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 work in be activated if you perfom a nonlinear static or nonlinear time-history analysis.
...