Fragility Analysis of Floating Cablestayed Bridge Under Nonuniform Seismic Excitation

Abstract:

The finite element model of a cablestayed bridge with the main span of 420 m was built with OpenSees software. Fragility analysis was performed under four conditions considering incoherence effect only, incoherence and wavepassage effects, incoherence and siteresponse effects and spatial variation due to incoherence, wavepassage and siteresponse effects. System fragility curves were generated combining joint probabilistic seismic demand model (JPSDM) with Monte Carlo simulation based on component fragility. The system vulnerability of the cablestayed bridge under nonuniform excitation considering different sources of spatial variation effects is higher than that under uniform excitation. The effects of incoherence and siteresponse are obvious to the seismic response of the cablestayed bridge. With the increase of incoherence factor, the bridge as a system becomes more fragile. The siteresponse effect is more complicated, and the bridge tends to be more vulnerable if the soil types of nearby exciting locations become more different. The vulnerability of the cablestayed bridge increases when the soil type along the direction of propagation turns from relative soft to firm than the inverse condition. Neglecting wavepassage effect in fragility analysis would not cause an obvious error. Above all, incoherence and siteresponse effects should be considered in the fragility analysis of the floating cablestayed bridge under nonuniform excitation. The widely adopted fragility analysis under uniform excitation at the current time overestimates the aseismic behavior of the system.