Help Desk Question: Nailhead pull-through adjustment factors

Posted At : September 25, 2008 2:36 PM | Posted By : Help Desk
Related Categories: Plywood,Roofs,Fasteners,Walls,Help Desk,OSB

APA Help DeskQuestion: What adjustment factor should be applied to the test values published in APA Technical Topic TT-070: Nailhead Pull-Through Strength of Wood Structural Panels?

Answer: When estimating allowable nailhead pull-through design values for plywood and OSB, APA recommends applying an adjustment factor of five (5) to the wet condition test values published in TT-070.

We are not aware of any standard establishing a methodology for developing this adjustment recommendation. Our recommendation is based on engineering judgment. The generalized supporting argument is that if nail withdrawal has a load factor of five (5) on ultimate (reference ASTM D 5456, Section A2.6) this number should also be reasonable for nailhead pull-through. We also believe that using the wet value is quite conservative. E.g. Even if roof covering were lost in a significant storm event, it is unlikely that rain exposure would saturate panels to + 30% moisture content during the event.

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