Update of Bridge Design Standards in Alabama for AASHTO LRFD Seismic Design Requirements

Abstract

The Alabama Department of Transportation (ALDOT) has been required to update their bridge design specifications from the Standard Specifications for Highway Bridges to the LRFD Bridge Design Specifications. This transition has resulted in changes to the seismic design standards of bridges in the state. These changes, as well as their resulting effects on the design of bridges, have been researched and are discussed in this thesis. One of the goals was to determine if standard drawings and details for bridges in Seismic Design Categories A and B, which are low to moderate seismic regions, could be generated. Multiple bridges, provided by ALDOT, were re-designed so that they satisfied the requirements of the LRFD Specifications. These new design details were used to create standard drawings for bridges in SDC A and B. The superstructure-to-substructure connection was also investigated to determine if it was adequate to resist the expected horizontal design forces. It was determined to be inadequate, but instead of proposing a new connection design, the original connection was recommended along with supplying an extended seat width in the longitudinal direction. A new equation for determining the minimum seat width was recommended, and this new design philosophy was incorporated into the re-design of the bridges.