Local Stability Design Of Q620 High Strength Steel Welded Box Section Axially Compressed Stub Column-the Continuous Strength Method

In recent years,high strength steel has been widely used in building structures and other fields.However,with the increasing of yield strength of steel,the bearing capacity of axially compressed members is controlled by stability rather than strength.At present,the effective width method and the direct strength method are the main methods for calculating local stability bearing capacity in the world.The current steel structure code GB50013-2014 limits the occurrence of local buckling of axially compressed members by strict width-thickness ratio limit,which makes the material properties of high strength steel not fully utilized.In this paper,the local stability performance of Q620 high strength steel welded box shaped axially compressed members is deeply studied by means of experimental and finite element numerical analysis methods,and a large number of experimental data of high strength steel axially compressed stub columns are collected.Based on the concept of the continuous strength method proposed by Gardener,a new method for calculating ultimate load of specimens with local buckling is proposed for high strength steel axially compressed members.The main work and achievements of this paper are as follows:(1)Summarized the development and concept of some existing international codes for calculating local buckling ultimate bearing capacity(including the effective width method and the direct strength method)and the new continuous strength method proposed in recent years,which provides a theoretical basis for the calculation of local buckling ultimate bearing capacity of high strength steel short columns.(2)Twenty Q620 E high strength steel short columns with welded box(square)cross section were tested under axial compression.Three specimens from the rolling direction of the original plate were tested and the test data were obtained.The initial geometric imperfections of the members are measured and the ultimate bearing capacity of the members after local buckling is obtained by experiments.The necessary parameters of the continuous strength method(the slenderness ratio of the whole section and the deformation capacity of the section)are obtained by analyzing the load-vertical displacement curve.(3)The finite element software ABAQUS 6.13 is used to simulate and verify the experiment of short column of Q620 E high strength steel welded box section.The effects of material nonlinearity,welding residual stress and initial geometric defects are considered in the analysis.The results show that the finite element model adopted in this paper can simulate the axial compression behavior of welded stub columns with high strength steel box section.(4)The local stability performance of welded box section members is parameterized by the verified finite element model.The effects of initial geometric imperfections and residual stresses on the ultimate bearing capacity and ultimate displacement of Q620 E high strength steel box-section short columns are studied.(5)The use of the finite strip software CUFSM is introduced for calculating the full-section slenderness of the transverse coordinates of the basic curve of the continuous strength method.(6)Based on the test data collected in this paper and the test data of high strength steel short columns at home and abroad,and according to the concept of the continuous strength method,a formula for calculating the local buckling ultimate bearing capacity of high strength steel short columns is proposed.The accuracy of the constitutive model and its sensitivity to parameters are verified.(7)Comparing the calculation results of the continuous strength method with those of other codes,the advantages and disadvantages of each method are summarized.