Behaviour of reinforced concrete structures in fire
Roger Plank2006
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Abstract
In the past two decades, a significant amount of research has been conducted into the performance of composite steel-framed structures in fire. However, the same level of development has not taken place for other forms of construction. In terms of reinforced concrete construction, design is still based on simplistic methods which have been developed from standard fire tests that do not necessarily represent real building behaviour. This makes it very difficult, if not impossible, to determine the level of safety achieved in real concrete structures, or whether an appropriate level of safety could be achieved more efficiently. In this study detailed analyses of a reinforced concrete structure subject to a standard fire regime are carried out. The building is designed to Eurocode 2 and represents a commercial office building. In order to study the interactions between the cool and hot zones of the structure, a series of analyses has been carried out for different extents and positions of localised fire compartments. It is clear that adjacent cool structure provides considerable restraint and continuity, increasing the fire resistance of the structure within the fire compartment. Relatively small areas of tensile membrane force are formed within the concrete slabs, and large areas are subject to compressive membrane action during the fire. As a result the downstand concrete beams experience enhanced tension during the fire, especially in the early stages, which is mainly carried by their tensile reinforcement. It is therefore very important to keep the temperature of beam reinforcement within certain limits. Eventual structural collapse in the studies is always due to column failure, and it is clear that the performance of columns is vitally important to the survival of reinforced concrete buildings in fire.
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