RC Columns Strengthened by Steel Jacket

[tristan861]

Hello guys;
I have a steel building of 4 floors with concrete columns. We decided to use circular plates around the concrete columns at the connection location (Please See attached) due to the high loads on the end steel beams.

Is there Any good reference for the design of this steel jacketing?. This would be so much appreciated guys

 

[briancpotter]

What sort of loading is this connection under? It's my understanding that partial-height steel jackets are mainly either for repairing damaged columns, or strengthening a column's plastic-hinge zone for seismic forces.

Brian C Potter, PE
Simple Supports - Back at it again with the engineering blog.

 

[tristan861]

The reason of the jacketing is to avoid connecting the steel beams to the concrete columns directly. Since the high moments on the beams will cause breakout problems in the concrete.

 

[JStephen]

It seems to me that moments in the beams will cause very high bending stresses in the sleeve. If you can use a heavy rolled piece or heavy pipe section and cast it into the column, it might be workable. If it is planned to use a thin sleeve, wrap it around the column and weld it, then I think the sleeve will be inadequate for the moment.
It would also be difficult to get the sleeve fitted to the column without some gap in between them.
Suggested approximate quick design check: Take half of the sleeve height, half of the diameter, assume it pinned at the ends, and check bending with the web tension force applied to it.
It might also be possible to come up with designs that used U-bolts to bolt around the column.

 

[tristan861]

When providing a steel ring or sleeve to the connection location, is it required to add anchors for shear transferring?. If not, How would it be guaranteed that there is bond between the steel and concrete in that location?

 

[Hokie93]

What is driving the requirement for round, cast-in-place concrete columns supporting structural steel-framed floors? In my experience and geographic practice area, this is atypical framing. Can the columns be concrete-encased steel columns? This would eliminate the beam/girder-to-column connection issues. Can the entire superstructure be cast-in-place concrete?

 

[KootK]

Are the concrete columns new or existing? Will they be in place prior to the steel showing up?

Can the beams be made pin supported at the columns?

If not, How would it be guaranteed that there is bond between the steel and concrete in that location?

Probably need the shear anchors if this thing is to be post installed. That, or some kind of adhesive.

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.

 

[tristan861]

Hokie93:
[Can the columns be concrete-encased steel columns? This would eliminate the beam/girder-to-column connection issues. Can the entire superstructure be cast-in-place concrete?]
Unfortunately, It can not

KootK:
[Are the concrete columns new or existing? Will they be in place prior to the steel showing up?]
They are new, cast in place columns.

KootK
[Can the beams be made pin supported at the columns?]
No, they are moment connection

 

[SAIL3]

transferring a moment thru the steel pipe jacket to the col would be a very complex problem to analyze....to begin with I could envision a ring stiffener @ the top and bottom of the pipe jacket with at least one vert stiff running from bottom ring stiff to the top ring stiff at the bm and one on the back side just for the jacket itself....then how to analyze the interaction of the jacket to the col is another problem that would require careful analysis of which I have no clue at the moment on how to address it .....

 

[KootK]

No, they are moment connection

What is the project goal that necessitates this? Are these moment frame beams? Cantilevers? As noted, there are a ton of great reasons not to create the moment connections. If we understand the intent here, we may be able provide more/better help.

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.

 

[SAIL3]

if possible , a rectangular col would present more viable options....

 

[tristan861]

KootK
Yes.those are moment frames. Ver. Bracing cannot be added for lateral stability. I tried to convince my manager to use steel columns instead of concrete ones to avoid the breakout problems but based on what he said it cant be done due to the project buudget.

Sail3
All I can do for those sleeves is to assume half the sleeve as a simply supported member and check it for bending due to tension and bearing. I have no idea how the bonding between the steel and the concrete would work or what extra analysis should be done here

 

[DETstru]

I think you'll blow any savings you make with concrete columns on this jacket system. It doesn't make much sense. What about using concrete beams instead?

Is your manager aware of the issues this will cause during construction? It will be very expensive to constantly switch between concrete and steel crews to build this as they go up the building.
If they're basing their cost solely on typical unit costs, they'll be in for a real treat once someone bids this and they realize how much it actually costs.

 

[KootK]

Hmmm... is it a visible connection? Maybe you could haunch the beam until the anchorage works? Or throughbolt through a square reinf cage out to washer plates etc?

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.

 

[briancpotter]

Assuming you're sticking with the steel beam/concrete column for the moment...

Why not instead of a jacket, use an embedded steel plate with 90 degree hooked bars welded to it? Something like that could be made as big as you needed it to be, really. Fabricating a plate to match the curvature of the column would be a hassle but it's light-years ahead of the difficulties involved in this steel jacket idea.

If you can't get something like that to work, I think you're better off re-examining your framing rather than looking into weird, untried connection ideas.

Brian C Potter, PE
Simple Supports - Back at it again with the engineering blog.