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Base Isolation of a Multi-Story Building Under a Harmonic Ground Motion - A Comparison of Performances of Various Systems

F-G. Fan, G. Ahmadi, I.G. Tadjbakhsh

NCEER-88-0010 | 5/18/1988 | 124 pages

About the Report:

TOC: The table of contents is provided.

Keywords: Base Isolation Devices, Ground Excitation, and Sliding Resilient-Friction System.

Abstract: Performances of several leading isolation devices (Pure-Friction/Sliding-Joint, Rubber Bearing, French System, New Zealand System, and Resilient-Friction) and a newly proposed system (Sliding Resilient-Friction) for a multi-story building subject to a horizontal harmonic ground motion are studied. The governing equations of motion of various systems and the criteria for stick-slip transitions are described and a computational algorithm for obtaining their numerical solutions is developed. The responses of the structure with different base isolation systems under various conditions are analyzed. The peak absolute acceleration, the maximum structural deflection, and the peak base displacement responses are obtained. A series of sensitivity analyses is also carried out. The effectiveness of various base isolators is studied and advantages and disadvantages of different systems are discussed. The results show that the base isolation devices effectively reduce the column stresses and the acceleration transmitted to the superstructure. Furthermore, the frictional base isolation systems are less sensiitive to severe frequency content of ground excitation. When the intensity of ground excitation is doubled, the peak responses of the frictional system increase by only about 10% to 25%. It is also observed that small variations in friction coefficient lead to slight changes in the peak responses of frictional isolators. Furthermore, the velocity-dependence of friction co-efficient, variations of mass ratio, and damping ratio of the isolator have negligible effects on peak responses of the base isolated structure.