Structural performance of a large-span bi-directional partially precast waffle slab system under fire exposure

This paper describes the evaluation of the structural performance under fire exposure of a partially precast waffle slab system employed in the 1970s for the construction of residences in high-mountain skying stations in the Italian Alpine arch. Full information is available about this structural arrangement, including geometry and reinforcement shop drawings, and material properties, adjuvated by on-site non-destructive detection tests. The bi-directional waffle slab system at study was not designed according to any specific rule or calculation concerning fire resistance. The performance of the slab system under fire exposure is investigated through numerical analysis employing non-linear equivalent beam elements under the standard ISO 834 temperature-time exposure, where sectional non-linear temperature distribution and moment-curvature diagrams are evaluated separately and attributed to the numerical model. The modelling is aimed at evaluating the structural performance of the waffle slab under fire exposure with an advanced method taking into account of indirect actions caused by the temperature rise in this highly-statically-undetermined structural arrangement, cheking the actual safety as well as stress and deformation profiles of the slab members under different time exposures. The simulation also aims at assessing the benefits brought in by structural redundancy and stress/force redistribution capacity, this being of primary importance for structures not designed to withstand the recent provisions in case of fire.