Direct strength method for the design of cold-formed steel hat sections under localised loading

Abstract

This thesis investigates the application of the Direct Strength Method (DSM) in predicting the localised loading capacity of cold-formed steel hat sections. Four loading cases with various fastening conditions are studied. Experimental data from this study and previous research are utilised to develop a yield/plastic mechanism model for use in the DSM, and to propose simplified and consistent DSM design equations for practical applications. The potential for utilising the DSM design equations for localised loading design is established through numerical, experimental and analytical investigations. Methods for calculating the two significant inputs for DSM design equations, the buckling load (P_cr) and the yield load (P_y), have been investigated.

The Finite Element Method (FEM) and the Finite Strip Method (FSM) are widely accepted for calculating the buckling loads of channel sections. A software program called THIN-WALL-PYTHON is developed and optimised for hat sections, employing the FSM to calculate the buckling loads which are benchmarked with the results obtained using the FEM software (ABAQUS).

Simplified yield/plastic mechanism models are developed for use with the hat sections under localised loading in various cases to calculate the yield load for DSM design equations. Experiments on hat sections with varying dimensions, particularly in the stocky range, are conducted to verify the analytical theory and numerical models.

Two sets of DSM design equations for hat sections under localised loading are developed based on experimental and numerical datasets. Deviation and reliability analyses are conducted using the experimental data, and design capacity reduction factors for both methods are proposed for all the investigated loading cases. The prediction results are compared with current standards and specifications (AS4600:2018 and AISI S100-16), demonstrating significant advancements in accuracy and applicability.