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 analyzed two systems: Example 1 is defined with a straight cable while the cable of Example 2 has a rise. Why there are recognizable differences here?

Answer

The "prestress" load is treated by the program as an external load like a member load and it affects the entire system. It "flows" off into the structural system and accordingly creates deformations and support reactions. The prestress is converted into a length change (strain). Which 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 deformation exists.

The prestress is thus comparable 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.

Keywords

Prestress Cable Support force Deformation Prestressing force

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