孔洞对木梁弯曲应变分布影响的试验研究

Experimental study on the effects of holes on bending strain distribution of wood beams

为了研究孔洞对木梁弯曲应变分布的影响,采用数字图像相关法进行了无疵木梁和含孔洞木梁的四点弯曲试验,分析了3种不同的孔洞位置(孔洞位于中心、受压区和受拉区)对木梁弯曲应变分布的影响,探讨了中性轴位置的偏移规律。结果表明:在极限载荷时,3种不同孔洞位置的木梁,其压应变区域均大于拉应变区域,其中孔洞位于受压区时木梁的压应变区域最大,孔洞位于中心时次之,孔洞位于受拉区时最小。并且在整个加载过程中,中性轴会随着载荷的增大向木梁下缘偏移,孔洞位于受压区时中性轴的偏移距离最大,孔洞位于中心时次之,孔洞位于受拉区时最小。在此基础上,依据平截面假定和弹塑性理论的Hoffman屈服准则,初步分析了含孔洞木梁弯曲应变分布和中性轴偏移规律的机理。研究结果为进一步从理论上定量推导含孔洞木梁的弯曲应变和应力计算公式提供了依据。

To analyze the deformation and strain distribution of wood beams which contained holes during loading, in this paper, four-point bending tests were performed on clear wood beams and wood beams containing holes using digital image correlation technique. The influence of three various locations of holes （a hole located at center, located at compression zone, and located at tension zone, respectively） on bending strain distributions of wood beams was analyzed, and the movement of the neutral axis during loading was discussed. The experiment results showed that strain distributions and neutral axis locations were significantly different for three various locations of holes. When beams were at the ultimate load, for beams containing holes at various locations, the compressive strain region was larger than the tensile strain region. Among three various locations of holes, wood beams containing a hole in the compression zone had the largest compressive strain region, beams containing a hole at center come second, and beams containing a hole in the tension zone had the smallest compressive strain region. Additionally, the neutral axis moved towards the bottom of the beam as the load increased during loading. The movement of neutral axis was largest when the hole located at the compression zone, secondly when the hole located at center, and smallest when the hole located at the tension zone. Based on plane-section assumption and Hoffman yield criterion in elastic-plastic theory, the theoretical analysis of strain distribution and movement of neutral axis was studied on wood beams which contained holes. The results provide proofs for further theoretical study on bending properties of wood beams containing holes.