Behaviour of externally confined high strength concrete column under uniaxial cyclic compression

Abstract

The behaviour of confined high-strength concrete under uniaxial cyclic compression is of vital important for the study either for seismic retrofitting technique of concrete columns or for the structure designs in seismic regions. Hence, the effectiveness of external wrapping with steel straps in reducing the brittleness and enhancing the strength and ductility of HSC column under uniaxial cyclic compression are to be properly understood. Twenty four high-strength concrete columns with diameter of 150 mm and 300 mm in height were cast, wrapped with pre-tensioned steel strap at spacing of 15 mm and tested to failure under both uniaxial monotonic and uniaxial cyclic compression load test. Test results obtained from steel strap-confined high-strength concrete cylinders are presented and examined, which allows a number of significant conclusions to be drawn, including the existence of an envelope curve, dependency of plastic strain to the number of layers of confinement, the cumulative effect of loading cycles, mode of failure under external confinement, etc. The present results are also compared with several results from previous study for various types of confined-concrete. The present study indicates that the column pre-tensioned with steel straps, performed better than the unconfined high-strength concrete columns. It is proved that externally confinement using steel straps do help to control the brittleness and at the same time, enhancing the ductility up to 56.2% and compressive strength up to 108.5% . The envelope curve of uniaxial cyclic loading almost coincides with the corresponding monotonic loading test, with a dependent plastic strain to the amount of layers of confinement.