Response Spectrum Analysis — Seismic & Shock
Response spectrum method, SRSS and CQC modal combination rules, floor spectra, and comparison with time-history analysis.
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Quick Explainer
What is a response spectrum and how is it different from a PSD?
A response spectrum is a plot of peak response of a single-DOF oscillator versus its natural frequency for a given input motion — used for seismic peak response. A PSD describes a random continuous signal. Response spectra are for transient peak-response problems; PSDs are for sustained random loading.
What is the difference between SRSS and CQC combination rules?
SRSS (Square Root of Sum of Squares) assumes modes respond independently and combines peaks by root-sum-square. CQC (Complete Quadratic Combination) accounts for correlation between closely spaced modes. CQC reduces to SRSS when modes are well-separated in frequency.