MODELLING OF SIMPLE ROCKING IN CHURCH FAÇADES: SENSITIVITY TO SEISMIC INPUT AND EFFECT OF ANCHORING

The paper is devoted to the large-scale assessment of the vulnerability of masonry church façades to out-of-plane mechanisms and of the positive effect provided by anchoring devices. In particular, attention is focused on the simple rocking of the main façade of masonry churches that is analysed by means of a displacement-based approach aimed to carry out pushover analysis. Non-linear static analyses, taking into account both geometric non-linearities and frictional resistances provided by the church sidewalls, are firstly performed on a reduced sample (14 façades) of churches located in the Ischia Island (Italy) and, then on an extended sample of 400 façades generated through the Monte Carlo simulation starting from the main geometric parameters of the 14 façades. The contribution of strengthening systems made of steel tie-rods to mitigate the simple rocking is analysed for both samples and their effect in terms of vulnerability reduction, as some design parameters of the tie-rod change, is highlighted by developing the fragility curves for both anchored and non-anchored façades. Fragility curves are, indeed, derived for the 14 and 400 façades using incremental static analysis (ISA) and multiple stripe analysis (MSA). Acceleration-displacement response spectra (ADRS) are considered for the three limit states corresponding to the onset of rocking, LS0, and to moderate and severe motions, i.e. LS1 and LS2, respectively. Finally, the influence of the seismic input variation is examined on both anchored and non-anchored façades and with reference only to the extended sample of 400 façades for LS1 and LS2.