A study was conducted with the primary objective of examining the efficacy of delamination test using cylindrical core specimens to assess the bond quality of cross laminated timber (CLT) products. A prototype coring drill bit was fabricated to prepare a cylindrical-shaped specimen, the height of which corresponds to the full thickness of the CLT panel. A secondary objective was to examine the effect of pressure, adhesive type, number of plies, and specimen shape on the delamination resistance of CLT panels. The wood material used for the CLT samples was Select grade nominal 1 x 6-inch Hem-Fir boards. Examples of three adhesive types were evaluated, which were designated as A, B, and C. The delamination tests used were as described in CAN / CSA O122-06 and EN 302-2.
Cylindrical specimen extracted as core was found satisfactory as a test specimen type for use in delamination testing of CLT product. Its efficacy was comparable to that of a square cross-section specimen. The former is recommended as it can be extracted from thicker panels and from any location in the panel. It would also be more convenient to plug the round hole.
Adhesive type had a strong effect on delamination resistance based on the two delamination tests used. Adhesive A exhibited the greatest delamination resistance, followed in decreasing order, by adhesives C and B. It should be noted that no effort was made to find the optimum CLT manufacturing parameters for each type of adhesive. Therefore the relative rankings of the adhesives tested may not be representative. However, for the purposes of this study, the different performance levels from the three adhesives are useful in providing insight into how the proposed delamination test responds to significant changes in CLT manufacturing parameters.
Pressure used in fabricating the CLT panel showed a strong effect on delamination resistance as demonstrated for one of the adhesives. Delamination resistance decreased with decreasing pressure. The effect of the number of plies in the CLT panel was dependent upon the type of adhesive, and this was probably related to the adhesive’s assembly time characteristic. These results provide support as to the effectiveness of delamination test in assessing the moisture durability of CLT panels. It was able to differentiate the performance in delamination resistance among different types of adhesives, and able to detect the effect of manufacturing parameters such as pressure and increased number of plies in CLT construction.
The test procedure described in CAN / CSA O122-06 appears to be reasonable in the delamination resistance assessment of CLT panels for qualification and quality control testing. Based on the results of the study along with some background information and guidelines, delamination requirements for CLT panels are proposed. The permitted delamination values are greater than those currently specified for laminated and fingerjoined lumber products. This is in recognition of the higher bond line stresses when bonded perpendicular laminations (i.e. CLT) are exposed to the delamination wetting and drying cycles, as opposed to parallel laminations (i.e. glulam or fingerjoints).
This project studied the effect of openings on the lateral performance of CLT shear walls
and the system behavior of the walls in a module. Three-layer Cross Laminated Timber
(CLT) was used for manufacturing the wall and module specimens. The laminar was
Spruce-Pine-Fir (SPF) #2&Better for both the major and minor layers. Each layer was 35
mm thick. The panel size was 2.44 m × 2.44 m.
Four configurations of walls were investigated: no opening, 25% opening, 37.5% opening,
and 50% opening. The opening was at the center of the wall and in the shape of a square.
A CLT module was made from two walls with 50% openings, with an overall thickness of
660 mm. The specimens were tested under monotonic loading and reverse-cyclic loading,
in accordance with ASTM E564-06 (2018) and ASTM E2126-19.
The wall without opening had an average peak load of 111.8 kN. It had little internal
deformation and the failure occurred at the connections. With a 25% opening, deformation
within the wall was observed but the failure remained at the connections. It had the same
peak load as the full wall. When the opening was increased to 37.5%, the peak load
decreased by 6% to 104.9 kN and the specimens failed in wood at the corners of the
opening. Further increasing the opening to 50%, the peak load dropped drastically to 63.4
kN, only 57% of the full wall.
The load-displacement relationship was approximately linear until the load reached 60%
of the peak or more. Compared to the full wall, the wall with 25% opening had 65% of the
stiffness. When the opening increased to 37.5% and 50%, the stiffness reduced to 50% and
24% of the full wall, respectively. The relationship between stiffness and opening ratio was
approximately linear. The loading protocol had effect on the peak load but not on the
stiffness. There was more degradation for larger openings under reverse-cyclic loading.
The performance of the module indicated the presence of system effect that improves the
ductility of the wall, which is important for the seismic performance of the proposed
midrise to tall wood buildings. The test data was compared to previous models found in
literature. Simplified analytical models were also developed to estimate the lateral stiffness
and strength of CLT wall with openings.