Problem of cracks in RC columns

[hamza41]

Hello,
The structure is a space frame supported on 15 RC columns (3x5). Columns height is about 12 m, their diameter is 60 cm. 5 columns, on the same axis, present vertical cracks in their mid-height in addition of a visible deflection.
A site visit will be arranged in the comming days and rebound hammer and cover meter tests will be performed. We suspect a lack of concrete resistance or cover.
Your opinions and suggestions are welcome.
Regards.

 

[SlideRuleEra]

..we may have to make an effort to convince (the Owner).

Propose to take cores of both defective areas on "bad" columns and similar locations on "good" columns. Test results will likely show no significant difference in the concrete. Explain that failure of some columns (to this date), but not others, is probably caused by either minor variations in concrete or just luck. As a former Owner, this is the type hard evidence that makes a convincing presentation.

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[SAIL3]

The deterioration of the space frames indicate a harsh environment.....it would be difficult to estimate the life-span of those cols going forward .....since the space frames are going to be replaced, perhaps that would require the bldg to be designed to current codes and render the current cols in need of replacement....

 

[MrHershey]

You are right, the columns replacement may be the solution to adopt, I'm expecting it, at least for the defected columns, and may be from the level of the cracked concrete. But the owner seems to refuse this solution, we may have to make an effort to convince him.

At least in the US I'd get a friendly contractor to weigh in (someone looking to be helpful, not just looking to make more work for themselves). And make sure they know the space frame is getting replaced too so they know they don't have to shore it up before removing the columns, also that there's no foundation work (assuming there actually isn't). Here in the US it would almost certainly be faster and very likely cheaper to just take the columns down and build new than to figure out what's wrong, design for what's wrong, and then build the fix. It's also possible you go through that whole process and the 'fix' is you still have to tear them down and rebuild.

I have never known an owner to insist on fixing an old structure for more money and more time when they have the option to tear it down and build a new one for less money and less time.

 

[hamza41]

Hello everyone,
I've come back to you again.
I've just finished investigation of the concrete columns. I'm waiting for laboratory results.
I've opened some cracks and noticed that concrete is fragile to a certain depth, until the rebars for some cracks, and the steel is corroded by different degrees. In one column,I've noticed a relatively advanced level of corrosion in one rebar, in the cracked zone,
and no corrosion in the next rebar, just below the cracked zone.
Similar cracks, but less wide, are noticed in some other columns in the two other axes. I've opened one of them and heve seen a relatively advanced level of corrosion with a relatively small cover comparing to others.
In the same column, at the same level, the concrete seems to be different from the north surfaces and the south ones, there is a difference in colour, look and sounds to hammer, escpecially the cracked ones, they sound very hollow from one side. It's almost the same for the 15 columns.
The problems seem to be due to carbonation or chloride attack on the concrete, accelerated by bad mix of concrete in these portions of these 5 columns and a lack of cover may be in another column.
We have taken 3 cores, 3 upv tests, some drill samples and some rebound hammer tests. We are waiting for compressive strength on the cores and chemical analysis.
What do you think ?

 

[jayrod12]

I think you've just solidified the knock it down course of action.

 

[rapt]

I would not think you need to ask! Replace them.

 

[hamza41]

I'm sorry jayrod12, I haven't understood your message.
If it was up to me, I would replace them, it would be too much easier and safer, but it's more complicated, the contract scope is about replacing the roof and repairing the columns.
The final tests will be more determinant.

 

[hokie66]

You have two situations with those columns, failures and imminent failures.

 

[jayrod12]

My comment was meant to say knock them down. Repair of that scope will likely be more expensive than remove and replace.

 

[MrHershey]

Go back to owner and give him the estimated time and cost for repair and the estimated time and cost for replacement. Contracts and scope can be (and often are) rewritten.

Again,

I have never known an owner to insist on fixing an old structure for more money and more time when they have the option to tear it down and build a new one for less money and less time.