SAN FRANCISCO-OAKLAND BAY BRIDGE SELF ANCHORED SUSPENSION SPAN STEEL DESIGN CHALLENGES AND DETAILING SOLUTIONS

The design of the new San Francisco Oakland Bay Bridge Self-Anchored Suspension Span will be completed by the end of the year 2001. A committee of structural engineers and architects representing the Bay Area selected the single tower asymmetric self-anchored suspension bridge design out of four other competing designs. This unique design has presented design challenges which required innovative yet practical solutions. The single steel tower is comprised of four shafts interlinked with shear links. These links are designed to yield during a strong seismic event to protect the tower shafts from any inelastic deformations. The tower shafts, which carry most of the bridge gravity load, are pentagonal in shape and taper in size along the height of the tower. The superstructure structural system of the bridge is a Vierendeel Frame which consists of dual steel box girders interconnected by steel crossbeams. Therefore the crossbeams resist the gravity loads as well as the lateral loads. This presented various challenges mainly due to the biaxial stresses in the box girder as well as fatigue considerations. Analytically, geometrically, and in the design of practical details for fabrication and durability, the Self-Anchored Suspension Span is a unique structure requiring unique solutions and departures from conventional design. Whether a similar bridge will ever again be proposed is unknown. However, the set of methods and technologies developed to meet these challenges offer an illustrative study of design for excellence.