# State-of-the-Art Review of Structural Vibration Control: Overview and Research Gaps
## 4 Semi-Active Control Systems
\begin{table}
\begin{tabular}{c c} \hline
**Control Systems** & **Key Features** \\ \hline Friction control devices & \(\bullet\) & Employed either as energy dispersers in the lateral bracing of a structure or as elements in sliding isolation systems. \\ \hline Friction-controllable sliding bearing & \(\bullet\) & The pressure between the two sliding surfaces can be adjusted to manage the friction between the bearing and the ground. \\ \hline Tuned mass dampers & \(\bullet\) & Tuned mass dampers essentially comprise a single-degree-of-freedom mass-spring-damper arrangement usually positioned on the uppermost floor of a multi-story building. \\ Tuned mass dampers & \(\bullet\) & The dynamic traits of the system are adjusted to manage the movement of the structure to which it is connected. \\ Tuned liquid dampers & \(\bullet\) & An effective control approach for managing a variety of dynamic loading scenarios. \\ \hline Tuned liquid dampers & \(\bullet\) & Commonly used when the lateral force-resisting consists of braces. \\ Tuned mass dampers & \(\bullet\) & It slips at the interface when the brace’s axial forces reach a predetermined threshold (the friction coefficient multiplied by the clamping force). \\ Semi-active slip bracing system & \(\bullet\) & Installing this type of device allows for the adjustment of a brace’s strength without changing its stiffness. \\ Tuned mass dampers & \(\bullet\) & Another benefit of this device over a passive one is its ability to operate effectively under minor forces (such as small earthquakes or winds) while still delivering effective performance under greater demands. \\ \hline Electro-inductive device & \(\bullet\) & Key factors in utilizing electro-inductive devices rather than fluid dampers include the following: \\ Electro-inductive device & \(\bullet\) & The behavior is essentially unaffected by outside temperature, as the device’s operating temperature consistently exceeds the air temperature and is achieved in just a few seconds. \\ Electro-inductive device & \(\bullet\) & Maintenance of the device is minimized due to the absence of aging or leakage issues, which are present in fluid dampers. \\ \hline Air-jet actuators & \(\bullet\) & They were introduced as an effective solution to the traditional concern that power would not be available when needed unless it was stored in advance. \\ Air-jet actuators & \(\bullet\) & The flow of compressed air supplies the actuator force, to be transmitted to the structure through the principle of momentum preservation. \\ \hline SMA actuators & \(\bullet\) & They are commonly adopted to realize passive devices, while the different (and long) reaction times for cooling and heating prevent their adoption in semi-active devices. \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._power consumption. This has been demonstrated in several scaled-down experimental investigations involving bridges and framed structures, e.g., [44; 45; 46; 47; 48; 49]. Table 3 lists publications on semi-active control for buildings and bridges. It has been observed that most of these studies focus on the controller's efficiency in mitigating seismic vibrations. However, little attention is given to addressing the practical issues in implementing the systems. Experimental studies with controllable devices demand focused efforts to address distinct aspects within the three stages of the semi-active control loop: acquisition, processing, and command. Additionally, the control system's efficiency is dramatically dependent on the control algorithm. [PERSON] et al. [158] examined the effectiveness of different control strategies for MR dampers, illustrating that the performance of the control system is significantly influenced by the algorithm selected for implementation. The subsequent section offers a comprehensive overview of the control algorithms employed in semi-active vibration control.