Nonlinear analysis of in-plane loaded masonry walls using an assumed-stress finite element and a single surface strength domain
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This work proposes a numerical approach for the efficient analysis of in-plane loaded masonry walls. The nonlinear behaviour of the material is described using a multi-failure strength domain. This describes different failure mechanisms through a micro-mechanical model. By intersecting the limit surfaces related to each mechanism, a homogenised multi-surface strength domain is derived. Then, a single surface representation of the strength domain is obtained by adopting the RealSoftMax function. This approach enhances the computational efficiency of the numerical model while preserving the multi-failure nature of masonry walls. The masonry structure is discretised by adopting a mixed finite element based on a stress interpolation that a-priori satisfies the equilibrium equations. The displacement field is assumed only along the element edges, while no explicit interpolation is required inside the domain. The element shows a quadratic convergence rate for both displacements and stresses, a low sensitivity to mesh distortion and provides accurate results on coarse discretisation. The integration of the nonlinear constitutive law is performed through a dual decomposition approach, preserving the assumed stress interpolation efficiently.
