Experimental Study On Bond-slip Performance Of Steel PVA Fiber Reinforced Concrete

Steel reinforced concrete structure is a kind of composite structure with excellent performance,which combines steel in concrete,so that it has the common advantages of concrete and steel,such as high stiffness,high bearing capacity and good seismic effect.It is widely used in practical engineering.with the continuous development of steel reinforced concrete composite structure,ordinary concrete has also exposed many shortcomings,such as brittleness.Therefore,in this thesis,PVA fiber is added into concrete to form a new type of steel reinforced PVA fiber concrete structure,which has the advantages of high bearing capacity,high stiffness,good seismic performance and good ductility.In order to popularize the application of steel PVA fiber reinforced concrete composite structure in practical engineering,the research on the bond-slip performance of the structure is crucial,which is related to the safety performance of the structure.Fourteen push-out specimens were designed to study their bond-slip performance,mainly considering the strength grade of concrete,the thickness of protective layer,the volume content of PVA fiber and the anchoring length of section steel,and a group of specimens welded with studs on section steel were the most contrasted.This thesis mainly focuses on the following work:(1)By optimizing the proportion design of PVA fiber concrete,five groups of fiber concrete samples with PVA fiber content of 0.2%,0.4%,0.6%,0.8% and 1% were made,and the splitting tensile strength of concrete was optimal when the fiber content was0.6%.(2)A typical failure mode and two main crack forms are summarized by studying the failure forms and crack forms of the specimens through experiments;The load-slip curves of the loading end are summarized and two types of curves are obtained,which are composed of four stages : no relative slip stage,relative slip stage,descending stage and residual slip stage;By analyzing the strain at different positions of the steel,it is found that the strain of the steel basically presents exponential distribution,and the strain of the web at the same position is smaller than that at the flange.(3)The bond strength is defined,and the influence of various factors on bond strength is analyzed.The mathematical expression of bond strength under single factor is regressed,and the mathematical expression under single factor is summarized to obtain the calculation formula of steel PVA fiber reinforced concrete bond strength considering multiple factors;Finally,the design suggestion of critical cover thickness is put forward,and the reference value of critical cover thickness of steel fiber reinforced concrete is given.(4)The characteristic slip value is defined,and the average bond stress and slip curve are obtained from the load-slip curve.According to the change rule of the curve,a constitutive model of linear plus hyperbolic combination is proposed,and the bond stress and slip curve are fitted by the model.The results show that the curve is in good agreement with the experimental curve.Finally,according to the strain changes of the flange and web of the steel,the equivalent strain of the steel is sorted out,and the regular change and strain expression of the steel along the buried depth direction are regressed.The relationship between the equivalent strain and the stress of the steel is obtained from the balance equation of force.Finally,it is concluded that the change trend of bond stress along the buried depth direction is the same as that of section steel strain,showing negative exponential distribution.