Unconventional Design:
Architectural mesh adds to bridge’s unique aesthetic
Marcy Marro, Managing Editor,
Posted
10/01/2012
An important pedestrian byway for San
Franciscans, the Iron Horse Trail Pedestrian Bridge in Contra Costa
County, Calif., connects the Dublin/Pleasanton and Pleasant Hill
BART stations.
Officially named the Robert I. Schroder Overcrossing, after a
former Contra Costa County supervisor and Walnut Creek mayor, the
$6.8 million bridge is 800 feet long and 10 feet wide. Crossing
over eight lanes of Treat Boulevard in East San Francisco, the
footbridge allows walkers and cyclists of the 33-mile Iron Horse
Trail to safely cross over the heavily trafficked road.
Lead designer/engineer and prime consultant Arup, San Francisco,
along with San Francisco-based Donald MacDonald Architects,
designed the bridge with an unorthodox curvature of architectural
mesh that gives it an unconventional design. Arup specified
Cambridge, Md.-based Cambridge Architectural's Plait pattern
architectural mesh system that uses a modified U-Binding
attachment.
"The stainless steel construction makes the mesh durable as well
as very attractive," says Ignacio Barandiaran, Arup principal and
project manager. "The pattern specified for the project was
specifically selected to have very small openings to discourage
people from being able to throw sizable objects down to the traffic
below, and to also discourage people from trying to climb the fence
since the short distance from wire to wire makes it hard to get a
grip either with one's fingers or toes/feet."
The bridge's angled semi-circle handrails give it an original
aesthetic that is perfect for San Francisco's modern and
unconventional style. "The mesh makes a pedestrian bridge that
crosses over arterial roads/highways that is at best a distraction,
and at worst a menacing-looking and ugly element, into a beautiful
and inviting element of the overall design," Barandiaran says.
The arches on either side of the bridge materialize from a
single common point at ground level before tilting away from one
another at approximately 20 degrees, leaving room in the middle for
the bridge deck to rest. The resulting support system only takes up
about half the space of a typical bridge.
The bridge's double arches are comprised of welded groupings of
three 10-inch-diameter hollow structural sections (HSS) members
that are joined by steel plate stiffeners at 14-foot intervals and
bent continuously to form curves. Lindon, Utah-based Mountain
States Steel Inc. fabricated the structural steel for the bridge.
Axis Steel Detailing Inc., Orem, Utah, was the steel detailer, and
Adams & Smith Inc., Lindon, was the steel erector.
The bridge is part of the new Pleasant Hill Bart Station
Specific Plan, which includes refined designs for streets and
parking lots, public open spaces, building massing and character
and allowed uses. It serves as the centerpiece of the Contra Costa
Centre Transit Village, a sustainable, mixed-use transit-oriented
development that includes a network of parks, plazas, open spaces,
public art displays and affordable housing.
Robert I. Schroder Overcrossing, Contra Costa County,
Calif.
Award: 2012 IDEAS2 award for innovation in
structural steel design from the American Institute of Steel
Construction
Owner: Contra Costa County Redevelopment Agency and
Public Works Department Designer/engineer/prime
consultant: Arup, San Francisco
Architect: Donald MacDonald Architects, San
Francisco
General contractor: Robert A. Bothman Inc., San
Jose, Calif.
Construction manager: TRC-Hanna Group, Rancho
Cordova, Calif.
Transportation planning/traffic engineer: Fehr
& Peers Transportation Consultants, Walnut Creek, Calif.
Engineering consultant: SPS Engineers, San
Francisco
Steel detailer: Axis Steel Detailing Inc., Orem,
Utah
Steel erector: Adams & Smith Inc., Lindon,
Utah
Architectural mesh: Cambridge Architectural,
Cambridge, Md., www.cambridgearchitectural.com
Steel fabricator: Mountain States Steel Inc.,
Lindon, Utah, www.mssteel.com