دانلود رایگان مقاله انگلیسی ارزیابی لرزه ای احتمالی ساده از قاب های RC با میراگرهای ویسکوز اضافه شده - الزویر 2017

ABSTRACT

The object of this paper is the study of simplified probabilistic procedures for the seismic assessment of nonlinear structures equipped with nonlinear fluid viscous dampers. The considered reference probabilistic approach is the SAC-FEMA method, which allows to obtain the probability of exceeding a given performance level. The specific purpose is to study the correlation between the results obtained through the probabilistic seismic assessment method for structures with and without dampers, with emphasis on these results in terms of dispersion. A wide set of recorded ground motions was therefore selected and applied to the considered RC frames. The study was performed without applying scaling factors to the earthquake records, but by selecting different sets of records for increasing values of seismic intensity. All the obtained results were examined considering different criteria, in order to determine the set of time-history analyses to be used for the probabilistic evaluation. Different methods were then applied to obtain the dispersion of the seismic demand. With reference to the application of the SAC-FEMA method, a sensitivity analysis was also performed, considering different procedures to interpolate the hazard curve. From the analyses, it was possible to derive the expressions that allow the results for structures with and without dampers to be correlated, as well as to offer suggestions for applying the SAC-FEMA method. A second purpose of the paper is to propose and apply, in the probabilistic assessment, a direct procedure. This procedure was recently presented by some of the authors as a method to be used for obtaining the response of nonlinear structures with nonlinear viscous dampers as an alternative to expensive nonlinear dynamic analyses.

6. Conclusions

Several investigations were performed, by means of nonlinear dynamic analyses, on the application of the simplified SAC-FEMA approach used in the probabilistic seismic assessment of RC structures with and without viscous dampers. The main results are summarized in the following. As expected, the median values obtained for the structure without dampers are greater than those obtained for the structure with dampers, regardless of the number of records considered. Regarding the application of the direct assessment method as an alternative to nonlinear dynamic analyses, the estimates derived from the method for the median curves of Droof are consistent with the results of the nonlinear dynamic analyses. These results show that the method is effective and can be used as a simplified alternative to nonlinear dynamic analyses for probabilistic assessment purposes. With reference to the dispersion parameter βregr, it is possible to notice several aspects. Dispersion increases with seismic intensity, it depends on the results of the nonlinear dynamic analyses and, in particular, on the number of records. The expected trend, i.e. greater dispersion for the structure without dampers than for the structure with dampers, was determined only for the higher number of records (180 records). Regarding the dispersion parameter βcost, the trend was as expected even when using a lower number of records. Additionally, βcost increases with the number of seismic events for both the structure with and without dampers. The relationships between the expressions for βcost and βregr for the structure with and without dampers were derived with the purpose of obtaining the dispersion for the structure with dampers, if that for the structure without dampers is known.