1075x
004574
2020-07-29

Question

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 Image 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:

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


Author

Mr. Rehm is responsible for developing products for timber structures, and he provides technical support for customers.