Research On Seismic Performance Of 735MPa High-strength Reinforced Concrete Frame Joints

In order to study the seismic performance of high-strength reinforced concrete frame joints,this paper carried out low-cycle reciprocating loading tests and finite element numerical simulations on six concrete beam-column joints assemblies with CRB735 new high-strength steel bars and one interior joint with HRB400 steel bars.And The effects of factors such as axial compression ratio,hoop ratio in the core area of the node,concrete strength,and steel reinforcement grade on the seismic performance of the node are obtained.The main research results of this paper are as following:（1）Low-cycle reciprocating loading tests were carried out on the concrete beam-column joints with CRB735 new high-strength steel or HRB400 ordinary steel.The failure form of beam-column joints,hysteresis curve,ductility coefficient,stiffness degradation,energy dissipation and other parameters are studied,which provides experimental data for the application of high-strength steel bars in reinforced concrete structures.（2）The test results show that increasing the axial compression ratio will make better the energy dissipation characteristics of high-strength steel reinforced joints,but the ultimate shear capacity of the joints cannot be increased effectively.Excessive axial compression ratios will cause earlier cracks in the core area and reduce the ductility of the specimens;Increasing the hoops in the core area of the joint will improve the joint’s shear resistance while increasing the failure displacement of the specimens;when the joint is equipped with new high-strength stirrups,it will delay the rate of stiffness degradation from the cracking of the joint core area to the yield stage of the member effectively;Compared with regular reinforced concrete specimens,joints with CRB735 high-strength steel have a shorter ultimate loading process,higher yield load and yield displacement,and the specimens are close to the limit state when they reach yield.（3）The shear bearing capacity of concrete beam-column joints equipped with CRB735 new high-strength steel bars can be calculated using the relevant shear bearing capacity formula in GB50010-2010 Code for Design of Concrete Structures,and has a certain safety reserve.In the formula,the yield strength of CRB735 steel bar is recommended to be 735MP.（4）The finite element parameter analysis results show that when the compressive strength of concrete and the yield strength of steel bars are in the range of C35～C60 and 400～735MPa,respectively,increasing the concrete strength and reinforcement grade can enhance the ultimate shear capacity of the joint,improve the pinch effect of the specimens,and increase the yield load and yield displacement of the joint while further reducing their ductility.In addition,increasing the material grade will also speed up the decline of the peak load of the joint.