how to use stiffener command in catia v5
1)Project the edges of the body where you want to give stiffener for support
2)connect the edges with a line & coincidence it with the edges
3)Make the projection lines as construction lines
4)Exit work bench
5)create a plane on the sketch support in the direction of the created line
6)Offset the plane as required .. Eg:- If you want to keep the plane in the middle;offset it by giving half value of the total body
(You can use "change sketch support" to bring the stiffener line in the created plane)
7)click on "stiffener" icon which is under "solid combine" and set the limits
"UNCHECK NEUTRAL FIBER"
Else it 'll show tropological error if it's checked"
8)Preview it & select ok
There you go :)