Cutting Bottom Flange of Steel Beam (In Place)
Cutting Bottom Flange of Steel Beam (In Place)
(OP)
I have a project under construction and have a beam that was specified as a W12x50, but they installed a W21x50. The other way around would have been a lot worse, but there are two ducts that need to pass under this beam and a certain ceiling height is required. This is an interior beam that supports a floor and is not part of the lateral system. The concrete deck has already been poured. The architect has asked if the bottom flange could be cut in the area the ducts need to go, so I'm looking into the possibility.
They want to cut out 5 1/2" from the bottom of the W21x50. That would leave enough depth to place horizontal stiffener plates at 14" below the top of beam. My quick preliminary check shows it wold work with that depth and appropriate stiffener design, but I realize there are a lot of things to consider: cutting heat, temporary shoring, preheating, welding inspection, stiffener design, etc.
I would make them shore the floor to take load off the beam and shore the beam on each side of the cut prior to work. I have enough depth to work with that I could add stiffener plates away from the cut edge about 1.5 inches. That will move the stiffener plates away from the heat-affected zone of the cut edge. All welds would be inspected.
I would appreciate any additional thoughts on this situation.
They want to cut out 5 1/2" from the bottom of the W21x50. That would leave enough depth to place horizontal stiffener plates at 14" below the top of beam. My quick preliminary check shows it wold work with that depth and appropriate stiffener design, but I realize there are a lot of things to consider: cutting heat, temporary shoring, preheating, welding inspection, stiffener design, etc.
I would make them shore the floor to take load off the beam and shore the beam on each side of the cut prior to work. I have enough depth to work with that I could add stiffener plates away from the cut edge about 1.5 inches. That will move the stiffener plates away from the heat-affected zone of the cut edge. All welds would be inspected.
I would appreciate any additional thoughts on this situation.






RE: Cutting Bottom Flange of Steel Beam (In Place)
If you're going with only horizontal stiffeners, I actually think that you could get away with no shoring / load removal here. You could install the stiffeners and then make the cut. I guess it depends how agressive and contractor friendly you want to be.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Cutting Bottom Flange of Steel Beam (In Place)
BA
RE: Cutting Bottom Flange of Steel Beam (In Place)
1) simple span beam?
2) where in the span(%) will the reduced section occur?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Cutting Bottom Flange of Steel Beam (In Place)
I like BA's concept of welding the new bottom flange, ie angles each side, prior to cutting off the existing bottom flange, as the reverse order would allow further accumulation of compressive stress in the top flange should there be any movements in the shores.
RE: Cutting Bottom Flange of Steel Beam (In Place)
RE: Cutting Bottom Flange of Steel Beam (In Place)
RE: Cutting Bottom Flange of Steel Beam (In Place)