Dynamic Effect of Tie-Bar Failure on Through Tied Arch Bridge

Abstract

Tie bars on through tied arch bridges are often in poor condition and may serve as an external cause of a tie-bar failure accident; nevertheless, bridge structural robustness contributes greatly in resisting progressive collapse, and poor robustness tends to be the essential internal cause of possible accident. To study the dynamic effect of tie-bar failure of a through tied arch bridge and to reveal the mechanism of how structural robustness reduces dynamic effects, a finite-element model of a typical rigid-frame through tied arch bridge is developed based on the most adverse tie-bar breaking time, a transient-unloading method with equivalent load is adopted to analyze the dynamic response of tie-bar failure, and the results under different working conditions are compared. Furthermore, parameter analysis of the arch-to-pier stiffness ratio is conducted for the dynamic-amplification effect. The results indicate that both the pier and the arch rib have significant dynamic-amplification effects with respect to tie-bar breakage, and the remaining tie bars are the most vulnerable elements of the bridge; thus, they should be considered the most important elements when conducting tie-bar failure analysis; the most adverse breaking time adopted in cable breakage analysis can be taken as 0.01 T; a greater arch-to-pier stiffness ratio is beneficial to reduce the dynamic response brought on by tie-bar breakage; therefore, a rigid-frame through tied arch bridge should be designed with a large pier thrust stiffness, while a simply supported tied arch bridge should not be used in future through arch bridges, and existing ones should be retrofitted as soon as possible.