In Situ Nail Withdrawal Strengths in Wood Roof Structures

Abstract

Premature failure of wood roof sheathing under wind loading has primarily been blamed on poor nail installation resulting in reduced nail withdrawal strengths. However, this increased vulnerability could also result from environmental effects and aging of the materials, but little information exists on the in situ withdrawal strengths of nails in actual wood buildings. To address this knowledge gap, the authors evaluated the withdrawal strengths of nails from 17 existing Florida homes, and they observed relatively low in situ nail withdrawal capacities in the tests. Further, laboratory tests compared the withdrawal strengths of nails determined using an industry-standard test protocol against an in situ nail test procedure. The study documented the effects of (1) through-sheathing nail installation, (2) nail withdrawal rate, and (3) sheathing removal methods on nail withdrawal capacity. The in situ nail test procedure consistently produced lower nail withdrawal capacities than did the industry-standard test protocol. Nail withdrawal capacity is reduced by combination of local sheathing removal methods to access the nail head, and by driving nails through sheathing. The results suggest empirically determined nail withdrawal capacity for nails provide nonconservative results.