Option 1 - Load Applied in a Global Direction

element-list  PRESSURE {GX | GY | GZ} p1 (x1 y1) (x2 y2) 

This is for specifying a pressure of magnitude p1 in one of the global axis directions on the full element or a small rectangular part of an element.

• Partial Pressure - If applied on a small part, (x1,y1,x2 and y2) define the corners of the rectangular region where the load is applied.
• Concentrated Load - If only x1, y1 is provided, the load is assumed as a concentrated load applied at the specified point defined by (x1,y1).
• Full Plate Pressure - If (x1,y1,x2,y2) is not provided, the load is assumed to act over the full area of the element.

p1 has units of force per square of length for pressure and units of force for concentrated load.

GX, GY and GZ represent the global axis directions.

Option 2 - Load Applied Normal to Plate (Local z)

element-list PRESSURE p1 (x1 y1) (x2 y2)

p1 has units of force per square of length for pressure and units of force for concentrated load.

Coordinate values, x1,y1 & x2,y2, in the local coordinate system used in options 1 and 2

Option 3 - Pressure on Full Plate in Local X or Y or Projection

element-list PRESSURE {LX | LY | PX | PY | PZ} p2

This is for specifying a constant pressure of magnitude p2 along the local X (LX) or Y (LY) axis of the element (parallel to the element surface) or along a global axis on the projected area of the plate. For example, in the case of a friction load you can use the LX or LY options.

A projected pressure is scaled down by a factor of the projected area onto the global plane perpendicular to the load direction to the element area. This is always equal to or less than the pressure in the global direction.

Projected pressure, p, in the PY direction

The resulting pressure, $p\text{'}=p\frac{A_{\mathrm{xz}}}{A_{\mathrm{xyz}}}$

p₂ has units of force per square of length.

Option 4 - Trapezoidal Plate Load

element-list TRAP  {GX | GY | GZ} {X | Y} f1 f2

This is for applying a trapezoidally varying load with the following characteristics:

1. The direction of action of the load is global (GX, GY or GZ), parallel to the surface (LX or LY as in friction type loads), or normal to the element surface (local Z). The last becomes the automatic direction of action if the global or tangential directions are not specified).

2. The load varies along the local X or Y directions (imagine the wall of a tank with hydrostatic pressure where pressure at the lower nodes is higher than at the upper nodes, and hence the load varies as one travels from the bottom edge of the elements to the top edge.)

   This type of load has to be applied over the full area of the element. f1 is the intensity at the I-J (or J-K) edge and f2 is the intensity at the K-L (or L-I) edge depending on whether the load varies along "X" or "Y".

Center of the element is the origin defining the rectangular area on which the pressure is applied in option 4

The TRAP option should be used when a linearly varying pressure needs to be specified. The variation must be provided over the entire element.

X or Y - Direction of variation of element pressure. The TRAP X/Y option indicates that the variation of the Trapezoid is in the local X or in the local Y direction. The load acts in the global or local direction if selected, otherwise along the local Z axis.    

• f1 - Pressure intensity at start.           
• f2 - Pressure intensity at end.   

Option 5 - Trapezoidal Loading Using Nodes

element-list TRAP {GX | GY | GZ | LX | LY} JT f3 f4 f5 f6

This is for specifying a trapezoidally varying load over the full area of the element where one happens to know the intensity at the joints (JT) of the element. The load is defined by intensities of f3, f4, f5, and f6 at the 4 corners of a 4-noded element. For triangular elements, f6 is not applicable. The load can act along the global directions (GX, GY and GZ) or along the local X and Y directions (LX and LY, like a friction load).

Notes

1. "Start" and "end" defined above are based on positive directions of the local X or Y axis.

2. Pressure intensities at the joints allows linear variation of pressure in both the X and Y local directions simultaneously.

3. The TRAP load with global directions may be used to apply a volumetric type of pressure. For example, consider a grain silo with a sloping wall. In the event of modeling it using non-uniform elements, by which we mean elements whose 3 or 4 nodes are all at different elevations, the grain height at each node will depend on the elevation of the node. One can apply the pressure by specifying the intensity at each node of each element.