County bridge under scrutiny

Span in Arizona Strip similar in design to one that collapsed in Minnesota

The Arizona Department of Transportation has identified five bridges in the state that are similar in construction to the Minneapolis freeway bridge that collapsed Aug. 1, according to an Associated Press story. One of those five bridges is located in Mohave County.

According to ADOT, the Sand Hollow Creek Bridge in the far northwestern corner of the county on old Highway 91 is a steel deck truss bridge, similar in design to the I-35W bridge in Minneapolis.

Mohave County Public Works Assistant Director Nick Hont said county bridges are inspected by the state every two years. The Sand Creek Hollow Bridge was last inspected in 2005 and is due to be inspected again in October.

The bridge has always received a good to satisfactory rating.

Hont confirmed that the bridge is a steel truss construction but didn't know how closely it matched the I-35W bridge. He estimated that the bridge is around 50 years old, which would make it 10 years older than the Minneapolis bridge.

The Sand Creek Hollow Bridge also has a weight limit of 14 tons. Hont said no oversize permits for vehicles are granted for the bridge. The typical weight limit for a bridge in the county is 40 tons. In 2001, the bridge underwent some minor repairs, which were completed by 2003. It passed state inspection in 2003.

The main difference between the two bridges is the size and traffic loads.

The Sand Creek Hollow Bridge is much smaller and doesn't carry nearly as much traffic as the I-35W did. Hont did not have figures on the amount of traffic that crosses the bridge on a daily basis.

According to Associated Press reports, the I-35W in Minneapolis was eight lanes wide and carried 140,000 cars daily. It is 1,900 feet long and sat 115 feet above the water.

The bridge was opened in 1967. It has been inspected annually since 1993. In 1990, the Minnesota Department of Transportation gave it a rating of "structurally deficient" due to corrosion. Cracking was found in the cross girders at the end of the approach spans in 1997. This was fixed, but the report noted a lack of redundancy in the bridge's construction to prevent failure.

The bridge again was rated structurally deficient and possibly in need of replacement in 2005, and in 2006 cracking and fatigue were found in the bridge structure.

At the time of the collapse, minor repairs were being done on the bridge. Four of the eight lanes were closed for resurfacing.

The investigation into the collapse is expected to take at least 18 months.

The Federal Highway Administration has identified what may be a design flaw in the bridge. Large steel sheets called gusset plates are used to connect the girders of steel deck truss bridges. These may have failed.

Arizona is conducting a review of all bridges in the state. It will start with the most heavily trafficked bridges. A report is due on Gov. Janet Napolitano's desk by Sept. 7.