Base plate holes for +ö dia anchor bolts

[WWTEng]

The steel fabricator is showing 1 1/16” dia holes for these anchor bolts. These seem a little large to me. Should they not be only 1/8” larger then the anchor size?

 

[ToadJones]

I have used many different hole sizes depending on application. 1/8" is pretty tight for anchor bolts as you are counting on accurate placement of the anchors if they are cast into the foundation.

AISC suggests a 1 5/16" hole for a 3/4" rod believe it or not.

 

[structSU10]

I agree with Toad. Cast in anchors need more tolerance.

If you need to transfer shear to the anchors, welding the anchor rod to the plate washer, then plate washer to the base plate is the way to go.

 

[MrHershey]

As long as you have an big enough (thickness and width) washer, it shouldn't really make much of a difference what the size of the hole is. Don't want to go crazy, but contractor may decide they'd rather pay the upfront cost with bigger washers and additional welding than risk expensive repairs (and delays) for the hole not being to accommodate miscast anchors.

Wish one of my recent jobs had done that. Concrete sub was utterly incapable of placing embed plates and anchor rods in the correct place. Sometimes were several feet off on embed plates. Nothing you can do on the embeds several feet off, but bigger base plate holes would have allowed us to avoid the miscast anchor issues.

 

[ToadJones]

My rule of thumb for shear is over 10 kips I use shear lugs

 

[WillisV]

Yes. Big Holes Good. AISC Table 14-2.

 

[WWTEng]

Thanks all. So it appears that if you have a high shear load, either use shear lugs or use welding between washers & base plate. I am assuming in that case the detail would need to specify the welds between AB to washer and washer to BP.

 

[ToadJones]

I have never specified welding plate washers, but I believe the idea is to have a std. hole size in the plate washer. The washer is plaed over the A.B. after the column is set and the washer is welded to the baseplate only.
I don't think welding to the A.B. itself is a great idea.

 

[structSU10]

As long as the AB is made of weldable steel, it will help insure all anchors get the load. There are plenty of instances that even within the plate washer, bolts aren't in the same location relative to the hole, thus only 2 or maybe even 1 of the AB could be taking the shear load until say, at worst case, 1/8" of movement occurs. If shear transfer is high, I like to embed within the slab if possible, and if I have to a shear lug. I tend to hear complaints about installing shear lugs.

 

[ToadJones]

problem is you are transferring shear to a anchor bolt which is essentially cantilevered from the grout and goes into bending.
I supposed you'd have to fill the annular space around the bolt with grout or something to mitigate this.

 

[PUEngineer]

I agree, oversized holes in the base plate with a plate washer. I've always detailed the plate washer to have a standard hole for the anchor rod and assumed all rods are in bearing for shear if shear is to be resisted. Obviously the plate washer needs to be welded to the base plate.

As far as bending in the anchor rod, AISC anchor rod design guide has a procedure for combined bending, shear and tension in the anchor rods. The procedure accounts for the the bending through the thickness of the base plate.

 

[SAIL3]

As WillisV said..big holes good...
I just used 1 5/16" dia holes for 3/4" dia AB's...2" grout...leveling nuts with oversised pl washers above and below base pl...I don't fool around with bolts taking out shear anymore...maybe 1 or 2 kips..if used I take bending from top of conc to bottom of leveling nut..fixed at both ends....it is not worth the trouble to mess around with any significant shear in the AB's...I put in shear keys and move on..

 

[Ron]

Oversize...OK...Use plate washer as others have noted. Min. 5/16" thickness.

 

[abusementpark]

Do you guys call for the thick plate washer per AISC for all anxhors bolts on the project or just the ones that have net uplift?