Asphalt Bearing Capacity. Wheel load vs Footing.

[Mr. Rogers]

How can I determine the capacity of an old asphalt test track road to support a gantry crane? I have a recent Geotech report from an adjacent building. In-situ bearing capacity is 2500 psf at a depth of 1-2ft and 4000psf at 2-4ft. I need to unload a piece of equipment with a temporary gantry crane. The equipment will be lifted from one truck and placed onto another. The max pressure below each gantry track is 2500 psf. Tracks are 5’ x 20’ and spaced at 35’.

Looking at basic passenger traffic loads as a minimum, I found an average tire contact patch area to be 36 in^2. And a typical vehicle weight of 4000 lb. That equals to 27.8 psi or 4000 psf per tire.

Can I equate the wheel load to the load of the gantry crane and say 4000psf wheel load is greater than the 2500psf crane load? Or is a vehicle load distributed over the wheelbase?

Thank you.

Edit: I don’t have information about the existing asphalt track. I’m assuming it was designed for basic passenger vehicles. Based on 4000psf wheel load of vehicle, can I say the asphalt will be adequate for the 2500psf gantry crane support?

 

[oldestguy]

One helluva difference. No way. I'd look to structural spread footings. Usually these footing pressure designations allow one inch deflection.

 

[fattdad]

as the geotechnical engineer. Foundation bearing capacity is often unrelated to ultimate failure. It's often (typically) related to settlement. Your crane load is transient. It's likely that if you lay in some gravel in the 12-inches below the wheels (or jacklegs), you'd distribute the load enough. Then too, it's transient - not like long-term foundation loads.

It could just be a phone call and a bit of reasoning.

f-d

ípapß gordo ainÆt no madre flaca!

 

[racookpe1978]

Jack leg loads (static on the bottom of the jack) will be greater than wheelbase (transient) loads because the crane is jacked up (off of 12 wheels) and onto the 4 jackstands.
Then the four pads expand the area enough to prevent excessive subsidence.

By definition, a little movement of the soil under the pad can be compensated for by leveling the crane. But, under load, no movement can be tolerated or the crane tips down, perhaps tipping over. If your pads are on asphalt, then the resistance will controlled by the soil immediately under the asphalt only, not a nearby building. (Unless, of course, the whole area is equal underground.)

 

[dik]

See what happens in the heat... same with motorcycle stand pegs...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[racookpe1978]

True, true.