摘要
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。
Since the fatigue load is much lower than the static limit load,glulam beams are apt to be damaged.Through the constant amplitude bending fatigue test and the static test of larch glulam beams,the fatigue failure pattern and failure mechanism of glulam beams are analyzed. The fatigue properties and stiffness degradation are studied. The results indicate that the fatigue damage of larch glulam beams grows from the compression side,and the depth of plastic zone on the compressive side expands to tension side of the glulam beam with the increase of fatigue load cycles. The failure of glulam beam is due to tension or parallel-to-grain shear because of the decreased flexural capacity of glulam beams; mid-span deflection,tensile and compressive strains of fatigue test beams increase gradually with the increase of fatigue load cycles. The amplitude of compressive strains is greater than that of tensile strains,but the strains distribution along section depth still complies with plane section assumption. After the larch glulam beams are subjected to fatigue load cycles,the flexural rigidity of beams decreases gradually and presents a linear degradation.The greater the stress level is,the more obviously the flexural stiffness reduces. Moreover,the stiffness degradation equations of larch glulam beams under different stress levels are given. The fatigue life of larch glulam beams is reduced with the increase of stress level. When the stress ratio is 0. 2 and stress level is 0. 55 times the static ultimate load,the fatigue cycles exceeds two million,which meets requirements of fatigue design of finite lifetime and indicates that the glulam beam has good fatigue properties. The mathematical expressions of S-N curves of larch glulam beam are obtained preliminarily by the linear regression analysis to experimental data.
出处
《建筑结构学报》
EI
CAS
CSCD
北大核心
2016年第10期27-35,共9页
Journal of Building Structures
基金
国际科技合作与交流专项(2014DFA53120)
国家自然科学基金项目(51578554)
