Seismic Retrofit of Existing Critical Structures Using Externally Connected Viscous Dampers

Abstract

To seismically retrofit existing critical structures like hospitals, it is not only necessary to guarantee that their performance is superior to that of general structures during and after earthquakes, but it is also very important to minimize the impact on daily operations and on patients during the reconstruction period. A seismic retrofit strategy involving external connections with linear viscous dampers whose damping coefficients are more efficiently distributed is proposed in this study. First, improper designs of added reaction structures and linked viscous dampers are effectively precluded by eliminating those that fall within undesired frequency ratio bands. Then, numerical examples are used to show that hospital structures retrofitted with viscous dampers at all stories and structures with dampers fitted only at lower stories perform satisfactorily. It is also shown that the higher the story linked by viscous dampers, the larger the damping coefficient and damper force required. In order to investigate the damping effect, a uniform distribution (UD) of the damping coefficient at all stories, a distribution based on the kinetic energy at all stories, and a more efficient distribution based on the kinetic energy at critical stories are analytically discussed and numerically examined. It is shown that adopting these three distributions can satisfactorily control performance, while adopting the first and third distributions requires the largest and smallest total damper forces, respectively. Consequently, adopting the distribution based on the kinetic energy at more important stories provides the most cost-effective retrofit strategy.