FAQ 000172 EN-US 12/01/2017

Robert Vogl Calculation RFEM RSTAB

In a cable structure with prestress, support forces are smaller than the prestressing force. I have analysed two systems: Example 1 is defined with a straight cable while the cable of Example 2 has a rise. Why there are recognisable differences here?

Answer

The program treats a 'prestress' load as an external load like a member load. Moreover, the 'prestress' load affects the entire model.

Let's say it 'flows' off into the structural system and accordingly creates deformations and support reactions.

The prestress is converted into a length change (strain).

The axial force that remains after the calculation depends on the member's restraint of deformation.

If the stiffness of the connected system is soft, nothing or only very little of the prestress remains but a deformation exists.

In the end, the prestress is to put on a same level with a temperature change.

Once it is expressed with a force, once it is expressed with a temperature.

In example 2, the prestressing force is more converted into a deformation, which leads to lower axial forces, and thus to lower support forces.

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