| Summary: | 博士 === 國立臺灣大學 === 土木工程學研究所 === 91 === In the study, the concept, framework and recent developments on performance-based seismic evaluation and design (PBSE and PBSD) procedures are discussed first. The simplified procedures for the construction of design displacement response spectra required for the implementation of displacement-based seismic design (DBSD) are then introduced. The resulting displacement response spectra are compared with the nonlinear displacement response spectra computed directly from the ground accelerations recorded from 10 sites located in Taichung Region during the 1999 Chi-Chi Taiwan earthquake. It is found that the nonlinear displacement demand estimated in the tentative seismic force provisions for building structures in Taiwan are unconservative? Moreover, modal contribution factor (MCF) spectra are constructed by using a simplified building structural model. By varying the stiffness ratio of the beams and columns and the fundamental period, individual modal contributions to the seismic response have been identified and can be used as a basis to develop multi-mode seismic design procedures. In the common range of structural fundamental period, the higher-mode contribution of base shear is about to 20% of the total base shear at most. For overturning moment, it is about 15% at most, and for roof displacement, the higher-mode contribution is only about 10% at most.
This research then reviewed the existing methods for seismic performance evaluation of building structures. It includes the capacity-spectra method and the displacement coefficient method. Some of these methods might be over-simplified: (1) only considers the contribution of the first mode; (2)or the manners considering the inelastic demands and the lateral deformation characteristics of the structural systems are too rough. The study discusses some possible improvements of these methods. Improved multi-mode displacement coefficient method incorporating the effects of the shear and flexure rigidity ratio is proposed. Some simple numerical examples are illustrated for the verification of the proposed method and the results are compared with some existing methods for seismic performance evaluation of building structures in different levels of seismic hazard. Analytical results confirm that the proposed method is more accurate in predicting the maximum response. Furthermore, by using the principle of displacement-based seismic design procedure of MDOF system developed by Calvi and Kingsley, this study assumes the shape of the lateral design story forces is transformed from the shape of the lateral design story displacements. Then the proposed multi-mode displacement-based seismic design procedure for building structures, in which the design lateral story displacements transformed from the shapes of the presumed dominant modal shapes along the building height is established. The proposed multi-mode displacement-based seismic design procedure is applied to the design of a three-storey CFT buckling restrained braced frame specimen and a twenty-storey steel ductile moment-resisting example building for verifying its feasibility. The analytical results show that the proposed displacement-based design method is more accurate than the current spectral acceleration-based design approach in achieving the target performance. The distribution of the seismic story deformations of the example buildings designed by the proposed displacement-based design procedure is more uniform along the building height. This research concludes with the future research needs for PBSE and PBSD.
|
|---|
