anchor rod holes in base plates

[rllo]

please help me understand AISC specs for anchor rod hole diameters in base plates

table 14-1 in AISC 16th edition (recommended sizes for washers and anchor rod holes in base plates) specs the maximum hole diameters as long as special washers are used, like square washers or round washers that meet the acceptable width in the same table.

if I want to use non-special washers (like ASTM F844 washers), Table 14-1 has a note at the bottom stating if F844 washers are used, the hole diameters are limited to
D + 5/16 (for D <= 1")
D + 1/2 (for 1" < D <= 2")
D + 1 (for 2" < D)

i've been taught to assumed contractors will use common F884 washers, so I follow the hole spec from the note. during QC I often get comments saying that hole sizes can just be D + 1/4" in all cases form one engineer, another engineer says just do D + 1/2" in all cases.

Does the note below table 14-1 also spec max hole sizes for F884 and engineers can spec anything less than that? for example 1/4" oversize is a more convenient spec than 5/16" oversize for D<= 1"

What is the correct way to size hole diameters for F844 washers?

 

[HDStructural]

The purpose of this rule is due to the difficulties of accurately placing anchor bolts in concrete. I have seen MANY MANY RFI's asking for anchor bolt fixes because they were put in the wrong spot. They can vary from 1/2" out of tolerance to more than a foot out of tolerance. The larger the hole, the less RFI's we will receive and more construction budget we can save for other items/profit.

I will always specify the original hole dimensions from the table (which used to be in AISC DG 1). I sometimes see smaller hole sizes on the shop drawings for my projects, and I comment that they are to be oversized per our project documents. If they choose to use a smaller hole, and there end up being alignment issues in the field, it is not our fault.

 

[RWW0002]

The footnote to the table [D + 5/16 (for D <= 1"), D + 1/2 (for 1" < D <= 2"), D + 1 (for 2" < D)] yields anchor rod holes similar to historic - i.e. "green book" - anchor rod hole sizes. Tons of projects have been successfully completed with the tolerances necessary to meet these hole sizes. I generally allow the use of the smaller holes, however I put a warning to the contractor to ensure that tighter tolerances are communicated with concrete subcontractors.

I agree that the larger bolt holes may reduce significance of field errors - although it is worth noting that extra clearance should be planned for for the larger plate washers+ anchor tolerance. I have seen many base plates where the larger holed and plate washers were used, but there was no extra room left between column and plate washers - there goes your "extra" tolerance"..

Also, be aware that plate washers may need to be welded to base plates for the case of significant shear transfer through anchors.

 

[rllo]

are the sizes in the footnote to the table (D + 5/16 (for D <= 1"), D + 1/2 (for 1" < D <= 2"), D + 1 (for 2" < D)) a maximum size and can engineers spec smaller sizes than than that?

I understand it will cause complications in the field. I'm trying to understand why someone would spec +1/4" instead of +5/16" (for D <= 1"). is there a standard size drill bit that is convenient to design to?