Study On Seismic Behavior Of Prefabricated Post Cast Steel Fiber Reinforced Concrete Beam Column Joints With Different Types

The joints and connection between prefabricated members are the weak areas of prefabricated frame structure.For a long time,joints are the focus of seismic performance research of prefabricated frame structures.The experimental consequence indicates what steel fiber strengthened concrete has excellent automatic properties such as shear,bending,tensile,toughness and fatigue resistance.Pouring steel strengthened concrete into the post pouring area of prefabricated joints can significantly improve the bearing capacity,ductility,crack resistance and seismic performance of prefabricated joints,replace some stirrups to bear shear force,reduce the amount of reinforcement,and facilitate construction.This paper focuses on the influence of steel fiber types on the seismic performance of post cast steel fiber reinforced concrete(SFRC)beam column joints in prefabricated frame.Five low cycle cyclic loading tests of mid beam column joints in prefabricated frame are carried out.(1)The crack development,bearing capacity change and failure mode of the joints under cyclic loading are observed and compared.The results show that each joint has experienced four stages: initial crack,through crack,ultimate crack and failure,and there are dense micro cracks in the core area and beam end of the joint.For the four joints A1-A4 poured with different types of steel fiber reinforced concrete in the core area,each type of steel fiber has good connection effect in the concrete,which effectually blocks the improvement of joint cracks and develops the crack resistance performance of prefabricated post cast beam column joints.Among them,the effect of adding corrugated steel fiber into the concrete in the core area is the best.(2)Based on the low cycle cyclic loading test,the hysterical curve,skeleton curve,displacement ductility and energy separation function of the joints are contrasted and investigated.The results show that: the prefabricated post cast steel fiber reinforced concrete beam column joints,even if the stirrup ratio in the core area is less than the normal stirrup ratio,can still stably bear the low cycle reciprocating load,Showing good shear capacity;the hysteresis curve of the joint is fuller,and the malleability and force separation function are better than that of post-cast ordinary concrete beam-column joints.The results show that the seismic performance of the joint has been significantly improved,which indicates the feasibility of steel fiber replacing part of the stirrups in the core area.By comparing the seismic performance of prefabricated beam column joints with different types of steel fiber in the core area concrete,it is found that the seismic performance of joints with corrugated steel fiber is the best,followed by copper plated round straight steel fiber.(3)The strain of lengthwise operation and stirrup of each beam column joint is analyzed.The conclusions indicate that: steel fiber can decrease the damage of joint reinforcement,improve the bond between reinforcement and concrete,reduce the slip of reinforcement,so as to improve the shear capacity of beam column joints.Among them,the stirrup strain is the smallest and the shear strength is the best,followed by the end hook steel fiber.(4)The seismic performance of post cast steel fiber concrete beam column joints is evaluated comprehensively,and the corresponding practical application suggestions are put forward.