Assessment of seismic vulnerability of continuous bridges considering soil-structure interaction and wave passage effects

Abstract

Identical ground motion excitations at all supports are typically assumed in practice for the design and seismic analysis of structures. Such assumption is customarily made despite the fact that ground motions do vary among supports especially for extended-in-plan structures such as long continuous bridges, tunnels, dams, pipelines, etc. This paper focuses on studying the effects of non-synchronized motion (due to the difference in the ground motion arrival time at different bridge supports) on the seismic performance of continuous box girder bridges, and the severity of such effects whether soil-structure interaction, SSI, is ignored or considered in the analysis. The study is carried out on a nine-span bridge with a total length of 430 m supported on deep (piled) foundation embedded in sandy soils. Three different sand soil profiles are investigated representing medium to stiff soil. Eighteen real bedrock earthquakes are extracted from PEER database and incremental nonlinear dynamic analyses are conducted for different apparent wave propagation velocities (namely, 100, 420, 1000 m/s, and ∞). Fragility curves are hence generated for three pre-selected performance levels (namely, Operational, Life Safety, and Complete Collapse) considering some modeling and capacity uncertainties. The fragility curves are finally compared to examine the joint effect and severity of non-synchronized support motions and soil-structure interaction on the seismic performance and vulnerability of investigated bridges. Results demonstrate that the wave passage effect and SSI significantly affect the bridge response and the probability of exceeding various pre-selected performance levels, especially for scenarios with low apparent velocity and schemes with soft soil.