Effects of Confinement and Flares on the Seismic Performance of ReinforcedConcrete Bridge Columns

摘要

This study examined the ductility capacity of rectangular reinforced concretebridge columns with moderate confinement and the effect of structural flares on the seismic performance of reinforced concrete bridge columns. Four half-scaled rectangular bridge columns were built and tested. The transverse reinforcement ratios provided in the strong direction of the column specimens corresponded to 46 percent and 60 percent of the minimum lateral reinforcement required by AASHTO for seismic detailing. Each specimen was tested under constant axial load while subjected to quasi-static cyclic lateral loading in the column strong direction. The axial load indexes were 10 percent and 25 percent. The specimens exhibited displacement ductilities ranging between 5 and 7. A new equation relating the amount of lateral steel to the attainable displacement ductility was developed. Push over analysis was performed on four existing bridges supported by columns with structural parabolic flares. In two bridges, the column longitudinal steel was placed in the core and along the flares whereas in the other two bridges the longitudinal steel was placed along the flares only. The results indicated that plastic hinges in columns with structural flares do not necessarily form at points of maximum bending moments. The location of the plastic hinges depended on the longitudinal steel amount placed in the core and along the flare. The analysis also showed that flared columns with main reinforcement placed along the flares only are more vulnerable to seismic loads than flared columns with most of the longitudinal steel placed in the core.