Removal of Structural Epoxy

[ticas]

I need to remove a section of epoxy from a column and need feedback from those
with experience.

Epoxy seem to drill softer than concrete. Is it normal? This means one can just
drill it around rebars to separate the epoxy from bars? What else do you suggest?

Picture of the column with epoxy is in the thread called "Epoxy Modulus and Creep".
Structural engineer told me to remove it as well as the concrete in a lift and just
put new one.

Also when epoxy and concrete are removed with only bars remaining and this is an eccentric
loading. Moment of inertia of the bars are 10% that of column. Magnification factor would
reach 1.4 at just over 4% column load. In other woreds, the entire column would bend during
the repair, how do you handle this? Thanks.

 

[JAE]

ticas - for your last paragraph - you should shore up the adjoining beams, slabs, etc. to remove load from a column if the amount of concrete removal and repair is significant.

 

[ticas]

If vertical one foot concrete is removed and only bars remaining, and the loading is eccentric at one side of the column. Do you think it's possible the bars can bend to the heavier side? The moment of inertia of just bars are very low and moment magnificant factor can reach 2 even with just 5% loading of the column. Inadequate shores can cause this? I need to know because if true so we need to put extensive shores to avoid the bars and column just bending during repair. What is anyone experience on this? My structural engineer wil be back after the holidays and I just need to know this to prepare and order extensive shores if columns with bars only 1 foot can bend permanently during repair.

 

[Ron]

JAE gave you the answer. Shore everything that contributes to loading the column!
Here we go again.

 

[ticas]

I'll shore everything. But if eccentric loading in column with only bars remaining can bend, then I'd put 3 times more shore to be sure. Massive amount of shores have to be ordered so I need to know this single fact. Someone wrote in other thread that a column with only bars is equal to no column at all. He wrote:

"In short: the column would have essentially zero capacity.

A 2mm gap is indeed too short for the rebar to buckle according to the Euler bucking equation. So what you have amounts to a section of the column with greatly reduced area and moment of inertia. For the information you've given, the area at that section is about 1.4% of the area of the full column - with 60ksi rebar, it's theoretically possible to actually have sufficient compression capacity if the column was lightly loaded in the first place.

But that's before taking into account second order effects.

The moment of inertia of the 4 bars in the example you've given is around 3% of the total column. Taking into account that steel has an E value of around 7.25 that of regular concrete, your moment magnification factor reaches 1.4 (the limit prescribed by ACI) at just over 4% of the full column capacity. And that's before you get into all the other reasons the code would forbid this.

Don't ever do this."

Does he mean the column with gap will literally bend? Someone pls. just answer this or rephase what he is saying because I have to order massive extra amount of shores and some to my own account if it will bend.

 

[msquared48]

Caan someone put some epoxy on this thread?

Mike McCann
MMC Engineering

 

[jwilki]

Tics, you are repairing a column. You need to take the column out of action by providing propping/shoring/bracing as required to completely take the load off the column... The rebars will not bend because there is no load on them.

 

[rowingengineer]

I suggest while you have the floor propped/shored/braced that you remove the concrete column minus the reo bar for starters and lapping above. Then pour a new column however this time make sure you use a good mix with a pencil vibrator, maybe reviewing the reo setup and positions with your structural engineer.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[ticas]

There is still load. Imagine you are repairing the column of the ground floor of a 10-storey building, the load of the column below is the axial load of all the columns above. Even if all the floor beams above are shored, the weight still goes to the column of each floor and the column below is the total of the column loads above.

So even though the structural engineer will compute next week the geometry and sizes of the shore and distances to the column. It's only in the ground floor. The column itself takes the load of all columns above.

 

[rowingengineer]

shoring should extended above the ground floor to at least 3 floors above (if there are this many) and should be designed by the structural engineer. This will ensure that the loads are directed to the shores instead of the column.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."