Horizontal cracks in beam below slabs

[releky]

http://img856.imageshack.us/img856/428/7cya.jpg

Has anyone encountered horizontal cracks in beam right below the slabs just like in the picture above? What could have caused it?

 

[Ingenuity]

'Cold' joint?

 

[msquared48]

Inadvertent at that. Probably too long a time between two truck loads, without adequate interstitial vibrating or mixing.

Mike McCann
MMC Engineering

 

[hokie66]

Looks like a plastic settlement crack to me. Inadequate vibration.

 

[Moamen2020]

but i think if it was a problem of an inadequate vibration, there would be no way for this crack to appear again after plastering and painting . may be it's because of the rusting of longitudinal bars. i think there r some marks of old wetness on the surface

 

[releky]

The designer who saw it told me it can't be from torsion because this only occurs in cantilevered slab. We don't want to chip if off yet and still discussing what it might be. Do you have any picture of how cracks from torsion looks like, or from the so called sliding failure where the T-beam flange has separated from the beam web?

 

[graybeach]

I have seen cracks like this due to corrosion of post-tensioning tendons. Do you have grouted draped PT tendons at the top of the beam over a cantilever? Bleed water from grouting can get trapped here and cause corrosion.

 

[Moamen2020]

this photo displays what happens because of rusting of steel. may be it looked like your beam on it's earlier stages .at this photo we can notice that the upper part of the damaged area is the most damaged part . which can tell that may be it begins with a crack at this part ..i can't see ur photo well but i think that there is another lower horizontal crack at the right side of the photo..

 

[Moamen2020]

Link

 

[Moamen2020]

http://www.google.com.sa/imgres?tbm...tart=70&ndsp=25&tx=158&ty=93&biw=1366&bih=638

 

[releky]

The beam is just one year old. It doesn't have the cracks a year ago. There is no post tensioning tendons. There are proper stirrups and bars. Perhaps in a T-beam, if the flange is very stiff and the beam twist, it can cause separation of the slab and beam?

 

[Moamen2020]

can u give more details about the static system

 

[releky]

Here, maybe when the secondary beam rotates, the girder at horizontal gets twisted and slab restrain cause the beam to separate from it? Has this happened before in recorded history?

http://img24.imageshack.us/img24/7697/ff1g.jpg

 

[VoyageofDiscovery]

The beam width to slab thickness ratio may be too large creating shrinkage issues.

 

[releky]

Here is a hi-res photo not compressed:

http://img823.imageshack.us/img823/6323/n0oi.jpg

The stain above is just portion not painted well since the beam is just 10 months old.

In a T-Beam, won't it be possible the flange just separate from the beam web? You have slabs forming very rigid plane, then the beam underneath it. The thickness of the slab is 4 inches, the width of the beam is 12 inches. Would this be considered too large a ratio?

 

[VoyageofDiscovery]

You will have to look into this more, I don't typically work with 4" slabs. CIRIA had publications on this.

 

[Moamen2020]

that static system tells that it's a solid slab ....if so, that may be the cause because the rigidity of the solid slab much smaller than the beam .but if it's a flat slab it will be hard to occure . or may be it's more than one cause ..i really started to believe that it could be a pouring problem. alot of engineers prefer to pour concrete in beams first to insure the equilibrium of the formwork . if u attended the concrete pouring u can tell us if that happened or not . that may cause separation between layers. they could act like two deferent materials. with torsion caused by the secondary beam they could make that problem .
anyway i think there is nothing to be afraid of . because of the similarity of the structure insures that it was an immediate torsion and with small value. may be because of some deferent settlements . another reason to be free from worry that the spans arn't too large . and from the photo, the beem looks to have a good depth.
where r u from eng. Releky?

 

[Moamen2020]

sorry eng. Releky i hadn't seen the dimension when i wrote my last reply ...i think with these dimensions 30 cm for this main beam and 10 cms for the slab ...may be u have to worry ....i think that this main beam doesn't have an adequate depth especially that there is no internal column and it carries the secondary beam alone ...what is that structre for? is it a roof?
i think u have to check loads and design.

 

[releky]

Moamen2020, the depth is 19.68 inches, width 12 inches and thickness of slab (flange of T-beam) 4 inches. I was there in the pour, the slabs and beam were poured at same time or monolithic. If there are really separation between layers. It's great cause of worry because the beam being separated from the flange can no longer make it work as one unit, the compression zone can be said to be broken (the horizontal cracks) and this may not make compression work property (just like column with vertical cracks) although there are 2 compression bars on top with a diameter of 0.8 inch and 60000 psi. The loads and member sizes and reinforcements are fully in line with design code so no problem with it.

 

[Ingenuity]

"...It's great cause of worry because the beam being separated from the flange can no longer make it work as one unit, the compression zone can be said to be broken (the horizontal cracks) and this may not make compression work property..."

But I assume you have vertical shear reinforcement passing through the horizontal crack...hopefully with fully developed hooks that engage to the top long't beam reinforcing bars.