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Column offset from pier & baseplate centerline

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P205

P205

Structural
Mar 2, 2008
136
This seems like a straightforward question but, given the picture below, do you see any issues with this offset? The architect is adamant on having the piers flush with the outside face of the foundation wall.

I'm only worried about the locations where we will have braced frames. With the uplift force being eccentric from the anchor rods, I would need to design the plate for the moment from the 2 anchor rods that are farther away. Or, conservatively, assume only the two closer anchor rods are taking all the tension load. Am I thinking about this right? Any thoughts?

Information:
- 2 story library addition
- Small building/small loads
- Low seismic area


The purple lines are the base plate and anchor rod holes. The blue/green lines are the pier. Hopefully this is clear enough.

Untitled_bjfckf.jpg
 
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If there is no moment at the base of the column, I don't see a big problem. If 2 rods will carry the uplift, have them do it. In my experience it is extremely rare for small columns and small piers on small buildings not to be flush on the outside, and the dimensions in your sketch definitely qualify for small. If it really concerns you, why not move the anchors toward the outside of the pier?
 
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Thank you for your response OldBldGuy. I just needed a sanity check.
 
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My experience is also that this is a very common arrangement, dictated by formwork simplification and interior/exterior aesthetics.

P205 said:
With the uplift force being eccentric from the anchor rods, I would need to design the plate for the moment from the 2 anchor rods that are farther away. Or, conservatively, assume only the two closer anchor rods are taking all the tension load. Am I thinking about this right? Any thoughts?
Click to expand...

I vote for something in between these extremes. Some designers will assume a uniform distribution of base plate compression stress or anchor bolt tension. I think that's erroneous given the relative flexibility of small columns versus the concrete pies etc. I'd estimate the tension in the anchor bolts imagining the column to be connected to the plate via a pin or ball joint (corner condition).
 
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Thanks KootK.

Being in somewhat of a silo at my current company, this website is invaluable and I really appreciate everyone's help.
 
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