Determining an Equipment load behind reinforced concrete wall 2

[piratecoach]

I am designing a reinforced concrete wall. I would like to design it to ensure it may withstand the maximum operating equipment load behind the wall. The area is paved behind the wall. ASCE code recommends a minimum of 250 pcf for tractor trailer and fire lanes, but how do I analyze a load for a loader having an operating weight of 100,000 pounds?

Is it reasonable to view the pavement as bearing the weight of the loader and treating it as a surcharge load, using the area between the center of the tires? Example, if the loader has an operating wt of 100,000 lbs, a 15' long wheel base and 12' wide axle length between tires, would it be unreasonable to call this a 555 psf surcharge behind the wall? My gut feeling is this is not an acceptable design procedure.

 

[BigInch]

It is reasonalbe to use the surcharge concept. What is not reasonable is to assume the 100 K load is concentrated. The loader has enough tire and contact area to distribute its full weight and load in such a manner that the load to the pavement is no worse than any 18 wheeler. Generally a highly loaded tracked or wheeled construction vehicle produces less load per ft2 on the track or large diameter wide tire than a well loaded passenger car does under its normal size tires.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[PEinc]

I disagree. 100,000# over 12' x 15' = 556 psf, much more than 250 psf. The 250 psf if for normal traffic. You need to give extra consideration to expected heavier loads. You may want to check the retaining wall for a concentrated load of AT LEAST 25,000# (100,000# / 4 tires) or 50,000# (100,000 / 2 tires). I doubt that your pavement is stiff enough to evenly distribute the load from the loader's 4 tires.

A normal highway truck has an axle load of about 32,000# or 16,000# on 2 adjacent tires. The loader would have significantly more load on a single, but larger, tire.

 

[DRC1]

Contact pressure will depend on if the tires are solid or air, and thhe load in the tires. The manufacterer or dealer can give you details. Th e area will not be that big and the area times the pressure will give you the wheel load.
For this condition, I would use 4 point loads at the tire locations. configure it as close to the wall as it will get. Loaders, like most heay equipment are not loaded evenly and weights are quoted w/o payload. With a full bucket, the load will go up substatially. as much as 2/3 of the load may be on the front tires. If the bucket is empty, The back tires probably carry considerably more weight than the front.
Find the most critical alignment (often this can be done by inspection) use 4 point loads for the tire contact points and compute the load. If the alignment is symetrical, you can use 2 points and double. Rember that for lateral pressure diagrams the theoretical load in the wall is twice the calulated value.

 

[BigInch]

They don't need pavement to distribute the load. Its already distributed quite well on the oversized tires. These things operate quite well on the edges of dirt slopes with no retaining wall.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[piratecoach]

Thanks all but I think I found the best answer on my own!

Book called Soil Engineering by Spangler and Handy, Third Edition, pg. 567, eq. 22-23, has the following equation:

P= applied truck-wheel load, lbs
x= horizontal distance from wall to load, ft.
y= lateral distance from point to load, ft.
z= vertical distance from point to load, ft
R= sqrt (x squared + y squared + z squared)
hc= horizontal unit pressure at any point on the wall, psf


Equation: hc= P (x squared * z)/ (R to the 5th power)

To find the maximum load to the wall, I would assume you would write a excel program or trial and error to find the depth below grade having the maximum applied load. Then use that depth below grade in your moment calculations.

Sorry I can't use upper/lower case letters here. This is the best information I've found yet, and appears to give reasonable results.

 

[eric1037]

There is a really good reference called "Productivity Tools for Geotechnical Engineers" by John T. Christian and Alfredo Urzua that was published by Magellen Press, Inc.

This book has many examples for analyzing soil stresses for many situations. The book also contains a disc with DOS-based software for formulating stress distributions for many different situations. Even though the software is very simplistic, it's also very useful.

Alternatively, you could determine stress distributions using the Boussinesq techniques or others.

 

[piratecoach]

The Boussinesq technique will under estimate the load by nearly half the pressure calculated from the provided equation (which was confirmed by experimental evidence). The increase in pressure is caused by the fact that a concrete retaining wall is rigid in comparison with the vertical plane through the soil (quoted from reference).

 

[eric1037]

piratecoach:

That's a good point. I retract my statement.

 

[BigInch]

me2

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com