列车荷载对板式无砟轨道力学性能的影响分析

为研究无砟轨道混凝土在客、货车作用下的劣化规律，基于损伤力学概念，引入损伤变量对混凝土室内循环加载进行试验研究. 首先，建立钢轨-扣件-轨道板-CA砂浆层-底座板-地基有限元实体模型，获取试件试验等效应力水平，通过列车车速确定加载频率，然后确定合理的荷载组合模拟工况；其次，应用MTS加载系统对混凝土试件进行循环加载测试，利用无损检测系统测试了不同加载次数下混凝土的动弹性模量以及抗折强度；最后，将动弹性模量和抗折强度作为损伤变量，根据测试结果得到不同应力水平、加载频率作用对轨道板材料力学性能劣化规律的影响. 试验结果表明:在客货车荷载作用下，动弹性模量的损伤程度在加载200万次时约为抗折强度的损伤程度的2倍；应力水平一定时，加载频率越小，混凝土动弹性模量以及抗折强度的损伤程度越大，并且在10 Hz与15 Hz频率之间较明显；加载频率一定时，应力水平越大，混凝土动弹性模量以及抗折强度的损伤越严重，应力水平为0.7的混凝土在1 000次左右的加载循环加载下发生破坏；低速的客货车荷载会加快混凝土初期损伤，较高速度的客货车荷载会加速无砟轨道结构后期损伤的发展. 

Influence of Train Load on Mechanical Property of Prefabricated Slab Track

To study the influence of passenger and freight trains on the mechanical deterioration of concrete for slab track, the indoor cyclic loading test was conducted and described by using the damage variables based on damage mechanics. First, the FE model consisting of the rail, fastening, slab, CA mortar, roadbed, and subgrade was established. In this model, the reasonable load combination was determined contemplating the equivalent stress levels for the test specimens, as well as the loading frequencies for passing trains. Next, a cyclic loading test for concrete specimens was performed using a MTS loading system. Besides, the dynamic elastic module and the flexural strength for concretes at various loading cycles were calculated with the help of nondestructive testing system. Finally, taking the dynamic elastic modulus and the flexural strength as damage variables, the influences of different stress levels and loading frequencies on the deterioration of mechanical properties for the track slab were obtained. The results reveal that: under passenger or freight train load, the damage of dynamic modulus is about twice that of flexural strength at 2 million loading cycles. Keeping the stress level constant, the damage of dynamic modulus and flexural strength for concrete are greater with the lower loading frequency, especially between 10 Hz and 15 Hz. At a constant loading frequency, the damage of dynamic elastic modulus and flexural strength of concrete accelerates as the stress level increases. Concrete with a stress level of 0.7 is broken after about 1 000 loading cycles. Trains running at a lower speed would fasten the damage accumulation at the beginning of the deterioration process, while trains running at a higher speed would aggravate the consequential damage development.