCTURE magazine

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December 2016

AWARD WINNER – CATEGORY 2

SANCTUARY FOR SUFISM REORIENTED

AWARD WINNER – CATEGORY 1

SLI 47+7 Seattle, WA

AWARD WINNER – CATEGORY 1

MOUNTAIN S HOME

DCI Engineers

SLI 47+7 is a six-story apartment structure built with revolutionary panelized and component-based design technology. A kit-of-parts allows a small construction team to swiftly assemble prefabricated panelized floor and wall systems containing plumbing, electrical, fire sprinklers, and finishes.

SLI 47+7 was topped out within 5.5 months – 50% faster than conventional building construction. The steel exoskeleton design strategy granted column-free living units and more interior space for tenants. This mid-rise was built on 6,426 square feet of land in Seattle, Washington.

Park City, UT

J.M. Williams and Associates, Inc.

This Mountain S Home is an “S” shaped house that steps and twists around its mountain site.

It has 30 individual kite shaped roofs. The perimeter walls are almost entirely glass, and each roof appears to be supported by glass.

The roofs are 16 inches thick and cantilever as much as 21 feet while supporting 235 psf of snow and maintaining a thin razor edge along the lower eaves. The roof is supported on 2- to 8-foot long piers averaging 16 feet in height and designed for gravity and seismic forces.

AWARD WINNER – CATEGORY 2

AWARD WINNER – CATEGORY 3

ORDWAY CENTER FOR THE PERFORMING ARTS – CONCERT HALL EXPANSION

EMERSON COLLEGE LOS ANGELES

Saint Paul, MN HGA Architects + Engineers

The Ordway Center for the Performing Arts Concert Hall expansion replaced an underutilized 300-seat theater with an 1,100-seat Concert Hall. Fitting the larger Concert Hall into the footprint of the small theater mandated creative structural solutions. Inventive sequencing was required to keep the Ordway Center operational through construction, including building a portion of the new structure inside the original theater before demolition. Innovative design features include bent post-tensioned transfer beams, curved folded-plate seating slabs, cantilevered tapered slab balconies without backspans, and an extension of the Ordway’s signature, two-story cantilevered lobby.

Walnut Creek, CA

Thornton Tomasetti

A central cast-in-place concrete shell dome surrounded by four smaller domes and eight minor domes in a circular footprint defines the new marble-clad Sanctuary for Sufism Reoriented. Two-thirds of the structure lies underground and helps the building fit into the surrounding residential neighborhood.

The project presented many challenges including high seismicity, unusual geometries, a high water table, and a desire for an unusually long design life with low maintenance. Through collaboration and ingenuity, the team delivered an elegant, unique, and durable worship space, fulfilling a long-time dream for the congregation.

Los Angeles, CA John A. Martin & Associates, Inc.

Emerson College Los Angeles is the West Coast home of Boston-based Emerson College. This $85 million, 250,000-squarefoot building is a small-scale university campus containing below-grade parking, classrooms, performance space, offices, and student housing.

The iconic structure, located on Sunset Boulevard in Hollywood, serves as a conduit for Emerson students to broaden their education and entertainment industry goals via internships within nearby studios and media companies. The complex forms and interconnecting spaces required creative structural problem-solving to maintain the efficiency of material and constructability while upholding the architect’s vision.

STRUCTURE magazine

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December 2016

AWARD WINNER – CATEGORY 3

45 EAST 22ND STREET New York, NY

DeSimone Consulting Engineers

45 East 22nd Street is a 61-story residential tower that reaches 777 feet at its pinnacle.

The ultra-luxury condominium building is located in the historic Flatiron neighborhood of Manhattan near Madison Square Park, only a block away from the Flatiron building itself.

The tower is sculpted so that the floor plate is as small as 62 feet wide by 52 feet deep near the base which gives a maximum slenderness ratio of about 13 to 1. The tower cantilevers outward to a maximum floor plate of 94 feet wide by 52 feet deep, compounding the overall slenderness.

Courtesy of Bruce Damonte AWARD WINNER – CATEGORY 4 AWARD WINNER – CATEGORY 4

THE TOWER AT PNC PLAZA Pittsburgh, PA

AWARD WINNER – CATEGORY 4

LOTTE WORLD TOWER

BuroHappold Engineering

Designed to be the greenest office building in the world, the new 800,000-square-foot Tower at PNC Plaza incorporates groundbreaking structural engineering and design, exceeding LEED Platinum criteria. The building features an unprecedented thermal break in a 6-inchdeep slab that cantilevers 4 feet 6 inches to support an occupiable, double-skin façade.

The design incorporates a story-deep, curved steel truss, supporting a 6-story cable net wall, using an ingenious approach to resist overturning. Complex structural challenges included economically supporting a heavy thermal mass for a solar chimney.

Seoul, South Korea Leslie E. Robertson Associates, R.L.L.P.

The 1,820-foot-tall Lotte World Tower in Seoul, South Korea is designed by Kohn Pedersen Fox Architects and Leslie E. Robertson Associates, structural engineers. It is a mixed-use building with 123 stories and a gross area of 3.7 million square feet.

The tower’s gently curving and tapering shape posed significant structural challenges as the mega-columns needed to follow the tower’s geometry. The floors have long-span spandrels that achieve 80-foot-clear main spans and 46-foot cantilevers at the building corners.

POLY INTERNATIONAL PLAZA Beijing, China Skidmore, Owings & Merrill LLP

Inspired by Chinese paper lanterns, the elliptically-shaped, faceted, Poly International Plaza Tower utilizes a column-free diagrid structural system in an area of high seismicity. The juxtaposition of diagrid modules on the elliptical shape of the tower made three dimensional helical load paths possible, allowing for large architecturally exciting atriums.

Many advanced analytical studies, including global buckling analysis, were performed on this non-prescriptive structure to justify the design. Scaled testing of prototypical portions of the diagrid system was conducted to validate the system’s behavior and performance under dynamic loads.

Courtesy of FDOT AWARD WINNER – CATEGORY 5

SECTION 5 PALMETTO SR 826/836 INTERCHANGE DESIGN-BUILD

AWARD WINNER – CATEGORY 5

Miami, FL

LITTLE CHUTE CANAL BRIDGE Little Chute, WI

exp

With its one-of-a-kind design, the new Little Chute Canal Bridge creates a gateway to Island Park, while permanently reopening the historic Little Chute Lock to marine navigation.

The design for the new pedestrian lift bridge embraces the Village of Little Chute’s Dutch heritage by utilizing counterweights on a lifting arm above the deck. The result is a unique new single leaf movable bridge that provides not only much-needed access over and through the Canal but also celebrates the rich history of the surrounding community.

Finley Engineering Group

The new interchange creates a safer and less congested route for 430,000 vehicles traveling through daily. Challenges included a location inside Miami International Airport’s flight path, FAA vertical height restrictions, canals in the middle of the project, aesthetic requirements and traffic flow maintenance.

The design-build team realized that design and material innovations were the keys to success. Innovations included the state’s first ever use of diabolos with external tendons, as well as haunched segments, polystyrene hollow pier columns, and top-down construction with an overhead gantry.

STRUCTURE magazine

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December 2016

AWARD WINNER – CATEGORY 6

WAR MEMORIAL VETERANS BUILDING San Francisco, CA

Simpson Gumpertz & Heger Inc.

The War Memorial Veterans Building was built in 1932 and is a designated historic landmark. The centerpiece of the building is the Herbst Theater, which hosts over 200 performances annually.

In 2011, the City and County of San Francisco initiated a $156 million project, including a seismic upgrade and complete replacement and improvement of building systems. The seismic upgrade incorporated rocking, concrete shear walls, eliminating the need for deep foundations and enhancing seismic performance.

AWARD WINNER – CATEGORY 6

AWARD WINNER – CATEGORY 6

MADISON SQUARE GARDEN V – THE TRANSFORMATION

CHRIST CATHEDRAL TOWER OF HOPE SEISMIC RETROFIT

New York, NY Severud Associates

Garden Grove, CA LPA, Inc.

The ambitious 985,000-square-foot transformation of Madison Square Garden involved the reconstruction of a new arena within the historic circular shell. The project included raising the entire upper bowl seating structure, allowing for new lower bowl luxury suites and courtside “bunker” suites.

Other transformations included raising the north and south arena roof structures, adding two 280-foot-long sky bridges, expanding and restructuring the 7th Avenue entrance, three levels of expansion on the 7th Avenue side, and a one-tier expansion of the existing west-side hung suites.

Richard Neutra’s iconic Tower of Hope on the Christ Cathedral campus has been an important landmark since it was built in 1968. The slender, 14-story concrete tower has been called a masterwork of modernist architecture.

The design team approached the challenging preservation and seismic retrofit project using an innovative, performance-based design strategy, combining fluid viscous dampers with fiberreinforced polymer. The completed seismic and architectural rehabilitation preserves the midcentury modernist design aesthetic, maximizes the functional interior space, and dramatically increases the seismic resiliency of the Tower.

2016 PANEL OF JUDGES The judging was held Wednesday, August 3, 2016, at the offices of Martin/Martin, Inc. in Lakewood, Colorado. The 2016 awards jury from the Structural Engineers Association of Colorado included the following individuals: Jonathan Akins, P.E. University of Colorado-Boulder Edward Buteyn, P.E., S.E. Jirsa Hedrick Structural Engineers Paul Doak, P.E., S.E. Martin/Martin, Inc.

Courtesy of Ball-Nogues Studio AWARD WINNER – CATEGORY 7

AWARD WINNER – CATEGORY 7

STRUCTURES OF LANDSCAPE

PULP PAVILION

Fishtail, MT Beaudette Consulting Engineers, Inc.

Indio, CA Nous Engineering

Structures of Landscape is an art installation of three enormous concrete sculptures at Tippet Rise Art Center in Fishtail, Montana.

At the base of the Beartooth Mountains, the Art Center spans across an 11,500-acre working cattle and sheep ranch.

To bring these sculptures to fruition, Beaudette Consulting Engineers had to utilize far-reaching creativity and ingenuity.

Challenges on this project spawned from the monumental scale of the sculptures, the irregular shapes of the pieces, and the unique approach to design and construction, combined with maintaining artistic integrity throughout the installation.

Paper exhibits unique sculptural capabilities when recycled into pulp. Using a blend of pulp, water, and pigment, a mix was sprayed onto a three-dimensional, woven lattice of natural rope to create the Pulp Pavilion, a large overhead structure featured at The Coachella Music and Arts Festival.

Because this building process has no known precedent, to engineer it meant gathering results from substantial material testing, establishing safe material properties, and using these in a 3-dimensional, finite element analysis to predict the behavior of the structure under anticipated loads.

STRUCTURE magazine

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December 2016

Lacey Goetz, P.E. Integral Engineering Carrie Johnson, P.E., SECB Wallace Engineering Structural Consultants, Inc. Susan Jorgensen, P.E., SECB, LEED Studio NYL Max Lehman, P.E. Wallace Engineering Structural Consultants, Inc. Chad S. Mitchell, P.E. S.A. Miro, Inc. Ben Nelson, P.E. Martin/Martin, Inc. Brian Tinkey, P.E. Martin/Martin, Inc. Jeannette Torrents, P.E. JVA, Inc.

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CHALLENGING FOUNDATION

BUILT IN THE HEART OF

By Douglas P. Gonzalez, P.E. and Joseph L. Yamin, P.E.

NEW YORK CITY

R

ising along the East River in Manhattan’s midtown is a brand new world-class hospital facility for one of New York’s major academic medical centers. This state-of-theart hospital building is fully integrated into the adjacent medical campus. Accomplishing this required locating the unique 21-story building on a congested urban site with numerous physical constraints that posed significant challenges. Designed by Ennead Architects in collaboration with NBBJ, the new hospital consists of a 7-level podium for operating rooms which also incorporates a fully enclosed and automated parking system, and a 14-story tower for single-bedded inpatient rooms.

The site originally had several hospital buildings and related construction that were demolished to make way for the new structure.

South of the construction site is the remaining campus with major hospital, academic, and research buildings. The new structure is located directly adjacent to the existing operational hospital to allow for passageways between the two.

Constraints in the ground that created challenges for the project included a major sewer and its easement, four tunnel tubes of the Amtrak commuter train lines, two ventilation buildings for the tunnels, as well as existing building foundations and underground utilities.

As is the case with much of Hospital Row along Manhattan’s east side, the ground surface is located a few feet above the nearby river level resulting in increased flood risk. With the site being the only remaining property available to build on, all these foundation and ground level challenges had to be overcome while not compromising the programmatic needs of the hospital and campus.

Foundations The project is located in midtown Manhattan’s east side, on land that is outboard of the original historical shoreline which was reclaimed from the East River. This reclamation process occurred in various stages from the mid-19th century through the early 20th century as Manhattan developed. The result is that the site subgrade consists of a 35-foot upper layer of uncontrolled fill, i.e. rubble, brick, and timber, over various layers of silt, clay, and sand that are then underlain by bedrock.

Much of the timber encountered is remnants of the historic shoreline bulkhead. The bedrock underlying the site consists of Manhattan schist and is located approximately 50 to 115 feet below grade, sloping down toward the river. Rock core results indicated bedrock of varying quality but, in general, below the weathered surface the rock is a minimum Class 1c Intermediate Rock. Given the poor soils and depth to bedrock, deep foundations were a natural choice for this site since they allow the load to be delivered directly to bedrock and their discrete nature minimized the impact to existing infrastructure.

