Targeted steel frames by means of innovative moment resisting connections

The present paper proposes the use of stepped cross section devices on steel frames aiming at reproducing a pre-established target push-over curve. To this aim a Limited Resistance Plastic Device (LRPD) to be inserted along selected structural members is proposed. The following two main specific features for LRPD are required: any elastic flexural stiffness variation of the original selected member must be avoided; an ultimate plastic bending moment value equal to an assigned percentage of the original limit resistance value must be ensured. Steel frames equipped with LRPD are modeled by means of an extension of a recently proposed Fibre Smart Displacement Based (FSDB) beam element model, characterized by the adoption of updating shape functions. The novelty of this research, with respect to previous studies, regards: i) the formulation of a targeted plane steel frame by means of a new optimal design procedure for the LRPD with assigned stiffness and resistance features, independent of each other; ii) the development of a FSDB beam element approach suitably devoted to such a special application of discontinuous cross sections devices. The design procedure and the FSDB model for the analysis of the real behaviour of the proposed LRPD device in the field of distributed plasticity is validated against detailed 3D finite element models.