A practical design method to retrofit existing RC buildings with viscous dampers

Many existing RC buildings have been designed using older versions of seismic standards and such buildings may be severely damaged due to earthquakes that may occur in the future. New buildings are designed to achieve a higher seismic performance compared to existing buildings, using updated seismic design maps. Hence, seismic performance enhancement is necessary for existing buildings, corresponding to the current earthquake design level. In this study, a non-iterative design procedure is proposed to determine the mechanical characteristics of additional linear viscous dampers that are needed, to achieve an enhanced seismic performance of existing RC buildings. The enhanced seismic performance of the buildings is based on the maximum Inter-story Drift Ratio (IDR) of the buildings. The viscous damper forces are calculated relative to the story shear forces in the unretrofitted buildings. The proposed design procedure is validated by considering 4-, 8-, and 12-story RC buildings, which were designed using IBC 2009, ASCE 7-05, and ACI 318-08. Seismic performance is enhanced according to the design level of IBC 2015. PERFORM-3D (CSI 2011) software is used for modeling and analysis of the buildings.