Open Ended Columns on Roof

[lejam]

A building was designed for 3 storeys with concrete roof slab. What if the beams and slabs of the roofslab won't be put yet but the 3 meter columns already arise that is open ended (without any beam connections on top of it). Is there any bad effects for this?

 

[briancpotter]

What type of columns are they (steel, concrete)? How long before the upper floors will be in place?

In general this shouldn't pose a problem - in precast buildings the upper floors of columns are often free for several days before the floor gets set. But it depends on the specifics of your situation.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[asixth]

As long as they have the capacity to freestand that 3m they will be okay.

 

[lejam]

brianc, it's concrete column and they will be left open ended for a year

 

[racookpe1978]

Hoow are you planning on protecting the exposed rebar and connecting bolts?

 

[lejam]

Spray with anti-rust paint?

But would the seismic resistance be better if beams would be added now to the columns or no difference if open ended at the 3rd level? Could adding beams now act like bracing? This is because longspan metal sheet may be used instead of roof slab one year or so from now.

 

[manstrom]

My only concern would be corrosion of the rebar

 

[lejam]

If you would temporary put weak cement-sand in the 0.5 meter open bars, how many bags of sands and cement in your experience so you can easily just remove it a year or two later with just light hammering?

 

[hokie66]

Why not finish the building now? Is the building to be occupied in the short term? If so, you will have to move out in order to provide shoring when you get around to casting the roof slab. How would you waterproof the top floor as a roof for the interim? Is this in one of those countries where you don't have to pay taxes on a building until it is finished?

 

[lejam]

Why would anyone have to move out when shoring for any roof slab when the floor supporting it is open to the skies.

The reason nothing is put yet is because it is not yet certain if the top floor will be used at all and only months later would we know. Of course we don't pay taxes until building is finished.

Do you think putting beams across the tops of the open columns can make it resist lateral seismic movement better? Imagine a building with 2 floors with beams versus 3 floors with beams. Would the latter produce better bracing against lateral movement?

 

[hokie66]

So you have designed the top floor to support the dead weight of the fresh concrete in the roof slab without shoring below the top floor? That is not the normal practice, but maybe you have thought of that.

If the top floor becomes your roof slab, will you waterproof it as such? I assume it is flat, and concrete is not inherently watertight. The reason for my question about taxes is that on my first visit to Northern African and Southern European countries, I marvelled at the number of unfinished buildings, with column reinforcement projecting above the topmost storey. When I was told the reason, I was amazed.

No, I don't think the beams would help.

 

[lejam]

Thank you.