Discrete element analysis of a stone masonry arch Axel Roland Tóth a , Zoltán Orbán b , Katalin Bagi c, * a Hungarian State Railways (MÁV Zrt.), Kerepesi út 3., H-1087 Budapest, Hungary b Department of Structural Engineering, University of Pécs, Faculty of Engineering, Boszorkány u. 2., H-7624 Pécs, Hungary c Department of Structural Mechanics, Budapest University of Technology and Economics, M} uegyetem rkp. 3. K.mf.35, H-1521 Budapest, Hungary article info Article history: Received 31 December 2007 Received in revised form 31 December 2008 Available online 22 January 2009 Keywords: UDEC Distinct element Discontinuous Computer simulation Rock Bridge abstract The aim of this study was to investigate the effect of the backfill on the mechanical behav- ior of a multi-span masonry arch with the help of the discrete element method. After defin- ing the geometry and identifying the mechanical properties of a one-span bridge model according to real experimental results from the literature, we extended the one-span model to a multi-span model and replaced the original backfill material with different sands and clays for investigations under live load in service loading conditions. We com- pared the deflections, the normal stresses in the arch and the plasticity state of the backfill under the live load. Then we also made load tests in different load cases to specify the effect of the stiffness, friction angle and cohesion of the backfill on load-bearing capacity. We found that the stiffness, the friction angle and the cohesion of the backfill largely influenced the load-bearing capacity of the structure. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The masonry arch is one of the oldest structural elements: stone and brick arches have been used for thousands of years as parts of bridges, aqueducts, cathedrals, castles etc. Masonry arches transmit the loads to the ground basically with the help of compression stresses. Rock blocks can resist huge compression (one can think of the enormous pressure deep down in the earth crust where rocks were formed); but masonry is not very strong for shear, and the tension-resisting capability of an old structure with spoiled mortar is very low. Hence in a well-designed, safe masonry arch the direction of the compres- sion principal stress should approximately follow the shape of the arch under the effect of those loads the structure was designed for. Multi-span masonry arch bridges play a significant role in the transportation infrastructure today: thousands of masonry railway and road bridges are in operation in Europe and throughout the world (Orbán, 2004). However, if the loads increase compared to those the bridge was designed for, or if some kind of a damage occurs, engineers have to face the problem of assessing the load-bearing capacity of the existing structure, and if a renewal of the bridge is necessary, approximate how the different strengthening methods would influence the mechanical behavior. Several methods are available for the assessment of the load-carrying capacity of masonry arch bridges. These include simple conservative methods (such as MEXE, see UIC Code 778-3R, 1994) and recently developed computerized methods such as adaptations of the mechanism method (Gilbert and Melbourne, 1994) or the different FEM and DEM systems. Besides their particular limitations, conservative methods often underestimate the load-carrying capacity, which may re- sult in uneconomical or unnecessary mitigation measures being taken to maintain or replace bridges. In addition, they are not valid for non-standard geometries or for arches with already displaced blocks. 0093-6413/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.mechrescom.2009.01.001 * Corresponding author. E-mail addresses: axeltoth@yahoo.co.uk (A.R. Tóth), kbagi@mail.bme.hu (K. Bagi). Mechanics Research Communications 36 (2009) 469–480 Contents lists available at ScienceDirect Mechanics Research Communications journal homepage: www.elsevier.com/locate/mechrescom