An Interface Constitutive Model for Mortar Joints with Embedded Rubber Layers

To improve the seismic performance of masonry structures, a novel multi-layer mortar bed joint has been recently conceived and experimentally tested, in which a soft-core rubber layer is enclosed by two extruded elastomer layers and positioned centrally within the mortar joint. Thus, it is essential to develop an effective constitutive model capable of describing its in-plane shear behaviour. The interface model is the most straightforward. In this study, the mechanical response of the interface is characterised by a constitutive relationship through four distinct stages, achieved by incorporating the Coulomb friction law into a trilinear traction–separation framework, while also accounting for the additional shear resistance arising from the deformation of the viscoelastic rubber layer. The developed model can provide a theoretical basis for further proposing either an analytical mechanical model or a direct implementation in a FEM software, facilitating efficient prediction and assessment of the seismic response of masonry structures incorporating multi-layer bottom bed joints.