Simplified fragility analysis methods for optimal protection level decision-making and minimum life-cycle cost design of aseismic structures

Probabilistic analysis of damage states of structures under seismic excitations is one of key problems in the optimal protection level decision-making and minimum life-cycle cost design of aseismic structures.The authors put forward two practical approaches to evaluation of seismic damage state probabilities of structures in the past,according to the three-level seismic design principle and results of probabilistic seismic hazard analysis of earthquake intensity.The foundation of seismic fragility theory is built for evaluation of seismic damage state probabilities of structures,in which the concepts and definitions of limit state seismic fragility and damage state seismic fragility are presented.The two practical analysis approaches for evaluation of seismic damage state probabilities of structure are analyzed thoroughly from the viewpoint of seismic fragility theory.It is found that the first approach is a semi-theoretical and semi-empirical seismic fragility analysis method,which considers the uncertainty in the macro-scope seismic capacity of structures;while the second approach is a simplified seismic fragility analysis method,which doesn't consider the uncertainty in the macro-scope seismic capacity of structures.The two approaches are compared on the basis of the computing results of seismic damage state probabilities of structures,and the suggestions of selection of two simplified seismic fragility methodologies for the optimal protection level decision-making and minimum life-cycle cost design of aseismic structures are offered.