Seismic Evaluation of Brent-Spence Bridge

This is the second part of a two-part paper on field testing and analytical studies related to seismic behavior of the Brent-Spence bridge, which connects Covington, Kentucky, and Cincinnati, Ohio, over the Ohio River. This part of the paper deals with seismic evaluation of the bridge, while the first part dealt with free and ambient vibration studies of the bridge by field testing and finite-element analysis. Site-specific ground motion scenarios are developed for the bridge to represent probable earthquakes that may occur in these seismic zones. The time histories of these events are then used in the seismic analysis of the main bridge and response spectra are used for analyzing the approach spans. A three-dimensional finite-element model of the main bridge was subjected to the time histories to determine maximum responses (displacements, forces, and stresses). The seismic analysis of approach spans dealt only with the potential for loss of span due to excessive longitudinal displacement along the highway main line. For the maximum credible earthquake of magnitude 8.5 surface wave magnitude (7.3 body wave magnitude) on the Richter scale at New Madrid, Missouri, the seismic evaluation indicates that the main bridge will survive the earthquake in the elastic range without significant damage and no loss of span. The approach spans are found to be vulnerable to loss of span failure in the event of a maximum credible earthquake.