Study On The Load-bearing Capacity Of RC Beam Strengthened With Near Surface Mounted Aluminum Alloy Bars Based On Interfacial Mechanical Model

The existing reinforced concrete structures in China are often damaged due to various unfavorable factors,which cause the structural load-bearing capacity to decline.Therefore,it is urgent to seek an efficient and economical strengthening method.Near Surface Mounted(NSM)technique is a new strengthening method of concrete structures.Combined with ductile material aluminum alloy,the concrete structure strengthened with aluminum alloy bar is proposed using NSM method.In order to study the flexural behavior of NSM aluminum alloy beams,writer statics experiment on seven reinforced concrete(RC)beams were carried out in this paper,and a calculation method for the load-bearing capacity of reinforced beams based on the interface mechanics model was established.The specific research results are as follows:(1)The flexural behavior experiment of NSM RC beams were completed,and the effects of NSM bars types and NSM bars amounts on the flexural behavior of concrete beams are contrastively studied,and the failure modes and failure processes of reinforced beams are analyzed.The experiment results show that the concrete beams strengthened with aluminum alloy bars have better deformability than concrete beams strengthened with GFRP bars/aluminum alloy bars and the concrete beams strengthened with PSB bars.The beams strengthened with aluminum alloy bars failed by the interface debonding following by concrete collapse,while the beams strengthened with GFRP bars failed by intermediate crack debonding.(2)According to the crack spacing of NSM reinforced concrete beams along the longitudinal section to establish interface analysis unit,each unit bond stress distribution is determined combining with the interfacial bond stress distribution model.Considering the influence of the interface relative slip reinforcing steel and concrete interface to solve,a model for calculating debonding load of reinforcement bars of embedded reinforced concrete beams is established.By limiting the boundary conditions,the interface bond stress control equation is re-solved,and a simplified calculation model of the interface load-bearing capacity is proposed.The experiment data of 19 beams strengthened with NSM bars with interfacial debonding failure are collected,and compared with three commonly used calculation models for the interface load-bearing capacity of strengthened concrete beams.The results show that the established model and the proposed simplified model has high accuracy.(3)Based on static equilibrium conditions and strain coordination relations,the calculation methods of flexural load-bearing capacity of NSM RC beams under different failure modes were established.At the stage before the longitudinal reinforcement yields,a calculation method for predicting the bending stiffness of the reinforced beam section is established based on the effective moment of inertia method;at the stage after the longitudinal reinforcement yields,the calculation formula for the secondary stiffness of the reinforced beam section is proposed based on the stiffness analysis method The method for calculating the mid-span deflection of beams strengthened with NSM bars finally established a simplified full-process analysis model of the reinforced beam load-mid-span deflection.The proposed analysis model was compared and verified with the experiment data,and the calculation results are in good agreement with the test results.