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Industrial single-storey buildings are the most diffuse typology of steel construction located in Italy. Most of these existing buildings were erected prior to the enforcement of adequate seismic provisions; hence, crucial attention is paid nowadays to the design of low-impact retrofit interventions which can restore a proper structural performance without interrupting productive activities. Within this framework, an existing industrial single-storey steel building located in Nusco (Italy) is selected in this paper as a case-study. The structure, which features moment resisting (MR) truss frames in both directions, is highly deformable and presents undersized MR bolted connections. Structural performance of the case-study was assessed by means of both global and local refined numerical analyses. As expected, the inadequate performance of connections, which fail due to brittle mechanisms, detrimentally affects the global response of the structure both in terms of lateral stiffness and resistance. This effect was accounted for in global analyses by means of properly calibrated non-linear links. Thus, both local and global retrofit interventions were designed and numerically investigated. Namely, lower chord connections were strengthened by means of rib stiffeners and additional rows of M20 10.9 bolts, whereas concentrically braced frames (CBFs) were placed on both directions' facades. Designed interventions proved to be effective for the full structural retrofitting against both seismic and wind actions without limiting building accessibility. [ABSTRACT FROM AUTHOR]

The non-linear monotonic and hysteretic behaviour of as-built and retrofitted beam-to-column joints of an existing non-code conforming steel multi-storey building was investigated by means of finite element simulations. The building case study was originally designed to resist only gravity and wind loads without any capacity design principle. The as-built joints have continuous beam and interrupted columns that are bolted with end-plate splice to the tapered flange of the beams in the nodal zone. These joints were analysed to assess their non-linear response. The finite element analyses showed adequate resistance against gravity loads, but poor performance under seismic and column loss scenarios. Two retrofit strategies were designed in order to enhance the local and global performance in order to guarantee the weak beam-strong column condition, namely: (i) strengthening the column and its connection; (ii) weakening of the beam. Different types of interventions were designed per examined strategy and numerically analysed to assess the global and local response of both external and internal joints. A TOPSIS multicriteria analysis was also performed to identify the most suitable type of intervention. • The response of steel joints from a non-code conforming building are investigated. • The as-built joints exhibit poor behaviour under seismic and column loss scenarios. • Both connection strengthening and beam weakening interventions are analysed. • The retrofitted joints show satisfactoy behaviour. • TOPSIS analysis is carried out to select the optimal retrofitting intervention. [ABSTRACT FROM AUTHOR]