Allowable Bending Strength Enhancement of 2 By 4 Lumber By Tension and Compression Proofloading

Simple 5th percentile and reliability analysis methods were used to evaluate increases in allowable bending strength from proofloading in tension and compression. The analysis included the use of realistic load data for residential roof and floor trusses, and combined stress present in truss chords was given consideration as part of the reliability analysis. Proofloading in tension or in compression both produced significant increases in allowable bending strength for 2 by 4 1650f-1.5E hem-fir. Proofloading in tension to a target 15% breakage level, or 2,838 psi, yielded for the survivors an increase of 72% in allowable bending strength. The allowable bending strength increased 60% because of compressive proofloading to a target 15% breakage level. Since relatively small sample sizes were used, the results are not definitive but provide justification for a comprehensive study