Fingerjoined lumber is widely used in manufacturing engineered wood products such as wood Ijoist
and cross-laminated timber. A shorter finger joint would waste less good quality lumber and
likely use less adhesive, thereby reducing the overall material cost of engineered wood products
made using fingerjoined lumber. This study was aimed at evaluating the structural performance
of I-joists produced with fingerjoined lumber made using a short finger joint profile. Properties
evaluated included stiffness (EI), moment capacity (Mr), creep recovery, and shear capacity. The
properties of the fingerjoined flange-stock lumber were also evaluated in terms of ultimate
tensile strength (UTS) and delamination resistance.
The test materials used were 2x3 black spruce lumber of two grades (NLGA SPS4 flange stock
grade FS-1.5E and FS-1.9E) for flange stock, 3/8-in thick oriented strand board (OSB) for web
stock, and three two-component polyurethane type adhesives for bonding finger-joined flange
stock lumber, web-to-web joint, and web-to-flange joint. The two flange stock grades led to
production of two grades of I-joists, I-1.5E and I-1.9E, in an industrial production line using the
cutter knives of a ½-in finger joint profile developed in the previous Value to Wood projects
conducted at the University of New Brunswick.
The key findings of this project were 1) The characteristic UTS values of fingerjoined lumber
fabricated using ½-in long cutter knives in this project were 25% higher and 11% lower than the
required characteristic UTS values of FS1.5E and FS1.9E, respectively; 2) As for the low grade
I-joists (I-1.5E) made in this project, the mean EI and characteristic Mr were about 2% and 32%
higher, regardless of the depth, than their respective target values; 3) As for the high grade Ijoists
(I-1.9E) made in this project, the mean EI and characteristic Mr were about 7% lower and
9% higher, regardless of the depth, than their respective target values; and 4) Shear capacities of
I-joists tested met the target values of the manufacturer.
In summary, the structural performance of wood I-joists produced with fingerjoined lumber
made using a short finger joint profile could be maintained, in comparison with those made with
the conventional length (1-1/8in) of finger joint profile. Therefore it is feasible to adopt a short
joint profile (e.g. ½in) for Canadian engineered wood products industry with a result of saving
high quality lumber and adhesives thereby reducing the cost of production.
Keywords: Creep recovery, delamination resistance, finger joint profile, finger-joined lumber,
wood I-joist, flange stock, shear capacity, stiffness, moment capacity, and ultimate tensile