重载铁路桥梁疲劳变形和裂缝扩展规律研究

Study on fatigue deflection and crack propagation laws of heavy-haul railway bridges

按照"动静结合,以静制动"的试验方法,通过6片1/6缩尺模型梁疲劳试验,研究重载铁路桥梁疲劳变形和裂缝扩展规律。研究表明:重载铁路预应力混凝土桥梁疲劳开裂后的跨中挠度和裂缝扩展基本符合快速增长、稳定发展和急剧变化的"三阶段"发展规律;重载铁路预应力混凝土桥梁疲劳开裂后的跨中挠度可以按残余挠度和瞬时挠度进行计算;疲劳开裂后的裂缝不仅包括纯弯段内的正截面裂缝,还包括剪跨区内的弯剪斜裂缝和腹剪斜裂纹,前者主要出现在疲劳稳态阶段,后者主要出现在疲劳破坏阶段。根据试验结果,提出"损伤梁单元模型"和"经验公式拟合"两种跨中挠度计算方法,结果表明在疲劳稳态过程中,跨中挠度的放大系数在20%～30%左右,临近疲劳破坏时在80%～100%左右。此外,利用统计方法提出一个用疲劳循环次数比表征的增大系数,以此来考虑循环次数和疲劳寿命的影响,进而描述疲劳裂缝发展的"三阶段"规律,计算结果表明混合配筋合适的预应力混凝土梁发生梁底普通钢筋疲劳断裂破坏时,对应纯弯段最大主裂缝宽度约在0.50～0.55mm左右,该方法可以满足工程上的精度要求。

According to the test method of dynamic-static loading combination loading test controlled analysis, totally of 6 1/6-scale PC model beams on the heavy-haul railway were made and the mid-span fatigue deflection and crack propagation laws were studied. Test results indicate that the evolution of mid-span deflection and crack propagation with the cycle frequency of increasing fatigue of 32m-span PC beams on the heavy-haul railway exhibits as three stages, i. e. , the swift growth stage, the stable development stage and the abrupt change stage. After cracking, the mid-span deflection of the beam can be calculated by the superimposition of residual deflection and instantaneous deflection. The cracks include normal section cracks in the pure flexure part, the shear cracks in the flexure-shear part. The normal section crack appears in the stable stage of fatigue damage evolution while the shear crack doesn＇ t emerge until the failure stage. According to test results of fatigue deflection, the two computation methods, damage beam model and fitting formula, were proposed. The calculation results show that the computation results agree well with the test results and the deflection magnification factor is about 20% - 30% in the stable stage of fatigue damage evolution and while 80% - 100% near the end of fatigue failure. Finally, the intensification factor indicating maximum crack width of normal section is put forward by the statistical method, which was characterized by the fatigue cycle ratio of n/Nf and used to consider the effect of fatigue cycle number （n） and fatigue life （Nf） and describe the law of three stages of fatigue crack propagation. The calculation results indicate that the maximum normal section crack width of PC beams with right mixed-reinforcement on the heavy-haul railway is about 0. 50 - 0. 55mm at the moment of fatigue failure. The test data validates the proposed method is effective and can satisfy the needs of engineering.