Tension-only elements can be modeled using the nonlinear version of ETABS. The process is as follows:
- Select the elements to be specified as tension-only.
- 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.
- 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:
- Select the case(s) through Define > Convert Combos to Nonlinear Cases.
- Run a static-linear analysis, then once complete, run a static-nonlinear analysis (only required in V9, in V13 linear and nonlinear cases will run in same analysis).
- Add the nonlinear case(s) to a user-defined combination with a scale factor of 1.0.
- Apply the nonlinear combination as design load.
- 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.
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