Study on human-induced vibration of a cable-stayed bridge without backstays located in abrupt valley

Abstract

This research aims to assess the pedestrian comfort and to control human-induced vibration of an arch tower cable-stayed bridge without backstays located in canyon. Dynamic simulations of human-induced vibration were carried out with a mode-by-mode approach, and the results indicated that a total of seven lateral and vertical modes of the bridge may suffer from excessive vibrations at the design crowd density. Based on the periodic walking force, the structure response under pedestrian loads was evaluated performing dynamic analyses with two Finite Element models of the footbridge. A single tuned mass damper (STMD) control system was developed for control of human-induced vibration, which consisted of four tuned mass dampers mounted on the mid-span of bridge to enhance damping ratios of lively modes. The results indicate that the maximum acceleration for the first-order lateral and second-order vertical vibration at the design crowd density exceed the associated threshold values referring to the comfort level 1 (CL1) Criteria. The critical pedestrian number of lateral dynamic instability estimated by the Dallard’s empirical formula is much smaller than the dynamic design pedestrian number; and the Dallard’s empirical formula is applicable to estimate the critical pedestrian number of lateral dynamic instability for this bridge by comparing with Pedroe Inês footbridge. The damping ratios for both the vertical and lateral modes increase appreciably after installing the tuned mass dampers and no evidence of large-amplitude vibrations has been observed, leading to the realization of satisfactory comfort levels, which can provide reference for vibration reduction design of this kind of bridge.