STRUCTURE magazine | December 2012

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

15 th Annual NCSEA Excellence in Structural Engineering Awards

December 2012 Soils & Foundations

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Martin/Martin gains the competitive edge with Tedds Patrick McManus, Technical Director, explains how Martin/Martin saved time, improved consistency and enhanced quality control by standardizing on structural calculation software, Tedds.

“At Martin/Martin we work on a variety of commercial projects and specialize in arena and stadium work, defensive design and construction services. To meet the requirements of such demanding and differing projects we historically used software packages from multiple vendors.

This was difficult to manage as each software package had its own interface and approached engineering problems differently.

No single engineer knew every product in-depth, which created problems with quality control, consistency, and it impacted project scheduling. What we really needed was a single software package that could reliably and accurately do everything we needed.”

“Tedds was our ideal solution because it provided an extensive library of calculations and created transparent output with detailed equations. It also reduced the need to perform calculations by hand, which had been very time consuming.

“Tedds has an extensive calculation library and produces transparent output with detailed equations.”

Tedds also offered us the capability to write our own calculations which has been invaluable. It works within the Microsoft Word interface, enabling us to develop custom tools that allow us to efficiently handle complicated problems that have not been well addressed by other software developers. This has given us a competitive advantage and we see great potential to take this further.”

“We have been able to write our own calculations in Tedds.”

“Since standardizing on Tedds we have decreased our number of vendors, which has saved time for our information technology teams and our engineers speak to fewer technical support teams.

“Tedds is fast and intuitive and is used by all our engineers.”

Tedds is really easy to use so it has become a staple tool for all our engineers, who now use the Tedds library daily for our quick component calculations. We have also standardized our output which immediately improved our consistency and quality control.

“Tedds has helped us to meet aggressive project demands and deliver a high quality service to our clients.”

Without Tedds, calculations would have taken considerably longer to develop and verify, with less transparent output. Tedds is flexible, it’s regularly updated and the size of the library means we can quickly respond to the changing needs of our clients.”

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CONTENTS

FEATURES

December 2012

22 NCSEA Excellence in Structural Engineering Awards

COLUMNS

The NCSEA Excellence in Structural Engineering Awards program annually highlights some of the best examples of structural ingenuity throughout the world.

The winners of the 2012 program were announced at the NCSEA annual meeting in St. Louis, Missouri on October 5. Read about the structural solutions developed for these unique projects, and join NCSEA in congratulating these exceptional winners.

9 Editorial On the Path to the Future: SEI’s Strategic Vision

By Sam A. Rihani, P.E.

10 Lessons Learned Mechanically Stabilized Earth Walls

By Scott J. DiFiore, P.E. and Bryan P. Strohman, P.E.

17 Structural Design

By Dan Eschenasy, P.E.

15 th Annual NCSEA Excellence in Structural Engineering Awards

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

®

Effect of Lateral Soil Pressure on Underpinning

December 2012 Soils & Foundations

ON

THE

COVER

30 Practical Solutions

A complex, three-dimensional expression of the work of Salvador Dali has been transformed into a structure housing the largest collection of Dali’s work outside of his hometown in Spain. Located in St. Petersburg, Florida, the structure is a result of engineering solutions that balanced aesthetic needs with protecting the art, providing a service life of 100 years, and withstanding a 165-mph storm and a storm surge of up to 25 feet. See NCSEA Excellence in Structural Engineering Awards on page 22.

Urban Fills

By Chris Woods, P.E.

DEPARTMENTS 35 InSights Don’t Get Burned

By Glen Robak, P.E., SECB

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. ®

42 Structural Forum Developing the Next Generation of Structural Engineers – Part 4

By Glenn R. Bell, P.E., S.E., SECB

Senior Structural Engineer

IN EVERY ISSUE

Design/Build Construction firm is seeking a senior level structural engineer to oversee its industrial design and construction process. With almost 40 years of experience in design, we offer an opportunity for career growth and stock ownership to the right person. Please send a resume or contact Stephanie Wood, HR Manager, at Fisher & Sons, Inc., 625 Fisher Lane, Burlington, WA 98233, (360) 757-5677, sw@fishersons.com. Website: www.fishersons.com.

6 Advertiser Index 34 Resource Guide (Earth Retention) 36 NCSEA News 38 SEI Structural Columns 40 CASE in Point

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STRUCTURE magazine

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December 2012

ADVERTISER INDEX

PLEASE SUPPORT THESE ADVERTISERS

Bentley Systems, Inc. ............................... 7 Computers & Structures, Inc. ............... 44 CSC, Inc. ................................................ 3 CTS Cement Manufacturing Corp........ 11 DBM Contractors, Inc. ......................... 14 Fisher & Sons, Inc. .................................. 5 Fyfe ....................................................... 19 Geopier Foundation Company.............. 21

Hayward Baker, Inc. ................................ 4 The IAPMO Group............................... 34 Integrated Engineering Software, Inc..... 12 KPFF Consulting Engineers .................... 6 NCSEA ................................................. 13 Pile Dynamics, Inc. ............................... 20 Polyguard Products, Inc........................... 8 Powers Fasteners, Inc. .............................. 2

Editorial Board

ADVERTISING ACCOUNT MANAGER

Chair

Interactive Sales Associates

Jon A. Schmidt, P.E., SECB

Burns & McDonnell, Kansas City, MO chair@structuremag.org

Craig E. Barnes, P.E., SECB

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Mike C. Mota, Ph.D., P.E.

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Evans Mountzouris, P.E.

CBI Consulting, Inc., Boston, MA

CRSI, Williamstown, NJ

Khatri International Inc., Pasadena, CA

The DiSalvo Ericson Group, Ridgefield, CT

Roger A. LaBoube, Ph.D., P.E.

Greg Schindler, P.E., S.E.

CCFSS, Rolla, MO

KPFF Consulting Engineers, Seattle, WA

Brian J. Leshko, P.E.

Stephen P. Schneider, Ph.D., P.E., S.E.

John A. Mercer, P.E.

John “Buddy” Showalter, P.E.

Mercer Engineering, PC, Minot, ND

Chuck Minor

Dick Railton

Eastern Sales 847-854-1666

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Davis, CA

Heath & Lineback Engineers, Inc., Marietta, GA

HDR Engineering, Inc., Pittsburgh, PA

Princeton University Press ..................... 35 PT&C Forensic Consulting Serv., P.A. .... 5 RISA Technologies ................................ 43 Simpson Strong-Tie............................... 15 Soilstructure.com .................................. 18 StructurePoint ....................................... 16 Struware, Inc. ........................................ 31 Subsurface Constructors, Inc. ................ 33

BergerABAM, Vancouver, WA

American Wood Council, Leesburg, VA

SEA-TAC INTERNATIONAL AIRPORT, SOUTH TERMINAL EXPANSION, SEATAC, WA

EDITORIAL STAFF Executive Editor Jeanne Vogelzang, JD, CAE

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STRUCTURE® (Volume 19, Number 12). ISSN 1536-4283.

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December 2012

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Editorial

On the Path to the Future: new trends, new techniques and current industry issues SEI’s Strategic Vision

By Sam A. Rihani, P.E., F. SEI, F. ASCE

A

t the conclusion of a 2008 strategic planning retreat that the Board of Governors of the Structural Engineering Institute (SEI) organized, the Board envisioned a more advanced, global, socially conscious, and professional structural engineer 25 years into the future. It was then believed that organizations like SEI have a decisive role in shaping the characteristics of this future engineer. Three and a half years later, the Board advanced this vision and developed strategic initiatives in support of this vision. Today, SEI has five special teams that are focused on two initiatives identified as the primary strategies for the Institute to adopt.

While it is nice to envision a future prominence of our profession, we also recognize that such prominence does not simply come about by maintaining the status quo. On the contrary, if we do not involve ourselves today to help in shaping our future, our profession is likely to become more and more dependent on software and computer technicians and less dependent on a structural engineer who is characterized by good intuition and creativity. If we believe that the roles and responsibilities of the future structural engineer are likely to be very different than those of today, then we, individually and collectively, have a very important role to play in helping shape the future status of our profession.

The two strategic visions that have been identified are: • The Future Structural Engineer Qualifications of the Structural Engineer Structural Licensure Globalization Continuing Education • Future Structural Codes and Standards Separate task committees have been established to address these two initiatives. From a strategic standpoint, it is critical that these teams work collaboratively together as there are natural overlaps between each of these topics and sub-topics.

Qualifications: Enabling a structural engineer to succeed and excel requires a sound and comprehensive education, and a strong and relevant experience. I recall, when I went to college nearly 40 years ago, the requirement to graduate with a Bachelor degree in civil engineering was 136 credits (then more commonly known as 204 term credits). In 1925, the requirement was 150 credits. With today’s advancements in structural engineering, be it in terms of new materials, more advanced structural software, and increasingly complex structures, one would argue that the requirements for basic education should be higher than the 136 credits mentioned above. This would lead to transitioning the current 4-5 year undergraduate program to a 6-year program. However, what has happened is the reverse, with a reduction of requirements down to 124-128 credits in most universities today. In addition to a sound and comprehensive education, the newly graduated engineer needs to be trained and mentored on the job to build on his/her knowledge and further expand on it to include such related (and practical) areas like project budgeting, project management, constructability, and creative solutions.

Structural Engineer (SE) Licensure: In the advent of increasingly higher requirements for the structural engineer to produce economical designs in a compressed time frame while complying with codes and standards that have become more complex than ever before, the practice STRUCTURE magazine

of structural engineering runs the risk of compromising the safety and welfare of the public if such designs are not produced by competent structural engineers. This is a risk that our profession cannot take. To significantly reduce this risk, SE licensing (now earned through a new 16-hour examination) is the best available tool. Although today there are only 11 states that have enacted some form of a SE licensing legislation, we believe that such a credential is critical to be adopted by all states.

Globalization: When we hear that a new engineering company that recently sprouted in our town won the project that we also bid on, but for half our price, and we learn that they were able to do so because 90% of the engineering work will be done in India or China with engineers earning 1/4 to 1/6 of U.S. engineers salaries, we have to ask ourselves where we fit in the current globalized market we live in. Is globalization a threat, or is it an opportunity? I believe it can be an opportunity. To deal with this challenging new reality, we must address, among other things, the need for an international structural engineering accreditation standard, the changing role we adopt on international projects, and the need for the structural engineer to acquire new skills such as foreign languages and a better understanding of different cultures. We have a significant role to play globally, but we have to prepare ourselves for it if we are to succeed in it.

Continuing Education: In today’s fast moving technology with improved tools made available to the general public on an ongoing basis, the need to acquire more knowledge beyond our formal education is more critical than ever before. The current continuing education programs should be enhanced by expanding them to include mentoring sessions, formal on-the-job training, and the traditional seminars/courses. Such programs should cover technical and non-technical topics.

Future Codes and Standards: Structural codes and standards have greatly increased in volume and complexity over the past 25-30 years.

While there are good reasons for these changes, the complexity seems unnecessarily burdensome for the majority of structures engineers deal with today. It is believed that as much as 80% of structures are not that complex, and more simplified provisions that would apply only to them (with limitations) would be adequate and desirable from a practice perspective. This initiative will explore the development of simplified codes and standards for certain classes of buildings and other structures. This will require close coordination between the structural engineering profession, building code officials, and standards development organizations.

Needless to say, there is abundant work to do regarding SEI’s strategic vision. This work cannot, and will not, be completed in one or two years, as it is an evolving process. I hope this will stimulate an engaged discussion in the structural engineering community, and lead each of us to be part of this very important transformation.▪ Sam Rihani, P.E., F. SEI, F. ASCE is President of the Structural Engineering Institute. He has also served on the Executive Committee of the Business & Professional Activities Division of SEI, is the past Chair of SEI’s Professional Activities Committee, and is former President of the Structural Engineers Association of Metropolitan Washington. He can be reached at SRihani@engineering.com.

9

December 2012

Lessons Learned problems and solutions encountered by practicing structural engineers

D

ue to advantages in economics, constructability, and aesthetics, the construction of mechanically stabilized earth (MSE) walls is now commonplace. An MSE wall consists of soil, reinforcement, and facing to retain earth and support overlying structures (Figure 1).

