Reliability Analysis for the Bending Strength of Larch 2×4 Lumber

A safety analysis for Larch (Larix gmelinii) 24 lumber, based on the requirements of Chinese national standards, is presented in this paper. Static, third-point bending tests were conducted using an MTS universal testing machine. The bending strength was adjusted to 15% moisture content (MOR15) and was fitted with three different probability distribution models. The best fitting MOR15 model for Larch 24 lumber possessed lognormal distribution. Furthermore, a procedure for calculation of a reliability index () was developed using the first-order second-moment method. Results of reliability analysis indicated that the reliability index decreased nonlinearly as both the design value of bending strength increased and the reduction of live to dead load ratio (). Finally, it was suggested that the design values for the bending strength of Larch 24 lumber were 18.4 MPa for grade SS, 11.6 MPa for grade No.1, 12.7 MPa for grade No.2, and 10.3 MPa for grade No.3, to meet the target reliability level.