Seismic upgrade of a non-code compliant multi-storey steel building: A case study

This study aims to develop a step-by-step design procedure for the seismic upgrade of existing steel buildings based on local strengthening interventions of the connections and the use of conventional X-concentrically bracings (X-CBFs), which are designed to account for both architectural and time/cost-saving constraints. The proposed procedure is applied to an existing non-code-compliant six-storey steel building, which is located in Naples (Italy). Both local and global numerical analyses are performed to investigate the effectiveness of the proposed procedure. The obtained results show that it is possible to decrease by up to 25 % the resistance and stiffness of new X-CBFs if the beam-to-column connections are strengthened to resist the flexural capacity of the connected beams. The pushover-based seismic fragility of as-built and upgraded structures is compared, and the seismic risk reduction is further quantified according to the Italian guidelines for the risk classification of constructions. The variation of seismic risk class induced by designed interventions is evaluated, thus confirming substantial risk mitigation of the upgraded building.