Testing rail joints for moveable bridges: moveable railroad bridges in Colorado? Not exactly - Ttci R&D

Railway Track and Structures, Sept, 2003 by Charity Sasaoka, David Davis, Duane Otter, Brian Doe

Where railroads and navigable waterways meet, the railroad often crosses on a moveable bridge. Moveable-bridge configurations include vertical lift spans, swing spans and bascule spans that raise, rotate horizontally of rotate vertically about one end to provide passage for ships. Special rail joints are required at each end of the bridge spans.

The pair of such special rail joints tested at Transportation Technology Center's Facility for Accelerated Service Testing, Pueblo, Colo., was comprised of two separate pieces of explosion hardened manganese steel and was designed specifically for bascule and vertical lift bridges.

After accumulating 54 million gross tons of 39-ton heavy-axle-load traffic, two-piece austenitic manganese steel casting rail joints for moveable bridges were removed from service due to maintenance issues. The following observations were made during the test:

* AMS easting joints had similar dynamic vertical loads to a typical mechanical rail joint as measured by instrumented wheelsets operated at 30 mph to 40 mph over the joints.

* Vertical movement of the joints caused the base-plate fasteners to fatigue.

* Approximately two-thirds of the coach screws used to fasten the base plate to the tie worked loose or broke.

* Some of the coach screws began to pull through the plate, enlarging and deforming the fastener holes.

* Several of the fastener base blocks used to hold the casting/rail to the plate had broken welds.

* Several of the elastic fasteners holding the casting to the plate failed under dynamic impact loads.

* AMS casting joint guards were subjected to high lateral loading, approximately 20 kips at 40 mph, due to trucks that did not straighten out and re-center on the rails in the short tangents before the joints. The high lateral loads likely contributed to the failure of the coach screws and other components.

* Line and surface of the joints deteriorated. Once the plate-to-timber fasteners began to fail, the AMS casting joints began to move laterally. Steel bars were placed on both sides of the plates to restrain them laterally, while allowing some vertical movement.

* The AMS casting special bridge rail joints had a shorter life under 39-ton axle loads than in revenue service under lighter axle loads.

* The joints were removed after 54 mgt of 39-ton axle loads of HAL traffic due to maintenance issues.

Previous evaluations of other types of special track work under 39-ton axle loads at FAST have shown a significant foreshortening of service life as compared to revenue-service conditions. (1)

The effect is greatest at high-angle frogs, where the largest impacts occur. Service life reductions of 25 to 50 percent and 50 to 90 percent were seen in low-angle (turnout) frogs and in high-angle crossing diamonds, respectively.

These special rail joints for moveable bridges are more like low-angle frogs in that, theoretically, the nominal profile wheel is always supported as it transfers from one rail to another. However impacts do routinely occur in turnout frogs and in these joints.

The objectives of this evaluation a FAST are to determine the effects of heavy axle loads on joint performance and to assist the industry in developing improved performance designs.

In turnout frog tests at FAST, initial evaluations of frogs originally designed for 33-ton axle loads have helped the industry develop improved performance designs for today's heavier axle loads. Railroads and suppliers have been able to significantly improve the performance of turnout frogs under increasing wheel loads.

Test and results

Two-piece AMS casting joints were installed and tested on the High Tonnage Loop at FAST. The joint consisted of two separate pieces of explosion-hardened manganese. Each piece was fastened to a base plate with elastic fasteners. The base plate was then fastened to the ties. One side of the joint was fixed (point side) and the other side was the moveable lift side. These AMS casting joints are designed specifically for bascule and vertical lift bridges (Figure 1).

[FIGURE 1 OMITTED]

The test train at FAST typically has 70 cars with 39-ton axle loads. HAL traffic runs in both directions with the number of cycles and tonnage documented. During testing, approximately four mgt of traffic ran over the joints each week. The AMS casting joints were installed in Section Five on an open-deck test bridge consisting of two steel deck plate girder spans. The longer span is 65 feet long and 69.25 inches deep. The other span is 55 feet, six inches long and 63 inches deep. The bridge is in the middle of a 210-foot-long tangent of Section Five, which has spirals and curves at each end.

The joints were installed between the two spans on the bridge. The fixed side of the joints was on the longer bridge span and the lift side was on the shorter bridge span. The two-piece AMS casting joints were installed to the manufacturer's specification of a four-inch gap at the base plate.

The AMS casting joints accumulated 54 mgt before being removed for increased maintenance demands. Approximately two-thirds of the coach screws used to fasten the plate to the tie worked loose or broke. Some of the fasteners began to pull through the plate, enlarging and deforming the fastener holes. Once these fasteners began to fail, the joints began to move laterally. Steel bars were placed on both sides of the plate restraining the joints laterally (Figure 1). The joints were still allowed to move vertically.