Local Buckling Analysis of Multi-Sided Steel Tube Sections

Multi-sided steel tubular sections are commonly used in many structures such as light posts, road signpost, transmission and telecommunication towers etc. These sections are generally subjected to axial compression, pure bending, combined bending and compression or torsion. From the design point of view, it is very important to make sure that these thin-walled sections do not buckle locally before reaching their capacity. Unlike Canadian bridge design standard (CSA S6-14), current AASHTO standard for Structural Supports for Highway Signs, Luminaires, and Traffic Signals provides slenderness limits to check for local buckling of Octagonal (8-sides), Dodecagonal (12-sides) and Hexadecagonal (16-sides) steel tube sections when they are subjected to axial compression and bending. While AASHTO recommends same slenderness limit for all the three sections when they are compact, the requirements are different for non-compact sections. In addition, no requirements are currently available to prevent local buckling of multi-sided sections subjected to torsion. Although many structures now use these multi-sided sections, very limited study has been conducted to evaluate slenderness limits of these thin-walled sections. This paper presents a finite element (FE) analysis based study of local buckling of multi-sided steel tubular sections. A nonlinear finite element model is developed for this study. The finite element model is validated against experimental results from stub column tests of 8-, 12, and 16-sided cross-sections. The validated FE model is then used to analyze a series of multi-sided steel tubular sections subjected to axial compression, pure bending, torsion and combined bending and compression. Results from FE analyses are used to evaluate the slenderness limits specified in different standards (AASHTO, ASCE, and Eurocode). FE analysis also shows that noncompact slenderness limit do not vary much with number of sides and same noncompact slenderness limit can be used for all three multi-sided sections. Finally, effects of initial imperfection and residual stress on capacities of multi-sided sections are investigated.

Keywords: Local buckling; Multi-sided tube; Slenderness limit; Finite element model; Residual stress

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