Evaluation of Polygonal Hollow Structural Steel Sections via Experimental and Finite Element Analyses

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Kabanda, John
Thin-walled Steel Sections , Local buckling , Polygonal hollow steel sections
Thin-walled hollow sections such as rectangular hollow sections (RHS) have very high torsional rigidity, and thus make a very economic choice for applications which are susceptible to lateral torsional buckling. However, as the depth of a thin-walled RHS increases to ensure adequate bending stiffness, its depth-to-thickness ratio increases and the section is now susceptible to webcrippling/local buckling failure. This causes a reduction in its moment rotation capacity. Therefore, deep thin-walled RHS are not efficient when used as long un-braced spans that require high bending strength and rotational capacity. As such, a new polygonal hollow section (PHS) was developed and a research project initiated to compare the PHS to typical RHS via experimental and numerical analyses comprising four-point, three-point and cantilever bending tests. The results showed that the PHS has almost four times the moment rotation capacity of a comparable RHS and the potential to minimize web-crippling failure in thin-walled hollow sections. Following completion of the flexural bending tests, cantilever bending tests using PHS and RHS beams were conducted. The results showed that lateral torsional bending is not significant for HSS as the lateral deflections recorded at the top and bottom flanges of all the beams were minimal (< 2 mm). Finally, numerical analyses were conducted to simulate the bending behavior of PHS beams and to consider the effects of varying specimen dimensions that were not considered in the experimental program. The results showed that PHS beams have a higher bending moment capacity, almost twice that of RHS beams. This is rather remarkable given that the PHS beams have 4% lower cross-sectional area and 18% lower moment of inertia than comparable RHS beams. It is speculated that the provision of bends in the flanges and webs of the cross-section gave rise to the increase in the moment capacity of the PHS beams. Furthermore, in comparison to the CAN/CSA-S16-14 design guidelines, the results showed that within limits of 32 ≤ h/t ≤ 85 and 19 ≤ b/t ≤ 64 the PHS beams can be classified as Class 1 sections while the RHS beams were confirmed to be Class 3 and Class 4 sections.
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