Fire protection assessment for the steel beams of a road bridge

Abstract

The impact of a fire in an open car park situated under a road bridge was evaluated. In a highly ventilated space such as an open car park, fire may develop by spreading from one car to another. High temperatures may appear locally above burning cars and, in the case of flames impacting the bridge deck, the heat flux from each burning car may be added to different sections of the steel beams of the bridge. The purpose of the study was to determine the most severe fire scenario leading to the highest temperatures in unprotected steel beams of a bridge situated above an open car park. As a function of these temperatures and using standard temperature-time curve equivalence, the necessary fire protection of the steel beams was assessed. Temperatures were determined using the localised fire models of BS EN 1991-1-2:2002, together with the results of some fire tests on isolated cars and car parks existing in the literature. Considering the positions of cars in the car park, the maximum temperatures in the unprotected steel beams were obtained considering no more than five cars in the fire, as corresponding to statistics regarding fires in open car parks.