Behaviour of reinforced concrete flat slab over column support using nonlinear stress field design

In the design of flat slabs, one of the problems is the congestion of reinforcement at the column/slab junction. From the construction point of view, it is useful to reduce this congestion of reinforcing steel. In the design of reinforced concrete framed structures a similar problem arises at the beam/column intersection, where the congestion is generally reduced by redistributing the support moments without affecting equilibrium of the structure. However it is important not to depart far from the elastic state of stress, otherwise problems due to early cracking arise. The object of the present paper is to explore a way of achieving a similar controlled reduction of support moments at the slab/column junction in the case of flat slabs. Using the procedure developed, a model of the local area around the column region is designed and made in reinforced concrete. The model is tested and the observed behaviour is compared with the predictions of a nonlinear finite-element analysis. The adopted procedure is shown to be viable from the serviceability and ultimate limit state point of view. Good agreement was obtained between predicted and experimental measurements.