San Francisco-Oakland Bay Bridge Cantilever Truss Demolition, California

NorCal Structural, Inc.

Bridge Demolition Engineering

Description: The existing San Francisco-Oakland Bay Bridge (SFOBB) includes a 2400 ft. long Cantilever Truss that will be demolished when the new bridge is opened. Constructed in 1934, the Cantilever Truss is composed of two cantilever arms that extend from opposite sides, supporting a suspended span in the middle, with a main span of 1400 ft. and two 500 ft. long side spans, supported by two 389 ft. high towers at E2 and E3. The structural members are either riveted box sections made up of angles, plates and latticed bracing or high tensile strength eyebars with pin connections. The towers are supported on massive caisson foundations extending up to 270 ft. into the soil. Caltrans engaged NorCal Structural, Inc. as a sub-consultant to T. Y. Lin International, to develop a BrIM model of the cantilever truss in Tekla Structures to capture all as-built structural details including all retrofits and rehabilitations of the structure since 1934, into one consolidated model. This model would be used to support engineering for deconstruction, including development of detailed stick-by-stick demolition sequences for the structure. The model would also be extensively used to develop 2D structural details for demolition. The Tekla model of the Cantilever Truss essentially captures a unique piece of engineering history for the San Francisco Bay Area. The model is approx. 220 MB in size with approx. 17,000 pieces and approx. 8000 assemblies modeled. Project is currently under deconstruction.

Special Challenges: Special challenges included modeling 1930's (very hard to read) as-built structural drawings to model extremely complicated truss member and connection details for a massive riveted structure composed of plates, angles, latticed bracing and eyebars. Another challenging aspect was managing the extremely large size of the model that captured every piece in the structure in a multi-user environment. Extensive use was made of the import of DWG details of the complicated truss members & joints.

Reason for Success: The Tekla BrIM model for the SFOBB Cantilever Truss is expected to be extensively used in the demolition of the structure, supporting both design and construction. The model will be used for production of 2D demolition details and 3D animated demolition sequences. This effort is expected to result in substantial cost savings to Caltrans in the demolition of the existing SFOBB structures.

 

Tekla BIMsight model