Face loads

Face loads should be used where a load distributed over the face of a 2D member or element is required. When loads are applied to members, they will be automatically expanded to load the appropriate finite elements.

Face loads can be applied in local, global or user defined axis directions. For face loads local is interpreted as element axis directions. If local axis is specified for a face load applied to a member, GSA will apply the load to the constituent elements in the direction of the elements' local axis. User axes can only be Cartesian; not cylindrical or spherical.

Face loads cannot be used for plane stress, plane strain or axisymmetric elements.

Face loads offer the option to specify the load as a projected load. When “projected” is set the distributed load is specified as the intensity applied to the projection of the member or element on the surface normal to the direction of the load; the load intensity actually applied to the member or element is then

$$W \times \cos θ$$

where $θ$ is the angle between the member or element and the surface normal to the direction of the load, and $W$ is the specified load intensity. A typical application of projected loads is for snow loading on an inclined roof.

Definition

Name

The name is only used as a convenient way of identifying a load. Optional.

Entity type

This specifies whether a list of members or elements will be used to define which entities the load will be applied onto.

In sculpt: The entity type is set to either members or elements based on what is in the current selection set.

Entity list

This specifies a list of 2D members or elements to load using any one of the forms detailed in our entry on lists. The list may be a single item.

In sculpt: The entity list is set to the 2D members or elements in the current selection set. The entity list cannot be edited in the dialog.

Load case

The load case in which the load applies. The load case gives a way of grouping load effects together.

Axis

The axis in which the load is applied.

The axis may be Global, Initial local, Deformed local or the number of an axis set specified in the Axes module. If local axis is specified for a face load applied to a member, GSA will apply the load to the constituent elements in the direction of the elements' local axis.

Loads applied in Initial local directions are applied in the element axis directions with the element axes being based on the undeformed state of the element.

Loads applied in Deformed local directions are applied in the element axis directions with the element axes being based on the deformed state of the element. Loads applied in Deformed Local directions may only be specified for nonlinear analysis.

Projected

By default, loads are applied at the specified intensity over the member or element. In some cases it may be more appropriate to project the loads on to the member or element, e.g. (vertical) snow loading on an inclined roof may be considered more easily as a projected load.

Type

The user has a choice of the type of loading applied to the members or elements.

• Uniform – uniform load applied over the whole face of the member or element.
• Variable – load which varies across the face of the elements interpolating between values specified at the corner nodes. This option is only available when the entity type is set to element.
• Point – force can be applied at a point on the face of the elements. The position of the point load on the face can be specified in ( r , s ) coordinates. (Based on two-dimensional shape function). This option is only available when the entity type is set to element.
• Equation – load magnitude is defined by an equation as a function, f(x,y,z), of the member or element's physical location.

If the elements to which this relates are load panels then the load type must be uniform.

Direction

The direction in which the load applies, with respect to the specified axis.

Pressure

This field applies to load types uniform, variable and point and represents the pressure to apply to the member or element.

For point type load, force at the point to be specified (not pressure). For a uniform face load a single pressure value is required and for the variable face load a value is required for each corner node on the element. The pressure over the face is interpolated from the corner values.

Position of load

Position of load is applicable for point load type. The position of the point load to be specified in ( r , s ) coordinates based on two-dimensional shape function.

• Coordinates vary from −1 to 1 for Quad 4 and Quad 8.
• Coordinates vary from 0 to 1 for Triangle 3 and Triangle 6.

Pressure value = f(x,y,z)

This field is applicable only if load type is equation and is used to define the pressure value as a function of x, y and z. Normal mathematical notation is used and the following list of operators and functions describe the syntax used in GSA.

The pressure unit and units associated with the variables x, y and z are defined explicitly. The default is current model units. The axis used to evaluate the location variables x, y and z can also be defined in the wizard. The default axis is Global.

Pressure type

The pressure type is applicable only if load type is set to Equation. Selecting this option defines what type of load to apply to each individual element of the loaded entity.

• Variable pressure across face of element - pressure will be evaluated at the corner nodes of the the element. The pressure over the face of each element is interpolated from the corner values.
• Constant pressure across face of element - pressure will be evaluated at the centre of the the element. The pressure over the face of each element is uniform.

The default is variable pressure across face of element.

2D loads in nonlinear analysis

Element loads are converted into nodal forces and moments and added to other nodal forces, GsRelax analysis being performed for nodal forces only. No nodal forces are applied to quad dummy nodes.

The vector of the equivalent nodal load will not change orientation as the element deflects, even if a local axis has been specified for the load direction. This can lead to inaccuracies in the case of large deflections and results should be checked.