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Laminated timbers offer the possibility of increased capacity and consistency over natural wood beams. The ability to select quality laminations eliminate the imperfections of natural wood (knots, cracks, wavy grain, rot, pith). I applied force to beams with various laminations to test the relationship between numbers of lamination and deflection.
I glued and bent 7 groups of 4 beams with layers ranging from 1 to 8. I used a bottle jack to apply force, a scale to monitor load and a machinist’s dial to measure the deflection.
My hypothesis was that beams with more layers would have less deflection because glue generally stiffens wood. In reality, beams with 4 layers were the stiffest: every other group, with fewer or greater layers, had more deflection.
When I graphed the deflection from the beams, the 8-layer beams had the highest deflection while the 4-layer beams had the lowest, with all other groups falling in between. The ANOVA test set the F-score at 95, well above the critical value of 2.32 (with degrees of freedom: 6,42) when p=0.05. The high F-score in relation to critical value indicates a strong correlation between layer quantity and deflection, well above the 5% p-value.
My data shows that laminated beams can be stiffer than solid beams, but laminating more or fewer than 4 layers yields less stiffness. Further tests of deflection in comparison to the breaking force including full scale beams would provide more complete data on the strength of laminated beams.