Tendon - Tension/Compression Limits

Form: Tendon T/C Limits

An upper limit on the amount of tension and compression force supported by a tendon object can be assigned. The behavior modeled is nonlinear but elastic. For example, assume a compression limit of zero has been set. If the object tries to go into axial compression, it will shorten without any stiffness. If the load reverses, it will recover its shortening with no stiffness, then engage with full stiffness when it reaches its original length.

Select the tendon(s) to be assigned axial force limits.
Use the Assign menu >Tendon > Tension/Compression Limits to access the Tendon T/C Limits form:

- Tension Limit. Specify a tension limit by checking the Tension Limit box and entering a value that is zero or positive.
- Compression Limit. Specify a compression limit by checking the Compression Limit box and entering a value that is zero or negative.

Note: If zero is specified for both the tension and compression limit, the object will carry no force in a nonlinear analysis.

Note:

Tension/Compression limits are nonlinear. Thus, the following apply:

Tension/compression limits will be activated in a nonlinear static or nonlinear direct-integration time-history analysis only. In general, use nonlinear analysis when tension/compression limits are present in the model.
If a linear analysis is performed using the stiffness at zero, the full axial stiffness (AE/L) of the element will be used as if there were no limits.
If a linear analysis is performed using the stiffness at the end of a nonlinear analysis, the axial stiffness will be zero or AE/L, depending on whether the object exceeded its limits at the end of the nonlinear case.

Tip: This feature is useful for modeling cables and braces that can reasonably be represented by a single straight object when the analysis is focused more on the effect of the cable/brace on the structure than on the detailed behavior of the cable/brace itself.

To model the deformation of the cable or brace in detail, break the cable/brace into several sub-objects, and use large-displacements analysis without compression limits. Under compression, the cable/brace will buckle out of the way in a more realistic representation of the true behavior.