Keywords: brick, elasto-plastic behaviour, interface elements, joint mortar, masonry, shear.

Masonry is a composite material made by either a regular or an irregular assembly of bricks with mortar joints. Many factors may influence the mechanical behaviour of such material: brick anisotropy, brick size and aspect ratio, joint dimensions, joint orientations, the relative position of head and bed joints, bricks, mortar and brick-mortar interface properties, workmanship and wall dimensions. Among these factors, the mortar joints, which represent planes of weakness, may have a significant influence on the masonry behaviour. In order to take into account this influence, the mechanical modelling of the masonry can be developed at a detailed scale. When this approach is adopted, bricks and joint mortar behaviour is described separately using a continuum and an interface model, respectively. This approach allows accurate analysis of the masonry behaviour since one may distinguish the phenomena that may occur either in the blocks or in the mortar joints.

The aim of this paper is to study the stress distribution in masonry shear walls and to investigate their failure mode using a detailed approach. The brick behaviour is expressed using an elasto-plastic damage model previously developed and validated by the authors [1]. The joint mortar behaviour is represented using a zero-thickness interface element defined by two failure modes: tensile failure and shear failure. The first leads to joint opening and the latter to joint sliding with friction. The joint model is developed using experimental results summarized in this paper [1,2].

The experimental study was carried out on half brick couplet specimens. First, load-unload shear tests are performed in order to assess the stiffness degradation, and consequently to determine the type of the mortar joint behaviour (elastic, elasto-plastic or damaged behaviour for instance). Then, monotonic shear tests are performed using two types of clay bricks (solid and hollow) in order to:

• analyse the possible influence of the holes,
• determinate the mortar joint mechanical features,
• study the joint failure modes.

Based on these experimental results, an interface model describing the mortar joint non-linearity is proposed [1,3]. As no stiffness degradation has been recorded experimentally, the joint mortar behaviour is assumed to be elasto-plastic for both solid and hollow bricks. Hence, an elastoplastic model based on a multisurface yield function is proposed. Rankine and the Mohr-Coulomb failure criteria are considered for the tensile and the shear behaviours, respectively. This model is implemented in the finite element code CAST3M and validated by comparison with the experimental results obtained on couplet specimens [1].

The model developed is used to simulate the mechanical behaviour of masonry shear walls using a detailed approach [1]. The theoretical predictions are compared to the experimental results obtained on a reinforced concrete frame with infill masonry [4]. A good accuracy is observed in the elastic phase, and the failure load is correctly predicted. Furthermore, it is shown that the compressive stresses are distributed on micro bands oriented according to the half brick diagonal. The evolution of the stress distribution enables the wall failure to be explained.

1

L. Abdou, "Modélisation du comportement mécanique des murs en maçonnerie chargés dans leur plan", Thèse de Doctorat, Université de Marne-La-Vallée, France, 2005.

2

L. Abdou, R. Ami Saada, F. Meftah, A. Mebarki, "Experimental investigations of the joint-mortar behaviour", Mechanics Research Communication, 33(3), 370-384, 2006. doi:10.1016/j.mechrescom.2005.02.026

3

P.B. Lourenço, "Computational strategies for masonry structures", Ph.D thesis, Delft University of Technology, Delft, The Netherlands, 1996.

4

J.I. Cruz Diaz, "Etude des murs de contreventement en maçonnerie d'éléments de terre cuite", Université de Marne-La-Vallée, France, 2002.

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