A Research On Seismic Performance Assessment Method And Application To Performance-based Design Of Reinforced Concrete Buildings

With the recognition of the highly uncertainty of earthquakes and the reasonable relationship between economics and structural safety, the ideas of multilevel seismic design fortification of“No Damage with Frequently Occurred Earthquakes, Repairable with Fortification Intensity Earthquakes and No Collapse with Rare Occurred Earthquakes”has been adopted by national seismic codes in some countries since early 1980s. While putting the code into practice, engineers consider life safety as the first design criteria. And the force-based design method is mainly used in seismic design. Earthquake hazard shows that many structures underwent considerable non-elastic deformations. Such deformations cause serious damages and enormous economic loss. Force-based seismic design is difficult to control the extent of damage in prospective earthquakes. Especially, with the progress of modern industrialization and urbanization, the number of cities in some countries and regions increase drastically, population and public wealth are highly concentrated. The damage caused by earthquake will bring serious burdens to the society.Performance-based seismic design considers both life safety and economic loss, in which the idea of multilevel fortification is further detailed and concrete. It is regarded as the future direction of development for seismic design. Therefore, it is of great academic significance and practical value to carry out research about performance-based seismic design.Combining with background and current problems of the research topic, this paper has completed the following works.Considering the fact that deformation-based indices can not account for the influence of the duration of ground motion on structural damage, based on Lemaitre equivalent strain theory and Rabotnov damage variable definition, and in accordance with existing experimental results, a new performance index associate with stiffness degradation is proposed. The analysis has shown that the proposed performance index with clear concept and simplicity in application, can easily assess structural seismic performance under different earthquake intensity.Earthquake input energy and hysteretic energy are important indicators to evaluate the seismic performance of structures. If no energy-dissipating device is used in a structure, the hysteretic energy dissipated during inelastic behavior which reflects some earthquake damage. It is of great advantage to evaluate the structural seismic performance from the viewpoint of energy. Therefore, methods of energy evaluation by nonlinear dynamic analysis and nonlinear static analysis are studied. Through numerical example, the earthquake input energy and structural hysteretic energy under the earthquake action with different peak ground acceleration levels, including the ratio between the two, are computed and analyzed, especially on the distribution pattern of hyteretic energy along the height of the structure and its allocation among the beam and column components. Then the weak storey or parts can be found out. Thus, the structure seismic performance can be effectively assesssed.Because of the complexity of energy evaluation and weak correlation with structural seismic parameters (deformation, displacement, internal force, etc.), from a practical viewpoint, engineers can not easily understand. The correlation between energy indicators and the proposed performance index is studied. The analysis results show that the proposed performance index highly correlates with the energy indicators, and some are even nearly perfect correlated. Therefore, the former can substitute for the latter to assess the seismic performance of structures.The performance-based seismic methodology has been first adopted by the new seismic code in 2010. The performance levels and index (interstorey drift), as well as its acceptance criteria, are suggested. Applications are studied. Based on cross-section fiber model, computation models for reinforced concrete frame structures with different storeys are designed. Five strong earthquake records are selected in the database of Pacific Earthquake Engieering Research Center, and the frames are analyzed through the nonlinear time history analysis with different earthquake intensities. It is found out that the interstorey drift is not so sensitive to the change of structural natural period, which is different from the fact that structure damages under earthquake action depend upon the ground motion characteristics as well as the structural dynamic characteristics.In order to comprehensively and systemtically assess the structural seismic performance, the designed structure frames based on fiber model are further studied. And the structural performances under different earthquake intensities are analyzed at three levels: overall performance, storey performance and component performance. The proposed index is adopted for the former two levels, and the component-level index is determined by the reference of The American Society of Civil Engineers Standard“Seismic Rehabilitation of Existing Buildings”. Moreover, comparisons between damage-based seimic evaluation and deformation-based evaluation is conducted at the overall performance level. The results indicate that according to 2010 new seismic code limiting the interstorey drift can prevent low-rise buildings from collapse. However, it may underestimate the damage of middle-rise to high-rise buildings. It is also shown that controlling interstorey drift of structure can not guarantee their safety because it does not account for the influences of the duration of earthquake.Since the limitations of pushover analysis, it needs analyses for variety of lateral load cases. Significantly, the analyses and results show that the proposed index is not sensitive to the pushover load cases. Thus, the results of pushover analysis are used to determine the proposed index. And it can avoid the uncertainty of computation of performance index, and can be used to quantify the structural damage. In addition, compared the development of plastic zone of components with the overall performance and storey performance, the results at the three levels are consistent. Consequently, the proposed index can be used easily and efficiently to assess the seismic performance of structures.Finally, further works are briefly discussed.