Overall Buckling Behaviours Investigation On Q460 High Strength Steel Welded I-section Two-span Continuous Beams

With the flourishing development of the building trades and the constantly improvement of steel manufacturing technique,high strength steel(the yield strength in excess of 460 MPa)with excellent performance has been widely used in the engineering field.Because the material properties of high strength steel are significantly different from those of normal strength steel,which affects the overall buckling behaviours of the component using high strength steel.The newly adopted Standard for Design of High Strength Steel Structures(JGJ/T483-2020)in my country provides the overall buckling design method for high strength steel flexural members,but design formula for the critical moment of two-span continuous beams is not proposed in this design method and the design formula of the elastic critical moment of continuous beams is the most critical.What’s more,there is no relevant test to verify the reliability and applicability of the design method.Therefore,the systematic and in-depth study on overall buckling behaviours and design methods of Q460 high strength steel welded Ⅰ-section two-span continuous beams was carried out in this paper,by combination of test and finite element analysis.The research results can provide reference for the future engineering application and the revision of relevant codes.The residual stress of Q460 high strength steel welded Ⅰ-section was measured by method of section,and the residual stress distribution model of the Q460 high strength steel welded Ⅰ-section was obtained.A total of six overall buckling behaviours test on Q460 high strength steel welded Ⅰ-section two-span continuous beams under concentrated loads in the middle of each span were carried out.The results show all specimens occurred overall buckling failure.The influence of height-to-width ratio and the span ratio on the overall buckling capacity of Q460 high strength steel two-span continuous beam were analyzed,and the overall buckling capacity of the two-span continuous beam can be increased by increasing the flange width and decreasing the span ratio.The finite element analysis(FEA)software ANSYS was used to establish the finite element model(FEM)considering the residual stresses and the initial geometric imperfections,and the test was simulated.The obtained failure mode,the overall buckling capacity and the load-displacement curve of the specimen were in good agreement with the test results,which verified the established FEM to be feasible for analyzing such components.On this basis,using the verified FEM,a large number of parameter analysis was carried out by transforming the span ratio,length of main-span,load position and height-to-width ratio,etc.The elastic critical moment and ultimate moment obtained from parameter analysis lay a foundation for the subsequent research on the solution of the elastic critical moment of two-span continuous beams and the study of the overall buckling method design of high strength steel two-span continuous beams.Based on the calculation formula for the elastic critical moment(Mcr)of simply supported beams given in the Standard for Design of Steel Structures(GB50017-2017),and combined with the FEA results,the calculation formula for the elastic critical moment(Mc)of two-span continuous beams was fitted.The fitting formula for calculating the elastic critical moment of two-span continuous beams was substituted into the calculating formula of the overall buckling factor for flexural members in Standard for Design of High Strength Steel Structures(JGJ/T483-2020)to obtain the curve of the overall buckling factor,which were compared with the test and the FEA results.The results show that when the load is applied on the top flange,between the design curve and the test or FEA results are in good agreement.However,when the load is applied on the bottom flange,the calculation result of the code is too conservative.The calculating formula of the overall buckling factor in this case is modified,and the modified curve of the overall buckling factor is close to the FEA results.It is shown that the modified formula can effectively predict the overall buckling factor of Q460 high strength steel weldedⅠ-section two-span continuous beam when the load is applied on the bottom flange.