What phenomenon arises when wind or movement across a bridge causes sustained oscillations?

• A. Flutter
• B. Damping
• C. Buckling
• D. Vibration/Resonance

Answer: (D)

When wind or movement provides energy to a bridge at a frequency that matches one of its natural modes, the structure begins to vibrate. If the forcing continues at that resonant frequency, each cycle adds to the motion and the oscillations can grow and persist, especially when damping is not strong enough to dissipate the energy. This sustained oscillation is what we call vibration through resonance.

Damping is simply the energy loss mechanism that would dampen these motions, so it prevents persistence. Buckling is a static instability under compression, not a sustained dynamic vibration. Flutter is a specific aeroelastic instability that can occur at higher wind speeds due to coupling between aerodynamic forces and structural motion; the broad, general phenomenon described here is best termed vibration/resonance.