Experimental Study On The Flexural Capacity Of Steel Beems Strengthened By Steel Plate Under Secondary Load

In recent years,threr is a increasing requirement to reform and reinforce exisiting steel structures,with the increase of steel structure buildings in China.Stick steel strengthening method is a traditional reinforcement method of concrete,which has the advantages of convenient construction and remarkable reinforcement effect without an open fire.The method,which has been widely used in the field of concrete structure reinforcement,also has wide application value in the field of steel structure reinforcement.The current technical code for strengthening steel structures was published in 1996,which is too old to cover the application of bonded steel method.Although the latest design code for strengthening steel structure has included the bonded steel method,the existing experimental research is still less,expecially considering the bonded steel reinforcement under secondary loading.In this paper,experimental study on flexural behavior of steel beams strengthened with bonded steel plates under secondary loads is carried out,which provides reference for the examination of relevant provisions and has guiding significance for related projects.In this paper,four steel beams strengthened with bonded steel plates and one unreinforced beam were designed as contrast beams.During the test,the deflection,strain and failure modes of the specimens were recorded in detail.The test results show that there are two main failure modes of steel beams strengthened with bonded steel plates: one is the failure of specimens due to excessive bending deformation to reach the ultimate deflection;the other is the peeling failure of the bonded steel plates at the end.The test data show that the yield load of the specimens decreases with the increase of initial stress level and increases with the increase of steel plate thickness,and the composite section of the specimens still conforms to the assumption of flat section.Compared with unreinforced beams,the stiffness of specimens after reinforcement increases significantly,and increases with the increase of steel plate thickness.The strain analysis of steel beam and steel plate shows that the main tensile stress is distributed in the middle of the span of the specimen,and there is stress concentration at the end.Based on the basic principle of steel structure and related research,this paper puts forward the calculation method of lag strain of steel plate bonded under secondary stress.The relationship between bending moment and curvature of reinforced specimens is used to further analyze the process of stress and deformation of reinforced steel beam.The calculation method of yield load and ultimate load of steel beam strengthened with bonded steel plate is obtained,and it is transformed into the expression commonly used in codes.The stress analysis of the interface of the specimens is carried out,and the calculation methods of bond shear stress and peel stress are put forward.Combining with the requirements of the main stress of the bond layer and the bond extension length in the code,it can provide guidance for engineering.Finally,this paper establishes the model of steel beam strengthened by bonding steel by ABAQUS software,uses cohesion element to simulate the bonding layer,and uses life and death element to establish the secondary stress relationship.The error between the simulation data and the test data is small,and the agreement is good.The theoretical calculation value is basically smaller than the simulation value,which shows that the calculation formula is basically accurate and reliable.By designing three groups of 12 simulated specimens,including initial stress level,thickness of bonded steel plate and bond elongation length,the corresponding load-deflection curve and stress nephogram are drawn,and the research and analysis are carried out.The results show that when the initial stress increases,the load-carrying capacity of the specimens decreases.When the initial stress increases,the reinforcement under low stress or stress-free conditions has the best effect,but it should be avoided.When the thickness of the bonded steel plate increases,the load-carrying capacity of the specimens increases,but when the thickness of the bonded steel plate reaches a certain level,the load-bearing capacity of the specimens increases.The increase of load-carrying capacity decreases with the increase of bond elongation length,and the load-carrying capacity of specimens increases with the increase of bond elongation length,but when the bond elongation length reaches a certain length,the load-carrying capacity of specimens no longer increases significantly.