STRUCTURE magazine | December 2017

EXCELLENCE IN STRUCTURAL ENGINEERING

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

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LeMessurier Calls on Tekla Structural Designer for Complex Projects Interoperability and Time Saving Tools

Tekla Structural Designer was developed specifically to maximize collaboration with other project parties, including technicians, fabricators and architects. Its unique functionality enables engineers to integrate the physical design model seamlessly with Tekla Structures or Autodesk Revit, and to round-trip without compromising vital design data.

“We’re able to import geometry from Revit, design in Tekla Structural Designer and export that information for import back into Revit. If an architect makes geometry updates or changes a slab edge, we’ll send those changes back into Tekla Structural Designer, rerun the analysis and design, and push updated design information back into Revit.”

Tekla Structural Design at Work: The Hub on Causeway

For over 55 years, LeMessurier has provided structural engineering services to architects, owners, contractors, developers and artists. Led by the example of legendary structural engineer and founder William LeMessurier, LeMessurier provides the expertise for some of the world’s most elegant and sophisticated designs while remaining true to the enduring laws of science and engineering.

Known for pushing the envelope of the latest technologies and even inventing new ones, LeMessurier engineers solutions responsive to their clients’ visions and reflective of their experience.

An early adopter of technology to improve their designs and workflow, LeMessurier put its own talent to work in the eighties to develop a software solution that did not exist commercially at the time. Their early application adopted the concept of Building Information Modeling (BIM) long before it emerged decades later.

While LeMessurier’s proprietary tool had evolved over three decades into a powerhouse of capability, the decision to evaluate commercial structural design tools was predicated on the looming effort required to modernize its software to leverage emerging platforms, support normalized data structure integration and keep up with code changes.

After a lengthy and thorough comparison of commercial tools that would “fill the shoes” and stack up to the company’s proprietary tool, LeMessurier chose Tekla Structural Designer for its rich capabilities that addressed all of their workflow needs. According to Derek Barnes, Associate at LeMessurier, ” Tekla Structural Designer offered the most features and the best integration of all the products we tested. They also offered us the ability to work closely with their development group to ensure we were getting the most out of the software.”

One Model for Structural Analysis & Design

From Schematic Design through Construction Documents, Tekla Structural Designer allows LeMessurier engineers to work from one single model for structural analysis and design, improving efficiency, workflow, and ultimately saving time. “Our engineers are working more efficiently because they don’t need to switch between multiple software packages for concrete and steel design. Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product,” said Barnes.

LeMessurier engineers use Tekla Structural Designer to create physical, information-rich models that contain the intelligence they need to automate the design of significant portions of their structures and efficiently manage project changes.

TRANSFORMING THE WAY THE WORLD WORKS

“Tekla Structural Designer has streamlined our design process,” said Craig Blanchet, P.E., Vice President of LeMessurier. “Because some of our engineers are no longer doubling as software developers, it allows us to focus their talents on leveraging the features of the software to our advantage. Had we not chosen to adopt Tekla Structural Designer, we would have needed to bring on new staff to update and maintain our in-house software. So Tekla Structural Designer is not just saving us time on projects, it is also saving us overhead.

Efficient, Accurate Loading and Analysis

Tekla Structural Designer automatically generates an underlying and highly sophisticated analytical model from the physical model, allowing LeMessurier engineers to focus more on design than on analytical model management. Regardless of a model’s size or complexity, Tekla Structural Designer’s analytical engine accurately computes forces and displacements for use in design and the assessment of building performance.

“Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product.”

Positioning a large scale mixed-use development next to an active arena, a below grade parking garage, and an interstate highway, and bridging it over two active subway tunnels makes planning, phasing and engineering paramount. Currently under construction, The Hub on Causeway Project will be the final piece in the puzzle that is the site of the original Boston Garden.

Despite being new to the software, LeMessurier decided to use Tekla Structural Designer for significant portions of the project. “Relying on a new program for such a big project was obviously a risk for us, but with the potential for time savings and other efficiencies, we jumped right in with Tekla Structural Designer. It forced us to get familiar the software very quickly.”

“Tekla Structural Designer allowed us to design the bulk of Phase 1 in a single model,” said Barnes. The project incorporates both concrete flat slabs and composite concrete and steel floor framing. “Tekla Structural Designer has the ability to calculate effective widths based on the physical model which is a big time saver,” said Barnes. “On this project, the integration with Revit, along with the composite steel design features enabled us to work more efficiently. Adding the ability to do concrete design in the same model was a bonus because we had both construction types in the same building.”

“Tekla Structural Designer helped this project run more efficiently, and in the end it was a positive experience,” said Blanchet.

“Tekla Structural Designer gives us multiple analysis sets to pull from, which gives us lots of control. Most programs don’t have the capability to do FE and grillage chase-down. For the design of beam supported concrete slabs, Tekla Structural Designer allows us to separate the slab stiffness from the beam stiffness, so if we choose to we can design the beams without considering the influence of the slab. In the same model we can use a separate analysis set to review the floor system with the beams and slab engaged,” said Barnes.

Barnes also shared similar benefits with concrete column design. “Tekla Structural Designer does grillage take-downs floor-by-floor, finds the reactions and applies them to the next floor. This allows us to view column results both for the 3-dimensional effects of the structure as a whole and from the more traditional floor-by-floor load take-down point of view.

Doing both has always required significant manual intervention, but Tekla Structural Designer puts it all in one place.” “We reduce the possibility for human error because with Tekla Structural Designer less user input is required,” said Barnes. “Tekla Structural Designer automatically computes many of the design parameters, such as column unbraced lengths. The assumptions made by the software are typically correct, but we can easily review and override them when necessary.”

“Tekla Structural Designer provided the best fit for our workflow compared to other commercially available software.”

Want to Evaluate Tekla Structural Designer? tekla.com/TryTekla

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CONTENTS Cover Feature

30 EXCELLENCE IN STRUCTURAL ENGINEERING AWARDS Announced at NCSEA’s 25th Annual Structural Engineering Summit in Washington, D.C., this year’s program saw a record number of entries.

Per Carrie Johnson, 2017 Awards Committee Chair, “The quality of the projects was outstanding.” This article provides overviews of all of the winning projects.

Courtesy of Blake Marvin

Features 22 GRANT STREET PIER DRILLED SHAFT REPAIR

Columns and Departments

By Benny I. Lujan, P.E. The city's fourth tallest building required an unconventional foundation to offset Colorado's Front Range soil and bedrock conditions. These soil types were classified as "difficult at best."

42 Structural Challenges for Space Architecture

By Valentina Sumini, Ph.D. and

EDITORIAL

By Dominic A. Webber, P.E., S.E. and Howard A. “Hod” Wells, P.E. Part of Vancouver's Waterfront Park redevelopment project, the Pier extends almost 110 feet over the Columbia River. During construction of the drilled piers, serious problems developed resulting in extensive repairs.

26 UNCONVENTIONAL FOUNDATION STABILIZES DENVER SKYSCRAPER

OUTSIDE THE BOX

Caitlin T. Mueller, Ph.D.

7 Building a Resilient Future David J. Odeh, P.E., S.E., SECB

INSIGHTS

47 Adhesive Anchor Systems STRUCTURAL DESIGN

10 Northwest Medical Office Building

By Marlo Sedki and David Martin

By Christopher Gamache, P.E.

CASE BUSINESS PRACTICES

49 Reframing Engineering

By Anthony H. LoCicero III, P.E.

CONSTRUCTION ISSUES

12 How to Standardize the Installation of Helical Piles

By Gary L. Seider, P.E.

STRUCTURAL FORUM

58 Women Designed to Move an Industry

By Kristin Killgore, P.E., S.E.

38 AN OASIS FOR CHILDREN IN THE RIVER CITY

STRUCTURAL PERFORMANCE

14 Feeling at Home in the Clouds

By Nathan C. Dumas, P.E, Jeffrey S. Davis, P.E. SECB, and Donna E. Adams, P.E. SECB Demolition of portions of an existing structure, design of a new 15-story building, and planning for future vertical and horizontal expansion resulted in unique foundations and excavation for Richmond’s new Children’s Hospital.

By Trevor Haskett, P.Eng. and Andy Smith, P.Eng.

HISTORIC STRUCTURES

18 Eads Bridge at St. Louis

By Frank Griggs, Jr., D.Eng., P.E.

IN EVERY ISSUE 8 Advertiser Index 50 Resource Guide – Earth Retention 52 NCSEA News 54 SEI Structural Columns 56 CASE in Point

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

STRUCTURE magazine

5

December 2017

Editorial

new trends, new techniques and current industry issues

Building a Resilient Future David J. Odeh, P.E., S.E., SECB, F.SEI, F.ASCE

T

he extraordinary devastation left by storms, earthquakes, and wildfires in 2017 dominated the news media for months. Many of our colleagues around the globe were directly affected by these events but still rose to the challenge by volunteering as emergency responders or by joining teams to study and report on lessons learned. Whether impacted or not, structural engineers keep the public safe from disasters every day.

We need to build on our shared strengths to achieve our common goal of an infrastructure that is both affordable and resilient, and solutions that can minimize the impact of disasters on people, property, and the economy. has grown tremendously through generous First, we need to update and improve our donations from individuals and companies. design standards continuously. Standards This endeavor is now able to fund impormust represent the combined wisdom of tant efforts such as the new SEI program for the global structural engineering comyounger member involvement on standards munity. While some may complain about committees, and scholarship opportunities for the increasing complexity and breadth of students and young professionals to travel to design standards, we cannot ignore the latest and attend the annual Structures Congress. knowledge yielded by research and studies of If you are passionate about the future of the disaster impacts. Our imperative is to create profession, please consider giving a year-end standards that respond to the day-to-day gift to the Futures Fund! Learn more and give needs of practicing professionals, but also at www.asce.org/SEIFuturesFund. allow them to apply the latest concepts accuThe common thread of this strategy is that rately. The complexity of predicting response we all must work together to make it happen. to extreme events shines a light on the need SEI, NCSEA, and CASE recently signed a new for performance-based design standards that Memorandum of Understanding to strengthen advance the state of the practice and leverage our bonds and promote more collaboration the creativity and judgment of the structural between these three interdependent organizaengineer. Investment in these performancetions. Right now, you are reading one of our most based standards is critical to balancing cost SEI leaders sign a collaboration agreement with successful collaborations: STRUCTURE magaand risk safely and effectively.

CASE and NCSEA. zine. Other activities include SEI’s Business and Second, we must improve the way that we Professional Activities Division, the Structural Engineering Licensure disseminate new knowledge to the practice. Continuing education Coalition, and the Structural Engineering Certification Board – all of requirements for licensure currently focus on attendance and durawhich have joint board membership from the three major organization of coursework, with little emphasis on content. We should turn tions. What other new initiatives can we create together this model on its head and create priorities for lifelong learning that that will help us to achieve our shared goals? With a emphasize the best practices of the design community. New models for combined effort, we can build a resilient future for our education, such as intensive guided online courses, offer the chance to profession and a resilient infrastructure for our society.▪ provide peer-reviewed and timely information to engineers that they can confidently use in their practice. Combining such coursework Encourage students and young professionals with incentives for engineers to achieve certification and advanced licensure credentials could create new opportunities for professional to get involved in SEI – www.asce.org/SEI. development and better ways to keep up with the latest information.

Students: Apply by January 5, 2018, for the Third and most important, we must continuously attract and retain the best and brightest in our profession to ensure its long-term viability. new scholarship to Structures Congress at To be the innovators and leaders that protect the public from disasters, we need a broad spectrum of well-educated young engineers to www.asce.org/SEI-Students. keep us moving forward. Our educational system should not focus on just teaching the “tried and true” methods of yesterday, but the David J. Odeh is Chair of the SEI Futures Fund Board, and a Past critical thinking skills that young engineers will need to create the President of the Structural Engineering Institute of ASCE. He is a innovations of tomorrow. To help fund these critical efforts to attract Principal at Odeh Engineers, Inc. of Providence, Rhode Island, and and retain younger members, we created the Structural Engineering teaches on the adjunct faculty at Brown University.

Institute Futures Fund in 2014. Since that time, the Futures Fund STRUCTURE magazine

7

December 2017

ADVERTISER INDEX

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Erratum In the November 2017 article, Preserving Navy History with Design-Build, the name of the Architect of Record was inadvertently misspelled. The correct name is Matsunaga & Associates, Inc. The authors apologize for the error.

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

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December 2017

Greg Schindler, P.E., S.E. KPFF Consulting Engineers, Seattle, WA Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA

December 2017, Volume 24, Number 12 ISSN 1536-4283. Publications Agreement No. 40675118.

STRUCTURE® is owned and published by the National Council of Structural Engineers Associations with a known office of publication of 645 N. Michigan Ave, Suite 540, Chicago, Illinois 60611. Structure is published in cooperation with CASE and SEI monthly. The publication is distributed as a benefit of membership to members of NCSEA, CASE and SEI; the non-member subscription rate is $65/yr domestic; $35/yr student; $90/yr Canada; $60/yr Canadian student; $125/yr foreign; $90/yr foreign student. Application to Mail at Periodical Postage Prices is Pending at Chicago and at additional Mailing offices.

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Structural DeSign design issues for structural engineers

T

hroughout the ages, humanity has been warned – do not build on weak foundations. Even the “Good Book” uses a parable of a home built on sand to emphasize the importance of a solid foundation in life.

However, the wise sages of the past did not live in today’s fast-paced world. As hard as most members of today’s society try to be good stewards of the land, some things get pushed to the wayside... literally.

As our superhighways were under construction following President Eisenhower’s Highway Act, all manner of materials were generated as waste. This waste was often pushed to the side in a landfill.

Moreover, being adjacent to a major interstate, that landfill, in turn, became prime real estate.

That is the background of Atlanta’s Northwest Medical Office Building (MOB) and parking deck. This state-of-the-art structure was built in the 1970s on fill containing organic materials

Northwest Medical Office Building

By Marlo Sedki and David Martin

and construction debris such as stone, brick, and concrete. The location was originally a dumping area for waste generated from constructing I-75 adjacent to the building site.

With that background, on to the problems – and there were many. The first floor of the parking deck, the service drive, and the terrace area between the parking lot and the MOB were built to bear on construction fill. The MOB was constructed using post-tensioned slab bearing on caissons. Over the years, the first-floor parking

deck began to settle unevenly, requiring continuous remedial work. It was jokingly described as having a roller coaster effect. The soils throughout the site were in deplorable condition, and the cavities under the slab-on-grade were far worse than expected.

With the major problems for the parking deck identified, the owner faced the fact that the MOB desperately needed to update the facility if they planned to keep their existing tenants and attract new ones. The lobbies needed updating, the building needed to be re-skinned, and the settlement needed to be corrected on the sidewalks and surrounding driveways.

If this facility was to be saved, it was time for some desperate measures. The design team of Sedki & Russ Structural Engineers, MSTSD Architects, and New South Construction was tasked to provide structural solutions.

The first problem addressed was that the slab-ongrade at the parking deck was not structural and rested on top of the construction fill. Through the years, the slab kept settling and the owner kept adding more concrete to level it. This, in turn, required additional ramps and stairs which may have compounded the issue by adding more weight and increasing the potential for further settlement. Consequently, the only solution left was to remove the slab and replace it with a structural slab bearing on a deep foundation.

The challenge was for the design team to develop a system that was economical, practical, and environmentally friendly. Several repair systems were considered, including auger cast piles, driven piles, and caissons. However, the cost of these methods was over budget and required removal of contaminated soil, exposing methane gas or causing excessive vibration to the structural frame during

Marlo Sedki is a former assistant industrial editor for AT&T. She has also done freelance feature writing and is the marketing manager for Sedki & Russ Structural Engineers, Inc. David Martin who served as the Senior Project Manager with New South Construction Company, was responsible for overseeing the construction on the N.W. Medical Center project.

View of the newly completed NW Medical MOB. Courtesy of Bob Hughes w/Brilliance Photography.

10 December 2017

The kickers holding the side form of the slab during the pouring of concrete, and also showing the holes where the helical piers are located. Courtesy of MSTSD Architects.

removal. The system that met all the requirements was to use helical piers with an allowable capacity of 40 kips and place a two-way reinforced concrete slab on top. The pier spacing varied to limit the total load on any pier to the 40-kip capacity. The slab at the parking area was designed for a live load of 40 psf and the driveway to meet HSS15 highway loading.

During the removal of the existing slab-ongrade, the clearances in the garage created two significant issues. First, there was not enough head height to use traditional equipment for installing the new piers and, second, there was not enough room to use traditional equipment for the slab removal. Thanks to the creativity of New South Construction Company, a small bobcat was rigged for the pier installation and a plow was welded to a bobcat to help break and remove the slab.

During the installation of the piers, an additional issue emerged – very few piers were able to be placed in their designated locations due to obstacles in the soil below. Thus, the structural slab was continually in redesign to accommodate the new pier locations and to avoid any delay in the construction schedule.

The second challenge that the design team faced on the NW Medical project involved the terrace level between the two buildings and the driveway connecting the buildings and the parking deck. The same issue with

Grade between columns and the overpour at each column base below the PT Slab.

Courtesy of New South Construction.

obstacles was encountered, but headroom was not a problem and removal of the slab was not complicated.

In this location, however, new storm and sanitary lines had to be placed deep below the slab. These lines cannot tolerate settlement and thus had to be supported by structures bearing on a deep foundation as well. Helical piers were installed with a continuous concrete pad on which these lines rested. Additionally, transformer pads and dumpster pads could not be removed and replaced; therefore, supports were added in these areas before the placement of the new slab.

At the existing terrace level at both buildings, the original structure was slab, beams, and girders. However, a few years after its initial occupancy, this slab was removed and replaced with an 8-inch post-tensioned (PT) flat plate.

At a few locations such as the perimeter girders, stair slabs and the mechanical floor of the original construction remained. The new slab had been attached to those existing elements.

The post-tensioned slab was performing well, but due to the low floor-to-floor height, the owner elected to remove the PT-slab and place a new, reinforced concrete slab bearing on helical piers and the existing caissons, to provide an additional 16 inches of headroom.

The slab at the terrace level had settled, in some areas close to ten feet. This complicated the

A view illustrating how much the existing grade has settled. Courtesy of MSTSD Architects.

STRUCTURE magazine

removal of the post-tensioned slab, where the slightest error could result in catastrophe. For instance, cutting the wrong cable could result in a slab failure, or projectiles of spalled concrete or actual tendons could cut through walls.

The next challenge encountered at the terrace level was that the owners wanted the slab to be removed in the areas the previous renovation had avoided. In these areas, the girders-on-grade were cantilevered beyond the caissons below and supporting four-story columns. To remove these girders would cause the columns to lose their support completely. Sedki & Russ Structural Engineers detailed a steel support outside the building, bearing on the existing caissons and on helical piers having a new concrete cap.

This system would support the columns once the slab and girder were removed. The steel frame was encased in concrete and placed below finish grade.

Working on a project of this nature with so many unknowns, challenges are many and require quick decision-making and resolution, like redesigning the slab and beams or changes to the architectural design. In the end, the challenges were met, and the structure was successfully completed.

For a project like this, one is reminded of Longfellow’s lines, “Ah, to build, to build!

That is the noblest art of all the arts.”▪

The steel frame before it was in place, designed by Sedki & Russ Engineers to pick up the four-story columns. Courtesy of MSTSD Architects.

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December 2017

ConstruCtion issues discussion of construction issues and techniques

H

elical piles are subject to special inspections, similar to deep foundations, but engineers have several choices when looking for the best way to install them. Currently, there are no standards for the installation of helical piles. However, helical piles should be installed and inspected in accordance with all relevant requirements listed in the governing building code.

Through the International Society of Helical Foundations program, engineers can obtain certification that allows them to provide inspection services. However, the engineering community would collectively benefit from the establishment of universal standards for installing helical piles to reduce the likelihood of building damage caused by pile failure. Pile failure may occur due to incorrect installation techniques or other unforeseen circumstances.

Standards establish qualitative and quantitative values and are integral to the field of civil engineering. An accepted standard for helical pile installation gives the engineer additional assurance that the pile will perform as intended by the design.

Adopting this kind of measure may help mitigate risks such as structural damage resulting from liquefaction.

Liquefaction occurs when a seismic event causes shaking, leading to soils acting more like liquids than solids. If the soil supporting the foundation of a building liquefies, the foundation is much more susceptible to extensive settlement, uniform and differential. These settlements may lead to significant structural damage, and in some cases, collapse.

How to Standardize the Installation of Helical Piles

By Gary L. Seider, P.E.

Gary L. Seider is an Engineering Manager of CHANCE® Civil and Utility Helical Products.

Obstacles to Standardization The primary obstacle to overcome when addressing standardization is – not surprisingly – cost.

For example, it is generally accepted that the risk of the occurrence of liquefaction and conditions like it are too low to justify the costs of prevention.

Many believe that adhering to certain helical pile installation standards would no doubt increase construction costs.

However, the increase in construction costs can occur if contractors are not supplied with standardized piles. Sites that hire contractors unaware of pile standards could see mounting change orders, overdesigns that camouflage pile issues, or piles being installed too deep into a foundation. These problems, and others, can send construction into cost overruns.

While a decrease in liquefaction risk is indeed a benefit, some may debate how valuable installation standards would be. Fortunately, specific tests and analysis can determine whether a residential area is

Crane operators begin installing a helical pile shaft into the site’s foundation. Soil type and a pile’s size and shape factor into installation resistance.

at a high risk for foundation issues. A soil analysis, for instance, can reveal that certain types of soil, such as clay-free deposits of sand and silt, are the most susceptible to damage, with that risk intensifying in areas that are most prone to seismic activity.

Piles are a long-term investment, with cracks in foundations and other issues possibly taking years to manifest. Cost concerns are a more immediate concern, ones that can be addressed by making standardized piles a priority early in the construction process.

Standardization Metrics Contractors and site managers looking for properly calibrated piles should put the following strategies in place.

1) Update torque indicators – Installation requires a torque indicator that directly measures torque. This requirement ensures that torque readings are accurate. Moreover, because torque is used to estimate the ultimate capacity of the helical pile, such a standard would result in more reliable estimates.

2) Work with a qualified installation inspector – Working with someone who provides inspection services is one option.

However, even if the project is not subject to special inspection, it is still important to use a third party to make sure everything is as it should be. The International Society of Helical Foundations (ISHF) provides certifications for any inspector interested in being credentialed.

Inspectors assess the following variables to make sure a pile is up to standards:

12 December 2017

• Pile location and attachment method • The pile shaft’s minimum size and type • Pile’s minimum depth • Required load-per-pile value and other safety factors • Minimum installation torque based on accepted torque correlation factors listed in ICC-ES AC358 or ESR-2794 Certified parties are trained in the proper means and methods of installation, including risk assessment. Hiring an inspector educated on installation standards and equipment specs can keep the building process as efficient as possible.

3) Complete installation logs – The installation contractor should complete installation logs for the specific project. Installation logs contain information obtained during drilling such as torque, depth, and more.

As-built plans for the construction project should include any logs created during construction. This ensures that each pile is installed to the minimum torque/capacity and depth in accordance with project construction documents.

4) Rate of penetration – The majority of helix plates have a 3-inch pitch. The helix pitch is the distance between the leading edge and trailing edge of the helix

plate. When the helical pile is installed, it should advance into the ground approximately one pitch per revolution.

The acceptable margin is between 2½ and 3 inches per revolution. If the helical pile is not advancing at the proper pace of one pitch per revolution, it is acting more like an auger and disturbing the soil, which can directly contribute to the risk of pile failure.

Helical piles are designed to be displacement piles that advance through the soil with minimal disturbance, so note that torque correlation to capacity is not valid for a helical pile that does not advance normally. Helical piles can stop advancing if they encounter obstructions or very dense soil. When that happens, use a load test to determine the capacity of the pile accurately.

Standardizing the practice of helical pile installation is an integral part of mitigating the risk of problems like liquefaction.

Minimum material standards help ensure helical piles manufactured by different companies meet basic requirements for strength, weldability, toughness, and corrosion protection. Most helical pile manufacturing standards require the use of structural-grade steel for both the helix plates and the central

A helical pile shaft nears the end of its site installation. Pile shafts use minimal equipment and quick install times to provide secure foundations with less disruption than other options.

shaft. In much the same way, standardizing pile installation ensures installation is done properly.▪

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Structural Performance performance issues relative to extreme events

M

odern engineering tools and techniques enable structural engineers to continually redefine the limits of possibility. Nowhere is this more evident than in supertall buildings, where controlling wind-induced sway has become a critical aspect of project success.

The use of tuned mass damping systems has become a mainstay in attaining this control, in large part because each custom-designed system can be tuned to match the as-built characteristics of the building. They also provide a much more efficient solution than adding more mass or stiffness.

One recent example is the Shanghai Tower which, when it opened in 2014, became China’s tallest building and the second tallest building in the world. Even though the design of the 2,073-foot (632-meter) tower was optimized to reduce wind effects, the developer also chose to include a tuned mass damper (TMD) to reduce accelerations further and eliminate any feeling of structural movement. The resulting 1,100-ton system is the world’s largest eddy current TMD, discussed in more detail below.

Feeling at Home in the Clouds

By Trevor Haskett, P.Eng. and Andy Smith, P.Eng.

Trevor Haskett is the Senior Technical Director and Principal and leads RWDI’s team that works on structural vibration and tuned mass damper projects.

Problems As buildings are designed to be taller and more slender, they also are designed to be lighter and, relatively speaking, not as stiff. As a result, wind tends to cause much more flexure in these structures than in shorter, more squat buildings. To put it another way, the taller and more slender a modern building is, the more lively it is likely to be.

If left uncontrolled, excessive wind-induced building movement can cause various problems.

For example, large oscillatory displacements may make it necessary to reduce the speed of elevators during strong wind events. Displacements can also damage more brittle secondary elements such

as partitions, glazing, and the façade. Beyond any noticeable harm caused by a single large displacement, the accumulation of many cycles of amplitude can also cause fatigue failures.

Wind-induced movement can cause two other significant problems that affect a building’s usability. The first, audible creaking and groaning, seems to be especially prevalent where there is the greatest amount of relative motion between building parts as the building deflects. Often occurring on the lower levels, these potentially loud noises can make even a new building sound like a rickety old ship.

The most common problem, however, is the perception of movement that comes from the acceleration of the building as it sways back and forth. This is an issue that designers must address to ensure occupants remain comfortable even as the building moves. Although their homes can be literally in the clouds, people want to feel like they are on solid ground.

The inherently low structural damping in modern high-rise structures is a significant factor in managing occupant perceptions of movement.

The challenge is made even more problematic because of the relatively high uncertainty in assuming an appropriate level of inherent structural damping.

Challenges Adding movement criteria to the building design process increases the complexity of coming up with a good design. Fortunately, a structure’s dynamic characteristics can be estimated using the structural engineer’s computer model through a back-and-forth approach.

Many years ago, wind tunnel testing on an instrumented flexure was used principally to come up with foundation loads to determine the building’s overturning moment. However,

Andy Smith is the Engineering Leader of mechanical design for RWDI’s tuned mass damper projects.

Wind tunnel testing of the tall and slender 432 Park Avenue played a key role in evaluating the effects of vortex shedding created by its very uniform shape.

14 December 2017

Located within blocks of New York’s Central Park, 432 Park Avenue is more than twice the height of any of its nearby neighbors, leaving the upper portion of the structure fully exposed to the wind.

in more recent times, it was realized that the test data already being collected could also be used to estimate accelerations. This is now a routine activity.

For many current projects, the structural engineer begins by laying out the structural system to resist the gravity loads vertically and the wind loads laterally – and sometimes earthquake loads, as applicable – based on the selected primary structural materials (which is to say concrete and steel) and their configuration. This initial layout includes the lion’s share of what determines the building’s mass and stiffness.

This typically leads to an initial design based on a finite element model. The output from that model provides the dynamic characteristics of the building. Using that information coupled with wind tunnel data and analysis, the structural engineer is given a set of equivalent distributed static wind loads, based on the specific dynamic characteristics of the building and local meteorological climate.

This data can be put back into the same finite element model to confirm the adequacy of all structural members for the ultimate design.

Another check is conducted to ensure serviceability requirements are met during regularly occurring wind events.

All of the secondary members in buildings – everything from the glazing to the interior drywall and partitions – also contribute to building stiffness in minor ways, but these additions are not taken into consideration by the structural engineer, making the findings a bit conservative with regard to safety. Conventional thinking is that, as far as loads are concerned, more stiffness is almost always better.

Researchers have gleaned a significant amount of data on building performance characteristics, including damping ratios as a function of height and building type. These characteristics help to estimate structural

Two 660-ton opposed pendulum tuned mass dampers (TMDs), located near the top of the tower on the east and west sides of the core, provide supplemental damping for 432 Park Avenue.

performance. However, data is less prevalent for a supertall building’s inherent damping except to know that it is going to be very low.

In fact, the trend is that the typical amount of inherent damping is decreasing in new buildings as designs get leaner and more efficient, which brings us back to the observation that new buildings tend to be more lively. So, what are the implications when you know you cannot expect much damping from the building structure, but you are going to reach for the sky anyway?

Setting Limits How people feel about perceived movement and acceleration is highly subjective, so trying to define how much acceleration is too much yields only a fuzzy threshold.

However, there is a consensus that building occupancy type and anticipated return periods (or mean recurrence intervals) factor into setting a reasonable range of such limits.

Residential buildings have tighter limits on movement than other buildings, such as offices or commercial space. People in a condominium or apartment are going to be much more particular about how comfortable their residence is, on an aroundthe-clock-basis, than the same people would be in an office building. When acceleration guidelines for buildings are set, they also include an anticipated recurrence interval.

For example, larger accelerations that the majority of people would sense might be acceptable if they occur only infrequently, such as once a year or once every 10 years.

For weekly or monthly occurrences, however, the acceleration would be limited to

a much smaller value that ideally should be imperceptible to most people.

Traditionally, the industry has found that keeping residential building accelerations below about 18 milli-g for the worst storm expected only once every 10 years heads off most complaints. For office towers, accelerations of 25 milli-g might be acceptable. That means, essentially, that weather patterns could be expected to produce building swaying that would be noticeable and uncomfortable on the uppermost floors – causing chandeliers or draperies to move, or doors to swing on their hinges – once in 10 years.

Although 10-year acceleration targets have proven to be useful guideposts for designers over the years, here again the liveliness of newer buildings comes into play. Whereas, for older buildings, most plots of peak acceleration versus average time between occurrences typically had roughly the same slope, such plots for lighter, more flexible structures can have much flatter slopes. In these cases, it is not unusual for the 1-month and 1-year accelerations to govern. Further complicating the picture, the cyclic frequency of the building’s sway also affects occupant sensitivity. One level of acceleration that is acceptable on a very slow swaying, lowfrequency building may be objectionable on a higher frequency building.

This type of limit is reflected in the International Standards Organization’s standard ISO 10137: 2007, which provides acceleration criteria for residential and office structures at the 1-year return period across a range of frequencies. By aligning these limits with logarithmic graphs showing a building’s total peak accelerations plotted against the typical mean time between

NOTE – The accelerations experienced in a swaying building are most frequently expressed in thousandths of a G, the constant acceleration due to gravity, which is 9.81 meters per second squared. Applying the metric prefix milli yields the term milli-g.

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these occurrences, when and to what extent structural performance improvements are necessary can be determined. (This is a very simplistic description of the process, as several key assumptions go into the actual plot generation.)

Resisting Wind Loads The process of determining appropriate wind loads for tall and supertall buildings is quite complex. It involves historical weather data, usually from a nearby airport, which may require interpretation to be more site-specific.

Further extrapolation is necessary because weather data typically are collected close to the ground. The most critical wind speeds for a supertall building occur several hundred yards above the ground surface.

When determining how much a high-rise building will oscillate in the wind, the controlling factor is damping. At one extreme, there is little or no resistance to oscillation and the building continues to sway back and forth indefinitely, unable to dissipate the energy that the wind transferred into it. The opposite behavior, known as critical damping, results in no oscillation at all, and the building simply returns to its at-rest position after any perturbation, in the shortest interval of time. Neither of these is the case in real-world tall buildings.

The amount of damping inherent in a tall or supertall building is impossible to predict with any certainty. In fact, inherent damping is the most uncertain structural variable. It, therefore, requires significant judgment and should be viewed together with other material behavior design assumptions. Observed damping ratios for scores of buildings confirm that the damping is very low, and trends lower with every story closer to the sky. A range of inherent damping, typically from 1% to 2% of critical, is used in the design.

It turns out that the challenge of designing a building to stay below specific acceleration targets is very sensitive to the as-built damping level in the structure, and that is not known until the building has been constructed.

By way of example, if the assumption is 1.5%, it could easily be as high as 1.8% or as low as 1.2%. That sounds like an insignificant absolute difference, but it can make a 20% relative difference in the acceleration levels. Instead of the target 18 milli-g at a 10-year return period, it could end up being as high as 22 milli-g or as low as 14.5 millig, which is quite a wide range of response.

So, even though it is understood that the damping levels are low, the uncertainty in predicting real-world accelerations is still very significant.

Staying in Control This essential uncertainty concerning a structure’s damping characteristics can be greatly reduced with the addition of a tuned mass damping system. Engineered to operate passively in response to building movement, these types of damping systems exert forces opposing the building’s movement.

A TMD system should be as high up in the building as possible to be most effective. Most damping systems are designed to be adjusted, or tuned, once the building is substantially complete to accommodate the uncertainty of the structure’s as-built sway frequency(ies).

These TMDs consist primarily of a large mass, either liquid or solid, some means of dissipating the energy, and an appropriate system of attachment to the structure. The mass is specifically sized for each building according to the demand for improved performance; for supertall buildings, this is typically several hundred tons.

Liquid dampers use a mass of moving water in various configurations, including tuned liquid column dampers and tuned sloshing dampers. Although water dampers are usually somewhat less expensive than their solid counterparts, they take more space and are not as high performance per ton of installed mass.

Solid TMDs usually consist of multiple steel plates that are transported to the TMD location and assembled in place. The mass can be suspended by cables, much like a simple pendulum, or supported by other low friction means. Other configurations in common use include a dual-stage pendulum, which requires only about half the vertical clearance, and an arrangement of opposing pendulums.

In the latter case, one mass held aloft by struts

is linked to a second mass supported pendulum-style. This configuration can be used to create a long period set up in the relatively low headspace.

After the building is structurally complete, the TMD must undergo a tuning and commissioning phase. With the TMD locked out, the final as-built frequency of the building must be measured. The TMD is then tuned to best interact with that frequency and release it to do its work of steadying the tower, keeping even its highest occupants feeling as stable and sure-footed as if they were on solid ground.

TMDs at Work Selecting a specific type of TMD for a given building is accomplished through an implementation assessment. Primary considerations include the force required and space constraints, although other factors also come into play.

432 Park Avenue This slender, taller-than-all-neighbors residential tower in the heart of New York City offered an extreme challenge in managing wind effects.

Despite extensive attempts to reduce wind effects through reshaping, which led to including wind floors at several levels of the structure, the need for a supplemental damping system was a foregone conclusion. The building’s long period, together with the required large movement of the damper mass, eliminated sloshing damper technology from consideration. To meet the space constraints, two 660-ton opposedpendulum TMDs, one on each side of the building core, were ultimately used.

