Base Plates/Anchorbolts

[eit09]

The company I work for now has a standard call out to provide double nuts on the anchor bolt for leveling of the base plates. Previous employer left this as a constructability issue in which the contractors just used shims for leveling. Both shims and nuts are covered by non shrink grout after leveling. Any pros, cons, or suggestions to either of the two leveling techniques?

I always provide holes in the base plates 1/2" larger than bolt for ease of placement when bolts are not exactly where they need to be ( seems to happen more often than not). I have been adding notes to weld plate washers to BP after column placement. This would allow all of the anchors to share the shear forces versus some anchors to yield before the rest of the anchors are bearing against BP. Is this overkill or does anyone else do something similar?

 

[rscassar]

What is your line of work? I am guessing the answer to this question is a regional thing because I once had a contractor from interstate ask the same question (shims vs levelling nuts).

My preference is to provide leveling nuts. This allows the builder (+/-) 1/2" construction tolerance.

I always provide holes in the base plates 1/2" larger than bolt for ease of placement when bolts are not exactly where they need to be

Common problem encountered on site is hold-down bolts being out of position. Good builders should be able to get the embedded items in the correct location. They should be able to do this without "wet-sticking" the embedded item after the concrete has been placed. This is critical to ensure the embedded item gets adequate concrete compaction around the bolt.

I don't know what any AISC code or specification says on the matter but the building standard which I comply with says:

Hole size The nominal diameter of a completed hole other than a hole in a base plate shall be 2mm larger than the nominal bolt diameter for a bolt not exceeding 24mm in diameter, and not more than 3mm larger for a bolt of greater diameter.

For a hole in a [highlight]base plate[/highlight], the hole diameter shall be not more than [highlight]6mm[/highlight] greater than the anchor bolt diameter. A special plate washer of minimum thickness 4mm shall be used under the nut if the hole diameter is 3mm or more larger than the bolt diameter.

I have always seen and specified 6mm increase in bolt size for baseplates (which is 1/4"). Generally, the note on the drawing follows: Provide each anchor bolt with two nuts and two oversized washers and provide sufficient thread to permit the levelling nut to be set below the baseplate.

 

[ToadJones]

we use 1/4" leveling plates that are set on leveling nuts and grouted-in prior to setting the column.
I oversize holes as I see fit depending on what type of building structure and the anchor bolt pattern.

 

[csd72]

The AISC field fixes video has a great section on anchor bolts:

http://www.aisc.org/content.aspx?id=2168

 

[eit09]

kikflip my line of work is also structural.

 

[sjohnAM]

I call for levelling nuts to be used to allow the contractor more control in making everything plumb. As for the hole diameters, I only call for the sizes stipulated in the AISC code (US). I have worked with other engineers that used different sizes than the AISC chart; however, this chart connects directly to the AISC Standard Code for fabrication and erection, which will directly hold the contractor responsible for bolt misalignment. Otherwise, the problem turns into 20 questions about how the hole diameter were chosen and what tolerances I was actually expecting.

 

[Lion06]

We don't call out hole sizes in baseplates. If the fabricator comes back with anything bigger than AISC recommends in their baseplates hole size table (which is in the 13th edition manual), we would ask why and look at the baseplates size again.

We typically show a grout bed with a 1/4" leveling plate, but we wouldn't complain if the contractor came back with shims or leveling nuts, but the leveling nuts do seem to need a thicker grout bed, and it's important to get the grout in before they get load on the columns.

You need to have plate washers to cover these large oversized holes, but we don't weld them unless we're counting on them for shear resistance, which is pretty rare (unless it's a moment frame building).

 

[nutte]

As for the hole diameters, I only call for the sizes stipulated in the AISC code (US). I have worked with other engineers that used different sizes than the AISC chart; however, this chart connects directly to the AISC Standard Code for fabrication and erection, which will directly hold the contractor responsible for bolt misalignment.

I would clarify that AISC does not specify base plate hole sizes. It is not in the AISC "code" (neither the Specification or Code of Standard Practice). Rather, in the Steel Construction Manual (not a "code"), there is a table of recommended hole sizes, as StructuralEIT mentioned.

 

[ToadJones]

I have always though that the AISC recommended hole sizes were way too big....but that's just me.

 

[eit09]

Are yall talking about AISC table 14-2 or is there another table for reccomended hole sizes? If 14-2 is what your referring to I believe these are just maximum recommended hole sizes not recommended hole sizes.

 

[nutte]

That's the table we're talking about.

 

[gbuell]

The same table appears in AISC Steel Design Guide 1 for base plates and anchor rods, but there they are called "Recommended" hole sizes, not "Maximums".