Experimental Study On Mechanism And Strength Calculation Of Twisting Damage Of Rebar ECC Columns Loading

Reinforced ECC structure has been widely used in bridges,dams,and high-rise buildings abroad,especially high-rise buildings that have strict requirements for seismic performance,due to many advantages such as excellent crack control performance,ductility and seismic performance.In recent years,there has been an increasing number of researches on reinforced steel ECC in China,but the main focus is on bending performance,shear performance and compression performance.There is very little research on its torsional performance,especially on composite torsional performance.Nor does the domestic and foreign codes give the calculation method of cracking torque and bearing capacity.In this paper,five reinforced ECC columns and one reinforced concrete column were designed and fabricated with PVA fiber content,longitudinal reinforcement ratio and stirrup spacing as the parameters.Monotonic loading composite torsion test was conducted to study the different parameters for the reinforcement ECC structural members are affected by torsion performance,focusing on describing the occurrence,development and distribution of cracks in all specimens,and discussing the effects of different parameters on the torque-torsion rate curve,stiffness and ductility.Based on the test results and the calculation theory of torsional strength of steel fiber concrete,a calculation method for cracking torque of reinforced ECC pure torsion members,a calculation method for cracking torque and ultimate torque strength of composite torsion members are proposed.As a basis,the main tensile stress of the shear stress superimposed surface is equal to the ECC axial tensile strength;the composite torsional limit torque calculation method is divided into two types,one based on the PVA fiber impact coefficient combined with the current specification,the other will be effective The PVA fiber in the wall thickness is equivalent to the steel bar,which is obtained by using the variable-angle space truss model.Finally,according to the experimental research,data analysis and strength formula derivation,the conclusion and prospect of the research on the torsional failure mechanism and strength calculation of reinforced ECC columns are given.Experimental research shows that: the reinforced ECC column mainly exhibits torsional failure,its cracks are more dense,the torque-torsion rate curve is relatively full,the stiffness and ductility are good,compared with the reinforced concrete column,its torsion performance is more excellent;the fiber content is The key factor that affects the torsional performance,as the fiber content increases,the torque-torsion rate curve of the component is more full,and the overall ductility and rigidity are also greatly improved;the longitudinal reinforcement ratio has little effect on the torsional performance;stirrup The distance affects the main factor of torsion performance.The calculation research shows that the calculation formula of the strength of the reinforced ECC column has certain feasibility,and the calculation result is close to the test result,but the overall trend is small,and the fiber impact coefficient and equivalent method need to be further explored.