Abstract:
In order to describe long term creep behavior of structural lumber in a natural
environment, a bending test with twenty Douglas-Fir beams subjected to a constant
load was set up in an open shed in the Forest Research Laboratory at Oregon State
University. Deflections of the beams were measured along with daily fluctuations in
temperature and relative humidity. An existing five-element creep model was used to
predict the creep strain and compared to the experimental data. The model did not
predict creep behavior of structural lumber in a natural environment. The general
observations showed that stiffness of the beams has a strong influence on the
magnitude of creep strain, and the creep strain closely follows the fluctuations in air
temperature. The mechano-sorptive creep strain in this experiment is likely to be the
shrinking and swelling on the surfaces of the beam and is not tied to the moisture
content (MC) of the entire beam, which changed very little over a one year period.
Four-element Burger model and power law empirical model were modified to include
the stiffness of the beams and air temperature effects. Both models fit the
experimental data very well.
