Block foundation for a press

[Robbiee]

Hi All,
Looking for some comments on designing a concrete foundation for a hydraulic press. It is not the first time we have designed a foundation for a press, but the first time for a big press like this one. The press is 13m tall and weighs 290 metric tones. This weight includes the weight of the oil and the molds. The supplier has indicated that the press applies 900KN dynamic load on the foundation. Considering two recommended criteria for the design of the foundation: a) limit the soil pressure to 0.25x(the allowable soil bearing pressure) and b) provide a foundation with a mass equals to 3 to 5 times the weight of the press, the foundation has to be 12mx12mx2m. Now, before sending my design to the soil consultant for their review I wish to know if the size is reasonable. To me it looks huge. Please comment. Thanks for the help.

 

[JAE]

3 to 5 times the weight seems appropriate. I do know that many presses also have very stringent requirements for stiffness in the foundation to limit differential settlements along the length.

With any "bending" in the footing the press looses its tight alignment for color overlay matching.

 

[kingnero]

What is the footprint of the press?
and DL = 900 kN, is that correct? that's about 1/3 of it's dead weight...
What is the capacity of the press?

 

[Robbiee]

Kingnero,
DL is the 290000 kg which includes the weight of the hydraulic fluid and two molds.The weight of the press only is 225000kg. 900kN is the dynamic load. I have memorized those numbers but I don't have answers right now to your other questions. Thanks

 

[kingnero]

I meant dynamic load with DL = 900 kN, I'm sorry for the confusion.
Looking forward for the other numbers...

 

[Forensic74]

Looks reasonable to me. I second the notion that this is mostly based on deflection requirements. You may want to cover your butt upfront and do a quick calc of drying shrinkage. On those thick footings, you start getting shrinkage that will be out of their deflection specs. You can quote ACI224 which shows you can expect around 900e-6 ue within the first year.

 

[concretemasonry]

Most manufacturers of heavy industrial equipment have examples of successful foundation types for "general information". They usually mirror the differences required depending on the frequency of operation (cycles per minute, etc.), vibration frequencies (cycles per minute or per second. etc.), percentage of total mass that is static and what percentage is rotary or vibratory and the rates for each.

The location of the source of power (on same footing or not) and whether it is electrical, hydraulic or mechanical could also be factor.

You depth does not seem excessive and could even be light depending on the equipment. We had a concrete block manufacturing machine that weighed only 20 metric tons (dry) that had minimal extra loads. All raw materials and ancillary equipment was supported separately. It required at least 4' deep concrete footing for proper operation because of the wide range of vibratory frequencies and the amplitude.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[racookpe1978]

Not a structural engineer, and have not designed heavy equipment foundations, so please forgive the question:

How would this foundation design be integrated into the building slab and floor? Or would it be (deliberately) kept completely separate from the building slab to avoid interferences due to settling and movement/vibration of the press into the rest of the building?

 

[cvg]

seismic loading causing overturning moment may also control the foundation sizing.

 

[JAE]

racookpe - usually these are thick, mass-pads of concrete that have expansion/separation joints around their perimeter where a slab-on-grade would provide the surrounding floor.

 

[Robbiee]

Thanks to everyone commented to date. The only info available to me now is what I have posted in addition to the size of the pit and the spacing of the four columns. I have asked a number of questions such as the frequency of the press (which I think is very low), Whether vibration isolators are used, and the allowable deflection in the footing. This footing and based on the type of soil, is expected to settle about 1mm(0.04 in) under total weight. Shrinkage deflections, well did not think about it, but planning to provide top and bottom reinforcing to minimize it. And as JAE mentined, the slab on grade will be isolated from this footing and its pit.

 

[Robbiee]

I thinck I missed the point of the shrinkage deflection in my previous post. Now, If the ultimate vertical deflection due to shrinkage is more than the allowed value by the manufacturer, can it be reduced by adding vertical reinforcing under the footprint of the press? what other option are available beside providing "good" concrete mix?

 

[Forensic74]

I only point it out so you dont make any sort of unconditional guarantee in your contract. I've seen way to many engineers go into press work and get stung by deflections because they weren't vocal upfront that Mechanical engineering tolerances dont mix with foundation tolerances. The press manufactures will always claim that they never have install issues, but in reality I think it's very common.

It gets expensive quickly when you have a press sitting there that the manufacturer wont warrant because they cant get it to remain level to their asinine one millionth of an inch tolerance.....and removing and replacing the press to do any remedial work costs $500,000.

You might be able to mitigate the risk with SRA admixtures. You wouldn't be able to put enough rebar in there to make much difference to the tolerances they require.

Only other option would be to drive steel H-piles, or wait for a specified period of time to allow it to shrink out.

 

[Robbiee]

Kingnero,
The footprint of the press is 4.6x6m. The capacity? Don't know. It has been challenging getting info from the European manufacturer. Thanks

 

[TLHS]

If you have incredibly tight tolerances it may be worthwhile to look into whether you could install some kind of leveling jacks on the equipment, or even the foundation itself, so that you can adjust as settlement occurs.

I actually know of a colleague who installed a jacking system for a whole building slab. There was highly compressible soil, so whenever settlement reached a certain point they'd jack it back to where it was supposed to be and grout the void.

 

[MiketheEngineer]

Must be independent foundation - otherwise you will be bouncing people off the john seats 100 feet away....