SEISMIC INSTRUMENTATION OF THE BILL EMERSON MEMORIAL MISSISSIPPI RIVER BRIDGE AT CAPE GIRARDEAU (MO): A COOPERATIVE EFFORT

摘要

This paper describes the seismic instrumentation scheme for the Bill Emerson Memorial Bridge in Cape Girardeau (MO). The new Mississippi River crossing is a cable-stayed bridge near the location of the 18 1 1-1 8 12 New Madrid earthquakes. This seismically active region requires hazard mitigation programs, including those related to investigation of strong shaking of structures and the potential for ground failures in the vicinity of structures. Design of the bridge accounted for the possibility of a strong earthquake (magnitude 7.5 or greater) during the design life of the bridge. Therefore, planning for its seismic instrumentation was initiated before the construction started. Seismic instrumentation plan for the Bill Emerson Memorial Bridge includes 84 accelerometers on the superstructure and pier foundations (caissons, tower and deck), in the vicinity of the bridge (e.g. free-field both surface and downhole), and in horizontal spatial arrays to assess the differential motions at the piers along the 1206 m (3956 ft) total span of the bridge. The real-time seismic monitoring system will support signal transmission via the internet from combinations of uniaxial and tri-axial accelerometers to the recorders at the site. The system will record events at the site and broadcast the data to outside users. Synchronized system-wide timing for all of all the accelerometers will assure time-variant response recording at one location of the structure with respect to another. Real-time streaming of the data will enable remote maintenance and data acquisition and retrieval capabilities. In addition, wind-related sensors (e.g. anemometers) will be deployed to record the response of the bridge to wind-related vibrations. The response data will be used by the owner, researchers and engineers to (1) assess the performance of the bridge, (2) check design parameters, including the comparison of dynamic characteristics with actual response, and (3) better design future similar bridges. By appropriate configuration of the streamed data, the instrumentation can also be used as a "health monitoring" tool (a) to serve as an early warning system of defects or unexpected behavior, and (b) to assess damage to the structure. Monitoring the response of structures in real-time or near real-time is usually adopted when rapid response information is needed such as with the recent emphasis on homeland security.