Unbraced concrete structures with Eurocode 2

[Pretty Girl]

Simple, yet considerably tall structures like overhead water tanks are common in many countries to be built with concrete. Further, they are commonly designed to have no significant bracing to prevent sway etc.
However I didn't notice a straight forward way to design "unbraced" concrete structures with Eurocode 2.

How to design an unbraced structure like the following, in accordance with Eurocode 2?
I feel like, the engineers in the Eurozone must be validating that the "column to beam" monolithic connection is strong enough to prevent sway, but how? is there any equation mentioned in the Eurocode?

 

[HTURKAK]

The elevated tank structures shown in the pictures have horizontal bracing beams.









Don't underestimate a nail. A nail saves a horseshoe, a horseshoe saves a horse, a horse saves a commander, a commander saves an army, an army saves a whole country.. GENGHIS KHAN

 

[Pretty Girl]

@HTURKAK
Thank you. You meant horizontal beams prevent sway? how? it should be diagonal to resist horizontal sway isn't it?
Or is it like making the "column to horizontal beam" connection stiff enough so that it prevents sway. How to do that? is there any seperate checks or a design method to comeup with the necessary r/f area or the beam area to make sure that the connection can prevent sway?

I felt like columns need to design to prevent sway in this case (pictures) than expecting horizontal beams to resist sway. I don't feel like beams like that can resist the sway it might be going through.

How to make sure the beams can resist lateral sway?

 

[GeorgeTheCivilEngineer]

Calculate the moment and design the connection for that. This is much preferred as a concrete diagonal member would be heavy and difficult to construct formwork for. Pure tension should also be avoided where possible.

Due to the normal orthogonal arrangement of reinforcement and the monolithic construction, getting a nominal pinned connection takes more care and detailing than a moment connection.

See also: vierendeel truss

 

[HTURKAK]

My points ;

- Horizontal beams ( the bracing beams in this case )reduce the sway .. while diagonal bracing elements resist ( essentially tension ) with axial resistance, the beams will resist to sway with bending..

- You should make some effort to understand the behavior of frames ...

- I will suggest you to model a plane frame with a software . First the beam is pin connected to columns.. see that the columns will resist as cantilever elements. Then make the beam connections then see the deflected shape and moment diagram . Then add intermediate beams with rigid connection and see how the beams reduce the sway with bending element behavior.








Don't underestimate a nail. A nail saves a horseshoe, a horseshoe saves a horse, a horse saves a commander, a commander saves an army, an army saves a whole country.. GENGHIS KHAN

 

[Pretty Girl]

@GeorgeTheCivilEngineer

Thank you for your reply. So is it just design the "column-beam" connection for combining "non-sway + sway moments"? like p-Delta analysis for wind load?

We anyway doing the sway analysis (p-delta) for wind loads (lateral) and all other loads (vertical loads etc) as standard basic structural analysis.
What I don't understand is what is the additional calculations that we should do to make the connection resist the lateral sway which does not have bracings?
Is superimposing "non-sway + sway moments" and design the reinforcement and section in normal way according to Eurocode2 sufficient to resist lateral loads without diagonal bracings?

Or is there any other calculations to be done to make the "column-beam" connection resist the moments in a "non-braced" structure?

 

[Pretty Girl]

@HTURKAK

Thank you for your reply and suggestions.

I made a simple frame today and I understand that making the "column-beam" connection stiff can make it stop sway.
Is it sufficient just to calculate moments due to sway (wind loads etc) + other vertical loads, and then designing according to the Eurocode2 in normal way?

I'm asking this because, we normally calculate moments for "sway (wind loads etc)(p-delta etc) + other vertical loads" (moment distribution etc) when we design "braced" structures anyways. So what's the "new" analysis/method that I should carry out to check the connection can resist the moments in an "un-braced" structure? There should be a different method for "un-braced" structures isn't it? as Eurocode states that their code is for braced structures only.

Are you saying, that we first make the "un-braced" structure to a "braced" structure with strong enough "column-beam" connection? If so, how to check (which calculation method or formula etc) the "column-beam" connection braced enough to call it a braced structure? Is there any other methods or formula that has not mentioned in the eurocode?