Thirty- to forty-foot high walls are not uncommon. Reinforcement often consists of geogrids or steel reinforcement strips, while the facing commonly consists of segmental precast concrete units, gabion baskets, metallic panels, or geosynthetic facing. There are many different MSE wall construction materials, making it more important for Contractors and design Engineers to understand how the products work with the remainder of the system.

For various reasons, some systems fail and require costly repair (Figure 2). Based on lessons learned from case studies, the authors discuss common pitfalls of MSE wall design and construction, in the form of a hypothetical case study.

Mechanically Stabilized Earth Walls Pitfalls in Design and Construction

By Scott J. DiFiore, P.E. and Bryan P. Strohman, P.E.

Scott J. DiFiore, P.E. is a senior project manager at Simpson Gumpertz & Heger Inc., Waltham, Massachusetts.

He can be reached at sjdifiore@sgh.com.

Bryan P. Strohman, P.E. is a Senior Staff II – Structures at Simpson Gumpertz & Heger Inc., Waltham, Massachusetts.

He can be reached at bpstrohman@sgh.com.

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

It’s Just a Retaining Wall…

Don’t Sweat It!

An Owner selects an affordable but complex site to construct a retail outlet with four, one-story buildings. The multiple-acre site slopes significantly from west to east, with more than 40-feet of grade differential, and a marsh at the lower elevations covering less than 10 percent of the site.

The Owner engages a Geotechnical Engineer to: drill one boring beneath each building, perform soil gradation tests, and prepare a report with site grading, building foundation, and generic retaining wall recommendations. Site soils, from the limited boring data, vary from clayey sand to sandy clay.

The Owner hires a Civil Engineer to layout the roadways, parking lot, buildings, and site utilities. Site utilities include pressurized waterlines, sanitary sewer lines, and a storm drainage pipe system to collect runoff from the roadway, parking lot, and roof drainage. The retaining wall is an

Figure 2: Costly repairs to failed MSE wall.

Figure 1: Typical MSE Wall Cross-Section.

afterthought. The plans show a bold black line at the property line to represent the retaining wall with the label “retaining wall – to be designed by others,” with a 30-foot grade change from the top to the bottom of the wall. The exposed side of the wall will be visible from local neighborhoods and a shopping center. The marsh is just outside the limit of the retaining wall.

The Contractor submits a bid that utilizes an MSE wall, and engages a Fabricator who provides proprietary masonry blocks for MSE systems. The Fabricator works with a design Engineer who is not local to the site, but regularly designs the proprietary MSE system. The Fabricator and his design Engineer assemble their standard design plans using subsurface information and recommendations from the geotechnical report. They do not visit the site, discuss the subsurface conditions with the Geotechnical Engineer, review the site topography and utilities with the Civil Engineer, or discuss whether soil backfill will be imported or reused from the site development work. The design plans provided to the Contractor contain notes stating that others are responsible to check the bearing capacity below the wall, the settlement of the wall, and the slope stability of the wall and retained backfill.

The Owner hires the Geotechnical Engineer at the start of construction to perform periodic site inspections. However, the Geotechnical Engineer was not involved with the project through the course of the site or retaining wall design. The Geotechnical Engineer assigns his recently promoted professional engineer (Inspector) to monitor site and retaining wall construction, who has no experience with MSE walls. The Inspector visits the site daily and diligently conducts compaction testing on the onsite clayey fill placed in the reinforced zone of the wall. The onsite soils vary significantly as the project progresses, due to the large amount of earthwork required, and the Inspector obtains new laboratory compaction data to correlate with the field-density tests. The Inspector observes water bearing utilities installed in the retained backfill, and storm drain manholes along the top of the wall at the edge of the pavement. The Fabricator and

10 December 2012

Figure 3: Water collecting in clay backfill immediately behind MSE wall facing.

The Imperfect Site Much of the easily-developed land has already been taken; this site has its development challenges. The primary development consists of four, simple one-story retail structures. Just bring the site to grade, install spread footings and pavement, and the development is off and running. What has the project team neglected that could come back to haunt them?

Subsurface Data By performing only four borings over a multiacre site, the team focused on the buildings, but neglected ancillary development which includes significant earthworks and soil reuse.

Retaining wall construction is near the edge of the marsh, which likely consists of unsuitable compressible soils. Could unsuitable soils extend beyond the marsh and into the MSE wall area? Backfilling over the unsuitable soils will result in settlement. What about other unclassified soils outside the building footprints? Incomplete soil characterization could cause construction problems or project delays.

Soil Backfill Clayey soils dominate the site, which are intended for reuse. MSE walls ideally use sand and gravel backfill in the reinforced zone.

How do clayey soils impact MSE wall design and construction?

Water, Enemy of the Wall Water comes from a variety of sources (Figure 4 ), including precipitation, leaky utilities, irrigation in landscaped areas, and groundwater. Unless actively managed by the project team, all sources can have detrimental effects on MSE walls. continued on next page

STRUCTURE magazine

11

December 2012

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his design Engineer provided no specific wall drainage systems in the design. The Contractor constructs the wall from the specified modular blocks and geogrid reinforcement, and the clayey site soils.

The project team is primarily focused on the building, utility, and pavement construction.

After all, the project is a retail center. But, as the project developed, the MSE wall became its own significant construction project. It is up to 30-feet high, next to an established neighborhood, with water sources in the wall backfill, supports building foundations and a parking lot. Treating the MSE wall as “incidental” to the project could be disastrous. Is the project team giving the wall its due consideration?

• Settlement: Sands and gravels undergo immediate settlement, whereas fine-grained soils (clays and silts) are susceptible to longterm settlement (consolidation).

The Geotechnical Engineer did not perform consolidation tests, and no one predicted the amount of wall settlement. If the wall settles over the long-term, the pavement, utilities, buildings, and other site features will go along for the ride.

• Geogrid-Soil Interaction: The geogrids interact with the soil through friction.

Together, the geogrids and soil act as a gravity structure. Geogrid and reinforcing manufacturers regularly test for interface friction with sand and gravel backfill, but not always for silts and clays, which have different behavior.

The reinforcing could also be more susceptible to creep in clayey soils.

• Compaction: Fine-grained soils require special attention to compaction methods and moisture content, more so than sands and gravels which are easier to compact. Poor compaction results in weaker soils, reducing soilreinforcement interface friction and increasing wall pressures.

• Soil Migration: As water flows through soil, it collects fine-grained particles and transports them. If the wall design did not include filter fabric or other protective measures against soil migration and erosion, the soil mass will lose volume and strength, resulting in additional wall pressures and settlement.

• Water Retention: Compared to sands and gravels, fine-grained soils are orders of magnitude less permeable.

Water readily collects on and within fine-grained soils (Figure 3), which, (a) introduces groundwater and seepage forces, (b) reduces soil strength (increasing wall pressures), (c) reduces interface friction between backfill and reinforcing, and (d) in colder environments introduces freeze-thaw cycles in soils at and below ground surface and just behind the facing, which can create frost-jacking pressures.

Figure 4: Water sources include: (A) groundwater, (B) pressurized water lines, (C) storm drain systems, (D) infiltration through open landscape areas, and (E) runoff through pavement cracks.

• Utilities: Water-bearing utilities are commonly placed directly within or behind the MSE wall, including pressurized water lines, storm drains and sewer lines. MSE walls are flexible structures and expected to move laterally as they reach an equilibrium condition. Can the utilities accommodate the anticipated movement without damage? What if they leak due to design or installation deficiencies? It is reasonable to expect that utilities will leak during their lifetime, possibly catastrophically, which introduces seepage or hydrostatic pressures.

• Landscaping: Most development projects include a landscaping component that requires irrigation.

Open landscape areas are often located immediately at the top of the wall behind a curb line, or perhaps in islands set back from the wall.

Irrigation lines and sprinkler systems, just like other water bearing utilities, are susceptible to leakage.

• Infiltration: Rainwater and snow melt infiltrate the ground through open landscape areas and act on the MSE wall. Rainwater also penetrates cracks in pavement. Significant storms can produce many inches of water in the course of just a day.

• Groundwater: Natural groundwater fluctuates over time and during different seasons. What happens during a flood? Is there a perched water table?

Site characterization, prior to design, should identify groundwater elevations and potential fluctuations during seasonal and extreme weather events.

MSE walls are typically designed without consideration for hydrostatic or seepage pressures. This design approach is acceptable provided that the design and construction effectively manages all water sources. It is essential to identify water sources and divert water away from the wall. Collection/retention of water within the wall backfill adds

Figure 5: Drainage swale at top of wall intended to collect water. However, open landscaping behind swale allows water to enter soil mass.

hydrostatic or seepage pressures. When water pressures are large enough, performance or stability problems occur. Drainage systems are particularly important where fine-grained soil backfill is used, since water does not readily flow through such soils.

Reference manuals by the Federal Highway Administration and National Concrete Masonry Association have provisions for wall drainage with varying site conditions. External and internal drainage systems, usually used in combination, collect and divert water away from the wall system. External systems typically include drainage swales and impermeable barriers to collect and divert surface runoff (Figure 5 ). Internal systems typically include chimney and blanket drains at the rear and bottom of the reinforced zone, respectively, with drain pipes and periodic outlets through the wall.

Has the Wall Received Its Due Attention?

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The retaining wall? It’s just a line on the drawings; incidental to the project, right? Engineers and contractors design and install them every day; they must be routine. As described above, challenges exist with site topography, soil conditions, and water sources.

Each project requires several players – Owner, Geotechnical Engineer, Civil Engineer, Contractor, Fabricator, Contractor/Fabricator’s Engineer–but many times each member may not have a full understanding of their role and responsibilities.

Project Delivery In this hypothetical case, the wall design flowed down to the Contractor, who passed it down to the Fabricator and his design Engineer. The Fabricator’s Engineer designs many walls and follows his typical protocol. He often assumes a “typical” soil type (sands and gravels), continued on page 14 STRUCTURE magazine

12

December 2012

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bearing capacity, and global stability of existing soils and subsurface water mitigation.”

The Owner and his Engineers, if they have limited experience, may miss this critical exclusion and neglect to act on it. Without design consideration of these potential failure modes, the wall is at risk.

Wall Performance

Figure 6: Vertical wall with no batter, leaning over adjacent roadway. Construction with inward batter could alleviate this performance problem.

with “typical” strength properties and gradation, to be verified by “others” during construction. All parties often assume that everything is fine, since the Contractor’s team has done this many times before. But, this site is going to use clayey backfill, which differs from the design assumptions and will alter the reported factors of safety. How does this impact wall performance?

Soils and Stability

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The Fabricator’s Engineer has a note on the drawings: “Fabricator and its Engineer accept no responsibility for settlement,

MSE walls are flexible and will move laterally, particularly during construction. The designer must consider this movement and design the wall with sufficient batter to compensate.

Building a vertical wall, which eventually leans outward, results in a perceived failure even if it is technically stable (Figure 6).

Miscellaneous Obstructions At this site, there may be utilities, manholes, parking lots, guardrails, and light poles that penetrate the soil reinforcement. Such obstructions result in additional loads (e.g., impact on guardrails) or decreased resistance (e.g., damage to reinforcing from installation). Did the design Engineer consider these obstructions? Has the Civil Engineer looked at the MSE wall plans, and considered how the civil improvements affect the wall? Are the Contractor and Owner’s Engineer experienced enough to acknowledge these issues if encountered during construction?

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Long-Term Stability Due to the limited subsurface investigation, no strength testing was performed on the foundation and backfill soils. What are the appropriate soil strengths for design, and how do they compare with the assumed parameters from the design drawings? It may be appropriate to consider residual strengths in some cases.

Quality Assurance and Quality Control The Inspector is prepared to make regular visits to the site, but has no MSE wall experience. The Contractor has not installed this specific facing block before, and has not talked to the Fabricator. What are the connection details at the wall facing? At what elevations are the geogrids installed? Has the Contractor installed the drainage controls? Regular, proactive project meetings are required to vet these issues; if not, they often remain unresolved.

Putting it All Together In this hypothetical project, there are many players, each with a different contract identifying their responsibility. But with so many players, and the MSE wall taking a back seat to the buildings, it is common for everyone to simply “assume” that the wall will be taken care of. It’s a bad assumption. Vigilance is required by all project team members, from the Owner, to his Geotechnical and Civil Engineer, to Contractor, Fabricator, Fabricator’s design Engineer, and the site Inspector.

