This paper describes numerical modelling of the fire behaviour of two-way reinforced concrete slabs using a special purpose non-linear finite-element program, SAFIR. Several two-way reinforced concrete and composite steel-concrete slabs are tested under exposure to the ISO standard fire in order to validate the shell finite element in the SAFIR program. The modelling results showed agreement with the fire tests and demonstrate that the SAFIR shell element can be used to predict tensile membrane behaviour of two-way reinforced concrete slabs in fire conditions. The analyses show that two-way slabs have excellent fire resistance if they deform in double curvature and develop tensile membrane action.
SUMMARYThis paper describes the numerical analyses of restrained concrete floor slabs exposed to fire. The analyses of the slabs were carried out with the SAFIR finite element program considering a 200 mm thick slab, spanning 5 m between two end supports. The slabs were exposed to the ISO standard fire for up to 4 h and were analysed with pinned and rotationally restrained supports. Different heights of the line of thrust at the supports and different levels of axial restraint were also investigated. The analyses show that fully restrained pin-supported slabs can survive the 4 h ISO fire without collapse if the position of the line of thrust is located near the soffit of the slab. If the position of the line of thrust is located much above the soffit of the slab, the slabs will rapidly undergo large deformations and sag into a catenary, imposing axial tensile forces at the supports. The analyses have shown that even if the line of thrust is located close to the soffit, the slab can still deform into a catenary if there is insufficient horizontal axial restraint. In this study, rotationally restrained slabs experience much smaller vertical deflections than pin-supported slabs when exposed to fires. Rotationally restrained slabs with low levels of horizontal restraint do not collapse, due to the beneficial effects of moment redistribution. However, high levels of horizontal restraint can be detrimental, causing slabs to collapse at advanced stages of the fire.
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