Issue 49

M. L. Puppio et alii, Frattura ed Integrità Strutturale, 49 (2019) 725-738; DOI: 10.3221/IGF-ESIS.49.65 734 A NALYSIS OF A RETROFITTED STATE t is worthy to evaluate the role of a retrofitting solution that could have impeded the wall collapse [34,35]. A traditional but effective technique is adopted: a steel tie-rod installed at a certain depth in the sandy soil beyond the artificially added soil (Fig. 8 - a). The designed length is 9.3 m and the tie is modelled as a non-linear truss beam element (Fig. 8 - b). The tensile force of the tie-rod is about 254 kN if the design actions displayed in Fig. 9 are considered. The tie is so designed considered the limit equilibrium of the wall also in case of drain obstruction. The tie is placed in the half of the wall and the uplift pressure of the water is also take into account in the design of the tie. Assuming the high resistance steel ASTM A416, a minimum diameter of 15 mm results. In the numerical modelling, fracture energy, elastic modulus and compressive strength of the wall are kept constant, not being so significant for the capacity curves, whereas the diameter is the only variable parameter assumed. (a) (b) Figure 8: Retrofitting of the historic wall by means of a steel tie rod at mid-height (a) and analyzed finite element model (b). Figure 9: Actions acting on the retaining wall restrained by a tie-rod. [31] The obtained results show a decisive increase in the water level necessary to cause the structural collapse. This improvement is due to the addition of a stabilizing force determining a beneficial effect for the internal stress distributions (Fig. 10 a - b). As for a quantitative assessment, the tensile stress of the wall is one order of magnitude lower than that without tie-rod (Fig. 10 - a) whereas the compressive stress at the foot corner does not significantly change. The crack pattern is consequently improved as well with a reduced cracking in the inner part of the wall but a wider spread in the inner wall (Fig. 10 - c). Another economic and effective solution is the restoration of the drain. This can be made by coring and it is recommended to produce alternate drainage both in height and in horizontal direction. This device is useful and recommendable even in the occurrence of a consolidation by means of tie elements. I