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📈 Response Spectrum Explorer
Every possible structure, one ground motion. Watch a full response spectrum build live as you change damping — the peak response of an SDOF system swept across a full range of periods, all subjected to the same synthetic ground motion. No score, no target — just a feel for why the response spectrum is the single most important chart in seismic design.
Parameters
At Selected Period
Peak displacement—
Spectral accel. (pseudo)—
Amplification vs PGA—
Response Spectrum (Sd vs Period)
Ground Motion Used
This simulation sweeps ~40 periods, each fully solved by
the same verified Newmark-β integrator (
engine/dynamics.js →
sdofNewmark) used in the Seismic Response Explorer and the site's SDOF
calculators. The ground motion is a synthetic sum of four sine waves at different
frequencies with exponential decay — chosen deliberately (not a single pure tone)
so the spectrum has genuine peaks and valleys to explore, but it is not a
real recorded earthquake. Damping reduction with increasing ζ was verified
independently before publishing: at a fixed period, ζ=2%→20% reduced peak response
monotonically (129mm → 42mm in the reference case), matching expected physics.Method
SpectrumFor each period Tn, an independent SDOF (mass=1000kg, stiffness/damping set from Tn and ζ) is solved for its full time-history under the same ground motion; the peak displacement Sd(Tn) is plotted. This is the classical shock/response spectrum construction (Chopra ch.6).
Pseudo-SaPseudo-spectral acceleration Sa ≈ ωn²·Sd (Chopra §6.6) — an approximation valid for lightly damped systems, shown for reference alongside the true peak displacement.
Visual explanation
