Behavior of FRP spiral strip-confined concrete under cyclic axial compression

Abstract

FRP spiral strip wrapping strengthening technique is effective in enhancing both strength and deformation capacity of reinforced concrete (RC) columns. Although some investigations have been conducted on axial monotonic compressive behaviour of FRP spiral strip-confined concrete, cyclic compressive behaviour of FRP spiral strip-confined concrete has never been studied. To this end, 18 FRP spiral strip wrapped concrete cylinders of three different levels of confinement under cyclic axial compression and 12 reference specimens under monotonic axial compression have been conducted. The test results show that the actual confinement effectiveness factor significantly influences the monotonic axial stress-strain curves of FRP spiral strip-confined concrete, which lie closely to the envelop curves of the corresponding cyclic stress-strain curves. However, the level of confinement has limited influence on reducing the plastic strain. The existing axial stress-strain model developed for FRP fully confined concrete cylinders under cyclic compression underestimates the plastic strain and overestimates the envelop stress for FRP spiral strip-confined concrete. A revised model is developed based on the test results, and the predicted cyclic axial stress-strain curves match reasonably well with the test results.