Technical Reports

Bridge Approaches and Track Stiffness

  • 01
  • Feb
  • 2008
AUTHOR: Donald Plotkin and David Davis
OFFICE: RPD
REPORT NUMBER: DOT/FRA/ORD-08/01
KEYWORDS: Bridge approach, track stiffness, track deflection, track modulus
ABSTRACT: Over time, it is not uncommon for a dip in the track to develop off the end of a bridge—on the bridge approach. This dip, or bump at the end of the bridge, is often a rough-riding spot and one that requires resurfacing at more frequent intervals than does the rest of the track. A commonly held belief is that this dip in the track is caused by dynamic forces resulting from wheel loads crossing an abrupt change in stiffness between the track on the bridge and the track off the bridge. A literature search found no documented field measurements to support this belief, only two modeling studies which predicted that the effect would be negligible. Five different methods were then employed to evaluate the potential for a track stiffness change to produce dynamic loads of practical significance. These methods ranged from the most technically sophisticated to the most basic. The results from all five pointed to the same conclusion—that changes in track stiffness at a bridge end have no practical effect on either track settlement or ride quality at a bridge approach.
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