It is important to know how buildings, utilities, or other adjacent construction could affect the MSE walls. It is also critical to verify the soils and drainage are appropriate for the wall, and that all relevant stability checks have been addressed. Periodic meetings with experienced personnel, both during project development and during construction, are effective in vetting out and coordinating the potential pitfalls.

MSE walls can be cost-effective, aesthetically pleasing, and a technically sound approach for permanent earth retention on a site, provided that they are given due consideration during design and construction. When the project team considers the retaining wall “incidental to the project,” and they lightly treat the site topography, soil type, water management, or project team coordination, the entire team may be faced with performance problems or even a wall failure.▪

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I

n New York City, there are over 100,000 masonry buildings that were erected prior to 1930. Typically these are three to six story unreinforced masonry (URM) bearing wall structures with wood floors and rubble foundations. As a consequence of the high number and density of these buildings, a high percentage of new developments occur adjoining an URM building. Excavating for deeper foundations of new buildings will require some type of underpinning. Although there are several methods available, New York City contractors seem to exclusively use strip (also called pin) underpinning.

In recent years, investigations of several incidents showed that some contractors were paying scant attention to some critical activities (e.g. jacking).

In some cases, strip underpinning might have been extended far beyond the range of where it had produced relatively safe results.

About six years ago, the New York City (NYC) Buildings Department established a special unit to focus on excavation and underpinning. As a result, the number and gravity of incidents has declined substantially. While engineering input has increased, the question of what the most appropriate method of analysis should be has not yet been entirely solved by the engineering community.

To motivate the profession towards a more in depth engineering approach to underpinning, the upcoming version of the NYC Building Code will require consideration of the effect of the soil lateral pressure on the structure of the building being underpinned. Given the high sensitivity of URM walls to out of plane loads, it is important to pay full consideration to the possibility that the soil lateral pressure acting on the underpinning might be partially transferred to the walls above. Although sometimes difficult, it is even more imperative to determine the effect of these pressures when the existing structure was erected based only on code prescribed empirical methods that did not fully include concepts like load path or wind design. Some of the engineering arguments that form the basis of this specific code requirement were presented in the May 2011 issue of this magazine (Cases of Failure of Unreinforced Brick Walls Due to Out-of-Plane Loads). This article presents a more detailed discussion of the lateral loads.

Empirical Methods and Lateral Loads As long as underpinning is required only to transfer vertical forces to a deeper soil level, one only needs to verify that the transfer system does not introduce any eccentricity or local overstress and that the removal of overburden does not alter the soil bearing capacity.

During the construction phase, strip underpinning functions as a soil retaining system as well, resisting pressures perpendicular to the wall.

This dual function (support of vertical loads of the existing wall and support of lateral pressures developed as a consequence of the excavation) provides significant savings that probably explains the present ubiquity of the method.

Transfer of Lateral Loads to the Structure Above The underpinning procedure requires jacking or shimming to ensure that the transfer of vertical forces occurs with minimal vertical displacement of the structure above. The jacking develops a high frictional resistance and, together with the subsequent grouting, produces a connection capable of transferring shear forces. Whether or not it is capable of transferring moments, the installation becomes continuous for shear loads. A load path is created.

This continuity of foundation-underpin makes impossible the prevention of transfer of lateral loads to the structure above.

One can minimize the loads transferred by approaching the soil retention function of the underpinning as a sheeting problem. This involves tying back the underpinning with anchors.

Similar to anchored sheeting jobs, the engineer is required to select the tieback, its pre-stressing level and its timing in the construction sequence.

Tie backs and horizontal shoring solutions are becoming common for deep underpinnings but are still rare for depths less than 6 feet. The analysis presented here concentrated on these lower ranges, since they are most common.

Neither the technical literature nor design practice provide good examples of engineering calculations that take into account the effect of lateral loads on existing structures. Many engineers consider such calculations unnecessary. They argue that the load or displacement transferred to the existing building is extremely small and gets dissipated in the system.

For these engineers, the success of the operations requires merely conforming to some empirical principles of execution such as controlling the run of sandy soils, providing a carefully designed box for the approach pit, careful jacking of the pin, keeping water away from the pit, etc.

Structural DeSign design issues for structural engineers

Effect of Lateral Soil Pressure on Underpinning

Sensitivity Analysis Due to modeling uncertainties and the large variety of possible conditions, a sensitivity analysis was deemed the best approach. Sensitivity analysis is a methodology that evaluates how the uncertainty in the output of a model can be apportioned to

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By Dan Eschenasy, P.E.

Dan Eschenasy, P.E. is the New York City Buildings Department Chief Structural Engineer. He is an Honorary Member of SEAoNY.

Figure 1: Phases of underpinning.

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different sources of uncertainty in the model input. In this case the output is the magnitude of horizontal forces transferred to the existing structure. Some relevant results are presented here. Obviously, these results are for particular cases, and should not be used in calculations by others. It is also important to note that the lateral pressure on the underpinning results in unequal distribution of stresses on the underlying soil, concentrating stresses at the toe of the pin.

The scope of the analysis was limited to underpinnings less than 6 feet in height and installed under walls of tenements less than 6 stories. The changes in pin toe pressure are described in terms of ratio of final toe pressure vs. pre-underpinning pressure. The large distance between the building’s shear walls restricting the out of plane movement of the bearing walls allowed us to neglect their direct effect on these bearing walls.

In this simplified model, the lateral loads can be transferred to the underlying soil or horizontal diaphragms only. A rigid support at diaphragm level was assumed.

The analysis used models that follow the steps of the installation process. The various static models are shown in Figure 2. Figures 3 to 6 depict the most relevant results, such as the theoretical effects on the underpin toe as well as the transfer of horizontal loads to

SOILSTRUCTURE.COM 1.

2.

3.

4.

5.

the structure above. A typical underpinning procedure would be as follows (Figure 1):

Figure 2: Structural models for underpinning Phase 3.

Underpinning Phase 1 A sheeted approach pit is executed to allow digging under the existing foundation. The safe removal of earth from under the existing foundation is possible but also limited by the capacity of masonry (brick or rubble) to span several feet unsupported. After the pit under the foundation has reached the desired dimensions, a pin is poured. The top of the pin leaves a gap of several inches to the bottom of the existing foundation. The typical sequence of operation allows the simultaneous digging of several pits.

Underpinning Phase 2 Jacking or shimming takes place to control the transfer of vertical forces from the foundation to the pin. The individual pin installation is finalized by packing grout in the gap between its top surface and the bottom of the existing foundation.

Underpinning Phase 3 The underpinning is complete as pins cover the entire length of the foundation. No backfill or additional supporting structure have been placed on the excavated side. Several possible conditions of the attachment of

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the masonry wall to the floor diaphragm were analyzed (Figure 2).

Case A: There is no positive connection to the floors. The resisting friction forces are small. The base of the underpinning prevents rotation. The case when the joist/wall friction is sufficient to transfer the horizontal forces is treated at Case B (see below).

Case B: The base of the underpinning prevents rotation. Case B(1) corresponds to positive diaphragm (joist) anchorage to the wall occurs at the first floor. In some structures, the first wall diaphragm connection occurs only at the second floor since the first floor joists were simply placed on the shoulder offered by the rubble foundation. This situation is labeled as Case B(2).

Case C: The base of the underpin cannot prevent rotation. For Case C(1) the first positive diaphragm-to-wall connection occurs at the first floor. Case C(2) corresponds to a first positive joist connection occurring at the second floor.

Discussion and Findings During Phase 1, per the analysis, some pins could overturn under lateral soil pressure.

This analysis, also confirmed by the findings

Figure 4: Variation in toe stress – at rest pressure.

Figure 5: Variation in toe stress – active pressure.

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of several incident investigations, clearly justifies the need to provide some system to counteract lateral pressures.

During Phase 2, jacking (or shimming) may result in an eccentric application of the load. The effects of various possible jack misalignments from the axis of the pin were evaluated. Misalignment from the center of the pin might increase the pin toe stresses by as much as 100%. Placing the jack perfectly at the middle of the pin avoids the application of a moment on the pin; but, since the position of the resultant of the existing vertical forces above is not exactly known, a misalignment might occur between the position of the jack and this resultant. As a consequence, some local stresses might double, but would probably be resolved within the masonry structure itself.

Both Phase 1 and Phase 2 are temporary. Most accidents during these phases can be attributed to contractor errors and, as such, is out of the scope of this study. Stresses and displacements present during Phase 3 are usually not temporary.

The presence of a new basement wall on the excavated side will only limit further rotation or horizontal displacement of the underpinning, but will not eliminate the stresses already present.

For Case A, the analysis shows that under at rest soil pressure and depending upon the load of floors above and the pin height, the increase in stresses concentrating at the toe of the pin will reach 350% for a 6-foot underpinning (Figure 4 ). Case A occurs when no transfer is available (e.g. walls not anchored to diaphragm) or when the transfer path is damaged (e.g. end of wood floor diaphragm is rotten). The analysis also shows clearly that the lower the vertical load, the higher the possibility of overturning (Figure 3). In fact, in 2005 there were two collapses of one story buildings that were being underpinned. continued on next page STRUCTURE magazine

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December 2012

The modeling of Case B implies that as long as the soil bearing capacity is not exceeded, it will not influence the magnitude of horizontal forces transferred. Under at rest soil pressure, a 6-foot high underpinning will see a 200% increase in the stresses, concentrated at the toe. For this case, the horizontal load transferred to the building above seems to vary around 4 to 8% of the total lateral pressure.

The load transferred to the first floor might exceed 50 pounds per linear foot, a relatively small but not to be neglected load (see example in Figure 6 ). Such load might be sufficient to break a deteriorating wall-to-diaphragm connection. Even though it would not drastically change the transfer of horizontal loads to the structure above, widening the pin towards the excavation side could significantly reduce the pressure on the soil. However, in NYC it is rarely possible to provide such enlargement.

In essence, Case C corresponds to a transfer of only vertical and shear forces to the soil (no moment restraint, rotation can occur). In Case C(1), the horizontal loads transferred to the first floor might exceed 200 pounds per linear foot (see example in Figure 6 ). For this case, the horizontal load transferred to the building above seems to vary around 15-25% of the total lateral pressure. If the wall-to-diaphragm ties at the first floor fail, the second floor diaphragm might be engaged. In this Case C(2), the horizontal load will diminish by about 40% compared with Case C(1). Case C requires verification of the capacity of the wall/foundation/underpin as a column under combined vertical and lateral forces. For Case C(2), the column might become too slender. For some Case C conditions, some overstressing tensile

Figure 6: Horizontal force transferred at 1st floor diaphragm (example).

stresses might develop and the compressive stresses might approach the allowable compressive capacity of rubble walls (as it was listed in old codes). Crushing and/or bowing of rubble walls were observed in several cases. When the grouted pin-foundation connection is not able to transfer applied moments, the column structure (bearing wall plus underpinning) might become unstable.

Old masonry buildings were never explicitly designed to sustain horizontal forces and, as a result, even smaller loads might crack or rake the structure. In some cases when interior plaster walls participate in the transfer of lateral forces, they might develop cracks.

The author has repeatedly seen such events.

Raking of walls is likely to introduce additional moments as it shifts the position of the resultant of the masonry weight.

Up to this point, the discussion of Case C and B involved only the at rest pressure that develops due to a stiff connection at the top of the wall. As noted, the size of the at rest lateral loads transferred to the structure might

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December 2012

reach levels enough to rake the wall or develop relatively significant horizontal deflections. For certain soils, these movements could change the nature of the lateral pressure from at rest to active. As the active lateral pressure is smaller than the at rest pressure, its effects might result in moments that the soil underlying the toe of the pin would be more likely to sustain.

Similarly, displacements and consequent active pressure can occur when the diaphragm does not provide a rigid support (e.g. deflects under load). The wall structure will be less stressed.

But the reduction in lateral pressure can occur only subsequent to some larger deflections or raking, that is, after some possible damage has occurred to the structure. A structural engineer might be summoned only at this late stage, when he/she will be able only to determine whether the damaged structure has the ability to sustain the smaller lateral loads.

