Leveling nuts and shims with grout pads 7

[nick24]

I'm currently installing some pumps and plan to use leveling nuts to level the pumps. They are self aligning so that is not my concern. Before I pour the grout pad, I've been told I need to come off of the leveling nuts so that the nuts are not bearing all of the weight but instead the grout pad is. The question is how do I come off of the leveling nuts before the grout is poured? The only thing I can think of is make a form which covers all areas except where the nuts are. Pour this and let it cure. Then come off the leveling nuts and pour the remainder of the grout pad. Is there another way to do it?

 

[dik]

It'll be interesting to see the response to this. I don't often use levelling nuts, but when I do... I grout them in and forget about them. See how others address this. There was a bit of a thread earlier on a similar topic.

Dik

 

[KootK]

I could be wrong but I thought that the usual way to address this was to use a slightly expansive grout.

 

[HTURKAK]

I understand the levelling nuts underside the baseplate for levelling purposes . The use of levelling nuts under the baseplate is not acceptable for the vibrating equipment foundations.

I copied and pasted my respond to thread407-462146
(..
HTURKAK (Structural)3 Jul 20 08:27

I just want to remind some critical points for grouting of vibrating machinery for more than 50 HP..

i =The grout shall support the equipment skid. The use of plate shims for adjustment will hinder this concept.

İİ=The use of adjustment nut underside the baseplate for levelling purpose , is not a good idea. This will hinder the loading of grout and tightening of the anchor nut will not be effective.

İİİ= The ( pump mass + grout mass + foundation mass ) shall vibrate as a unique mass to minimize the pump vibration effects. In order to justify this, the anchor bolt sahll be preloaded to a level , such that ,the concrete foundation will receive compression stress around tension strength or the preload shall overcome an externally applied cyclic load.

The following picture is copy and paste from the book ;The Grouting Handbook A Step-by-Step Guide for Foundation
Design and Machinery Installation (Donald M. Harrison ))

IMO, you have two options; either use levelling screw set up as shown on the picture or plastic levelling nuts..

 

[r13]

HTURKAK provided an excellent leveling/grouting method. In the past, for heavy, vibrating machinery, sleeve was used to perform the functions of leveling, allowing small adjustment on anchor rod position, post tensioning. The sleeve can be grouted, or leave it without grout for future retightening.

 

[nick24]

HTURKAK - Thanks for the insight. Can you provide a little more detail on that drawing you provided. How would the leveling screw work, is the equipment base plate tapped? Wouldn't that act similar to a leveling nut? How do you pre-load the anchor bolts? Lastly, I'm confused as to what the sleeve in the concrete foundation is and what purpose it serves?

Thanks

 

[dik]

thanks

Dik

 

[HTURKAK]

Yes...the equipment base plate is tapped... Alternatively the hole for adjustment screw drilled and a nut is welded at the top of the hole but this alternative is not preferable.


No...the levelling screw will be taken out after grout is hardened.. In case of levelling nut, one cannot take it out and preloading of the anchor bolt will be resisted by levelling nut so, preloading will not be effective..


The steps of construction: the equipment base shall be levelled using adjustment screws by turning the double nuts ( although single nut shown on the picture , there must be double nut to turn the screw.), then epoxy grouting is performed, then take out the adjustment screws, then preloading of the anchor bolts will be performed to a level , such that ,the concrete foundation will receive compression stress around tension strength or the preload shall overcome an externally applied cyclic load.

The sleeve is provided to avoid bond for a preloaded free length of the anchor bolt. The common practice, the anchor bolts with base plates are used and flexible conduit or duct tape wrapped for this purpose.

You may consider the use of plastic levelling nuts if the subject pumps are small..

 

[dik]

so, you could tack weld a nut to the underside to prevent it from turning and use a bolt from above to level it... and then remove the bolt? tack welding the nut is not an issue since it's only temporary and has no effect on the rest of the assembly?

Dik

 

[nick24]

HTURKAK - thanks again for all of the information. So if I understand this correctly, you're wrapping the leveling screw in duct tape so that the epoxy will not adhere to it? That way you can remove the screw once the epoxy grout as hardened? If that's the case, wouldnt there be a void in your grout pad where the screw was? Couldnt it also crack or affect the area around it as its being removed?

Thanks,

 

[r13]

dik,

I don't think it works this way. The screw hole is threaded, so once the screw is set/turned to desirable position, the plate wouldn't be able to drop down or backout because of the threads. The entire assembly is then fastened by the anchor bolt's nut after pre-tension/load, just prior to grout.

