The Brick Development Association, London
Jenkins and Potter, Consulting Engineers, London


The vertical loadbearing capacity of a masonry wall is dependent on the masonry compressive strength, the dimensions of the wall and the eccentricity of the load. EN 1996-1-1 requires that a calculation model be set up and allows the bending moments to be calculated from the material properties, the joint behaviour and the principles of structural mechanics. A simplified method for calculating out of plane eccentricities is given in Annex C of the standard where the moment at a joint is distributed among the joint members in proportion to their relative stiffnesses. For ‘thick’ masonry walls the magnitude of the moment allocated to the wall tends to be relatively large. This moment is further increased with increasing fk. In this paper a number of cases are considered where cavity walls with different compressive strengths are loaded by insitu concrete slabs having different thicknesses and load spans. It is demonstrated that the suggested method in EN 1996-1-1 Annex C does not suit all cases of masonry walls and in fact a very conservative outcome may result as thickness and wall strength are increased. This outcome is further aggravated when floor spans are relatively short.
An improvement to the Annex C method is suggested together with a method for calculating load eccentricity.

Key words
joint behaviour; eccentricity; vertical loadbearing capacity