Work out resonant frequency (mechanical) instantly with clear inputs, formula shown and shareable results.
A structure's natural frequency is (1/2pi) sqrt(k/m) - the frequency at which a small driving force builds a large response. A 60 kg mass on 15,000 N/m of stiffness resonates at 2.52 Hz, uncomfortably close to walking cadence, which is why floor and footbridge design targets keeping the first mode above about 5 Hz.
Resonant frequency
f = (1 / 2 pi) sqrt(k / m)
Static deflection link
f is approximately 15.76 / sqrt(deflection in mm)
At resonance the response is limited only by damping, so a modest repeated force can build displacements large enough to fail the structure.
Add stiffness to raise it or mass to lower it; frequency scales with the square root, so a 4x stiffness change only doubles it.