Circular Column Ties - Retrofit

[robcatstruct]

Hi All,

I am working on a rehab project where we are adding ties around a column that had broken ties and spalled cover concrete. For new columns we would lap by min 6" and hook the bars around the vertical bars. That is not feasible.

Lap for a #4 bar is 19", but the contractor has made ties that have a lap of about 12 inches. We are trying to utilize these ties if possible, but I am not seeing anything in ACI that talks about circular ties that just lap, but this is not new construction it is a retrofit to an existing column.

My question is, is there a way of estimating what is required in terms of tie tension based on the column profile and loading to see if the 12" lap would provide enough development?

Thanks in advance for your help!

 

[KootK]

Depends a bit on what you intend to use the ties for.

- If this needs so support serious, inelastic, bending excursions -- ala seismic -- then laps may not cut it no matter how long they are. In this case, you may need to modify the detailing or, perhaps, weld the laps.

- Are the ties needed for shear capacity?

- Are the ties needed for confinement to improve axial capacity?

- Are the ties only needed for vertical bar buckling restraint?

 

[Harbringer80]

Wow that column looks awful. How are you restoring capacity to the vertical bars? In lieu of ties you could pour new concrete around the column and wrap with FRP to provide confinement.

Regarding the reduced lap for ties, I'd make them correct their mistake. When doing restoration/strengthening to a seriously compromised member like this I tend not to cut corners.

 

[robcatstruct]

Depends a bit on what you intend to use the ties for.

- If this needs so support serious, inelastic, bending excursions -- ala seismic -- then laps may not cut it no matter how long they are. In this case, you may need to modify the detailing or, perhaps, weld the laps.

- Are the ties needed for shear capacity?

- Are the ties needed for confinement to improve axial capacity?

- Are the ties only needed for vertical bar buckling restraint?

KootK this is in a low seismic area, ties are for vertical bar buckling restraint. They will be forming up the column and pouring new concrete around the perimeter. The original plan was to weld the laps but my boss is trying to avoid it. Thanks for your input!

 

[robcatstruct]

Wow that column looks awful. How are you restoring capacity to the vertical bars? In lieu of ties you could pour new concrete around the column and wrap with FRP to provide confinement.

Regarding the reduced lap for ties, I'd make them correct their mistake. When doing restoration/strengthening to a seriously compromised member like this I tend not to cut corners.

It sure does look awful. The vertical bars are actually not bad, minor section loss on the bars that are exposed. I agree I dont like cutting any corners either. The original plan was to weld the lap splice that's why they were shorter but my boss is against it. Thats why I posed the question. I think I need to talk him into letting them weld them.

 

[KootK]

KootK this is in a low seismic area, ties are for vertical bar buckling restraint. They will be forming up the column and pouring new concrete around the perimeter. The original plan was to weld the laps but my boss is trying to avoid it. Thanks for your input!

Meh, I wouldn't get to excited about the lap if it's just bar buckling restraint.