Bending, shear, and compressive properties of three- and five-layer cross-laminated timber fabricated with black spruce

Xiaofeng Sun,Wei Feng,Zheng Li,Minjuan He

doi:10.1186/s10086-020-01886-z

Abstract

Cross-laminated timber (CLT) is an innovative engineering wood product made by gluing layers of solid-sawn lumber at perpendicular angles. The commonly used wood species for CLT manufacturing include spruce-pine-fir (SPF), douglas fir-larch, and southern pine lumber. With the hope of broadening the wood species for CLT manufacturing, the purposes of this study include evaluating the mechanical properties of black spruce CLT and analyzing the influence of CLT thickness on its bending or shear properties. In this paper, bending, shear, and compressive tests were conducted respectively on 3-layer CLT panels with a thickness of 105 mm and on 5-layer CLT panels with a thickness of 155 mm, both of which were fabricated with No. 2-grade Canadian black spruce. Their bending or shear resisting properties as well as the failure modes were analyzed. Furthermore, comparison of mechanical properties was conducted between the black spruce CLT panels and the CLT panels fabricated with some other common wood species. Finally, for both the CLT bending panels and the CLT shear panels, their numerical models were developed and calibrated with the experimental results. For the CLT bending panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios can even slightly reduce the characteristic bending strength of the black spruce CLT. For the CLT shear panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios has little enhancement on their characteristic shear strength. For the CLT bending panels, their effective bending stiffness based on the Shear Analogy theory can be used as a more accurate prediction on their experiment-based global bending stiffness. The model of the CLT bending specimens is capable of predicting their bending properties; whereas, the model of the CLT shear specimens would underestimate their ultimate shear resisting capacity due to the absence of the rolling shear mechanism in the model, although the elastic stiffness can be predicted accurately. Overall, it is attested that the black spruce CLT can provide ideal bending or shear properties, which can be comparable to those of the CLT fabricated with other commonly used wood species. Besides, further efforts should focus on developing a numerical model that can consider the influence of the rolling shear mechanism.

Highlights

Cross-laminated timber (CLT) is one kind of prefabricated engineered wood products, made of at least three orthogonal cross-wise layers of graded sawn lumber thatHe et al J Wood Sci (2020) 66:38Since CLT has illustrated its potentials and competitiveness of using as dominant building materials for the mid- and high-rise timber buildings, a series of studies have focused on comprehending the mechanical properties of CLT panels based on tests
Ukyo et al [7] tested the rolling shear properties of CLT fabricated with Japanese cedar, and found that its rolling shear strength was highly correlated with the shear modulus
For the 3-layer CLT shear specimens, their average ultimate shear resisting capacity (FVmax) is 51.639 kN with a coefficient of variation (COV) of 7.5%; for the 5-layer CLT shear specimens, their average FVmax is 69.806 kN with a COV of 5.6%. For both the 3-layer and the 5-layer CLT shear specimens, their characteristic shear strength can be calculated using Eqs. (6) and (7) from CLT Handbook [21], in which EIeff,shear is the effective bending stiffness calculated based on the Shear Analogy theory; Ei represents El,0 for the longitudinal lamination and represents El,90 for the transverse lamination, respectively; hi is the thickness of lamination i, except for the middle

Summary

Introduction

Cross-laminated timber (CLT) is one kind of prefabricated engineered wood products, made of at least three orthogonal cross-wise layers of graded sawn lumber thatHe et al J Wood Sci (2020) 66:38Since CLT has illustrated its potentials and competitiveness of using as dominant building materials for the mid- and high-rise timber buildings, a series of studies have focused on comprehending the mechanical properties (e.g., bending, rolling shear, compression, tension, etc.) of CLT panels based on tests.

Results

Conclusion