How do I get the actual member length of cables, for example, after the calculation in RF‑FORM‑FINDING?

Answer

This information is available in the Results navigator for members (see Figure 01). The member lengths are displayed with regard to the stressed structural system and the unstressed system. The "stressed length" is obtained from the form-finding under consideration of prestresses.

The recalculation to the "stressed length" can be done manually using Hooke's law:

${\mathrm l}_{\mathrm{unstressed}}\;=\;{\mathrm l}_{\mathrm{stressed}}\;-\;\mathrm{Δl}\\\\\mathrm\sigma\;=\;\mathrm E\;\cdot\;\mathrm\varepsilon\\\frac{\mathrm F}{\mathrm A}\;=\;\mathrm E\;\cdot\;\frac{\mathrm{Δl}}{\mathrm l}\\\mathrm{Δl}\;=\;\frac{\mathrm F\;\cdot\;\mathrm l}{\mathrm E\;\cdot\;\mathrm A}\\\\{\mathrm l}_{\mathrm{unstressed}}\;=\;{\mathrm l}_{\mathrm{stressed}}\;-\;\frac{\mathrm F\;\cdot\;{\mathrm l}_{\mathrm{stressed}}}{\mathrm E\;\cdot\;\mathrm A}\;=\;{\mathrm l}_{\mathrm{stressed}}\;\cdot\;\left(1-\;\frac{\mathrm F\;}{\mathrm E\;\cdot\;\mathrm A}\right)$

Keywords

Length Cable Form-finding

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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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RF-FORM-FINDING 5.xx

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Form-finding of tensile membrane and cable structures

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