The Tensile Strength of Laminated Members

An exploratory project to determine the tensile strength of laminated members was undertaken to lay groundwork for a more extended study. Material was Coast Region Douglas-fir 2 by 4’s, Eight of these were tested singly. Five specimens each of 2, 3, 4, 5, 6 and 7 laminations were fabricated and tested. The effective length of members under test was six feet. Member moisture content was about 10 percent. The minimum strength of laminated members was about equal to the average strength of single members and more than 2 l/2 times that of the weakest single member. For the laminated members, no dependency of tensile strength on number of laminations was evident. Neither was there conclusive evidence that the variability of strength had an inverse dependency on number of laminations. The tests failed to justify the established allowable stress, for that species and grade.

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