Kinetic friction calculation for rail buffer stop 1

[Temporaryworks]

Hi,

I am a structural engineer designing a rail buffer stop to resist a force of 200kN @ 10kmph. The buffer stop works by small clamps at the bottom which are tensioned against the rail shoe to provide a known force (see attached sketch for an example). This known force can then be used to calculate the frictional force required to overcome the inertia i.e. static friction - this is very important for my structural steel design as this will determine the greatest force that will be applied to the structure.

At the point of sliding, the clamp will move with the train and dissipate the energy along the rail. The kinetic friction then takes over and the train strike energy gets dissapated as the clamp slides to a stop. I need to calculate the kinetic frictional co-efficient here because this will determine the distance over which it takes the train to stop after it has started sliding.

This is where I get a bit lost and am looking for help - how do I calulcate this kinetic friction reistance, plus the friction resistance would never be constant as the train is decelerating. My head is spinning - any advice?

Thanks in advance.

 

[RolMec]

This concerns railway material, there should imo be some specific standard to applicable frictional coefficients.
If there is not, then similar standards might help: FEM 2.132 / 2.133 give applicable statical and kinetical c.o.f.
This need to be approved by the authority concerned.
As friction is probabilistic, the big number of rail clamps shall allow for a sufficiently narrow range to be assumed for the c.o.f.'s

Regards

Roland Heilmann

 

[Compositepro]

Coefficient of friction is determined by testing. The suppliers of friction materials have the data.

 

[IRstuff]

Google is your friend:

https://www.researchgate.net/publication/319893402_FRICTION_BUFFER_STOP_DESIGN

http://www.railway-research.org/IMG/pdf/329.pdf

https://www.rawie.de/en/portfolio-item/special-friction-buffer-stop/

https://ojs.cvut.cz/ojs/index.php/APP/article/view/4441/4319

https://extranet.artc.com.au/docs/eng/track-civil/guidelines/track-civil/ETH-00-01.pdf

TTFN (ta ta for now)
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[handleman]

Sorry. Nothing you can do will stop a train travelling at 10,000 miles per hour.

 

[dvd]

It is really not a 200 kN force at 10 kmph - it is 200 kN x stopping distance + 1/2mv^2. The stop has to absorb all of the energy of the moving train. The frictional energy the rail clamp absorbs is rail clamping force x coefficient of friction x stopping distance. Here is a picture of one that I saw that I like because it combined dampers and friction.

 

[handleman]

it is 200 kN x stopping distance + 1/2mv^2.

I think maybe you accidentally hit "shift"? 200 kN x stopping distance = 1/2mv^2.

 

[dvd]

Handleman - nope, as stated the OP indicates a 200 kN force. Without further knowledge, I have to assume that the 200 kN force is applied throughout the stopping motion - thus total energy to be absorbed is kinetic energy + work energy.

 

[handleman]

Ah, gotcha. Your interpretation is that the train is powering into the buffer with 200kN of force in addition to its inertia. I read it as 200kN is the target force spec for stopping a coasting train at 10kph, with part of the design being that you must make the sliding portion long enough to dissipate the 1/2mv^2 of the coasting train.

Of course, the huge design parameter that's unstated is the mass of the train. If it's a fully loaded freight train of 5700 metric tons (per a quick Google search), 200kN would require 110m of distance to stop. Pretty unreasonable. However, if it's a single 120t locomotive, that drops to 2.3m, which seems reasonable...

 

[LittleInch]

I think you're lost because as others have pointed out your first sentence doesn't make sense. A force at a speed? Means nothing without the mass of the train.

And where does 20 tonne force come from?

These sort of buffers are not intended to stop trains running at 10 kph. They are way too puny to stop anything more than 1 to 2 kph or maybe a single engine at 5kph.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dvd]

The force at speed requirement makes sense in terms of a moving mass which is still being powered as it engages a shock absorbing device. It may be beneficial to look at an article on shock absorber sizing. Or maybe see what a shock absorber sizing program takes into consideration.

 

[dvd]

The original request is for assistance with calculating frictional coefficient. I would recommend a product versus an invented gizmo due to the variation in friction that needs to be anticipated, and someone has already learned. Here is an easy read on the topic. Another source of information would be vendors. I have some experience with storm/parking brakes for large equipment that grip the rails. This might give you some ideas.

 

[Temporaryworks]

Yes, dvd, it makes more sense when you think of it as a problem to try to dissapate the energy from the impact rather than talking strictly about forces as it is not a static problem.

Thanks all for your input, those references have proved very useful.

 

[Temporaryworks]

The buffer is being used to stop an exacavator with 20t mass moving at 10km/hr. I am also imposing a maximum decleration of 2.5m/s-2. The main other unknown was the friction force but RolMec's source helped with that. One of IRStuff's references also assisted with the design process, it was a paper on the design of buffer stops using friction clamps, so thanks for that.

 

[chicopee]

Check the internet for the article "Hydraulic Bumpers for the Protection of Buildings, Cranes and Operators from Impact Damage" by Paul G. Kit.. The article is in PDF format and may help you.

 

[BUGGAR]

Is it possible to submit a spreadsheet here?