This paper is presented to establish a concept which is supposed to take an important role in predicting the uniaxial strength of masonry, that is to say prism strength. Prism strength has been regarded as the basic strength for the structural design of masonry buildings in many masonry structural codes.

As far as we know, there are many factors affecting prism strength. Some generalized concepts are necessary and the concepts are thought to be a function of the various factors concerning basic component materials, masonry unit and joint.

Firstly, a primary concept, "Biaxial Stress Coefficient", is proposed for the prediction of prism strength. The concept can be estimated from the various elastic constants of the component materials. The calculation method of prism strength is also shown on the foundation of the concept.

Secondly, the relationship between prism strength and the value of the coefficient is discussed on the basis of the theory and some past experimental data. Some necessary items of study are clarified for the precise estimation of prism strength.

Finally, the possible range of efficiency is presented for ungrouted masonry. A fundamental direction for improving the mechanical properties of this type of masonry is also discussed.

This study reported herein was conducted as part of the Research Project of the Development of Reinforced Brick Masonry.

^*1 Head of Construction Techniques Division, Building Research Institute