Experimental Study On Bond-slip Performance Of Partly Encased Concrete Composite Structure

PEC(Partially Encased Concrete)structure is characterized by its prefabrication,high degree of assembly and fast construction speed compared with reinforced concrete structure.At the same time,its seismic performance,bearing capacity and fire resistance are excellent and recently received wide attention.The problem of bond-slip is the basic problem of steel and concrete structures.Similarly,this problem also exists in PEC steel-concrete structures.The design of PEC structures and components needs to consider the influence of bonding slip,but at present there are relatively few studies on the bonding properties of partially wrapped concrete at home and abroad.Therefore,it is necessary to carry out research on the behavior of PEC steel concrete members bond slip,and to introduce the influence of bond-slip into the design of PEC steel concrete members.In this paper,a combination of experimental research and theoretical analysis is used to study the natural bonding and slipping properties of PEC steel concrete members,which provides a reference for the design and construction of PEC steel-concrete components.In this paper the natural bond-slip performance of PEC composite structure was studied by launching experiments.In the test,the anchoring length of section steel and concrete,the strength of concrete,and the amount of concrete expansion agent(internal content)were the influencing factors.Six PEC test pieces were designed and manufactured.The test phenomenon,the failure mode of the test piece,the steel strain,the concrete strain,and the load-side and free-side slip were examined in the test.The research results show that the anchoring length of steel and concrete and the strength of concrete have a significant effect on the bond strength of members,and the amount of expansion agent affects the strength of concrete,thus affecting its bonding performance.The initial bonding strength and ultimate bonding strength of the specimen are directly proportional to the anchor length and concrete strength.When the anchorage length of steel and concrete increases from 300 mm to 400 mm and then to 500 mm,the ultimate bond strength increases by 10.7% and 62.4% respectively.At the same time,it is found that the initial slip bond strength is about 20% of the ultimate bond strength,and the stability is between 20% and 35%.When the slip value at the loading end reaches about 0.8 mm,the specimen is basically in a large slip state,and the bonding strength at this time is 39% to 87% of the ultimate bonding strength.According to the test results,the formula for calculating the characteristic bond strength was regressed.According to the standard force equilibrium condition of the test piece,the distribution law of equivalent strain along the anchorage length was established,and the equivalent strain expression was fitted,so that the equivalent stress distributed along the anchorage length was obtained.The local bonding stress of the section steel can be obtained by establishing the force balance equation in the micro section of the section steel.It is found that the local bonding stress of the web in the micro section is about 1.2 ~ 1.6 times of the flange.Based on the average bond stress and the slip at the loading end,a basic constitutive relationship mechanical model of the test specimen is established.The model curve is in good agreement with the test curve,and it can reflect the average bond stress and slip from a macro perspective relationship.Based on the measured strain of the profile steel and the concrete at the corresponding position,the test curve of local slip distribution along the anchorage length was obtained.During the entire loading process,the section steel has not undergone significant deformation and is basically in an elastic state.Based on the elastic theory,the calculated values of the slip at the loading end under various loads are given.Based on the study of the distribution of local bonding stress and local slip along the length of the anchor,the position function ?(x)is given,and the constitutive relationship of the bonding slip with position is determined.