13.281. SHELL281 - 8-Node Shell

Matrix or VectorGeometryShape FunctionsIntegration Points
Stiffness Matrix and Thermal Load VectorQuadEquation 11–82, Equation 11–83, and Equation 11–84

In-plane:  2 x 2

Thru-the-thickness:
1, 3, 5, 7, or 9 per layer
for section data input for
general shell option 
(KEYOPT(1) = 0)

Thru-the-thickness:
1 per layer for section
data input for membrane
shell option 
(KEYOPT(1) = 1)

TriangleEquation 11–58, Equation 11–59, and Equation 11–60

In-plane:  3

1, 3, 5, 7, or 9 per layer
for section  data input for
general shell option 
(KEYOPT(1) = 0)

1 per layer for section 
data input for membrane
shell option 
(KEYOPT(1) = 1)

Consistent Mass and Stress Stiffness MatricesQuadEquation 11–82, Equation 11–83, and Equation 11–84Same as stiffness matrix
TriangleEquation 11–58, Equation 11–59, and Equation 11–60Same as stiffness matrix
Lumped Mass MatrixQuadEquation 11–82, Equation 11–83, and Equation 11–84Same as stiffness matrix
TriangleEquation 11–58, Equation 11–59, and Equation 11–60Same as stiffness matrix
Transverse Pressure Load VectorQuadEquation 11–842 x 2
TriangleEquation 11–603
Edge Pressure Load VectorSame as in-plane mass matrix, specialized to the edge2
Load TypeDistribution
Element TemperatureLinear thru thickness, bilinear in plane of element
Nodal TemperatureConstant thru thickness, bilinear in plane of element
PressureBilinear in plane of element, linear along each edge

References: Ahmad([1]), Cook([5]), Dvorkin([97]), Dvorkin([98]), Bathe and Dvorkin([99]), Allman([114]), Cook([115]), MacNeal and Harder([116])

13.281.1. Other Applicable Sections

Structures describes the derivation of structural element matrices and load vectors as well as stress evaluations.

13.281.2. Assumptions and Restrictions

Normals to the centerplane are assumed to remain straight after deformation, but not necessarily normal to the centerplane.

Each set of integration points thru a layer (in the r direction) is assumed to have the same element (material) orientation.

13.281.3. Membrane Option

A membrane option is available for SHELL281 if KEYOPT(1) = 1. For this option, there is no bending stiffness or rotational degrees of freedom. There is only one integration point per layer, regardless of other input.

13.281.4. Shear Correction

The element uses an equivalent energy method to compute shear-correction factors. These factors are predetermined based on the section lay-up at the start of solution.