Abstract

Multi-sided steel tubular sections are commonly used in many structures such as road side light posts, road signposts, 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. Current AASHTO 2015 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. The new Canadian steel standard, CAN/CSA S16-19 has recently adopted the same slenderness limit for compact multi-sided tube sections as suggested in AASHTO. While AASHTO recommends the same width-thickness limit for all the three multi-sided sections when they are compact, the requirements for non-compact sections are different for different sections. ASCE/SEI 48-11 provides limits for the non-compact sections, which are very close to the non-compact limits of AASHTO. Although many structures now use these multi-sided sections, no study has been conducted to evaluate AASHTO slenderness limits of these thin-walled sections. In addition, no study is currently available on local buckling of multi-sided sections subjected to bending and axial compression. Thus, a detailed study is required to investigate the local buckling behavior of multi-sided steel tube sections and evaluate these limits. This thesis 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 and validated against experimental results from stub column tests of 8, 12, and 16-sided cross-sections. The FE model is further validated against experimental test results of 16-sided cross-sections subjected to pure bending. The validated FE model is then used to analyze a series of multi-sided steel tubular sections subjected to axial compression, pure bending, combined bending and compression, and pure torsion. Three different geometry, namely, eight, twelve, and sixteen-sided polygonal sections are considered. FE analyses show that AASHTO provided compact limit for members under flexure might need to be revised. However, AASHTO provided non-compact 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 sections subjected to flexure. 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. Furthermore, FE results are used to evaluate capacity equations provided in different standards (i.e., AASHTO, ASCE/SEI 48-11, Eurocode 3, and EN 50341-1) for multi-sided tubes subjected to different loading conditions. FE analyses show that while AASHTO provides a pretty good prediction for the Octagonal and Dodecagonal sections under combined bending and compression, it overestimates the capacities of several selected Hexadecagonal sections. It is also observed that torsional capacities for the Octagonal and Dodecagonal sections are predicted well for the compact sections in AASHTO and ASCE/SEI 48-11 and for a large number of selected Hexadecagonal compact sections, both codes are predicting higher torsional resistance.