Vibration control of Elevated Water Tanks using viscous dampers

For the last thirty years or so, the reduction of structural response caused by dynamic effects has become a subject of intensive research. Many structural control concepts have been evolved for this purpose, and quite a few of them have been implemented in practice. There are a number of mechanisms by which the structural control action is achieved. For example, in the category of passive control base isolation devices, linear viscous dampers, nonlinear viscous dampers, visco-elastic dampers, tuned mass dampers, liquid column dampers, liquid-mass dampers, metallic yield dampers, and friction dampers have been proposed. Out of these, base isolation devices have been widely implemented in practice. In active control, active mass/tuned mass dampers (ATMD), active tendon systems, actuators/controllers have been used. Out of these, active mass/tuned mass dampers have been implemented for the response reduction of tall buildings in controlling wind-induced vibrations. In hybrid control, the concepts using base isolation and ATMD, and visco-elastic dampers and ATMD have been proposed. The objective of the study is to investigate the uncontrolled and controlled response of RCC Elevated Water reservoirs of different H/R ratios (height of the container to its radius) viz. 0.6 and 1.85 with time period of tower (T_s) as 0.5s and subjected to different strong ground motion earthquakes. Also to obtain the controlled response of RCC Elevated water tank with linear viscous damper (LVD) placed in the staging of the tank. The simulation of water tank using three-mass model concept is carried out through MATLAB using State Space Method. Time history analysis has been carried out. In the first phase, the response of the tanks to different real earthquake ground excitations viz. Loma Prieta (1989) earthquake, Northridge (1994) earthquake, El-Centro (1940) earthquake and Kobe (1995) earthquake is investigated using simplified three mass model of the tank. The tank is modeled- as 3 DOF system viz. sloshing displacements (d_c), rigid mass displacement or tower drift (d_r) and base mass displacement (d_b). Response quantities and response of the damper are further obtained in the form of Force Vs Displacement curves. It is observed that the response quantities such as base shear and tower drift are highly influenced by introduction of linear viscous damper.