Static equivalent force procedure in Etabs

[luungoclinh]

Dear all,
I am doing static equivalent force procedure for my shear wall building (no column is considered) in Etabs, but only for 2D analysis. I conduct 2 studied cases: one without eccentricity and the other with eccentricity of 0.1. I use the same response spectra for two cases. The fundamental period is selected by the user (less than mechanical value).
I expect to get very similar base shear from 2 cases because torque (eccentricity) does not influence base shear, but I get 2 different base shear values (20% difference).
Could anyone explain that to me? any help could be appreciate.
Thanks
Lisu

 

[pkjr618]

Hi luungoclinh,

Can you post the .edb file so that we can inspect the model for possible causes of this effect.

Thanks and regards,
pkjr618

 

[luungoclinh]

here is the model. I consider the YZ plane, just look at 2 load case labelling TORPOY (without eccentricity) and TORNEY (with eccentricity of 0.1)
Thanks
Lisu

 

[pkjr618]

Hi Lisu,

The peak acceleration is different for the two load cases. However, the most significant source of the difference lies on the story range specification where one of the two load cases considers a higher range than the other.

Regards,
pkjr618

 

[luungoclinh]

oh, yes. Thanks. It is solved. It seems that Etabs does take the time period value from user define, automatically, it still compares that value to empirical value calculated basing on height of the structure. Please correct me if I am wrong
Thanks again.
Lisu