EFFECT OF VARYING FOUNDATION STIFFNESS ON SEISMICALLY INDUCED LOADS IN BRIDGE BENTS: A SENSITIVITY STUDY

Research was undertaken to assist the Tennessee Department of Transportation (TnDOT) in its analysis of bridges subjected to seismic loading. Specifically, consideration was given to the modeling of the soil-pile interface where friction piles are used in loessial soil. TnDOT uses the SEISAB bridge analysis program, developed by Imbsen and Associates, for the seismic analysis of its bridges. This program was used for all analysis of the research. Current TnDOT modeling practice is to consider that the bridge piers are fixed at the top of the pile cap rather than to assign values of stiffness to springs used to model the resistance of the soil to foundation movement. Elastic spring coefficients, developed using methods presented previously, and the traditional beam-on-elastic-foundation theory are used in the modeling of the bridges. The primary focus of this study is the sensitivity of the calculated axial loads and moments to variations in these spring coefficients. The results from this study underscore the need for more experimental data that could lead to more realistic and reliable values for spring stiffness.