Experimental And Theoretical Studies Of The Flexural Behavior Of RC Beam Strengthened With Aluminum Alloy

The aluminum alloy has a lot of advantages,such as lightweight structure materials with high specific strength,corrosion resistance,good deformation performance,easy extrusion and low susceptibility in low temperature.The RC beam strengthened with aluminum alloy has good ductility and energy dissipation ability while improving bearing capacity.Thus the aluminum alloy can be used for structural reinforcement engineering,especially in erosion and cold temperature environments.The study of RC beam strengthened with aluminum alloy is a beneficial exploration and perfection of reinforcement theory of RC structure.As the study foundation of RC beam strengthened with aluminum alloy plate,the experimental and theoretical studies on bond behavior between aluminum alloy plate and concrete were given.First,in-plane shear tests of 129 specimens were carried out.Secondly the influencing factors on bond behavior,such as concrete strength,width and thickness of aluminum alloy plate,bonding length,additional anchor(U-shaped stirrup and chemical bolt)and interface treatment,were discussed.Then typical characteristics of bond failure,ultimate bond loads,shear stresses distribution curves and bond-slip curves of the connections between aluminum alloy plate and concrete were analyzed.Finally,based on statistics regression analysis of experiment data,the modified Niedermeier model of bond strength was put forward,and the calculation formula for effective bond length was obtained.Above work provide a theoretical basis for RC beam strengthened with aluminum alloy plate.The bending tests of 4 RC beams and 24 RC beams strengthened with aluminum alloy plate were carried out.Then the strain values of aluminum alloy plate,steel bars and concretes,deflection changing of beam and process of crack development were measured during the whole process of the test.The failure law,strain development,stress distribution and deformation characteristics of RC beams strengthened with aluminum alloy plate were studied.The effects of additional anchor methods,reinforcement ratio,aluminum alloy plate ratio and concrete strength on failure mode,cracking load,yield load and ultimate load of RC beams strengthened with aluminum alloy plate were also studied.It provides theoretical basis for the design of RC beam strengthened with aluminum alloy plate.In experiment,adequate reinforcement failure occurred in 4 RC reference beams.The failure modes of 24 RC beams strengthened with aluminum alloy plate are as follows:(1)Adequate reinforcement failure;(2)Debonding failure at plate end;(3)Intermediate crack induced debonding failure;(4)Over-reinforced failure.The test results show that,the aluminum alloy plate and RC beam are in cooperative working to resist external load,and their anti-cracking performances are improved,especially the bearing capacities are greatly improved,meanwhile their ductility are not obviously reduced for RC beam strengthened with aluminum alloy plate with effective additional anchor methods.The mechanical behavior of RC beams strengthened with aluminum alloy plate with adequate reinforcement failure was theoretically analyzed.Then the whole process analysis of normal section under load for RC beams strengthened with aluminum alloy plate was analyzed with computer program.In order to facilitate engineering application,simplified design method of RC beams strengthened with aluminum alloy plate was discussed in combination with characteristics of strengthening beams.Based on theory of ordinary RC beams,theory of calculating maximum crack width and method of checking deformation of RC beams strengthened with aluminum alloy plate were put forward.The theoretical results were in good agreement with experimental results.As basis of studying effect of load status on mechanical behavior of RC beams strengthened with aluminum alloy plate,the post-strain tests of 4 RC beams with different loading and unloading conditions were carried out.Then the change law of the strains of steel bars and concretes,beam deflection during unloading were obtained,and the post-strains under different loading history were got.Then,considering three loading histories of complete unloading,partial unloading and no-unloading,bending tests of 7 RC beams strengthened with aluminum alloy plate subjected to secondary load were carried out.The effects of initial damage on crack resistance,bearing capacity and deformation property of strengthened RC beams subjected to secondary load were studied.According to different initial state of stress and strain,the theoretical calculation formulas of post-strain were derived classified as 3 types,complete unloading,partial unloading and no-unloading.Based on analysis of influencing factors of post-strains,a simplified formula for calculating post-strain was put forward.Combined with results of bending tests of RC beams strengthened with aluminum alloy plate subjected to secondary load,the simplified design methods were proposed.The theoretical results are in good agreement with experimental results.In order to eliminate negative effect of post-strains of RC beams subjected to secondary load,and to improve mechanical properties such as crack resistance,flexural stiffness,ductility and bearing capacity,a new structure of RC beam strengthened with external prestressed aluminum alloy bars was presented.Meanwhile a new technology of simple and effective to construct the prestress of aluminum alloy bar was presented.Then the bending tests of 8 RC beams strengthened with external prestressed aluminum alloy bars were carried out,and the effects of influencing factors,such as prestress level,loading history and position of aluminum alloy bars on mechanical properties of strengthened RC beams were investigated.The test results show that RC beams strengthened with external prestressed aluminum alloy bars can overall improve crack resistance,bending stiffness,ductility and bearing capacity of beams.Different from brittle failure of other traditional prestressed structures,typical plastic failure occurs due to good deformation properties of aluminum alloy materials.Then a simplified design method was proposed,and theoretical results compared with test results.