Issue 49

M. L. Puppio et alii, Frattura ed Integrità Strutturale, 49 (2019) 725-738; DOI: 10.3221/IGF-ESIS.49.65 736 collapsed section. This suggests that a fast investigation of the safety of the retaining wall can be done section by section, indagating the safety of several point with a 2-dim model. (a) (b) Figure 12: Out-of-plane displacements (a) and crack pattern (b) at collapse. C ONCLUSIONS n this paper the safety of the historical wall of Volterra is analyzed in order to evaluate the cause of the collapse occurred in 2014. Non-linear static analyses are carried out considering a growing hydrostatic head varying the fracture energy G f an the tensile strength f t . Among all the considered parameters, only masonry tensile strength is demonstrated to play a crucial role for the assessment of the retaining wall. On the other hand, this parameter is difficult to evaluate, in particular for historical wall (with a significant thickness) and can have a significant variation section by section. Under the assumptions of an increasing groundwater level from the wall base, given the evidence of what observed after the actual collapse occurred (i.e. the wall base stayed in place), it is possible to consider that the failure took place according to the first mechanism case (f t < f t.lim ). Hence, it was possible to trace the maximum masonry tensile strength, which does not exceed the value of f t = 15 kN/m 2 . This value can help in any subsequent safety analysis to be carried out in the remaining medieval urban walls, as they were built in the same period. Cracking path and displacement fields have been analyzed in order to evaluate the more likely failure mechanism and to propose retrofitting strategies. The effectiveness of a sub-horizontal tie placed in the middle of the wall, together with the installation of new drains, was also discussed. This intervention produced a significant increasing of the capacity of the wall in particular towards equilibrium but also in terms of resistance. A CKNOWLEDGEMENT he Authors thank the Municipality of Volterra, Prof. Mauro Sassu and Dr. Giorgia Giardina for the support in obtaining information about the case study and modelling, and Gianmarco Passera for developing part of the numerical models. The Authors also cite the MICHe (Mitigation of the Impact of natural hazard on Cultural Heritage) project for the financial support. R EFERENCES [1] Alecci, V., De Stefano, M., Focacci, F., Luciano, R., Rovero, L., Stipo, G. (2017). Strengthening Masonry Arches with Lime-Based Mortar Composite, Buildings, 7(2), pp. 49, DOI: 10.3390/buildings7020049. [2] Alecci, V., Focacci, F., Rovero, L., Stipo, G., Stefano, M. De. (2017). Intrados strengthening of brick masonry arches with different FRCM composites: Experimental and analytical investigations, Compos. Struct., 176, pp. 898–909, DOI: https://DOI.org/10.1016/j.compstruct.2017.06.023. [3] C. Casapulla; L. U. Argiento. (n.d.). In-plane frictional resistances in dry block masonry walls and rocking-sliding failure modes revisited and experimentally validated. I T