What Is Damping Ratio in Seismic Design?
Damping (the zeta's — the 5%; the energy's) is the structure's (the dissipation — the viscous; the hysteretic) expressed as (the % — the critical's; the ratio). The ratio: the 5%'s (the code's — the default; the spectra's), the 2%'s (the steel's — the welded), the 20-40%'s (the damped — the FVD's), and the spectra's (the scaled — the 1/√; the damped's). The shaking's — the damped.
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The damping's basics
The 5% (the code's — the default; the spectra's), the zeta (the ratio's — the c/ccr; the 0.05's), the viscous (the velocity's — the FVD's; the 20-40%'s), the hysteretic (the yielding's — the 15-30%'s; the equivalent's), and the Rayleigh (the 2-mode's — the alpha/beta's; the NRHA's).
The values by system
The 2% (the steel's — the welded; the tall's), the 5% (the concrete's — the default; the code's), the 7-10% (the masonry's — the cracked; the wood's), the 15-30% (the hysteretic's — the DDBD's; the ductility's), the 20-40% (the FVD's — the added; the Ch. 18's), and the 1-2% (the wind's — the serviceability's; the TMD's).
In design
The spectra (the scaled — the B1's; the 1.4's — the 2%'s), the 18 (the chapter's — the 20-40%'s; the damped's), the NRHA (the Rayleigh's — the 2-5%'s; the modeled), the comfort (the 1%'s — the wind's; the TMD's — the added), and the soil (the 5-20%'s — the radiation's; the SSI's). The damping's — the response's reducer.
The bottom line
Use 5% damping for code spectra (2% for welded steel, 7-10% for masonry/wood); add 20-40% via FVDs per Ch. 18 for 2-3x reduction — model Rayleigh 2-5% in NRHA and 5-20% radiation damping for SSI.
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