Oh gosh do you live there? Remember all the chest beating and tearing of robes that had to take place to get that built even though it was private money? Oy!
Have flown into and out of MCI on two occasions - it was dry weather both times.
One thing I will say - if you have a rental car, don’t expect to find a gas station to fill it up before you return it at MCI.
My obsevation of trackside physics is that I see the track and ties bounce up and down under the weght of the cars so I assumed that a type of floating displacement is taking effect here and that the stone ballast pushes up against the ties. Has the Ballast not been there the weight of the train would push the tracks deeper and deeper into the dirt and be unusable. The original builders and contracter that built the Union Pacific build the road bed so shoddly that most of the railroad had to be rebuilt after the Golden Spike.
So maybe the question is this: The weight of the cars presses the track down tight against the load bearing ballast. So why does the track rebound and rise up from the load bearing ballast when the cars are not passing over the track? What causes the track to levitate when there is no car loading upon the track?
That would be an indication that the track structure is not fully supported by the ballast. Think of placing a long board on two bricks at the ends - if you step in the middle, the board will sag, at least until it reaches the floor.
The answer would be to tamp/surface the roadbed so the track structure is fully supported.
This could be an indication that there are problems with the subroadbed - soft spots, etc.
As rigid as one might think 132 pound rail would be, simply watching a CWR replacement operation will show that it is, indeed, quite flexible.
Primarily elasticity in the wood ties, most likely in the large bearing area between the bottom of the tie and all the points where it locks into the ballast. Even well-laid track with ‘breathe’ as weight comes on and passes off a particular section of ties.
It doesn’t “levitate” under normal conditions, due in part to colossal damping factor in the tie material. It just comes to level line and surface, with normal relaxation in the ties, again mostly in the large aggregate contact area between tie and ballast. "Rebound’ would only be if there were substantial subsidence, for example over a ‘wet spot’ in the ballast, where the weight of the train produces higher vertical acceleration and any resultant, and thence higher compression in the ties.
You’ll notice that concrete-tie track ‘breathes’ less when properly installed, but shock absorption and reflected impact motion may cause it to move too.
If there were much ‘spring’ in the rail, the fixation would either accommodate or, as in the case of Pandrol clips, deform elastically. You can set up nodes of vibration in CWR, but that is not ‘spring levitation’ as a restoring force to loading, and it will stop reasonably promptly as long as a train is not actively ‘pushing’ it. Note also the effect of rail anchors in restraining longitudinal force along the rail.
What I have observed is track compressing downward then rebounding upward under the passage of each truck. It appears to be a natural, normal response, although it can become abnormal in the case of an actual soft spot from a local defect that is compressing and rebounding more than average.
There would be no compression and rebound in clean, aggregate rock ballast, but there may be some in the subgrade. The empty track has its natural elevation repose. Adding equipment weight on a truck compresses the track downward into the combination of imperfect ballast and subgrade.
The weight pressing down on the track at each truck causes a lever reaction that raises the track, primarily between two trucks of each car. In this cycling lever reaction under a passing train, the rebound reaction to the down-pressure raises the track higher than its normal elevation repose.
So the up and down movements are both outside of the natural repose elevation. So overall, the weight of the train applied at each truck compresses the track down, and in response, it lifts the track higher than normal between trucks. Then when the train passes, the track comes to rest in its natural elevation repose approximately midway between the high and low elevations during the incremental loading and unload
Rock is more elastic than you might think, so there would be some compression and rebound in rock ballast.
Bucky is in over his head. He also cannot handle the idea of simply supported beam deflection being part of what one sees.
I don’t doubt that rock generally can be compressed and then rebound when the compression is released. However, I would not expect that phenomena to play a practical role in the cycle of rising and falling track associated with the passage of a train. That role would be every rock in the ballast shrinking in volume when the wheel loading passes, and then expanding back to its normal size when the loading is reduced.
What I have described above works like this: The train lowers the track elevation to below normal, as each truck passes, and th
What you have described has the plausibility of your average Bugs Bunny cartoon. As the train rolls over a soft spot, the track depress under the weight. You can’t even see that track depress. What you see is the motion of the tie depressing. When the train passes that spot, the track rises back up to where it started. To suggest that it is bouncing higher than when it had no load is just silly. Do you really think your human eye could even see that, if it did happen?
