GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.2 GNGTS 2023 Specific reference is made to the "Irpinia 1980" earthquake (D'Amico et al., 2020), and we consider the horizontal ground displacement (direction East-West) recorded on Nov 23rd, 1980, with the identification code IT-1980-0012 (station latitude 41.021298, station longitude 15.116339, Italy). In the numerical model, the ground motion is applied along the x direction of Fig. 1. Five different scenarios are considered: colonnade as built (Fig. 2a), colonnade tied by iron rods (Fig. 2b), colonnade with additional lateral walls (Fig. 2c), colonnade with additional lateral walls and tie rod (Fig. 2d), colonnade strengthened with glass-based diaphragms and tie rod (Fig. 2e). The as-built structure is not well tied in the longitudinal direction and tends to "open up" (Fig. 2a). More specifically, the structure is subjected to huge oscillations, and it loses equilibrium and collapses. The quantitative results, reported in Fig. 3a, show that, after 6 seconds from the beginning of the seismic time history, the position of the reference brick diverges, as the structure collapses. A first attempt to improve the seismic performance of the colonnade relies on the insertion of iron rods. In the DEM model, these can slacken under compression and behave as linear elastic springs under tension. The structure is now tied up in the longitudinal direction and responds to the earthquake by oscillating with all its parts moving in phase (Fig. 2b). However, the oscillations are still large and cause the damaging of the base and the top of the masonry buttresses. The colonnade still stands after the seismic event, but it is highly damaged and probably difficult to repair. Quantitative results in Fig. 3a show the large displacements attained during the earthquake. Consider now the traditional retrofitting, where the two lateral fornices are infilled with solid masonry walls, with regular texture and thickness 50 cm. These new members stiffen the colonnade and act as shear walls, thus reducing seismic oscillations (Fig. 2c). However, since the structure is not well tied in the longitudinal direction, cracks open in the masonry work. With the addition of a tie rod, this vulnerability is highly reduced (Fig. 2d), but cracks still open during the earthquake because of the lack of vertical tensile-resistant elements. The quantitative results, in terms of displacement of the reference block, are reported in Fig. 3a: with the presence of infill walls, the structure survives the earthquake and follows the ground motion, though the displacements are slightly amplified. The behaviour obviously improves when the tie rod is present. The innovative glass-based bracing (Fig. 3b) is a shear diaphragm consisting of a (laminated) glass pane surrounded by a thin steel frame, which hoops the glass providing a restraint against the pane rotation and can be directly anchored to the ground and to the masonry structure. Critical stress concentrations at the corners of the glass pane are limited by a system of aluminum inserts and gaskets. A system of micropiles forms the foundations. When these diaphragms are inserted inside the lateral fornices, connected to the masonry at the level of the tie rod and with additional inclined links at the top of the frame (Fig. 2e), the structure withstands the seismic event very well, and does not show any significant damage. The quantitative results of Fig. 3a show that the colonnade essentially follows the ground motion as a whole. In fact, in this case, the colonnade is tied up by the horizontal rod, while the bracing provides additional stiffness to reduce oscillations,