Base Plates/Anchorbolts
Base Plates/Anchorbolts
(OP)
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?
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?






RE: Base Plates/Anchorbolts
My preference is to provide leveling nuts. This allows the builder (+/-) 1/2" construction tolerance.
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 base plate, the hole diameter shall be not more than 6mm 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.
RE: Base Plates/Anchorbolts
I oversize holes as I see fit depending on what type of building structure and the anchor bolt pattern.
RE: Base Plates/Anchorbolts
http://www.aisc.org/content.aspx?id=2168
RE: Base Plates/Anchorbolts
RE: Base Plates/Anchorbolts
RE: Base Plates/Anchorbolts
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).
RE: Base Plates/Anchorbolts
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.
RE: Base Plates/Anchorbolts
RE: Base Plates/Anchorbolts
RE: Base Plates/Anchorbolts
RE: Base Plates/Anchorbolts