Development of fragility curves for underground box tunnels from nonlinear frame analysis

Abstract

We develop seismic fragility curves ofa double box tunnel for three damage states from nonlinear frame analyses. A suite of site profiles is used to evaluate the effect of soil characteristics on the calculated fragility curve. We use two ground motion intensity measures, which are peak ground acceleration (PGA) and the ratio of the peak ground velocity to the average shear wave velocity within 30m from the surface (PGV/Vs30 ). The fragility curve is demonstrated to be highly dependent on the site profile. The influence of the site effects on the fragility curve is reduced when PGV/Vs30 is used. This is because both the intensity of the ground motion and the soil stiffness is accounted for in the parameter PGV/Vs30. It is therefore recommended that PGV/Vs30 be used instead of PGA to generate fragility curves for underground structures. ? 2019 Associazione Geotecnica Italiana, Rome, Italy.