Seismic analysis - results / combinations

[micp_rsa]

Hello,

I think I need a bit of explanation for the seismic analysis principals in Robot.

OK, what’s the issue:

2D Steel frame. Very simple.
Firtstly I run modal analysis. Got whay I have expected.
Than I go for Seismic case with Newmark comb CQC (+ proper combination sign).
Now I read results ie. bending moments for each CQC combination.
Should I get results of moments from earthquake acting in +X direction and acting in -X direction? Results from cqc combination looks like earthquake acted only in one direction – towards X+.

Basically, based on modal shapes structure was deforming (sway deformation) the same to the right +X and the same to the left -X. So my understanding  is seismic should act in a similar way, giving utilization once in X+ and X- dir

I do not know if my understanding of a problem is right…. What you think of it?

[Krzysztof_Wasik]

Hi @micp_rsa 

Opposite seismic action direction should be considered by seismic combination definition. It can be done manualy (+ and - sign defined in manual combination including seismic cases), or it can be done automatically in Automatic combination module when Seismic Accidental combinations are chosen. Then combination module uses + and - for seismic cases in generated seismic combinations.

[micp_rsa]

Thank you @Krzysztof_Wasik 

I should have gone one step ahead to see that RSA cobines load with "+" and "-" sign automatically. Thought I need to have all simple cases as for example like wind.

One more question. I want to prepare automatic combinations.

I turned off case 4 and 5 to get involved only seismic cases 6to9. Is is the right approach?

Still have 4 and 5 in com list...

[Krzysztof_Wasik · Accepted solution]

Hi @micp_rsa 

It is correct, cases 4 and 5 are components of combinations 6 to 9. Robot presents components of seismic combinations in Definition column. Generates combinations represent cases 6 to 9 multiplied by "1" or " -1" combined with cases 1 and 2

[Simau · Accepted solution]

@micp_rsa 

1)I turned off case 4 and 5 to get involved only seismic cases 6to9. Is is the right approach?

Yes

2)

Still have 4 and 5 in com list...

Yes they they still appearin the list, just don't select them to create the groupe

[micp_rsa]

thanks @Simau and @Krzysztof_Wasik 

So basically I will not see cases 6to9 in the definition of Seismic automatic combination table, despite I have them checkboxed in automatic combination defnition as a cases?

They will allway be represented by simple cases 4 and 5. Is it right?  Please see screen below.

 

[Krzysztof_Wasik]

Hi @micp_rsa 

Yes you are right

[micp_rsa]

Thank you!

[manuel.gomes]

Hi @Krzysztof_Wasik

When we perform a spectral analysis Robot has the possibility of specify the acidental eccentricity. In a seismic analysis, in some codes too. But on other codes like NP EN 1998-1:2013 (Portugal EC8) Robot simply doesn't have that option. Do you have any idea why and how to solve it?

Thanks!