Problem with vertical slope of ramp and trucks with multiple axles

[MonsieurR]

Hello everyone,

We currently have a problem with an access to a property which will require a ramp inside the property to compensate for the level difference. We are trying to design the ramp (in the property) such that a truck has no problems. At the beginning we thought a ramp with a 7.5% average slope would suffice, since this looked reasonable and is less than the recommended recipe of 10-12% max for normal ramps, yet with simple autocad exercise presents to us the problem that if a truck with 2 or 3 axles (tandem or tridem) tries to pass, one of the axles would be "in the air". See attached .dwg. I'm aware this tandem systems can compensate some level differences, but I don't know how much, I suppose this depends on the manufacturer.

Does the AASHTO or any other reference provide a solution to this problem in a prescriptive fashion?
Is it ok for the truck to have one axle bearing more load than the others?

Any comment is highly welcomed. Thanks

 

[JGard1985]

In my real world experience, I dont think this would be a problem, since truck suspension is pretty flexible.

I would look at the crest of the ramp and if it can strike the undercarriage of a truck. Its especially painful for semis with low ground clearance typically used for hauling construction equipment. You dont want a truck to bottom out at the top of the ramp and get stuck at the top

Jeff
Pipe Stress Analysis
Finite Element Analysis

http://www.xceed-eng.com

 

[SwinnyGG]

The ramp configuration you're showing- constant grade, sharp transition at the top, etc is basically exactly the same as a loading dock. I would suggest loading dock design guidelines as a good starting point.

 

[racookpe1978]

Your file is a .dwg (AutoCAD formatted) file. Request you provide a non-proprietary image only file like .png, .bmp .pdf or .jpg file as well.

 

[dhengr]

MonsieurR:
I’d talk with a few truck/tractor manuf’ers., and trailer manuf’ers. or shops which sell this type of equipment. They should be able to get you the info. you need. What you are really interested in is vertical curve negotiation capability of the tandem or tri-axle running gear. They normally have some vert. curve negotiating ability, through several different mechanical features, but then at some point they bottom out on some hard spots, or reaction points on the truck frame. And, this will vary a little bit depending on who makes the specific running gear and upon the axle spacing, etc. You should normally not be running over two planes which meet at the PI (point of intersection) of the two planes. But rather over some short vert. curves which are convex or concave. And, you want to know what this min. vert. curve radius is, but I wouldn’t design to that. And, while it is not desirable the axles and tires can take much more loading than the perfect max. load distribution.