Dynamic response of rocking masonry elements to long period strong ground motion

Damage and collapse in masonry structures often take place locally. Due to the dynamic action, the damage mechanisms develop as loss of equilibrium of rigid blocks capable of sliding and rotating. Actually the rocking mechanisms of masonry elements, typically non-linear, show high displacement capacity until collapse, high fundamental period of vibration in the non-linear range that can further increase because of the nearly non-tensile strength of masonry. Recent works (e.g. Resemini et al. 2006) propose an approach based on the Equilibrium Limit Analyses (kinematic theorem), in order to describe these out-of-plane mechanisms. Nevertheless, the chaotic dynamic response of these rocking elements needs further studies. The rocking behaviour and its relation to different input and structural parameters are investigated by means of non-linear numerical simulations, with special attention to the long period range. Using a non-linear dynamic model, several step-by-step dynamic analyses on the equivalent SDOF systems are performed. In these analyses, the ground motion characterization is a crucial topic: from a selection of digital recorded accelerograms (Paolucci et al. 2008, Cauzzi and Faccioli, 2008), long period strong ground motions representative of different conditions (magnitude, focal distance, etc.) are used as input for the structural analyses, both dynamic and simplified (proposing a method based on overdamped response spectra). The aim is to verify the applicability of response spectra parameters to simplified procedures for the structural verification of damage mechanisms in masonry structures. Moreover, the influence on the response of ground motion characteristics (PGA, PGV, PGD, Housner intensity, etc.) is analysed.

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