Study On The Bond Strength Between Steel-polypropylene Hybrid Fiber Reinforced Concrete And Deformed Bar Under Cyclic Loading

Our country has frequent earthquake,the main cause of the collapse of the building is closely related to the bonding performance,thus using plain concrete in some seismic structures is limited.It is an urgent need to modify the conventional reinforced concrete and resolve the current problem of the brittleness.To solve the problem,adding fiber to concrete is one of the effective solutions.Fiber reinforces concrete has been more and more widely used in the field of civil engineering for its superior tensile strength,crack resistance,impermeability,shock resistance,durability and other mechanical properties.Single fiber incorporation can only improve or enhance a particular phase of concrete performance,while the hybrid fiber reinforced concrete can be at different levels and different phases.The research results for bonding behavior between reinforced bars and single doped fiber concrete has been abundant,but end research of the hybrid fiber concrete of this field is still relatively lacking.So it is important to study the bond behavior between steel-polypropylene hybrid fiber reinforced concrete and deformed bar under cyclic loading in the theory and application,Based on this,mix steel fiber and polypropylene fiber in concrete to study the bonding properties of deformed steel and polypropylene fiber concrete.The subject comes from the National Natural Science Fund Project "bonding properties and seismic performance of steel-polypropylene hybrid fiber reinforced concrete under cyclic loading"(No.51278388).In this paper,using previous research results on steel and concrete bonding behavior for preference,experimental and theoretical analysis are used to study deformed steel bars and steel-polypropylene hybrid fiber concrete bonding performance.The main work and the results are as follows:(1)On the basis of the experiments and the theoretical research,by means of the test phenomenon and the bond stress and slip curve of experiments,found the failure mode and reveal the mechanism of the bond failure process.The results showed that:the failure process of the cyclic bond strength between the steel rebar and steel-polypropylene hybrid fiber reinforced concrete is slow and steady,the whole process can be divided into six stages:elastic stages,initial cracks propagation stage,stable cracks propagation stage,unstable cracks propagation stage,cracks closure stage,friction stage,steel fibers and polypropylene fibers play distinct roles in various stages.(2)Based on the experimental results,in order to research the ultimate bond stress,the corresponding slip and the bond stress and slip curve of the bond properties between hybrid fiber reinforced concrete and deformed bar deeply,the effects of steel fiber and polypropylene fiber volume fraction,aspect ratio of steel fiber and polypropylene fiber were analyzed.Steel fiber exhibited a more pronounced influence.For the HFRC specimen,whose volume fraction and aspect ratio of PF were 0.15%and 167,the bond strength could be increased by 20.57%and 9.49%respectively,when the volume fraction of SF varied from 0.5%to 1.5%,and 30 to 80 for the aspect ratio.However,no significant influence could be observed when the volume fraction and aspect ratio of PF varied.(3)Furthermore,based on the failure mode,actual stress state and theory of thick-walled cylinder,a calculation method was proposed to calculate the bond strength between steel rebar and FRC.The analytical solutions were then validated by the results from current study and other literatures.