Comparison between Allowable Properties Method and Reliability Analysis Method to Determine Design Values of Visually Graded Chinese Larch 40 x 65 mm Lumber

The reliability analysis method and the allowable stress method were both applied in this study to determine design values of ultimate compression strength (UCS) of visually-graded 40 x 65 mm dimension Chinese larch lumber. A total of 784 lumber samples were tested on the static full-size compression strength, according to Chinese National Standards. The goodness-of-fit for the UCS distribution of four visual grades of lumber were analyzed, and first-order, second-moment reliability analyses under different load cases were performed based on all of the test data. The log-normal distribution was found to optimize the fitted distribution of the ultimate compression strength of Chinese larch dimension lumber. Design values of the compression strength of grades Ic, IIc, IIIc, and IVc were suggested to have the minimum reliability index of 3.2 for the reliability analysis method, and the reduction factor of 1/1.9 for the allowable stress method. The results showed that the design values in the Chinese Code were the most conservative for high visual grade dimension lumber compared to the reliability analysis and allowable stress methods. The reliability analysis method was more suitable for developing design values of lower visually-graded lumber.