Effect of Juvenile Wood and Choice of Parametric Property Distributions on Reliability-Based Beam Design

A comparison is made of the effect of choice of the SB distribution, Weibull distribution, or log-normal distribution on reliability-based design of a 2 x 4 southern pine beam, No. 2 grade. The SB distribution provided most flexibility in describing the lumber properties.The presence of juvenile wood in lumber may affect the distributional characterization of lumber properties and in turn affect reliability-based design results. This study shows that juvenile wood had a significant effect on the reliability-based design results when stiffness was the limiting state. Unless juvenile wood lumber is separated from mature wood lumber in the grading process, a considerable loss in efficiency in utilizing lumber from fast-grown trees will occur where stiffness is critical