Tension-only elements can be modeled using the nonlinear version of ETABS. The process is as follows:

1. Select the elements to be specified as tension-only.
   
   
2. Specify the tension limit (usually a limit higher than expected maximum tension capacity) and a compression limit of zero (or negative) through Assign > Frame/Line > Tension/Compression Limits.
   
   
3. Run a nonlinear static or nonlinear time-history analysis. This is necessary since tension-only assignment is a nonlinear feature.

Any load case or combination may be converted to a nonlinear analysis as follows:

1. Select the case(s) through Define > Convert Combos to Nonlinear Cases.
   
   
2. Run a static-linear analysis, then once complete, run a static-nonlinear analysis.
   
   
3. Add the nonlinear case(s) to a user-defined combination with a scale factor of 1.0.
   
   
4. Apply the nonlinear combination as design load.
   
   
5. Perform design.

When full nonlinear behavior must be considered, nonlinear time-history analysis should be run since response-spectrum analysis only applies to linear systems. Further, response-spectrum loads cannot be converted to nonlinear cases.

See Also

• Tension and compression limits article

• Response-spectrum analysis and nonlinear properties article