What's the best way to calculate tire contact areas?
What's the best way to calculate tire contact areas?
(OP)
I'm attempting to place a CAT 930 or larger on a 7" thick slab an am trying to determine the contact area so I can calculate the load vs the soil bearing capacity.
Any ideas?
Any ideas?





RE: What's the best way to calculate tire contact areas?
RE: What's the best way to calculate tire contact areas?
RE: What's the best way to calculate tire contact areas?
So if the load per tire is in pounds and you are dividing by pounds per square inch... You will end up with an area in square inches...
Probably, unless of course, the tire is completly flat and resting on the rim...
RE: What's the best way to calculate tire contact areas?
Why do you want to check the bearing capacity under the slab? You are not likely to get a bearing capacity failure in confined soil.
RE: What's the best way to calculate tire contact areas?
RE: What's the best way to calculate tire contact areas?
The bridging effect of the 3000 psi concrete becomes negligibe when supported by the underlying soil with an allowable bearing capacity of 2500 psf and no effective tensioning strength from the 40 ksi steel...
Also, I'm facing a modulus of vertical sub-grade reaction of 3 tons per cubic foot... Which, if I'm looking at this right, yields a deflection of 0.007 inches or there abouts and craking is a REAL issue with the governing agency...
Further input would be greatly appreciated... I feel that this is a compressional rather than a slab bending problem...
The largest piece of equipment I've been able to prove that will not damage the slab so far is a Cat 963 Track loader with a track pressure of approximately 1500 psf...
RE: What's the best way to calculate tire contact areas?
Further, I can't imagine that your modulus of subgrade reaction is that low in a soil with your stated bearing capacity.
Assuming your 930 loader has a wheel load of say 8000 lb and it has standard tires, you probably have a contact area of about 70 to 80 square inches. Considering this, and the 7-inch slab thickness, the vertical deflection in the soil will be about 0.010 inches directly under the load. At 24 inches from the load, the deflection is about 0.008 inches, thus the load is being bridged (if the load were not being bridged, you would have no deflection that far away from the load and the concrete would have failed in shear). You may compute these stresses and load influence radii with most any convenient pavement analysis program or do it by hand using the PCA method. I did it by elastic layer analysis, considering the concrete and the underlying soil as a 2-layer elastic system. Check Yoder and Witczak for a quick dissertation on elastic layer analysis.
The stress in the concrete at the bottom of the slab directly under the load is about 200 psi in tension. If you are using a concrete with a coarse aggregate of No. 57 stone or larger, you are likely getting a modulus of rupture of greater than about 400 psi, so cracking with a reasonable number of load repetitions is not likely. In fact, in working stress design, we consider that if the actual stresses do not exceed 50 percent of the working stress limit, you will get unlimited cycles of load allowable.