A novel approach for assessing the interaction of masonry walls under vertical loads Márcio R.S. Corrêa and Adrian W. Page Abstract: This paper investigates the behaviour of masonry load-bearing walls subjected to differential vertical load. A new approach for evaluating the interaction of intersecting walls is used, focusing on the mechanism of load transfer and the resulting shear stresses. The study is carried out using finite element modelling. Previous full-scale tests are used to verify the features of the numerical model. Once confirmed, the model is then used to study the phenomenon, varying parameters such as the number of floors and the dimensions of the walls. It is shown that the distance down the wall at which homogenization of the applied loads occurs can be predicted by application of the Saint Venant’s Principle. The distribution of shear stresses along the interface can be simulated by a simple parabolic distribution. A simple design procedure is proposed, allowing more realistic, cost-effective designs of load-bearing masonry structures. Key words: masonry, walls, vertical loads, finite elements, interaction of walls. Résumé : Cet article étudie le comportement des murs porteurs en maçonnerie soumis à une charge verticale différen- tielle. Une nouvelle approche pour évaluer l’interaction des murs d’intersection est utilisée, ciblant le mécanisme de transfert de charge et les contraintes de cisaillement qui en résultent. L’étude est effectuée par modélisation par éléments finis. Des essais antérieurs à pleine échelle sont utilisés pour vérifier les caractéristiques du modèle numérique. Une fois confirmé, le modèle est ensuite utilisé pour étudier le phénomène, en variant des paramètres tels que le nombre d’étages et les dimensions des murs. Il est démontré que la distance le long du mur à laquelle survient l’homogénéisation des charges appliquées peut être prédite en appliquant le principe de Saint Venant. La distribution des contraintes de cisaillement le long de l’interface peut être simulée par une simple distribution parabolique. Une procédure de conception simple est proposée, permettant des conceptions plus réalistes et rentables des structures portantes en maçonnerie. Mots clés : maçonnerie, murs, charges verticales, éléments finis, interaction des murs. [Traduit par la Rédaction] Corrêa and Page 614 Introduction Two intersecting load-bearing walls will interact provided there is some form of structural connection crossing the plane of the interface (steel bars, connectors, or bonded units), resulting in an interface that has sufficient strength to transmit the transferred forces. This interaction will result from loading conditions such as out-of-plane bending or differential compressive loading on different parts of the wall system. Compared to walls subjected to horizontal loads, the differential vertical loading phenomenon has not been widely studied. It is common for load-bearing walls at the same floor level to be subjected to different levels of vertical load due to their different tributary areas, with internal walls usually supporting higher loads than external walls. The ratio of internal wall load to external wall load can be up to two in residential buildings. Normally the most heavily loaded wall governs the masonry strength, since the same masonry units will normally be used for all walls. In the case of block work it is also possible to use grout to vary the masonry strength, although this can create site control difficulties. If two intersecting walls are subjected to different levels of vertical load, they will shorten differentially, with resulting interaction at the interface. If the interface has sufficient shear strength, the more heavily loaded wall will transfer load to the other, leading to progressive vertical stress homogenization across the complete wall system. This sharing of the load uses the walls more efficiently, thus enabling a more cost-effective design, particularly for tall load-bearing walls. This homogenization of the load is not as important in low-rise structures where load levels are low, but even in this case it is useful to gain a more complete understanding of the mechanism of this interaction. Stockbridge (1967) carried out one of the first research projects on this subject at the University of Edinburgh. The author monitored wall strains on a five-storey full-scale building and found evidence of the homogenization of Can. J. Civ. Eng. 31: 601–614 (2005) doi: 10.1139/L05-010 © 2005 NRC Canada 601 Received 6 September 2004. Revision accepted 17 January 2005. Published on the NRC Research Press Web site at http://cjce.nrc.ca on 5 July 2005. M.R.S. Corrêa. University of São Paulo, Av. Trabalhador Saocarlense 400, Sao Carlos, SP, Brazil. A.W. Page. 1 Faculty of Engineering and Built Environment, University of Newcastle, University Drive, Callaghan, NSW 2308, Australia. Written discussion of this article is welcomed and will be received by the Editor until 31 December 2005. 1 Corresponding author (Adrian.Page@newcastle.edu.au).