Effects of Long-Term Creep on the Integrity of Modern Wood Structures

Short-term creep tests in tension and in compression were conducted on southern pine, Douglas-fir, yellow-poplar, and Parallam™ samples at temperatures ranging between 20 and 80° C and at 6, 9 and 12% moisture content. The principle of time-temperature superposition was applied to form a master curve that extended for a maximum of 2 years. The horizontal shift factors followed an Arrhenius relation with activation energies ranging between 75 and 130 kJ/mole. It was not possible to superpose the compliance curves at 70 and 80° C, this is attributed to the presence of multiple components in wood with different temperature dependence.

Long-term creep tests were also conducted in tension and in compression at 20° C and 12% moisture content for over 2 years. The resulting compliance curves were fitted to the power law equation using a nonlinear fitting procedure. The results were compared with those of the short-term creep tests.

Finite element analysis was conducted on selected wood structures to determine the effect of creep on serviceability and stability.