Evaluation of rolling shear modulus and strength of Japanese cedar cross-laminated timber (CLT) laminae

Seiichiro Ukyo,Kenta Shindo,Atsushi Miyatake

doi:10.1186/s10086-019-1810-8

Seiichiro Ukyo, Kenta Shindo + Show 1 more

Open Access

https://doi.org/10.1186/s10086-019-1810-8

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Abstract

Cross-laminated timber (CLT) panels are fabricated with their layers stacked crosswise. Owing to the low shear modulus and strength in the rolling shear direction, the shear properties of cross-layers influence the overall deflection and shear capacities of CLT panels. The aim of the present study is to determine the rolling shear properties of Japanese cedar and investigate how annual ring patterns and lamina geometry influence shear properties. Using a test configuration similar to the standard shear test configuration prescribed in European Standards (EN 408), a single lamina shear test was conducted. To investigate the influence of thickness-to-width aspect ratio of the lamina on the rolling shear properties, samples with three different widths, including 62, 88, and 112 mm, with a constant thickness of 24 mm were tested. The geometrical features of the annual ring patterns of each test sample were measured. The mean rolling shear moduli were 72, 91, and 109 MPa, and the mean rolling shear strengths were 1.54, 1.83, and 2.02 MPa for the 62-, 88-, and 112-mm sample widths, respectively. Shear strength was highly correlated with shear modulus. The mean shear modulus and strength, in addition to the 5% quantile, increased with an increase in lamina width. Across all sample widths, rolling shear modulus and strength decreased with an increasing radial distance from the pith. Using the principle of continuum mechanics, the influence of the annual ring angle relative to the shear force direction was examined quantitatively using the finite element method. The results suggest that shear modulus and its variance are influenced greatly by the annual ring structure.

Highlights

Cross-laminated timber (CLT) panels are fabricated with layers stacked crosswise
A shear test configuration similar to the shear test prescribed in the EN 408 standard was conducted to obtain the rolling shear properties of Japanese cedar with different lamina sizes
The rolling shear modulus based on the areal strain of laminae (G str ) was 16% higher than the shear modulus based on the relative displacement of the side plates (G dsp)

Summary

Introduction

Cross-laminated timber (CLT) panels are fabricated with layers stacked crosswise. When the panels are subjected to close out-of-plane loads, a critical shear stress is introduced to the cross-layers. Aicher and Dill-langer [1] studied the effects of sawing patterns on rolling shear modulus using polar anisotropic finite element analysis. They concluded that the shear modulus at the macro-level (i.e., lamina size) is not an intrinsic material property, but a global apparent quantity that is highly dependent on the sawing pattern. Ehrhart et al [2] studied the rolling shear properties of single lamina prepared from various European timber species using a shear test configuration similar to the EN 408 timber test standard [3] They conducted a parametric study on Norway spruce to assess the effect of various radial distances from the pith (i.e., sawing pattern) and aspect ratios of laminae on the rolling shear properties. The annual ring patterns were classified into four established sawing patterns based on the mathematical descriptions of the orientation of the annual rings

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