SSI Bridge: Evaluation of Soil-Structure Interaction Effects of PNW Bridges – year 1 (2012-13)
The Pacific Northwest (PNW) is prone to large subduction zone earthquakes, large basin-and-range earthquakes, and smaller, shallow, crustal earthquakes. Each of these different types of creates a different type of demand on a soil-bridge system. A subduction zone event, for instance, creates large magnitude, long-duration and long-period events that can damage long, flexible bridges. A shallow, crustal event, when it occurs near a bridge, can create an intense velocity pulse that can damage shorter, more brittle bridges. In addition to the challenges presented by considering multiple earthquake scenarios, the soil underlying bridge columns and abutments can significantly affect the seismic response of the overlying bridge superstructure. To truly examine the seismic performance of a bridge, one must consider soil-structure interaction.
In this research we propose to create a finite element model of a typical PNW soil-bridge system within the program OpenSees. We will consider different soil conditions by using a series of complex, nonlinear Winkler springs. For this research, we will focus on large, subduction zone earthquakes, becasue this scenario is possibly the most damaging event in the PNW. However, for completeness, we will also examine shallow, crustal earthquakes as well as longer-return period basin-and-range earthquakes. The end-product of the reasearch will be guidance for how a typical bridge in varying soil conditions performs during differing, realistic earthquake motions. Future research will examine different bridge-foundation-soil models and earthquake motions.