Tensile Strength of Varied-Angle Mortise and Tenon Connections in Timber Frames

Abstract

The tensile strength of varied-angle mortise and tenon connections in timber frames is discussed in this paper. Twelve full-size mortise and tenon connections (four 90°, four 67.5°, and four 45°) were tested under monotonic tensile loading. Initial yield modes observed during testing included peg bending, peg shear, tenon tear out, and mortise splitting. Decreased connection angle corresponded to equal or increased tensile strength but decreased ductility. A theoretical method to calculate the tensile strength of mortise and tenon connections is also developed. The method uses a modified set of yield-limit equations supplemented with local-stress-effect (mortise splitting and row tear out) equations to predict tensile strength. The governing theoretical yield modes agree well with yield modes observed during testing. The theoretical tensile strength is reasonably accurate, averaging 14% higher to 9% lower compared with test results. The findings indicate that mortise and tenon connections are significantly stronger when the tenon is oriented radially with respect to the mortise grain, especially in orthogonal connections. As a consequence, tangential loading of the mortise should be avoided.