Frictional behaviour of masonry interfaces: Experimental investigation on two dry-jointed tuff blocks

In historical masonry structures, featured by dry or weak mortar joints, limit analysis of 3D assemblages of blocks represents a useful tool for the prediction of failure mechanism and collapse load. Results of limit analysis, with no-tension and frictional contact interfaces, are based on the definition of accurate block interface yield domains: experimental and numerical investigations on the frictional contact con- ditions are required. Despite the characterization of shear behaviour of frictional contact was widely studied in the past, limited research is available on the behaviour of dry masonry joints implying interac- tions among shear, bending and torsion. This work aims at presenting an extensive experimental investigation conducted in order to analyse the frictional behaviour of two dry-jointed tuff blocks subjected to load- ing patterns reproducing several possible yield conditions. Besides pro- viding fundamental parameters required for limit analysis formulations, the adopted testing program investigates 3D yield domains of a sin- gle contact interface through different loading scenarios. Moreover, the experimental results are compared with those obtained by a numerical model based on the assumption of rigid blocks which interact through no-tension, frictional interfaces. From the comparison, it is found that the usual modelling hypothesis of ideal interface with all points between blocks perfectly in contact is not always reliable. In fact, depending on the actual contact area and especially in presence of torsion moment, the predicted 3D yield domains may differ significantly from the experimental results.