Lifting steel bridge superstructures in washington state is described. The use of jacks is an effective means for raising existing plate girder bridges to increase vertical clearance, to remove and replace defective bridge bearings, and to transfer the superstructure dead load from one existing bridge substructure to another. Case studies are presented for two successful jacking operations that involved connecting permanent steel jacking beams to the girders and jacking upward from the substructure. Generally, data on jacking operations do not appear in the technical literature. In one case study presented, data were recorded from jack gauges, and a comparison betweencalculated and recorded lifting loads is presented that indicates the transverse distribution of loads to the jacks. The total lifting loads recorded exceeded the calculated loads by 22 to 32%. Possible reasons for these discrepancies and recommendations for lifting bridge superstructures are given. It is recommended that jacks be sized for at least 1 1/2 times the calculated lifting loads. This paper appears in transportation research record no. 1319, Bridge and hydrology research 1991.
Samenvatting