Railway Track & Structures - February 2009 - (Page 33) Figure 1. Track settlement at a bridge approach. What causes track settlement at bridge approaches and how can railroad engineering departments deal with the problem safely and efficiently? Track settlement at bridge approaches by Dave Davis, TTCI, and Don Plotkin, FRA O ver time, it is not uncommon for a dip to develop in the track off the end of a bridge—on the bridge approach, as shown in Figure 1 above. This dip, or bump, off the end of a bridge is often a roughriding spot and one that requires resurfacing at more frequent intervals than does the rest of the track. A common belief is that this dip in the track is caused by dynamic forces from wheel loads crossing an abrupt change in stiffness between the track on the bridge and the track off the bridge. Figure 2 shows one case of the measured difference in track stiffness (or track modulus) between the track on a ballast deck bridge and the track off the bridge. Track stiffness difference theory As normally constructed, track on a bridge is relatively stiff, supported by a rigid bridge structure and supporting piers (or bents) and abutments. Track off a bridge is supported by an earth subgrade, which permits more deflection when subjected to the same load. As a loaded wheel rolls over the end of a bridge and passes from the stiffer track on the bridge to the less stiff track off the bridge, an abrupt difference in vertical deflection occurs, which creates a bump in the track—a track surface deviation. Figure 3 illustrates this concept, showing a difference in deflection as wheels of a www.rtands.com Figure 2, top. Track stiffness change at a bridge approach. Measurements are averaged over a 30-foot moving window. Figure 3. Stiffness difference concept, illustrating an abrupt change in track modulus from 10,000 to 2,000 lbs./in./in. Railway Track & Structures February 2009 33 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 Railway Track & Structures - February 2009 - Railway Track and Structures - February 2009 (Page Cover1) Railway Track & Structures - February 2009 - Railway Track and Structures - February 2009 (Page Cover2) Railway Track & Structures - February 2009 - Contents (Page 1) Railway Track & Structures - February 2009 - Contents (Page 2) Railway Track & Structures - February 2009 - On Track (Page 3) Railway Track & Structures - February 2009 - Industry Today (Page 4) Railway Track & Structures - February 2009 - Industry Today (Page 5) Railway Track & Structures - February 2009 - Industry Today (Page 6) Railway Track & Structures - February 2009 - Supplier News (Page 7) Railway Track & Structures - February 2009 - AREMA News (Page 8) Railway Track & Structures - February 2009 - AREMA News (Page 9) Railway Track & Structures - February 2009 - AREMA News (Page 10) Railway Track & Structures - February 2009 - AREMA News (Page 11) Railway Track & Structures - February 2009 - AREMA News (Page 12) Railway Track & Structures - February 2009 - AREMA News (Page 13) Railway Track & Structures - February 2009 - AREMA News (Page 14) Railway Track & Structures - February 2009 - AREMA News (Page 15) Railway Track & Structures - February 2009 - NRC News (Page 16) Railway Track & Structures - February 2009 - TTCI R&D (Page 17) Railway Track & Structures - February 2009 - TTCI R&D (Page 18) Railway Track & Structures - February 2009 - TTCI R&D (Page 19) Railway Track & Structures - February 2009 - TTCI R&D (Page 20) Railway Track & Structures - February 2009 - TTCI R&D (Page 21) Railway Track & Structures - February 2009 - TTCI R&D (Page 22) Railway Track & Structures - February 2009 - Railroads Stepping Up Use of Technology to Locate Rail Flaws (Page 23) Railway Track & Structures - February 2009 - Railroads Stepping Up Use of Technology to Locate Rail Flaws (Page 24) Railway Track & Structures - February 2009 - Railroads Stepping Up Use of Technology to Locate Rail Flaws (Page 25) Railway Track & Structures - February 2009 - Railroads Stepping Up Use of Technology to Locate Rail Flaws (Page 26) Railway Track & Structures - February 2009 - Rail Lubrication Realizing Great Potential (Page 27) Railway Track & Structures - February 2009 - Rail Lubrication Realizing Great Potential (Page 28) Railway Track & Structures - February 2009 - Rail Lubrication Realizing Great Potential (Page 29) Railway Track & Structures - February 2009 - Rail Lubrication Realizing Great Potential (Page 30) Railway Track & Structures - February 2009 - Rail Lubrication Realizing Great Potential (Page 31) Railway Track & Structures - February 2009 - Rail Lubrication Realizing Great Potential (Page 32) Railway Track & Structures - February 2009 - M/W Challenges: Track Settlement at Bridge Approaches (Page 33) Railway Track & Structures - February 2009 - M/W Challenges: Track Settlement at Bridge Approaches (Page 34) Railway Track & Structures - February 2009 - M/W Challenges: Track Settlement at Bridge Approaches (Page 35) Railway Track & Structures - February 2009 - M/W Challenges: Track Settlement at Bridge Approaches (Page 36) Railway Track & Structures - February 2009 - M/W Challenges: Track Settlement at Bridge Approaches (Page 37) Railway Track & Structures - February 2009 - M/W Challenges: Track Settlement at Bridge Approaches (Page 38) Railway Track & Structures - February 2009 - Supplier Profiles (Page 39) Railway Track & Structures - February 2009 - People (Page 40) Railway Track & Structures - February 2009 - Calendar (Page 41) Railway Track & Structures - February 2009 - Sales Representatives (Page 42) Railway Track & Structures - February 2009 - Website Directory (Page 43) Railway Track & Structures - February 2009 - Professional Directory (Page 44) Railway Track & Structures - February 2009 - Classified Advertising (Page 45) Railway Track & Structures - February 2009 - Classified Advertising (Page 46) Railway Track & Structures - February 2009 - Classified Advertising (Page 47) Railway Track & Structures - February 2009 - Chicago Perspective (Page 48) Railway Track & Structures - February 2009 - Chicago Perspective (Page Cover3) Railway Track & Structures - February 2009 - Chicago Perspective (Page Cover4)
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