The site contains four Amtrak Rail Tunnels as well as a combined sewer outfall (CSO) for New York City. The tunnels, which are approximately 65 feet below grade, are clustered in pairs with two tunnels toward the north end of the site and two at the south end of the site below the CSO. The agreed upon easement for deep foundations was 10 feet clear in plan from the tunnel spring line. An extensive study of the impact of caisson elements near the existing tunnels was performed by the Geotechnical Engineer. Given that these rail tunnels STRUCTURE magazine

The 21-story, 830,000-square-foot hospital is the crowning jewel of an extensive campus transformation. Courtesy of Ennead Architects.

The existing site conditions presented a challenge for the structure and its foundations.

34

December 2016

Caisson installation, given the tight site constraints. Note, installation began before the demolition of adjacent structures.

Revit model of the foundation system showing the pressure slab and concrete flood walls. Note, openings between perimeter walls are infilled with barriers to create the “bathtub” system.

are critical infrastructure, it was necessary to confirm there was no detrimental impact to the tunnels. As a result of the study, caissons near the tunnels have isolated portions of their socket length above the tunnel spring line to avoid possible load shedding to the tunnels.

Given the tunnel diameters, spacing, and easement requirements, there is an 80-foot zone running northeast through the southern half of the site where no deep foundations could occur. As a result, long span transfers of the building structure, spanning 100 feet or more, were provided. Also, the building’s services and structural core had

to be shifted eccentric to the building massing to avoid this tunnel zone. A similar zone occurs at the north end where the new building only partially extends over the tunnel zone. This was accomplished with cantilever foundation plate girders, which in some cases were 6 feet deep, as well as cantilevered floor framing above.

The building transfers in the superstructure resulted in large column loads on many of the foundations, which led to the decision to use high capacity drilled caissons. A schedule of multiple caisson types was proposed that ranged in capacity from 3,000 kips to

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8,000 kips. The caissons are 36 inches in hydrostatic pressure, as well as flood walls diameter and consist of steel reinforced to resist lateral hydrostatic and dynamic concrete within a permanent steel casing wave loads. The pressure slab is typically that is seated into bedrock. The casing was 12 inches thick with drop panels at supinstalled via vibratory hammer and the porting caissons. At the building perimeter, rock socket was accomplished with concantilevering concrete flood walls behind ventional rotary drilling methods using façade elements are supported by a thickreverse circulation heads to clean out the ened pressure slab. The concrete bathtub spoils. Both operations were coordinated is protected by a continuous pre-applied with the hospital to minimize disruption. waterproofing system. Also, the pressure Also, it was agreed with Amtrak that caisslab supports a 3-foot interstitial MEP zone sons located nearest the tunnels would be of crushed stone with a bearing slab above, installed with tight tolerance controls on allowing services to run throughout the verticality and deviation.

Ground Floor within the bathtub system.

In addition to tunnel proximity, caisThe real challenge was protecting the sons were carefully installed as close as large openings throughout the building 5 feet to the existing hospital, as well as for entrances and loading docks. To do through the abandoned basements of the this, the project uses every conceivable, demolished buildings and old shoreline deployable flood barrier type from mulbulkheads. A comprehensive monitoring tiple vendors. These include 1) flip-up program was implemented above grade Perimeter foundation detail to support proprietary selfbarriers at the loading dock and parking and within the tunnels to measure the closing flood barrier at the storefront entrance. entrances; 2) swing barriers at the loadeffects of foundation construction on the ing dock ramp; 3) sliding barrier at the tunnels and existing buildings. ambulatory entrance; 4) redundant submarine doors at points of The caissons were originally designed with studded core steel consist- egress; 5) redundant deployable stacking barriers at Ground Floor ing of heavy rolled shapes. However, because there were large lead times elevator entrances; and 6) a self-closing flood barrier at the 225 feet for the core steel and the final caisson tip elevations were determined long entrance storefront. The majority of these barriers represent based on actual rock quality encountered, there was concern that the common flood protection technology. However, the self-closing contractor could not meet the foundation schedule. This resulted in barrier at the entrance storefront is less common. This barrier type the use of threadbar as the caisson steel reinforcement instead of the employs a passive wall system constructed of fiberglass encased core steel. Benefits of this approach included shorter lead times and foam, which is less dense than water thereby allowing the barrier flexibility to accommodate varying rock socket lengths, especially since to deploy itself as flood waters rise. This system was chosen at the longer threadbar lengths could be achieved quickly with mechanical main entrance because the system is completely hidden below grade couplers instead of field welding extensions to the rolled core steel. when closed except for a metal strip in the sidewalk pavement. The The threadbar reinforcement was specified as Grade 75 with sizes barrier withstands flood loads as a simple bearing force couple, ranging from #18 to #28 bars, depending on the caisson capacity. resisted by prying on a 24-inch-thick foundation trench structure Bars were spaced equally in a circumferential ring, typically one to which houses the barrier. two layers, with an opening in the center to allow for a tremie pipe.

Another challenge was extending the pressure slab over the existing Before installation of the rebar cage and concrete operations, the rock sewer and providing flood uplift support on either side within the easesocket was flushed out to remove any remaining spoils and then video ment zone. Here, shallower soil-anchors were specified and installed inspected to confirm rock quality. in the top 30 feet of soil to maintain the minimum required vertical clearance above the crown of the tunnels. These tie-down anchors consist of small diameter casings, with a #10 threadbar grouted into Ground Floor Construction soil that resists uplift by mobilizing the soil mass.

Given the proximity to the East River and the existing ground water elevation, the new hospital building’s lowest level is at grade. With Summary its main entrance and its loading docks on street level, the hospital needs to protect numerous open entrances from the risk of rising flood The existing site constraints, coupled with the challenge of providwaters. While the original flood risk for this site, as defined by the ing a flood resistant structure, presented significant challenges to the Federal Emergency Management Agency (FEMA) flood maps, was foundation and ground level construction. However, with careful mitigated by slightly elevating the majority of the ground level, the consideration and thoughtful design, the team was able revision of the FEMA flood elevations post-Hurricane Sandy resulted to overcome these challenges and bring to reality a statein the need for a wholesale rethinking of the flood protection strategy. of-the-art, resilient hospital to serve the surrounding The resulting increase in the Design Flood Elevation of approximately community well into the 21st century.▪ 7 feet, which also included an allowance for sea level rise, could only realistically be accommodated by providing a building-wide resilient Douglas P. Gonzalez, P.E. (doug.gonzalez@lera.com) is an “bathtub” or “boat” system to keep flood waters out of the building.

Associate Partner at Leslie E. Robertson Associates (LERA) and leads This approach, coupled with the elevating of critical MEP services and the firm’s Healthcare, Renovation, and Adaptive Reuse efforts. hospital functions above the ground floor, provided a system-wide Joseph L. Yamin, P.E. (joseph.yamin@lera.com) is an Associate at resilient building. The upgraded ground level includes a building-wide Leslie E. Robertson Associates (LERA). spanning pressure slab with additional mini-caissons to resist uplift from STRUCTURE magazine

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December 2016

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Structural analySiS

discussing problems, solutions, and analysis methods

Fatigue Analysis of Concrete Structures

By Dilip Khatri, Ph.D., S.E.

