Nonlinear frame behavior is modeled using either concentrated plastic hinges or fiber hinges. Nonlinear material properties are only applicable when hinges are assigned to frame objects. The hinge force-deformation relationship, also known as the backbone curve, may be input manually, may be determined from the cross-section fiber model, or may be calculated from FEMA or Caltrans code-based equations. Once hinges are assigned, material nonlinearity may then characterize the inelastic response of frame objects.
NOTE: The P-M2-M3 hinge is best suited for nonlinear static pushover, whereas the fiber hinge is best for hysteretic dynamics.
- Nonlinear tension-only or compression-only axial behavior may be modeled by following the process outlined in the Tension and compression limits article.