Yes, but…
Think for a moment about a typical two-truck railcar sitting on a piece of track. The areas under the trucks are depressed by the weight, bending the rail into a slight curve. At no point is this curve ‘above’ resting level, as you’ll see if you approximate the bending moments, say every foot or so if you’re not into calculus.
Put this into motion, and the track ‘between’ trucks of a moving train always goes down to spread the load. If a piece of rail had bridge hinges at the quarter points in the ‘span’ between trucks, then you’d see a deflection upward at midspan with the ends loaded. But that is NOT fully the case even in poorly maintained track, and it’s arguable that it was a factor even in the days of chaired fishbelly rail on granite plinths and relatively short cars.
Now, if you had a severe soft spot, perhaps combined with a track-tuning issue like a crossing or bridge transition, you might see lifting in part of the span between the effective ‘hinge point’ ahead of the truck in the soft spot and the point where the rail is ‘pinned’ under the next truck ahead. Places like this probably exist, but they are anomalous and have to be explained with different geometry and physical explanation.
Something else that might be added is that there are ‘some’ track transitions that produce significant unloading of suspension going over them. There was one such at the east end of the Collierville passing siding, I believe at one of the last grade crossings,
Actually, yes. Although I think Euclid’s use of the term “bounce” is inaccurate.
We have molten sulphur trains come through here. And there is a neglected spot on the former PRR where the track comes off a bridge. when the trailing bogey on those sulphur cars hit that soft spot, it actually bows the rail between bogeys sufficiently that the ties attached to the rails are lifted a good 6" off the road bed.
It is a violent movement, and repeats between every car. So an uninformed observer could rationalize that the track is “bouncing”…in a narrow field of view it would look that way.
But I think it’s more the result of lever action, when the trailing truck comes off the bridge abutment and sinks into the soft spot.
Theorizing, but the weight of the lead bogey pinning the track to the roadbed might be a factor in making the raised track appear to “bounce” back to the ground.
But it does happen.
What makes it especially noticable is that not all ties are still attached to the rail. So when some ties go up with the rail, while others do not…it is a real attention getter.
I would theorize there is a much more subtle but interesting efffect on the ‘lead bogie’ – its wheelset angular speed might change very slightly during the period the rail is lifting and falling. The ‘rear’ wheelset in the three-piece truck is pinning the ‘beam’ of the rail as the following truck goes into the hole, but since both the wheelset and the three-piece sideframe can rotate, it is a near-frictionless ‘pinning’ and if the sideframe doesn’t ‘articulate’ as the beam deflects, you’d see the wheel rotation very slightly change.
Although I’d bet it would be a comparatively small change, impossible to measure without sensitive encoding…
What’s more interesting to consider is what makes the action so violent.
(Incidentally ‘bogey’ is an enemy aircraft or radar indication. The term for a railroad truck ought to be ‘bogie’.)
When you witness the still-attached ties rise with the rails, while the derelict ties lay flat on the roadbed, one doesn’t have to be a weatherman to know which way the wind blows. [st][8o|][:o)]
So sayeth the boogieman. 
I never said the track “bounces” upward when it returns to normal after being depressed. Murphy Siding used that description for what I meant.
I did use the term “rebound” as meaning the opposite of being compressed. But this simply refers to the return of the track level to its normal elevation repose when no train is passing. Compress and rebound are the terms used to define elasticity of material. Materials that can be compressed under load and rebound when the load is removed are said to have “memory,” that is that they remember their original uncompressed size, and thus return to that size when the pressure is removed. It is the action of a spring.
But anyway, to the point:
This thread is making me think of the ND&W
I should have realized that…I’m sorry. [A]
Perhaps with twin fulcrums? Additionally, it’s probably worth noting there are another pair of heavily loaded axles immediately beyond each coupler.
There is a magic speed for trains that can cause derailments which is about 15 miles per hour. This effect is caused “Harmonic Rock” happens most often on jointed stick rail is poorly maintained track is seasonal climates. quote from the WAYBACK machine from 2004-This isn’t going to be the most scientific explanation. Derailments can happen due to harmonic rocking of cars. This generally happens at speeds between approximately 12 and 25 miles per hour on stick (jointed) rail. Cars at that speed tend to rock back and forth as it moves down the line over the offset rail joints. The heavy weight of the cars, speed and type of track all contribute to the amplification of the rocking that eventually results in wheels leaving the track.
I understand that under certain conditions this effect can be felt at higher speeds but the speed range above is the greatest risk.