Experimental Study On Fatigue Behavior Of Bonding Strengthened RC Beam Under The Alternating Load And Hygrothermal Environment

Adhesive CFRP and bonding steel reinforced concrete structure is an economical and effective way to strengthen,in the critical,old bridge reinforcement project is a large number of applications,but the reinforcement of the structure in the environment and load the role of the service,its durability will degenerate with time to reduce the reinforcement effect.In this paper,under the support of the Ministry of Transport,the research and development of the key technology of the durability of the reinforced girder bridge under the coupling of the load and the hygrothermal environment No.2015318814190,the reinforced concrete beams strengthened with the alternating load and the hygrothermal environment The effects of the interaction between the alternating load and the hygrothermal environment on the mechanical properties of the strengthened beams are analyzed.The main research work and the conclusions are as follows.Firstly,the fracture modes of CFRP reinforcement beams under the interaction of alternating load and hygrothermal environment are the interface peeling failure between the CFRP sheet and the concrete.The interface failure modes are the failure of the fracture at the middle and the steel plate.Of the failure mode is cross-section steel cross-section yield,steel and concrete between the local stripping damage,and only by the hygrothermal environment and by the constant load and hygrothermal environment compared to the reinforcement of the test beam in the destruction of the form of failure mode is not But the peel value at the beginning of the peeling failure becomes smaller,and the CFRP is exhibited at the time of loading,and the peeling failure occurs at the interface between the steel plate and the concrete.The crack resistance of the test beam strengthened with CFRP reinforcement was weakened,the number of cracks in the test beam increased,the crack width increased,the average spacing of the crack distribution decreased,and the crack distribution was more concentrated in the middle and middle areas.Secondly,compared with the hygrothermal environment,under the action of constant load and hygrothermal environment,the tensile strain of the cross-section concrete under the alternating load and hygrothermal environment increases,the compressive strain decreases,the neutral axis rises and turns.The interaction between load and hygrothermal environment accelerates the degradation of concrete beam.Thirdly,the ultimate bearing capacity and deformation bending behavior of CFRP and steel plate reinforced under the interaction of alternating load and hygrothermal environment show a decreasing trend.Compared with the test beam which is not subjected to the environment and load,it is subjected to corrosion fatigue for 15 days and 30 days.The ultimate bearing capacity of the test beam with CFRP reinforcement decreased by 16.4% and 26.3% respectively,and the ultimate deflection decreased by 20.9% and 39.3% respectively.The ultimate bearing capacity of the test piece was 18.6% and 25.9%,and the ultimate deflection 31.5% and 12.7%,respectively,show a decreasing trend in the ultimate bearing capacity and ultimate deflection compared with the test beam subjected only to the hygrothermal environment and subjected to constant load and hygrothermal environment.The stiffness decreases and the ductility decreases.,The decrease of the ultimate bearing capacity of the test beam and the degradation of the mechanical properties of the test beam are accelerated by the extension of the interaction period between the hygrothermal environment and the alternating load.Fourthly,in the interaction between the alternating load and the hygrothermal environment,the CFRP,the steel plate reinforcement test beam is subjected to the CFRP limit strain,the steel plate ultimate strain steel limit strain,compared with the test beam subjected only to the hygrothermal environment and subjected to the constant load and hygrothermal environment.The stress-concentrated distribution area is closer to the end,and the decrease in the bonding performance across the middle layer weakens the middle and lower part of the CFRP,and the steel plate participates in the structure.The CFRP,Force,so that near the end of the region of the CFRP,steel load to increase,participate in the structure of the joint force to deeply.Finally,the coupling capacity and bending performance of the CFRP and steel plate reinforced concrete beams are affected by the interaction between the alternating load and the hygrothermal environment.The reason is that the fatigue failure of the reinforced concrete is affected by the alternating load,The water vapor in the hygrothermal environment provides a new invasion point,water molecules through the cracks into the concrete layer to accelerate the degradation of concrete durability,in the cross-cracks at the water molecules more easily through the expansion of the cracks into the adhesive layer,At the same time,due to the deformation of the test beam under the action of the load,the bonding interface between the CFRP or steel and the concrete produces a relative slip,and the stress concentration at the bonding interface leads to the decrease of the sealing property into the water molecule.The failure of CFRP or steel to participate in the structural force,so that the original should be borne by the CFRP or steel to reduce the load and bear the load of the main reinforcement,while fatigue crack growth to improve the neutral axis position,The height of the nip,the two together to accelerate the load under the tension of the main tendons yield,the main buckling yield After the CFRP or steel began to bear the load of the main force,but because of the adhesive layer of the adhesive layer of the decline in the bond strength of the shear strength decreased under the action of peeling failure began earlier,when the CFRP or steel into the stripping stage In the case of small load growth will soon be stripping damage.