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For [nonlinear|kb:Nonlinear] static and nonlinear direct-integration [time-history|kb:Time-history analysis] analyses, users may simulate [post-yield|kb:Material nonlinearity] behavior by assigning *concentrated plastic hinges* to [frame|kb:Frame] and [tendon|kb:Tendon] objects. The [P-M2-M3|P-M2-M3 hinges] hinge is best suited for nonlinear static pushover, whereas the [fiber hinge|kb:Caltrans vs. fiber hinge] is best for hysteretic dynamics. Elastic behavior occurs over member length, then deformation beyond the elastic limit occurs entirely within hinges, which are modeled as discrete points. !Figure 1.png|align=right,border=0,width=250pxpxpxpxpxpxpxpx,hspace=15,vspace=15px! Inelastic behavior is obtained through integration of the plastic strain and plastic curvature which occurs within a user-defined hinge length, typically on the order of member depth (FEMA-356). To capture plasticity distributed along member length, a series of hinges may be modeled. Multiple hinges may also coincide at the same point.

Plasticity may be associated with force-displacement behaviors (axial and shear) or moment-rotation (torsion and bending). Hinges may be assigned (uncoupled) to any of the six DOF. Post-yield behavior is described by the general backbone relationship shown to the right. The modeling of strength loss is discouraged, to mitigate load redistribution (which may lead to progressive collapse) and to ensure numerical convergence. {new-tab-link:http://www.csiberkeley.com/}CSI{new-tab-link} Software automatically limits negative slope to 10% of elastic stiffness, though overwrite options are available. For informational purposes, additional limit states (IO, LS, CP) may be specified which are reported in analysis, but do not affect results. Unloading from the point of plastic deformation follows the slope of initial stiffness.

Both [P-M2-M3|P-M2-M3 hinges] and [fiber hinges|kb:Caltrans vs. fiber hinge] are available to capture coupled axial and biaxial-bending behavior. Additional information on hinges can be found in the {new-tab-link:http://www.csiberkeley.com/}CSI{new-tab-link} [_Analysis Reference Manual_|doc:CSI Analysis Reference Manual] (Frame Hinge Properties, page 131).

{list-of-resources2:label=hinge|drafts-root=Hinge drafts}