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TR.32.3.1 Element Load Specification - Plates

This command may be used to specify various types of ELEMENT LOADS for plates.

Plate element loads must be applied following the expression

ELEMENT LOAD (PLATE)

using the format explained under the following options.

Option 1

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. If applied on a small part, (x1,y1,x2 and y2) define the corners of the rectangular region where the load is applied. If only x1, y1 is provided, the load is assumed as a concentrated load applied at the specified point defined by (x1,y1). If (x1,y1,x2,y2) is not provided, the load is assumed to act over the full area of the element. (x1,y1, x2 and y2) are measured from the center of the element in the local axis system (see figure later in this section). There is no option to apply the load over a projected area.

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

element-list PRESSURE p1 (x1 y1 x2 y2)

This is for specifying a constant pressure of magnitude p1 acting perpendicular to the plane of the element on the full element or a small rectangular part of an element. This coincides with the element’s local Z axis. If applied on a small part, (x1,y1,x2 and y2) define the corners of the rectangular region where the load is applied. If only x1, y1 is provided, the load is assumed as a concentrated load applied at the specified point defined by (x1,y1). If (x1,y1,x2,y2) is not provided, the load is assumed to act over the full area of the element. (x1,y1, x2 and y2) are measure from the center of the element in the local axis system (see figure later in this section). There is no option to apply the load over a projected area.

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

element-list PRESSURE {LX | LY} {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). An example of this type of load is friction load. With this option, a load can be applied only on the full area of the element.

p2 has units of force per square of length.

Option 4

element-list TRAP  {GX | GYGZ |      LX | LY} {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

element-list TRAP {GX | GYGZ |      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.

Example

LOAD 4
ELEMENT LOAD
1 7 TO 10 PR 2.5     
11 12 PR 2.5 1.5 2.5 5.5 4.5       
15 TO 25 TRAP X 1.5 4.5      
15 TO 20 TRAP GY JT 1.5 4.5 2.5 5.5         
34 PR 5.0 2.5 2.5    
35 TO 45 PR -2.5    
15 25 TRAP GX Y 1.5 4.5      
29 95 TRAP LX Y 3.7 8.7