Modeling tension-only members

Tension-only members may be modeled through the following process:

1. Select all frame objects which will only carry tension.
2. Set the compression limit to zero through Assign > Frame > Tension/Compression Limits.

Note that the assignment of tension/compression limits is a nonlinear analysis feature, and some applicable points, taken from Context Help, include:

• Tension/compression limits will only be activated in a nonlinear static or nonlinear direct-integration time-history analysis load case. In general, use a nonlinear analysis technique when tension/compression limits are present in the model.

• When linear analysis is performed using the initial stiffness of a member (stiffness at zero), computation will use the full axial stiffness (AE/L) as though no limits are assigned.

• When linear analysis uses the stiffness at the end of a nonlinear analysis load case, axial frame behavior depends on whether or not the tension/compression limits are exceeded at the end of the case, conditions for which are described as follows:
  
  
  • Limits exceeded. Axial frame behavior is replaced with a sufficiently soft spring (1e-6*EA/L) which simulates zero stiffness.
  • Limits not exceeded. The software uses full axial stiffness (AE/L) as though no limits are assigned.

Tension-only members in moving-load analysis

The only method available to account for the nonlinear properties of members which are assigned tension and compression limits during moving-load analysis is step-by-step time-history moving-load analysis. Additional information is available in the CSI Analysis Reference Manual (Step-By-Step Analysis > Time-History Analysis, page 466).

See Also

• Tension-only elements in ETABS article

• Response-spectrum analysis and nonlinear properties article