Strength and stiffness of built-up section columns abstract

Abstract

Cold-formed steel (CFS) built-up structural members are formed by connecting several single sections using discrete fasteners such as screws, bolts and welds. This research project aims to investigate the stiffness and strength of built-up members subjected to different loading types including bending, torsion and compression. This research project comprises four main components. The first part involves a comprehensive experimental study on the shear characteristics of various fasteners for a range of section thicknesses. These connection properties are then incorporated into the analyses of built-up members in the subsequent research stages. The second component involves studies on the effects of fastener configurations on the effective flexural rigidity of built-up I-sections. The obtained flexural rigidity results are adapted more generally to study the stiffness and strength of built-up members experiencing global buckling. The third part comprises studies on the torsion and warping rigidities of built-up I-sections subjected to torsion. Effective torsion and warping rigidities are key parameters affecting the deformation and strength of built-up members subject to torsional and flexural-torsional deformations. The last part integrates the results of the first three sessions to embark on the study of CFS built-up section columns composed of more than two single channels. The studied cross-sectional shapes include singly-symmetric columns composed of three channel sections, for which the failure mode is either local, distortional and/or flexural-torsional buckling, and doubly-symmetric columns formed by four sections which fail in local, distortional and/or flexural buckling modes. The obtained experimental and finite element results are subsequently compared with strengths predicted by the current direct strength method. A design proposal is suggested for the design of CFS built-up section columns.