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How are initial free-vibration conditions applied to the beginning of a time-history analysis?

Extended Question: I am interested in subjecting a SAP2000 model to an initial displacement and velocity at the start of a time-history analysis. Is this possible and how would it be done?

Answer: The initial conditions of a time-history load case may either be zero, or may continue from the end of a previous nonlinear analysis. Initial free-vibration conditions would have to be induced in the previous case before that state carries over into the time-history analysis.