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胶合木梁的疲劳极限荷载远低于静力极限荷载而易于破坏,通过落叶松胶合木梁的等幅疲劳试验及静力对比试验,分析了落叶松胶合木梁疲劳破坏形态与破坏机理,并研究了其疲劳特性,探讨了弯曲刚度退化规律。结果表明:落叶松胶合木梁的疲劳损伤从受压侧展开,受压侧塑性区高度随循环次数增加而逐渐向受拉侧扩展,最后因试件承载力降低而发生受拉破坏或顺纹剪切破坏;随着疲劳循环次数的增加,疲劳试验梁跨中挠度及拉、压应变逐渐增大,且压应变增幅大于拉应变,但其截面应变分布仍符合平截面假定;经疲劳荷载作用后,梁的弯曲刚度逐渐降低,基本呈线性退化,应力水平越高,其刚度退化越明显,并得出了不同应力水平下落叶松胶合木梁的刚度退化方程;落叶松胶合木梁的疲劳寿命随应力水平的提高而降低,在应力比为0.2,应力水平为0.55倍静力极限荷载时,疲劳极限超过200万次,满足构件有限寿命疲劳设计的要求,说明胶合木梁具有较好的疲劳特性。此外,通过对试验数据进行线性回归分析,初步得出了落叶松胶合木梁的S-N曲线数学表达式。
The fatigue limit load of glulam wood beam is much lower than the static limit load and it is easy to destroy. Through the equal-amplitude fatigue test and static comparison test of larch-bonded wood beam, the fatigue failure morphology and failure mechanism of larch-bonded wood beam are analyzed. The fatigue characteristics were studied and the law of bending stiffness degradation was discussed. The results show that the fatigue damage of the larch-glued wood beam expands from the pressure side, and the height of the plastic area at the compression side gradually expands to the tension side with the increase of the number of cycles. Finally, the tensile strength of the specimen is damaged or the grain is damaged. Shear failure; With the increase of the number of fatigue cycles, the mid-span deflection, tensile strain and compressive strain of the fatigue test beam increase gradually, and the increase of the compressive strain is greater than the tensile strain, but the cross-sectional strain distribution still meets the flat section assumption; Afterwards, the bending stiffness of the beam decreases gradually, and it basically degenerates linearly. The higher the stress level, the more obvious the degradation of its stiffness, and the stiffness degradation equations of larch-glued wood beams under different stress levels are obtained; the fatigue of larch-glued wood beams is obtained. The service life decreases with the increase of the stress level. When the stress ratio is 0.2 and the stress level is 0.55 times the static limit load, the fatigue limit exceeds 2 million times, which meets the requirements of the limited life fatigue design of the components, indicating that the glued wood beam has better Fatigue characteristics. In addition, through the linear regression analysis of the experimental data, the mathematical expression of the S-N curve of the larch-glued wooden beam was preliminarily obtained.