Numerical and experimental study on CFS spherically-hinged equal-leg angle columns: stability, strength and DSM design

Abstract

This paper reports a numerical and experimental investigation on the stability/buckling, elastic and elastic-plastic behaviour and strength, and Direct Strength Method (DSM) design of cold-formed steel (CFS) spherically-hinged short-to-intermediate equal-leg angle columns. It extends the scope of similar studies recently carried out for CFS fixed-ended and pin-ended (cylindrically-hinged) columns with the same characteristics. Initially, the paper addresses the stability/buckling behaviour of spherically-hinged columns − the results presented and discussed, which include the selection of the column geometries to be analysed (numerically and experimentally), are obtained by means of Generalised Beam Theory (GBT). Then, the post-buckling behaviour and strength of columns containing initial geometrical imperfections is investigated, by means of Ansys shell finite element analyses, and an experimental study, carried out at UFRJ (Federal University of Rio de Janeiro) and whose results are subsequently used to validate the previously developed numerical model, intended to perform a parametric study to obtain numerical failure load data covering a wide slenderness range for the columns considered. Such results comprise (i) initial imperfection measurements, (ii) load-displacement equilibrium paths, (iii) deformed configurations (including the collapse modes) and (iv) failure loads. The experimental and numerical failure loads obtained are then used to develop, validate and assess the merits of a DSM-based rational design approach that adopts the same concepts and procedures that were previously employed for cylindrically-hinged columns. The need for modifications arises from the new major-axis flexure support conditions, which affect the column flexural-torsional behaviour significantly. It is shown that the proposed/modified DSM strength curves lead to safe and reliable failure load estimates for spherically-hinged short-to-intermediate equal-leg angle columns exhibiting a wide slenderness range, thus making it possible to extend the scope of the existing DSM-based design approach to cover also columns with these end support conditions. The very high prediction quality achieved is attested by the fact that the LRFD resistance factors obtained are well above ϕc = 0.85 (value prescribed by the North American Specification for compression members).