Development of Analytical Models for Earthquake Analysis of Steel Moment Frames

Moment resisting steel frames (MRFs) designed according to current building codes are expected to deform well into the inelastic range during severe earthquake ground motions. Inelastic deformations of MRFs are typically concentrated in critical regions at the ends of girders and columns, and in column panel zones. The accurate prediction of the mechanical behavior of the structure during earthquake excitations depends on the development of reliable analytical models which describe the hysteretic behavior of the critical regions. The development of such analytical models is the subject of this study.

The multi-linear hinge element (a one component series hinge type model), nonlinear panel zone element (a rotational spring element), and composite beam element (a one component series hinge type model) were developed to model bare steel beams and columns, column panel zones, and composite beams. The multi-linear hinge element employes multilinear force deformation relationships, and accounts for the effects of beam end connection type, for the case of fully welded as well as welded flange-bolted web type connections. The element also models plastic axial deformations and changes in axial stiffness due to hinge formation under combined bending and axial force. Hardening rules handle monotonic, cyclic or random loading. In the hysteretic models of the nonlinear panel zone element and the composite beam element, a smooth transition from the elastic stage to the inelastic stage was considered. In the composite beam element, the capability to account for a moving inflection point was implemented. The member behavior predicted by the developed elements match well with available experimental results and with predictions made by a fiber model.

The multi-linear hinge element, the nonlinear panel zone element, and the composite beam element were combined into thirteen steel subassemblages and five steel frames to investigate their local and overall response. The analytically predicted overall responses matched reasonably well with experimental data. The analyses by the multi-linear hinge elements and the nonlinear panel zone elements produced better overall and local response predictions than the analyses by existing bilinear hinge elements and bilinear panel zone elements.