中文摘要：

为了研究上大下小拼合木梁受弯时的破坏形式、抗弯承载力、截面应变分布等抗弯性能,基于传统构造做法对不同材质、不同尺寸的上大下小拼合梁抗弯性能进行试验研究。基于理论公式推导,结合试验数据修正,提出杉木和松木材质的上大下小拼合木梁抗弯承载力的计算公式。研究结果表明：杉木和松木材质的上大下小拼合木梁的受弯破坏模式均为上梁底部木纤维脆性拉断。2种材质的上下拼合梁的截面应变沿梁截面高度方向的分布均符合平截面假定。为防止拼合木梁出现不可预见的早期脆性破坏,在工程设计和施工时应避免将节疤缺陷放置在木梁的受拉边。

英文摘要：

In order to study the bending behavior including failure mode and bending beating capacity and strain distribution at mid-span section of timber stitching beams with big top and small bottom, the bending tests on eight specimens with traditional conformation were carried out. Based on the theoretical analysis and the experimental results, the computing formulas of bending bearing capacity of this kind of timber stitching beams made of pine and fir were presented. The results show that the failure modes of this kind of stitching beams are all the brittle breaking at the bottoms of the top beams for the stitching pine beams and the stitching fir beams. The distribution of the section strain along the height of the stitching timber beam basically obeys plane hypothesis. Moreover, in order to avoid the early brittle failure of the stitching beam, the wood knot should not be put on the tensile side of beam.