Reliability analysis for critical reaction forces of lumber members with an end notch

Abstract

The basis of new design provisions for avoidance of brittle failures in sawn lumber members with an end notch is explained. Linear elastic fracture mechanics and structural reliability concepts are combined with material property data to determine appropriate forms of equations for limiting the reaction force, when a notch is made on either the tension or compression face of a member. Following from this, the factored reaction force resistance of a member designed to the 1994 edition of the CSA Standard 086.1 "Engineering design in wood (limit states design)" depends upon the depth of the member and the geometry and size of an end notch if the notch is located on the tension face. A new property, the specified reaction force strength, which is a measure of the capability of the material to resist fracture, is taken to be independent of the timber species and stress grade of the lumber. Design variables such as duration of load and moisture service condition influence assignments of factored reaction force resistances for members end notched on the tension face. When a notch is located on the compression face of a member the resistance is simply the factored shear resistance of the residual cross section. As in previous editions of CSA Standard 086.1, notches are not permitted to have a depth greater than 0.25 times the depth of the section. Key words: lumber, fracture, structural reliability, notched beam, design criterion.