Proposed Updates to the ASCE 41 Nonlinear Modeling Parameters for Wide-Flange Steel Columns in Support of Performance-Based Seismic Engineering

Nonlinear static and dynamic analyses are utilized by engineers for performance-based seismic risk evaluation of new and existing structures. In this context, nonlinear component modeling criteria are typically based on ASCE 41 guidelines. Experiments on wide-flange steel columns suggest that the ASCE 41-13 nonlinear component models do not adequately reflect the expected steel column behavior under cyclic loading. To help bridge the gap between state-of-the-art research and engineering practice, this paper proposes new modeling criteria for the first-cycle envelope and monotonic backbone curves of steel wide-flange columns for use in nonlinear static and dynamic frame analyses. The proposed nonlinear provisions include new parameters for concentrated hinge models to facilitate modeling of strength and stiffness deterioration of steel columns under seismic loading. The associated variability in the model parameters is also quantified to facilitate reliability analyses and development of probabilistic acceptance criteria for design. Recommendations are made to account for the influence of bidirectional lateral loading and varying axial load demands on the steel column’s hysteretic behavior. Also proposed is an increase in the compression axial force limit for characterizing columns as force-controlled versus deformation-controlled in line with the new ASCE 41 provisions. The proposed modeling parameters are validated against test data and continuum finite-element analyses, and they are proposed for consideration in future updates to ASCE 41 requirements for nonlinear static and dynamic analyses of steel frame buildings with wide-flange columns.