problem of beam moment-curvature figure

[wunico]

I use the nonlinearBeamColumn element to build a portal frame, and import an acceleration of ground motion(taft) to this frame,and finish the Transient analysis.
but when i analyze the beam's end section moment-curvature time–history curve, I find the figure is very secund? the column's is proper.
Normally,the section moment-curvature time–history curve surrounds the origin .why this beam section’s figure is like this? which factors may
cause that? And how can I resolve this problem?

[silvia]

is this still a problem?

[wunico]

i found the section moment-curvature time–history curve is secund,when the section is yield under the positive moment after yield under negative moment.i think the section be yield at negative curvature under positive moment is right,becouse the area of top steel is more than the bottom's.

[silvia]

okey, i am assuming secund means not symmetric.
but that's okey, right, if this is a portal frame gravity moments impose a symmetric bending-moment diagram, while lateral loads impose antisymmetric one. the symmetric (gravity) and antisymmetric (lateral) axial load affects the flexural strength.

the ground motion is not symmetric either.

so are things okey or not?