Proposed Seismic Retrofitting Method for Bridges With Multicolumn Bents

Economical efficiency of an innovative seismic retrofitting technique for typical Illinois bridges with multi-column bents was studied in this paper. The proposed retrofitting technique is based on modifying the fixity conditions of the bearings for response modification purposes so as to eliminate the need for costly retrofitting of substructures. For this purpose, a typical seismically vulnerable bridge, representative of those with multi-column bents in the state of Illinois, was selected. Detailed seismic analyses of the bridge were conducted using synthetic ground motions representative of the seismicity of the bridge site. It was found that the bearings, wing-walls and pier foundations of the bridge needed to be retrofitted. A conventional retrofitting strategy was developed for the bridge and the cost of retrofit was estimated. Next, the abutment bearings were fixed longitudinally to reduce the seismic forces transferred to vulnerable pier foundations. It was observed that the proposed retrofitting technique effectively mitigated the seismic forces transferred to the pier foundations and eliminated the need for their costly retrofitting. Thus, the proposed seismic retrofitting method may be used effectively for economical seismic retrofitting of such bridges in the state of Illinois or in regions of low to moderate risk of seismic activity.