Development of seismic fragility curves of high-rise structures and introducing a method for selecting optimum probability distribution function for different performance levels

Fragility curves are powerful tools to assess and control of possible damages to the existing structures and estimate the exceedance probability from the seismic behavior of the structures under the influence of different earthquake levels. these curves present the probability of damage as a function of the ground motion characteristics. The main goal of the current study is to examine the existing methods and the presentation of a suitable method for the production of analytical seismic fragility curves and propose appropriate relationships for the exceedance probability from different performance levels. For this purpose, three high-rise building with 20, 25, and 30 stories with a slimming ratio greater than π, according to the standard 2800 and the sixth issues and tenth issues of the national building regulations of Iran, were designed. Then after extracting the perimeter frame, by using appropriate software, their analytical model was defined and validated. To evaluate the seismic response demand of frames, incremental nonlinear dynamic analysis (IDA) was performed. For IDA analysis, the 22 recommended records in the FEMAP695 guideline and two earthquakes in Iran were used. Spectral acceleration of the first mode of the structure with damping of 5 Percentage (Sa (T1.5%)) was used to introduce the intensity of the earthquake (IM) and the inter story drift ratio was used to introduce the engineering demand parameter (EDP) Or damage measure (DM). To find the appropriate function of the exceedance probability from limit states and use them in the production of fragility curves, the results of IDA analysis and nineteen different probability functions using the suitable program were used. in order that the used distribution describes the sample data in the best manner, the goodness of fit tests was used. the results obtained from the goodness of fit tests show that The probability distribution rank used by researchers (log normal) versus other probability distribution functions varies in ranking the best fitted probability distribution. and selecting the appropriate probability distribution is effective in the conclusions and determining the probability exceedance of the structure from the desired limit states. Therefore, in order to reduce the uncertainty related to the mathematical model (epistemic uncertainty) in the template of a comprehensive view and according to accuracy and the required seismic target, a suitable method for developing fragility curves for types of structural systems with different heights here called “intelligent seismic fragility curve (ISFC)” is introduced and presented. Such that if among the probability functions examined in this paper, the use of only one distribution is desired to compare several options, including deciding how to reinforce or comparing the seismic performance of several structures with duel system of special steel moment resisting frames with eccentric lateral bracings to plot the fragility curve, it is recommended: to use the probability distribution "Generalized Extreme Value", due to the ability to fit better than the distribution "log normal", but for more sensitive structures, such as nuclear power plants and hospitals that are of great importance and require high precision or in order to achieve the most accurate fitted possible to decide on about the vulnerability estimation for types of structural systems with different heights, It is then recommended: to estimate the exceedance probability from performance levels at the structure, before fragility analysis, by probabilistic evaluation and using the goodness of fit tests on suitable probability functions, at first, a best fitted probability distribution should be selected at all performance levels and then the vulnerability of structures is estimated by fragility curves.