Behaviour and design of cold-formed stainless steel hollow section structural components in fire

Abstract

The focus of this thesis is on the behaviour and design of cold-formed stainless steel hollow section structural components in fire conditions. Currently, codified methods for fire design of stainless steel structures are based largely upon those for carbon steel structures. The main aim of this research study was to develop safe, reliable and efficient design methods for stainless steel structural elements that are in line with the observed actual response of the stainless steel structures at elevated temperatures. An extensive numerical modelling programme was conducted to investigate the behaviour of cold-formed stainless steel columns and beam-columns in fire conditions. The finite element models were rigorously validated against existing test data provided in the literature. The validated models were subsequently utilised to perform a series of parametric studies that allowed the evaluation of key parameters on the structural response of columns and beam-columns at elevated temperatures to be carried out. It is demonstrated that, due to the existing differences in the material behaviour between carbon steel and stainless steel, it is not possible to utilise the same design formulae for the member stability calculations, as proposed in the existing codified design methods. Furthermore, the results indicate that the existing design formulae to predict the resistance of column and beam-column members are not on the safe side in fire conditions, and improvements and amendments are necessary. Based on the comparisons between the resistance predictions from the numerical data and the codified design methods for of cold-formed stainless steel tubular columns and beam-columns, new modified design rules have been proposed in this thesis. For columns, this included revised flexural buckling curves for square, rectangular and circular hollow sections of austenitic, duplex and ferritic stainless steel grades. The proposed buckling curves were shown to offer significant improvements over the existing buckling curves and comply with the required reliability levels for design at fire conditions. For beam-columns, new combined loading interaction factors were proposed, which in combination with the proposed flexural buckling curves allow the determination of the member resistance with high degree of predictive accuracy. Overall, these proposed revisions were shown to lead to a more accurate and reliable determination of resistance of stainless steel columns and beam-columns at elevated temperatures, enabling a more efficient use of the material in structural applications.