Many people have asked me how I calculate shock load for a moving piece. Here's what I came up with. (Refer to the disclaimer at the end)
Assuming that a 2 brake Tour Rig or Tour Lift will stop the load within 0.09s average under a loss of power, you get the following calculation:
F = ma
where
F = force applied
m = mass
a = (Vf - Vi)/ t
a = acceleration
Vf = velocity final in m/s
Vi = velocity initial in m/s
t = time
16'/min = 0.082m/s
32'/min = 0.163m/s
85'/min = 0.435m/s
104'/min = 0.53m/s
You can now determine that you have:
16'/min = 0.907x the load on the structure (minimum of 1x)
32'/min = 1.81481x the load on the structure
85'/min = 4.83x the load on the structure
104'/min = 5.89x the load on the structure
Another consideration is the time to brake. If you have weaker brakes, the shock load will be drastically reduced. It is also non linear on a 1/2 and 1/4 ton tourlift as the brake will slip, so these values are if the brakes are operating at 100% efficiency, which is never the case. In real world, the brakes will operate at 60-80% efficiency, which drags these numbers down by 20-40%. These are only to calculate MAXIMUM shock load in theory on a structure.
DISCLAIMER: As usual, for liability issues, i must write this: THESE ARE ONLY APPROXIMATIONS. Do not use these numbers or calculations for actual engineering purposes. Not liable for mistakes.
If anyone has a different way of calculating this, please do share.
Seb
