RAPID: Spectral Analysis of Sub-Track Accelerations Subjected to Long Term Heavy Axle Load Conditions

该奖项是根据2009年《美国复苏和再投资法案》(Public Law 111-5)资助的。这一快速奖项是为了利用一个独特的机会，在即将开始的现有行业测试计划中增加基础研究部分。通过利用运输技术中心公司(TTCI)在其加速服务测试设施(FAST)计划的一个项目，这项研究可以作为一个独立的研究项目，以其成本的一小部分完成。与工业界的密切合作也增加了技术转让的机会。研究小组将研究轨道下岩土材料对列车交通引起的动态激励的动态响应之间的关系。特别是，动态响应将由放置在测试部分中的六个三轴压电式加速度计监测，每个部分一个。试验台由六个部分组成，在轨道道床中的污垢百分比(通过3/8“筛网)材料和施工中使用的绑带类型有不同的变化。安装和测量的目的是记录重轴列车通过时的加速度时程。利用功率谱密度(PSD)可以识别出主要频率。通过记录随时间的加速时间历史，可以将PSD与基线PSD进行比较。主要频率的变化将与子轨道岩土材料的材料行为的变化有关。基本理论是，随着材料刚度的变化，频率响应也会随之变化。将这一变化与基线条件进行比较，将提供材料硬度变化的指示。研究项目的第二部分是对道碴和系杆结构进行平面应变箱试验。这将使用用于建造测试部分的相同材料来完成。这些试验将被用来评估试验区段的刚度和变形能力。研究的主要目标是确定固有频率的变化是否可以与子轨材料的维护需求相关联，并提供一种在沉降和挠度的物理表现之前预测维护需求的方法，而沉降和挠度可以通过传统方法测量。如果成功，这项研究可能会带来一种在自动化和连续过程中评估镇流器的全新方法，从而减少因镇流器退化而导致的事故数量。

This award is funded under the American Recovery and Reinvestment Act of 2009(Public Law 111-5).This RAPID award was made to take advantage of a unique opportunity to add a basic research component to an existing industry testing program that is about to begin. By taking advantage of a project being planned by the Transportation Technology Center, Inc. (TTCI) at their Facility for Accelerated Service Testing (FAST), this research can be accomplished for a small fraction of its costs as a stand-alone research project. The close collaboration with industry also enhances the opportunities for technology transfer. The research team will investigate the relationship between the dynamic response of sub-track geo-materials to dynamic excitation resulting from train traffic. In particular, the dynamic response will be monitored by six triaxial piezoelectric accelerometers placed in a test section, one in each subsection. The test bed consists of six sections with variations in percent fouling (passing 3/8" sieve) material in the track ballast and the type of tie used in the construction. The purpose of the installation and measurement is to record the acceleration time history when a heavy axle load (HAL) train passes over. Using the power spectral density (PSD), predominant frequencies can be identified. By recording the acceleration time histories over time, the PSD can be compared with the baseline PSD. Changes in the predominant frequencies will relate to the changes in the material behavior of the sub-track geo-materials. The fundamental theory is that as material stiffness changes, the frequency response will also subsequently change. Comparing the change to a baseline conditions would provide an indication of changes in material stiffness. A second part of the research project is to conduct plane strain box tests on the ballast and tie configuration. This is to be done with the same materials used to construct the test section. These tests will be used to evaluate stiffness and deformability of the test section.The primary objective of the research is to determine if the changes in natural frequency can be correlated to the need for maintenance of the sub-track material and provide a means to predict the need for maintenance prior to the physical manifestation of settlement and deflection that can be measured by conventional means. If successful, this research could lead to a fundamentally new method of evaluating ballast in an automated and continuous process, thereby reducing the number of accidents resulting from ballast degradation.