Design Considerations for Laminated Wood Beams Composed of Two Species

The strength and stiffness limitations of two-species laminated beams have been considered as being affected by the interaction between face and core properties as well as by the face to core depth ratios in various composite beams tested. A theoretical basis for predicting the strength and stiffness of two-species beams was developed using classic flexure analysis, modified to take into account shear deformations introduced by both the face and core components of the composite. Two-species laminated beams, 1 inch by 1 inch in cross section and 8 and 16 inches long, were tested to failure in static bending as simple beams with center loading. Actual values of strength and modulus of elasticity were compared with predicted values from theoretical analysis. The beams were constructed from six species which varied in specific gravity from 0.32 to l.10. Face to core specific gravity ratios ranged from 1.56 to 2.04. The average error between predicted and actual value of modulus of elasticity of all composites except those having a core of the lowest density species was 3.4 percent. The error in predicting maximum bending moment for the same group of composites was 4.5 percent. The analysis failed to predict properties accurately with basswood, the low density species, as a core material because of distortion of the cross section of the beam under the loading head. There was no significant difference in percentage errors between composite beams with thick and thin faces.

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