Technical Knowledgebase

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This page is devoted to frequently asked questions (FAQ) related to cables.

 

On this page:

Modeling

How are cables imported from AutoCAD?

ANSWER: AutoCAD lines, and therefore cables which are drawn as lines, are imported into CSI Software as frame objects. Cables may be drawn over these frame objects, then frames may either be deleted or assigned null properties.

As an alternative, one cable may be drawn to activate the tendon connectivity table, then interactive database editing is available to copy the connectivity-frame data into the connectivity-cable table to create cables within the model.

Large Displacement should be included in analysis when cables are modeled using frame objects.

Why are the cables of my model returning nonzero moment values?

ANSWER: It is possible that the cables were modeled using straight frame objects. Frame objects generate a bending response. If moment values are returned, cables should be modeled as catenary elements by unchecking the Model Cable Using Straight Frame option on the Cable Geometry menu.

Why does the cable shape calculator generate an asymmetrical profile for multiple segments?

ANSWER: Once load is applied to the original geometry, a symmetric shape should result.

Loading

Should I apply a load which represents initial cable conditions before running subsequent nonlinear analyses?

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 in which 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.

 

How can I display the wind load which is applied to cables?

ANSWER: The wind load which acts on cables may be displayed by selecting Display > Show Load Assign > Frame/Cable/Tendon. To assign wind load to cable objects, the auto load pattern should be defined using the Exposure from Frame Object option.

Formulation

Is cable stiffness considered during static linear analysis?

ANSWER: Nonlinear analysis is necessary to generate meaningful results which concern cable behavior. Linear analysis may be performed, though cable stiffness values should be taken from a nonlinear static-analysis load case in which cables are subjected to all loading conditions, including self-weight, transverse, etc.

When a cable with slack is not subjected to any form of transverse loading, a negligible self-weight is imposed to enable the formulation. However, it is best to apply this self-weight load manually such that it is of realistic magnitude.

See Also