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Abstract

The increased use of sustainable building products, such as glued-laminated timber (glulam), can help mitigate the significant global carbon emissions generated by the construction sector. This study investigates the weak-axis bending performance of glulam to address the overly conservative design assumptions in the Canadian Code of Engineering. The current CSA O86 design standard assigns a conservatively low specified bending strength of 11.0 MPa for Hem-Fir glulam weak-axis applications, without accounting for the actual layup configuration. Even with the inclusion of the 1.1 system factor permitted under repetitive member provisions, the adjusted strength only reaches 12.1 MPa, which remains relatively low. Experimental tests were conducted on 117 individual Hem-Fir laminations (T1, B, C, and D grades) and 240 full-scale Hem-Fir glulam specimens, including homogeneous (16c-E) and non-homogeneous (24f-EX) layups with 2 to 16 layers. Results demonstrated that the weak-axis bending capacity significantly exceeds current code-specified strength values: 16c-E members showed increasing strength as the number of laminations increased (average MOR: 42.1 MPa for 2 layers to 51.8 MPa for 12 layers), while 24f-EX beams exhibited stable performance (average MOR: 55.1–48.4 MPa). A Monte Carlo simulation model was developed to predict the weak-axis bending strength of the 16c-E and 24f-EX members. The model incorporated lamination-level variability and a strength adjustment factor (1.35–1.49 for 24f-EX; 0.93–1.40 for 16c-E) and was validated against the experimental data. A simplified layered stiffness method was employed to simulate the weak-axis modulus of elasticity (MOE) in glulam. This is based on the law of mixtures, incorporating corrected stress wave-based MOE values. The predicted MOE results consistently underestimated experimental values, indicating the simulation provides conservative yet reliable stiffness predictions. This study developed technical evidence in support of a code change proposal for: (1) a weak-axis specified bending strength of 35 MPa for 24f-EX (excluding width effects), (2) a lamination factor (𝐾𝑙𝑎) for homogeneous layups (e.g., 16c-E) to scale strength with layer count, and (3) removal of width adjustments in size factors for weak-axis design. Limitations include sample size constraints and simplified simulation assumptions. Future work should explore additional species, advanced modeling, and environmental effects to further refine design guidelines.