Railway Track & Structures - February 2009 - (Page 38)

BRIDGE APPROACH SETTLING sons. Insufficient lateral confinement on a steep approach embankment, inadequate drainage or low-strength subgrade soil are just a few of these. So, any proposed solution will need to correctly address at least the main cause or combination of causes where more than one has a significant effect. In addition to where most of the settlement occurs within the track support, and the specific causes of the settlement, bridge approaches also differ in the relative amount of settlement incurred. Figure 10 shows an example of both common profiles. On the right, the approach has settled about the same amount as the adjacent track. On the left, the approach has settled more than the adjacent track. In such cases the additional settlement at the approach is sometimes quite pronounced nearest the bridge end. These two different types of profiles suggest the need for different solutions to control the settlement in each case. FRA will be working with TTCI and others throughout the rail industry to find effective and affordable ways to produce more durable track surface transitions at bridge approaches and at other locations where track construction changes. Acknowledgments Steve Chrismer of LTK Engineering Services conducted the general literature review. Stan Gurule of TTCI produced the computer modeling data showing vertical forces below the rail. Brian Whitten and Brent Selby of ENSCO provided the instrumented wheelset data from the Northeast Corridor. Their work is gratefully acknowledged. The authors also acknowledge Amtrak for granting permission to use data from the Northeast Corridor. References 1. Plo tk in , D., and D av i s, D . (2008). Bridge Approaches and Track Stiffness. Washington, D.C. Federal Railroad Administration. Technical Report No. DOT/FRA/ ORD-08/ 2. Hay, W. (1982). “Railroad Engineering.” John Wiley & Sons, New York. pp. 247-252. 3. Recent data from instrumented wheelsets and wheel load impact detectors suggest that good wheels (not out-of-round or with flat spots) on good track with welded rail and traveling near the highest speed allowable for that FRA track class commonly produce a dynamic load about 15 percent higher than their static load. For a 286,000-lb car, the static wheel load is 36,000 lbs and the total dynamic load would be 1.15 x 36,000, or about 41,500 lbs. 4. Briaud, J. L., Nicks, J. E., and Smith, B. J. (December. 2006). “The Bump at the End of the Railway Bridge.” Texas A&M University. 5. Briaud, J. L., and Hoffman, S. B. (1997). “Settlement of Bridge Approaches.” Trans. Research Board, National Cooperative Highway Research Program, Synthesis of Highway Practice 234. 6. Hoppe, E. J. (1999). “Guidelines for the Use, Design, and Construction of Bridge Approach Slabs.” Virginia Transportation Research Council, Charlottesville, Va, VTRC 00-04. 38 Railway Track & Structures February 2009 www.rtands.com http://www.fcmrail.com/ http://www.fcmrail.com/ http://www.rtands.com

Table of Contents Feed for the Digital Edition of Railway Track & Structures - February 2009

Railway Track and Structures - February 2009 Contents On Track Industry Today Supplier News AREMA News NRC News TTCI R&D Railroads Stepping Up Use of Technology to Locate Rail Flaws Rail Lubrication Realizing Great Potential M/W Challenges: Track Settlement at Bridge Approaches Supplier Profiles Products and Literature People Calendar Advertisers Index Sales Representatives Website Directory Professional Directory Classified Advertising Chicago Perspective

Railway Track & Structures - February 2009

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.