From motoring to construction, from power lines to wind generators. The mass damper, also known as dynamic absorber, is a device that is mounted on different types of structures in order to mitigate the negative effects of vibrations.
Which concept is the mass damper based on?
The purpose of the mass damper is to transfer the energy introduced by a force field into a vibrating system, deliberately sending a part into resonance so that the remaining portion of the system is kept still. Buildings, including skyscrapers, are easily subject to swaying caused by wind gusts or earthquake tremors.
There are two types of mass dampers: passive, as in the case of the tuned mass damper (TMD), and active, the active mass damper (AMD).
The TMD is an oscillating mass capable of discharging forces on the structural elements it is anchored to via a spring-damper connection. It allows for “capturing” the motion energy of the structure around its resonant frequency.
Active mass dampers (AMDs), the most advanced active version of the passive device called tuned mass damper, consist of an auxiliary oscillating mass, actuated by an actuator, which exerts a force on the mass, causing it to vibrate. The controlling force exerted on the structure is given by the inertia force of the mass, thanks to the action and reaction principle.
Who invented mass dampers?
The mass damping technique was first invented by Herman Frahm in 1901. Later on, in 1909, the concept of tuned mass damper (TMD) was developed when Frahm invented a vibration control device called a dynamic vibration absorber.
In the early 1970s, the mass damper was then applied to earthquakes by Bill Robinson, who developed the seismic damper, built using high-density lead and rubber to absorb the force of earthquakes.
From Asia to Europe – The evolution of the mass damper
Mass dampers are systems adopted especially in Asia, where for decades they have been common earthquake-resistant devices, able to withstand any type of vibration, including that of the wind, and for this reason they are used on very tall buildings, such as skyscrapers.
The most famous example of a TMD in existence is on the Taipei 101 skyscraper in Taiwan, where a 660-ton pendulum equipped with a total of eight huge hydraulic dampers has been installed.
The Taipei 101 Building in Taiwan
The first implementation of an active control device on a building was with the adoption, in 1989, of an AMD system in Tokyo inside the Kyobashi Seiwa building.
This 11-storey structure has two active masses of 5 tons (the weight of the building is about 400 tons) to withstand both the transverse motion of the building and the twisting motion of the wind.
Active mass dampers in Europe and Italy: ISAAC’s cases
ISAAC has patented the first AMD type active control system in Europe that can significantly improve the overall behaviour of a structure prone to earthquakes.
The system involves the installation of actuators on the roof of the building being protected and accelerometer sensors positioned at strategic points on the structure. A central computer coordinates and controls the entire system. The purpose of the latter is to withstand the movement of the building during earthquakes, reducing the oscillation amplitude of the building and consequently lessening the intensity of the forces acting on resistant structural elements. This process takes place through the generation of forces by machines, determined by the control algorithm implemented within the central computer. The latter measures the accelerations of the building at the points where the sensors are and, consequently, calculates the forces that the machines must generate.
The adoption of active control systems on civil structures makes it possible to obtain improvements to the building’s dynamic behaviour if an earthquake strikes that are comparable to those obtainable with the adoption of passive systems, but taking advantage of lesser invasiveness during installation. A system of this type, in fact, allows for intervening on buildings without disturbing the occupants and allows for minimizing preparatory accessory work for installation of the system.
The future of seismic protection has arrived. Learn more about ISAAC’s active protection systems.
