Seismic retrofit of reinforced concrete structures using magnetorheological mass driver: Evolving a design methodology

Abstract

This paper proposes a design methodology for a damping enhancement-based seismic retrofitting of a damaged reinforced concrete (RC) model frame with a mass driver (MD) and magnetorheological (MR) damper. The MR-MD is applied with preset constant current inputs and the structure + MR-MD system is subjected to harmonic and seismic base excitations. Equivalent effective damping for a biviscous MR damper is derived both from energy and secant damping considerations. The effect of yielding force of the MR damper, mass value of the secondary system, and non-linearity associated with input accelerations are discussed. The paper proposes a suboptimum frequency tuning, that is, the frequency of the secondary MR-MD is marginally lower than the optimum value, anticipating a degrading stiffness and frequency drop of the target structure, typical of materials like masonry and concrete. Experimental investigations with undertuned, overtuned, and near-optimum tuned conditions of the secondary MR-MD system are performed to highlight that operation with near optimum damping plays a significant role, particularly when MR dampers are used. Higher effective damping associated with higher preset current inputs have a tendency to be counter-productive, which is proved experimentally and analytically. Four seismic performance parameters are calculated, which showed a substantial reduction of acceleration and displacement responses on the experimental structure when the damper is operated at lower input currents. From analytical and experimental investigations, a simplified retrofit design methodology for a degraded RC superstructure is proposed and experimentally validated through incorporating a mass driver coupled with a non-linear damper.