Fire resistance assessment of reinforced concrete slabs and beams under vehicle fires in mechanical parking structures

This study evaluated the fire resistance performance of reinforced concrete (RC) slabs and beams subjected to vehicle fires in mechanical parking structures. A fire simulation was conducted using the Fire Dynamics Simulator (FDS) for a prototype structure with vertically stacked vehicles, and time–temperature curves at the bottom surface of upper members were derived. These results were applied to a nonlinear finite element analysis to assess the thermo-structural response of RC members under varying load ratios. The analysis showed that slabs exceeded the allowable deflection limit of 254.4 mm at load ratios of 0.6 and above, with maximum mid-span deflections of 290.3, 451.7, and 573.3 mm at 0.6, 0.7, and 0.8, respectively. Beams maintained integrity up to 0.6 but exceeded the limit of 518.6 mm at 0.7. Strength reduction of reinforcing steel under high temperatures was identified as a critical factor affecting stability. Peak surface temperatures reached approximately 1,250 °C, indicating severe thermal exposure in confined parking environments. Application of a 5 mm fireproof board effectively suppressed thermal penetration, keeping rebar temperatures below 250 °C. Maximum deflections were limited to 43.6 mm for slabs and 68.9 mm for beams, confirming substantial improvements in fire resistance. These findings provide insight into the thermo-structural behavior of RC members under vehicle fire exposure and emphasize the need for fire-resistant design strategies in mechanical parking structures. The results also offer reference data for the development of future performance-based fire resistance guidelines.