Printing Press Footing 2

[B16A2]

I'm looking at a possible project for a printing press that would require an insanely small deflection tolerance (0.03mm/m). I think there's so many things that could go wrong. Heck, the natural shrinkage of the footing concrete could exceed this. How would one go about getting a geotechnical recommendation to satisfy?

Not that I'm going to go after this one, but I am interested if any of you have actually designed for something like this and how you have approached it. Almost seems impossible with structural engineering tolerances.

 

[TDAA]

I was asked to provide recommendations for an 8-foot diameter Kugel. The tolerance provided was for 1/8-inch over the approximately 10-foot footing. We ended up with three 18-inch diameter piers founded on dense material at a depth of 21 feet. Totally overkill for the weight of the ball.

 

[FixedEarth]

Not sure even if the surveyor can measure that small a difference!

 

[countervail]

Hmm

Would it be total settlement or differential settlement thats the problem.

I would think as long as the entire printing press and surrounding equipment settled at the same rate that might be acceptable.

 

[ishvaaag]

On counterval opinion, extend a rigid foundation for as much length they want the differential settlement limited; use a soft soil modulus of subgrade reaction, this will make them aware of the price of what asked; if go ahead, finish the envelope and then ensure operational temperature is kept stable; use low shrinkage concrete to level; enter the parts in the building and let them stabilize in temperature prior to assemblage.

 

[hawkaz]

Caissons all the way to bedrock. This is how many of the Washington DC monuments that are designed to last "forever" are supported. To do this, it helps to have an unlimited budget.

 

[B16A2]

Caissons all the way to bedrock would definitely not work. Concrete shrinks hundreds of microstrain in the first weeks, and continues on in the range of 50ue per week thereafter. If you place a 20' caisson, you're way out of movement spec just on shrinkage.

I do agree that the temperature would need to be stable. The foundation has a CTE of about 10 so even a 10 degree temperature change would put it out of spec.

 

[JLNJ]

This seems to me to be an unreasonable requirement. I don't think your degree of accuracy would allow for you to make a settlement or dynamic deflection prediction to three hundredths of a millimeter.

Maybe you can talk to the guy who wrote the specification and find out what he is after.

 

[TLHS]

The only real way I can see to be sure of that level of precision, unless you can build directly on bedrock and then grout to level once your concrete's set is to build the foundation using fairly normal tolerances and then adjust the level for the equipment afterwards. Possibly design in a way to modify it after construction so that periodic adjustments could be made to maintain the level as the foundation settles.

You could maybe put the equipment on a large skid with shim points where it sits on the foundation, then leave clearance underneath for a jack. Then you can jack the equipment a tiny amount up and shim it to make fine adjustments.

If the press isn't insanely large, you could probably attach some sort of screw jacks directly to the support points and adjust those directly.

 

[JedClampett]

When I worked in the power industry, we had large turbines that were very sensitive to settlement. A couple of questions come to my mind. Have you talked to the printing press engineers to verify that this is really what they want? Is this a differential settlement that they're worried about? That's easier to control than absolute settlement. And is this settlement for the press only (just for its weight) or the whole structure (press weight + DL)?
Some advice if it's just a differential settlement issue. Put survey points in corners of the foundation. Survey the foundation right after the manufacturer balances the machine. That way, if the machine goes out of balance, you can resurvey and eliminate the foundation as the cause.

 

[B16A2]

Yes, I spoke to the press engineers and they were adamant about this deflection criteria. They are most concerned about differential settlement, but honestly at such a small tolerance, the difference between differential and absolute movement isn't clear cut.

I hear what you're saying about getting a surveyor to measure the foundation. Even if I could find one willing to measure to that degree of accuracy (which I cant) I still see it as a can of worms that could be dragged into litigation.

The press manufacturer would come out and relevel once if there was a problem. But any more than that, it would be on the owners dime and the press would not be warranted. Crazy! One would think the press manufacturer would design their own rigid platform that could sit on some sort of pads that could sustain normal movement.

