Behaviour of multi-sided tube sections under combined bending and compression or pure torsion

Multi-sided steel tubular sections are often used in structures like roadside light posts, road signposts, transmission, telecommunication towers, etc. These sections are generally subjected to axial compression, pure bending, combined bending and compression or torsion. 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. However, no separate limit is provided for the sections subjected to combined bending and compression, and currently, no study is available on multi-sided tube sections subjected to combined bending and compression. Dalia et al. [1]. studied the behaviour of multi-sided steel tube sections having 8, 12, and 16-sides under axial compression and pure bending. The current paper extends the previous research and investigates the behaviour of multi-sided steel tube sections under combined bending and compression. In addition, the behaviour of multi-sided tube sections under pure torsion is studied. A series of multi-sided steel tubular sections subjected to combined bending and compression and pure torsion is analysed. Results from FE analyses are used to evaluate the slenderness limits specified in different standards (AASHTO, ASCE/SEI 48-11, Eurocode 3 and EN 50341-1). Based on FE results, it is observed that current AASHTO limits for Octagonal multi-sided tube sections can be considered adequate for combined bending and compression. However, the current AASHTO compact limit is found to be unconservative for Dodecagonal and Hexadecagonal multi-sided tube sections when subjected to combined axial compression and bending. It is also observed that torsional capacities for the Octagonal and Dodecagonal sections are predicted well for the compact sections in the AASHTO and ASCE/SEI 48-11, and for a large number of selected Hexadecagonal compact sections, both codes predict higher torsional resistance.