Experimental Research On Seismic Shear Behavior Of Reinforced Concrete Columns With CRB600H High-strength Stirrups

High-strength stirrups are beneficial to reduce the brittleness,improve ductility and energy dissipation capacity of concrete columns,at the same time diminish the amount of reinforcement,avoid the congestion of steel bars,facilitate construction,save mineral resources and energy,and have great significance for maintaining sustainable economic development.At present,the research on the seismic behavior of high-strength stirrup columns is mainly focused on the normal section behavior of the column end,and the experimental research on the seismic shear behavior is relatively few,especially on the seismic shear capacity of meeting certain deformation capacity and the level of stirrup stress.How about the seismic shear behavior of high-strength stirrup columns,does it has the seismic shear capacity and deformation capacity not less than that of ordinary stirrup columns and the level of stress of high-strength stirrups under cyclic load reversals are the main concerns of researchers.In addition,researchers are also focusing on whether the calculation formula of the seismic shear capacity of the columns in the current concrete code in China is suitable for high strength stirrup columns and the influence law of various parameters on the seismic shear behavior of high-strength stirrup columns.Therefore,in this paper,the seismic shear behavior of high-strength stirrup columns is studied as follows:Seven CRB600 H high-strength stirrup concrete columns and a HRB400normal-strength stirrup concrete column under cyclic load reversals were carried out.According to the test results and other experimental data of CRB600 H high-strength stirrup columns in the research group,it was investigated the adaptability of the current code to high strength stirrup columns,whether the CRB600 H high-strength stirrup columns has good deformation capacity,the level of stirrups stress were also evaluated.Then comparing the differences in crack development and failure characteristics,shear bearing capacity,deformation capacity,stiffness degradation and energy dissipation capacity of "equal strength replacement","equal quantity replacement" high-strength stirrup columns and ordinary stirrup columns,and combined with the rest of the CRB600 H high-strength stirrup columns in the research group and the collected400 MPa grade normal-stirrup columns test data,the difference of seismic shear capacity and deformation capacity between CRB600 H high strength stirrup columns and ordinary stirrup columns were further studied.In addition,the influences of stirrup ratio,stirrup diameter and spacing,concrete compression strength on the seismic shear behavior of high-strength stirrup columns were studied.The main conclusions are as follows:(1)The calculation formula of the seismic shear capacity of the columns in the current concrete code is not suitable for high strength stirrup concrete columns.The CRB600 H high-strength stirrup columns with proper stirrups have good ductility and ultimate deformation capacity.Under the stirrup ratio of this paper,the strength of CRB600 H high-strength stirrups can be fully developed.Since the uniform elongation of CRB600 H reinforcement is lower than that of HRB400 reinforcement,CRB600 H stirrups are easy to be broken under cyclic load reversals,which should be avoided by proper measures such as limiting the axial compression ratios of columns and the reasonable determination of the minimum spacing of stirrups.(2)Under the equal strength replacement and equal quantity replacement,the hysteretic curves of CRB600 H high strength stirrup concrete columns have no obvious difference,the stiffness degradation process is basically the same,and the energy dissipation capacity is relatively poor.Compared with 400 MPa grade stirrup columns,CRB600 H stirrup columns have little difference in shear capacity,while have better ductility and ultimate deformation capacity.(3)Increasing stirrup ratio has not significantly improve the shear capacity and ductility of the high-strength stirrup columns,but it has great effect on improving the ultimate deformation capacity of the columns.At a given stirrup ratio,seismic behavior of columns with small stirrup spacing is better than those with large stirrup spacing and diameter.Within a certain range,using the higher strength concrete is beneficial to improve the seismic shear behavior of high-strength stirrup columns.The innovation points of this paper:(1)The stress of the stirrups in CRB600 H stirrup concrete columns is investigated,and the stress level of the stirrups is analyzed,so as to provide experimental basis for determining the strength of the stirrups for the seismic shear capacity of the frame columns with high strength stirrups.(2)Through the test data,it is tested whether the code formula is suitable for calculating the seismic shear capacity of high-strength stirrup concrete columns.