Investigations of the bond wrench method of testing masonry

The bond wrench is a simple and practical piece of equipment which can be used to test masonry bond for laboratory as well as site investigations. The bond wrench test method provides more data from a single masonry test specimen relative to other known methods. However, it has produced variable results and there are mixed opinions on its validity. This paper describes some of the deficiencies associated with the present bond wrench commonly used in Australia. The effect of geometrical configuration of the wrench and the clamping effect of the restraining frame on the stress distribution were investigated by experimental and analytical means using an Aluminium calibration block and finite element analysis. It is shown that the current bond wrench does not produce the assumed stress distribution in the test specimen and as a result it underestimates the masonry strength. Suitable parameters for a new bond wrench are proposed, which eliminate the ill effects of the present apparatus.