Behaviour and design of steel members with web openings under combined bending, shear and compression

Abstract

This paper examines the behaviour of steel beams with web openings under combined axial compression, bending moment and shear force through numerical simulation modelling. The numerical simulation results show that under either pure compression or pure bending, the plastic axial or bending capacities of beams are limited by buckling of the compressive tee-section with the reduction being much more significant in the case of axial compression. The numerical study results also show that when dealing with the general situation of a beam under combined axial compression, bending moment and shear force, the effect of compressive force and consequent tee-section buckling should be included to reduce both the bending moment and shear resistances of the perforated section.Based on the numerical simulation results, an analytical method has been derived. The method was developed by modifying existing shear-moment interaction equations for the Vierendeel mechanism to incorporate the influences of tee-section buckling and additional compressive force in reducing the bending moment and shear capacities.To account for the effects of additional compression force on bending resistance, the plastic moment-axial compression interaction equation may be used, however, the plastic bending moment capacity (without axial compression) and the plastic compression resistance (without bending) should be replaced by those under the influence of T-section buckling. To allow for T-section buckling, an effective T-section buckling length of 0.5L or L (where L is the T-section length) should be used when calculating the bending moment or compression resistance of the perforated section. The shear resistance of the perforated section is obtained by calculating a critical shear stress in the T-section. This critical shear stress -direct stress interaction is according to the von Mises equation, but the square power in the von Mises equation is replaced by a function that reflects the influence of T-section buckling.A comparison between the numerical simulation results and the analytical results using the proposed method indicates very good agreement, with the inaccuracy mainly attributed to inaccurate calculation of the bending – shear interaction of the existing methods which do not consider the effects of additional compression and T-section buckling.