An Analysis of Creep-Inducing Stress in Sitka Spruce

Abstract

Sniall specimens of Sitka spruce (Yicea sitchensis) were placed under a parallel-to-thegrain compressive loading situation in a water-sat~~rated state to exk~mine the adequacy of three-elrment and four-elenlent spring and dashpot model analogs in describing creep response curves for \\,ood.Stress levels of 10, 20, 40, and 60% of lllti~~late comprcssivc \trength were studied for loatl durations u p to 20 clays.Deforniation-time rllcasuremcnts wclre analyzecl statistically l)y means of a eo~nputrrized, uonlinear, least squares regression analysis and \vith the aid of graphic analysis.Creep defonnation mas found to occm at stress levels as low as 10% and a t very short time periods.In general, three-or four-elrment model analogs were adequate to describe time-dependent deformation phenomena for applied pnrposes; further refinements were tlee~nctl superfluous.For time periods of 24 hr or longer, the use of a four-element niodel is advised, particularly at higher stress levels.