Bulging of CFT walls

[jaskamakkara]

Hi guys, just wondering what you make of this concrete-filled tube that we found during a frame inspection. It looks like all the side of the column are bulging - indeed it looks like the concrete socle at the base is restraining the deformation which is why some concrete is spalling off. At the upper end there is a brace connection and that is also clearly restraining the deformation. Very strange to me that the walls of the column are bulging over such a long distance, I would have expected some buckling deformations to be more local. Anyone seen this kind of thing before? Interestingly, the other similarly loaded columns do not show this same bulging.

It's a 180x180x5 SHS with plain concrete filling, it's total height is around 7,5m. I have included a stick diagram showing the arrangement - the column takes some compression from the top but also resists some bending moment from the entrance canopy brace that is attached between the stiff points formed by the bracing. Sorry it might all be a bit hard to see but hopefully you get the idea.

 

[dik]

I assume it's restrained at the top. The connection appears to have rotated a bit. It's a thin wall and with 25' of concrete, there could be a slight 'bulge' depending on how concrete was placed. I've never encountered this and I've never done calculations for this. If designed properly, there is little reason to be concerned.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[centondollar]

I do not see any buckling in those pictures. The beam is probably restrained at both top and bottom, and since it seems embedded deeply into the socle, it may experience stresses due to thermal gradients and imposed deformation from frame action. A remedy would´ve been (not sure if it´s worth fixing now) to install the column onto a baseplate and not into a hole in the poorly reinforced socle.

 

[jaskamakkara]

Thanks for the input, guys. Yes, I agree that this doesn't seem to concerning and it doesn't look like anything is buckling. I think the column is rotating a little and it gives the impression that it is bulging - I think I'll go back on site with a nice long straight edge and have a look myself.

Cheers

 

[gte447f]

Is freezing of entrapped water a possibility? I have seen several instances of freezing water inside a column resulting in the column walls bulging, although not usually over the entire length of the column.

 

[jayrod12]

I was going to suggest water intrusion and freezing as a possibility. Although it appears to be interior so freezing would be unlikely it is possible. We actually have a project locally where a HSS12x12 filled with water and froze, it split the column right down the weld. It was an interior column, however it was within an exit stair case that was only heating at the bottom floor by a small radiant heater.

 

[jaskamakkara]

Hi guys, sorry for not responding earlier my email notifications were going to junk for some reason.

I guess water entry is a possibility, there are some weird connections at the top of the columns and it's possible a weld or two is missing or incomplete, leaving some space for water to get in. As you mentioned, it is unlikely that freezing would be an issue but it's not beyond the realms of possibility if the shop had been empty for some time and the heating switched off. I'll investigate this a little further.