Shanghai Tower This tower was one of those rare cases with accelerations below the ISO standards to

Visitors to the observation area at the top of the Shanghai Tower can see the slow movements of a 70-ton jade sculpture mounted atop the tower’s pendulum-like tuned mass damper.

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Supported by the crown structure of the tower, the simple pendulum of the tuned mass damper at the top of the Shanghai Tower is suspended over an eddy current damping system by 12 cables, three on each of four corners.

Conclusion Supplemental damping technology is something that should be in every tall building designer’s toolbox. Especially when used in conjunction with shaping techniques that reduce wind effects, TMDs can make living and working in high-rise buildings every bit as comfortable as more traditional, shorter buildings. And that allows people to relax and enjoy the spectacular view.▪

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begin with, but the owner wanted them to be even lower – and was prepared to spend significantly more to achieve that. The goal was to give the impression that the structure simply does not move.

That led to the installation of a 1,100ton TMD, which the owner also wanted to display as an architectural feature visible within the observation levels. Also, a unique form of damping was added to the system. Typically, TMDs have sizeable viscous damping devices (VDDs), similar to shock absorbers, which are used to drain energy from the TMD and also control its response in high winds. For the Shanghai Tower, a large array of rare earth magnets was attached to the pendulum, and a layer of copper plate was fixed to the floor. As the TMD travels back and forth, electrical eddy currents are passively formed that create a force that resists the motion of the pendulum mass relative to the tower. This system replaced the eight large, inclined VDDs that otherwise would have been used, making the installation much more aesthetically pleasing. This installation is the world’s largest eddy current TMD.

MAKING NEW AND EXISTING STRUCTURES STRONGER AND LAST LONGER

Historic structures significant structures of the past

T

he Eads Bridge was, perhaps, the best-known bridge of the 19th century after the Brooklyn Bridge. A bridge across the Mississippi River had been projected as early as 1839 when Charles Ellet Jr. (STRUCTURE, October 2006) proposed a 1,200-foot span suspension bridge. John A. Roebling (STRUCTURE, November 2006) also proposed a hybrid bridge, with a pier at midriver, a short time later. The St. Louis and Illinois Bridge Company was formed in 1855, but nothing was done until February 1864 when the State of Missouri granted a charter. James B. Eads was named Chief Engineer on March 23, 1867, after he submitted preliminary plans in early March.

By May 1867, Eads decided to build his bridge as a three-span arch bridge over the Mississippi River with the arches made of steel. To assist him, the Company named Jacob Hays Linville (STRUCTURE, July 2007) of the Pennsylvania Railroad and Keystone Bridge Company as a consulting engineer.

The design was based on a bridge across the Rhine River at Koblenz (Coblenz), Prussia.

Eads first design had a central span of 515 feet and two flanking arches of 497 feet, with a minimum clearance of 50 feet above high water. He recruited Henry Flad, Charles Pfeifer, and W. Milnor Roberts as his assistant engineers. When Eads made his design known to the public in 1867, the St. Louis Democrat wrote, “What a triumph for St. Louis, the noblest river, the most glorious bridge, and the finest engineer in the world. His arch ribs were to be made of steel in the form of steel tubes in straight pieces

Eads Bridge at St. Louis

By Frank Griggs, Jr., Dist.

M.ASCE, D.Eng., P.E., P.L.S.

connected together to form a polygon of 800 sides.” Upper and lower arches were to be connected by trussing, and the arches were to be fixed at the ends making them statically indeterminate.

The easterly approach in Illinois consisted of a long iron viaduct with masonry arches flanking the end spans of his arches. Railroad tracks were on the lower deck, and roadways and pedestrian walkways on the upper deck.

In the meantime, Lucius Boomer was also proposing a bridge in the same area under the name of the Illinois and St. Louis Bridge Company. He had Simeon Post work out a design consisting of six wrought iron Post Trusses with two spans of 368 feet and four of 264 feet. To promote his plan, Boomer called a convention of engineers to look over all plans but with special attention to his plan. The Convention favored Boomer’s plan and recommended in their Report spans of no more than 350 feet. Eads went on the offensive and responded with “If there were no engineering precedent for 500-feet (stet) spans, can it be possible that our knowledge of the science of engineering is so limited as not to teach us whether such plans are safe and practicable? Must we admit that because a thing never has been done, it never can be, when our knowledge and judgment assure us that it is entirely practicable? This shallow reasoning would have defeated the laying of the Atlantic Cable, the spanning of the Menai Straits, the conversion of Harlem Lake into a garden, and left the terrors of the Eddystone without their warning light. The Rhine and the sea would still be alternately claiming dominion over one-half of the territory of a powerful kingdom, if this miserable argument had been suffered to prevail against men who knew, without ‘an engineering precedent,’ that the river could be controlled,

Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges having restored many 19 th Century cast and wrought iron bridges. He is a Professor Emeritus of Civil Engineering at Merrimack College in N. Andover, Massachusetts and is currently an independent consulting engineer. Dr. Griggs can be reached at fgriggsjr@twc.com.

Eads Bridge with St. Louis Arch in the background. Courtesy of HAER.

18 December 2017

East pier caisson.

and a curb put upon the ocean itself.” The two bridge companies later merged.

When Linville saw the preliminary design, he wrote, “The bridge if built upon these plans will not stand up; it will not carry its own weight… I cannot consent to imperil my reputation by appearing to encourage or approve its adoption. I deem it entirely unsafe and impracticable, as well as in fault in the qualities of durability.” Linville later, as Chief Engineer of the Keystone Bridge Company, would be in charge of building the superstructure of the bridge.

When making a case for his bridge, Eads told his investors that he could build the bridge for $3,000,000 and have it opened for traffic within 3 years. He had never built a bridge before, especially a bridge that was going to have a great deal of steel in it. Steel was used for many years, but not in bridge building or major building construction. Wrought iron by this time had generally replaced cast iron and wood in bridge construction, with much of the progress attributable to Linville and the Keystone Bridge Company plus the Phoenix Bridge Company, the Detroit Bridge Company, and others.

His first construction task was to place foundations for his two river piers and two abutments. Given his knowledge of the

shifting sands of the the arches in bars of 9 feet length, and of such Mississippi River bed, form that ten of them shall fill the circumferhe insisted his founda- ence of a 9-inch lap-welded tube one-eighth tions rested on bedrock inch thick, in the manner that the staves of and looked at various a barrel fill the hoops. This would virtually methods to accomplish form a steel tube 9 inches in diameter and of this. Bedrock on the west 6 inches bore, the steel being about 1½ inches abutment was near the thick, and would be much less expensive than surface, so it presented if the tube were rolled or drawn in one piece. no problems. His east The manufacture of the steel in such small and west piers, however, bars will ensure a more uniform quality in the would have to be sunk to metal, and in the tube each bar will be supdepths of 95 feet and 86 ported against deflection in every direction. feet below the river sur- The tubes will be retained in their positions face. His east abutment by an effective system of bracing, which will would have to reach a sustain the voussoirs or pieces against which depth of 110 feet. the tubes are butted throughout the arch...

Eads learned about The tubing in which the steel bars will be pneumatic caissons on enclosed will effectually protect the latter from a trip to Europe. Even the weather.” though no one had ever His tubes were made of steel staves covered used them at the depths with a steel casing similar to wooden barrels. required at St. Louis, he The length of staves varied, as did the thickdecided they were the ness. Eads had to compromise his original only possible means to specifications. He had significant problems reach bedrock. While in getting the quality steel he wanted for placing the foundations, the staves as well as for the couplings that 14 men were lost, mostly connected the tubes. Once the staves were on the west pier, to what encased, he had to mill the ends to ensure was to become known as full bearing from one set of staves to the next. caisson’s disease or the bends. By May 1870, all of the foundations were in place, and Eads could begin erecting his superstructure.

His original arches were doubled steel tubes, top and bottom, with diameters of nine inches. He later changed this to single tubes with 12-inch diameters, and even later to diameters of 18 inches. He also changed the vertical spacing between the top and bottom tubes from 8 to 12 feet, as well as having the lower arch come up tangent to the deck chords of the railroad tracks. The spans were revised to 520 feet on the center span and 502 feet on the flanking spans.

Transversely, the two center arches would be 13 feet 9½ inches apart and the outer arches 15 feet 1¾ inches off the center arches.

He knew the uniqueness of his use of steel and in 1867 wrote: “To ensure a uniform quality and high grade of steel at the lowest prices, and at the same time avail myself of the advantages of the tubular form of construction, I propose to have the steel rolled for Coupling and pin to connect diagonals to tubes.

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He also had to cut-in the threads to receive the couplings. He retained Theodore Cooper (STRUCTURE, April 2011) to handle the fabrication of the staves and couplings.

Cooper was later in charge of the erection of the tubes.

Since falsework could not be placed in the river, Eads developed a way to build the superstructure by cantilever methods. He, Flad, and the Keystone Bridge Company erected wooden towers on the piers and abutments and ran links down to the arch segments to support them before the closing of the arches. He had major problems in fitting his final arch segments (the equivalent to a keystone) and had to modify them by making them adjustable.

The bridge was opened to pedestrians on May 24, 1874. The first train crossed on June 9, and it was test loaded on July 2.

It was formally dedicated on July 4, 1874, with a grand celebration. Eads, in his speech, stated, in part: “The love of praise is, I believe, common to all men, and whether it be a frailty or a virtue, I plead no exemption from its fascination. The wish to merit the good opinion of our fellow-citizens, and especially of those whom we respect and esteem, is a laudable stimulus to effort…Yon graceful forms of stone and steel, which prompt this wonderful display, stand forth, not as the result of one man’s talents, but as the crystallized thought of many, aye, very many minds, and as the enduring evidence of the toil of very many hands; therefore I would forfeit my self-respect and be unworthy of these pleasing evidences of your good will, if on this or any other occasion, I should appropriate to myself more than a humble share of the great compliment you are paying to those who created the bridge. It is of itself a high privilege to feel that I stand before you as the representative of a community of earnest men, whose combined labor, brains, and wealth, have built up this monument of usefulness for their fellowmen. For them and in their names I thank you for this magnificent evidence of your approbation…

Everything which prudence, judgment and the present state of science could suggest to me and my assistants has been carefully observed, in its design and construction.

Every computation involving its safety has been made by different individuals thoroughly competent to make them, and they have been carefully revised time and again, and verified and re-examined until the possibility of error nowhere exists. When its first deep pier reached the bedrock 110 feet below the surface, those who knew nothing about the care

that was used in ensuring success, expressed their gladness that my mind was relieved by the occasion. I felt no relief, however, for I knew that it must go there safely…Yesterday friends expressed to me their pleasure at the thought that my mind was relieved after testing the bridge, but I felt no relief because I had felt no anxiety on the subject. I could get no more engines or I should have imposed still greater loads upon it; for if I knew that thrice fourteen locomotives were to be put on each span and the densest crowd of humanity which was ever packed together stood upon the upper roadway above them, I should feel no anxiety whatever for the safety of the structure, for I know it is capable of bearing up vastly more than that, and I trust that those who use it hereafter will put the same implicit faith in its strength that I have. Its ability to sustain its burden depends upon laws which are as immutable as the Creator Himself, and when these laws are properly applied in estimating its strength, there need be no fear of the result…

This is a feature in its construction possessed by no other similar work in the world, and it justifies me in saying that this bridge will endure as long as it is useful to man. He, alone, will destroy it, for the earthquakes may rock its piers and shake its elastic arches in vain…

Let us not today forget these faithful toilers, no matter how humble they were, who contributed their lives in the erection of

the structure, whose completion you signalize so notably…”

The bridge ended up costing $6,536,729, twice as much as Eads originally estimated.

With construction starting in 1867 and opening on July 4, 1874, the bridge had taken seven years to build, also more than twice as long as Eads estimated. W. W. W. Evans stated in 1869, “Captain Eads is a bold man to design an arched bridge with spans of 500 feet and will deserve credit for his boldness and nerve if successful, but I doubt if he will deserve or receive much credit for spending two or three times the amount the circumstances called for.”

Eads resigned as Chief Engineer on July 28, 1874, and Theodore Cooper was named as his successor. After the bridge opened, it did not carry as much railroad traffic as anticipated, as the railroads needed a terminal in St. Louis and the ferry operators cut their rates for the use of rail car ferries across the river. The Bridge Company went into bankruptcy on April 19, 1875, as it could not pay the interest on its bonds. So, while an engineering success, it was a financial failure. It stands today, however, almost a century and a half after its erection still carrying traffic across the Mississippi River. It is an icon to 19th-century engineering. It was placed on the National Register of Historic Places in 1966 and was named a National Historic Civil Engineering Landmark in 1971.▪

Tubes showing packing, thickness, casing, and threaded ends.

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Grant Street Pier D S R

By Dominic A. Webber, P.E., S.E. and Howard A. “Hod” Wells, P.E., LEED AP, ENV SP

Grand Street Pier rendering.

C

urrently under construction in Vancouver, Washington, Waterfront Park is part of a 32-acre mixed-use urban redevelopment project on a site that is being reclaimed, having previously been used as a paper mill. Developed by the City of Vancouver, the 7.3-acre Waterfront Park features open lawns, picnic areas, viewpoints, and shoreline paths along nearly 2,500 feet of Columbia River waterfront. When completed in the Spring of 2018, the Grant Street Pier will become the focal point of the new park.

The Grant Street Pier is a concrete, cable-stayed structure projecting almost 110 feet over the Columbia River. The 2½-inch diameter steel cables are anchored at the end of the pier and at two concrete backstays. They are supported at the center by a 75-foot-tall steel pipe mast.

The pier deck is three-foot-thick post-tensioned concrete that tapers to only six inches thick at the outside edges. A concrete abutment supports the pier deck, the mast, and one of the two backstays. The second mast backstay is anchored into an independent mat footing supported on 11 micropiles. Sliding of the backstay anchor footing is restrained by three grade-beams attached to the abutment slab.

The concrete abutment wall is two feet thick at the base and tapers up to six-and-a-half feet thick at the top. The wall taper was a desired aesthetic for the pier base just above the waterline. Seven 18-inch-thick counterfort walls, orthogonal to the abutment wall, anchor the pier slab to the mat foundation. The mat foundation is a six-foot-thick concrete slab supported by twenty-seven five-foot-diameter drilled shafts.

Serious problems developed during the construction of the drilled piers, resulting in extensive and expensive repairs.

Foundation Design The overall abutment foundation layout was highly constrained by the site – the Columbia River on the south edge, a property line boundary to the north, and a large sewer pipe that runs through the center of the footprint that could not be realigned for this project.

One requirement of the permit was that the foundation could not be located waterward of the biological ordinary-high-water mark (OHWM). Thus, the alignment of the OHWM dictated that the STRUCTURE magazine

foundation orientation be non-perpendicular to the primary axis of the pier span over the water. This resulted in a skewed axis of the mat slab foundation and drilled shafts relative to the main axis of the abutment walls and pier, resulting in a substantial torsion on the foundation mat slab in addition to the expected flexure and shear.

The underlying soil consisted of 25 feet of loose fill over ten feet of sand and then gravel and cobbles to depth. The loose fill contained sand, organics, some silt, wood debris, and large pieces of concrete debris. The concrete debris was not discovered by the geotechnical borings. The fill material and sand are subject to liquefaction during a seismic event. Because of the topography of the underlying gravels and the riverbank, these materials are also subject to lateral spread toward the river, with an estimated lateral spread of up to 15 feet.

Because the excavation for the foundation was below the river level, a sheet pile cofferdam was needed to facilitate the pier foundation construction. The portion of the cofferdam that encroached on the OHWM was required to be removed; however, the landside portion of the cofferdam could remain. It was decided to utilize this portion of the cofferdam to resist demands due to liquefaction. As such, 36 tieback anchors were needed along the back face of the sheet pile cofferdam to resisting the primary demand of lateral spread. The tops of the sheet piles were cut off five feet below grade; since this was below the top of the pier slab, the abutment and drilled shafts were required to resist the portion of liquefaction demand not supported by the sheet pile wall.

The bottom of the mat slab foundation is 14 feet below the OHWM and approximately 15 feet above the gravel and cobble layer. The result is that 15 feet of soil below the mat foundation has the potential to liquefy due to a seismic event. This resulted in the drilled piers being designed as cantilever elements when subject to seismic demands.

The seismic overturning, when combined with the overturning of the cantilever pier, created axial loads of almost 2,000-kips compression and bending moments of 45,000 kip-ft in the forward most drilled shafts, and tension loads of 610-kips and bending moments of 42,000 kip-ft in the rearmost drilled shafts based on allowable load combinations. These demands and the geotechnical conditions required drilled

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shafts with up to 70 feet of embedment into the gravel, resulting in a total shaft length of 90 feet.

Construction The shafts were installed with oscillating sectional casing using a Bauer BG40 track-mounted drill rig. Material inside of the casing was excavated using a digging bucket, a cleanout bucket, a flight auger, and a rock auger depending on the material encountered. During the drilling process, a water head was maintained above the river elevation to prevent heaving.

After the shafts were drilled and cleaned, the reinforcing cage was lowered into the shaft and concrete was placed using a tremie pipe. As the concrete level rose, the casing was retracted.

The drilling occurred from a bench CSL Data: compromised drilled shaft on the left, sound drilled shaft on the right. elevation 10 feet above the top of the drilled pier. The contractor excavated for the cofferdam tremie seal these shafts happened to be the deepest and most heavily loaded and mat foundation after the drilled shafts were installed. This shafts on the pier abutment. difference in elevation was taken up by a weak concrete mixture that could easily be chipped away from the shaft dowels once the Testing excavation for the mat slab was complete. During the retraction of the casing of the two final shafts, some construction problems Each drilled shaft was evaluated using Crosshole Sonic Logging were encountered. The issues for both shafts were similar – as the (CSL) in accordance with ASTM D 6760. The tests are performed last segments of casing were withdrawn, the top of concrete fell by a transmitter probe that converts electrical pulses into ultrasonic about 2.5 feet below the bottom of the top collar leaving a portion waves. A receiver probe measures the ultrasonic waves. The probes of shaft uncased. The soil around the top collar settled as the con- are sent down parallel steel pipes that are cast in the shafts. There tractor continued to place concrete in the shaft. One shaft took 14 are a total of five pipes for CSL per drilled shaft. The CSL data more yards of concrete than the estimated shaft volume, while the indicated possible flaws in the top 8 feet of one shaft and the top other shaft took on 20 more yards than expected. Coincidentally, 3 feet in the other shaft.

