This article presents findings from projects conducted by the Transportation Technology Center, Inc. concerning track maintenance problems associated with bridge approaches of railway track. Field tests for determining root causes of, and evaluating remedies for, such problems were conducted at the Facility for Accelerated Service Testing near Pueblo, Colorado, and at a number of revenue service sites in the United States. Investigations covered ballast deck concrete bridges with concrete ties, open deck steel bridges with wood ties, and their approaches.
This paper describes an effort to understand the types of railway bridge irregularities that cause service interruptions and to use this information to evaluate the need to develop bridge monitoring systems. Existing monitoring systems and other mitigation techniques were also considered. The study described in this paper considered the frequency and severity of such service interruptions and estimated that the annual risk exposure from bridge irregularities cost tens of millions of dollars; the estimate did not include the cost of consequent train delays. The analysis showed that the largest contributors to irregularities were scour and other bridge hydraulic issues. The next most frequent causes were strikes from marine traffic and strikes from highway traffic. Other large contributors were damage by derailed trains, fire, failed structural members, and movable bridge irregularities. The number of train delays from structural failures was minimal, primarily because of effective inspection and maintenance procedures implemented by North American railroads. A risk control matrix was developed to match potential irregularities with existing control measures and to identify those areas in which additional controls might be warranted. Results suggested that track displacement detectors, tilt monitors, and midspan displacement monitors should undergo additional investigation. Bridge inspection is an effective way to avert many potential losses and presents an opportunity for railway workers to detect defects as well. Workers trained to recognize bridge-related irregularities may be a cost-effective way to reduce losses from bridge service interruptions.
Railway bridges are critical in the transportation network and vital to the profitability of the industry. Thousands of U.S. bridge spans of more than 50 years of age are still in service. Transportation Technology Center, Inc.’s current work under the Association of American Railroads Strategic Research Initiatives Program on bridge life extension focuses on the effects of increased axle loads, on extending the safe service life of existing steel bridge spans, and on onboard inspection of bridge structural integrity. The program includes various tests at the Bridge Deflection Test Facility (BDTF) at the Transportation Technology Center, Pueblo, Colorado, as well as vehicle–track–bridge interaction modeling. This paper presents simulation and test results of a freight car and locomotive running on a railway bridge located at the BDTF. Simulation and test results of an onboard system installed on an instrumented freight car indicated that it is a useful tool for identifying some bridge condition issues. The BDTF provides adjustable bridge strength and geometry conditions. Various tests were conducted on the BDTF to investigate the potential for using onboard technology to detect bridge impairment or changes in bridge behavior. Test results were used to validate the NUCARS three-layer track model of the BDTF. Experimental and analytical case studies were conducted to develop onboard systems for dynamic inspection of bridges under varying loads.
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