Modelling Thermal Profiles in Fire-Exposed Concrete Filled Hollow Steel Sections Protected with Intumescent Paint

Abstract

Concrete filled hollow steel (CFS) sections are increasingly used in multi-storey buildings and can, in some cases, provide adequate fire resistance without the need for supplemental fire protection. When calculations show that unprotected CFS sections have inadequate structural capacity at the required fire resistance period (FR), these sections require applied fire protection. For plain steel sections (i.e. unfilled hollow steel sections) the design structural capacity at the required FR is typically assumed to depend only on the limiting steel temperature, and is assumed to be the same for both unprotected and protected sections; however, for CFS sections this assumption does not apply. Heated CFS sections develop thermal gradients within their concrete cores. The cross-sectional thermal gradients, upon which the material properties and structural capacities of CFS sections depend, are influenced by many factors such as: the limiting steel tube temperature assumed in design; the required fire resistance period; and the cross-sectional dimensions. This paper presents a parametric analysis on the effect of these three key parameters on the thermal gradients within CFS sections exposed to an assumed steel temperaturetime history. This is performed using ABAQUS finite element (FE) modelling. This is used to develop a simplified design equation to predict the thermal gradients within CFS columns based on these parameters, supporting a rational, simplified approach for fire resistance prediction of protected CFS columns