Plastic mechanism analysis of fabricated square and triangular sections under axial compression

This paper presents a plastic mechanism analysis to predict the complete load-shortening behaviour of fabricated square and triangular section (FSTS) stub columns. Very high strength (VHS) circular steel tubes with a nominal yield stress of 1350 MPa are placed at each corner of the section and welded to Grade 350 steel plates to form a FSTS. Three stages are considered in the analysis: (1) both the VHS tube and steel plate are elastic, (2) plastic mechanism starts to form in steel plates while the VHS tube remains elastic (3) plastic mechanism occurs in both steel plates and the VHS tubes. Discussions are made on the factors affecting the types of mechanism (“flip-disc” versus “roof-type”) in steel plates and the effect of initial geometrical imperfection of the plates on the analysis. Simplified formulae were given for an easy application of the theory developed. The predicted load-axial shortening curves are in good agreement with those obtained by experiments. The predicted ultimate load carrying capacity is about 6% to 8% lower on average than the experimental capacity.