BENDING AND MEMBRANE ACTION IN CONCRETE

It has become apparent from the series of fire tests carried out at Cardington, UK that the response of steel-concrete composite structures in fire conditions is largely governed by the behaviour of the reinforced concrete floor slabs. This paper obtains a detailed understanding of the strength of heated concrete floor slabs when subject to the combined bending and membrane forces that typically result from restrained thermal expansion. To analyse such slabs the computer program FEAST is used. Initially the behaviour of the floor slab in the Cardington frame under pure bending and pure membrane forces is described and explained. The paper then explores the effect that interaction between bending and membrane behaviour has on the strength of the slab when it is uniformly heated, heated with a linear thermal gradient and heated with the non-linear thermal gradient observed during the Cardington tests. Finally, the effects of varying the area and location of the reinforcement in the slab are analysed