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Joseph LoPresti and Semih Kalay
Traffic Growth and Heavy Axle Load Research at FAST
North American railroads have experienced significant traffic growth over the past 20 years. Some studies have projected that rail freight traffic will double in the next 20 years. Railroads are continuing to develop cost-effective ways to safely increase capacity. One strategy that North American railroads have used is to raise the allowable axle loads for freight cars. Research funded by the Association of American Railroads (AAR) and the industry has been helping minimize the adverse effects of increased axle loads.
Since 1988, testing at Facility for Accelerated Service Testing (FAST), Pueblo, Colo., has been a mainstay in the AAR heavy axle load research program. Tests are updated at the direction of railroad committees to assure that the program meets the changing needs of the industry. In the past year, there have been significant changes and additions to FAST.
Figure 1 shows a different train that is now operating at FAST, which should enhance safety, increase productivity, and reduce maintenance costs. The Union Pacific (UP) Railroad provided 110 current generation 315,000-pound gross rail load aluminum coal cars for use. Norfolk Southern, UP, and CSX provided the use of modern, high-horsepower, fuel-efficient EMD SD 70M and SD 70 MAC locomotives. Fuel consumption has been reduced by about 20 percent, and the new locomotives facilitate unmanned train operations that are now standard practice at FAST.
A riveted steel bridge span built in 1912 replaced a 40-year-old welded steel span. The riveted span is typical of hundreds of spans currently in service in North America. Testing at FAST will provide a better understanding of how these spans react to heavy axle loads, which will be valuable as railroads make decisions on upgrading or replacing them to accommodate heavier cars. Strain data collected at FAST can be used in fatigue models to estimate remaining bridge life.
In 2008, U.S. railroads spent over $3 billion to renew and maintain the rails, which are their most valuable track asset. Accelerated testing in the controlled and well-maintained environment at FAST plays an important role in finding ways to increase the service life and decrease the life-cycle costs of modern rail steels. In 2010, over 1/3 of a mile of new state-of-the art rail was installed in two 5-degree curves at FAST for performance evaluation under heavy axle loads.
Premium rails developed to provide better wear and rolling contact fatigue (RCF) resistance were installed in a 5-degree nonlubricated curve at FAST. Rail manufacturers from North America, Europe, and Asia provided the eight high-hardness (413 HB average) premium rails being tested. An experimental rail developed by Transportation Technology Center, Inc. and the University of Pittsburgh and produced by voestalpine AG was added to the test later. After 110 MGT of heavy axle load traffic, all rail types are showing shallow RCF.
Intermediate-hardness (340 HB average) rails from several manufacturers were installed in a lubricated 5-degree curve at FAST. These rails are intended to provide satisfactory performance under moderately demanding conditions, at a lower cost than premium rail. All of the intermediate-hardness rails are showing shallow RCF. There is less wear on the intermediate-hardness rails in the lubricated curve than on the premium rails in the nonlubricated curve, which demonstrates the effectiveness of gage face lubrication in reducing rail wear.
Heavier, faster, and longer trains have created the need for innovative types of track structures. Heavy-duty concrete ties (Figure 3) and state-of-the practice conventional concrete ties were installed at FAST as part of a test to evaluate improved strength track. Goals are to reduce surfacing requirements, increase resistance to track buckling, and reduce the need for track maintenance. After 160 MGT of testing, the heavy-duty concrete tie track is very stable, but some of the ties have developed minor cracks. Modifications are being considered. Ballast movement is affected by the tie type.
Reducing the dynamic loads heavier cars produce is another way to improve track performance. Flange bearing turnout frogs have been installed and tested at FAST to evaluate dynamic performance and wear. Test results show a 70-percent reduction in dynamic forces on the mainline side of the turnout for the flange bearing turnout frogs compared to conventional turnout frogs.
Another concept being considered is a continuous (mainline) running surface switch point based on earlier vertical switch designs. It would eliminate cars transitioning from switch point to stock rail and vice versa when traversing the mainline side of a turnout. Set-out track where diverging traffic is extremely limited is one example where it could be used. Individual components that could become parts of a prototype switch are being tested at FAST.
After 100 MGT, no welds have been removed in second generation thermite, head-repair welds installed at FAST. The welds are improvements based on earlier tests at FAST. For comparison, approximately 40 percent of the earlier head-repair welds had been removed by 100 MGT. In summer 2010, welds were installed in rail directly over concrete ties. Also, repair welds were recently installed over electric flash butt welds.
An in-track electric flash butt welder donated by UP is changing maintenance rail welding at FAST. It will allow the welder to reduce the number of thermite welds in track, which should reduce the number of service failures. Although thermite welds are relatively easy and inexpensive to install, they typically have lives substantially shorter than rail.
In late 2010, a new, 42-foot hybrid composite concrete (HCB) bridge span will be installed and tested at FAST. It will replace a 42-foot high-strength concrete span. The HCB span is a tied-arch design that reduces the weight of a span and is capable of supporting 315,000-pound cars.
A similar 30-foot HCB bridge span at FAST was replaced with a 30-foot box-girder span. After 240 MGT, the HCB span has performed as expected, with deflections similar to reinforced concrete.
Other concrete bridge spans being tested at FAST are performing well through 900 MGT.
In summer 2010, the track and ballast were removed from one of the bridges and the ballast depth was reduced from 12 to 8 inches for the first of a series of tests on the effects of ballast depth. Earlier tests showed that using tie materials and ballast mats to modify track modulus is an effective method of lowering the stress state and reducing track maintenance requirements.
Hardwood, softwood, and concrete ties being tested at FAST have accumulated 255 MGT of heavy axle load traffic. Gage restraint and gage widening are being evaluated. The effects of heavy axle loads on screw spikes, insulators, and other components continue to be monitored. Component failures have been documented and components were replaced when necessary.
Unmanned trains operate regularly at FAST. The automated system, which was moved to one of the new locomotives, is activated by the test controller and is then in control of the train. The test controller can also stop the train remotely in an emergency.