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

 

[KootK]

Having corporate buy you one of these would be a good place to start I think. Were I in your shoes, I'd be engaging the services of a structural engineer.

 

[dik]

Can the equipment tolerate movement? How is it currently supported? What s the soil?

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

-Dik

 

[ThatShouldHaveWorked]

It doesn't require a ridged surface. It does align with other equipment.

8 years ago they cut out the existing 5" slab and poured a thicker one in it's place. That section is all covered by the machine so I don't have access to run a drill bit through it to measure it that way unfortunately.

I may be able to find the original plans from when the building was built. Which would give me a better idea of what it's built on. It's all sand around here though. A plant went up across the street and they spent two or three months wetting and compacting.

Thank you

 

[AgMechEngr]

When I was in industry, equipment installation was rarely engineered. The contractor would typically just "go big and heavy".

As a general rule, dynamic equipment blocktype foundations will be 3-5 times the weight of the equipment. Koot's literature recommendation should address this rule-of-thumb. You should engage a geotech and a structural engineer. Their analysis is worth it on this one.

 

[ThatShouldHaveWorked]

dik the original plans list the site soils as "composed of sandy and silty sand soils". Where the machine foundation will go the existing floor is just 5" unreinforced on grade.

I did order the report. It looks like the right place to start my homework. At the very least I'll know a bunch more about concrete after reading it.

I did get a we think we poured a 3' foundation under it when it was installed message today.

I agree AgMechEngr there seems to be a lot of well what we usually do / what we've done before.

It's definitely my preference to have a local engineer do the analysis. Selling it is a whole different story. I've only won that once when I told them if they want to hang things from the bar joists they need to get someone else to sign off on it because I never will.

I just won a 2 year long battle that while air compressor X may be sufficient for a plant located at sea level with relatively cool ambient temperatures. That same compressor is not sufficient at 5,300 ft above and 115 degrees ambient. Finally got irritated enough with constantly being told there had to be massive air leaks in the plant and we needed to get our act together that I researched the math.

Doubt I really made them understand that altitude makes a significant difference though. I will find out when it comes to buying a new boiler next year.

 

[SlideRuleEra]

I've had a project to relocate several pieces of equipment in one of our plants assigned to me.
It (equipment) does align with other equipment.
It's definitely my preference to have a local engineer do the analysis. Selling it is a whole different story.

What are the horizontal dimensions of the proposed slabs?

 

[ThatShouldHaveWorked]

6' x 6' would give me 1' from the edge of the feet.

 

[dik]

35K/36ft^2 is about 1ksf... which seems to be OK, including concrete weight. Still should check with a geotekkie...

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

-Dik

 

[SlideRuleEra]

Per dik's calcs, soil bearing pressure is certainly ok, unless the slab is in a swamp. I would not consult a geotech, but spend money saved by not hiring a geotech to make the slab "conservatively" thick, say the 3' you have heard mentioned(4 yd[sup]3[/sup] concrete).

I've been in your shoes, you have got to balance creating an acceptable design with looking very "foolish" to Management if your solution to a problem you have not encountered before is to hire a consultant every time. Others can disagree, but "I've walked the walk, so I'll talk the talk."

 

[dik]

SRE... just being cautious, but a geotekkie isn't likely required. The concrete weight is about half of the load with a 3' thick slab...

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

-Dik

 

[SlideRuleEra]

dik - Agree with your comment on 3' thickness. Only reason I went that high was because the OP has reason to believe 3' thick works on this site. If that was not known, I would say 18" thick.

Edit: Also a 3' thickness is not as "heavy" as it seems. Most of the 3' will be below grade where the 150 lb/ft[sup]3[/sup] concrete displaces soil at 100+ lb/ft[sup]3[/sup]. This results in an increased load on bearing soil based on the difference, 50+ lb/ft[sup]3[/sup].

 

[ThatShouldHaveWorked]

I think I missed a few step. The ACI book will be here tomorrow.

Above there was a general rule "dynamic equipment blocktype foundations will be 3-5 times the weight of the equipment."

Is this the weight to use to calculate the load to be born, or the actual weight the concrete should be?

It did seem like a GIANT block of concrete if it was 3 times the machine weight in concrete weight.

 

[SlideRuleEra]

SPurvis - 3 to 5 times weight of equipment is weight of concrete foundation (called an "inertia block"). The 3 to 5 times weight that AgMechEngr provided is an excellent time-tested (approximate) rule for foundations for vibrating (often rotating) equipment. But, there may be something missing from information provided: 15,300 Kg seems unusually heavy for equipment that will easily fit on a 6' x 6' foundation... unless the equipment is very tall.

Do some math: Equipment weight = 15,300 Kg = 33,700 lb.

3 x 33,700 lb. = 101,000 lb. (weight of inertia block concrete)

Volume of concrete = 101,000 lb / 150 lb/ft[sup]3[/sup] = 673 ft[sup]3[/sup] of concrete

Thickness for 6' x 6' inertia block = 673 ft[sup]3[/sup] / 36 ft[sup]2[/sup] = 18.7' thick

This is NOT right... there is something wrong with the information or assumed foundation size. Now sounds like it is time for you (Electrical Engineer) to call in a consultant.

 

[dik]

From the bearing, the area seems to be of the correct magnitude. I would have thought a 2' or 3' pad with vibration isolators would be adequate. If movement can occur it should be OK with good founding soil. The problem occurs if the equipment is part of a 'line' and movement cannot be tolerated... then maybe a pile type foundation is in order.+

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

-Dik

 

[SlideRuleEra]

dik - You make good points. The OP does say "It (equipment) does align with other equipment."
As I mentioned above, to me, the balance of "In-House" vs. "Consultant" has tipped to "Consultant", for this OP.

 

[ThatShouldHaveWorked]

It wasn't my intention to offend and I definitely wasn't questioning your experience.

The lack of information is my fault. I'm looking at a 56 bar extraction press. It's about 13' tall.

Similar to this

https://www.youtube.com/watch?v=BE835bJh7pE

Forces are:
when the conveyor kicks on to discharge every 2 minutes
once in a while a cake will stick to the ram and 250ish lbs falls 1 or 2'
a 22kw hydraulic pump that is mount on dampers to the top plate.

Definitely doesn't require precision alignment. We're talking within an inch or two in any direction. likely even more.

I really do appreciate the conversation.

 

[dik]

There was nothing at all offensive about any of this thread... SRE and myself are not of that ilk...

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

-Dik

 

[SlideRuleEra]

SPurvis - As dik says, absolutely no offense intended or taken. If anything, I admire you (Electrical Engineer) for having the moxie to take on a project of this nature.
[sub]Note: If I may say so, reminds me of myself a few decades ago.[/sub]

 

[dik]

me too... just slowed down a tad...

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

-Dik