Behaviour of Steel Beams Exposed to Parametric Design Fires: A Study on Fire Duration and Intensity

Simplified design techniques based on common fire curves, such as ISO 834 (International Organization for Standardization standard fire curve), are commonly used to evaluate the structural behaviour of steel members in fire situations. However, these approaches do not capture the variable nature of real fire events, particularly in terms of the heating rates and durations. To address this limitation, the thermo-mechanical behaviour of steel beams exposed to parametric fire exposure is examined in this study, with particular attention paid to two different scenarios: a long-duration, low-temperature fire (long-cool) and a short-duration, high-temperature fire (short-hot). Both the unprotected and protected steel beams were evaluated. A validated finite element model was developed to simulate the coupled thermal and structural responses of the steel beams. The thermal analysis used the properties of fire insulation and the methodologies of EN 1991-1-2 (European Standard: Eurocode 1 - Actions on structures exposed to fire) related to parametric fires. The results revealed that for unprotected beams, the steel temperature aligned with that of the gas, resulting in rapid degradation and notable mid-span deflection. In contrast, the protected beams exhibited a delayed thermal response and loss of deformation, although in the case of long-duration fires, there was cumulative heating and sustained axial force. The findings indicate that fire duration can be as critical as peak temperature in governing the structural response of steel beams. Accordingly, performance-based fire assessments should consider realistic parametric fire scenarios and evaluate the effectiveness of fire protection systems under prolonged fire exposure.