Jacketing or Strengthening for Existing Columns 1

[MSUK90]

I was checking columns for a ground villa where they have increased the floor height by 1m more than the approved height.
Many columns are failing in buckling now. However, when I change the column thickness from 200mm to 250mm, the columns passed the buckling check.
My question is regarding jacketing at site. Is it possible to just increase the concrete thickness to existing columns(without adding reinforcement)?
Has someone has experience doing such thing?
I would like to get some detailing drawings for this type of work or even drawings for jacketing with additional reinforcement.

 

[DCBII]

I would be very hesitant to jacket columns with concrete. First, the concrete outside the rebar cage is unconfined and is the first to crumble and fall off when overstressed. The further away from the cage, the larger the cracks. In high seismic regions you can usually plan on losing any concrete outside the rebar cage. Second, how do you ensure you get good bond? ACI 546 has some guidelines for adhering new concrete to existing concrete, but can you really get the project team to adhere to all those guidelines?

If you truly want to jacket it, I suggest looking into an external CFRP wrap to provide confinement to the concrete.

 

[jayrod12]

We've jacketed concrete columns before, however the jacketing was a minimum of 6" thick all around so we could fit additional verts and rings in the jacket.

All in all it went well. There's a 40 storey tower sitting on those columns now.

 

[DCBII]

I should clarify... jacketing with unreinforced concrete would concern me.

 

[STrctPono]

I was checking columns for a ground villa where they have increased the floor height by 1m more than the approved height.
Many columns are failing in buckling now.

1m increase in height has now caused the columns to buckle!? Really? When you say buckle, are you actually running a buckling capacity check or is this that it violates the kl/r ratio? Are you the designer of record or hired by the Contractor to fix a change?

 

[MSUK90]

ACI 546 has some guidelines for adhering new concrete to existing concrete, but can you really get the project team to adhere to all those guidelines?

I will look into the guidelines from ACI 546. I don't know if they are totally going to follow it but I believe they will.

 

[MSUK90]

1m increase in height has now caused the columns to buckle!? Really? When you say buckle, are you actually running a buckling capacity check or is this that it violates the kl/r ratio?

Yes, the height increased from 5.25m to 6.25m. Secondly, I am not running a detailed buckling analysis, it just the kl/r ratio or you can say the violation of clause 6.2.6 and 6.6.4.5.1 of ACI 318-14 where DeltaNS exceeds the allowed value of 1.4.

 

[MSUK90]

We've jacketed concrete columns before, however the jacketing was a minimum of 6" thick all around so we could fit additional verts and rings in the jacket.

I can't really increase the column width that much. When I check, they did work out in 250mm width. Just 50mm added concrete. Curios if I can add that without extra rebar(as extra rebar is not really required).

 

[HTURKAK]

You may post some sketches showing the structural plan and some details...
Jacketing of the RC columns ( in our region ) is a minimum of 4" thick all around and so one could fit additional vertical bars and and ties in the jacket.

In your case, strenghtening of the columns with steel plates could be a viable option.( pls look 6.2.5.2 For composite columns, the radius of gyration, r,...)

 

[NewbieInSE]

This type of detailing is followed in our office.

 

[DCBII]

MSUK90:
1. I still don't like it - extra unconfined concrete. I hope its not in a seismic region.
2. Expecting the contractor to do a good job bonding concrete to concrete is playing with fire. Lot's of surface preparation and probably some pull-testing required to validate it.
3. Have you thought about re-examining your analysis parameters. For example:
-Are you using moment magnification? Could a second-order analysis of another type remove some fat from your design?
-Live load reduction?
-Parabolic stress block?

 

[MSUK90]

You may post some sketches showing the structural plan and some details...

Here are the drawings which are approved for construction at site(please ignore the mark ups as I don't want to share the regional/company details).
The marked columns need amendment.

 

[MSUK90]

This type of detailing is followed in our office.

Thanks for sharing. I have seen a lot of sketches showing similar details. However, I am still looking for some details(or data) for jacketing only one or two sides of column(with and without added rebar). Please share if you get any info about it.

 

[MSUK90]

1. I still don't like it - extra unconfined concrete. I hope its not in a seismic region.
2. Expecting the contractor to do a good job bonding concrete to concrete is playing with fire. Lot's of surface preparation and probably some pull-testing required to validate it.
3. Have you thought about re-examining your analysis parameters. For example:
-Are you using moment magnification? Could a second-order analysis of another type remove some fat from your design?
-Live load reduction?
-Parabolic stress block?

1) Not in a seismic prone region and not even designed for seismic or wind loads.
2) Understood your concern, but that is the only hope I can keep with the contractor.
3) I didn't play with the parameters still. Was hoping to get some solution without that.

 

[HTURKAK]

MSUK90,

As far as i understand, you are hesitant for jacketing all around the columns with 100 mm thk. or the use steel plates and convert the critical columns to composite as per 6.2.5.2 ..

In this case, i will suggest you to speak with local construction chemical supplier ( may be with SIKA ) and use one of the repair mortars ( e.g. Sika MonoTop®-612) ..

But perform a detailed analysis including second order effects and try to see the situation .

I would prefer strenghtening with steel plates or angles ..

 

[JLNJ]

Not designed for wind loads?

 

[Enable]

...details

How does the contractor get the stirrup around the existing column when it's detailed as a single closed stirrup? Unless the contractor bends them quite significantly, the stirrups cannot get around the column as detailed. Typically such opening / closing is frowned upon at least by EOR's around here.

In restoration it's common for us to weld stirrups together in a U-configuration when doing such things for that reason.

You also want to take care with specifying a bonding agent. Certain agents have longer windows than others, but typically that window is 12 hours or less (temp dependent). And if the contractor doesn't apply the agent, form, and pour on the same day the bonding agent acts as a bond breaker.

However, I am still looking for some details(or data) for jacketing only one or two sides of column(with and without added rebar).

I've never jacketed anything for a structural purpose without some sort of additional reinforcing steel to add confinement. Jacketing to add cover, sure. But to increase strength? Never seen that without steel.

Anyways, here is a picture of a jacket on 2 sides of a column that I did a few months ago. I'll find the engineered details from the consultant and post later once I find them in the archives.

 

[MSUK90]

As far as i understand, you are hesitant for jacketing all around the columns with 100 mm thk

Yes, as that means added 200mm of column showing off the walls into the rooms and the client doesn't want it.

the use steel plates and convert the critical columns to composite as per 6.2.5.2 ..

This I can try but have never done/seen before.

 

[MSUK90]

Not designed for wind loads?

Yes. Here, the authority accepts mostly everything below 15m height to be designed without considering wind or seismic affects.

 

[MSUK90]

I've never jacketed anything for a structural purpose without some sort of additional reinforcing steel to add confinement. Jacketing to add cover, sure. But to increase strength? Never seen that without steel.

Anyways, here is a picture of a jacket on 2 sides of a column that I did a few months ago

Thanks for sharing your experience.

I'll find the engineered details from the consultant and post later once I find them in the archives.

Looking forward.