Critical analysis of ultimate rotation formula for R.C. columns subjected to cyclic loadings

Performance-based earthquake engineering relies on the availability of analytical models that can be used to predict structural performance, including collapse. Current code prescriptions allow evaluating the ultimate rotational capacity of hybrid (mechanical-empirical) or empirical formulations, for R.C. members both seismically and not-seismically detailed. The aim of the present work is to present a critical analysis of the empirical relationship proposed by Eurocode 8 Part 3 and Italian Seismic Code. These relationships formerly similar have been compared with the original formulations introduced by Biskinis and Fardis [1,2]. A databank of cyclic tests on rectangular column sections failing in flexure, shear and flexure-shear, have been selected from an available database and research reports. Their ultimate chord rotation corresponding to an ultimate strength of 80% has been compared with the results provided by the available relationships, to check the accuracy and the reliability of codes proposals. Finally, a new formulation based on an empirical approach is proposed.