Modal analysis question

[RamiHabchi93]

Hi, I have a question:
In modal analysis, to get the displacement of a story we combine story displacements obtained from each mode.what is the reason behind this?

 

[BigInch]

When waves of different periods add constructively, you get a bigger wave.

Reaction to change doesn't stop it

 

[chicopee]

To the OP, a course on vibration analysis should have been a requirement in your line of work.