FAQ 001074 EN

1 December 2017

Robert Vogl Calculation RFEM RSTAB

How is the change in the torsional moment Iy taken into account for variable cross-sections (tapers)?

Answer

RFEM and RSTAB interpolate the variable stiffnesses along the member by higher-order polynomials. The internal determination of tapered cross-sections is done by using the taper shape (see Figure 01). If different cross-sections are defined for the member start and end, you can select the 'linear' or 'quadratic' taper shape. In this way, it is possible to represent the taper geometry for the determination of the interpolated cross-section properties.

In most cases, the layout of the taper is linear, that is, the member only tapers and extends regularly over the depth of the start to the end section. However, if the cross-section width and depth changes, the quadratic shape is recommended for the interpolation of the cross-section properties.

For more precise results, it can also be reasonable to divide the tapered member and create additional cross-sections.

The influence on the calculation of tapers also has the division of taper and foundation members that is controlled in the calculation parameters (see Figure 02).

Keywords

taper variable cross-section cross-section distribution member stiffness

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RFEM Main Program
RFEM 5.xx

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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

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RSTAB 8.xx

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The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions

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