Printing Press Foundation Design (Dynamic and Settlement Issues)

[structengr23]

I've not designed a foundation for a printing press. This one is for a client in Arkansas. The soils are good. Low PI and shale at 4' and beyond. Allowable bearing is around 2500 psf and expected settlement for shallow rigid foundations is less than 1", but the differential settlement tolerance required by the machine manufacturer (Koenig & Bauer) is like 0.05mm/m. That's very strict and similar to another thread I read thru on this site. In that thread, it was discussed to use piles down to bedrock. The weight of this machine is 422 kips spread out over a footprint that is 87'x9', long and narrow. The out of balance forces don't appear to be that bad. But, I typically try to get a foundation weight that is 3/1 ratio to equipment weight as a starting point. That requires a thick foundation that puts me right into the hard shale without any piers, since shale is 4' below grade. The client is whining about piles, so he is really going to whine about the extra plinth size for 3/1 ratio. The client say I don't need to anchor the equipment down, that all the supports can just bear on the concrete foundation with no embed steel plates.

I was hoping for some feedback on foundations done on typical printing presses. I don't want to over think it, but then again the cost of concrete and installation is much cheaper than replacing a damaged machine.

Thanks in advance.

 

[HTURKAK]

Absolutely you need detailed geotechnical investigation showing the soil stiffness values and predicted settlement for the proposed strip raft.
IMO, There are two options;

- Strip raft 12' X 92' with thick. 2.5 -3.0 ft . supported on compacted sand +gravel layer on shale.

- Similar raft extending to the shale , the loose weathered shale will be stripped.

If you post the soil stiffness values and predicted long therm settlement values you may get better responds..

 

[JLNJ]

0.05 mm/m may just not be possible, even with concrete down to the shale.

 

[SlideRuleEra]

I've not designed a foundation for a printing press.
But, I typically try to get a foundation weight that is 3/1 ratio to equipment weight as a starting point.

Maybe this machine does not need the typical preliminary foundation design you use.

I assume you make a machine's foundation massive so that it acts as an inertia block to dampen vibration. If so, the machine / foundation need to be securely connected so they vibrate as a single unit. Does the machine have provisions for numerous, "large" anchor bolts, or other secure anchorage to guarantee they vibrate together?

From your other comments, I don't think so.

With limited differential settlement as the primary requirement (instead of vibration dampening) the design approach shoud be very different.

http://www.SlideRuleEra.net

 

[WARose]

0.05 mm/m sounds pretty outrageous to me as well. (As far as foundation settlements go.) I can see leveling to that down the line.....but I couldn't guarantee that based on concrete shrinkage alone.

As far as settlement goes (for dynamic pressures).....most geotechs will recommend compacting to 70-75% relative density to eliminate the dynamic settlement issue. (In case you wind up on something besides that shale.)

 

[structengr23]

The modulus of subgrade reaction, k, is 100 lbs/per si/in. And the SPT-N values when you get to shale at 4' depth is 50 blows per foot roughly. I have a top block of 9' width x 4' depth (machine is around that width) and I added a plinth underslab (plinth) of 17' width x 3 foot depth that is dowel connected. I also have momentarily added micropiles under the bottom slab. Not sure if I need those if I'm resting right on top of the shale with the underslab (plinth).

The building manufacturer says we don't need to anchor the press to the slab. So it just bears on the slab. That was surprising. So, it must be fairly balanced with negligible uplift.

The max speed is 17000 Bg/h
Basic frequency for specified machine speed is 4.72 Hz
Max. circulating forces per printing unit are 317 lbf
Amplitude of 1st harmonic is 799 lbf
Amplitude of 9th harmonic is 16 lbf

I attached the design requirements from the manufacturer's drawings.

Thanks for the feedback!

 

[structengr23]

I also uploaded a snapshot of the press foundation with block and plinth combination on micropiles. Maybe a bit of overkill, but can always scale back in conservatism later. Basically the bottom of the plinth (lower foundation) is into the shale. So, may not need the micropiles at the end of the day. Also, attached is the general arrangement of the press inside the PEMB.

 

[structengr23]

Attached is the press foundation snapshot.

 

[WARose]

That makes a little more sense. The 0.05 mm/m is (apparently) a limiting rocking/vertical vibration limit. And that is doable by some quick numbers I ran. (Given the relatively low unbalanced forces.) I misunderstood your OP to say that was static criteria.

I'd have a wider foundation than that. (If I follow what you are saying it's only 17' wide.) But the numbers (for natural frequency and so on) will dictate that.

EDIT:

The modulus of subgrade reaction, k, is 100 lbs/per si/in.

That's static. The dynamic spring constants should be much greater than that.

 

[structengr23]

Yeah I was thinking the 100 lbs/si/in was a little low. I think it's stiffer than that. The micropile consultant says we can get some pretty stiff springs with the micropiles. Thanks for the feedback folks. I really appreciate it. As usual, the clients wig out with robust structures, but it's cheaper than replacing a damaged machine down the road, that's for sure.

 

[HTURKAK]

The amplitude of 1st harmonic 799 lb-f , basic frequency 4.72 Hz do not cause critical unbalanced forces.. If the wt of eq. 422000 lbs, seems no need to anchorage..

Apparently ,the subject upper limit 0.05 mm/m is for oscillation amplitude rather than the differential settlement tolerance.

However, flatness tolerance +,- 4 mm/ m or max. 15 mm should be assumed as tolerance for screed and differential settlements.

I do not have any idea for the reason for low tolerance for the differential settlement but i heard that the quality of color printing is sensitive to flatness and differential settlement.

I will suggest to analize the raft with piles and without piles and see the difference. IMO, the raft thk. around 4 ft ( extending to sound shale ) should be O.K.

 

[structengr23]

Thanks, Hturkak! Yeah, the unbalanced forces are not large at all. Yes, with the combined upper block and lower raft (plinth), I'm definitely into the shale enough for firm resistance. I agree with you that the underpinning may be a little overboard, but I will analyze both ways (with and without piles) and compare the deflection. If it doesn't required anchoring, that's a good sign that it's very balanced. The mass of the concrete to equipment is 3/1 right now. So, it will be robust. I appreciate the feedback.

 

[1503-44]

Printer dynamics isn't demanding, but that deflection is. Without rock, i'd think you'd be looking at roughly 6 to 8ft slab thickness, depending on actual mach wt distribution.

 

[dik]

If movement is critical, can you not excavate to the shale, and remove any loose/weathered shale and anchor it to the shale?... maybe 25M anchors on a 2'x2' grid?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[structengr23]

Yeah, you guys have confirmed what I read previously, that movement is a very big concern and can damage the machine. I hit shale at 4' below grade per the soils investigation. The soils guy introduced me to a micropile contractor, but I'm thinking if my total slab thickness is 7', I'm well into the shale. Is that enough stiffness, or do I need to add the micropiles to be sure? I mean that's like 60 micropiles. They wouldn't need to be that deep, but still. It's not cheap. Yeah, dik, I've got the shale cut down a bit and am anchoring into the shale also. Man, that should be plenty. My foundation mass is now 3 times my machine mass, i'm founded in shale, and I have micropiles. Very conservative.

 

[dik]

with the blessing of the geotekkie... done like a turkey.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik