Study On Seismic Performance Of RC Column With High Compressive Ratio Retrofitted By Prestressing Steel Plate Hoops

Nine half-scale RC short column specimens based on substandard shear design and details with and without seismic retrofitting have been tested under cyclic loading to investigate the effectiveness of externally prestressing in transverses direction of rectangular columns as a seismic retrofit methodology. The main variables of this test are the axial compressive ratio n, the prestressing levelαin steel plate hoop(SPH), configuration parameter of SPHηand longitudinal reinforcement ratioρs. The main objectives of present study are to obtain information on: (a) the seismic performance of RC short columns retrofitted by prestressing steel plate hoop(PSPH) with high axial compressive ratio; (b) the effect ofηon the seismic performance of the retrofitted short columns; (c) the effect ofαon the seismic performance of the retrofitted short columns; (d) the shear carring capacity of the RC short column retrofitted by PSPH. Based on the test results, the failure mechanism, hysteretic curves, skeleton curves, stiffness degradation, deformability and energy dissipation capacity are comprehensively analyzed and the following can be concluded:(1) The proposed retrofitted scheme can substantially improve the seismic performance of RC short columns. The ductility index reduces with an increase of axial compressive ratio under the same confinement.(2) The ductility index increases with an increase ofη. The RC short columns with small axial compressive ratio have a good ductility whenηis equal to 0.35, but only whenηis equal to or larger than 0.53, the specimens with high axial compressive ratio can achieve desirable seismic performance.(3) The seismic performance of a retrofitted column can be improved by increasing the value of prestressing level of steel plate hoops. Comparing PC3 and PC2(n=0.28), the ductility index increases from 5.19 to 7.40 with an enhancement ofαfrom 0 to 0.35, and it increases from 5.22 to 7.01 due to an increase ofαfrom 0.35 to 0.45 when comparing PC9 with PC7(n=0.56).(4) The specimen PC8 which is retrofitted by PSPH withηequal to 0.35 have experienced shear failure due to an increase of longitudinal reinforcement ratioρs from 1.34% to 2.23% and a deficiency on shear strength, and the ductility index of PC8 is only 2.89. Compared with the unretrofitted specimen, the shear capacity of PC8 has an improvement of 24 percent.(5)The cumulative energy dissipation of the retrofitted specimen increases with the increasing ofηandα, and decreases with the increasing of n. The energy dissipation of the specimen PC7(n=0.56,η=0.53 andα=0.45) is still better than that of the specimen PC2(n=0.28,η=0.35 andα=0.35).The FEM model of the RC short columns retrofitted by PSPH are established and an elastic-plastic analysis of the monotonic loading are carried out with the versatile FEM software-ANSYS. The comparison between the analysis and experimental result shows that, the calculated P-? curves have a good agreement with the experimental ones.