Proofroll Loading
Proofroll Loading
(OP)
We need to proofroll a heavy haul road using a minimum simulated wheel loading of 90 psi. The tandem axle dump truck we are planning on using will have a tire pressure of 110 psi. The issue is, what do you base the loading on; the 110 psi tire pressure or the weight of the load divided over the contact area of each tire? The measured contact area is very subjective based on the squatting of the tires under load. The text books I have studied provide formulas for defining the tires contact area, however, it all comes back to the tire pressure (110 psi). If this is the case, what is the rational for proofrolling with a fully loaded tandem axle dump truck, if the tire pressure is what governs.
Sorry for the long winded scenario. Looking for some opinions.
Thanks
Bagger
Sorry for the long winded scenario. Looking for some opinions.
Thanks
Bagger





RE: Proofroll Loading
If the tire pressure at the end of a loaded axle is 110 psi, and you raise up the truck body and axle with a floor lift, the tire pressure is still going to be close to 110 psi, with no ground load.
Discussions about tire pressure and ground pressure sometimes do not address the radial tension in the tire correctly.
Contact area estimates are not perfect, but this is what you should use, as this is what the ground "feels."
RE: Proofroll Loading
Tire pressure (actual pressure - not cold, unloaded, inflation pressure) roughly limits the peak pressure that a tire can apply to a flat surface. As load on the tire increases, the contact area increases, and the tire pressure will rise slightly.
RE: Proofroll Loading
however a total load of 110 lbs applied over one square inch will not be sufficient to test your road...
Total load is more important, thus the requirement for a large, fully loaded trailer
you should proof roll with the heaviest vehicle that you can reasonably expect to use the road. Let the mechanics worry about how much air to put in the tires. most proof-roll specs do not specifiy tire pressure but they all seem to specify the vehicle - minimum 30 tons up to 50 tons.
RE: Proofroll Loading
You can get 110 psi ground pressure with a flat tire (0 psi internal pressure) or with a solid rubber or steel wheel, given adequate truck load.
A pressurized tire under asymmetric loading with non-linear constitution is a complicated thing, and using tire pressure to find ground pressure is unnecessarily complicated. Worse, if you ignore hoop tension in the body of the tire, conclusions relating tire pressure to ground pressure will be incorrect.
cvg is correct that you want a very heavy load to increase your area of influence.
RE: Proofroll Loading
ATSE said it nicely...forget the pressure. Concentrate on the total load. For proofrolling, a loaded dump truck works just fine. Almost any equipment with heavy loads and rubber tires will work.
RE: Proofroll Loading
1. Determined the tire pressure with the truck empty. (110 psi)
2. Loaded the truck with the maximum load it could carry.(68,880#)
3. Measured the tire pressure. (remained at 110 psi)
4. Measured the contact area of the squatted tire (12.5"x8")
5. Calculated the individual tire load (68,880/8=8610 lbs).
6. Calculated the contact area (110 psi/8610 lbs.=78.27 sq in.
7. Contact area assummed to be an ellipse per Boeing.
8. Calculated the major and minor axis of an ellipse.
9. Major axis=12.66", Minor axis=7.91".
10. Compared the calculated values with the physical measurements. 12.5" vs. 12.66" and 7.91" vs. 8.00" OK
11. Based on this procedure we should be >90 psi, closer to 110 psi.
The proofroll went well. The road failed where you would anticipate it to fail (at the edges) and was ok near the centerline. Thanks again for your input.
RE: Proofroll Loading
www.FoundEng.com
RE: Proofroll Loading