不同测试方法下杉木锯材抗弯性能指标的确定

Determination of bending properties index of Chinese fir lumber affected by different test methods

锯材力学性能指标的确定方法包括清材小试件和足尺试件两种测试方法。我国传统原木方木结构体系中木材的设计指标主要是基于清材小试件获得,而基于足尺试件确定设计指标的差异性相关研究有待深入。因此,选取774根目测分级杉木锯材,开展足尺试件和清材小试件抗弯性能的力学测试、数理统计、可靠度分析和相互关系研究。研究结果表明:目测等级对足尺试件抗弯性能的影响大于其对清材小试件抗弯性能的影响;采用Lognormal分布能够较好地拟合抗弯强度尾部概率分布;清材小试件、足尺试件目测等级为Ⅰ_(c)、Ⅱ_(c)/Ⅲ_(c)、Ⅳ_(c)满足目标可靠度要求的抗弯承载力抗力分项系数分别为1.34、1.11、1.15、1.42;足尺试件目测等级为Ⅰ_(c)、Ⅱ_(c)/Ⅲ_(c)、Ⅳ_(c)的抗弯弹性模量平均值分别为清材小试件抗弯弹性模量平均值的1.16、1.13、1.08倍,抗弯强度设计值分别为清材小试件抗弯强度设计值的1.37、1.12、0.76倍。

Two testing methods,i.e.,those using clear wood specimens(CS)and full-scale specimens(FS),are often used to determine the mechanical properties of lumber.The design index of wood in the traditional sawn and log timber structures is determined by the method of CS,and the result is different from that determined by the method of FS.However,there is no relevant research on the relationship or difference between these two methods.Therefore,774 pieces of Chinese fir lumber graded by visual were selected,and then mechanical test,mathematical statistics,reliability analysis and mutual relationship were carried out or obtained to investigate the bending properties of both CS and FS.Results indicate that the influence of visual grade on the bending properties of FS is greater than that on the bending properties of CS.Lognormal distribution could provide a good fit for the tail probability distribution of bending strength for both CS and FS.The partial coefficients of flexural bearing capacity resistance that meet the requirements of target reliability are 1.34 for CS,and 1.11,1.15,1.42 for Ⅰ_(c),Ⅱ_(c)/Ⅲ_(c) and Ⅳ_(c) FS,respectively.The mean value of the bending elastic modulus of Ⅰ_(c),Ⅱ_(c)/Ⅲ_(c) and Ⅳ_(c) FS is 1.16,1.13 and 1.08 times of the mean value of the bending elastic modulus of CS,and the design value of bending strength is 1.37,1.12 and 0.76 times of the design value of flexural strength of CS.