Experimental And Theoretical Research On Shear Performance Of ECC Beams Reinforced By Steel Bars Without Web Reinforcement

The research on the shear performance of reinforced concrete members is one of the classic problems in the basic theory of concrete structures.Due to the numerous influencing factors of shear failure and the complex failure modes,the current understanding of the shear mechanism of concrete is still insufficient,and a complete theoretical system has not been established so far.When calculating the shear bearing capacity of beams,the dowel action of longitudinal steel bars is usually ignored or included in the shear contribution of concrete.So far,there is no quantitative analysis of the dowel action shear contribution.The shear failure of reinforced concrete beams is usually brittle failure.There is no obvious warning before failure,which can easily lead to catastrophic consequences.Fiber-reinforced cement-based composite material with high ductility（ECC）is a fiber-reinforced cement-based composite material with ultra-high ductility and superior crack control ability,and its ultimate tensile strain reaches 2%~6% at a fiber volume of 2% with pseudo strain hardening characteristics and multiple cracks cracking mechanism.ECC also has good performance in shear resistance.Applying it to key parts of structural members can effectively improve the serious problem of concrete structure shear failure brittleness.Therefore,studying the shear resistance of ECC beams reinforced by steel bars without web reinforcement has important theoretical significance and practical value.This paper conducted an in-depth study on the shear performance of ECC beams reinforced by steel bars without web reinforcement from three aspects: experimental research,numerical simulation,and theoretical derivation.The details are as follows:（1）ECC basic mechanics test and steel bar property test were carried out.By analyzing the preparation of ECC and pouring a cylindrical test block for compression test and dog bone test block for tensile test,the compression and tensile stress-strain curves of the test piece are obtained.At the same time,the material properties of the steel bars used in this test were tested,and the stress-strain curves of the steel bars were obtained,which provided a basis for further theoretical analysis and numerical simulation.（2）The shear test of ECC beams reinforced by steel bars without web reinforcement was carried out.Taking base material,reinforcement ratio,and shear span ratio as control parameters,four-point bending static load resistance test was carried out on nine ECC beams,one concrete beam,and one mortar beam.The test results showed that the shear resistance of ECC members is far superior to concrete specimens and mortar specimens.Under the same conditions,the shear capacity of ECC beams is 1.67 times that of concrete beams and twice that of mortar beams.Compared with ordinary concrete beams,ECC beams have good shear resistance and crack control capabilities.When the shear-span ratio increases from 2.0 to 3.0,the fiberreinforced ECC beam without web reinforcement gradually changes from diagonal compression failure to shear tension failure,and the load-bearing capacity decreases in turn.The increase of the longitudinal reinforcement ratio can restrain the development of diagonal cracks to a certain extent,and the shear capacity of the beam increases with the increase of the longitudinal reinforcement ratio.（3）The contribution of the dowel action of the longitudinal steel bars to the total shear capacity of beams without web reinforcement were quantitatively studied.First,the finite element analysis of fiber-reinforced ECC beams and concrete beams without web reinforcement were carried out based on the ABAQUS software.The results confirm that the numerical analysis can more accurately study the shear resistance of beams.Secondly,a model were established for a single steel bar embedded in concrete,which mainly discusses the influence of factors such as matrix material,different crack opening values,matrix material strength,ECC tensile strength and other factors on the bearing capacity of the pin.Finally,a dowel action model of multiple steel bars in a beam without web reinforcement were established,and combined with the experimental measurement data,the change curve of the dowel force with deflection during the whole loading process were obtained,and its contribution to the shear resistance of the beam without web reinforcement were quantitatively studied.The results showed that the contribution of the dowel to the shear resistance of concrete beams without web reinforcement was not significant,and the peak load is only about 2%;the role of the dowel action in the reinforced ECC beam without web reinforcement contributes more to the shear resistance,and the peak load reaches about 35%.（4）The formula for calculating the shear capacity of ECC beams without web reinforcement were established.Based on the concrete truss-arch shear theoretical model,considering the shear contribution of the longitudinal reinforcement dowel action,a formula for calculating the shear bearing capacity of ECC beams without web reinforcement were proposed and compared with the experimental results.The comparison results showed that the proposed formula can better predict the shear capacity of ECC beams without web reinforcement.