Bidirectional Section

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This command allows the user to construct a Bidirectional section, which is a stress-resultant plasticity model of two coupled forces. The yield surface is circular and there is combined isotropic and kinematic hardening.

section Bidirectional $secTag $E $Fy $Hiso $Hkin <$code1 $code2>

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$secTag	unique section tag
$E	elastic modulus
$Fy	yield force
$Hiso	isotropic hardening modulus
$Hkin	kinematic hardening modulus
$code1	section force code for direction 1 (default = Vy)
$code2	section force code for direction 2 (default = P)

NOTES:

• The implementation is a generalization of the uniaxial return map algorithm for rate independent plasticity (page 45, Simo and Hughes, 1998) with the same input parameters as the Hardening Material uniaxial material model.
• The bidirectional section is a suitable base isolator model and should be used in conjunction with a ZeroLengthSection element to this end. It can also be used in a nonlinear beam element to define stress resultant plasticity at an integration point.
• The optional code1 and code2 values correspond to the beam cross-section analogy with respect to the local axes of the calling element (P, Vy, and Vz = force along section local x, y, and z axes, respectively; T, My, and Mz = moment about section local x, y, and z axes, respectively)

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Code Developed by: Michael H. Scott