胶缝缺陷对木梁承载能力的影响

The Influence of Glue Line Defects on Bearing Capacity of Glulam Beam

采用兴安落叶松板材、水基聚氨酯胶粘剂,分5层板胶合,制作含有不同胶缝缺陷率的3组胶合木梁试件,胶缝缺陷设置在梁的跨中。通过静力弯曲破坏试验,测试构件应力、变形及极限承载力。试验表明,胶合木梁弯曲破坏属于脆性破坏,存在受拉区外侧木纤维被拉断及胶缝缺陷处破坏两种正常破坏形态。胶缝缺陷使得木梁抗弯刚度和承载能力均降低,胶缝缺陷率2%、4%的木梁相对胶合完好的构件,极限承载能力分别降低8. 8%、13. 5%;正常使用承载能力分别降低11. 3%、14. 7%。承载能力降低幅度与胶缝缺陷率不完全成比例关系,是由于内层胶缝缺陷比外层胶缝缺陷对木梁抗弯能力影响小的原因,这表明木梁抗弯承载能力不仅与胶缝缺陷率有关,还与缺陷的位置有关。

In this paper,employing Xingan larch plank and water-based polyurethane adhesive,three groups of five-layer glulam beams were manufactured and each has different rate of glue line defects,the glue line defect is located in the midspan of the beam.The strain,deformation and ultimate bearing capacity of the components are tested by static bending destructive test.Tests showed that the bending failure of glulam beam belongs to brittle failure,there are two kinds of normal failure modes,which are the lateral wood fiber of the tensile zone is broken and the glue line defect is damaged.The flexural stiffness and bearing capacity of glulam beam will be reduced by glue line defects.Compared with an intact beam,the ultimate bearing capacity of glulam beams with a ratio of 2%and 4%glue line defect was reduced by 8.8%and 13.5%respectively;and the bearing capacity of normal working was reduced by 11.3%and 14.7%respectively.Defects in inner glue seam have less effect on the bending resistance ability of the glulam beam than external,so that the reduction of bearing capacity is not proportional to the rate of glue line defects completely.This indicates that the bending resistance ability of the glulam beam is not only related to the defect rate,but also to the location of the defects.