Elevated Slab Crack Repair after water damage

[McStructures30]

Hello! I am dealing with an elevated formed one-way concrete slab spanning between steel beams that are cast into concrete as well where cracks have formed in the slab apparently due to sprinkler lines going off and flooding that first floor. The concrete slab is pretty old, the steel beams within the concrete are WF shapes. The claim is that these cracks were not present before the flooding and there is already moisture showing from the underside, see pic attached. The concrete around the steel beams are also cracks all the way under and around.

I am wondering how would you recommend to reinforce the slab or repair these cracks? there is only about 3 or 4 large cracks in an isolated area where the water was above. I am thinking to bolt a channel to the concrete encased beams with end plates along the cracks between the beams which are about 6 to 8 ft apart. most of the beams are parallel with the slab span (perp to beams) but about 2 or 3 are maybe 4 ft wide and parallel to the beams, I'd be more worried about these parallel to beam ones running across the slab. I am thinking of an epoxy injection into the beam cracks (concrete around beams is likely only for shear and fireproofing) just to seal those up.
Let me know your thoughts how to repair!


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[KootK]

1) Structurally, an encased steel beam like this would likely have been used one of two ways:

a) As a completely non-composite member with the concrete just there for fireproofing etc or;

b) Composite with the concrete but only the concrete above the neutral axis.

2) [1] leads me to believe that:

a) adding a channel to the underside of the beam would accomplish nothing at all structurally. The soffit concrete was never being utilized structurally in bending.

b) I'm not sure that you even need to fix the cracks on the bottom and sides of the beam. You really just need them to stay put for fire proofing. The epoxy injection business is appealing on some levels but, on the other hand, if the concrete cover is thin, the very act of performing the work might cause the concrete to fall off.

3) If there is a structural concern here, I think that it is that, whatever the water intrusion did here, it might have somehow compromised the shear bond between the concrete and the top flange which is necessary for composite action. I find that pretty unlikely though.

4) My gut feel here is that these cracks existed prior to the food as micro cracks. Then, when the water came, these cracks were enlarged and made more visible by way of:

a) Slight volumetric changes during the wetting and drying and;

b) The water scouring the cracks as it made its way through them en route to exiting.

b) Perhaps the weight of the water deflecting the beam a bit.

 

[McStructures30]

Thanks KOOTK, I agree with everything you said. I am really not concerned with the cracks down and around the beams, and I checked the steel members encased and they are adequate without composite action of the concrete. My thoughts were the cracks were existing prior to the flood also and the beam cracks would not make a huge difference if fixed or epoxied (potentially worse as you said).

However the cracks I am concerned about are the ones in the slab, first and third pic are looking directly up to the underside of slab with cracks both parallel and perp to the one way slab. I was mentioning the channel or bottom reinforcing members to run on the underside of slab along the cracks, not the beams. My concern would be slab failure over time

 

[jayrod12]

I think the same argument applies regarding the slab cracks in my mind.

There's no way those cracks are brand new, granted the photo quality isn't great, but they don't look "sharp" enough to be new cracks. They're likely shrinkage cracking from the original pour. But no one notices or pays attention to them until something like this happens and everyone starts actually looking.

Assuming that the reinforcing in the slab is adequate, I'd be non-concerned about the slab cracks as well. But in those scenarios, you could specify an epoxy injection just to satisfy the worry worts.

 

[KootK]

Agree with jarod12 in the slabs. The same logic would apply unless you've reason to believe that the slab bars have corroded somehow, which I'd not expect from a single wetting and drying. And, yeah, epoxy injection on the slab doesn't present the same spalling issue that it would on the encased beam.