## 2 Types of Dampers on Structural Buildings
### Tuned Mass Dampers  
Tuned mass dampers (TMDs) are a type of passive device often used to control the response of buildings and bridges. A TMD consists of a mass-spring system attached to the main structure of a building or bridge and is usually installed on the roof of the structure to counteract the ground's motion to reduce the dynamic response of the structure. The dissipation of energy is achieved by the inertial damper forces acting on the structure [104; 105]. These systems are primarily efficient at controlling wind-generated vibrations in lean structures, such as towers and tall buildings. TMDs can be classified into three categories: tuned liquid dampers; TMDs; and tuned liquid column dampers. A TMD is the classic configuration of a tuned damper and consists of a properly adjusted damping element and a secondary mass with a spring to increase the attenuation of a primary structure resulting from frequency-dependent hysteresis. Therefore, TMDs can be credited with increasing the damping of a structural system. Although these devices effectively reduce wind-excited responses to stationary narrowband stimuli, they are less effective for broadband excitations, such as earthquakes [105]. The scheme of a TMD is shown in Figure 1[106]. It consists of a mass, spring stiffness in the structure, and damping for earthquake excitations. Numerous numerical, analytical, experimental, and optimal structural studies have been carried out to determine the efficacy of TMDs in reducing the seismic response of structures. [PERSON] et al. developed and implemented TMDs in building structures [106]. The study used real earthquake data in its numerical and statistical analysis of torsion in an installation in a five-story building. The results show that passive TMDs effectively reduced the response of the building during an earthquake. A similar experimental study conducted by [PERSON] et al. developed a TMD with multiple degrees of freedom and optimized the two degree of freedom system [107]. During its development, the TMD was quite a popular device, and it has been applied to several building structures. Several theoretical and experimental studies have been conducted on TMDs. [PERSON] (2006) theoretically and experimentally analyzed TMDs. [PERSON] et al. (2007) used linear TMDs to control seismic excitation in buildings with limited reliability based on technical optimizations. While both [PERSON] et al. (2007) and [PERSON] (2006) agree that TMDs optimize a building's response to seismic loads [108,109], [PERSON] et al. found that TMDs were not effective at reducing vibrations [110]. Not all studies on TMDs have analyzed their performance. Other studies investigated TMDs in terms of cost optimizations [111, 112, 113, 114, 115]. [PERSON] et al. compared the redistribution of structural materials and the application of TMDs to benchmarks for reinforced concrete structures with a 60-story steel belt frame with wind loading. The study concluded that a redesign of the building's standards, to meet inter-story deviations and the peak acceleration, would require a 14% increase in initial material costs, while using adjustable mass dampers would only require a 3.6% increase in the initial structural material costs [112]. However, TMDs can only reduce the free vibrations of a tall building structure. This also only happens when the earthquake ends. This is because TMDs have the task of mitigating the structural acceleration caused by wind on tall buildings. Various types of TMDs, including both passive and active TMDs, have been applied in several buildings in multiple countries. The most recent application of a TMD is shown in Figure 2.  
The development of the TMD also gave rise to the new idea of using liquid as a mass to balance the structure of a building when it vibrates. A tuned liquid damper (TLD) is a type of TMD. In this case, the mass used is replaced with a liquid (usually water). The effects of external vibrations are balanced through the movement of water in the tube or tank.