Finite element modelling of compressive behavior of back to back lipped channel sections

Abstract

Cold Formed Steel (CFS) as a construction material has many advantages like lightness in weight, no requirement of formwork etc. Because of these reasons use of built-up CFS members are increasing. Although extensive experimental and numerical studies have been carried out by a number of researchers on such sections under compression, limited research work has been reported that investigates the effect of width-to-thickness ratio (b/t) and lip height-to-thickness ratio (c/t) on the strength and stability of such channels under axial compression. Moreover, present design codes like Eurocode (EC), American Iron and Steel Institute (AISI) and the Australian and New Zealand standards (AS/NZ) include limited guidance on the approximation of capacity of built-up CFS columns considering different width-to-thickness ratio and lip height-to-thickness ratio.

This thesis presents a numerical investigation on the behavior of built-up CFS lipped channels considering different width-to-thickness ratios and lip height-to-thickness ratios of different columns. Nonlinear finite element model was developed based on thirty available experimental results considering different material models and geometric imperfections. The axial compression strengths obtained from finite element model shows good agreement with experimental results of previous researchers validating the reliability of the model. A parametric study comprising of total eighty-eight models was then carried out by using the principles of validated model, with various width-to-thickness ratios and lip height-to-thickness ratios for four types of column sections covering a range of lengths (stub, short, intermediate and slender) which has generated sufficient information about the axial strength of such channels. Obtained axial column strengths were compared against the design strengths calculated in accordance with the AISI standard. It was observed that the AISI standard have predicted somewhat higher strength values with respect to finite element results in most of the cases for all four types of columns. A design guideline was proposed through linear regression analysis between FEA and AISI strength and a multiplier of AISI equation for obtaining better strength result is suggested followed by deriving some curves which can be used while predicting the buckling behavior of such channels.