Conclusions The sensitivity analysis was able to verify that the magnitude of the lateral forces transferred to the structure is dependent on the location and rigidity of the diaphragm, and on the capacity of the base of the underpinning to prevent rotation. The percentage of the total lateral force transferred to the building increases as the stresses at the bottom of the underpinning concentrate toward its toe, making rotation likely. The horizontal forces that develop can reach levels sufficient to damage the wall diaphragm connections and even rake some poorly built or deteriorating structures. These modes of damage match some of the distressed unreinforced masonry walls that were investigated following underpinning incidents.

The New York City Building Code’s upcoming requirement of considering the effect of lateral forces on structures being underpinned seems fully justified.

Underpinning might be more effectively designed by a collaboration of structural and geotechnical engineers.▪

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ExcEllEncE in Structural EnginEEring NCSEA 15 th ANNuAl AwArdS ProgrAm

2012 Panel of Judges The judging was held Wednesday August 7, 2012 in Orlando, Florida at the offices of Cuhaci & Peterson.

The 2012 awards jury included the following individuals from the Florida Structural Engineers Association: Roberto Archila, P.E.

Cuhaci & Peterson

Luis Bedoya, P.E. BBM Structural Kevin Casey, P.E. Paul J. Ford & Company Luis Correa, P.E.

Integral Engineering, Inc.

Justin Gatzemeyer, P.E. Tom Grogan, P.E.

Amore Engineering

The Haskell Company

Roger Jeffery, P.E. AMEC Environmental & Infrastructure Amy Miller, P.E. National Ready Mixed Concrete Association Ron Milmed, P.E.

FSEA Southern Florida

Brett Rylands, P.E. Cuhaci & Peterson Mark Scala, P.E. A. Mark Scala, P.E., Inc.

A

t their annual meeting in St. Louis, Missouri on October 5, NCSEA announced the winners of the 2012 Excellence in Structural Engineering Awards. This awards program annually highlights some of the best examples of structural ingenuity throughout the world.

Awards are divided into eight categories: four building categories which are separated based on construction cost, bridge or transportation structures, international structures, forensic-renovation-retrofit-rehabilitation structures and an “other” category which encompasses all types of non-building or bridge structures. In each category, three award winners were named with one project being named the Outstanding Project. All structures must have been completed, or substantially completed, within the past three calendar years.

The 2012 Awards Committee was chaired by Carrie Johnson (Wallace Engineering, Tulsa OK). Ms. Johnson noted: “We had an outstanding group of projects this year and the variety of entries was fascinating. The quality of entries and the complexity of projects continues to grow. The judges had an enormous task to evaluate all of the projects and they did an outstanding job. The judging was really close in several of the categories, and the judges indicated that they had an interesting time reading about the various creative ways structural engineers resolve unique and challenging problems. It continues to make me proud to be a structural engineer.”

Please join STRUCTURE® magazine and NCSEA in congratulating all of the winners. More in-depth articles on several of the 2012 winners will appear in the Spotlight Department of the magazine over the course of the 2013 editorial year.

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CATEGORY

Outstanding Project

1

Robert Wood Johnson University Hospital’s New Proton Therapy building is designed to house two MEVION S250 Proton Beam Therapy treatment machines which emit positively charged atomic particles that can be focused precisely on tumors.

The 4,900 square-foot, three-story below grade concrete structure is located directly adjacent to a one-story medical office building, beneath its parking lot. Due to the confined site, deep excavation, radiation shielding requirements and coordination requirements with the medical equipment’s tight tolerances, the team had to incorporate many unconventional and innovative solutions into the design to produce a cost effective project on a tight schedule.

New BuildiNgs

Robert Wood Johnson University Hospital Proton Therapy Vault New Brunswick, NJ O’Donnell & Naccarato, Inc.

uNder

$10 M illioN

CATEGORY

2

Outstanding Project

New BuildiNgs

Salvador Dali Museum St. Petersburg, FL Walter P Moore

$10 M illioN

Located in downtown St. Petersburg, Florida, the new 66,400 squarefoot Salvador Dali Museum is an engineered work of surrealistic art that houses the largest collection of Salvador Dali’s work outside of his hometown in Spain. The challenge for the engineering team was to balance the aesthetic needs of a building of architectural significance while protecting the art and providing a structure capable of withstanding hurricane-force winds and flooding. Perhaps the most stunning feature – both architecturally and structurally – is the 60-inch-tall helical central stair that is supported by a singular stringer beam and was inspired by Dali’s life-long fascination with DNA structure.

to

$30 M illioN STRUCTURE magazine

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December 2012

CATEGORY

Outstanding Project

3

New BuildiNgs

Milstein Hall, Cornell University Ithaca, NY Robert Silman Associates Cornell University’s new building for the College of Architecture, Art and Planning befits its role as a place where design is taught. The two-story structure contains flexible studio space, a presentation area, gallery space, and a 250-seat auditorium. The challenging design incorporates a reinforced concrete dome at the basement level that rises from the concrete foundation wall up through the first floor, where it is crossed by a reinforced concrete bridge. On the second floor, a series of five steel hybrid trusses, that incorporate features of conventional and Vierendeel trusses, allows the building to cantilever dramatically fifty feet over University Avenue.

$30 M illioN to

$100 M illioN

CATEGORY

4

Outstanding Project

New BuildiNgs

Crystal Bridges Museum of American Art Bentonville, AR Buro Happold Consulting Engineers, PC The 201,000 square-foot Crystal Bridges Museum of Art is an iconic museum inspired by the local Arkansas landscape and the exotic suspension bridges of Bhutan. Its complex geometric forms were made possible because of creative design, cutting-edge engineering solutions, BIM technologies, and a thoroughly integrated design team. Unique among the eight-structure campus are two of the “water” buildings. Their foundation acts as a weir creating a pool and serves as the floor. The roof, constructed of glulam beams and clad in copper with skylights, is suspended from stainless steel cables.

over

$100 M illioN Photos courtesy of Timothy Hursley.

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December 2012

CATEGORY

Outstanding Project

5

The Harbor Drive Pedestrian Bridge is one of the longest self-anchored suspension bridges in the world. It was constructed to provide a safe, elevated footbridge over the busy Harbor Drive and existing train and trolley tracks.

The main span of the bridge is 354 feet and the pylon is 131 feet tall. The pylon is inclined at a 60 degree angle from the horizontal and leans over the deck to support the single pair of suspension cables. For this bridge, the main cable is completely enclosed in a continuous stainless steel guide pipe.

The Harbor Drive Pedestrian Bridge serves as a southern gateway to downtown San Diego and truly is a bridge fitting for America’s Finest City.

CATEGORY

6

Photos courtesy of Brooke Duthie.

Outstanding Project

iNterNatioNal structures

Regent Emirate Pearl Hotel Abu Dhabi, UAE DeSimone Consulting Engineers Located amongst palaces and high profile skyscrapers on the Cornich Street of Abu Dhabi, the new mixed-use $287 million Regent Emirates Pearl development will rise and twist 840 feet above ground. The expansive plot area of 146,500 square feet provides some of the best views of the Capital City.

over

$100 M illioN

The Pearl’s signature feature is the 45-story twisting elliptical floor plan and columns which contains 60 luxury serviced apartments occupying levels 1 thru 10 and a 5-star hotel occupying levels 11 thru the Roof.

In plan, each floor rotates 0.56 degrees each level, with a total of 25 degrees of total rotation from Level 1 to the Roof. The expansive podium area includes five levels of restaurants, retail areas, spas, swimming pools, gym and more, with another 5 levels of underground parking. The total project build up area is 55 stories and 1.4 million square feet.

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December 2012

New Bridge & traNsportatioN structures

Harbor Drive Pedestrian Bridge San Diego, CA T.Y. Lin International

CATEGORY

Outstanding Project

7 Geiger Gossen Campbell Engineers, PC

Decades after its opening, BC Place Stadium required updating. The stadium’s primary systems, the roof aside, remained sound and renovation was preferable to new construction. The original air-supported roof was deflated in May 2010 and renovations completed in September 2011.

The new retractable roof and clerestory provide an open-air, or an enclosed but naturally-lit, configuration. The energy-intensive snowmelt required by the old air-supported roof is eliminated. Programmable, energy-efficient architectural lighting animates the venue.

Revitalization was achieved with minimum intrusion and avoided costly and time-consuming structural alterations, resulting in a world-class, modern facility that is a new iconic Vancouver landmark.

Photo courtesy of David M. Campbell.

Photo courtesy of Michael Elkan.

CATEGORY

8

Outstanding Project

other structures

Van Alen Books New York, NY Robert Silman Associates Van Alen Books was conceived of as an installation for the Van Alen Institute’s small storefront, intended to extend their mission of “promoting inquiry into the processes that shape the design of the public realm”. The store’s primary design feature is a seating area created from cantilevering recycled door stacks suspended

dramatically by steel rods from the existing wood joists above. Visitors to the store are encouraged to use the “steps” to peruse the design-related books that line the signature yellow walls. The effect is a sustainable, stunning, and interactive environment that both reflects and supports the Institute’s vision.

Photos courtesy of Danny Bright.

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December 2012

ForeNsic/reNovatioN/ retroFit/rehaBilitatioN structures

BC Place Revitalization Vancouver, British Columbia

Category 1 Award Winners

Category 2 Award Winners

Category 3 Award Winners

Killam Oil Company, Ltd. Hollywood Park, TX Beicker Martinez Engineering

Centra Iselin, NJ DeSimone Consulting Engineers

Centre for Interactive Research on Sustainability Vancouver, British Columbia Fast + Epp

When the client requested a building with an architectural design that dictated concrete wall spandrels with horizontal ribbons of glass, the designers invented new technology.

Using typical tilt up wall panel construction, the building design connected spandrels of all the floor levels together with steel columns embedded into panels with standard stud anchors. As a result, the panels could be lifted like typical tilt up panels. The outcome was the creation of a new patentpending product: ClearView Composite Wall System™. Unlike traditional tilt walls, the resulting panels provide true horizontal bands of unobstructed ribbon glass with load bearing tilt wall cost efficiency.

Located in Iselin, New Jersey, Centra at Metropark involves renovating and adding to an existing 4-story office building. The design utilizes existing basement space by adding light wells and a central oculus, creating 20,000 square feet of usable below grade office space.

An additional 10,000 square feet were added above the fourth floor roofline, creating a new fifth floor. The floor plate of the addition is rectangular in shape while the existing floor plate is L-shaped. A signature tree-like column was created to support this addition and also create a dramatic entrance. The completed building epitomizes the concept of sustainability by updating the codes, standards of efficiency, and function of an existing yet outdated facility.

A cutting-edge facility for environmental development, The Centre for Interactive Research on Sustainability (CIRS) at the University of British Columbia was designed as a research and education facility focusing on the importance of sustainability. With a target of LEED Platinum and the Living Building Challenge status in mind, the designers and architects set out to maximize the use of wood in the project.

The 59, 202 square-foot (5,500 square meters) building was constructed entirely of the local renewable resource, a rarity in multi-storey academic structures. CIRS encompasses offices, lecture halls, exhibition spaces, and laboratories for research and testing.

Buckner Companies Home Office Graham, NC Stewart Engineering, Inc.

VanDusen Botanical Gardens Visitor Centre Vancouver, British Columbia Fast + Epp

Sanford Consortium for Regenerative Medicine (SCRM) La Jolla, CA Hope Engineering, Inc.

Courtesy of Nic Lehoux.

Courtesy of Bill Robinson Photography.

The new 19,000 square-foot visitor centre at VanDusen Botanical Gardens provides an iconic entrance point to the grounds.

Engineers and architects collaborated to develop a dramatic free-form roof, made almost entirely of timber. Three-dimensional technology, a product of the use of three different modeling programs, ensured accuracy and precision in the design and construction of the multifaceted geometrical shape of the unique roof. The building targets LEED Platinum and Living Building Challenge status, as its 71 unique, prefabricated panels champion innovation, economy and sustainability.

SCRM unites San Diego’s top research scientists under the “Collaboratory”, a 150,000 square foot facility with a total construction cost of approximately $85 million.

