Facial distributed loading

Distributed loading is triggered by the *DLOAD card. Facial distributed loads are entered as pressure loads on the element faces, which are for that purpose numbered according to Figures 155, 156 and 157.

**Figure 155:** Face numbering for hexahedral elements
$\begin{figure}\epsfig{file=HexFace.eps,width=9cm}\end{figure}$

**Figure 156:** Face numbering for tetrahedral elements
$\begin{figure}\epsfig{file=TetFace.eps,width=8cm}\end{figure}$

**Figure 157:** Face numbering for wedge elements
$\begin{figure}\epsfig{file=WedFace.eps,width=8cm}\end{figure}$

Thus, for hexahedral elements the faces are numbered as follows:

Face 1: 1-2-3-4
Face 2: 5-8-7-6
Face 3: 1-5-6-2
Face 4: 2-6-7-3
Face 5: 3-7-8-4
Face 6: 4-8-5-1

for tetrahedral elements:

Face 1: 1-2-3
Face 2: 1-4-2
Face 3: 2-4-3
Face 4: 3-4-1

for wedge elements:

Face 1: 1-2-3
Face 2: 4-5-6
Face 3: 1-2-5-4
Face 4: 2-3-6-5
Face 5: 3-1-4-6

for quadrilateral plane stress, plane strain and axisymmetric elements:

Face 1: 1-2
Face 2: 2-3
Face 3: 3-4
Face 4: 4-1

for triangular plane stress, plane strain and axisymmetric elements:

Face 1: 1-2
Face 2: 2-3
Face 3: 3-1

for beam elements:

Face 1: pressure in 1-direction
Face 2: pressure in 2-direction

For shell elements no face number is needed since there is only one kind of loading: pressure in the direction of the normal on the shell.

Applying a pressure to a face for which a pressure was specified in a previous step replaces this pressure. The parameter OP=NEW on the *DLOAD card removes all previous distributed loads. It only takes effect for the first *DLOAD card in a step. A buckling step always removes all previous loads.

In a large deformation analysis the pressure is applied to the deformed face of the element. Thus, if you pull a rod with a constant pressure, the total force will decrease due to the decrease of the cross-sectional area of the rod. This effect may or may not be intended. If not, the pressure can be replaced by nodal forces. Figures 158 and 159 show the equivalent forces for a unit pressure applied to a face of a C3D20(R) and C3D10 element. Notice that the force is zero (C3D10) or has the opposite sign (C3D20(R)) for quadratic elements. For the linear C3D8(R) elements, the force takes the value 1/4 in each node of the face.

**Figure 158:** Equivalent nodal forces for a face of a C3D20(R) element
$\begin{figure}\epsfig{file=HexPres.eps,width=10cm}\end{figure}$

**Figure 159:** Equivalent nodal forces for a face of a C3D10 element
$\begin{figure}\epsfig{file=TetPres.eps,width=10cm}\end{figure}$