Although core samples taken from the center of shafts did not reveal flaws, the concern was about the cover around the reinforcing cage. Thus, a request was made for the top four feet of the shafts to be exposed for visual observation, where moderate-sized chunks of concrete from the loose fill were found embedded in the sides of the shaft. The contractor was then required to probe the six inches of concrete cover using a rotor hammer drill with the longest available drill bits. On more than one occasion, while drilling vertically into the cover, the concrete offered little to no resistance. Also, the air from the drill would periodically force water out of holes on the opposite sides of the shaft. This process revealed weak, porous concrete cover of the shafts.

Drilled Shaft Repair The design team had little confidence that these shafts had adequate corrosion protection for the reinforcing steel, and were thus considered unreliable for long-term performance. Consequently, the capacity of these drilled shafts had to be replaced. The solution preferred by the contractor was to drive H-piles locally around the compromised shafts to replace the missing capacity. However, even with as many H-piles as could physically fit within the mat foundation geometry, this solution was not practical because of the stiffness incompatibility between the new H-piles and the adjacent drilled shafts. Variations of

Installation of drilled shaft.

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Structural components of foundation abutment.

the repair option to excavate, remove the concrete cover, and re-cast concrete were attempted, but ultimately were abandoned because of worker safety and constructability concerns. One option dismissed early on in the process was revisited – to core the center of each drilled shaft and insert a concrete-filled steel pipe through the region of the compromised shaft. This was made possible only by an ability to core a large diameter hole in the center of the existing shaft using a rock auger without interfering with the existing reinforcing cage.

Ultimately, a 36-inch diameter auger was used to core the center of each shaft a minimum of 12 feet below the location where it was believed, based on drilling and CSL data, each existing shaft was compromised. This allowed a 33-inch diameter x 1.25-inch thick steel pipe to be placed inside the core and extend 42 inches into the mat slab.

Overall, a 28-foot length of pipe was needed for Altered structural conditions at the top of the concrete-filled steel pipe repair. each shaft. This allowed the concrete-filled pipe to act over the compromised portion of the drilled shaft and ultimately transfer loads back to the existing shaft below.

Lessons Learned The analytical model used in the original evaluation was revised using the structural properties of the repaired shaft, with particular During shaft excavation and repair, the engineers and the contractor attention given to the boundary conditions at the top of the pipe. suspected that the excavations for the drilled shafts encountered a Although there was an approximate 7% shift of axial demand local subsurface area fill that contained sizeable concrete rubble and to the adjacent uncompromised shafts, the concrete-filled pipe large void areas. When these voids were exposed by the removal of recovered most of the stiffness of the original shaft to make the the temporary casing, the concrete flowed into the voids. compromised shafts effective. The analysis also showed that it was The contractor’s sequence called for the drilled shafts to be conessential to develop as much bending capacity at the top of the pipe structed before excavation for the cofferdam tremie seal or mat slab. as possible to minimize the redistribution effect. Consequently, When the tremie seal and mat slab excavation occurred, the contractor this bending resistance was achieved considering three compo- pulled out broken concrete slabs in the vicinity of the problem shafts, nents – the addition of a spirally tied reinforcing cage to help validating the suspicions. engage the concrete core of the pipe, the embedded portion of the Drilled shaft repairs are expensive and time-consuming. The repair pipe extension above the bottom layer of slab reinforcement, and for the drilled shafts cost approximately 120% of the original drilled headed studs added around the pipe perimeter to directly engage shaft installation. When projects are constrained by short in-water the pipe wall in bending. Additional detailing was needed in the work periods, schedule delays can be particularly troublesome. For mat slab to support the high local demands from the pipe flexure waterfront structures with deep foundations in areas of historic waterat the top. This bending moment at the bottom of the pipe was front development, the risk associated with unknown and variable redistributed to the shaft by the socketed 12-foot embed length, subsurface conditions is high. This risk can be partially mitigated by where the shear demand to engage bending was limited to the performing more exploratory geotechnical borings, or limited-depth shear capacity of the shaft reinforcement. This determined the potholing, than would be typical for an upland or undeveloped site. effective embedment of the pipe in the competent portion of the The pre-design geotechnical borings performed at the site indicated original drilled shaft below. fill and woody debris but did not indicate concrete. It is possible that STRUCTURE magazine

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Foundation under construction: a repaired shaft (left) and bottom layer of reinforcement in mat slab (right).

a more comprehensive geotechnical exploration program would have alerted the designers to the concrete debris field, and provisions could have been established within the design documents (such as requiring permanent casing within the fill zone at the concrete debris field) to lessen the risk. However, designing to account for all unknowns can be expensive as well. The balance of risk associated with deep foundations is often the trickiest part of waterfront project development, and owners may not be fully aware of the risks.

The construction of the Grant Street Pier foundation provides a case study in the potential risk associated with drilled-shaft deep foundations.▪

Dominic A. Webber, P.E., S.E,. is a Structural Engineer with BergerABAM, Inc. He is involved with building and marine structure design as well as design/build projects with geotechnical construction firms. Dominic can be reached at dominic.webber@ abam.com.

Howard A. “Hod” Wells, P.E., LEED AP, ENV SP, is a Senior Project Manager with BergerABAM, Inc. He is involved with transportation and marine structure design in the Pacific Northwest.

Howard can be reached at howard.wells@abam.com.

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BIM Integration

Unconventional Foundation Stabilizes Denver Skyscraper

By Benny I. Lujan, P.E.

I North face of iconic 1144 Fifteenth at topping-out ceremony in July 2017.

n the heart of Denver’s Theatre District, the city’s fourth tallest building is steadily rising from the ground. The 42-story, 603-foot-high LEED Pre-Certified Gold building, called 1144 Fifteenth, is the first Class A office tower built in the downtown area in more than 30 years. The soaring glass structure is an emblem to the city’s future.

The building will rise above the rest – literally and figuratively. However, securing its strong foundation presented a long list of challenges.

First and foremost was the ground itself. There is a reason the buildings of Denver’s skyline are primarily low compared to the skylines of other U.S. cities. As compared to New York, that is underlain by strong bedrock like schist, the comparatively soft rock (intermediate geomaterial) prevalent throughout Colorado’s Front Range cannot withstand the loads induced by very tall buildings, particularly with a dense office use. Moreover, soil and bedrock conditions can vary significantly within any individual foundation area.

Secondly, land is scarce in Denver and the 1144 Fifteenth site – in a prime location – is a tight one, bound by downtown streets on three sides with the equally iconic Four Seasons Hotel on the fourth. The architectural team needed as wide a base as possible, so the foundation was designed “property line to property line.”

Needless to say, when Martin/Martin Consulting Engineers tapped CTL|Thompson’s geotechnical engineers Marc Cleveland, David Glater, and Benny I. Lujan, it was with a pretty sizable task: design a building foundation for a very visible and very heavily-loaded skyscraper in a tight building envelope and sitting on the area’s sedimentary bedrock.

The team had to dig deep, but ultimately they came up with a way to get the difficult job done – create a foundation design using a shoring system that allowed lateral loads from the drilled pier/tie-beam core foundation to be transferred directly to undisturbed bedrock.

Problem Solving

A downhole view of the reinforcing cage and concrete placement for a drilled pier used in the foundation for 1144 Fifteenth Street.

During soil testing, the CTL team identified that bedrock was at the elevation of the building’s lower level. The shallow bedrock could have presented an additional challenge, but CTL, along with Martin/Martin engineers, used it to their advantage. Instead of excavating the bedrock to support a conventional drilled pier and thick monolithic reinforced concrete mat core, the team designed a system using a tie-beam connecting and supported by drilled piers. This system would rely on undisturbed bedrock around the perimeter lateral face of the tie-beam system to transmit a portion of the lateral load to the bedrock. The process would require the piers to be poured 7 feet below basement grade and the installation of vertical concrete and steel beam soldier

Reinforcing steel cages form the drilled piers used in the foundation for 1144 Fifteenth Street. Due to the length of the piers, the reinforcing steel was built in two sections that were spliced together. Here the second section is hoisted into place.

Team members prepare to form the tie beam system that will support the foundation of 1144 Fifteenth Street. The bedrock is covered with an earth retention system and shotcrete; drilled piers line the top and right.

piles around the perimeter before excavating. The excavation at the core perimeter would expose the top of the foundation piers, soldier piles, and bedrock. After the bedrock surface was cleaned, the reinforcing mesh would be placed and attached to the soldier piles; then shotcrete would be applied pneumatically to protect the bedrock and preserve its strength.

The tie-beams were designed using one-sided forms and the hollow areas filled with a non-shrink, flowable fill mix, instead of soil or concrete. This design approach resulted in a value-added, more economical solution compared to the typical monolithic reinforced concrete core foundation.

The Execution

Foundation Design Before the non-conventional process could be attempted, the foundation needed to be designed. Martin/Martin and CTL created a tie-beam and drilled pier system with a footprint of 120 feet by 47 feet. The system included eight drilled piers, each ten feet in diameter and boring more than 100 feet into the bedrock, which supported seven-foot deep, seven-foot-wide tie-beams. Two longer beams would run along the longitudinal axis of the building and be pulled together by four shorter, perpendicular beams. It was designed to “kiss” the undisturbed bedrock at 29 feet below street grade and seven feet below the lower-level parking garage floor. As a result, lateral loads on the drilled piers that support the core foundation were reduced by using the bedrock’s passive resistance, in conjunction with lateral resistance provided by the drilled piers.

With the foundation designed, the engineering team began to outline a plan to carefully excavate the core foundation footprint to the top of the core drilled piers, keeping the bedrock intact and limiting any impact on the neighboring building.

First, the perimeter of the core excavation was drilled and soldier piles installed along the outside edge of the planned face of the core excavation. A shotcrete-faced earth retention system was recommended for the perimeter to achieve the highest possible passive resistance.

Because the bedrock is an overly consolidated sedimentary claystone which can become weathered, excavation for the site needed to be both careful and quick. When exposed to the elements for too long, the bedrock dries and disintegrates, reducing the strength that the design team was relying on for lateral support. To counter this issue, the contractor excavated in two phases and operated at about 1.5

Workers splice together two sections of reinforcing steel that form drilled piers used in the foundation for 1144 Fifteenth Street.

Drilled piers on either side of the excavated bedrock with the first phase of shotcrete applied.

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The tie beam system used in the foundation of 1144 Fifteenth Street.

The architect’s rendering of the skyline-changing 1144 Fifteenth Street, the first Class A office tower built in downtown Denver in 30 years.

times a traditional pace. In the first phase, the contractor excavated three feet, installed reinforcing mesh tied to the soldier pile system, used compressed air to clean the exposed bedrock surface, and then applied shotcrete to protect it. After completion of the first 3-foot layer, the contractor extended the excavation to the design depth of 7 feet and the top of the ten-foot diameter piers, and repeated the process.

A special concrete mixture was designed to minimize temperatures during the initial curing of the concrete. About the process, geotechnical engineer Benny I. Lujan of CTL|Thompson said, “Massive amounts of concrete generate significant heat during curing, which can be detrimental to the quality and strength of the concrete. Each pier had 300 yards of concrete, and we had eight piers. That is 30 truckloads of concrete for each pier. I have never seen anything like it.”

Due to the volume of concrete needed for the piers and tie-beam system, a concrete mix design was created by the concrete supplier Martin Marietta, with assistance from fellow engineers at Martin/ Martin and CTL|Thompson. The mix included as much as 40 percent fly ash to create a lower heat of hydration and slow down the curing process. During placement, concrete temperatures were carefully monitored to keep within a tolerable range. Since the strength gain was slowed, the allowable minimum strength at 28 days was relaxed to a 56-day strength requirement.

Playing Nice with the Neighbors Another solution was needed to negotiate the earth retention system for the site’s neighbor, the Four Seasons Hotel. The southern wall of the hotel had an older system of grouted tie-back anchors and soldier piles, with lagging and drilled piers remaining in place. The team created a tension system via counterforts to excavate the old system while avoiding the existing drilled piers supporting the structure. The process involved moving piers inward and doubling them up, then placing the newly designed piers.

The team also had to find a creative way to design the tie-beam system along this southern edge, as the caissons could not be placed over existing piles. The design team moved planned columns from the south to the north side and designed a transfer beam system to support the southern edge to overcome the issue.

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Throughout foundation construction, surveyors monitored deflection, while lateral movement was monitored carefully and extensively by the construction team to ensure work on 1144 Fifteenth would not result in tilting, cracking, or vibration to the hotel’s below-grade parking garage and its foundation.

Bringing Downtown Denver to New Heights The unique, sky-line changing office building “topped out” in July 2017, right on schedule, and is expected to be complete in Q1, 2018.

When complete, visitors and users will never notice the ground beneath them, but the foundation is just as unique as the building, with extensive, nonconventional engineering solutions that overcame potentially project-derailing issues. The result is a foundation that will not only withstand the heavy loads of the building but will also serve as an example to the industry.

“Approaching this extensive project required research, speculation, experience, calculation, patience, and creativity,” said Lujan.

“We were faced with an enormous challenge, and our goal was to determine the most effective engineering solutions to complete the project without compromising quality. It was not easy, but together with our friends at Hines and Martin/Martin, we developed an unconventional, innovative, and costeffective technique to building the core foundation for 1144 Fifteenth.”▪

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Benny I. Lujan, P.E., is a Geotechnical Engineer with CTL|Thompson, a full-service geotechnical, structural, environmental and materials engineering firm.

Project Team Owner: Hines Interests Limited Partnership Engineer of Record: Martin/Martin Consulting Engineers Architect of Record: Kendall/Heaton Associates Contractor: Hensel Phelps Construction Company December 2017

T

20th Annual

he National Council of Structural Engineers Associations (NCSEA) is pleased to announce the winners of the 2017 Excellence in Structural Engineering Awards. The awards were announced on the evening of October 13 at NCSEA’s 25th Annual Structural Engineering Summit in Washington, D.C. The awards have been given annually since 1998 and, each year, highlight work from the best and brightest in our profession.

Awards were given in seven categories, with one project in each category named the Outstanding Project. The categories for 2017 were: • New Buildings under $20 Million • New Buildings $20 Million to $100 Million • New Buildings over $100 Million • New Bridges and Transportation Structures • Forensic/Renovation/Retrofit/Rehabilitation Structures up to $20 Million • Forensic/Renovation/Retrofit/Rehabilitation Structures over $20 Million • Other Structures The 2017 Awards Committee was chaired by Carrie Johnson (Wallace Engineering Structural Consultants, Inc., Tulsa OK). Ms. Johnson noted: “We had a record number of entries this year and the quality of projects was outstanding. Our judges for 2017 were from the Structural Engineers Association of Illinois. They had an enormous task of trying to determine winners from an excellent group of submittals. They did a great job of thoroughly analyzing each entry and thoughtfully discussing which ones should receive the award.”

More in-depth articles on several of the 2017 winners will appear in the Spotlight section of the magazine over the course of the 2018 editorial year.

EXCELLENCE IN STRUCTURAL ENGINEERING AWARDS

Courtesy of HOK

Category 1: New Buildings under $20 Million

OUTSTANDING PROJECT

The Exchange at 100 Federal Street

Boston, MA | McNamara • Salvia Structural Engineers The Exchange at 100 Federal Street is a pavilion that was envisioned as a dynamic, faceted form in structural steel with a glass façade.

A variety of steel shapes were considered, but none could be costeffectively sized for the 75-foot main spans and still achieve the vision for the structure. The solution was solid plate members with exposed bolted connections, limited by steel availability to 4 inches thick. The original architectural desire for narrow steel shapes and a dynamic form was realized. The benefits of collaborative design loops, open communications, and creative thinking provided a final form that shows dynamic character from every viewing angle.

All photos courtesy of Perkins+Will

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Category 2: New Buildings $20 Million to $100 Million

OUTSTANDING PROJECT

U.S. Air Force Academy Center for Character and Leadership Development

Colorado Springs, CO | Skidmore, Owings & Merrill, LLP The Center for Character & Leadership Development’s (CCLD) dramatic cantilevering, 105-foot Skylight structure consists of a triangulated system of Architecturally Exposed Structural Steel plates of varying depth and calibrated to resist lateral forces due to wind loadings. This glass-enclosed structure aligns precisely with the North Star, Polaris, signifying and reinforcing the Academy’s mission to integrate character and leadership development into all aspects of the Cadet experience. The Skylight is designed as a series of “stacked trusses” to minimize the number of field connections as one measure to ensure that the building could be constructed easily.

Category 3: New Buildings over $100 Million

Courtesy of Mercedes-Benz Stadium

OUTSTANDING PROJECT Mercedes-Benz Stadium

Atlanta, GA | BuroHappold Engineering The multi-purpose Mercedes-Benz Stadium, home for the NFL’s Atlanta Falcons and the new Atlanta United, a Major League Soccer team, will cover almost 2 million square feet. It will accommodate seating for approximately 80,000 fans. BuroHappold developed a unique retractable roof concept that opens in 19 minutes or less by moving eight “petals” that create an exciting pinwheel appearance when in motion. The petals are clad in over 120,000 square feet of double-skin ETFE cushions, a transparent, lightweight material that exerts minimal weight on the petals and their long, cantilevering spans.

