Using Result Beam in RFEM

Technical Article

Since the release of RFEM 5, the ‘Result Beam’ member type has been available. The result beam is a virtual member that does not have any stiffness nor require any support. It can be used in various situations in order to integrate the results from members, surfaces, and solids, and to display them as member internal forces.

Input

After selecting the ‘Result Beam’ member type, it is necessary to set further parameters. There are four options available for specifying the integration area:

  • Within cuboid - quadratic
    A quadratic integration area is used, whose centroid is located in the member axis.
  • Within cuboid - general
    A rectangular integration area is used, whose centroid may vary.
  • Within cylinder
    A circular integration area is used, whose centroid is located in the member axis.
  • From listed including objects
    Only the elements for evaluation are used, which are in the list of ‘Including Objects’ and are within the possible effective area (see below).

If the integration area overlaps the objects which should not be taken into account, these objects can be defined in the list ‘Except from Including Objects’.

Effective Area of Result Beam

A result beam can only provide results of the elements located within a rectangular axis of the member start and end. All elements outside these boundaries are not taken into account.

This is illustrated in Figure 01: The results do not apply to the areas marked in red. The turquoise areas were manually modelled as auxiliary areas and represent the boundaries of the result beam.

Figure 01 - Effective Area

Cross-Section

For the internal forces of the member, it is irrelevant which cross‑section is used. So if you want to apply the result beam to only determine the internal forces, you can use any cross‑section. However, if you want to perform further design in the add‑on modules such as RF‑STEEL EC3 or RF‑CONCRETE Members, the cross‑section plays an important role and thus should be specifically defined.

Member Division of Results

Since the distribution of internal forces is not much reliable, it is necessary to set a higher number of member divisions for result diagrams in the global calculation parameters.

Figure 02 - Division of Members

Position of Result Beam

For the internal forces N, Vy, and Vz, the parallel distance of the result beam to the centroid of the including objects does not matter. So if you want to only evaluate the axial and shear forces, you can model the result member on or above the structure to get a clear display.

However, it is crucial for the internal forces Mt, My, and Mz to place the result beam in the centroid of the including objects. In addition to including moments, the axial forces multiplied by the distance of each FE mesh point are added to the centroid of the result beam.

Figure 03 - Position of Result Beam

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RFEM Main Program
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements