Hysteretic Behavior of bridge columns with FRP-Jacketed lap splices designed for moderate ductility enhancement

This paper presents test results of six specimens representing older bridge columns with inadequate reinforcement detailing consisting of short lap splices at the base and widely spaced transverse reinforcement. Four of these specimens were rehabilitated using fiber-reinforced polymer (FRP) jackets of two different composite materials (carbon and aramid) to avoid premature failure of the lapped bars after a limited number of postyield cycles. The test results indicate that thin FRP jackets can be used to avoid failure of short lap splices at moderate displacement ductilities. Displacement capacities consistent with expected demands in regions of moderate or low seismicity were achieved after jacket retrofitting. The hysteretic behavior of rehabilitated columns was assessed with emphasizing issues related to variation of stiffness and damping ratio as a function of ductility demand for this class of columns. Equations that account for the effect of axial load level on estimates of effective stiffness and damping as a function of displacement ductility are proposed for this class of columns.