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Structural Engineering and Mechanics Volume 23, Number 5, July30 2006 , pages 543-562 DOI: https://doi.org/10.12989/sem.2006.23.5.543 |
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Vertical distributions of lateral forces on base isolated structures considering higher mode effects |
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C. S. Tsai, Wen-Shin Chen, Bo-Jen Chen and Wen-Shen Pong
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| Abstract | ||
| Base isolation technology has been accepted as a feasible and attractive way in improving seismic resistance of structures. The seismic design of new seismically isolated structures is mainly governed by the Uniform Building Code (UBC-97) published by the International Conference of Building Officials. In the UBC code, the distribution formula of the inertial (or lateral) forces leads to an inverted triangular shape in the vertical direction. It has been found to be too conservative for most isolated structures through experimental, computational and real earthquake examinations. In this paper, four simple and reasonable design formulae, based on the first mode of the base-isolated structures, for the lateral force distribution on isolated structures have been validated by a multiple-bay three-story base-isolated steel structure tested on the shaking table. Moreover, to obtain more accurate results for base-isolated structures in which higher mode contributions are more likely expected during earthquakes, another four inertial force distribution formulae are also proposed to include higher mode effects. Besides the experimental verification through shaking table tests, the vertical distributions of peak accelerations computed by the proposed design formulae are in good agreement with the recorded floor accelerations of the USC University Hospital during the Northridge earthquake. | ||
| Key Words | ||
| base isolation; structural control; UBC code; lateral force distribution; higher mode effect. | ||
| Address | ||
| C. S. Tsai; Department of Civil Engineering, Feng Chia University, Taichung, Taiwan, ROC Wen-Shin Chen; Graduate Institute of Civil and Hydraulic Engineering, Feng Chia University, Taichung, Taiwan, ROC Bo-Jen Chen; R&D Department, Earthquake Proof System, Inc., Taichung, Taiwan, ROC Wen-Shen Pong; School of Engineering, San Francisco State University, USA | ||