Retrofit design assessment methods

Return period can also be used for the assessment of structural capacity and vulnerability of a structure in order to design proper mitigation measures. In other words, it can be used to quantify the safety levels and structural deficiencies in a more straightforward manner and to assess the improvement of structural performance after certain retrofitting interventions. For this purpose, Raffaele and Fiore (2013) presented a simple methodology (based on the reverse application of the well-known N2 method) that allows the assessment of the return period when the elastic period and the capacity of the examined structure for a given limit state are available. Subsequently, this so-called capacitive return period can be used to determine the seismic capacity and the reference life for any limit state considered. 

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