Let’s start by building out a simple frame, this will be what we’re lifting using the cable elements. We’re going to make the most of the following handy modeling features:

• Pen Tool – model quickly using the pen tool
• Multi-edit – hold CTRL and drag the mouse to select and multi-edit parts of your model
• Search Sections – quick add sections from our library in seconds, using search
• Area Loads – one way, two way and wind load area loads that automatically calculate (and readjust!) the tributary areas of members.

So now we add the cables. Cables are non-linear elements, so are basically added the same way you would add any other member. The main difference is that cables are never in compression, have zero flexural, torsional or shear capacity (they are tension-only) and they often exhibit large displacements and non-linear behavior. So analysing these types of elements is treated slightly different to regular steel elements that have flexural and other strength.

Modeling the cable elements is done the same way you would any other element. However, when you are assigning the attributes, you would select Type: Cable. This will automatically assign the element with pinned end fixities and have it treated as a cable element in the solver.

Opening up the Renderer view, clearly shows the cable elements (in this model, denoted as Section ID 2).

Applying equipment loads to your frame structure is the same as in regular analysis models. In this case we have applied an equipment load (using two-way area loads) and some other dead load (using one-way area loads).

Cables typically undergo large deformations when subjected to significant loads. Geometric nonlinearity accounts for the changes in cable geometry as it deforms. The initial assumption of linearity in the cable’s response (as in linear static analysis) becomes invalid when the deformations become significant.

It is necessary to use a non-linear analysis when cable elements are present, since non-linear analysis considers these geometric changes and provides more accurate results. When you load or tension a cable, after each step the structure has moved so much that the loads are not necessarily being applied in the same position as before.

Therefore, for this structure we will need to perform a non-linear analysis. Note: if user selects Linear Static Analysis, it will automatically revery to non-linear analysis.

Once the analysis is successfully completed, it’s a good idea to check the deflections to (a) ensure the numbers are reasonable and (b) animate the deflection of the structure to see if it deforms in a way you’d expect. If cable elements are not solving correctly, you will see jagged deflection curves and could be an indication that the cables are under or overloaded.

A well behaving cable element should be smooth, sagging and showing tension-only deformations, as seen in the example model:

Another result worth reviewing, is the axial stress in the cable tendons. Obviously, since the cable has no shear or flexural capacity, all of the force is transferred via tension in the element. By default the structure will highlight any stresses that exceed the material yield/ultimate strength. You can also enter in your own custom allowable stress, so that you can easily identify elements that exceed your stress limits:

If your cable structure is failing to solve (a lot of times due to instability or the inability to converge), here are some common things to check or try:

1. Check diameter size
2. Check Cables are Not Over/Under Loaded
3. Reduce your Convergence Accuracy
4. Add Extra Supports
5. Check Your Other Members

• Cable Elements
• How Cable analysis is different from linear static analysis
• 5 tips for better cable convergence
• Non-Linear Static Analysis