Abstract: [Objective] For the safety design and the rational application of domestic dimension lumber in timber structure, the objective of this study was to develop a determination method of the design value of tension strength of domestic dimension lumber.[Method] The Chinese larch dimension lumber (Larix gmelinii) was selected as the research object. Full-size tensile test results of different visual grades (grade Ⅰc, Ⅱc, Ⅲc, Ⅳc) dimension lumber were summarized. By the least square method, the fitted parameters and results for tension strength were obtained under different probability distribution models and different fitting data points. The characteristic values of tension strength were also determined based on the nonparametric method. Finally, the relationships between the reliability index and the partial factor under different fitting data points, probability distribution models, load combinations, and load ratios were investigated by the reliability analysis theory.[Result] The results indicated that there were significant difference of tension strength between different visual grades. The average and the coefficient of variance of tension strength displayed the following order:Ⅰc > Ⅲc > Ⅳc > Ⅱc, Ⅱc < Ⅰc < Ⅲc < Ⅳc, respectively. Compared with the fitting results, the end probability distribution fitted by different models (Normal, Lognormal and 2-P-Weibull) begun to be identical with the decrease of the fitting data points, which was close to the tested values. The calculated reliability index with the lognormal probability distribution model was the highest, and that with the normal probability distribution model was the lowest. With the decrease of the fitting data points, the calculated reliability indexes with different probability distribution models (Normal, Lognormal and 2-P-Weibull) begun to be identical. If the partial factor was the same, with the increase of the load ratio, the calculated reliability indexes under dead load plus residential live load (D+R), or dead load plus office live load (D+O) were increased, however, the calculated reliability indexes under dead load plus snow live load (D+S), or dead load plus wind live load (D+W) changed very little. The partial factor for D+W or D+S was the highest while that for D+O was the lowest.[Conclusion] To determine the design value of tension strength of domestic dimension lumber, this study suggested that the lognormal probability distribution model be selected for the tested probability distribution of tension strength, the parameters of the selected lognormal probability distribution model be determined by the 25 per cent tested data points, the load type of dead load plus residential live load be selected, and the load ratio be 1.0. For Chinese larch dimension lumber, the design values of tension strength of grade Ⅰc, Ⅱc, Ⅲc, Ⅳc were 9.0, 6.8, 5.6 and 2.9 MPa, respectively.

Key words: domestic dimension lumber, design value of tension strength, timber structure, reliability