Research On Energy Spectrum And The Selection Of Earthquake Accelerograms For Dynamic Analysis Based On Energy

The current seismic analysis of structure is usually based on the strength and displacement, and the duration of ground motion on the progressive damage of structure is not taken into account. Energy analysis can not only reflect the intensity of ground motion and spectral characteristics, and can also effectively take account of earthquake duration of the progressive damage to the structure. Therefore, the extensive researches of the energy analysis method have been carried out since this method was put forward, and in current the energy-based design approach is developing.Although the method of energy analysis has been obtained a lot of research results, there are still many problems to be solved. In this thesis, combined with the research project“Research on the inelastic seismic response and energy analysis of super high-rise mega-frame structure”financed by the Major Research Program from the Committee of National Natural Science Foundation of China, the problems of the index of ground motion intensity, the design input energy spectrum, the cumulative energy spectrum and the selection of the ground motion input and so on related to the energy analysis method are studied. Through the detailed research on these problems the following conclusions and research results are obtained.1. 694 horizontal records are selected and classified according to Chinese standards of site classification. Intensity parameter is proposed to characterize the demand of energy input and dissipation of the structure, and the different intensity parameters of each ground motion record are calculated. Analysis on the correlation among the different parameters and between the parameters and the input energy and hysteretic energy of the single degree of freedom system and the multi- degree of freedom system is carried out, and the results show that the proposed intensity parameters can be well to characterize structural characteristics of energy demand, and it can be used in energy analysis and design methods as a intensity index.2. Influences of the ductility, damping ratio and the hysteretic model on the input energy spectrum (IES) and hysteretic energy spectra (HES) are studied. The results show that with the increase of ductility, the peak values of IES and HES are reduced, and the period corresponding to the spectral peak is shorter. With the increase of damping ratio, the peak values of IES and HES are also reduced. While in the scope of long-period, the value of the energy spectrum increases with the damping ratio increased. When the period is less than the period corresponding to spectral peak value, elastic-perfectly plastic model is non-conservative model relative to other models. The group parameter for establishing the design equivalent velocity spectra of input energy is proposed, and considering different damping ratio, a multi-segment design equivalent velocity spectra of input energy is established, in which the recommended values of spectral parameters are presented.3. The mathematical model to estimate the equivalent velocity spectra of input energy is established. The model can take into account the impact of ductility and damping ratio, and does not depend on the spectral period. The inelastic input energy spectrum can be estimated through Fourier amplitude spectrum directly. Considering the influence of period, damping ratio and ductility on the HES and IES, the mathematical model for estimating the ratio of equivalent velocity spectrum of hysteretic energy and input energy is established, and it is compared with other existing models. The results show that the proposed model can estimate well on the ratio of spectrum, and the period can also be considered.4. An optimal method for choosing a set of records which makes the average spectrum of the records be better matched with the target spectrum using genetic algorithm and greedy algorithm is proposed. Methods of ground motion simulation such as superposition of trigonometric series for synthetic records, adjusting real record in frequency domain using the wavelet transform and adjusting real record in time domain are introduced. Characteristics of frequency domain, time-frequency domain based on Hilbert-Huang transform and the calculated structural responses for each type of simulated records and real records are analyzed. The results show that the characteristics of the synthetic records are quite different with the real ground motion records, and compared with other type of records, synthetic record have larger input energy. The characteristics of the record through adjusting real record in time-domain are closer to the real record, and it is a better method to generate simulated ground motion records.5. The program EQSYS is developed for solving the problem of managing and analyzing the ground motion records, selecting the real ground motion records and generating simulated ground motion records for analysis and design of the actual structure. The program is compiled using the visual way, and have friendly interface. It can be used as a tool of ground motion records management, analysis and selection of ground motion.6. The properties of different macro-models are analyzed. Simulation on two reinforced concrete columns and two pieces of reinforced concrete shear walls is carried out, and the simulating results are compared with test results. The results show that the accuracy of the fiber model is better than the MS model, but when the proper plastic hinge length of the MS model are chosen it can also be used to reach a certain accuracy.7. Methods of selecting ground motion records for the energy analysis are proposed, and the detailed implementation steps are given. Inelastic dynamic analysis on a real structure by using different methods of selecting ground motion records is carried out, and the analysis results show that the proposed method is effective.8. Correlations between different types of strong motion duration indexes and energy responses of the single degree of freedom system and multi degree of freedom system are studied. The results show that within certain limits the uniform duration has a high correlation with the energy response.In summary, the researches on the intensity index of analysis method based energy, the properties of energy spectrum, establishment of design input energy spectrum, estimation of inelastic energy spectrum, selection of real ground motion records and simulated records for dynamic analysis, selection of ground motion records for energy-based analysis and strong motion index and so on are carried out, and a lot of useful conclusions are obtained. Reference and basis can be provided for the energy-based analysis in seismic analysis and design.