Study On Energy-based Seismic Design Methodology And Application For RC Frames

In this thesis, the state of the art of the energy-based seismic design methodology is expatiated. The analysis and design method based on deformation and energy response of seismic structures is studied and the main achievements of this dissertation are as follows:1. Based on elasto-plastic single-degree-of-freedom (SDOF) and elasto-plastic multi-degree-of-freedom (MDOF) systems, the correlation between different structural seismic responses and variant intensity indices is analyzed using 60 earthquake records. According to the analysis of the correlation, the rational ground motion intensity indices for seismic analysis purpose are suggested.2. Based on the results of the incremental dynamic analysis (IDA), the accuracy of traditional pushover analysis and modal pushover analysis (MPA) to the seismic responses of RC frame structures, especially to the deformation of structures, are analyzed and compared. Finally, the applicability of the commonly-used nonlinear static analysis procedures for RC frame structures is summarized.3. The influence of post-yielding stiffness to the seismic response of structures is studied with 19,600 nonlinear time-history analysis cases mainly based on MDOF systems, and the methods of improving post-yielding stiffness of structures are summarized. It is indicated that, the seismic structures should have enhanced behavior after the structure yielding. For RC frames, the total failure mechanism of structures is preferred.4. The design methods for weak-beam-strong-column RC frames in several national codes are introduced, and the problems in Chinese code are summarized and studied. It is shown that, the excessive amount of reinforcement of beam, the case-in-place floor slabs, the value of column-to-beam strength ratio and several other uncertain factors may influent the weak-beam-strong-column design. Finally, the design suggestions are proposed and the design method is improved.5. A simplified procedure for evaluating the story drifts of RC frames with total failure mechanism is proposed based on several rational assumptions, which is relatively accurate compared with nonlinear static analysis procedures. The proposed estimating procedure can also reflect the dispersion of seismic responses and avoids the large amount of calculation of nonlinear time-history analysis. Consequently, the nonlinear static analysis procedure is used to estimate the deformation demand of structural elements by taking the evaluated story drift as target performance point of each story.6. The distribution of cumulated seismic hysteretic energy of RC frames with different column-to-beam strength ratios are studied based on 3-story, 6-story, 8-story and 10-story frames. The simplified calculating method is proposed according to the results of frames in line with the design requirements for deformation and seismic energy dissipation.7. Based on the two-stage design approaches and the failure criterion determined by deformation and hysteretic energy, the combined energy and displacement-based design methodologies are suggested. A practical example is used to illustrate the design procedure, and it is validated by time history analysis. The results indicate that the suggested energy-based seismic design method for the RC frames can provide adequate deformation and seismic energy dissipating capacities to achieve the designed performance objectives.