Stress path adapting Strut-and-Tie models in cracked and uncracked R.C. elements

In this paper, a general method for the automatic search for Strut-and-Tie (S&T) modelsrepresentative of possible resistant mechanisms in reinforced concrete elements is proposed. Therepresentativeness criterion here adopted is inspired to the principle of minimum strain energy andrequires the consistency of the model with a reference stress field. In particular, a highly indeterminatepin-jointed framework of a given layout is generated within the assigned geometry of the concreteelement and an optimum truss is found by the minimisation of a suitable objective function. Such afunction allows us to search the optimum truss according to a reference stress field deduced through aF.E.A. and assumed as representative of the given continuum. The theoretical principles and themathematical formulation of the method are firstly explained; the search for a S&T model suitable for thedesign of a deep beam shows the method capability in handling the reference stress path. Finally, sincethe analysis may consider the structure as linear-elastic or cracked and non-linear in both the componentmaterials, it is shown how the proposed procedure allows us to verify the possibilities of activation of thedesign model, oriented to the serviceability condition and deduced in the linear elastic field, by followingthe evolution of the resistant mechanisms in the cracked non-linear field up to the structural failure.