Experimental study of CLT panels under combined out-of-plane bending and compression

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Combined out-of-plane bending and compression is an inevitable loading condition for cross-laminated timber (CLT) walls due to the out of plumbness, initial panel curvature and load eccentricity. Because of the weaker cross layers, the mechanical performance and failure mode of the CLT panels under such loading significantly differ from those of the other wood members, such as sawn timber and glulam. This experimental study focuses on investigating the behavior of CLT panels under the stated loading scenario. The experimental program consisted of 36 specimens, including 12 five-layer CLT panels provided by two Canadian manufacturers, as well as 12 three-layer and 12 five-layer CLT panels provided by a Chinese manufacturer. All the specimens were tested in Canada and China, respectively, using the same test setup. It was found that in the majority of the specimens, the damage was caused by the local buckling near the mid-height of the outer layer on the concave compression side at about 45%–60% of the ultimate failure load and 25%–35% of the ultimate deflection. The dominant failure mode was characterized as the crushing yield of the outer layer on the concave side (fibers in compression) near the mid-height after the local buckling progressed. Signs of shear failure of cross layers were evident almost simultaneously with the outer layer failure. Hence, although the dominant failure mode was likely triggered by the fracture in the cross layers due to rolling shear, the load-carrying capacity of the CLT panels under the combined out-of-plane bending and compression is governed by the compression failure of the longitudinal outer layers. It was found that a cross-layered panel can maintain its integrity before failure. It was also noted that the interaction equations specified in the Canadian design standard are appropriate for the CLT panels under small load eccentricity, while for panels that have large load eccentricity, the appropriateness of the interaction equation is questionable. Based on the test results obtained, the validity of the interaction equation for the prediction of the load-carrying capacity of CLT columns, specified in the CSA O86-19, is confirmed for cases in which Pf/Pr>0.5 and Mf/Mr<0.3. For the cases of Pf/Pr<0.5 and Mf/Mr>0.3, modification of the equation is needed.