Failure mechanisms of roof sheathing under fluctuating wind loads

Roof sheathing on typical North American timber frame house construction is subjected to high uplift loads during severe windstorms resulting in commonly observed failures. To investigate such failures in detail, ramp and fluctuating wind loads were applied to oriented strand board and plywood panels fixed to rafters with twisted and ring-shank nail varieties, as well as staples. It was observed for panels fixed with twist-shank nails that the panels separate from the rafters in small increments associated with the large peak pressures. In contrast, the failure progression for ring-shank nails is much more sudden. With both types of failure progression, however, it is observed that it is the short duration peak gusts which damage and fail the panels, and always at the nails with the largest tributary areas in the interior of the panel. Tests were also conducted with different missing nail configurations and the capacities assessed. It was observed that fasteners with the incremental failure mechanism were able to more effectively distribute the load such that the effects of missing nails are reduced compared to the panels which fail by the sudden mechanism.

► Realistic fluctuating wind and ramp loads were applied to roof sheathing panels.
► Incremental, pull-out failures for twist shank nails were found.
► Sudden, pull-over failures for panels with ring shank nails were found.
► Effects of missing nails and tributary area effects were examined.
► The incremental, pull-out failure mechanism allowed greater load sharing.