10.3 Element Section

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The section keyword *ELEMENT has as options

*TYPE=<element type>

specifies the element type (mandatory)

*ELSET=<name>

specifies a name which basically may be freely chosen (mandatory)



The data lines describe the following element data

<element number>,

<1st node number>,

<2nd node number>

....



Values have to be separated by commas. The number of nodes which have to be specified depends on the element type. Nodes have to be specified in a counter clockwise direction sequence regarding plate, slab and shell elements.

The whole of these lines form an element set which is referred to by the name specified above. The particular element set is closed with a new section keyword. More element sets may be created starting with the section keyword *ELEMENT.

The following element types are currently implemented:

   

number

ndof indices

book section

internal type index

   

of nodes

see Section 8

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see also Section 13.1

B23E   

Extended 2D Bernoulli beam

3

1,2,6

3.3.2

10

B23   

2D Bernoulli beam

2

1,2,6

3.3.2

10

B21E   

Extended 3D Timoshenko beam

3

1,2,6

3.3.3

11

B21   

3D Timoshenko beam

2

1,2,6

3.3.3

11

T1D2   

1D truss / bar

2

1

1.3

1

T2D2   

2D truss / bar

2

1,2

1.3

1

T3D2   

3D truss / bar

2

1,2,3

 

1

S1D2   

1D spring

2

1

1.3

99

S2D6   

2D spring

2

1,2,6

 

98

CPE3   

2D continuum plane strain

3

1,2

 

2

CPE4   

2D continuum plane strain

4

1,2

1.3

2

CPS3   

2D continuum plane stress

3

1,2

 

2

CPS4   

2D continuum plane stress

4

1,2

1.3

2

SB3   

2D slab

3

3

7.4.2

20

SH4   

3D continuum based shell

4

1,2,3,4,5

8.1-2

21



The section keyword *ELEMENT has no own keywords.

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10.3.1 Special remarks concerning shell elements SH4

Every shell node has a local 3D right-handed cartesian coordinate system, see Fig. 4 and Section 8.1 of the Book ($\rightarrow $ http://www.concrete-fem.com). It is basically defined through a director more or less normal to the shell surface. The director defines the cross sectional planes which are assumed to remain straight during a deformation. The other two directions define the axes of the rotational degrees of freedom.

\includegraphics[scale=0.70]{Figures/C8_ShellKinemat1}
Figure 4: Nodal shell coordinate system



Furthermore, the node directors co-determine the relations between global and local coordinates in shell integration points. In particular – regarding an integration point –, they co-determine the Jacobian matrix and thus the integration point director which is more or less normal to the shell’s reference surface.

Another local 3D right-handed cartesian coordinate system is used with the integration point director as local $n$-direction. The local $\alpha $-direction is generally derived by the cross product of the director and the global $y$-direction, i.e. it aligns to to the global $x-z$-plane. The local $\beta $-direction is derived from the cross product of the director and and the local $\alpha $-direction.

The material behavior is described with respect to this integration point coordinate system, see Section 8.3 of the Book ($\rightarrow $ http://www.concrete-fem.com). In particular, stress directions and directions of derived normal forces, bending moments and shear forces relate to this coordinate system. The components of $\bf {V}_\alpha ,\, \bf {V}_\beta $ – measured in the global system – are appended to the shell element output, see Section 12.2. This indicates how moments, forces and stresses are acting. The orientation angle of a reinforcement layer – acting uniaxially within the shell surface by definition – refers to $\bf {V}_\alpha $. The orientation angle is measured counterclockwise with the director $\bf {V}_ n$ as rotation axis.

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