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Abstract
In recent years, the effect of fire on materials and buildings is considered one of the most important fields of research in structural engineering. Concrete is one of the most resistant construction materials to fire. It can to retain for a relatively long time, thus limits crack propagation. Furthermore, it can be repaired if exposed to moderate fire for a limited time. However, it loses its strength dramatically when exposed to fire for long duration due to a series of complex physical and chemical phenomena which take place within the concrete. Variables such as duration of exposure at a particular level of temperature and cooling methods are expected to have an influence on the strength of concrete subject to fire. One of the methods of increasing the fire resistance of a building is to coat the structural elements with fire retardant plasters to delay failure. More research work should be carried out to evaluate the effect of these parameters. The objectives of this work are to study the effect of fire on the behaviour of strengthened and un-strengthened R.C slabs under load and to evaluate the efficiency of protection layers against fire. The studied parameters of this research are: Fire temperature degrees (300,500 and 7000C), fire durations (one, two and three hours), methods of cooling (water-air), effect of loading during fire, fire resistance of different strengthening systems and effectiveness of protection layer.
The present study has two phases: experimental and theoretical. The experimental program includes fabrication and testing of twenty R.C slab specimens with dimensions (1800x500x100 mm), thirty cubes coated and uncoated with fire protective layer and twelve cylinders under different fire durations.
The theoretical program applies a nonlinear finite element program namely ANSYS (version 10) for modelling the tested reinforced concrete slabs.
Finally, it is concluded that the residual modulus of elasticity, strength and failure load of tested slabs after firing and cooling reduced by increasing the fire temperature degree and fire duration, leading to reduction in stiffness and decrease in ductility. It is also concluded that cooling the specimens by water causes great loss of stiffness and decreases the failure load more than cooling by air.
Keywords: Reinforced concrete slabs, Fire, Strengthening, FRP, Finite element.