Experimental Study On Seismic Performance Of PVA-steel Hybrid Fiber Reinforced Cementitious Composite Frame Mid-joints

At present,the reinforced concrete structure is a more commonly used construction form in my country’s industrial and civil buildings.When subjected to an earthquake load,the force and bending moments transmitted by the column end and beam end of the frame structure act on the joints together,making it the weakest point of the structure,which is prone to brittle failure.The beam-column joints serve as the transmission of the entire structure.The performance of the force and the stressed parts is the key to ensure that the overall structure does not collapse.To improve the performance of the node,the traditional method is mainly to encrypt the stirrups in the core area of the node,but this can not avoid the construction difficulties due to the large number of stirrups.Therefore,some scholars have proposed that the incorporation of fibers in the joints can not only improve the failure form of the joints,but also improve the seismic performance of the beam-column joints and reduce the amount of stirrups in the core area.This paper conducts pseudo-static tests on PVA-steel hybrid fiber-reinforced cement-based composites and ordinary concrete frame joints,and compares and analyzes the effects of the experimental axial compression ratio and the volumetric hoop ratio of the core area on the seismic performance of frame joints.The main contents are as follows:(1)The related theories,experimental studies and practical engineering applications of PVA fiber,steel fiber and hybrid fiber are summarized.According to the research direction of the subject,the stress mechanism,failure process and influence factors of seismic performance of ordinary concrete beam and column joints are summarized.On the basis of summarizing the two aspects,PVA and steel fiber were selected as joint toughening materials,and axial compression ratio and core volume stirrup ratio were selected as test variables.(2)The crack development path and failure mode of each joint in the test process are simply described,which shows that all beam-column joints experience four processes: initial crack,penetration,limit and final failure.After mixing the hybrid fiber,the crack width in the core area was significantly reduced,the speed of crack development was slowed,and the small cracks in the core area increased significantly,showing the characteristics of multiple crack development.The core area concrete did not fall off from the beginning of the test to the final failure.(3)The hysteresis curve,skeleton curve,ductility performance,stiffness degradation,energy dissipation capacity and rotation capacity of the plastic hinge area at the beam end were analyzed for each specimen.It was found that after the hybrid fiber was mixed,the bridge caused by PVA and steel fiber The effect of joint stress transfer makes the joint’s plastic deformation capacity and energy dissipation capacity and other seismic performance significantly improved;in the hybrid fiber joint,with the increase of the test axial compression ratio,its bearing capacity,ductility,stiffness,energy consumption and The rotational capacity of the plastic hinge area at the beam end has been improved;as the volumetric hooping ratio of the core area increases,its bearing capacity,energy consumption and stiffness degradation increase,and the ductility coefficient does not change significantly;in this experiment the volume hooping ratio in the core area is reduced by 50% Under the circumstances,the seismic performance of hybrid fiber nodes is significantly better than that of ordinary concrete nodes with stirrups in the core area;indicating the hybrid fiber Incorporation can reduce the amount of stirrups in the core area or even replace stirrups.