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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.

The slim floor beams, characterized by the steel profile embedded in the concrete slab, may be found in different configurations, based on the shape of the steel profile cross-section, which can vary from a rectangular to double-T section. While the most common shape used nowadays is the double-T cross-section, the Eurocodes do not provide a simplified method for the fire resistance assessment. The literature offers a simplified method for computation of bending resistance under elevated temperature, based on existing research on thermal models, and was validated for a particular type of slim floor beams (SFB). The current study extends the scope of application of this method, for different types of slim floor beam, which include an asymmetric double-T steel cross-section. The objective was reached through a numerical procedure, by analyzing 162 configurations subjected to four different fire requirements (R30, R60, R90, R120), resulting in a total of 648 analyses, performed with a validated numerical model in SAFIR software. The results in terms of bending resistance showed that the simplified method represents a strong tool for the fire design of slim floor beams.

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