Mechanisms governing the compressive strength of unconfined and confined rubble stone masonry

In the safety assessment of masonry constructions the estimate of the compressive strength of masonry is often required, especially for those structures subjected to high stresses or stress concentration. Focusing on rubble stone and conglomerate-like masonries, a typology which is quite common in historical constructions, a theoretical formulation identifying the phenomena governing the collapse mechanism was recently proposed for the evaluation of the compressive strength of unconfined and confined masonries. The theoretical formulation also provides useful insights on the design of the necessary confinement stress level, anytime improvement of the compressive strength and ductility of the masonry walls is needed. In this paper the reliability of the theoretical predictions is substantiated by an experimental study. Specific and challenging tests on masonry samples replicating historical rubble stone masonry elements and the inner core of three leaf walls are conceived to offer experimental evidences of the phenomena governing collapse, such as the cohesion, the aggregate interlocking and the residual tensile strength after cracking, as well as the possible confinement stress level. The experimental investigation also provides preliminary values of the parameters affecting the masonry compressive strength.