Iowa DOT Mississippi River Bridge Inspections

The project involved completing an in-depth inspection of the Iowa 9 bridge over the Mississippi River at Lansing in Allamakee County and a routine inspection of the Iowa 136 bridge over the Mississippi River at North Clinton in Clinton County. Ayres was a subconsultant to Burgess & Niple, Inc., on this Iowa Department of Transportation project.

The inspections included a hands-on inspection of fracture critical members and inspection of the remaining above-water portions of the structures, following National Bridge Inspection Standards (NBIS).

The Iowa 9 bridge inspection resulted in the discovery of a crack in a floor beam under the bridge deck, prompting a temporary bridge closure and fast-track repairs. This bridge is fracture critical, and the fracture critical members were inspected within arm’s reach of the bridge. The fracture critical floor beams were known to have cracks in the webs at the ends of the beams where they frame into the lower chord. Special attention was given to the floor beams. Access to the bridge was gained through bridge climbing, rope access, and a pick board. These methods eliminated the need for traffic control and therefore avoided congestion on the bridge. The bridge climbing and rope access methods positioned the inspector within arm’s reach of the fracture critical diagonals and top chord members in the main span and approach spans. The pick board positioned the inspector within arm’s reach of the floor beams and lower chord. Detailed notes on the condition of the fracture critical members and associated condition states were recorded by the inspector while climbing or on the pick board. The inspector’s notes were compiled into one report with bridge elements, quantities for each element, and quantities of each element for each respective condition state observed. Non-destructive testing (NDT) was completed as needed.

The Iowa 136 (North Clinton) bridge is fracture critical, and the fracture critical members were inspected within arm’s reach of the inspector. Access to the bridge was gained through rope access, bridge climbing, and an under-bridge inspection vehicle. These methods were intended to reduce traffic control and congestion on the bridge. Rope access was used to inspect the fracture critical members of the top chord and each hanger in the main spans. Bridge climbing was used to access the lower chord and floor beams of the main spans. The under-bridge inspection vehicle was used to inspect the approach spans. The inspector’s notes were compiled into one report with bridge elements, quantities for each element, and quantities of each element for each respective condition state observed. NDT was completed as needed.

• Fracture Critical Member
• In-Depth
• Routine Bridge