Development of fragility curves for seismic vulnerability assessment of high-rise R/C buildings with added viscous dampers

Abstract

The fragility curves are used to represent the probabilities that the structural damages, under various level of seismic excitation, exceed specified damage states by means of earthquake intensity-damage relations. This, in turn, can be utilized for prioritizing retrofit, pre-earthquake planning, and loss estimation tools such as cost-benefit analysis. Therefore, the fragility analysis is also particularly useful in regions of moderate and high seismicity, such as İstanbul. In this study, a twelve storey non-ductile R/C office building, which represents the typical properties of the high rise office buildings located in Mecidiyeköy region, was selected and fragility curves were developed for the economic loss estimation as well as a basis for assigning retrofit prioritization for the R/C office buildings in Mecidiyeköy region. For the purpose of seismic retrofitting, external passive fluid viscous damper systems were designed to provide the structure with different effective damping ratios (ζ) of 10, 15 and 20 per cent; and the improvement of the system reliability achieved through the use of the dampers was assessed through fragility, risk and cost-benefit analysis. In order to be able to compare the innovative technique applied with the conventional retrofitting techniques, the building was also retrofitted by shear walls. In the fragility analysis, a set of 240 artificially generated earthquake ground motions compatible with the design spectrum selected to represent the variability in ground motion were developed to study nonlinear dynamic responses of the structures before and after retrofit. Fragility curves represented by lognormal distribution functions were constructed as a function of peak ground acceleration, spectral acceleration and displacement. By combining fragility analysis results with the seismic hazard risk of the region, the effectiveness of viscous damper systems and shear walls in the retrofit of the high rise R/C building is further investigated based on economic point of view by performing seismic risk analysis and cost-benefit analysis.