Abstract | A methodology is introduced for applying the FUSEIS beam-link steel lateral-load-resisting system for strengthening existing reinforced-concrete buildings. The purpose is to take advantage of the easy replaceability and architectural versatility of the FUSEIS systems to strengthen a deficient structure, while minimizing the economic impact of the rehabilitation works due to suspension of the operation of the building. Additionally, a case study is presented, where an existing building is upgraded by introducing FUSEIS beam-link systems, first by performing response spectra analysis using an initial behaviour factor, then refining the results via the INNOSEIS performance-based methodology. This necessitates the use of nonlinear dynamic analyses to quantify a risk-consistent behaviour factor that incorporates the effect of aleatory and epistemic uncertainty on the actual systems’ performance. Finally, a pre-normative assessment for the q-factor of FUSEIS-beam link systems is achieved, for use in existing reinforced concrete buildings within Eurocode 8.