Greetings everyone.

To define the interface between mortar and brick during the modeling of masonry, I need normal and shear stiffness (Kn and Kt).

I have tried some relationships found in the literature:

the one from P. B. Lourenço in his thesis document, Vladimír Červenka from the named "ATHENA" software documentation, and the one from the named "FLAC" software documentation. the formulas are displayed in the enclosed images.

In those formulas, the interface's thickness value taken as the joint's thickness overestimates the results. Furthermore, compared to our experimental results for compression on masonry samples, the model does not restitute the over-yield strength point curve since the numerical curves are linear compared to experimental results.

Note that the blocks used are natural stones. We define a detailed micro-model with linear orthotropic material for the joints and the blocks and a combined cracking-shearing-crushing for the interface material.

Could you please help me with this issue?