The seismic response of reinforced concrete bridges must include consideration of the whole system including soil-foundation-structure interaction (SFSI). Simulation models validated against the results of experimental tests are required to provide an accurate prediction of the bridge system response. Performance-based engineering necessitates large-scale parameter studies of these simulation models to quantify the demand for varying levels of seismic hazard. The goal of this research is to characterize the SFSI effects for a range of hazard levels by using calibrated models from the experimental tests.
Two projects administered by the Network for Earthquake Engineering Simulation (NEES) have facilitated the study of this system effect through the collaboration of researchers within the earthquake engineering community. Shaking table tests of both a two-span and a four-span bridge at 1/4-scale were conducted at the University of Nevada, Reno. Nonlinear dynamic analyses of three-dimensional finite element models performed using OpenSees were evaluated based on the experimental test results. For the two-span bridge, the simulation model matches well both the global and local response until the onset of failure. The highly nonlinear pounding at the abutments and complicated test protocol of the four-span bridge produces less agreement in the simulation results.
A simulation model for the prototype bridge system incorporates the influence of the abut- ments, drilled shaft foundations, and site response effects. The cyclic response of the soil at the abutments is calibrated using results from full-scale tests. P-y, t-z, and q-z springs model the in- ertial interaction between the soil and pile foundations. A total of 1280 site response analyses are computed at four locations along the bridge for two soil profiles using SHAKE to obtain the free-field motions at the location of each soil spring.
Large-scale parameter studies of four prototype bridge models with and without the SFSI effect were conducted in parallel on a supercomputer using the multiple-interpreter capability of OpenSees. The response is determined for a suite of 80 ground motions of varying magnitude and distance from the fault. Linear regressions of the simulation results produce demand models that elucidate the effect of SFSI for both the global and local response. The demand models demon- strate that the SFSI effect is significant for the prototype bridge system and should be considered.
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