Duration of Load Tests for Dry Lumber Subjected to Shear

Tubular specimens made from clear material and material containing knots were subjected to shear. The load was applied using step-wise ramp loadings. A total of six rates of loadings varying from 0.015 psi/MIN to 1440 psi/MIN were used. The results indicated that the relationship between Strength reduction, time and strength is more complicated than the presently used concept. It was found that initially strong material did loose strength approximately as indicated by our present design concept but that weak material did not lose strength. Since the allowable stresses are based upon the lower 5th percentile value the validity of our present design method is questioned.

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