| Summary: | Cold-formed steel is a popular material with various advantages. Its easy production and assembly give engineer an option to speed the construction process. However, thinness relates to the major issue of buckling, especially when dealing with high temperature. The unprotected cold-formed steel behaviour under fire is expected to have a little strength as compared to hot-rolled steel. Information on such behaviour is still limited. Fire resistance testing on built-up box CFS column was presented in this paper. Two fire resistance tests were carried out under compression load. The Standard ISO 834 Fire Resistance Test under 50% and 70% degree of utilisation measured the temperatures at several points of the steel column surface by using a surface thermocouple and axial column deformation. For reference purpose, one same static test at ambient temperature was carried out to assess the load bearing capacity. Results found that the failure temperature of built-up CFS could reach up to 515 °C and 443 °C within 8 minutes and 7 minutes resistant time for 50 % and 70% degree of utilisation, respectively. Based on deformation analysis, buckling temperature of the column was 448 °C and 394 °C with a critical time of 7 minutes for 50 % and 70% degree of utilisation, respectively. This concluded that the higher degree of utilisation results in lower critical temperatures of the columns.
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