Construction of the main building consists of two-way concrete flat-slabs, concrete columns, and shear walls on a conventional foundation system. “Punched” exterior shear walls serve to maximize interior natural light and provide seismic resistance. Exterior steel framed office “Pods” rest on cantilevered tapered concrete slabs extending over 16 feet from the supporting exterior wall. The auditorium building consists of elevated floors of composite steel beams with metal deck and concrete fill. The cantilevered perimeter framing creates an illusion of a floating structure.

Buckner Companies, a North Carolina-based steel erector, envisioned a unique headquarters that highlighted past projects and exposed the building’s structure. The result is a structure composed of salvaged structural pieces of projects that have been recovered and stored

by Buckner over the last 62 years. Examples include the conference room which was built from girders recovered from a renovation of Clemson University’s Littlejohn Coliseum and a connecting bridge originally erected by Buckner in 1972 on the campus of UNC Chapel Hill.

Instead of components resulting from design decisions, on this project, the components drove the design. Structural engineers were challenged to reinvent the component’s intended purposes.

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Category 4 Award Winners 8 Spruce Street–Beekman Tower New York, NY WSP Cantor Seinuk 8 Spruce Street – Beekman Tower is Manhattan’s tallest residential building.

Designed by Frank Gehry, for client Forest City Ratner, the 870-foot tower rises to 76 stories.

The tower boasts a striking rippled facade, made possible by a ground-breaking structural design. Floor plates and slab edges are unique to each level, and innovative column, beam, and shear wall configurations accommodate the steel curtain walls, providing flexibility for a wide range of interior space configurations while also ensuring structural stability in high winds. At the foot of the building, a six-story podium contains a public school and ambulatory care center.

Category 5 Award Winners Lake Champlain Bridge Replacement – Crown Point, NY Chimney Point, VT HNTB Corporation

The Lake Champlain Pedestrian Bridge is a lifeline connecting two communities, Crown Point (NY) and Chimney Point (VT). The replacement bridge maintained the signature aesthetics that fit the landscape and provided a stronger, longer lasting bridge from start to finish in just over two years. Several team innovations helped to fast-track construction activities, including the decision to construct the arch span offsite, concurrently with the approach spans, and then float it into place. The team’s accelerated project delivery resulted in the bridge opening to traffic in just 20 months – a dramatically shorter time frame than normally associated with traditional methods.

Tempe Town Lake Pedestrian Bridge Tempe, AZ T.Y. Lin International

Kauffman Center for the Performing Arts Kansas City, MO Arup

The 356,000 square-foot Kauffman Center for the Performing Arts serves as the focal point of Kansas City’s burgeoning arts district.

To achieve the architect’s ambitious vision while providing excellent sound quality within the performance spaces, engineers helped design a box-in-box facility that is actually three separate buildings: two dense concrete performance halls covered by a lightweight steel structure with a glass wall and roof supported by a cable net.

Structural engineers worked closely with other disciplines to achieve elegant solutions for fire protection, climate control and other issues.

The thoughtful use of steel and concrete for different areas of the facility saved the client time and money.

Category 6 Award Winners Marina Bay Sands Singapore Arup

The Marina Bay Sands Integrated Resort was unrivaled in scale, complexity and speed of execution. The engineering design included a number of firsts for the construction industry as a whole. Project highlights include three curving, uniquely shaped high-rise hotel towers topped by a SkyPark (the world’s largest public cantilever, lifted into place with one of the highest strand-jacking operations ever undertaken), a lotus-shaped museum, and extensive casino, convention, retail and entertainment spaces. The development necessitated deep excavations across the site.

Four cofferdams, among the largest ever used, were deployed at the unusual depth of 62 feet.

Photo courtesy of Timothy Hursley.

Al Hamra Tower Kuwait City, Kuwait Skidmore, Owings & Merrill LLP

The Tempe Town Lake Bridge connects bike and pedestrian paths from the north and south sides of the lake, allowing runners, walkers and cyclists to cross without having to compete with vehicular traffic at major intersections.

The structure is a 4 span simple tied arch bridge, each comprised of tubular parabolic arches that lean into each other and cross at the quarter points, lending to its distinctive shape. Exposed “up-close” connections and simple railing details invite users to observe elegant, yet simple “engineering”.

At 413 meters (1,355 feet), Al Hamra Tower is among the tallest buildings in the world. Its unique sculpted form sets it apart from other towers. The structural system and exterior were developed symbiotically through digital design. A spiraling slice subtracted from a prismatic volume generates the building geometry and results in a cantilevered office wing that wraps around a courtyard. The two resultant cut surfaces are hyperbolic paraboloid reinforced-concrete walls that extend the full height of the tower and participate in the lateral and gravity force resisting systems.

Photo courtesy of Tom Pavia.

Photo courtesy of Tim Griffith.

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December 2012

Category 7 Award Winners

Category 8 Award Winners

J. Paul Leonard and Sutro Library San Francisco, CA Simpson Gumpertz and Heger

Atrium Operable Roof – California Academy of Sciences San Francisco, CA Walter P Moore

In 2007, San Francisco State University undertook an extensive program to remodel, retrofit and expand their existing library.

The expansion included a complete seismic upgrade, architecturally significant study spaces, and a high-density vault to house the majority of the library’s collection. This was a design-build project, which allowed Structural Engineers to work closely with the architect, owner and contractors while developing design solutions. A performancebased approach to the retrofit resulted in an economical and effective design. For example, engineers designed concrete shear walls to rock on new shallow foundations, eliminating a need for new micropiles.

The California Academy of Sciences commissioned the design of a replacement operable roof over the Piazza, a glass-covered central atrium. Key factors in the design were visual integration with the Renzo Piano-designed Academy, a high-tech aesthetic, durability, and ease of operation. Eight stainless steel arches span 64 feet across the existing glass roof, blending seamlessly with the existing structure. Lightweight, translucent polycarbonate panels slide along the top of the arches via highstrength, low-friction slide pad assemblies. To ease operation and maintenance requirements, engineered plastics requiring no lubrication were used for exposed components, and roof movement is operated remotely via iPad.

Photo courtesy of David Wakely.

Photo courtesy of David Wakely.

Chelsea Piers, Connecticut Stamford, CT WSP Cantor Seinuk

Miami Beach Soundscape Miami Beach, FL Douglas Wood Associates, Inc.

Chelsea Piers, Connecticut is a 400,000 square-foot sports, entertainment and educational facility. Formerly a Clairol manufacturing plant, the adaptive reuse design saved the old building from being demolished and ending up in a landfill. An economic solution to remove 23 existing columns was necessary in order to achieve 100-foot column free zones. Leaving the entire roof structure in place, king post trusses constructed out of the in-place existing roof structure allowed for the columns to be cut away. The structural engineering solutions were creative, economical and sustainable, resulting in limited demolition and limited use of new materials.

Soundscape is a small park in lively South Beach.

It’s also a state-of-the-art theater for live projection of concerts from the adjacent symphony and for public movie and art presentations.

The park’s primary structures are three large aluminum pergolas (shaped to resemble cumulus clouds) and numerous outdoor theater elements, including giant “Ballet Bars” and a project tower (enshrouded in its own “cloud”).

Undulating concrete seating walls and a maze of concrete walkways complete the project.

This project stands out for accommodation of its complex audio-visual systems within a sculptural expression of its structural systems.

Photo courtesy of Robin Hill.

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December 2012

Practical SolutionS solutions for the practicing structural engineer

Urban Fills How Ground Improvement Can Eliminate the Need for a Costly Deep Foundation System

By Chris Woods, P.E., LEED AP BD+C

Chris Woods, P.E., LEED AP BD+C (dchipurdue@hotmail.com), is the Chief Engineer for the Paeonian Springs, Virginia based Densification, Inc., and presently serves on the Ground Improvement Committee of the Deep Foundations Institute (DFI).

T

hese days, finding an urban site, particularly in our older cities, that has not been impacted by previous developments might best be described as….impossible. Many sites developed in urban settings have been built and rebuilt throughout the years, and experience speaks to the fact that as the vast majority of these prior structures were demolished, little thought or care was given to what was left beneath the surface. When combined with factors beyond the developer’s control, such as the existence of foundation systems Figure 1: Typical foundation remnants on an urban site. supporting adjacent structures, buried utilities or transit tunnels, developTypical Foundation Solutions ing an appropriate foundation solution that can be designed, permitted, and most important, Once the site has been characterized from a geoconstructed in an economical way, becomes a technical standpoint, the first step is always to significant challenge for the design team. In identify the main concerns raised by the results most instances, the approach of the investigation, and then to outline potential taken by the geotechnical foundations solutions that can address the issues and structural engineers will and be constructed in an economical manner. determine whether or not the Generally, there are two solution paths that can given site challenges are suc- be followed: deep foundations such as driven or cessfully overcome. drilled piles or caissons, or shallow or mat foundations constructed following the implementation appropriate ground improvement measures.

Typical Challenges to Foundation ofAfter development of a list of feasible engineering solutions, two main factors, schedule and Design on Urban Sites cost, generally determine the most appropriate Depending on the location or age of the site and solution. Ground improvement often provides the nature of the previous development on a site, the advantage in both categories, and as it relates there could be a virtual cornucopia of foundation to cost, can be significantly more appealing. construction issues that need to be addressed.

Additionally, ground improvement programs can There could be uncontrolled fill material (often of be strategically implemented in localized areas of poor quality) which was simply dumped back into poor soils, rather than the all-or-nothing approach a site after a former structure was razed or placed that is generally required by deep foundations centuries ago if the site was reclaimed land near and structural floor slab systems. There will be water. There could be decades-old foundation occasions where there is no option but to use deep remnants that were left in place (or former bulkfoundations, perhaps as to not damage immedihead elements on reclaimed land sites). The most ately adjacent structures or to avoid imposing common example is basement structures in which loads on adjacent transit structures; however, the superstructure above grade was knocked into the use of ground improvement should never the basement and the site leveled, with foundabe readily dismissed in the urban setting, as it is tion walls and basement slabs left in the ground often completely viable and more economical.

(Figure 1). There could be elements of excavation support systems, such as soldier piles and lagging, that were installed to facilitate the construction Common Ground Improvement of former development at the site. There could Techniques in the Urban Setting be environmentally-impacted soils resulting from the nature in which a site was used. In some Of the potential issues that could exist at an urban rare instances, there could also be archaeologi- redevelopment site, urban fill material is more cal considerations such as former cemeteries or often than not the primary issue to deal with human remains that were undocumented. Sites during foundation design (Figure 2). The reality may have one or more of these issues. No matter is, while some of the other issues can exist, the site which way you look at it, any of these scenarios would have been disturbed to create most of those creates headaches from a foundation design and conditions, leading to the placement of fill mateconstruction standpoint. rial. With this in mind, let’s review some of the

30 December 2012

Figure 2: Typical urban fill material.

Figure 3: Typical stone column layout and footing location.

generally applicable types of ground improvement for improving urban fill material.

Improvement methods discussed below are generally more applicable to granular types of material, rather than plastic silts or clays soils, as this tends to be the more common occurrence with urban fill. Specifically, the desired result of these methods is to densify the materials in-place, improving the engineering properties of the existing fill materials to the point that the materials are uniform and can be relied on to provide foundation support.

Stone Columns

Removal and Replacement Removal and replacement consists of removing the fill material in question and replacing it as a structural fill. Constructability-wise, this option is generally feasible from depths on the order of 15-20 feet or less. The deeper you go, the more likely it is that excavation support measures will be required. In congested urban settings, this can easily become an issue.

Another key design consideration with removal and replacement is to understand the foundation conditions of the structures bordering the site. If the required depth of excavation will go below the adjacent foundation levels and underpinning becomes required, it is likely that an in-situ option for ground improvement (such as stone columns or grouting) will be more cost effective and certainly more attractive from a risk management standpoint.

Removal and replacement can be an economically attractive option if you have suitable materials on-site, as the cost then generally boils down to the equipment and labor to perform the work. Typical earthwork costs are $3-4 per cubic yard for soil being excavated, and $4-5 per cubic yard of material being placed and compacted. If this option seems feasible based on preliminary studies, then high-end site characterization is generally recommended. Large amount of debris, obstructions, or environmentally-impacted soils can lead to a need for off-site disposal (usually at a premium) of significant quantities of material and a subsequent requirement for import of suitable material at additional cost and impact on the project schedule. Should these conditions be present, removal and replacement quickly becomes a less attractive option from a cost perspective.

