PSI - Issue 78

Alessandro Fulco et al. / Procedia Structural Integrity 78 (2026) 2054–2061

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gives positive results, with values of ζ E >1,0, corresponding to the full retrofitting (seismic adaptation) of the building, even with reference to the very high seismic demand characterized the buildings belonging to the Class of Use IV (strategic building) as requested by the client. 3.2. Design works The works for the seismic retrofitting of the structure consists of seismic isolation at the base and detachments and joints along the perimeter. The latter include some new r/c retaining wall alignments and a new steel frame to support the ground level floor on the east side. The main seismic isolation works also provide for the strengthening of the lift shaft walls at the first level, the reconstruction of the lift shaft and of the first r/c staircase ramp. Seismic isolation at the base The isolation works include the installation of 39 double curved surface sliding isolators with a radius of curvature of 3100 mm and variable friction coefficient, as described before, correspondently to all vertical structural elements. The installation of the devices involves the insertion of steel caps on the two pillar, above and below the cut for inserting the isolators, in order to accommodate the plates of the devices, which, as usual, are larger than the dimensions of the existing columns. The steel caps have different dimensions depending on the columns/walls on which they have to be installed and on the device to be installed: in total 15 types of caps are provided. The upper caps have vertical plates with a height of 200 mm that contrast against the column without the need for through anchors. The lower caps consist of a plate to which the contrast angles are bolted only after the installation phase: this sequence is necessary in order to allow for the shimming and grouting required during the devices' loading phase. Fig. 5a shows a design sketch of one of the cap types adopted for the columns. Correspondently at the 5 walls defining the stairwell, the isolation devices are installed at a lower level, that is at the level of the foundation (0,0 m). This choice was necessary in order to limit the functional-architectural impact in relation to the vertical paths. Therefore pockets are provided in the two r/c walls of the stairwell devoted to host the devices, and for the other three walls defining the lift shaft, the same number of widening steel brackets are provided in order to keep the lift run free. To isolate the lift shaft, the demolition of the slab of the existing pit (located at -1,50 m) and its reconstruction at a higher level (-0,40 m) are foreseen. It is also planned the strengthening of the three walls completing the lift shaft, obtained with the insertion of vertical steel plates on both sides, tied with grouted bars passing through the walls, extended vertically up to the intradox of the first level deck. The curbs are applied not only to the lift shaft partitions but also to the two walls adjacent the stairwell (Fig. 5b e Fig. 5c).

Fig. 5 Project excerpts: a) types of caps for the seismic isolation devices; b) device installation on lift shaft walls; c) types of caps for the r/c walls of the stairwell Solutions for perimeter joints The intervention is aimed at guaranteeing the necessary displacement gap for the oscillations during the seismic phase, conservatively defined as 250 mm wide. The demolition of the structural elements connecting the columns on which the devices are installed is planned: the r/c walls incorporating the perimeter columns will be partially demolished up to the intrados of the devices installed on columns. A top demolition (limited to approximately 10 cm) is also planned for the above-mentioned perimeter retaining walls to allow their detachment from the isolated mobile portion of the building. The demolitions described above require the construction of new r/c retaining walls to replace the demolished elements. The new walls are located approximately 40 cm outside to allow for the excursions of the isolated structure, they are 25 cm thick with a height of approximately 2,40 m and are connected to the "fixed" part of the structure at a distance of -1,40 m to allow for the works. The demolition of a portion of the existing slab joined to the main structure is also foreseen, which performs the function of a ground floor "buffer" between the perimeter alignment of the structure and an independent r/c retaining wall against the ground.