PSI - Issue 44

Simona Coccia et al. / Procedia Structural Integrity 44 (2023) 1356–1363 Simona Coccia et al. / Structural Integrity Procedia 00 (2022) 000–000

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Cracks open and close without contrast. If the pulse magnitude does not reach high values, the wall initiates its motion when the intensity of the acceleration pulses reaches the limit static value A L and the wall starts to oscillate with alternated mechanisms. On the contrary, when the acceleration pulses become stronger and reaches the limit dynamical intensity A 0 the behaviour of the wall changes and two new relevant features take place: - a continuous growth of the deformation of the wall under the sequence of pulses, notwithstanding their alternating action - the occurrence of the dynamical collapse of the wall when, once it has reached the critical configuration - where any opposing action of the dead loads vanishes - the last pulse of the sequence pushes the wall to further overturn. The arrangement of the seismic action in a sequence of regular pulses of alternating sign allows to determine, for any assigned value of the pulse length, the specific minimum collapse acceleration ratio A 0 / A L , able to drag the wall to the collapse. We understand that this ratio gives, from a new dynamical point of the view, the so called “strength reduction or performance factor” of the wall (see foe example Anooshehpoor et al., 1999; Coccia et al., 2022; Dimitrakopoulos et al., 2016; Dimitrakopoulos & DeJong, 2012, Housner, 1963; Ishiyama, 1982; Makris, N., & Vassiliou, M. F., 2013; Ther & Kollár, 2018; Voyagaki et al. 2013; Zhang & Makris, 2001). Due to the intrinsic seismic weakness of the wall under this loading condition, we assume that suitable reinforcements are applied to improve the connection of the wall to the other building walls as, for example, by using FRP strips or similar systems, ads shown in Fig.1(a).

(a)

(b)

Fig. 1. (a) first picture; (b) second picture.

The transversal section of Fig. 1(b) thus shows the presence of a horizontal constraint at the head of the wall. The presence of a vertical weight applied at this head helps the occurrence of a vertical arching action in the wall and to improve the out of plane strength of the wall. We make reference to the last floor facade wall of the masonry building where the horizontal acceleration intensities are larger than at the ground. The wall is at the limit of the collapse under the horizontal seismic loads A L . The vertical and the horizontal loads acting on the wall are shown in Fig. 1(b). The pressure line runs inside the wall and touches one of its edges. 2. Motion of the wall hit by horizontal accelerations. Geometry changes during the motion The motion of the wall starts as soon as the acceleration intensity reaches the static limit value ! = " (1) The motion of the wall starts with the mechanism of Fig. 2 having its centers fixed at the initial vertical configuration. The collapse mechanism of the wall, is composed by three hinges: one at the foot (C 1 in Fig. 2), the other ( C 12 ) on the opposite side at the distance x from the basis of the wall (Fig. 1(b)), and the last ( C 2 ) at the head of the wall, at