How to select a limited number of ground motion records (GMRs) is an important challenge for the nonlinear analysis of structures. Since epsilon (ε Sa ) is an indicator of spectral shape, which has a significant correlation with the non-linear response of a structure, the selection of GMRs based on the hazard-related target ε Sa is a reasonable approach. In this paper, an alternative indicator of spectral shape is proposed, which results in a more reliable prediction of the non-linear response for the structures with the natural period of 0.25 to 3.0 s. This new parameter, named eta ( ), is a linear combination of ε Sa and the peak ground velocity epsilon (ε PGV ). It is shown that , as a non-linear response predictor, is remarkably more efficient than the well-known and convenient parameter ε Sa . The influence of -filtration in the collapse analysis of an eight-story reinforced concrete structure with special moment-resisting frames was studied. Statistical analysis of the results confirmed that the difference between ε-filtration and -filtration can be very significant at some hazard levels. In the case of this structure, the resulting annual frequency of collapse was found to be lower in the case of -based record selection, in comparison with the ε-based record-selection approach.

A methodology has been proposed which can be used to reduce the number of ground motion records needed for the reliable prediction of the median seismic response of structures by means of incremental dynamic analysis (IDA). This methodology is presently limited to predictions of the median IDA curve only. The reduction in the number of ground motion records needed to predict the median IDA curve is achieved by introducing a precedence list of ground motion records. The determination of such a list is an optimization problem, which is solved in the paper by means of (1) a genetic algorithm and (2) a proposed simple procedure. The seismic response of a simple, computationally non-demanding structural model has been used as input data for the optimization problem. The presented example is a three-storey-reinforced concrete building, subjected to two sets of ground motion records, one a free-field set and the other a near-field set. It is shown that the median IDA curves can be predicted with acceptable accuracy by employing only four ground motion records instead of the 24 or 30 records, which are the total number of ground motion records for the free-field and near-field sets, respectively.

Incremental dynamic analysis (IDA) is a widely-used method for assessing structural performance under earthquake excitations. It enables direct evaluation of the record-to-record variability in structural response through a set of ground motion records. If the number of ground motion records is large then, the method becomes computationally demanding. To facilitate its practical application, a precedence list of ground motion records has been introduced, aiming at selecting the most representative ground motion records for IDA analysis. In progressive IDA analysis the IDA curves are computed progressively, starting from the first ground motion record in the precedence list. After an acceptable tolerance has been achieved, the analysis is terminated. This approach may significantly reduce the computational effort for first-mode dominated structures, since the seismic response can be computed only for a certain number of ground motion records from the precedence list in order to achieve an acceptable level of confidence in the prediction of the summarized (16 th, 50 th and 84 th fractiles) IDA curves. The proposed implementation of incremental dynamic analysis, which is demonstrated using an example of a four-storey reinforced concrete frame, can also be used for the selection of ground motion records from a very large set of records, provided that all the records properly represent the seismic scenario for a given site.