Which of the following are typical examples of fracture-critical elements?

• A. Key pin connections, primary load-carrying members without redundancy, critical gusset plates, and suspension hanger connections
• B. Decorative railings and pedestrian barriers
• C. Non-load-carrying cosmetic features
• D. Asphalt road surface and guardrails

Answer: (A)

Fracture-critical elements are parts of a bridge whose fracture would remove a load path with no redundant path to carry the load, so a crack or break could lead to rapid loss of capacity or collapse. Key pin connections in certain truss bridges are fracture-critical because the pin directly carries forces between members; if the pin fractures, the connected members can separate and the structure loses its primary load transfer path. Primary load-carrying members that have no redundancy are fracture-critical because there isn’t an alternate route to carry that portion of the load if that member fails. Critical gusset plates tie together multiple members; a crack or fracture there can compromise the entire joint and cascade into broader member failures. Suspension hanger connections are fracture-critical as they transfer the main cable forces to the deck; a failure there removes a major load path and can lead to collapse without another path to share the load.

Decorative railings and pedestrian barriers, non-load-carrying cosmetic features, and components like asphalt surface and guardrails do not constitute the main structural load path in the same way, so they are not typically fracture-critical.