Local buckling of multi-sided steel tube sections under axial compression and bending

Abstract

Multi-sided steel tubular sections are commonly used in many structures such as high mast lighting and sign supports. Current AASHTO standard for Structural Supports for Highway Signs, Luminaires, and Traffic Signals provides width-thickness 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. Although multi-sided tubes are used in many structures, very limited study has been conducted to evaluate the 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 FE model is developed for this study and validated against experimental results from stub column tests of 8-, 12-, and 16-sided cross-sections. The FE model is then used to analyze a series of multi-sided tubular sections subjected to axial compression or pure bending. Results from FE analyses are used to evaluate the slenderness limits specified in different standards (AASHTO, ASCE, and Eurocode 3). FE analyses show that AASHTO provided compact limit for many multi-sided tube sections are non-conservative when subjected to flexure and might need to be revised. Also, current non-compact section limits are quite relaxed for the sections subjected to pure bending. Based on FE results, revised compact and non-compact limits have been proposed for octagonal, dodecagonal, and hexadecagonal multi-sided tubular sections. Moreover, FE analyses indicate that the non-compact limit of the hexadecagonal section can also be used for the other two sections under axial compression.