A "fracture critical" component is by definition a component that will cause a structure to collapse should it fail :D We know what that "fracture critical" co

A "fracture critical" component is by definition a component that will cause a structure to collapse should it fail :D We know what that "fracture critical" components of a structure through analysis of the design. So what the NTSB is saying here is that none of the components of this bridge that were identified as being fracture critical are the cause of failure. Of course that doesn't mean there wasn't a single component failure, it is possible that there was an error in the analysis and a fracture critical component was not identified. Alternatively an error in construction could result in weaknesses in the structure leading to more fracture critical components. It's also possible there were existing failures in non-fracture critical components that had not been detected, in which case you are getting closer and closer to every component being critical.