A Study on the Strengths of Compression Members Undergoing Buckling Interaction

The ultimate strengths of compression members composed of thin-walled steel plates is dependent on the width-thickness ratio of plate elements and the member slenderness. If the component element has a large width-thickness ratio, an elastic or inelastic local buckling may occur first and be interacted with the overall buckling. The local buckling causes a negative effect on the column strength. In this paper, a series of compression tests performed on welded H-section and C-section columns fabricated from SM400 steel plate of thickness 6.0 mm is described. The ultimate strength and performance of the compression members undergoing the nonlinear interaction between local and overall buckling were investigated experimentally and theoretically. The compression tests indicated that the interaction has a negative effect on the ultimate strength of thin-walled welded steel section columns. The allowable stress of the sections with buckling interaction can not be predicted properly by the Korean Highway Bridge Design Specifications. The Direct Strength Method, which was newly developed and adopted as an alternative to the effective width method for the cold-formed steel sections recently by NAS (AISI, 2004) and AS/NZS4600 (2005), was calibrated for the application to the welded steel sections by the experimental and numerical results. The paper proposes the effective width method and the Direct Strength Method to predict properly the ultimate strength of welded steel section columns whether the local buckling and overall buckling occurs nearly simultaneously or not.