Application of Gyro-Mass Dampers to Mitigate the Seismic Failure in Soft First Story Buildings

Abstract

Sudden changes in stiffness and strength of the structures present a structural vulnerability leading to damage and collapse during strong earthquakes. This paper investigates the possibility of improving the seismic performance of soft first story structures by incorporating gyro-mass dampers (GMDs) as an alternative and effective novel solution to this problem. GMDs are newly developed passive energy dissipation devices for which the generated force by the element is proportional to the relative acceleration applied at the end nodes. These mechanical devices use a gear assembly to counteract dynamic forces by transforming the transitional motion into rotational one. Dynamic properties of GMDs are adjustable by changing the dimension of the physical components. Moreover, the application of compound gears makes it possible to amplify the small rotational inertial forces and make the GMDs (with/without additional viscous damping mechanism) a viable passive control strategy. Here, GMDs are used to control the drift at the first floor and to correct the mode shapes of the unbraced structure. These dampers are envisioned to be installed in each floor at the bottom of Chevron braces in the associated frame. Consequently, the brace-damper system acts like a Maxwell-element, which modifies the stiffness and equivalent mass of the original frame. Utilizing this concept, the governing equations including the equivalent mass and lateral stiffness contributed by a damper-brace system are formulated; used for design and an application example is presented.