Reliability of reused sawn lumber: Effect of fastener holes

The results of a comprehensive research study on the effect of fastener hol es on the reliability of structural timbers, specifically No. 2 Douglas fir 102 x 303 mm (nominal 4 x 8 in.) structural joists and planks, is reported . Through this study, adjustment factors are developed to account for the p resence of a hole as a function of its size and location within the member. Such adjustment factors could be used in design by the engineer, or perhap s more appropriately, grading agencies to develop appropriate grading proce dures and design values for reused or recycled timbers to ensure acceptable levels of safety. The specific objectives of this paper are, therefore, to (1) quantify and determine the effect of a fastener hole on the reliabilit y of wood beams when various diameter holes are located at various position s throughout the depth; and (2) develop and recommend possible adjustment f actors to account for the reduction in reliability created by the presence of a fastener hole. The reduction in reliability caused by a 44.5 mm hole w as found not to be significantly different from that caused by a 25.4 mm ho le. The reliability, however, is significantly affected by hole location. I f the hole is located at the point of maximum moment, the reduction in reli ability is over twice as much as when the hole is located randomly within t he central third of the length, which is similar to the grading criteria fo r knots. For a flexural member containing a 25.4-44.5 mm hole anywhere with in the central third of the length, the recommended adjustment factor is om ega' = 0.90. In other words, a 10% reduction in design capacity is recommen ded when such a fastener hole is present in the central third of the member 's length.