Building Displacement Shape

[ThisMustBeAJoke]

Hello, why my model showing this kind of behaviour under dead + eqx combination , at the Y direction it's like a normal flex. But in X direction it's like this.
Please help me, Thanks.

 

[JoshPlumSE]

Is this a response spectra earthquake load? An equivalent static lateral force earthquake load. A time-history response or what?

I suspect that it could be a response spectra analysis. If so, then this is likely due to the statistical combination of the results for each mode shape. Think of it as Square Root some of the squares where:

Total Displacement = Square Root (displacement_mode^2 + Displ_mode2^2 + Displ_mode3^2...).

Notice how this will always be a positive value? Even if all those displacements were originally negative?

 

[ThisMustBeAJoke]

Sorry forgot to mention, yes it was response spectra earthquake load. I understand your point but this does not apply for Y (dead + eqy combination) direction. And normally i don't see this kind of shape. What should i do or should i do something about this ? Boss i am confused

 

[JoshPlumSE]

Could the Y direction be a brace frame or shear wall? The type of weirdness in deflection is often because the plotted positive rotation of a joint doesn't match the positive displacement of that joint.

Regardless, I wouldn't read too much into it. See the Wiki articles on CSI's website.

https://wiki.csiamerica.com/display/kb/Deflected+configuration

https://wiki.csiamerica.com/display/kb/Base+reactions+for+response-spectrum+analysis

PS While I work for CSI, I'm not one of their technical experts. I participate in this forum on my own, not at a representative of the company. If you need an expert response to this, you should probably contact their technical support.