11 th Canadian Masonry Symposium, Toronto, Ontario, May 31- June 3, 2009 IDENTIFICATION OF SHEAR MECHANICAL PARAMETERS OF MASONRY PIERS FROM DIAGONAL COMPRESSION TEST C.Calderini 1 , S.Cattari 2 and S.Lagomarsino 3 1 Research Assistant, Dept. of Civil, Environmental and Architectural Engineering , University of Genoa, Italy, chiara.calderini@unige.it 2 Research Assistant, Dept. of Civil, Environmental and Architectural Engineering , University of Genoa, Italy, serena.cattari@unige.it 3 Full Professor, Dept. of Civil, Environmental and Architectural Engineering , University of Genoa, Italy, sergio.lagomarsino@unige.it ABSTRACT In the seismic design and assessment of ordinary masonry buildings the prediction of the strength of masonry piers subject to in-plane lateral forces plays a crucial role. Different simplified models are present in literature and codes to describe the failure modes of piers (Rocking/Crushing, Bed Joint Sliding, Diagonal Cracking) and to predict their load bearing capacity. In general, they are based on simple idealizations of the limit strength domain of masonry through few mechanical parameters. Referring in particular to the Diagonal Cracking failure mode, two models are usually adopted: that of Turnšek and Čačovič (1970) and that of Mann and Müller (1980). These models are dependent on two main mechanical parameters: the cohesion of mortar joints, usually obtained through the triplet test, and the tensile strength of masonry, usually derived by the diagonal compression test. Aim of this paper is to synthetically analyse the physical meaning, the experimental evaluation and the proper use of these parameters. Moreover, a method to relate the result of the diagonal compression test to a “mean” value of the cohesion is proposed. This latter test offers two main advantages: a versatile application to different types of masonry (also irregular ones); the capability of providing “mean” mechanical parameters, representative of the whole masonry. KEYWORDS: masonry, pier strength, in-plane shear behaviour, diagonal compression test. INTRODUCTION The prediction of the strength of masonry piers subject to in-plane lateral forces plays a crucial role in the seismic design and assessment of ordinary masonry buildings. A “direct” approach to the estimation of the strength of masonry piers consists in performing experimental tests able to simulate reality as closely as possible, in terms of boundary conditions and acting forces. Through these tests, the limit strength domain of piers of given slenderness and given masonry type may be obtained in the space of the applied forces. Although quite accurate and reliable, such approach is costly and time-consuming since it requires a large number of tests to be performed. Moreover, in most cases, it is technically inapplicable to