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（公法111-5）资助的。RAPID项目是为了利用一个独特的机会，为即将开始的现有行业测试项目增加基础研究的组成部分。通过利用交通技术中心公司（TTCI）在其加速服务测试设施（FAST）中计划的一个项目，该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土工材料的动力响应与列车交通动力激励的关系。特别是，动态响应将通过放置在测试部分的六个三轴压电加速度计来监测，每个部分一个。试验台由六个部分组成，在轨道道砟中有不同百分比的污垢（通过3/8“筛子）材料和施工中使用的领带类型。安装和测量的目的是记录重载列车通过时的加速度时程。利用功率谱密度（PSD），可以确定主频。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。主频的变化将与亚轨道土工材料的材料特性的变化有关。基本理论是，随着材料刚度的变化，频率响应也将随之改变。将变化与基线条件进行比较将提供材料刚度变化的指示。研究项目的第二部分是对镇流器和拉杆结构进行平面应变箱试验。这是用同样的材料来建造测试部分。这些测试将用于评估测试截面的刚度和可变形性。研究的主要目的是确定固有频率的变化是否与子轨道材料的维护需求相关，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，这些物理表现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全新的方法，在自动化和连续的过程中评估镇流器，从而减少由镇流器降解引起的事故数量。

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.