Tie down requirement for rail road cars 1

[shin25]

I was looking into the tie down design requirements for products shipped on flat bed rail road cars. The requirements are- forward and backward-3g, transverse-2g, up and down-2g. I find these requirements quite unbelievable. As far as I am concerned, 3g is about the acceleration during the launch of a space rocket (?). The product that I am trying to tie down is about 90 tons. Can you imagine the force that the system has to be designed for.

 

[csd72]

I imagine it is to allow for a collision. If the train hits a solid object at full speed it would be easy to imagine a deceleration of 3g. If you are the driver in this situation you really dont want your ten ton load flying through your back windscreen.

The space rockets have acceleration greater than 3g I believe, some jets give 5 or 6g when turning (which the pilots have to wear special suits for).

csd

 

[shin25]

csd72,

I seem to agree with you. But,

These rail cars with heavy loads that I am mentioning probably cannot achieve more than 40 miles/hr at full speed. So, for an example, if it meets with a collision and comes to a complete stop in 2 seconds (which is unlikely considering all types of deformations,etc), then deceleration is only 29 ft/sec^2, which is even less than 1g (32.2 ft/sec^2).

 

[csd72]

29ft/sec^2 is your average deceleration.

If you think of the impact as a spring then your deceleration curve will be more like a triangle with the instantaneous maximum being about twice the average (58).

You are also thinking likely scenarios whereas these are base on worst case (i.e. if the brakes fail going down a hill).

Do not mess with it, you dont want to be facing a court with your only defence being 'I didnt think it was likely'.

csd

 

[JStephen]

These are probably shock loads, as well, not sustained loads. For example, pulling the slack out of couplers sends a shock down the train that could be the 3g force. If the floor under you accelerates at 3g for 1 or 2 inches, it's not going to bother you much, but on a rigid item, that could be a large force.

I think there is a rail engineering forum here, you might check there as well.

 

[IFRs]

In my experience, the railroad will not transport a load that is not tied down to their specifications. I recently transported several million pounds of steel about 1200 miles via rail. It seemed that no matter how well we tied down the loads, they shifted when the cars were bumped.