I recently had a discussion with some fellow engineers about the species adjustment factor in shear wall tables using staples in the International Building Code. When determining the allowable shear for wood structural panel shear walls, IBC Table 2306 footnote (a) requires adjusting the Structural I capacities for staples, using a flat adjustment of 0.82 for most framing species (those with a specific gravity of 0.42 or greater) or 0.65 for others. The footnote also requires adjusting the shear values for the framing with nails and the type of sheathing used based on a formula of (1-(0.5-SG)) but not more than 1.

The (1-(0.5-SG)) adjustment factor was based on a study APA conducted on nails. The underlying basis of this adjustment factor is the yield equations in the National Design Specification that were introduced in 1991. Based on this study, APA engineers determined that the old adjustment factors (pre 1991, which are currently being used for staples) were very conservative for nails. We never considered the use of staples in our study. When staples were added to the shear wall table (2000 IBC), the proponent of this code change choose to use the old adjustment factors.