Bend Rebar for a Large Radius?

[umrce]

I primarily design bridges where I often run into a very large radius on a curved bridge deck. I've never specified pre-bending the deck reinforcing that runs longitudinally along the length of the bridge. I've always assuming that since these bars are typically no larger than a #6, that they can flex the rebar enough to tie it in place. Does anyone have any experience with this or maybe some reference material as to when pre-bending rebar for a large radius might be necessary? I'd primarily be interested in #4 or #5 bars but every once in a while we have #6's as well.