On the extension of the yield-line method to the design of SFRC slabs on grade

Pavements are one of the main applications of steel fiber-reinforced concrete, since steel fibers are particularly suitable both for limiting shrinkage effects and for increasing the bearing capacity and fatigue resistance. This is one of the few applications where steel fibers can even replace conventional reinforcement. The design of steel-fiber reinforced concrete pavements requires a non linear approach. In this paper the yield-line method is proposed for the evaluation of the ultimate bearing capacity of slabs on grade. Yield lines allow to predict the collapse load, if the collapse mechanism indicated by the crack pattern is known and if the mutual ratios among the applied forces are a-priori fixed. Unfortunately, this is not the case in slabs on grade, since the reaction forces exerted by the subgrade depend on the displacement field and are a-priori unknown. Consequently, a specific assumption on the displacement field at collapse must be introduced. In this paper the extension of the yield-line method to slabs on grade proposed by Bauman and Weisgerber is recalled and applications to steel fiber-reinforce concrete slabs are performed, with the objective of fitting (a) the results obtained with a FE code based on nonlinear fracture mechanics, and (b) the results from full-scale tests. The comparison shows that yield lines slightly underestimate the bearing capacity of slabs on grade. However, in spite of this limit, the yield-line method shows (once more) to he highly effective in the design of 2-D plane members subjected to bending, owing to its handiness and closeness to the actual structural behavior.