原竹材料抗弯性能试验研究

Experimental Study on Bending Resistance of Original Bamboo Material

开展了原竹材料抗弯性能试验,探究了竹材抗弯强度和弹性模量与高度、壁厚、周长的关系,采用Bootstrap法分析了竹材抗弯强度标准值,基于可靠度理论研究了原竹材料的抗弯强度设计值。结果表明:竹片抗弯加载经历较长的弹性阶段,塑性阶段较短,竹材抗弯承载力随高度增加而减小;竹片抗弯强度和弹性模量随高度增加而增大,随壁厚和周长增大而减小,竹片抗弯强度、弹性模量与高度、壁厚和周长具有较好的拟合优度,拟合公式可对竹材力学性能进行预测;样本数量对竹材抗弯强度的抽样误差具有显著影响,通过Bootstrap重抽样法分析标准值能够有效减小误差,采用该法进行10000次重抽样分析得到的原竹材料强度标准值为126.75 MPa;可靠度指标β随抗力分项系数γR和荷载比ρ的增大而增大;荷载比ρ>0时,目标可靠度下的抗力分项系数γR在恒载+雪荷载情况下最大,在恒载+办公楼面活荷载情况下最小,计算得到的3个安全等级下的原竹材料抗弯强度设计值分别为27.670,29.884,32.084 MPa。

The bending resistance test of the original bamboo material was carried out,the relationship between the bending strength,elastic modulus of bamboo and the height,wall thickness,and circumference was explored.The Bootstrap method was used to analyze the standard value of bending strength of bamboo.Based on the reliability theory,the design value of bending strength of the original bamboo material was calculated.The results show that the bending loading of bamboo slices goes through a longer elastic stage,and the plastic stage is shorter.The bending bearing capacity of bamboo decreases with the increase of height.The bending strength and elastic modulus of bamboo slices increase with the increase of height,and decrease with the increase of the wall thickness and circumference.The bending strength and elastic modulus of bamboo have good goodness of fit with height,wall thickness and circumference.The fitting formula can predict the mechanical properties of bamboo.The number of samples has a significant impact on the sampling error of the bending strength of bamboo.The standard value of the Bootstrap re-sampling method can effectively reduce the error.The standard value of original bamboo material strength obtained by the method for 10000 re-sampling analysis is 126.75 MPa.The reliability indexβincreases with the increase of the resistance sub-factorγR and the load ratioρ.When the load ratioρ>0,the resistance sub-factorγR under target reliability in the case of dead load+snow load is the largest,and is the smallest in the case of dead load+office floor live load.The calculated bending strength design values of the original bamboo material under the three safety levels are 27.670,29.884,32.084 MPa respectively.