SHEAR BEHAVIOUR AND DESIGN OF COLD-FORMED CHANNEL SECTIONS WITH ELONGATED OPENINGS BASED ON DIRECT STRENGTH METHOD

This thesis presents a detailed study on shear buckling and shear strength of high strength cold-formed channel sections with elongated openings. The main purposes are to investigate experimentally and numerically the shear behaviour of perforated cold-formed steel plain C-lipped sections and to further develop a Direct Strength Method (DSM) of design to predict the shear capacity of such sections. Firstly, in order to achieve the primary aims as stated, an experimental program of thirty tests was performed to observe the shear behaviour of channel members with both non-elongated and elongated web holes. Based on the capability of minimising the bending moments at two ends of the shear span, a testing apparatus namely ‘Dual Actuator Test Rig’ previously developed at the University of Sydney was used throughout the test program to capture a state close to pure shear and to obtain the predominantly shear capacity of perforated members with an aspect ratio (shear span / web depth) up to 2.0. The experimental results were used to study the shear strength reduction due to enlarged web openings. Further, these test results were also used as the input to the current Direct Strength Method (DSM) equations for further comparisons, calibrations and validations. Secondly, in order to achieve more insights into the shear behaviour of cold-formed members with elongated web openings, numerical nonlinear simulations based on the Finite Element Method (FEM) using ABAQUS/Standard were developed to compare with and calibrate against the experimental results. Moreover, to study shear buckling behaviour and to generate shear buckling loads which is also a required input to the DSM in shear, a simplified method for shear buckling analysis using simplified finite element (FE) models including web holes were introduced in this study. The buckling results obtained from these models were calibrated against those of the full FE models which have the same configuration as the actual tests. On the basis of the accuracy of the finite element modelling, the FE models for both shear buckling and shear strength analyses were employed for parametric studies to extend the result database used for further verification of new proposals in this study. Finally, on the basis of the results from experimental and numerical investigations, a new DSM design for cold-formed channel sections subjected to shear with both non-elongated and elongated web openings was introduced. The new proposal is based on the use of the existing DSM design rules for shear together with introduced modifications of the shear yield loads as a result of the Vierendeel mechanism approach. As a consequence of the parametric study for shear buckling analyses, a dimensional transformation was also proposed to determine the equivalent hole dimensions in design

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