Semi-Active Fluid Viscous Dampers for Seismic Mitigation of RC Elevated Liquid Storage Tanks

The effectiveness of the semi-active control strategies using fluid viscous dampers (SAFVDs) for seismic mitigation of reinforced concrete (RC) elevated liquid storage tanks is investigated. Three control algorithms are employed for regulating the damping coefficient of the SAFVDs: (1) Passive-OFF, (2) Passive-ON, and (3) Clipped Optimal Control (COC). The uncontrolled response of the tank is compared with those installed with SAFVD of different control algorithms. Focus is also placed on various positions of the dampers, viz., dampers installed at alternate levels (Configurations I, II, IV, and V) and at all levels (Configurations III and VI) of the staging. A discrete two-mass model for the liquid and multi-degree-of-freedom system for the staging, installed with the dampers, is developed for the RC elevated liquid storage tanks. The response of the broad and slender tanks is studied, for which the ratios of the height of the liquid to the radius of the container are 0.5 and 2.0, respectively. The time-history response of the elevated tank is evaluated for eight different earthquake ground motions, including near- and far-field earthquakes. A MATLAB code was developed to solve the coupled differential equations of motion of the system using the state-space approach. Key parameters, viz., convective displacement, rigid mass displacement, base shear, overturning moment, and damper force, are evaluated. The results show that all the control systems considered herein are beneficial in reducing the seismic responses. The frequency response function for the uncontrolled and semi-actively controlled liquid storage tank in frequency domain exhibits significant response reduction, highlighting the effectiveness of the SAFVDs. The structural response is effectively controlled using the SAFVDs with Passive-OFF (valve closed) and COC algorithms. The COC algorithm employed in this study is a promising candidate for the seismic mitigation of RC elevated liquid storage tanks using the semi-active control.