Necessity investigation of tie-down devices for single-pylon cable-stayed bridges to resist near-fault earthquakes with finite element models updated by vibration measurements

Abstract

This paper aims to thoroughly investigate the necessity of designing tie-down devices at the boundaries of cable-stayed bridges to sustain near-fault earthquakes. The medium-span Chi-Lu Bridge, the long-span Kao-Pin-Hsi Bridge and the low-pylon Ma-Zu Bridge are chosen for a broad coverage. The finite element models for these three bridges are first updated with ambient vibration measurements and then modified by considering the compression-only feature of bearings to suit for seismic analyses. For Chi-Lu Bridge, the possibility of its deck to vertically jump out of the shear keys at the girder-pier connection under an exceptional near-fault earthquake is explicitly verified. The subsequent lateral swung of deck end in this case is further found to reach a significant level that can easily induce the damages near the pylon-deck intersection observed in the Chi-Chi earthquake. Therefore, the installation of tie-down devices is suggested for a medium-span cable-stayed bridge like Chi-Lu Bridge. In the case of Kao-Pin-Hsi Bridge, the analyzed results indicate that the capacity of tie-down devices originally designed to limit the uplift movement produced by live loads is not satisfactory to resist near-fault earthquakes. As for Ma-Zu Bridge, the corresponding results demonstrate that the addition of tie-down devices is normally not necessary.