Abstract
By extending the previous investigation of the machine grading classification, this study examined the visual
grading classification to determine the size effect parameter for the size adjustment factor used to reduce the
design bending strength in the Japanese agricultural standard for sawn lumber (JAS 1083). First, by examining the relationship between the specimen depth and bending strength of various species and grades, including the machine grading classification, it was deemed realistic to adopt at present a single value for the size effect parameter for all species and grades, rather not by species and grades. Then, after comparing the size adjustment factor for the design strength for the visual grades with a 5% lower limit/design strength, it was considered logical to assume the same value for the size effect parameter of the visual grading classification as to be 0.4-0.5 that obtained from the machine grading classification. However, some problems persist, and the values of the size effect parameters need to be reexamined after accumulating bending strength data obtained from the large-diameter lumber, which will increase in the future.
