Citation

Leichti RJ, Tang RC. Math. Comput. Model. 1989; 12(2): 153-161.

Copyright

(Copyright © 1989, Elsevier Publishing)

DOI

10.1016/0895-7177(89)90430-5

PMID

unavailable

Abstract

Elastic displacement of wood is considered within current and envisioned structural design methods in the U.S.A., but viscoelastic displacement is treated only by rule of thumb. This study examined the reliability of wood as a viscoelastic material, based on the premise that timber structural members have two failure modes: (1) serviceability and (2) ultimate collapse. In the laboratory, full-scale solid sawn lumber and wood-composite I-beams were loaded for 110 days in a controlled environment. Data on initial elastic and creep displacements were recorded and fitted to a four-element mechanical analog to model creep. The mathematical description of the four-element mode was then used as the failure surface in a second-moment reliability analysis. Reliability was shown to be a function of time for lumber and I-beams when the limit state was serviceability; however, reliability may not have changed or may have changed at a different rate when the limit state was ultimate failure. It seems reasonable to expect reliabilities to change over time in viscoelastic materials whose serviceability state precedes ultimate failure.