Influence of number of finger joints per stud on mechanical performance of wood shearwalls

Finger-joined lumber studs are considered equivalent to, and can be used interchangeably with, unjoined lumber of the same grade in residential construction in Canada. However, there have been concerns expressed by engineers and users that there is no data available on the mechanical performance of shearwalls built with finger-joined studs to support this equivalency. This study was intended to address this information gap. Two groups of finger-joined studs were fabricated using ‘No. 2 or better’ grade spruce-pine-fir (SPF) lumber and a heat resistant polyvinyl acetate (PVA) adhesive. One group had 2–3 joints per stud, while the second group had 5–6 joints per stud. A control group of unjoined ‘No. 2 or better’ grade SPF lumber was sampled as a reference for comparison between groups. The stud dimensions were 38 mm × 89 mm × 2.44 m. Sheathing used was oriented strand board (OSB) panels with dimensions of 1.22 m × 2.44 m × 12.5 mm. The stud frame was fastened using 12d common wire nails and the sheathing was fastened to the stud frame using 8d common wire nails. A total of 12 shearwall test specimens of dimensions 2.44 m × 2.44 m were fabricated and tested. Test results showed that there was no statistically significant difference in the mechanical performance in terms of peak racking load and stiffness between shearwalls containing finger-joined studs (up to 5–6 joints) and shearwalls containing unjointed studs. The failure mode for each test wall was a combined sheathing nail withdrawal and sheathing nail head pull through. This study provides confirmation that finger-joined studs made using the PVA adhesive in this study could be deemed to be equivalent to unjoined studs in fabrication of shearwalls.