Numerical Analysis On Seismic Behavior Of Polypropylene Fiber Concrete Beam-column Joints

China is a country with many earthquakes,which cause damage to houses and structures.In order to reduce the loss caused by earthquakes,it is necessary to improve the ability of houses and structures to resist earthquakes.With the rapid development of the construction industry,frame structure,shear wall structure,frame shear and barrel structure have gradually become the main structural forms in China.But all previous earthquake damage investigation indicate that the destruction of reinforced concrete frame concentrated in the joint core and its nearby area,and normal concrete has low tensile strength,easy cracking and other defects.By adding polypropylene fiber as reinforcing material to concrete can have the effect of crack resistance toughening,improve the structure ductility.With the development of numerical methods,finite element analysis plays an increasingly important role in the field of civil engineering.This study adopts the method of experiment and numerical analysis.The cubic compressive test,axial compressive test and splitting tensile test were carried out on the concrete with polypropylene fiber volume content of 0%,0.07%,0.1%,0.13%and 0.16%to study the influence of polypropylene fiber content on the mechanical property,and the damage constitutive model of polypropylene fiber concrete was proposed.On this basis,the finite element software ABAQUS was used to establish the polypropylene fiber concrete beam-column joint model and study its seismic behavior.The main research contents are as follows:1.The influence of the content of polypropylene fiber on the compressive strength of concrete cube,axial compressive strength and splitting tensile strength of concrete was studied through the cube compressive strength,axial compressive strength and splitting tensile strength tests.The results show that when the content of polypropylene fiber is0.1%,the compressive strength of concrete cube is increased by 15.3%,the compressive strength of concrete axis is increased by 21.96%,and the tensile strength of concrete splitting is increased by 41.99%.When the content of polypropylene fiber is 0.07%,the mechanical properties of concrete are the lowest.When the content of polypropylene fiber reaches 0.13%,the mechanical properties of concrete are lower than that of ordinary concrete,but tend to be stable.2.In the uniaxial compressive test,the micrometer was used to measure the concrete deformation,and the influence of polypropylene fiber content on the peak stress,peak strain,ultimate strain and toughness of concrete was studied.The damage constitutive model of polypropylene fiber concrete is established.The results show that with the increase of polypropylene fiber content,the peak strain and the ultimate strain of concrete under monotonic compression increase,and the peak stress and compressive strength have similar rules.The toughness of polypropylene fiber concrete is higher than that of ordinary concrete,which obviously improves the toughness of concrete.Polypropylene fiber concrete toughness index η_c3 increased than those of normal concrete is not obvious,but the polypropylene fiber concrete toughness index η_c5.5 were compared with normal concrete increased greatly.When the fiber content is 0.16%,the toughness index increase was most pronounced than those of normal concrete,increased by 14%,show that toughening effect of polypropylene fiber concrete is mainly embodied in the specimen with larger deformation occurs.3.ABAQUS was used to establish the beam-column joint model of polypropylene fiber concrete.The influence of polypropylene fiber content,axial pressure ratio and core zone volume collar ratio on the failure mode,hysteretic curve,skeleton curve,strength and stiffness degradation and ductility of beam-column joints were studied.The results show that:According to the cloud map of concrete and steel stress and the cloud map of concrete tensile and compressive damage variables of the model,it is found that the failure characteristics of the model established by ABAQUS are consistent with the failure characteristics of test members.Adding polypropylene fiber into concrete to strengthen the joint core area,appropriately increasing the axial pressure ratio and increasing the core area volume hoop ratio can increase the energy dissipation capacity of the joint members.The model is consistent with the hysteresis curve,and the skeleton curve is in good agreement with each characteristic point.