Numerical simulations of flat-jack test setups for the local shear characterisation of masonry panels

The present numerical investigation concerns the characterisation of local in-plane shear strength and failure of masonry panels. A testing geometry has been conceived at design stage so as to experiment the non-linear shear response of masonry wall specimens at the laboratory scale by using pressure-controlled shear flat-jack testing. Before implementing real experimental tests, advanced finite element method (FEM) simulations have been devised and carried out here (with the LS-DYNA code), with the aim of assessing and optimising the conceived experimental test geometry and the shear flat-jack configuration. Both bricks and mortar are appropriately modelled through the Karagozian & Case (K&C) damage plasticity model. Two different shear flat-jack setups, placed in couples within through-thickness vertical wall cuts, are analysed, in order to enquire the local shear response and damage field arising in the centre of the wall panel. Numerical outcomes show that the shear flat-jack configurations look reasonably well set and put forward first benchmark results useful for further setup optimisation and for possible later comparison to real future experimental outcomes, in view of a qualitative and quantitative interpretation and consistent identification of local shear structural properties and response of masonry panels. The proposed configuration indeed allows to ingenerate a shear stress state concentrated in the central part of the panel, ultimately leading to extensive localised damage and failure. The resulting damage field predicts mortar fracture in the middle of the masonry wall.