TR.32.3.3 Element Load Specification - Joints

This command may be used to specify various types of element-like loads for joints.

Three or four joints are specified that form a plane area. Pressure is specified for that area as either uniform or trapezoidally varying. Then STAAD.Pro computes the equivalent joint loads. This command may be used as an alternative or supplement for the Area Load, Floor Load, and the other Element Load commands.

The pressure may be provided either in global (GX, GY, GZ) directions or in local Z direction (normal to the element). If the global direction is omitted, the applied loading is assumed to be in the local Z direction as if the joints defined a plate. The loads are proportional to the area, not the projected area.

Note: This load command can be applied to any joints to form a loaded region in addition to element vertices. The command ELEMENT LOAD here is used for backwards compatibility with older models. Equivalent joint loads are generated, and any elements, solids, or members are not loaded as a result of this command.

General Format

ELEMENT LOAD JOINTS

i₁ (BY i₂) i₃ (BY i₄) i₅ (BY i₆) i₇ (BY i₈) -

FACETS j₁ PRESSURE ({ GX | GY | GZ }) f₁ f₂ f₃ f₄

Note: If this data is on more than one line, the hyphens must be within the joint data.

Where:

f₁ f₂ f₃ f₄ = Pressure values at the joints for each 3 or 4 joint facet defined. Only f₁ needs to be specified for uniform pressure. In any case the pressure is provided over the entire element.
j₁ = number of facets loaded.
i₁, i₃, i₅, i₇ = Joint numbers that define the first facet.
i₂, i₄, i₆, i₈ = each joint number is incremented by the BY value (1 if omitted).

Example

LOAD 4
ELEMENT LOAD JOINT
1 BY 1 2 BY 1 32 BY 1 31 BY 1 -
FACETS 5 PR GY 10 10 15 15

The above data is equivalent to the following:

LOAD 4
ELEMENT LOAD JOINT
1 2 32 31 FACETS 1 PRESSURE GY 10 10 15 15
2 3 33 32 FACETS 1 PRESSURE GY 10 10 15 15
3 4 34 33 FACETS 1 PRESSURE GY 10 10 15 15
4 5 35 34 FACETS 1 PRESSURE GY 10 10 15 15
5 6 36 35 FACETS 1 PRESSURE GY 10 10 15 15

So, the value following the word FACETS is like a counter for generation, indicating how many element faces the load command must be created for. Thus a value of 5 for facets means, a total of 5 imaginary element faces have been loaded.

BY is the value by which the individual corner node number is being incremented during the generation. In this example, the value is 1, which is same as the default. Instead, if it had been say,

1 BY 22 BY 2 32 BY 1 31 BY 1 -
FACETS 5 PRESSURE GY 10 10 15 15

we would have obtained

1 2 32 31 FACETS 1 PRESSURE GY 10 10 15 15
3 5 33 32 FACETS 1 PRESSURE GY 10 10 15 15
5 8 34 33 FACETS 1 PRESSURE GY 10 10 15 15
8 11 35 34 FACETS 1 PRESSURE GY 10 10 15 15
9 14 36 35 FACETS 1 PRESSURE GY 10 10 15 15

Notes

If a pressure or volumetric load is acting on a region or surface, and the entity which makes up the surface, like a slab, is not part of the structural model, one can apply the pressure load using this facility. The load is defined in terms of the pressure intensity at the 3 or 4 nodes which can be treated as the corners of the triangular or quadrilateral plane area which makes up the region. This command may be used as an alternative or supplement for the Area Load, Floor Load, Wind Load, and other pressure load situations.

In other words, the element pressure load can be applied along a global direction on any surface, without actually having elements to model that surface. Thus, for a sloping face of a building, if one wants to apply a wind pressure on the sloping face, one can do so by specifying the joints which make up the boundary of that face. Three or four joints are specified that form a plane area; pressure is specified for that area; then STAAD.Pro computes the equivalent joint loads.