Modeling of the nonlinear behavior of semi-rigid connections in steel framed structures and its influence on three dimensional analysis of structural systems

Özel, Halil Fırat
In steel frame structures, introducing the nonlinear force-deformation behavior of frame members with flexible joints will show closer results to the actual behavior. In this thesis, a mixed formulation frame finite element is developed from a nonlinear force-based method that can include localized semi-rigid connection response. The formulation of the element uses the three-fields Hu-Washizu-Barr principle, where displacement shape function approximation is omitted with the use of a force-based approach. The proposed element formulation can accurately capture the spread of plasticity along element length and section depth with a single element for each beam and column member. Introducing flexible connections to frame members does not necessitate additional nodes where the degrees of freedom do not increase. Also, nonlinear geometric effects and a correct shear area definition are applied to the elements with the use of the proposed element. Accuracy and robustness of the proposed element are presented at both member level and structural level for both the two-dimensional and three-dimensional rigid and semi-rigid steel frame structures. Verifications are conducted by considering studies presented in the literature, as well as the results obtained using advanced nonlinear finite element programs.