Number of Strength Reducing Features—How does it Affect the Strength of Laminated Beams?

Abstract

SYNOPSISTest done by the author and others have shown that the strength oflaminated beams is usually governed by the strength of the finger joints in the extreme tension laminate. The author illustrates how the influence of the number of finger joints in a laminate can be quantified. He also points out that the variability of the finger joint strength can have a big influence on the strength, especially at the lower end of the strength distribution.The stress in laminate 1 is 70 % ofstress in laminate 2. The load sharing factor is thus 1,429.If one now assumes that the laminate with the knot is weaker than the defect-free laminate and that failure will occur in the knot, it is possible to calculate the "reinforcement" offered to the knot. The total load carried by the combined member is given by:

Finger Joint Strength. A Laminated Beam Strength Predictor?

“…The factor for the strength of the laminate due to the number of finger joints in the laminate, has been described by Burdzik (1996), and depends on the distribution of the finger joint strengths and at which percentile we define the characteristic stress. The probability P(X n Sa) = 1 -P (X n > a) of the strength of a series ofn finger joints being less thana is given by…”