Modeling of inelastic cyclic behavior of members, connections and joint panels of steel frames

Research is presented on methods for including inelastic cyclic behavior of beam-column members, connections and joint panels for the nonlinear dynamic analysis of three-dimensional steel framed structures. A stress-resultant bounding surface model is proposed for modeling strain-hardening behavior of materials or gradual plastification in beam-column members. Surface contraction can be included to model the cyclic softening behavior which usually occurs in semi-rigid connections. A transit surface model is developed for handling the cyclic pinching behavior of connections. These models can be applied to structural components such as inelastic members, semi-rigid connections and joint panels for nonlinear analysis.;An inelastic member model is developed for including the effects of gradual plastification in the member. This model is combined with the bounding surface model for representing cross section response together with a factor to take account of moment distribution along the member length. A semi-rigid connection model is based on a multi-dimensional force-space surface model which accounts for the interaction of moment, shear, and axial loads in the connection. Strain-hardening behavior of connections is described using the bounding surface model, and cyclic pinching behavior is predicted using the transit surface model. A joint panel model is developed for incorporating joint panel effects in line-element type finite element analysis of framed structures, and joint panel distortion due to joint shear forces is included. Aspects of computer implementation of these models and preliminary studies of the effects of the inelastic members and semi-rigid connections on the nonlinear response of framed structures subjected to ground accelerations are also presented.;The study shows that (1) the inelastic member model requires fewer elements and is more computationally efficient than fiber- and finite-element models, (2) the semi-rigid connection model is capable of handling both strain-hardening and cyclic pinching behavior, and (3) the joint panel model which is applicable for planar joints allows its use in three-dimensional structures. In reality, the effects of members, connections and joint panels are coupled, and the proposed models can be combined for modeling complex behavior of these structural components for nonlinear dynamic analysis.