Seismic bridge response modification due to degradation of viscous dampers performance.

摘要

The goal of this thesis is to analyze the variation of a seismic response of a bridge in case of degradation of installed viscous fluid dampers.;The study was conducted with nonlinear time-history analyses of a detailed three-dimensional FE model of the Vincent Thomas Bridge, provided by Caltrans. Three different type of excitations were used (two white noises and a real measured earthquake). Such numerical model, including cables, suspenders, suspended structure, towers, cable bents and anchorages, reflects the state of the structure after the last retrofit phase, when dampers and fuses were installed and towers were stiffened.;A preliminary validation of the numerical model of the bridge, aimed to ensuring the reliability of the FE model, has been carried out by comparing the numerical response with recorded signals.;The degraded performance of the dampers was simulated through the use of gap, spring and viscous elements and validated against experimental results of real devices. The parametric study was intended to investigate the effects of progressive degradation of the energy dissipators on the bridge structural performance, both under service load conditions and seismic excitations. Results indicated a significant level of relative displacement experienced by the devices during daily loading conditions, potentially resulting in a premature degradation due to wear of the internal components of the units. For this reason an alternative device was proposed at least in conceptual terms, in order to decompose the dampers during service loading and to engage then only in case of seismic event.;A solution to the early degradation of the damper devices has been proposed.