Dynamic Soil-Foundation-Structure Interaction Analysis of Large Caissons

Keywords: Reinforced concrete.  Caissons.  Long span bridges.  Equivalent linear analysis.  Nonlinear analysis.  Soil structure interaction.

Abstract: Large cellular reinforced concrete caissons exist as foundations of major long span bridges across waterways in many parts of the country.  The purpose of this study is to qualitatively assess the effects of  various factors affecting the seismic response of such caissons.  Several equivalent linear and nonlinear analyses were performed for a typical caisson, idealized from the large caisson at Pier W3 of the west spans of the San Francisco-Oakland Bay Bridge.  The results indicate that the effects of the superstructure on the response of the caisson were insignificant.  The lateral earth pressure, base bearing pressure, and soil stresses computed by the equivalent linear analysis indicate the possibility of soil foundation separation (gapping and uplift).  The results of nonlinear analyses indicate that motions and stresses developed in the caisson are sensitive to the soil-caisson and rock-caisson interface properties.  More sensitivity analyses of caissons founded in different materials are needed to address the effects of soil embedment on the caisson response.