Creep of lumber beams under constant bending load

Two sets of data are analyzed in the thesis. The first set was derived from the long term deformations of 2 in x 6 in x 12 ft (40 mm x 140 mm x 3600 mm) joists of Douglas-Fir loaded under constant bending stress to levels lower than or equal to 3110 psi (21.44 MPa). The second set was derived from the long term deformations of 2 in x 6 in x 12 ft joists of Hemlock loaded under constant bending stress to levels of 3000 psi (20.68 MPa) and 4500 psi (31.0 2 MPa) . The analysis shows that the creep behaviour of structural size beams depends upon the material characteristics; specifically, material with a strength lower than 5000 psi (34.33 MPa) appeared to creep 1.5 times more than, material with a strength higher than that level, over a three month period. In addition, the test results support the assumption of a linear relationship between the creep deformation of a structural-size timber beam and applied stress. A method is presented to predict the creep behaviour of a structural-size specimen at discrete times over a three month period. The method consists of expressing the creep deformation, Δ[sub c], in terms of the elastic deformation, δ[sub e], or equivalently, the fractional creep (f = δ[sub c] / δ[sub e]) in terms of δ[sub e] or in terms of the modulus of elasticity. This work is limited to the stress levels investigated and to specific temperature (10°C< θ <30°C) and moisture content (8%<MC