Transcript POINT PLEASANT PowerPoint.ppt

POINT PLEASANT
BRIDGE
Stress Corrosion
&
Corrosion Fatigue
Group 19
POINT PLEASANT BRIDGE


Connecting West Virginia & Ohio
Two lane eye-bar suspension bridge
WHAT HAPPENED?

December 15, 1967

Eye-bar in chain fractures
Complete Structural Failure

46 lives lost

Major transportation route now useless
FAILURE
 Stress
Corrosion
 Corrosion
Fatigue
STRESS CORROSION

Tensile Stress

Environment

Brittle cracks in normally sound
material

Failure loads << Yield stress

Catastrophic Failure
CORROSION FATIGUE

Cyclic stress

Environment

Failure loads << Tensile strength

Fatigue damages protective film on steel

Corrosion accelerated
FAILURE-TECHNICAL FACTORS
Casting & heat treatment of steel
Residual stress
 Microscopic Cracks
 Corrosive Environment
 Actual Loads >> Design Loads
 Chain inaccessible for inspection
 No detection equipment available 1960’s

FAILURE-TECHNICAL FACTORS

Tensile Stress
+ Corrosive environment
+ Increased Loads
= Stress Corrosion Cracking

Cyclical Stress
+ Corrosive environment
+ Increased Loads
= Corrosion Fatigue
FAILURE-TECHNICAL FACTORS

Stress corrosion cracking
+ Corrosion fatigue
+ Microscopic crack
= Critical size flaw
Cleavage Fracture & Ductile Fracture
Eye-bar in chain fails
FAILURE - HUMAN FACTORS

Engineers did not
anticipate traffic loads x 3

No inspection of eye-bars

Stress corrosion &
Corrosion fatigue
unknown in particular
environment and material
LESSONS LEARNT
New detection devices
 Research on material properties
 Bridge inspections
 Stress corrosion & Corrosion fatigue
mechanisms known
 Single element should not cause
catastrophic failure

Finally...
Thank You