Evaluation of behaviour factors on the basis of ductility and overstrength studies

The paper focuses on the evaluation of behaviour factors for seismic design of structures, with due consideration to both their ductility and overstrength. Firstly, inelastic strength spectra for typical target ductilities are presented for earthquake motions representative of those expected in Southern Europe, in particular Greece, the country with the highest seismicity in Europe. Mean spectra for different soil conditions are derived, using a scaling procedure, which is different from that usually found in previous studies, and reduces the associated scatter. The ductility-dependent component of the behaviour factor is then estimated on the basis of the corresponding inelastic spectra and comparisons with previously suggested values are made. The overstrength-dependent component is subsequently addressed, with particular emphasis on low-rise and medium-rise reinforced concrete structures designed to procedures typical in current European construction; both inelastic time-history and pushover analyses are used to this purpose. A tentative proposal for an appropriate (period-dependent) form of the behaviour factor is made, and it is found that the expression for the behaviour factor adopted in Eurocode 8 is reasonably conservative and can be used if more complex procedures are to be avoided.