Explain modal analysis and its application in dynamic structural analysis.

Modal analysis determines natural frequencies and mode shapes of a structure by solving the eigenvalue problem [K - omega^2*M]{phi} = 0. Each mode has a frequency, shape, and participation factor. For dynamic loading, response is computed by superposing modal responses using modal superposition. Response spectrum analysis uses these modes with spectral accelerations. Key concepts include modal mass, effective modal mass, and SRSS/CQC combination rules. Sufficient modes must be included to capture 90% of total mass in each direction.