Bulging on SHS steel column

[SSM_27]

Hello everyone,

Does anybody know why this "bulging" occurred on these SHS steel columns (see photos attached)? They appear in different places along the columns. Freeze-thaw maybe? They're closed off, maybe some water got inside though porous welds? The structure is near a large river (not saltwater) and it's unloaded (just self weight). Wall thickness is 4mm from what I understand.
Also what about those white spots on that galvanized steel members (last photo)? Because of the technological process?
Thoughts? Thank you in advance.

 

[Tomfh]

Local buckling due to fit up stresses. When they rattled up the bolts it’s caused the goal post frame to bend and yield at those points.

Note the way the U-shaped saddles are bulging/crushing.

 

[hokie66]

If I am looking at what you described as bulging, it just looks like a site welded splice to me. The weld projects beyond the face of the member. Not sure about the spots.

 

[SSM_27]

@Tomfh
This also happened lower down some columns, not near the connection. It's visible if you zoom in the 3rd photo, left column.

 

[SSM_27]

@hokie66
That's what I thought at first. But you can see in the first photo, it's not all around the cross section; usually they are for welded splices. Also it's seems they weren't there from the beginning, they appeared recently.

 

[Tomfh]

This also happened lower down some columns, not near the connection. It's visible if you zoom in the 3rd photo, left column.

There appears to be a connection on the other side of that buckle too? There is a secondary frame structure within the main frame, and it appears to connect at that location.

 

[SSM_27]

@Tomfh
It seems so, yes. But no bolted connection there. I'm not sure if those gussets (or whatever they are) are site welded or not, if that would make a difference. Anyway, they would be visible from the beginning, not later on. It was cold and it got warmer recently, that's why I was thinking freeze-thaw cycle effects. I've never seen local buckling for something like this (no major loads applied, 4mm steel).

 

[Tomfh]

The fact it occurs at the location of connections is too much coincidence for me. The connection points are likely applying point loads (possibly amplified by temperature) which is causing excess bending stress.

Are you sure it’s 4mm wall thickness?

 

[human909]

Yeah it looks a little thinner than 4mm. Both by the corner radius and the way it has locally buckled.

I highly doubt thermal would do this. Site workers trying to get bring a prefabricated out of square shape back into square is the more likely answer.

 

[dik]

I'd tap it with a hammer to see if the column makes a ringing sound...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik