Researches On Slant Shear Behavior Of New And Old Concrete Interfaces Under Different Loading Rates

In the construction process of new concrete structure and in the reinforcement and repair of existing concrete structure,there are often cases of concrete pouring at different times.These new and old concrete joints formed by the combination of concrete of different ages usually become the weak part of concrete structure.As the concrete is easy to crack and destroy in the shear state,the performance of the new and old concrete interface in the shear state is the key to whether the new and old concrete can form a whole and bear the force together.To solve this problem,researchers have done a lot of research work.However,the existing researches are all aimed at the static mechanical properties of the new and old concrete interface.In addition to static load,concrete structure may also be subjected to dynamic load,such as earthquake,explosion,vehicle or ship collision,etc.For this reason,this paper designs 95 slant shear specimens of new and old concrete interface.Slant shear tests were carried out under quasi-static and dynamic loads.The effects of strain rate,joint roughness,joint age and joint angle on failure mode,shear strength,dissipation energy,quasi-static load displacement curve,dynamic stress-strain curve and transmission wave shape of new and old concrete joint are studied.There are five different failure modes after the test.With the increase of strain rate,the shear strength increases.In the dynamic loading,the dissipated energy also increases with the increase of strain rate,and the dissipated energy of the specimen in the quasi-static test can be used as the threshold value in the SHPB test.From the quasi-static load displacement curve,it can be seen that with the increase of the age of the joint,the deformation ability of the specimen is obviously enhanced.In addition,under the influence of strain rate,due to the existence of the interface,the dynamic stress-strain curve has an obvious transition stage when rising.In SHPB test,the transmitted wave can be divided into four types.Then,the finite element model of slant shear specimen of new and old concrete interface is established by using ABAQUS.Based on the accuracy of the model,the mechanism of shear failure of new and old concrete interface is analyzed.Through parameter analysis,the influence of strain rate and joint roughness on the shear behavior of new and old concrete joint is studied,and the formulas for calculating the cohesion and friction angle of new and old concrete joint under different strain rate and roughness are obtained.