Evaluation of the End Effect Impact on the Torsion Test for Determining the Shear Modulus of a Timber Beam through a Photogrammetry Approach

The timber beam end effect in the torsion test is
evaluated using binocular stereo vision system. It is recommended by
BS EN 408:2010+A1:2012 to exclude a distance of two to three times
of cross-sectional thickness (b) from ends to avoid the end effect;
whereas, this study indicates that this distance is not sufficiently far
enough to remove this effect in slender cross-sections. The shear
modulus of six timber beams with different aspect ratios is determined
at the various angles and cross-sections. The result of this experiment
shows that the end affected span of each specimen varies depending
on their aspect ratios. It is concluded that by increasing the aspect
ratio this span will increase. However, by increasing the distance
from the ends to the values greater than 6b, the shear modulus trend
becomes constant and end effect will be negligible. Moreover, it is
concluded that end affected span is preferred to be depth-dependent
rather than thickness-dependant.

Authors:

• Niaz Gharavi
• Hexin Zhang
• Yanjun Xie

Keywords:

• End effect
• structural-size torsion test
• shear properties
• timber engineering
• binocular stereo vision.

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