F

or many structural engineers, the subject of fatigue analysis has been limited to a few simplified evaluations based on the American Institute of Steel Construction (AISC) Steel Construction Manual that says less than 2,000,000 cycles implies no problem. For concrete structures, the presumption of any fatigue loss was never even a design consideration in typical coursework or practice. Therefore, professional structural engineers in the U.S. have never actually been trained in understanding the effects of fatigue and fracture mechanics, except Northridge Earthquake’s impact on welded steel moment frame connections.

The industrial age (1920 to 1960) saw a proliferation of new buildings, bridges, and infrastructure elements built under this methodology. As the profession continues to evolve into more esoteric, analytical, and focused areas, structural engineers realize that the issue of fatigue is more than just a textbook discussion and has very real implications on the long term considerations of structures. Structures are now passing 50 years. Some have well over 100 years of service life and are beginning to show severe signs of long-term wear and tear. This is particularly true of bridges of both steel and concrete where cracking, corrosion, and fractures are limiting the extended life of these vital arteries of our economy. Why is fatigue analysis important? Here are the fundamental reasons: 1) Fatigue loading leads to fractures, cracking, and eventual collapse/failure because the structure will likely fail before it reaches its yield point. Even though the structure is elastic, it still poses a life-safety threat to occupants.

Structures subjected to earthquakes

Bridges

Structures subjected to storm

0

10 1

SUPERHIGH-CYCLE FATIGUE

HIGH-CYCLE FATIGUE

LOW-CYCLE FATIGUE

10 2

10 3

Wind power plants

Mass rapid transit structures

Airport pavement

Sea structures

10 4

10 5

10 6

10 7

10 8

10 9

NUMBER OF CYCLES

Spectra of fatigue loading in structures.

2) Designing for strength, ductility, dynamic response, strain compatibility, and serviceability are fundamental but have no correlation to fatigue analysis. A structure can be compliant with all of the basic tenets of structural design and still fail in fatigue. Increasing the strength (i.e. yield strength/stiffness) does not necessarily contribute to better fatigue strength.

3) Fatigue failure is the result of a high number of cycles with low to moderate stress over an extended period that eventually fractures the material and causes failure. These fractures will grow and ultimately undermine the structural strength of the member and the system.

The purpose of this brief introduction to fatigue analysis is to raise awareness. It is an important part of design for the long-term performance of concrete and steel structures.

log S

Fatigue in Concrete Structures Concrete fatigue is due to long term low amplitude force or stress, with many cycles occurring over the life of the structure, that leads to concrete fracture. This can happen in tension, shear, and compression failure zones. Concrete fatigue is addressed by one internationally accepted code: FIB Model Code 2010, part of Eurocode 2. The basic tenets of fatigue analysis and analytical models are contained in this document.

The principle of fatigue analysis relies on an empirical design model: 1) A stress-cycle (S-N) curve is developed based on cyclic fatigue load test data. This is the Envelope of Failure for the structure.

2) The analysis is based on summing the various fatigue loads to determine if the final structure “fits” within this Envelope.

Stress, σ Curve obtained from test data

Strain softening ƒc

Curve used in practice

Strain, ε

log N S-N curve for fatigue analysis.

Strain softening in the concrete structure.

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December 2016

3) The basic rule is the Palmer-Migren Summation or the Minor’s Rule method of fatigue analysis.

With concrete material, the fatigue cracking is not physically visible; because concrete experiences a strain softening at high cycles, the crack propagation will continue un-noticed.

Think about all of the concrete structures that are impacted by this type of loading: a) Bridges b) Concrete Buildings (mostly commercial structures) c) Hospitals d) Pavements e) Theaters f ) Stadiums

Fatigue in Steel Structures Steel structures experience strain hardening with high cycle fatigue, so failure patterns are different. With steel, the critical points are stress concentrations, welds, and bolted connections.

Steel structures with fracture failure mechanics that are impacted by fatigue loading include: a) Steel Bridges b) Reinforcement in Concrete Structures c) Steel Moment Frame Buildings

Stress, σ

considered in their design methodology.

The same principle applies to buildings and other structures.

Strain hardening

Long Term Considerations

ƒy

Strain, ε Strain hardening in steel structures.

Wind Tower Projects The author’s experience with fatigue analysis comes from 20 years of practice in the wind energy industry. In this field, the topic of fatigue check surpasses the normal strength design issues and usually governs on wind tower projects. The reasons are obvious; the wind tower supports a functioning machine (wind turbine) that will generate 20 million cycles of loading over a 25-year service life. It stands to reason that when structural engineers think of bridges, which are expected to last for 75+ years (sometimes over 100 years), fatigue analysis should be

The U.S. should seriously look at our design codes to incorporate this relevant topic into our design process. Currently, there is minimal guidance. Bridge codes (AASHTO) do have some requirements for fatigue analysis, but these are not as sophisticated as European codes. As for buildings, there are no requirements for these considerations. As we see more of our structures surpass 80 to 100-year service lives, we will recognize the importance of fatigue analysis as part and parcel of structural design.▪ Dilip Khatri is the Principal of Khatri International Inc, Civil and Structural Engineers, based in Las Vegas, NV, and Pasadena, CA. He was a Professor of Civil Engineering at Cal Poly Pomona for 10 years. He serves as a member of the STRUCTURE Editorial Board and may be reached at dkhatri@gmail.com.

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December 2016

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InSIghtS

new trends, new techniques and current industry issues

The Virtual Toolbelt A Contractors Use of BIM

By Elizabeth Angel and Daniel Shirkey

I

t is no novelty that communication and visualization in the Architecture, Engineering and Construction industry are continuously evolving. With more challenging project types, owners requesting “the next best thing,” and digital tools and more sophisticated software advancement, it is our duty to stay current and relevant with the latest innovative trends and tools. To stay competitive, embracing technology and the digital world is a must. Contractors are no exception to this trend. Making changes from traditional handheld tools, such as paper plans, and embracing virtual/visualization tools, like BIM (Building Information Modeling) and VDC (Virtual Design and Construction), has truly revolutionized the way structures are being designed, visualized and built. At Balfour Beatty Construction, the virtual toolbelt is equipped with BIM and its multiple workflows to encourage team collaboration and drive efficiency on every project, every day.

First and foremost, how do contractors define BIM and what are the possible uses? BIM includes anything from creating 3D models, generating shop drawings for self-performed concrete work, running clash detection/conflict resolution for 3D MEP coordination, laser scanning of as-built conditions, 4D scheduling (model simulation based on project schedule), 5D estimating (model quantity extraction plus cost), and creating sensory enhancing virtual environments using virtual or augmented realities (VR or AR, respectively).

