A single-surface multi-failure strength domain for masonry

In this paper, we propose a simple approach to derive a single-surface multi-failure strength domain for the in-plane behaviour of masonry. The approach, that lays the basis for homogeneous continuum model developments relies on micro-mechanical analyses employing a block-based model for masonry in which blocks, modelled as finite strength continuum bodies, interact through zero-thickness interfaces. In order to derive the strength domain, firstly three failure mechanism typologies are identified, namely crushing failure, joint failure and mixed joint-block failure. Then, the limit surface for each mechanism is obtained relying on limit equilibrium considerations, also introducing a novel rational treatment of the mixed mechanism. Accordingly, a multi-surface strength domain is built by intersecting all the limit surfaces. Finally, such multi-surface strength domain is reduced to a single-surface one exploiting the RealSoftMax function, which allows to preserve the multi-failure nature of the approach, i.e. the explicit distinction between all the failure mechanisms. Following the proposed procedure, the resulting strength domain inherits the material parameters characterizing the block-based model. A finite element block-based model and available experimental data are employed to validate the proposed strength domain. The good agreement obtained with reference results confirms the soundness of the approach.