Measurement of rolling shear modulus and strength of cross laminated timber fabricated with black spruce

• Two-plate shear test was proposed for measuring the rolling shear modulus of a cross layer in 3-layer CLT.
• Two-plate shear test could be used to determine the load capacity of 3-layer CLT at a relatively large span-to-depth ratio.
• The apparent modulus of elasticity and shear modulus of 3-layer CLT beam specimens were independent of the specimen width.
• An adjustment factor was proposed for predicting the deflection of a CLT beam specimen at a given range of span-to-depth ratios.
• Wooden cross layer specimens under the two-plate shear test failed in a ductile manner.

The design and application of cross laminated timber (CLT) is strongly influenced by the rolling shear properties of cross layers. Hence, to predict the performance of CLT requires accurate information about its rolling shear properties. In this study, a wooden cross layer (WCL) specimen was made of 38 mm by 89 mm black spruce lumber of a grade of No. 3. The average rolling shear modulus of the WCL specimens measured by the two-plate shear test was 136 MPa. The rolling shear modulus measured was then used as input to predict, using the shear analogy method, the deflection (dc) of a 3-layer CLT beam subjected to the centre-point bending load. Subsequently, the bending test was conducted to directly obtain the deflection (dm) of a 3-layer CLT beam for validation. It was found that dc could, with an adjustment factor (α), provide a good estimate of dm at different span-to-depth ratios under the centre-point bending test. Additionally, the bending test results showed that the specimen width did not have a statistically significant effect on apparent modulus of elasticity (Eapp) and apparent shear modulus (Gapp) of 3-layer CLT beam specimens.