Non linear time history analysis

[ankit2609]

hello everyone,
I am trying to do time history analysis (both linear and non linear) on a simple frame. The result obtained are seems quite absurd to me, which I am enlisting in here. Kindly throw some light on the possible mistake I might be committing.
Base shear from linear modal analysis= 1554 kN
Base shear from non-linear modal analysis= 1554 kN
Base shear from linear direct integration analysis= 1183 kN
Base shear from non-linear direct integration analysis= 1532 kN

I am also not clear about how to provide non-linearity in the structure, as I am not considering geometric non-linearity. Only non linearity to be considered is material non-linearity.

your guidance will be highly appreciated.

 

[PicoStruc]

Note 1 : Of course, the result of linear direct integration analysis will depend mainly of the time history accelerogram used !

Generally, many are used and a average is done for design.

Note 2 : If you want to compare, you need to model with the same damping for all analysis.

Note 3 : If you want to do Non-Linear Analysis in earthquake engineering, the most important aspect is off cource the material non-linearity and not the geometric non-linearity !

Geometric non-linearity, as negative stiffness, will soften you structure (increase you periods and then decrease force response) Be cautious of that !