Issue 51

G. Ramaglia et alii, Frattura ed Integrità Strutturale, 51 (2020) 288-312; DOI: 10.3221/IGF-ESIS.51.23 292 The Eqn. (5) is an algebraic second order equation in the unknown parameter, 3  . The positive solution of the previous equation provides the maximum compressive strength, 3  for different lateral stress states 1 2    :   2 3 1 1 1 1 1 2 1 2 12 12 2                (6) The envelope of the 3  points to change the internal lateral stress state 1 2    represents the confinement curve. Henky-Von Mises model Henky-Von Mises model [27, 28] was developed for homogeneous materials with compressive strength, 0 m f equal to the tensile strength, mt f (i.e. 1   ). This assumption is certainly not justified for the masonry, where 1   , but it is interesting in order to assess the drawbacks of the other models. This model provides the boundaries of the failure surface by means of the following equation:       2 2 2 2 1 2 3 1 2 3 0 1 2 2 3 1 3 0 0 , , H VM m m m f f f f                     (7) The Eqn. (7), expressed in normalized form and under an uniform lateral stress state, becomes: 2 2 1 2 3 1 1 3 3 0 0 , 1 2 l mc H VM m m f f f f f                       (8) Fig. 3 shows the three-dimensional failure surface model independent on  . Figure 3 : Failure surface according to a Henky-Von Mises model independent on  . The solution of the Eqn. (8) for confinement is represented by the positive stress, 3  : 3 1 1     (9)