Effects of welding to RC structures, Cracks

[Rejido]

Any thoughts?

Just today I found a crack line located at the mid-span of my 6-m (500mm x 700mm) RC girder. The girder was designed to be connected with a wide flange steel beam at the mid-point of it.

The connection used was a 10mm thick plate anchor bolted to the RC girder with 6pcs M20 chemical bolts.

The steel beam was then full welded to the plate.

What do you think? does the increase of temperature during welding caused the RC girder to crack? or please share if you also have the same experiences...

 

[frv]

Seems like the fixity of the wide flange would result in some torsion in the girder.

 

[civilperson]

Depends on the weld proceedure. A qualified welder will use short increments of weld on alternate sides and on alternate flanges. This will keep the overall temperature increase small and minimize stress. The cured concrete should have enough strength to survive the welding process crack free. Please give some details of the connection orientation and the crack alignment, size and depth. Is the plate on the bottom or top of the beam, (best), or attached to the side face of the beam, (torsion inducing)? Is the crack horizontal or vertical? Does it show on both sides?

 

[csd72]

What about the chemical anchors? will the chemicals still be okay after they have been heated?

 

[hokie66]

Tell us about the crack. If it is vertical and at midspan, it is probably a normal flexural crack.

Why was the connection made in this manner? More standard practice would be to bolt a tee to the concrete, and in turn bolt the steel beam to the tee.

 

[Rejido]

@civilperson: the plate was attach to the one side face of the girder. yeah, it is torsion inducing. but it was design to withstand torsion.

the crack is parallel to the girder... the cracks (one at the top surface of the beam and one at the bottom/soffit of the beam) are 3 times the plates width long and the cracks width is approximately 1-3mm.

My initial assessment on this is that the welding process really caused the cracks. It suddenly appeared during the welding process... we all know that of about 500-600 deg F can really weaken the concrete.

Any thoughts of any solution to this?

Thanks to all your replies.

 

[civeng80]

Interesting and disturbing. So your saying that that RC beam was designed for a torsional moment requiring full full welding of the steel section to the plate?

It would then seem to me that the RC would be heavily reinforced at midspan. I would suggest that the heat generated by the welding may have expanded the chemset anchors and this may have caused the crack in the concrete.