  Lumber and wood-based products are versatile construction materials that are
susceptible to weakening as a result of applied stresses. To assess the effects
of load duration and rate, experiments have been carried out by applying preset
load profiles to sample specimens. This paper studies these effects via a
damage modeling approach, by considering three models in the literature: the
Gerhards and Foschi accumulated damage models, and a degradation model based on
the gamma process. We present a statistical framework for fitting these models
to failure time data generated by a combination of ramp and constant load
settings, and show how estimation uncertainty can be quantified. The models and
methods are illustrated and compared via a novel analysis of a Hemlock lumber
dataset. Practical usage of the fitted damage models is demonstrated with an
application to long-term reliability prediction under stochastic future
loadings.
