The influence of tensile membrane action in concrete slabs on the behaviour of composite steel-framed buildings in fire

A computer program VULCAN has been progressively developed for some years at the University of Sheffield, with the objective of enabling three-dimensional modelling of the behaviour of composite buildings in fire. In this paper the theoretical basis of the non-linear layered procedure used to model the reinforced concrete floor slabs, which includes both geometric and material non-linearity, is briefly outlined. Several of the full-scale fire tests carried out in 1995–96 on the composite frame at Cardington, representing cases in which different degrees of in-plane restraint are provided by the adjacent structure, are modelled to evaluate the influence of tensile membrane action in the concrete slabs on the structural behaviour in fire. In order to illustrate the influence of membrane action and its relationship with boundary restraint, all cases have been analysed using both geometrically linear and non-linear slab elements. A series of parametric studies has been carried out as an initial investigation into the characteristics of steel reinforcement which allow this action to take place. It is clear that the influence of tensile membrane action of concrete slabs on the behaviour of such composite structures in fire is very important, and should be accounted for in later additions and amendments to structural fire engineering design codes.