FE Analysis Of Welded Steel Beam Strengthened By CFRP

Fatigue damage is one of the most important failure modes for welded steel structures. It is reported that seventy percent to ninety percent of damages in the welded steel structures is due to the fatigue failure in welded joints. It leads that the application of welded steel structure is restricted to a certain extent, because of the fatigue damage. Fatigue properties of welded steel structures reinforced by CFRP (carbon fiber reinforced polymer) are studied by the finite element method in this thesis. The theory about fatigue analysis and the conventional analyical methods used to investigate the fatigue properties are introduced.In the thesis, the finite element method and ANSYS are adopted to analyze the stress fields and fatigue life of welded I-beam reinforced by CFRP.Firstly, the stress distributions of the reinforced weld I-beam with static bending load are obtained by ANSYS. According to the computed results we knew that, the CFRP enhances the rigidity and reduces the maximum stress of welded steel beams. However, because the elastic modulus of CFRP is similar to steel, the stiffness of the steel beam reinforced by CFRP only has a little change.Secondly, the fatigue lifes of the welded I-beam with CFRP in several cases are predicted by ANSYS. Then the analytical results are compared with the published experimental results. The cycle limits of the fatigue lifes of welded steel beams without any reinforcement, with one sheet of carbon fiber sheet, with two sheet of carbon fiber sheets and with one carbon fiber plate are, respectively, 1629000, 2217000, 272800, 2269000. Thus, in contrast with the I-beam without reinforcement, the fatigue life of the reinforced welded I-beam is increased by 36.1%, 67.5%, 39.3%, respectively.In conclusion, the present study indicates that the carbon fiber sheet and carbon fiber plate can share the load of welded steel structure, reduce the stress peak values of the welded joints. The reinforced technigue with CFRP can effectively improve the fatigue properties of welded steel structures. By compared with the published experimental results at the same cases, the fatigue lifes of welded steel beams with CFRP obtained by the finite element analysis are longer than the experimental results. Finally the reasons for the differences between the two results are discussed.The present results can be used to instruct the reinforced design of the welded steel beam strengthened by CFRP.