2016 年 81 巻 725 号 p. 1071-1079
Recently, Inertia Mass Dampers have been developed and realized. The damper can exert negative stiffness with neither energy supply from outside nor complicated electronic control devices. It is possible for the damper to exert inertia mass much greater than physical mass. In practical applications to controlling relatively large structures, great mass would be required inertia mass. But in the case of controlling small structures, smaller inertia force yielded by flowing fluid would be enough.
In this paper, we propose a Linked Fluid Inertia Mass Damper (LFIMD) which is effective to reduce seismic response of low-rise structure. The damper is composed of two cylinders, two piston rods and two link tubes that connect two oil chambers of each cylinder. There is no orifice in the piston and the fluid runs in the tube at high velocity when piston rod moves back and forth. The ratio of two piston displacements can be adjusted based on the ratio of cross section area of two oil chambers linked with a tube. The damper works in three ways. They are viscous damping effect by flowing fluid, negative stiffness by inertia mass effect with moving fluid at high velocity in the tube and the displacement control by hydraulic link mechanism. The damper is quite effective in reducing acceleration response, because load-displacement relationship of the damper has negative stiffness by inertia force, decreasing the maximum shear force of a total structure. The LFIMD yields negative stiffness by means of simple passive mechanism. It can prevent damage concentration to a specific part of a multi-story building, as well as the torsional vibration of a building with stiffness or strength eccentricity.
In the first part of the paper, we propose seismic response control method with LFIMD and show its dynamic mechanical properties by performance test on a LFIMD. Important findings are; there exists constant internal friction force between the cylinder and the piston, the damping force depends on the squared piston velocity, inertia force depends on frequency and linking force depends on the compression stiffness of the fluid and rigidity of the tube. It was confirmed that the test results conclude with simulated results fairly well.
We perform seismic response analysis of a wooden house with LFIMDs. It is shown that LFIMD is capable of exerting seismic response control in multiple ways. In the case of no damper, the deformation and absorbed energy are concentrated to either of the story. On the other hand, in the case of using LFIMDs, it is possible to make structural deflection distribution uniform and to reduce the maximum deformation with link mechanism. Maximum acceleration is reduced due to negative stiffness by inertia force. Finally, we confirmed the use of LFIMD is quite effective in reducing seismic response of low to mid rise building structure.