BRIDGE BEARING REPLACEMENT

The Washington State Department of Transportation (WSDOT) has removed and replaced nonfunctioning bridge bearings to extend the service lives of existing bridges. Inoperable roller nests and seismically vulnerable steel rocker bearings with excessive tipping have been removed and replaced to restore expansion capability. The superstructure must be raised to replace bridge bearings. Case studies that show three recent bridge bearing replacement projects designed by WSDOT are presented. In the first case study, a 113.0-m single-span truss built in 1925 was raised from below by placing two hydraulic jacks and the upper steel distribution plates directly under the bearing pin gusset plates. The unreinforced pier cap was post-tensioned to prevent spalling. A sliding disc bearing was installed in place of the frozen roller nest. In the second case study, the bearings were removed and were replaced as part of an overall structural rehabilitation project. The existing concrete deck was removed and the ends of seven 54.9-m single-span trusses were lifted sequentially from above with a pair of jacking beams consisting of two W36 x 245 steel beams. Hanger rods were attached directly to the jacking beams and the floor beam top flange. Four 50-metric-ton jacks (two per jacking beam) simultaneously raised the ends of the trusses. Sliding fabric pad bearings were used to replace the frozen expansion roller nests. In the final case study, seismically vulnerable tipping rocker bearings were replaced with elastomeric bearings. Jacking diaphragms were located in the exterior bays at the girder centerline of bearings so that the lifting loads would not cause tipping of the pier. Additional shelf width was provided by adding a continuous corbel to the pier cap. Superstructure lifting recommendations are given. Jacks are sized for at least 1.5 times the calculated lifting loads. Bearing design loads, replacement bearing costs, and costs for lifting bridge superstructures are presented.