With these uses of BIM identified, designers, including structural engineers, can be of huge help to contractors and, in turn, help themselves simply by focusing on the accuracy of their 3D model. It is unrealistic to expect structural design models to be fully detailed and “build ready.” In most cases, fees are not available for engineers to fully detail and develop models, nor is it typically in their scope. It truly makes the most sense for contractors to re-create structural models altogether (especially if they self-perform work), and virtually assess problems and back check for inconsistencies to bridge any design gaps before actual construction. The structural design team can transmit accuracy by clearly providing edge of slab details (accounting

for exterior wall treatment, curbs, etc.), fully dimensioning plans from gridlines to edge of concrete and steps, providing top of slab and wall elevations, clearly identifying control joints, modeling of zones-of-influence, or by penetration allowance details. If this level of detail is provided, there is less opportunity for mistakes of information interpretation due to unclear data. Moreover, there will be a reduction in RFIs. For contractors who self-perform concrete work, there is always a need to have critical dimensions to edge of slabs and curbs to create concrete shop or lift drawings, and also to locate embeds. When recreating a structural model, the detailer can learn and study head heights, wall layout, and steps and, moreover, provide a constructability review for the team. This also presents a prime opportunity for vertical and horizontal penetrations to be modeled and submitted for review and approval by the engineer.

With BIM, the structural detailer is also at liberty to include critical objects that can be used in the clash detection process.

Adding 3D elements for PT tendons, stud

With the use of an inexpensive cardboard headset kit and a smartphone, viewers can experience VR at their fingertips. Featured here is an as-built prepour panoramic view with comments.

rails at columns, zones of influence/clearance zones, shoring, tiebacks, and any other critical structural elements can help coordinate the location of MEP systems that need to penetrate a slab or structural wall. This is where real savings are realized. Resolving a conflict between a structural element and a piece of equipment virtually and before construction, rather than in the field, can save both money and time and helps build trust. Having accurate dimensions can also contribute to defining pour schedules and help break up a model if 4D simulations are going to be part of project tools.

Recently, the use of virtual and augmented reality has been making great strides by

With the use of 3D modeling, virtual objects/placeholders can be created for PT tendons and stud rails to assist in MEP clash detection and conflicts can be resolved before construction.

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Elizabeth Angel is a Senior Process Manager at Howard S. Wright, a Balfour Beatty company, in Seattle, WA, where she oversees the Virtual Design and Construction and Innovative Technologies Group. Elizabeth may be contacted at angele@hswc.com.

Daniel Shirkey is the Senior Director of Technology and Operational Improvement for the California Division of Balfour Beatty Construction. Additionally, Daniel is an Adjunct Professor at San Diego State University (SDSU) where he teaches Virtual Design and Construction to Civil and Construction Engineering students. Daniel is also a member of the steering committee for the San Diego Lean Construction Institute (LCI) Community of Practice.

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allowing more users to experience a space in an immersive environment. These environments are typically created by taking the 3D coordination models and processing them through a gaming engine that exports the data into a Virtual Reality (VR) headset.

VR allows BIM to be more accessible to people with varying technical abilities since it is easier to navigate, explore, and much more impactful as users are immersed in the experience. These benefits carry through into enhancing constructability review, providing design assistance, and enhanced planning.

VR can also be utilized on something as simple as a mobile smartphone with the use of cardboard viewers and a panoramic camera. This is a straightforward and quick way to document a slab pre-pour or document what is in a wall before it is framed.

Another means of documenting pre-pour conditions or capturing as-built conditions for an existing structure is the use of laser scanning. This is an excellent workflow to capture and document the location of sleeves, PT tendons, and Smurf tubes (flexible conduit), and be able to memorialize the as-built condition. Laser scans can also be used to measure slab flatness. Software continues to improve to automate the conversion of scanned pixelated information into solid 3D objects which can be incorporated in composite MEP models for spatial reference and even clash detection.

With the integration of all these tools, and the more they become embedded in our day to day use, it begs the question of whether 3D models are on their way to being approved to record construction documents in the near future. Nonetheless, the use of BIM by contractors presently enhances collaboration, visualization, and information sharing, and will only continue to improve.▪

CASE BuSinESS PrACtiCES

business issues

Do You Know the Standard of Care?

By John A. Dal Pino, S.E. and Kirk Haverland, P.E., SECB

M

ost structural engineers understand that they should perform their engineering services with no less than the skill customarily exercised by other structural engineers in similar circumstances. Most likely, their employer or a colleague told them so at some point in their early careers, or they overheard other engineers discussing the issue in the context of a legal action.

Beyond this probably brief introduction to the issue, and perhaps a few casual conversations here and there, it is reasonable to assume (without the benefit of a poll) that most engineers are not particularly familiar with professional liability laws governing their profession, are not conversant on legal specifics or potential legal pitfalls, or know how the legal system would deal with them should their professional acts or omissions be alleged to have caused harm to another party.

Why should structural engineers be expected to be better informed? The topic is not addressed in most university engineering curricula or in the professional licensing examinations, both of which are mostly technical in nature.

Moreover, thanks to the 10th Amendment to the U.S. Constitution, the legal landscape for engineers is largely shaped at the state level. And, every state has its own set of rules, regulations, and legal precedents, phrased with different words and emphasis by various legislators and judges. What might be acceptable in one state might not be acceptable in another, even neighboring, state. Reviewing in detail a state’s Professional Engineering Act and the associated Administrative Rules, and reading precedentsetting court opinions, is not high on the to-do lists of many engineers. And if you are registered in many states... Well, you get the picture. So it is easy to understand why an engineer might struggle to stay abreast of and understand in detail what is expected of him or her.

They say, “ignorance of the law is no excuse.”

Having a good understanding of your legal responsibilities is more important than ever because many engineers are licensed and practice in several states. What is customary in one, may not be so in another. Also, codes and standards are becoming more standardized and national in nature, meaning more uniformity and perhaps a higher level of required engineering skills across the country. Gone may be the days when an engineer can say that “we do not do that around here.”

Negligence as the Standard of Care In today’s engineering world, negligence has become the common tort standard for judging whether damages are due to the injured, as a kind of middle ground between the law of the jungle and strict liability. You might think of it as a judicial system, rather than an administrative or legislative system, “designed” to optimize the cost spent on preventing damaging events. Over time, the collective actions and reactions of thousands of engineers to market pressures and legal actions define what society expects from professionals.

So what is the definition of negligence and under what circumstances could a structural engineer be found negligent? Negligence has been defined as the failure to exercise the care that a reasonable person would in similar circumstances. Putting this in an engineering context, negligence is a failure to exercise the care that is customarily exercised by similarly competent or experienced engineers in performing professional engineering services under similar circumstances. To be found negligent and in breach of the standard of care, several issues have to be proven by the plaintiff: 1) the defendant owed a legal duty to the plaintiff, 2) the defendant breached that duty by failing to exercise reasonable care through his or her actions or non-actions, 3) there is an actual and legal cause-and-effect relationship between the alleged negligent acts and the harm, and 4) the plaintiff suffered harm.

