Weight per square inch

[BellaBo]

I'm trying to determine brick paver driveway weight support for the RV.
Does anyone have their weight for four points? If so, does anyone know the formula to calculate the weight per square inch?
Thanks,

[BellaBo]

I'm trying to determine brick paver driveway weight support for the RV.
Does anyone have their weight for four points? If so, does anyone know the formula to calculate the weight per square inch?
Thanks,

[DriVer]

I gave up trying to figure it out. I had our contractor pour 3,000 psi concrete.

[BellaBo]

Thanks DriVer.
I'm looking at brick pavers rated at 2000psi for the driveway.
If I take 22000Lbs/4 (4 point jacks) it comes to 5500 lbs per jack. Each jack is about 8x8 so, 64 square inches. Therefore 5500/64=85.98lb/psi.

I know this is rough and I also know there is more weight to the rear, but there seems plenty of margin. This seems a worse case scenario as the jacks should never have the full weight of the coach anyway.
Guess the easy answer would be to put 3-4 bricks under each jack, raise the coach and see if they crack. Too simple though!

[rogueii]

When I built my garage, I had 3000 # psi/with fiber, poured. I t has been working fine. I have had the full weight on the jacks.
If I was on pavers, I would get a sheet of 3/4" plywood, cut it into 8 equal pieces. Double these under each Jack an you transfer the weight over a larger area. Be close to 2'x2' square.

[wa7hra]

Look at your tire pressure gage. If it says 90 lbs, you are exerting a pressure on the ground of 90 lbs/sq inch on each tire.

[TXiceman]

wa7hra, the tire pressure of "90 #" is not the same as the loading on the slab or ground. The 90# is the pressure exerted by the air in the tires on the tire internal surface. To get the loading on the slab, you need to know the weight on the axle and divide by the number of square inches of tire contact area.

If your coach has a front axle loading of say 8000# and you have 2 tires with a contact area of 10" by 10" (100 square inches), you will have a loading of 40 #/Sq. In.
40#/ Sq/ in = (8000 #)/(2*10"*10")

Or this would be 5,760 #/sq. ft.

Ken

[DriVer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by DriVer:
I had our contractor pour 3,000 psi concrete. </div></BLOCKQUOTE>I would like to revise my remarks to fiber filled 4,000 psi concrete.

They used 3K psi on the car side.

[Cruzer]

You need to consider both thickness of the concrete as well as the mix ratio. Standard 5-1/2 bag mix concrete is rated at 3500 PSI. 6 bag mix is rated at 4,000 PSI. Adding rebar, mesh, or fiberglass is another way to add strength by helping bind it together. I prefer the fiber myself.

Thickness also determines the amount of weight you can support. If PSI was the only issue, then why do they build roads at a minimum 11" thickness? A 4" slab is fine for automotive and light truck use but if you drive a redi-mix truck over it it'll crack into pieces. I have a 5" 3500 PSI slab with wire mesh as my driveway and there are a few cracks in it. Had I known at the time that I would be parking an RV on it I would have gone to 6" 4,000 PSI concrete with fiber. The fiber is especially important in cold weather climates (like Wisconsin ) where the frost level can go down to 4' below ground. That causes lots of shifting and heaving on the slab and the fiber helps tie it all together. I'd also cut 1-1/2" deep control joints in 10' squares and use a 3/4" tarred expansion joint where the driveway meets the garage.

Once I get the hover conversion on my RV then I won't have to worry about that any more.

[Tom N]

Or, you could use asphalt, as I did.

Tom

[rogueii]

My slab and footing was a single pour, footings are 18" wide x 18" deep, with 4' x 4' x 18' deep footing in the center, on the sides with a Hairpin. Tied Rebar in footings, Heavy Mesh over pad. Pad is 6" deep / 3000 #psi with fiber. 18" x 3/4" "J" anchor rods secure Red Iron Girts to slab. Approx. 34 yards of concrete for 30' x 40' garage. Meets FL Code, withstand 120 mph wind.

[troth]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">So, if you'd drop your tire preassure to 10#, you'd have 10# of preassure per sq ft??? </div></BLOCKQUOTE>


We need a knee-slapping emoticon!

[tderonne]

At 10 psi, your contact patch would grow. Probably not exactly nine times, but the psi of the air isn't a bad way to think about it.

Guess there's a calculator on my knee...

[TXiceman]

The pressure in your tire has not much to do with the loading of the concrete. Yes a lower pressure in the tire will create a slightly larger foot print, but dropping the pressure to 1/2 will not increase the foot print by a factor of two.

Just use the basic mechanics to look at this.

ken