Question

define period in nature defination very short

Answer 1

In order to calculate the ductility factor, you have to find first the peak response (displacement) of the elastoplastic and the equivalent linear elastic structure, as well as the normalized yield strength of the elastoplastic system (namely the ratio of its yield force to its maximum force supposing that the system is linear elastic). All the above are valid only for a specific earthquake ground motion.

Therefore, you have to find the eigenperiod of the structure, then find the peak response from the elastoplastic response spectrum and the linear elastic response spectrum of the earthquake-induced ground motion, and then calculate the ductility factor, or ductility demand of the selected earthquake motion.

You can find some code to produce the linear elastic response spectrum and the constant ductility response spectrum of an arbitrary earthquake motion, and then you can find from them the maximum response. 

Answer 2

short-period. Adjective. (not comparable) (astronomy) Having an orbital period of less than 200 years, especially said of comets. HOPE THIS HELPS!!!