Seismic retrofit of a reinforced concrete flat-slab structure: Part II — seismic fragility analysis

An assessment of seismic fragility was conducted for a reinforced concrete (RC) frame structure representative of 1980s construction in the Central United States. The performance of the unretrofitted structure is presented in terms of fragility relationships that relate the probability of exceeding a performance level to the earthquake intensity. In addition, seismic fragility relationships were developed for the retrofitted structure based on three possible retrofit techniques and several performance levels. Fragility curves for the retrofitted structure were compared with those for the unretrofitted structure.For development of seismic fragility curves, the FEMA 356 global drift limits were compared with drift limits based on the FEMA 356 member-level criteria. In addition, a punching shear prediction model was used to establish an upper bound drift limit. Performance levels based on additional quantitative limits were also considered. Varying degrees of reduction in the seismic fragility were demonstrated through the use of the three selected retrofit techniques. The fragility curves were compared to those for RC structures derived in other studies and it was found that the results based on this study are comparable.