Enhancement of the fire resistance of concrete-filled steel tubular columns by using high performance steels

Abstract

[EN] In recent years, innovative solutions have been developed with the purpose of increasing both the load-bearing capacity and fire resistance of concrete-filled steel tubular (CFST) columns. One of these solutions are the so-called concrete-filled dual steel tubular (CFDST) columns. In this configuration, the inner steel tube is thermally protected by the outer concrete ring and therefore its degradation is delayed, which may thus help resisting the applied load for a longer period of fire exposure time. An alternative solution that might be interesting to evaluate under fire conditions is to embed an inner steel profile inside the CFST section, such as an HEB profile. In addition to the development of new types of composite sections, the use of high strength steels (HSS) in construction is increasing, owing to their excellent mechanical properties, which may also be used for an enhanced fire resistance. In the same line, stainless steels (SS) are also becoming widely used in construction due to their beneficial characteristics such as corrosion resistance, high ductility or good aesthetics. Besides, the degradation of their strength and stiffness at elevated temperature is slower than for carbon steels, hence SS may withstand higher temperatures without significantly altering their mechanical properties. This paper aims at obtaining strategies for enhancing the fire resistance of concrete-filled steel tubular columns with the use of innovative solutions (CFDST sections or embedded HEB profiles) combining high performance steels such as HSS or SS. Taking advantage of the improved mechanical properties of these steels at elevated temperatures and using the appropriate thickness ratio between the outer and inner tube or embedded steel profile, it may be possible to attain the required fire resistance without the need for external protection. A three-dimensional finite element model is used in this paper for conducting parametric studies with the different section types and material combinations, in order to evaluate the interest of using HSS and SS for improving the fire performance of steel-concrete composite columns.