Seismic retrofitting of highway bridges in Illinois using friction pendulum seismic isolation bearings and modeling procedures

In this paper, the economical and structural efficiency of friction pendulum bearings (FPB) for retrofitting typical seismically vulnerable bridges in the State of Illinois is studied. For this purpose, a bridge was carefully selected by the Illinois Department of Transportation (IDOT) to represent typical seismically vulnerable bridges commonly used in the State of Illinois. A comprehensive structural model of the bridge was first constructed for seismic analysis. An iterative multi-mode response spectrum (MMRS) analysis of the bridge was then conducted to account for the nonlinear behavior of the bridge components and soil-bridge interaction. The calculated seismic demands were compared with the estimated capacities of the bridge components to determine those that need to be retrofitted. It was found that the bearings, wingwalls and pier foundations of the considered typical bridge need to be retrofitted. A conventional retrofitting strategy was developed for the bridge and the cost of retrofit was estimated. Next, the bridge was further studied to develop appropriate techniques for upgrading its seismic capacity using FPB to eliminate the need for seismic retrofitting of its vulnerable substructure components. It was observed that the use of FPB mitigated the seismic forces and eliminated the need for retrofitting of the substructure components of the bridge. An average retrofitting cost using FPB was calculated and found to be less than the cost of conventional retrofitting considered in this study. Thus, FPB may successfully be used for economical seismic retrofitting of typical bridges in the State of Illinois or in regions of low to moderate risk of seismic activity. (C) 2003 Elsevier Science Ltd. All rights reserved.