concrete pressure 3

[qbubba]

I am installing a machine with the weight of 12,500 kg. The concrete floor is 6inchs thick and rate for 3,500lbs per square inch. What is the formula to figure if the concrete is able to handle this weight?

 

[olynyk]

Assuming you're on Earth, your machine with a mass of 12500 kg has a weight of 27567 pounds. Then you need to know the surface area of the base plates of the machine. If it's (for example) four plates, 6"x6" each, then there's 6*6*4 = 144 square inches of base plate. Then divide the weight of the machine (27567 lb.) by the contact area (144 sq. in. in my example) to get the pressure. In the example, the pressure is 191 psi.

 

[unclesyd]

I think you had better get a civil engineer in on the job as soon as possible, especially if the slab wasn't designed to carry that type loads.

 

[EddyC]

The 3500psi is not the allowable stress of concrete. Think also about the allowable soil pressure under the concrete floor. And also consider any dynamic loads resulting from the machine. But I too think you better get a civil/structural engineer for this. Your machine is quite heavy.

 

[CanuckMiner]

No offense intended to others here, but how exactly did Olynyk earn a star for the response? Olynyk did respond to the (unasked?) question posed in the title, but failed to point out the obvious problems with just looking at bearing stress on the concrete pad. I see no mention of starting torques, overturning loads, starting loads, nor the other myriad of questions ALWAYS posed by civil/structural engineers when preparing foundation loading calculations. As others have indicated, seek the expertise offered by a qualified civil/structural engineer...preferably one who understands the term "rebar" given your rather large loading condition.

I urge you...Do not just base the loading on the compressive strength of the concrete alone.

Cheers,
CanuckMiner

 

[UcfSE]

Canuck is right in that you have more to consider than simple bearing alone. You don't mention if this is a slab-on-grade (s.o.g.), i.e. supported completely by soil, or a structurally elevated slab. If it's a s.o.g. you need the modulus of subgrade reaction or will need to assume a value. You need to know how the weight of the machine is distributed, is it 4 point loads, 3 or 6, and so on. There are many things to consider for the concrete itself, and then there are the loads the machine will impose on the concrete during start-up and operation plus the anchorage of the machine to the concrete. Since this machine is so large you may or may not have a significant seismic load depending on your location. I'm sorry I can't really be more helpful than to tell you some of what I would look for but here is no single equation to help you out.

 

[boo1]

Don't forget about maachinery vibrations too. A rule of thumb was 2x machinery wt. for a starting point for foundation pad design.

 

[mrMikee]

I would like to point out that the first thing to do is to find out what the manufactures recommendations are? If the machine in question here is a machine tool it will require more in terms of foundation rigidity. Some machines need foundations that are both strong enough to support the weight of the machine and rigid enough to maintain critical alignments required.

Shock and vibrations can be important too so you may need to know the dynamic loads generated by its operation. For example, a machine tool (lathe, milling machine, etc.) are smooth running machines that are sensitive to disturbances coming in. On the other hand, a punch press or shear can cause shock loads that not only put significant loads on their own foundations, but can travel out to other machines to cause more problems.

So the answer is that it just depends. However, you should in my opinion have a Civil or Structural engineer look at your problem and visit the site.

Regards,
-Mike

 

[olynyk]

CanuckMiner, I made no warranty as to whether the concrete could support the weight, since I don't know about this. If you read my post all I said was how to calculate pressure given a loading and a surface area. Obviously others have stepped in and added their more educated opinions and qbubba now has a good starting point for his problem.

I do however agree with you that I probably shouldn't have been given a star for that post since what I said was so basic.

 

[CanuckMiner]

Olynyk,

I re-read my original post and must apologize for my rudeness. My concern was that qbubba was going to use the information you presented and not consider the other factors involved.

I should have written my post more directly, instead of taking "shots" at others.

Again, my apologies.

Cheers,
CanuckMiner

 

[Cockroach]

Full strength concrete, 28 MPa. Stay below this by some factor of safety 1.5, more if vibrations worry you. Don't exceed this number as normal surface load.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada