The study reports on block shear investigations with bondlines of face-glued laminations and matched solid wood specimens from hardwood glulam (GLT) beams produced industrially from eight technically and stand volume-wise important species. The European hardwoods comprised oak, beech, sweet chestnut and ash and the tropical species were teak, keruing, melangangai and light red meranti. The adhesives were phenol-resorcinol and melamine-urea. When combining all species in one sample, a rather strong linear relationship of bond and wood shear strength was observed. The ratio of bond vs. wood shear strength was for all species on the mean value level = 0.9, and likewise (with one exception) for the respective strengths’ 5%-quantiles. Consistent with literature, the test results showed no significant correlations between bond shear strength and density, wood shear strength and wood failure percentage of individual species, respectively. The investigations render the methodological basics of some international standards on bond quality verification as being inappropriate. New, empirically validated hardwood GLT bond requirements are proposed for discussion and implementation at the CEN and ISO levels. The strength ratio specifications reflect respective ANSI provisions, yet the reference quantity wood shear strength is now determined in an unbiased manner from matched GLT specimens. The wood failure verification proposal is based on the 10%-quantile and mean level for initial type testing and factory production control. The requirements further account for the pronounced difference observed in scatter of wood failure between European and tropical species.
The North American product standard for performance-rated cross-laminated timber (CLT), ANSI/APA PRG 320, was published in 2012. The standard recognizes the use of all major Canadian and US softwood species groups for CLT manufacturing and provides design properties for specific CLT layups with visually graded and E-rated/MSR laminations. While design properties for CLT layups with Spruce-Pine-Fir and Douglas fir-Larch laminations are specified in the current standard, no design properties are indicated for CLT layups with Hem-Fir laminations.
Design properties for two proposed CLT grades manufactured with Hem-Fir lumber were developed. These include a CLT layup with visually graded laminations and another layup with E-rated/MSR laminations. Design properties for these two CLT layups were calculated separately for use in Canada and the US.
Supporting information for the addition of design properties for Hem-Fir grades to the CLT product standard was generated. Recommended amendments to the CLT product standard include durability and wood failure requirements of bondlines, and design properties for Hem-Fir layups.
This project was conducted to quantify the performance of adhesives bond lines under
shear load subject to elevated temperature. The results add to the understanding of the
performance of polyurethane adhesive bond lines under elevated temperatures to address
areas of fire safety concern under the current building codes.
The project focused on studying the shear bond capacity of three wood species by using 3
types of adhesives with/without nanoclay treatment at 4 temperature levels. The three
wood species are Douglas-Fir, Hemlock and SPF. The adhesives are polyurethane (PU),
Phenol-Resorcinol-Formaldehyde (PRF) and Epoxy. PU and PRF specimens were also
tested with nanoclay treatment and without nanoclay treatment. Epoxy specimens were
tested without nanoclay treatment only. The temperature levels considered were room
temperature (about 20 °C), 60°C, 80°C and 100°C. The results indicate that the influence
of elevated temperature on the shear bond strength of PU and PRF adhesive was in the
range of 20 to 30% regardless of nanoclay treatment. Regardless of species, PU or PRF,
with or without nanoclay, the average shear strength for 100°C oven temperature
treatment ranged from 6.0 to 7.5 MPa. In the case of SPF PU specimens treatment with
nanoclay reduced the variability of shear strength significantly from 12% at room
temperature to 5% after 100°C oven treatment. This is an important aspect that needs
further verification for enhancement of performance. Finally the data in this study can be
used to support modeling of timber component subjected to elevated temperature.
