Fluid viscous is a term used in building design that usually involves proportioning the elements of the structure. Such as constraints on strength and serviceability limit states are satisfied. The conventional approach is to proportion the components to satisfy the strength limit states and then follow it up with serviceability checks. But based on the modern control theory, structural control has emerged to mitigate the negative effects that the external disturbances impose on the structures. Structural control has been investigated and shown great potential for reducing vibrations in various civil structures under dynamic loading.
Structural control is usually classified by its method, or the type of device used to impart the control force. The three classes of structural control system are passive energy dissipation, active and semi-active energy dissipation. The first class of energy dissipating system, the passive systems are uncontrollable. The basic function of the passive devices is to absorb a part of input energy, reducing energy dissipation on structural members and minimizing the damage on structures. Contrary to semi-active or active systems there is no need of external power supply. The second class of energy dissipating devices, the active devices are controllable and require significant amount of external supply. The third class includes the semi-active devices which combine the aspects of active and passive devices.
Passive devices are frequently used type of control system implemented because they involve no external power and such devices are inherently stable. Passive devices encompasses a range of materials and devices for enhancing damping and strength such as fluid viscous dampers, friction dampers and metallic dampers have been developed since the 1990’s.