Have not had any experience with "fracture mechanics" in bridge design, unless you mean shear failure. Of course, I haven't had much experience at all. Here's a good link on the subject:
Someone had posted a question about the T&S requirements in the AASHTO LRFD. I thought the switch from #4@18" to the new code (which from what I read is the same as ACI) might be an indirect attempt at curtailing fracture in large structures. Of course, I could be way off base and it is all for the sake of servicability.
Why are you asking? That's a really general question.
Fatigue and fracture are very important concerns for bridges. Usually it's fatigue that is addressed directly; the fracture mechanics aspect is looked at in research aimed at developing requirements, or sometimes in repair situations.
