tunedmass

A tuned mass, in the context of engineering, usually refers to the tuned mass damper (TMD), a device designed to reduce unwanted vibrations in structures. A TMD consists of a secondary mass connected to the structure through a spring and a damper. The system is tuned so that its natural frequency matches the target vibration mode of the structure, allowing it to counteract motions caused by wind, earthquakes, or other dynamic loads.

The operating principle is that when the structure is excited near its resonant frequency, the attached mass begins to move out of phase with the structure. Through the spring-damper connection, energy is transferred from the structure to the TMD, and the damper dissipates part of that energy as heat. The result is a reduction in peak displacements and accelerations, improving comfort and safety and potentially extending the life of structural components. The effectiveness depends on the mass ratio, stiffness, damping, and how closely the TMD is tuned to the dominant vibration modes.

Design and variants: A TMD is typically a passive system, but there are semi-active and active versions that adjust stiffness or damping in response to changing conditions. Mass ratios in tall buildings often range from a few tenths of a percent to a few percent of the structure’s modal mass. Common configurations place the TMD near or above the structure’s center of gravity to target the key modes. Materials and mechanisms must tolerate long-term loads and maintenance needs.

Applications: TMDs are widely used in tall skyscrapers and long-span bridges to mitigate wind-induced or seismic vibrations. Notable installations include large urban towers and major bridges, where the device contributes to reduced sway and improved occupant comfort.