I-35 Bridge Collapse, Minneapolis, MN

Structurally Deficient 

• Structurally deficient means there are elements of the bridge that need to be monitored and/or repaired.  The fact that a bridge is "deficient" does not imply that it is likely to collapse or that it is unsafe. It means they must be monitored, inspected and maintained.

• Most “deficient" bridges are left open to traffic while it undergoes maintenance and repair.

• If inspectors find unsafe conditions they will restrict access or close the bridge.  Nothing in the inspection reports indicated that it was necessary to limit access or close the I-35 Bridge. 

Inspection History and Results

• The I-35 bridge has been inspected annually by MnDOT

• A recent inspection was conducted by MnDOT on May 2, 2007, to address some minor concerns regarding weld details.  MnDOT planned to continue inspecting the bridge in the fall.  No imminent dangers were observed.

• Prior to that inspection, the bridge was inspected in June 2006.  The bridge was rated 4 over all.  The 4 rating means that the state can continue to operate the bridge without load restrictions (0= shut down, 9 = perfect).

Background

The National Bridge Inspection Program:

·        The National Bridge Inspection Standards (NBIS), in place since the early 1970s, requires biennial safety inspections for bridges in excess of approximately 20 feet in total length on public roads.

·        Safety is ensured through hands-on inspections and rating of components, such as the deck, superstructure, and sub-structure.  This composition and condition information is maintained in the national bridge inventory (NBI) database, maintained by the FHWA.

·        Certain structures can be inspected every 4 years if they are deemed to be in very good condition.   Approximately 83 percent of bridges are inspected once every 2 years, 12 percent are inspected annually, and 5 percent are inspected on a 4 year cycle.

·        Over $4 billion is apportioned annually from the Federal government to State DOTs for bridge replacement, rehabilitation and preventative maintenance.   

Bridge Facts:

• Opened in November 1967

• Dimensions: 

Length:  1907 ft (structure length; 458 ft (length of max. span)

Width:  8 traffic lanes, 108 ft

Height:  64 ft above water

• Location:  I-35 West at Mississippi River mile marker 853.20 and 1 mile northeast of junction TH94 

• Type structure:  Steel Arch Deck Truss

• This bridge is unique because it was constructed with a single 458 ft steel arch to avoid putting piers in the water which would impede river navigation.

• Daily Traffic:  141,000 vehicles per day as of 2004 count.

• Detour status:  MnDOT has a detour in place and expects it to minimally impact traffic.