What signifies a fracture critical bridge?

A fracture critical bridge is defined by the critical nature of its structural components and the implications of failure. Specifically, the correct answer highlights that the failure of a single member could lead to the collapse of the entire bridge. This characteristic emphasizes that these bridges rely heavily on each of their primary load-bearing elements. If one of these critical components fails, there is no alternative load path to redistribute the weight or forces, hence resulting in a potentially catastrophic failure.

Understanding this concept is important for bridge safety assessments. Engineers and inspectors must recognize the vulnerability associated with such structures, ensuring they are monitored and maintained effectively. The lack of redundancy in load paths means that all primary components must be in good condition, and any signs of distress in any one of them is a serious concern.

In contrast, the other options, while related to bridge safety and structural integrity, do not capture the essence of what defines a fracture critical bridge. For instance, while it is true that these bridges have no redundancy, that characteristic alone does not encompass the consequences of a member's failure. Additionally, the notion of sustaining positive load under all conditions or having all members connected with one type of fastening does not directly relate to the criticality of individual member failures that mainly characterizes fracture critical bridges.