疲劳荷载后重载铁路桥梁剩余静载承载力试验研究

Experimental Study on Post-cyclic-loading Residual Static Bearing Capacity of Heavy-haul Railway Bridges

基于应变和振幅的疲劳试验实时测试系统，通过10片1/6缩尺模型梁疲劳试验，研究重载铁路桥梁疲劳后静载破坏形态以及振幅、刚度、非预应力筋和预应力筋应变、混凝土应变随反复荷载次数的变化规律。研究表明：重载铁路32 m预应力混凝土梁疲劳后剩余静载承载力演变呈现“Z”字形三折线的3个阶段，即基本不变阶段、直线下降阶段和压弯失稳破坏阶段。第一阶段，疲劳后试件静载破坏形态与普通静载破坏形态相同，试件静载承载力基本保持不变；第二阶段，试件静载承载力直线下降，直至压弯失稳破坏，最终梁的剩余静载承载力降至原有承载力的50％～60％，主要由预应力筋提供。与普通静载破坏试验相比，疲劳后静载破坏试验不同的地方主要表现在混凝土、梁底普通钢筋和预应力筋等材料的应力-应变本构关系上，受压区混凝土残余应变不断增加，变形模量降低了20％～30％，普通钢筋和预应力筋残余应变也明显增加，但弹性模量和屈服强度（预应力筋极限强度）基本不变。

A real-time railway bridge fatigue test system was built for measurement of beam strains and vibration amplitudes .The fatigue test of a total of 10 1/6 reduced-scale PC model beams of heavy-haul railway bridges was made to study the development of static and post-cyclic-loading failure patterns and the changing law of vertical beam vibration amplitudes ,stiffness ,strains of non-prestressed and prestressed reinforcing bars and concrete strains with the frequency of repeated cyclic loading .Test results indicate as follows ：Evolution of the post-cyclic-loading residual static bearing capacity of 32m-span PC beams of heavy-haul railway bridges is fea-tured by the Z-shaped curve ,w hich undergoes three stages ,i .e .,the basically unchanging stage ,the straight-line falling stage and the bending failure stage .In the first stage ,the post-cyclic-loading static failure pattern is the same with the ordinary failure pattern of a specimen under static loads ,the static bearing capacity of the specimen remains basically unchanged .In the second stage ,the static bearing capacity of the specimen declines in the straight-line manner until buckled to failure and the residual static bearing capacity is reduced to 50% ~60% of the original bearing capacity ,which is provided largely by prestressed tendons .In comparison with the ordinary static failure tests ,the difference of the post-cyclic-loading static failure tests largely lies in the consti-tutive stress-strain relationship of the materials of concrete ,ordinary beam-bottom bars and prestresed bars and so on .After fatigue loading ,the residual concrete strains in the compression zone reep on going up and up and the deformation modulus gets dow n by 20% ~30% ;at the same time ,the residual strains of prestressed and non-prestressed steel bars increase obviously ,but the elastic modulus and yield strength （the ultimate strength of prestressing steel bar ） remain basically unchanged .