Portal milling machine stringent foundation deflection requirement

[hetgen]

We are task to design a foundation for this type of portal milling machine. The deflection requirement specified by the supplier appears very unreal.

See the diagram below showing the foundation layout, the length from D to F is 15m [~49 ft], and A to C, which is the width of the portal, is 4m [13.1 ft].
The maximum allowed deflection in operation are:
1) 0.01mm /m [ 0.00001 in/in ] along the length of the mill (from D to F or E to G, and
2) 0.01mm from A to C or 0.005mm/m [0.000005 in/in]

The deflection restriction only applies to the moving parts. The moving parts are heavy, the portal is 9ton [~19800lb], and the vertical slide is 5t [~11000 lb]. Even assuming the soil is extremely stiff, a massive concrete section will be required. The steel columns that support the portal do add a bit of stiffness too. (see the hatched area in the sketch above)

The project geotechnical engineer did provide us with a modulus of subgrade reaction, but caution using it to size anything that requires this kind of accuracy? he suggests we use piles extending to bedrock 20m below, but a pile that long will have large strain too?

We did ask the supplier for guidance. They said, assuming that we have good site condition, the deflection requirement can normally be achieved by providing a concrete base 5 x the weight of the milling machine.

Has anyone here dealt with this type of foundation design?

What is very strange is that they allow very thick grouting ~100mm [~4in] with a maximum swell of 1.5%. Which is huge compare to the deflection requirements?

See the detail below.

 

[phamENG]

Sounds like vibration limits, not static deflection limits. The response from the supplier mentioning the mass of the concrete base supports this, I think.

 

[dik]

Even if founded on bedrock, can you achieve those deflection limits?

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

-Dik

 

[hetgen]

@dik

We approach the deflection limits assuming 40MN/m3 (250psi/in) subgrade modulus and 3.0m [9.8ft] thick concrete foundation, but the geotechnical engineer is not happy.

Hoping to convince him, we said the loading is similar to wheel load so it should be okay if we use the subgrade modulus for short-term loading. But he is not accepting the assumption.

He said, considering the stringent deflection requirements, he can only vouch for the accuracy of measured rock elastic modulus, but not for soil subgrade reaction.

 

[phamENG]

Here's a recent thread that was going through a similar requirement: thread507-485226

Might prove a little useful.

 

[HTURKAK]

But you did not provide the modulus of subgrade reaction to us ... I assume , soft subgrade and the geotekkie proposed piling..
Better provide soil data and modulus of subgrade...

with a maximum swell of 1.5%. Which is huge compare to the deflection requirements?]

Apparently ,the thickness of grouting is 30 mm.. and the subject ( a maximum swell of 1.5%.).. is the limit for shrinkage of the grout.

 

[BAretired]

The specified deflection limits are unattainable. If they are made part of the contract, no one in his right mind would undertake the project.

BA

 

[dik]

even if founded on bedrock, I suspect...

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

-Dik

 

[phamENG]

That's why I think it must be referring to some relative, vibration induced movement. If the piece being machined and the mill itself share a foundation, and the foundation is sufficiently stiff, the relative deflection between the head and the piece can be drastically reduced. .01mm still feels pretty unobtainable, though. Hey. That's it! Build your foundation from unobtanium!

Jokes aside, I really think it's looking at relative dynamic displacements and not absolute static deflection. The supplier recommended a foundation 5x the weight of the mill. That strongly suggests to me the goal isn't settlement prevention but rather some sort of inertial damping.

And the <1.5% swell for the grout...I'm guessing that's in case your using a metallic grout designed to swell to counteract the cement shrinkage for a net stable or slight swell to prevent adverse shrinkage. And while it is huge, it will be compensated for after installation when they calibrate the mill. The deflections are for operations, so any movement prior to turning it on is irrelevant.

I don't have this and haven't used it, but seems like it could be helpful: ACI 531

 

[hetgen]

@phamENG

We will inquire again, but I think the requirements are static deflections curvatures (see clip below). It's similar to an overhead crane support beam deflection limit.

ACI 531's scope is limited to rotating; reciprocating; and Impact / impulsive machinery.

The mill portal and head move slowly. Once in a milling position, the deflection requirement should not be exceeded.

 

[hetgen]

Thanks, @dik & @BAretired.

I think we have to ask the supplier what they really want?

 

[phamENG]

Wow. That's kind of nuts. As a point of reference, that's the amount of deflection you'd get in a W8x10 spanning 3feet with a 9 pound point load at mid-span.

Good luck. Be sure to let us know what the supplier has to say.

 

[dik]

We likely have 100 years of good experience between us.

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

-Dik

 

[Brad805]

That milling machine will be capable of producing parts milled to within 0.003". Every little error is important. That said, it is easy to add unreasonable specs to a design table when it does not cost you anything. CR Onsrud makes similar machines (Link)