Cracks on beam

[concreteworld]

Dear All;

We received a complaint from one Owner of the building for cracks in the beam at 2nd floor of a 16 storeyed building; Below are details..
1. The building contains 16 floors
2. Design submittal 400 kg/cm² BS standards
3. Subject beam is 1.5 m thickness, 6 m length and 2 m width. Beam design strength is 40 MPa BS
4. Showing two different concrete surface soundness.
5. There is a clear horizontal line crossing beam along its length at its one 3rd level. It is not clear to be consider as a pour line or cold joint. We were not able to take Rebound No. due to rough face.
6. Along the line there are micro surface cracks with 10 to 20 cm length distributed perpendicular to the horizontal line.
7. There are three main cracks two of them at the above Right wall and one at Left wall.
8. Core failed (25 Mpa as against 40 Mpa) and core locations showing less distribution of coarse agg from inside

Please shed some light of the possible reasons for such cracks and low compressive strength of the cores.

Regards

 

[hokie66]

By the dimensions of this beam, I assume that it is a transfer beam, supporting a number of floors above. Although the roughly vertical cracks appear to be flexural in nature, there are many possible causes. Without knowing a lot more about the structural design, and perhaps more importantly, how the construction was staged, guessing is the best you can hope for here.

The horizontal line does have the appearance of a cold joint. That, along with the apparently low strength concrete, is certainly cause for concern and indication of poor construction practice and supervision.

 

[JAE]

The horizontal crack - surface is even across it so I would tend to agree with hokie66 that it is not a cold joint but there is a color difference it appears between the lower and upper sections.

The vertical crack on the right appears to veer off at an angle near the top implying some shear is getting involved higher up.

Is that a cantilever on the right side of the support? I see light but not sure if that is an end of the beam with the main span to the left.

 

[Ron]

The horizontal line is a cold joint. I would suggest low frequency ultrasonic testing to determine integrity. Surface tests will be irrelevant.

The width of the vertical crack starting near the column edge and progressing upward is wider just below the horizontal line than above it. This could indicate slippage along the cold joint.

Further, the vertical cracks appear wider at the top in general than at the bottom, indicating reverse bending over the column.

As noted, I would be very suspicious of the quality of the construction, including top steel placement.

 

[concreteworld]

Thanks for the analysis.

Please see attached pictures of the structure. The concrete cubes samples passed the compressive strength tests. But the Owner suspects that there is problem with the concrete itself rather than the poor construction practice.

 

[concreteworld]

another pic

 

[concreteworld]

See attached

 

[msquared48]

With the shape and aqppearance of the curved cold joint, I suspect that there was little to no rodding or vibrating between the two pours seen here, and with the crack pattern you show in your last pic, it seems like they could have been two different mix designs.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

The concrete only tells part of the story. The way the beam is reinforced is probably more important. Is it a post-tensioned beam?

Your last attachment shows a new support under the outboard column. Probably the right choice. Why wasn't it done that way the first time?

 

[rapt]

For the cracks at the right column, my guess would be that the top reinforcement into the cantilever has no or limited developement at the end of the cantilever (no cog at the end and probably large bars used!). So it is not developing sufficiently at the face of the support.

As it looks like a Deep Beam, that reinforcement should have been fully developed at the free end of the cantilever to act as a tension tie. So it needed to be either anchored prestressing tendons or a welded plate to develop bars to the end.

If it is actually a flexural beam, the top reinforcement still needs to develop full capacity at D from the face of the support, which would still require full or nearly full development of the bars at the end, depending on the dimensions.

For the other cracks, a beam of this size would require a lot of side face reinforcement, both for shrinkage/temperature and, if a deep beam as suspected, for shear. I doubt that sufficient has been provided.