The Seismic Fragility Analysis Of RC Frame Structures Based On Damage Index

Quantitative assessment of structural damage is a crucial issue in the field ofperformance based seismic design. Due to the clear physical interpretation and simpledefinition, the Park-Ang damage index has been widely adopted to estimate structuraldamage. However, the Park-Ang damage index still has a problem about thesignificant discreteness. Seismic fragility curve is widely used to assess seismicperformance of structures. Currently, the drift is selected as the engineering demandparameter for seismic fragility, which means that it only considers the damageassociated with ductility and neglects the damage caused by cumulative energydissipation. Therefore, some research work has been done in this thesis:(1) The main reasons for the discreteness problem of the Park-Ang damage indexare: the artificial linear combination of ductility and energy dissipation and missingsome necessary factors. In order to improve this problem, a modified damage indexbased on Jiang’s model was proposed. The modification model was constructed with8variables in exponential form. With experimental database, Bayesian updating wasimplemented to determine the values of the unknown parameters. A simplificationprocedure was conducted to obtain the optimal modification model. It has been foundthat the concrete core area and cross sectional area ratio, the longitudinalreinforcement ratio and the experimental setup are the critical variables influencingthe discreteness of the damage index. Through the modification process, the scatter ofthe original damage index has decreased by35%.(2) Under earthquake excitations, building structures are subjected todeformation and energy dissipation. The drift only considers the structural damagecaused by the deformation, while the Park-Ang damage index considers not only theductility damage but also the energy dissipation damage. Three types of engineeringdemand parameters, i.e. the drift, the local damage index and the global damage indexwere selected. And a corresponding incremental dynamic analysis was conducted.Thereafter, the seismic fragility curves for each type were obtained. They reveal that:the seismic fragility based on the damage index is larger than the one based on thedrift; the seismic fragility based on the local damage index is larger than the onebased on the global damage index.