 

[BAretired]

I am trying to understand your units of deflection tolerance, i.e. 0.03mm/m...per meter of what?

BA

 

[MikeHalloran]

So, they're asking for a stiff structure, e.g.
1/33,333
instead of say
1/360.
Is that right?

If you could design a structure that stiff, settlement in the substrate would not affect it; it would just rest on the highest three points.




Mike Halloran
Pembroke Pines, FL, USA

 

[dik]

If you have competent bearing (aka stiff and relatively unyielding)then you can create a foundation with enough area (or embedded structural steel if necessary for stiffness) to achieve the deflection requirement. It's then a matter of casting a 'sub-cap' on this with a final cap to minimise shrinkage. It may be necessary to embed composite steel sections.

It's a matter of timing so that shrinkage can occur as well as size for stiffness. There is a real premium for high strength concrete (a balance between Ec and shrinkage), low slump, low w/c and possibly superP, mass and delay in doing the work to let shrinkage occur.

It's a challenge and very costly... unreasonable specs have a price.

Can the proper elevations be maintained using a flowable grout under the equipment?

Dik

 

[PMR06]

Here's another thread discussing a similar situation:

http://www.eng-tips.com/viewthread.cfm?qid=264282

 

[concretemasonry]

Just look at the difference between settlement and deflection. A rigid foundation will not deflect, no matter what it is placed on. A "structure" (no matter how rigid can settle) depending on the support. soil and even rock can move.

Precision equipment is set by millwrights that make sure the equipment is aligned and functional according to the equipment manufacturers specs. It can be re-leveled later if there is a problem that affects the process operation, but the foundation must be rigid. The manufacturers specs are to make sure there is a satisfactory base to install and operate on even if the is some long term settlement, plus they get paid for adjusting the equipment of the rigid foundation.

Mass, minimal foundation deflection are the keys in the end. Concrete is cheap and rigid. I had a project where the proposed foundation (16'x40') for a heavy (40,000#) piece of equipment which had very strong cyclical vibrations. It was supported on piling and the foundation was originally about 3' thick and both the owner and the equipment supplier insisted on at least 6' thick because it was just some cheap concrete.

Dick

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

 

[Bobber1]

I've done similar foundations using a fabricated base frame that can be relevelled by adjusting screws. The base frame had to be very stout! The frame also accomodated and concrete shrinkage without affecting the machine above. The millwrights would periodically relevel the unit using electronic levels.

Bob G.

 

[B16A2]

Thanks for the thoughts guys. I think some of you grasp what that deflection entails and the altered definition of "rigid".

I think just designing a huge hunk of concrete is a risky approach because at these tolerances nothing is rigid. Concrete shrinks even if you use SRA's. Look up self dessication. High strength concrete is VERY bad in this respect.

My approach would be steel H piles down to bedrock, to heavy honkin steel structure connected together with slip critical connections, and make the owner temperature control the entire environment.

 

[Den32]

We have done many of these press foundations. It really depends on the Press Manufacturer (not sure which you are involved with) as well as soils and height of press.

Is there an elevated press platform?

Typically, the mat foundation is supported by drilled piers or auger-cast piles.

The Press Manufacturer always makes (crazy) claims/requirements which the contractor cannot reasonably meet. I can go on and on, but it is beyond this single post.

Basically, it needs to be reasonably stout (carry design loads, minimal deflection and settlement) and contractor has to meet the tolerances. In all the ones we have done, the worst case is the contractor may have to come back and grind some areas - but even though the Press Manuf. won't admit it, they have 'adjustable' bases that can tolerate some construction differences.

 

[doka1]

I work for a concrete contractor that finished a printing press in the ny metro area. There was pile foundation with a massive footing slab (thick). The only portion that required precision within an 1/8" was the elevated press table and the topping slab on top of the footing. And yes den32 you may be correct, but the press manufacturer had a few disaster stories.