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Dynamic or Rapid-Impact Compaction Dynamic compaction and rapid-impact compaction (RIC) are two distinct methods that consist of imparting high-level energy into the ground to densify soils in place. Dynamic compaction achieves this by dropping a weight ranging from 5 to 15 tons from a height varying from 60 to 100 feet across the site at multiple points on a grid pattern (Figure 4 , page 32). This is generally effective to treat soils to a depth of about 30 feet. Alternatively, RIC is conducted using a hydraulic pile hammer mounted to the arm of a track-mounted backhoe. Given the scale of the equipment being used, RIC is generally effective to treat soils to a depth of 10 feet or less.

The biggest drawback to these methods is the level of vibration that is generated during execution. If sensitive buildings or utility structures exist within 80 or 90 feet of the site, this may not be the best solution for the project. However, there are techniques, such as seismic trenches, that can be employed to minimize the effects of vibrations off-site.

Where practical, dynamic compaction or RIC are almost always one of the most attractive options from a cost consideration, generally

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Stone columns are also known in the industry by proprietary names such as Geo-Piers or Vibro-piers. The idea behind stone columns is to introduce stiff stone elements into the ground, while simultaneously densifying the surrounding soils during installation of each element. The columns are generally installed in clusters at foundation locations (Figure 3) and, if needed, on a grid pattern throughout the remaining areas of the site to provide floor-slab support. Stone columns tend to be slightly more applicable to soils having elevated quantities of fine-grained soils, but are still generally less applicable in areas of soft silts, clays, or organic materials, as some amount of confining pressure in the ground is required to facilitate installation of the columns. Stone column installation is possible to depths of up to about 100 feet, but generally used to depths of 50 feet or less.

The costs for stone columns generally ranges from $2 to $6 per cubic yard of soil to be improved; mobilization of the installation equipment is on the order of $10,000 to $20,000. There are not many situations that preclude the use of stone columns, as the vibration levels associated with installation are usually tolerable to adjacent structures.

However, on sites with significant obstructions, a thorough pre-excavation job will be required to facilitate installation. Additionally, a site can

be optimized to include stone columns in areas of poor quality soils within the site, but omit them in areas of better quality soils, providing flexibility and cost efficiency to the project.

costing on the order of $2 per square foot of treated area and no spoils or excess materials from the process that require off-site disposal.

Additionally, obstructions typical of urban fill that are encountered during the process are able to be removed as they are discovered.

Grouting There are several types of grouting that can be utilized in ground improvement. For improvement of miscellaneous urban fills, compaction grouting tends to be the more cost-effective and readily used option. Compaction grouting consists of injecting low-slump grout on a grid pattern across a site to densify a given soil mass. Compaction grouting can be effective to depths of up to 50 feet or so, but does require some amount of overburden pressure, that is to say mass on top of the zone being grouted, to be effective.

Of the ground improvement methods discussed in this article, compaction grouting is on the higher end of the cost spectrum. Costs generally range from $100 to $300 per cubic yard of grout, with mobilization costing on the order of $10,000 to $15,000. Additional grouting treatment types can consist of chemical grouting or jet grouting; however, these methods tend to be more expensive than other methods and, as a result, are not as widely used.

It is always advantageous to involve specialty geotechnical contractors early in the process, as they may have specific insight on the chosen solution or input regarding potential techniques and the limitations of each. This will be beneficial for the development of accurate foundation and project cost estimates.

Design Considerations in Applying Ground Improvement On a typical shallow foundation job, the geotechnical engineer performs an investigation and provides foundation design recommendations and seismic parameters to the structural engineer, usually with minimal interaction between the two. When it comes to the successful implementation of a ground improvement program, however, a constant dialogue between the two is required in an iterative process to optimize the ground improvement design. Specifically: • Regardless of the level of improvement achieved, some level of post-construction settlement can always be anticipated with a shallow foundation solution. To that end, the geotechnical engineer will need a realistic understanding of the actual column loads in the proposed

structure, along with how much total and differential settlement can be tolerated.

At this stage, the dialogue between the geotechnical and structural engineers should be constant. When it relates to successfully implementing a ground improvement program, make no mistake – this interaction is critical.

• What are the boundary constraints? The design team Figure 4: General photograph of dynamic compaction. needs to work together to understand the nature and composition to compare Standard Penetration of any bordering foundation systems, Test N-values or Cone Penetration utilities, or transit tunnels in proximity Test Soundings before and after the to the site so that educated decisions can treatment to verify that the level be made when it comes to assessing the of improvement required has impact of a given ground improvement been achieved. technique beyond the limits of the site.

• testing to obtain site-specific modulus Understanding the boundary conditions values. On projects where design is of particular importance when it parameters, such as allowable bearing comes to evaluating a given ground pressure, need to be optimized for the improvement technique in conjunction overall foundation design, flat-plate with necessary underpinning or dilatometer testing can be performed to excavation support measures, or how obtain site-specific modulus values for construction-related vibrations could use in fine-tuning settlement estimates impact adjacent structures. for the project.

From a site characterization standpoint, This is by no means an exhaustive list of there are several key issues which will likely tasks, but rather the most commonly applibe addressed by the geotechnical engineer; cable in urban redevelopment projects. however, the entire design team should have a good understanding of the objectives of Conclusions the exploration process so that pertinent information can be shared amongst the team There are several foundation-related issues that as it is obtained. Specific exploration-related can arise on an urban site, almost all of them tasks completed by the geotechnical engineer relate to the way a site has been utilized over typically include: time. These encumbrances can impact an entire • soil borings to evaluate the general site, part of a site, or the areas immediately subsurface conditions at the site. As surrounding a site. In any case, ways to successthe design concept is developed and fully overcome them during construction need advanced, supplemental investigations to be evaluated and developed in the design can be conducted in specific locations phase of a project. When considering the varito collect information critical to a ous options for foundation support of an urban successful design. structure, it is important to not immediately • test pits to better evaluate and jump to the conclusion that deep foundations assess the surficial conditions at the are the only viable solution, as it is highly likely site. In the urban setting, test pits that alternative solutions exist. There are several become invaluable for investigating types of ground improvements applicable to an and identifying former foundation urban environment that are cost effective and elements or structures that might exist flexible from an implementation standpoint, beneath the site. and that can help with schedule. However, • a comparison of pre-treatment for ground improvement solutions to be truly investigation data to post-treatment effective, constant and effective communicainvestigation data, which is how tion between the geotechnical engineer and most ground improvement methods the structural engineer during the design phase are evaluated. Specifically, when should always exists; if not, it most assuredly methods that are being used to densify will be during the construction and litigation a given soil mass, it is most common phases of a project.▪

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December 2012

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All Resource Guides and Updates for the 2013 Editorial Calendar are now available on the website, www.STRUCTUREmag.org. Listings are provided as a courtesy. STRUCTURE® magazine is not responsible for errors.

new trends, new techniques and current industry issues

InSIghtS

Don’t Get Burned Emerging Technology Simplifies Fire-Rated Floor/Ceiling Assemblies in Wood-Framed Buildings

By Glen Robak, P.E., SECB

F

ire-resistant building materials provide crucial “passive” protection for buildings by limiting the damaging effects of fire. It is especially important that designers select materials and assemblies that protect a building’s structural elements–thereby extending the time for occupants to escape a burning building and for firefighters to enter safely and put-out the flames.

In wood-framed buildings, codes require various forms of fire protection for wall assemblies and floor/ceiling assemblies. Typically, floor/ceiling assemblies in multi-family buildings using engineered wood I-joists must include a protective “membrane” to provide a one-hour fire-resistance rating. The typical membrane is two layers of gypsum attached to the joist flange or resilient channels. For single-family homes with unfinished basements, the International Residential Code (IRC) requires a single-layer of gypsum board.

and edges of the bottom flange. The coating swells in a fire, thereby decreasing heat transfer to the joists’ wood fiber. The result is enhanced fire resistance and a longer time to burn than uncoated I-joists.

For this product, the factory-applied intumescent is durable and does not reduce the structural properties of the engineered wood I-joists. The intumescing action occurs at high temperatures and is thus not activated by temperature ranges of typical building mechanical systems. Finally, these fire-resistant engineered wood I-joists do not require special tools or training to use.

Builders can cut and drill them similar to other I-joists, and use standard hangers for quick and smooth installation.

One-hour Fire-rated Assemblies

These types of products are being evaluated and approved through code evaluation reports such as those developed by ICC-Evaluation Services AC14 Acceptance Criteria for Prefabricated Wood I-Joists. Product testing is in compliance with ASTM E-119 Standard Test Methods for Fire Tests of Building Construction and Materials.

Glen Robak, P.E., SECB is a senior engineer for Weyerhaeuser. The company offers a range of wood structural frame materials, technical support and design software for residential, multi-family and light commercial construction. www.woodbywy.com.

Wind Wizard Alan G. Davenport and the Art of Wind Engineering

Siobhan Roberts Chronicling Davenport’s innovations by analyzing select projects, this book gives an illuminating behind-the-scenes view into the practice of wind engineering, and insight into Davenport’s steadfast belief that there is neither a structure too tall nor too long, as long as it is supported by sound wind science.

Emerging Technology One wood I-joist innovation introduced in 2012 is a product with a specialty coating that helps simplify design and construction of one-hour fire-rated floor/ ceiling assemblies. Specifically, for multifamily buildings, the joists can provide a one-hour fire-rated floor/ceiling assembly with only a single layer of gypsum (versus double layer) and no mineral wool. In single-family homes with unfinished basements, these joists can also be approved for installation without the gypsum layer.

This particular I-joist has an intumescent coating applied to the joists’ web surfaces STRUCTURE magazine

Engineered wood I-joists with factory-applied fire resistive coatings will likely have a higher unit cost than uncoated I-joists, yet a net savings is possible from eliminating the material and labor costs of installing one of the gypsum layers in multi-family residences and eliminating the gypsum membrane in singlefamily homes.▪

“Wind Wizard is a masterpiece of science writing at its best: informative, interesting, and entertaining. I warmly recommend it to anyone interested in the important issues of our time. Roberts is one of our best writers on science and mathematics today.”

—Amir Aczel, author of Fermat’s Last Theorem Cloth $29.95 978-0-691-15153-3

See our E-Books at press.princeton.edu

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December 2012

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Chapter 7 of the International Building Code (IBC) contains prescriptive one-hour fireresistance protection for wood I-joists (see especially Table 721.1(3), rows 21 – 28).

These prescriptive one-hour assemblies generally fall into two category types: 1) Assemblies that require two layers of gypsum board, and 2) single-layer assemblies requiring a minimum 2x4 flange size with the addition of mineral wool.

ICC-Evaluation Services (AC14)

Cost/Benefit

Brent Perkins, P.E., S.E. is a project engineer with Dudley Williams and Associates, P.A. in Wichita, KS.

Concrete I (Reinforced Concrete) Topics 1.

2.

3.

4.

5.

6.

Materials.

Flexural behavior and design.

Deflections.

Shear.

Development of reinforcement.

Columns.

Concrete II (Prestressed and Posttensioned Concrete) Topics 1. Introduction, general design principle, material and anchorages.

2. Loss of prestress.

3. Analysis of flexural sections.

4. Design of flexural sections.

5. Design of composite sections.

6. Design of shear.

7. Prestress transfer bond, anchorage zone.

8. Cable profile, deflection.

9. Partial prestressed and non-prestressed reinforcement 10. Design of continuous beams.

11. Post-tensioning two-way slabs.

Modified Concrete Coursework Concrete I (Reinforced Concrete) Topics 1.

2.

3.

4.

5.

6.

Materials.

Flexural behavior and design.

Serviceability and deflections.

Shear.

Development of reinforcement.

Columns.

Concrete II (Advanced Reinforced Concrete) Topics 1.

2.

3.

4.

5.

6.

7.

Slender and biaxial column design.

Design for torsion.

Two-way slab design.

Structural wall design.

Earthquake-resistant design.

Strut and tie models.

Anchoring to concrete.

