Size Effects in Visually Graded Softwood Structural Lumber

A unified size-effect model based on the weakest-link brittle fracture theory has been developed to represent statistical size effects in visually graded structural lumber. Test results from published studies and new results from a comprehensive study of strength properties of Canadian visually graded lumber have been used to develop the model parameters. Analyses have shown that size-effect factors are not statistically different across grades, species, or strength levels. For international harmonization of size-effect adjustment procedures for characteristic lumber strength properties, factors have been suggested for (1) Length and width effects for tension and bending members to equal 0.2; and (2) length and width effects for compression members to equal 0.1.