Issue 43

P. Zampieri et alii, Frattura ed Integrità Strutturale, 43 (2018) 182-190; DOI: 10.3221/IGF-ESIS.43.14 185 If this condition is not verified, the hinge points (1, 2 and 3) are moved to the local maximum and minimum points of the thrust line before applying PVW again. This procedure is reiterated until the thrust line condition is verified. It should be emphasised that for a given displacement d k the hinges may not be correctly positioned (1, 2, 3) in relation to the displacement in the previous step d k-1, but rather the hinge positions are updated (1 ‘, 2’, 3 ‘) as shown in Fig. 3. This procedure can therefore assess (step-by-step) whether the collapse hinge positions have changed (Fig. 3) as the displacement d k increases. The procedure described is repeated for incremental values of d k and ends when the arch collapse condition is verified due to alignment of the three crack hinges. Fig. 4 shows a flow chart of the algorithm described above. Figure 4 : Algorithm implemented. E XPERIMENTAL TESTING xperimental analysis was carried out on a masonry arch made of solid bricks bound with traditional mortar. A plastic caisson was used in order to obtain a great geometrically regular element instead of using bricks without mortar as in Ochsendorf [22] tests. The mortar employed for this experimental has low tensile property according with the hypothesis assumed by Clemente [26]. The masonry arch was fixed to a steel frame with a movable springing along a 45° direction (Fig. 5). This applied displacement system represents an innovative case never studied before by other authors. The arch made from 37 bricks measuring 250 x 125 x 50 mm 3 has a span length of 2281 mm, an arch rise of 585 mm and an embrace angle (β) equal to 107.356°. Fig. 5 shows the experimental test diagram and the graphical representation of the mechanical system capable of applying an incremental displacement along an inclined direction of 45°, providing instant-by-instant the imposed displacement value. Results of experimental testing During the test, images were continuously recorded that allowed the displacement imposed by the mechanical system to be associated with the configuration of the arch collapse mechanism (Fig. 6). Specifically, in the images shown in Fig. 6, three different collapse mechanism configurations can be identified for different values of displacement d k , as shown in the graph in Fig. 9. E