Weak Axis Bending Moment Capacity of Polygonal Hollow Steel Sections

Hollow structural sections (HSS) have high torsional rigidity, which makes them an ideal candidate for structural applications to combat lateral-torsional buckling. However, as the bending moment applied on HSS members increase, the risk of local buckling of the HSS members also increases. In recent studies, polygonal hollow sections (PHS) with discrete bends have been shown to be effective in reducing local buckling and improving rotational capacity under strong axis bending. However, the effectiveness of these bends under weak axis bending has not been studied. This paper investigates the structural performance of PHS as well as that of rectangular hollow sections (RHS) with comparative dimensions through a series of four-point bending tests about weak axis with the aid of distributed fiber optic strain sensors (DFOS). The smaller RHS305 beam reached its theoretical yield moment capacity, while the moment capacity of the larger RHS356 beam was 14% less than the theoretical yield moment capacity. The moment capacity of the smaller PHS305 beam is 10% less than its theoretical yield moment, while that of the larger PHS356 beam is 23% less. DFOS was found to be effective in identifying and quantifying stress concentration as well as in monitoring the progress of local buckling in thin-walled PHS and RHS beams.