Issue 51

G. Ramaglia et alii, Frattura ed Integrità Strutturale, 51 (2020) 288-312; DOI: 10.3221/IGF-ESIS.51.23 291 In the Eqn. (1) the confinement effect is provided by the lateral stresses 1 2    ; while, 3  represents the axial stress applied on the masonry columns. The confinement curve is provided by the maximum 3  related to the lateral stress state 1 2    (i.e. the confinement effect). In particular, the Eqn. (2) provides a second order equation in the unknown parameter, 3  . In order to obtain the confinement curve, only the compressive component must be considered for the analysis: 3 1 3 1 2             (3) The Eqn. (3) can be used to assess the confinement curve of strengthened masonry columns. It represents one solution (maximum compressive stress) of the algebraic Eqn. (2). The second solution regards the negative value of the stress 3  (i.e. tensile stress), useless for this discussion. Stassi-D’Alia model The Stassi-D’Alia model [19, 20] provides the boundaries of the failure surface, S D f  with the following equation:         2 2 2 2 1 2 3 0 1 2 3 1 2 3 1 2 2 3 1 3 0 0 , , 1 S D m m m f f f f                               (4) The Eqn. (4), assuming an axisymmetric confinement, can be rewritten in normalized form as follow:     2 2 1 2 3 1 1 3 3 1 3 0 0 , 2 1 2 l mc S D m m f f f f f                             (5) Fig. 2 shows the three-dimensional failure surface assuming the value,  changing from 0 up to 1 with a step of 0.2. Figure 2 : Failure surface according to a Stassi-D’Alia model assuming  changing from 0 up to 1 with a step of 0.2.