Figure 2: Current versus modified Basic Structural Engineering Education Concrete Coursework

January 7: Structural General Notes & Specifications: Integration Issues & Recommendations, Greg Markling

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Announcing the Wind Series Webinars: January 29: Wind Series #1 – Basics of MWFRS & CC Loads, John O’Brien February 12: Wind series #2 – Components & Cladding Roof Loads, John Hutton & Michael Stenstrom February 26: Wind series #3 – Components & Cladding Wall Loads & Other Structures, Tom DiBlasi & Bob Paullus March 12: Wind series #4 – Basics of Wind Tunnel Testing, Jim Swanson & Don Scott March 26: Wind series #5 – Wind Loads on Non-Standard Building Configurations, Don Scott

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News form the National Council of Structural Engineers Associations

Is it time to change the concrete coursework recommended by the National Council of Structural Engineers Associations (NCSEA)?

Since 2002, the Basic Education Basic Structural Engineering Committee for the NCSEA has recomEducation Curriculum mended a core 12-course schematic for the Basic Structural Engineering Education Analysis I Curriculum (see Figure 1). This curriculum Analysis II includes a myriad of topics deemed necMatrix Methods essary by the profession for all structural Dynamic Behavior engineers. However, since the inception of Steel Design I the curriculum, NCSEA has continually Steel Design II sought feedback and input concerning Concrete I the curriculum. In the years since the Concrete II implementation of this schematic, eduTimber cators have consistently suggested that the Masonry concrete coursework needs to be revised Foundation Design/ to include one more course: Advanced Soil Mechanics Reinforced Concrete Design. As practicing Technical Writing engineers and educators, do you agree?

Figure 1: NCSEA 12-Course The American Concrete Institute (ACI) Basic Structural Engineering Faculty Network has provided beneficial Education Curriculum Schematic. feedback to the NCSEA Basic Education Committee concerning the need of adding another course extending students’ understanding of concrete. Many members of the ACI Faculty Network have voiced this concern. Currently, Concrete I coursework consists of reinforced concrete topics, while Concrete II consists of prestressed and post-tensioned concrete topics (see Figure 2). The ACI Faculty Network members have suggested that Concrete II be revised to cover advanced reinforced concrete design, while adding another concrete course concerning prestressed and posttensioned concrete topics (see Figure 2 ). Is this change needed? Should some of the content be an elective course? How can collegiate institutions meet this challenge of adding yet another course to the recommended curriculum?

The Basic Education Committee has continually sought feedback concerning the recommended curriculum through forums at the NCSEA Annual Conference, articles in STRUCTURE magazine, and discussions with practitioners and educators. Now the committee needs input from a broader spectrum of professionals to move forward and make a final recommendation. Tell us what you think. Should the curriculum remain unchanged or be modified as outlined?

Provide feedback to the Basic Education Committee by contacting Brent Perkins, NCSEA Basic Education Committee Vice Chair, at bperkins@dwase.com.

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NCSEA News

Current Concrete Coursework

Should the focus of concrete coursework in the Basic Structural Engineering Education Curriculum be modified?

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Curing the Concrete Question

Upcoming Webinars

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Diamond Reviewed

SPECIAL OFFER for the Wind Series! Buy four webinars, get the fifth FREE! These courses will award 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program. Time: 10:00 AM Pacific, 11:00 AM Mountain, 12:00 PM Central, 1:00 PM Eastern. Register at www.ncsea.com.

STRUCTURE magazine

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December 2012

Re-Engineering your Firm for the New Economy

16 Hours of Learning and Sharing the Strategies of Success Eight sessions to include: • Hard Choices in a Soft Economy – 5 Mistakes You Cannot Afford to Make by Kelly Riggs of VMax Performance Group • Key Financial Indicators to Look for When Running a Structural Engineering Firm by Scott Braley of Braley Consulting & Training • Coaching for Leadership: Transforming Potential into Performance by Kelly Riggs of VMax Performance Group • Roundtable Panel Discussion: Diversified practice?

Multi-state practice? What works? What doesn’t? with moderator Carrie Johnson of Wallace Engineering • Developing the Next Generation of Structural Engineers by Glenn R. Bell, senior principal & CEO of Simpson Gumpertz & Heger • Setting up a Technical Training Program for New Engineers by Ben Nelson, P.E., SECB, principal of Martin/Martin Inc. • Ten Keys to Managing Multiple Deadlines by Jon Stigliano of Strategic Solutions Group • Motivational Climate – Does Your Firm have one? by Jon Stigliano of Strategic Solutions Group

News from the National Council of Structural Engineers Associations

The changing landscape of the economy has forced many professions to examine their business practices, operations and leadership skills.

NCSEA’s Winter Leadership Forum is gathering the best and brightest for two days, March 7-8 in Tucson, to learn how to improve and maintain the practice of structural engineering.

The Forum includes educational sessions, roundtable discussions, and opportunities to network and share ideas in a casual and interactive atmosphere.

The sessions will offer management ideas, practices and resources that can be implemented in your firm, noted Bill Warren, principal structural engineer for SESOL. “Facing challenges with your business? Direction not clear? How do you survive, let alone grow? Is there any answer or any help? Yes, there is. Come to the Winter Leadership Forum to discuss your ideas with those around the country who are facing the same situation. Develop a circle of those you can talk to.”

Registration for the Forum is $995 for the two day event and includes breakfasts, lunches and a reception. A one-day registration may be purchased for $595.

The Forum will be held at the Westin La Paloma Resort in Tucson, Arizona, with a room rate of $179 per night. The Resort includes 27 holes of Jack Nicklaus signature golf on property, an Elizabeth Arden Red Door Spa, seven dining options, and five swimming pools, including a private adult pool.

“The NCSEA Winter Leadership Forum is the perfect setting to learn how to grow and improve your business because you will learn from top performers and leaders how to handle important issues that affect your business and bottom line,” stated Barry Arnold, principal of ARW Engineers.

NCSEA News

2013 Winter Leadership Forum

Detailed information on presenters can be found at www.NCSEA.com.

Why I am attending the NCSEA Winter Leadership Forum…

“The new economy provides fresh opportunities for those who will change and adapt. Success demands understanding the economy, business operations, leadership styles, the direction the profession is heading, and how to reposition a firm. This leadership forum tackles all those issues and will allow those who attend to share ideas and jump-start their re-engineering.”

Chris D. Poland Chairman & Senior Principal Degenkolb Engineers

“The development and training of engineers is important for the future of the profession and the bottom line of engineering firms.

I like the fact that this forum has sessions which will help principals of firms ensure that their engineers are both competent and peak performers.”

Bill Thornton Corporate Consultant Cives Corporation

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The Newsletter of the Structural Engineering Institute of ASCE

Structural Columns

Make your plans to attend the Structures 2013 Congress in Pittsburgh, PA, May 2-4, 2013. The focus of this highly regarded specialty conference is Bridging Your Passion with Your Profession.

The ASCE/SEI Structures Congress is your annual opportunity to broaden your technical knowledge, sharpen your business skills, deepen your understanding of cutting-edge research, and network with your peers and colleagues. In addition to eleven technical tracks, the congress will offer Pre-conference seminars.

Pre-conference Seminars Design of Bridges for Accelerated Bridge Construction The workshop will include information on the current state of ABC in the United States including the most common technologies and details that are in use. The focus will be in the design development process as it relates to ABC projects. Discussion will include the design of precast concrete deck panels, modular superstructure elements, substructures, foundations, and full scale bridge installations using Self Propelled Modular Transporters and lateral sliding techniques. The basis of the workshop will be a manual entitled Engineering Design, Fabrication, and Erection of

New Concrete Transmission Pole Structures Manual Now Available Prestressed Concrete Transmission Pole Structures: Recommended Practice for Design and Installation is a complete engineering reference on static-cast and spun-cast prestressed concrete poles for electric distribution and transmission power lines.

This Manual of Practice contains critical information for all aspects of a prestressed concrete pole project, including applications, concepts, materials, connections, foundations, manufacture, installation, and testing. This manual was prepared by SEI’s Task Committee on Concrete Transmission Pole Structures of the Committee of Electrical Transmission Structures.

Topics in this manual include: considerations for the design process; specifications for concrete and steel materials; design choices, criteria, and methodology; quality assurance during manufacture; assembly and erection; and inspection, maintenance, and repair.

Appendixes offer sample documents showing specifications for the purchase of static and spun cast prestressed concrete poles.

Utility engineers responsible for the design of transmission and distribution lines, pole manufacturers, power line constructors, and inspectors will find this manual to be useful for basic training and as an ongoing reference.

To order, visit the ASCE Bookstore website: www.asce.org/bookstore.

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Prefabricated Bridge Elements and Systems, that is under development by the Federal Highway Administration.

New Essentials for Your Sustainability Tool Kit This interactive seminar will provide attendees with a hands-on overview of the new list of “essentials” that every engineer should have in their Sustainability Tool Kit. The seminar will focus on: how to decipher and use Life Cycle Assessment on a project; exploring how disaster resilience can help you avoid unsustainable rebuilding both before and after failures caused by natural disasters; how to recognize and design around thermal bridges; what green infrastructure means, and what resources are available to lower the environmental impact of infrastructure projects.

Attendees will participate in interactive exercises designed to support the information that was shared in presentations. By attending the seminar, participants will gain a functional understanding of the tools and strategies presented and be better prepared to apply this knowledge on their next project.

For more information and to see the matrix of Technical Sessions, visit the Congress website: http://content.asce.org/conferences/structures2013/.

SEI Endowment Fund The SEI Endowment Fund keeps SEI at the forefront of serving structural engineers by providing continuing education, advancement of pre-standards, and outreach to students.

Gifts are fully deductible for income tax purposes. Please consider the SEI Endowment Fund as part of your year-end giving. To make an individual, corporate or commemorative gift, visit the SEI Endowment Page on the SEI Website at www.asce.org/SEI.

SEI’s Efforts Continue on S.E. Licensure As a reminder for those who may not follow the topic closely, SEI adopted Policy Statement 101 on Structural Engineering Licensure in 2010. However, the Institute continues to work towards its goals for S.E. licensure. In fact, the following is one of the stated desired outcome of its 2011 strategic initiatives: Enact legislation for structural engineering licensure requirements in all jurisdictions by creating a plan for working proactively with local engineers, stakeholders, and engineering organizations, and developing resources such as statistical data, white papers, case studies, etc. to support the efforts of local structural engineers.

Visit the SEI Website at www.asce.org/SEI to learn more about SEI’s Strategic Vision and Strategic Initiatives and SEI’s efforts on S.E. licensure.

December 2012

The 2012 SEI Local Leadership Conference was held October 12-13 in Salt Lake City with representatives from 25 local SEI groups and the SEI Local Activities Executive Committee participating. In addition to the general session meeting, the event included a technical tour of the LDS Tabernacle Seismic Retrofit and Conference Center, a technical presentation on UDOT Accelerated Bridge Construction, and a Post-Disaster Safety Evaluations (PDSE) Workshop sponsored by SEI and the ASCE Committee on Critical Infrastructure, in cooperation with the California Emergency Management Agency (CalEMA) and the Applied Technology Council (ATC). Participants learned more about SEI programs and local best practices, earned 10.0 PDHs, and 25 were registered as CalEMA Safety Assessment Program (SAP) Evaluators.

To get involved with the events and activities of your local SEI Chapter or Structural Technical Group (STG) http://content.seinstitute.org/committees/local.html.

Local groups offer a variety of opportunities for professional development, student and community outreach, mentoring, scholarships, networking, and technical tours.

SEI Young Professional Scholarship Bridges 2013 Calendar to attend Structures 2013 Congress $10 each when you buy 2 or more

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

ASCE Calendar2013_FinalArt.indd 1

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SEI/ASCE Student Structural Design Competition Call For Applications

SEI sponsors a structural design competition for student teams.

Innovative projects demonstrating excellence in structural engineering are invited for submission. A written submission will be judged and three finalist teams will be invited to present their designs at the Structures 2013 Congress in Pittsburgh, PA, May 2 – 4, 2013. The finalist teams will be judged on an oral presentation during the conference and 1st, 2nd, and 3rd place awards will be determined as a combination of the written and oral presentations. Awards include cash prizes and complimentary registration to the conference for the three finalist teams (up to three student registrations and one full registration for the faculty advisor).

ELIGIBILITY: Any team of undergraduate civil engineering students is eligible to submit a structural design. Projects from classes and other university assignments may be used (e.g. capstone design classes, senior assignments, class design projects).

