Fire modelling and resistance of RC columns subjected to natural fire

Currently, the fire resistance design of reinforced concrete (RC) columns is essentially based on standard fire curves such as ISO 834 or ASTM E119. A more scientific approach based on realistic fire curves is useful to structural engineers as the method can take account of the actual fire load, ventilation openings and thermal properties of boundary walls in a fire compartment. In this paper, a simple and rational design method called the Rankine method is extended to natural fire conditions, which requires the concept of time equivalence for calculating the column fire resistance. By applying a time equivalence formula recommended in the Eurocode, the proposed Rankine method can be extended to different fire curves. As gas temperature plays a pivotal role in fire resistance calculations, a comparison study of time equivalence, zone modelling and Eurocode parametric fire equations is conducted. The study shows that the time equivalence approach is reasonably accurate and robust. A finite element code - SAFIR and a zone modelling program - Ozone are used to benchmark the simplified fire resistance calculation for RC columns.