Rate of Loading Adjustment for Proof Testing of Lumber in Tension

Tension proof loading of truss lumber could provide practical, economic benefits to several industries. One implementation difficulty is that current allowable design stresses are tied to tests conducted at a slow ASTM rate. The influence of a load rate of 19.8 times the ASTM D198 standard on the tensile strength of No. 2 KD15 southern pine was evaluated. Four hundred twenty-four specimens, divided into two balanced samples, were tested in tension. Lognormal distributions were fit to the resulting tensile strength populations. Tensile strength was found to be moderately higher when tested at a faster, more economical rate than the standard. Unlike previous studies of high quality lumber, the rate of loading has a positive effect on the entire sample population but material in the upper percentiles was most affected. The development of a rate adjustment factor for truss lumber proof testing is demonstrated. This factor can be used in obtaining code approval of proof tested lumber and is necessary to establish a proof test level needed to maintain any desired allowable tension strength.

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