When the petals slide open, the oval-shaped roof opening spans the length of the field past each end zone.

Courtesy of Mercedes-Benz Stadium

Courtesy of HOK

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Category 4: New Bridges or Transportation Structures

OUTSTANDING PROJECT

Sellwood Bridge Replacement

Portland, OR | T.Y.Lin International The Sellwood Bridge is located on a vital route in Portland, Oregon. A unique design solution was developed where the entire 1,100-foot-long four-span continuous steel deck truss of the old bridge was slid over to temporary piers on a detour alignment to accommodate construction of the new bridge. The new 1,976.5-foot-long bridge, 1,275 feet of which is steel deck arch, carries two 12-foot wide vehicular lanes, two 6.5-foot-wide bike lanes, and two 12-foot-wide sidewalks, and will accommodate future streetcar service. The new structure has an advanced ductility-based seismic design for both operating and strength level earthquakes.

Category 5: Forensic/Renovation/Retrofit/Rehabilitation Structures under $20 Million

OUTSTANDING PROJECT The Desmond Building

Los Angeles, CA | Skidmore, Owings & Merrill LLP Located in downtown Los Angeles’ South Park commercial district, The Desmond Building has recently been infused with new life through a full renovation and seismic retrofit. The 1916 era building stood empty for many years and, with the city’s focus on seismic safety of non-ductile concrete buildings, had been identified as “at-risk.” Renovated for highend creative office use, the building maintains its original industrial aesthetic and historic character. A successful implementation of a rigorous, code prescriptive retrofit solution enabled the addition of a lightweight, income-generating sixth story. The Desmond exemplifies how other historic properties can be safely renovated while including new additions.

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Category 6: Forensic/Renovation/Retrofit/Rehabilitation Structures over $20 Million

Photos courtesy of Blake Marvin

OUTSTANDING PROJECT Bay Area Metro Center

San Francisco, CA | Holmes Structures Serving as the regional headquarters for various government transportation entities, The Bay Area Metro Center was built in 1942 as a WWII tank assembly plant. With a limited budget, this heavy reinforced concrete structure required a seismic retrofit for its change to commercial offices.

Holmes Structures “lightened” the building by removing mass from the interior floor plates and added selective perimeter strengthening without altering the foundation. Performance-based engineering was used to design a retrofit that leveraged the capacity of the existing structure. The solution spread lateral resisting members around the perimeter, distributing the loads over a larger area and eliminating the need for new, deeper foundations.

Category 7: Other Structures

Courtesy of Hunter Kerhart

OUTSTANDING PROJECT Broad Museum Veil

Los Angeles, CA | John A Martin & Associates, Inc. An innovative design that features a “veil and vault” concept defined the project at the Broad Museum in Los Angeles. The veil is a structural exoskeleton, a honeycomb-like structure that drapes over the building’s interior vault. This porous yet absorptive screen is made of 2,500 fiberglass reinforced concrete (FRC) panels and 650 tons of steel. It forms a 3-D series of open cellular components that channels light into public spaces and galleries and connects the museum to the Downtown Streetscape. An elegant steel frame realized through the use of rigorous analysis, testing, and creative support strategies allow this stand-alone piece an expression that fulfills dual functional and aesthetic roles.

Courtesy of Benny Chan Fotoworks

Courtesy of Benny Chan Fotoworks

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Courtesy of Albert Vecerka/Esto

AWARD WINNER – CATEGORY 1

AWARD WINNER – CATEGORY 1

AWARD WINNER – CATEGORY 2

Berkeley, CA | Tipping Structural Engineers

Tulsa, OK | Wallace Engineering – Structural Consultants, Inc.

Amherst, MA | Simpson Gumpertz & Heger Inc.

1908 Shattuck

The Collegiate Center at Edison

This downtown Berkeley project includes a restaurant-brewery at street level and an office space on the second and third floors.

Given the area’s high seismicity, engineers elected to design an essentially earthquakeproof building employing seismic isolation.

Because retaining walls already existed on three sides of the lot, alternative isolation configurations were considered. Exposed bearings, spliced into the ground-floor columns ten feet above grade, are visible to the public. Practice would dictate employing isolation bearings with a 36-inch allowable horizontal movement at this site. To maximize real estate, TSE customized isolators for a 24-inch allowable movement.

The Collegiate Center at Edison presented a unique challenge: design a facility incorporating diverse functions such as safe rooms, lecture halls, and an academic hall while creating a building that was iconic as well.

The student lounge is the most striking feature of the building, appearing to hover fourteen feet above an outdoor plaza located along a busy arterial street. The lecture halls serve as ICC-500, FEMA-361 safe rooms.

Designed to resist the wind pressures and debris impact from an EF-5 tornado, or approximately 250 mph wind speeds, they provide shelter for up to 300 people during a tornadic event.

Courtesy of Forestry Innovation Investment

The University of Massachusetts (UMass) wanted to bring their design programs – Architecture, Landscape Architecture and Regional Planning, and Building and Construction Technology – together in one creatively designed building exemplifying sustainable construction practices. While a steel- or concrete-framed structure would be conventional for this building’s size and use, the new Design Building features a timber-framed superstructure with an innovative composite floor system. The exposed wood structure emphasizes the potential of engineered wood elements while complementing and influencing the aesthetics inside and out.

Courtesy of Morphosis

AWARD WINNER – CATEGORY 2

AWARD WINNER – CATEGORY 2

TallWood House at Brock Commons Vancouver, BC | Fast + Epp

University of Massachusetts Design Building

The TallWood House at Brock Commons is an 18-story, mass timber hybrid, student residence at the University of British Columbia (UBC) in Vancouver, Canada. It has been recognized as the tallest mass timber hybrid building in the world, reaching 174 feet (53m). The building is comprised of 17 stories of unique structure: five-ply crosslaminated timber (CLT) floor panels, point supported by glue-laminated timber columns, all resting on a concrete transfer slab at level two. Two full height concrete cores provide the lateral stability. Eighteen fullscale load tests were performed to verify the custom CLT panel’s capacity.

California Polytechnic University, Student Recreation Center Pomona, CA | LPA, Inc.

Located on the campus of California State Polytechnic University in Pomona, California, the Student Recreation Center has become a focal point of student activity on the primarily commuter campus since the facility opened in 2014. The dramatic three-story structure seems to defy gravity even more than the rock climbers inside, featuring several substantial cantilevered floor areas, the largest of which extends nearly 60 feet to support an indoor running track. The 165,000-square-foot facility addresses multiple structural challenges by marrying the performance of structural steel framing to this unique building form.

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AWARD WINNER – CATEGORY 3

Hanking Tower (Rolansburg) Shenzhen, China | WSP

The Hanking Center in Shenzhen is a 1,150-foot-tall (350m) innovative architectural form, including a detached core and folded angled exterior. The challenges of the eccentric core design are overcome by a unique structural steel solution – a ‘mega-braced’ tube structure, using composite columns linked by steel diagonal bracing organized over multi-story modules around and through the tower. The result is a closed tube structure, efficiently engaging the entire tower depth and integrated within the architectural design. Minimal floor links, as envisioned between the tower and offset core, are maintained with light bracing integrated only at select levels.

AWARD WINNER – CATEGORY 3

AWARD WINNER – CATEGORY 3

JTI Headquarters

Geneva, Switzerland | Skidmore, Owings & Merrill LLP

Framed in structural steel, the 10-story JTI Headquarters in Geneva, Switzerland, was achieved by using creative structural engineering design and an innovative application of both design and construction techniques.

The building’s striking form was primarily dictated by the triangular shape of the site, and 157-foot (48m) and 197-foot (60m) cantilevers created by lifting the northeast corner to allow for public space and scenic views. Combined moment frames and nested Pratt trusses at the building faces support both gravity and lateral loads. Potential excessive deflections were controlled during construction through a combination of camber, jacking, and tie-downs.

AWARD WINNER – CATEGORY 4

SR 520 Floating Bridge and Landings Seattle, WA | KPFF Consulting Engineers

Sutter Health, California Pacific Medical Center, Viscous Wall Damper

Torre Reforma

Mexico City, Mexico | Arup

The CPMC hospital at the Van Ness and Geary Street campus is currently under construction.

The hospital, to be completed in 2018, will consolidate the acute care services from two older CPMC campuses. The structure includes 274 patient beds, diagnostic and treatment centers, and subterranean parking. The structural system is a steel moment resisting frame with supplemental viscous wall dampers to reduce earthquake demands, the first use of this technology in the US. The project is being delivered using the Integrated Project Delivery method. The team was able to reduce waste in the design and construction of Sutter’s most significant project.

At 807 feet (246m), Torre Reforma will be the tallest skyscraper in Mexico. The 57-floor, 344,500-square-foot (40,000 m2) building includes office space, along with restaurants, shopping, and a 4-floor fitness club. Set along the bustling new commercial corridor of Paseo de la Reforma, the building’s unique triangular form responds to the setback limitations of the site and the preservation of a historic building on the site. A vital element of the project was to demonstrate how, through the integration of engineering and architecture, a high degree of sustainability and building performance could be achieved. Torre Reforma has been certified LEED Platinum.

AWARD WINNER – CATEGORY 4

AWARD WINNER – CATEGORY 5

San Francisco, CA | Degenkolb Engineers

The New Dresbach Bridge

LaCrescent, WI | FIGG Bridge Engineers, Inc.

The new SR 520 floating bridge replaces an old, structurally vulnerable floating bridge with a stronger, more resilient structure. The new bridge spans 7,708.5 feet across Lake Washington, forming the longest floating bridge in the world.

Four structural types form the new bridge, each selected to address unique challenges and serve distinct purposes. On land, dual concrete box girders form the approaches. Steel transition spans connect the fixed structures to the floating bridge, allowing for differential movement between the structures. The floating bridge itself consists of floating concrete pontoons, concrete girder supported high-rises, and an innovative precast ribbed-slab low-rise structure.

AWARD WINNER – CATEGORY 3

The New Dresbach Bridge crosses the Mississippi River between LaCrescent, MN, and LaCrosse, WI. It demonstrates how innovative engineering can result in a beautiful, efficient, variable-depth, long span bridge thoughtfully built in sensitive environmental areas and during harsh winter conditions, all while achieving a new record span length (508 feet) for Minnesota. Its concrete segmental structures and custom formwork achieved context sensitive, signature shapes while being highly economical and delivered ahead-of-schedule. It met or exceeded all of Minnesota DOT’s project constraints, criteria, and goals: built rapidly, minimizing impacts on the public, achieving outstanding context-sensitive aesthetics, and being highly economical.

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Duke University Chapel: Investigation and Restoration of Cracked Stone Arches

Durham, NC | Wiss, Janney, Elstner Associates, Inc.

Duke University Chapel has a vaulted ceiling system that consists of rib arches constructed with individual stone voussoirs and a Guastavino ceiling system (clay tile and precast concrete) that spans between the arches. Unusual conditions that include cracks in mortar joints between voussoirs developed in the stone arches due to tensile stresses from long-term moisture expansion of the clay tile component of the Guastavino ceiling system. Restoration that included tuckpointing of mortar joints between voussoirs was completed August 2015, and the Chapel was subsequently reopened.

Courtesy of David Wakely

AWARD WINNER – CATEGORY 5

AWARD WINNER – CATEGORY 6

St. Helena, CA | ZFA Structural Engineers

Brooklyn, NY | Silman

Freemark Abbey Winery

Empire Stores

Originally constructed in 1886, Freemark Abbey Winery has undergone several modifications over the last 130 years. When purchased by Jackson Family Wines in 2006, their vision was to celebrate the history of the structure while bringing it into the modern era. Coined by SB Architects as the “rebirth” of the historic stone building, the $15M retrofit and alteration project is providing Freemark Abbey, one of the original gravity fed stone wineries, with an iconic hospitality and events center located in the heart of Napa Valley. Structural solutions included utilizing existing stone walls, adding structural steel trusses and braced frames, and selectively placing new concrete foundations.

Empire Stores is a landmarked structure on the DUMBO waterfront in Brooklyn Bridge Park.

It is a series of seven interconnected structures constructed between 1870 and 1885 for use in the shipping industry, and, later, as a coffee warehouse. Silman participated in its rehabilitation and renovation, which consisted of the restoration of the existing structure and the addition of two new stories. Also, the roof was transformed into a public park, and a public courtyard was created that cut a large slice through two of the buildings and includes a winding staircase that grants access to the roof.

Overhead, at levels 3 and 4, two bridges fly through the courtyard and connect the interior spaces on either side.

AWARD WINNER – CATEGORY 6

UC Berkeley Bowles Hall Seismic Retrofit and Renewal Berkley, CA | Maffei Structural Engineering

Built in 1929 in the Collegiate Gothic style, Bowles Hall is the University of California’s first residence hall. A western trace of the Hayward earthquake fault passes beneath two corners of the building. The 2016 renovation and retrofit is the University’s first public-private partnership for a seismic retrofit project. The renovation revises the dormitory room layout to include bathrooms within units, adds wheelchair accessibility, replaces utilities, restores dining, and expands common spaces. Seismic retrofit work includes concrete walls and a buttress at strategic locations to blend with the existing architecture while strengthening the structure for the site’s extreme earthquake hazard.

2017 Panel of Judges

The judging was held on Monday, July 24, 2017, at the NCSEA offices in Chicago, Illinois. The judges for this year’s Excellence in Structural Engineering Awards were:

Courtesy of christian phillips photography

AWARD WINNER – CATEGORY 7

AWARD WINNER – CATEGORY 7

Black Rock Lighthouse Service

Black Rock City, NV | Holmes Structures

Chicago Riverwalk

Ben Nelson, P.E., SECB Martin/Martin, Inc.

The new 1.3-mile Chicago Riverwalk transformed discontinuous riverfront spaces along the Chicago River into 2,800 feet of continuous walkway that connects the Lakefront to Chicago’s West Loop. As Chicago’s “second shoreline,” the Riverwalk now serves as a premier, sustainable urban space consisting of six uniquely designed sections that integrate the original Riverwalk walls. The innovative project includes precast underbridges supported on drilled shafts that seamlessly connect each section along the walkway. The Riverwalk not only enhances the environment but enables residents, workers, and visitors to connect with the many recreational, cultural and economic amenities offered by the Chicago River.

Kevin Conroy, P.E., S.E. Simpson Gumpertz & Heger

Chicago, IL | Alfred Benesch & Company

The Black Rock Lighthouse Service was the largest independent art installation at Burning Man 2016, featuring four octagonal lighthouses connected with suspension bridges. The installation experienced 60+ mph wind and dust storms without sustaining structural damage and sheltered 70,000 attendees over the course of the festival. The engineering team provided extensive prototyping to ensure life-safety for structures with an unstable aesthetic. Prefabricated panels were prototyped and tested for mandatory rapid onsite assembly. Additionally, a flexible anchorage system and meticulous clean-up procedures were implemented to respect Burning Man’s strict “leave no trace” policy.

Carrie Johnson, P.E., SECB Wallace Engineering Structural Consultants, Inc.

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An

Oasis for

Children in the River City

By Nathan C. Dumas, P.E., Jeffrey S. Davis, P.E. SECB, LEED AP BD+C, and Donna E. Adams, P.E. SECB

The Sky Lobby garden is perhaps one of the most inviting features to families seeking pediatric medical care at this facility. Courtesy of Michael Stavaridis.

T

his is the type of project that gives geotechnical, geostructural, and structural engineers goosebumps – in a good way. VCU Health’s vision for a new Children’s Hospital of Richmond at VCU Children’s Pavilion required designing in the fourth dimension, where the past, present, and future of the physical facilities critical to this ambitious undertaking were simultaneously considered. Goals were lofty. Not only would it become the largest and most advanced outpatient facility dedicated to children in the region, but the reimagined pavilion was also expected to serve as a gateway to Virginia Commonwealth University’s urban medical campus in downtown Richmond. And that was just for starters.

On the surface, the program directive to the design team, led by HKS Architects, Inc., was clear and concise. With an all-in budget of $200 million, on a site adjacent and practically connected to the existing Children’s Pavilion, design and construct a 640,000-squarefoot, 15-story building rising 11 floors above grade and descending four stories below it. The design had to incorporate structural systems that would allow for seven floors of future vertical expansion and also extend the below-grade levels to the north, occupying the entire block. Last but not least, although the plan required demolition of a portion of the existing pavilion, it had to remain open and operational during construction.

Together, these factors formed an irresistible challenge for two local engineering firms to surmount. As part of the HKS team, structural engineer Dunbar Milby Williams Pittman & Vaughan (DMWPV) and geotechnical/geostructural engineer Schnabel Engineering were charged with designing the support of excavation, the structural support and underpinning of the existing pavilion, and structural support of the new building.

Location, Location, Location Previously a surface parking lot, the project site occupies less than an acre and is bounded by busy East Broad Street, and North 10th and STRUCTURE magazine

11th Streets. With the adjacent pediatric pavilion already in place, VCU saw the expansion as a means to enhance their brand and re-energize the neighborhood and campus gateway while consolidating services from various locations under one roof to better serve the community.

The new Pavilion at 1000 E. Broad Street is on a GRTC Transit System bus route and features a 600-space attached parking garage.

Diving into a Deep Excavation Extensive subsurface exploration – 23 test borings, a cone penetrometer test, three pressuremeter tests, and strength and consolidation testing on Shelby tube samples – confirmed the site geology to be typical of downtown Richmond. The good news was that the Miocene clay and silt soils were heavily pre-consolidated and suitable for support of heavy building loads.

The real challenge lay in the fact that the excavation for the new Pavilion extended 55 feet below street level, which is 35 feet below the foundations of the existing pediatric care facility. This prompted creative thinking and serious teamwork on the part of DMWPV and Schnabel to address two pivotal issues: excavation support and existing building support.

