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2meterman (Structural) (OP)
19 Jul 07 15:06
Hello All,

I'm working on a residential design that has a full basement below a one-story house.  One of the basement walls is adjacent to the attached garage.  So this wall has a full backfill of 8'-4" plus a wheel load that is about 2' horizontal from the front axle to the face of the basement wall.

How do I convert the axle load of the vehicle into a surcharge load to place next to the basement wall?  All the design examples that I can find start out with a wheel load already give in psf.  What I am looking for is a method to convert a known wheel load of 2,000 lb to a psf surcharge load placed at the top of the wall.  I know the footprint of the vehicle's tire and its air pressure.  But I'm a bit hazy on how to convert this to a psf loading for the wall.

Does it matter that the wheel load cannot get any closer to the wall than 2 feet?

Any suggestions or references would be greatly appreciated!

I humbly await the responses of my fellow engineers.  Thanks for your time and help!
DarthSoilsGuy (Geotechnical)
19 Jul 07 15:23
Instead of directly running the numbers, i think using the IBC table 1607.1  40 psf live load for garages is more appropriate.
DWHA (Structural)
19 Jul 07 15:33
Is the garage floor a concrete slab? If so you can distribute the load over a larger area and reduce the surcharge. I would use a 2:1 slope to distribute the load thru the slab.

In terms of distance from the wall, Das has a good section in his text that deals with either a line load at a known distance from a wall, or a area load at a known distance from a wall.
csd72 (Structural)
19 Jul 07 15:56
Include the weight of the slab in the surcharge load.
shin25 (Structural)
19 Jul 07 16:24
I believe you are asking how the wheel load will distribute in the soil and inturn create lateral load on the wall.  I think you should get your answer in any of geotechnical engineering book. But the best reference would be "geotechnical engineering" by Braja M. Das. Look under "insitu stresses".
strguy11 (Structural)
23 Jul 07 17:52
The AASHTO code requires a 2' surcharge on retaining walls.
dbuzz (Structural)
23 Jul 07 23:35
Lateral earth pressure from point loads near a retaining wall are fairly easily determined using the Boussinesq equation.
Whodapookie (Structural)
23 Jul 07 23:43
Wouldn't this depend on the type of garage slab you have?  If the slab is like mine in my home, with a grade beam and turned down rebar tied into the basement (retaining) wall, I could technially remove all the dirt under this slab and it would still support the weight of my vehicles.  In this case, the surcharge from the garage wheel would be zero.  

I talked to the super when they were building my home, and asked why a self supporting slab.  The answer is the expense of compacting the soil to 95% and time involved is more than just reinforcing the slab.  A little overkill, but you get what you pay for.
Tomfh (Structural)
24 Jul 07 1:20
I agree with DarthSoilGuy. Pick an appropriate psf from somewhere and use that.

For a retaining wall like this I would use minimum 100 psf surcharge.

There are many lateral pressure formulas for point-loads/line-loads/ramp-loads at various distance from retaining walls but it's a bit complicated.

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