Treatment-Processing Effects Model for WBP-Treated Lumber

A rationally based procedure has long been needed for assigning design adjustments to Southern Pine lumber treated with waterborne preservative. This paper attempts to develop such a procedure by evaluating a series of models to predict the short-term effects of waterborne preservative treatments on the strength of U.S. Southern Pine lumber. Input data consisted of non-parametric treated to untreated strength ratios normalized from data of seven recent reports. Input variables included material quality factors, such as grade and size, and treatment processing factors, such as preservative retention and redrying temperature. For the best models evaluated, the loss in bending strength from preservative treatment was significantly related to the differential between the pH of the treating solution and that of the untreated wood, post-treatment redrying temperature, and initial material quality. Mechanisticbased models were found to fit the compiled data set as well as or better than the best empirical models. Both mechanistic and empirical models provided a reasonable level of predictive capability, but neither was flawless. When used with the recently developed short-term load– duration adjustment model for waterborne-preservativetreated lumber, this accumulated treatment-processing effects model can result in a rationally based procedure for assigning design adjustments to waterbornepreservative-treated Southern Pine lumber.