Seismic assessment and dissipative bracing retrofit-based protection of infills and partitions in RC structures

A balanced performance improvement of the constituting structural members, infills and partitions is a fundamental requirement in seismic retrofit design of frame buildings. In order to pursue this objective, the response of the non-structural elements must be accurately simulated, so as to evaluate their damage evolution and the correlation with the response of the structural skeleton. In the study presented in this article, diagonal no-tension struts with multilinear “pivot”-type hysteretic behaviour are adopted as substitute elements for masonry infill and partition panels. A trilinear axial force–displacement backbone curve is generated for the equivalent struts and transformed in the lateral force-drift curve of the panels. The latter is then scanned in terms of sequential performance limits and ranges. This model is demonstratively applied to a real case study, i.e. a reinforced concrete frame building damaged by the 2016 Central Italy earthquake, although a retrofit intervention had been carried out a few years before. Based on the results of the time-history assessment analyses in its original conditions, an alternative retrofit solution is proposed, consisting in the incorporation of dissipative braces equipped with pressurized fluid viscous dampers. This technology was selected for its high-damping capacity, as well as for the prompt activation of the constituting devices starting from the early stages of the building seismic response. The verification analyses developed in retrofitted configuration for the main shock records of the 2016 earthquake confirm this property, showing slight damage only in a small number of partitions—instead of the diffused moderate-to-irreparable damage actually surveyed in the building partitions and infills—and safe response of all structural members.