Transcript Mianus_River_Bridge_Collapse.ppt

Mianus River Bridge Collapse
Group 11
Introduction
• The Mianus River Bridge is an 810m long multi-span
structure
• It is part of Route 95 that links Connecticut & New York
• On June 28th 1983 at 1.30 am a 30m section collapsed
• Three were killed and three seriously injured
Bridge Design
• The Bridge is 6 lanes wide with an expansion joint in the
centre dividing it into two parallel bridges
• There are 24 spans in total, 19 of which are approach
• Two of the spans are hung using a pin and hanger
system from the main and anchor spans
Design Flaw
• The Pin & Hanger system is an inherent design flaw
• The system was structurally determinate with no
redundant members. If the pin failed, the bridge failed
• The pin and hanger system was used on the ends
connected to the anchor slab
• The hanger allowed for expansion / contraction
• It was commonly used in the 1950’s to reduce cost
Mode of Failure
• Failure began when the inside
hanger of the southwest span
dislodged from the lower pin
due to corrosion
• This transferred all the weight
onto the remaining hanger
• Fatigue cracks grew in the top
of the upper pin and led to the
fracturing of the pin
• This caused the sudden
collapse of the slab
Reasons for Failure
• Corrosion in the pin
– Maintenance works blocked drainage ducts 10 years previously
– Caused the water to flow over the pins
• Poor Maintenance and Inspection
– Under funded and under staffed
– 12 engineers working in pairs to inspect 3,425 bridges
– Corrosion of pin went undetected
• Inherent design flaw
– High risk of failure
– Only realised in 1968 following Silver Bridge failure
Conclusions
• The Connecticut Dep. Of Transport judged responsible
– Insufficient inspection & maintenance
• The Designers were cleared of all responsibility
• Interstate reopened after 6 months
– Temporary truss
– Repairs cost $20 million
• $5.5 Billion repair package initiated
• In 2007
– 25% of U.S. Bridges structurally deficient of functionally obsolete
– 33.5% of Connecticut Bridges structurally deficient or functionally
obsolete
Thank you!
• Any questions?