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000269
2023-12-12

Member Loads

Member loads are forces, moments, masses, temperature effects, or imposed deformations that act on members.

In the list, select the 'Load Case' to which you want to assign the load.

Base

The Main tab manages the basic load parameters.

Categories

The following options are available in the 'Load type' list:

Load Type Description
Force Concentrated load(s), uniform or variable distributed load
Moment Single moment(s), uniform or variable distributed moment
Mass Mass continuously distributed over member length, which is relevant for Dynamic Analyses.
Temperature Temperature load uniformly distributed (Tt = Tb) or unevenly distributed (Tt ≠ Tb) over member cross-section
Temperature Change Difference in temperature between member top and member bottom, considering a constant temperature change if applicable (positive load value: top side of member heats up)
Axial Strain Imposed or compressive strain ε of member (positive load value: member is stretched)
Axial Displacement Imposed or compressive strain Δl of member
Precamber Imposed curvature of member
Initial prestress Prestressing force acting on member before calculation starts (positive load value: member is stretched)
Displacement Imposed displacement by magnitude Δ for determining influence lines
Rotation Imposed rotation about angle φ for influence lines
Pipe Content - Full Distributed load due to complete filling of a pipe
Pipe Content - Partial Distributed load due to partial filling of a pipe
Pipe Internal Pressure Uniform internal pressure of a pipe
Rotary Motion Centrifugal force from mass and angular velocity ω on member
End prestress Prestressing force that should be available in member after calculation with iterative determination (positive load value: member is in tension)

The load type as well as the effect of the signs are illustrated in the upper dialog graphic.

Important

To consider a mass in the calculation, activate the Active mass option in the 'Static Analysis Settings' dialog box (see Figure Basic Settings ).

The 'Load distribution' list provides various options for displaying the arrangement of the load.

The load distribution scheme is illustrated in the upper dialog graphic. In the 'Parameters' dialog section, you can then specify the values, distances, and other parameters of the load.

In the 'Coordinate system' list, define whether the load acts in the direction of the local xyz-member axes, the local principal axes xuv, or the global XYZ-axes. Alternatively, you can select a user-defined coordinate system or create a new one.

The local x-axis represents the longitudinal axis of the member. In the case of a symmetrical cross-section, the y-axis is the "major" axis of the member cross-section; the z-axis is the "minor" axis. In the case of an asymmetrical cross-section, these are the axes u and v.

Select the 'Load direction' from the list to define the effect of the load. Depending on the coordinate system, the local member axes x, y, z, the principal axes x, u, v, the global axes X, Y, Z, or the user-defined axes U, V, W are available for selection.

The member load can be related to the true length (such as a weight load) or the projected length (such as a snow load). The load direction is illustrated in the dialog sketch.

Important

For calculations according to the linear static analysis, it does not matter whether a load is defined as local or equivalent global. However, for geometrically nonlinear calculations, differences are possible: The global load keeps its direction when finite elements are twisting. In contrast, a locally defined load is twisting on the member in accordance with the twist of the elements.

Parameters

Specify the load value of the force, moment, or mass. For concentrated or variable loads, several input fields are available where you can describe the member load. The meaning of the respective parameters is illustrated in the load sketch.

Info

A positive moment acts clockwise about the corresponding positive axis. The global axes of coordinates in the work window help you to define the sign. For locally defined loads, you can apply member axes with the Model View (see Image Varying Member Load).

When defining concentrated or trapezoidal loads, you can use the button Relative/Absolute Input Switch between relative and absolute distance input.

For varying loads, a table is displayed where you can specify the load locations x with the corresponding load values.

Options

Usually, the load acts separately on each of the members that you define in the 'Assigned to Members' dialog section. If you tick the 'Reference to list of members' check box, the member load acts on the total length of the members: This way, in the case of trapezoidal loads, RFEM does not apply the parameters to each member, but to all members of the list as a whole.

Tip

A 'list of members' allows you to apply the load across members without defining a member set.

The 'Refer distance to the member end' check box is only accessible for loads not acting over the entire length of the member. If you activate it, you can specify the distances in relation to the member end in the 'Parameters' dialog section.

When defining trapezoidal loads, you can use the 'Load over total length of member' check box to control whether the linearly variable load is arranged continuously from the member start to the member end.

The 'Eccentricity' check box is available for the 'Force' load type. If you tick it, you can define an eccentric effect of the member load in the Force Eccentricity tab.

The 'Import support reaction' check box allows you to import support forces from another model. After ticking it, you can enter the specifications in another tab (see the image Defining Model, Load, and Line to Import Support Reaction ).

You can affect the display of the load vectors by the 'Display on opposite side' option.

Force Eccentricity

If the force does not act in the shear center of the cross-section, you can define the location of the load application in the Force Eccentricity tab.

Eccentricity Settings

Nine "Reference" check boxes symbolize distinctive locations on the cross-section. The point in the middle represents the centroid, and the eight edge points represent the intersections of the member axes y and z with the edge lines of a rectangle circumscribing the cross-section. If you activate one of the points, RFEM applies the member load at the corresponding distance from the centroid.

Alternatively, you can apply the load in the 'Center of gravity' or in the 'Shear center' and define the 'Offset at member start' manually in the text boxes below. The distances refer to the local member axes y and z.

Options

If the eccentricity is not uniform along the member, activate the 'Offset on member end different than on member start' check box. Then, you can specify the 'Offset at member end' in the dialog section above. This way, it is possible to describe a linear distribution of the eccentricity from the member start to the member end.

Important

When calculating according to second-order or large deformation analysis, the load keeps the defined eccentricity. It is not adjusted to the member's rotation.

Parent section