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Problem of cracks in RC columns

Problem of cracks in RC columns

(OP)
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.







RE: Problem of cracks in RC columns

Quite a spindly structure, including the footings, columns, and space frame.

Based on the condition of the space frame, I would say the environment is quite severe.

I would check for carbonation depth in the columns. Carbonation to a significant depth, leading to corrosion of the reinforcement, would be my guess.

The cover meter would be useful, but forget the rebound hammer. That won't give you any useful information.

RE: Problem of cracks in RC columns

Agree with hokie66.

Chip off a cracked/spalled piece of concrete, break it in two to expose a 'fresh' surface and use phenolphthalein indicator solution to check for depth of carbonation.

If the structure is in a coastal environment you may also have increased chloride content, and it is easy to take samples and get them lab tested.

If it gets more 'complicated' you could take cores samples and do petrographic analysis/testing.


RE: Problem of cracks in RC columns

During construction, the columns appear to have been jump formed. Notice in the marked up photo that cracks more or less stop at the residual form marks. Compare test results from all sampled areas on all five columns - there may have been problems with specific batches of concrete, contractor's means and methods on certain days, weather conditions, etc. during construction.



www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Problem of cracks in RC columns

(OP)
Thank you for your answers.
Indeed, the structure is in a coastal environment is Saudi Arabia.
We thinked about coring samples and performing resistance, carbonation and chloride and sulphate content tests , but we were afraid this could cause damage to the columns since the cores are 100mm in diameter and up to 300mm long for only 600mm of diameter fo the column.
The problem is that the cracks are located only in the mid-length, between construction joints, for only 5 aligned columns, we think the quality of the concrete mix for these parts is pour. Is there any possibilities of repairs if carbonation or chloride content is proven ?
Thank you.

RE: Problem of cracks in RC columns

(OP)
Indeed SlideRuleEra, we first suspected the concrete batch in these parts.

RE: Problem of cracks in RC columns

I took an FRP class and this seems like a perfect circumstance for confining the columns with an FRP wrap....But I don't have experience with the carbonation and chloride damage. Is that a chemical process that can be stopped, or once it starts; it just keeps going?

RE: Problem of cracks in RC columns

Or, rather than some high tech magic, you could shore the structure and repour the columns.
The space frame also looks to be in bad shape. I see peeling paint in your pictures and I suspect it is corroded. Maybe it's time to price a new structure and replace.

RE: Problem of cracks in RC columns

(OP)
I forgot to tell you that the space frame will be replaced. The columns will have to withstand the reactions of the new one.

RE: Problem of cracks in RC columns

Tend to side with Jed on this one. May want to price out just replacing the columns if this is a widespread issue. It very well may be cheaper than tests plus repairs (assuming repairs actually address issue rather than just hide it), especially since you'll already be mobilized for the space frame replacement. And in the end you have brand new columns, not refurbished ones.

RE: Problem of cracks in RC columns

How was it poured and formed? Are the joints shown 'cold joints'; cracking seems to indicate that.

Really spindally, what type of bracing? Looks to be too recent for carbonation to be an issue. Doesn't look like a rebar problem, but, if near coastal areas, you should have a couple of inches of cover and maybe HDG rebar.

Dik

RE: Problem of cracks in RC columns

Quote (hamza41)

but we were afraid this could cause damage to the columns since the cores are 100mm in diameter and up to 300mm long for only 600mm of diameter fo the column.

Why do you need such large dia core samples?

2" dia cores for a 4" depth will usually be satisfactory for Cl- testing and petrographic analysis. 2" cores can be sometime used for compression strength testing too after you factor in H/D ratio and use adequate test capping.

RE: Problem of cracks in RC columns

I would think that 2" would be OK for some testing, but not compression testing... too small a sample to be meaningful. The columns are too small to take bigger cores, but could be patched. Rebar locator is essential.

None of this leads to 'why the cracks formed'; the procedure for construction has to be reviewed.

Dik

RE: Problem of cracks in RC columns

I was just looking at the web members. They are very slender and thin, and are exhibiting substantial corrosion already. Whatever coating system appears to have failed. The columns may be the least of your problems.

Dik

RE: Problem of cracks in RC columns

(OP)
Thank you all.
The structure was constructed in the 1980's, unfortunately, we don't have any information about its construction procedure.

RE: Problem of cracks in RC columns

Agree with hokie66....look at the concrete. A small core can tell a lot with proper evaluation, but can be misleading as well. I would shore the structure and do some destructive observation and sampling. Take as large a core as possible in multiple locations. It takes quite a bit of prepared surface area to do a proper voids assessment with petrography. As dik notes, a larger core is also better for strength evaluation. Chip away around rebar to assess condition directly.

RE: Problem of cracks in RC columns

If the structure is that old, carbonation may be an issue that should be checked.

Dik

RE: Problem of cracks in RC columns

Agree with MrHershey, it would probably be better to replace the columns as well if you are replacing the spaceframe!

RE: Problem of cracks in RC columns

If that space frame was not being replaced, I would spend some effort testing with the hope to limit to selectively repairing. But, since that frame is being replaced, I wouldn't bother. Spending all that money to replace the frame and not spending the extra effort to provide a long-term solution for the columns sounds like a waste.

One in the hand is worth two in the bush.

RE: Problem of cracks in RC columns

(OP)
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.

RE: Problem of cracks in RC columns

Quote (hamza41)

..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.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Problem of cracks in RC columns

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....

RE: Problem of cracks in RC columns

Quote (hamza41)

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.

RE: Problem of cracks in RC columns

(OP)
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 ?

RE: Problem of cracks in RC columns

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

RE: Problem of cracks in RC columns

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

RE: Problem of cracks in RC columns

(OP)
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.

RE: Problem of cracks in RC columns

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

RE: Problem of cracks in RC columns

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

RE: Problem of cracks in RC columns

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,

Quote (MrHershey)

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.

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