连续道床板拉伸开裂模型试验研究

为验证连续式无砟轨道温度裂缝型式和温度力荷载取值方法的正确性，针对目前高速铁路上普遍采用的连续道床板及底座板结构，考虑混凝土标号、配筋率及钢筋直径等影响连续无砟轨道设计的关键因素，设计了450 mm×80 mm×80 mm、中心配置直径10 mm带肋钢筋的混凝土构件，利用万能试验机进行张拉，模拟了连续道床板降温时的裂缝开展过程，测试了构件开裂前后的轴力及应力重分布情况.测试结果表明，张拉过程中，裂缝呈现出不稳定和稳定两种状态；裂缝出现后，钢筋与混凝土应力分布不均匀，裂缝位置处的钢筋应力增加至300 MPa以上；构件在全断面开裂后轴力会突然降低，开裂前后瞬间的轴力超过或达到了混凝土开裂轴力.对于采用C40混凝土的连续道床板，为保证结构的安全使用，应配置0.9%以上的钢筋使之满足强度要求，并将裂缝控制为不稳定裂缝状态，作为设计荷载之一的最大温度力荷载建议采用开裂后的轴力进行计算. 

Model Experiment Study of Continuous Track Slab Tension Cracks

To investigate the thermal cracking patterns in continuous ballastless track and verify the rationality of its thermal force determination method, several reinforced concrete specimens were built to model the continuous track slab and base plate which was widely used in China's high-speed railways. Taking into account the key design factors of the continuous track slab, such as concrete grade, reinforcement ratio, rebar diameter, etc., all the specimens were designed as 450 mm long, with an 80 mm×80 mm cross section; and a ribbed rebar of 10 mm diameter was deployed at the center of the cross section. The test specimens were tensioned using the universal testing machine to simulate the development of cracks under the tensile thermal force in the process of temperature drop. The axial force of the specimens and the stress distribution in concrete and reinforcement were recorded before and after cracking. The results show that cracks in specimens during the tensile process were in two states: unstable and stable. Reinforcement and concrete stress was extremely uneven distributed after cracks appear, and reinforcement stress increased to more than 300 MPa at the crack position. The axial force of the specimen would drop suddenly when cracks occurred to the whole section, and the axial force just before and after cracking was higher than or equal to the theoretical cracking axial force of the concrete. For continuous track slab using C40 concrete, more than 0.9% reinforcement should be configured to ensure the safety of the structure. Cracks in track slab should be controlled in unstable stage. As one of the design loads of the continuous track slab, the maximum thermal force load should be calculated using the axial tensile force after cracking.