SEISMIC SCREENING AND RETROFITTING OF DELAWARE'S BRIDGES

Existing bridges in the eastern United States have historically been designed predominately to resist gravity loads, without any regard for seismic loads. This leaves many of the bridges in this country vulnerable to extensive damage and possible collapse, due to earthquakes. The current trend of seismically retrofitting bridges to mitigate the risk has become increasingly popular in highly active seismic areas, as well as low activity areas, throughout the U.S. The goal in performing the research work in this thesis was to develop a program for assessing the seismic risk of bridges in Delaware and to prescribe applicable retrofit procedures. A Delaware Seismic Risk Algorithm for Bridges was developed to identify and prioritize all of the bridges in the state, according to their seismic vulnerability. The detailed evaluation of specific structural components on bridges deemed most vulnerable to seismic motion is presented. This evaluation involves comparing the actual strength of specific bridge components to the required strength in resisting the design earthquake loading. In some cases this may require performing a dynamic analysis of the bridge. Following the detailed evaluation procedure, specific retrofit strategies applicable to the bridges in Delaware are presented. The goal of the retrofit action is to prevent total collapse of a bridge by increasing the seismic resistance of the structure.