The effects of in-plane shear displacements at the springings of Gothic cross vaults

Extensive damages recorded during recent strong Italian earthquakes highlighted how vulnerable masonry vaults are and what deformations they receive from the rest of the building, which can be simulated as two phenomena: (i) a dynamic response of the vault itself, above the lateral walls and piers, and (ii) a pseudo-static response of the vault to imposed displacements at its springings, triggered by significant movement from the lateral walls and piers. This paper aims at improving knowledge in this field by simulating the second of these phenomena as static shear deformation at the springings. An experimental programme was set on a model of a typical quadripartite square Gothic cross vault (from the aisle of the Holyrood Abbey in Edinburgh). The test on a 1:4 scaled model had the shear displacement applied by moving two abutments in the longitudinal sense until failure, recording the crack pattern evolution and displacements of the ridges, identifying the diagonal cracks normal to the shear displacement that cause the damage and collapse in the vault. The crack pattern was validated with linear and non-linear numerical models, confirming particular observations like the uplift of the ridges and concentration of damage along the notional shear diagonal. Non-linear models are capable of capturing not only the crack pattern evolution, but also the vertical and horizontal displacements of the structure

Pseudo-static response of masonry cross vaults to imposed shear displacements at the springings

The static and dynamic performances of historical masonry churches are closely related to the behaviour of each substructure, as well as to the mechanical properties of the constituent materials. Information on damage location and extent, collected after recent violent Italian earthquakes, highlighted that masonry vaults are among the most vulnerable elements. The investigation of their dynamic behaviour under earthquake excitation (stress and deformation states) is a fundamental issue for effective structural interventions. During an earthquake ground motion, cross vaults are basically subjected to two phenomena: (i) the "shaking"/dynamic response of the vault system itself, vibrating above the lateral walls and piers, and (ii) the response of the vault to imposed displacements at its springings, accommodating the significant movements of the lateral walls and piers. Within this context, this paper aims at improving the knowledge of the structural behaviour of cross vaults under static shear deformation at the springings, by means of an experimental test representative of a Gothic cross vault from the aisle of the Holyrood Abbey in Edinburgh (UK). The experimental test was performed on a 1:4 scaled specimen built with timber and lime mortar. The shear displacement was applied by moving two abutments until failure. The deformation of the vault was recorded in space with a Total Station. The results of the tests are reported in this paper in terms of crack pattern evolution, vertical displacements of the transverse ridge, identifying the shear displacement levels corresponding to significant damages in the vault