ANALYTICAL MODEL FOR STEEL-JACKETED RC CIRCULAR BRIDGE COLUMNS

The current approach for seismic retrofit of bridge columns in California involves extensive use of steel jacketing, which has been shown to be very effective in enhancing the flexural and shear performance of deficient bridge columns. In this paper, an analytical model is developed for the first-yield limit state and the ultimate limit state of flexurally dominated steel-jacketed circular bridge columns. Lateral stiffening of column is taken into account by considering the effective bond transfer between the steel jacket and column. Two possible ultimate limit states are identified: (1) A limit state that corresponds to the ultimate compressive strain of concrete; and (2) a limit state that corresponds to low-cycle fatigue fracture of the longitudinal steel. An equation based on the energy balance method is proposed for predicting the ultimate compressive strain of concrete confined by the steel jacket. The ultimate limit state governed by low-cycle fatigue fracture of the longitudinal steel is assessed using an energy-based damage model. The proposed model is shown to correlate well with the lateral response of tested steel-jacketed columns.