Excavation Support A permanently tied-back soldier pile and lagging support of excavation (SOE) system was selected based on consideration of the subsurface conditions, and site and design constraints. The system can resist the lateral earth pressures instead of relying on the building framing and facilitates future expansion to the north.

Schnabel performed the initial SOE design, which was subsequently optimized by design-builder Nicholson Construction.

The system consisted of 143 drilled and set piles and 472 tiebacks and was designed to limit horizontal and vertical deflection of the adjacent building to one inch.

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systems to compensate for unbalanced lateral earth pressure and to keep the building from moving toward the excavation.

The structure to remain in place after demolition was modeled using Autodesk Revit and Bentley RAM Elements finite element analysis software. Multiple options to support the lateral loads on the structure and transfer approximately 2,300 kips of service level lateral load to the soils below were considered; internal buttresses and shear walls was the option of choice. The buttresses consist of seven 9-foot by 6.75-foot, full-height concrete columns spaced at 24 feet on-center along the cut plane, each with an integral 2-foot-thick concrete shear wall perpendicular to the line of excavation. The continuous underpinning grade beam at the cut plane connects the buttresses and is supported by the system of vertical micropiles detailed above. The groups of micropiles are centered Site location and position of the new building relative to the existing pediatric care building. between the SOE tiebacks.

To resist the lateral forces and prevent the building from moving Existing Building Support towards the excavation, an A-frame system of post-tensioned battered The excavation below and adjacent to the pediatric care facility at piles coupled with vertical micropiles was constructed 30 feet away the demolition cut plane necessitated supporting the existing shallow from the building cut plane, in line with the vertical micropiles along foundations. Because the two structures were to remain independent, the front grade beam, to avoid the SOE tiebacks. Horizontal tie beams neither gravity nor lateral loads from the existing building could be consisting of post-tensioned tie rods were used to transfer the lateral transmitted to the new one. loads from the grade beam at the cut plane back to the line of the Gravity loads at the cut plane were supported on a 10-foot, 8-inch A-frame micropiles. Thirty-four coupled battered pile assemblies conwide by 3-foot, 6-inch deep concrete underpinning-style grade beam nected to 30 horizontal tie beams containing a total of 60 horizontal along the entire length of the cut plane. The underpinning grade post-tensioned tie rods were constructed. beam was supported on 95 vertical micropiles designed to transfer A sophisticated instrumentation and monitoring system provided gravity forces from the structure to below the bottom of the SOE. real-time data that was used to verify the performance of the SOE The micropiles were typically installed in groups of three and spaced and underpinning. The total horizontal movement of the existing at 6 feet on-center. The installation took place in the building’s lowest building during the monitoring period was approximately 0.4 inches. parking level under headroom conditions of nine feet or less. The vertical micropiles were each designed for a service level compression New Building Structural Elements load of 96 kips, bonded in the Miocene stratum, and were a total length of 52 feet.

The new building is supported on a mat foundation on Miocene soils.

Demolition of a portion of the pediatric care facility, and excava- Typical mat thickness is 6 feet with 5,000 psi compressive strength tion adjacent to it, also required the design of new lateral support concrete, which eliminated the need for shear reinforcing where the columns bear on it. The contractor developed a detailed mass concrete plan that addressed logistics and thermal control during curing. The specifications limited maximum internal temperature of the concrete to 160°F to avoid damage by delayed ettringite formation. A maximum temperature differential of 35°F was stipulated to mitigate cracking of the concrete due to thermal stresses. The concrete supplier chose to use mix designs with 60 percent slag cement to assist with meeting thermal control limitations. The mat was poured in four quadrants totaling 1,100 cubic yards.

The four floors below and four levels above grade were constructed from CIP concrete. For reasons of future flexibility while making building modifications, VCU Health requested a non-post-tensioned design so 12-inch-thick two-way slabs spanned the typical 30-foot by 30-foot bays without the need for any drop panels or slab shear reinforcing in most cases. Measures taken to push deck repair projects many decades into the future included dosing parking level slabs with three gallons/cubic yard of calcium nitrite corrosion inhibitor; a 2-inch concrete cover over top reinforcing Partial demolition of the existing VCU Children’s Pavilion. New SOE/ underpinning to be installed below remaining three-story portion. bars; maintaining a low water/cement ratio between 0.39 and STRUCTURE magazine

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Taken from the pediatric care building, excavation, and SOE at the start of mat foundation construction.

Historic Old City Hall is in the background. Courtesy of Skanska USA.

0.42; and limiting chloride ion penetrability to 1,000 coulombs in 28 days per ASTM C1202. Typical gravity columns were 36 inches by 36 inches using 8,000 psi compressive strength concrete at the lower levels. ASTM A615 Grade 65 KSI reinforcing steel was used in the columns to assist with rebar congestion at beam intersections and column splices.

The six outpatient floors plus mechanical penthouse were constructed to accommodate the addition of another seven levels above.

Typical floor slab construction consisted of 3.5 inches of lightweight concrete over a 2-inch composite deck for a two-hour fire rating.

While typical 30-foot by 30-foot bays of all clinical levels were framed with W16 beams and W24 girders, the first steel level above the concrete framing had beams as deep as W33 connecting into W36 girders in order to meet vibration requirements for sensitive imaging equipment.

Steel-braced frames in the upper levels align atop CIP concrete shear walls of the parking levels to provide lateral force resistance.

A Seismic Response Modification Coefficient (R) value of 3.0 was used to avoid prescriptive joint design requirements of AISC 341.

Wind loads for this structure were close in value to seismic forces so there was little to gain by using a larger R-value.

Schematic of the system of underpinning and bracing below the existing pediatric care building.

The Sky Lobby is constructed on the uppermost level of CIP concrete framing. This portion of concrete framing is depressed several feet to accommodate the depth of planters and allow for the structural slabs to slope to drains. The floor system was designed for heavy concentrated loads of landscaping boulders, as well as a 20,000-pound allowance for mature trees in each planting well.

Conclusion In the second decade of the 21st century, few projects have as much social resonance as those connected with health care and those connected with children. This one exemplifies the best of both. The new Children’s Pavilion opened on March 21, 2016, to the kind of enthusiasm one might expect when outpatient pediatric services expand from a 54,000-square-foot facility well past its prime to a gleaming high-tech tower housing clinics, radiology, same-day surgery, lab testing, dialysis, infusions, family amenities and more, in an environment custom-tailored for kids.

Even before construction was finished, the Pavilion had been recognized for its innovative design. Awards include the 2013 Honor Award of Excellence in Architecture (AIA Richmond Chapter), 2014 National Healthcare Design Award (AIA Academy of Architecture for Health), 2015 Future Healthy Built Environment Award (Design & Health International), and 2015 Concrete Excellence Award (American Concrete Institute Virginia Chapter).

By the time it was completed after five years of planning and preparation, compiled data spoke volumes about the scope of this undertaking: $200 million invested, 2,450 tons of steel, 523,000 pounds of sheet metal, 41,000 cubic yards of concrete, seven floors of structured parking, and 83 new exam rooms.

Now, after more than a year in operation, the building has become a downtown Richmond landmark, revitalizing the historic and vital Broad Street corridor as it has improved the lives of many children and their families. After all, that is something worthy of support.▪ Nathan C. Dumas, P.E. (ndumas@schnabel-eng.com), is a Geotechnical Engineer with Schnabel Engineering in Glen Allen, VA. Jeffrey S. Davis, P.E. SECB, LEED AP BD+C (jdavis@dmwpv. com), is a Structural Engineer with Dunbar Milby Williams Pittman & Vaughan in Richmond, VA. Donna E. Adams, P.E. SECB (dadams@dmwpv.com), is a Structural Engineer with Dunbar Milby Williams Pittman & Vaughan in Richmond, VA.

The completed Pavilion stands at the northwest corner of East Broad Street and North 11th Street in Downtown Richmond, Virginia. Courtesy of Michael Stavaridis.

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Outside the BOx highlighting the out-of-theordinary within the realm of structural engineering

S

everal decades after the first space age, there is renewed interest in space exploration and specifically in future human habitation far beyond the Earth’s surface. NASA recently received funding with an ambitious target: to send a manned mission to Mars by the 2030s and allow for future human habitats and even cities. This is a challenging, multi-disciplinary problem that requires expertise from a wide variety of fields: aerospace engineering, environmental engineering, social science, urban planning, design, architecture – and especially structural engineering. Unlike structural engineering for the built environment on Earth, there are virtually zero rules of thumb or design precedents to draw on for construction on Mars or the Moon. There is exciting potential to shape this discussion with fundamental structural engineering principles and forward-looking material and fabrication strategies.

one-third on Mars as compared to Earth), thermoelastic loads, and micrometeoroid impact.

Because of the lack of atmosphere on the Moon and Mars, a pressure differential of up to 2090 psf across the habitat enclosure is required to sustain Earth-level pressures inside. This results in outward pressures on the structure that are several orders of magnitude greater than conventional structural loads due to gravity and environmental loading on Earth.

Therefore, the structure will be mainly subjected to tensile stresses instead of the compression induced in Earth-bound structures under gravity loading. In comparison, a tension structure on Earth, such as an air-inflated sports dome, typically withstands a net pressure of 1 psf (Herzog, 1976) and the pressure differential on an airplane may be between 1100 and 1400 psf. Furthermore, since the loss of pressure is catastrophic to human life, the structure must be designed with redundancy and safety measures against decompression disasters caused by accidental and natural impacts.

According to NASA research, it is possible to safely reduce the internal pressure to values that are lower than those typical on Earth. Minimum pressures of 1150 psf and 1100 psf are recommended for the Moon and Mars, respectively, for normal operations. However, these lower pressures require increasing the percentage of oxygen in the air from 21% to 32%. This higher oxygen concentration corresponds to the maximum nonmetallic materials flammability certification level currently used in operational human space flight programs. These recommendations must be studied further before the development of requirements for surface habitats.

Thermo-elastic loading is related to the presence of the Sun that produces a thermal gradient of about 630 °F on the Moon (in 29 days) and 148 °F on Mars (in 24.6 hours). These gradients occur between the sunlit and the shadow-exposed parts of the structure, as well as between the internal and external face of the envelope.

Regolith is loose, fractured soil or rock and is commonly available on the moon, Mars, and Earth. An external thick regolith layer on structures could be used to provide thermal mass to dampen temperature swings. This layer can also

Structural Challenges for Space Architecture Engineering Habitats for the Moon and Mars

By Valentina Sumini, Ph.D. and Caitlin T. Mueller, Ph.D.

Valentina Sumini is a postdoctoral fellow at Massachusetts Institute of Technology in the Department of Civil and Environmental Engineering. Sumini’s research aims to explore form-finding and structural optimization strategies for deep-space exploration habitats on the Moon and Mars. She can be reached at vsumini@mit.edu.

Caitlin T. Mueller is an Assistant Professor at the Massachusetts Institute of Technology in the Departments of Architecture and Civil and Environmental Engineering. She leads the Digital Structures research group, which focuses on new digital technologies for the design and fabrication of innovative structures.

Much like their Earth-based counterparts, the requirements of future space habitat structures are defined by their ability to protect their occupants and provide usable space to live and work. On Mars, the environmental loads are more extreme and the settlements more confined and isolated.

Due to the high cost of transporting resources from Earth, up to $2 million for a single brick, recent efforts have focused on using in-situ materials for long-term sustainability. Throughout human history, settlers have adapted their construction methods to the locally available resources: snow huts, adobe walls, thatch roofs, and bamboo structures are just a few examples. Martian soil may be next on this list.

Loading and Structural Considerations Structural systems for space habitats must be designed for four main loading types: internal pressure, reduced gravity (one-sixth on the Moon and

Loading on the Earth, the Moon, and Mars.

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NASA 3D printed Habitat Challenge. Project: Ouroboros. Team Digital Structures Research Group.

Faculty Advisor Caitlin Mueller.

serve as shielding from solar and cosmic radiation fields. The thickness of the layer would be variable, with thicker construction in the directions with greater sun exposure.

Micrometeoroids are small space projectiles (up to 0.1 inches in diameter) that do not survive entry through Earth’s atmosphere but do reach the surface of the Moon and Mars at velocities up to 45 mps. Habitat structures must protect their interiors from penetration by these cosmic bullets. While it is impossible to predict this phenomenon deterministically, researchers have proposed that a habitat should resist projectile penetration with a probability of 99% over a mission time of 10 years. A commonly proposed strategy also involves utilizing the external regolith layer with a thickness of 3 to 6 feet to achieve this.

was essentially a kind of mechanical worm three meters (10 feet) in diameter. It would be transported and installed in a compact position and then its length would be extended telescopically using compressed liquid air stored in cylinders inside the unit.

To date, other inflatable solutions for Moon habitats have been explored by prominent architectural firms such as Foster & Partners and Andreas Vogler. The project conceptualized

by Foster & Partners has an internal inflatable membrane covered by a shelter made of regolith which could be constructed using robotic fabrication processes (such as 3D printers).

The state-of-the-art about rapid prototyping of building blocks is seen in research by the engineer Enrico Dini (Monolite Ltd.) who designed a 3D-printer, called D-shape technology. The technology has allowed for the construction of several prototype projects on Earth including housing, sculpture, military structures, and furniture. For the moon outpost (Foster & Partners in collaboration with AltaSpace), the 3D printer built a section through a regolith simulant.

The NASA Innovative Advanced Concepts Fellow, Neil Leach, is involved in a research project that aims to develop a robotic fabrication technology capable of printing structures on the Moon and Mars using lunar dust. The mechanical properties of the lunar regolith simulant (available at Orbitec of Madison, WI, USA, called JSC-1A) appear promising from a structural point of view, as the compression resistance is about 2900 psi and the Elastic modulus is equal to 341,000 psi. Density data for the regolith can be estimated from samples collected in space missions: the density of Moon regolith from the Apollo 15 mission data ranges from 84 pcf for the top foot, to 115 pcf at a depth of 2 feet. The powdered regolith with naturally occurring metallic oxides is mixed with chemical admixtures that react to form a type of concrete.

One of the analyzed regolith mix design techniques is known as Contour Crafting, which is a digitally controlled construction process developed by Behrokh Khoshnevis that fabricates components directly from computer models. The material used is a form of rapidhardening cement that gains sufficient strength

Design Concepts and Fabrication Strategies Since 1986, several types of structures have been proposed as concept settlements for both the Moon and Mars. As internal pressurization is the controlling load on the structural system, several inflatable architectural concepts have been explored over time. The first one from Archigram in 1966, with the Living Pod project, was a free-roving exploratory house inspired by the Lunar Modules that NASA was preparing for a moon landing. A few decades later, the architect Dante Bini developed design proposals in collaboration with Harrison Schmitt, the twelfth astronaut to set foot on the Moon in 1971 during the Apollo 17 mission. These projects are interesting because they are self-shaping, pressurized units. One of the proposals, Lunit,

Redwood Forest City – Mars City DesignTM Competition 2017. Team: Valentina Sumini, Alpha Arsano, George Lordos, Meghan Maupin, Zoe N. Lallas, Sam Wald, Matthew Moraguez, John Stillman, Mark Tam, Alejandro Trujillo and Luis Fernando Herrera Arias. Faculty advisor: Caitlin Mueller.

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Application of sphere packing as a form-finding strategy for inflatable Moon exploration habitats.

to be self-supporting almost immediately after extrusion. At the moment, other 3D printing technologies are also being developed by private companies such as Made In Space and Redworks.

For the Mars regolith, indirect evaluations suggest densities from 75 to 100 pcf. In these respects, regolith is not very different from typical concrete aggregate used on Earth. Recent studies at Northwestern’s McCormick School of Engineering highlighted that a concrete mix design that includes Martian regolith exhibits characteristics similar to terrestrial concrete, as well as easy handling, fast curing, high strength, recyclability, and adaptability in a dry and cold environment. The mix uses molten sulfur which is abundant on Mars. The regolith can be properly proportioned to allow the optimization of both the coefficient of thermal expansion and the mechanical strength.

Andrea Vogler’s design, Moon Capital, is composed of domes, positioned over inflatable modules, which form a unique intelligent skin using a 3-meter (10-foot) thick layer of smallregolith sandbags. The weight of the regolith sandbags will provide protection from radiation and impact; however, it will not counterbalance the internal pressure of the entire structure.

An innovative aspect of this project relies on the use of small swarm robots that will fill and mount the regolith sandbags on the smart skin.

The potential application of swarm robotic systems is becoming very attractive because of their miniaturization and reduced costs, especially for areas with difficult or dangerous access. On Earth, drones have been used

by University researchers at the Swiss Federal Institute of Technology (ETH), Zurich, to build a prototype rope bridge between two sets of scaffolding. While drones come to mind when picturing swarm robots, drones could only fly in indoor pressurized environments.

Swarm robots operating on Mars or the Moon, exterior to the habitat, would be surface robots with collecting and hauling capabilities, similar to a robotic ant colony.

Another interesting conceptual design that explores a temporary inflatable module on the Moon has been developed by MIT’s Department of Aeronautics and Astronautics and Brown University’s Department of Geological Sciences. The inflatable habitat will be folded and packaged into a manageable volume to fit on the Apollo Lunar Rover. To deploy the habitat, the astronauts will remove the habitat from its container and unfold it on a flat surface. The ribs will then be inflated, establishing the habitat structure. This ribbing consists of a frame of small-diameter inflatable tubes that, when inflated to high pressure, provide a rigid structure for the habitat. The structure can be used for protection on overnight missions while the astronauts remain in their space suits.

Habitat Organization and Current Projects Previous and current space habitat design examples mirror the evolution of a spacecraft interior design that mostly follows activity functions. Typically, the organization of the interior layout follows the functional needs of the crew, such as working, hygiene, personal spaces, and preparing and eating food.

