In the present work the ultimate failure load and the collapse mechanism of a stone arch bridge are estimated by the usage of (a) a multi - part elastic model with unilateral contact frictional interfaces and (b) a continuous damage model. According to the contact model, contact interfaces simulating potential cracks are considered and their opening or sliding indicates crack initiation. | Vietnam Journal of Mechanics, VAST, Vol. 31, No. 3 &4 (2009), pp. 185 – 190 UNILATERAL CONTACT AND DAMAGE ANALYSIS IN MASONRY ARCHES M. Campo1 , . Drosopoulos2 and . Stavroulakis2 1 Departamento de Matemática Aplicada, Facultade de Matemáticas, Universidade de Santiago de Compostela, ES-15782 Santiago de Compostela, Spain 2 Instiute of Computational Mechanics and Optimization, Department of Production Engineering and Management, Technical University of Crete, GR-73132, Chania, Greece Abstract. In the present work the ultimate failure load and the collapse mechanism of a stone arch bridge are estimated by the usage of (a) a multi - part elastic model with unilateral contact frictional interfaces and (b) a continuous damage model. According to the contact model, contact interfaces simulating potential cracks are considered and their opening or sliding indicates crack initiation. The second model deals with the material damage consisting in the development of internal microcracks that affect the load bearing capacity of the material. Satisfactory comparison of the results is reported here. Keywords: masonry arch, limit analysis, unilateral contact, continuum damage models 1. DESCRIPTION OF THE UNILATERAL CONTACT AND THE DAMAGE MODEL In this paper is presented a first step in the cooperation between a discrete and a continuum model. Objective goal of this cooperation is to study as accurately as possible structures with non linear behavior, like masonry arches. A stone bridge consists of stone blocks and the mortar joints. Low tensile strength of the arch, which is found in the joints, contrary to the high compressive strength of the blocks, make the whole structure highly non linear. In the present study two models are used for the calculation of the failure load and the collapse mechanism of the arch bridge. The first model [1] uses unilateral contact friction interfaces in order to describe the mechanical behavior of the arch. The model has been .