I think I understand what you are getting at but could you clarify harmonic speed? [:)]
You referrenced it in the Amtrak tracks post.
Thanks
Mike
Mike-
Sorry, I almost missed your question with everything else that has been going on.
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.
LC
Limitedclear is correct. A bit in addition — the problem centers around the distance between truck centers and car height and the length of jointed rail.
This problem first surfaced with 50 foot Exceed Plate C cars. The distance between the center pin locations as measured along the center sill is almost exactly the same as the length of most jointed rail (30 to 36 feet, normally about 33). This caused the car to have both ends of the car drop into the sag at the rail joints at the same time. That would cause a significant rocking motion. Add to that the “moment of rock” is increased by the additional 12" to 18" of car height so instead of rocking just a bit, the cars can actually rock so much that they can turn over between (about) 13 and 18 MPH. If the cars are high enough and loaded up to the roof, that rollover speed can extend to 25 MPH as Limitedclear states. Even at 8 MPH, I have seen the “high side” wheels lift off the rail.
This problem is not limited to 50 foot Excess Plate C cars, but to most long and high cars (such as autoracks and 89 foot pigs), but the Superliner cars have a very high center of gravity and are also light cars, so with so much of their weight up high (the upper passenger deck) they can really rock. Don’t know of any that have turned over.
An interesting point – I have not noticed articulated double-stack cars to subject to harmonic rock to a great degree.
Guilford Must have a lot of problems with this since over 200+ miles of there lines are 15-25 mph on poorly mantained track,B&M
At one time, the CNW had a rule that one could not operate a freight train in the “critical speed” range, which they stated to be between 12-22 mph. The only exceptions were if the train was accelerating or braking through the range, or if the entire train was on welded rail.
And our suburban equipment (bi-level coaches) were prone to severe rocking when operating at coach yards speeds (5-10mph).
The few SD45’s that the CNW had, when operated on the Kenosha Subdivision, frequently felt as though they were going over, and that was between 25-30 mph on the poorly maintained track north of Kenosha.
Any rail equipment could be in danger of tipping if the speed and lengthand condition of the rail was just right.
You wouldn’t believe on a video I saw. A NS train heading to Buffalo from CN Niagara Falls Yard (Ontario) started to hunt on the wye from the Grimsby Sub to the Stamford Sub. He couldn’t have been going more than 10mph and still he was walking the track.
There were times when riding Amtrak a few years back, I experienced the rocking…know I realize what it is.
When I was living in central Illinois ('70s) I would fan the ICG from the platform of the Rantoul station. There were several times when I wondered if I should be thinking of an escape route, as the motive power was doing some serious rocking as it approached the station, particularly the northbounds, which track was right next to the platform.
For some reason, I always thought jointed rail was normally 39 feet…
Eric,
Articulated cars behave differently and are affected by the platforms in front and behind. I have a couple of HO TGV models with quite different articulation systems (in the model) and they both run really smoothly even on quite rough track.
But most articulated cars would be at least 50 feet or more long, (to carry 48 feet containers in the well), and the trucks are at the extreme ends, relatively much further apart than the 50 feet single cars. And each platform has side bearings both sides on the truck, so that should prevent a single platform starting a harmonic roll.
I just don’t want to think about double stack 9’6" high containers swaying from side to side on rough track! It’s enough to make you only take photos with a telephoto, or from bridges over the track.
Peter
Harmonic speed is a speed where resonant vibratory motion is excited in this case rigid body rocking. The cause of the rocking is the car passing over closely spaced joints in the track. Most U.S. track using jointed rail have stagered joints that are not placed opposite each other. Instead they are staggered so the joint in one rail is 19 1/2 feet away from the joint in the opposite rail.
Peter — just think of this – The situation of wheel lift I mentioned above, I was the telegrapher, standing out there on the platform, with those brand new EFCX Excess Plate C insulated box cars, loaded-full-visable-capacity (right to the ceiling of the car), rolling by at 8 MPH, wheel lift on the right, rock, wheel lift on the left, rock, wheel lift on the right, rock, wheel lift — you get the idea. Sometimes high enough to clear the flanges. Then comes the caboose to make the “hand-up”, and I have to get close enough that a car rocking could actually bump me.
And we call that the good old days.
Rudy
Fortunatly, not much track had the staggerg joints 1/2 way (15-18 feet) along the opposit rail. That situation causes the absolute worst rocking. The closer to being opposed (European standard) the less the rocking. European opposed joints cause a pitching motion rather than rocking.
Was an Operater on the B&O for one month while a bridge was being replaced in Hicksville, Ohio. Six feet max from everything.
kenneo, I know what you mean !
Eric,
I think I could cope with a box car rocking and get out of the way. It’s the thought of the upper container on a double stack breaking away during the roll that scares me! I’ve seen a yard after a 40’ container, single stacked, decided to swing out to 90 degrees to the car while passing under a semaphore signal bridge! They had about two weeks of pilotman operation and everything coming to a dead stand each end of town until they found the equipment to build a simpler replacement set of signals on four posts. Ironically, the station houses the CTC control for most of the 400 miles of line, they just never got the yard modernised. Nobody ever came to take what was left of the container away, either!
Peter
I have ridden cabooses with loaded 100-ton covered hoppers on the rear of the train, and from the cupola read the car number on the end of the third hopper ahead of the caboose.
No, I didn’t enjoy that trip.
Old Timer
Whatever speed I happen to be travelling at.
Gadzooks! That is an image that is absolutely hair-raising!
In the late 60’s with the advent of the so called ‘Hi-Cube’ Covered hoppers (4500 cu.ft. or greater) a number of derailments occured on terrirories with 6 degree or greater curvature with grain trains traveling between 10 & 25 MPH. At that time most main line track was laid in jointed rail. The standard jointed rail length is 39 feet, with staggered rail joints. The combination of the cars having a 45 foot truck center, and the nominal center distance between the wheels on a truck, caused the cars, with their high center of gravity, to develop a rocking couple that when operated between 10 & 25 MPH around 6 degree or greater curves would rock the cars right off the rail…of course 6 degree (which in the scheme of main line railroading, is a rather tight curve) curves are mostly found in mountainous territory where the minimium continuous speed of the locomotive comes into play (MCS for freight locomotives ranges from 9 MPH to 12 MPH in most cases). The cars and the restrictions created many train handling situations as loaded trains tried to pull up the hills.
The implementation of welded rail and a good surfacing operation after the installation of the welded rail caused most of the restrictions that were in place for the high-cube covered hoppers to be removed.
My dad managed a feed mill at the end of a branch that, at posted speeds, took a local 5.5 hours to make the run one end unless the train had one of his CH’s in it, and then it was a 10 MPH run for 110 miles. … And almost every train had at least 2. The crews loved it. The railroad did not. I just never could understand why[:D][yeah]
I’ve been in a similar situation watching the UP take its intermodal train from the Iowa Interstate yard to their yard in Council Bluffs. Standing on the platform of the old Rock Island depot in Council Bluffs I’d wonder how long before one of the rocking double stacks actually touches the roof of the depot. I think they finally fixed the problem with a little ballast and some track work. I don’t notice the rocking nearly as much anymore.