Fire resistance of high-strength steel tubes infilled with ultra-high-strength concrete under compression

Ultra-high strength concrete (UHSC) and high strength steel (HSS) have been found to be attractive alternatives to normal strength materials for high-rise construction. The uses of HSS and UHSC can reduce member sizes and payload acting on foundation, which will free up more usable floor space and require less construction materials and handling works. The combination of them to form concrete-filled steel tubular (CFST) columns is more attractive compared with the columns employing either UHSC or HSS due to enhanced strength and stiffness. To better understand the structural behavior of CFST columns using UHSC and HSS, experimental and analytical studies on their fire resistance are presented in this paper. Fire tests were carried out on square S690 HSS tubes infilled with C170/185 UHSC to form the CFST columns. The fire resistance time under Standard ISO fire was recorded and checked against the conventional simple calculation model of EN1994-1-2 and the newly proposed axial force and moment interaction model. It is revealed that the column buckling curve in EN1993-1-1 can be used for fire-resistant design of CFST columns employing UHSC and HSS when the load level is less than 0.65. The use of UHSC is beneficial to improve the fire resistance of CFST columns but the use of high strength steel is not when compared with their counterparts using normal strength materials. (C) 2020 Elsevier Ltd. All rights reserved.