Guidelines on nonlinear dynamic analysis for seismic design of steel moment frames

Nonlinear dynamic (response history) analysis is being used increasingly in design practice for the performance-based seismic design of buildings. In contrast to nonlinear static analysis, dynamic analyses require more explicit modeling of cyclic response including strength and stiffness degradation as well as special consideration to selection and scaling of ground motions, definition of viscous damping, and other dynamic effects. To help bridge the gap between state-of-the-art in research and practice, the National Institute of Standards and Technology has funded ATC-114 project to develop improved modeling criteria and guidelines for nonlinear dynamic analysis. The guidelines address both overall considerations, such as recommendations for modeling floor diaphragms and equivalent viscous damping, along with component modeling criteria that are specific to steel moment frame systems. Nonlinear analysis provisions for steel moment frames include new parameters for concentrated hinge models to facilitate modeling of strength and stiffness degradation under random cyclic loading. The new parameters are calibrated to testing and detailed finite element analyses of beam-to-column connections and columns subjected to bending and axial loads. The guidelines also include recommendations for modeling fracturecritical welded connections using fiber-type hinge models. An example analysis of a four-story steel moment frame building is included to illustrate application of the guidelines, following the new ASCE 7-16 requirements for nonlinear response history analysis.