Two Unique Bridges for the New I-880 Freeway in California USA

摘要

Bridges are an integral part of our lifeline transportation system and must remain operational after an earthquake. The collapse of the I-880 Cypress Viaduct in Oakland California USA changed the way Caltrans (California Department of Transportation) designed it's bridges to withstand earthquake forces. The I-880 replacement freeway was realigned in downtown Oakland to be adjacent to railroad corridor and switchyards rather than continuing to divide a residential neighbourhood. A series of bridges were built. About half of the bridges are steel plate girder bridges built over active freeways and the other half are post-tension concrete box girders built with falsework. Two unique bridges were part of this group. One unique bridge is the curved steel Orthotropic Maritime Off-Ramp that has a 180 degree or "horseshoe" shape. Another unique bridge is a post-tensioned cradle bridge that allowed the new freeway to be built below an existing BART (Bay Area Rapid Transit) elevated concrete trestle viaduct. Both solutions were selected to minimise their impact on commuters.