Mississippi River Bridge Collapse (2007)
What was the sequence of events that lead up to the disaster?
SETTING FOR COLLAPSE
- Minor construction on bridge during few weeks prior
- Four of the eight lanes were closed for resurfacing
- 575,000 lbs. of construction supplies and equipment on bridge
- Rush hour traffic, about 100 vehicles on bridge
- August 1, 2007 at 6:05 pm (was built in 1967)
- Central span collapsed, then the adjoining
- South part toppled eastward 81 ft
Facts and figures- loss of life, injuries, financial losses.
- 13 deaths, about 100 more injured
- Traffic congestion, rerouting
- Cost of emergency response: +$8 million
- Cost of collapse to state: $400,000 – 1 million/day
- Cost of rebuilding
What was to blame?
ROAD TO FAILURE
- Bridge inspections must occur at least every two years by federal law
- I- 35W bridge rated “structurally deficient” since 1990
- Annual inspections since 1993
- 2005 Bridge sufficiency rating: 50%
Only 4% similar bridges scored below 50%
- “Structurally deficient” due to corrosion in bearings
- Found signs of cracking and fatigue
- Only patch-up repairs conducted
- Scheduled for reconstruction in 2020-2025
What was the physics behind the failure?
TOOLS AND TECHNIQUES USED TO ANALYZE THE BRIDGE COLLAPSE
- Helicopters use lasers to produce a detailed map of the debris
- Then the images are uploaded to a computer where software can recreate the bridge
- The software recreates different scenarios that could have made the bridge collapse, then determines where it failed
- Results are then analyzed in case the computer assumptions are incorrect
POSSIBLE REASONS IT COLLAPSED
- In past inspections fatigue cracks were found and if part of the truss gave way the bridge would collapse
- The bridge was under larger amounts of pressure with the construction work being done
- Some say a design flaw-steel plates connected to girders(large support beams) were under larger amounts of stress with the construction equipment which caused the plates to separate and collapse
- Classified in inspections as a non redundant structure, meaning if one part failed the whole thing would collapse, and it wasn’t due for replacement until 2020
What new regulations, designs, policies, etc. have come about because of the disaster?
- The I-35W bridge crisis prompted governors of several states to call for extra inspections on bridge conditions
- Federal Highway Administration issued special advisories
- The issue has in general made the nation more aware of the poor state of US bridges
- Spending on bridge repair is increasing, but so are construction costs
- 25% of bridges are now deficient, down from 29% in 1998
- At the current construction rate, it will take 50 years to bring all bridges up to safety standards
- This incident shows what we will face if more action is not taken to make our bridges structurally sound and safe for the use of the public for years to come.