“Primary” and “secondary” structural elements in seismic retrofitting of RC buildings

The paper deals with a design approach aimed at the seismic retrofitting of an existing RC building. The methodology is based on the classification of structural members into “primary” and “secondary” seismic members, where the former possess a seismic-resisting capacity while the latter are neglected in the evaluation of the seismic resistance, as indicated in both EC8 and NTC2018. This approach can be particularly advantageous for the design of seismic retrofit of existing buildings since it enables to focus the seismic design on the new bracing elements. If these elements have a very high lateral stiffness than the existing structure, they can be classified as primary, while the existing structure is classified as secondary, and it is only required to maintain its load-bearing capacity against vertical loads during seismic events. The design approach has been applied to a RC building that is part of the Florentine public housing stock of the 1970s.