Development of Design Procedure for Cold Formed Steel Channel Composite with Polyurethane Foam

Abstract

This thesis is part of an on-going development of cold formed steel and polyurethane foam composite channels. Cold formed steel channels are roll-formed from sheets of mild steel less than 3 mm thick. Recent developments made in design procedures and roll-forming process has allowed rapid growth of cold formed steel members. They are commonly used as wall studs and purlins in residential and light commercial construction. The composite is made by filling the cavity with the foaming ingredients and restraining with formwork. Cold formed steel are highly susceptible to many forms of buckling. The project seeks to improve upon this weakness with the foam filling with the end goal of producing a more economical product. This thesis was to assist in this endeavour by making modifications to the existing cold formed steel design procedures to include the properties and influence of the foam. The direct strength method was chosen as the procedure to modify for its growing popularity and superior analysis. The new design procedure was validated with experimental tests and finite element modelling of channels of different lengths, foam and cross section. The compression and bending tests were performed on composite channels of 6 different configurations. The procedure and results are discussed in this thesis. The experimental tests performed on small specimens showed the material properties of foam can vary significantly from different foaming conditions. Hence the material properties were only found after the main tests have been completed. The final design procedure made very little modifications to the existing procedure. Local effects of the foam on the steel are modelled by a series of springs with stiffness representing the elastic modulus of the foam. The global properties were based on steel only with the assumption torsion buckling is not critical. The design procedure matched the experimental tests very well and in most cases was more accurate than the finite element model. This project was funded by Materials Accelerator, a research group, and FrameCad, a cold form steel specialist.