Typical architectural tools for the interior organization of terrestrial buildings, such as bubble diagrams and adjacency matrices, could also be used to explore the relationships among the sizes, adjacencies, and approximate shapes of the spaces needed for various activities in space habitats.

A project underway by MIT’s Digital Structures research group is investigating

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this potential, developing a new sphere packing form-finding approach for conceptual space habitat design. The method aims to optimize the location of different functional systems and subsystems inside a space habitat. Spherical bubbles representing different functional programs can combine in 3D space by prioritizing the preferred connections and maintaining the requested volume. The sphere packing achieved through a dynamic relaxation algorithm allows for the combination of both bubble diagrams and adjacency matrices, allocating all activities and respecting all required linkages between functions and subsystems. The obtained functional diagram is also considered as a pressurized architectural space, made of spherical components, and evaluated, in terms of its structural performance, through finite element analysis tools.

The individual spheres may be pressurized, and the encapsulating envelope can be pressurized, creating a layer of redundancy if one membrane is breached.

Designers and researchers are also working on proposals for human habitation at the urban scale, including the recent Mars City DesignTM competition that aims to develop concepts for future Martian cities.

One winning proposal from MIT, called Redwood Forest, is located in an unusual circular depression where a network of bright, green, and water-rich pressurized habitats are proposed to nurture 10,000 people. The city will exist both above and below ground, mimicking the structure of trees. Within the root network, residents will have their private spaces protected from harsh radiation, meteoroid impact, and thermal environment. The root network will house most of the machines that process, store, and distribute resources vital to everyday life. The public spaces will exist above ground, in enclosed structures

which filter daylight down to the root network. The main transportation network will be an underground thoroughfare modeled after rhizomes present in various plant species.

The radiation protection will be enhanced by the inclusion of a layer in the shield consisting of a water reservoir. The regolith that was dug out for the initial root system will be used as a catalyst to start water production and extract other mineral resources for construction.

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Going Forward Designing a structure on an extraterrestrial surface includes numerous challenges, including the internal pressure, the dead loads/live loads under reduced gravity, the consideration of new failure modes such as those due to high-velocity micrometeoroid impacts, and the relationships between severe Lunar/Martian temperature cycles and structural and material fatigue. Also of concern is the structural sensitivity to temperature differentials between different sections of the same component, the very extreme thermal variations and possibility of embrittlement of metals, the out-gassing for exposed steels and other effects of high vacuum on steel, alloys, and advanced materials. In addition, the factors of safety and the reliability (and risk) must be major components for lunar structures, as they are for significant Earth structures.

When considering a permanent settlement on another planet, one of the crucial aspects involves an evaluation of the total life cycle of the structure. That is, taking a system from conception through retirement and disposition or the recycling of the system and its components. Many factors affecting system life cannot be predicted due to the nature of the Lunar/Martian environment and inability to realistically assess the system before it is built and utilized. Therefore, even if the challenges in space exploration are very peculiar, the colonization of satellites and planets could teach us to be wiser in our consumption of natural resources, pushing us to pursue efficiency and sustainability here on Earth. The multidisciplinary methodology connected to space exploration research will be a wise starting point for optimizing the terrestrial consumption of natural resources for designing more sustainable architectures and improving ground logistics research.▪

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For more on Mars regolith densities, see K. Seiferlin et al., Simulating Martian regolith in the laboratory, Planetary and Space Science, vol. 56, 2009-2025 (2008).

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InSIghtS

Adhesive Anchor Systems

The Effects of Base Material Temperature during Installation and In-Service Use

By Christopher Gamache, P.E.

P

ost-installed adhesive anchor systems have been used for many years for the attachment of threaded rods and reinforcing bars to concrete and other masonry base materials. The code that governs the design of adhesive anchor systems is the American Concrete Institute’s ACI 31814, Building Code Requirements for Structural Concrete, Chapter 17 “Anchoring to Concrete.”

The test reference is ACI 355.4, Qualification of Post-Installed Adhesive Anchors in Concrete.

In addition, the International Code Council’s (ICC) Evaluation Services (ICC-ES) Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements (AC308) is a test criterion that supplements ACI 355.4, which then allows a product to be issued as a third party evaluation report from ICC-ES or other third party evaluation services, such as the International Association of Plumbing and Mechanical Officials (IAPMO) Evaluation Service.

In general, the design of post-installed adhesive anchor systems is very similar to the design of cast-in-place anchors and post-installed mechanical anchors. However, for the design engineer, there are additional bond strength considerations and additional temperature considerations for product testing. The base material temperature at the time of the installation of the adhesive anchor system, and during the in-service lifetime of the anchor, also must be considered. Additionally, there have been changes in ACI 318 and ACI 355.4 in recent years that affect the overall design bond strength.

High Temperatures The most significant change in adhesive anchors has been in the adoption of the 2012 International Building Code (IBC), which references ACI 318-11. Appendix D, “Anchoring to Concrete,” referenced adhesive anchors for the first time and appropriate bond strength failure modes were added. Appendix D referenced the test criterion ACI 355.4, which was also first published in 2011. ACI 355.4 followed the testing procedure and evaluation of adhesive anchor systems from AC308 very closely, but some changes were made. The most glaring difference was that ACI 355.4 required that the minimum base material temperature for long-term temperature testing and design was increased from room temperature to 110°F (43°C).

In general, a high base material temperature has a negative effect on the bond strength of an

adhesive anchor. Anchors that previously had testing in accordance with AC308 prior to the publication of ACI 355.4 would have published technical data typically showing a minimum long-term base material temperature of 70°F to 80°F (21°C to 27°C). After the publication of ACI 355.4 and with the increase in the minimum long-term base material temperature to 110°F (43°C), some adhesive anchor systems had reductions in the published bond strength.

In general, slow-cure products, such as pure epoxies, were most affected, as higher temperatures can have significant effects on the bond strength. Fast-cure products were not as affected since their high-temperature resistance is better.

Cure Time and Installation Direction Temperature Tests Also in ACI 355.4 and AC308, additional tests for the base material temperature at the time of installation have been updated, as well as the installation direction. Previously, testing for bond stress at cure time was not done or was considered optional. The manufacturer was responsible for providing the relevant working and cure time for the adhesive product at the minimum and maximum published base material temperatures during installation. ACI 355.4 and AC308 were modified in 2011 to include additional testing at the minimum and maximum installation basematerial temperatures that the manufacturer recognizes for the specific product.

Similarly, AC308 had tests for installation direction that were used to show that anchors installed vertically downward had the same bond strength as for anchors installed overhead. This applied for anchors with the largest diameter threaded rod or reinforcing bar and at the maximum embedment depth. These tests were all performed at room temperature. ACI 355.4, when published, had the same tests but also required that the tests be performed at the revised minimum and maximum installation base material temperatures.

Low Temperature and Freeze-Thaw Low-temperature in and of itself, is not typically a problem. Bond strength of adhesive anchor systems at room temperature and the minimum published base-material temperature are essentially the same. ACI 355.4 carried over the AC308 freeze-thaw tests which do test the ability of the adhesive anchor system

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to maintain the published bond strengths over the lifetime of the anchorage when exposed to freeze-thaw cycles.

One additional optional test has been added in AC308 for adhesive systems that are permitted to be installed at a base material temperature less than 40°F (4°C). After installation and full curing of the adhesive at or below 40°F, the concrete temperature is raised to more than 80°F (27°C) in a 12-hour period while a sustained load is applied. This situation is unlikely in practice, as the concrete must be exposed to a large temperature fluctuation. An ambient temperature change from 40°F to 80°F, which is possible during the day, would not be able to increase the temperature over the full thickness of a concrete member at the same rate that same day. Thus, this situation would only be applicable where direct sun or heat exposure is concentrated on a thin concrete slab with a shallow adhesive anchor embedment, and the adhesive happened to be installed below 40°F. Summary Adhesive anchor systems used with threaded rod and rebar are covered under the current design codes of ACI 318-14 for use in concrete. It is known that unlike cast-in and post-installed mechanical anchors, the adhesive bond strength must be evaluated and the bond strength is affected by low and high temperatures of the base material. ACI 355.4 and AC308 test procedures are established to cover the effects of temperature on the adhesive not only during the installation process but also throughout the service life of the anchorage. Designers should be aware of the various in-service temperature considerations on the design of the anchorage by referring to the adhesive system’s 3rd party evaluation report and applying the applicable bond stress to a proper anchor design in accordance with ACI 318-14 Chapter 17.▪ Christopher Gamache is the Manager of Approvals and Project Engineering / Anchors for Hilti North America. He is responsible for creating the technical data for the Hilti North American Product Technical Guide, Volume 2, for Anchor Fastening, and publishing external evaluation reports such as ICC-ES ESR’s. He can be reached at christopher.gamache@hilti.com.

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business issues

CASE BuSinESS PrACtiCES

Reframing Engineering

The Importance of Project Management

By Anthony H. LoCicero III, P.E., LEED AP

S

tructural engineers take classes in calculus, physics, statics, mechanics, structural analysis, and structural design during their undergraduate years. In graduate school, they take courses in structural dynamics, earthquake engineering, advanced structural analysis, and advanced structural design. In theory, with this knowledge, the newly minted graduates are ready to make the transition from academia to the realities of working in an engineering firm.

However, a few years after graduation, the question usually arises, “How does my firm make money?” Admittedly, this seems like a silly question. But, up until this point, it is a question that the typical structural engineer was never taught, exposed to, or even asked to think about. And then one day, bang! This structural engineer is spending his or her days interfacing with clients, managing personnel and project budgets, writing proposals, and reviewing invoices, often during the evening after everyone else has gone home. How did this transition occur?

Conversations among project managers and principals of engineering firms rarely center on problems with code provisions, solving complex equations, or performing detailed design work. This should not be a surprise – structural engineers have years of training in these complex technical tasks, but they do not use this knowledge any longer. Usually, upper management’s chief concerns include developing new client relationships and maintaining existing relationships. So if the leaders of most structural engineering firms believe that relationships are a vital component of their firm’s future success, why are structural engineers not trained in how to foster and maintain relationships? The same could be asked about other non-technical aspects of an engineering business such as managing risk, reading contracts, managing accounts receivable, forecasting workload, and controlling project budgets.

Responsibilities and job titles vary from firm to firm depending on the organizational structure, market sector, and other factors.

The non-technical aspects of running a project typically fall to the Project Manager. In many cases, the Project Manager role is the “Peter Principle” in action – the most technically adept

engineers are “promoted” to project manager where they are asked to set aside their technical proficiencies and are thrust into a new role for which they are largely untrained. Moreover, to compound this problematic situation, how are our talented engineers trained in the soft skills of management? They learn by observation and from the habits and practices (good and bad) of the previous generation of engineer-turned-project managers. And thus, the cycle continues.

A parallel and opposite scenario is also running at the same time. Engineers who cannot master advanced technical concepts are considered underperformers and are not given the opportunity to try their hand at project management. If given a chance, they might have an affinity for that role because of the skills they naturally have but which they have never been asked to employ.

So, how does the structural engineering profession break this pattern? How can staff members (technically and non-technically skilled) be encouraged to develop managerial soft-skills that successful project managers need so that those best suited for management careers are identified?

The profession’s architecture counterparts have it right. The recently updated Architect Registration Examination (ARE) 5.0 includes the following modules: Practice Management (PcM) focuses on the management of an architectural practice, including professional ethics, fiduciary responsibilities, and the regulations governing the practice of architecture. The professional should be able to demonstrate an understanding of and abilities in business structure, business development, and asset development and protection.

Project Management (PjM) focuses on the management of architectural projects, including organizing principles, contract management, and consultant management.

The professional should be able to demonstrate an understanding of and abilities in quality control, project team configuration, and project scheduling.

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Courses in these professional practice skills are also required in most, if not all, Bachelor of Architecture curricula. As a result, architects are exposed to both sides of their field early in their careers, and they can decide where their passion and skills lie and where they can be most successful. The structural engineering profession needs to find a way to give young engineers the same exposure to business practicum.

Yes, some universities are starting to pick up the slack with programs in Engineering Management. Maybe this is a start, but it is likely that few students realize the opportunities these programs offer. They just don’t yet understand or appreciate the importance of the business of engineering. No one has told them how their future firms make money.

The CASE Toolkit Committee is currently developing Tool 5-5, Project Management Training Guide, which will be available soon. Tool 5-5 is a template curriculum of 24 topics that should be taught to budding Project Managers, and how they relate to eight overarching corporate goals: Smooth Project Execution, Reputation, Profitability, Marketing, Employee Retention and Growth, Firm Growth, Risk Management, and Contributions to the Profession. The 24 topics include both financial and technical management skills and are applied chronologically through the life of a sample project, from Business Development and Project Selection Go/No Go Decisions to Archiving and the Promotion of Successful Projects.▪ Anthony H. LoCicero III is a Project Manager at Burns Engineering in their Philadelphia, PA, and New York, NY, offices. He serves as a member of the CASE Toolkit Committee. He can be reached at alocicero@burns-group.com.

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All 2018 Resource Guide forms, including the 2018 TRADE SHOW IN PRINT, are now available on our website: www.STRUCTUREmag.org.

Structural Engineering Summit Draws Record Attendance “This year’s Summit showcased the best our profession has to offer in terms of education, technical capabilities, and excitement,” said NCSEA Past President Tom Grogan.

The 2017 Summit featured a keynote by Martina Driscoll, P.E., and Terrence Paret of Wiss, Janney, Elstner Associates, discussing the magnitude 5.8 Mineral, Virginia, earthquake and its effect on the Washington Monument and the Washington National Cathedral. A panel also was held on How to Improve ASCE 7, led by Ron Hamburger, P.E., S.E., SECB, John Hooper, P.E., S.E., and Don Scott, S.E. This panel’s goal was to collect feedback on how to make the loading standard more effective and efficient to use.

The NCSEA Awards Banquet at the Summit featured the presentation of NCSEA Special Awards, including:

In addition, six NCSEA SEAs were awarded funding as part of NCSEA’s Grant Program.

NCSEA Service Award to James O. Malley, S.E., SECB, for work on behalf of NCSEA that is beyond the norm of volunteerism.

Structural Engineers Association of Georgia (SEAOG)

James M. Delahay Award to Michael O’Rourke, Ph.D., P.E., for outstanding contributions towards the development of building codes and standards.

Structural Engineers Association of Hawaii (SEAOH)

Robert Cornforth Award to Theodore E. (Ted) Smith, P.E., S.E., for exceptional dedication and exemplary service to an NCSEA Member Organization and to the profession.

Susan M. Frey NCSEA Educator Award to Edwin T. Huston, S.E., for genuine interest in, and extraordinary talent for, effective instruction to practicing structural engineers.

Also presented at the Banquet were the NCSEA Excellence in Structural Engineering Awards (highlighted in last month’s NCSEA News column). Overviews of all award winners are included elsewhere in this issue (pp. 30-36). In addition, you can visit www.ncsea.com to see a complete list and descriptions.

Awarded $1000 to promote visibility for the profession.

Awarded $500 for a shake table.

Structural Engineers Association of Illinois (SEAOI)

Awarded $1000 to host a Young Engineers Symposium.

Structural Engineers Association of Massachusetts (SEAMass)

Awarded $2000 to host an ACE Mentor Program.

Structural Engineers Association of New York (SEAoNY)

Awarded $2000 for a diversity launch party with the SE3 committee and to host networking skills events.

Structural Engineers Association of Ohio (SEAoO)

Awarded $3000 to enhance their existing student mentoring program.

We look forward to next year’s Structural Engineering Summit, to be held October 24-27 at the Sheraton Grand in Chicago, IL.

NCSEA News

News form the National Council of Structural Engineers Associations

The National Council of Structural Engineers Associations attracted more than 500 attendees from across the country to Washington D.C. from October 11-14 to celebrate the profession at the annual Structural Engineering Summit. The event featured education sessions for the practicing structural engineer, social and networking events, and a trade show with 59 exhibitors.

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NCSEA is pleased to announce the addition of two new directors to the Board of Directors. David Horos of SEAOI and Stephanie Young of MNSEA join the 2017-2018 Board with standing members: Williston “Bill” Warren IV, President; Jon Schmidt, Vice President; Emily Guglielmo, Secretary; Susan Jorgensen, Treasurer; Chun C. Lau, Director; Ed Quesenberry, Director; and Thomas A. Grogan Jr., Past President. NCSEA thanks Brian Dekker, past NCSEA Board President, and Jonathan Hernandez, Director, for their service on the NCSEA Board of Directors.

From left to right: Chun Lau, Emily Guglielmo, David Horos, Susan Jorgensen, Ed Quesenberry, Bill Warren, Jon Schmidt, Stephanie Young, and Tom Grogan.

2018 Call for Abstracts

Enhanced Subscription Plan

The NCSEA Structural Engineering Summit Committee is seeking presentations for the 2018 Summit in Chicago, IL. The Summit deliver pertinent and useful information that the attendees can apply in their structural engineering practices. Submissions on best-design practices, new codes and standards, recent projects, advanced analysis techniques, management, business practices, and other topics that would be of interest to practicing structural engineers are desired. The 2018 Summit will feature education specific to the practicing structural engineer, in both technical and non-technical tracks.

Visit www.ncsea.com to download the Call for Abstract form.

In response to your input, NCSEA is excited to announce an enhanced Webinar Subscription Program that provides unprecedented access to the highest-quality webinars available for structural engineers.

The enhanced annual subscription includes:

• An unlimited number of free CE certificates for each webinar so multiple viewers at the same location can receive credit for every live webinar with the same subscription.

• New and enhanced education website that will be launched in the first quarter of 2018 to provide easy access to all your education content and records.

Visit www.ncsea.com for more information about this subscription plan and to register for upcoming webinars.