Projects solely performed as an employee of a design firm for STRUCTURE magazine

which no university credit was obtained are not eligible. A maximum of one design from each university will be allowed.

Any structural engineering design will be accepted, including but not limited to new building and bridge design, and existing building and bridge retrofit.

Competition deadline is January 15, 2013.

For more information about the Student Structural Design Competition and how to enter, visit the SEI website: www.asce.org/SEI.

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December 2012

The Newsletter of the Structural Engineering Institute of ASCE

SEI is committed to the future of structural engineering and offers a scholarship for Young Professionals (age 35 and under) to attend Structures Congress. Many young professionals have found Structures Congress to be a career-changing and energizing experience, opening up networking opportunities and expanding horizons to new and emerging trends. Visit the SEI Website at www.asce.org/SEI for more information and to apply.

A must-have for bridge lovers, the ASCE Bridges 2013 calendar continues to delight and inform! Bridges 2013 offers spectacular images of bridges from the United States and around the world. This BRIDGES calendar celebrates the unique blend of technology and art that is the hallmark of great engineering.

Each month features a different bridge accompanied by an explanation of its technical or historical significance and an inset highlighting a unique characteristic. With brilliant photographic detail, this collection of distinguished bridges celebrates the form, function, and style central to excellence in civil engineering. To view bridge photos, visit www.asce.org/calendar.

Advertise Your Business. Advertise your company name and logo on the Bridges 2013 calendar, printed on upgraded, premium paper stock that displays your message professionally all year long. For more information, visit www.asce.org/calendar.

2013

Apply by January 14, 2013

Structural Columns

Local Activities

The Newsletter of the Council of American Structural Engineers

Tool No. 6-2: Scope of Work for Engaging Sub-consultants Tool 6-2, Scope of Work for Engaging Subconsultants, provides structural engineers with sample scopes of work that cover the key scope issues to consider when hiring a sub-consultant. The tool will be used when a structural engineer is asked by the prime consultant or owner to provide input on sub-consultant selection and scope of work, or when the structural engineer is required to retain the sub-consultant directly.

When the structural engineer retains these services directly, it is recommended that CASE Contract #3 or #10 be used.

CASE Contract #3 provides an agreement for retaining the services of an Architect or other Consulting Design Professional (CDP). CASE Contract #10 provides a sample agreement that may be used when the Structural Engineer of Record (SER) is required to contract directly with the Geotechnical Engineer of Record (GER).

You can purchase all CASE products at www.booksforengineers.com.

Great Turnout, Programming at CASE Convocation CASE held its biannual convocation alongside ACEC’s Fall Conference on Monday, October 15th in Boca Raton, FL. CASE kicked off the day with a session lead by Randy Lewis of the XL Group on managing project risk, highlighting that communication is key, but what defines “communication” is fluid over generational lines. Stephen Cox of GHD had his participants break into small groups to identify, evaluate, and

manage project risk. He left them with tools that will aid firm leaders in training their project managers. Finally, CASE was thrilled to have Eric Sohn, of Wiss, Janney, Elstener Associates, Inc. dazzle them with his work in repairing the Washington Monument and National Cathedral, both in Washington, DC, including pictures of the presenter himself dangling from the tops of these structures.

CASE would like to thank all of its presenters for a great convocation.

CASE is on LinkedIn LinkedIn is a great virtual resource for networking, education, and now, connecting with CASE. Join the CASE LinkedIn Group today! www.linkedin.com.

You can follow ACEC Coalitions on Twitter – @ACECCoalitions.

Get an ACEC Designation

CASE in Point

Set the Standard for Management and Leadership Excellence Executives at engineering firms develop a unique skill set that transcends the technical practice of engineering – the skill and adroitness of running an engineering business. Experience managing programs, projects, personnel and budgets will drive a firm’s profitability. These vital skills are not learned in technical programs, but are acquired through company programs, from industry groups, such as ACEC, and via direct business practice experience.

ACEC, as the industry leader in best business practices, recognizes that business acumen is critical to success, but difficult to quantify for a client. ACEC is proud to offer its designation program – a way for our members to codify their experience and use it to market their services.

ACEC’s Professional Designation programs are designed to recognize a singular attainment of relevant experience and education by worthy professionals in the engineering industry.

ACEC’s Professional Designation programs set the national standards for business management and leadership excellence STRUCTURE magazine

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in the engineering industry. ACEC offers three professional designations, and each has a different set of criteria for eligibility to capture an individual’s level of experience and education.

The Management Engineer – MgtEng SM – is designed for professionals working in project, program, or business management roles within an engineering firm or related to the engineering industry.

The Executive Engineer – ExecEng SM – is designed for leaders in the industry. Executive Engineers have attained the highest level of achievement in industry leadership and experience.

The Management Professional – MgtPro SM – is designed for non-P.E. managers working in non-profits or government agencies related to the engineering industry or business managers within engineering firms.

Contact Kerri McGovern at kmcgovern@acec.org for more information or visit www.acec.org/education/designations/.

December 2012

This year, the Coalitions awarded its very first Distinguished Service Award. The Coalition Distinguished Service Award is intended to recognize the accomplishments of an individual that has contributed significantly and/or has sustained volunteer performance within ACEC’s Coalitions.

The inaugural award went to Blake N. Murillo, P.E., LEED AP, CEO and chairman of the board of Psomas, a consulting engineering firm located in Los Angeles, CA. Mr. Murillo not only serves as Senior Vice Chair of The American Council of Engineering Companies (www.acec.org), but was instrumental in the development and launch of the Land Development Coalition, serving as its first Chair.

The nominees were all outstanding individuals who have demonstrated a sustained commitment to the Coalitions over multiple years.

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

Red Flag for “Duty to Defend” Language in Your Contracts There is no law requiring a consultant to defend its client against third party lawsuits. It can only happen if someone inserts the language into a contract. As such, it is generally not covered by liability insurance through the liability insurance exclusion of an errors and omissions policy. If this language appears in a contract courts have interpreted it to mean the consultant must defend its client…which means paying legal fees for ongoing litigation. Advice from insurance professionals is that any duty to defend language is uninsurable and should be struck from the contract. Contract language can also be drafted that explicitly excludes the duty to defend.

Twenty-One New Contracts The General Conditions of the Construction Contract (C-700) is the backbone of contract documents and is the product of long deliberation and careful thinking by EJCDC. In many ways, it is similar to AIA’s General Conditions but is directed toward a project where engineering is the primary design discipline. EJCDC is close to finishing the latest version of its STRUCTURE magazine

construction series. The last one was 2007. The whole series contains 21 documents including bond forms, bidding procedures, payment forms, change orders, field orders and more.

Among other things, the updated documents will have clearer language on who is responsible for site safety. They should be available early next year. Watch this space for exactly when.

Electronic Document Retention Options Engineers tend to keep information. How do you balance the cost and burden of storage with the need to retain documents?

Some firms do a random audit to insure retention complies with any laws. Statutes of Repose offer a rule of thumb, but sometimes even these may not be relied on. There are online products that will retain documents for you. Some firms keep all documents forever. Some firms do a yearly review of projects that have ended that year to determine how to close the file. A company should expect all employees to fully comply with any published records retention policy. Public agencies often demand ownership of documents created by consultants. Engineers should try to restrict granting ownership to public agencies and, if not possible, limit it to final deliverables.

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CASE is a part of the American Council of Engineering Companies

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

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

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

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

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

Blake Murillo Receives the Coalitions Distinguished Service Award at ACEC’S Fall Conference

CASE in Point

Donate to the CASE Scholarship Fund!

Structural Forum

opinions on topics of current importance to structural engineers

Developing the Next Generation of Structural Engineers Part 4: Industry Reform/Conclusions Glenn R. Bell, P.E., S.E., SECB This is the final article of a four-part series on the opportunities and challenges we face in developing the next generation of structural engineers. It is based on the author’s keynote address at the SEI Structures Congress in March 2012. This article reviews some of the ongoing reform efforts by ASCE and others, and closes with a call for action by all in the structural engineering community.

Thought Leadership to Date Many organizations and individuals have provided excellent thought leadership about the future of engineering, in general, and our ability to compete in a global marketplace.

The National Academy of Engineering and various academic leaders have focused heavily on educational reform. Some of their ideas are quite far-reaching.

SEI’s parent organization, ASCE, has shown outstanding leadership on behalf of the broad civil engineering community. ASCE Policy Statement 465 sets forth a certain body of knowledge for licensure that would be met by a combination of a baccalaureate degree in civil engineering, a master’s degree or 30 graduate or professional practice credits, and appropriate practical experience.

In June 2006, ASCE held a summit of leaders in civil engineering and related disciplines on the future of civil engineering. The result was ASCE Vision 2025, published in 2007. Vision 2025 sets forth an inspiring view of our future.

Finally, ASCE’s Committee on Academic Prerequisites for Professional Practice (CAP3) has been studying proposed changes in the way civil engineering is taught and learned.

The Body of Knowledge (BOK) committee published its second-edition report (known as BOK2) in 2008. It is a monumental work, laying out 24 desired “outcomes,” or areas of competence, that a well-trained civil engineer should possess. The report offers a roadmap for achieving those proficiencies through undergraduate training, graduate training, and professional experience. But the thinking stops at attainment of licensure.

Industry Leadership We are not alone in the structural engineering community. We have the strength and resources of all of ASCE behind us. ASCE is working on many of these issues through its CAP3 and

associated subcommittees. SEI has partners in the other ASCE Institutes. Beyond ASCE, there are many other organizations worldwide with which we need to build coalitions.

Most importantly, our engineering community needs to do a better job of talking to the rest of the world; by that I mean more public outlets within the structural engineering community in the US and outside our country’s borders. My colleagues around the globe tell me that they observe that most US structural engineers are relatively sheltered in their view of the world.

I am pleased to see that the SEI Board of Governors has taken on a number of strategic initiatives that are exactly in line with the need to develop a new breed of structural engineer.

Our Profession at a Crossroads Our profession today is at a critical crossroads.

If we fail to act boldly now, our work will become trivialized and we will get run over by the steamrollers of automation and global competition. Our current position of strength in engineering in the United States, and our fundamental culture of promoting leadership, innovation, and entrepreneurship, position us well to take on the grand challenges of the world in the 21st century. We have a wonderful opportunity to contribute to global society in a profound way. The future for structural engineers offers us the chance to attract and retain our best and brightest into a profession where they can be challenged, continuously learn and develop, and shape the future of the world. To succeed, we must overcome our fears and inertia and lead change now.

This is not a challenge that will be met only by the leaders and committees of our engineering societies. This is not a challenge only for the young professionals among us. This is not a challenge only for academic leaders.

Each one of us must get involved.

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, C3Ink, or the STRUCTURE magazine Editorial Board.

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Professors and Academic Leaders I encourage professors and academic leaders to work and advocate for academic reform along the lines of the developing ASCE Body of Knowledge. Develop rubrics specific to structural engineering. Fight to change the evaluation and reward systems in academia to assure a proper focus on teaching and professional development. Work with industry to improve the integration and overlap of teaching, research, and practice. Spend some sabbaticals in industry practice. Invite more practitioners into your classrooms. Leverage the value of effective industry-academic advisory boards.

Engineering Managers and Leaders If you are a project team leader or company CEO, the most important thing you can do is invest in your staff. Not only do we have to make financial investments in training and professional development programs, we have to enhance the power of experiential learning. We must commit to restore the waning art of mentoring. More creative, confident, value-producing engineers will return your investment in them with productivity and loyalty to your organization.

Young Professionals and Students To young professionals and students I say, “This is your future.” Take charge of it. No one is going to do it for you. Ensure you always have a long-range professional development plan and work toward it. Expect to invest your own time in self-study. Read prodigiously and broadly, not only in subjects related to your practice, but in other areas that will help you become a better global leader. And invest yourself at an early age in professional society work.

Closing As we stand at our profession’s crossroads, let us resolve to choose the path of greatness. If we work together with passion, energy, focus, and unyielding determination, we can take this great profession to even greater heights, and in the process change the world.▪ Glenn R. Bell, P.E., S.E., SECB (GRBell@sgh.com), is the Chief Executive Officer at Simpson Gumpertz & Heger in Waltham, Massachusetts.