Slab on grade design 3

[ThatShouldHaveWorked]

I've had a project to relocate several pieces of equipment in one of our plants assigned to me. I have the various utilities covered. However these machines are going to require thicker slabs under them. So far the best I've been able to get out of corporate is cut the existing out and pour deeper one in it's place. I know next to nothing about concrete.

The specs I have from the OEM are.

Operating weight - 15,300 Kg
Static point load at foot 0.94 N/mm[sup]2[/sup]
Dynamic point load - 15 kN
Excitation frequency of the dynamic point load <0.01 Hz
Number of feet - 4
Surface of individual foot 40,000 mm[sup]2[/sup]

I don't mind doing the homework but I have no idea where to start.

Any help will be greatly appreciated

 

[AgMechEngr]

Thanks for the video. The dynamic effects are minimal if the video is accurate. My "3-5 times the weight of the equipment" comment is not accurate for this application.

 

[ThatShouldHaveWorked]

Thanks I actually do enjoy stretching myself a bit and taking on a challenge.

I did a quick flip through of the ACI materials. Based on the rigid nature of the machine I think what I'm really looking at is a rigid mat foundation.

Using T[sub]M[/sub] > 2 + L[sub]M[/sub] / 30

Minimum thickness is 2.2', so 3' should have a good margin of safety.

With 136 PSI at the feet I think 4000 psi concrete will be more then enough.

Still have more reading to do.

 

[dik]

Check with your local codes... 36" may trigger some mass concrete issues where 35" won't...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

Unless there are some other issues for durability, 20MPa or 3000psi will likely do the job... is less costly and more ecological... also 1-1/2" aggregate... check to see what the savings are...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BigH]

Forgive me but what type of machine are you talking about?? Rules of thumb is that the weight of the foundation is a multiple of the weight/mass of the machine - and can range from 3x to 5x . . . Arya has a good book on machine foundations but this paper might help :

https://www.researchgate.net/public..._Thumb/link/594c44d0a6fdcc14c97d9414/download

 

[SlideRuleEra]

SPurvis - After watching the video, I'll flip my previous recommendation to retain a Consultant back to being an In-House project - you can do this. Except for you being an EE, your job duties seem similar to mine. I retired from a mid-size electric utility where I had civil/structural/geotechnical engineering responsibility for major projects at all of our electric generating stations. I say this for a reason, performing engineering as an Owner is different than the same project by a Consultant. Before I say more, let me ask you a few questions:

1) As Owner, is your top priority by your employer "saving money" or ensuring your plants remain operational and reliable?

2) Are your in-house (industrial) project plans & specs exempt from submittals to and review by building officials?

3) Are your in-house project designs exempt from building codes?

4) Is a PE seal required on your in-house plans?

The answers will determine whether I "go away" or make comments that contradict some of our Engineer-Tips colleagues. I don't want to create a situation that confuses the advice offered to you.

 

[ThatShouldHaveWorked]

SlideRuleEra no need to go away.

1) I'd say both but they lean towards as economical as possible. They do tend to question how necessary every piece is, but with a solid explanation or a hard no they come around.

As to the other questions

I try to do everything as the various codes would require on my projects. Unless it's a major project (building expansions, service upgrades, new plants, boilers) we generally don't involve the building department and inspectors.

No requirements for seals for corporate.

 

[ThatShouldHaveWorked]

36" may trigger some mass concrete issues where 35" won't...

Did I say 36"? I meant 35"

Thank you

 

[dik]

I often spec 29" deep grade beams because 30" triggers intermediate face reinforcing. I've outgrown it, but when I was younger, when a new code came out the first thing I did was to go through it looking for exceptions, like the above.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SlideRuleEra]

TSHW - This project appears fairly simple and straight forward, but I'll over emphasize the various aspects of doing this type work in-house.

You will be the Project Manager, Structural, Civil, Geotechnical & Mechanical Engineer, and also (I assume) Construction Manager and responsible for technical side of contractor Procurement and bid evaluation.

Here is a conceptual sketch of a few of the issues you need to plan and address:

Also establishing potential foundation loading from equipment operation, maintenance, seismic, etc.

The equipment is not necessarily centered on the foundation. It's important to position the equipment's center of gravity as shown below. If this is not done, load on the foundation will be "eccentric" which will effect how supporting soil is loaded. The center 1/3 of a footing (in all directions) is called the "kern". Google on "footing kern" for more info.

Some of the items I have listed above will be the Contractor's responsibility (like getting concrete to the work site), but if you don't think things through they become your problem when his actions effect plant operation. Read over the above and let us know your thoughts.

 

[dik]

That's an awful lot of reinforcing in your 6'x6'x3' blob... shrinkage? in a 6' length?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[ATSE]

Not to change the subject, but...
I am on a project in a electrical yard, and all of our electrical engineers are busy, so even though I'm a structural engineer, I am going to try my hand at cross discipline work.
I know next to nothing about electrical or power engineering.
The task at hand is to re-wire a delta-wye transformer. I think it is 480 3P, but not sure. Real big copper wires. I don't mind learning new things, and I'm hoping you can help me...
[When you don't know what you don't know, hire an expert. Eng-tips and YouTube are good when you're close, but will not prevent you from making a costly mistake.]

 

[dik]

I occasionally stray into small mechanical issues... but other than doing an electrical design review for the 6 storey apartment building down the street about 50 years back... I don't do electrical stuff... real electrical stuff is really intensive.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[ATSE]

Hey guys, that was just my attempt at satire. I would never even think of tackling something so far outside my expertise - especially when rotating machinery is involved.

 

[ThatShouldHaveWorked]

Hey guys, that was just my attempt at satire.

In that case lick your middle and pointer finger. Put one on the big brown wire lug and the other on the big orange wire lug. Always want to check that the power is off first.

Then you will most likely need a wire stretcher. You'll have to ask around but I'm sure you can find an electrician that will lend you one.

 

[dik]

I thought it was just called a stretcher?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik