I don't know the name of the tool in english but litteraly in french it would be " path gradient ". Its like a color gradient but instead of color it duplicate forms as many time as you want between two path with an equal number of point. Then I just ad a clipping mask to fit all of this into the form I expect.. After that I made the different parts of the bar with gradient form delimited by gradient mesh opacity mask (yeah all at a time). Hope it help ( and that my explanation isn't a total mess )