OVS Holes on Braced Bay Columns 1

[Veer007]

Hello All,

I am currently working on the base plate connection at the braced bay column. I have a doubt that is it structurally acceptable to provide oversized holes in the base plate for braced bay columns (even with a plate washer that has an STD hole).

I am under the impression that I should provide STD holes (anchor rod dia + 1/16"), but it will be very hard to erect the column at the site, Can you help me out with this?

Thanks in advance!!

 

[jayrod12]

I believe it is relatively common to provide oversized holes with welded washers, however I'm in non-seismic area so that may change things.

 

[KootK]

I agree with jayrod. Seismic or not, anchor bolt placement tolerances necessitate the use of oversized holes and weld washers for this kind of connection. The shear lug looks very skimpy here. Maybe that's just a graphical thing.

 

[Veer007]

Thank you...Here is the comment that I have received from EOR regarding the oversized hole in the base plate at braced bay columns.

Thanks in advance!!

 

[jayrod12]

I don't see anywhere that the washers are indicated as welded. Also his other comment doesn't make sense, 19 1/4" does fit within the drop. And didn't he detail the plate size to begin with?

I agree withhim that oversized holes and loose washers are not allowed. But welded washers should be acceptable.

 

[phamENG]

If they are going to insist on standard steel to steel hole sizes for the connection, they should also specify the tolerance for setting anchor bolts. 'Standard' size holes are not standard for base plates, so fit up tolerances should be specified by the EOR.

I've had to do this before - the location made it impractical to field weld and the steel was a prefab tower that we couldn't modify and the manufacturer wouldn't play ball. So I worked with the contractor (a great one, fortunately) and the worked up a field adjustable anchor setting template. It fastened to the top of the forms and could be adjusted in two directions by turning an adjusting screw. It had a couple layers of steel plate to align the anchors vertically and a precision machined centering point in the middle. Once placed, a surveyor located the center to make sure it lined up. The tower legs went on nicely, but it was a long and expensive process. Better to just detail in the tolerances and use either a suitable shear key or welded washers.

 

[WinelandV]

A couple random thoughts:

- regarding the baseplate size, I wonder if the 24" drop is centered on the column, making the off-center 19.25" plate not fit

- regarding the hole sizes, my hunch is the EOR sized the rods for some of the shear load, but not any of the bending that DG1 lays out for oversized holes and plate washers.

- at any rate, you'll want the GC and erector to bug the EOR about this as it will make construction more difficult. In my area, I've had a TERRIBLE time with anchor placement - the concrete subs here appear to eye in the anchors at best.

 

[Veer007]

Thank you all...Hope welded washers can help solve this issue..
Interesting to read this, however, most of the time the anchor bolts are not placed vertically, so it can be an expansive process as you said...


Thanks in advance!!