Displacement Control Design Concept for Long-Period Structures: Design Strategies for High-Rise and Seismic Isolated Buildings Subjected To Strong Ground Motions

Abstract eng:
The earthquake-resistant design code provision at the beginning in Japan required that structures resist seismic force produced by response acceleration. The design concept subsequently, in accordance with the increase of heights of structures to be constructed, evolved to take response displacement as well as response acceleration into account to utilize ductility of structures in reduction of required strength on the basis of energy balance concept. It is attracting much attention that excessive displacements in long-period structures such as high-rise or seismic isolated buildings, the number of which are designed and constructed is increasing nowadays, might occur due to long-period components of extreme ground motions. The excessive displacement may not necessarily cause structural damage, whereas the excessive displacement itself is harmful. It is considered to be effective to incorporate some damping devices that control vibrations in direct response to the response displacement. The authors define this concept as “displacement control design” and have developed some control strategies and devices to realize it. This paper outlines the basic concept of displacement control design and the mechanisms and application of the newly developed dampers. The basic concept is utilizing a damper that generates resistant force in response to displacement without velocity dependency. Theoretical representation of such damping element is complex stiffness. Although the present damping element can be realized by using magneto-rheological (MR) fluid damper, the damper is unreliable in seismic events because of power source failure. The problem of non-causality of complex stiffness makes realization of such damping device more difficult. To solve these problems, we developed tuned viscous mass dampers for seismic control, rotational viscous mass dampers, performance variable oil dampers, and friction dampers with coupling mechanism for seismic isolation. By using these devices, we can build systems that can reduce response displacements without deterioration of floor response accelerations in response to each criterion for the corresponding earthquake input level. These devices can be, so to speak, categorized as smart passive damper and are effective in response control of structures against expected extreme seismic events.

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