This page is devoted to frequently asked questions (FAQ) related to cables.
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Should a load which represents initial cable conditions be applied before subsequent nonlinear analyses are run for additional external loads?
Answer: Yes, in most cases, it is a good practice to assign a load which represents initial cable conditions. This is done using the Cable Geometry menu. Initial cable tension is dependent upon initial geometry and applied loading. Given distributed loading on a single cable with fixed supports, the cable drawing tool can calculate this tension. Full analysis must be implemented for systems of cables, cables connected to flexible structures, and conditions where additional loads are applied. The best approach depends on what information is known and how the structure is to be built. If cable length is known, a simple nonlinear analysis procedure should be sufficient. Otherwise, initial-geometry iteration or target-force loading may be necessary.
Once the initial shape and tension of a cable is determined, further analysis is necessary when additional loading is applied. Nonlinear analysis is also recommended. Video 16 of the SAP2000
Watch & Learn
video series provides excellent instruction on this topic.
In normal static linear analysis, is the cable stiffness considered in calculations or not?
Nonlinear analysis DRAFT is required to get meaningful results with the cable element. Linear analysis can be performed, but they should always use the stiffness from the end of a nonlinear static analysis case in which all cables are loaded by their self weight or other transverse loads. For cases where no transverse load is present on a slack cable elements, the program will internally assume a very small self-weight load in order to obtain a unique shape. However, it is better if you apply a realistic load for this purpose.
Why do I see nonzero moment diagram on the cables in my model?
You may be modeling the cable using straight frame objects. If this is the case, please uncheck the "Model Cable Using Straight Frame Option" on the "Cable Geometry" form to model the cable as a catenary.
How can I display the wind loading applied to the cables?
You are able to use the Display>Show Load Assign>Frame/Cable/Tendon menu command to display the wind loading on the cables. Please note that to generate wind loading on cable elements; you should define the auto load pattern to use Exposure from Frame Object.