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h1. Modeling Tension-Only Members

You can model tension-only members as indicated below:

- Select all frames which you want to carry only tension

- Use "Assign > Frame > Tension/Compression Limits" menu command to specify zero compression limit

However, please note that T/C limits are a nonlinear feature of SAP2000 and that the following applies (the information below is taken from the F1 context help launched when the "Frame T/C Limits" form is active):

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 (more precisely, when tension/compression limits are used, the program replaces the behavior with a very soft spring (1e-6*EA/L)) or AE/L, depending on whether the object exceeded its limits at the end of the nonlinear case.

h1. Tension-Only Members in Moving Load Analysis

Please note that tension-only members (members with T/C limits) are nonlinear by their nature. Currently the only way to consider nonlinear properties in moving load analysis is to run step-by-step time history moving load analysis as described above. Please refer to CSI Analysis Reference Manual, chapter "Bridge Analysis", section "Step-By-Step Analysis > Time-History Analysis" for additional information.

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Related emails:
* [8/11/20032008 email from fh: Compression limits not enforced|$3703206]
* [8/10/2010 email from ok: When member reaches T/C limit, the stiffness used is not zero but approximately 1e-6 times the axial stiffness|$3703398]
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