Nakamura et al. 2008
The authors explain a CSI system, a new type of structural system. The mechanics of this system are clarified using the results of shake table tests and static loading tests. An overview of the first building using the CSI system is then given.
System Concept
The core-suspended isolation system is composed of a reinforced concrete core, double layer of inclined rubber bearings and a hat truss. The double layer of inclined rubber bearings seismically isolate the structure and are installed on top of the reinforced concrete core, creating a pendulum isolation mechanism. An office or residential structure can then be suspended from a hat-truss constructed to the seismic isolation mechanism, effectively isolating it from the motion of the core. As a result, the seismic isolation mechanism allows sway and swing motions of the hanging structure, as well as rocking motion of the core.
Experimental Study, Results, and Discussion
A 1/16 scale model 21-story building with the CSI system was tested on a shake table. In order to study the effect of the tilt angle, the shake table tests were conducted at two angles: 1/10 and 1/5. The first and the second mode periods were obtained from sinusoidal sweep tests and eigenvalue analyses. The first mode caused the hung structure to sway, while the second mode resulted in rocking. It was concluded that, based on the maximum amplitude of response for each part of the model, the CSI mechanism significantly isolates the suspended structure.
Static load tests were conducted to investigate the hysteresis characteristics of full-scale rubber bearings under imposed rotational and horizontal displacements. The results of static loading tests of inclined rubber bearings demonstrate that the horizontal stiffness of a rubber bearing slightly decreased with increasing inclination.
Implementation of CSI system
The first building using the CSI system was constructed in Tokyo, Japan. The seismic isolation mechanism of the 4-story building consists of two layers of four inclined rubber bearings installed at the top of a reinforced concrete core, from which three floors of office structure are suspended by high-strength steel rods.
Reference
Nakamura, Y., Masaaki, S., Nakanishi, T., Wada, A., Takeuchi, T., Hikone, S., and Takahashi, T. (2008). “Development of the Core-Suspended Isolation System,” Proceedings of the 14th World Conference on Earthquake Engineering, Beijing, China, October 12-17.