The Future It is probably safe to say that “negligence” will be the measure by which our performance is judged for the foreseeable future. However, custom and industry norms will change and what constitutes negligence will likely change too. Computer analysis of structures was not the norm a generation ago. Building information modeling (BIM) is on its way to becoming the standard for documenting structural designs and for assessing and mitigating possible construction problems (clash detection, fit-up, etc.). Advances in technology are lowering the costs of previously prohibitively expensive actions (nonlinear analysis, finite element analysis, etc.) to the

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point where they may become the custom or industry norm at some point as well.

An example of expanding liability can be found in the famous T.J. Hooper case (see T.J. Hooper v. Northern Barge Corp. 60 F.2d 737 (2d Cir. 1932)). The plaintiff argued that the barge company was negligent for losing its cargo by failing to use a radio to check for inclement weather. The barge company argued that the use of radios was not yet the custom in the industry. The court ruled that the industry custom was not of a sufficient level to protect against obvious and easily mitigated hazards, and had not evolved as it should have to protect the public. If society decides that markets are flawed, then custom will change and the obligation of precaution might fall on the person (i.e. engineer) most able to make the relevant calculation of risks and take precautions. Might society hold engineers responsible for earthquake damage and loss of life for the poor performance of known unsafe structures that owners were not legally required to upgrade?

It is also possible that to whom an engineer owes a duty of care might change. Historically, engineers have been protected from thirdparty lawsuits by the “economic loss rule,” which holds that an engineer cannot be sued for negligence by a third party for purely economic losses. In a recent case before the California Supreme Court, Beacon Residential Community Association v. Skidmore, Owings and Merrill LLP, the court found that SOM owed a duty to the homeowners mainly due to their professional involvement and “closeness” to the project, and not necessarily due to any negligent action on their part.

So, as was asked at the beginning, why should structural engineers be expected to be better informed about the standard of care? Would their livelihood be a good enough reason?▪ John A. Dal Pino is a Principal with FTF Engineering located in San Francisco, California. He serves as a member of the STRUCTURE Editorial Board and may be reached at jdalpino@ftfengineering.com.

Kirk Haverland is a Principal and Regional Manager for Larson Engineering, Inc. He is also the Chair of the CASE Guidelines Committee. He can be reached at khaverland@larsonengr.com.

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NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

SEER Database Provides Roster of Post-Disaster Professionals All too often in the aftermath of a disaster, few municipalities have trained or certified Second Responder Damage Assessment Professionals who can determine whether buildings in the postdisaster environment can be safely reoccupied.

NCSEA’s Structural Engineering Emergency Response (SEER) Committee has developed a national database of properly trained and certified damage assessment professionals who are capable of assisting with post-disaster efforts. Contact information from the database will be shared with local, state

and federal agencies requesting post-disaster assessment assistance on an as-needed basis.

The database is a self-reporting system where engineers can update their contact information, training and certifications, and deployment experience. The new database, www.ncsea-seer.com, allows volunteers to update their information and certifications at any time.

For more information, contact the SEER Committee Co-Chairs William Bracken at wbracken@brackenengineering.com and Scott Nacheman at Scott.Nacheman@de-simone.com.

Last Chance to Participate in SE Curriculum Practioner Survey Are you interested in the future of the structural engineering profession? The NCSEA Basic Education Committee (BEC) strongly values the opinion of the practitioners and has developed a survey on the core education required to begin a career as a structural engineer. Access the survey at www.surveymonkey.com/r/NCSEAcurriculum. The survey will close on December 19. Some of the questions under consideration are: • Is a matrix methods course still needed?

• Should structural analysis courses only include classical “hand” methods or should they de-emphasize “hand”

methods to allow more time for students to model structures using computer programs?

• Should the recommended curriculum include design courses for other materials such as cold-formed steel?

• Do we recommend too many or not enough courses?

Currently, NCSEA recommends a curriculum that includes 12 courses in 9 core topics (Analysis, Matrix Methods, Steel, Concrete, Timber, Masonry, Dynamics, Foundations/Soils, and Technical Writing).

The results of this survey may influence the NCSEA’s recommended structural engineering curriculum.

NCSEA Webinars January 17, 2017 Masonry Movement Joints Pat Conway, AIA, Director of Architectural Education, International Masonry Insititute January 26, 2017 Draining Low-Sloped Roof Structures – Rain Issues for the Structural Engineer John Lawson, S.E., Associate Professor, Cal Poly San Luis Obispo

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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.

December 2016

MO Delegates discussing improvements to resource documents at the 2016 Summit.

News from the National Council of Structural Engineers Associations

NCSEA has developed and published several new resources for Member Organization (MO) leadership. MO resources and information are available in the Member-Only Portal at www.ncsea.com, accessible by member login.

“These can be valuable resources for our Member Organizations, and are in line with NCSEA’s mission to support our MOs,” stated NCSEA Executive Director Al Spada.

The new resources are: • 2016-2017 Delegate Handbook – This annual handbook provides NCSEA Delegates and Alternate Delegates, as well as MO Executive Directors and Board Members, with information on the MO Delegate role within NCSEA, and NCSEA programs and benefits. The Handbook also includes reports from each of NCSEA’s 44 Member Organizations.

• MO Recommended Speakers List – This list is a compilation of the speakers and topics recommended

by Member Organizations over the last year. It includes speaker contact information as well as the MO that recommended the presentation.

• MO Committee Contact List – This list contains committees and contacts from the MOs, organized by committee. If your MO committees are interested in reaching out to other MOs with similar committees, this is a resource to do that.

• 2016 MO Summary Report – This benchmarking and analysis document includes statistics from the MOs including programs, dues structure, revenue, and membership.

NCSEA News

New Member Organization Resources Available

• MO Toolbox – Developed in 2015, this tool includes information and feedback from the Delegate Interaction Sessions at the past two NCSEA Summits.

Helpful ideas for MOs focus on attracting new members, leadership development, maintaining active committees, quality content for seminars, building a steady revenue and dues structure, and geographical challenges of member engagement.

2017 Summit Call for Abstracts Open

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Here is your opportunity to share in the spotlight! Help your field and help your peers by presenting your success and that of your firm at the 2017 NCSEA Structural Engineering Summit, the field’s gathering place for practicing structural engineers. Abstract submission for the 2017 NCSEA Structural Engineering Summit is now open.

The 2017 NCSEA Structural Engineering Summit Committee is seeking presentations that deliver pertinent and useful information that the attendees can apply in their structural engineering practices.

Submissions on best-design practices, new codes and standards, recent projects, advanced analysis techniques and other topics that would be of interest to practicing structural engineers are desired.

The 2017 Summit will feature education specific to the practicing structural engineer, in both technical and non-technical tracks. The Summit will take place at the Washington Hilton in Washington, DC, October 11–14.

