Dynamical assessment of the performance factor "Q" for the masonry wall under the out of plane seismic action

The non-linear out of plane dynamical response of the masonry wall, suitably reinforced at the top and hit by sequences of acceleration pulses, alternating in sign and with different intensity and duration, is the subject of the paper. The wall moves out of its plane with a gradually changing failure mechanism and two relevant aspects characterize this motion: the occurrence of a rotational build up under the action of the pulse sequence, in spite of their alternating in sign and the occurrence of the dynamical collapse. This last takes place when, under the second last pulse of the sequence, the increasing mechanism has reached the critical configuration in which all resistance of the wall is lost. The arriving of the last pulse, pushing the wall to further increase its rotation, yields the collapse. The ratio between the dynamical and the statical collapse accelerations – the so-called strength reduction or performance factors – is thus directly determined following the dynamical response of the wall to the pulse sequences. The paper, which is part of an ongoing research (Coccia et al. 2022) reveals how the wall, so vulnerable under the out of plane seismic actions, can mobilize collapse mechanisms capable of defending it by the destructive action of the quakes.