Non-linear analysis of damage local mechanisms for monumental structures (In Italian)
Because of their intrinsic typological vulnerability (architectonic complexity, geometry, constructive phases, transformations, etc.) and the poor tensile strength of the masonry, the damage and collapse in monumental structures often take place locally. Due to the dynamic action, the structure is subdivided into “macroelements”, which are characterized by an autonomous structural behaviour. It was pointed out that, if the masonry shows good characteristics, the damage mechanisms develop as loss of equilibrium of rigid blocks capable of sliding and rotating. The static loss of equilibrium does not correspond to the collapse, and the kinematism is able to sustain some horizontal action even after its activation. Actually the out-of-plane local mechanisms of monuments, 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. This implies an accurate definition of the safety check methods referring to the high period range (T>2 s). In this research, overdamped elastic spectra were introduced in order to evaluate the maximum response in terms of displacement for macroelements belonging to monumental structures. The simplified procedure introduces the non-linear kinematic approach for the determination of the capacity curve and overdamped elastic spectra for the evaluation of the earthquake demand in terms of displacement. In case of damage mechanisms located at a certain height in the building, quite far from the ground (for instance, the gable overturning in the church façade or the belfry collapse in the tower), an ad hoc procedure was developed in order to account for the amplified seismic demand at a certain height. A non-linear dynamic model was finalized in order to completely describe the seismic response of a macroelement representing a part of a monumental building. Using this model, several step-by-step non-linear dynamic analyses on the equivalent SDOF systems are performed, employing different input ground motions, to validate the simplified method.