The abstract submittal form can be found on the Summit page of www.ncsea.com, and must be returned by February 24, 2017. Speakers will be notified of abstract acceptance by March 22, 2017.

COUNCI L

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.

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.

Convention Hotel: Hyatt Regency Denver 650 15th Street Denver, CO 80202 The Congress also provides an opportunity to recruit the best and brightest structural engineering students at the SEI Student Career Networking Event.

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

Guided Online Courses on Seismic and Retrofit 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.

ASCE Week Orlando Florida

Tsunami Loads and Effects Articles for Free Download

Earn up to 42 PDHs in one week

The Tsunami Loads and Effects Subcommittee of the ASCE/ SEI 7 Standards Committee has developed a new Chapter 6 – “Tsunami Loads and Effects” for the 2016 edition of the ASCE 7 Standard, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. The ASCE 7-16 “Tsunami Loads and Effects” chapter will become the first national, consensusbased standard for tsunami resilience for use in the states of Alaska, Washington, Oregon, California, and Hawaii. Articles highlighting the need for tsunami load design requirements for critical infrastructure are now available for free download from the ASCE Library at http://ascelibrary.org/page/tsunamidesign through December 31, 2016.

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Don’t miss ASCE Week, March 26 – 31, 2017, at the Wyndham Grand Orlando Resort Bonnet Creek. ASCE Week offers ASCE’s most popular face-to-face seminars in one location.

Structural seminars include Designing Nonbuilding Structures Using ASCE/SEI 7-16, Earthquake-Induced Ground Motions, Application of Soil-Structure Interaction to Buildings and Bridges, Financial Management for the Professional Engineer, Investigation, Analysis, and Remediation of Building Failures, Public-Private Partnerships for Transportation Infrastructure, and Seismic Loads for Buildings and Other Structures (newly updated for ASCE 7-16). Also, there will be a special behind-the-scenes tour of Disney. Register by March 3 for special discounts. Learn more at www.asce.org/asceweek.

December 2016

SEI Local Activities Georgia Tech Graduate Student Chapter The Georgia Tech SEI Graduate Student Chapter conducted two seminars in October. The first was on Retrofit of the Chirag 1 Platform in the Caspian Sea, by David Grimm on October 27.

The second one was on The Right Bridge, by Joshua Orton, the current chairman of the Georgia SEI Chapter, on October 31.

Get Involved in Local SEI Activities

Become a SEI Sustaining Organization Member

Local Leaders Conference Leaders of SEI Chapters met in San Juan, Puerto Rico October 14 – 15 for the annual SEI Local Leaders Conference.

Representatives from more than 30 SEI professional and graduate student chapters learned about new SEI initiatives and best practices, shared insights from their local group activities, and were trained on Post-Disaster Safety Evaluation of Buildings & Infrastructure. The group also enjoyed a presentation by SEI President Andy Herrmann on the Vision for the Future of SE; a presentation on development and construction of the walled city of San Juan by Jose Izquierdo, President of the PR Chamber of Commerce and of the Professional College of Engineers & Land Surveyors; and a structural tour of the San Cristobal Castle (largest fortress in America) and the La Fortaleza Governor’s Mansion. Many thanks to ASCE Puerto Rico and Mr. Izquierdo and his colleagues for their gracious hospitality. Learn more about SEI Local Activities at www.asce.org/structural-engineering/sei-local-groups.

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

2017 Bridges Calendar Bridges 2017 is the must-have wall calendar for anyone who designs, builds, crosses, or simply loves bridges. Each month highlights a spectacular bridge with an awesome photograph and a thumbnail history highlighting the bridge’s engineering significance. Plus, each month has a bonus bridge mini-photo.

Chock-full of photos from the United States and around the world, this full-sized calendar is perfect for jotting down daily activities or appointments.

STRUCTURE magazine

The Bridges 2017 calendar celebrates the magical combination of technology and inspiration that is the hallmark of great engineering. These civil engineering masterpieces inspire photographers, too! Every photo in the calendar was selected from entries to ASCE’s Bridges Photo Contest, and all winning photographers are identified. Order your copy at http://ascelibrary.org/page/bridgescalendar.

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The Newsletter of the Structural Engineering Institute of ASCE

Raise recognition for your organization in the structural engineering community, and increase visibility to more than 30,000 SEI members via the SEI website, SEI Update e-newsletter, and STRUCTURE magazine. Learn more at www.asce.org/SEI.

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 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.

Structural Columns

Thank You to 2016 SEI Sustaining Organization Members

CASE Practice Guidelines Currently Available

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE 962 – National Practice Guidelines for the Structural Engineer of Record 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 usually a member of a multidiscipline 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, CASE 962 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.

CASE 962-A – National Practice Guidelines for the Preparation of Structural Engineering Reports for Buildings The purpose of this document is to provide the structural engineer with a guide for conducting conditional surveys, code reviews, special purpose investigations and related reports for buildings, as well as describing services to aid with the client risk management communication issues. This Guideline is intended to promote and enhance the quality of engineering reports.

A section of this Guideline deals specifically with outlines for various reports. While it is not intended to establish a specific format for reports, it is believed there may be certain minimal information that might be contained in a report. The Appendix includes disclaimer language which identifies statements one might consider to clarify the depth of responsibility accepted by the report writer.

CASE 962-B – National Practice Guidelines for Specialty Structural Engineers This document has been prepared to supplement CASE’s National Practice Guidelines for the Structural Engineer of Record by defining the concept of a specialty structural engineer and clarifies the interrelation between the specialty structural engineer and the Structural Engineer of Record. CASE encourages the concept of one Structural Engineer of Record for an entire project. However, for many, if not most projects, there may be portions of the project that will be designed by different specialty structural engineers.

The primary purpose of this document is to define the relationships between the SER and the SSE better, and to outline the usual duties and responsibilities related to specific trades.

This is done for the benefit of the owners, the PDP, the SER, the SSE and the other members of the construction team. The goal is to help create positive coordination and cooperation among the various parties.

CASE 962-D – A Guideline Addressing Coordination and Completeness of Structural Construction Documents The guidelines presented in this document will assist not only the Structural Engineer of Record (SER) but also everyone involved with building design and construction in improving STRUCTURE magazine

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the process by which the owner is provided with a successfully completed project. The intent is to help the practicing structural engineer understand the importance of preparing coordinated and complete construction documents and to provide guidance and direction toward achieving that goal.

Currently, the coordination and completeness of Documents vary substantially within the structural engineering profession and among the various professional disciplines comprising the design team. The SER’s goal should be meeting both the owner’s and the contractor’s needs by producing a complete and coordinated set of Documents. Owners and contractors generally understand that some changes to the Documents will occur because they realize that no set of Documents is perfect. The SER must focus on completeness, coordination, constructability, and the reduction of errors to minimize potential changes.

You can purchase these and the other Risk Management Tools at www.acec.org/coalitions/coalition-publications.

