Plastic-hinge approach for inelastic analysis of steel–concrete framed structures

This paper presents an application of a computational tool, denoted as SAAFE Program, developed to provide a nonlinear inelastic analysis of steel and composite (steel–concrete) 2D framed structures. This procedure allows an accurate description of the structural nonlinear response, with less computational effort when compared to the general FEM formulation. The method, although similar in concept to earlier plastic-hinge approaches, differs with regard to numerical implementation methodology and precision. The proposed plastic-hinge model is formulated in a succinct format based on the following characteristics: (i) stiffness parameter ηη, evaluated as a function of the yielding progress at each plastic-hinge location; (ii) effective tangent modulus EtEt concept which reduces the modulus of elasticity in the element stiffness calculation, considering both the residual stress and out-of-straightness effects; (iii) second-order formulation, based on an incremental stiffness approach in which conventional stability functions are used to reflect the effect (on member stiffness) of axial loads on displacements, allowing accurate identification of member instability. Verification examples are analysed by the proposed approach, in which results are compared with those of FEM numerical and available experimental data, showing good agreement. Based on the obtained results, it is possible to infer about the efficiency and robustness of the proposed model to perform inelastic analysis for isolated and full frame members, incorporating geometric and material nonlinearity.