Repair Options for Buckling Wide Flange.

[tmoe]

See attached photo for reference.

Basically, this W10x12 outrigger had its bottom flange removed for aesthetic purposes without coordination of the structural team.
While the original beam was well designed for conservative eave snow loads, particularly heavy cornices have developed at the eaves, and in combination with the altered beam section, the web is buckling near the support.

Looking for recommendations on a field repair for the damaged beam.
I was hypothesizing that perhaps heat treatment to form the web back to vertical and then add welded side plates to strengthen the section.
I'm unclear on the pitfalls of heat treatment on a yielding member though.

 

[canwesteng]

I would weld the bottom flange back on, and add a doubler plate where the web has buckled. I don't believe there is a problem with residual stresses or metallurgy if you heat treat and hot bent the web back, if it is done properly, but the beam needs to be unloaded, and the cladding needs to be protected from the heat (which is true of welding as well).

 

[Rabbit12]

Has there been any talk of shoring that thing so it doesn't completely fail?

 

[tmoe]

@canwesteng - yeah that my initial thought, but the web is tapered from the end back to roughly the buckling locations. Perhaps cutting out the tapered portion of the web and replacing that with a full depth plate at the same time as the new bottom flange plate.

 

[jayrod12]

Why couldn't you put a flange on the tapered web? I assume it's a straight taper, not a rounded one?

 

[KootK]

To my eye, this looks like web sidesway buckling at a beam over column condition. Any chance this thing lacks web stiffeners at that connection? If so, this might be a viable solution:

1) Fabricate a pair of thick angles that will eventually serve as web stiffeners.

2) Bolt the angles to the existing web such that it straightens the web +/-. You might need to oversize some or all of the holes for tolerance.

3) Weld the angles to the beam web and bottom flange such that they're doing the stiffener job properly.

If this is sidesway buckling, then it likely has little to do with the tapered cantilever.

Did someone actually fit the wall cladding around the web?

 

[tmoe]

@Rabbit12 - yes the large eave snow load is being removed and the beam temporarily shored.

@jayrod12 - yeah I suppose the tapper could remain. no sense making things more difficult.

@KootK - The column connection detail does have stiffeners but the WT section left over as a result of cutting the bottom flange off is woefully under capacity for the cantilever length and snow load.

Just some more context for those curious: It appears from the details that the contractor cut the flange back at least 2x more than the should have. It was originally defined as 1.5x beam depth max which would be about 15" in this case. The cantilevers are roughly 36" from face of wall.
Also see picture where longer cantilevers are doing fine, but the its the shorter ones that are buckling.

 

[phamENG]

So that's what snow looks like...yikes.

 

[tmoe]

phamENG - Welcome to Tahoe, CA! Client was not happy when we previously told him he needs to be removing cornices like this at least once a season to prevent damage or injury/death.
these are particularly large due to the heavy winter we got this year, but either way, some due diligence is clearly going to be required at this site with regards to snow management.

 

[Rabbit12]

That is impressive! I've worked on projects in Yellowstone NP and they have serious snow loads there too.

 

[jerseyshore]

So buckling does exist. Who knew that cutting off those pesky bottom flanges were so important.

I like the idea of welding on a new web plate (ideally one on each side if you can straighten this buckled web back out) and then welding on a new bottom flange. Have to take the load off obviously and run the plates back as far as needed. Would be similar to a built-up/ rust repair type detail, just with a cantilever.

 

[3DDave]

Has that buckled vertically? It's tough to see if the top flange is bent or if the problem is the web can't take the concentrated vertical load.

Edit: Looking closer it's just buckling due to bending moment. If that's not continuing to increase the buckling and failing entirely means that it just needed enough deflection in the upper flange to take all the bending moment and the wrinkle means the web isn't doing much anymore.

It might look nicer to jack up the beam end and pound that web flat and weld on a bottom flange that is tapered to echo the taper of the web.

 

[TLHS]

My brain isn't comprehending the geometry right, because from that photo it looks like it's buckled at the point where it goes through the wall, but the wall isn't damaged, so that can't be what's actually happening. Is the buckling set out a bit from the wall face and then stops at the wall where it's restrained by that wood siding?

 

[Flotsam7018]

You've got to love steel, it let's you know when something is wrong.

I agree straightening the web and replacing the bottom flange to the designs original intent is likely the best path forward. Though as canwesteng mentioned, the amount of heat that will need to go into this repair will be quite tricky with all the surrounding finishes. I used to be a certified welder and I would have dreaded this repair - if you don't need a CJP weld here looking into stitch fillet welds based on the shear flow demand would make this repair a bit less daunting.