Wood Shear Wall Performance: Influence of Sheathing Nail Head Geometry

Wood shear wall performance is affected by the materials used for construction including the sheathing fasteners. The model building codes permit different fasteners for sheathing attachment in terms of diameter and length. In general, the nail head geometry is designated in the fastener schedule footnotes by terminology, such as “common,” “sinker,” “casing,” or “finish.” Power-driven nails are collated and the heads are formed to facilitate collation, so the heads may be flat and round with full round geometries or the flat round head may be clipped or notched. The European Yield Limit equations of the National Design Specification assume a smooth round dowel with no head, which leaves the engineering community without a rational basis for specification of head geometry requirements for shear wall construction. To address this issue, three types of nails distinguished by different head geometries were used in shear wall tests to investigate the potential effects of sheathing nail head geometry on shear wall performance. The head geometries were full-round heads (FRH), clipped heads (CLP), and casing heads (CSE), but the nails were otherwise the same. The head-area ratios for these fasteners were 0.83, 0.74, and 0.55 for the FRH, CLP, and CSE nails, respectively. These were used to fabricate shear walls sheathed one side with plywood (height/length ratio=2.0) that were tested using the sequential phase displacement method of fully-reversed cyclic testing. Shear walls with the FRH nails and the CLP nails had the same nominal strength while the CSE nails had a nominal strength that was 78% of the nominal strength of the shear walls with FRH nails. The elastic stiffness’ of shear walls were not statistically different when the source of variation was sheathing-nail head geometry. The test performance was compared to nominal strength calculated from published design values. The walls with FRH and CLP exceeded the expected nominal shear while shear walls with CSE nails underperformed the design value. Nails with FRH and CLP heads cannot be distinguished in performance and are interchangeable for design and construction. Even though CSE nails produce shear walls with the same elastic stiffness, they cause shear capacity to be less than that of walls built with FRH and CLP nails and about 8% less than allowable shear design.