The first questions is why do you have black bars? There should never be black bars in your project. If you want to work in a different aspect ratio then set your project up for that aspect and edit in that aspect and then have the black bars added when you render to a different aspect. This will keep any FX from affecting the black bars.
If you insist on working with black bars in your project you could use a Mask and set it to limit the FX (i.e., Apply to FX):

But that’s a lot of work. You could also create black bas with generated media and drop them on a track above your entire project but it’s better to not have black bars in your project at all.
~jr
http://www.johnrofrano.com
http://www.vasst.com