Research On Shear Performance Of Joints Of UHPC-based Gravity-type Assembly Column

With the economic growth and urbanization development in China,the requirements for construction efficiency and environmental protection have been increased.The application of fabricated structures have been popularized,and the bridge column has also begun to be produced by the construction technology of prefabrication and assembly.The grouting sleeve has been widely used because of its simple structure and reliable performance.To improve the shortcomings of traditional grouting sleeve connection,the UHPC based gravity grouting technology is applied to the grouting sleeve connection,but the shear behavior of the connection interface in the new assembled column with UHPC is not clear.In this paper,such a shear behavior was studied.The main contents and conclusions are as follows:(1)The static direct shear tests of 8 grouting sleeve connections were carried out,and the effects of grouting material type,axial pressure,concrete strength and reinforcement ratio on the shear resistance of the joint were studied.The results showed that the joint surface between cushion and concrete far from the sleeve side is the weak surface of grouting sleeve joint,and the use of UHPC grouting material can effectively improve the shear resistance of grouting sleeve joint.Besides,by increasing the concrete strength,applying axial pressure and increasing the reinforcement ratio of the joint surface,the shear strength of the joint of the grouting sleeve can be improve.(2)By analyzing the shear mechanism of the new UHPC based grouting sleeve connection,it was found that the main factors affecting its shear strength are bonding force,bite force,friction effect,reinforcement clamping effect and dowel action of reinforcing steel bars.Based on such conclusions,this study proposed the formula of new UHPC based grouting sleeve joint referencing the national codes,and the results were in good agreement with the tests.(3)The simplified finite element model of the static direct shear test of the grouting sleeve connection joint is established.By analyzing the results of the static direct shear test,the sleeve and the concrete joint far from the sleeve side are simplified.The simulation results are in good agreement with the test results,which shows that the simplified finite element model in this paper can effectively simulate the bearing mechanism process of the grouting sleeve connection members under static load.(4)Nine drop hammer impact tests of UHPC based grouting sleeve connection were carried out,and the effects of grouting material type,axial pressure,concrete strength,reinforcement ratio of shear plane and impact energy on the dynamic shear behavior of grouting sleeve connection joint were studied.It was found that the dynamic shear resistance of the joint in grouting sleeve can be improved by using the UHPC grouting material with high strength,increasing the axial pressure,improving the concrete strength of the structure and increasing the longitudinal reinforcement ratio of the joint surface.The damage of the joint of the grouting sleeve was exacerbate with the increase of the impact energy.Under the same impact energy,the large mass with low velocity resulted in greater peak displacement than that of the small mass with high velocity,and the final residual displacement of the former was slightly large.(5)The finite element models of drop hammer impact test of Z-shaped direct shear specimen of grouting sleeve connection joint were established,and the numerical simulation results are in good agreement with the experimental results.It was found that increasing the shear strength,tensile strength and friction coefficient of the interface can improve the shear bearing capacity of the grouting sleeve joint,based on parameter analysis.