D. LANGE-KORNBAK Danish Building Research Institute, Hctrsholm


High strength mortars are commonly used to improve the strength of masonry but with limited or no gain in the load-carrying and deformation capacity. This is explained in the paper by the accompanied reduction in material ductility, and a ductility measure for inclusion in the design of unreinforced masonry is therefore introduced. The ductility measure is based on a Mohr-Coulomb description of the unit-mortar interface and is valid for brittle matrix masonry. New relations for the fracture energy and modulus of elasticity are established, allowing an examination of the importance of the mortar composition, unit type and unit configuration to the load-carrying and deformation capacity of masonry. An analytical design is established which maximizes material ductility and tensile strength simultaneously for a prescribed compressive strength by using nonlinear mathematical programming techniques. In this way, optimal unit configurations (unit length, unit height, unit embedment length and joint thickness) are given for a wide range of compressive strengths.