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POSSIBLE CAUSES OF FAILURE
Substructure
Overstress
Wind Excitation
External Event
- Anchorage Move
- Pier Displacement
- Pier Scour
- Design error
- Excessive Load
- Dynamic Effects
- Secondary Effects
- Aeroelastic Instability
- Fatigue from wind induced oscillation
- Static wind load
- Sabotage
- Vehicle collision
- Sonic boom
Superstructure Defect
Articulation
Trusses
Hangers
Towers
- Chain Bent Post Slots
- Toggle Links
- Chain Bent Post, Ohio N.
- Gussett Plate U7N
- Connection Box at U13N Direction of Loads ?
- Cleavage Fractures in Hangers 17N, 19N
- Screw Pin Dowels at base
- Bracing Failure
- Buckling Failure
Fracture L12-L13N
Other Fractures
Evidence of Critical Flaws in Fractures
Direction of Loads At Fracture
Pro-existent flaw ?
Evidence of "Triggers" ?
Fatigue ?
Paint on Fracture Surface
Fatigue ?
Erection ?
Later Painting ? Critical ?
Eyebal Chain
Ohio Side Span ?
Main Span ?
W. Vs. Side Span ?
Joint C13N
Eyebal No. 33 Slipped Off pin ?
Fracture in Eyebal No. 330
Overstress on Normal Section
Normal Stress, Pre-existent defect
Dynamic Effects Live Load ?
Abnormal Loading Due to prior failure ?
Actual Stress Level
Critical Stress Intensity Factor for Material At 32°F
Shock Loading Due to "trigger" fracture ?
Residual Stresses Due to Heat Treatment
Stress Concentration Effects, Plastic
Mechanism of Flaw Growth
Hydrogen-Embrittlement ?
Stress-Corrosion ?
Fatigue ?
Atmospheric Agent ?
Corrosion-Fatigue ?
Fretting Effects ?
LOGIC FRAMEWORK FOR CONDUCT OF INVESTIGATION
Figure 3