Structural damping

Damping refers to a structure’s ability to reduce its vibration energy over time on its own. When a structure undergoes vibration, energy is typically exchanged between kinetic energy, in the form of velocity swaying through its resting point, and potential energy, in the form of bending when the structure rests momentarily at its peak deflection. Damping comes into play to dissipate this energy, reducing the amplitude of the oscillation or vibration until the system comes to rest.

The most commonly understood form of damping is linear damping, where there is an opposite force proportional to the velocity of the structure’s movement. As the force is in the opposite direction of its velocity, it acts like a braking force, removing energy from the system. The more force is generated per unit velocity, the more the structure is damped. Damping is usually expressed by the damping coefficient [force per velocity] divided by the system’s critical damping coefficient. The critical damping coefficient equals 4×pi×moving mass×resonance frequency. As a reference, commonly a fixed steel member naturally has a damping of 0.16% or higher.

Without the addition of a dedicated damper system on a structure, such as tuned mass dampers, a structure damping is usually dominated by structural damping. This is aside from aerodynamic damping during high wind speeds, which adds damping in the wind direction of the structure. This damping is from structural elements within the system, such as joints or connections, and material damping, the material’s natural ability to reduce its vibration energy. However, structural damping is usually very low, and causes the structure to be sensitive to a phenomena called resonance.