Performance-based seismic design of steel structures accounting for fuzziness in their joint flexibility

This paper presents a performance-based earthquake engineering framework to explicitly take into account fuzziness in the design parameters, with application to steel structures. Semi-rigidity of column-to-foundation and beam-to-column connections is considered as a relevant example of design parameters that can be conveniently modelled using fuzzy variables. Without lack of generality, their fixity factors are described by means of triangular membership functions, fully defined by lower and upper values of admissibility and their most likely value, i.e. their reference value. For demonstration purposes, the procedure is applied to analyse two different case studies, namely a 5-storey single-bay plane frame and an industrial 3D modular structure. The analyses are performed accounting for the fuzziness of the connections, which is then propagated onto representative engineering demand parameters, within a general performance-based design (PBD) approach.