Murede skivers styrke: Murværk påvirket til plane spændingstilstande

This report considers the strength of masonry disks. The problem of determining the uniaxial strength as well as the strength under biaxial stresses are approached through the theory of plasticity by considering upper and lower bound solutions.

Methods are developed for determining the uniaxial tensile and compressive strengths parallel and perpendicular to the bed joints. Later on the uniaxial strength of week planes are examined. The term week planes is used for yield lines running in the interface between brick and mortar since the strength of the interface is normally significantly smaller than the strengths of brick and mortar, respectively.

Plasticity approaches to determine the compressive strength perpendicular to and the tensile strength parallel to the bed joints have formerly been examined by Hagsten [1999.1] and [1999.2]. This report aims at determining simpler expressions not depending on optimisation with respect to variables. The expressions are compared to the expressions given by Hagsten as well as to experimental result available from the literature. The agreement is found to be good.

When examining the strength of week planes plane strain is assumed in the yield lines. Failure in week planes as a consequence involves dilatation since the relative displacement between opposite parts on each side of the yield line is restricted to take place under angles greater than or equal to the angle of friction in the line.

Finally the report attends the problem of determining the yield surface for masonry disks of massive bricks. Knowing the yield surface its possible to determine the strength of masonry disks for any combination of stresses. The yield surface is created using the basic theories applied for developing the yield surface for reinforced concrete disks with orthogonal reinforcement. The basic strength of masonry is described using the modified Coulomb failure criterion. The basic strength thus is isotropic. The orthotropic properties of masonry are taken into account by considering the masonry bond as an inner reinforcement. Stress substitutions are submitted in agreement with known differences in the uniaxial compressive and tensile strengths parallel and perpendicular to the bed joints. The orthotropic yield surface developed in this way is modified by introducing cut-offs representing failure in week planes. The yield surface is compared to experimental results concerning masonry disks.

Ganz [1985.3] introduced a similar yield surface for masonry made of perforated bricks. A simple version of the yield surface introduced by Ganz has been adopted in the Swiss national brick code.

The possibilities of using the yield surface on reinforced masonry are shortly commented upon.