Strut-and-tie models to design bridge floors subjected to horizontal actions

Strut-and-Tie Model (STM), conceived by the French builder François Hennebique as a simple representation of a reinforced concrete element subjected to shear and bending, has been later developed by Ritter and Mörsch. In the twentieth century several studies have been carried out about STM and the results constitute the fundamentals of some prescriptions in many international codes. Schlaich et al. 19871 proposed a global approach to the structural design by means of STM. Even though nowadays STM is widely used, several difficulties can be still encountered when dealing with the choice of the model that can best fit the actual configuration (i.e. the ‘optimum’ model). Such problems can be even more relevant when dealing with non-standard cases. In this paper, the case of bridge decks subjected to horizontal actions is presented. Different methods to reach STM are shown: from FEM to Load Path Method to Bi-directional Evolutionary Structural Optimization method. The aim is to use the examined case to evaluate the efficacy of these methods to gain experience in designing r.c. structures with STM. Moreover, in the paper the influence on the model of the geometry of the bridge slab as well as the distribution of longitudinal and transversal deck beams have been investigated.