Precast Concrete Industrial Portal Frames Subjected to Simulated Fire

Precast concrete industrial frames made with tall columns cantilevering from their base and with simply supported prestressed horizontal beam/roof members, widely diffused in Europe and abroad, host most of the industrial activities of the continent, including the many characterised by high fire risk due to production or handling of materials/products having high combustion potential. The typical structural checks under fire action of such structures consists in a simplified cross-section analysis under the action of nominal temperature curves over time. However, this sort of analysis neglects the thermal-mechanical deformation induced by the exposure to fires of the structural elements. This contribution may become critical if considering the beam-column portal sub-assemblies, especially whenever peripheral columns are provided with infill walls. In this case, unlike central columns exposed to somehow uniform fire at all sides, a relevant differential thermal gradient occurs in the slender element, bringing it to large outward deformation activating 2nd order effects and coming into geometrical conflict with the beam, possibly leading to the collapse of the beam due to loss of support. This article presents a case study based on a real precast industrial building carried out employing a full Fire Safety Engineering workflow: (a) realistic fire scenarios encompassing different fire load distributions are simulated by computational fluid dynamics based on experimental curves of rate of heat release found in literature; (b) temperature distribution within the concrete elements was obtained with non-linear thermal analysis in variable regime; (c) strength and deformation of the concrete elements were checked with non-linear thermal-mechanical analysis based on parallel stripes in straight bending.