The member modeling requirements in this section are invoked by the applicable requirements for each system, as specified in Section 1.7.
1.5.1 Beams
Modeling of beams shall address the following as applicable:
- (a) Force-deformation and moment-rotation models for beams shall include inelastic flexural deformations, taking into account material yielding, strain hardening, and degradation due to local buckling and lateral-torsional buckling effects. The model shall consider interaction unless the ratio of is 0.1 or less.
- (b) Where concentrated beam hinge models are used, the moment-rotation response shall be determined using the parameters in ANSI/AISC 342, Chapter C.
- (c) Where fiber-type beam hinge or distributed plasticity models are used, strain hardening shall be considered when appropriate. Unless the fiber model accounts for local buckling and fracture effects, the inelastic beam rotations shall be limited to the hinge rotation at the peak strength of an equivalent concentrated plastic hinge model.
- (d) Beam hinge properties shall be modeled considering the cross-sectional characteristics of the beam. Concentrated hinge or fiber hinge models shall be located at the expected plastic hinge locations. Locating the concentrated hinge away from the actual hinge location is permitted, provided that the hinge properties are adjusted to account for the discrepancy in locations, considering the beam moment gradient and the difference between actual and modeled beam lengths.
- (e) Where the steel beam acts compositely with a concrete floor slab (solid slab or slab on steel deck), adjusting the beam stiffness and hinge strength to account for composite action under positive and negative bending shall be considered, taking into account the force transfer mechanisms in the beam-to-column (or beam-to-wall) connections.
1.5.2 Links
Modeling of links shall address the following as applicable:
- (a) Shear and flexural yielding or buckling, post-yielding or post-buckling, peak strength of the link.
- (b) The component properties of the link shall be determined per ANSI/AISC 342, Chapter C, taking into account the effect of axial force in the link.
1.5.3 Columns
Modeling of columns shall address the following as applicable:
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(a) Force-deformation model for columns shall include inelastic flexural deformations under combined flexure and axial loading, taking into account yielding, strain hardening, local buckling effects, and flexural-torsional response.
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(b) Where concentrated hinge models are used, the moment-rotation response shall be determined using the parameters in ANSI/AISC 342, Chapter C.
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(c) Where fiber-type beam hinge or distributed plasticity models are used, strain hardening shall be considered. Unless the fiber model properties are adjusted to account for local buckling and flexural-torsional effects, the inelastic column rotations shall be limited to the peak point of the plastic hinge rotation of an equivalent concentrated hinge model.
1.5.4 Braces (Except Buckling-Restrained Braces)
Modeling of braces shall address the following as applicable:
- (a) Brace yielding and elongation, including accumulation of permanent elongation due to cyclic loading
- (b) Brace buckling, including effects of initial imperfections, residual stress, equilibrium on the deformed brace geometry, and axial-flexural interaction
- (c) Post-buckling strength degradation under cyclic loading
- (d) Fracture due to low-cycle fatigue degradation and peak ductility effects. If fracture is not included in the brace model, the peak deformation shall not exceed the values specified in ANSI/AISC 342, Section C3.
- (e) Rotational restraint of end connections
- (f) Restraint effects and appropriate constraints at locations where braces overlap or intersect
- (g) Actual brace end locations that are offset from workpoint locations
1.5.5 Buckling-Restrained Braces
Modeling of buckling-restrained braces shall address the following as applicable:
- (a) Elastic stiffness considering variations in brace cross-sectional area along the length
- (b) Brace yielding in tension and compression, including accumulation of permanent axial deformation due to cyclic loading
- (c) The peak deformation demand and cumulative deformation demand for brace element models shall be limited to capacities determined from representative cyclic tests conducted in accordance with Section K3.
- (d) Difference between tension and compression yield forces, as specified in Section F4.2
- (e) Actual brace end locations that are offset from workpoint locations
1.5.6 Steel Plate Shear Walls
Modeling of steel plate shear walls shall address the following as applicable:
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(a) Yielding and elongation of the steel plate
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(b) Pinching of the hysteretic loop due to shear buckling
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(c) Distribution of transverse forces on horizontal and vertical boundary elements
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(d) The valid range of steel plate shear wall element models shall not extend beyond 15Δy, where Δy is the yield elongation of a diagonal strip of the web plate. For methods other than strip modeling, an equivalent displacement measure shall be used.
1.5.7 Composite Plate Shear Walls
Modeling of composite plate shear walls shall address the following as applicable:
- (a) Yielding of steel plates
- (b) Inelastic local buckling of steel plates in compression
- (c) Concrete compression behavior including effects of confinement on infill concrete
- (d) Concrete tension cracking
- (e) Pinching of hysteretic loops due to concrete crack closure and steel cyclic local buckling
- (f) Fracture of steel plates due to plastic strain accumulation