毛竹杆纯弯构件受力性能试验研究

为研究毛竹杆的受弯性能，先对取自10根毛竹的40组竹条标准材性件进行抗弯试验，得到其破坏模式和抗弯强度；再对直径为90、120 mm，跨距为3 000、3 600 mm的24根毛竹杆进行弯曲试验，研究其荷载—位移曲线、初始抗弯刚度、极限承载力、挠度、破坏模式等相关力学性能；理论推导毛竹梁破坏受压区高度及受拉区边缘应力。结果表明：毛竹梁跨距变化对挠度的影响大于直径变化对挠度的影响，毛竹梁直径越大、跨距越小，初始抗弯刚度越大；根据试验数据，按弹性理论计算出毛竹杆受弯破坏时的受压区高度在3R/2处，在小挠度条件下，毛竹梁受弯符合平截面假定，大挠度条件下，截面受压区高度上移，计算出的破坏边缘拉应力与平截面假定计算的结果不一致，建议毛竹梁受弯破坏弯矩按上边缘顺纹抗压强度达到最大进行计算。

Experimental study of flexural performance of raw bamboo

In order to study the flexural performance of bamboo member, 40 groups of bamboo standard wood strips from 10 raw bamboos were tested to obtain their failure modes and flexural strength. Then, the 24 raw bamboo beams with diameters of 90 mm and 120 mm making the spans of 3 000 mm and 3 600 mm were subjected to bending collapse tests. And the load-displacement curves, initial bending stiffness, ultimate bearing capacity, deflection and failure modes were analyzed. The height of compressive zone and edge stress of tensile zone of the raw bamboo beams were deduced theoretically. The results show that the influence of span change on deflection of bamboo beam is greater than that of diameter at breast height. The larger diameter at breast height and the smaller span, the greater the initial bending stiffness of the bamboo beams. According to the test data and the classical elastic theory, it is calculated that the compressive zone height of the bamboo beam is about 3R/2 height of the cross-section. Under the condition of small deflection, the bending of Phyllostachys pubescents beam conforms to the assumption of flat section, while under the condition of large deflection, the height of compression zone of section moves up, and the calculated tensile stress of failure edge is inconsistent with the calculated result of the assumption of flat section. It is suggested that the bending moment of Phyllostachys pubescents beam should be calculated according to the maximum compressive strength of the upper edge along the grain.