The relationship between proof load level of fingerjoined lumber and degree of cure of adhesive bonds was investigated. Tension tests were completed for two different degrees of cure for two different adhesives. The proof load level determined for the partially cured joints did not cause damage to the joints that survived the proof test.
Preliminary guidelines for determining appropriate proof load levels for testing fingerjoined lumber with partially cured joints were proposed. The proposed guidelines will need to be validated through mill trials to demonstrate their efficacy and reliability to the manufacturer and third party inspection agency.
Keywords: fingerjoined lumber; tension proof testing/loading; partially cured adhesive bonds.
Test results for three representative adhesives were obtained for use in the development of a proposed standard for limited moisture exposure (CSA O112.10). The adhesives tested were an emulsion polymer isocyanate (EPI), a polyurethane (PUR) and a melamine-urea formaldehyde with 40% melamine resin content (MUF40). Currently, EPI and PUR are used for I-joists and fingerjoined lumber. MUF40 was included in the study as a non-conforming adhesive. The range of performance of these adhesives, along with that of melamine formaldehyde (MF) and polyvinyl acetate (PVA) evaluated in a previous study, is baseline information used in defining acceptable performance levels for adhesives undergoing block shear tests required in the proposed standard.
Specimens in this study were evaluated under five test conditions: dry, vacuum-pressure wet or re-dried, and three-cycle boil-dry-freeze wet or re-dried. Dry and re-dried test conditions are the proposed test protocols for the draft CSA O112.10 standard.
In terms of shear strength and percentage of wood failure, EPI and MUF40 met the requirements of CSA O112.9 for the dry test condition, and PUR did not.
The following block shear test requirements are recommended for CSA O112.10, based on the 95% lower confidence limit of the EPI test results, and structured to be analogous to the requirements of CSA O112.9:
Median dry shear strength = 10 MPa (1450 psi) (adopted from CSA O112.9);
Vacuum-pressure re-dried median shear strength = 7.4 MPa (1070 psi);
Median percentage wood failure = 85% for all the proposed tests (adopted from CSA O112.9); and
Lower quartile percentage wood failure = 75% for all the proposed tests (adopted from CSA O112.9).
The above requirements will be discussed in the CSA Task Group, which will eventually make recommendations to the CSA Standards Committee.