Hollow Pot Slab Visualised And Detailed As Simply Supported Developing Cracks At Line of Support

[YuleMsee]

I have been called to give an opinion as to why cracks are developing on the upper surface of a hollow Pot Slab and to give recommendations. The slab is formed by 230mm thick concrete pots, with a width of 380mm and 130mm wide ribs and a concrete topping 75mm thick to give a total slab depth of 305mm.
The assumption was the spans are simply supported so no top steel was provided in the ribs at the supporting beams. Only BRC mesh a142 is provided on the 75mm thick concrete topping.
6 years after construction cracks are opening up at the line of supporting beams.
From analysis the structure is okay, what advice should I give the client in terms of dealing with the cracks.
A drawing of the slab is attached

 

[JAE]

Is the BRC mesh truly laid out in diagonal fashion as shown?
Usually for me there are top bars on concrete joists over beams - not sure why they didn't do that on these.

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[BAretired]

If analysis shows the structure to be okay, you could advise the owner to either live with the cracks or fill them with epoxy.

I wonder why it took six years before the cracks became noticeable with no top steel over the beams (other than wire mesh).

BA

 

[rapt]

Do the beams have top reinforcement?

 

[YuleMsee]

@rapt, yes, the beams are well reinforced

@JAE, no, 0it was not laid diagonally.

@BAretired, I think I phrased that wrong, I'm being called 6 years after construction, not sure when exactly they appeared, will definitely try to find this out from the client. The owner cannot live with this cracks since it's a front office and the cracks show on the ceramic tile finish. Do I introduce a joint in the finishes too after filling the cracks with epoxy?

 

[dik]

With a brittle surface, have you checked the deflections? maybe use a different flooring material? If deflection is an issue, any brittle surface will likely suffer the same fate.

Dik

 

[BAretired]

Cracks will show through a ceramic tile floor. Carpet might be a better solution.

BA