SEISMIC INVESTIGATIONS FOR THE DESIGN OF THE NEW MISSISSIPPI RIVER BRIDGE AT ST. LOUIS

This paper describes the proposed New Mississippi River Bridge at St. Louis and the preliminary seismic analyses. A high seismic performance level is set for the bridge, and a site specific design spectrum is developed. The bridge will be a cable stayed structure with a main span of 2000 ft carrying 8 lanes of traffic and 4 full shoulders resulting in 12 design lanes. The sidespans will be cast-in-place post-tensioned concrete cellular structures, connected integrally with the towers, and will extend approximately 70 ft into the main span. The remainder of the main span will consist of steel edge box girders supporting steel floor beams and a concrete deck. The important mode shapes and periods in the three principle directions of the bridge were investigated. The results of a preliminary multi-modal response spectrum analysis are presented, and the response of the bridge is evaluated.