Trackwork

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Asketh Ron:


>>

Thanks Abe, but wouldn't that have happened with jointed rail also? 
<<

I'm an operating guy, Ron, and not a track expert.  And I'm a philologist, not an engineer. So I speak from very limited knowledge.

Did you ever walk along "jointed track" in the Summertime, and notice how much the rail had "run" longitudinally in the tie plates, as indicated by the shiney abrasions of the spike heads on the base of the rails?  Each rail joint is in effect an "expansion joint" for taking up and relieving longitudinal stresses.  

That doesn't happen on track with welded rail.  The rail is anchored tightly to the ties with Woodring anchors or Pandrol clips, so that it will not "run" longitudinally.  When the expansive forces and pressures build up under these conditions, the rails move laterally and move the ties with them, which amounts to a "kink" in the track.

I remember some years ago, not long after ribbon rail became popular, that railroads were having numerous derailments on "buckled track," but most of them were happening about 15 or 20 car lengths behind the engine.

The DOT Pueblo facility fitted some welded rail track with all kinds of instrumentation and even took movies of track buckling in the hot sun.  What they discovered is that the sun heated the rail to the high-130's, and then the friction caused by a train moving over the track added a couple more degrees to the rail temperature and pushed the track over the critical temperature threshold, and the track buckled horizontally right under the train.  I recall seeing an AAR movie (viedeo ???) of these experiments in the late 1970s.

This showed the railroads why they were having "track buckled derailments," and the response was to "regulate" gobs of ballast against the ends of the ties on continuously welded track, to keep the ties from moving laterally.

That's a brakeman's explanation for you.  I'm sure a civil or mechanical engineer could put perfume and a ribbon my my pig of an explanation.

-- abram burnett
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