Seismic Fragility Analysis Based On Story Plastic Energy Dissipation Index

Seismic fragility analysis is one of the three important parts of seismic hazard risk analysis, which also is the main part of structural damage analysis. Conditional probability of different damage degree under different intensity earthquake for engineering structures can be predicted indicated in a fragility curve. Fragility analysis of a structure not only improves seismic capacity and provides the effective way to reduce the loss, but also provides the basis for disaster prevention and mitigation, reinforcement and maintenance measures. At present, there are mainly empirical methods and theoretical analysis methods for seismic fragility analysis. Theoretical analysis methods have become a hot spot that most researchers study due to the limitations and difficulty to obtain of empirical method. There are two important decisive factors for theoretical analysis method, namely, nonlinear analysis method and damage index of fragility. Compared with other methods of fragility analysis, this paper made a new try. Force analogy method is proposed to be adopt as nonlinear analysis method that a kind of calculation analysis with variable displacements. Since constant initial stiffness matrix was used in the operation process, amount and speed of calculation were better than others. Moreover, it could obtain high accuracy. For the damage index of fragility, story plastic energy dissipation is used according to force analogy method. The plastic characteristics of structure is highlighted by the selected index and a new train of thought for the development of energy index is provided. Based on two above factors, seismic fragility analysis of a steel structure and the steel structure with viscous damper is analyzed in this paper. The main research content is as follows.(1) The core idea, the basic equation and energy equation of force analogy method were elaborated. The stiffness matrix relationship based on force analogy method was checked roundly. Nonlinear analysis of a structure with viscous dampers expands the application for force analogy method in the field of nonlinear time history analysis.(2) According to energy analysis theory of force analogy method, a new damage index termed story plastic energy dissipation was proposed and its calculation formula was established right now. Furthermore, the weighting coefficients were discussed. Combined with story drift angle that widely used at present, this paper compared the damage analysis of two damage indexes and manifested the effectiveness and rationality of story plastic energy dissipation. On this basis, the damage analysis method about energy dissipation structure was proposed by story plastic energy dissipation.(3) With the theory of fragility analysis, seismic fragility analysis of a steel frame structure was executed based on force analogy method and story plastic energy dissipation that proposed in this paper. The seismic fragility curves was obtained in four kinds of damage state. Afterwards, the difference of two kinds of seismic fragility curves was analyzed by story drift angle as contrast which verifies the rationality of seismic fragility analysis based on story energy dissipation. Finally, seismic fragility analysis of energy dissipation structure with viscous damper was executed which expands the application value of force analogy method and story plastic energy dissipation.