Seismic performance of benchmark highway bridge installed with passive control devices

Abstract

Major earthquakes of the last few decades have generated a great deal of interest in structural control systems, to mitigate seismic hazards to lifeline structures -in particular, bridges. The vast destruction and economic losses during earthquakes underscore the importance of finding more rational and substantiated solutions for protection of bridges. One of the most promising devices, considered as a structural control system, is a passive device. Although, there has been substantial work in the recent past in the development of seismic isolators and structural control systems, their effectiveness could not be compared by a systematic study, because they were applied to different types of structures subjected to different types of loadings. A benchmark problem on highway bridges has been developed to compare the performance and effectiveness of different control systems in protecting bridges from earthquakes. In the present study, seismic response of the Benchmark Highway Bridge, with passive controllers is investigated. The problem is based on the 91/5 highway over-crossing at Southern California, USA. In the first phase, the deck is fixed to the outriggers, and in the second phase, the deck is isolated from the outriggers. Using an analytical frame work, a thorough investigation of the isolation devices has been carried out to evaluate their effectiveness under different earthquakes. The response of the bridge to six different real earthquake ground excitations is investigated using simplified lumped mass finite element model of the bridge. The optimum device parameters are investigated to improve response of the benchmark highway bridge. The study explores the use of seismic isolators, namely, Friction Pendulum System (FPS), Double Concave Friction Pendulum System (DCFPS), Variable Friction Pendulum System (VFPS) and Variable Frequency Pendulum Isolator (VFPI). The governing equations of motion are solved by Newmark-beta solver in MATLAB and SIMULINK toolbox. The effectiveness of the devices is explored in terms of reduction of the specified evaluation criteria, considering maximum and norm values. The analytical simulation results demonstrate that these isolators, under optimum parameters are quite effective and can be practically implemented for the vibration control of bridges.