Research On Seismic Behavior Of High Toughness Concrete Frame Joints

With the vigorous development of the construction industry,high toughness concrete has been applied in practical engineering.High toughness concrete has two major branches: steel fiber reinforced concrete and PVA fiber reinforced concrete.Although the research on the seismic behavior of these two kinds of concrete frame joints has been done at home and abroad,the research is carried out independently and lacks horizontal comparison.At present,domestic and foreign scholars have not systematically compared the seismic performance of steel fiber reinforced concrete joints,PVA fiber reinforced concrete joints and ordinary concrete joints.In this paper,the seismic behavior of beam-column joints of high toughness concrete frame structures is analyzed and studied systemically by using reciprocating load test and finite element analysis.The main works are as follows:1.The seismic performance of ordinary concrete,steel fiber reinforced concrete and PVA fiber reinforced concrete beam-column joints are compared and analyzed from the aspects of hysteretic curve,skeleton curve,stiffness degradation curve and energy dissipation capacity.The results show that the seismic performance of high toughness concrete frame joints is better than ordinary concrete joints,and the seismic performance of PVA fiber reinforced concrete joints is slightly better than steel fiber reinforced concrete joints.2.Some nonlinear characteristics of rebar,concrete and fiber reinforced concrete are introduced theoretically,including the stress-strain relation of rebar,steel fiber reinforced concrete and PVA fiber reinforced concrete,which can provide the basis for the determination of constitutive model.By using the ABAQUS software,the hysteretic curve,stiffness degradation curve and equivalent viscous damping coefficient of three kinds of joints are simulated and the results are in good agreement with the experimental results,which verify the accuracy and rationality of the selected constitutive model3.Based on ABAQUS,the impact factors of the seismic performance of frame joints are analyzed.The influence of beam section size,concrete strength grade,longitudinal reinforcement yield strength and stirrup reinforcement ratio on the seismic performance of joints are discussed.The results show that stirrups used in the PVA fiber reinforced concrete joint is less than the steel fiber reinforced concrete joint;When the impact factors are bad for the seismic performance of the joint,the seismic performance of the steel fiber reinforced concrete joint is worse than the PVA fiber reinforced concrete joint;When the impact factors are beneficial to the seismic performance of the joints,the seismic performance of the PVA fiber reinforced concrete joint is better than the steel fiber reinforced concrete joint.4.The time-history analysis of the high toughness concrete frame is carried out to simulate the stress state of the frame when the earthquake occurred,getting the result of weak points,story drift,inter-story displacement angle and failure mode of the frame structure,further affirmed the high toughness of concrete material,especially the superiority of PVA fiber reinforced concrete material in seismic performance in the frame joints.