What It Means
A fracture critical member (FCM) is a steel tension member or tension component of a member whose failure would be expected to result in the collapse of the bridge or an inability of the bridge to perform its function. Bridges containing one or more FCMs are designated fracture critical and receive heightened inspection scrutiny under the National Bridge Inspection Standards. Typical fracture critical configurations include two-girder steel bridges, single-tub-girder bridges, two-column steel bent piers, pin-and-hanger assemblies, tied arch bridges, and certain truss bridges where failure of a single tension chord would trigger collapse. The concept gained national attention after the Silver Bridge collapse on the Ohio River in December 1967, which killed 46 people when a single eyebar chain link fractured due to stress corrosion cracking at a welded detail, directly motivating Congress to establish the NBIS in 1971. The 2022 NBIS update formalized fracture critical inspection requirements: FCMs must receive a hands-on inspection (within arm's reach, close enough to detect cracks of 1/16 inch or less) at intervals not exceeding 24 months, and inspectors must be specifically qualified in fracture critical inspection techniques through FHWA-NHI course 130078. Hands-on inspection typically requires snooper trucks, scaffolding, man-lifts, or climbing access, making fracture critical inspections significantly more expensive than routine inspections, often $15,000-$100,000 per bridge versus $1,000-$5,000 for standard inspections. FHWA maintains a subset inventory of fracture critical bridges, and the 2022 NBIS also introduced the concept of "System Redundant Member" (SRM) analysis, allowing engineers to re-classify some previously fracture-critical bridges as redundant through rigorous finite element analysis demonstrating that failure of the member in question would not cause collapse, potentially reducing inspection burden without compromising safety. Approximately 18,000 U.S. bridges are currently designated fracture critical.
Fracture Critical is one of the bridge-engineering or FHWA-policy concepts that recurs across BridgeSafety. Below is how the concept connects to the National Bridge Inventory data behind every page on the site.
Within the BridgeSafety Condition Score, each primary component (deck, superstructure, substructure) contributes about a third of the rating, with an age penalty applied to bridges past their typical design life. The methodology page describes the scoring in full detail.
Frequently Asked Questions
What does "Fracture Critical" mean?
A bridge containing non-redundant steel tension members whose failure would likely cause partial or complete collapse.
Why does Fracture Critical matter for bridge safety?
A fracture critical member (FCM) is a steel tension member or tension component of a member whose failure would be expected to result in the collapse of the bridge or an inability of the bridge to perform its function. Bridges containing one or more FCMs are designated fracture critical and receive ...