Pedestrian Bridge at Stockton, Calif. Medical Center Wins National Architecture and Engineering Award
October 16, 2012 from American Institute of Steel Construction
(Chicago, IL) – The pedestrian walkway at St. Joseph’s Medical Center in Stockton, 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 bridge on Friday, October 19 at 10:30 a.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 St. Joseph’s Medical Center, Stockton, Calif.
- architect Anshen+Allen Architects, San Francisco
- structural engineer ESE Consulting Engineers, Benicia, Calif.
- general contractor Turner Construction Co., Sacramento, Calif.
- steel fabricator, detailer and erector Olson Steel, San Leandro, Calif. (AISC Member/AISC Certified Fabricator/AISC Advanced Certified Erector)
The St. Joseph’s pedestrian walkway is a Merit award winner in the category of projects Less than $15 Million, making it one of only four projects around the country to receive the Merit 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 pedestrian bridge is a 320-ft-long steel-framed covered structure that connects the existing hospital to a new patient pavilion.
The bridge has five equal main spans, each about 60 ft long, and one end span that is 20 ft long. The main columns are 20-in.-diameter HSS members located 6 ft outside of the walkway footprint. These columns extend vertically about 17 ft above the walkway roof. The walkway is hung from these main columns with rigid diagonal tension/compression members. The main columns penetrate the existing plaza level waffle structure and are supported by new footings at the basement level. The walkway at both ends is separated from the existing and new hospital buildings by seismic expansion joints.
“Interesting visually because of its geometry and attention to attractive detailing, interesting technically because of its efficient design, showing weight savings,” commented Andy Johnson, previous AISC vice president of marketing (retired) and current board president for the Taos Center for the Arts, Taos, N.M., and a judge in the competition.
The overall structural configuration is relied upon to effectively reduce column eccentricity by placing columns on both sides of the walkway so that the center of mass of the overall bridge is located very close to the center of rigidity of the columns. Internal redistribution of torsional forces is made possible by designing the walkway walls, floor and roof as full trusses. The resulting effective eccentricity in columns below the floor level is less than 1 ft whereas the apparent eccentricity at each column is about 11 ft. The torsional strength and stiffness of the walkway are also used to effectively “fix” the top of all eccentrically placed columns in two horizontal directions. The resulting lateral resisting system is equivalent to a moment frame structure in two horizontal directions even though it uses only one continuous “beam” (walkway truss) eccentrically placed outside the column lines.
The main columns and walkway longitudinal top and bottom chords are detailed and designed as continuous. All other members are designed as simply connected, including columns to the foundation, in order to reduce forces in the members and the foundation and to reduce the stress gradient in the joints and connections. The existing waffle slab at the plaza level is used as a lever point along with the foundation pin connection to efficiently create fixity at the base of columns, and the walkway structure is used to create fixity at the top of the columns. Therefore, the columns in this bridge act as though they are fixed at top and bottom in both directions all by using simple end connections.
The resulting final configuration is very efficient as a structural system with a steel weight of about 830 plf. For comparison, an earlier design scheme with cantilevered wide-flange columns located directly under the bridge had an estimated structural steel weight of about 1,080 plf.
The bridge embraces the main arrival plaza linking the services of the new Women’s and Children’s Pavilion with the existing hospital. The overall shape of the bridge is very pleasing and dramatic in its curves, giving the viewer a feeling that the structure is floating in space since the slender supporting columns are placed eccentrically outside of the walkway footprint. HSS were used to reduce the overall dimensions and twin round HSS members were used as wall diagonals to visually reduce the profile while at the same time increasing the number of connections and thus reducing the length and stress at each connection point.
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 St. Joseph’s pedestrian walkway project team has shown how structural steel can be used to create structures that combine beauty and practicality. The result is a pedestrian bridge that serves the hospital extremely well, while providing an example of what can be achieved when designing and constructing projects with steel.”
High-resolution images of the St. Joseph’s pedestrian walkway project are available upon request by contacting AISC’s Tasha Weiss at 312.670.5439, [email protected].
Photo by Joe Fletcher Photography
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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