Line elements
Line elements can only be used for linear static and dynamic problems.
Each element is described in the name.i1 file using one EL batch:
EL T 51 E IE N IN$_1$ IN$_2$ A $A$
in the case of a bar, or
EL T 53 E IE N IN$_1$ IN$_2$ A $A$ $I_k$ $W_k$ $I_\eta$ $W_\eta$ $I_\zeta$ $W_\zeta$ C $p_x$ $p_y$ $p_z$
in the case of a beam.
The T group can be omitted if $\mathtt{ITE}={}$$\mathtt{ITED}$${}=51$ or $53$, respectively.
The geometric properties of the element are specified in the local coordinate system, see the Reference Manual. If the A or C groups are missing, the default values apply.
| $\mathtt{IE}$ | The element number. | |
|---|---|---|
| $\mathtt{IN}_1,\mathtt{IN}_2$ | The global node numbers of the element; the order does not matter. | |
| $A$ | The cross-sectional area $[\text{m}^2]$. | |
| $I_k$ | The torsion constant $[\text{m}^4]$. | |
| $W_k$ | The torsional section modulus $[\text{m}^3]$. | |
| $I_\eta$ | The second moment of area about the local axis $\eta$ $[\text{m}^4]$. | |
| $W_\eta$ | The bending section modulus about the local axis $\eta$ $[\text{m}^3]$. | |
| $I_\zeta$ | The second moment of area about the local axis $\zeta$ $[\text{m}^4]$. | |
| $W_\zeta$ | The bending section modulus about the local axis $\zeta$ $[\text{m}^3]$. | |
| $p_x,p_y,p_z$ | The components of the direction vector $\mathbf{p}$. | |
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 assume $h>b$. The geometric properties of the cross-section will be:
| $h/b$ | $1.0$ | $1.2$ | $1.5$ | $2.0$ | $3.0$ | $\infty$ |
|---|---|---|---|---|---|---|
| $\alpha$ | $0.2080$ | $0.2190$ | $0.2310$ | $0.2460$ | $0.2670$ | $1/3$ |
| $\gamma$ | $0.1406$ | $0.1661$ | $0.1958$ | $0.2287$ | $0.2633$ | $1/3$ |
Example
Let us consider a beam with global node numbers 32 and 45, whose coordinates $[x,y,z]$ are written in square brackets in the figure. The beam runs at a height of $5~\text{m}$, parallel to the $x$ axis. Its length is $1~\text{m}$.
The $\xi$ axis always points from the node with the lower global number to the node with the higher global number.
The order of the numbers in the EL batch therefore does not matter, and it is possible to write N 32 45 the same as N 45 32.
Let us further assume that the entire structure is made of a single profile. In that case, the cross-sectional properties are specified within the RP line, and the A group is not used. It remains to specify the direction of the principal axis $\eta$ using the vector $\mathbf{p}$. If, for example, one of the principal axes has the direction of the global axis $y$, the simplest choice is $\mathbf{p}'=\mathbf{p}\equiv[0,1,0]$. The same effect is achieved by the different specification $\mathbf{p}'\ne\mathbf{p}\equiv[1,1,0]$. However, $\mathbf{p}\equiv[1,0,0]$ must not be specified, since then $\mathbf{p}'\equiv\mathbf{0}$.
A typical form of the EL batch will be:
EL T 53 E 211 N 45 32 C 0 1 0
or equivalently
EL T 53 E 211 N 45 32 C 1 1 0