PSI - Issue 78

Angelo Masi et al. / Procedia Structural Integrity 78 (2026) 686–693

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displacement and the distance from the theoretical device’s point of rotation, see sketches in the corner of Figs. 4a and 4b), as obtained from experimental tests. From the test results, the following remarks can be drawn: • For a given target displacement, the hysteretic response appears stable, without significant intra-cycle degradation; • The cycles recorded at all target displacements are quite symmetric. For example, considering the last cycles before failure, the peak force in the loading (positive) direction is about 152 kN, while it reaches -163 kN in unloading (negative) direction. In terms of maximum drift, the values are 1.8% and 1.9% in positive and negative directions, respectively; • During the final test, i.e. target 11 in Table 1, the specimen reached the maximum drift ratio of 2.75%. Subsequently, the ‘hourglass’ elements exhibited shear failure (Fig. 4d) prior to completing the first loading cycle; • In terms of energy dissipated during the loading cycles, Fig. 4c shows the relationship between the equivalent viscous damping value (ζ eq ) as a function of drift. It can be observed that ζ eq linearly increases after yielding (drift of about 0.8%), reaching a peak value of about 30%. This value, which refers to a key characteristic of the proposed device, will be further investigated in the following phases of the study in order to optimize both the geometric dimensions of the device and the shape of hourglasses.

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Fig. 4. Experimental results: (a) cyclic response, (b) envelop curve, (c) equivalent viscous damping vs drift relationship, and (d) shear failure of the hourglass elements. 4. Conclusions The SAFER-REBUILT project aims at defining innovative and sustainable solutions for reducing the vulnerability of constructions. In this context, the effectiveness of SPEAD, a local, non-invasive, dissipative retrofit technique to