A note on selection of time-histories for seismic analysis of bridges in Eurocode

Eurocode 8 (EC8) allows the use of real earthquake records as an input for time-history analysis of structures. In its Part 2, the code discusses the preparation of seismic input for bridges; although referring to the same target spectral shapes of Part 1, which applies to buildings. The prescriptions are somewhat differently specified in the two drafts. However, the main requirement the chosen record set should satisfy in both cases, is the compatibility of the horizontal average spectrum with the target in a broad range of periods. The set has to be made of at least three recordings, but seven is the minimum set size to consider the mean structural response as the design value. The code, at least for bridges, seems to indicate real records as the principal source of ground-motions the practitioners should rely on; however the selection of real records is not straightforward. In another study, the authors discussed the record selection prescriptions of EC8 Part 1 with respect to the current best practice, and the actual possibility of finding real record sets compliant with EC8 spectra was investigated. This paper represents an extension of the same study to EC8 Part 2 and bridges. To this aim the European Strong-Motion Database is searched to identify real record sets matching the design spectral shapes for several hazard levels and site conditions in a broad range of periods up to 4s. It resulted that combinations well approximating the target may be found for some soil classes, at least for low-to-moderate seismicity sites and if the condition of matching specific source parameters is released and large record-to-record variability is accepted. Finally the record sets presented have been used to compare spectral compatibility prescriptions of EC8 Part 1 and Part 2, which have been found to be equivalent to some extent.