Shell elements

Semi-loof elements, which model thin shells, can be used for all problem types except materially nonlinear problems.

Each element is described in the name.i1 file using one EL batch:

EL T 61 E IE N IN$_1$ IN$_2$ $\dots$ IN$_\mathtt{NNE}$ G NG H $h_1$ $h_2$ $\dots$ $h_\mathtt{NNE}$

The T group can be omitted if $\mathtt{ITE}={}$$\mathtt{ITED}$${}=61$.

$\mathtt{IE}$	The element number.
$\mathtt{IN}_j$	The node numbers of the element in the prescribed order, see the Reference Manual. Midside nodes must not be omitted.
$j$	The local number of the element node, $1\le j\le\mathtt{NNE}$.
$\mathtt{NNE}$	The number of nodes in the element.
$\mathtt{NG}$	The order of numerical integration for the element, $2\le\mathtt{NG}\le4$. If the G group is missing, the value $\mathtt{NGD}$ applies. Usually $\mathtt{NG}=\mathtt{NGD}=3$.
$h_j$	The nodal thicknesses of the element. If only one value is specified, it applies to all nodes of the element. If the H group is missing, the value $\mathtt{THDEF}$ applies to all nodes of the element. The thicknesses are automatically multiplied by the $\mathtt{SCALE}$ scale factor; for example, the value $\mathtt{SCALE}=0.001$ means that all thicknesses are given in millimeters.

Note
The EL batch can have any number of continuation lines. Data are written from column 3 to column 72 (the first two columns are generally reserved for two-letter batch names), see the Reference Manual.

Example

Let us consider a triangular shell element. The global node numbers follow from the specific numbering of the mesh.

According to the Reference Manual, the node numbers can be written in three ways:

22 24 77 23 44 43
24 77 22 44 43 23
77 22 24 43 23 44

in which case the $\zeta$ axis will point upward as in the figure, or in three further ways:

22 77 24 43 44 23
77 24 22 44 23 43
24 22 77 23 43 44

in which case the $\zeta$ axis will point downward.

A typical form of the EL batch, corresponding to the orientation of the coordinate system $\xi,\eta,\zeta$ and the order of the edges shown in the figure, will be:

EL T 61 E 211 N 22 24 77 23 44 43

The order of numerical integration and the thickness of the element will be given by the default values $\mathtt{NGD}$ and $\mathtt{THDEF}$. If only shell elements occurred in the mesh, the notation could be simplified by specifying $\mathtt{ITED}=61$, and the T 61 group would be omitted.

Stiffeners

A semi-loof element can be stiffened along one or more edges, see the Reference Manual.

Each stiffener is described by one pair of S and R groups, which are appended to the end of the corresponding EL batch:

EL $\dots$ S IH R $I_\eta$ $I_\zeta$ $A$ $\alpha_v$ $h_T$ $h_v$

$\mathtt{IH}$	The local number of the edge of the shell element.
$I_\eta$	The second moment of area about the local axis $\eta_v$ $[\text{m}^4]$.
$I_\zeta$	The second moment of area about the local axis $\zeta_v$ $[\text{m}^4]$.
$A$	The cross-sectional area $[\text{m}^2]$.
$\alpha_v$	The angle between the local axis $\eta_v$ and the tangent plane $[^\circ]$.
$h_T$	The distance of the centroid from the surface $[\text{m}]$ (entered as negative if the stiffener is attached to the bottom of the surface).
$h_v$	The height $[\text{m}]$ (entered as negative if the stiffener is attached to the bottom of the surface).

Example

Let us consider a triangular shell element. The local edge numbers follow from the specific numbering of the mesh. Let us assume that edge 24–44–77 is to be longitudinally stiffened by a rib attached to the bottom.

A typical form of the EL batch will be:

EL T 61 E 211 N 22 24 77 23 44 43
␣␣S 2 R <Ieta> <Izeta> <A> <αᵥ> -<hᴛ> -<hᵥ>

where the corresponding values of the stiffener’s geometric properties are written in place of the expressions <…>. The heights $h_T$ and $h_v$ will be entered as negative.