What Is Rayleigh Damping in Structural Analysis?

How Rayleigh works

The C=αM+βK (the proportional's — the mass's + stiffness'; the 1877's), the alpha (the 2ζω1ω2/(ω1+ω2)'s — the mass's; the 1st's), the beta (the 2ζ/(ω1+ω2)'s — the stiffness'; the 2nd's), the 2-5% (the target's — the 1st/2nd's; the NRHA's), and the 2-mode (the anchored — the 1st's + 2nd's; the interpolated).

The pitfalls

The higher (the modes' — the overdamped; the beta's — the stiffness'), the 20%+ (the spurious's — the 10th's; the filtered), the initial (the stiffness' — the P-delta's; the committed), the tangent (the updated — the NRHA's; the preferred), and the 1st/3rd (the alternative's — the modes'; the sometimes).

Practice

The 2-5% (the NRHA's — the 1st/2nd's; the target), the tangent (the stiffness' — the updated; the 1st's), the 1st/3rd (the modes' — the alternative; the tall's), the modal (the alternative's — the 5%'s; the RSA's), and the 1877 (the Lord's — the 150-year; the still used). The Rayleigh's — the 2-mode's anchor; the tangent's — the preferred.

The bottom line

Set Rayleigh damping (C=αM+βK: α=2ζω1ω2/(ω1+ω2), β=2ζ/(ω1+ω2)) at 2-5% anchored to 1st/2nd modes for NRHA — use tangent stiffness to avoid spurious higher-mode overdamping; consider modal damping for RSA.

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