Analysis of lifetime and residual strength of wood

The present paper is thought of as a working paper for the CTBA-seminar on Thematic network in the field for reliability based design of timber structures, Topic: Numerical methods for structural analysis. It is preliminary and quite informal in its structure. The intention is to present some wood technological problems which can be solved with respect to lifetime and residual strength by the so-called DVM-theory (Damaged Viscoelastic Material). The outlines of the paper is straight on: Expressions are presented by which the analysis is made. then some examples are considered with solutions presented graphically. The examples are subdivided in two groups. The first group is considered as an average of wood. Another group is considered respecting that each piece of wood is an individual.Constant loads and variable loads are considered. The latter are assumed to have "seasonal frequencies" with periods greater than 1-2 months. It is also assumed in this paper that loads do not change sign. These assumptions are introduced for simplicity only. The DVM-theory has recently been generalized to apply in general for any frequency of load variations with arbitrary average. Two examples are presented just to illustrate the capability of the DVM-theory also to confider such problems.Some basics of the DVM-theory are presentes in sections at the end of the paper. Finally, most often time to start of damage propagation (t_s) is ignored in this paper because it is very often negligible relative to total lifetime (t_CAT).