Title: Numerical modelling on the behaviour of concrete-filled steel tube (CFST) with ferrochrome slag as a fine aggregate at elevated temperatures. Since laboratory testing is costly and requires considerable amount of time especially in concrete tests, numerical simulation becomes a matter of great interest in the last few decades. Finite element modelling method using computers permits the simulation of structural elements composed of concrete and high strength concrete. On the other hand, modelling the response of concrete containing waste materials and industrial by-products is difficult due to the deficiency in the definition of material properties contrasting normal and common types of concrete. Existing constitutive models for concrete materials do not account for the presence of aggregate replacement such as Ferrochrome slag (FCS). FCS is an industrial by-product of the ferrochrome manufacturing and one of the waste materials that is used in various construction applications. As experimental tests were already performed on FCS concrete that is used in concrete-filled steel tube (CFST) composite column, it is necessary to further investigate the behaviour of this type of concrete utilizing finite element modelling. This research focuses on the numerical simulation of concrete filled steel tube (CFST) stub column with ferrochrome slag as a fine aggregate after exposure to elevated temperatures. The study aims to investigate the behaviour of such columns at ambient temperature and under fire conditions through finite element modelling and simulation. The numerical models were validated against previous experimental data, and parametric studies were conducted to assess the effect of various factors, such as steel tube thickness and concrete strength. Modifications on existing concrete stress-strain relations after cooling from high temperatures were proposed to consider confinement and FCS aggregate replacement. The results are matching well with experiment at normal and high temperature in terms of failure mode, ultimate load capacity and overall behaviour trend. The outcomes of this research can help in understanding the behaviour of concrete-filled steel tube stub columns with ferrochrome slag as a fine aggregate and aid in the design of exceptional/innovative fire-resistant structures that contains new type of materials.