## 2 Types of Dampers on Structural Buildings
### Viscous Dampers  
One of the countermeasures for reducing seismic vibrations is to use an evaluation of the seismic design approach. In order to evaluate such a seismic design approach with nonlinear dynamic analysis, a robust model for the steel device and damper depending on the rating is required. Accurate models have been proposed for viscous, viscoelastic, and elastomeric fluids that are rate dependent [122; 123]. Fully active control systems apply both dissipative and non-dissipative forces to a structure. A properly designed fully active control system is capable of significantly increasing the damping in comparison with a passive system. However, controlling these devices requires a large amount of power and suffers from instabilities due to time delays. Moreover, these active systems will probably malfunction in the event of an electrical failure or damage as the control system ceases to operate and the damping device cannot change the system to a passive system. In this case, an active system provides a wider range of technologies. However, the actuator controller relies on an external power source to apply force to the structure. Therefore, providing optimal responses in relation to demand can be accomplished by adding or removing the applied force [124]. In control engineering, an active system consists of four interconnected components: (1) the plant (i.e., the building); (2) the sensors; (3) the controller or control computer; and (4) the actuators. Each of these components functions as a subsystem and is integrated in a closed feedback control loop such that the output of one component is the input of another component [125]. Although full-scale active systems have been implemented in research structures, the lack of reliability and the lack of cost-effectiveness have limited their widespread use in non-research models, which prefer to adopt passive systems instead. Therefore, full-scale active systems are still under investigation by many users  
Figure 2: Tuned mass damper applications: (**a**) 101-Taipei, Taipei—Taiwan; (**b**) Aspire Tower, Doha—Qatar; (**c**) Sanghai World Financial Center, Sanghai—China. and researchers. However, many studies have developed damping devices that optimize the cost-effectiveness and the potential reliability to provide a solution for both passive and active systems. As such, researchers have shifted their focus to semi-active systems in recent times [126; 127]. The development of damping devices that use semi-active systems progressed rapidly as they require significantly less energy to control than active systems. This is because semi-active systems do not require the addition of mechanical energy to the structural system. Therefore, the bounded input guarantees the stability of the bounded output. This type of device is also referred to as a controllable passive system [126; 128]. Semi-active systems provide electrical safety as, if the electrical device malfunctions or fails, the system converts into a passive system. This differs greatly from an active system, which relies on a considerable amount of power to control the system and increase performance. Semi-active systems do not require tremendous amounts of power to increase performance as feedback from the external sensors in the internal control mechanism dictates its dissipative or resistive power. This enables the system to inversely combine elements from active to passive or vice versa [128]. Semi-active systems effectively minimize structural damage under large environmental loads and provide three main advantages over active and passive systems. As they are very dissipative, they do not add energy to the system, thereby guaranteeing stability. Unlike passive systems, semi-active systems are also able to change their structural behavior due to nonlinearity, degradation, or damage over time. A recent study on semi-active systems demonstrated their efficacy for seismic control using viscous fluid dampers.