topic Re: Sway steel structure in Robot Structural Analysis Forum

Sway steel structure

RRufino — Tue, 29 Dec 2020 18:00:25 GMT

Hello all,

I was reading other topics and testing some procedures on steel portal frames and i'm not sure if the following procedure is correct for a sway portal:

1) make a buckling analysis proofing thas i'm in presence of a sway structure (as seen on other topics by calculating alfacr for global buckling mode)

2) change linear combinations to "P-Delta" (not large displacements)

3) set member definitions as non-sway and define proper buckling lenghts

4) run steel design

Is this correct?

Do i've to break columns and beams in order to have several intermediate points?

Thanks in advance,

Happy new year,

Re: Sway steel structure

Simau — Wed, 30 Dec 2020 12:07:15 GMT

Hi @RRufino

could you specify what code you are using?

Re: Sway steel structure

RRufino — Wed, 30 Dec 2020 12:13:47 GMT

Hi @Simau ,

I'm using Eurocode 3.

Tks.

Re: Sway steel structure

Simau — Wed, 30 Dec 2020 13:10:53 GMT

I usually try to avoid alphacr < 10 for a global blucking.
So i can't tell you if your point 3 is correct.
You have to read carefully EC3 &5.2 &6.3
It's better if you have a concret example

Re: Sway steel structure

RRufino — Wed, 30 Dec 2020 16:16:01 GMT

Thanks @Simau , me too but i'm evaluating an existing structure. It's a single portal truss where alfacr=7. Nevertheless i'm also interest in general procedure and robot approach to study further structures.

Thanks,

Re: Sway steel structure

Simau — Wed, 30 Dec 2020 18:34:24 GMT

For what mode?

Could you post the structure deformation for this mode?

Re: Sway steel structure

RRufino — Mon, 04 Jan 2021 09:53:25 GMT

Hi @Simau ,

As requested,

But as i said previously i'm also interest in general procedure and robot approach to study further structures.

Thanks in advance,

Re: Sway steel structure

Simau — Mon, 04 Jan 2021 18:55:55 GMT

@RRufino

This deformation shape shows that there is a global buckling of the structure.
As I said you previously, I try to avoid Alpha cr < 10 by changing elements step by step to reach alpha > 10.
In case of existing structure With alpha-cr <10, I would try this ( but not sure @Krzysztof_Wasik 😞
Run a the second order with a “static analysis + P_Delta.” And check the displacements and resistance of the elements. The buckling lengths of bars are calculated according to your code using Robot features.