Issue 51

M.G. Masciotta et alii, Frattura ed Integrità Strutturale, 51 (2020) 423-441; DOI: 10.3221/IGF-ESIS.51.31 431 and subjected to horizontal settlements of the right support. Snapshots were taken at the settlement onset (Fig. 8a), in correspondence to a movement of 4.5 cm (Fig. 8b), 7.5 cm (Fig. 8c) and in the last configuration before collapse (Figs. 8d- e), respectively. (a) (b) (c) (d) (e) Figure 8: Experimental kinematic configurations of the segmental masonry arch subjected to horizontal settlements of the right support: (a) 0.5 cm; (b) 4.5 cm; (c) 7.5 cm; (d) and (e) 10.5 cm settlements. The maximum measured displacement before collapse (10.5 cm) was reached with an increment of 5.5% with respect to the nominal span. At this stage, the position of the thrust line still lies inside the profile of the arch (even if it is close to touch the intrados in correspondence of the 11th joint from the right) confirming that the equilibrium of the structure with 10.5 cm settlement is still ensured. Afterwards, the right support is left free to slide horizontally over the clearance remaining between support and actuator (3 cm) with consequent loss of stability of the arch and activation of a pure rotational collapse mechanism when the thrust line becomes tangent to the arch profile in another point [19], presumably the 11th joint (counting from the moving support). The position of both intrados and extrados crack hinges remains unchanged throughout the development of the mechanism. Collapse occurs with a limit displacement capacity of approximately 12 cm, corresponding to an ultimate span increment of 6.3%. In Fig. 9 the instant immediately after the collapse is shown. Figure 9: Masonry arch specimen after collapsing due to increasing horizontal settlements of the right support.