Estimating the Peak Longitudinal Near-Field Seismic Response of an Isolated Bridge Using Basic Pulse Motions

The peak dynamic responses of a typical isolated bridge under basic pulse motions and a set of near-field (NF) earthquake records were investigated in this study. A numerical model of the isolated bridge was constructed and validated using seismic response measurements. Nonlinear time-history analyses were conducted for the isolated bridge by considering various post-yield stiffness ratios of the isolators and dominant pulse periods of the ground motions. The analysis results revealed that the peak pulse response and mean-plus-one standard deviation of the peak NF seismic response had similar trends of variation with the stiffness ratio. The ratio of the mean-plus-one standard deviation of the peak NF seismic response to the peak pulse response was described using a simple empirical formula. Using this formula, the NF seismic response of the isolated bridge could be estimated from the one-cycle Type-A pulse motion. The aforementioned ratio was approximated to 0.75 if the pulse period was larger than 6 s. However, the aforementioned ratio varied from 0.1 to 0.5 when the post-yield stiffness ratio varied from 0.1 to 0.45 if the pulse period was 1 s.