Please I need to ask, is mode superposition method used in the time history analysis in SACS sample 19 of blast Analysis?
If yes (as I think) why is the modal combination is not used?
Thanks a lot
Modal combination (SRSS or CQC) does not give a realistic representation of the behavior at any given time step. We square the response when performing modal combination which means that the response will always be positive and isn't necessarily reflective of the actual response. Those modal combination methods represent the maximum response for each element and therefore do not give a realistic global response. These methods are used simply to design each element for the expected worst case during the dynamic event.
The time history response uses super-position because we need a realistic global response at each time step to estimate the dynamic response at the next time step.