Seismic Performance Experimental Research Of PVA-steel Fiber Reinforced Cementitious Composite Beam-column Joints

Concrete is a brittle material,but with the development of social economy in China,engineering structure gradually tends to be higher and longer span,which puts forward higher requirements for the seismic performance of the building structure.Starting from the material level,it is considered to be a good means of improving the ductility of the structure that mixing fibers in matrix.For this reason,engineered cementitious composites(ECC)came into being with advantages not only conforms to the current green building requirements,but also takes into account ductility and strain hardening characteristic.As the weakest part of the frame structure,beam column joint is the key to improve the ductility of the structure.Research for hybrid fiber reinforced cement composite beam column joints seismic behavior is still in a small range with the existing research is mainly for ordinary concrete and single doped fiber cement composite beam column joints.In summary,the study on seismic behavior of beam column joints of hybrid fiber reinforced cement based composite structures is both necessary and has space for further study.The main contents of this paper are as follows:(1)The experimental study of steel fiber,PVA fiber and hybrid fiber and the seismic performance of beam and column are summarized.Based on this,the seismic performance of beam and column joints is studied by using PVA fiber and steel fiber as the toughening material.(2)The stress-strain curves of the cubes were analyzed by axial compression test.The test results show that the specimens under axial compression condition,PVAsteel fiber reinforced specimens bearing capacity were improved to different extent.Compared to the result of ordinary concrete test block,the pre peak strain energy does not increase significantly,while the peak energy after the strain can be improved obviously.Available from the correlation coefficient of toughness,adding fiber in cement or concrete matrix can improve the toughness.(3)Seismic behavior of PVA-steel fiber reinforced cement composite beam column joints were studied by pseudo static test method.There are some conclusions can be obtained through analysis of the hysteretic curves,skeleton curves,stiffness degradation,ductility coefficient and energy dissipation: the brittle damage occurred in the joint area of ordinary concrete,and more stirrups can improve the seismic resistance performance,while the ductile fracture of PVA-steel fiber reinforced specimens appeared in the joints as well as the cracks were slow.In addition of ordinary concrete specimens,other specimens showed the plastic deformation ability is efficient.When the volume content of PVA fiber is constant,the stiffness increases with the volume fraction steel fiber and slow degradation,energy dissipation capacity also increases.When the volume fraction of steel fiber is constant,with the increase of volume fraction of PVA fiber,the stiffness degradation rate of each specimen does not change greatly,and the law of energy dissipation is not obvious.It can achieve better seismic performance than PVA fibers by join steel fibers in place of part of PVA.In summary: Based on PVA-steel fiber reinforced cement composite beam column joints of seismic performance experiment,it is showed that the matrix with PVA-steel fiber can effectively improve the seismic performance of reinforced concrete frame beam column joints,which demonstrates the feasibility of structure to develope high ductility and has very important practical significance for promoting application hybrid fiber reinforced cement composite material in the construction field.