Honors College Thesis

The Location of the Neutral Axis in Wood Beams with Multiple Knots

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  • In a homogenous and isotropic material, the location of the neutral axis coincides with the location of the centroid of the beam. Wood is anisotropic, meaning that it has different properties in different directions. It is also non-homogenous, meaning that the beam exhibits different properties at different locations throughout its length due to the presence of knots as well as grain characteristics. Since wood is not homogenous or isotropic, the location of the neutral axis varies throughout the length of the beam and is different for each individual beam. Because of this variability, research is needed to better understand the movement of the neutral axis as it reacts to different combinations of knots and grain angles. This thesis explores this in 38 mm by 89 mm (nominal 2X4) Douglas Fir beams with different patterns of knots. The analysis was done using Digital Image Correlation equipment and VIC-3D software which displays the strains and thus the location of the neutral axis. It was found in a clear nominal 2 in x 4 in beam that the neutral axis was slightly above the center of the beam. In the beams containing knots, the location of the neutral axis tended to move away from the knots except in situations where the knots were located longitudinally close to each other. In this case, the neutral axis moved very minimally or not at all.
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