NCSEA Webinars January 11, 2018 Structural Concrete Special Inspections Chris Kimball, S.E., P.E., MCP, CBO This seminar will discuss, in detail, the specific special inspection requirements for concrete construction as listed in Chapter 17 of the 2015 International Building Code (IBC) and will cover in detail the specific items requiring special inspection and testing such as reinforcement, formwork, concrete materials, anchors, placement, and curing techniques.

January 25, 2018 Multi-Family Wood Construction: Engineering Mid-Rise Buildings Ricky McLain, P.E., S.E. This presentation is intended for structural engineers who are seeking a full system understanding of the unique design considerations associated with 4-6 story wood structures.

February 15, 2018 Structural Stability During Construction Matthew Pavelchak This course provides an overview of common areas of concern regarding structural stability during the construction process and will highlight issues that are often overlooked or missed during construction which can create unsafe conditions leading to partial or complete structural collapse.

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News from the National Council of Structural Engineers Associations

• Access to 20+ live webinars annually, featuring the highestquality speakers available. Check out our upcoming schedule at www.ncsea.com.

• Unlimited access to NCSEA’s Recorded Webinar Library 24/7/365 – more than 100 webinars.

STRUCTURE magazine

NCSEA News

NCSEA Announces 2017–18 Board

Learning / Networking

Structural Materials and Global Climate

Structural Columns

The Newsletter of the Structural Engineering Institute of ASCE

A Primer on Global Emissions for Structural Engineers http://bit.ly/2yE6P4J

SEI/ASCE Live Webinars – Learn from the Experts December 8: Wind Design for Components and Cladding Using ASCE 7-16 December 11: Joints in Buildings December 19: Alternative Designs for Anchorage to Concrete Individual Certificate Fee Discontinued. Register at Mylearning.asce.org for these and much more.

Check out P.E./S.E. Exam Review Courses – www.asce.org/live_exam_reviews.

SEI Local Leaders Conference Fifty local SEI leaders from SEI Chapters and Graduate Student Chapters met October 20-21 in Chicago for the SEI Local Leaders Conference to learn about new initiatives and share Chapter best practices. Attendees also participated in ASCE Communications and Media Training and a presentation/tour of the Riverwalk Expansion Project. The gathering included the first meeting of the SEI Graduate Student Chapter Leadership Council. Learn more about SEI Chapters at www.asce.org/SEILocal.

Register now and plan your participation using the new interactive planner at www.structurescongress.org.

NOW AVAILABLE – ASCE/SEI 41-17 Seismic Evaluation and Retrofit of Existing Buildings The new edition describes deficiency-based and systematic procedures that use performance-based principles to evaluate and retrofit existing buildings to withstand the effects of earthquakes. A primary reference for structural engineers addressing the seismic resilience of existing buildings. www.asce.org/SEI.

Students and Young Professionals

NEW Scholarship for Students to Structures Congress Expand your Horizons!

Participating at Structures Congress opens doors to many SEI opportunities, including meeting leaders of the profession, the latest knowledge from research, standards and business practices, and fun networking events.

Encourage a student and/or young professional to join you at Structures Congress in Ft. Worth.

Students: Apply by January 5 at www.asce.org/SEI-Students.

Made possible by the SEI Futures Fund in partnership with the ASCE Foundation.

SEI Student Career Networking Event April 20 at Structures Congress in Ft. Worth

Employers: Sign up now to participate, be included in event promotions, and receive student profiles in advance of the event. www.asce.org/SEI-Sustaining-Org-Membership.

Students: Plan now to connect one-on-one with employers for SE positions and internships. Learn more at www.asce.org/SEI-Students.

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SEI Elite Sustaining Organization Members

As an SEI Elite Sustaining Organization Member, Michael Baker enjoys complimentary participation in the SEI Student Career Networking Event April 20 at Structures Congress 2018 in Ft. Worth.

Reach more than 30,000 SEI members year-round with SEI Sustaining Organization Membership. Show your support for SEI to advance and serve the structural engineering profession. Learn more and join today at www.asce.org/SEI-Sustaining-Org-Membership.

SEI Futures Fund

Investing in the Future of Structural Engineering

Membership

Join or Renew SEI/ASCE membership For innovative solutions and learning, to connect with leaders and colleagues, and enjoy member benefits.

Check out the NEW mobile-first landing page and news features at www.asce.org/SEI including: Get Involved Early by Lizhong Wang, A.M.ASCE. Make sure to select SEI with ASCE membership to receive benefits such as SEI Member Update monthly e-news opportunities and resources – visit www.asce.org/myprofile or call ASCE Customer Service at 800-548-ASCE (2723).

Congratulations to SEI Members in the 2017 Class of ASCE Distinguished Members Bilal M. Ayyub, Ph.D., P.E., Dist.M.ASCE; University of Maryland James O. Jirsa, Ph.D., P.E., Dist.M.ASCE, NAE; University of Texas, Austin Kincho H. Law, Ph.D., Dist.M.ASCE; Stanford University John G. Tawresey, P.E., F.SEI, Dist.M.ASCE; KPFF Consulting Engineers http://news.asce.org/asce-announces-new-class-of-distinguished-members

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Errata SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI-Errata. If you would like to submit errata, contact Jon Esslinger at jesslinger@asce.org.

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The Newsletter of the Structural Engineering Institute of ASCE

More than ever, structural engineers have a critical role as leaders and innovators to improve the safety and well-being of our communities.

The SEI Vision for the Future is our plan to ensure a bright and dynamic future for structural engineering – to prepare the next generation of structural engineers to be leaders and innovators. The SEI Futures Fund, in partnership with the ASCE Foundation, leverages contributions to fund SEI Vision initiatives such as student and young professional scholarships, global initiatives, and professional development.

What You Can Do Your gift to the SEI Futures Fund will strengthen SEI efforts to build a vibrant community of structural engineers to lead into the future! Learn more and give at www.asce.org/SEIFuturesFund.

Structural Columns

Advancing the Profession

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE Practice Guidelines Currently Available CASE 962-F – A Guideline Addressing the Bidding and Construction Administration Phases for the Structural Engineer This document has been developed to assist all the parties associated with the bidding and construction administration phases of a project, with the primary emphasis on those issues associated with the structural engineer (SER). It is essential that the design team remains proactive in communicating with the contractor and the owner after the construction documents have been issued. This communication during the construction phase, as well as during the pricing and bidding process, should have as its primary goal the assistance, interpretation, and documentation for the improvement of the constructed project. This is a guide to the SER’s roles after the construction documents have been issued for construction.

It provides guidance on pre-bid and pre-construction activities through the completion of the project. The appendices contain tools and forms to assist the SER in applying this guide to their practice.

CASE 962-G – Guidelines for Performing Project Specific Peer Reviews on Structural Projects Increasing complexity of structural design and code requirements, compressed schedules, and financial pressures are among many factors that have prompted the greater frequency of peer review of structural engineering projects. The peer review of a project by a qualified third party is intended to result in an improved project with less risk to all parties involved, including

the engineer, owner, and contractor. Many aspects of the peer review process are important to establish before the start of the review to ensure that the desired outcome is achieved. These items include the specific goals, scope, and effort, the required documentation, the qualifications and independence of the peer reviewer, the process for the resolution of differences, the schedule, and the fee. These guidelines intend to increase awareness of such issues, assist in establishing a framework for the review, and improve the process for all interested parties.

CASE 962-H – National Practice Guideline on Project and Business Risk Management This guideline is intended to assist structural engineering companies in the management of risk associated with projects and to provide commentary regarding the management of risk associated with business practices. The guideline is organized in two sections that correspond to these two areas of risk, namely Project Risk Management and Business Practices Risk Management. The goal of the guideline is to educate and inform structural engineers about risk issues so that the risks they face in their practices can be effectively mitigated, making structural engineering firms more successful.

You can purchase these and the other CASE Risk Management Tools at www.acec.org/case/news/publications.

CASE Winter Planning Meeting February 1 – 2, 2018; Austin, TX

The agenda for the meeting is: Thursday – February 1 6:15pm – 7:15pm Coalition Welcome Reception Sponsored by the Small Firm Council Friday – February 2 7:30am – 8:30am Shared Breakfast 8:00am – 12:00pm CASE General / Toolkit Committee Meeting CASE Contracts Committee Meeting CASE Guidelines Committee Meeting CASE Programs & Communications Committee Meeting

12:00pm – 2:00pm Joint Coalition Roundtable Lunch Moderator: Andy Rauch, BKBM Engineers 2:15pm – 6:00pm CASE General / Toolkit Committee Meeting CASE Contracts Committee Meeting CASE Guidelines Committee Meeting CASE Programs & Communications Committee Meeting 6:00pm – 6:15pm Committee Wrap-up Session If you are interested in attending the meeting or have any suggested topics/ideas from a firm perspective for the committees to pursue, please contact Heather Talbert at htalbert@acec.org.

CASE Risk Management Convocation in Fort Worth, TX The CASE Risk Management Convocation will be held in conjunction with the Structures Congress in Fort Worth, TX, April 19 – 21, 2018. For more information and updates go to www.structurescongress.org.

The following CASE Convocation sessions are scheduled to take place on Friday, April 20: 9:30 am – 10:30 am Managing Design Professionals’ Risk in the Design and Construction of Property Line Building Structures Moderator: Benjamin M Cornelius, Leslie E. Robertson Associates, R.L.L.P. Speaker: Kriton A. Pantelidis, Esq., Welby, Brady & Greenblatt, LLP STRUCTURE magazine

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11:00 am – 12:30 pm The Good and the Bad of Delegated Design: How to Work With/As a Specialty Structural Engineer Moderator / Speaker: Kevin Chamberlain, DeStefano & Chamberlain Inc. 1:30 pm – 3:30 pm Construction Dispute Resolution through Forensic Engineering Moderator/Speaker: Benjamin M Cornelius, Leslie E. Robertson Associates, R.L.L.P. 3:30 pm – 5:00 pm Tackling Today’s Business Practice Challenges – A Structural Engineering Roundtable Moderator: Corey Matsuoka P.E., SSFM International, Inc. December 2017

CASE’s Toolkit committee has released the following new tools for firms to use: Tool 4-6: Project Team Coordination and Prioritization Log Project planning and coordination are crucial to reducing your firm’s risk and to avoiding claims. One major facet of project planning is organizing coordination items and prioritizing when you need that information to complete your work. The CASE Tool 4-6: Project Team Coordination and Prioritization Log provides a simple to use and easy to manipulate spreadsheet-based tool for coordinating project information required to complete the structural design with the other project team members.

Tool 5-5: Project Management Training Guide In the structural design profession, engineers learn project management in an ad hoc manner as they advance from purely technical tasks to situations that require management skills.

Often, self-learning combined with one-on-one mentoring are the only things that develop the management skills of engineers as they acquire more responsibility. Learning in this fashion can result in project management practices that vary significantly with the individual’s exposure to various project and mentorship experiences. A management training program that provides a formal indoctrination into a firm’s preferred management practices and the firm’s values as reflected in those practices can be a powerful tool that can increase the firm’s effectiveness and profitability.

CASE in Point

New CASE Risk Management Tools Released

2018 Small Firm Council Winter Seminar Looking to grow your business? Who isn’t!

Whether it is how to market, what key firm positions to fill, how to organize the firm into teams, or when it is time to delegate more, it is your leadership that ultimately grows your business. That is why you will want to join other small firm leaders from around the county for an in-depth examination of three strategic agendas your firm should implement to become more successful and profitable.

Seminar topics will focus on: • Sustainability – Promoting on-the-job learning and growth, and seeking new ways to improve your management process and protocols • Serviceability – Creating client value and a superior client experience through firm innovation and thought leadership • Survivability – Focusing on consistently generating and investing profits to expand your firm’s influence into current and prospective target markets This seminar is for firm leadership tasked with making decisions, such as owners, principals, HR professionals, CEOs, CFOs.

Registration:

ACEC Coalition Members – $399 ACEC Members – $499 | Non-members – $599

Location:

Hilton Garden Inn Austin Downtown & Convention Center 500 North IH 35, Austin, Texas 78701 Phone: 877-782-9444 use group code: ACEC Special Rate – $189/night until January 4, 2018, or until block sells out

About the Speaker Mark Goodale is a co-founder of Morrissey Goodale. His breadth of experience includes organizational development, strategic planning, mergers and acquisitions, marketing, and executive search. He is a trusted advisor and coach to dozens of industry executives.

Before helping to establish Morrissey Goodale, Mark was the Corporate Strategic Marketing Manager at PBS&J (now a part of Atkins) where he was charged with improving and implementing progressive corporate initiatives geared to position the firm for successful, large-scale client pursuits.

Before that, he worked at ZweigWhite for over a decade and headed the firm’s strategic business planning and marketing business units.

Mark has authored numerous articles for industry magazines such as Civil Engineering Magazine, CE News, and Consulting Specifying Engineer. He has been quoted many times in various industry publications and newspapers and is featured in the Morrissey Goodale/Axium video series, Building High-Performance Organizations. Mark was also a frequent contributor to ZweigWhite’s publications and events, and authored The Healthcare Market for AEP and Environmental Consulting Firms, the first of ZweigWhite’s market intelligence reports.

Always a top-rated speaker, Mark delivers presentations around the country on a wide variety of management topics at AIA, ACEC, NSPE, CSE, and ZweigWhite events.

Mark received his MBA from the Sawyer School of Business at Suffolk University where he now teaches Business.

To register for the seminar: http://bit.ly/2z2Mbrn Questions? Call 202-682-4377 or email at htalbert@acec.org.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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December 2017

CASE is a part of the American Council of Engineering Companies

Leading Innovation, Fostering Growth: Essentials to Achieving a Sustainable, Profitable Business February 1 – 3, 2018; Austin, TX

Structural Forum

opinions on topics of current importance to structural engineers

Women Designed to Move an Industry

By Kristin Killgore, P.E., S.E., LEED AP

T

here are questions in life that become routine. Where do you live?

How old are you? What do you do for a living?

There are also questions specifically directed to our profession. What is structural engineering? Does that mean you are an architect? What type of structures do you design?

As a female structural engineer, I routinely receive additional questions that open the door for self-reflection. These questions are honest, real, discussion-worthy questions specific to my gender. They are not intended to be offensive but are based on continued gender stereotyping in our society and a real need for conversation at all career levels within the structural engineering workplace.

I have been asked; Can you be a mom and be a structural engineer? How do you balance home and work life? How do the men in the profession treat you? How many women structural engineers do you know? How many hours do you work in a week and how many hours are you expected to work in a week?

These questions came from mentoring sessions with young high school women and early career engineers. Our conversations begin with general professional questions regarding how I chose my career path, but then quickly move to the treatment of women and integration of work and home life. It frustrates me that even with a full generation of women in the workforce, these young women already have perceived a struggle for women in the engineering profession and workplace.

The good news is that most of the ladies are not derailed by honest answers and perceive the conversation as a tool to effectively overcome any hurdle they may encounter through their careers. Young engineers today, both men and women, yearn for answers to career development questions while maintaining a desire to create a life and identity for themselves outside of their career. How would you answer such questions?

Cheryl Sandburg wrote the book Lean In – Women, Work, and the Will to Lead, encouraging women to advocate for themselves as they progress in their careers.

Sandburg argues that young women, with

the expectation of one-day forming families, may not pursue as many opportunities for advancement as their male colleagues, even years before they become mothers. The “lean in” mentality is one of pursuing every opportunity available until a conflict prevents you from doing so.

Leslie Gallery-Dilworth, FAIA, the author of Luck is Not a Plan for Your Future, argues that work-life balance does not exist. She stresses integration.

Integration is a realistic approach for managing the life of a spouse, parent, and career.

In my career, I have struggled to come to terms with the notion that a balance between work and life does not exist and integration is HARD. I continually feel as if I am failing in every aspect of my life and a good week is the week that I feel I have hit mediocrity.

For most people, I know this family expectation of balance is unrealistic. This constant dichotomy is a struggle for families.

I believe most men and women in today’s workplace environment desire an understanding from their employers that integration of personal time and professional time must be respected and encouraged. The profession of structural engineering is plagued with stereotypes of long hours, impossible deadlines, low pay compared to other engineering disciplines, and high expectations. People desire enrichment, personal and professional; our industry provides that enrichment for most who enter it, but often at the cost of burn out and dedicated talent leaving the industry.

Discussing gender sheds light on a person’s story and priorities, and it advocates for all people in an organization to develop a positive team environment, crucial to company success. Gender, though, must not be the defining factor in determining expectations for employee performance or position.

Mentoring in all professions, and through life, is a powerful tool to appreciate wisdom, avoid pitfalls, and provide accountability.

Mentoring has enriched my life, but at times I have often felt isolated by my profession.

Someone once asked me, “Do you know any women older than you, with children,

currently practicing structural engineering full time and in a leadership position?” I immediately felt my gut wrench and my brain spin as I raced through female engineers that I knew.

I knew of some, but did I have relationships with them, no. Most didn’t really live close, and I could not attest to their level of leadership. It was with this question that I realized I might have had professional women mentors outside of the industry who provided guidance, but I did not have a mentor who understood the structural engineering profession. The difference, though small, feels tremendous. A woman structural engineer and mom in a leadership position to glean any advice and knowledge from seems like a simple request to me, a 21st-century woman.

I hope that current and future professional leaders, both men and women, develop work cultures that erode employees’ incorrect perceptions about the engineering profession. In doing so, the gender line will become a gender sieve parsing ideas and influence. We need to assess our business practices and decide if we are encouraging our engineers to invest in themselves. As changes in practice infiltrate the engineering profession, students contemplating the start of a career in engineering will experience the long-term support they desire from their chosen profession.▪ Kristin Killgore is an Associate/Project Engineer with ZFI Engineering in Oklahoma City, Oklahoma. She is Co-Chair of the NCSEA Licensure Committee and a founding member of the Oklahoma City Chapter of Commercial Real Estate Women.

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, the Publisher, or the STRUCTURE® magazine Editorial Board.

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December 2017

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