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27. January 2020

Fatigue check for steel pipes with 5x10^6 load cycles permissible - TM 4-2019 published

Technical note regulates procedure according to EC

The DWA-A 161 is no longer to be used for the proof of fatigue strength. In future, jacking pipes made of steel can be verified in accordance with DIN EN 1993-1-9 (Eurocode 3: Design and construction of steel structures - Part 1-9: Fatigue).

In March 2014, the worksheet DWA-A 161 Static calculation of jacking pipes was released. As a rule, it requires the fatigue proof for jacking pipes crossing railways under not predominantly static loads at 1x10^8 load cycles.

For comparison: Other regulations in pipe construction require the "dynamic proof" for 2x10^6 cycles.

Since 2014, it has been common practice in pipe statics to verify fatigue against a 50-fold increase in the number of passes. The German Rail (DB) justified this, among other things, by the increased number of or generally longer freight trains with more axles.

This DB approach leads to the following phenomena in application:

  • Railway crossing with a reinforced concrete jacking pipe required significantly higher reinforcement. A pipe under load model 71 (LM71) with 1x10^8 load cycles required twice as much reinforcement as the UIC71 with 2x10^6 load cycles.
  • Railway crossing with a steel jacking pipe: Double the wall thickness. Pipes could no longer be manufactured or welded on site.

In the meantime, a commission of experts from the Federal Railway Authority (EBA), pipe manufacturers, engineering offices and university professors took up the matter. Steel pipes were reassessed. The boundary conditions have been published in TN: 4-2019-10152 I.NPF 2, which can be found as a PDF file at

Our software for pipe statics IngSoft EasyPipe completely implements TM 4-2019 from version 2.7.6.2. Summarized in key points:

  • Affected are
    • Jacking pipes according to worksheet DWA-A 161
    • Made of steel
    • Under Deutsche Bahn tracks
    • In the fatigue check
  • DWA-A 161 Section 9.4.5.3 Fatigue check for steel pipes with Table 22 is invalid.
  • Pipes in accordance with Ril 877 may be used under certain circumstances.
  • Notch case 71 (Kerbfall, KF 71) shall be applied.
  • Wall thickness ≤ 25 mm → characteristic limit stress: 52 N/mm²
  • Minimum cover for the reduction of the number of load cycles: 1.5 m
  • Lower axle loads and/or fewer overruns over the planned service life of 50 years are undesirable.

A calculation example for IngSoft EasyPipe with comparison and explanations can be found here:

We would be happy to discuss the changes to your specific project with you. Please contact us.

 

 

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