Layer model for finite element limit analysis of concrete slabs with shear reinforcement

In the last decades, finite element limit analysis has shown to be an efficient method to determine the load-carrying capacity of slab bridges in bending. However, the load-carrying capacity of concrete slabs can be limited by the shear capacity and the redistribution of shear forces when subjected to high-intensity loads such as tire pressure from heavy vehicles.

In this paper, an optimised layer model is presented which include limitations on both shear and bending. The layer model is based on a sandwich model, which provides a simple way to determine a safe stress distribution for reinforced concrete slabs with shear reinforcement subjected to shear and bending.

The yield criteria in the layer model are formulated as second-order cones which enables an efficient implementation in finite element limit analysis where general convex optimisation algorithms are used. The interaction of section forces is investigated for different combinations of shear forces, moments and torsion.

The optimised layer model is used, in combination with finite element limit analysis, to evaluate concrete slabs subjected to different load configurations. The results show that the layer model performs very well with finite element limit analysis and it is possible to determine a safe distribution of shear forces, moments and torsion very efficiently.

However, the model cannot handle local effects such as punching shear and concentrated loads near the support.