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🌍 Seismic Response Explorer

A single-degree-of-freedom structure subjected to a ground motion pulse. Change the structure's natural period and damping ratio, and watch how its displacement response over time changes shape and magnitude — no score, no target, just a feel for why period and damping matter so much in seismic design.

Structure Properties

Natural period T_n 0.50 s

Damping ratio ζ 5%

Ground Motion Pulse

Pulse period T_p 0.60 s

Peak ground accel. 0.30 g

Live Response

Peak displacement—

Ductility demand proxy—

T_n / T_p ratio—

Response trend—

This simulation runs the exact same Newmark-β time-integration solver (engine/dynamics.js → sdofNewmark) used in the SDOF response calculators elsewhere on this platform. This engine was found to have a real coefficient bug during this session's verification work (an incorrect mass term caused up to 69% error against an independent Duhamel-integral cross-check on another page) — it was fixed, then re-verified against a closed-form step-load case (DLF=2.0, exact) and an independent scipy RK45 numerical integration (matching to <0.03% at well-conditioned points). See tests/dynamics.test.js for the full record.

Method

ModelSDOF system under base excitation, integrated by Newmark average-acceleration (β=¼, γ=½), unconditionally stable (Chopra §5.3).

PulseA single-cycle sine ground acceleration pulse — a simplified, illustrative "earthquake-like" input, not a real recorded ground motion.

Observed behaviorFor this single-cycle pulse, peak response increases roughly monotonically as Tn/Tp grows (a swept check from 0.2 to 2.8 showed no peak-then-decay). This differs from steady-state harmonic resonance, which does peak sharply near Tn=Tp — a genuine distinction between shock/pulse response and sustained-forcing resonance (Chopra ch.4 on shock spectra).

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