Seismic Design and Retrofitting of Structures by Using Mass Isolation System with Visco-Elastic Dampers

Abstract eng:
This paper presents results of using mass isolation system, MIS, with visco-elastic dampers in seismic design of structures or retrofitting of existing buildings. Herein, MIS consists of two separate frames, a flexible moment resisting frame, which bears main part of structure mass and a relatively rigid braced frame, which carries the remained little mass of the structure and these two frames are connected to each other with visco-elastic dampers. Use of visco-elastic dampers in MIS is here proposed instead of other dampers types, due to their smaller sizes, which make them more applicable specially for retrofitting of existing buildings, and their stiffness, which have very important role on regulating of the flexibility rate of the flexible frame and stability control of the system. Three steel structures with 4, 8, 12 stories are selected and nonlinear dynamic analysis under 7 time-histories acceleration records of the ground strong motions have been carried out for the structures, Drain-2DX software is used for modeling and nonlinear analysis of the structures. From economy point of view, numbers and vertical arrangement of visco-elastic dampers between the two frames of the structures are optimized considering story drift limitations, structures responses and using various mechanical characteristics, stiffness and damping of the dampers. Input energy of earthquakes are obtained and compared with the dissipated energies in the systems. The results show that MIS effectively causes reduction of input energies of earthquakes and visco-elastic dampers dissipate nearly 50% of the input energy and most of structural elements remain at the elastic ranges, which can be inferred that the performance levels of the structures have been significantly improved by using this system.

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