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Using [CSiBridge|csibridge:home], *initial cable forces* may be obtained *for a cable-stayed bridge* by following the process outlined in this article.



h1. Modify undeformed geometry

* Model the final geometry of the bridge in its deformed configuration.

* On the Cable Shape Definition menu, select the option for Relative Undeformed Length.

* Use a nonlinear [load case|kb:Load case] to analyze the bridge under applied dead loads.

* Run analysis again by selecting Analysis > Shape Finding > Modify Geometry. Iterate until deformed shape converges to the geometry desired.

* Extract the [cable|kb:Cable] forces.


h1. Verify cable forces

The procedure used to verify these cable forces is as follows:

* Apply the dead loads and the cable target forces (previously determined), then run a [nonlinear|kb:Nonlinear] static analysis for this loading condition.

* If the cable forces are optimal, then the structure, when modeled in its final configuration, should experience negligible deflection under dead-load and target-cable forces.


h1. Use the unit-load method to tune cable forces

* If deflection is not negligible, then the unit-load method may be manually applied to determine how cable forces should be adjusted.


h1. See Also

* [kb:Accounting for deformed shape in staged construction] article


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