 

[dik]

Does the screw hole need to be threaded? What is the advantage? If threaded, the anchor rods have to be attached when the installed. Can you drill the holes out and use a levelling nut with a 1/2" neoprene spacer below and use the new anchorage to hold it in tension and the grout in compression? If you are concerned about transferring load to the anchor rods by means of the levelling nut. Something doesn't make sense or are there two sets of holes? One for anchorage and one for levelling? If two sets, abandon the threaded ones and use a double nut on the real anchor rod. Sorry, I missed the washer... or does the anchorage need a preload?

Dik

 

[dik]

Something like:

Dik

 

[1503-44]

Critical leveling points may not coincide with anchor bolt locations. Detail would need good wrench access to be able to reach and turn the nut. May also require more grout due to higher profile. May not always be convenient for all anchor bolt locations, especially if any are located close to equipment centerline at an interior point. Nut for leveling screw should be welded to top of skid flange, or skid flange must be tapped.

 

[BJI]

It is a separate hole that is tapped, the anchor hole is not. A welded nut should also work if preferred over tapping the base plate. After the grout sets the levelling bolt is removed, anchors tensioned and the hole filled with epoxy grout. Grease or wax can also be used on the stud to allow it to be removed after the grout has set. This level of effort would only be used in dynamic or very heavy load applications but could be used on any base plate. Usually the shims or levelling nuts just get grouted in if you can't temporarily support the structure elsewhere, but could lead to cracking over time. The below is a good reference that includes a similar detail.

https://www.parchem.com.au/public/pdfs/brochures/Filling-The-Gap-Guide-.pdf

 

[HTURKAK]

The answer is, the nut should be tack welded above the baseplate (if the hole is drilled , not tapped ) .The nut will support the base plate and equipment and provide the adjustment screw can level the base.

.

It is true that the wrapping the leveling screw with duct tape to ensure that the epoxy grout will not adhere to it and the screw will be removed once the grout is hardened. The void may be filled with epoxy and tapped hole may be closed with a short hexagonal headed bolt. The removal of levelling screw will not affect the area around and hardened grout..


Dear Dik; Yes ..the screw hole need to be threaded ( tapped ). The purpose of adjustment screw is for levelling of the base and after the grout is hardened will be removed.With this set up , one can preload the anchor bolts and prestress the RC foundation and grout. The picture that you released will work also if the neopren washer is above the nut, that is , the base plate shall not be supported by nuts directly on permanent anchor bolts . the steps for ( your picture set-up), provide nuts with neopren washers above at permanent anchor bolts,install the equipment and level ( using nuts + neopren washers ) , finger tightening of above permanent nuts, grouting of the foundation and preloading of anchor bolts. The preloading will be effective since the rubber washer will compress. Alternatively , you may use plastic adjustment nuts instead of (steel nut+ rubber washer).

 

[dik]

Neoprene washer should be below the nut in the event the nut is loaded it will not be transferred to the concrete. Baseplate can be supported by the nut, temporarily, but load not transferred to the concrete. If machine base has to be level at specific points and not all anchor rod locations, then threaded levelling screws can be used, else levelling nuts can be levelled by instrument or by machinist's level. I suspect it's unlikely that parts of the baseplate have to be level and not others. I don't see why the levelling nut if attached to the base plate cannot be located on the bottom... just means the nut is in the grout space after the bolt is removed, just like part of the baseplate.

Dik

 

[HTURKAK]

The purpose of preloading of anchor bolts for vibrating equipment foundation is tightening of foundation +grout and equipment and to obtain vibrating unique mass to minimize the pump vibration effects.

If you provide adjustment steel nut underside the baseplate for levelling purpose and neoprene washer below, the preloading of the anchor bolts after grout hardened , will not prestress the grout and foundation concrete. Just will tighten the bolt portion between two nuts..

The use of adjustment nut underside the baseplate for levelling purposes is a common practice for lighting masts, simple architectural buildings..However , the same concept is killing the behavior for anchor bolts of vibrating equipment and when fatigue loading is an issue..

 

[dik]

got it... to isolate the load from the anchor rods... thanks and does't work for preload.

Dik

 

[humanengr]

API 686, Ch. 5, Fig. H.1 - Mounting Plate Leveling Pads are Stainless Steel.