P. JUKES* AND J.R. RIDDINGTON**
* School of Engineering & Information Technology, University of Sussex & K W Ltd., Leatherhead, Surrey ** School of Engineering & Information Technology, University of Sussex
Although the triple! test is a standard test used to determine masonry shear strength properties, the factors determining the failure load are not fully understood. In this paper test and finite element results are reported. They support the hypothesis that the relative importance of different forms of failure change as the level of precompression stress changes, and that at any particular precompression stress level one particular form of failure can be considered to be most important. On an idealised plot of average shear stress at failure against precompression stress, precompression stress regions are identified where different forms of failure will be most important, in practice, however, for any particular brick-mortar combination, not all of these regions may be evident. It is concluded that if shear strength characteristics, as defined by the Coulomb line are required, a test arrangement should be used that minimises bending, and the level of precompression stress applied should not exceed 2N/mm”. The precompression loading levels and the shear loading arrangement specified in the draft European shear strength test prEN 1053-3 meet these requirements.