SSI-Bridge: Soil-Bridge Interaction During Long-Duration Earthquake Motions

Abstract

The seismic response of a complete soil-bridge system during shallow, crustal and subduction zone earthquakes is the topic of this report. Specifically, the effects of earthquake duration on the seismic performance of soil-bridge systems are examined. This topic is important, because many bridges worldwide are located in tectonic regions characterized by a subducting plate boundary, where high-intensity, long-duration earthquake motions are possible. To date, the effects of earthquake duration are not widely considered during seismic design of bridges. In this report, a model of a soil-bridge system is developed in the finite element framework OpenSees. The soilbridge system is subjected to earthquake motions of varying durations using the direct method. Comparative results show that the number of inelastic excursions in the bridge column and pile increase significantly with earthquake duration, even though other traditional measures of damage such as maximum bending moments and peak column drifts are independent of duration. The results also indicate that the number of inelastic excursions is strongly correlated with earthquake intensity measures that incorporate earthquake duration, such as significant duration, and cumulative absolute velocity. The results imply that earthquake duration needs to be considered when designing and retrofitting bridge superstructures, especially when these are designed to fail in flexure, which is the desired mode of failure in current design methodologies.