Local Buckling Behaviour And Design Method Of High Strength Steel Welded I-section Beams

With the progress in metallurgical technique and steel production process,the high strength steel(HSS)with excellent processing performance has been more and more widely used in the field of structural engineering.Because the material properties of HSS are clearly different from conventional strength steel(CSS),the stability performance of HSS members may be influenced significantly.In order to further improve the design method of HSS structure and promote the engineering application of HSS,the systematic study on local buckling behaviour and design method of HSS welded I-section beams was carried out in this dissertation,by means of a considerable amount of experimental,numerical and theoretical research.The main research works are as follows:(1)Elastic buckling analysis on steel plate subjected to combined stresses was performed by using the mathematical software Matlab and Mathematica cooperatively.The local buckling of a total of 198 plates under independent bending stress and shear stress were analysed.The checking calculations of local buckling for plates with four edges simply supported and plates with four edges clamped were obtained by data fitting.Then the local buckling of a total of 132 plates under moment gradient were also analysed.Based on the analysis result,the elastic buckling calculation method for web panels was proposed.(2)A total of 15 full-scale local buckling test on HSS welded I-section beams were conducted,including 5 specimens under uniform moement,6 specimens under moment gradient and 4 specimens under patch loading.The material properties of HSS,local buckling behavior and resistances of HSS specimens were explored.The test results were further compared with the design results from different design specifications for steel structure to investigate whether the current local buckling criteria are also applicable to HSS beams.(3)Using the general finite element(FE)software ANSYS,refined FE models were established accounting for the material nonlinearity,initial geometric imperfection,welding-induced residual stress and initial deviation of load,which were detailedly validated against test results of HSS beams from this dissertation and other references.Using the validated FE models,parametric analysis on HSS beams under uniform moment,moment gradient and patch loading were carried out,to investigate the influence of residual stress,initial local geometric imperfection,steel material properties and plate slenderness on the local buckling behavior of HSS I-section beams.(4)Using the curvature integral method,the flexural mechanical performance of CSS beam and HSS beam subjected to uniform moment and moment gradient was qualitatively analysed.Based on the FE analysis results,the calculation formula of rotation capacity for the HSS I-section beam under uniform moment was proposed.According to the cross-section classification principle in Eurocode 3,new cross-section classification method for HSS flexural member was also proposed.(5)Numerical simulation on a total of 315 I-section beams under uniform moment,600 I-section beams under moment gradient and 200 I-section beams under patch loading were carried out.Based on the FE analysis results and existing test results,new design formulas of the post-buckling ultimate resistance for HSS I-section beams under uniform moment,moment gradient and patch loading were respectively proposed according to the concept of interactive width-to-thickness ratio of component plates.The design results calculated by this method were further compared with the results from American,European and Chinese specifications for design of steel structures.