Wood Joist Floors: Probabilistic Analysis of Joist Stiffness Measured at Retail Lumberyards.

A systematic sampling of joint lumber was carried out at retail lumber yards over two summers to observe and measure physical and mechanical properties close to point of purchase and use. The study sought to define acceptable performance of the dimension lumber in terms of floor system performance using a composite of current standards. Measured properties of the material were discussed in terms of that tentative criterion. This interim report emphasizes sampling procedures, testing methods, and techniques of statistical analysis used. In a first phase of the study , joist lumber was sampled in serial lots to develop statistical data on joist properties. In a second phase, the effect of time on serial sampling was considered. The survey showed that approximately 50 percent of 3 x 8 joists were of smaller dimensions than would be anticipated by reference to the ruling standards. Some differences occurred in sample properties over the sampling interval of 1 year, even in material from the same lumberyards.