Effect of pounding on the seismic response of non-isolated bridges considering spatial variability of ground motion and soil-structure interaction

Pounding between the bridge structural components might cause serious damage and may lead to unseating and even collapse of the entire bridge. The motivation and objective of the present study are to investigate the influence of non-linear viscoelastic pounding on the seismic response of non-isolated multi-span simply-supported (MSSS) bridges, considering the effect of both frequency-independent (FI-SSI) and frequency-dependent (FD-SSI) soil-structure interactions. The investigation considers both pulse-type and non-pulse-type near-field uniform ground motions, as well as non-uniform ground motions considering the spatial variability of ground motion (SVGM) in hard, medium, and soft soil conditions. The study considers a spectral-representation-based simulation approach that generates sample functions of a multivariate non-stationary stochastic process with evolutionary power based on its mandated non-stationary cross-spectral density matrix. This approach, which incorporates the effects of wave passage, incoherence, and differential site response, is employed for simulating arrays of SVGM. Parametric studies have been carried out using the state-space formulation to analyze the effects of SVGM and FD-SSI on the pounding forces, which consequently influence the seismic response of bridges. It is observed that the influence of FD-SSI and SVGM on pounding phenomena are most significant for soft and hard soils, respectively. The study highlights that consideration of SVGM and FD-SSI reduces the maximum pounding force in bridges, and the effect of pounding on the structural response is greatly influenced by gap sizes. Thus, it may be concluded from the results that consideration of FD-SSI and SVGM leads to a more realistic and economical design of bridges.