Collapse behaviour of steel columns in fire.

Abstract

The three years' work undertaken in this project is a purely numerical analysis of the inelastic behaviour of steel columns in fire. This is made up of three main parts, each devoted to the development and use of a numerical technique to study the behaviour of steel columns in fire. The first two chapters report on the state of the art on plate analysis, plasticity theories, column behaviour at room temperature, finite strip method and the behaviour of columns at elevated temperature. Part 1, consisting of Chapters 3 to 5, reports on the development of the small deflection finite strip method which includes the effect of plastification of component plates using deformation theory of plasticity. The validity of the method is tested by comparing with published test data on steel columns at ambient and elevated temperature. The comparisons show that the method gives good correlation with test data. Parametric studies have been carried out to assess the effects of slenderness ratios, different stress-strain-temperature representations, residual stresses, eccentricity of loading and local budding of columns. In addition the inelastic behaviour of an H-section under uniform end couples is studied. Part 2, consisting of Chapters 6 and 7, reports on the development of a finite element method which includes the effect of thermal gradients over the member cross-section. The method is compared with test data on both uniformly and non-uniformly heated columns. This shows a good correlation between the method and experiment. Parametric studies have been carried out to assess the effects of initial out-of-straightness, different end conditions, thermal gradients and interaction of eccentricity of loading with thermal gradients on columns. In addition a simple Shanley's column theory is utilised to demonstrate the interaction effect of eccentricity of loading with thermal gradients on columns. Part 3, consisting of Chapter 8, reports on the development of a large deflection finite strip method which includes flow theory of plasticity. The method has not been used for any parametric study. Finally, general conclusions and recommendations for future works are presented in Chapter 9. It is hoped that the valuable information provided in this thesis will be useful in providing a better understanding on the real behaviour of steel columns in fire.