Investigation of Buckling Behaviour of Cold- Formed Steel Columns with Built-up Sections Subjected to Fire

In recent years, the use of Cold-formed steel (CFS) as load bearing structural members in residential and commercial buildings has become widespread. There are a few researches about fire performance of CFS columns. In particular, CFS columns with a built-up section, which are more common in construction, have been less studied. Also, the existing standards for the design of cold-formed steel structures do not provide sufficient design criteria for designing against fire. In this research project, a numerical study will be conducted to investigate the buckling behavior of CFS columns with built-up cross sections, in fire conditions. Numerical analysis method using ABAQUS finite element software has been used to evaluate the models. After numerical modeling and validation using the results of previous experiments, parametric studies have been performed to investigate the effect of various parameters such as cross-sectional thickness, type of steel, etc. on the buckling behavior of CFS columns at elevated temperatures.The load bearing capacity of CFS columns is extracted from load-displacement curve obtained from numerical analysis. Also, using the direct strength method (DSM), the axial resistance of the CFS columns is computed and compared with the results of numerical analysis. Failure modes of CFS columns have also been obtained and discussed. The results showed that the DSM method estimates the ultimate load capacity of the columns very close to the values obtained from the numerical analysis method. Also, the use of high-strength steel has increased the load-bearing capacity of the columns at different temperatures, although the amount of increase is not very significant.