Is "Modal Response Spectrum Analysis" the same as response spectrum analysis? How about modal superposition analysis? This is the same or different? Or all are same?


A building with several degrees of freedom under a certain dynamic vibration, such as earthquake ground motion, will vibrate in several mode shapes. Each with a different frequency.

Modal response spectrum design involves imposing the predetermined response spectra of that particular frequency to that mode and after calculating the mass participation factor of individual modes add them together with as many modes as it takes to have at least 90% or either what the code requires mass participation.

There are several ways to add these modes together.

One is the square root of the sum of the squares SRSS method, there are other methods as well.

These are linear dynamic methods, ie, structure assumed never go beyond elastic range.

If we want to allow the structure to deform beyond yield stress into the plastic range we have to use complicated nonlinear methods.

Harvard University link

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    $\begingroup$ Thanks, good information, which I benefitted, but my question was simpler, I only asked if "Modal Response Spectrum Analysis" the same as "Response Spectrum Analysis?".Are these two the same thing? Only different ways of calling the same method? $\endgroup$ – user3600630 Apr 23 '20 at 10:50
  • $\begingroup$ Response spectrum analysis can be done with one DOF. In simplified version with no mode shapes to add. $\endgroup$ – kamran Apr 23 '20 at 19:50

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