"Short-term" mechano-sorptive creep of well-defined spruce timber

In this paper creep test results in bending in a variable climate, 30-90% r elative humidity (RH), are presented. Eighty-one specimens, 45 x 70 x 1100 mm, from fifteen both fast-grown and slow-grown trees with well-documented history were tested. The duration of the creep tests was at least 42 days. Simple statistical methods were used to evaluate the creep test results. Fo r a part of the material the short-term creep, after 1-1.5 moisture cycles, was compared with relative creep after additional moisture cycles. The rel ative creep after 1-1.5 moisture cycles was a good predictor of the relativ e creep after additional moisture cycles. The wide range in material proper ties was not completely reflected in the relative creep test results. It se emed like the variation in relative creep decreased with increasing amount of moisture cycles. It was not possible to confirm a statistically signific ant difference in relative creep between specimens from the slow-grown and the fast-grown stands. For specimens assumed to contain juvenile wood and m ature wood, there was a statistically significant difference in relative cr eep after 1-1.5, 3-3.5 and 5-5.5 moisture cycles. Specimens assumed to cont ain juvenile wood showed the largest relative creep values. In the test mat erial, 81 specimens, a variation in deformation during the first moisture c hange of 14%-97% of the initial elastic deformation was found. The correlat ion between this deformation and material parameters was weak. However, the largest deformations during the first moisture change were obtained for sp ecimens from three trees. The moisture conditions when the creep tests star ted (30% RH or 90% RH) were not a governing factor for the creep behaviour.