ABSTRACT
Nowadays, railway bridges are evaluated using the load rating method specified by the American Railway Engineering and Maintenance-Way Association (AREMA) (AREMA 2008). The load rating of existing bridges in terms of the carrying capacity is determined by computing the stresses based on an authentic record of the design, geometric details, materials, workmanship, and physical condition. The input data come from the most recent inspections performed on the target bridge. If deemed advisable, field determination of stresses shall be made and the results given due consideration in the final assignment of the structure’s carrying capacity. For a specific service the location and behavior under load shall be taken into account (AREMA 2010). Two levels of load rating are considered in AREMA Specifications: 1) normal and 2) maximum ratings. Normal rating considers the load level that can be carried during the expected life of the bridge while maximum rating considers the load level that can be carried at infrequent intervals with any applicable speed restrictions. The load rating method specified by AREMA uses the simple beam analysis to analyze the behavior of the structural member. While this simplification is warranted and provides a quick but conservative estimate of the load carrying capacity, the bridge behaves more like a structural system with complex interaction between different members and boundary conditions. Furthermore, since the input data for the load rating calculations come from the recent inspection reports, the most recent changes in section properties due to repairs or deterioration might not be included. Therefore, in order to obtain a more accurate evaluation of the bridge performance, a refined method needs to be developed.
In this paper, three load rating methods were applied and compared: (1) Traditional method based on AREMA Specifications, (2) Refined traditional method using data from field tests, (3) Load rating using data from field tests and FE modeling. In order to evaluate the efficiency and accuracy of these methods, a typical railway bridge was investigated using data from SHM and field-testing and FE modeling. Based on the load rating results, a refined traditional method was proposed to be used for the load rating of railway bridges especially those that are critical to rail network and freight services. Field testing equipment, instrumentation, and target bridges: (a) Strain gauges, (b) Junction nodes, (c) Main unit, (d) Laptop computer, (e) Helium neon Class II laser head, (f) Decoder unit, (g) Reflective target. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig161_1.jpg"/>
