Behavior and design of cold-formed and hot-finished steel elliptical tubular stub columns

Abstract

Significant progress has been made on structural behavior of hot-finished (HF) steel members with elliptical hollow sections (EHS) in the past few years. However, there is very limited research on cold-formed (CF) steel members with EHS. In this study, both CF and HF steel elliptical tubular stub columns are investigated. The investigation includes laboratory testing, numerical analysis and design evaluations. The geometric imperfection measurements, full load-end shortening relationships and load-strain curves of the stub columns are detailed in this paper. A non-linear finite element model was developed and validated against test results obtained from the present study as well as from the literature. The validated numerical model was employed to perform an extensive parametric study, where the CF and HF stub columns with EHS were carefully designed to include a broad range of the cross-section slenderness and aspect ratio. The cold-forming effect on the CF sections was taken into account in a conservative manner. The ultimate strengths obtained from the tests and numerical analysis were compared with the predictions in the design strengths predicted by the design methods proposed in the existing literature and the Direct Strength Method (DSM). The comparisons showed that the strengths predicted by the equivalent diameter method, the DSM and the modified DSM are generally conservative and reliable. The modified DSM provides the most accurate and the least scattered predictions among these design methods. Therefore, the modified DSM is recommended for the design of CF and HF steel elliptical tubular stub columns.