(1) Professor, Department of Civil Engineering, Aristotle University of Thessaloniki, Thessaloniki,Greece
(2) Research assistant ,Department of Civil Engineering, Aristotle University of Thessaloniki, Thessaloniki,Greece

The aim of this paper is to study the shear transfer mechanism through the horizontal contact surface of two rigid blocks. The shear resistance offered by the interface is the main mechanism mobilized by the structural elements of many historical stone masonry structures in order to transfer horizontal actions from earthquakes and wind forces to the foundations. In some cases, a certain connection exists between two blocks at the contact surface, which is created by wooden or metal parts at the central area of the blocks (poles, empolia). The role of this connection in transferring horizontal forces and its influence on the seismic behaviour is a point debated by the research community. Cyclic experiments were performed at the laboratory in order to study this sliding behaviour at the interface between two rigid blocks. The parameters of the experimental sequence under investigation can be divided in two groups. The first group includes specimens without any connection between the rigid blocks, while the second group includes specimens with poles and empolia connecting the rigid blocks. During all tests the imposed cyclic horizontal sliding displacement was combined with a constant level of vertical load applied at the top of the upper block. Through this experimental process, it became possible to describe the shear transfer mechanism through diagrams of horizontal sliding displacement versus horizontal load, and study the effects on the shear transfer behaviour between these rigid blocks without or with the connection with poles and empolia between them. Numerical simulations of the problems described were also performed by finite element analysis utilizing two commercial Finite Element Software packages.

Key words
Rigid blocks, poles, empolia