Hello everyone. I cannot find where to define ultimate and service load combos in the menu. How does Etabs distinguish ultimate and service load combos for strength and stiffness check? Thank you.
You define all load combinations in the same location (Define -> Load Combinations)
If you want to use certain load combinations for ULS vs SLS, you will assign them to a category in the design load combination menus for whatever type of element you are designing. Example: Design->Steel Design->Select Design Load Combinations, then you can switch the tab between ultimate and serviceability.