Column Repair/Shoring

[mijowe]

We have been asked to come up with a column repair detail and procedure for a column damaged by a contractor during a renovation. Two concrete columns sit back to back at a building expansion joint, 2" gap. The gap was filled with stuff/gunk, and in attempt to remove it they used a core drill. While core drilling they not only removed part of the concrete cover but also cut rebar at the top of the column.

Each column is 32"x16" with 6 bars on each of the long faces of the column and the bars on the expansion joint face of both columns were effectively 100% removed. The columns are near the bottom of the building and have factored loads of about 900 kips each.

Any thoughts?

 

[jike]

Major Problem!

The only two thoughts that I can come up with are:

1) Pour new columns alongside the existing.

2) combine the two columns into one column, if you can justify not having an expansion joint or otherwise modify the expansion joint.

Good luck to the contractor who caused this damage!

 

[ishvaaag]

Prior to any works enough shoring to complete discharge the loads should be provided, according to engineering judgement.


1. Steel plates Option

One could drill completely at the centers of the 32" faces and insert a steel plate at the expansion joints' side to be taken with nut + expoxy there. Either the plate goes to the upper level to deliver proper tensile transfer or you provide by drilling the same.

2. Substitution of the entire column

You may do with proper shoring.

3. Adding additional steel members and parts

Some Shapes adequate to the problem may be added. One can ensure transfer of the tensile force by drilling into the sane columns.

 

[mijowe]

I like the idea of tying the two columns together. Right now the two columns sit on a single round column below, so the expansion joint goes away anyhow. The stuff that was cleaned out never allowed the joint to contract in the first place. And the building is old enough that the shrinkage of the concrete is no longer an issue, only thermal shrinkage would be an issue and since it is internal to the building these temperature changes would be small.

 

[ishvaaag]

If you opt for the single column then check for thermal acommodation of the annual cycle, especially with attached masonries and irregular plans. Either follow mandatory code separation or calculate thermal movement, and take proper measures.

 

[JedClampett]

I recently had a similar issue. A column was falling apart due to water infiltration corroding the bars. The cleanest approach in my judgement was to shore the beam above, knock out the column and replace it. In my case the dead load was relatively small (25 kips) so the shoring was not a huge deal. I used a small pipe (4 inch), timber cribbing, steel beams to distribute the load and had the contractor jack the beam above until they got a 25,000 lb reading.
The shoring was so tight that when the sun hit the 4 inch pipe, the reading on the jack would go up a couple of thousand pounds.
When you say 900 kips factored, what is the actual dead and live load? If you can design a shoring system for 200 kips or so (unfactored dead load), maybe replacement is the best way.

 

[AHaddad1]

In the worst case scenerio, the column has now created a hinge at the top of the column.

I have the following suggestion assuming you can solve the accessibility issue:

1) Shore the column that has the rebars cut, you can probably use two W14 Column Section on both side of the damaged column at the underside of the spandrel beams delivering the shear. Install cap plates at the end of the W14 section and use tapered shims welded in place after a tight fit. you might want to do the same at the floor above since there is also a load coming down from the upper floors.

2) dig 2 inches around all the cut rebars.

3) use a CADWELD(R) Rebar Splicer [or equal] to reconnect the cut bars.

4) Form and Inject high strength non-shrink / non-metalic grout to original Column shape and size.

 

[csd72]

there was a recent post similar to this on which I posted a very useful link.

Use the google search at the top of the page.