The Local And Global Interaction Buckling Study Of The High-strength Steel Box Sections Biaxial Bending Beam-columns

Recently, high strength steel(HSS, fy≥460MPa) welded box sections have been successfully used in many steel structures, and better economic profit have been obtained. The limit of the width-to-thickness ratio in the Code for design of steel structures is too strict to take advantage of using the post buckling strength of plates. In order to save steel and reduce cost we should relax the limit of the width-to-thickness ratio, the members with the large width-to-thickness ratio often show the local and overall interaction buckling. In addition, the initial deflections and the accidental eccentricity at the any direction are taken into account, the axial columns or the beam-column is the biaxial bending beam-columns. Domestic and foreign research for the local-overall interaction buckling still focus on axial compression and one-way bending member, the study of the biaxial bending beam-columns is less. So, the study for local and overall interaction buckling of the high strength steel box section biaxial bending beam-columns has an important practical and theoretical significance.The ultimate capacities of welded box sections column under biaxial load made of high strength steel(nominal yield stress is 460MPa), were analyzed by the ANSYS program. The initial geometric imperfections(both the global and local deflections) and residual stresses, as well as the geometrical and material nonlinearities were be considered. The influence of the width-to-thickness ratio, the slenderness ratio, the relative eccentricity ratio, the residual stress, the strength of steel for the local-overall interaction ultimate capacity was studied. To consider the influence of the geometric parameters for the ultimate bearing capacity, the coefficients of effective yield strength was introduced. According to the Code for design of steel structures, the effective yield strength method and the direct strength method, the formula of the ultimate bearing capacity about the local and global interaction buckling of the high strength steel box sections biaxial bending beam-columns is put forward by using the gross section area, the gross section modulus and the coefficients of effective yield strength.It shows that the developed ?nite element model can simulate the local–overall interaction buckling behavior of the high-strength steel box sections columns. What the width-to-thickness ratio increases will make the ultimate bearing capacity increase and the non-dimensional ultimate bearing capacity decrease. What the slenderness ratio increases will make the ultimate bearing capacity and the non-dimensional ultimate bearing capacity decrease. What the relative eccentricity ratio increases will make the ultimate bearing capacity decrease, the damping of the non-dimensional ultimate bearing capacity with the width-to-thickness ratio or the slenderness ratio increasing will decrease when the relative eccentricity ratio increases. The interaction curves between the axial force and ?exural moment for the high-strength steel box sections biaxial bending beam-columns are nearly linear. Using the high-strength steel can obviously improve the ultimate bearing capacity of specimens. The residual stress will reduce the ultimate bearing capacity of specimens. The coefficients of effective yield strength can consider the influence of the parameters for the ultimate bearing capacity. The proposed formula can precisely predict the local–overall interactive buckling strength of the high- strength steel biaxial bending beam-columns; the proposed modified formulas are good agreement with the numerical results.