Allowable Bearing Capacity

[OOcram]

This might be simple to many, but I have some difficulties. I will build an area (which will be backfilled with soil material) which will house the cranes I have. I have a maximum component load of 125 metric tons of 4-wheel cranes. The crane has a wheel with an area of about 1 square meter each when it sets/touches the ground. Question: What should be the allowable bearing capacity of the ground (soil) to hold all my cranes?

 

[oldestguy]

It all depends. For instance if these are rubber tires and you have no outriggers and you don't mind if there is some rotation or tilt angle of the machine on ground that has no give, such as solid concrete. In that case how much can those tires deflect without causing trouble? So how much tilt is OK? What is the spacing of the wheel supports? Is there an occasion where almost all your load can apply to only one tire? So you see there are mechanical calculations you may need to do to show the actual load to each tire that you will apply as well as how much can that loaded area deflect downward and still be acceptable?

If you have some allowable tilt angle under those circumstances, then you provide the geotech some information as to how much that compacted fill can settle. Thus, the allowable bearing capacity that someone may say you need, will depend on the allowable settlement under load.

Do you have adjustment potential for taking up such settlement at each support? Is this just a temporary job thing or a permanent support situation? What tire pressure do you require, since that may be the required bearing capacity of the ground below, as a rough answer.

 

[msquared48]

Point being that in order to solve the problem, you need to identify the loading conditions and desoign constraints.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[OOcram]

Thank you guys for the replies. (oldestguy) Yes, the tires are made of rubber and yes, I don't mind if there is some rotation or tilt angle of the machine.
The area will just be a place where I can park the heavy equipment. It may also be a place where we can fix and maintain the equipment (some sort of a workshop). So the plan is to fill the area with earth fill and compact it, no more concrete.

There is no occasion where all the load will apply to only 1 tire. We are assuming that the weight of the crane which is 125MT will be divided equally to 4 (number of tires), so each tire will carry 31.25 metric tons.

I believe this will be a permanent support situation. I will be using this for about 1.5 to 2 decades.

Is it safe to assume, having said 31.25MT per square meter (area of 1 tire), I will have about 306kPa of allowable bearing capacity?

 

[MiketheEngineer]

Crane mats??

 

[dhengr]

Do I understand correctly? You have a mobile crane on 4 wheels which weights 125MT, as a light weight? And, each wheel has a foot print of about 1 meter square, under this loading? The four wheels will not likely each carry one quarter of the weight. Those must be some pretty big tires. What diameter and width are they, and what width btwn. tire centers, and length btwn. tire centers. What kind of a crane is this, please explain?