| Steel has the advantages of light weight,high strength,high rigidity and excellent plasticity,and it has been used more and more for long-span structures such as bridge engineering.Steel structures have been inevitably affected by natural disasters,man-made damage and other factors during the service period.These factors may cause a variety of damage in the structure,and even lead to a decline in the bearing capacity of the structure.Therefore,it is an urgent research task in the field of engineering to find a safe,economical and effective reinforcement measure to restore the bearing capacity of damaged steel structures so that they can continue to serve safely during their service life.In this paper,aiming at the research object of I-section steel beam,the mechanisms of reinforcing bending steel beams with prestressed CFRP plates and the improvement effect on bending behavior are studied by theoretical derivation,experimental research and finite element simulation analysis.The main research contents are as follows:Based on the reinforcing principle of reverse arch method,bending tests were carried out on four steel beams strengthened with CFRP plates(one is strengthened with non-pre-stressed CFRP plate and three are strengthened with pre-stressed CFRP plate).The effects of different pre-stress levels on the flexural behavior of the strengthened steel beams were studied.The test results show that: compared with the steel beam strengthened by non-prestressed CFRP plate,the yield bearing capacity,ultimate bearing capacity and flexural rigidity of the steel beam strengthened by prestressed CFRP plate have been improved,and the range of improvement will be greater if the level of the prestress is higher.Under different loads,the strain of the carbon plate at the loading point is the largest,and the strain at the end of the carbon plate is the smallest.When the strengthened beam yields or fails,the utilization ratio of carbon plate of the steel beam strengthened with pre-stressed CFRP plate is higher than the steel beam strengthened with non-pre-stressed CFRP plate.Therefore,considering the utilization ratio of materials,the reinforcement method of prestressed CFRP plate has more advantages.A three-dimensional solid-spring-shell element model is established by using finite element software ANSYS to simulate the non-linear behavior of steel beams strengthened with pre-stressed CFRP plates.The load-deflection curves of the test beams obtained by numerical simulation are basically in agreement with those obtained by experiments,and the error is within acceptable range,which shows that the finite element model established in this paper has high accuracy.Furthermore,the results of finite element analysis show that the maximums of shear stress and peeling stress of bonding interface occur at the end of CFRP plate,and both of them decrease rapidly from the end of the carbon plate to the middle of the span.It indicates that the end of the CFRP plate is the most disadvantageous place where peeling failure may occur.When CFRP plate is used to reinforce steel beams,it is necessary to effectively anchor the end of carbon plate.Based on the steel structure design theory,the design method of steel beam strengthened by prestressed CFRP plate is discussed theoretically,and the formulas for calculating yield and ultimate bearing capacity of steel beams strengthened with pre-stressed CFRP plates are derived.By comparison,it is found that the calculated results are in good agreement with the experimental results,which shows that the theoretical formula established in this paper is feasible and can be used as a theoretical reference for the reinforcement design of steel structures.Based on the principle of virtual work and the approximate differential equation of deflection curve,the deflection calculation formula of steel beams strengthened with pre-stressed CFRP plates is deduced.The calculated theoretical deflection values are basically consistent with the experimental results. |
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