Study On Seismic Behavior Of RC Short Columns Retrofitted By Prestressing Steel Plate Hoops

Many existing reinforced concrete buildings are seismically deficient due to changes in codes, poor detailing practice, rezoning of seismic intensity. A new scheme for the rehabilitation of seismically deficient reinforced concrete columns is proposed that makes use of external prestressing steel plate hoop (PSPH) in transverses direction of rectangular RC columns to improve their seismic performance.Six rectangular RC column specimens (one nonretrofitted as built specimen and five retrofitted 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 and the prestressing ratio α in steel plate hoop.Test results indicate that the transverse prestressing steel plate hoop can be highly effective in controlling diagonal tension cracks caused by shear. Premature shear failure of columns was prevented and the failure mode was changed from shear to flexure. The ductility of the retrofitted specimens show an enhancement over 3 times than that of "as built" nonretrofitted columns and the displacement ductility ratio can be enhanced with the augment of the transverse prestressing ratio.The ductility ratio reduce slightly with an increase in axial load on the columns under the same prestressing ratio. The specimen still can reach the displacement ductility ratio 5.6, when compression ratio equal to 0.53. The energy dissipation of the specimen will be enhanced with the increasing of the prestressing ratio. The PSPH with the prestressing ratio 0.35 still can form favorable confinement to high axial load columns. The energy dissipation of the specimen PC4 (α=0.35, n = 0.53) is better than that of PC5(α=0.15, n=0.29) when the drift angle reach 1/15.Based on the analysis of the theory and the experimental study on the confinedconcrete, it is pointed out that the steel jacket bear partial axial load inevitably in the experimental study of the constitutive relationship. The model of the concrete confined by the steel jacket which exclude the influence of the longitudinal interaction are developed with the versatile FEM software — ANSYS. The constitutive relationship of the confined columns, in which the prestressing ratio is taken into account, is established based on FEM elasto-plastic analysis of the uniaxial loading.The FEM model of the RC short columns retrofitted by PSPH are developed and the elastic-plastic analysis are carried out based on analysis and experimental results of the paper. The comparison between the analysis and experimental result show that the element type, material model and the technique of simulating the transverse prestressing adopted in this paper can simulate the experimental process well and the P-A curve from calculation data have a good agreement with the skeleton curve of experimental result. The effect of the steel plate hoop configuration parameter 77 on the strength and ductility of the specimen is studied based on FEM analysis. It is suggested that the steel plate hoop configuration parameter 77 be controlled between 0.74 and 0.99. This conclusion can be referenced for further experimental study.