الفهرس 
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Abstract
Concrete-filled steel tubular columns are currently used in a large number of structures. Conventionally, carbon steel tubes have been used to fabricate the composite columns, but it is now widely believed that stainless steel is a beneficial and innovative alternative material. Stainless steel is corrosion-resistant, it is highly durable, performs well in fire conditions, and it is easily maintained. One of the main advantages of stainless steel is its attractive architectural appearance, which has encouraged engineers to use it in a range of different structures. The initial high cost of stainless steel is offset by its lower lifetime cost, since it requires less maintenance than carbon steel. The amount of stainless steel needed is reduced by filling hollow structural sections with concrete. Because of this, concrete-filled stainless steel tubes (CFSST) have the potential for wide use for structural members. Fire safety is of great concern in structural design. This thesis describes a study of the behavior of CFSST columns in fire conditions. First, the literature was reviewed to obtain a better understanding of the behavior of concrete-filled stainless steel and carbon steel composite columns in fire situations. All the available and reliable fire test data that has accumulated on the subject of concrete-filled carbon steel tubular (CFST) and CFSST columns was compiled and used to validate the numerical models of heat transfer and stress analysis developed in the thesis. Two kinds of fire tests were carried out on CFSST columns. Six columns of either circular or square cross-section were subjected to fire-resistance tests in which each column was subjected to a given constant load level at ambient temperature, then heated until the column failed. Another six columns were tested in simulated post-fire conditions to investigate their strength deterioration, wherein each column was subjected to a constant load at ambient temperature and heated for a certain time, then left to cool to ambient temperature while the load was maintained. Following the heating and cooling phases, the applied load was increased until the column failed .The effects of different parameters were studied in the test program: load level, the existence of steel reinforcement or not, section type (circular or square) and the effect of initial imperfections in the column. A photogrammetrical method was adopted for measuring the initial imperfections in the column prior to testing and to measure the axial and lateral deformations and strains during the tests. The data obtained from the tests (e.g., temperature developments, axial and lateral deformations, fire resistance times and failure modes) have increased the understanding of the performance of CFSST columns under different fire conditions. The test data was also used to verify the proposed finite element modelling approach in which a finite element model, based on ABAQUS software, simulates the behaviour of CFSST columns while taking account of the measured initial imperfections and profile of each stainless steel tube. A simplified finite element model is also proposed, which assumes a sinusoidal shape for the overall buckling mode of the columns. This simplified model was verified by comparison with the present test results, and also by reference to test results reported by others. The influences of different parameters on the behaviour of the CFSST columns were also investigated, and the differences in the behaviour of stainless steel and carbon steel composite columns were recognised. A new simplified program based on the finite difference method was developed using MATLAB software to calculate the temperature field in both types of steel columns during fire exposure.Finally, simplified design guidelines are proposed for CFST and CFSST stub columns and for slender CFSST columns. The guidelines show the calculated allowable load capacity for specific columns at different fire rating times. Design examples illustrate the use of the proposed simplified design methods. Practical design tables have also been compiled to show the temperature field for columns of different dimensions and different fire duration times. Other design tables are also presented for the calculation of the load capacity of CFSST and CFST columns.