BbarQuad u-p Element

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bbarQuadUP is a four-node plane-strain mixed volume/pressure element, which uses a tri-linear isoparametric formulation. This element is implemented for simulating dynamic response of solid-fluid fully coupled material, based on Biot's theory of porous medium. Each element node has 3 degrees-of-freedom (DOF): DOF 1 and 2 for solid displacement (u) and DOF 3 for fluid pressure (p).

Please click here for examples.

OUTPUT INTERFACE: Pore pressure can be recorded at an element node using OpenSees Node Recorder:

recorder Node <-file $fileName> <-time> <-node ($nod1 $nod2 …)> -dof 3 vel

See OpenSees command manual (McKenna and Fenves 2001) for nodal displacement, velocity, or acceleration recorders.

The valid queries to a bbarQuadUP element when creating an ElementRecorder are 'force', 'stiffness', or 'material matNum matArg1 matArg2 ...', where matNum represents the material object at the corresponding integration point.

element bbarQuadUP $eleTag $iNode $jNode $kNode $lNode $thick $matTag $bulk $fmass $hPerm $vPerm <$b1=0 $b2=0 $t=0>

$eleTag	A positive integer uniquely identifying the element among all elements
$iNode, $jNode, $kNode, $lNode	Four element node (previously defined) numbers in counter-clockwise order around the element
$thick	Element thickness
$matTag	Tag of an NDMaterial object (previously defined) of which the element is composed
$bulk	Combined undrained bulk modulus Bc relating changes in pore pressure and volumetric strain, may be approximated by: Bc ≈ Bf/n where Bf is the bulk modulus of fluid phase (2.2x106 kPa (or 3.191x105 psi) for water), and n the initial porosity.
$fmass	Fluid mass density
$hPerm, $vPerm	Permeability coefficient in horizontal and vertical directions respectively.
$b1, $b2	Optional gravity acceleration components in horizontal and vertical directions respectively (defaults are 0.0)
$t	Optional uniform element normal traction, positive in tension (default is 0.0)

TYPICAL RANGE OF PERMEABILITY COEFFICIENT

Gravel	Sand	Silty Sand	Silt	Clay
>1.0x10-1 cm/s (or 3.94x10-2 in/s)	1.0x10-3 cm/s (or 3.94 x10-4 in/s) ~ 1.0x10-1 cm/s (or 3.94 x10-2 in/s)	1.0x10-5 cm/s (or 3.94 x10-6 in/s) ~ 1.0x10-3 cm/s (or 3.94 x10-4 in/s)	1.0x10-7 cm/s (or 3.94 x10-8 in/s) ~ 1.0x10-5 cm/s (or 3.94 x10-6 in/s)	<1.0x10-7 cm/s (or 3.94x10 -8 in/s)

Code Developed by: UC San Diego (Dr. Zhaohui Yang):

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UC San Diego Soil Model:

• Element Command
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    • Twenty Eight Node Brick u-p Element

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  • UC San Diego soil models (Linear/Nonlinear, dry/drained/undrained soil response under general 2D/3D static/cyclic loading conditions (please visit UCSD for examples)
    • PressureIndependMultiYield Material
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  • UC San Diego Saturated Undrained soil
    • FluidSolidPorousMaterial
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