# Bidirectional Section
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.
```tcl
section Bidirectional $secTag $E $Fy $Hiso $Hkin <$code1 $code2>
```
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)
Code Developed by: Michael H. Scott