Experimental modal-based damage evaluation of masonry cross-vaults under quasi-static and dynamic cyclic loading

Masonry cross-vaults are double-curvature structural systems widely employed in historic churches and monumental buildings, which exhibit a pronounced vulnerability to seismic actions owing to the mechanical characteristics of their constituent materials. In such structures, diagonal cracking induced by in-plane shear deformation represents a typical failure mechanism under seismic loading. Despite this, limited experimental and numerical research has been conducted to assess the seismic response of masonry cross-vaults associated with this failure mechanism. Furthermore, the effect of structural damage on the dynamic properties of masonry cross-vaults remains insufficiently investigated in the existing literature. Accordingly, this study aimed to provide additional insight into the seismic response and modal-based damage evolution of a cross-vault made of alternative materials, namely Compressed Earth Blocks (CEBs), characterised by in-plane shear behaviour. Two specimens were tested under controlled laboratory conditions: one subjected to quasi-static cyclic loading, previously investigated by the authors, and the other subjected to dynamic excitation on a uniaxial shaking table. At predefined loading phases, modal parameters were identified through Operational Modal Analysis using the time-domain stochastic subspace identification (SSI) method. Structural damage was evaluated at both the detection and localisation levels through global indicators derived from modal properties as well as spatially distributed local indicators. Experimental observations confirmed the development of shear-related cracking patterns consistent with the expected structural behaviour of cross-vaults under lateral actions. The evolution of modal properties provided reliable information on damage progression across loading stages. Furthermore, a comparison of loading conditions revealed differences in the cracking pattern and vibration-based indicators of masonry cross-vaults.