2017 Small Firm Council Winter Seminar: Defining HR for Your Firm February 17–18, 2017; San Diego, CA Why is human resources management (HRM) important to your small A/E firm?

At its heart, it is all about managing people, your most vital asset. A strong HRM focus will help you find and retain new talent, helping them perform better and stay motivated so you can concentrate on profitable growth and a strong bottom line.

Presented by Barbara Irwin, Principal and Founder of HR Advisors Groups, this 1½ day seminar will focus on how firms can create programs, processes, and procedures that meet the needs of the workforce while continuing to focus on the bottom line.

This seminar is for any employee in a small firm tasked with making human resources decisions, such as owners, principals, HR professionals, CEOs, CFOs. Registration: ACEC Coalition Members – $399 ACEC Members – $499 Non-members – $599 Location: DoubleTree by Hilton Hotel San Diego – Mission Valley 7450 Hazard Center Drive San Diego, California, 92108, USA Phone: 619-297-5466 Special Rate – $139/night until January 15, 2017 To register for the seminar: www.acec.org/calendar/calendar-seminar/2017-small-firmcouncil-winter-seminar-defining-hr-for-your-firm.

Questions? Call 202-682-4377 or email at htalbert@acec.org.

December 2016

February 17 – 18, 2017; San Diego, CA 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 Saturday, February 18 8:30 am – 12:00 pm CASE Toolkit Committee CASE Contracts Committee Meeting CASE Guidelines Committee Meeting CASE Programs & Communications Committee Meeting 12:00 pm – 12:30 pm Wrap-up Meeting

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

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

One way to enhance the ability of students to pursue 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 do not have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

CASE Risk Management Convocation in Denver, CO April 7, 2017 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:

2:00 pm – 3:30 pm

4:00 pm – 5:30 pm

8:00 am – 9:30 am

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Structural Forum

opinions on topics of current importance to structural engineers

Structural Engineers and... Energy Codes?

By Jim D’Aloisio, P.E., SECB

I

recently asked a group of about 20 structural engineers in Pittsburgh if they thought that structural engineers have any role in addressing energy code requirements. Less than half of them responded affirmatively – this was apparently the first time that many of them had considered such a notion! So we explored the topic further.

Perhaps the disconnect begins with the way we “frame” our profession (pun intended).

If engineers who provide structural services for building design projects identify themselves as the project’s “structural engineer,” it implies their role on the project is limited to ensuring the load-resisting integrity of beams, columns, foundations, the lateral system, and other primary or secondary structural items.

The truth is, on most successful building projects with which I have been involved, our role might have been better defined as the project’s consulting structural engineer – implying not just the design of the structural components but a willingness to consult on nonstructural aspects of the project that relate to the building structure. This includes not only deflection and vibration, but acoustics (ever specify an acoustic roof deck?), aesthetics (such as Architecturally Exposed Structural Steel or appearance-grade concrete forms), and yes, the effect of the structure on the thermal performance of the building envelope.

We once worked on a project where our scope carefully limited our role to providing the structural design for wind and gravity load resistance of the building facade elements, specifically excluding any other performance aspects of the exterior envelope. The wall system involved cold-formed steel studs and hat channels, horizontal aluminum channel girts, and thin cementitious rain screen panels. The structural design requirements were met but the energy performance was subpar, primarily due to the thick aluminum girts (aluminum conducts heat about five times better than carbon steel) that thermally bridge across the mineral wool insulation. Because of our carefully worded scope, we were clearly not culpable for the problem. However, we were in as good a position as anyone on the design team to identify this condition as problematic and help develop more appropriate solutions.

Here are a few items to consider: ▪ Is compliance with the Energy Code any less important than compliance with the International Building Code (IBC)? Of course, a structural engineer must consider the structural portions of the IBC of paramount importance to their work in assuring safety, integrity, and reliability. So how can energy efficiency be considered in the same category of importance? Well, the fact is, the project must conform to all parts of the applicable building codes – Code requirements are code requirements.

▪ For those structural engineers who feel the design and detailing of a building envelope is a task for others, how many engineers have shown a vapor barrier under a slab-on-grade?

The purpose of this barrier is to mitigate vapor migration through the building envelope. It has nothing to do with the structural performance.

In this way, we have incorporated building science principles into our designs for years.

▪ Some structural engineers show foundation insulation in climate zones where it is appropriate, and some do not. The problem develops when the insulation integrates with, or interrupts, the foundation and perimeter slab edge detail. Building envelope professionals now realize that minimizing thermal breaks in continuous insulation can significantly affect the energy loss through the envelope, as well as reduce the potential for condensation, material deterioration, and organic growth, increase occupant comfort, and can be an essential aspect of compliance with energy code requirements.

▪ A serious issue developed with steel shelf angles while we were not paying attention: the prevalence of continuous wall insulation has obliged us to design these elements with thick, horizontal projecting legs that span across the insulation layer to support masonry veneer.

Ironically, these conditions allow tremendous building energy loss due to thermal bridging of the steel angle. These thick, continuous, conductive plates through the insulated envelope are essentially prohibited by European Union energy codes, which set clear limits to the amount of thermal bridging allowed.

The U.S. should follow suit. In fact, such details may make compliance with the ICC Energy Conservation Construction Code and

ASHRAE 90.1 requirements extremely difficult. Alternatives include vertical discrete steel “fin plates” that extend across the insulation plane and support a smaller-sized angle from the spandrel beam or the careful use of nonconductive shims at supports. Recently completed research should soon provide helpful design guides to practitioners.

▪ Many other structural conditions at the building perimeter warrant consideration of thermal transfer effects, including balconies, canopies, lintels, steel-framed roof overhangs, and cold-formed steel framing conditions.

These represent opportunities to actively engage with architects, owners, and other members of the design team to address these details, which can lead to very positive results.

Coordinating building perimeter details with the need for continuous air barriers, which are different than vapor barriers, is a new frontier for project team collaboration. Should this nonstructural design consideration change what we do structurally? Perhaps not, but it depends on the building system being used.

Awareness of this requirement, when it is necessary or appropriate, and how the architect or others intend to address it, is the first step.

Considering the discussion above, I share the following opinion: Structural engineers who design building structures should have a basic working knowledge of building science, and how a building’s structure influences heat transfer through the building envelope.

It may seem radical to some and rational to others, but hopefully, this provides a useful perspective in your approach to structural design. As a licensed Professional and Structural Engineer, it is important to have a high level of control in what is designed and constructed under one’s stamp. Accordingly, structural details to improve the energy performance of the building envelope should be done by the Structural Engineer. A truly integrated design is the path to better buildings.▪ Jim D’Aloisio is a Principal with Klepper, Hahn & Hyatt in Syracuse, NY. He is also an NYS energy code trainer for the Urban Green Council, a trained thermographer, on the steering committee of the Structural Engineering Institute (SEI) Thermal Bridging Task Committee, and former Chair of the SEI Sustainability Committee.

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

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December 2016