Walnut Creek, Calif., Pedestrian Bridge Wins National Architecture and Engineering Award
July 26, 2012 from American Institute of Steel Construction
(Chicago, IL) – The Robert I. Schroder Pedestrian Overcrossing in Walnut Creek, Calif., has earned national recognition in the 2012 Innovative Design in Engineering and Architecture with Structural Steel awards program (IDEAS2). In honor of this achievement, members of the project team will be presented with awards from the American Institute of Steel Construction (AISC) during a ceremony at the north end of the bridge on Tuesday, July 31 at 4 p.m. Conducted annually by AISC, the IDEAS2 awards recognize outstanding achievement in engineering and architecture on structural steel projects across the country. The IDEAS2 award is the highest, most prestigious honor bestowed on building projects by the structural steel industry in the U.S.
The project team members include:
- owner/developer Contra Costa County Public Works Department
- architect MacDonald Architects, San Francisco
- structural engineer Arup, San Francisco
- general contractor Robert A. Bothman, Inc., San Jose, Calif.
- steel fabricator Mountain States Steel, Lindon, Utah (AISC Member/AISC Certified Fabricator)
- steel detailer Axis Steel Detailing Inc., Orem, Utah (AISC Member)
- steel erector Adams & Smith Inc., Lindon, Utah (AISC Member/AISC Advanced Certified Steel Erector)
The Robert I. Schroder Pedestrian Overcrossing is a National award winner in the category of projects Less than $15 Million, making it one of only five projects around the country to receive the National honor. Each year, the IDEAS2 awards honor National and Merit award winners in three categories, based on constructed value: projects less than $15 million; projects $15 million to $75 million; and projects greater than $75 million. Each project is judged on its use of structural steel from both an architectural and structural engineering perspective, with an emphasis on: creative solutions to project requirements; design innovation; aesthetic and visual impact of the project; innovative use of architecturally exposed structural steel; technical or architectural advances in the use of the steel; the use of innovative design and construction methods; and sustainable design and construction.
The new overcrossing provides safe passage for pedestrians and bicyclists over a major traffic intersection in Walnut Creek, Calif. The bridge is the centerpiece of a transit village consisting of a commuter railway station and a high-density, residential and commercial development, and serves both commuters approaching the station and recreational users of the 33-mile long Iron Horse Trail.
Surrounding elements – transit easements on the trail’s surface for a future light-rail or streetcar system, 115kV power lines hanging directly over the project site, oak trees that the community was determined to preserve, underground utilities and multiple property rights issues – created boundaries within which the bridge’s design needed to fall (although the overhead power lines were eventually moved slightly). To avoid hitting the trees and utilities, the design team twisted the bridge’s body into an elongated S-shape.
In order to take up as little surface space as possible and avoid hitting any underground utilities, the structure relies on an unusual support system; the arches on either side emerge from a single common point at ground level, then tilt away from one another at approximately 20-degrees as they rise, leaving room in the middle for the bridge deck to rest. As a result, the support infrastructure underneath takes up only about half the space of a typical bridge.
“A very unique bridge that brilliantly uses steel as not only a structural element but as an architectural element too,” commented Eric Liobis, an honors student who recently completed his senior year at Rose-Hulman Institute of Technology in Terre Haute, Ind., and a judge in the competition.
To encourage community buy-in and create a lasting point of pride for the region, the team placed a great deal of emphasis on the bridge's aesthetics. While there are no parts on the bridge that are exclusively decorative—every element serves either a structural or safety function—each design decision was carefully considered from a visual and a functional perspective. For structural components, this meant making each piece as light and elegant as possible. The most visible structural support, the double arches, comprise welded groupings of three 10-in.-diameter hollow structural sections (HSS) members, which are joined by steel plate stiffeners at 14-ft intervals and bent continuously to form curves. The three-pipe grouping creates intricate shadow displays that change throughout the day and a visual rhythm that gives the structure a sense of dynamism. The two ground-level support structures consist of three slim concrete pillars, two of which are tilted to the angle of the arches, and appear almost too slim and delicate to support the bridge’s weight.
To create a feeling of openness, structural engineer Arup also eliminated the need for the arch segments to touch above the deck. A steel beam linking the two pairs of inclined buttress columns that support them under the deck ensures adequate structural support, giving pedestrians and bikers an unobstructed view of the sky.
The underside also received consideration due to its visual prominence from the ground. Because it acts as a continuous beam running throughout the bridge, suspended from the arches by structural hangers, Schroder's deck requires only about 2 ft of depth at its thickest point, rendering it considerably less bulky than most comparably sized bridge decks. This slender profile is enhanced by the curving underside, shaped to resemble the hull of a boat, a modification that also increases rigidity. Regularly shaped ribs provide visual rhythm to the deck, making visible the structural action of the hangers supporting it.
The project team’s emphasis on intelligent, efficient use of materials translated directly into a more environmentally friendly project. The push to craft a lightweight, minimal design with no superfluous elements significantly reduced the amount of steel used in the bridge; the total count was only 230 tons, or an average of 66 lbs per square foot, of deck plan across the entire structure—a very small figure compared to most bridges of this type.
The 10 IDEAS2 winners for 2012 were chosen from nearly 100 submissions received from architectural and engineering firms throughout the U.S. Each submission is reviewed and award winners are selected by a nationally recognized panel of design and construction industry professionals.
The IDEAS2 award dates back more than 70 years to the earliest years of AISC’s existence. Roger E. Ferch, P.E., president of AISC, said, “The entire Robert I. Schroder Pedestrian Overcrossing project team has shown how structural steel can be used to create structures that combine beauty and practicality. The result is a bridge that serves the public extremely well, while providing an example of what can be achieved when designing and constructing projects with steel.”
High resolution images of the Robert I. Schroder Pedestrian Overcrossing are available upon request by contacting AISC’s Tasha Weiss at 312.670.5439, [email protected].
Photo by Paul Mourraille
For more information contact:
American Institute of Steel Construction
The American Institute of Steel Construction, headquartered in Chicago, is a not-for-profit technical institute and trade association established in 1921 to serve the structural steel design community and construction industry. AISC’s mission is to make structural steel the material of choice by being the leader in structural steel-related technical and market-building activities, including: specification and code development, research, education, technical assistance, quality certification, standardization, and market development. AISC has a long tradition of service to the steel construction industry of providing timely and reliable information.
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