Shear cracks in concrete Beams.

[nisha1980]

Hi

I am investigating causes for cracks in a 5 storey apartment concrete frame building about 8 years old building . . We have band beams in the ground floor and other all floors we have transfer slabs and no beams. we have identified cracks in beams across the width and ma of 0.35mm crack width. and crack spacing is about 200mm and similar to stirrup spacing . We analysis the Beam in RAPT and gave the results that shear R/f in not enough.
so i think these are shear cracks .Attached are pictures of these cracks

1. Is there any other causes for these type of cracks ?

2. Whats the best economical solution to avoid further propagating these cracks ?

Appreciated your answers and thanks in Advance

 

[BAretired]

You are calling them shear cracks, but most of the cracks have the appearance of moment cracks, possibly amplified by temperature and shrinkage effects.​

The most economical solution is to leave the building alone. After eight years, it is unlikely that the cracks will propagate.​

BA

 

[JAE]

I would tend to agree with BAretired - although I don't know whether your photos are comprehensive of all the different conditions.

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[hokie66]

The cracks, as BA said, look like flexural cracks, and are not alarming. Are there other concerns about the building, e.g. distress in the walls of the upper floors?

The structural framing description bothers me. You said that the floors above are transfer slabs with no beams. But don't you mean that the floor with the band beams is the transfer floor, and that the other floors are flat plates, supported by the transfer floor?

Another thing of concern is the picture which shows the band beam offset on the columns, but that probably has nothing to do with the cracking.

 

[Ingenuity]

Are the band beams post-tensioned?

The photo shows the columns offset from the C/L of band beam, but the part framing plan does not show the same magnitude of offset:

The supportING columns (under) are those that you highlighted in YELLOW, and the columns OVER are those I shaded in RED, right?

 

[KootK]

I've seen similar flexura/restraint cracks in many buildings with band beam construction. For many years, I parked beneath such a beam with such cracks. While shallow, wide beams make sense for a number of reasons, I suspect that, on account of their limited depth, they are more prone to developing flexural cracks than are beams of more conventional proportions.

 

[nisha1980]

Thank you for everyone's comments and appreciated.

]for Ingenuity- No those are not post- tensioned. correct picture for the referring band beam is attached. "The supporting columns (under) are those that you highlighted in YELLOW, and the columns OVER are those I shaded in RED, right? " -yes that is correct. All these columns highlighted in red runs from Ground floor to 5th floor.

for hokie66- yes all other floors ( 1 to 5th ) are flat plates( flat slabs) and ground floor with band beams is a transfer slab .

this building has numerous cracks in the building supper structure , can be seen externally.haven't noticed any cracks in upper floors internally pictures attached.

Thanks everyone

 

[hokie66]

Those cracks in what you call the superstructure all seem to be related to openings in the external wall. But are they structural cracks, or cracks in finish material? Do you know the details of construction of those external walls, including the finishes?