Shear strength of rubble stone-and-brick masonry panels. A new proposal for the interpretation of Sheppard test results

This paper provides some insights on the identification of the shear strength parameters of masonry panels with irregular texture. Non-linear finite element analyses have been first used to simulate the diagonal compression and the Sheppard tests, which are among the most common experimental layouts used in-situ to investigate the shear strength. The constitutive parameters of the non-linear models have been calibrated considering the results of past experimental tests carried out on rubble stone-and-brick masonry panels. Results show that in the Sheppard test the first-cracking load and the collapse load are clearly separated. Based on this observation, a new methodology to interpret the Sheppard test results is proposed where the shear strengths at first-cracking and at collapse are introduced. This new interpretation, which overcomes some of the drawbacks of the classical interpretation, envisages a local stress criterion for the assessment of the first-cracking shear strength and a global limit equilibrium criterion for the assessment of the collapse shear strength. Eventually, a practical procedure for the experimental implementation of the procedure here proposed is provided.