Tension only elements can be modeled on the non-linear version of ETABS. Select the elements you want to be “tension only” and go to Assign menu > Frame/Line > Tension/Compression Limits command, once you are there you have to specify a compression limit of zero (you can also use any negative number) in order for the element to be tension only. The tension limit can be entered as a positive number much higher that the tension you expect to have on your analysis. Keep in mind that this is a non-linear feature; therefore, it will only be activated if you perfom a nonlinear static or nonlinear time-history analysis.
Any load case/combination can easily be converted to a nonlinear case as follows:
1) Click on Define > Convert combos to Nonlinear cases, chose the specific cases as required.
2) Run static linear and when this finalizes run a static nonlinear analysis.
4) Add nonlinear cases in a user defined combination with scale factor 1.
5) Use nonlinear combination as a design load combination as required.
6) Perform design.
For linear analysis, frames take both tension and compression.