|Session 1.1 - Structural Base Isolation|
L.-Y. Lu, M.-H. Shih, S.-W. Tzeng and C.-S. Chang Chien
In this paper, the experimental results of a shaking-table test that was performed on a sliding isolated structure, subjected to both near-fault and far-field ground motions are presented and compared. In the test, a set of pulse accelerations with various pulse periods were also artificially generated and imposed on the isolated structure, in order to study the effect of the pulse wave component possessed in a near-fault earthquake. Based on the test data, several effects of near-fault earthquakes on the response of the isolated structure are investigated and discussed. These effects include the vertical ground motion, the over-turning moment of the structure and the period of the pulse wave. The test results show that the pulse component in the near-fault earthquake wave can lead to an isolation motion similar to resonant response. As a result, and the isolator displacement of the sliding isolated structure is considerably amplified in the near-fault earthquake as compared with that in the far-field earthquake.
Keywords: near-fault earthquake, seismic isolation, shaking table test, sliding bearing, friction pendulum system
Impact of Decentralized Semi-active Control on the Stability of Tall Structures under Seismic Loading
Recent research in the area of semi-active control has led to the development of an impressive array of smart dampers and resetable devices. These actuators typically employ control algorithms that are a function of local structural response measurements. However, the structural response of tall structures under seismic loading can have significant contribution from higher modes that can negatively interact with the decentralized nature of the control laws. The interaction of higher modes, non-linear effects and decentralized control on the stability of tall structures is investigated for the SAC-9 steel, moment resisting frame structure. The research is presented in terms of semi-active resetable actuators that use the compressibility of air to create non-linear springs that optimally release stored energy before it is returned to the structure. The action of these devices is governed by local measurements of relative velocity and displacement that can lead to actuator-to-actuator interaction when higher modes are present in the response. These interactions are shown to be a function of non-linear effects and higher mode contributions that result in increased permanent deformations, accelerations and structural hysteretic energy. Highly effective control architectures that mitigate these effects are presented in contrast.
Keywords: semi-active, structural control, decentralized, non-linear control, hysteresis, SAC-9
A large seismic-isolated telecommunications building with a guyed mast tower was planned to be constructed upon liquefiable subsoil. The foundation and superstructure have to be designed taking soil conditions into account. In order to penetrate the soft soil layers to reach the underlying firm layers, a continuous wall pile system was adopted. For seismic analysis, seven seismic waves were used to measure the dynamic response. The results showed that the higher modes of the site waves were dominated the structural response. To reduce this response, viscous wall dampers were installed in the building. The project was therefore able to be achieved, and through the application of various structural means such as continuous wall piles, seismic isolators, viscous dampers and by conducting a thorough seismic analysis, the level of safety of the structure was greatly improved.
Keywords: seismic isolation, liquefiable subsoil, wall pile, viscous damper, guyed tower, tuned mass damper